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Algebraic surface

In mathematics, an algebraic surface is an algebraic variety of dimension two. In the case of geometry over the field of complex numbers, an algebraic surface has complex dimension two (as a complex manifold, when it is non-singular) and so of dimension four as a smooth manifold.

The theory of algebraic surfaces is much more complicated than that of algebraic curves (including the compact Riemann surfaces, which are genuine surfaces of (real) dimension two). Many results were obtained, but, in the Italian school of algebraic geometry, and are up to 100 years old.

Classification by the Kodaira dimension
In the case of dimension one, varieties are classified by only the topological genus, but, in dimension two, one needs to distinguish the arithmetic genus $$p_a$$ and the geometric genus $$p_g$$ because one cannot distinguish birationally only the topological genus. Then, irregularity is introduced for the classification of varieties. A summary of the results (in detail, for each kind of surface refers to each redirection), follows:

Examples of algebraic surfaces include (κ is the Kodaira dimension):

 * κ = −∞: the projective plane, quadrics in P3, cubic surfaces, Veronese surface, del Pezzo surfaces, ruled surfaces
 * κ = 0 : K3 surfaces, abelian surfaces, Enriques surfaces, hyperelliptic surfaces
 * κ = 1: elliptic surfaces
 * κ = 2: surfaces of general type.

For more examples see the list of algebraic surfaces.

The first five examples are in fact birationally equivalent. That is, for example, a cubic surface has a function field isomorphic to that of the projective plane, being the rational functions in two indeterminates. The Cartesian product of two curves also provides examples.

Birational geometry of surfaces
The birational geometry of algebraic surfaces is rich, because of blowing up (also known as a monoidal transformation), under which a point is replaced by the curve of all limiting tangent directions coming into it (a projective line). Certain curves may also be blown down, but there is a restriction (self-intersection number must be −1).

Castelnuovo's Theorem
One of the fundamental theorems for the birational geometry of surfaces is Castelnuovo's theorem. This states that any birational map between algebraic surfaces is given by a finite sequence of blowups and blowdowns.

Properties
The Nakai criterion says that:
 * A Divisor D on a surface S is ample if and only if D2 > 0 and for all irreducible curve C on S ''D•C > 0.

Ample divisors have a nice property such as it is the pullback of some hyperplane bundle of projective space, whose properties are very well known. Let $$\mathcal{D}(S)$$ be the abelian group consisting of all the divisors on S. Then due to the intersection theorem
 * $$\mathcal{D}(S)\times\mathcal{D}(S)\rightarrow\mathbb{Z}:(X,Y)\mapsto X\cdot Y$$

is viewed as a quadratic form. Let
 * $$\mathcal{D}_0(S):=\{D\in\mathcal{D}(S)|D\cdot X=0,\text{for all } X\in\mathcal{D}(S)\}$$

then $$\mathcal{D}/\mathcal{D}_0(S):=Num(S)$$ becomes to be a numerical equivalent class group of S and
 * $$Num(S)\times Num(S)\mapsto\mathbb{Z}=(\bar{D},\bar{E})\mapsto D\cdot E$$

also becomes to be a quadratic form on $$Num(S)$$, where $$\bar{D}$$ is the image of a divisor D on S. (In the below the image $$\bar{D}$$ is abbreviated with D.)

For an ample line bundle H on S, the definition
 * $$\{H\}^\perp:=\{D\in Num(S)|D\cdot H=0\}.$$

is used in the surface version of the Hodge index theorem:
 * for $$D\in\{\{H\}^\perp|D\ne0\}, D\cdot D < 0$$, i.e. the restriction of the intersection form to $$\{H\}^\perp$$ is a negative definite quadratic form.

This theorem is proven using the Nakai criterion and the Riemann-Roch theorem for surfaces. The Hodge index theorem is used in Deligne's proof of the Weil conjecture.

Basic results on algebraic surfaces include the Hodge index theorem, and the division into five groups of birational equivalence classes called the classification of algebraic surfaces. The general type class, of Kodaira dimension 2, is very large (degree 5 or larger for a non-singular surface in P3 lies in it, for example).

There are essential three Hodge number invariants of a surface. Of those, h1,0 was classically called the irregularity and denoted by q; and h2,0 was called the geometric genus pg. The third, h1,1, is not a birational invariant, because blowing up can add whole curves, with classes in H1,1. It is known that Hodge cycles are algebraic and that algebraic equivalence coincides with homological equivalence, so that h1,1 is an upper bound for ρ, the rank of the Néron-Severi group. The arithmetic genus pa is the difference

 * geometric genus − irregularity.

This explains why the irregularity got its name, as a kind of 'error term'.

Riemann-Roch theorem for surfaces
The Riemann-Roch theorem for surfaces was first formulated by Max Noether. The families of curves on surfaces can be classified, in a sense, and give rise to much of their interesting geometry.

title: Algebraic surface


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Pterophyllum

Pterophyllum is a small genus of freshwater fish from the family Cichlidae known to most aquarists as angelfish. All Pterophyllum species originate from the Amazon Basin, Orinoco Basin and various rivers in the Guiana Shield in tropical South America. The three species of Pterophyllum are unusually shaped for cichlids being greatly laterally compressed, with round bodies and elongated triangular dorsal and anal fins. This body shape allows them to hide among roots and plants, often on a vertical surface. Naturally occurring angelfish are frequently striped transversely, colouration which provides additional camouflage. Angelfish are ambush predators and prey on small fish and macroinvertebrates. All Pterophyllum species form monogamous pairs. Eggs are generally laid on a submerged log or a flattened leaf. As is the case for other cichlids, brood care is highly developed.

Pterophyllum should not be confused with marine angelfish, perciform fish found on shallow ocean reefs.

Species
The currently recognized species in this genus are:

History
The freshwater angelfish (P. scalare) was described in 1824 by F. Schultze. Pterophyllum is derived from the Greek πτερον, pteron (fin/sail) and φυλλον, phyllon (leaf).

In 1906, J. Pellegrin described P. altum. In 1963, P. leopoldi was described by J. P. Gosse. Undescribed species may still exist in the Amazon Basin. New species of fish are discovered with increasing frequency, and, like P. scalare and P. leopoldi, the differences may be subtle. Scientific notations describe the P. leopoldi as having 29–35 scales in a lateral row and straight predorsal contour, whereas, P. scalare is described as having 35–45 scales in a lateral row and a notched predorsal contour. P. leopoldi shows the same coloration as P. scalare, but a faint stripe shows between the eye stripe and the first complete body stripe and a third incomplete body stripe exists between the two main (complete) body stripes that extends three-fourths the length of the body. P. scalare's body does not show the stripe between the eye stripe and first complete body stripe at all, and the third stripe between the two main body stripes rarely extends downward more than a half inch, if even present. P. leopoldi fry develop three to eight body stripes, with all but one to five fading away as they mature, whereas P. scalare only has two in true wild form throughout life.

Angelfish were bred in captivity for at least 30 years prior to P. leopoldi being described.

In the aquarium
Angelfish are one of the most commonly kept freshwater aquarium fish, as well as the most commonly kept cichlid. They are praised for their unique shape, color, and behavior. It was not until the late 1920s to early 1930s that the angelfish was bred in captivity in the United States.

Species
The most commonly kept species in the aquarium is Pterophyllum scalare. Most of the individuals in the aquarium trade are captive-bred. Sometimes, captive-bred Pterophyllum altum is available. Pterophyllum leopoldi is the hardest to find in the trade.

Care
Angelfish are kept in a warm aquarium, ideally around 80 °F (27 °C), with soft and acidic (<6.5ph) water. Though angelfish are members of the cichlid family, they are generally peaceful when not mating; however, they still may feed on very small species of fishes. Suitable tank mates include catfishes of the families Doradidae and Callichthyidae which have their own armor for protection.

Breeding
P. scalare is relatively easy to breed in the aquarium, although one of the results of generations of inbreeding is that many breeds have almost completely lost their rearing instincts, resulting in the tendency of the parents to eat their young. In addition, it is very difficult to accurately identify the sex of any individual until it is nearly ready to breed.

Angelfish pairs form long-term relationships where each individual will protect the other from threats and potential suitors. Upon the death or removal of one of the mated pair, breeders have experienced the total refusal of the remaining mate to pair up with any other angelfish and successfully breed with subsequent mates.

Depending upon aquarium conditions, P. scalare reaches sexual maturity at the age of six to 12 months or more. In situations where the eggs are removed from the aquarium immediately after spawning, the pair is capable of spawning every seven to 10 days. Around the age of three years, spawning frequency decreases and eventually ceases.

When the pair is ready to spawn, they choose an appropriate medium upon which to lay the eggs, and spend one or two days picking off detritus and algae from the surface. This medium may be a broad-leaf plant in the aquarium, a flat surface such as a piece of slate placed vertically in the aquarium, a length of pipe, or even the glass sides of the aquarium. The female deposits a line of eggs on the spawning substrate, followed by the male, which fertilizes the eggs. This process is repeated until a total of 100 to more than 1,200 eggs are laid, depending on the size and health of the female fish. As both parents care for the offspring throughout development, the pair takes turns maintaining a high rate of water circulation around the eggs by swimming very close to the eggs and fanning them with their pectoral fins. In a few days, the eggs hatch and the fry remain attached to the spawning substrate. During this period, the fry survive by consuming the remnants of their yolk sacs. At one week, the fry detach and become free-swimming. Successful parents keep close watch on the eggs until then. At the free-swimming stage, the fry can be fed suitably sized live food.

P. altum is notably difficult to breed in an aquarium environment.

Lifespan
Freshwater Angelfish with quality genetics are known to live approximately 12 years in captivity, if the ideal living conditions are provided. In the wild they are thought to live as long as 15 years if unthreatened by their numerous natural predators.

Compatibility with other fish
In pet stores, the freshwater angelfish is typically placed in the semiaggressive category. Some tetras and barbs are compatible with angelfish, but ones small enough to fit in the mouth of the angelfish may be eaten. Generous portions of food should be available so the angelfish do not get hungry and turn on their tank mates.

P. scalare and P. altum are described to be peaceful but territorial. While freshwater angelfish are often recommended for community aquaria, it has been reported that fin-nippers such as Tiger barb often target their long fins, and that freshwater angelfish become aggressive towards their companions as they grow. It is thus recommended that freshwater angelfish be kept instead in single-species aquaria.

Ich (White Spot Disease)
Ich, also known as "White Spot Disease," is caused by the parasitic protozoan Ichthyophthirius multifiliis. Fish infected with Ich exhibit small, white, grain-like spots on their body, fins, and gills. These spots are cysts where the parasites reside. Infected fish often display signs of discomfort, frequently scratching against objects in the aquarium. The primary cause of an Ich outbreak is usually stress, which can result from factors such as poor water quality, sudden temperature changes, or the introduction of new fish without proper quarantine. To treat Ich, increasing the aquarium's temperature gradually to 78-86 °F (25-30 °C) for a few days can speed up the parasite's life cycle. Simultaneously, using commercially available Ich treatments, based on copper or formalin, can be effective in eradicating the disease.

Fin Rot
Fin Rot is a common bacterial infection affecting the fins of aquarium fish. It is characterized by the fraying, discoloration, and gradual degradation of the fish's fins, giving them a ragged appearance. If left untreated, the condition can progress from the fins to the body, leading to a more severe form known as body rot. The primary causes of fin rot are poor water quality, overcrowding, and physical damage, all of which stress the fish and make them more susceptible to infections. In terms of treatment, the first step is to improve water quality by conducting regular water changes, removing waste, and ensuring proper filtration.

Swim Bladder Disease
Swim Bladder Disease refers to a collection of issues affecting a fish's swim bladder, the organ responsible for buoyancy. Fish afflicted with this condition may struggle to maintain their position in the water, often floating upside-down, sinking to the bottom, or swimming at unusual angles. The causes can be diverse, ranging from overfeeding, constipation, and rapid water temperature changes to physical injury and bacterial infections. To treat swim bladder disease, it's advised to first fast the fish for 24–48 hours, followed by feeding them a diet of cooked, skinned peas, which can help alleviate constipation. If the condition is thought to be due to a bacterial infection, antibiotic treatments can be considered.

Bacterial Infections
Bacterial Infections in aquarium fish can manifest in various ways and are caused by harmful bacteria proliferating within the tank. Symptoms can range from visible ulcers, sores, and red streaks on the fish's body to bloating, erratic swimming, and a loss of appetite. The primary triggers for bacterial infections often include poor water quality, overcrowded tanks, stress, and injuries. Overfeeding, which leads to excess waste, can also contribute to bacterial blooms. To treat bacterial infections, the first step is always to improve water conditions by conducting regular water changes, enhancing filtration, and removing any decaying organic matter. Specialized antibacterial medications, available at pet and aquarium stores, can be administered based on the specific type of bacterial infection. In severe or persistent cases, isolating the affected fish in a quarantine tank during treatment is recommended.

Aquarium varieties
Most strains of angelfish available in the fishkeeping hobby are the result of many decades of selective breeding. For the most part, the original crosses of wild angelfish were not recorded and confusion between the various species of Pterophyllum, especially P. scalare and P. leopoldi, is common. This makes the origins of "domestic angelfish" unclear. Domestic strains are most likely a collection of genes resulting from more than one species of wild angelfish, combined with the selection of mutations in domesticated lines over the last 60 or more years. The result of this is a domestic angelfish that is a true hybrid, with little more than a superficial resemblance to wild Pterophyllum species. Much of the research into the known genetics of P. scalare is the result of the research of Dr. Joanne Norton, who published a series of 18 articles in Freshwater and Marine Aquarium Magazine. The genome of P. scalare was first sequenced and assembled by Indeever Madireddy, a high school student in October 2022.

 * Silver (+/+): The silver angelfish most commonly resembles the wild form of angelfish, and is also referred to as "wild-type". It is not, however, caught in the wild and is considered domestic. The fish has a silver body with red eyes, and three vertical black stripes that can fade or darken depending on the mood of the fish.
 * Gold (g/g): The genetic trait for the gold angelfish is recessive, and causes a light golden body with a darker yellow or orange color on the crown of the fish. It does not have the vertical black stripes or the red eye seen in the wild angelfish.
 * Zebra (Z/+ or Z/Z): The zebra phenotype results in four to six vertical stripes on the fish that in other ways resembles a silver angelfish. It is a dominant mutation that exists at the same locus as the stripeless gene.
 * Black lace (D/+) or zebra lace (D/+ - Z/+): A silver or zebra with one copy of the dark gene results in very attractive lacing in the fins, considered by some to the most attractive of all angelfish varieties.
 * Smokey (Sm/+): A variety with a dark brownish grey back half and dark dorsal and anal fins
 * Chocolate (Sm/Sm): Homozygous for smokey with more of the dark pattern, sometimes only the head is silver

 * Halfblack (h/h): Silver with a black rear portion, halfblack can express along with some other color genes, but not all. The pattern may not develop or express if the fish are in stressful conditions.
 * Sunset blushing (g/g S/S): The sunset blushing has two genes of gold and two genes of stripeless. The upper half of the fish exhibits orange on the best specimens. The body is mostly white in color, and the fins are clear. The amount of orange showing on the fish can vary. On some, the body is a pinkish or tangerine color. The term blushing comes from the clear gill plates found on juveniles, with pinkish gills underneath.

 * Koi (Gm/Gm S/S) or (Gm/g S/S): The koi has a double or single gene of gold marble with a double gene of stripeless. Their expression of orange varies with stress levels. The black marbling varies from 5%-40% coverage.
 * Leopard (Sm/Sm Z/Z) or (Sm/Sm Z/+): Leopards are very popular fish when young, having spots over most of their bodies. Most of these spots grow closer together as adults, so they look like chocolates with dots.
 * Blue blushing (S/S): This wild-type angelfish has two stripeless genes. The body is actually grey with a bluish tint under the right light spectrum. An iridescent pigment develops as they age. This iridescence usually appears blue under most lighting.
 * Silver gold marble (Gm/+): A silver angel with a single gold marble gene, this is a co-dominant expression.
 * Ghost (S/+): Heterozygous for stripeless results in a mostly silver fish with just a stripe through the eye and tail. Sometimes, portions of the body stripes will express.
 * Gold marble (Gm/g or Gm/Gm)'''
 * Depending on whether the Gold Marble is single or double dose, the marbling will range from 5% to 40% coverage.

 * Marble (M/+ or M/M or M/g or M/Gm): Marble expresses with much more black pattern than gold marble. The marbling varies from 50% to 95%.
 * Black hybrid (D/g or D/Gm): A cross of black with a gold, the result is black hybrids, a very vigorous black that may look brassy when young. This cross does not breed true.

 * Pearlscale (p/p): Pearlscale is a scale mutation, also called the "diamond" angelfish in some regions due to the gem-like iridescence on its scales. The scales have a wrinkled, wavy look that reflects light to create a sparkling effect. Pearl develops slowly, starting at around 9 weeks of age. In can be inhibited by stressful conditions. It is recessive, requiring both parents to contribute the allele.
 * Black ghost (D/+ - S/+): Similar to a ghost, it has a darker appearance due to the dark gene, and very similar to a black lace without complete stripes. Ghosts generally have more iridescence than normal.
 * Albino (a/a): Albino removes dark pigments in most varieties. Some, like albino marble still have a little black remaining on a percentage of the fish. The eye pupils are pink as in all albino animals. The surrounding iris can be red or yellow depending on the variety.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Pterophyllum


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Nachman Syrkin

Nachman Syrkin (or Nahman Syrkin or Nahum Syrkin; Нахман Сыркин; 11 February 1868 – 6 September 1924) was a political theorist, founder of Labor Zionism and a prolific writer in the Hebrew, Yiddish, Russian, German and English languages.

Biography
Nachum Syrkin was born to a Lithuanian Jewish family in Mogilev, Russian Empire (now Belarus). He was influenced by Hovevei Zion and socialism in his youth and dedicated himself to synthesizing the two concepts. In this task he was joined by Ber Borochov. Syrkin's daughter Marie was a noted writer, educator and American Zionist activist.

Zionist career
Syrkin was one of the leaders of the socialist Zionist faction at the First Zionist Congress in 1897 and was an early proponent of the Jewish National Fund. He was also the first person to propose that olim to Palestine form collective settlements.

Unlike other socialist thinkers of the time, Syrkin was comfortable with his Jewish heritage and, although he does not spell it out explicitly in his essay "The Jewish Question and the Jewish Socialist State" (1898), it is clear that he had in mind the biblical emphasis on strict social justice, irrespective of wealth, power or privilege. However, he saw Zionism as a replacement for traditional Judaism: "The new, Zionist Judaism stands in complete contrast to the Judaism of exile … Zionism uproots religious Judaism in a stronger way than Reform or assimilation, by creating new standards of 'Judaism' which will constitute a new ideology that can be elevated to the status of a religion."In "The Jewish Question and the Socialist Jewish State," Syrkin sought to reconcile his conception of socialism and his strong devotion to Zionism, arguing against what he considered bourgeois Zionists, such as Theodor Herzl, that only the Jewish working class could realize Zionism. He also argued against anti-Zionist Jewish socialists that there could be no solution to the Jewish problem without the creation of a Jewish state.

Syrkin worked to establish socialist Zionist groups throughout Central Europe. After studying and working in Germany and France and after being banned from Germany in 1904, Syrkin returned to Russia after the Russian Revolution of 1905. He took part at the 1905 Basle Seventh Zionist Congress as a delegate of the new Zionist Socialist Workers Party.

In 1919, Syrkin was a member of the American Jewish delegation to the Versailles Peace Conference. He was also a leading figure in the World Poale Zion conference that year and was given the task of visiting Palestine to develop a plan for kibbutz settlement. He intended to relocate to Palestine, but died of a heart attack in 1924 in New York City.

Legacy
In 1951, his remains were buried in the Kibbutz Kinneret beside the other founders of Labour Zionism. Kfar Sirkin, founded in 1933 close to Petach Tikva, is named for him.

Published works (English)

 * Essays on socialist Zionism (New York, Young Poale Zion Alliance of America, 1935, 64p). Includes:
 * The Jewish Question and the Jewish Socialist State (1898)
 * National independence and international unity (1917)

title: Nachman Syrkin


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Münsterländer

Münsterländer may refer to:

 * A person from the German region of Münster
 * One of two breeds of dogs of the gun dog type originating in the Münster region of Germany:
 * Large Münsterländer, a breed of dog weighing approximately 30 kg (66 lbs)
 * Small Münsterländer, a breed of dog weighing approximately 16 kg (35 lbs)

title: Münsterländer


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Soundscape

A soundscape is the acoustic environment as perceived by humans, in context. The term was originally coined by Michael Southworth, and popularised by R. Murray Schafer. There is a varied history of the use of soundscape depending on discipline, ranging from urban design to wildlife ecology to computer science. An important distinction is to separate soundscape from the broader acoustic environment. The acoustic environment is the combination of all the acoustic resources, natural and artificial, within a given area as modified by the environment. The International Organization for Standardization (ISO) standardized these definitions in 2014. (ISO 12913-1:2014)

A soundscape is a sound or combination of sounds that forms or arises from an immersive environment. The study of soundscape is the subject of acoustic ecology or soundscape ecology. The idea of soundscape refers to both the natural acoustic environment, consisting of natural sounds, including animal vocalizations, the collective habitat expression of which is now referred to as the biophony, and, for instance, the sounds of weather and other natural elements, now referred to as the geophony; and environmental sounds created by humans, the anthropophony through a sub-set called controlled sound, such as musical composition, sound design, and language, work, and sounds of mechanical origin resulting from use of industrial technology. Crucially, the term soundscape also includes the listener's perception of sounds heard as an environment: "how that environment is understood by those living within it" and therefore mediates their relations. The disruption of these acoustic environments results in noise pollution.

The term "soundscape" can also refer to an audio recording or performance of sounds that create the sensation of experiencing a particular acoustic environment, or compositions created using the found sounds of an acoustic environment, either exclusively or in conjunction with musical performances.

Pauline Oliveros, composer of post-World War II electronic art music, defined the term "soundscape" as "All of the waveforms faithfully transmitted to our audio cortex by the ear and its mechanisms".

Historical context
The origin of the term soundscape is somewhat ambiguous. It is often miscredited as having been coined by Canadian composer and naturalist, R. Murray Schafer, who indeed led much of the groundbreaking work on the subject from the 1960s and onwards. According to an interview with Schafer published in 2013 Schafer himself attributes the term to city planner Michael Southworth. Southworth, a former student of Kevin Lynch, led a project in Boston in the 1960s, and reported the findings in a paper entitled "The Sonic Environment of Cities", in 1969, where the term is used.

Around the same time as Southworth's project in Boston, Schafer initiated the World Soundscape Project together with colleagues like Barry Truax and Hildegard Westerkamp. Schafer subsequently collected the findings from the world soundscape project and fleshed out the soundscape concept in more detail in his seminal work about the sound environment, "Tuning of the World". Schafer has also used the concept in music education.

In music
In music, soundscape compositions are often a form of electronic music, or electroacoustic music. Composers who use soundscapes include real-time granular synthesis pioneer Barry Truax, Hildegard Westerkamp, and Luc Ferrari, whose Presque rien, numéro 1 (1970) is an early soundscape composition. Soundscape composer Petri Kuljuntausta has created soundscape compositions from the sounds of sky dome and Aurora Borealis and deep sea underwater recordings, and a work entitled "Charm of Sound" to be performed at the extreme environment of Saturn's moon Titan. The work landed on the ground of Titan in 2005 after traveling inside the spacecraft Huygens over seven years and four billion kilometres through space.

Irv Teibel's Environments series (1969–79) consisted of 30-minute, uninterrupted environmental soundscapes and synthesized or processed versions of natural sound.

Music soundscapes can also be generated by automated software methods, such as the experimental TAPESTREA application, a framework for sound design and soundscape composition, and others.

The soundscape is often the subject of mimicry in timbre-centered music such as Tuvan throat singing. The process of Timbral Listening is used to interpret the timbre of the soundscape. This timbre is mimicked and reproduced using the voice or rich harmonic producing instruments.

The environment
In Schafer's analysis, there are two distinct soundscapes, "hi-fi" and "lo-fi", created by the environment. A hi-fi system possesses a positive signal-to-noise ratio. These settings make it possible for discrete sounds to be heard clearly since there is no background noise to obstruct even the smallest disturbance. A rural landscape offers more hi-fi frequencies than a city because the natural landscape creates an opportunity to hear incidences from nearby and afar. In a lo-fi soundscape, signals are obscured by too many sounds, and perspective is lost within the broad-band of noises. In lo-fi soundscapes everything is very close and compact. A person can only listen to immediate encounters; in most cases even ordinary sounds have to be exuberantly amplified in order to be heard.

All sounds are unique in nature. They occur at one time in one place and cannot be replicated. In fact, it is physically impossible for nature to reproduce any phoneme twice in exactly the same manner.

According to Schafer there are three main elements of the soundscape:

 * Keynote sounds

 * This is a musical term that identifies the key of a piece, not always audible ... the key might stray from the original, but it will return. The keynote sounds may not always be heard consciously, but they "outline the character of the people living there" (Schafer).  They are created by nature (geography and climate): wind, water, forests, plains, birds, insects, animals.  In many urban areas, traffic has become the keynote sound.

 * Sound signals

 * These are foreground sounds, which are listened to consciously; examples would be warning devices, bells, whistles, horns, sirens, etc.

 * Soundmark

 * This is derived from the term landmark. A soundmark is a sound which is unique to an area. In his 1977 book, The Soundscape: Our Sonic Environment and the Tuning of the World, Schafer wrote, "Once a Soundmark has been identified, it deserves to be protected, for soundmarks make the acoustic life of a community unique."

The elements have been further defined as to essential sources:

Bernie Krause, naturalist and soundscape ecologist, redefined the sources of sound in terms of their three main components: geophony, biophony, and anthropophony.

 * Geophony

 * Consisting of the prefix, geo (gr. earth), and phon (gr. sound), this refers to the soundscape sources that are generated by non-biological natural sources such as wind in the trees, water in a stream or waves at the ocean, and earth movement, the first sounds heard on earth by any sound-sentient organism.

 * Biophony

 * Consisting of the prefix, bio (gr. life) and the suffix for sound, this term refers to all of the non-human, non-domestic biological soundscape sources of sound.

 * Anthropophony

 * Consisting of the prefix, anthro (gr. human), this term refers to all of the sound signatures generated by humans.

In health care
Research has traditionally focused mostly on the negative effects of sound on human beings, as in exposure to environmental noise. Noise has been shown to correlate with health-related problems like stress, reduced sleep and cardiovascular disease. More recently however, it has also been shown that some sounds, like sounds of nature and music, can have positive effects on health,  some of which might be explained by natural sounds increasing cognitive restoration and feelings of calm, for example. While the negative effects of sound has been widely acknowledged by organizations like EU (END 2002/49) and WHO (Burden of noise disease), the positive effects have as yet received less attention. The positive effects of nature sounds can be acknowledged in everyday planning of urban and rural environments, as well as in specific health treatment situations, like nature-based sound therapy and nature-based rehabilitation.

Soundscapes from a computerized acoustic device with a camera may also offer synthetic vision to the blind, utilizing human echolocation, as is the goal of the seeing with sound project.

Soundscapes and noise pollution
Papers on noise pollution are increasingly taking a holistic, soundscape approach to noise control. Whereas acoustics tends to rely on lab measurements and individual acoustic characteristics of cars and so on, soundscape takes a top-down approach. Drawing on John Cage's ideas of the whole world as composition, soundscape researchers investigate people's attitudes to soundscapes as a whole rather than individual aspects – and look at how the entire environment can be changed to be more pleasing to the ear. This body of knowledge approaches the sonic environment subjectively as well, as in how some sounds are tolerated while others disdained, with still others preferred, as seen in Fong's 2016 research comparing the soundscapes of Bangkok, Thailand and Los Angeles, California. To respond to unwanted sounds, however, a typical application of this is the use of masking strategies, as in the use of water features to cover unwanted white noise from traffic. It has been shown that masking can work in some cases, but that the successful outcome is dependent on several factors, like sound pressure levels, orientation of the sources, and character of the water sound.

Research has shown that variation is an important factor to consider, as a varied soundscape give people the possibility to seek out their favorite environment depending on preference, mood and other factors. One way to ensure variation is to work with "quiet areas" in urban situations. It has been suggested that people's opportunity to access quiet, natural places in urban areas can be enhanced by improving the ecological quality of urban green spaces through targeted planning and design and that in turn has psychological benefits.

Soundscaping as a method to reducing noise pollution incorporates natural elements rather than just man made elements. Soundscapes can be designed by urban planners and landscape architects. By incorporating knowledge of soundscapes in their work, certain sounds can be enhanced, while others can be reduced or controlled. It has been argued that there are three main ways in which soundscapes can be designed: localization of functions, reduction of unwanted sounds and introduction of wanted sounds, each of which should be considered to ensure a comprehensive approach to soundscape design.

In United States National Parks
The National Park Service Natural Sounds and Night Skies Division actively protects the soundscapes and acoustic environments in national parks across the country. Acoustic resources are physical sound sources, including both natural sounds (wind, water, wildlife, vegetation) and cultural and historic sounds (battle reenactments, tribal ceremonies, quiet reverence). The acoustic environment is the combination of all the acoustic resources within a given area – natural sounds and human-caused sounds – as modified by the environment. The acoustic environment includes sound vibrations made by geological processes, biological activity, and even sounds that are inaudible to most humans, such as bat echolocation calls. Soundscape is the component of the acoustic environment that can be perceived and comprehended by the humans. The character and quality of the soundscape influence human perceptions of an area, providing a sense of place that differentiates it from other regions. Noise refers to sound which is unwanted, either because of its effects on humans and wildlife, or its interference with the perception or detection of other sounds. Cultural soundscapes include opportunities for appropriate transmission of cultural and historic sounds that are fundamental components of the purposes and values for which the parks were established.

title: Soundscape


text:
STS

STS, or sts, may refer to:

Medicine

 * Secondary traumatic stress, a condition which leads to a diminished ability to empathize
 * Sequence-tagged site, a gene-reference in genomics
 * Soft-tissue sarcoma
 * Staurosporine, an antibiotic
 * STS (gene), which codes for steroid sulfatase
 * Superior temporal sulcus
 * Sinus tarsi syndrome, a foot condition

Places

 * Semipalatinsk Test Site for Soviet nuclear weapons
 * Staffordshire, county in England, Chapman code

Transport

 * Cadillac STS, a luxury car
 * NASA Space Transportation System, the system in which the NASA shuttle is part of and only surviving component of; starting as a 1969 NASA proposal system for reusable space vehicles
 * NASA Space Shuttle program, the shuttle program itself, whose mission were referred to with STS-numbering
 * Sail training ship, a ship prefix
 * Satellite Transit System, now called the SEA Underground, airport transit in Seattle-Tacoma International Airport
 * Ship-to-ship transfer, between seagoing ships
 * Société de transport de Sherbrooke, a public bus system in Sherbrooke, Quebec, Canada
 * Société de transport du Saguenay, a public bus system in Saguenay, Quebec, Canada
 * Sonar Technician Submarine, a US Navy rating
 * STS, the IATA airport code for Charles M. Schulz - Sonoma County Airport
 * STS, the National Rail code for Saltash railway station, Cornwall, UK

Science and technology

 * Space Tourism Society
 * Scanning tunneling spectroscopy
 * Science and technology studies, a.k.a. science, technology, and society
 * Sociotechnical system
 * Special treatment steel, used by the US Navy c.1910
 * Static transfer switch, a semiconductor switch
 * STS 5 an Australopithecus specimen
 * Suomenkielisten teknikkojen seura, now incorporated into Academic Engineers and Architects in Finland TEK

Computing and communications

 * HTTP Strict Transport Security
 * Security token service, a web service
 * Set Transmit State, hex 93 in the C1 set of control codes
 * Spring Tool Suite, IDE for Spring Framework
 * Station-to-Station protocol, a cryptographic key agreement scheme
 * Synergy Teleconferencing System, a PC-based chat server
 * Serviciul de Telecomunicaţii Speciale, the Romanian special telecommunication service
 * STS Relay, US speech to speech relay service for people with a speech disability
 * STS (TV channel), Russia
 * Synchronous transport signal, in synchronous optical networking
 * Saga Television Station, a Japanese commercial broadcaster

Culture

 * Satanas, a Filipino-American gang
 * Stepover toehold sleeper, a wrestling hold
 * S.T.S. (band), an Austropop band

Societies, organizations and companies

 * Scottish Tartans Society, a defunct Scottish society
 * Sisu Terminal Systems, a former terminal tractor producer
 * Society of the Holy Trinity (Societas Trinitatis Sanctae – STS), Lutheran ministerium
 * Suomen Työväen Säästöpankki, a defunct Finnish commercial bank
 * Hitachi Rail STS, formerly known as Ansaldo STS, a company specializing in railway signalling and control systems

Other uses

 * Saints, the plural of Saint, for example: Sts. Peter and Paul
 * Short-term business statistics
 * Strathcona-Tweedsmuir School, Alberta, Canada
 * Susquehannock Trail System, Pennsylvania, US

title: STS


text:
Karl Ludwig Fernow

Karl Ludwig Fernow (19 November 1763 – 4 December 1808) was a German art critic and archaeologist.

Early life
Fernow was born in Pomerania, the son of a servant in the household of the lord of Blumenhagen. At the age of twelve he became clerk to a notary, and was afterwards apprenticed to a druggist. While serving his time he had the misfortune accidentally to shoot a young man who came to visit him; and although through the intercession of his master he escaped prosecution, the untoward event weighed heavily on his mind, and led him at the close of his apprenticeship to quit his native place.

Art career
He obtained a situation at Lübeck, where he had leisure to cultivate his natural taste for drawing and poetry. Having formed an acquaintance with the painter Asmus Jacob Carstens, whose influence was an important stimulus and help to him, he renounced his trade of druggist, and set up as a portrait-painter and drawing-master. At Ludwigslust he fell in love with a young girl, and followed her to Weimar; but failing in his suit, he went next to Jena. There he was introduced to Professor Reinhold, and in his house met the Danish poet Jens Immanuel Baggesen. The latter invited him to accompany him to Switzerland and Italy, a proposal which in 1794 he eagerly accepted for the sake of the opportunity of furthering his studies in the fine arts. On Baggesen's return to Denmark, Fernow, assisted by some of his friends, visited Rome and made some stay there. He now renewed his intercourse with Carstens, who had settled at Rome, and applied himself to the study of the history and theory of the fine arts and of the Italian language and literature. Fernow's critiques and opinions have been questioned and poorly received due to his lack of formal qualification. His personal attacks on artists are thought to reflect his own lack of artistic talent and insight. Fernow self-proclaimed to have made rapid progress, he was soon semi-qualified to give a course of lectures on archaeology, which was attended by the principal artists then at Rome. Having married a Roman lady, he returned in 1802 to Germany, and was appointed in the following year professor extraordinary of Italian literature at Jena.

Librarian
In 1804, he accepted the post of librarian to Amalia, Dowager Duchess of Weimar, which gave him the leisure he desired for the purpose of turning to account the literary and archaeological researches in which he had engaged at Rome. Fernow died in 1808 at Weimar, where he is buried in the Jacobsfriedhof.

Works and biography
His most valuable work, the Romische Studien, appeared in 3 volumes between 1806 and 1808. Among his other works are Das Leben des Kunstlers Carstens (1806), Ariostos Lebenslauf (1809), and Francesco Petrarca (1818).

A memoir of his life by Johanna Schopenhauer, mother of the philosopher, Arthur Schopenhauer, appeared in 1810, and a complete edition of his works in 1829.

title: Karl Ludwig Fernow


text:
Quantum Zeno effect

The quantum Zeno effect (also known as the Turing paradox) is a feature of quantum-mechanical systems allowing a particle's time evolution to be slowed down by measuring it frequently enough with respect to some chosen measurement setting.

Sometimes this effect is interpreted as "a system cannot change while you are watching it". One can "freeze" the evolution of the system by measuring it frequently enough in its known initial state. The meaning of the term has since expanded, leading to a more technical definition, in which time evolution can be suppressed not only by measurement: the quantum Zeno effect is the suppression of unitary time evolution in quantum systems provided by a variety of sources: measurement, interactions with the environment, stochastic fields, among other factors. As an outgrowth of study of the quantum Zeno effect, it has become clear that applying a series of sufficiently strong and fast pulses with appropriate symmetry can also decouple a system from its decohering environment.

The first rigorous and general derivation of the quantum Zeno effect was presented in 1974 by Degasperis, Fonda, and Ghirardi, although it had previously been described by Alan Turing. The comparison with Zeno's paradox is due to a 1977 article by Baidyanath Misra & E. C. George Sudarshan.The name comes by analogy to Zeno's arrow paradox, which states that because an arrow in flight is not seen to move during any single instant, it cannot possibly be moving at all. In the quantum Zeno effect an unstable state seems frozen – to not 'move' – due to a constant series of observations.

According to the reduction postulate, each measurement causes the wavefunction to collapse to an eigenstate of the measurement basis. In the context of this effect, an observation can simply be the absorption of a particle, without the need of an observer in any conventional sense. However, there is controversy over the interpretation of the effect, sometimes referred to as the "measurement problem" in traversing the interface between microscopic and macroscopic objects.

Another crucial problem related to the effect is strictly connected to the time–energy indeterminacy relation (part of the indeterminacy principle). If one wants to make the measurement process more and more frequent, one has to correspondingly decrease the time duration of the measurement itself. But the request that the measurement last only a very short time implies that the energy spread of the state in which reduction occurs becomes increasingly large. However, the deviations from the exponential decay law for small times is crucially related to the inverse of the energy spread, so that the region in which the deviations are appreciable shrinks when one makes the measurement process duration shorter and shorter. An explicit evaluation of these two competing requests shows that it is inappropriate, without taking into account this basic fact, to deal with the actual occurrence and emergence of Zeno's effect.

Closely related (and sometimes not distinguished from the quantum Zeno effect) is the watchdog effect, in which the time evolution of a system is affected by its continuous coupling to the environment.

Description
Unstable quantum systems are predicted to exhibit a short-time deviation from the exponential decay law. This universal phenomenon has led to the prediction that frequent measurements during this nonexponential period could inhibit decay of the system, one form of the quantum Zeno effect. Subsequently, it was predicted that measurements applied more slowly could also enhance decay rates, a phenomenon known as the quantum anti-Zeno effect.

In quantum mechanics, the interaction mentioned is called "measurement" because its result can be interpreted in terms of classical mechanics. Frequent measurement prohibits the transition. It can be a transition of a particle from one half-space to another (which could be used for an atomic mirror in an atomic nanoscope ) as in the time-of-arrival problem, a transition of a photon in a waveguide from one mode to another, and it can be a transition of an atom from one quantum state to another. It can be a transition from the subspace without decoherent loss of a qubit to a state with a qubit lost in a quantum computer. In this sense, for the qubit correction, it is sufficient to determine whether the decoherence has already occurred or not. All these can be considered as applications of the Zeno effect. By its nature, the effect appears only in systems with distinguishable quantum states, and hence is inapplicable to classical phenomena and macroscopic bodies.

The mathematician Robin Gandy recalled Turing's formulation of the quantum Zeno effect in a letter to fellow mathematician Max Newman, shortly after Turing's death:

As a result of Turing's suggestion, the quantum Zeno effect is also sometimes known as the Turing paradox. The idea is implicit in the early work of John von Neumann on the mathematical foundations of quantum mechanics, and in particular the rule sometimes called the reduction postulate. It was later shown that the quantum Zeno effect of a single system is equivalent to the indetermination of the quantum state of a single system.

Various realizations and general definition
The treatment of the Zeno effect as a paradox is not limited to the processes of quantum decay. In general, the term Zeno effect is applied to various transitions, and sometimes these transitions may be very different from a mere "decay" (whether exponential or non-exponential).

One realization refers to the observation of an object (Zeno's arrow, or any quantum particle) as it leaves some region of space. In the 20th century, the trapping (confinement) of a particle in some region by its observation outside the region was considered as nonsensical, indicating some non-completeness of quantum mechanics. Even as late as 2001, confinement by absorption was considered as a paradox. Later, similar effects of the suppression of Raman scattering was considered an expected effect, not a paradox at all. The absorption of a photon at some wavelength, the release of a photon (for example one that has escaped from some mode of a fiber), or even the relaxation of a particle as it enters some region, are all processes that can be interpreted as measurement. Such a measurement suppresses the transition, and is called the Zeno effect in the scientific literature.

In order to cover all of these phenomena (including the original effect of suppression of quantum decay), the Zeno effect can be defined as a class of phenomena in which some transition is suppressed by an interaction – one that allows the interpretation of the resulting state in the terms 'transition did not yet happen' and 'transition has already occurred', or 'The proposition that the evolution of a quantum system is halted' if the state of the system is continuously measured by a macroscopic device to check whether the system is still in its initial state.

Periodic measurement of a quantum system
Consider a system in a state $$A$$, which is the eigenstate of some measurement operator. Say the system under free time evolution will decay with a certain probability into state $$B$$. If measurements are made periodically, with some finite interval between each one, at each measurement, the wave function collapses to an eigenstate of the measurement operator. Between the measurements, the system evolves away from this eigenstate into a superposition state of the states $$A$$ and $$B$$. When the superposition state is measured, it will again collapse, either back into state $$A$$ as in the first measurement, or away into state $$B$$. However, its probability of collapsing into state $$B$$ after a very short amount of time $$t$$ is proportional to $$t^2$$, since probabilities are proportional to squared amplitudes, and amplitudes behave linearly. Thus, in the limit of a large number of short intervals, with a measurement at the end of every interval, the probability of making the transition to $$B$$ goes to zero.

According to decoherence theory, the collapse of the wave function is not a discrete, instantaneous event. A "measurement" is equivalent to strongly coupling the quantum system to the noisy thermal environment for a brief period of time, and continuous strong coupling is equivalent to frequent "measurement". The time it takes for the wave function to "collapse" is related to the decoherence time of the system when coupled to the environment. The stronger the coupling is, and the shorter the decoherence time, the faster it will collapse. So in the decoherence picture, a perfect implementation of the quantum Zeno effect corresponds to the limit where a quantum system is continuously coupled to the environment, and where that coupling is infinitely strong, and where the "environment" is an infinitely large source of thermal randomness.

Experiments and discussion
Experimentally, strong suppression of the evolution of a quantum system due to environmental coupling has been observed in a number of microscopic systems.

In 1989, David J. Wineland and his group at NIST observed the quantum Zeno effect for a two-level atomic system that was interrogated during its evolution. Approximately 5,000 ^{9}Be+ ions were stored in a cylindrical Penning trap and laser-cooled to below 250 mK. A resonant RF pulse was applied, which, if applied alone, would cause the entire ground-state population to migrate into an excited state. After the pulse was applied, the ions were monitored for photons emitted due to relaxation. The ion trap was then regularly "measured" by applying a sequence of ultraviolet pulses during the RF pulse. As expected, the ultraviolet pulses suppressed the evolution of the system into the excited state. The results were in good agreement with theoretical models.

In 2001, Mark G. Raizen and his group at the University of Texas at Austin observed the quantum Zeno effect for an unstable quantum system, as originally proposed by Sudarshan and Misra. They also observed an anti-Zeno effect. Ultracold sodium atoms were trapped in an accelerating optical lattice, and the loss due to tunneling was measured. The evolution was interrupted by reducing the acceleration, thereby stopping quantum tunneling. The group observed suppression or enhancement of the decay rate, depending on the regime of measurement.

In 2015, Mukund Vengalattore and his group at Cornell University demonstrated a quantum Zeno effect as the modulation of the rate of quantum tunnelling in an ultracold lattice gas by the intensity of light used to image the atoms.

The quantum Zeno effect is used in commercial atomic magnetometers and proposed to be part of birds' magnetic compass sensory mechanism (magnetoreception).

It is still an open question how closely one can approach the limit of an infinite number of interrogations due to the Heisenberg uncertainty involved in shorter measurement times. It has been shown, however, that measurements performed at a finite frequency can yield arbitrarily strong Zeno effects. In 2006, Streed et al. at MIT observed the dependence of the Zeno effect on measurement pulse characteristics.

The interpretation of experiments in terms of the "Zeno effect" helps describe the origin of a phenomenon. Nevertheless, such an interpretation does not bring any principally new features not described with the Schrödinger equation of the quantum system.

Even more, the detailed description of experiments with the "Zeno effect", especially at the limit of high frequency of measurements (high efficiency of suppression of transition, or high reflectivity of a ridged mirror) usually do not behave as expected for an idealized measurement.

It was shown that the quantum Zeno effect persists in the many-worlds and relative-states interpretations of quantum mechanics.

title: Quantum Zeno effect


text:
Conversion to Judaism

Conversion to Judaism (גִּיּוּר or גֵּרוּת) is the process by which non-Jews adopt the Jewish religion and become members of the Jewish ethnoreligious community. It thus resembles both conversion to other religions and naturalization. The procedure and requirements for conversion depend on the sponsoring denomination. Furthermore, a conversion done in accordance with one Jewish denomination is not a guarantee of recognition by another denomination. Normally, though not always, the conversions performed by more stringent denominations are recognized by less stringent ones, but not the other way around. A formal conversion is also sometimes undertaken by individuals whose Jewish ancestry is questioned or uncertain, even if they were raised Jewish, but may not actually be considered Jews according to traditional Jewish law.

There are some groups that have adopted Jewish customs and practices. For example, in Russia the Subbotniks have adopted most aspects of Judaism without formal conversion to Judaism. However, if Subbotniks, or anyone without a formal conversion, wish to marry into a traditional Jewish community or immigrate to Israel under the Law of Return, they must have a formal conversion.

According to Israel Bartal, then dean of the humanities faculty of the Hebrew University, "conversions to Judaism had a major impact on Jewish history in the ancient period and in the early Middle Ages".

Terminology
The word ger comes from the Hebrew verb  meaning "to reside" or "to sojourn [with]". In the Hebrew Bible ger is defined as a "foreigner", or "sojourner". Rabbi Marc Angel writes: "The Hebrew ger (in post-Biblical times translated as "proselyte") literally means "resident" and refers to a non-Israelite who lived among the Israelite community. When the Torah commands compassion and equal justice for the ger, it is referring to these "residents". Rabbinic tradition interpreted the word ger as referring to proselytes...""

Angel's explanation of the literal meaning of "ger" as alien is borne out in biblical verses such as : "The stranger that sojourneth with you shall be unto you as the home-born among you, and thou shalt love him as thyself; for ye were strangers in the land of Egypt: I am the LORD your God."

Another verse which has been interpreted as referring to non-Jews converting to Judaism is Esther 8:17, although no process is described. .

The word is rendered by the Greek "proselyte" as used in the Septuagint to denote a "stranger". A formal male convert to Judaism is referred to by the Hebrew word ' (גר, plural גרים ') and a formal female convert is a giyoret. In all branches of Judaism, a ger or giyoret is considered a full Jew; the literal meaning of "stranger", "resident", or "foreigner" refers to the convert's origin, not present status. In Karaite Judaism the term  only refers to a non-Jew who has yet to fully convert to Judaism, and once converted to Karaitism, is no longer called ger.

In the Talmud, ger is used in two senses: ger tzedek refers to a "righteous convert", a proselyte to Judaism, and ger toshav, a non-Jewish inhabitant of the Land of Israel who observes the Seven Laws of Noah and has repudiated all links with idolatry. In Modern Hebrew, the unqualified term ger means ger tzedek.

Overview
According to Maimonides (Isurei Biah 13:14), converts were accepted since the beginning of Jewish history, and the foreign wives of Jewish leaders—such as Samson and Solomon—were converts. Yet he says (Isurei Biah 13:15), that in the times of Jewish political power, such as the days of Kings David and Solomon, batei din (Jewish courts) did not accept converts who may have not had the right intention, and they had to wait and prove their intentions to be legally accepted.

With the notable exception of some Syrian Jewish communities (primarily the Brooklyn, New York, and Deal, New Jersey communities), all mainstream forms of Judaism today are open to sincere converts, with all denominations accepting converts converted by their denominations. The rules vary between denominations, as does acceptance of some denominations' converts by other denominations.

For Rabbinic Judaism, the laws governing conversion (gerut) are based on codes of law and texts, including discussions in the Talmud, through the Shulkhan Arukh and subsequent interpretations. (Many of the guidelines of accepting converts are based on the Book of Ruth and the manner whereby Ruth was brought into the fold through her mother-in-law, Naomi). These rules are held as authoritative by Orthodox Judaism and Conservative Judaism.

Within Orthodoxy it is commonly understood that Halacha somewhat discourages proselytizing, and religious gerut is somewhat discouraged. The majority of rabbis reject potential converts three times, and if the potential convert remains adamant in their desire to convert, the rabbi will then allow them to begin the process. These practices do not have any solid basis in the written text, and while they may have been the practice in some locations, it was not universal, and a number of rabbis have not followed these practices.

In order to convert, the conversion candidate must have a circumcision (if male) and immerse in the mikveh before a kosher beth din, comprising three Jewish males who are shomer Shabbat. There is also a requirement to accept the Jewish commandments (although not necessarily a commitment to keep them).

Today, the process has become more centralized, with the conversion candidate having to convince a rabbi and the beth din of their sincerity, and there will usually be a considerable amount of study. In addition to studying, potential converts are typically expected to become involved in the Jewish community. This includes attending services, participating in holidays and rituals, and building relationships with other Jews in the community. They will then be tested and formally accepted, the convert is issued with a Shtar geirut ("Certificate of Conversion"). As the conversion process becomes more centralized there are only a limited number of permanent conversion courts that are acceptable to the Chief Rabbinate of Israel.

However, there are a number of rabbis who are willing to conduct decentralized conversions, and are recognized by each other. Two of the more prominent of these rabbis are Chuck Davidson and Haim Amsalem.

Conservative Judaism takes a more lenient approach to the halakhic rules than Modern Orthodox Judaism. Its approach to the validity of conversions is based on whether the conversion procedure followed rabbinic norms, rather than the reliability of those performing it or the nature of the obligations the convert undertook. Accordingly, it may accept the validity of some Reform and Reconstructionist conversions, but only if they include immersion in a ritual bath (mikvah), appearance before a rabbinical court (beit din) and, for men, circumcision (brit milah) or a symbolic circumcision for those already circumcised (hatafat dam brit).

The requirements of Reform Judaism for conversions are extremely different, and far more lenient. The denomination states that "people considering conversion are expected to study Jewish theology, rituals, history, culture and customs, and to begin incorporating Jewish practices into their lives. The length and format of the course of study will vary from rabbi to rabbi and community to community, though most now require a course in basic Judaism and individual study with a rabbi, as well as attendance at services and participation in home practice and synagogue life."

Although an infant conversion might be accepted in some circumstances (such as in the case of adopted children or children whose parents convert), children who convert would typically be asked if they want to remain Jewish after reaching religious adulthood – which is 12 years of age for a girl and 13 for a boy. This standard is applied by Orthodox and Conservative Judaism, which accept halakha as binding.

Reconstructionist Judaism values the symbolism of the conversion ritual, and encourages those who were not born of Jewish parents and who wish to convert to undergo this rite of passage. The Reconstructionist course of study for a prospective convert, which is determined by the rabbi and congregation the individual is working with, includes history, observance and beliefs, and learning how to make educated choices. The completion of the process is marked by ritual immersion for men and women; circumcision or hatafat dam brit (symbolic drop of blood) for men (unless there exists an extraordinary physical or emotional hazard); a valid Bet Din (a dialogue with three knowledgeable Jews, at least one of whom is a rabbi), and often a public welcoming ceremony.

Karaite Judaism does not accept the Talmud and therefore has different requirements for conversion. Traditionally non-proselytizing, Karaite Judaism's long standing abstention from conversions was recently lifted. On 1 August 2007, the Karaites reportedly converted their first new members in 500 years. At a ceremony in their Northern California synagogue, ten adults and four minors swore fealty to Judaism after completing a year of study. This conversion comes 15 years after the Karaite Council of Sages reversed its centuries-old ban on accepting converts.

Humanistic Judaism postulates that "conversion" does not suit the process of becoming a Jew, as it implies a change in belief, which is not chosen like behavioral changes. The shift is better described as naturalization, affiliation, or adoption, reflecting alterations in family ties and cultural aspirations rather than fundamental belief changes.

In ancient times
Louis Feldman's views on active Jewish missionizing have changed. While viewing classical Judaism as being receptive to converts, especially from the second century BC through the first century AD, he points to a lack of either missionizing tracts or records of the names of rabbis who sought converts as evidence for the lack of active Jewish missionizing. Feldman maintains that conversion to Judaism was common and the Jewish population was large both within the Land of Israel and in the Diaspora. Other historians believe that conversion during the Roman era was limited in number and did not account for much of the Jewish population growth, due to various factors such as the illegality of male conversion to Judaism in the Roman world from the mid-second century. Another factor that made conversion difficult in the Roman world was the halakhic requirement of circumcision, a requirement that proselytizing Christianity quickly dropped. The Fiscus Judaicus, a tax imposed on Jews in 70 AD and relaxed to exclude Christians in 96 AD, also limited Judaism's appeal.

Early debate on requirement for circumcision
According to The Jewish Encyclopedia article on circumcision of proselytes, in the first century AD, before the Mishnah was edited, the requirement for circumcision of proselytes was an open issue between the Zealots and liberal parties in ancient Israel. Joshua ben Hananiah argued that besides accepting Jewish beliefs and laws, a prospective convert to Judaism must undergo immersion in a mikveh. In contrast, Eliezer ben Hurcanus makes circumcision a condition for the conversion. A similar controversy between the Shammaites and the Hillelites is given regarding a proselyte born without a foreskin: the former demanding the spilling of a drop of blood symbolic of the Brit Milah, thereby entering into the covenant; the latter declaring it to be unnecessary.

In discussions about the necessity of circumcision for those born of a Jewish mother, lending some support to the need for circumcision of converts, the Midrash states: "If thy sons accept My Godhead [by undergoing circumcision] I shall be their God and bring them into the land; but if they do not observe My covenant in regard either to circumcision or to the Sabbath, they shall not enter the land of promise" (Midrash Genesis Rabbah xlvi). "The Sabbath-keepers who are not circumcised are intruders, and deserve punishment" (Midrash Deut. Rabbah i).

However, the opposing view is supported in the Babylonian Talmud by Joshua ben Hananiah: "A male convert who has been immersed but not circumcised, or circumcised but not immersed, is a convert." Note this view is later rejected by the Talmud.

Josephus in Antiquities of the Jews, Book 20 Chapter 2, recorded the story of King Izates of Adiabene who decided to follow the Law of Moses at the advice of a Jewish merchant named Ananias. He was going to get circumcised, but his mother, Helen, who herself embraced the Jewish customs, advised against it on the grounds that the subjects would not stand to be ruled by someone who followed such "strange and foreign rites". Ananias likewise advised against it, on the grounds that worship of God was superior to circumcision (Robert Eisenman in James the Brother of Jesus claims that Ananias is Paul the Apostle, who held similar views, although this is a novel interpretation lacking support in mainstream scholarship) and that God would forgive him for fear of his subjects. So Izates decided against it. However, later, "a certain other Jew that came out of Galilee, whose name was Eleazar," who was well versed in the Law, convinced him that he should, on the grounds that it was one thing to read the Law and another thing to practice it, and so he did. Once Helen and Ananias found out, they were struck by great fear of the possible consequences, but as Josephus put it, God looked after Izates. As his reign was peaceful and blessed, Helen visited the Second Temple to thank God, and since there was a terrible famine at the time, she brought much food and aid to the people of Jerusalem.

Requirements
The Amoraim who produced the Talmud set out basic requirements for conversion to Judaism (Keritot 8b), which must be witnessed and affirmed by a beth din (a rabbinical court composed of three Jewish males above the age of Bar Mitzvah). The judges on the Beth Din should be observant of Jewish law. Common Orthodox practice is for all of the judges to be Rabbis or Orthodox clergy. Today conversion requirements and the time required to complete conversion differ according to denomination and rabbinic sponsor. The basic requirements set out in the Talmud include:

 * Circumcision (Brit milah or hatafat dam brit) for men. If the male is already circumcised, a single drop of blood is drawn as a symbolic circumcision
 * Immersion (tevilah) in a ritual bath (mikveh) for both men and women
 * Offering a certain sacrifice (korban) in the Temple (the Beit Hamikdash) – (this is not currently required as a part of modern conversion to Judaism. )
 * Offering a certain sacrifice (korban) in the Temple (the Beit Hamikdash) – (this is not currently required as a part of modern conversion to Judaism. )

The consensus of halakhic authorities also requires a convert to understand and formally accept the duties of classical Jewish law. This is not stated explicitly in the Talmud, but was inferred by subsequent commentators.

After confirming that all these requirements have been met, the beth din issues a "Certificate of Conversion" (Shtar Giur), certifying that the person is now a Jew.

Modern practice
The requirements for conversions vary somewhat within the different branches of Judaism, so whether or not a conversion is recognized by another denomination is often an issue fraught with religious politics. The Orthodox rejection of non-Orthodox conversions is derived less from qualms with the conversion process itself, since Conservative and even some Reform conversions are very similar to Orthodox conversions with respect to duration and content, but rather from that the Orthodox presumption that convert was not properly instructed in Jewish Law to Orthodox Jewish standards.

In general, immersion in the mikveh is an important part of a traditional conversion. If the person who is converting is male, circumcision is a part of the traditional conversion process as well. If the male who is converting has already been circumcised, then a ritual removal of a single drop of blood will take place (hatafat dam brit). However, more liberal branches of Judaism have a more relaxed requirement of immersion and circumcision.

Maturity
Someone who converts as a minor (younger than 12 for a girl and 13 for a boy) is required to fulfill the requirements of conversion, that is circumcision and mikvah, but are not required to perform an 'acceptance of the mitzvoth'. The conversion instead is done al daat beth din, i.e. the acceptance is done by the Beth Din presiding over the conversion. The child lives as a Jew until their bar/bat mitzvah and they then have the option of rejecting their conversion. Once they have accepted to continue as a Jew the conversion can no longer be rejected.

Reform Jewish views
In the United States, Reform Judaism rejects the concept that any rules or rituals should be considered necessary for conversion to Judaism. In the late 19th century, the Central Conference of American Rabbis, the official body of American Reform rabbis, formally resolved to permit the admission of converts "without any initiatory rite, ceremony, or observance whatsoever." (CCAR Yearbook 3 (1893), 73–95; American Reform Responsa (ARR), no. 68, at 236–237.)

Although this resolution has often been examined critically by many Reform rabbis, the resolution still remains the official policy of American Reform Judaism (CCAR Responsa "Circumcision for an Eight-Year-Old Convert" 5756.13 and Solomon Freehof, Reform Responsa for Our Time, no. 15.) Thus, American Reform Judaism does not require ritual immersion in a mikveh, circumcision, or acceptance of mitzvot as normative. Appearance before a Beth Din is recommended, but is not considered necessary. Converts are asked to commit to religious standards set by the local Reform community.

In actual practice, the requirements for conversion of any individual are determined by the Rabbi who sponsors the convert. Typically, Reform Rabbis require prospective converts to take a course of study in Judaism, such as an "Introduction to Judaism" course, to participate in worship at a synagogue, and to live as a Jew (however that is interpreted by the individual Rabbi) for a period of time. A period of one year is common, although individual Rabbis' requirements vary. When the sponsoring Rabbi feels that the candidate is ready, a Beth Din may be convened. Other rituals such as immersion in a mikvah, circumcision (or Hatafat dam brit), and a public ceremony to celebrate the conversion, are also at the discretion of the Rabbi.

Interdenominational views
In response to the tremendous variations that exist within the Reform community, the Conservative Jewish movement attempted to set a nuanced approach. The Conservative Committee on Jewish Law and Standards has issued a legal opinion stating that Reform conversions may be accepted as valid only when they include the minimal Conservative halachic requirements of milah and t'vilah, appearance before a Conservative Beth Din, and a course of Conservative study. (Proceedings of Committee on Jewish Law and Standards: 1980–1985, pp. 77–101.)

In general, branches of Orthodox Judaism consider non-Orthodox conversions either inadequate or of questionable halachic compliance, and such conversions are therefore not accepted by these branches of Judaism. Conversely, both Conservative and Reform Judaism accept the Orthodox conversion process as being valid. Since 2008, Haredi Orthodox religious courts in Israel have been rejecting conversions from a number of Orthodox rabbis, since the Chief Rabbinate do not accept the authority of the presiding rabbis.

Intra-Orthodox controversy
In 2008, a Haredi-dominated Badatz in Israel annulled thousands of conversions performed by the Military Rabbinate in Israel. The Chief Rabbinate of Israel, which is the only state-recognized authority on religious matters, backed by Rabbi Ovadia Yosef, ruled against this, making the annulment legally invalid for purposes of Israeli law.

Karaite views
As of 2006, the Moetzet Hakhamim (Council of Sages) began to accept converts to Karaite Judaism through the Karaite Jewish University. The process requires one year of learning, circumcision (for males), and the taking of the vow that Ruth took:

"For whither thou goest, I will go; and where thou lodgest, I will lodge; thy people shall be my people, and thy God my God; where thou diest, will I die, and there will I be buried; the do so to me, and more also, if aught but death part thee and me."

1950s: proposed joint beth din
In the 1950s Rabbi Joseph Soloveitchik and other members of the Rabbinical Council of America engaged in a series of private negotiations with the leaders of Conservative Judaism's Rabbinical Assembly, including Saul Lieberman; their goal was to create a joint Orthodox-Conservative national beth din for all Jews in the United States. It would create communal standards of marriage and divorce. It was to be modeled after the Israeli Chief Rabbinate, where all the judges would have been Orthodox, while it would have been accepted by the larger Conservative movement as legitimate. Conservative rabbis in the Rabbinical Assembly created a Joint Conference on Jewish Law, devoting a year to this effort.

For a number of reasons, the project did not succeed. According to Orthodox Rabbi Louis Bernstein, the major reason for its failure was the Orthodox rabbis' insistence that the Conservative Rabbinical Assembly agree to expel Conservative rabbis for actions they took prior to the formation of the new beth din, and the RA refused to do so. According to Orthodox Rabbi Emanuel Rackman, former president of the RCA, the major reason for its failure was pressure from haredi Orthodox rabbis, who held that any cooperation between Orthodoxy and Conservatism was forbidden. In 1956, Rabbi Harry Halpern, of the Joint Conference wrote a report on the demise of this beth din. He writes that negotiations between the Orthodox and Conservative denominations were completed and agreed upon, but then a new requirement was demanded by the RCA: The RA must "impose severe sanctions" upon Conservative rabbis for actions they took before this new beth din was formed. Halpern writes that the RA "could not assent to rigorously disciplining our members at the behest of an outside group." He goes on to write that although subsequent efforts were made to cooperate with the Orthodox, a letter from eleven Rosh Yeshivas was circulated declaring that Orthodox rabbis are forbidden to cooperate with Conservative rabbis.

1978–1983: Denver program, patrilineal descent
In Denver, Colorado, a joint Orthodox, Traditional, Conservative and Reform Bet Din was formed to promote uniform standards for conversion to Judaism. A number of rabbis were Orthodox and had semicha from Orthodox yeshivas, but were serving in synagogues without a mechitza; these synagogues were called traditional Judaism. Over a five-year period they performed some 750 conversions to Judaism. However, in 1983 the joint Beth Din was dissolved, due to the unilateral American Reform Jewish decision to change the definition of Jewishness:

"The move was precipitated by the resolution on patrilineality adopted that year by the Central Conference of American Rabbis. This decision to redefine Jewish identity, as well as the designation of Denver as a pilot community for a new Reform out reach effort to recruit converts, convinced the Traditional and Conservative rabbis that they could no longer participate in the joint board...the national decision of the Reform rabbinate placed the Traditional and Conservative rabbis in an untenable position. They could not cooperate in a conversion program with rabbis who held so different a conception of Jewish identity. And furthermore, they could not supervise conversions that would occur with increasing frequency due to a Reform outreach effort that was inconsistent with their own understanding of how to relate to potential proselytes."

- Wertheimer

Specifically, in 1983, the Central Conference of American Rabbis passed a resolution waiving the need for formal conversion for anyone with at least one Jewish parent who has made affirmative acts of Jewish identity. This departed from the traditional position requiring formal conversion to Judaism for children without a Jewish mother. The 1983 resolution of the American Reform movement has had a mixed reception in Reform Jewish communities outside of the United States. Most notably, the Israel Movement for Progressive Judaism has rejected patrilineal descent and requires formal conversion for anyone without a Jewish mother. However, in 2015 the majority of Britain's Assembly of Reform Rabbis voted in favor of a position paper proposing "that individuals who live a Jewish life, and who are patrilineally Jewish, can be welcomed into the Jewish community and confirmed as Jewish through an individual process." Britain's Assembly of Reform Rabbis stated that rabbis "would be able to take local decisions – ratified by the Beit Din – confirming Jewish status."

The end of the joint Beth Din program was welcomed by Haredi Orthodox groups, who saw the program as illegitimate. Further, Haredi groups attempted to prevent non-Orthodox rabbis from following the traditional requirements of converts using a mikveh. In the Haredi view, it is better to have no conversion at all than a non-Orthodox conversion, as all non-Orthodox conversions are not true conversions at all according to them.

1980s: proposed Israeli joint beth din
In the 1980s Modern Orthodox Rabbi Norman Lamm, Rosh Yeshiva of Yeshiva University, along with other American and Israeli Orthodox rabbis, worked with Conservative and Reform rabbis to come up with solution to the "Who is a Jew?" issue. In 1989 and 1990 Israeli Prime Minister Yitzhak Shamir spearheaded an effort to find a way to resolve the impasse.

A plan was developed by Israeli Cabinet Secretary Elyakim Rubenstein, who negotiated secretly for many months with rabbis from Conservative, Reform and Orthodox Judaism, including faculty at Yeshiva University, with Lamm as Rosh Yeshiva. They were planning to create a joint panel that interviewed people who were converting to Judaism and considering making aliyah (moving to the State of Israel), and would refer them to a beth din that would convert the candidate following traditional halakha. All negotiating parties came to agreement:
 * 1) Conversions must be carried out according to halakha
 * 2) the beth din (rabbinic court) overseeing the conversion would be Orthodox, perhaps appointed by the Chief Rabbinate of Israel, and
 * 3) there would be three-way dialogue throughout the process.

Many Reform rabbis took offense at the notion that the beth din must be strictly halakhic and Orthodox, but they acquiesced. However, when word about this project became public, a number of leading haredi rabbis issued a statement denouncing the project, condemning it as a "travesty of halakha". Rabbi Moshe Sherer, Chairman of Agudath Israel World Organization, stated that "Yes we played a role in putting an end to that farce, and I'm proud we did." Norman Lamm condemned this interference by Sherer, stating that this was "the most damaging thing that he [Sherer] ever did in his forty year career."

Rabbi Lamm wanted this to be only the beginning of a solution to Jewish disunity. He stated that had this unified conversion plan not been destroyed, he wanted to extend this program to the area of halakhic Jewish divorces, thus ending the problem of mamzerut.

1997: Neeman Commission proposal
In 1997 the issue of "Who is a Jew?" again arose in the State of Israel, and Orthodox leaders such as Rabbi Norman Lamm publicly backed the Neeman commission, a group of Orthodox, Conservative and Reform rabbis working to develop joint programs for conversion to Judaism. In 1997 Lamm gave a speech at the World Council of Orthodox Leadership, in Glen Springs, New York, urging Orthodox Jews to support this effort:

"Lamm told his listeners that they should value and encourage the efforts of non-Orthodox leaders to more seriously integrate traditional Jewish practices into the lives of their followers. They should welcome the creation of Reform and Conservative day schools and not see them as a threat to their own, Lamm said. In many communities, Orthodox day schools, or Orthodox-oriented community day schools, have large numbers of students from non-Orthodox families. The liberal movements should be appreciated and encouraged because they are doing something Jewish, even if it is not the way that Orthodox Jews would like them to, he said. "What they are doing is something, and something is better than nothing," he said in his speech. "I'm very openly attacking the notion that we sometimes find in the Orthodox community that 'being a goy is better than being a non-Orthodox Jew, he said in an interview." The committee recommended the establishment of a joint institute for Jewish studies, which would be a joint effort by all three streams of Judaism. The committee also recommended that conversion proceedings themselves be held in special conversion courts, to be recognized by all denominations in Judaism. The purpose of the proposal was to prevent a rift in the Jewish people, while at the same time bringing about a state-sponsored arrangement for conversion. On 7 September 1998, the government adopted the Ne'eman Commission Report.

A year later, the Joint Institute for Jewish Studies was established, and since then it has been the official state operator of conversion courses in Israel, including the military conversion courses. In 2015 the institute's name was changed to Nativ – The National Center for Jewish Studies, Identity and Conversion.

Conversion annulments
A recent development has been the idea of annulling conversions to Judaism, sometimes many years after they have taken place, due to a reduction in religious observance or change of community by the convert. Chuck Davidson, a Modern Orthodox expert on this conversion crisis explains "From the Middle Ages onwards, the greatest of the rabbis wrote explicitly that even if immediately after the conversion the convert goes off to worship idols, the person is still considered Jewish." The justification given for the change in approach is that the original conversion must never have been valid in the first place as it is clear from the convert's subsequent actions they were insincere at the time of conversion.

A situation of confusion in Jewish identity in Israel was made worse when Haredi Rabbi Avraham Sherman of Israel's supreme religious court (בית הדין הרבני הגדול) called into question the validity of over 40,000 Jewish conversions when he upheld a ruling by the Ashdod Rabbinical Court to retroactively annul the conversion of a woman who came before them because in their eyes she failed to observe Jewish law.

This crisis deepened, when Israel's Rabbinate called into question the validity of soldiers who had undergone conversion in the army, meaning a soldier killed in action could not be buried according to Jewish law. In 2010, the rabbinate created a further distrust in the conversion process when it began refusing to recognize orthodox converts from the United States as Jewish. Indeed, the great-niece of the renowned Zionist Nahum Sokolow was recently deemed "not Jewish enough" to marry in Israel, after she failed to prove the matrilineal Jewish descent for four generations.

Following a scandal in which U.S. Rabbi Barry Freundel was arrested on charges of installing hidden cameras in a mikveh to film women converts undressing, the Israeli Chief Rabbinate said it would review the validity of all past conversions performed by Freundel, then quickly reversed its decision, clarifying that it was joining the Orthodox Rabbinical Council of America in affirming the validity of the conversions.

In December 2014 an Israeli court decided that a conversion could be annulled. In his decision Justice Neal Hendel wrote: "Just as the civil court has the inalienable authority to reverse – in extremely rare cases – a final judgment, so too does the special religious conversion court. For otherwise, we would allow for judgments that are flawed from their inception to exist eternally."

Consequences
Once undergone, a valid religious conversion to Judaism cannot be overturned. However, a Beth Din may determine that the conversion is void as it was never undertaken correctly in the first place. For example, if the rite of mikveh was performed incorrectly. In recent years, many Orthodox conversions have been overturned. In 2008 Israel's highest religious court invalidated the conversion of 40,000 Jews, mostly from Russian immigrant families, even though they had been approved by an Orthodox rabbi. Debate on what constitutes a valid Beth Din for conversion and for annulling conversions has caused divisions in the Orthodox world. It is an implicit judgment on the character and uprightness of the rabbis in that religious court. For example, when Rabbi Barry Freundel was arrested on charges of voyeurism for filming women converts at the mikveh he supervised, Israel's Chief Rabbinate initially threatened to review and possibly invalidate the conversions Freundel had been involved in approving. A crisis between American and Israeli rabbis was averted when the Chief Rabbinate agreed that all conversions completed by Freundel would be considered valid.

Relations between Jews and proselytes
Judaism is not an openly proselytizing religion. Judaism teaches that the righteous of all nations have a place in the afterlife. Much like in the other Abrahamic faiths, Jewish law requires the sincerity of a potential convert. In view of the foregoing considerations, most authorities are very careful about it. Essentially, they want to be sure that the convert knows what they are getting into, and that they are doing it for sincerely religious reasons. However, while conversion for the sake of love for Judaism is considered the best motivation, a conversion for the sake of avoiding intermarriage is gaining acceptance also.

There is a tradition that a prospective convert should be turned away three times as a test of sincerity, though most rabbis no longer follow the tradition. Neither the Rabbinical Council of America nor the Rabbinical Assembly, the leading American Orthodox and Conservative organizations, suggest taking this action in their conversion policies, with the Central Conference of American Rabbis (CCAR) and Union for Reform Judaism (URJ) actively opposing its practice.

Halakhic considerations
Halakha forbids the mistreatment of a convert, including reminding a convert that they were once not a Jew. Hence, little to no distinction is made in Judaism between those who are born Jewish and those who are Jewish as a result of conversion. However, despite Halakha protecting the rights of converts, some Jewish communities have been accused of treating converts as second-class Jews. For example, many communities of Syrian Jews have banned conversion and refuse to recognise any Jewish conversion, including those done under Orthodox auspices (possibly influenced by sects in Syria like the Druze which do not accept converts).

According to Orthodox interpretations of Halakha, converts face a limited number of restrictions. A marriage between a female convert and a kohen (members of the priestly class) is prohibited and any children of the union do not inherit their father's kohen status. While a Jew by birth may not marry a mamzer, a convert can. Descendants of converts can become rabbis. For instance, Rabbi Meir Baal Ha Nes is thought to be a descendant of a proselyte. Rabbi Akiva was also a very well-known son of converts. The Talmud lists many of the Jewish nation's greatest individuals who had either descended from or were themselves converts. Asenath, the wife of Joseph (son of Jacob), is mentioned as a possible convert. There are Midrash attesting to her conversion along with other women. This includes Hagar, Zipporah, Shiphrah, Puah, the Daughter Of Pharaoh, Rahab, Ruth, and Jael. In fact, King David is descended from Ruth, a convert to Judaism. In Orthodox and Conservative communities that maintain tribal distinctions, converts become Yisraelim (Israelites), ordinary Jews with no tribal or inter-Jewish distinctions. Converts typically follow the customs of their congregations. So, a convert who prays at a Sephardi synagogue would follow Sephardi customs and learn Sephardi Hebrew.

A convert chooses his or her own Hebrew first name upon conversion but is traditionally known as the son or daughter of Abraham and Sarah, the first patriarch and matriarch in the Torah, often with the additional qualifier of "Avinu" (our father) and "Imenu" (our mother). Hence, a convert named Akiva would be known, for ritual purposes in a synagogue, as "Akiva ben Avraham Avinu"; in cases where the mother's name is used, such as for the prayer for recovery from an illness, he would be known as "Akiva ben Sarah Imenu".

Talmudic opinions on converts are numerous; some positive, some negative. A quote from the Talmud labels the convert "hard on Israel as a scab". Many interpretations explain this quote as meaning converts can be unobservant and lead Jews to be unobservant or converts can be so observant that born Jews feel ashamed.

Jews by choice
The term "Jews by choice" is often used to describe people who chose to convert to Judaism, many of whom have no ancestral connection to the Jewish people. It is often contrasted with such terms as "Jew by birth" (or "Jew by chance"). The practice of conversion to Judaism is sometimes understood within Orthodox Judaism in terms of reincarnation. According to this school of thought in Judaism, when non-Jews are drawn to Judaism, it is because they had been Jews in a former life. Such souls may "wander among nations" through multiple lives, until they find their way back to Judaism, including through finding themselves born in a gentile family with a "lost" Jewish ancestor.

Bnei Anusim
In recent decades, there has been a renewed Jewish conversion interest with some Bnei Anusim, that is, the descendants of Jews who were forced to convert to other faiths.

The Hebrew term for forced converts is "Anusim" (lit. "forced [converts]"), while the descendants of said converts are called "Bnei Anusim" (lit. "children of forced [converts]").

In the modern era, the single most notable and numerous group of Bnei Anusim converts are the Sephardic Bnei Anusim, descendants of those Sephardic Jews who were forced to convert to Christianity during the Spanish and Portuguese Inquisition. They are found throughout Iberia (Spain and Portugal) and Iberoamerica (the Hispanic countries of the Americas plus Brazil). There has been a continuous steady growth among them who are now prospective converts, actively seeking conversions back to Judaism.

Since many Bnei Anusim (i.e. descendants of forced converts) lack an unbroken matrilineal Jewish line of descent or lack satisfactory documentary evidence to that effect (even if they can prove Jewish ancestry along one or all other of their lineages besides their direct matrilineal lineage), conversion has been a growing option for them to return to Judaism.

title: Conversion to Judaism