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In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino; or, conversely a proton is converted into a neutron by the emission of a positron with a neutrino in what is called positron emission. Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus prior to beta decay, but are created in the decay process. By this process, unstable atoms obtain a more stable ratio of protons to neutrons. The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy. The binding energies of all existing nuclides form what is called the nuclear band or valley of stability. For either electron or positron emission to be energetically possible, the energy release (see below) or Q value must be positive. Beta decay is a consequence of the weak force, which is characterized by relatively long decay times. Nucleons are composed of up quarks and down quarks, and the weak force allows a quark to change its flavour by means of a virtual W boson leading to creation of an electron/antineutrino or positron/neutrino pair. For example, a neutron, composed of two down quarks and an up quark, decays to a proton composed of a down quark and two up quarks. Electron capture is sometimes included as a type of beta decay, because the basic nuclear process, mediated by the weak force, is the same. In electron capture, an inner atomic electron is captured by a proton in the nucleus, transforming it into a neutron, and
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an electron neutrino is released. == Description == The two types of beta decay are known as beta minus and beta plus. In beta minus (β−) decay, a neutron is converted to a proton, and the process creates an electron and an electron antineutrino; while in beta plus (β+) decay, a proton is converted to a neutron and the process creates a positron and an electron neutrino. β+ decay is also known as positron emission. Beta decay conserves a quantum number known as the lepton number, or the number of electrons and their associated neutrinos (other leptons are the muon and tau particles). These particles have lepton number +1, while their antiparticles have lepton number −1. Since a proton or neutron has lepton number zero, β+ decay (a positron, or antielectron) must be accompanied with an electron neutrino, while β− decay (an electron) must be accompanied by an electron antineutrino. An example of electron emission (β− decay) is the decay of carbon-14 into nitrogen-14 with a half-life of about 5,700 years: 146C → 147N + e− + νe In this form of decay, the original element becomes a new chemical element in a process known as nuclear transmutation. This new element has an unchanged mass number A, but an atomic number Z that is increased by one. As in all nuclear decays, the decaying element (in this case 146C) is known as the parent nuclide while the resulting element (in this case 147N) is known as the daughter nuclide. Another example is the decay of hydrogen-3 (tritium) into helium-3 with a half-life of about 12.3 years: 31H → 32He + e− + νe An example of positron emission (β+ decay) is the decay of magnesium-23 into sodium-23 with a half-life of about 11.3 s: 2312Mg → 2311Na + e+ +
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νe β+ decay also results in nuclear transmutation, with the daughter element having an atomic number that is decreased by one. The beta spectrum, or distribution of energy values for the beta particles, is continuous. The total energy of the decay process is divided between the electron, the antineutrino, and the recoiling nuclide. In the figure to the right, an example of an electron with 0.40 MeV energy from the beta decay of 210Bi is shown. In this example, the total decay energy is 1.16 MeV, so the antineutrino has the remaining energy: 1.16 MeV − 0.40 MeV = 0.76 MeV. An electron at the far right of the curve would have the maximum possible kinetic energy, leaving the energy of the neutrino to be only its small rest mass. == History == === Discovery and initial characterization === Radioactivity was discovered in 1896 by Henri Becquerel in uranium, and subsequently observed by Marie and Pierre Curie in thorium and in the newly discovered elements polonium and radium. In 1899, Ernest Rutherford separated radioactive emissions into two types: alpha and beta (now beta minus), based on penetration of objects and ability to cause ionization. Alpha rays could be stopped by thin sheets of paper or aluminium, whereas beta rays could penetrate several millimetres of aluminium. In 1900, Paul Villard identified a still more penetrating type of radiation, which Rutherford identified as a fundamentally new type in 1903 and termed gamma rays. Alpha, beta, and gamma are the first three letters of the Greek alphabet. In 1900, Becquerel measured the mass-to-charge ratio (m/e) for beta particles by the method of J.J. Thomson used to study cathode rays and identify the electron. He found that m/e for a beta particle is the same as for Thomson's electron, and therefore suggested that the
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beta particle is in fact an electron. In 1901, Rutherford and Frederick Soddy showed that alpha and beta radioactivity involves the transmutation of atoms into atoms of other chemical elements. In 1913, after the products of more radioactive decays were known, Soddy and Kazimierz Fajans independently proposed their radioactive displacement law, which states that beta (i.e., β−) emission from one element produces another element one place to the right in the periodic table, while alpha emission produces an element two places to the left. === Neutrinos === The study of beta decay provided the first physical evidence for the existence of the neutrino. In both alpha and gamma decay, the resulting alpha or gamma particle has a narrow energy distribution, since the particle carries the energy from the difference between the initial and final nuclear states. However, the kinetic energy distribution, or spectrum, of beta particles measured by Lise Meitner and Otto Hahn in 1911 and by Jean Danysz in 1913 showed multiple lines on a diffuse background. These measurements offered the first hint that beta particles have a continuous spectrum. In 1914, James Chadwick used a magnetic spectrometer with one of Hans Geiger's new counters to make more accurate measurements which showed that the spectrum was continuous. The results, which appeared to be in contradiction to the law of conservation of energy, were validated by means of calorimetric measurements in 1929 by Lise Meitner and Wilhelm Orthmann. If beta decay were simply electron emission as assumed at the time, then the energy of the emitted electron should have a particular, well-defined value. For beta decay, however, the observed broad distribution of energies suggested that energy is lost in the beta decay process. This spectrum was puzzling for many years. A second problem is related to the conservation of angular
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momentum. Molecular band spectra showed that the nuclear spin of nitrogen-14 is 1 (i.e., equal to the reduced Planck constant) and more generally that the spin is integral for nuclei of even mass number and half-integral for nuclei of odd mass number. This was later explained by the proton-neutron model of the nucleus. Beta decay leaves the mass number unchanged, so the change of nuclear spin must be an integer. However, the electron spin is 1/2, hence angular momentum would not be conserved if beta decay were simply electron emission. From 1920 to 1927, Charles Drummond Ellis (along with Chadwick and colleagues) further established that the beta decay spectrum is continuous. In 1933, Ellis and Nevill Mott obtained strong evidence that the beta spectrum has an effective upper bound in energy. Niels Bohr had suggested that the beta spectrum could be explained if conservation of energy was true only in a statistical sense, thus this principle might be violated in any given decay.: 27 However, the upper bound in beta energies determined by Ellis and Mott ruled out that notion. Now, the problem of how to account for the variability of energy in known beta decay products, as well as for conservation of momentum and angular momentum in the process, became acute. In a famous letter written in 1930, Wolfgang Pauli attempted to resolve the beta-particle energy conundrum by suggesting that, in addition to electrons and protons, atomic nuclei also contained an extremely light neutral particle, which he called the neutron. He suggested that this "neutron" was also emitted during beta decay (thus accounting for the known missing energy, momentum, and angular momentum), but it had simply not yet been observed. In 1931, Enrico Fermi renamed Pauli's "neutron" the "neutrino" ('little neutral one' in Italian). In 1933, Fermi published his
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landmark theory for beta decay, where he applied the principles of quantum mechanics to matter particles, supposing that they can be created and annihilated, just as the light quanta in atomic transitions. Thus, according to Fermi, neutrinos are created in the beta-decay process, rather than contained in the nucleus; the same happens to electrons. The neutrino interaction with matter was so weak that detecting it proved a severe experimental challenge. Further indirect evidence of the existence of the neutrino was obtained by observing the recoil of nuclei that emitted such a particle after absorbing an electron. Neutrinos were finally detected directly in 1956 by the American physicists Clyde Cowan and Frederick Reines in the Cowan–Reines neutrino experiment. The properties of neutrinos were (with a few minor modifications) as predicted by Pauli and Fermi. === β+ decay and electron capture === In 1934, Frédéric and Irène Joliot-Curie bombarded aluminium with alpha particles to effect the nuclear reaction 42He + 2713Al → 3015P + 10n, and observed that the product isotope 3015P emits a positron identical to those found in cosmic rays (discovered by Carl David Anderson in 1932). This was the first example of β+ decay (positron emission), which they termed artificial radioactivity since 3015P is a short-lived nuclide which does not exist in nature. In recognition of their discovery, the couple were awarded the Nobel Prize in Chemistry in 1935. The theory of electron capture was first discussed by Gian-Carlo Wick in a 1934 paper, and then developed by Hideki Yukawa and others. K-electron capture was first observed in 1937 by Luis Alvarez, in the nuclide 48V. Alvarez went on to study electron capture in 67Ga and other nuclides. === Non-conservation of parity === In 1956, Tsung-Dao Lee and Chen Ning Yang noticed that there was no evidence that parity
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was conserved in weak interactions, and so they postulated that this symmetry may not be preserved by the weak force. They sketched the design for an experiment for testing conservation of parity in the laboratory. Later that year, Chien-Shiung Wu and coworkers conducted the Wu experiment showing an asymmetrical beta decay of 60Co at cold temperatures that proved that parity is not conserved in beta decay. This surprising result overturned long-held assumptions about parity and the weak force. In recognition of their theoretical work, Lee and Yang were awarded the Nobel Prize for Physics in 1957. However Wu, who was female, was not awarded the Nobel prize. == β− decay == In β− decay, the weak interaction converts an atomic nucleus into a nucleus with atomic number increased by one, while emitting an electron (e−) and an electron antineutrino (νe). β− decay generally occurs in neutron-rich nuclei. The generic equation is: AZX → AZ+1X′ + e− + νe where A and Z are the mass number and atomic number of the decaying nucleus, and X and X′ are the initial and final elements, respectively. Another example is when the free neutron (10n) decays by β− decay into a proton (p): n → p + e− + νe. At the fundamental level (as depicted in the Feynman diagram on the right), this is caused by the conversion of the negatively charged (−1/3 e) down quark to the positively charged (+2/3 e) up quark, which is promoted by a virtual W− boson; the W− boson subsequently decays into an electron and an electron antineutrino: d → u + e− + νe. == β+ decay == In β+ decay, or positron emission, the weak interaction converts an atomic nucleus into a nucleus with atomic number decreased by one, while emitting a positron (e+)
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and an electron neutrino (νe). β+ decay generally occurs in proton-rich nuclei. The generic equation is: AZX → AZ−1X′ + e+ + νe This may be considered as the decay of a proton inside the nucleus to a neutron: p → n + e+ + νe However, β+ decay cannot occur in an isolated proton because it requires energy, due to the mass of the neutron being greater than the mass of the proton. β+ decay can only happen inside nuclei when the daughter nucleus has a greater binding energy (and therefore a lower total energy) than the mother nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron, and a neutrino and into the kinetic energy of these particles. This process is opposite to negative beta decay, in that the weak interaction converts a proton into a neutron by converting an up quark into a down quark resulting in the emission of a W+ or the absorption of a W−. When a W+ boson is emitted, it decays into a positron and an electron neutrino: u → d + e+ + νe. == Electron capture (K-capture/L-capture) == In all cases where β+ decay (positron emission) of a nucleus is allowed energetically, so too is electron capture allowed. This is a process during which a nucleus captures one of its atomic electrons, resulting in the emission of a neutrino: AZX + e− → AZ−1X′ + νe An example of electron capture is one of the decay modes of krypton-81 into bromine-81: 8136Kr + e− → 8135Br + νe All emitted neutrinos are of the same energy. In proton-rich nuclei where the energy difference between the initial and final states is less than 2mec2, β+ decay is not energetically possible, and electron
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capture is the sole decay mode. If the captured electron comes from the innermost shell of the atom, the K-shell, which has the highest probability to interact with the nucleus, the process is called K-capture. If it comes from the L-shell, the process is called L-capture, etc. Electron capture is a competing (simultaneous) decay process for all nuclei that can undergo β+ decay. The converse, however, is not true: electron capture is the only type of decay that is allowed in proton-rich nuclides that do not have sufficient energy to emit a positron and neutrino. == Nuclear transmutation == If the proton and neutron are part of an atomic nucleus, the above described decay processes transmute one chemical element into another. For example: Beta decay does not change the number (A) of nucleons in the nucleus, but changes only its charge Z. Thus the set of all nuclides with the same A can be introduced; these isobaric nuclides may turn into each other via beta decay. For a given A there is one that is most stable. It is said to be beta stable, because it presents a local minimum of the mass excess: if such a nucleus has (A, Z) numbers, the neighbour nuclei (A, Z−1) and (A, Z+1) have higher mass excess and can beta decay into (A, Z), but not vice versa. For all odd mass numbers A, there is only one known beta-stable isobar. For even A, there are up to three different beta-stable isobars experimentally known; for example, 12450Sn, 12452Te, and 12454Xe are all beta-stable. There are about 350 known beta-decay stable nuclides. === Competition of beta decay types === Usually unstable nuclides are clearly either "neutron rich" or "proton rich", with the former undergoing beta decay and the latter undergoing electron capture (or more
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rarely, due to the higher energy requirements, positron decay). However, in a few cases of odd-proton, odd-neutron radionuclides, it may be energetically favorable for the radionuclide to decay to an even-proton, even-neutron isobar either by undergoing beta-positive or beta-negative decay. Three types of beta decay in competition are illustrated by the single isotope 6429Cu (29 protons, 35 neutrons), which has a half-life of about 12.7 hours. This isotope has one unpaired proton and one unpaired neutron, so either the proton or the neutron can decay. This particular nuclide is almost equally likely to undergo proton decay (by positron emission, 18% or by electron capture, 43%; both forming 64Ni) or neutron decay (by electron emission, 39%; forming 64Zn). === Stability of naturally occurring nuclides === Most naturally occurring nuclides on earth are beta stable. Nuclides that are not beta stable have half-lives ranging from under a second to periods of time significantly greater than the age of the universe. One common example of a long-lived isotope is the odd-proton odd-neutron nuclide 4019K, which undergoes all three types of beta decay (β−, β+ and electron capture) with a half-life of 1.277×109 years. == Conservation rules for beta decay == === Baryon number is conserved === B = n q − n q ¯ 3 {\displaystyle B={\frac {n_{q}-n_{\bar {q}}}{3}}} where n q {\displaystyle n_{q}} is the number of constituent quarks, and n q ¯ {\displaystyle n_{\overline {q}}} is the number of constituent antiquarks. Beta decay just changes neutron to proton or, in the case of positive beta decay (electron capture) proton to neutron so the number of individual quarks doesn't change. It is only the baryon flavor that changes, here labelled as the isospin. Up and down quarks have total isospin I = 1 2 {\textstyle I={\frac {1}{2}}} and isospin projections I z
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= { 1 2 up quark − 1 2 down quark {\displaystyle I_{\text{z}}={\begin{cases}{\frac {1}{2}}&{\text{up quark}}\\-{\frac {1}{2}}&{\text{down quark}}\end{cases}}} All other quarks have I = 0. In general I z = 1 2 ( n u − n d ) {\displaystyle I_{\text{z}}={\frac {1}{2}}(n_{\text{u}}-n_{\text{d}})} === Lepton number is conserved === L ≡ n ℓ − n ℓ ¯ {\displaystyle L\equiv n_{\ell }-n_{\bar {\ell }}} so all leptons have assigned a value of +1, antileptons −1, and non-leptonic particles 0. n → p + e − + ν ¯ e L : 0 = 0 + 1 − 1 {\displaystyle {\begin{matrix}&{\text{n}}&\rightarrow &{\text{p}}&+&{\text{e}}^{-}&+&{\bar {\nu }}_{\text{e}}\\L:&0&=&0&+&1&-&1\end{matrix}}} === Angular momentum === For allowed decays, the net orbital angular momentum is zero, hence only spin quantum numbers are considered. The electron and antineutrino are fermions, spin-1/2 objects, therefore they may couple to total S = 1 {\displaystyle S=1} (parallel) or S = 0 {\displaystyle S=0} (anti-parallel). For forbidden decays, orbital angular momentum must also be taken into consideration. == Energy release == The Q value is defined as the total energy released in a given nuclear decay. In beta decay, Q is therefore also the sum of the kinetic energies of the emitted beta particle, neutrino, and recoiling nucleus. (Because of the large mass of the nucleus compared to that of the beta particle and neutrino, the kinetic energy of the recoiling nucleus can generally be neglected.) Beta particles can therefore be emitted with any kinetic energy ranging from 0 to Q. A typical Q is around 1 MeV, but can range from a few keV to a few tens of MeV. Since the rest mass of the electron is 511 keV, the most energetic beta particles are ultrarelativistic, with speeds very close to the speed of light. In the case of 187Re, the maximum speed of the
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beta particle is only 9.8% of the speed of light. The following table gives some examples: Tritium β− decay being used in the KATRIN experimental search for sterile neutrinos. === β− decay === Consider the generic equation for beta decay AZX → AZ+1X′ + e− + νe. The Q value for this decay is Q = [ m N ( X Z A ) − m N ( X Z + 1 A ′ ) − m e − m ν ¯ e ] c 2 {\displaystyle Q=\left[m_{N}\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)-m_{N}\left({\ce {^{\mathit {A}}_{{\mathit {Z}}+1}X'}}\right)-m_{e}-m_{{\overline {\nu }}_{e}}\right]c^{2}} , where m N ( X Z A ) {\displaystyle m_{N}\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)} is the mass of the nucleus of the AZX atom, m e {\displaystyle m_{e}} is the mass of the electron, and m ν ¯ e {\displaystyle m_{{\overline {\nu }}_{e}}} is the mass of the electron antineutrino. In other words, the total energy released is the mass energy of the initial nucleus, minus the mass energy of the final nucleus, electron, and antineutrino. The mass of the nucleus mN is related to the standard atomic mass m by m ( X Z A ) c 2 = m N ( X Z A ) c 2 + Z m e c 2 − ∑ i = 1 Z B i . {\displaystyle m\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)c^{2}=m_{N}\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)c^{2}+Zm_{e}c^{2}-\sum _{i=1}^{Z}B_{i}.} That is, the total atomic mass is the mass of the nucleus, plus the mass of the electrons, minus the sum of all electron binding energies Bi for the atom. This equation is rearranged to find m N ( X Z A ) {\displaystyle m_{N}\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)} , and m N ( X Z + 1 A ′ ) {\displaystyle m_{N}\left({\ce {^{\mathit {A}}_{{\mathit {Z}}+1}X'}}\right)} is found similarly. Substituting these nuclear
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masses into the Q-value equation, while neglecting the nearly-zero antineutrino mass and the difference in electron binding energies, which is very small for high-Z atoms, we have Q = [ m ( X Z A ) − m ( X Z + 1 A ′ ) ] c 2 {\displaystyle Q=\left[m\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)-m\left({\ce {^{\mathit {A}}_{{\mathit {Z}}+1}X'}}\right)\right]c^{2}} This energy is carried away as kinetic energy by the electron and antineutrino. Because the reaction will proceed only when the Q value is positive, β− decay can occur when the mass of atom AZX is greater than the mass of atom AZ+1X′. === β+ decay === The equations for β+ decay are similar, with the generic equation AZX → AZ−1X′ + e+ + νe giving Q = [ m N ( X Z A ) − m N ( X Z − 1 A ′ ) − m e − m ν e ] c 2 . {\displaystyle Q=\left[m_{N}\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)-m_{N}\left({\ce {^{\mathit {A}}_{{\mathit {Z}}-1}X'}}\right)-m_{e}-m_{\nu _{e}}\right]c^{2}.} However, in this equation, the electron masses do not cancel, and we are left with Q = [ m ( X Z A ) − m ( X Z − 1 A ′ ) − 2 m e ] c 2 . {\displaystyle Q=\left[m\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)-m\left({\ce {^{\mathit {A}}_{{\mathit {Z}}-1}X'}}\right)-2m_{e}\right]c^{2}.} Because the reaction will proceed only when the Q value is positive, β+ decay can occur when the mass of atom AZX exceeds that of AZ−1X′ by at least twice the mass of the electron. === Electron capture === The analogous calculation for electron capture must take into account the binding energy of the electrons. This is because the atom will be left in an excited state after capturing the electron, and the binding energy of the captured innermost electron is significant. Using the generic equation
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for electron capture AZX + e− → AZ−1X′ + νe we have Q = [ m N ( X Z A ) + m e − m N ( X Z − 1 A ′ ) − m ν e ] c 2 , {\displaystyle Q=\left[m_{N}\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)+m_{e}-m_{N}\left({\ce {^{\mathit {A}}_{{\mathit {Z}}-1}X'}}\right)-m_{\nu _{e}}\right]c^{2},} which simplifies to Q = [ m ( X Z A ) − m ( X Z − 1 A ′ ) ] c 2 − B n , {\displaystyle Q=\left[m\left({\ce {^{\mathit {A}}_{\mathit {Z}}X}}\right)-m\left({\ce {^{\mathit {A}}_{{\mathit {Z}}-1}X'}}\right)\right]c^{2}-B_{n},} where Bn is the binding energy of the captured electron. Because the binding energy of the electron is much less than the mass of the electron, nuclei that can undergo β+ decay can always also undergo electron capture, but the reverse is not true. == Beta emission spectrum == Beta decay can be considered as a perturbation as described in quantum mechanics, and thus Fermi's Golden Rule can be applied. This leads to an expression for the kinetic energy spectrum N(T) of emitted betas as follows: N ( T ) = C L ( T ) F ( Z , T ) p E ( Q − T ) 2 {\displaystyle N(T)=C_{L}(T)F(Z,T)pE(Q-T)^{2}} where T is the kinetic energy, CL is a shape function that depends on the forbiddenness of the decay (it is constant for allowed decays), F(Z, T) is the Fermi Function (see below) with Z the charge of the final-state nucleus, E = T + mc2 is the total energy, p = ( E / c ) 2 − ( m c ) 2 {\displaystyle p={\sqrt {(E/c)^{2}-(mc)^{2}}}} is the momentum, and Q is the Q value of the decay. The kinetic energy of the emitted neutrino is given approximately by Q minus the kinetic energy of the beta.
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As an example, the beta decay spectrum of 210Bi (originally called RaE) is shown to the right. === Fermi function === The Fermi function that appears in the beta spectrum formula accounts for the Coulomb attraction / repulsion between the emitted beta and the final state nucleus. Approximating the associated wavefunctions to be spherically symmetric, the Fermi function can be analytically calculated to be: F ( Z , T ) = 2 ( 1 + S ) Γ ( 1 + 2 S ) 2 ( 2 p ρ ) 2 S − 2 e π η | Γ ( S + i η ) | 2 , {\displaystyle F(Z,T)={\frac {2(1+S)}{\Gamma (1+2S)^{2}}}(2p\rho )^{2S-2}e^{\pi \eta }|\Gamma (S+i\eta )|^{2},} where p is the final momentum, Γ the Gamma function, and (if α is the fine-structure constant and rN the radius of the final state nucleus) S = 1 − α 2 Z 2 {\displaystyle S={\sqrt {1-\alpha ^{2}Z^{2}}}} , η = ± Z e 2 E / ( ℏ c p ) {\displaystyle \eta =\pm Ze^{2}E/(\hbar cp)} (+ for electrons, − for positrons), and ρ = r N / ℏ {\displaystyle \rho =r_{N}/\hbar } . For non-relativistic betas (Q ≪ mec2), this expression can be approximated by: F ( Z , T ) ≈ 2 π η 1 − e − 2 π η . {\displaystyle F(Z,T)\approx {\frac {2\pi \eta }{1-e^{-2\pi \eta }}}.} Other approximations can be found in the literature. === Kurie plot === A Kurie plot (also known as a Fermi–Kurie plot) is a graph used in studying beta decay developed by Franz N. D. Kurie, in which the square root of the number of beta particles whose momentum (or energy) lies within a certain narrow range, divided by the Fermi function, is plotted against beta-particle energy. It is a straight
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line for allowed transitions and some forbidden transitions, in accord with the Fermi beta-decay theory. The energy-axis (x-axis) intercept of a Kurie plot corresponds to the maximum energy imparted to the electron/positron (the decay's Q value). With a Kurie plot one can find the limit on the effective mass of a neutrino. == Helicity (polarization) of neutrinos, electrons and positrons emitted in beta decay == After the discovery of parity non-conservation (see History), it was found that, in beta decay, electrons are emitted mostly with negative helicity, i.e., they move, naively speaking, like left-handed screws driven into a material (they have negative longitudinal polarization). Conversely, positrons have mostly positive helicity, i.e., they move like right-handed screws. Neutrinos (emitted in positron decay) have negative helicity, while antineutrinos (emitted in electron decay) have positive helicity. The higher the energy of the particles, the higher their polarization. == Types of beta decay transitions == Beta decays can be classified according to the angular momentum (L value) and total spin (S value) of the emitted radiation. Since total angular momentum must be conserved, including orbital and spin angular momentum, beta decay occurs by a variety of quantum state transitions to various nuclear angular momentum or spin states, known as "Fermi" or "Gamow–Teller" transitions. When beta decay particles carry no angular momentum (L = 0), the decay is referred to as "allowed", otherwise it is "forbidden". Other decay modes, which are rare, are known as bound state decay and double beta decay. === Fermi transitions === A Fermi transition is a beta decay in which the spins of the emitted electron (positron) and anti-neutrino (neutrino) couple to total spin S = 0 {\displaystyle S=0} , leading to an angular momentum change Δ J = 0 {\displaystyle \Delta J=0} between the initial and final states of
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the nucleus (assuming an allowed transition). In the non-relativistic limit, the nuclear part of the operator for a Fermi transition is given by O F = G V ∑ a τ ^ a ± {\displaystyle {\mathcal {O}}_{F}=G_{V}\sum _{a}{\hat {\tau }}_{a\pm }} with G V {\displaystyle G_{V}} the weak vector coupling constant, τ ± {\displaystyle \tau _{\pm }} the isospin raising and lowering operators, and a {\displaystyle a} running over all protons and neutrons in the nucleus. === Gamow–Teller transitions === A Gamow–Teller transition is a beta decay in which the spins of the emitted electron (positron) and anti-neutrino (neutrino) couple to total spin S = 1 {\displaystyle S=1} , leading to an angular momentum change Δ J = 0 , ± 1 {\displaystyle \Delta J=0,\pm 1} between the initial and final states of the nucleus (assuming an allowed transition). In this case, the nuclear part of the operator is given by O G T = G A ∑ a σ ^ a τ ^ a ± {\displaystyle {\mathcal {O}}_{GT}=G_{A}\sum _{a}{\hat {\sigma }}_{a}{\hat {\tau }}_{a\pm }} with G A {\displaystyle G_{A}} the weak axial-vector coupling constant, and σ {\displaystyle \sigma } the spin Pauli matrices, which can produce a spin-flip in the decaying nucleon. === Forbidden transitions === When L > 0, the decay is referred to as "forbidden". Nuclear selection rules require high L values to be accompanied by changes in nuclear spin (J) and parity (π). The selection rules for the Lth forbidden transitions are: Δ J = L − 1 , L , L + 1 ; Δ π = ( − 1 ) L , {\displaystyle \Delta J=L-1,L,L+1;\Delta \pi =(-1)^{L},} where Δπ = 1 or −1 corresponds to no parity change or parity change, respectively. The special case of a transition between isobaric analogue states, where the
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structure of the final state is very similar to the structure of the initial state, is referred to as "superallowed" for beta decay, and proceeds very quickly. The following table lists the ΔJ and Δπ values for the first few values of L: == Rare decay modes == === Bound-state β− decay === A very small minority of free neutron decays (about four per million) are "two-body decays": the proton, electron and antineutrino are produced, but the electron fails to gain the 13.6 eV energy necessary to escape the proton, and therefore simply remains bound to it, as a neutral hydrogen atom. In this type of beta decay, in essence all of the neutron decay energy is carried off by the antineutrino. For fully ionized atoms (bare nuclei), it is possible in likewise manner for electrons to fail to escape the atom, and to be emitted from the nucleus into low-lying atomic bound states (orbitals). This cannot occur for neutral atoms with low-lying bound states which are already filled by electrons. Bound-state β− decays were predicted by Daudel, Jean, and Lecoin in 1947, and the phenomenon in fully ionized atoms was first observed for 163Dy66+ in 1992 by Jung et al. of the Darmstadt Heavy-Ion Research Center. Though neutral 163Dy is stable, fully ionized 163Dy66+ undergoes β− decay into the K and L shells with a half-life of 47 days. The resulting nucleus – 163Ho66+ – is stable only in this almost fully ionized state and will decay via electron capture into 163Dy in the neutral state. Likewise, while being stable in the neutral state, the fully ionized 205Tl81+ undergoes bound-state β− decay to 205Pb81+ with a half-life of 291+33−27 days. The half-lives of neutral 163Ho and 205Pb are respectively 4570 years and 1.73×107 years. In addition, it is estimated
|
{
"page_id": 4651,
"source": null,
"title": "Beta decay"
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|
that β− decay is energetically impossible for natural atoms but theoretically possible when fully ionized also for 193Ir, 194Au, 202Tl, 215At, 243Am, and 246Bk. Another possibility is that a fully ionized atom undergoes greatly accelerated β decay, as observed for 187Re by Bosch et al., also at Darmstadt. Neutral 187Re does undergo β− decay, with half-life 4.12×1010 years, but for fully ionized 187Re75+ this is shortened to only 32.9 years. This is because 187Re75+ is energetically allowed to undergo β− decay to the first-excited state in 187Os75+, a process energetically disallowed for natural 187Re. Similarly, neutral 241Pu undergoes β− decay with a half-life of 14.3 years, but in its fully ionized state the beta-decay half-life of 241Pu94+ decreases to 4.2 days. For comparison, the variation of decay rates of other nuclear processes due to chemical environment is less than 1%. Moreover, current mass determinations cannot decisively determine whether 222Rn is energetically possible to undergo β− decay (the decay energy given in AME2020 is (−6 ± 8) keV), but in either case it is predicted that β− will be greatly accelerated for fully ionized 222Rn86+. === Double beta decay === Some nuclei can undergo double beta decay (2β) where the charge of the nucleus changes by two units. Double beta decay is difficult to study, as it has an extremely long half-life. In nuclei for which both β decay and 2β are possible, the rarer 2β process is effectively impossible to observe. However, in nuclei where β decay is forbidden but 2β is allowed, the process can be seen and a half-life measured. Thus, 2β is usually studied only for beta stable nuclei. Like single beta decay, double beta decay does not change A; thus, at least one of the nuclides with some given A has to be stable with regard
|
{
"page_id": 4651,
"source": null,
"title": "Beta decay"
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|
to both single and double beta decay. "Ordinary" 2β results in the emission of two electrons and two antineutrinos. If neutrinos are Majorana particles (i.e., they are their own antiparticles), then a decay known as neutrinoless double beta decay will occur. Most neutrino physicists believe that neutrinoless 2β has never been observed. == See also == Common beta emitters Neutrino Betavoltaics Particle radiation Radionuclide Tritium illumination, a form of fluorescent lighting powered by beta decay Pandemonium effect Total absorption spectroscopy == References == == Bibliography == Tomonaga, S.-I. (1997). The Story of Spin. University of Chicago Press. Tuli, J. K. (2011). Nuclear Wallet Cards (PDF) (8th ed.). Brookhaven National Laboratory. Archived (PDF) from the original on 2022-10-09. == External links == The Live Chart of Nuclides - IAEA with filter on decay type Beta decay simulation [1]
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{
"page_id": 4651,
"source": null,
"title": "Beta decay"
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Meibomian glands (also called tarsal glands, palpebral glands, and tarsoconjunctival glands) are sebaceous glands along the rims of the eyelid inside the tarsal plate. They produce meibum, an oily substance that prevents evaporation of the eye's tear film. Meibum prevents tears from spilling onto the cheek, traps them between the oiled edge and the eyeball, and makes the closed lids airtight. There are about 25 such glands on the upper eyelid, and 20 on the lower eyelid. Dysfunctional meibomian glands is believed to be the most often cause of dry eyes. They are also the cause of posterior blepharitis. == History == The glands were mentioned by Galen in 200 AD and were described in more detail by Heinrich Meibom (1638–1700), a German physician, in his work De Vasis Palpebrarum Novis Epistola in 1666. This work included a drawing with the basic characteristics of the glands. == Anatomy == Although the upper lid have greater number and volume of meibomian glands than the lower lid, there is no consensus whether it contributes more to the tearfilm stability. The glands do not have direct contact with eyelash follicles. The process of blinking releases meibum into the lid margin. == Function == === Meibum === ==== Lipids ==== Lipids are the major components of meibum (also known as "meibomian gland secretions"). The term "meibum" was originally introduced by Nicolaides et al. in 1981. The biochemical composition of meibum is extremely complex and very different from that of sebum. Lipids are universally recognized as major components of human and animal meibum. An update was published in 2009 on the composition of human meibum and on the structures of various positively identified meibomian lipids. Currently, the most sensitive and informative approach to lipidomic analysis of meibum is mass spectrometry, either with direct infusion or
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{
"page_id": 2167346,
"source": null,
"title": "Meibomian gland"
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|
in combination with liquid chromatography. The lipids are the main component of the lipid layer of the tear film, preventing rapid evaporation and it is believed they lower the surface tension which helps to stabilize the tear film. ==== Proteins ==== In humans, more than 90 different proteins have been identified in meibomian gland secretions. == Clinical significance == Dysfunctional meibomian glands often cause dry eyes, one of the more common eye conditions. They may also contribute to blepharitis. Inflammation of the meibomian glands (also known as meibomitis, meibomian gland dysfunction, or posterior blepharitis) causes the glands to be obstructed by thick, cloudy-to-yellow, more opaque and viscous-like, oily and waxy secretions, a change from the glands' normal clear secretions. Besides leading to dry eyes, the obstructions can be degraded by bacterial lipases, resulting in the formation of free fatty acids, which irritate the eyes and sometimes cause punctate keratopathy. Meibomian gland dysfunction is more often seen in women and is regarded as the main cause of dry eye disease. Factors that contribute to meibomian gland dysfunction can include things such as a person's age and/or hormones, or severe infestation of Demodex brevis mite. Treatment can include warm compresses to thin the secretions and eyelid scrubs with a commercial eyelid cleanser or baby shampoo, or emptying ("expression") of the gland by a professional. Lifitegrast and ciclosporin are topical medication commonly used to control the inflammation and improve the oil quality. In some cases, topical steroids and topical (drops or ointment)/oral antibiotics (to reduce bacteria on the lid margin) are also prescribed to reduce inflammation. Intense pulsed light (IPL) treatments have also been shown to reduce inflammation and improve gland function. Meibomian gland probing is also used on patients who experience deep clogging of the glands. Meibomian gland dysfunction may be caused
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{
"page_id": 2167346,
"source": null,
"title": "Meibomian gland"
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|
by some prescription medications, notably isotretinoin. A blocked meibomian gland can cause a chalazion (or "meibomian cyst") to form in the eyelid. == See also == Gland of Zeis List of specialized glands within the human integumentary system Meibomian gland dysfunction Moll's gland == References == == External links == synd/541 at Whonamedit? Rethinking Meibomian Gland Dysfunction: How to Spot It, Stage It and Treat It
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{
"page_id": 2167346,
"source": null,
"title": "Meibomian gland"
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|
Roman Ulrich Sexl (19 October 1939 – 10 July 1986) was one of the leading Austrian theoretical physicists. He is famous for his textbooks on special relativity. == Life == His most cited work is "On the gravitational field of a massless particle" together with Peter C. Aichelburg. Since 1972 he was professor for Cosmology and General Relativity at the University of Vienna, where, from 1969, he was director of the Institute of Theoretical Physics. From 1971 to 1975 he was the director of the Institute for Space Exploration at the Austrian Academy of Sciences. In 1980 he received the Robert Wichard-Pohl prize. Today there is the annual Roman-Ulrich-Sexl-Prize for extraordinary achievements in teaching physics. == Publications == Relativity (1972) Gravitation and Cosmology (1975) Relativity, Groups and Particles (1975) Aichelburg, Peter C.; Sexl, Roman U. (1979). Albert Einstein: his influence on physics, philosophy and politics. Braunschweig; Wiesbaden. ISBN 3-528-08425-1. {{cite book}}: |work= ignored (help)CS1 maint: location missing publisher (link) == References == == External links == Literature by and about Roman Ulrich Sexl in the German National Library catalogue
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{
"page_id": 13177394,
"source": null,
"title": "Roman Ulrich Sexl"
}
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Electromechanical Film (EMFI, EMFIT, trademarks of Emfit Ltd) is a thin, flexible film that can function as a sensor or actuator. It is composed of a charged polymer coated with two conductive layers, making it an electret. It was invented and first made by Finnish inventor Kari Kirjavainen. Its voided internal structure and high resistivity allow it to hold a high electric charge and make the film very sensitive to force. Changes in the film's thickness create an electric charge and make it operate as a sensor, or when an electric voltage is applied, it can function as an actuator. This gives the film applications in different fields of technology, including, but not limited to, mechanical vibration and ultrasound sensors, microphones, loudspeaker panels, keyboards, and physiological touch sensors. Other than being cheap, its main advantage is its versatility; it can be cut, reshaped, and resized depending on its surface of application. == Manufacturing and structure == The base film is first made from bi-axially orienting a polypropylene film. It is created through a "film-blowing" process, in which the plastic is extruded using a film blowing machine in the shape of a tube. Through the process of foaming, gaseous bubbles can be formed at a fixed density in the tube, which would give rise to EMFi's "voided internal structure". It is then expanded into two different directions depending on the desired thickness and orientation (bi-axial orientation). The tube is then coated with some electrically conductive material and then cut open into a film. This film is then charged using the Corona Treatment, and the electrically conductive layers create electrodes. EMFiT sensor has three layers, two of which that are homogeneous and act as electrodes as mentioned above, and a middle layer that is filled with flat, disk-shaped voids. Upon receiving charge
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{
"page_id": 14488117,
"source": null,
"title": "Electromechanical film"
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|
from the Corona method, electrical breakdowns occur and the surfaces of the voids are permanently charged. There is one basic type of EMFFIT sensor film manufactured currently, the thicknesses being 70 μm respectively. == Operation == === Sensor === The film can be used as a sensor. As the film is charged, it creates an electric field. When pressure is applied to the film, the film's thickness is reduced and changes in the shapes of the individual voids in its structure occur. Any electric charges residing in these voids will move and create mirror charges at the electrode surfaces of the film. These charges are proportional to the force applied to the film, which is given by the equation: Δq = kΔF where ΔF is the dynamic force, Δq is the charge generated, and k is the sensitivity factor. === Actuator === The same sensor film can also be used as an actuator. Changes in thickness can be induced by applying a voltage on the film; compression and expansion of the film depends on the polarity of the voltage, and it occurs when both the outer surfaces of the film either attract or repel from each other. The attractive force between the surfaces while the film is uncharged is given by the equation: F = 12CU2x where C is the capacitance of the film and x is the film's thickness. == Applications == EMFIT sensor film has a diverse range of applications due to it being flexible, durable, and sensitive to a wide range of frequencies. These properties are attributed to its base material: cellular voided Ferro-electret film. Due to these properties, in conjunction with the two modes of operation, it has already seen use in vandalism-proof keyboards, guitar pickups, flat speakers, and vital signs ballistocardiography sensors. esmicrophones. In active
|
{
"page_id": 14488117,
"source": null,
"title": "Electromechanical film"
}
|
noise cancellation, a part of a sensor product can be used in the sensor mode to identify sound signals, and a part can be used as an actuator and then be used to produce sound signals that cancel out the first. EMFIT sensors has been implemented in physiological bio-signal sensors where no direct contact with the skin is required, such as a BCG, as its application is non-invasive. == Limits == Due to the thermal constraints faced by using polypropylene as base material, applications where high sensitivity is needed, long-term temperatures should be below 70 °C, which limits its scope in terms of some potential applications such as the automotive industry. The air voids present in the structure become smaller and higher in pressure as force is applied to the film. This means that the film becomes harder to compress as it goes under more load, meaning that in the sensor mode, the charge output is non-linear, which can make calibrating the sensor difficult. == References ==
|
{
"page_id": 14488117,
"source": null,
"title": "Electromechanical film"
}
|
In organic chemistry, a primary carbon is a carbon atom which is bound to only one other carbon atom. It is thus at the end of a carbon chain. In case of an alkane, three hydrogen atoms are bound to a primary carbon (see propane in the figure on the right). A hydrogen atom could also be replaced by a hydroxy group (−OH), which would make the molecule a primary alcohol. == References ==
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{
"page_id": 16912952,
"source": null,
"title": "Primary carbon"
}
|
In quantum mechanics, an unextendible product basis is a set of orthogonal, non-entangled state vectors for a multipartite system, with the property that local operations and classical communication are insufficient to distinguish one member of the set from the others. Because these states are product states and yet local measurements cannot tell them apart, they are sometimes said to exhibit "nonlocality without entanglement". They provide examples of non-entangled states that pass the Peres–Horodecki criterion for entanglement. == See also == Bound entanglement == References ==
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{
"page_id": 78582329,
"source": null,
"title": "Unextendible product basis"
}
|
The flora of Turkey consists of almost 10,000 species of plants, as well as a number of fungi and algae. Around 32% of Turkey's plants are found only in the country. One reason for the high proportion of endemics is that Anatolia is both mountainous and quite fragmented. The country is divided into three main floristic areas: the Mediterranean, Euro-Siberian, and Irano-Tranian area. The flora of the European part of Turkey is similar to that of adjoining Greece. The ecoregions here include Balkan mixed forests dominated by oaks, and Aegean and Western Turkey sclerophyllous and mixed forests where some of the main species are oaks, strawberry tree, Greek strawberry tree, Spanish broom and laurel. The country is at a meeting point of three phytogeographical regions Mediterranean, Euro-Siberian, and Irano-Turonian. The region played a key role in the early cultivation of wheat, other cereals, and various horticultural crops. The Euro-Siberian area is a mountainous part of western Turkey. Here the flora transitions from the Mediterranean vegetation type to the Anatolian plateau. The dominant vegetation cover here is forests of oak and pine, especially Anatolian black pine and Turkish pine. Further east is the Anatolian plateau, a largely treeless area of plains and river basins at an average altitude of 1,000 m (3,300 ft). This area is characterised by hot dry summers and cold winters. Salt steppes and lakes are found here, as well salt-free grassland areas, marshes and freshwater systems. Immediately around the large Lake Tuz and other saline areas, saltmarsh plants grow, and beyond this is a sharp divide, with the flora being dominated by members of the families Chenopodiaceae and Plumbaginaceae. The mountainous eastern half of the country is separated floristically from the rest of the country by the Anatolian diagonal, a floral break that crosses the country from
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{
"page_id": 24646202,
"source": null,
"title": "Flora of Turkey"
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the eastern end of the Black Sea to the northeastern corner of the Mediterranean Sea. Many species found to the east of this break are not found to the west and vice versa, and about four hundred species are only found along this divide. The natural vegetation in eastern Turkey is the Eastern Anatolian deciduous forests; in these oaks such as Brant's oak, Lebanon oak, Aleppo oak and Mount Thabor's oak predominate in open woodland with Scots pine, burnet rose, dog-rose, oriental plane, alder, sweet chestnut, maple, Caucasian honeysuckle (Lonicera caucasica) and common juniper. Most European species are found in Turkey. The most important reasons for the high plant biodiversity are believed to be the relatively high proportion of endemics, together with the high variety of soils and climate of Turkey. In Anatolia the Pleistocene glaciations only covered the highest peaks, so there are many species with small ranges. In other words: Anatolia as a whole is a big “massif de refuge”, showing all degrees of past and recent speciation. Naturally much of the vegetation would be steppe and forest, however people have cleared much forest and their animals have changed the vegetation by grazing. == Diversity and endemism == === Vascular plants === A third of Turkish plant species are endemic to Turkey: one reason there are so many is because the surface of Anatolia is both mountainous and quite fragmented. In fact, the Anatolian mountains resemble archipelagos like the famous Galapagos Islands. Since Darwin we know that geographic isolation between islands or separated mountains is an important means of speciation, leading to high spatial diversity. For Anatolia this assumption is confirmed by concentrations of endemism on highly isolated and relatively old massifs such as Uludağ and Ilgaz Dağ, whereas very young volcanic cones such as Erciyes Dağ and
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{
"page_id": 24646202,
"source": null,
"title": "Flora of Turkey"
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|
Hassan Dağ are surprisingly poor in endemics. For a visitor from Central Europe, climatic diversity within Turkey is quite astonishing. All climatic zones present in Europe can be found in Turkey on a somewhat smaller scale. The Black Sea coast is humid all year round, with the highest rainfall between Rize and Hopa. South of the Pontic Range there is much less rain so Central Anatolia is dry; also it is cold in the winter. Approaching the southern and western coasts, the climate turns more and more Mediterranean, with mild but very rainy winters and dry, hot summers. This simple scheme is complicated a lot by the mountainous surface of Anatolia. On the high mountains, harsh climatic conditions persist all the year round and, as of 2019, there are glaciers in Turkey, for example on Mount Ararat. Anatolia’s diversity of soils is astonishingly high. Saline soils are quite common in the driest parts of central Anatolia; addtionally, the Aras valley between Kağızman and Armenia is full of impressive salt outlets, some pouring directly out of the mountains and thus resembling snow patches from a distance. South of Sivas and around Gürün there are extensive gypsum hills with a very special flora. A further lot of endemics have been described from the extensive serpentine areas in South-West Anatolia, especially Sandras Dağ (Cicekbaba D.) near Köyceğiz. The Anatolian diagonal is an ecological dividing line that runs slant-wise across central and eastern Turkey from the northeastern corner of the Mediterranean Sea to the southeastern part of the Black Sea. Many species of plants that exist west of the diagonal are not present to the east, while others found to the east are not in the west. Of 550 species analysed, 135 were found to be "eastern" and 228 "western". Besides the Anatolian diagonal
|
{
"page_id": 24646202,
"source": null,
"title": "Flora of Turkey"
}
|
forming a barrier to floral biodiversity, about four hundred species of plant are endemic to the diagonal itself. With almost 400 species the genus Astragalus (milk-vetch, goat's-thorn; Fabaceae) has by far the most species of the Turkish flora; as historically humans have dramatically expanded its favored treeless, dry and heavily grazed habitats. But not as many as Central Asia: the former USSR has twice as many. The plasticity of this genus is astonishingly high. Depending on environmental conditions a big variety of life forms evolved, ranging from tiny annuals to small woody and thorny bushes. Speciation seems to be in plain progress in Astragalus. Nearly all of its different sections consists of clusters of closely related species whose determination is one of the hardest tasks in a closer study of the Anatolian flora. One of the most successful growth forms of Turkish Astragali is the thorn cushion, which is very characteristic of the dry mountains of inner Anatolia. Such thorn cushions were not exclusively invented by many Astragali. Really striking examples of convergent evolution are the impressive thorn cushions of Onobrychis cornuta, also belonging to the Fabaceae. But there are a lot of thorn cushions also in Acantholimon (Plumbaginaceae). Even some Asteraceae (in Turkey e.g. Centaurea urvillei, C. iberica) and Caryophyllaceae (e.g. Minuartia juniperina) evolved in that direction. Second in importance comes Verbascum (Scrophulariaceae) and third is Centaurea (Asteraceae). For Verbascum Turkey evidently is the centre of distribution. Of approximately 360 species worldwide no less than 232 are to be found in Turkey, almost 80% of them being Anatolian endemics! Most Verbascum species are protected against water loss and hungry cattle by a dense cover of tree-shaped micro hairs. Centaurea species rarely have woolly hairs, but in defence against heavy grazing developed thorny phyllaries, or evolved to have no visible
|
{
"page_id": 24646202,
"source": null,
"title": "Flora of Turkey"
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|
stem or a very short one. === Non-vascular plants === There are over 700 species of moss. === Fungi === There are over 12,000 varieties of mushroom in Turkey, some of which are edible. === Algae === There are over 2000 taxa of freshwater algae. == Vegetation types == Steppe grassland is mostly in Central and southeast Anatolia. Above 2000m in the Black Sea Region there is Alpine grassland. The distribution of plants uses the World Geographical Scheme for Recording Plant Distributions (WGSRPD). See List of codes used in the World Geographical Scheme for Recording Plant Distributions for its coding system. Turkey is divided into two botanical areas: TUE – Turkey in Europe – part of 13 Southeastern Europe – part of 1 Europe → Category:Flora of European Turkey TUR – (the rest of) Turkey – part of 34 Western Asia – part of 3 Temperate-Asia → Category:Flora of Turkey The Pontic mountain range along the north Anatolian coast is a more or less continuous barrier against humid air from the Black Sea, causing high precipitation on the northern slopes of the Pontus all year. Climatic conditions on the northern coast therefore resemble those in central Europe and so does the vegetation. A limited Mediterranean influence is noticeable only on a very narrow coastal strip, but almost completely missing in the northeast. In the lower forest zone often Hornbeam (Carpinus betulus) prevails, frequently intermingled with Sweet Chestnut (Castanea sativa). Further up Oriental Beech (Fagus orientalis) and/or Nordmann Fir (Abies nordmanniana) form extensive forests. Humidity becomes extremely high in Lazistan, where the Pontic barrier culminates in the nearly 4000 m high Kaçkar Mountains. East of Trabzon therefore vegetation becomes somewhat sub-tropic, with a lot of evergreens in the forest and tea plantations everywhere on the slopes. South of the Pontic watershed
|
{
"page_id": 24646202,
"source": null,
"title": "Flora of Turkey"
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|
the climate immediately gets drier. In the mountains first Abies nordmanniana, but then soon Pinus becomes dominant. In the western parts of Anatolia this is often Black Pine (Pinus nigra), in the east nearly exclusively Scots Pine (Pinus sylvestris). Penetrating further into the central parts of inner Anatolia leads to still dryer, wintercold conditions. Today the lower parts of central Anatolia are virtually treeless. Fields on deep alluvial soils alternate with steppe on the dryer hills. But it is still an open question where and to what degree this central Anatolian steppe is due to aridity or to human deforestation. Aridity is most pronounced around Tuz Gölü south of Ankara and in the Aras-valley near the Armenian border. Between Kağizman and Tuzluca this valley is so dry, that here and there pure salt deposits glitter like white snowfields on the bare slopes. The Taurus Mountains form the southern edge of the central Anatolian Plateau and are already very influenced by the Mediterranean, with a lot of snow in winter, but dry and warm summers. Climax forests are formed by Black Pine, Cilician Fir (Abies cilicica) and Lebanon Cedar (Cedrus libani). Unfortunately, there has been a lot of deforestation in the Taurus, most gravely affecting the stands of cedar. On the Aegean and Mediterranean coasts pronounced Mediterranean conditions prevail, with very hot and dry summers and very rainy winters. Antalya Province has considerably more total precipitation than, for example, the south of England (1071 mm versus 759 mm), but its seasonal distribution is completely different and the average temperature is of course much higher (18.3 °C versus 9.7°). But due to massive forest destruction hills and slopes in coastal West and South Anatolia are nowadays mostly covered with maquis shrubland. Where fertile alluvial soils prevail, e.g. in the Cilician Plain around
|
{
"page_id": 24646202,
"source": null,
"title": "Flora of Turkey"
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Adana, there is intense agriculture. Mediterranean vegetation is resilient to drought. == Origins and evolution == As local endemics take a long time to evolve, we also have to compare the history of the central and north European mountains with the Anatolian ones. During each of the glacial periods the former were covered by thick shields of permanent ice, which destroyed most pre-glacial endemism and hindered neo-endemics from forming. Only less glaciated, peripheral areas, the so-called “massifs de refuge”, offered suitable conditions for the survival of local endemics during glacial periods. In Anatolia the Pleistocene glaciations only covered the highest peaks, so there are many species with small ranges. In other words: Anatolia as a whole is a big "massif de refuge", showing all degrees of past and recent speciation. == Human impact == Without humans the main vegatation types would be steppe and forest. Rangeland in Central Anatolia was overgrazed, and rangeland management to limit soil erosion has been suggested. There is a national biodiversity action plan to 2028, and an IUCN SSC Turkey Plant Red List Authority. Potentially there could be more forest in Turkey. Technology is being used to revegetate steep slopes to try to prevent desertification. == Botanical resources == "The Flora of Turkey and the East Aegean Islands", 9 volumes, 1965-1985, ed. P H Davis, followed by two supplementary volumes 10 (1988) & 11 (2000, Güner, A. & al.). All volumes are in English, mostly text. "Resimli Türkiye Florası" (Illustrated Flora of Turkey), projected to be 30 volumes, ed. Adil Güner, released in PDF and print format, currently published (May 2024) vols. 1,2,3a,3b,4a,4b, primarily distributed via ANG. All volumes are in Turkish, with keys, descriptive text, illustrations and details and map of herbarium specimens used for each taxon. "Check-list of additional taxa to the supplement
|
{
"page_id": 24646202,
"source": null,
"title": "Flora of Turkey"
}
|
of flora of Turkey I... X" are 10 (as of May 2024) supplemental lists of new taxa that have been found in Turkey (released as PDFs). "Orchids of Europe, North Africa and the Middle East, ed 3", 2006, 640 pp, by Pierre Delforge (English, includes the entirety of Turkey). "Endemism in Mainland Regions – Case Studies: Turkey", 2013, by Pils, p. 240-255 in: Endemism in Vascular Plants, Springer Verlag, ed. C Hobohm [1] Turkish Journal Of Botany AVCI. M. 2005. "Çeşitlilik Ve Endemizm Açısından Türkiye’nin Bitki Örtüsü-Diversity and endemism in Turkey's Vegetation", İstanbul Üniversitesi Edebiyat Fakültesi Coğrafya Bölümü Coğrafya Dergisi 13:27-55. Information for this article was taken mainly from: Flowers of Turkey - a photo guide.- 448 pp.– Eigenverlag Gerhard Pils (2006). == Notes == == References == == External links == Plant List with Maps (bizimbitkiler.org.tr) (to search, type a genus or species and click Ara (or hit enter), against a plant Göster provides details and map, tab "Geçerli İsimler" provides current names, "Eşisimler" obsolete names; the maps are mostly from old herbarium data and some latitude is needed) Threatened Plants List by Category (tehditaltindabitkiler.org.tr) (click a threat category to view taxon list, as of 2024-12 these categories are from 2012) Some new Flora PDFs and images (turkiyeflorasi.org.tr) (images can be found using the upper right search box) 30-volume Flora of Turkey on ang.org.tr (e-kitap items are the PDFs) Primary National Plant Gallery and Breaking News (turkiyebitkileri.com) Primary National Botany ID Forum (FB) Primary National Orchid ID Forum (FB)
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{
"page_id": 24646202,
"source": null,
"title": "Flora of Turkey"
}
|
One use of the concept of biocontainment is related to laboratory biosafety and pertains to microbiology laboratories in which the physical containment of pathogenic organisms or agents (bacteria, viruses, and toxins) is required, usually by isolation in environmentally and biologically secure cabinets or rooms, to prevent accidental infection of workers or release into the surrounding community during scientific research. Another use of the term relates to facilities for the study of agricultural pathogens, where it is used similarly to the term "biosafety", relating to safety practices and procedures used to prevent unintended infection of plants or animals or the release of high-consequence pathogenic agents into the environment (air, soil, or water). == Terminology == The World Health Organization's 2006 publication, Biorisk management: Laboratory biosecurity guidance, defines laboratory biosafety as "the containment principles, technologies and practices that are implemented to prevent the unintentional exposure to pathogens and toxins, or their accidental release". It defines biorisk management as "the analysis of ways and development of strategies to minimize the likelihood of the occurrence of biorisks". The term "biocontainment" is related to laboratory biosafety. Merriam-Webster's online dictionary reports the first use of the term in 1966, defined as "the containment of extremely pathogenic organisms (such as viruses) usually by isolation in secure facilities to prevent their accidental release especially during research". The term laboratory biosafety refers to the measures taken "to reduce the risk of accidental release of or exposure to infectious disease agents", whereas laboratory biosecurity is usually taken to mean "a set of systems and practices employed in legitimate bioscience facilities to reduce the risk that dangerous biological agents will be stolen and used maliciously". == Containment types == === Laboratory context === Primary containment is the first container in direct contact with biohazardous material as well as protection of personnel
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and the immediate laboratory environment from exposure to infectious agents. Primary containment requires using proper storage containers, good microbiological technique, and the use of appropriate safety equipment such as biological safety cabinets. Secondary containment is the protection of the environment external to the laboratory from exposure to infectious materials and is provided by a combination of facility design and operational practices. Biological safety cabinets (BSC), first commercially available in 1950, are fairly common devices designed to provide effective primary biocontainment in laboratories working with highly infectious agents. Three general levels and types have been devised (Class I, Class II, and Class III). Biosafety suites are suites of laboratory rooms which are essentially equivalent to large Class III cabinets in which positive pressure personnel suits ("space suits") serve as the "outside" environment for workers. Examples include the biosafety suites at USAMRIID at Fort Detrick, Maryland, USA and the Maximum Containment Facility (MCF) of the CDC in Atlanta, Georgia, USA. === Agricultural context === The term “biocontainment” is used differently in facilities for the study of human pathogens versus those used for the study of agricultural pathogens. In agricultural facilities, the definition for “biocontainment” resembles that for “biosafety,” i.e., the safety practices and procedures used to prevent unintended infection of plants or animals or the release of high-consequence pathogenic agents into the environment (air, soil, or water). In the agricultural setting, worker protection and public health are always considerations; however, emphasis is placed on reducing the risk that agents under study could escape into the environment. == Biosafety levels == A "biosafety level" (BSL) is the level of the biocontainment precautions required to isolate dangerous biological agents in an enclosed laboratory facility. The levels of containment range from the lowest biosafety level 1 (BSL-1) to the highest at level 4 (BSL-4). In
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the United States, the Centers for Disease Control and Prevention (CDC) have specified these levels. In the European Union, the same biosafety levels are defined in a directive. == Guidelines == Today, guiding publications for biosafety and containment in the US are set by the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH). Since 1984, the CDC and the NIH have jointly authored the Biosafety in Microbiological and Medical Laboratories (BMBL). The BMBL is an advisory document providing national recommendations for Biosafety Levels, Containment, Decontamination and Disinfection, Transportation, and Disposal of biohazardous agents. In Canada the government publication "Laboratory biosafety guidelines" was current between 1990 and 2013, and has been superseded by the "Canadian Biosafety Standards and Guidelines". OECD Best Practice Guidelines for Biological Resource Centres is a consensus report created in 2001 after experts from OECD countries came together, calling upon "national governments to undertake actions to bring the BRC concept into being in concert with the international scientific community". BRCs are "repositories and providers of high-quality biological materials and information". == Laboratory program == Components of a laboratory biosecurity program include: Physical security Personnel security Material control and accountability Transport security Information security Program management == See also == Aeromedical Isolation Team – Former US Army aeromobile biocontainment team Biorisk – Risk associated with biological materials and/or infectious agents ("pathogens") Biosafety – Prevention of large-scale loss of biological integrity Biosafety level – Set of biocontainment precautions Biosecurity – Preventive measures designed to reduce the risk of infectious disease transmission Biological hazard – Biological material that poses serious risks to the health of living organisms Chemical hazard – Non-biological hazards of hazardous materials Safety engineering – Engineering discipline which assures that engineered systems provide acceptable levels of safety Security engineering – Process of
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incorporating security controls into an information system Select agent – Controlled biological agents in the United States == References == Citations Other sources Biosafety in Microbiological and Biomedical Laboratories (1999), 4th Edition, U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institutes of Health, Washington, DC: U.S. Government Printing Office. The 2013 International Conference on Biocontainment Facilities The 2014 International Conference on Biocontainment Facilities eBook Reference: Management Principles for Building and Operating Biocontainment Facilities (Kindle Edition) Archived 2013-05-26 at the Wayback Machine Wedum, A.G., W.E. Barkley, and A. Hellman (1972), "Handling of infectious agents", Journal of the American Veterinary Medical Association, 161(11):1557-1567. == Further reading == Biorisk Management: Laboratory Biosecurity Guidance. WHO, 2006 Biosafety in Microbiological and Biomedical Laboratories, 5th edition, 2007 (CDC) Clevestig, Peter (28 June 2009). Handbook of Applied Biosecurity for Life Science Laboratories (PDF). Stockholm International Peace Research Institute. ISBN 978-91-85114-61-0. (Website here) Kanabrocki, Joseph (20 January 2017). "Biosafety and Biosecurity in the Realm of Dual-Use Research of Concern" (PDF). p. 2. Retrieved 23 May 2020. National Academies of Sciences, Engineering, and Medicine (14 September 2017). "3. Managing Dual Use Research of Concern". Dual Use Research of Concern in the Life Sciences: Current Issues and Controversies. Washington DC: National Academies Press. doi:10.17226/24761. ISBN 978-0-309-45888-7. PMID 29001489. Retrieved 23 May 2020 – via NCBI Bookshelf.{{cite book}}: CS1 maint: multiple names: authors list (link) PDF Laboratory Biosafety Manual, 3rd edition, 2004 (4th edition slideshow and draft - Section 8 on Laboratory Biosecurity) Laboratory Biosecurity Handbook. CRC Press. 2007. ISBN 978-0-8493-6475-4.
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Species distribution, or species dispersion, is the manner in which a biological taxon is spatially arranged. The geographic limits of a particular taxon's distribution is its range, often represented as shaded areas on a map. Patterns of distribution change depending on the scale at which they are viewed, from the arrangement of individuals within a small family unit, to patterns within a population, or the distribution of the entire species as a whole (range). Species distribution is not to be confused with dispersal, which is the movement of individuals away from their region of origin or from a population center of high density. == Range == In biology, the range of a species is the geographical area within which that species can be found. Within that range, distribution is the general structure of the species population, while dispersion is the variation in its population density. Range is often described with the following qualities: Sometimes a distinction is made between a species' natural, endemic, indigenous, or native range, where it has historically originated and lived, and the range where a species has more recently established itself. Many terms are used to describe the new range, such as non-native, naturalized, introduced, transplanted, invasive, or colonized range. Introduced typically means that a species has been transported by humans (intentionally or accidentally) across a major geographical barrier. For species found in different regions at different times of year, especially seasons, terms such as summer range and winter range are often employed. For species for which only part of their range is used for breeding activity, the terms breeding range and non-breeding range are used. For mobile animals, the term natural range is often used, as opposed to areas where it occurs as a vagrant. Geographic or temporal qualifiers are often added, such as in
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British range or pre-1950 range. The typical geographic ranges could be the latitudinal range and elevational range. Disjunct distribution occurs when two or more areas of the range of a taxon are considerably separated from each other geographically. == Factors affecting species distribution == Distribution patterns may change by season, distribution by humans, in response to the availability of resources, and other abiotic and biotic factors. === Abiotic === There are three main types of abiotic factors: climatic factors consist of sunlight, atmosphere, humidity, temperature, and salinity; edaphic factors are abiotic factors regarding soil, such as the coarseness of soil, local geology, soil pH, and aeration; and social factors include land use and water availability. An example of the effects of abiotic factors on species distribution can be seen in drier areas, where most individuals of a species will gather around water sources, forming a clumped distribution. Researchers from the Arctic Ocean Diversity (ARCOD) project have documented rising numbers of warm-water crustaceans in the seas around Norway's Svalbard Islands. ARCOD is part of the Census of Marine Life, a huge 10-year project involving researchers in more than 80 nations that aims to chart the diversity, distribution and abundance of life in the oceans. Marine Life has become largely affected by increasing effects of global climate change. This study shows that as the ocean temperatures rise species are beginning to travel into the cold and harsh Arctic waters. Even the snow crab has extended its range 500 km north. === Biotic === Biotic factors such as predation, disease, and inter- and intra-specific competition for resources such as food, water, and mates can also affect how a species is distributed. For example, biotic factors in a quail's environment would include their prey (insects and seeds), competition from other quail, and their predators,
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such as the coyote. An advantage of a herd, community, or other clumped distribution allows a population to detect predators earlier, at a greater distance, and potentially mount an effective defense. Due to limited resources, populations may be evenly distributed to minimize competition, as is found in forests, where competition for sunlight produces an even distribution of trees. One key factor in determining species distribution is the phenology of the organism. Plants are well documented as examples showing how phenology is an adaptive trait that can influence fitness in changing climates. Physiology can influence species distributions in an environmentally sensitive manner because physiology underlies movement such as exploration and dispersal. Individuals that are more disperse-prone have higher metabolism, locomotor performance, corticosterone levels, and immunity. Humans are one of the largest distributors due to the current trends in globalization and the expanse of the transportation industry. For example, large tankers often fill their ballasts with water at one port and empty them in another, causing a wider distribution of aquatic species. == Patterns on large scales == On large scales, the pattern of distribution among individuals in a population is clumped. === Bird wildlife corridors === One common example of bird species' ranges are land mass areas bordering water bodies, such as oceans, rivers, or lakes; they are called a coastal strip. A second example, some species of bird depend on water, usually a river, swamp, etc., or water related forest and live in a river corridor. A separate example of a river corridor would be a river corridor that includes the entire drainage, having the edge of the range delimited by mountains, or higher elevations; the river itself would be a smaller percentage of this entire wildlife corridor, but the corridor is created because of the river. A further example
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of a bird wildlife corridor would be a mountain range corridor. In the U.S. of North America, the Sierra Nevada range in the west, and the Appalachian Mountains in the east are two examples of this habitat, used in summer, and winter, by separate species, for different reasons. Bird species in these corridors are connected to a main range for the species (contiguous range) or are in an isolated geographic range and be a disjunct range. Birds leaving the area, if they migrate, would leave connected to the main range or have to fly over land not connected to the wildlife corridor; thus, they would be passage migrants over land that they stop on for an intermittent, hit or miss, visit. == Patterns on small scales == On large scales, the pattern of distribution among individuals in a population is clumped. On small scales, the pattern may be clumped, regular, or random. === Clumped === Clumped distribution, also called aggregated distribution, clumped dispersion or patchiness, is the most common type of dispersion found in nature. In clumped distribution, the distance between neighboring individuals is minimized. This type of distribution is found in environments that are characterized by patchy resources. Animals need certain resources to survive, and when these resources become rare during certain parts of the year animals tend to "clump" together around these crucial resources. Individuals might be clustered together in an area due to social factors such as selfish herds and family groups. Organisms that usually serve as prey form clumped distributions in areas where they can hide and detect predators easily. Other causes of clumped distributions are the inability of offspring to independently move from their habitat. This is seen in juvenile animals that are immobile and strongly dependent upon parental care. For example, the bald eagle's
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nest of eaglets exhibits a clumped species distribution because all the offspring are in a small subset of a survey area before they learn to fly. Clumped distribution can be beneficial to the individuals in that group. However, in some herbivore cases, such as cows and wildebeests, the vegetation around them can suffer, especially if animals target one plant in particular. Clumped distribution in species acts as a mechanism against predation as well as an efficient mechanism to trap or corner prey. African wild dogs, Lycaon pictus, use the technique of communal hunting to increase their success rate at catching prey. Studies have shown that larger packs of African wild dogs tend to have a greater number of successful kills. A prime example of clumped distribution due to patchy resources is the wildlife in Africa during the dry season; lions, hyenas, giraffes, elephants, gazelles, and many more animals are clumped by small water sources that are present in the severe dry season. It has also been observed that extinct and threatened species are more likely to be clumped in their distribution on a phylogeny. The reasoning behind this is that they share traits that increase vulnerability to extinction because related taxa are often located within the same broad geographical or habitat types where human-induced threats are concentrated. Using recently developed complete phylogenies for mammalian carnivores and primates it has been shown that in the majority of instances threatened species are far from randomly distributed among taxa and phylogenetic clades and display clumped distribution. A contiguous distribution is one in which individuals are closer together than they would be if they were randomly or evenly distributed, i.e., it is clumped distribution with a single clump. === Regular or uniform === Less common than clumped distribution, uniform distribution, also known as even
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distribution, is evenly spaced. Uniform distributions are found in populations in which the distance between neighboring individuals is maximized. The need to maximize the space between individuals generally arises from competition for a resource such as moisture or nutrients, or as a result of direct social interactions between individuals within the population, such as territoriality. For example, penguins often exhibit uniform spacing by aggressively defending their territory among their neighbors. The burrows of great gerbils for example are also regularly distributed, which can be seen on satellite images. Plants also exhibit uniform distributions, like the creosote bushes in the southwestern region of the United States. Salvia leucophylla is a species in California that naturally grows in uniform spacing. This flower releases chemicals called terpenes which inhibit the growth of other plants around it and results in uniform distribution. This is an example of allelopathy, which is the release of chemicals from plant parts by leaching, root exudation, volatilization, residue decomposition and other processes. Allelopathy can have beneficial, harmful, or neutral effects on surrounding organisms. Some allelochemicals even have selective effects on surrounding organisms; for example, the tree species Leucaena leucocephala exudes a chemical that inhibits the growth of other plants but not those of its own species, and thus can affect the distribution of specific rival species. Allelopathy usually results in uniform distributions, and its potential to suppress weeds is being researched. Farming and agricultural practices often create uniform distribution in areas where it would not previously exist, for example, orange trees growing in rows on a plantation. === Random === Random distribution, also known as unpredictable spacing, is the least common form of distribution in nature and occurs when the members of a given species are found in environments in which the position of each individual is independent of
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the other individuals: they neither attract nor repel one another. Random distribution is rare in nature as biotic factors, such as the interactions with neighboring individuals, and abiotic factors, such as climate or soil conditions, generally cause organisms to be either clustered or spread. Random distribution usually occurs in habitats where environmental conditions and resources are consistent. This pattern of dispersion is characterized by the lack of any strong social interactions between species. For example; When dandelion seeds are dispersed by wind, random distribution will often occur as the seedlings land in random places determined by uncontrollable factors. Oyster larvae can also travel hundreds of kilometers powered by sea currents, which can result in their random distribution. Random distributions exhibit chance clumps (see Poisson clumping). == Statistical determination of distribution patterns == There are various ways to determine the distribution pattern of species. The Clark–Evans nearest neighbor method can be used to determine if a distribution is clumped, uniform, or random. To utilize the Clark–Evans nearest neighbor method, researchers examine a population of a single species. The distance of an individual to its nearest neighbor is recorded for each individual in the sample. For two individuals that are each other's nearest neighbor, the distance is recorded twice, once for each individual. To receive accurate results, it is suggested that the number of distance measurements is at least 50. The average distance between nearest neighbors is compared to the expected distance in the case of random distribution to give the ratio: R = ( mean distance ) × 2 density {\displaystyle R=({\text{mean distance}})\times 2{\sqrt {\text{density}}}} If this ratio R is equal to 1, then the population is randomly dispersed. If R is significantly greater than 1, the population is evenly dispersed. Lastly, if R is significantly less than 1, the population
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is clumped. Statistical tests (such as t-test, chi squared, etc.) can then be used to determine whether R is significantly different from 1. The variance/mean ratio method focuses mainly on determining whether a species fits a randomly spaced distribution, but can also be used as evidence for either an even or clumped distribution. To utilize the Variance/Mean ratio method, data is collected from several random samples of a given population. In this analysis, it is imperative that data from at least 50 sample plots is considered. The number of individuals present in each sample is compared to the expected counts in the case of random distribution. The expected distribution can be found using Poisson distribution. If the variance/mean ratio is equal to 1, the population is found to be randomly distributed. If it is significantly greater than 1, the population is found to be clumped distribution. Finally, if the ratio is significantly less than 1, the population is found to be evenly distributed. Typical statistical tests used to find the significance of the variance/mean ratio include Student's t-test and chi squared. However, many researchers believe that species distribution models based on statistical analysis, without including ecological models and theories, are too incomplete for prediction. Instead of conclusions based on presence-absence data, probabilities that convey the likelihood a species will occupy a given area are more preferred because these models include an estimate of confidence in the likelihood of the species being present/absent. They are also more valuable than data collected based on simple presence or absence because models based on probability allow the formation of spatial maps that indicates how likely a species is to be found in a particular area. Similar areas can then be compared to see how likely it is that a species will occur there also;
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this leads to a relationship between habitat suitability and species occurrence. == Species distribution models == Species distribution can be predicted based on the pattern of biodiversity at spatial scales. A general hierarchical model can integrate disturbance, dispersal and population dynamics. Based on factors of dispersal, disturbance, resources limiting climate, and other species distribution, predictions of species distribution can create a bio-climate range, or bio-climate envelope. The envelope can range from a local to a global scale or from a density independence to dependence. The hierarchical model takes into consideration the requirements, impacts or resources as well as local extinctions in disturbance factors. Models can integrate the dispersal/migration model, the disturbance model, and abundance model. Species distribution models (SDMs) can be used to assess climate change impacts and conservation management issues. Species distribution models include: presence/absence models, the dispersal/migration models, disturbance models, and abundance models. A prevalent way of creating predicted distribution maps for different species is to reclassify a land cover layer depending on whether or not the species in question would be predicted to habit each cover type. This simple SDM is often modified through the use of range data or ancillary information, such as elevation or water distance. Recent studies have indicated that the grid size used can have an effect on the output of these species distribution models. The standard 50x50 km grid size can select up to 2.89 times more area than when modeled with a 1x1 km grid for the same species. This has several effects on the species conservation planning under climate change predictions (global climate models, which are frequently used in the creation of species distribution models, usually consist of 50–100 km size grids) which could lead to over-prediction of future ranges in species distribution modeling. This can result in the misidentification
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of protected areas intended for a species future habitat. == Species Distribution Grids Project == The Species Distribution Grids Project is an effort led out of the University of Columbia to create maps and databases of the whereabouts of various animal species. This work is centered on preventing deforestation and prioritizing areas based on species richness. As of April 2009, data are available for global amphibian distributions, as well as birds and mammals in the Americas. The map gallery Gridded Species Distribution contains sample maps for the Species Grids data set. These maps are not inclusive but rather contain a representative sample of the types of data available for download: == See also == Geographic range limit Animal migration Biogeography Colonisation Cosmopolitan distribution Occupancy frequency distribution == Notes == == External links == Livestock Grazing Distribution Patterns: Does Animal Age Matter? Discrete Uniform Random Distribution
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The Olmec colossal heads are stone representations of human heads sculpted from large basalt boulders. They range in height from 1.17 to 3.4 metres (3.8 to 11.2 ft). The heads date from at least 900 BCE and are a distinctive feature of the Olmec civilization of ancient Mesoamerica. All portray mature individuals with fleshy cheeks, flat noses, and slightly-crossed eyes; their physical characteristics correspond to a type that is still common among the inhabitants of Tabasco and Veracruz. The backs of the monuments are often flat. The boulders were brought from the Sierra de Los Tuxtlas mountains of Veracruz. Given that the extremely large slabs of stone used in their production were transported more than 150 kilometres (93 mi), requiring a great deal of human effort and resources, it is thought that the monuments represent portraits of powerful individual Olmec rulers. Each of the known examples has a distinctive headdress. The heads were variously arranged in lines or groups at major Olmec centres, but the method and logistics used to transport the stone to these sites remain unclear. The heads all display distinctive headgear and one theory is that these were worn as protective helmets, maybe worn for war or to take part in a ceremonial Mesoamerican ballgame. The discovery of the first colossal head at Tres Zapotes in 1862 by José María Melgar y Serrano was not well documented nor reported outside Mexico. The excavation of the same colossal head by Matthew Stirling in 1938 spurred the first archaeological investigations of Olmec culture. Seventeen confirmed examples are known from four sites within the Olmec heartland on the Gulf Coast of Mexico. Most colossal heads were sculpted from spherical boulders but two from San Lorenzo Tenochtitlán were re-carved from massive stone thrones. An additional monument, at Takalik Abaj in Guatemala,
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is a throne that may have been carved from a colossal head. This is the only known example from outside the Olmec heartland. Dating the monuments remains difficult because many were removed from their original contexts prior to archaeological investigation. Most have been dated to the Early Preclassic period (1500–1000 BC) with some to the Middle Preclassic (1000–400 BC) period. The smallest weigh 5 tonnes (6 short tons), while the largest is estimated to weigh 36 to 45 t (40 to 50 short tons); it was abandoned and left uncompleted close to the source of its stone. == Olmec civilization == The Olmec civilization developed in the lowlands of southeastern Mexico between 1500 and 400 BC. The Olmec heartland lies on the Gulf Coast of Mexico within the states of Veracruz and Tabasco, an area measuring approximately 275 kilometres (171 mi) east to west and extending about 100 kilometres (62 mi) inland from the coast. The Olmecs are regarded as the first civilization to develop in Mesoamerica and the Olmec heartland is one of six cradles of civilization worldwide, the others being the Norte Chico culture of South America, the Erlitou culture of China's Yellow River, the Indus Valley civilization of the Indian subcontinent, the civilization of ancient Egypt in Africa, and the Sumerian civilization of ancient Iraq. Of these, only the Olmec civilization developed in a lowland tropical forest setting. The Olmecs were one of the first inhabitants of the Americas to construct monumental architecture and to settle in towns and cities, predated only by the Caral civilization. They were also the first people in the Americas to develop a sophisticated style of stone sculpture. In the first decade of the 21st century, evidence emerged of Olmec writing, with the earliest examples of Olmec hieroglyphs dating to around 650
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BC. Examples of script have been found on roller stamps and stone artefacts; the texts are short and have been partially deciphered based on their similarity to other Mesoamerican scripts. The evidence of complex society developing in the Olmec heartland has led to the Olmecs being regarded as the "Mother Culture" of Mesoamerica, although this concept remains controversial. Some of the Olmecs' rulers seem to have served religious functions. The city of San Lorenzo was succeeded as the main centre of the civilization by La Venta in about 900 BC, with Tres Zapotes and Laguna de los Cerros possibly sharing the role; other urban centres were much less significant. The nature and degree of the control exercised by the centres over a widespread rural population remains unclear. Very fine Olmec art, much clearly made for an elite, survives in several forms, notably Olmec figurines, and larger sculptures such as The Wrestler. The figurines have been recovered in large numbers and are mostly in pottery; these were presumably widely available to the population. Together with these, of particular relevance to the colossal heads are the "Olmec-style masks" in stone, so called because none has yet been excavated in circumstances that allow the proper archaeological identification of an Olmec context. These evocative stone face masks present both similarities and differences to the colossal heads. Two thirds of Olmec monumental sculptures represent the human form, and the colossal heads fall within this major theme of Olmec art. == Dating == The colossal heads cannot be precisely dated. However, the San Lorenzo heads were buried by 900 BC, indicating that their period of manufacture and use was earlier still. The heads from Tres Zapotes had been moved from their original context before they were investigated by archaeologists and the heads from La Venta were
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found partially exposed on the modern ground surface. The period of production of the colossal heads is therefore unknown, as is whether it spanned a century or a millennium. Estimates of the time span during which colossal heads were produced vary from 50 to 200 years. The San Lorenzo heads are believed to be the oldest, and are the most skilfully executed. All of the stone heads have been assigned to the Preclassic period of Mesoamerican chronology, generally to the Early Preclassic (1500–1000 BC), although the two Tres Zapotes heads and the La Cobata Head are attributed to the Middle Preclassic (1000–400 BC). == Characteristics == Olmec colossal heads vary in height from 1.47 to 3.4 metres, or from 4.8 to 11.2 feet, and weigh between 6 and 50 tons. All of the Olmec colossal heads depict mature men with flat noses and fleshy cheeks; the eyes tend to be slightly crossed. The general physical characteristics of the heads are of a type that is still common among people in the Olmec region in modern times. The backs of the heads are often flat, as if the monuments were originally placed against a wall. All examples of Olmec colossal heads wear distinctive headdresses that probably represent cloth or animal hide originals. Some examples have a tied knot at the back of the head, and some are decorated with feathers. A head from La Venta is decorated with the head of a bird. There are similarities between the headdresses on some of the heads that has led to speculation that specific headdresses may represent different dynasties, or perhaps identify specific rulers. Most of the heads wear large earspools inserted into the ear lobes. All of the heads are realistic, unidealised and frank depictions of the men. It is likely that they
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"page_id": 35721801,
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were portraits of living (or recently deceased) rulers well known to the sculptors. Each head is distinct and naturalistic, displaying individualised features. They were once thought to represent ballplayers although this theory is no longer widely held; it is possible, however, that they represent rulers equipped for the Mesoamerican ballgame. Facial expressions depicted on the heads vary from stern through placid to smiling. The most naturalistic Olmec art is the earliest, appearing suddenly without surviving antecedents, with a tendency towards more stylised sculpture as time progressed. Some surviving examples of wooden sculpture recovered from El Manatí demonstrate that the Olmecs are likely to have created many more perishable sculptures than works sculpted from stone. In the late 19th century, José Melgar y Serrano described a colossal head as having "Ethiopian" features, and speculations that the Olmec had African origins resurfaced in 1960 in the work of Alfonso Medellín Zenil and in the 1970s in the writings of Ivan van Sertima. Such speculation is not taken seriously by Mesoamerican scholars such as Richard Diehl and Ann Cyphers. Genetic studies have shown that, rather than Africa, the earliest Americans had ancestry closer to Ancient Paleo-Siberian. Although all the colossal heads are broadly similar, there are distinct stylistic differences in their execution. One of the heads from San Lorenzo bears traces of plaster and red paint, suggesting that the heads were originally brightly decorated. Heads did not just represent individual Olmec rulers; they also incorporated the very concept of rulership itself. == Manufacture == The production of each colossal head must have been carefully planned, given the effort required to ensure the necessary resources were available; it seems likely that only the more powerful Olmec rulers were able to mobilise such resources. The workforce would have included sculptors, labourers, overseers, boatmen, woodworkers and
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other artisans producing the tools to make and move the monument, in addition to the support needed to feed and otherwise attend to these workers. The seasonal and agricultural cycles and river levels needed to have been taken into account to plan the production of the monument and the whole project may well have taken years from beginning to end. Archaeological investigation of Olmec basalt workshops suggest that the colossal heads were first roughly shaped using direct percussion to chip away both large and small flakes of stone. The sculpture was then refined by retouching the surface using hammerstones, which were generally rounded cobbles that could be of the same basalt as the monument itself, although this was not always the case. Abrasives were found in association with workshops at San Lorenzo, indicating their use in the finishing of fine detail. Olmec colossal heads were fashioned as in-the-round monuments with varying levels of relief on the same work; they tended to feature higher relief on the face and lower relief on the earspools and headdresses. Monument 20 at San Lorenzo is an extensively damaged throne with a figure emerging from a niche. Its sides were broken away and it was dragged to another location before being abandoned. It is possible that this damage was caused by the initial stages of re-carving the monument into a colossal head, left uncompleted. All seventeen of the confirmed heads in the Olmec heartland were sculpted from basalt mined in the Sierra de los Tuxtlas mountains of Veracruz. Most were formed from coarse-grained, dark-grey basalt known as Cerro Cintepec basalt after a volcano in the range. Investigators have proposed that large Cerro Cintepec basalt boulders found on the southeastern slopes of the mountains are the source of the stone for the monuments. These boulders are
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found in an area affected by large lahars (volcanic mudslides) that carried substantial blocks of stone down the mountain slopes, which suggests that the Olmecs did not need to quarry the raw material for sculpting the heads. Roughly spherical boulders were carefully selected to mimic the shape of a human head. The stone for the San Lorenzo and La Venta heads was transported a considerable distance from the source. The La Cobata head was found on El Vigia hill in the Sierra de los Tuxtlas and the stone from Tres Zapotes Colossal Head 1 and Nestepe Colossal Head 1 (also known as Tres Zapotes Monuments A and Q) came from the same hill. The boulders were transported over 150 kilometres (93 mi) from the source of the stone. The exact method of transport of such large masses of rock are unknown, especially since the Olmecs lacked beasts of burden and functional wheels, and they were likely to have used water transport whenever possible. Coastal currents of the Gulf of Mexico and in river estuaries might have made the waterborne transport of monuments weighing 20 tons or more impractical. Two badly damaged Olmec sculptures depict rectangular stone blocks bound with ropes. A largely destroyed human figure rides upon each block, with their legs hanging over the side. These sculptures may well depict Olmec rulers overseeing the transport of the stone that would be fashioned into their monuments. When transport over land was necessary, the Olmecs are likely to have used causeways, ramps and roads to facilitate moving the heads. The regional terrain offers significant obstacles such as swamps and floodplains; avoiding these would have necessitated crossing undulating hill country. The construction of temporary causeways using the suitable and plentiful floodplain soils would have allowed a direct route across the floodplains to
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the San Lorenzo Plateau. Earth structures such as mounds, platforms and causeways upon the plateau demonstrate that the Olmec possessed the necessary knowledge and could commit the resources to build large-scale earthworks. The flat backs of many of the colossal heads represented the flat bases of the monumental thrones from which they were reworked. Only four of the seventeen heartland heads do not have flattened backs, indicating the possibility that the majority were reworked monuments. Alternatively, the backs of many of these massive monuments may have been flattened to ease their transport, providing a stable form for hauling the monuments with ropes. Two heads from San Lorenzo have traces of niches that are characteristic of monumental Olmec thrones and so were definitely reworked from earlier monuments. == Known monuments == Seventeen confirmed examples are known. An additional monument, at Takalik Abaj in Guatemala, is a throne that may have been carved from a colossal head. This is the only known example outside the Olmec heartland on the Gulf Coast of Mexico. Possible fragments of additional colossal heads have been recovered at San Lorenzo and at San Fernando in Tabasco. Crude colossal stone heads are also known in the Southern Maya area where they are associated with the potbelly style of sculpture. Although some arguments have been made that they are pre-Olmec, these latter monuments are generally believed to be influenced by the Olmec style of sculpture. === San Lorenzo === The ten colossal heads from San Lorenzo originally formed two roughly parallel lines running north-south across the site. Although some were recovered from ravines, they were found close to their original placements and had been buried by local erosion. These heads, together with monumental stone thrones, probably formed a processional route across the site, powerfully displaying its dynastic history. Two
|
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of the San Lorenzo heads had been re-carved from older thrones. San Lorenzo Colossal Head 1 (also known as San Lorenzo Monument 1) was lying facing upwards when excavated. The erosion of a path passing on top of the monument uncovered its eye and led to the discovery of the Olmec site. Colossal Head 1 is 2.84 metres (9.3 ft) high; it measures 2.11 metres (6.9 ft) wide and it weighs 25.3 tons. The monument was discovered partially buried at the edge of a gully by Matthew Stirling in 1945. When discovered, it was lying on its back, looking upwards. It was associated with a large number of broken ceramic vessels and figurines. The majority of these ceramic remains have been dated to between 800 and 400 BC; some pieces have been dated to the Villa Alta phase (Late Classic period, 800–1000 AD). The headdress possesses a plain band that is tied at the back of the head. The upper portion of the headdress is decorated with a U-shaped motif. This element descends across the front of the headdress, terminating on the forehead. On the front portion it is decorated with five semicircular motifs. The scalp piece does not meet the horizontal band, leaving a space between the two pieces. On each side of the face a strap descends from the headdress and passes in front of the ear. The forehead is wrinkled in a frown. The lips are slightly parted without revealing the teeth. The cheeks are pronounced and the ears are particularly well executed. The face is slightly asymmetric, which may be due to error on the part of the sculptors or may accurately reflect the physical features of the portrait's subject. The head has been moved to the Xalapa Museum of Anthropology. San Lorenzo Colossal Head 2
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(also known as San Lorenzo Monument 2) was reworked from a monumental throne. The head stands 2.69 metres (8.8 ft) high and measures 1.83 metres (6.0 ft) wide by 1.05 metres (3.4 ft) deep; it weighs 20 tons. Colossal Head 2 was discovered in 1945 when Matthew Stirling's guide cleared away some of the vegetation and mud that covered it. The monument was found lying on its back, facing the sky, and was excavated in 1946 by Stirling and Philip Drucker. In 1962 the monument was removed from the San Lorenzo plateau in order to put it on display as part of "The Olmec tradition" exhibition at the Museum of Fine Arts in Houston in 1963. San Lorenzo Colossal Head 2 is currently in the Museo Nacional de Antropología in Mexico City. The head was associated with ceramic finds which have been dated to the Early Preclassic and Late Classic periods. Colossal Head 2 wears a complex headdress that sports a horizontal band tied at the back of the head; this is decorated with three bird's heads that are located above the forehead and temples. The scalp piece is formed from six strips running towards the back of the head. The front of the headdress above the horizontal band is plain. Two short straps hang down from the headdress in front of the ears. The ear jewellery is formed by large squared hoops or framed discs. The left and right ornaments are different, with radial lines on the left earflare, a feature absent on the right earflare. The head is badly damaged due to an unfinished reworking process. This process has pitmarked the entire face with at least 60 smaller hollows and 2 larger holes. The surviving features appear to depict an ageing man with the forehead creased into a
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frown. The lips are thick and slightly parted to reveal the teeth; the head has a pronounced chin. San Lorenzo Colossal Head 3 is also known as San Lorenzo Monument 3. The head measures 1.78 metres (5.8 ft) high by 1.63 metres (5.3 ft) wide by 0.95 metres (3.1 ft) deep and weighs 9.4 tons. The head was discovered in a deep gully by Matthew Stirling in 1946; it was found lying face down and its excavation was difficult due to the wet conditions in the gully. The monument was found 0.8 kilometres (0.50 mi) southwest of the main mound at San Lorenzo, however, its original location is unknown; erosion of the gully may have resulted in significant movement of the sculpture. Head 3 has been moved to the Xalapa Museum of Anthropology. The headdress is complex, with the horizontal basal band being formed by four horizontal cords, with diagonal folds above each eye. A small skullcap tops the headdress. A large flap formed of four cords drops down both sides of the head, completely covering the ears. The face has a typically frowning brow and, unusually, has clearly defined eyelids. The lips are thick and slightly parted; the front of the lower lip has broken away completely, and the lower front of the headdress is pitted with 27 irregularly spaced artificial depressions. San Lorenzo Colossal Head 4 (also known as San Lorenzo Monument 4) weighs 6 tons and has been moved to the Xalapa Museum of Anthropology. Colossal Head 4 is 1.78 metres (5.8 ft) high, 1.17 metres (3.8 ft) wide and 0.95 metres (3.1 ft) deep. The head was discovered by Matthew Stirling in 1946, 550 metres (600 yd) northwest of the principal mound, at the edge of a gully. When excavated, it was found to be lying
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on its right-hand side and in a very good state of preservation. Ceramic materials excavated with the head became mixed with ceramics associated with Head 5, making ceramic dating of the monument difficult. The headdress is decorated with a horizontal band formed of four sculpted cords, similar to those of Head 3. On the right-hand side, three tassels descend from the upper portion of the headdress; they terminate in a total of eight strips that hang down across the horizontal band. These tassels are judged to represent hair rather than cords. Also on the right hand side, two cords descend across the ear and continue to the base of the monument. On the left-hand side, three vertical cords descend across the ear. The earflare is only visible on the right hand side; it is formed of a plain disc and peg. The face is that of an ageing man with a creased forehead, low cheekbones and a prominent chin. The lips are thick and slightly parted. San Lorenzo Colossal Head 5 is also known as San Lorenzo Monument 5. The monument stands 1.86 metres (6.1 ft) high and measures 1.47 metres (4.8 ft) wide by 1.15 metres (3.8 ft) deep. It weighs 11.6 tons. The head was discovered by Matthew Stirling in 1946, face down in a gully to the south of the principal mound. The head is particularly well executed and is likely to have been found close to its original location. Ceramics recovered during its excavation became mixed with those from the excavation of Head 4. The mixed ceramics have been dated to the San Lorenzo and Villa Alta phases (approximately 1400–1000 BC and 800–1000 AD respectively). Colossal Head 5 is particularly well preserved, although the back of the headdress band was damaged when the head was moved
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from the archaeological site. The band of the headdress is set at an angle and has a notch above the bridge of the nose. The headdress is decorated with jaguar paws; this general identification of the decoration is contested by Beatriz de la Fuente since the "paws" have three claws each; she identifies them as the claws of a bird of prey. At the back of the head, ten interlaced strips form a net decorated with disc motifs. Two short straps descend from the headdress in front of the ears. The ears are adorned with disc-shaped earspools with pegs. The face is that of an ageing man with wrinkles under the eyes and across the bridge of the nose, and a forehead that is creased in a frown. The lips are slightly parted. Colossal Head 5 has been moved to the Xalapa Museum of Anthropology. San Lorenzo Colossal Head 6 (also known as San Lorenzo Monument 17) is one of the smaller examples of colossal heads, standing 1.67 metres (5.5 ft). It measures 1.41 metres (4.6 ft) wide by 1.26 metres (4.1 ft) deep and is estimated to weigh between 8 and 10 tons. The head was discovered by a local farmworker and was excavated in 1965 by Luis Aveleyra and Román Piña Chan. The head had collapsed into a ravine under its own weight and was found face down on its left hand side. In 1970 it was transported to the Metropolitan Museum of Art in New York for the museum's centenary exhibition. After its return to Mexico, it was placed in the Museo Nacional de Antropología in Mexico City. It is sculpted with a net-like head covering joined together with sculpted beads. A covering descends from under the headdress to cover the back half of the neck. The
|
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headband is divided into four strips and begins above the right ear, extending around the entire head. A short strap descends from either side of the head to the ear. The ear ornaments are complex and are larger at the front of the ear than at the back. The face is that of an ageing male with the forehead creased in a frown, wrinkles under the eyes, sagging cheeks and deep creases on either side of the nose. The face is somewhat asymmetric, possibly due to errors in the execution of the monument. San Lorenzo Colossal Head 7 (also known as San Lorenzo Monument 53) measures 2.7 metres (8.9 ft) high by 1.85 metres (6.1 ft) wide by 1.35 metres (4.4 ft) deep and weighs 18 tons. San Lorenzo Colossal Head 7 was reworked from a monumental throne; it was discovered by a joint archaeological project by the Instituto Nacional de Antropología e Historia and Yale University, as a result of a magnetometer survey. It was buried at a depth of less than 1 metre (3.3 ft) and was lying facing upwards, leaning slightly northwards on its right hand side. The head is poorly preserved and has suffered both from erosion and deliberate damage. The headdress is decorated with a pair of human hands; a feathered ornament is carved at the back of the headband and two discs adorn the front. A short strap descends from the headband and hangs in front of the right ear. The head sports large earflares that completely cover the earlobes, although severe erosion makes their exact form difficult to distinguish. The face has wrinkles between the nose and cheeks, sagging cheeks and deep-set eyes; the lips are badly damaged and the mouth is open, displaying the teeth. In 1986 the head was transported to
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the Xalapa Museum of Anthropology. San Lorenzo Colossal Head 8 (also known as San Lorenzo Monument 61) stands 2.2 metres (7.2 ft) high; it measures 1.65 metres (5.4 ft) wide by 1.6 metres (5.2 ft) deep and weighs 13 tons. It is one of the finest examples of an Olmec colossal head. It was found lying on its side to the south of a monumental throne. The monument was discovered at a depth of 5 metres (16 ft) during a magnetometer survey of the site in 1968; it has been dated to the Early Preclassic. After discovery it was initially reburied; it was moved to the Xalapa Museum of Anthropology in 1986. The headdress is decorated with the talons or claws of either a jaguar or an eagle. It has a headband and a cover that descends from under the headdress proper behind the ears. Two short straps descend in front of the ears. The head sports large ear ornaments in the form of pegs. The face is that of a mature male with sagging cheeks and wrinkles between these and the nose. The forehead is gathered in a frown. The mouth is slightly parted to reveal the teeth. Most of the head is carved in a realistic manner, the exception being the ears. These are stylised and represented by one question mark shape contained within another. The head is very well preserved and displays a fine finish. San Lorenzo Colossal Head 9 is also known as San Lorenzo Monument 66. It measures 1.65 metres (5.4 ft) high by 1.36 metres (4.5 ft) wide by 1.17 metres (3.8 ft) deep. The head was exposed in 1982 by erosion of the gullies at San Lorenzo; it was found leaning slightly on its right hand side and facing upwards, half covered by
|
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the collapsed side of a gully and washed by a stream. Although it was documented by archaeologists, it remained for some time in its place of discovery before being moved to the Xalapa Museum of Anthropology. The headdress is of a single piece without a distinct headband. The sides display features that are possibly intended to represent long hair trailing to the bottom of the monument. The earflares are rectangular plates with an additional trapezoid element at the front. The head is also depicted wearing a nose-ring. The face is smiling and has wrinkles under the eyes and at the edge of the mouth. It has sagging cheeks and wide eyes. The mouth is closed and the upper lip is badly damaged. The sculpture suffered some mutilation in antiquity, with nine pits hollowed into the face and headdress. San Lorenzo Colossal Head 10 (also known as San Lorenzo Monument 89) has been moved to the Museo Comunitario de San Lorenzo Tenochtitlán near Texistepec. It stands 1.8 metres (5.9 ft) tall and measures 1.43 metres (4.7 ft) wide by 0.92 metres (3.0 ft) deep; it weighs 8 tons. The head was discovered by a magnetometer survey in 1994; it was found buried, lying face upwards in the bottom of a ravine and was excavated by Ann Cyphers. The headdress is formed of 92 circular beads that completely cover the upper part of the head and descend across the sides and back. Above the forehead is a large element forming a three-toed foot with long nails, possibly the foot of a bird. The head wears large earspools that protrude beyond the beads of the headdress. The spools have the form of a rounded square with a circular sunken central portion. The face is that of a mature man with the mouth closed,
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sagging cheeks and lines under the eyes. The mouth is sensitively carved and the head possesses a pronounced chin. === La Venta === Three of the La Venta heads were found in a line running east-west in the northern Complex I; all three faced northwards, away from the city centre. The other head was found in Complex B to the south of the Great Pyramid, in a plaza that included other sculptures. The latter, the first of the La Venta heads to be discovered, was found during archaeological exploration of La Venta in 1925; the other three remained unknown to archaeologists until a local boy guided Matthew Stirling to them while he was excavating the first head in 1940. They were located approximately 0.9 kilometres (0.56 mi) to the north of Monument 1. La Venta Monument 1 is speculated to have been the portrait of La Venta's final ruler. Monument 1 measures 2.41 metres (7.9 ft) high by 2.08 metres (6.8 ft) wide by 1.95 metres (6.4 ft) deep; it weighs 24 tons. The front of the headdress is decorated with three motifs that apparently represent the claws or fangs of an animal. Above these symbols is an angular U-shaped decoration descending from the scalp. On each side of the monument a strap descends from the headdress, passing in front of the ear. Each ear has a prominent ear ornament that descends from the earlobe to the base of the monument. The features are those of a mature man, with wrinkles around the mouth, eyes and nose. Monument 1 is the best preserved head at La Venta but has suffered from erosion, particularly at the back. The head was first described by Franz Blom and Oliver La Farge who investigated the La Venta remains on behalf of Tulane University in
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1925. When discovered, it was half-buried; its massive size meant that the discoverers were unable to excavate it completely. Matthew Stirling fully excavated the monument in 1940, after clearing the thick vegetation that had covered it in the intervening years. Monument 1 has been moved to the Parque-Museo La Venta in Villahermosa. The head was found in its original context; associated finds have been radiocarbon dated to between 1000 and 600 BC. La Venta Monument 2 measures 1.63 metres (5.3 ft) high by 1.35 metres (4.4 ft) wide by 0.98 metres (3.2 ft) deep; the head weighs 11.8 tons. The face has a broadly smiling expression that reveals four of the upper teeth. The cheeks are given prominence by the action of smiling; the brow that is normally visible in other heads is covered by the rim of the headdress. The face is badly eroded, distorting the features. In addition to the severe erosion damage, the upper lip and a part of the nose have been deliberately mutilated. The head was found in its original context a few metres north of the northwest corner of pyramid-platform A-2. Radiocarbon dating of the monument's context dates it to between 1000 and 600 BC. Monument 2 has suffered erosion damage from its exposure to the elements prior to discovery. The head has a prominent headdress but this is badly eroded and any individual detail has been erased. A strap descends in front of the ear on each side of the head, descending as far as the earlobe. The head is adorned with ear ornaments in the form of a disc that covers the earlobe, with an associated clip or peg. The surviving details of the headdress and earflares are stylistically similar to those of Tres Zapotes Monument A. The head has been moved
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to the Museo del Estado de Tabasco in Villahermosa. La Venta Monument 3 stands 1.98 metres (6.5 ft) high and measures 1.6 metres (5.2 ft) wide by 1 metre (3.3 ft) deep; it weighs 12.8 tons. Monument 3 was located a few metres to the east of Monument 2, but was moved to the Parque-Museo La Venta in Villahermosa. Like the other La Venta heads, its context has been radiocarbon dated to between 1000 and 600 BC. It appears unfinished and has suffered severe damage through weathering, making analysis difficult. It had a large headdress that reaches to the eyebrows but any details have been lost through erosion. Straps descend in front of each ear and continue to the base of the monument. The ears are wearing large flattened rings that overlap the straps; they probably represent jade ornaments of a type that have been recovered in the Olmec region. Although most of the facial detail is lost, the crinkling of the bridge of the nose is still evident, a feature that is common to the frowning expressions of the other Olmec colossal heads. La Venta Monument 4 measures 2.26 metres (7.4 ft) high by 1.98 metres (6.5 ft) wide and 1.86 metres (6.1 ft) deep. It weighs 19.8 tons. It was found a few metres to the west of Monument 2 and has been moved to the Parque-Museo La Venta. As with the other heads in the group, its archaeological context has been radiocarbon dated to between 1000 and 600 BC. The headdress is elaborate and, although damaged, various details are still discernible. The base of the headdress is formed by three horizontal strips running over the forehead. One side is decorated with a double-disc motif that may have been repeated on the other; if so, damage to the
|
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right side has obliterated any trace of it. The top of the headdress is decorated with the clawed foot of a bird of prey. Either straps or plaits of hair descend on either side of the face, from the headdress to the base of the monument. Only one earspool survives; it is flat, in the form of a rounded square, and is decorated with a cross motif. The ears have been completely eroded away and the lips are damaged. The surviving features display a frown and creasing around the nose and cheeks. The head displays prominent teeth. === Tres Zapotes === The two heads at Tres Zapotes, with the La Cobata head, are stylistically distinct from the other known examples. Beatriz de la Fuente views them as a late regional survival of an older tradition while other scholars argue that they are merely the kind of regional variant to be expected in a frontier settlement. These heads are sculpted with relatively simple headdresses; they have squat, wide proportions and distinctive facial features. The two Tres Zapotes heads are the earliest known stone monuments from the site. The discovery of one of the Tres Zapotes heads in the 19th century led to the first archaeological investigations of Olmec culture, carried out by Matthew Stirling in 1938. Tres Zapotes Monument A (also known as Tres Zapotes Colossal Head 1) was the first colossal head to be found, discovered by accident in the middle of the 19th century, 1 kilometre (0.62 mi) to the north of the modern village of Tres Zapotes. After its discovery it remained half-buried until it was excavated by Matthew Stirling in 1939. At some point it was moved to the plaza of the modern village, probably in the early 1960s. It has since been moved to the Museo
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Comunitario de Tres Zapotes. Monument A stands 1.47 metres (4.8 ft) tall; it measures 1.5 metres (4.9 ft) wide by 1.45 metres (4.8 ft) deep, and is estimated to weigh 7.8 tons. The head is sculpted with a simple headdress with a wide band that is otherwise unadorned, and wears rectangular ear ornaments that project forwards onto the cheeks. The face is carved with deep creases between the cheeks and the nose and around the mouth; the forehead is creased into a frown. The upper lip has suffered recent damage, with the left portion flaking away. Tres Zapotes Monument Q (also known as the Nestape Head and Tres Zapotes Colossal Head 2) measures 1.45 metres (4.8 ft) high by 1.34 metres (4.4 ft) wide by 1.26 metres (4.1 ft) deep and weighs 8.5 tons. Its exact date of discovery is unknown but is estimated to have been some time in the 1940s, when it was struck by machinery being used to clear vegetation from Nestape hill. Monument Q was the eleventh colossal head to be discovered. It was moved to the plaza of Santiago Tuxtla in 1951 and remains there to this day. Monument Q was first described by Williams and Heizer in an article published in 1965. The headdress is decorated with a frontal tongue-shaped ornament, and the back of the head is sculpted with seven plaits of hair bound with tassels. A strap descends from each side of the headdress, passing over the ears and to the base of the monument. The face has pronounced creases around the nose, mouth and eyes. === La Cobata === The La Cobata region was the source of the basalt used for carving all of the colossal heads in the Olmec heartland. The La Cobata colossal head was discovered in 1970 and
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was the fifteenth to be recorded. It was discovered in a mountain pass in the Sierra de los Tuxtlas, on the north side of El Vigia volcano near to Santiago Tuxtla. The head was largely buried when found; excavations uncovered a Late Classic (600–900 AD) offering associated with the head consisting of a ceramic vessel and a 12-centimetre (4.7 in) long obsidian knife placed pointing northwards towards the head. The offering is believed to have been deposited long after the head was sculpted. The La Cobata head has been moved from its original location to the main plaza at Santiago. The La Cobata head is more or less rounded and measures 3 by 3 metres (9.8 by 9.8 ft) by 3.4 metres (11 ft) high, making it the largest known head. This massive sculpture is estimated to weigh 40 tons. It is stylistically distinct from the other examples, and Beatriz de la Fuente placed it late in the Olmec time frame. The characteristics of the sculpture have led to some investigators suggesting that it represents a deceased person. Norman Hammond argues that the apparent stylistic differences of the monument stem from its unfinished state rather than its late production. The eyes of the monument are closed, the nose is flattened and lacks nostrils and the mouth was not sculpted in a realistic manner. The headdress is in the form of a plain horizontal band. The original location of the La Cobata head was not a major archaeological site and it is likely that the head was either abandoned at its source or during transport to its intended destination. Various features of the head suggest that it was unfinished, such as a lack of symmetry below the mouth and an area of rough stone above the base. Rock was not removed
|
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from around the earspools as on other heads, and does not narrow towards the base. Large parts of the monument seem to be roughed out without finished detail. The right hand earspool also appears incomplete; the forward portion is marked with a sculpted line while the rear portion has been sculpted in relief, probably indicating that the right cheek and eye area were also unfinished. The La Cobata head was almost certainly carved from a raw boulder rather than being sculpted from a throne. === Takalik Abaj === Takalik Abaj Monument 23 dates to the Middle Preclassic period, and is found in Takalik Abaj, an important city in the foothills of the Guatemalan Pacific coast, in the modern department of Retalhuleu. It appears to be an Olmec-style colossal head re-carved into a niche figure sculpture. If originally a colossal head then it would be the only known example from outside the Olmec heartland. Monument 23 is sculpted from andesite and falls in the middle of the size range for confirmed colossal heads. It stands 1.84 metres (6.0 ft) high and measures 1.2 metres (3.9 ft) wide by 1.56 metres (5.1 ft) deep. Like the examples from the Olmec heartland, the monument features a flat back. Lee Parsons contests John Graham's identification of Monument 23 as a re-carved colossal head; he views the side ornaments, identified by Graham as ears, as rather the scrolled eyes of an open-jawed monster gazing upwards. Countering this, James Porter has claimed that the re-carving of the face of a colossal head into a niche figure is clearly evident. Monument 23 was damaged in the mid-20th century by a local mason who attempted to break its exposed upper portion using a steel chisel. As a result, the top is fragmented, although the broken pieces were recovered
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by archaeologists and have been put back into place. == Collections == All of the 17 confirmed colossal heads remain in Mexico. Two heads from San Lorenzo are on permanent display at the Museo Nacional de Antropología in Mexico City. Seven of the San Lorenzo heads are on display in the Xalapa Museum of Anthropology. Five of them are in Sala 1, one is in Sala 2, and one is in Patio 1. The remaining San Lorenzo head is in the Museo Comunitario de San Lorenzo Tenochtitlán near Texistepec. All four heads from La Venta are now in Villahermosa, the state capital of Tabasco. Three are in the Parque-Museo La Venta and one is in the Museo del Estado de Tabasco. Two heads are on display in the plaza of Santiago Tuxtla; one from Tres Zapotes and the La Cobata Head. The other Tres Zapotes head is in the Museo Comunitario de Tres Zapotes. Several colossal heads have been loaned to temporary exhibitions abroad; San Lorenzo Colossal Head 6 was loaned to the Metropolitan Museum of Art in New York in 1970. San Lorenzo colossal heads 4 and 8 were lent to the Olmec Art of Ancient Mexico exhibition in the National Gallery of Art, Washington, D.C., which ran from 30 June to 20 October 1996. San Lorenzo Head 4 was again loaned in 2005, this time to the de Young Museum in San Francisco. The de Young Museum was loaned San Lorenzo colossal heads 5 and 9 for its Olmec: Colossal Masterworks of Ancient Mexico exhibition, which ran from 19 February to 8 May 2011. === Vandalism === On 12 January 2009, at least three people, including two Mexicans and one American, entered the Parque-Museo La Venta in Villahermosa and damaged just under 30 archaeological pieces, including the four
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La Venta colossal heads. The vandals were all members of an evangelical church and appeared to have been carrying out a supposed pre-Columbian ritual, during which salts, grape juice, and oil were thrown on the heads. It was estimated that 300,000 pesos (US$21,900) would be needed to repair the damage, and the restoration process would last four months. The three vandals were released soon after their arrest after paying 330,000 pesos each. === Replicas === The majority of replicas around the world, though not all, were placed under the leadership of Miguel Alemán Velasco, former governor of the state of Veracruz. The following is a list of replicas and their locations: Austin, Texas. A replica of San Lorenzo Head 1 was placed in the Teresa Lozano Long Institute of Latin American Studies at the University of Texas in November 2008. Chicago, Illinois. A replica of San Lorenzo Head 8 made by Ignacio Perez Solano was placed in the Field Museum of Natural History in 2000. Covina, California. A replica of San Lorenzo Head 5 was donated to Covina in 1989, originally intended to be placed in Jalapa Park. Due to concerns over potential vandalism it was instead installed outside the police station. It was removed in 2011 and relocated to Jobe's Glen, Jalapa Park in June 2012. McAllen, Texas. A replica of San Lorenzo Head 8 is located in the International Museum of Art & Science. The placement was dedicated by Fidel Herrera Beltrán, then governor of Veracruz. This was done in 2010. The head is one of 12 sculpted by Ignacio Perez Solano and sent to various cities around the world. New York. A replica of San Lorenzo Head 1 was placed next to the main plaza in the grounds of Lehman College in the Bronx, New York. It
|
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"title": "Olmec colossal heads"
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was installed in 2013 to celebrate the first anniversary of the CUNY Institute of Mexican Studies, housed at the college. The replica was a gift by the government of Veracruz state, Cumbre Tajín and Mexico Trade; it was first placed in Dag Hammerskjold Park, outside the United Nations, in 2012. Paris. Since 2013, the Musée du Quai Branly – Jacques Chirac displays a replica of San Lorenzo Head 8 in its public gardens. San Francisco, California. A replica of San Lorenzo Head 1 created by Ignacio Perez Solano was placed in San Francisco City College, Ocean Campus in October 2004. Washington, D.C. A replica of San Lorenzo Head 4 sculpted by Ignacio Perez Solano was placed near the Constitution Avenue entrance of the Smithsonian National Museum of Natural History in October 2001. West Valley City, Utah. A replica of San Lorenzo Head 8 was placed in the Utah Cultural Celebration Center in May 2004. Todos Santos, Baja California Sur. A replica of a San Lorenzo Head 8 was sculpted in July 2018 by Mexican sculptor Benito Ortega Vargas. It is on the mound on the Camino a Las Playitas just north of Todos Santos. Mexican Government of Veracruz donated a resin replica of an Olmec colossal head to Belgium; it is on display in the Tournay Solvay Park in Brussels. In February 2010, the Secretaría de Relaciones Exteriores (Secretariat of Foreign Affairs) announced that the Instituto Nacional de Antropología e Historia would be donating a replica Olmec colossal head to Ethiopia. It was placed in Plaza Mexico in Addis Ababa in May 2010 and is locally known as the "Mexican Warrior". Online conspiracy theory memes have surfaced claiming this is 'proof' of Africans arriving in the Americas before Columbus. In November 2017, President Enrique Peña Nieto donated a full-size replica
|
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"page_id": 35721801,
"source": null,
"title": "Olmec colossal heads"
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of San Lorenzo Head 8 to the people of Belize. It was installed in Belmopan at the roundabout facing the Embassy of Mexico. == See also == Maya stelae Moai Monte Alto culture Stone spheres of Costa Rica == Footnotes == == References == == Further reading ==
|
{
"page_id": 35721801,
"source": null,
"title": "Olmec colossal heads"
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The molecular formula C21H24O10 (molar mass: 436.41 g/mol, exact mass: 436.136947 u) may refer to: Nothofagin, a C-linked phloretin glucoside Phlorizin, an O-linked phloretin glucoside
|
{
"page_id": 24318538,
"source": null,
"title": "C21H24O10"
}
|
This list of sequenced plant genomes contains plant species known to have publicly available complete genome sequences that have been assembled, annotated and published. Unassembled genomes are not included, nor are organelle only sequences. For all kingdoms, see the list of sequenced genomes. See also List of sequenced algae genomes. == Bryophytes == == Vascular plants == === Lycophytes === === Ferns === === Gymnosperms === === Angiosperms === ==== Amborellales ==== ==== Chlorantales ==== Magnoliales ==== Eudicots ==== ===== Proteales ===== ===== Ranunculales ===== ===== Trochodendrales ===== ===== Caryophyllales ===== ===== Rosids ===== ===== Asterids ===== ==== Monocots ==== ===== Grasses ===== ===== Other non-grasses ===== == Press releases announcing sequencing == Not meeting criteria of the first paragraph of this article in being nearly full sequences with high quality, published, assembled and publicly available. This list includes species where sequences are announced in press releases or websites, but not in a data-rich publication in a refereed peer-review journal with DOI. Corchorus olitorius (Jute mallow), fibre plant 2017 Corchorus capsularis 2017 Fraxinus excelsior, European ash (2013 draft) == See also == List of sequenced eukaryotic genomes List of sequenced animal genomes List of sequenced archaeal genomes List of sequenced bacterial genomes List of sequenced fungi genomes List of sequenced plastomes List of sequenced protist genomes == External links == http://plabipd.de/timeline_view.ep http://genomevolution.org/wiki/index.php/Sequenced_plant_genomes https://phytozome.jgi.doe.gov/pz/portal.html https://bioinformatics.psb.ugent.be/plaza/ == References ==
|
{
"page_id": 33362511,
"source": null,
"title": "List of sequenced plant genomes"
}
|
Arginine carboxypeptidase may refer to: Lysine carboxypeptidase, an enzyme Carboxypeptidase U, an enzyme
|
{
"page_id": 39260751,
"source": null,
"title": "Arginine carboxypeptidase"
}
|
Dilution cloning or cloning by limiting dilution describes a procedure to obtain a monoclonal cell population starting from a polyclonal mass of cells. This is achieved by setting up a series of increasing dilutions of the parent (polyclonal) cell culture. A suspension of the parent cells is made. Appropriate dilutions are then made, depending on cell number in the starting population, as well as the viability and characteristics of the cells being cloned. After the final dilutions are produced, aliquots of the suspension are plated or placed in wells and incubated. If all works correctly, a monoclonal cell colony will be produced. Applications for the procedure include cloning of parasites, T cells, transgenic cells, macrophages. and hematopoietic stem cells. == References == == External links == Robert Staszewski "Cloning by Limiting Dilution: an improved estimate that an interesting culture is monoclonal" [1] John A. Ryan "Cell Cloning by Serial Dilution in 96 Well Plates". Vilma Maldonado,Jorge Meléndez-Zajgla "A modified method for cloning adherent mammalian cells". "Cloning by Limiting Dilution". "Cloning by limiting dilution". Nanci Donacki "Cloning by Limiting Dilution of Hybridoma".
|
{
"page_id": 6885971,
"source": null,
"title": "Dilution cloning"
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|
The molecular formula C21H32O3 (molar mass: 332.48 g/mol) may refer to: Alfaxalone Androstenediol 3β-acetate Androstenediol 17β-acetate BNN-27 Dihydrodeoxycorticosterone Dihydrotestosterone acetate Hydroxydione, a neurosteroid Hydroxypregnenolones 17α-Hydroxypregnenolone 21-Hydroxypregnenolone Hydroxyhexahydrocannabinols 9-Hydroxyhexahydrocannabinol 11-Hydroxyhexahydrocannabinol Oxymetholone 5α-Pregnan-17α-ol-3,20-dione
|
{
"page_id": 23663191,
"source": null,
"title": "C21H32O3"
}
|
Neurocriminology is an emerging sub-discipline of biocriminology and criminology that applies brain imaging techniques and principles from neuroscience to understand, predict, and prevent crime. == Concept == While crime is partially a social and environmental problem, the main idea behind neurocriminology (also known as neurolaw) is that the condition of an individual's brain often needs to be included in the analysis for a complete understanding. This can include conditions such as brain tumors, psychoses, sociopathy, sleepwalking, and many more. Deviant brain theories have always been part of biocriminology, which explains crime with biological reasons. Neurocriminology has become mainstream during the past two decades, since contemporary biocriminologists focus almost exclusively on brain due to significant advances in neuroscience. Even though neurocriminology is still at odds with traditional sociological theories of crime, it is becoming more popular in the scientific community. == Origins == The origins of neurocriminology go back to one of the founders of modern criminology, 19th-century Italian psychiatrist and prison doctor Cesare Lombroso, whose beliefs that the crime originated from brain abnormalities were partly based on phrenological theories about the shape and size of the human head. Lombroso conducted a postmortem on a serial killer and rapist, who had an unusual indentation at the base of the skull. Lombroso discovered a hollow part in the killer's brain where the cerebellum would be. Lombroso's theory was that crime originated in part from abnormal brain physiology and that violent criminals where throwbacks to less evolved human types identifiable by ape-like physical characteristics. Criminals, he believed, could be identified by physical traits, such as a large jaw and sloping forehead. The contemporary neuroscientists further developed his idea that physiology and traits of the brain underlie all crime. The term “neurocriminology” was first introduced by James Hilborn (Cognitive Centre of Canada) and adopted
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"title": "Neurocriminology"
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by the leading researcher in the field, Dr. Adrian Raine, the chair of the Criminology Department at University of Pennsylvania. He was the first to conduct brain imaging study on violent criminals. == Major studies == Many recent studies have revealed that sometimes structural and functional abnormalities are so striking that anyone can see them. Some violent offenders, however, have subtle structural or functional abnormalities and even highly experienced neuroradiologists cannot detect these irregularities right away. Yet, the abnormalities can be detected using brain imaging and state-of-the-art analytic tools. == Neurophysiological studies == Studies on structural deficiencies suggest that people consistently behaving antisocially have structurally impaired brains. The abnormalities can be either of general character or affect specific regions of the brain that control emotions, aggression or are responsible for ethical decisions: Low number of neurons in the prefrontal cortex. A study in 2000 determined that people with a history of persistent antisocial behavior had an 11 percent reduction in the volume of gray matter in the prefrontal cortex, while white matter volume was normal. Similarly, A 2009 meta-analysis study, which pooled together the findings of 12 anatomical brain-imaging studies conducted on offender populations, found that the prefrontal cortex of the brain is indeed structurally impaired in offenders. Underdeveloped amygdalae. Two studies found that both the left and especially the right amygdalae are impaired in psychopaths. The psychopaths had on average 18 percent reduction in the volume of the right amygdala. Cavum septi pellucidi maldevelopment. A study in 2010 suggested that people with cavum septi pellucidi were prone to psychopathy, antisocial personality disorder, and had more charges and convictions for criminal offenses. This brain maldevelopment was especially linked to lifelong antisocial behavior, i.e. a reckless disregard for self and others, lack of remorse, and aggression. Bigger right hippocampus. A 2004
|
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"page_id": 32379480,
"source": null,
"title": "Neurocriminology"
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study suggested that the psychopaths’ right hippocampus that partially controls emotions and regulates aggression was significantly bigger than the left. This asymmetry was also true in normal people, but it was much more noticeable in psychopaths. Increase in the volume of the striatum. A study in 2010 found that psychopathic individuals showed a 10 percent increase in the volume of the striatum. Damage by foreign objects. A large number of studies on structural damage by foreign objects convincingly shows that adults suffering head injuries damaging the prefrontal cortex show impulsive and antisocial behavior that does not conform to the norms of society. There is a number of famous life stories showing the same causal connection. For example, P. Gage was a well-respected, well-liked, and responsible gentleman. In 1848 because of a construction accident he suffered a serious damage to his brain when a metal rod propelled by an explosive entered his lower left cheek and exited from the top-middle part of his head. Gage healed quickly. After that accident, however, he became erratic, disrespectful, and vulgar. Gage had been transformed from a well-controlled, well-respected person to an individual with psychopathic traits. Damage by tumors. There is also a number of famous U.S. criminal cases showing that damage of the brain by tumors can result in the same transformation as the damage by foreign objects. Charles Whitman, for instance, was a young man who studied architectural engineering at the University of Texas. Whitman had no history of violence or crime. As a child, he scored 138 on the Stanford-Binet IQ test, placing in the 99th percentile. He was an Eagle Scout, volunteered as a scoutmaster, and served in Marine Corps. In 1966 Whitman unexpectedly killed his mother as well as wife, ascended the belltower of the University of Texas, Austin, and
|
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fired a rifle at students below. He killed 15 people and wounding 31 more before police officers shot him. Whitman in his final note complained of inability to control his thoughts and requested an autopsy, which revealed a brain tumor in the hypothalamus region of his brain, a growth that, some hypothesized, put pressure on his amygdala. Another example would be Michael Oft. Oft was a teacher in Virginia who had no prior psychiatric nor deviant behavior history. At the age of forty, his behavior suddenly changed. He began to frequent massage parlors, collect child pornography, abuse his step-daughter, and was soon found guilty of child molestation. Mr. Oft opted for a treatment program for pedophiles, but still couldn't resist soliciting sexual favors from staff and other clients at the rehabilitation center. A neurologist advised a brain scan, which showed a tumor growing at the base of his orbitofrontal cortex, compressing the right prefrontal region of his brain. After the tumor was removed, Mr. Oft's emotion, behavior and sexual activity returned to normal. But after several months of normal behavior Mr. Oft again began to collect child pornography. Neurologists rescanned his brain and found that the tumor had grown back. After the second surgery removing the tumor, his behavior has been totally appropriate. == Neurofunctional studies == Similarly to neurophysiological studies neurofunctional showed that brains of criminals and psychopaths not only are structures differently but also operate in a different way. As you can see below, both structural and functional abnormalities tend to affect the same areas of the brain. These are the major abnormalities found: Lack of Activation in the Prefrontal Cortex. A number of studies replicated the observance that violent criminals’ brains showed a significant reduction in prefrontal glucose metabolism. Reduced Activity In The Amygdala. A study found
|
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that individuals with high psychopathy scores showed reduced activity in the amygdala during emotional, personal moral decision-making. Dysfunctional Posterior Cingulate. Two studies found that posterior cingulate functions poorly in adult criminal psychopaths and aggressive patients. Reduced Cerebral Blood Flow in Angular Gyrus. A couple of studies found reduced cerebral blood flow in angular gyrus of murderers and impulsive, violent criminals. Higher Activation of Subcortical Limbic Regions. A 1998 study showed higher activation of subcortical limbic regions of two groups of reactive and proactive murderers, especially in the more “emotional” right hemisphere of the brain. Functional Disturbances of the Hippocampus and Its Parahippocampal Gyrus. A number of studies suggest that this region of the brain is not working properly in murders and violent offenders in general. Differences in hormone levels: A 2022 study observed reported crime and hormone levels–mainly that of testosterone and cortisol–within a population of university students as consenting participants. Results from the research found that there was a positive direct correlation between testosterone levels and criminal behavior, particularly in terms of impulsive behavior and aggression. However, further tests may need to be conducted to determine if those behaviors are connected to criminal behavior through dominance-seeking behavior associated with testosterone or if it is more so due to testosterone’s influence in the mesolimbic reward system by instant gratification related to committing crime. It was also found that cortisol–a major hormone in the stress response system–in both high and low levels is correlated with an increase in criminal behavior. In response to stress or threats, high levels of cortisol boost energy, suppress the immune system and increase cardiovascular activity while low levels are associated with signs of psychopathy including a lack of empathy. The two hormones were found to interact to create influence on criminal behavior with low levels of
|
{
"page_id": 32379480,
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cortisol and baseline levels of testosterone correlating with income-generating crime. Effects of drugs: Illegal drug use and drug abuse are found to be highly correlated with antisocial behaviors leading to crime. Drugs function to mimic and take the place of naturally-occurring neurotransmitters–or chemical brain signals–that activate brain chemical receptors and affect arousal, mood, as well as physiological and cognitive function among other neurophysiological effects. In cases of addiction, particular drugs may affect the brain’s rewards system, making it overly sensitive to the drug: thus making naturally occurring, healthy behaviors less rewarding and increasing deviant behaviors like attention-seeking, impulsivity, and aggression–often related to withdrawal behavioral traits–all of which can promote criminal behavior. In particular, inhibition caused by drug use can impair regular brain functioning, especially that of the pre-frontal cortex, impairing the ability to make decisions and perform higher-level thinking and reasoning that is otherwise critical in preventing criminal and deviant behaviors. == Ethical Concerns == === Free Will === Unlike the founding father of criminology, Cesare Lombroso, who thought that crime was fundamentally biological in its origin and criminals lacked free will altogether, contemporary neurocriminologists seem to take the middle ground approach. They do not argue that biological factors alone cause behavioral problems, but recognize that behavior results from interaction between biology and environment. Some authors, however, are more determinist in their views. As Stanford neuroscientist David Eagleman writes: "Free will may exist (it may simply be beyond our current science), but one thing seems clear: if free will does exist, it has little room in which to operate. It can at best be a small factor riding on top of vast neural networks shaped by genes and environment. In fact, free will may end up being so small that we eventually think about bad decision-making in the same way
|
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we think about any physical process, such as diabetes or lung disease." == Legal use == US legal defense teams increasingly use brain scans as mitigating evidence in trials of violent criminals and sex offenders. See Neurolaw for more. Here are some of the most famous cases: === Herbert Weinstein === In 1991, a sixty-five-year-old advertising executive with no prior history of crime or violence after an argument strangled his wife, opened the window and threw her out of their 12th-floor apartment. His defense team had a structural brain scan done using MRI and PET scan. The images showed a big piece missing from the prefrontal cortex of the brain, i.e., a subarachnoid cyst was growing in his left frontal lobe. The defense team used these images to argue that Weinstein had an impaired ability to regulate his emotions and make rational decisions. The team went with an insanity defense, and the prosecution and defense agreed to a plea of manslaughter. As a result, Weinstein was given a seven-year sentence in contrast to the twenty-five-year sentence he would have served if he had been convicted of second-degree murder. He ended up serving until 2006. === Antonio Bustamante === Bustamante was a well-behaved teenager who suddenly at the age of 22 became a career criminal. His crimes included theft, breaking and entering, drug offenses, and robbery. In 1990 Bustamante was charged with a homicide. The defense team discovered that the client had suffered a head injury from a crowbar at the age of twenty. Bustamante's behavior changed fundamentally after that, transforming him from a normal individual into an impulsive and emotionally labile criminal. The defense team had his client's brain scanned, which revealed malfunctioning of the prefrontal cortex. At the end the jury believed that Bustamante's brain was not normal and
|
{
"page_id": 32379480,
"source": null,
"title": "Neurocriminology"
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spared him from the death penalty. === Donta Page === In 1999, Page robbed, raped and killed a female student in Denver. He later was found guilty of first-degree murder and was a candidate for the death penalty. Professor A. Raine from the University of Pennsylvania was an expert witness for defense and brought Page into a laboratory to assess his brain function. Brain imaging scans revealed a distinct lack of activation in the ventral prefrontal cortex. Professor Raine argued for a deep-rooted biological explanation for Mr. Page's violence, who escaped death penalty partly on the basis of his brain pathology. == Crime prevention == Even though currently there are no preventive programs in place utilizing the recent discoveries in neurocriminology, there are a number of offender rehabilitation programs (Cognitive Centre of Canada). === Decisions based on brain imaging === Some scientists propose using brain imaging to help decide which soon-to-be-released offenders are at greater risk for reoffending. The brain imaging data would be used along with common factors like age, prior arrests, and marital status. To support this idea, in a 2013 study, Professor Kent Kiehl from the University of New Mexico studying the population of 96 male offenders in the state's prisons found that offenders with low activity in the anterior cingulate cortex where twice as likely to commit an offense in the four years after their release as those who had high activity in this region. Similarly, Dustin Pardini conducted that which shows that men with a smaller amygdala are three times more likely to commit violence three years after their release. === Neurochemistry === Trials demonstrated the efficacy of a number of medications, i.e. stimulants antipsychotics, antidepressants and mood stabilizers, in diminishing aggression in adolescents and children. Even a simple omega-3 supplements in the diets of
|
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young offenders reduces offending and aggression. However, drug treatment is subject to vary based on biological and environmental influences. Variation in genes predisposes differences in biological systems and brain structure and function within individuals, influencing outcomes. === Meditation === Meditation can also affect brains, and even change them permanently. In 2003 Professor Richie Davidson from the University of Wisconsin performed a revolutionary study. People were randomly selected into either a mindfulness training group or a control group that was put on a waiting list for training. Davidson showed that even eight weekly sessions of meditation enhanced left frontal EEG functioning. Similar study was later replicated by Professor Holzel. === Stigma === In preventing crime on the basis of association to neurobiological function, there could also be adverse effects in increased stigma around those with atypical brain functioning and mental disorders. Although much research has been discovered in relation to neurocriminology, all atypical brain functions do not objectively result in deviant, criminal, or problematic behaviors. This bias can potentially bring bias towards those with divergent mental functionings into being categorized as those who are unable to make–morally–correct decisions. It is also worth considering that while focusing on neurobiological aspects, the social-environmental facets and causes of criminal behaviors cannot be ignored. Research has found that although an early intervention may benefit those who are at risk of violent, anti-social behaviors–especially in children and adolescents–it can adversely cause negative effects. When stigma is associated with the labeling of mental functions, it can increase anxiety and potentially trigger the development of maladaptive cognitions and narratives. Although neurological research is important in crime prevention, performing intervention in light of the criminal justice system is ideally done while respecting the rights of people and earning consent to perform prevention strategies. == See also == Criminology Social
|
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"page_id": 32379480,
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|
neuroscience Neurolaw Neuropsychiatry == References ==
|
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"page_id": 32379480,
"source": null,
"title": "Neurocriminology"
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A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature spatial gradient is a vector quantity with dimension of temperature difference per unit length. The SI unit is kelvin per meter (K/m). Temperature gradients in the atmosphere are important in the atmospheric sciences (meteorology, climatology and related fields). == Mathematical description == Assuming that the temperature T is an intensive quantity, i.e., a single-valued, continuous and differentiable function of three-dimensional space (often called a scalar field), i.e., that T = T ( x , y , z ) {\displaystyle T=T(x,y,z)} where x, y and z are the coordinates of the location of interest, then the temperature gradient is the vector quantity defined as ∇ T = ( ∂ T ∂ x , ∂ T ∂ y , ∂ T ∂ z ) {\displaystyle \nabla T={\begin{pmatrix}{\frac {\partial T}{\partial x}},{\frac {\partial T}{\partial y}},{\frac {\partial T}{\partial z}}\end{pmatrix}}} == Physical processes == === Meteorology === Differences in air temperature between different locations are critical in weather forecasting and climate. The absorption of solar light at or near the planetary surface increases the temperature gradient and may result in convection (a major process of cloud formation, often associated with precipitation). Meteorological fronts are regions where the horizontal temperature gradient may reach relatively high values, as these are boundaries between air masses with rather distinct properties. Clearly, the temperature gradient may change substantially in time, as a result of diurnal or seasonal heating and cooling for instance. This most likely happens during an inversion. For instance, during the day the temperature at ground level may be cold while it's warmer up in the atmosphere. As the day shifts over to night the temperature might drop rapidly while at
|
{
"page_id": 1446490,
"source": null,
"title": "Temperature gradient"
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|
other places on the land stay warmer or cooler at the same elevation. This happens on the West Coast of the United States sometimes due to geography. === Weathering === Expansion and contraction of rock, caused by temperature changes during a wildfire, through thermal stress weathering, may result in thermal shock and subsequent structure failure. == Indoor temperature == == See also == Atmospheric temperature for gradient of Earth's atmosphere Geothermal gradient Gradient Lapse rate Weak temperature gradient approximation == References == Edward N. Lorenz (1967). The Nature and Theory of the General Circulation of the Atmosphere. Publication No. 218. Geneva, Switzerland: World Meteorological Organization. M. I. Budyko (1978). Climate and Life. International Geophysics Series. Vol. 18. Academic Press. ISBN 0-12-139450-6. Robert G. Fleagle; Joost A. Businger (1980). An introduction to atmospheric physics. International Geophysics Series. Vol. 25. Academic Press. ISBN 0-12-260355-9. David Miller (1981). Energy at the surface of the earth : an introduction to the energetics of ecosystems. Academic Press. ISBN 978-0-08-095460-8. John M. Wallace; Peter V. Hobbs (2006). Atmospheric Science: An Introductory Survey. Elsevier. ISBN 978-0-08-049953-6. == External links == IPCC Third Assessment Report Pictorial Representation of Temperature Gradient (Tools).
|
{
"page_id": 1446490,
"source": null,
"title": "Temperature gradient"
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|
In radiological physics, charged-particle equilibrium (CPE) occurs when the number of charged particles leaving a volume is equal to the number entering, for each energy and type of particle. When CPE exists in an irradiated medium, the absorbed dose in the volume is equal to the collision kerma. In order for this to occur, energy is needed. == References ==
|
{
"page_id": 22221404,
"source": null,
"title": "Charged-particle equilibrium"
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|
In humans, males and females differ in their strategies to acquire mates and focus on certain qualities. There are two main categories of strategies that both sexes utilize: short-term and long-term. Human mate choice, an aspect of sexual selection in humans, depends on a variety of factors, such as ecology, demography, access to resources, rank/social standing, genes, and parasite stress. While there are a few common mating systems seen among humans, the amount of variation in mating strategies is relatively large. This is due to how humans evolved in diverse niches that were geographically and ecologically expansive. This diversity, as well as cultural practices and human consciousness, have all led to a large amount of variation in mating systems. Below are some of the overarching trends of mate choice. == Female mate choice == Although human males and females are both selective in deciding with whom to mate, females exhibit more mate choice selectivity than males, as is seen in nature. Relative to most other animals however, female and male mating strategies are found to be more similar to each other. According to Bateman's principle of Lifespan Reproductive Success (LRS), human females display the least variance of the two sexes in their LRS due to their high obligatory parental investment, that is a nine-month gestational period, as well as lactation following birth in order to feed offspring so that their brain can grow to the required size. Human female sexual selection can be examined by looking at ways in which males and females are sexually dimorphic, especially in traits that serve little other evolutionary purpose. For example, male traits such as the presence of beards, overall lower voice pitch, and average greater height are thought to be sexually selected traits as they confer benefits to either the women selecting for
|
{
"page_id": 70324833,
"source": null,
"title": "Mate choice in humans"
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them, or to their offspring. Experimentally, women have reported a preference for men with beards and lower voices. Female mate choice hinges on many different coinciding male traits, and the trade-off between many of these traits must be assessed. The ultimate traits most salient to female human mate choice, however, are parental investment, resource provision and the provision of good genes to offspring. Many phenotypic traits are thought to be selected for as they act as an indication of one of these three major traits. The relative importance of these traits when considering mate selection differ depending on the type of mating arrangement females engage in. Human women typically employ long-term mating strategies when choosing a mate, however they also engage in short-term mating arrangements, so their mate choice preferences change depending on the function of the type of arrangement. == Mating strategies == === Female short-term === David Buss outlines several hypotheses as to the function of women's short-term mate choices: Resource hypothesis: Women may engage in short-term mating in order to gain resources that they may not be able to gain from a long-term partner, or that a long-term partner may not be able to provide consistently. These resources may be food, protection for the woman and her children from aggressive men who may capture or sexually coerce them, or status, by providing the woman with a higher social standing. Women may also benefit from having several short-term mating arrangements through paternity confusion—if the paternity of her offspring is not certain, she may be able to accrue resources from several men as a result of this uncertainty. Genetic benefit hypothesis: Women may choose to engage in short-term mating arrangements in order to aid conception if her long-term partner is infertile, to gain superior genes to those of her
|
{
"page_id": 70324833,
"source": null,
"title": "Mate choice in humans"
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long-term partner, or to acquire different genes to those of her partner and increase the genetic diversity of her offspring. This relates to what is known as the sexy son hypothesis; if a woman acquires genes from a high quality male, her offspring will likely have higher mate value, resulting in their increased reproductive success. Mate expulsion and mate switching: Women may engage in a short-term mating arrangement in order to cause an end to a long-term relationship; in other words, to facilitate a break-up. Women may also use short-term mating if their current partner has depreciated in value, and they wish to 'trade up' and find a partner that they believe has higher value. Short-term for long-term goals: Women may use short-term sexual relationships in order to assess a mate's value as a long-term partner, or in the hopes that the short-term arrangement will result in one that is long-term. === Female long-term === The provision of economic resources, or the potential to acquire many economic resources, is the most obvious cue towards the ability of a man to provide resources, and women in the United States have been shown experimentally to rate the importance of their partner's financial status more highly than men. However, many other traits exist that may act as cues towards a man's ability to provide resources that have been sexually selected for in women's evolutionary history. These include older age—older males have had more time to accrue resources—industriousness, dependability and stability—if a woman's long-term partner is not emotionally stable or is not dependable then their provision of resources to her and her offspring are likely to be inconsistent. Additionally, the costs associated with an emotionally unstable partner such as jealousy and manipulation may outweigh the benefits associated with the resources they are able to
|
{
"page_id": 70324833,
"source": null,
"title": "Mate choice in humans"
}
|
provide. Women's mate choices will also be constrained by the context in which they are making them, resulting in conditional mate choices. Some of the conditions that may influence female mate choice include the woman's own perceived attractiveness, the woman's personal resources, mate copying and parasite stress. Romantic love is the mechanism through which long-term mate choice occurs in human females. === Male short-term === When finding a short-term mate, males highly value women with sexual experience and physical attractiveness. Men seeking short-term sexual relationships are likely to avoid women who are interested in commitment or require investment. In short-term sexual relationships, men are less choosy because of low parental investment. Examples of short-term mating strategies in males: Multiple sexual partners: When looking for short-term sexual relationships, men may wish for there to be as little time as possible between each partner. Physical attractiveness: Men who are interested in a short-term sexual relationship are more likely to prioritise information about the body of potential partners, rather than their faces. When finding a female for a short-term relationship, compared with a long-term relationship, males are less likely to prioritise factors such as commitment. Relaxation of standards: It has been reported that men are more likely to engage in a sexual relationship with women who have lower levels of intelligence, independence, honesty, generosity, athleticism, responsibility and cooperativeness, when this relationship is short-term. Men may be more accepting of lower standards, than what they usually prefer, because they are not entering a long-term relationship with this person. Sexual experience: Many men assume that women who have engaged in sexual experiences beforehand are likely to have a higher sex drive than women who haven't. These women may also be more accessible and require less courtship. === Male long-term === Humans have the ability to
|
{
"page_id": 70324833,
"source": null,
"title": "Mate choice in humans"
}
|
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