text stringlengths 26 3.6k | page_title stringlengths 1 71 | source stringclasses 1
value | token_count int64 10 512 | id stringlengths 2 8 | url stringlengths 31 117 | topic stringclasses 4
values | section stringlengths 4 49 ⌀ | sublist stringclasses 9
values |
|---|---|---|---|---|---|---|---|---|
For any , the ideal generated by is also generated by any associate of , that is, ; no other element generates the same ideal. As all the generators of an ideal have the same norm, the norm of an ideal is the norm of any of its generators.
In some circumstances, it is useful to choose, once for all, a generator for each ideal. There are two classical ways for doing that, both considering first the ideals of odd norm. If the has an odd norm , then one of and is odd, and the other is even. Thus has exactly one associate with a real part that is odd and positive. In his original paper, Gauss made another choice, by choosing the unique associate such that the remainder of its division by is one. In fact, as , the norm of the remainder is not greater than 4. As this norm is odd, and 3 is not the norm of a Gaussian integer, the norm of the remainder is one, that is, the remainder is a unit. Multiplying by the inverse of this unit, one finds an associate that has one as a remainder, when divided by .
If the norm of is even, then either or , where is a positive integer, and is odd. Thus, one chooses the associate of for getting a which fits the choice of the associates for elements of odd norm.
Gaussian primes
As the Gaussian integers form a principal ideal domain, they also form a unique factorization domain. This implies that a Gaussian integer is irreducible (that is, it is not the product of two non-units) if and only if it is prime (that is, it generates a prime ideal).
The prime elements of are also known as Gaussian primes. An associate of a Gaussian prime is also a Gaussian prime. The conjugate of a Gaussian prime is also a Gaussian prime (this implies that Gaussian primes are symmetric about the real and imaginary axes).
A positive integer is a Gaussian prime if and only if it is a prime number that is congruent to 3 modulo 4 (that is, it may be written , with a nonnegative integer) . The other prime numbers are not Gaussian primes, but each is the product of two conjugate Gaussian primes. | Gaussian integer | Wikipedia | 484 | 48628 | https://en.wikipedia.org/wiki/Gaussian%20integer | Mathematics | Basics | null |
A Gaussian integer is a Gaussian prime if and only if either:
one of is zero and the absolute value of the other is a prime number of the form (with a nonnegative integer), or
both are nonzero and is a prime number (which will not be of the form ).
In other words, a Gaussian integer is a Gaussian prime if and only if either its norm is a prime number, or is the product of a unit () and a prime number of the form .
It follows that there are three cases for the factorization of a prime natural number in the Gaussian integers:
If is congruent to 3 modulo 4, then it is a Gaussian prime; in the language of algebraic number theory, is said to be inert in the Gaussian integers.
If is congruent to 1 modulo 4, then it is the product of a Gaussian prime by its conjugate, both of which are non-associated Gaussian primes (neither is the product of the other by a unit); is said to be a decomposed prime in the Gaussian integers. For example, and .
If , we have ; that is, 2 is the product of the square of a Gaussian prime by a unit; it is the unique ramified prime in the Gaussian integers.
Unique factorization
As for every unique factorization domain, every Gaussian integer may be factored as a product of a unit and Gaussian primes, and this factorization is unique up to the order of the factors, and the replacement of any prime by any of its associates (together with a corresponding change of the unit factor).
If one chooses, once for all, a fixed Gaussian prime for each equivalence class of associated primes, and if one takes only these selected primes in the factorization, then one obtains a prime factorization which is unique up to the order of the factors. With the choices described above, the resulting unique factorization has the form | Gaussian integer | Wikipedia | 426 | 48628 | https://en.wikipedia.org/wiki/Gaussian%20integer | Mathematics | Basics | null |
where is a unit (that is, ), and are nonnegative integers, are positive integers, and are distinct Gaussian primes such that, depending on the choice of selected associates,
either with odd and positive, and even,
or the remainder of the Euclidean division of by equals 1 (this is Gauss's original choice).
An advantage of the second choice is that the selected associates behave well under products for Gaussian integers of odd norm. On the other hand, the selected associate for the real Gaussian primes are negative integers. For example, the factorization of 231 in the integers, and with the first choice of associates is , while it is with the second choice.
Gaussian rationals
The field of Gaussian rationals is the field of fractions of the ring of Gaussian integers. It consists of the complex numbers whose real and imaginary part are both rational.
The ring of Gaussian integers is the integral closure of the integers in the Gaussian rationals.
This implies that Gaussian integers are quadratic integers and that a Gaussian rational is a Gaussian integer, if and only if it is a solution of an equation
with and integers. In fact is solution of the equation
and this equation has integer coefficients if and only if and are both integers.
Greatest common divisor
As for any unique factorization domain, a greatest common divisor (gcd) of two Gaussian integers is a Gaussian integer that is a common divisor of and , which has all common divisors of and as divisor. That is (where denotes the divisibility relation),
and , and
and implies .
Thus, greatest is meant relatively to the divisibility relation, and not for an ordering of the ring (for integers, both meanings of greatest coincide).
More technically, a greatest common divisor of and is a generator of the ideal generated by and (this characterization is valid for principal ideal domains, but not, in general, for unique factorization domains).
The greatest common divisor of two Gaussian integers is not unique, but is defined up to the multiplication by a unit. That is, given a greatest common divisor of and , the greatest common divisors of and are , and .
There are several ways for computing a greatest common divisor of two Gaussian integers and . When one knows the prime factorizations of and , | Gaussian integer | Wikipedia | 505 | 48628 | https://en.wikipedia.org/wiki/Gaussian%20integer | Mathematics | Basics | null |
where the primes are pairwise non associated, and the exponents non-associated, a greatest common divisor is
with
Unfortunately, except in simple cases, the prime factorization is difficult to compute, and Euclidean algorithm leads to a much easier (and faster) computation. This algorithm consists of replacing of the input by , where is the remainder of the Euclidean division of by , and repeating this operation until getting a zero remainder, that is a pair . This process terminates, because, at each step, the norm of the second Gaussian integer decreases. The resulting is a greatest common divisor, because (at each step) and have the same divisors as and , and thus the same greatest common divisor.
This method of computation works always, but is not as simple as for integers because Euclidean division is more complicated. Therefore, a third method is often preferred for hand-written computations. It consists in remarking that the norm of the greatest common divisor of and is a common divisor of , , and . When the greatest common divisor of these three integers has few factors, then it is easy to test, for common divisor, all Gaussian integers with a norm dividing .
For example, if , and , one has , , and . As the greatest common divisor of the three norms is 2, the greatest common divisor of and has 1 or 2 as a norm. As a gaussian integer of norm 2 is necessary associated to , and as divides and , then the greatest common divisor is .
If is replaced by its conjugate , then the greatest common divisor of the three norms is 34, the norm of , thus one may guess that the greatest common divisor is , that is, that . In fact, one has .
Congruences and residue classes
Given a Gaussian integer , called a modulus, two Gaussian integers are congruent modulo , if their difference is a multiple of , that is if there exists a Gaussian integer such that . In other words, two Gaussian integers are congruent modulo , if their difference belongs to the ideal generated by . This is denoted as . | Gaussian integer | Wikipedia | 458 | 48628 | https://en.wikipedia.org/wiki/Gaussian%20integer | Mathematics | Basics | null |
The congruence modulo is an equivalence relation (also called a congruence relation), which defines a partition of the Gaussian integers into equivalence classes, called here congruence classes or residue classes. The set of the residue classes is usually denoted , or , or simply .
The residue class of a Gaussian integer is the set
of all Gaussian integers that are congruent to . It follows that if and only if .
Addition and multiplication are compatible with congruences. This means that and imply and .
This defines well-defined operations (that is independent of the choice of representatives) on the residue classes:
With these operations, the residue classes form a commutative ring, the quotient ring of the Gaussian integers by the ideal generated by , which is also traditionally called the residue class ring modulo (for more details, see Quotient ring).
Examples
There are exactly two residue classes for the modulus , namely (all multiples of ), and , which form a checkerboard pattern in the complex plane. These two classes form thus a ring with two elements, which is, in fact, a field, the unique (up to an isomorphism) field with two elements, and may thus be identified with the integers modulo 2. These two classes may be considered as a generalization of the partition of integers into even and odd integers. Thus one may speak of even and odd Gaussian integers (Gauss divided further even Gaussian integers into even, that is divisible by 2, and half-even).
For the modulus 2 there are four residue classes, namely . These form a ring with four elements, in which for every . Thus this ring is not isomorphic with the ring of integers modulo 4, another ring with four elements. One has , and thus this ring is not the finite field with four elements, nor the direct product of two copies of the ring of integers modulo 2.
For the modulus there are eight residue classes, namely , whereof four contain only even Gaussian integers and four contain only odd Gaussian integers.
Describing residue classes
Given a modulus , all elements of a residue class have the same remainder for the Euclidean division by , provided one uses the division with unique quotient and remainder, which is described above. Thus enumerating the residue classes is equivalent with enumerating the possible remainders. This can be done geometrically in the following way. | Gaussian integer | Wikipedia | 508 | 48628 | https://en.wikipedia.org/wiki/Gaussian%20integer | Mathematics | Basics | null |
In the complex plane, one may consider a square grid, whose squares are delimited by the two lines
with and integers (blue lines in the figure). These divide the plane in semi-open squares (where and are integers)
The semi-open intervals that occur in the definition of have been chosen in order that every complex number belong to exactly one square; that is, the squares form a partition of the complex plane. One has
This implies that every Gaussian integer is congruent modulo to a unique Gaussian integer in (the green square in the figure), which its remainder for the division by . In other words, every residue class contains exactly one element in .
The Gaussian integers in (or in its boundary) are sometimes called minimal residues because their norm are not greater than the norm of any other Gaussian integer in the same residue class (Gauss called them absolutely smallest residues).
From this one can deduce by geometrical considerations, that the number of residue classes modulo a Gaussian integer equals its norm (see below for a proof; similarly, for integers, the number of residue classes modulo is its absolute value ).
Residue class fields
The residue class ring modulo a Gaussian integer is a field if and only if is a Gaussian prime.
If is a decomposed prime or the ramified prime (that is, if its norm is a prime number, which is either 2 or a prime congruent to 1 modulo 4), then the residue class field has a prime number of elements (that is, ). It is thus isomorphic to the field of the integers modulo .
If, on the other hand, is an inert prime (that is, is the square of a prime number, which is congruent to 3 modulo 4), then the residue class field has elements, and it is an extension of degree 2 (unique, up to an isomorphism) of the prime field with elements (the integers modulo ). | Gaussian integer | Wikipedia | 416 | 48628 | https://en.wikipedia.org/wiki/Gaussian%20integer | Mathematics | Basics | null |
Primitive residue class group and Euler's totient function
Many theorems (and their proofs) for moduli of integers can be directly transferred to moduli of Gaussian integers, if one replaces the absolute value of the modulus by the norm. This holds especially for the primitive residue class group (also called multiplicative group of integers modulo ) and Euler's totient function. The primitive residue class group of a modulus is defined as the subset of its residue classes, which contains all residue classes that are coprime to , i.e. . Obviously, this system builds a multiplicative group. The number of its elements shall be denoted by (analogously to Euler's totient function for integers ).
For Gaussian primes it immediately follows that and for arbitrary composite Gaussian integers
Euler's product formula can be derived as
where the product is to build over all prime divisors of (with ). Also the important theorem of Euler can be directly transferred:
For all with , it holds that .
Historical background
The ring of Gaussian integers was introduced by Carl Friedrich Gauss in his second monograph on quartic reciprocity (1832). The theorem of quadratic reciprocity (which he had first succeeded in proving in 1796) relates the solvability of the congruence to that of . Similarly, cubic reciprocity relates the solvability of to that of , and biquadratic (or quartic) reciprocity is a relation between and . Gauss discovered that the law of biquadratic reciprocity and its supplements were more easily stated and proved as statements about "whole complex numbers" (i.e. the Gaussian integers) than they are as statements about ordinary whole numbers (i.e. the integers).
In a footnote he notes that the Eisenstein integers are the natural domain for stating and proving results on cubic reciprocity and indicates that similar extensions of the integers are the appropriate domains for studying higher reciprocity laws.
This paper not only introduced the Gaussian integers and proved they are a unique factorization domain, it also introduced the terms norm, unit, primary, and associate, which are now standard in algebraic number theory.
Unsolved problems
Most of the unsolved problems are related to distribution of Gaussian primes in the plane. | Gaussian integer | Wikipedia | 496 | 48628 | https://en.wikipedia.org/wiki/Gaussian%20integer | Mathematics | Basics | null |
Gauss's circle problem does not deal with the Gaussian integers per se, but instead asks for the number of lattice points inside a circle of a given radius centered at the origin. This is equivalent to determining the number of Gaussian integers with norm less than a given value.
There are also conjectures and unsolved problems about the Gaussian primes. Two of them are:
The real and imaginary axes have the infinite set of Gaussian primes 3, 7, 11, 19, ... and their associates. Are there any other lines that have infinitely many Gaussian primes on them? In particular, are there infinitely many Gaussian primes of the form ?
Is it possible to walk to infinity using the Gaussian primes as stepping stones and taking steps of a uniformly bounded length? This is known as the Gaussian moat problem; it was posed in 1962 by Basil Gordon and remains unsolved. | Gaussian integer | Wikipedia | 196 | 48628 | https://en.wikipedia.org/wiki/Gaussian%20integer | Mathematics | Basics | null |
The English term lance is derived, via Middle English launce and Old French lance, from the Latin lancea, a generic term meaning a spear or javelin employed by both infantry and cavalry, with English initially keeping these generic meanings. It developed later into a term for spear-like weapons specially designed and modified to be part of a "weapon system" for use couched under the arm during a charge, being equipped with special features such as grappers to engage with lance rests attached to breastplates, and vamplates, small circular plates designed to prevent the hand sliding up the shaft upon impact. These specific features were in use by the beginning of the late 14th century.
Though best known as a military and sporting weapon carried by European knights and men-at-arms, the use of lances was widespread throughout East Asia, the Middle East, and North Africa wherever suitable mounts were available. Lances were the main weapon of lancers of the medieval period and beyond, and these troops also carried secondary weapons such as swords, battle axes, war hammers, maces, and daggers for use in hand-to-hand combat, since the lance was often a one-use-per-engagement weapon, becoming embedded in their targets or being broken on impact. Assuming the lance survived the initial impact without breaking, it could also prove inappropriate for more static, closer engagements where its length became a hindrance.
Etymology
The name is derived from the word , the Roman auxiliaries' javelin or throwing spear; although according to the OED, the word may be of Iberian origin. Also compare (), a Greek term for "spear" or "lance".
A lance in the original sense is a light throwing spear or javelin. The English verb to launch "fling, hurl, throw" is derived from the term (via Old French ), as well as the rarer or poetic to lance. The term from the 17th century came to refer specifically to spears not thrown, used for thrusting by heavy cavalry, and especially in jousting. The longer types of thrusting spear used by infantry are usually referred to simply as spears or later as pikes, though many other terms existed.
History of use
Late Roman
During the late 3rd century the weapons of the cavalry attached to each Roman legion evolved from javelins and swords to sometimes include long reaching lances (contus). These required the use of both hands to thrust. | Lance | Wikipedia | 490 | 48774 | https://en.wikipedia.org/wiki/Lance | Technology | Polearms | null |
Middle Ages
The Byzantine cavalry used lances (kontos or kontarion) almost exclusively, often in mixed formations of mounted archers and lancers (cursores et defensores). The Byzantines used lances in both overarm and underarm grips, as well as being couched under the arm (held horizontally). The length of the standard kontarion is estimated at , which is shorter than that of the medieval knight of Western Europe.
Formations of knights were known to use underarm-couched military lances in full-gallop closed-ranks charges against lines of opposing infantry or cavalry. Two variants on the couched lance charge developed, the French method, en haie, with lancers in a double line, and the German method, with lancers drawn up in a deeper formation which was often wedge-shaped. It is commonly believed that this became the dominant European cavalry tactic in the 11th century after the development of the cantled saddle and stirrups (the Great Stirrup Controversy), and of rowel spurs (which enabled better control of the mount). Cavalry thus outfitted and deployed had a tremendous collective force in their charge, and could shatter most contemporary infantry lines.
Because of the extreme stopping power of a thrusting spear, it quickly became a popular weapon of infantry in the Late Middle Ages. These eventually led to the rise of the longest type of spears, the pike. This adaptation of the cavalry lance to infantry use was largely tasked with stopping lance-armed cavalry charges. During the 14th, 15th, and 16th centuries, these weapons, both mounted and unmounted, were so effective that lancers and pikemen not only became a staple of every Western army, but also became highly sought-after mercenaries. (However, the pike had already been used by Philip II of Macedon in antiquity to great effect, in the form of the sarissa.) | Lance | Wikipedia | 385 | 48774 | https://en.wikipedia.org/wiki/Lance | Technology | Polearms | null |
In Europe, a jousting lance was a variation of the knight's lance which was modified from its original war design. In jousting, the lance tips would usually be blunt, often spread out like a cup or furniture foot, to provide a wider impact surface designed to unseat the opposing rider without spearing him through. The centre of the shaft of such lances could be designed to be hollow, in order for it to break on impact, as a further safeguard against impalement. They were on average long, and had hand guards built into the lance, often tapering for a considerable portion of the weapon's length. These are the versions that can most often be seen at medieval reenactment festivals. In war, lances were much more like stout spears, long and balanced for one-handed use, and with sharpened tips.
Lance (unit organization)
As a small unit that surrounded a knight when he went into battle during the 14th and 15th centuries, a lance might have consisted of one or two squires, the knight himself, one to three men-at-arms, and possibly an archer. Lances were often combined under the banner of a higher-ranking nobleman to form companies of knights that would act as an ad hoc unit.
17th and 18th century decline in Western Europe
The advent of wheellock technology spelled the end of the lance in Western Europe, with newer types of heavy cavalry such as reiters and cuirassiers spurning the old one-use weapon and increasingly supplanting the older gendarme type Medieval cavalry. While many Renaissance captains such as Sir Roger Williams continued to espouse the virtues of the lance, many such as François de la Noue openly encouraged its abandonment in the face of the pistol's greater armor piercing power, handiness and greater general utility. At the same time the adoption of pike and shot tactic by most infantry forces would neuter much of the power of the lancer's breakneck charge, making them a non-cost effective type of military unit due to their expensive horses in comparison to cuirassiers and reiters, who usually charging only at a trot could make do with lower quality mounts. After the success of pistol-armed Huguenot heavy horse against their Royalist counterparts during the French Wars of Religion, most Western European powers started rearming their lancers with pistols, initially as an adjunct weapon and eventually as a replacement, with the Spanish retaining the lance the longest. | Lance | Wikipedia | 504 | 48774 | https://en.wikipedia.org/wiki/Lance | Technology | Polearms | null |
Only the Polish–Lithuanian Commonwealth with its far greater emphasis on cavalry warfare, large population of Szlachta nobility and general lower military technology level among its foes retained the lance to a considerable degree, with the famously winged Polish hussars having their glory period during the 17th and 18th centuries against a wide variety of enemy forces.
Indigenous use in North America
After the Western introduction of the horse to Native Americans, the Plains Indians used the bow and lance, probably independently, as American cavalry of the time were armed with the pistol and sabre, firing forward at full gallop.
19th century revival in Western Europe
The mounted lancer experienced a renaissance in the 19th century. This followed on the demise of the pike and of body armor during the early 18th century, with the reintroduction of lances coming from Hungary and Poland, having retained large formations of lance-armed cavalry when they had become more or less obsolescent elsewhere in Europe. Lancers became especially prevalent during and after the Napoleonic Wars: a period when almost all the major European powers reintroduced the lance into their respective cavalry arsenals. Formations of uhlans and other types of cavalry used lances between in length as their primary weapons. The lance was usually employed in initial charges in close formation, with sabers being used in the melee that followed.
The Crimean War saw the use of the lance in the Charge of the Light Brigade. One of the four British regiments involved in the charge, plus the Russian Cossacks who counter-attacked, were armed with this weapon.
During the War of the Triple Alliance (1864–1870), the Paraguayan cavalry made effective use of locally manufactured lances, both of conventional design and of an antique pattern used by gauchos for cattle herding.
The 1860s and 1870s saw the increasing common usage of ash, bamboo, beech, or pine wood for lance shafts of varying lengths, each with steel points and butts, adopted by the uhlan regiments of the Saxon, Württemberg, Bavarian, and Prussian armies.
Twilight of use
In the American Civil War, the 6th Pennsylvania Cavalry Regiment was equipped with lances modeled after Napoleon Bonaparte's forces in France. American troops had never previously used the lance in combat. The lances proved ineffective in battle and were replaced with carbine rifles in 1863. | Lance | Wikipedia | 465 | 48774 | https://en.wikipedia.org/wiki/Lance | Technology | Polearms | null |
The Franco-Prussian War of 1870 saw the extensive deployment of cavalry armed with lances on both sides. While the opportunities for decisive use of this weapon proved infrequent during the actual conflict, the entire cavalry corps (93 regiments of hussars, dragoons, cuirassiers, and uhlans) of the post-war Imperial German Army subsequently adopted the lance as a primary weapon. After 1893 the standard German cavalry lance was made of drawn tubular steel, covered with clear lacquer and with a hemp hand-grip. At it was the longest version then in use.
The Austrian cavalry had included regiments armed with lances since 1784. In 1884, the lance ceased to be carried either as an active service or parade weapon. However the eleven Uhlan regiments continued in existence until 1918, armed with the standard cavalry sabre.
During the Second Boer War, British troops successfully used the lance on one occasion - against retreating Boers at the Battle of Elandslaagte (21 October 1899). However, the Boers made effective use of trench warfare, rapid-fire field artillery, continuous-fire machine guns, and accurate long-range repeating rifles from the beginning of the war. The combined effect was devastating, so much of the British cavalry was deployed as mounted infantry, dismounting to fight on foot. For some years after the Boer War, the six British lancer regiments officially carried the lance only for parades and other ceremonial duties. At the regimental level, training in the use of the lance continued, ostensibly to improve recruit riding skills. In 1909, the bamboo or ash lance with a steel head was reauthorized for general use on active service.
The Russian cavalry (except for the Cossacks) discarded the lance in the late 19th century, but in 1907, it was reissued for use by the front line of each squadron when charging in open formation. In its final form, the Russian lance was a long metal tube with a steel head and leather arm strap. It was intended as a shock weapon in the charge, to be dropped after impact and replaced by the sword for close combat in a melee. While demoralizing to an opponent, the lance was recognized as being an awkward encumbrance in forested regions. | Lance | Wikipedia | 457 | 48774 | https://en.wikipedia.org/wiki/Lance | Technology | Polearms | null |
The relative value of the lance and the sword as a principal weapon for mounted troops was an issue of dispute in the years immediately preceding World War I. Opponents of the lance argued that the weapon was clumsy, conspicuous, easily deflected, and inefficient in a melee. Arguments favoring the retention of the lance focused on the impact on morale of having charging cavalry preceded by "a hedge of steel" and on the effectiveness of the weapon against fleeing opponents.
World War I and after
Lances were still in use by the British, Turkish, Italian, Spanish, French, Belgian, Indian, German, and Russian armies at the outbreak of World War I. In initial cavalry skirmishes in France this antique weapon proved ineffective, German uhlans being "hampered by their long lances and a good many threw them away". A major action involving repeated charges by four regiments of German cavalry, all armed with lances, at Halen on 12 August 1914 was unsuccessful. Amongst the Belgian defenders was one regiment of lancers who fought dismounted.
With the advent of trench warfare, lances and the cavalry that carried them ceased to play a significant role. A Russian cavalry officer whose regiment carried lances throughout the war recorded only one instance where an opponent was killed by this weapon.
The Greco-Turkish War (1919–1922), saw an unexpected revival of lances amongst the cavalry of the Turkish National Army. During the successful Turkish offensives of the final stages of the war across the open plains of Asia Minor, Turkish mounted troops were armed with bamboo shafted-lances taken from military storage and inflicted heavy losses on the retreating Greek Army.
The cavalry branches of most armies which still retained lances as a service weapon at the end of World War I generally discarded them for all but ceremonial occasions during the 1920s and 1930s. There were exceptions during this era, such as the Polish cavalry, which retained the lance for combat use until either 1934 or 1937, but contrary to popular legend did not make use of it in World War II. The German cavalry retained the lance (Stahlrohrlanze) as a service weapon until 1927, as did the British cavalry until 1928. The Argentine cavalry were documented as carrying lances until the 1940s, but this appears to have been used as part of recruit riding school training, rather than serious preparation for use in active service.
Use as flagstaff
The United States Cavalry used a lance-like shaft as a flagstaff. | Lance | Wikipedia | 497 | 48774 | https://en.wikipedia.org/wiki/Lance | Technology | Polearms | null |
Mounted police use
When the Canadian North-West Mounted Police was established, it was modeled after certain British cavalry units that used lances. It made limited use of this weapon in small detachments during the 1870s, intended to impress indigenous peoples.
The modern Royal Canadian Mounted Police, the North-West Mounted Police's descendant, employs ceremonial, though functional, lances made of male bamboo. They feature a crimped swallowtail pennant, red above and white below.
The New South Wales Mounted Police, based at Redfern Barracks, Sydney, Australia, carry a lance with a navy blue and white pennant on ceremonial occasions.
Other weapons
"Lance" is also the name given by some anthropologists to the light flexible javelins (technically darts) thrown by atlatls (spear-throwing sticks), but these are usually called "atlatl javelins". Some were not much larger than arrows, and were typically feather-fletched like an arrow and unlike the vast majority of spears and javelins (one exception would be several instances of the many types of ballista bolt, a mechanically thrown spear).
A "tilting-spear" is a heraldric term for a lance. | Lance | Wikipedia | 239 | 48774 | https://en.wikipedia.org/wiki/Lance | Technology | Polearms | null |
A halberd (also called halbard, halbert or Swiss voulge) is a two-handed polearm that came to prominent use from the 13th to 16th centuries. The halberd consists of an axe blade topped with a spike mounted on a long shaft. It can have a hook or thorn on the back side of the axe blade for grappling mounted combatants and protecting allied soldiers, typically musketeers. The halberd was usually long.
The word halberd is cognate with the German word Hellebarde, deriving from Middle High German halm (handle) and barte (battleaxe) joined to form helmbarte. Troops that used the weapon were called halberdiers. The word has also been used to describe a weapon of the early Bronze Age in Western Europe. This consisted of a blade mounted on a pole at a right angle.
History
The halberd is first mentioned (as ) in a work by 13th-century German poet Konrad von Würzburg. John of Winterthur described it as a new weapon used by the Swiss at the Battle of Morgarten of 1315. The halberd was inexpensive to produce and very versatile in battle. As the halberd was eventually refined, its point was more fully developed to allow it to better deal with spears and pikes (and make it able to push back approaching horsemen), as was the hook opposite the axe head, which could be used to pull horsemen to the ground. A Swiss peasant used a halberd to kill Charles the Bold, the Duke of Burgundy, at the Battle of Nancy, decisively ending the Burgundian Wars.
The halberd was the primary weapon of the early Swiss armies in the 14th and early 15th centuries. Later, the Swiss added the pike to better repel knightly attacks and roll over enemy infantry formations, with the halberd, hand-and-a-half sword, or the dagger known as the Schweizerdolch used for closer combat. The German Landsknechte, who imitated Swiss warfare methods, also used the pike, supplemented by the halberd—but their side arm of choice was a short sword called the Katzbalger. | Halberd | Wikipedia | 460 | 48775 | https://en.wikipedia.org/wiki/Halberd | Technology | Polearms | null |
As long as pikemen fought other pikemen, the halberd remained a useful supplemental weapon for push of pike, but when their position became more defensive, to protect the slow-loading arquebusiers and matchlock musketeers from sudden attacks by cavalry, the percentage of halberdiers in the pike units steadily decreased. By 1588, official Dutch infantry composition was down to 39% arquebuses, 34% pikes, 13% muskets, 9% halberds, and 2% one-handed swords. By 1600, troops armed exclusively with swords were no longer used and the halberd was only used by sergeants.
Researchers suspected that a halberd or a bill sliced through the back of King Richard III's skull at the Battle of Bosworth Field on 22 August 1485, leaving his brain visible before killing him during the battle, and were later able to confirm that it was a halberd.
While rarer than it had been from the late 15th to mid-16th centuries, the halberd was still used infrequently as an infantry weapon well into the mid-17th century. The armies of the Catholic League in 1625, for example, had halberdiers comprising 7% of infantry units, with musketeers comprising 58% and armored pikemen 35%. By 1627 this had changed to 65% muskets, 20% pikes, and 15% halberds. A near-contemporary depiction of the 1665 Battle of Montes Claros at Palace of the Marquises of Fronteira depicts a minority of the Portuguese and Spanish soldiers as armed with halberds. Antonio de Pereda's 1635 painting El Socorro a Génova depicting the Relief of Genoa has all the soldiers armed with halberds. The most consistent users of the halberd in the Thirty Years' War were German sergeants who would carry one as a sign of rank. While they could use them in melee combat, more often they were used for dressing the ranks by grasping the shaft in both hands and pushing it against several men simultaneously. They could also be used to push pikes or muskets up or down, especially to stop overexcited musketeers from firing prematurely. | Halberd | Wikipedia | 463 | 48775 | https://en.wikipedia.org/wiki/Halberd | Technology | Polearms | null |
The halberd has been used as a court bodyguard weapon for centuries, and is still the ceremonial weapon of the Swiss Guard in the Vatican and the Alabarderos (Halberdiers) Company of the Spanish Royal Guard. The halberd was one of the polearms sometimes carried by lower-ranking officers in European infantry units in the 16th through 18th centuries. In the British army, sergeants continued to carry halberds until 1793, when they were replaced by spontoons. The 18th-century halberd had, however, become simply a symbol of rank with no sharpened edge and insufficient strength to use as a weapon. It served as an instrument for ensuring that infantrymen in ranks stood correctly aligned with each other and that their muskets were aimed at the correct level.
The development of the halberd
The word helmbarte or variations thereof show up in German texts from the 13th century onwards. At that point, the halberd is not too distinct from other types of broad axes or bardiches used all over Europe. In the late 13th century the weapon starts to develop into a distinct weapon, with the top of the blade developing into a more acute thrusting point. This form of the halberd is erroneously sometimes called a voulge or a swiss voulge, but there is no evidence for the usage of these terms for this weapon historically. There were variations of these weapons with spikes on the back, though also plenty without. In the early 15th century the construction changes to incorporate sockets into the blade, instead of hoops as the previous designs had. With this development back spikes are directly integrated into the blade construction and become a universal part of the halberd design.
Similar and related polearms | Halberd | Wikipedia | 353 | 48775 | https://en.wikipedia.org/wiki/Halberd | Technology | Polearms | null |
Bardiche, a type of two-handed battle axe known in the 16th and 17th centuries in Eastern Europe
Bill, similar to a halberd but with a hooked blade form
Ge or dagger-axe, a Chinese weapon in use from the Shang dynasty (est. 1500 BC) that had a dagger-shaped blade mounted perpendicular to a spearhead
Fauchard, a curved blade atop a pole that was used in Europe between the 11th and 14th centuries
Guisarme, a medieval bladed weapon on the end of a long pole; later designs implemented a small reverse spike on the back of the blade
Glaive, a large blade, up to long, on the end of a pole
Guandao, a Chinese polearm from the 3rd century AD that had a heavy curved blade with a spike at the back
Ji (戟), a Chinese polearm combining a spear and dagger-axe
Kamayari, a Japanese spear with blade offshoots
Lochaber axe, a Scottish weapon that had a heavy blade attached to a pole in a similar fashion to a voulge
Naginata, a Japanese weapon that had a blade attached by a sword guard to a wooden shaft
Partisan, a large double-bladed spearhead mounted on a long shaft that had protrusions on either side for parrying sword thrusts
Poleaxe, a type of polearm with an axehead or hammerhead on the sides with either a spike or spearhead at the top and mounted on a long shaft. It was developed in the 14th century and remained in use until the 16th century to breach the plate armour worn by European knights and men-at-arms
Ranseur, a polearm consisting of a spearhead affixed with a cross hilt at its base derived from the earlier spetum
Spontoon, a 17th-century weapon that consisted of a large blade with two side blades mounted on a long pole, considered a more elaborate pike
Voulge, a crude single-edged blade bound to a wooden shaft
Tabarzin, a type of battle axe from Middle East.
War scythe, an improvised weapon that consisted of a blade from a scythe attached vertically to a shaft
Welsh hook, similar to a halberd and thought to originate from a forest-bill
Woldo, A Korean polearm that had a crescent-shaped blade mounted on a long shaft, similar in construction to the Chinese guandao, and primarily served as a symbol of the Royal Guard
Yue, a Chinese axe with long shaft.
Gallery | Halberd | Wikipedia | 505 | 48775 | https://en.wikipedia.org/wiki/Halberd | Technology | Polearms | null |
Pathology is the study of disease. The word pathology also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in the context of modern medical treatment, the term is often used in a narrower fashion to refer to processes and tests that fall within the contemporary medical field of "general pathology", an area that includes a number of distinct but inter-related medical specialties that diagnose disease, mostly through analysis of tissue and human cell samples. Idiomatically, "a pathology" may also refer to the predicted or actual progression of particular diseases (as in the statement "the many different forms of cancer have diverse pathologies", in which case a more proper choice of word would be "pathophysiologies"). The suffix pathy is sometimes used to indicate a state of disease in cases of both physical ailment (as in cardiomyopathy) and psychological conditions (such as psychopathy). A physician practicing pathology is called a pathologist.
As a field of general inquiry and research, pathology addresses components of disease: cause, mechanisms of development (pathogenesis), structural alterations of cells (morphologic changes), and the consequences of changes (clinical manifestations). In common medical practice, general pathology is mostly concerned with analyzing known clinical abnormalities that are markers or precursors for both infectious and non-infectious disease, and is conducted by experts in one of two major specialties, anatomical pathology and clinical pathology. Further divisions in specialty exist on the basis of the involved sample types (comparing, for example, cytopathology, hematopathology, and histopathology), organs (as in renal pathology), and physiological systems (oral pathology), as well as on the basis of the focus of the examination (as with forensic pathology).
Pathology is a significant field in modern medical diagnosis and medical research.
Etymology
The Latin term pathology derives from the Ancient Greek roots pathos (), meaning "experience" or "suffering", and -logia (), meaning "study of". The term is of early 16th-century origin, and became increasingly popularized after the 1530s.
History | Pathology | Wikipedia | 450 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
The study of pathology, including the detailed examination of the body, including dissection and inquiry into specific maladies, dates back to antiquity. Rudimentary understanding of many conditions was present in most early societies and is attested to in the records of the earliest historical societies, including those of the Middle East, India, and China. By the Hellenic period of ancient Greece, a concerted causal study of disease was underway (see Medicine in ancient Greece), with many notable early physicians (such as Hippocrates, for whom the modern Hippocratic Oath is named) having developed methods of diagnosis and prognosis for a number of diseases. The medical practices of the Romans and those of the Byzantines continued from these Greek roots, but, as with many areas of scientific inquiry, growth in understanding of medicine stagnated somewhat after the Classical Era, but continued to slowly develop throughout numerous cultures. Notably, many advances were made in the medieval era of Islam (see Medicine in medieval Islam), during which numerous texts of complex pathologies were developed, also based on the Greek tradition. Even so, growth in complex understanding of disease mostly languished until knowledge and experimentation again began to proliferate in the Renaissance, Enlightenment, and Baroque eras, following the resurgence of the empirical method at new centers of scholarship. By the 17th century, the study of rudimentary microscopy was underway and examination of tissues had led British Royal Society member Robert Hooke to coin the word "cell", setting the stage for later germ theory. | Pathology | Wikipedia | 310 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Modern pathology began to develop as a distinct field of inquiry during the 19th Century through natural philosophers and physicians that studied disease and the informal study of what they termed "pathological anatomy" or "morbid anatomy". However, pathology as a formal area of specialty was not fully developed until the late 19th and early 20th centuries, with the advent of detailed study of microbiology. In the 19th century, physicians had begun to understand that disease-causing pathogens, or "germs" (a catch-all for disease-causing, or pathogenic, microbes, such as bacteria, viruses, fungi, amoebae, molds, protists, and prions) existed and were capable of reproduction and multiplication, replacing earlier beliefs in humors or even spiritual agents, that had dominated for much of the previous 1,500 years in European medicine. With the new understanding of causative agents, physicians began to compare the characteristics of one germ's symptoms as they developed within an affected individual to another germ's characteristics and symptoms. This approach led to the foundational understanding that diseases are able to replicate themselves, and that they can have many profound and varied effects on the human host. To determine causes of diseases, medical experts used the most common and widely accepted assumptions or symptoms of their times, a general principle of approach that persists in modern medicine.
Modern medicine was particularly advanced by further developments of the microscope to analyze tissues, to which Rudolf Virchow gave a significant contribution, leading to a slew of research developments.
By the late 1920s to early 1930s pathology was deemed a medical specialty. Combined with developments in the understanding of general physiology, by the beginning of the 20th century, the study of pathology had begun to split into a number of distinct fields, resulting in the development of a large number of modern specialties within pathology and related disciplines of diagnostic medicine.
General pathology
The modern practice of pathology is divided into a number of subdisciplines within the distinct but deeply interconnected aims of biological research and medical practice. Biomedical research into disease incorporates the work of a vast variety of life science specialists, whereas, in most parts of the world, to be licensed to practice pathology as a medical specialty, one has to complete medical school and secure a license to practice medicine. Structurally, the study of disease is divided into many different fields that study or diagnose markers for disease using methods and technologies particular to specific scales, organs, and tissue types.
Anatomical pathology | Pathology | Wikipedia | 504 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Anatomical pathology (Commonwealth) or anatomic pathology (United States) is a medical specialty that is concerned with the diagnosis of disease based on the gross, microscopic, chemical, immunologic and molecular examination of organs, tissues, and whole bodies (as in a general examination or an autopsy). Anatomical pathology is itself divided into subfields, the main divisions being surgical pathology, cytopathology, and forensic pathology. Anatomical pathology is one of two main divisions of the medical practice of pathology, the other being clinical pathology, the diagnosis of disease through the laboratory analysis of bodily fluids and tissues. Sometimes, pathologists practice both anatomical and clinical pathology, a combination known as general pathology.
Cytopathology
Cytopathology (sometimes referred to as "cytology") is a branch of pathology that studies and diagnoses diseases on the cellular level. It is usually used to aid in the diagnosis of cancer, but also helps in the diagnosis of certain infectious diseases and other inflammatory conditions as well as thyroid lesions, diseases involving sterile body cavities (peritoneal, pleural, and cerebrospinal), and a wide range of other body sites. Cytopathology is generally used on samples of free cells or tissue fragments (in contrast to histopathology, which studies whole tissues) and cytopathologic tests are sometimes called smear tests because the samples may be smeared across a glass microscope slide for subsequent staining and microscopic examination. However, cytology samples may be prepared in other ways, including cytocentrifugation.
Dermatopathology | Pathology | Wikipedia | 326 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Dermatopathology is a subspecialty of anatomic pathology that focuses on the skin and the rest of the integumentary system as an organ. It is unique, in that there are two paths a physician can take to obtain the specialization. All general pathologists and general dermatologists train in the pathology of the skin, so the term dermatopathologist denotes either of these who has reached a certain level of accreditation and experience; in the US, either a general pathologist or a dermatologist can undergo a 1 to 2 year fellowship in the field of dermatopathology. The completion of this fellowship allows one to take a subspecialty board examination, and becomes a board certified dermatopathologist. Dermatologists are able to recognize most skin diseases based on their appearances, anatomic distributions, and behavior. Sometimes, however, those criteria do not lead to a conclusive diagnosis, and a skin biopsy is taken to be examined under the microscope using usual histological tests. In some cases, additional specialized testing needs to be performed on biopsies, including immunofluorescence, immunohistochemistry, electron microscopy, flow cytometry, and molecular-pathologic analysis. One of the greatest challenges of dermatopathology is its scope. More than 1500 different disorders of the skin exist, including cutaneous eruptions ("rashes") and neoplasms. Therefore, dermatopathologists must maintain a broad base of knowledge in clinical dermatology, and be familiar with several other specialty areas in Medicine.
Forensic pathology | Pathology | Wikipedia | 333 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Forensic pathology focuses on determining the cause of death by post-mortem examination of a corpse or partial remains. An autopsy is typically performed by a coroner or medical examiner, often during criminal investigations; in this role, coroners and medical examiners are also frequently asked to confirm the identity of a corpse. The requirements for becoming a licensed practitioner of forensic pathology varies from country to country (and even within a given nation) but typically a minimal requirement is a medical doctorate with a specialty in general or anatomical pathology with subsequent study in forensic medicine. The methods forensic scientists use to determine death include examination of tissue specimens to identify the presence or absence of natural disease and other microscopic findings, interpretations of toxicology on body tissues and fluids to determine the chemical cause of overdoses, poisonings or other cases involving toxic agents, and examinations of physical trauma. Forensic pathology is a major component in the trans-disciplinary field of forensic science.
Histopathology
Histopathology refers to the microscopic examination of various forms of human tissue. Specifically, in clinical medicine, histopathology refers to the examination of a biopsy or surgical specimen by a pathologist, after the specimen has been processed and histological sections have been placed onto glass slides. This contrasts with the methods of cytopathology, which uses free cells or tissue fragments. Histopathological examination of tissues starts with surgery, biopsy, or autopsy. The tissue is removed from the body of an organism and then placed in a fixative that stabilizes the tissues to prevent decay. The most common fixative is formalin, although frozen section fixing is also common. To see the tissue under a microscope, the sections are stained with one or more pigments. The aim of staining is to reveal cellular components; counterstains are used to provide contrast. Histochemistry refers to the science of using chemical reactions between laboratory chemicals and components within tissue. The histological slides are then interpreted diagnostically and the resulting pathology report describes the histological findings and the opinion of the pathologist. In the case of cancer, this represents the tissue diagnosis required for most treatment protocols.
Neuropathology | Pathology | Wikipedia | 436 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Neuropathology is the study of disease of nervous system tissue, usually in the form of either surgical biopsies or sometimes whole brains in the case of autopsy. Neuropathology is a subspecialty of anatomic pathology, neurology, and neurosurgery. In many English-speaking countries, neuropathology is considered a subfield of anatomical pathology. A physician who specializes in neuropathology, usually by completing a fellowship after a residency in anatomical or general pathology, is called a neuropathologist. In day-to-day clinical practice, a neuropathologist generates diagnoses for patients. If a disease of the nervous system is suspected, and the diagnosis cannot be made by less invasive methods, a biopsy of nervous tissue is taken from the brain or spinal cord to aid in diagnosis. Biopsy is usually requested after a mass is detected by medical imaging. With autopsies, the principal work of the neuropathologist is to help in the post-mortem diagnosis of various conditions that affect the central nervous system. Biopsies can also consist of the skin. Epidermal nerve fiber density testing (ENFD) is a more recently developed neuropathology test in which a punch skin biopsy is taken to identify small fiber neuropathies by analyzing the nerve fibers of the skin. This test is becoming available in select labs as well as many universities; it replaces the traditional nerve biopsy test as less invasive.
Pulmonary pathology
Pulmonary pathology is a subspecialty of anatomic (and especially surgical) pathology that deals with diagnosis and characterization of neoplastic and non-neoplastic diseases of the lungs and thoracic pleura. Diagnostic specimens are often obtained via bronchoscopic transbronchial biopsy, CT-guided percutaneous biopsy, or video-assisted thoracic surgery. These tests can be necessary to diagnose between infection, inflammation, or fibrotic conditions.
Renal pathology | Pathology | Wikipedia | 411 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Renal pathology is a subspecialty of anatomic pathology that deals with the diagnosis and characterization of disease of the kidneys. In a medical setting, renal pathologists work closely with nephrologists and transplant surgeons, who typically obtain diagnostic specimens via percutaneous renal biopsy. The renal pathologist must synthesize findings from traditional microscope histology, electron microscopy, and immunofluorescence to obtain a definitive diagnosis. Medical renal diseases may affect the glomerulus, the tubules and interstitium, the vessels, or a combination of these compartments.
Surgical pathology
Surgical pathology is one of the primary areas of practice for most anatomical pathologists. Surgical pathology involves the gross and microscopic examination of surgical specimens, as well as biopsies submitted by surgeons and non-surgeons such as general internists, medical subspecialists, dermatologists, and interventional radiologists. Often an excised tissue sample is the best and most definitive evidence of disease (or lack thereof) in cases where tissue is surgically removed from a patient. These determinations are usually accomplished by a combination of gross (i.e., macroscopic) and histologic (i.e., microscopic) examination of the tissue, and may involve evaluations of molecular properties of the tissue by immunohistochemistry or other laboratory tests. | Pathology | Wikipedia | 277 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
There are two major types of specimens submitted for surgical pathology analysis: biopsies and surgical resections. A biopsy is a small piece of tissue removed primarily for surgical pathology analysis, most often in order to render a definitive diagnosis. Types of biopsies include core biopsies, which are obtained through the use of large-bore needles, sometimes under the guidance of radiological techniques such as ultrasound, CT scan, or magnetic resonance imaging. Incisional biopsies are obtained through diagnostic surgical procedures that remove part of a suspicious lesion, whereas excisional biopsies remove the entire lesion, and are similar to therapeutic surgical resections. Excisional biopsies of skin lesions and gastrointestinal polyps are very common. The pathologist's interpretation of a biopsy is critical to establishing the diagnosis of a benign or malignant tumor, and can differentiate between different types and grades of cancer, as well as determining the activity of specific molecular pathways in the tumor. Surgical resection specimens are obtained by the therapeutic surgical removal of an entire diseased area or organ (and occasionally multiple organs). These procedures are often intended as definitive surgical treatment of a disease in which the diagnosis is already known or strongly suspected, but pathological analysis of these specimens remains important in confirming the previous diagnosis.
Clinical pathology
Clinical pathology is a medical specialty that is concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids such as blood and urine, as well as tissues, using the tools of chemistry, clinical microbiology, hematology and molecular pathology. Clinical pathologists work in close collaboration with medical technologists, hospital administrations, and referring physicians. Clinical pathologists learn to administer a number of visual and microscopic tests and an especially large variety of tests of the biophysical properties of tissue samples involving automated analysers and cultures. Sometimes the general term "laboratory medicine specialist" is used to refer to those working in clinical pathology, including medical doctors, Ph.D.s and doctors of pharmacology. Immunopathology, the study of an organism's immune response to infection, is sometimes considered to fall within the domain of clinical pathology.
Hematopathology | Pathology | Wikipedia | 446 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Hematopathology is the study of diseases of blood cells (including constituents such as white blood cells, red blood cells, and platelets) and the tissues, and organs comprising
the hematopoietic system. The term hematopoietic system refers to tissues and organs that produce and/or primarily host hematopoietic cells and includes bone marrow, the lymph nodes, thymus, spleen, and other lymphoid tissues. In the United States, hematopathology is a board certified subspecialty (licensed under the American Board of Pathology) practiced by those physicians who have completed a general pathology residency (anatomic, clinical, or combined) and an additional year of fellowship training in hematology. The hematopathologist reviews biopsies of lymph nodes, bone marrows and other tissues involved by an infiltrate of cells of the hematopoietic system. In addition, the hematopathologist may be in charge of flow cytometric and/or molecular hematopathology studies.
Molecular pathology
Molecular pathology is focused upon the study and diagnosis of disease through the examination of molecules within organs, tissues or bodily fluids. Molecular pathology is multidisciplinary by nature and shares some aspects of practice with both anatomic pathology and clinical pathology, molecular biology, biochemistry, proteomics and genetics. It is often applied in a context that is as much scientific as directly medical and encompasses the development of molecular and genetic approaches to the diagnosis and classification of human diseases, the design and validation of predictive biomarkers for treatment response and disease progression, and the susceptibility of individuals of different genetic constitution to particular disorders. The crossover between molecular pathology and epidemiology is represented by a related field "molecular pathological epidemiology". Molecular pathology is commonly used in diagnosis of cancer and infectious diseases. Molecular Pathology is primarily used to detect cancers such as melanoma, brainstem glioma, brain tumors as well as many other types of cancer and infectious diseases. Techniques are numerous but include quantitative polymerase chain reaction (qPCR), multiplex PCR, DNA microarray, in situ hybridization, DNA sequencing, antibody-based immunofluorescence tissue assays, molecular profiling of pathogens, and analysis of bacterial genes for antimicrobial resistance. Techniques used are based on analyzing samples of DNA and RNA. Pathology is widely used for gene therapy and disease diagnosis. | Pathology | Wikipedia | 508 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Oral and maxillofacial pathology
Oral and Maxillofacial Pathology is one of nine dental specialties recognized by the American Dental Association, and is sometimes considered a specialty of both dentistry and pathology. Oral Pathologists must complete three years of post doctoral training in an accredited program and subsequently obtain diplomate status from the American Board of Oral and Maxillofacial Pathology. The specialty focuses on the diagnosis, clinical management and investigation of diseases that affect the oral cavity and surrounding maxillofacial structures including but not limited to odontogenic, infectious, epithelial, salivary gland, bone and soft tissue pathologies. It also significantly intersects with the field of dental pathology. Although concerned with a broad variety of diseases of the oral cavity, they have roles distinct from otorhinolaryngologists ("ear, nose, and throat" specialists), and speech pathologists, the latter of which helps diagnose many neurological or neuromuscular conditions relevant to speech phonology or swallowing. Owing to the availability of the oral cavity to non-invasive examination, many conditions in the study of oral disease can be diagnosed, or at least suspected, from gross examination, but biopsies, cell smears, and other tissue analysis remain important diagnostic tools in oral pathology.
Medical training and accreditation
Becoming a pathologist generally requires specialty-training after medical school, but individual nations vary some in the medical licensing required of pathologists. In the United States, pathologists are physicians (D.O. or M.D.) who have completed a four-year undergraduate program, four years of medical school training, and three to four years of postgraduate training in the form of a pathology residency. Training may be within two primary specialties, as recognized by the American Board of Pathology: [anatomical pathology and clinical pathology, each of which requires separate board certification. The American Osteopathic Board of Pathology also recognizes four primary specialties: anatomic pathology, dermatopathology, forensic pathology, and laboratory medicine. Pathologists may pursue specialised fellowship training within one or more subspecialties of either anatomical or clinical pathology. Some of these subspecialties permit additional board certification, while others do not. | Pathology | Wikipedia | 451 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
In the United Kingdom, pathologists are physicians licensed by the UK General Medical Council. The training to become a pathologist is under the oversight of the Royal College of Pathologists. After four to six years of undergraduate medical study, trainees proceed to a two-year foundation program. Full-time training in histopathology currently lasts between five and five and a half years and includes specialist training in surgical pathology, cytopathology, and autopsy pathology. It is also possible to take a Royal College of Pathologists diploma in forensic pathology, dermatopathology, or cytopathology, recognising additional specialist training and expertise and to get specialist accreditation in forensic pathology, pediatric pathology, and neuropathology. All postgraduate medical training and education in the UK is overseen by the General Medical Council.
In France, pathology is separated into two distinct specialties, anatomical pathology, and clinical pathology. Residencies for both lasts four years. Residency in anatomical pathology is open to physicians only, while clinical pathology is open to both physicians and pharmacists. At the end of the second year of clinical pathology residency, residents can choose between general clinical pathology and a specialization in one of the disciplines, but they can not practice anatomical pathology, nor can anatomical pathology residents practice clinical pathology.
Overlap with other diagnostic medicine
Though separate fields in terms of medical practice, a number of areas of inquiry in medicine and
medical science either overlap greatly with general pathology, work in tandem with it, or contribute significantly to the understanding of the pathology of a given disease or its course in an individual. As a significant portion of all general pathology practice is concerned with cancer, the practice of oncology makes extensive use of both anatomical and clinical pathology in diagnosis and treatment. In particular, biopsy, resection, and blood tests are all examples of pathology work that is essential for the diagnoses of many kinds of cancer and for the staging of cancerous masses. In a similar fashion, the tissue and blood analysis techniques of general pathology are of central significance to the investigation of serious infectious disease and as such inform significantly upon the fields of epidemiology, etiology, immunology, and parasitology. General pathology methods are of great importance to biomedical research into disease, wherein they are sometimes referred to as "experimental" or "investigative" pathology. | Pathology | Wikipedia | 473 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Medical imaging is the generating of visual representations of the interior of a body for clinical analysis and medical intervention. Medical imaging reveals details of internal physiology that help medical professionals plan appropriate treatments for tissue infection and trauma. Medical imaging is also central in supplying the biometric data necessary to establish baseline features of anatomy and physiology so as to increase the accuracy with which early or fine-detail abnormalities are detected. These diagnostic techniques are often performed in combination with general pathology procedures and are themselves often essential to developing new understanding of the pathogenesis of a given disease and tracking the progress of disease in specific medical cases. Examples of important subdivisions in medical imaging include radiology (which uses the imaging technologies of X-ray radiography) magnetic resonance imaging, medical ultrasonography (or ultrasound), endoscopy, elastography, tactile imaging, thermography, medical photography, nuclear medicine and functional imaging techniques such as positron emission tomography. Though they do not strictly relay images, readings from diagnostics tests involving electroencephalography, magnetoencephalography, and electrocardiography often give hints as to the state and function of certain tissues in the brain and heart respectively.
Pathology informatics
Pathology informatics is a subfield of health informatics. It is the use of information technology in pathology. It encompasses pathology laboratory operations, data analysis, and the interpretation of pathology-related information.
Key aspects of pathology informatics include:
Laboratory information management systems (LIMS): Implementing and managing computer systems specifically designed for pathology departments. These systems help in tracking and managing patient specimens, results, and other pathology data.
Digital pathology: Involves the use of digital technology to create, manage, and analyze pathology images. This includes side scanning and automated image analysis.
Telepathology: Using technology to enable remote pathology consultation and collaboration.
Quality assurance and reporting: Implementing informatics solutions to ensure the quality and accuracy of pathology processes.
Psychopathology | Pathology | Wikipedia | 393 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Psychopathology is the study of mental illness, particularly of severe disorders. Informed heavily by both psychology and neurology, its purpose is to classify mental illness, elucidate its underlying causes, and guide clinical psychiatric treatment accordingly. Although diagnosis and classification of mental norms and disorders is largely the purview of psychiatry—the results of which are guidelines such as the Diagnostic and Statistical Manual of Mental Disorders, which attempt to classify mental disease mostly on behavioural evidence, though not without controversy—the field is also heavily, and increasingly, informed upon by neuroscience and other of the biological cognitive sciences. Mental or social disorders or behaviours seen as generally unhealthy or excessive in a given individual, to the point where they cause harm or severe disruption to the person's lifestyle, are often called "pathological" (e.g., pathological gambling or pathological liar).
Non-humans
Although the vast majority of lab work and research in pathology concerns the development of disease in humans, pathology is of significance throughout the biological sciences. Two main catch-all fields exist to represent most complex organisms capable of serving as host to a pathogen or other form of disease: veterinary pathology (concerned with all non-human species of kingdom of Animalia) and phytopathology, which studies disease in plants.
Veterinary pathology
Veterinary pathology covers a vast array of species, but with a significantly smaller number of practitioners, so understanding of disease in non-human animals, especially as regards veterinary practice, varies considerably by species. Nevertheless, significant amounts of pathology research are conducted on animals, for two primary reasons: 1) The origins of diseases are typically zoonotic in nature, and many infectious pathogens have animal vectors and, as such, understanding the mechanisms of action for these pathogens in non-human hosts is essential to the understanding and application of epidemiology and 2) those animals that share physiological and genetic traits with humans can be used as surrogates for the study of the disease and potential treatments as well as the effects of various synthetic products. For this reason, as well as their roles as livestock and companion animals, mammals generally have the largest body of research in veterinary pathology. Animal testing remains a controversial practice, even in cases where it is used to research treatment for human disease. As in human medical pathology, the practice of veterinary pathology is customarily divided into the two main fields of anatomical and clinical pathology.
Plant pathology | Pathology | Wikipedia | 494 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
Although the pathogens and their mechanics differ greatly from those of animals, plants are subject to a wide variety of diseases, including those caused by fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Damage caused by insects, mites, vertebrate, and other small herbivores is not considered a part of the domain of plant pathology. The field is connected to plant disease epidemiology and especially concerned with the horticulture of species that are of high importance to the human diet or other human utility. | Pathology | Wikipedia | 129 | 48791 | https://en.wikipedia.org/wiki/Pathology | Biology and health sciences | Fields of medicine | Health |
In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic events occurring in distant galaxies which represent the brightest and "most powerful class of explosion in the universe." These extreme electromagnetic events are second only to the Big Bang as the most energetic and luminous phenomenon ever known. Gamma-ray bursts can last from a few milliseconds to several hours. After the initial flash of gamma rays, a longer-lived §afterglow is emitted, usually in the longer wavelengths of X-ray, ultraviolet, optical, infrared, microwave or radio frequencies.
The intense radiation of most observed GRBs is thought to be released during a supernova or superluminous supernova as a high-mass star implodes to form a neutron star or a black hole. From gravitational wave observations, short-duration (sGRB) events describe a subclass of GRB signals that are now known to originate from the cataclysmic merger of binary neutron stars.
The sources of most GRB are billions of light years away from Earth, implying that the explosions are both extremely energetic (a typical burst releases as much energy in a few seconds as the Sun will in its entire 10-billion-year lifetime) and extremely rare (a few per galaxy per million years). All GRBs in recorded history have originated from outside the Milky Way galaxy, although a related class of phenomena, soft gamma repeaters, are associated with magnetars within our galaxy. This may be self-evident, since a gamma-ray burst in the Milky Way pointed directly at Earth would likely sterilize the planet or effect a mass extinction. The Late Ordovician mass extinction has been hypothesised by some researchers to have occurred as a result of such a gamma-ray burst.
GRB signals were first detected in 1967 by the Vela satellites, which were designed to detect covert nuclear weapons tests; after an "exhaustive" period of analysis, this was published as academic research in 1973. Following their discovery, hundreds of theoretical models were proposed to explain these bursts, such as collisions between comets and neutron stars. Little information was available to verify these models until the 1997 detection of the first X-ray and optical afterglows and direct measurement of their redshifts using optical spectroscopy, and thus their distances and energy outputs. These discoveries—and subsequent studies of the galaxies and supernovae associated with the bursts—clarified the distance and luminosity of GRBs, definitively placing them in distant galaxies.
History | Gamma-ray burst | Wikipedia | 509 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
Gamma-ray bursts were first observed in the late 1960s by the U.S. Vela satellites, which were built to detect gamma radiation pulses emitted by nuclear weapons tested in space. The United States suspected that the Soviet Union might attempt to conduct secret nuclear tests after signing the Nuclear Test Ban Treaty in 1963. On July 2, 1967, at 14:19 UTC, the Vela 4 and Vela 3 satellites detected a flash of gamma radiation unlike any known nuclear weapons signature. Uncertain what had happened but not considering the matter particularly urgent, the team at the Los Alamos National Laboratory, led by Ray Klebesadel, filed the data away for investigation. As additional Vela satellites were launched with better instruments, the Los Alamos team continued to find inexplicable gamma-ray bursts in their data. By analyzing the different arrival times of the bursts as detected by different satellites, the team was able to determine rough estimates for the sky positions of 16 bursts and definitively rule out a terrestrial or solar origin. Contrary to popular belief, the data was never classified. After thorough analysis, the findings were published in 1973 as an Astrophysical Journal article entitled "Observations of Gamma-Ray Bursts of Cosmic Origin".
Most early hypotheses of gamma-ray bursts posited nearby sources within the Milky Way Galaxy. From 1991, the Compton Gamma Ray Observatory (CGRO) and its Burst and Transient Source Explorer (BATSE) instrument, an extremely sensitive gamma-ray detector, provided data that showed the distribution of GRBs is isotropicnot biased towards any particular direction in space. If the sources were from within our own galaxy, they would be strongly concentrated in or near the galactic plane. The absence of any such pattern in the case of GRBs provided strong evidence that gamma-ray bursts must come from beyond the Milky Way. However, some Milky Way models are still consistent with an isotropic distribution. | Gamma-ray burst | Wikipedia | 391 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
Counterpart objects as candidate sources
For decades after the discovery of GRBs, astronomers searched for a counterpart at other wavelengths: i.e., any astronomical object in positional coincidence with a recently observed burst. Astronomers considered many distinct classes of objects, including white dwarfs, pulsars, supernovae, globular clusters, quasars, Seyfert galaxies, and BL Lac objects. All such searches were unsuccessful, and in a few cases particularly well-localized bursts (those whose positions were determined with what was then a high degree of accuracy) could be clearly shown to have no bright objects of any nature consistent with the position derived from the detecting satellites. This suggested an origin of either very faint stars or extremely distant galaxies. Even the most accurate positions contained numerous faint stars and galaxies, and it was widely agreed that final resolution of the origins of cosmic gamma-ray bursts would require both new satellites and faster communication.
Afterglow
Several models for the origin of gamma-ray bursts postulated that the initial burst of gamma rays should be followed by afterglow: slowly fading emission at longer wavelengths created by collisions between the burst ejecta and interstellar gas. Early searches for this afterglow were unsuccessful, largely because it is difficult to observe a burst's position at longer wavelengths immediately after the initial burst. The breakthrough came in February 1997 when the satellite BeppoSAX detected a gamma-ray burst (GRB 970228) and when the X-ray camera was pointed towards the direction from which the burst had originated, it detected fading X-ray emission. The William Herschel Telescope identified a fading optical counterpart 20 hours after the burst. Once the GRB faded, deep imaging was able to identify a faint, distant host galaxy at the location of the GRB as pinpointed by the optical afterglow. | Gamma-ray burst | Wikipedia | 375 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
Because of the very faint luminosity of this galaxy, its exact distance was not measured for several years. Well after then, another major breakthrough occurred with the next event registered by BeppoSAX, GRB 970508. This event was localized within four hours of its discovery, allowing research teams to begin making observations much sooner than any previous burst. The spectrum of the object revealed a redshift of z = 0.835, placing the burst at a distance of roughly 6 billion light years from Earth. This was the first accurate determination of the distance to a GRB, and together with the discovery of the host galaxy of 970228 proved that GRBs occur in extremely distant galaxies. Within a few months, the controversy about the distance scale ended: GRBs were extragalactic events originating within faint galaxies at enormous distances. The following year, GRB 980425 was followed within a day by a bright supernova (SN 1998bw), coincident in location, indicating a clear connection between GRBs and the deaths of very massive stars. This burst provided the first strong clue about the nature of the systems that produce GRBs.
More recent instruments - launched from 2000 | Gamma-ray burst | Wikipedia | 244 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
BeppoSAX functioned until 2002 and CGRO (with BATSE) was deorbited in 2000. However, the revolution in the study of gamma-ray bursts motivated the development of a number of additional instruments designed specifically to explore the nature of GRBs, especially in the earliest moments following the explosion. The first such mission, HETE-2, was launched in 2000 and functioned until 2006, providing most of the major discoveries during this period. One of the most successful space missions to date, Swift, was launched in 2004 and as of May 2024 is still operational. Swift is equipped with a very sensitive gamma-ray detector as well as on-board X-ray and optical telescopes, which can be rapidly and automatically slewed to observe afterglow emission following a burst. More recently, the Fermi mission was launched carrying the Gamma-Ray Burst Monitor, which detects bursts at a rate of several hundred per year, some of which are bright enough to be observed at extremely high energies with Fermi's Large Area Telescope. Meanwhile, on the ground, numerous optical telescopes have been built or modified to incorporate robotic control software that responds immediately to signals sent through the Gamma-ray Burst Coordinates Network. This allows the telescopes to rapidly repoint towards a GRB, often within seconds of receiving the signal and while the gamma-ray emission itself is still ongoing.
The Space Variable Objects Monitor is a small X-ray telescope satellite for studying the explosions of massive stars by analysing the resulting gamma-ray bursts, developed by China National Space Administration (CNSA), Chinese Academy of Sciences (CAS) and the French Space Agency (CNES), launched on 22 June 2024 (07:00:00 UTC).
The Taiwan Space Agency is launching a cubesat called The Gamma-ray Transients Monitor to track GRBs and other bright gamma-ray transients with energies ranging from 50 keV to 2 MeV in Q4 2026.
Short bursts and other observations
New developments since the 2000s include the recognition of short gamma-ray bursts as a separate class (likely from merging neutron stars and not associated with supernovae), the discovery of extended, erratic flaring activity at X-ray wavelengths lasting for many minutes after most GRBs, and the discovery of the most luminous and the former most distant objects in the universe. Prior to a flurry of discoveries from the James Webb Space Telescope, was the most distant known object in the universe. | Gamma-ray burst | Wikipedia | 502 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
In October 2018, astronomers reported that (detected in 2015) and GW170817, a gravitational wave event detected in 2017 (which has been associated with , a burst detected 1.7 seconds later), may have been produced by the same mechanism—the merger of two neutron stars. The similarities between the two events, in terms of gamma ray, optical, and x-ray emissions, as well as to the nature of the associated host galaxies, were considered "striking", suggesting the two separate events may both be the result of the merger of neutron stars, and both may be a kilonova, which may be more common in the universe than previously understood, according to the researchers.
The highest energy light observed from a gamma-ray burst was one teraelectronvolt, from in 2019. Although enormous for such a distant event, this energy is around 3 orders of magnitude lower than the highest energy light observed from closer gamma ray sources within our Milky Way galaxy, for example a 2021 event of 1.4 petaelectronvolts.
Classification
The light curves of gamma-ray bursts are extremely diverse and complex. No two gamma-ray burst light curves are identical, with large variation observed in almost every property: the duration of observable emission can vary from milliseconds to tens of minutes, there can be a single peak or several individual subpulses, and individual peaks can be symmetric or with fast brightening and very slow fading. Some bursts are preceded by a "precursor" event, a weak burst that is then followed (after seconds to minutes of no emission at all) by the much more intense "true" bursting episode. The light curves of some events have extremely chaotic and complicated profiles with almost no discernible patterns. | Gamma-ray burst | Wikipedia | 360 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
Although some light curves can be roughly reproduced using certain simplified models, little progress has been made in understanding the full diversity observed. Many classification schemes have been proposed, but these are often based solely on differences in the appearance of light curves and may not always reflect a true physical difference in the progenitors of the explosions. However, plots of the distribution of the observed duration for a large number of gamma-ray bursts show a clear bimodality, suggesting the existence of two separate populations: a "short" population with an average duration of about 0.3 seconds and a "long" population with an average duration of about 30 seconds. Both distributions are very broad with a significant overlap region in which the identity of a given event is not clear from duration alone. Additional classes beyond this two-tiered system have been proposed on both observational and theoretical grounds.
Short gamma-ray bursts
Events with a duration of less than about two seconds are classified as short gamma-ray bursts (sGRB). These account for about 30% of gamma-ray bursts, but until 2005, no afterglow had been successfully detected from any short event and little was known about their origins. Following this, several dozen short gamma-ray burst afterglows were detected and localized, several of them associated with regions of little or no star formation, such as large elliptical galaxies. This ruled out a link to massive stars, confirming the short events to be physically distinct from long events. In addition, there had been no association with supernovae. | Gamma-ray burst | Wikipedia | 309 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
The true nature of these objects was thus initially unknown, but the leading hypothesis was that they originated from the mergers of binary neutron stars or a neutron star with a black hole. Such mergers were hypothesized to produce kilonovae, and evidence for a kilonova associated with short GRB 130603B was reported in 2013. The mean duration of sGRB events of around 200 milliseconds implied (due to causality) that the sources must be of very small physical diameter in stellar terms: less than 0.2 light-seconds (60,000 km or 37,000 miles)—about four times the Earth's diameter. The observation of minutes to hours of X-ray flashes after an sGRB was seen as consistent with small particles of a precursor object like a neutron star initially being swallowed by a black hole in less than two seconds, followed by some hours of lower-energy events as remaining fragments of tidally disrupted neutron star material (no longer neutronium) would remain in orbit, spiraling into the black hole over a longer period of time. The origin of short gamma-ray bursts in kilonovae was finally conclusively established in 2017, when short GRB 170817A co-occurred with the detection of gravitational wave GW170817, a signal from the merger of two neutron stars.
Unrelated to these cataclysmic origins, short-duration gamma-ray signals are also produced by giant flares from soft gamma repeaters in our own—or nearby—galaxies.
Long gamma-ray bursts
Most observed events (70%) have a duration of greater than two seconds and are classified as long gamma-ray bursts. Because these events constitute the majority of the population and because they tend to have the brightest afterglows, they have been observed in much greater detail than their short counterparts. Almost every well-studied long gamma-ray burst has been linked to a galaxy with rapid star formation, and in many cases to a core-collapse supernova as well, unambiguously associating long GRBs with the deaths of massive stars. Long GRB afterglow observations, at high redshift, are also consistent with the GRB having originated in star-forming regions. | Gamma-ray burst | Wikipedia | 459 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
In December 2022, astronomers reported the observation of GRB 211211A for 51 seconds, the first evidence of a long GRB likely associated with mergers of "compact binary objects" such as neutron stars or white dwarfs. Following this, GRB 191019A (2019, 64s) and GRB 230307A (2023, 35s) have been argued to signify an emerging class of long GRB which may originate from these types of progenitor events.
Ultra-long gamma-ray bursts
ulGRB are defined as GRB lasting more than 10,000 seconds, covering the upper range to the limit of the GRB duration distribution. They have been proposed to form a separate class, caused by the collapse of a blue supergiant star, a tidal disruption event or a new-born magnetar. Only a small number have been identified to date, their primary characteristic being their gamma ray emission duration. The most studied ultra-long events include GRB 101225A and GRB 111209A. The low detection rate may be a result of low sensitivity of current detectors to long-duration events, rather than a reflection of their true frequency. A 2013 study, on the other hand, shows that the existing evidence for a separate ultra-long GRB population with a new type of progenitor is inconclusive, and further multi-wavelength observations are needed to draw a firmer conclusion.
Energetics
Gamma-ray bursts are very bright as observed from Earth despite their typically immense distances. An average long GRB has a bolometric flux comparable to a bright star of our galaxy despite a distance of billions of light years (compared to a few tens of light years for most visible stars). Most of this energy is released in gamma rays, although some GRBs have extremely luminous optical counterparts as well. GRB 080319B, for example, was accompanied by an optical counterpart that peaked at a visible magnitude of 5.8, comparable to that of the dimmest naked-eye stars despite the burst's distance of 7.5 billion light years. This combination of brightness and distance implies an extremely energetic source. Assuming the gamma-ray explosion to be spherical, the energy output of GRB 080319B would be within a factor of two of the rest-mass energy of the Sun (the energy which would be released were the Sun to be converted entirely into radiation). | Gamma-ray burst | Wikipedia | 497 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
Gamma-ray bursts are thought to be highly focused explosions, with most of the explosion energy collimated into a narrow jet. The jets of gamma-ray bursts are ultrarelativistic, and are the most relativistic jets in the universe. The matter in gamma-ray burst jets may also become superluminal, or faster than the speed of light in the jet medium, with there also being effects of time reversibility. The approximate angular width of the jet (that is, the degree of spread of the beam) can be estimated directly by observing the achromatic "jet breaks" in afterglow light curves: a time after which the slowly decaying afterglow begins to fade rapidly as the jet slows and can no longer beam its radiation as effectively. Observations suggest significant variation in the jet angle from between 2 and 20 degrees.
Because their energy is strongly focused, the gamma rays emitted by most bursts are expected to miss the Earth and never be detected. When a gamma-ray burst is pointed towards Earth, the focusing of its energy along a relatively narrow beam causes the burst to appear much brighter than it would have been were its energy emitted spherically. The total energy of typical gamma-ray bursts has been estimated at 3 × 1044 J,which is larger than the total energy (1044 J) of ordinary supernovae (type Ia, Ibc, II), with gamma-ray bursts also being more powerful than the typical supernova. Very bright supernovae have been observed to accompany several of the nearest GRBs. Further support for focusing of the output of GRBs comes from observations of strong asymmetries in the spectra of nearby type Ic supernovae and from radio observations taken long after bursts when their jets are no longer relativistic.
However, a competing model, the binary-driven hypernova model, developed by Remo Ruffini and others at ICRANet, accepts the extreme isotropic energy totals as being true, with there being no need to correct for beaming. They also note that the extreme beaming angles in the standard "fireball" model have never been physically corroborated. | Gamma-ray burst | Wikipedia | 443 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
With the discovery of GRB 190114C, astronomers may have been missing half of the total energy that gamma-ray bursts produce, with Konstancja Satalecka, an astrophysicist at the German Electron Synchrotron, stating that "Our measurements show that the energy released in very-high-energy gamma-rays is comparable to the amount radiated at all lower energies taken together".
Short (time duration) GRBs appear to come from a lower-redshift (i.e. less distant) population and are less luminous than long GRBs. The degree of beaming in short bursts has not been accurately measured, but as a population they are likely less collimated than long GRBs or possibly not collimated at all in some cases.
Progenitors
Because of the immense distances of most gamma-ray burst sources from Earth, identification of the progenitors, the systems that produce these explosions, is challenging. The association of some long GRBs with supernovae and the fact that their host galaxies are rapidly star-forming offer very strong evidence that long gamma-ray bursts are associated with massive stars. The most widely accepted mechanism for the origin of long-duration GRBs is the collapsar model, in which the core of an extremely massive, low-metallicity, rapidly rotating star collapses into a black hole in the final stages of its evolution. Matter near the star's core rains down towards the center and swirls into a high-density accretion disk. The infall of this material into a black hole drives a pair of relativistic jets out along the rotational axis, which pummel through the stellar envelope and eventually break through the stellar surface and radiate as gamma rays. Some alternative models replace the black hole with a newly formed magnetar, although most other aspects of the model (the collapse of the core of a massive star and the formation of relativistic jets) are the same. | Gamma-ray burst | Wikipedia | 403 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
However, a new model which has gained support and was developed by the Italian astrophysicist Remo Ruffini and other scientists at ICRANet is that of the binary-driven hypernova (BdHN) model. The model succeeds and improves upon both the fireshell model and the induced gravitational collapse (IGC) paradigm suggested before, and explains all aspects of gamma-ray bursts. The model posits long gamma-ray bursts as occurring in binary systems with a carbon–oxygen core and a companion neutron star or a black hole. Furthermore, the energy of GRBs in the model is isotropic instead of collimated. The creators of the model have noted the numerous drawbacks of the standard "fireball" model as motivation for developing the model, such as the markedly different energetics for supernova and gamma-ray bursts, and the fact that the existence of extremely narrow beaming angles have never been observationally corroborated.
The closest analogs within the Milky Way galaxy of the stars producing long gamma-ray bursts are likely the Wolf–Rayet stars, extremely hot and massive stars, which have shed most or all of their hydrogen envelope. Eta Carinae, Apep, and WR 104 have been cited as possible future gamma-ray burst progenitors. It is unclear if any star in the Milky Way has the appropriate characteristics to produce a gamma-ray burst.
The massive-star model probably does not explain all types of gamma-ray burst. There is strong evidence that some short-duration gamma-ray bursts occur in systems with no star formation and no massive stars, such as elliptical galaxies and galaxy halos. The favored hypothesis for the origin of most short gamma-ray bursts is the merger of a binary system consisting of two neutron stars. According to this model, the two stars in a binary slowly spiral towards each other because gravitational radiation releases energy until tidal forces suddenly rip the neutron stars apart and they collapse into a single black hole. The infall of matter into the new black hole produces an accretion disk and releases a burst of energy, analogous to the collapsar model. Numerous other models have also been proposed to explain short gamma-ray bursts, including the merger of a neutron star and a black hole, the accretion-induced collapse of a neutron star, or the evaporation of primordial black holes. | Gamma-ray burst | Wikipedia | 484 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
An alternative explanation proposed by Friedwardt Winterberg is that in the course of a gravitational collapse and in reaching the event horizon of a black hole, all matter disintegrates into a burst of gamma radiation.
Tidal disruption events
This class of GRB-like events was first discovered through the detection of Swift J1644+57 (originally classified as GRB 110328A) by the Swift Gamma-Ray Burst Mission on 28 March 2011. This event had a gamma-ray duration of about 2 days, much longer than even ultra-long GRBs, and was detected in many frequencies for months and years after. It occurred at the center of a small elliptical galaxy at redshift 3.8 billion light years away. This event has been accepted as a tidal disruption event (TDE), where a star wanders too close to a supermassive black hole, shredding the star. In the case of Swift J1644+57, an astrophysical jet traveling at near the speed of light was launched, and lasted roughly 1.5 years before turning off.
Since 2011, only 4 jetted TDEs have been discovered, of which 3 were detected in gamma-rays (including Swift J1644+57). It is estimated that just 1% of all TDEs are jetted events.
Emission mechanisms
The means by which gamma-ray bursts convert energy into radiation remains poorly understood, and as of 2010 there was still no generally accepted model for how this process occurs. Any successful model of GRB emission must explain the physical process for generating gamma-ray emission that matches the observed diversity of light curves, spectra, and other characteristics. Particularly challenging is the need to explain the very high efficiencies that are inferred from some explosions: some gamma-ray bursts may convert as much as half (or more) of the explosion energy into gamma-rays. Early observations of the bright optical counterparts to GRB 990123 and to GRB 080319B, whose optical light curves were extrapolations of the gamma-ray light spectra, have suggested that inverse Compton scattering may be the dominant process in some events. In this model, pre-existing low-energy photons are scattered by relativistic electrons within the explosion, augmenting their energy by a large factor and transforming them into gamma-rays. | Gamma-ray burst | Wikipedia | 479 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
The nature of the longer-wavelength afterglow emission (ranging from X-ray through radio) that follows gamma-ray bursts is better understood. Any energy released by the explosion not radiated away in the burst itself takes the form of matter or energy moving outward at nearly the speed of light. As this matter collides with the surrounding interstellar gas, it creates a relativistic shock wave that then propagates forward into interstellar space. A second shock wave, the reverse shock, may propagate back into the ejected matter. Extremely energetic electrons within the shock wave are accelerated by strong local magnetic fields and radiate as synchrotron emission across most of the electromagnetic spectrum. This model has generally been successful in modeling the behavior of many observed afterglows at late times (generally, hours to days after the explosion), although there are difficulties explaining all features of the afterglow very shortly after the gamma-ray burst has occurred.
Rate of occurrence and potential effects on life
Gamma ray bursts can have harmful or destructive effects on life. Considering the universe as a whole, the safest environments for life similar to that on Earth are the lowest density regions in the outskirts of large galaxies. Our knowledge of galaxy types and their distribution suggests that life as we know it can only exist in about 10% of all galaxies. Furthermore, galaxies with a redshift, z, higher than 0.5 are unsuitable for life as we know it, because of their higher rate of GRBs and their stellar compactness.
All GRBs observed to date have occurred well outside the Milky Way galaxy and have been harmless to Earth. However, if a GRB were to occur within the Milky Way within 5,000 to 8,000 light-years and its emission were beamed straight towards Earth, the effects could be harmful and potentially devastating for its ecosystems. Currently, orbiting satellites detect on average approximately one GRB per day. The closest observed GRB as of March 2014 was GRB 980425, located away (z=0.0085) in an SBc-type dwarf galaxy. GRB 980425 was far less energetic than the average GRB and was associated with the Type Ib supernova SN 1998bw. | Gamma-ray burst | Wikipedia | 454 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
Estimating the exact rate at which GRBs occur is difficult; for a galaxy of approximately the same size as the Milky Way, estimates of the expected rate (for long-duration GRBs) can range from one burst every 10,000 years, to one burst every 1,000,000 years. Only a small percentage of these would be beamed towards Earth. Estimates of rate of occurrence of short-duration GRBs are even more uncertain because of the unknown degree of collimation, but are probably comparable.
Since GRBs are thought to involve beamed emission along two jets in opposing directions, only planets in the path of these jets would be subjected to the high energy gamma radiation. A GRB could potentially vaporize anything in its beams' paths within a range of around 200 light-years.
Although nearby GRBs hitting Earth with a destructive shower of gamma rays are only hypothetical events, high energy processes across the galaxy have been observed to affect the Earth's atmosphere.
Effects on Earth
Earth's atmosphere is very effective at absorbing high energy electromagnetic radiation such as x-rays and gamma rays, so these types of radiation would not reach any dangerous levels at the surface during the burst event itself. The immediate effect on life on Earth from a GRB within a few kiloparsecs would only be a short increase in ultraviolet radiation at ground level, lasting from less than a second to tens of seconds. This ultraviolet radiation could potentially reach dangerous levels depending on the exact nature and distance of the burst, but it seems unlikely to be able to cause a global catastrophe for life on Earth. | Gamma-ray burst | Wikipedia | 319 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
The long-term effects from a nearby burst are more dangerous. Gamma rays cause chemical reactions in the atmosphere involving oxygen and nitrogen molecules, creating first nitrogen oxide then nitrogen dioxide gas. The nitrogen oxides cause dangerous effects on three levels. First, they deplete ozone, with models showing a possible global reduction of 25–35%, with as much as 75% in certain locations, an effect that would last for years. This reduction is enough to cause a dangerously elevated UV index at the surface. Secondly, the nitrogen oxides cause photochemical smog, which darkens the sky and blocks out parts of the sunlight spectrum. This would affect photosynthesis, but models show only about a 1% reduction of the total sunlight spectrum, lasting a few years. However, the smog could potentially cause a cooling effect on Earth's climate, producing a "cosmic winter" (similar to an impact winter, but without an impact), but only if it occurs simultaneously with a global climate instability. Thirdly, the elevated nitrogen dioxide levels in the atmosphere would wash out and produce acid rain. Nitric acid is toxic to a variety of organisms, including amphibian life, but models predict that it would not reach levels that would cause a serious global effect. The nitrates might in fact be of benefit to some plants.
All in all, a GRB within a few kiloparsecs, with its energy directed towards Earth, will mostly damage life by raising the UV levels during the burst itself and for a few years thereafter. Models show that the destructive effects of this increase can cause up to 16 times the normal levels of DNA damage. It has proved difficult to assess a reliable evaluation of the consequences of this on the terrestrial ecosystem, because of the uncertainty in biological field and laboratory data.
Hypothetical effects on Earth in the past
There is a very good chance (but no certainty) that at least one lethal GRB took place during the past 5 billion years close enough to Earth as to significantly damage life. There is a 50% chance that such a lethal GRB took place within two kiloparsecs of Earth during the last 500 million years, causing one of the major mass extinction events. | Gamma-ray burst | Wikipedia | 445 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
The major Ordovician–Silurian extinction event 450 million years ago may have been caused by a GRB. Estimates suggest that approximately 20–60% of the total phytoplankton biomass in the Ordovician oceans would have perished in a GRB, because the oceans were mostly oligotrophic and clear. The late Ordovician species of trilobites that spent portions of their lives in the plankton layer near the ocean surface were much harder hit than deep-water dwellers, which tended to remain within quite restricted areas. This is in contrast to the usual pattern of extinction events, wherein species with more widely spread populations typically fare better. A possible explanation is that trilobites remaining in deep water would be more shielded from the increased UV radiation associated with a GRB. Also supportive of this hypothesis is the fact that during the late Ordovician, burrowing bivalve species were less likely to go extinct than bivalves that lived on the surface.
A case has been made that the 774–775 carbon-14 spike was the result of a short GRB, though a very strong solar flare is another possibility.
GRB candidates in the Milky Way
No gamma-ray bursts from within our own galaxy, the Milky Way, have been observed, and the question of whether one has ever occurred remains unresolved. In light of evolving understanding of gamma-ray bursts and their progenitors, the scientific literature records a growing number of local, past, and future GRB candidates. Long duration GRBs are related to superluminous supernovae, or hypernovae, and most luminous blue variables (LBVs) and rapidly spinning Wolf–Rayet stars are thought to end their life cycles in core-collapse supernovae with an associated long-duration GRB. Knowledge of GRBs, however, is from metal-poor galaxies of former epochs of the universe's evolution, and it is impossible to directly extrapolate to encompass more evolved galaxies and stellar environments with a higher metallicity, such as the Milky Way. | Gamma-ray burst | Wikipedia | 428 | 48803 | https://en.wikipedia.org/wiki/Gamma-ray%20burst | Physical sciences | Stellar astronomy | null |
A gravitational lens is matter, such as a cluster of galaxies or a point particle, that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein's general theory of relativity. If light is treated as corpuscles travelling at the speed of light, Newtonian physics also predicts the bending of light, but only half of that predicted by general relativity.
Orest Khvolson (1924) and Frantisek Link (1936) are generally credited with being the first to discuss the effect in print, but it is more commonly associated with Einstein, who made unpublished calculations on it in 1912 and published an article on the subject in 1936.
In 1937, Fritz Zwicky posited that galaxy clusters could act as gravitational lenses, a claim confirmed in 1979 by observation of the Twin QSO SBS 0957+561.
Description
Unlike an optical lens, a point-like gravitational lens produces a maximum deflection of light that passes closest to its center, and a minimum deflection of light that travels furthest from its center. Consequently, a gravitational lens has no single focal point, but a focal line. The term "lens" in the context of gravitational light deflection was first used by O. J. Lodge, who remarked that it is "not permissible to say that the solar gravitational field acts like a lens, for it has no focal length". If the (light) source, the massive lensing object, and the observer lie in a straight line, the original light source will appear as a ring around the massive lensing object (provided the lens has circular symmetry). If there is any misalignment, the observer will see an arc segment instead.
This phenomenon was first mentioned in 1924 by the St. Petersburg physicist Orest Khvolson, and quantified by Albert Einstein in 1936. It is usually referred to in the literature as an Einstein ring, since Khvolson did not concern himself with the flux or radius of the ring image. More commonly, where the lensing mass is complex (such as a galaxy group or cluster) and does not cause a spherical distortion of spacetime, the source will resemble partial arcs scattered around the lens. The observer may then see multiple distorted images of the same source; the number and shape of these depending upon the relative positions of the source, lens, and observer, and the shape of the gravitational well of the lensing object. | Gravitational lens | Wikipedia | 505 | 48824 | https://en.wikipedia.org/wiki/Gravitational%20lens | Physical sciences | Basics_2 | Astronomy |
Strong lensing Where there are easily visible distortions such as the formation of Einstein rings, arcs, and multiple images. Despite being considered "strong", the effect is in general relatively small, such that even a galaxy with a mass more than 100 billion times that of the Sun will produce multiple images separated by only a few arcseconds. Galaxy clusters can produce separations of several arcminutes. In both cases the galaxies and sources are quite distant, many hundreds of megaparsecs away from our Galaxy.
Weak lensing Where the distortions of background sources are much smaller and can only be detected by analyzing large numbers of sources in a statistical way to find coherent distortions of only a few percent. The lensing shows up statistically as a preferred stretching of the background objects perpendicular to the direction to the centre of the lens. By measuring the shapes and orientations of large numbers of distant galaxies, their orientations can be averaged to measure the shear of the lensing field in any region. This, in turn, can be used to reconstruct the mass distribution in the area: in particular, the background distribution of dark matter can be reconstructed. Since galaxies are intrinsically elliptical and the weak gravitational lensing signal is small, a very large number of galaxies must be used in these surveys. These weak lensing surveys must carefully avoid a number of important sources of systematic error: the intrinsic shape of galaxies, the tendency of a camera's point spread function to distort the shape of a galaxy and the tendency of atmospheric seeing to distort images must be understood and carefully accounted for. The results of these surveys are important for cosmological parameter estimation, to better understand and improve upon the Lambda-CDM model, and to provide a consistency check on other cosmological observations. They may also provide an important future constraint on dark energy.
Microlensing Where no distortion in shape can be seen but the amount of light received from a background object changes in time. The lensing object may be stars in the Milky Way in one typical case, with the background source being stars in a remote galaxy, or, in another case, an even more distant quasar. In extreme cases, a star in a distant galaxy can act as a microlens and magnify another star much farther away. The first example of this was the star MACS J1149 Lensed Star 1 (also known as Icarus), thanks to the boost in flux due to the microlensing effect. | Gravitational lens | Wikipedia | 510 | 48824 | https://en.wikipedia.org/wiki/Gravitational%20lens | Physical sciences | Basics_2 | Astronomy |
Gravitational lenses act equally on all kinds of electromagnetic radiation, not just visible light, and also in non-electromagnetic radiation, like gravitational waves. Weak lensing effects are being studied for the cosmic microwave background as well as galaxy surveys. Strong lenses have been observed in radio and x-ray regimes as well. If a strong lens produces multiple images, there will be a relative time delay between two paths: that is, in one image the lensed object will be observed before the other image.
History
Henry Cavendish in 1784 (in an unpublished manuscript) and Johann Georg von Soldner in 1801 (published in 1804) had pointed out that Newtonian gravity predicts that starlight will bend around a massive object as had already been supposed by Isaac Newton in 1704 in his Queries No.1 in his book Opticks. The same value as Soldner's was calculated by Einstein in 1911 based on the equivalence principle alone. However, Einstein noted in 1915, in the process of completing general relativity, that his (and thus Soldner's) 1911-result is only half of the correct value. Einstein became the first to calculate the correct value for light bending.
The first observation of light deflection was performed by noting the change in position of stars as they passed near the Sun on the celestial sphere. The observations were performed in 1919 by Arthur Eddington, Frank Watson Dyson, and their collaborators during the total solar eclipse on May 29. The solar eclipse allowed the stars near the Sun to be observed. Observations were made simultaneously in the cities of Sobral, Ceará, Brazil and in São Tomé and Príncipe on the west coast of Africa. The observations demonstrated that the light from stars passing close to the Sun was slightly bent, so that stars appeared slightly out of position. | Gravitational lens | Wikipedia | 359 | 48824 | https://en.wikipedia.org/wiki/Gravitational%20lens | Physical sciences | Basics_2 | Astronomy |
The result was considered spectacular news and made the front page of most major newspapers. It made Einstein and his theory of general relativity world-famous. When asked by his assistant what his reaction would have been if general relativity had not been confirmed by Eddington and Dyson in 1919, Einstein said "Then I would feel sorry for the dear Lord. The theory is correct anyway." In 1912, Einstein had speculated that an observer could see multiple images of a single light source, if the light were deflected around a mass. This effect would make the mass act as a kind of gravitational lens. However, as he only considered the effect of deflection around a single star, he seemed to conclude that the phenomenon was unlikely to be observed for the foreseeable future since the necessary alignments between stars and observer would be highly improbable. Several other physicists speculated about gravitational lensing as well, but all reached the same conclusion that it would be nearly impossible to observe.
Although Einstein made unpublished calculations on the subject, the first discussion of the gravitational lens in print was by Khvolson, in a short article discussing the "halo effect" of gravitation when the source, lens, and observer are in near-perfect alignment, now referred to as the Einstein ring.
In 1936, after some urging by Rudi W. Mandl, Einstein reluctantly published the short article "Lens-Like Action of a Star By the Deviation of Light In the Gravitational Field" in the journal Science.
In 1937, Fritz Zwicky first considered the case where the newly discovered galaxies (which were called 'nebulae' at the time) could act as both source and lens, and that, because of the mass and sizes involved, the effect was much more likely to be observed.
In 1963 Yu. G. Klimov, S. Liebes, and Sjur Refsdal recognized independently that quasars are an ideal light source for the gravitational lens effect.
It was not until 1979 that the first gravitational lens would be discovered. It became known as the "Twin QSO" since it initially looked like two identical quasistellar objects. (It is officially named SBS 0957+561.) This gravitational lens was discovered by Dennis Walsh, Bob Carswell, and Ray Weymann using the Kitt Peak National Observatory 2.1 meter telescope. | Gravitational lens | Wikipedia | 479 | 48824 | https://en.wikipedia.org/wiki/Gravitational%20lens | Physical sciences | Basics_2 | Astronomy |
In the 1980s, astronomers realized that the combination of CCD imagers and computers would allow the brightness of millions of stars to be measured each night. In a dense field, such as the galactic center or the Magellanic clouds, many microlensing events per year could potentially be found. This led to efforts such as Optical Gravitational Lensing Experiment, or OGLE, that have characterized hundreds of such events, including those of OGLE-2016-BLG-1190Lb and OGLE-2016-BLG-1195Lb.
Approximate Newtonian description
Newton wondered whether light, in the form of corpuscles, would be bent due to gravity. The Newtonian prediction for light deflection refers to the amount of deflection a corpuscle would feel under the effect of gravity, and therefore one should read "Newtonian" in this context as the referring to the following calculations and not a belief that Newton held in the validity of these calculations.
For a gravitational point-mass lens of mass , a corpuscle of mass feels a force
where is the lens-corpuscle separation. If we equate this force with Newton's second law, we can solve for the acceleration that the light undergoes:
The light interacts with the lens from initial time to , and the velocity boost the corpuscle receives is
If one assumes that initially the light is far enough from the lens to neglect gravity, the perpendicular distance between the light's initial trajectory and the lens is b (the impact parameter), and the parallel distance is , such that . We additionally assume a constant speed of light along the parallel direction, , and that the light is only being deflected a small amount. After plugging these assumptions into the above equation and further simplifying, one can solve for the velocity boost in the perpendicular direction. The angle of deflection between the corpuscle’s initial and final trajectories is therefore (see, e.g., M. Meneghetti 2021)
Although this result appears to be half the prediction from general relativity, classical physics predicts that the speed of light is observer-dependent (see, e.g., L. Susskind and A. Friedman 2018) which was superseded by a universal speed of light in special relativity.
Explanation in terms of spacetime curvature | Gravitational lens | Wikipedia | 473 | 48824 | https://en.wikipedia.org/wiki/Gravitational%20lens | Physical sciences | Basics_2 | Astronomy |
In general relativity, light follows the curvature of spacetime, hence when light passes around a massive object, it is bent. This means that the light from an object on the other side will be bent towards an observer's eye, just like an ordinary lens. In general relativity the path of light depends on the shape of space (i.e. the metric). The gravitational attraction can be viewed as the motion of undisturbed objects in a background curved geometry or alternatively as the response of objects to a force in a flat geometry. The angle of deflection is
toward the mass M at a distance r from the affected radiation, where G is the universal constant of gravitation, and c is the speed of light in vacuum.
Since the Schwarzschild radius is defined as , and escape velocity is defined as , this can also be expressed in simple form as
Search for gravitational lenses
Most of the gravitational lenses in the past have been discovered accidentally. A search for gravitational lenses in the northern hemisphere (Cosmic Lens All Sky Survey, CLASS), done in radio frequencies using the Very Large Array (VLA) in New Mexico, led to the discovery of 22 new lensing systems, a major milestone. This has opened a whole new avenue for research ranging from finding very distant objects to finding values for cosmological parameters so we can understand the universe better. | Gravitational lens | Wikipedia | 276 | 48824 | https://en.wikipedia.org/wiki/Gravitational%20lens | Physical sciences | Basics_2 | Astronomy |
A similar search in the southern hemisphere would be a very good step towards complementing the northern hemisphere search as well as obtaining other objectives for study. If such a search is done using well-calibrated and well-parameterized instruments and data, a result similar to the northern survey can be expected. The use of the Australia Telescope 20 GHz (AT20G) Survey data collected using the Australia Telescope Compact Array (ATCA) stands to be such a collection of data. As the data were collected using the same instrument maintaining a very stringent quality of data we should expect to obtain good results from the search. The AT20G survey is a blind survey at 20 GHz frequency in the radio domain of the electromagnetic spectrum. Due to the high frequency used, the chances of finding gravitational lenses increases as the relative number of compact core objects (e.g. quasars) are higher (Sadler et al. 2006). This is important as the lensing is easier to detect and identify in simple objects compared to objects with complexity in them. This search involves the use of interferometric methods to identify candidates and follow them up at higher resolution to identify them. Full detail of the project is currently under works for publication.
Microlensing techniques have been used to search for planets outside our solar system. A statistical analysis of specific cases of observed microlensing over the time period of 2002 to 2007 found that most stars in the Milky Way galaxy hosted at least one orbiting planet within 0.5 to 10 AU.
In 2009, weak gravitational lensing was used to extend the mass-X-ray-luminosity relation to older and smaller structures than was previously possible to improve measurements of distant galaxies.
the most distant gravitational lens galaxy, J1000+0221, had been found using NASA's Hubble Space Telescope. While it remains the most distant quad-image lensing galaxy known, an even more distant two-image lensing galaxy was subsequently discovered by an international team of astronomers using a combination of Hubble Space Telescope and Keck telescope imaging and spectroscopy. The discovery and analysis of the IRC 0218 lens was published in the Astrophysical Journal Letters on June 23, 2014. | Gravitational lens | Wikipedia | 443 | 48824 | https://en.wikipedia.org/wiki/Gravitational%20lens | Physical sciences | Basics_2 | Astronomy |
Research published Sep 30, 2013 in the online edition of Physical Review Letters, led by McGill University in Montreal, Québec, Canada, has discovered the B-modes, that are formed due to gravitational lensing effect, using National Science Foundation's South Pole Telescope and with help from the Herschel space observatory. This discovery would open the possibilities of testing the theories of how our universe originated.
Solar gravitational lens
Albert Einstein predicted in 1936 that rays of light from the same direction that skirt the edges of the Sun would converge to a focal point approximately 542 AU from the Sun. Thus, a probe positioned at this distance (or greater) from the Sun could use the Sun as a gravitational lens for magnifying distant objects on the opposite side of the Sun. A probe's location could shift around as needed to select different targets relative to the Sun.
This distance is far beyond the progress and equipment capabilities of space probes such as Voyager 1, and beyond the known planets and dwarf planets, though over thousands of years 90377 Sedna will move farther away on its highly elliptical orbit. The high gain for potentially detecting signals through this lens, such as microwaves at the 21-cm hydrogen line, led to the suggestion by Frank Drake in the early days of SETI that a probe could be sent to this distance. A multipurpose probe SETISAIL and later FOCAL was proposed to the ESA in 1993, but is expected to be a difficult task. If a probe does pass 542 AU, magnification capabilities of the lens will continue to act at farther distances, as the rays that come to a focus at larger distances pass further away from the distortions of the Sun's corona. A critique of the concept was given by Landis, who discussed issues including interference of the solar corona, the high magnification of the target, which will make the design of the mission focal plane difficult, and an analysis of the inherent spherical aberration of the lens.
In 2020, NASA physicist Slava Turyshev presented his idea of Direct Multipixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravitational Lens Mission. The lens could reconstruct the exoplanet image with ~25 km-scale surface resolution, enough to see surface features and signs of habitability.
Measuring weak lensing | Gravitational lens | Wikipedia | 471 | 48824 | https://en.wikipedia.org/wiki/Gravitational%20lens | Physical sciences | Basics_2 | Astronomy |
Kaiser, Squires and Broadhurst (1995), Luppino & Kaiser (1997) and Hoekstra et al. (1998) prescribed a method to invert the effects of the point spread function (PSF) smearing and shearing, recovering a shear estimator uncontaminated by the systematic distortion of the PSF. This method (KSB+) is the most widely used method in weak lensing shear measurements.
Galaxies have random rotations and inclinations. As a result, the shear effects in weak lensing need to be determined by statistically preferred orientations. The primary source of error in lensing measurement is due to the convolution of the PSF with the lensed image. The KSB method measures the ellipticity of a galaxy image. The shear is proportional to the ellipticity. The objects in lensed images are parameterized according to their weighted quadrupole moments. For a perfect ellipse, the weighted quadrupole moments are related to the weighted ellipticity. KSB calculate how a weighted ellipticity measure is related to the shear and use the same formalism to remove the effects of the PSF.
KSB's primary advantages are its mathematical ease and relatively simple implementation. However, KSB is based on a key assumption that the PSF is circular with an anisotropic distortion. This is a reasonable assumption for cosmic shear surveys, but the next generation of surveys (e.g. LSST) may need much better accuracy than KSB can provide.
Gallery | Gravitational lens | Wikipedia | 315 | 48824 | https://en.wikipedia.org/wiki/Gravitational%20lens | Physical sciences | Basics_2 | Astronomy |
Kava or kava kava (Piper methysticum: Latin 'pepper' and Latinized Greek 'intoxicating') is a plant in the pepper family, native to the Pacific Islands. The name kava is from Tongan and Marquesan, meaning 'bitter.’ Other names for kava include ʻawa (Hawaiʻi), ʻava (Samoa), yaqona or yagona (Fiji), sakau (Pohnpei), seka (Kosrae), and malok or malogu (parts of Vanuatu). Kava can refer to either the plant or a beverage made from its root. The beverage has sedative, anesthetic, psychoactive and mildly euphoriant properties. It is consumed throughout the Pacific Ocean cultures of Polynesia, including Hawaii and Vanuatu, Melanesia, some parts of Micronesia, such as Pohnpei and Kosrae, and the Philippines.
Kava consists of sterile cultivars clonally propagated from its wild ancestor, Piper wichmanii. It originated in northern Vanuatu, where it was domesticated by farmers around 3,000 years ago through selective cultivation. Historically, the beverage was made from fresh kava; preparation from dry kava emerged in response to the efforts of Christian missionaries in the 18th and 19th centuries to prohibit the drinking of kava.
Its active compounds are known as kavalactones. Systematic reviews and meta-analyses conducted in the last decade have typically indicated a modest positive effect of kava on anxiety and Generalized Anxiety Disorder, though the evidence is mixed and further research is frequently recommended.
Moderate consumption of kava in its traditional form, as a water-based suspension of kava roots, is considered by the World Health Organization to present an “acceptably low level of health risk.” However, consumption of kava extracts produced with organic solvents or excessive amounts of low-quality kava products may be linked to an increased risk of adverse health outcomes, including liver injury.
History and names
Kava is conspecific with Piper wichmannii, indicating Kava was domesticated from Piper wichmannii (syn. Piper subbullatum). | Kava | Wikipedia | 456 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
It was spread by the Austronesian Lapita culture after contact eastward into the rest of Polynesia. It is endemic to Oceania and is not found in other Austronesian groups. Kava reached Hawaii, but it is absent in New Zealand, where it cannot grow. Consumption of kava is also believed to be the reason why betel nut chewing, ubiquitous elsewhere, was lost for Austronesians in Oceania.
According to Lynch (2002), the reconstructed Proto-Polynesian term for the plant, *kava, was derived from the Proto-Oceanic term *kawaR in the sense of a "bitter root" or "potent root [used as fish poison]". It may have been related to reconstructed *wakaR (in Proto-Oceanic and Proto-Malayo-Polynesian) via metathesis. It originally referred to Zingiber zerumbet, used to make a similar mildly psychoactive bitter drink in Austronesian rituals. Cognates for *kava include Pohnpeian sa-kau; Tongan, Niue, Rapa Nui, Tuamotuan, and Rarotongan kava; Samoan, Tahitian, and Marquesan ava; and Hawaiian awa. In some languages, most notably Māori kawa, the cognates have come to mean "bitter", "sour", or "acrid" to the taste. | Kava | Wikipedia | 285 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
In the Cook Islands, the reduplicated forms of kawakawa or kavakava are also applied to the unrelated members of the genus Pittosporum. In other languages, such as Futunan, compound terms like kavakava atua refer to other species belonging to the genus Piper. The reduplication of the base form is indicative of falsehood or likeness, in the sense of "false kava". In New Zealand, it was applied to the kawakawa (Piper excelsum), which is endemic to New Zealand and nearby Norfolk Island and Lord Howe Island. It was exploited by the Māori based on previous knowledge of the kava, as the latter could not survive in the colder climates of New Zealand. The Māori name for the plant, kawakawa, is derived from the same etymon as kava, but reduplicated. It is a sacred tree among the Māori people. It is seen as a symbol of death, corresponding to the rangiora (Brachyglottis repanda), which is the symbol of life. However, kawakawa has no psychoactive properties. Its connection to kava is linked to its similarity in appearance and bitter taste.
Characteristics
Kava was historically grown only in the Pacific islands of Hawaii, Federated States of Micronesia, Vanuatu, Fiji, the Samoas, and Tonga. It appears to have originated in Vanuatu; an inventory of P. methysticum distribution showed it was cultivated on numerous islands of Micronesia, Melanesia, Polynesia, and Hawaii, whereas specimens of P. wichmannii were all from Papua New Guinea, the Solomon Islands, and Vanuatu.
Traditionally, plants are harvested around four years of age, as older plants have higher concentrations of kavalactones. After reaching about in height, plants grow a wider stalk and additional stalks, but not much taller. The roots can reach a depth of .
Cultivars
Kava consists of sterile cultivars cloned from its wild ancestor, Piper wichmanii. Today it comprises hundreds of different cultivars grown across the Pacific. Each cultivar has not only different requirements for successful cultivation, but also displays unique characteristics both in terms of its appearance and its psychoactive properties. | Kava | Wikipedia | 462 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
Noble and non-noble kava
Scholars make a distinction between the so-called noble and non-noble kava. The latter category comprises the so-called tudei (or "two-day") kavas, medicinal kavas, and wild kava (Piper wichmanii, the ancestor of domesticated Piper methysticum). Traditionally, only noble kavas have been used for regular consumption, due to their more favourable composition of kavalactones and other compounds that produce more pleasant effects and have lower potential for causing negative side effects, such as nausea, or "kava hangover".
The perceived benefits of noble cultivars explain why only these cultivars were spread around the Pacific by Polynesian and Melanesian migrants, with presence of non-noble cultivars limited to the islands of Vanuatu, from which they originated. More recently, it has been suggested that the widespread use of tudei cultivars in the manufacturing of several kava products might have been the key factor contributing to the rare reports of adverse reactions to kava observed among the consumers of kava-based products in Europe.
Tudei varieties have traditionally not been grown in Hawaii and Fiji, but in recent years there have been reports of farmers attempting to grow "isa" or "palisi" non-noble cultivars in Hawaii, and of imports of dried tudei kava into Fiji for further re-exporting. The tudei cultivars may be easier and cheaper to grow: while it takes up to 5 years for noble kava to mature, non-noble varieties can often be harvested just one year after being planted.
The concerns about the adverse effects of non-noble varieties, produced by their undesirable composition of kavalactones and high concentrations of potentially harmful compounds (flavokavains, which are not present in any significant concentration in the noble varieties), have led to legislation prohibiting exports from countries such as Vanuatu. Likewise, efforts have been made to educate non-traditional customers about the difference between noble and non-noble varieties and that non-noble varieties do not offer the same results as noble cultivars. In recent years, government regulatory bodies and non-profit NGOs have been set up with the declared aim of monitoring kava quality; producing regular reports; certifying vendors selling proper, noble kava; and warning customers against products that may contain tudei varieties. | Kava | Wikipedia | 498 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
Growing regions
In Vanuatu, exportation of kava is strictly regulated. Only cultivars classified as noble are allowed to be exported. Only the most desirable cultivars for everyday drinking are classified as noble to maintain quality control. In addition, their laws mandate that exported kava must be at least five years old and farmed organically. Their most popular noble cultivars are "Borogu" or "Borongoru" from Pentecost Island, "Melomelo" from Aoba Island (called Sese in the north Pentecost Island), and "Palarasul" kava from Espiritu Santo. In Vanuatu, Tudei ("two-day") kava is reserved for special ceremonial occasions and exporting it is not allowed. "Palisi" is a popular Tudei variety.
In Hawaii, there are many other cultivars of kava (). Some of the most popular cultivars are Mahakea, Moʻi, Hiwa, and Nene. The Aliʻi (kings) of precolonial Hawaii coveted the Moʻi variety, which had a strong cerebral effect due to a predominant amount of the kavalactone kavain. This sacred variety was so important to them that no one but royalty could ever experience it, "lest they suffer an untimely death". The reverence for Hiwa in old Hawaiʻi is evident in this portion of a chant recorded by Nathaniel Bright Emerson and quoted by E. S. Craighill and Elizabeth Green Handy: "This refers to the cup of sacramental ʻawa brewed from the strong, black ʻawa root (ʻawa hiwa), which was drunk sacramentally by the kumu hula":
Winter describes a hula prayer for inspiration that contains the line, He ʻike pū ʻawa hiwa. Pukui and Elbert translated this as "a knowledge from kava offerings". Winter explains that ʻawa, especially of the Hiwa variety, was offered to hula deities in return for knowledge and inspiration.
More recently, specialized kava varieties have been introduced to South Florida which have been acclimated and adapted to grow well in South Florida's unique soil and climate and have significant resistance to pest and disease pressures. As of 2024, cultivation of these varieties is limited to a small number of commercial farms and backyard growers.
Relationship with kawakawa | Kava | Wikipedia | 496 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
The Kawakawa (Piper excelsum) plant, known also as "Māori kava", may be confused with kava. While the two plants look similar and have similar names, they are different, but related, species. Kawakawa is a small tree endemic to New Zealand, having importance to traditional medicine and Māori culture. As noted by the Kava Society of New Zealand, "in all likelihood, the kava plant was known to the first settlers of Aotearoa [New Zealand]. It is also possible that (just like the Polynesian migrants that settled in Hawaii) the Maori explorers brought some kava with them. Unfortunately, most of New Zealand is simply too cold for growing kava and hence the Maori settlers lost their connection to the sacred plant." Further, "in New Zealand, where the climate is too cold for kava, the Maori gave the name kawa-kawa to another Piperaceae M. excelsum, in memory of the kava plants they undoubtedly brought with them and unsuccessfully attempted to cultivate. The Maori word kawa also means "ceremonial protocol", recalling the stylized consumption of the drug typical of Polynesian societies". Kawakawa is commonly used in Maori traditional medicine for the treatment of skin infections, wounds, and cuts, and (when prepared as a tea) for stomach upsets and other minor illnesses.
Composition
Fresh kava root contains on average 80% water. Dried root contains approximately 43% starch, 20% dietary fiber, 15% kavalactones, 12% water, 3.2% sugars, 3.6% protein, and 3.2% minerals.
In general, kavalactone content is greatest in the roots and decreases higher up the plant into the stems and leaves. Relative concentrations of 15%, 10%, and 5% have been observed in the root, stump, and basal stems, respectively. The relative content of kavalactones depends not only on plant segment but also on the kava plant variety, plant maturity, geographic location, and time of harvest. The kavalactones present are kavain, demethoxyyangonin, and yangonin, which are higher in the roots than in the stems and leaves, with dihydrokavain, methysticin, and dihydromethysticin also present. | Kava | Wikipedia | 481 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
The mature roots of the kava plant are harvested after a minimum of four years (at least five years, ideally) for peak kavalactone content. Most kava plants produce around of root when they are harvested. Kava root is classified into two categories: crown root (or chips) and lateral root. Crown roots are the large-diameter pieces that look like -diameter wooden poker chips. Most kava plants consist of approximately 80% crown root upon harvesting. Lateral roots are smaller-diameter roots that look more like a typical root. A mature kava plant is about 20% lateral roots. Kava lateral roots have the highest content of kavalactones in the kava plant. "Waka" grade kava is made of lateral roots only.
Pharmacology
Constituents
A total of 18 different kavalactones (or kavapyrones) have been identified to date, at least 15 of which are active. However, six of them, including kavain, dihydrokavain, methysticin, dihydromethysticin, yangonin, and desmethoxyyangonin, have been determined to be responsible for about 96% of the plant's pharmacological activity. Some minor constituents, including three chalcones — flavokavain A, flavokavain B, and flavokavain C — have also been identified, as well as a toxic alkaloid (not present in the consumable parts of the plant), pipermethystine. Alkaloids are present in the roots and leaves.
Pharmacodynamics
The following pharmacological actions have been reported for kava and/or its major active constituents:
Potentiation of GABAA receptor activity (by kavain, dihydrokavain, methysticin, dihydromethysticin, and yangonin).
Inhibition of the reuptake of norepinephrine (by kavain and methysticin) and possibly also of dopamine (by kavain and desmethoxyyangonin).
Binding to the CB1 receptor (by yangonin).
Inhibition of voltage-gated sodium channels and voltage-gated calcium channels (by kavain and methysticin).
Monoamine oxidase B reversible inhibition (by all six of the major kavalactones). | Kava | Wikipedia | 505 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
Receptor binding assays with botanical extracts have revealed direct interactions of leaf extracts of kava (which appear to be more active than root extracts) with the GABA (i.e., main) binding site of the GABAA receptor, the D2 receptor, the μ- and δ-opioid receptors, and the H1 and H2 receptors. Weak interaction with the 5-HT6 and 5-HT7 receptors and the benzodiazepine site of the GABAA receptor was also observed.
Potentiation of GABAA receptor activity may underlie the anxiolytic effects of kava, while elevation of dopamine levels in the nucleus accumbens likely underlie the moderately psychotropic effects the plant can produce. Changes in the activity of 5-HT neurons could explain the sleep-inducing action. However, failure of the GABAA receptor inhibitor flumazenil to reverse the anxiolytic effects of kava in mice suggests that benzodiazepine-like effects are not contributing to the pharmacological profile of kava extracts.
Heavy, long-term use of kava has been found to be free of association with reduced ability in saccade and cognitive tests, but has been associated with elevated liver enzymes.
Detection
Recent usage of kava has been documented in forensic investigations by quantitation of kavain in blood specimens. The principal urinary metabolite, conjugated 4'-OH-kavain, is generally detectable for up to 48 hours.
Preparations
Traditional preparation
Kava is consumed in various ways throughout the Pacific Ocean cultures of Polynesia, Vanuatu, Melanesia, and some parts of Micronesia and Australia. Traditionally, it is prepared by either chewing, grinding, or pounding the roots of the kava plant. Grinding is done by hand against a cone-shaped block of dead coral; the hand forms a mortar and the coral a pestle. The ground root/bark is combined with only a little water, as the fresh root releases moisture during grinding. Pounding is done in a large stone with a small log. The product is then added to cold water and consumed as quickly as possible.
The extract is an emulsion of kavalactone droplets in starch. The taste is slightly pungent, while the distinctive aroma depends on whether it was prepared from dry or fresh plant, and on the variety. The colour is grey to tan to opaque greenish. | Kava | Wikipedia | 502 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
Kava prepared as described above is much more potent than processed kava. Chewing produces the strongest effect because it produces the finest particles. Fresh, undried kava produces a stronger beverage than dry kava. The strength also depends on the species and techniques of cultivation.
In Vanuatu, a strong kava drink is normally followed by a hot meal or tea. The meal traditionally follows some time after the drink so that the psychoactives are absorbed into the bloodstream more quickly. Traditionally, no flavoring is added.
In Papua New Guinea, the locals in Madang province refer to their kava as waild koniak ("wild cognac" in English).
Fijians commonly share a drink called grog, made by pounding sun-dried kava root into a fine powder, straining and mixing it with cold water. Traditionally, grog is drunk from the shorn half-shell of a coconut, called a bilo. Grog is very popular in Fiji, especially among young men, and often brings people together for storytelling and socializing. Drinking grog for a few hours brings a numbing and relaxing effect to the drinker; grog also numbs the tongue, and grog drinking typically is followed by a "chaser" or sweet or spicy snack to follow a bilo.
Supplements and pharmaceutical preparations
Water extraction is the traditional method for preparation of the plant. Pharmaceutical and herbal supplement companies extract kavalactones from the kava plant using solvents such as supercritical carbon dioxide, acetone, and ethanol to produce pills standardized with between 30% and 90% kavalactones.
Concerns
Numerous scholars and regulatory bodies have raised concerns over the safety profile of such products.
One group of scholars say that organic solvents introduce compounds that may affect the liver into the standardized product; these compounds are not extracted by water and are consequently largely absent from kava prepared with water. For instance, when compared with water extraction, organic solvents extract vastly larger amounts of flavokavains, compounds associated with adverse reactions to kava that are present in very low concentrations in noble kava, but significant in non-noble. | Kava | Wikipedia | 436 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
Also, "chemical solvents used do not extract the same compounds as the natural water extracts in traditional use. The extraction process may exclude important modifying constituents soluble only in water". In particular, it has been noted that, unlike traditional water-based preparations, products obtained with the use of organic solvents do not contain glutathione, an important liver-protecting compound. Another group of researchers noted: "The extraction process (aqueous vs. acetone in the two types of preparations) is responsible for the difference in toxicity as extraction of glutathione in addition to the kava lactones is important to provide protection against hepatotoxicity".
It has also been argued that kavalactone extracts have often been made from low-quality plant material, including the toxic aerial parts of the plant that contain the hepatotoxic alkaloid Pipermethystine, non-noble kava varieties, or plants affected by mold — which, in light of the chemical solvents' ability to extract far greater amounts of the potentially toxic compounds than water, makes them particularly problematic.
In the context of these concerns, the World Health Organization advises against the consumption of ethanolic and acetonic kavalactone extracts, and says that "products should be developed from water-based suspensions of kava". The government of Australia prohibits the sales of such kavalactone extracts, and only permits the sale of kava products in their natural form or produced with cold water.
Kava culture
Kava is used for medicinal, religious, political, cultural, and social purposes throughout the Pacific. These cultures have a great respect for the plant and place a high importance on it. In Fiji, for example, a formal yaqona (kava) ceremony will often accompany important social, political, or religious functions, usually involving a ritual presentation of the bundled roots as a sevusevu (gift) and drinking of the yaqona itself. Due to the importance of kava in religious rituals and the seemingly (from the Western point of view) unhygienic preparation method, its consumption was discouraged or even banned by Christian missionaries.
Kava bars
With kava's increasing popularity, bars serving the plant in its liquid state are beginning to open up outside of the South Pacific. | Kava | Wikipedia | 473 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
While some bars have been committed to only serving the traditional forms and types of kava, other establishments have been accused of serving non-traditionally consumed non-noble kava varieties, which are cheaper but far more likely to cause unpleasant effects and adverse reactions, or of serving kava with other substances, including alcohol.
Effects of consumption
The nature of effects will largely depend on the cultivar of the kava plant and the form of its consumption. Traditionally, only noble kava cultivars have been consumed, as they are accepted as safe and produce desired effects. The specific effects of various noble kavas depend on various factors, such as the cultivar used (and the related specific composition of kavalactones), age of the plant, and method of consumption. However, it can be stated that in general, noble kava produces a state of calmness, relaxation, and well-being without diminishing cognitive performance. Kava may produce an initial talkative period, followed by muscle relaxation and eventual sleepiness.
As noted in one of the earliest Western publications on kava (1886): "A well prepared Kava potion drunk in small quantities produces only pleasant changes in behavior. It is therefore a slightly stimulating drink which helps relieve great fatigue. It relaxes the body after strenuous efforts, clarifies the mind and sharpens the mental faculties".
Other effects include euphoria, feelings of happiness and relaxation, reduced appetite, relaxed muscles and sedation.
In very high doses for some people it can cause a “dream” or “trance” like State, mild dissociation, stronger euphoric effects, and mild hallucinations but most of these effects come from drastically abusing kava. Kava is not a psychedelic like magic mushrooms or LSD or a dissociative like ketamine and it should not be used for psychedelic or dissociative purposes. This use is highly dangerous and can result in liver damage or other serious side effects.
Despite its psychoactive effects, kava is not considered to be physically addictive and its use does not lead to dependency.
Toxicity, safety, and potential side effects
General observations
There is limited safety information available on the effects of kava consumption, but in general, moderate consumption appears unlikely to be harmful, while there is evidence of harm from heavy use. | Kava | Wikipedia | 475 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
Effects on the liver
There is published evidence of the hepatotoxicity of kava extracts, and concerns about this led to kava being omitted from the US Pharmacopeia.
Other adverse reactions
Adverse reactions may result from the poor quality of kava raw material used in the manufacturing of various kava products. In addition to the potential for hepatotoxicity, adverse reactions from chronic use may include visual impairment, rashes or dermatitis, seizures, weight loss, and malnutrition, but there is only limited high-quality research on these possible effects.
On the basis of research findings and long history of safe use across the South Pacific, experts recommend using water-based extractions of high-quality peeled rhizome and roots of the noble kava cultivars to minimize the potential of adverse reactions to chronic use.
Potential interactions
Several adverse interactions with drugs have been documented, both prescription and nonprescription — including, but not limited to, anticonvulsants, alcohol, anxiolytics (central nervous system depressants such as benzodiazepines), antipsychotics, levodopa, diuretics, and drugs metabolized by CYP450 in the liver. | Kava | Wikipedia | 259 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
A few notable potential drug interactions are, but are not limited to:
Alcohol: It has been reported that combined use of alcohol and kava extract can have additive sedative effects. Regarding cognitive function, kava has been shown to have additive cognitive impairments while taken with alcohol when compared to taking placebo and alcohol alone.
Anxiolytics (CNS depressants such as benzodiazepines and barbiturates): Kava may have potential additive CNS depressant effects (such as sedation and anxiolytic effects) with benzodiazepines and barbiturates. Kava taken in combination with alprazolam can cause a semicomatose state in humans.
Dopamine agonist — levodopa: One of levodopa's chronic side effects that Parkinson's patients experience is the "on-off phenomenon" of motor fluctuations, where there will be periods of oscillations between "on", where the patient experiences symptomatic relief, and "off", where the therapeutic effect wears off early. When taking levodopa and kava together, it has been shown that there is an increased frequency of this "on-off phenomenon".
Kava dermopathy
Long-term and heavy kava consumption is associated with a reversible skin condition known as "kava dermopathy", or kanikani (in the Fijian language), characterised by dry and scaly skin covering the palms of the hands, soles of the feet, and back. The first symptom to appear is usually dry, peeling skin; some Pacific Islanders deliberately consume large quantities of kava for several weeks in order to get the peeling effect, resulting in a layer of new skin. These effects appeared at consumption levels between to a week of kava powder. Despite numerous studies, the mechanism that causes kava dermopathy is poorly understood "but may relate to interference with cholesterol metabolism". The condition is easily treatable with abstinence or lowering of kava intake as the skin appears to be returning to its normal state within a couple of weeks of reduced or no kava use. Kava dermopathy should not be confused with rare instances of allergic reactions to kava that are usually characterised by itchy rash or puffy face. | Kava | Wikipedia | 481 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
Research
Kava is under preliminary research for its potential psychoactive — primarily anxiolytic — sleep-inducing, and sleep-enhancing properties. Preliminary analysis of kava effects in people with short-term anxiety disorders indicated a small level of improvement.
Traditional medicine
Over centuries, kava has been used in the traditional medicine of the South Pacific Islands for central nervous system and peripheral effects. As noted in one literature review: "Peripherally, kava is indicated in traditional Pacific medicine for urogenital conditions (gonorrhea infections, chronic cystitis, difficulty urinating), reproductive and women's health (...), gastrointestinal upsets, respiratory ailments (asthma, coughs, and tuberculosis), skin diseases and topical wounds, and as an analgesic, with significant subtlety and nuance attending the precise strain, plant component (leaf, stem, root) and preparative method to be used".
Regulation
Kava remains legal in most countries. Regulations often treat it as a food or dietary supplement.
Australia
In Australia, the supply of kava is regulated through the National Code of Kava Management. Travellers to Australia are allowed to bring up to 4 kg of kava in their baggage, provided they are at least 18 years old and the kava is in root or dried form. Commercial import of larger quantities is allowed, under licence for medical or scientific purposes. These restrictions were introduced in 2007 after concern about abuse of kava in indigenous communities. Initially, the import limit was 2 kg per person; it was raised to 4 kg in December 2019, and a pilot program allowing for commercial importation was implemented on 1 December 2021.
The Australian Therapeutic Goods Administration has recommended no more than 250 mg of kavalactones be taken in a 24‑hour period.
Kava possession is limited to 2 kg per adult in the Northern Territory. While it was previously banned in Western Australia in the 2000s, the Western Australian Health Department announced the lifting of the ban in February 2017, bringing Western Australia "into line with other States" where it has always remained legal, albeit closely regulated. | Kava | Wikipedia | 431 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
Europe
Following discussions on the safety of certain pharmaceutical products derived from kava and sold in Germany, the EU imposed a temporary ban on imports of kava-based pharmaceutical products in 2002. The sale of kava plant became regulated in Switzerland, France, and in prepared form in the Netherlands. Some Pacific island states which had been benefiting from the export of kava to the pharmaceutical companies have attempted to overturn the EU ban on kava-based pharmaceutical products by invoking international trade agreements at the WTO: Fiji, Samoa, Tonga, and Vanuatu argued that the ban was imposed with insufficient evidence. The pressure prompted Germany to reconsider the evidence base for banning kava-based pharmaceutical products. On 10 June 2014, the German Administrative Court overturned the 2002 ban, making selling kava as a medicine legal (personal possession of kava has never been illegal), albeit strictly regulated. In Germany, kava-based pharmaceutical preparations are currently prescription drugs. Furthermore, patient and professional information brochures have been redesigned to warn about potential side effects. These strict measures have been opposed by some of the leading kava scientists. In early 2016, a court case was filed against the Bundesinstitut für Arzneimittel und Medizinprodukte (BfArM/German Federal Institute for Drugs and Medical Devices), arguing that the new regulatory regime is too strict and not justified.
In the United Kingdom, it is a criminal offence to sell, supply, or import any medicinal product containing kava for human consumption. It is legal to possess kava for personal use or to import it for purposes other than human consumption (e.g., for animals).
Until August 2018, Poland was the only EU country with an "outright ban on kava" and where the mere possession of kava was prohibited and may have resulted in a prison sentence. Under the new legislation, kava is no longer listed among prohibited substances and it is therefore legal to possess, import, and consume the plant, but it remains illegal to sell it within Poland for the purpose of human consumption.
In the Netherlands, for unknown reasons, the ban was never lifted, and it is still prohibited to prepare, manufacture, or trade kava or goods containing kava. | Kava | Wikipedia | 459 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
New Zealand
When used traditionally, kava is regulated as a food under the Food Standards Code. Kava may also be used as an herbal remedy, where it is currently regulated by the Dietary Supplements Regulations. Only traditionally consumed forms and parts of the kava plant (i.e., pure roots of the kava plant, water extractions prepared from these roots) can legally be sold as food or dietary supplements in New Zealand. The aerial parts of the plant (growing up and out of the ground), unlike the roots, contain relatively small amounts of kavalactones; instead, they contain a mildly toxic alkaloid, pipermethysticine. While not normally consumed, the sale of aerial plant sections and non-water based extract (such as , acetonic, or ethanol extractions) is prohibited for the purpose of human consumption (but can be sold as an ingredient in cosmetics or other products not intended for human consumption).
North America
In 2002, Health Canada issued an order prohibiting the sale of any product containing kava. While the restrictions on kava were lifted in 2012, Health Canada lists five kava ingredients as of 2017.
In 2002, the U.S. Food and Drug Administration issued a Consumer Advisory: "Kava-Containing Dietary Supplements May be Associated with Severe Liver Injury". No legal action was taken, and this advisory has since been archived.
Vanuatu
The Pacific island-state of Vanuatu has passed legislation to regulate the quality of its kava exports. Vanuatu prohibits the export or consumption of non-noble kava varieties or the parts of the plant that are unsuitable for consumption (such as leaves and stems). | Kava | Wikipedia | 333 | 48836 | https://en.wikipedia.org/wiki/Kava | Biology and health sciences | Piperales | Plants |
Sidereal time ("sidereal" pronounced ) is a system of timekeeping used especially by astronomers. Using sidereal time and the celestial coordinate system, it is easy to locate the positions of celestial objects in the night sky. Sidereal time is a "time scale that is based on Earth's rate of rotation measured relative to the fixed stars".
Viewed from the same location, a star seen at one position in the sky will be seen at the same position on another night at the same time of day (or night), if the day is defined as a sidereal day (also known as the sidereal rotation period). This is similar to how the time kept by a sundial (Solar time) can be used to find the location of the Sun. Just as the Sun and Moon appear to rise in the east and set in the west due to the rotation of Earth, so do the stars. Both solar time and sidereal time make use of the regularity of Earth's rotation about its polar axis: solar time is reckoned according to the position of the Sun in the sky while sidereal time is based approximately on the position of the fixed stars on the theoretical celestial sphere.
More exactly, sidereal time is the angle, measured along the celestial equator, from the observer's meridian to the great circle that passes through the March equinox (the northern hemisphere's vernal equinox) and both celestial poles, and is usually expressed in hours, minutes, and seconds. (In the context of sidereal time, "March equinox" or "equinox" or "first point of Aries" is currently a direction, from the center of the Earth along the line formed by the intersection of the Earth's equator and the Earth's orbit around the Sun, toward the constellation Pisces; during ancient times it was toward the constellation Aries.) Common time on a typical clock (using mean Solar time) measures a slightly longer cycle, affected not only by Earth's axial rotation but also by Earth's orbit around the Sun. | Sidereal time | Wikipedia | 427 | 48837 | https://en.wikipedia.org/wiki/Sidereal%20time | Physical sciences | Celestial mechanics | Astronomy |
The March equinox itself precesses slowly westward relative to the fixed stars, completing one revolution in about 25,800 years, so the misnamed "sidereal" day ("sidereal" is derived from the Latin sidus meaning "star") is 0.0084 seconds shorter than the stellar day, Earth's actual period of rotation relative to the fixed stars.
The slightly longer stellar period is measured as the Earth rotation angle (ERA), formerly the stellar angle. An increase of 360° in the ERA is a full rotation of the Earth.
A sidereal day on Earth is approximately 86164.0905 seconds (23 h 56 min 4.0905 s or 23.9344696 h).
(Seconds are defined as per International System of Units and are not to be confused with ephemeris seconds.)
Each day, the sidereal time at any given place and time will be about four minutes shorter than local civil time (which is based on solar time), so that for a complete year the number of sidereal "days" is one more than the number of solar days.
Comparison to solar time
Solar time is measured by the apparent diurnal motion of the Sun. Local noon in apparent solar time is the moment when the Sun is exactly due south or north (depending on the observer's latitude and the season). A mean solar day (what we normally measure as a "day") is the average time between local solar noons ("average" since this varies slightly over a year).
Earth makes one rotation around its axis each sidereal day; during that time it moves a short distance (about 1°) along its orbit around the Sun. So after a sidereal day has passed, Earth still needs to rotate slightly more before the Sun reaches local noon according to solar time. A mean solar day is, therefore, nearly 4 minutes longer than a sidereal day.
The stars are so far away that Earth's movement along its orbit makes nearly no difference to their apparent direction (except for the nearest stars if measured with extreme accuracy; see parallax), and so they return to their highest point at the same time each sidereal day. | Sidereal time | Wikipedia | 456 | 48837 | https://en.wikipedia.org/wiki/Sidereal%20time | Physical sciences | Celestial mechanics | Astronomy |
Another way to understand this difference is to notice that, relative to the stars, as viewed from Earth, the position of the Sun at the same time each day appears to move around Earth once per year. A year has about 365.24 solar days but 366.24 sidereal days. Therefore, there is one fewer solar day per year than there are sidereal days, similar to an observation of the coin rotation paradox. This makes a sidereal day approximately times the length of the 24-hour solar day.
Effects of precession
Earth's rotation is not a simple rotation around an axis that remains always parallel to itself. Earth's rotational axis itself rotates about a second axis, orthogonal to the plane of Earth's orbit, taking about 25,800 years to perform a complete rotation. This phenomenon is termed the precession of the equinoxes. Because of this precession, the stars appear to move around Earth in a manner more complicated than a simple constant rotation.
For this reason, to simplify the description of Earth's orientation in astronomy and geodesy, it was conventional to chart the positions of the stars in the sky according to right ascension and declination, which are based on a frame of reference that follows Earth's precession, and to keep track of Earth's rotation, through sidereal time, relative to this frame as well. (The conventional reference frame, for purposes of star catalogues, was replaced in 1998 with the International Celestial Reference Frame, which is fixed with respect to extra-galactic radio sources. Because of the great distances, these sources have no appreciable proper motion.) In this frame of reference, Earth's rotation is close to constant, but the stars appear to rotate slowly with a period of about 25,800 years. It is also in this frame of reference that the tropical year (or solar year), the year related to Earth's seasons, represents one orbit of Earth around the Sun. The precise definition of a sidereal day is the time taken for one rotation of Earth in this precessing frame of reference. | Sidereal time | Wikipedia | 433 | 48837 | https://en.wikipedia.org/wiki/Sidereal%20time | Physical sciences | Celestial mechanics | Astronomy |
Modern definitions
During the past, time was measured by observing stars with instruments such as photographic zenith tubes and Danjon astrolabes, and the passage of stars across defined lines would be timed with the observatory clock. Then, using the right ascension of the stars from a star catalog, the time when the star should have passed through the meridian of the observatory was computed, and a correction to the time kept by the observatory clock was computed. Sidereal time was defined such that the March equinox would transit the meridian of the observatory at 0 hours local sidereal time.
Beginning during the 1970s, the radio astronomy methods very-long-baseline interferometry (VLBI) and pulsar timing overtook optical instruments for the most precise astrometry. This resulted in the determination of UT1 (mean solar time at 0° longitude) using VLBI, a new measure of the Earth Rotation Angle, and new definitions of sidereal time. These changes became effective 1 January 2003.
Earth rotation angle
The Earth rotation angle (ERA) measures the rotation of the Earth from an origin on the celestial equator, the Celestial Intermediate Origin, also termed the Celestial Ephemeris Origin, that has no instantaneous motion along the equator; it was originally referred to as the non-rotating origin. This point is very close to the equinox of J2000.
ERA, measured in radians, is related to UT1 by a simple linear relation:
where tU is the Julian UT1 date (JD) minus 2451545.0.
The linear coefficient represents the Earth's rotation speed around its own axis.
ERA replaces Greenwich Apparent Sidereal Time (GAST). The origin on the celestial equator for GAST, termed the true equinox, does move, due to the movement of the equator and the ecliptic. The lack of motion of the origin of ERA is considered a significant advantage.
The ERA may be converted to other units; for example, the Astronomical Almanac for the Year 2017 tabulated it in degrees, minutes, and seconds.
As an example, the Astronomical Almanac for the Year 2017 gave the ERA at 0 h 1 January 2017 UT1 as 100° 37′ 12.4365″. Since Coordinated Universal Time (UTC) is within a second or two of UT1, this can be used as an anchor to give the ERA approximately for a given civil time and date.
Mean and apparent varieties | Sidereal time | Wikipedia | 493 | 48837 | https://en.wikipedia.org/wiki/Sidereal%20time | Physical sciences | Celestial mechanics | Astronomy |
Although ERA is intended to replace sidereal time, there is a need to maintain definitions for sidereal time during the transition, and when working with older data and documents.
Similarly to mean solar time, every location on Earth has its own local sidereal time (LST), depending on the longitude of the point. Since it is not feasible to publish tables for every longitude, astronomical tables use Greenwich sidereal time (GST), which is sidereal time on the IERS Reference Meridian, less precisely termed the Greenwich, or Prime meridian. There are two varieties, mean sidereal time if the mean equator and equinox of date are used, and apparent sidereal time if the apparent equator and equinox of date are used. The former ignores the effect of astronomical nutation while the latter includes it. When the choice of location is combined with the choice of including astronomical nutation or not, the acronyms GMST, LMST, GAST, and LAST result.
The following relationships are true:
The new definitions of Greenwich mean and apparent sidereal time (since 2003, see above) are:
such that θ is the Earth Rotation Angle, EPREC is the accumulated precession, and E0 is equation of the origins, which represents accumulated precession and nutation. The calculation of precession and nutation was described in Chapter 6 of Urban & Seidelmann.
As an example, the Astronomical Almanac for the Year 2017 gave the ERA at 0 h 1 January 2017 UT1 as 100° 37′ 12.4365″ (6 h 42 m 28.8291 s). The GAST was 6 h 43 m 20.7109 s. For GMST the hour and minute were the same but the second was 21.1060.
Relationship between solar time and sidereal time intervals
If a certain interval I is measured in both mean solar time (UT1) and sidereal time, the numerical value will be greater in sidereal time than in UT1, because sidereal days are shorter than UT1 days. The ratio is:
such that t represents the number of Julian centuries elapsed since noon 1 January 2000 Terrestrial Time. | Sidereal time | Wikipedia | 445 | 48837 | https://en.wikipedia.org/wiki/Sidereal%20time | Physical sciences | Celestial mechanics | Astronomy |
Sidereal days compared to solar days on other planets
Six of the eight solar planets have prograde rotation—that is, they rotate more than once per year in the same direction as they orbit the Sun, so the Sun rises in the east. Venus and Uranus, however, have retrograde rotation. For prograde rotation, the formula relating the lengths of the sidereal and solar days is:
or, equivalently:
When calculating the formula for a retrograde rotation, the operator of the denominator will be a plus sign (put another way, in the original formula the length of the sidereal day must be treated as negative). This is due to the solar day being shorter than the sidereal day for retrograde rotation, as the rotation of the planet would be against the direction of orbital motion.
If a planet rotates prograde, and the sidereal day exactly equals the orbital period, then the formula above gives an infinitely long solar day (division by zero). This is the case for a planet in synchronous rotation; in the case of zero eccentricity, one hemisphere experiences eternal day, the other eternal night, with a "twilight belt" separating them.
All the solar planets more distant from the Sun than Earth are similar to Earth in that, since they experience many rotations per revolution around the Sun, there is only a small difference between the length of the sidereal day and that of the solar day – the ratio of the former to the latter never being less than Earth's ratio of 0.997. But the situation is quite different for Mercury and Venus. Mercury's sidereal day is about two-thirds of its orbital period, so by the prograde formula its solar day lasts for two revolutions around the Sun – three times as long as its sidereal day. Venus rotates retrograde with a sidereal day lasting about 243.0 Earth days, or about 1.08 times its orbital period of 224.7 Earth days; hence by the retrograde formula its solar day is about 116.8 Earth days, and it has about 1.9 solar days per orbital period.
By convention, rotation periods of planets are given in sidereal terms unless otherwise specified. | Sidereal time | Wikipedia | 449 | 48837 | https://en.wikipedia.org/wiki/Sidereal%20time | Physical sciences | Celestial mechanics | Astronomy |
In astronomy and celestial navigation, the hour angle is the dihedral angle between the meridian plane (containing Earth's axis and the zenith) and the hour circle (containing Earth's axis and a given point of interest).
It may be given in degrees, time, or rotations depending on the application.
The angle may be expressed as negative east of the meridian plane and positive west of the meridian plane, or as positive westward from 0° to 360°. The angle may be measured in degrees or in time, with 24h = 360° exactly.
In celestial navigation, the convention is to measure in degrees westward from the prime meridian (Greenwich hour angle, GHA), from the local meridian (local hour angle, LHA) or from the first point of Aries (sidereal hour angle, SHA).
The hour angle is paired with the declination to fully specify the location of a point on the celestial sphere in the equatorial coordinate system.
Relation with right ascension
The local hour angle (LHA) of an object in the observer's sky is
or
where LHAobject is the local hour angle of the object, LST is the local sidereal time, is the object's right ascension, GST is Greenwich sidereal time and is the observer's longitude (positive east from the prime meridian). These angles can be measured in time (24 hours to a circle) or in degrees (360 degrees to a circle)—one or the other, not both.
Negative hour angles (−180° < LHAobject < 0°) indicate the object is approaching the meridian, positive hour angles (0° < LHAobject < 180°) indicate the object is moving away from the meridian; an hour angle of zero means the object is on the meridian.
Right ascension is frequently given in sexagesimal hours-minutes-seconds format (HH:MM:SS) in astronomy, though may be given in decimal hours, sexagesimal degrees (DDD:MM:SS), or, decimal degrees.
Solar hour angle | Hour angle | Wikipedia | 425 | 48838 | https://en.wikipedia.org/wiki/Hour%20angle | Physical sciences | Celestial sphere: General | Astronomy |
Observing the Sun from Earth, the solar hour angle is an expression of time, expressed in angular measurement, usually degrees, from solar noon. At solar noon the hour angle is zero degrees, with the time before solar noon expressed as negative degrees, and the local time after solar noon expressed as positive degrees. For example, at 10:30 AM local apparent time the hour angle is −22.5° (15° per hour times 1.5 hours before noon).
The cosine of the hour angle (cos(h)) is used to calculate the solar zenith angle. At solar noon, so , and before and after solar noon the cos(± h) term = the same value for morning (negative hour angle) or afternoon (positive hour angle), so that the Sun is at the same altitude in the sky at 11:00AM and 1:00PM solar time.
Sidereal hour angle
The sidereal hour angle (SHA) of a body on the celestial sphere is its angular distance west of the March equinox generally measured in degrees. The SHA of a star varies by less than a minute of arc per year, due to precession, while the SHA of a planet varies significantly from night to night. SHA is often used in celestial navigation and navigational astronomy, and values are published in astronomical almanacs. | Hour angle | Wikipedia | 274 | 48838 | https://en.wikipedia.org/wiki/Hour%20angle | Physical sciences | Celestial sphere: General | Astronomy |
Gadiformes , also called the Anacanthini, are an order of ray-finned fish that include the cod, hakes, pollock, haddock, burbot, rocklings and moras, many of which are food fish of major commercial value. They are mostly marine fish found throughout the world and the vast majority are found in temperate or colder regions (tropical species are typically deep-water) while a few species may enter brackish estuaries. Pacific tomcods, one of the two species that makes up the genus Microgadus, are able to enter freshwater, but there is no evidence that they breed there. Some populations of landlocked Atlantic tomcod on the other hand, complete their entire life cycle in freshwater. Yet only one species, the burbot (Lota lota), is a true freshwater fish.
Common characteristics include the positioning of the pelvic fins (if present), below or in front of the pectoral fins. Gadiformes are physoclists, which means their swim bladders do not have a pneumatic duct. The fins are spineless. Gadiform fish range in size from the codlets, which may be as small as in adult length, to the Atlantic cod, Gadus morhua, which reaches up to .
The earliest gadiforms are Palaeogadus weltoni from the Maastrichtian of the United States and the undescribed, informally named "Protocodus" from the Early Paleocene of Greenland.
Timeline of genera | Gadiformes | Wikipedia | 321 | 48866 | https://en.wikipedia.org/wiki/Gadiformes | Biology and health sciences | Acanthomorpha | Animals |
Sparidae is a family of ray-finned fishes belonging to the order Spariformes, the seabreams and porgies, although they were traditionally classified in the order Perciformes. They are found in shallow temperate and tropical waters around the world and are demersal carnivores.
Taxonomy
Sparidae was first proposed as a family in 1818 by the French polymath and naturalist Constantine Samuel Rafinesque. Traditionally the taxa within the Spariformes were classified within the Perciformes, with some authorities using the term "Sparoid lineage" for the families Centracanthidae, Nemipteridae, Lethrinidae and Sparidae. Since then the use of molecular phylogenetics in more modern classifications has meant that the Spariformes is recognised as a valid order within the Percomorpha containing six families, with Callanthidae, Sillaginidae and Lobotidae included. Other workers have found that the Centracanthidae is synonymous with Sparidae and that the Spariformes contains only the remaining three families of the "Sparoid lineage".
In the past workers recognised six subfamilies within the Sparidae. These were Boopsinae, Denticinae, Diplodinae, Pagellinae, Pagrinae, and Sparinae. However, these taxa did not resolve as monophyletic in all the analyses undertaken. These analyses support Sparidae as a monophyletic family if Spicara, a genus formerly in the family Centracanthidae, was included. This meant that Spicara and Centracanthus were both now classified within Sparidae, so that Centracanthidae is a junior synonym of Sparidae.
Etymology
Sparidae takes its name from its type genus, Sparus, that name coming from the Greek for its only species the gilt-head bream (Sparus aurata).
Genera
The family Sparidae contains about 155 species in 38 genera:
Fossil genera include: | Sparidae | Wikipedia | 421 | 48868 | https://en.wikipedia.org/wiki/Sparidae | Biology and health sciences | Acanthomorpha | Animals |
†Abromasta Day, 2003
†Burtinia van Beneden, 1873
†Crommyodus Cope, 1875
†Ctenodentex Storms, 1896
†Ellaserrata Day, 2003
†Kreyenhagenius David, 1946
†Paracalamus Arambourg, 1927
†Plectrites Jordan & Gilbert, 1920
†Pseudosparnodus Day, 2003
†Pshekharus Bannikov & Kotylar, 2015
†Rhythmias Jordan & Gilbert, 1920
†Sciaenurus Agassiz, 1845
†Sparnodus Agassiz, 1838 | Sparidae | Wikipedia | 117 | 48868 | https://en.wikipedia.org/wiki/Sparidae | Biology and health sciences | Acanthomorpha | Animals |
Characteristics
Sparidae breams have oblong, moderately deep and compressed bodies. The head is large, with a characteristic steep dorsal slant. There are no scales on the snout but there are scales on the cheeks. The preoperculum may or may not have scales and has no spines or serrations on its margin. The operculum is scaled and also has no spines. The mouth is slightly oblique and can be protruded a little. The upper jaw never extends back past a vertical line through the centre of the eye. There are teeth in the jaws which vary from conical or flattened but there are no teeth on the roof of the mouth. There is one dorsal fin which is supported by between 10 and 13 spines and 9 and 17 soft rays, with the ultimate ray being split into 2, and no incision separated the spines from the soft rays. The rearmost spines in the dorsal fin may be elongated or filamentous. The anal fin is supported by 3 robust spines and between 7 and 15 soft rays. The caudal fin varies from moderately deeply emarginate to forked. The pectoral fins are typically long and pointed and the pelvic fins are under or immediately to the rear of the bases of the pectoral fins, supported a single spine and 5 soft rays, with a scale in the axilla, referred to as the axillary pelvic process. The scales are typically smooth, cycloid, or slightly rough to the touch, weakly ctenoid, The lateral line is single and continuous and reached the base of the caudal fin. They are very variable in colour and may be pinkish or reddish to yellowish or greyish, frequently with tints of silver or gold and dark or coloured spots, stripes or bars. The two largest species of Sparid are the white steenbras (Lithognathus lithognathus) and the red steenbras (Petrus rupestris), both of which have a maximum published total length of , while the smallest species is the cherry seabream (Polysteganus cerasinus).
Distribution and habitat
Sparidae breams are found in tropical and temperate coastal waters around the world. They are demersal fishes on the continental shelf and slope. A few species are found in brackish water, and a few of these will enter fresh water. | Sparidae | Wikipedia | 491 | 48868 | https://en.wikipedia.org/wiki/Sparidae | Biology and health sciences | Acanthomorpha | Animals |
Biology
Sparidae breams are predatory with most feeding on benthic invertebrates. Smaller species in the family usually gather in schools, as do the juveniles of the larger species. The larger adult fishes are normally solitary or, at least, are less sociable and prefer deeper waters. The juveniles and subadults are often markedly different in shape and colour patterns, and may be much more colourful. Many sparids are hermaphroditic and some have both male and female sex organs at the same time. Others change sex as the grow, either changing from male to female, i.e. protandrous. or from female to male, protogynous.
Fisheries
Sparids are highly regarded as food fish and are important target species for commercial fisheries wherever they occur. Between 1990 and 1995, the FAO Yearbook of Fishery Statistics reported that the annual weight of landings was between of sparids in the Western Central Pacific.
Cookery
The most celebrated of the breams in cookery are the gilt-head bream and the common dentex. | Sparidae | Wikipedia | 219 | 48868 | https://en.wikipedia.org/wiki/Sparidae | Biology and health sciences | Acanthomorpha | Animals |
Clupeiformes is the order of ray-finned fish that includes the herring family, Clupeidae, and the anchovy family, Engraulidae and sardines. The group includes many of the most important forage and food fish.
Clupeiformes are physostomes, which means that their gas bladder has a pneumatic duct connecting it to the gut. They typically lack a lateral line, but still have the eyes, fins and scales that are common to most fish, though not all fish have these attributes. They are generally silvery fish with streamlined, spindle-shaped bodies, and they often school. Most species eat plankton which they filter from the water with their gill rakers.
The former order of Isospondyli was subsumed mostly by Clupeiformes, but some isospondylous fishes (isospondyls) were assigned to Osteoglossiformes, Salmoniformes, Cetomimiformes, etc.
Their sister group were the extinct Ellimmichthyiformes, which were dominant throughout much of the Cretaceous and into the Paleogene, and often coexisted with clupeiforms at many known localities. Both groups closely resembled each other morphologically, although the ellimmichthyiformes evolved some highly divergent body plans later in the Cretaceous.
Several fossil clupeiforms are known from the Early Cretaceous of South America that appear to be more closely allied with Clupeioidei over the Denticipitidae. This suggests a very deep divergence within the crown group Clupeiformes that must have occurred during the Early Cretaceous or before. | Clupeiformes | Wikipedia | 347 | 48869 | https://en.wikipedia.org/wiki/Clupeiformes | Biology and health sciences | Clupeiformes | Animals |
Families
The order includes about 405 species in ten families:
Order Clupeiformes
Genus †Histiothrissa Woodward, 1901
Genus ?†Jhingrania Misra & Saxena, 1959 (possibly a clupavid)
Genus †Santanaclupea Maisey, 1993
Genus †Spratticeps Patterson, 1970
Suborder Denticipitoidei Grande, 1982
Family Denticipitidae Clausen, 1959 (denticle herring)
Suborder Clupeoidei Bleeker, 1849
Genus †Beksinskiella Granica, Bieńowska-Wasiluki & Paldyna, 2004
Genus †Nolfia De Figueiredo, 2009
Genus †Pseudoellima De Figueiredo, 2009
Family †Cynoclupeidae Malabarba & Di Dario, 2017
Family Spratelloididae D. S. Jordan 1925 (dwarf herrings or small round herrings)
Family Engraulidae Gill, 1861 (anchovies)
Family Clupeidae Cuvier, 1816 (herrings and sprats)
Family Chirocentridae Bleeker, 1849 (wolf herrings)
Family Dussumieriidae Gill, 1861 (round herrings or rainbow sardines)
Family Pristigasteridae Bleeker, 1872 (longfin herrings)
Family Ehiravidae Deraniyagala, 1929 (river sprats)
Family Alosidae Svetovidov, 1952 (shads and sardines)
Family Dorosomatidae Gill, 1861 (thread herrings or gizzard shads and sardinellas)
Timeline of genera | Clupeiformes | Wikipedia | 333 | 48869 | https://en.wikipedia.org/wiki/Clupeiformes | Biology and health sciences | Clupeiformes | Animals |
Clupeidae is a family of clupeiform ray-finned fishes, comprising, for instance, the herrings and sprats. Many members of the family have a body protected with shiny cycloid (very smooth and uniform) scales, a single dorsal fin, and a fusiform body for quick, evasive swimming and pursuit of prey composed of small planktonic animals. Due to their small size and position in the lower trophic level of many marine food webs, the levels of methylmercury they bioaccumulate are very low, reducing the risk of mercury poisoning when consumed.
The earliest known fossil members of this group are the stem-clupeids Italoclupea and Lecceclupea from the late Campanian/early Maastrichtian of Italy.
Description and biology
Clupeids are mostly marine forage fish, although a few species are found in fresh water. No species has scales on the head, and some are entirely scaleless. The lateral line is short or absent, and the teeth are unusually small where they are present at all. Clupeids typically feed on plankton, and range from in length.
Clupeids spawn huge numbers of eggs (up to 200,000 in some species) near the surface of the water. After hatching, the larvae live among the plankton until they develop a swim bladder and transform into adults. These eggs and fry are not protected or tended to by parents. The adults typically live in large shoals, seeking protection from piscivorous predators such as birds, sharks and other predatory fish, toothed whales, marine mammals, and jellyfish. They also form bait balls.
Commercially important species of the Clupeidae include the Atlantic and Baltic herrings (Clupea harengus), and the Pacific herring (C. pallasii). | Clupeidae | Wikipedia | 387 | 48870 | https://en.wikipedia.org/wiki/Clupeidae | Biology and health sciences | Clupeiformes | Animals |
Feeding physiology
The Clupeidae family primarily feed on small planktonic organisms. The teeth of members of this family are either reduced or absent, reduced teeth are miniature teeth that would be barely visible and line the interior of the fish's mouth. The structure of these teeth indicate that these organisms do not need to cut or tear their prey items as they would need fully formed teeth to complete this process. They do, however, possess long gill rakers that are designed for sifting plankton and other small particles out of the water as it passes through their gills. Gill rakers are protrusions along the gill arch, opposing the gill filaments, that help aquatic organisms to trap food particles.
The diet of many clupeids primarily consists of phytoplankton and plant matter during their larval stages. As the fish mature this diet begins to shift towards larger and more substantive organisms, including more zooplankton and copepods. This change in diet is possible due to their increase in body and gill raker size, which allows them to capture and process larger organisms to support themselves. Small organisms like these do not need to be ground or torn apart for consumption so pronounced teeth would not serve a purpose in the feeding habits of Clupeidae, instead the use of filter feeding allows for much more efficient nutrient collection.
The fusiform body shape of Clupeidae is also advantageous to their trophic ecology. The tapering body form is a highly hydrodynamic form that allows for quick increases in speed and a high maximum speed. Moving at high speeds allows the members of this family to regulate their feeding habits and avoid predators. Clupeidae can moderate the speed at which they swim to increase their uptake of nutrients. As with all filter feeders, Clupeidae cannot take in food if nutrient rich water does not pass over their gills. To moderate this, members of this family have been found to increase their swimming speed when they sense that there is a high concentration of food items in order to take advantage of this feeding period. Keeping a high swimming speed during periods of low food availability would not be efficient to maintain over long periods of time as the organisms would not net as much energy as they may need to in order to sustain themselves and increase their fitness. Increasing their swimming speed during feeding periods would allow them to take in more plankton while not suffering consequences from maintaining that speed.
Taxonomy
The following genera are classified within the family: | Clupeidae | Wikipedia | 505 | 48870 | https://en.wikipedia.org/wiki/Clupeidae | Biology and health sciences | Clupeiformes | Animals |
Clupea Linnaeus, 1758
Ethmidium W. F. Thompson, 1916
Hyperlophus Ogilby, 1892
Potamalosa Ogilby, 1897
Ramnogaster Whitehead, 1965
Sprattus Girgensohn 1846
Strangomera Whitehead,genera from ECoF 1965
The family arguably also contains the "Sundasalangidae", a paedomorphic taxon first thought to be a distinct salmoniform family, but then discovered to be deeply nested in the Clupeidae.
Until recently, the concept of Clupeidae was broader, but it has been subdivided into several distinct families (e.g. Alosidae)
Fossil genera
The following fossil genera have been variously suggested to be sensu stricto members of Clupeidae. Many were formerly placed in the subfamily Clupeinae:
?†Audenaerdia Taverne, 1973 (alternatively Clupeidae or Alosidae)
†Italoclupea Taverne, 2007
†Knightia Jordan, 1907
†Lecceclupea Taverne, 2011
†Xyne Jordan, 1921 (likely closely related to Clupea)
Disputed fossil genera
Known fossil genera classified under the sensu lato concept of Clupeidae include:
†Alisea
†Austroclupea
†Bolcaichthys
†Chasmoclupea
†Clupeidarum [otolith]
†Clupeops
†Eoalosa
†Eosardinella
†Etringus
†Ganoessus
†Ganolytes
†Gosiutichthys
†Horaclupea
†?Hypsospondylus
†Karaganops
†Marambionella
†Maicopiella
†Moldavichthys
†Paleopiquitinga
†Primisardinella
†Pseudohilsa
†Quisque
†Rupelia
†Sarmatella (=†Illusionella)
†Trollichthys
†Waihaoclupea
†Wisslerius
†Xenophanis
†Xyrinius | Clupeidae | Wikipedia | 414 | 48870 | https://en.wikipedia.org/wiki/Clupeidae | Biology and health sciences | Clupeiformes | Animals |
The mackerel, tuna, and bonito family, Scombridae, includes many of the most important and familiar food fishes. The family consists of 51 species in 15 genera and two subfamilies. All species are in the subfamily Scombrinae, except the butterfly kingfish, which is the sole member of subfamily Gasterochismatinae.
Scombrids have two dorsal fins and a series of finlets behind the rear dorsal fin and anal fin. The caudal fin is strongly divided and rigid, with a slender, ridged base. The first (spiny) dorsal fin and the pelvic fins are normally retracted into body grooves. Species lengths vary from the of the island mackerel to the recorded for the immense Atlantic bluefin tuna.
Scombrids are generally predators of the open ocean, and are found worldwide in tropical and temperate waters. They are capable of considerable speed, due to a highly streamlined body and retractable fins. Some members of the family, in particular the tunas, are notable for being partially endothermic (warm-blooded), a feature that also helps them to maintain high speed and activity. Other adaptations include a large amount of red muscle, allowing them to maintain activity over long periods. Scombrids like the yellowfin tuna can reach speeds of 22 km/h (14 mph).
Classification
Jordan, Evermann, and Clark (1930) divide these fishes into the four families: Cybiidae, Katsuwonidae, Scombridae, and Thunnidae, but taxonomists later classified them all into a single family, the Scombridae.
The World Wildlife Fund and the Zoological Society of London jointly issued their "Living Blue Planet Report" on 16 September 2015 which states that a dramatic fall of 74% occurred in worldwide stocks of scombridae fish between 1970 and 2010, and the global overall "population sizes of mammals, birds, reptiles, amphibians and fish fell by half on average in just 40 years".
Extant genera
The 51 extant species are in 15 genera and two subfamilies – with the subfamily Scombrinae further grouped into four tribes, as: | Scombridae | Wikipedia | 448 | 48872 | https://en.wikipedia.org/wiki/Scombridae | Biology and health sciences | Acanthomorpha | Animals |
Family Scombridae
Subfamily Gasterochismatinae
Genus Gasterochisma
Subfamily Scombrinae
Tribe Scombrini – mackerels
Genus Rastrelliger
Genus Scomber
Tribe Scomberomorini – Spanish mackerels
Genus Acanthocybium
Genus Grammatorcynus
Genus Orcynopsis
Genus Scomberomorus
Tribe Sardini – bonitos
Genus Sarda
Genus Cybiosarda
Genus Gymnosarda
Tribe Thunnini – tunas
Genus Allothunnus
Genus Auxis
Genus Euthynnus
Genus Katsuwonus
Genus Thunnus
Fossil genera
The following fossil genera are known:
Genus †Aramichthys (fossil; middle Eocene of Syria)
Genus †Eoscomber (fossil; early Eocene of Senegal)
Genus †Eoscombrus (fossil; late Eocene of California)
Genus †Godsilia (fossil; early Eocene of Italy)
Genus †Landanichthys (fossil; middle Paleocene of Angola)
Genus †Palaeocybium (fossil; Eocene to Oligocene of the United States and parts of Europe)
Genus †Pseudauxides (fossil; early Eocene of Italy)
Genus †Scombrinus (fossil; early Eocene of England)
Genus †Thunnoscomberoides (fossil; early Eocene of Italy)
Genus †Wetherellus (fossil; early Eocene of England)
Subfamily Scombrinae
Tribe †Eocoelopomini
Genus †Eocoelopoma (early Eocene of England & Turkmenistan)
Genus †Palaeothunnus (early Eocene of Turkmenistan)
Genus †Micrornatus (early Eocene of England)
Tribe Scomberomorini
Genus †Neocybium (Late Eocene of Kazakhstan, Early Oligocene of Germany & Georgia)
Tribe Scombrini
Genus †Auxides (early Eocene of Senegal, Turkmenistan, and much of Europe) | Scombridae | Wikipedia | 404 | 48872 | https://en.wikipedia.org/wiki/Scombridae | Biology and health sciences | Acanthomorpha | Animals |
Serranidae is a large family of fishes belonging to the order Perciformes. The family contains about 450 species in 65 genera, including the sea basses and the groupers (subfamily Epinephelinae). Although many species are small, in some cases less than , the giant grouper (Epinephelus lanceolatus) is one of the largest bony fishes in the world, growing to in length and in weight. Representatives of this group live in tropical and subtropical seas worldwide.
Characteristics
Many serranid species are brightly colored, and many of the larger species are caught commercially for food. They are usually found over reefs, in tropical to subtropical waters along the coasts. Serranids are generally robust in form, with large mouths and small spines on the gill coverings. They typically have several rows of sharp teeth, usually with a pair of particularly large, canine-like teeth projecting from the lower jaw.
All serranids are carnivorous. Although some species, especially in the Anthiadinae subfamily, only feed on zooplankton, the majority feed on fish and crustaceans. They are typically ambush predators, hiding in cover on the reef and darting out to grab passing prey. Their bright colours are most likely a form of disruptive camouflage, similar to the stripes of a tiger.
Many species are protogynous hermaphrodites, meaning they start out as females and change sex to male later in life. They produce large quantities of eggs and their larvae are planktonic, generally at the mercy of ocean currents until they are ready to settle into adult populations.
Like other fish, serranids harbour parasites, including nematodes, cestodes, digeneans, monogeneans, isopods, and copepods. A study conducted in New Caledonia has shown that coral reef-associated serranids harbour about 10 species of parasites per fish species.
Classification
In recent times, this family has been proposed to be split. The two hypothetical families emerging from the remains of the possibly-obsolete taxon are the families Epinephilidae and Anthiadidae. This taxonomic separation is recognized by some authorities, including the IUCN.
Recent molecular classifications challenge the validity of the genera Cromileptes (sometimes spelled Chromileptes) and Anyperodon. Each of these two genera has a single species, which were included in the same clade as species of Epinephelus in a study based on five different genes. | Serranidae | Wikipedia | 503 | 48873 | https://en.wikipedia.org/wiki/Serranidae | Biology and health sciences | Acanthomorpha | null |
The subfamilies and genera are as follows: | Serranidae | Wikipedia | 11 | 48873 | https://en.wikipedia.org/wiki/Serranidae | Biology and health sciences | Acanthomorpha | null |
Salmonidae (, ) is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes (, lit. "salmon-shaped"), consisting of 11 extant genera and over 200 species collectively known as "salmonids" or "salmonoids". The family includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), char, graylings, freshwater whitefishes, taimens and lenoks, all coldwater mid-level predatory fish that inhabit the subarctic and cool temperate waters of the Northern Hemisphere. The Atlantic salmon (Salmo salar), whose Latin name became that of its genus Salmo, is also the eponym of the family and order names.
Salmonids have a relatively primitive appearance among teleost fish, with the pelvic fins being placed far back, and an adipose fin towards the rear of the back. They have slender bodies with rounded scales and forked tail fins, and their mouths contain a single row of sharp teeth. Although the smallest salmonid species is just long for adults, most salmonids are much larger, with the largest reaching .
All salmonids are migratory fish that spawn in the shallow gravel beds of freshwater headstreams, spend the growing juvenile years in rivers, creeks, small lakes and wetlands, but migrate downstream upon maturity and spend most of their adult lives at much larger waterbodies. Many salmonid species are euryhaline and migrate to the sea or brackish estuaries as soon as they approach adulthood, returning to the upper streams only to reproduce. Such sea-run life cycle is described as anadromous, and other freshwater salmonids that migrate purely between lakes and rivers are considered potamodromous. Salmonids are carnivorous predators of the middle food chain, feeding on smaller fish, crustaceans, aquatic insects and larvae, tadpoles and sometimes fish eggs (even those of their own kind), and in turn being preyed upon by larger predators. Many species of salmonids are thus considered keystone organisms important for both freshwater and terrestrial ecosystems due to the biomass transfer provided by their mass migration from oceanic to inland waterbodies.
Evolution | Salmonidae | Wikipedia | 453 | 48878 | https://en.wikipedia.org/wiki/Salmonidae | Biology and health sciences | Salmoniformes | null |
Current salmonids comprise three main clades taxonomically treated as subfamilies: Coregoninae (freshwater whitefishes), Thymallinae (graylings), and Salmoninae (trout, salmon, char, taimens and lenoks). Generally, all three lineages are accepted to allocate a suite of derived traits indicating a monophyletic group.
The order Salmoniformes first appeared during the Santonian and Campanian stages of the Late Cretaceous, and is most closely related to pike and mudminnows in the order Esociformes, to the extent that some authors have grouped the Esociformes within the Salmoniformes. Although it is assumed that salmon and pike diverged from one another during the Cretaceous, no definitive salmonids appear before the Eocene. The Salmonidae first appear in the fossil record in the Early Eocene with Eosalmo driftwoodensis, a stem-salmonine, which was first described from fossils found at Driftwood Creek, central British Columbia, and has been recovered from most sites in the Eocene Okanagan Highlands. This genus shares traits found in all three subfamily lineages. Hence, E. driftwoodensis is an archaic salmonid, representing an important stage in salmonid evolution. Fossil scales of coregonines are known from the Late Eocene or Early Oligocene of California.
A gap appears in the salmonine fossil record after E. driftwoodensis until about 7 million years ago (mya), in the Late Miocene, when trout-like fossils appear in Idaho, in the Clarkia Lake beds. Several of these species appear to be Oncorhynchus — the current genus for Pacific salmon and Pacific trout. The presence of these species so far inland established that Oncorhynchus was not only present in the Pacific drainages before the beginning of the Pliocene (~5–6 mya), but also that rainbow and cutthroat trout, and Pacific salmon lineages had diverged before the beginning of the Pliocene. Consequently, the split between Oncorhynchus and Salmo (Atlantic salmon and European trout) must have occurred well before the Pliocene. Suggestions have gone back as far as the Early Miocene (about 20 mya).
Genetics | Salmonidae | Wikipedia | 469 | 48878 | https://en.wikipedia.org/wiki/Salmonidae | Biology and health sciences | Salmoniformes | null |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.