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In mathematics , a sesquilinear form is a generalization of a bilinear form that, in turn, is a generalization of the concept of the dot product of Euclidean space . A bilinear form is linear in each of its arguments, but a sesquilinear form allows one of the arguments to be "twisted" in a semilinear manner, thus the name; which originates from the Latin numerical prefix sesqui- meaning "one and a half". The basic concept of the dot product – producing a scalar from a pair of vectors – can be generalized by allowing a broader range of scalar values and, perhaps simultaneously, by widening the definition of a vector.
A motivating special case is a sesquilinear form on a complex vector space , V . This is a map V × V → C that is linear in one argument and "twists" the linearity of the other argument by complex conjugation (referred to as being antilinear in the other argument). This case arises naturally in mathematical physics applications. Another important case allows the scalars to come from any field and the twist is provided by a field automorphism .
An application in projective geometry requires that the scalars come from a division ring (skew field), K , and this means that the "vectors" should be replaced by elements of a K -module . In a very general setting, sesquilinear forms can be defined over R -modules for arbitrary rings R .
Sesquilinear forms abstract and generalize the basic notion of a Hermitian form on complex vector space . Hermitian forms are commonly seen in physics , as the inner product on a complex Hilbert space . In such cases, the standard Hermitian form on C n is given by
where w ¯ i {\displaystyle {\overline {w}}_{i}} denotes the complex conjugate of w i . {\displaystyle w_{i}~.} This product may be generalized to situations where one is not working with an orthonormal basis for C n , or even any basis at all. By inserting an extra factor of i {\displaystyle i} into the product, one obtains the skew-Hermitian form , defined more precisely, below. There is no particular reason to restrict the definition to the complex numbers; it can be defined for arbitrary rings carrying an antiautomorphism , informally understood to be a generalized concept of "complex conjugation" for the ring.
Conventions differ as to which argument should be linear. In the commutative case, we shall take the first to be linear, as is common in the mathematical literature, except in the section devoted to sesquilinear forms on complex vector spaces. There we use the other convention and take the first argument to be conjugate-linear (i.e. antilinear) and the second to be linear. This is the convention used mostly by physicists [ 1 ] and originates in Dirac's bra–ket notation in quantum mechanics . It is also consistent with the definition of the usual (Euclidean) product of w , z ∈ C n {\displaystyle w,z\in \mathbb {C} ^{n}} as w ∗ z {\displaystyle w^{*}z} .
In the more general noncommutative setting, with right modules we take the second argument to be linear and with left modules we take the first argument to be linear.
Over a complex vector space V {\displaystyle V} a map φ : V × V → C {\displaystyle \varphi :V\times V\to \mathbb {C} } is sesquilinear if
for all x , y , z , w ∈ V {\displaystyle x,y,z,w\in V} and all a , b ∈ C . {\displaystyle a,b\in \mathbb {C} .} Here, a ¯ {\displaystyle {\overline {a}}} is the complex conjugate of a scalar a . {\displaystyle a.}
A complex sesquilinear form can also be viewed as a complex bilinear map V ¯ × V → C {\displaystyle {\overline {V}}\times V\to \mathbb {C} } where V ¯ {\displaystyle {\overline {V}}} is the complex conjugate vector space to V . {\displaystyle V.} By the universal property of tensor products these are in one-to-one correspondence with complex linear maps V ¯ ⊗ V → C . {\displaystyle {\overline {V}}\otimes V\to \mathbb {C} .}
For a fixed z ∈ V {\displaystyle z\in V} the map w ↦ φ ( z , w ) {\displaystyle w\mapsto \varphi (z,w)} is a linear functional on V {\displaystyle V} (i.e. an element of the dual space V ∗ {\displaystyle V^{*}} ). Likewise, the map w ↦ φ ( w , z ) {\displaystyle w\mapsto \varphi (w,z)} is a conjugate-linear functional on V . {\displaystyle V.}
Given any complex sesquilinear form φ {\displaystyle \varphi } on V {\displaystyle V} we can define a second complex sesquilinear form ψ {\displaystyle \psi } via the conjugate transpose : ψ ( w , z ) = φ ( z , w ) ¯ . {\displaystyle \psi (w,z)={\overline {\varphi (z,w)}}.} In general, ψ {\displaystyle \psi } and φ {\displaystyle \varphi } will be different. If they are the same then φ {\displaystyle \varphi } is said to be Hermitian . If they are negatives of one another, then φ {\displaystyle \varphi } is said to be skew-Hermitian . Every sesquilinear form can be written as a sum of a Hermitian form and a skew-Hermitian form.
If V {\displaystyle V} is a finite-dimensional complex vector space, then relative to any basis { e i } i {\displaystyle \left\{e_{i}\right\}_{i}} of V , {\displaystyle V,} a sesquilinear form is represented by a matrix A , {\displaystyle A,} and given by φ ( w , z ) = φ ( ∑ i w i e i , ∑ j z j e j ) = ∑ i ∑ j w i ¯ z j φ ( e i , e j ) = w † A z . {\displaystyle \varphi (w,z)=\varphi \left(\sum _{i}w_{i}e_{i},\sum _{j}z_{j}e_{j}\right)=\sum _{i}\sum _{j}{\overline {w_{i}}}z_{j}\varphi \left(e_{i},e_{j}\right)=w^{\dagger }Az.} where w † {\displaystyle w^{\dagger }} is the conjugate transpose . The components of the matrix A {\displaystyle A} are given by A i j := φ ( e i , e j ) . {\displaystyle A_{ij}:=\varphi \left(e_{i},e_{j}\right).}
A complex Hermitian form (also called a symmetric sesquilinear form ), is a sesquilinear form h : V × V → C {\displaystyle h:V\times V\to \mathbb {C} } such that h ( w , z ) = h ( z , w ) ¯ . {\displaystyle h(w,z)={\overline {h(z,w)}}.} The standard Hermitian form on C n {\displaystyle \mathbb {C} ^{n}} is given (again, using the "physics" convention of linearity in the second and conjugate linearity in the first variable) by ⟨ w , z ⟩ = ∑ i = 1 n w ¯ i z i . {\displaystyle \langle w,z\rangle =\sum _{i=1}^{n}{\overline {w}}_{i}z_{i}.} More generally, the inner product on any complex Hilbert space is a Hermitian form.
A minus sign is introduced in the Hermitian form w w ∗ − z z ∗ {\displaystyle ww^{*}-zz^{*}} to define the group SU(1,1) .
A vector space with a Hermitian form ( V , h ) {\displaystyle (V,h)} is called a Hermitian space .
The matrix representation of a complex Hermitian form is a Hermitian matrix .
A complex Hermitian form applied to a single vector | z | h = h ( z , z ) {\displaystyle |z|_{h}=h(z,z)} is always a real number . One can show that a complex sesquilinear form is Hermitian if and only if the associated quadratic form is real for all z ∈ V . {\displaystyle z\in V.}
A complex skew-Hermitian form (also called an antisymmetric sesquilinear form ), is a complex sesquilinear form s : V × V → C {\displaystyle s:V\times V\to \mathbb {C} } such that s ( w , z ) = − s ( z , w ) ¯ . {\displaystyle s(w,z)=-{\overline {s(z,w)}}.} Every complex skew-Hermitian form can be written as the imaginary unit i := − 1 {\displaystyle i:={\sqrt {-1}}} times a Hermitian form.
The matrix representation of a complex skew-Hermitian form is a skew-Hermitian matrix .
A complex skew-Hermitian form applied to a single vector | z | s = s ( z , z ) {\displaystyle |z|_{s}=s(z,z)} is always a purely imaginary number .
This section applies unchanged when the division ring K is commutative . More specific terminology then also applies: the division ring is a field, the anti-automorphism is also an automorphism, and the right module is a vector space. The following applies to a left module with suitable reordering of expressions.
A σ -sesquilinear form over a right K -module M is a bi-additive map φ : M × M → K with an associated anti-automorphism σ of a division ring K such that, for all x , y in M and all α , β in K ,
The associated anti-automorphism σ for any nonzero sesquilinear form φ is uniquely determined by φ .
Given a sesquilinear form φ over a module M and a subspace ( submodule ) W of M , the orthogonal complement of W with respect to φ is
Similarly, x ∈ M is orthogonal to y ∈ M with respect to φ , written x ⊥ φ y (or simply x ⊥ y if φ can be inferred from the context), when φ ( x , y ) = 0 . This relation need not be symmetric , i.e. x ⊥ y does not imply y ⊥ x (but see § Reflexivity below).
A sesquilinear form φ is reflexive if, for all x , y in M ,
That is, a sesquilinear form is reflexive precisely when the derived orthogonality relation is symmetric.
A σ -sesquilinear form φ is called ( σ , ε ) -Hermitian if there exists ε in K such that, for all x , y in M ,
If ε = 1 , the form is called σ - Hermitian , and if ε = −1 , it is called σ - anti-Hermitian . (When σ is implied, respectively simply Hermitian or anti-Hermitian .)
For a nonzero ( σ , ε ) -Hermitian form, it follows that for all α in K ,
It also follows that φ ( x , x ) is a fixed point of the map α ↦ σ ( α ) ε . The fixed points of this map form a subgroup of the additive group of K .
A ( σ , ε ) -Hermitian form is reflexive, and every reflexive σ -sesquilinear form is ( σ , ε ) -Hermitian for some ε . [ 2 ] [ 3 ] [ 4 ] [ 5 ]
In the special case that σ is the identity map (i.e., σ = id ), K is commutative, φ is a bilinear form and ε 2 = 1 . Then for ε = 1 the bilinear form is called symmetric , and for ε = −1 is called skew-symmetric . [ 6 ]
Let V be the three dimensional vector space over the finite field F = GF( q 2 ) , where q is a prime power . With respect to the standard basis we can write x = ( x 1 , x 2 , x 3 ) and y = ( y 1 , y 2 , y 3 ) and define the map φ by:
The map σ : t ↦ t q is an involutory automorphism of F . The map φ is then a σ -sesquilinear form. The matrix M φ associated to this form is the identity matrix . This is a Hermitian form.
In a projective geometry G , a permutation δ of the subspaces that inverts inclusion, i.e.
is called a correlation . A result of Birkhoff and von Neumann (1936) [ 7 ] shows that the correlations of desarguesian projective geometries correspond to the nondegenerate sesquilinear forms on the underlying vector space. [ 5 ] A sesquilinear form φ is nondegenerate if φ ( x , y ) = 0 for all y in V (if and) only if x = 0 .
To achieve full generality of this statement, and since every desarguesian projective geometry may be coordinatized by a division ring , Reinhold Baer extended the definition of a sesquilinear form to a division ring, which requires replacing vector spaces by R -modules . [ 8 ] (In the geometric literature these are still referred to as either left or right vector spaces over skewfields.) [ 9 ]
The specialization of the above section to skewfields was a consequence of the application to projective geometry, and not intrinsic to the nature of sesquilinear forms. Only the minor modifications needed to take into account the non-commutativity of multiplication are required to generalize the arbitrary field version of the definition to arbitrary rings.
Let R be a ring , V an R - module and σ an antiautomorphism of R .
A map φ : V × V → R is σ -sesquilinear if
for all x , y , z , w in V and all c , d in R .
An element x is orthogonal to another element y with respect to the sesquilinear form φ (written x ⊥ y ) if φ ( x , y ) = 0 . This relation need not be symmetric, i.e. x ⊥ y does not imply y ⊥ x .
A sesquilinear form φ : V × V → R is reflexive (or orthosymmetric ) if φ ( x , y ) = 0 implies φ ( y , x ) = 0 for all x , y in V .
A sesquilinear form φ : V × V → R is Hermitian if there exists σ such that [ 10 ] : 325
for all x , y in V . A Hermitian form is necessarily reflexive, and if it is nonzero, the associated antiautomorphism σ is an involution (i.e. of order 2).
Since for an antiautomorphism σ we have σ ( st ) = σ ( t ) σ ( s ) for all s , t in R , if σ = id , then R must be commutative and φ is a bilinear form. In particular, if, in this case, R is a skewfield, then R is a field and V is a vector space with a bilinear form.
An antiautomorphism σ : R → R can also be viewed as an isomorphism R → R op , where R op is the opposite ring of R , which has the same underlying set and the same addition, but whose multiplication operation ( ∗ ) is defined by a ∗ b = ba , where the product on the right is the product in R . It follows from this that a right (left) R -module V can be turned into a left (right) R op -module, V o . [ 11 ] Thus, the sesquilinear form φ : V × V → R can be viewed as a bilinear form φ ′ : V × V o → R . | https://en.wikipedia.org/wiki/Sesquilinear_form |
In materials science , the sessile drop technique is a method used for the characterization of solid surface energies , and in some cases, aspects of liquid surface energies. [ 1 ] The main premise of the method is that by placing a droplet of liquid with a known surface energy and contact angle , the surface energy of the solid substrate can be calculated. [ 2 ] The liquid used for such experiments is referred to as the probe liquid, and the use of several different probe liquids is required.
The surface energy is measured in units of joules per square meter, which is equivalent in the case of liquids to surface tension, measured in newtons per meter . The overall surface tension /energy of a liquid can be acquired through various methods using a tensiometer or using the pendant drop method and maximum bubble pressure method .
The interface tension at the interface of the probe liquid and the solid surface can additionally be viewed as being the result of different types of intermolecular forces . As such, surface energies can be subdivided according to the various interactions that cause them, such as the surface energy due to dispersive (e.g. van der Waals forces ) and other interactions (e.g. hydrogen bonding , polar interactions , acid–base interactions , etc.). It is often useful for the sessile drop technique to use liquids that are known to be incapable of some of those interactions (see table 1 [ dead link ] ). For example, the surface tension of all straight alkanes is said to be entirely dispersive, and all of the other components are zero. This is algebraically useful, as it eliminates a variable in certain cases and makes these liquids essential testing materials.
The overall surface energy, both for a solid and a liquid, is assumed traditionally to simply be the sum of the components considered. For example, the equation describing the subdivision of surface energy into the contributions of dispersive interactions and polar interactions would be
where σ S is the total surface energy of the solid, σ S D and σ S P are respectively the dispersive and polar components of the solid surface energy,
σ L is the total surface tension/surface energy of the liquid, and
σ L D and σ L P are respectively the dispersive and polar components of the surface tension.
In addition to the tensiometer and pendant drop techniques, the sessile drop technique can be used in some cases to separate the known total surface energy of a liquid into its components. This is done by reversing the above idea with the introduction of a reference solid surface that is assumed to be incapable of polar interactions, such as polytetrafluoroethylene (PTFE).
The contact angle is defined as the angle made by the intersection of the liquid/solid interface and the liquid/air interface. It can be alternately described as the angle between solid sample's surface and the tangent of the droplet's ovate shape at the edge of the droplet. A high contact angle indicates a low solid surface energy or chemical affinity. This is also referred to as a low degree of wetting. A low contact angle indicates a high solid surface energy or chemical affinity, and a high or sometimes complete degree of wetting. For example, a contact angle of zero degrees will occur when the droplet has turned into a flat puddle; this is called complete wetting .
The simplest way of measuring the contact angle of a sessile drop is with a contact angle goniometer , which allows the user to measure the contact angle visually. A droplet is deposited by a syringe which is positioned above the sample surface, and a high resolution camera captures the image from the profile or side view. The image can then be analyzed either by eye (with a protractor) or more often is measured using image analysis software. This type of measurement is referred to as a static contact angle measurement. [ 3 ]
The contact angle is affected not only by the surface chemistry but also by the surface roughness. The Young equation, which is the basis for the contact angle, assumes a homogeneous surface with no surface roughness. In case surface roughness is present, the droplet can be in Wenzel state (homogeneous wetting), Cassie-Baxter state (heterogeneous wetting) or in an intermediary state. The surface roughness amplifies the wetting behavior caused by the surface chemistry.
In order to measure the contact angle hysteresis, the sessile droplet can be increased gradually in volume. The maximum possible contact angle is referred to as the advancing contact angle. The receding contact angle can be measured by removing volume from the drop until dewetting occurs. The minimum possible contact angle is referred to as the receding contact angle. [ 3 ] The contact angle hysteresis is the difference between the advancing and receding contact angle. [ 3 ]
The advantage of this method, aside from its relatively straightforward nature, is the fact that with a large enough solid surface, multiple droplets can be deposited in various locations on the sample to determine heterogeneity. The reproducibility of particular values of the contact angle will reflect the heterogeneity of the surface's energy properties. Conversely, the disadvantage is that if the sample is only large enough for one droplet, then it will be difficult to determine heterogeneity, or consequently to assume homogeneity. This is particularly true because conventional, commercially available goniometers do not swivel the camera/backlight set up relative to the stage, and thus can only show the contact angle at two points: the right and the left edge of the droplet. In addition to this, this measurement is hampered by its inherent subjectivity, as the placement of the lines is determined either by the user looking at the pictures or by the image analysis software's definition of the lines.
An alternative method for measuring the contact angle is the Wilhelmy method, which employs a sensitive force meter of some sort to measure a force that can be translated into a value of the contact angle. In this method, a small plate-shaped sample of the solid in question, attached to the arm of a force meter, is vertically dipped into a pool of the probe liquid (in actuality, the design of a stationary force meter would have the liquid being brought up, rather than the sample being brought down), and the force exerted on the sample by the liquid is measured by the force meter. This force is related to the contact angle by the following equation:
where F is the total force measured by the force meter, F b is the force of buoyancy due to the solid sample displacing the liquid, I is the wetted length, and σ is the known surface tension of the liquid.
The advantage of this method is that it is fairly objective and the measurement yields data which is inherently averaged over the wetted length. Although this does not help determine heterogeneity, it does automatically give a more accurate average value. Its disadvantages, aside from being more complicated than the goniometer method, include the fact that sample of an appropriate size must be produced with a uniform cross section in the submersion direction, and the wetted length must be measured with some precision. In addition, this method is only appropriate if both sides of the sample are identical, otherwise the measured data will be a result of two completely different interactions. [ 4 ]
Strictly speaking, this is not a sessile drop technique, as we are using a small submerging pool, rather than a droplet. However, the calculations described in the following sections, which were derived for the relation of the sessile drop contact angle to the surface energy, apply just as well.
While surface energy is conventionally defined as the work required to build a unit of area of a given surface, [ 5 ] when it comes to its measurement by the sessile drop technique, the surface energy is not quite as well defined. The values obtained through the sessile drop technique depend not only on the solid sample in question, but equally on the properties of the probe liquid being used, as well as the particular theory relating the parameters mathematically to one another.
There are numerous such theories developed by various researchers. These methods differ in several regards, such as derivation and convention, but most importantly they differ in the number of components or parameters which they are equipped to analyze. The simpler methods containing fewer components simplify the system by lumping surface energy into one number, while more rigorous methods with more components are derived to distinguish between various components of the surface energy. Again, the total surface energy of solids and liquids depends on different types of molecular interactions, such as dispersive (van der Waals), polar, and acid/base interactions, and is considered to be the sum of these independent components. Some theories account for more of these phenomena than do other theories. These distinctions are to be considered when deciding which method is appropriate for the experiment at hand. The following are a few commonly used such theories.
The Zisman theory is the simplest commonly used theory, as it is a one-component theory, and is best used for non-polar surfaces. This means that polymer surfaces that have been subjected to heat treatment , corona treatment , plasma cleaning , or polymers that contain heteroatoms do not lend themselves to this particular theory, as they tend to be at least somewhat polar . The Zisman theory also tends to be more useful in practice for surfaces with lower energies.
The Zisman theory simply defines the surface energy as being equal to the surface energy of the highest surface energy liquid that wets the solid completely. That is to say, the droplet will disperse as much as possible, i.e. completely wetting the surface, for this liquid and any liquids with lower surface energies, but not for liquids with higher surface energies. Since this probe liquid could hypothetically be any liquid, including an imaginary liquid, the best way to determine the surface energy by the Zisman method is to acquire data points of contact angles for several probe liquids on the solid surface in question, and then plot the cosine of that angle against the known surface energy of the probe liquid. By constructing the Zisman plot, one can extrapolate the highest liquid surface energy, real or hypothetical, that would result in complete wetting of the sample with a contact angle of zero degrees.
The line coefficient (Fig 5) [ where? ] suggests that this is a fairly accurate result, however this is only the case for the pairing of that particular solid with those particular liquids. In other cases, the fit may not be so great (such is the case if we replace polyethylene with poly(methyl methacrylate), wherein the line coefficient of the plot results using the same list of liquids would be significantly lower). This shortcoming is a result of the fact that the Zisman theory treats the surface energy as one single parameter, rather than accounting for the fact that, for example, polar interactions are much stronger than dispersive ones, and thus the degree to which one is happening versus the other greatly affects the necessary calculations. As such, it is a simple but not particularly robust theory. Since the premise of this procedure is to determine the hypothetical properties of a liquid, the precision of the result depends on the precision to which the surface energy values of the probe liquids are known.
The Owens/Wendt theory [ 6 ] (after D. K. Owens and R. C. Wendt) divides the surface energy into two components: surface energy due to dispersive interactions and surface energy due to polar interactions. This theory is derived from the combination of Young's relation , which relates the contact angle to the surface energies of the solid and liquid and to the interface tension, and Good's equation (after R. J. Good), which relates the interface tension to the polar and dispersive components of the surface energy. The resulting principle [ clarify ] equation is
Note that this equation has the form of y = mx + b , with
As such, the polar and dispersive components of the solid's surface energy are determined by the slope and intercept of the resulting graph. Of course, the problem at this point is that in order to make that graph, knowing the surface energy of the probe liquid is not enough, as it is necessary to know specifically how it breaks down into its polar and dispersive components as well.
To do this, one can simply reverse the procedure by testing the probe liquid against a standard reference solid that is not capable of polar interactions, such as PTFE. If the contact angle of a sessile drop of the probe liquid is measured on a PTFE surface with
the principle equation reduces to
Since the total surface tension of the liquid is already known, this equation determines the dispersive component, and the difference between the total and dispersive components gives the polar component.
The accuracy and precision of this method is supported largely by the confidence level of the results for appropriate liquid/solid combinations (as seen, for example, in fig 6 [ where? ] ). The Owens/Wendt theory is typically applicable to surfaces with low charge and moderate polarity. Some good examples are polymers that contain heteroatoms, such as PVC , polyurethanes , polyamides , polyesters , polyacrylates , and polycarbonates
The Fowkes theory (after F. M. Fowkes) is derived in a slightly different way from the Owens/Wendt theory, although the Fowkes theory's principle equation is mathematically equivalent to that of Owens and Wendt:
Note that by dividing both sides of the equation by σ L D {\displaystyle {\sqrt {\sigma _{\text{L}}^{\text{D}}}}} , the Owens/Wendt principle equation is recovered. As such, one of the options for the proper determination of the surface energy components is the same.
In addition to that method, it is also possible to simply do tests using liquids with no polar component to their surface energies, and then liquids that do have both polar and dispersive components, and then linearize the equations (see table 1 ). First, one performs the standard sessile drop contact angle measurement for the solid in question and a liquid with a polar components of zero ( σ L p = 0 {\displaystyle \sigma _{\text{L}}^{\text{p}}=0} ; σ L = σ L D {\displaystyle \sigma _{\text{L}}=\sigma _{\text{L}}^{\text{D}}} ) The second step is to use a second probe liquid that has both a dispersive and a polar component to its surface energy, and then solve for the unknowns algebraically. The Fowkes theory generally requires the use of only two probe liquids, as described above, and the recommended ones are diiodomethane , which should have no polar component due to its molecular symmetry, and water , which is commonly known to be a very polar liquid.
Though the principle equation is essentially identical to that of Owens and Wendt, the Fowkes theory in a larger sense has slightly different applications. Because it is derived from different principles than Owens/Wendt, the rest of the information that Fowkes theory is concerned with is related to adhesion . As such, it is more applicable to situations where adhesion occurs, and in general works better than does the Owens/Wendt theory when dealing with higher surface energies.
In addition, there is an extended Fowkes theory, rooted in the same principles, but dividing the total surface energy into a sum of three rather than two components: surface energy due to dispersive interactions, polar interactions, and hydrogen bonding.
The Wu theory (after Souheng Wu) is also essentially similar to the Owens/Wendt and Fowkes theories, in that it divides surface energy into a polar and a dispersive component. The primary difference is that Wu uses the harmonic means rather than the geometric means of the known surface tensions, and subsequently the use of more rigorous mathematics is employed.
The Wu theory provides more accurate results than do the other two component theories, particularly for high surface energies. It does, however, suffer from one complication: because of the mathematics involved, the Wu theory yields two results for each component, one being the true result, and one being simply a consequence of the mathematics. The challenge at this point lies in interpreting which is the true result. Sometimes this is as simple as eliminating the result that makes no physical sense (a negative surface energy) or the result that is clearly incorrect by virtue of being many orders of magnitude larger or smaller than it should be. Sometimes interpretation is more tricky.
The Schultz theory (after D. L. Schultz) is applicable only for very high energy solids. Again, it is similar to the theories of Owens, Wendt, Fowkes, and Wu, but is designed for a situation where conventional measurement required for those theories is impossible. In the class of solids with sufficiently high surface energy, most liquids wet the surface completely with a contact angle of zero degrees, and thus no useful data can be gathered. The Schultz theory and procedure calls to deposit a sessile drop of probe liquid on the solid surface in question, but this is all done while the system is submerged in yet another liquid, rather than being done in the open air. As a result, the higher "atmospheric" pressure due to the surrounding liquid causes the probe liquid droplet to compress so that there is a measurable contact angle.
This method is designed to be robust where the other methods don't even provide any results in particular. As such, it is indispensable, since it is the only way to use the sessile drop technique on very high surface energy solids. Its major drawback is the fact that it is far more complex, both in its mathematics and experimentally. The Schultz theory requires one to account for many more factors, as there is now the unusual interaction of the probe liquid phase with the surrounding liquid.
The van Oss theory [ 7 ] separates the surface energy of solids and liquids into three components. It includes the dispersive surface energy, as before, and subdivides the polar component as being the sum of two more specific components: the surface energy due to acidic interactions ( σ + {\displaystyle \sigma ^{+}} ) and due to basic interactions ( σ − {\displaystyle \sigma ^{-}} ). The acid component theoretically describes a surface's propensity to have polar interactions with a second surface that has the ability to act basic by donating electrons. Conversely, the base component of the surface energy describes the propensity of a surface to have polar interactions with another surface that acts acidic by accepting electrons. The principle equation for this theory is
Again, the best way to deal with this theory, much like the two-component theories, is to use at least three liquids (more can be used to get more results for statistical purposes) – one with only a dispersive component in its surface energy ( σ L = σ L D {\displaystyle \sigma _{\text{L}}=\sigma _{\text{L}}^{\text{D}}} ), one with only a dispersive and an acidic or basic component ( σ L = σ L D + σ L ± {\displaystyle \sigma _{\text{L}}=\sigma _{L}^{\text{D}}+\sigma _{\text{L}}^{\pm }} ), and finally either a liquid with a dispersive and a basic or acidic component (whichever the second probe liquid did not have ( σ L = σ L D + σ L ∓ {\displaystyle \sigma _{\text{L}}=\sigma _{\text{L}}^{\text{D}}+\sigma _{\text{L}}^{\mp }} )), or a liquid with all three components ( σ L = σ L D + σ L + + σ L − {\displaystyle \sigma _{\text{L}}=\sigma _{\text{L}}^{\text{D}}+\sigma _{\text{L}}^{+}+\sigma _{\text{L}}^{-}} ) – and linearizing the results.
It is naturally more robust than other theories, particularly in cases where there is a great imbalance between the acid and base components of the polar surface energy. The van Oss theory is most suitable for testing the surface energies of inorganics, organometallics, and surface containing ions.
The most significant difficulty of applying the van Oss theory is the fact that there is not much of an agreement in regards to a set of reference solids that can be used to characterize the acid and base components of potential probe liquids. There are however some liquids that are generally agreed to have known dispersive/acid/base components to their surface energies. Two of them are listed in table 1 [ dead link ] .
The presence of surface active elements such as oxygen and sulfur will have a large impact on the measurements obtained with this technique. Surface active elements will exist in larger concentrations at the surface than in the bulk of the liquid, meaning that the total levels of these elements must be carefully controlled to a very low level. For example, the presence of only 50 ppm sulphur in liquid iron will reduce the surface tension by approximately 20%. [ 9 ]
The sessile drop technique has various applications for both materials engineering and straight characterization. In general, it is useful in determining the surface tension of liquids through the use of reference solids, with a similar technique being the Captive Bubble Method . There are various other specific applications which can be subdivided according to which of the above theories is most likely to be applicable to the circumstances:
The Zisman theory is mostly used for low energy surfaces and characterizes only the total surface energy. As such, it is probably most useful in cases that recall the conventional definition of surfaces, for example if a chemical engineer wants to know what the energy associated with fabricating a surface is. It may also be useful in cases where the surface energy has some effect on a spectroscopic technique being used on the solid in question.
The two component theories would most likely be applicable to materials engineering questions about the practical interactions of liquids and solids. The Fowkes theory, since it is more suited for higher energy solid surfaces, and since much of it is rooted in theories about adhesion , would likely be suited for the characterization of interactions where the solids and liquids have a high affinity for one another, such as, logically enough, adhesives and adhesive coatings . The Owens/Wendt theory, which deals in low energy solid surfaces, would be helpful in characterizing the interactions where the solids and liquids do not have a strong affinity for one another – for example, the effectiveness of waterproofing . Polyurethanes and PVC are good examples of waterproof plastics.
The Schultz theory is best used for the characterization of very high energy surfaces for which the other theories are ineffective, the most significant example being bare metals .
The van Oss theory is most suitable for cases in which acid/base interaction is an important consideration. Examples include pigments , pharmaceuticals , and paper . Specifically, notable examples include both paper used for the regular purpose of printing, and the more specialized case of litmus paper , which in itself is used to characterize acidity and basicity.
Shimizu, R. N., & Demarquette, N. R. (2000). Evaluation of surface energy of solid polymers using different models. Journal of Applied Polymer Science, 76(12), 1831-1845. | https://en.wikipedia.org/wiki/Sessile_drop_technique |
Sessility is the biological property of an animal describing its lack of a means of self-locomotion. Sessile animals for which natural motility is absent are normally immobile. This is distinct from the botanical concept of sessility , which refers to an organism or biological structure attached directly by its base without a stalk.
Sessile animals can move via external forces (such as water currents), but are usually permanently attached to something. Organisms such as corals lay down their own substrate from which they grow. Other organisms grow from a solid object, such as a rock, a dead tree trunk, or a human-made object such as a buoy or ship's hull. [ 1 ]
Sessile animals typically have a motile phase in their development. Sponges have a motile larval stage and become sessile at maturity. Conversely, many jellyfish develop as sessile polyps early in their life cycle. In the case of the cochineal , it is in the nymph stage (also called the crawler stage) that the cochineal disperses. The juveniles move to a feeding spot and produce long wax filaments. Later they move to the edge of the cactus pad where the wind catches the wax filaments and carries the tiny larval cochineals to a new host.
Many sessile animals, including sponges, corals and hydra , are capable of asexual reproduction in situ by the process of budding . Sessile organisms such as barnacles and tunicates need some mechanism to move their young into new territory. This is why the most widely accepted theory explaining the evolution of a larval stage is the need for long-distance dispersal ability. Biologist Wayne Sousa 's 1979 study in intertidal disturbance added support for the theory of nonequilibrium community structure, "suggesting that open space is necessary for the maintenance of diversity in most communities of sessile organisms". [ 2 ]
Clumping is a behavior in sessile organisms in which individuals of a particular species group closely to one another for beneficial purposes instead of motility , as can be seen in coral reefs and cochineal populations. This allows for faster reproduction and better protection from predators but make sessile organisms walk. [ 3 ]
The circalittoral zone of coastal environments and biomes are dominated by sessile organisms such as oysters . Carbonate platforms grow due to the buildup of skeletal remains of sessile organisms, usually microorganisms , which induce carbonate precipitation through their metabolism.
In anatomy and botany, sessility refers to an organism or biological structure that has no peduncle or stalk. A sessile structure has no stalk.
See : peduncle (anatomy) , peduncle (botany) and sessility (botany) . | https://en.wikipedia.org/wiki/Sessility_(motility) |
In architecture and masonry , the term set-off or off-set is given to the part of a wall or other architectural feature, which is exposed when the portion above is of a reduced thickness. [ 1 ] In plinths , this is generally simply chamfered. In other parts of stonework, the set-off is generally concealed by a projecting string course . In parapets , where the upper part projects (or is proud of) the lower, the break is generally hidden by a corbel . The portions of buttress caps which recede one behind another are also called sets-off. [ 2 ] The term for a set-off near ground level is water table , often sloped at the top to throw off water. [ 3 ]
This architectural element –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Set-off_(architecture) |
{ n ∣ ∃ k ∈ Z , n = 2 k } {\displaystyle \{n\mid \exists k\in \mathbb {Z} ,n=2k\}}
In mathematics and more specifically in set theory , set-builder notation is a notation for specifying a set by a property that characterizes its members. [ 1 ]
Specifying sets by member properties is allowed by the axiom schema of specification . This is also known as set comprehension and set abstraction .
Set-builder notation can be used to describe a set that is defined by a predicate , that is, a logical formula that evaluates to true for an element of the set, and false otherwise. [ 2 ] In this form, set-builder notation has three parts: a variable, a colon or vertical bar separator, and a predicate. Thus there is a variable on the left of the separator, and a rule on the right of it. These three parts are contained in curly brackets:
or
The vertical bar (or colon) is a separator that can be read as " such that ", "for which", or "with the property that". The formula Φ( x ) is said to be the rule or the predicate . All values of x for which the predicate holds (is true) belong to the set being defined. All values of x for which the predicate does not hold do not belong to the set. Thus { x ∣ Φ ( x ) } {\displaystyle \{x\mid \Phi (x)\}} is the set of all values of x that satisfy the formula Φ . [ 3 ] It may be the empty set , if no value of x satisfies the formula.
A domain E can appear on the left of the vertical bar: [ 4 ]
or by adjoining it to the predicate:
The ∈ symbol here denotes set membership , while the ∧ {\displaystyle \land } symbol denotes the logical "and" operator, known as logical conjunction . This notation represents the set of all values of x that belong to some given set E for which the predicate is true (see " Set existence axiom " below). If Φ ( x ) {\displaystyle \Phi (x)} is a conjunction Φ 1 ( x ) ∧ Φ 2 ( x ) {\displaystyle \Phi _{1}(x)\land \Phi _{2}(x)} , then { x ∈ E ∣ Φ ( x ) } {\displaystyle \{x\in E\mid \Phi (x)\}} is sometimes written { x ∈ E ∣ Φ 1 ( x ) , Φ 2 ( x ) } {\displaystyle \{x\in E\mid \Phi _{1}(x),\Phi _{2}(x)\}} , using a comma instead of the symbol ∧ {\displaystyle \land } .
In general, it is not a good idea to consider sets without defining a domain of discourse , as this would represent the subset of all possible things that may exist for which the predicate is true. This can easily lead to contradictions and paradoxes. For example, Russell's paradox shows that the expression { x | x ∉ x } , {\displaystyle \{x~|~x\not \in x\},} although seemingly well formed as a set builder expression, cannot define a set without producing a contradiction. [ 5 ]
In cases where the set E is clear from context, it may be not explicitly specified. It is common in the literature for an author to state the domain ahead of time, and then not specify it in the set-builder notation. For example, an author may say something such as, "Unless otherwise stated, variables are to be taken to be natural numbers," though in less formal contexts where the domain can be assumed, a written mention is often unnecessary.
The following examples illustrate particular sets defined by set-builder notation via predicates. In each case, the domain is specified on the left side of the vertical bar, while the rule is specified on the right side.
An extension of set-builder notation replaces the single variable x with an expression . So instead of { x ∣ Φ ( x ) } {\displaystyle \{x\mid \Phi (x)\}} , we may have { f ( x ) ∣ Φ ( x ) } , {\displaystyle \{f(x)\mid \Phi (x)\},} which should be read
For example:
When inverse functions can be explicitly stated, the expression on the left can be eliminated through simple substitution. Consider the example set { 2 t + 1 ∣ t ∈ Z } {\displaystyle \{2t+1\mid t\in \mathbb {Z} \}} . Make the substitution u = 2 t + 1 {\displaystyle u=2t+1} , which is to say t = ( u − 1 ) / 2 {\displaystyle t=(u-1)/2} , then replace t in the set builder notation to find
Two sets are equal if and only if they have the same elements. Sets defined by set builder notation are equal if and only if their set builder rules, including the domain specifiers, are equivalent. That is
if and only if
Therefore, in order to prove the equality of two sets defined by set builder notation, it suffices to prove the equivalence of their predicates, including the domain qualifiers.
For example,
because the two rule predicates are logically equivalent:
This equivalence holds because, for any real number x , we have x 2 = 1 {\displaystyle x^{2}=1} if and only if x is a rational number with | x | = 1 {\displaystyle |x|=1} . In particular, both sets are equal to the set { − 1 , 1 } {\displaystyle \{-1,1\}} .
In many formal set theories, such as Zermelo–Fraenkel set theory , set builder notation is not part of the formal syntax of the theory. Instead, there is a set existence axiom scheme , which states that if E is a set and Φ( x ) is a formula in the language of set theory, then there is a set Y whose members are exactly the elements of E that satisfy Φ :
The set Y obtained from this axiom is exactly the set described in set builder notation as { x ∈ E ∣ Φ ( x ) } {\displaystyle \{x\in E\mid \Phi (x)\}} .
A similar notation available in a number of programming languages (notably Python and Haskell ) is the list comprehension , which combines map and filter operations over one or more lists .
In Python, the set-builder's braces are replaced with square brackets, parentheses, or curly braces, giving list, generator , and set objects, respectively. Python uses an English-based syntax. Haskell replaces the set-builder's braces with square brackets and uses symbols, including the standard set-builder vertical bar.
The same can be achieved in Scala using Sequence Comprehensions, where the "for" keyword returns a list of the yielded variables using the "yield" keyword. [ 6 ]
Consider these set-builder notation examples in some programming languages:
The set builder notation and list comprehension notation are both instances of a more general notation known as monad comprehensions , which permits map/filter-like operations over any monad with a zero element . | https://en.wikipedia.org/wiki/Set_comprehension |
In mathematics, especially measure theory , a set function is a function whose domain is a family of subsets of some given set and that (usually) takes its values in the extended real number line R ∪ { ± ∞ } , {\displaystyle \mathbb {R} \cup \{\pm \infty \},} which consists of the real numbers R {\displaystyle \mathbb {R} } and ± ∞ . {\displaystyle \pm \infty .}
A set function generally aims to measure subsets in some way. Measures are typical examples of "measuring" set functions. Therefore, the term "set function" is often used for avoiding confusion between the mathematical meaning of "measure" and its common language meaning.
If F {\displaystyle {\mathcal {F}}} is a family of sets over Ω {\displaystyle \Omega } (meaning that F ⊆ ℘ ( Ω ) {\displaystyle {\mathcal {F}}\subseteq \wp (\Omega )} where ℘ ( Ω ) {\displaystyle \wp (\Omega )} denotes the powerset ) then a set function on F {\displaystyle {\mathcal {F}}} is a function μ {\displaystyle \mu } with domain F {\displaystyle {\mathcal {F}}} and codomain [ − ∞ , ∞ ] {\displaystyle [-\infty ,\infty ]} or, sometimes, the codomain is instead some vector space , as with vector measures , complex measures , and projection-valued measures .
The domain of a set function may have any number properties; the commonly encountered properties and categories of families are listed in the table below.
Additionally, a semiring is a π -system where every complement B ∖ A {\displaystyle B\setminus A} is equal to a finite disjoint union of sets in F . {\displaystyle {\mathcal {F}}.} A semialgebra is a semiring where every complement Ω ∖ A {\displaystyle \Omega \setminus A} is equal to a finite disjoint union of sets in F . {\displaystyle {\mathcal {F}}.} A , B , A 1 , A 2 , … {\displaystyle A,B,A_{1},A_{2},\ldots } are arbitrary elements of F {\displaystyle {\mathcal {F}}} and it is assumed that F ≠ ∅ . {\displaystyle {\mathcal {F}}\neq \varnothing .}
In general, it is typically assumed that μ ( E ) + μ ( F ) {\displaystyle \mu (E)+\mu (F)} is always well-defined for all E , F ∈ F , {\displaystyle E,F\in {\mathcal {F}},} or equivalently, that μ {\displaystyle \mu } does not take on both − ∞ {\displaystyle -\infty } and + ∞ {\displaystyle +\infty } as values. This article will henceforth assume this; although alternatively, all definitions below could instead be qualified by statements such as "whenever the sum/series is defined". This is sometimes done with subtraction, such as with the following result, which holds whenever μ {\displaystyle \mu } is finitely additive :
Null sets
A set F ∈ F {\displaystyle F\in {\mathcal {F}}} is called a null set (with respect to μ {\displaystyle \mu } ) or simply null if μ ( F ) = 0. {\displaystyle \mu (F)=0.} Whenever μ {\displaystyle \mu } is not identically equal to either − ∞ {\displaystyle -\infty } or + ∞ {\displaystyle +\infty } then it is typically also assumed that:
Variation and mass
The total variation of a set S {\displaystyle S} is | μ | ( S ) = def sup { | μ ( F ) | : F ∈ F and F ⊆ S } {\displaystyle |\mu |(S)~{\stackrel {\scriptscriptstyle {\text{def}}}{=}}~\sup\{|\mu (F)|:F\in {\mathcal {F}}{\text{ and }}F\subseteq S\}} where | ⋅ | {\displaystyle |\,\cdot \,|} denotes the absolute value (or more generally, it denotes the norm or seminorm if μ {\displaystyle \mu } is vector-valued in a ( semi ) normed space ).
Assuming that ∪ F = def ⋃ F ∈ F F ∈ F , {\displaystyle \cup {\mathcal {F}}~{\stackrel {\scriptscriptstyle {\text{def}}}{=}}~\textstyle \bigcup \limits _{F\in {\mathcal {F}}}F\in {\mathcal {F}},} then | μ | ( ∪ F ) {\displaystyle |\mu |\left(\cup {\mathcal {F}}\right)} is called the total variation of μ {\displaystyle \mu } and μ ( ∪ F ) {\displaystyle \mu \left(\cup {\mathcal {F}}\right)} is called the mass of μ . {\displaystyle \mu .}
A set function is called finite if for every F ∈ F , {\displaystyle F\in {\mathcal {F}},} the value μ ( F ) {\displaystyle \mu (F)} is finite (which by definition means that μ ( F ) ≠ ∞ {\displaystyle \mu (F)\neq \infty } and μ ( F ) ≠ − ∞ {\displaystyle \mu (F)\neq -\infty } ; an infinite value is one that is equal to ∞ {\displaystyle \infty } or − ∞ {\displaystyle -\infty } ).
Every finite set function must have a finite mass .
A set function μ {\displaystyle \mu } on F {\displaystyle {\mathcal {F}}} is said to be [ 1 ]
Arbitrary sums
As described in this article's section on generalized series , for any family ( r i ) i ∈ I {\displaystyle \left(r_{i}\right)_{i\in I}} of real numbers indexed by an arbitrary indexing set I , {\displaystyle I,} it is possible to define their sum ∑ i ∈ I r i {\displaystyle \textstyle \sum \limits _{i\in I}r_{i}} as the limit of the net of finite partial sums F ∈ FiniteSubsets ( I ) ↦ ∑ i ∈ F r i {\displaystyle F\in \operatorname {FiniteSubsets} (I)\mapsto \textstyle \sum \limits _{i\in F}r_{i}} where the domain FiniteSubsets ( I ) {\displaystyle \operatorname {FiniteSubsets} (I)} is directed by ⊆ . {\displaystyle \,\subseteq .\,} Whenever this net converges then its limit is denoted by the symbols ∑ i ∈ I r i {\displaystyle \textstyle \sum \limits _{i\in I}r_{i}} while if this net instead diverges to ± ∞ {\displaystyle \pm \infty } then this may be indicated by writing ∑ i ∈ I r i = ± ∞ . {\displaystyle \textstyle \sum \limits _{i\in I}r_{i}=\pm \infty .} Any sum over the empty set is defined to be zero; that is, if I = ∅ {\displaystyle I=\varnothing } then ∑ i ∈ ∅ r i = 0 {\displaystyle \textstyle \sum \limits _{i\in \varnothing }r_{i}=0} by definition.
For example, if z i = 0 {\displaystyle z_{i}=0} for every i ∈ I {\displaystyle i\in I} then ∑ i ∈ I z i = 0. {\displaystyle \textstyle \sum \limits _{i\in I}z_{i}=0.} And it can be shown that ∑ i ∈ I r i = ∑ r i = 0 i ∈ I , r i + ∑ r i ≠ 0 i ∈ I , r i = 0 + ∑ r i ≠ 0 i ∈ I , r i = ∑ r i ≠ 0 i ∈ I , r i . {\displaystyle \textstyle \sum \limits _{i\in I}r_{i}=\textstyle \sum \limits _{\stackrel {i\in I,}{r_{i}=0}}r_{i}+\textstyle \sum \limits _{\stackrel {i\in I,}{r_{i}\neq 0}}r_{i}=0+\textstyle \sum \limits _{\stackrel {i\in I,}{r_{i}\neq 0}}r_{i}=\textstyle \sum \limits _{\stackrel {i\in I,}{r_{i}\neq 0}}r_{i}.} If I = N {\displaystyle I=\mathbb {N} } then the generalized series ∑ i ∈ I r i {\displaystyle \textstyle \sum \limits _{i\in I}r_{i}} converges in R {\displaystyle \mathbb {R} } if and only if ∑ i = 1 ∞ r i {\displaystyle \textstyle \sum \limits _{i=1}^{\infty }r_{i}} converges unconditionally (or equivalently, converges absolutely ) in the usual sense.
If a generalized series ∑ i ∈ I r i {\displaystyle \textstyle \sum \limits _{i\in I}r_{i}} converges in R {\displaystyle \mathbb {R} } then both ∑ r i > 0 i ∈ I r i {\displaystyle \textstyle \sum \limits _{\stackrel {i\in I}{r_{i}>0}}r_{i}} and ∑ r i < 0 i ∈ I r i {\displaystyle \textstyle \sum \limits _{\stackrel {i\in I}{r_{i}<0}}r_{i}} also converge to elements of R {\displaystyle \mathbb {R} } and the set { i ∈ I : r i ≠ 0 } {\displaystyle \left\{i\in I:r_{i}\neq 0\right\}} is necessarily countable (that is, either finite or countably infinite ); this remains true if R {\displaystyle \mathbb {R} } is replaced with any normed space . [ proof 1 ] It follows that in order for a generalized series ∑ i ∈ I r i {\displaystyle \textstyle \sum \limits _{i\in I}r_{i}} to converge in R {\displaystyle \mathbb {R} } or C , {\displaystyle \mathbb {C} ,} it is necessary that all but at most countably many r i {\displaystyle r_{i}} will be equal to 0 , {\displaystyle 0,} which means that ∑ i ∈ I r i = ∑ r i ≠ 0 i ∈ I r i {\displaystyle \textstyle \sum \limits _{i\in I}r_{i}~=~\textstyle \sum \limits _{\stackrel {i\in I}{r_{i}\neq 0}}r_{i}} is a sum of at most countably many non-zero terms.
Said differently, if { i ∈ I : r i ≠ 0 } {\displaystyle \left\{i\in I:r_{i}\neq 0\right\}} is uncountable then the generalized series ∑ i ∈ I r i {\displaystyle \textstyle \sum \limits _{i\in I}r_{i}} does not converge.
In summary, due to the nature of the real numbers and its topology, every generalized series of real numbers (indexed by an arbitrary set) that converges can be reduced to an ordinary absolutely convergent series of countably many real numbers. So in the context of measure theory, there is little benefit gained by considering uncountably many sets and generalized series. In particular, this is why the definition of " countably additive " is rarely extended from countably many sets F 1 , F 2 , … {\displaystyle F_{1},F_{2},\ldots \,} in F {\displaystyle {\mathcal {F}}} (and the usual countable series ∑ i = 1 ∞ μ ( F i ) {\displaystyle \textstyle \sum \limits _{i=1}^{\infty }\mu \left(F_{i}\right)} ) to arbitrarily many sets ( F i ) i ∈ I {\displaystyle \left(F_{i}\right)_{i\in I}} (and the generalized series ∑ i ∈ I μ ( F i ) {\displaystyle \textstyle \sum \limits _{i\in I}\mu \left(F_{i}\right)} ).
A set function μ {\displaystyle \mu } is said to be/satisfies [ 1 ]
If a binary operation + {\displaystyle \,+\,} is defined, then a set function μ {\displaystyle \mu } is said to be
If τ {\displaystyle \tau } is a topology on Ω {\displaystyle \Omega } then a set function μ {\displaystyle \mu } is said to be:
If μ {\displaystyle \mu } and ν {\displaystyle \nu } are two set functions over Ω , {\displaystyle \Omega ,} then:
Examples of set functions include:
The Jordan measure on R n {\displaystyle \mathbb {R} ^{n}} is a set function defined on the set of all Jordan measurable subsets of R n ; {\displaystyle \mathbb {R} ^{n};} it sends a Jordan measurable set to its Jordan measure.
The Lebesgue measure on R {\displaystyle \mathbb {R} } is a set function that assigns a non-negative real number to every set of real numbers that belongs to the Lebesgue σ {\displaystyle \sigma } -algebra. [ 5 ]
Its definition begins with the set Intervals ( R ) {\displaystyle \operatorname {Intervals} (\mathbb {R} )} of all intervals of real numbers, which is a semialgebra on R . {\displaystyle \mathbb {R} .} The function that assigns to every interval I {\displaystyle I} its length ( I ) {\displaystyle \operatorname {length} (I)} is a finitely additive set function (explicitly, if I {\displaystyle I} has endpoints a ≤ b {\displaystyle a\leq b} then length ( I ) = b − a {\displaystyle \operatorname {length} (I)=b-a} ).
This set function can be extended to the Lebesgue outer measure on R , {\displaystyle \mathbb {R} ,} which is the translation-invariant set function λ ∗ : ℘ ( R ) → [ 0 , ∞ ] {\displaystyle \lambda ^{\!*\!}:\wp (\mathbb {R} )\to [0,\infty ]} that sends a subset E ⊆ R {\displaystyle E\subseteq \mathbb {R} } to the infimum λ ∗ ( E ) = inf { ∑ k = 1 ∞ length ( I k ) : ( I k ) k ∈ N is a sequence of open intervals with E ⊆ ⋃ k = 1 ∞ I k } . {\displaystyle \lambda ^{\!*\!}(E)=\inf \left\{\sum _{k=1}^{\infty }\operatorname {length} (I_{k}):{(I_{k})_{k\in \mathbb {N} }}{\text{ is a sequence of open intervals with }}E\subseteq \bigcup _{k=1}^{\infty }I_{k}\right\}.} Lebesgue outer measure is not countably additive (and so is not a measure) although its restriction to the 𝜎-algebra of all subsets M ⊆ R {\displaystyle M\subseteq \mathbb {R} } that satisfy the Carathéodory criterion : λ ∗ ( M ) = λ ∗ ( M ∩ E ) + λ ∗ ( M ∩ E c ) for every S ⊆ R {\displaystyle \lambda ^{\!*\!}(M)=\lambda ^{\!*\!}(M\cap E)+\lambda ^{\!*\!}(M\cap E^{c})\quad {\text{ for every }}S\subseteq \mathbb {R} } is a measure that called Lebesgue measure . Vitali sets are examples of non-measurable sets of real numbers.
As detailed in the article on infinite-dimensional Lebesgue measure , the only locally finite and translation-invariant Borel measure on an infinite-dimensional separable normed space is the trivial measure . However, it is possible to define Gaussian measures on infinite-dimensional topological vector spaces . The structure theorem for Gaussian measures shows that the abstract Wiener space construction is essentially the only way to obtain a strictly positive Gaussian measure on a separable Banach space .
The only translation-invariant measure on Ω = R {\displaystyle \Omega =\mathbb {R} } with domain ℘ ( R ) {\displaystyle \wp (\mathbb {R} )} that is finite on every compact subset of R {\displaystyle \mathbb {R} } is the trivial set function ℘ ( R ) → [ 0 , ∞ ] {\displaystyle \wp (\mathbb {R} )\to [0,\infty ]} that is identically equal to 0 {\displaystyle 0} (that is, it sends every S ⊆ R {\displaystyle S\subseteq \mathbb {R} } to 0 {\displaystyle 0} ) [ 6 ] However, if countable additivity is weakened to finite additivity then a non-trivial set function with these properties does exist and moreover, some are even valued in [ 0 , 1 ] . {\displaystyle [0,1].} In fact, such non-trivial set functions will exist even if R {\displaystyle \mathbb {R} } is replaced by any other abelian group G . {\displaystyle G.} [ 7 ]
Theorem [ 8 ] — If ( G , + ) {\displaystyle (G,+)} is any abelian group then there exists a finitely additive and translation-invariant [ note 1 ] set function μ : ℘ ( G ) → [ 0 , 1 ] {\displaystyle \mu :\wp (G)\to [0,1]} of mass μ ( G ) = 1. {\displaystyle \mu (G)=1.}
Suppose that μ {\displaystyle \mu } is a set function on a semialgebra F {\displaystyle {\mathcal {F}}} over Ω {\displaystyle \Omega } and let algebra ( F ) := { F 1 ⊔ ⋯ ⊔ F n : n ∈ N and F 1 , … , F n ∈ F are pairwise disjoint } , {\displaystyle \operatorname {algebra} ({\mathcal {F}}):=\left\{F_{1}\sqcup \cdots \sqcup F_{n}:n\in \mathbb {N} {\text{ and }}F_{1},\ldots ,F_{n}\in {\mathcal {F}}{\text{ are pairwise disjoint }}\right\},} which is the algebra on Ω {\displaystyle \Omega } generated by F . {\displaystyle {\mathcal {F}}.} The archetypal example of a semialgebra that is not also an algebra is the family S d := { ∅ } ∪ { ( a 1 , b 1 ] × ⋯ × ( a 1 , b 1 ] : − ∞ ≤ a i < b i ≤ ∞ for all i = 1 , … , d } {\displaystyle {\mathcal {S}}_{d}:=\{\varnothing \}\cup \left\{\left(a_{1},b_{1}\right]\times \cdots \times \left(a_{1},b_{1}\right]~:~-\infty \leq a_{i}<b_{i}\leq \infty {\text{ for all }}i=1,\ldots ,d\right\}} on Ω := R d {\displaystyle \Omega :=\mathbb {R} ^{d}} where ( a , b ] := { x ∈ R : a < x ≤ b } {\displaystyle (a,b]:=\{x\in \mathbb {R} :a<x\leq b\}} for all − ∞ ≤ a < b ≤ ∞ . {\displaystyle -\infty \leq a<b\leq \infty .} [ 9 ] Importantly, the two non-strict inequalities ≤ {\displaystyle \,\leq \,} in − ∞ ≤ a i < b i ≤ ∞ {\displaystyle -\infty \leq a_{i}<b_{i}\leq \infty } cannot be replaced with strict inequalities < {\displaystyle \,<\,} since semialgebras must contain the whole underlying set R d ; {\displaystyle \mathbb {R} ^{d};} that is, R d ∈ S d {\displaystyle \mathbb {R} ^{d}\in {\mathcal {S}}_{d}} is a requirement of semialgebras (as is ∅ ∈ S d {\displaystyle \varnothing \in {\mathcal {S}}_{d}} ).
If μ {\displaystyle \mu } is finitely additive then it has a unique extension to a set function μ ¯ {\displaystyle {\overline {\mu }}} on algebra ( F ) {\displaystyle \operatorname {algebra} ({\mathcal {F}})} defined by sending F 1 ⊔ ⋯ ⊔ F n ∈ algebra ( F ) {\displaystyle F_{1}\sqcup \cdots \sqcup F_{n}\in \operatorname {algebra} ({\mathcal {F}})} (where ⊔ {\displaystyle \,\sqcup \,} indicates that these F i ∈ F {\displaystyle F_{i}\in {\mathcal {F}}} are pairwise disjoint ) to: [ 9 ] μ ¯ ( F 1 ⊔ ⋯ ⊔ F n ) := μ ( F 1 ) + ⋯ + μ ( F n ) . {\displaystyle {\overline {\mu }}\left(F_{1}\sqcup \cdots \sqcup F_{n}\right):=\mu \left(F_{1}\right)+\cdots +\mu \left(F_{n}\right).} This extension μ ¯ {\displaystyle {\overline {\mu }}} will also be finitely additive: for any pairwise disjoint A 1 , … , A n ∈ algebra ( F ) , {\displaystyle A_{1},\ldots ,A_{n}\in \operatorname {algebra} ({\mathcal {F}}),} [ 9 ] μ ¯ ( A 1 ∪ ⋯ ∪ A n ) = μ ¯ ( A 1 ) + ⋯ + μ ¯ ( A n ) . {\displaystyle {\overline {\mu }}\left(A_{1}\cup \cdots \cup A_{n}\right)={\overline {\mu }}\left(A_{1}\right)+\cdots +{\overline {\mu }}\left(A_{n}\right).}
If in addition μ {\displaystyle \mu } is extended real-valued and monotone (which, in particular, will be the case if μ {\displaystyle \mu } is non-negative ) then μ ¯ {\displaystyle {\overline {\mu }}} will be monotone and finitely subadditive : for any A , A 1 , … , A n ∈ algebra ( F ) {\displaystyle A,A_{1},\ldots ,A_{n}\in \operatorname {algebra} ({\mathcal {F}})} such that A ⊆ A 1 ∪ ⋯ ∪ A n , {\displaystyle A\subseteq A_{1}\cup \cdots \cup A_{n},} [ 9 ] μ ¯ ( A ) ≤ μ ¯ ( A 1 ) + ⋯ + μ ¯ ( A n ) . {\displaystyle {\overline {\mu }}\left(A\right)\leq {\overline {\mu }}\left(A_{1}\right)+\cdots +{\overline {\mu }}\left(A_{n}\right).}
If μ : F → [ 0 , ∞ ] {\displaystyle \mu :{\mathcal {F}}\to [0,\infty ]} is a pre-measure on a ring of sets (such as an algebra of sets ) F {\displaystyle {\mathcal {F}}} over Ω {\displaystyle \Omega } then μ {\displaystyle \mu } has an extension to a measure μ ¯ : σ ( F ) → [ 0 , ∞ ] {\displaystyle {\overline {\mu }}:\sigma ({\mathcal {F}})\to [0,\infty ]} on the σ-algebra σ ( F ) {\displaystyle \sigma ({\mathcal {F}})} generated by F . {\displaystyle {\mathcal {F}}.} If μ {\displaystyle \mu } is σ-finite then this extension is unique.
To define this extension, first extend μ {\displaystyle \mu } to an outer measure μ ∗ {\displaystyle \mu ^{*}} on 2 Ω = ℘ ( Ω ) {\displaystyle 2^{\Omega }=\wp (\Omega )} by μ ∗ ( T ) = inf { ∑ n μ ( S n ) : T ⊆ ∪ n S n with S 1 , S 2 , … ∈ F } {\displaystyle \mu ^{*}(T)=\inf \left\{\sum _{n}\mu \left(S_{n}\right):T\subseteq \cup _{n}S_{n}{\text{ with }}S_{1},S_{2},\ldots \in {\mathcal {F}}\right\}} and then restrict it to the set F M {\displaystyle {\mathcal {F}}_{M}} of μ ∗ {\displaystyle \mu ^{*}} -measurable sets (that is, Carathéodory-measurable sets ), which is the set of all M ⊆ Ω {\displaystyle M\subseteq \Omega } such that μ ∗ ( S ) = μ ∗ ( S ∩ M ) + μ ∗ ( S ∩ M c ) for every subset S ⊆ Ω . {\displaystyle \mu ^{*}(S)=\mu ^{*}(S\cap M)+\mu ^{*}(S\cap M^{\mathrm {c} })\quad {\text{ for every subset }}S\subseteq \Omega .} It is a σ {\displaystyle \sigma } -algebra and μ ∗ {\displaystyle \mu ^{*}} is sigma-additive on it, by Caratheodory lemma.
If μ ∗ : ℘ ( Ω ) → [ 0 , ∞ ] {\displaystyle \mu ^{*}:\wp (\Omega )\to [0,\infty ]} is an outer measure on a set Ω , {\displaystyle \Omega ,} where (by definition) the domain is necessarily the power set ℘ ( Ω ) {\displaystyle \wp (\Omega )} of Ω , {\displaystyle \Omega ,} then a subset M ⊆ Ω {\displaystyle M\subseteq \Omega } is called μ ∗ {\displaystyle \mu ^{*}} –measurable or Carathéodory-measurable if it satisfies the following Carathéodory's criterion : μ ∗ ( S ) = μ ∗ ( S ∩ M ) + μ ∗ ( S ∩ M c ) for every subset S ⊆ Ω , {\displaystyle \mu ^{*}(S)=\mu ^{*}(S\cap M)+\mu ^{*}(S\cap M^{\mathrm {c} })\quad {\text{ for every subset }}S\subseteq \Omega ,} where M c := Ω ∖ M {\displaystyle M^{\mathrm {c} }:=\Omega \setminus M} is the complement of M . {\displaystyle M.}
The family of all μ ∗ {\displaystyle \mu ^{*}} –measurable subsets is a σ-algebra and the restriction of the outer measure μ ∗ {\displaystyle \mu ^{*}} to this family is a measure .
Proofs | https://en.wikipedia.org/wiki/Set_function |
In mathematics , set inversion is the problem of characterizing the preimage X of a set Y by a function f , i.e., X = f −1 ( Y ) = { x ∈ R n | f ( x ) ∈ Y }. It can also be viewed as the problem of describing the solution set of the quantified constraint " Y ( f ( x ))", where Y ( y ) is a constraint, e.g. an inequality , describing the set Y .
In most applications, f is a function from R n to R p and the set Y is a box of R p (i.e. a Cartesian product of p intervals of R ).
When f is nonlinear the set inversion problem can be solved [ 1 ] using interval analysis combined with a branch-and-bound algorithm. [ 2 ]
The main idea consists in building a paving of R p made with non-overlapping boxes. For each box [ x ], we perform the following tests:
To check the two first tests, we need an interval extension (or an inclusion function) [ f ] for f . Classified boxes are stored into subpavings , i.e., union of non-overlapping boxes.
The algorithm can be made more efficient by replacing the inclusion tests by contractors .
The set X = f −1 ([4,9]) where f ( x 1 , x 2 ) = x 2 1 + x 2 2 is represented on the figure.
For instance, since [−2,1] 2 + [4,5] 2 = [0,4] + [16,25] = [16,29] does not intersect the interval [4,9], we conclude that the box [−2,1] × [4,5] is outside X . Since [−1,1] 2 + [2, √ 5 ] 2 = [0,1] + [4,5] = [4,6] is inside [4,9], we conclude that the whole box [−1,1] × [2, √ 5 ] is inside X .
Set inversion is mainly used for path planning , for nonlinear parameter set estimation , [ 3 ] [ 4 ] for localization [ 5 ] [ 6 ] or for the characterization of stability domains of linear dynamical systems . [ 7 ] | https://en.wikipedia.org/wiki/Set_inversion |
Set packing is a classical NP-complete problem in computational complexity theory and combinatorics , and was one of Karp's 21 NP-complete problems . Suppose one has a finite set S and a list of subsets of S . Then, the set packing problem asks if some k subsets in the list are pairwise disjoint (in other words, no two of them share an element).
More formally, given a universe U {\displaystyle {\mathcal {U}}} and a family S {\displaystyle {\mathcal {S}}} of subsets of U {\displaystyle {\mathcal {U}}} , a packing is a subfamily C ⊆ S {\displaystyle {\mathcal {C}}\subseteq {\mathcal {S}}} of sets such that all sets in C {\displaystyle {\mathcal {C}}} are pairwise disjoint. The size of the packing is | C | {\displaystyle |{\mathcal {C}}|} . In the set packing decision problem , the input is a pair ( U , S ) {\displaystyle ({\mathcal {U}},{\mathcal {S}})} and an integer t {\displaystyle t} ; the question is whether
there is a set packing of size t {\displaystyle t} or more. In the set packing optimization problem , the input is a pair ( U , S ) {\displaystyle ({\mathcal {U}},{\mathcal {S}})} , and the task is to find a set packing that uses the most sets.
The problem is clearly in NP since, given t {\displaystyle t} subsets, we can easily verify that they are pairwise disjoint in polynomial time .
The optimization version of the problem, maximum set packing , asks for the maximum number of pairwise disjoint sets in the list. It is a maximization problem that can be formulated naturally as an integer linear program , belonging to the class of packing problems .
The maximum set packing problem can be formulated as the following integer linear program .
The set packing problem is not only NP-complete, but its optimization version (general maximum set packing problem) has been proven as difficult to approximate as the maximum clique problem ; in particular, it cannot be approximated within any constant factor. [ 1 ] The best known algorithm approximates it within a factor of O ( | U | ) {\displaystyle O({\sqrt {|{\mathcal {U}}|}})} . [ 2 ] The weighted variant can also be approximated as well. [ 3 ]
The problem does have a variant which is more tractable. Given any positive integer k ≥3, the k -set packing problem is a variant of set packing in which each set contains at most k elements.
When k =1, the problem is trivial. When k =2, the problem is equivalent to finding a maximum cardinality matching , which can be solved in polynomial time.
For any k ≥3, the problem is NP-hard, as it is more general than 3-dimensional matching . However, there are constant-factor approximation algorithms :
In another more tractable variant, if no element occurs in more than d of the subsets, the answer can be approximated within a factor of d . This is also true for the weighted version.
Hypergraph matching is equivalent to set packing: the sets correspond to the hyperedges.
The independent set problem is also equivalent to set packing – there is a one-to-one polynomial-time reduction between them:
This is also a bidirectional PTAS reduction , and it shows that the two problems are equally difficult to approximate.
In the special case when each set contains at most k elements (the k-set packing problem ), the intersection graph is ( k +1)- claw-free . This is because, if a set intersects some k +1 sets, then at least two of these sets intersect, so there cannot be a ( k +1)-claw. So Maximum Independent Set in claw-free graphs [ 6 ] can be seen as a generalization of Maximum k -Set Packing.
Graph matching is a special case of set packing in which the size of all sets is 2 (the sets correspond to the edges). In this special case, a maximum-size matching can be found in polynomial time.
3-dimensional matching is a special case in which the size of all sets is 3, and in addition, the elements are partitioned into 3 colors and each set contains exactly one element of each color. This special case is still NP-hard, though it has better constant-factor approximation algorithms than the general case.
In the set cover problem , we are given a family S {\displaystyle {\mathcal {S}}} of subsets of a universe U {\displaystyle {\mathcal {U}}} , and the goal is to determine whether we can choose t sets that together contain every element of U {\displaystyle {\mathcal {U}}} . These sets may overlap. The optimization version finds the minimum number of such sets. The maximum set packing need not cover every possible element.
In the exact cover problem, every element of U {\displaystyle {\mathcal {U}}} should be contained in exactly one of the subsets. Finding such an exact cover is an NP-complete problem, even in the special case in which the size of all sets is 3 (this special case is called exact 3 cover or X3C ). However, if we create a singleton set for each element of S and add these to the list, the resulting problem is about as easy as set packing.
Karp originally showed set packing NP-complete via a reduction from the clique problem . | https://en.wikipedia.org/wiki/Set_packing |
In computer science and information theory , set redundancy compression are methods of data compression that exploits redundancy between individual data groups of a set, usually a set of similar images.
It is wide used on medical and satellital images. [ 1 ] [ 2 ] [ 3 ] [ 4 ] The main methods are min-max differential , min-max predictive and centroid method .
In the min-max differential (or MMD ), for each position (pixel) selects the highest or the lowest. And then in each image is stored the difference of each of their positions with respect to the value previously selected. | https://en.wikipedia.org/wiki/Set_redundancy_compression |
Seth Lloyd (born August 2, 1960) is a professor of mechanical engineering and physics at the Massachusetts Institute of Technology .
His research area is the interplay of information with complex systems , especially quantum systems. He has performed seminal work in the fields of quantum computation , quantum communication and quantum biology , including proposing the first technologically feasible design for a quantum computer , demonstrating the viability of quantum analog computation, proving quantum analogs of Shannon's noisy channel theorem , and designing novel methods for quantum error correction and noise reduction. [ 1 ]
Lloyd was born on August 2, 1960. He graduated from Phillips Academy in 1978 and received a bachelor of arts degree from Harvard College in 1982. He earned a certificate of advanced study in mathematics and a master of philosophy degree from Cambridge University in 1983 and 1984, while on a Marshall Scholarship . [ 2 ] Lloyd was awarded a doctorate by Rockefeller University in 1988 (advisor Heinz Pagels ) after submitting a thesis on Black Holes, Demons, and the Loss of Coherence: How Complex Systems Get Information, and What They Do With It.
From 1988 to 1991, Lloyd was a postdoctoral fellow in the High Energy Physics Department at the California Institute of Technology , where he worked with Murray Gell-Mann on applications of information to quantum-mechanical systems. From 1991 to 1994, he was a postdoctoral fellow at Los Alamos National Laboratory , where he worked at the Center for Nonlinear Systems on quantum computation. In 1994, he joined the faculty of the Department of Mechanical Engineering at MIT . Starting in 1988, Lloyd was an external faculty member at the Santa Fe Institute for more than 30 years.
In his 2006 book, Programming the Universe , Lloyd contends that the universe itself is one big quantum computer producing what we see around us, and ourselves, as it runs a cosmic program . According to Lloyd, once we understand the laws of physics completely, we will be able to use small-scale quantum computing to understand the universe completely as well.
Lloyd states that we could have the whole universe simulated in a computer in 600 years provided that computational power increases according to Moore's Law . [ 3 ] However, Lloyd shows that there are limits to rapid exponential growth in a finite universe, and that it is very unlikely that Moore's Law will be maintained indefinitely.
Lloyd directs the Center for Extreme Quantum Information Theory (xQIT) at MIT. [ 4 ] He has made influential contributions to a broad range of topics, mostly in the wider field of quantum information science . Among his most cited works are the first proposal for a digital quantum simulator , [ 5 ] a general framework for quantum metrology , [ 6 ] the first treatment of quantum computation with continuous variables , [ 7 ] dynamical decoupling as a method of quantum error avoidance, [ 8 ] quantum algorithms for equation solving [ 9 ] and machine learning [ 10 ] [ 11 ] or research on the possible relevance of quantum effects in biological phenomena, especially photosynthesis , [ 12 ] [ 13 ] [ 14 ] an effect he has also collaborated to exploit technologically. [ 15 ]
According to Clarivate he had in July 2023 in total 199 peer-reviewed publications which were cited more than 22,600 times leading to an h index of 61. [ 16 ]
During July 2019, reports surfaced that MIT and other institutions had accepted funding from convicted sex offender Jeffrey Epstein . [ 17 ] In the ensuing scandal, [ 18 ] the director of the MIT Media Lab , Joi Ito , resigned from MIT as a result of his association with Epstein. [ 19 ] Lloyd's connections to Epstein also drew criticism: Lloyd had acknowledged receiving funding from Epstein in 19 of his papers. [ 20 ] On August 22, 2019, Lloyd published a letter [ 21 ] apologizing for accepting grants (totaling $225,000) from Epstein. Despite this, the controversy continued. [ 22 ] [ 23 ] [ 24 ] In January 2020, at the request of the MIT Corporation , the law firm Goodwin Procter issued a report [ 18 ] on all of MIT's interactions with Epstein. As a result of the report, on January 10, 2020, Lloyd was placed on paid administrative leave . [ 25 ] Lloyd has vigorously denied that he misled MIT about the source of the funds he received from Epstein. [ 26 ] This denial was validated by a subsequent MIT investigation that concluded that Lloyd did not attempt to circumvent the MIT vetting process, nor try to conceal the name of the donor, and Lloyd was allowed to continue his tenured faculty position at MIT. [ 27 ] However, most but not all members of MIT's fact-finding committee concluded that Lloyd had violated MIT's conflict of interest policy by not revealing crucial publicly known information about Epstein's background to MIT, as a result of which Lloyd will be subject to a series of administrative actions for 5 years. [ 27 ] | https://en.wikipedia.org/wiki/Seth_Lloyd |
In mathematics , a setoid ( X , ~) is a set (or type ) X equipped with an equivalence relation ~. A setoid may also be called E-set , Bishop set , or extensional set . [ 1 ]
Setoids are studied especially in proof theory and in type-theoretic foundations of mathematics . Often in mathematics, when one defines an equivalence relation on a set, one immediately forms the quotient set (turning equivalence into equality ). In contrast, setoids may be used when a difference between identity and equivalence must be maintained, often with an interpretation of intensional equality (the equality on the original set) and extensional equality (the equivalence relation, or the equality on the quotient set).
In proof theory, particularly the proof theory of constructive mathematics based on the Curry–Howard correspondence , one often identifies a mathematical proposition with its set of proofs (if any). A given proposition may have many proofs, of course; according to the principle of proof irrelevance, normally only the truth of the proposition matters, not which proof was used. However, the Curry–Howard correspondence can turn proofs into algorithms , and differences between algorithms are often important. So proof theorists may prefer to identify a proposition with a setoid of proofs, considering proofs equivalent if they can be converted into one another through beta conversion or the like.
In type-theoretic foundations of mathematics, setoids may be used in a type theory that lacks quotient types to model general mathematical sets. For example, in Per Martin-Löf 's intuitionistic type theory , there is no type of real numbers , only a type of regular Cauchy sequences of rational numbers . To do real analysis in Martin-Löf's framework, therefore, one must work with a setoid of real numbers, the type of regular Cauchy sequences equipped with the usual notion of equivalence. Predicates and functions of real numbers need to be defined for regular Cauchy sequences and proven to be compatible with the equivalence relation. Typically (although it depends on the type theory used), the axiom of choice will hold for functions between types (intensional functions), but not for functions between setoids (extensional functions). [ clarification needed ] The term "set" is variously used either as a synonym of "type" or as a synonym of "setoid". [ 2 ]
In constructive mathematics , one often takes a setoid with an apartness relation instead of an equivalence relation, called a constructive setoid. One sometimes also considers a partial setoid using a partial equivalence relation or partial apartness (see e.g. Barthe et al. , section 1). | https://en.wikipedia.org/wiki/Setoid |
In cybernetics and control theory , a setpoint ( SP ; [ 1 ] also set point ) is the desired or target value for an essential variable, or process value (PV) of a control system , [ 2 ] which may differ from the actual measured value of the variable. Departure of such a variable from its setpoint is one basis for error-controlled regulation using negative feedback for automatic control. [ 3 ] A setpoint can be any physical quantity or parameter that a control system seeks to regulate, such as temperature, pressure, flow rate, position, speed, or any other measurable attribute.
In the context of PID controller , the setpoint represents the reference or goal for the controlled process variable. It serves as the benchmark against which the actual process variable (PV) is continuously compared. The PID controller calculates an error signal by taking the difference between the setpoint and the current value of the process variable . Mathematically, this error is expressed as:
where e ( t ) {\displaystyle e(t)} is the error at a given time t {\displaystyle t} , S P {\displaystyle SP} is the setpoint, P V ( t ) {\displaystyle PV(t)} is the process variable at time t {\displaystyle t} .
The PID controller uses this error signal to determine how to adjust the control output to bring the process variable as close as possible to the setpoint while maintaining stability and minimizing overshoot .
Cruise control
The S P − P V {\displaystyle SP-PV} error can be used to return a system to its norm. An everyday example is the cruise control on a road vehicle; where external influences such as gradients cause speed changes (PV), and the driver also alters the desired set speed (SP). The automatic control algorithm restores the actual speed to the desired speed in the optimum way, without delay or overshoot, by altering the power output of the vehicle's engine. In this way the S P − P V {\displaystyle SP-PV} error is used to control the PV so that it equals the SP. A widespread of S P − P V {\displaystyle SP-PV} error is classically used in the PID controller .
Industrial applications
Special consideration must be given for engineering applications. In industrial systems, physical or process restraints may limit the determined set point. For example, a reactor which operates more efficiently at higher temperatures may be rated to withstand 500°C. However, for safety reasons, the set point for the reactor temperature control loop would be well below this limit, even if this means the reactor is running less efficiently.
This technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Setpoint_(control_system) |
Setsuban Kanri (節番管理) is the name of a production management methodology for make-to-order business companies. [ 1 ] More specifically, it indicates a "management system by synchronized process blocks" which had been originally set and implemented as a management model for the control of the manufacturing progress with makers whose products were very much tailored upon the requests of their customers. It is specific to organizations where the production model is one of the following: DTO ("Design-to-order"), ETO ("Engineer-to-order"), ATO ("Assembly-to-order") or MTO ("Make-to-order").
The first applications of this model concerned the Japanese railways and the aviation industry, which in the operational management of activities had been referring to a block by block workflow progress management system (what is meant literally by the expression "suishin kusei kōtei kanri" 推進区制工程管理).
This one was the root of the so-called Oiban kanri for series production management, of the Seiban kanri for discontinuous productions and of the Setsuban Kanri for make-to-order productions. The study and formalization of this threefold approach were run later on by JMA – the Japan Management Association , who could base their work on the most significant industrial experiences to date (such as the application of the oiban kanri at Kawasaki Heavy Industries ). Besides, they could enrich and tune the methodological contents with specific implementation tools and gave meaningful contributions to the definition of the methodology itself, which was named Setsuban Kanri from the reading of the ideographic characters 節 (setsu = period/temporal unit) and 番 (ban = ordinal number) + 管理 (kanri = management, control).
Employed until the 1970s in many companies operating as make-to-order in Japan , for some decades it has fallen out of practice and knowledge. Since 2006, thanks to the direct initiative of Akira Kōdate , a Japanese engineer who launched it and promoted its application in Italy with JMAC Europe. Its name had a revival and it is now being adopted by several companies (among machine tools makers especially).
The basic principles of the Setsuban Kanri are:
1. Awareness of both the "axes" (nijiku kanri 二軸管理) to be managed .
Make-order productions need a continuous monitoring to grant for integration and fair balance in-between the following:
a. the X axis represents the made-to-order flow, where attention must be paid to quality , cost , time , and customer satisfaction issues per each order, throughout all work phases – from the order receipt to the delivery to customer.
b. the Y axis represents the department/function where attention should be paid in managing the load/capacity, know-how and priorities to complete all the orders which go through a single dept./function.
The targets for every order can be achieved only by managing at the same time both axes according to a production plan which allows the various production flows get synchronized one another. Actually, the current Project Management practices generally result too unbalanced on the X axis; the normal practices of production management , on the contrary, tend to focus almost exclusively to the governance of the Y axis.
2. Synchronization .
It is like what happens with the Japanese railway system: the on time arrival of trains is not granted by forcing a check on each single train on the run. Instead, it is the result of careful synchronization of the entry and departure of all the trains from/to each railway station. Each train is considered with reference to the train running before and the one to follow. That is to say that the sequence can be effectively managed only by synchronizing the entire system and verifying the consistency among the drawings release plan, the supply plan and the production plan.
3. Backward planning starting from point zero .
Every single order must be planned backwards starting prom a point zero (the point after which it is no longer necessary to have processes monitored because there is a minimum risk of jamming). Choosing a reference time unit called Setsuban (can be days, weeks, decades or months), a number of time units are accounted for in the calendar and the duration of each stage in the working flow is fixed accordingly, and referred to by using delivery indicators called teban (see below).
4. The fourfold multilevel planning .
The planning system consists of 4 levels:
a. Level 0 or portfolio planning : all orders to all departments/functions
b. Level 1 or make-to-order planning : each order through all departments
c. Level 2 or department planning : all the orders with each department/function
d. Level 3 or block planning : plan by block, that is a set of activities related to every single order being realized inside a single department/function.
Workflow progress block (Suishin-ku 推進区):
A set of activities realized for a production order within the department or office where a person is clearly identified to be in charge of the correct (qualitative) completion and of meeting the production plan as well.
Reference time unit (Setsuban 節番):
The unit in which the time available is divided and the basis on which the plan is organized. For simplicity the week is generally preferred (the work shift or a period of time – e.g. 10 days – can be chosen instead).
Delivery turn (Teban手番):
The number showing the moment of time when the object planned should reach or leave a specific division or office (e.g. piece to be worked at dept. Y supposed to get in the dept. at teban 23 and to leave the same department at teban 25).
Workflow progress assistant (Shinkōin 進行員):
The person in charge of the due progress of the job /activity block in the department where the part/product is being manufactured. It is not necessarily an assigned job role, as it can be performed by the shift leader, by the head of department, by single operators or even by the in-house logistic workforce (e.g. the forklift operator).
The management system (Suishin kusei kōtei kanri 推進区制工程管理):
The true name of the organizational and managerial system and the concept the "setsuban kanri" has been referring to from its origins. The term refers to the set of processes, roles, coordination mechanisms and supporting visual tools which allow the management of processes/organizational functions by "blocks of stepping progress (advancement)".
One of the founding principles of Setsuban Kanri is that the work progress control can take place only by combining to electronic tools some visual tools the use of which is the closest possible to the physical place where things happen (e.g. Assembly Dept., R&D office). Four types of tools are used:
• Tools for controlling the quality, cost, time, and customer satisfaction progress over each order for all the y axes
• Tools for managing the workload and capacity, priorities and competences through all the y axes
• Tools for synchronization and portfolio control (e.g. Portfolio plans, aggregated KPIs , etc.)
• Tools for the know-how retrieval and for the execution speed-up of each activity.
The method shares many aspects with the Lean Thinking techniques. Inspired by the Toyota Production System (TPS), it facilitates the application of the same approach to make-to-order business companies, while overcoming some of its limits. As a matter of fact, the Setsuban Kanri is adopting approaches which meet the needs of discontinuous production, high product customization and strict cross-relation among the sale, design and production phases. | https://en.wikipedia.org/wiki/Setsuban_Kanri |
Settling is the process by which particulates move towards the bottom of a liquid and form a sediment . Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force. For gravity settling, this means that the particles will tend to fall to the bottom of the vessel, forming sludge or slurry at the vessel base.
Settling is an important operation in many applications, such as mining , wastewater and drinking water treatment, biological science, space propellant reignition, [ 1 ] and scooping.
For settling particles that are considered individually, i.e. dilute particle solutions, there are two main forces enacting upon any particle. The primary force is an applied force, such as gravity, and a drag force that is due to the motion of the particle through the fluid . The applied force is usually not affected by the particle's velocity, whereas the drag force is a function of the particle velocity.
For a particle at rest no drag force will be exhibited, which causes the particle to accelerate due to the applied force. When the particle accelerates, the drag force acts in the direction opposite to the particle's motion, retarding further acceleration, in the absence of other forces drag directly opposes the applied force. As the particle increases in velocity eventually the drag force and the applied force will approximately equate , causing no further change in the particle's velocity. This velocity is known as the terminal velocity , settling velocity or fall velocity of the particle. This is readily measurable by examining the rate of fall of individual particles.
The terminal velocity of the particle is affected by many parameters, i.e. anything that will alter the particle's drag. Hence the terminal velocity is most notably dependent upon grain size , the shape (roundness and sphericity) and density of the grains, as well as to the viscosity and density of the fluid.
For dilute suspensions, Stokes' law predicts the settling velocity of small spheres in fluid , either air or water. This originates due to the strength of viscous forces at the surface of the particle providing the majority of the retarding force. Stokes' law finds many applications in the natural sciences, and is given by:
where w is the settling velocity, ρ is density (the subscripts p and f indicate particle and fluid respectively), g is the acceleration due to gravity, r is the radius of the particle and μ is the dynamic viscosity of the fluid.
Stokes' law applies when the Reynolds number , Re, of the particle is less than 0.1. Experimentally Stokes' law is found to hold within 1% for R e ≤ 0.1 {\displaystyle Re\leq 0.1} , within 3% for R e ≤ 0.5 {\displaystyle Re\leq 0.5} and within 9% R e ≤ 1.0 {\displaystyle Re\leq 1.0} . [ 2 ] With increasing Reynolds numbers, Stokes law begins to break down due to the increasing importance of fluid inertia, requiring the use of empirical solutions to calculate drag forces.
Defining a drag coefficient , C d {\displaystyle C_{d}} , as the ratio of the force experienced by the particle divided by the impact pressure of the fluid, a coefficient that can be considered as the transfer of available fluid force into drag is established. In this region the inertia of the impacting fluid is responsible for the majority of force transfer to the particle.
For a spherical particle in the Stokes regime this value is not constant, however in the Newtonian drag regime the drag on a sphere can be approximated by a constant, 0.44. This constant value implies that the efficiency of transfer of energy from the fluid to the particle is not a function of fluid velocity.
As such the terminal velocity of a particle in a Newtonian regime can again be obtained by equating the drag force to the applied force, resulting in the following expression
In the intermediate region between Stokes drag and Newtonian drag, there exists a transitional regime, where the analytical solution to the problem of a falling sphere becomes problematic. To solve this, empirical expressions are used to calculate drag in this region. One such empirical equation is that of Schiller and Naumann, and may be valid for 0.2 ≤ R e ≤ 1000 {\displaystyle 0.2\leq Re\leq 1000} : [ 3 ]
Stokes, transitional and Newtonian settling describe the behaviour of a single spherical particle in an infinite fluid, known as free settling. However this model has limitations in practical application. Alternate considerations, such as the interaction of particles in the fluid, or the interaction of the particles with the container walls can modify the settling behaviour. Settling that has these forces in appreciable magnitude is known as hindered settling. Subsequently, semi-analytic or empirical solutions may be used to perform meaningful hindered settling calculations.
The solid-gas flow systems are present in many industrial applications, as dry, catalytic reactors, settling tanks, pneumatic conveying of solids, among others. Obviously, in industrial operations the drag rule is not simple as a single sphere settling in a stationary fluid. However, this knowledge indicates how drag behaves in more complex systems, which are designed and studied by engineers applying empirical and more sophisticated tools.
For example, 'settling tanks ' are used for separating solids and/or oil from another liquid. In food processing , the vegetable is crushed and placed inside of a settling tank with water. The oil floats to the top of the water then is collected. In drinking water and waste water treatment a flocculant or coagulant is often added prior to settling to form larger particles that settle out quickly in a settling tank or ( lamella ) clarifier , leaving the water with a lower turbidity .
In winemaking , the French term for this process is débourbage . This step usually occurs in white wine production before the start of fermentation . [ 4 ]
Settleable solids are the particulates that settle out of a still fluid. Settleable solids can be quantified for a suspension using an Imhoff cone. The standard Imhoff cone of transparent glass or plastic holds one liter of liquid and has calibrated markings to measure the volume of solids accumulated in the bottom of the conical container after settling for one hour. A standardized Imhoff cone procedure is commonly used to measure suspended solids in wastewater or stormwater runoff . The simplicity of the method makes it popular for estimating water quality . To numerically gauge the stability of suspended solids and predict agglomeration and sedimentation events, zeta potential is commonly analyzed. This parameter indicates the electrostatic repulsion between solid particles and can be used to predict whether aggregation and settling will occur over time.
The water sample to be measured should be representative of the total stream. Samples are best collected from the discharge falling from a pipe or over a weir, because samples skimmed from the top of a flowing channel may fail to capture larger, high-density solids moving along the bottom of the channel. The sampling bucket is vigorously stirred to uniformly re-suspend all collected solids immediately before pouring the volume required to fill the cone. The filled cone is immediately placed in a stationary holding rack to allow quiescent settling. The rack should be located away from heating sources, including direct sunlight, which might cause currents within the cone from thermal density changes of the liquid contents. After 45 minutes of settling, the cone is partially rotated about its axis of symmetry just enough to dislodge any settled material adhering to the side of the cone. Accumulated sediment is observed and measured fifteen minutes later, after one hour of total settling time. [ 5 ] | https://en.wikipedia.org/wiki/Settleable_solids |
Settlement is the downward movement or the sinking of a structure's foundation . It is mostly caused by changes in the underlying soil, such as drying and shrinking, wetting and softening, or compression due to the soil being poorly compacted when construction started. [ 1 ] Some settlement is quite normal after construction has been completed.
Unequal settlement or differential settlement is non-uniform settlement. It may cause significant problems for buildings. Distortion or disruption of parts of a building may occur due to
Settlement should not be confused with subsidence which results from the load-bearing ground upon which a building sits reducing in level, for instance in areas of mine workings where shafts collapse underground.
Traditional green oak-framed buildings are designed to settle with time as the oak seasons and warps, lime mortar rather than Portland cement is used for its elastic properties and glazing will often employ small leaded lights which can accept movement more readily than larger panes.
The magnitude of settlements can be measured using different techniques such as: | https://en.wikipedia.org/wiki/Settlement_(structural) |
Settling is the process by which particulates move towards the bottom of a liquid and form a sediment . Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force. For gravity settling, this means that the particles will tend to fall to the bottom of the vessel, forming sludge or slurry at the vessel base.
Settling is an important operation in many applications, such as mining , wastewater and drinking water treatment, biological science, space propellant reignition, [ 1 ] and scooping.
For settling particles that are considered individually, i.e. dilute particle solutions, there are two main forces enacting upon any particle. The primary force is an applied force, such as gravity, and a drag force that is due to the motion of the particle through the fluid . The applied force is usually not affected by the particle's velocity, whereas the drag force is a function of the particle velocity.
For a particle at rest no drag force will be exhibited, which causes the particle to accelerate due to the applied force. When the particle accelerates, the drag force acts in the direction opposite to the particle's motion, retarding further acceleration, in the absence of other forces drag directly opposes the applied force. As the particle increases in velocity eventually the drag force and the applied force will approximately equate , causing no further change in the particle's velocity. This velocity is known as the terminal velocity , settling velocity or fall velocity of the particle. This is readily measurable by examining the rate of fall of individual particles.
The terminal velocity of the particle is affected by many parameters, i.e. anything that will alter the particle's drag. Hence the terminal velocity is most notably dependent upon grain size , the shape (roundness and sphericity) and density of the grains, as well as to the viscosity and density of the fluid.
For dilute suspensions, Stokes' law predicts the settling velocity of small spheres in fluid , either air or water. This originates due to the strength of viscous forces at the surface of the particle providing the majority of the retarding force. Stokes' law finds many applications in the natural sciences, and is given by:
where w is the settling velocity, ρ is density (the subscripts p and f indicate particle and fluid respectively), g is the acceleration due to gravity, r is the radius of the particle and μ is the dynamic viscosity of the fluid.
Stokes' law applies when the Reynolds number , Re, of the particle is less than 0.1. Experimentally Stokes' law is found to hold within 1% for R e ≤ 0.1 {\displaystyle Re\leq 0.1} , within 3% for R e ≤ 0.5 {\displaystyle Re\leq 0.5} and within 9% R e ≤ 1.0 {\displaystyle Re\leq 1.0} . [ 2 ] With increasing Reynolds numbers, Stokes law begins to break down due to the increasing importance of fluid inertia, requiring the use of empirical solutions to calculate drag forces.
Defining a drag coefficient , C d {\displaystyle C_{d}} , as the ratio of the force experienced by the particle divided by the impact pressure of the fluid, a coefficient that can be considered as the transfer of available fluid force into drag is established. In this region the inertia of the impacting fluid is responsible for the majority of force transfer to the particle.
For a spherical particle in the Stokes regime this value is not constant, however in the Newtonian drag regime the drag on a sphere can be approximated by a constant, 0.44. This constant value implies that the efficiency of transfer of energy from the fluid to the particle is not a function of fluid velocity.
As such the terminal velocity of a particle in a Newtonian regime can again be obtained by equating the drag force to the applied force, resulting in the following expression
In the intermediate region between Stokes drag and Newtonian drag, there exists a transitional regime, where the analytical solution to the problem of a falling sphere becomes problematic. To solve this, empirical expressions are used to calculate drag in this region. One such empirical equation is that of Schiller and Naumann, and may be valid for 0.2 ≤ R e ≤ 1000 {\displaystyle 0.2\leq Re\leq 1000} : [ 3 ]
Stokes, transitional and Newtonian settling describe the behaviour of a single spherical particle in an infinite fluid, known as free settling. However this model has limitations in practical application. Alternate considerations, such as the interaction of particles in the fluid, or the interaction of the particles with the container walls can modify the settling behaviour. Settling that has these forces in appreciable magnitude is known as hindered settling. Subsequently, semi-analytic or empirical solutions may be used to perform meaningful hindered settling calculations.
The solid-gas flow systems are present in many industrial applications, as dry, catalytic reactors, settling tanks, pneumatic conveying of solids, among others. Obviously, in industrial operations the drag rule is not simple as a single sphere settling in a stationary fluid. However, this knowledge indicates how drag behaves in more complex systems, which are designed and studied by engineers applying empirical and more sophisticated tools.
For example, 'settling tanks ' are used for separating solids and/or oil from another liquid. In food processing , the vegetable is crushed and placed inside of a settling tank with water. The oil floats to the top of the water then is collected. In drinking water and waste water treatment a flocculant or coagulant is often added prior to settling to form larger particles that settle out quickly in a settling tank or ( lamella ) clarifier , leaving the water with a lower turbidity .
In winemaking , the French term for this process is débourbage . This step usually occurs in white wine production before the start of fermentation . [ 4 ]
Settleable solids are the particulates that settle out of a still fluid. Settleable solids can be quantified for a suspension using an Imhoff cone. The standard Imhoff cone of transparent glass or plastic holds one liter of liquid and has calibrated markings to measure the volume of solids accumulated in the bottom of the conical container after settling for one hour. A standardized Imhoff cone procedure is commonly used to measure suspended solids in wastewater or stormwater runoff . The simplicity of the method makes it popular for estimating water quality . To numerically gauge the stability of suspended solids and predict agglomeration and sedimentation events, zeta potential is commonly analyzed. This parameter indicates the electrostatic repulsion between solid particles and can be used to predict whether aggregation and settling will occur over time.
The water sample to be measured should be representative of the total stream. Samples are best collected from the discharge falling from a pipe or over a weir, because samples skimmed from the top of a flowing channel may fail to capture larger, high-density solids moving along the bottom of the channel. The sampling bucket is vigorously stirred to uniformly re-suspend all collected solids immediately before pouring the volume required to fill the cone. The filled cone is immediately placed in a stationary holding rack to allow quiescent settling. The rack should be located away from heating sources, including direct sunlight, which might cause currents within the cone from thermal density changes of the liquid contents. After 45 minutes of settling, the cone is partially rotated about its axis of symmetry just enough to dislodge any settled material adhering to the side of the cone. Accumulated sediment is observed and measured fifteen minutes later, after one hour of total settling time. [ 5 ] | https://en.wikipedia.org/wiki/Settling |
A settling basin , settling pond or decant pond is an earthen or concrete structure using sedimentation to remove settleable matter and turbidity from wastewater . The basins are used to control water pollution in diverse industries such as agriculture , [ 1 ] aquaculture , [ 2 ] and mining . [ 3 ] [ 4 ] Turbidity is an optical property of water caused by scattering of light by material suspended in that water. Although turbidity often varies directly with weight or volumetric measurements of settleable matter, correlation is complicated by variations in size, shape, refractive index , and specific gravity of suspended matter. [ 5 ] Settling ponds may be ineffective at reducing turbidity caused by small particles with specific gravity low enough to be suspended by Brownian motion . [ 6 ]
Settling basins are used as a separation mechanism to eliminate rejected products (i.e. waste solids management strategies) of a specified size and quantity in various fields, such as aquaculture, mining, dairy, food processing, alcohol production and wine making. Regular draining and desilting of settling basins is required to maintain satisfactory performance. [ 7 ]
All materials not removed from the system during harvesting are categorized as wastes including uneaten feed, excreta, chemicals and therapeutics, dead and moribund fish, escaped fish and pathogens. Settling basins in the field are simple ponds dug downstream of the farm to optimally remove suspended solids effectively, produce clarified effluent, and accumulate and thicken sludge to minimal volume. If impairment occurs in any of these functions, this might have a great impact on pond performance, which could lead to damaging the effectiveness of the process. [ 8 ]
Wastewater produced by mining industries contribute to the acidity, suspended material and dissolved heavy metal ions in the aquatic environment, causing environmental problems for biological life and discoloration of the receiving waters. The application of settling basins by the Coeur d'Alene mining district of northern Idaho, United States, globally known to produce lead, zinc and silver, to treat wastewater has greatly improved the quality of water discharge from mining operations. [ 9 ]
By reducing flow velocity to limit solids being transported along with fast flowing liquid, separation can occur. Approximately 35–60% of the solids is removed from dilute liquid slurry, with 10 minutes detention time, with a common detention time of 30 to 60 minutes. Due to the inadequate consideration of critical design criteria, most settling basins built were oversized and had low efficiency. [ 10 ]
Settling basins used in dairy production reduce the nutrient-loading on a vegetative filter strip from lot runoff, thus decreasing the required lagoon volume for a new facility. Moreover, settling basins are useful to remove unwanted solid materials, such as hay, straw and feathers from the waste stream before flowing to the lagoon, aids to reduce smell and avoid crust formation on the lagoon surface. A baffle may be used to retain the floating solids removed. There are two types of settling basins, based on the method of removing solids. With one type, the solids are removed mechanically (after the free water has drained away), usually with a front-end or skid-steer loader. The other type uses hydraulic (pump) removal of the solids. Typically, pumping is initiated when the basin is half full of solids and the remainder is water. Vigorous agitation is needed to mix the liquid and the solids, preferably by propeller-type agitators or pumps with agitation nozzles. [ 11 ]
Settling basins are designed to retain water long enough so that suspended solids can settle to obtain a high purity water in the outlet and to provide the opportunity for pH adjustment. [ 12 ] Other processes that could be used: thickeners, clarifiers, hydro cyclones and membrane filtration are highly used techniques in the field. [ 13 ] Compared to those processes, settling basins have a simpler and cheaper design, with fewer moving parts, demanding less maintenance, despite requiring cleaning and vacuuming of the quiescent zones at least once every two weeks.
However, settling basins can introduce new kinds of water contamination, particularly if the water supply is from a well. The basin can catch windblown contaminants, and if the water is retained for a long period, algae grows in the pool, leading to greater filtration problems. Settling ponds may also be ineffective at reducing turbidity caused by small particles with specific gravity low enough to be suspended by Brownian motion. Usually, it can only remove particles ranging from sand (2 mm in diameter) to silt (0.002 mm in diameter).
Wastewater enters the basin and very fine particles in the water are separated by means of gravity . The water must be in the basin long enough for the desired particle size to be removed. Smaller particles require longer periods for removal and thus larger basins. In some basins a flocculant may be added to help smaller particles stick together and form larger particles. Stokes' law can be used to calculate the size of a settling basin needed in order to remove a desired particle size. Stokes' law gives a settling velocity determining an effective settling basin depth; so solids removal depends upon effective settling basin surface area, while the depth component of settling basin volume remains important for storage of settled solids. [ 14 ]
Translation of required settling time surface area to settling basin geometry requires consideration of short circuiting and turbulence induced by wind, bottom scour, or inlet and overflow design. Settling basin geometry is important because effective time of settling within the basin will be the time a volume of water spends in non-turbulent conditions before reaching the settling basin overflow. Median time is always less than the mean time calculated by dividing available volume by anticipated flow. The median time of passage through a short, wide settling basin may be significantly less than that through a long, narrow settling basin. Settling basins with overflow structures near the entrance points may hold a large volume of stagnant water while newly admitted water rapidly reaches the overflow point before settling can occur. Effective surface area for settling seldom extends perpendicularly more than a tenth the distance of a flow line from basin entrance to overflow unless baffles are installed. [ 15 ] Effective surface area and geometry may change as accumulating sediment fills part of the originally constructed volume. Short cut channels may rapidly form through heavier sediment accumulations near the entrance to the settling basin. Flow through shallow portions of the settling basin may cause turbulence resuspending sediment from the bottom of the basin. Two feet has been recommended as a minimum settling basin depth to avoid bottom scour. [ 15 ] | https://en.wikipedia.org/wiki/Settling_basin |
The Seven Bridges of Königsberg is a historically notable problem in mathematics. Its negative resolution by Leonhard Euler , in 1736, [ 1 ] laid the foundations of graph theory and prefigured the idea of topology . [ 2 ]
The city of Königsberg in Prussia (now Kaliningrad , Russia ) was set on both sides of the Pregel River , and included two large islands— Kneiphof and Lomse —which were connected to each other, and to the two mainland portions of the city, by seven bridges. The problem was to devise a walk through the city that would cross each of those bridges once and only once.
By way of specifying the logical task unambiguously, solutions involving either
are explicitly unacceptable.
Euler proved that the problem has no solution. The difficulty he faced was the development of a suitable technique of analysis , and of subsequent tests that established this assertion with mathematical rigor.
Euler first pointed out that the choice of route inside each land mass is irrelevant and that the only important feature of a route is the sequence of bridges crossed. This allowed him to reformulate the problem in abstract terms (laying the foundations of graph theory ), eliminating all features except the list of land masses and the bridges connecting them. In modern terms, one replaces each land masses with an abstract " vertex " or node, and each bridge with an abstract connection, an " edge ", which only serves to record which pair of vertices (land masses) is connected by that bridge. The resulting mathematical structure is a graph .
→ →
Since only the connection information is relevant, the shape of pictorial representations of a graph may be distorted in any way, without changing the graph itself. Only the number of edges (possibly zero) between each pair of nodes is significant. It does not, for instance, matter whether the edges drawn are straight or curved, or whether one node is to the left or right of another.
Next, Euler observed that (except at the endpoints of the walk), whenever one enters a vertex by a bridge, one leaves the vertex by a bridge. In other words, during any walk in the graph, the number of times one enters a non-terminal vertex equals the number of times one leaves it. Now, if every bridge has been traversed exactly once, it follows that, for each land mass (except for the ones chosen for the start and finish), the number of bridges touching that land mass must be even (half of them, in the particular traversal, will be traversed "toward" the landmass; the other half, "away" from it). However, all four of the land masses in the original problem are touched by an odd number of bridges (one is touched by 5 bridges, and each of the other three is touched by 3). Since, at most, two land masses can serve as the endpoints of a walk, the proposition of a walk traversing each bridge once leads to a contradiction.
In modern language, Euler shows that the possibility of a walk through a graph, traversing each edge exactly once, depends on the degrees of the nodes. The degree of a node is the number of edges touching it. Euler's argument shows that a necessary condition for the walk of the desired form is that the graph be connected and have exactly zero or two nodes of odd degree. This condition turns out also to be sufficient—a result stated by Euler and later proved by Carl Hierholzer . Such a walk is now called an Eulerian trail or Euler walk in his honor. Further, if there are nodes of odd degree, then any Eulerian path will start at one of them and end at the other. Since the graph corresponding to historical Königsberg has four nodes of odd degree, it cannot have an Eulerian path.
An alternative form of the problem asks for a path that traverses all bridges and also has the same starting and ending point. Such a walk is called an Eulerian circuit or an Euler tour . Such a circuit exists if, and only if, the graph is connected and all nodes have even degree. All Eulerian circuits are also Eulerian paths, but not all Eulerian paths are Eulerian circuits.
Euler's work was presented to the St. Petersburg Academy on 26 August 1735, and published as Solutio problematis ad geometriam situs pertinentis (The solution of a problem relating to the geometry of position) in the journal Commentarii academiae scientiarum Petropolitanae in 1741. [ 3 ] It is available in English translation in The World of Mathematics by James R. Newman .
In the history of mathematics , Euler's solution of the Königsberg bridge problem is considered to be the first theorem of graph theory and the first true proof in the network theory , [ 4 ] a subject now generally regarded as a branch of combinatorics . Combinatorial problems of other types such as the enumeration of permutations and combinations had been considered since antiquity.
Euler's recognition that the key information was the number of bridges and the list of their endpoints (rather than their exact positions) presaged the development of topology . The difference between the actual layout and the graph schematic is a good example of the idea that topology is not concerned with the rigid shape of objects.
Hence, as Euler recognized, the "geometry of position" is not about "measurements and calculations" but about something more general. That called in question the traditional Aristotelian view that mathematics is the "science of quantity ". Though that view fits arithmetic and Euclidean geometry, it did not fit topology and the more abstract structural features studied in modern mathematics. [ 5 ]
Philosophers have noted that Euler's proof is not about an abstraction or a model of reality, but directly about the real arrangement of bridges. Hence the certainty of mathematical proof can apply directly to reality. [ 6 ] The proof is also explanatory, giving insight into why the result must be true. [ 7 ]
Two of the seven original bridges did not survive the bombing of Königsberg in World War II . Two others were later demolished and replaced by a highway. The three other bridges remain, although only two of them are from Euler's time (one was rebuilt in 1935). [ 8 ] These changes leave five bridges existing at the same sites that were involved in Euler's problem. In terms of graph theory, two of the nodes now have degree 2, and the other two have degree 3. Therefore, an Eulerian path is now possible, but it must begin on one island and end on the other. [ 9 ]
The University of Canterbury in Christchurch has incorporated a model of the bridges into a grass area between the old Physical Sciences Library and the Erskine Building, housing the Departments of Mathematics, Statistics and Computer Science. [ 10 ] The rivers are replaced with short bushes and the central island sports a stone tōrō . Rochester Institute of Technology has incorporated the puzzle into the pavement in front of the Gene Polisseni Center , an ice hockey arena that opened in 2014, [ 11 ] and the Georgia Institute of Technology also installed a landscape art model of the seven bridges in 2018. [ 12 ]
A popular variant of the puzzle is the Bristol Bridges Walk . [ 13 ] Like historical Königsberg, Bristol occupies two river banks and two river islands. [ 14 ] However, the configuration of the 45 major bridges in Bristol is such that an Eulerian circuit exists. [ 15 ] This cycle has been popularized by a book [ 15 ] and news coverage [ 16 ] [ 17 ] and has featured in different charity events. [ 18 ] | https://en.wikipedia.org/wiki/Seven_Bridges_of_Königsberg |
The seven management and planning tools have their roots in operations research work done after World War II and the Japanese total quality control (TQC) research. [ 1 ] [ 2 ]
Affinity diagrams are a special kind of brainstorming tool that organize large amount of disorganized data and information into groupings based on natural relationships.
It was created in the 1960s by the Japanese anthropologist Jiro Kawakita. It is also known as KJ diagram, after Jiro Kawakita. An affinity diagram is used when:
Interrelationship diagrams (IDs) displays all the interrelated cause-and-effect relationships and factors involved in a complex problem and describes desired outcomes. The process of creating an interrelationship diagram helps a group analyze the natural links between different aspects of a complex situation.
This tool is used to break down broad categories into finer and finer levels of detail. It can map levels of details of tasks that are required to accomplish a goal or solution or task. Developing a tree diagram directs concentration from generalities to specifics.
This tool is used to prioritize items and describe them in terms of weighted criteria. It uses a combination of tree and matrix diagramming techniques to do a pair-wise evaluation of items and to narrow down options to the most desired or most effective. Popular applications for the prioritization matrix include return on investment (ROI) or cost–benefit analysis (investment vs. return), time management matrix (urgency vs. importance), etc.
This tool shows the relationship between two or more sets of elements. At each intersection, a relationship is either absent or present. It then gives information about the relationship, such as its strength, the roles played by various individuals or measurements. The matrix diagram enables you to analyze relatively complex situations by exposing interactions and dependencies between things. Six differently shaped matrices are possible: L, T, Y, X, C, R and roof-shaped, depending on how many groups must be compared.
A useful way of planning is to break down tasks into a hierarchy, using a tree diagram. The process decision program chart (PDPC) extends the tree diagram a couple of levels to identify risks and countermeasures for the bottom level tasks. Different shaped boxes are used to highlight risks and identify possible countermeasures (often shown as "clouds" to indicate their uncertain nature). The PDPC is similar to the failure modes and effects analysis (FMEA) in that both identify risks, consequences of failure, and contingency actions; the FMEA also rates relative risk levels for each potential failure point.
This tool is used to plan the appropriate sequence or schedule for a set of tasks and related subtasks. It is used when subtasks must occur in parallel. The diagram helps in determining the critical path (longest sequence of tasks). The purpose is to help people sequentially define, organize, and manage a complex set of activities. | https://en.wikipedia.org/wiki/Seven_management_and_planning_tools |
The Sevenfold Sun Miracle was an atmospheric phenomenon witnessed in Gdańsk in 1661. It was a complex halo phenomenon , and was described by Georg Fehlau, the pastor of the St Marien church , in a sermon two weeks later, which was then published under the title Siebenfältiges Sonnenwunder oder sieben Nebensonnen, so in diesem 1661 Jahr den 20. Februar neuen Stils am Sonntage Sexagesima um 11 Uhr bis nach 12 am Himmel bei uns sind gesehen worden ("Sevenfold sun miracle or seven sun dogs which were seen in our skies on Sexagesima Sunday, 20th of February of the year 1661 from 11 o'clock until after 12 o'clock") The same event was also described by the astronomer Johan Hevelius the following year in his book Mercurius in Sole visus Gedani .
On 20 February 1661 a complex halo phenomenon was observed by more than 1000 people, including Fehlau and Hevelius, both astronomers, in the city of Gdańsk on the Baltic .
As well as the true Sun, two mock Suns ( parhelia ) and an anthelion were seen, with halos at 22° and 46° , and topped with an upper tangent arc and a circumzenithal arc , respectively. Of particular interest to modern scientists were the mention of three further mock Suns, one at the intersection of the 22° halo and the upper tangent arc, and two others at 90° to the Sun, also at the intersections of an immense but incomplete halo.
The first is thought to be a particularly bright Parry arc , mistakenly described as a parhelion. The other two and the associated halo, which has been labelled "Hevel's halo", [ 1 ] [ 2 ] have no theoretical explanation, and have not been recorded since (though one possible sighting was reported in 1909 [ 3 ] ). In the absence of conclusive evidence these observations are regarded as possibly being a misidentification of the rare but not unusual 120° parhelia . [ 1 ] [ 4 ] [ 5 ]
On 6 March, two weeks after the event, Fehlau preached at St Mary's church; taking the event, and the widespread interest it created, as his inspiration. His sermon was later published, and contains a full account of the phenomenon.
The following year Hevelius published his book Mercurius in Sole visus Gedani ("Mercury appeared in the Sun, at Gdansk"), principally on the observation of a transit of Mercury , but containing other astronomical information, including an account of the 1661 halos. [ 6 ]
As the two accounts are virtually identical, and as Fehlau is known to have visited Hevelius on 3 March at his observatory to look at a comet, modern astronomers believe Fehlau and Hevelius collaborated on the text, though they generally give Hevelius (being the better-known of the two) the credit for the account. [ 5 ]
The translation of Fehlau's account [ 5 ] reads ( notes added for clarity ):
We now come to the description of the recently appeared sundogs or parhelia, which had been observed a fortnight ago and which we talk of now. They were like this: A fortnight ago it was February 20 at about 11 a.m. when the sun was in the southeast and the air was all bright and clear. There were seven suns clearly visible in the sky at the same time, three colourful and three white ones additionally to the real sun. Around the latter one ( the real sun ) appeared a rather big and almost closed circle with very beautiful colours like a rainbow ( the 22° halo ), on which at both sides two colourful sundogs were visible which were at the same elevation as the real sun. Both of them had long clear and white tails, tapering like comets, one pointing to the east and the other one to the west ( the ends of the parhelic circle ).
Second, on just that circle ( the 22° halo ), directly above the sun, under a vertical line ( possible sun pillar ), there was a part of an inverted circle or rainbow, also with very beautiful colours ( the upper tangent arc ), with another, a bit less bright sundog in it ( possible Parry arc ).
Third there was a very much larger circle with also a lot of beautiful colours around the Sun ( the 46° halo ), surrounding the other one, a bit fainter and not totally closed as the horizon was too near and the diameter of the circle too big, on which near the uppermost point an inverted part of a rainbow was visible ( the circumzenithal arc ), very bright and with beautiful colours.
Fourth there was a very white and silvery circle emerging from the two sundogs beside the real Sun ( the parhelic circle ), which surrounded the whole horizon and was in all parts at the same distance, which was about 20 degrees: On this circle there were three other silver Suns, one in the northwest, opposite the real Sun ( the anthelion ). The other one in the northeast and the third one in the southwest ( Hevelius's 90° parhelia; though possibly 120° parhelia in fact ). Through these two latter ones as eastern and western one passed a white piece of an arc coming from above ( "Hevel's halo" ), also through the big circle they were standing upon. So that through these two white sundogs a white cross seemed to pass, which appeared very amazing for about one hour and a half before everything disappeared. It was an overwhelmingly beautiful picture, in which seven suns were visible at the same time, which never had been observed before. Yes, scholars ( possibly Hevelius ) believe that, if this picture had been observed a little earlier, there would have been visible nine suns at the same time. | https://en.wikipedia.org/wiki/Sevenfold_Sun_miracle |
In arithmetic and algebra , the seventh power of a number n is the result of multiplying seven instances of n together. So:
Seventh powers are also formed by multiplying a number by its sixth power , the square of a number by its fifth power , or the cube of a number by its fourth power .
The sequence of seventh powers of integers is:
In the archaic notation of Robert Recorde , the seventh power of a number was called the "second sursolid ". [ 1 ]
Leonard Eugene Dickson studied generalizations of Waring's problem for seventh powers, showing that every non-negative integer can be represented as a sum of at most 258 non-negative seventh powers [ 2 ] (1 7 is 1, and 2 7 is 128). All but finitely many positive integers can be expressed more simply as the sum of at most 46 seventh powers. [ 3 ] If powers of negative integers are allowed, only 12 powers are required. [ 4 ]
The smallest number that can be represented in two different ways as a sum of four positive seventh powers is 2056364173794800. [ 5 ]
The smallest seventh power that can be represented as a sum of eight distinct seventh powers is: [ 6 ]
The two known examples of a seventh power expressible as the sum of seven seventh powers are
and
any example with fewer terms in the sum would be a counterexample to Euler's sum of powers conjecture , which is currently only known to be false for the powers 4 and 5.
This algebra -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Seventh_power |
Severyn Marcel Sternhell AO (30 May 1930 – 18 November 2022) was a Polish-born Australian academic and organic chemist . He was professor of Chemistry at the University of Sydney and a Fellow of the Australian Academy of Science . His research focused on the induction of chirality into mesophases, aspects of steric hindrance and the mechanochemistry of organic compounds. [ 1 ]
Sternhell was born in Lwow , then in Poland but now in western Ukraine. His father was Samson Sternhell, a lawyer. Before the war he attended a Zionist Hebrew language primary school for five years. Having survived the Bergen-Belsen concentration camp , he emigrated to Australia with his parents to join members of the Sternhell family who had left Europe prior to World War II . Arriving in Sydney in February 1947, he enrolled as a boarder at Newington College a few days after the commencement of the first term. [ 2 ] Having had no formal education since primary school, and only learnt English recently in Palestine , he spent the next nine months studying for the Leaving Certificate. He sat for his exams and received four A's and a B in English. Following Newington, he attended the University of Sydney and graduated with a BSc (hons) in 1951 and a MSc in 1953. [ 3 ] In 1961, he was awarded a PhD and DIC from the University of London . After further study in London, he received a DSc from Imperial College .
Sternhell began his career as a research chemist in private industry with Monsanto in 1953. Two years later, he was appointed a senior research officer at CSIRO and remained in that position until 1964. Sternhell was a senior lecturer in the Department of Organic Chemistry at the University of Sydney, from 1964 until 1967. He spent a further ten years as a reader in organic chemistry at the University of Sydney before being appointed Professor of Organic Chemistry. He was an Emeritus Professor from 1999. In 1991–92, he was chairman of the Australian Research Council Chemical Sciences Panel. [ 4 ]
Sternhell was a Fellow, of the Australian Academy of Science and of the Royal Australian Chemical Institute . In 2001, he was awarded the Centenary Medal for his service to Australian society and science in organic chemistry and molecular engineering. [ 5 ] In June 2018, he was made an Officer of the Order of Australia "for distinguished service to education in the field of organic chemistry, specifically to nuclear magnetic resonance, as an academic and researcher, and to scientific institutions." [ 6 ]
Sternhell died in Naremburn , Sydney on 18 November 2022, at the age of 92. [ 7 ] | https://en.wikipedia.org/wiki/Sever_Sternhell |
Severe plastic deformation ( SPD ) is a generic term describing a group of metalworking techniques involving very large strains typically involving a complex stress state or high shear, resulting in a high defect density and equiaxed "ultrafine" grain (UFG) size ( d < 1000 nm) or nanocrystalline (NC) structure (d < 100 nm). [ 1 ]
The significance of SPD was known from the ancient times, at least during the transition from the Bronze Age to the Iron Age, when repeated hammering and folding was employed for processing strategic tools such as swords. [ 2 ] The development of the principles underlying SPD techniques goes back to the pioneering work of P.W. Bridgman at Harvard University in the 1930s. [ 3 ] This work concerned the effects on solids of combining large hydrostatic pressures with concurrent shear deformation and it led to the award of the Nobel Prize in Physics in 1946. [ 4 ] Very successful early implementations of these principles, described in more detail below, are the processes of equal-channel angular pressing (ECAP) developed by V.M. Segal and co-workers in Minsk in the 1970s [ 5 ] and high-pressure torsion , derived from Bridgman's work, but not widely developed until the 1980s at the Russian Institute of Metals Physics in modern-day Yekaterinburg . [ 4 ]
Some definitions of SPD describe it as a process in which high strain is applied without any significant change in the dimensions of the workpiece, resulting in a large hydrostatic pressure component. [ 6 ] However, the mechanisms that lead to grain refinement in SPD are the same as those originally developed for mechanical alloying, a powder process [ 7 ] that has been characterized as "severe plastic deformation" by authors as early as 1983. [ 8 ] Additionally, some more recent processes such as asymmetric rolling, do result in a change in the dimensions of the workpiece, while still producing an ultrafine grain structure. [ 9 ] The principles behind SPD have even been applied to surface treatments. [ 10 ]
SPD methods are classified into three main groups of bulk-SPD methods, surface-SPD methods and powder-SPD methods. [ 11 ] Here some popular SPD methods are briefly explained.
Equal channel angular extrusion (ECAE, sometimes called Equal channel angular pressing, ECAP) was developed in the 1970s. In this process, a metal billet is pressed through an angled (typically 90 degrees) channel. To achieve optimal results, the process may be repeated several times, changing the orientation of the billet with each pass. This produces a uniform shear throughout the bulk of the material. [ 5 ]
High pressure torsion (HPT) can be traced back to the experiments that won Percy Bridgman the 1946 Nobel Prize in Physics , though its use in metal processing is considerably more recent. In this method, a disk of the material to be strained is placed between 2 anvils. A large compressive stress (typically several gigapascals ) is applied, while one anvil is rotated to create a torsion force. HPT can be performed unconstrained, in which the material is free to flow outward, fully constrained, or to some degree between in which outward flow is allowed, but limited. [ 4 ]
In accumulative roll bonding (ARB), 2 sheets of the same material are stacked, heated (to below the recrystallization temperature), and rolled , bonding the 2 sheets together. This sheet is cut in half, the 2 halves are stacked, and the process is repeated several times. Compared to other SPD processes, ARB has the benefit that it does not require specialized equipment or tooling, only a conventional rolling mill. However, the surfaces to be joined must be well-cleaned before rolling to ensure good bonding. [ 12 ]
Repetitive corrugation and straightening (RCS) is a severe plastic deformation technique used to process sheet metals. In RCS, a sheet is pressed between two corrugated dies followed by pressing between two flat dies. RCS has gained wide popularity to produce fine grained sheet metals. [ 13 ] Endeavors to improve this technique lead to introduce Repetitive Corrugation and Straightening by Rolling (RCSR), a novel SPD method. [ 14 ] Applicability of this new method approved in the various materials. [ 14 ] [ 15 ] [ 16 ] [ 17 ] [ 18 ]
In asymmetric rolling (ASR), a rolling mill is modified such that one roll has a higher velocity than the other. This is typically done with either independent speed control or by using rolls of different size. This creates a region in which the frictional forces on the top and bottom of the sheet being rolled are opposite, creating shear stresses throughout the material in addition to the normal compressive stress from rolling. Unlike other SPD processes, ASR does not maintain the same net shape, but the effect on the microstructure of the material is similar. [ 9 ] [ 19 ]
Mechanical alloying/milling (MA/MM) performed in a high-energy ball mill such as a shaker mill or planetary mill will also induce severe plastic deformation in metals. During milling, particles are fractured and cold welded together, resulting in large deformations. The end product is generally a powder that must then be consolidated in some way (often using other SPD processes), but some alloys have the ability to consolidate in-situ during milling. Mechanical alloying also allows powders of different metals to be alloyed together during processing. [ 20 ] [ 21 ]
More recently, the principles behind SPD have been used to develop surface treatments that create a nanocrystalline layer on the surface of a material. In the surface mechanical attrition treatment (SMAT), an ultrasonic horn is connected to an ultrasonic (20 kHz) transducer), with small balls on top of the horn. The workpiece is mounted a small distance above the horn. The high frequency results in a large number of collisions between the balls and the surface, creating a strain rate on the order of 10 2 –10 3 s −1 . The NC surface layer developed can be on the order of 50 μm thick. [ 10 ] The process is similar to shot peening , but the kinetic energy of the balls is much higher in SMAT. [ 22 ]
An ultrasonic nanocrystalline surface modification (UNSM) technique is also one of the newly developed surface modification technique. In the UNSM process, not only the static load, but also the dynamic load are exerted. The processing is conducted striking a workpiece surface up to 20K or more times per second with shots of an attached ball to the horn in the range of 1K-100K per square millimeter. The strikes, which can be described as cold-forging, introduce SPD to produce a NC surface layer by refining the coarse grains until nanometer scale without changing the chemical composition of a material which render the high strength and high ductility. This UNSM technique does not only improve the mechanical and tribological properties of a material, but also produces a corrugated structure having numerous of desired dimples on the treated surface. [ 23 ]
Most research into SPD has focused on grain refinement, which has obvious applications in the development of high-strength materials as a result of the Hall-Petch relation. Conventionally processed industrial metals typically have a grain size from 10–100 μm. Reducing the grain size from 10 μm to 1 μm can increase the yield strength of metals by more than 100%. Techniques that use bulk materials such as ECAE can provide reliable and relatively inexpensive ways of producing ultrafine grain materials compared to rapid solidification techniques such as melt spinning . [ 24 ]
However, other effects of SPD, such as texture modification also have potential industrial applications as properties such as the Lankford coefficient (important for deep drawing processes) and magnetic properties of electrical steel are highly dependent on texture. [ 24 ]
Processes such as ECAE and HPT have also been used to consolidate metal powders and composites without the need for the high temperatures used in conventional consolidation processes such as hot isostatic pressing , allowing desirable characteristics such as nanocrystalline grain sizes or amorphous structures to be retained. [ 24 ] [ 25 ]
Some known commercial application of SPD processes are in the production of Sputtering targets by Honeywell [ 24 ] and UFG titanium for medical implants. [ 26 ]
The presence of a high hydrostatic pressure, in combination with large shear strains, is essential for producing high densities of crystal lattice defects, particularly dislocations , which can result in a significant refining of the grains . Grain refinement in SPD processes occurs by a multi-step process:
The mechanism by which the subgrains rotate is less understood. Wu et al. describe a process in which dislocation motion becomes restricted due to the small subgrain size and grain rotation becomes more energetically favorable. [ 28 ] Mishra et al. propose a slightly different explanation, in which the rotation is aided by diffusion along the grain boundaries (which is much faster than through the bulk). [ 27 ]
F.A. Mohamad has proposed a model for the minimum grain size achievable using mechanical milling . The model is based on the concept that the grain size is dependent on the rates at which dislocations are generated and annihilated. The full model is given by
d m i n b = A 3 ( e − β Q 4 R T ) ( D p 0 G b 2 ν 0 k T ) 0.25 ( γ G b ) 0.5 ( G H ) 1.25 {\displaystyle {\frac {d_{min}}{b}}=A_{3}\left(e^{-{\tfrac {\beta Q}{4RT}}}\right){\left({\frac {D_{p0}Gb^{2}}{\nu _{0}kT}}\right)}^{0.25}{\left({\frac {\gamma }{Gb}}\right)}^{0.5}{\left({\frac {G}{H}}\right)}^{1.25}}
While the model was developed specifically for mechanical milling, it has also been successfully applied to other SPD processes. Frequently only a portion of the model is used (typically the term involving the stacking fault energy) as the other terms are often unknown and difficult to measure. This is still useful as it implies that all other things remaining equal, reducing the stacking fault energy, a property that is a function of the alloying elements, will allow for better grain refinement. [ 4 ] [ 7 ] A few studies, however, suggested that despite the significance of stacking fault energy on the grain refinement at the early stages of straining, the steady-state grain size at large strains is mainly controlled by the homologous temperature in pure metals [ 30 ] and by the interaction of solute atoms and dislocations in single-phase alloys. [ 31 ] | https://en.wikipedia.org/wiki/Severe_plastic_deformation |
The Severinghaus electrode is an electrode that measures carbon dioxide (CO 2 ). It was developed by Dr. John W. Severinghaus and his technician A. Freeman Bradley in 1958. [ 1 ]
It utilizes a CO 2 -sensitive glass electrode in a surrounding film of bicarbonate solution covered by a thin plastic carbon dioxide permeable membrane , but impermeable to water and electrolytic solutes . The carbon dioxide pressure of a sample gas or liquid equilibrates through the membrane and the glass electrode measures the resulting pH of the bicarbonate solution.
Clark, galvanic, and paramagnetic electrodes measure oxygen. Severinghaus electrode measures CO 2 . Sanz electrode measures pH. [ 2 ]
This electrochemistry -related article is a stub . You can help Wikipedia by expanding it .
This article about analytical chemistry is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Severinghaus_electrode |
The Severnside Sirens are a system of Civil defense sirens located along the South Severn Estuary coastline from Redcliffe Bay to Pilning , northwest of Bristol . They are activated by Avon and Somerset Police [ 1 ] in the event of a potential incident at one of the COMAH sites located in the area, mainly in and near Avonmouth . [ 2 ] The system was setup in 1997 following a fire [ 3 ] at the Albright and Wilson site in 1996. [ 4 ]
Severnside Sirens Trust Limited is the organisation responsible for maintaining the system. It is a registered company (number 3348008) and charity (number 1063224) [ 5 ] and was incorporated on 9 April 1997. [ 6 ] The trust's activities are funded by the 3 local authorities whose constituents the sirens serve, North Somerset Council , Bristol City Council , and South Gloucestershire Council , and from donations from the organisations running the COMAH sites themselves.
The sirens themselves are mounted on dedicated poles and all but one [ citation needed ] are manufactured by the Federal Signal Corporation . Most of them are Federal Signal Modulators . They are operated via radio signal from a control system at Avon and Somerset Police Headquarters in Portishead .
The sirens are tested at 1500 on the 3rd of every month. The test comprises the following: [ 9 ]
Local volunteers monitor the sirens on test day. [ 10 ] | https://en.wikipedia.org/wiki/Severnside_Sirens |
Sevoflurane , sold under the brand name Sevorane , among others, is a sweet-smelling, nonflammable, highly fluorinated methyl isopropyl ether used as an inhalational anaesthetic for induction and maintenance of general anesthesia . After desflurane , it is the volatile anesthetic with the fastest onset. [ 8 ] While its offset may be faster than agents other than desflurane in a few circumstances, its offset is more often similar to that of the much older agent isoflurane . While sevoflurane is only half as soluble as isoflurane in blood, the tissue blood partition coefficients of isoflurane and sevoflurane are quite similar. For example, in the muscle group: isoflurane 2.62 vs. sevoflurane 2.57. In the fat group: isoflurane 52 vs. sevoflurane 50. As a result, the longer the case, the more similar will be the emergence times for sevoflurane and isoflurane. [ 9 ] [ 10 ] [ 11 ]
It is on the World Health Organization's List of Essential Medicines . [ 12 ]
It is one of the most commonly used volatile anesthetic agents, particularly for outpatient anesthesia, [ 13 ] across all ages, but particularly in pediatric anesthesia, as well as in veterinary medicine. Together with desflurane , sevoflurane is replacing isoflurane and halothane in modern anesthesia practice. It is often administered in a mixture of nitrous oxide and oxygen.
Sevoflurane is a potent vasodilator . As such, it induces a dose dependent reduction in blood pressure and cardiac output. It is a bronchodilator , however, in patients with pre-existing lung pathology, it may precipitate coughing and laryngospasm . It reduces the ventilatory response to hypoxia and hypercapnia , and impedes hypoxic pulmonary vasoconstriction. Sevoflurane vasodilatory properties also cause it to increase intracranial pressure and cerebral blood flow. However, it reduces cerebral metabolic rate. [ 14 ] [ 15 ]
Sevoflurane has an excellent safety record, [ 13 ] but is under review for potential hepatotoxicity , and may accelerate Alzheimer's. [ 16 ] There were rare reports involving adults with symptoms similar to halothane hepatotoxicity . [ 13 ] Sevoflurane is the preferred agent for mask induction due to its lesser irritation to mucous membranes .
Sevoflurane is an inhaled anesthetic that is often used to induce and maintain anesthesia in children for surgery. [ 17 ] During the process of awakening from the medication, it has been associated with a high incidence (>30%) of agitation and delirium in preschool children undergoing minor noninvasive surgery. [ 17 ] It is not clear if this can be prevented. [ 17 ]
Studies examining a current significant health concern, anesthetic-induced neurotoxicity (including with sevoflurane, and especially with children and infants) are "fraught with confounders, and many are underpowered statistically", and so are argued to need "further data... to either support or refute the potential connection". [ 18 ]
Concern regarding the safety of anaesthesia is especially acute with regard to children and infants, where preclinical evidence from relevant animal models suggest that common clinically important agents, including sevoflurane, may be neurotoxic to the developing brain, and so cause neurobehavioural abnormalities in the long term; two large-scale clinical studies (PANDA and GAS) were ongoing as of 2010, in hope of supplying "significant [further] information" on neurodevelopmental effects of general anaesthesia in infants and young children, including where sevoflurane is used. [ 19 ]
In 2021, researchers at Massachusetts General Hospital published in Communications Biology research that sevoflurane may accelerate existing Alzheimer's or existing tau protein to spread: "These data demonstrate anesthesia-associated tau spreading and its consequences. [...] This tau spreading could be prevented by inhibitors of tau phosphorylation or extracellular vesicle generation." According to Neuroscience News, "Their previous work showed that sevoflurane can cause a change (specifically, phosphorylation, or the addition of phosphate) to tau that leads to cognitive impairment in mice. Other researchers have also found that sevoflurane and certain other anesthetics may affect cognitive function." [ 16 ]
Additionally, there has been some investigation into potential correlation of sevoflurane use and renal damage (nephrotoxicity). [ 20 ] However, this should be subject to further investigation, as a recent study shows no correlation between sevoflurane use and renal damage as compared to other control anesthetic agents. [ 21 ] There is also evidence that renal damage may be caused by compound A, a product of the degradation of sevoflurane. [ 22 ]
The exact mechanism of the action of general anaesthetics has not been delineated . [ 23 ] Sevoflurane acts as a positive allosteric modulator of the GABA A receptor in electrophysiology studies of neurons and recombinant receptors. [ 24 ] [ 25 ] [ 26 ] [ 27 ] However, it also acts as an NMDA receptor antagonist , [ 28 ] potentiates glycine receptor currents, [ 27 ] and inhibits nAChR [ 29 ] and 5-HT 3 receptor currents. [ 30 ] [ 31 ] [ 32 ]
Sevoflurane was discovered by Ross Terrell alongside Louise Speers in the early 1960s researching at Airco Industrial Gases . [ 33 ] Sevoflurane was concurrently synthesized by Richard Wallen. [ 33 ] The rights for sevoflurane worldwide were held by AbbVie . It is available as a generic drug .
Sevoflurane is a greenhouse gas . The twenty-year global-warming potential , GWP(20), for sevoflurane is 349, however this is significantly lower than isoflurane or desflurane. [ 34 ]
Sevoflurane will degrade into what is most commonly referred to as compound A (fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether) when in contact with CO 2 absorbents, and this degradation tends to enhance with decreased fresh gas flow rates, increased temperatures, and increased sevoflurane concentration. [ 35 ] Compound A may be correlated with renal damage. [ 22 ] | https://en.wikipedia.org/wiki/Sevoflurane |
Sewage (or domestic sewage , domestic wastewater , municipal wastewater ) is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system . [ 1 ] : 175 Sewage consists of wastewater discharged from residences and from commercial, institutional and public facilities that exist in the locality. [ 2 ] : 10 Sub-types of sewage are greywater (from sinks, bathtubs, showers, dishwashers, and clothes washers) and blackwater (the water used to flush toilets , combined with the human waste that it flushes away). Sewage also contains soaps and detergents. Food waste may be present from dishwashing , and food quantities may be increased where garbage disposal units are used. In regions where toilet paper is used rather than bidets , that paper is also added to the sewage. Sewage contains macro-pollutants and micro-pollutants, and may also incorporate some municipal solid waste and pollutants from industrial wastewater .
Sewage usually travels from a building's plumbing either into a sewer , which will carry it elsewhere, or into an onsite sewage facility . Collection of sewage from several households together usually takes places in either sanitary sewers or combined sewers . The former is designed to exclude stormwater flows whereas the latter is designed to also take stormwater. The production of sewage generally corresponds to the water consumption. A range of factors influence water consumption and hence the sewage flowrates per person. These include: Water availability (the opposite of water scarcity ), water supply options, climate (warmer climates may lead to greater water consumption), community size, economic level of the community, level of industrialization , metering of household consumption, water cost and water pressure. [ 2 ] : 20
The main parameters in sewage that are measured to assess the sewage strength or quality as well as treatment options include: solids, indicators of organic matter, nitrogen, phosphorus, and indicators of fecal contamination. [ 2 ] : 33 These can be considered to be the main macro-pollutants in sewage. Sewage contains pathogens which stem from fecal matter . The following four types of pathogens are found in sewage: pathogenic bacteria , viruses , protozoa (in the form of cysts or oocysts) and helminths (in the form of eggs). [ 3 ] [ 4 ] In order to quantify the organic matter, indirect methods are commonly used: mainly the Biochemical Oxygen Demand (BOD) and the Chemical Oxygen Demand (COD). [ 2 ] : 36
Management of sewage includes collection and transport for release into the environment, after a treatment level that is compatible with the local requirements for discharge into water bodies, onto soil or for reuse applications. [ 2 ] : 156 Disposal options include dilution (self-purification of water bodies, making use of their assimilative capacity if possible), marine outfalls , land disposal and sewage farms . All disposal options may run risks of causing water pollution .
Sewage (or domestic wastewater) consists of wastewater discharged from residences and from commercial, institutional and public facilities that exist in the locality. [ 2 ] : 10 Sewage is a mixture of water (from the community's water supply ), human excreta ( feces and urine ), used water from bathrooms , food preparation wastes, laundry wastewater, and other waste products of normal living.
Sewage from municipalities contains wastewater from commercial activities and institutions, e.g. wastewater discharged from restaurants , laundries , hospitals , schools , prisons , offices , stores and establishments serving the local area of larger communities. [ 2 ] : 21
Sewage can be distinguished into "untreated sewage" (also called "raw sewage") and "treated sewage" (also called "effluent" from a sewage treatment plant ).
The term "sewage" is nowadays often used interchangeably with "wastewater" – implying "municipal wastewater" – in many textbooks, policy documents and the literature. [ 2 ] [ 5 ] [ 6 ] To be precise, wastewater is a broader term, because it refers to any water after it has been used in a variety of applications. [ 5 ] : 1 Thus it may also refer to " industrial wastewater ", agricultural wastewater and other flows that are not related to household activities.
Blackwater in a sanitation context denotes wastewater from toilets which likely contains pathogens that may spread by the fecal–oral route . Blackwater can contain feces , urine , water and toilet paper from flush toilets . Blackwater is distinguished from greywater , which comes from sinks, baths, washing machines, and other household appliances apart from toilets. Greywater results from washing food, clothing, dishes, as well as from showering or bathing. [ 7 ]
Greywater (or grey water, sullage, also spelled gray water in the United States) refers to domestic wastewater generated in households or office buildings from streams without fecal contamination, i.e., all streams except for the wastewater from toilets. Sources of greywater include sinks , showers , baths , washing machines or dishwashers . As greywater contains fewer pathogens than blackwater , it is generally safer to handle and easier to treat and reuse onsite for toilet flushing , landscape or crop irrigation , and other non- potable uses. Greywater may still have some pathogen content from laundering soiled clothing or cleaning the anal area in the shower or bath.
The overall appearance of sewage is as follows: [ 2 ] : 30 The temperature tends to be slightly higher than in drinking water but is more stable than the ambient temperature. The color of fresh sewage is slightly grey, whereas older sewage (also called "septic sewage") is dark grey or black. The odor of fresh sewage is "oily" and relatively unpleasant, whereas older sewage has an unpleasant foul odor due to hydrogen sulfide gas and other decomposition by-products. [ 10 ] : 9–38 Sewage can have high turbidity from suspended solids.
The pH value of sewage is usually near neutral, and can be in the range of 6.7–8.0. [ 2 ] : 57
Sewage consists primarily of water and usually contains less than one part of solid matter per thousand parts of water. In other words, one can say that sewage is composed of around 99.9% pure water, and the remaining 0.1% are solids, which can be in the form of either dissolved solids or suspended solids . [ 2 ] : 28 The thousand-to-one ratio is an order of magnitude estimate rather than an exact percentage because, aside from variation caused by dilution, solids may be defined differently depending upon the mechanism used to separate those solids from the liquid fraction. Sludges of settleable solids removed by settling or suspended solids removed by filtration may contain significant amounts of entrained water, while dried solid material remaining after evaporation eliminates most of that water but includes dissolved minerals not captured by filtration or gravitational separation. [ 11 ] The suspended and dissolved solids include organic and inorganic matter plus microorganisms. [ 2 ] : 28
About one-third of this solid matter is suspended by turbulence , while the remainder is dissolved or colloidal . For the situation in the United States in the 1950s it was estimated that the waste contained in domestic sewage is about half organic and half inorganic . [ 10 ] : 9–38
The organic matter in sewage can be classified in terms of form and size: Suspended (particulate) or dissolved (soluble). Secondly, it can be classified in terms of biodegradability : either inert or biodegradable. [ 2 ] : 35 The organic matter in sewage consists of protein compounds (about 40%), carbohydrates (about 25–50%), oils and grease (about 10%) and urea , surfactants , phenols , pesticides and others (lower quantity). [ 2 ] : 35 In order to quantify the organic matter content, it is common to use "indirect methods" which are based on the consumption of oxygen to oxidize the organic matter: mainly the Biochemical Oxygen Demand (BOD) and the Chemical Oxygen Demand (COD). [ 2 ] : 36 These indirect methods are associated with the major impact of the discharge of organic matter into water bodies: the organic matter will be food for microorganisms, whose population will grow, and lead to the consumption of oxygen, which may then affect aquatic living organisms.
The mass load of organic content is calculated as the sewage flowrate multiplied with the concentration of the organic matter in the sewage. [ 2 ] : 55
Typical values for physical–chemical characteristics of raw sewage is provided further down below.
Apart from organic matter, sewage also contains nutrients. The major nutrients of interest are nitrogen and phosphorus . If sewage is discharged untreated, its nitrogen and phosphorus content can lead to pollution of lakes and reservoirs via a process called eutrophication . [ 2 ] : 77
In raw sewage, nitrogen exists in the two forms of organic nitrogen or ammonia . The ammonia stems from the urea in urine . Urea is rapidly hydrolyzed and therefore not usually found in raw sewage. [ 2 ] : 43
Total phosphorus is mostly present in sewage in the form of phosphates .They are either inorganic (polyphosphates and orthophosphates) and their main source is from detergents and other household chemical products. The other form is organic phosphorus, where the source is organic compounds to which the organic phosphorus is bound. [ 2 ] : 45
Human feces in sewage may contain pathogens capable of transmitting diseases. [ 10 ] : 9–38 The following four types of pathogens are found in sewage: [ 3 ] [ 4 ]
In most practical cases, pathogenic organisms are not directly investigated in laboratory analyses. An easier way to assess the presence of fecal contamination is by assessing the most probable numbers of fecal coliforms (called thermotolerant coliforms), especially Escherichia coli . Escherichia coli are intestinal bacteria excreted by all warm blooded animals, including human beings, and thus tracking their presence in sewage is easy, because of their substantially high concentrations (around 10 to 100 million per 100 mL). [ 2 ] : 52
The ability of a flush toilet to make things "disappear" is soon recognized by young children who may experiment with virtually anything they can carry to the toilet. [ 13 ] Adults may be tempted to dispose of toilet paper , wet wipes , diapers , sanitary napkins , tampons , tampon applicators, condoms , and expired medications , even at the risk of causing blockages. The privacy of a toilet offers a clandestine means of removing embarrassing evidence by flushing such things as drug paraphernalia , pregnancy test kits, combined oral contraceptive pill dispensers, and the packaging for those devices. There may be reluctance to retrieve items like children's toys or toothbrushes which accidentally fall into toilets, and items of clothing may be found in sewage from prisons or other locations where occupants may be careless. [ 14 ] Trash and garbage in streets may be carried to combined sewers by stormwater runoff.
Sewage contains environmental persistent pharmaceutical pollutants . Trihalomethanes can also be present as a result of past disinfection . Sewage may contain microplastics such as polyethylene and polypropylene beads, or polyester and polyamide fragments [ 15 ] from synthetic clothing and bedding fabrics abraded by wear and laundering, or from plastic packaging and plastic-coated paper products disintegrated by lift station pumps. Pharmaceuticals , endocrine disrupting compounds, and hormones [ 16 ] [ 17 ] [ 18 ] may be excreted in urine or feces if not catabolized within the human body.
Some residential users tend to pour unwanted liquids like used cooking oil , [ 19 ] : 228 lubricants , [ 19 ] : 228 adhesives , paint , solvents , detergents , [ 19 ] : 228 and disinfectants into their sewer connections. This behavior can result in problems for the treatment plant operation and is thus discouraged.
The composition of sewage varies with climate, social and economic situation and population habits. [ 2 ] : 28 In regions where water use is low, the strength of the sewage (or pollutant concentrations) is much higher than that in the United States where water use per person is high. [ 5 ] : 183 Household income and diet also plays a role: For example, for the case of Brazil, it has been found that the higher the household income, the higher is the BOD load per person and the lower is the BOD concentration. [ 2 ] : 57
Typical values for physical–chemical characteristics of raw sewage in developing countries have been published as follows: 180 g/person/d for total solids (or 1100 mg/L when expressed as a concentration), 50 g/person/d for BOD (300 mg/L), 100 g/person/d for COD (600 mg/L), 8 g/person/d for total nitrogen (45 mg/L), 4.5 g/person/d for ammonia-N (25 mg/L) and 1.0 g/person/d for total phosphorus (7 mg/L). [ 2 ] : 57 The typical ranges for these values are: 120–220 g/person/d for total solids (or 700–1350 mg/L when expressed as a concentration), 40–60 g/person/d for BOD (250–400 mg/L), 80–120 g/person/d for COD (450–800 mg/L), 6–10 g/person/d for total nitrogen (35–60 mg/L), 3.5–6 g/person/d for ammonia-N (20–35 mg/L) and 0.7–2.5 g/person/d for total phosphorus (4–15 mg/L). [ 2 ] : 57
For high income countries, the "per person organic matter load" has been found to be approximately 60 gram of BOD per person per day. [ 6 ] This is called the population equivalent (PE) and is also used as a comparison parameter to express the strength of industrial wastewater compared to sewage.
Values for households in the United States have been published as follows, whereby the estimates are based on the assumption that 25% of the homes have kitchen waste-food grinders (sewage from such households contain more waste): 95 g/person/d for total suspended solids (503 mg/L concentration), 85 g/person/d for BOD (450 mg/L), 198 g/person/d for COD (1050 mg/L), 13.3 g/person/d for the sum of organic nitrogen and ammonia nitrogen (70.4 mg/L), 7.8 g/person/d for ammonia-N (41.2 mg/L) and 3.28 g/person/d for total phosphorus (17.3 mg/L). The concentration values given here are based on a flowrate of 190 L per person per day. [ 5 ] : 183
A United States source published in 1972 estimated that the daily dry weight of solid wastes per capita in sewage is estimated as 20.5 g (0.72 oz) in feces, 43.3 g (1.53 oz) of dissolved solids in urine, 20 g (0.71 oz) of toilet paper, 86.5 g (3.05 oz) of greywater solids, 30 g (1.1 oz) of food solids (if garbage disposal units are used), and varying amounts of dissolved minerals depending upon salinity of local water supplies, volume of water use per capita, and extent of water softener use. [ 19 ] : 234
Sewage contains urine and feces. The mass of feces varies with dietary fiber intake. An average person produces 128 grams of wet feces per day, or a median dry mass of 29 g/person/day. [ 20 ] The median urine generation rate is about 1.42 L/person/day, as was determined by a global literature review. [ 20 ]
The volume of domestic sewage produced per person (or " per capita ", abbreviated as "cap") varies with the water consumption in the respective locality. [ 2 ] : 11 A range of factors influence water consumption and hence the sewage flowrates per person. These include: Water availability (the opposite of water scarcity ), water supply options, climate (warmer climates may lead to greater water consumption), community size, economic level of the community, level of industrialization , metering of household consumption, water cost and water pressure. [ 2 ] : 20
The production of sewage generally corresponds to the water consumption. However water used for landscape irrigation will not enter the sewer system, while groundwater and stormwater may enter the sewer system in addition to sewage. [ 2 ] : 22 There are usually two peak flowrates of sewage arriving at a treatment plant per day: One peak is at the beginning of the morning and another peak is at the beginning of the evening. [ 2 ] : 24
With regards to water consumption, a design figure that can be regarded as "world average" is 35–90 L per person per day (data from 1992). [ 5 ] : 163 The same publication listed the water consumption in China as 80 L per person per day, Africa as 15–35 L per person per day, Eastern Mediterranean in Europe as 40–85 L per person per day and Latin America and Caribbean as 70–190 L per person per day. [ 5 ] : 163 Even inside a country, there may be large variations from one region to another due to the various factors that determine the water consumption as listed above.
A flowrate value of 200 liters of sewage per person per day is often used as an estimate in high income countries , and is used for example in the design of sewage treatment plants. [ 6 ]
For comparison, typical sewage flowrates from urban residential sources in the United States are estimated as follows: 365 L/person/day (for one person households), 288 L/person/day (two person households), 200 L/person/day (four person households), 189 L/person/day (six person households). [ 5 ] : 156 This means the overall range for this example would be 189–365 L (42–80 imp gal; 50–96 US gal).
Sewage can be monitored for both disease-causing and benign organisms with a variety of techniques. Traditional techniques involve filtering, staining, and examining samples under a microscope. Much more sensitive and specific testing can be accomplished with DNA sequencing , such as when looking for rare organisms, attempting eradication , testing specifically for drug-resistant strains, or discovering new species. [ 22 ] [ 23 ] [ 24 ] Sequencing DNA from an environmental sample is known as metagenomics .
Sewage has also been analyzed to determine relative rates of use of prescription and illegal drugs among municipal populations. [ 25 ] General socioeconomic demographics may be inferred as well. [ 26 ]
Sewage is commonly collected and transported in gravity sewers , either in a sanitary sewer or in a combined sewer . The latter also conveys urban runoff ( stormwater ) which means the sewage gets diluted during rain events. [ 2 ] : 9
Infiltration is groundwater entering sewer pipes through defective pipes, connections, joints or manholes . [ 2 ] : 26 [ 5 ] : 164 Contaminated or saline groundwater may introduce additional pollutants to the sewage. The amount of such infiltrated water depends on several parameters, such as the length of the collection network, pipeline diameters, drainage area, soil type, water table depth, topography and number of connections per unit area. [ 2 ] : 26 Infiltration is increased by poor construction procedures, and tends to increase with the age of the sewer. The amount of infiltration varies with the depth of the sewer in comparison to the local groundwater table . [ 10 ] : 9–1, 9–9 Older sewer systems that are in need of rehabilitation may also exfiltrate sewage into groundwater from the leaking sewer joints and service connections. [ 5 ] : 167 This can lead to groundwater pollution . [ 28 ]
Combined sewers are designed to transport sewage and stormwater together. This means that sewage becomes diluted during rain events. There are other types of inflow that also dilute sewage, e.g. "water discharged from cellar and foundation drains, cooling-water discharges, and any direct stormwater runoff connections to the sanitary collection system". [ 5 ] : 163 The "direct inflows" can result in peak sewage flowrates similar to combined sewers during wet weather events. [ 5 ] : 165
Sewage from communities with industrial facilities may include some industrial wastewater , generated by industrial processes such as the production or manufacture of goods. Volumes of industrial wastewater vary widely with the type of industry. [ 2 ] : 27 Industrial wastewater may contain very different pollutants at much higher concentrations than what is typically found in sewage. [ 5 ] : 188 Pollutants may be toxic or non- biodegradable waste including pharmaceuticals , [ 29 ] biocides , heavy metals , radionuclides , or thermal pollution .
An industry may treat its wastewater and discharge it into the environment (or even use the treated wastewater for specific applications), or, in case it is located in the urban area, it may discharge the wastewater into the public sewerage system. In the latter case, industrial wastewater may receive pre-treatment at the factories to reduce the pollutant load . [ 2 ] : 27 Mixing industrial wastewater with sewage does nothing to reduce the mass of pollutants to be treated, but the volume of sewage lowers the concentration of pollutants unique to industrial wastewater, and the volume of industrial wastewater lowers the concentration of pollutants unique to sewage.
When wastewater is discharged into a water body (river, lakes, sea) or land, its relative impact will depend on the assimilative capacity of the water body or ecosystem . [ 2 ] : 78 Water bodies have a self-purification capacity, so that the concentration of a pollutant may decrease along the distance from the discharge point. Furthermore, water bodies provide a dilution to the pollutants concentrations discharged, although it does not decrease their mass. In principle, the higher the dilution capacity (ratio of volume or flow of the receiving water and volume or flow of sewage discharged), the lower will be the concentration of pollutants in the receiving water, and probably the lower will be the negative impacts. But if the water body already arrives very polluted at the point of discharge, the dilution will be of limited value. [ 30 ]
In several cases, a community may treat partially its sewage, and still count on the assimilative capacity of the water body. However, this needs to be analyzed very carefully, taking into account the quality of the water in the receiving body before it receives the discharge of sewage, the resulting water quality after the discharge and the impact on the intended water uses after discharge. There are also specific legal requirements in each country. Different countries have different regulations regarding the specifications of the quality of the sewage being discharged and the quality to be maintained in the receiving water body. [ 2 ] : 152 The combination of treatment and disposal must comply with existing local regulations.
The assimilative capacity depends – among several factors – on the ability of the receiving water to sustain dissolved oxygen concentrations necessary to support organisms catabolizing organic waste. [ 19 ] : 9, 673 For example, fish may die if dissolved oxygen levels are depressed below 5 mg/L. [ 31 ] : 573
Application of sewage to land can be considered as a form of final disposal or of treatment, or both. [ 2 ] : 189 Land disposal alternatives require consideration of land availability, groundwater quality, and possible soil deterioration. [ 32 ]
Sewage may be discharged to an evaporation or infiltration basin . [ 10 ] : 9–41 Groundwater recharge is used to reduce saltwater intrusion , or replenish aquifers used for agricultural irrigation . Treatment is usually required to sustain percolation capacity of infiltration basins, and more extensive treatment may be required for aquifers used as drinking water supplies. [ 19 ] : 700–703
Before the 20th century in Europe, sewers usually discharged into a body of water such as a river, lake, or ocean. There was no treatment, so the breakdown of the human waste was left to the ecosystem . This could lead to satisfactory results if the assimilative capacity of the ecosystem is sufficient which is nowadays not often the case due to increasing population density. [ 35 ] : 78
Sewage treatment is beneficial in reducing environmental pollution. Bar screens can remove large solid debris from sewage, [ 19 ] : 274–275 and primary treatment can remove floating and settleable matter . [ 19 ] : 446 Primary treated sewage usually contains less than half of the original solids content and approximately two-thirds of the BOD in the form of colloids and dissolved organic compounds. [ 43 ] Secondary treatment can reduce the BOD of organic waste in undiluted sewage, [ 31 ] : 575 but is less effective for dilute sewage. [ 44 ] Water disinfection may be attempted to kill pathogens prior to disposal, and is increasingly effective after more elements of the foregoing treatment sequence have been completed. [ 19 ] : 359
An alternative to discharge into the environment is to reuse the sewage in a productive way (for agricultural, urban or industrial uses), in compliance with local regulations and requirements for each specific reuse application. Public health risks of sewage reuse in agriculture can be minimized by following a "multiple barrier approach" according to guidelines by the World Health Organization . [ 45 ]
There is also the possibility of resource recovery which could make agriculture more sustainable by using carbon , nitrogen , phosphorus , water and energy recovered from sewage. [ 46 ] [ 4 ]
Sewage management includes collection and transport for release into the environment after a treatment level that is compatible with the local requirements for discharge into water bodies, onto soil, or for reuse applications. [ 2 ] : 156 In most countries, uncontrolled discharges of wastewater to the environment are not permitted under law, and strict water quality requirements are to be met. For requirements in the United States, see Clean Water Act .
Sewage management regulations are often part of a country's broader sanitation policies. These may also include the management of human excreta (from non-sewered collection systems ), solid waste and stormwater. | https://en.wikipedia.org/wiki/Sewage |
Sewage fungus [ 1 ] (also known as undesirable river biofilms, URBs) is a polymicrobial biofilm (a microbial mat ) that proliferates in saprobic rivers [ 2 ] and has been frequently used as a bioindicator [ 3 ] [ 4 ] of organic river pollution for the past century. [ 5 ] Its presence has been strongly associated with discharges of untreated or inadequately treated sewage, [ 6 ] [ 7 ] [ 8 ] [ 9 ] yet its presence extends beyond these areas, with contributors including airport de-ice fluid runoff, [ 10 ] [ 11 ] [ 12 ] papermill effluents, [ 13 ] and agricultural runoff. [ 14 ] [ 15 ]
The name "sewage fungus" is somewhat of a misnomer, [ 5 ] as these growths are not primarily fungal in nature. Instead, they are complex poly microbial mats bound within a matrix of extracellular polymeric substances . The bacterial taxa most frequently associated with this phenomenon include Sphaerotilus natans , Zoogloea spp . , Beggiatoa spp . , and Rhodoferax spp . [ 11 ] [ 16 ] [ 17 ]
In addition to being a bioindicator of organic pollution in rivers and playing a vital role utilizing excess organic carbon in fluvial systems, sewage fungus causes significant ecological impacts through direct and indirect ecological pathways.
Sewage fungus thrives in the low dissolved oxygen (DO) environment of an organically polluted river. [ 4 ] [ 17 ] [ 18 ] [ 19 ] Whilst DO is required for sewage fungus growth, it readily outcompetes other benthic organisms at low DO, [ 20 ] [ 21 ] [ 22 ] quickly smothering riverbeds, greatly altering the benthic habitat for invertebrates [ 23 ] [ 24 ] and fish spawning. [ 2 ] [ 25 ] [ 26 ] The dominating growth of sewage fungus also reduces hyporheic exchange flows, an important part of a rivers self-cleaning system. [ 27 ] [ 28 ] Similar river biofilms are also reported to accumulate heavy metals [ 29 ] [ 30 ] and other toxic substances. [ 31 ] within their matrix causing ecological impacts throughout the food web. [ 32 ] [ 33 ] As a heterotroph, sewage fungus uses considerably higher DO than an aquatic macrophyte of the same mass, [ 34 ] it can maintain DO concentrations below thresholds required for other organisms. Once sewage fungus becomes established, it is difficult to remove, [ 35 ] unless all sources of organic nutrients (pollution) are addressed, causing a further loss in biodiversity [ 36 ] and other flora and fauna [ 37 ] [ 38 ] in the river. These ecological impacts and the striking visible presence of sewage fungus growth on a riverbed further affects people's perceptions and use of rivers. [ 7 ] [ 39 ]
Sewage fungus is a type of microbial mat , the specific composition of which is affected by the available nutrients (especially organic carbon sources) and the environmental drivers of each unique occurrence. However, several key taxa are reported as highly frequent and dominant within sewage fungus.
Sphaerotilus natans , has been strongly associated with this phenomenon since it was first studied [ 5 ] and continues to be regarded as a key sewage fungus organism. [ 11 ] [ 12 ] Consequently, Sphaerotilus has been used seemingly synonymously with sewage fungus and a series of laboratory studies use S. natans as sewage fungus. [ 25 ] [ 40 ] [ 41 ]
Other key taxa include the bacteria Zoogloea spp . , Beggiatoa spp. , Thiothrix spp. , Flavobacterium spp. , and Flexibacter spp. . [ 16 ] [ 17 ] However, fungi (e.g., Leptomitus lacteus , Geotrichum candidum , and Fusarium aquaeductuum ), algae (e.g., Cladophora glomerata ) along with archaea and protozoa (e.g., Carchesium polypinum ) also form integral and important pasts of the biofilm.
Recent genomic studies of sewage fungus composition have identified some of these taxa within airport de-icer implicated occurrences but have also identified new taxa not previously associated with sewage fungus: Rhodoferax as a dominant component of sewage fungus, [ 11 ] and the presence of Thiothrix . [ 12 ]
Alongside the complex nutrient utilisation requirements of sewage fungus, there are several key environmental drivers including substrate type, flow velocity, temperature, shading/sunlight, and water chemistry (e.g. pH).
Flowing water is a requirement for sewage fungus growth, to provide a constant replenishment of nutrients. [ 2 ] [ 4 ] [ 42 ] However, if the velocity of the river is too fast, then growths are scoured away, especially on more readily mobilised substrates. In turn, the specific flow of the river shapes the morphotype and structure of the biofilm. [ 43 ] Intrinsically the substrate affects the upper limit of flow as more stable riverbeds are less readily mobilised in periods of higher flows. Surfaces such as large cobbles, anthropogenic litter (e.g., bricks), and concrete channels facilitate excellent sewage fungus growth, whereas fine sediments and gravel provide a less stable substrate. | https://en.wikipedia.org/wiki/Sewage_fungus |
Sewage disposal regulation and administration describes the governance of sewage treatment and disposal.
Sewage treatment systems in the United States are subject to the Clean Water Act (CWA) and are regulated by federal and state environmental agencies. In most states, local sewage plants receive discharge permits from state agencies; in the remaining states and territories , permits are issued by the United States Environmental Protection Agency (EPA). [ 1 ] The treatment plants, known as publicly owned treatment works (POTW) in CWA parlance, must protect the health and welfare of the local population by ensuring that wastewater does not contaminate the local potable water supply, nor violate additional water quality standards that protect the ecological health of the water body.
The basic national standard for U.S. municipal treatment plants is the Secondary Treatment Regulation . [ 2 ] Most plants in the U.S. must meet this secondary treatment standard. The permit authority (state agency or EPA) can compel a POTW to meet a higher standard, if there are applicable water quality standards for the receiving water body. For water bodies with stringent standards, such as Lake Tahoe , POTWs must treat their discharges to tertiary treatment levels, and then pump all treated water out of the drainage basin so that no effluent ever drains to a certain body of water. [ 3 ] Such higher standards may require the POTW to construct improvements to its plant(s). If not in compliance with its permit and regulations, POTWs may be subject to heavy fines. Regulation is therefore often the driving force behind increasing sewage treatment costs in the United States, and is directly linked to the high cost of constructing or expanding a sewage treatment facility.
Many large cities in the U.S. operate combined sewers , which collect sewage and stormwater runoff in a single pipe system leading to the treatment plant. Combined sewers can cause serious water pollution problems due to combined sewer overflows, which are caused by large variations in flow between dry and wet weather. These overflows can lead to violation of the Secondary Treatment Regulation and/or water quality standards. Discharge permits for these POTWs typically have additional requirements that require facility improvements to reduce or eliminate the overflows. [ 4 ]
Ships at sea are forbidden from discharging their sewage overboard unless three miles or more from shore. [ 5 ]
In England and Wales, Ofwat regulates charges and service standards. [ 6 ] In England environmental standards and their achievement for sewage disposal are regulated by the Environment Agency . In Wales environmental regulation is undertaken by Natural Resources Wales . In Scotland the Scottish Environment Protection Agency fulfils the environmental regulation role and the Water Industry Commission for Scotland undertakes the economic regulatory role. [ 7 ]
Sewer systems are usually administered on the local level, usually citywide, and usually by the city itself. These systems, which may operate independently or as a subdivision of a city or other municipal agency, are typically operated as Enterprises , meaning that they produce enough revenues to fund their own activities.
Revenues are usually generated through two charges to customers: connection fees and use charges . Connection fees are charged once to new customers as they connect to the sanitary sewer collection system, and are usually designed to recover capital investments made by the enterprise to serve its customers. Use charges are periodic charges for ongoing use of the system, and are designed to recover operations and maintenance expenses. Both connection fees and use charges are typically proportionate to the amount and strength of wastewater expected to be generated by each customer. Therefore, a single family residence would pay much smaller fees and charges than a food processing plant.
Some POTWs are eligible for low-interest loans to finance system improvements, from the Clean Water State Revolving Fund . This program is administered by EPA and state agencies, using a combination of federal and state funds. [ 8 ]
In England sewerage and sewage disposal is undertaken by relatively few large private companies, including several multi-national companies. In Wales and Scotland a "not for profit" company is the responsible body, however in Wales almost all the operational work is sub- contracted by others. Charges to domestic users are based either on the metered volume of incoming water or on the notional value of the property ( rateable basis). [ 9 ] | https://en.wikipedia.org/wiki/Sewage_regulation_and_administration |
Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges. [ 2 ] Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater . There are a high number of sewage treatment processes to choose from. These can range from decentralized systems (including on-site treatment systems) to large centralized systems involving a network of pipes and pump stations (called sewerage ) which convey the sewage to a treatment plant. For cities that have a combined sewer , the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment , while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter (measured as biological oxygen demand ) from sewage, using aerobic or anaerobic biological processes. A so-called quaternary treatment step (sometimes referred to as advanced treatment) can also be added for the removal of organic micropollutants , such as pharmaceuticals. This has been implemented in full-scale for example in Sweden. [ 3 ]
A large number of sewage treatment technologies have been developed, mostly using biological treatment processes. Design engineers and decision makers need to take into account technical and economical criteria of each alternative when choosing a suitable technology. [ 4 ] : 215 Often, the main criteria for selection are: desired effluent quality, expected construction and operating costs, availability of land, energy requirements and sustainability aspects. In developing countries and in rural areas with low population densities, sewage is often treated by various on-site sanitation systems and not conveyed in sewers. These systems include septic tanks connected to drain fields , on-site sewage systems (OSS), vermifilter systems and many more. On the other hand, advanced and relatively expensive sewage treatment plants may include tertiary treatment with disinfection and possibly even a fourth treatment stage to remove micropollutants. [ 3 ]
At the global level, an estimated 52% of sewage is treated. [ 5 ] However, sewage treatment rates are highly unequal for different countries around the world. For example, while high-income countries treat approximately 74% of their sewage, developing countries treat an average of just 4.2%. [ 5 ]
The treatment of sewage is part of the field of sanitation . Sanitation also includes the management of human waste and solid waste as well as stormwater (drainage) management. [ 6 ] The term sewage treatment plant is often used interchangeably with the term wastewater treatment plant . [ 4 ] [ page needed ] [ 7 ]
The term sewage treatment plant (STP) (or sewage treatment works ) is nowadays often replaced with the term wastewater treatment plant (WWTP). [ 7 ] [ 8 ] Strictly speaking, the latter is a broader term that can also refer to industrial wastewater treatment.
The terms water recycling center or water reclamation plants are also in use as synonyms.
The overall aim of treating sewage is to produce an effluent that can be discharged to the environment while causing as little water pollution as possible, or to produce an effluent that can be reused in a useful manner. [ 9 ] This is achieved by removing contaminants from the sewage. It is a form of waste management .
With regards to biological treatment of sewage, the treatment objectives can include various degrees of the following: to transform or remove organic matter, nutrients (nitrogen and phosphorus), pathogenic organisms, and specific trace organic constituents (micropollutants). [ 7 ] : 548
Some types of sewage treatment produce sewage sludge which can be treated before safe disposal or reuse. Under certain circumstances, the treated sewage sludge might be termed biosolids and can be used as a fertilizer .
Typical values for physical–chemical characteristics of raw sewage in developing countries have been published as follows: 180 g/person/d for total solids (or 1100 mg/L when expressed as a concentration), 50 g/person/d for BOD (300 mg/L), 100 g/person/d for COD (600 mg/L), 8 g/person/d for total nitrogen (45 mg/L), 4.5 g/person/d for ammonia-N (25 mg/L) and 1.0 g/person/d for total phosphorus (7 mg/L). [ 10 ] : 57 The typical ranges for these values are: 120–220 g/person/d for total solids (or 700–1350 mg/L when expressed as a concentration), 40–60 g/person/d for BOD (250–400 mg/L), 80–120 g/person/d for COD (450–800 mg/L), 6–10 g/person/d for total nitrogen (35–60 mg/L), 3.5–6 g/person/d for ammonia-N (20–35 mg/L) and 0.7–2.5 g/person/d for total phosphorus (4–15 mg/L). [ 10 ] : 57
Sewerage (or sewage system) is the infrastructure that conveys sewage or surface runoff ( stormwater , meltwater , rainwater ) using sewers. It encompasses components such as receiving drains , manholes , pumping stations , storm overflows, and screening chambers of the combined sewer or sanitary sewer . Sewerage ends at the entry to a sewage treatment plant or at the point of discharge into the environment . It is the system of pipes, chambers, manholes or inspection chamber, etc. that conveys the sewage or storm water.
Sewage can be treated close to where the sewage is created, which may be called a decentralized system or even an on-site system ( on-site sewage facility , septic tanks , etc.). Alternatively, sewage can be collected and transported by a network of pipes and pump stations to a municipal treatment plant. This is called a centralized system (see also sewerage and pipes and infrastructure ).
A large number of sewage treatment technologies have been developed, mostly using biological treatment processes (see list of wastewater treatment technologies ). Very broadly, they can be grouped into high tech (high cost) versus low tech (low cost) options, although some technologies might fall into either category. Other grouping classifications are intensive or mechanized systems (more compact, and frequently employing high tech options) versus extensive or natural or nature-based systems (usually using natural treatment processes and occupying larger areas) systems. This classification may be sometimes oversimplified, because a treatment plant may involve a combination of processes, and the interpretation of the concepts of high tech and low tech, intensive and extensive, mechanized and natural processes may vary from place to place.
Examples for more low-tech, often less expensive sewage treatment systems are shown below. They often use little or no energy. Some of these systems do not provide a high level of treatment, or only treat part of the sewage (for example only the toilet wastewater ), or they only provide pre-treatment, like septic tanks. On the other hand, some systems are capable of providing a good performance, satisfactory for several applications. Many of these systems are based on natural treatment processes, requiring large areas, while others are more compact. In most cases, they are used in rural areas or in small to medium-sized communities.
For example, waste stabilization ponds are a low cost treatment option with practically no energy requirements but they require a lot of land. [ 4 ] : 236 Due to their technical simplicity, most of the savings (compared with high tech systems) are in terms of operation and maintenance costs. [ 4 ] : 220–243
Examples for systems that can provide full or partial treatment for toilet wastewater only:
Examples for more high-tech, intensive or mechanized, often relatively expensive sewage treatment systems are listed below. Some of them are energy intensive as well. Many of them provide a very high level of treatment. For example, broadly speaking, the activated sludge process achieves a high effluent quality but is relatively expensive and energy intensive. [ 4 ] : 239
There are other process options which may be classified as disposal options, although they can also be understood as basic treatment options. These include: Application of sludge , irrigation , soak pit , leach field , fish pond , floating plant pond, water disposal/ groundwater recharge , surface disposal and storage. [ 12 ] : 138
The application of sewage to land is both: a type of treatment and a type of final disposal. [ 4 ] : 189 It leads to groundwater recharge and/or to evapotranspiration. Land application include slow-rate systems, rapid infiltration, subsurface infiltration, overland flow. It is done by flooding, furrows, sprinkler and dripping. It is a treatment/disposal system that requires a large amount of land per person.
The per person organic matter load is a parameter used in the design of sewage treatment plants. This concept is known as population equivalent (PE). The base value used for PE can vary from one country to another. Commonly used definitions used worldwide are: 1 PE equates to 60 gram of BOD per person per day, and it also equals 200 liters of sewage per day. [ 13 ] This concept is also used as a comparison parameter to express the strength of industrial wastewater compared to sewage.
When choosing a suitable sewage treatment process, decision makers need to take into account technical and economical criteria. [ 4 ] : 215 Therefore, each analysis is site-specific. A life cycle assessment (LCA) can be used, and criteria or weightings are attributed to the various aspects. This makes the final decision subjective to some extent. [ 4 ] : 216 A range of publications exist to help with technology selection. [ 4 ] : 221 [ 12 ] [ 14 ] [ 15 ]
In industrialized countries , the most important parameters in process selection are typically efficiency, reliability, and space requirements. In developing countries , they might be different and the focus might be more on construction and operating costs as well as process simplicity. [ 4 ] : 218
Choosing the most suitable treatment process is complicated and requires expert inputs, often in the form of feasibility studies . This is because the main important factors to be considered when evaluating and selecting sewage treatment processes are numerous. They include: process applicability, applicable flow, acceptable flow variation, influent characteristics, inhibiting or refractory compounds, climatic aspects, process kinetics and reactor hydraulics , performance, treatment residuals, sludge processing, environmental constraints, requirements for chemical products, energy and other resources; requirements for personnel, operating and maintenance; ancillary processes, reliability, complexity, compatibility, area availability. [ 4 ] : 219
With regards to environmental impacts of sewage treatment plants the following aspects are included in the selection process: Odors, vector attraction, sludge transportation, sanitary risks, air contamination , soil and subsoil contamination, surface water pollution or groundwater contamination , devaluation of nearby areas, inconvenience to the nearby population. [ 4 ] : 220
Odors emitted by sewage treatment are typically an indication of an anaerobic or septic condition. [ 16 ] Early stages of processing will tend to produce foul-smelling gases, with hydrogen sulfide being most common in generating complaints. Large process plants in urban areas will often treat the odors with carbon reactors, a contact media with bio-slimes, small doses of chlorine , or circulating fluids to biologically capture and metabolize the noxious gases. [ 17 ] Other methods of odor control exist, including addition of iron salts, hydrogen peroxide , calcium nitrate , etc. to manage hydrogen sulfide levels. [ 18 ]
The energy requirements vary with type of treatment process as well as sewage strength. For example, constructed wetlands and stabilization ponds have low energy requirements. [ 19 ] In comparison, the activated sludge process has a high energy consumption because it includes an aeration step. Some sewage treatment plants produce biogas from their sewage sludge treatment process by using a process called anaerobic digestion . This process can produce enough energy to meet most of the energy needs of the sewage treatment plant itself. [ 7 ] : 1505
For activated sludge treatment plants in the United States, around 30 percent of the annual operating costs is usually required for energy. [ 7 ] : 1703 Most of this electricity is used for aeration, pumping systems and equipment for the dewatering and drying of sewage sludge . Advanced sewage treatment plants, e.g. for nutrient removal, require more energy than plants that only achieve primary or secondary treatment. [ 7 ] : 1704
Small rural plants using trickling filters may operate with no net energy requirements, the whole process being driven by gravitational flow, including tipping bucket flow distribution and the desludging of settlement tanks to drying beds. This is usually only practical in hilly terrain and in areas where the treatment plant is relatively remote from housing because of the difficulty in managing odors. [ 20 ] [ 21 ]
In highly regulated developed countries, industrial wastewater usually receives at least pretreatment if not full treatment at the factories themselves to reduce the pollutant load , before discharge to the sewer. The pretreatment has the following two main aims: Firstly, to prevent toxic or inhibitory compounds entering the biological stage of the sewage treatment plant and reduce its efficiency. And secondly to avoid toxic compounds from accumulating in the produced sewage sludge which would reduce its beneficial reuse options. Some industrial wastewater may contain pollutants which cannot be removed by sewage treatment plants. Also, variable flow of industrial waste associated with production cycles may upset the population dynamics of biological treatment units. [ citation needed ]
Urban residents in many parts of the world rely on on-site sanitation systems without sewers, such as septic tanks and pit latrines , and fecal sludge management in these cities is an enormous challenge. [ 22 ]
For sewage treatment the use of septic tanks and other on-site sewage facilities (OSSF) is widespread in some rural areas, for example serving up to 20 percent of the homes in the U.S. [ 23 ]
Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes. [ 13 ] Different types of sewage treatment may utilize some or all of the process steps listed below.
Preliminary treatment (sometimes called pretreatment) removes coarse materials that can be easily collected from the raw sewage before they damage or clog the pumps and sewage lines of primary treatment clarifiers .
The influent in sewage water passes through a bar screen to remove all large objects like cans, rags, sticks, plastic packets, etc. carried in the sewage stream. [ 24 ] This is most commonly done with an automated mechanically raked bar screen in modern plants serving large populations, while in smaller or less modern plants, a manually cleaned screen may be used. The raking action of a mechanical bar screen is typically paced according to the accumulation on the bar screens and/or flow rate. The solids are collected and later disposed in a landfill, or incinerated. Bar screens or mesh screens of varying sizes may be used to optimize solids removal. If gross solids are not removed, they become entrained in pipes and moving parts of the treatment plant, and can cause substantial damage and inefficiency in the process. [ 25 ] : 9
Grit consists of sand , gravel , rocks, and other heavy materials. Preliminary treatment may include a sand or grit removal channel or chamber, where the velocity of the incoming sewage is reduced to allow the settlement of grit. Grit removal is necessary to (1) reduce formation of deposits in primary sedimentation tanks, aeration tanks, anaerobic digesters, pipes, channels, etc. (2) reduce the frequency of tank cleaning caused by excessive accumulation of grit; and (3) protect moving mechanical equipment from abrasion and accompanying abnormal wear. The removal of grit is essential for equipment with closely machined metal surfaces such as comminutors, fine screens, centrifuges, heat exchangers, and high pressure diaphragm pumps.
Grit chambers come in three types: horizontal grit chambers, aerated grit chambers, and vortex grit chambers. Vortex grit chambers include mechanically induced vortex, hydraulically induced vortex, and multi-tray vortex separators. Given that traditionally, grit removal systems have been designed to remove clean inorganic particles that are greater than 0.210 millimetres (0.0083 in), most of the finer grit passes through the grit removal flows under normal conditions. During periods of high flow deposited grit is resuspended and the quantity of grit reaching the treatment plant increases substantially. [ 7 ]
Equalization basins can be used to achieve flow equalization. This is especially useful for combined sewer systems which produce peak dry-weather flows or peak wet-weather flows that are much higher than the average flows. [ 7 ] : 334 Such basins can improve the performance of the biological treatment processes and the secondary clarifiers. [ 7 ] : 334
Disadvantages include the basins' capital cost and space requirements. Basins can also provide a place to temporarily hold, dilute and distribute batch discharges of toxic or high-strength wastewater which might otherwise inhibit biological secondary treatment (such was wastewater from portable toilets or fecal sludge that is brought to the sewage treatment plant in vacuum trucks ). Flow equalization basins require variable discharge control, typically include provisions for bypass and cleaning, and may also include aerators and odor control. [ 26 ]
In some larger plants, fat and grease are removed by passing the sewage through a small tank where skimmers collect the fat floating on the surface. Air blowers in the base of the tank may also be used to help recover the fat as a froth. Many plants, however, use primary clarifiers with mechanical surface skimmers for fat and grease removal.
Primary treatment is the "removal of a portion of the suspended solids and organic matter from the sewage". [ 7 ] : 11 It consists of allowing sewage to pass slowly through a basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface and are skimmed off. These basins are called primary sedimentation tanks or primary clarifiers and typically have a hydraulic retention time (HRT) of 1.5 to 2.5 hours. [ 7 ] : 398 The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment. Primary settling tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank where it is pumped to sludge treatment facilities. [ 25 ] : 9–11
Sewage treatment plants that are connected to a combined sewer system sometimes have a bypass arrangement after the primary treatment unit. This means that during very heavy rainfall events, the secondary and tertiary treatment systems can be bypassed to protect them from hydraulic overloading, and the mixture of sewage and storm-water receives primary treatment only. [ 27 ]
Primary sedimentation tanks remove about 50–70% of the suspended solids, and 25–40% of the biological oxygen demand (BOD). [ 7 ] : 396
The main processes involved in secondary sewage treatment are designed to remove as much of the solid material as possible. [ 13 ] They use biological processes to digest and remove the remaining soluble material, especially the organic fraction. This can be done with either suspended-growth or biofilm processes. The microorganisms that feed on the organic matter present in the sewage grow and multiply, constituting the biological solids, or biomass. These grow and group together in the form of flocs or biofilms and, in some specific processes, as granules. The biological floc or biofilm and remaining fine solids form a sludge which can be settled and separated. After separation, a liquid remains that is almost free of solids, and with a greatly reduced concentration of pollutants. [ 13 ]
Secondary treatment can reduce organic matter (measured as biological oxygen demand) from sewage, using aerobic or anaerobic processes. The organisms involved in these processes are sensitive to the presence of toxic materials, although these are not expected to be present at high concentrations in typical municipal sewage.
Advanced sewage treatment generally involves three main stages, called primary, secondary and tertiary treatment but may also include intermediate stages and final polishing processes. The purpose of tertiary treatment (also called advanced treatment ) is to provide a final treatment stage to further improve the effluent quality before it is discharged to the receiving water body or reused. More than one tertiary treatment process may be used at any treatment plant. If disinfection is practiced, it is always the final process. It is also called effluent polishing . Tertiary treatment may include biological nutrient removal (alternatively, this can be classified as secondary treatment), disinfection and partly removal of micropollutants, such as environmental persistent pharmaceutical pollutants .
Tertiary treatment is sometimes defined as anything more than primary and secondary treatment in order to allow discharge into a highly sensitive or fragile ecosystem such as estuaries , low-flow rivers or coral reefs . [ 28 ] Treated water is sometimes disinfected chemically or physically (for example, by lagoons and microfiltration ) prior to discharge into a stream , river , bay , lagoon or wetland , or it can be used for the irrigation of a golf course, greenway or park. If it is sufficiently clean, it can also be used for groundwater recharge or agricultural purposes.
Sand filtration removes much of the residual suspended matter. [ 25 ] : 22–23 Filtration over activated carbon , also called carbon adsorption, removes residual toxins . [ 25 ] : 19 Micro filtration or synthetic membranes are used in membrane bioreactors and can also remove pathogens. [ 7 ] : 854
Settlement and further biological improvement of treated sewage may be achieved through storage in large human-made ponds or lagoons. These lagoons are highly aerobic, and colonization by native macrophytes , especially reeds, is often encouraged.
Disinfection of treated sewage aims to kill pathogens (disease-causing microorganisms) prior to disposal. It is increasingly effective after more elements of the foregoing treatment sequence have been completed. [ 29 ] : 359 The purpose of disinfection in the treatment of sewage is to substantially reduce the number of pathogens in the water to be discharged back into the environment or to be reused. The target level of reduction of biological contaminants like pathogens is often regulated by the presiding governmental authority. The effectiveness of disinfection depends on the quality of the water being treated (e.g. turbidity , pH, etc.), the type of disinfection being used, the disinfectant dosage (concentration and time), and other environmental variables. Water with high turbidity will be treated less successfully, since solid matter can shield organisms, especially from ultraviolet light or if contact times are low. Generally, short contact times, low doses and high flows all militate against effective disinfection. Common methods of disinfection include ozone , chlorine , ultraviolet light , or sodium hypochlorite . [ 25 ] : 16 Monochloramine , which is used for drinking water, is not used in the treatment of sewage because of its persistence.
Chlorination remains the most common form of treated sewage disinfection in many countries due to its low cost and long-term history of effectiveness. One disadvantage is that chlorination of residual organic material can generate chlorinated-organic compounds that may be carcinogenic or harmful to the environment. Residual chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated, adding to the complexity and cost of treatment.
Ultraviolet (UV) light can be used instead of chlorine, iodine, or other chemicals. Because no chemicals are used, the treated water has no adverse effect on organisms that later consume it, as may be the case with other methods. UV radiation causes damage to the genetic structure of bacteria, viruses , and other pathogens , making them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that the target microorganisms are not shielded from the UV radiation (i.e., any solids present in the treated effluent may protect microorganisms from the UV light). In many countries, UV light is becoming the most common means of disinfection because of the concerns about the impacts of chlorine in chlorinating residual organics in the treated sewage and in chlorinating organics in the receiving water.
As with UV treatment, heat sterilization also does not add chemicals to the water being treated. However, unlike UV, heat can penetrate liquids that are not transparent. Heat disinfection can also penetrate solid materials within wastewater, sterilizing their contents. Thermal effluent decontamination systems provide low resource, low maintenance effluent decontamination once installed.
Ozone ( O 3 ) is generated by passing oxygen ( O 2 ) through a high voltage potential resulting in a third oxygen atom becoming attached and forming O 3 . Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, thereby destroying many pathogenic microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site (highly poisonous in the event of an accidental release), ozone is generated on-site as needed from the oxygen in the ambient air. Ozonation also produces fewer disinfection by-products than chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the requirements for special operators. Ozone sewage treatment requires the use of an ozone generator , which decontaminates the water as ozone bubbles percolate through the tank.
Membranes can also be effective disinfectants, because they act as barriers, avoiding the passage of the microorganisms. As a result, the final effluent may be devoid of pathogenic organisms, depending on the type of membrane used. This principle is applied in membrane bioreactors .
Sewage may contain high levels of the nutrients nitrogen and phosphorus . Typical values for nutrient loads per person and nutrient concentrations in raw sewage in developing countries have been published as follows: 8 g/person/d for total nitrogen (45 mg/L), 4.5 g/person/d for ammonia -N (25 mg/L) and 1.0 g/person/d for total phosphorus (7 mg/L). [ 4 ] : 57 The typical ranges for these values are: 6–10 g/person/d for total nitrogen (35–60 mg/L), 3.5–6 g/person/d for ammonia-N (20–35 mg/L) and 0.7–2.5 g/person/d for total phosphorus (4–15 mg/L). [ 4 ] : 57
Excessive release to the environment can lead to nutrient pollution , which can manifest itself in eutrophication . This process can lead to algal blooms , a rapid growth, and later decay, in the population of algae. In addition to causing deoxygenation, some algal species produce toxins that contaminate drinking water supplies.
Ammonia nitrogen, in the form of free ammonia (NH 3 ) is toxic to fish. Ammonia nitrogen, when converted to nitrite and further to nitrate in a water body, in the process of nitrification, is associated with the consumption of dissolved oxygen. Nitrite and nitrate may also have public health significance if concentrations are high in drinking water , because of a disease called metahemoglobinemia . [ 4 ] : 42
Phosphorus removal is important as phosphorus is a limiting nutrient for algae growth in many fresh water systems. Therefore, an excess of phosphorus can lead to eutrophication. It is also particularly important for water reuse systems where high phosphorus concentrations may lead to fouling of downstream equipment such as reverse osmosis .
A range of treatment processes are available to remove nitrogen and phosphorus. Biological nutrient removal (BNR) is regarded by some as a type of secondary treatment process, [ 7 ] and by others as a tertiary (or advanced ) treatment process.
Nitrogen is removed through the biological oxidation of nitrogen from ammonia to nitrate ( nitrification ), followed by denitrification , the reduction of nitrate to nitrogen gas. Nitrogen gas is released to the atmosphere and thus removed from the water.
Nitrification itself is a two-step aerobic process, each step facilitated by a different type of bacteria. The oxidation of ammonia (NH 4 + ) to nitrite (NO 2 − ) is most often facilitated by bacteria such as Nitrosomonas spp. ( nitroso refers to the formation of a nitroso functional group). Nitrite oxidation to nitrate (NO 3 − ), though traditionally believed to be facilitated by Nitrobacter spp. (nitro referring the formation of a nitro functional group ), is now known to be facilitated in the environment predominantly by Nitrospira spp.
Denitrification requires anoxic conditions to encourage the appropriate biological communities to form. Anoxic conditions refers to a situation where oxygen is absent but nitrate is present. Denitrification is facilitated by a wide diversity of bacteria. The activated sludge process , sand filters , waste stabilization ponds , constructed wetlands and other processes can all be used to reduce nitrogen. [ 25 ] : 17–18 Since denitrification is the reduction of nitrate to dinitrogen (molecular nitrogen) gas, an electron donor is needed. This can be, depending on the wastewater, organic matter (from the sewage itself), sulfide , or an added donor like methanol . The sludge in the anoxic tanks (denitrification tanks) must be mixed well (mixture of recirculated mixed liquor, return activated sludge, and raw influent) e.g. by using submersible mixers in order to achieve the desired denitrification.
Over time, different treatment configurations for activated sludge processes have evolved to achieve high levels of nitrogen removal. An initial scheme was called the Ludzack–Ettinger Process. It could not achieve a high level of denitrification. [ 7 ] : 616 The Modified Ludzak–Ettinger Process (MLE) came later and was an improvement on the original concept. It recycles mixed liquor from the discharge end of the aeration tank to the head of the anoxic tank. This provides nitrate for the facultative bacteria. [ 7 ] : 616
There are other process configurations, such as variations of the Bardenpho process. [ 30 ] : 160 They might differ in the placement of anoxic tanks, e.g. before and after the aeration tanks.
Studies of United States sewage in the late 1960s estimated mean per capita contributions of 500 grams (18 oz) in urine and feces, 1,000 grams (35 oz) in synthetic detergents, and lesser variable amounts used as corrosion and scale control chemicals in water supplies. [ 31 ] Source control via alternative detergent formulations has subsequently reduced the largest contribution, but naturally the phosphorus content of urine and feces remained unchanged.
Phosphorus can be removed biologically in a process called enhanced biological phosphorus removal . In this process, specific bacteria, called polyphosphate-accumulating organisms (PAOs), are selectively enriched and accumulate large quantities of phosphorus within their cells (up to 20 percent of their mass). [ 30 ] : 148–155
Phosphorus removal can also be achieved by chemical precipitation , usually with salts of iron (e.g. ferric chloride ) or aluminum (e.g. alum ), or lime. [ 25 ] : 18 This may lead to a higher sludge production as hydroxides precipitate and the added chemicals can be expensive. Chemical phosphorus removal requires significantly smaller equipment footprint than biological removal, is easier to operate and is often more reliable than biological phosphorus removal. Another method for phosphorus removal is to use granular laterite or zeolite . [ 32 ] [ 33 ]
Some systems use both biological phosphorus removal and chemical phosphorus removal. The chemical phosphorus removal in those systems may be used as a backup system, for use when the biological phosphorus removal is not removing enough phosphorus, or may be used continuously. In either case, using both biological and chemical phosphorus removal has the advantage of not increasing sludge production as much as chemical phosphorus removal on its own, with the disadvantage of the increased initial cost associated with installing two different systems.
Once removed, phosphorus, in the form of a phosphate-rich sewage sludge , may be sent to landfill or used as fertilizer in admixture with other digested sewage sludges. In the latter case, the treated sewage sludge is also sometimes referred to as biosolids. 22% of the world's phosphorus needs could be satisfied by recycling residential wastewater. [ 34 ] [ 35 ]
Micropollutants such as pharmaceuticals, ingredients of household chemicals, chemicals used in small businesses or industries, environmental persistent pharmaceutical pollutants (EPPP) or pesticides may not be eliminated in the commonly used sewage treatment processes (primary, secondary and tertiary treatment) and therefore lead to water pollution. [ 36 ] Although concentrations of those substances and their decomposition products are quite low, there is still a chance of harming aquatic organisms. For pharmaceuticals , the following substances have been identified as toxicologically relevant: substances with endocrine disrupting effects, genotoxic substances and substances that enhance the development of bacterial resistances . [ 37 ] They mainly belong to the group of EPPP.
Techniques for elimination of micropollutants via a fourth treatment stage during sewage treatment are implemented in Germany, Switzerland, Sweden [ 3 ] and the Netherlands and tests are ongoing in several other countries. [ 38 ] In Switzerland it has been enshrined in law since 2016. [ 39 ] Since 1 January 2025, there has been a recast of the Urban Waste Water Treatment Directive in the European Union. Due to the large number of amendments that have now been made, the directive was rewritten on November 27, 2024 as Directive (EU) 2024/3019, published in the EU Official Journal on December 12, and entered into force on January 1, 2025. The member states now have 31 months, i.e. until July 31, 2027, to adapt their national legislation to the new directive ("implementation of the directive").
The amendment stipulates that, in addition to stricter discharge values for nitrogen and phosphorus, persistent trace substances must at least be partially separated. The target, similar to Switzerland, is that 80% of 6 key substances out of 12 must be removed between discharge into the sewage treatment plant and discharge into the water body. At least 80% of the investments and operating costs for the fourth treatment stage will be passed on to the pharmaceutical and cosmetics industry according to the polluter pays principle in order to relieve the population financially and provide an incentive for the development of more environmentally friendly products. In addition, the municipal wastewater treatment sector is to be energy neutral by 2045 and the emission of microplastics and PFAS is to be monitored.
The implementation of the framework guidelines is staggered until 2045, depending on the size of the sewage treatment plant and its population equivalents (PE). Sewage treatment plants with over 150,000 PE have priority and should be adapted immediately, as a significant proportion of the pollution comes from them. The adjustments are staggered at national level in:
Wastewater treatment plants with 10,000 to 150,000 PE that discharge into coastal waters or sensitive waters are staggered at national level in:
The latter concerns waters with a low dilution ratio, waters from which drinking water is obtained and those that are coastal waters, or those used as bathing waters or used for mussel farming. Member States will be given the option not to apply fourth treatment in these areas if a risk assessment shows that there is no potential risk from micropollutants to human health and/or the environment. [ 40 ] [ 41 ]
Such process steps mainly consist of activated carbon filters that adsorb the micropollutants. The combination of advanced oxidation with ozone followed by granular activated carbon (GAC) has been suggested as a cost-effective treatment combination for pharmaceutical residues. For a full reduction of microplasts the combination of ultrafiltration followed by GAC has been suggested. Also the use of enzymes such as laccase secreted by fungi is under investigation. [ 42 ] [ 43 ] Microbial biofuel cells are investigated for their property to treat organic matter in sewage. [ 44 ]
To reduce pharmaceuticals in water bodies, source control measures are also under investigation, such as innovations in drug development or more responsible handling of drugs. [ 37 ] [ 45 ] In the US, the National Take Back Initiative is a voluntary program with the general public, encouraging people to return excess or expired drugs, and avoid flushing them to the sewage system. [ 46 ]
Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge treatment is focused on reducing sludge weight and volume to reduce transportation and disposal costs, and on reducing potential health risks of disposal options. Water removal is the primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during thermophilic digestion, composting , or incineration . The choice of a sludge treatment method depends on the volume of sludge generated, and comparison of treatment costs required for available disposal options. Air-drying and composting may be attractive to rural communities, while limited land availability may make aerobic digestion and mechanical dewatering preferable for cities, and economies of scale may encourage energy recovery alternatives in metropolitan areas.
Sludge is mostly water with some amounts of solid material removed from liquid sewage. Primary sludge includes settleable solids removed during primary treatment in primary clarifiers . Secondary sludge is sludge separated in secondary clarifiers that are used in secondary treatment bioreactors or processes using inorganic oxidizing agents . In intensive sewage treatment processes, the sludge produced needs to be removed from the liquid line on a continuous basis because the volumes of the tanks in the liquid line have insufficient volume to store sludge. [ 47 ] This is done in order to keep the treatment processes compact and in balance (production of sludge approximately equal to the removal of sludge). The sludge removed from the liquid line goes to the sludge treatment line. Aerobic processes (such as the activated sludge process) tend to produce more sludge compared with anaerobic processes. On the other hand, in extensive (natural) treatment processes, such as ponds and constructed wetlands , the produced sludge remains accumulated in the treatment units (liquid line) and is only removed after several years of operation. [ 48 ]
Sewage treatment plants can have significant effects on the biotic status of receiving waters and can cause some water pollution, especially if the treatment process used is only basic. For example, for sewage treatment plants without nutrient removal, eutrophication of receiving water bodies can be a problem.
In 2024, The Royal Academy of Engineering released a study into the effects wastewater on public health in the United Kingdom. [ 55 ] The study gained media attention, with comments from the UKs leading health professionals, including Sir Chris Whitty . Outlining 15 recommendations for various UK bodies to dramatically reduce public health risks by increasing the water quality in its waterways , such as rivers and lakes.
After the release of the report, The Guardian newspaper interviewed Whitty, who stated that improving water quality and sewage treatment should be a high level of importance and a "public health priority". He compared it to eradicating cholera in the 19th century in the country following improvements to the sewage treatment network. [ 56 ] The study also identified that low water flows in rivers saw high concentration levels of sewage , as well as times of flooding or heavy rainfall. While heavy rainfall had always been associated with sewage overflows into streams and rivers, the British media went as far to warn parents of the dangers of paddling in shallow rivers during warm weather. [ 57 ]
Whitty's comments came after the study revealed that the UK was experiencing a growth in the number of people that were using coastal and inland waters recreationally. This could be connected to a growing interest in activities such as open water swimming or other water sports . [ 58 ] Despite this growth in recreation, poor water quality meant some were becoming unwell during events. [ 59 ] Most notably, the 2024 Paris Olympics had to delay numerous swimming-focused events like the triathlon due to high levels of sewage in the River Seine . [ 60 ]
Increasingly, people use treated or even untreated sewage for irrigation to produce crops. Cities provide lucrative markets for fresh produce, so are attractive to farmers. Because agriculture has to compete for increasingly scarce water resources with industry and municipal users, there is often no alternative for farmers but to use water polluted with sewage directly to water their crops. There can be significant health hazards related to using water loaded with pathogens in this way. The World Health Organization developed guidelines for safe use of wastewater in 2006. [ 61 ] They advocate a 'multiple-barrier' approach to wastewater use, where farmers are encouraged to adopt various risk-reducing behaviors. These include ceasing irrigation a few days before harvesting to allow pathogens to die off in the sunlight, applying water carefully so it does not contaminate leaves likely to be eaten raw, cleaning vegetables with disinfectant or allowing fecal sludge used in farming to dry before being used as a human manure. [ 62 ]
Before the 20th century in Europe, sewers usually discharged into a body of water such as a river, lake, or ocean. There was no treatment, so the breakdown of the human waste was left to the ecosystem . This could lead to satisfactory results if the assimilative capacity of the ecosystem is sufficient which is nowadays not often the case due to increasing population density. [ 4 ] : 78
Today, the situation in urban areas of industrialized countries is usually that sewers route their contents to a sewage treatment plant rather than directly to a body of water. In many developing countries , however, the bulk of municipal and industrial wastewater is discharged to rivers and the ocean without any treatment or after preliminary treatment or primary treatment only. Doing so can lead to water pollution . Few reliable figures exist on the share of the wastewater collected in sewers that is being treated worldwide. A global estimate by UNDP and UN-Habitat in 2010 was that 90% of all wastewater generated is released into the environment untreated. [ 66 ] A more recent study in 2021 estimated that globally, about 52% of sewage is treated. [ 5 ] However, sewage treatment rates are highly unequal for different countries around the world. For example, while high-income countries treat approximately 74% of their sewage, developing countries treat an average of just 4.2%. [ 5 ] As of 2022, without sufficient treatment, more than 80% of all wastewater generated globally is released into the environment. High-income nations treat, on average, 70% of the wastewater they produce, according to UN Water. [ 34 ] [ 67 ] [ 68 ] Only 8% of wastewater produced in low-income nations receives any sort of treatment. [ 34 ] [ 69 ] [ 70 ]
The Joint Monitoring Programme (JMP) for Water Supply and Sanitation by WHO and UNICEF report in 2021 that 82% of people with sewer connections are connected to sewage treatment plants providing at least secondary treatment. [ 71 ] : 55 However, this value varies widely between regions. For example, in Europe, North America, Northern Africa and Western Asia, a total of 31 countries had universal (>99%) wastewater treatment. However, in Albania, Bermuda, North Macedonia and Serbia "less than 50% of sewered wastewater received secondary or better treatment" and in Algeria, Lebanon and Libya the value was less than 20% of sewered wastewater that was being treated. The report also found that "globally, 594 million people have sewer connections that don't receive sufficient treatment. Many more are connected to wastewater treatment plants that do not provide effective treatment or comply with effluent requirements.". [ 71 ] : 55
Sustainable Development Goal 6 has a Target 6.3 which is formulated as follows: "By 2030, improve water quality by reducing pollution, eliminating,dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally." [ 65 ] The corresponding Indicator 6.3.1 is the "proportion of wastewater safely treated". It is anticipated that wastewater production would rise by 24% by 2030 and by 51% by 2050. [ 34 ] [ 72 ] [ 73 ]
Data in 2020 showed that there is still too much uncollected household wastewater: Only 66% of all household wastewater flows were collected at treatment facilities in 2020 (this is determined from data from 128 countries). [ 8 ] : 17 Based on data from 42 countries in 2015, the report stated that "32 per cent of all wastewater flows generated from point sources received at least some treatment". [ 8 ] : 17 For sewage that has indeed been collected at centralized sewage treatment plants, about 79% went on to be safely treated in 2020. [ 8 ] : 18
The history of sewage treatment had the following developments: It began with land application ( sewage farms ) in the 1840s in England, followed by chemical treatment and sedimentation of sewage in tanks, then biological treatment in the late 19th century, which led to the development of the activated sludge process starting in 1912. [ 74 ] [ 75 ]
It was not until the late 19th century that it became possible to treat the sewage by biologically decomposing the organic components through the use of microorganisms and removing the pollutants. Land treatment was also steadily becoming less feasible, as cities grew and the volume of sewage produced could no longer be absorbed by the farmland on the outskirts.
Edward Frankland conducted experiments at the sewage farm in Croydon , England during the 1870s and was able to demonstrate that filtration of sewage through porous gravel produced a nitrified effluent (the ammonia was converted into nitrate) and that the filter remained unclogged over long periods of time. [ 76 ] This established the then revolutionary possibility of biological treatment of sewage using a contact bed to oxidize the waste. This concept was taken up by the chief chemist for the London Metropolitan Board of Works , William Dibdin, in 1887:
In most countries, sewage collection and treatment are subject to local and national regulations and standards .
In the European Union, 0.8% of total energy consumption goes to wastewater treatment facilities. [ 34 ] [ 80 ] The European Union needs to make extra investments of €90 billion in the water and waste sector to meet its 2030 climate and energy goals. [ 34 ] [ 81 ] [ 82 ]
In October 2021, British Members of Parliament voted to continue allowing untreated sewage from combined sewer overflows to be released into waterways. [ 83 ] [ 84 ]
The ' Delhi Jal Board ' (DJB) is currently operating on the construction of the largest sewage treatment plant in India. It will be operational by the end of 2022 with an estimated capacity of 564 MLD. It is supposed to solve the existing situation wherein untreated sewage water is being discharged directly into the river 'Yamuna'.
In Libya, municipal wastewater treatment is managed by the general company for water and wastewater in Libya, which falls within the competence of the Housing and Utilities Government Ministry. There are approximately 200 sewage treatment plants across the nation, but few plants are functioning. In fact, the 36 larger plants are in the major cities; however, only nine of them are operational, and the rest of them are under repair. [ 91 ] | https://en.wikipedia.org/wiki/Sewage_treatment |
Sewbo is an industrial sewing robot invented by Sewbo, Inc., a company based in Seattle , Washington .
The company Sewbo, Inc was founded by Jonathan Zornow in 2015. [ 1 ] [ 2 ] The robot capable of handling fabric components throughout the entire garment production process. The operation relies on a water-soluble, non-toxic polymer called polyvinyl alcohol , which stiffens the fabric to facilitate manipulation during sewing. While Sewbo is currently optimized for producing T-shirts . It can sew a T-shirt from start to the end. The process involves cutting fabric panels, stiffening them with a polymer solution, and feeding them into a sewing machine using a robotic arm equipped with suction cups. [ 3 ] | https://en.wikipedia.org/wiki/Sewbo |
A sewer dosing unit (SDU) is a plumbing device to allow effective sewage disposal with low liquid-flow rates. With a global emphasis on water saving, many new buildings and renovations are seeing the installation of water saving fixtures such as low flow shower heads and low flush toilets . With the decrease in wastewater flows problems are arising from waste solids not being carried completely to the main sewers, often causing blockages.
In 2006, Ducane R&D Pty Ltd conceived the idea of a device that can store wastewater and release it in large batches to replace the drain clearing action of large volume toilet flushes. After prototyping and development the devices became available for sale in Australia, New Zealand and the United Kingdom under the brand name Drainwave in 2010.
Independent testing has shown that the use of an SDU allows for the use of low flush toilets using as little as 0.8 L to push general waste solids more than 25 metres along a typical wastewater drainpipe.
An advantage of the SDU is that it can use more than just the toilet wastewater to keep drains clear of blockages. | https://en.wikipedia.org/wiki/Sewer_dosing_unit |
Sewer mining (or sewage mining ) is a concept where municipal wastewater ( sewage ) is pumped from a trunk sewer and treated on-site to accommodate a range of local, nonpotable water needs. [ 1 ] It is a strategy for combating water scarcity . It combines decentralized wastewater management and water reclamation . [ 1 ] Since 2012, it is used as a tool for improving water management and promoting reuse of water in Australia. [ 2 ]
A sewer mining scheme typically consists of: [ 3 ]
One of the advantages of sewer mining is the decrease in transportation costs, since sewage can be treated locally. Another benefit derives from the fact that no further capital costs for sewer infrastructure are needed, because a treatment scheme can be directly linked to the already existing pipeline system. With the combination of new, emerging technologies, such as the membrane bioreactor (MBR) , further reduction of operating costs became possible, making the average cost of retrieved water comparable to potable water costs. [ 3 ]
Most of sewer mining cases are realised in Australia and involve residential non-drinking uses. More specifically, in Sydney Olympic Park, a large scale sewer mining unit has been installed for using recycled water for irrigational purposes. The retrieved water is being produced in such quantities that substitutes more than 50% of the potable water that would be sustaining green sites in the Sydney Olympic Park and the Newington Estate. Another realisation of sewer mining takes place in Pennant Hills Golf Club, where the recycling scheme produced up to 100 million litres of reclaimed water that is used for irrigating the golf course. [ 4 ] In this case, the nutrients from the sewage are used as fertilizer on the golf course rather than being removed in a sewage treatment plant. [ 5 ]
In Greece, an example that applies sewer mining as a decentralised wastewater treatment method is the DESSIN Athens pilot plant, which is implemented under the European Union Seventh Framework Programme . [ 6 ] The Athens demonstration site pumps municipal sewage directly from the central sewage network and treats it by the use of a membrane bioreactor, while a reverse osmosis unit assures that the water quality lies within the legislation limits. The treated effluent is used to irrigate a nearby area of 50 square meters. [ 3 ] | https://en.wikipedia.org/wiki/Sewer_mining |
Dosage compensation is the process by which organisms equalize the expression of genes between members of different biological sexes. Across species, different sexes are often characterized by different types and numbers of sex chromosomes . In order to neutralize the large difference in gene dosage produced by differing numbers of sex chromosomes among the sexes, various evolutionary branches have acquired various methods to equalize gene expression among the sexes. Because sex chromosomes contain different numbers of genes , different species of organisms have developed different mechanisms to cope with this inequality. Replicating the actual gene is impossible; thus organisms instead equalize the expression from each gene. For example, in humans , female (XX) cells randomly silence the transcription of one X chromosome , and transcribe all information from the other, expressed X chromosome. Thus, human females have the same number of expressed X-linked genes per cell as do human males (XY), both sexes having essentially one X chromosome per cell, from which to transcribe and express genes. [ 1 ]
Different lineages have evolved different mechanisms to cope with the differences in gene copy numbers between the sexes that are observed on sex chromosomes. Some lineages have evolved dosage compensation, an epigenetic mechanism which restores expression of X or Z specific genes in the heterogametic sex to the same levels observed in the ancestor prior to the evolution of the sex chromosome. [ 2 ] [ 3 ] Other lineages equalize the expression of the X- or Z- specific genes between the sexes, but not to the ancestral levels, i.e. they possess incomplete compensation with "dosage balance". One example of this is X-inactivation which occurs in humans. The third documented type of gene dose regulatory mechanism is incomplete compensation without balance (sometimes referred to as incomplete or partial dosage compensation). In this system gene expression of sex-specific loci is reduced in the heterogametic sex i.e. the females in ZZ/ZW systems and males in XX/XY systems. [ 4 ]
There are three main mechanisms of achieving dosage compensation which are widely documented in the literature and which are common to most species. These include random inactivation of one female X chromosome (as observed in humans and Mus musculus ; this is called X-inactivation ), a two-fold increase in the transcription of a single male X chromosome (as observed in Drosophila melanogaster ), and decreased transcription by half in both of the X chromosomes of a hermaphroditic organism (as observed in Caenorhabditis elegans ). These mechanisms have been widely studied and manipulated in model organisms commonly used in the laboratory research setting. A summary of these forms of dosage compensation is illustrated below. However, there are also other less common forms of dosage compensation, which are not as widely researched and are sometimes specific to only one species (as observed in certain bird and monotreme species).
One logical way to equalize gene expression amongst males and females that follow a XX/XY sex differentiation scheme would be to decrease or altogether eliminate the expression of one of the X chromosomes in an XX, or female, homogametic individual, such that both males and females then express only one X chromosome. This is the case in many mammalian organisms, including humans and mice. [ 1 ]
The evidence for this mechanism of dosage compensation was discovered prior to scientists' understanding of what its implications were. In 1949, Murray Barr and Ewert Bertram published data describing the presence of "nucleolar satellites, [ 5 ] which they observed were present in the mature somatic tissue of different female species. Further characterization of these satellites revealed that they were actually packages of condensed heterochromatin , but a decade would pass before scientists grasped the significance of this specialized DNA. [ citation needed ]
Then, in 1959 Susumu Ohno proved that these satellite-like structures found exclusively in female cells were actually derived from female X chromosomes. [ 6 ] He called these structures Barr bodies after one of the investigators who originally documented their existence. Ohno's studies of Barr bodies in female mammals with multiple X chromosomes revealed that such females used Barr bodies to inactivate all but one of their X chromosomes. Thus, Ohno described the "n-1" rule to predict the number of Barr bodies in a female with n number of X chromosomes in her karyotype. [ 6 ]
Simultaneously, Mary F. Lyon began investigating manipulations of X-linked traits that had phenotypically visible consequences, particularly in mice, whose fur color is a trait intimately linked to the X chromosome. Building on work done by Ohno and his colleagues, Lyon eventually proved that either the maternal or paternal X chromosome is randomly inactivated in every cell of the female body in the species she was studying, [ 7 ] which explained the heterogeneous fur patterns she observed in her mosaic mice. This process is known as X-inactivation , and is sometimes referred to as "lyonization". [ 1 ] This discovery can be easily extrapolated to explain the mixed color patterns observed in the coats of tortoiseshell cats . The fur patterns characteristic of tortoiseshell cats are found almost exclusively in females, because only they randomly inactivate one X chromosome in every somatic hair cell. [ 8 ] Thus, presuming that hair color determining genes are X-linked, it makes sense that whether the maternal or paternal X chromosome is inactivated in a particular hair cell can result in differential fur color expression.
Compounding on Lyon's discoveries, in 1962 Ernest Beutler used female fibroblast cell lineages grown in culture to demonstrate the heritability of lyonization or random X-inactivation. [ 9 ] By analyzing the differential expression of two existing, viable alleles for the X-linked enzyme glucose-6-phosphate dehydrogenase (G6PD) gene, Beutler observed that the inactivation of the gene was heritable across passaged generations of the cells. [ 10 ]
This pattern of dosage compensation, caused by random X-inactivation, is regulated across development in female mammals, following concerted patterns throughout development; for example, at the beginning of most female mammal development, both X chromosomes are initially expressed, but gradually undergo epigenetic processes to eventually achieve random inactivation of one X. [ 10 ] In germ cells , inactivated X chromosomes are then once again activated to ensure their expression in gametes produced by female mammals. [ 1 ]
Thus, dosage compensation in mammals is largely achieved through the silencing of one of two female X chromosomes via X-inactivation. This process involves histone tail modifications, DNA methylation patterns, and reorganization of large-scale chromatin structure encoded by the X-ist gene. [ 1 ] In spite of these extensive modifications, not all genes along the X chromosome are subject to X-inactivation; active expression at some loci is required for homologous recombination with the pseudo-autosomal region ( PAR ) of the Y chromosome during meiosis. [ 11 ] Additionally, 10-25% of human X chromosome genes, [ 12 ] and 3-7% of mouse X chromosome genes [ 13 ] outside of the PARs show weak expression from the inactive X chromosome.
Random X-inactivation demands that the cell can determine if it contains more than one active X-chromosome before acting to silence any extraneous X-chromosome(s). This process is known as "counting". [ 1 ] The exact molecular mechanism of counting is still unknown, but a popular model posits that autosomes produce factors that repress X-inactivation, while X-chromosome products that promote X-inactivation. These two conflicting forces are balanced such that if there is more than one X-chromosome X-inactivation will occur, but if there is only one, the autosomal products will successfully prevent the process. [ 1 ]
Not all random X-inactivation is entirely random. Some alleles, generally mutations in the X-inactivation center on the X-chromosome have been demonstrated to confer a bias towards inactivation for the chromosome on which they sit. [ 1 ] Truly random X-inactivation may also appear to be non-random if one X-chromosome carries a deleterious mutation. This can result in fewer cells which express the lower-fitness X-chromosome to be present in the body as these cells are selected against. [ 1 ]
Another mechanism common for achieving equal X-related genetic expression between males and females involves two-fold increased transcription of a single male X chromosome. Thus, heterogametic male organisms with one X chromosome may match the level of expression achieved in homogametic females with two active X chromosomes. This mechanism is observed in Drosophila . [ 14 ]
The concept of dosage compensation actually originated from an understanding of organisms in which males upregulated X-linked genes two-fold, and was much later extended to account for the observation of the once mysterious Barr bodies. As early as 1932, H.J. Muller carried out a set of experiments which allowed him to track the expression of eye color in flies, which is an X-linked gene. Muller introduced a mutant gene that caused loss of pigmentation in fly eyes, and subsequently noted that males with only one copy of the mutant gene had similar pigmentation to females with two copies of the mutant gene. This led Muller to coin the phrase "dosage compensation" to describe the observed phenomenon of gene expression equalization. [ 15 ]
Despite these advances, it was not until Ardhendu Mukherjee and W. Beermann performed more advanced autoradiography experiments in 1965 that scientists could confirm that transcription of genes in the single male X chromosome was double that observed in the two female X chromosomes. [ 16 ] Mukherjee and Beermann confirmed this by designing a cellular autoradiography experiment that allowed them to visualize incorporation of [3H]uridine into ribonucleic acid of the X chromosomes. Their studies showed equal levels of [3H]uridine incorporation in the single male X chromosome and the two female X chromosomes. Thus, the investigators concluded that the two-fold increase in the rate of RNA synthesis in the X chromosome of the male relative to those of the female could account for Muller's hypothesized dosage compensation.
In the case of two-fold increased transcription of a single male X chromosome, there is no use for a Barr body, and the male organism must use different genetic machinery to increase the transcriptional output of their single X chromosome. It is common in such organisms for the Y chromosome to be necessary for male fertility , but not for it to play an explicit role in sex determination . [ 17 ] [ 18 ] In Drosophila , for example, the sex lethal (SXL) gene acts as a key regulator of sexual differentiation and maturation in somatic tissue ; in XX animals, SXL is activated to repress increased transcription, while in XY animals SXL is inactive and allows male development to proceed via increased transcription of the single X. [ 18 ] Several binding sites exist on the Drosophila X chromosome for the dosage compensation complex (DCC), a ribonucleoprotein complex; these binding sites have varying levels of affinity, presumably for varying expression of specific genes. [ 19 ] The Male Specific Lethal complex, composed of protein and RNA binds and selectively modifies hundreds of X-linked genes, [ 20 ] [ 21 ] increasing their transcription to levels comparable to female D. melanogaster .
In organisms that use this method of dosage compensation, the presence of one or more X chromosomes must be detected early on in development, as failure to initiate the appropriate dosage compensation mechanisms is lethal. [ 17 ] Male specific lethal proteins (MSLs) are a family of four proteins that bind to the X chromosome exclusively in males. The name "MSL" is used because mutations in these genes cause inability to effectively upregulate X-linked genes appropriately, and are thus lethal to males only and not their female counterparts. [ 17 ] SXL regulates pre-messenger RNA in males to differentially splice MSLs and result in the appropriate increase in X chromosome transcription observed in male Drosophila . The immediate target of SXL is male specific lethal-2 (MSL-2). [ 22 ] Current dogma suggests that the binding of MSL-2 at multiple sites along the SXL gene in females prevents proper MSL-2 translation, and thus, as previously stated, represses the possibility for X-linked genetic upregulation in females. However, all other transcription factors in the MSL family—maleless, MSL-1, and MSL-3—are able to act when SXL is not expressed, as in the case in males. These factors act to increase male X chromosome transcriptional activity. Histone acetylation and the consequent upregulation of X-linked genes in males is dictated by the MSL complex. [ 23 ] Specifically, special roX non-coding RNAs on the MSL complexes facilitate binding to the single male X chromosome, and dictate acetylation of specific loci along the X chromosome as well as the formation of euchromatin. [ 24 ] Though these RNAs bind at specific sites along the male X chromosome, their effects spread along the length of the chromosome and have the ability to influence large-scale chromatin modifications. The implications of this spreading epigenetic regulation along the male X chromosome is thought to have implications for understanding the transfer of epigenetic activity along long genomic stretches. [ 14 ]
Other species that do not follow the previously discussed conventions of XX females and XY males must find alternative ways to equalize X-linked gene expression among differing sexes. For example, in Caenorhabditis elegans (or C. elegans ), sex is determined by the ratio of X chromosomes relative to autosomes; [ 25 ] worms with two X chromosomes (XX worms) develop as hermaphrodites , whereas those with only one X chromosome (XO worms) develop as males. [ 26 ] This system of sex determination is unique, because there is no male specific chromosome, as is the case in XX/XY sex determination systems. However, as is the case with the previously discussed mechanisms of dosage compensation, failure to express X-linked genes appropriately can still be lethal. [ 27 ]
In this XX/XO sex determination system, gene expression on the X chromosome is equalized by downregulating expression of genes on both X chromosomes of hermaphroditic XX organisms by half. [ 26 ] In these XX organisms, the dosage compensation complex (DCC) is assembled on both X chromosomes to allow for this tightly regulated change in transcription levels. The DCC is often compared to the condensin complex, [ 28 ] which is conserved across the mitotic and meiotic processes of many species. This complex is crucial to the condensation and segregation of chromosomes during both meiosis and mitosis. Because data substantiates the theory that dosage compensation in other species is caused by chromatin-wide modifications, many theorize that the DCC in particular functions similar to the condensin complex in its ability to condense or remodel the chromatin of the X chromosome. [ 29 ]
The role of the DCC in this form of dosage compensation was postulated by Barbara J. Meyer in the 1980s, and its individual components and their cooperative function were later parsed out by her lab. Notably, in 1999, data from Meyer's lab showed that SDC-2 is a particularly important transcriptional factor for targeting the DCC to the X chromosome and for assembling DCC components onto the X chromosomes in XX embryos. [ 30 ] More recently, Meyer's lab has shown that proteins known as X-linked signal elements (XSEs) operate in concert with SDC-2 to differentially repress and activate other genes in the dosage compensation pathway. [ 31 ] By selectively mutating a panel of genes hypothesized to contribute to dosage compensation in worms, Meyer's group demonstrated which XSEs specifically play a role in determining normal dosage compensation. They found that during embryonic development, several X-linked genes—including sex-1, sex-2, fox-1, and ceh-39—act in a combinatorial fashion to selectively repress transcriptional activity of the xol-1 gene in hermaphrodites. [ 32 ] [ 33 ] Xol-1 expression is tightly regulated during early development, and is considered the most upstream gene in sex determination of C. elegans. In fact, xol-1 is often referred to in the literature as the master sex regulatory gene of C. elegans. XX C. elegans embryos have much lower xol-1 expression than their XO counterparts, resulting from overall increases in the amount of SEX-1, SEX-2, CEH-39, and FOX-1 transcription produced in the female embryos. This consequent decrease in xol-1 expression then allows higher SDC-2 expression levels, which aids in the formation and function of the DCC complex in the XX hermaphroditic worms, and in turn results in equalized expression of X-linked genes in the hermaphrodite. [ citation needed ]
Though all of the above-mentioned XSEs act to reduce xol-1 expression, experimentally reducing expression levels of these individual XSEs has been shown to have a minimal effect on sex determination and successful dosage compensation. [ 31 ] This could be in part because these genes encode different proteins that act cooperatively rather than in an isolated fashion; for example, SEX-1 is a nuclear hormone receptor, while FOX-1 is an RNA-binding protein with properties capable of inducing post-transcriptional modifications in the xol-1 target. [ 31 ] [ 33 ] [ 34 ] However, reducing the level of more than one XSE in different combinational permutations seems to have an additive effect on ensuring proper sex determination and resultant dosage compensation mechanics. [ 31 ] This supports the hypothesis that these XSEs act together to achieve the desired sex determination and dosage compensation fate. Thus, in this model organism, the achieved level of X-chromosome expression is directly correlated to the activation of multiple XSEs that ultimately function to repress xol-1 expression in a developing worm embryo. A summary of this C. elegans mechanism of dosage compensation is illustrated below.
The ZZ/ZW sex system is used by most birds, as well as some reptiles and insects. In this system the Z is the larger chromosome so the males (ZZ) must silence some genetic material to compensate for the female's (ZW) smaller W chromosome. Instead of silencing the entire chromosome as humans do, male chickens (the model ZZ organism) seem to engage in selective Z silencing, in which they silence only certain genes on the extra Z chromosome. [ 35 ] [ 36 ] Thus, male chickens express an average of 1.4-1.6 of the Z chromosome DNA expressed by female chickens. [ 37 ] The Z chromosome expression of male zebra finches and chickens is higher than the autosomal expression rates, whereas X chromosome expression in female humans is equal to autosomal expression rates, [ 38 ] illustrating clearly that both male chickens and male zebra finches practice incomplete silencing. Few other ZZ/ZW Systems have been analyzed as thoroughly as the chicken; however a recent study on silkworms [ 39 ] revealed similar levels of unequal compensation across male Z chromosomes. Z-specific genes were over-expressed in males when compared to females, and a few genes had equal expression in both male and female Z chromosomes. [ citation needed ]
In chickens, most of the dosage compensated genes exist on the Zp, or short, arm of the chromosome while the non-compensated genes are on the Zq, or long, arm of the chromosome. The compensated (silenced) genes on Zp resemble a region on the primitive platypus sex chromosome, suggesting an ancestor to the XX/XY system. [ 40 ]
The sex chromosomes of birds evolved separately from those of mammals and share very little sequence homology with the XY chromosomes. [ 41 ] As such, scientists refer to bird sex chromosomes as a ZW sex-determining system, with males possessing two Z chromosomes, and females possessing one Z chromosome and one W. Thus, dosage compensation in birds could be hypothesized to follow a pattern similar to the random X-inactivation observed in most mammals. Alternatively, birds might show decreased transcription of the two Z chromosomes present in the male heterogametic sex, similar to the system observed in the two hermaphrodite X chromosomes of C. elegans . However, bird mechanisms of dosage compensation differ significantly from these precedents. Instead, male birds appear to selectively silence only a few genes along one of their Z chromosomes, rather than randomly silencing one entire Z chromosome. [ 42 ] This type of selective silencing has led some people to label birds as "less effective" at dosage compensation than mammals. [ 38 ] However, more recent studies have shown that those genes on the Z chromosome which are not inactivated in birds may play an important role in recruiting dosage compensation machinery to the Z chromosome in ZZ organisms. [ 43 ] In particular, one of these genes, ScII has been demonstrated to be an ortholog of xol-1, the master sex regulator gene in C. elegans. [ 43 ] [ 44 ] Thus, the function of the selective silencing may be to spare dosage compensation of genes crucial for sex determination of homologous pairing. [ citation needed ]
Recent studies are focusing on how epigenetic mechanisms could contribute to dosage compensation in birds, with a particular emphasis on methylation . It is already known that some regions on the Z chromosome of birds are heavily methylated, called MHM regions. So far, only two such regions have been well studied: one located at around 27.3 Mb and the other at 73.16–73.17 Mb (designated MHM2). The first MHM region discovered consists of tandem repeats of a BamHI 2.2-kb sequence and has a high degree of methylation on the cytosine of CpG islands (segments of cytosine-phosphate-guanine that are more readily methylated and silenced than other DNA segments) in both copies of the Z chromosome in males, and less so in the Z chromosome of females. This region is transcribed only in females and produces a long non-coding RNA, which gathers at the transcription site next to the DMRT1 gene. [ 4 ] The second MHM region, at 73.16 Mb, is not as extensively studied due to its recent discovery. It appears to be smaller in size and contains three long non-coding RNA sequences with higher expression in females. [ 9 ]
Findings also suggest that the mechanism is more gene-specific, as certain genetic variants, called methylation quantitative trait loci (meQTLs), can affect methylation. These meQTLs are hypothesized to impact a larger part of the Z chromosome in males and are mostly located on autosomes, affecting the Z chromosome in a trans manner. [ 3 ]
Monotremes are a class of basal mammals that also lay eggs. [ 45 ] They are an order of mammals that includes platypuses and four species of echidna, all of which are egg-laying mammals. While monotremes use an XX/XY system, unlike other mammals, monotremes have more than two sex chromosomes. The male short-beaked echidna, for example, has nine sex chromosomes—5 Xs and 4 Ys, and the male platypus has 5 Xs and 5 Ys. [ citation needed ]
Platypuses are a monotreme species whose mechanism of sex determination has been extensively studied. There is some contention in academia about the evolutionary origin and the proper taxonomy of platypuses. A recent study [ 46 ] revealed that four platypus X chromosomes, as well as a Y chromosome, are homologous to some regions on the avian Z chromosome. Specifically, platypus X1 shares homology with the chicken Z chromosome, and both share homology with the human chromosome 9. This homology is important when considering the mechanism of dosage compensation in monotremes. In 50% of female platypus cells, only one of the alleles on these X chromosomes is expressed while in the remaining 50% multiple alleles are expressed. This, combined with the portions that are homologous to chicken Z and human 9 chromosomes imply that this level of incomplete silencing may be the ancestral form of dosage compensation.
Regardless of their ambiguous evolutionary history, platypuses have been empirically determined to follow an XY sex-determination system , with females possessing five pairs of X chromosomes as the homogametic sex, and males possessing five X and five Y chromosomes as the heterogametic sex. [ 47 ] Because the entire genome of the platypus has yet to be completely sequenced (including one of the X chromosomes), [ 46 ] there is still continued investigation as to the definitive mechanism of dosage compensation that Platypuses follow. Research from the laboratory of Jennifer Graves used qPCR and SNP analysis of BACs containing various genes from X chromosomes in order to find whether multiple alleles for particular X-linked genes were being expressed at once, or were otherwise being dosage compensated. [ 46 ] Her group found that in female platypuses, some X-linked genes only expressed an allele from one X chromosomes, while other genes expressed multiple alleles. [ 46 ] This appears to be a system similar to the selective silencing method of dosage compensation observed in birds. However, about half of all X-linked genes also seemed to stochastically express only one active copy of said gene, [ 46 ] alluding to the system of random X-inactivation observed in humans. These findings suggest that platypuses may employ a hybrid form of dosage compensation that combines feature from mammals as well as birds. Understanding the evolution of such a system may have implications for solidifying the true ancestral lineage of monotremes.
In addition to humans and flies, some plants also make use of the XX/XY dosage compensation systems. Silene latifolia plants are also either male (XY) or female (XX), with the Y chromosome being smaller, with fewer genes expressed, than the X chromosome. Two separate studies [ 48 ] have shown male S. latifolia expression of X-linked genes to be about 70% of the expression in females. If the S. latifolia did not practice dosage compensation, the expected level of X-linked gene expression in males would be 50% that of females, thus the plant practices some degree of dosage compensation but, because male expression is not 100% that of females, it has been suggested that S. latiforia and its dosage compensation system is still evolving. Additionally, in plant species that lack dimorphic sex chromosomes, dosage compensation can occur when aberrant meiotic events or mutations result in either aneuploidy or polyploidy . Genes on the affected chromosome may be upregulated or down-regulated to compensate for the change in the normal number of chromosomes present.
Research into dosage compensation has been carried out in six species of toxicoferan reptiles and in one species of softshell turtle. Two species of caenophidian snake (one which belongs to the family Viperidae and the other to the family Colubridae) have been investigated and both of these exhibit female heterogametic sex determination systems (ZZ\ZW) and have incomplete compensation without balance. [ 49 ] The Komodo dragon exhibits incomplete compensation without dosage balance in their independently evolved ZZ/ZW system. [ 50 ] In the XX/XY system of Basiliscus vittatus and multiple neo-sex chromosomes with male heterogamety in the pygopodid gecko Lialis burtonis incomplete compensation without dosage balance were also seen. [ 51 ] [ 52 ] The Green anole ( Anolis carolinensis ; Dactyloidea), has XX/XY sex determination and unlike the other squamates studied to date has complete dosage compensation with dosage balance. [ 53 ] In the Florida softshell turtle ( Apalone ferox) with ZZ/ZW sex chromosomes, the lack of dosage balance in the expression of Z-linked genes was also found. [ 54 ]
XCI is initiated very early during female embryonic development or upon differentiation of female embryonic stem (ES) cells and results in inactivation of one X chromosome in every female somatic cell. This process is initiated very early during development, around the two- to eight-cell stage and is maintained in the developing extra-embryonic tissues of the embryo, including the fetal placenta. [ 55 ] Xist RNA induces heterochromatinization of the X chromosome by attracting chromatin modifiers, involved in gene silencing. Xist RNA is tightly associated with the Xi and it is required for X Chromosome Inactivation to occur in cis. Knockout studies in female ES cells and mice have shown that X chromosomes bearing a deletion of the Xist gene are unable to inactivate the mutated X. Most of the human female ES cell lines display an inactivated X chromosome already in the undifferentiated state characterized by XIST expression, XIST coating and accumulated markers of heterochromatin on the Xi. [ 55 ]
It is widely thought that human embryos do not employ XCI prior to implantation. [ 56 ] Female embryos have an accumulation of Xist RNA on one of the two X chromosomes, beginning around the 8-cell stage. Xist RNA accumulates at the morula and blastocyst stages and is shown to be associated with transcriptional silencing of the Xist-coated chromosomal region, therefore indicating dosage compensation has occurred. [ 56 ] Recently, however, it has become increasingly apparent that XCI of the paternal X chromosome is already present from the 4-cell stage onward in all cells of preimplantation mouse embryos, not the 8-cell stages. [ citation needed ]
Xite and Xist, are both long non-coding RNAs that regulate and facilitate the process of X-inactivation and are important in the silencing of genes within the X chromosome that is being inactivated. [ 57 ] These work in combination with Tsix, which is non-coding RNA that is an antisense which downregulates the effects of Xist on the X chromosome in which it is expressed on the maternal X chromosome upon the start regulation of X-inactivation. [ 58 ] These three RNAs regulate the X-X pair in a cis orientation in order to be able to have both chromosomes available for inhibitory actions. Tsix and Xite have basic lncRNAs functions in addition to X-inactivation and regulate the X-X pair in the trans orientation. This ensures exclusive silencing for both X chromosomes. Xite and Tsix are both essential within the orientational directional processes in cis and trans as it is seen that without Tsix and Xite in trans it perturbs pairing and counting of genes. [ 57 ] [ 58 ]
Once the Xist is turned off and no longer regulates the process, the Tsix will slowly decrease in expression as well until both RNAs are no longer being changed by Xic. [ 58 ] Xite is the locus that harbors intergenic transcription start sites from hypersensitive sites of allelic crossovers/differences. [ 57 ] When X-inactivation begins, the transcription of Xite increases and signals for the downregulation of Tsix in cis orientation, which is on the silent X chromosome, all while promoting the Tsix persistence on the active X chromosome. [ 59 ] Xite also has major roles to play in the asymmetry of Tsix expression and generates X chromosome inequality through moving and helping orient the chromosomes to be acted upon by the correct subsequent lncRNA, either Tsix or Xist. [ 58 ]
The monarch butterfly Danaus plexippus belongs to the order Lepidoptera and has 30 chromosomes one of which is a neo-sex chromosome which is the result of a fusion between one of the sex chromosomes and an autosome. A study using a combination of methods (Hi-C assembly, coverage analysis and ChIp-seq) found that the neo-Z segment exhibits complete dosage compensation which is achieved by increased transcription in ZW females. Interestingly, the ancestral Z segment exhibits dosage balance with transcription levels being equal between both genders but less than the expected ancestral level, and this is achieved by decreased transcription in ZZ males. [ 60 ] | https://en.wikipedia.org/wiki/Sex-chromosome_dosage_compensation |
Sex-limited genes are genes that are present in both sexes of sexually reproducing species but are expressed in only one sex and have no penetrance , or are simply 'turned off' in the other. [ 1 ] In other words, sex-limited genes cause the two sexes to show different traits or phenotypes , despite having the same genotype . This term is restricted to autosomal traits, and should not be confused with sex-linked characteristics, which have to do with genetic differences on the sex chromosomes (see sex-determination system ). Sex-limited genes are also distinguished from sex-influenced genes, where the same gene will show differential expression in each sex. Sex-influenced genes commonly show a dominant/recessive relationship, where the same gene will have a dominant effect in one sex and a recessive effect in the other (for example, male pattern baldness ). However, the resulting phenotypes caused by sex-limited genes are present in only one sex and can be seen prominently in various species that typically show high sexual dimorphism . [ 2 ]
Sex-limited genes are responsible for sexual dimorphism , which is a phenotypic (directly observable) difference between males and females of the same species regardless of genotype . [ 3 ] These differences can be reflected in size, color, behavior (ex: levels of aggression), and morphology . An example of sex-limited genes are genes which control horn development in sheep: [ 4 ] while both males and females possess the same genes controlling horn development, they are only expressed in males. Sex-limited genes are also responsible for some female beetles' inability to grow exaggerated mandibles, [ 5 ] research that is discussed in detail later in this article.
Sex-limited genes were first hypothesized by Charles Darwin and though he was unsuccessful in distinguishing the previously mentioned sex-linked traits, his hypothesis was the starting point for future study of the subject. [ 6 ] His studies on sex-limited traits have been further substantiated and supported over time, distinguishing sex-limited genes and sex-linked traits. Modern study of sex-limited genes includes research on epigenetics , which is the study of inheritable phentotypic changes with no change in DNA sequence. Modern research suggests that a substantial portion of the expression of sex-limited genes and sexual dimorphism may be influenced by certain epigenetic marks. [ 7 ]
The purpose of sex-limited genes is to resolve sexual conflict . These genes try to resolve the "push-pull" between males and females over trait values for optimal phenotype. Without these genes, organisms would be forced to settle on an average trait value, incurring costs on both sexes. With these genes, it is possible to 'turn off' the genes in one sex, allowing both sexes to attain (or at least, approach very closely) their optimal phenotypes. This phenotypic variation can play a key role in the evolution of various species and their sexual differentiation . [ 3 ]
The idea of sex-limited genes was initially developed by Charles Darwin in 1871 in his book The Descent of Man and Selection in Relation to Sex. [ 6 ] He did not distinguish between sex-limited, sex-linked, and sex-influenced genes, but referred to any gene that expresses differently between sexes as sex-limited. Thomas Hunt Morgan , aware of this confusing terminology, published an article in The American Naturalist in 1914 titled "Sex-Linked and Sex-Limited Inheritance," which proposed definitions of sex-linked genes and sex-limited genes (as defined in the introduction above). [ 8 ] Morgan's paper was followed by several others involving sex-limited genes and their expression as traits. One of the more notable examples is John H. Gerould's "Inheritance of White Wing Color, a Sex-Limited (Sex-Controlled) Variation in Yellow Pierid Butterflies," published in Genetics in 1923 (and edited slightly in 1924). [ 9 ] Gerould observed the phenotypic differences between male and female Pierid Butterflies and determined colouration to be a sex-limited trait.
The notable advancements in the early stages of the development of sex-limited genes, a brief discussion of R. A. Fisher is necessary. Commonly hailed as one of the most significant evolutionary biologists of his time, Fisher was also a talented geneticist. His book The Genetical Theory of Natural Selection , published in 1930, over 20 years before the double-helix shape of DNA was discovered, was the first attempt to explain Darwin's theories within the foundation of genetics . [ 10 ] Chapter 6 of this book is titled "Sexual Reproduction and Sexual Selection" and includes a genetic interpretation of Darwin's initial idea of sex-limited genes. After these groundbreaking works, papers continue to be published further exploring the causes, mechanisms, evolutionary advantages, and more of sex-limited genes.
The genetic study of sexual dimorphism, published in Evolution , hypothesizes two methods which leads to different ornamental characteristics in male and female birds. [ 11 ] The alleles (different versions of the same gene) responsible for sexual dimorphism can be limited to expression in only one sex when they first appear, or the alleles could begin by being expressed in both sexes then become modified (repressed or promoted) in one sex by modifier genes or regulatory elements. The concept of this study was to examine female hybrids from species where males displayed different types of ornamental traits (elongated feathers, wattles, color patches). The assumption is that different hypotheses about male-specific expression will yield different results in female hybrids. The methods and materials of the experiment are discussed in detail in the paper, but the important result that emerged was that NO female hybrids expressed any of the ornamental traits found in the parent males. Two interpretations of these results are possible: the dimorphic alleles were initially only expressed in males, or the alleles were initially expressed in both and then were suppressed in females or became limited to males by regulatory regions that are completely dominant in hybrids. The most likely genomic explanation for initial expression in both species then modification is involvement of cis -dominance, where the factors that modify the gene are located next to the gene on the chromosome . (This is in contrast to trans -dominance, where mobile products that can affect distant genes are produced.) These factors can be in the form of promoter regions , which can be either suppressed or activated by hormones . This experiment also demonstrates that these alleles come under regulatory control very quickly. This is because none of the ornamentation seen in males is seen in the very next generation. These conclusions make it likely that at least some male-specific (thus, sex-limited) genes cue their expression by hormone levels, such as threshold ratios of estrogen and testosterone.
Because sex-limited genes are present in both sexes but only expressed in one, this allows the unexpressed genes to be hidden from selection. On a short-term scale, this means that during one generation, only the sex that expresses the sex-limited trait(s) of interest will be affected by selection. The remaining half of the gene pool for these traits will be unaffected by selection because they are hidden (unexpressed) in the genes of the other sex. Since a portion of the alleles for these sex-limited traits are hidden from selection, this occurrence has been termed 'storage-effect'. On a long-term scale, this storage effect can have significant effects on selection, especially if selection is fluctuating over a long period of time. It is inarguable that selection will fluctuate over time with varying levels of environmental stability. For example, fluctuations in population density can drive selection on sex-limited traits. In less dense populations, females will have less opportunity to choose between males for reproduction. In this case, attractive males may experience both reduced reproductive success and increased predation pressure. Thus, selection on males for sex-limited traits such as increased size (elephant seals) and weaponry (claws on fiddler crabs, horns on rhinoceros beetles) will change direction with fluctuation in population density. [ 12 ]
John Parsch and Hans Ellegren defined "genes that differ in expression between females and males" as sex-biased genes. While this definition is more broad, sex-limited genes are certainly included in this category. One of the key principles of sex-biased gene expression that Parsch and Ellegren stressed in their paper in February 2013 [ 13 ] is that of rapid evolution. They assert that a gene's sex bias can vary among different types of tissues throughout the body or throughout development, making the level of sex bias a fluid, rather than static, property. This makes it possible, then, that the rapid evolution seen in sex-biased genes is not an inherent property of their sex bias, but a property of some other feature. The paper offers expression breadth, the number of tissue types in which the genes are expressed, as an example of a feature correlated to sex-biased genes. It is known that genes with limited expression (in only one type of tissue) generally evolve faster than those with a higher expression breadth, and sex-biased genes are often restricted in their expression, such as to only the testes or ovaries. Thus, it is likely that sex-biased (including sex-limited) genes will evolve faster than the average genetic information. Parsch and Ellegren also assert that "sex-biased genes expressed only in sex-limited reproductive tissues evolve faster than unbiased genes that are expressed only in a single, non-reproductive tissue." That is, genes that have a bias toward any kind of reproductive tissue (testes or ovaries) seem to show faster evolution than genes expressed in non-gonadal tissues, despite the number of tissues in which they are expressed. This makes sense in the context of genes with reproductive function evolving more quickly, a generally observed pattern in evolutionary biology .
Sexual antagonism occurs when two species have conflicting optimal fitness strategies concerning reproduction (see link in introduction paragraph). Multiple matings is a classic example of competing optimal strategies. Males, who typically have a much lower overall investment in reproduction, may benefit from more frequent matings. Females, however, invest much more in reproduction and can be endangered, harmed, or even killed by multiple matings. [ 14 ]
Animal behavior (see ethology ) encompasses so many disciplines that it is impossible not to see it in some capacity in almost all primary literature involving live animals. While the examples above certainly contain aspects of animal behavior, a more overt example of it in relation to sex-limited traits is detailed in a Teplitsky et al. paper (2010) centering on breeding time in red-billed gulls. [ 15 ] This experiment deals with breeding time, an aspect of reproductive biology. Reproduction and sexual behavior are two key aspects of animal behavior, as they are universally expressed in some way throughout the animal kingdom.
Breeding time in red-billed gulls is expressed only in females, because only females lay eggs. Male care, however, affects female breeding performance substantially. This qualifies breeding time as a sex-limited trait because it is expressed only in one sex but can be affected by both (similarly to Hosken's beetle experiment above). By following a natural population of red-billed gulls for 46 years, Teplitsky et al. came to an unexpected conclusion - while laying date (aka breeding time) is only expressed in females, the trait is only heritable in males. This is atypical because sex-limited traits are almost always heritable within the sex in which they are expressed.
For this species, the timing of egg-laying has much to do with male behavior. Males can affect female reproductive success so strongly because for the 20 days up to egg-laying, females spend up to 80% of their time in the nest. This leaves males with the responsibility of providing food regularly and securing (and maintaining) a high-quality territory for nesting. This phenomenon of the genetics of one individual affecting those of another individual is known as indirect genetic effects . For this population, at least, possible explanations for this atypical heritability pattern exist. While controlling female health and safety, males are responsible for the timing of the start of courtship feeding, as well. These populations also typically have excesses of females, allowing males to exert even further choice in the form of mate choice . These factors in combination give males a great opportunity to express their "laying date genotype". In spite of the presence of directional selection and significant male heritability for breeding time, no advancement of breeding time was seen during the 46 years of this experiment. This does not discount the significance of the paper's other results however - one of the most significant being that here a "female trait (laying date) is largely determined by genetic characteristics of its mate". [ 15 ]
Epigenetics is the study of heritable phenotype changes, caused by modification of gene expression and does not entail a change in the genetic code. These epigenetic factors may also be sex-limited. Genomic imprinting for example, silencing of one parental allele by DNA methylation , for which sex-limited imprinting has been proposed to resolve intralocus conflict . Genomic imprinting has been shown to be indistinguishable from non-imprinted systems at the population level in some cases, having equivalent evolutionary models. However, this does not hold for sex-limited models of sex-limited imprinting which behave differently depending on which sex imprinting occurs and the parental sex of imprinted allele. Specifically, this affects whether alleles are imprinted in consecutive generations with different evolutionary trajectories (under the same selection fitnesses) arising purely due to sex-limited epigenetics. The X chromosome for example, has been very prevalent in the field of epigenetics. The X chromosome percentage between males and females is largely due to X chromosome inactivation. In humans, the process of X chromosome inactivation occurs in the beginning stages of development which is one of the main reasons why this topic has been challenging to study. In differentiating between the XX and the XY chromosomes, the amount of X-linked genes compared to XY males are due to the silencing of one of the two chromosomes in XX female. RNA X inactive specific transcript (Xist) regulates this whole process which results in a genome wide silencing. This is also a concept that is poorly understood which makes for great study and prolonged analysis. Indeed, over 20% of X-linked genes are expressed from the inactive X chromosome and they contribute to sexually dimorphic traits. The X chromosome makes a very small percentage of the total human genome and the epigenetics of this chromosome is a major contributor to certain diseases. Thus sex-limited epigenetic traits may have played a pivotal role in the evolution of mammals and other species, particularly as a mechanism to ameliorate intralocus conflict between the sexes. | https://en.wikipedia.org/wiki/Sex-limited_genes |
Sex-linked barring is a plumage pattern on individual feathers in chickens, which is characterized by alternating pigmented and apigmented bars. [ 1 ] The pigmented bar can either contain red pigment ( phaeomelanin ) or black pigment ( eumelanin ) whereas the apigmented bar is always white. The locus is therefore often referred to as an ‘eumelanin diluter’ or ‘melanin disruptor’. [ 2 ] Typical sex-linked barred breeds include the Barred Plymouth Rock , Delaware, Old English Crele Games as well as Coucou de Renne . [ 3 ]
The presence of a white bar on a dark background is distinguishing sex-linked barring from Autosomal barring, another plumage pattern in chickens which is created by a black bar on a light color background (white/ beige or brown) as exemplified by the breed Egyptian Fayoumi . [ 1 ] The absence of pigment in the white bar has been attributed to a lack of pigment producing cells ( melanocytes ) in the feather follicle during feather growth. [ 4 ] [ 5 ] Initially it was proposed that this lack was the result of cell death as a consequence of the B locus mutation but later research demonstrated that the lack is the result of premature cell differentiation rather than apoptosis . [ 6 ]
Male chicken of traditional sex-linked barred breeds like the Barred Plymouth Rock usually show much wider and clearer white bands than females of the same breed. [ 3 ] Further characteristics of sex-linked barred chickens are the dilution of skin pigment in the legs as well as a white dot at the top of the head of freshly hatched chicks which can be used for autosexing : homozygous males have a much bigger spot than hemizygous females. [ 3 ]
Sex-linked barring has been established as the dominant locus B by traditional mendelian genetics in the beginning of the 20th century. [ 3 ] The responsible gene was predicted to be located on the Z chromosome [ 7 ] [ 8 ] and since male birds are homogametic (ZZ), they can be either hetero - or homozygous for sex-linked barring. Females are always hemizygous at this locus (ZW).
In 2010 Swedish scientist have identified four mutations located in or around the tumor suppressor locus CDKN2A , which appear to be associated with sex-linked barring. [ 1 ] The four mutations are organized in 3 different alleles named B0 , B1 and B2 . All alleles carry two non-coding mutation located in regulatory regions of the gene (the promoter and intron ) but only B1 and B2 carry two additional missense mutations in a functional important domain of the protein . The B1 allele is causing the typical sex-linked barring phenotype / appearance and is present in most modern sex-linked barred chicken breeds. Females or male chickens carrying the B2 allele in the heterozygous condition show a defined barring pattern but in the homozygous condition, males are essentially white with very little pigmentation . [ 9 ] This phenotype has been initially described as a distinct but closely related mutation , [ 10 ] however, it was later assigned to the same gene and termed ‘Sex-linked Dilution'. [ 9 ]
The B0 allele only carries the two non-coding mutations and its contribution to the barring pattern remained unknown as it only occurred in breeds that also carry the Dominant white mutation which is masking the effect at the B locus . [ 1 ] ). Recently scientists have removed the Dominant white mutation from chickens of those lines and were able to show that those chickens show a very light barring pattern. They named the phenotype ‘Sex-linked Extreme Dilution’. [ 11 ] As chickens with the B0 allele show the weakest barring pattern compared to those that have the coding mutation in addition, the scientists propose an evolutionary scenario in which the non-coding mutations occurred first and the two missense mutations later in time and independently. As only the combination of both non-coding and missense mutations give the desired and pronounced barring pattern, B0 alone is not present in modern Sex-linked barred breeds anymore. [ 11 ]
Scientists were able to show that either both or one of the non-coding mutations present in all B alleles , cause an up-regulation of the activity of CDKN2A . [ 11 ] ). With more of the gene product, which is called ARF (Alternate Reading frame Protein) in the cell, more of p53 is protected from degradation. p53 is a transcription factor which in turn activates more genes involved in cell cycle regulation and apoptosis . As a consequence the cell stops dividing and starts to prematurely produce pigment.
The missense mutations in the B1 and B2 allele , however, have an opposite effect. [ 11 ] Both missense mutations lead to a malfunctioning ARF protein, which is counteracting the effect of the higher activity of the gene to some degree. The premature production of pigment is still obvious but less strong as observed in the B0 allele. It is intriguing that the missense mutation in the B1 allele is much more disruptive for the protein function than the one in the B2 allele and the scientists believe that this is the reason for the observed phenotypic differences between those two alleles .
When the melanocyte progenitor cells start to migrate up from the bottom of the follicle into the barbs where they will make pigment, they further divide until a sufficient number of pigment cells is achieved. As a consequence of the up-regulation of CDKN2A , most cells will stop dividing and make new cells but instead start producing pigment- a black bar is emerging from the feather. But eventually, there will not be enough pigment cells anymore. As they are recruited from the bottom of the feather follicle, the feather keeps on growing, creating the white bar. With the new set of pigment cells, the cyclic behavior starts again, creating alternating pigmented and apigmented bars.
Mutations in CDKN2A have been associated with the occurrence of familial melanoma in humans. [ 12 ] [ 13 ] [ 14 ] Changes in its gene product ARF often cause the cell to lose their ability for self-induced cell death or cell cycle arrest , which are mechanisms of cells to manage uncontrolled cell divisions and therefore the occurrence of cancer. It is intriguing that chickens carrying the B1 or B2 allele with a malfunctioning ARF do not show any higher prevalence to any type of cancer and are usually considered very sturdy and easy to keep breeds. It is also astonishing that the majority of the egg and meat production industry is relying on chickens, which have a defect in a tumor suppressor gene . [ 11 ] | https://en.wikipedia.org/wiki/Sex-linked_barring |
Sex and drugs refers to the influence of substances on sexual function and experience. Sex and drugs date back to ancient humans and have been interlocked throughout human history. Sexual performance is known as the execution of the act of sex and the quality of sexual activity . This includes elements such as libido (a person's sexual drive), sexual function (including erection in males and vaginal lubrication in females), sensation (the ability to achieve orgasm ). Drugs are termed as any chemical substance that produces a physiological and or psychological change in an organism. Drugs categorized as psychoactive drugs , antihypertensive drugs , antihistamines , cancer treatment , and hormone medication have a significant impact on sexual performance. Various drugs result in different effects, both positive and negative. Negative effects may include low libido, erection issues (in males), vaginal dryness (in females) and anorgasmia . Positive effects usually address these issues, overall enhancing sexual performance and contributing to a more enjoyable sexual experience. It is crucial to know that the impact of drugs on sexual performance varies among individuals, especially among different genders.
Understanding sexual performance involves recognizing various factors that are responsible for a person's combined sexual experience and function. This includes libido, a person's overall sexual desire, and drive; sexual function, which encompasses the male's erectile function and a female's vaginal lubrication; and sensations, which in this context refers to a person's ability to have orgasms and/or ejaculations.
Libido is primarily regulated by the hypothalamus , where sex hormones ( testosterone and estrogen ), and neurotransmitters ( dopamine , oxytocin and serotonin ), are the main components that influence sex drive. [ 1 ] [ 2 ] A decreased libido is predominantly caused by low testosterone in males [ 2 ] For females, serotonin acts as a inhibitor for sexual desire as it reduces the ability of stimulatory systems for sexual cues. [ 3 ]
Penile erection for men is a vascular event caused by the innervation of both autonomic (sympathetic and parasympathetic) and somatic nervous systems (sensory and motor). [ 4 ] Sensory information is received from the genitals towards these nervous systems, in which neurotransmitters such as serotonin , dopamine , noradrenaline , and adrenaline would be released to control erectile function. [ 5 ]
Vaginal dryness refers to the situation when the vagina lacks lubrication which leads to serious pain during sexual intercourse. [ 6 ] The production of lubricants in the vagina are highly sensitive to changes in hormones such as estrogen and testosterone, that are also responsible for blood flow. [ 7 ] Low estrogen and testosterone circulating in the body contributes to vaginal dryness. [ 7 ]
Orgasms are sensory phenomena that take place in the cerebral cortex with an association with the spinal reflex . [ 8 ] Men can achieve orgasm through the penis, and can be categorised to two parts: emission and ejaculation. Neurotransmitters such as serotonin , norepinephrine and dopamine affect ejaculation in males the most. [ 9 ] For women, orgasms are induced by stimulation of erotic sites, currently there are no definitive explanations on the chemical triggers for female orgasm. [ 10 ]
Drugs are frequently associated with reduced sexual inhibition, both when used voluntarily in social circumstances, and involuntarily, as in the case of some date rape drugs . Because the use of drugs, including alcohol , is commonly presented as an excuse for risky or socially unacceptable behavior, it is necessary to treat the idea of a direct causal relation between drug use and unsafe sex with caution. Drugs may provide a socially acceptable excuse for engaging in sexual behaviors in which people may want to engage but perhaps feel that they should not. [ 11 ]
Some forms of sexual dysfunction such as erectile dysfunction can be treated with drugs. Because of their effects, erectile dysfunction drugs are sometimes used for recreational purposes. Many drugs, both legal and illegal, some sold online, have side effects that affect the user's sexual function. Many drugs can cause loss of libido as a side effect. [ 12 ]
Since a partial cause of the refractory period is the inhibition of dopamine by an orgasm-induced secretion of prolactin , [ 13 ] such potent dopamine receptor agonists as cabergoline may help achieve multiple orgasms as well as the retention of sexual arousal for longer periods of time. [ 13 ]
According to some studies, up to 22.1% of teenagers abused substances during their most recent sexual experience. [ 14 ]
Likewise, studies have shown adolescents who regularly abuse substances are more likely to initiate sexual activity at an earlier age, [ 15 ] have a more significant number of sexual partners, [ 16 ] and engage in unprotected sex more often. [ 17 ]
Additionally, substance abuse has been linked to an increased risk of sexually transmitted infection (STI). [ 18 ]
Drugs on the market provide both benefits and detrimental effects to the person, especially regarding sexual performance, depending on the use and dosage. [ 19 ] Drugs are classified into different categories in respect to their functions, including psychoactive drugs, antihypertensive drugs, antihistamines, cancer treatment drugs and hormone medication.
Psychoactive drugs refer to chemical substances that affect an individual's mental processes, such as emotions, cognition, perception, and consciousness. [ 20 ] These substances directly impact the central nervous system (CNS) , which also has an impact on the neurophysiologic phases of sexual response. [ 21 ] Antidepressants are a group of drugs that treat individuals with clinical depression, as well as other mental disorders. [ 22 ] This group of drugs have shown to affect sexual functions in both male and females. [ 23 ] Alcohol is a group of psychoactive substances where signals of pleasure, rewards are sent to the human brain. It also causes a series of adverse effects on the body, including the brain and the liver, leading to health problems and sexual dysfunction. [ 24 ] [ 25 ] Antipsychotics are drugs that treat mental disorders such as schizophrenia, and other psychoses. [ 26 ] These drugs block certain pathways in humans that contribute to sexual dysfunction, including reduced arousal and sexual desire. [ 27 ]
Alcohol inhibits neuronal excitability through acting on gamma-aminobutyric acid (GABA) receptors. [ 28 ] Alcohol is often accessible in a number of social situations across many cultures and is frequently connected with uninhibited social activities. Alcohol has been shown in human research to have surprising effects on the human libido.
While some studies indicates that alcohol improves sexual behavior and desire, other research indicates that alcohol impairs sexual function.
The conditions under which the drinking occurs, laboratory research vs self-report studies from users, as well as the amounts of alcohol consumed, may all contribute to these controversial outcomes. [ 29 ] [ 30 ]
Laboratory studies have demonstrated that while low blood alcohol levels have no effect on or slightly enhance sexual arousal and responsiveness in men, elevated blood alcohol levels result in decreased erectile responsiveness, decreased arousal, and impaired ability to ejaculate. [ 29 ] [ 30 ] Other laboratory research, on the other hand, found no significant influence of either low or high blood alcohol levels on measures of arousal. [ 31 ]
Even with mild alcohol use, women have decreased vaginal flow responses. In apparent contrast, women self-report heightened sexual desire and pleasure when they consume more alcohol and are more likely to engage in sexual activities with someone when intoxicated. [ 30 ]
Heavy alcohol intake impairs sexual and reproductive function, erectile, and ejaculatory dysfunction in males, and sexual arousal, interest, and orgasm in women. [ 29 ] [ 32 ]
Alcohol and sex although alcohol may have varying impacts on sexual performance depending on the amount drank, it generally impairs sexual functioning and contributes to increased sexual risk taking. [ 33 ] [ 34 ]
Psychiatrists and doctors commonly prescribe different types of antidepressants to patients. SSRIs , SNRIs , and NDRIs are the most common types of antidepressants. [ 35 ] Each has slightly different effects on sexual functioning, but generally, it has been found that antidepressants can delay/decrease orgasms and cause females to have breast enlargement . [ 36 ] Dapoxetine in particular takes advantage of the side effect of delayed orgasm and is approved specifically as a medication for the treatment of premature ejaculation rather than as an antidepressant.
The side effects on sexual functioning can impact mental health and quality of life. [ 36 ] However, the decrease in depressive symptoms from antidepressants make it worth the sexual side effects for many people. They can be managed by changing the dose, switching drugs, or taking "antidotes". [ 37 ] Maca , a plant that grows in central Peru, aids with sexual dysfunction caused by antidepressant drugs for women. There are specific Maca products that can also increase sexual desire in men. [ citation needed ]
2C-B was first sold commercially in 5 mg pills as a purported aphrodisiac under the trade name "Erox", which was manufactured by the German pharmaceutical company Drittewelle. [ 38 ] While being primarily a psychedelic it is also a mild entactogen . 5-MeO-MiPT is another psychedelic that some users find to be euphoric and tactile in low to moderate doses of 4-8 milligrams. [ 39 ]
Antihypertensive drugs are a group of drugs that prevent, control and treat hypertension. Hypertension imposes negative sexual effects on both men and women, where antihypertensive drugs help alleviate erectile dysfunction in men. [ 40 ]
Antihistamines are used for relieving symptoms of allergies and hay fever. [ 41 ] Antihistamines may cause a drying effect of the mouth, nose and throat but can also cause a drying effect on other parts of the body, such as the vagina, decreasing moisture and lubrication. [ 42 ]
There are a variety of treatment types for cancer , depending on the cancer type. [ 43 ] The therapies for treating cancer vary, including hormone therapy, medications that treat pain, depression, nerves and blood vessels. These therapies will affect one's sexual desire and pose possible consequences on sexual response. [ 44 ]
Hormone therapy directs its treatment towards hormones in the body, including reproductive hormones. One type is hormonal replacement therapy (HRT), which is used to supply menopausal women that lack estrogen and progesterone, increasing vaginal lubrication. [ 45 ] Another type is testosterone replacement therapy, which treats men with hypogonadism and it helps increase libido. [ 46 ] On the contractionary, selective oestrogen receptor modulators (SERMs) lead to a drop in oestrogen levels that would cause vaginal dryness. [ 47 ]
Amphetamines may lead to an increase in sexual drive and delay in orgasm. [ 48 ]
Cocaine is a potent psycho-stimulant that boosts dopamine levels by inhibiting dopamine transporters. It has been often linked to enhanced libido and risk-taking behavior in humans. [ 49 ]
Cocaine has been observed to increase sexual arousal or to trigger spontaneous erections and orgasms. [ 50 ]
In contrast, other data has shown that persistent cocaine use impairs sexual desire and the capacity of both men and women to achieve orgasm. [ 30 ]
Cannabis is the most commonly used illicit substance. [ 51 ] [ 52 ] Studies on cannabis and sex have shown that THC has been linked to improved sexual desire and function. Specifically, in one study, 70 percent of users said marijuana was an aphrodisiac , and 81 percent said it improved their sexual pleasure and satisfaction. [ 53 ]
Other research has found that long-term marijuana use lowers testosterone levels and other reproductive hormones, causing erectile dysfunction in males. [ 54 ] [ 48 ]
MDMA or "ecstasy" originally gained popularity in the 1980s among college students. According to a survey conducted, 10% of college students at a big US institution reported using MDMA , with alcohol and marijuana being the most often used substances. [ 55 ] MDMA users report increased enjoyment in physical contact and proximity rather than a sexual experience . [ 56 ] [ 57 ] MDMA has been shown to impair sexual performance, including erectile dysfunction and delayed orgasm , [ 58 ] [ 59 ] as well as to suppress sex desire . [ 60 ] [ 61 ] [ 62 ]
Opioids (also known as narcotics ) such as morphine and heroin attach to opioid receptors in the brain. These substances have long been known to inhibit sexual behavior. [ 63 ]
Similar to the effects of psycho-stimulants , both men and women who use heroin report engaging in high-risk sexual practices.
Subjects typically report having several sexual partners, using condoms seldom or not at all, and having a high frequency of STI diagnosis. [ 64 ]
While small doses of heroin may enhance sexual desire and performance, [ 65 ] chronic opiate use, including methadone and buprenorphine , synthetic and semi-synthetic opiates prescribed for opiate addiction treatment , results in decreased sexual desire, response, and orgasms for both men and women, as well as erectile , ejaculatory dysfunction , and vaginismus . [ 50 ] [ 65 ] [ 30 ]
Libido refers to a person's overall sexual desire and drive. Since low testosterone levels are associated with low sexual desire, testosterone replacement therapy can be prescribed for increasing testosterone in the body, increasing libido and restoring hormonal balance. [ 66 ] While Phosphodiesterase-5 (PDE5) inhibitors such as sildenafil, tadalafil, vardenafil, and avanafil are primarily known for treating erectile dysfunction, it also has a positive effect on libido. [ 67 ]
Flibanserin is a drug that is both a serotonin antagonist and agonist that treats hypoactive sexual desire disorder (HSDD) for premenopausal women. The drug acts as antagonist and agonist on two different receptors. The binding of flibanserin causes downstream release of dopamine and noradrenaline and reduces the production of serotonin, increasing sex drive. [ 68 ] However, currently there is still no evidence that this drug would enhance sexual performance, therefore this drug still needs to be further investigated. [ 68 ]
For males, several drugs increases the blood flow to the penis which allows for the achievement and maintenance of an erection. [ 69 ] Phosphodiesterase-5 (PDE5) inhibitors are widely known and commonly prescribed for erectile dysfunction. [ 70 ] PDE5 enzymes are blocked by PDE5 inhibitors to prevent their function, this allows for the relaxation of penile blood vessels and muscles, facilitating increased blood circulation to the penis. [ 71 ] Alprostadil injections as a vasodilator are also used for the treatment of erectile dysfunction, expanding blood vessels that result in increasing blood flow to the penis. [ 72 ]
For females, vaginal lubricant production can be increased by hormone replacement therapy (HRT) medicine such as vaginal estrogen . [ 73 ] Vaginal dryness results from a declined level in circulating estrogen within the body, most likely during menopause . [ 74 ] Treatment for vaginal dryness typically involves the use of localised estrogen, such as HRT medicine. This drug works by increasing estrogen in the body circulation, thereby enhancing lubrication production in the vaginal area. [ 74 ]
Delayed ejaculation , a type of male sexual disorder that is characterised by the delay of ejaculation or inability to achieve ejaculation. [ 75 ] There are no approved drugs for the treatment of delayed ejaculation as of now, The majority of medications used for treating delayed ejaculation are primarily intended for treating different medical conditions. [ 76 ] Amantadine , a Parkinson's medication, is known to enhance dopamine agonist release and activate dopamine receptors , which helps with ejaculation. [ 77 ] However, there is not sufficient evidence to support the effectiveness of these medications on delayed ejaculation. [ 77 ]
Several common medications can contribute to low libido. Antidepressants, especially selective serotonin reuptake inhibitors (SSRIs) antidepressants, increase serotonin levels that decrease testosterone, leading to a decrease in libido. [ 78 ] Antipsychotic drugs create blockages of dopamine D2 receptors that are responsible for dopamine production can lead to a low libido. [ 27 ] Additionally, these drugs can increase production of prolactin in males which contribute to lower levels of testosterone. [ 27 ] [ 79 ] Chemotherapy drugs also lead to a decrease in testosterone but it is only temporary during the course of therapy. [ 27 ]
Drinking large amounts of alcohol regularly can lead to low libido due to a process called aromatisation . [ 80 ] This process refers to the conversion of testosterone or its precursors into estrogen , leading to a decrease in testosterone levels in circulation. [ 80 ]
Impotence refers to the inability of a male's penis to become erect for sexual intercourse, in which the male is not able to get or maintain an erection. [ 81 ] The medical term for this phenomenon is erectile dysfunction. Drugs such as antihypertensives including thiazide diuretics , loop diuretics , and beta-blockers used for lowering blood pressure limiting blood flow to the penis area, making it difficult to get or maintain an erection. [ 82 ] Direct effects caused by antihypertensives on the penile vascular smooth muscle lead to vasoconstriction which leads to impaired perfusion . [ 83 ] Antipsychotic drugs are also responsible for several mechanisms that lead to erectile dysfunction. Mechanisms such as acetylcholine receptor antagonism and alpha-adrenergic receptor antagonism reduces periphery vasodilation, inducing erectile dysfunction. [ 27 ]
Overindulgence in alcohol may also cause temporary inability to achieve an erection. Alcohol, being a diuretic , can cause a person to urinate more frequently, resulting in dehydration . [ 84 ] Dehydration reduces the volume of blood in the body, consequently decreasing blood flow towards the penis [ 84 ] Additionally, dehydration also increases angiotensin levels in the body, which is a hormone associated with erectile dysfunction. [ 84 ]
Birth control pills affect hormone levels in the body such as a decrease in estrogen, leading to vaginal dryness by thinning and shrinking of the vaginal tissue. [ 7 ] Moreover, SERMs such as Evista and Tamoxifen which are used to treat breast cancer, results in vaginal dryness. [ 47 ]
Antihistamines narrow blood vessels, leading to lowering of moisture levels as well as mucous production, which includes lubricant production in the vagina. [ 47 ] Anti-hypertensive drugs help reduce blood pressure by decreasing blood flow to organs in the body, resulting in decreased vaginal lubrication as well. [ 85 ]
Antidepressants, particularly SSRIs, cause delayed ejaculation and orgasm due to its function of retaining serotonin, which inhibits ejaculation. [ 86 ] Similarly, antipsychotics also contribute to delayed ejaculation by affecting dopamine transporters , where dopamine plays a role in ejaculation via D2 receptors . [ 87 ] [ 88 ]
SSRI prevents reuptake of serotonin, thereby increasing serotonin in the body and decreasing their ability to produce lubricant in the vagina. It has been reported that around 42% of women that intake this type of medication have problems with orgasm production. [ 23 ] Other medications such as antipsychotic drugs also reported signs of impaired orgasm. [ 89 ]
Intake of too much alcohol can potentially cause depressant effects on the central nervous system (CNS). [ 90 ] These effects contribute to sensory dullness, which leads to a delay effect on orgasm and ejaculation. [ 90 ]
A date rape drug is any drug that is an incapacitating agent which—when administered to another person—incapacitates the person and renders them vulnerable to a drug-facilitated sexual assault (DFSA), including rape . One of the most common types of DFSA are those in which a victim consumes a recreational drug such as alcohol that was administered surreptitiously. [ 91 ] The other most common form of DFSA involves the non-surreptitiously administered consumption of alcohol. [ 92 ] Here, the victims in these cases are drinking voluntarily which then makes them unable to make informed decisions or give consent .
Party and play , or chemsex, is the consumption of drugs to facilitate sexual activity . Sociologically, both terms refer to a subculture of recreational drug users who engage in high-risk sexual activities under the influence of drugs within groups. [ 93 ] The term PnP is commonly used by gay men [ 93 ] [ failed verification ] and other men who have sex with men (MSM) in North America, while chemsex is more associated with the gay scene in Europe. [ 94 ] The drug of choice is typically methamphetamine , known as tina or T, [ 95 ] but other drugs are also used, such as mephedrone , GHB , GBL [ 96 ] and alkyl nitrites (known as poppers ). [ 97 ]
Drug-based contraception has been available since the development of the contraceptive pill . As well as their contraceptive effects, contraceptive drugs can also have adverse sexual and reproductive side-effects. Prior to the availability of effective contraceptives, some substances were also used as abortifacients to terminate pregnancy; medical abortion exists as a modern medical practice. | https://en.wikipedia.org/wiki/Sex_and_drugs |
Sex as a biological variable ( SABV ) is a research policy recognizing sex as an important variable to consider when designing studies and assessing results. Research including SABV has strengthened the rigor and reproducibility of findings. Public research institutions including the European Commission , Canadian Institutes of Health Research , and the U.S. National Institutes of Health have instituted SABV policies. Editorial policies were established by various scientific journals recognizing the importance and requiring research to consider SABV.
In 1999, the Institute Of Medicine established a committee on understanding the biology of sex and gender differences . In 2001, they presented a report that sex is an important variable in designing studies and assessing results. The quality and generalizability of biomedical research depends on the consideration of key biological variables, such as sex . To improve the rigor and reproducibility of research findings, the European Commission , Canadian Institutes of Health Research , and the U.S. National Institutes of Health (NIH) established policies on sex as a biological variable (SABV). [ 1 ] Enrolling both men and women in clinical trials can impact the application of results and permit the identification of factors that affect the course of disease and the outcome of treatment. [ 2 ]
In 2003, the European Commission (EC) began influencing investigators to include sex and gender in their research methodologies. The Canadian Institutes of Health Research (CIHR) requires four approaches: sex and gender integration in research proposals, sex and gender expertise among research teams, sex and gender platform in large consortiums, and starting in September 2015, the completion of sex and gender online training programs. [ 1 ]
In May 2014, the NIH announced the formation of SABV policy. The policy came into effect in 2015 which specified that "SABV is frequently ignored in animal study designs and analyses, leading to an incomplete understanding of potential sex-based differences in basic biological function, disease processes, and treatment response. NIH expects that sex as a biological variable will be factored into research designs, analyses, and reporting in vertebrate animal and human studies. [ 4 ] Strong justification from the scientific literature, preliminary data or other relevant considerations must be provided for applications proposing to study only one sex." [ 2 ] [ 1 ] The review criteria should assess the extent to which the sex of participants has been incorporated into the research plan. [ 5 ]
In 2010, the National Centre for the Replacement, Refinement and Reduction of Animals in Research published the ARRIVE guidelines which promotes incorporating SABV in animal studies. [ 6 ] In 2012, the American Physiological Society (APS) journals began requiring sex and gender to be reported in studies involving cells, tissues, animals, and humans. [ 7 ] This APS editorial policy was not widely accepted by reviewers and researchers. [ 8 ]
The European Association of Science Editors established the gender policy committee (GPC) in 2012. The GPC published Sex and Gender Equity in Research (SAGER) guidelines in 2016. [ 9 ] In January 2017, the Journal of Neuroscience Research began requiring the consideration of SABV. [ 10 ] The December 2017 ICMJE recommendations encouraged the use of SABV by researchers. [ 1 ]
Research incorporating sex as a biological variable increases the rigor and reproducibility of results. [ 11 ] [ 12 ] After publishing the NIH published SABV policy, there were increases in the percentage of scientists understanding and recognizing its importance. [ 13 ] Some investigators were critical of the NIH SABV policy, saying it would increase cost and labor requirements. [ 14 ] [ 15 ] Including SABV in basic research and preclinical studies can reduce costs and time requirements to test sex differences in clinical trials. [ 16 ] [ 17 ]
Historically, there were concerns among researchers of the female reproductive system impacting findings in animal studies. [ 18 ] Other studies using mice models found that despite the estrous cycle , variability was the same among sexes. [ 19 ] Studies following SABV policies can identify potential hormonal variability in earlier phases of biomedical research. [ 20 ]
In 2020, the NIH Office on Women's Health and the Food and Drug Administration Office of Women's Health created an educational tool, Bench-to-Bedside : Integrating Sex and Gender to Improve Human Health. [ 21 ] | https://en.wikipedia.org/wiki/Sex_as_a_biological_variable |
Sex is influenced by water pollutants that are encountered in everyday life. These sources of water can range from the simplicity of a water fountain to the entirety of the oceans. The pollutants within the water range from endocrine disruptor chemicals (EDCs) in birth control to Bisphenol A (BPA). Foreign substances such as chemical pollutants that cause an alteration of sex have been found in growing prevalence in the circulating waters of the world. These pollutants have affected not only humans, but also animals in contact with the pollutants.
Endocrine disruptor chemicals (EDCs) are a type of chemical that directly influences sex hormones . [ 1 ] They have acquired these names due to the fact that they are anti-estrogens and anti-androgens . [ 1 ] By inhibiting the function of these hormones, fertility decreases, and an imbalance of such hormones has been shown to cause feminizing effects in males. [ citation needed ] This is not only a human issue, but has become increasingly noticeable in fish populations worldwide. [ 2 ] Scientists believe that these chemicals present in the water supply leads to increasing feminizing effects in male fish. [ 2 ] Estrogens accumulate in body fat and tissue, and because of the cycle of the food chain, the artificial estrogens/EDCs bioaccumulate as they rise up the different levels of the food chain.
EDCs are present in the environment, whether naturally or artificially. [ 1 ] Although the EDCs from birth control are obviously causing a great effect on the humans, it turns out that, in the United States, the estrogens given to livestock are even more prevalent. [ 3 ]
Sex-altering pollutants come from many sources. One source that is becoming more visible is water pollution through pharmaceuticals . Pharmaceutical products may contain microscopic pollutants that imitate the chemical structure of hormones found in living organisms. These compounds are called Endocrine Disrupting Chemicals. They usually mimic the chemical structures of estrogens and androgens. [ 4 ] The sources of these artificial EDCs are surprisingly common in human production and usage of many household and industrial products. For example, EDCs such as parabens, phthalates, and triclosans can be found in everyday household items such as generic shampoos, conditioners, soaps, perfumes, makeup, and lotions. EDCs are either applied to the skin and are absorbed, ingested and then excreted in urine, or are washed off in the shower or sink and have been documented in multiple water analyses. Below are some of the most commonly tested, used, and analyzed EDCs found in pharmaceuticals and personal care products:
Aside from these microscopic EDCs, some of the other more common types of pharmaceuticals found in water analyses are " anti-depressants , anti-seizure drugs , and one that is very well known: birth control." [ 3 ]
However, pharmaceuticals are not the largest contributor to the growing amount of gender-altering pollution in the water. Scientists at the University of California, San Francisco (UCSF) stated that there are many other sources of chemicals like the ones found in various pharmaceuticals that produce the same effects. [ 3 ] " Crop fertilizers along with dairy cows , and various industrial chemicals like BPA" are increasingly seen as a source for pollution causing certain specific effects in those who consume them or products that are manufactured from them. [ 3 ] Specifically shifting to industrial chemicals, when they, along with other products containing these chemicals, are disposed of, they end up in landfills . [ 3 ] Runoff from said landfills eventually finds its way to a larger source of water and the contamination begins.
Another source from which pollutants originate is fossil fuel combustion. [ 5 ] The organic pollutants and trace metals released into the air from this combustion end up in the oceans and influence the chemistry of the ocean. One specific process that has a great impact on the global nitrogen cycle which affects ocean climate, the Haber-Bosch process , is used for an agricultural fertilizer. [ 5 ]
There are also humans. The chemicals that alter gender are constantly produced and excreted by a human being on a normal everyday basis. Along with this, pregnant women contain greater amounts of the chemicals thus releasing greater amounts of it with every excretion. [ 3 ] Because of this, one can see that the source of gender-altering pollutants is not natural, but due to man-made chemicals that, globally, are being released.
Chemicals such as EDCs and artificial estrogens are in constant circulation around the planet through a variety of mediums. Humans have become a main contributor to the toxic buildup of these chemicals in our ecosystem. [ 6 ] Main sources of drinking water, such as rivers, lakes, streams, and eventually the ocean are just a few of such mediums that carry these chemicals from place to place. Most chemical exposure to impoverished people around the world who live in rural areas is linked to their exposure to polluted water sources. [ 7 ]
The process of the EDCs entering the water source all begins with a source. Whether it comes from an industrial plant , pharmaceutical, or human source, it eventually finds its way to a larger water source, usually in the form of a waste product. The Environmental Protection Agency (EPA) has documented the amount of pharmaceuticals released into the environment from manufacturing plants, however, this documentation is not as prevalent on a household level. [ 8 ] There are some on-going efforts to attempt to minimize this pollution. For example, 80 percent of pharmacies in Clark County, Washington , have contributed to efforts emphasizing the safe disposal of noncontrolled drugs. [ 8 ] Attempts to control water pollution are gaining support as pollution gradually becomes more visible. However, these efforts are still in the process of being implemented on a large scale. The polluted water is then sent to a number of places.
One possibility is that the water is sent to a waste management facility to be treated and then recirculated. However, experts have found that sewage treatment does not remove these chemicals completely from drinking supplies. Any type of water that is flushed down the shower, toilet, or sink usually carries with it some sort of EDC. These drains lead to pipes that lead to a waste water management plant. A typical waste water treatment plant involves a multiple step process of water cleaning but due to the microscopic size of EDC particles, it usually is not a 100% successful process. For example, Boulder, Colorado Waste Water Management receives water in inceptor pipes, which lead into larger holding pools at the facility. The typical treatment usually lasts between 12 and 24 hours and consists of three main treatment processes. First, physical treatments remove solid and organic materials from the waste water. Then, microbiological treatments follow. Bacteria in these waste tanks feed on carbon and nitrogenous compounds left in the sewage. And finally, the water is treated with ultraviolet blue light to disinfect the remaining water. The effluent water is feed back into local creeks, streams, and freshwater resources. This basic waste water treatment plan is effective in targeting larger contaminants, however, it is ineffective in removing microscopic EDCs. [ 9 ] Thus, EDC micro-pollution is causing a toxic buildup of chemical soups in freshwater habitats. [ 10 ]
In response to this, the water industry has stated that there is no evidence of a risk to overall health as a result of exposure to these chemicals. However, the Food and Drug Administration (FDA) states in its review of water pollution that many contaminants survive wastewater treatment and biodegradation , and are detectable in the environment. Therefore, the tainted source is recycled through a community, exposing more people and releasing more chemicals along the way. [ citation needed ]
A second source of circulation is water as it follows its natural path through the water cycle . The water cycle, put simply, represents the path that water takes as it circulates around planet earth. [ 11 ] It follows a series of stages in which the water changes state multiple times until it finally falls back to earth where it will once again be circulated. In the water cycle, both organic and inorganic pollutants are biodegraded or filtered out whereas they no longer present much of a threat. [ 11 ] This is also true for small amounts of chemicals present in the water. However, when there are very large amounts of chemicals, organic or inorganic, present in the water as it cycles through the atmosphere, harmful effects can be seen in areas where this water falls as precipitation . This precipitation re-enters the ongoing circulation of water pollution.
Another path in which the water can circulate is by flowing directly to the ocean. Pollutants are prevalent in coastal and open-ocean waters as contaminated water flows from point sources to the sea. [ 5 ] These pollutants are then distributed globally due to the circulation of the ocean currents and migration of exposed marine life. [ 5 ] This becomes an explanation of how the chemicals, once again, find their way to a human consumer. Marine wildlife in a polluted area exists in and consumes contaminated water daily. When it is harvested, it has accumulated an amount of harmful chemicals/EDCs relatively high to that compared to ambient ocean levels. [ 5 ] This is then passed on to consumers of the seafood: humans, whereas the chemicals bioaccumulate in their bodies eventually causing sex-related health problems.
These chemicals have an effect on the sex of many humans because of constant exposure. The pollutants found in the water have been observed in many studies that produce concrete data describing the effects they have on the hormones in both males and females. Studies have been conducted on animals, but the observed trends are also associated with effects noticed in humans. Scientists observing EDCs in women's blood found that these chemicals mimic human hormones and trigger changes in the sex-determining process of unborn children. [ 12 ] Some scientists suggest that this hormonal influence on the sex-determining process has led to a decrease in the male/female ratio. [ 12 ] Other effects directly influencing the sex of an individual include a decrease in number and quality of sperm and increased deficiency in a male's reproductive system. [ 13 ]
Specifically looking at the effects of EDCs on sperm, these chemicals cause a premature release of a chemical that the sperm cells use to penetrate the egg's outer layer. [ 1 ] Results collected from a study help to explain why the sperm act the way they do. In respect to the deficiency of the male's reproductive system, these chemicals begin affecting a male as early as birth. As the testes are developing, an occurrence taking place early in the development process, a specific type of cells, Sertoli cells , differentiates. [ 1 ] During this period, exposure to an EDC such as oestrogen causes a reduction in Sertoli cells produced. [ 1 ] The reduction of Sertoli cells causes a decrease in the production of sperm thus rendering the male reproductive system less effective. [ 1 ] EDCs have also been linked to early puberty , infertility, and developmental defects. [ 3 ] Not only have these effects been found in human subjects, but aquatic life has also been studied as these animals are in direct contact with EDCs as a part of their lifestyle. Populations of fish have been largely affected by EDC's prevalence in their native ecosystems.
In an effort to better filter these trace pollutants out of effluent water leaving waste management plants, studies conducted by Westerhoff et al. [ 16 ] and Schafer et al. [ 17 ] explore the water filtration systems that are best at removal of EDCs from effluent waters. They found that Powdered Activated Carbon (PAC), membrane filtration (nonfiltration and biofiltration), and reverse osmosis were the best at removal of EDCs. | https://en.wikipedia.org/wiki/Sex_effects_of_water_pollution |
Sex linkage describes the sex-specific patterns of inheritance and expression when a gene is present on a sex chromosome (allosome) rather than a non-sex chromosome ( autosome ). Genes situated on the X-chromosome are thus termed X-linked, and are transmitted by both males and females, while genes situated on the Y-chromosome are termed Y-linked, and are transmitted by males only. As human females possess two X-chromosomes and human males possess one X-chromosome and one Y-chromosome , the phenotype of a sex-linked trait can differ between males and females due to the differential number of alleles (polymorphisms) possessed for a given gene. In humans, sex-linked patterns of inheritance are termed X-linked recessive , X-linked dominant and Y-linked . The inheritance and presentation of all three differ depending on the sex of both the parent and the child. This makes sex-linked patterns of inheritance characteristically different from autosomal dominance and recessiveness . [ 1 ] This article will discuss each of these patterns of inheritance, as well as diseases that commonly arise through these sex-linked patterns of inheritance. Variation in these inheritance patterns arising from aneuploidy of sex chromosomes, sex-linkage in non-human animals, and the history of the discovery of sex-linked inheritance are briefly introduced.
In humans (and mammals in general), biological sex is determined by genetics; however this is not the case for all animals, for instance, the biological sex of some reptiles is environmentally determined, and the sex of some worms is dependent on location. [ 2 ]
22 of the 23 pairs of human chromosomes are autosomal (not involved in sex determination), while the 23rd pair of human chromosomes are the sex chromosomes. The possession of two X-chromosomes defines a biological female, while the possession of one X and one Y chromosome defines a biological male. [ 3 ] The two sex chromosomes differ in size and gene content, and unlike the sets of autosomal chromosomes, are not homologous. The X-chromosome contains an estimated 1400 genes, most of which are involved in tissue development and the development of human disorders. [ 4 ] [ 5 ] The Y-chromosome is host to the SRY gene, which is involved in the development of several male sex characteristics, while the identified functions of many of the remaining approximately 200 genes on the Y-chromosome are associated with human disease. [ 6 ] Sex linkage thus refers to the association of a trait encoded by one of the genes on these sex chromosomes. There are many more X-linked conditions than Y-linked conditions due to the larger size of the X-chromosome and greater number of genes encoded within it. [ 1 ]
In classical genetics , a mating experiment called a reciprocal cross is performed to test if an animal's trait is sex-linked. [ 7 ]
A disease or trait determined by a gene on the X-chromosome demonstrates X-linked inheritance. Historically, X-linked inheritance has been divided into the patterns of X-linked dominant inheritance and X-linked recessive inheritance as synonymous with classical Mendelian inheritance of genes on autosomal chromosomes. [ 8 ] However, more recently scholars have suggested the discontinuation of the use of the terms dominant and recessive when referring to X-linked inheritance, stating that the highly variable penetrance of X-linked traits in females as a result of mechanisms such as skewed X-inactivation or somatic mosaicism is difficult to reconcile with standard definitions of dominance and recessiveness. [ 9 ]
X-linked dominant inheritance is the pattern by which a trait encoded by an allele on the X-chromosome is passed down through generations, wherefore only one copy of that allele is sufficient for an individual to be affected ( dominance ). [ 11 ] Unlike with X-linked recessive traits, females are more often affected by X-linked dominant traits than males as females have two X-chromosomes as opposed to one. Moreover, some X-linked dominant conditions (for example, Aicardi syndrome ) are embryonically or neonatally lethal in hemizygous males (XY), and thus can be seen to only affect heterozygous females, who experience less severe symptoms. [ 12 ]
In X-linked dominant inheritance, the transmission of the gene depends on the genotype of each of the parents. A mother heterozygous for an X-linked dominant trait will be affected, and half of her children (whether female or male) will inherit her affected X-chromosome and be affected themselves, assuming an unaffected father. Of the children of a father affected by an X-linked dominant trait and an unaffected mother, all daughters will be affected (having inherited their father's only affected X-chromosome), while no sons will be affected (having received their father's Y-chromosome). A child affected by an X-linked dominant condition will always have at least one affected parent, and an affected son will always have an affected mother. [ 13 ] [ 14 ]
X-linked recessive inheritance describes one of the patterns of inheritance of genetic traits or disorders encoded by an allele (version of a gene) situated on the X-chromosome. In X-linked recessive inheritance, females (XX) must have two copies of the allele (homozygous), while males (XY) require only one copy of the allele (hemizygous) to display the phenotype. Thus, it is far more common for males to be affected by X-linked recessive traits. [ 15 ] [ 16 ]
A female heterozygous for an X-linked recessive trait is considered a carrier . [ 17 ] While a carrier female most often does not display the phenotype, rare cases of skewed X-chromosome inactivation , can lead to varied levels of expression. This would occur when, during the normal process of inactivating half of a female's X-chromosomes, inactivation preferentially targets X-chromosomes inherited from a single parent, thus the remaining active X-chromosomes from the other parent are disproportionately expressed. [ 18 ]
There are characteristic patterns for X-linked recessive inheritance. As each parent contributes one sex chromosome to their offspring, sons cannot receive the X-linked trait from affected fathers, who provide only a Y-chromosome. Consequently, affected males must inherit the X-linked recessive trait from their mothers. Sons of a healthy carrier female have a 50% change of being affected, while sons of an affected female will always be affected. Females must inherit a X-linked recessive allele from each parent. All daughters of an affected father and healthy non-carrier mother will be carriers. Daughters of an affected father and carrier mother will have a 50% chance of being affected, and daughters of two affected parents will always be affected. [ 17 ] [ 19 ] While there is no male-to-male transmission of X-linked recessive traits, an affected male can pass his recessive X allele to a grandson through his unaffected carrier daughter. [ 15 ]
Alport syndrome is a genetic disorder that primarily affects the kidneys by damaging the glomeruli, which are tiny filtering units inside the kidneys. [ 24 ]
It is caused by inherited mutations in the COL 4A3 , COL4A4 , and COL4A5 genes, which are responsible for producing type IV collagen . [ 24 ] These mutations disrupt the formation of basement membranes, particularly in the kidneys , inner ears , and eyes , where this collagen network plays a key structural role. [ 25 ] The specific gene affected determines the form of Alport syndrome: mutations in COL4A5 cause the X-linked form (XLAS), while mutations in COL4A3 or COL4A4, located on chromosome 2, are associated with autosomal recessive (ARAS) or autosomal dominant (ADAS) forms. [ 26 ]
Common signs and symptoms of Alport syndrome include hematuria (blood in urine), proteinuria (protein in urine), hearing loss, and eye abnormalities. [ 27 ]
Diagnosis typically involves urine and blood tests, hearing and vision assessments, and genetic testing to confirm the mutation and identify the specific type of Alport syndrome. Kidney biopsy can reveal a characteristic 'basketweave' appearance of the glomerular basement membrane under electron microscopy. [ 28 ] In some cases, skin or kidney tissue may be tested for the absence of type IV collagen proteins. Genetic testing is especially useful when biopsy is inconclusive or unavailable.
While there is no cure, treatments focus on slowing the progression of the kidney disease and managing symptoms. ACE inhibitors are commonly used to control blood pressure and reduce proteinuria. [ 29 ] If kidney failure develops, dialysis or kidney transplant is often effective. Rarely, transplant recipients may develop anti-GBM disease due to antibodies against type IV collagen. [ 30 ]
Fragile X syndrome is a genetic neurodevelopmental disorder caused by a CGG trinucleotide repeat expansion in the FMR1 gene on the X chromosome . [ 31 ] It is inherited in an X-linked dominant pattern and is the most common known inherited genetic cause of autism spectrum disorder . [ 32 ] The condition affects approximately 1 in 3,600 males and 1 in 4,000 to 6,000 females. [ 33 ]
Fragile X syndrome occurs when the CGG repeat expansion exceeds 200 repeats, causing methylation and silencing of the FMR1 gene. This leads to a deficiency of FMRP, a protein essential for normal synaptic development and brain plasticity. [ 32 ]
Fragile X syndrome typically presents with learning disabilities to severe intellectual impairment , along with distinct physical features such as a long face, large or protruding ears , flat feet , and low muscle tone . [ 32 ] Many individuals, especially males, also exhibit behavioural traits including social anxiety , hyperactivity , hand-flapping, and self-injurious behaviors such as biting. Females, who have two X chromosomes, are generally less severely affected due to X-inactivation. [ 34 ]
Diagnosis typically involves identifying a mutation in the FMR1 gene using polymerase chain reaction (PCR) and Southern blot analysis to measure CGG repeat expansions and methylation status. [ 35 ] Earlier cytogenetic methods, such as detecting " fragile sites " on the X chromosome, have largely been replaced due to low reliability, particularly in females. [ 36 ] Early diagnosis is important to support timely intervention and genetic counseling.
Rett syndrome is a severe neurodevelopmental disorder that primarily affects females, with a prevalence of approximately 1 in 8,500. [ 37 ] It is caused by mutations in the MECP2 gene located on the X chromosome and is inherited in an X-linked dominant pattern. [ 37 ] However, the vast majority (over 99%) of cases result from de novo mutations , often from the paternal germline. [ 38 ]
Following a period of seemingly normal development, Rett syndrome progresses through four clinical stages. Stage I, or early-onset, typically begins between 6 and 18 months of age with subtle developmental delays. [ 39 ] Stage II, the rapid destructive phase, involves a sudden loss of purposeful hand use and spoken language, often accompanied by repetitive hand movements, breathing irregularities, and autistic-like behaviours. [ 39 ] In Stage III, or the plateau phase, some behavioural improvements may occur, though motor dysfunction, apraxia , and seizures remain common. [ 39 ] Stage IV, the late motor deterioration phase, is characterized by progressive loss of mobility and muscle rigidity, while communication and cognition generally stabilize. [ 39 ]
The condition is rarely seen in males, as those with MECP2 mutations typically do not survive infancy unless they have Klinefelter's syndrome or mosaicism . [ 37 ] [ 40 ] In contrast, affected females often survive into middle age, with symptom severity influenced by the specific mutation and patterns of X-chromosome inactivation.
Diagnosis is based on clinical presentation and confirmed through genetic testing for MECP2 mutations once the established diagnostic criteria are met. [ 41 ] [ 42 ] While there is no cure, treatment focuses on managing symptoms with physical and speech therapy, medications for seizures, and supportive care. [ 39 ] In 2023, trofinetide became the first medication approved in the United States specifically for Rett syndrome. [ 43 ]
X-linked hypophosphatemia is a rare genetic form of rickets caused by mutations in the PHEX gene on the X chromosome. [ 44 ] Unlike nutritional rickets, X-linked hypophosphatemia does not respond to vitamin D supplements. Instead, the PHEX mutation leads to overproduction of the hormone FGF23, which causes the kidneys to waste phosphate and impairs bone mineralization. [ 45 ] [ 46 ] Reduced PHEX enzyme activity allows the accumulation of osteopontin , a mineralization-inhibiting protein, to accumulate in bones and teeth. [ 47 ] These combined effects result in soft bones (osteomalacia), dental issues (odontomalacia), short stature, and bow-leggedness. [ 48 ] The condition affects approximately 1 in 20,000. [ 49 ]
Symptoms vary by age. In children, common signs include rickets , fatigue , delayed growth, craniostenosis (premature fusion of skull bones), and more. [ 50 ] [ 51 ] [ 52 ] Adults may experience osteomalacia (soft bones), fractures or pseudofractures, dental abscesses, hearing loss, and joint pain. [ 50 ] [ 53 ] [ 54 ]
Diagnosis is based on clinical and biochemical findings, including low serum phosphate, elevated alkaline phosphatase, and excessive urinary phosphate loss. [ 55 ]
Treatment has traditionally included phosphate supplements and active vitamin D analogs. [ 56 ] More recently, burosumab , a monoclonal antibody that targets FGF23, has been approved and shown to normalize phosphate levels and improve skeletal outcomes in both children and adults. [ 57 ]
The incidence of X-linked recessive conditions in females is the square of that in males. For example, if 1 in 20 males in a human population are red–green color blind , then 1 in 400 females in the population are expected to be color-blind ( 1 / 20 )*( 1 / 20 ). Examples include:
Duchenne muscular dystrophy is a severe neuromuscular disease causing progressive weakness and damage of muscle tissues , [ 58 ] leading to mobility loss and difficulties in daily activities. In a later stage of Duchenne muscular dystrophy, as respiratory and cardiac muscles start to degenerate, affected individuals are likely to develop complications such as respiratory failure , cardiomyopathy and heart failure . [ 58 ] 1 in 3,600 male births worldwide are affected by Duchenne muscular dystrophy, moreover, it presents itself at around ages 2–4 and progressively worsens. Most cases of Duchenne muscular dystrophy are inherited from the mother who is a carrier of the X-linked recessive trait, however, approximately 30% occur due to random mutations that are not inherited. [ 59 ]
Duchenne muscular dystrophy arises from a mutation, likely to be the deletion of the exons , [ 60 ] [ 61 ] a nucleotide sequence in the DMD gene that codes for dystrophin . Dystrophin is a protein responsible for strengthening and stabilizing muscle fibres. [ 62 ] With the loss of the dystrophin complex, the muscle cells would no longer be protected and therefore result in progressive damage or degeneration. Although interventions vary case by case, corticosteroids are often used to delay the progressive degeneration of muscle cells. [ 59 ]
X-linked agammaglobulinemia is a primary immunodeficiency disorder that impairs the body’s ability to produce antibodies , which are proteins protecting us from disease-causing antigens , resulting in severe bacterial infections . [ 63 ]
X-linked agammaglobulinemia is associated with a mutation in the Bruton's tyrosine kinase ( BTK ) gene, a cytoplasmic signalling molecule, on the X chromosome. The gene is responsible for producing BTK, an enzyme regulating B cells development and maturation within the bone marrow. It is also involved in the further development of the B cells that migrate into the secondary lymphoid tissues like the lymph nodes and spleen. [ 64 ] B cells are a type of white blood cells essential in the production of antibodies, when at an early stage, called pre-B cells , they rely on expansion and survival signals involving BTK to mature. [ 65 ]
In affected individuals, their BTK gene mutations can range from point mutations to indels that alter the amino acid sequence and the structure of BTK making it faulty. [ 64 ] Therefore, the loss of BTK gene functions, prevents the maturation from pre-B cell to B cell lymphocytes hence, not able to differentiate into antibodies -producing plasma cells. With low antibodies, individuals are highly vulnerable to bacterial and viral infections. [ 66 ]
Red-green colour blindness is a type of colour vision deficiency caused by a mutation in X-linked genes, affecting cone cells responsible for absorbing red or green light. [ 67 ] Primarily affecting males (1 in 12) compared to females (1 in 200), as the condition requires all the X chromosomes to have the mutations. [ 68 ]
The perception of red and green light is attributed to the Long (L) and Medium (M) wavelength cones, respectively. [ 69 ] In Red-green colour blindness, mutations take place on the OPN1LW which impairs L-cones, and OPN1MW genes, which impairs the medium cones [ 70 ] coding for the photopigments in the cones. In milder cases, those affected exhibit reduced sensitivity to red or green light, as a result of hybridization of the genes, [ 70 ] shifting the response of one cone towards that of the other. [ 69 ] In the more extreme conditions, there is a deletion or replacement of the respective coding genes, [ 71 ] resulting in the absence of L or M cones photopigments and thus losing the ability to differentiate between red or green light completely.
Haemophilia A is a blood clotting disease caused by a genetic defect in clotting factor VIII . It causes significant susceptibility to both internal and external bleeding. [ 72 ] 1 in 5,617 live male births is affected, and the condition primarily affects males, while females are usually carriers with mild low clotting factor level symptoms, due to X-inactivation . The X-linked mutations are inherited from the mother, however, about ⅓ cases are mutations like point mutations or indels that have occurred spontaneously. [ 73 ] Mutations in the F8 gene cause hemophilia A, while mutations in the F9 gene cause hemophilia. The F8 gene encodes for coagulation factor VIII , hence with missing proteins there cannot be effective clotting of the blood. [ 74 ]
Individuals having more severe haemophilia can experience more frequent and intense bleeding, and typically severe hemophilia A affects most patients. Patients with mild haemophilia often do not experience heavy bleeding except for surgeries and significant trauma. [ 72 ]
Glucose-6-phosphate dehydrogenase deficiency
Glucose-6-phosphate dehydrogenase (G6PD) deficiency, is characterized by when the enzyme that helps red blood cells to work properly. Without the enzyme red blood cells will prematurely break down leading to hemolytic anemia . This is a condition that shows a low red blood cell count since the body cannot compensate for the quick degrading cells. Glucose-6-phosphate dehydrogenase is an enzyme that protects red blood cells from oxidative stress caused by reactive oxygen species , it will reduce the amount of ROS accumulation of ROS in the red blood cells. A mutation in the G6PD gene causes this deficiency, leaving the cells with no protective enzyme. Approximately 400 million individuals have been affected by G6PD deficiency. Since the gene is located on the X- chromosome, therefore, the condition usually affects males more than females. Since males received have the mutated gene on the X-chromosome from the carrier mothers, they tend to show the symptoms of G6PD deficiency. Since females have two X chromosomes, they are typically carriers. However, when the healthy G6PD gene-carrying chromosome is inactivated females may exhibit mild symptoms. [ 75 ]
Wiskott–Aldrich syndrome
Wiskott-Aldrich syndrome is an X-linked recessive disorder that is caused by mutations in the WAS gene that encodes for the WASp protein. It is characterized by weakened immune function , eczema , and problems with blood clotting. This protein is responsible for cell movement and cell-to-cell adhesions . It relays the signals from the surface of all blood cells to the actin cytoskeleton of the cells to trigger movement and adhesion. When there is the loss of WASp due to the mutation it causes the actin cytoskeleton to not properly form, or not form at all. In white blood cells , this becomes a problem as the lack of actin cytoskeleton does not allow it to respond to the environment and foreign invaders. Therefore, having impaired immune responses causes increased vulnerability to infections and autoimmune diseases. Moreover, a lack of WASp proteins can impair cell growth and induce early cell death. The WAS gene is located on the X-chromosome, hence primarily affecting the males who inherit the mutated X-chromosome. Females tend to be the carriers and typically do not show symptoms until the healthy X-chromosome is inactivated. [ 76 ]
Genetic screening , which includes carrier screening , prenatal screening and newborn screening may be performed to enable early detection of genetic defects.
Carrier screening is conducted on prospective parent(s) to determine if they are carriers (heterozygous) for an X-linked recessive or autosomal recessive disease. Individuals who undergo carrier screening commonly have a family history of genetic disease or belong to an at-risk population and wish to determine the likelihood of having a child with a genetic disorder. Carrier screening is performed by taking a blood sample, saliva sample or buccal swab and using laboratory techniques such as next-generation sequencing or Polymerase Chain Reaction (PCR) to determine if the parent carries the allele implicated in the genetic disease. [ 77 ] [ 78 ] [ 79 ] [ 80 ]
Prenatal screening is can be conducted on pregnant females to test for a number of genetic conditions. It is more commonly used to test for aneuploidy (for example, Down syndrome or trisomy 21), but can also be used to detect X-linked recessive or X-linked dominant disorders (for example, fragile X-syndrome ). Prenatal screening involves maternal blood tests and ultrasound to defect such defects in the developing fetus . This can confirm the diagnosis of a genetic condition, allowing parents to prepare or consider terminating the pregnancy . [ 81 ] [ 82 ] [ 83 ]
Newborn screening is conducted on infants less than a week old to test for a variety of genetic disorders, specifically those with high morbidity and mortality rates to enable early intervention. Newborn screening is conducted by analyzing the biochemistry of a spot of dried blood (often obtained via a heel prick test ). This form of screening is also used to detect endocrine and metabolic disorders. [ 84 ] [ 85 ]
The Y chromosome is comprised of approximately 59 million base pairs and 200 genes, entailing approximately 66 protein-coding genes. [ 86 ] [ 87 ] [ 88 ] Since only biological males possess the Y chromosome, it is essential in male sexual differentiation , which results in the production of male sex hormones that lead to the development of male sex organs, reproduction, fertility, and spermatogenesis , commonly known as sperm production. [ 87 ] [ 89 ] [ 90 ] Additionally, due to the small length of the Y chromosome in comparison to the X chromosome, recombination is mostly suppressed, and thus it remains relatively distinct from the X chromosome, maintaining important genes for male fertility and sexual differentiation. [ 86 ] Particularly, the SRY gene on the Y chromosome is known to be involved in sex determination . [ 86 ] As well, AZF, azoospermia factor region encodes for 16 proteins, and are thus related to the production of sperm. [ 91 ]
The Y chromosome has a highly repetitive sequence, and thus had many gaps that were not able to be sequenced until recently. [ 86 ] Based on advances in the Makova Lab at Penn State and Phillippy at the Human Genome Research Institute, they successfully filled in the missing sequence gaps. [ 86 ]
The SRY gene , being the sex-determining region of the Y chromosome, gives the genetic information required for the body to code for proteins that are involved in male sexual differentiation. [ 92 ] The expression of the SRY gene is regulated via a myriad of transcription factors , which is a protein that can bind to genes of interest and increase or decrease their expression. [ 92 ] Specific to SRY these include, Six1, WT1, and Gata4. [ 86 ] SRY expression is regulated spatially and temporally in a strict manner. [ 86 ] The SRY gene encodes a transcription factor called the Testes Determining Factor (Tdf), and Tdf binds to and activates another gene called Sox9 . [ 86 ] Sox9 then codes a transcription factor that leads to the development of the testes via many downstream pathways that ultimately result in the targeting of Sertoli cell which is where sperm is produced and the Lydig cell, also called testicular somatic cells, which is where the androgen hormone is produced, that is essential for male sexual differentiation. [ 86 ] [ 93 ] Therefore, SRY expression leads to testis development in biological XY males, and absence of SRY in biological XX females, leads to ovary development. [ 94 ]
Swyer syndrome , also known as complete gonadal dysgenesis or pure gonadal dysgenesis, is a condition that impairs the process of sexual differentiation in males. [ 92 ] Male individuals with this condition have a normal XY genotype , yet due to the impairment of the SRY gene, the protein critical in male sexual determination is non-functional or is not produced at all. [ 92 ] As a result, male sexual differentiation is prevented, and an affected individual will lack male sexual characteristics such as gonads, and will instead develop biological female-typical sex characteristics, such as a uterus, fallopian tubes, etc. [ 92 ]
Y-linked inheritance, also known as Holandric inheritance, refers to genes that are inherited via the Y chromosome. [ 95 ] In other words, Y-linked inheritance involves genes that are only carried on the Y chromosome, also known as Y-linked genes .
Inheritance of Y-linked genes can occur in two ways: complete inheritance and incomplete inheritance. [ 96 ] Complete Y-linkage results when a gene is only found on a certain area on the Y chromosome either because there is no allele i.e. a copy of that gene, on the X chromosome or because it does not exchange with the X chromosome's allele. [ 96 ] Complete Y linkage of heterogamous organisms can result in the following possible outcomes:
Conversely, incomplete Y linkage is when traits on a gene cross-over and exchange information between the X and Y chromosome. [ 96 ]
The first few Y-linked inheritance cases were recognized in the early 20th century, with initial theories proposing certain traits were passed exclusively from father to son. [ 97 ] However, it was not until genetic advancements and cytogenetic techniques that enabled researchers to have a better understanding of the Y chromosome in greater detail. [ 98 ] When scientist began mapping the Y chromosome and identifying traits that followed a paternal lineage, it became evident that certain genetic conditions were linked to the male-specific chromosome. The identification of Y-linked inheritance marked a significant milestone in laying the groundwork for expanding research into male-specific conditions. Further understanding led to exploration of developmental disorders, allowing of diagnostic and therapeutic strategies to be explored in medical genetics. Eventually, ongoing investigations into Y chromosome revealed the broader picture in human biology, evolution and disease susceptibility. [ 99 ]
Hypertrichosis is a genetic condition that results in the excessive growth of hair on a specific area of the body, that is abnormal for the age, sex or race of an individual. [ 100 ] Specifically, hypertrichosis centralized to the outer ear, also known as the auricle, is a Y-linked disordered, commonly referred to as hypertrichosis pinnae auris. [ 100 ] Since hypertrichosis pinnae auris is a Y-linked disorder, this means only biological men and subsequent male offspring can be affected by this disorder. [ 100 ] Tommasi C. was crucial in determining the Y-linked origin of this disorder, by creating a pedigree that elicited holandric inheritance. [ 100 ] Conversely, hypertrichosis cannot be confused with Hirustism , which is characterized by excessive androgen sensitive hair growth, and thus is most often diagnosed in women and children that tend to have male-typical hair patterns.
Considered to be relatively rare as the congenital form is classified in 2 categories; generalized hypertrichosis (CGH) and localized hypertrichosis (CLH). [ 101 ]
CGH is seen amongst individuals with excessive hair growth that cover most of the body while CLH affects a specific area of the body, typically a patch of area. Although the incidence is unknown, it seen that CGH is extremely rare with very few cases documented worldwide compared to CLH is more commonly seen. [ 101 ] Now Acquired hypertrichosis is a type that can develop later in life, typically from medicinal triggers or from underlying medical conditions. [ 101 ]
Webbing of the toes is the result of premature arrested development in the fetal stage. [ 102 ] The premature arrest of development results in second and third digit fusion of the skin. [ 102 ] The Y-linked trait of webbed toes causes a skin connection between the second and third digit. [ 88 ] Research studies based in a pedigree analysis have shown that webbed toes follow holandric inheritance in biological males. [ 102 ] [ 100 ]
Considered to be the most prevalent congential limb malformation where the occurrence is 1 in 2000-3000 in live births, accounting for 20% of congenial hand malformation. [ 103 ] The condition is more frequently seen in males where it is a 2:1 ratio for male-to-females. Syndactyl can present as an “isolated anomaly” where it occurs as a standalone condition often with no known cause. [ 104 ] In other scenarios, syndactyl is a features amongst other symptoms of a larger genetic disorder (ie. Holt-Oram syndrome).
Y-linked genes responsible for spermatogenesis can result in male infertility, characterized by azoospermia , [ 105 ] [ 106 ] or hypo-fertility, which is the hindered production of sperm. [ 95 ] Azoospermia is the absence of functional sperm in male ejaculate due to issues in sperm motility or lack of sperm production. [ 106 ] As a result, Y-chromosome linked infertility is characterized as the inability to fertilize an egg and produce children. [ 105 ] Sperm infertility results from the failure of the sperm to mature or a disfigured sperm that is not able to travel and fertilize an egg effectively. [ 105 ]
Male infertility affects 1 in 20 men, at 0.05% and primary spermatogenic failure accounts for a large portion of these cases. [ 91 ] More specifically, Y chromosome infertility is relatively rare at a 0.03-0.05% frequency. [ 105 ]
Mutations to the male-specific region of the Y chromosome (MSY) are typically the cause of spermatogenic failure, which is the reduced or absent sperm production in semen. [ 107 ] More specifically, deletions in long arm of the Y chromosome are associated with spermatogenic failure, as well some paternal lineages of the Y chromosome are associated with reduced sperm counts. [ 108 ] Y chromosome deletions are determined as the most frequent cause of genetic azoopermia, however other instances such as rearrangements, deletions and duplications may contribute to infertile biological males. [ 108 ]
Thus far, this article has discussed the patterns of inheritance of sex-linked genes / traits in diploid organisms with the canonical XX (female) or XY (male) genotype. However, there exists a very small fraction of the human population with aneuploidy (an abnormal number) of the sex chromosomes. [ 109 ] This includes monosomy of the X-chromosome (XO genotype), also called Turner syndrome, in which up to 0.04% of females are born with one X-chromosome as supposed to two. Turner syndrome can result in developmental and health-related issues, including short stature, problems with ovarian development, and congenital heart defects. [ 110 ] Females can also present with trisomy of the X-chromosome, or the XXX genotype, which can result in tall stature, and in some cases, delayed development of speech, language, and motor functions. [ 111 ] Sex chromosome aneuploidy which results in male development includes the XXY genotype, and very rarely, the XXYY genotype. [ 109 ] XXY, also known as Klinefelter syndrome, can result in a variety of symptoms, the severity of which is widely variable. Symptoms may include tall stature and reduced testosterone production, leading to delayed or incomplete development of male sex characteristics. Those with Klinefelter syndrome will also be at greater risk for developing of learning disorders, Attention-Deficit Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD), and metabolic syndromes. [ 112 ] Males with the XXYY genotype exhibit similar but often more severe symptoms to Klinefelter syndrome, and are infertile. [ 113 ]
It is notable that, while sex chromosome aneuploidy is not an inherited condition (and instead arises due to nondisjunction of the sex chromosomes during meiosis) in individuals with an abnormal number of sex chromosomes, the patterns of inheritance and expression of sex-linked genes and traits will vary from those discussed for XX and XY individuals. This is largely due to the dosage imbalance of one or both of the sex-chromosomes. For instance, a XO female with Turner syndrome would be affected by X-linked recessive traits in the same way as XY males, lacking a second X-chromosome encoding a dominant allele to mask the recessive phenotype. Moreover, inactivation of all but one X-chromosomes by Xist, and the fact that nondisjunction during meiosis can lead to aneuploidy in either all or some of the body's cells, can lead to genetic mosaicism and intermediate phenotypes. [ 109 ]
Most mammals, including humans, use the XY sex determination system and thus follow the same patterns of sex-linked inheritance discussed herein so long as the sex chromosomes are present in normal ploidy (diploidy). [ 114 ] However, patterns of inheritance of sex-linked traits differ in animals that use sex-determination systems other than XY . For instance, in the ZW sex-determination system used by birds, the mammalian pattern is reversed, since the male is the homogametic (ZZ) and the female is heterogametic (ZW). [ 115 ]
Drosophila melanogaster , a common model organism in genetics and developmental biology, carry both the X and Y sex chromosomes. However, the rules of sex determination are not the same as in humans and other placental mammals in which sex is determined by the presence or absence of the Y-chromosome. Instead, sex is determined by the ratio of X-chromosomes to autosomes, the X:A ratio. A ratio of 1:2 results in male development, while a ratio of 1:1 results in female development. Drosophila have two autosomes, thus XO and XY flies are males (1X:2A), while XX flies are females (2X:2A). As the X-chromosome makes up a far more significant portion of the genome, far more genes are sex-linked in Drosophila as compared to humans. [ 116 ] Moreover, the mechanism of dosage compensation in Drosophila is not X-inactivation in females, but the two-fold upregulation of expression of genes encoded on the X-chromosome in males. [ 117 ]
Much of the scientific knowledge on sex-linked traits was derived from observations and experimental evidence made in non-human animals. Some of the discoveries instrumental to forming this body of knowledge include:
The relationship between sex chromosomes and Mendelian inheritance was first discovered by Nettie Stevens. [ 86 ] Steven's was influenced by McClung's work highlighting, that some insect species, the difference in chromosome counts possibly determined whether cells develop into males or females. [ 122 ] In Steven's study called Studies in spermatogenesis, she found that biological females carry two X chromosomes, whereas males carry one X and a smaller Y chromosome. [ 86 ] By identifying the male unique role of the Y chromosome, Stevens was able to confirm a chromosomal role in sex determination . [ 86 ] She had done this by using a microscope Tenebrio molitor, mealworm beetles, to observe that there were 20 chromosome in both the male and females. However, in the males, she had found that the 20th chromosome was significantly smaller than the other 19 chromosomes. Steven's continued Studies in spermatogenesis, and found the same pattern in 18 other species. Additionally, her work contradicted the common theories that attributed to sex determination, including role of environmental factors. [ 122 ]
Red-green colour blindness was the first described on paper, in 1794 by John Dalton , who was affected by the disorder himself. [ 123 ] However, its recognition of its X-linked inheritance characterisitc was only established later. The X-chromosome was discovered in 1890 by Hermann Henking , [ 124 ] which he discovered while studying spermatocyte divisions of the firebug. He found that one chromosome behaved different from all the others, and did not divide during meiosis . Instead, he found that it went into one of the two germ cells. This cell that did not divide became known as the X-chromosome. [ 125 ] Then in 1910, Thomas Hunt Morgan discovered an X-linked mutation on a Drosophila , [ 126 ] who then conducted experiments and observations to understand the X-linked inheritance. He observed a white-eye male fruit fly, which is rare, and through cross-breeding experiments, he found that the mutation was inherited differently in males and females. He found that males, who had the only one X-chromosomes displayed the condition, if the mutated gene was present. [ 127 ]
In 1961, Mary Lyon proposed that one of the two X chromosomes in female mammalian cells would experience random inactivation (see X-chromosome inactivation ) in the early embryonic stage . [ 128 ] According to her hypothesis, both males and females should have one single X chromosome that is active. This enhanced the understanding of the fundamental mechanisms of X-linked inheritance.
It is important to distinguish between sex-linked characters, which are controlled by genes on sex chromosomes, and two other categories. [ 129 ]
Sex-influenced or sex-conditioned traits are phenotypes affected by whether they appear in a male or female body. [ 130 ] Even in a homozygous dominant or recessive female the condition may not be expressed fully. Example: baldness in humans.
These are characters only expressed in one sex. They may be caused by genes on either autosomal or sex chromosomes. [ 130 ] Examples: female sterility in Drosophila ; and many polymorphic characters in insects, especially in relation to mimicry . Closely linked genes on autosomes called " supergenes " are often responsible for the latter. [ 131 ] [ 132 ] [ 133 ] | https://en.wikipedia.org/wiki/Sex_linkage |
Sex pheromones are pheromones released by an organism to attract an individual of the same species, encourage them to mate with them, or perform some other function closely related with sexual reproduction .
Sex pheromones specifically focus on indicating females for breeding, attracting the opposite sex, and conveying information on species, age, sex and genotype. Non-volatile pheromones, or cuticular contact pheromones, are more closely related to social insects as they are usually detected by direct contact with chemoreceptors on the antennae or feet of insects.
Insect sex pheromones have found uses in monitoring and trapping of pest insects.
Sex pheromones have evolved in many species. The many types of pheromones (i.e. alarm, aggregation, defense, sexual attraction ) all have a common cause acting as chemical cues to trigger a response. However, sex pheromones are particularly associated with signaling mating behaviors or dominance. The odors released can be seen as a favorable trait selected by either the male or female leading to attraction and copulation . Chemical signaling is also used to find genetically different mates and thus avoid inbreeding. [ 2 ] Females are often selective when deciding to mate , and chemical communication ensures that they find a high-quality mate that satisfies their reproductive needs.
Odours may be a kind of male "ornament" selected for by female choice . They meet the criteria for such ornaments that Charles Darwin set out in The Descent of Man, and Selection in Relation to Sex . After many years of study the importance of such chemical communication is becoming clear. [ 4 ]
Males usually compete for scarce females , which make adaptive choices based on male traits. The choice can benefit the female directly and/or genetically. In tiger moths ( Utetheisa ornatrix ), females choose the males that produce the most pheromone; an honest signal of the amount of protective alkaloids the male has, as well as an indicator of the size of female offspring (females fertilised by such males lay more eggs). [ 4 ] Male cockroaches form dominance hierarchies based on pheromone "badges", while females use the same pheromone for male choice. [ 5 ] In oriental beetles ( Exomala Orientalis ), females release the pheromone and passively wait for a male to find them. The males with superior detection and flying abilities are most likely to reach the female beetle first which leads to a selection for genetically-advantageous males. [ 6 ]
In most species, pheromones are released by the non-limiting sex. Some female moths signal, but this is cheap and low risk; it means the male has to fly to her, taking a high risk. This mirrors communication with other sensory modalities, e.g. male frogs croak; male birds are usually colourful. Male long-range pheromone signals may be associated with patchy resources for the female. In some species, both sexes signal. Males can sometimes attract other males instead, the sex pheromone acting as an aggregation pheromone . [ 4 ]
It is likely that most externally fertilizing species (e.g. marine worms , sea urchins ) coordinate their sexual behaviour (release of sperm and eggs ) using pheromones. This coordination is very important because sperm are diluted easily, and are short-lived. Coordination therefore provides a selective advantage to both males and females: individuals that do not coordinate are unlikely to achieve fertilisation and hence to leave offspring. [ 4 ]
The main selective advantage of outcrossing is that it promotes the masking of deleterious recessive alleles, while inbreeding promotes their harmful expression. [ 7 ] [ 8 ]
No study has led to the isolation of true human sex pheromones . [ 9 ] [ 10 ] While humans are highly dependent upon visual cues, when in close proximity, smells also play a role in sociosexual behaviors. An inherent difficulty in studying human pheromones is the need for cleanliness and odorlessness in human participants. [ 11 ]
Different species use a wide variety of chemical substances to send sexual signals. The first to be described chemically was bombykol , the silkworm moth 's sex pheromone, which is a complex alcohol, (E,Z)-10,12-hexadecadienol, discovered in 1959. It is detected in the antennae of the male moth by a pheromone-binding protein which carries the bombykol to a receptor bound to the membrane of a nerve cell. [ 12 ] The chemicals used by other moths are species-specific. For example, the Eastern spruce budworm Choristoneura fumiferana female pheromones contain a 95:5 mix of E- and Z 11-tetradecenal aldehydes , while the sex pheromones of other species of spruce budworm contain acetates and alcohols . [ 13 ]
Sexual development in the freshwater green alga Volvox is initiated by a glycoprotein pheromone. [ 14 ] It is one of the most potent known biological effector molecules, as it can trigger sexual development at a concentration as low as 10 −16 moles per litre. [ 14 ] Kirk and Kirk showed that sex-inducing pheromone production can be triggered experimentally in somatic cells by heat shock. [ 15 ]
Sex pheromones have found applications in pest monitoring and pest control . For monitoring, pheromone traps are used to attract and catch a sample of pest insects to determine whether control measures are needed. For control, much larger quantities of a sex pheromone are released to disrupt the mating of a pest species. This can be either by releasing enough pheromone to prevent males from finding females, effectively drowning out their signals, or by mass trapping, attracting and removing pests directly. [ 16 ] For example, research on the control of the spruce bud moth ( Zeiraphera canadensis ) has focused on the use of the pheromone E-9-tetradecenyl-acetate, a chemical the spruce bud moth releases during mating. [ 17 ] | https://en.wikipedia.org/wiki/Sex_pheromone |
Sex segregation , sex separation , sex partition, gender segregation, gender separation, or gender partition [ 1 ] [ 2 ] is the physical, legal, or cultural separation of people according to their gender or biological sex at any age. Sex segregation can simply refer to the physical and spatial separation by sex without any connotation of illegal discrimination . In other circumstances, sex segregation can be controversial. Depending on the circumstances, it can be a violation of capabilities and human rights and can create economic inefficiencies; on the other hand, some supporters argue that it is central to certain religious laws and social and cultural histories and traditions. [ 3 ] [ 4 ]
Sex segregation is a global phenomenon manifested differently in varying localities. [ 5 ] Sex segregation and integration considered harmless or normal in one country can be considered radical or illegal in others. [ 6 ] At the same time, many laws and policies promoting segregation or desegregation recur across multiple national contexts. Safety and privacy concerns, traditional values and cultural norms, and belief that sex segregation can produce positive educational and overall social outcomes all shape public policy regarding sex segregation.
The term "sex" in "sex segregation" refers to the biological distinctions between men and women, used in contrast to " gender ". [ 7 ] The term "segregation" refers to separation of the sexes, which can be enforced by rules, laws, and policies, or be a de facto outcome in which people are separated by sex. Even as a de facto outcome, sex segregation taken as a whole can be caused by societal pressures, historical practices, socialized preferences and “fundamental biological differences”. [ 8 ] Sex segregation can refer to literal physical and spatial separation by sex. The term is also used for the exclusion of one sex from participation in an occupation, institution, or group. Sex segregation can be complete or partial, as when members of one sex predominate within, but do not exclusively constitute, a group or organization. [ 7 ]
In the United States some scholars use the term sex separation and not sex segregation . [ 9 ] [ 10 ] [ 11 ] [ 12 ] [ undue weight? – discuss ]
The term gender apartheid (or sexual apartheid) also has been applied to segregation of people by gender, [ 13 ] implying that it is sexual discrimination . [ 14 ] If sex segregation is a form of sex discrimination, its effects have important consequences for gender equality and equity . [ 7 ]
Sex segregation can occur in both public and private contexts, and be classified in many ways. It is the practice of separating people based on their gender and can take a variety of forms in different contexts. Legal and gender studies scholar David S. Cohen offers one taxonomy in categorizing sex segregation as mandatory, administrative, permissive, or voluntary. Mandatory and administrative sex segregation are required and enforced by governments in public environments, while permissive and voluntary sex segregation are stances chosen by public or private institutions, but within the capacity of the law. [ 7 ] Example: Separate restrooms and locker rooms for men and women in public buildings. Sex-segregated prisons or detention centers. Sex-specific sports competitions, especially where physical differences are considered important.
Mandatory sex segregation is legally required and enforces separation based on sex. [ 7 ] Examples include separation of men and women in prisons , law enforcement , military service , public toilets , and housing. These mandatory rules can be nuanced, as in military service, where sexes are often separated in laws about conscription, in housing, and in regulations on which sexes can participate in certain roles, like frontline infantry. [ 7 ] Mandatory sex segregation also includes less obvious cases of separation, as when men and women are required to have same-sex attendants for body searches. Mandatory sex segregation can thus dictate parameters for employment in sex segregated spaces, including medical and care work contexts, and can be a form of occupational segregation . [ 7 ] For example, a government may mandate that clinics hire female nurses to care for female patients.
Administrative sex segregation involves public and government institutions segregating by sex in their operating capacity, rather than as the result of a formal mandate. [ 7 ] This segregation often stems from practical considerations, organizational norms, or social expectations, rather than formal legal requirements. Examples of administrative sex segregation include sex segregation in government sponsored medical research, sports leagues, public hospitals with shared rooms, rehabilitation programs, and some public education facilities. Administrative sex segregation can occur in these environments simply as through the provisioning of sex segregated public toilets despite limited explicit legal requirements to do so. [ 7 ]
Permissive sex segregation is segregation which is explicitly permitted by law, i.e. affirmatively authorized, but not necessarily legally required or encouraged. [ 7 ] Permissive sex segregation exempts certain things from anti- sex-discrimination laws, often allowing for, among others, segregation of religious and military schools, undergraduate schools that have traditionally admitted based on sex, health clubs, athletic teams, social fraternities and sororities, choirs and choruses, voluntary youth service organizations such as the Girl Scouts and Boy Scouts , father/son and mother/daughter activities, and sex-exclusive beauty pageants and scholarships. [ 7 ]
Sex segregation that is neither legally mandated, nor enacted in an administrative capacity, nor explicitly permitted by law, is recognized as voluntary sex segregation. [ 7 ] Voluntary sex segregation refers to lack of explicit legal prescriptions; it does not necessarily indicate the free choice of either the segregated or the segregators, and it may be imposed by social and cultural norms. Voluntary sex segregation takes place in numerous national professional and interest-based membership organizations, local and larger clubs, professional sports teams, private recreational facilities, religious institutions, performing arts, and more. [ 7 ]
Libertarian feminist theory stems from ideologies similar to libertarian political theory; that legal and governmental institutions should not regulate choices and should allow people's free will to govern their life trajectories. [ 15 ] Libertarianism takes a free market approach to sex segregation saying that women have a natural right and are the most informed to make decisions for themselves but rejects special protections specifically for women. [ 16 ] Autonomy is central to libertarianism, so theorists believe that the government should not interfere with decision making or be concerned with reasoning behind such decisions since men and women culturally and naturally make different and often diverging choices. Policies and laws enforced by the government should not act to change any inherent differences between the sexes. [ 7 ] [ 17 ] Libertarianism most directly relates to voluntary sex segregation as it maintains that the government should not regulate private institutions or entities' segregation by sex and should not regulate how individuals privately group themselves. [ 7 ] Libertarian feminist David Berstein argues that while sex segregation can cause harm, guarding the freedom of choice for men and women is more important than preventing such sex segregation since methods of prevention can often cause more harm than good for both sexes. Women's health clubs are an example of how sex segregation benefits women since desegregation would interfere with women's abilities to exercise without the distraction of men and 'ogling' without any direct benefit to allowing men a membership. [ 18 ] Additionally, libertarians would allow for permissive sex segregation since it allows people to choose how to organize their interactions and relationships with others. [ 7 ] Libertarian feminists acknowledge that there is legal precedence for sex segregation laws, but argue for such parameters to ensure equal treatment of similarly situated men and women. As such, libertarianism could allow or reject specific forms of sex segregation created to account for natural or biological differences between the sexes. [ 19 ]
Equal treatment theory or formal equity often works in tandem with libertarianism in that equal treatment theorists believe governments should treat men and women similarly when their situations are similar. [ 20 ] [ 21 ] In countries whose governments have taken to legislation eliminating sex segregation, equal treatment theory is most frequently used as support for such rules and regulation. [ 22 ] For example, equal treatment theory was adopted by the many feminists during the United States' feminist movement in the 1970s. This utilization of equal treatment theory led to the adoption of intermediate scrutiny as a standard for sex discrimination on the basis that men and women should be treated equally when in similar situations. [ 22 ] While equal treatment theory provides a sound framework for equality, application is quite tricky, as many critics question the standards by which men and women should be treated similarly or differently. [ 21 ] In this manner, libertarianism and equal treatment theory provide good foundations for their agendas in sex segregation, but conceptually do not prevent it, leaving room for mandatory and administrative sex segregation to remain as long as separation is based on celebrated differences between men and women. Some forms of mandatory and administrative segregation may perpetuate sex segregation by depicting a difference between male and female employees where there is no such difference, as in combat exclusion policies. [ 7 ] [ 23 ]
Difference feminism arose from libertarianism and equal treatment theories' perceived failure to create systemic equality for women. Difference feminism celebrates biological, psychological, moral differences between men and women, accusing laws concerning sex segregation of diluting these important differences. [ 24 ] Difference feminists believe that such laws not only ignore these important differences, but also can exclude participation of women in the world. Difference feminism's goal is to bring about a consciousness of women's femininity and to cause the revaluation of women's attributes in a more respectful, reverent manner. [ 21 ] Difference feminism and equal treatment theory are quite contrasting feminist theories of sex segregation. Difference feminism often justifies sex segregation through women's and men's differences while equal treatment theory does not support separation because of differences in sex. Difference feminism, however, argues against segregation that stems from societal and "old-fashioned" differences between men and women, but believes that segregation that takes women's differences into account and promotes equality is acceptable, even going so far as to say that some forms of sex segregation are necessary to ensure equality, such as athletics and education, and policies such as Title IX. [ 7 ]
Anti-subordination feminist theory examines sex segregation of power to determine whether women are treated or placed subordinately compared to men in a law or situation. [ 7 ] The theory focuses on male dominance and female subordination and promotes destroying a sex-based hierarchy in legal and social institutions and preventing future hierarchies from arising. [ 25 ] Anti-subordination also supports laws that promote the status of women even if they lower men's status as a consequence. [ 26 ] Controversial applications of anti-subordination that can either perpetuate the subordination of women or create the subordination of men include sex segregation in education and in the military. [ 27 ]
Critical race feminism developed due to the lack of racial inclusivity of feminist theories and lack of gender inclusivity of racial theories. [ 28 ] This theory is more global than the others, attempting to take into account the intersectionality of gender and race. Critical race feminism demands that theorists reexamine surface-level segregation and focus on how sex segregation stems from different histories, causing different effects based on race, especially for [ 29 ] women of color. This segregation is evident in many racially divided countries, especially in the relationship between the end of race-segregated schools and sex segregation. [ 7 ] [ 30 ] Critical race feminism critiques other theories' failure to take into account their different applications once race, class, sexual orientation, or other identity factors are included in a segregated situation. [ 31 ] It creates the need to examine mandatory and administrative sex segregation to determine whether or if they sustain racial stereotypes, particularly towards women of color. Additionally, critical race feminists wonder whether permissive and voluntary sex segregation are socially acceptable manners by which to separate races and sexes or whether they maintain and perpetuate inequalities. [ 7 ] Critical race feminism is a form of anti-essentialism (below). [ 28 ]
Anti-essentialists maintain that sex and gender categories are limiting and fail to include the unlimited variety of difference in human identity and impose identities rather than simply note their differences. [ 32 ] [ 33 ] Theorists believe that there is variation in what it means to be a man and what it means to be a woman, and by promoting the differences through sex segregation, people are confined to categories, limiting freedom. [ 7 ] Anti-essentialists examine how society imposes specific identities within the sex dichotomy and how subsequently sex and gender hierarchies are created, perpetuated, and normalized. [ 7 ] This theory requires that there is a specific disentanglement between sex and gender. [ 34 ] [ 35 ] Anti-essentialists believe that there should not be an idea of what constitutes masculinity or femininity, but that individual characteristics should be fluid to eliminate sex and gender-based stereotypes. [ 36 ] No specific types of sex segregation are outwardly promoted or supported by anti-essentialists since mandatory and administrative sex segregation reinforce power struggles between the sexes and genders while permissive or voluntary forms of sex segregation allow institutions and society to sort individuals into categories with differential access to power, and supporting the government's elimination of such permission for certain institutions and norms to continue to exist. [ 37 ]
Some sex segregation occurs for reasons of safety and privacy. Worldwide, laws often mandate sex segregation in public toilets, changing rooms , showers, and similar spaces, based on a common perceived need for privacy. [ 7 ] This type of segregation policy can protect against sexual harassment and sexual abuse . [ 38 ] To combat groping , street harassment , and eve teasing of women in crowded public places, some countries have also designated women only spaces . For example, sex-segregated buses, women-only passenger cars , and compartments on trains have been introduced in Mexico , Japan , the Philippines , the UAE and other countries to reduce sexual harassment. [ 39 ] [ 40 ] [ 41 ] [ 42 ]
Some places in Germany , Korea , and China all have women's parking spaces , often for related safety issues. [ 43 ] [ 44 ] [ 45 ] Many more countries, including Canada , the United States , Italy , Japan , and the United Kingdom also grant parking privileges to pregnant women, for safety or access reasons.
Sex segregation rooted in safety considerations can furthermore extend beyond the physical to the psychological and emotional as well. A refuge for battered mothers or wives may refuse to admit men, even those who are themselves the victims of domestic violence, both to exclude those who might commit or threaten violence to women and because women who have been subjected to abuse by a male might feel threatened by the presence of any man. [ 46 ] Women's health clinics and women's resource centers, whether in Africa or North America , are further examples of spaces where sex segregation may facilitate private and highly personal decisions. Women-only banks may be similarly intended to provide autonomy to women's decision making.
Sex segregation can also be motivated by religious or cultural ideas about men and women. Such cultural assumptions may even exist in the aforementioned policies enacted under the pretenses of safety or privacy concerns. Gender separation in Judaism and gender segregation in Islam reflect religiously motivated sex segregation. In Buddhism , Christianity , and Hinduism , monastic orders , prayer spaces, and leadership roles have also been segregated by sex. [ 49 ]
From a policy perspective, theocracies and countries with a state religion have sometimes made sex segregation laws based partially in religious traditions. Even when not legally enforced, such traditions can be reinforced by social institutions and in turn result in sex segregation. In the South Asian context, one institution conducive to sex segregation, sometimes but not always rooted in national law, is purdah . [ 50 ]
The Muslim world and the Middle East have been particularly scrutinized by scholars analyzing sex segregation resulting from the consequences of Sharia , the moral and religious code of Islam that, in the strictest version, Muslims hold to be the perfect law created by God. Saudi Arabia has been called an epicenter of sex segregation, stemming partially from its conservative Sunni Islamic practices and partially from its monarchy's legal constraints. [ 51 ] Sex segregation in Saudi Arabia is not inherent to the country's culture, but was promoted in the 1980s and 1990s by the government, the Sahwa movement, and conservative and religious behavioral enforcers (i.e. police, government officers, etc.). [ 51 ]
Israel has also been noted both for its military draft of both sexes and its sex-segregated Mehadrin bus lines . [ 52 ]
Sex segregation is sometimes pursued through policy because it is thought to produce better educational outcomes. In some parts of the world, especially in Europe, where education is available to girls as well as boys, educational establishments were frequently single-gender. Such single-sex schools are still found in many countries, including but not limited to, Australia , the United Kingdom, and the United States. [ 53 ] [ 54 ]
In the United States in particular, two federal laws give public and private entities permission to segregate based on sex: Title VII of the Civil Rights Act of 1964 and Title IX of the Educational Amendments of 1972. [ 7 ] These laws permit sex segregation of contact sports, choruses, sex education, and in areas such as math and reading, within public schools. [ 7 ]
Studies have analyzed whether single-sex or co-ed schools produce better educational outcomes. Teachers and school environments tend to be more conducive to girls' learning habits and participation rates improve in single-sex schools. [ 55 ] [ 56 ] [ 57 ] [ 58 ] In developing countries, single-sex education provides women and girls an opportunity to increase female education and future labor force participation. [ 59 ] Girls in single-sex schools outperform their counterparts in co-educational schools in math, average class scores for girls are higher, girls in single-sex math and science classes are more likely to continue to take math and science classes in higher education, and in case studies, boys and girls have reported that single-sex classes and single-sex teachers create a better environment for learning for both sexes. [ 60 ] [ 61 ] [ 62 ] [ 63 ] [ 64 ]
Critics of single-sex schools and classes claim that single-sex schooling is inherently unequal and that its physical separation contributes to gender bias on an academic and social basis. Single-sex schooling also allegedly limits the socialization between sexes that co-educational schools provide. Coeducational school settings have been shown to foster less anxiety, have happier classrooms, and enable students to participate in a simulated social environment with the tools to maneuver, network, and succeed in the world outside of school. [ 65 ] [ 66 ] [ 67 ] [ 68 ] Even in co-ed schools, certain classes, such as sex education , are sometimes segregated on the basis of sex. Parallel education occurs in some schools, when administrators decide to segregate students only in core subjects. [ 69 ] Segregation by specialization is also evident in higher education and actually increases with economic development of a country. [ 70 ] Cambodia , Laos , Morocco , and Namibia are countries with the least amount of gender segregation in tertiary studies while Croatia , Finland , Japan, and Lithuania have the most. [ 71 ]
Even outside of educational settings women's sports are sex segregated from men's sports . [ 72 ]
Sex segregation is very prevalent in the administration of prisons. Radical feminist Catharine MacKinnon says that the policy is in place for ease of management and not for protecting women, examplified by the fact that women's prisons put women who have been convicted of rape or murder in the same wards as women who have been convicted of prostitution , or killing their batterers . [ 73 ]
For most children, sex segregation manifests itself early in the socialization process via group socialization theory , where children are expected to behave in certain sex-typed manners and form sex in and out-groups. [ 74 ] In pre-school classrooms, for example, making gender more salient to children has been shown to lead to stronger gender stereotypes and inter-group biases between sex groups. These evident tendencies were also manifested in decreased playtime with children of the opposite sex, or a kind of early, selective sex segregation based on preconceived social norms. [ 75 ] While specifically segregating by sex for playtime has not been linked to any long-lasting effects on women's rights compared to men, these different manners of socialization often lead to communication and power struggles between men and women and to differential life decisions by each sex based on these long-established gendered identities. [ 76 ]
In elementary and secondary education, sex segregation sometimes yields and perpetuates gender bias in the form of treatment by teachers and peers that perpetuates traditional gender roles and sex bias, underrepresentation of girls in upper level math, science, and computer classes, fewer opportunities for girls to learn and solve problems, girls receiving less attention compared to the boys in their classes, and significantly different performance levels between boys and girls in reading and math classes. Sometimes in elementary schools teachers force the students to sit boy, girl, boy girl. [ 77 ] Sex segregation in educational settings can also lead to negative outcomes for boys such as boys in co-educational classrooms having academic scores higher than boys in single-sex classrooms. On the contrary, girls in single-sex classrooms have academic scores higher than girls in co-educational classrooms. Boys academically benefit from a coeducational environment while girls do from a single-sex environment, so critics and proponents of both types of education argue that either single-sex or coeducational classrooms create a comparative disadvantage for either sex. [ 78 ] [ 79 ] [ 80 ] Athletic participation and physical education are examples where appeals to differences in biological sex may encourage segregation within education systems. [ 81 ] These differences can impact access to competition, gender identity construction, and external as well as internalized perceptions of capabilities, especially among young girls. [ 82 ]
Separation of public toilets by sex is very common around the world. In certain settings the sex separation can be critical to ensure the safety of females, in particular schoolgirls, from male abuse. [ 38 ] At the same time, sex segregated public toilets may promote a gender binary that excludes transgender people. [ 83 ] Unisex public toilets can be a suitable alternative and/or addition to sex-segregated toilets in many cases.
A special case presents with choirs and choruses, especially in the tradition of the choir school which uses ensemble and musical discipline to ground academic discipline. Male and female voices are distinctive both solo and in ensemble, and segregated singing has an evolved and established aesthetic. Male voices, unlike female voices, break in early adolescence, and accommodating this break in an educational program is challenging in a coed environment. Coeducation tends to stigmatize males, as is often the case in expressive arts, unlike athletics. [ citation needed ]
During the Taiping Rebellion (1851–64) against the Qing dynasty , areas controlled by the Taiping Heavenly Kingdom had strict sex separation enforced. Even married couples were not allowed to live together until 1858. Okinoshima is a Japanese island where women are not allowed. Athos is a Greek peninsula where women are not allowed.
The preference of same-sex friendships ( homosociality ) compared to cross-sex friendships differs by country and is associated with sex segregation. [ 84 ]
Physical sex separation is popular in many institutions on a tertiary level (between types of institutions), while fields of study or majors are not highly gendered, such as later life decisions such as work/care work conflicts. Men tend to occupy engineering, manufacturing, science, and construction fields while women dominate education, humanities and arts, social sciences, business, law, and health and welfare fields. [ 3 ] [ 85 ] However, important life decisions as occupations can yield other instances of sex segregation by impacting occupational sex imbalances and further male and female socialization . [ 86 ] Vicki Schultz (1990) indicates that although Title VII of the Civil Rights Act of 1964 prohibits sex discrimination in employment and promised working women change, "most women continue to work in low paying, low status, and traditionally female jobs." Schultz (1990) states that "employers have argued that women lack interest in male-dominated jobs, which are highly rewarded and nontraditional for women." According to Schultz, the courts have accepted this argument, subsequently not holding employers liable. Schultz contends that "the courts have failed to recognize the role of employers in shaping women's work aspirations." (Schultz, 1990:1750,1756) [ 87 ] ) Schultz states that the judicial framework that has been established by the courts "has created an unduly narrow definition of sex discrimination and an overly restrictive role for the law in dismantling sex segregation." (Schultz, 1990:1757) [ 87 ] Schultz concludes by saying, "courts can acknowledge their own constructive power and use it to help create a work world in which women are empowered to choose the more highly rewarded occupations that Title VII has long promised." (Schultz, 1990:1843) [ 87 ] Even at psychological levels, socialized preferences for or against sex segregation can also have significant effects. In one study, women in male-dominated work settings were the most satisfied psychologically with their jobs while women in occupational settings with only 15-30% men were less satisfied due to favored treatment of the male minority in such a segregated atmosphere. [ 88 ] Stark segregation by occupation can lead to a sexual division of labor, influencing the access and control men and women have over inputs and outputs required for labor. Additionally, occupational sex segregation has certain health and safety hazards for each sex, since employment conditions, type of work, and contract and domestic responsibilities vary for types of employment. In many areas of work, women tend to dominate the production line jobs while men occupy managerial and technical jobs. [ 89 ] These types of workplace factors and interactions between work and family have been cited by social stratification research as key causes for social inequality. Family roles are especially influential for predicting significant differences in earnings between married couples. Men benefit financially from family roles such as a husband and a father, while women's incomes are lowered when becoming a wife and mother. [ 90 ]
Other gender disparities via sex segregation between men and women include differential asset ownership, house and care work responsibilities, and agency in public and private spheres for each sex. [ 90 ] These segregations have persisted because of governmental policy, blocked access for a sex, and/or the existence of sex-based societal gender roles and norms. Perpetuation of gender segregation, especially in economic spheres, creates market and institutional failures. For example, women often occupy jobs with flexible working environments in order to take on care work as well as job responsibilities, but since part-time, flexible hourly jobs pay less and have lower levels of benefits, large numbers of women in these lower income jobs lowers incentives to participate in the same market work as their male counterparts, perpetuating occupational gender lines in societies and within households. [ 3 ] Schultz (1990) article indicates that "working-class women have made it a priority to end job segregation for they want opportunities that enable them to support them and their families." (Schultz, 1990:1755) [ 87 ] Additionally, economic development in countries is positively correlated with female workers in wage employment occupations and negatively correlated with female workers in unpaid or part-time work, self-employment, or entrepreneurship, job sectors often seen occupied by women in developing countries. [ 3 ] Many critics of sex segregation see globalization processes as having the potential to promote systemic equality among the sexes. [ 3 ]
Some literary works of social science fiction and gender , sex and sexuality in speculative fiction that consider sex segregation are the books Swastika Night or The Handmaid's Tale (later converted into a TV series ).
Desegregation policies often seek to prevent sex discrimination , or alleviate occupational segregation . These policies encourage women and men to participate in environments typically predominated by the opposite sex. Examples include government quotas , gender-specific scholarships, co-ed recreational leagues, or programming designed to change social norms.
In China, deputies to the National People's Congress and members of the Chinese People's Political Consultative Conference National Committee proposed that the public should be more attentive to widespread instances of occupational segregation in China. Often employers reject specifically women applicants or create sex requirements in order to apply. The Labour Contract Law of the People's Republic of China and Law of the People's Republic of China on the Protection of Rights and Interests of Women state that no employer can refuse to employ women based on sex or raise application standards for women specifically, but also do not currently have clear sanctions for those who do segregate based on sex. [ 91 ] China has also begun to encourage women in rural villages to take up positions of management in their committees. Specifically, China's Village Committee Organization Law mandates that women should make up one third or more of the members of village committees. The Dunhuang Women's Federation of Dunhuang City, in China's Gansu Province, provided training for their village's women in order to build political knowledge. [ 92 ]
In March 2013 in the European Union, a resolution was passed to invest in training and professional development for women, promote women-run businesses, and include women on company boards. [ 93 ] In Israel, the Minister of Religious Services, Yaakov Margi Shas, has recently supported removal of signs at cemeteries segregating women and men for eulogies and funerals, prohibiting women from taking part in the services. The Minister agreed with academic and politician, Yesh Atid MK Aliza Lavie, who questioned him about segregation policies enacted by rabbis and burial officials, that governmental opposition to sex segregation was necessary to combat these practices not supported by Jewish or Israeli law. [ 94 ]
In other cases, sex segregation in one arena can be pursued to enable sex desegregation in another. For example, separation of boys and girls for early math and science education may be part of an effort to increase the representation of women in engineering or women in science .
Sometimes, countries will also argue that segregation in other nations violates human rights . For example, the United Nations and Western countries have encouraged kings of Saudi Arabia to end its strict segregation of institutions such as schools, government institutions, hospitals, and other public spaces in order to secure women's rights in Saudi Arabia [ 95 ] Even though the removal of certain religious and government heads has made way for liberal agendas to promote desegregation, the public largely still subscribes to the idea of a segregated society, while institutions and the government itself still technically remain under the control of Wahhabism . Reform is small in size, since there is no constitution to back up policy changes concerning sex segregation. The Saudi people refer to this segregation as Khilwa and violation of the separation is punishable by law. This separation is tangibly manifested in the recently erected wall in places that employ both men and women, a feat possible by a law passed in 2011 allowing Saudi women to work in lingerie shops in order to lower female unemployment rates. The public views the 1.6 meter wall favorably, saying that it will lead to less instances of harassment by men visiting the expatriate women in the shops. [ 96 ] The Luthan hotel in Saudi Arabia was the country's first women's only hotel, acting more as a vacation spot for women than a mandated segregated institution. Upon entering the hotel, women are allowed to remove their headscarves and abayas and the hotel employs only women, calling their bellhops the world's first bellgirls, providing opportunities for Saudi women in IT and engineering jobs where, outside the Luthan, are quite scarce. [ 97 ] | https://en.wikipedia.org/wiki/Sex_segregation |
A sextant is a doubly reflecting navigation instrument that measures the angular distance between two visible objects. The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation .
The estimation of this angle, the altitude, is known as sighting or shooting the object, or taking a sight . The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart —for example, sighting the Sun at noon or Polaris at night (in the Northern Hemisphere) to estimate latitude (with sight reduction ). Sighting the height of a landmark can give a measure of distance off and, held horizontally, a sextant can measure angles between objects for a position on a chart . [ 1 ] A sextant can also be used to measure the lunar distance between the moon and another celestial object (such as a star or planet) in order to determine Greenwich Mean Time and hence longitude .
The principle of the instrument was first implemented around 1731 by John Hadley (1682–1744) and Thomas Godfrey (1704–1749), but it was also found later in the unpublished writings of Isaac Newton (1643–1727). [ 2 ]
In 1922, it was modified for aeronautical navigation by Portuguese navigator and naval officer Gago Coutinho .
Like the Davis quadrant , the sextant allows celestial objects to be measured relative to the horizon, rather than relative to the instrument. This allows excellent precision. Also, unlike the backstaff , the sextant allows direct observations of stars. This permits the use of the sextant at night when a backstaff is difficult to use. For solar observations, filters allow direct observation of the Sun.
Since the measurement is relative to the horizon, the measuring pointer is a beam of light that reaches to the horizon. The measurement is thus limited by the angular accuracy of the instrument and not the sine error of the length of an alidade , as it is in a mariner's astrolabe or similar older instrument.
A sextant does not require a completely steady aim, because it measures a relative angle. For example, when a sextant is used on a moving ship, the image of both horizon and celestial object will move around in the field of view. However, the relative position of the two images will remain steady, and as long as the user can determine when the celestial object touches the horizon, the accuracy of the measurement will remain high compared to the magnitude of the movement.
The sextant is not dependent upon electricity (unlike many forms of modern navigation) or any human-controlled signals (such as GPS). For these reasons it is considered to be an eminently practical back-up navigation tool for ships.
The frame of a sextant is in the shape of a sector which is approximately 1 ⁄ 6 of a circle (60°), [ 3 ] hence its name ( sextāns, sextantis is the Latin word for "one sixth"). Both smaller and larger instruments are (or were) in use: the octant , quintant (or pentant ) and the (doubly reflecting) quadrant [ 4 ] span sectors of approximately 1 ⁄ 8 of a circle (45°), 1 ⁄ 5 of a circle (72°) and 1 ⁄ 4 of a circle (90°), respectively. All of these instruments may be termed "sextants".
Attached to the frame are the "horizon mirror", an index arm which moves the index mirror , a sighting telescope, Sun shades, a graduated scale and a micrometer drum gauge for accurate measurements. The scale must be graduated so that the marked degree divisions register twice the angle through which the index arm turns. The scales of the octant, sextant, quintant and quadrant are graduated from below zero to 90°, 120°, 140° and 180° respectively. For example, the sextant illustrated has a scale graduated from −10° to 142°, which is basically a quintant: the frame is a sector of a circle subtending an angle of 76° at the pivot of the index arm.
The necessity for the doubled scale reading follows from consideration of the relations of the fixed ray (between the mirrors), the object ray (from the sighted object) and the direction of the normal perpendicular to the index mirror. When the index arm moves by an angle, say 20°, the angle between the fixed ray and the normal also increases by 20°. But the angle of incidence equals the angle of reflection so the angle between the object ray and the normal must also increase by 20°. The angle between the fixed ray and the object ray must therefore increase by 40°. This is the case shown in the graphic.
There are two types of horizon mirrors on the market today. Both types give good results.
Traditional sextants have a half-horizon mirror, which divides the field of view in two. On one side, there is a view of the horizon; on the other side, a view of the celestial object. The advantage of this type is that both the horizon and celestial object are bright and as clear as possible. This is superior at night and in haze, when the horizon and/or a star being sighted can be difficult to see. However, one has to sweep the celestial object to ensure that the lowest limb of the celestial object touches the horizon.
Whole-horizon sextants use a half-silvered horizon mirror to provide a full view of the horizon. This makes it easy to see when the bottom limb of a celestial object touches the horizon. Since most sights are of the Sun or Moon, and haze is rare without overcast, the low-light advantages of the half-horizon mirror are rarely important in practice.
In both types, larger mirrors give a larger field of view, and thus make it easier to find a celestial object. Modern sextants often have 5 cm or larger mirrors, while 19th-century sextants rarely had a mirror larger than 2.5 cm (one inch). In large part, this is because precision flat mirrors have grown less expensive to manufacture and to silver .
An artificial horizon is useful when the horizon is invisible, as occurs in fog, on moonless nights, in a calm, when sighting through a window or on land surrounded by trees or buildings. There are two common designs of artificial horizon. An artificial horizon can consist simply of a pool of water shielded from the wind, allowing the user to measure the distance between the body and its reflection, and divide by two. Another design allows the mounting of a fluid-filled tube with bubble directly to the sextant.
Most sextants also have filters for use when viewing the Sun and reducing the effects of haze. The filters usually consist of a series of progressively darker glasses that can be used singly or in combination to reduce haze and the Sun's brightness. However, sextants with adjustable polarizing filters have also been manufactured, where the degree of darkness is adjusted by twisting the frame of the filter.
Most sextants mount a 1 or 3-power monocular for viewing. Many users prefer a simple sighting tube, which has a wider, brighter field of view and is easier to use at night. Some navigators mount a light-amplifying monocular to help see the horizon on moonless nights. Others prefer to use a lit artificial horizon. [ citation needed ]
Professional sextants use a click-stop degree measure and a worm adjustment that reads to a minute , 1/60 of a degree . Most sextants also include a vernier on the worm dial that reads to 0.1 minute. Since 1 minute of error is about a nautical mile , the best possible accuracy of celestial navigation is about 0.1 nautical miles (190 m). At sea, results within several nautical miles, well within visual range, are acceptable. A highly skilled and experienced navigator can determine position to an accuracy of about 0.25-nautical-mile (460 m). [ 5 ]
A change in temperature can warp the arc, creating inaccuracies. Many navigators purchase weatherproof cases so that their sextant can be placed outside the cabin to come to equilibrium with outside temperatures. The standard frame designs (see illustration) are supposed to equalise differential angular error from temperature changes. The handle is separated from the arc and frame so that body heat does not warp the frame. Sextants for tropical use are often painted white to reflect sunlight and remain relatively cool. High-precision sextants have an invar (a special low-expansion steel) frame and arc. Some scientific sextants have been constructed of quartz or ceramics with even lower expansions. Many commercial sextants use low-expansion brass or aluminium. Brass is lower-expansion than aluminium, but aluminium sextants are lighter and less tiring to use. Some say they are more accurate because one's hand trembles less. Solid brass frame sextants are less susceptible to wobbling in high winds or when the vessel is working in heavy seas, but as noted are substantially heavier. Sextants with aluminum frames and brass arcs have also been manufactured. Essentially, a sextant is intensely personal to each navigator, and they will choose whichever model has the features which suit them best.
Aircraft sextants are now out of production, but had special features. Most had artificial horizons to permit taking a sight through a flush overhead window. Some also had mechanical averagers to make hundreds of measurements per sight for compensation of random accelerations in the artificial horizon's fluid. Older aircraft sextants had two visual paths, one standard and the other designed for use in open-cockpit aircraft that let one view from directly over the sextant in one's lap. More modern aircraft sextants were periscopic with only a small projection above the fuselage . With these, the navigator pre-computed their sight and then noted the difference in observed versus predicted height of the body to determine their position.
A sight (or measure ) of the angle between the Sun , a star , or a planet , and the horizon is done with the 'star telescope ' fitted to the sextant using a visible horizon. On a vessel at sea even on misty days a sight may be done from a low height above the water to give a more definite, better horizon. Navigators hold the sextant by its handle in the right hand, avoiding touching the arc with the fingers. [ 6 ]
For a Sun sight, a filter is used to overcome the glare such as "shades" covering both index mirror and the horizon mirror designed to prevent eye damage. Initially, with the index bar set to zero and the shades covering both mirrors, the sextant is aimed at the sun until it can be viewed on both mirrors through the telescope, then lowered vertically until the portion of the horizon directly below it is viewed on both mirrors. It is necessary to flip back the horizon mirror shade to be able to see the horizon more clearly on it. Releasing the index bar (either by releasing a clamping screw, or on modern instruments, using the quick-release button), and moving it towards higher values of the scale, eventually the image of the Sun will reappear on the index mirror and can be aligned to about the level of the horizon on the horizon mirror. Then the fine adjustment screw on the end of the index bar is turned until the bottom curve (the lower limb ) of the Sun just touches the horizon. " Swinging " the sextant about the axis of the telescope ensures that the reading is being taken with the instrument held vertically. The angle of the sight is then read from the scale on the arc, making use of the micrometer or vernier scale provided. The exact time of the sight must also be noted simultaneously, and the height of the eye above sea-level recorded. [ 6 ]
An alternative method is to estimate the current altitude (angle) of the Sun from navigation tables, then set the index bar to that angle on the arc, apply suitable shades only to the index mirror, and point the instrument directly at the horizon, sweeping it from side to side until a flash of the Sun's rays are seen in the telescope. Fine adjustments are then made as above. This method is less likely to be successful for sighting stars and planets. [ 6 ]
Star and planet sights are normally taken during nautical twilight at dawn or dusk , while both the heavenly bodies and the sea horizon are visible. There is no need to use shades or to distinguish the lower limb as the body appears as a mere point in the telescope. The Moon can be sighted, but it appears to move very fast, appears to have different sizes at different times, and sometimes only the lower or upper limb can be distinguished due to its phase . [ 6 ]
After a sight is taken, it is reduced to a position by looking at several mathematical procedures. The simplest sight reduction is to draw the equal-altitude circle of the sighted celestial object on a globe. The intersection of that circle with a dead-reckoning track, or another sighting, gives a more precise location.
Sextants can be used very accurately to measure other visible angles, for example between one heavenly body and another and between landmarks ashore. Used horizontally, a sextant can measure the apparent angle between two landmarks such as a lighthouse and a church spire, which can then be used to find the distance off or out to sea (provided the distance between the two landmarks is known). Used vertically, a measurement of the angle between the lantern of a lighthouse of known height and the sea level at its base can also be used for distance off. [ 6 ]
Due to the sensitivity of the instrument it is easy to knock the mirrors out of adjustment. For this reason a sextant should be checked frequently for errors and adjusted accordingly.
There are four errors that can be adjusted by the navigator, and they should be removed in the following order. | https://en.wikipedia.org/wiki/Sextant |
In astronomy , sextants are devices depicting a sixth of a circle, used primarily for measuring the position of stars . There are two types of astronomical sextants, mural instruments and frame-based instruments.
They are of significant historical importance, but have been replaced over time by transit telescopes , other astrometry techniques, and satellites such as Hipparcos .
The first known mural sextant was constructed in Ray, Iran , by Abu-Mahmud al-Khujandi in 994. [ 1 ] To measure the obliquity of the ecliptic , al-Khujandī invented a device that he called al-Fakhri sextant (al-suds al Fakhrī), a reference to his patron, Buwayhid ruler, Fakhr al Dawla (976–997). This instrument was a sixty-degree arc on a wall aligned along a meridian (north–south) line. Al Khujandi's instrument was larger than previous instruments; it had a radius of about twenty meters. [ 2 ] The main improvement incorporated in al-Fakhri sextants over earlier instruments was bringing the precision of reading to seconds while older instruments could only be read in degrees and minutes. This was confirmed by al-Birūni , al-Marrākushī and al-Kāshī . Al-Khujandī used his device to measure the sun's angle above the horizon at the summer and winter solstices ; these two measurements allow computation of the latitude of the sextant's location and the obliquity of the ecliptic. [ 1 ]
Ulugh Beg constructed a Fakhri Sextant that had a radius of 40.4 meters, the largest instrument of its type in the 15th century. Housed in the Ulugh Beg Observatory , the sextant had a finely constructed arc with a staircase on either side to provide access for the assistants who performed the measurements. [ citation needed ]
A sextant based on a large metal frame had an advantage over a mural instrument in that it could be used at any orientation. This allows the measure of angular distances between astronomical bodies. [ citation needed ]
These instruments differ substantially from a navigator's sextant in that the latter is a reflecting instrument. The navigator's sextant uses mirrors to bring the image of the sun, moon or a star to the horizon and measure the altitude of the object. Due to the use of the mirrors, the angle measured is twice the length of the instrument's arc. Hence, the navigator's sextant measures 120° on an arc with an included angle of 60°. By comparison, the astronomical sextants are large and measure angles directly — a 60° arc will measure at most 60°. [ citation needed ]
These large sextants are made primarily of wood, brass or a combination of both materials. The frame is heavy enough to be stiff and provide reliable measures without flexural changes in the instrument compromising the quality of the observation. The frame is mounted on a support structure that holds it in position while in use. In some cases, the position of the sextant can be adjusted to allow measurements to be made with any instrument orientation. Owing to the size and weight of the instrument, attention was paid to balancing it so that it could be moved with ease. [ citation needed ]
Observations were typically made with an alidade , though newer versions could use a telescope . In some cases, a system of counter-weights and pulleys were used to allow the observer to manipulate the instrument in spite of its size.
These instruments were used in much the same way as smaller instruments, with effort possibly scaled due to the size. Some of the instruments might have needed more than one person to operate.
If the sextant is permanently fixed in position, only the position of the alidade or similar index need be determined. In that case, the observer moved the alidade until the object of interest is centered in the sights and then reads the graduations marked on the arc.
For instruments that could be moved, the process was more complex. It was necessary to sight the object with two lines. The edge of the instrument would typically be supplied with sights and the instrument was aligned with one of the two objects of interest. The alidade was then aligned with the second object as well. Once each object was centred in one set of sights, the reading could be taken. This could be a challenge for a moving star observed with a very large instrument as a single person might not be able to confirm both sights with ease; an assistant was a great benefit. The illustration of the Hevelius instrument to the right shows how two persons would use such a sextant: his wife Elisabetha is aligning the instrument while Johannes sets the alidade. | https://en.wikipedia.org/wiki/Sextant_(astronomy) |
In algebra , a sextic (or hexic ) polynomial is a polynomial of degree six.
A sextic equation is a polynomial equation of degree six—that is, an equation whose left hand side is a sextic polynomial and whose right hand side is zero. More precisely, it has the form:
where a ≠ 0 and the coefficients a , b , c , d , e , f , g may be integers , rational numbers , real numbers , complex numbers or, more generally, members of any field .
A sextic function is a function defined by a sextic polynomial. Because they have an even degree, sextic functions appear similar to quartic functions when graphed, except they may possess an additional local maximum and local minimum each. The derivative of a sextic function is a quintic function .
Since a sextic function is defined by a polynomial with even degree, it has the same infinite limit when the argument goes to positive or negative infinity . If the leading coefficient a is positive, then the function increases to positive infinity at both sides and thus the function has a global minimum. Likewise, if a is negative, the sextic function decreases to negative infinity and has a global maximum.
Some sixth degree equations, such as ax 6 + dx 3 + g = 0 , can be solved by factorizing into radicals, but other sextics cannot. Évariste Galois developed techniques for determining whether a given equation could be solved by radicals which gave rise to the field of Galois theory .
It follows from Galois theory that a sextic equation is solvable in terms of radicals if and only if its Galois group is contained either in the group of order 48 which stabilizes a partition of the set of the roots into three subsets of two roots or in the group of order 72 which stabilizes a partition of the set of the roots into two subsets of three roots.
There are formulas to test either case, and, if the equation is solvable, compute the roots in term of radicals. [ 1 ]
Watt's curve , which arose in the context of early work on the steam engine , is a sextic in two variables.
One method of solving the cubic equation involves transforming variables to obtain a sextic equation having terms only of degrees 6, 3, and 0, which can be solved as a quadratic equation in the cube of the variable.
The describer "sextic" comes from the Latin stem for 6 or 6th ("sex-t-"), and the Greek suffix meaning "pertaining to" ("-ic"). The much less common "hexic" uses Greek for both its stem ( hex- 6) and its suffix ( -ik- ). In both cases, the prefix refers to the degree of the function. Often, these type of functions will simply be referred to as "6th degree functions". | https://en.wikipedia.org/wiki/Sextic_equation |
A sextuple bond is a type of covalent bond involving 12 bonding electrons and in which the bond order is 6. The only known molecules with true sextuple bonds are the diatomic dimolybdenum ( Mo 2 ) and ditungsten ( W 2 ), which exist in the gaseous phase and have boiling points of 4,639 °C (8,382 °F) and 5,930 °C (10,710 °F) respectively.
Roos et al argue that no stable element can form bonds of higher order than a sextuple bond, because the latter corresponds to a hybrid of the s orbital and all five d orbitals , and f orbitals contract too close to the nucleus to bond in the lanthanides . [ 1 ] Indeed, quantum mechanical calculations have revealed that the dimolybdenum bond is formed by a combination of two σ bonds , two π bonds and two δ bonds . (Also, the σ and π bonds contribute much more significantly to the sextuple bond than the δ bonds.) [ 2 ]
Although no φ bonding has been reported for transition metal dimers, it is predicted that if any sextuply-bonded actinides were to exist, at least one of the bonds would likely be a φ bond as in quintuply-bonded diuranium and dineptunium . [ 3 ] No sextuple bond has been observed in lanthanides or actinides. [ 1 ]
For the majority of elements, even the possibility of a sextuple bond is foreclosed, because the d electrons ferromagnetically couple , instead of bonding. The only known exceptions are dimolybdenum and ditungsten. [ 1 ]
The formal bond order (FBO) of a molecule is half the number of bonding electrons surplus to antibonding electrons; for a typical molecule, it attains exclusively integer values. A full quantum treatment requires a more nuanced picture, in which electrons may exist in a superposition, contributing fractionally to both bonding and antibonding orbitals. In a formal sextuple bond, there would be P = 6 different electron pairs; an effective sextuple bond would then have all six contributing almost entirely to bonding orbitals.
In Roos et al 's calculations, the effective bond order (EBO) could be determined by the formula E B O = ( 1 2 ) ∑ p = 1 P ( η b , p − η a b , p ) − c {\displaystyle EBO=\left({\frac {1}{2}}\right)\sum _{p=1}^{P}(\eta _{b,p}-\eta _{ab,p})-c} where η b is the proportion of formal bonding orbital occupation for an electron pair p , η ab is the proportion of the formal antibonding orbital occupation, and c is a correction factor accounting for deviations from equilibrium geometry. [ 1 ] Several metal -metal bonds' EBOs are given in the table at right, compared to their formal bond orders.
Dimolybdenum and ditungsten are the only molecules with effective bond orders above 5, with a quintuple bond and a partially formed sixth covalent bond . Dichromium , while formally described as having a sextuple bond, is best described as a pair of chromium atoms with all electron spins exchange-coupled to each other. [ 5 ]
While diuranium is also formally described as having a sextuple bond, relativistic quantum mechanical calculations have determined it to be a quadruple bond with four electrons ferromagnetically coupled to each other rather than in two formal bonds. [ 4 ] Previous calculations on diuranium did not treat the electronic molecular Hamiltonian relativistically and produced higher bond orders of 4.2 with two ferromagnetically coupled electrons. [ 6 ]
Laser evaporation of a molybdenum sheet at low temperatures (7 K ) produces gaseous dimolybdenum (Mo 2 ). The resulting molecules can then be imaged with, for instance, near-infrared spectroscopy or UV spectroscopy . [ 7 ]
Both ditungsten and dimolybdenum have very short bond lengths compared to neighboring metal dimers. [ 1 ] For example, sextuply-bonded dimolybdenum has an equilibrium bond length of 1.93 Å. This equilibrium internuclear distance is significantly lower than in the dimer of any neighboring 4d transition metal , and suggestive of higher bond orders. [ 8 ] [ 9 ] [ 10 ] However, the bond dissociation energies of ditungsten and dimolybdenum are rather low, because the short internuclear distance introduces geometric strain. [ 1 ] [ 11 ]
One empirical technique to determine bond order is spectroscopic examination of bond force constants . Linus Pauling investigated the relationships between bonding atoms [ 12 ] and developed a formula that predicts that bond order is roughly [ 13 ] proportional to the force constant; that is, k e = n ⋅ k e ( 1 ) {\displaystyle k_{e}=n\cdot k_{e}^{(1)}} where n is the bond order, k e is the force constant of the interatomic interaction and k e (1) is the force constant of a single bond between the atoms. [ 14 ]
The table at right shows some select force constants for metal-metal dimers compared to their EBOs; consistent with a sextuple bond, molybdenum's summed force constant is substantially more than quintuple the single-bond force constant.
Like dichromium, dimolybdenum and ditungsten are expected to exhibit a 1 Σ g + singlet ground state . [ 15 ] [ 16 ] However, in tungsten, this ground state arises from a hybrid of either two 5 D 0 ground states or two 7 S 3 excited states. Only the latter corresponds to the formation of a stable, sextuply-bonded ditungsten dimer . [ 8 ]
Although sextuple bonding in homodimers is rare, it remains a possibility in larger molecules.
Theoretical computations suggest that bent dimetallocenes have a higher bond order than their linear counterparts. [ 17 ] For this reason, the Schaefer lab has investigated dimetallocenes for natural sextuple bonds. However, such compounds tend to exhibit Jahn–Teller distortion , rather than a true sextuple bond.
For example, dirhenocene is bent. Calculating its frontier molecular orbitals suggests the existence of relatively stable singlet and triplet states, with a sextuple bond in the singlet state. But that state is the excited one ; the triplet ground state should exhibit a formal quintuple bond. [ 17 ] Similarly, for the dibenzene complexes Cr 2 (C 6 H 6 ) 2 , Mo 2 (C 6 H 6 ) 2 , and W 2 (C 6 H 6 ) 2 , molecular bonding orbitals for the triplet states with symmetries D 6h and D 6d indicate the possibility of an intermetallic sextuple bond. Quantum chemistry calculations reveal, however, that the corresponding D 2h singlet geometry is stabler than the D 6h triplet state by 3–39 kcal/mol , depending on the central metal. [ 18 ]
Both quantum mechanical calculations and photoelectron spectroscopy of the tungsten oxide clusters W 2 O n (n = 1–6) indicate that increased oxidation state reduces the bond order in ditungsten. At first, the weak δ bonds break to yield a quadruply-bonded W 2 O; further oxidation generates the ditungsten complex W 2 O 6 with two bridging oxo ligands and no direct W–W bonds. [ 19 ] | https://en.wikipedia.org/wiki/Sextuple_bond |
Sexual antagonistic co-evolution is the relationship between males and females where sexual morphology changes over time to counteract the opposite's sex traits to achieve the maximum reproductive success . This has been compared to an arms race between sexes. In many cases, male mating behavior is detrimental to the female's fitness . [ 1 ] For example, when insects reproduce by means of traumatic insemination , it is very disadvantageous to the female's health. During mating, males will try to inseminate as many females as possible, however, the more times a female's abdomen is punctured, the less likely she is to survive. [ 2 ] Females that possess traits to avoid multiple matings will be more likely to survive, resulting in a change in morphology . In males, genitalia is relatively simple and more likely to vary among generations compared to female genitalia . This results in a new trait that females have to avoid in order to survive.
Additionally, sexual antagonistic co-evolution can be the cause of rapid evolution, as is thought to be the case in seminal proteins known as Acps in species of Drosophila melanogaster . While Acps facilitate the mutually beneficial outcome of increased progeny production, several Acps have detrimental effects on female fitness as they are toxic and shorten her lifespan. This leads to antagonistic co-evolution, as the female must evolve in order to defend herself. When female Drosophila melanogaster are experimentally prevented from co-evolving with males, males rapidly adapt to the static female phenotype . [ 3 ] This male adaptation leads to a reduction in female survivorship, which is mediated by an increased rate of remating and increased toxicity of Acps in seminal fluid. Since non-reproductive proteins do not feel the same evolutionary pressure as Acps, they are not evolving nearly as quickly. Consistent with the arms race theory, DNA analyses reveal a two-fold increase in Acp divergence relative to non-reproductive proteins. [ 4 ] [ 5 ] [ 6 ]
For many females, reproduction can be very dangerous and disadvantageous as in the case of bed bugs mentioned previously. Therefore, females who possess traits where they can lessen the impacts of male behavior are the ones who will survive and go on to reproduce. There are many ways a female can "defend" herself to the onslaught of potential mates. [ citation needed ]
Females have a very complex and an extremely variable reproductive system , commonly known as a spermatheca . Some species do not have a spermatheca in the traditional sense, but do possess pseudospermatheca . Both forms play an essential role in sperm storage and fertilization . In the family Tingidae , pseudospermatheca are located at the base of the oviduct and are hypothesized to have functioned as spermatheca at one point in time. [ 7 ] They now serve as storage units for sperm , where a female can introduce the stored sperm to her eggs when she finds it optimal. It is this factor that has put females in the driver seat of evolution. These organs give females the ability to pick and choose which sperm they will use to fertilize their eggs. Males now have another factor they need to overcome. In the case of D. melanogaster , females will mate multiple times and then expel the excess sperm that she does not need. However, neither the first nor the second mate know if it is his sperm that was dispelled, because at any postcopulatory moment a female can store the sperm of more than one male. [ 8 ]
Enzymes secreted by female reproductive tracts may also play a role in sexual antagonistic coevolution with males. In Drosophila species, a large group of enzymes known as serine proteases have been associated with female sperm storage organs (most notably, the spermatheca) through genetic sequencing and analysis. It is hypothesized that these proteases break down various proteins in male seminal fluid . [ 9 ] This would result in females choosing for males that can overcome these digestive enzymes , whether through genetic variation or physiological ability to produce greater quality or quantity of sperm. [ citation needed ]
Before a male even has to begin worrying if the female will use his sperm or not, he must mate with her, which can be a problem within itself. Potential mates often play a game of persistence and resistance. In the case of water striders (genus Gerris ) males will harass females and try to grasp them by chasing and lunging at them. Females can be extremely evasive and often fend off these aggressive attacks. Even when a female is finally grasped she continues to struggle. However, this type of avoidance is very costly to a female, so she ends up having to balance the cost of mating and the cost of resistance. [ 10 ] However, in species with singly mating females like the fly Prochyliza xanthostoma , the cost of resisting mating is low relative to the benefit of evading a low quality male. [ 11 ]
Like females, males have developed responses to counter evolutionary adaptations of the opposite sex. Responses in insects can vary in both genitalia and sperm structures, along with variations in behavior. [ citation needed ]
Male genitalia evolve more rapidly and divergently in animals. Spiny genitalia can aid in male-male competition. In seed beetles , spiny genitalia help with anchor during copulation and allow a rapid passage to the female's reproductive tract, thus overcoming female barriers to sperm. Females suffer costs as a result of injuries, but males do not benefit directly from harm inflicted on their mates. Damage, such as scarring , increases in the female tract with the number of matings. In seed beetles, a positive correlation exists between the degree of harmfulness of the male's genitalia and the thickness or reinforcement of the wall of the bursa copulatrix in the female's reproductive tract. As a result, females’ connective tissue in the copulatory tract increased in thickness. [ 12 ] However, females with a thicker copulatory tract correlated positively to the amount of scarring, suggesting that scarring is a poor measure of costs for females. Females have evolved in other ways such as investing in immunocapacity to help with trauma associated during copulation. [ citation needed ]
Male bed bugs have a unique way to copulate called traumatic insemination. Males use their intromittent organ to stab and inseminate females through their abdominal wall even though females contain a genital tract. Male bed bugs can also adjust their ejaculate volume and time of copulation through the presence of ejaculates in females to conserve sperm and determine paternity outcomes. [ 2 ] Females have evolved a paragenital system to counter traumatic inseminations. The paragenital system contains a mesospermalege where sperm is deposited. The sperm migrates through the blood to the sperm storage site and oviducts, and then to the ovaries to fertilize eggs. Female bed bugs have also evolved physiological by the presence of phagocytic cells in the mesospermalege that ingest sperm after mating. [ citation needed ]
Selection on development time is often sexually antagonistic. In seed beetles, populations differed in development time and growth rate between sexes. Population fitness is not significant to either body size or growth rate, but variation in development time was significantly related to population fitness. [ 13 ] In females, genes associated with long development time lead to high fecundity and mate immediately upon eclosion . Males have shorter development time and emerge early ( protandry ) resulting in greater fertilization opportunities. [ citation needed ]
Competition between differing male phenotypes also exists at the microscale level. It has been found in Drosophila that there is a positive correlation between the length of male sperm tails and the size of the seminal receptacle found in females. [ 14 ] It has been found that females with larger seminal receptacles “choose” sperm with long tails over sperm with short tails. Although females seem to “favor” this trait, no reproductive advantage for long tails has been found except for better correspondence to females with large seminal receptacles. This discrimination is reminiscent of the Fisherian runaway model, as females may choose for long tails based solely on inherited desirability, and would want to pass on that trait, which would improve the sexual success of their male progeny. This also could be an example of the “good genes” model of sexual selection , as correlations have been found between sperm tail length and the physiological condition of the male. [ citation needed ]
In the case of the Neriid fly, Derocephalus angusticollis , males have been observed to have coevolved to have a flexible aedeagus . In this species females have coiled oviducts that lead to the spermatheca that in turn make it hard for males to reach the area needed to release their sperm. Once copulation is initiated the males are able to unfold their aedeagus and use its flexibility to maneuver the coiled oviducts. [ 15 ] | https://en.wikipedia.org/wiki/Sexual_antagonistic_coevolution |
Sexual coercion among animals is the use of violence, threats, harassment, and other tactics to help them forcefully copulate . [ 1 ] Such behavior has been compared to sexual assault , including rape , among humans. [ 2 ]
In nature, males and females usually differ in reproductive fitness optima. [ 3 ] Males generally prefer to maximize their number of offspring, and therefore their number of mates; females, on the other hand, tend to care more for their offspring and have fewer mates. [ 4 ] Because of this, there are generally more males available to mate at a given time, making females a limited resource. [ 4 ] [ 5 ] This leads males to evolve aggressive mating behaviors which can help them acquire mates. [ 5 ]
Sexual coercion has been observed in many clades , including mammals, birds, insects, and fish. [ 6 ] While sexual coercion does help increase male fitness , it is very often costly to females. [ 5 ] Sexual coercion has been observed to have consequences, such as intersexual coevolution, speciation, and sexual dimorphism . [ 4 ] [ 7 ]
Harassment is a technique used by males of many species to force females to submit to mating. [ 8 ] It has been observed in numerous species, including mammals, birds, insects and fish. [ 6 ] Aggression and harassment have been documented in the males of guppies ( Poecilia reticulata ), [ 4 ] bottlenose dolphins ( Tursiops aduncus ), botos ( Inia geoffrensis ), dusky dolphins ( Lagenorhynchus obscurus ), Hector's dolphins ( Cephalorhynchus hectori ), grizzly bears , polar bears , and ungulates . [ 9 ] It is also seen in Chinook salmon ( Oncorhynchus tshawytscha ), [ 6 ] red-spotted newts ( Notophthalmus viridescens ), and seed-eating true bugs ( Neacoryphus spp.). [ 10 ] Furthermore, it is prevalent in spider monkeys , [ 1 ] wild Barbary macaques ( Macaca sylvanus ) and many other primates. [ 11 ]
In basically all major primate taxa, aggression is used by the dominant males when herding females and keeping them away from other males. [ 1 ] In hamadryas baboons , the males often bite the females' necks and threaten them. [ 12 ] Wild chimpanzees can charge at females, shake branches, hit, slap, kick, pound, drag, and bite them. Orangutans are among the most forceful of mammals. Bornean orangutans ( Pongo pygmaeus ) exhibited aggression in almost 90 percent of their copulations, including when the females were not resisting. [ 13 ] A possible explanation for aggressive behaviors in primates is that it is a way for males to train females to be afraid of them and be more likely to surrender to future sexual advances. [ 1 ]
Males may also use more indirect techniques to mate with females, such as intimidation . While most female water striders ( Gerridae ) have their genitalia exposed, females of the water strider species Gerris gracilicornis have evolved a shield over their genitals. As a result, males cannot physically coerce females because mating is difficult unless the female exposes her genitalia. Therefore, males intimidate females into mating by attracting predators; they tap on the water's surface and create ripples that catch the attention of predatory fish. From there, it is in the best interest of the female to mate, and as quickly as possible, to avoid being eaten by predators. Typical mating positions of water striders have the females on the bottom, closer to predators, so the risk of predation is much higher for them. Females succumb to copulation to get males to cease signaling to predators. [ 14 ] [ 15 ]
Another indirect form of sexual coercion occurs in red-sided garter snakes, Thamnophis sirtalis parietalis . When males "court" females, they line their bodies up to the females' and produce caudocephalic waves, which are a series of muscle contractions that travel through their bodies from tail to head. The exact reason for this behavior is unknown, but some studies show that it relates to stress. Females have nonrespiratory air sacs containing anoxic air, and the waving pushes this air into her lungs. The resulting stress causes her cloaca to open, and aids the male in inserting his hemipenis . The stronger and more frequent the caudocephalic waves and the closer the male's cloaca to the female's, the more likely the male is to mate successfully. [ 16 ]
Males of certain species have evolved mating behaviors in which they forcefully attempt to mate with and inseminate females, often employing grasping techniques. These male grasping devices exist to increase the duration of copulation and restrict females from mating with other males. They are in some ways a form of mate guarding . While some males have evolved different types of modifications to aid in grasping, others just grab females and attempt to force copulation.
One type of grasping modification is spiky male genitalia . In seed beetles (Coleoptera: Bruchidae), males possess sclerotized spines on their genitalia. These spines are used during copulation to help overcome female resistance and penetrate into their copulatory duct. In addition to aiding penetration, these spines promote the passage of seminal fluids, and act as an anchor to keep the female from fleeing. Furthermore, spiny genitals can injure the females and make them less likely to remate. [ 7 ] Sepsidae fly males have modifications on their forelegs to help them grasp onto female wing bases. These modifications include cuticular outgrowths, indentations, and bristles, and males use them to secure themselves onto females after jumping on them. Once the males grab on, a struggle ensues akin to a rodeo , where males try to hold on while females violently shake them off. [ 17 ]
Another type of modification is found in male diving beetles (of the family Dytiscidae ), who are equipped with suction cup structures on their front legs. They use these to grab passing females and attach to their dorsal surfaces. To get the females to submit, males shake the females violently and keep them submerged underwater (diving beetles cannot go long without atmospheric oxygen). Unable to get air, female diving beetles submit to the male's advances in order to avoid drowning (and they lose the energy to resist). Once the males attach, copulation can occur. [ 18 ]
Male waterfowl have developed another modification; while most male birds have no external genitalia, male waterfowl (Aves: Anatidae ) have a phallus (length 1.5–4.0 centimetres [0.59–1.57 in]). Most birds mate with the males balancing on top of the females and touching cloacas in a “cloacal kiss”; this makes forceful insemination very difficult. The phallus that male waterfowl have evolved everts out of their bodies (in a clockwise coil) and aids in inseminating females without their cooperation. [ 19 ]
Another such technique is having a "lock-like" mechanism, found in Drosophila montana , dogs, wolves, and pigs. Towards the end of copulation, females struggle to try to dislodge the males, whose genital organs take much longer to deflate than females do; the locking (most commonly known in canids as a "tie") allows the males to copulate for as long as they need to until they are finished. In dogs, the male has a knot in his penis that gets engorged with blood and ties the female, locking them together during copulation, until the act is complete. Male dogs have evolved this mechanism during mating in order to prevent other males from penetration whilst they are and the use of the tie enables them to be more likely to inseminate the female and produce a healthy litter of pups. Breaking this "tie" can be physically harmful to both females and males. [ 20 ]
Males of many species simply grab the females and force a mating. Coercive mating is very common in water striders ( Gerridae ) because in most of the species, the female genitalia are often exposed and easily accessible to males. [ 3 ] Without any courtship behavior, males initiate by forcefully trying to mount the females. Carrying the males on their backs is energetically costly to females, so they try to resist and throw off the males. The males fight back even harder and use their forelegs to tightly grasp the female's thorax and keep them from escaping. [ 21 ] The males then forcefully insert their genitalia into the female vulvar opening. [ 3 ] In the newt species Notophthalmus viridescens , males carry out a courtship behavior called amplexus . It consists of males capturing females that do not want to mate with them and using their hind limbs to grasp the females by their pectoral regions. [ 5 ]
Male guppies ( Poecilia reticulata ) have been observed to forcefully copulate with females by trying to insert their gonopodium (male sex organ) into female's genital pores, whether or not they are accepting. [ 6 ] Sometimes, male guppies also try to forcefully mate with Skiffia bilineata (goodeid) females, which resemble guppy females and tend to share the same habitat, even when guppy females are available. A possible explanation for this is the deeper genital cavity of S. bilineata , which stimulates the males more than when mating with guppy females. [ 10 ]
Males of some species are able to immobilize females and force copulation. In pigs and boars, males grab females and maneuver the pelvis to lift the vaginal opening and facilitate copulation. The stimulation following intromission causes the female to be immobilized. The male can then freely continue copulation without worrying about the female escaping. [ 22 ] Immobilization of the female also occurs in muscovy ducks .
Grasping and/or grappling mating situations have also been documented in Calopteryx haemorrhoidalis haemorrhoidalis ( Odonata ), [ 23 ] fallow deer ( Dama dama ), [ 6 ] wild orangutans (Smuts 1993), wild chimpanzees, [ 1 ] water voles (semi-aquatic rats) Arvicola amphibius , [ 22 ] feral fowl, [ 24 ] mallard ( Anas platyrhynchos ), [ 25 ] hamadryas baboons [ 26 ] and many other primates, [ 1 ] coho salmon ( Oncorhynchus kisutch ), [ 6 ] and others.
In some mammal species, it is common for males to commit infanticide to mate with females. This happens often in species that live in groups, such as Old and New World monkeys, apes, prosimians, and hamadryas baboons. [ 26 ] There is usually a single breeding male in a group, and when an outside male aggressively takes over, he kills off all of the young offspring. The males kill infants that are not their own to assert their strength and position, and mate with the females. [ 1 ] Killing infants may also bring breastfeeding females out of lactational amenorrhea and back into fecundity, improving the male’s chance of fertilising the female if he returns to mate with her again soon.
Sometimes, multiple males will invade a troop and gang up on females, killing their offspring and subsequently mating with them. This occurs in spider monkeys , red-backed squirrel monkeys , chimpanzees, and red howlers . [ 1 ]
In the newt species Notophthalmus viridescens , the males rub off hormonal secretions onto the skin of the females they are courting. These hormones have been shown to make the female more receptive to mating with the male. When the male deposits the secretions, he detaches from the female and releases a spermatophore (containing spermatozoa). It is then the female's decision to either accept it and pick it up or reject it by running away; these hormones make her more likely to accept it. [ 5 ]
Another form of coercion is male mate guarding, used to keep females from mating with other males, and often involves aggression. [ 8 ] Guarding allows the males to ensure their paternity. A classic example occurs in diving beetles, family Dytiscidae. After copulation, males continue to guard females for up to six hours. They hold them underwater, occasionally tilting them up for air. [ 18 ] Guarding also occurs in water striders where, once males complete their sperm transfer, they often remain on top of the females. This guarding duration varies, lasting from several minutes to several weeks. The purpose of such long guarding periods is for the males to see the females lay their eggs and be assured that the offspring are theirs. [ 21 ] This behavior also occurs in hamadryas baboons ( Papio hamadryas ), where the leader males practice intensive mate guarding. [ 26 ] In Drosophila montana , studies have shown that following mate guarding, the chances of a female mating with or being inseminated by another male were greatly diminished. This shows that the mate guarding tactic can be very effective. [ 20 ]
Males of some species use bodily fluids, such as seminal fluid from their ejaculate, to aid in the coercion of females. Seminal fluid in males of Drosophila melanogaster may contain chemicals that increase the amount of time it takes for females to remate, decrease the length of successive matings, or keep her from remating at all. The less a female mates with other males after copulation with a male, the more likely it is for him to ensure his paternity. These chemicals may also serve to increase the female's reproductive success, but at the cost of decreased longevity and immune response. [ 20 ]
In many species, seminal fluid can be used as a sort of mating plug . Males of these species transfer their sperm at the beginning of copulation and use the rest of copulation to transfer substances that help build up the mating plugs. These plugs are effective in ensuring that the female does not mate with any other males and that the male's paternity is secured. [ 20 ]
A major direct cost of sexual coercion is physical injury. [ 6 ] Male seed beetles (Coleoptera: Bruchidae) have sclerotized spines on their genitalia, which penetrate the female and leave melanized scars. Females can be physically injured from just one mating, and the more a female mates, the more scarring forms in the copulatory duct. [ 7 ] In guppies, the male's gonopodium can cause damage when forcefully inserted, causing cloacal damage to the females. [ 10 ] In fowl, females can be physically injured during forceful copulations. Also, semen transferred from the males can contain pathogens and fecal matter, which can lead to disease and decrease female fitness. [ 24 ] In elephant seals, physical injury happens very often. In fact, mating leads to 1 in every 1,000 female elephant seals getting killed. [ 22 ] Other species in which the females (and/or their offspring) are injured or even killed include lions , rodents , farm cats , crabeater seals , grey seals , [ 27 ] sea lions , [ 1 ] bottle-nosed dolphins ( Tursiops truncatus ), [ 9 ] red-sided garter snakes ( Thamnophis sirtalis parietalis ), [ 16 ] and newts ( N. viridescens ). [ 5 ]
Another cost is the excess energy and time expenditure that comes with mating. For example, female water striders, Gerridae, [ 21 ] and marine snails of the genus Littorina have to carry the males on their backs while they mate. First of all, this is a great loss of energy. [ 21 ] Second, both the male and the female are at a much greater risk of predation in this position. [ 6 ] Furthermore, the time spent mating interferes with the time that could have been spent foraging [ 6 ] and feeding. [ 28 ]
In addition, sexual coercion can lower body condition and immunity in ways other than physical damage. Harassment can lead to stress, which can result in weight loss, decreased immune function and energy stores, and less feeding, which has been seen in red-spotted newts. [ 5 ] Furthermore, when females are constantly moving around to avoid violent males, they are not able to form female social ties (for example, Grévy's zebra /Equus grevyi). [ 28 ] This also happens in species where herding males sometimes do not permit females to join their family in different groups, like in hamadryad baboons. [ 1 ]
Indirect costs are those that affect females in the future. One such cost happens because sexual coercion does not allow females to choose the males they want to mate with, which are usually males that are higher quality, compatible, and/or have good genes that will increase their offspring's survival and fitness. Coercion decreases this choice and can lead to their offspring having lower genetic quality. Studies of the rose bitterling (Rhodeus ocellatus), have shown that offspring of females with mate choice had higher survival rates than offspring of females that did not. [ 6 ] Another ultimate cost comes from when males commit infanticide to obtain mating access. This loss of offspring leads to a decrease in fitness of females. [ 1 ]
As a response to sexual coercion and the costs that females face, one of their counter-adaptations is the evolution of anatomical protection. [ 3 ] Females of some species, such as the water striders , developed morphological shields to protect their genitalia from males that want to forcefully copulate. [ 14 ] Some Gerridae females have also evolved abdominal spines and altered the shapes of their abdomens to make them less accessible to males. [ 3 ]
Waterfowl males of the family Aves: Anatidae have evolved a phallus to aid in coercion. This phallus everts out of the male body (when it's time to mate) in a counter-clockwise coil. As a response, females have developed vaginal structures called dead end sacs and clockwise coils to protect themselves from forceful intromission. [ 19 ] Waterfowl females have evolved these “convoluted vaginal morphologies” to make it harder for males to insert themselves without the female's consent. [ 29 ]
Another female tactic to counter coercion is to try to avoid males that may cause them harm. To do this, females often change their habitats to get away from aggressive males, as is seen in wild Trinidadian guppies ( Poecilia reticulata ). [ 9 ] Female bottlenose dolphins behave in similar ways by moving into shallow waters where there are not too many males. [ 9 ] Other species that practice mate avoidance are Calopteryx haemorrhoidalis , a species of damselfly, who often try to hide from large groups of males to avoid harassment. [ 23 ]
Females of the marine intertidal periwinkle species (genus Littorina ) have another way to avoid males. Males usually recognize female snails by cues in their mucous trails. However, females try to mask their sex by altering these cues. [ 30 ] In damselflies, females also try to mask their gender by mimicking male colors, which make them less attractive to males. [ 30 ]
An effective female strategy is the employment of protection and alliances. Some females, such as wild Trinidadian guppies (Poecilia reticulate) associate themselves with protective males who come to their rescue. [ 31 ] This also occurs in hamadryas, savanna, and olive baboons, where males and females form friendships where the female gets male protection. [ 26 ] In northern elephant seals , the females give loud cries when mounted by undesirable or subordinate males, which attract dominant males to help. A similar phenomenon occurs in elephants, bighorn sheep , and fallow deer, where the females stay close to dominant males for protection. [ 1 ]
Females can also form alliances with other females for protection against aggressive males. [ 1 ] Researchers have observed such alliances in many other female-bonded species, including other Old World monkeys such as macaques , olive baboons , patas and rhesus monkeys, and gray langurs ; New World monkeys such as the capuchin; and prosimians such as the ring-tailed lemur . In African vervet monkeys, related females often form groups and “gang up” on males. [ 32 ] Females of high rank create networks of female alliances; together, they fight away persistent suitors. [ 1 ]
Resisting males and fighting back are important tactics some species use to counter male coercion. Many females try to vigorously shake off males to dislodge them and flee; this is seen in female sepsid flies [ 17 ] and diving beetles. [ 18 ] Sepsids also try to bend their abdomen in such a way that males cannot copulate forcefully. [ 17 ] Females are especially likely to fight back when they are protecting their offspring. This is seen in mountain gorillas, red howlers, and grey langur females, where males are often infanticidal. [ 1 ]
Female resistance has rarely been found to be effective. Male mammals and birds are usually larger than females, and the sheer size and strength difference makes this very difficult. [ 1 ] However, it has been observed in some species, such as squirrel monkeys, patas monkeys, vervets, and captive chimpanzees, that females can “gang up” on males when they are being aggressive. They will even try to protect a female in distress. Females have even been observed to kill immigrant males in wild red colobus monkeys. [ 1 ]
Sometimes, females choose not to struggle and simply acquiesce to forceful matings. This can happen when they decide that the cost of resisting would be greater than the cost of mating. [ 23 ] They use submission to avoid further harassment or aggression, which could end in death or injury. [ 28 ] This is often seen in primate species, such as chimpanzees and hamadryas baboons. [ 1 ]
Some possible benefits of sexual coercion for the species have been hypothesized.
A possible proximate benefit for females is that sometimes after a male mates with a female, he becomes her mate. Then, he would defend and protect her. [ 23 ] This is seen in many primate species. [ 1 ]
A possible benefit of sexual coercion that would come out in the long run is the “good genes” hypothesis. [ 18 ] If males can overcome a female's resistance, then they must possess good genes that would increase the survival or mating success of male offspring. The hypothesis is that females can use the sexual coercion process to assess the quality of a male. [ 3 ]
Sexual coercion often leads to an intersexual coevolutionary arms race. This consists of females evolving adaptations to male advances and males evolving counter-adaptations as a response. [ 4 ] Males persist in violent behavior, which favors the evolution of female resistance to defend themselves. [ 3 ] [ 7 ] In organisms where males have genitalia harmful to females, such as in certain insects, females tend to evolve thicker, less sensitive copulatory tracts. [ 7 ] Also, they may evolve a shield over their genital openings to prevent intromission. [ 14 ] Females of some species of water striders have evolved protection from forceful insemination, such as abdominal spines and downward-bent abdomens to make it harder for males to mate. In response, however, males have counter evolved, also changing the shape of their abdomens to those that would facilitate forceful mating. [ 3 ]
The male waterfowl (Aves: Anatidae) evolution of a phallus to forcefully copulate with females has led to counteradaptations in females in the form of vaginal structures called dead end sacs and clockwise coils. These structures make it harder for males to achieve intromission. The clockwise coils are significant because the male phallus everts out of their body in a counter-clockwise spiral; therefore, a clockwise vaginal structure would impede forceful copulation. Studies have shown that, the longer a male's phallus, the more elaborate the corresponding vaginal structures. [ 19 ]
Speciation has been observed to be a possible consequence of sexual coercion. In diving beetle species family Dytiscidae , an intersexual arms race occurs between males and females. Males have evolved suction cup structures on their forelegs to help grasp females; females have counter-evolved setose dorsal furrows to impede forceful copulation. This continuous evolution (in both the forward and reverse directions) has led to the recent speciation of A. japonicus and A. kishii , where females of A. kishii have lost their dorsal furrows while those of A. japonicus have not. [ 18 ]
Sexual coercion can lead to sexual dimorphisms, in which males and females have significant morphological differences. For example, in some species, larger males are more successful in forcefully mating/insemination, leading to a higher fitness. [ 4 ] In red-sided garter snakes , Thamnophis sirtalis parietalis , it has been shown that heavier-bodied males were better courters and their size gave them an advantage over smaller bodied snakes. [ 16 ] This helps lead to an evolution of sexual dimorphism, with males larger than females. [ 4 ] In other species, males that are smaller than females have higher fitness. As such, many sex-specific morphological adaptations (for example, in Dytiscidae diving beetles, females have setose dorsal furrows that males do not and males have suction cups on their forelegs that females do not [ 18 ] ) are sexual dimorphisms caused by sexual coercion. | https://en.wikipedia.org/wiki/Sexual_coercion_among_animals |
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Sexual communication is a conversation between partners about sex, which is necessary to obtain sexual consent, to learn about likes and dislikes, and to obtain sexual satisfaction. [ 1 ]
Sexual communication is a transitional stage from the romantic period of a relationship to a closer intimate and sexual relationship between partners.
Sexual communication in different countries is based on the partners' chosen religion and marriage customs, so it can start at different stages of the partners' relationship. Sexual communication is not primary in the relationship of partners, and in harmonious relationships it occurs after the spiritual perception of the partner. [ 2 ]
Sexual communication occurs in various forms:
According to research conducted by scientists, sexual communication is important for maintaining healthy sexual function. Studies of different years, starting from the 1970s. show that couples with more sexual difficulties have problems with sexual communication and sexual expression. Research conducted in 2014 shows that that couples who have more sexual difficulties have problems with sexual communication and sexual expression. Research conducted in 2014 shows that sexual self-disclosure is important for the health of sexual function and sexual satisfaction, which is one of the prevention methods for sexual dysfunction. Sexual self-disclosure involves discussing sexual preferences with partners, the desire to participate in a certain sexual activity, about sexual values and past experiences. [ 5 ]
Sexual communication is widespread in biology, and occurs in many organisms, e.g. bacteria , fungi , protozoa , insects , vertebrates and flowering plants . [ 6 ] Sexual communication, in general, refers to the use of signals to promote or modulate sexual interaction, and appears to operate at three different levels. [ 6 ] (a) At the primary level sexual communication increases the likelihood of sexual interaction between two individuals leading to the production of progeny. (b) At the secondary level, signaling is modulated to avoid inbreeding and to facilitate outbreeding, presumably because outbreeding promotes hybrid vigor and the avoidance of expression of deleterious alleles in progeny ( inbreeding depression ). (c) Sexual communication is also used to facilitate selection among potential mates based on fitness characteristics in order to facilitate vigor among progeny. [ 6 ] | https://en.wikipedia.org/wiki/Sexual_communication |
Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction , particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females . [ 1 ] [ 2 ] In one example, males may benefit from multiple matings, while multiple matings may harm or endanger females due to the anatomical differences of that species. [ 3 ] Sexual conflict underlies the evolutionary distinction between male and female. [ 4 ]
The development of an evolutionary arms race can also be seen in the chase-away sexual selection model , [ 5 ] which places inter-sexual conflicts in the context of secondary sexual characteristic evolution, sensory exploitation, and female resistance. [ 1 ] According to chase-away selection, continuous sexual conflict creates an environment in which mating frequency and male secondary sexual trait development are somewhat in step with the female's degree of resistance. [ 1 ] It has primarily been studied in animals , though it can in principle apply to any sexually reproducing organism, such as plants and fungi . There is some evidence for sexual conflict in plants. [ 6 ]
Sexual conflict takes two major forms:
Sexual conflict may lead to antagonistic co-evolution , in which one sex (usually male) evolves a favorable trait that is offset by a countering trait in the other sex. Similarly, interlocus sexual conflict can be the result of what is called a perpetual cycle. The perpetual cycle begins with the traits that favor male reproductive competition, which eventually manifests into male persistence. These favorable traits will cause a reduction in the fitness of females due to their persistence. Following this event, females may develop a counter-adaptation, that is, a favorable trait that reduces the direct costs implemented by males. This is known as female resistance. After this event, females' fitness depression decreases, and the cycle starts again. [ 5 ] Interlocus sexual conflict reflects interactions among mates to achieve their optimal fitness strategies and can be explained through evolutionary concepts.
Sensory exploitation by males is one mechanism that involves males attempting to overcome female reluctance. It can result in chase-away selection, which then leads to a co-evolutionary arms race. There are also other mechanisms involved in sexual conflict such as traumatic insemination , forced copulation , penis fencing , love darts and others.
Female resistance traditionally includes reducing negative effects to mechanisms implemented by males, but outside the norm may include sexual cannibalism , increased fitness in females on offspring and increased aggression to males.
Some regard sexual conflict as a subset of sexual selection (which was traditionally regarded as mutualistic [ citation needed ] ), while others suggest it is a separate evolutionary phenomenon. [ 10 ]
The differences between male and female general evolutionary interests can be better understood through the analysis of the various factors that affect sexual conflict. In situations involving a male and female, only the relative positions of the optimal trait values are important as it is their comparative positions that provide insight into the resulting conflict. The trait value bar at the bottom of the accompanying figure indicates the relative intensity of each trait. The left side represents the poorly developed end of intensity range, while the right side represents the strongly developed end of the range.
Males and females differ in the following general components of fitness, thus leading to sexual conflict. Refer to the accompanying figure in this section.
Mating rate: Males generally increase their fitness by mating with multiple mates, while females are on the middle section of the range because they do not favor a particular side of the spectrum. For instance, females tend to be the choosier sex, but the presence of female sexual promiscuity in Soay sheep show that females might not have an established mating preference. [ 11 ] However, Soay sheep are a breed of domestic sheep, ergo might not be a subject to traditional evolutionary mechanisms due to human interference.
Female stimulation threshold: Generally, females benefit from being more selective than males would like them to be. For example, the Neotropical spider, Paratrechalea ornata , displays nuptial gift -giving behaviors during courtship as a part of their male mating efforts. These nuptials gifts allow the male to control copulation duration and to increase the speed of female oviposition. [ 12 ]
Degree of female fidelity: Because female fidelity depends on the species' particular mating system, therefore they are in the middle section of the spectrum. However, males seeking mates have different preferences depending on whether they are unpaired or paired. Paired males benefit from high female fidelity, while unpaired males benefit from low female fidelity in order to increase their mating frequencies.
Toxicity of seminal fluid: Females benefit from low seminal fluid toxicity, while males benefit from a high toxicity level as it increases their competitive edge. [ vague ] [ 8 ]
Female fecundity: Males benefit from a high female fecundity as it means that females can produce more offspring and have a higher potential for reproduction. It is important to note that females also benefit from high fecundity, and thus this trait is probably more affected by classical natural selection.
Maternal investment: In many species, males benefit from high maternal investment as it allows them to preserve more energy and time for additional matings rather than investing their resources on one offspring. Females are expected to invest a certain amount of time and resources, but it can also be detrimental to the female if too much maternal investment is expected.
Natural and/or sexual selection on traits that influence the fitness of either male or female give rise to fundamental phenotypic and behavioral differences between them referred to as sexual dimorphism . Selective pressures on such traits give rise to differences in expression of these genes either at transcriptional or translational level. In certain cases these differences are as dramatic as genes not being expressed at all in either of the sexes. These differences in gene expression are the result of either natural selection on reproductive potential and survival traits of either sex or sexual selection on traits relevant to intra-sexual competition and inter-sexual mate choice. [ 13 ]
Sex-biased genes could either be male- or female-biased and sequence analysis of these protein coding genes have revealed their faster rate of evolution which has been attributed to their positive selection vs. reduced selective constraint. Apart from sex specific natural selection and sexual selection that includes both intersexual and intrasexual selection, a third phenomenon also explains the differences in gene expressions between two sexes – sexual antagonism. Sexual antagonism represents an evolutionary conflict at a single or multiple locus that contribute differentially to the male and female fitness. The conflict occurs as the spread of an allele at one locus in either male or female that lowers the fitness of the other sex. This gives rise to different selection pressure on males and females. Since the allele is beneficial for one sex and detrimental to the other, counter adaptations in the form of suppressor alleles at different genetic loci can develop that reduce the effects of deleterious allele, giving rise to differences in gene expression. Selection on such traits in males would select for suppressor alleles in females thus increasing the chances of retaining the deleterious allele in the population in interlocus sexual conflict . [ 14 ]
The retention of such antagonistic alleles in a population could also be explained in terms of increase in the net fitness of the maternal line, for example, the locus for male sexual orientation in humans was identified on subtelomeric regions of X chromosomes after studies conducted on 114 families of homosexual men. Same sex orientation was found to be higher in maternal uncles and male cousins of the gay subjects. [ 15 ] An evolutionary model explained this finding in terms of increased fertility of the females in maternal lines, hence adding to net fitness gain. [ 16 ]
Combined data from coding sequence studies in C. elegans , Drosophila , Humans and Chimps show a similar pattern of molecular evolution in sex-biased genes, i.e. most of the male- and female-biased genes when compared to genes equally expressed in both had higher Ka/Ks ratio . [ 17 ] Male-biased genes show greater divergence than female-biased genes. The Ka/Ks ratio was higher for male-biased genes which are expressed exclusively in reproductive tissues e.g. testis in primate lineages. In C. elegans , which is an androdioecious species (a population consisting of only hermaphrodites and males), the rate of evolution for genes expressed during spermatogenesis was higher in males than in hermaphrodites. In Drosophila , interspecies divergence was found to be higher than intraspecific polymorphism at non synonymous sites of male-biased genes which elucidated the role of positive selection and showed that male-biased genes undergo frequent adaptive evolution. [ 18 ] Although positive evolution is associated with most of the male and female-biased genes, it's difficult to isolate genes which shown bias solely due to sexual conflict/antagonism. Nevertheless, since sexually antagonistic genes give rise to biased expression and most biased genes are under positive selection we can argue the same in favor of sexually antagonistic genes. A similar trend as seen in coding sequence evolution was seen with gene expression levels. Interspecific expression divergence was higher than intraspecific expression polymorphism. Positive selection in Accessory gland proteins (Acps) (produced by males) and Female Reproductive Tract Proteins (Frtps) has also been reported previously.
Although X chromosomes have been considered as hot spots for accumulating sexually antagonistic alleles, other autosomal locations have also been reported to harbor sexually antagonistic alleles. The XY, XX and ZW, ZZ system of sex determination allows accelerated fixation of alleles that are sex-linked recessive, male-beneficial and female-detrimental due to constant exposure to positive selection acting on heterogametic sex (XY, ZW) as compared to purifying selection removing the alleles only in homozygous state. In case of partial or completely dominant sex linked traits which are detrimental to male, the probability of selecting for the allele would be 2/3 as compared to selecting against probability of 1/3. Considering the above scenario it is likely that X and W chromosomes would harbor many sexually antagonistic alleles. However, recently Innocenti et al. identified sexually antagonistic candidate genes in Drosophila melanogaster that contributed about 8% of the total genes. These were distributed on X, second and third chromosomes. Accessory gland proteins which are male-biased and shows positive selection reside entirely on autosomes. They are partially sexually antagonistic as they are not expressed in females and dominant in nature and hence under represented on X. [ 19 ]
Interlocus sexual conflict involves numerous evolutionary concepts that are applied to a wide range of species in order to provide explanations for the interactions between sexes. The conflict between the interactions of male and females can be described as an ongoing evolutionary arms race.
According to Darwin (1859), sexual selection occurs when some individuals are favored over others of the same sex in the context of reproduction. Sexual selection and sexual conflict are related because males usually mate with multiple females while females typically mate with fewer males. It is hypothesized that both chase away selection and sexual conflict may be the result of males use of sensory exploitation. Males are able to exploit females' sensory biases due to the existence of female choice . For example, females may behave in ways that are considerably biased towards mating and fertilization success due to the attractiveness of males who exhibit a deceptive or exaggerated secondary sex characteristic . Since some male traits are detrimental to females, the female becomes insensitive to these traits. Sexually antagonistic co-evolution entails the cyclic process between the exaggerated (persistent) traits and the resistant traits by the sexes. If male traits that decrease female fitness spread, then female preference will change. [ 9 ]
Female resistance is an evolutionary concept where females develop traits to counter the males' influence. This concept can be supported by the examples of sexual conflict in the water strider and pygmy fish.
Male water striders exhibit forced copulation on the female. As a result, the female will struggle with the male to reduce the detrimental effects. Female struggle is a by-product of female resistance. [ 9 ]
The population of pygmy fish Xiphophorus pygmaeus or pygmy sword-tail fish initially consisted of small males. [ 20 ] A study tested female choice using large hetero-specific males. They found that the female pigmy swordtail fish favored larger sized males, indicating that females changed their preference from small males to large males. [ 21 ] This pattern of female preference for larger male body size disappeared in populations consisting of smaller males. The study concluded that this behavior is caused by female resistance and not due to a general preference for larger body size males. [ 5 ]
Sperm competition is an evolutionary concept developed by Geoff Parker (1970) and describes a mechanism by which different males will compete to fertilize a female's egg. [ 1 ] Sperm competition selects for both offensive and defensive traits. Offensive sperm competition consists of males displacing sperm from the previous male as well as the use of toxic sperm to destroy rival sperm. [ 1 ] Conversely, defensive sperm competition consists of males preventing females from remating by prolonging the duration of their own mating or by restricting the females' interest in other males. Sperm competition can be exhibited throughout behavioral, morphological and physiological male adaptations. Some examples of behavioral adaptations are mate guarding or forced copulation. Morphological adaptations may include male claspers, altered genitalia (e.g. spiky genitals) and copulatory plugs (i.e. mating plugs ). Physiological adaptations may consist of toxic sperm or other chemicals in the seminal fluid that delays a female's ability to remate. [ 22 ]
Sexual conflict is exhibited when males target other males through sperm competition. For example, Iberian rock lizard ( Lacerta monticola ) males create hard mating plugs. These mating plugs are placed within the female cloaca instantly after copulation, which was hypothesized to function as a " chastity belt ." However, the study found no evidence to support the hypothesis, as males were able to displace the mating plugs of other males. [ 23 ] There is no direct conflict between males and females, but males may evolve manipulative traits to counter the removal of their mating plugs.
Males also develop different behaviors for paternity assurance. A study of sperm competition revealed that there was a positive relationship between testis size and levels of sperm competition within groups. Higher levels of sperm competition were correlated to larger accessory reproductive glands, seminal vesicles, and interior prostates. Larger mating plugs were less likely to be removed. [ 24 ]
Males inflicting harm on females is a by-product of male adaptation in the context of sperm competition. The advantages to males may include: a) a decrease in the likelihood of females remating, b) the ability to produce more offspring, c) sperm maintenance, and d) sperm storage. [ 25 ] These advantages are seen throughout all variations of mate traits such as toxic sperm, spiky genitalia, forced copulation, sexual cannibalism, penis fencing, love darts, mate guarding, harassment/aggressive behavior, and traumatic insemination.
Females can experience a wide range of detrimental effects from males. This may include: a) longevity reduction, b) distortion in feeding behaviors (which could increase food intake as seen in Drosophila fruit flies) c) increased risk of infection, d) wound repair through energy consumption, [ 25 ] e) male manipulation of female reproductive schedules, [ 26 ] f) susceptibility to predators, [ 9 ] and g) reduced female immune response. [ 25 ]
Hermaphrodites are organisms that have both male and female reproductive organs. It is possible for there to be sexual conflict within a species that is entirely hermaphroditic. An example of such is seen in some hermaphroditic flatworms such as Pseudobiceros bedfordi . Their mating ritual involves penis fencing in which both try to stab to inseminate the other and at the same time avoid being stabbed. Being inseminated represents a cost because striking and hypodermic insemination can cause considerable injury; as a result, the conflict lies in adapting to be more adept at striking and parrying and avoiding being stabbed. [ 9 ]
Also the earthworm Lumbricus terrestris show behavior where both parts try to make sure as much sperm as possible is absorbed by their partner. To do this they use 40 to 44 copulatory setae to pierce into the partner's skin, causing substantial damage. [ 27 ]
There are cases where hermaphrodites can fertilize their own eggs, but this is usually rare. Most hermaphrodites take on the role of a male or female to reproduce. [ 9 ] Sexual conflict over mating can cause hermaphrodites to either cooperate or display aggressive behavior in the context of gender choice.
Infanticide is a behavior that occurs in many species in which an adult kills the younger individuals, including eggs. Sexual conflict is one of the most common causes, although there are exceptions as demonstrated by the male bass eating their own juvenile descendants. [ 28 ] Although males usually exhibit such behavior, females can also behave in the same way.
Infanticide has been extensively studied in vertebrates such as hanuman langurs , big cats, house sparrows and mice . However, this behavior also occurs in the invertebrates . For example, in the spider Stegodyphus lineatus , males invade female nests and toss out their egg sacs. [ 29 ] Females only have one clutch in their lifetime, and experience reduced reproductive success if the clutch is lost. This results in vicious battles where injury and even death can occur. Jacana jacana , a tropical wading bird , provides an example of infanticide by the female sex. [ 30 ] Females guard a territory while males care for their young. As males are a limited resource, other females will commonly displace or kill their young. Males can then mate again and care for the young of the new female.
This behavior is costly to both sides, and counter-adaptations have evolved in the affected sex ranging from cooperative defense of their young to loss minimization strategies such as aborting existing offspring upon the arrival of a new male (the Bruce effect ).
Traumatic insemination describes the male's tactics of piercing a female and depositing sperm in order to ensure paternity success. Traumatic insemination in this sense incorporates species which display extra-genitalic traumatic insemination. [ 31 ] Males have a needle-like intromittent organ . Examples include bed bugs, bat bugs and spiders.
In bed bugs Cimex lectularius , for example, males initiate mating by climbing onto the female and piercing her abdomen. The male will then directly inject his sperm along with the accessory gland fluids into the female's blood. As a result, the female will have a distinct melanized scar in the region the male pierced. It was observed that males not only pierce females but also other males and nymphs. The females may suffer detrimental effects which can include blood leaking, wounds, the risk of infection, and the immune system having difficulty fighting off sperm in the blood. [ 32 ]
A study focused on the mating effects of bed bugs of other species such as female Hesperocimex sonorensis and a male Hesperocimex cochimiensis . It was observed that H. sonorensis females died in a period of 24 to 48 hours after mating with H. cochimiensis males. When examining the females, it was evident that their abdomens were blackened and swollen due to an enormous number of immunoreactions. [ 33 ] There is a direct relationship between the increase of mating and the decrease in female's lifespan. [ 34 ]
Female bed bug mortality rate due to traumatic insemination could be related more to STDs rather than just the open wound. The same environmental microbes that were found on the male's genital were also found within the female. A study found a total of nine microbes, with five microbes actually causing mortality of females during copulation. [ 35 ]
African bat bugs Afrocimex constrictus also perform extra-genitalic traumatic insemination. Males will puncture the female outside her genitals and ultimately inseminate them. It was observed that both males and females suffer from traumatic insemination. Males suffer from traumatic insemination because they expressed female like genitals, and were often at times mistaken for females. Females also displayed polymorphism because some females had distinct "female-like" genitals while others had a "male-like" appearance. The results showed that males along with females who had "male-like" genitals suffer less traumatic insemination compared to the distinct females. Female polymorphism could in fact be a result of evolution due to sexual conflict. [ 36 ]
Male spiders Harpactea sadistica perform extra-genitalic traumatic insemination with their needle-like intromittent organs that puncture the female's wall, resulting in direct insemination. Males also puncture females with their cheliceral fangs during courtship. Females have atrophied spermathecae (sperm-storage organs). The sperm storage organ removes sperm from males who mate later, which reflects cryptic female choice . Cryptic female choice refers to a female's opportunity to choose with which sperm to fertilize her eggs. It has been suggested that males may have developed this aggressive mate tactic as a result of the female sperm storage organ. [ 31 ]
Toxic semen is most associated with Drosophila melanogaster fruit flies. Drosophila fruit flies exhibit toxic semen along with intra-genitalic traumatic insemination. The male places his intromittent organ within the female genitalia, following the piercing of her inner wall, to inject toxic semen.
Frequent mating in D. melanogaster is associated with a reduction in female lifespan. [ 37 ] This cost of mating in D. melanogaster females is not due to receipt of sperm but is instead mediated by accessory gland proteins (Acps) . [ 38 ] Acps are found in male seminal fluid. The toxic effects of Acps on females may have evolved as a side effect of the other functions of Acps (e.g. male-male competition or increased egg production). Drosophila males may benefit from transferring toxic semen but it is not likely that their main reproductive benefit is directly from reducing female lifespan. [ 25 ]
After Acps are transferred to the female, they cause various changes in her behavior and physiology. [ 25 ] Studies have revealed that females who received Acps from males suffered decreased lifespan [ 8 ] and fitness. [ 39 ] Currently it has been estimated that there are more than 100 different Acps in D. melanogaster . [ 9 ] [ 40 ] Acp genes have been found in a variety of species and genera. Acps have been described as displaying a conservation function because they reserve protein biochemical classes within the seminal fluid. [ 25 ]
Drosophila hibisci use mating plugs rather than traumatic insemination. The mating plugs of Drosophila hibisci are gelatinous, hard composites that adhere to the uterus of the female in the event of copulation. A study tested two hypotheses concerning mating plugs: a) that they were nutritional gifts for females to digest to provide maintenance of the eggs during maturation, or b) that they could serve as a chastity device to prevent sperm of rivals. The study found that mating plugs had no effect on female nutrition and serve as an enforcement device against rival males. [ 41 ] Although this species of fruit flies ( Drosophila hibisci ) found success in mating plugs, they are ineffective for other Drosophila species. A study found that males who insert their mating plugs within females were unable to prevent females from remating just four hours after mating. [ 42 ] Therefore, the assumption can be made that male Drosophila melanogaster develop other male adaptations to compensate for mating plug insufficiency, including intra-genitalic traumatic insemination to directly deposit their sperm.
Bruchid beetle or bean weevil Callosobruchus maculatus males are known to express extra-genitalic traumatic insemination on females. [ 31 ] The male Bruchid beetle's intromittent organ is described as having spines that are used to pierce the reproductive tract of the female.
Males which had multiple copulations with the same female caused greater damage to her genitals. However, those same males transferred a small quantity of ejaculate compared to the virgin males. [ 43 ] It was also observed that males that participated in copulation with females sometimes deposit no sperm through the wounds they created on the females. [ 3 ]
Females which mated with more than one male suffered higher mortality. Females had a decrease in longevity as a result of receiving a large single ejaculate from males. However, females which received a total of two ejaculates were less likely to die compared to those that received just one ejaculate. The assumption could be made that females that mated 48 hours after the first copulation were lacking nutrition as they do not drink or eat. The ejaculate that was provided after the second copulation was nutritionally beneficial and lengthened female longevity, allowing them to produce more offspring. [ 43 ]
Females which mated with virgin males were less likely to suffer genital damage compared to those which mated with sexually experienced males. It was suggested that factors contributing to male virgins being less harmful were ejaculate size and the amount of sperm contained. [ 43 ]
Hermaphroditic gastropod snails mate using love darts . The love darts are described as a sharp "stiletto," created by the males. The love darts are shot at the females during courtship. A single love dart is shot at a time, due to the lengthy process of regeneration. [ 44 ] Snails of the genus Helix are model organisms for the study of love darts. It was observed that snails that rub against their mates, will forcefully place the love dart into their mate. It has been shown that though darts may aid in mating, they do not necessarily ensure mating success. [ 9 ] However, love darts do in fact aid in mating success. Hermaphroditic snails will selectively take on a female or male role. Snails transmitted darts into these females so that they would store more sperm (about twice as much) compared to males who were not as successful. [ 45 ] Males who successfully hit females with love darts had higher paternity assurance. Many snails inflicted with love darts suffer open wounds and sometimes death. [ 46 ]
Forced copulation (sexual coercion) by males occurs in a wide range of species and may elicit behaviors such as aggression, harassment and grasping. In the time prior to or during copulation, females suffer detrimental effects due to forceful male mating tactics. Ultimately, females are forced to copulate against their will (a.k.a. "rape").
Harassment is a behavior displayed during or prior to forced copulation. A male may follow the female at a distance in preparation to attack. In the Malabar ricefish Horaichthys setnai ( Beloniformes ), males harass females of interest from a distance. This behavior may consist of swimming below or behind the females, and even following them at a distance. When the male Malabar ricefish is ready to copulate, he dashes at high speed towards the female and release his club-shaped organ, the gonopodium also known as an anal fin. The purpose of the gonopodium is to deliver the spermatophore. The male takes his gonopodium and forcefully places it near the female genitalia. The sharp end of the spermatophore stabs the female's skin. As a result, the male is firmly attached to the female. Following this event, the male's spermatophore bursts, releasing sperm that travel towards the female's genital opening. [ 9 ]
Forced copulation can lead to aggressive behaviors such as grasping. Males express grasping behaviors during the event of copulation with a desired female. Darwin (1871) described males with grasping qualities as having "organs for prehension." His view was that males perform these aggressive behaviors in order to prevent the female from leaving or escaping. The purpose of male grasping devices is to increase the duration of copulation along with restricting females from other males. Grasping traits can also be considered as a way of males expressing mate-guarding. [ 9 ] Examples of species with grasping traits are water striders , diving beetles, and the dung fly Sepsis cynipsea .
During forced copulation, male water striders (genus Gerris ) attack females. As a result, a struggle occurs because the female is resistant. When the male water strider is successfully attached to the female, the female carries the male during and after copulation. This can be energetically costly to the female because she has to support the heavy weight of the male at the same time as she is gliding on the water surface. The speed of the female is usually reduced by 20% when the male is attached. The purpose of long copulation is for the male to achieve paternity assurance in order to restrict the female from other males. Long periods of copulation can strongly affect females because females will depart from the water surface after mating and discontinue foraging. The duration of copulation can be extremely long. For water strider Aquarius najas it was a total of 3 months. For water strider Gerris lateralis the time ranged from 4 to 7 minutes. [ 47 ]
In water strider Gerris odontogaster , males have an abdominal clasping mechanism that grasps females in highly complex struggles before mating. Males that have clasps that are longer than those of other males were able to endure more somersaults by resistant females and achieved mating success. Males' genital structures had a particular shape to aid in female resistance. [ 48 ]
Water striders G. gracilicornis have a behavioral mechanism and grasping structures allowing grasping. Male water striders use what is called an "intimidating courtship". This mechanism involves males using a signal vibration to attract predators in order to manipulate females to mate. Females face more risks of being captured by predators since they idle on the water's surface for long periods of time. If a male were attached to the female, it would be less likely for the male to be harmed by the predators because he would be resting on top of the female. Therefore, males will tap their legs in order to create ripples in the water to attract predators. The female become fearful, causing her to be less resistant towards the male. As a result, copulation occurs faster, during which the male stops signaling. [ 49 ]
Male water striders Gerris odontogaster have grasping structures that can prolong copulation depending on the size of their abdominal processes. Males who had longer abdominal processes were able to restrain females longer than males who had shorter abdominal processes. [ 50 ]
In diving beetles Dytiscidae , males approach females in the water with a grasping mechanism before copulation. When this occurs, females repeatedly resist. Males evolved an anatomical advantage towards grasping. Males have a particular structure located on their tarsae that enhances grasping of female anatomical structures, pronotum and elytra, which are located on her dorsal surface. [ 51 ]
Sepsis cynipsea is another example of sexual conflict via grasping. Males cannot force copulation; however, while females lay eggs fertilized from a previous mating, a new male mounts the female and guards her from other males. Although the females are larger than the males, the males are still able to grasp onto a female. Females are also known to attempt to shake off the male from her back. If she does not shake him off successfully, they mate. [ 52 ]
Sexual cannibalism contradicts the traditional male-female relationship in terms of sexual conflict. Sexual cannibalism involves females slaying and consuming males during attempted courtship or copulation, [ 9 ] as in the interaction between male and female funnel-web spider ( Hololena curta ). [ 53 ]
A possible explanation for sexual cannibalism occurring across taxa is "paternal investment". This means that females kill and consume males, sometimes after sperm exchange, in order to enhance the quality and number of her offspring. Male consumption by females serves as a blood meal since they volunteer their soma. The idea of "paternal investment" supports the concept of female choice because female spiders consume males in order to receive an increase in quality of offspring. Males may tap into female sensory biases that may influence female mate selection. Male gift-giving spiders are known to provide gifts to females in order to avoid being eaten. This is a tactic that males may use in order to manipulate females to not kill them. Females may have a strong, uncontrollable appetite, which males may use to their advantage by manipulating females through edible gifts. [ 54 ]
Males of several species of Heliconius butterflies, such as Heliconius melpomene and Heliconius erato , have been found to transfer an antiaphrodisiac to the female during copulation. [ 55 ] This compound is only produced in the male and is how males identify one another as male. Therefore, when it is transferred to the female, she then smells like a male. This prevents future males from attempting to copulate with her. This behavior both benefits the female because harassment from males post mating has been found to decrease reproductive success by disturbing the production of eggs, and increases the reproductive success of the male by ensuring that his sperm will be used to fertilize the egg. [ 55 ]
The most well known examples of sexual conflict occur before and during mating, but conflicts of interest do not end once mating has happened. Initially there may be a conflict over female reproductive patterns such as reproductive rate, remating rate, and sperm utilization. In species with parental care, there may be a conflict over which sex provides care and the amount of care given to the offspring.
Cryptic female choice falls under the conflict in reproductive patterns. Cryptic female choice results from process that occurs after intromission which allows the female to preferentially fertilize or produce offspring with a particular male phenotype. It is thought that if the female's cryptic choice provides her with indirect genetic benefits in the form of more fit offspring, any male phenotype that limits female cryptic choice will induce a cost on the female. Often, cryptic female choice occurs in polyandrous or polygamous species.
The cricket species, Gryllus bimaculatus , is a polygamous species. Multiple matings increases the hatching success of clutch of eggs which is hypothesized to be a result of increased chances of finding compatible sperm. Therefore, it is in the female's best interest to mate with multiple males to increase the offspring genetic fitness; [ 56 ] however, males would prefer to sire more of the females' offspring and will try to prevent the female from having multiple matings by mate guarding to exclude rival males. [ 57 ]
Similarly, the polyandrous species of spider Pisaura mirabilis has been demonstrated to have cryptic female choice. The presence of a nuptial gift by a male increases the proportion of sperm retained by the female (With copulation duration controlled for). [ 58 ]
Parental investment is when either parent cares for eggs or offspring resulting in increased offspring fitness. Though intuitively one might assume that since providing care to offspring would provide indirect genetic benefits to both parents, there would not be much sexual conflict; however, since neither is interested in the other's genetic fitness, it is more beneficial to be selfish and push the costs of parental care onto the other sex. Therefore, each partner would exert selection on the other partner to provide more care, creating sexual conflict. Additionally, since it is beneficial for one partner to develop adaptations in parental care at the expense of the other, the other partner is likely to evolve counter adaptations to avoid being exploited, creating a situation to be predicted by game theory. [ 9 ]
In the species Nicrophorus defodiens , the burying beetle, there is biparental care; however, males of the species will resume releasing pheromones after mating with the primary female in order to attract more females to increase his reproductive output. However, it is in the female's best interest if she can monopolize the male's parental care and food providence for her offspring. Therefore, the female will bite and attempt to push the male off his signaling perch and interfere with the male's secondary mating attempts in order to impose monogamy on the male. [ 9 ]
In Remiz pendulinus , the Eurasian penduline tit , the male will build an elaborate nest and may or may not be joined by a female at any stage of construction. After eggs are laid, it is strictly uniparental incubation and offspring care; however, either parent may take the role of caregiver. Females will give care 50-70% of initiated breedings while males will give care 5-20% of the time, and approximately 30%-35% of the time, the eggs, which consist of four to five viable eggs, will be left to die, which is a considerable cost to both parents. However, being deserted also represents a large cost for the deserted parent. Therefore, timing of desertion becomes very important. Optimal timing for the males depends on the status of the clutch, and as a result the male frequently enters and remains near the nest during the egg-laying period. For females it is important not to desert too early so that the male does not also desert the eggs, but also not too late else the male deserts before the female does. Females adapt by being very aggressive towards males that try to approach the nest as well as hiding one or more eggs so that males do not have full information on the clutch status. [ 9 ]
Breeding success of Eurasian penduline tits suggests conflicting interests between males and females in a wild population: [ 59 ] by deserting the clutch each parent increases her (or his) reproductive success although desertion reduces the reproductive success of their mate. This tug-of-war between males and females over care provisioning has been suggested to drive flexible parenting strategies in this species. [ 60 ] In the closely related Cape penduline tit Anthoscopus minutus, however, both parents incubate the eggs and rear the young. A contributing factor to parenting decision is extra-pair paternity since in Cape penduline tit less than 8% of young were extra-pair whereas in Eurasian penduline tit over 24% young resulted from extra-pair paternity. [ 61 ]
In other species such as the Guianan cock-of-the-rock , as well as other lekking species, sexual conflict may not even manifest itself in parental care. The females of these species have the tendency to select males to mate with, become fertilized, and the females raise the offspring on their own in their nests. [ 62 ] [ 63 ] | https://en.wikipedia.org/wiki/Sexual_conflict |
Sexual differentiation in humans is the process of development of sex differences in humans . It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination. [ 1 ] Sexual differentiation includes development of different genitalia and the internal genital tracts and body hair plays a role in sex identification. [ 2 ]
The development of sexual differences begins with the XY sex-determination system that is present in humans, and complex mechanisms are responsible for the development of the phenotypic differences between male and female humans from an undifferentiated zygote . [ 3 ] Females typically have two X chromosomes , and males typically have a Y chromosome and an X chromosome. At an early stage in embryonic development, both sexes possess equivalent internal structures. These are the mesonephric ducts and paramesonephric ducts . The presence of the SRY gene on the Y chromosome causes the development of the testes in males, and the subsequent release of hormones which cause the paramesonephric ducts to regress. In females, the mesonephric ducts regress.
Disorders of sexual development (DSD), encompassing conditions characterized by the appearance of undeveloped genitals that may be ambiguous, or look like those typical for the opposite sex, sometimes known as intersex , can be a result of genetic and hormonal factors. [ 4 ]
Most mammals , including humans, have an XY sex-determination system : the Y chromosome carries factors responsible for triggering male development. In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene. [ 5 ] Thus, male mammals typically have an X and a Y chromosome (XY), while female mammals typically have two X chromosomes (XX).
Chromosomal sex is determined at the time of fertilization ; a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell. Gonadal sex refers to the gonads, that is the testicles or ovaries, depending on which genes are expressed. Phenotypic sex refers to the structures of the external and internal genitalia. [ 6 ]
Six weeks elapse after fertilization before the first signs of sex differentiation can be observed in human embryos. [ 5 ] The embryo and subsequent early fetus appear to be sexually indifferent, looking neither like a male or a female. Over the next several weeks, hormones are produced that cause undifferentiated tissue to transform into either male or female reproductive organs. This process is called sexual differentiation. The precursor of the internal female sex organs is called the Müllerian system .
Differentiation between the sexes of the sex organs occurs throughout embryological, fetal and later life. In both males and females, the sex organs consist of two structures: the internal genitalia and the external genitalia. In males, the gonads are the testicles and in females, they are the ovaries . These are the organs that produce gametes (egg and sperm), the reproductive cells that will eventually meet to form the fertilized egg ( zygote ).
As the zygote divides, it first becomes the embryo (which means 'growing within'), typically between zero and eight weeks, then from the eighth week until birth, it is considered the fetus (which means 'unborn offspring'). The internal genitalia are all the accessory glands and ducts that connect the gonads to the outside environment. The external genitalia consist of all the external reproductive structures. The sex of an early embryo cannot be determined because the reproductive structures do not differentiate until the seventh week. Prior to this, the child is considered bipotential because it cannot be identified as male or female.
The internal genitalia consist of two accessory ducts: mesonephric ducts (Woffian duct) and paramesonephric ducts (Müllerian ducts). The mesonephric system is the precursor to the male genitalia and the paramesonephric to the female reproductive system. [ 8 ] As development proceeds, one of the pairs of ducts develops while the other regresses. This depends on the presence or absence of the sex determining region of the Y chromosome, also known as the SRY gene . [ 5 ] In the presence of a functional SRY gene, the bipotential gonads develop into testes. Gonads are histologically distinguishable by 6–8 weeks of gestation.
Subsequent development of one set and degeneration of the other depends on the presence or absence of two testicular hormones: testosterone and anti-Müllerian hormone (AMH) . Disruption of typical development may result in the development of both, or neither, duct system, which may produce morphologically intersex individuals.
Males: The SRY gene when transcribed and processed produces SRY protein that binds to DNA and directs the development of the gonad into testes. Male development can only occur when the fetal testis secretes key hormones at a critical period in early gestation. The testes begin to secrete three hormones that influence the male internal and external genitalia: they secrete anti-Müllerian hormone (AMH), testosterone , and dihydrotestosterone (DHT). Anti-Müllerian hormone causes the paramesonephric ducts to regress. Testosterone converts the mesonephric ducts into male accessory structures, including the epididymides , vasa deferentia , and seminal vesicles . Testosterone will also control the descending of the testes from the abdomen. [ 1 ] Many other genes found on other autosomes , including WT1 , SOX9 and SF1 also play a role in gonadal development. [ 9 ]
Females: Without testosterone and AMH, the mesonephric ducts degenerate and disappear. The paramesonephric ducts develop into the uterus , fallopian tubes , and upper vagina (the lower vagina develops from the urogenital sinus). [ 9 ] There still remains a broad lack of information about the genetic controls of female development (as of 1992), and much remains unknown about the female embryonic process. [ 10 ] The mesonephric ducts are not completely useless in the female case: they secrete WNT9B , which is necessary for the elongation of the paramesonephric ducts. Elongation also happens through the active migration of the paramesonephric epithelium, which happens through a phosphoinositide 3-kinase pathway. [ 11 ]
By 7 weeks, a fetus has a genital tubercle , urogenital sinus , urogenital folds and labioscrotal swellings . In females, without excess androgens, these become the vulva ( clitoris , vestibule , labia minora and labia majora respectively). Males become externally distinct between 8 and 12 weeks, as androgens enlarge the genital tubercle and cause the urogenital groove and sinus to fuse in the midline, producing an unambiguous penis with a phallic urethra, and the labioscrotal swellings become a thinned, rugate scrotum where the testicles are situated. Dihydrotestosterone will differentiate the remaining male characteristics of the external genitalia. [ 1 ]
A sufficient amount of any androgen can cause external masculinization . The most potent is dihydrotestosterone (DHT), generated from testosterone in skin and genital tissue by the action of 5α-reductase. A male fetus may be incompletely masculinized if this enzyme is deficient . In some diseases and circumstances, other androgens may be present in high enough concentrations to cause partial or (rarely) complete masculinization of the external genitalia of a genetically female fetus. The testes begin to secrete three hormones that influence the male internal and external genitalia. They secrete anti-Müllerian hormone, testosterone, and Dihydrotestosterone. Anti-Müllerian hormone (AMH) causes the paramesonephric ducts to regress. Testosterone, which is secreted and converts the mesonephric ducts into male accessory structures, such as epididymis, vas deferens and seminal vesicle. Testosterone will also control the descending of the testes from the abdomen into the scrotum. Dihydrotestosterone, also known as (DHT) will differentiate the remaining male characteristics of the external genitalia. [ 12 ]
Further sex differentiation of the external genitalia occurs at puberty , when androgen levels again become disparate. Male levels of testosterone directly induce growth of the penis, and indirectly (via DHT) the prostate .
Alfred Jost observed that while testosterone was required for mesonephric duct development, the regression of the paramesonephric duct was due to another substance. This was later determined to be paramesonephric inhibiting substance (MIS), a 140 kD dimeric glycoprotein that is produced by Sertoli cells . MIS blocks the development of paramesonephric ducts , promoting their regression. [ 13 ] Today it’s better known as the anti-Müllerian hormone (AMH).
Visible differentiation occurs at puberty , when estradiol and other hormones cause breasts to develop in typical females.
Human adults and children show many psychological and behavioral sex differences. Some (e.g. dress) are learned and cultural. Others are demonstrable across cultures and have both biological and learned determinants. For example, some studies claim girls are, on average, more verbally fluent than boys, but boys are, on average, better at spatial calculation. [ 14 ] [ 15 ] Some have observed that this may be due to two different patterns in parental communication with infants, noting that parents are more likely to talk to girls and more likely to engage in physical play with boys. [ 10 ]
Disorders of sex determination (DSD) are classified into a multitude of categories. [ 16 ] These categories consists of different types of female disorders along with categories specifically for male DSDs. There are also sex chromosomal DSDs such as, the later mentioned, Klinefelter and Turner syndrome [ 16 ]
The following are some of the conditions associated with atypical determination and differentiation process: [ 17 ] | https://en.wikipedia.org/wiki/Sexual_differentiation_in_humans |
Sexual maturity is the capability of an organism to reproduce . In humans, it is related to both puberty and adulthood . [ 1 ] Puberty is the biological process of sexual maturation, while adulthood , the condition of being socially recognized as an independent person capable of giving consent and taking responsibility, generally implies sexual maturity (certain disorders of sexual development notwithstanding), but depends on other criteria, defined by specific cultural expectations . [ 1 ] [ 2 ]
Most multicellular organisms are unable to sexually reproduce at birth (animals) or germination (e.g. plants): depending on the species, it may be days, weeks, or years until they have developed enough to be able to do so; in addition, certain cues may trigger an organism to become sexually mature. These may be external, such as drought, or fire, that triggers sexual maturation of certain plants, or internal, such as percentage of body fat (certain animals). Internal cues are not to be confused with hormones , the chemical signals that initiate cellular processes leading to sexual maturity, but the production and secretion of hormones is triggered by such cues. In some species, immature males may delay sexual maturation in the presence of another sexually mature male, as in the male chicken (rooster), due to the intense, often lethal, combat engaged in by mature males. The female honeybee only becomes sexually mature if it is fed a special substance (" royal jelly ") during the larval stage.
Sexual maturity is brought about by a maturing of the reproductive organs and the production of gametes . It may also be accompanied by a growth spurt or other physical changes which distinguish the immature organism from its adult form. In animals these are termed secondary sex characteristics , and often represent an increase in sexual dimorphism . [ clarification needed ]
After sexual maturity is achieved, [ clarification needed ] some organisms become infertile , or even change their sex . Some organisms are hermaphrodites and may or may not be able to "completely" mature and/or to produce viable offspring. Also, while in many organisms sexual maturity is strongly linked to age, many other factors are involved, and it is possible for some to display most or all of the characteristics of the adult form without being sexually mature. Conversely it is also possible for the "immature" form of an organism to reproduce. This is called progenesis , in which sexual development occurs faster than other physiological development (in contrast, the term neoteny refers to when non-sexual development is slowed – but the result is the same - the retention of juvenile characteristics into adulthood). [ citation needed ]
In some species, there is a difference between puberty and sexual maturity. For example, in bulls , puberty is characterized by the accelerated growth of the genital system, an increase in luteinizing hormone (LH) secretion, and the onset of spermatogenesis . Sexual maturity, however, signifies the attainment of full reproductive capacity, which may take up to 6–9 months after puberty. [ 3 ] | https://en.wikipedia.org/wiki/Sexual_maturity |
Sexual mimicry occurs when one sex mimics the opposite sex in its behavior, appearance, or chemical signalling. [ 1 ]
It is more commonly seen within invertebrate species, although sexual mimicry is also seen among vertebrates such as spotted hyenas.
Sexual mimicry is commonly used as a mating strategy to gain access to a mate, a defense mechanism to avoid more dominant individuals, or a survival strategy. It can also be a physical characteristic that establishes an individual's place in society. Sexual mimicry is employed differently across species and it is part of their strategy for survival and reproduction.
Examples of intraspecific sexual mimicry in animals include the spotted hyena , certain types of fish, passerine birds and some species of insect.
Interspecific sexual mimicry can also occur in some plant species, especially orchids. In plants employing sexual mimicry, flowers mimic mating signals of their pollinator insects. These insects are attracted and pollinate the flowers through pseudocopulations or other sexual behaviors performed on the flower.
Sexual mimicry can play a role in the development of a species' social system. Perhaps the most extreme example of this can be seen in the spotted hyena , Crocuta crocuta . [ 2 ] Female hyenas of all ages possess pseudomasculinized genitalia, including a pseudopenis formed from the clitoris, and a false scrotum formed from the labia. These characteristics likely initially evolved to reduce rates of intrasex aggression received by cub and juvenile females from adult females. However, the trait has evolved beyond its initial use to become highly relevant to spotted hyena communication. Subordinate hyenas will greet dominant individuals by erecting their penis or pseudopenis and allowing the dominant individual to lick it. This likely initially evolved as a means of discerning the sex of the subordinate individual, as the pseudopenis less closely resembles a genuine penis when erect, and tasting the area could allow for the detection of sex specific hormone concentrations. However, this behaviour continues to be engaged in by adult, parous females which no longer convincingly resemble males, visually or olifactorily.
In the spotted hyenas, the only way for the males to mate with the females is if they have the female's full cooperation because of the female's peniform clitoris. An increase in the male's status gave them more access to dominant females in the clan. Non-dominant females are observed copulating more often with lower-ranking males. [ 3 ] It is costly for female hyenas to give birth through their long peniform clitoris. The umbilical cord is 12–18 cm long, while the journey from the uterus to the clitoris end is 40 cm. The umbilical cord often breaks before the cub emerges, leading to death by anoxia for many young. This journey is not only harmful for the cubs, but also for the mother. The tissue of the clitoris will sometimes rip open when giving birth for the first time which can be fatal to the mother. [ 4 ]
Sexual mimicry is also used as a mate-guarding strategy by some species. Mate-guarding is a process in which a member of a species prevents another member of the same species from mating with their partner. Mate-guarding is seen in Cotesia rubecula , a parasitic wasp from the family Braconidae whose mating system is polygynous . Males are attracted to females through pheromones and they induce females to mate through vibrations, to which the female responds by assuming a specific position. When a male who has copulated with a female sees another male trying to court her, he will often adopt the female receptive position. Post-copulatory female mimicry by the male offers an advantage by acting as a mate-guarding mechanism. If a second male arrives soon enough after the female copulates with the first male, the second male may be able to induce a second copulation which will compete with the first one. However, if the first male who copulated with her mimics the female, it distracts the second male long enough that the female becomes unreceptive. [ 5 ]
Sneaky copulation is a strategy used by many aquatic organisms who portray sexual mimicry. Several studies have found that small male fish will look and behave like the female of their species in order to gain access to female territory and copulate with them. [ 6 ] [ 7 ] In the fish family Blenniidae , the female Salaria pavo will show a specific colour pattern and movement when they want to approach a male and copulate with him. The male guards a territory, and when the female lays her eggs, the parental male protects that territory until the eggs hatch. A second type of males, the sneaker males, is parasitic and resembles the female bleniid fish in their small size, colour, and movement patterns. This allows them to intrude into the nest guarded by the parental males. Sneaker males approach the nests with the same colour patterns and movements that the females hold. Most cases of sneaker males are seen when there is a female already inside the nest although sometimes the sneaker fish enters the nest alongside a female. This species of fish releases the sperm before the female releases her eggs into the water [ 8 ] making it possible for the sneaker fish to fertilize an egg, even if the female is not present in the nest. [ 6 ]
In the Sepiina family, the giant cuttlefish , Sepia apama , have some males that are large and able to guard a female's nest while other males are small and resemble females in order to sneak in copulations. In the giant cuttlefish, the male courts the female and transfers its sperm to a pouch below the female's beak. During this process, the female displays a body pattern of black splotches on a white background. Once the eggs are laid, the male guards the nest from any possible suitors and opponents. A ‘second female’ is sometimes seen during male-female interaction in close proximity to the couple. This female-looking cuttlefish has the same black blotches as a real female. If the male leaves to fight other males, this individual approaches the female and copulates with her, usually with success. However, in the absence of rivals, these 'mimicking female' males display the phenotype of a mature male. [ 7 ]
A similar phenomenon to the sneaker fish males is observed in the dark-edged splitfin , Girardinichthys multiradiatus . The juveniles resemble the pregnant females in the species by having a dark spot near the vent. In this case, however, the mimicking males have the capability to resemble the females or become a morphologically mature male throughout most of their adult life. This dark spot allows the female-looking males to escape aggression from more dominant males, as well as reducing the chance of having a female nearby flee due to persisting courting males. The mature males do not attack the subordinate fish and the subordinate fish decides when to initiate the fights, which gives it an advantage as the mature male is not expecting this. The dark spot also permits access of subordinate males to females, a characteristic that is advantageous because females' eggs can only be fertilized during a five-day fertilizing window. [ 9 ]
Sexual mimicry to avoid aggression is also seen in birds. In some bird species, males have a female-like plumage colour during their second year of life (SY males). These SY males are sexually mature and able to breed, but their morphology differs greatly from the older, after second year (ASY) males. Various studies have looked into this delayed plumage maturation (DPM) and found that the DPM in SY males reduces aggression from ASY males. [ 10 ] [ 11 ] [ 12 ] Female mimicry in birds was first found in European pied flycatcher , Ficedula hypoleuca . When a dull-coloured male is in the area, mature males reduce their aggressiveness and behave as if the intruder is a female. The dull plumage is seen mostly in younger males, likely due to being born later in the previous spring. The resemblance to females benefit these young males when trying to occupy a territory with many males already present because the young males can gain information and access to a territory that would not be accessible to them otherwise. [ 11 ]
There is a big cost to not looking like a male when it comes to defending a territory or attracting a mate. Females show aggression against dull-coloured males, making it harder for them to mate. [ 11 ] However, DPM has some benefits: as mentioned above, it reduces aggression from older males. [ 11 ] As well, these female-looking birds are able to get access to territories, mates, and food that may be not be available to them otherwise. Another benefit is that DPM provides SY birds with a longer lifespan; because they do not have to compete with other males, their mortality rate is lower. This advantage, however, only benefits individuals of species that have a longer potential lifespan and, therefore, DPM would not benefit a short-lived species. [ 10 ] This is known as the breeding threshold hypothesis, and states that SY males should only delay breeding if there is a large mortality difference between the SY males who attempt to breed and the ones who do not. [ 10 ]
Most studies addressed DPM as a type of sexual mimicry, [ 10 ] [ 11 ] which is done through deception: male ASY birds should not be able to tell females or SY males apart. However, Muheter et al. (1997) found that territorial males perceive the dull-coloured males as males but they show less aggression because their dull-coloured plumage promotes low competitive ability. They referred to this as honest signalling and not sexual mimicry. [ 12 ]
Another example of sexual mimicry occurs in Broadley's Flat Lizard, Platysaurus broadleyi , where some males mimic females. Flat lizard males tend to be territorial and aggressive towards other males. Therefore, it is beneficial for some males to mimic females in order to avoid aggressive encounters and move freely through the male's territory, looking for mates. There are two types of males in this population; she-males, who mimic females, and he-males, who look like males. The she-males can visually fool the he-males into believing that they are female due to their female morphology. However, the she-males cannot fool the he-males through scent, as he-males can detect the difference. Therefore, the most successful she-males are those who avoid close contact with other males, thereby reducing the chances of detection through chemical signals. [ 13 ]
In a lekking shorebird species, the ruff , or Philomachus pugnax , there are three distinct male morphs: independent males, the primary, dark-feathered morph, which establishes and aggressively defends a lekking territory, satellite males, a light-feathered morph which does not defend its own territory but which seeks prominent independent males to display alongside, and faeder males, which lack the typical male breeding plumage, instead more closely resembling females, possess a smaller body size, intermediate between a typical male and female, and which do not consistently occupy a single territory, but move freely between different independent male territories, perhaps owing to their female-like plumage, and engage in sneak copulations with females. [ 14 ]
When testosterone is administered to reeves (female ruffs), male courtship behaviour and male feather colouration are expressed in the reeves. Testosterone, in this case, expresses sex-limited characteristics by acting on the single autosomal gene. [ 15 ]
A different example is seen in mature female fruit flies, Drosophila melanogaster , who are very attractive but their level of attractiveness decreases by half or more after three minutes of mating. [ 16 ] Males release a compound, 7-tricosene, into the female during courtship that lowers female attractiveness. However, the researcher found that the females release this compound as well, six hours after mating. This compound lowers the female's levels of attractiveness both times, when the male is courting her and during mating. This way, the female mimics the male and with this compound, she lowers her levels of attractiveness. [ 17 ]
Some organisms' sexual mimicry is genetically determined by specific alleles. In the marine isopod, Paracerceis sculpta , there are three different male morphologies: the alpha male is the largest morph, it matures last, and it is the one who gets privileged access to the females. The beta male is of intermediate size, and it mimics the female to get access to females. Last, the gamma male is the smallest morph and it invades harems, where females go to mate with alpha males, for mating opportunities. This morphology is associated with a single autosomal gene and three different alleles. Beta is the most dominant allele, followed by gamma, which is followed by alpha. Selection on these alleles acts according to the Hardy-Weinberg equilibrium and mating success is equivalent among all three morphs. [ 18 ]
The alpha males, who are homozygous for the alpha allele, mate with many females in a harem. The females prefer to aggregate with other females in the harem, which gives the alpha male a bigger selection of mating partners. Shuster (1992) looked at the behaviour and relationship of each morph with respect to the harem and found that beta and gamma males could locate harems that have sexually receptive females. They were also able to differentiate between a harem with a sexually receptive female, i.e. one that is able to mate, and a non-sexually receptive female, i.e. one that has already deposited the embryo into her pouch and can no longer mate. While it is still unclear how the beta males do this or how their mating strategies work, they are not harassed by alpha males due to their mimicry of females: the beta males can attract other females into the harem since females like to go where other females are, and this provides the alpha males with more mates. [ 19 ]
Another order of organisms whose sexual mimicry is influenced by their DNA is the Odonata , carnivorous insects known as dragonflies and damselflies. In these species, it is the female who sometimes mimics the male. Within a species, groups of females will differ in colour: one group mimics the males' colour and they are known as androchromes. Other groups will have their own female colouration and they are known as gynochromes. In Ischnura elegans , androchromes comprise 6-30% of the female population and their colour is usually blue, like the males; in some populations, androchromes are larger in size than gynochromes. This polymorphism is controlled by an autosomal allele and some studies have looked at the reason for the polymorphism's maintenance. [ 20 ]
The most likely theory for the maintenance of the polymorphism in Odonata is the density dependence theory [ 21 ] that states that at a high male density, the androchromes are not bothered by the males and their existence is not threatened by male harassment. This hypothesis also assumes that males cannot distinguish between androchromes and other males. This advantage, however, is counteracted with the fact that they will not get a lot of mating opportunities (if any) and their reproduction is limited. This theory is the most likely explanation for the maintenance of polymorphism, since studies have shown that there is an advantage for androchromes in high male-density populations. [ 22 ]
In the swordtail fish Xiphophorus birchmanni , 40% of males develop a "false gravid spot," a trait that allows males to mimic the " pregnancy spot " found in females. [ 23 ] The false gravid spot is caused by structural variation which up-regulates expression of the nearby gene kit-ligand . [ 23 ] Males with the spot experience reduced aggression from other males; however, they are disdained by females but receive more attention from males. [ 23 ]
While, as seen before, most organisms which portray sexual mimicry are born with this morphology/behaviour, this is not always the case. The giant cuttlefish, Sepia apama , mentioned above in the section “sneaky copulations”, is born with the capacity to choose whether to change its morphology to look like a female or a mature male. When no competition is seen nearby, the cuttlefish will look like a mature male and mate with the female. However, when a mature male and a female are copulating, the giant cuttlefish will resemble a female and stay at a close distance of the couple, hoping for a chance to mate with the female if the mature male leaves to fight other males. [ 7 ] Another example of an organism that has the capability to remain small and look like a female, or become a morphologically mature male, is the dark-edged splitfin, Girardinichthys multiradiatus . The purpose for their female mimicry was seen before, in the “sexual mimicry against aggression” section where the female-looking males will escape aggression from dominant males and avoid females fleeing their company due to persisting courting males. [ 9 ]
Interspecific sexual mimicry can also occur in some plant species. The most common example of this is known as sexually deceptive pollination and is found among some orchids. [ 24 ] The orchid mimics its pollinator's females, usually hymenopterans such as wasps and bees, attracting the males to the flower. Orchid flowers mimic the sex pheromones and to some degree the visual appearance of the female insect of its pollinator species. The primacy of olfactory over visual cues has been demonstrated in many cases, such as in the European orchid genus Ophrys as well as many Australian sexually deceptive orchids. In few other cases, such as the South African daisy Gorteria diffusa , visual signals seem to be of primary importance. [ 25 ] Visual signals also enhance the attractiveness of the flowers of some Ophrys species to their pollinators. [ 26 ] [ 27 ] Some male scoliid wasps such as Campsoscolia ciliata are more attracted to the Ophrys flowers' odours than to the odours of the female wasps, although they both attract the males with the same compounds. This is most likely a result of a higher amount of scent coming from the orchid flowers; female wasps tend to produce less scent to avoid attracting predators. [ 28 ] Regardless of whether orchids use appearances, fragrances or both, they mimic the female pollinator for their own benefit. | https://en.wikipedia.org/wiki/Sexual_mimicry |
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell ) with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes ( diploid ). [ 1 ] This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes . [ 2 ] [ 3 ]
In placental mammals , sperm cells exit the penis through the male urethra and enter the vagina during copulation , [ 4 ] [ 5 ] while egg cells enter the uterus through the oviduct . Other vertebrates of both sexes possess a cloaca for the release of sperm or egg cells.
Sexual reproduction is the most common life cycle in multicellular eukaryotes, such as animals , fungi and plants . [ 6 ] [ 7 ] Sexual reproduction also occurs in some unicellular eukaryotes. [ 2 ] [ 8 ] Sexual reproduction does not occur in prokaryotes , unicellular organisms without cell nuclei , such as bacteria and archaea . However, some processes in bacteria, including bacterial conjugation , transformation and transduction , may be considered analogous to sexual reproduction in that they incorporate new genetic information. [ 9 ] Some proteins and other features that are key for sexual reproduction may have arisen in bacteria, but sexual reproduction is believed to have developed in an ancient eukaryotic ancestor. [ 10 ]
In eukaryotes, diploid precursor cells divide to produce haploid cells in a process called meiosis . In meiosis, DNA is replicated to produce a total of four copies of each chromosome. This is followed by two cell divisions to generate haploid gametes. After the DNA is replicated in meiosis, the homologous chromosomes pair up so that their DNA sequences are aligned with each other. During this period before cell divisions, genetic information is exchanged between homologous chromosomes in genetic recombination . Homologous chromosomes contain highly similar but not identical information, and by exchanging similar but not identical regions, genetic recombination increases genetic diversity among future generations. [ 11 ]
During sexual reproduction, two haploid gametes combine into one diploid cell known as a zygote in a process called fertilization . The nuclei from the gametes fuse, and each gamete contributes half of the genetic material of the zygote. Multiple cell divisions by mitosis (without change in the number of chromosomes) then develop into a multicellular diploid phase or generation. In plants, the diploid phase, known as the sporophyte , produces spores by meiosis. These spores then germinate and divide by mitosis to form a haploid multicellular phase, the gametophyte , which produces gametes directly by mitosis. This type of life cycle, involving alternation between two multicellular phases, the sexual haploid gametophyte and asexual diploid sporophyte, is known as alternation of generations .
The evolution of sexual reproduction is considered paradoxical, [ 12 ] because asexual reproduction should be able to outperform it as every young organism created can bear its own young. This implies that an asexual population has an intrinsic capacity to grow more rapidly with each generation. [ 13 ] This 50% cost is a fitness disadvantage of sexual reproduction. [ 14 ] The two-fold cost of sex includes this cost and the fact that any organism can only pass on 50% of its own genes to its offspring. However, one definite advantage of sexual reproduction is that it increases genetic diversity and impedes the accumulation of harmful genetic mutations . [ 15 ] [ 11 ]
Sexual selection is a mode of natural selection in which some individuals out-reproduce others of a population because they are better at securing mates for sexual reproduction. [ 16 ] [ failed verification ] [ 17 ] It has been described as "a powerful evolutionary force that does not exist in asexual populations". [ 18 ]
The first fossilized evidence of sexual reproduction in eukaryotes is from the Stenian period, about 1.05 billion years old. [ 19 ] [ 20 ]
Biologists studying evolution propose several explanations for the development of sexual reproduction and its maintenance. These reasons include reducing the likelihood of the accumulation of deleterious mutations, increasing rate of adaptation to changing environments , [ 21 ] dealing with competition , DNA repair , masking deleterious mutations, and reducing genetic variation on the genomic level. [ 22 ] [ 23 ] [ 24 ] [ 25 ] All of these ideas about why sexual reproduction has been maintained are generally supported, but ultimately the size of the population determines if sexual reproduction is entirely beneficial. Larger populations appear to respond more quickly to some of the benefits obtained through sexual reproduction than do smaller population sizes. [ 26 ]
However, newer models presented in recent years suggest a basic advantage for sexual reproduction in slowly reproducing complex organisms .
Sexual reproduction allows these species to exhibit characteristics that depend on the specific environment that they inhabit, and the particular survival strategies that they employ. [ 27 ]
In order to reproduce sexually, both males and females need to find a mate . Generally in animals mate choice is made by females while males compete to be chosen. This can lead organisms to extreme efforts in order to reproduce, such as combat and display, or produce extreme features caused by a positive feedback known as a Fisherian runaway . Thus sexual reproduction, as a form of natural selection , has an effect on evolution . Sexual dimorphism is where the basic phenotypic traits vary between males and females of the same species . Dimorphism is found in both sex organs and in secondary sex characteristics , body size, physical strength and morphology, biological ornamentation , behavior and other bodily traits. However, sexual selection is only implied over an extended period of time leading to sexual dimorphism. [ 28 ]
Animals have different ways about going about sexual selection. One common example is with male peacocks fanning out their wings in order to show all their colors and attract a female mate. Lions with bigger and fuller manes are more likely to attract a female mate. Male deer with larger antlers are more likely to gain a female mate. These are just few of many examples in nature that show how sexual selection would be used in nature when females are choosing a mate.
A few arthropods, such as barnacles , are hermaphroditic , that is, each can have the organs of both sexes . However, individuals of most species remain of one sex their entire lives. [ 29 ] A few species of insects and crustaceans can reproduce by parthenogenesis , especially if conditions favor a "population explosion". However, most arthropods rely on sexual reproduction, and parthenogenetic species often revert to sexual reproduction when conditions become less favorable. [ 30 ] The ability to undergo meiosis is widespread among arthropods including both those that reproduce sexually and those that reproduce parthenogenetically . [ 31 ] Although meiosis is a major characteristic of arthropods, understanding of its fundamental adaptive benefit has long been regarded as an unresolved problem, [ 32 ] that appears to have remained unsettled.
Aquatic arthropods may breed by external fertilization, as for example horseshoe crabs do, [ 33 ] or by internal fertilization , where the ova remain in the female's body and the sperm must somehow be inserted. All known terrestrial arthropods use internal fertilization. Opiliones (harvestmen), millipedes , and some crustaceans use modified appendages such as gonopods or penises to transfer the sperm directly to the female. However, most male terrestrial arthropods produce spermatophores , waterproof packets of sperm , which the females take into their bodies. A few such species rely on females to find spermatophores that have already been deposited on the ground, but in most cases males only deposit spermatophores when complex courtship rituals look likely to be successful. [ 29 ]
Insect species make up more than two-thirds of all extant animal species. Most insect species reproduce sexually, though some species are facultatively parthenogenetic . Many insect species have sexual dimorphism , while in others the sexes look nearly identical. Typically they have two sexes with males producing spermatozoa and females ova. The ova develop into eggs that have a covering called the chorion , which forms before internal fertilization. Insects have very diverse mating and reproductive strategies most often resulting in the male depositing a spermatophore within the female, which she stores until she is ready for egg fertilization. After fertilization, and the formation of a zygote, and varying degrees of development, in many species the eggs are deposited outside the female; while in others, they develop further within the female and the young are born live. [ 37 ]
There are three extant kinds of mammals: monotremes , placentals and marsupials , all with internal fertilization. In placental mammals, offspring are born as juveniles: complete animals with the sex organs present although not reproductively functional. After several months or years, depending on the species, the sex organs develop further to maturity and the animal becomes sexually mature . Most female mammals are only fertile during certain periods during their estrous cycle, at which point they are ready to mate. [ 38 ] For most mammals, males and females exchange sexual partners throughout their adult lives . [ 39 ] [ 40 ] [ 41 ]
The vast majority of fish species lay eggs that are then fertilized by the male. [ 42 ] Some species lay their eggs on a substrate like a rock or on plants, while others scatter their eggs and the eggs are fertilized as they drift or sink in the water column.
Some fish species use internal fertilization and then disperse the developing eggs or give birth to live offspring. Fish that have live-bearing offspring include the guppy and mollies or Poecilia . Fishes that give birth to live young can be ovoviviparous , where the eggs are fertilized within the female and the eggs simply hatch within the female body, or in seahorses , the male carries the developing young within a pouch, and gives birth to live young. [ 43 ] Fishes can also be viviparous , where the female supplies nourishment to the internally growing offspring. Some fish are hermaphrodites , where a single fish is both male and female and can produce eggs and sperm. In hermaphroditic fish, some are male and female at the same time while in other fish they are serially hermaphroditic; starting as one sex and changing to the other. In at least one hermaphroditic species, self-fertilization occurs when the eggs and sperm are released together. Internal self-fertilization may occur in some other species. [ 44 ] One fish species does not reproduce by sexual reproduction but uses sex to produce offspring; Poecilia formosa is a unisex species that uses a form of parthenogenesis called gynogenesis , where unfertilized eggs develop into embryos that produce female offspring. Poecilia formosa mate with males of other fish species that use internal fertilization, the sperm does not fertilize the eggs but stimulates the growth of the eggs which develops into embryos. [ 45 ]
Reptiles generally reproduce sexually, though some are capable of asexual reproduction. All reproductive activity occurs through the cloaca, the single exit/entrance at the base of the tail where waste is also eliminated. Most reptiles have copulatory organs, which are usually retracted or inverted and stored inside the body. In turtles and crocodilians, the male has a single median penis, while squamates, including snakes and lizards, possess a pair of hemipenes, only one of which is typically used in each session. Tuatara, however, lack copulatory organs, and so the male and female simply press their cloacas together as the male discharges sperm. Most reptiles lay amniotic eggs covered with leathery or calcareous shells.
Asexual reproduction has been identified in squamates in six families of lizards and one snake. In some species of squamates, a population of females is able to produce a unisexual diploid clone of the mother.
Animals have life cycles with a single diploid multicellular phase that produces haploid gametes directly by meiosis. Male gametes are called sperm, and female gametes are called eggs or ova. In animals, fertilization of the ovum by a sperm results in the formation of a diploid zygote that develops by repeated mitotic divisions into a diploid adult. Plants have two multicellular life-cycle phases, resulting in an alternation of generations . Plant zygotes germinate and divide repeatedly by mitosis to produce a diploid multicellular organism known as the sporophyte. The mature sporophyte produces haploid spores by meiosis that germinate and divide by mitosis to form a multicellular gametophyte phase that produces gametes at maturity. The gametophytes of different groups of plants vary in size. Mosses and other pteridophytic plants may have gametophytes consisting of several million cells, while angiosperms have as few as three cells in each pollen grain.
Flowering plants are the dominant plant form on land [ 46 ] : 168, 173 and they reproduce either sexually or asexually. Often their most distinctive feature is their reproductive organs, commonly called flowers. The anther produces pollen grains which contain the male gametophytes that produce sperm nuclei. For pollination to occur, pollen grains must attach to the stigma of the female reproductive structure ( carpel ), where the female gametophytes are located within ovules enclose within the ovary . After the pollen tube grows through the carpel's style, the sex cell nuclei from the pollen grain migrate into the ovule to fertilize the egg cell and endosperm nuclei within the female gametophyte in a process termed double fertilization . The resulting zygote develops into an embryo, while the triploid endosperm (one sperm cell plus two female cells) and female tissues of the ovule give rise to the surrounding tissues in the developing seed. The ovary, which produced the female gametophyte(s), then grows into a fruit , which surrounds the seed(s). Plants may either self-pollinate or cross-pollinate .
In 2013, flowers dating from the Cretaceous (100 million years before present) were found encased in amber, the oldest evidence of sexual reproduction in a flowering plant. Microscopic images showed tubes growing out of pollen and penetrating the flower's stigma. The pollen was sticky, suggesting it was carried by insects. [ 47 ]
Ferns produce large diploid sporophytes with rhizomes , roots and leaves. Fertile leaves produce sporangia that contain haploid spores . The spores are released and germinate to produce small, thin gametophytes that are typically heart shaped and green in color. The gametophyte prothalli , produce motile sperm in the antheridia and egg cells in archegonia on the same or different plants. [ 48 ] After rains or when dew deposits a film of water, the motile sperm are splashed away from the antheridia, which are normally produced on the top side of the thallus, and swim in the film of water to the archegonia where they fertilize the egg. To promote out crossing or cross fertilization the sperm are released before the eggs are receptive of the sperm, making it more likely that the sperm will fertilize the eggs of different thallus. After fertilization, a zygote is formed which grows into a new sporophytic plant. The condition of having separate sporophyte and gametophyte plants is called alternation of generations .
The bryophytes , which include liverworts , hornworts and mosses , reproduce both sexually and vegetatively . They are small plants found growing in moist locations and like ferns, have motile sperm with flagella and need water to facilitate sexual reproduction. These plants start as a haploid spore that grows into the dominant gametophyte form, which is a multicellular haploid body with leaf-like structures that photosynthesize . Haploid gametes are produced in antheridia (male) and archegonia (female) by mitosis. The sperm released from the antheridia respond to chemicals released by ripe archegonia and swim to them in a film of water and fertilize the egg cells thus producing a zygote. The zygote divides by mitotic division and grows into a multicellular, diploid sporophyte. The sporophyte produces spore capsules ( sporangia ), which are connected by stalks ( setae ) to the archegonia. The spore capsules produce spores by meiosis and when ripe the capsules burst open to release the spores. Bryophytes show considerable variation in their reproductive structures and the above is a basic outline. Also in some species each plant is one sex ( dioicous ) while other species produce both sexes on the same plant ( monoicous ). [ 49 ]
Fungi are classified by the methods of sexual reproduction they employ. The outcome of sexual reproduction most often is the production of resting spores that are used to survive inclement times and to spread. There are typically three phases in the sexual reproduction of fungi: plasmogamy , karyogamy and meiosis . The cytoplasm of two parent cells fuse during plasmogamy and the nuclei fuse during karyogamy. New haploid gametes are formed during meiosis and develop into spores. The adaptive basis for the maintenance of sexual reproduction in the Ascomycota and Basidiomycota ( dikaryon ) fungi was reviewed by Wallen and Perlin. [ 50 ] They concluded that the most plausible reason for maintaining this capability is the benefit of repairing DNA damage , caused by a variety of stresses, through recombination that occurs during meiosis . [ 50 ]
Three distinct processes in prokaryotes are regarded as similar to eukaryotic sex : bacterial transformation , which involves the incorporation of foreign DNA into the bacterial chromosome; bacterial conjugation , which is a transfer of plasmid DNA between bacteria, but the plasmids are rarely incorporated into the bacterial chromosome; and gene transfer and genetic exchange in archaea .
Bacterial transformation involves the recombination of genetic material and its function is mainly associated with DNA repair . Bacterial transformation is a complex process encoded by numerous bacterial genes, and is a bacterial adaptation for DNA transfer. [ 22 ] [ 23 ] This process occurs naturally in at least 40 bacterial species. [ 51 ] For a bacterium to bind, take up, and recombine exogenous DNA into its chromosome, it must enter a special physiological state referred to as competence (see Natural competence ). Sexual reproduction in early single-celled eukaryotes may have evolved from bacterial transformation, [ 24 ] or from a similar process in archaea (see below).
On the other hand, bacterial conjugation is a type of direct transfer of DNA between two bacteria mediated by an external appendage called the conjugation pilus. [ 52 ] Bacterial conjugation is controlled by plasmid genes that are adapted for spreading copies of the plasmid between bacteria. The infrequent integration of a plasmid into a host bacterial chromosome, and the subsequent transfer of a part of the host chromosome to another cell do not appear to be bacterial adaptations. [ 22 ] [ 53 ]
Exposure of hyperthermophilic archaeal Sulfolobus species to DNA damaging conditions induces cellular aggregation accompanied by high frequency genetic marker exchange [ 54 ] [ 55 ] Ajon et al. [ 55 ] hypothesized that this cellular aggregation enhances species-specific DNA repair by homologous recombination. DNA transfer in Sulfolobus may be an early form of sexual interaction similar to the more well-studied bacterial transformation systems that also involve species-specific DNA transfer leading to homologous recombinational repair of DNA damage. | https://en.wikipedia.org/wiki/Sexual_reproduction |
In biology , sexual segregation is the differential use of space , habitats , and resources by males and females, or the separation of males and females into different social groups outside the breeding season. Sexual segregation is widespread among animals , especially among vertebrates that live in groups , and has also been observed in plants. [ 1 ] [ 2 ] [ 3 ] [ 4 ] It was first formally proposed by Charles Darwin in his book The Descent of Man, and Selection in Relation to Sex . [ 1 ]
Sexual segregation has traditionally been defined as the differential use of space (spatial segregation) or habitat (habitat segregation) by males and females. Recently, it has also been defined as the separation of males and females into different social groups (social segregation) outside the breeding season. Some authors consider social segregation to be a by-product of habitat segregation but it is now known that social segregation can occur independently of habitat segregation. [ 1 ] [ 2 ] [ 5 ] Conradt (2005) argued that spatial segregation should be treated as a auxiliary concept as both habitat segregation and social segregation can lead to spatial segregation. [ 6 ]
This zoology –related article is a stub . You can help Wikipedia by expanding it .
This ecology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Sexual_segregation_(biology) |
Sexual selection has been observed in fungi as a part of their reproduction , although they also often reproduce asexually. In the basidiomycetes , the sex ratio is biased towards males, implying sexual selection there. Male–male competition to fertilize occurs in fungi including yeasts. Pheromone signaling is used by female gametes and by conidia, implying male choice in these cases. Female–female competition may also occur, indicated by the much faster evolution of female-biased genes in fungi.
Most fungi can produce asexually and sexually. Currently, sexual selection has been studied to occur more predominantly in the Ascomycota and Basidiomycota phyla. Although different sexes are not present within fungi, sexual selection can act due to the presence of different sex roles as well as different mating types as most fungi are hermaphroditic . [ 1 ] Sex roles can be distinguished in sexually producing filamentous fungi . For example, sexually producing ascomycetes can produce anisogamous gametes . The larger immobile gametes act as female gametes, while the smaller, motile gametes act as male gametes. Increased difference in the operational sex ratio (OSR) due to asymmetry between the sex roles leads to the production of more male gametes. In addition, variation within gamete quality which could affect offspring viability or fitness can also lead to differences in female/male gamete ratios. [ 2 ]
In addition, sexual selection can occur within fungi if there is a limiting number of a certain type of gamete. [ 1 ] The limiting gamete is typically the female gamete as they tend to be more costly to produce and invest more, energetically, in the zygote. [ 2 ]
Most fungi have a haploid-diploid life cycle . Sexual selection is much more crucial in the diploid phase as the product of the phase immediately undergoes meiosis and can no longer be fertilized again.
Mushroom-forming fungi within the phylum Basidiomycota produce sexually by the reciprocal migration of nuclei and have a male-biased OSR which aids in supporting that sexual selection is present within fungi. Although there are no traditional males present, there is variation between the mating types responsible for acting as the male or female sex role. Receiving mycelia act as the female gametes while the donating nucleus acts as the male gamete. Sexual selection might occur through male–male competition or by female choice . A study demonstrated that sexual selection does occur between the donating nucleus of the heterokaryon and the receiving homokaryon through the two nuclear types within the heterkaryon. These two nuclear types are in competition with each other to fertilize the homokaryon. Female choice between the nuclear types is also possible as there is a strong bias for one of the two nuclei. [ 1 ] However, it is more supported that competition between the donating nuclei is more responsible as it has been shown that there is a variation in the success of various nuclei independent of the receiving mycelium. [ 2 ] Some factors that may affect the nuclei's success include faster mitotic division, increased migration, and possibly a mechanism that suppresses mitotic division in the competition. [ 1 ]
Most basidiomycetes have two mating types, A and B, which are unlinked. However, the B locus codes for a larger amount of pheromones through subloci. Each subloci can produce many pheromones yet codes only one receptor resulting in a high redundancy of these pheromones. Although only one pheromone is necessary to fertilize, the presence of such a high amount increases the likelihood of that individual's pheromones to be received. This characteristic is hypothesized to have evolved as a result of sexual selection . [ 1 ]
Competition can occur within fungi as it does in plants and animals if an inequality in the ability to access one sex role or mating type is present. This inequality could result in increased competition for access to the other mating type. Competition can also occur if there is a variation in the quality of the gametes. Within fungi, there is competition to fertilize, which can be seen as the equivalent of male–male competition in plants and animals. Sexual selection in fungi aids in explaining certain characteristics including the high redundancy of pheromones in the B mating-type locus as well as strong pheromone signaling in yeasts. [ 1 ]
Male gametes have the ability to reproduce asexually as asexual spores if they fail to reproduce sexually. Some fungal species are capable of producing male gametes of two different sizes. Throughout evolution, the smaller gametes have lost the ability to produce asexually in order to increase the likelihood of fertilizing a female gamete by decreasing size and increasing both the amount and motility of the male gamete. This is most likely a result of direct competition as a trade-off was made in order to increase the likelihood of fertilization. [ 1 ]
Pheromone signaling is used within fungi to either attract a mate or to assess the quality of that gamete; and tends to be more effective when occurring over small distances. Female gametes are typically the ones responsibly for producing pheromones in order to attract a mate. [ 1 ] However, pheromones can also be released by conidia. [ 3 ] Male choice can occur in populations where there is a low concentration of male gametes, allowing them to be selective in which female to fertilize. The female with the highest concentration of pheromone is usually chosen. [ 1 ] In situations where fertilization may have to occur over long distances, water-soluble pheromones may be secreted as seen in the female gametes of an aquatic Chytridiomycetes . [ 2 ] The same similarly occurs within an aquatic oomycete algae species; also, a variation in the pheromone production related to the male reaction has been observed. Variations within the pheromone production as well as the response have been studied and found be affected by environmental conditions as well as developmental differences between the fungi. [ 3 ] Although not proven, the production of pheromones may lead to Fisherian runaway selection in which the production of pheromone increases due to the increase in its preference throughout generations. [ 1 ] [ 2 ]
In addition to pheromone signaling being used as a method in finding a mate, it also appears to be utilized as a method to assess mate quality. Pheromones are costly to produce due to post-translational modification and therefore may be subject to the handicap principle in which an organism cannot fake its fitness by producing pheromones. [ 1 ] In the isogamous budding yeast , Saccharomyces cerevisiae , pheromones are used to distinguish between different mating types and show a preference for higher concentrations of pheromones along with a rejection of lower concentrations. [ 2 ] However, all of the pheromone studies within fungi have been performed in a laboratory. More research is necessary on the effects of natural gamete density, motility, and pheromone production in nature. [ 1 ] [ 2 ]
Post-copulatory mechanisms may also be present within fungi through polyandry in which zygote -level sexual selection might occur. Within multicellular ascomycete fungi, a haploid mycelium produces a fruiting body which in turn produces many offspring that are also haploid. Each fruiting body has the potential to be fertilized by more than one male gamete. Laboratory experiments have shown that multiple matings are possible and the female has the ability to selectively abort fruiting bodies that have been inappropriately fertilized by a closely related yet incompatible species. [ 4 ]
A study has shown that female-biased genes evolve much faster than male-biased genes demonstrated by a rapid protein-level evolution . In most other eukaryotes, male-biased genes demonstrate a faster evolution. This may be due to specific reproductive traits within fungi, possibly allowing female–female competition to occur rather than male–male competition . This is also supported the passive nature of conidia during mating. Due to the presence of pheromones as well as the dispersal of male gametes, two or more female gametes may be attracted to one conidium, or male gamete. The presence of karyogamy further supports the possibility of female–female competition . Within N. crassa, the haploid mycelium undergoes growth as vegetative tissue prior to entering the mating cycle. This vegetative tissue can be used as a source of fertilization and can fuse with the trichogyne . This causes the female gamete to no longer be subject to male–male competition and further fertilization by a conidium. The female-biased genes that were studied and seen to evolve more rapidly than male-biased genes did so regardless of the mechanism of fertilization. Fertilization occurring by the fusion of a female nucleus and male conidium nucleus or between a female nucleus or nucleus from vegetative tissue did not alter this rate of evolution. [ 4 ] | https://en.wikipedia.org/wiki/Sexual_selection_in_fungi |
A sexual system is a distribution of male and female functions across organisms in a species . [ 1 ] [ 2 ] The terms reproductive system and mating system have also been used as synonyms. [ 3 ]
Sexual systems play a key role in genetic variation and reproductive success , and may also have led to the origin or extinction of certain species . [ 4 ] In flowering plants and animals, sexual reproduction involves meiosis , an adaptive process for repairing damage in the germline DNA transmitted to progeny. [ 5 ] The distinctions between different sexual systems is not always clear due to phenotypic plasticity . [ 2 ]
Interest in sexual systems goes back to Charles Darwin , who found that barnacles include some species that are androdioecious and some that are dioecious . [ 6 ]
Flowering plants may have dimorphic or monomorphic sexual systems . In monomorphic sexual systems, a combination of hermaphrodite , male , and/or female flowers may be present on the same plant. Monomorphic sexual systems include monoecy , gynomonoecy , andromonoecy , and trimonoecy . In dimorphic sexual systems , individual plants within a species only produce one sort of flower, either hermaphrodite or male, or female. Dimorphic sexual systems include dioecy , gynodioecy , androdioecy , and trioecy . [ 7 ]
Male ( a.k.a. staminate) flowers have a stamen but no pistil and produce only male gametes. Female (a.k.a. pistillate) flowers only have a pistil. Hermaphrodite (a.k.a. perfect, or bisexual) flowers have both a stamen and pistil. The sex of a single flower may differ from the sex of the whole organism: for example, a plant may have both staminate and pistillate flowers, making the plant as a whole a hermaphrodite. Hence although all monomorphic plants are hermaphrodites, different combinations of flower types (staminate, pistillate, or perfect) produces distinct monomorphic sexual systems. [ 8 ]
In animals, androdioecy , gynodioecy , and trioecy are referred to as mixed sexual systems ; [ 9 ] where hermaphrodites coexist with single sexed individuals. [ 10 ]
The term "gonochorism" is usually applied to animals while "dioecy" is applied to plants. [ 21 ] Gonochorism is the most common sexual system in animals, occurring in 95% of animal species. [ 22 ]
Leonard, Janet (2019-05-21), Transitions Between Sexual Systems: Understanding the Mechanisms Of, and Pathways Between, Dioecy, Hermaphroditism and Other Sexual Systems , Springer Publishing , ISBN 978-3-319-94139-4 | https://en.wikipedia.org/wiki/Sexual_system |
Sexually active life expectancy is the average number of years remaining for a person to be sexually active . This population-based indicator extends the concept of health expectancy to the measure of sexuality (via sexual activity). Calculation of sexually active life expectancy uses the age-specific prevalence data on sexual activity in conjunction with life table data on survival probabilities to partition the number of person-years into years with and without sexual activity, which is based on the Sullivan method. [ 1 ] The Sullivan method's objective is to understand the change of health in a given population over time. [ 2 ]
The measure of sexually active life expectancy was introduced by Lindau and Gavrilova. [ 3 ] [ 4 ] [ 5 ] Through their study of two cohorts, researchers Lindau and Gavrilova found that sexual activity, a good quality sex life, and interest in sex were associated with self rated health in a positive way. [ 6 ] Their research focused on midlife and later life health. This included ages 27 to 74 years and 57 to 85 years. In their findings, they concluded that a gender difference was present with increasing age. Evidence proved that men were more likely than women to be engaging in sexual activity. Men were also more likely to report that they were even interested in having sex and that they were having good quality sex. In addition, the research demonstrated that only 51.8% of women in a later stage of life reported being satisfied by their sexual life compared to 71.1% of men. [ 7 ] Furthermore, their research showed that men in good or excellent health participated in regular sexual activity lived an extra five to seven years, and women in substantially good health lived three to six years longer. Even though the gender gap is evident, the research provides a clear association between health and sexual activity.
A study of two large population-based U.S. surveys found that, on average, women expect fewer years of sexual activity, mainly due to prevalent widowhood among older women. This gender disparity is attenuated for people with a spouse or other intimate partner. The study also found that men tend to lose more years of sexually active life due to poor health. [ 5 ]
Sexually active life expectancy is associated with self-reports of good health in both men and women. Sexuality has been identified as an important attribute to overall health and a marker of quality of life . Sexual desire has also been attributed to good health, good sexual functioning, positive sexual self-esteem, and a skillful partner. [ 8 ] Physicians may find that sexually active life expectancy can be used as an incentive for patients to become (and stay) healthy. [ 5 ] Institutional settings such as residential care facilities should focus on offering an accepting environment for sexually active older people.
Although some people generalize that older adults do not participate in sex often, research shows that many older people enjoy participating in a variety of sexual activities. Barriers, both physically and mentally, is an important factor that influences older adults' sexual activities. These barriers can be seen at the individual, societal, and structural level. Some barriers include: lack of privacy, availability of sexual partner, mental health, and the impact of prescriptions on sexual desires. [ 9 ]
Age-related factors can be identified through the decline of health. This can include declining fitness and mobility levels. Biological changes, such as menopause for women, can cause an unpleasant experience during sex. This can include painful intercourse and a lack of sex drive, however, many women have reported that not having to worry about becoming pregnant made them enjoy sexual activity more. The presence of diseases such as arthritis , can also greatly affect a person's sexual activities, however, this is evident for any age range. [ 10 ] Factors such as a decrease in self esteem, confidence, and cognitive function can prohibit an older person from participating in sex or romantic partnerships. [ 11 ] Having to live in an assisted living home has also created a physical behavior. People are less likely to have the privacy that they want when they are surrounded by other elderly people and nurses. [ 9 ]
Despite the known benefits of continued sexual activity on physical, mental, and emotional health, nursing home residents often face barriers to sexual expression. These barriers rob them of fundamental aspects of self-worth, emphasizing the need for societal and institutional changes to support the sexual rights of the elderly. [ 12 ] A study conducted in Wisconsin nursing homes found that elderly residents believe sexual activity is appropriate for their peers but often do not engage in it themselves, mainly due to lack of opportunity. This study also highlighted the reluctance of medical and behavioral personnel to discuss the topic, indicating a need for more open and supportive environments. [ 13 ]
One of the main reasons residential homes do not care to facilitate intimate relationships is because employees may have a hard time distinguishing a desired sexual partnership from an undesired one. The residential care faces possible issues if a resident is being taken advantage of, especially if they are physically or mentally incapable to protect themselves. Facilities usually have a safeguarding and protection policy which monitors any relationship to prevent abuse. [ 14 ]
Addressing inappropriate sexual behaviors in nursing homes can be challenging for staff. Strategies for managing such behaviors include improving privacy, educating staff, allowing conjugal or home visits, and assessing the decision-making capacity of cognitively impaired residents. Physicians can play a key role in removing barriers to sexual expression. [ 15 ] | https://en.wikipedia.org/wiki/Sexually_active_life_expectancy |
The sexy son hypothesis in evolutionary biology and sexual selection , proposed by Patrick J. Weatherhead and Raleigh J. Robertson of Queen's University in Kingston, Ontario in 1979, [ 1 ] states that a female's ideal mate choice among potential mates is one whose genes will produce males with the best chance of reproductive success . This implies that other benefits the father can offer the mother or offspring are less relevant than they may appear, including his capacity as a parental caregiver, territory and any nuptial gifts . Fisher's principle means that the sex ratio (except in certain eusocial insects ) is always near 1:1 between males and females, yet what matters most are her "sexy sons'" future breeding successes, more likely if they have a promiscuous father, in creating large numbers of offspring carrying copies of her genes. [ 2 ] [ clarification needed ] This sexual selection hypothesis has been researched in species such as the European pied flycatcher . [ 1 ]
Female mating preferences are widely recognized as being responsible for the rapid and divergent evolution of male secondary sex characteristics . [ 3 ] In 1915, Ronald Fisher wrote: [ 4 ]
Granted that while this taste and preference prevails among the females of the species, the males will grow more and more elaborate and beautiful tail feathers, the question must be answered "Why have the females this taste? Of what use is it to the species that they should select this seemingly useless ornament?"
The first step to a solution lies in the fact that the success of an animal in the struggle for existence is not measured only by the number of offspring which it produces and rears, but also by the probable success of these offspring. So that in selecting a mate from a number of different competitors, it is important to select that one which is most likely to produce successful children. [ 4 ]
In 1976, prior to Weatherhead and Robertson's paper, [ 1 ] Richard Dawkins had written in his book The Selfish Gene :
In a society where males compete with each other to be chosen as he-men by females, one of the best things a mother can do for her genes is to make a son who will turn out in his turn to be an attractive he-man. If she can ensure that her son is one of the fortunate few males who wins most of the copulations in the society when he grows up, she will have an enormous number of grandchildren. The result of this is that one of the most desirable qualities a male can have in the eyes of a female is, quite simply, sexual attractiveness itself. [ 5 ]
Ronald Fisher 's principle, as published in his book The Genetical Theory of Natural Selection , is one of several possible explanations for the highly diverse and often astonishing ornaments of animals. [ 6 ] [ 7 ] [ 8 ] If females choose physically attractive males, they will tend to get physically attractive sons, and, thus more grandchildren, because other choosy females will prefer their attractive, sexy sons. The theory will function regardless of the physical or behavioral trait a female chooses, as long as it is heritable (that is, the trait varies between individuals of the population), because it is possessing the trait that makes males attractive, and not the qualities of the trait in itself.
Once a preference becomes established, females choosing males with elaborate secondary sexual traits will produce sons that carry alleles for the trait and produce daughters that carry alleles for the preference, generating genetic coupling that will drive self-reinforcing coevolution of both trait and preference, due to the mating advantage of males with the trait, creating a Fisherian runaway sexy sons process. [ 8 ] Similar models have been proposed for postcopulatory female preferences, such as the time at which females removed the male's sperm ampulla after mating. Sexual selection by direct and/or indirect benefits as well as sexual conflict determine the evolution of animal mating systems. [ 9 ]
In its original context, the "narrow-sense sexy son hypothesis" of Weatherhead and Robertson refers to mating systems with care from both parents. In these mating systems, females that mate with a polygynous male normally receive less assistance than females mated with a monogamous male, [ 10 ] and thus suffer from direct fitness consequences that have to be (at least) compensated for by the breeding successes of their sexy sons. On the other hand, a "broad-sense sexy son hypothesis" encompasses both polygyny and promiscuous mating systems, with and without care from both parents. Alatalo (1998) [ 11 ] argues that the costs of any additional choice may be so minor that female choice for honestly signaling males, that is good genes, may evolve even if the indirect benefits on offspring quality are small. A similar argument can be made for the sexy son hypothesis if mates of attractive males do not suffer any direct fitness consequences. [ 12 ]
Sexual conflict refers to the conflicting goals of breeding males and females. It describes the diverging interests of males and females in optimizing their fitness. From the viewpoint of any one partner, the best outcome would be for the partner's mate to care for the young, thus freeing up his or her own resources (e.g., time and energy) that s/he—but typically he—can invest in further sex that may create additional offspring. In polygynous mating systems, sexual conflict means the optimization of male reproductive success by having mated with multiple females, even though the reproductive success of a polygynously mated female is thereby reduced. [ 12 ] Such can be the case for the Guianan cock-of-the-rocks , whose male members spend a majority of their time and energy maintaining their plumage and attempting to seek the most matings. Females, on the other hand, spend their time building and maintaining their nest where they will lay their eggs and raise the young.
"Good genes" theory proposes that females select males seen to have genetic advantages that increase offspring quality. Increased viability of offspring provides compensation for any lower reproductive success that results from their being "picky". The good-gene hypothesis for polyandry proposes that when females encounter better males than their previous mates, they re-mate in order to fertilize their eggs with the better male's sperm. [ 7 ]
Dung beetles who have selected mates with better genetics tend to have offspring that survive longer and are more able to reproduce than those that do not pick mates with genetic quality. This suggests that carefully choosing a mate is beneficial. [ 13 ]
Another study notes that pronghorn females engage in an obvious and energetically expensive mate sampling process to identify vigorous males. Though each female selects independently, the outcome is that a small proportion of the herd's males sire most young. Offspring of attractive males were more likely to survive to weaning and to age classes as late as 5 years, apparently due to faster growth rates. [ 14 ] Because pronghorn males do not have costly ornaments , the authors conclude that female choice for good genes can exist in the absence of obvious sexual selection cues such as elaborate antlers.
The sexy son hypothesis is closely related to the good genes assumption and the Fisherian runaway selection process. Like good genes, the sexy son hypothesis assumes the existence of indirect genetic benefits that are able to compensate for any inferior direct reproductive success (i.e., fewer offspring). The main difference between good genes and the sexy son hypothesis is that the latter assumes an indirect effect due to the attractiveness of the sons, whereas good genes focus on the viability of both sons and daughters. However, "attractiveness" is not narrowly defined, and can refer to every trait that increases a male's probability to become polygynous.
Good-sperm models predict positive genetic associations between a male's sperm competitiveness and the general viability of his offspring, [ 7 ] whereas sexy-sperm models predict that multiple-mating females produce more grandchildren. [ 15 ] [ 16 ] As with precopulatory processes, postcopulatory models predict that the trait in males that determines fertilization success will become genetically coupled with the mechanism by which females choose the sperm of preferred males. [ 17 ] | https://en.wikipedia.org/wiki/Sexy_son_hypothesis |
The Seyferth–Gilbert homologation is a chemical reaction of an aryl ketone 1 (or aldehyde ) with dimethyl (diazomethyl)phosphonate 2 and potassium tert-butoxide to give substituted alkynes 3 . [ 1 ] [ 2 ] Dimethyl (diazomethyl)phosphonate 2 is often called the Seyferth–Gilbert reagent . [ 3 ]
This reaction is called a homologation because the product has exactly one additional carbon more than the starting material.
Deprotonation of the Seyferth–Gilbert reagent A gives an anion B , which reacts with the ketone to form the oxaphosphetane D . Elimination of dimethylphosphate E gives the vinyl diazo -intermediate Fa and Fb . The generation of nitrogen gas gives a vinyl carbene G , which via a 1,2-migration forms the desired alkyne H .
The dimethyl (diazomethyl)phosphonate carbanion can be generated in situ from dimethyl-1-diazo-2-oxopropylphosphonate (also called the Ohira-Bestmann reagent ) by reaction with methanol and potassium carbonate as the base by cleavage of the acetyl group as methyl acetate . Reaction of Bestmann's reagent with aldehydes gives terminal alkynes often in very high yield and fewer steps than the Corey–Fuchs reaction . [ 4 ] [ 5 ]
The use of the milder potassium carbonate makes this procedure much more compatible with a wide variety of functional groups .
Recently a safer and more scalable approach has been developed for the synthesis of alkynes from aldehydes. This protocol takes advantage of a stable sulfonyl azide, rather than tosyl azide, for the in situ generation of the Ohira−Bestmann reagent. [ 6 ]
Another modification for less reactive aldehydes is made by replacement of potassium carbonate with caesium carbonate in MeOH and results in a drastic [ quantify ] yield increase. [ 7 ] | https://en.wikipedia.org/wiki/Seyferth–Gilbert_homologation |
Sfold is a software program developed to predict probable RNA secondary structures through structure ensemble sampling and centroid predictions [ 1 ] [ 2 ] with a focus on assessment of RNA target accessibility, [ 3 ] for major applications to the rational design of siRNAs [ 4 ] in the suppression of gene expressions, and to the identification of targets for regulatory RNAs particularly microRNAs . [ 5 ] [ 6 ]
The core RNA secondary structure prediction algorithm is based on rigorous statistical (stochastic) sampling of Boltzmann ensemble of RNA secondary structures, enabling statistical characterization of any local structural features of potential interest to experimental investigators. In a review on nucleic acid structure and prediction, [ 7 ] the potential of structure sampling described in a prototype algorithm [ 8 ] was highlighted. With the publication of the mature algorithms for Sfold, [ 1 ] [ 2 ] the sampling approach became the focus of a review [ 9 ] Both the sampling approach and the centroid predictions were discussed in a comprehensive review. [ 10 ] As an application module of the Sfold package, the STarMir program [ 11 ] has been widely used for its capability in modeling target accessibility. [ 6 ] STarMir was described in an independent study on microRNA target prediction [ 12 ] STarMir predictions have been used in an attempt to derive improved predictions. [ 13 ] Predictions by Sfold have led to new biological insights. [ 14 ] The novel ideas of ensemble sampling and centroids have been adopted by others not only for RNA problems, but also for other fundamental problems in computational biology and genomics . [ 15 ] [ 16 ] [ 17 ] [ 18 ] [ 19 ]
An implementation of stochastic sampling has been included in two widely used RNA software packages, RNA Structure [ 20 ] and the ViennaRNA Package , [ 21 ] which are also based on the Turner RNA thermodynamic parameters. [ 22 ] Sfold was featured on a Nucleic Acids Research cover, [ 23 ] and was highlighted in Science NetWatch. [ 24 ] The underlying novel model for STarMir [ 11 ] was featured in the Cell Biology section of Nature Research Highlights . [ 25 ]
Sfold runs on Linux , and is freely available to the scientific community for non-commercial applications, and is available under license for commercial applications. Both the source code and the executables are available at GitHub . | https://en.wikipedia.org/wiki/Sfold |
Sha-Mail ( 写メール , Sha Mēru ) was a 2G mailing and picture messaging service launched by J-Phone (now Softbank ) in 2000 that allowed users to take a photo with their mobile phone and send it to another user on the service as an email attachment. [ 1 ] A related service introduced in 2002, Video Sha-Mail, let users record and send videos as well. [ 2 ] Sha-Mail was widely successful upon its launch, became a household name in Japan, [ 3 ] and sparked a boom in camera phone services worldwide. [ 4 ] The term derives from sha , the first part of the Japanese word shashin ( 写真 , 'picture') , and mail (from email ). [ 5 ]
Sha-Mail development was led by Keiji Takao, who previously worked for Mazda . Takao came up with the idea on a sight-seeing trip to Hakone with his parents, where he saw a woman on a cable car using her mobile phone, apparently struggling to operate the device and unable to send a photo of the view. [ 2 ] He recalled: "Here she was, a lady furiously typing into her handset and trying to relay her feelings and excitement to her children or husband. I said to myself, 'Gee, wouldn't it be easier if there was some sort of an image to send with?'" [ 6 ] Takao also reportedly took inspiration from a survey he had read about adolescent girls keeping disposable cameras alongside their phones in their purse. [ 7 ] J-Phone, meanwhile, was under pressure from competitors KDDI , which had a faster network, and NTT Docomo , which was preparing to move to 3G , and the company believed it could differentiate itself by focusing on email. [ 6 ]
J-Phone launched the Sha-Mail service in November 2000 with the help of electronics company Sharp Corporation , who developed the J-SH04 phone with a built-in, back-facing CCD camera. [ 2 ] The J-SH04 was among the first phones in the world with a fully-integrated camera, and at the time, Sha-Mail was Japan's only service of its kind. [ 3 ]
The service was quite successful on the market, particularly with young people. J-Phone had sold around 3 million handsets with Sha-Mail enabled by January 2022. [ 1 ] Almost three years later, 10 million users were on the service, [ 2 ] with around 5 million users using Movie Sha-Mail. In 2002 Vodafone , which had by that point acquired J-Phone, launched Vodafone live! as a global service. By December 2002, the European launch of Vodafone live! brought in more than 380,000 users. [ 6 ]
This rapid growth helped J-Phone move from #3 to #2 in total wireless data subscribers. J-Phone's competitors followed suit. Market leader NTT Docomo introduced a similar service with Sharp called i-shot and another named Foma, KDDI's au introduced "Photo Mail" and "Movie Mail" services, and KDDI subsidiary TU-KA introduced "Picture Mail." [ 7 ] In the US, AT&T (a NTT Docomo affiliate) launched the mMode Pix feature on Sony Ericsson T68i devices. [ 4 ] Sha-Mail's popularity also spawned tie-ins such as a magazine called "J-Phone Sha-mail Hearts" [ 7 ] and the TV Aichi series Syamekke , which encouraged users to send in photos and text messages relating to weekly topics, later to be broadcast on the program. [ 1 ]
In November 2002, Japan's fair trade commission raided Vodafone's headquarters upon an accusation that the company had prevented retailers from lowering the cost of Sha-Mail enabled handsets upon launch. [ 8 ]
Though Vodafone planned to make Sha-Mail a centerpiece of its 3G service, [ 4 ] the company lagged well behind its competitors in moving to 3G and capturing users; as of 2004 fewer than 20% of Vodafone subscribers were subscribed to 3G. [ 9 ] Thus the now-obsolete Sha-Mail never upgraded to 3G, effectively ending Sha-Mail once support for 2G networks ceased. [ citation needed ]
The word Japanese word shamēru , often abbreviated to shame ( 写メ ), now commonly refers to any text message with an image attached. [ 3 ] | https://en.wikipedia.org/wiki/Sha-Mail |
Shading coefficient (SC) is a measure of thermal performance of a glass unit (panel or window ) in a building .
It is the ratio of solar gain (due to direct sunlight) passing through a glass unit to the solar energy which passes through 3mm Clear Float Glass. [ 1 ] It is an indicator of how well the glass is thermally insulating ( shading ) the interior when there is direct sunlight on the panel or window.
The shading coefficient depends on the color of glass and degree of reflectivity . It also depends on the type of reflective metal oxides for the case of reflective glass. Sputter -coated reflective and/or sputter -coated low-emissivity glasses tend to have lower SC compared to the same pyrolitically -coated reflective and/or low-emissivity glass.
The value ranges between 1.00 and 0.00, but experiments [ which? ] show that the value of the SC is typically between 0.98 and 0.10. The lower the rating, the less solar heat is transmitted through the glass, and the greater its shading ability.
Solar properties play a significant role in the selection of glass, especially in regions or cardinal directions with high solar exposure. It becomes less significant in situations where direct sunlight is not a major factor (e.g., windows completely shaded by overhangs).
Window design methods have moved away from Shading Coefficient to Solar Heat Gain Coefficient (SHGC), which is defined as the fraction of incident solar radiation that actually enters a building through the entire window assembly as heat gain (not just the glass portion). Though shading coefficient is still mentioned in manufacturer product literature and some industry computer software, [ 2 ] it is no longer mentioned as an option in the handbook widely used by building energy engineers [ 3 ] or model building codes. [ 4 ] Industry technical experts recognized the limitations of SC and pushed towards SHGC before the early 1990s. [ 5 ]
A conversion from SC to SHGC is not necessarily straightforward, as they each take into account different heat transfer mechanisms and paths (window assembly vs. glass-only). To perform an approximate conversion from SC to SHGC, multiply the SC value by 0.87. | https://en.wikipedia.org/wiki/Shading_coefficient |
ShadowTV , founded in 2001, provides all-digital continuous-access to live and archived television content via the web. ShadowTV operates two divisions: ShadowTV Monitoring, and ShadowMedia.
In 2008, the Republican National Convention and Democratic National Convention named ShadowTV as their official monitoring service. [ 1 ] [ 2 ]
In 2009, Cengage announced it would use video from ShadowTV's seven-year archive to supplement its current archive of news broadcasts . [ 3 ]
This article about an IT-related or software-related company or corporation is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/ShadowTV |
In organizations, shadow IT refers to information technology (IT) systems deployed by departments other than the central IT department, to bypass [ 1 ] limitations and restrictions that have been imposed by central information systems. [ 2 ] While it can promote innovation and productivity, shadow IT introduces security risks and compliance concerns, especially when such systems are not aligned with corporate governance. [ 3 ]
Information systems in large organizations can be a source of frustration for their users. [ 2 ] In order to bypass limitations of solutions provided by a centralized IT department, as well as restrictions that are deemed detrimental to individual productivity, non-IT departments might develop independent IT resources and for the specific or urgent need or requirements. [ 4 ] In some cases, IT specialists could be recruited or software solutions procured outside of the centralized IT department, sometimes without the knowledge, or approval of corporate governance channels.
Although often perceived as attempts to undermine corporate governance, the existence of shadow IT often is an indicator of needs from individual departments not being satisfied from a centrally managed information ecosystem. Thus the immediate benefits of shadow IT are as follows:
In addition to information security risks, some of the implications of shadow IT are: [ 6 ] [ 7 ]
Shadow IT increases the likelihood of uncontrolled data flows, making it more difficult to comply with various legislations, regulations or sets of best practices.
These include, but are not limited to:
Within an organization, the amount of shadow IT activity is by definition unknown, especially since departments often hide their shadow IT activities as a preventive measure to ensure their ongoing operations. Even when figures are known, organizations are reluctant to voluntarily admit their existence. As a notable exception, The Boeing Company has published an experience report [ 1 ] describing the number of shadow applications which various departments have introduced to work around the limitations of their official information system.
According to Gartner, by 2015, 35 percent of enterprise IT expenditures for most organizations will be managed outside the central IT department's budget. [ 11 ]
A 2012 French survey [ 12 ] of 129 IT managers revealed some examples of shadow IT :
Examples of these unofficial data flows include USB flash drives or other portable data storage devices, instant messaging software, Gmail or other online e-mail services, Google Docs or other online document sharing and Skype or other online VOIP software—and other less straightforward products: self-developed Access databases and self-developed Excel spreadsheets and macros . Security risks arise when data or applications move outside protected systems, networks, physical location, or security domains.
BankAmerica employees began deploying personal computers within the company in late 1981. While the financial firm already extensively used large computers, as the data processing budget did not account for personal computers, individual employees and offices bought them and expensed them as office supplies . After the purchasing department in summer 1982 discovered unusually large purchases from Computerland stores, Bank of America allotted a acquisition budget for small computers and standardized on the IBM PC . By early 1983 all executives including president Sam Armacost reportedly had IBM PCs. [ 13 ] | https://en.wikipedia.org/wiki/Shadow_IT |
Shadow matching (a.k.a. Shadow mapping) is a new positioning method that improves positioning accuracy of global navigation satellite systems (GNSS) in urban environments. The shadow matching positioning principle was first proposed and the name 'shadow matching' was first introduced by Paul D Groves. [ 1 ] The principle of shadow matching combines two commonly known principles together: GNSS signal availability determination using 3D building models and the fingerprinting-like positioning techniques.
The principle of shadow matching is simple. Due to obstruction by buildings in urban canyons, some of the GNSS satellites will be receivable in some parts of a street, but not all of them. Whether each direct signal is receivable can be predicted using a 3D city model. Consequently, by determining whether a direct signal is being received from a given satellite, the user can localize their position to within one of two areas of the street. By considering other satellites, the position solution may be refined further. At each epoch, a set of candidate user positions is generated close to the user's low-accuracy conventional GNSS positioning solution. At each candidate user position, the predicted satellite visibility is matched with the real observations. The candidate position that has the best match between the prediction and the real observations can be deemed the shadow matching positioning solution. This process can be conducted epoch by epoch, so the GNSS user can be either static or dynamic. | https://en.wikipedia.org/wiki/Shadow_Matching |
A shadow biosphere is the hypothesis of a hypothetical microbial biosphere of Earth that would use radically different biochemical and molecular processes from that of currently known life. Although life on Earth is relatively well studied, if a shadow biosphere exists, it may still remain unnoticed because the exploration of micro-organisms targets primarily the biochemistry of macro-organisms.
It has been proposed that the early Earth hosted multiple origins of life, some of which produced chemical variations on life as we know it. [ 1 ] [ 2 ] Some argue that these alternative life forms could have become extinct, either by being out-competed by other forms of life, or they might have become one with the present day life via mechanisms like lateral gene transfer . [ 1 ] Others, however, argue that this other form of life might still exist to this day.
Steven A. Benner, Alonso Ricardo, and Matthew A. Carrigan, biochemists at the University of Florida , argued that if organisms based on RNA once existed, they might still be alive today, unnoticed because they do not contain ribosomes , which are usually used to detect living microorganisms. They suggest searching for them in environments that are low in sulfur , environments that are spatially constrained (for example, minerals with pores smaller than one micrometre ), or environments that cycle between extreme hot and cold. [ 3 ]
Other proposed candidates for a shadow biosphere include organisms using different suites of amino acids in their proteins or different molecular units (e.g., bases or sugars) in their nucleic acids, [ 4 ] having a chirality opposite of ours, using some of the nonstandard amino acids , or using arsenic instead of phosphorus , [ 5 ] having a different genetic code , or even another kind of chemical for its genetic material that are not nucleic acids ( DNA nor RNA ) chains or biopolymers . [ 6 ] Carol Cleland , a philosopher of science at the University of Colorado (Boulder), argues that desert varnish , whose status as biological or nonbiological has been debated since the time of Darwin, should be investigated as a potential candidate for a shadow biosphere. [ 1 ] [ 2 ] [ improper synthesis? ]
Existence of a shadow biosphere could mean that life has independently evolved on Earth more than once, which means that microorganisms may exist on Earth which have no evolutionary connection with any other known form of life. [ 6 ] [ 7 ] [ 8 ] It is suggested that if an alternate form of microbial life on Earth is discovered, the odds are good that life is also common elsewhere in the universe. [ 6 ] [ 7 ]
Methods used by proponents and conclusions drawn from experiments that purport to show evidence of shadow biospheres have been criticized. For example, evidence that once seemed to support arsenic as a substitute for phosphorus in DNA could have resulted from lab or field contamination, and DNA that includes arsenic is chemically unstable. [ 9 ] | https://en.wikipedia.org/wiki/Shadow_biosphere |
A shadow board is a type of tool board for organizing a set of tools; the board defines where particular tools should be placed when they are not in use. [ 1 ] Shadow boards have the outlines of a work station's tools marked on them, allowing operators to identify quickly which tools are in use or missing. The boards are commonly located near the work station where the tools are used. Shadow boards are often used in the manufacturing environment to improve a facility's lean six sigma capabilities. [ 2 ]
Shadow boards reduce time spent looking for tools and also reduce losses. [ 3 ] They improve work station safety because tools are replaced safely after use, rather than becoming potential hazards. [ citation needed ] | https://en.wikipedia.org/wiki/Shadow_board |
The shadow effect [ 1 ] is a phenomenon seen in genetic studies that use noninvasive genetic data collection methods. It occurs when there are not enough loci and/or loci that have low variance of alleles within the population. As a result, researchers can capture two separate individuals and mistakenly label them as the same individual. This can create a negative bias in the data and portray a population as smaller and less genetically diverse than it is. This is most commonly seen in collection methods that rely on environmental DNA (eDNA) which is collected directly from the environment (such as feces or hair removed from the ground). [ 2 ] The accuracy of non-invasive collection data can be increased by increasing the amount of loci being examined during the study. [ 1 ]
There are several types of rarefaction methods that can be used to estimate the size of a hard monitor species. The study of population size and density falls under demography , the study of populations of any kind of organism. [ citation needed ]
Mark and recapture is a common form of data collection involving species with large populations. Being able to capture and mark a species in a noninvasive way allows for accurate readings of the population's size, both total and effective over several rounds of recapture. However, for species that are difficult to capture or view directly such as endangered species , it can be near impossible to use the mark-recapture method to obtain genetic samples. [ citation needed ]
Another method for population size estimation is a real-time polymerase chain reaction (qPCR). qPCR is a molecular approach that measures the amplification of DNA over time rather than just at the end of the reaction. [ 3 ] This method is useful because it can rely on eDNA to give an estimate of how abundant a species is in a given habitat. [ citation needed ]
Noninvasive forms of data collection can be achieved through the collection of fur, feces or other fragments of DNA-rich material left behind (eDNA). [ 1 ] Once considered costly, modern advancements have allowed for non-invasive data collection to become easier and provide more genetic information about a population. [ 4 ] DNA-Barcoding is a method of species identification that uses eDNA to determine the unique genetic makeup of individuals and their species. This method is that it requires a balancing act: Maintaining enough loci markers in the genetic data, and remaining cost-effective. [ citation needed ]
Probability of Identity (PI AV ) is the probability of a randomly selected sample from a population producing the same genotype twice if not enough loci are used during the study. Should loci with little genetic variation or few loci are selected, it is likely that multiple individuals will be identified as too genetically similar, with individuals being excluded from the data set. This creates a negative statistical bias , pushing the results towards a smaller, less genetically diverse mean than is accurate to the population. This is known as the shadow effect. [ 1 ]
The Cabrera vole ( Microtus cabrerae ) is a small, endangered rodent that belongs to the Microtus genus. Existing primarily in Portugal, populations can be difficult to estimate using typical mark-recapture methods due to their small size and ability to quickly disperse over large swaths of prairie land. [ 4 ] With the introduction and reduced cost of using environmental DNA (in this case feces) were able to be used in a relatively low cost experiment to estimate the population size of the Cabrera vole in southern Portugal in return for sacrificing demographic (age, sex, health) information. [ 4 ] | https://en.wikipedia.org/wiki/Shadow_effect |
Shadow enhancers are groups of DNA regulatory sequences that function alongside primary enhancers to regulate gene expression . Originally discovered in Drosophila , shadow enhancers have since been identified in a wide range of organisms, including insects , plants , and mammals . [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] Shadow enhancers work alongside primary enhancers to drive overlapping gene expression patterns, which stabilizes gene expression against genetic and environmental fluctuations. [ 6 ] [ 1 ] [ 7 ] [ 8 ] Shadow enhancers can act at a large genomic range, are highly evolutionarily conserved and interact with many molecules to drive gene expression patterns. [ 7 ] [ 8 ] [ 9 ] Shadow enhancers play a crucial role in development and early embryogenesis by maintaining stable expression of a variety of genes. [ 8 ] [ 6 ]
Shadow enhancers were first described in 2008 by Michael Levine and his research group at the University of California, Berkeley. [ 1 ] [ 7 ] Their research in Drosophila investigated the transcription factor Dorsal and its target genes. Through characterization of enhancers using ChIP-chip assays , they found that some enhancers appeared to produce gene expression patterns that overlap with those produced by the primary enhancer. Initially, shadow enhancers were believed to act redundantly to the function of the primary enhancer to ensure proper gene expression, despite environmental or genetic variability. [ 1 ]
Shadow enhancers are regulatory DNA elements that play a critical role in stabilizing gene expression and minimizing variability. They work alongside primary enhancers to ensure consistent transcriptional activity, even under fluctuating environmental conditions or genetic disturbances. [ 10 ] [ 11 ] One of their primary functions is to provide a backup mechanism for gene regulation; if a primary enhancer is mutated or damaged, shadow enhancers can compensate and maintain proper gene expression patterns. [ 12 ] Therefore, genes that are regulated by these redundant enhancer regions are more resistant to mutations within their non-coding regions. [ 8 ]
Shadow enhancers, like any enhancer, do not directly interact with the promoter of a gene to regulate gene expression. Shadow enhancers instead directly bind transcription factors, which can then interact with the promoter. [ 7 ] Different shadow enhancers can interact with many different transcription factors in order to indirectly interact and affect the promoter of a gene. Shadow enhancers are a part of a multi-enhancer complex, therefore they can compete with one another to influence a single promoter. In contrast, multiple shadow enhancers can also have an additive effect on a single promoter, therefore boosting its intensity or activity. As well, shadow enhancers can work on multiple non-connected promoters in order to influence development at its different stages. [ 13 ]
A key characteristic of shadow enhancers is their functional redundancy, which arises from their ability to functionally overlap with primary enhancers in controlling gene expression. This redundancy enhances the strength of gene regulation by ensuring that multiple enhancers contribute to the expression of a single gene. If a gene is regulated not only by a primary enhancer but also by two or more shadow enhancers, then the gene has additional protection against the failure of a single regulatory element. In contrast, genes regulated solely by a primary enhancer lack this redundancy, making them more vulnerable to regulatory disruptions. [ 8 ] Shadow enhancers exhibit varying levels of redundancy across different contexts and timeframes. Some shadow enhancers' redundant function can be restricted to a small timeframe or a small number of cells, while others can have a more extensive overlap and thus are more functionally redundant. [ 2 ]
While shadow enhancers' primary function is to drive overlapping gene expression patterns in order to fine-tune gene expression patterns, some shadow enhancers also play important non-redundant roles. Shadow enhancers may be redundant in one developmental stage or tissue type and non-redundant in another, indicating they can have their own essential functions. [ 2 ] Some shadow enhancers are redundant under normal conditions but non-redundant under extreme conditions, highlighting their importance in stabilizing gene expression in unfavourable conditions. [ 2 ] [ 10 ] [ 11 ]
Shadow enhancers can be positioned at various distances from their target genes, often farther away compared to primary enhancers. [ 7 ] Shadow enhancers are cis-acting regulatory elements , thus they are located on the same DNA molecule as the gene they regulate. [ 9 ] They may reside within intronic regions or beyond adjacent genes, exerting their regulatory influence over a broad genomic range. [ 7 ] Although both shadow and primary enhancers contribute to gene expression, shadow enhancers tend to operate from more distal genomic locations. [ 8 ]
Shadow enhancers are evolutionary conserved sequences that are present in a wide range of organisms, including both vertebrate and invertebrate species. [ 8 ] Shadow enhancers have been shown to be more conserved than non-redundant enhancers, which suggests their function is crucial not only in the development of an organism but also throughout evolutionary time. Genes important in development have complex and highly conserved regulation, which explains why shadow enhancers that regulate these genes are highly conserved. Shadow enhancers' partial redundancy also explains why they are maintained over evolutionary time, as they serve important redundant and non-redundant functions that contributes to the proper development of organisms. [ 2 ] The conservation of shadow enhancers across taxonomic groups showcases just how important shadow enhancers are in the viability of organisms. [ 8 ]
Shadow enhancers must interact with many factors in order to regulate and reduce variability in gene expression. [ 1 ] [ 2 ] [ 6 ] [ 7 ] Shadow enhancers contain clustered binding sites, and the binding of a transcription factor to these sites can either activate or repress gene expression. [ 7 ] Shadow enhancers have a higher proportion of functional sites than non-redundant enhancers, suggesting they are involved in complex regulation of gene expression. [ 2 ]
Shadow enhancers play a critical role in embryogenesis, particularly in defining body patterning. [ 14 ] [ 15 ] By modulating transcriptional activation strength, timing, and location, they ensure precise control of gene expression during development. [ 14 ] Their ability to fine-tune gene expression levels helps maintain stability, allowing organisms to grow and develop properly despite environmental stresses. [ 16 ] [ 6 ] [ 12 ] Shadow enhancers can compensate for mutations in primary enhancers, acting as a buffer against genetic and environmental fluctuations. [ 8 ] [ 11 ] [ 12 ] This buffering capacity ensures consistent and precise gene expression patterns, which are crucial for proper body development and overall developmental stability. [ 8 ] [ 6 ] Mutations to shadow enhancers confer a higher fitness consequence than mutations to non-redundant enhancers, highlighting their importance in proper development and thus viability of organisms. [ 2 ] Shadow enhancers are important in the regulation of many genes involved in development and have been well characterized in Drosophila . [ 16 ] [ 11 ] [ 12 ] [ 15 ]
Shadow enhancers are important in the regulation of the twin of eyeless ( toy ) gene in Drosophila. The toy gene is crucial for eye development, therefore these shadow enhancers work together to drive toy expression during early embryogenesis. Their overlapping yet distinct expression patterns ensures consistent toy expression during critical developmental processes. [ 11 ]
Shadow enhancers play a crucial role in regulation of the snail gene during Drosophila embryogenesis. The snail gene encodes a transcription factor that is essential for epithelial-mesenchymal transitions in many developmental processes. Shadow enhancers maintain snail expression under environmental and genetic disturbances in order to ensure proper gastrulation . [ 12 ]
Shadow enhancers are important in the regulation of the Krüppel ( Kr ) gene in Drosophila. The Krüppel gene is involved in early segmentation and creates precise patterning along the anterior-posterior axis of the Drosophila embryo. Shadow enhancers are crucial in facilitating Kr expression, ultimately ensuring accurate spacial and temporal expression of Krüppel . Shadow enhancers are important in fine-tuning gene expression patterns during critical developmental stages. [ 15 ] [ 16 ]
Two shadow enhancers have been identified to be involved in the regulation of the sonic hedgehog (SHH) gene in mice. [ 1 ] In vertebrates, SHH is important in forming the ventral midline of the central nervous system . Without shadow enhancers to ensure proper expression of Shh, the brain can become malformed. Therefore, shadow enhancers are crucial in ensuring proper development and stabilizing gene expression of important developmental genes, like SHH. [ 17 ] | https://en.wikipedia.org/wiki/Shadow_enhancer |
The shadow square , also known as an altitude scale , [ 1 ] was an instrument used to determine the linear height of an object, in conjunction with the alidade , for angular observations. An early example was described in an Arabic treatise likely dating to 9th or 10th-century Baghdad . [ 2 ] Shadow squares are often found on the backs of astrolabes .
The main use of a shadow square is to measure the linear height of an object using its shadow. It does so by simulating the ratio between an object, generally a gnomon , and its shadow. If the Sun's ray is between 0 degrees and 45 degrees the umbra versa (Vertical axis) is used, between 45 degrees and 90 degrees the umbra recta (Horizontal axis) is used and when the Sun's ray is at 45 degrees its shadow falls exactly on the umbra media (y=x) [ 3 ] It was used during the time of medieval astronomy to determine the height of, and to track the movement of celestial bodies such as the Sun when more advanced measurement methods were not available. These methods can still be used today to determine the altitude, with reference to the horizon, of any visible celestial body.
A gnomon is used along with a shadow box commonly. A gnomon is a stick placed vertically in a sunny place so that it casts a shadow that can be measured. Studying the shadow of the gnomon provides information about the motion of the Sun. Gnomons were most likely independently discovered by many ancient civilizations, but it is known that they were used in the 5th century BC in Greece. Most likely for the measurement of the winter and summer solstices. " Herodotus says in his Histories written around 450 B.C., that the Greeks learned the use of the gnomon from the Babylonians . [ 4 ]
If a shadow of a human being is 4 feet long then what is the altitude of the sun? This problem can be solved through the use of the shadow box. The shadow box is divided in half, one half is calibrated by sixes the other by tens. Because it is a shadow cast by the human body the sixes are more convenient. By moving the alidade to the four (the same as the shadows length) and then reading the altitude scale shows the Sun is at an altitude of 56.3 degrees. [ 5 ]
The Shadow box can also be used with long shadows using a slightly modified method. If a human's shadow is 18 feet long, then what is the altitude of the Sun? Using the sixes side of the shadow box (using a human body as measurement) the longest shadow marked on a shadow box is six feet. This creates a problem any time the shadow is longer than the gnomon that casts it. By performing a simple calculation, by figuring out how tall a gnomon would be if it cast a six-foot shadow in the same situation, in this situation the gnomon would be only two feet tall in order to cast a six-foot shadow. If the shadow is longer than the gnomon, first turn the astrolabe upside down then set the alidade at two, the height of the projected gnomon, then read off the altitude from the altitude scale. It should read that the Sun is at 19 degrees above the horizon. [ 6 ] | https://en.wikipedia.org/wiki/Shadow_square |
In the theory of dynamical systems , the shadowing lemma is a lemma describing the behaviour of pseudo-orbits near a hyperbolic invariant set . Informally, the theory states that every pseudo-orbit (which one can think of as a numerically computed trajectory with rounding errors on every step [ 1 ] ) stays uniformly close to some true trajectory (with slightly altered initial position)—in other words, a pseudo-trajectory is "shadowed" by a true one. [ 2 ] This suggests that numerical solutions can be trusted to represent the orbits of the dynamical system. However, caution should be exercised as some shadowing trajectories may not always be physically realizable. [ 3 ]
Given a map f : X → X of a metric space ( X , d ) to itself, define a ε-pseudo-orbit (or ε-orbit ) as a sequence ( x n ) {\displaystyle (x_{n})} of points such that x n + 1 {\displaystyle x_{n+1}} belongs to a ε-neighborhood of f ( x n ) {\displaystyle f(x_{n})} .
Then, near a hyperbolic invariant set, the following statement holds: [ 4 ] Let Λ be a hyperbolic invariant set of a diffeomorphism f. There exists a neighborhood U of Λ with the following property: for any δ > 0 there exists ε > 0, such that any (finite or infinite) ε-pseudo-orbit that stays in U also stays in a δ-neighborhood of some true orbit.
This mathematical analysis –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shadowing_lemma |
In civil engineering a shaft is an underground vertical or inclined passageway. Shafts are often entered through a manhole and closed by a manhole cover . They are constructed for a number of reasons including:
There are a number of methods for the construction of shafts, the most significant being:
Shafts can be sunk either dry or for methods such as the caisson method they can be sunk wet. Sinking a dry shaft means that any water that flows into the excavation is pumped out to leave no significant standing or flowing water in the base of the shaft. When wet sinking a shaft the shaft is allowed to flood and the muck is excavated out of the base of the shaft underwater using a grab on the end of a crane or similar excavation method. Because the shaft is flooded, the lining can not be constructed at the excavation level of the shaft so this method only suits methods where the lining is installed before shaft sinking (such as the use of sheet piles) or where the lining is sunk down with the shaft such as the caisson method. | https://en.wikipedia.org/wiki/Shaft_(civil_engineering) |
In mechanical engineering , a shaft is a rotating machine element , usually circular in cross section, which is used to transmit power from one part to another, or from a machine which produces power to a machine which absorbs power.
They are mainly classified into two types.
The material used for ordinary shafts is mild steel . When high strength is required, an alloy steel such as nickel , nickel-chromium or chromium-vanadium steel is used. Shafts are generally formed by hot rolling and finished to size by cold drawing or turning and grinding . [ citation needed ]
Source: [ 1 ]
The standard lengths of the shafts are 5 m, 6 m and 7 m.
Usually 1m to 5m is used.
The following stresses are induced in the shafts. | https://en.wikipedia.org/wiki/Shaft_(mechanical_engineering) |
Shaft alignment is the process of aligning two or more shafts with each other to within a tolerated margin. The resulting fault if alignment is not achieved within the demanded specifications is shaft misalignment , which may be offset or angular. Faults can lead to premature wear and damage to systems.
When a driver like an electric motor or a turbine is coupled to a pump, generator, or any other piece of equipment, the shafts of the two pieces must be aligned. Any misalignment increases the stress on the shafts and will almost certainly result in excessive wear and premature breakdown of the equipment. [ citation needed ] This can be very costly. [ 1 ] [ 2 ] When the equipment is down, production requiring the equipment may be delayed. Bearings or mechanical seals may be damaged and need to be replaced.
Shaft alignment is the process of aligning two or more shafts with each other to within a tolerated margin. The process is used for machinery before the machinery is put in service.
Before shaft alignment can be done, the foundations for the driver and the driven piece must be designed and installed correctly. [ citation needed ]
Flexible couplings are designed to allow a driver (e.g., electric motor, engine, turbine, hydraulic motor) to be connected to the driven equipment. Flexible couplings use an elastomeric insert to allow a slight degree of misalignment. Flexible couplings can also use shim packs. [ citation needed ] These couplings are called disc couplings .
Tools used to achieve alignment may be mechanical, optical (e.g., laser shaft alignment), or gyroscope–based. The gyroscopic systems can be operated very time efficiently and can also be used if the shafts have a large distance (e.g., on marine vessels).
The resulting fault if alignment is not achieved within the demanded specifications is shaft misalignment, which may be offset, angular, or both. Misalignment can cause increased vibration and loads on the machine parts for which they have not been designed (i.e. improper operation). [ citation needed ]
There are two types of misalignment: offset or parallel misalignment and angular, gap, or face misalignment. [ 3 ] [ 4 ] With offset misalignment, the center lines of both shafts are parallel but they are offset. With angular misalignment, the shafts are at an angle to each other. Errors of alignment can be caused by parallel misalignment, angular misalignment, or a combination of the two.
Offset misalignment can be further divided into horizontal and vertical misalignment. Horizontal misalignment is misalignment of the shafts in the horizontal plane and vertical misalignment is misalignment of the shafts in the vertical plane:
Similarly, angular misalignment can be divided into horizontal and vertical misalignment: | https://en.wikipedia.org/wiki/Shaft_misalignment |
Shaft mining or shaft sinking is the action of excavating a mine shaft from the top down, where there is initially no access to the bottom. [ 1 ] Shallow shafts , typically sunk for civil engineering projects, differ greatly in execution method from deep shafts, typically sunk for mining projects.
Shaft sinking is one of the most difficult of all mining development methods: restricted space, gravity, groundwater and specialized procedures make the task quite formidable. [ 2 ] Shafts may be sunk by conventional drill and blast or mechanised means.
Historically, mine shaft sinking has been among the most dangerous of all the mining occupations and the preserve of mining contractors called sinkers . [ 3 ] Today shaft sinking contractors are concentrated in Canada , Germany , China and South Africa .
The modern shaft sinking industry is gradually shifting further towards greater mechanisation. Recent innovations in the form of full-face shaft boring [ 4 ] (akin to a vertical tunnel boring machine ) have shown promise but the use of this method is, as of 2019, not widespread. [ 5 ]
Mine shafts are vertical or near-vertical tunnels , which are "sunk" as a means of accessing an underground ore body, during the development of an underground mine.
The shape (in plan view ), dimensions and depth of mine shafts vary greatly in response to the specific needs of the mine they are part of and the geology they are sunk through. For example, in North and South America, smaller shafts are designed to be rectangular in plan view with timber supports. Larger shafts are round in plan and are concrete lined. [ 6 ]
Mine shafts may be used for a variety of purposes, including as a means of escape in the event of an emergency underground and allowing for the movement of:
When the top of the excavation is the ground surface, it is referred to as a shaft ; when the top of the excavation is underground, it is called a winze or a sub-shaft . Small shafts may be excavated upwards from within an existing mine as long as there is access at the bottom, in which case they are called raises .
A shaft may be either vertical or inclined (between 80 and 90 degrees to the horizontal), although most modern mine shafts are vertical. If access exists at the bottom of the proposed shaft, and ground conditions allow, then raise boring may be used to excavate the shaft from the bottom up; such shafts are called borehole shafts .
Following the Hartley Colliery disaster where the single shaft at the mine became blocked, [ 7 ] the United Kingdom made single shaft mines illegal in 1862, establishing the practice that all underground mines must have " a second means of egress ". Many other global mining jurisdictions have adopted this rule and shafts are therefore often found in pairs (although there are multiple alternative methods of providing a second means of egress).
Currently, the deepest continuous single-lift mine shaft in the world is the main shaft at South Deep Mine in South Africa, owned by Gold Fields Limited , which has a depth of 2991 meters. [ 8 ] Along with its twin ventilation shafts, it took ten years to sink and equip.
The most visible feature of a traditionally-built mine shaft is the headframe (or winding tower, poppet head or pit head) which stands above the shaft. Depending on the type of hoist (or winder) used, the top of the headframe will either house a hoist motor or a sheave wheel (with the hoist motor mounted on the ground). The headframe will also typically contain bins for storing ore being transferred to the processing facility.
At ground level beneath and around the headframe is the Shaft Collar (also called the Bank or Deck), which provides the foundation necessary to support the weight of the headframe and provides a means for workers, materials and services to enter and exit the shaft. Collars are usually massive reinforced concrete structures with more than one level. If the shaft is used for mine ventilation , a plenum space or casing is incorporated into the collar to ensure the proper flow of air into and out of the mine.
Beneath the collar the part of the shaft which continues into the ground is called the shaft barrel . [ citation needed ]
At locations where the shaft barrel meets horizontal workings there is a shaft station (or inset) which allows men, materials and services to enter and exit the shaft. From the station tunnels (drifts, galleries or levels) extend towards the ore body , sometimes for many kilometers. The lowest shaft station is most often the point where rock leaves the mine levels and is transferred to the shaft, if so a loading pocket is excavated on one side of the shaft at this location to allow transfer facilities to be built.
Beneath the lowest shaft station the shaft continues on for some distance; this area is referred to as the shaft bottom . A tunnel called a ramp typically connects the bottom of the shaft with the rest of the mine. This ramp often contains the mine's water handling facility, called the sump , as water will naturally flow to the lowest point in the mine.
Many (although not all) shafts are lined following excavation and the installation of temporary ground support . The shaft lining performs several functions; it is first and foremost a safety feature preventing loose or unstable rock from falling into the shaft, then a place for shaft sets to bolt into, and lastly a smooth surface to minimise resistance to airflow for ventilation.
Final choice of shaft lining is dependent on the geology of the rock which the shaft passes through, some shafts have several liners sections as required [ 9 ] Where shafts are sunk in very competent rock there may be no requirement for lining at all, or just the installation of welded mesh and rock bolts . The material of choice for shaft lining is mass concrete which is poured behind shaft forms in lifts of 6 m as the shaft advances (gets deeper).
Shotcrete , fibrecrete, brick , cast iron tubing, and precast concrete segments have all been used at one time or another. Additionally, the use of materials like bitumen and even squash balls have been required by specific circumstances. In extreme cases, particularly when sinking through halite , composite liners consisting of two or more materials may be required. [ 10 ]
The shaft liner does not reach right to the bottom of the shaft during sinking, but lags behind by a fixed distance. This distance is determined by the methodology of excavation and the design thickness of the permanent liner. To ensure the safety of persons working on the shaft bottom temporary ground support is installed, usually consisting of welded mesh and rock bolts . The installation of the temporary ground support (called bolting ) is among the most physically challenging parts of the shaft sinking cycle as bolts must be installed using pneumatic powered rock drills.
For this reason, and to minimise the number of persons on the shaft bottom a number of projects have successfully switched to shotcrete for this temporary lining. Research and development in this area is focusing on the robotic application of shotcrete and the commercialisation of thin sprayed polymer liners.
Where the shaft is to be used for hoisting it is frequently split into multiple compartments by shaft sets , these may be made of either timber or steel . Vertical members in a shaft set are called guides , horizontal members are called buntons . For steel shaft guides, the main two options are hollow structural sections and top hat sections. Top hat sections offer a number of advantages over hollow structural sections including simpler installation, improved corrosion resistance and increased stiffness. Mine conveyances run on the guides in a similar way to how a steel roller coaster runs on its rails, both having wheels which keep them securely in place.
Some shafts do not use guide beams but instead utilize steel wire rope (called guide rope ) kept in tension by massive weights at shaft bottom called cheese weights (because of their resemblance to a truckle or wheel of cheese) as these are easier to maintain and replace.
The largest compartment is typically used for the mine cage , a conveyance used for moving workers and supplies below the surface, which is suspended from the hoist on steel wire rope. It functions in a similar manner to an elevator . Cages may be single-, double-, or rarely triple-deck, always having multiple redundant safety systems in case of unexpected failure.
The second compartment is used for one or more skips , used to hoist ore to the surface. Smaller mining operations use a skip mounted underneath the cage, rather than a separate device, while some large mines have separate shafts for the cage and skips. The third compartment is used for an emergency exit; it may house an auxiliary cage or a system of ladders. An additional compartment houses mine services such as high voltage cables and pipes for transfer of water, compressed air or diesel fuel .
A second reason to divide the shaft is for ventilation . One or more of the compartments discussed above may be used for air intake, while others may be used for exhaust. Where this is the case a steel or concrete wall called a brattice is installed between the two compartments to separate the air flow. At many mines there are one or more complete additional separate auxiliary shafts with separate head gear and cages.
The lowest point in a sinking shaft is known as the "shaft bottom". Shaft projects differ from some other forms of mine development in that all activities that take place on the shaft bottom become part of the critical path for the project schedule. The infrastructure required to sink a shaft is referred to as "the sinking set-up".
It is typical for progress (the "sinking rate") in the sinking phase (that is excavation, ground support and lining) of a shaft project to follow a learning curve as the project team repeats the same series of activities over and over in what is called "the sinking cycle", eventually approaching the theoretical maximum rate for that sinking set up over time. The use of experienced shaft sinkers is necessary to reduce the length of this learning curve and thus the duration of the project as much as possible.
Key to a successful shaft sinking project are:
Although significant emphasis is placed on the rate of progress of a project sinking cycle by shaft sinkers, sinking is only one of a number of phases in the conventional construction of a new shaft, as follows;
As with the depth and design of shafts, significant variations may exist in this sequence depending on local conditions. For example, shafts in the Canadian Shield generally do not need a deep and complex shaft collar since the bedrock is both strong and close to the surface. This reduces the amount of time required to establish the shaft collar.
Traditionally, sinking contractors would build a temporary headframe for the sinking set-up, which would then be dismantled to make way for a permanent headframe. With the growth in complexity and duration of shaft sinking projects over time it has become more common to incorporate more of the permanent shaft set-up into the sinking phase. This results in a reduced overall project duration, as for example, if the service piping used to sink the shaft does not need to be stripped out to make way for permanent piping.
With the advancements made in raise boring technology, raise borers have been used to create a pilot hole for shaft sinking, where access exists at the bottom of the new shaft, in this case the sinking phase is dedicated to enlarging this pilot hole to full diameter (a process usually called "slashing"). This methodology can be considerably faster than full face sinking as muck (waste rock) from sinking falls down the pilot hole and is handled using existing mine infrastructure off critical path. | https://en.wikipedia.org/wiki/Shaft_sinking |
Shallow is an elevation of the bottom in the sea , river , lake , which impedes navigation . It is a type of an underwater relief where the depth of the water is low compared to that of the surrounding points.
Usually formed by sand or pebble deposits, can also be of volcanic origin or the result of human or animal activities.
Stranded near the shore of a reservoir or watercourse is called a shoal ; the shallow ocean area adjacent to the mainland is the continental shelf .
Shallows can be permanently hidden under water or appear on the surface of the water periodically (for example, during low tide in the seas, changes in the water level in rivers from water content) in the form of islands, sediments, side streams, spits, etc.
On river shoals , if possible, to cross the river on foot, or by land transport, arrange fords.
This hydrology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shallow_(underwater_relief) |
A shallow foundation is a type of building foundation that transfers structural load to the Earth very near to the surface, rather than to a subsurface layer or a range of depths, as does a deep foundation . Customarily, a shallow foundation is considered as such when the width of the entire foundation is greater than its depth. [ 1 ] In comparison to deep foundations, shallow foundations are less technical, thus making them more economical and the most widely used for relatively light structures.
Footings are always wider than the members that they support. Structural loads from a column or wall are usually greater than 1,000 kPa, while the soil's bearing capacity is commonly less than that (typically less than 400 kPa). By possessing a larger bearing area, the foundation distributes the pressure to the soil, decreasing the bearing pressure to within allowable values. [ 2 ] A structure is not limited to one footing. Multiple types of footings may be used in a construction project.
Also called strip footing , a wall footing is a continuous strip that supports structural and non-structural load-bearing walls. Found directly under the wall, Its width is commonly 2-3 times wider than the wall above it. [ 3 ]
Also called single-column footing , an isolated footing is a square, rectangular, or circular slab that supports the structural members individually. Generally, each column is set on an individual footing to transmit and distribute the load of the structure to the soil underneath. Sometimes, an isolated footing can be sloped or stepped at the base to spread greater loads. This type of footing is used when the structural load is relatively low, columns are widely spaced, and the soil's bearing capacity is adequate at a shallow depth.
When more than one column shares the same footing, it is called a combined footing . A combined footing is typically utilized when the spacing of the columns is too restricted such that if isolated footing were used, they would overlap one another. Also, when property lines make isolated footings eccentrically loaded, combined footings are preferred.
When the load among the columns is equal, the combined footing may be rectangular. Conversely, when the load among the columns is unequal, the combined footing should be trapezoidal .
A strap footing connects individual columns with the use of a strap beam. The general purpose of a strap footing is alike to those of a combined footing, where the spacing is possibly limited and/or the columns are adjacent to the property lines.
Also called raft foundation, a mat foundation is a single continuous slab that covers the entirety of the base of a building. Mat foundations support all the loads of the structure and transmit them to the ground evenly. Soil conditions may prevent other footings from being used. Since this type of foundation distributes the load coming from the building uniformly over a considerably large area, it is favored when individual footings are unfeasible due to the low bearing capacity of the soil.
Slab-on-grade or floating slab foundations are a structural engineering practice whereby the reinforced concrete slab that is to serve as the foundation for the structure is formed from formwork set into the ground. The concrete is then poured into the formwork, leaving no space between the ground and the structure. This type of construction is most often seen in warmer climates, where ground freezing and thawing is less of a concern and where there is no need for heat ducting underneath the floor. Frost Protected Shallow Foundations (or FPSF) which are used in areas of potential frost heave, are a form of slab-on-grade foundation. [ 4 ]
Remodeling or extending such a structure may be more difficult. Over the long term, ground settling (or subsidence ) may be a problem, as a slab foundation cannot be readily jacked up to compensate; proper soil compaction prior to pour can minimize this. The slab can be decoupled from ground temperatures by insulation, with the concrete poured directly over insulation (for example, extruded polystyrene foam panels), or heating provisions (such as hydronic heating ) can be built into the slab.
Slab-on-grade foundations should not be used in areas with expansive clay soil. While elevated structural slabs actually perform better on expansive clays, it is generally accepted by the engineering community that slab-on-grade foundations offer the greatest cost-to-performance ratio for tract homes . Elevated structural slabs are generally only found on custom homes or homes with basements.
Copper piping, commonly used to carry natural gas and water , reacts with concrete over a long period, slowly degrading until the pipe fails. This can lead to what is commonly referred to as slab leaks. These occur when pipes begin to leak from within the slab. Signs of a slab leak range from unexplained dampened carpet spots, to drops in water pressure and wet discoloration on exterior foundation walls. [ 5 ] Copper pipes must be lagged (that is, insulated ) or run through a conduit or plumbed into the building above the slab. Electrical conduits through the slab must be water-tight, as they extend below ground level and can potentially expose wiring to groundwater . | https://en.wikipedia.org/wiki/Shallow_foundation |
Shamir Optical Industry Ltd. is an international company headquartered in Kibbutz Shamir, Israel that develops and manufactures optical lenses for eyeglasses . [ 2 ] [ failed verification ] In 2005, the company issued dual listings, on the Tel Aviv Stock Exchange and NASDAQ , becoming the first company from the kibbutz industry to be listed on NASDAQ. [ 3 ]
The optics factory was established in Kibbutz Shamir in 1972 to meet the need of kibbutz members for non-agricultural work. [ 4 ] [ non-primary source needed ] To this end, the kibbutz signed an agreement with the American company "KMS Industries" (owned by Kip Siegel ), to establish a bi-focal lens factory in Israel, with production intended entirely for export. [ 5 ] [ 6 ]
As part of the agreement, the company, which produced optics for televisions, agreed to provide know-how to the factory and even to buy all its products for the first two years. [ 7 ] In 1972, about two years after signing the agreement, Shamir Optical Industry Ltd was established, and the kibbutz optics factory for the production of bi-focal lenses was inaugurated by Pinchas Sapir , Israel Minister of Trade and Industry . [ 8 ]
The company expanded its production and started manufacturing progressive lenses in addition to its existing line of lenses in 1984. During that year, the factory's turnover was half a million dollars, and about 20% of the country's optics industry sector originated in the Kibbutz Shamir factory. [ 9 ]
In 1990, the company gained a foothold in the United States, with the establishment of its subsidiary, Shamir USA. Eleven years later, Shamir set up a distribution center to supply semi-finished lenses to laboratories across the United States, and for that purpose it set up another company called Shamir Insight Inc. [ 10 ]
In 2005, Shamir Optics became a public company, issued on both the Tel Aviv Stock Exchange and NASDAQ at a value of $225.4 million, making it the first kibbutz company to be issued on NASDAQ, and was the only company which has been listed on the American stock exchange that develops multifocal lenses. [ 3 ] [ 2 ] [ 11 ]
In 2008, Shamir strengthened its position in Europe by making the German distribution company, Altra Trading, a wholly owned subsidiary following the acquisition of 49% of its shares, adding to the 51% already held. [ 12 ]
The company merged with the French optics company Essilor in 2011. [ 13 ] The merger was carried out through the purchase of 37% of shares from the public and another 13% of shares from Shamir Optical Industry Ltd., totaling 50% of the company, for $130 million. Upon completion of the merger with Essilor, Shamir was delisted from NASDAQ and became a private company. [ 14 ]
In 2011, Dymotech Ltd filed a $28 million lawsuit against Shamir and its partly owned subsidiary Inray Ltd. Dymotech Ltd. alleged that Shamir and Inray were illegally used Technion 's intellectual property, and requested restraining order against them to prevent future use of its alleged intellectual property . [ 15 ]
In May 2021, Shamir completed acquisition of Lenstec Optical Group on behalf of its owner Essilor. [ 16 ]
In August 2022, EssilorLuxottica completed acquisition of 100% Shamir. [ 17 ] | https://en.wikipedia.org/wiki/Shamir_Optical_Industry |
Shang-Ping Xie [ a ] is a climatology and oceanography researcher who holds the Roger Revelle Chair at Scripps Institution of Oceanography . Known best for his research on interaction between the world's oceans and atmosphere and on El Niño–Southern Oscillation , Xie is noted as a Highly Cited Researcher by Clarivate . [ 2 ]
Xie was born in Quzhou in 1963. [ 3 ] He entered university after the Cultural Revolution had ended, and studied oceanography, though he had never seen the ocean before. [ 4 ] His education includes: [ 5 ]
He was a visiting scientist to Princeton University from 1991 to 1993, and a research associate for the University of Washington from 1993 to 1994. [ 5 ]
Xie had been employed at the University of Hawaiʻi as a professor of meteorology until he joined the Scripps Institution of Oceanography of the University of California, San Diego in 2012 as the inaugural Roger Revelle Chair, [ b ] [ 7 ] a title named for pioneering researcher Roger Revelle , [ 8 ] established with an endowment from the Revelle family. [ 9 ] While at Hawaiʻi, he was faculty in the International Pacific Research Center of the School of Ocean and Earth Science and Technology . [ 10 ]
In April 2016, as a Scripps professor, Xie returned to the University of Washington as an endowed lecturer—he gave a lecture on El Niño in the Graduate Students' Distinguished Visiting Lecture series. [ 11 ]
In 2013, a study co-authored by Xie and published in Nature suggested that the slowdown in global warming was tied to cooling in parts of the Pacific Ocean . [ 12 ] [ 13 ] Further research into the slowdown was published in 2015, in the journal Nature Climate Change . [ 14 ] [ 15 ] Xie has also published research on modeling the role of human activity to global warming; a 2015 co-authored paper in Nature Geoscience modeled the evolution of global temperature, creating a new method of tracking anthropogenic global warming . [ 16 ] [ 17 ] The modelling was reported on again in 2016, when Xie and others modelled human activities' impact on warming. [ 18 ] Other papers on climate change have included collaboration with authors affiliated with Duke University and University of Wisconsin–Madison . [ 19 ] [ 20 ] In 2019, Xie published research with scientists from the Lawrence Berkeley National Laboratory , where they modelled Hadley cells to predict changes in the monsoon season of parts of Asia. [ 21 ] [ 22 ] In a 2022 article published by the World Economic Forum and The Conversation and co-authored by Xie, the authors claim that tropical cyclones have been increasing in intensity over time. [ 23 ]
In 2016, Xie was the organizer of a special issue of Advances in Atmospheric Sciences . [ c ] [ 24 ]
Xie has been included as a Highly Cited Researcher by Clarivate in the field of geosciences . [ 25 ] | https://en.wikipedia.org/wiki/Shang-Ping_Xie |
Shanghai Astronomy Museum is a planetarium opened in 2021 in Lingang New City , Pudong New Area district, Shanghai . Its dome covers 38,000 square meters. It is the world's largest planetarium in terms of building scale. [ 1 ] The planetarium, designed by New York City based Ennead Architects , serves as an educational and entertainment site for visitors. [ 2 ] It is part of Shanghai Science and Technology Museum .
With no straight lines or right angles, the building was designed to reflect the shapes, movement and geometry of the universe. Ennead Architects design partner, Thomas J Wong, explained that the foundational design concept of the museum was to “abstractly embody within the architecture some of the fundamental laws of astrophysics, which are the rule in space.” [ 3 ]
This astronomy -related article is a stub . You can help Wikipedia by expanding it .
This article about a building or structure in China is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shanghai_Astronomy_Museum |
The Shanghai Stem Cell Institute is an institute in Shanghai , People's Republic of China dedicated to stem cell research .
The institute, located within the Shanghai Jiao Tong University under the School of Medicine faculty, is entirely funded by the government of the People's Republic of China. [ 1 ]
In 2007, the first Shanghai International Symposium on Stem Cell Research took place at Shanghai Jiatong University. [ citation needed ]
On July 24, 2009, the first publication of a successful breakthrough in Stem cell research was released, [ 2 ] [ 3 ] where Chinese researchers from the Shanghai Stem Cell Institute, led by Professor Fanyi Zeng, successfully reprogrammed adult stem cells to be able to differentiate into any body cell, as in the case with standard embryonic stem cells , the cells in question known as " induced pluripotent stem cells " (IPS cells). The IPS cells were obtained by genetically reprogramming the skin cells of mice to acts like embryonic stem cells , which then were able to differentiate into all forms of body tissue. [ 4 ] The researchers have managed to use the IPS cells to create every type of cell in a mouse, creating entire mouse pups using the technique. This is the first time the technique has been used to make an entire mouse.
This breakthrough, published in the journals Nature and Cell Stem Cell and developed independently by two teams in China, may possibly depreciate the usage of stem cells obtained from human embryos. [ 5 ] The oldest living mice created by the technique are nine months old and are reproducing, albeit showing signs of abnormalities. "This gives us hope for future therapeutic intervention using patients' own re-programmed cells in our far future," according to Professor Zeng Fanyi . [ 5 ] A total of 27 mice were successfully born from the first generation of mice created from the IPS cells which were able to reproduce without any issues. [ 4 ] | https://en.wikipedia.org/wiki/Shanghai_Stem_Cell_Institute |
In information theory , Shannon's source coding theorem (or noiseless coding theorem ) establishes the statistical limits to possible data compression for data whose source is an independent identically-distributed random variable , and the operational meaning of the Shannon entropy .
Named after Claude Shannon , the source coding theorem shows that, in the limit, as the length of a stream of independent and identically-distributed random variable (i.i.d.) data tends to infinity, it is impossible to compress such data such that the code rate (average number of bits per symbol) is less than the Shannon entropy of the source, without it being virtually certain that information will be lost. However it is possible to get the code rate arbitrarily close to the Shannon entropy, with negligible probability of loss.
The source coding theorem for symbol codes places an upper and a lower bound on the minimal possible expected length of codewords as a function of the entropy of the input word (which is viewed as a random variable ) and of the size of the target alphabet.
Note that, for data that exhibits more dependencies (whose source is not an i.i.d. random variable), the Kolmogorov complexity , which quantifies the minimal description length of an object, is more suitable to describe the limits of data compression. Shannon entropy takes into account only frequency regularities while Kolmogorov complexity takes into account all algorithmic regularities, so in general the latter is smaller. On the other hand, if an object is generated by a random process in such a way that it has only frequency regularities, entropy is close to complexity with high probability (Shen et al. 2017). [ 1 ]
Source coding is a mapping from (a sequence of) symbols from an information source to a sequence of alphabet symbols (usually bits) such that the source symbols can be exactly recovered from the binary bits (lossless source coding) or recovered within some distortion (lossy source coding). This is one approach to data compression .
In information theory, the source coding theorem (Shannon 1948) [ 2 ] informally states that (MacKay 2003, pg. 81, [ 3 ] Cover 2006, Chapter 5 [ 4 ] ):
N i.i.d. random variables each with entropy H ( X ) can be compressed into more than N H ( X ) bits with negligible risk of information loss, as N → ∞ ; but conversely, if they are compressed into fewer than N H ( X ) bits it is virtually certain that information will be lost.
The N H ( X ) {\displaystyle NH(X)} coded sequence represents the compressed message in a biunivocal way, under the assumption that the decoder knows the source. From a practical point of view, this hypothesis is not always true. Consequently, when the entropy encoding is applied the transmitted message is N H ( X ) + ( i n f . s o u r c e ) {\displaystyle NH(X)+(inf.source)} . Usually, the information that characterizes the source is inserted at the beginning of the transmitted message.
Let Σ 1 , Σ 2 denote two finite alphabets and let Σ ∗ 1 and Σ ∗ 2 denote the set of all finite words from those alphabets (respectively).
Suppose that X is a random variable taking values in Σ 1 and let f be a uniquely decodable code from Σ ∗ 1 to Σ ∗ 2 where |Σ 2 | = a . Let S denote the random variable given by the length of codeword f ( X ) .
If f is optimal in the sense that it has the minimal expected word length for X , then (Shannon 1948):
Where E {\displaystyle \mathbb {E} } denotes the expected value operator.
Given X is an i.i.d. source, its time series X 1 , ..., X n is i.i.d. with entropy H ( X ) in the discrete-valued case and differential entropy in the continuous-valued case. The Source coding theorem states that for any ε > 0 , i.e. for any rate H ( X ) + ε larger than the entropy of the source, there is large enough n and an encoder that takes n i.i.d. repetition of the source, X 1: n , and maps it to n ( H ( X ) + ε ) binary bits such that the source symbols X 1: n are recoverable from the binary bits with probability of at least 1 − ε .
Proof of Achievability. Fix some ε > 0 , and let
The typical set , A ε n , is defined as follows:
The asymptotic equipartition property (AEP) shows that for large enough n , the probability that a sequence generated by the source lies in the typical set, A ε n , as defined approaches one. In particular, for sufficiently large n , P ( ( X 1 , X 2 , ⋯ , X n ) ∈ A n ε ) {\displaystyle P((X_{1},X_{2},\cdots ,X_{n})\in A_{n}^{\varepsilon })} can be made arbitrarily close to 1, and specifically, greater than 1 − ε {\displaystyle 1-\varepsilon } (See AEP for a proof).
The definition of typical sets implies that those sequences that lie in the typical set satisfy:
Since | A n ε | ≤ 2 n ( H ( X ) + ε ) , n ( H ( X ) + ε ) {\displaystyle \left|A_{n}^{\varepsilon }\right|\leq 2^{n(H(X)+\varepsilon )},n(H(X)+\varepsilon )} bits are enough to point to any string in this set.
The encoding algorithm: the encoder checks if the input sequence lies within the typical set; if yes, it outputs the index of the input sequence within the typical set; if not, the encoder outputs an arbitrary n ( H ( X ) + ε ) digit number. As long as the input sequence lies within the typical set (with probability at least 1 − ε ), the encoder does not make any error. So, the probability of error of the encoder is bounded above by ε .
Proof of converse : the converse is proved by showing that any set of size smaller than A ε n (in the sense of exponent) would cover a set of probability bounded away from 1 .
For 1 ≤ i ≤ n let s i denote the word length of each possible x i . Define q i = a − s i / C {\displaystyle q_{i}=a^{-s_{i}}/C} , where C is chosen so that q 1 + ... + q n = 1 . Then
where the second line follows from Gibbs' inequality and the fifth line follows from Kraft's inequality :
so log C ≤ 0 .
For the second inequality we may set
so that
and so
and
and so by Kraft's inequality there exists a prefix-free code having those word lengths. Thus the minimal S satisfies
Define typical set A ε n as:
Then, for given δ > 0 , for n large enough, Pr( A ε n ) > 1 − δ . Now we just encode the sequences in the typical set, and usual methods in source coding show that the cardinality of this set is smaller than 2 n ( H n ¯ ( X ) + ε ) {\displaystyle 2^{n({\overline {H_{n}}}(X)+\varepsilon )}} . Thus, on an average, H n ( X ) + ε bits suffice for encoding with probability greater than 1 − δ , where ε and δ can be made arbitrarily small, by making n larger. | https://en.wikipedia.org/wiki/Shannon's_source_coding_theorem |
The shannon (symbol: Sh) is a unit of information named after Claude Shannon , the founder of information theory . IEC 80000-13 defines the shannon as the information content associated with an event when the probability of the event occurring is 1 / 2 . It is understood as such within the realm of information theory , and is conceptually distinct from the bit , a term used in data processing and storage to denote a single instance of a binary signal . A sequence of n binary symbols (such as contained in computer memory or a binary data transmission) is properly described as consisting of n bits, but the information content of those n symbols may be more or less than n shannons depending on the a priori probability of the actual sequence of symbols. [ 1 ]
The shannon also serves as a unit of the information entropy of an event, which is defined as the expected value of the information content of the event (i.e., the probability-weighted average of the information content of all potential events). Given a number of possible outcomes, unlike information content, the entropy has an upper bound, which is reached when the possible outcomes are equiprobable. The maximum entropy of n bits is n Sh. A further quantity that it is used for is channel capacity , which is generally the maximum of the expected value of the information content encoded over a channel that can be transferred with negligible probability of error, typically in the form of an information rate.
Nevertheless, the term bits of information or simply bits is more often heard, even in the fields of information and communication theory , rather than shannons ; just saying bits can therefore be ambiguous. Using the unit shannon is an explicit reference to a quantity of information content, information entropy or channel capacity, and is not restricted to binary data, [ 2 ] whereas bits can as well refer to the number of binary symbols involved, as is the term used in fields such as data processing.
The shannon is connected through constants of proportionality to two other units of information: [ 3 ]
The hartley , a seldom-used unit, is named after Ralph Hartley , an electronics engineer interested in the capacity of communications channels. Although of a more limited nature, his early work, preceding that of Shannon, makes him recognized also as a pioneer of information theory. Just as the shannon describes the maximum possible information capacity of a binary symbol, the hartley describes the information that can be contained in a 10-ary symbol, that is, a digit value in the range 0 to 9 when the a priori probability of each value is 1 / 10 . The conversion factor quoted above is given by log 10 (2).
In mathematical expressions, the nat is a more natural unit of information, but 1 nat does not correspond to a case in which all possibilities are equiprobable, unlike with the shannon and hartley. In each case, formulae for the quantification of information capacity or entropy involve taking the logarithm of an expression involving probabilities. If base-2 logarithms are employed, the result is expressed in shannons, if base-10 ( common logarithms ) then the result is in hartleys, and if natural logarithms (base e ), the result is in nats. For instance, the information capacity of a 16-bit sequence (achieved when all 65536 possible sequences are equally probable) is given by log(65536), thus log 10 (65536) Hart ≈ 4.82 Hart , log e (65536) nat ≈ 11.09 nat , or log 2 (65536) Sh = 16 Sh .
In information theory and derivative fields such as coding theory , one cannot quantify the 'information' in a single message (sequence of symbols) out of context, but rather a reference is made to the model of a channel (such as bit error rate ) or to the underlying statistics of an information source. There are thus various measures of or related to information , all of which may use the shannon as a unit. [ citation needed ]
For instance, in the above example, a 16-bit channel could be said to have a channel capacity of 16 Sh, but when connected to a particular information source that only sends one of 8 possible messages, one would compute the entropy of its output as no more than 3 Sh. And if one already had been informed through a side channel in which set of 4 possible messages the message is, then one could calculate the mutual information of the new message (having 8 possible states) as no more than 2 Sh. Although there are infinite possibilities for a real number chosen between 0 and 1, so-called differential entropy can be used to quantify the information content of an analog signal, such as related to the enhancement of signal-to-noise ratio or confidence of a hypothesis test . [ citation needed ] | https://en.wikipedia.org/wiki/Shannon_(unit) |
The Centre for Applied Bioscience Research (Formerly Shannon Applied Biotechnology Centre) is a partnership between the Munster Technological University (MTU) and Technological University of the Shannon: Midlands Midwest (TUS:MM,) and is co-located between these research institutes in Ireland. CABR applies bioprocessing to a variety of different source materials to derive added value from them in the area of biological products (e.g. anti-oxidants , anti-microbials , immunomodulators, value added food, waste optimisation, etc.) [ 1 ]
CABR was established through core funding from Enterprise Ireland as an Applied Research Enhancement Centre and continues to enjoy support from this organisation as well as:
CABR has a large multidisciplinary team of research scientists, highly experienced in the commercial application of science through industry collaboration. In addition to the identification of bioactive molecules through bioprocessing, [ 2 ] CABR also provides a contract research facility to companies who wish to optimise scientific processes within their company.
In July 2010 CABR formed a strategic life sciences cluster with the Pharmaceutical & Molecular Biotechnology Research Centre (PMBRC) [ 3 ] and the Ion Channel Biotechnology Centre (ICBC). This cluster was developed with the intention of providing further expertise to industry while taking advantage of complementary capabilities in the centres. [ citation needed ]
The key aim of CABR is to assist in the continued prosperity of industry by offering access to wide-ranging expertise and know how, state of the art equipment and facilities and access to a wide variety of national and international funding programmes.
CABR provides biotechnology services on a range of levels. Companies can use Enterprise Ireland funded schemes (such as Innovation Vouchers and Innovation Partnerships) to carry out research, or they can fund the work themselves as contract research.
Industry partners include those from a range of industries, including: Food, Agriculture, Marine, Pharmaceutical, Healthcare, Cosmetics, etc.
Funding from Enterprise Ireland for the initial period of existence of CABR provided for the development of niche expertise areas of the Centre, as well as providing for a critical mass of experienced, commercially focused researchers. Initial waste streams that were mined included spent yeast, horse chestnut waste and fish waste. [ 4 ] A further area of expertise includes investigation of raw materials, such as seaweed, [ 5 ] for a variety of bioactive compounds.
From these core activities the Centre has developed a bioactivity screening process applicable to any natural waste process or product. In the absence of bioactivity, competencies within the Centre can be used to recommend other ways to add value to waste processes.
A key research, development and innovation area for CABR are bioactive molecules. Bioactive molecules are those derived from biological origin that exhibit an active effect, and can include anti-oxidants , immunomodulatory compounds, anti microbials , prebiotics , etc. Bioactive molecules are extracted by traditional solvent extraction techniques or by super critical fluid extraction. Activity can then be screened for and molecules of interest identified. | https://en.wikipedia.org/wiki/Shannon_Applied_Biotechnology_Centre |
In the field of data compression , Shannon coding , named after its creator, Claude Shannon , is a lossless data compression technique for constructing a prefix code based on a set of symbols and their probabilities (estimated or measured). It is suboptimal in the sense that it does not achieve the lowest possible expected code word length like Huffman coding does, and never better than but sometimes equal to the Shannon–Fano coding (Fano's method).
The method was the first of its type, the technique was used to prove Shannon's noiseless coding theorem in his 1948 article "A Mathematical Theory of Communication", [ 1 ] and is therefore a centerpiece of the information age.
Shannon–Fano coding methods gave rise to the field of information theory and without its contributions, the world would not have any of the many successors; for example Huffman coding, or arithmetic coding . Much of our day-to-day lives are significantly influenced by digital data and this would not be possible without Shannon-Fano coding and the ongoing evolution of its methods. [ 2 ] [ page needed ]
In Shannon coding, the symbols are arranged in order from most probable to least probable, and assigned codewords by taking the first l i = ⌈ − log 2 p i ⌉ {\displaystyle l_{i}=\left\lceil -\log _{2}p_{i}\right\rceil } bits from the binary expansions of the cumulative probabilities ∑ k = 1 i − 1 p k . {\displaystyle \sum \limits _{k=1}^{i-1}p_{k}.} Here ⌈ x ⌉ {\displaystyle \lceil x\rceil } denotes the ceiling function (which rounds x {\displaystyle x} up to the next integer value).
In the table below is an example of creating a code scheme for symbols a 1 to a 6 . The value of l i gives the number of bits used to represent the symbol a i . The last column is the bit code of each symbol.
Shannon, Claude Elwood. "A Mathematical Theory of Communication." ACM SIGMOBILE mobile computing and communications review 5.1 (2001): 3-55. | https://en.wikipedia.org/wiki/Shannon_coding |
In the field of data compression , Shannon–Fano coding , named after Claude Shannon and Robert Fano , is one of two related techniques for constructing a prefix code based on a set of symbols and their probabilities (estimated or measured).
Shannon–Fano codes are suboptimal in the sense that they do not always achieve the lowest possible expected codeword length, as Huffman coding does. [ 1 ] However, Shannon–Fano codes have an expected codeword length within 1 bit of optimal. Fano's method usually produces encoding with shorter expected lengths than Shannon's method. However, Shannon's method is easier to analyse theoretically.
Shannon–Fano coding should not be confused with Shannon–Fano–Elias coding (also known as Elias coding), the precursor to arithmetic coding .
Regarding the confusion in the two different codes being referred to by the same name, Krajči et al. write: [ 2 ]
Around 1948, both Claude E. Shannon (1948) and Robert M. Fano (1949) independently proposed two different source coding algorithms for an efficient description of a discrete memoryless source. Unfortunately, in spite of being different, both schemes became known under the same name Shannon–Fano coding .
There are several reasons for this mixup. For one thing, in the discussion of his coding scheme, Shannon mentions Fano’s scheme and calls it “substantially the same” (Shannon, 1948, p. 17 [reprint]). [ 3 ] For another, both Shannon’s and Fano’s coding schemes are similar in the sense that they both are efficient, but suboptimal prefix-free coding schemes with a similar performance.
Shannon's (1948) method, using predefined word lengths, is called Shannon–Fano coding by Cover and Thomas, [ 4 ] Goldie and Pinch, [ 5 ] Jones and Jones, [ 6 ] and Han and Kobayashi. [ 7 ] It is called Shannon coding by Yeung. [ 8 ]
Fano's (1949) method, using binary division of probabilities, is called Shannon–Fano coding by Salomon [ 9 ] and Gupta. [ 10 ] It is called Fano coding by Krajči et al. [ 2 ]
Shannon's method starts by deciding on the lengths of all the codewords, then picks a prefix code with those word lengths.
Given a source with probabilities p 1 , p 2 , … , p n {\displaystyle p_{1},p_{2},\dots ,p_{n}} the desired codeword lengths are l i = ⌈ − log 2 p i ⌉ {\displaystyle l_{i}=\lceil -\log _{2}p_{i}\rceil } . Here, ⌈ x ⌉ {\displaystyle \lceil x\rceil } is the ceiling function , meaning the smallest integer greater than or equal to x {\displaystyle x} .
Once the codeword lengths have been determined, we must choose the codewords themselves. One method is to pick codewords in order from most probable to least probable symbols, picking each codeword to be the lexicographically first word of the correct length that maintains the prefix-free property.
A second method makes use of cumulative probabilities. First, the probabilities are written in decreasing order p 1 ≥ p 2 ≥ ⋯ ≥ p n {\displaystyle p_{1}\geq p_{2}\geq \cdots \geq p_{n}} . Then, the cumulative probabilities are defined as
so c 1 = 0 , c 2 = p 1 , c 3 = p 1 + p 2 {\displaystyle c_{1}=0,c_{2}=p_{1},c_{3}=p_{1}+p_{2}} and so on.
The codeword for symbol i {\displaystyle i} is chosen to be the first l i {\displaystyle l_{i}} binary digits in the binary expansion of c i {\displaystyle c_{i}} .
This example shows the construction of a Shannon–Fano code for a small alphabet. There 5 different source symbols. Suppose 39 total symbols have been observed with the following frequencies, from which we can estimate the symbol probabilities.
This source has entropy H ( X ) = 2.186 {\displaystyle H(X)=2.186} bits.
For the Shannon–Fano code, we need to calculate the desired word lengths l i = ⌈ − log 2 p i ⌉ {\displaystyle l_{i}=\lceil -\log _{2}p_{i}\rceil } .
We can pick codewords in order, choosing the lexicographically first word of the correct length that maintains the prefix-free property. Clearly A gets the codeword 00. To maintain the prefix-free property, B's codeword may not start 00, so the lexicographically first available word of length 3 is 010. Continuing like this, we get the following code:
Alternatively, we can use the cumulative probability method.
Note that although the codewords under the two methods are different, the word lengths are the same. We have lengths of 2 bits for A, and 3 bits for B, C, D and E, giving an average length of
which is within one bit of the entropy.
For Shannon's method, the word lengths satisfy
Hence the expected word length satisfies
Here, H ( X ) = − ∑ i = 1 n p i log 2 p i {\displaystyle H(X)=-\textstyle \sum _{i=1}^{n}p_{i}\log _{2}p_{i}} is the entropy , and Shannon's source coding theorem says that any code must have an average length of at least H ( X ) {\displaystyle H(X)} . Hence we see that the Shannon–Fano code is always within one bit of the optimal expected word length.
In Fano's method, the symbols are arranged in order from most probable to least probable, and then divided into two sets whose total probabilities are as close as possible to being equal. All symbols then have the first digits of their codes assigned; symbols in the first set receive "0" and symbols in the second set receive "1". As long as any sets with more than one member remain, the same process is repeated on those sets, to determine successive digits of their codes. When a set has been reduced to one symbol this means the symbol's code is complete and will not form the prefix of any other symbol's code.
The algorithm produces fairly efficient variable-length encodings; when the two smaller sets produced by a partitioning are in fact of equal probability, the one bit of information used to distinguish them is used most efficiently. Unfortunately, Shannon–Fano coding does not always produce optimal prefix codes; the set of probabilities {0.35, 0.17, 0.17, 0.16, 0.15} is an example of one that will be assigned non-optimal codes by Shannon–Fano coding.
Fano's version of Shannon–Fano coding is used in the IMPLODE compression method, which is part of the ZIP file format . [ 11 ]
A Shannon–Fano tree is built according to a specification designed to define an effective code table. The actual algorithm is simple:
We continue with the previous example.
All symbols are sorted by frequency, from left to right (shown in Figure a). Putting the dividing line between symbols B and C results in a total of 22 in the left group and a total of 17 in the right group. This minimizes the difference in totals between the two groups.
With this division, A and B will each have a code that starts with a 0 bit, and the C, D, and E codes will all start with a 1, as shown in Figure b. Subsequently, the left half of the tree gets a new division between A and B, which puts A on a leaf with code 00 and B on a leaf with code 01.
After four division procedures, a tree of codes results. In the final tree, the three symbols with the highest frequencies have all been assigned 2-bit codes, and two symbols with lower counts have 3-bit codes as shown table below:
This results in lengths of 2 bits for A, B and C and per 3 bits for D and E, giving an average length of
We see that Fano's method, with an average length of 2.28, has outperformed Shannon's method, with an average length of 2.62.
It is shown by Krajči et al [ 2 ] that the expected length of Fano's method has expected length bounded above by E L ≤ H ( X ) + 1 − p min {\displaystyle \mathbb {E} L\leq H(X)+1-p_{\text{min}}} , where p min = min i p i {\displaystyle p_{\text{min}}=\textstyle \min _{i}p_{i}} is the probability of the least common symbol.
Neither Shannon–Fano algorithm is guaranteed to generate an optimal code. For this reason, Shannon–Fano codes are almost never used; Huffman coding is almost as computationally simple and produces prefix codes that always achieve the lowest possible expected code word length, under the constraints that each symbol is represented by a code formed of an integral number of bits. This is a constraint that is often unneeded, since the codes will be packed end-to-end in long sequences. If we consider groups of codes at a time, symbol-by-symbol Huffman coding is only optimal if the probabilities of the symbols are independent and are some power of a half, i.e., 1 / 2 k {\displaystyle \textstyle 1/2^{k}} . In most situations, arithmetic coding can produce greater overall compression than either Huffman or Shannon–Fano, since it can encode in fractional numbers of bits which more closely approximate the actual information content of the symbol. However, arithmetic coding has not superseded Huffman the way that Huffman supersedes Shannon–Fano, both because arithmetic coding is more computationally expensive and because it is covered by multiple patents. [ 12 ]
A few years later, David A. Huffman (1952) [ 13 ] gave a different algorithm that always produces an optimal tree for any given symbol probabilities. While Fano's Shannon–Fano tree is created by dividing from the root to the leaves, the Huffman algorithm works in the opposite direction, merging from the leaves to the root.
We use the same frequencies as for the Shannon–Fano example above, viz:
In this case D & E have the lowest frequencies and so are allocated 0 and 1 respectively and grouped together with a combined probability of 0.282. The lowest pair now are B and C so they're allocated 0 and 1 and grouped together with a combined probability of 0.333. This leaves BC and DE now with the lowest probabilities so 0 and 1 are prepended to their codes and they are combined. This then leaves just A and BCDE, which have 0 and 1 prepended respectively and are then combined. This leaves us with a single node and our algorithm is complete.
The code lengths for the different characters this time are 1 bit for A and 3 bits for all other characters.
This results in the lengths of 1 bit for A and per 3 bits for B, C, D and E, giving an average length of
We see that the Huffman code has outperformed both types of Shannon–Fano code, which had expected lengths of 2.62 and 2.28. | https://en.wikipedia.org/wiki/Shannon–Fano_coding |
In information theory , Shannon–Fano–Elias coding is a precursor to arithmetic coding , in which probabilities are used to determine codewords. [ 1 ] It is named for Claude Shannon , Robert Fano , and Peter Elias .
Given a discrete random variable X of ordered values to be encoded, let p ( x ) {\displaystyle p(x)} be the probability for any x in X . Define a function
Algorithm:
Let X = { A , B , C , D }, with probabilities p = {1/3, 1/4, 1/6, 1/4}.
Shannon–Fano–Elias coding produces a binary prefix code , allowing for direct decoding.
Let bcode( x ) be the rational number formed by adding a decimal point before a binary code. For example, if code( C ) = 1010 then bcode( C ) = 0.1010. For all x , if no y exists such that
then all the codes form a prefix code.
By comparing F to the CDF of X , this property may be demonstrated graphically for Shannon–Fano–Elias coding.
By definition of L it follows that
And because the bits after L ( y ) are truncated from F ( y ) to form code( y ), it follows that
thus bcode( y ) must be no less than CDF( x ).
So the above graph demonstrates that the bcode ( y ) − bcode ( x ) > p ( x ) ≥ 2 − L ( x ) {\displaystyle \operatorname {bcode} (y)-\operatorname {bcode} (x)>p(x)\geq 2^{-L(x)}} , therefore the prefix property holds.
The average code length is L C ( X ) = ∑ x ∈ X p ( x ) L ( x ) = ∑ x ∈ X p ( x ) ( ⌈ log 2 1 p ( x ) ⌉ + 1 ) {\displaystyle LC(X)=\sum _{x\in X}p(x)L(x)=\sum _{x\in X}p(x)\left(\left\lceil \log _{2}{\frac {1}{p(x)}}\right\rceil +1\right)} . Thus for H ( X ), the entropy of the random variable X ,
Shannon Fano Elias codes from 1 to 2 extra bits per symbol from X than entropy, so the code is not used in practice. | https://en.wikipedia.org/wiki/Shannon–Fano–Elias_coding |
In information theory , the Shannon–Hartley theorem tells the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise . It is an application of the noisy-channel coding theorem to the archetypal case of a continuous-time analog communications channel subject to Gaussian noise . The theorem establishes Shannon's channel capacity for such a communication link, a bound on the maximum amount of error-free information per time unit that can be transmitted with a specified bandwidth in the presence of the noise interference, assuming that the signal power is bounded, and that the Gaussian noise process is characterized by a known power or power spectral density. The law is named after Claude Shannon and Ralph Hartley .
The Shannon–Hartley theorem states the channel capacity C {\displaystyle C} , meaning the theoretical tightest upper bound on the information rate of data that can be communicated at an arbitrarily low error rate using an average received signal power S {\displaystyle S} through an analog communication channel subject to additive white Gaussian noise (AWGN) of power N {\displaystyle N} :
where
During the late 1920s, Harry Nyquist and Ralph Hartley developed a handful of fundamental ideas related to the transmission of information, particularly in the context of the telegraph as a communications system. At the time, these concepts were powerful breakthroughs individually, but they were not part of a comprehensive theory. In the 1940s, Claude Shannon developed the concept of channel capacity, based in part on the ideas of Nyquist and Hartley, and then formulated a complete theory of information and its transmission.
In 1927, Nyquist determined that the number of independent pulses that could be put through a telegraph channel per unit time is limited to twice the one-sided bandwidth of the channel. In symbolic notation,
where f p {\displaystyle f_{p}} is the pulse frequency (in pulses per second) and B {\displaystyle B} is the one-sided bandwidth [ clarification needed ] (in hertz). The quantity 2 B {\displaystyle 2B} later came to be called the Nyquist rate , and transmitting at the limiting pulse rate of 2 B {\displaystyle 2B} pulses per second as signalling at the Nyquist rate . Nyquist published his results in 1928 as part of his paper "Certain topics in Telegraph Transmission Theory". [ 1 ]
During 1928, Hartley formulated a way to quantify information and its line rate (also known as data signalling rate R bits per second). [ 2 ] This method, later known as Hartley's law, became an important precursor for Shannon's more sophisticated notion of channel capacity.
Hartley argued that the maximum number of distinguishable pulse levels that can be transmitted and received reliably over a communications channel is limited by the dynamic range of the signal amplitude and the precision with which the receiver can distinguish amplitude levels. Specifically, if the amplitude of the transmitted signal is restricted to the range of [− A ... + A ] volts, and the precision of the receiver is ±Δ V volts, then the maximum number of distinct pulses M is given by
By taking information per pulse in bit/pulse to be the base-2- logarithm of the number of distinct messages M that could be sent, Hartley [ 3 ] constructed a measure of the line rate R as:
where f p {\displaystyle f_{p}} is the pulse rate, also known as the symbol rate, in symbols/second or baud .
Hartley then combined the above quantification with Nyquist's observation that the number of independent pulses that could be put through a channel of one-sided bandwidth B {\displaystyle B} hertz was 2 B {\displaystyle 2B} pulses per second, to arrive at his quantitative measure for achievable line rate.
Hartley's law is sometimes quoted as just a proportionality between the analog bandwidth , B {\displaystyle B} , in Hertz and what today is called the digital bandwidth , R {\displaystyle R} , in bit/s. [ 4 ] Other times it is quoted in this more quantitative form, as an achievable line rate of R {\displaystyle R} bits per second: [ 5 ]
Hartley did not work out exactly how the number M should depend on the noise statistics of the channel, or how the communication could be made reliable even when individual symbol pulses could not be reliably distinguished to M levels; with Gaussian noise statistics, system designers had to choose a very conservative value of M {\displaystyle M} to achieve a low error rate.
The concept of an error-free capacity awaited Claude Shannon, who built on Hartley's observations about a logarithmic measure of information and Nyquist's observations about the effect of bandwidth limitations.
Hartley's rate result can be viewed as the capacity of an errorless M -ary channel of 2 B {\displaystyle 2B} symbols per second. Some authors refer to it as a capacity. But such an errorless channel is an idealization, and if M is chosen small enough to make the noisy channel nearly errorless, the result is necessarily less than the Shannon capacity of the noisy channel of bandwidth B {\displaystyle B} , which is the Hartley–Shannon result that followed later.
Claude Shannon 's development of information theory during World War II provided the next big step in understanding how much information could be reliably communicated through noisy channels. Building on Hartley's foundation, Shannon's noisy channel coding theorem (1948) describes the maximum possible efficiency of error-correcting methods versus levels of noise interference and data corruption. [ 6 ] [ 7 ] The proof of the theorem shows that a randomly constructed error-correcting code is essentially as good as the best possible code; the theorem is proved through the statistics of such random codes.
Shannon's theorem shows how to compute a channel capacity from a statistical description of a channel, and establishes that given a noisy channel with capacity C {\displaystyle C} and information transmitted at a line rate R {\displaystyle R} , then if
there exists a coding technique which allows the probability of error at the receiver to be made arbitrarily small. This means that theoretically, it is possible to transmit information nearly without error up to nearly a limit of C {\displaystyle C} bits per second.
The converse is also important. If
the probability of error at the receiver increases without bound as the rate is increased, so no useful information can be transmitted beyond the channel capacity. The theorem does not address the rare situation in which rate and capacity are equal.
The Shannon–Hartley theorem establishes what that channel capacity is for a finite-bandwidth continuous-time channel subject to Gaussian noise. It connects Hartley's result with Shannon's channel capacity theorem in a form that is equivalent to specifying the M in Hartley's line rate formula in terms of a signal-to-noise ratio, but achieving reliability through error-correction coding rather than through reliably distinguishable pulse levels.
If there were such a thing as a noise-free analog channel, one could transmit unlimited amounts of error-free data over it per unit of time (Note that an infinite-bandwidth analog channel could not transmit unlimited amounts of error-free data absent infinite signal power). Real channels, however, are subject to limitations imposed by both finite bandwidth and nonzero noise.
Bandwidth and noise affect the rate at which information can be transmitted over an analog channel. Bandwidth limitations alone do not impose a cap on the maximum information rate because it is still possible for the signal to take on an indefinitely large number of different voltage levels on each symbol pulse, with each slightly different level being assigned a different meaning or bit sequence. Taking into account both noise and bandwidth limitations, however, there is a limit to the amount of information that can be transferred by a signal of a bounded power, even when sophisticated multi-level encoding techniques are used.
In the channel considered by the Shannon–Hartley theorem, noise and signal are combined by addition. That is, the receiver measures a signal that is equal to the sum of the signal encoding the desired information and a continuous random variable that represents the noise. This addition creates uncertainty as to the original signal's value. If the receiver has some information about the random process that generates the noise, one can in principle recover the information in the original signal by considering all possible states of the noise process. In the case of the Shannon–Hartley theorem, the noise is assumed to be generated by a Gaussian process with a known variance. Since the variance of a Gaussian process is equivalent to its power, it is conventional to call this variance the noise power.
Such a channel is called the Additive White Gaussian Noise channel, because Gaussian noise is added to the signal; "white" means equal amounts of noise at all frequencies within the channel bandwidth. Such noise can arise both from random sources of energy and also from coding and measurement error at the sender and receiver respectively. Since sums of independent Gaussian random variables are themselves Gaussian random variables, this conveniently simplifies analysis, if one assumes that such error sources are also Gaussian and independent.
Comparing the channel capacity to the information rate from Hartley's law, we can find the effective number of distinguishable levels M : [ 8 ]
The square root effectively converts the power ratio back to a voltage ratio, so the number of levels is approximately proportional to the ratio of signal RMS amplitude to noise standard deviation.
This similarity in form between Shannon's capacity and Hartley's law should not be interpreted to mean that M {\displaystyle M} pulse levels can be literally sent without any confusion. More levels are needed to allow for redundant coding and error correction, but the net data rate that can be approached with coding is equivalent to using that M {\displaystyle M} in Hartley's law.
In the simple version above, the signal and noise are fully uncorrelated, in which case S + N {\displaystyle S+N} is the total power of the received signal and noise together. A generalization of the above equation for the case where the additive noise is not white (or that the S / N {\displaystyle S/N} is not constant with frequency over the bandwidth) is obtained by treating the channel as many narrow, independent Gaussian channels in parallel:
where
Note: the theorem only applies to Gaussian stationary process noise. This formula's way of introducing frequency-dependent noise cannot describe all continuous-time noise processes. For example, consider a noise process consisting of adding a random wave whose amplitude is 1 or −1 at any point in time, and a channel that adds such a wave to the source signal. Such a wave's frequency components are highly dependent. Though such a noise may have a high power, it is fairly easy to transmit a continuous signal with much less power than one would need if the underlying noise was a sum of independent noises in each frequency band.
For large or small and constant signal-to-noise ratios, the capacity formula can be approximated:
When the SNR is large ( S / N ≫ 1 ), the logarithm is approximated by
in which case the capacity is logarithmic in power and approximately linear in bandwidth (not quite linear, since N increases with bandwidth, imparting a logarithmic effect). This is called the bandwidth-limited regime .
where
Similarly, when the SNR is small (if S / N ≪ 1 {\displaystyle S/N\ll 1} ), applying the approximation to the logarithm:
then the capacity is linear in power. This is called the power-limited regime .
In this low-SNR approximation, capacity is independent of bandwidth if the noise is white, of spectral density N 0 {\displaystyle N_{0}} watts per hertz, in which case the total noise power is N = B ⋅ N 0 {\displaystyle N=B\cdot N_{0}} . | https://en.wikipedia.org/wiki/Shannon–Hartley_theorem |
The Shannon–Weaver model is one of the first models of communication . Initially published in the 1948 paper " A Mathematical Theory of Communication ", it explains communication in terms of five basic components: a source, a transmitter, a channel , a receiver, and a destination. The source produces the original message. The transmitter translates the message into a signal , which is sent using a channel. The receiver translates the signal back into the original message and makes it available to the destination. For a landline phone call, the person calling is the source. They use the telephone as a transmitter, which produces an electric signal that is sent through the wire as a channel. The person receiving the call is the destination and their telephone is the receiver.
Shannon and Weaver distinguish three types of problems of communication: technical, semantic , and effectiveness problems. They focus on the technical level, which concerns the problem of how to use a signal to accurately reproduce a message from one location to another location. The difficulty in this regard is that noise may distort the signal. They discuss redundancy as a solution to this problem: if the original message is redundant then the distortions can be detected, which makes it possible to reconstruct the source's original intention .
The Shannon–Weaver model of communication has been influential in various fields, including communication theory and information theory . Many later theorists have built their own models on its insights. However, it is often criticized based on the claim that it oversimplifies communication. One common objection is that communication should not be understood as a one-way process but as a dynamic interaction of messages going back and forth between both participants. Another criticism rejects the idea that the message exists prior to the communication and argues instead that the encoding is itself a creative process that creates the content.
The Shannon–Weaver model is one of the earliest models of communication . [ 2 ] [ 3 ] [ 4 ] It was initially published by Claude Shannon in his 1948 paper " A Mathematical Theory of Communication ". [ 5 ] The model was further developed together with Warren Weaver in their co-authored 1949 book The Mathematical Theory of Communication . [ 6 ] [ 7 ] It aims to provide a formal representation of the basic elements and relations involved in the process of communication . [ 8 ]
The model consists of five basic components: a source, a transmitter, a channel , a receiver, and a destination. [ 5 ] [ 2 ] [ 9 ] The source of information is usually a person and decides which message to send. The message can take various forms, such as a sequence of letters, sounds, or images. The transmitter is responsible for translating the message into a signal . To send the signal, a channel is required. [ 2 ] [ 5 ] [ 10 ] [ 7 ] Channels are ways of transmitting signals, like light, sound waves, radio waves, and electrical wires. [ 10 ] The receiver performs the opposite function of the transmitter: it translates the signal back into a message and makes it available to the destination. The destination is the person for whom the message was intended. [ 5 ] [ 2 ] [ 10 ]
Shannon and Weaver focus on telephonic conversation as the paradigmatic case of how messages are produced and transmitted through a channel. But their model is intended as a general model that can be applied to any form of communication. [ 9 ] [ 10 ] [ 11 ] For a regular face-to-face conversation, the person talking is the source, the mouth is the transmitter, the air is the channel transmitting the sound waves, the listener is the destination, and the ear is the receiver. In the case of a landline phone call, the source is the person calling, the transmitter is their telephone, the channel is the wire, the receiver is another telephone and the destination is the person using the second telephone. [ 10 ] [ 2 ] [ 5 ] To apply this model accurately to real-life cases, some of the components may have to be repeated. For the telephone call, for example, the mouth is also a transmitter before the telephone itself as a second transmitter. [ 10 ]
Shannon and Weaver identify and address problems in the study of communication at three basic levels: technical, semantic, and effectiveness problems (referred to as levels A, B, and C). [ 12 ] [ 10 ] Shannon and Weaver hold that models of communication should provide good responses to all three problems, ideally by showing how to make communication more accurate and efficient. [ 10 ] The prime focus of their model is the technical level, which concerns the issue of how to accurately reproduce a message from one location to another location. [ 5 ] [ 10 ] For this problem, it is not relevant what meaning the message carries. By contrast, it is only relevant that the message can be distinguished from different possible messages that could have been sent instead of it. [ 5 ]
Semantic problems go beyond the symbols themselves and ask how they convey meaning. Shannon and Weaver assumed that the meaning is already contained in the message but many subsequent communication theorists have further problematized this point by including the influence of cultural factors and the context in their models. The effectiveness problem is based on the idea that the person sending the message has some goal in mind concerning how the person receiving the message is going to react. In this regard, effectivity means that the reaction matches the speaker's goal. [ 12 ] [ 10 ] The problem of effectivity concerns the question of how to achieve this. Many critics have rejected this aspect of Shannon and Weaver's theory since it seems to equate communication with manipulation or propaganda . [ 10 ]
To solve the technical problem at level A, it is necessary for the receiver to reconstruct the original message from the signal. However, various forms of noise can interfere and distort it. [ 10 ] [ 12 ] [ 7 ] [ 11 ] Noise is not intended by the source and makes it harder for the receiver to reconstruct the source's intention found in the original message. Crackling sounds during a telephone call or snow on a television screen are examples of noise. One way to solve this problem is to make the information in the message partially redundant . This way, distortions can often be identified and the original meaning can be reconstructed. A very basic form of redundancy is to repeat the same message several times. But redundancy can take various other forms as well. For example, the English language is redundant in the sense that many possible combinations of letters are meaningless. So the term "comming" does not have a distinct meaning. For this reason, it can be identified as a misspelling of the term "coming", thus revealing the source's original intention. Redundancy makes it easier to detect distortions but its drawback is that messages carry less information. [ 10 ] [ 12 ]
The Shannon–Weaver model of communication has been influential, inspiring subsequent work in the field of communication studies . [ 10 ] [ 13 ] [ 11 ] Erik Hollnagel and David D. Woods even characterize it as the "mother of all models." [ 14 ] It has been widely adopted in various other fields, including information theory , organizational analysis, and psychology. Many later theorists expanded this model by including additional elements in order to take into account other aspects of communication. For example, Wilbur Schramm includes a feedback loop to understand communication as an interactive process and George Gerbner emphasizes the relation between communication and the reality to which the communication refers. Some of these models, like Gerbner's, are equally universal in that they apply to any form of communication. Others apply to more specific areas. For example, Lasswell's model and Westley and MacLean's model are specifically formulated for mass media . [ 13 ] Shannon's concepts were also popularized in John Robinson Pierce 's Symbols, Signals, and Noise , which introduces the topic to non-specialists. [ 15 ]
Many criticisms of the Shannon–Weaver model focus on its simplicity by pointing out that it leaves out vital aspects of communication. In this regard, it has been characterized as "inappropriate for analyzing social processes" [ 16 ] and as a "misleading misrepresentation of the nature of human communication". [ 17 ] A common objection is based on the fact that it is a linear transmission model: it conceptualizes communication as a one-way process going from a source to a destination. Against this approach, it is argued that communication is usually more interactive with messages and feedback going back and forth between the participants. This approach is implemented by non-linear transmission models, also termed interaction models. [ 18 ] [ 3 ] [ 19 ] They include Wilbur Schramm's model , Frank Dance's helical-spiral model, a circular model developed by Lee Thayer, and the "sawtooth" model due to Paul Watzlawick, Janet Beavin , and Don Jackson. [ 9 ] [ 20 ] These approaches emphasize the dynamic nature of communication by showing how the process evolves as a multi-directional exchange of messages. [ 21 ] [ 3 ] [ 20 ]
Another criticism focuses on the fact that Shannon and Weaver understand the message as a form of preexisting information. I. A. Richards criticizes this approach for treating the message as a preestablished entity that is merely packaged by the transmitter and later unpackaged by the receiver. [ 13 ] This outlook is characteristic of all transmission models. They contrast with constitutive models, [ 18 ] which see meanings as "reflexively constructed, maintained, or negotiated in the act of communicating". [ 22 ] Richards argues that the message does not exist before it is articulated. This means that the encoding is itself a creative process that creates the content. Before it, there is a need to articulate oneself but no precise pre-existing content. [ 13 ] The communicative process may not just affect the meaning of the message but also the social identities of the communicators, which are established and modified in the ongoing communicative process. [ 22 ] | https://en.wikipedia.org/wiki/Shannon–Weaver_model |
Shanon Shah (born 14 August 1978 in Alor Star , Kedah), is a singer-songwriter, playwright and academic from Malaysia . He released two albums Dilanda Cinta (2005) [ 1 ] and Suara Yang Ku Dengar (2010) [ 2 ] on the InterGlobal Music Malaysia independent label. He is noted for his emotive voice and cabaret-style piano playing.
Trained as a chemical engineer, [ 3 ] Shanon has previously worked as a credit risk analyst, [ 4 ] human rights advocate and journalist. [ 5 ] In his various writings, he focuses on issues relating to gender , sexuality and Islam .
In 2003, Shanon won the Mandarin Oriental Fan of the Arts Most Promising Artist Award at the 2nd Annual Boh Cameronian Arts Awards. [ 6 ] Two years later, he went on to win the Anugerah Industri Muzik award for best male vocal in an album for Dilanda Cinta . [ 7 ]
In 2007, he entered the Ikon Malaysia televised competition which looked for an icon among existing Southeast Asian artistes. The Malaysian level of the competition was ultimately won by Jaclyn Victor .
Shanon has also performed as a duo with fellow singer-songwriter Azmyl Yunor and with his backing band the Cintas. Fellow singer-songwriter Ariff Akhir has also performed as part of the Cintas, and produced Shanon's second album, Suara Yang Ku Dengar . [ 8 ]
Shanon's musical influences include Leonard Cohen , Aimee Mann and Sam Phillips . [ 4 ]
Shanon Shah is also a playwright. His play Air Con was by the Instant Cafe Theatre Company's FIRSTWoRKS programme. [ 9 ] The play, directed by Jo Kukathas and Zalfian Fuzi, was performed to critical acclaim prompting a revival in 2009.
One reviewer praised not only the play's take on issues such as hate crimes against transsexuals, homophobic bullying in schools, racism and religious fundamentalism, but also its comedic touches and bilingual dialogue. [ 10 ] Shanon has said he is greatly influenced by award-winning Malaysian actor and playwright Jit Murad. [ 11 ]
Air Con was nominated in nine categories for the 7th BOH Cameronian Arts Awards, winning four awards, including Best Original Script (Bahasa Malaysia). [ 12 ]
Shanon also co-wrote the screenplay and four original songs for Chris Chong Chan Fui's first full-length feature film Karaoke , [ 13 ] [ 14 ] which in 2009 was selected for the Directors' Fortnight of the Cannes Film Festival . The songs for Karaoke eventually made it into Suara Yang Ku Dengar .
Shanon Shah was also the former full-time Columns and Comments Editor at The Nut Graph , a bilingual, independent, Malaysian online news site aiming "to provide space for columnists and reader comments from as broad a political spectrum, and from as many sectors of interest, as possible". [ 15 ] He contributed several English-language features, commentaries and interviews on the politics of Islam in Malaysia. His fortnightly Malay-language column, Secubit Garam , often took a light-hearted approach to serious political concerns through the fictional agony aunt Kak Nora. [ 16 ]
Shanon has also been published in other print anthologies. His 5,000-word essay "The Khutbah Diaries" was published in New Malaysian Essays 2 in 2009. In the same year his essay, "Muslim 2 Muslim", was published in Body 2 Body , [ 17 ] an English-language anthology of fiction and non-fiction on sexual diversity in Malaysia. Body 2 Body was published by writer-director Amir Muhammad 's publishing company, Matahari Books .
In June 2012, Shanon's essay "Lot's Legacy" was published in the third issue of Critical Muslim ( Fear and Loathing ), [ 18 ] a British "quarterly magazine of ideas and issues showcasing ground-breaking thinking on Islam and what it means to be a Muslim in a rapidly changing, interconnected world". [ 19 ] The magazine is co-edited by London-based Muslim scholar and critic Ziauddin Sardar .
In 2010, Shanon was awarded the Chevening Scholarship to pursue his Master of Arts (MA) in Religion in Contemporary Society at King's College London . [ 3 ] He completed his MA in 2011 and won the Shelford MA Prize from King's School of Arts and Humanities. [ 20 ]
He is currently a doctoral candidate at King's College London. [ 21 ] | https://en.wikipedia.org/wiki/Shanon_Shah |
In metallurgy , a shape-memory alloy ( SMA ) is an alloy that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. It is also known in other names such as memory metal , memory alloy , smart metal , smart alloy , and muscle wire . [ citation needed ] The "memorized geometry" can be modified by fixating the desired geometry and subjecting it to a thermal treatment, for example a wire can be taught to memorize the shape of a coil spring.
Parts made of shape-memory alloys can be lightweight, solid-state alternatives to conventional actuators such as hydraulic , pneumatic , and motor-based systems. They can also be used to make hermetic joints in metal tubing, and it can also replace a sensor-actuator closed loop to control water temperature by governing hot and cold water flow ratio.
The two most prevalent shape-memory alloys are copper - aluminium - nickel and nickel - titanium ( NiTi ), but SMAs can also be created by alloying zinc , copper , gold and iron .
Although iron-based and copper-based SMAs, such as Fe -Mn-Si, Cu-Zn-Al and Cu-Al-Ni, are commercially available and cheaper than NiTi, NiTi-based SMAs are preferable for most applications due to their stability and practicability [ 1 ] [ 2 ] [ 3 ] as well as their superior thermo-mechanical performance. [ 4 ] SMAs can exist in two different phases, with three different crystal structures (i.e. twinned martensite, detwinned martensite, and austenite) and six possible transformations. [ 5 ] [ 6 ] The thermo-mechanic behavior of the SMAs is governed by a phase transformation between the austenite and the martensite.
NiTi alloys change from austenite to martensite upon cooling starting from a temperature below M s ; M f is the temperature at which the transition to martensite completes upon cooling. Accordingly, during heating A s and A f are the temperatures at which the transformation from martensite to austenite starts and finishes.
Applying a mechanical load to the martensite leads to a re-orientation of the crystals, referred to as “de-twinning”, which results in a deformation which is not recovered (remembered) after releasing the mechanical load. De-twinning starts at a certain stress σ s and ends at σ f above which martensite continue exhibiting only elastic behavior (as long as the load is below the yield stress). The memorized deformation from detwinning is recovered after heating to austenite.
The phase transformation from austenite to martensite can also occur at constant temperature by applying a mechanical load above a certain level. The transformation is reversed when the load is released.
The transition from the martensite phase to the austenite phase is only dependent on temperature and stress, not time, as most phase changes are, as there is no diffusion involved. Similarly, the austenite structure receives its name from steel alloys of a similar structure. It is the reversible diffusionless transition between these two phases that results in special properties. While martensite can be formed from austenite by rapidly cooling carbon - steel , this process is not reversible, so steel does not have shape-memory properties.
In this figure the vertical axis represents the martensite fraction. The difference between the heating transition and the cooling transition gives rise to hysteresis where some of the mechanical energy is lost in the process. The shape of the curve depends on the material properties of the shape-memory alloy, such as the alloy's composition [ 7 ] and work hardening . [ 8 ]
The shape memory effect (SME) [ 9 ] occurs because a temperature-induced phase transformation reverses deformation, as shown in the previous hysteresis curve. Typically the martensitic phase is monoclinic or orthorhombic (B19' or B19 ). Since these crystal structures do not have enough slip systems for easy dislocation motion, they deform by twinning —or rather, detwinning. [ 10 ]
Martensite is thermodynamically favored at lower temperatures, while austenite ( B2 cubic) is thermodynamically favored at higher temperatures. Since these structures have different lattice sizes and symmetry, cooling austenite into martensite introduces internal strain energy in the martensitic phase. To reduce this energy, the martensitic phase forms many twins—this is called "self-accommodating twinning" and is the twinning version of geometrically necessary dislocations . Since the shape memory alloy will be manufactured from a higher temperature and is usually engineered so that the martensitic phase is dominant at operating temperature to take advantage of the shape memory effect, SMAs "start" highly twinned. [ 11 ]
When the martensite is loaded, these self-accommodating twins provide an easy path for deformation. Applied stresses will detwin the martensite, but all of the atoms stay in the same position relative to the nearby atoms—no atomic bonds are broken or reformed (as they would be by dislocation motion). Thus, when the temperature is raised and austenite becomes thermodynamically favored, all of the atoms rearrange to the B2 structure which happens to be the same macroscopic shape as the B19' pre-deformation shape. [ 12 ] This phase transformation happens extremely quickly and gives SMAs their distinctive "snap".
Repeated use of the shape-memory effect may lead to a shift of the characteristic transformation temperatures (this effect is known as functional fatigue, as it is closely related with a change of microstructural and functional properties of the material). [ 13 ] The maximum temperature at which SMAs can no longer be stress induced is called M d , where the SMAs are permanently deformed. [ 14 ]
Shape-memory alloys have different shape-memory effects. The two common effects are one-way SMA and two-way SMA. A schematic of the effects is shown below.
The procedures are very similar: starting from martensite, adding a deformation, heating the sample and cooling it again.
When a shape-memory alloy is in its cold state (below M f ), the metal can be bent or stretched and will hold those shapes until heated above the transition temperature. Upon heating, the shape changes to its original. When the metal cools again, it will retain the shape, until deformed again.
With the one-way effect, cooling from high temperatures does not cause a macroscopic shape change. A deformation is necessary to create the low-temperature shape. On heating, transformation starts at A s and is completed at A f (typically 2 to 20 °C or hotter, depending on the alloy or the loading conditions). A s is determined by the alloy type and composition and can vary between −150 °C and 200 °C .
The two-way shape-memory effect is the effect that the material remembers two different shapes: one at low temperatures, and one at the high temperature.
A material that shows a shape-memory effect during both heating and cooling is said to have two-way shape memory. This can also be obtained without the application of an external force (intrinsic two-way effect).
The reason the material behaves so differently in these situations lies in training. Training implies that a shape memory can "learn" to behave in a certain way.
Under normal circumstances, a shape-memory alloy "remembers" its low-temperature shape, but upon heating to recover the high-temperature shape, immediately "forgets" the low-temperature shape. However, it can be "trained" to "remember" to leave some reminders of the deformed low-temperature condition in the high-temperature phases. One way of training the SMA consists in applying a cyclic thermal load under constant stress field. During this process, internal defects are introduced into the microstructure which generates internal permanent stresses that facilitate the orientation of the martensitic crystals. [ 15 ] Therefore, while cooling a trained SMA in austenitic phase under no applied stress, the martensite is formed detwinned due to the internal stresses, which leads to the material shape change. And while heating back the SMA into austenite, it recovers its initial shape.
There are several ways of doing this. [ 16 ] A shaped, trained object heated beyond a certain point will lose the two-way memory effect.
SMAs display a phenomenon sometimes called superelasticity, but is more accurately described as pseudoelasticity . “Superelasticity” implies that the atomic bonds between atoms stretch to an extreme length without incurring plastic deformation. Pseudoelasticity still achieves large, recoverable strains with little to no permanent deformation, but it relies on more complex mechanisms.
SMAs exhibit at least 3 kinds of pseudoelasticty. The two less-studied kinds of pseudoelasticity are pseudo-twin formation and rubber-like behavior due to short range order. [ 17 ]
The main pseudoelastic effect comes from a stress-induced phase transformation. The figure on the right exhibits how this process occurs.
Here a load is isothermally applied to a SMA above the austenite finish temperature, A f , but below the martensite deformation temperature, M d . The figure above illustrates how this is possible, by relating the pseudoelastic stress-induced phase transformation to the shape memory effect temperature induced phase transformation. For a particular point on A f, it is possible to choose a point on the M s line with a higher temperature, as long as that point M d also has a higher stress . The material initially exhibits typical elastic-plastic behavior for metals. However, once the material reaches the martensitic stress, the austenite will transform to martensite and detwin. As previously discussed, this detwinning is reversible when transforming back from martensite to austenite. If large stresses are applied, plastic behavior such as detwinning and slip of the martensite will initiate at sites such as grain boundaries or inclusions. [ 19 ] [ 20 ] If the material is unloaded before plastic deformation occurs, it will revert to austenite once a critical stress for austenite is reached (σ as ). The material will recover nearly all strain that was induced from the structural change, and for some SMAs this can be strains greater than 10 percent. [ 21 ] [ 22 ] This hysteresis loop shows the work done for each cycle of the material between states of small and large deformations, which is important for many applications.
In a plot of strain versus temperature, the austenite and martensite start and finish lines run parallel. The SME and pseudoelasticity are actually different parts of the same phenomenon, as shown on the left.
The key to the large strain deformations is the difference in crystal structure between the two phases. Austenite generally has a cubic structure while martensite can be monoclinic or another structure different from the parent phase, typically with lower symmetry. For a monoclinic martensitic material such as Nitinol, the monoclinic phase has lower symmetry which is important as certain crystallographic orientations will accommodate higher strains compared to other orientations when under an applied stress. Thus it follows that the material will tend to form orientations that maximize the overall strain prior to any increase in applied stress. [ 23 ] One mechanism that aids in this process is the twinning of the martensite phase. In crystallography, a twin boundary is a two-dimensional defect in which the stacking of atomic planes of the lattice are mirrored across the plane of the boundary. Depending on stress and temperature, these deformation processes will compete with permanent deformation such as slip.
σ ms is dependent on parameters such as temperature and the number of nucleation sites for phase nucleation. Interfaces and inclusions will provide general sites for the transformation to begin, and if these are great in number, it will increase the driving force for nucleation. [ 24 ] A smaller σ ms will be needed than for homogeneous nucleation. Likewise, increasing temperature will reduce the driving force for the phase transformation, so a larger σ ms will be necessary. One can see that as you increase the operational temperature of the SMA, σ ms will be greater than the yield strength, σ y , and superelasticity will no longer be observable.
The first reported steps towards the discovery of the shape-memory effect were taken in the 1930s. According to Otsuka and Wayman, Arne Ölander discovered the pseudoelastic behavior of the Au-Cd alloy in 1932. Greninger and Mooradian (1938) observed the formation and disappearance of a martensitic phase by decreasing and increasing the temperature of a Cu-Zn alloy. The basic phenomenon of the memory effect governed by the thermoelastic behavior of the martensite phase was widely reported a decade later by Kurdjumov and Khandros (1949) and also by Chang and Read (1951). [ 13 ]
The nickel-titanium alloys were first developed in 1962–1963 by the United States Naval Ordnance Laboratory and commercialized under the trade name Nitinol (an acronym for Nickel Titanium Naval Ordnance Laboratories). Their remarkable properties were discovered by accident. A sample that was bent out of shape many times was presented at a laboratory management meeting. One of the associate technical directors, Dr. David S. Muzzey, decided to see what would happen if the sample was subjected to heat and held his pipe lighter underneath it. To everyone's amazement the sample stretched back to its original shape. [ 25 ] [ 26 ]
There is another type of SMA, called a ferromagnetic shape-memory alloy (FSMA), that changes shape under strong magnetic fields. These materials are of particular interest as the magnetic response tends to be faster and more efficient than temperature-induced responses.
Metal alloys are not the only thermally-responsive materials; shape-memory polymers have also been developed, and became commercially available in the late 1990s.
Many metals have several different crystal structures at the same composition, but most metals do not show this shape-memory effect. The special property that allows shape-memory alloys to revert to their original shape after heating is that their crystal transformation is fully reversible. In most crystal transformations, the atoms in the structure will travel through the metal by diffusion, changing the composition locally, even though the metal as a whole is made of the same atoms. A reversible transformation does not involve this diffusion of atoms, instead all the atoms shift at the same time to form a new structure, much in the way a parallelogram can be made out of a square by pushing on two opposing sides. At different temperatures, different structures are preferred and when the structure is cooled through the transition temperature, the martensitic structure forms from the austenitic phase.
Shape-memory alloys are typically made by casting, using vacuum arc melting or induction melting. These are specialist techniques used to keep impurities in the alloy to a minimum and ensure the metals are well mixed. The ingot is then hot rolled into longer sections and then drawn to turn it into wire.
The way in which the alloys are "trained" depends on the properties wanted. The "training" dictates the shape that the alloy will remember when it is heated. This occurs by heating the alloy so that the dislocations re-order into stable positions, but not so hot that the material recrystallizes . They are heated to between 400 °C and 500 °C for 30 minutes, shaped while hot, and then are cooled rapidly by quenching in water or by cooling with air.
The copper-based and NiTi-based shape-memory alloys are considered to be engineering materials. These compositions can be manufactured to almost any shape and size.
The yield strength of shape-memory alloys is lower than that of conventional steel, but some compositions have a higher yield strength than plastic or aluminum. The yield stress for Ni Ti can reach 500 MPa . The high cost of the metal itself and the processing requirements make it difficult and expensive to implement SMAs into a design. As a result, these materials are used in applications where the super elastic properties or the shape-memory effect can be exploited. The most common application is in actuation.
One of the advantages to using shape-memory alloys is the high level of recoverable plastic strain that can be induced. The maximum recoverable strain these materials can hold without permanent damage is up to 8% for some alloys. This compares with a maximum strain 0.5% for conventional steels.
SMA have many advantages over traditional actuators, but do suffer from a series of limitations that may impede practical application. In numerous studies, it was emphasised that only a few of patented shape memory alloy applications are commercially successful due to material limitations combined with a lack of material and design knowledge and associated tools, such as improper design approaches and techniques used. [ 27 ] The challenges in designing SMA applications are to overcome their limitations, which include a relatively small usable strain, low actuation frequency, low controllability, low accuracy and low energy efficiency. [ 28 ]
SMA actuators are typically actuated electrically, where an electric current results in Joule heating . Deactivation typically occurs by free convective heat transfer to the ambient environment. Consequently, SMA actuation is typically asymmetric, with a relatively fast actuation time and a slow deactuation time. A number of methods have been proposed to reduce SMA deactivation time, including forced convection, [ 29 ] and lagging the SMA with a conductive material in order to manipulate the heat transfer rate.
Novel methods to enhance the feasibility of SMA actuators include the use of a conductive " lagging ". this method uses a thermal paste to rapidly transfer heat from the SMA by conduction. This heat is then more readily transferred to the environment by convection as the outer radii (and heat transfer area) are significantly greater than for the bare wire. This method results in a significant reduction in deactivation time and a symmetric activation profile. As a consequence of the increased heat transfer rate, the required current to achieve a given actuation force is increased. [ 30 ]
SMA is subject to structural fatigue – a failure mode by which cyclic loading results in the initiation and propagation of a crack that eventually results in catastrophic loss of function by fracture. The physics behind this fatigue mode is accumulation of microstructural damage during cyclic loading. This failure mode is observed in most engineering materials, not just SMAs.
SMAs are also subject to functional fatigue, a failure mode not typical of most engineering materials, whereby the SMA does not fail structurally but loses its shape-memory/superelastic characteristics over time. As a result of cyclic loading (both mechanical and thermal), the material loses its ability to undergo a reversible phase transformation. For example, the working displacement in an actuator decreases with increasing cycle numbers. The physics behind this is gradual change in microstructure—more specifically, the buildup of accommodation slip dislocations . This is often accompanied by a significant change in transformation temperatures. [ 32 ] Design of SMA actuators may also influence both structural and functional fatigue of SMA, such as the pulley configurations in SMA-Pulley system. [ 33 ]
SMA actuators are typically actuated electrically by Joule heating . If the SMA is used in an environment where the ambient temperature is uncontrolled, unintentional actuation by ambient heating may occur.
Boeing , General Electric Aircraft Engines , Goodrich Corporation , NASA , Texas A&M University and All Nippon Airways developed the Variable Geometry Chevron using a NiTi SMA. Such a variable area fan nozzle (VAFN) design would allow for quieter and more efficient jet engines in the future. In 2005 and 2006, Boeing conducted successful flight testing of this technology. [ 34 ]
SMAs are being explored as vibration dampers for launch vehicles and commercial jet engines. The large amount of hysteresis observed during the superelastic effect allow SMAs to dissipate energy and dampen vibrations. These materials show promise for reducing the high vibration loads on payloads during launch as well as on fan blades in commercial jet engines, allowing for more lightweight and efficient designs. [ 35 ] SMAs also exhibit potential for other high shock applications such as ball bearings and landing gear. [ 36 ]
There is also strong interest in using SMAs for a variety of actuator applications in commercial jet engines, which would significantly reduce their weight and boost efficiency. [ 37 ] Further research needs to be conducted in this area, however, to increase the transformation temperatures and improve the mechanical properties of these materials before they can be successfully implemented. A review of recent advances in high-temperature shape-memory alloys (HTSMAs) is presented by Ma et al. [ 21 ]
A variety of wing-morphing technologies are also being explored. [ 35 ]
The first high-volume product (> 5Mio actuators / year) is an automotive valve used to control low pressure pneumatic bladders in a car seat that adjust the contour of the lumbar support / bolsters. The overall benefits of SMA over traditionally-used solenoids in this application (lower noise/EMC/weight/form factor/power consumption) were the crucial factor in the decision to replace the old standard technology with SMA.
The 2014 Chevrolet Corvette became the first vehicle to incorporate SMA actuators, which replaced heavier motorized actuators to open and close the hatch vent that releases air from the trunk, making it easier to close. A variety of other applications are also being targeted, including electric generators to generate electricity from exhaust heat and on-demand air dams to optimize aerodynamics at various speeds.
There have also been limited studies on using these materials in robotics , for example the hobbyist robot Stiquito (and "Roboterfrau Lara" [ 38 ] ), as they make it possible to create very lightweight robots. Recently, a prosthetic hand was introduced by Loh et al. that can almost replicate the motions of a human hand [Loh2005]. Other biomimetic applications are also being explored. Weak points of the technology are energy inefficiency, slow response times , and large hysteresis .
SMAs are also used for actuating valves . [ 39 ] The SMA valves are particularly compact in design.
There is some SMA-based prototypes of robotic hand that using shape memory effect (SME) to move fingers. [ 40 ]
SMAs find a variety of applications in civil structures such as bridges and buildings. In the form of rebars or plates, they can be used for flexural, shear and seismic strengthening of concrete and steel structures. Another application is Intelligent Reinforced Concrete (IRC), which incorporates SMA wires embedded within the concrete. These wires can sense cracks and contract to heal micro-sized cracks. Also the active tuning of structural natural frequency using SMA wires to dampen vibrations is possible, as well as the usage of SMA fibers in concrete. [ 41 ]
The first consumer commercial application was a shape-memory coupling for piping, e.g. oil pipe lines, for industrial applications, water pipes and similar types of piping for consumer/commercial applications.
Several smartphone companies have released handsets with optical image stabilisation (OIS) modules incorporating SMA actuators, manufactured under licence from Cambridge Mechatronics.
Shape-memory alloys are applied in medicine, for example, as fixation devices for osteotomies in orthopaedic surgery , as the actuator in surgical tools; active steerable surgical needles for minimally invasive percutaneous cancer interventions in the surgical procedures such as biopsy and brachytherapy , [ 42 ] in dental braces to exert constant tooth-moving forces on the teeth, in Capsule Endoscopy they can be used as a trigger for biopsy action.
The late 1980s saw the commercial introduction of Nitinol as an enabling technology in a number of minimally invasive endovascular medical applications. While more costly than stainless steel, the self expanding properties of Nitinol alloys manufactured to BTR (Body Temperature Response), have provided an attractive alternative to balloon expandable devices in stent grafts where it gives the ability to adapt to the shape of certain blood vessels when exposed to body temperature. On average, 50% of all peripheral vascular stents currently available on the worldwide market are manufactured with Nitinol.
Eyeglass frames made from titanium-containing SMAs are marketed under the trademarks Flexon and TITANflex. These frames are usually made out of shape-memory alloys that have their transition temperature set below the expected room temperature. This allows the frames to undergo large deformation under stress, yet regain their intended shape once the metal is unloaded again. The very large apparently elastic strains are due to the stress-induced martensitic effect, where the crystal structure can transform under loading, allowing the shape to change temporarily under load. This means that eyeglasses made of shape-memory alloys are more robust against being accidentally damaged.
Memory metal has been utilized in orthopedic surgery as a fixation-compression device for osteotomies , typically for lower extremity procedures. The device, usually in the form of a large staple, is stored in a refrigerator in its malleable form and is implanted into pre-drilled holes in the bone across an osteotomy. As the staple warms it returns to its non-malleable state and compresses the bony surfaces together to promote bone union. [ 43 ]
The range of applications for SMAs has grown over the years, a major area of development being dentistry. One example is the prevalence of dental braces using SMA technology to exert constant tooth-moving forces on the teeth; the nitinol archwire was developed in 1972 by orthodontist George Andreasen . [ 44 ] This revolutionized clinical orthodontics. Andreasen's alloy has a patterned shape memory, expanding and contracting within given temperature ranges because of its geometric programming.
Harmeet D. Walia later utilized the alloy in the manufacture of root canal files for endodontics .
Traditional active cancellation techniques for tremor reduction use electrical, hydraulic, or pneumatic systems to actuate an object in the direction opposite to the disturbance. However, these systems are limited due to the large infrastructure required to produce large amplitudes of power at human tremor frequencies. SMAs have proven to be an effective method of actuation in hand-held applications, and have enabled a new class active tremor cancellation devices. [ 45 ] One recent example of such device is the Liftware spoon, developed by Verily Life Sciences subsidiary Lift Labs .
Experimental solid state heat engines, operating from the relatively small temperature differences in cold and hot water reservoirs, have been developed since the 1970s, including the Banks Engine, developed by Ridgway Banks .
Sold in small round lengths for use in affixment-free bracelets.
German scientists at Saarland University have produced a prototype machine that transfers heat using a nickel-titanium ("nitinol") alloy wire wrapped around a rotating cylinder. As the cylinder rotates, heat is absorbed on one side and released on the other, as the wire changes from its "superelastic" state to its unloaded state. According to a 2019 article released by Saarland University, the efficiency by which the heat is transferred appears to be higher than that of a typical heat pump or air conditioner. [ 46 ]
Almost all air conditioners and heat pumps in use today employ vapor-compression of refrigerants . Over time, some of the refrigerants used in these systems leak into the atmosphere and contribute to global warming . If the new technology, which uses no refrigerants, proves economical and practical, it might offer a significant breakthrough in the effort to reduce climate change. [ citation needed ]
Shape memory alloys (SMAs), such as nickel-titanium (Nitinol) , are used in clamping systems due to their unique thermo-responsive behavior. [ 47 ] The clamps made from SMA are used in the dentofacial surgery to heal mandibular fractures . [ 48 ]
A variety of alloys exhibit the shape-memory effect. Alloying constituents can be adjusted to control the transformation temperatures of the SMA. Some common systems include the following (by no means an exhaustive list):
Media related to Shape-memory materials at Wikimedia Commons
Veritasium - How NASA Reinvented The Wheel | https://en.wikipedia.org/wiki/Shape-memory_alloy |
Shape-memory coupling is a system for connecting pipes using shape-memory alloys . In its typical form the technique uses an internally ribbed sleeve of alloy such as Tinel (see Nitinol ) that is slightly smaller in diameter than the pipes it is to connect. The sleeve is cooled in liquid nitrogen then, in this low-temperature state, mechanically expanded with a mandrel to fit easily over the two pipe ends to be joined. After fitting, it is allowed to rewarm, when the memory effect causes the sleeve to shrink back to its original smaller size, creating a tight joint.
It was first produced in the late 1960s or early 1970s by the Raychem Corporation under the trade name CryoFit. Manufacture of these couplings for aerospace hydraulic connections was later transferred to AMCI (Advanced Metal Components Inc.) and then later to Aerofit Products Inc. Additional products using the same shape-memory alloy technology are produced under Cryolive and CryoFlare trade names.
This industry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shape-memory_coupling |
Shape-memory polymers (SMPs) are polymeric smart materials that have the ability to return from a deformed state (temporary shape) to their original (permanent) shape when induced by an external stimulus (trigger), such as temperature change. [ 1 ]
Polymer that, after heating and being subjected to a plastic deformation, resumes its original shape
when heated above its glass-transition or melting temperature [ 2 ]
Note:
SMPs can retain two or sometimes three shapes, and the transition between those is often induced by temperature change. In addition to temperature change, the shape change of SMPs can also be triggered by an electric or magnetic field , [ 3 ] light [ 4 ] or solution. [ 5 ] Like polymers in general, SMPs cover a wide range of properties from stable to biodegradable , from soft to hard, and from elastic to rigid, depending on the structural units that constitute the SMP. SMPs include thermoplastic and thermoset (covalently cross-linked) polymeric materials. SMPs are known to be able to store up to three different shapes in memory. [ 6 ] SMPs have demonstrated recoverable strains of above 800%. [ 7 ]
Two important quantities that are used to describe shape-memory effects are the strain recovery rate ( R r ) and strain fixity rate ( R f ). The strain recovery rate describes the ability of the material to memorize its permanent shape, while the strain fixity rate describes the ability of switching segments to fix the mechanical deformation.
where N {\displaystyle N} is the cycle number, ε m {\displaystyle \varepsilon _{m}} is the maximum strain imposed on the material, and ε p ( N ) {\displaystyle \varepsilon _{p}(N)} and ε p ( N − 1 ) {\displaystyle \varepsilon _{p}(N-1)} are the strains of the sample in two successive cycles in the stress-free state before yield stress is applied.
Shape-memory effect can be described briefly as the following mathematical model: [ 8 ]
where E g {\displaystyle E_{g}} is the glassy modulus, E r {\displaystyle E_{r}} is the rubbery modulus, f I R {\displaystyle f_{IR}} is viscous flow strain and f α {\displaystyle f_{\alpha }} is strain for t >> t r {\displaystyle t>>t_{r}} .
While most traditional shape-memory polymers can only hold a permanent and temporary shape, recent technological advances have allowed the introduction of triple-shape-memory materials. Much as a traditional double-shape-memory polymer will change from a temporary shape back to a permanent shape at a particular temperature, triple-shape-memory polymers will switch from one temporary shape to another at the first transition temperature, and then back to the permanent shape at another, higher activation temperature. This is usually achieved by combining two double-shape-memory polymers with different glass transition temperatures [ 9 ] or when heating a programmed shape-memory polymer first above the glass transition temperature and then above the melting transition temperature of the switching segment. [ 10 ] [ 11 ]
Polymers exhibiting a shape-memory effect have both a visible, current (temporary) form and a stored (permanent) form. Once the latter has been manufactured by conventional methods, the material is changed into another, temporary form by processing through heating, deformation, and finally, cooling. The polymer maintains this temporary shape until the shape change into the permanent form is activated by a predetermined external stimulus. The secret behind these materials lies in their molecular network structure, which contains at least two separate phases. The phase showing the highest thermal transition, T perm , is the temperature that must be exceeded to establish the physical crosslinks responsible for the permanent shape. The switching segments, on the other hand, are the segments with the ability to soften past a certain transition temperature ( T trans ) and are responsible for the temporary shape. In some cases this is the glass transition temperature ( T g ) and others the melting temperature ( T m ). Exceeding T trans (while remaining below T perm ) activates the switching by softening these switching segments and thereby allowing the material to resume its original (permanent) form. Below T trans , flexibility of the segments is at least partly limited. If T m is chosen for programming the SMP, strain-induced crystallization of the switching segment can be initiated when it is stretched above T m and subsequently cooled below T m . These crystallites form covalent netpoints which prevent the polymer from reforming its usual coiled structure. The hard to soft segment ratio is often between 5/95 and 95/5, but ideally this ratio is between 20/80 and 80/20. [ 12 ] The shape-memory polymers are effectively viscoelastic and many models and analysis methods exist.
In the amorphous state, polymer chains assume a completely random distribution within the matrix. W represents the probability of a strongly coiled conformation, which is the conformation with maximum entropy, and is the most likely state for an amorphous linear polymer chain. This relationship is represented mathematically by Boltzmann's entropy formula S = k ln W , where S is the entropy and k is the Boltzmann constant .
In the transition from the glassy state to a rubber-elastic state by thermal activation, the rotations around segment bonds become increasingly unimpeded. This allows chains to assume other possibly, energetically equivalent conformations with a small amount of disentangling. As a result, the majority of SMPs will form compact, random coils because this conformation is entropically favored over a stretched conformation. [ 1 ]
Polymers in this elastic state with number average molecular weight greater than 20,000 stretch in the direction of an applied external force. If the force is applied for a short time, the entanglement of polymer chains with their neighbors will prevent large movement of the chain and the sample recovers its original conformation upon removal of the force. If the force is applied for a longer period of time, however, a relaxation process takes place whereby a plastic, irreversible deformation of the sample takes place due to the slipping and disentangling of the polymer chains. [ 1 ]
To prevent the slipping and flow of polymer chains, cross-linking can be used, both chemical and physical.
Representative shape-memory polymers in this category are polyurethanes , [ 13 ] [ 14 ] polyurethanes with ionic or mesogenic components made by prepolymer method. Other block copolymers also show the shape-memory effect, such as, block copolymer of polyethylene terephthalate (PET) and polyethyleneoxide (PEO), block copolymers containing polystyrene and poly(1,4-butadiene), and an ABA triblock copolymer made from poly(2-methyl-2-oxazoline) and polytetrahydrofuran .
A linear, amorphous polynorbornene (Norsorex, developed by CdF Chemie/Nippon Zeon) or organic-inorganic hybrid polymers consisting of polynorbornene units that are partially substituted by polyhedral oligo silsesquioxane (POSS) also have shape-memory effect.
Another example reported in the literature is a copolymer consisting of polycyclooctene (PCOE) and poly(5-norbornene-exo,exo-2,3-dicarboxylic anhydride) (PNBEDCA), which was synthesized through ring-opening metathesis polymerization (ROMP). Then the obtained copolymer P(COE-co-NBEDCA) was readily modified by grafting reaction of NBEDCA units with polyhedral oligomeric silsesquioxanes (POSS) to afford a functionalized copolymer P(COE-co-NBEDCA-g-POSS). It exhibits shape-memory effect. [ 15 ]
The main limitation of physically crosslinked polymers for the shape-memory application is irreversible deformation during memory programming due to the creep . The network polymer can be synthesized by either polymerization with multifunctional (3 or more) crosslinker or by subsequent crosslinking of a linear or branched polymer. They form insoluble materials which swell in certain solvents. [ 1 ]
This material can be made by using excess diisocyanate or by using a crosslinker such as glycerin , trimethylol propane . Introduction of covalent crosslinking improves in creep, increase in recovery temperature and recovery window. [ 16 ]
The PEO-PET block copolymers can be crosslinked by using maleic anhydride , glycerin or dimethyl 5-isophthalates as a crosslinking agent. The addition of 1.5 wt% maleic anhydride increased in shape recovery from 35% to 65% and tensile strength from 3 to 5 MPa. [ 17 ]
While shape-memory effects are traditionally limited to thermosetting plastics , some thermoplastic polymers, most notably PEEK , can be used as well. [ 18 ]
Light-activated shape-memory polymers (LASMP) use processes of photo-crosslinking and photo-cleaving to change T g . Photo-crosslinking is achieved by using one wavelength of light, while a second wavelength of light reversibly cleaves the photo-crosslinked bonds. The effect achieved is that the material may be reversibly switched between an elastomer and a rigid polymer. Light does not change the temperature, only the cross-linking density within the material. [ 19 ] For example, it has been reported that polymers containing cinnamic groups can be fixed into predetermined shapes by UV light illumination (> 260 nm) and then recover their original shape when exposed to UV light of a different wavelength (< 260 nm). [ 19 ] Examples of photoresponsive switches include cinnamic acid and cinnamylidene acetic acid .
The use of electricity to activate the shape-memory effect of polymers is desirable for applications where it would not be possible to use heat and is another active area of research. Some current efforts use conducting SMP composites with carbon nanotubes , [ 20 ] short carbon fibers (SCFs), [ 21 ] [ 22 ] carbon black, [ 23 ] or metallic Ni powder. These conducting SMPs are produced by chemically surface-modifying multi-walled carbon nanotubes (MWNTs) in a mixed solvent of nitric acid and sulfuric acid , with the purpose of improving the interfacial bonding between the polymers and the conductive fillers. The shape-memory effect in these types of SMPs have been shown to be dependent on the filler content and the degree of surface modification of the MWNTs, with the surface modified versions exhibiting good energy conversion efficiency and improved mechanical properties.
Another technique being investigated involves the use of surface-modified super-paramagnetic nanoparticles. When introduced into the polymer matrix, remote actuation of shape transitions is possible. An example of this involves the use of oligo (e-caprolactone)dimethacrylate/butyl acrylate composite with between 2 and 12% magnetite nanoparticles . Nickel and hybrid fibers have also been used with some degree of success. [ 21 ]
Shape-memory polymers differ from shape memory alloys (SMAs) [ 25 ] by their glass transition or melting transition from a hard to a soft phase which is responsible for the shape-memory effect. In shape-memory alloys martensitic / austenitic transitions are responsible for the shape-memory effect.
There are numerous advantages that make SMPs more attractive than shape memory alloys . They have a high capacity for elastic deformation (up to 200% in most cases), much lower cost, lower density, a broad range of application temperatures which can be tailored, easy processing, potential biocompatibility and biodegradability, [ 24 ] and probably exhibit superior mechanical properties to those of SMAs. [ 26 ]
One of the first conceived industrial applications was in robotics where shape-memory (SM) foams were used to provide initial soft pretension in gripping. [ 27 ] These SM foams could be subsequently hardened by cooling, making a shape adaptive grip. Since this time, the materials have seen widespread usage in, for example, the building industry (foam which expands with warmth to seal window frames), sports wear (helmets, judo and karate suits) and in some cases with thermochromic additives for ease of thermal profile observation. [ 28 ] Polyurethane SMPs are also applied as an autochoke element for engines. [ 29 ]
One field in which SMPs are having a significant impact is photonics. Due to the shape changing capability, SMPs enable the production of functional and responsive photonic gratings. [ 30 ] By using modern soft lithography techniques such as replica molding, it is possible to imprint periodic nanostructures, with sizes of the order of magnitude of visible light, onto the surface of shape memory polymeric blocks. As a result of the refractive index periodicity, these systems diffract light. By taking advantage of the polymer's shape memory effect, it is possible to reprogram the lattice parameter of the structure and consequently tune its diffractive behavior. Another application of SMPs in photonics is shape changing random lasers. [ 31 ] By doping SMPs with highly scattering particles such as titania it is possible to tune the light transport properties of the composite. Additionally, optical gain may be introduced by adding a molecular dye to the material. By configuring both the amount of scatters and of the organic dye, a light amplification regime may be observed when the composites are optically pumped. Shape memory polymers have also been used in conjunction with nanocellulose to fabricate composites exhibiting both chiroptical properties and thermo-activated shape memory effect. [ 32 ]
Most medical applications of SMP have yet to be developed, but devices with SMP are now beginning to hit the market. Recently, this technology has expanded to applications in orthopedic surgery . [ 18 ] Additionally, SMPs are now being used in various ophthalmic devices including punctal plugs, glaucoma shunts and intraocular lenses.
SMPs are smart materials with potential applications as, e.g., intravenous cannula, [ 29 ] self-adjusting orthodontic wires and selectively pliable tools for small scale surgical procedures where currently metal-based shape-memory alloys such as Nitinol are widely used. Another application of SMP in the medical field could be its use in implants: for example minimally invasive, through small incisions or natural orifices, implantation of a device in its small temporary shape. Shape-memory technologies have shown great promise for cardiovascular stents, since they allow a small stent to be inserted along a vein or artery and then expanded to prop it open. [ 33 ] After activating the shape memory by temperature increase or mechanical stress, it would assume its permanent shape. Certain classes of shape-memory polymers possess an additional property: biodegradability . This offers the option to develop temporary implants. In the case of biodegradable polymers, after the implant has fulfilled its intended use, e.g. healing/tissue regeneration has occurred, the material degrades into substances which can be eliminated by the body. Thus full functionality would be restored without the necessity for a second surgery to remove the implant. [ 34 ] Examples of this development are vascular stents and surgical sutures . When used in surgical sutures, the shape-memory property of SMPs enables wound closure with self-adjusting optimal tension, which avoids tissue damage due to overtightened sutures and does support healing and regeneration. [ 35 ] SMPs have also potential for use as compression garments [ 36 ] and hands-free door openers, whereby the latter can be produced via so-called 4D printing. [ 37 ]
Further potential applications include self-repairing structural components, such as e.g. automobile fenders in which dents are repaired by application of temperature. [ 38 ] After an undesired deformation, such as a dent in the fender, these materials "remember" their original shape. Heating them activates their "memory". In the example of the dent, the fender could be repaired with a heat source, such as a hair-dryer. The impact results in a temporary form, which changes back to the original form upon heating—in effect, the plastic repairs itself. SMPs may also be useful in the production of aircraft which would morph during flight. Currently, the Defense Advanced Research Projects Agency DARPA is testing wings which would change shape by 150%. [ 6 ]
The realization of a better control over the switching behavior of polymers is seen as key factor to implement new technical concepts. For instance, an accurate setting of the onset temperature of shape recovering can be exploited to tune the release temperature of information stored in a shape memory polymer. This may pave the way for the monitoring of temperature abuses of food or pharmaceuticals. [ 39 ]
Recently, a new manufacturing process, mnemosynation, was developed at Georgia Tech to enable mass production of crosslinked SMP devices, which would otherwise be cost-prohibitive using traditional thermoset polymerization techniques. [ 40 ] Mnemosynation was named for the Greek goddess of memory, Mnemosyne , and is the controlled imparting of memory on an amorphous thermoplastic materials utilizing radiation-induced covalent crosslinking, much like vulcanization imparts recoverable elastomeric behavior on rubbers using sulfur crosslinks. Mnemosynation combines advances in ionizing radiation and tuning the mechanical properties of SMPs to enable traditional plastics processing ( extrusion , blow molding , injection molding , resin transfer molding , etc.) and allows thermoset SMPs in complex geometries. The customizable mechanical properties of traditional SMPs are achievable with high throughput plastics processing techniques to enable mass producible plastic products with thermosetting shape-memory properties: low residual strains, tunable recoverable force and adjustable glass transition temperatures.
Shape memory polymers may serve as technology platform for a safe way of information storage and release. [ 41 ] Overt anti-counterfeiting labels have been constructed that display a visual symbol or code when exposed to specific chemicals. [ 42 ] Multifunctional labels may even make counterfeiting increasingly difficult. [ 43 ] [ 44 ] Shape memory polymers have already been made into shape memory film by extruder machine, with covert and overt 3D embossed pattern internally, and 3D pattern will be released to be embossed or disappeared in just seconds irreversibly as soon as it is heated; Shape memory film can be used as label substrates or face stock for anti-counterfeiting, brand protection , tamper-evident seals, anti-pilferage seals, etc.
Using shape memory polymers as matrices, multifunctional composite materials can be produced. Such composites can have temperature dependant shape morphing (i.e. shape memory) characteristics. [ 45 ] [ 46 ] This phenomenon allows these composites to be potentially used to create deployable structures [ 47 ] such as booms, [ 48 ] hinges, [ 49 ] wings [ 50 ] [ 51 ] etc. While using SMPs can help produce one-way shape morphing structures, it has been reported that using SMPs in combination with shape memory alloys allows creation of more complex shape memory composites that is capable of two-way shape memory deformation. [ 52 ] | https://en.wikipedia.org/wiki/Shape-memory_polymer |
ShapeWriter (previously known as Shorthand-Aided Rapid Keyboarding (SHARK) ) was a keyboard text input method for tablet, handheld PCs, and mobile phones invented by Shumin Zhai and Per Ola Kristensson at IBM Almaden Research Center and the Department of Computer and Information Science at Linköping University .
Using ShapeWriter text entry software, a user draws words on a graphical keyboard using a pen. Instead of tapping the keys, the user draws a pen gesture that connects all the letters in the desired word. After some usage the user learns the movement pattern for the commonly used words and can write them faster than is possible on a traditional virtual keyboard .
The first system described by Shumin Zhai and Per Ola Kristensson (2003) was only a prototype system that could recognize about 100 pen gestures for the top 100 words used in the English language. It used a handwriting recognition algorithm that relied on dynamic programming to recognize the word patterns drawn from a lexicon. The next version described by Per Ola Kristensson and Shumin Zhai (2004) has a fundamentally different recognition engine that can recognize 50,000 - 60,000 words with low latency . This system introduced the notion that every word in a large lexicon should be possible to write by tracing the letters. It is this system that was the basis for the software release on IBM alphaWorks that is generally associated with the term "ShapeWriter".
ShapeWriter was acquired by Nuance Communications , and taken off the market in 2010; [ 1 ] its technology presumably incorporated as part of Nuance's FlexT9 app in 2011. [ 2 ] [ 3 ]
ShapeWriter was made available for the iPhone approximately in 2008 and was revised several times (including ShapeWriter Lite and ShapeWriter Pro or Plus) before being pulled due to its sale to Nuance Communications (see following entry).
Those who purchased the iPhone version continued to use it and it also functioned on iPads v. 1 and 2 until 2013.
As of 2013 it no longer functions on iOS devices and is no longer available in Apple's App Store.
ShapeWriter software was made available as a free application for Android (operating system) smartphones through the Android Market . As a touchscreen keyboard replacement, it had over 50,000 users on Android worldwide. It was available only for Android OS versions 1.6 or higher. ShapeWriter for Android was available in 7 European languages including English, Spanish, and German. There was also a Beta release for Android 1.5 phones including the HTC Hero and Droid Eris .
ShapeWriter, Inc. was purchased by Nuance Communications and the ShapeWriter software was removed from the Android Market indefinitely on June 20, 2010. | https://en.wikipedia.org/wiki/ShapeWriter |
This article describes shape analysis to analyze and process geometric shapes .
Shape analysis is the (mostly) [ clarification needed ] automatic analysis of geometric shapes, for example using a computer to detect similarly shaped objects in a database or parts that fit together. For a computer to automatically analyze and process geometric shapes, the objects have to be represented in a digital form. Most commonly a boundary representation is used to describe the object with its boundary (usually the outer shell, see also 3D model ). However, other volume based representations (e.g. constructive solid geometry ) or point based representations ( point clouds ) can be used to represent shape.
Once the objects are given, either by modeling ( computer-aided design ), by scanning ( 3D scanner ) or by extracting shape from 2D or 3D images, they have to be simplified before a comparison can be achieved. The simplified representation is often called a shape descriptor (or fingerprint, signature). These simplified representations try to carry most of the important information, while being easier to handle, to store and to compare than the shapes directly.
A complete shape descriptor is a representation that can be used to completely reconstruct the original object (for example the medial axis transform).
Shape analysis is used in many application fields:
Shape descriptors can be classified by their invariance with respect to the transformations allowed in the associated shape definition. Many descriptors are invariant with respect to congruency , meaning that congruent shapes (shapes that could be translated, rotated and mirrored) will have the same descriptor (for example moment or spherical harmonic based descriptors or Procrustes analysis operating on point clouds).
Another class of shape descriptors (called intrinsic shape descriptors) is invariant with respect to isometry . These descriptors do not change with different isometric embeddings of the shape. Their advantage is that they can be applied nicely to deformable objects (e.g. a person in different body postures) as these deformations do not involve much stretching but are in fact near-isometric. Such descriptors are commonly based on geodesic distances measures along the surface of an object or on other isometry invariant characteristics such as the Laplace–Beltrami spectrum (see also spectral shape analysis ).
There are other shape descriptors, such as graph-based descriptors like the medial axis or the Reeb graph that capture geometric and/or topological information and simplify the shape representation but can not be as easily compared as descriptors that represent shape as a vector of numbers.
From this discussion it becomes clear, that different shape descriptors target different aspects of shape and can be used for a specific application. Therefore, depending on the application, it is necessary to analyze how well a descriptor captures the features of interest. | https://en.wikipedia.org/wiki/Shape_analysis_(digital_geometry) |
Shape coding is a method of design of a control that allows the control's function to be signified by the shape of the control. It was used successfully by Alphonse Chapanis on airplane controls to improve aviation safety .
This design -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Shape_coding |
The shape correction function is a ratio of the surface area of a growing organism and that of an isomorph as function of the volume. The shape of the isomorph is taken to be equal to that of the organism for a given reference volume, so for that particular volume the surface areas are also equal and the shape correction function has value one.
For a volume V {\displaystyle V} and reference volume V d {\displaystyle V_{d}} , the shape correction function M ( V ) {\displaystyle M(V)} equals: [ 1 ]
Static mixtures between a V0 and a V1-morph can be found as: M ( V ) = w ( V / V d ) − 2 / 3 + ( 1 − w ) ( V / V d ) 1 / 3 {\displaystyle M(V)=w(V/V_{d})^{-2/3}+(1-w)(V/V_{d})^{1/3}} for 0 < w < 1 {\displaystyle 0<w<1}
The shape correction function is used in Dynamic Energy Budget theory to correct equations for isomorphs to organisms that change shape during growth. The conversion is necessary for accurately modelling food (substrate) acquisition and mobilization of reserve for use by metabolism. | https://en.wikipedia.org/wiki/Shape_correction_function |
In theoretical physics , shape dynamics is a theory of gravity that implements Mach's principle , developed with the specific goal to obviate the problem of time and thereby open a new path toward the resolution of incompatibilities between general relativity and quantum mechanics .
Shape dynamics is dynamically equivalent to the canonical formulation of general relativity, known as the ADM formalism . Shape dynamics is not formulated as an implementation of spacetime diffeomorphism invariance , but as an implementation of spatial relationalism based on spatial diffeomorphisms and spatial Weyl symmetry . [ 1 ] An important consequence of shape dynamics is the absence of a problem of time in canonical quantum gravity . [ 2 ] The replacement of the spacetime picture with a picture of evolving spatial conformal geometry opens the door for a number of new approaches to quantum gravity . [ 3 ]
An important development in this theory was contributed in 2010 by Henrique Gomes, Sean Gryb and Tim Koslowski, building on an approach initiated by Julian Barbour .
Mach's principle has been an important inspiration for the construction of general relativity , but the physical interpretation of Einstein's formulation of general relativity still requires external clocks and rods and thus fails to be manifestly relational. [ 4 ] Mach's principle would be fully implemented if the predictions of general relativity were independent of the choice of clocks and rods. Barbour and Bertotti conjectured that Jacobi's principle and a mechanism they called "best matching" were construction principles for a fully Machian theory. [ 5 ]
Barbour implemented these principles in collaboration with Niall Ó Murchadha, Edward Anderson, Brendan Foster and Bryan Kelleher to derive the ADM formalism in constant mean curvature gauge. [ 6 ] This did not implement Mach's principle, because the predictions of general relativity in constant mean curvature gauge depend on the choice of clocks and rods. Mach's principle was successfully implemented in 2010 by Henrique Gomes, Sean Gryb and Tim Koslowski [ 7 ] who drew on the work of Barbour and his collaborators to describe gravity in a fully relational manner as the evolution of the conformal geometry of space. [ 8 ]
Shape dynamics possesses the same dynamics as general relativity, but has different gauge orbits. [ 9 ] The link between general relativity and shape dynamics can be established using the ADM formalism in the following way: Shape dynamics can be gauge fixed in such a way that its initial value problem and its equations of motion coincide with the initial value problem and equations of motion of the ADM formalism in constant mean extrinsic curvature gauge. This equivalence ensures that classical shape dynamics and classical general relativity are locally indistinguishable. However, there is the possibility for global differences. [ 10 ] [ 11 ] [ 12 ] [ 13 ]
The shape dynamics formulation of gravity possesses a physical Hamiltonian that generates evolution of spatial conformal geometry. This disentangles the problem of time in quantum gravity: The gauge problem (the choice of foliation in the spacetime description) is replaced by the problem of finding spatial conformal geometries, leaving an evolution that is comparable to a system with time dependent Hamiltonian. [ 14 ] The problem of time is suggested to be completely solved by restricting oneself to "objective observables," which are those observables that do not depend on any external clock or rod. [ 15 ]
Recent work by Julian Barbour, Tim Koslowski and Flavio Mercati [ 16 ] demonstrates that Shape Dynamics possesses a physical arrow of time given by the growth of complexity and the dynamical storage of locally accessible records of the past. This is a property of the dynamical law and does not require any special initial condition. | https://en.wikipedia.org/wiki/Shape_dynamics |
Shape factors are dimensionless quantities used in image analysis and microscopy that numerically describe the shape of a particle, independent of its size. Shape factors are calculated from measured dimensions , such as diameter , chord lengths, area , perimeter , centroid , moments , etc. The dimensions of the particles are usually measured from two-dimensional cross-sections or projections , as in a microscope field, but shape factors also apply to three-dimensional objects. The particles could be the grains in a metallurgical or ceramic microstructure , or the microorganisms in a culture , for example. The dimensionless quantities often represent the degree of deviation from an ideal shape, such as a circle , sphere or equilateral polyhedron . [ 1 ] Shape factors are often normalized , that is, the value ranges from zero to one. A shape factor equal to one usually represents an ideal case or maximum symmetry, such as a circle, sphere, square or cube.
The most common shape factor is the aspect ratio , a function of the largest diameter and the smallest diameter orthogonal to it:
The normalized aspect ratio varies from approaching zero for a very elongated particle, such as a grain in a cold-worked metal, to near unity for an equiaxed grain. The reciprocal of the right side of the above equation is also used, such that the AR varies from one to approaching infinity.
Another very common shape factor is the circularity (or isoperimetric quotient ), a function of the perimeter P and the area A :
The circularity of a circle is 1, and much less than one for a starfish footprint. The reciprocal of the circularity equation is also used, such that f circ varies from one for a circle to infinity.
The less-common elongation shape factor is defined as the square root of the ratio of the two second moments i n of the particle around its principal axes. [ 2 ]
The compactness shape factor is a function of the polar second moment i n of a particle and a circle of equal area A . [ 2 ]
The f comp of a circle is one, and much less than one for the cross-section of an I-beam .
The waviness shape factor of the perimeter is a function of the convex portion P cvx of the perimeter to the total. [ 2 ]
Some properties of metals and ceramics, such as fracture toughness , have been linked to grain shapes. [ 3 ] [ 4 ]
Greenland , the largest island in the world, has an area of 2,166,086 km 2 ; a coastline (perimeter) of 39,330 km; a north–south length of 2670 km; and an east–west length of 1290 km. The aspect ratio of Greenland is
The circularity of Greenland is
The aspect ratio is agreeable with an eyeball-estimate on a globe. Such an estimate on a typical flat map, using the Mercator projection , would be less accurate due to the distorted scale at high latitudes . The circularity is deceptively low, due to the fjords that give Greenland a very jagged coastline (see the coastline paradox ). A low value of circularity does not necessarily indicate a lack of symmetry, and shape factors are not limited to microscopic objects. | https://en.wikipedia.org/wiki/Shape_factor_(image_analysis_and_microscopy) |
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