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As a model species
Populus trichocarpa has several qualities that makes it a good model species for trees:
Model genome size (although significantly larger than the other model plant, Arabidopsis thaliana)
Rapid growth (for a tree)
Reaches reproductive maturity 4–6 years
Economically important
It represents a phenotypically diverse genus
For these reasons, the species has been extensively studied. Its genome sequence was published in 2006. More than 121,000 expressed sequence tags have been sequenced from it. The wide range of topics studied by using P. trichocarpa include the effects of ethylene, lignin biosynthesis, drought tolerance, and wood formation.
Cultural significance
The Chehalis believed that the tree was intelligent and had a form of special physical agency, moving on its own without the need of wind. Due to this belief, they refused to use it for firewood.
Genome
The sequence of P. trichocarpa is that of an individual female specimen "Nisqually-1", named after the Nisqually River in Washington, where the specimen was collected. The sequencing was performed at the Joint Genome Institute using the shotgun method. The depth of the sequencing was about 7.5 x (meaning that each base pair was sequenced on average 7.5 times). Genome annotation was done primarily by the Joint Genome Institute, the Oak Ridge National Laboratory, the Umeå Plant Science Centre, and Genome Canada.
Prior to the publication of P. trichocarpa genome the only available plant genomes were those of thale cress and rice, both of which are herbaceous. P. trichocarpa is the first woody plant genome to be sequenced. Considering the economic importance of wood and wood products, the availability of a tree genome was necessary. The sequence also allows evolutionary comparisons and the elucidation of basic molecular differences between herbaceous and woody plants.
Characteristics
Size: 485 million base pairs (human genome: 3 billion base pairs)
Proportion of heterochromatin to euchromatin: 3:7
Number of chromosomes: 19
Number of putative genes: 45,555, the largest number of genes ever recorded (estimate in September 2008)
Mitochondrial genome: 803,000 base pairs, 52 genes
Chloroplast genome: 157,000 base pairs, 101 genes | Populus trichocarpa | Wikipedia | 481 | 7189344 | https://en.wikipedia.org/wiki/Populus%20trichocarpa | Biology and health sciences | Malpighiales | Plants |
Somatic mosaicism
Genome-wide analysis of 11 clumps of P. trichocarpa trees reveals significant genetic differences between the roots and the leaves and branches of the same tree. The variation within a specimen is as much as found between unrelated trees. These results may be important in resolving debate in evolutionary biology regarding somatic mutation (that evolution can occur within individuals, not solely among populations), with a variety of implications. | Populus trichocarpa | Wikipedia | 87 | 7189344 | https://en.wikipedia.org/wiki/Populus%20trichocarpa | Biology and health sciences | Malpighiales | Plants |
Tarski's axioms are an axiom system for Euclidean geometry, specifically for that portion of Euclidean geometry that is formulable in first-order logic with identity (i.e. is formulable as an elementary theory). As such, it does not require an underlying set theory. The only primitive objects of the system are "points" and the only primitive predicates are "betweenness" (expressing the fact that a point lies on a line segment between two other points) and "congruence" (expressing the fact that the distance between two points equals the distance between two other points). The system contains infinitely many axioms.
The axiom system is due to Alfred Tarski who first presented it in 1926. Other modern axiomizations of Euclidean geometry are Hilbert's axioms (1899) and Birkhoff's axioms (1932).
Using his axiom system, Tarski was able to show that the first-order theory of Euclidean geometry is consistent, complete and decidable: every sentence in its language is either provable or disprovable from the axioms, and we have an algorithm which decides for any given sentence whether it is provable or not.
Overview
Early in his career Tarski taught geometry and researched set theory. His coworker Steven Givant (1999) explained Tarski's take-off point:
From Enriques, Tarski learned of the work of Mario Pieri, an Italian geometer who was strongly influenced by Peano. Tarski preferred Pieri's system [of his Point and Sphere memoir], where the logical structure and the complexity of the axioms were more transparent.
Givant then says that "with typical thoroughness" Tarski devised his system:
What was different about Tarski's approach to geometry? First of all, the axiom system was much simpler than any of the axiom systems that existed up to that time. In fact the length of all of Tarski's axioms together is not much more than just one of Pieri's 24 axioms. It was the first system of Euclidean geometry that was simple enough for all axioms to be expressed in terms of the primitive notions only, without the help of defined notions. Of even greater importance, for the first time a clear distinction was made between full geometry and its elementary — that is, its first order — part. | Tarski's axioms | Wikipedia | 487 | 2181360 | https://en.wikipedia.org/wiki/Tarski%27s%20axioms | Mathematics | Axiomatic systems | null |
Like other modern axiomatizations of Euclidean geometry, Tarski's employs a formal system consisting of symbol strings, called sentences, whose construction respects formal syntactical rules, and rules of proof that determine the allowed manipulations of the sentences. Unlike some other modern axiomatizations, such as Birkhoff's and Hilbert's, Tarski's axiomatization has no primitive objects other than points, so a variable or constant cannot refer to a line or an angle. Because points are the only primitive objects, and because Tarski's system is a first-order theory, it is not even possible to define lines as sets of points. The only primitive relations (predicates) are "betweenness" and "congruence" among points.
Tarski's axiomatization is shorter than its rivals, in a sense Tarski and Givant (1999) make explicit. It is more concise than Pieri's because Pieri had only two primitive notions while Tarski introduced three: point, betweenness, and congruence. Such economy of primitive and defined notions means that Tarski's system is not very convenient for doing Euclidean geometry. Rather, Tarski designed his system to facilitate its analysis via the tools of mathematical logic, i.e., to facilitate deriving its metamathematical properties. Tarski's system has the unusual property that all sentences can be written in universal-existential form, a special case of the prenex normal form. This form has all universal quantifiers preceding any existential quantifiers, so that all sentences can be recast in the form This fact allowed Tarski to prove that Euclidean geometry is decidable: there exists an algorithm which can determine the truth or falsity of any sentence. Tarski's axiomatization is also complete. This does not contradict Gödel's first incompleteness theorem, because Tarski's theory lacks the expressive power needed to interpret Robinson arithmetic .
The axioms | Tarski's axioms | Wikipedia | 420 | 2181360 | https://en.wikipedia.org/wiki/Tarski%27s%20axioms | Mathematics | Axiomatic systems | null |
Alfred Tarski worked on the axiomatization and metamathematics of Euclidean geometry intermittently from 1926 until his death in 1983, with Tarski (1959) heralding his mature interest in the subject. The work of Tarski and his students on Euclidean geometry culminated in the monograph Schwabhäuser, Szmielew, and Tarski (1983), which set out the 10 axioms and one axiom schema shown below, the associated metamathematics, and a fair bit of the subject. Gupta (1965) made important contributions, and Tarski and Givant (1999) discuss the history.
Fundamental relations
These axioms are a more elegant version of a set Tarski devised in the 1920s as part of his investigation of the metamathematical properties of Euclidean plane geometry. This objective required reformulating that geometry as a first-order theory. Tarski did so by positing a universe of points, with lower case letters denoting variables ranging over that universe. Equality is provided by the underlying logic (see First-order logic#Equality and its axioms). Tarski then posited two primitive relations:
Betweenness, a triadic relation. The atomic sentence Bxyz denotes that the point y is "between" the points x and z, in other words, that y is a point on the line segment xz. (This relation is interpreted inclusively, so that Bxyz is trivially true whenever x=y or y=z).
Congruence (or "equidistance"), a tetradic relation. The atomic sentence Cwxyz or commonly wx ≡ yz can be interpreted as wx is congruent to yz, in other words, that the length of the line segment wx is equal to the length of the line segment yz.
Betweenness captures the affine aspect (such as the parallelism of lines) of Euclidean geometry; congruence, its metric aspect (such as angles and distances). The background logic includes identity, a binary relation denoted by =.
The axioms below are grouped by the types of relation they invoke, then sorted, first by the number of existential quantifiers, then by the number of atomic sentences. The axioms should be read as universal closures; hence any free variables should be taken as tacitly universally quantified.
Congruence axioms
Reflexivity of Congruence
Identity of Congruence | Tarski's axioms | Wikipedia | 507 | 2181360 | https://en.wikipedia.org/wiki/Tarski%27s%20axioms | Mathematics | Axiomatic systems | null |
Transitivity of Congruence
Commentary
While the congruence relation is, formally, a 4-way relation among points, it may also be thought of, informally, as a binary relation between two line segments and . The "Reflexivity" and "Transitivity" axioms above, combined, prove both:
that this binary relation is in fact an equivalence relation
it is reflexive: .
it is symmetric .
it is transitive .
and that the order in which the points of a line segment are specified is irrelevant.
.
.
.
The "transitivity" axiom asserts that congruence is Euclidean, in that it respects the first of Euclid's "common notions".
The "Identity of Congruence" axiom states, intuitively, that if xy is congruent with a segment that begins and ends at the same point, x and y are the same point. This is closely related to the notion of reflexivity for binary relations.
Betweenness axioms
Identity of Betweenness
The only point on the line segment is itself.
Axiom of Pasch
Axiom schema of Continuity
Let φ(x) and ψ(y) be first-order formulae containing no free instances of either a or b. Let there also be no free instances of x in ψ(y) or of y in φ(x). Then all instances of the following schema are axioms:
Let r be a ray with endpoint a. Let the first order formulae φ and ψ define subsets X and Y of r, such that every point in Y is to the right of every point of X (with respect to a). Then there exists a point b in r lying between X and Y. This is essentially the Dedekind cut construction, carried out in a way that avoids quantification over sets.
Note that the formulae φ(x) and ψ(y) may contain parameters, i.e. free variables different from a, b, x, y. And indeed, each instance of the axiom scheme that does not contain parameters can be proven from the other axioms.
Lower Dimension
There exist three noncollinear points. Without this axiom, the theory could be modeled by the one-dimensional real line, a single point, or even the empty set.
Congruence and betweenness | Tarski's axioms | Wikipedia | 477 | 2181360 | https://en.wikipedia.org/wiki/Tarski%27s%20axioms | Mathematics | Axiomatic systems | null |
Upper Dimension
Three points equidistant from two distinct points form a line. Without this axiom, the theory could be modeled by three-dimensional or higher-dimensional space.
Axiom of Euclid
Three variants of this axiom can be given, labeled A, B and C below. They are equivalent to each other given the remaining Tarski's axioms, and indeed equivalent to Euclid's parallel postulate.
A:
Let a line segment join the midpoint of two sides of a given triangle. That line segment will be half as long as the third side. This is equivalent to the interior angles of any triangle summing to two right angles.
B:
Given any triangle, there exists a circle that includes all of its vertices.
C:
Given any angle and any point v in its interior, there exists a line segment including v, with an endpoint on each side of the angle.
Each variant has an advantage over the others:
A dispenses with existential quantifiers;
B has the fewest variables and atomic sentences;
C requires but one primitive notion, betweenness. This variant is the usual one given in the literature.
Five Segment
Begin with two triangles, xuz and x'u'z'. Draw the line segments yu and y'u', connecting a vertex of each triangle to a point on the side opposite to the vertex. The result is two divided triangles, each made up of five segments. If four segments of one triangle are each congruent to a segment in the other triangle, then the fifth segments in both triangles must be congruent.
This is equivalent to the side-angle-side rule for determining that two triangles are congruent; if the angles uxz and u'x'z' are congruent (there exist congruent triangles xuz and x'u'z'), and the two pairs of incident sides are congruent (xu ≡ x'u' and xz ≡ x'z'), then the remaining pair of sides is also congruent (uz ≡ u'z).
Segment Construction
For any point y, it is possible to draw in any direction (determined by x) a line congruent to any segment ab. | Tarski's axioms | Wikipedia | 465 | 2181360 | https://en.wikipedia.org/wiki/Tarski%27s%20axioms | Mathematics | Axiomatic systems | null |
Discussion
According to Tarski and Givant (1999: 192-93), none of the above axioms are fundamentally new. The first four axioms establish some elementary properties of the two primitive relations. For instance, Reflexivity and Transitivity of Congruence establish that congruence is an equivalence relation over line segments. The Identity of Congruence and of Betweenness govern the trivial case when those relations are applied to nondistinct points. The theorem xy≡zz ↔ x=y ↔ Bxyx extends these Identity axioms.
A number of other properties of Betweenness are derivable as theorems including:
Reflexivity: Bxxy ;
Symmetry: Bxyz → Bzyx ;
Transitivity: (Bxyw ∧ Byzw) → Bxyz ;
Connectivity: (Bxyw ∧ Bxzw) → (Bxyz ∨ Bxzy).
The last two properties totally order the points making up a line segment.
The Upper and Lower Dimension axioms together require that any model of these axioms have dimension 2, i.e. that we are axiomatizing the Euclidean plane. Suitable changes in these axioms yield axiom sets for Euclidean geometry for dimensions 0, 1, and greater than 2 (Tarski and Givant 1999: Axioms 8(1), 8(n), 9(0), 9(1), 9(n) ). Note that solid geometry requires no new axioms, unlike the case with Hilbert's axioms. Moreover, Lower Dimension for n dimensions is simply the negation of Upper Dimension for n - 1 dimensions.
When the number of dimensions is greater than 1, Betweenness can be defined in terms of congruence (Tarski and Givant, 1999). First define the relation "≤" (where is interpreted "the length of line segment is less than or equal to the length of line segment "): | Tarski's axioms | Wikipedia | 397 | 2181360 | https://en.wikipedia.org/wiki/Tarski%27s%20axioms | Mathematics | Axiomatic systems | null |
In the case of two dimensions, the intuition is as follows: For any line segment xy, consider the possible range of lengths of xv, where v is any point on the perpendicular bisector of xy. It is apparent that while there is no upper bound to the length of xv, there is a lower bound, which occurs when v is the midpoint of xy. So if xy is shorter than or equal to zu, then the range of possible lengths of xv will be a superset of the range of possible lengths of zw, where w is any point on the perpendicular bisector of zu.
Betweenness can then be defined by using the intuition that the shortest distance between any two points is a straight line:
The Axiom Schema of Continuity assures that the ordering of points on a line is complete (with respect to first-order definable properties). As was pointed out by Tarski, this first-order axiom schema may be replaced by a more powerful second-order Axiom of Continuity if one allows for variables to refer to arbitrary sets of points. The resulting second-order system is equivalent to Hilbert's set of axioms. (Tarski and Givant 1999)
The Axioms of Pasch and Euclid are well known. The Segment Construction axiom makes measurement and the Cartesian coordinate system possible—simply assign the length 1 to some arbitrary non-empty line segment. Indeed, it is shown in (Schwabhäuser 1983) that by specifying two distinguished points on a line, called 0 and 1, we can define an addition, multiplication and ordering, turning the set of points on that line into a real-closed ordered field. We can then introduce coordinates from this field, showing that every model of Tarski's axioms is isomorphic to the two-dimensional plane over some real-closed ordered field.
The standard geometric notions of parallelism and intersection of lines (where lines are represented by two distinct points on them), right angles, congruence of angles, similarity of triangles, tangency of lines and circles (represented by a center point and a radius) can all be defined in Tarski's system. | Tarski's axioms | Wikipedia | 449 | 2181360 | https://en.wikipedia.org/wiki/Tarski%27s%20axioms | Mathematics | Axiomatic systems | null |
Let wff stand for a well-formed formula (or syntactically correct first-order formula) in Tarski's system. Tarski and Givant (1999: 175) proved that Tarski's system is:
Consistent: There is no wff such that it and its negation can both be proven from the axioms;
Complete: Every wff or its negation is a theorem provable from the axioms;
Decidable: There exists an algorithm that decides for every wff whether is it is provable or disprovable from the axioms. This follows from Tarski's:
Decision procedure for the real closed field, which he found by quantifier elimination (the Tarski–Seidenberg theorem);
Axioms admitting the above-mentioned representation as a two-dimensional plane over a real closed field.
This has the consequence that every statement of (second-order, general) Euclidean geometry which can be formulated as a first-order sentence in Tarski's system is true if and only if it is provable in Tarski's system, and this provability can be automatically checked with Tarski's algorithm. This, for instance, applies to all theorems in Euclid's Elements, Book I. An example of a theorem of Euclidean geometry which cannot be so formulated is the Archimedean property: to any two positive-length line segments S1 and S2 there exists a natural number n such that nS1 is longer than S2. (This is a consequence of the fact that there are real-closed fields that contain infinitesimals.) Other notions that cannot be expressed in Tarski's system are the constructability with straightedge and compass and statements that talk about "all polygones" etc.
Gupta (1965) proved the Tarski's axioms independent, excepting Pasch and Reflexivity of Congruence.
Negating the Axiom of Euclid yields hyperbolic geometry, while eliminating it outright yields absolute geometry. Full (as opposed to elementary) Euclidean geometry requires giving up a first order axiomatization: replace φ(x) and ψ(y) in the axiom schema of Continuity with x ∈ A and y ∈ B, where A and B are universally quantified variables ranging over sets of points. | Tarski's axioms | Wikipedia | 481 | 2181360 | https://en.wikipedia.org/wiki/Tarski%27s%20axioms | Mathematics | Axiomatic systems | null |
Comparison with Hilbert's system
Hilbert's axioms for plane geometry number 16, and include Transitivity of Congruence and a variant of the Axiom of Pasch. The only notion from intuitive geometry invoked in the remarks to Tarski's axioms is triangle. (Versions B and C''' of the Axiom of Euclid refer to "circle" and "angle," respectively.) Hilbert's axioms also require "ray," "angle," and the notion of a triangle "including" an angle. In addition to betweenness and congruence, Hilbert's axioms require a primitive binary relation "on," linking a point and a line.
Hilbert uses two axioms of Continuity, and they require second-order logic. By contrast, Tarski's Axiom schema of Continuity consists of infinitely many first-order axioms. Such a schema is indispensable; Euclidean geometry in Tarski's (or equivalent) language cannot be finitely axiomatized as a first-order theory.
Hilbert's system is therefore considerably stronger: every model is isomorphic to the real plane (using the standard notions of points and lines). By contrast, Tarski's system has many non-isomorphic models: for every real-closed field F, the plane F2'' provides one such model (where betweenness and congruence are defined in the obvious way).
The first four groups of axioms of Hilbert's axioms for plane geometry are bi-interpretable with Tarski's axioms minus continuity. | Tarski's axioms | Wikipedia | 329 | 2181360 | https://en.wikipedia.org/wiki/Tarski%27s%20axioms | Mathematics | Axiomatic systems | null |
Macrobrachium rosenbergii, also known as the giant river prawn or giant freshwater prawn, is a commercially important species of palaemonid freshwater prawn. It is found throughout the tropical and subtropical areas of the Indo-Pacific region, from India to Southeast Asia and Northern Australia. The giant freshwater prawn has also been introduced to parts of Africa, Thailand, China, Japan, New Zealand, the Americas, and the Caribbean. It is one of the biggest freshwater prawns in the world, and is widely cultivated in several countries for food. While M. rosenbergii is considered a freshwater species, the larval stage of the animal depends on estuarine brackish water. Once the individual shrimp has grown beyond the planktonic stage and becomes a juvenile, it migrants from the estuary and lives entirely in fresh water.
It is also known as the Malaysian prawn, freshwater scampi (India), or cherabin (Australia). Locally, it is known as golda chingri () in Bangladesh and India, udang galah in Indonesia and Malaysia, uwáng or uláng in the Philippines, Thailand prawn in Southern China and Taiwan (Chinese: Tàiguó xiā 泰國蝦), and (กุ้งแม่น้ำ) or (กุ้งก้ามกราม) in Thailand.
Description
M. rosenbergii can grow to a length over . They are predominantly brownish in colour, but can vary. Smaller individuals may be greenish and display faint vertical stripes. The rostrum is very prominent and contains 11 to 14 dorsal teeth and 8 to 11 ventral teeth. The first pair of walking legs (pereiopods) is elongated and very thin, ending in delicate claws (chelipeds), which are used as feeding appendages. The second pair of walking legs are much larger and powerful, especially in males. The movable claws of the second pair of walking legs are distinctively covered in dense bristles (setae) that give them a velvety appearance. The colour of the claws in males varies according to their social dominance.
Females can be distinguished from males by their wider abdomens and smaller second pereiopods. The genital openings are found on the body segments containing the fifth pereiopods and the third pereiopods in males and females, respectively. | Macrobrachium rosenbergii | Wikipedia | 477 | 2183839 | https://en.wikipedia.org/wiki/Macrobrachium%20rosenbergii | Biology and health sciences | Shrimps and prawns | Animals |
This sexual dimorphism is driven by the IAG physiological sexual switch, discovered by Prof. Amir Sagi and his research group, and monosex biotechnologies were established for all-male and all-female culture. The all-male technology includes the first application of temporal RNA interference (RNAi) in the field of aquaculture. Also, all-female culture technology was established. Crustacean monosex technologies are applied in Vietnam, Thailand, China, Malaysia and Israel.
Morphotypes
Three different morphotypes of males exist. The first stage is called "small male" (SM); this smallest stage has short, nearly translucent claws. If conditions allow, small males grow and metamorphose into "orange claws" (OC), which have large orange claws on their second chelipeds, which may have a length of 0.8 to 1.4 times their body size. OC males later may transform into the third and final stage, the "blue claw" (BC) males. These have blue claws, and their second chelipeds may become twice as long as their bodies.
Males of M. rosenbergii have a strict hierarchy; the territorial BC males dominate the OCs, which in turn dominate the SMs. The presence of BC males inhibits the growth of SMs and delays the metamorphosis of OCs into BCs; an OC keeps growing until it is larger than the largest BC male in its neighbourhood before transforming. All three male stages are sexually active, and females that have undergone their premating moult cooperate with any male to reproduce. BC males protect the females until their shells have hardened; OCs and SMs show no such behaviour.
Life cycle
In mating, the male deposits spermatophores on the underside of the female's thorax, between the walking legs. The female then extrudes eggs, which pass through the spermatophores. The female carries the fertilised eggs with her until they hatch; the time may vary, but is generally less than 3 weeks. Females lay 10,000–50,000 eggs up to five times per year. | Macrobrachium rosenbergii | Wikipedia | 444 | 2183839 | https://en.wikipedia.org/wiki/Macrobrachium%20rosenbergii | Biology and health sciences | Shrimps and prawns | Animals |
From these eggs hatch zoeae, the first larval stage of crustaceans. They go through several larval stages in brackish water before metamorphosing into postlarvae, at which stage they are long and resemble adults. This metamorphosis usually takes place about 32 to 35 days after hatching. These postlarvae then migrate back into fresh water. | Macrobrachium rosenbergii | Wikipedia | 80 | 2183839 | https://en.wikipedia.org/wiki/Macrobrachium%20rosenbergii | Biology and health sciences | Shrimps and prawns | Animals |
Boiling-point elevation is the phenomenon whereby the boiling point of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent. This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water. The boiling point can be measured accurately using an ebullioscope.
Explanation
The boiling point elevation is a colligative property, which means that boiling point elevation is dependent on the number of dissolved particles but not their identity. It is an effect of the dilution of the solvent in the presence of a solute. It is a phenomenon that happens for all solutes in all solutions, even in ideal solutions, and does not depend on any specific solute–solvent interactions. The boiling point elevation happens both when the solute is an electrolyte, such as various salts, and a nonelectrolyte. In thermodynamic terms, the origin of the boiling point elevation is entropic and can be explained in terms of the vapor pressure or chemical potential of the solvent. In both cases, the explanation depends on the fact that many solutes are only present in the liquid phase and do not enter into the gas phase (except at extremely high temperatures).
The vapor pressure affects the solute shown by Raoult's Law while the free energy change and chemical potential are shown by Gibbs free energy. Most solutes remain in the liquid phase and do not enter the gas phase, except at very high temperatures.
In terms of vapor pressure, a liquid boils when its vapor pressure equals the surrounding pressure. A nonvolatile solute lowers the solvent’s vapor pressure, meaning a higher temperature is needed for the vapor pressure to equalize the surrounding pressure, causing the boiling point to elevate.
In terms of chemical potential, at the boiling point, the liquid and gas phases have the same chemical potential. Adding a nonvolatile solute lowers the solvent’s chemical potential in the liquid phase, but the gas phase remains unaffected. This shifts the equilibrium between phases to a higher temperature, elevating the boiling point.
Relationship between Freezing-point Depression
Freezing-point depression is analogous to boiling point elevation, though the magnitude of freezing-point depression is higher for the same solvent and solute concentration. These phenomena extend the liquid range of a solvent in the presence of a solute. | Boiling-point elevation | Wikipedia | 500 | 2184383 | https://en.wikipedia.org/wiki/Boiling-point%20elevation | Physical sciences | Thermodynamics | Chemistry |
Related equations for Calculating Boiling Point
The extent of boiling-point elevation can be calculated by applying Clausius–Clapeyron relation and Raoult's law together with the assumption of the non-volatility of the solute. The result is that in dilute ideal solutions, the extent of boiling-point elevation is directly proportional to the molal concentration (amount of substance per mass) of the solution according to the equation:
ΔTb = Kb · bc
where the boiling point elevation, is defined as Tb (solution) − Tb (pure solvent).
Kb, the ebullioscopic constant, which is dependent on the properties of the solvent. It can be calculated as Kb = RTb2M/ΔHv, where R is the gas constant, and Tb is the boiling temperature of the pure solvent [in K], M is the molar mass of the solvent, and ΔHv is the heat of vaporization per mole of the solvent.
bc is the colligative molality, calculated by taking dissociation into account since the boiling point elevation is a colligative property, dependent on the number of particles in solution. This is most easily done by using the van 't Hoff factor i as bc = bsolute · i, where bsolute is the molality of the solution. The factor i accounts for the number of individual particles (typically ions) formed by a compound in solution. Examples:
i = 1 for sugar in water
i = 1.9 for sodium chloride in water, due to the near full dissociation of NaCl into Na+ and Cl− (often simplified as 2)
i = 2.3 for calcium chloride in water, due to nearly full dissociation of CaCl2 into Ca2+ and 2Cl− (often simplified as 3)
Non integer i factors result from ion pairs in solution, which lower the effective number of particles in the solution.
Equation after including the van 't Hoff factor
ΔTb = Kb · bsolute · i | Boiling-point elevation | Wikipedia | 417 | 2184383 | https://en.wikipedia.org/wiki/Boiling-point%20elevation | Physical sciences | Thermodynamics | Chemistry |
The above formula reduces precision at high concentrations, due to nonideality of the solution. If the solute is volatile, one of the key assumptions used in deriving the formula is not true because the equation derived is for solutions of non-volatile solutes in a volatile solvent. In the case of volatile solutes, the equation can represent a mixture of volatile compounds more accurately, and the effect of the solute on the boiling point must be determined from the phase diagram of the mixture. In such cases, the mixture can sometimes have a lower boiling point than either of the pure components; a mixture with a minimum boiling point is a type of azeotrope.
Ebullioscopic constants
Values of the ebullioscopic constants Kb for selected solvents:
Uses
Together with the formula above, the boiling-point elevation can be used to measure the degree of dissociation or the molar mass of the solute. This kind of measurement is called ebullioscopy (Latin-Greek "boiling-viewing"). However, superheating is a factor that can affect the precision of the measurement and would be challenging to avoid because of the decrease in molecular mobility. Therefore, ΔTb would be hard to measure precisely even though superheating can be partially overcome by the invention of the Beckmann thermometer. In reality, cryoscopy is used more often because the freezing point is often easier to measure with precision. | Boiling-point elevation | Wikipedia | 300 | 2184383 | https://en.wikipedia.org/wiki/Boiling-point%20elevation | Physical sciences | Thermodynamics | Chemistry |
The common ringtail possum (Pseudocheirus peregrinus, Greek for "false hand" and Latin for "pilgrim" or "alien") is an Australian marsupial.
It lives in a variety of habitats and eats a variety of leaves of both native and introduced plants, as well as flowers, fruits and sap. This possum also consumes caecotropes, which is material fermented in the caecum and expelled during the daytime when it is resting in a nest. This behaviour is called caecotrophy and is similar to that seen in rabbits.
Taxonomy
The common ringtail possum is currently classified as one of the two living species in the genus Pseudocheirus; the species of Pseudochirulus and other ringtail genera were formerly also classified in Pseudocheirus. Several subspecies have been described:
Pseudocheirus peregrinus pereginus, the type subspecies based on a collection made at Endeavour River
Pseudocheirus peregrinus convolutor, (Eastern ringtail possum or Southeastern ringtail possum)
Pseudocheirus peregrinus pulcher, (Rufous ringtail possum)
Pseudocheirus occidentalis (Ngwayir, or the Western ringtail possum), found in the south west of Australia, used to be considered a subspecies of Pseudocheirus peregrinus; however, it is now formally considered a separate species.
Description
The common ringtail possum weighs between and is approximately cm long when grown (excluding the tail, which is roughly the same length again). It has grey or black fur with white patches behind the eyes and usually a cream-coloured belly. It has a long prehensile tail which normally displays a distinctive white tip over 25% of its length. The back feet are syndactyl, which helps it to climb. The ringtail possum's molars have sharp and pointed cusps. | Common ringtail possum | Wikipedia | 404 | 2184516 | https://en.wikipedia.org/wiki/Common%20ringtail%20possum | Biology and health sciences | Diprotodontia | Animals |
Distribution and habitat
The common ringtail possum ranges on the east coast of Australia, as well as Tasmania and a part of southwestern Australia. They generally live in temperate and tropical environments and are rare in drier environments. Ringtail possums prefer forests of dense brush, particularly eucalyptus forests. The common ringtail possum and its relatives occupy a range of niches similar to those of lemurs, monkeys, squirrels, and bushbabies in similar forests on other continents. It is less prolific and less widespread than the common brushtail possum.
Behaviour
The common ringtail possum is nocturnal and well adapted to arboreal life. It relies on its prehensile tail and sometimes will descend to the ground. They communicate with soft, high-pitched, and twittering calls.
Diet and foraging
The common ringtail possum feeds on a wide variety of plants in the family Myrtaceae including the foliage, flowers and fruits from shrubs and lower canopy. Some populations are also known to feed on the leaves of cypress pine (Callitris), wattles (Acacia spp.) and plant gum or resins.
When foraging, ringtail possums prefer young leaves over old ones. One study found the emergence of young possums from their pouches corresponds to the flowering and fruiting of the tea-tree, Leptospermum and the peak of fresh plant growth. Young eucalypt leaves are richer in nitrogen and have less dense cell walls than older leaves; however, the protein gained from them is less available due to higher amounts of tannins. When feeding, the possum's molars slice through the leaves, slitting them into pieces. The possum's gastrointestinal tract sends the fine particles to the caecum and the coarse ones to the colon. These particles stay in the caecum for up to 70 hours where the cell walls and tanned cytoplasts are partially digested. | Common ringtail possum | Wikipedia | 405 | 2184516 | https://en.wikipedia.org/wiki/Common%20ringtail%20possum | Biology and health sciences | Diprotodontia | Animals |
What distinguishes the digestive system of the common ringtail possum from that of the koala and the greater glider is the caecal contents are expelled as caecotropes, reingested and passed into the stomach. Because of this, the ringtail possum is able to gain more protein. This is also done by lagomorphs (rabbits, hares and pikas). Hard faeces are produced during the night while feeding and are not eaten, while caecotropes are produced during the day during rests and are eaten.
Metabolism
The re-ingestion of caecotropes also serves to maintain the ringtail possum's energy balance. Ringtail possums gain much of their gross energy from reingestion. The common ringtail possum has a daily maintenance nitrogen requirement (MNR) of 290 mg N/kg0.75. Common ringtail possums gain much of their MNR from consuming their nitrogen-rich caecotropes. They would have to gain 620 mg N/kg0.75 otherwise. The ringtail possum recycles 96% of its liver's urea, which is then transferred into the caecum and made into bacterial protein. Only re-ingestion makes this effective and the bacterial protein must be digested in the stomach and the amino acids subsequently absorbed in the small intestine. This recycling also allows the possum to conserve water and urinate less. Reingestion allows the possum to live on low nitrogen eucalyptus leaves which is particularly important during late lactation. It has been found that at higher temperatures, the common ringtail possum consumes less food due to a limited ability to metabolize toxins found in their diet. Because 55% of their water intake comes from the leaves and foliage they consume, their metabolic rate must remain low and stable while facing water loss. In response to this challenge, common ringtail possums can control their body temperature and conserve water by using facultative hyperthermia to temporarily raise their internal body temperature, ranging from . | Common ringtail possum | Wikipedia | 439 | 2184516 | https://en.wikipedia.org/wiki/Common%20ringtail%20possum | Biology and health sciences | Diprotodontia | Animals |
Nesting
Common ringtail possums live a gregarious lifestyle which centres on their communal nests, also called dreys. Ringtail possums build nests from tree branches and occasionally use tree hollows. A communal nest is made up of an adult female and an adult male, their dependant offspring and immature offspring of the previous year. A group of ringtail possums may build several dreys at different sites. Ringtail possums are territorial and will drive away any strange conspecifics from their nests. A group has a strong attachment to their site. In one experiment, in which a group was removed from their territory, it remained uncolonised for the following two years. Ringtail possum nests tend to be more common in low scrub and less common in heavily timbered areas with little under-story. Dreys contribute to the survival of the young when they are no longer carried on their mother's back.
Reproduction and growth
The common ringtail possum carries its young in a pouch, where it develops. Depending on the area, the mating season can take place anywhere between April and December. The majority of the young are born between May and July. The oestrous cycle of ringtail possum lasts 28 days. It is both polyoestrous and polyovular. If a female prematurely loses her litter, she can return to oestrous and produce a second litter in October as a replacement if conditions are right. The average litter is two, although there are very occasionally triplets. Common ringtail possum young tend to grow relatively slowly due to dilute milk with low lipid levels that is provided to the young. As with other marsupials, the common ringtail possum's milk changes through lactation. During the second phase of lactation, more solid foods are eaten, especially when the young first emerges from the pouch. During this time, the concentration of carbohydrates fall, while those of proteins and lipids reach their highest. The long lactation of the ringtail possums may give the young more time to learn skills in the communal nest as well as to climb and forage in the trees. | Common ringtail possum | Wikipedia | 454 | 2184516 | https://en.wikipedia.org/wiki/Common%20ringtail%20possum | Biology and health sciences | Diprotodontia | Animals |
The young are first able to vocalise and open their eyes between 90 and 106 days of age. They leave their mother's pouch at 120–130 days. However, lactation usually continues until 180–220 days after birth but sometimes ends by 145 days. Both sexes become sexually mature in the first mating season after their birth.
Status
Common ringtail possum populations severely declined during the 1950s. However, populations seem to have recovered in recent times. Because they are largely arboreal, common ringtail possums are particularly affected by deforestation in Australia. They are also heavily preyed upon by the introduced red fox. They are also hit by cars, or killed by snakes, cats and dogs in suburban areas. | Common ringtail possum | Wikipedia | 146 | 2184516 | https://en.wikipedia.org/wiki/Common%20ringtail%20possum | Biology and health sciences | Diprotodontia | Animals |
A quadrant is an instrument used to measure angles up to 90°. Different versions of this instrument could be used to calculate various readings, such as longitude, latitude, and time of day. Its earliest recorded usage was in ancient India in Rigvedic times by Rishi Atri to observe a solar eclipse. It was then proposed by Ptolemy as a better kind of astrolabe. Several different variations of the instrument were later produced by medieval Muslim astronomers. Mural quadrants were important astronomical instruments in 18th-century European observatories, establishing a use for positional astronomy.
Etymology
The term quadrant, meaning one fourth, refers to the fact that early versions of the instrument were derived from astrolabes. The quadrant condensed the workings of the astrolabe into an area one fourth the size of the astrolabe face; it was essentially a quarter of an astrolabe.
History
During Rigvedic times in ancient India, quadrants called 'Tureeyam's were used to measure the extent of a great solar eclipse. The use of a Tureeyam for observing a solar eclipse by Rishi Atri is described in the fifth mandala of the Rigveda, most likely between c. 1500 and 1000 BCE.
Early accounts of a quadrant also come from Ptolemy's Almagest around AD 150. He described a "plinth" that could measure the altitude of the noon sun by projecting the shadow of a peg on a graduated arc of 90 degrees. This quadrant was unlike later versions of the instrument; it was larger and consisted of several moving parts. Ptolemy's version was a derivative of the astrolabe and the purpose of this rudimentary device was to measure the meridian angle of the sun.
Islamic astronomers in the Middle Ages improved upon these ideas and constructed quadrants throughout the Middle East, in observatories such as Marageh, Rey and Samarkand. At first these quadrants were usually very large and stationary, and could be rotated to any bearing to give both the altitude and azimuth for any celestial body. As Islamic astronomers made advancements in astronomical theory and observational accuracy they are credited with developing four different types of quadrants during the Middle Ages and beyond. The first of these, the sine quadrant, was invented by Muhammad ibn Musa al-Khwarizmi in the 9th century at the House of Wisdom in Baghdad. The other types were the universal quadrant, the horary quadrant and the astrolabe quadrant. | Quadrant (instrument) | Wikipedia | 502 | 13352174 | https://en.wikipedia.org/wiki/Quadrant%20%28instrument%29 | Technology | Navigation | null |
During the Middle Ages the knowledge of these instruments spread to Europe. In the 13th century Jewish astronomer Jacob ben Machir ibn Tibbon was crucial in further developing the quadrant. He was a skilled astronomer and wrote several volumes on the topic, including an influential book detailing how to build and use an improved version of the quadrant. The quadrant that he invented came to be known as the novus quadrans, or new quadrant. This device was revolutionary because it was the first quadrant to be built that did not involve several moving parts and thus could be much smaller and more portable.
Tibbon's Hebrew manuscripts were translated into Latin and improved upon by Danish scholar Peter Nightingale several years later. Because of the translation, Tibbon, or Prophatius Judaeus as he was known in Latin, became an influential name in astronomy. His new quadrant was based upon the idea that the stereographic projection that defines a planispheric astrolabe can still work if the astrolabe parts are folded into a single quadrant. The result was a device that was far cheaper, easier to use and more portable than a standard astrolabe. Tibbon's work had a far reach and influenced Copernicus, Christopher Clavius and Erasmus Reinhold; and his manuscript was referenced in Dante's Divine Comedy.
As the quadrant became smaller and thus more portable, its value for navigation was soon realized. The first documented use of the quadrant to navigate at sea is in 1461, by Diogo Gomes. Sailors began by measuring the height of Polaris to ascertain their latitude. This application of quadrants is generally attributed to Arab sailors who traded along the east coast of Africa and often travelled out of sight of land. It soon became more common to take the height of the sun at a given time due to the fact that Polaris is not visible south of the equator.
In 1618, the English mathematician Edmund Gunter further adapted the quadrant with an invention that came to be known as the Gunter quadrant. This pocket sized quadrant was revolutionary because it was inscribed with projections of the tropics, the equator, the horizon and the ecliptic. With the correct tables one could use the quadrant to find the time, the date, the length of the day or night, the time of sunrise and sunset and the meridian. The Gunter quadrant was extremely useful but it had its drawbacks; the scales only applied to a certain latitude so the instrument's use was limited at sea.
Types | Quadrant (instrument) | Wikipedia | 501 | 13352174 | https://en.wikipedia.org/wiki/Quadrant%20%28instrument%29 | Technology | Navigation | null |
There are several types of quadrants:
Mural quadrants, used for determining the time by measuring the altitudes of astronomical objects. Tycho Brahe created one of the largest mural quadrants. In order to tell time he would place two clocks next to the quadrant so that he could identify the minutes and seconds in relation to the measurements on the side of the instrument.
Large frame-based instruments used for measuring angular distances between astronomical objects.
Geometric quadrant used by surveyors and navigators.
Davis quadrant a compact, framed instrument used by navigators for measuring the altitude of an astronomical object.
They can also be classified as: | Quadrant (instrument) | Wikipedia | 124 | 13352174 | https://en.wikipedia.org/wiki/Quadrant%20%28instrument%29 | Technology | Navigation | null |
Altitude – The plain quadrant with plumb line, used to take the altitude of an object.
Gunner's – A type of clinometer used by an artillerist to measure the elevation or depression angle of a gun barrel of a cannon or mortar, both to verify proper firing elevation, and to verify the correct alignment of the weapon-mounted fire control devices.
Gunter's – A quadrant used for time determination as well as the length of day, when the sun had risen and set, the date, and the meridian using scales and curves of the quadrant along with related tables. It was invented by Edmund Gunter in 1623. Gunter's quadrant was fairly simple which allowed for its widespread and long-lasting use in the 17th and 18th centuries. Gunter expanded the basic features of other quadrants to create a convenient and comprehensive instrument. Its distinguishable feature included projections of the tropics, equator, ecliptic, and the horizon.
Islamic – King identified four types of quadrants that were produced by Muslim astronomers.
The sine quadrant (Arabic: Rubul Mujayyab) – also known as the Sinecal Quadrant – was used for solving trigonometric problems and taking astronomical observations. It was developed by al-Khwarizmi in 9th century Baghdad and prevalent until the nineteenth century. Its defining feature is a graph-paper like grid on one side that is divided into sixty equal intervals on each axis and is also bounded by a 90 degree graduated arc. A cord was attached to the apex of the quadrant with a bead, for calculation, and a plumb bob. They were also sometimes drawn on the back of astrolabes.
The universal (shakkāzīya) quadrant – used for solving astronomical problems for any latitude: These quadrants had either one or two sets of shakkāzīya grids and were developed in the fourteenth century in Syria. Some astrolabes are also printed on the back with the universal quadrant like an astrolabe created by Ibn al-Sarrāj. | Quadrant (instrument) | Wikipedia | 407 | 13352174 | https://en.wikipedia.org/wiki/Quadrant%20%28instrument%29 | Technology | Navigation | null |
The horary quadrant – used for finding the time with the sun: The horary quadrant could be used to find the time either in equal or unequal (length of the day divided by twelve) hours. Different sets of markings were created for either equal or unequal hours. For measuring the time in equal hours, the horary quadrant could only be used for one specific latitude while a quadrant for unequal hours could be used anywhere based on an approximate formula. One edge of the quadrant had to be aligned with the sun, and once aligned, a bead on the plumbline attached to the centre of the quadrant showed the time of the day. A British version dated 1311 was listed by Christie's in December 2023, with the claim of being "the earliest dated English scientific instrument" without showing any provenance. A further example exists dated 1396, from European sources (Richard II of England). The oldest horary quadrant was found during an excavation in 2013 in the Hanseatic town of Zutphen (Netherlands), is dated ca. 1300, and is in the local Stedelijk Museum in Zutphen.
The astrolabe/almucantar quadrant – a quadrant developed from the astrolabe: This quadrant was marked with one half of a typical astrolabe plate as astrolabe plates are symmetrical. A cord attached from the centre of the quadrant with a bead at the other end was moved to represent the position of a celestial body (sun or a star). The ecliptic and star positions were marked on the quadrant for the above. It is not known where and when the astrolabe quadrant was invented, existent astrolabe quadrants are either of Ottoman or Mamluk origin, while there have been discovered twelfth century Egyptian and fourteenth century Syrian treatises on the astrolabe quadrant. These quadrants proved to be very popular alternatives to astrolabes. | Quadrant (instrument) | Wikipedia | 395 | 13352174 | https://en.wikipedia.org/wiki/Quadrant%20%28instrument%29 | Technology | Navigation | null |
Geometric quadrant
The geometric quadrant is a quarter-circle panel usually of wood or brass. Markings on the surface might be printed on paper and pasted to the wood or painted directly on the surface. Brass instruments had their markings scribed directly into the brass.
For marine navigation, the earliest examples were found around 1460. They were not graduated in degrees but rather had the latitudes of the most common destinations directly scribed on the limb. When in use, the navigator would sail north or south until the quadrant indicated he was at the destination's latitude, turn in the direction of the destination and sail to the destination maintaining a course of constant latitude. After 1480, more of the instruments were made with limbs graduated in degrees.
Along one edge there were two sights forming an alidade. A plumb bob was suspended by a line from the centre of the arc at the top.
In order to measure the altitude of a star, the observer would view the star through the sights and hold the quadrant so that the plane of the instrument was vertical. The plumb bob was allowed to hang vertical and the line indicated the reading on the arc's graduations. It was not uncommon for a second person to take the reading while the first concentrated on observing and holding the instrument in proper position.
The accuracy of the instrument was limited by its size and by the effect the wind or observer's motion would have on the plumb bob. For navigators on the deck of a moving ship, these limitations could be difficult to overcome.
Solar observations
In order to avoid staring into the sun to measure its altitude, navigators could hold the instrument in front of them with the sun to their side. By having the sunward sighting vane cast its shadow on the lower sighting vane, it was possible to align the instrument to the sun. Care would have to be taken to ensure that the altitude of the centre of the sun was determined. This could be done by averaging the elevations of the upper and lower umbra in the shadow.
Back observation quadrant
In order to perform measurements of the altitude of the sun, a back observation quadrant was developed. | Quadrant (instrument) | Wikipedia | 429 | 13352174 | https://en.wikipedia.org/wiki/Quadrant%20%28instrument%29 | Technology | Navigation | null |
With such a quadrant, the observer viewed the horizon from a sight vane (C in the figure on the right) through a slit in the horizon vane (B). This ensured the instrument was level. The observer moved the shadow vane (A) to a position on the graduated scale so as to cause its shadow to appear coincident with the level of the horizon on the horizon vane. This angle was the elevation of the sun.
Framed quadrant
Large frame quadrants were used for astronomical measurements, notably determining the altitude of celestial objects. They could be permanent installations, such as mural quadrants. Smaller quadrants could be moved. Like the similar astronomical sextants, they could be used in a vertical plane or made adjustable for any plane.
When set on a pedestal or other mount, they could be used to measure the angular distance between any two celestial objects.
The details on their construction and use are essentially the same as those of the astronomical sextants; refer to that article for details.
Navy: Used to gauge elevation on ships cannon, the quadrant had to be placed on each gun's trunnion in order to judge range, after the loading. The reading was taken at the top of the ship's roll, the gun adjusted, and checked, again at the top of the roll, and he went to the next gun, until all that were going to be fired were ready. The ship's Gunner was informed, who in turn informed the captain...You may fire when ready...at the next high roll, the cannon would be fired.
In more modern applications, the quadrant is attached to the trunnion ring or of a large naval gun to align it to benchmarks welded to the ship's deck. This is done to ensure firing of the gun hasn't "warped the deck." A flat surface on the mount gunhouse or turret is also checked against benchmarks, also, to ensure large bearings and/or bearing races haven't changed... to "calibrate" the gun.
Customization
During the Middle Ages, makers often added customization to impress the person for whom the quadrant was intended. In large, unused spaces on the instrument, a sigil or badge would often be added to denote the ownership by an important person or the allegiance of the owner. | Quadrant (instrument) | Wikipedia | 474 | 13352174 | https://en.wikipedia.org/wiki/Quadrant%20%28instrument%29 | Technology | Navigation | null |
Speech–language pathology (a.k.a. speech and language pathology or logopedics) is a healthcare and academic discipline concerning the evaluation, treatment, and prevention of communication disorders, including expressive and mixed receptive-expressive language disorders, voice disorders, speech sound disorders, speech disfluency, pragmatic language impairments, and social communication difficulties, as well as swallowing disorders across the lifespan. It is an allied health profession regulated by professional bodies including the American Speech-Language-Hearing Association (ASHA) and Speech Pathology Australia. The field of speech-language pathology is practiced by a clinician known as a speech-language pathologist (SLP) or a speech and language therapist (SLT). SLPs also play an important role in the screening, diagnosis, and treatment of autism spectrum disorder (ASD), often in collaboration with pediatricians and psychologists.
History
The development of speech-language pathology into a profession took different paths in the various regions of the world. Three identifiable trends influenced the evolution of speech-language pathology in the United States during the late 19th century to early 20th century: the elocution movement, scientific revolution, and the rise of professionalism. Groups of "speech correctionists" formed in the early 1900s. The American Academy of Speech Correction was founded in 1925, which became ASHA in 1978. | Speech–language pathology | Wikipedia | 272 | 7032057 | https://en.wikipedia.org/wiki/Speech%E2%80%93language%20pathology | Biology and health sciences | Disabilities | Health |
Profession
Speech-language pathologists (SLPs) provide a wide range of services, mainly on an individual basis, but also as support for families, support groups, and providing information for the general public. SLPs work to assess levels of communication needs, make diagnoses based on the assessments, and then treat the diagnoses or address the needs. Speech/language services begin with initial screening for communication and/or swallowing disorders and continue with assessment and diagnosis, consultation for the provision of advice regarding management, intervention, and treatment, and providing counseling and other followup services for these disorders. Services are provided in the following areas:
Developmental language and early feeding neurodevelopment and prevention;
Cognitive aspects of communication (e.g., attention, memory, problem-solving, executive functions);
Speech (phonation, articulation, fluency, resonance, and voice including aeromechanical components of respiration);
Language (phonology, morphology, syntax, semantics, and pragmatic/social aspects of communication) including comprehension and expression in oral, written, graphic, and manual modalities; language processing; preliteracy and language-based literacy skills, phonological awareness;
Augmentative and alternative communication (AAC) for individuals with severe language and communication impairments;
Swallowing or other upper aerodigestive functions such as infant feeding and aeromechanical events (evaluation of esophageal function is for the purpose of referral to medical professionals);
Voice (hoarseness, dysphonia), poor vocal volume (hypophonia), abnormal (e.g., rough, breathy, strained) vocal quality. Research demonstrates voice therapy to be especially helpful with certain patient populations; individuals with Parkinson's Disease often develop voice issues as a result of their disease.
Sensory awareness related to communication, swallowing, or other upper aerodigestive functions.
Speech, language, and swallowing disorders result from a variety of causes, such as a stroke, brain injury, hearing loss, developmental delay, a cleft palate, cerebral palsy, or emotional issues. | Speech–language pathology | Wikipedia | 437 | 7032057 | https://en.wikipedia.org/wiki/Speech%E2%80%93language%20pathology | Biology and health sciences | Disabilities | Health |
A common misconception is that speech–language pathology is restricted to the treatment of articulation disorders (e.g., helping English-speaking individuals enunciate the traditionally difficult r) and/or the treatment of individuals who stutter but, in fact, speech–language pathology is concerned with a broad scope of speech, language, literacy, swallowing, and voice issues involved in communication, some of which include:
Word-finding and other semantic issues, either as a result of a specific language impairment (SLI) such as a language delay or as a secondary characteristic of a more general issue such as dementia.
Social communication difficulties involving how people communicate or interact with others (pragmatics).
Language impairments, including difficulties creating sentences that are grammatical (syntax) and modifying word meaning (morphology).
Literacy impairments (reading and writing) related to the letter-to-sound relationship (phonics), the word-to-meaning relationship (semantics), and understanding the ideas presented in a text (reading comprehension).
Voice difficulties, such as a raspy voice, a voice that is too soft, or other voice difficulties that negatively impact a person's social or professional performance.
Cognitive impairments (e.g. attention, memory, executive function) to the extent that they interfere with communication.
Parent, caregiver, and other communication partner coaching.
Primary pediatric speech and language disorders include: receptive and expressive language disorders, speech sound disorders, childhood apraxia of speech (CAS), stuttering, and language-based learning disabilities. Speech-language pathologists (SLPs) work with people of all ages.
Swallowing disorders include difficulties in any phase of the swallowing process (i.e., oral, pharyngeal, esophageal), as well as functional dysphagia and feeding disorders. Swallowing disorders can occur at any age and can stem from multiple causes.
Multi-discipline collaboration | Speech–language pathology | Wikipedia | 399 | 7032057 | https://en.wikipedia.org/wiki/Speech%E2%80%93language%20pathology | Biology and health sciences | Disabilities | Health |
SLPs collaborate with other health care professionals, often working as part of a multidisciplinary team. They can provide information and referrals to audiologists, physicians, dentists, nurses, nurse practitioners, occupational therapists, rehabilitation psychologists, dietitians, educators, behavior consultants (applied behavior analysis), and parents as dictated by the individual client's needs. For example, the treatment for patients with cleft lip and palate often requires multidisciplinary collaboration. Speech–language pathologists can be very beneficial in helping resolve speech problems associated with cleft lip and palate. Research has indicated that children who receive early language intervention are less likely to develop compensatory error patterns later in life, although speech therapy outcomes are usually better when surgical treatment is performed earlier. Another area of collaboration relates to auditory processing disorders, where SLPs can collaborate in assessments and provide intervention where there is evidence of speech, language, and/or other cognitive-communication disorders.
Working environments
SLPs work in a variety of clinical and educational settings. SLPs work in public and private hospitals, private practices, skilled nursing facilities (SNFs), long-term acute care (LTAC) facilities, hospice, and home healthcare. SLPs may also work as part of the support structure in the education system, working in both public and private schools, colleges, and universities. Some SLPs also work in community health, providing services at prisons and young offenders' institutions or providing expert testimony in applicable court cases.
Following ASHA's 2005 approval of the delivery of speech/language services via video conference or telepractice, SLPs in the United States have begun to use this service model.
Children with speech, language, and communication needs (SLCN) are particularly at risk of not being heard because of communication challenges. Speech-language pathologists (SLPs) can explain the significance of supporting communication as a tool for the child to shape and influence choices available to them in their lives, even though it is advised that children with SLCN can and should be actively involved as equal partners in decision-making about their communication needs. Building these skills is especially crucial for SLPs working in settings related to traditional education.
Research
SLPs conduct research related to communication sciences and disorders, swallowing disorders, or other upper aerodigestive functions. | Speech–language pathology | Wikipedia | 477 | 7032057 | https://en.wikipedia.org/wiki/Speech%E2%80%93language%20pathology | Biology and health sciences | Disabilities | Health |
Experimental, empirical, and scientific methodologies that build on hypothesis testing and logical, deductive reasoning have dominated research in speech-language pathology. Other types of research in the field are complemented by qualitative research.
Education and training
United States
In the United States, speech–language pathologists must hold a master's degree from an ASHA-accredited program. Following graduation and passing a nation-wide board exam, SLPs typically begin their Clinical Fellowship Year, during which they are granted a provisional license and receive guidance from their supervisor. At the end of this process, SLPs may choose to apply for ASHA's Certificate of Clinical Competence and apply for full state licensure. SLPs may additionally choose to earn advanced degrees such as a clinical doctorate in speech–language pathology, PhD, or EdD.
Methods of assessment
Many approaches exist to assess language, communication, speech and swallowing. Two main aspects of assessment can be to determine the extent of breakdown (impairment-level), or how communication can be supported (functional level). When evaluating impairment-based level of breakdown, therapists are trained to use a cognitive neuropsychological approach to assessment, to precisely determine what aspect of communication is impaired. Some therapists use assessments that are based on historic anatomical models of language, that have since been shown to be unreliable. These tools are often preferred by therapists working within a medical model, where medics request a 'type' of impairment, and a 'severity' rating. The broad tools available allow clinicians to precisely select the aspect of communication that they wish to assess.
Because school-based speech therapy is run under state guidelines and funds, the process of assessment and qualification is more strict. To qualify for in-school speech therapy, students must meet the state's criteria on language testing and speech standardization. Due to such requirements, some students may not be assessed in an efficient time frame or their needs may be undermined by criteria. For a private clinic, students are more likely to qualify for therapy because it is a paid service with more availability.
Clients and patients
Speech–language pathologists work with clients and patients who may present with a wide range of issues. | Speech–language pathology | Wikipedia | 442 | 7032057 | https://en.wikipedia.org/wiki/Speech%E2%80%93language%20pathology | Biology and health sciences | Disabilities | Health |
Infants and children
Premature infants are at higher risk of feeding and later language needs and SLTS work with this cohort to prevent developmental difficulties and support neonatal care
Infants with injuries due to complications at birth, feeding and swallowing difficulties, including dysphagia
Children with mild, moderate or severe:
Genetic disorders that adversely affect speech, language and/or cognitive development including cleft palate, Down syndrome, DiGeorge syndrome
Attention deficit hyperactivity disorder
Autism spectrum disorders, including Asperger syndrome
Developmental delay
Feeding disorders, including oral motor deficits
Cranial nerve damage
Hearing loss
Craniofacial anomalies that adversely affect speech, language and/or cognitive development
Language delay
Specific language impairment
Specific difficulties in producing sounds, called articulation disorders, (including vocalic /r/ and lisps)
Pediatric traumatic brain injury
Developmental verbal dyspraxia
Cleft palate
United States
In the US, some children are eligible to receive speech therapy services, including assessment and lessons through the public school system. If not, private therapy is readily available through personal lessons with a qualified speech–language pathologist or the growing field of telepractice. Teleconferencing tools such as Skype are being used more commonly as a means to access remote locations in private therapy practice, such as in the geographically diverse south island of New Zealand. More at-home or combination treatments have become readily available to address specific types of articulation disorders. The use of mobile applications in speech therapy is also growing as an avenue to bring treatment into the home. | Speech–language pathology | Wikipedia | 319 | 7032057 | https://en.wikipedia.org/wiki/Speech%E2%80%93language%20pathology | Biology and health sciences | Disabilities | Health |
United Kingdom
In the UK, children are entitled to an assessment by local NHS speech- and language-therapy teams, usually after referral by health visitors or education settings, but parents are also entitled to request an assessment directly. If treatment is appropriate, an educational plan will be drawn up. Speech therapists often play a role in multi-disciplinary teams when a child has speech delay or disorder as part of a wider health condition. The Children's Commissioner for England reported in June 2019 that there was a postcode lottery; £291.65 a year per head was spent on services in some areas, while the budget in some areas was £30.94 or less. In 2018, 193,971 children in English primary schools were on the special educational needs register needing speech-therapy services.
Speech and language therapists work in acute settings and are often
integrated into the MDT in multiple areas of speciality for neonatal, children and adult services. Areas include but not limited to; neonatal care, respiratory, ENT, gastrointestinal, stroke, Neurology,ICU, oncology and geriatric care
Children and adults
Puberphonia
Neonatal care
Respiratory
ENT
Cerebral palsy
Head injury (Traumatic brain injury)
Hearing loss and impairments
Learning difficulties including
Dyslexia
Specific language impairment (SLI)
Auditory processing disorder
Physical disabilities
Speech disorders (such as oral dyspraxia)
Stammering, stuttering (disfluency)
Stroke
Voice disorders (dysphonia)
Language delay
Motor speech disorders (dysarthria or developmental verbal dyspraxia)
Naming difficulties (anomia)
Dysgraphia, agraphia
Cognitive communication disorders
Pragmatics
Laryngectomies
Tracheostomies
Oncology (ear, nose or throat cancer) | Speech–language pathology | Wikipedia | 372 | 7032057 | https://en.wikipedia.org/wiki/Speech%E2%80%93language%20pathology | Biology and health sciences | Disabilities | Health |
Adults
Adults with aphasia
Adults with mild, moderate, or severe eating, feeding and swallowing difficulties, including dysphagia
Adults recovering from significant tumors in the bronchus, lung, oropharynx, breast, and brain
Adults with mild, moderate, or severe language difficulties as a result of:
Motor neuron diseases,
Alzheimer's disease,
Dementia,
Huntington's disease,
Hearing loss
Multiple sclerosis,
Parkinson's disease,
Traumatic brain injury,
Mental health issues
Stroke
Progressive neurological conditions such as cancer of the head, neck and throat (including laryngectomy)
Aphasic
Adults seeking transgender-specific voice training, including voice feminization and voice masculinization | Speech–language pathology | Wikipedia | 143 | 7032057 | https://en.wikipedia.org/wiki/Speech%E2%80%93language%20pathology | Biology and health sciences | Disabilities | Health |
Human fertilization is the union of an egg and sperm, occurring primarily in the ampulla of the fallopian tube. The result of this union leads to the production of a fertilized egg called a zygote, initiating embryonic development. Scientists discovered the dynamics of human fertilization in the 19th century.
The process of fertilization involves a sperm fusing with an ovum. The most common sequence begins with ejaculation during copulation, follows with ovulation, and finishes with fertilization. Various exceptions to this sequence are possible, including artificial insemination, in vitro fertilization, external ejaculation without copulation, or copulation shortly after ovulation. Upon encountering the secondary oocyte, the acrosome of the sperm produces enzymes which allow it to burrow through the outer shell called the zona pellucida of the egg. The sperm plasma then fuses with the egg's plasma membrane and their nuclei fuse, triggering the sperm head to disconnect from its flagellum as the egg travels down the fallopian tube to reach the uterus.
In vitro fertilization (IVF) is a process by which egg cells are fertilized by sperm outside the womb, in vitro.
History
Fertilization was not understood in antiquity. Hippocrates believed that the embryo was the product of male semen and a female factor. Aristotle held that only male semen gave rise to an embryo, while the female only provided a place for the embryo to develop, a concept he acquired from the preformationist Pythagoras. Aristotle argued for form and function emerging gradually, in a mode called by him as epigenetic. In 1651 William Harvey refuted Aristotle's idea, that menstrual blood could be involved in the formation of a fetus, asserting that eggs from the female were somehow caused to become a fetus as a result of sexual intercourse. Sperm cells were discovered in 1677 by Antonie van Leeuwenhoek, who believed that Aristotle had been proven correct. Some observers believed they could see an entirely pre-formed little human body in the head of a sperm. The human ova was first observed in 1827 by Karl Ernst von Baer. Only in 1876 did Oscar Hertwig prove that fertilization is due to fusion of an egg and sperm cell.
Sperm and oocyte meet
Ampulla | Human fertilization | Wikipedia | 501 | 3016568 | https://en.wikipedia.org/wiki/Human%20fertilization | Biology and health sciences | Human reproduction | Biology |
Fertilization occurs in the ampulla of the fallopian tube, the section that curves around the ovary. Capacitated sperm are attracted to progesterone, which is secreted from the cumulus cells surrounding the oocyte. Progesterone binds to the CatSper receptor on the sperm membrane and increases intracellular calcium levels, causing hyperactive motility. The sperm will continue to swim towards higher concentrations of progesterone, effectively guiding it to the oocyte. Around 200 out of 200 million spermatozoa reach the ampulla.
Sperm preparation
At the beginning of the process, the sperm undergoes a series of changes, as freshly ejaculated sperm is unable or poorly able to fertilize. The sperm must undergo capacitation in the female's reproductive tract, which increases its motility and hyperpolarizes its membrane, preparing it for the acrosome reaction, the enzymatic penetration of the egg's tough membrane, the zona pellucida, which surrounds the oocyte.
Corona radiata
The sperm binds through the corona radiata, a layer of follicle cells on the outside of the secondary oocyte. The corona radiata sends out chemicals that attract the sperm in the fallopian tube to the oocyte. It lies above the zona pellucida, a membrane of glycoproteins that surrounds the oocyte.
Cone of attraction and perivitelline membrane
Where the spermatozoan is about to pierce, the yolk (ooplasm) is drawn out into a conical elevation, termed the cone of attraction or reception cone. Once the spermatozoon has entered, the peripheral portion of the yolk changes into a membrane, the perivitelline membrane, which prevents the passage of additional spermatozoa.
Zona pellucida and acrosome reaction
After binding to the corona radiata the sperm reaches the zona pellucida, which is an extracellular matrix of glycoproteins. A ZP3 glycoprotein on the zona pellucida binds to a receptor on the cell surface of the sperm head. This binding triggers the acrosome to burst, releasing acrosomal enzymes that help the sperm penetrate through the thick zona pellucida layer surrounding the oocyte, ultimately gaining access to the egg's cell membrane. | Human fertilization | Wikipedia | 508 | 3016568 | https://en.wikipedia.org/wiki/Human%20fertilization | Biology and health sciences | Human reproduction | Biology |
Some sperm cells consume their acrosome prematurely on the surface of the egg cell, facilitating the penetration by other sperm cells. As a population, mature haploid sperm cells have on average 50% genome similarity, so the premature acrosomal reactions aid fertilization by a member of the same cohort. It may be regarded as a mechanism of kin selection.
Recent studies have shown that the egg is not passive during this process. In other words, they too appear to undergo changes that help facilitate such interaction.
Fusion
Cortical reaction
After the sperm enters the cytoplasm of the oocyte, the tail and the outer coating of the sperm disintegrate. The fusion of sperm and oocyte membranes causes cortical reaction to occur. Cortical granules inside the secondary oocyte fuse with the plasma membrane of the cell, causing enzymes inside these granules to be expelled by exocytosis to the zona pellucida. This in turn causes the glycoproteins in the zona pellucida to cross-link with each other — i.e. the enzymes cause the ZP2 to hydrolyse into ZP2f — making the whole matrix hard and impermeable to sperm. This prevents fertilization of an egg by more than one sperm.
Fusion of genetic material
Preparation
In preparation for the fusion of their genetic material both the oocyte and the sperm undergo transformations as a reaction to the fusion of cell membranes.
The oocyte completes its second meiotic division. This results in a mature haploid ovum and the release of a polar body. The nucleus of the oocyte is called a pronucleus in this process, to distinguish it from the nuclei that are the result of fertilization.
The sperm's tail and mitochondria degenerate with the formation of the male pronucleus. This is why all mitochondria in humans are of maternal origin. Still, a considerable amount of RNA from the sperm is delivered to the resulting embryo and likely influences embryo development and the phenotype of the offspring.
Fusion
The sperm nucleus then fuses with the ovum, enabling fusion of their genetic material. | Human fertilization | Wikipedia | 460 | 3016568 | https://en.wikipedia.org/wiki/Human%20fertilization | Biology and health sciences | Human reproduction | Biology |
Blocks of polyspermy
When the sperm enters the perivitelline space, a sperm-specific protein Izumo on the head binds to Juno receptors on the oocyte membrane. Once it is bound, two blocks to polyspermy then occur. After approximately 40 minutes, the other Juno receptors on the oocyte are lost from the membrane, causing it to no longer be fusogenic. Additionally, the cortical reaction will happen which is caused by ovastacin binding and cleaving ZP2 receptors on the zona pellucida. These two blocks of polyspermy are what prevent the zygote from having too much DNA.
Replication
The pronuclei migrate toward the center of the oocyte, rapidly replicating their DNA as they do so to prepare the zygote for its first mitotic division.
Mitosis
Usually 23 chromosomes from spermatozoon and 23 chromosomes from egg cell fuse (approximately half of spermatozoons carry X chromosome and the other half Y chromosome). Their membranes dissolve, leaving no barriers between the male and female chromosomes. During this dissolution, a mitotic spindle forms between them. The spindle captures the chromosomes before they disperse in the egg cytoplasm. Upon subsequently undergoing mitosis (which includes pulling of chromatids towards centrioles in anaphase) the cell gathers genetic material from the male and female together. Thus, the first mitosis of the union of sperm and oocyte is the actual fusion of their chromosomes.
Each of the two daughter cells resulting from that mitosis has one replica of each chromatid that was replicated in the previous stage. Thus, they are genetically identical.
Fertilization age
Fertilization is the event most commonly used to mark the beginning point of life, in descriptions of prenatal development of the embryo or fetus. The resultant age is known as fertilization age, fertilizational age, conceptional age, embryonic age, fetal age or (intrauterine) developmental (IUD) age. | Human fertilization | Wikipedia | 427 | 3016568 | https://en.wikipedia.org/wiki/Human%20fertilization | Biology and health sciences | Human reproduction | Biology |
Gestational age, in contrast, takes the beginning of the last menstrual period (LMP) as the start point. By convention, gestational age is calculated by adding 14 days to fertilization age and vice versa. Fertilization though usually occurs within a day of ovulation, which, in turn, occurs on average 14.6 days after the beginning of the preceding menstruation (LMP). There is also considerable variability in this interval, with a 95% prediction interval of the ovulation of 9 to 20 days after menstruation even for an average woman who has a mean LMP-to-ovulation time of 14.6. In a reference group representing all women, the 95% prediction interval of the LMP-to-ovulation is 8.2 to 20.5 days.
The average time to birth has been estimated to be 268 days (38 weeks and two days) from ovulation, with a standard deviation of 10 days or coefficient of variation of 3.7%.
Fertilization age is sometimes used postnatally (after birth) as well to estimate various risk factors. For example, it is a better predictor than postnatal age for risk of intraventricular hemorrhage in premature babies treated with extracorporeal membrane oxygenation.
Diseases affecting human fertility
Various disorders can arise from defects in the fertilization process. Whether that results in the process of contact between the sperm and egg, or the state of health of the biological parent carrying the zygote cell. The following are a few of the diseases that can occur and be present during the process. | Human fertilization | Wikipedia | 344 | 3016568 | https://en.wikipedia.org/wiki/Human%20fertilization | Biology and health sciences | Human reproduction | Biology |
Polyspermy results from multiple sperm fertilizing an egg, leading to an offset number of chromosomes within the embryo. Polyspermy, while physiologically possible in some species of vertebrates and invertebrates, is a lethal condition for the human zygote.
Polycystic ovary syndrome is a condition in which the woman does not produce enough follicle stimulating hormone and excessively produces androgens. This results in the ovulation period between contact of the egg being postponed or excluded.
Autoimmune disorders can lead to complications in implantation of the egg in the uterus, which may be the immune system's attack response to an established embryo on the uterine wall.
Cancer ultimately affects fertility and may lead to birth defects or miscarriages. Cancer severely damages reproductive organs, which affects fertility.
Endocrine system disorders affect human fertility by decreasing the body's ability to produce the level of hormones needed to successfully carry a zygote. Examples of these disorders include diabetes, adrenal disorders, and thyroid disorders.
Endometriosis is a condition that affects women in which the tissue normally produced in the uterus proceeds to grow outside of the uterus. This leads to extreme amounts of pain and discomfort and may result in an irregular menstrual cycle. | Human fertilization | Wikipedia | 265 | 3016568 | https://en.wikipedia.org/wiki/Human%20fertilization | Biology and health sciences | Human reproduction | Biology |
In quantum mechanics, spin is an intrinsic property of all elementary particles. All known fermions, the particles that constitute ordinary matter, have a spin of . The spin number describes how many symmetrical facets a particle has in one full rotation; a spin of means that the particle must be rotated by two full turns (through 720°) before it has the same configuration as when it started.
Particles having net spin include the proton, neutron, electron, neutrino, and quarks. The dynamics of spin- objects cannot be accurately described using classical physics; they are among the simplest systems which require quantum mechanics to describe them. As such, the study of the behavior of spin- systems forms a central part of quantum mechanics.
Stern–Gerlach experiment
The necessity of introducing half-integer spin goes back experimentally to the results of the Stern–Gerlach experiment. A beam of atoms is run through a strong heterogeneous magnetic field, which then splits into N parts depending on the intrinsic angular momentum of the atoms. It was found that for silver atoms, the beam was split in two—the ground state therefore could not be an integer, because even if the intrinsic angular momentum of the atoms were the smallest (non-zero) integer possible, 1, the beam would be split into 3 parts, corresponding to atoms with Lz = −1, +1, and 0, with 0 simply being the value known to come between −1 and +1 while also being a whole-integer itself, and thus a valid quantized spin number in this case. The existence of this hypothetical "extra step" between the two polarized quantum states would necessitate a third quantum state; a third beam, which is not observed in the experiment. The conclusion was that silver atoms had net intrinsic angular momentum of .
General properties
Spin- objects are all fermions (a fact explained by the spin–statistics theorem) and satisfy the Pauli exclusion principle. Spin- particles can have a permanent magnetic moment along the direction of their spin, and this magnetic moment gives rise to electromagnetic interactions that depend on the spin. One such effect that was important in the discovery of spin is the Zeeman effect, the splitting of a spectral line into several components in the presence of a static magnetic field. | Spin-1/2 | Wikipedia | 464 | 3017092 | https://en.wikipedia.org/wiki/Spin-1/2 | Physical sciences | Quantum numbers | Physics |
Unlike in more complicated quantum mechanical systems, the spin of a spin- particle can be expressed as a linear combination of just two eigenstates, or eigenspinors. These are traditionally labeled spin up and spin down. Because of this, the quantum-mechanical spin operators can be represented as simple 2 × 2 matrices. These matrices are called the Pauli matrices.
Creation and annihilation operators can be constructed for spin- objects; these obey the same commutation relations as other angular momentum operators.
Connection to the uncertainty principle
One consequence of the generalized uncertainty principle is that the spin projection operators (which measure the spin along a given direction like x, y, or z) cannot be measured simultaneously. Physically, this means that the axis about which a particle is spinning is ill-defined. A measurement of the z-component of spin destroys any information about the x- and y-components that might previously have been obtained.
Mathematical description
A spin- particle is characterized by an angular momentum quantum number for spin s of . In solutions of the Schrödinger equation, angular momentum is quantized according to this number, so that total spin angular momentum
However, the observed fine structure when the electron is observed along one axis, such as the z-axis, is quantized in terms of a magnetic quantum number, which can be viewed as a quantization of a vector component of this total angular momentum, which can have only the values of .
Note that these values for angular momentum are functions only of the reduced Planck constant (the angular momentum of any photon), with no dependence on mass or charge.
Complex phase
Mathematically, quantum mechanical spin is not described by a vector as in classical angular momentum. It is described by a complex-valued vector with two components called a spinor. There are subtle differences between the behavior of spinors and vectors under coordinate rotations, stemming from the behavior of a vector space over a complex field. | Spin-1/2 | Wikipedia | 393 | 3017092 | https://en.wikipedia.org/wiki/Spin-1/2 | Physical sciences | Quantum numbers | Physics |
When a spinor is rotated by 360° (one full turn), it transforms to its negative, and then after a further rotation of 360° it transforms back to its initial value again. This is because in quantum theory the state of a particle or system is represented by a complex probability amplitude (wavefunction) ψ, and when the system is measured, the probability of finding the system in the state ψ equals , the absolute square (square of the absolute value) of the amplitude. In mathematical terms, the quantum Hilbert space carries a projective representation of the rotation group SO(3).
Suppose a detector that can be rotated measures a particle in which the probabilities of detecting some state are affected by the rotation of the detector. When the system is rotated through 360°, the observed output and physics are the same as initially but the amplitudes are changed for a spin- particle by a factor of −1 or a phase shift of half of 360°. When the probabilities are calculated, the −1 is squared, , so the predicted physics is the same as in the starting position. Also, in a spin- particle there are only two spin states and the amplitudes for both change by the same −1 factor, so the interference effects are identical, unlike the case for higher spins. The complex probability amplitudes are something of a theoretical construct which cannot be directly observed.
If the probability amplitudes rotated by the same amount as the detector, then they would have changed by a factor of −1 when the equipment was rotated by 180° which when squared would predict the same output as at the start, but experiments show this to be wrong. If the detector is rotated by 180°, the result with spin- particles can be different from what it would be if not rotated, hence the factor of a half is necessary to make the predictions of the theory match the experiments.
In terms of more direct evidence, physical effects of the difference between the rotation of a spin- particle by 360° as compared with 720° have been experimentally observed in classic experiments in neutron interferometry. In particular, if a beam of spin-oriented spin- particles is split, and just one of the beams is rotated about the axis of its direction of motion and then recombined with the original beam, different interference effects are observed depending on the angle of rotation. In the case of rotation by 360°, cancellation effects are observed, whereas in the case of rotation by 720°, the beams are mutually reinforcing. | Spin-1/2 | Wikipedia | 511 | 3017092 | https://en.wikipedia.org/wiki/Spin-1/2 | Physical sciences | Quantum numbers | Physics |
Non-relativistic quantum mechanics
The quantum state of a spin- particle can be described by a two-component complex-valued vector called a spinor. Observable states of the particle are then found by the spin operators Sx, Sy, and Sz, and the total spin operator S.
Observables
When spinors are used to describe the quantum states, the three spin operators (Sx, Sy, Sz,) can be described by 2 × 2 matrices called the Pauli matrices whose eigenvalues are .
For example, the spin projection operator Sz affects a measurement of the spin in the z direction.
The two eigenvalues of Sz, , then correspond to the following eigenspinors:
These vectors form a complete basis for the Hilbert space describing the spin- particle. Thus, linear combinations of these two states can represent all possible states of the spin, including in the x- and y-directions.
The ladder operators are:
Since , it follows that and . Thus:
Their normalized eigenspinors can be found in the usual way. For Sx, they are:
For Sy, they are:
Relativistic quantum mechanics
While non relativistic quantum mechanics defines spin with 2 dimensions in Hilbert space with dynamics that are described in 3-dimensional space and time, relativistic quantum mechanics defines the spin with 4 dimensions in Hilbert space and dynamics described by 4-dimensional space-time.
Observables
As a consequence of the four-dimensional nature of space-time in relativity, relativistic quantum mechanics uses 4×4 matrices to describe spin operators and observables.
History
When physicist Paul Dirac tried to modify the Schrödinger equation so that it was consistent with Einstein's theory of relativity, he found it was only possible by including matrices in the resulting Dirac equation, implying the wave must have multiple components leading to spin.
The 4π spinor rotation was experimentally verified using neutron interferometry in 1974, by Helmut Rauch and collaborators, after being suggested by Yakir Aharonov and Leonard Susskind in 1967. | Spin-1/2 | Wikipedia | 440 | 3017092 | https://en.wikipedia.org/wiki/Spin-1/2 | Physical sciences | Quantum numbers | Physics |
The Cartwheel Galaxy (also known as ESO 350-40 or PGC 2248) is a lenticular ring galaxy about 500 million light-years away in the constellation Sculptor. It has a D25 isophotal diameter of , and a mass of about solar masses; its outer ring has a circular velocity of .
It was discovered by Fritz Zwicky in 1941. Zwicky considered his discovery "one of the most complicated structures awaiting its explanation on the basis of stellar dynamics."
The Third Reference Catalogue of Bright Galaxies (RC3) measured a D25 isophotal diameter for the Cartwheel Galaxy at about 60.9 arcseconds, giving it a diameter of based on a redshift-derived distance of .
This diameter is slightly smaller than that of the Andromeda Galaxy.
The large Cartwheel Galaxy is the dominant member of the Cartwheel Galaxy group, consisting of four physically associated spiral galaxies. The three companions are referred to in several studies as G1, the smaller irregular blue Magellanic spiral; G2, the yellow compact spiral with a tidal tail; and G3, a more distant spiral often seen in wide field images.
One supernova has been observed in the Cartwheel Galaxy. SN 2021afdx (type II, mag. 18.8) was discovered by ATLAS on 23 November 2021.
Structures
The structure of the Cartwheel Galaxy is noted to be highly complicated and heavily disturbed. The Cartwheel consists of two rings: the outer ring, the site of massive ongoing star formation due to gas and dust compression; and the inner ring that surrounds the galactic center. A ring of dark absorbing dust is also present in the nucleic ring. Several optical arms or "spokes" are seen connecting the outer ring to the inner. Observations show the presence of both non-thermal radio continuum and optical spokes, but the two do not seem to overlap. | Cartwheel Galaxy | Wikipedia | 388 | 3019076 | https://en.wikipedia.org/wiki/Cartwheel%20Galaxy | Physical sciences | Notable galaxies | Astronomy |
Evolution
The galaxy was once a normal spiral galaxy before it apparently underwent a head-on "bullseye" style collision with a smaller companion approximately 200–300 million years prior to how we see the system today. When the nearby galaxy passed through the Cartwheel Galaxy, the force of the collision caused a powerful gravitational shock wave to expand through the galaxy. Moving at high speed, the shock wave swept up and compressed gas and dust, creating a Starburst region around the galaxy's center portion that went unscathed as it expanded outwards. This explains the bluish ring around the center, which is the brighter portion. It can be noted that the galaxy is beginning to retake the form of a normal spiral galaxy, with arms spreading out from a central core. These arms are often referred to as the cartwheel's “spokes”.
Alternatively, a model based on the gravitational Jeans instability of both axisymmetric (radial) and nonaxisymmetric (spiral) small-amplitude gravity perturbations allows an association between growing clumps of matter and the gravitationally unstable axisymmetric and nonaxisymmetric waves which take on the appearance of a ring and spokes. Based on observational data, however, this theory of ring galaxy evolution does not appear to apply to this specific galaxy.
While most images of the Cartwheel display three galaxies close together, a fourth physically associated companion (also known as G3) is known to be associated with the group through an HI (or neutral hydrogen) tail that connects G3 to the cartwheel. Due to the presence of the HI tail, it is widely believed that G3 is the "bullet" galaxy that plunged through the disk of the cartwheel, creating its current shape, not G1 or G2. This hypothesis makes sense given the size and predicted age of the current structure (~300 million years old as mentioned before). Considering how close G1 and G2 are to the Cartwheel still, it is much more widely believed that the roughly 88 kpc (~287,000 light years) distant G3 is the intruding galaxy. | Cartwheel Galaxy | Wikipedia | 433 | 3019076 | https://en.wikipedia.org/wiki/Cartwheel%20Galaxy | Physical sciences | Notable galaxies | Astronomy |
HI tail mapping is extremely useful in determining “culprit” galaxies in similar cases where the solution is relatively unclear. Hydrogen gas, being the lightest and most abundant gas in galaxies, is easily torn away from parent galaxies through gravitational forces. Evidence of this can be seen in the Jellyfish Galaxy and the Comet Galaxy, which are undergoing a type of gravitational effect called ram pressure stripping, and other galaxies with tidal tails and star forming stellar streams associated with collisions and mergers. Ram pressure stripping will almost always cause trailing-dominant tails of HI gas as a galaxy infalls into a galaxy cluster, while mergers and collisions like the ones involving in Cartwheel galaxy often create leading-dominant tails as the culprit galaxy’s gravity attracts and pulls on the victim galaxy’s gas in the direction of the culprit's motion.
The existing structure of the cartwheel is expected to disintegrate over the next few hundred million years as the remaining gas, dust and stars that haven’t escaped the galaxy begin to infall back towards the center. It is likely that the galaxy will regain a spiral shape after the infall process completes and spiral density waves have a chance to reform. This is only possible if companions G1, G2 and G3 remain distant and do not undergo an additional collision with the cartwheel.
X-ray sources
The unusual shape of the Cartwheel Galaxy may be due to a collision with a smaller galaxy such as one of those in the lower left of the image. The most recent starburst has lit up the Cartwheel rim, which has a diameter larger than that of the Milky Way. Star formation via starburst galaxies, such as the Cartwheel Galaxy, results in the formation of large and extremely luminous stars. When massive stars explode as supernovas, they leave behind neutron stars and black holes. Some of these neutron stars and black holes have nearby companion stars, and become powerful sources of X-rays as they pull matter off their companions (also known as ultra and hyperluminous X-ray sources). The brightest X-ray sources are likely black holes with companion stars, appearing as the white dots that lie along the rim of the X-ray image. The Cartwheel contains an exceptionally large number of these black hole binary X-ray sources, because many massive stars formed in the ring. | Cartwheel Galaxy | Wikipedia | 475 | 3019076 | https://en.wikipedia.org/wiki/Cartwheel%20Galaxy | Physical sciences | Notable galaxies | Astronomy |
In thermodynamics, the entropy of mixing is the increase in the total entropy when several initially separate systems of different composition, each in a thermodynamic state of internal equilibrium, are mixed without chemical reaction by the thermodynamic operation of removal of impermeable partition(s) between them, followed by a time for establishment of a new thermodynamic state of internal equilibrium in the new unpartitioned closed system.
In general, the mixing may be constrained to occur under various prescribed conditions. In the customarily prescribed conditions, the materials are each initially at a common temperature and pressure, and the new system may change its volume, while being maintained at that same constant temperature, pressure, and chemical component masses. The volume available for each material to explore is increased, from that of its initially separate compartment, to the total common final volume. The final volume need not be the sum of the initially separate volumes, so that work can be done on or by the new closed system during the process of mixing, as well as heat being transferred to or from the surroundings, because of the maintenance of constant pressure and temperature.
The internal energy of the new closed system is equal to the sum of the internal energies of the initially separate systems. The reference values for the internal energies should be specified in a way that is constrained to make this so, maintaining also that the internal energies are respectively proportional to the masses of the systems.
For concision in this article, the term 'ideal material' is used to refer to either an ideal gas (mixture) or an ideal solution.
In the special case of mixing ideal materials, the final common volume is in fact the sum of the initial separate compartment volumes. There is no heat transfer and no work is done. The entropy of mixing is entirely accounted for by the diffusive expansion of each material into a final volume not initially accessible to it.
In the general case of mixing non-ideal materials, however, the total final common volume may be different from the sum of the separate initial volumes, and there may occur transfer of work or heat, to or from the surroundings; also there may be a departure of the entropy of mixing from that of the corresponding ideal case. That departure is the main reason for interest in entropy of mixing. These energy and entropy variables and their temperature dependences provide valuable information about the properties of the materials. | Entropy of mixing | Wikipedia | 489 | 3021875 | https://en.wikipedia.org/wiki/Entropy%20of%20mixing | Physical sciences | Thermodynamics | Physics |
On a molecular level, the entropy of mixing is of interest because it is a macroscopic variable that provides information about constitutive molecular properties. In ideal materials, intermolecular forces are the same between every pair of molecular kinds, so that a molecule feels no difference between other molecules of its own kind and of those of the other kind. In non-ideal materials, there may be differences of intermolecular forces or specific molecular effects between different species, even though they are chemically non-reacting. The entropy of mixing provides information about constitutive differences of intermolecular forces or specific molecular effects in the materials.
The statistical concept of randomness is used for statistical mechanical explanation of the entropy of mixing. Mixing of ideal materials is regarded as random at a molecular level, and, correspondingly, mixing of non-ideal materials may be non-random.
Mixing of ideal species at constant temperature and pressure
In ideal species, intermolecular forces are the same between every pair of molecular kinds, so that a molecule "feels" no difference between itself and its molecular neighbors. This is the reference case for examining corresponding mixing of non-ideal species.
For example, two ideal gases, at the same temperature and pressure, are initially separated by a dividing partition.
Upon removal of the dividing partition, they expand into a final common volume (the sum of the two initial volumes), and the entropy of mixing
is given by
where is the gas constant, the total number of moles and the mole fraction of component , which initially occupies volume . After the removal of the partition, the moles of component may explore the combined volume , which causes an entropy increase equal to for each component gas.
In this case, the increase in entropy is entirely due to the irreversible processes of expansion of the two gases, and involves no heat or work flow between the system and its surroundings.
Gibbs free energy of mixing
The Gibbs free energy change determines whether mixing at constant (absolute) temperature and pressure is a spontaneous process. This quantity combines two physical effects—the enthalpy of mixing, which is a measure of the energy change, and the entropy of mixing considered here.
For an ideal gas mixture or an ideal solution, there is no enthalpy of mixing (), so that the Gibbs free energy of mixing is given by the entropy term only: | Entropy of mixing | Wikipedia | 479 | 3021875 | https://en.wikipedia.org/wiki/Entropy%20of%20mixing | Physical sciences | Thermodynamics | Physics |
For an ideal solution, the Gibbs free energy of mixing is always negative, meaning that mixing of ideal solutions is always spontaneous. The lowest value is when the mole fraction is 0.5 for a mixture of two components, or 1/n for a mixture of n components.
Solutions and temperature dependence of miscibility
Ideal and regular solutions
The above equation for the entropy of mixing of ideal gases is valid also for certain liquid (or solid) solutions—those formed by completely random mixing so that the components move independently in the total volume. Such random mixing of solutions occurs if the interaction energies between unlike molecules are similar to the average interaction energies between like molecules. The value of the entropy corresponds exactly to random mixing for ideal solutions and for regular solutions, and approximately so for many real solutions.
For binary mixtures the entropy of random mixing can be considered as a function of the mole fraction of one component.
For all possible mixtures, , so that and are both negative and the entropy of mixing is positive and favors mixing of the pure components.
The curvature of as a function of is given by the second derivative
This curvature is negative for all possible mixtures , so that mixing two solutions to form a solution of intermediate composition also increases the entropy of the system. Random mixing therefore always favors miscibility and opposes phase separation.
For ideal solutions, the enthalpy of mixing is zero so that the components are miscible in all proportions. For regular solutions a positive enthalpy of mixing may cause incomplete miscibility (phase separation for some compositions) at temperatures below the upper critical solution temperature (UCST). This is the minimum temperature at which the term in the Gibbs energy of mixing is sufficient to produce miscibility in all proportions.
Systems with a lower critical solution temperature
Nonrandom mixing with a lower entropy of mixing can occur when the attractive interactions between unlike molecules are significantly stronger (or weaker) than the mean interactions between like molecules. For some systems this can lead to a lower critical solution temperature (LCST) or lower limiting temperature for phase separation. | Entropy of mixing | Wikipedia | 415 | 3021875 | https://en.wikipedia.org/wiki/Entropy%20of%20mixing | Physical sciences | Thermodynamics | Physics |
For example, triethylamine and water are miscible in all proportions below 19 °C, but above this critical temperature, solutions of certain compositions separate into two phases at equilibrium with each other. This means that is negative for mixing of the two phases below 19 °C and positive above this temperature. Therefore, is negative for mixing of these two equilibrium phases. This is due to the formation of attractive hydrogen bonds between the two components that prevent random mixing. Triethylamine molecules cannot form hydrogen bonds with each other but only with water molecules, so in solution they remain associated to water molecules with loss of entropy. The mixing that occurs below 19 °C is due not to entropy but to the enthalpy of formation of the hydrogen bonds.
Lower critical solution temperatures also occur in many polymer-solvent mixtures. For polar systems such as polyacrylic acid in 1,4-dioxane, this is often due to the formation of hydrogen bonds between polymer and solvent. For nonpolar systems such as polystyrene in cyclohexane, phase separation has been observed in sealed tubes (at high pressure) at temperatures approaching the liquid-vapor critical point of the solvent. At such temperatures the solvent expands much more rapidly than the polymer, whose segments are covalently linked. Mixing therefore requires contraction of the solvent for compatibility of the polymer, resulting in a loss of entropy.
Statistical thermodynamical explanation of the entropy of mixing of ideal gases
Since thermodynamic entropy can be related to statistical mechanics or to information theory, it is possible to calculate the entropy of mixing using these two approaches. Here we consider the simple case of mixing ideal gases. | Entropy of mixing | Wikipedia | 340 | 3021875 | https://en.wikipedia.org/wiki/Entropy%20of%20mixing | Physical sciences | Thermodynamics | Physics |
Proof from statistical mechanics
Assume that the molecules of two different substances are approximately the same size, and regard space as subdivided into a square lattice whose cells are the size of the molecules. (In fact, any lattice would do, including close packing.) This is a crystal-like conceptual model to identify the molecular centers of mass. If the two phases are liquids, there is no spatial uncertainty in each one individually. (This is, of course, an approximation. Liquids have a "free volume". This is why they are (usually) less dense than solids.) Everywhere we look in component 1, there is a molecule present, and likewise for component 2. After the two different substances are intermingled (assuming they are miscible), the liquid is still dense with molecules, but now there is uncertainty about what kind of molecule is in which location. Of course, any idea of identifying molecules in given locations is a thought experiment, not something one could do, but the calculation of the uncertainty is well-defined.
We can use Boltzmann's equation for the entropy change as applied to the mixing process
where is the Boltzmann constant. We then calculate the number of ways of arranging molecules of component 1 and molecules of component 2 on a lattice, where
is the total number of molecules, and therefore the number of lattice sites.
Calculating the number of permutations of objects, correcting for the fact that of them are identical to one another, and likewise for ,
After applying Stirling's approximation for the factorial of a large integer m:
,
the result is
where we have introduced the mole fractions, which are also the probabilities of finding any particular component in a given lattice site.
Since the Boltzmann constant , where is the Avogadro constant, and the number of molecules , we recover the thermodynamic expression for the mixing of two ideal gases,
This expression can be generalized to a mixture of components, , with
The Flory–Huggins solution theory is an example of a more detailed model along these lines.
Relationship to information theory | Entropy of mixing | Wikipedia | 423 | 3021875 | https://en.wikipedia.org/wiki/Entropy%20of%20mixing | Physical sciences | Thermodynamics | Physics |
The entropy of mixing is also proportional to the Shannon entropy or compositional uncertainty of information theory, which is defined without requiring Stirling's approximation. Claude Shannon introduced this expression for use in information theory, but similar formulas can be found as far back as the work of Ludwig Boltzmann and J. Willard Gibbs. The Shannon uncertainty is not the same as the Heisenberg uncertainty principle in quantum mechanics which is based on variance. The Shannon entropy is defined as:
where pi is the probability that an information source will produce the ith symbol from an r-symbol alphabet and is independent of previous symbols. (thus i runs from 1 to r ). H is then a measure of the expected amount of information (log pi) missing before the symbol is known or measured, or, alternatively, the expected amount of information supplied when the symbol becomes known. The set of messages of length N symbols from the source will then have an entropy of NH.
The thermodynamic entropy is only due to positional uncertainty, so we may take the "alphabet" to be any of the r different species in the gas, and, at equilibrium, the probability that a given particle is of type i is simply the mole fraction xi for that particle. Since we are dealing with ideal gases, the identity of nearby particles is irrelevant. Multiplying by the number of particles N yields the change in entropy of the entire system from the unmixed case in which all of the pi were either 1 or 0. We again obtain the entropy of mixing on multiplying by the Boltzmann constant .
So thermodynamic entropy with r chemical species with a total of N particles has a parallel to an information source that has r distinct symbols with messages that are N symbols long.
Application to gases
In gases there is a lot more spatial uncertainty because most of their volume is merely empty space. We can regard the mixing process as allowing the contents of the two originally separate contents to expand into the combined volume of the two conjoined containers. The two lattices that allow us to conceptually localize molecular centers of mass also join. The total number of empty cells is the sum of the numbers of empty cells in the two components prior to mixing. Consequently, that part of the spatial uncertainty concerning whether any molecule is present in a lattice cell is the sum of the initial values, and does not increase upon "mixing". | Entropy of mixing | Wikipedia | 486 | 3021875 | https://en.wikipedia.org/wiki/Entropy%20of%20mixing | Physical sciences | Thermodynamics | Physics |
Almost everywhere we look, we find empty lattice cells. Nevertheless, we do find molecules in a few occupied cells. When there is real mixing, for each of those few occupied cells, there is a contingent uncertainty about which kind of molecule it is. When there is no real mixing because the two substances are identical, there is no uncertainty about which kind of molecule it is. Using conditional probabilities, it turns out that the analytical problem for the small subset of occupied cells is exactly the same as for mixed liquids, and the increase in the entropy, or spatial uncertainty, has exactly the same form as obtained previously. Obviously the subset of occupied cells is not the same at different times. But only when there is real mixing and an occupied cell is found do we ask which kind of molecule is there. | Entropy of mixing | Wikipedia | 161 | 3021875 | https://en.wikipedia.org/wiki/Entropy%20of%20mixing | Physical sciences | Thermodynamics | Physics |
A javelin is a light spear designed primarily to be thrown, historically as a ranged weapon. Today, the javelin is predominantly used for sporting purposes such as the javelin throw. The javelin is nearly always thrown by hand, unlike the sling, bow, and crossbow, which launch projectiles with the aid of a hand-held mechanism. However, devices do exist to assist the javelin thrower in achieving greater distances, such as spear-throwers or the amentum.
A warrior or soldier armed primarily with one or more javelins is a javelineer.
The word javelin comes from Middle English and it derives from Old French javelin, a diminutive of javelot, which meant spear. The word javelot probably originated from one of the Celtic languages.
Prehistory
There is archaeological evidence that javelins and throwing sticks were already in use by the last phase of the Lower Paleolithic. Seven spear-like objects were found in a coal mine in the city of Schöningen, Germany. Stratigraphic dating indicates that the weapons are about 400,000 years old. The excavated items were made of spruce (Picea) trunk and were between long. They were manufactured with the maximum thickness and weight situated at the front end of the wooden shaft. The frontal centre of gravity suggests that these weapons were used as javelins. A fossilized horse shoulder blade with a projectile wound, dated to 500,000 years ago, was revealed in a gravel quarry in the village of Boxgrove, England. Studies suggested that the wound was probably caused by a javelin.
Classical age
Ancient Egypt
In History of Ancient Egypt: Volume 1 (1882), George Rawlinson depicts the javelin as an offensive weapon used by the Ancient Egyptian military. It was lighter in weight than that used by other nations. He describes the Ancient Egyptian javelin's features:
It consisted of a long thin shaft, sometimes merely pointed, but generally armed with a head, which was either leaf-shaped, or like the head of a spear, or else four-sided, and attached to the shaft by projections at the angles.
A strap or tasseled head was situated at the lower end of the javelin: it allowed the javelin thrower to recover his javelin after throwing it.
Egyptian military trained from a young age in special military schools. Focusing on gymnastics to gain strength, hardiness, and endurance in childhood, they learned to throw the javelin – along with practicing archery and the battle-axe – when they grew older, before entering a specific regiment. | Javelin | Wikipedia | 508 | 8700358 | https://en.wikipedia.org/wiki/Javelin | Technology | Ranged weapons | null |
Javelins were carried by Egyptian light infantry, as a main weapon, and as an alternative to a bow or spear, generally along with a shield. They also carried a curved sword, club, or hatchet as a sidearm. An important part in battles is often assigned to javelin-men, "whose weapons seem to inflict death at every blow".
Multiple javelins were also sometimes carried by Egyptian war-chariots, in a quiver and/or bow case.
Beyond its military purpose, the javelin was likely also a hunting instrument, for food and sport.
Ancient Greece
The peltasts, usually serving as skirmishers, were armed with several javelins, often with throwing straps to increase stand-off power. The peltasts hurled their javelins at the enemy's heavier troops, the hoplite phalanx, in order to break their lines so that their own army's hoplites could destroy the weakened enemy formation. In the battle of Lechaeum, the Athenian general Iphicrates took advantage of the fact that a Spartan hoplite phalanx operating near Corinth was moving in the open field without the protection of any missile-throwing troops. He decided to ambush it with his force of peltasts. By launching repeated hit-and-run attacks against the Spartan formation, Iphicrates and his men were able to wear the Spartans down, eventually routing them and killing just under half. This marked the first recorded occasion in ancient Greek military history in which a force entirely made up of peltasts had defeated a force of hoplites.
The thureophoroi and thorakitai, who gradually replaced the peltasts, carried javelins in addition to a long thrusting spear and a short sword.
Javelins were often used as an effective hunting weapon, the strap adding enough power to take down large game. Javelins were also used in the Ancient Olympics and other Panhellenic games. They were hurled in a certain direction and whoever hurled it the farthest, as long as it hit tip-first, won that game.
Ancient Rome
Republic and early empire | Javelin | Wikipedia | 428 | 8700358 | https://en.wikipedia.org/wiki/Javelin | Technology | Ranged weapons | null |
In 387 BC, the Gauls invaded Italy, inflicted a crushing defeat on the Roman Republican army, and sacked Rome. After this defeat, the Romans undertook a comprehensive reform of their army and changed the basic tactical formation from the Greek-style phalanx armed with the hasta spear and the clipeus round shield to a more flexible three-line formation. The hastati stood in the first line, the principes in the second line and the triarii in the third line. While the triarii were still armed with hastae, the hastati and the principes were rearmed with short swords and heavy javelins. Each soldier from the hastati and principes lines carried two javelins. This heavy javelin, known as a pilum (plural pila), was about two metres long overall, consisting of an iron shank, about 7 mm in diameter and 60 cm long, with pyramidal head, secured to a wooden shaft. The iron shank was either socketed or, more usually, widened to a flat tang. A pilum usually weighed between , with the versions produced during the empire being somewhat lighter. Pictorial evidence suggests that some versions of the weapon were weighted with a lead ball at the base of the shank in order to increase penetrative power, but no archaeological specimens have been found. Recent experiments have shown pila to have a range of about , although the effective range is only . Pila were sometimes referred to as "javelins", but the archaic term for the javelin was "verutum". | Javelin | Wikipedia | 323 | 8700358 | https://en.wikipedia.org/wiki/Javelin | Technology | Ranged weapons | null |
From the third century BC, the Roman legion added a skirmisher type of soldier to its tactical formation. The velites were light infantry armed with short swords (the gladius or pugio), small round shields, and several small javelins. These javelins were called "veruta" (singular verutum). The velites typically drew near the enemy, hurled javelins against their formation, and then retreated behind the legion's heavier infantry. The velites were considered highly effective in turning back war elephants, on account of discharging a hail of javelins at some range and not presenting a "block" that could be trampled on or otherwise smashed – unlike the close-order infantry behind them. At the Battle of Zama in 202 BC, the javelin-throwing velites proved their worth and were no doubt critical in helping to herd Hannibal's war elephants through the formation to be slaughtered. The velites would slowly have been either disbanded or re-equipped as more-heavily armed legionaries from the time when Gaius Marius and other Roman generals reorganised the army in the late second and early first centuries BC. Their role would most likely have been taken by irregular auxiliary troops as the republic expanded overseas. The verutum was a cheaper missile weapon than the pilum. The verutum was a short-range weapon, with a simply made head of soft iron.
Legionaries of the late republic and early empire often carried two pila, with one sometimes being lighter than the other. Standard tactics called for a Roman soldier to throw his pilum (both if there was time) at the enemy just before charging to engage with his gladius. Some pila had small hand-guards, to protect the wielder if he intended to use it as a melee weapon, but it does not appear that this was common. | Javelin | Wikipedia | 382 | 8700358 | https://en.wikipedia.org/wiki/Javelin | Technology | Ranged weapons | null |
Late Empire
In the late Roman Empire, the Roman infantry came to use a differently-shaped javelin from the earlier pilum. This javelin was lighter and had a greater range. Called a plumbata, it resembled a thick stocky arrow, fletched with leather vanes to provide stability and rotation in flight (which increased accuracy). To overcome its comparatively small mass, the plumbata was fitted with an oval-shaped lead weight socketed around the shaft just forward of the center of balance, giving the weapon its name. Even so, plumbatae were much lighter than pila, and would not have had the armour penetration or shield transfixing capabilities of their earlier counterparts.
Two or three plumbatae were typically clipped to a small wooden bracket on the inside of the large oval or round shields used at the time. Massed troops would unclip and hurl plumbatae as the enemy neared, hopefully stalling their movement and morale by making them clump together and huddle under their shields. With the enemy deprived of rapid movement and their visibility impaired by their own raised shields, the Roman troops were then better placed to exploit the tactical situation. It is unlikely plumbatae were viewed by the Romans as the killing blow, but more as a means of stalling the enemy at ranges greater than previously provided by the heavier and shorter ranged pilum.
Gaul
The Gallic cavalry used to hurl several javelin volleys to soften the enemy before a frontal attack. The Gallic cavalry used their javelins in a tactic similar to that of horse archers' Parthian shot. The Gauls knew how to turn on horseback to throw javelins backwards while appearing to retreat.
Iberia
The Hispanic cavalry was a light cavalry armed with falcatas and several light javelins. The Cantabri tribes invented a military tactic to maximize the advantages of the combination between horse and javelin. In this tactic the horsemen rode around in circles, toward and away from the enemy, continually hurling javelins. The tactic was usually employed against heavy infantry. The constant movement of the horsemen gave them an advantage against slow infantry and made them hard to target. The maneuver was designed to harass and taunt the enemy forces, disrupting close formations. This was commonly used against enemy infantry, especially the heavily armed and slow moving legions of the Romans. This tactic came to be known as the Cantabrian circle. In the late Republic various auxiliary cavalry completely replaced the Italian cavalry contingents and the Hispanic auxiliary cavalry was considered the best. | Javelin | Wikipedia | 511 | 8700358 | https://en.wikipedia.org/wiki/Javelin | Technology | Ranged weapons | null |
Numidia
The Numidians were indigenous tribes of northwest Africa. The Numidian cavalry was a light cavalry usually operating as skirmishers. The Numidian horseman was armed with a small shield and several javelins. The Numidians had a reputation as swift horsemen, cunning soldiers and excellent javelin throwers. It is said that Jugurtha, the Numidian king "...took part in the national pursuits of riding, javelin throwing and competed with other young men in running." [Sallust The Jugurthine War: 6]. The Numidian Cavalry served as mercenaries in the Carthaginian Army and played a key role in assisting both Hannibal and Scipio during the Second Punic War.
Middle ages
Norse
There is some literary and archeological evidence that the Norse were familiar with and used the javelin for hunting and warfare, but they commonly used a spear designed for both throwing and thrusting. The Old Norse word for javelin was frakka.
Anglo-Saxons
The Anglo-Saxon term for javelin was france. In Anglo-Saxon warfare, soldiers usually formed a shield wall and used heavy weapons like Danish axes, swords and spears. Javelins, including barbed angons, were used as an offensive weapon from behind the shield wall or by warriors who left the protective formation and attacked the enemy as skirmishers. Designed to be difficult to remove from either flesh or wood, the Angon javelin used by Anglo-Saxon warriors was an effective means of disabling an opponent or his shield, thus having the potential to disrupt opposing shield-walls.
Iberia
The Almogavars were a class of Aragonese infantrymen armed with a short sword, a shield and two heavy javelins, known as azcona. The equipment resembled that of a Roman legionary and the use of the heavy javelins was much the same.
The Jinetes were Arabic light horsemen armed with several javelins, a sword, and a shield. They were proficient at skirmishing and rapid maneuver, and played an important role in Arabic mounted warfare throughout the Reconquista until the sixteenth century. These units were widespread among the Italian infantrymen of the fifteenth century. | Javelin | Wikipedia | 441 | 8700358 | https://en.wikipedia.org/wiki/Javelin | Technology | Ranged weapons | null |
Wales
The Welsh, particularly those of North Wales, used the javelin as one of their main weapons. During the Norman and later English invasions, the primary Welsh tactic was to rain javelins on the tired, hungry, and heavily armoured English troops and then retreat into the mountains or woods before the English troops could pursue and attack them. This tactic was very successful, since it demoralized and damaged the English armies while the Welsh ranks suffered little.
Ireland
The kern of Ireland used javelins as their main weapon as they accompanied the more heavily armoured galloglass.
Chinese
Various kingdoms and dynasties in China have used javelins, such as the iron-headed javelin of the Qing dynasty.
Qi Jiguang's anti-pirate army included javelin throwers with shields.
Modern age
Africa
Many African kingdoms have used the javelin as their main weapon since ancient times. Typical African warfare was based on ritualized stand-off encounters involving throwing javelins without advancing for close combat. In the flag of Eswatini there is a shield and two javelins, which symbolize the protection from the country's enemies.
Zulu
The Zulu warriors used a long version of the assegai javelin as their primary weapon. The Zulu legendary leader Shaka initiated military reforms in which a short stabbing spear, with a long, swordlike spearhead named iklwa, had become the Zulu warrior's main weapon and was used as a mêlée weapon. The assegai was not discarded, but was used for an initial missile assault. With the larger shields, introduced by Shaka to the Zulu army, the short spears used as stabbing swords and the opening phase of javelin attack; the Zulu regiments were quite similar to the Roman legion with its Scutum, Gladius and Pilum tactical combination.
Mythology
Norse mythology
In Norse mythology, Odin, the chief god, carried a javelin or spear called Gungnir. It was created by a group of dwarves known as the Sons of Ivaldi who also fashioned the ship of Freyr called Skidbladnir and the golden hair of Sif. It had the property of always finding its mark ("the spear never stopped in its thrust"). During the final conflict of Ragnarok between the gods and giants, Odin will use Gungnir to attack the wolf Fenrir before being devoured by him. | Javelin | Wikipedia | 469 | 8700358 | https://en.wikipedia.org/wiki/Javelin | Technology | Ranged weapons | null |
During the war (and subsequent alliance) between the Aesir and Vanir at the dawn of time, Odin hurled a javelin over the enemy host which, according to custom, was thought to bring good fortune or victory to the thrower. Odin also wounded himself with a spear while hanging from Yggdrasil, the World Tree, in his ritual quest for knowledge but in neither case is the weapon referred to specifically as Gungnir.
When the god Baldr began to have prophetic dreams of his own death, his mother Frigg extracted an oath from all things in nature not to harm him. However, she neglected the mistletoe, thinking it was too young to make, let alone respect, such a solemn vow. When Loki learned of this weakness, he had a javelin or dart made from one of its branches and tricked Hod, the blind god, into hurling it at Baldr and causing his death.
Lusitanian mythology
The god Runesocesius is identified as a "god of the javelin". | Javelin | Wikipedia | 208 | 8700358 | https://en.wikipedia.org/wiki/Javelin | Technology | Ranged weapons | null |
Nanofiltration is a membrane filtration process that uses nanometer sized pores through which particles smaller than about 1–10 nanometers pass through the membrane. Nanofiltration membranes have pore sizes of about 1–10 nanometers, smaller than those used in microfiltration and ultrafiltration, but a slightly bigger than those in reverse osmosis. Membranes used are predominantly polymer thin films. It is used to soften, disinfect, and remove impurities from water, and to purify or separate chemicals such as pharmaceuticals.
Membranes
Membrane materials that are commonly used are polymer thin films such as polyethylene terephthalate or metals such as aluminium. Pore dimensions are controlled by pH, temperature and time during development with pore densities ranging from 1 to 106 pores per cm2.
Membranes made from polyethylene terephthalate (PET) and other similar materials, are referred to as "track-etch" membranes, named after the way the pores on the membranes are made. "Tracking" involves bombarding the polymer thin film with high energy particles. This results in making tracks that are chemically developed into the membrane, or "etched" into the membrane, which are the pores.
Membranes created from metal such as alumina membranes, are made by electrochemically growing a thin layer of aluminum oxide from aluminum in an acidic medium.
Range of applications
Historically, nanofiltration and other membrane technology used for molecular separation was applied entirely on aqueous systems. The original uses for nanofiltration were water treatment and in particular water softening. Nanofilters "soften" water by retaining scale-forming divalent ions (e.g. Ca2+, Mg2+).
Nanofiltration has been extended into other industries such as milk and juice production as well as pharmaceuticals, fine chemicals, and flavour and fragrance industries.
Advantages and disadvantages | Nanofiltration | Wikipedia | 389 | 8702779 | https://en.wikipedia.org/wiki/Nanofiltration | Physical sciences | Other separations | Chemistry |
One of the main advantages of nanofiltration as a method of softening water is that during the process of retaining calcium and magnesium ions while passing smaller hydrated monovalent ions, filtration is performed without adding extra sodium ions, as used in ion exchangers. Many separation processes do not operate at room temperature (e.g. distillation), which greatly increases the cost of the process when continuous heating or cooling is applied. Performing gentle molecular separation is linked with nanofiltration that is often not included with other forms of separation processes (centrifugation). These are two of the main benefits that are associated with nanofiltration.
Nanofiltration has a very favorable benefit of being able to process large volumes and continuously produce streams of products. Still, Nanofiltration is the least used method of membrane filtration in industry as the membrane pores sizes are limited to only a few nanometers. Anything smaller, reverse osmosis is used and anything larger is used for ultrafiltration. Ultrafiltration can also be used in cases where nanofiltration can be used, due to it being more conventional.
A main disadvantage associated with nanotechnology, as with all membrane filter technology, is the cost and maintenance of the membranes used. Nanofiltration membranes are an expensive part of the process. Repairs and replacement of membranes is dependent on total dissolved solids, flow rate and components of the feed. With nanofiltration being used across various industries, only an estimation of replacement frequency can be used. This causes nanofilters to be replaced a short time before or after their prime usage is complete.
Design and operation
Industrial applications of membranes require hundreds to thousands of square meters of membranes and therefore an efficient way to reduce the footprint by packing them is required. Membranes first became commercially viable when low cost methods of housing in 'modules' were achieved.
Membranes are not self-supporting. They need to be stayed by a porous support that can withstand the pressures required to operate the NF membrane without hindering the performance of the membrane. To do this effectively, the module needs to provide a channel to remove the membrane permeation and provide appropriate flow condition that reduces the phenomena of concentration polarisation. A good design minimises pressure losses on both the feed side and permeate side and thus energy requirements.
Concentration polarisation | Nanofiltration | Wikipedia | 465 | 8702779 | https://en.wikipedia.org/wiki/Nanofiltration | Physical sciences | Other separations | Chemistry |
Concentration polarization describes the accumulation of the species being retained close to the surface of the membrane which reduces separation capabilities. It occurs because the particles are convected towards the membrane with the solvent and its magnitude is the balance between this convection caused by solvent flux and the particle transport away from the membrane due to the concentration gradient (predominantly caused by diffusion.) Although concentration polarization is easily reversible, it can lead to fouling of the membrane.
Spiral wound module
Spiral wound modules are the most commonly used style of module and are 'standardized' design, available in a range of standard diameters (2.5", 4" and 8") to fit standard pressure vessel that can hold several modules in series connected by O-rings. The module uses flat sheets wrapped around a central tube. The membranes are glued along three edges over a permeate spacer to form 'leaves'. The permeate spacer supports the membrane and conducts the permeate to the central permeate tube. Between each leaf, a mesh like feed spacer is inserted. The reason for the mesh like dimension of the spacer is to provide a hydrodynamic environment near the surface of the membrane that discourages concentration polarisation. Once the leaves have been wound around the central tube, the module is wrapped in a casing layer and caps placed on the end of the cylinder to prevent 'telescoping' that can occur in high flow rate and pressure conditions
Tubular module
Tubular modules look similar to shell and tube heat exchangers with bundles of tubes with the active surface of the membrane on the inside. Flow through the tubes is normally turbulent, ensuring low concentration polarisation but also increasing energy costs. The tubes can either be self-supporting or supported by insertion into perforated metal tubes. This module design is limited for nanofiltration by the pressure they can withstand before bursting, limiting the maximum flux possible. Due to both the high energy operating costs of turbulent flow and the limiting burst pressure, tubular modules are more suited to 'dirty' applications where feeds have particulates such as filtering raw water to gain potable water in the Fyne process. The membranes can be easily cleaned through a 'pigging' technique with foam balls are squeezed through the tubes, scouring the caked deposits.
Flux enhancing strategies | Nanofiltration | Wikipedia | 467 | 8702779 | https://en.wikipedia.org/wiki/Nanofiltration | Physical sciences | Other separations | Chemistry |
These strategies work to reduce the magnitude of concentration polarisation and fouling. There is a range of techniques available however the most common is feed channel spacers as described in spiral wound modules. All of the strategies work by increasing eddies and generating a high shear in the flow near the membrane surface. Some of these strategies include vibrating the membrane, rotating the membrane, having a rotor disk above the membrane, pulsing the feed flow rate and introducing gas bubbling close to the surface of the membrane.
Characterisation
Performance parameters
Retention of both charged and uncharged solutes and permeation measurements can be categorised into performance parameters since the performance under natural conditions of a membrane is based on the ratio of solute retained/ permeated through the membrane.
For charged solutes, the ionic distribution of salts near the membrane-solution interface plays an important role in determining the retention characteristic of a membrane. If the charge of the membrane and the composition and concentration of the solution to be filtered is known, the distribution of various salts can be found. This in turn can be combined with the known charge of the membrane and the Gibbs–Donnan effect to predict the retention characteristics for that membrane.
Uncharged solutes cannot be characterised simply by Molecular Weight Cut Off (MWCO,) although in general an increase in molecular weight or solute size leads to an increase in retention. The charge and structure, pH of the solute, influence the retention characteristics.
Morphology parameters
The morphology of a membrane is usually established by microscopy. Atomic force microscopy (AFM) is one method used to characterise the surface roughness of a membrane by passing a small sharp tip (<100 Ă) across the surface of a membrane and measuring the resulting Van der Waals force between the atoms in the end of the tip and the surface. This is useful as a direct correlation between surface roughness and colloidal fouling has been developed. Correlations also exist between fouling and other morphology parameters, such as hydrophobe, showing that the more hydrophobic a membrane is, the less prone to fouling it is. See membrane fouling for more information. | Nanofiltration | Wikipedia | 433 | 8702779 | https://en.wikipedia.org/wiki/Nanofiltration | Physical sciences | Other separations | Chemistry |
Methods to determine the porosity of porous membranes have also been found via permporometry, making use of differing vapour pressures to characterise the pore size and pore size distribution within the membrane. Initially all pores in the membrane are completely filled with a liquid and as such no permeation of a gas occurs, but after reducing the relative vapour pressure some gaps will start to form within the pores as dictated by the Kelvin equation. Polymeric (non-porous) membranes cannot be subjected to this methodology as the condensable vapour should have a negligible interaction within the membrane.
Solute transport and rejection
Unlike membranes with larger and smaller pore sizes, passage of solutes through nanofiltration is significantly more complex.
Because of the pore sizes, there are three modes of transport of solutes through the membrane. These include 1) diffusion (molecule travel due to concentration potential gradients, as seen through reverse osmosis membranes), 2) convection (travel with flow, like in larger pore size filtration such as microfiltration), and 3) electromigration (attraction or repulsion from charges within and near the membrane).
Additionally, the exclusion mechanisms in nanofiltration are more complex than in other forms of filtration. Most filtration systems operate solely by size (steric) exclusion, but at small length scales seen in nanofiltration, important effects include surface charge and hydration (solvation shell). The exclusion due to hydration is referred to as dielectric exclusion, a reference to the dielectric constants (energy) associated with a particles precense in solution versus within a membrane substrate. Solution pH strongly impacts surface charge, providing a method to understand and better control rejection.
The transport and exclusion mechanisms are heavily influenced by membrane pore size, solvent viscosity, membrane thickness, solute diffusivity, solution temperature, solution pH, and membrane dielectric constant. The pore size distribution is also important. Modeling rejection accurately for NF is very challenging. It can be done with applications of the Nernst–Planck equation, although a heavy reliance on fitting parameters to experimental data is usually required.
In general, charged solutes are much more effectively rejected in NF than uncharged solutes, and multivalent solutes like (valence of 2) experience very high rejection.
Typical figures for industrial applications | Nanofiltration | Wikipedia | 496 | 8702779 | https://en.wikipedia.org/wiki/Nanofiltration | Physical sciences | Other separations | Chemistry |
Keeping in mind that NF is usually part of a composite system for purification, a single unit is chosen based on the design specifications for the NF unit. For drinking water purification many commercial membranes exist, coming from chemical families having diverse structures, chemical tolerances and salt rejections.
NF units in drinking water purification range from extremely low salt rejection (<5% in 1001A membranes) to almost complete rejection (99% in 8040-TS80-TSA membranes.) Flow rates range from 25 to 60 m3/day for each unit, so commercial filtration requires multiple NF units in parallel to process large quantities of feed water. The pressures required in these units are generally between 4.5 and 7.5 bar.
For seawater desalination using a NF-RO system a typical process is shown below.
Because NF permeate is rarely clean enough to be used as the final product for drinking water and other water purification, is it commonly used as a pre treatment step for reverse osmosis (RO) as is shown above.
Post-treatment
As with other membrane based separations such as ultrafiltration, microfiltration and reverse osmosis, post-treatment of either permeate or retentate flow streams (depending on the application) – is a necessary stage in industrial NF separation prior to commercial distribution of the product. The choice and order of unit operations employed in post-treatment is dependent on water quality regulations and the design of the NF system. Typical NF water purification post-treatment stages include aeration and disinfection & stabilisation.
Aeration
A Polyvinyl chloride (PVC) or fibre-reinforced plastic (FRP) degasifier is used to remove dissolved gases such as carbon dioxide and hydrogen sulfide from the permeate stream. This is achieved by blowing air in a countercurrent direction to the water falling through packing material in the degasifier. The air effectively strips the unwanted gases from the water.
Disinfection and stabilisation | Nanofiltration | Wikipedia | 417 | 8702779 | https://en.wikipedia.org/wiki/Nanofiltration | Physical sciences | Other separations | Chemistry |
The permeate water from a NF separation is demineralised and may be disposed to large changes in pH, thus providing a substantial risk of corrosion in piping and other equipment components. To increase the stability of the water, chemical addition of alkaline solutions such as lime and caustic soda is employed. Furthermore, disinfectants such as chlorine or chloroamine are added to the permeate, as well as phosphate or fluoride corrosion inhibitors in some cases.
Research trends
Challenges in nanofiltration (NF) technology include minimising membrane fouling and reducing energy requirements. Thin film composite membranes (TFC), which consist of a number of extremely thin selective layers interfacially polymerized over a microporous substrate, have had commercial success in industrial membrane applications. Electrospunnanofibrous membrane layers (ENMs) enhances permeate flux.
Energy-efficient alternatives to the commonly used spiral wound arrangement are hollow fibre membranes, which require less pre-treatment. Titanium Dioxide nanoparticles have been used to minimize for membrane fouling. | Nanofiltration | Wikipedia | 227 | 8702779 | https://en.wikipedia.org/wiki/Nanofiltration | Physical sciences | Other separations | Chemistry |
In computing, a directory is a file system cataloging structure which contains references to other computer files, and possibly other directories. On many computers, directories are known as folders, or drawers, analogous to a workbench or the traditional office filing cabinet. The name derives from books like a telephone directory that lists the phone numbers of all the people living in a certain area.
Files are organized by storing related files in the same directory. In a hierarchical file system (that is, one in which files and directories are organized in a manner that resembles a tree), a directory contained inside another directory is called a subdirectory. The terms parent and child are often used to describe the relationship between a subdirectory and the directory in which it is cataloged, the latter being the parent. The top-most directory in such a filesystem, which does not have a parent of its own, is called the root directory.
The freedesktop.org media type for directories within many Unix-like systems – including but not limited to systems using GNOME, KDE Plasma 5, or ROX Desktop as the desktop environment – is "inode/directory". This is not an IANA registered media type.
Overview
Historically, and even on some modern embedded systems, the file systems either had no support for directories at all or had only a "flat" directory structure, meaning subdirectories were not supported; there were only a group of top-level directories, each containing files. In modern systems, a directory can contain a mix of files and subdirectories.
A reference to a location in a directory system is called a path.
In many operating systems, programs have an associated working directory in which they execute. Typically, file names accessed by the program are assumed to reside within this directory if the file names are not specified with an explicit directory name.
Some operating systems restrict a user's access only to their home directory or project directory, thus isolating their activities from all other users. In early versions of Unix the root directory was the home directory of the root user, but modern Unix usually uses another directory such as for this purpose. | Directory (computing) | Wikipedia | 449 | 5515027 | https://en.wikipedia.org/wiki/Directory%20%28computing%29 | Technology | Data storage and memory | null |
In keeping with Unix philosophy, Unix systems treat directories as a type of file. Caveats include not being able to write to a directory file except indirectly by creating, renaming and removing file system objects in the directory and only being able to read from a directory file using directory-specific library routines and system calls that return records, not a byte-stream.
Folder metaphor
The name folder, presenting an analogy to the file folder used in offices, and used in a hierarchical file system design for the Electronic Recording Machine, Accounting (ERMA) Mark 1 published in 1958 as well as by Xerox Star, is used in almost all modern operating systems' desktop environments. Folders are often depicted with icons which visually resemble physical file folders.
There is a difference between a directory, which is a file system concept, and the graphical user interface metaphor that is used to represent it (a folder). For example, Microsoft Windows uses the concept of special folders to help present the contents of the computer to the user in a fairly consistent way that frees the user from having to deal with absolute directory paths, which can vary between versions of Windows, and between individual installations. Many operating systems also have the concept of "smart folders" or virtual folders that reflect the results of a file system search or other operation. These folders do not represent a directory in the file hierarchy. Many email clients allow the creation of folders to organize email. These folders have no corresponding representation in the filesystem structure.
If one is referring to a container of documents, the term folder is more appropriate. The term directory refers to the way a structured list of document files and folders are stored on the computer. The distinction can be due to the way a directory is accessed; on Unix systems, is usually referred to as a directory when viewed in a command line console, but if accessed through a graphical file manager, users may sometimes call it a folder.
Lookup cache
Operating systems that support hierarchical filesystems (practically all modern ones) implement a form of caching to RAM of recent path lookups. In the Unix world, this is usually called Directory Name Lookup Cache (DNLC), although it is called dcache on Linux.
For local filesystems, DNLC entries normally expire only under pressure from other more recent entries. For network file systems a coherence mechanism is necessary to ensure that entries have not been invalidated by other clients. | Directory (computing) | Wikipedia | 502 | 5515027 | https://en.wikipedia.org/wiki/Directory%20%28computing%29 | Technology | Data storage and memory | null |
Scops owls are typical owls in family Strigidae belonging to the genus Otus and are restricted to the Old World. Otus is the largest genus of owls with 59 species. Scops owls are colored in various brownish hues, sometimes with a lighter underside and/or face, which helps to camouflage them against the bark of trees. Some are polymorphic, occurring in a greyish- and a reddish-brown morph. They are small and agile, with both sexes being compact in size and shape. Female scops owls are usually larger than males.
For most of the 20th century, this genus included the American screech owls, which are now again separated in Megascops based on a range of behavioral, biogeographical, morphological and DNA sequence data.
Taxonomy
The genus Otus was introduced in 1769 by the Welsh naturalist Thomas Pennant for the Indian scops owl (O. bakkamoena). The name is derived from the Latin word and the Greek word ōtos meaning horned or eared owl (cf. οὖς, ὠτός, "ear"). The generic name Scops that was proposed by Marie Jules César Savigny in 1809 is a junior synonym and is derived from the Greek (skōps) meaning small kind of owl, Otus scops.
By the mid-19th century, it was becoming clear that Otus encompassed more than one genus. First, in 1848, the screech owls were split off as Megascops. The white-faced owls of Africa, with their huge eyes and striking facial coloration, were separated in Ptilopsis in 1851. In 1854, the highly apomorphic white-throated screech owl of the Andes was placed in the monotypic genus Macabra. Gymnasio was established in the same year for the Puerto Rican owl, and the bare-legged owl (or "Cuban screech owl") was separated in Gymnoglaux the following year; the latter genus was sometimes merged with Gymnasio by subsequent authors. The Palau scops owl, described only in 1872 and little-known to this day, was eventually separated in Pyrroglaux by Yoshimaro Yamashina in 1938. | Scops owl | Wikipedia | 454 | 585682 | https://en.wikipedia.org/wiki/Scops%20owl | Biology and health sciences | Strigiformes | Animals |
In the early 20th century, the lumping-together of taxa had come to be preferred. The 3rd edition of the AOU checklist in 1910 placed the screech owls back in Otus. Although this move was never unequivocally accepted, it was the dominant treatment throughout most of the 20th century. In 1988 it was attempted to resolve this by re-establishing all those genera split some 140 years earlier at subgenus rank inside Otus. Still, the diversity and distinctness of the group failed to come together in a good evolutionary and phylogenetic picture, and it was not until the availability of DNA sequence data that this could be resolved. In 1999, a preliminary study of mtDNA cytochrome b across a wide range of owls found that even the treatment as subgenera was probably unsustainable and suggested that most of the genera proposed around 1850 should be accepted. Though there was some debate about the reliability of these findings at first, they have been confirmed by subsequent studies. In 2003, the AOU formally re-accepted the genus Megascops again.
Species
The genus Otus contains 59 species (including 3 extinct species): | Scops owl | Wikipedia | 233 | 585682 | https://en.wikipedia.org/wiki/Scops%20owl | Biology and health sciences | Strigiformes | Animals |
Giant scops owl, Otus gurneyi
White-fronted scops owl, Otus sagittatus
Reddish scops owl, Otus rufescens
Serendib scops owl, Otus thilohoffmanni
Sandy scops owl, Otus icterorhynchus
Sokoke scops owl, Otus ireneae
Andaman scops owl, Otus balli
Flores scops owl, Otus alfredi
Mountain scops owl, Otus spilocephalus
Javan scops owl, Otus angelinae
Mindanao scops owl, Otus mirus
Luzon scops owl, Otus longicornis
Mindoro scops owl, Otus mindorensis
São Tomé scops owl, Otus hartlaubi
Torotoroka scops owl, Otus madagascariensis – formerly included in O. rutilus
Rainforest scops owl, Otus rutilus
Mayotte scops owl, Otus mayottensis – formerly included in O. rutilus
Karthala scops owl, Otus pauliani
Anjouan scops owl, Otus capnodes
Moheli scops owl, Otus moheliensis
† Réunion scops owl, Otus grucheti – extinct, formerly placed in the genus Mascarenotus
† Mauritius scops owl, Otus sauzieri – extinct, formerly placed in the genus Mascarenotus
† Rodrigues scops owl, Otus murivorus – extinct, formerly placed in the genus Mascarenotus
Pemba scops owl, Otus pembaensis
Eurasian scops owl, Otus scops
Cyprus scops owl, Otus cyprius – formerly included in O. scops
Pallid scops owl, Otus brucei
Arabian scops owl, Otus pamelae
African scops owl, Otus senegalensis
Annobón scops owl, Otus feae – formerly included in O. senegalensis
Socotra scops owl, Otus socotranus
Oriental scops owl, Otus sunia
Ryūkyū scops owl, Otus elegans
Moluccan scops owl, Otus magicus
Wetar scops owl, Otus tempestatis
Sula scops owl, Otus sulaensis
Biak scops owl, Otus beccarii
Sulawesi scops owl, Otus manadensis
Banggai scops owl, Otus mendeni
Siau scops owl, Otus siaoensis | Scops owl | Wikipedia | 504 | 585682 | https://en.wikipedia.org/wiki/Scops%20owl | Biology and health sciences | Strigiformes | Animals |
Sangihe scops owl, Otus collari
Mantanani scops owl, Otus mantananensis
Seychelles scops owl, Otus insularis
Nicobar scops owl, Otus alius
Simeulue scops owl, Otus umbra
Enggano scops owl, Otus enganensis
Mentawai scops owl, Otus mentawi
Rajah scops owl, Otus brookii
Indian scops owl, Otus bakkamoena
Collared scops owl, Otus lettia – formerly included in O. bakkamoena
Japanese scops owl, Otus semitorques – formerly included in O. bakkamoena
Sunda scops owl, Otus lempiji – formerly included in O. bakkamoena
Philippine scops owl, Otus megalotis
Negros scops owl, Otus nigrorum – formerly included in O. megalotis
Everett's scops owl, Otus everetti – formerly included in O. megalotis
Palawan scops owl, Otus fuliginosus
Wallace's scops owl, Otus silvicola
Rinjani scops owl, Otus jolandae
Palau scops owl, Otus podarginus – formerly placed in the monotypic genus Pyrroglaux
Principe scops owl, Otus bikegila
Two extinct species are sometimes placed in the genus:
† Madeiran scops owl, Otus mauli (extinct, c. 15th century)
† São Miguel scops owl, Otus frutuosoi (extinct, c. 15th century) | Scops owl | Wikipedia | 338 | 585682 | https://en.wikipedia.org/wiki/Scops%20owl | Biology and health sciences | Strigiformes | Animals |
An apparent Otus owl was heard calling at about 1,000 meters ASL south of the summit of Camiguin in the Philippines on May 14, 1994. No scops owls had previously known from this island, and given that new species of Otus are occasionally discovered, it may have been an undescribed taxon.
In July 2016, an unknown Otus species was photographed on Príncipe. The image was published on Ornithomedia. Dubbed Otus bikegila, it was formally described in 2022.
Formerly placed here
As noted above, the fossil record of scops owls gives an incomplete picture of their evolution at present. While older sources cite many species of supposed extinct Otus (or "Scops"), these are now placed in entirely different genera:
"Otus" henrici was a barn owl of the genus Selenornis
"Otus" providentiae was a burrowing owl, probably a paleosubspecies
"Otus" wintershofensis may be close to extant genus Ninox and some material assigned to it belongs into Intutula
"Scops" commersoni is a junior synonym of the recently extinct Mauritius owl, referring to pictures and descriptions which mention ear tufts; the subfossil material of this species had been erroneously assigned to tuftless owls. | Scops owl | Wikipedia | 273 | 585682 | https://en.wikipedia.org/wiki/Scops%20owl | Biology and health sciences | Strigiformes | Animals |
Evolution
The evolutionary relationships of the scops and screech owls are not entirely clear. What is certain is that they are very closely related; they may be considered sister lineages which fill essentially the same ecological niche in their allopatric ranges. A screech-owl fossil from the Late Pliocene of Kansas – which is almost identical to eastern and western screech owls – indicate a long-standing presence of these birds in the Americas, while coeval scops owl fossils very similar to the Eurasian scops-owl have been found at S'Onix on the Spanish island Majorca. The scops and screech owl lineage probably evolved at some time during the Miocene (like most other genera of typical owls), and the three (see below) modern lineages separated perhaps roughly 5 million years ago. Note that there is no reliable estimate of divergence time, as Otus and Megascops are osteologically very similar, as is to be expected from a group that has apparently conserved its ecomorphology since before its evolutionary radiation. As almost all scops and screech owls today, their common ancestor was in all probability already a small owl, with ear tufts and at least the upper tarsus ("leg") feathered.
However that may be, the hypothesis that the group evolved from Old World stock is tentatively supported by cytochrome b sequence data.
Ecology and behaviour
While late 19th-century ornithologists knew little of the variation of these cryptic birds which often live in far-off places, with every new taxon being described a few differences between the Old and New World "scops" owls became more and more prominent. Namely, the scops owls give a whistling call or a row of high-pitched hoots with less than four individual hoots per second. This call is given in social interaction or when the owl tries to scare away other animals. The screech owls on the other hand are named for their piercing trills of more than four individual notes per second. They also have a kind of song, which is a short sequence of varying calls given by the males when they try to attract females to their nests, or between members of a pair. There are a few other differences such as the screech owls almost never being brown below which is common in scops owls, but the difference in vocalizations is most striking. | Scops owl | Wikipedia | 488 | 585682 | https://en.wikipedia.org/wiki/Scops%20owl | Biology and health sciences | Strigiformes | Animals |
Scops owls hunt from perches in semi-open landscapes. They prefer areas which contain old trees with hollows; these are home to their prey which includes insects, reptiles, small mammals such as bats and mice and other small birds. The owls will also eat earthworms, amphibians and aquatic invertebrates. Scops owls have a good sense of hearing which helps them locate their prey in any habitat. They also possess well-developed raptorial claws and a curved bill, both of which are used for tearing their prey into pieces small enough to swallow easily.
Scops owls are primarily solitary birds. Most species lay and incubate their eggs in a cavity nest that was originally made by another animal. During the incubation period, the male will feed the female. These birds are monogamous, with biparental care, and only fledge one young per year. The young of most scops owls are altricial to semialtricial.
As opposed to screech owls, scops owls have only a single type of call. This consists of a series of whistles or high-pitched hoots, given with a frequency of 4 calls per second or less, or of a single, drawn-out whistle. Calls differ widely between species in type and pitch, and in the field are often the first indication of these birds' presence, as well as the most reliable means to distinguish between species. Some, like the recently described Serendib scops owl (Otus thilohoffmanni), were discovered because their vocalizations were unfamiliar to experts in birdcalls. | Scops owl | Wikipedia | 327 | 585682 | https://en.wikipedia.org/wiki/Scops%20owl | Biology and health sciences | Strigiformes | Animals |
The radius or radial bone (: radii or radiuses) is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is longer than the radius, but the radius is thicker. The radius is a long bone, prism-shaped and slightly curved longitudinally.
The radius is part of two joints: the elbow and the wrist. At the elbow, it joins with the capitulum of the humerus, and in a separate region, with the ulna at the radial notch. At the wrist, the radius forms a joint with the ulna bone.
The corresponding bone in the lower leg is the tibia.
Structure
The long narrow medullary cavity is enclosed in a strong wall of compact bone. It is thickest along the interosseous border and thinnest at the extremities, same over the cup-shaped articular surface (fovea) of the head.
The trabeculae of the spongy tissue are somewhat arched at the upper end and pass upward from the compact layer of the shaft to the fovea capituli (the humerus's cup-shaped articulatory notch); they are crossed by others parallel to the surface of the fovea. The arrangement at the lower end is somewhat similar. It is missing in radial aplasia.
The radius has a body and two extremities. The upper extremity of the radius consists of a somewhat cylindrical head articulating with the ulna and the humerus, a neck, and a radial tuberosity. The body of the radius is self-explanatory, and the lower extremity of the radius is roughly quadrilateral in shape, with articular surfaces for the ulna, scaphoid and lunate bones. The distal end of the radius forms two palpable points, radially the styloid process and Lister's tubercle on the ulnar side. Along with the proximal and distal radioulnar articulations, an interosseous membrane originates medially along the length of the body of the radius to attach the radius to the ulna.
Near the wrist
The distal end of the radius is large and of quadrilateral form. | Radius (bone) | Wikipedia | 492 | 585732 | https://en.wikipedia.org/wiki/Radius%20%28bone%29 | Biology and health sciences | Skeletal system | Biology |
Joint surfaces
It is provided with two articular surfaces – one below, for the carpus, and another at the medial side, for the ulna.
The carpal articular surface is triangular, concave, smooth, and divided by a slight antero-posterior ridge into two parts. Of these, the lateral, triangular, articulates with the scaphoid bone; the medial, quadrilateral, with the lunate bone.
The articular surface for the ulna is called the ulnar notch (sigmoid cavity) of the radius; it is narrow, concave, smooth, and articulates with the head of the ulna.
These two articular surfaces are separated by a prominent ridge, to which the base of the triangular articular disk is attached; this disk separates the wrist-joint from the distal radioulnar articulation.
Other surfaces
This end of the bone has three non-articular surfaces – volar, dorsal, and lateral.
The volar surface, rough and irregular, affords attachment to the volar radiocarpal ligament.
The dorsal surface is convex, affords attachment to the dorsal radiocarpal ligament, and is marked by three grooves. Enumerated from the lateral side:
The first groove is broad, but shallow, and subdivided into two by a slight ridge: the lateral of these two, transmits the tendon of the extensor carpi radialis longus muscle; the medial, the tendon of the extensor carpi radialis brevis muscle.
The second is deep but narrow, and bounded laterally by a sharply defined ridge; it is directed obliquely from above downward and lateralward, and transmits the tendon of the extensor pollicis longus muscle.
The third is broad, for the passage of the tendons of the extensor indicis proprius and extensor digitorum communis.
The lateral surface is prolonged obliquely downward into a strong, conical projection, the styloid process, which gives attachment by its base to the tendon of the brachioradialis, and by its apex to the radial collateral ligament of wrist joint. The lateral surface of this process is marked by a flat groove, for the tendons of the abductor pollicis longus muscle and extensor pollicis brevis muscle. | Radius (bone) | Wikipedia | 488 | 585732 | https://en.wikipedia.org/wiki/Radius%20%28bone%29 | Biology and health sciences | Skeletal system | Biology |
Body
The body of the radius (or shaft of radius) is prismoid in form, narrower above than below, and slightly curved, so as to be convex lateralward. It presents three borders and three surfaces.
Borders
The volar border (margo volaris; anterior border; palmar;) extends from the lower part of the tuberosity above to the anterior part of the base of the styloid process below, and separates the volar from the lateral surface. Its upper third is prominent, and from its oblique direction has received the name of the oblique line of the radius; it gives origin to the flexor digitorum superficialis muscle (also flexor digitorum sublimis) and flexor pollicis longus muscle; the surface above the line gives insertion to part of the supinator muscle. The middle third of the volar border is indistinct and rounded. The lower fourth is prominent, and gives insertion to the pronator quadratus muscle, and attachment to the dorsal carpal ligament; it ends in a small tubercle, into which the tendon of the brachioradialis muscle is inserted.
The dorsal border (margo dorsalis; posterior border) begins above at the back of the neck, and ends below at the posterior part of the base of the styloid process; it separates the posterior from the lateral surface. is indistinct above and below, but well-marked in the middle third of the bone.
The interosseous border (internal border; crista interossea; interosseous crest;) begins above, at the back part of the tuberosity, and its upper part is rounded and indistinct; it becomes sharp and prominent as it descends, and at its lower part divides into two ridges which are continued to the anterior and posterior margins of the ulnar notch. To the posterior of the two ridges the lower part of the interosseous membrane is attached, while the triangular surface between the ridges gives insertion to part of the pronator quadratus muscle. This crest separates the volar from the dorsal surface, and gives attachment to the interosseous membrane. The connection between the two bones is actually a joint referred to as a syndesmosis joint. | Radius (bone) | Wikipedia | 462 | 585732 | https://en.wikipedia.org/wiki/Radius%20%28bone%29 | Biology and health sciences | Skeletal system | Biology |
Surfaces
The volar surface (facies volaris; anterior surface) is concave in its upper three-fourths, and gives origin to the flexor pollicis longus muscle; it is broad and flat in its lower fourth, and affords insertion to the Pronator quadratus. A prominent ridge limits the insertion of the Pronator quadratus below, and between this and the inferior border is a triangular rough surface for the attachment of the volar radiocarpal ligament. At the junction of the upper and middle thirds of the volar surface is the nutrient foramen, which is directed obliquely upward.
The dorsal surface (facies dorsalis; posterior surface) is convex, and smooth in the upper third of its extent, and covered by the Supinator. Its middle third is broad, slightly concave, and gives origin to the Abductor pollicis longus above, and the extensor pollicis brevis muscle below. Its lower third is broad, convex, and covered by the tendons of the muscles which subsequently run in the grooves on the lower end of the bone.
The lateral surface (facies lateralis; external surface) is convex throughout its entire extent and is known as the convexity of the radius, curving outwards to be convex at the side. Its upper third gives insertion to the supinator muscle. About its center is a rough ridge, for the insertion of the pronator teres muscle. Its lower part is narrow, and covered by the tendons of the abductor pollicis longus muscle and extensor pollicis brevis muscle. | Radius (bone) | Wikipedia | 335 | 585732 | https://en.wikipedia.org/wiki/Radius%20%28bone%29 | Biology and health sciences | Skeletal system | Biology |
Near the elbow
The upper extremity of the radius (or proximal extremity) presents a head, neck, and tuberosity.
The radial head has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum (or capitellum) of the humerus. The circumference of the head is smooth; it is broad medially where it articulates with the radial notch of the ulna, narrow in the rest of its extent, which is embraced by the annular ligament. The deepest point in the fovea is not axi-symmetric with the long axis of the radius, creating a cam effect during pronation and supination.
The head is supported on a round, smooth, and constricted portion called the neck, on the back of which is a slight ridge for the insertion of part of the supinator muscle.
Beneath the neck, on the medial side, is an eminence, the radial tuberosity; its surface is divided into a posterior, rough portion, for the insertion of the tendon of the biceps brachii muscle, and an anterior, smooth portion, on which a bursa is interposed between the tendon and the bone.
Development
The radius is ossified from three centers: one for the body, and one for each extremity. That for the body makes its appearance near the center of the bone, during the eighth week of fetal life.
Ossification commences in the lower end between 9 and 26 months of age. The ossification center for the upper end appears by the fifth year.
The upper epiphysis fuses with the body at the age of seventeen or eighteen years, the lower about the age of twenty.
An additional center sometimes found in the radial tuberosity, appears about the fourteenth or fifteenth year.
Function | Radius (bone) | Wikipedia | 390 | 585732 | https://en.wikipedia.org/wiki/Radius%20%28bone%29 | Biology and health sciences | Skeletal system | Biology |
Muscle attachments
The biceps muscle inserts on the radial tuberosity of the upper extremity of the bone. The upper third of the body of the bone attaches to the supinator, the flexor digitorum superficialis, and the flexor pollicis longus muscles.
The middle third of the body attaches to the extensor ossis metacarpi pollicis, extensor primi internodii pollicis, and the pronator teres muscles.
The lower quarter of the body attaches to the pronator quadratus muscle and the tendon of the supinator longus.
Clinical significance
Radial aplasia refers to the congenital absence or shortness of the radius.
Fracture
Specific fracture types of the radius include:
Proximal radius fracture. A fracture within the capsule of the elbow joint results in the fat pad sign or "sail sign" which is a displacement of the fat pad at the elbow.
Essex-Lopresti fracture – a fracture of the radial head with concomitant dislocation of the distal radio-ulnar joint with disruption of the interosseous membrane.
Radial shaft fracture
Distal radius fracture
Galeazzi fracture – a fracture of the radius with dislocation of the distal radioulnar joint
Colles' fracture – a distal fracture of the radius with dorsal (posterior) displacement of the wrist and hand
Smith's fracture – a distal fracture of the radius with volar (ventral) displacement of the wrist and hand
Barton's fracture – an intra-articular fracture of the distal radius with dislocation of the radiocarpal joint.
History
The word radius is Latin for "ray". In the context of the radius bone, a ray can be thought of rotating around an axis line extending diagonally from center of capitulum to the center of distal ulna. While the ulna is the major contributor to the elbow joint, the radius primarily contributes to the wrist joint.
The radius is named so because the radius (bone) acts like the radius (of a circle). It rotates around the ulna and the far end (where it joins to the bones of the hand), known as the styloid process of the radius, is the distance from the ulna (center of the circle) to the edge of the radius (the circle). The ulna acts as the center point to the circle because when the arm is rotated the ulna does not move. | Radius (bone) | Wikipedia | 503 | 585732 | https://en.wikipedia.org/wiki/Radius%20%28bone%29 | Biology and health sciences | Skeletal system | Biology |
Other animals
In four-legged animals, the radius is the main load-bearing bone of the lower forelimb. Its structure is similar in most terrestrial tetrapods, but it may be fused with the ulna in some mammals (such as horses) and reduced or modified in animals with flippers or vestigial forelimbs.
Gallery | Radius (bone) | Wikipedia | 70 | 585732 | https://en.wikipedia.org/wiki/Radius%20%28bone%29 | Biology and health sciences | Skeletal system | Biology |
A sabot (, ) is a supportive device used in firearm/artillery ammunitions to fit/patch around a projectile, such as a bullet/slug or a flechette-like projectile (such as a kinetic energy penetrator), and keep it aligned in the center of the barrel when fired. It allows a narrower projectile with high sectional density to be fired through a barrel of much larger bore diameter with maximal accelerative transfer of kinetic energy. After leaving the muzzle, the sabot typically separates from the projectile in flight, diverting only a very small portion of the overall kinetic energy.
The sabot component in projectile design is the relatively thin, tough and deformable seal known as a driving band or obturation ring needed to trap propellant gases behind a projectile, and also keep the projectile centered in the barrel, when the outer shell of the projectile is only slightly smaller in diameter than the caliber of the barrel. Driving bands and obturators are used to seal these full-bore projectiles in the barrel because of manufacturing tolerances; there always exists some gap between the projectile outer diameter and the barrel inner diameter, usually a few thousandths of an inch; enough of a gap for high pressure gasses to slip by during firing. Driving bands and obturator rings are made from material that will deform and seal the barrel as the projectile is forced from the chamber into the barrel.
Sabots use driving bands and obturators, because the same manufacturing tolerance issues exist when sealing the saboted projectile in the barrel, but the sabot itself is a more substantial structural component of the in-bore projectile configuration. Refer to the two armor-piercing fin-stabilized discarding sabot (APFSDS) pictures to see the substantial material nature of a sabot to fill the bore diameter around the sub-caliber arrow-type flight projectile, compared to the very small gap sealed by a driving band or obturator to mitigate what is known classically as windage. More detailed cutaways of the internal structural complexity of advanced APFSDS saboted long rod penetrator projectiles can be found in #External links.
Design | Sabot (firearms) | Wikipedia | 441 | 585842 | https://en.wikipedia.org/wiki/Sabot%20%28firearms%29 | Technology | Ammunition | null |
The function of a sabot is to provide a larger bulkhead structure that fills the entire bore area between an intentionally designed sub-caliber flight projectile and the barrel, giving a larger surface area for propellant gasses to act upon than just the base of the smaller flight projectile. Efficient aerodynamic design of a flight projectile does not always accommodate efficient interior ballistic design to achieve high muzzle velocity. This is especially true for arrow-type projectiles, which are long and thin for low drag efficiency, but too thin to shoot from a gun barrel of equal diameter to achieve high muzzle velocity. The physics of interior ballistics demonstrates why the use of a sabot is advantageous to achieve higher muzzle velocity with an arrow-type projectile. Propellant gasses generate high pressure, and the larger the base area that pressure acts upon the greater the net force on that surface. Force (pressure times area) provides an acceleration to the mass of the projectile. Therefore, for a given pressure and barrel diameter, a lighter projectile can be driven from a barrel to a higher muzzle velocity than a heavier projectile. However, a lighter projectile may not fit in the barrel, because it is too thin. To make up this difference in diameter, a properly designed sabot provides less parasitic mass than if the flight projectile were made full-bore, in particular providing dramatic improvement in muzzle velocity for APDS (Armor-piercing discarding sabot) and APFSDS (Armor-piercing fin-stabilized discarding sabot) ammunition. | Sabot (firearms) | Wikipedia | 301 | 585842 | https://en.wikipedia.org/wiki/Sabot%20%28firearms%29 | Technology | Ammunition | null |
Seminal research on two important sabot configurations for long rod penetrators used in APFSDS ammunition, namely the "saddle-back" and "double-ramp" sabot was performed by the US Army Ballistics Research Laboratory during the development and improvement of modern 105mm and 120mm kinetic energy APFSDS penetrators and published in 1978, permitted by the significant advancement in the computerized finite element method in structural mechanics at that time; and now represents the existing fielded technology standard. (See for example the development of the M829 series of anti-tank projectiles beginning with the base model M829 in the early 1980s, to the 2016 M829A4 model, employing ever longer "double-ramp" sabots). Upon muzzle exit, the sabot is discarded, and the smaller flight projectile flies to the target with less drag resistance than a full-bore projectile. In this manner, very high velocity and slender, low drag projectiles can be fired more efficiently, (see external ballistics and terminal ballistics). Nevertheless, the weight of the sabot represents parasitic mass that must also be accelerated to muzzle velocity, but does not contribute to the terminal ballistics of the flight projectile. For this reason, great emphasis is placed on selecting strong yet lightweight structural materials for the sabot, and configuring the sabot geometry to efficiently employ these parasitic materials at minimum weight penalty. | Sabot (firearms) | Wikipedia | 289 | 585842 | https://en.wikipedia.org/wiki/Sabot%20%28firearms%29 | Technology | Ammunition | null |
Made of some lightweight material (usually high strength plastic in small caliber rifles, (see SLAP Saboted light armor penetrator), shotguns and muzzle loader ammunition; aluminium, steel, and carbon fiber reinforced plastic for modern anti-tank kinetic energy ammunition; and, in classic times, wood or papier-mâché – in muzzle loading cannons). The sabot usually consists of several longitudinal pieces held in place by the cartridge case, an obturator or driving band. When the projectile is fired, the sabot blocks the gas, provides significant structural support against launch acceleration, and carries the projectile down the barrel. When the sabot reaches the end of the barrel, the shock of hitting still air pulls the parts of the sabot away from the projectile, allowing the projectile to continue in flight. Modern sabots are made from high strength aluminum and graphite fiber reinforced epoxy. They are used primarily to fire long rods of very dense materials, such as tungsten heavy alloy and depleted uranium. (see for example the M829 series of anti-tank projectiles).
Sabot-type shotgun slugs were marketed in the United States from about 1985, and became legal for hunting in most U.S. states. When used with a rifled slug barrel, they are very much more accurate than normal shotgun slugs.
Types
Cup sabot
A cup sabot supports the base and rear end of a projectile, and the cup material alone can provide both structural support and barrel obturation. When the sabot and projectile exit the muzzle of the gun, air pressure alone on the sabot forces the sabot to release the projectile. Cup sabots are found typically in small arms ammunition, smooth-bore shotgun and smooth-bore muzzleloader projectiles.
Expanding cup sabot
Used typically in rifled small arms (SLAP, shotguns, and muzzleloaders), an expanding cup sabot has a one piece sabot surrounding the base and sides of a projectile, providing both structural support and obturation. Upon firing, when the sabot and projectile leave the muzzle of the gun, centrifugal force from the rotation of the projectile, due to barrel rifling, opens up the segments surrounding the projectile, rapidly presenting more surface area to air pressure, quickly releasing it. | Sabot (firearms) | Wikipedia | 471 | 585842 | https://en.wikipedia.org/wiki/Sabot%20%28firearms%29 | Technology | Ammunition | null |
Although the use of cup sabots of various complexity are popular with rifle ammunition hand-loaders, in order to achieve significantly higher muzzle velocity with a lower drag, smaller diameter and lighter bullet, successful saboted projectile design has to include the resulting bullet stability characteristics. For example, simply inserting a commercially available 5.56mm (.224) bullet into a sabot that will fire it from a commercially available 7.62mm (.300) barrel may result in that 5.56mm bullet failing to achieve sufficient gyroscopic stability to fly accurately without tumbling. To achieve gyroscopic stability of longer bullets in smaller diameter requires faster rifling. Therefore, if a bullet requires at least 1 turn in 7 inch twist, (1:7 rifling), in 5.56mm, it will also require at least 1:7 rifling when saboted in 7.62mm. However, larger caliber commercial rifles generally don't need such fast twist rates; 1:10 being a readily available standard in 7.62mm. As a result, the twist rate of the larger barrel will dictate which smaller bullets can be fired with sufficient stability out of a sabot. In this example, using 1:10 rifling in 7.62mm restricts saboting to 5.56mm bullets that require 1:10 twist or slower, and this requirement will tend to restrict saboting to the shorter (and lighter) 5.56mm bullets.
Base sabot
A base sabot has a one piece base which supports the bottom of the projectile, and separate pieces that surround the sides of the projectile and center it. The base sabot can have better and cleaner sabot/projectile separation than cup or expanding cup sabots for small arms ammunition, but may be more expensive to manufacture and assemble.
In larger caliber APDS ammunition, based on the cup, expanding cup, and base sabot concepts, significantly more complex assemblies are required. | Sabot (firearms) | Wikipedia | 405 | 585842 | https://en.wikipedia.org/wiki/Sabot%20%28firearms%29 | Technology | Ammunition | null |
Spindle sabot
A spindle sabot uses a set of at least two and upwards of four matched longitudinal rings or "petals" which have a center section in contact with a long arrow-type projectile; a front section or "bore-rider" which centers that projectile in the barrel and provides an air scoop to assist in sabot separation upon muzzle exit, and a rear section which both centers the projectile, provides a structural "bulkhead", and seals propellant gases with an obturator ring around the outside diameter. Spindle sabots are the standard type used in modern large caliber armor-piercing ammunition. Three-petal spindle-type sabots are shown in the illustrations at the right of this paragraph. The "double-ramp" and "saddle-back" sabots used on modern APFSDS ammunition are a form of spindle sabot.
Shotgun slugs often use a cast plastic sabot similar to the spindle sabot. Shotgun sabots in general extend the full length of the projectile and are designed to be used more effectively in rifled barrels.
Ring sabot
A ring sabot uses the rear fins on a long rod projectile to help center the projectile and ride the bore, and the multi-petal sabot forms only a single bulkhead ring around the projectile near the front, with an obturator sealing gases from escaping past it, and centering the front of the projectile. The former Soviet Union favored armor-piercing sabot projectiles using ring sabots, which performed acceptably for that era, manufactured from high strength steel for both the long rod penetrator and ring sabot. The strength of the steel ring was sufficient to withstand launch accelerations without the need for sabot ramps to also support the steel flight projectile. | Sabot (firearms) | Wikipedia | 360 | 585842 | https://en.wikipedia.org/wiki/Sabot%20%28firearms%29 | Technology | Ammunition | null |
The tailed frogs are two species of frogs in the genus Ascaphus, the only taxon in the family Ascaphidae . The "tail" in the name is actually an extension of the male cloaca. The tail is one of two distinctive anatomical features adapting the species to life in fast-flowing streams. These are the only North American frog species that reproduce by internal fertilization. They are among the most primitive known families of frogs.
Its scientific name means 'without a spade', from the privative prefix a- and the Ancient Greek (, 'spade, shovel'), referring to the metatarsal spade, which these frogs do not have.
Taxonomy
Until 2001, the genus was believed to be monotypic, the single species being the tailed frog (Ascaphus truei Stejneger, 1899). However, in that year, Nielson, Lohman, and Sullivan published evidence that promoted the Rocky Mountain tailed frog (Ascaphus montanus) from a subspecies to its own species. Since then, the former species has been formally called the coastal tailed frog.
The genus "Ascaphus", through mtDNA comparisons, has been grouped into a clade with the genus "Leiopelma" creating a sister taxon to all modern anurans.
General morphology
The existence of the visible "tail" appendage makes this frog family distinct from all other frogs. It is usually classified in the ancient frog suborder Archaeobatrachia and further organized into a basal clade with Leiopelma that is considered a sister taxon to all other frogs.
The "tail" is found only in males, and is actually part of the cloaca, used to insert sperm into the female during mating. This anatomical feature improves breeding success by minimizing loss of sperm in the turbulent, fast-flowing streams inhabited by this species. Thus, the tailed frogs exhibit internal fertilisation, rather than the external fertilisation found in other frogs. | Tailed frog | Wikipedia | 405 | 586353 | https://en.wikipedia.org/wiki/Tailed%20frog | Biology and health sciences | Frogs and toads | Animals |
Ascaphidae and Leiopelmatidae are primitive to almost all other frogs in having nine amphicoelous vertebrae and a caudalipuboischiotibialis tail-wagging muscle in adults. a type of vertebrae seen mostly in fish and early terrestrial tetrapod fossils (such as fossil salamanders and fossil frogs. The joints in amphicoelous vertebrae allow for significant lateral movement of the vertebral column, seen most clearly when fish use their tail to generate propulsive force. An additional plesiomorphy is the presence of free ribs in adults, a characteristic only present in the basal group archaeobatrachia.
Ascaphids lack the ability to vocalise, are small – around long – and are found in steep, fast-flowing streams in Montana, Idaho, Washington, Oregon, and northern California in the northwest United States, and southeastern British Columbia (Rocky Mountain Tailed Frog) and coastal BC (Coastal Tailed Frog).
Unique to the tailed frogs is the ability to secrete a series of antimicrobial peptides called ascaphins. These peptides share minimal genetic characteristics with other peptides secreted by frogs, yet show some similarities with antibacterial peptides found in African scorpions Pandinus imperator and Opistophthalmus carinatus. The ascaphin peptides are secreted through the skin and imperative in fighting bacteria such as E. coli and S. aureus.
The tailed frogs share certain characteristics with the Leiopelma, a genus of primitive frogs native to New Zealand, with which they are a phylogenetic sister taxa to all other anurans.
Mating practices
When attempting to mate, males will lunge at the female, wrapping a forelimb around them to secure them initially in an inguinal amplexus formation (males wrap their digits around female anterior to the pelvic region, placing their head on the back and close to the rear of the female) and then in a ventral amplexus formation (female is flipped over and male and female venters face each other). From here, the male inserts the "tail" into the female, and squeezes the female to gain leverage before thrusting. During this process the female is relatively still, occasionally kicking during the insertion process. | Tailed frog | Wikipedia | 470 | 586353 | https://en.wikipedia.org/wiki/Tailed%20frog | Biology and health sciences | Frogs and toads | Animals |
In some situations there is male-male competition for the female. In these situations, both males compete to enter the amplexus formation, eventually one establishing a better hold on the female and expelling the other male from the breeding process. Usually the male that is larger is more likely to succeed.
General habitat
The habitat of the tailed frog is cold, fast-moving streams with cobblestone bottoms. They are mostly aquatic, but adults may emerge during cool, wet conditions to forage terrestrially. Breeding season lasts from May through September, and females deposit their eggs in strings under rocks in fast-moving streams. Larvae take one to four years to metamorphose in the cool, fast-moving mountain streams. The amount of cobbles and fines (sand and similarly sized fine particles) in streams have been shown to be good indicators of tadpole abundance, with tadpole abundance being inversely proportional to concentration of fines and proportional to concentration of cobbles.
Thermal tolerance range in adults is exceptionally low relative to other North American anurans, with eggs rarely found above 20 °C and adults and larvae regularly migrating along microhabitats to reach temperatures below 20 °C whenever possible. It would appear that they prefer temperatures 16 °C and below. Eggs develop best at temperatures between 5° and 13
5 °C.
Because of this very narrow thermal tolerance, Adults may exhibit philopatry where temperatures are stable and low. However it has also been hypothesized that they may migrate to colder waters in autumn. Unfortunately, movements and migrational habits in Ascaphus have not been well documented, preventing any conclusive statements on migratory behavior or philopatry from being made with confidence.
Adults forage primarily terrestrially along stream banks, but also occasionally feed underwater. A wide variety of food items is taken, including both aquatic and terrestrial larval and adult insects, other arthropods (especially spiders), and snails. Tadpoles consume small quantities of filamentous green algae and desmids. Large quantities of conifer pollen are consumed seasonally by tadpoles. | Tailed frog | Wikipedia | 423 | 586353 | https://en.wikipedia.org/wiki/Tailed%20frog | Biology and health sciences | Frogs and toads | Animals |
During the day, adults seek cover under submerged substrates in the stream, or occasionally under similar surface objects close to the stream. Individuals have also been found in crevices in spray-drenched cliff walls near waterfalls. During winter, individuals are less active, especially inland, and appear to retreat beneath large logs and boulders. Tadpoles require cool streams with smooth-surfaced stones with a minimum diameter of . Tadpoles probably spend most of their time attached to such substrates by a large oral sucker. The large, sucker-like mouth parts of the tadpoles are a second distinctive feature of the species, enabling survival in turbulent water unsuitable for other frogs. They prefer turbulent water to smooth, swiftly flowing water. | Tailed frog | Wikipedia | 143 | 586353 | https://en.wikipedia.org/wiki/Tailed%20frog | Biology and health sciences | Frogs and toads | Animals |
Artificial general intelligence (AGI) is a type of artificial intelligence (AI) that matches or surpasses human cognitive capabilities across a wide range of cognitive tasks. This contrasts with narrow AI, which is limited to specific tasks. Artificial superintelligence (ASI), on the other hand, refers to AGI that greatly exceeds human cognitive capabilities. AGI is considered one of the definitions of strong AI.
Creating AGI is a primary goal of AI research and of companies such as OpenAI and Meta. A 2020 survey identified 72 active AGI research and development projects across 37 countries.
The timeline for achieving AGI remains a subject of ongoing debate among researchers and experts. As of 2023, some argue that it may be possible in years or decades; others maintain it might take a century or longer; a minority believe it may never be achieved; and another minority claims that it is already here. Notable AI researcher Geoffrey Hinton has expressed concerns about the rapid progress towards AGI, suggesting it could be achieved sooner than many expect.
There is debate on the exact definition of AGI and regarding whether modern large language models (LLMs) such as GPT-4 are early forms of AGI. AGI is a common topic in science fiction and futures studies.
Contention exists over whether AGI represents an existential risk. Many experts on AI have stated that mitigating the risk of human extinction posed by AGI should be a global priority. Others find the development of AGI to be too remote to present such a risk.
Terminology
AGI is also known as strong AI, full AI, human-level AI, human-level intelligent AI, or general intelligent action.
Some academic sources reserve the term "strong AI" for computer programs that experience sentience or consciousness. In contrast, weak AI (or narrow AI) is able to solve one specific problem but lacks general cognitive abilities. Some academic sources use "weak AI" to refer more broadly to any programs that neither experience consciousness nor have a mind in the same sense as humans.
Related concepts include artificial superintelligence and transformative AI. An artificial superintelligence (ASI) is a hypothetical type of AGI that is much more generally intelligent than humans, while the notion of transformative AI relates to AI having a large impact on society, for example, similar to the agricultural or industrial revolution. | Artificial general intelligence | Wikipedia | 480 | 586357 | https://en.wikipedia.org/wiki/Artificial%20general%20intelligence | Technology | Artificial intelligence concepts | null |
A framework for classifying AGI in levels was proposed in 2023 by Google DeepMind researchers. They define five levels of AGI: emerging, competent, expert, virtuoso, and superhuman. For example, a competent AGI is defined as an AI that outperforms 50% of skilled adults in a wide range of non-physical tasks, and a superhuman AGI (i.e. an artificial superintelligence) is similarly defined but with a threshold of 100%. They consider large language models like ChatGPT or LLaMA 2 to be instances of emerging AGI.
Characteristics
Various popular definitions of intelligence have been proposed. One of the leading proposals is the Turing test. However, there are other well-known definitions, and some researchers disagree with the more popular approaches.
Intelligence traits
Researchers generally hold that intelligence is required to do all of the following:
reason, use strategy, solve puzzles, and make judgments under uncertainty
represent knowledge, including common sense knowledge
plan
learn
communicate in natural language
if necessary, integrate these skills in completion of any given goal
Many interdisciplinary approaches (e.g. cognitive science, computational intelligence, and decision making) consider additional traits such as imagination (the ability to form novel mental images and concepts) and autonomy.
Computer-based systems that exhibit many of these capabilities exist (e.g. see computational creativity, automated reasoning, decision support system, robot, evolutionary computation, intelligent agent). There is debate about whether modern AI systems possess them to an adequate degree.
Physical traits
Other capabilities are considered desirable in intelligent systems, as they may affect intelligence or aid in its expression. These include:
the ability to sense (e.g. see, hear, etc.), and
the ability to act (e.g. move and manipulate objects, change location to explore, etc.)
This includes the ability to detect and respond to hazard. | Artificial general intelligence | Wikipedia | 381 | 586357 | https://en.wikipedia.org/wiki/Artificial%20general%20intelligence | Technology | Artificial intelligence concepts | null |
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