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Thus, dimensional analysis may be used as a sanity check of physical equations: the two sides of any equation must be commensurable or have the same dimensions. This has the implication that most mathematical functions, particularly the transcendental functions, must have a dimensionless quantity, a pure number, as the argument and must return a dimensionless number as a result. This is clear because many transcendental functions can be expressed as an infinite power series with dimensionless coefficients. All powers of" x" must have the same dimension for the terms to be commensurable. But if" x" is not dimensionless, then the different powers of" x" will have different, incommensurable dimensions. However, power functions including root functions may have a dimensional argument and will return a result having dimension that is the same power applied to the argument dimension. This is because power functions and root functions are, loosely, just an expression of multiplication of quantities. Even when two physical quantities have identical dimensions, it may nevertheless be meaningless to compare or add them. For example, although torque and energy share the dimension, they are fundamentally different physical quantities. To compare, add, or subtract quantities with the same dimensions but expressed in different units, the standard procedure is first to convert them all to the same units. For example, to compare 32 metres with 35 yards, use 1 yard= 0. 9144 m to convert 35 yards to 32. 004 m. A related principle is that any physical law that accurately describes the real world must be independent of the units used to measure the physical variables. For example, Newton' s laws of motion must hold true whether distance is measured in miles or kilometres. This principle gives rise to the form that conversion factors must take between units that measure the same dimension: multiplication by a simple constant. It also ensures equivalence; for example, if two buildings are the same height in feet, then they must be the same height in metres. The factor- label method for converting units. The factor- label method is the sequential application of conversion factors expressed as fractions and arranged so that any dimensional unit appearing in both the numerator and denominator of any of the fractions can be cancelled out until only the desired set of dimensional units is obtained. For example, 10 miles per hour can be converted to meters per second by using a sequence of conversion factors as shown below: Each conversion factor is chosen based on the relationship between one of the original units and one of the desired units( or some intermediary unit), before being re- arranged to create a factor that cancels out the original unit. For example, as" mile" is the numerator in theoriginalfractionandformula_4," mile" will need to be the denominator in the conversion factor. Dividing both sides of the equation by 1mileyieldsformula_5, which when simplified results inthedimensionlessformula_6. Multiplying any quantity( physical quantity or not) by the dimensionless 1 does not change that quantity. Once this and the conversion factor for seconds per hour have been multiplied by the original fraction | to cancel out the units" |
mile" and" hour", 10 miles per hour converts to 4. 4704 meters per second. As a more complex example, the concentration of nitrogen oxides( i. e.,formula_7) in the flue gas from an industrial furnace can be converted to a mass flow rate expressed in grams per hour( i. e., g/ h)offormula_8 by using the following information as shown below: After canceling out any dimensional units that appear both in the numerators and denominators of the fractions in the above equation, the NOx concentration of 10 ppmv converts to mass flow rate of 24. 63 grams per hour. Checking equations that involve dimensions. The factor- label method can also be used on any mathematical equation to check whether or not the dimensional units on the left hand side of the equation are the same as the dimensional units on the right hand side of the equation. Having the same units on both sides of an equation does not ensure that the equation is correct, but having different units on the two sides( when expressed in terms of base units) of an equation implies that the equation is wrong. For example, check the Universal Gas Law equation of, when: As can be seen, when the dimensional units appearing in the numerator and denominator of the equation' s right hand side are cancelled out, both sides of the equation have the same dimensional units. Dimensional analysis can be used as a tool to construct equations that relate non- associated physico- chemical properties. The equations may reveal hitherto unknown or overlooked properties of matter, in the form of left- over dimensions– dimensional adjusters– that can then be assigned physical significance. It is important to point out that such' mathematical manipulation' is neither without prior precedent, nor without considerable scientific significance. Indeed, the Planck constant, a fundamental constant of the universe, was' discovered' as a purely mathematical abstraction or representation that built on the Rayleigh– Jeans law for preventing the ultraviolet catastrophe. It was assigned and ascended to its quantum physical significance either in tandem or post mathematical dimensional adjustment– not earlier. Limitations. The factor- label method can convert only unit quantities for which the units are in a linear relationship intersecting at 0.( Ratio scale in Stevens' s typology) Most units fit this paradigm. An example for which it cannot be used is the conversion between degrees Celsius and kelvins( or degrees Fahrenheit). Between degrees Celsius and kelvins, there is a constant difference rather than a constant ratio, while between degrees Celsius and degrees Fahrenheit there is neither a constant difference nor a constant ratio. There is, however, an affine transform(formula_11, rather thanalineartransformformula_12) between them. For example, the freezing point of water is 0° C and 32° F, and a 5° C change is the same as a 9° F change. Thus, to convert from units of Fahrenheit to units of Celsius, one subtracts 32° F( the offset from the point of reference), divides by 9° F and multiplies by 5° C( scales by the ratio of units), and adds 0° C( the offset from the | point of reference). Reversing this |
yields the formula for obtaining a quantity in units of Celsius from units of Fahrenheit; one could have started with the equivalence between 100° C and 212° F, though this would yield the same formula at the end. Hence, to convert the numerical quantity value of a temperature" T"[ F] in degrees Fahrenheit to a numerical quantity value" T"[ C] in degrees Celsius, this formula may be used: To convert" T"[ C] in degrees Celsius to" T"[ F] in degrees Fahrenheit, this formula may be used: Applications. Dimensional analysis is most often used in physics and chemistry– and in the mathematics thereof– but finds some applications outside of those fields as well. Mathematics. A simple application of dimensional analysis to mathematics is in computing the form of the volume of an" n"- ball( the solid ball in" n" dimensions), or the area of its surface, the" n"- sphere: being an" n"- dimensional figure,thevolumescalesasformula_13 while the surface area,beingformula_14- dimensional,scalesasformula_15 Thus the volume of the" n"-ballintermsoftheradiusisformula_16forsomeconstantformula_17 Determining the constant takes more involved mathematics, but the form can be deduced and checked by dimensional analysis alone. Finance, economics, and accounting. In finance, economics, and accounting, dimensional analysis is most commonly referred to in terms of the distinction between stocks and flows. More generally, dimensional analysis is used in interpreting various financial ratios, economics ratios, and accounting ratios. Fluid mechanics. In fluid mechanics, dimensional analysis is performed to obtain dimensionless pi terms or groups. According to the principles of dimensional analysis, any prototype can be described by a series of these terms or groups that describe the behaviour of the system. Using suitable pi terms or groups, it is possible to develop a similar set of pi terms for a model that has the same dimensional relationships. In other words, pi terms provide a shortcut to developing a model representing a certain prototype. Common dimensionless groups in fluid mechanics include: History. The origins of dimensional analysis have been disputed by historians. The first written application of dimensional analysis has been credited to an article of François Daviet at the Turin Academy of Science. Daviet had the master Lagrange as teacher. His fundamental works are contained in acta of the Academy dated 1799. This led to the conclusion that meaningful laws must be homogeneous equations in their various units of measurement, a result which was eventually later formalized in the Buckingham π theorem. Simeon Poisson also treated the same problem of the parallelogram law by Daviet, in his treatise of 1811 and 1833( vol I, p. 39). In the second edition of 1833, Poisson explicitly introduces the term" dimension" instead of the Daviet" homogeneity". In 1822, the important Napoleonic scientist Joseph Fourier made the first credited important contributions based on the idea that physical laws like should be independent of the units employed to measure the physical variables. James Clerk Maxwell played a major role in establishing modern use of dimensional analysis by distinguishing mass, length, and time as fundamental units, while referring to other units as derived. Although Maxwell defined length, time and mass to be" | the three fundamental units", he |
also noted that gravitational mass can be derived from length and time by assuming a form of Newton' s law of universal gravitation in which the gravitational constant" G" is taken as unity, thereby defining. By assuming a form of Coulomb' s law in which Coulomb' s constant" k" e is taken as unity, Maxwell then determined that the dimensions of an electrostatic unit of charge were, which, after substituting his equation for mass, results in charge having the same dimensions as mass, viz.. Dimensional analysis is also used to derive relationships between the physical quantities that are involved in a particular phenomenon that one wishes to understand and characterize. It was used for the first time in this way in 1872 by Lord Rayleigh, who was trying to understand why the sky is blue. Rayleigh first published the technique in his 1877 book" The Theory of Sound". The original meaning of the word" dimension", in Fourier' s" Theorie de la Chaleur", was the numerical value of the exponents of the base units. For example, acceleration was considered to have the dimension 1 with respect to the unit of length, and the dimension− 2 with respect to the unit of time. This was slightly changed by Maxwell, who said the dimensions of acceleration are T−2L, instead of just the exponents. Mathematical formulation. The Buckingham π theorem describes how every physically meaningful equation involving" n" variables can be equivalently rewritten as an equation of dimensionless parameters, where" m" is the rank of the dimensional matrix. Furthermore, and most importantly, it provides a method for computing these dimensionless parameters from the given variables. A dimensional equation can have the dimensions reduced or eliminated through nondimensionalization, which begins with dimensional analysis, and involves scaling quantities by characteristic units of a system or natural units of nature. This gives insight into the fundamental properties of the system, as illustrated in the examples below. Definition. The dimension of a physical quantity can be expressed as a product of the basic physical dimensions such as length, mass and time, each raised to a rational power. The" dimension" of a physical quantity is more fundamental than some" scale" unit used to express the amount of that physical quantity. For example," mass" is a dimension, while the kilogram is a particular scale unit chosen to express a quantity of mass. Except for natural units, the choice of scale is cultural and arbitrary. There are many possible choices of basic physical dimensions. The SI standard recommends the usage of the following dimensions and corresponding symbols: time( T), length( L), mass( M), electric current( I), absolute temperature( Θ), amount of substance( N) and luminous intensity( J). The symbols are by convention usually written in roman sans serif typeface. Mathematically, the dimension of the quantity" Q" is given bywhere" a"," b"," c"," d"," e"," f"," g" are the dimensional exponents. Other physical quantities could be defined as the base quantities, as long as they form a linearly independent basis– for instance, one could replace the dimension( I) of electric current of the SI | basis with a dimension( Q) |
of electric charge, since Q= TI. As examples, the dimension of the physical quantity speed" v" isand the dimension of the physical quantity force" F" isThe unit chosen to express a physical quantity and its dimension are related, but not identical concepts. The units of a physical quantity are defined by convention and related to some standard; e. g., length may have units of metres, feet, inches, miles or micrometres; but any length always has a dimension of L, no matter what units of length are chosen to express it. Two different units of the same physical quantity have conversion factors that relate them. For example, 1 in= 2. 54 cm; in this case 2. 54 cm/ in is the conversion factor, which is itself dimensionless. Therefore, multiplying by that conversion factor does not change the dimensions of a physical quantity. There are also physicists who have cast doubt on the very existence of incompatible fundamental dimensions of physical quantity, although this does not invalidate the usefulness of dimensional analysis. Mathematical properties. The dimensions that can be formed from a given collection of basic physical dimensions, such as T, L, and M, form an abelian group: The identity is written as 1;, and the inverse of L is 1/ L or L− 1. L raised to any rational power" p" is a member of the group, having an inverse of L−" p" or 1/ L" p". The operation of the group is multiplication, having the usual rules for handling exponents(). This group can be described as a vector space over the rational numbers, with the dimensional symbol corresponding to the vector. When physical measured quantities( be they like- dimensioned or unlike- dimensioned) are multiplied or divided by one other, their dimensional units are likewise multiplied or divided; this corresponds to addition or subtraction in the vector space. When measurable quantities are raised to a rational power, the same is done to the dimensional symbols attached to those quantities; this corresponds to scalar multiplication in the vector space. A basis for such a vector space of dimensional symbols is called a set of base quantities, and all other vectors are called derived units. As in any vector space, one may choose different bases, which yields different systems of units( e. g., choosing whether the unit for charge is derived from the unit for current, or vice versa). The group identity, the dimension of dimensionless quantities, corresponds to the origin in this vector space. The set of units of the physical quantities involved in a problem correspond to a set of vectors( or a matrix). The nullity describes some number( e. g.," m") of ways in which these vectors can be combined to produce a zero vector. These correspond to producing( from the measurements) a number of dimensionless quantities,.( In fact these ways completely span the null subspace of another different space, of powers of the measurements.) Every possible way of multiplying( and exponentiating) together the measured quantities to produce something with the same units as some derived quantity" X" can be expressed in | the general formConsequently, every possible |
commensurate equation for the physics of the system can be rewritten in the formKnowing this restriction can be a powerful tool for obtaining new insight into the system. Mechanics. The dimension of physical quantities of interest in mechanics can be expressed in terms of base dimensions T, L, and M– these form a 3- dimensional vector space. This is not the only valid choice of base dimensions, but it is the one most commonly used. For example, one might choose force, length and mass as the base dimensions( as some have done), with associated dimensions F, L, M; this corresponds to a different basis, and one may convert between these representations by a change of basis. The choice of the base set of dimensions is thus a convention, with the benefit of increased utility and familiarity. The choice of base dimensions is not entirely arbitrary, because they must form a basis: they must span the space, and be linearly independent. For example, F, L, M form a set of fundamental dimensions because they form a basis that is equivalent to T, L, M: the former can be expressed as[ F= LM/T2], L, M, while the latter can be expressed as[ T=( LM/ F) 1/ 2], L, M. On the other hand, length, velocity and time do not form a set of base dimensions for mechanics, for two reasons: Other fields of physics and chemistry. Depending on the field of physics, it may be advantageous to choose one or another extended set of dimensional symbols. In electromagnetism, for example, it may be useful to use dimensions of T, L, M and Q, where Q represents the dimension of electric charge. In thermodynamics, the base set of dimensions is often extended to include a dimension for temperature, Θ. In chemistry, the amount of substance( the number of molecules divided by the Avogadro constant,≈) is also defined as a base dimension, N. In the interaction of relativistic plasma with strong laser pulses, a dimensionless relativistic similarity parameter, connected with the symmetry properties of the collisionless Vlasov equation, is constructed from the plasma-, electron- and critical- densities in addition to the electromagnetic vector potential. The choice of the dimensions or even the number of dimensions to be used in different fields of physics is to some extent arbitrary, but consistency in use and ease of communications are common and necessary features. Polynomials and transcendental functions. Scalar arguments to transcendental functions such as exponential, trigonometric and logarithmic functions, or to inhomogeneous polynomials, must be dimensionless quantities.( Note: this requirement is somewhat relaxed in Siano' s orientational analysis described below, in which the square of certain dimensioned quantities are dimensionless.) While most mathematical identities about dimensionless numbers translate in a straightforward manner to dimensional quantities, care must be taken with logarithms of ratios: the identity log(" a"/" b")= log" a"− log" b", where the logarithm is taken in any base, holds for dimensionless numbers" a" and" b", but it does" not" hold if" a" and" b" are dimensional, because in this case the left- hand side is well- | defined but the right- hand |
side is not. Similarly, while one can evaluate monomials(" x"" n") of dimensional quantities, one cannot evaluate polynomials of mixed degree with dimensionless coefficients on dimensional quantities: for" x" 2, the expression( 3 m) 2=9m2 makes sense( as an area), while for" x" 2+" x", the expression( 3 m) 2+ 3 m=9m2+ 3 m does not make sense. However, polynomials of mixed degree can make sense if the coefficients are suitably chosen physical quantities that are not dimensionless. For example, This is the height to which an object rises in time" t" if the acceleration of gravity is 9. 8 and the initial upward speed is 500. It is not necessary for" t" to be in" seconds". For example, suppose" t"= 0. 01 minutes. Then the first term would beIncorporating units. The value of a dimensional physical quantity" Z" is written as the product of a unit[" Z"] within the dimension and a dimensionless numerical factor," n". When like- dimensioned quantities are added or subtracted or compared, it is convenient to express them in consistent units so that the numerical values of these quantities may be directly added or subtracted. But, in concept, there is no problem adding quantities of the same dimension expressed in different units. For example, 1 meter added to 1 foot is a length, but one cannot derive that length by simply adding 1 and 1. A conversion factor, which is a ratio of like- dimensioned quantities and is equal to the dimensionless unity, is needed:Thefactorformula_32 is identical to the dimensionless 1, so multiplying by this conversion factor changes nothing. Then when adding two quantities of like dimension, but expressed in different units, the appropriate conversion factor, which is essentially the dimensionless 1, is used to convert the quantities to identical units so that their numerical values can be added or subtracted. Only in this manner is it meaningful to speak of adding like- dimensioned quantities of differing units. Position vs displacement. Some discussions of dimensional analysis implicitly describe all quantities as mathematical vectors.( In mathematics scalars are considered a special case of vectors; vectors can be added to or subtracted from other vectors, and, inter alia, multiplied or divided by scalars. If a vector is used to define a position, this assumes an implicit point of reference: an origin. While this is useful and often perfectly adequate, allowing many important errors to be caught, it can fail to model certain aspects of physics. A more rigorous approach requires distinguishing between position and displacement( or moment in time versus duration, or absolute temperature versus temperature change). Consider points on a line, each with a position with respect to a given origin, and distances among them. Positions and displacements all have units of length, but their meaning is not interchangeable: This illustrates the subtle distinction between" affine" quantities( ones modeled by an affine space, such as position) and" vector" quantities( ones modeled by a vector space, such as displacement). Properly then, positions have dimension of" affine" length, while displacements have dimension of" vector" length. To assign a number to | an" affine" unit, one must |
not only choose a unit of measurement, but also a point of reference, while to assign a number to a" vector" unit only requires a unit of measurement. Thus some physical quantities are better modeled by vectorial quantities while others tend to require affine representation, and the distinction is reflected in their dimensional analysis. This distinction is particularly important in the case of temperature, for which the numeric value of absolute zero is not the origin 0 in some scales. For absolute zero, where the symbol≘ means" corresponds to", since although these values on the respective temperature scales correspond, they represent distinct quantities in the same way that the distances from distinct starting points to the same end point are distinct quantities, and cannot in general be equated. For temperature differences,( Here° R refers to the Rankine scale, not the Réaumur scale). Unit conversion for temperature differences is simply a matter of multiplying by, e. g., 1° F/ 1 K( although the ratio is not a constant value). But because some of these scales have origins that do not correspond to absolute zero, conversion from one temperature scale to another requires accounting for that. As a result, simple dimensional analysis can lead to errors if it is ambiguous whether 1 K means the absolute temperature equal to− 272. 15° C, or the temperature difference equal to 1° C. Orientation and frame of reference. Similar to the issue of a point of reference is the issue of orientation: a displacement in 2 or 3 dimensions is not just a length, but is a length together with a" direction".( This issue does not arise in 1 dimension, or rather is equivalent to the distinction between positive and negative.) Thus, to compare or combine two dimensional quantities in a multi- dimensional space, one also needs an orientation: they need to be compared to a frame of reference. This leads to the extensions discussed below, namely Huntley' s directed dimensions and Siano' s orientational analysis. Examples. A simple example: period of a harmonic oscillator. What is the period of oscillation of a mass attached to an ideal linear spring with spring constant suspended in gravity of strength? That period is the solution for of some dimensionless equation in the variables,,, and. The four quantities have the following dimensions:[ T];[ M];[ M/T2]; and[ L/T2]. From these we can form only one dimensionless product of powers of our chosen variables,formula_33=formula_34,andputtingformula_35 for some dimensionless constant gives the dimensionless equation sought. The dimensionless product of powers of variables is sometimes referred to as a dimensionless group of variables; here the term" group" means" collection" rather than mathematical group. They are often called dimensionless numbers as well. Note that the variable does not occur in the group. It is easy to see that it is impossible to form a dimensionless product of powers that combines with,, and, because is the only quantity that involves the dimension L. This implies that in this problem the is irrelevant. Dimensional analysis can sometimes yield strong statements about the" irrelevance" of some quantities in a | problem, or the need for |
additional parameters. If we have chosen enough variables to properly describe the problem, then from this argument we can conclude that the period of the mass on the spring is independent of: it is the same on the earth or the moon. The equation demonstrating the existence of a product of powers for our problem can be written in an entirely equivalent way:formula_36, for some dimensionless constant(equaltoformula_37 from the original dimensionless equation). When faced with a case where dimensional analysis rejects a variable(, here) that one intuitively expects to belong in a physical description of the situation, another possibility is that the rejected variable is in fact relevant, but that some other relevant variable has been omitted, which might combine with the rejected variable to form a dimensionless quantity. That is, however, not the case here. When dimensional analysis yields only one dimensionless group, as here, there are no unknown functions, and the solution is said to be" complete"– although it still may involve unknown dimensionless constants, such as. A more complex example: energy of a vibrating wire. Consider the case of a vibrating wire of length" ℓ"( L) vibrating with an amplitude" A"( L). The wire has a linear density" ρ"( M/ L) and is under tension" s"( LM/T2), and we want to know the energy" E"(L2M/T2) in the wire. Let" π" 1 and" π" 2 be two dimensionless products of powers of the variables chosen, given byThe linear density of the wire is not involved. The two groups found can be combined into an equivalent form as an equationwhere" F" is some unknown function, or, equivalently aswhere" f" is some other unknown function. Here the unknown function implies that our solution is now incomplete, but dimensional analysis has given us something that may not have been obvious: the energy is proportional to the first power of the tension. Barring further analytical analysis, we might proceed to experiments to discover the form for the unknown function" f". But our experiments are simpler than in the absence of dimensional analysis. We' d perform none to verify that the energy is proportional to the tension. Or perhaps we might guess that the energy is proportional to" ℓ", and so infer that. The power of dimensional analysis as an aid to experiment and forming hypotheses becomes evident. The power of dimensional analysis really becomes apparent when it is applied to situations, unlike those given above, that are more complicated, the set of variables involved are not apparent, and the underlying equations hopelessly complex. Consider, for example, a small pebble sitting on the bed of a river. If the river flows fast enough, it will actually raise the pebble and cause it to flow along with the water. At what critical velocity will this occur? Sorting out the guessed variables is not so easy as before. But dimensional analysis can be a powerful aid in understanding problems like this, and is usually the very first tool to be applied to complex problems where the underlying equations and constraints are poorly understood. In such cases, the | answer may depend on a |
dimensionless number such as the Reynolds number, which may be interpreted by dimensional analysis. A third example: demand versus capacity for a rotating disc. Consider the case of a thin, solid, parallel- sided rotating disc of axial thickness" t"( L) and radius" R"( L). The disc has a density" ρ"( M/L3), rotates at an angular velocity" ω"( T− 1) and this leads to a stress" S"( T−2L−1M) in the material. There is a theoretical linear elastic solution, given by Lame, to this problem when the disc is thin relative to its radius, the faces of the disc are free to move axially, and the plane stress constitutive relations can be assumed to be valid. As the disc becomes thicker relative to the radius then the plane stress solution breaks down. If the disc is restrained axially on its free faces then a state of plane strain will occur. However, if this is not the case then the state of stress may only be determined though consideration of three- dimensional elasticity and there is no known theoretical solution for this case. An engineer might, therefore, be interested in establishing a relationship between the five variables. Dimensional analysis for this case leads to the following( 5− 3= 2) non- dimensional groups: Through the use of numerical experiments using, for example, the finite element method, the nature of the relationship between the two non- dimensional groups can be obtained as shown in the figure. As this problem only involves two non- dimensional groups, the complete picture is provided in a single plot and this can be used as a design/ assessment chart for rotating discsExtensions. Huntley' s extension: directed dimensions and quantity of matter. Huntley has pointed out that a dimensional analysis can become more powerful by discovering new independent dimensions in the quantities under consideration,thusincreasingtherankformula_41 of the dimensional matrix. He introduced two approaches to doing so: As an example of the usefulness of the first approach, suppose we wish tocalculatethedistanceacannonballtravelswhenfiredwithaverticalvelocitycomponentformula_42andahorizontalvelocitycomponentformula_43, assuming it is fired on a flat surface. Assuming no use of directed lengths,thequantitiesofinterestarethenformula_43,formula_42, both dimensioned as T−1L,, the distance travelled, having dimension L, and the downward acceleration of gravity, with dimension T−2L. With these four quantities, we may conclude that the equation for the range may be written:Ordimensionallyfromwhichwemaydeducethatformula_48andformula_49, which leaves one exponent undetermined. This is to be expected since we have two fundamental dimensions T and L, and four parameters, with one equation. If, however, we use directed length dimensions,thenformula_43 will be dimensioned as T−1L,formula_42 as T−1L, as L and as T−2L. The dimensional equation becomes: andwemaysolvecompletelyasformula_53,formula_54andformula_55. The increase in deductive power gained by the use of directed length dimensions is apparent. In his second approach, Huntley holds that it is sometimes useful( e. g., in fluid mechanics and thermodynamics) to distinguish between mass as a measure of inertia( inertial mass), and mass as a measure of the quantity of matter. Quantity of matter is defined by Huntley as a quantity( a) proportional to inertial mass, but( b) not implicating inertial properties. No further restrictions are added to its definition. For example, consider | the derivation of Poiseuille' s |
Law. We wish to find the rate of mass flow of a viscous fluid through a circular pipe. Without drawing distinctions between inertial and substantial mass we maychooseastherelevantvariablesTherearethreefundamentalvariablessotheabovefiveequationswillyieldtwodimensionlessvariableswhichwemaytaketobeformula_58andformula_59 and we may express the dimensional equation aswhere and are undetermined constants.Ifwedrawadistinctionbetweeninertialmasswithdimensionformula_61andquantityofmatterwithdimensionformula_62, then mass flow rate and density will use quantity of matter as the mass parameter, while the pressure gradient and coefficient of viscosity will use inertial mass. We now have four fundamental parameters, and one dimensionless constant, so that the dimensional equation may be written: where now only is an undetermined constant(foundtobeequaltoformula_64 by methods outside of dimensional analysis). This equation may be solved for the mass flow rate to yield Poiseuille' s law. Huntley' s recognition of quantity of matter as an independent quantity dimension is evidently successful in the problems where it is applicable, but his definition of quantity of matter is open to interpretation, as it lacks specificity beyond the two requirements( a) and( b) he postulated for it. For a given substance, the SI dimension amount of substance, with unit mole, does satisfy Huntley' s two requirements as a measure of quantity of matter, and could be used as a quantity of matter in any problem of dimensional analysis where Huntley' s concept is applicable. Huntley' s concept of directed length dimensions however has some serious limitations: It also is often quite difficult to assign the L, L, L, L, symbols to the physical variables involved in the problem of interest. He invokes a procedure that involves the" symmetry" of the physical problem. This is often very difficult to apply reliably: It is unclear as to what parts of the problem that the notion of" symmetry" is being invoked. Is it the symmetry of the physical body that forces are acting upon, or to the points, lines or areas at which forces are being applied? What if more than one body is involved with different symmetries? Consider the spherical bubble attached to a cylindrical tube, where one wants the flow rate of air as a function of the pressure difference in the two parts. What are the Huntley extended dimensions of the viscosity of the air contained in the connected parts? What are the extended dimensions of the pressure of the two parts? Are they the same or different? These difficulties are responsible for the limited application of Huntley' s directed length dimensions to real problems. Siano' s extension: orientational analysis. Angles are, by convention, considered to be dimensionless quantities. As an example, consider again the projectile problem in which a point mass is launched from the origin at a speed and angle above the" x"- axis, with the force of gravity directed along the negative" y"- axis. It is desired to find the range, at which point the mass returns to the" x"- axis. Conventional analysis will yield the dimensionless variable, but offers no insight into the relationship between and. has suggested that the directed dimensions of Huntley be replaced by using" orientational symbols" to denote vector directions, and an orientationless symbol 10. Thus, Huntley' s L becomesL1 | with L specifying the dimension |
of length, and specifying the orientation. Siano further shows that the orientational symbols have an algebra of their own. Along with the requirement that, the following multiplication table for the orientation symbols results: Note that the orientational symbols form a group( the Klein four- group or" Viergruppe"). In this system, scalars always have the same orientation as the identity element, independent of the" symmetry of the problem". Physical quantities that are vectors have the orientation expected: a force or a velocity in the z- direction has the orientation of. For angles, consider an angle that lies in the z- plane. Form a right triangle in the z- plane with being one of the acute angles. The side of the right triangle adjacent to the angle then has an orientation and the side opposite has an orientation. Since( using to indicate orientational equivalence) we conclude that an angle in the xy- plane must have an orientation, which is not unreasonable. Analogous reasoning forces the conclusion that has orientation while has orientation 10. These are different, so one concludes( correctly), for example, that there are no solutions of physical equations that are of the form, where and are real scalars.Notethatanexpressionsuchasformula_66 is not dimensionally inconsistent since it is a special case of the sum of angles formula and should properly be written:whichforformula_68andformula_69yieldsformula_70. Siano distinguishes between geometric angles, which have an orientation in 3- dimensional space, and phase angles associated with time- based oscillations, which have no spatial orientation, i. e.theorientationofaphaseangleisformula_71. The assignment of orientational symbols to physical quantities and the requirement that physical equations be orientationally homogeneous can actually be used in a way that is similar to dimensional analysis to derive a little more information about acceptable solutions of physical problems. In this approach one sets up the dimensional equation and solves it as far as one can. If the lowest power of a physical variable is fractional, both sides of the solution is raised to a power such that all powers are integral. This puts it into" normal form". The orientational equation is then solved to give a more restrictive condition on the unknown powers of the orientational symbols, arriving at a solution that is more complete than the one that dimensional analysis alone gives. Often the added information is that one of the powers of a certain variable is even or odd. As an example, for the projectile problem, using orientational symbols,, being in the xy- plane will thus have dimension and the range of the projectile will be of the form: Dimensional homogeneity will now correctly yield and,andorientationalhomogeneityrequiresthatformula_73. In other words, that must be an odd integer. In fact the required function of theta will be which is a series consisting of odd powers of. It is seen that the Taylor series of and are orientationally homogeneous using the above multiplication table, while expressions like and are not, and are( correctly) deemed unphysical. Siano' s orientational analysis is compatible with the conventional conception of angular quantities as being dimensionless, and within orientational analysis, the radian may still be considered a dimensionless | unit. The orientational analysis of |
a quantity equation is carried out separately from the ordinary dimensional analysis, yielding information that supplements the dimensional analysis. Dimensionless concepts. Constants. The dimensionless constants that arise in the results obtained, such as the C in the Poiseuille'sLawproblemandtheformula_74 in the spring problems discussed above, come from a more detailed analysis of the underlying physics and often arise from integrating some differential equation. Dimensional analysis itself has little to say about these constants, but it is useful to know that they very often have a magnitude of order unity. This observation can allow one to sometimes make" back of the envelope" calculations about the phenomenon of interest, and therefore be able to more efficiently design experiments to measure it, or to judge whether it is important, etc. Formalisms. Paradoxically, dimensional analysis can be a useful tool even if all the parameters in the underlying theory are dimensionless, e. g., lattice models such as the Ising model can be used to study phase transitions and critical phenomena. Such models can be formulated in a purely dimensionless way. As we approach the critical point closer and closer, the distance over which the variables in the lattice model are correlated( the so- called correlation length,formula_75) becomes larger and larger. Now, the correlation length is the relevant length scale related to critical phenomena, so one can, e. g., surmise on" dimensional grounds" that the non-analyticalpartofthefreeenergyperlatticesiteshouldbeformula_76whereformula_77 is the dimension of the lattice. It has been argued by some physicists, e. g., M. J. Duff, that the laws of physics are inherently dimensionless. The fact that we have assigned incompatible dimensions to Length, Time and Mass is, according to this point of view, just a matter of convention, borne out of the fact that before the advent of modern physics, there was no way to relate mass, length, and time to each other. The three independent dimensionful constants:" c"," ħ", and" G", in the fundamental equations of physics must then be seen as mere conversion factors to convert Mass, Time and Length into each other. Just as in the case of critical properties of lattice models, one can recover the results of dimensional analysis in the appropriate scaling limit; e. g., dimensional analysis in mechanics can be derived by reinserting the constants" ħ"," c", and" G"( but we can now consider them to be dimensionless) and demanding that anonsingularrelationbetweenquantitiesexistsinthelimitformula_78,formula_79andformula_80. In problems involving a gravitational field the latter limit should be taken such that the field stays finite. Dimensional equivalences. Following are tables of commonly occurring expressions in physics, related to the dimensions of energy, momentum, and force. Natural units. If, where" c" is the speed of light and" ħ" is the reduced Planck constant, and a suitable fixed unit of energy is chosen, then all quantities of time" T", length" L" and mass" M" can be expressed( dimensionally) as a power of energy" E", because length, mass and time can be expressed using speed" v", action" S", and energy" E": though speed and action are dimensionless( and)– so the only remaining quantity with dimension is energy. In terms of | powers of dimensions: This is |
particularly useful in particle physics and high energy physics, in which case the energy unit is the electron volt( eV). Dimensional checks and estimates become very simple in this system. However, if electric charges and currents are involved, another unit to be fixed is for electric charge, normally the electron charge" e" though other choices are possible. See also. Programming languages. Dimensional correctness as part of type checking has been studied since 1977. Implementations for Ada and C++ were described in 1985 and 1988. Kennedy' s 1996 thesis describes an implementation in Standard ML, and later in F#. There are implementations for Haskell, OCaml, and Rust, Python, and a code checker for Fortran. Griffioen' s 2019 thesis extended Kennedy' s Hindley– Milner type system to support Hart' s matrices. Digital television( DTV) is the transmission of television audiovisual signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development itwasconsideredaninnovativeadvancementandrepresentedthefirstsignificantevolutionintelevisiontechnologysincecolortelevisioninthe1950s. Modern digital television is transmitted in high- definition television( HDTV) with greater resolution than analog TV. It typically uses a widescreen aspect ratio( commonly 16: 9) in contrast to the narrower format of analog TV. It makes more economical use of scarce radio spectrum space; it can transmit up to seven channels in the same bandwidth as a single analog channel, and provides many new features that analog television cannot. A transition from analog to digital broadcasting began around 2000. Different digital television broadcasting standards have been adopted in different parts of the world; below are the more widely used standards: History. Background. Digital television' s roots have been tied very closely to the availability of inexpensive, high performance computers.Itwasnotuntilthe1990s that digital TV became a real possibility. Digital television was previously not practically feasible due to the impractically high bandwidth requirements of uncompressed digital video,requiringaround200Mbit/ s(25MB/ s) for a standard- definition television( SDTV) signal,andover1Gbit/ s for high- definition television( HDTV).DigitalTVbecamepracticallyfeasibleintheearly1990s due to a major technological development, discrete cosine transform( DCT) video compression. DCT coding is a lossy compression technique that was first proposed for image compression by Nasir Ahmed in 1972, and was later adapted into a motion- compensated DCT video coding algorithm, for video coding standards such as the H.26x formats from 1988 onwards and the MPEG formats from 1991 onwards. Motion- compensated DCT video compression significantly reduced the amount of bandwidth required for a digital TV signal. DCT coding compressed down the bandwidth requirements ofdigitaltelevisionsignalstoabout34Mpps for SDTV and around 70140 Mbit/ s for HDTV while maintaining near- studio- quality transmission, making digital televisionapracticalrealityinthe1990s. Development. In the mid-1980s, Toshiba released a television set with digital capabilities, using integrated circuit chips such as a microprocessor to convert analog television broadcast signals to digital video signals, enabling features such as freezing pictures and showing two channels at once. In 1986, Sony and NEC Home Electronics announced their own similar TV sets with digital video capabilities. However, they still relied on analog TV broadcast signals, with true digital TV broadcasts not yet being available at the time. A digital TV broadcast service was | proposed in 1986 by Nippon |
Telegraph and Telephone( NTT) and the Ministry of Posts and Telecommunication( MPT) in Japan, where there were plans to develop an" Integrated Network System" service. However, it was not possible to practically implement such a digital TV service until the adoption of discrete cosine transform( DCT)videocompressiontechnologymadeitpossibleintheearly1990s. In the mid-1980s, as Japanese consumer electronics firms forged ahead with the development of HDTV technology, and as the MUSE analog format was proposed by Japan' s public broadcaster NHK as a worldwide standard, Japanese advancements were seen as pacesetters that threatened to eclipse U. S. electronics companies. Until June 1990, the Japanese MUSE standard— based on an analog system— was the front- runner among the more than 23 different technical concepts under consideration. Between 1988 and 1991, several European organizations were working on DCT- based digital video coding standards for both SDTV and HDTV. The EU 256 project by the CMTT and ETSI, along with research by Italian broadcaster RAI,developedaDCTvideocodecthatbroadcastSDTVat34Mbit/ s and near- studio- quality HDTV at about 70140 Mbit/ s. RAI demonstrated this with a 1990 FIFA World Cup broadcast in March 1990. An American company, General Instrument, also demonstrated the feasibility of a digital television signal in 1990. This led to the FCC being persuaded to delay its decision on an ATV standard until a digitally based standard could be developed. In March 1990, when it became clear that a digital standard was feasible, the FCC made a number of critical decisions. First, the Commission declared that the new TV standard must be more than an enhanced analog signal, but be able to provide a genuine HDTV signal with at least twice the resolution of existing television images. Then, to ensure that viewers who did not wish to buy a new digital television set could continue to receive conventional television broadcasts, it dictated that the new ATV standard must be capable of being" simulcast" on different channels. The new ATV standard also allowed the new DTV signal to be based on entirely new design principles. Although incompatible with the existing NTSC standard, the new DTV standard would be able to incorporate many improvements. The final standard adopted by the FCC did not require a single standard for scanning formats, aspect ratios, or lines of resolution. This outcome resulted from a dispute between the consumer electronics industry( joined by some broadcasters) and the computer industry( joined by the film industry and some public interest groups) over which of the two scanning processes— interlaced or progressive— is superior. Interlaced scanning, which is used in televisions worldwide, scans even- numbered lines first, then odd- numbered ones. Progressive scanning, which is the format used in computers, scans lines in sequences, from top to bottom. The computer industry argued that progressive scanning is superior because it does not" flicker" in the manner of interlaced scanning. It also argued that progressive scanning enables easier connections with the Internet, and is more cheaply converted to interlaced formats than vice versa. The film industry also supported progressive scanning because it offers a more efficient means of converting filmed programming into digital | formats. For their part, the |
consumer electronics industry and broadcasters argued that interlaced scanning was the only technology that could transmit the highest quality pictures then( and currently) feasible, i. e., 1, 080 lines per picture and 1, 920 pixels per line. Broadcasters also favored interlaced scanning because their vast archive of interlaced programming is not readily compatible with a progressive format. Inaugural launches. DirecTV in the U. S. launched the first commercial digital satellite platform in May 1994, using the Digital Satellite System( DSS) standard. Digital cable broadcasts were tested and launched in the U. S. in 1996 by TCI and Time Warner. The first digital terrestrial platform was launched in November 1998 as ONdigital in the United Kingdom, using the DVB- T standard. Technical information. Formats and bandwidth. Digital television supports many different picture formats defined by the broadcast television systems which are a combination of size and aspect ratio( width to height ratio). With digital terrestrial television( DTT) broadcasting, the range of formats can be broadly divided into two categories: high- definition television( HDTV) for the transmission of high- definition video and standard- definition television( SDTV). These terms by themselves are not very precise, and many subtle intermediate cases exist. One of several different HDTV formats that can be transmitted over DTV is: 1280× 720 pixels in progressive scan mode( abbreviated"720p") or 1920× 1080 pixels in interlaced video mode("1080i"). Each of these uses a aspect ratio. HDTV cannot be transmitted over analog television channels because of channel capacity issues. SDTV, by comparison, may use one of several different formats taking the form of various aspect ratios depending on the technology used in the country of broadcast. In terms of rectangular pixels, NTSC countries can deliver a 640× 480 resolution in 4: 3 and 854× 480 in, while PAL can give 768× 576 in and 1024× 576 in. However, broadcasters may choose to reduce these resolutions to reduce bit rate( e. g., many DVB- T channels in the United Kingdom use a horizontal resolution of 544 or 704 pixels per line). Each commercial broadcasting terrestrial television DTV channel in North America is permitted to be broadcast at a bit rate up to 19 megabits per second. However, the broadcaster does not need to use this entire bandwidth for just one broadcast channel. Instead the broadcast can use the channel to include PSIP and can also subdivide across several video subchannels( a. k. a. feeds) of varying quality and compression rates, including non- video datacasting services that allow one- way high- bit- rate streaming of data to computers like National Datacast. A broadcaster may opt to use a standard- definition( SDTV) digital signal instead of an HDTV signal, because current convention allows the bandwidth of a DTV channel( or" multiplex") to be subdivided into multiple digital subchannels,( similar to what most FM radio stations offer with HD Radio), providing multiple feeds of entirely different television programming on the same channel. This ability to provide either a single HDTV feed or multiple lower- resolution feeds is often referred to as distributing one' s" bit budget" or multicasting. | This can sometimes be arranged |
automatically, using a statistical multiplexer( or" stat- mux"). With some implementations, image resolution may be less directly limited by bandwidth; for example in DVB- T, broadcasters can choose from several different modulation schemes, giving them the option to reduce the transmission bit rate and make reception easier for more distant or mobile viewers. Receiving digital signal. There are several different ways to receive digital television. One of the oldest means of receiving DTV( and TV in general) is from terrestrial transmitters using an antenna( known as an" aerial" in some countries). This way is known as Digital terrestrial television( DTT). With DTT, viewers are limited to channels that have a terrestrial transmitter in range of their antenna. Other ways have been devised to receive digital television. Among the most familiar to people are digital cable and digital satellite. In some countries where transmissions of TV signals are normally achieved by microwaves, digital MMDS is used. Other standards, such as Digital multimedia broadcasting( DMB) and DVB- H, have been devised to allow handheld devices such as mobile phones to receive TV signals. Another way is IPTV, that is receiving TV via Internet Protocol, relying on digital subscriber line( DSL) or optical cable line. Finally, an alternative way is to receive digital TV signals via the open Internet( Internet television),whetherfromacentralstreamingserviceoraP2P( peer- to- peer) system. Some signals carry encryption and specify use conditions( such as" may not be recorded" or" may not be viewed on displays larger than 1 m in diagonal measure") backed up with the force of law under the World Intellectual Property Organization Copyright Treaty( WIPO Copyright Treaty) and national legislation implementing it, such as the U. S. Digital Millennium Copyright Act. Access to encrypted channels can be controlled by a removable smart card, for example via the Common Interface( DVB- CI) standard for Europe and via Point Of Deployment( POD) for IS or named differently CableCard. Protection parameters for terrestrial DTV broadcasting. Digital television signals must not interfere with each other, and they must also coexist with analog television until it is phased out. The following table gives allowable signal- to- noise and signal- to- interference ratios for various interference scenarios. This table is a crucial regulatory tool for controlling the placement and power levels of stations. Digital TV is more tolerant of interference than analog TV, and this is the reason a smaller range of channels can carry an all- digital set of television stations. Interaction. People can interact with a DTV system in various ways. One can, for example, browse the electronic program guide. Modern DTV systems sometimes use a return path providing feedback from the end user to the broadcaster. This is possible with a coaxial or fiber optic cable, a dialup modem, or Internet connection but is not possible with a standard antenna. Some of these systems support video on demand using a communication channel localized to a neighborhood rather than a city( terrestrial) or an even larger area( satellite). 1- segment broadcasting.1seg( 1- segment) is a special form of ISDB. Each channel is further divided into | 13 segments. The 12 segments |
of them are allocated for HDTV and remaining segment,the13th, is used for narrow- band receivers such as mobile television or cell phone. Comparison of analog vs digital. DTV has several advantages over analog TV, the most significant being that digital channels take up less bandwidth, and the bandwidth needs are continuously variable, at a corresponding reduction in image quality depending on the level of compression as well as the resolution of the transmitted image. This means that digital broadcasters can provide more digital channels in the same space, provide high- definition television service, or provide other non- television services such as multimedia or interactivity. DTV also permits special services such as multiplexing( more than one program on the same channel), electronic program guides and additional languages( spoken or subtitled). The sale of non- television services may provide an additional revenue source. Digital and analog signals react to interference differently. For example, common problems with analog television include ghosting of images, noise from weak signals, and many other potential problems which degrade the quality of the image and sound, although the program material may still be watchable. With digital television, the audio and video must be synchronized digitally, so reception of the digital signal must be very nearly complete; otherwise, neither audio nor video will be usable. Short of this complete failure," blocky" video is seen when the digital signal experiences interference. Analog TV began with monophonic sound, and later developed multichannel television sound with two independent audio signal channels. DTV allows up to 5 audio signal channels plus a subwoofer bass channel, with broadcasts similar in quality to movie theaters and DVDs. Digital TV signals require less transmission power than analog TV signals to be broadcast and received satisfactorily. Compression artifacts, picture quality monitoring, and allocated bandwidth. DTV images have some picture defects that are not present on analog television or motion picture cinema, because of present- day limitations of bit rate and compression algorithms such as MPEG- 2. This defect is sometimes referred to as" mosquito noise". Because of the way the human visual system works, defects in an image that are localized to particular features of the image or that come and go are more perceptible than defects that are uniform and constant. However, the DTV system is designed to take advantage of other limitations of the human visual system to help mask these flaws, e. g. by allowing more compression artifacts during fast motion where the eye cannot track and resolve them as easily and, conversely, minimizing artifacts in still backgrounds that may be closely examined in a scene( since time allows). Broadcast, cable, satellite, and Internet DTV operators control the picture quality of television signal encodes using sophisticated, neuroscience- based algorithms, such as the structural similarity( SSIM) video quality measurement tool, which was accorded each of its inventors a Primetime Emmy because of its global use. Another tool, called Visual Information Fidelity( VIF), is a top- performing algorithm at the core of the Netflix VMAF video quality monitoring system, which accounts for about 35% of all U. S. | bandwidth consumption. Effects of poor |
reception. Changes in signal reception from factors such as degrading antenna connections or changing weather conditions may gradually reduce the quality of analog TV. The nature of digital TV results in a perfectly decodable video initially, until the receiving equipment starts picking up interference that overpowers the desired signal or if the signal is too weak to decode. Some equipment will show a garbled picture with significant damage, while other devices may go directly from perfectly decodable video to no video at all or lock up. This phenomenon is known as the digital cliff effect. Block error may occur when transmission is done with compressed images. A block error in a single frame often results in black boxes in several subsequent frames, making viewing difficult. For remote locations, distant channels that, as analog signals, were previously usable in a snowy and degraded state may, as digital signals, be perfectly decodable or may become completely unavailable. The use of higher frequencies will add to these problems, especially in cases where a clear line- of- sight from the receiving antenna to the transmitter is not available, because usually higher frequency signals can' t pass through obstacles as easily. Effect on old analog technology. Television sets with only analog tuners cannot decode digital transmissions. When analog broadcasting over the air ceases, users of sets with analog- only tuners may use other sources of programming( e. g. cable, recorded media) or may purchase set- top converter boxes to tune in the digital signals. In the United States, a government- sponsored coupon was available to offset the cost of an external converter box. Analog switch- off( of full- power stations) took place on December 11, 2006 in The Netherlands, June 12, 2009 in the United States for full- power stations, and later for Class- A Stations on September 1, 2016, July 24, 2011 in Japan, August 31, 2011 in Canada, February 13, 2012 in Arab states, May 1, 2012 in Germany, October 24, 2012 in the United Kingdom and Ireland, October 31, 2012 in selected Indian cities, and December 10, 2013 in Australia. Completion of analog switch- off is scheduled for December 31, 2017 in the whole of India, December 2018 in Costa Rica and around 2020 for the Philippines. Disappearance of TV- audio receivers. Prior to the conversion to digital TV, analog television broadcast audio for TV channels on a separate FM carrier signal from the video signal. This FM audio signal could be heard using standard radios equipped with the appropriate tuning circuits. However, after the transition of many countries to digital TV, no portable radio manufacturer has yet developed an alternative method for portable radios to play just the audio signal of digital TV channels; DTV radio is not the same thing. Environmental issues. The adoption of a broadcast standard incompatible with existing analog receivers has created the problem of large numbers of analog receivers being discarded during digital television transition. One superintendent of public works was quoted in 2009 saying;" some of the studies I’ ve read in the trade magazines say up | to a quarter of American |
households could be throwing a TV out in the next two years following the regulation change". In 2009, an estimated 99 million analog TV receivers were sitting unused in homes in the US alone and, while some obsolete receivers are being retrofitted with converters, many more are simply dumped in landfills where they represent a source of toxic metals such as lead as well as lesser amounts of materials such as barium, cadmium and chromium. According to one campaign group, a CRT computer monitor or TV contains an average of of lead. According to another source, the lead in glass of a CRT varies from 1. 08 lb to 11. 28 lb, depending on screen size and type, but the lead is in the form of" stable and immobile" lead oxide mixed into the glass. It is claimed that the lead can have long- term negative effects on the environment if dumped as landfill. However, the glass envelope can be recycled at suitably equipped facilities. Other portions of the receiver may be subject to disposal as hazardous material. Local restrictions on disposal of these materials vary widely; in some cases second- hand stores have refused to accept working color television receivers for resale due to the increasing costs of disposing of unsold TVs. Those thrift stores which are still accepting donated TVs have reported significant increases in good- condition working used television receivers abandoned by viewers who often expect them not to work after digital transition. In Michigan in 2009, one recycler estimated that as many as one household in four would dispose of or recycle a TV set in the following year. The digital television transition, migration to high- definition television receivers and the replacement of CRTs with flatscreens are all factors in the increasing number of discarded analog CRT- based television receivers. The Declaration of Arbroath(;;) is the name usually given to a letter, dated 6 April 1320 at Arbroath, written by Scottish barons and addressed to Pope John XXII. It constituted King Robert I' s response to his excommunication for disobeying the pope' s demand in 1317 for a truce in the First War of Scottish Independence. The letter asserted the antiquity of the independence of the Kingdom of Scotland, denouncing English attempts to subjugate it. Generally believed to have been written in Arbroath Abbey by Bernard of Kilwinning( or of Linton), then Chancellor of Scotland and Abbot of Arbroath, and sealed by fifty- one magnates and nobles, the letter is the sole survivor of three created at the time. The others were a letter from the King of Scots, Robert I, and a letter from four Scottish bishops which all made similar points. The" Declaration" was intended to assert Scotland' s status as an independent, sovereign state and defend Scotland' s right to use military action when unjustly attacked. Submitted in Latin, the" Declaration" was little known until thelate17th century and is unmentioned by any of Scotland' smajor16th century historians. In the1680s, the Latin text was printed for the first time and translated into English in the wake | of the Glorious Revolution, after |
which time it was sometimes described as a declaration of independence. Overview. The" Declaration" was part of a broader diplomatic campaign, which sought to assert Scotland' s position as an independent kingdom, rather than its being a feudal land controlled by England' s Norman kings, as well as lift the excommunication of Robert the Bruce. The pope had recognised Edward I of England' s claim to overlordship of Scotland in 1305 and Bruce was excommunicated by the Pope for murdering John Comyn before the altar at Greyfriars Church in Dumfries in 1306. This excommunication was lifted in 1308; subsequently the pope threatened Robert with excommunication again if Avignon' s demands in 1317 for peace with England were ignored. Warfare continued, and in 1320 John XXII again excommunicated Robert I. In reply, the" Declaration" was composed and signed and, in response, the papacy rescinded King Robert Bruce' s excommunication and thereafter addressed him using his royal title. The wars of Scottish independence began as a result of the deaths of King Alexander III of Scotland in 1286 and his heir the" Maid of Norway" in 1290, which left the throne of Scotland vacant and the subsequent succession crisis of 1290- 1296 ignited a struggle among the Competitors for the Crown of Scotland, chiefly between the House of Comyn, the House of Balliol, and the House of Bruce who all claimed the crown. After July 1296' s deposition of King John Balliol by Edward of England and then February 1306' s killing of John Comyn III, Robert Bruce' s rivals to the throne of Scotland were gone, and Robert was crowned king at Scone that year. Edward I, the" Hammer of Scots", died in 1307; his son and successor Edward II did not renew his father' s campaigns in Scotland. In 1309 a parliament held at St Andrews acknowledged Robert' s right to rule, received emissaries from the Kingdom of France recognising the Bruce' s title, and proclaimed the independence of the kingdom from England. By 1314 only Edinburgh, Berwick- upon- Tweed, Roxburgh, and Stirling remained in English hands. In June 1314 the Battle of Bannockburn had secured Robert Bruce' s position as King of Scots; Stirling, the Central Belt, and much of Lothian came under Robert' s control while the defeated Edward II' s power on escaping to England via Berwick weakened under the sway of his cousin Henry, Earl of Lancaster. King Robert was thus able to consolidate his power, and sent his brother Edward Bruce to claim the Kingdom of Ireland in 1315 with an army landed in Ulster the previous year with the help of Gaelic lords from the Isles. Edward Bruce died in 1318 without achieving success, but the Scots campaigns in Ireland and in northern England were intended to press for the recognition of Robert' s crown by King Edward. At the same time, it undermined the House of Plantagenet' s claims to overlordship of the British Isles and halted the Plantagenets' effort to absorb Scotland as had been done in Ireland and Wales. Thus were the Scots | nobles confident in their letters |
to Pope John of the distinct and independent nature of Scotland' s kingdom; the" Declaration of Arbroath" was one such. According to historian David Crouch," The two nations were mutually hostile kingdoms and peoples, and the ancient idea of Britain as an informal empire of peoples under the English king' s presidency was entirely dead." The text makes claims about the ancient history of Scotland and especially the" Scoti", forbears of the Scots, who the" Declaration" claims originated in" Scythia Major" and migrated via Spain to Britain, dating their migration to" 1, 200 years from the Israelite people' s crossing of the Red Sea". The" Declaration" describes how the Scots had" thrown out the Britons and completely destroyed the Picts", resisted the invasions of" the Norse, the Danes and the English", and" held itself ever since, free from all slavery". It then claims that in the Kingdom of Scotland," one hundred and thirteen kings have reigned of their own Blood Royal, without interruption by foreigners". The text compares Robert Bruce with the Biblical warriors Judah Maccabee and Joshua. The" Declaration" made a number of points: that Edward I of England had unjustly attacked Scotland and perpetrated atrocities; that Robert the Bruce had delivered the Scottish nation from this peril; and, most controversially, that the independence of Scotland was the prerogative of the Scottish people, rather than the King of Scots. Debates. Some have interpreted this last point as an early expression of' popular sovereignty'– that government is contractual and that kings can be chosen by the community rather than by God alone. It has been considered to be the first statement of the contractual theory of monarchy underlying modern constitutionalism. It has also been argued that the" Declaration" was not a statement of popular sovereignty( and that its signatories would have had no such concept) but a statement of royal propaganda supporting Bruce' s faction. A justification had to be given for the rejection of King John Balliol in whose name William Wallace and Andrew de Moray had rebelled in 1297. The reason given in the" Declaration" is that Bruce was able to defend Scotland from English aggression whereas King John could not. Whatever the true motive, the idea of a contract between King and people was advanced to the Pope as a justification for Bruce' s coronation whilst John de Balliol, who had abdicated the Scottish throne, still lived in as a Papal prisoner. Text. For the full text in Latin and a translation in English, See on WikiSource. Signatories. There are 39 names— eight earls and thirty- one barons— at the start of the document, all of whom may have had their seals appended, probably over the space of some time, possibly weeks, with nobles sending in their seals to be used. The folded foot of the document shows that at least eleven additional barons and freeholders( who were not noble) who were not listed on the head were associated with the letter. On the extant copy of the" Declaration" there are only 19 seals, and of those 19 people | only 12 are named within |
the document. It is thought likely that at least 11 more seals than the original 39 might have been appended. The" Declaration" was then taken to the papal court at Avignon by Sir Adam Gordon, Sir Odard de Maubuisson, and Bishop Kininmund who was not yet a bishop and probably included for his scholarship. The Pope heeded the arguments contained in the" Declaration", influenced by the offer of support from the Scots for his long- desired crusade if they no longer had to fear English invasion. He exhorted Edward II in a letter to make peace with the Scots. However, it did not lead to his recognising Robert as King of Scots, and the following year was again persuaded by the English to take their side and issued six bulls to that effect. Eight years later, on 1 March 1328, the new English king, Edward III, signed a peace treaty between Scotland and England, the Treaty of Edinburgh– Northampton. In this treaty, which was in effect until 1333, Edward renounced all English claims to Scotland. In October 1328, the interdict on Scotland, and the excommunication of its king, were removed by the Pope. Manuscript. The original copy of the" Declaration" that was sent to Avignon is lost. The only existing manuscript copy of the" Declaration" survives among Scotland' s state papers,measuring540mmwideby675mm long( including the seals), it is held by the National Archives of Scotland in Edinburgh, a part of the National Records of Scotland. The most widely known English language translation was made by Sir James Fergusson, formerly Keeper of the Records of Scotland, from text that he reconstructed using this extant copy and early copies of the original draft. G. W. S. Barrow has shown that one passage in particular, often quoted from the Fergusson translation, was carefully written using different parts of" The Conspiracy of Catiline" by the Roman author, Sallust( 86– 35 BC) as the direct source: List of signatories. Listed below are the signatories of the Declaration of Arbroath in 1320. The letter itself is written in Latin. It uses the Latin versions of the signatories' titles, and in some cases, the spelling of names has changed over the years. This list generally uses the titles of the signatories' Wikipedia biographies. In addition, the names of the following do not appear in the document' s text, but their names are written on seal tags and their seals are present: Legacy. In 1998 former majority leader Trent Lott succeeded in instituting an annual" National Tartan Day" on 6 April by resolution of the United States Senate. US Senate Resolution 155 of 10 November 1997 states that" the Declaration of Arbroath, the Scottish Declaration of Independence, was signed on April 6, 1320 and the American Declaration of Independence was modeled[ sic] on that inspirational document". However, although this influence is accepted by some historians, it is disputed by others. In 2016 the Declaration of Arbroath was placed on the UK Memory of the World Register, part of UNESCO' s Memory of the World Programme. 2020 was the700th anniversary of the | Declaration of Arbroath' s composition; |
an" Arbroath 2020" festival was arranged but postponed due to the COVID- 19 pandemic. The National Museum of Scotland in Edinburgh planned to display the document to the public for the first time in fifteen years. Digital data, in information theory and information systems, is information represented as a string of discrete symbols each of which can take on one of only a finite number of values from some alphabet, such as letters or digits. An example is a text document, which consists of a string of alphanumeric characters. The most common form of digital data in modern information systems is" binary data", which is represented by a string of binary digits( bits) each of which can have one of two values, either 0 or 1. Digital data can be contrasted with" analog data", which is represented by a value from a continuous range of real numbers. Analog data is transmitted by an analog signal, which not only takes on continuous values, but can vary continuously with time, a continuous real- valued function of time. An example is the air pressure variation in a sound wave. The word" digital" comes from the same source as the words digit and" digitus"( the Latin word for" finger"), as fingers are often used for counting. Mathematician George Stibitz of Bell Telephone Laboratories used the word" digital" in reference to the fast electric pulses emitted by a device designed to aim and fire anti- aircraft guns in 1942. The term is most commonly used in computing and electronics, especially where real- world information is converted to binary numeric form as in digital audio and digital photography. Symbol to digital conversion. Since symbols( for example, alphanumeric characters) are not continuous, representing symbols digitally is rather simpler than conversion of continuous or analog information to digital. Instead of sampling and quantization as in analog- to- digital conversion, such techniques as polling and encoding are used. A symbol input device usually consists of a group of switches that are polled at regular intervals to see which switches are switched. Data will be lost if, within a single polling interval, two switches are pressed, or a switch is pressed, released, and pressed again. This polling can be done by a specialized processor in the device to prevent burdening the main CPU. When a new symbol has been entered, the device typically sends an interrupt, in a specialized format, so that the CPU can read it. For devices with only a few switches( such as the buttons on a joystick), the status of each can be encoded as bits( usually 0 for released and 1 for pressed) in a single word. This is useful when combinations of key presses are meaningful, and is sometimes used for passing the status of modifier keys on a keyboard( such as shift and control). But it does not scale to support more keys than the number of bits in a single byte or word. Devices with many switches( such as a computer keyboard) usually arrange these switches in a scan matrix, with the individual switches | on the intersections of x |
and y lines. When a switch is pressed, it connects the corresponding x and y lines together. Polling( often called scanning in this case) is done by activating each x line in sequence and detecting which y lines then have a signal, thus which keys are pressed. When the keyboard processor detects that a key has changed state, it sends a signal to the CPU indicating the scan code of the key and its new state. The symbol is then encoded or converted into a number based on the status of modifier keys and the desired character encoding. A custom encoding can be used for a specific application with no loss of data. However, using a standard encoding such as ASCII is problematic if a symbol such as' ß' needs to be converted but is not in the standard. It is estimated that in the year 1986 less than 1% of the world' s technological capacity to store information was digital and in 2007 it was already 94%. The year 2002 is assumed to be the year when humankind was able to store more information in digital than in analog format( the" beginning of the digital age"). States. Digital data come in these three states: data at rest, data in transit and data in use. The confidentiality, integrity and availability have to be managed during the entire lifecycle from' birth' to the destruction of the data. Properties of digital information. All digital information possesses common properties that distinguish it from analog data with respect to communications: Historical digital systems. Even though digital signals are generally associated with the binary electronic digital systems used in modern electronics and computing, digital systems are actually ancient, and need not be binary or electronic. Deduction may refer to: A demon is a supernatural entity, typically associated with evil, prevalent historically in religion, occultism, literature, fiction, mythology, and folklore; as well as in media such as comics, video games, movies, anime, and television series. In Ancient Near Eastern religions and in the Abrahamic traditions, including ancient and medieval Christian demonology, a demon is considered a harmful spiritual entity which may cause demonic possession, calling for an exorcism. Large portions of the Jewish demonology, a key influence on Christianity and Islam, originated from a later form of Zoroastrianism, and were transferred to Judaism during the Persian era. In Western occultism and Renaissance magic, which grew out of an amalgamation of Greco- Roman magic, Jewish Aggadah and Christian demonology, a demon is believed to be a spiritual entity that may be conjured and controlled. The supposed existence of demons remains an important concept in many modern religions and occultist traditions. Demons are still feared largely due to their alleged power to possess living creatures. In the contemporary Western occultist tradition( perhaps epitomized by the work of Aleister Crowley), a demon( such as Choronzon, which is Crowley' s interpretation of the so- called" Demon of the Abyss") is a useful metaphor for certain inner psychological processes( inner demons), though some may also regard it as an objectively real phenomenon. The | original Greek word" daimon" did |
not carry negative connotations. The Ancient Greek word" daimōn" denotes a spirit or divine power. The Greek conception of a" daimōn" notably appears in the works of Plato, where it describes the divine inspiration of Socrates. In Christianity morally ambivalent daimons were replaced by demons, forces of evil only striving for corruption. Such demons are not the Greek intermediary spirits, but hostile entities, already known in Iranian beliefs. Etymology. The Ancient Greek word" daemon" denotes a spirit or divine power, much like the Latin" genius" or" numen"." Daimōn" most likely came from the Greek verb" daiesthai"( to divide, distribute). The Greek conception of a" daimōn" notably appears in the works of Plato, where it describes the divine inspiration of Socrates. The original Greek word" daimon" does not carry the negative connotation initially understood by implementation of the Koine(" daimonion"), and later ascribed to any cognate words sharing the root. The Greek terms do not have any connotations of evil or malevolence. In fact," eudaimonia",( literally good- spiritedness) means happiness. By the early Roman Empire, cult statues were seen, by pagans and their Christian neighbors alike, as inhabited by the numinous presence of the gods:" Like pagans, Christians still sensed and saw the gods and their power, and as something, they had to assume, lay behind it, by an easy traditional shift of opinion they turned these pagan" daimones" into malevolent' demons', the troupe of Satan. Far into the Byzantine period Christians eyed their cities' old pagan statuary as a seat of the demons' presence. It was no longer beautiful, it was infested." The term had first acquired its negative connotations in the Septuagint translation of the Hebrew Bible into Greek, which drew on the mythology of ancient Semitic religions. This was then inherited by the Koine text of the New Testament. The Western medieval and neo- medieval conception of a" demon" derives seamlessly from the ambient popular culture of Late Antiquity. The Hellenistic" daemon" eventually came to include many Semitic and Near Eastern gods as evaluated by Christianity. The English use of" demon" as synonym for devils goes back at least as far as about 825. The German word(" Dämon") however, is different from devil(" Teufel") and demons as evil spirits. Ancient Egypt. Both deities and demons can act as intermediaries to deliver messages to humans. Thus they share some resemblance to the Greek daimonion. The exact definition of" demon" in Egyptology posed a major problem for modern scholarship, since the borders between a deity and a demon are sometimes blurred and the ancient Egyptian language lacks a term for the modern English" demon". However, magical writings indicate that ancient Egyptians acknowledged the existence of malevolent demons by highlighting the demon names with red ink. Demons in this culture appeared to be subordinative and related to a specific deity, yet they may have occasionally acted independently of the divine will. The existence of demons can be related to the realm of chaos, beyond the created world. But even this negative connotation cannot be denied in light of the magical texts. The role | of demons in relation to |
the human world remains ambivalent and largely depends on context. Ancient Egyptian demons can be divided into two classes:" guardians" and" wanderers."" Guardians" are tied to a specific place; their demonic activity is topographically defined and their function can be benevolent towards those who have the secret knowledge to face them. Demons protecting the underworld may prevent human souls from entering paradise. Only by knowing right charms is the deceased able to enter the" Halls of Osiris". Here, the aggressive nature of the guardian demons is motivated by the need to protect their abodes and not by their evil essence. Accordingly, demons guarded sacred places or the gates to the netherworld. During the Ptolemaic and Roman period, the guardians shifted towards the role of Genius loci and they were the focus of local and private cults. The" wanderers" are associated with possession, mental illness, death and plagues. Many of them serve as executioners for the major deities, such as Ra or Osiris, when ordered to punish humans on earth or in the netherworld. Wanderers can also be agents of chaos, arising from the world beyond creation to bring about misfortune and suffering without any divine instructions, led only by evil motivations. The influences of the wanderers can be warded off and kept at the borders on the human world by the use of magic, but they can never be destroyed. A sub- category of" wanderers" are nightmare demons, which were believed to cause nightmares by entering a human body. Mesopotamia. The ancient Mesopotamians believed that the underworld was home to many demons, which are sometimes referred to as" offspring of" arali"". These demons could sometimes leave the underworld and terrorize mortals on earth. One class of demons that were believed to reside in the underworld were known as" galla"; their primary purpose appears to have been to drag unfortunate mortals back to Kur. They are frequently referenced in magical texts, and some texts describe them as being seven in number. Several extant poems describe the" galla" dragging the god Dumuzid into the underworld. Like other demons, however," galla" could also be benevolent and, in a hymn from King Gudea of Lagash( 2144– 2124 BCE), a minor god named Ig- alima is described as" the great" galla" of Girsu". Lamashtu was a demonic goddess with the" head of a lion, the teeth of a donkey, naked breasts, a hairy body, hands stained( with blood?), long fingers and fingernails, and the feet of Anzû." She was believed to feed on the blood of human infants and was widely blamed as the cause of miscarriages and cot deaths. Although Lamashtu has traditionally been identified as a demoness, the fact that she could cause evil on her own without the permission of other deities strongly indicates that she was seen as a goddess in her own right. Mesopotamian peoples protected against her using amulets and talismans. She was believed to ride in her boat on the river of the underworld and she was associated with donkeys. She was believed to be the daughter of An. Pazuzu | is a demonic god who |
was well known to the Babylonians and Assyrians throughout the first millennium BCE. He is shown with" a rather canine face with abnormally bulging eyes, a scaly body, a snake- headed penis, the talons of a bird and usually wings." He was believed to be the son of the god Hanbi. He was usually regarded as evil, but he could also sometimes be a beneficent entity who protected against winds bearing pestilence and he was thought to be able to force Lamashtu back to the underworld. Amulets bearing his image were positioned in dwellings to protect infants from Lamashtu and pregnant women frequently wore amulets with his head on them as protection from her. Šul- pa- e' s name means" youthful brilliance", but he was not envisioned as youthful god. According to one tradition, he was the consort of Ninhursag, a tradition which contradicts the usual portrayal of Enki as Ninhursag' s consort. In one Sumerian poem, offerings made to Šhul- pa- e in the underworld and, in later mythology, he was one of the demons of the underworld. According to" The"" Jewish Encyclopedia", originally published in 12 volumes from 1901 to 1906," In Chaldean mythology the seven evil deities were known as" shedu", storm- demons, represented in ox- like form." They were represented as winged bulls, derived from the colossal bulls used as protective jinn of royal palaces. Judaism. There are differing opinions in Judaism about the existence or non- existence of demons(" shedim" or" se' irim"). There are" practically nil" roles assigned to demons in the Hebrew Bible. In Judaism today, beliefs in demons or evil spirits are either" midot hasidut"( Hebrew for" customs of the pious"), and therefore not" halakha", or notions based on a superstition that are non- essential, non- binding parts of Judaism, and therefore not normative Jewish practice. That is to say, Jews are not obligated to believe in the existence of" shedim", as posek rabbi David Bar- Hayim points out. Hebrew Bible. The Hebrew Bible mentions two classes of demonic spirits, the" se' irim" and the" shedim". The word" shedim"( sing" shed" or" sheyd") appears in two places in the Hebrew Bible. The" se' irim"( sing." sa' ir"," male goat") are mentioned once in Leviticus 17: 7, probably a recollection of Assyrian demons in the shape of goats. The" shedim", however, are not pagan demigods, but the foreign gods themselves. Both entities appear in a scriptural context of animal or child sacrifice to non- existent false gods. From Chaldea, the term" shedu" traveled to the Israelites. The writers of the Tanach applied the word as a dialogism to Canaanite deities. There are indications that demons in popular Hebrew mythology were believed to come from the nether world. Various diseases and ailments were ascribed to them, particularly those affecting the brain and those of internal nature. Examples include catalepsy, headache, epilepsy and nightmares. There also existed a demon of blindness," Shabriri"( lit." dazzling glare") who rested on uncovered water at night and blinded those who drank from it. Demons supposedly entered the body and caused the | disease while overwhelming or" seizing" |
the victim. To cure such diseases, it was necessary to draw out the evil demons by certain incantations and talismanic performances, at which the Essenes excelled. Josephus, who spoke of demons as" spirits of the wicked which enter into men that are alive and kill them", but which could be driven out by a certain root, witnessed such a performance in the presence of the Emperor Vespasian and ascribed its origin to King Solomon. In mythology, there were few defences against Babylonian demons. The mythical mace Sharur had the power to slay demons such as Asag, a legendary" gallu" or" edimmu" of hideous strength. Talmudic tradition and Midrashim. In the Jerusalem Talmud, notions of" shedim"(" demons" or" spirits") are almost unknown or occur only very rarely, whereas in the Babylonian Talmud there are many references to" shedim" and magical incantations. The existence of" shedim" in general was not questioned by most of the Babylonian Talmudists. As a consequence of the rise of influence of the Babylonian Talmud over that of the Jerusalem Talmud, late rabbis in general took as fact the existence of" shedim", nor did most of the medieval thinkers question their reality. However, rationalists like Maimonides, Saadia Gaon and Abraham ibn Ezra and others explicitly denied their existence, and completely rejected concepts of demons, evil spirits, negative spiritual influences, attaching and possessing spirits. They thought, the essential teaching about" shedim" and similar spirits is, that they should not be an object of worship, not a reality to be acknowledged or feared. Their point of view eventually became mainstream Jewish understanding. Occasionally an angel is called" satan" in the Babylon Talmud. But" satans" do not refer to demons as they remain at the service of God:" Stand not in the way of an ox when coming from the pasture, for Satan dances between his horns". Aggadic tales from the Persian tradition describe the" shedim", the" mazziḳim"(" harmers"), and the" ruḥin"(" spirits"). There were also" lilin"(" night spirits")," ṭelane"(" shade", or" evening spirits")," ṭiharire"(" midday spirits"), and" ẓafrire"(" morning spirits"), as well as the" demons that bring famine" and" such as cause storm and earthquake". According to some aggadic stories, demons were under the dominion of a king or chief, usually Asmodai. Kabbalah. In Kabbalah, demons are regarded a necessary part of the divine emanation in the material world and a byproduct of human sin( Qliphoth). However, spirits such as the" shedim" may also be benevolent and were used in kabbalistic ceremonies( as with the golem of Rabbi Yehuda Loevy) and malevolent" shedim"(" Mazikin", from the root meaning" to damage") were often credited with possession. Second Temple Judaism. The sources of demonic influence were thought to originate from the Watchers or Nephilim, who are first mentioned in Genesis 6 and are the focus of 1 Enoch Chapters 1– 16, and also in Jubilees 10. The Nephilim were seen as the source of the sin and evil on Earth because they are referenced in Genesis 6: 4 before the story of the Flood. In Genesis 6: 5, God sees evil in the hearts | of men. Ethiopic Enoch refers |
to Genesis 6: 4– 5, and provides further description of the story connecting the Nephilim to the corruption of humans. According to the Book of Enoch, sin originates when angels descend from heaven and fornicate with women, birthing giants. The Book of Enoch shows that these fallen angels can lead humans to sin through direct interaction or through providing forbidden knowledge. Most scholars understand the text, that demons originate from the evil spirits of the deceased giants, cursed by God to wander the Earth. Dale Martin disagrees with this interpretation, arguing that the ghosts of the Nephilim are distinct. The evil spirits would make the people sacrifice to the demons, but they were not demons themselves. The spirits are stated in Enoch to" corrupt, fall, be excited, and fall upon the earth, and cause sorrow." The Book of Jubilees conveys that sin occurs when Cainan accidentally transcribes astrological knowledge used by the Watchers. This differs from Enoch in that it does not place blame on the angels. However, in Jubilees 10: 4 the evil spirits of the Watchers are discussed as evil and still remain on Earth to corrupt the humans. God binds only 90% of the Watchers and destroys them, leaving 10% to be ruled by Mastema. Because the evil in humans is great, only 10% would be needed to corrupt and lead humans astray. These spirits of the giants also referred to as" the bastards" in the apotropaic prayer Songs of the Sage, which lists the names of demons the narrator hopes to expel. To the Qumran community during the Second Temple period, this apotropaic prayer was assigned, stating:" And, I the Sage, declare the grandeur of his radiance in order to frighten and terri[ fy] all the spirits of the ravaging angels and the bastard spirits, demons, Liliths, owls"(" Dead Sea Scrolls"," Songs of the Sage," Lines 4– 5). Hinduism. Hindu beliefs include numerous varieties of creatures with materialistic or non- material form such as Vetalas, Bhutas and Pishachas. Rakshasas and Asuras are demons. Asuras." Asura", in the earliest hymns of the Rigveda, originally meant any supernatural spirit, either good or bad. Since the/ s/ of the Indic linguistic branch is cognate with the/ h/ of the Early Iranian languages, the word" Asura", representing a category of celestial beings, is a cognate with Old Persian" Ahura". Ancient Hinduism tells that Devas( also called" suras") and Asuras are half- brothers, sons of the same father Kashyapa; although some of the Devas, such as Varuna, are also called Asuras. Later, during Puranic age, Asura and Rakshasa came to exclusively mean any of a race of anthropomorphic, powerful, possibly evil beings. Daitya( lit. sons of the mother" Diti"), Maya Danava, Rakshasa( lit. from" harm to be guarded against"), and Asura are incorrectly translated into English as" demon". In post- Vedic Hindu scriptures, pious, highly enlightened Asuras, such as Prahlada and Vibhishana, are not uncommon. The Asura are not fundamentally against the gods, nor do they tempt humans to fall. Many people metaphorically interpret the Asura as manifestations of the ignoble passions in | the human mind and as |
symbolic devices. There were also cases of power- hungry Asuras challenging various aspects of the gods, but only to be defeated eventually and seek forgiveness. Evil spirits. Hinduism advocates the reincarnation and transmigration of souls according to one' s karma. Souls( Atman) of the dead are adjudged by the Yama and are accorded various purging punishments before being reborn. Humans that have committed extraordinary wrongs are condemned to roam as lonely, often mischief mongers, spirits for a length of time before being reborn. Many kinds of such spirits( Vetalas, Pishachas, Bhūta) are recognized in the later Hindu texts. Iranian demons. Zoroastrianism. The Zorastrian belief in demons(" Daeva") had strong influence on the Abrahamic religions, especially Christianity and Islam. The daevas seem to be a Zorastrian interpretation of the Hindu pantheon. Particularly Indra, one of the most eminent individual deities of Vedic texts, is portrayed as a malicious force only next to Ahriman, the principle of evil( devil). But daevas are not merely the false gods of a past religion, but also embodiment of vices and fierce side of nature. Thraotona slays the daeva Azhi Dahāka, a serpentine or dragon- like creature with three heads. Thraotona' s victory over a serpentine or dragon- like creature with three heads, is not the victory of a great warrior, but to show that people who live in accordance with" Asha" can overcome evil. Aeshma, a demon of wrath and destruction, appears to be the direct forerunner of Asmodeus(" Sakhr" in Islam) from Abrahamic religion. Winter too became associated with one of the daeva. In Zarathustra' s personal revelation, there are no individual Daevas. They are always referred to as in a group and their worshippers are associated with violence and destruction: but ye Daevas are all spawned from Evil Thought/ as is the grandee who worships you, and from wrong and contempt... ever since you have been enjoiing those worst of things that mortals are to do/ to wax to the daevas' favor retreating from Good Thought/ losing the way from the Mindful Lord' s wisdom and from Right. In their state of wickedness, they lead mankind into sin and death: So ye lure the mortal from good living and security from death/ as the Evil Will does you who are daevas, by evil thought/ and that evil speech with which he assigns the deed to the wrongfil one' s control. The daevas however, are merely subordinate to the absolute power of evil, the Evil Will, embodied in Ahriman/ Angra Manyu. The daeva are thus both corrupted by evil, but also evil themselves. People who worship them are blamed too. in the Gathas, the primary way for demons to corrupt humans and cause suffering, manifests through their worshippers. The Vendidad( Law against Daeva) is mainly concerned to ward off the daevas. It offers laws for general ritual purity. Not only acts in favor for the demons might increase their power, but so does any act against Ahura Mazda. Cutting one' s hair or nails and keeping them on the ground can be considered a sacrifice to | the demons. As the demon' |
s power increase by human' s acts of wickedness, they are weakened by good deeds, especially performance of invocation of Ahura Mazda. The Vendidad further explores the possibility for humans to become a daeva. A human who performs sexual immoralities and/ or worships the daeva, becomes one themselves after death. During life, the person is considered to be equal to them, but turns truly into one after death. The Bundahishn gives an overview about the creation of demons. The text explains that Ahura Mazda and Ahriman existed before the material world, one in light and the other in the abyss of darkness. When Ahriman assaulted Ahura Mazda, Ahura Mazda created a world as a battle place and Ahriman could be defeated. The first beings created by Ahura Mazda were the six Amesha Spenta, whereupon Ahriman counters by creating six daevas. The demons are not tempted but directly created by the principle of evil. According to the Bundahishn, the demons revive Ahriman, whereby calling him their father: Rise up, thou father of us! for we will cause a conflict in the world, the distress and injury from which will become those of Ohrmazd and the archangelsDaevas assault the souls when passing the Chinvat Bridge. While virtuous people ward them off and succeed on entering heaven, wicked souls fail and are seized by the demons. In hell, daevas continue to torment the damned. Manichaeism. In Manichaean mythology demons had a real existence, as they derived from the Kingdom of Darkness, they were not metaphors expressing the absence of good nor are they fallen angels, that means they are not originally good, but entities purely evil. The demons came into the world after the Prince of Darkness assaulted the Realm of Light. The demons ultimately failed their attack and ended up imprisoned in the structures and matter of the contemporary world. Lacking virtues and being in constant conflict with both the divine creatures and themselves, they are inferior to the divine entities and overcome by the divine beings at the end of time. They are not sophisticated or inventive creatures, but only driven by their urges. Simultaneously, the Manichaean concept of demons remains abstract and is closely linked to ethical aspects of evil that many of them appear as personified evil qualities such as: The Watcher, another group of demonic entities, known from the Enochian writings, appear in the canonical Book of Giants. The Watchers came into existence after the demons were chained up in the sky by Living Spirit. Later, outwitted by Third Messenger, they fall to earth, there they had intercourse with human women and beget the monstrous Nephilim. Thereupon they establish a tyrannical rule on earth, suppressing mankind, until they are defeated by the angels of punishment, setting an end to their rule. In the" Shahnameh". In Shahnameh, written by the Persian poet Ferdowsi between c. 977 and 1010 CE the term" div"( from the Avestan" Daeva") includes both demons as well as evil humans. The divs of the legendary Mazandaran might reflect human enemies of Iran. Zahak, inspired by the daeva" | Azhi Dahāka", is not a |
degraced deity, but a human tyrant, identified as an Arab, who slayed his father in exchange for power. It is only after he was tricked by the devil for power, he grows serpentine heads on his shoulders and becomes less human. Divs are often black, long teeth, claws as hands; a monstrous but humanoid shape. Despite their human form, many divs are masters of supernatural sorcery, reflecting their former associations with the daevas. Div- e Sepid, leader of the divs, is both an outstanding warrior and a master of magic, who causes storms to overcome hostile armies. After divs are defeated, they might join their enemy. The poem begins with the kings of the Pishdadian dynasty. They defeat and subjugate the demonic divs. Tahmuras commanded the divs and became known as" dīvband"( binder of demons). Jamshid, the fourth king of the world, ruled over both angels and div and served as a high priest of Ahura Mazda( Hormozd). After a just reign over hundreds of years, Jamshid grew haughty and claims, because of his wealth and power, divinity for himself. His people get unsatisfied with their king and Zahhak usurps the throne, aided by demons. Jamshid dies sawn in two by two divs. Tricked by Ahriman( or Iblis), Zahhak grew two snakes on his shoulders and becomes athe demonic serpant- king. The King Kay Kāvus fails to conquer the legendary Mazdaran, the land of divs and gets captured. To save his king, Rustam takes a journey and fights through seven trials. Divs are among the common enemies Rustam faces, the last one the Div- e Sepid, the demonic king of Mazdaran. Native North American demons. Wendigo. The Algonquian people traditionally believe in a spirit called a wendigo. The spirit is believed to possess people who then become cannibals. In Athabaskan folklore, there is a belief in wechuge, a similar cannibal spirit. Christianity. Old Testament. The existence of demons as inherently malicious spirits within Old Testamental texts is absent. Though there are evil spirits sent by YHWH, they can hardly be called" demons", since they serve and do not oppose the governing deity. First then the Hebrew Bible was translated into Greek, the" gods of other nations" were merged into a single category of demons( daimones) with implied negativity. The Greek Daimons were associated with demi- divine entities, deities, illnesses and fortune- telling. The Jewish translators rendered them all as demons, depicting their power as nullified comparable to the description of shedim in the Tanakh. Although all these supernatural powers were translated, none were angels, despite sharing a similar function to that of the Greek Daimon. This established a dualism between the angels on God' s side and negatively evaluated demons of pagan origin. Their relationship to the God- head became the main difference between angels and demons, not their degree of benevolence. Both angels and demons might be fierce and terrifying. However, the angels act always at service of the high god of the Israelites, differing from the pagan demons, who represent the powers of foreign deities. The Septuagint refers to evil | spirits as demons( daimon). New |
Testament. Through the New Testament, demons appear 55 times, 46 times in reference to demonic possession or exorcisms. Some old English Bible translations such as King James Version do not have the word' demon' in their vocabulary and translate it as' devil'. As adversaries of Jesus, demons are not morally ambivalent spirits, but evil; cause of misery, suffering and death. They are not tempters, but cause of pain, suffering and maladies, both physical and mental. Temptation is reserved for the devil only. Unlike spirits in pagan beliefs, demons are not intermediary spirits whom must be sacrificed for appeasement of a deity. Possession also shows no trace of positivity contrary to some pagan depictions of spirit possession. They are explicitly said to be ruled by the devil or Beelzebub. Their origin is unclear, the texts take the existence of demons for granted. Many early Christians, like Irenaeus, Justin Martyr, Clement of Alexandria and Lactantius assumed demons were ghosts of the Nephilim, known from Intertestamental writings. Because of references to Satan as the lord of demons, and evil angels of Satan throughout the New Testament, other scholars identified fallen angels with demons. Demons as entirely evil entities, who have been born evil, may not fit the proposed origin of evil in free- will, taught in alternate or opposing theologies. Pseudepigrapha and deuterocanonical books. Demons are included into biblical interpretation. In the story of Passover, the Bible tells the story as" the Lord struck down all the firstborn in Egypt"(). In the Book of Jubilees, which is considered canonical only by the Ethiopian Orthodox Church, this same event is told slightly differently:" All the powers of[ the demon] Mastema had been let loose to slay all the first- born in the land of Egypt. And the powers of the Lord did everything according as the Lord commanded them."( Jubilees 49: 2– 4) In the Genesis flood narrative the author explains how God was noticing" how corrupt the earth had become, for all the people on earth had corrupted their ways"(). In Jubilees the sins of man are attributed to" the unclean demons[ who] began to lead astray the children of the sons of Noah, and to make to err and destroy them"( Jubilees 10: 1). In Jubilees, Mastema questions the loyalty of Abraham and tells God to" bid him offer him as a burnt offering on the altar, and Thou wilt see if he will do this command"( Jubilees 17: 16). The discrepancy between the story in Jubilees and the story in Genesis 22 exists with the presence of Mastema. In Genesis, God tests the will of Abraham merely to determine whether he is a true follower, however; in Jubilees Mastema has an agenda behind promoting the sacrifice of Abraham' s son," an even more demonic act than that of the Satan in Job". In Jubilees, where Mastema, an angel tasked with the tempting of mortals into sin and iniquity, requests that God give him a tenth of the spirits of the children of the watchers, demons, in order to aid the process( Jubilees 10: | 7– 9). These demons are |
passed into Mastema' s authority, where once again, an angel is in charge of demonic spirits. The Testament of Solomon, written sometime in the first three centuries C. E., the demon Asmodeus explains what he is the son of an angel and a human mother. Another demon describes himself as having died in the" massacre in the age of giants"." Beelzeboul", the prince of demons, appears as a fallen angel not as a demon, but makes people worship demons as their gods. Christian demonology. Since Early Christianity, demonology has developed from a simple acceptance of demons to a complex study that has grown from the original ideas taken from Jewish demonology and Christian scriptures. Christian demonology is studied in depth within the Roman Catholic Church, although many other Christian churches affirm and discuss the existence of demons. Building upon the few references to" daimon" in the New Testament, especially the poetry of the Book of Revelation,Christianwritersofapocryphafromthe2nd century onwards created a more complicated tapestry of beliefs about" demons" that was largely independent of Christian scripture. While daimons were considered as both potentially benevolent or malevolent, Origen argued against Celsus that daimons are exclusively evil entities, supporting the later idea of( evil) demons. According to Origen' s cosmology, increasing corruption and evil within the soul, the more estranged the soul gets from God. Therefore, Origen opinned that the most evil demons are located underground. Besides the fallen angels known from Christian scriptures, Origen talks about Greek daemons, like nature spirits and giants. These creatures were thought to inhabit nature or air and nourish from pagan sacrifices roaming the earth. However, there is no functional difference between the spirits of the underworld and of earth, since both have fallen from perfection into the material world. Origen sums them up as fallen angels and thus equal to demons. Many ascetics, like Origen and Anthony the Great, described demons as psychological powers, tempting to evil, in contrast to benevolent angels advising good. According to" Life of Anthony", written in Greek around 360 by Athanasius of Alexandria, most of the time, the demons were expressed as an internal struggle, inclinations and temptations. But after Anthony successfully resisted the demons, they would appear in human form to tempt and threat him even more intense. Pseudo- Dionysius the Areopagite described" evil" as" defiancy" and does not give" evil" an ontological existence. He explains demons are deficiant creatures, who willingly turn themselves towards the unreal and non- existence. Their dangerous nature results not from power of their nature, but from their tendency to drag others into the" void" and the unreal, away from God. Michael Psellos proposed the existence of several types of demons, deeply influenced by the material nature of the regions they dwell. The highest and most powerful demons attack the mind of people using their" imaginative action"( phantastikos) to produce illusions in the mind. The lowest demons on the other hand are almost mindless, gross and grunting spirits, which try to possess people instinctively, simply attracted by the warmth and life of humans. These cause diseases, fatal accidents | and animalistic behavior in their |
victims. They are unable to speak, while other lower types of demons might give out false oracles. The demons are divided into: Invocation of Saints, holy men and women, especially ascetics, reading the Gospel, holy oil or water is said to drive them out. However, Psellos' schemes have been too inconsistent to answer questions about the hierarchy of fallen angels. The devil' s position is impossible to assign in this scheme and it does not respond to living perceptions of felt experience and was considered rather impractical to have a lasting effect or impact on Christian demonology. The contemporary Roman Catholic Church unequivocally teaches that angels and demons are real beings rather than just symbolic devices. The Catholic Church has a cadre of officially sanctioned exorcists which perform many exorcisms each year. The exorcists of the Catholic Church teach that demons attack humans continually but that afflicted persons can be effectively healed and protected either by the formal rite of exorcism, authorized to be performed only by bishops and those they designate, or by prayers of deliverance, which any Christian can offer for themselves or others. At various times in Christian history, attempts have been made to classify demons according to various proposed demonic hierarchies. Mandaeism. In Mandaeism, the World of Darkness(), also referred to as Sheol, is the underworld located below Tibil( Earth). It is ruled by its king Ur( Leviathan) and its queen Ruha, mother of the seven planets and twelve constellations. The great dark Ocean of Sup( or Suf) lies in the World of Darkness. The great dividing river of Hitpun, analogous to the river Styx in Greek mythology, separates the World of Darkness from the World of Light. Prominent infernal beings found in the World of Darkness include" lilith"," nalai"( vampire)," niuli"( hobgoblin)," gadalta"( ghost)," satani"( Satan) and various other demons and evil spirits. Gnosticism. Examples of Gnostic portrayals of demons can be found in the" Apocryphon of John" in which they are said to have helped construct the physical Adam and in" Pistis Sophia" which states they are ruled over by Hekate and punish corrupt souls. Islam." Shayāṭīn"( or" Daeva" of Indo- Iranian religion) are the usual terms for demons in Islamic belief. In Islam demons try to lead humans astray from God, by tempting them to sin, teaching them sorcery and cause mischief among humans. Occult practises albeit not forbidden per se, may include conjuring demons, which requires acts against God' s laws and are therefore forbidden, such as illicit blood- sacrifices, abandoning prayer and rejecting fasting. Based on the Islamic view on Solomon, who is widely believed to have been a ruler over genies and demons, Islam has a rich tradition about conjuring demons. Among the demons are the devils(" shayatin") and the fiends(" div"). Both are believed to have worked for Solomon as slaves. While the devils usually appear within a Judeo- Christian background, the" div" frequently feature in beliefs of Persian and Indian origin. But it is to be noted that in Islam both angels and demons are considered to be the creatures | of God and so God |
has ultimate power over all of them. According to exegisis of the Quran the devils are the offspring of Iblis( Satan). They are said to live until the world ceases to exist, always shadow in humans( and jinn) whispering onto their hearts to lead them astray. Prayers are used to ward off their attacks, dissolving them temporarily. As the counterpart of the angels, they try to go against God' s will and their abode in Hell is pre- destined. They lack free will and are bound to evil. The ifrit and marid are more powerful classes of devils. Jinn are different from devils in that they have free will and not all of them are wrongdoers. According to Abu Ali Bal' ami' s work on the history of the world, Wahb ibn Munabbih explained that the divs were the first beings created by God. Some argue the devils were created good, but turned evil by Iblis' act of arrogance, the div were created as vicious creatures and embodiment of evil. When Iblis was still among the angels, he led an army against the spirits on the earth. Among them were the div, who formed two orders; one of which sided with the jinn and were banished with them, condemned to roam the earth. The other, treacherous div joined Iblis in battle, and exiled to Hell with him. The div are often depicted as sorcerers whose misdeeds are not bound to temptation only. They could cause sickness, mental illnesses, or even turn humans to stone by touching. While the devils frequently appear to ordinary humans to tempt them into everything disapproved by society, the div usually appear to specific heroes. Bahá' í Faith. In the Bahá' í Faith, demons are not regarded as independent evil spirits as they are in some faiths. Rather, evil spirits described in various faiths' traditions, such as Satan, fallen angels, demons and jinn, are metaphors for the base character traits a human being may acquire and manifest when he turns away from God and follows his lower nature. Belief in the existence of ghosts and earthbound spirits is rejected and considered to be the product of superstition. Ceremonial magic. While some people fear demons, or attempt to exorcise them, others willfully attempt to summon them for knowledge, assistance, or power. The ceremonial magician usually consults a grimoire, which gives the names and abilities of demons as well as detailed instructions for conjuring and controlling them. Grimoires are not limited to demons– some give the names of angels or spirits which can be called, a process called theurgy. The use of ceremonial magic to call demons is also known as goetia, the name taken from a section in the famous grimoire known as the" Lesser Key of Solomon". Wicca. According to Rosemary Ellen Guiley," Demons are not courted or worshipped in contemporary Wicca and Paganism. The existence of negative energies is acknowledged." Modern interpretations. Psychologist Wilhelm Wundt remarked that" among the activities attributed by myths all over the world to demons, the harmful predominate, so that in popular belief | bad demons are clearly older |
than good ones." Sigmund Freud developed this idea and claimed that the concept of demons was derived from the important relation of the living to the dead:" The fact that demons are always regarded as the spirits of those who have died" recently" shows better than anything the influence of mourning on the origin of the belief in demons." M. Scott Peck, an American psychiatrist, wrote two books on the subject," People of the Lie: The Hope For Healing Human Evil" and" Glimpses of the Devil: A Psychiatrist' s Personal Accounts of Possession, Exorcism, and Redemption". Peck describes in some detail several cases involving his patients. In" People of the Lie" he provides identifying characteristics of an evil person, whom he classified as having a character disorder. In" Glimpses of the Devil" Peck goes into significant detail describing how he became interested in exorcism in order to debunk the" myth" of possession by evil spirits– only to be convinced otherwise after encountering two cases which did not fit into any category known to psychology or psychiatry. Peck came to the conclusion that possession was a rare phenomenon related to evil and that possessed people are not actually evil; rather, they are doing battle with the forces of evil. Although Peck' s earlier work was met with widespread popular acceptance, his work on the topics of evil and possession has generated significant debate and derision. Much was made of his association with( and admiration for) the controversial Malachi Martin, a Roman Catholic priest and a former Jesuit, despite the fact that Peck consistently called Martin a liar and a manipulator. Richard Woods, a Roman Catholic priest and theologian, has claimed that Dr. Peck misdiagnosed patients based upon a lack of knowledge regarding dissociative identity disorder( formerly known as multiple personality disorder) and had apparently transgressed the boundaries of professional ethics by attempting to persuade his patients into accepting Christianity. Father Woods admitted that he has never witnessed a genuine case of demonic possession in all his years. According to S. N. Chiu, God is shown sending a demon against Saul in 1 Samuel 16 and 18 in order to punish him for the failure to follow God' s instructions, showing God as having the power to use demons for his own purposes, putting the demon under his divine authority. According to the" Britannica Concise Encyclopedia", demons, despite being typically associated with evil, are often shown to be under divine control, and not acting of their own devices. A domino effect or chain reaction is the cumulative effect produced when one event sets off a chain of similar events. This term is best known as a mechanical effect and is used as an analogy to a falling row of dominoes. It typically refers to a linked sequence of events where the time between successive events is relatively small. It can be used literally( an observed series of actual collisions) or metaphorically( causal linkages within systems such as global finance or politics). The term" domino effect" is used both to imply that an event is | inevitable or highly likely( as |
it has already started to happen), and conversely to imply that an event is impossible or highly unlikely( the one domino left standing). Demonstration of the effect. The domino effect can easily be visualized by placing a row of dominoes upright, each separated by a small distance. Upon pushing the first domino, the next domino in line will be knocked over, and so on, thus firing a linear chain in which each domino' s fall is triggered by the domino immediately preceding it. The effect is the same regardless of the length of the chain. The energy used in this chain reaction is the potential energy of the dominoes due to them being in a meta- stable state; when the first domino is toppled, the energy transferred by the fall is greater than the energy needed to knock over the following domino, and so on. The domino effect is exploited in Rube Goldberg machines. See also. Relevant physical theory: Mathematical theoryPolitical theorySocialDiffusion pumps use a high speed jet of vapor to direct gas molecules in the pump throat down into the bottom of the pump and out the exhaust. They were the first type of high vacuum pumps operating in the regime of free molecular flow, where the movement of the gas molecules can be better understood as diffusion than by conventional fluid dynamics. Invented in 1915 by Wolfgang Gaede, he named it a" diffusion pump" since his design was based on the finding that gas cannot diffuse against the vapor stream, but will be carried with it to the exhaust. However, the principle of operation might be more precisely described as gas- jet pump, since diffusion plays a role also in other high vacuum pumps. In modern textbooks, the diffusion pump is categorized as a momentum transfer pump. The diffusion pump is widely used in both industrial and research applications. Most modern diffusion pumps use silicone oil or polyphenyl ethers as the working fluid. History.Inthelate19th century, most vacuums were created using a Sprengel pump, which had the advantage of being very simple to operate, and capable of achieving quite good vacuum given enough time. Compared to later pumps, however, the pumping speed was very slow and the vapor pressure of the mercury limited the ultimate vacuum. Following his invention of the molecular pump, the diffusion pump was invented in 1915 by Wolfgang Gaede, and originally used elemental mercury as the working fluid. After its invention, the design was quickly commercialized by Leybold. It was then improved by Irving Langmuir and W. Crawford. Cecil Reginald Burch discovered the possibility of using silicone oil in 1928. Oil diffusion pumps. An oil diffusion pump is used to achieve higher vacuum( lower pressure) than is possible by use of positive displacement pumps alone. Although its use has been mainly associated within the high- vacuum range, down to, diffusion pumps today can produce pressures approachingwhen properly used with modern fluids and accessories. The features that make the diffusion pump attractive for high and ultra- high vacuum use are its high pumping speed for all gases and | low cost per unit pumping |
speed when compared with other types of pump used in the same vacuum range. Diffusion pumps cannot discharge directly into the atmosphere, so a mechanical forepump is typically used to maintain an outlet pressure aroundThe oil diffusion pump is operated with an oil of low vapor pressure. The high speed jet is generated by boiling the fluid and directing the vapor through a jet assembly. Note that the oil is gaseous when entering the nozzles. Within the nozzles, the flow changes from laminar to supersonic and molecular. Often, several jets are used in series to enhance the pumping action. The outside of the diffusion pump is cooled using either air flow, water lines or a water- filled jacket. As the vapor jet hits the outer cooled shell of the diffusion pump, the working fluid condenses and is recovered and directed back to the boiler. The pumped gases continue flowing to the base of the pump at increased pressure, flowing out through the diffusion pump outlet, where they are compressed to ambient pressure by the secondary mechanical forepump and exhausted. Unlike turbomolecular pumps and cryopumps, diffusion pumps have no moving parts and as a result are quite durable and reliable. They can function over pressure ranges ofThey are driven only by convection and thus have a very low energy efficiency. One major disadvantage of diffusion pumps is the tendency to backstream oil into the vacuum chamber. This oil can contaminate surfaces inside the chamber or upon contact with hot filaments or electrical discharges may result in carbonaceous or siliceous deposits. Due to backstreaming, oil diffusion pumps are not suitable for use with highly sensitive analytical equipment or other applications which require an extremely clean vacuum environment, but mercury diffusion pumps may be in the case of ultra high vacuum chambers used for metal deposition. Often cold traps and baffles are used to minimize backstreaming, although this results in some loss of pumping speed. The oil of a diffusion pump cannot be exposed to the atmosphere when hot. If this occurs, the oil will oxidise and has to be replaced. If a fire occurs, the smoke and residue may contaminate other parts of the system. Oil types. The least expensive diffusion pump oils are based on hydrocarbons which have been purified by double- distillation. Compared with the other fluids, they have higher vapor pressure, so are usually limited to a pressure ofThey are also the most likely to burn or explode if exposed to oxidizers. The most common silicone oils used in diffusion pumps are trisiloxanes, which contain the chemical group Si- O- Si- O- Si, to which various phenyl groups or methyl groups are attached. These are available as the so called 702 and 703 blends, which were formerly manufactured by Dow Corning. These can be further separated into 704 and 705 oils, which are made up of the isomers of tetraphenyl tetramethyl trisiloxane and pentaphenyl trimethyl trisiloxane respectively. For pumping reactive species, usually a polyphenyl ether based oil is used. These oils are the most chemical and heat resistant type of diffusion | pump oil. Steam ejectors. The |
steam ejector is a popular form of pump for vacuum distillation and freeze- drying. A jet of steam entrains the vapour that must be removed from the vacuum chamber. Steam ejectors can have single or multiple stages, with and without condensers in between the stages. While both steam ejectors and diffusion pumps use jets of vapor to entrain gas, they work on fundamentally different principles- steam ejectors rely on viscous flow and mixing to pump gas, whereas diffusion pumps use molecular diffusion. This has several consequences. In diffusion pumps, the inlet pressure can be much lower than the static pressure of jet, whereas in steam ejectors the two pressures are about the same. Also, diffusion pumps are capable of much higher compression ratios, and cannot discharge directly to atmosphere. Domenico Alberti( c. 1710– 14 October 1740 or 1746) was an Italian singer, harpsichordist, and composer. Alberti was born in Venice and studied music with Antonio Lotti. He wrote operas, songs, and sonatas for keyboard instruments, for which he is best known today. His sonatas frequently employ arpeggiated accompaniment in the left hand in one of several patterns that are now collectively known as" Alberti bass". Alberti was one of the earliest composers to use those patterns, but was not the first or only one. The most well- known of these patterns consists of regular broken chords, with the lowest note sounding first, then the highest, then the middle and then the highest again, with the pattern repeated. Today, Alberti is regarded as a minor composer, and his works are played or recorded only irregularly. However, the Alberti bass was used by many later composers, and it became an important element in much keyboard music of the classical music era. An example of Alberti bass( Mozart' s" Piano Sonata, K 545"): In his own lifetime, Alberti was known as a singer, and often used to accompany himself on the harpsichord. In 1736, he served as a page for Pietro Andrea Cappello, the Venetian ambassador to Spain. While at the Spanish court, the famous castrato singer Farinelli heard him sing. Farinelli was said to have been impressed, although Alberti was an amateur. Alberti' s best known pieces are his keyboard sonatas, although even they are very rarely performed. It is thought he wrote around 36 sonatas, of which 14 have survived. They all have two movements, each in binary form. It is probable that Mozart' s first violin sonatas, written at the age of seven, were modeled on Alberti' s work. Alberti died in Rome in 1740 or 1746. Doris Day( born Doris Mary Anne Kappelhoff; April 3, 1922– May 13, 2019) was an American actress, singer, and animal welfare activist. She began her career as a big band singer in 1939, achieving commercial success in 1945 with two No. 1 recordings," Sentimental Journey" and" My Dreams Are Getting Better All the Time" with Les Brown& amp; His Band of Renown. She left Brown to embark on a solo career and recorded more than 650 songs from 1947 to 1967. Day was one of | the biggest film stars of |
the1950s–1960s. Day' s film career began during the Golden Age of Hollywood with the film" Romance on the High Seas"( 1948). She starred in films of many genres, including musicals, comedies, dramas, and thrillers. She played the title role in" Calamity Jane"( 1953) and starred in Alfred Hitchcock' s" The Man Who Knew Too Much"( 1956) with James Stewart. Her best- known films are those in which she co- starred with Rock Hudson, chief among them 1959' s" Pillow Talk", for which she was nominated for the Academy Award for Best Actress. She also worked with James Garner on both" Move Over, Darling"( 1963) and" The Thrill of It All"( 1963), and starred alongside Clark Gable, Cary Grant, James Cagney, David Niven, Ginger Rogers, Jack Lemmon, Frank Sinatra, Kirk Douglas, Lauren Bacall, and Rod Taylor in various movies. After ending her film career in 1968, only briefly removed from the height of her popularity, she starred in her own sitcom" The Doris Day Show"( 1968– 1973). In 1989, she was awarded the Golden Globe Cecil B. DeMille Award for lifetime achievement in motion pictures. In 2004, she was awarded the Presidential Medal of Freedom. In 2008, she received the Grammy Lifetime Achievement Award as well as a Legend Award from the Society of Singers. In 2011, she was awarded the Los Angeles Film Critics Association' s Career Achievement Award. The same year,shereleasedher29th studio album," My Heart", which contained new material and became a UK Top 10 album., she was one of eight record performers to have been the top box- office earner in the United States four times. Early life. Day was born Doris Mary Anne Kappelhoff on April 3, 1922 in Cincinnati, Ohio, the daughter of Alma Sophia(" née" Welz; 1895– 1976) and William Joseph Kappelhoff( 1892– 1967). Her mother was a homemaker, and her father was a music teacher and choirmaster. Doris was named after actress Doris Kenyon. Her maternal and paternal grandparents were German; her paternal grandfather Franz Joseph Wilhelm Kappelhoff immigrated to the United States in 1875 and settled in Cincinnati which had a large German community with its own churches, clubs, and German- language newspapers. For most of her life, Day stated she was born in 1924;itwasnotuntilher95th birthday– when the Associated Press found her birth certificate, showing a 1922 date of birth– that she stated otherwise. The youngest of three siblings, she had two older brothers: Richard( who died before her birth) and Paul, two to three years older. Due to her father' s infidelity, her parents separated. She developed an early interest in dance, and in the mid-1930s formed a dance duo with Jerry Doherty that performed in competitions throughout the United States. A car accident on October 13, 1937 shattered her right leg and curtailed her prospects as a professional dancer. Career. Early career( 1938– 1947). While recovering from her car accident, Kappelhoff started to sing along with the radio and discovered a talent she did not know she had." During this long, boring period, I used to while away a lot of time listening | to the radio, sometimes singing |
along with the likes of Benny Goodman, Duke Ellington, Tommy Dorsey, and Glenn Miller", she told A. E. Hotchner, one of Day' s biographers." But the one radio voice I listened to above others belonged to Ella Fitzgerald. There was a quality to her voice that fascinated me, and I' d sing along with her, trying to catch the subtle ways she shaded her voice, the casual yet clean way she sang the words." Observing her daughter sing rekindled Alma' s interest in show business, and she decided Doris must have singing lessons. She engaged a teacher, Grace Raine. After three lessons, Raine told Alma that young Doris had" tremendous potential"; Raine was so impressed that she gave Doris three lessons a week for the price of one. Years later, Day said that Raine had the biggest effect on her singing style and career. During the eight months she was taking singing lessons, Kappelhoff had her first professional jobs as a vocalist, on the WLW radio program" Carlin' s Carnival", and in a local restaurant, Charlie Yee' s Shanghai Inn. During her radio performances, she first caught the attention of Barney Rapp, who was looking for a female vocalist and asked if she would like to audition for the job. According to Rapp, he had auditioned about 200 singers when Kappelhoff got the job. While working for Rapp in 1939, she adopted the stage surname" Day", at Rapp' s suggestion. Rapp felt that" Kappelhoff" was too long for marquees, and he admired her rendition of the song" Day After Day". After working with Rapp, Day worked with bandleaders Jimmy James, Bob Crosby, and Les Brown. In 1941, Day appeared as a singer in three Soundies with the Les Brown band. While working with Brown, Day recorded her first hit recording," Sentimental Journey", released in early 1945. It soon became an anthem of the desire of World War II demobilizing troops to return home. The song continues to be associated with Day, and she re- recorded it on several occasions, including a version in her 1971 television special. During 1945– 46, Day( as vocalist with the Les Brown Band) had six other top ten hits on the" Billboard" chart:" My Dreams Are Getting Better All the Time", Tain' t Me"," Till The End of Time"," You Won' t Be Satisfied( Until You Break My Heart)"," The Whole World is Singing My Song", and" I Got the Sun in the Mornin. Les Brown said," As a singer Doris belongs in the company of Bing Crosby and Frank Sinatra."( Aljean Harmetz( 2019)." Wholesome Box- Office Star and Golden Voice of' Que Sera, Sera'"." The New York Times." p. 1) Early film career( 1948– 1954). While singing with the Les Brown band and for nearly two years on Bob Hope' s weekly radio program, she toured extensively across the United States. Her performance of the song" Embraceable You" impressed songwriter Jule Styne and his partner, Sammy Cahn, and they recommended her for a role in" Romance on the High Seas"( 1948). Day was cast for the | role after auditioning for director |
Michael Curtiz. She was shocked at being offered the role in the film, and admitted to Curtiz that she was a singer without acting experience. But he said he liked that" she was honest", not afraid to admit it, and he wanted someone who" looked like the All- American Girl". Day was the discovery of which Curtiz was proudest during his career. The film provided her with a hit recording as a soloist," It' s Magic", which followed by two months her first hit(" Love Somebody" in 1948) recorded as a duet with Buddy Clark. Day recorded" Someone Like You", before the film" My Dream Is Yours"( 1949), which featured the song. In 1950, U. S. servicemen in Korea voted her their favorite star. She continued to make minor and frequently nostalgic period musicals such as" On Moonlight Bay"( 1951)," By the Light of the Silvery Moon"( 1953), and" Tea For Two"( 1950) for Warner Brothers. Her most commercially successful film for Warner was" I' ll See You in My Dreams"( 1951), which broke box- office records of 20 years. The film is a musical biography of lyricist Gus Kahn. It was Day' s fourth film directed by Curtiz. Day appeared as the title character in the comedic western- themed musical," Calamity Jane"( 1953). A song from the film," Secret Love", won the Academy Award for Best Original Song and became Day' s fourth No. 1 hit single in the United States. Between 1950 and 1953, the albums from six of her movie musicals charted in the Top 10, three of them at No. 1. After filming" Lucky Me"( 1954) with Bob Cummings and" Young at Heart"( 1955) with Frank Sinatra, Day chose not to renew her contract with Warner Brothers. During this period, Day also had her own radio program," The Doris Day Show". It was broadcast on CBS in 1952– 1953. Breakthrough( 1955– 1958). Having become primarily recognized as a musical- comedy actress, Day gradually took on more dramatic roles to broaden her range. Her dramatic star turn as singer Ruth Etting in" Love Me or Leave Me"( 1955), with top billing above James Cagney, received critical and commercial success, becoming Day' s biggest hit thus far. Cagney said she had" the ability to project the simple, direct statement of a simple, direct idea without cluttering it", comparing her to Laurette Taylor' s Broadway performance in" The Glass Menagerie"( 1945), one of the greatest performances by an American actor. Day said it was her best film performance. Producer Joe Pasternak said," I was stunned that Doris did not get an Oscar nomination." The soundtrack album from that movie was a No. 1 hit. Day starred in Alfred Hitchcock' s suspense film" The Man Who Knew Too Much"( 1956) with James Stewart. She sang two songs in the film," Que Sera, Sera( Whatever Will Be, Will Be)" which won an Academy Award for Best Original Song, and" We' ll Love Again". The film was Day's10th movie to be in the Top 10 at the box office. Day played the title role | in the thriller/ noir" Julie"( |
also 1956) with Louis Jourdan. After three successive dramatic films, Day returned to her musical/ comedic roots in" The Pajama Game"( 1957) with John Raitt. The film was based on the Broadway play of the same name. She worked with Paramount Pictures for the comedy" Teacher' s Pet"( 1958), alongside Clark Gable and Gig Young. She co- starred with Richard Widmark and Gig Young in the romantic comedy film" The Tunnel of Love"( also 1958), but found scant success opposite Jack Lemmon in" It Happened to Jane"( 1959)." Billboard" annual nationwide poll of disc jockeys had ranked Day as the No. 1 female vocalist nine times in ten years( 1949 through 1958), but her success and popularity as a singer was now being overshadowed by her box- office appeal. Box- office success( 1959– 1968). In 1959, Day entered her most successful phase as a film actress with a series of romantic comedies. This success began with" Pillow Talk"( 1959), co- starring Rock Hudson who became a lifelong friend, and Tony Randall. Day received a nomination for an Academy Award for Best Actress. It was the only Oscar nomination she received in her career. Day, Hudson, and Randall made two more films together," Lover Come Back"( 1961) and" Send Me No Flowers"( 1964). Along with David Niven and Janis Paige, Day starred in" Please Don' t Eat the Daisies"( 1960) and with Cary Grant in the comedy" That Touch of Mink"( 1962). During 1960 and the 1962 to 1964 period, she ranked number one at the box office, the second woman to be number one four times, an accomplishment equalled by no other actress except Shirley Temple. She set a record that has yet to be equaled, receiving seven consecutive Laurel Awards as the top female box office star. Day teamed up with James Garner starting with" The Thrill of It All", followed by" Move Over, Darling"( both 1963). The film' s theme song," Move Over Darling", co- written by her son, reached in the UK. In between these comedic roles, Day co- starred with Rex Harrison in the movie thriller" Midnight Lace"( 1960), an updating of the stage thriller" Gaslight".Bythelate1960s, the sexual revolution of the baby boomer generation had refocused public attitudes about sex. Times changed, but Day' s films did not. Day' s next film" Do Not Disturb"( 1965) was popular with audiences, but her popularity soon waned. Critics and comics dubbed Day" The World' s Oldest Virgin", and audiences began to shy away from her films. As a result, she slipped from the list of top box- office stars, last appearing in the top ten with the hit film" The Glass Bottom Boat"( 1966). One of the roles she turned down was that of Mrs. Robinson in" The Graduate", a role that eventually went to Anne Bancroft. In her published memoirs, Day said she had rejected the part on moral grounds: she found the script" vulgar and offensive". She starred in the western film" The Ballad of Josie"( 1967). That same year, Day recorded" The Love Album", although it was | not released until 1994. The |
following year( 1968), she starred in the comedy film" Where Were You When the Lights Went Out?" which centers on the Northeast blackout of November 9, 1965. Her final feature, the comedy" With Six You Get Eggroll", was released in 1968. From 1959 to 1970, Day received nine Laurel Award nominations( and won four times) for best female performance in eight comedies and one drama. From 1959 through 1969, she received six Golden Globe nominations for best female performance in three comedies, one drama(" Midnight Lace"), one musical(" Jumbo"), and her television series. Bankruptcy and television career. After her third husband Martin Melcher died on April 20, 1968, a shocked Day discovered that Melcher and his business partner and" adviser" Jerome Bernard Rosenthal had squandered her earnings, leaving her deeply in debt. Rosenthal had been her attorney since 1949, when he represented her in her uncontested divorce action against her second husband, saxophonist George W. Weidler. Day filed suit against Rosenthal in February 1969, won a successful decision in 1974, but did not receive compensation until a settlement in 1979. Day also learned to her displeasure that Melcher had committed her to a television series, which became" The Doris Day Show". Day hated the idea of performing on television, but felt obligated to do it. The first episode of" The Doris Day Show" aired on September 24, 1968, and, from 1968 to 1973, employed a rerecorded version of" Que Sera, Sera" as its theme song. Day persevered( she needed the work to help pay off her debts), but only after CBS ceded creative control to her and her son. The successful show enjoyed a five- year run, and functioned as a curtain raiser for the" Carol Burnett Show". It is remembered today for its abrupt season- to- season changes in casting and premise. By the end of its run in 1973, public tastes had changed, as had those of the television industry, and her firmly established persona was regarded as passé. She largely retired from acting after" The Doris Day Show", but did complete two television specials," The Doris Mary Anne Kappelhoff Special"( 1971) and" Doris Day Today"( 1975),andwasaguestonvariousshowsinthe1970s. In the 1985– 86 season, Day hosted her own television talk show," Doris Day' s Best Friends", on the Christian Broadcasting Network( CBN). The network canceled the show after 26 episodes, despite the worldwide publicity it received. Much of that attention came from the episode featuring Rock Hudson, in which Hudson was showing the first public symptoms of AIDS including severe weight loss and admitted fatigue; Hudson would die from the disease a year later. Day later said," He was very sick. But I just brushed that off and I came out and put my arms around him and said,' Am I glad to see you'."1980sand1990s. Day' s husband and agent, Martin Melcher, had Beverly Hills lawyer Jerome Rosenthal handle his wife' s moneysincethe1940s." During that period, Rosenthal committed breaches of professional ethics that are difficult to exaggerate", as one court put it. In October 1985, the California Supreme Court rejected Rosenthal' s | appeal of the multimillion- dollar |
judgment against him for legal malpractice, and upheld conclusions of a trial court and a Court of Appeal that Rosenthal acted improperly. In April 1986, the U. S. Supreme Court refused to review the lower court' s judgment. In June 1987, Rosenthal filed a$ 30 million lawsuit against lawyers he claimed cheated him out of millions of dollars in real estate investments. He named Day as a co- defendant, describing her as an" unwilling, involuntary plaintiff whose consent cannot be obtained". Rosenthal claimed that millions of dollars Day lost were in real estate sold after Melcher died in 1968, in which Rosenthal asserted that the attorneys gave Day bad advice, telling her to sell, at a loss, three hotels, in Palo Alto, California, Dallas, Texas, and Atlanta, Georgia, plus some oil leases in Kentucky and Ohio. He claimed he had made the investments under a long- term plan, and did not intend to sell them until they appreciated in value. Two of the hotels sold in 1970 for about$ 7 million, and their estimated worth in 1986 was$ 50 million. Terry Melcher stated that his adoptive father' s premature death saved Day from financial ruin. It remains unresolved whether Martin Melcher had himself also been duped. Day stated publicly that she believed her husband innocent of any deliberate wrongdoing, stating that he" simply trusted the wrong person". According to Day' s autobiography, as told to A. E. Hotchner, the usually athletic and healthy Martin Melcher had an enlarged heart. Most of the interviews on the subject given to Hotchner( and included in Day' s autobiography) paint an unflattering portrait of Melcher. Author David Kaufman asserts that one of Day' s costars, actor Louis Jourdan, maintained that Day herself disliked her husband, but Day' s public statements regarding Melcher appear to contradict that assertion. Day was scheduled to present, along with Patrick Swayze and Marvin Hamlisch,theBestOriginalScoreOscaratthe61st Academy Awards in March 1989 but she suffered a deep leg cut and was unable to attend. She had been walking through the gardens of her hotel when she cut her leg on a sprinkler. The cut required stitches. Day was inducted into the Ohio Women' s Hall of Fame in 1981 and received the Cecil B. DeMille Award for career achievement in 1989. In 1994, Day' s" Greatest Hits" album became another entry into the British charts. Her cover of" Perhaps, Perhaps, Perhaps" was included in the soundtrack of the Australian film" Strictly Ballroom."2000s. Day participated in interviews and celebrations of her birthday with an annual Doris Day music marathon. In July 2008, she appeared on the Southern California radio show of longtime friend and newscaster George Putnam. Day turned down a tribute offer from the American Film Institute and from the Kennedy Center Honors because they require attendance in person. In 2004, she was awarded the Presidential Medal of Freedom by President George W. Bush for her achievements in the entertainment industry and for her work on behalf of animals. President Bush stated: Columnist Liz Smith and film critic Rex Reed mounted vigorous campaigns to | gather support for an Honorary |
Academy Award for Day to herald her film career and her status as the top female box- office star of all time. According to" The Hollywood Reporter" in 2015, the Academy offered her the Honorary Oscar multiple times, but she declined as she saw the film industry as a part of her past life. Day received a Grammy for Lifetime Achievement in Music in 2008, albeit again in absentia. She received three Grammy Hall of Fame Awards, in 1998, 1999 and 2012, for her recordings of" Sentimental Journey"," Secret Love", and" Que Sera, Sera", respectively. Day was inducted into the Hit Parade Hall of Fame in 2007, and in 2010 received the first Legend Award ever presented by the Society of Singers.2010s. Day, aged 89, released" My Heart" in the United Kingdom on September 5, 2011, her first new album in nearly two decades since the release of" The Love Album", which, although recorded in 1967, was not released until 1994. The album is a compilation of previously unreleased recordings produced by Day' s son, Terry Melcher, before his death in 2004.Tracksincludethe1970s Joe Cocker hit" You Are So Beautiful", the Beach Boys'" Disney Girls" and jazz standards such as" My Buddy", which Day originally sang in the film" I' ll See You in My Dreams"( 1951). After the disc was released in the United States it soon climbed to No. 12 on Amazon' s bestseller list, and helped raise funds for the Doris Day Animal League. Day became the oldest artist to score a UK Top 10 with an album featuring new material. In January 2012, the Los Angeles Film Critics Association presented Day with a Lifetime Achievement Award. In April 2014, Day made an unexpected public appearance to attend the annual Doris Day Animal Foundation benefit. The benefit raises money for her Animal Foundation. Clint Eastwood offered Day a role in a film he was planning to direct in 2015. Although she reportedly was in talks with Eastwood, her neighbor in Carmel, about a role in the film, she eventually declined. Day granted ABC a telephone interview on her birthday in 2016, which was accompanied by photos of her life and career. In a rare interview with" The Hollywood Reporter" on April 4, 2019,thedayafterher97th birthday, Day talked about her work on the Doris Day Animal Foundation, founded in 1978. On the question of what her favorite film was, she answered" Calamity Jane":" I was such a tomboy growing up, and she was such a fun character to play. Of course, the music was wonderful, too—' Secret Love,' especially, is such a beautiful song." To commemorate her birthday, her fans gathered each year to take part in a three- day party in her hometown of Carmel, California, in late March. The event was also a fundraiser for her Animal Foundation. During the 2019 event, there was a special screening of her film" Pillow Talk"( 1959) tocelebrateits60th anniversary. About the film, Day stated in the same interview that she" had such fun working with my pal, Rock. We laughed our way through three | films we made together and |
remained great friends. I miss him." Animal welfare activism. Day' s interest in animal welfare and related issues apparently dated to her teen years. While recovering from an automobile accident, she took her dog Tiny for a walk without a leash. Tiny ran into the street and was killed by a passing car. Day later expressed guilt and loneliness about Tiny' s untimely death. It was during the making of" The Man Who Knew Too Much", when she saw how camels, goats, and other" animal extras" in a marketplace scene were being treated, that Day began actively preventing animal abuse. She was so appalled at the conditions the animals used in filming were kept in that she refused to work unless they were properly fed and cared for. The production company had to set up" feeding stations" for the various goats, sheep, camels, etc., and feed them every day before Day would agree to go back to work. In 1971, she co- founded Actors and Others for Animals, and appeared in a series of newspaper advertisements denouncing the wearing of fur, alongside Mary Tyler Moore, Angie Dickinson, and Jayne Meadows. In 1978, Day founded the Doris Day Pet Foundation, now the Doris Day Animal Foundation( DDAF). A non- profit 501( c)( 3) grant- giving public charity, DDAF funds other non- profit causes throughout the US that share DDAF' s mission of helping animals and the people who love them. The DDAF continues to operate independently. To complement the Doris Day Animal Foundation, Day formed the Doris Day Animal League( DDAL) in 1987, a national non- profit citizens' lobbying organization whose mission is to reduce pain and suffering, and protect animals through legislative initiatives. Day actively lobbied the United States Congress in support of legislation designed to safeguard animal welfare on a number of occasions, and in 1995 she originated the annual Spay Day USA. The DDAL merged into The Humane Society of the United States( HSUS) in 2006. The HSUS now manages World Spay Day, the annual one- day spay/ neuter event that Day originated. A facility bearing her name, the Doris Day Horse Rescue and Adoption Center, which helps abused and neglected horses, opened in 2011 in Murchison, Texas, on the grounds of an animal sanctuary started by her late friend, author Cleveland Amory. Day contributed$ 250, 000 toward the founding of the center. A posthumous auction of 1, 100 of Day' s possessions in April 2020 generated$ 3 million for the Doris Day Animal Foundation. Personal life. After her retirement from films, Day lived in Carmel- by- the- Sea, California. She had many pets and adopted stray animals. She was a lifelong Republican. Her only child was music producer and songwriter Terry Melcher, who had a hit inthe1960s with" Hey Little Cobra" under the name The Rip Chords before becoming a successful producer whose acts included The Byrds, Paul Revere& amp; the Raiders, and The Beach Boys; he died of melanoma in November 2004. Since the1980s Day owned a hotel in Carmel- by- the- Sea called the Cypress Inn which | she originally co- owned with |
her son. It was an early pet– friendly hotel and was featured in" Architectural Digest" in 1999. Marriages. Day was married four times. From March 1941 to February 1943, she was married to trombonist Al Jorden( 1917– 1967), whom she met in Barney Rapp' s Band. Jorden had schizophrenia and was violent, and died by suicide. When Day became pregnant and refused to have an abortion, he beat her in an attempt to force a miscarriage. Their son, Terrence" Terry" Paul Jorden, was born in 1942; he changed his name to Terrence Paul Melcher when he was adopted by Day' s third husband. Her second marriage was to George William Weidler( 1926– 1989) from March 30, 1946, to May 31, 1949, a saxophonist and the brother of actress Virginia Weidler. Weidler and Day met again several years later during a brief reconciliation, and he introduced her to Christian Science. Day married American film producer Martin Melcher( 1915– 1968) on April 3, 1951,her29th birthday, and this marriage lasted until he died in April 1968. Melcher adopted Day' s son Terry, who became a successful musician and record producer under the name Terry Melcher. Martin Melcher produced many of Day' s movies. They were both Christian Scientists, resulting in her not seeing a doctor for some time for symptoms which suggested cancer. Day' s fourth marriage was to Barry Comden( 1935– 2009) from April 14, 1976, until April 2, 1982. He was the" maître d' hôtel" at one of Day' s favorite restaurants. He knew of her great love of dogs and endeared himself to her by giving her a bag of meat scraps and bones on her way out of the restaurant. He later complained that she cared more for her" animal friends" than she did for him. Death. Day died on May 13, 2019, at the age of 97, after having contracted pneumonia. Her death was announced by her charity, the Doris Day Animal Foundation. Per Day' s requests, the Foundation announced that there would be no funeral services, grave marker, or other public memorials. Discography. Studio albums." Source" Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. Dry distillation is the heating of solid materials to produce gaseous products( which may condense into liquids or solids). Dry distillation may involve chemical changes such as destructive distillation or cracking and is not discussed under this article. Distillation may result in essentially complete separation( nearly pure components), or it may be a partial separation that increases the concentration of selected components in the mixture. In either case, the process exploits differences in the relative volatility of the mixture' s components. In industrial applications, distillation is a unit operation of practically universal importance, but it is a physical separation process, not a chemical reaction. Distillation has many applications. For example: An installation used for distillation, especially of distilled beverages, is a distillery. The distillation equipment itself is a still. History. Early evidence of distillation was found on Akkadian tablets dated | c. 1200 BCE describing perfumery |
operations. The tablets provided textual evidence that an early primitive form of distillation was known to the Babylonians of ancient Mesopotamia.EarlyevidenceofdistillationwasalsofoundrelatedtoalchemistsworkinginAlexandriainRomanEgyptinthe1st century CE. Distillation was practiced in the ancient Indian subcontinent, which is evident from baked clay retorts and receivers found at Taxila, Shaikhan Dheri, and Charsadda in modern Pakistan, dating to the early centuries of the Common Era. These" Gandhara stills" were only capable of producing very weak liquor, as there was no efficient means of collecting the vapors at low heat. Distilled water has been in use since at least c. 200 CE, when Alexander of Aphrodisias described the process. WorkondistillingotherliquidscontinuedinearlyByzantineEgyptunderZosimusofPanopolisinthe3rd century. Distillation in China may have begun during the Eastern Han dynasty(1st–2nd centuries CE), but the distillation of beverages began in the Jin(12th–13th centuries) and Southern Song(10th–13th centuries) dynasties, according to archaeological evidence. Medieval Muslim chemists such as Jābir ibn Ḥayyān( Latin: Geber, ninth century) and Abū Bakr al- Rāzī( Latin: Rhazes,) experimented extensively with the distillation of various substances. The distillation of wine is attested in Arabic works attributed to al- Kindī( c. 801– 873 CE) and to al- Fārābī( c. 872– 950),andinthe28th book of al- Zahrāwī' s( Latin: Abulcasis, 936– 1013)" Kitāb al- Taṣrīf"( later translated into Latin as" Liber servatoris"). In the twelfth century, recipes for the production of" aqua ardens"(" burning water", i. e., ethanol) by distilling wine with salt started to appear in a number of Latin works, and by the end of the thirteenth century it had become a widely known substance among Western European chemists. The works of Taddeo Alderotti( 1223– 1296) describe a method for concentrating alcohol involving repeated distillation through a water- cooled still, by which an alcohol purity of 90% could be obtained. The invention of steam distillation is attributed to the Persian physician Avicenna. The fractional distillation of organic substances plays an important role in the works attributed to Jābir ibn Ḥayyān, such as in the(' The Book of Seventy'), translated into Latin by Gerard of Cremona( c. 1114– 1187) under the title. The Jabirian experiments with fractional distillation of animal and vegetable substances, and to a lesser degree also of mineral substances, is the main topic of the, an originally Arabic work falsely attributed to Avicenna that was translated into Latin and would go on to form the most important alchemical source for Roger Bacon(). A still was found in an archaeological site in Qinglong, Hebei province, in China,datingbacktothe12th century. Distilled beverages were common during the Yuan dynasty(13th–14th centuries). In 1500, German alchemist Hieronymus Braunschweig published" Liber de arte destillandi"(" The Book of the Art of Distillation"), the first book solely dedicated to the subject of distillation, followed in 1512 by a much expanded version. In 1651, John French published" The Art of Distillation", the first major English compendium on the practice, but it has been claimed that much of it derives from Braunschweig' s work. This includes diagrams with people in them showing the industrial rather than bench scale of the operation. As alchemy evolved into the science of chemistry, vessels called retorts became used for | distillations. Both alembics and retorts |
are forms of glassware with long necks pointing to the side at a downward angle to act as air- cooled condensers to condense the distillate and let it drip downward for collection. Later, copper alembics were invented. Riveted joints were often kept tight by using various mixtures, for instance a dough made of rye flour. These alembics often featured a cooling system around the beak, using cold water, for instance, which made the condensation of alcohol more efficient. These were called pot stills. Today, the retorts and pot stills have been largely supplanted by more efficient distillation methods in most industrial processes. However, the pot still is still widely used for the elaboration of some fine alcohols, such as cognac, Scotch whisky, Irish whiskey, tequila, rum, and some vodkas. Pot stills made of various materials( wood, clay, stainless steel) are also used by bootleggers in various countries. Small pot stills are also sold for use in the domestic production of flower water or essential oils. Early forms of distillation involved batch processes using one vaporization and one condensation. Purity was improved by further distillation of the condensate. Greater volumes were processed by simply repeating the distillation. Chemists reportedly carried out as many as 500 to 600 distillations in order to obtain a pure compound.Intheearly19th century, the basics of modern techniques, including pre- heating and reflux, were developed. In 1822, Anthony Perrier developed one of the first continuous stills, and then, in 1826, Robert Stein improved that design to make his patent still. In 1830, Aeneas Coffey got a patent for improving the design even further. Coffey' s continuous still may be regarded as the archetype of modern petrochemical units. The French engineer Armand Savalle developed his steam regulator around 1846. In 1877, Ernest Solvay was granted a U. S. Patent for a tray column for ammonia distillation, and the same and subsequent years saw developments in this theme for oils and spirits. With the emergence of chemical engineeringasadisciplineattheendofthe19th century, scientific rather than empirical methods could be applied.Thedevelopingpetroleumindustryintheearly20th century provided the impetus for the development of accurate design methods, such as the McCabe– Thiele method by Ernest Thiele and the Fenske equation. The first industrial plant in the United States to use distillation as a means of ocean desalination opened in Freeport, Texas in 1961 with the hope of bringing water security to the region. The availability of powerful computers has allowed direct computer simulations of distillation columns. Applications. The application of distillation can roughly be divided into four groups: laboratory scale, industrial distillation, distillation of herbs for perfumery and medicinals( herbal distillate), and food processing. The latter two are distinctively different from the former two in that distillation is not used as a true purification method but more to transfer all volatiles from the source materials to the distillate in the processing of beverages and herbs. The main difference between laboratory scale distillation and industrial distillation are that laboratory scale distillation is often performed on a batch basis, whereas industrial distillation often occurs continuously. In batch distillation, the composition of the source | material, the vapors of the |
distilling compounds, and the distillate change during the distillation. In batch distillation, a still is charged( supplied) with a batch of feed mixture, which is then separated into its component fractions, which are collected sequentially from most volatile to less volatile, with the bottoms– remaining least or non- volatile fraction– removed at the end. The still can then be recharged and the process repeated. In continuous distillation, the source materials, vapors, and distillate are kept at a constant composition by carefully replenishing the source material and removing fractions from both vapor and liquid in the system. This results in a more detailed control of the separation process. Idealized model. The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the pressure around the liquid, enabling bubbles to form without being crushed. A special case is the normal boiling point, where the vapor pressure of the liquid equals the ambient atmospheric pressure. It is a misconception that in a liquid mixture at a given pressure, each component boils at the boiling point corresponding to the given pressure, allowing the vapors of each component to collect separately and purely. However, this does not occur, even in an idealized system. Idealized models of distillation are essentially governed by Raoult' s law and Dalton' s law and assume that vapor– liquid equilibria are attained. Raoult' s law states that the vapor pressure of a solution is dependent on 1) the vapor pressure of each chemical component in the solution and 2) the fraction of solution each component makes up, a. k. a. the mole fraction. This law applies to ideal solutions, or solutions that have different components but whose molecular interactions are the same as or very similar to pure solutions. Dalton' s law states that the total pressure is the sum of the partial pressures of each individual component in the mixture. When a multi- component liquid is heated, the vapor pressure of each component will rise, thus causing the total vapor pressure to rise. When the total vapor pressure reaches the pressure surrounding the liquid, boiling occurs and liquid turns to gas throughout the bulk of the liquid. A mixture with a given composition has one boiling point at a given pressure when the components are mutually soluble. A mixture of constant composition does not have multiple boiling points. An implication of one boiling point is that lighter components never cleanly" boil first". At boiling point, all volatile components boil, but for a component, its percentage in the vapor is the same as its percentage of the total vapor pressure. Lighter components have a higher partial pressure and, thus, are concentrated in the vapor, but heavier volatile components also have a( smaller) partial pressure and necessarily vaporize also, albeit at a lower concentration in the vapor. Indeed, batch distillation and fractionation succeed by varying the composition of the mixture. In batch distillation, the batch vaporizes, which changes its composition; in fractionation, liquid higher in the fractionation column contains more lights and boils at lower temperatures. Therefore, | starting from a given mixture, |
it appears to have a boiling range instead of a boiling point, although this is because its composition changes: each intermediate mixture has its own, singular boiling point. The idealized model is accurate in the case of chemically similar liquids, such as benzene and toluene. In other cases, severe deviations from Raoult' s law and Dalton' s law are observed, most famously in the mixture of ethanol and water. These compounds, when heated together, form an azeotrope, which is when the vapor phase and liquid phase contain the same composition. Although there are computational methods that can be used to estimate the behavior of a mixture of arbitrary components, the only way to obtain accurate vapor– liquid equilibrium data is by measurement. It is not possible to completely purify a mixture of components by distillation, as this would require each component in the mixture to have a zero partial pressure. If ultra- pure products are the goal, then further chemical separation must be applied. When a binary mixture is vaporized and the other component, e. g., a salt, has zero partial pressure for practical purposes, the process is simpler. Batch or differential distillation. Heating an ideal mixture of two volatile substances, A and B, with A having the higher volatility, or lower boiling point, in a batch distillation setup( such as in an apparatus depicted in the opening figure) until the mixture is boiling results in a vapor above the liquid that contains a mixture of A and B. The ratio between A and B in the vapor will be different from the ratio in the liquid. The ratio in the liquid will be determined by how the original mixture was prepared, while the ratio in the vapor will be enriched in the more volatile compound, A( due to Raoult' s Law, see above). The vapor goes through the condenser and is removed from the system. This, in turn, means that the ratio of compounds in the remaining liquid is now different from the initial ratio( i. e., more enriched in B than in the starting liquid). The result is that the ratio in the liquid mixture is changing, becoming richer in component B. This causes the boiling point of the mixture to rise, which results in a rise in the temperature in the vapor, which results in a changing ratio of A: B in the gas phase( as distillation continues, there is an increasing proportion of B in the gas phase). This results in a slowly changing ratio of A: B in the distillate. If the difference in vapour pressure between the two components A and B is large– generally expressed as the difference in boiling points– the mixture in the beginning of the distillation is highly enriched in component A, and when component A has distilled off, the boiling liquid is enriched in component B. Continuous distillation. Continuous distillation is an ongoing distillation in which a liquid mixture is continuously( without interruption) fed into the process and separated fractions are removed continuously as output streams occur over time during the | operation. Continuous distillation produces a |
minimum of two output fractions, including at least one volatile distillate fraction, which has boiled and been separately captured as a vapor and then condensed to a liquid. There is always a bottoms( or residue) fraction, which is the least volatile residue that has not been separately captured as a condensed vapor. Continuous distillation differs from batch distillation in the respect that concentrations should not change over time. Continuous distillation can be run at a steady state for an arbitrary amount of time. For any source material of specific composition, the main variables that affect the purity of products in continuous distillation are the reflux ratio and the number of theoretical equilibrium stages, in practice determined by the number of trays or the height of packing. Reflux is a flow from the condenser back to the column, which generates a recycle that allows a better separation with a given number of trays. Equilibrium stages are ideal steps where compositions achieve vapor– liquid equilibrium, repeating the separation process and allowing better separation given a reflux ratio. A column with a high reflux ratio may have fewer stages, but it refluxes a large amount of liquid, giving a wide column with a large holdup. Conversely, a column with a low reflux ratio must have a large number of stages, thus requiring a taller column. General improvements. Both batch and continuous distillations can be improved by making use of a fractionating column on top of the distillation flask. The column improves separation by providing a larger surface area for the vapor and condensate to come into contact. This helps it remain at equilibrium for as long as possible. The column can even consist of small subsystems(' trays' or' dishes') which all contain an enriched, boiling liquid mixture, all with their own vapor– liquid equilibrium. There are differences between laboratory- scale and industrial- scale fractionating columns, but the principles are the same. Examples of laboratory- scale fractionating columns( in increasing efficiency) includeLaboratory procedures. Laboratory scale distillations are almost exclusively run as batch distillations. The device used in distillation, sometimes referred to as a" still", consists at a minimum of a reboiler or" pot" in which the source material is heated, a condenser in which the heated vapor is cooled back to the liquid state, and a receiver in which the concentrated or purified liquid, called the distillate, is collected. Several laboratory scale techniques for distillation exist( see also). A completely sealed distillation apparatus could experience extreme and rapidly varying internal pressure, which could cause it to burst open at the joints. Therefore, some path is usually left open( for instance, at the receiving flask) to allow the internal pressure to equalize with atmospheric pressure. Alternatively, a vacuum pump may be used to keep the apparatus at a lower than atmospheric pressure. If the substances involved are air- or moisture- sensitive, the connection to the atmosphere can be made through one or more drying tubes packed with materials that scavenge the undesired air components, or through bubblers that provide a movable liquid barrier. Finally, the entry of | undesired air components can be |
prevented by pumping a low but steady flow of suitable inert gas, like nitrogen, into the apparatus. Simple distillation. In simple distillation, the vapor is immediately channeled into a condenser. Consequently, the distillate is not pure but rather its composition is identical to the composition of the vapors at the given temperature and pressure. That concentration follows Raoult' s law. As a result, simple distillation is effective only when the liquid boiling points differ greatly( rule of thumb is 25° C) or when separating liquids from non- volatile solids or oils. For these cases, the vapor pressures of the components are usually different enough that the distillate may be sufficiently pure for its intended purpose. A cutaway schematic of a simple distillation operation is shown at right. The starting liquid 15 in the boiling flask 2 is heated by a combined hotplate and magnetic stirrer 13 via a silicone oil bath( orange, 14). The vapor flows through a short Vigreux column 3, then through a Liebig condenser 5, is cooled by water( blue) that circulates through ports 6 and 7. The condensed liquid drips into the receiving flask 8, sitting in a cooling bath( blue, 16). The adapter 10 has a connection 9 that may be fitted to a vacuum pump. The components are connected by ground glass joints( gray). Fractional distillation. For many cases, the boiling points of the components in the mixture will be sufficiently close that Raoult' s law must be taken into consideration. Therefore, fractional distillation must be used in order to separate the components by repeated vaporization- condensation cycles within a packed fractionating column. This separation, by successive distillations, is also referred to as rectification. As the solution to be purified is heated, its vapors rise to the fractionating column. As it rises, it cools, condensing on the condenser walls and the surfaces of the packing material. Here, the condensate continues to be heated by the rising hot vapors; it vaporizes once more. However, the composition of the fresh vapors are determined once again by Raoult' s law. Each vaporization- condensation cycle( called a" theoretical plate") will yield a purer solution of the more volatile component. In reality, each cycle at a given temperature does not occur at exactly the same position in the fractionating column;" theoretical plate" is thus a concept rather than an accurate description. More theoretical plates lead to better separations. A spinning band distillation system uses a spinning band of Teflon or metal to force the rising vapors into close contact with the descending condensate, increasing the number of theoretical plates. Steam distillation. Like vacuum distillation, steam distillation is a method for distilling compounds which are heat- sensitive. The temperature of the steam is easier to control than the surface of a heating element, and allows a high rate of heat transfer without heating at a very high temperature. This process involves bubbling steam through a heated mixture of the raw material. By Raoult' s law, some of the target compound will vaporize( in accordance with its partial pressure). The vapor mixture is | cooled and condensed, usually yielding |
a layer of oil and a layer of water. Steam distillation of various aromatic herbs and flowers can result in two products; an essential oil as well as a watery herbal distillate. The essential oils are often used in perfumery and aromatherapy while the watery distillates have many applications in aromatherapy, food processing and skin care. Vacuum distillation. Some compounds have very high boiling points. To boil such compounds, it is often better to lower the pressure at which such compounds are boiled instead of increasing the temperature. Once the pressure is lowered to the vapor pressure of the compound( at the given temperature), boiling and the rest of the distillation process can commence. This technique is referred to as vacuum distillation and it is commonly found in the laboratory in the form of the rotary evaporator. This technique is also very useful for compounds which boil beyond their decomposition temperature at atmospheric pressure and which would therefore be decomposed by any attempt to boil them under atmospheric pressure. Short path and molecular distillation. Molecular distillation is vacuum distillation below the pressure of 0. 01 torr. 0. 01 torr is one order of magnitude above high vacuum, where fluids are in the free molecular flow regime, i. e. the mean free path of molecules is comparable to the size of the equipment. The gaseous phase no longer exerts significant pressure on the substance to be evaporated, and consequently, rate of evaporation no longer depends on pressure. That is, because the continuum assumptions of fluid dynamics no longer apply, mass transport is governed by molecular dynamics rather than fluid dynamics. Thus, a short path between the hot surface and the cold surface is necessary, typically by suspending a hot plate covered with a film of feed next to a cold plate with a line of sight in between. Molecular distillation is used industrially for purification of oils. Short path distillation is a distillation technique that involves the distillate travelling a short distance, often only a few centimeters, and is normally done at reduced pressure. A classic example would be a distillation involving the distillate travelling from one glass bulb to another, without the need for a condenser separating the two chambers. This technique is often used for compounds which are unstable at high temperatures or to purify small amounts of compound. The advantage is that the heating temperature can be considerably lower( at reduced pressure) than the boiling point of the liquid at standard pressure, and the distillate only has to travel a short distance before condensing. A short path ensures that little compound is lost on the sides of the apparatus. The Kugelrohr apparatus is a kind of short path distillation method which often contains multiple chambers to collect distillate fractions. Air- sensitive vacuum distillation. Some compounds have high boiling points as well as being air sensitive. A simple vacuum distillation system as exemplified above can be used, whereby the vacuum is replaced with an inert gas after the distillation is complete. However, this is a less satisfactory system if one desires | to collect fractions under a |
reduced pressure. To do this a" cow" or" pig" adaptor can be added to the end of the condenser, or for better results or for very air sensitive compounds a Perkin triangle apparatus can be used. The Perkin triangle, has means via a series of glass or Teflon taps to allows fractions to be isolated from the rest of the still, without the main body of the distillation being removed from either the vacuum or heat source, and thus can remain in a state of reflux. To do this, the sample is first isolated from the vacuum by means of the taps, the vacuum over the sample is then replaced with an inert gas( such as nitrogen or argon) and can then be stoppered and removed. A fresh collection vessel can then be added to the system, evacuated and linked back into the distillation system via the taps to collect a second fraction, and so on, until all fractions have been collected. Zone distillation. Zone distillation is a distillation process in a long container with partial melting of refined matter in moving liquid zone and condensation of vapor in the solid phase at condensate pulling in cold area. The process is worked in theory. When zone heater is moving from the top to the bottom of the container then solid condensate with irregular impurity distribution is forming. Then most pure part of the condensate may be extracted as product. The process may be iterated many times by moving( without turnover) the received condensate to the bottom part of the container on the place of refined matter. The irregular impurity distribution in the condensate( that is efficiency of purification) increases with the number of iterations. Zone distillation is the distillation analog of zone recrystallization. Impurity distribution in the condensate is described by known equations of zone recrystallization– with the replacement of the distribution co- efficient k of crystallization- for the separation factor α of distillation. Other types. The unit process of evaporation may also be called" distillation": Other uses: Azeotropic process. Interactions between the components of the solution create properties unique to the solution, as most processes entail non- ideal mixtures, where Raoult' s law does not hold. Such interactions can result in a constant- boiling azeotrope which behaves as if it were a pure compound( i. e., boils at a single temperature instead of a range). At an azeotrope, the solution contains the given component in the same proportion as the vapor, so that evaporation does not change the purity, and distillation does not effect separation. For example, ethyl alcohol and water form an azeotrope of 95. 6% at 78. 1° C. If the azeotrope is not considered sufficiently pure for use, there exist some techniques to break the azeotrope to give a pure distillate. This set of techniques are known as azeotropic distillation. Some techniques achieve this by" jumping" over the azeotropic composition( by adding another component to create a new azeotrope, or by varying the pressure). Others work by chemically or physically removing or sequestering the impurity. For example, to | purify ethanol beyond 95%, a |
drying agent( or desiccant, such as potassium carbonate) can be added to convert the soluble water into insoluble water of crystallization. Molecular sieves are often used for this purpose as well. Immiscible liquids, such as water and toluene, easily form azeotropes. Commonly, these azeotropes are referred to as a low boiling azeotrope because the boiling point of the azeotrope is lower than the boiling point of either pure component. The temperature and composition of the azeotrope is easily predicted from the vapor pressure of the pure components, without use of Raoult' s law. The azeotrope is easily broken in a distillation set- up by using a liquid– liquid separator( a decanter) to separate the two liquid layers that are condensed overhead. Only one of the two liquid layers is refluxed to the distillation set- up. High boiling azeotropes, such as a 20 percent by weight mixture of hydrochloric acid in water, also exist. As implied by the name, the boiling point of the azeotrope is greater than the boiling point of either pure component. To break azeotropic distillations and cross distillation boundaries, such as in the DeRosier Problem, it is necessary to increase the composition of the light key in the distillate. Breaking an azeotrope with unidirectional pressure manipulation. The boiling points of components in an azeotrope overlap to form a band. By exposing an azeotrope to a vacuum or positive pressure, it' s possible to bias the boiling point of one component away from the other by exploiting the differing vapor pressure curves of each; the curves may overlap at the azeotropic point, but are unlikely to remain identical further along the pressure axis to either side of the azeotropic point. When the bias is great enough, the two boiling points no longer overlap and so the azeotropic band disappears. This method can remove the need to add other chemicals to a distillation, but it has two potential drawbacks. Under negative pressure, power for a vacuum source is needed and the reduced boiling points of the distillates requires that the condenser be run cooler to prevent distillate vapors being lost to the vacuum source. Increased cooling demands will often require additional energy and possibly new equipment or a change of coolant. Alternatively, if positive pressures are required, standard glassware can not be used, energy must be used for pressurization and there is a higher chance of side reactions occurring in the distillation, such as decomposition, due to the higher temperatures required to effect boiling. A unidirectional distillation will rely on a pressure change in one direction, either positive or negative. Pressure- swing distillation. Pressure- swing distillation is essentially the same as the unidirectional distillation used to break azeotropic mixtures, but here both positive and negative pressures may be employed. This improves the selectivity of the distillation and allows a chemist to optimize distillation by avoiding extremes of pressure and temperature that waste energy. This is particularly important in commercial applications. One example of the application of pressure- swing distillation is during the industrial purification of ethyl acetate after its catalytic synthesis | from ethanol. Industrial process. Large |
scale industrial distillation applications include both batch and continuous fractional, vacuum, azeotropic, extractive, and steam distillation. The most widely used industrial applications of continuous, steady- state fractional distillation are in petroleum refineries, petrochemical and chemical plants and natural gas processing plants. To control and optimize such industrial distillation, a standardized laboratory method,ASTMD86, is established. This test method extends to the atmospheric distillation of petroleum products using a laboratory batch distillation unit to quantitatively determine the boiling range characteristics of petroleum products. Industrial distillation is typically performed in large, vertical cylindrical columns known as distillation towers or distillation columns with diameters ranging from about and heights ranging from about or more. When the process feed has a diverse composition, as in distilling crude oil, liquid outlets at intervals up the column allow for the withdrawal of different" fractions" or products having different boiling points or boiling ranges. The" lightest" products( those with the lowest boiling point) exit from the top of the columns and the" heaviest" products( those with the highest boiling point) exit from the bottom of the column and are often called the bottoms. Industrial towers use reflux to achieve a more complete separation of products. Reflux refers to the portion of the condensed overhead liquid product from a distillation or fractionation tower that is returned to the upper part of the tower as shown in the schematic diagram of a typical, large- scale industrial distillation tower. Inside the tower, the downflowing reflux liquid provides cooling and condensation of the upflowing vapors thereby increasing the efficiency of the distillation tower. The more reflux that is provided for a given number of theoretical plates, the better the tower' s separation of lower boiling materials from higher boiling materials. Alternatively, the more reflux that is provided for a given desired separation, the fewer the number of theoretical plates required. Chemical engineers must choose what combination of reflux rate and number of plates is both economically and physically feasible for the products purified in the distillation column. Such industrial fractionating towers are also used in cryogenic air separation, producing liquid oxygen, liquid nitrogen, and high purity argon. Distillation of chlorosilanes also enables the production of high- purity silicon for use as a semiconductor. Design and operation of a distillation tower depends on the feed and desired products. Given a simple, binary component feed, analytical methods such as the McCabe– Thiele method or the Fenske equation can be used. For a multi- component feed, simulation models are used both for design and operation. Moreover, the efficiencies of the vapor– liquid contact devices( referred to as" plates" or" trays") used in distillation towers are typically lower than that of a theoretical 100% efficient equilibrium stage. Hence, a distillation tower needs more trays than the number of theoretical vapor– liquid equilibrium stages. A variety of models have been postulated to estimate tray efficiencies. In modern industrial uses, a packing material is used in the column instead of trays when low pressure drops across the column are required. Other factors that favor packing are: vacuum systems, smaller diameter | columns, corrosive systems, systems prone |
to foaming, systems requiring low liquid holdup, and batch distillation. Conversely, factors that favor plate columns are: presence of solids in feed, high liquid rates, large column diameters, complex columns, columns with wide feed composition variation, columns with a chemical reaction, absorption columns, columns limited by foundation weight tolerance, low liquid rate, large turn- down ratio and those processes subject to process surges. This packing material can either be random dumped packing( wide) such as Raschig rings or structured sheet metal. Liquids tend to wet the surface of the packing and the vapors pass across this wetted surface, where mass transfer takes place. Unlike conventional tray distillation in which every tray represents a separate point of vapor– liquid equilibrium, the vapor– liquid equilibrium curve in a packed column is continuous. However, when modeling packed columns, it is useful to compute a number of" theoretical stages" to denote the separation efficiency of the packed column with respect to more traditional trays. Differently shaped packings have different surface areas and void space between packings. Both of these factors affect packing performance. Another factor in addition to the packing shape and surface area that affects the performance of random or structured packing is the liquid and vapor distribution entering the packed bed. The number of theoretical stages required to make a given separation is calculated using a specific vapor to liquid ratio. If the liquid and vapor are not evenly distributed across the superficial tower area as it enters the packed bed, the liquid to vapor ratio will not be correct in the packed bed and the required separation will not be achieved. The packing will appear to not be working properly. The height equivalent to a theoretical plate( HETP) will be greater than expected. The problem is not the packing itself but the mal- distribution of the fluids entering the packed bed. Liquid mal- distribution is more frequently the problem than vapor. The design of the liquid distributors used to introduce the feed and reflux to a packed bed is critical to making the packing perform to it maximum efficiency. Methods of evaluating the effectiveness of a liquid distributor to evenly distribute the liquid entering a packed bed can be found in references. Considerable work has been done on this topic by Fractionation Research, Inc.( commonly known as FRI). Multi- effect distillation. The goal of multi- effect distillation is to increase the energy efficiency of the process, for use in desalination, or in some cases one stage in the production of ultrapure water. The number of effects is inversely proportional to the kW· h/m3 of water recovered figure, and refers to the volume of water recovered per unit of energy compared with single- effect distillation. One effect is roughly 636 kW· h/m3. There are many other types of multi- effect distillation processes, including one referred to as simply multi- effect distillation( MED), in which multiple chambers, with intervening heat exchangers, are employed. In food processing. Beverages. Carbohydrate- containing plant materials are allowed to ferment, producing a dilute solution of ethanol in the process. Spirits | such as whiskey and rum |
are prepared by distilling these dilute solutions of ethanol. Components other than ethanol, including water, esters, and other alcohols, are collected in the condensate, which account for the flavor of the beverage. Some of these beverages are then stored in barrels or other containers to acquire more flavor compounds and characteristic flavors. David Hilbert(;; 23 January 1862– 14 February 1943)wasaGermanmathematicianandoneofthemostinfluentialmathematiciansofthe19thandearly20th centuries. Hilbert discovered and developed a broad range of fundamental ideas in many areas, including invariant theory, the calculus of variations, commutative algebra, algebraic number theory, the foundations of geometry, spectral theory of operators and its application to integral equations, mathematical physics, and the foundations of mathematics( particularly proof theory). Hilbert adopted and defended Georg Cantor' s set theory and transfinite numbers. In 1900,hepresentedacollectionofproblemsthatsetthecourseformuchofthemathematicalresearchofthe20th century. Hilbert and his students contributed significantly to establishing rigor and developed important tools used in modern mathematical physics. Hilbert is known as one of the founders of proof theory and mathematical logic. Life. Early life and education. Hilbert, the first of two children and only son of Otto and Maria Therese( Erdtmann) Hilbert, was born in the Province of Prussia, Kingdom of Prussia, either in Königsberg( according to Hilbert' s own statement) or in Wehlau( known since 1946 as Znamensk) near Königsberg where his father worked at the time of his birth. In late 1872, Hilbert entered the Friedrichskolleg Gymnasium(" Collegium fridericianum", the same school that Immanuel Kant had attended 140 years before); but, after an unhappy period, he transferred to( late 1879) and graduated from( early 1880) the more science- oriented Wilhelm Gymnasium. Upon graduation, in autumn 1880, Hilbert enrolled at the University of Königsberg, the" Albertina". In early 1882, Hermann Minkowski( two years younger than Hilbert and also a native of Königsberg but had gone to Berlin for three semesters), returned to Königsberg and entered the university. Hilbert developed a lifelong friendship with the shy, gifted Minkowski. Career. In 1884, Adolf Hurwitz arrived from Göttingen as an Extraordinarius( i. e., an associate professor). An intense and fruitful scientific exchange among the three began, and Minkowski and Hilbert especially would exercise a reciprocal influence over each other at various times in their scientific careers. Hilbert obtained his doctorate in 1885, with a dissertation, written under Ferdinand von Lindemann, titled" Über invariante Eigenschaften spezieller binärer Formen, insbesondere der Kugelfunktionen"(" On the invariant properties of special binary forms, in particular the spherical harmonic functions"). Hilbert remained at the University of Königsberg as a" Privatdozent"( senior lecturer) from 1886 to 1895. In 1895, as a result of intervention on his behalf by Felix Klein, he obtained the position of Professor of Mathematics at the University of Göttingen. During the Klein and Hilbert years, Göttingen became the preeminent institution in the mathematical world. He remained there for the rest of his life. Göttingen school. Among Hilbert' s students were Hermann Weyl, chess champion Emanuel Lasker, Ernst Zermelo, and Carl Gustav Hempel. John von Neumann was his assistant. At the University of Göttingen, Hilbert was surrounded by a social circle of some of the most important mathematicians of the20th century, such | as Emmy Noether and Alonzo |
Church. Among his 69 Ph. D. students in Göttingen were many who later became famous mathematicians, including( with date of thesis): Otto Blumenthal( 1898), Felix Bernstein( 1901), Hermann Weyl( 1908), Richard Courant( 1910), Erich Hecke( 1910), Hugo Steinhaus( 1911), and Wilhelm Ackermann( 1925). Between 1902 and 1939 Hilbert was editor of the" Mathematische Annalen", the leading mathematical journal of the time. Personal life. In 1892, Hilbert married Käthe Jerosch( 1864– 1945), who was the daughter of a Königsberg merchant, an outspoken young lady with an independence of mind that matched[ Hilbert' s]." While at Königsberg they had their one child,( 1893– 1969). Franz suffered throughout his life from an undiagnosed mental illness. His inferior intellect was a terrible disappointment to his father and this misfortune was a matter of distress to the mathematicians and students at Göttingen. Hilbert considered the mathematician Hermann Minkowski to be his" best and truest friend". Hilbert was baptized and raised a Calvinist in the Prussian Evangelical Church. He later left the Church and became an agnostic. He also argued that mathematical truth was independent of the existence of God or other" a priori" assumptions. When Galileo Galilei was criticized for failing to stand up for his convictions on the Heliocentric theory, Hilbert objected:" But[ Galileo] was not an idiot. Only an idiot could believe that scientific truth needs martyrdom; that may be necessary in religion, but scientific results prove themselves in due time." Later years. Like Albert Einstein, Hilbert had closest contacts with the Berlin Group whose leading founders had studied under Hilbert in Göttingen( Kurt Grelling, Hans Reichenbach and Walter Dubislav). Around 1925, Hilbert developed pernicious anemia, a then- untreatable vitamin deficiency whose primary symptom is exhaustion; his assistant Eugene Wigner described him as subject to" enormous fatigue" and how he" seemed quite old", and that even after eventually being diagnosed and treated, he" was hardly a scientist after 1925, and certainly not a Hilbert." Hilbert lived to see the Nazis purge many of the prominent faculty members at University of Göttingen in 1933. Those forced out included Hermann Weyl( who had taken Hilbert' s chair when he retired in 1930), Emmy Noether and Edmund Landau. One who had to leave Germany, Paul Bernays, had collaborated with Hilbert in mathematical logic, and co- authored with him the important book" Grundlagen der Mathematik"( which eventually appeared in two volumes, in 1934 and 1939). This was a sequel to the Hilbert– Ackermann book" Principles of Mathematical Logic" from 1928. Hermann Weyl' s successor was Helmut Hasse. About a year later, Hilbert attended a banquet and was seated next to the new Minister of Education, Bernhard Rust. Rust asked whether" the" Mathematical Institute" really suffered so much because of the departure of the Jews". Hilbert replied," Suffered? It doesn' t exist any longer, does it!" Death. By the time Hilbert died in 1943, the Nazis had nearly completely restaffed the university, as many of the former faculty had either been Jewish or married to Jews. Hilbert' s funeral was attended by fewer than a dozen people, only two of | whom were fellow academics, among |
them Arnold Sommerfeld, a theoretical physicist and also a native of Königsberg. News of his death only became known to the wider world six months after he died. The epitaph on his tombstone in Göttingen consists of the famous lines he spoke at the conclusion of his retirement address to the Society of German Scientists and Physicians on 8 September 1930. The words were given in response to the Latin maxim:" Ignoramus et ignorabimus" or" We do not know, we shall not know": The day before Hilbert pronounced these phrases at the 1930 annual meeting of the Society of German Scientists and Physicians, Kurt Gödel— in a round table discussion during the Conference on Epistemology held jointly with the Society meetings— tentatively announced the first expression of his incompleteness theorem. Gödel' s incompleteness theorems show that even elementary axiomatic systems such as Peano arithmetic are either self- contradicting or contain logical propositions that are impossible to prove or disprove. Contributions to mathematics and physics. Hilbert solves Gordan' s Problem. Hilbert' s first work on invariant functions led him to the demonstration in 1888 of his famous" finiteness theorem". Twenty years earlier, Paul Gordan had demonstrated the theorem of the finiteness of generators for binary forms using a complex computational approach. Attempts to generalize his method to functions with more than two variables failed because of the enormous difficulty of the calculations involved. To solve what had become known in some circles as" Gordan' s Problem", Hilbert realized that it was necessary to take a completely different path. As a result, he demonstrated" Hilbert' s basis theorem", showing the existence of a finite set of generators, for the invariants of quantics in any number of variables, but in an abstract form. That is, while demonstrating the existence of such a set, it was not a constructive proof— it did not display" an object"— but rather, it was an existence proof and relied on use of the law of excluded middle in an infinite extension. Hilbert sent his results to the" Mathematische Annalen". Gordan, the house expert on the theory of invariants for the" Mathematische Annalen", could not appreciate the revolutionary nature of Hilbert' s theorem and rejected the article, criticizing the exposition because it was insufficiently comprehensive. His comment was: Klein, on the other hand, recognized the importance of the work, and guaranteed that it would be published without any alterations. Encouraged by Klein, Hilbert extended his method in a second article, providing estimations on the maximum degree of the minimum set of generators, and he sent it once more to the" Annalen". After having read the manuscript, Klein wrote to him, saying: Later, after the usefulness of Hilbert' s method was universally recognized, Gordan himself would say: For all his successes, the nature of his proof created more trouble than Hilbert could have imagined. Although Kronecker had conceded, Hilbert would later respond to others' similar criticisms that" many different constructions are subsumed under one fundamental idea"— in other words( to quote Reid):" Through a proof of existence, Hilbert had been able to | obtain a construction";" the proof"( |
i. e. the symbols on the page)" was"" the object". Not all were convinced. While Kronecker would die soon afterwards, his constructivist philosophy would continue with the young Brouwer and his developing intuitionist" school", much to Hilbert' s torment in his later years. Indeed, Hilbert would lose his" gifted pupil" Weyl to intuitionism—" Hilbert was disturbed by his former student' s fascination with the ideas of Brouwer, which aroused in Hilbert the memory of Kronecker". Brouwer the intuitionist in particular opposed the use of the Law of Excluded Middle over infinite sets( as Hilbert had used it). Hilbert responded: Axiomatization of geometry. The text" Grundlagen der Geometrie"( tr.:" Foundations of Geometry") published by Hilbert in 1899 proposes a formal set, called Hilbert' s axioms, substituting for the traditional axioms of Euclid. They avoid weaknesses identified in those of Euclid, whose works at the time were still used textbook- fashion. It is difficult to specify the axioms used by Hilbert without referring to the publication history of the" Grundlagen" since Hilbert changed and modified them several times. The original monograph was quickly followed by a French translation, in which Hilbert added V. 2, the Completeness Axiom. An English translation, authorized by Hilbert, was made by E. J. Townsend and copyrighted in 1902. This translationincorporatedthechangesmadeintheFrenchtranslationandsoisconsideredtobeatranslationofthe2nd edition. Hilbert continued to make changes in the text and several editions appeared in German.The7th edition was the last to appear in Hilbert' s lifetime.Neweditionsfollowedthe7th, but the main text was essentially not revised. Hilbert' s approach signaled the shift to the modern axiomatic method. In this, Hilbert was anticipated by Moritz Pasch' s work from 1882. Axioms are not taken as self- evident truths. Geometry may treat" things", about which we have powerful intuitions, but it is not necessary to assign any explicit meaning to the undefined concepts. The elements, such as point, line, plane, and others, could be substituted, as Hilbert is reported to have said to Schoenflies and Kötter, by tables, chairs, glasses of beer and other such objects. It is their defined relationships that are discussed. Hilbert first enumerates the undefined concepts: point, line, plane, lying on( a relation between points and lines, points and planes, and lines and planes), betweenness, congruence of pairs of points( line segments), and congruence of angles. The axioms unify both the plane geometry and solid geometry of Euclid in a single system. The 23 problems. Hilbert put forth a most influential list of 23 unsolved problems at the International Congress of Mathematicians in Paris in 1900. This is generally reckoned as the most successful and deeply considered compilation of open problems ever to be produced by an individual mathematician. After re- working the foundations of classical geometry, Hilbert could have extrapolated to the rest of mathematics. His approach differed, however, from the later' foundationalist' Russell– Whitehead or' encyclopedist' Nicolas Bourbaki, and from his contemporary Giuseppe Peano. The mathematical community as a whole could enlist in problems, which he had identified as crucial aspects of the areas of mathematics he took to be key. The problem set was launched as a | talk" The Problems of Mathematics" |
presented during the course of the Second International Congress of Mathematicians held in Paris. The introduction of the speech that Hilbert gave said: He presented fewer than half the problems at the Congress, which were published in the acts of the Congress. In a subsequent publication, he extended the panorama, and arrived at the formulation of the now- canonical 23 Problems of Hilbert. See also Hilbert' s twenty- fourth problem. The full text is important, since the exegesis of the questions still can be a matter of inevitable debate, whenever it is asked how many have been solved. Some of these were solved within a short time.Othershavebeendiscussedthroughoutthe20th century, with a few now taken to be unsuitably open- ended to come to closure. Some even continue to this day to remain a challenge for mathematicians. Formalism. In an account that had become standard by the mid- century, Hilbert' s problem set was also a kind of manifesto, that opened the way for the development of the formalist school,oneofthreemajorschoolsofmathematicsofthe20th century. According to the formalist, mathematics is manipulation of symbols according to agreed upon formal rules. It is therefore an autonomous activity of thought. There is, however, room to doubt whether Hilbert' s own views were simplistically formalist in this sense. Hilbert' s program. In 1920, Hilbert proposed a research project in metamathematics that became known as Hilbert' s program. He wanted mathematics to be formulated on a solid and complete logical foundation. He believed that in principle this could be done by showing that: He seems to have had both technical and philosophical reasons for formulating this proposal. It affirmed his dislike of what had become known as the ignorabimus, still an active issue in his time in German thought, and traced back in that formulation to Emil du Bois- Reymond. This program is still recognizable in the most popular philosophy of mathematics, where it is usually called" formalism". For example, the Bourbaki group adopted a watered- down and selective version of it as adequate to the requirements of their twin projects of( a) writing encyclopedic foundational works, and( b) supporting the axiomatic method as a research tool. This approach has been successful and influential in relation with Hilbert' s work in algebra and functional analysis, but has failed to engage in the same way with his interests in physics and logic. Hilbert wrote in 1919: Hilbert published his views on the foundations of mathematics in the 2- volume work, Grundlagen der Mathematik. Gödel' s work. Hilbert and the mathematicians who worked with him in his enterprise were committed to the project. His attempt to support axiomatized mathematics with definitive principles, which could banish theoretical uncertainties, ended in failure. Gödel demonstrated that any non- contradictory formal system, which was comprehensive enough to include at least arithmetic, cannot demonstrate its completeness by way of its own axioms. In 1931 his incompleteness theorem showed that Hilbert' s grand plan was impossible as stated. The second point cannot in any reasonable way be combined with the first point, as long as the axiom system is genuinely finitary. | Nevertheless, the subsequent achievements of |
proof theory at the very least" clarified" consistency as it relates to theories of central concern to mathematicians. Hilbert' s work had started logic on this course of clarification; the need to understand Gödel'sworkthenledtothedevelopmentofrecursiontheoryandthenmathematicallogicasanautonomousdisciplineinthe1930s. The basis for later theoretical computer science, in the work of Alonzo Church and Alan Turing, also grew directly out of this' debate'. Functional analysis. Around 1909, Hilbert dedicated himself to the study of differential and integral equations; his work had direct consequences for important parts of modern functional analysis. In order to carry out these studies, Hilbert introduced the concept of an infinite dimensional Euclidean space, later called Hilbert space. His work in this part of analysis provided the basis for important contributions to the mathematics of physics in the next two decades, though from an unanticipated direction. Later on, Stefan Banach amplified the concept, defining Banach spaces. Hilbert spaces are an important class of objects in the area of functional analysis, particularly of the spectral theory of self- adjoint linear operators,thatgrewuparounditduringthe20th century. Physics. Until 1912, Hilbert was almost exclusively a pure mathematician. When planning a visit from Bonn, where he was immersed in studying physics, his fellow mathematician and friend Hermann Minkowski joked he had to spend 10 days in quarantine before being able to visit Hilbert. In fact, Minkowski seems responsible for most of Hilbert' s physics investigations prior to 1912, including their joint seminar on the subject in 1905. In 1912, three years after his friend' s death, Hilbert turned his focus to the subject almost exclusively. He arranged to have a" physics tutor" for himself. He started studying kinetic gas theory and moved on to elementary radiation theory and the molecular theory of matter. Even after the war started in 1914, he continued seminars and classes where the works of Albert Einstein and others were followed closely. By 1907, Einstein had framed the fundamentals of the theory of gravity, but then struggled for nearly 8 years to put the theory into its final form. By early summer 1915, Hilbert' s interest in physics had focused on general relativity, and he invited Einstein to Göttingen to deliver a week of lectures on the subject. Einstein received an enthusiastic reception at Göttingen. Over the summer, Einstein learned that Hilbert was also working on the field equations and redoubled his own efforts. During November 1915, Einstein published several papers culminating in" The Field Equations of Gravitation"( see Einstein field equations). Nearly simultaneously, Hilbert published" The Foundations of Physics", an axiomatic derivation of the field equations( see Einstein– Hilbert action). Hilbert fully credited Einstein as the originator of the theory and no public priority dispute concerning the field equations ever arose between the two men during their lives. See more at priority. Additionally, Hilbert' s work anticipated and assisted several advances in the mathematical formulation of quantum mechanics. His work was a key aspect of Hermann Weyl and John von Neumann' s work on the mathematical equivalence of Werner Heisenberg' s matrix mechanics and Erwin Schrödinger' s wave equation, and his namesake Hilbert space plays an important | part in quantum theory. In |
1926, von Neumann showed that, if quantum states were understood as vectors in Hilbert space, they would correspond with both Schrödinger' s wave function theory and Heisenberg' s matrices. Throughout this immersion in physics, Hilbert worked on putting rigor into the mathematics of physics. While highly dependent on higher mathematics, physicists tended to be" sloppy" with it. To a pure mathematician like Hilbert, this was both ugly, and difficult to understand. As he began to understand physics and how physicists were using mathematics, he developed a coherent mathematical theory for what he found– most importantly in the area of integral equations. When his colleague Richard Courant wrote the now classic" Methoden der mathematischen Physik"(" Methods of Mathematical Physics") including some of Hilbert' s ideas, he added Hilbert' s name as author even though Hilbert had not directly contributed to the writing. Hilbert said" Physics is too hard for physicists", implying that the necessary mathematics was generally beyond them; the Courant- Hilbert book made it easier for them. Number theory. Hilbert unified the field of algebraic number theory with his 1897 treatise" Zahlbericht"( literally" report on numbers"). He also resolved a significant number- theory problem formulated by Waring in 1770. As with the finiteness theorem, he used an existence proof that shows there must be solutions for the problem rather than providing a mechanism to produce the answers. He then had little more to publish on the subject; but the emergence of Hilbert modular forms in the dissertation of a student means his name is further attached to a major area. He made a series of conjectures on class field theory. The concepts were highly influential, and his own contribution lives on in the names of the Hilbert class field and of the Hilbert symbol of local class field theory. Results were mostly proved by 1930, after work by Teiji Takagi. Hilbert did not work in the central areas of analytic number theory, but his name has become known for the Hilbert– Pólya conjecture, for reasons that are anecdotal. Works. His collected works(" Gesammelte Abhandlungen") have been published several times. The original versions of his papers contained" many technical errors of varying degree"; when the collection was first published, the errors were corrected and it was found that this could be done without major changes in the statements of the theorems, with one exception— a claimed proof of the continuum hypothesis. The errors were nonetheless so numerous and significant that it took Olga Taussky- Todd three years to make the corrections. Down syndrome or Down' s syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual disability, and characteristic facial features. The average IQ of a young adult with Down syndrome is 50, equivalent to the mental ability of an eight- or nine- year- old child, but this can vary widely. The parents of the affected individual are usually genetically normal. The probability increases from less | than 0. 1% in 20- |
year- old mothers to 3% in those of age 45. The extra chromosome is believed to occur by chance, with no known behavioral activity or environmental factor that changes the probability. Down syndrome can be identified during pregnancy by prenatal screening followed by diagnostic testing or after birth by direct observation and genetic testing. Since the introduction of screening, Down syndrome pregnancies are often aborted. There is no cure for Down syndrome. Education and proper care have been shown to improve quality of life. Some children with Down syndrome are educated in typical school classes, while others require more specialized education. Some individuals with Down syndrome graduate from high school, and a few attend post- secondary education. In adulthood, about 20% in the United States do paid work in some capacity, with many requiring a sheltered work environment. Support in financial and legal matters is often needed. Life expectancy is around 50 to 60 years in the developed world with proper health care. Regular screening for health problems common in Down syndrome is recommended throughout the person' s life. Down syndrome is one of the most common chromosome abnormalities in humans. It occurs in about 1 in 1, 000 babies born each year. In 2015, Down syndrome was present in 5. 4 million individuals globally and resulted in 27, 000 deaths, down from 43, 000 deaths in 1990. It is named after British doctor John Langdon Down, who fully described the syndrome in 1866. Some aspects of the condition were described earlier by French psychiatrist Jean- Étienne Dominique Esquirol in 1838 and French physician Édouard Séguin in 1844. The genetic cause of Down syndrome was discovered in 1959. Signs and symptoms. Those with Down syndrome nearly always have physical and intellectual disabilities. As adults, their mental abilities are typically similar to those of an 8- or 9- year- old. They also typically have poor immune function and generally reach developmental milestones at a later age. They have an increased risk of a number of other health problems, including congenital heart defect, epilepsy, leukemia, thyroid diseases, and mental disorders. Physical. People with Down syndrome may have some or all of these physical characteristics: a small chin, slanted eyes, poor muscle tone, a flat nasal bridge, a single crease of the palm, and a protruding tongue due to a small mouth and relatively large tongue. These airway changes lead to obstructive sleep apnea in around half of those with Down syndrome. Other common features include: a flat and wide face, a short neck, excessive joint flexibility, extra space between big toe and second toe, abnormal patterns on the fingertips and short fingers. Instability of the atlantoaxial joint occurs in about 20% and may lead to spinal cord injury in 1– 2%. Hip dislocations may occur without trauma in up to a third of people with Down syndrome. Growth in height is slower, resulting in adults who tend to have short stature— the average height for men is 154 cm( 5 ft 1 in) and for women is 142 cm( 4 ft 8 in). Individuals | with Down syndrome are at |
increased risk for obesity as they age. Growth charts have been developed specifically for children with Down syndrome. Neurological. This syndrome causes about a third of cases of intellectual disability. Many developmental milestones are delayed with the ability to crawl typically occurring around 8 months rather than 5 months and the ability to walk independently typically occurring around 21 months rather than 14 months. Most individuals with Down syndrome have mild( IQ: 50– 69) or moderate( IQ: 35– 50) intellectual disability with some cases having severe( IQ: 20– 35) difficulties. Those with mosaic Down syndrome typically have IQ scores 10– 30 points higher. As they age, people with Down syndrome typically perform worse than their same- age peers. Commonly, individuals with Down syndrome have better language understanding than ability to speak. Between 10 and 45% have either a stutter or rapid and irregular speech, making it difficult to understand them. After reaching 30 years of age, some may lose their ability to speak. They typically do fairly well with social skills. Behavior problems are not generally as great an issue as in other syndromes associated with intellectual disability. In children with Down syndrome, mental illness occurs in nearly 30% with autism occurring in 5– 10%. People with Down syndrome experience a wide range of emotions. While people with Down syndrome are generally happy, symptoms of depression and anxiety may develop in early adulthood. Children and adults with Down syndrome are at increased risk of epileptic seizures, which occur in 5– 10% of children and up to 50% of adults. This includes an increased risk of a specific type of seizure called infantile spasms. Many( 15%) who live 40 years or longer develop Alzheimer' s disease. In those who reach 60 years of age, 50– 70% have the disease. Senses. Hearing and vision disorders occur in more than half of people with Down syndrome. Vision problems occur in 38 to 80%. Between 20 and 50% have strabismus, in which the two eyes do not move together. Cataracts( cloudiness of the lens of the eye) occur in 15%, and may be present at birth. Keratoconus( a thin, cone- shaped cornea) and glaucoma( increased eye pressure) are also more common, as are refractive errors requiring glasses or contacts. Brushfield spots( small white or grayish/ brown spots on the outer part of the iris) are present in 38 to 85% of individuals. Hearing problems are found in 50– 90% of children with Down syndrome. This is often the result of otitis media with effusion which occurs in 50– 70% and chronic ear infections which occur in 40 to 60%. Ear infections often begin in the first year of life and are partly due to poor eustachian tube function. Excessive ear wax can also cause hearing loss due to obstruction of the outer ear canal. Even a mild degree of hearing loss can have negative consequences for speech, language understanding, and academics. It is important to rule out hearing loss as a factor in social and cognitive deterioration. Age- related hearing loss of the sensorineural type occurs | at a much earlier age |
and affects 10– 70% of people with Down syndrome. Heart. The rate of congenital heart disease in newborns with Down syndrome is around 40%. Of those with heart disease, about 80% have an atrioventricular septal defect or ventricular septal defect with the former being more common. Mitral valve problems become common as people age, even in those without heart problems at birth. Other problems that may occur include tetralogy of Fallot and patent ductus arteriosus. People with Down syndrome have a lower risk of hardening of the arteries. Cancer. Although the overall risk of cancer in Down syndrome is not changed, the risk of testicular cancer and certain blood cancers, including acute lymphoblastic leukemia( ALL) and acute megakaryoblastic leukemia( AMKL) is increased while the risk of other non- blood cancers is decreased. People with Down syndrome are believed to have an increased risk of developing cancers derived from germ cells whether these cancers are blood- or non- blood- related. Blood cancers. Leukemia is 10 to 15 times more common in children with Down syndrome. In particular, acute lymphoblastic leukemia is 20 times more common and the megakaryoblastic form of acute myeloid leukemia( acute megakaryoblastic leukemia), is 500 times more common. Acute megakaryoblastic leukemia( AMKL) is a leukemia of megakaryoblasts, the precursors cells to megakaryocytes which form blood platelets. Acute lymphoblastic leukemia in Down syndrome accounts for 1– 3% of all childhood cases of ALL. It occurs most often in those older than nine years or having a white blood cell count greater than 50, 000 per microliter and is rare in those younger than one year old. ALL in Down syndrome tends to have poorer outcomes than other cases of ALL in people without Down syndrome. In Down syndrome, AMKL is typically preceded by transient myeloproliferative disease( TMD), a disorder of blood cell production in which non- cancerous megakaryoblasts with a mutation in the"GATA1" gene rapidly divide during the later period of pregnancy. The condition affects 3– 10% of babies with Down. While it often spontaneously resolves within three months of birth, it can cause serious blood, liver, or other complications. In about 10% of cases, TMD progresses to AMKL during the three months to five years following its resolution. Non- blood cancers. People with Down syndrome have a lower risk of all major solid cancers, including those of lung, breast, and cervix, with the lowest relative rates occurring in those aged 50 years or older. This low risk is thought due to an increase in the expression of tumor suppressor genes present on chromosome 21. One exception is testicular germ cell cancer which occurs at a higher rate in Down syndrome. Endocrine. Problems of the thyroid gland occur in 20– 50% of individuals with Down syndrome. Low thyroid is the most common form, occurring in almost half of all individuals. Thyroid problems can be due to a poorly or nonfunctioning thyroid at birth( known as congenital hypothyroidism) which occurs in 1% or can develop later due to an attack on the thyroid by the immune system resulting in Graves' disease or | autoimmune hypothyroidism. Type 1 diabetes |
mellitus is also more common. Gastrointestinal. Constipation occurs in nearly half of people with Down syndrome and may result in changes in behavior. One potential cause is Hirschsprung' s disease, occurring in 2– 15%, which is due to a lack of nerve cells controlling the colon. Other frequent congenital problems include duodenal atresia, pyloric stenosis, Meckel diverticulum, and imperforate anus. Celiac disease affects about 7– 20% and gastroesophageal reflux disease is also more common. Teeth. People with Down syndrome tend to be more susceptible to gingivitis as well as early, severe periodontal disease, necrotising ulcerative gingivitis, and early tooth loss, especially in the lower front teeth. While plaque and poor oral hygiene are contributing factors, the severity of these periodontal diseases cannot be explained solely by external factors. Research suggests that the severity is likely a result of a weakened immune system. The weakened immune system also contributes to increased incidence of yeast infections in the mouth( from" Candida albicans"). People with Down syndrome also tend to have a more alkaline saliva resulting in a greater resistance to tooth decay, despite decreased quantities of saliva, less effective oral hygiene habits, and higher plaque indexes. Higher rates of tooth wear and bruxism are also common. Other common oral manifestations of Down syndrome include enlarged hypotonic tongue, crusted and hypotonic lips, mouth breathing, narrow palate with crowded teeth, class III malocclusion with an underdeveloped maxilla and posterior crossbite, delayed exfoliation of baby teeth and delayed eruption of adult teeth, shorter roots on teeth, and often missing and malformed( usually smaller) teeth. Less common manifestations include cleft lip and palate and enamel hypocalcification( 20% prevalence). Taurodontism, an elongation of the pulp chamber, has a high prevalence in people with DS. Fertility. Males with Down syndrome usually do not father children, while females have lower rates of fertility relative to those who are unaffected. Fertility is estimated to be present in 30– 50% of females. Menopause usually occurs at an earlier age. The poor fertility in males is thought to be due to problems with sperm development; however, it may also be related to not being sexually active. As of 2006, three instances of males with Down syndrome fathering children and 26 cases of females having children have been reported. Without assisted reproductive technologies, around half of the children of someone with Down syndrome will also have the syndrome. Cause. Down syndrome is caused by having three copies of the genes on chromosome 21, rather than the usual two. The parents of the affected individual are typically genetically normal. Those who have one child with Down syndrome have about a 1% possibility of having a second child with the syndrome, if both parents are found to have normal karyotypes. The extra chromosome content can arise through several different ways. The most common cause( about 92– 95% of cases) is a complete extra copy of chromosome 21, resulting in trisomy 21. In 1. 0 to 2. 5% of cases, some of the cells in the body are normal and others have trisomy 21, known as mosaic Down | syndrome. The other common mechanisms |
that can give rise to Down syndrome include: a Robertsonian translocation, isochromosome, or ring chromosome. These contain additional material from chromosome 21 and occur in about 2. 5% of cases. An isochromosome results when the two long arms of a chromosome separate together rather than the long and short arm separating together during egg or sperm development. Trisomy 21. Trisomy 21( also known by the karyotype 47, XX,+ 21 for females and 47, XY,+ 21 for males)iscausedbyafailureofthe21st chromosome to separate during egg or sperm development( nondisjunction). As a result, a sperm or egg cell is produced with an extra copy of chromosome 21; this cell thus has 24 chromosomes. When combined with a normal cell from the other parent, the baby has 47 chromosomes, with three copies of chromosome 21. About 88% of cases of trisomy 21 result from nonseparation of the chromosomes in the mother, 8% from nonseparation in the father, and 3% after the egg and sperm have merged. Translocation. The extra chromosome 21 material may also occur due to a Robertsonian translocation in 2– 4% of cases. In this situation, the long arm of chromosome 21 is attached to another chromosome, often chromosome 14. In a male affected with Down syndrome,itresultsinakaryotypeof46XY, t(14q21q). This may be a new mutation or previously present in one of the parents. The parent with such a translocation is usually normal physically and mentally; however, during production of egg or sperm cells, a higher chance of creating reproductive cells with extra chromosome 21 material exists. This results in a 15% chance of having a child with Down syndrome when the mother is affected and a less than 5% probability if the father is affected. The probability of this type of Down syndrome is not related to the mother' s age. Some children without Down syndrome may inherit the translocation and have a higher probability of having children of their own with Down syndrome. In this case it is sometimes known as familial Down syndrome. Mechanism. The extra genetic material present in Down syndrome results in overexpression of a portion of the 310 genes located on chromosome 21. This overexpression has been estimated at around 50%, due to the third copy of the chromosome present. Some research has suggestedtheDownsyndromecriticalregionislocatedatbands21q22. 1–q22. 3, with this area including genes for the amyloid precursor protein, superoxide dismutase,andlikelytheETS2 proto oncogene. Other research, however, has not confirmed these findings. MicroRNAs are also proposed to be involved. The dementia that occurs in Down syndrome is due to an excess of amyloid beta peptide produced in the brain and is similar to Alzheimer' s disease, which also involves amyloid beta build- up. Amyloid beta is processed from amyloid precursor protein, the gene for which is located on chromosome 21. Senile plaques and neurofibrillary tangles are present in nearly all by 35 years of age, though dementia may not be present. Those with Down syndrome also lack a normal number of lymphocytes and produce less antibodies which contributes to their increased risk of infection. Epigenetics. Down syndrome is associated with an increased risk of many | chronic diseases that are typically |
associated with older age such as Alzheimer' s disease. The accelerated aging suggest that trisomy 21 increases the biological age of tissues, but molecular evidence for this hypothesis is sparse. According to a biomarker of tissue age known as epigenetic clock, trisomy 21 increases the age of blood and brain tissue( on average by 6. 6 years). Diagnosis. Before birth. When screening tests predict a high possibility of Down syndrome, a more invasive diagnostic test( amniocentesis or chorionic villus sampling) is needed to confirm the diagnosis. The false- positive rate with screening is about 2– 5%( see section Screening below). Amniocentesis and chorionic villus sampling are more reliable tests, but they increase the risk of miscarriage by between 0. 5 and 1%. The risk of limb problems may be increased in the offspring if chorionic villus sampling is performed before 10 weeks. The risk from the procedure is greater the earlier it is performed, thus amniocentesis is not recommended before 15 weeks gestational age and chorionic villus sampling before 10 weeks gestational age. Abortion rates. About 92% of pregnancies in Europe with a diagnosis of Down syndrome are terminated. As a result, there is almost no one with Down' s in Iceland and Denmark, where screening is commonplace. In the United States, the termination rate after diagnosis is around 75%, but varies from 61% to 93% depending on the population surveyed. Rates are lower among women who are younger and have decreased over time. When asked if they would have a termination if their fetus tested positive, 23– 33% said yes, when high- risk pregnant women were asked, 46– 86% said yes, and when women who screened positive are asked, 89– 97% say yes. After birth. The diagnosis can often be suspected based on the child' s physical appearance at birth. An analysis of the child' s chromosomes is needed to confirm the diagnosis, and to determine if a translocation is present, as this may help determine the chances of the child' s parents having further children with Down syndrome. Parents generally wish to know the possible diagnosis once it is suspected and do not wish pity. Screening. Guidelines recommend screening for Down syndrome to be offered to all pregnant women, regardless of age. A number of tests are used, with varying levels of accuracy. They are typically used in combination to increase the detection rate. None can be definitive, thus if screening is positive, either amniocentesis or chorionic villus sampling is required to confirm the diagnosis. Screening in both the first and second trimesters is better than just screening in the first trimester. The different screening techniques in use are able to pick up 90– 95% of cases, with a false- positive rate of 2– 5%. If Down syndrome occurs in one in 500 pregnancies with a 90% detection rate and the test used has a 5% false- positive rate, this means, of 26 women who test positive on screening, only one will have Down syndrome confirmed. If the screening test has a 2% false- positive rate, this means one of | eleven who test positive on |
screening have a fetus with Down syndrome. Ultrasound. Ultrasound imaging can be used to screen for Down syndrome. Findings that indicate increased chances when seen at 14 to 24 weeks of gestation include a small or no nasal bone, large ventricles, nuchal fold thickness, and an abnormal right subclavian artery, among others. The presence or absence of many markers is more accurate. Increased fetal nuchal translucency( NT) indicates an increased possibility of Down syndrome picking up 75– 80% of cases and being falsely positive in 6%. Blood tests. Several blood markers can be measured to predict the chances of Down syndrome during the first or second trimester. Testing in both trimesters is sometimes recommended and test results are often combined with ultrasound results. In the second trimester, often two or three tests are used in combination with two or three of: α- fetoprotein, unconjugated estriol, total hCG, and free βhCG detecting about 60– 70% of cases. Testing of the mother' s blood for fetal DNA is being studied and appears promising in the first trimester. The International Society for Prenatal Diagnosis considers it a reasonable screening option for those women whose pregnancies are at a high likelihood of trisomy 21. Accuracy has been reported at 98. 6% in the first trimester of pregnancy. Confirmatory testing by invasive techniques( amniocentesis, CVS) is still required to confirm the screening result. Management. Efforts such as early childhood intervention, screening for common problems, medical treatment where indicated, a good family environment, and work- related training can improve the development of children with Down syndrome. Education and proper care can improve quality of life. Raising a child with Down syndrome is more work for parents than raising an unaffected child. Typical childhood vaccinations are recommended. Health screening. A number of health organizations have issued recommendations for screening those with Down syndrome for particular diseases. This is recommended to be done systematically. At birth, all children should get an electrocardiogram and ultrasound of the heart. Surgical repair of heart problems may be required as early as three months of age. Heart valve problems may occur in young adults, and further ultrasound evaluation may be needed in adolescents and in early adulthood. Due to the elevated risk of testicular cancer, some recommend checking the person' s testicles yearly. Cognitive development. Hearing aids or other amplification devices can be useful for language learning in those with hearing loss. Speech therapy may be useful and is recommended to be started around nine months of age. As those with Down syndrome typically have good hand- eye coordination, learning sign language may be possible. Augmentative and alternative communication methods, such as pointing, body language, objects, or pictures, are often used to help with communication. Behavioral issues and mental illness are typically managed with counseling or medications. Education programs before reaching school age may be useful. School- age children with Down syndrome may benefit from inclusive education( whereby students of differing abilities are placed in classes with their peers of the same age), provided some adjustments are made to the curriculum. Evidence to support | this, however, is not very |
strong. In the United States, the Individuals with Disabilities Education Act of 1975 requires public schools generally to allow attendance by students with Down syndrome. Individuals with Down syndrome may learn better visually. Drawing may help with language, speech, and reading skills. Children with Down syndrome still often have difficulty with sentence structure and grammar, as well as developing the ability to speak clearly. Several types of early intervention can help with cognitive development. Efforts to develop motor skills include physical therapy, speech and language therapy, and occupational therapy. Physical therapy focuses specifically on motor development and teaching children to interact with their environment. Speech and language therapy can help prepare for later language. Lastly, occupational therapy can help with skills needed for later independence. Other. Tympanostomy tubes are often needed and often more than one set during the person' s childhood. Tonsillectomy is also often done to help with sleep apnea and throat infections. Surgery, however, does not always address the sleep apnea and a continuous positive airway pressure( CPAP) machine may be useful. Physical therapy and participation in physical education may improve motor skills. Evidence to support this in adults, however, is not very good. Efforts to prevent respiratory syncytial virus( RSV) infection with human monoclonal antibodies should be considered, especially in those with heart problems. In those who develop dementia there is no evidence for memantine, donepezil, rivastigmine, or galantamine. Plastic surgery has been suggested as a method of improving the appearance and thus the acceptance of people with Down syndrome. It has also been proposed as a way to improve speech. Evidence, however, does not support a meaningful difference in either of these outcomes. Plastic surgery on children with Down syndrome is uncommon, and continues to be controversial. The U. S. National Down Syndrome Society views the goal as one of mutual respect and acceptance, not appearance. Many alternative medical techniques are used in Down syndrome; however, they are poorly supported by evidence. These include: dietary changes, massage, animal therapy, chiropractic and naturopathy, among others. Some proposed treatments may also be harmful. Prognosis. Between 5 and 15% of children with Down syndrome in Sweden attend regular school. Some graduate from high school; however, most do not. Of those with intellectual disability in the United States who attended high school about 40% graduated. Many learn to read and write and some are able to do paid work. In adulthood about 20% in the United States do paid work in some capacity. In Sweden, however, less than 1% have regular jobs. Many are able to live semi- independently, but they often require help with financial, medical, and legal matters. Those with mosaic Down syndrome usually have better outcomes. Individuals with Down syndrome have a higher risk of early death than the general population. This is most often from heart problems or infections. Following improved medical care, particularly for heart and gastrointestinal problems, the life expectancy has increased. This increase has been from 12 years in 1912, to 25 years inthe1980s, to 50 to 60 years in the developed world inthe2000s. | Currently between 4 and 12% |
die in the first year of life. The probability of long- term survival is partly determined by the presence of heart problems. In those with congenital heart problems, 60% survive to 10 years and 50% survive to 30 years of age. In those without heart problems, 85% survive to 10 years and 80% survive to 30 years of age. About 10% live to 70 years of age. The National Down Syndrome Society provide information regarding raising a child with Down syndrome. Epidemiology. Down syndrome is the most common chromosomal abnormality in humans. Globally,, Down syndrome occurs in about 1 per 1, 000 births and results in about 17, 000 deaths. More children are born with Down syndrome in countries where abortion is not allowed and in countries where pregnancy more commonly occurs at a later age. About 1. 4 per 1, 000 live births in the United States and 1. 1 per 1, 000 live births in Norway are affected.Inthe1950s, in the United States, it occurred in 2 per 1000 live births with the decrease since then due to prenatal screening and abortions. The number of pregnancies with Down syndrome is more than two times greater with many spontaneously aborting. It is the cause of 8% of all congenital disorders. Maternal age affects the chances of having a pregnancy with Down syndrome. At age 20, the chance is 1 in 1, 441; at age 30, it is 1 in 959; at age 40, it is 1 in 84; and at age 50 it is 1 in 44. Although the probability increases with maternal age, 70% of children with Down syndrome are born to women 35 years of age and younger, because younger people have more children. The father' s older age is also a risk factor in women older than 35, but not in women younger than 35, and may partly explain the increase in risk as women age. History. English physician John Langdon Down first described Down syndrome in 1862, recognizing it as a distinct type of mental disability, and again in a more widely published report in 1866. Édouard Séguin described it as separate from cretinism in 1844.Bythe20th century, Down syndrome had become the most recognizable form of mental disability. In antiquity, many infants with disabilities were either killed or abandoned. In June 2020, the earliest incidence of Down syndrome was found in genomic evidence from an infant that was buried before 3200 BC at Poulnabrone dolmen in Ireland. Researchers believe that a number of historical pieces of art portray Down syndrome, including pottery from the pre- Columbian Tumaco- La Tolita culture in present- day Colombia and Ecuador,andthe16th- century painting" The Adoration of the Christ Child".Inthe20th century, many individuals with Down syndrome were institutionalized, few of the associated medical problems were treated, and most people died in infancy or early adulthood. With the rise of the eugenics movement, 33 of the then 48 U. S. states and several countries began programs of forced sterilization of individuals with Down syndrome and comparable degrees of disability. ActionT4 in Nazi Germany made public | policy of a program of |
systematic involuntary euthanization.Withthediscoveryofkaryotypetechniquesinthe1950s it became possible to identify abnormalities of chromosomal number or shape. In 1959 Jérôme Lejeune reported the discovery that Down syndrome resulted from an extra chromosome. However, Lejeune' s claim to the discovery has been disputed, and in 2014 the Scientific Council of the French Federation of Human Genetics unanimously awarded its Grand Prize to his colleague Marthe Gautier for her role in this discovery. The discovery took place in the laboratory of Raymond Turpin at the Hôpital Trousseau in Paris, France. Jérôme Lejeune and Marthe Gautier were both his students. As a result of this discovery, the condition became known as trisomy 21. Even before the discovery of its cause, the presence of the syndrome in all races, its association with older maternal age, and its rarity of recurrence had been noticed. Medical texts had assumed it was caused by a combination of inheritable factors that had not been identified. Other theories had focused on injuries sustained during birth. Society and culture. Name. Due to his perception that children with Down syndrome shared facial similarities with those of Blumenbach' s Mongolian race, John Langdon Down used the term" mongoloid". He felt that the existence of Down syndrome confirmed that all peoples were genetically related.Inthe1950s with discovery of the underlying cause as being related to chromosomes, concerns about the race- based nature of the name increased. In 1961, a group of nineteen scientists suggested that" mongolism" had" misleading connotations" and had become" an embarrassing term". The World Health Organization( WHO) dropped the term in 1965 after a request by the delegation from the Mongolian People' s Republic. While the term mongoloid( also mongolism, Mongolian imbecility or idiocy)continuedtobeuseduntiltheearly1980s, it is now considered unacceptable and is no longer in common use. In 1975, the United States National Institutes of Health( NIH) convened a conference to standardize the naming and recommended replacing the possessive form," Down' s syndrome" with" Down syndrome". However, both the possessive and nonpossessive forms remain in use by the general population. The term" trisomy 21" is also commonly used. Ethics. Most obstetricians argue that not offering screening for Down syndrome is unethical. As it is a medically reasonable procedure, per informed consent, people should at least be given information about it. It will then be the woman' s choice, based on her personal beliefs, how much or how little screening she wishes. When results from testing become available, it is also considered unethical not to give the results to the person in question. Some bioethicists deem it reasonable for parents to select a child who would have the highest well- being. One criticism of this reasoning is that it often values those with disabilities less. Some parents argue that Down syndrome should not be prevented or cured and that eliminating Down syndrome amounts to genocide. The disability rights movement does not have a position on screening, although some members consider testing and abortion discriminatory. Some in the United States who are anti- abortion support abortion if the fetus is disabled, while others do not. Of a group of | 40 mothers in the United |
States who have had one child with Down syndrome, half agreed to screening in the next pregnancy. Within the US, some Protestant denominations see abortion as acceptable when a fetus has Down syndrome while Orthodox Christianity and Roman Catholicism do not. Some of those against screening refer to it as a form of" eugenics". Disagreement exists within Islam regarding the acceptability of abortion in those carrying a fetus with Down syndrome. Some Islamic countries allow abortion, while others do not. Parents may be stigmatized whichever decision they make. Advocacy groups. Advocacy groups for individuals with Down syndrome began to be formed after the Second World War. These were organizations advocating for the inclusion of people with Down syndrome into the general school system and for a greater understanding of the condition among the general population, as well as groups providing support for families with children living with Down syndrome. Before this individuals with Down syndrome were often placed in mental hospitals or asylums. Organizations included the Royal Society for Handicapped Children and Adults founded in the UK in 1946 by Judy Fryd, Kobato Kai founded in Japan in 1964, the National Down Syndrome Congress founded in the United States in 1973 by Kathryn McGee and others, and the National Down Syndrome Society founded in 1979 in the United States. The first Roman Catholic order of nuns for women with Down Syndrome, Little Sisters Disciples of the Lamb, was founded in 1985 in France. The first World Down Syndrome Day was held on 21 March 2006. The day and month were chosen to correspond with 21 and trisomy, respectively. It was recognized by the United Nations General Assembly in 2011. Research. Efforts are underway to determine how the extra chromosome 21 material causes Down syndrome, as currently this is unknown, and to develop treatments to improve intelligence in those with the syndrome. Two efforts being studied are the use stem cells and gene therapy. Other methods being studied include the use of antioxidants, gamma secretase inhibition, adrenergic agonists, and memantine. Research is often carried out on an animal model,theTs65Dn mouse. Other hominids. Down syndrome may also occur in hominids other than humans. In great apes chromosome 22 corresponds to the human chromosome 21 and thus trisomy 22 causes Down syndrome in apes. The condition was observed in a common chimpanzee in 1969 and a Bornean orangutan in 1979, but neither lived very long. The common chimpanzee Kanako( born around 1993, in Japan) has become the longest- lived known example of this condition. Kanako has some of the same symptoms that are common in human Down syndrome. It is unknown how common this condition is in chimps but it is plausible it could be roughly as common as Down syndrome is in humans. Dyslexia, also known as reading disorder, is a disorder characterized by difficulty reading in individuals with otherwise unaffected intelligence. Different people are affected to different degrees. Problems may include difficulties in spelling words, reading quickly, writing words," sounding out" words in the head, pronouncing words when reading aloud and understanding what | one reads. Often these difficulties |
are first noticed at school. When someone who previously could read loses their ability, it is known as" alexia". The difficulties are involuntary and people with this disorder have a normal desire to learn. People with dyslexia have higher rates of attention deficit hyperactivity disorder( ADHD), developmental language disorders, and difficulties with numbers. Dyslexia is believed to be caused by the interaction of genetic and environmental factors. Some cases run in families. Dyslexia that develops due to a traumatic brain injury, stroke, or dementia is called" acquired dyslexia". The underlying mechanisms of dyslexia result from differences within the brain' s language processing. Dyslexia is diagnosed through a series of tests of memory, vision, spelling, and reading skills. Dyslexia is separate from reading difficulties caused by hearing or vision problems or by insufficient teaching or opportunity to learn. Treatment involves adjusting teaching methods to meet the person' s needs. While not curing the underlying problem, it may decrease the degree or impact of symptoms. Treatments targeting vision are not effective. Dyslexia is the most common learning disability and occurs in all areas of the world. It affects 3– 7% of the population; however, up to 20% of the general population may have some degree of symptoms. While dyslexia is more often diagnosed in men, it has been suggested that it affects men and women equally. Some believe that dyslexia should be best considered as a different way of learning, with both benefits and downsides. Classification. Dyslexia is divided into developmental and acquired forms. This article is primarily about" developmental dyslexia", i. e., dyslexia that begins in early childhood. Acquired dyslexia occurs subsequent to neurological insult, such as traumatic brain injury or stroke. People with acquired dyslexia exhibit some of the signs or symptoms of the developmental disorder, but requiring different assessment strategies and treatment approaches. Signs and symptoms. In early childhood, symptoms that correlate with a later diagnosis of dyslexia include delayed onset of speech and a lack of phonological awareness. A common myth closely associates dyslexia with mirror writing and reading letters or words backwards. These behaviors are seen in many children as they learn to read and write, and are not considered to be defining characteristics of dyslexia. School- age children with dyslexia may exhibit signs of difficulty in identifying or generating rhyming words, or counting the number of syllables in words– both of which depend on phonological awareness. They may also show difficulty in segmenting words into individual sounds or may blend sounds when producing words, indicating reduced phonemic awareness. Difficulties with word retrieval or naming things is also associated with dyslexia. People with dyslexia are commonly poor spellers, a feature sometimes called dysorthographia or dysgraphia, which depends on orthographic coding. Problems persist into adolescence and adulthood and may include difficulties with summarizing stories, memorization, reading aloud, or learning foreign languages. Adults with dyslexia can often read with good comprehension, though they tend to read more slowly than others without a learning difficulty and perform worse in spelling tests or when reading nonsense words– a measure of phonological awareness. Associated | conditions. Dyslexia often co- occurs |
with other learning disorders, but the reasons for this comorbidity have not been clearly identified. These associated disabilities include: Causes. Researchers have been trying to find the neurobiological basis of dyslexia since the condition was first identified in 1881. For example, some have tried to associate the common problem among people with dyslexia of not being able to see letters clearly to abnormal development of their visual nerve cells. Neuroanatomy. Neuroimaging techniques, such as functional magnetic resonance imaging( fMRI) and positron emission tomography( PET), have shown a correlation between both functional and structural differences in the brains of children with reading difficulties. Some people with dyslexia show less electrical activation in parts of the left hemisphere of the brain involved with reading, such as the inferior frontal gyrus, inferior parietal lobule, and the middle and ventral temporal cortex. Over the past decade, brain activation studies using PET to study language have produced a breakthrough in the understanding of the neural basis of language. Neural bases for the visual lexicon and for auditory verbal short- term memory components have been proposed, with some implication that the observed neural manifestation of developmental dyslexia is task- specific( i. e., functional rather than structural). fMRIs of people with dyslexia indicate an interactive role of the cerebellum and cerebral cortex as well as other brain structures in reading. The cerebellar theory of dyslexia proposes that impairment of cerebellum- controlled muscle movement affects the formation of words by the tongue and facial muscles, resulting in the fluency problems that some people with dyslexia experience. The cerebellum is also involved in the automatization of some tasks, such as reading. The fact that some children with dyslexia have motor task and balance impairments could be consistent with a cerebellar role in their reading difficulties. However, the cerebellar theory has not been supported by controlled research studies. Genetics. Research into potential genetic causes of dyslexia has its roots in post- autopsy examination of the brains of people with dyslexia. Observed anatomical differences in the language centers of such brains include microscopic cortical malformations known as ectopias, and more rarely, vascular micro- malformations, and microgyrus— a smaller than usual size for the gyrus. The previously cited studies and others suggest that abnormal cortical development, presumed to occur before or during the sixth month of fetal brain development, may have caused the abnormalities. Abnormal cell formations in people with dyslexia have also been reported in non- language cerebral and subcortical brain structures. Several genes have been associated with dyslexia,includingDCDC2andKIAA0319 on chromosome 6,andDYX1C1 on chromosome 15. Gene– environment interaction. The contribution of gene– environment interaction to reading disability has been intensely studied using twin studies, which estimate the proportion of variance associated with a person' s environment and the proportion associated with their genes. Both environmental and genetic factors appear to contribute to reading development. Studies examining the influence of environmental factors such as parental education and teaching quality have determined that genetics have greater influence in supportive, rather than less optimal, environments. However, more optimal conditions may just allow those genetic risk factors | to account for more of |
the variance in outcome because the environmental risk factors have been minimized. As environment plays a large role in learning and memory, it is likely that epigenetic modifications play an important role in reading ability. Measures of gene expression, histone modifications, and methylation in the human periphery are used to study epigenetic processes; however, all of these have limitations in the extrapolation of results for application to the human brain. Language. The orthographic complexity of a language directly affects how difficult it is to learn to read it. English and French have comparatively" deep" phonemic orthographies within the Latin alphabet writing system, with complex structures employing spelling patterns on several levels: letter- sound correspondence, syllables, and morphemes. Languages such as Spanish, Italian and Finnish primarily employ letter- sound correspondence— so- called" shallow" orthographies— which makes them easier to learn for people with dyslexia. Logographic writing systems, such as Chinese characters, have extensive symbol use; and these also pose problems for dyslexic learners. Pathophysiology. For most people who are right- hand dominant, the left hemisphere of their brain is more specialized for language processing. With regard to the mechanism of dyslexia, fMRI studies suggest that this specialization is less pronounced or absent in people with dyslexia. In other studies, dyslexia is correlated with anatomical differences in the corpus callosum, the bundle of nerve fibers that connects the left and right hemispheres. Data via diffusion tensor MRI indicate changes in connectivity or in gray matter density in areas related to reading and language. Finally, the left inferior frontal gyrus has shown differences in phonological processing in people with dyslexia. Neurophysiological and imaging procedures are being used to ascertain phenotypic characteristics in people with dyslexia, thus identifying the effects of dyslexia- related genes. Dual route theory. The dual- route theoryofreadingaloudwasfirstdescribedintheearly1970s. This theory suggests that two separate mental mechanisms, or cognitive routes, are involved in reading aloud. One mechanism is the lexical route, which is the process whereby skilled readers can recognize known words by sight alone, through a" dictionary" lookup procedure. The other mechanism is the nonlexical or sublexical route, which is the process whereby the reader can" sound out" a written word. This is done by identifying the word' s constituent parts( letters, phonemes, graphemes) and applying knowledge of how these parts are associated with each other, for example, how a string of neighboring letters sound together. The dual- route system could explain the different rates of dyslexia occurrence between different languages( e. g., the consistency of phonological rules in the Spanish language could account for the fact that Spanish- speaking children show a higher level of performance in non- word reading, when compared to English- speakers). Diagnosis. Dyslexia is a heterogeneous, dimensional learning disorder that impairs accurate and fluent word reading and spelling. Typical— but not universal— features include difficulties with phonological awareness; inefficient and often inaccurate processing of sounds in oral language(" phonological processing"); and verbal working memory deficits. Dyslexia is a neurodevelopmental disorder, subcategorized in diagnostic guides as a" learning disorder with impairment in reading"( ICD- 11 prefixes" developmental" to" learning | disorder"; DSM- 5 uses" specific"). |
Dyslexia is not a problem with intelligence. Emotional problems often arise secondary to learning difficulties. The National Institute of Neurological Disorders and Stroke describes dyslexia as" difficulty with phonological processing( the manipulation of sounds), spelling, and/ or rapid visual- verbal responding". The British Dyslexia Association defines dyslexia as" a learning difficulty that primarily affects the skills involved in accurate and fluent word reading and spelling" and is characterized by" difficulties in phonological awareness, verbal memory and verbal processing speed"." Phonological awareness" enables one to identify, discriminate, remember( working memory), and mentally manipulate the sound structures of language— phonemes, onsite- rime segments, syllables, and words. Assessment. Assessment tests. There is a wide range of tests that are used in clinical and educational settings to evaluate the possibility that a person might have dyslexia. If initial testing suggests that a person might have dyslexia, such tests are often followed up with a full diagnostic assessment to determine the extent and nature of the disorder. Some tests can be administered by a teacher or computer; others require specialized training and are given by psychologists. Some test results indicate how to carry out teaching strategies. Because a variety of different cognitive, behavioral, emotional, and environmental factors all could contribute to difficultly learning to read, a comprehensive evaluation should consider these different possibilities. These tests and observations can include: Screening. Screening procedures seek to identify children who show signs of possible dyslexia. In the preschool years, a family history of dyslexia, particularly in biological parents and siblings, predicts an eventual dyslexia diagnosis better than any test. In primary school( ages 5– 7), the ideal screening procedure consist of training primary school teachers to carefully observe and record their pupils' progress through the phonics curriculum, and thereby identify children progressing slowly. When teachers identify such students they can supplement their observations with screening tests such as the" Phonics screening check" used by United Kingdom schools during Year one. In the medical setting, child and adolescent psychiatrist M. S. Thambirajah emphasizes that"[ g] iven the high prevalence of developmental disorders in school- aged children, all children seen in clinics should be systematically screened for developmental disorders irrespective of the presenting problem/ s." Thambirajah recommends screening for developmental disorders, including dyslexia, by conducting a brief developmental history, a preliminary psychosocial developmental examination, and obtaining a school report regarding academic and social functioning. Management. Through the use of compensation strategies, therapy and educational support, individuals with dyslexia can learn to read and write. There are techniques and technical aids that help to manage or conceal symptoms of the disorder. Reducing stress and anxiety can sometimes improve written comprehension. For dyslexia intervention with alphabet- writing systems, the fundamental aim is to increase a child' s awareness of correspondences between graphemes( letters) and phonemes( sounds), and to relate these to reading and spelling by teaching how sounds blend into words. Reinforced collateral training focused on reading and spelling may yield longer- lasting gains than oral phonological training alone. Early intervention can be successful in reducing reading failure. Research does not suggest that specially- | tailored fonts( such as Dyslexie |
and OpenDyslexic) help with reading. Children with dyslexia read text set in a regular font such as Times New Roman and Arial just as quickly, and they show a preference for regular fonts over specially- tailored fonts. Some research has pointed to increased letter- spacing being beneficial. There is currently no evidence showing that music education significantly improves the reading skills of adolescents with dyslexia. Prognosis. Dyslexic children require special instruction for word analysis and spelling from an early age. The prognosis, generally speaking, is positive for individuals who are identified in childhood and receive support from friends and family. The New York educational system( NYED) indicates" a daily uninterrupted 90- minute block of instruction in reading", furthermore" instruction in phonemic awareness, phonics, vocabulary development, reading fluency" so as to improve the individual' s reading ability. Epidemiology. The percentage of people with dyslexia is unknown, but it has been estimated to be as low as 5% and as high as 17% of the population. While it is diagnosed more often in males, some believe that it affects males and females equally. There are different definitions of dyslexia used throughout the world, but despite significant differences in writing systems, dyslexia occurs in different populations. Dyslexia is not limited to difficulty in converting letters to sounds, and Chinese people with dyslexia may have difficulty converting Chinese characters into their meanings. The Chinese vocabulary uses logographic, monographic, non- alphabet writing where one character can represent an individual phoneme. The phonological- processing hypothesis attempts to explain why dyslexia occurs in a wide variety of languages. Furthermore, the relationship between phonological capacity and reading appears to be influenced by orthography. History. Dyslexia was clinically described by Oswald Berkhan in 1881, but the term" dyslexia" was coined in 1883 by Rudolf Berlin, an ophthalmologist in Stuttgart. He used the term to refer to the case of a young boy who had severe difficulty learning to read and write, despite showing typical intelligence and physical abilities in all other respects. In 1896, W. Pringle Morgan, a British physician from Seaford, East Sussex, published a description of a reading- specific learning disorder in a report to the" British Medical Journal" titled" Congenital Word Blindness". The distinction between phonological versus surface types of dyslexia is only descriptive, and without any etiological assumption as to the underlying brain mechanisms. However, studies have alluded to potential differences due to variation in performance. Society and culture. As is the case with any disorder, society often makes an assessment based on incomplete information.Beforethe1980s, dyslexia was thought to be a consequence of education, rather than a neurological disability. As a result, society often misjudges those with the disorder. There is also sometimes a workplace stigma and negative attitude towards those with dyslexia. If the instructors of a person with dyslexia lack the necessary training to support a child with the condition, there is often a negative effect on the student' s learning participation. Since at leastthe1960s in the UK, the children diagnosed with developmental dyslexia have consistently been from privileged families. Although half of prisoners in | the UK have significant reading |
difficulties, very few have ever been evaluated for dyslexia. Access to some special educational resources and funding is contingent upon having a diagnosis of dyslexia. As a result, when Staffordshire and Warwickshire proposed in 2018 to teach reading to all children with reading difficulties, using techniques proven to be successful for most children with a diagnosis of dyslexia, without first requiring the families to obtain an official diagnosis, dyslexia advocates and parents of children with dyslexia were fearful that they were losing a privileged status. Research. Most dyslexia research relates to alphabetic writing systems, and especially to European languages. However, substantial research is also available regarding people with dyslexia who speak Arabic, Chinese, Hebrew, or other languages. The outward expression of individuals, with reading disability and regular poor readers is the same in some respects. Delft() is a city and municipality in the province of South Holland, Netherlands. It is located between Rotterdam, to the southeast, and The Hague, to the northwest. Together with them, it is part of both Rotterdam– The Hague metropolitan area and the Randstad. Delft is a popular tourist destination in the Netherlands, famous for its historical connections with the reigning House of Orange- Nassau, for its blue pottery, for being home to the painter Jan Vermeer, and for hosting Delft University of Technology( TU Delft). Historically, Delft played a highly influential role in the Dutch Golden Age. In terms of science and technology, thanks to the pioneering contributions of Antonie van Leeuwenhoek and Martinus Beijerinck, Delft can be considered to be the birthplace of microbiology. History. Early history. The city of Delft came into being beside a canal, the' Delf', which comes from the word" delven", meaning to delve or dig, and this led to the name Delft. At the elevated place where this' Delf' crossed the creek wall of the silted up river Gantel, a Count established his manor, probably around 1075. Partly because of this, Delft became an important market town, the evidence for which can be seen in the size of its central market square. Having been a rural village in the early Middle Ages, Delft developed into a city, and on 15 April 1246, Count Willem II granted Delft its city charter. Trade and industry flourished. In 1389 the Delfshavensche Schie canal was dug through to the river Maas, where the port of Delfshaven was built, connecting Delft to the sea.Untilthe17th century, Delft was one of the major cities of the then county( and later province) of Holland. In 1400, for example, the city had 6, 500 inhabitants, making it the third largest city after Dordrecht( 8, 000) and Haarlem( 7, 000). In 1560, Amsterdam, with 28, 000 inhabitants, had become the largest city, followed by Delft, Leiden and Haarlem, which each had around 14, 000 inhabitants. In 1536, a large part of the city was destroyed by the great fire of Delft. The town' s association with the House of Orange started when William of Orange( Willem van Oranje), nicknamed William the Silent( Willem de Zwijger), took up residence in 1572 in | the former Saint- Agatha convent( |
subsequently called the Prinsenhof). At the time he was the leader of growing national Dutch resistance against Spanish occupation, known as the Eighty Years' War. By then Delft was one of the leading cities of Holland and it was equipped with the necessary city walls to serve as a headquarters. In October 1573, an attack by Spanish forces was repelled in the Battle of Delft. After the Act of Abjuration was proclaimed in 1581, Delft became the" de facto" capital of the newly independent Netherlands, as the seat of the Prince of Orange. When William was shot dead on 10 July 1584 by Balthazar Gerards in the hall of the Prinsenhof( now the Prinsenhof Museum), the family' s traditional burial place in Breda was still in the hands of the Spanish. Therefore, he was buried in the Delft Nieuwe Kerk( New Church), starting a tradition for the House of Orange that has continued to the present day. Around this time, Delft also occupied a prominent position in the field of printing. A number of Italian glazed earthenware makers settled in the city and introduced a new style. The tapestry industry also flourished when famous manufacturer François Spierincx moved to the city.Inthe17th century, Delft experienced a new heyday, thanks to the presence of an office of the Dutch East India Company( VOC)( opened in 1602) and the manufacture of Delft Blue china. A number of notable artists based themselves in the city, including Leonard Bramer, Carel Fabritius, Pieter de Hoogh, Gerard Houckgeest, Emanuel de Witte, Jan Steen, and Johannes Vermeer. Reinier de Graaf and Antonie van Leeuwenhoek received international attention for their scientific research. Explosion. The Delft Explosion, also known in history as the Delft Thunderclap, occurred on 12 October 1654 when a gunpowder store exploded, destroying much of the city. Over a hundred people were killed and thousands were injured. About of gunpowder were stored in barrels in a magazine in a former Clarist convent in the Doelenkwartier district, where the Paardenmarkt is now located. Cornelis Soetens, the keeper of the magazine, opened the store to check a sample of the powder and a huge explosion followed. Luckily, many citizens were away, visiting a market in Schiedam or a fair in The Hague. Today, the explosion is primarily remembered for killing Rembrandt' s most promising pupil, Carel Fabritius, and destroying almost all of his works. Delft artist Egbert van der Poel painted several pictures of Delft showing the devastation. The gunpowder store( Dutch: Kruithuis) was subsequently re- housed, a' cannonball' s distance away', outside the city, in a new building designed by architect Pieter Post. Sights. The city centre retains a large number of monumental buildings, while in many streets there are canals of which the banks are connected by typical bridges, altogether making this city a notable tourist destination. Historical buildings and other sights of interest include: Culture. Delft is well known for the Delft pottery ceramic products which were styled on the imported Chinese porcelain ofthe17th century. The city had an early start in this area since it was a | home port of the Dutch |
East India Company. It can still be seen at the pottery factories De Koninklijke Porceleyne Fles( or Royal Delft) and De Delftse Pauw, while new ceramics and ceramic art can be found at the Gallery Terra Delft. The painter Johannes Vermeer( 1632– 1675) was born in Delft. Vermeer used Delft streets and home interiors as the subject or background in his paintings. Several other famous painters lived and worked in Delft at that time, such as Pieter de Hoogh, Carel Fabritius, Nicolaes Maes, Gerard Houckgeest and Hendrick Cornelisz. van Vliet. They were all members of the Delft School. The Delft School is known for its images of domestic life and views of households, church interiors, courtyards, squares and the streets of Delft. The painters also produced pictures showing historic events, flowers, portraits for patrons and the court as well as decorative pieces of art. Delft supports creative arts companies. From 2001 the, a building that had been disused since 1951, began to house small companies in the creative arts sector. Its demolition started in December 2009, making way for the new railway tunnel in Delft. The occupants of the building, as well as the name' Bacinol', moved to another building in the city. The name Bacinol relates to Dutch penicillin research during WWII. Education. Delft University of Technology( TU Delft) is one of four universities of technology in the Netherlands. It was founded as an academy for civil engineering in 1842 by King William II. Today, well over 21, 000 students are enrolled. The UNESCO- IHE Institute for Water Education, providing postgraduate education for people from developing countries, draws on the strong tradition in water management and hydraulic engineering of the Delft university. Economy. In the local economic field, essential elements are: Nature and recreation. East of Delft lies a relatively large nature and recreation area called the" Delftse Hout"(" Delft Wood"). Through the forest lie bike, horse- riding and footpaths. It also includes a vast lake( suitable for swimming and windsurfing), narrow beaches, a restaurant, and community gardens, plus camping ground and other recreational and sports facilities.( There is also a facility for renting bikes from the station.) Inside the city, apart from a central park, there are several smaller town parks, including" Nieuwe Plantage"," Agnetapark"," Kalverbos". There is also the Botanical Garden of the TU and an arboretum in Delftse Hout. Notable people. Delft is the birthplace of: International relations. Twin towns. Delft is twinned with: Transport. Trains stopping at these stations connect Delft with, among others, the nearby cities of Rotterdam and The Hague, as often as every five minutes, for most of the day. There are several bus routes from Delft to similar destinations. Trams frequently travel between Delft and The Hague via special double tracks crossing the city. The Duesberg hypothesis is the claim, associated with University of California, Berkeley professor Peter Duesberg, that various noninfectious factors such as but not limited to, recreational and pharmaceutical drug use are the cause of AIDS, and that HIV( human immunodeficiency virus) is merely a harmless passenger virus. The scientific | consensus is that the Duesberg |
hypothesis is incorrect and that HIV is the cause of AIDS. The most prominent supporters of this hypothesis are Duesberg himself, biochemist vitamin proponent David Rasnick, and journalist Celia Farber. The scientific community contends that Duesberg' s arguments are the result of cherry- picking predominantly outdated scientific data and selectively ignoring evidence in favor of HIV' s role in AIDS. Role of legal and illegal drug use. Duesberg argues that there is a statistical correlation between trends in recreational drug use and trends in AIDS cases.HearguesthattheepidemicofAIDScasesinthe1980s corresponds to a supposed epidemic of recreational drug use in the United States and Europe during the same time frame. These claims are not supported by epidemiologic data. The average yearly increase in opioid- related deaths from 1990 to 2002 was nearly three times the yearly increase from 1979– 90, with the greatest increase in 2000– 02, yet AIDS cases and deaths fell dramatically during the mid- to- late-1990s. Duesberg' s claim that recreational drug use, rather than HIV, was the cause of AIDS has been specifically examined and found to be false. Cohort studies have found that only HIV- positive drug users develop opportunistic infections; HIV- negative drug users do not develop such infections, indicating that HIV rather than drug use is the cause of AIDS. Duesberg has also argued that nitrite inhalants were the cause of the epidemic of Kaposi sarcoma( KS) in gay men. However, this argument has been described as an example of the fallacy of a statistical confounding effect; it is now known that a herpesvirus, potentiated by HIV, is responsible for AIDS- associated KS. Moreover, in addition to recreational drugs, Duesberg argues that anti- HIV drugs such as zidovudine( AZT) can cause AIDS. Duesberg' s claim that antiviral medication causes AIDS is regarded as disproven by the scientific community. Placebo- controlled studies have found that AZT as a single agent produces modest and short- lived improvements in survival and delays the development of opportunistic infections; it certainly did not cause AIDS, which develops in both treated and untreated study patients. With the subsequent development of protease inhibitors and highly active antiretroviral therapy, numerous studies have documented the fact that anti- HIV drugs prevent the development of AIDS and substantially prolong survival, further disproving the claim that these drugs" cause" AIDS. Scientific study and rejection of Duesberg' s risk- AIDS hypothesis. Several studies have specifically addressed Duesberg' s claim that recreational drug abuse or sexual promiscuity were responsible for the manifestations of AIDS. An early study of his claims, published in" Nature" in 1993, found Duesberg' s drug abuse- AIDS hypothesis to have" no basis in fact." A large prospective study followed a group of 715 homosexual men in the Vancouver, Canada, area; approximately half were HIV- seropositive or became so during the follow- up period, and the remainder were HIV- seronegative. After more than 8 years of follow- up, despite similar rates of drug use, sexual contact, and other supposed risk factors in both groups, only the HIV- positive group suffered from opportunistic infections. Similarly,CD4 counts dropped in the patients | who were HIV- infected, but |
remained stable in the HIV- negative patients, despite similar rates of risk behavior. The authors concluded that" the risk- AIDS hypothesis... is clearly rejected by our data," and that" the evidence supports the hypothesis that HIV-1hasanintegralroleintheCD4 depletion and progressive immune dysfunction that characterise AIDS." Similarly, the Multicenter AIDS Cohort Study( MACS) and the Women' s Interagency HIV Study( WIHS)— which between them observed more than 8, 000 Americans— demonstrated that" the presence of HIV infection is the only factor that is strongly and consistently associated with the conditions that define AIDS." A 2008 study found that recreational drug use( including cannabis, cocaine, poppers, and amphetamines)hadnoeffectonCD4orCD8 T- cell counts, providing further evidence against a role of recreational drugs as a cause of AIDS. Current AIDS definitions. Duesberg argued in 1989 that a significant number of AIDS victims had died without proof of HIV infection. However, with the use of modern culture techniques and polymerase chain reaction testing, HIV can be demonstrated in virtually all patients with AIDS. Since AIDS is now defined partially by the presence of HIV, Duesberg claims it is impossible by definition to offer evidence that AIDS doesn' t require HIV. However, the first definitions of AIDS mentioned no cause and the first AIDS diagnoses were made before HIV was discovered. The addition of HIV positivity to surveillance criteria as an absolutely necessary condition for case reporting occurred only in 1993, after a scientific consensus was established that HIV caused AIDS. AIDS in Africa. According to the Duesberg hypothesis, AIDS is not found in Africa. What Duesberg calls" the myth of an African AIDS epidemic," among people" exists for several reasons, including: Duesberg states that African AIDS cases are" a collection of long- established, indigenous diseases, such as chronic fevers, weight loss, alias" slim disease," diarrhea, and tuberculosis" that result from malnutrition and poor sanitation. African AIDS cases, though, have increased in the last three decades as HIV' s prevalence has increased but as malnutrition percentages and poor sanitation have declined in many African regions. In addition, while HIV and AIDS are more prevalent in urban than in rural settings in Africa, malnutrition and poor sanitation are found more commonly in rural than in urban settings. According to Duesberg, common diseases are easily misdiagnosed as AIDS in Africa because" the diagnosis of African AIDS is arbitrary" and does not include HIV testing. A definition of AIDS agreed upon in 1985 by the World Health Organization in Bangui did not require a positive HIV test, but since 1985, many African countries have added positive HIV tests to the Bangui criteria for AIDS or changed their definitions to match those of the U. S. Centers for Disease Control. One of the reasons for using more HIV tests despite their expense is that, rather than overestimating AIDS as Duesberg suggests, the Bangui definition alone excluded nearly half of African AIDS patients." Duesberg notes that diseases associated with AIDS differ between African and Western populations, concluding that the causes of immunodeficiency must be different. Tuberculosis is much more commonly diagnosed among AIDS patients in | Africa than in Western countries, |
while PCP conforms to the opposite pattern. Tuberculosis, though, had higher prevalence in Africa than in the West before the spread of HIV. In Africa and the United States, HIV has spurred a similar percentage increase in tuberculosis cases. PCP may be underestimated in Africa: since machinery" required for accurate testing is relatively rare in many resource- poor areas, including large parts of Africa, PCP is likely to be underdiagnosed in Africa. Consistent with this hypothesis, studies that report the highest rates of PCP in Africa are those that use the most advanced diagnostic methods" Duesberg also claims that Kaposi' s Sarcoma is" exclusively diagnosed in male homosexual risk groups using nitrite inhalants and other psychoactive drugs as aphrodisiacs", but the cancer is fairly common among heterosexuals in some parts of Africa, and is found in heterosexuals in the United States as well. Because reported AIDS cases in Africa and other parts of the developing world include a larger proportion of people who do not belong to Duesberg' s preferred risk groups of drug addicts and male homosexuals, Duesberg writes on his website that" There are no risk groups in Africa, like drug addicts and homosexuals." However, many studies have addressed the issue of risk groups in Africa and concluded that the risk of AIDS is not equally distributed. In addition, AIDS in Africa largely kills sexually active working- age adults. South African president Thabo Mbeki accepted Duesberg' s hypothesis and, through the mid-2000s, rejected offers of medical assistance to fight HIV infection, a policy of inaction that cost over 300, 000 lives. Duesberg claims that retroviruses like HIV must be harmless to survive. Duesberg argues that retroviruses like HIV must be harmless to survive: they do not kill cells and they do not cause cancer, he maintains. Duesberg writes," retroviruses do not kill cells because they depend on viable cells for the replication of their RNA from viral DNA integrated into cellular DNA." Duesberg elsewhere states that" the typical virus reproduces by entering a living cell and commandeering the cell' s resources in order to make new virus particles, a process that ends with the disintegration of the dead cell." Duesberg also rejects the involvement of retroviruses and other viruses in cancer. To him, virus- associated cancers are" freak accidents of nature" that do not warrant research programs such as the war on cancer. Duesberg rejects a role in cancer for numerous viruses, including leukemia viruses, Epstein– Barr virus, human papilloma virus, hepatitis B, feline leukemia virus, and human T- lymphotropic virus. Duesberg claims that the supposedly innocuous nature of all retroviruses is supported by what he considers to be their normal mode of proliferation: infection from mother to child" in utero". Duesberg does not suggest that HIV is an endogenous retrovirus, a virus integrated into the germline and genetically heritable: Scientific response to the Duesberg hypothesis. The consensus in the scientific community is that the Duesberg hypothesis has been refuted by a large and growing mass of evidence showing that HIV causes AIDS, that the amount of virus in the | blood correlates with disease progression, |
that a plausible mechanism for HIV' s action has been proposed, and that anti- HIV medication decreases mortality and opportunistic infection in people with AIDS. In issue of" Science"( Vol. 266, No. 5191), Duesberg' s methods and claims were evaluated in a group of articles. The authors concluded thatEffectiveness of antiretroviral medication. The vast majority of people with AIDS have never received antiretroviral drugs, including those in developed countries prior to the licensure of AZT( zidovudine) in 1987, and people in developing countries today where very few individuals have access to these medications. The NIAID reports thatOpponents claim that nearly all HIV- positive people will develop AIDS. Duesberg claims as support for his idea that many drug- free HIV- positive people have not yet developed AIDS; HIV/ AIDS scientists note that many drug- free HIV- positive people have developed AIDS, and that, in the absence of medical treatment or rare genetic factors postulated to delay disease progression, it is very likely that nearly all HIV- positive people will eventually develop AIDS. Scientists also note that HIV- negative drug users do not suffer from immune system collapse. DSL or digital subscriber line is a family of technologies that provide digital data transmission over the wires of a local telephone network. DSL may also refer to: Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233. 23 million years ago, although the exact origin and timing of the evolution of dinosaurs is the subject of active research. They became the dominant terrestrial vertebrates after the Triassic– Jurassic extinction event 201. 3 million years ago; their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are modern feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage to survive the Cretaceous– Paleogene extinction event approximately 66 million years ago. Dinosaurs can therefore be divided into avian dinosaurs, or birds; and the extinct non- avian dinosaurs, which are all dinosaurs other than birds. Dinosaurs are a varied group of animals from taxonomic, morphological and ecological standpoints. Birds, at over 10, 700 living species, are among the most diverse group of vertebrates. Using fossil evidence, paleontologists have identified over 900 distinct genera and more than 1, 000 different species of non- avian dinosaurs. Dinosaurs are represented on every continent by both extant species( birds) and fossil remains. Throughthefirsthalfofthe20th century, before birds were recognized as dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold- blooded. Mostresearchconductedsincethe1970s, however, has indicated that dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction. Some were herbivorous, others carnivorous. Evidence suggests that all dinosaurs were egg- laying; and that nest- building was a trait shared by many dinosaurs, both avian and non- avian. While dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, and some | extinct groups developed skeletal modifications |
such as bony armor and spines. While the dinosaurs' modern- day surviving avian lineage( birds) are generally small due to the constraints of flight, many prehistoric dinosaurs( non- avian and avian) were large- bodied— the largest sauropod dinosaurs are estimated to have reached lengths of and heights of and were the largest land animals of all time. The misconception that non- avian dinosaurs were uniformly gigantic is based in part on preservation bias, as large, sturdy bones are more likely to last until they are fossilized. Many dinosaurs were quite small, some measuring about in length.Thefirstdinosaurfossilswererecognizedintheearly19th century, with the name" dinosaur"( meaning" terrible lizard") having been coined by Sir Richard Owen in 1841 to refer to these" great fossil lizards". Since then, mounted fossil dinosaur skeletons have been major attractions at museums worldwide, and dinosaurs have become an enduring part of popular culture. The large sizes of some dinosaurs, as well as their seemingly monstrous and fantastic nature, have ensured their regular appearance in best- selling books and films, such as" Jurassic Park". Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, and new discoveries are regularly covered by the media. Definition. Under phylogenetic nomenclature, dinosaurs are usually defined as the group consisting of the most recent common ancestor( MRCA) of" Triceratops" and modern birds( Neornithes), and all its descendants. It has also been suggested that Dinosauria be defined with respect to the MRCA of" Megalosaurus" and" Iguanodon", because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria. Both definitions result in the same set of animals being defined as dinosaurs:" Dinosauria= Ornithischia+ Saurischia". This definition includes major groups such as ankylosaurians( armored herbivorous quadrupeds), stegosaurians( plated herbivorous quadrupeds), ceratopsians( bipedal or quadrupedal herbivores with neck frills), pachycephalosaurians( bipedal herbivores with thick skulls), ornithopods( bipedal or quadrupedal herbivores including" duck- bills"), theropods( mostly bipedal carnivores and birds), and sauropodomorphs( mostly large herbivorous quadrupeds with long necks and tails). Birds are now recognized as being the sole surviving lineage of theropod dinosaurs. In traditional taxonomy, birds were considered a separate class that had evolved from dinosaurs, a distinct superorder. However, a majority of contemporary paleontologists concerned with dinosaurs reject the traditional style of classification in favor of phylogenetic taxonomy; this approach requires that, for a group to be natural, all descendants of members of the group must be included in the group as well. Birds are thus considered to be dinosaurs and dinosaurs are, therefore, not extinct. Birds are classified as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs. Research by Matthew G. Baron, David B. Norman, and Paul M. Barrett in 2017 suggested a radical revision of dinosaurian systematics. Phylogenetic analysis by Baron" et al." recovered the Ornithischia as being closer to the Theropoda than the Sauropodomorpha, as opposed to the traditional union of theropods with sauropodomorphs. They resurrected the clade Ornithoscelida to refer to the group containing Ornithischia and Theropoda. Dinosauria itself was re- defined as the last common ancestor | of" Triceratops horridus"," Passer domesticus" |
and" Diplodocus carnegii", and all of its descendants, to ensure that sauropods and kin remain included as dinosaurs. General description. Using one of the above definitions, dinosaurs can be generally described as archosaurs with hind limbs held erect beneath the body. Other prehistoric animals, including pterosaurs, mosasaurs, ichthyosaurs, plesiosaurs, and" Dimetrodon", while often popularly conceived of as dinosaurs, are not taxonomically classified as dinosaurs. Pterosaurs are distantly related to dinosaurs, being members of the clade Ornithodira. The other groups mentioned are, like dinosaurs and pterosaurs, members of Sauropsida( the reptile and bird clade), except" Dimetrodon"( which is a synapsid). None of them had the erect hind limb posture characteristic of true dinosaurs. Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic Era, especially the Jurassic and Cretaceous periods. Other groups of animals were restricted in size and niches; mammals, for example, rarely exceeded the size of a domestic cat, and were generally rodent- sized carnivores of small prey. They have always been recognized as an extremely varied group of animals; over 900 non- avian dinosaur genera have been identified with certainty as of 2018, and the total number of genera preserved in the fossil record has been estimated at around 1850, nearly 75% of which remain to be discovered, and 1124 species by 2016. A 1995 study predicted that about 3, 400 dinosaur genera ever existed, including many that would not have been preserved in the fossil record. In 2016, the estimated number of dinosaur species that existed in the Mesozoic was 1, 543– 2, 468. In 2021, the number of modern- day birds( avian dinosaurs) was estimated to be at 10, 806 species. Some are herbivorous, others carnivorous, including seed- eaters, fish- eaters, insectivores, and omnivores. While dinosaurs were ancestrally bipedal( as are all modern birds), some prehistoric species were quadrupeds, and others, such as" Anchisaurus" and" Iguanodon", could walk just as easily on two or four legs. Cranial modifications like horns and crests are common dinosaurian traits, and some extinct species had bony armor. Although known for large size, many Mesozoic dinosaurs were human- sized or smaller, and modern birds are generally small in size. Dinosaurs today inhabit every continent, and fossils show that they had achieved global distribution by at least the Early Jurassic epoch. Modern birds inhabit most available habitats, from terrestrial to marine, and there is evidence that some non- avian dinosaurs( such as" Microraptor") could fly or at least glide, and others, such as spinosaurids, had semiaquatic habits. Distinguishing anatomical features. While recent discoveries have made it more difficult to present a universally agreed- upon list of their distinguishing features, nearly all dinosaurs discovered so far share certain modifications to the ancestral archosaurian skeleton, or are clearly descendants of older dinosaurs showing these modifications. Although some later groups of dinosaurs featured further modified versions of these traits, they are considered typical for Dinosauria; the earliest dinosaurs had them and passed them on to their descendants. Such modifications, originating in the most recent common ancestor of a certain taxonomic group, are called the synapomorphies of such a | group. A detailed assessment of |
archosaur interrelations by Sterling Nesbitt confirmed or found the following twelve unambiguous synapomorphies, some previously known: Nesbitt found a number of further potential synapomorphies and discounted a number of synapomorphies previously suggested. Some of these are also present in silesaurids, which Nesbitt recovered as a sister group to Dinosauria, including a large anterior trochanter, metatarsals II and IV of subequal length, reduced contact between ischium and pubis, the presence of a cnemial crest on the tibia and of an ascending process on the astragalus, and many others. A variety of other skeletal features are shared by dinosaurs. However, because they are either common to other groups of archosaurs or were not present in all early dinosaurs, these features are not considered to be synapomorphies. For example, as diapsids, dinosaurs ancestrally had two pairs of Infratemporal fenestrae( openings in the skull behind the eyes), and as members of the diapsid group Archosauria, had additional openings in the snout and lower jaw. Additionally, several characteristics once thought to be synapomorphies are now known to have appeared before dinosaurs, or were absent in the earliest dinosaurs and independently evolved by different dinosaur groups. These include an elongated scapula, or shoulder blade; a sacrum composed of three or more fused vertebrae( three are found in some other archosaurs, but only two are found in" Herrerasaurus"); and a perforate acetabulum, or hip socket, with a hole at the center of its inside surface( closed in" Saturnalia tupiniquim", for example). Another difficulty of determining distinctly dinosaurian features is that early dinosaurs and other archosaurs from the Late Triassic epoch are often poorly known and were similar in many ways; these animals have sometimes been misidentified in the literature. Dinosaurs stand with their hind limbs erect in a manner similar to most modern mammals, but distinct from most other reptiles, whose limbs sprawl out to either side. This posture is due to the development of a laterally facing recess in the pelvis( usually an open socket) and a corresponding inwardly facing distinct head on the femur. Their erect posture enabled early dinosaurs to breathe easily while moving, which likely permitted stamina and activity levels that surpassed those of" sprawling" reptiles. Erect limbs probably also helped support the evolution of large size by reducing bending stresses on limbs. Some non- dinosaurian archosaurs, including rauisuchians, also had erect limbs but achieved this by a" pillar- erect" configuration of the hip joint, where instead of having a projection from the femur insert on a socket on the hip, the upper pelvic bone was rotated to form an overhanging shelf. History of study. Pre- scientific history. Dinosaur fossils have been known for millennia, although their true nature was not recognized. The Chinese considered them to be dragon bones and documented them as such. For example," Huayang Guo Zhi"(), a gazetteer compiled by Chang Qu() during the Western Jin Dynasty( 265– 316), reported the discovery of dragon bones at Wucheng in Sichuan Province. Villagers in central China have long unearthed fossilized" dragon bones" for use in traditional medicines. In Europe, dinosaur fossils were generally | believed to be the remains |
of giants and other biblical creatures. Early dinosaur research.Scholarlydescriptionsofwhatwouldnowberecognizedasdinosaurbonesfirstappearedinthelate17th century in England. Part of a bone, now known to have been the femur of a" Megalosaurus", was recovered from a limestone quarry at Cornwell near Chipping Norton, Oxfordshire, in 1676. The fragment was sent to Robert Plot, Professor of Chemistry at the University of Oxford and first curator of the Ashmolean Museum, who published a description in his" The Natural History of Oxford- shire"( 1677). He correctly identified the bone as the lower extremity of the femur of a large animal, and recognized that it was too large to belong to any known species. He, therefore, concluded it to be the femur of a huge human, perhaps a Titan or another type of giant featured in legends. Edward Lhuyd, a friend of Sir Isaac Newton, published" Lithophylacii Britannici ichnographia"( 1699), the first scientific treatment of what would now be recognized as a dinosaur when he described and named a sauropod tooth," Rutellum impicatum", that had been found in Caswell, near Witney, Oxfordshire. Between 1815 and 1824, the Rev William Buckland, the first Reader of Geology at the University of Oxford, collected more fossilized bones of" Megalosaurus" and became the first person to describe a non- avian dinosaur in a scientific journal. The second non- avian dinosaur genus to be identified," Iguanodon", was discovered in 1822 by Mary Ann Mantell– the wife of English geologist Gideon Mantell. Gideon Mantell recognized similarities between his fossils and the bones of modern iguanas. He published his findings in 1825. The study of these" great fossil lizards" soon became of great interest to European and American scientists, and in 1841 the English paleontologist Sir Richard Owen coined the term" dinosaur", using it to refer to the" distinct tribe or sub- order of Saurian Reptiles" that were then being recognized in England and around the world. The term is derived. Though the taxonomic name has often been interpreted as a reference to dinosaurs' teeth, claws, and other fearsome characteristics, Owen intended it to also evoke their size and majesty. Owen recognized that the remains that had been found so far," Iguanodon"," Megalosaurus" and" Hylaeosaurus", shared a number of distinctive features, and so decided to present them as a distinct taxonomic group. With the backing of Prince Albert, the husband of Queen Victoria, Owen established the Natural History Museum, London, to display the national collection of dinosaur fossils and other biological and geological exhibits. Discoveries in North America. In 1858, William Parker Foulke discovered the first known American dinosaur, in marl pits in the small town of Haddonfield, New Jersey.( Although fossils had been found before, their nature had not been correctly discerned.) The creature was named" Hadrosaurus foulkii". It was an extremely important find:" Hadrosaurus" was one of the first nearly complete dinosaur skeletons found( the first was in 1834, in Maidstone, England), and it was clearly a bipedal creature. This was a revolutionary discovery as, until that point, most scientists had believed dinosaurs walked on four feet, like other lizards. Foulke' s discoveries sparked a wave of | interests in dinosaurs in the |
United States, known as dinosaur mania. Dinosaur mania was exemplified by the fierce rivalry between Edward Drinker Cope and Othniel Charles Marsh, both of whom raced to be the first to find new dinosaurs in what came to be known as the Bone Wars. This fight between the two scientists lasted for over 30 years, ending in 1897 when Cope died after spending his entire fortune on the dinosaur hunt. Unfortunately, many valuable dinosaur specimens were damaged or destroyed due to the pair' s rough methods: for example, their diggers often used dynamite to unearth bones. Modern paleontologists would find such methods crude and unacceptable, since blasting easily destroys fossil and stratigraphic evidence. Despite their unrefined methods, the contributions of Cope and Marsh to paleontology were vast: Marsh unearthed 86 new species of dinosaur and Cope discovered 56, a total of 142 new species. Cope' s collection is now at the American Museum of Natural History, while Marsh' s is at the Peabody Museum of Natural History at Yale University." Dinosaur renaissance" and beyond.Thefieldofdinosaurresearchhasenjoyedasurgeinactivitythatbeganinthe1970s and is ongoing. This was triggered, in part, by John Ostrom' s discovery and 1969 description of" Deinonychus", an active predator that may have been warm- blooded, in marked contrast to the then- prevailing image of dinosaurs as sluggish and cold- blooded. Vertebrate paleontology has become a global science. Major new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including India, South America, Madagascar, Antarctica, and most significantly China( the well- preserved feathered dinosaurs in China have further consolidated the link between dinosaurs and their living descendants, modern birds). The widespread application of cladistics, which rigorously analyzes the relationships between biological organisms, has also proved tremendously useful in classifying dinosaurs. Cladistic analysis, among other modern techniques, helps to compensate for an often incomplete and fragmentary fossil record. Soft tissue and DNA. One of the best examples of soft- tissue impressions in a fossil dinosaur was discovered in the Pietraroia Plattenkalk in southern Italy. The discovery was reported in 1998, and described the specimen of a small, juvenile coelurosaur," Scipionyx samniticus". The fossil includes portions of the intestines, colon, liver, muscles, and windpipe of this dinosaur. In the March 2005 issue of" Science", the paleontologist Mary Higby Schweitzer and her team announced the discovery of flexible material resembling actual soft tissue inside a 68- million- year- old" Tyrannosaurus rex" leg bone from the Hell Creek Formation in Montana. After recovery, the tissue was rehydrated by the science team. When the fossilized bone was treated over several weeks to remove mineral content from the fossilized bone- marrow cavity( a process called demineralization), Schweitzer found evidence of intact structures such as blood vessels, bone matrix, and connective tissue( bone fibers). Scrutiny under the microscope further revealed that the putative dinosaur soft tissue had retained fine structures( microstructures) even at the cellular level. The exact nature and composition of this material, and the implications of Schweitzer' s discovery, are not yet clear. In 2009, a team including Schweitzer announced that, using even more careful methodology, they had duplicated | their results by finding similar |
soft tissue in a duck- billed dinosaur," Brachylophosaurus canadensis", found in the Judith River Formation of Montana. This included even more detailed tissue, down to preserved bone cells that seem to have visible remnants of nuclei and what seem to be red blood cells. Among other materials found in the bone was collagen, as in the" Tyrannosaurus" bone. The type of collagen an animal has in its bones varies according to its DNA and, in both cases, this collagen was of the same type found in modern chickens and ostriches. The extraction of ancient DNA from dinosaur fossils has been reported on two separate occasions; upon further inspection and peer review, however, neither of these reports could be confirmed. However, a functional peptide involved in the vision of a theoretical dinosaur has been inferred using analytical phylogenetic reconstruction methods on gene sequences of related modern species such as reptiles and birds. In addition, several proteins, including hemoglobin, have putatively been detected in dinosaur fossils. In 2015, researchers reported finding structures similar to blood cells and collagen fibers, preserved in the bone fossils of six Cretaceous dinosaur specimens, which are approximately 75 million years old. Evolutionary history. Origins and early evolution. Dinosaurs diverged from their archosaur ancestors during the Middle to Late Triassic epochs, roughly 20 million years after the devastating Permian– Triassic extinction event wiped out an estimated 96% of all marine species and 70% of terrestrial vertebrate species approximately 252 million years ago. Radiometric dating of the Ischigualasto Formation of Argentina where the early dinosaur genus" Eoraptor" was found date it as 231. 4 million years old." Eoraptor" is thought to resemble the common ancestor of all dinosaurs; if this is true, its traits suggest that the first dinosaurs were small, bipedal predators. The discovery of primitive, dinosaur- like ornithodirans such as" Lagosuchus" and" Lagerpeton" in Argentina in the Carnian epoch of the Triassic, around 233 million years ago, supports this view; analysis of recovered fossils suggests that these animals were indeed small, bipedal predators. Dinosaurs may have appeared as early as the Anisian epoch of the Triassic, 245 million years ago, as evidenced by remains of the genus" Nyasasaurus" from that period. However, its known fossils are too fragmentary to tell if it was a dinosaur or only a close relative. Paleontologist Max C. Langer" et al."( 2018) determined that" Staurikosaurus" from the Santa Maria Formation dates to 233. 23 million years ago, making it older in geologic age than" Eoraptor". When dinosaurs appeared, they were not the dominant terrestrial animals. The terrestrial habitats were occupied by various types of archosauromorphs and therapsids, like cynodonts and rhynchosaurs. Their main competitors were the pseudosuchians, such as aetosaurs, ornithosuchids and rauisuchians, which were more successful than the dinosaurs. Most of these other animals became extinct in the Triassic, in one of two events. First, at about 215 million years ago, a variety of basal archosauromorphs, including the protorosaurs, became extinct. This was followed by the Triassic– Jurassic extinction event( about 201 million years ago), that saw the end of most of the | other groups of early archosaurs, |
like aetosaurs, ornithosuchids, phytosaurs, and rauisuchians. Rhynchosaurs and dicynodonts survived( at least in some areas) at least as late as early– mid Norian and late Norian or earliest Rhaetian stages, respectively, and the exact date of their extinction is uncertain. These losses left behind a land fauna of crocodylomorphs, dinosaurs, mammals, pterosaurians, and turtles. The first few lines of early dinosaurs diversified through the Carnian and Norian stages of the Triassic, possibly by occupying the niches of the groups that became extinct. Also notably, there was a heightened rate of extinction during the Carnian pluvial event. Evolution and paleobiogeography. Dinosaur evolution after the Triassic followed changes in vegetation and the location of continents. In the Late Triassic and Early Jurassic, the continents were connected as the single landmass Pangaea, and there was a worldwide dinosaur fauna mostly composed of coelophysoid carnivores and early sauropodomorph herbivores. Gymnosperm plants( particularly conifers), a potential food source, radiated in the Late Triassic. Early sauropodomorphs did not have sophisticated mechanisms for processing food in the mouth, and so must have employed other means of breaking down food farther along the digestive tract. The general homogeneity of dinosaurian faunas continued into the Middle and Late Jurassic, where most localities had predators consisting of ceratosaurians, megalosauroids, and allosauroids, and herbivores consisting of stegosaurian ornithischians and large sauropods. Examples of this include the Morrison Formation of North America and Tendaguru Beds of Tanzania. Dinosaurs in China show some differences, with specialized metriacanthosaurid theropods and unusual, long- necked sauropods like" Mamenchisaurus". Ankylosaurians and ornithopods were also becoming more common, but primitive sauropodomorphs had become extinct. Conifers and pteridophytes were the most common plants. Sauropods, like earlier sauropodomorphs, were not oral processors, but ornithischians were evolving various means of dealing with food in the mouth, including potential cheek- like organs to keep food in the mouth, and jaw motions to grind food. Another notable evolutionary event of the Jurassic was the appearance of true birds, descended from maniraptoran coelurosaurians. By the Early Cretaceous and the ongoing breakup of Pangaea, dinosaurs were becoming strongly differentiated by landmass. The earliest part of this time saw the spread of ankylosaurians, iguanodontians, and brachiosaurids through Europe, North America, and northern Africa. These were later supplemented or replaced in Africa by large spinosaurid and carcharodontosaurid theropods, and rebbachisaurid and titanosaurian sauropods, also found in South America. In Asia, maniraptoran coelurosaurians like dromaeosaurids, troodontids, and oviraptorosaurians became the common theropods, and ankylosaurids and early ceratopsians like" Psittacosaurus" became important herbivores. Meanwhile, Australia was home to a fauna of basal ankylosaurians, hypsilophodonts, and iguanodontians. The stegosaurians appear to have gone extinct at some point in the late Early Cretaceous or early Late Cretaceous. A major change in the Early Cretaceous, which would be amplified in the Late Cretaceous, was the evolution of flowering plants. At the same time, several groups of dinosaurian herbivores evolved more sophisticated ways to orally process food. Ceratopsians developed a method of slicing with teeth stacked on each other in batteries, and iguanodontians refined a method of grinding with dental batteries, taken to its extreme | in hadrosaurids. Some sauropods also |
evolved tooth batteries, best exemplified by the rebbachisaurid" Nigersaurus". There were three general dinosaur faunas in the Late Cretaceous. In the northern continents of North America and Asia, the major theropods were tyrannosaurids and various types of smaller maniraptoran theropods, with a predominantly ornithischian herbivore assemblage of hadrosaurids, ceratopsians, ankylosaurids, and pachycephalosaurians. In the southern continents that had made up the now- splitting supercontinent Gondwana, abelisaurids were the common theropods, and titanosaurian sauropods the common herbivores. Finally, in Europe, dromaeosaurids, rhabdodontid iguanodontians, nodosaurid ankylosaurians, and titanosaurian sauropods were prevalent. Flowering plants were greatly radiating, with the first grasses appearing by the end of the Cretaceous. Grinding hadrosaurids and shearing ceratopsians became very diverse across North America and Asia. Theropods were also radiating as herbivores or omnivores, with therizinosaurians and ornithomimosaurians becoming common. The Cretaceous– Paleogene extinction event, which occurred approximately 66 million years ago at the end of the Cretaceous, caused the extinction of all dinosaur groups except for the neornithine birds. Some other diapsid groups, including crocodilians, dyrosaurs, sebecosuchians, turtles, lizards, snakes, sphenodontians, and choristoderans, also survived the event. The surviving lineages of neornithine birds, including the ancestors of modern ratites, ducks and chickens, and a variety of waterbirds, diversified rapidly at the beginning of the Paleogene period, entering ecological niches left vacant by the extinction of Mesozoic dinosaur groups such as the arboreal enantiornithines, aquatic hesperornithines, and even the larger terrestrial theropods( in the form of" Gastornis", eogruiids, bathornithids, ratites, geranoidids, mihirungs, and" terror birds"). It is often stated that mammals out- competed the neornithines for dominance of most terrestrial niches but many of these groups co- existed with rich mammalian faunas for most of the Cenozoic Era. Terror birds and bathornithids occupied carnivorous guilds alongside predatory mammals, and ratites are still fairly successful as mid- sized herbivores; eogruiids similarly lasted from the Eocene to Pliocene, only becoming extinct very recently after over 20 million years of co- existence with many mammal groups. Classification. Dinosaurs belong to a group known as archosaurs, which also includes modern crocodilians. Within the archosaur group, dinosaurs are differentiated most noticeably by their gait. Dinosaur legs extend directly beneath the body, whereas the legs of lizards and crocodilians sprawl out to either side. Collectively, dinosaurs as a clade are divided into two primary branches, Saurischia and Ornithischia. Saurischia includes those taxa sharing a more recent common ancestor with birds than with Ornithischia, while Ornithischia includes all taxa sharing a more recent common ancestor with" Triceratops" than with Saurischia. Anatomically, these two groups can be distinguished most noticeably by their pelvic structure. Early saurischians—" lizard- hipped", from the Greek'() meaning" lizard" and'() meaning" hip joint"— retained the hip structure of their ancestors, with a pubis bone directed cranially, or forward. This basic form was modified by rotating the pubis backward to varying degrees in several groups(" Herrerasaurus", therizinosauroids, dromaeosaurids, and birds). Saurischia includes the theropods( exclusively bipedal and with a wide variety of diets) and sauropodomorphs( long- necked herbivores which include advanced, quadrupedal groups). By contrast, ornithischians—" bird- hipped", from the Greek" ornitheios"( ὀρνίθειος) meaning" of | a bird" and" ischion"( ἰσχίον) |
meaning" hip joint"— had a pelvis that superficially resembled a bird' s pelvis: the pubic bone was oriented caudally( rear- pointing). Unlike birds, the ornithischian pubis also usually had an additional forward- pointing process. Ornithischia includes a variety of species that were primarily herbivores. Despite the terms" bird hip"( Ornithischia) and" lizard hip"( Saurischia), birds are not part of Ornithischia. Birds instead belong to Saurischia, the“ lizard- hipped” dinosaurs— birds evolved from earlier dinosaurs with" lizard hips". Taxonomy. The following is a simplified classification of dinosaur groups based on their evolutionary relationships, and organized based on the list of Mesozoic dinosaur species provided by Holtz( 2007). A more detailed version can be found at Dinosaur classification. The dagger(†) is used to signify groups with no living members. Timeline of major groups. Timeline of major dinosaur groups per Holtz( 2007). Paleobiology. Knowledge about dinosaurs is derived from a variety of fossil and non- fossil records, including fossilized bones, feces, trackways, gastroliths, feathers, impressions of skin, internal organs and other soft tissues. Many fields of study contribute to our understanding of dinosaurs, including physics( especially biomechanics), chemistry, biology, and the Earth sciences( of which paleontology is a sub- discipline). Two topics of particular interest and study have been dinosaur size and behavior. Size. Current evidence suggests that dinosaur average size varied through the Triassic, Early Jurassic, Late Jurassic and Cretaceous. Predatory theropod dinosaurs, which occupied most terrestrial carnivore niches during the Mesozoic, most often fall into the category when sorted by estimated weight into categories based on order of magnitude, whereas recent predatory carnivoran mammals peak in the category. The mode of Mesozoic dinosaur body masses is between. This contrasts sharply with the average size of Cenozoic mammals, estimated by the National Museum of Natural History as about. The sauropods were the largest and heaviest dinosaurs. For much of the dinosaur era, the smallest sauropods were larger than anything else in their habitat, and the largest was an order of magnitude more massive than anything else that has since walked the Earth. Giant prehistoric mammals such as" Paraceratherium"( the largest land mammal ever) were dwarfed by the giant sauropods, and only modern whales approach or surpass them in size. There are several proposed advantages for the large size of sauropods, including protection from predation, reduction of energy use, and longevity, but it may be that the most important advantage was dietary. Large animals are more efficient at digestion than small animals, because food spends more time in their digestive systems. This also permits them to subsist on food with lower nutritive value than smaller animals. Sauropod remains are mostly found in rock formations interpreted as dry or seasonally dry, and the ability to eat large quantities of low- nutrient browse would have been advantageous in such environments. Largest and smallest. Scientists will probably never be certain of the largest and smallest dinosaurs to have ever existed. This is because only a tiny percentage of animals were ever fossilized and most of these remain buried in the earth. Few of the specimens that are recovered | are complete skeletons, and impressions |
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