Game Theory (album)

Game Theory is the seventh studio album by American hip-hop band the Roots, released August 29, 2006, on Def Jam Recordings. The group's first release for the label after leaving Geffen Records, the album was recorded by the Roots mostly using the Apple-developed software application GarageBand. A darker, grittier album with minimal emphasis on hooks in comparison to their previous work, Game Theory features a stripped-down sound similar to the work of Public Enemy, with lyrics that concern sociological themes and the late hip-hop producer J Dilla.
The album debuted at number nine on the U.S. Billboard 200 chart, selling 61,000 copies in its first week. It produced two singles and achieved moderate sales success. Upon its release, Game Theory received acclaim from most music critics and earned a Grammy Award nomination for Best Rap Album. To date, the album has sold over 200,000 copies in the United States.


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Annihilation

In particle physics, annihilation is the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons. The total energy and momentum of the initial pair are conserved in the process and distributed among a set of other particles in the final state. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of such an original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy, conservation of momentum, and conservation of spin are obeyed.
During a low-energy annihilation, photon production is favored, since these particles have no mass. High-energy particle colliders produce annihilations where a wide variety of exotic heavy particles are created.
The word "annihilation" takes its use informally for the interaction of two particles that are not mutual antiparticles –  not charge conjugate. Some quantum numbers may then not sum to zero in the initial state, but conserve with the same totals in the final state. An example is the "annihilation" of a high-energy electron antineutrino with an electron to produce a W− boson.
If the annihilating particles are composite, such as mesons or baryons, then multiple different particles are typically produced in the final state.
The inverse of annihilation is pair production, the process in which a high-energy photon converts its energy into mass.


Boson

In particle physics, a boson ( ) is a subatomic particle whose spin quantum number has an integer value (0, 1, 2, ...). The class of bosons is one of the two fundamental classes of subatomic particle, the other being fermions, which have half odd-integer spin (1/2, 3/2, 5/2, ...). Every observed subatomic particle is either a boson or a fermion. Paul Dirac coined the term boson to classify the fundamental particles that obey Bose–Einstein statistics, the quantum framework pioneered by Satyendra Nath Bose.
Some bosons are elementary particles occupying a special role in particle physics, distinct from the role of fermions (which are sometimes described as the constituents of "ordinary matter"). Certain elementary bosons (e.g. gluons) act as force carriers, which give rise to forces between other particles, while one (the Higgs boson) contributes to the phenomenon of mass. Other bosons, such as mesons, are composite particles made up of smaller constituents.
Outside the realm of particle physics, multiple identical composite bosons behave at high densities or low temperatures in a characteristic manner described by Bose–Einstein statistics: for example, a gas of helium-4 atoms becomes a superfluid at temperatures close to absolute zero. Similarly, superconductivity arises because some quasiparticles, such as Cooper pairs, behave in this characteristic manner.


CERN

The European Organization for Nuclear Research, also called European Laboratory for Particle Physics, known as CERN (; French pronunciation: [sɛʁn]; Organisation européenne pour la recherche nucléaire), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, a western suburb of Geneva, on the France–Switzerland border. It comprises 25 member states. Israel, admitted in 2013, is the only full member geographically out of Europe. CERN is an official United Nations General Assembly observer.
The acronym CERN is also used to refer to the laboratory; in 2024, it had 2,704 scientific, technical, and administrative staff members, and hosted about 12,406 users from institutions in more than 80 countries. In 2016, CERN generated 49 petabytes of data.
CERN's main function is to provide the particle accelerators and other infrastructure needed for high-energy physics research – consequently, numerous experiments have been constructed at CERN through international collaborations. CERN is the site of the Large Hadron Collider (LHC), the world's largest and highest-energy particle collider. The main site at Meyrin hosts a large computing facility, which is primarily used to store and analyze data from experiments, as well as simulate events. As researchers require remote access to these facilities, the lab has historically been a major wide area network hub. CERN is also the birthplace of the World Wide Web.


Calorimeter (particle physics)

In experimental particle physics, a calorimeter is a type of detector that measures the energy of particles.  Particles enter the calorimeter and initiate a particle shower  in which their energy is deposited in the calorimeter, collected, and measured. The energy may be measured in its entirety, requiring total containment of the particle shower, or it may be sampled. Typically, calorimeters are segmented transversely to provide information about the direction of the particle or particles, as well as the energy deposited, and longitudinal segmentation can provide information about the identity of the particle based on the shape of the shower as it develops. Calorimetry design is an active area of research in particle physics.


Cross section (physics)

In physics, the cross section is a measure related to the probability that a specific process will take place in a collision of two particles.  For example, the Rutherford cross section is a measure of probability that an alpha particle will be deflected by a given angle during an interaction with an atomic nucleus. Cross section is typically denoted σ (sigma) and has dimension of area, with units of square meter or more often in barns. In a way, it can be thought of as the size of the object that the excitation must hit in order for the process to occur, but more exactly, it is a parameter of a stochastic process.
When two discrete particles interact in classical physics, their mutual cross section is the area transverse to their relative motion within which they must meet in order to scatter from each other. If the particles are hard hard spheres that interact only upon contact, their scattering cross section is related to their geometric size. If the particles interact through some action-at-a-distance force, such as electromagnetism or gravity, their scattering cross section is generally larger than their geometric size.
When a cross section is specified as the differential limit of a function of some final-state variable, such as particle angle or energy, it is called a differential cross section (see detailed discussion below). When a cross section is integrated over all scattering angles (and possibly other variables), it is called a total cross section or integrated total cross section. For example, in Rayleigh scattering, the intensity scattered at the forward and backward angles is greater than the intensity scattered sideways, so the forward differential scattering cross section is greater than the perpendicular differential cross section, and by adding all of the infinitesimal cross sections over the whole range of angles with integral calculus, we can find the total cross section.
Scattering cross sections may be defined in nuclear, atomic, and particle physics for collisions of accelerated beams of one type of particle with targets (either stationary or moving) of a second type of particle. The probability for any given reaction to occur is in proportion to its cross section. Thus, specifying the cross section for a given reaction is a proxy for stating the probability that a given scattering process will occur.
The measured reaction rate of a given process depends strongly on experimental variables such as the density of the target material, the intensity of the beam, the detection efficiency of the apparatus, or the angle setting of the detection apparatus. However, these quantities can be factored away, allowing measurement of the underlying two-particle collisional cross section.
Differential and total scattering cross sections are among the most important measurable quantities in nuclear, atomic, and particle physics.
With light scattering off of a particle, the cross section specifies the amount of optical power scattered from light of a given irradiance (power per area). Although the cross section has the same units as area, the cross section may not necessarily correspond to the actual physical size of the target given by other forms of measurement. It is not uncommon for the actual cross-sectional area of a scattering object to be much larger or smaller than the cross section relative to some physical process. For example, plasmonic nanoparticles can have light scattering cross sections for particular frequencies that are much larger than their actual cross-sectional areas.

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Desert (particle physics)

In the Grand Unified Theory of particle physics (GUT), the desert refers to a theorized gap in energy scales, between approximately the electroweak energy scale–conventionally defined as roughly the vacuum expectation value or VEV of the Higgs field (about 246 GeV)–and the GUT scale, in which no known interactions appear.
It can also be described as a gap in the lengths involved, with no new physics below 10−18 m (the currently probed length scale) and above 10−31 m (the GUT length scale).
The idea of the desert was motivated by the observation of approximate, order of magnitude, gauge coupling unification at the GUT scale. When the values of the gauge coupling constants of the weak nuclear, strong nuclear, and electromagnetic forces are plotted as a function of energy, the 3 values appear to nearly converge to a common single value at very high energies. This was one theoretical motivation for Grand Unified Theories themselves, and adding new interactions at any intermediate energy scale generally disrupts this gauge coupling unification. The disruption arises from the new quantum fields- the new forces and particles- which introduce new coupling constants and new interactions that modify the existing Standard Model coupling constants at higher energies. The fact that the convergence in the Standard Model is actually inexact, however, is one of the key theoretical arguments against the Desert, since making the unification exact requires new physics below the GUT scale.


Don Lincoln

Don Lincoln (born 1964) is an American physicist, author, host of the YouTube channel Fermilab, and science communicator. He conducts research in particle physics at Fermi National Accelerator Laboratory, and was an adjunct professor of physics at the University of Notre Dame, although he is no longer affiliated with the university. He received a Ph.D. in experimental particle physics from Rice University in 1994. In 1995, he was a co-discoverer of the top quark. He has co-authored hundreds of research papers, and more recently, was a member of the team that discovered the Higgs boson in 2012.


Elementary particle

In the Standard Model of particle physics, an elementary particle or fundamental particle is a  subatomic particle that is not composed of other particles. The Standard Model recognizes seventeen distinct particles—twelve fermions and five bosons. As a consequence of flavor and color combinations and antimatter, the fermions and bosons are known to have 48 and 13 variations, respectively. These 61 elementary particles include electrons and other leptons, quarks, and the fundamental bosons. Subatomic particles such as protons or neutrons, which contain two or more elementary particles, are known as composite particles.

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European Strategy for Particle Physics

The European Strategy for Particle Physics is a prioritisation of European ambitions to advance particle physics science for the long-term future and is the cornerstone of Europe's decision-making process in the field. The European Strategy is mandated by the CERN Council, and is formed through a broad consultation of the grass-roots particle physics community. The opinions of physicists from around the world are actively solicited and the European Strategy is developed in close coordination with similar processes in the US and Japan in order to ensure coordination and optimal use of resources globally.
The European Strategy takes into account the worldwide particle physics landscape and developments in related fields, and was initiated by the CERN Council to coordinate activities across a large, international and fast-moving community with the aim to maximise scientific returns.
The CERN Council began discussions in 2005 that led to the European Strategy's first document being adopted in 2006. The Large Hadron Collider (LHC) was cited as the top scientific priority of European particle physics with a discussion of a possible significant luminosity upgrade. Other priorities included research and development of future accelerators, coordination with a potential International Linear Collider, and participation in a global neutrino program.
An update to the original European Strategy was prepared in 2012 and formally adopted in 2013 following the discovery of the Higgs boson.
Input from the particle physics community for the next update was requested to be submitted by 18 December 2018. This update for the decade of the 2020s was adopted in June 2020.


Fermion

In particle physics, a fermion is a subatomic particle that follows Fermi–Dirac statistics. Fermions have a half-integer spin (spin 1/2, spin 3/2, etc.) and obey the Pauli exclusion principle. These particles include all quarks and leptons and all composite particles made of an odd number of these, such as all baryons and many atoms and nuclei. Fermions differ from bosons, which obey Bose–Einstein statistics.
Some fermions are elementary particles (such as electrons), and some are composite particles (such as protons). For example, according to the spin-statistics theorem in relativistic quantum field theory, particles with integer spin are bosons. In contrast, particles with half-integer spin are fermions.
In addition to the spin characteristic, fermions have another specific property: they possess conserved baryon or lepton quantum numbers. Therefore, what is usually referred to as the spin-statistics relation is, in fact, a spin statistics-quantum number relation.
As a consequence of the Pauli exclusion principle, only one fermion can occupy a particular quantum state at a given time. Suppose multiple fermions have the same spatial probability distribution, then, at least one property of each fermion, such as its spin, must be different. Fermions are usually associated with matter, whereas bosons are generally force carrier particles. However, in the current state of particle physics, the distinction between the two concepts is unclear. Weakly interacting fermions can also display bosonic behavior under extreme conditions. For example, at low temperatures, fermions show superfluidity for uncharged particles and superconductivity for charged particles.
Composite fermions, such as protons and neutrons, are the key building blocks of everyday matter.
English theoretical physicist Paul Dirac coined the name fermion from the surname of Italian physicist Enrico Fermi.

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Flavour (particle physics)

In particle physics, flavour or flavor refers to the species of an elementary particle. The Standard Model counts six flavours of quarks and six flavours of leptons. They are conventionally parameterized with flavour quantum numbers that are assigned to all subatomic particles. They can also be described by some of the family symmetries proposed for the quark-lepton generations.


Generation (particle physics)

In particle physics, a generation or family is a division of the elementary particles. Between generations, particles differ by their flavour quantum number and mass, but their electric and strong interactions are identical.
There are three generations according to the Standard Model of particle physics. Each generation contains two types of leptons and two types of quarks. The two leptons may be classified into one with electric charge −1 (electron-like) and neutral (neutrino); the two quarks may be classified into one with charge −1⁄3 (down-type) and one with charge +2⁄3 (up-type). The basic features of quark–lepton generation or families, such as their masses and mixings etc., can be described by some of the proposed family symmetries.


Hadron

In particle physics, a hadron is a composite subatomic particle made of two or more quarks that are held together by the strong nuclear force. Pronounced  , the name is derived from Ancient Greek  ἁδρός (hadrós) 'stout, thick'. They are analogous to molecules, which are held together by the electromagnetic force. Most of the mass of ordinary matter comes from two hadrons: the proton and the neutron, while most of the mass of the protons and neutrons is in turn due to the binding energy of their constituent quarks, due to the strong force.
Hadrons are categorized into two broad families: baryons, made of an odd number of quarks (usually three), and mesons, made of an even number of quarks (usually two: one quark and one antiquark). Protons and neutrons (which make the majority of the mass of an atom) are examples of baryons; pions are an example of a meson. A tetraquark state (an exotic meson), named the Z(4430)−, was discovered in 2007 by the Belle Collaboration and confirmed as a resonance in 2014 by the LHCb collaboration. Two pentaquark states (exotic baryons), named P+c(4380) and P+c(4450), were discovered in 2015 by the LHCb collaboration. There are several other "Exotic" hadron candidates and other colour-singlet quark combinations that may also exist.
Almost all "free" hadrons and antihadrons (meaning, in isolation and not bound within an atomic nucleus) are believed to be unstable and eventually decay into other particles. The only known possible exception is free protons, which appear to be stable, or at least, take immense amounts of time to decay (order of 1034+ years). By way of comparison, free neutrons are the longest-lived unstable particle, and decay with a half-life of about 611 seconds, and have a mean lifetime of 879 seconds (see Free neutron decay).
Hadron physics is studied by colliding hadrons, e.g. protons, with each other or the nuclei of dense, heavy elements, such as lead (Pb) or gold (Au), and detecting the debris in the produced particle showers. A similar process occurs in the natural environment, in the extreme upper-atmosphere, where muons and mesons such as pions are produced by the collisions of cosmic rays with rarefied gas particles in the outer atmosphere.

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Helicity (particle physics)

In physics, helicity is the projection of the spin onto the direction of momentum.
Mathematically, helicity is the sign of the projection of the spin vector onto the momentum vector: "left" is negative, "right" is positive. Thus, it can be represented with the operator

                      p

                    ^

              ⋅

                      Σ

                    ^

                |

                      p

                    ^

                |

    {\displaystyle {\frac {{\hat {\mathbf {p} }}\cdot {\hat {\mathbf {\Sigma } }}}{|{\hat {\mathbf {p} }}|}}}

, where

                p

              ^

    {\displaystyle {\hat {\mathbf {p} }}}

 is the momentum operator and

                Σ

              ^

    {\displaystyle {\hat {\mathbf {\Sigma } }}}

 is the spin operator.


Higgs boson

The Higgs boson, sometimes called the Higgs particle, is an elementary particle in the Standard Model of particle physics produced by the quantum excitation of the Higgs field, one of the fields in particle physics theory. In the Standard Model, the Higgs particle is a massive scalar boson that couples to (interacts with) particles whose mass arises from their interactions with the Higgs field, has zero spin, even (positive) parity, no electric charge, and no color charge. It is also very unstable, decaying into other particles almost immediately upon generation.
The Higgs field is a scalar field with two neutral and two electrically charged components that form a complex doublet of the weak isospin SU(2) symmetry. Its "sombrero potential" leads it to take a nonzero value everywhere (including otherwise empty space), which breaks the weak isospin symmetry of the electroweak interaction and, via the Higgs mechanism, gives a rest mass to all massive elementary particles of the Standard Model, including the Higgs boson itself. The existence of the Higgs field became the last unverified part of the Standard Model of particle physics, and for several decades was considered "the central problem in particle physics".
Both the field and the boson are named after physicist Peter Higgs, who in 1964, along with five other scientists in three teams, proposed the Higgs mechanism, a way for some particles to acquire mass. All fundamental particles known at the time should be massless at very high energies, but fully explaining how some particles gain mass at lower energies had been extremely difficult. If these ideas were correct, a particle known as a scalar boson (with certain properties) should also exist. This particle was called the Higgs boson and could be used to test whether the Higgs field was the correct explanation.
After a 40-year search, a subatomic particle with the expected properties was discovered in 2012 by the ATLAS and CMS experiments at the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland. The new particle was subsequently confirmed to match the expected properties of a Higgs boson. Physicists from two of the three teams, Peter Higgs and François Englert, were awarded the Nobel Prize in Physics in 2013 for their theoretical predictions. Although Higgs's name has come to be associated with this theory, several researchers between about 1960 and 1972 independently developed different parts of it.
In the media, the Higgs boson has often been called the "God particle" after the 1993 book The God Particle by Nobel Laureate Leon M. Lederman. The name has been criticised by physicists, including Peter Higgs.


History of subatomic physics

The idea that matter consists of smaller particles and that there exists a limited number of sorts of primary, smallest particles in nature has existed in natural philosophy at least since the 6th century BC. Such ideas gained physical credibility beginning in the 19th century, but the concept of "elementary particle" underwent some changes in its meaning: notably, modern physics no longer deems elementary particles indestructible. Even elementary particles can decay or collide destructively; they can cease to exist and create (other) particles in result.
Increasingly small particles have been discovered and researched: they include molecules, which are constructed of atoms, that in turn consist of subatomic particles, namely atomic nuclei and electrons. Many more types of subatomic particles have been found. Most such particles (but not electrons) were eventually found to be composed of even smaller particles such as quarks. Particle physics studies these smallest particles; nuclear physics studies atomic nuclei and their (immediate) constituents: protons and neutrons.


Jet (particle physics)

A jet is a narrow cone of hadrons and other particles produced by the hadronization of quarks and gluons in a particle physics or heavy ion experiment. Particles carrying a color charge, i.e. quarks and gluons, cannot exist in free form because of quantum chromodynamics (QCD) confinement which only allows for colorless states. When protons collide at high energies, their color charged components each carry away some of the color charge. In accordance with confinement, these fragments create other colored objects around them to form colorless hadrons. The ensemble of these objects is called a jet, since the fragments all tend to travel in the same direction, forming a narrow "jet" of particles. Jets are measured in particle detectors and studied in order to determine the properties of the original quarks.
A jet definition includes a jet algorithm and a recombination scheme. The former defines how some inputs, e.g. particles or detector objects, are grouped into jets, while the latter specifies how a momentum is assigned to a jet. For example, jets can be characterized by the thrust. The jet direction (jet axis) can be defined as the thrust axis. In particle physics experiments, jets are usually built from clusters of energy depositions in the detector calorimeter. When studying simulated processes, the calorimeter jets can be reconstructed based on a simulated detector response. However, in simulated samples, jets can also be reconstructed directly from stable particles emerging from fragmentation processes. Particle-level jets are often referred to as truth-jets. A good jet algorithm usually allows for obtaining similar sets of jets at different levels in the event evolution. Typical jet reconstruction algorithms are, e.g., the anti-kT algorithm, kT algorithm, cone algorithm. A typical recombination scheme is the E-scheme, or 4-vector scheme, in which the 4-vector of a jet is defined as the sum of 4-vectors of all its constituents.
In relativistic heavy ion physics, jets are important because the originating hard scattering is a natural probe for the QCD matter created in the collision, and indicate its phase. When the QCD matter undergoes a phase crossover into quark gluon plasma, the energy loss in the medium grows significantly, effectively quenching (reducing the intensity of) the outgoing jet.
Example of jet analysis techniques are:

jet correlation
flavor tagging (e.g., b-tagging)
jet substructure.
The Lund string model is an example of a jet fragmentation model.


Large Hadron Collider

The Large Hadron Collider (LHC)  is the world's largest and highest-energy particle accelerator. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008, in collaboration with over 10,000 scientists, and hundreds of universities and laboratories across more than 100 countries. It lies in a tunnel 27 kilometres (17 mi) in circumference and as deep as 175 metres (574 ft) beneath the France–Switzerland border near Geneva.
The first collisions were achieved in 2010 at an energy of 3.5 tera-electronvolts (TeV) per beam, about four times the previous world record. The discovery of the Higgs boson at the LHC was announced in 2012. Between 2013 and 2015, the LHC was shut down and upgraded; after those upgrades it reached 6.5 TeV per beam (13.0 TeV total collision energy). At the end of 2018, it was shut down for maintenance and further upgrades, and reopened over three years later in April 2022.
The collider has four crossing points where the accelerated particles collide. Nine detectors, each designed to detect different phenomena, are positioned around the crossing points. The LHC primarily collides proton beams, but it can also accelerate beams of heavy ions, such as in lead–lead collisions and proton–lead collisions.
The LHC's goal is to allow physicists to test the predictions of different theories of particle physics, including measuring the properties of the Higgs boson, searching for the large family of new particles predicted by supersymmetric theories, and studying other unresolved questions in particle physics.


Linear particle accelerator

A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of oscillating electric potentials along a linear beamline. The principles for such machines were proposed by Gustav Ising in 1924, while the first machine that worked was constructed by Rolf Widerøe in 1928 at the RWTH Aachen University.
Linacs have many applications: they generate X-rays and high energy electrons for medicinal purposes in radiation therapy, serve as particle injectors for higher-energy accelerators, and are used directly to achieve the highest kinetic energy for light particles (electrons and positrons) for particle physics.
The design of a linac depends on the type of particle that is being accelerated: electrons, protons or ions. Linacs range in size from a cathode-ray tube (which is a type of linac) to the 3.2-kilometre-long (2.0 mi) linac at the SLAC National Accelerator Laboratory in Menlo Park, California.


List of accelerators in particle physics

A list of particle accelerators used for particle physics experiments. Some early particle accelerators that more properly did nuclear physics, but existed prior to the separation of particle physics from that field, are also included. Although a modern accelerator complex usually has several stages of accelerators, only accelerators whose output has been used directly for experiments are listed.


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17th century in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science.  This article records significant discoveries and events related to paleontology that occurred or were published in the 17th century.


1821 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1821.


1830 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1830.


1862 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1862.


1889 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1889.


18th century in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science.  This article records significant discoveries and events related to paleontology that occurred or were published in the 18th century.


1962 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1962.


1979 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1979.


1987 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1987.


1994 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1994.


2001 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2001.


2002 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2002.


2006 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2006.


2007 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2007.


2008 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2008.


2009 in archosaur paleontology

The year 2009 in archosaur paleontology was eventful.  Archosaurs include the only living dinosaur group — birds — and the reptile crocodilians, plus all extinct dinosaurs,  extinct crocodilian relatives, and pterosaurs. Archosaur paleontology is the scientific study of those animals, especially as they existed before the Holocene Epoch began about 11,700 years ago.  The year 2009 in paleontology included various significant developments regarding archosaurs.
This article records new taxa of fossil archosaurs of every kind that have been described during the year 2009, as well as other significant discoveries and events related to paleontology of archosaurs that occurred in the year 2009.


2010 in archosaur paleontology

The year 2010 in archosaur paleontology was eventful.  Archosaurs include the only living dinosaur group — birds — and the reptile crocodilians, plus all extinct dinosaurs,  extinct crocodilian relatives, and pterosaurs. Archosaur palaeontology is the scientific study of those animals, especially as they existed before the Holocene Epoch began about 11,700 years ago.  The year 2010 in paleontology included various significant developments regarding archosaurs.
This article records new taxa of fossil archosaurs of every kind that have been described during the year 2010, as well as other significant discoveries and events related to paleontology of archosaurs that occurred in the year 2010.


2010 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2010.


2013 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2013.


2014 in archosaur paleontology

This article records new taxa of fossil archosaurs of every kind that are scheduled described during the year 2014, as well as other significant discoveries and events related to paleontology of archosaurs that are scheduled to occur in the year 2014.


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Moscow Paleontological Museum

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Adaptive immune system

The adaptive immune system (AIS), also known as the acquired immune system or specific immune system, is a subsystem of the immune system that is composed of specialized cells, organs, and processes that eliminate pathogens specifically. The acquired immune system is one of the two main immunity strategies found in vertebrates (the other being the innate immune system).
Like the innate system, the adaptive immune system includes both humoral immunity components and cell-mediated immunity components and destroys invading pathogens. Unlike the innate immune system, which is pre-programmed to react to common broad categories of pathogen, the adaptive immune system is highly specific to each particular pathogen the body has encountered.
Adaptive immunity creates immunological memory after an initial response to a specific pathogen, and leads to an enhanced response to future encounters with that pathogen. Antibodies are a critical part of the adaptive immune system. Adaptive immunity can provide long-lasting protection, sometimes for the person's entire lifetime. For example, someone who recovers from measles is now protected against measles for their lifetime; in other cases it does not provide lifetime protection, as with chickenpox. This process of adaptive immunity is the basis of vaccination.
The cells that carry out the adaptive immune response are white blood cells known as lymphocytes. B cells and T cells, two different types of lymphocytes, carry out the main activities: antibody responses, and cell-mediated immune response. In antibody responses, B cells are activated to secrete antibodies, which are proteins also known as immunoglobulins. Antibodies travel through the bloodstream and bind to the foreign antigen causing it to inactivate, which does not allow the antigen to bind to the host. Antigens are any substances that elicit the adaptive immune response. Sometimes the adaptive system is unable to distinguish harmful from harmless foreign molecules; the effects of this may be hayfever, asthma, or any other allergy.
In adaptive immunity, pathogen-specific receptors are "acquired" during the lifetime of the organism (whereas in innate immunity pathogen-specific receptors are already encoded in the genome). This acquired response is called "adaptive" because it prepares the body's immune system for future challenges (though it can actually also be maladaptive when it results in allergies or autoimmunity).
The system is highly adaptable because of two factors. First, somatic hypermutation is a process of accelerated random genetic mutations in the antibody-coding genes, which allows antibodies with novel specificity to be created. Second, V(D)J recombination randomly selects one variable (V), one diversity (D),
and one joining (J) region for genetic recombination and discards the rest, which produces a highly unique combination of antigen-receptor gene segments in each lymphocyte. This mechanism allows a small number of genetic segments to generate a vast number of different antigen receptors, which are then uniquely expressed on each individual lymphocyte. Since the gene rearrangement leads to an irreversible change in the DNA of each cell, all progeny (offspring) of that cell inherit genes that encode the same receptor specificity, including the memory B cells and memory T cells that are the keys to long-lived specific immunity.


Affective forecasting

Affective forecasting, also known as hedonic forecasting or the hedonic forecasting mechanism, is the prediction of one's affect (emotional state) in the future. As a process that influences preferences, decisions, and behavior, affective forecasting is studied by both psychologists and economists, with broad applications.


Antibody

An antibody (Ab), or immunoglobulin (Ig), is a large protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as those that exist on bacteria and virus cells, including those that cause disease. Each individual antibody recognizes one or more specific antigens, and antigens (a portmanteau of "antibody generator") of virtually any size and chemical composition can be recognized. Each of the branching chains comprising the "Y" of an antibody contains a paratope (the antigen-binding site) that specifically binds to one particular epitope (a specific part of an antigen bound by the paratope) on an antigen, allowing the two molecules to bind together with precision. Using this mechanism, antibodies can effectively "tag" the antigen (or a microbe or an infected cell bearing such an antigen) for attack by cells of the immune system, or can neutralize it directly (for example, by blocking a part of a virus that is essential for its ability to invade a host cell).
Antibodies may be borne on the surface of an immune cell, as in a B cell receptor, or they may exist freely by being secreted into the extracellular space. The term antibody generally refers to the free (secreted) form, while the term immunoglobulin can refer to either forms. Since they are, broadly speaking, the same protein, the terms are often treated as synonymous.
To allow the immune system to recognize millions of different antigens, the antigen-binding paratopes at each tip of the antibody come in an equally wide variety. The rest of an antibody's structure is much less variable; in humans, antibodies occur in five classes or isotypes: IgA, IgD, IgE, IgG, and IgM. Human IgG and IgA antibodies are also divided into discrete subclasses (IgG1, IgG2, IgG3, and IgG4; IgA1 and IgA2). The class refers to the functions triggered by the antibody (also known as effector functions), in addition to some other structural features. Antibodies from different classes also differ in where they are released in the body and at what stage of an immune response. Between species, while classes and subclasses of antibodies may be shared (at least in name), their function and distribution throughout the body may be different, which complicates the use of animal models in studying antibodies. For example, mouse IgG1 is closer to human IgG2 than to human IgG1 in terms of its function.
The term humoral immunity is often treated as synonymous with the antibody response, describing the function of the immune system that exists in the body's humors (fluids) in the form of soluble proteins, as distinct from cell-mediated immunity, which generally describes the responses of T cells (especially killer T cells). In general, antibodies are considered part of the adaptive immune system, though this classification can become complicated. For example, natural IgM, which are made by B-1 cells that have properties more similar to innate immune cells than adaptive, refers to IgM antibodies made independently of an immune response that demonstrate polyreactivity—i.e. they recognize multiple distinct (unrelated) antigens. These can work with the complement system in the earliest phases of an immune response to help facilitate clearance of the offending antigen and delivery of the resulting immune complexes to the lymph nodes or spleen for initiation of an immune response. Hence in this capacity, the functions of antibodies are more akin to that of innate immunity than adaptive. Nonetheless, in general, antibodies are regarded as part of the adaptive immune system because they demonstrate exceptional specificity (with some exceptions), are produced through genetic rearrangements (rather than being encoded directly in the germline), and are a manifestation of immunological memory.

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Artificial immune system

Artificial immune systems (AIS) are a class of rule-based machine learning systems inspired by the principles and processes of the vertebrate immune system. The algorithms are typically modeled after the immune system's characteristics of learning and memory for problem-solving, specifically for biological computational techniques.


Autoimmune disease

An autoimmune disease is a condition causing disease that results from an anomalous response of the adaptive immune system, wherein it mistakenly targets and attacks healthy, functioning parts of the body as if they were foreign organisms. It is estimated that there are more than 80 recognized autoimmune diseases, with recent scientific evidence suggesting the existence of potentially more than 100 distinct conditions. Nearly any body part can be involved.
Autoimmune diseases are a separate class from autoinflammatory diseases. Both are characterized by an immune system malfunction which may cause similar symptoms, such as rash, swelling, or fatigue, but the cardinal cause or mechanism of the diseases is different. A key difference is a malfunction of the innate immune system in autoinflammatory diseases, whereas in autoimmune diseases there is a malfunction of the adaptive immune system.
Symptoms of autoimmune diseases can significantly vary, primarily based on the specific type of the disease and the body part that it affects. Symptoms are often diverse and can be fleeting, fluctuating from mild to severe, and typically comprise low-grade fever, fatigue, and general malaise. However, some autoimmune diseases may present with more specific symptoms such as joint pain, skin rashes (e.g., urticaria), or neurological symptoms.
The exact causes of autoimmune diseases remain unclear and are likely multifactorial, involving both genetic and environmental influences. While some diseases like lupus exhibit familial aggregation, suggesting a genetic predisposition, other cases have been associated with infectious triggers or exposure to environmental factors, implying a complex interplay between genes and environment in their etiology.
Some of the most common diseases that are generally categorized as autoimmune include coeliac disease, type 1 diabetes, Graves' disease, inflammatory bowel diseases (such as Crohn's disease and ulcerative colitis), multiple sclerosis, alopecia areata, Addison's disease, pernicious anemia, psoriasis, rheumatoid arthritis, and systemic lupus erythematosus. Diagnosing autoimmune diseases can be challenging due to their diverse presentations and the transient nature of many symptoms.
Treatment modalities for autoimmune diseases vary based on the type of disease and its severity. Therapeutic approaches primarily aim to manage symptoms, reduce immune system activity, and maintain the body's ability to fight diseases. Nonsteroidal anti-inflammatory drugs (NSAIDs) and immunosuppressants are commonly used to reduce inflammation and control the overactive immune response. In certain cases, intravenous immunoglobulin may be administered to regulate the immune system. Despite these treatments often leading to symptom improvement, they usually do not offer a cure and long-term management is often required.
In terms of prevalence, a UK study found that 10% of the population were affected by an autoimmune disease. Women are more commonly affected than men. Autoimmune diseases predominantly begin in adulthood, although they can start at any age. The initial recognition of autoimmune diseases dates back to the early 1900s, and since then, advances in understanding and management of these conditions have been substantial, though much more is needed to fully unravel their complex etiology and pathophysiology.


Autoimmunity

In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an "autoimmune disease". Prominent examples include celiac disease, diabetes mellitus type 1, Henoch–Schönlein purpura, systemic lupus erythematosus, Sjögren syndrome, eosinophilic granulomatosis with polyangiitis, Hashimoto's thyroiditis, Graves' disease, idiopathic thrombocytopenic purpura, Addison's disease, rheumatoid arthritis, ankylosing spondylitis, polymyositis, dermatomyositis, and multiple sclerosis. Autoimmune diseases are very often treated with steroids.
Autoimmunity means presence of antibodies or T cells that react with self-protein and is present in all individuals, even in normal health state. It causes autoimmune diseases if self-reactivity can lead to tissue damage.


Autonomic nervous system

The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal. The fight-or-flight response, also known as the acute stress response, is set into action by the autonomic nervous system.
The autonomic nervous system is regulated by integrated reflexes through the brainstem to the spinal cord and organs. These functions include control of respiration, cardiac regulation, vasomotor activity, and certain reflex actions such as coughing, sneezing, swallowing and vomiting. Those are then subdivided into other areas and are also linked to autonomic subsystems and the peripheral nervous system. The hypothalamus, just above the brain stem, acts as an integrator for autonomic functions, receiving autonomic regulatory input from the limbic system.
Although conflicting reports about its subdivisions exist in the literature, the autonomic nervous system has historically been considered a purely motor system, and has been divided into three branches: the sympathetic nervous system, the parasympathetic nervous system, and the enteric nervous system. The enteric nervous system however is a less recognized part of the autonomic nervous system. The sympathetic nervous system is responsible for setting off the fight-or-flight response. The parasympathetic nervous system is responsible for the body's rest and digestion response. In many cases, both of these systems have "opposite" actions where one system activates a physiological response and the other inhibits it. An older simplification of the sympathetic and parasympathetic nervous systems as "excitatory" and "inhibitory" was overturned due to the many exceptions found. A more modern characterization is that the sympathetic nervous system is a "quick response mobilizing system" and the parasympathetic is a "more slowly activated dampening system", but even this has exceptions, such as in sexual arousal and orgasm, wherein both play a role.
There are inhibitory and excitatory synapses between neurons. A third subsystem of neurons has been named as non-noradrenergic, non-cholinergic transmitters because they use other transmitters such as nitric oxide as a neurotransmitter. These functions are integral in autonomic function, in particular in the gut and the lungs.
Although the ANS is also known as the visceral nervous system and although most of its fibers carry non-somatic information to the CNS, many authors still consider it only connected with the motor side. Most autonomous functions are involuntary but they can often work in conjunction with the somatic nervous system which provides voluntary control. Overall, the ANS ensures the maintenance of vital functions and allows the body to effectively adapt to cycles of stress and recovery.


Avian immune system

The avian immune system is the system of biological structures and cellular processes that protects birds from disease.
The avian immune system resembles that of mammals since both evolved from a common reptilian ancestor and have inherited many commonalities.  They have also developed a number of different strategies that are unique to birds. Most avian immunology research has been carried out on the domestic chicken, Gallus gallus domesticus.  Birds have lymphoid tissues, B cells, T cells, cytokines and chemokines like many other animals. They can also have tumours, immune deficiency and autoimmune diseases.


Behavioral immune system

The behavioral immune system is a phrase coined by the psychological scientist Mark Schaller to refer to a suite of psychological mechanisms that allow individual organisms to detect the potential presence of infectious parasites or pathogens in their immediate environment, and to engage in behaviors that prevent contact with those objects and individuals.
The existence of a behavioral immune system has been documented across many animal species, including humans. It is theorized that the mechanisms that comprise the behavioral immune system evolved as a crude first line of defense against disease-causing pathogens.
In humans and animals, activating a physiological immune response to pathogens is effective, but metabolically costly. Immune responses are activated at the expense of other fitness enhancing activities. Inflammation after infection can also be harmful to the body (e.g., contribute to diseases of aging). In addition to cultural adaptations to avoid pathogens, the behavioral immune system acts as a set of defense mechanisms to protect against pathogens before infection occurs


Cancer immunotherapy

Cancer immunotherapy (immuno-oncotherapy) is the stimulation of the immune system to treat cancer, improving the immune system's natural ability to fight the disease. It is an application of the basic science of cancer immunology (immuno-oncology) and a growing subspecialty of oncology.
Cancer immunotherapy exploits the fact that cancer cells often have tumor antigens, molecules on their surface that can bind to antibody proteins or T-cell receptors, triggering an immune system response. The tumor antigens are often proteins or other macromolecules (e.g., carbohydrates). Normal antibodies bind to external pathogens, but the modified immunotherapy antibodies bind to the tumor antigens marking and identifying the cancer cells for the immune system to inhibit or kill. The clinical success of cancer immunotherapy is highly variable between different forms of cancer; for instance, certain subtypes of gastric cancer react well to the approach whereas immunotherapy is not effective for other subtypes.
Major types of cancer immunotherapy include immune checkpoint inhibitors, which block inhibitory pathways such as PD-1/PD-L1 and CTLA-4 to enhance T cell activity against tumors. These therapies have shown effectiveness in treating cancers such as melanoma and lung cancer.
Adoptive cell therapies, including chimeric antigen receptor (CAR) T cell therapy, involve modifying a patient's immune cells to recognize cancer-specific antigens. These therapies have been particularly effective in certain blood cancers. Natural killer cell (NK) therapies and CAR-NK cell approaches are also being explored, leveraging NK cells' innate ability to target tumor cells. Other strategies include cancer vaccines, which aim to provoke an immune response against tumor-associated antigens, and may be either preventive or therapeutic. Immunomodulatory agents such as cytokines (e.g., interleukin-2, interferon-alpha) and Bacillus Calmette-Guerin (BCG) are used to enhance immune activity or alter the tumor microenvironment. Oncolytic virus therapies, which employ engineered viruses to selectively kill cancer cells while promoting systemic immunity, are also under investigation.
In 2018, American immunologist James P. Allison and Japanese immunologist Tasuku Honjo received the Nobel Prize in Physiology or Medicine for their discovery of cancer therapy by inhibition of negative immune regulation.


Cell-mediated immunity

Cellular immunity, also known as cell-mediated immunity, is an immune response that does not rely on the production of antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T cells (a.k.a. cytotoxic T lymphocytes), and the release of various cytokines in response to an antigen.


Chondrichthyes

Chondrichthyes (; from Ancient Greek  χόνδρος (khóndros) 'cartilage' and  ἰχθύς (ikhthús) 'fish') is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquatic vertebrates with paired fins, paired nares, placoid scales, and conus arteriosus in the heart. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.
The class is divided into two subclasses: Elasmobranchii (sharks, rays, skates and sawfish) which lack opercula, and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class).  Extant chondrichthyans range in size from the 10 cm (3.9 in) finless sleeper ray to the over 10 m (33 ft) whale shark.

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Circulatory system

In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart and blood vessels (from Greek kardia meaning heart, and Latin vascula meaning vessels). The circulatory system has two divisions, a systemic circulation or circuit, and a pulmonary circulation or circuit. Some sources use the terms cardiovascular system and vascular system interchangeably with circulatory system.
The network of blood vessels are the great vessels of the heart including large elastic arteries, and large veins; other arteries, smaller arterioles, capillaries that join with venules (small veins), and other veins. The circulatory system is closed in vertebrates, which means that the blood never leaves the network of blood vessels. Many invertebrates such as arthropods have an open circulatory system with a heart that pumps a hemolymph which returns via the body cavity rather than via blood vessels. Diploblasts such as sponges and comb jellies lack a circulatory system.
Blood is a fluid consisting of plasma, red blood cells, white blood cells, and platelets; it is circulated around the body carrying oxygen and nutrients to the tissues and collecting and disposing of waste materials. Circulated nutrients include proteins and minerals and other components include hemoglobin, hormones, and gases such as oxygen and carbon dioxide. These substances provide nourishment, help the immune system to fight diseases, and help maintain homeostasis by stabilizing temperature and natural pH.
In vertebrates, the lymphatic system is complementary to the circulatory system. The lymphatic system carries excess plasma (filtered from the circulatory system capillaries as interstitial fluid between cells) away from the body tissues via accessory routes that return excess fluid back to blood circulation as lymph. The lymphatic system is a subsystem that is essential for the functioning of the blood circulatory system; without it the blood would become depleted of fluid.
The lymphatic system also works with the immune system. The circulation of lymph takes much longer than that of blood and, unlike the closed (blood) circulatory system, the lymphatic system is an open system. Some sources describe it as a secondary circulatory system.
The circulatory system can be affected by many cardiovascular diseases. Cardiologists are medical professionals which specialise in the heart, and cardiothoracic surgeons specialise in operating on the heart and its surrounding areas. Vascular surgeons focus on disorders of the blood vessels, and lymphatic vessels.


Complement system

The complement system, also known as complement cascade, is a part of the humoral, innate immune system and enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. Despite being part of the innate immune system, the complement system can be recruited and brought into action by antibodies generated by the adaptive immune system.
The complement system consists of a number of small, inactive, liver synthesized protein precursors circulating in the blood. When stimulated by one of several triggers, proteases in the system cleave specific proteins to release cytokines and initiate an amplifying cascade of further cleavages. The result of this complement activation or complement fixation cascade is stimulation of phagocytes to clear foreign and damaged material, inflammation to attract additional phagocytes, and activation of the cell-killing membrane attack complex. About 50 proteins and protein fragments make up the complement system, including plasma proteins, and cell membrane receptors. They account for about 10% of the globulin fraction of blood serum.
Three biochemical pathways activate the complement system: the classical complement pathway, the alternative complement pathway, and the lectin pathway. The alternative pathway accounts for the majority of terminal pathway activation and so therapeutic efforts in disease have revolved around its inhibition.


Corporate immune system

The term corporate immune system, or corporate immune response, refers to a process within corporations that demands organizations within the company accomplish activities in a certain way, a form of conformity tendencies. It is, in effect, the active form of groupthink, when the past outcome of groupthink processes forces itself on organizations that are otherwise different.
The term is most commonly used to describe such processes that drive out innovation and entrepreneurial activity within organizations. This is often found in large multi-divisional companies, where it manifests itself as inter-divisional fighting, often subtle or unintended. Multinational corporations are particularly common examples, as divisional differences can be compounded by different corporate structures, languages and even time zones.


Earth immune system

The Earth immune system is a controversial proposal, claimed to be a consequence of  the Gaia hypothesis. The Gaia hypothesis holds that the entire earth may be considered a single organism (Gaia). As a self-maintaining organism, Earth would have an immune system of some sort in order to maintain its health.
Some proponents of this speculative concept, for example, hold that humankind can be considered an "infection" of Gaia, and that AIDS is an attempt by this immune system to reject the infection.
"Cancer" might be a more accurate term, as humans evolved within Gaia, and are not external invaders.
An opposite view is that humankind is Gaia's immune system itself, perhaps evolved to avert future catastrophes such as the Permian and Cretaceous mass extinctions of species.
James Lovelock's book "The Revenge of Gaia" suggests that Gaia has many mechanisms for eliminating civilizations that do harm through greenhouse gas emissions and global warming, but suggests that with increasing heat being received from the sun, Gaia's ability to "bounce back" as it did after the Permian and Cretaceous extinction events, may be increasingly compromised.
Paul Hawken suggests in Blessed Unrest that when Earth is considered a living system then Earth's immune system is made up of the million or so organizations all around the globe that are working for social justice, the environment, and indigenous people's rights. Many of these groups are linked through the Internet and other means so there is a vast network of interconnected people and groups working to protect the planet, its people, and all beings. For example, one organization that serves to link groups working on sustainable energy is Inforse in Denmark.


Fish anatomy

Fish anatomy is the study of the form or morphology of fish. It can be contrasted with fish physiology, which is the study of how the component parts of fish function together in the living fish. In practice, fish anatomy and fish physiology complement each other, the former dealing with the structure of a fish, its organs or component parts and how they are put together, as might be observed on a dissecting table or under a microscope, and the latter dealing with how those components function together in living fish.
The anatomy of fish is often shaped by the physical characteristics of water, the medium in which fish live. Water is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does. The body of a fish is divided into a head, trunk and tail, although the divisions between the three are not always externally visible. The skeleton, which forms the support structure inside the fish, is either made of cartilage (cartilaginous fish) or bone (bony fish). The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles. The main external features of the fish, the fins, are composed of either bony or soft spines called rays which, with the exception of the caudal fins, have no direct connection with the spine. They are supported by the muscles that make up most of the trunk.
The heart has two chambers and pumps the blood through the respiratory surfaces of the gills and then around the body in a single circulatory loop. The eyes are adapted for seeing underwater and have only local vision. There is an inner ear but no external or middle ear. Low-frequency vibrations are detected by the lateral line system of sense organs that run along the length of the sides of fish, which responds to nearby movements and to changes in water pressure.
Sharks and rays are basal fish with numerous primitive anatomical features similar to those of ancient fish, including skeletons composed of cartilage. Their bodies tend to be dorso-ventrally flattened, and they usually have five pairs of gill slits and a large mouth set on the underside of the head. The dermis is covered with separate dermal placoid scales. They have a cloaca into which the urinary and genital passages open, but not a swim bladder. Cartilaginous fish produce a small number of large yolky eggs. Some species are ovoviviparous, having the young develop internally, but others are oviparous and the larvae develop externally in egg cases.
The bony fish lineage shows more derived anatomical traits, often with major evolutionary changes from the features of ancient fish. They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an operculum, and a mouth at or near the tip of the snout. The dermis is covered with overlapping scales. Bony fish have a swim bladder which helps them maintain a constant depth in the water column, but not a cloaca. They mostly spawn a large number of small eggs with little yolk which they broadcast into the water column.


Gastrointestinal tract

The gastrointestinal tract (also called the GI tract, digestive tract, and the alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is one of the largest of the body's systems. The GI tract contains all the major organs of the digestive system, in humans and other animals, including the esophagus, stomach, and intestines. Food taken in through the mouth is digested to extract nutrients and absorb energy, and the waste expelled at the anus as feces. Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines.
Most animals have a "through-gut" or complete digestive tract. Exceptions are more primitive ones: sponges have small pores (ostia) throughout their body for digestion and a larger dorsal pore (osculum) for excretion, comb jellies have both a ventral mouth and dorsal anal pores, while cnidarians and acoels have a single pore for both digestion and excretion.
The human gastrointestinal tract consists of the esophagus, stomach, and intestines, and is divided into the upper and lower gastrointestinal tracts. The GI tract includes all structures between the mouth and the anus, forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine. The complete human digestive system is made up of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder). The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment. The whole human GI tract is about nine meters (30 feet) long at autopsy. It is considerably shorter in the living body because the intestines, which are tubes of smooth muscle tissue, maintain constant muscle tone in a halfway-tense state but can relax in different areas to allow for local distension and peristalsis.
The human gut microbiota is made up of around 4,000 different strains of bacteria, archaea, viruses and eukaryotes, with diverse roles in the maintenance of immune health and metabolism. Enteroendocrine cells of the GI tract release hormones to help regulate the digestive process. These digestive hormones, including gastrin, secretin, cholecystokinin, and ghrelin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.


Giardiasis

Giardiasis is a parasitic disease caused by the protist enteropathogen Giardia duodenalis (also known as G. lamblia and G. intestinalis), especially common in children and travelers. Infected individuals experience steatorrhea, a type of diarrhea with fatty sticky stool; abdominal pain, weight loss, and weakness due to dehydration and malabsorption. Less common symptoms include skin rash, hives and joint swelling. Symptoms usually begin one to three weeks after exposure and, without treatment, may last two to six weeks or longer. Some infected individuals experience mild or no symptoms and remain symptom-free even if the infection persists for a long time.
Giardiasis spreads via the fecal-oral route, when Giardia cysts excreted with feces contaminate food or water that is later consumed orally. The disease can also spread between people and between people and animals, mainly via pets. Cysts may survive for nearly three months in cold water.
The microscopic identification of Giardia and its cysts in fecal samples is considered the gold standard method for diagnosing giardiasis. Immunoassays, such as ELISA and PCR for giardia gene loci, are also available as diagnostic tools, although are not widely used due to methods complexity and costs.
Prevention may be improved through proper personal hygiene practices and by cooking and sanitizing food. Asymptomatic cases often do not need treatment. When symptoms are present, treatment is typically provided with either tinidazole or metronidazole. Other drugs, such as nitazoxanide, albendazole, quinacrine, chloroquine, paromomycin, and other drug combinations are also used in clinics. Refractory giardiasis and resistant strains are reported more and more often. Infection may cause a person to become lactose intolerant, so it is recommended to temporarily avoid lactose following an infection or use lactase supplements.
Giardiasis occurs worldwide. It is one of the most common parasitic human diseases. Infection rates are as high as 7% in the developed world and 30% in the developing world. In 2013, there were approximately 280 million people worldwide with symptomatic cases of giardiasis. The World Health Organization classifies giardiasis as a neglected disease. It is popularly known as beaver fever in North America.


HIV/AIDS

The human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a preventable disease. It can be managed with treatment and become a manageable chronic health condition. While there is no cure or vaccine for HIV, antiretroviral treatment can slow the course of the disease, and, if used before significant disease progression, can extend the life expectancy of someone living with HIV to a nearly standard level. An HIV-positive person on treatment can expect to live a normal life, and die with the virus, not of it. Effective treatment for HIV-positive people (people living with HIV) involves a life-long regimen of medicine to suppress the virus, making the viral load undetectable.  Early testing can show if treatment is needed to stop progression and to prevent infecting others.
Treatment is recommended as soon as the diagnosis is made. An HIV-positive person who has an undetectable viral load as a result of long-term treatment has effectively no risk of transmitting HIV sexually. Campaigns by UNAIDS and other organizations around the world have communicated this as Undetectable = Untransmittable.
Without treatment the infection can interfere with the immune system, and eventually progress to AIDS, sometimes taking many years. Following initial infection an individual may not notice any symptoms, or may experience a brief period of influenza-like illness. During this period the person may not know that they are HIV-positive, yet they will be able to pass on the virus. Typically, this period is followed by a prolonged incubation period with no symptoms. Eventually the HIV infection increases the risk of developing other infections such as tuberculosis, as well as other opportunistic infections, and tumors which are rare in people who have normal immune function. The late stage is often also associated with unintended weight loss. Without treatment, the life expectancy of an individual with HIV is around 11 years.
HIV is spread primarily by unprotected sex (including anal, oral and vaginal sex), contaminated hypodermic needles or blood transfusions, and from mother to child during pregnancy, delivery, or breastfeeding. Some bodily fluids, such as saliva, sweat, and tears, do not transmit the virus. Oral sex has little risk of transmitting the virus. Ways to avoid catching HIV and preventing the spread include safe sex, treatment to prevent infection ("PrEP"), treatment to stop infection in someone who has been recently exposed ("PEP"), treating those who are infected, and needle exchange programs. Disease in a baby can often be prevented by giving both the mother and child antiretroviral medication.
Recognized worldwide in the early 1980s, HIV/AIDS has had a large impact on society, both as an illness and as a source of discrimination. The disease also has large economic impacts. There are many misconceptions about HIV/AIDS, such as the belief that it can be transmitted by casual non-sexual contact. The disease has become subject to many controversies involving religion, including the Catholic Church's position not to support condom use as prevention. It has attracted international medical and political attention as well as large-scale funding since it was identified in the 1980s.
HIV made the jump from other primates to humans in west-central Africa in the early-to-mid-20th century. AIDS was first recognized by the U.S. Centers for Disease Control and Prevention (CDC) in 1981 and its cause—HIV infection—was identified in the early part of the decade. Between the first time AIDS was readily identified through 2024, the disease is estimated to have caused at least 42.3 million deaths worldwide. In 2025, 1.2 million people acquired HIV and an estimated 40.9 million people worldwide were living with HIV. HIV/AIDS is considered a pandemic—a disease outbreak which is present over a large area and is actively spreading. The United States' National Institutes of Health (NIH) and the Gates Foundation have pledged $200 million focused on developing a global cure for AIDS.


Human body

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Humoral immunity


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Immune checkpoint


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Immunity (medicine)


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List of systems of the human body


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White blood cell


Anna Magdalena Bach

Anna Magdalena Bach (née Wilcke; 22 September 1701 – 27 February 1760) was a German professional singer and the second wife of Johann Sebastian Bach.


BACH motif

In music, the BACH motif is a succession of notes important or characteristic to a piece, which consists of the notes B♭, A, C, B♮:

In German musical nomenclature, in which the note B natural is named H and the B flat named B, it forms Johann Sebastian Bach's family name. One of the most frequently occurring examples of a musical cryptogram, the motif has been used by countless composers, especially after the Bach Revival in the first half of the 19th century.


Bach's Nekrolog

The 1754 obituary of Johann Sebastian Bach is usually called the "Nekrolog." It was published four years after his death.


Bach-Werke-Verzeichnis

The Bach-Werke-Verzeichnis (German: [ˈbax ˌvɛʁkə fɐˈtsaɪçnɪs], lit. 'Bach Works Catalogue'; BWV) is a catalogue of compositions by Johann Sebastian Bach. It was first published in 1950, edited by Wolfgang Schmieder. The catalogue's second edition appeared in 1990 and the third edition in 2022.
The catalogue groups compositions by genre. Even within a genre, compositions are not necessarily collated chronologically.
In part this reflects the fact that some compositions cannot be dated. However, an approximate or precise date can be assigned to others: for example, BWV 992 was composed many years before BWV 1.


Bach Church, Arnstadt

Bach Church is the common name of a Protestant parish church in Arnstadt, Thuringia, Germany. It was officially named Johann-Sebastian-Bach-Kirche in 1935 because of its association with the composer Johann Sebastian Bach.
It was in this church that Bach played a harpsichord concerto after working for Johann Ernst III, Duke of Saxe-Weimar for 7 months.
A church on the premises named after St. Boniface burned down in 1581. A new church was built from 1676 to 1683 and simply named Neue Kirche (New church). It is a Baroque hall church with three tiers on all sides.

The organ builder Johann Friedrich Wender from Mühlhausen built from 1699 to 1703 on the third tier of the church an organ with two manuals and 21 stops. It was inspected in June 1703 by Johann Sebastian Bach, then 18 years old, who was hired afterwards for the post of the organist at the church, his first position as an organist. He was succeeded in 1707 by his cousin Johann Ernst Bach who held the post to 1728. The organ was changed and restored several times. A replica of the organ was installed in the church of Pontaumur, Auvergne, which is used also for a regional Bach festival, Bach en Combrailles.


Bach Medal

The Bach Medal (German: Bach-Medaille) is awarded by the Lord Mayor of Leipzig during the Bachfest Leipzig in recognition of efforts to promote the work of Johann Sebastian Bach. The Bach Medal of the City of Leipzig is an annual award.


Bach family

The Bach family is a family of notable composers of the Baroque and Classical periods of music, the best-known of whom was Johann Sebastian Bach (1685–1750). There are surviving descendants of the Erfurt Line, such as the great-great-great-grandson of Frederich Leopold Bach or the daughters of Philip Frederick Bach, Susan Jean Weaver and Nancy Louis Hertzog Bach. A family genealogy was drawn up by Johann Sebastian Bach himself in 1735 when he was 50 and was continued by his son Carl Philipp Emanuel Bach.


Biographies of Johann Sebastian Bach

The first major biographies of Johann Sebastian Bach, including those by Johann Nikolaus Forkel and Philipp Spitta, were published in the 19th century. Many more were published in the 20th century by, among others, Albert Schweitzer, Charles Sanford Terry, Christoph Wolff and Klaus Eidam.


Church cantata (Bach)

Throughout his life as a musician, Johann Sebastian Bach composed cantatas for both secular and sacred use. He composed his church cantatas for use in the Lutheran church, mainly intended for the occasions of the liturgical year.


Clavier-Übung (Bach)

There are four Clavier-Übung (keyboard practice) volumes by Johann Sebastian Bach, all of them published during his lifetime:

Clavier-Übung I, for harpsichord, contains six partitas, BWV 825–830, which were published separately from 1726 to 1730, and then grouped into one publication in 1731
Clavier-Übung II, for harpsichord with two manuals, contains the Italian Concerto, BWV 971 and the Overture in the French style, BWV 831, and was published in 1735
Clavier-Übung III, for organ, contains the Prelude and Fugue in E flat major, BWV 552, 21 chorale preludes, BWV 669–689, and the Four Duets, BWV 802–805, and was published in 1739
Clavier-Übung IV, better known as the Goldberg Variations, for harpsichord with two manuals, was published in 1741


The International Johann Sebastian Bach Competition (German: Internationaler Bach Wettbewerb Leipzig) is a music competition in Leipzig, Germany, held by the Bach-Archiv Leipzig. It was founded in 1950 and was held every four years from 1964 to 1996 with five subjects and is now held every two years with three changing subjects violin / baroque violin, piano, harpsichord or in the fields of voice, cello / baroque violoncello and organ. From 1965 the competition is a member of the World Federation of International Music Competitions in Geneva.


Johann Ambrosius Bach

Johann Ambrosius Bach (22 February 1645 – 20 February 1695) was a German musician, father to Johann Sebastian Bach.


Johann Bernhard Bach

Johann Bernhard Bach (23 May 1676 – 11 June 1749) was a German composer, and second cousin of J. S. Bach.


Johann Christian Bach

Johann Christian Bach (5 September 1735 – 1 January 1782) was a German composer of the Classical era and the youngest son of Johann Sebastian Bach.
Bach received his early musical training from his father, and later from his half-brother, Carl Philipp Emanuel Bach in Berlin. After his time in Berlin he made his way to Italy to study with the famous Padre Martini in Bologna. While in Italy, J.C. Bach was appointed as an organist at the Milan Cathedral. In 1762 he became a composer to the King’s Theatre in London where he wrote a number of successful Italian operas and became known as "The English Bach".
Bach is responsible for the development of the sinfonia concertante form. He became one of the most influential figures of the classical period, influencing compositional styles of prolific composers like Joseph Haydn and Wolfgang Amadeus Mozart. There are two others named Johann Christian Bach in the Bach family tree, but neither was a composer.


Johann Christoph Bach

Johann Christoph Bach (baptised 18 December [O.S. 8 December] 1642 – 31 March 1703) was a German composer and organist of the Baroque period. Johann Christoph was an older cousin of Johann Sebastian Bach who would later describe him in his Genealogy (Ursprung, 1735) as "the profound composer", suggesting a solid reputation not only within the family but also in wider musical society. He is not to be confused with Johann Sebastian Bach's son, Johann Christoph Friedrich Bach.


Johann Christoph Bach (organist at Ohrdruf)

Johann Christoph Bach (16 June 1671 – 22 February 1721) was a musician of the Bach family. He was the eldest of the brothers of Johann Sebastian Bach who survived childhood.


Johann Ludwig Bach

Johann Ludwig Bach (14 February [O.S. 4 February] 1677 – 1 May 1731) was a German composer and violinist.
He was born in Thal (Ruhla) near Eisenach on 4 February 1677. At the age of 22 he moved to Meiningen eventually being appointed cantor there, and later Kapellmeister. He wrote a large amount of music and regularly oversaw performances, both at Meiningen and neighbouring courts.
He was a third cousin of Johann Sebastian Bach, who made copies of several of his cantatas and performed them at Leipzig. The cantata Denn du wirst meine Seele nicht in der Hölle lassen, BWV 15, once thought to be by Johann Sebastian, and listed as BWV 15 in Wolfgang Schmieder's catalogue of his works, is now thought to be by Johann Ludwig.
Bach died on 1 May 1731 in Meiningen.


Johann Michael Bach

Johann Michael Bach (baptised 19 August [O.S. 9 August] 1648, Arnstadt, Schwarzburg-Sondershausen – 27 May [O.S. 17 May] 1694, Gehren) was a German composer of the Baroque period.  He was the brother of Johann Christoph Bach, as well as first cousin, once removed and father-in-law of Johann Sebastian Bach (he was the father of J.S. Bach's first wife Maria Barbara Bach). He is sometimes referred to as the "Gehrener Bach" to distinguish him from the "Wuppertaler Bach", Johann Michael Bach (musician at Wuppertal).


Johann Pachelbel

Johann Pachelbel (also Bachelbel; baptised 11 September [O.S. 1 September] 1653 – buried 9 March 1706) was a German composer, organist, and teacher who brought the south German organ schools to their peak. He composed a large body of sacred and secular music, and his contributions to the development of the chorale prelude and fugue have earned him a place among the most important composers of the middle Baroque era.
Pachelbel's music enjoyed enormous popularity during his lifetime; he had many pupils and his music became a model for the composers of south and central Germany. Pachelbel is most famous for the Canon in D; other well known works include the Chaconne in F minor, the Toccata in E minor for organ, and the Hexachordum Apollinis, a set of keyboard variations.
He was influenced by southern German composers, such as Johann Jakob Froberger and Johann Caspar Kerll, Italians such as Girolamo Frescobaldi and Alessandro Poglietti, French composers, and the composers of the Nuremberg tradition. He preferred a lucid, uncomplicated contrapuntal style that emphasized melodic and harmonic clarity. His music is less virtuosic and less adventurous harmonically than that of Dieterich Buxtehude, although, like Buxtehude, Pachelbel experimented with different ensembles and instrumental combinations in his chamber music and, most importantly, his vocal music, much of which features exceptionally rich instrumentation. Pachelbel explored many variation forms and associated techniques, which manifest themselves in various diverse pieces, from sacred concertos to harpsichord suites.

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German classical composers of church music