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23,568,658 | https://en.wikipedia.org/wiki/Radioanalytical%20chemistry | Radioanalytical chemistry focuses on the analysis of sample for their radionuclide content. Various methods are employed to purify and identify the radioelement of interest through chemical methods and sample measurement techniques.
History
The field of radioanalytical chemistry was originally developed by Marie Curie with contributions by Ernest Rutherford and Frederick Soddy. They developed chemical separation and radiation measurement techniques on terrestrial radioactive substances. During the twenty years that followed 1897 the concepts of radionuclides was born. Since Curie's time, applications of radioanalytical chemistry have proliferated. Modern advances in nuclear and radiochemistry research have allowed practitioners to apply chemistry and nuclear procedures to elucidate nuclear properties and reactions, used radioactive substances as tracers, and measure radionuclides in many different types of samples.
The importance of radioanalytical chemistry spans many fields including chemistry, physics, medicine, pharmacology, biology, ecology, hydrology, geology, forensics, atmospheric sciences, health protection, archeology, and engineering. Applications include: forming and characterizing new elements, determining the age of materials, and creating radioactive reagents for specific tracer use in tissues and organs. The ongoing goal of radioanalytical researchers is to develop more radionuclides and lower concentrations in people and the environment.
Radiation decay modes
Alpha-particle decay
Alpha decay is characterized by the emission of an alpha particle, a 4He nucleus. The mode of this decay causes the parent nucleus to decrease by two protons and two neutrons. This type of decay follows the relation:
Beta-particle decay
Beta decay is characterized by the emission of a neutrino and a negatron which is equivalent to an electron. This process occurs when a nucleus has an excess of neutrons with respect to protons, as compared to the stable isobar. This type of transition converts a neutron into a proton; similarly, a positron is released when a proton is converted into a neutron. These decays follows the relation:
Gamma-ray decay
Gamma ray emission follows the previously discussed modes of decay when the decay leaves a daughter nucleus in an excited state. This nucleus is capable of further de-excitation to a lower energy state by the release of a photon. This decay follows the relation:
Radiation detection principles
Gas ionization detectors
Gaseous ionization detectors collect and record the electrons freed from gaseous atoms and molecules by the interaction of radiation released by the source. A voltage potential is applied between two electrodes within a sealed system. Since the gaseous atoms are ionized after they interact with radiation they are attracted to the anode which produces a signal. It is important to vary the applied voltage such that the response falls within a critical proportional range.
Solid-state detectors
The operating principle of Semiconductor detectors is similar to gas ionization detectors: except that instead of ionization of gas atoms, free electrons and holes are produced which create a signal at the electrodes. The advantage of solid state detectors is the greater resolution of the resultant energy spectrum. Usually NaI(Tl) detectors are used; for more precise applications Ge(Li) and Si(Li) detectors have been developed. For extra sensitive measurements high-pure germanium detectors are used under a liquid nitrogen environment.
Scintillation detectors
Scintillation detectors uses a photo luminescent source (such as ZnS) which interacts with radiation. When a radioactive particle decays and strikes the photo luminescent material a photon is released. This photon is multiplied in a photomultiplier tube which converts light into an electrical signal. This signal is then processed and converted into a channel. By comparing the number of counts to the energy level (typically in keV or MeV) the type of decay can be determined.
Chemical separation techniques
Due to radioactive nucleotides have similar properties to their stable, inactive, counterparts similar analytical chemistry separation techniques can be used. These separation methods include precipitation, Ion Exchange, Liquid Liquid extraction, Solid Phase extraction, Distillation, and Electrodeposition.
Radioanalytical chemistry principles
Sample loss by radiocolloidal behaviour
Samples with very low concentrations are difficult to measure accurately due to the radioactive atoms unexpectedly depositing on surfaces. Sample loss at trace levels may be due to adhesion to container walls and filter surface sites by ionic or electrostatic adsorption, as well as metal foils and glass slides. Sample loss is an ever present concern, especially at the beginning of the analysis path where sequential steps may compound these losses.
Various solutions are known to circumvent these losses which include adding an inactive carrier or adding a tracer. Research has also shown that pretreatment of glassware and plastic surfaces can reduce radionuclide sorption by saturating the sites.
Carrier or tracer addition
Since small amounts of radionuclides are typically being analyzed, the mechanics of manipulating tiny quantities is challenging. This problem is classically addressed by the use of carrier ions. Thus, carrier addition involves the addition of a known mass of stable ion to radionuclide-containing sample solution. The carrier is of the identical element but is non-radioactive. The carrier and the radionuclide of interest have identical chemical properties. Typically the amount of carrier added is conventionally selected for the ease of weighing such that the accuracy of the resultant weight is within 1%. For alpha particles, special techniques must be applied to obtain the required thin sample sources. The use of carries was heavily used by Marie Curie and was employed in the first demonstration of nuclear fission.
Isotope dilution is the reverse of tracer addition. It involves the addition of a known (small) amount of radionuclide to the sample that contains a known stable element. This additive is the "tracer." It is added at the start of the analysis procedure. After the final measurements are recorded, sample loss can be determined quantitatively. This procedure avoids the need for any quantitative recovery, greatly simplifying the analytical process.
Typical radionuclides of interest
Quality assurance
As this is an analytical chemistry technique quality control is an important factor to maintain. A laboratory must produce trustworthy results. This can be accomplished by a laboratories continual effort to maintain instrument calibration, measurement reproducibility, and applicability of analytical methods. In all laboratories there must be a quality assurance plan. This plan describes the quality system and procedures in place to obtain consistent results. Such results must be authentic, appropriately documented, and technically defensible." Such elements of quality assurance include organization, personnel training, laboratory operating procedures, procurement documents, chain of custody records, standard certificates, analytical records, standard procedures, QC sample analysis program and results, instrument testing and maintenance records, results of performance demonstration projects, results of data assessment, audit reports, and record retention policies.
The cost of quality assurance is continually on the rise but the benefits far outweigh this cost. The average quality assurance workload was risen from 10% to a modern load of 20-30%. This heightened focus on quality assurance ensures that quality measurements that are reliable are achieved. The cost of failure far outweighs the cost of prevention and appraisal. Finally, results must be scientifically defensible by adhering to stringent regulations in the event of a lawsuit.
References
Further reading
Chemical Analysis by Nuclear Methods, by Z.B. Alfassi
Radioanalytical chemistry by J. Tölgyessy, & M. Kyrš.
Nuclear analytical chemistry by J. Tölgyessy, Š. Varga and V. Kriváň. English translation: P. Tkáč.
Chemistry
Analytical chemistry
Radiometric dating
Environmental isotopes
Radioactivity
Nuclear technology
Nuclear chemistry
Quaternary
Radiobiology | Radioanalytical chemistry | Physics,Chemistry,Biology | 1,581 |
52,197,659 | https://en.wikipedia.org/wiki/Permutational%20analysis%20of%20variance | Permutational multivariate analysis of variance (PERMANOVA), is a non-parametric multivariate statistical permutation test. PERMANOVA is used to compare groups of objects and test the null hypothesis that the centroids and dispersion of the groups as defined by measure space are equivalent for all groups. A rejection of the null hypothesis means that either the centroid and/or the spread of the objects is different between the groups. Hence the test is based on the prior calculation of the distance between any two objects included in the experiment.
PERMANOVA shares some resemblance to ANOVA where they both measure the sum-of-squares within and between groups, and make use of F test to compare within-group to between-group variance. However, while ANOVA bases the significance of the result on assumption of normality, PERMANOVA draws tests for significance by comparing the actual F test result to that gained from random permutations of the objects between the groups. Moreover, whilst PERMANOVA tests for similarity based on a chosen distance measure, ANOVA tests for similarity of the group averages.
Calculation of the statistic
In the simple case of a single factor with p groups and n objects in each group, the total sum-of-squares is determined as:
where is the total number of objects, and is the squared distance between objects i and j.
Similarly, the within groups sum-of-squares is determined as:
where is 1 if the observations i and j belong to the same group, and 0 otherwise.
Then, the between groups sum-of-squares () can be calculated as the difference between the overall and the within groups sum-of-squares:
Finally, a pseudo F-statistic is calculated:
where p is the number of groups.
Drawing significance
Finally, the PERMANOVA procedure draws significance for the actual F statistic by performing multiple permutations of the data. In each permutation the items are shuffled between groups, and the F-ratio is calculated for it, . The P-value is then calculated by:
Implementation and use
PERMANOVA is widely used in the field of ecology and is implemented in several software packages including the PERMANOVA software, PRIMER and R (programming language) Vegan, lmPerm and Python (programming language) skbio packages.
References
Statistical hypothesis testing
Ecology | Permutational analysis of variance | Biology | 483 |
156,998 | https://en.wikipedia.org/wiki/Action%20potential | An action potential occurs when the membrane potential of a specific cell rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of excitable cells, which include animal cells like neurons and muscle cells, as well as some plant cells. Certain endocrine cells such as pancreatic beta cells, and certain cells of the anterior pituitary gland are also excitable cells.
In neurons, action potentials play a central role in cell–cell communication by providing for—or with regard to saltatory conduction, assisting—the propagation of signals along the neuron's axon toward synaptic boutons situated at the ends of an axon; these signals can then connect with other neurons at synapses, or to motor cells or glands. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction. In beta cells of the pancreas, they provoke release of insulin. Action potentials in neurons are also known as "nerve impulses" or "spikes", and the temporal sequence of action potentials generated by a neuron is called its "spike train". A neuron that emits an action potential, or nerve impulse, is often said to "fire".
Action potentials are generated by special types of voltage-gated ion channels embedded in a cell's plasma membrane. These channels are shut when the membrane potential is near the (negative) resting potential of the cell, but they rapidly begin to open if the membrane potential increases to a precisely defined threshold voltage, depolarising the transmembrane potential. When the channels open, they allow an inward flow of sodium ions, which changes the electrochemical gradient, which in turn produces a further rise in the membrane potential towards zero. This then causes more channels to open, producing a greater electric current across the cell membrane and so on. The process proceeds explosively until all of the available ion channels are open, resulting in a large upswing in the membrane potential. The rapid influx of sodium ions causes the polarity of the plasma membrane to reverse, and the ion channels then rapidly inactivate. As the sodium channels close, sodium ions can no longer enter the neuron, and they are then actively transported back out of the plasma membrane. Potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state. After an action potential has occurred, there is a transient negative shift, called the afterhyperpolarization.
In animal cells, there are two primary types of action potentials. One type is generated by voltage-gated sodium channels, the other by voltage-gated calcium channels. Sodium-based action potentials usually last for under one millisecond, but calcium-based action potentials may last for 100 milliseconds or longer. In some types of neurons, slow calcium spikes provide the driving force for a long burst of rapidly emitted sodium spikes. In cardiac muscle cells, on the other hand, an initial fast sodium spike provides a "primer" to provoke the rapid onset of a calcium spike, which then produces muscle contraction.
Overview
Nearly all cell membranes in animals, plants and fungi maintain a voltage difference between the exterior and interior of the cell, called the membrane potential. A typical voltage across an animal cell membrane is −70 mV. This means that the interior of the cell has a negative voltage relative to the exterior. In most types of cells, the membrane potential usually stays fairly constant. Some types of cells, however, are electrically active in the sense that their voltages fluctuate over time. In some types of electrically active cells, including neurons and muscle cells, the voltage fluctuations frequently take the form of a rapid upward (positive) spike followed by a rapid fall. These up-and-down cycles are known as action potentials. In some types of neurons, the entire up-and-down cycle takes place in a few thousandths of a second. In muscle cells, a typical action potential lasts about a fifth of a second. In plant cells, an action potential may last three seconds or more.
The electrical properties of a cell are determined by the structure of its membrane. A cell membrane consists of a lipid bilayer of molecules in which larger protein molecules are embedded. The lipid bilayer is highly resistant to movement of electrically charged ions, so it functions as an insulator. The large membrane-embedded proteins, in contrast, provide channels through which ions can pass across the membrane. Action potentials are driven by channel proteins whose configuration switches between closed and open states as a function of the voltage difference between the interior and exterior of the cell. These voltage-sensitive proteins are known as voltage-gated ion channels.
Process in a typical neuron
All cells in animal body tissues are electrically polarized – in other words, they maintain a voltage difference across the cell's plasma membrane, known as the membrane potential. This electrical polarization results from a complex interplay between protein structures embedded in the membrane called ion pumps and ion channels. In neurons, the types of ion channels in the membrane usually vary across different parts of the cell, giving the dendrites, axon, and cell body different electrical properties. As a result, some parts of the membrane of a neuron may be excitable (capable of generating action potentials), whereas others are not. Recent studies have shown that the most excitable part of a neuron is the part after the axon hillock (the point where the axon leaves the cell body), which is called the axonal initial segment, but the axon and cell body are also excitable in most cases.
Each excitable patch of membrane has two important levels of membrane potential: the resting potential, which is the value the membrane potential maintains as long as nothing perturbs the cell, and a higher value called the threshold potential. At the axon hillock of a typical neuron, the resting potential is around –70 millivolts (mV) and the threshold potential is around –55 mV. Synaptic inputs to a neuron cause the membrane to depolarize or hyperpolarize; that is, they cause the membrane potential to rise or fall. Action potentials are triggered when enough depolarization accumulates to bring the membrane potential up to threshold. When an action potential is triggered, the membrane potential abruptly shoots upward and then equally abruptly shoots back downward, often ending below the resting level, where it remains for some period of time. The shape of the action potential is stereotyped; this means that the rise and fall usually have approximately the same amplitude and time course for all action potentials in a given cell. (Exceptions are discussed later in the article). In most neurons, the entire process takes place in about a thousandth of a second. Many types of neurons emit action potentials constantly at rates of up to 10–100 per second. However, some types are much quieter, and may go for minutes or longer without emitting any action potentials.
Biophysical basis
Action potentials result from the presence in a cell's membrane of special types of voltage-gated ion channels. A voltage-gated ion channel is a transmembrane protein that has three key properties:
It is capable of assuming more than one conformation.
At least one of the conformations creates a channel through the membrane that is permeable to specific types of ions.
The transition between conformations is influenced by the membrane potential.
Thus, a voltage-gated ion channel tends to be open for some values of the membrane potential, and closed for others. In most cases, however, the relationship between membrane potential and channel state is probabilistic and involves a time delay. Ion channels switch between conformations at unpredictable times: The membrane potential determines the rate of transitions and the probability per unit time of each type of transition.
Voltage-gated ion channels are capable of producing action potentials because they can give rise to positive feedback loops: The membrane potential controls the state of the ion channels, but the state of the ion channels controls the membrane potential. Thus, in some situations, a rise in the membrane potential can cause ion channels to open, thereby causing a further rise in the membrane potential. An action potential occurs when this positive feedback cycle (Hodgkin cycle) proceeds explosively. The time and amplitude trajectory of the action potential are determined by the biophysical properties of the voltage-gated ion channels that produce it. Several types of channels capable of producing the positive feedback necessary to generate an action potential do exist. Voltage-gated sodium channels are responsible for the fast action potentials involved in nerve conduction. Slower action potentials in muscle cells and some types of neurons are generated by voltage-gated calcium channels. Each of these types comes in multiple variants, with different voltage sensitivity and different temporal dynamics.
The most intensively studied type of voltage-dependent ion channels comprises the sodium channels involved in fast nerve conduction. These are sometimes known as Hodgkin-Huxley sodium channels because they were first characterized by Alan Hodgkin and Andrew Huxley in their Nobel Prize-winning studies of the biophysics of the action potential, but can more conveniently be referred to as NaV channels. (The "V" stands for "voltage".) An NaV channel has three possible states, known as deactivated, activated, and inactivated. The channel is permeable only to sodium ions when it is in the activated state. When the membrane potential is low, the channel spends most of its time in the deactivated (closed) state. If the membrane potential is raised above a certain level, the channel shows increased probability of transitioning to the activated (open) state. The higher the membrane potential the greater the probability of activation. Once a channel has activated, it will eventually transition to the inactivated (closed) state. It tends then to stay inactivated for some time, but, if the membrane potential becomes low again, the channel will eventually transition back to the deactivated state. During an action potential, most channels of this type go through a cycle deactivated→activated→inactivated→deactivated. This is only the population average behavior, however – an individual channel can in principle make any transition at any time. However, the likelihood of a channel's transitioning from the inactivated state directly to the activated state is very low: A channel in the inactivated state is refractory until it has transitioned back to the deactivated state.
The outcome of all this is that the kinetics of the NaV channels are governed by a transition matrix whose rates are voltage-dependent in a complicated way. Since these channels themselves play a major role in determining the voltage, the global dynamics of the system can be quite difficult to work out. Hodgkin and Huxley approached the problem by developing a set of differential equations for the parameters that govern the ion channel states, known as the Hodgkin-Huxley equations. These equations have been extensively modified by later research, but form the starting point for most theoretical studies of action potential biophysics.
As the membrane potential is increased, sodium ion channels open, allowing the entry of sodium ions into the cell. This is followed by the opening of potassium ion channels that permit the exit of potassium ions from the cell. The inward flow of sodium ions increases the concentration of positively charged cations in the cell and causes depolarization, where the potential of the cell is higher than the cell's resting potential. The sodium channels close at the peak of the action potential, while potassium continues to leave the cell. The efflux of potassium ions decreases the membrane potential or hyperpolarizes the cell. For small voltage increases from rest, the potassium current exceeds the sodium current and the voltage returns to its normal resting value, typically −70 mV. However, if the voltage increases past a critical threshold, typically 15 mV higher than the resting value, the sodium current dominates. This results in a runaway condition whereby the positive feedback from the sodium current activates even more sodium channels. Thus, the cell fires, producing an action potential. The frequency at which a neuron elicits action potentials is often referred to as a firing rate or neural firing rate.
Currents produced by the opening of voltage-gated channels in the course of an action potential are typically significantly larger than the initial stimulating current. Thus, the amplitude, duration, and shape of the action potential are determined largely by the properties of the excitable membrane and not the amplitude or duration of the stimulus. This all-or-nothing property of the action potential sets it apart from graded potentials such as receptor potentials, electrotonic potentials, subthreshold membrane potential oscillations, and synaptic potentials, which scale with the magnitude of the stimulus. A variety of action potential types exist in many cell types and cell compartments as determined by the types of voltage-gated channels, leak channels, channel distributions, ionic concentrations, membrane capacitance, temperature, and other factors.
The principal ions involved in an action potential are sodium and potassium cations; sodium ions enter the cell, and potassium ions leave, restoring equilibrium. Relatively few ions need to cross the membrane for the membrane voltage to change drastically. The ions exchanged during an action potential, therefore, make a negligible change in the interior and exterior ionic concentrations. The few ions that do cross are pumped out again by the continuous action of the sodium–potassium pump, which, with other ion transporters, maintains the normal ratio of ion concentrations across the membrane. Calcium cations and chloride anions are involved in a few types of action potentials, such as the cardiac action potential and the action potential in the single-cell alga Acetabularia, respectively.
Although action potentials are generated locally on patches of excitable membrane, the resulting currents can trigger action potentials on neighboring stretches of membrane, precipitating a domino-like propagation. In contrast to passive spread of electric potentials (electrotonic potential), action potentials are generated anew along excitable stretches of membrane and propagate without decay. Myelinated sections of axons are not excitable and do not produce action potentials and the signal is propagated passively as electrotonic potential. Regularly spaced unmyelinated patches, called the nodes of Ranvier, generate action potentials to boost the signal. Known as saltatory conduction, this type of signal propagation provides a favorable tradeoff of signal velocity and axon diameter. Depolarization of axon terminals, in general, triggers the release of neurotransmitter into the synaptic cleft. In addition, backpropagating action potentials have been recorded in the dendrites of pyramidal neurons, which are ubiquitous in the neocortex. These are thought to have a role in spike-timing-dependent plasticity.
In the Hodgkin–Huxley membrane capacitance model, the speed of transmission of an action potential was undefined and it was assumed that adjacent areas became depolarized due to released ion interference with neighbouring channels. Measurements of ion diffusion and radii have since shown this not to be possible. Moreover, contradictory measurements of entropy changes and timing disputed the capacitance model as acting alone. Alternatively, Gilbert Ling's adsorption hypothesis, posits that the membrane potential and action potential of a living cell is due to the adsorption of mobile ions onto adsorption sites of cells.
Maturation of the electrical properties of the action potential
A neuron's ability to generate and propagate an action potential changes during development. How much the membrane potential of a neuron changes as the result of a current impulse is a function of the membrane input resistance. As a cell grows, more channels are added to the membrane, causing a decrease in input resistance. A mature neuron also undergoes shorter changes in membrane potential in response to synaptic currents. Neurons from a ferret lateral geniculate nucleus have a longer time constant and larger voltage deflection at P0 than they do at P30. One consequence of the decreasing action potential duration is that the fidelity of the signal can be preserved in response to high frequency stimulation. Immature neurons are more prone to synaptic depression than potentiation after high frequency stimulation.
In the early development of many organisms, the action potential is actually initially carried by calcium current rather than sodium current. The opening and closing kinetics of calcium channels during development are slower than those of the voltage-gated sodium channels that will carry the action potential in the mature neurons. The longer opening times for the calcium channels can lead to action potentials that are considerably slower than those of mature neurons. Xenopus neurons initially have action potentials that take 60–90 ms. During development, this time decreases to 1 ms. There are two reasons for this drastic decrease. First, the inward current becomes primarily carried by sodium channels. Second, the delayed rectifier, a potassium channel current, increases to 3.5 times its initial strength.
In order for the transition from a calcium-dependent action potential to a sodium-dependent action potential to proceed new channels must be added to the membrane. If Xenopus neurons are grown in an environment with RNA synthesis or protein synthesis inhibitors that transition is prevented. Even the electrical activity of the cell itself may play a role in channel expression. If action potentials in Xenopus myocytes are blocked, the typical increase in sodium and potassium current density is prevented or delayed.
This maturation of electrical properties is seen across species. Xenopus sodium and potassium currents increase drastically after a neuron goes through its final phase of mitosis. The sodium current density of rat cortical neurons increases by 600% within the first two postnatal weeks.
Neurotransmission
Anatomy of a neuron
Several types of cells support an action potential, such as plant cells, muscle cells, and the specialized cells of the heart (in which occurs the cardiac action potential). However, the main excitable cell is the neuron, which also has the simplest mechanism for the action potential.
Neurons are electrically excitable cells composed, in general, of one or more dendrites, a single soma, a single axon and one or more axon terminals. Dendrites are cellular projections whose primary function is to receive synaptic signals. Their protrusions, known as dendritic spines, are designed to capture the neurotransmitters released by the presynaptic neuron. They have a high concentration of ligand-gated ion channels. These spines have a thin neck connecting a bulbous protrusion to the dendrite. This ensures that changes occurring inside the spine are less likely to affect the neighboring spines. The dendritic spine can, with rare exception (see LTP), act as an independent unit. The dendrites extend from the soma, which houses the nucleus, and many of the "normal" eukaryotic organelles. Unlike the spines, the surface of the soma is populated by voltage activated ion channels. These channels help transmit the signals generated by the dendrites. Emerging out from the soma is the axon hillock. This region is characterized by having a very high concentration of voltage-activated sodium channels. In general, it is considered to be the spike initiation zone for action potentials, i.e. the trigger zone. Multiple signals generated at the spines, and transmitted by the soma all converge here. Immediately after the axon hillock is the axon. This is a thin tubular protrusion traveling away from the soma. The axon is insulated by a myelin sheath. Myelin is composed of either Schwann cells (in the peripheral nervous system) or oligodendrocytes (in the central nervous system), both of which are types of glial cells. Although glial cells are not involved with the transmission of electrical signals, they communicate and provide important biochemical support to neurons. To be specific, myelin wraps multiple times around the axonal segment, forming a thick fatty layer that prevents ions from entering or escaping the axon. This insulation prevents significant signal decay as well as ensuring faster signal speed. This insulation, however, has the restriction that no channels can be present on the surface of the axon. There are, therefore, regularly spaced patches of membrane, which have no insulation. These nodes of Ranvier can be considered to be "mini axon hillocks", as their purpose is to boost the signal in order to prevent significant signal decay. At the furthest end, the axon loses its insulation and begins to branch into several axon terminals. These presynaptic terminals, or synaptic boutons, are a specialized area within the axon of the presynaptic cell that contains neurotransmitters enclosed in small membrane-bound spheres called synaptic vesicles.
Initiation
Before considering the propagation of action potentials along axons and their termination at the synaptic knobs, it is helpful to consider the methods by which action potentials can be initiated at the axon hillock. The basic requirement is that the membrane voltage at the hillock be raised above the threshold for firing. There are several ways in which this depolarization can occur.
Dynamics
Action potentials are most commonly initiated by excitatory postsynaptic potentials from a presynaptic neuron. Typically, neurotransmitter molecules are released by the presynaptic neuron. These neurotransmitters then bind to receptors on the postsynaptic cell. This binding opens various types of ion channels. This opening has the further effect of changing the local permeability of the cell membrane and, thus, the membrane potential. If the binding increases the voltage (depolarizes the membrane), the synapse is excitatory. If, however, the binding decreases the voltage (hyperpolarizes the membrane), it is inhibitory. Whether the voltage is increased or decreased, the change propagates passively to nearby regions of the membrane (as described by the cable equation and its refinements). Typically, the voltage stimulus decays exponentially with the distance from the synapse and with time from the binding of the neurotransmitter. Some fraction of an excitatory voltage may reach the axon hillock and may (in rare cases) depolarize the membrane enough to provoke a new action potential. More typically, the excitatory potentials from several synapses must work together at nearly the same time to provoke a new action potential. Their joint efforts can be thwarted, however, by the counteracting inhibitory postsynaptic potentials.
Neurotransmission can also occur through electrical synapses. Due to the direct connection between excitable cells in the form of gap junctions, an action potential can be transmitted directly from one cell to the next in either direction. The free flow of ions between cells enables rapid non-chemical-mediated transmission. Rectifying channels ensure that action potentials move only in one direction through an electrical synapse. Electrical synapses are found in all nervous systems, including the human brain, although they are a distinct minority.
"All-or-none" principle
The amplitude of an action potential is often thought to be independent of the amount of current that produced it. In other words, larger currents do not create larger action potentials. Therefore, action potentials are said to be all-or-none signals, since either they occur fully or they do not occur at all. This is in contrast to receptor potentials, whose amplitudes are dependent on the intensity of a stimulus. In both cases, the frequency of action potentials is correlated with the intensity of a stimulus.
Despite the classical view of the action potential as a stereotyped, uniform signal having dominated the field of neuroscience for many decades, newer evidence does suggest that action potentials are more complex events indeed capable of transmitting information through not just their amplitude, but their duration and phase as well, sometimes even up to distances originally not thought to be possible.
Sensory neurons
In sensory neurons, an external signal such as pressure, temperature, light, or sound is coupled with the opening and closing of ion channels, which in turn alter the ionic permeabilities of the membrane and its voltage. These voltage changes can again be excitatory (depolarizing) or inhibitory (hyperpolarizing) and, in some sensory neurons, their combined effects can depolarize the axon hillock enough to provoke action potentials. Some examples in humans include the olfactory receptor neuron and Meissner's corpuscle, which are critical for the sense of smell and touch, respectively. However, not all sensory neurons convert their external signals into action potentials; some do not even have an axon. Instead, they may convert the signal into the release of a neurotransmitter, or into continuous graded potentials, either of which may stimulate subsequent neuron(s) into firing an action potential. For illustration, in the human ear, hair cells convert the incoming sound into the opening and closing of mechanically gated ion channels, which may cause neurotransmitter molecules to be released. In similar manner, in the human retina, the initial photoreceptor cells and the next layer of cells (comprising bipolar cells and horizontal cells) do not produce action potentials; only some amacrine cells and the third layer, the ganglion cells, produce action potentials, which then travel up the optic nerve.
Pacemaker potentials
In sensory neurons, action potentials result from an external stimulus. However, some excitable cells require no such stimulus to fire: They spontaneously depolarize their axon hillock and fire action potentials at a regular rate, like an internal clock. The voltage traces of such cells are known as pacemaker potentials. The cardiac pacemaker cells of the sinoatrial node in the heart provide a good example. Although such pacemaker potentials have a natural rhythm, it can be adjusted by external stimuli; for instance, heart rate can be altered by pharmaceuticals as well as signals from the sympathetic and parasympathetic nerves. The external stimuli do not cause the cell's repetitive firing, but merely alter its timing. In some cases, the regulation of frequency can be more complex, leading to patterns of action potentials, such as bursting.
Phases
The course of the action potential can be divided into five parts: the rising phase, the peak phase, the falling phase, the undershoot phase, and the refractory period. During the rising phase the membrane potential depolarizes (becomes more positive). The point at which depolarization stops is called the peak phase. At this stage, the membrane potential reaches a maximum. Subsequent to this, there is a falling phase. During this stage the membrane potential becomes more negative, returning towards resting potential. The undershoot, or afterhyperpolarization, phase is the period during which the membrane potential temporarily becomes more negatively charged than when at rest (hyperpolarized). Finally, the time during which a subsequent action potential is impossible or difficult to fire is called the refractory period, which may overlap with the other phases.
The course of the action potential is determined by two coupled effects. First, voltage-sensitive ion channels open and close in response to changes in the membrane voltage Vm. This changes the membrane's permeability to those ions. Second, according to the Goldman equation, this change in permeability changes the equilibrium potential Em, and, thus, the membrane voltage Vm. Thus, the membrane potential affects the permeability, which then further affects the membrane potential. This sets up the possibility for positive feedback, which is a key part of the rising phase of the action potential. A complicating factor is that a single ion channel may have multiple internal "gates" that respond to changes in Vm in opposite ways, or at different rates. For example, although raising Vm opens most gates in the voltage-sensitive sodium channel, it also closes the channel's "inactivation gate", albeit more slowly. Hence, when Vm is raised suddenly, the sodium channels open initially, but then close due to the slower inactivation.
The voltages and currents of the action potential in all of its phases were modeled accurately by Alan Lloyd Hodgkin and Andrew Huxley in 1952, for which they were awarded the Nobel Prize in Physiology or Medicine in 1963. However, their model considers only two types of voltage-sensitive ion channels, and makes several assumptions about them, e.g., that their internal gates open and close independently of one another. In reality, there are many types of ion channels, and they do not always open and close independently.
Stimulation and rising phase
A typical action potential begins at the axon hillock with a sufficiently strong depolarization, e.g., a stimulus that increases Vm. This depolarization is often caused by the injection of extra sodium cations into the cell; these cations can come from a wide variety of sources, such as chemical synapses, sensory neurons or pacemaker potentials.
For a neuron at rest, there is a high concentration of sodium and chloride ions in the extracellular fluid compared to the intracellular fluid, while there is a high concentration of potassium ions in the intracellular fluid compared to the extracellular fluid. The difference in concentrations, which causes ions to move from a high to a low concentration, and electrostatic effects (attraction of opposite charges) are responsible for the movement of ions in and out of the neuron. The inside of a neuron has a negative charge, relative to the cell exterior, from the movement of K+ out of the cell. The neuron membrane is more permeable to K+ than to other ions, allowing this ion to selectively move out of the cell, down its concentration gradient. This concentration gradient along with potassium leak channels present on the membrane of the neuron causes an efflux of potassium ions making the resting potential close to EK ≈ –75 mV. Since Na+ ions are in higher concentrations outside of the cell, the concentration and voltage differences both drive them into the cell when Na+ channels open. Depolarization opens both the sodium and potassium channels in the membrane, allowing the ions to flow into and out of the axon, respectively. If the depolarization is small (say, increasing Vm from −70 mV to −60 mV), the outward potassium current overwhelms the inward sodium current and the membrane repolarizes back to its normal resting potential around −70 mV. However, if the depolarization is large enough, the inward sodium current increases more than the outward potassium current and a runaway condition (positive feedback) results: the more inward current there is, the more Vm increases, which in turn further increases the inward current. A sufficiently strong depolarization (increase in Vm) causes the voltage-sensitive sodium channels to open; the increasing permeability to sodium drives Vm closer to the sodium equilibrium voltage ENa≈ +55 mV. The increasing voltage in turn causes even more sodium channels to open, which pushes Vm still further towards ENa. This positive feedback continues until the sodium channels are fully open and Vm is close to ENa. The sharp rise in Vm and sodium permeability correspond to the rising phase of the action potential.
The critical threshold voltage for this runaway condition is usually around −45 mV, but it depends on the recent activity of the axon. A cell that has just fired an action potential cannot fire another one immediately, since the Na+ channels have not recovered from the inactivated state. The period during which no new action potential can be fired is called the absolute refractory period. At longer times, after some but not all of the ion channels have recovered, the axon can be stimulated to produce another action potential, but with a higher threshold, requiring a much stronger depolarization, e.g., to −30 mV. The period during which action potentials are unusually difficult to evoke is called the relative refractory period.
Peak phase
The positive feedback of the rising phase slows and comes to a halt as the sodium ion channels become maximally open. At the peak of the action potential, the sodium permeability is maximized and the membrane voltage Vm is nearly equal to the sodium equilibrium voltage ENa. However, the same raised voltage that opened the sodium channels initially also slowly shuts them off, by closing their pores; the sodium channels become inactivated. This lowers the membrane's permeability to sodium relative to potassium, driving the membrane voltage back towards the resting value. At the same time, the raised voltage opens voltage-sensitive potassium channels; the increase in the membrane's potassium permeability drives Vm towards EK. Combined, these changes in sodium and potassium permeability cause Vm to drop quickly, repolarizing the membrane and producing the "falling phase" of the action potential.
Afterhyperpolarization
The depolarized voltage opens additional voltage-dependent potassium channels, and some of these do not close right away when the membrane returns to its normal resting voltage. In addition, further potassium channels open in response to the influx of calcium ions during the action potential. The intracellular concentration of potassium ions is transiently unusually low, making the membrane voltage Vm even closer to the potassium equilibrium voltage EK. The membrane potential goes below the resting membrane potential. Hence, there is an undershoot or hyperpolarization, termed an afterhyperpolarization, that persists until the membrane potassium permeability returns to its usual value, restoring the membrane potential to the resting state.
Refractory period
Each action potential is followed by a refractory period, which can be divided into an absolute refractory period, during which it is impossible to evoke another action potential, and then a relative refractory period, during which a stronger-than-usual stimulus is required. These two refractory periods are caused by changes in the state of sodium and potassium channel molecules. When closing after an action potential, sodium channels enter an "inactivated" state, in which they cannot be made to open regardless of the membrane potential—this gives rise to the absolute refractory period. Even after a sufficient number of sodium channels have transitioned back to their resting state, it frequently happens that a fraction of potassium channels remains open, making it difficult for the membrane potential to depolarize, and thereby giving rise to the relative refractory period. Because the density and subtypes of potassium channels may differ greatly between different types of neurons, the duration of the relative refractory period is highly variable.
The absolute refractory period is largely responsible for the unidirectional propagation of action potentials along axons. At any given moment, the patch of axon behind the actively spiking part is refractory, but the patch in front, not having been activated recently, is capable of being stimulated by the depolarization from the action potential.
Propagation
The action potential generated at the axon hillock propagates as a wave along the axon. The currents flowing inwards at a point on the axon during an action potential spread out along the axon, and depolarize the adjacent sections of its membrane. If sufficiently strong, this depolarization provokes a similar action potential at the neighboring membrane patches. This basic mechanism was demonstrated by Alan Lloyd Hodgkin in 1937. After crushing or cooling nerve segments and thus blocking the action potentials, he showed that an action potential arriving on one side of the block could provoke another action potential on the other, provided that the blocked segment was sufficiently short.
Once an action potential has occurred at a patch of membrane, the membrane patch needs time to recover before it can fire again. At the molecular level, this absolute refractory period corresponds to the time required for the voltage-activated sodium channels to recover from inactivation, i.e., to return to their closed state. There are many types of voltage-activated potassium channels in neurons. Some of them inactivate fast (A-type currents) and some of them inactivate slowly or not inactivate at all; this variability guarantees that there will be always an available source of current for repolarization, even if some of the potassium channels are inactivated because of preceding depolarization. On the other hand, all neuronal voltage-activated sodium channels inactivate within several milliseconds during strong depolarization, thus making following depolarization impossible until a substantial fraction of sodium channels have returned to their closed state. Although it limits the frequency of firing, the absolute refractory period ensures that the action potential moves in only one direction along an axon. The currents flowing in due to an action potential spread out in both directions along the axon. However, only the unfired part of the axon can respond with an action potential; the part that has just fired is unresponsive until the action potential is safely out of range and cannot restimulate that part. In the usual orthodromic conduction, the action potential propagates from the axon hillock towards the synaptic knobs (the axonal termini); propagation in the opposite direction—known as antidromic conduction—is very rare. However, if a laboratory axon is stimulated in its middle, both halves of the axon are "fresh", i.e., unfired; then two action potentials will be generated, one traveling towards the axon hillock and the other traveling towards the synaptic knobs.
Myelin and saltatory conduction
In order to enable fast and efficient transduction of electrical signals in the nervous system, certain neuronal axons are covered with myelin sheaths. Myelin is a multilamellar membrane that enwraps the axon in segments separated by intervals known as nodes of Ranvier. It is produced by specialized cells: Schwann cells exclusively in the peripheral nervous system, and oligodendrocytes exclusively in the central nervous system. Myelin sheath reduces membrane capacitance and increases membrane resistance in the inter-node intervals, thus allowing a fast, saltatory movement of action potentials from node to node. Myelination is found mainly in vertebrates, but an analogous system has been discovered in a few invertebrates, such as some species of shrimp. Not all neurons in vertebrates are myelinated; for example, axons of the neurons comprising the autonomous nervous system are not, in general, myelinated.
Myelin prevents ions from entering or leaving the axon along myelinated segments. As a general rule, myelination increases the conduction velocity of action potentials and makes them more energy-efficient. Whether saltatory or not, the mean conduction velocity of an action potential ranges from 1 meter per second (m/s) to over 100 m/s, and, in general, increases with axonal diameter.
Action potentials cannot propagate through the membrane in myelinated segments of the axon. However, the current is carried by the cytoplasm, which is sufficient to depolarize the first or second subsequent node of Ranvier. Instead, the ionic current from an action potential at one node of Ranvier provokes another action potential at the next node; this apparent "hopping" of the action potential from node to node is known as saltatory conduction. Although the mechanism of saltatory conduction was suggested in 1925 by Ralph Lillie, the first experimental evidence for saltatory conduction came from Ichiji Tasaki and Taiji Takeuchi and from Andrew Huxley and Robert Stämpfli. By contrast, in unmyelinated axons, the action potential provokes another in the membrane immediately adjacent, and moves continuously down the axon like a wave.
Myelin has two important advantages: fast conduction speed and energy efficiency. For axons larger than a minimum diameter (roughly 1 micrometre), myelination increases the conduction velocity of an action potential, typically tenfold. Conversely, for a given conduction velocity, myelinated fibers are smaller than their unmyelinated counterparts. For example, action potentials move at roughly the same speed (25 m/s) in a myelinated frog axon and an unmyelinated squid giant axon, but the frog axon has a roughly 30-fold smaller diameter and 1000-fold smaller cross-sectional area. Also, since the ionic currents are confined to the nodes of Ranvier, far fewer ions "leak" across the membrane, saving metabolic energy. This saving is a significant selective advantage, since the human nervous system uses approximately 20% of the body's metabolic energy.
The length of axons' myelinated segments is important to the success of saltatory conduction. They should be as long as possible to maximize the speed of conduction, but not so long that the arriving signal is too weak to provoke an action potential at the next node of Ranvier. In nature, myelinated segments are generally long enough for the passively propagated signal to travel for at least two nodes while retaining enough amplitude to fire an action potential at the second or third node. Thus, the safety factor of saltatory conduction is high, allowing transmission to bypass nodes in case of injury. However, action potentials may end prematurely in certain places where the safety factor is low, even in unmyelinated neurons; a common example is the branch point of an axon, where it divides into two axons.
Some diseases degrade myelin and impair saltatory conduction, reducing the conduction velocity of action potentials. The most well-known of these is multiple sclerosis, in which the breakdown of myelin impairs coordinated movement.
Cable theory
The flow of currents within an axon can be described quantitatively by cable theory and its elaborations, such as the compartmental model. Cable theory was developed in 1855 by Lord Kelvin to model the transatlantic telegraph cable and was shown to be relevant to neurons by Hodgkin and Rushton in 1946. In simple cable theory, the neuron is treated as an electrically passive, perfectly cylindrical transmission cable, which can be described by a partial differential equation
where V(x, t) is the voltage across the membrane at a time t and a position x along the length of the neuron, and where λ and τ are the characteristic length and time scales on which those voltages decay in response to a stimulus. Referring to the circuit diagram on the right, these scales can be determined from the resistances and capacitances per unit length.
These time and length-scales can be used to understand the dependence of the conduction velocity on the diameter of the neuron in unmyelinated fibers. For example, the time-scale τ increases with both the membrane resistance rm and capacitance cm. As the capacitance increases, more charge must be transferred to produce a given transmembrane voltage (by the equation Q = CV); as the resistance increases, less charge is transferred per unit time, making the equilibration slower. In a similar manner, if the internal resistance per unit length ri is lower in one axon than in another (e.g., because the radius of the former is larger), the spatial decay length λ becomes longer and the conduction velocity of an action potential should increase. If the transmembrane resistance rm is increased, that lowers the average "leakage" current across the membrane, likewise causing λ to become longer, increasing the conduction velocity.
Termination
Chemical synapses
In general, action potentials that reach the synaptic knobs cause a neurotransmitter to be released into the synaptic cleft. Neurotransmitters are small molecules that may open ion channels in the postsynaptic cell; most axons have the same neurotransmitter at all of their termini. The arrival of the action potential opens voltage-sensitive calcium channels in the presynaptic membrane; the influx of calcium causes vesicles filled with neurotransmitter to migrate to the cell's surface and release their contents into the synaptic cleft. This complex process is inhibited by the neurotoxins tetanospasmin and botulinum toxin, which are responsible for tetanus and botulism, respectively.
Electrical synapses
Some synapses dispense with the "middleman" of the neurotransmitter, and connect the presynaptic and postsynaptic cells together. When an action potential reaches such a synapse, the ionic currents flowing into the presynaptic cell can cross the barrier of the two cell membranes and enter the postsynaptic cell through pores known as connexons. Thus, the ionic currents of the presynaptic action potential can directly stimulate the postsynaptic cell. Electrical synapses allow for faster transmission because they do not require the slow diffusion of neurotransmitters across the synaptic cleft. Hence, electrical synapses are used whenever fast response and coordination of timing are crucial, as in escape reflexes, the retina of vertebrates, and the heart.
Neuromuscular junctions
A special case of a chemical synapse is the neuromuscular junction, in which the axon of a motor neuron terminates on a muscle fiber. In such cases, the released neurotransmitter is acetylcholine, which binds to the acetylcholine receptor, an integral membrane protein in the membrane (the sarcolemma) of the muscle fiber. However, the acetylcholine does not remain bound; rather, it dissociates and is hydrolyzed by the enzyme, acetylcholinesterase, located in the synapse. This enzyme quickly reduces the stimulus to the muscle, which allows the degree and timing of muscular contraction to be regulated delicately. Some poisons inactivate acetylcholinesterase to prevent this control, such as the nerve agents sarin and tabun, and the insecticides diazinon and malathion.
Other cell types
Cardiac action potentials
The cardiac action potential differs from the neuronal action potential by having an extended plateau, in which the membrane is held at a high voltage for a few hundred milliseconds prior to being repolarized by the potassium current as usual. This plateau is due to the action of slower calcium channels opening and holding the membrane voltage near their equilibrium potential even after the sodium channels have inactivated.
The cardiac action potential plays an important role in coordinating the contraction of the heart. The cardiac cells of the sinoatrial node provide the pacemaker potential that synchronizes the heart. The action potentials of those cells propagate to and through the atrioventricular node (AV node), which is normally the only conduction pathway between the atria and the ventricles. Action potentials from the AV node travel through the bundle of His and thence to the Purkinje fibers. Conversely, anomalies in the cardiac action potential—whether due to a congenital mutation or injury—can lead to human pathologies, especially arrhythmias. Several anti-arrhythmia drugs act on the cardiac action potential, such as quinidine, lidocaine, beta blockers, and verapamil.
Muscular action potentials
The action potential in a normal skeletal muscle cell is similar to the action potential in neurons. Action potentials result from the depolarization of the cell membrane (the sarcolemma), which opens voltage-sensitive sodium channels; these become inactivated and the membrane is repolarized through the outward current of potassium ions. The resting potential prior to the action potential is typically −90mV, somewhat more negative than typical neurons. The muscle action potential lasts roughly 2–4 ms, the absolute refractory period is roughly 1–3 ms, and the conduction velocity along the muscle is roughly 5 m/s. The action potential releases calcium ions that free up the tropomyosin and allow the muscle to contract. Muscle action potentials are provoked by the arrival of a pre-synaptic neuronal action potential at the neuromuscular junction, which is a common target for neurotoxins.
Plant action potentials
Plant and fungal cells are also electrically excitable. The fundamental difference from animal action potentials is that the depolarization in plant cells is not accomplished by an uptake of positive sodium ions, but by release of negative chloride ions. In 1906, J. C. Bose published the first measurements of action potentials in plants, which had previously been discovered by Burdon-Sanderson and Darwin. An increase in cytoplasmic calcium ions may be the cause of anion release into the cell. This makes calcium a precursor to ion movements, such as the influx of negative chloride ions and efflux of positive potassium ions, as seen in barley leaves.
The initial influx of calcium ions also poses a small cellular depolarization, causing the voltage-gated ion channels to open and allowing full depolarization to be propagated by chloride ions.
Some plants (e.g. Dionaea muscipula) use sodium-gated channels to operate plant movements and "count" stimulation events to determine if a threshold for movement is met. Dionaea muscipula, also known as the Venus flytrap, is found in subtropical wetlands in North and South Carolina. When there are poor soil nutrients, the flytrap relies on a diet of insects and animals. Despite research on the plant, there lacks an understanding behind the molecular basis to the Venus flytraps, and carnivore plants in general.
However, plenty of research has been done on action potentials and how they affect movement and clockwork within the Venus flytrap. To start, the resting membrane potential of the Venus flytrap (−120 mV) is lower than animal cells (usually −90 mV to −40 mV). The lower resting potential makes it easier to activate an action potential. Thus, when an insect lands on the trap of the plant, it triggers a hair-like mechanoreceptor. This receptor then activates an action potential that lasts around 1.5 ms. This causes an increase of positive calcium ions into the cell, slightly depolarizing it. However, the flytrap does not close after one trigger. Instead, it requires the activation of two or more hairs. If only one hair is triggered, it disregards the activation as a false positive. Further, the second hair must be activated within a certain time interval (0.75–40 s) for it to register with the first activation. Thus, a buildup of calcium begins and then slowly falls after the first trigger. When the second action potential is fired within the time interval, it reaches the calcium threshold to depolarize the cell, closing the trap on the prey within a fraction of a second.
Together with the subsequent release of positive potassium ions the action potential in plants involves an osmotic loss of salt (KCl). Whereas, the animal action potential is osmotically neutral because equal amounts of entering sodium and leaving potassium cancel each other osmotically. The interaction of electrical and osmotic relations in plant cells appears to have arisen from an osmotic function of electrical excitability in a common unicellular ancestors of plants and animals under changing salinity conditions. Further, the present function of rapid signal transmission is seen as a newer accomplishment of metazoan cells in a more stable osmotic environment. It is likely that the familiar signaling function of action potentials in some vascular plants (e.g. Mimosa pudica) arose independently from that in metazoan excitable cells.
Unlike the rising phase and peak, the falling phase and after-hyperpolarization seem to depend primarily on cations that are not calcium. To initiate repolarization, the cell requires movement of potassium out of the cell through passive transportation on the membrane. This differs from neurons because the movement of potassium does not dominate the decrease in membrane potential. To fully repolarize, a plant cell requires energy in the form of ATP to assist in the release of hydrogen from the cell – utilizing a transporter called proton ATPase.
Taxonomic distribution and evolutionary advantages
Action potentials are found throughout multicellular organisms, including plants, invertebrates such as insects, and vertebrates such as reptiles and mammals. Sponges seem to be the main phylum of multicellular eukaryotes that does not transmit action potentials, although some studies have suggested that these organisms have a form of electrical signaling, too. The resting potential, as well as the size and duration of the action potential, have not varied much with evolution, although the conduction velocity does vary dramatically with axonal diameter and myelination.
Given its conservation throughout evolution, the action potential seems to confer evolutionary advantages. One function of action potentials is rapid, long-range signaling within the organism; the conduction velocity can exceed 110 m/s, which is one-third the speed of sound. For comparison, a hormone molecule carried in the bloodstream moves at roughly 8 m/s in large arteries. Part of this function is the tight coordination of mechanical events, such as the contraction of the heart. A second function is the computation associated with its generation. Being an all-or-none signal that does not decay with transmission distance, the action potential has similar advantages to digital electronics. The integration of various dendritic signals at the axon hillock and its thresholding to form a complex train of action potentials is another form of computation, one that has been exploited biologically to form central pattern generators and mimicked in artificial neural networks.
The common prokaryotic/eukaryotic ancestor, which lived perhaps four billion years ago, is believed to have had voltage-gated channels. This functionality was likely, at some later point, cross-purposed to provide a communication mechanism. Even modern single-celled bacteria can utilize action potentials to communicate with other bacteria in the same biofilm.
Experimental methods
The study of action potentials has required the development of new experimental methods. The initial work, prior to 1955, was carried out primarily by Alan Lloyd Hodgkin and Andrew Fielding Huxley, who were, along John Carew Eccles, awarded the 1963 Nobel Prize in Physiology or Medicine for their contribution to the description of the ionic basis of nerve conduction. It focused on three goals: isolating signals from single neurons or axons, developing fast, sensitive electronics, and shrinking electrodes enough that the voltage inside a single cell could be recorded.
The first problem was solved by studying the giant axons found in the neurons of the squid (Loligo forbesii and Doryteuthis pealeii, at the time classified as Loligo pealeii). These axons are so large in diameter (roughly 1 mm, or 100-fold larger than a typical neuron) that they can be seen with the naked eye, making them easy to extract and manipulate. However, they are not representative of all excitable cells, and numerous other systems with action potentials have been studied.
The second problem was addressed with the crucial development of the voltage clamp, which permitted experimenters to study the ionic currents underlying an action potential in isolation, and eliminated a key source of electronic noise, the current IC associated with the capacitance C of the membrane. Since the current equals C times the rate of change of the transmembrane voltage Vm, the solution was to design a circuit that kept Vm fixed (zero rate of change) regardless of the currents flowing across the membrane. Thus, the current required to keep Vm at a fixed value is a direct reflection of the current flowing through the membrane. Other electronic advances included the use of Faraday cages and electronics with high input impedance, so that the measurement itself did not affect the voltage being measured.
The third problem, that of obtaining electrodes small enough to record voltages within a single axon without perturbing it, was solved in 1949 with the invention of the glass micropipette electrode, which was quickly adopted by other researchers. Refinements of this method are able to produce electrode tips that are as fine as 100 Å (10 nm), which also confers high input impedance. Action potentials may also be recorded with small metal electrodes placed just next to a neuron, with neurochips containing EOSFETs, or optically with dyes that are sensitive to Ca2+ or to voltage.
While glass micropipette electrodes measure the sum of the currents passing through many ion channels, studying the electrical properties of a single ion channel became possible in the 1970s with the development of the patch clamp by Erwin Neher and Bert Sakmann. For this discovery, they were awarded the Nobel Prize in Physiology or Medicine in 1991. Patch-clamping verified that ionic channels have discrete states of conductance, such as open, closed and inactivated.
Optical imaging technologies have been developed in recent years to measure action potentials, either via simultaneous multisite recordings or with ultra-spatial resolution. Using voltage-sensitive dyes, action potentials have been optically recorded from a tiny patch of cardiomyocyte membrane.
Neurotoxins
Several neurotoxins, both natural and synthetic, function by blocking the action potential. Tetrodotoxin from the pufferfish and saxitoxin from the Gonyaulax (the dinoflagellate genus responsible for "red tides") block action potentials by inhibiting the voltage-sensitive sodium channel; similarly, dendrotoxin from the black mamba snake inhibits the voltage-sensitive potassium channel. Such inhibitors of ion channels serve an important research purpose, by allowing scientists to "turn off" specific channels at will, thus isolating the other channels' contributions; they can also be useful in purifying ion channels by affinity chromatography or in assaying their concentration. However, such inhibitors also make effective neurotoxins, and have been considered for use as chemical weapons. Neurotoxins aimed at the ion channels of insects have been effective insecticides; one example is the synthetic permethrin, which prolongs the activation of the sodium channels involved in action potentials. The ion channels of insects are sufficiently different from their human counterparts that there are few side effects in humans.
History
The role of electricity in the nervous systems of animals was first observed in dissected frogs by Luigi Galvani, who studied it from 1791 to 1797. Galvani's results inspired Alessandro Volta to develop the Voltaic pile—the earliest-known electric battery—with which he studied animal electricity (such as electric eels) and the physiological responses to applied direct-current voltages.
In the 19th century scientists studied the propagation of electrical signals in whole nerves (i.e., bundles of neurons) and demonstrated that nervous tissue was made up of cells, instead of an interconnected network of tubes (a reticulum). Carlo Matteucci followed up Galvani's studies and demonstrated that injured nerves and muscles in frogs could produce direct current. Matteucci's work inspired the German physiologist, Emil du Bois-Reymond, who discovered in 1843 that stimulating these muscle and nerve preparations produced a notable diminution in their resting currents, making him the first researcher to identify the electrical nature of the action potential. The conduction velocity of action potentials was then measured in 1850 by du Bois-Reymond's friend, Hermann von Helmholtz. Progress in electrophysiology stagnated thereafter due to the limitations of chemical theory and experimental practice. To establish that nervous tissue is made up of discrete cells, the Spanish physician Santiago Ramón y Cajal and his students used a stain developed by Camillo Golgi to reveal the myriad shapes of neurons, which they rendered painstakingly. For their discoveries, Golgi and Ramón y Cajal were awarded the 1906 Nobel Prize in Physiology. Their work resolved a long-standing controversy in the neuroanatomy of the 19th century; Golgi himself had argued for the network model of the nervous system.
The 20th century saw significant breakthroughs in electrophysiology. In 1902 and again in 1912, Julius Bernstein advanced the hypothesis that the action potential resulted from a change in the permeability of the axonal membrane to ions. Bernstein's hypothesis was confirmed by Ken Cole and Howard Curtis, who showed that membrane conductance increases during an action potential. In 1907, Louis Lapicque suggested that the action potential was generated as a threshold was crossed, what would be later shown as a product of the dynamical systems of ionic conductances. In 1949, Alan Hodgkin and Bernard Katz refined Bernstein's hypothesis by considering that the axonal membrane might have different permeabilities to different ions; in particular, they demonstrated the crucial role of the sodium permeability for the action potential. They made the first actual recording of the electrical changes across the neuronal membrane that mediate the action potential. This line of research culminated in the five 1952 papers of Hodgkin, Katz and Andrew Huxley, in which they applied the voltage clamp technique to determine the dependence of the axonal membrane's permeabilities to sodium and potassium ions on voltage and time, from which they were able to reconstruct the action potential quantitatively. Hodgkin and Huxley correlated the properties of their mathematical model with discrete ion channels that could exist in several different states, including "open", "closed", and "inactivated". Their hypotheses were confirmed in the mid-1970s and 1980s by Erwin Neher and Bert Sakmann, who developed the technique of patch clamping to examine the conductance states of individual ion channels. In the 21st century, researchers are beginning to understand the structural basis for these conductance states and for the selectivity of channels for their species of ion, through the atomic-resolution crystal structures, fluorescence distance measurements and cryo-electron microscopy studies.
Julius Bernstein was also the first to introduce the Nernst equation for resting potential across the membrane; this was generalized by David E. Goldman to the eponymous Goldman equation in 1943. The sodium–potassium pump was identified in 1957 and its properties gradually elucidated, culminating in the determination of its atomic-resolution structure by X-ray crystallography. The crystal structures of related ionic pumps have also been solved, giving a broader view of how these molecular machines work.
Quantitative models
Mathematical and computational models are essential for understanding the action potential, and offer predictions that may be tested against experimental data, providing a stringent test of a theory. The most important and accurate of the early neural models is the Hodgkin–Huxley model, which describes the action potential by a coupled set of four ordinary differential equations (ODEs). Although the Hodgkin–Huxley model may be a simplification with few limitations compared to the realistic nervous membrane as it exists in nature, its complexity has inspired several even-more-simplified models, such as the Morris–Lecar model and the FitzHugh–Nagumo model, both of which have only two coupled ODEs. The properties of the Hodgkin–Huxley and FitzHugh–Nagumo models and their relatives, such as the Bonhoeffer–Van der Pol model, have been well-studied within mathematics, computation and electronics. However the simple models of generator potential and action potential fail to accurately reproduce the near threshold neural spike rate and spike shape, specifically for the mechanoreceptors like the Pacinian corpuscle. More modern research has focused on larger and more integrated systems; by joining action-potential models with models of other parts of the nervous system (such as dendrites and synapses), researchers can study neural computation and simple reflexes, such as escape reflexes and others controlled by central pattern generators.
See also
Anode break excitation
Bioelectricity
Biological neuron model
Bursting
Central pattern generator
Chronaxie
Frog battery
Law of specific nerve energies
Neural accommodation
Single-unit recording
Soliton model in neuroscience
Notes
References
Footnotes
Journal articles
Books
Web pages
Further reading
External links
Ionic flow in action potentials at Blackwell Publishing
Action potential propagation in myelinated and unmyelinated axons at Blackwell Publishing
Generation of AP in cardiac cells and generation of AP in neuron cells
Resting membrane potential from Life: The Science of Biology, by WK Purves, D Sadava, GH Orians, and HC Heller, 8th edition, New York: WH Freeman, .
Ionic motion and the Goldman voltage for arbitrary ionic concentrations at The University of Arizona
A cartoon illustrating the action potential
Action potential propagation
Production of the action potential: voltage and current clamping simulations
Open-source software to simulate neuronal and cardiac action potentials at SourceForge.net
Introduction to the Action Potential, Neuroscience Online (electronic neuroscience textbook by UT Houston Medical School)
Khan Academy: Electrotonic and action potential
Capacitors
Neural coding
Electrophysiology
Electrochemistry
Computational neuroscience
Cellular neuroscience
Cellular processes
Membrane biology
Plant intelligence
Action potentials | Action potential | Physics,Chemistry,Biology | 13,629 |
62,187,817 | https://en.wikipedia.org/wiki/Schw%C3%A4bisch%20Gm%C3%BCnd%20Prize | The Schwäbisch Gmünd Prize for Young Scientists is an annual award given by the European Academy of Surface Technology (EAST) to an early career researcher active in Europe on the grounds of originality, creativity and excellence in surface technology. The prize aims to promote science, research and education in the field of surface technology as part of EAST efforts to promote friendship and integration within the European scientific and technological community.
The award is named in honor of the town of Schwäbisch Gmünd and its long tradition of craftsmanship of precious metals. The town has also been the location of EAST headquarters since its foundation in 1989. The prize is presented in a public lecture during an event sponsored by or co-organised by EAST, such as electrochemistry, corrosion or surface finishing related conferences.
Recipients of the Schwäbisch Gmünd Prize
To the date, three early career researchers have received the prize:
2017 - J. Zhang
2018 - N. T. Nguyen
2019 - L. F. Arenas
2020 - M. Leimbach
2021 - K. Eiler
See also
List of engineering awards
Electroplating
References
External links
The Schwäbisch Gmünd Prize for Young Scientists
The European Academy of Surface Technology
The Research Institute for Precious Metals and Metal Chemistry
The International Union for Surface Finishing
European science and technology awards
Early career awards
Research awards
Awards established in 2017
2017 establishments in Europe | Schwäbisch Gmünd Prize | Technology | 278 |
2,137,332 | https://en.wikipedia.org/wiki/Boomerang%20attack | In cryptography, the boomerang attack is a method for the cryptanalysis of block ciphers based on differential cryptanalysis. The attack was published in 1999 by David Wagner, who used it to break the COCONUT98 cipher.
The boomerang attack has allowed new avenues of attack for many ciphers previously deemed safe from differential cryptanalysis.
Refinements on the boomerang attack have been published: the amplified boomerang attack, and the rectangle attack.
Due to the similarity of a Merkle–Damgård construction with a block cipher, this attack may also be applicable to certain hash functions such as MD5.
The attack
The boomerang attack is based on differential cryptanalysis. In differential cryptanalysis, an attacker exploits how differences in the input to a cipher (the plaintext) can affect the resultant difference at the output (the ciphertext). A high probability "differential" (that is, an input difference that will produce a likely output difference) is needed that covers all, or nearly all, of the cipher. The boomerang attack allows differentials to be used which cover only part of the cipher.
The attack attempts to generate a so-called "quartet" structure at a point halfway through the cipher. For this purpose, say that the encryption action, E, of the cipher can be split into two consecutive stages, E0 and E1, so that E(M) = E1(E0(M)), where M is some plaintext message. Suppose we have two differentials for the two stages; say,
for E0, and
for E1−1 (the decryption action of E1).
The basic attack proceeds as follows:
Choose a random plaintext and calculate .
Request the encryptions of and to obtain and
Calculate and
Request the decryptions of and to obtain and
Compare and ; when the differentials hold, .
Application to specific ciphers
One attack on KASUMI, a block cipher used in 3GPP, is a related-key rectangle attack which breaks the full eight rounds of the cipher faster than exhaustive search (Biham et al., 2005). The attack requires 254.6 chosen plaintexts, each of which has been encrypted under one of four related keys and has a time complexity equivalent to 276.1 KASUMI encryptions.
References
(Slides in PostScript)
External links
Boomerang attack — explained by John Savard
Cryptographic attacks | Boomerang attack | Technology | 505 |
24,551,397 | https://en.wikipedia.org/wiki/C21H26NO3 | {{DISPLAYTITLE:C21H26NO3}}
The molecular formula C21H26NO3 (molar mass: 340.44 g/mol, exact mass: 340.1913 u) may refer to:
Mepenzolate
Methantheline
Poldine
Molecular formulas | C21H26NO3 | Physics,Chemistry | 62 |
1,881,722 | https://en.wikipedia.org/wiki/External%20memory%20algorithm | In computing, external memory algorithms or out-of-core algorithms are algorithms that are designed to process data that are too large to fit into a computer's main memory at once. Such algorithms must be optimized to efficiently fetch and access data stored in slow bulk memory (auxiliary memory) such as hard drives or tape drives, or when memory is on a computer network. External memory algorithms are analyzed in the external memory model.
Model
External memory algorithms are analyzed in an idealized model of computation called the external memory model (or I/O model, or disk access model). The external memory model is an abstract machine similar to the RAM machine model, but with a cache in addition to main memory. The model captures the fact that read and write operations are much faster in a cache than in main memory, and that reading long contiguous blocks is faster than reading randomly using a disk read-and-write head. The running time of an algorithm in the external memory model is defined by the number of reads and writes to memory required. The model was introduced by Alok Aggarwal and Jeffrey Vitter in 1988. The external memory model is related to the cache-oblivious model, but algorithms in the external memory model may know both the block size and the cache size. For this reason, the model is sometimes referred to as the cache-aware model.
The model consists of a processor with an internal memory or cache of size , connected to an unbounded external memory. Both the internal and external memory are divided into blocks of size . One input/output or memory transfer operation consists of moving a block of contiguous elements from external to internal memory, and the running time of an algorithm is determined by the number of these input/output operations.
Algorithms
Algorithms in the external memory model take advantage of the fact that retrieving one object from external memory retrieves an entire block of size . This property is sometimes referred to as locality.
Searching for an element among objects is possible in the external memory model using a B-tree with branching factor . Using a B-tree, searching, insertion, and deletion can be achieved in time (in Big O notation). Information theoretically, this is the minimum running time possible for these operations, so using a B-tree is asymptotically optimal.
External sorting is sorting in an external memory setting. External sorting can be done via distribution sort, which is similar to quicksort, or via a -way merge sort. Both variants achieve the asymptotically optimal runtime of to sort objects. This bound also applies to the fast Fourier transform in the external memory model.
The permutation problem is to rearrange elements into a specific permutation. This can either be done either by sorting, which requires the above sorting runtime, or inserting each element in order and ignoring the benefit of locality. Thus, permutation can be done in time.
Applications
The external memory model captures the memory hierarchy, which is not modeled in other common models used in analyzing data structures, such as the random-access machine, and is useful for proving lower bounds for data structures. The model is also useful for analyzing algorithms that work on datasets too big to fit in internal memory.
A typical example is geographic information systems, especially digital elevation models, where the full data set easily exceeds several gigabytes or even terabytes of data.
This methodology extends beyond general purpose CPUs and also includes GPU computing as well as classical digital signal processing. In general-purpose computing on graphics processing units (GPGPU), powerful graphics cards (GPUs) with little memory (compared with the more familiar system memory, which is most often referred to simply as RAM) are utilized with relatively slow CPU-to-GPU memory transfer (when compared with computation bandwidth).
History
An early use of the term "out-of-core" as an adjective is in 1962 in reference to devices that are other than the core memory of an IBM 360. An early use of the term "out-of-core" with respect to algorithms appears in 1971.
See also
Cache-oblivious algorithm
External memory graph traversal
Online algorithm
Parallel external memory
Streaming algorithm
References
External links
Out of Core SVD and QR
Out of core graphics
Scalapack design
Algorithms
Models of computation
Cache (computing)
Analysis of algorithms
External memory algorithms | External memory algorithm | Mathematics | 886 |
3,103,836 | https://en.wikipedia.org/wiki/Hypholoma%20capnoides | Hypholoma capnoides is a mushroom in the family Strophariaceae. Found in both the Old and New World, it grows on decaying wood and is edible, though may resemble some poisonous species.
Description
The cap is up to in diameter with yellow-to-orange-brownish or matt yellow colour, sometimes viscid. It is convex then flattens in age. The stipe is yellowish, somewhat rust-brown below. The mushroom grows to tall. The flesh is yellow. The taste is mild, compared to most Hypholomas which are bitter.
The gills are initially pale orangish-yellow, pale grey when mature, later darker purple/brown. The spore print is dark burgundy to brown.
Similar species
The poisonous sulphur tuft is more common in many areas. H. capnoides has greyish gills due to the dark color of its spores, whereas sulphur tuft has greenish gills. It could also perhaps be confused with the deadly Galerina marginata or the good edible Kuehneromyces mutabilis.
Distribution and habitat
Like its poisonous relative H. fasciculare ('sulphur tuft'), H. capnoides grows in clusters on decaying wood, for example in tufts on old tree stumps, in North America, Europe, and Asia.
Edibility
Though edible when cooked, it could be confused with some poisonous species.
References
Edible fungi
capnoides
Fungi described in 1818
Fungi of Europe
Taxa named by Elias Magnus Fries
Fungus species | Hypholoma capnoides | Biology | 314 |
55,536,169 | https://en.wikipedia.org/wiki/Hypercalculia | Hypercalculia is "a specific developmental condition in which the ability to perform mathematical calculations is significantly superior to general learning ability and to school attainment in maths." A 2002 neuroimaging study of a child with hypercalculia suggested greater brain volume in the right temporal lobe. Serial SPECT scans revealed hyperperfusion over right parietal areas during performance of arithmetic tasks.
Math and reading achievement profiles in autistic individuals
Children at any age may be stronger in language or in mathematics, but very rarely in both. Autistic children are no different. A rare example of a child with multiple savant tendencies is a case study of a thirteen-year-old girl. Pacheva, Panoy, Gillberg, and Neville discovered this individual has not only hypercalculia abilities, but also showcases hyperlexia, and hypermnesia capabilities.
A study published in 2014 examined the reading and math achievement profiles and their changes over time within a sample of children between the ages 6–9 diagnosed with an autism spectrum disorder. What they found was that there are four distinct achievement profiles: higher-achieving (39%), hyperlexia (9%), hypercalculia (20%) and lower-achieving (32%). A previous study conducted in 2009 estimated the rate of hypercalculia at 16.2% in ASD adolescents.
According to Wei, Christiano, Yu, Wagner, and Spiker, research of the ASD achievement profile, hypercalculia, is sometimes overlooked in academic settings. Sometimes this oversight is a result of more resources being spent on understanding the capabilities of children who exhibit hyperlexia. Children with an ASD have shown various results during testing for hypercalculia. Some of these varied results indicate: below average performance of mathematical and problem solving tasks, average proficiency, and high-achievers topping the 99th percentile on 'standardized math achievement measures.'
There is an ongoing debate concerning the cause of hypercalculia along with other savant perceptions. Some researchers theorize that obsessive tendencies may trigger greater attention to certain areas of their lives.
Individuals with autism will sometimes focus a lot of their time, energy, and attention on schedules or routines, calendar calculations, numbers or counting, and/or music.
Other researchers speculate that people with savant tendencies may use different brain areas while they are processing subjects of their higher abilities. Among other debate arguments are hypotheses with regards to neural processes and working memory storage capabilities.
Wallace sometimes refers to these individuals as "mathematical savants" or "arithmetic savants." In his experience, individuals with this ability tend to prefer a chunking or segmentation method of sorts. Their proclivities tend to push them towards breaking bigger things down to smaller things like numbers or equations. This data led Wallace to research, "prime number savants." Prime number savants can calculate which numbers are prime by breaking up the number over and over numerous times until they are at its lowest form. The next step is figuring out if that number can be evenly divided.
Behavioral research of children with higher-achieving intellectual abilities
There are five different types of disorders that have been labeled on the autism spectrum. According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), the five different types of disorders on the autism spectrum are listed as: Autistic disorder, Asperger disorder, childhood disintegrative disorder, Rett disorder, and pervasive developmental disorder - not otherwise specified (PPD-NOS).
In a 2013 study, the behavior of children on the autism spectrum who exhibited intellectual abilities was observed. The behavior of these children was compared to children of normal intellectual status. Research shows that these children tended to internalize their problems. Further investigation proffers the suggestion that this internalization is due to social and language impairments. Many children on the autism spectrum with different savant perceptions such as hypercalculia, hyperlexia, and semantic hypermnesia tended to internalize their problems. These children were more likely to experience anxiety, low self-esteem, perfectionism and struggles in their social life. These social issues stem from withdrawal in social circumstances and an unwillingness to share. A lot of these children that were observed fell into two types of disorders on the spectrum, PPD and Asperger syndrome. The results show that there is little difference in the behavior of children considered to be high-achieving in their intellectual abilities and those children not as intellectually gifted.
Education of children with savant abilities
Towards the end of the twentieth century, recognition of autistic children, including autistic children with savant abilities, has increased awareness in the educational system.
There are just a few main names for savant children. The first category of savants was first discovered in London in 1887 by Dr. J. Langdon Down. Down coined the term 'idiot savant.' This term is given to individuals who have an IQ score below 25. These individuals show below average intelligence in most areas, but still show gifted expertise among such areas as music, arithmetic, reading, writing, or art to name a few. Idiot savant is no longer an acceptable name of categorization. It is not used very much anymore and was mainly discontinued after the first century of its discovery. Almost all individuals diagnosed with savant aptitudes test with an IQ of 40 or above.
The second name often used for these children is 'autistic savant.' Just like Down's term, autistic savant is not always appropriate for all savant cases. Only half of individuals with savant syndrome are autistic. The other half of the savant population suffer from other central nervous system deficiencies caused by injuries or other disorders.
Savant syndrome is the more overarching and accurate name to identify children with these higher-cognition skills.
Awareness of savant syndrome has increased, but the limited number of affected individuals has complicated finding educational resources to meet their needs. Better diagnostic tools over the years has helped identify these children and their needs. For the benefit of the students, educators should keep in mind that although these children are skilled in certain areas and may even take courses for the gifted, they may come across as rude and perhaps disrespectful. These behaviors might be shown to classmates and teachers because these students will not always be adept at communication and social cues.
Other concepts to consider in the educational system are the child's weaknesses and strengths. These will be unique to each child. In some examples of children with mathematical savant talents, individual children can be exhibit human calculator abilities, but be unable to use those skills in every day functions. There is sometimes a disconnection between their savant abilities and practical situations.
See also
Acalculia
Dyscalculia
Mental calculator
Numerical cognition
Savant syndrome
References
Further reading
Cognitive psychology
Cognitive neuroscience
Developmental psychology
Autism
Symptoms and signs: Nervous system | Hypercalculia | Biology | 1,428 |
75,122,057 | https://en.wikipedia.org/wiki/Maria%20Gatu%20Johnson | Maria Gatu Johnson (born 1978) is a Swedish-American plasma physicist whose research involves the use of neutron spectrometry to study inertial confinement fusion and stellar nucleosynthesis. She works at the Massachusetts Institute of Technology as a principal research scientist in the MIT Plasma Science and Fusion Center.
Education and career
Gatu Johnson earned a master's degree in engineering physics from Uppsala University in Sweden in 2003, and completed a Ph.D. in applied nuclear physics there in 2010. Her work there involved the application of neutron spectrometry to the Joint European Torus, a magnetic confinement fusion experiment in England.
She was a postdoctoral researcher at the MIT Plasma Science and Fusion Center from 2010 to 2013, before becoming a permanent member of the research staff there. In 2023 she was promoted to principal research scientist. At the Plasma Science and Fusion Center, she has been in charge of the Magnetic Recoil Neutron Spectrometer (MRS) beginning in 2013.
Recognition
Gatu Johnson was the 2019 recipient of the Katherine E. Weimer Award of the American Physical Society (APS), given biennially to recognize early-career research excellence by a female plasma physicist. She is a recipient of the 2022 National Nuclear Security Administration Secretary's Honor Award, and of the 2023 Department of Energy Secretary's Achievement Award.
In 2022, the Burning Plasma Team of the National Ignition Facility, including Gatu Johnson, received the John Dawson Award for Excellence in Plasma Physics Research of the APS, given "for the first laboratory demonstration of a burning deuterium-tritium plasma where alpha heating dominates the plasma energetics".
She was named a Fellow of the American Physical Society in 2023, after a nomination from the APS Division of Plasma Physics, "for pioneering efforts in the cross-cut field of plasma-nuclear science and for groundbreaking studies of macroscopic plasma flows in Inertial Confinement Fusion implosions".
References
External links
1978 births
Living people
Swedish emigrants to the United States
Swedish physicists
Swedish women physicists
American physicists
American women physicists
Plasma physicists
Uppsala University alumni
Fellows of the American Physical Society | Maria Gatu Johnson | Physics | 435 |
12,423,014 | https://en.wikipedia.org/wiki/C3H8O2 | {{DISPLAYTITLE:C3H8O2}}
The molecular formula C3H8O2 may refer to:
Dimethoxymethane
2-Methoxyethanol
Propanediol
1,2-Propanediol (propylene glycol), a vicinal diol
1,3-Propanediol (trimethylene glycol)
1,1-Propanediol (geminal diol)
2,2-Propanediol (geminal diol)
See also
Diol (Glycol)
Geminal diol
Vicinal diol | C3H8O2 | Chemistry | 131 |
17,182,647 | https://en.wikipedia.org/wiki/Hunter%E2%80%93Saxton%20equation | In mathematical physics, the Hunter–Saxton equation
is an integrable PDE that arises in the theoretical study of nematic liquid crystals. If the molecules in the liquid crystal are initially all aligned, and some of them are then wiggled slightly, this disturbance in orientation will propagate through the crystal, and the Hunter–Saxton equation describes certain aspects of such orientation waves.
Physical background
In the models for liquid crystals considered here, it is assumed that there is no fluid flow, so that only the orientation of the molecules is of interest.
Within the elastic continuum theory, the orientation is described by a field of unit vectors n(x,y,z,t). For nematic liquid crystals, there is no difference between orienting a molecule in the n direction or in the −n direction, and the vector field n is then called a director field.
The potential energy density of a director field is usually assumed to be given by the Oseen–Frank energy functional
where the positive coefficients , , are known as the elastic coefficients of splay, twist, and bend, respectively. The kinetic energy is often neglected because of the high viscosity of liquid crystals.
Derivation of the Hunter–Saxton equation
Hunter and Saxton investigated the case when viscous damping is ignored and a kinetic energy term is included in the model. Then the governing equations for the dynamics of the director field are the Euler–Lagrange equations for the Lagrangian
where is a Lagrange multiplier corresponding to the constraint |n|=1.
They restricted their attention to "splay waves" where the director field takes the special form
This assumption reduces the Lagrangian to
and then the Euler–Lagrange equation for the angle φ becomes
There are trivial constant solutions φ=φ0
corresponding to states where the molecules in the liquid crystal are
perfectly aligned.
Linearization around such an equilibrium leads to the linear wave equation
which allows wave propagation in both directions with speed
,
so the nonlinear equation can be expected to behave similarly.
In order to study right-moving waves for large t,
one looks for asymptotic solutions of the form
where
Inserting this into the equation, one finds at the order that
A simple renaming and rescaling of the variables
(assuming that )
transforms this into the Hunter–Saxton equation.
Generalization
The analysis was later generalized by Alì and Hunter, who allowed the director field to point in any direction, but with the spatial dependence still only in the x direction:
Then the Lagrangian is
where
The corresponding Euler–Lagrange equations are coupled nonlinear wave equations for the angles φ and ψ, with φ corresponding to "splay waves" and ψ to "twist waves". The previous Hunter–Saxton case (pure splay waves) is recovered by taking ψ constant, but one can also consider coupled splay-twist waves where both φ and ψ vary. Asymptotic expansions similar to that above lead to a system of equations, which, after renaming and rescaling the variables, takes the form
where u is related to φ and v to ψ.
This system implies that u satisfies
so (rather remarkably) the Hunter–Saxton equation arises in this context too, but in a different way.
Variational structures and integrability
The integrability of the Hunter–Saxton equation, or, more precisely, that of its x derivative
was shown by Hunter and Zheng, who exploited that this equation is obtained from the Camassa–Holm equation
in the "high frequency limit"
Applying this limiting procedure to a Lagrangian for the Camassa–Holm equation, they obtained a Lagrangian
which produces the Hunter–Saxton equation after elimination of v and w from the Euler–Lagrange equations for u, v, w. Since there is also the more obvious Lagrangian
the Hunter–Saxton has two inequivalent variational structures. Hunter and Zheng also obtained a bihamiltonian formulation and a Lax pair from the corresponding structures for the Camassa–Holm equation in a similar way.
The fact that the Hunter–Saxton equation arises physically in two different ways (as shown above) was used by Alì and Hunter to explain why it has this bivariational (or bihamiltonian) structure.
Geometric Formulation
The periodic Hunter-Saxton equation can be given a geometric interpretation as the geodesic equation on an infinite-dimensional Lie group, endowed with an appropriate Riemannian metric. In more detail, consider the group of diffeomorphisms of the unit circle . Choose some and denote by the subgroup of consisting diffeomorphisms which fix :
The group is an infinite-dimensional Lie group, whose Lie algebra consists of vector fields on which vanish at :
Here is the standard coordinate on . Endow with the homogeneous inner product:
where the subscript denotes differentiation. This inner product defines a right-invariant Riemannian metric on (on the full group this is only a semi-metric, since constant vector fields have norm 0 with respect to . Note that is isomorphic to the right quotient of by the subgroup of translations, which is generated by constant vector fields).
Let
be a time-dependent vector field on such that for all , and let be the flow of , i.e. the solution to:
Then is a periodic solution to the Hunter-Saxton equation if and only if the path is a geodesic on with respect to the right-invariant metric.
In the non-periodic case, one can similarly construct a subgroup of the group of diffeomorphisms of the real line, with a Riemannian metric whose geodesics correspond to non-periodic solutions of the Hunter-Saxton equation with appropriate decay conditions at infinity.
Notes
References
Further reading
Mathematical physics
Solitons
Partial differential equations
Equations of fluid dynamics | Hunter–Saxton equation | Physics,Chemistry,Mathematics | 1,208 |
36,737,310 | https://en.wikipedia.org/wiki/C7H13NO2 | {{DISPLAYTITLE:C7H13NO2}}
The molecular formula C7H13NO2 (molar mass: 143.19 g/mol) may refer to:
Dimethylaminoethyl_acrylate
N-(2-Hydroxypropyl)_methacrylamide
Stachydrine
Molecular formulas | C7H13NO2 | Physics,Chemistry | 75 |
14,879,114 | https://en.wikipedia.org/wiki/TIAF1 | TGFB1-induced anti-apoptotic factor 1 is a protein that in humans is encoded by the TIAF1 gene.
Interactions
TIAF1 has been shown to interact with Janus kinase 3 and TRIB3.
References
Further reading | TIAF1 | Chemistry | 53 |
8,591,903 | https://en.wikipedia.org/wiki/List%20of%20stars%20in%20Volans | This is the list of notable stars in the constellation Volans, sorted by decreasing brightness.
See also
List of stars by constellation
References
List
Volans | List of stars in Volans | Astronomy | 31 |
71,550,747 | https://en.wikipedia.org/wiki/Lanthanum%20diiodide | Lanthanum diiodide is an iodide of lanthanum, with the chemical formula of LaI2. It is an electride, actually having a chemical formula of La3+[(I−)2e−].
Preparation
Lanthanum diiodide can be obtained from the reduction of lanthanum(III) iodide with lanthanum metal under a vacuum at 800 to 900 °C:
It can also be obtained by reacting lanthanum and mercury(II) iodide:
It was first created by John D. Corbett in 1961.
Properties
Lanthanum diiodide is a blue-black solid with metallic lustre, which is easily hydrolyzed into the iodide oxide. It has a MoSi2-type structure, with the space group I4/mmm (No. 139).
References
Lanthanum compounds
Iodides
Electrides
Substances discovered in the 1960s | Lanthanum diiodide | Chemistry | 193 |
16,643,486 | https://en.wikipedia.org/wiki/Emotional%20aperture | Emotional aperture has been defined as the ability to perceive features of group emotions. This skill involves the perceptual ability to adjust one's focus from a single individual's emotional cues to the broader patterns of shared emotional cues that comprise the emotional composition of the collective.
Some examples of features of group emotions include the level of variability of emotions among members (i.e., affective diversity), the proportion of positive or negative emotions, and the modal (i.e., most common) emotion present in a group. The term “emotional aperture” was first defined by the social psychologist, Jeffrey Sanchez-Burks, and organizational theorist, Quy Huy. It has since been referenced in related work such as in psychologist, journalist, and author of the popular book Emotional Intelligence Daniel Goleman's most recent book "Focus: The Hidden Driver of Excellence." Academic references to emotional aperture and related work can be found on the references site for the Consortium for Research on Emotional Intelligence in Organizations.
Emotional Aperture abilities have been measured using the EAM. The EAM consists of a series of short movie clip showing groups that have various brief reactions to an unspecified event. Following each movie clip, individuals are asked to report the proportion of individuals that had a positive or negative reaction.
Emotional aperture, the ability to pick up such subtle signals in a group, works on essentially the same principle as the aperture of a camera, so he says. We can zoom in to focus on a person's feelings, or, conversely, zoom out to encompass everyone gathered - whether it's a school class or a workgroup. This concept is closely linked to emotional intelligence since it includes abilities such as the ability to develop motivation and persistence. Aperture enables managers to read information more accurately and understand, for example, whether their proposal is met with enthusiasm or rejection. Accurate perception of these signals can prevent failure and help make useful adjustments during project implementation.
Origin
The construct, emotional aperture, was developed to address the need to expand existing models of individual emotion perception (e.g., emotional intelligence) to take into account the veracity of group-based emotions and their action tendencies.
See also
Social intelligence
References
Emotion
Interpersonal relationships | Emotional aperture | Biology | 451 |
60,447,421 | https://en.wikipedia.org/wiki/Vkernel | A virtual kernel architecture (vkernel) is an operating system virtualisation paradigm where kernel code can be compiled to run in the user space, for example, to ease debugging of various kernel-level components, in addition to general-purpose virtualisation and compartmentalisation of system resources. It is used by DragonFly BSD in its vkernel implementation since DragonFly 1.7, having been first revealed in , and first released in the stable branch with DragonFly 1.8 in .
The long-term goal, in addition to easing kernel development, is to make it easier to support internet-connected computer clusters without compromising local security.
Similar concepts exist in other operating systems as well; in Linux, a similar virtualisation concept is known as user-mode Linux; whereas in NetBSD since the summer of 2007, it has been the initial focus of the rump kernel infrastructure.
The virtual kernel concept is nearly the exact opposite of the unikernel concept — with vkernel, kernel components get to run in userspace to ease kernel development and debugging, supported by a regular operating system kernel; whereas with a unikernel, userspace-level components get to run directly in kernel space for extra performance, supported by baremetal hardware or a hardware virtualisation stack. However, both vkernels and unikernels can be used for similar tasks as well, for example, to self-contain software to a virtualised environment with low overhead. In fact, NetBSD's rump kernel, originally having a focus of running kernel components in userspace, has since shifted into the unikernel space as well (going after the anykernel moniker for supporting both paradigms).
The vkernel concept is different from a FreeBSD jail in that a jail is only meant for resource isolation, and cannot be used to develop and test new kernel functionality in the userland, because each jail is sharing the same kernel. (DragonFly, however, still has FreeBSD jail support as well.)
In DragonFly, the vkernel can be thought of as a first-class computer architecture, comparable to i386 or amd64, and, according to Matthew Dillon circa 2007, can be used as a starting point for porting DragonFly BSD to new architectures.
DragonFly's vkernel is supported by the host kernel through new system calls that help manage virtual memory address space (vmspace) — vmspace_create() et al., as well as extensions to several existing system calls like mmap's madvise — mcontrol.
See also
user-mode Linux
rump kernel
References
External links
2006 software
BSD software
Computer architecture
Computer performance
DragonFly BSD
Free software programmed in C
Free virtualization software
Operating system kernels
Operating system security
Operating system technology
System administration
Virtual machines
Virtualization software
Software using the BSD license | Vkernel | Technology,Engineering | 602 |
3,865,332 | https://en.wikipedia.org/wiki/Genomic%20convergence | Genomic convergence is a multifactor approach used in genetic research that combines different kinds of genetic data analysis to identify and prioritize susceptibility genes for a complex disease.
Early applications
In January 2003, Michael Hauser along with fellow researchers at the Duke Center for Human Genetics (CHG) coined the term “genomic convergence” to describe their endeavor to identify genes affecting the expression of Parkinson disease (PD). Their work successfully combined serial analysis of gene expression (SAGE) with genetic linkage analysis. The authors explain, “While both linkage and expression analyses are powerful on their own, the number of possible genes they present as candidates for PD or any complex disorder remains extremely large”. The convergence of the two methods allowed researchers to decrease the number of possible PD genes to consider for further study.
Their success prompted further use of the genomic convergence method at the CHG, and in July 2003 Yi-Ju Li, et al. published a paper revealing that glutathione S-transferase omega-1 (GSTO1) modifies the age-at-onset (AAO) of Alzheimer disease (AD) and PD.
In May 2004, Dr. Margaret Pericak-Vance, currently the director of the John P. Hussman Institute for Human Genomics at the University of Miami Miller School of Medicine and then the director of the CHG, articulated the value of the genomic convergence method at a New York Academy of Sciences (NYAS) keynote address entitled "Novel Methods in Genetic Exploration of Neurodegenerative Disease." She stated, "No single method is going to get us where we need to be with these complex traits. It is going to take a combination of methods to dissect the underlying etiology of these disorders".
Recent and future applications
Genomic convergence has a countless number of creative applications that combine the strengths of different analyses and studies. Maher Noureddine et al., note in their 2005 paper, “One of the growing problems in the study of complex diseases is how to prioritize research and make sense of the immense amount of data now readily available at the click of a computer mouse...The best approach may be to take advantage of the strengths of both…SAGE …and microarrays”.
The results of combining methods of analysis have continued to be promising. Sofia Oliveira et al. (2005) combined gene expression, linkage data, and “iterative association mapping” to identify several genes associated with PD AAO.
Future studies will continue to apply genomic convergence to elucidate the etiology of complex diseases. Dr. Jeff Vance, Director of the Morris K. Udall PD Research Center of Excellence, notes, “Genomic convergence is really no different from mathematical convergence – the more angles from which you can come at a problem, the better chance you have of solving it”.
References
Genetics | Genomic convergence | Biology | 593 |
2,566,769 | https://en.wikipedia.org/wiki/Happy%20Tooth | The Happy Tooth is a registered trademark of Toothfriendly International. It stands for guaranteed toothfriendly quality.
The Happy Tooth mark distinguishes products that are not harmful for teeth. In order for products to carry the logo they have to be scientifically tested and proven not to be cariogenic or erosive. The test is based on the measurement of the pH of dental plaque and saliva and is carried out by three appointed independent university institutes.
The compliance of a product is tested by means of intra-oral pH telemetry. Applying a standardized method, the plaque pH is measured at least in four volunteers during and for 30 minutes after consumption of the product with an indwelling, interproximally placed, plaque-covered electrode. Products which do not lower plaque pH below 5.7 under the conditions of this test, lack a cariogenic potential. The erosive potential is measured with a plaque free electrode. The acid exposure of the teeth must not exceed 40 mmol H min. Schachtele Ch.F. et al. (1986). Human plaque acidity models – Working Group Consensus Report. J. Dent. Res., 65 (Spec. Iss.): 1530–1531.
Toothfriendly International grants the rights to use the trademark.
References
Dental erosion in the 21st century: what is happening to nutritional habits and lifestyle in our society?
External links
Toothfriendly International
Certification marks
Dentistry | Happy Tooth | Mathematics | 297 |
75,874,752 | https://en.wikipedia.org/wiki/Radium%20fad | The radium fad or radium craze of the early 20th century was an early form of radioactive quackery that resulted in widespread marketing of radium-infused products as being beneficial to health. Many radium products contained no actual radium, in part because it was prohibitively expensive, which turned out to be a grace, as high levels of radium exposure can result in radiation-induced cancer.
The fad began to fizzle out following the emergence of research that radium could be hazardous to health, and high-profile cases such as the Radium Girls and the death of Eben Byers, which proved this fact.
In the United States, the 1938 Federal Food, Drug and Cosmetic Act outlawed deceptive packaging, further preventing companies being able to use radium as a marketing tool.
Radium-infused products
Radium was added to, or used to market, a number of consumer goods. These included cosmetics, such as the brand Tho-Radia, toothpaste, hair cream, and hemorrhoid cream.
Radium was also used to market foods and drinks, although products such as Radium Brand Creamery Butter did not actually contain any radium. Radithor, an "energy drink" of distilled water with traces of radium, was marketed as a panacea. One of its most famous advocates, golfer Eben Byers, died in 1932 of radium poisoning through his consumption of the product. A number of water sources (such as bottlers or artesian hot-spring spa hotels) rebranded themselves as "radium water" or radium springs to capitalize on the craze.
Radium was also used to give products a glowing appearance, as in the case of watches painted with radium-containing paint.
Radium was also used in some ceramics, including in the production of radium water crocks, whose purpose was to irradiate drinking water.
Gallery
See also
Uranium glass
Lead pipes
Arsenic green (disambiguation)
Asbestos
Electrical quackery
History of radiation protection
References
Radioactive quackery
20th-century fads and trends
Radium | Radium fad | Chemistry | 434 |
1,041,955 | https://en.wikipedia.org/wiki/Project%2025 | Project 25 (P25 or APCO-25) is a suite of standards for interoperable digital two-way radio products. P25 was developed by public safety professionals in North America and has gained acceptance for public safety, security, public service, and commercial applications worldwide. P25 radios are a direct replacement for analog UHF (typically FM) radios, adding the ability to transfer data as well as voice for more natural implementations of encryption and text messaging. P25 radios are commonly implemented by dispatch organizations, such as police, fire, ambulance and emergency rescue service, using vehicle-mounted radios combined with repeaters and handheld walkie-talkie use.
Starting around 2012, products became available with the newer phase 2 modulation protocol, the older protocol known as P25 became P25 phase 1. P25 phase 2 products use the more advanced AMBE2+ vocoder, which allows audio to pass through a more compressed bitstream and provides two TDMA voice channels in the same RF bandwidth (12.5 kHz), while phase 1 can provide only one voice channel. The two protocols are not compatible. However, P25 Phase 2 infrastructure can provide a "dynamic transcoder" feature that translates between Phase 1 and Phase 2 as needed. In addition to this, phase 2 radios are backwards compatible with phase 1 modulation and analog FM modulation, per the standard. The European Union has created the Terrestrial Trunked Radio (TETRA) and Digital mobile radio (DMR) protocol standards, which fill a similar role to Project 25.
Suite of standards overview
History
Public safety radios have been upgraded from analog FM to digital since the 1990s because of an increased use of data on radio systems for such features as GPS location, trunking, text messaging, metering, and encryption.
Various user protocols and different public safety radio spectrum made it difficult for Public Safety agencies to achieve interoperability and widespread acceptance. However, lessons learned during disasters the United States faced in the past decades have forced agencies to assess their requirements during a disaster when basic infrastructure has failed. To meet the growing demands of public safety digital radio communication, the United States Federal Communications Commission (FCC) at the direction of the United States Congress initiated a 1988 inquiry for recommendations from users and manufacturers to improve existing communication systems. Based on the recommendations, to find solutions that best serve the needs of public safety management, in October 1989 APCO Project 25 came into existence in a coalition with:
Association of Public-Safety Communications Officials-International (APCO)
National Association of State Telecommunications Directors (NASTD)
National Telecommunications and Information Administration (NTIA)
National Communications System (NCS)
National Security Agency (NSA)
Department of Defense (DoD)
A steering committee consisting of representatives from the above-mentioned agencies along with FPIC (Department of Homeland Security Federal Partnership for Interoperable Communication), Coast Guard and the Department of Commerce's National Institute of Standards and Technology (NIST), Office of Law Enforcement Standards was established to decide the priorities and scope of technical development of P25.
Introduction
Interoperable emergency communication is integral to initial response, public health, community safety, national security and economic stability. Of all the problems experienced during disaster events, one of the most serious is poor communication due to lack of appropriate and efficient means to collect, process, and transmit important information in a timely fashion. In some cases, radio communication systems are incompatible and inoperable not just within a jurisdiction but within departments or agencies in the same community. Non-operability occurs due to use of outdated equipment, limited availability of radio frequencies, isolated or independent planning, lack of coordination, and cooperation, between agencies, community priorities competing for resources, funding and ownership, and control of communications systems. Recognizing and understanding this need, Project 25 (P25) was initiated collaboratively by public safety agencies and manufacturers to address the issue with emergency communication systems. P25 is a collaborative project to ensure that two-way radios are interoperable. The goal of P25 is to enable public safety responders to communicate with each other and, thus, achieve enhanced coordination, timely response, and efficient and effective use of communications equipment.
P25 was established to address the need for common digital public safety radio communications standards for first-responders and homeland security/emergency response professionals. The Telecommunications Industry Association's TR-8 engineering committee facilitates such work through its role as an ANSI-accredited standards development organization (SDO) and has published the P25 suite of standards as the TIA-102 series of documents, which now include 49 separate parts on Land Mobile Radio and TDMA implementations of the technology for public safety.
P25-compliant systems are being increasingly adopted and deployed throughout the United States, as well as other countries. Radios can communicate in analog mode with legacy radios, and in either digital or analog mode with other P25 radios. Additionally, the deployment of P25-compliant systems will allow for a high degree of equipment interoperability and compatibility.
P25 standards use the proprietary Improved Multi-Band Excitation (IMBE) and Advanced Multi-Band Excitation (AMBE+2) voice codecs which were designed by Digital Voice Systems, Inc. to encode/decode the analog audio signals. It is rumored that the licensing cost for the voice-codecs that are used in P25 standard devices is the main reason that the cost of P25 compatible devices is so high.
P25 may be used in "talk around" mode without any intervening equipment between two radios, in conventional mode where two radios communicate through a repeater or base station without trunking or in a trunked mode where traffic is automatically assigned to one or more voice channels by a Repeater or Base Station.
The protocol supports the use of Data Encryption Standard (DES) encryption (56 bit), 2-key Triple-DES encryption, three-key Triple-DES encryption, Advanced Encryption Standard (AES) encryption at up to 256 bits keylength, RC4 (40 bits, sold by Motorola as Advanced Digital Privacy), or no encryption.
The protocol also supports the ACCORDION 1.3, BATON, Firefly, MAYFLY and SAVILLE Type 1 ciphers.
P25 open interfaces
P25's Suite of Standards specify eight open interfaces between the various components of a land mobile radio system. These interfaces are:
Common Air Interface (CAI) – standard specifies the type and content of signals transmitted by compliant radios. One radio using CAI should be able to communicate with any other CAI radio, regardless of manufacturer
Subscriber Data Peripheral Interface – standard specifies the port through which mobiles and portables can connect to laptops or data networks
Fixed Station Interface – standard specifies a set of mandatory messages supporting digital voice, data, encryption and telephone interconnect necessary for communication between a Fixed Station and P25 RF Subsystem
Console Subsystem Interface – standard specifies the basic messaging to interface a console subsystem to a P25 RF Subsystem
Network Management Interface – standard specifies a single network management scheme which will allow all network elements of the RF subsystem to be managed
Data Network Interface – standard specifies the RF Subsystem's connections to computers, data networks, or external data sources
Telephone Interconnect Interface – standard specifies the interface to Public Switched Telephone Network (PSTN) supporting both analog and ISDN telephone interfaces.
Inter RF Subsystem Interface (ISSI) – standard specifies the interface between RF subsystems which will allow them to be connected into wide area networks
P25 phases
P25-compliant technology has been deployed over two main phases with future phases yet to be finalized.
Phase 1
Phase 1 radio systems operate in 12.5 kHz digital mode using a single user per channel access method. Phase 1 radios use Continuous 4 level FM (C4FM) modulation—a special type of 4FSK modulation—for digital transmissions at 4,800 baud and 2 bits per symbol, yielding 9,600 bits per second total channel throughput. Of this 9,600, 4,400 is voice data generated by the IMBE codec, 2,800 is forward error correction, and 2,400 is signalling and other control functions. Receivers designed for the C4FM standard can also demodulate the "Compatible quadrature phase shift keying" (CQPSK) standard, as the parameters of the CQPSK signal were chosen to yield the same signal deviation at symbol time as C4FM. Phase 1 uses the IMBE voice codec.
These systems involve standardized service and facility specifications, ensuring that any manufacturers' compliant subscriber radio has access to the services described in such specifications. Abilities include backward compatibility and interoperability with other systems, across system boundaries, and regardless of system infrastructure. In addition, the P25 suite of standards provides an open interface to the radio frequency (RF) subsystem to facilitate interlinking of different vendors' systems.
Phase 2
To improve spectrum use, P25 Phase 2 was developed for trunking systems using a 2-slot TDMA scheme and is now required for all new trunking systems in the 700 MHz band. Phase 2 uses the AMBE+2 voice codec to reduce the needed bitrate so that one voice channel will only require 6,000 bits per second (including error correction and signalling). Phase 2 is not backwards compatible with Phase 1 (due to the TDMA operation), although multi-mode TDMA radios and systems are capable of operating in Phase 1 mode when required, if enabled. A subscriber radio cannot use TDMA transmission without a synchronization source; therefore direct radio to radio communication resorts to conventional FDMA digital operation. Multi-band subscriber radios can also operate on narrow-band FM as a lowest common denominator between almost any two way radios. This makes analog narrow-band FM the de facto "interoperability" mode for some time.
Originally the implementation of Phase 2 was planned to split the 12.5 kHz channel into two 6.25 kHz slots, or Frequency-Division Multiple Access (FDMA). However it proved more advantageous to use existing 12.5 kHz frequency allocations in Time Division Multiple Access (TDMA) mode for a number of reasons. It allowed subscriber radios to save battery life by only transmitting half the time which also yields the ability for the subscriber radio to listen and respond to system requests between transmissions.
Phase 2 is what is known as 6.25 kHz "bandwidth equivalent" which satisfies an FCC requirement for voice transmissions to occupy less bandwidth. Voice traffic on a Phase 2 system transmits with the full 12.5 kHz per frequency allocation, as a Phase 1 system does, however it does so at a faster data rate of 12 kbit/s allowing two simultaneous voice transmissions. As such subscriber radios also transmit with the full 12.5 kHz, but in an on/off repeating fashion resulting in half the transmission and thus an equivalent of 6.25 kHz per each radio. This is accomplished using the AMBE voice coder that uses half the rate of the Phase 1 IMBE voice coders.
Beyond Phase 2
From 2000 to 2009, the European Telecommunications Standards Institute (ETSI) and TIA were working collaboratively on the Public Safety Partnership Project or Project MESA (Mobility for Emergency and Safety Applications), which sought to define a unified set of requirements for a next-generation aeronautical and terrestrial digital wideband/broadband radio standard that could be used to transmit and receive voice, video, and high-speed data in wide-area, multiple-agency networks deployed by public safety agencies.
The final functional and technical requirements have been released by ETSI and were expected to shape the next phases of American Project 25 and European DMR, dPMR, and TETRA, but no interest from the industry followed, since the requirements could not be met by available commercial off-the-shelf technology, and the project was closed in 2010.
During the United States 2008 wireless spectrum auction, the FCC allocated 20 MHz of the 700 MHz UHF radio band spectrum freed in the digital TV transition to public safety networks. The FCC expects providers to employ LTE for high-speed data and video applications.
Conventional implementation
P25 systems do not have to resort to using in band signaling such as Continuous Tone-Coded Squelch System (CTCSS) tone or Digital-Coded Squelch (DCS) codes for access control. Instead they use what is called a Network Access Code (NAC) which is included outside of the digital voice frame. This is a 12-bit code that prefixes every packet of data sent, including those carrying voice transmissions.
The NAC is a feature similar to CTCSS or DCS for analog radios. That is, radios can be programmed to only pass audio when receiving the correct NAC. NACs are programmed as a three-hexadecimal-digit code that is transmitted along with the digital signal being transmitted.
Since the NAC is a three-hexadecimal-digit number (12 bits), there are 4,096 possible NACs for programming, far more than all analog methods combined.
Three of the possible NACs have special functions:
0x293 ($293) – the default NAC
0xf7e ($F7E) – a receiver set for this NAC will pass audio on any decoded signal received
0xf7f ($F7F) – a repeater receiver set for this NAC will allow all incoming decoded signals and the repeater transmitter will retransmit the received NAC.
Adoption
Adoption of these standards has been slowed by budget problems in the US; however, funding for communications upgrades from the Department of Homeland Security usually requires migrating to Project 25. It is also being used in other countries worldwide including Australia, New Zealand, Brazil, Canada, India and Russia. As of mid-2004 there were 660 networks with P25 deployed in 54 countries. At the same time, in 2005, the European Terrestrial Trunked Radio (TETRA) was deployed in sixty countries, and it is the preferred choice in Europe, China, and other countries. This was largely based on TETRA systems being many times cheaper than P25 systems ($900 vs $6,000 for a radio) at the time. However P25 radio prices are rapidly approaching parity with TETRA radio prices through increased competition in the P25 market. The majority of P25 networks are based in Northern America where it has the advantage that a P25 system has the same coverage and frequency bandwidth as the earlier analog systems that were in use so that channels can be easily upgraded one by one. Some P25 networks also allow intelligent migration from the analog radios to digital radios operating within the same network. Both P25 and TETRA can offer varying degrees of functionality, depending on available radio spectrum, terrain and project budget.
While interoperability is a major goal of P25, many P25 features present interoperability challenges. In theory, all P25 compliant equipment is interoperable. In practice, interoperable communications isn't achievable without effective governance, standardized operating procedures, effective training and exercises, and inter-jurisdictional coordination. The difficulties inherent in developing P25 networks using features such as digital voice, encryption, or trunking sometimes result in feature-backlash and organizational retreat to minimal "feature-free" P25 implementations which fulfill the letter of any Project 25 migration requirement without realizing the benefits thereof. Additionally, while not a technical issue per se, frictions often result from the unwieldy bureaucratic inter-agency processes that tend to develop in order to coordinate interoperability decisions.
Naming of P25 technology in regions
Statewide P25 systems in Australia were deployed using the name Government Radio Network (GRN) in New South Wales, South Australia, and Tasmania; Government Wireless Network (GWN) in Queensland; Territory Radio Network (TRN) in the Australian Capital Territory; and Melbourne Metropolitan Radio (MMR) and Rural Mobile Radio (RMR) in Victoria. In New South Wales, the GRN is now called the Public Safety Network (PSN).
Project 25 Compliance Assessment Program (P25 CAP)
The United States DHS's Project 25 Compliance Assessment Program (P25 CAP) aims for interoperability among different vendors by testing to P25 Standards. P25 CAP, a voluntary program, allows suppliers to publicly attest to their products' compliance.
Independent, accredited labs test vendor's P25 radios for compliance to P25 Standards, derived from TIA-102 Standards and following TIA-TR8 testing procedures. Only approved products may be purchased using US federal grant dollars. Generally, non-approved products should not be trusted to be meet P25 standards for performance, conformance, and interoperability.
P25 product labeling varies. "P25" and "P25 compliant" mean nothing while high standards apply for a vendor to claim a product is "P25 CAP compliant" or "P25 compliant with the Statement of Requirements (P25 SOR)"
Security flaws
OP25 Project—Encryption flaws in DES-OFB and ADP ciphers
At the Securecomm 2011 conference in London, security researcher Steve Glass presented a paper, written by himself and co-author Matt Ames, that explained how DES-OFB and Motorola's proprietary ADP (RC4 based) ciphers were vulnerable to brute force key recovery. This research was the result of the OP25 project which uses GNU Radio and the Ettus Universal Software Radio Peripheral (USRP) to implement an open source P25 packet sniffer and analyzer. The OP25 project was founded by Steve Glass in early 2008 while he was performing research into wireless networks as part of his PhD thesis.
The paper is available for download from the NICTA website.
University of Pennsylvania research
In 2011, the Wall Street Journal published an article describing research into security flaws of the system, including a user interface that makes it difficult for users to recognize when transceivers are operating in secure mode. According to the article, "(R)esearchers from the University of Pennsylvania overheard conversations that included descriptions of undercover agents and confidential informants, plans for forthcoming arrests and information on the technology used in surveillance operations." The researchers found that the messages sent over the radios are sent in segments, and blocking just a portion of these segments can result in the entire message being jammed. "Their research also shows that the radios can be effectively jammed (single radio, short range) using a highly modified pink electronic child's toy and that the standard used by the radios 'provides a convenient means for an attacker' to continuously track the location of a radio's user. With other systems, jammers have to expend a lot of power to block communications, but the P25 radios allow jamming at relatively low power, enabling the researchers to prevent reception using a $30 toy pager designed for pre-teens."
The report was presented at the 20th USENIX Security Symposium in San Francisco in August 2011. The report noted a number of security flaws in the Project 25 system, some specific to the way it has been implemented and some inherent in the security design.
Encryption lapses
The report did not find any breaks in the P25 encryption; however, they observed large amounts of sensitive traffic being sent in the clear due to implementations problems. They found switch markings for secure and clear modes difficult to distinguish (∅ vs. o). This is exacerbated by the fact that P25 radios when set to secure mode continue to operate without issuing a warning if another party switches to clear mode. In addition, the report authors said many P25 systems change keys too often, increasing the risk that an individual radio on a net may not be properly keyed, forcing all users on the net to transmit in the clear to maintain communications with that radio.
Jamming vulnerability
One design choice was to use lower levels of error correction for portions of the encoded voice data that are deemed less critical for intelligibility. As a result, bit errors may be expected in typical transmissions, and while harmless for voice communication, the presence of such errors force the use of stream ciphers, which can tolerate bit errors, and prevents the use of a standard technique, message authentication codes (MACs), to protect message integrity from stream cipher attacks. The varying levels of error correction are implemented by breaking P25 message frames into subframes. This allows an attacker to jam entire messages by transmitting only during certain short subframes that are critical to reception of the entire frame. As a result, an attacker can effectively jam Project 25 signals with average power levels much lower than the power levels used for communication. Such attacks can be targeted at encrypted transmissions only, forcing users to transmit in the clear.
Because Project 25 radios are designed to work in existing two-way radio frequency channels, they cannot use spread spectrum modulation, which is inherently jam-resistant. An optimal spread spectrum system can require an effective jammer to use 1,000 times as much power (30 dB more) as the individual communicators. According to the report, a P25 jammer could effectively operate at 1/25th the power (14 dB less) than the communicating radios. The authors developed a proof-of-concept jammer using a Texas Instruments CC1110 single chip radio, found in an inexpensive toy.
Traffic analysis and active tracking
Certain metadata fields in the Project 25 protocol are not encrypted, allowing an attacker to perform traffic analysis to identify users. Because Project 25 radios respond to bad data packets addressed to them with a retransmission request, an attacker can deliberately send bad packets forcing a specific radio to transmit even if the user is attempting to maintain radio silence. Such tracking by authorized users is considered a feature of P25, referred to as "presence".
The report's authors concluded by saying "It is reasonable to wonder why this protocol, which was developed over many years and is used for sensitive and critical applications, is so difficult to use and so vulnerable to attack." The authors separately issued a set of recommendations for P25 users to mitigate some of the problems found. These include disabling the secure/clear switch, using Network Access Codes to segregate clear and encrypted traffic, and compensating for the unreliability of P25 over-the-air rekeying by extending key life.
Comparison between P25 and TETRA
P25 and TETRA are used in more than 53 countries worldwide for both public safety and private sector radio networks. There are some differences in features and capacities:
TETRA is optimized for high population density areas, and has spectral efficiency of 4 time slots in 25 kHz. (Four communications channels per 25 kHz channel, an efficient use of spectrum). It supports full-duplex voice communication, data, and messaging. It does not provide simulcast.
P25 is optimized for wider area coverage with low population density, and also supports simulcast. It is, however, limited with respect to data support. There is a major subdivision within P25 radio systems: Phase I P25 operates analogue, digital, or mixed mode in a single 12.5 kHz channel. Phase II uses a 2-timeslot TDMA structure in each 12.5 kHz channel.
See also
APCO-16, an earlier standard that specified trunking formats and radio operation
Digital Audio Broadcasting
Digital terrestrial television
Government radio networks in Australia, examples deployment of P25 technology
NXDN, a two-way digital radio standard with similar characteristics (Optional TDMA)
Terrestrial Trunked Radio, TETRA, the European(EU) standard equivalent to P25
Notes
External links
P25 Overview TIA Standards Development Activities for Public Safety
https://web.archive.org/web/20110223005820/http://www.apco911.org/frequency/project25.php APCO International Project 25 page
http://www.apco.ca/ APCO Canada
http://www.dvsinc.com/papers/p25_training_guide.pdf Daniels' P25 Radio System Training Guide
https://valid8.com/solutions/p25-issi-cssi-conformance P25 Compliance Test Tools for ISSI & CSSI
https://web.archive.org/web/20170611161725/http://www.dvsinc.com/prj25.htm DVSI P25 Vocoder Software and Hardware
http://www.p25phase2.com Radio users and experts discuss P25 Phase 2
Trunked radio systems
Telecommunications standards
Computer security exploits | Project 25 | Technology | 5,070 |
40,309,522 | https://en.wikipedia.org/wiki/Thermomechanical%20cuttings%20cleaner | The thermomechanical cuttings cleaner (TCC) is a patented technology mainly used by service providers in the oil and gas industry to separate and recover the components of oil-contaminated drilling waste. A TCC converts kinetic energy to thermal energy in a thermal desorption process which efficiently transforms drilling waste into re-usable products. Using kinetic energy instead of indirect heating allows for very short retention times and as a consequence the quality of the separated components is not affected by the treatment. Thus the recovered water, base oil and solids can be re-used after the treatment process.
References
Waste treatment technology
Industrial machinery
Mechanical engineering
Waste management | Thermomechanical cuttings cleaner | Physics,Chemistry,Engineering | 129 |
36,791,572 | https://en.wikipedia.org/wiki/Gastric%20balloon | A gastric balloon, also known as an intragastric balloon (IGB) or a stomach balloon, is an inflatable medical device that is temporarily placed into the stomach to help reduce weight. It is designed to help provide weight loss when diet and exercise have failed and surgery is not wanted by or recommended for the patient.
Medical uses
Intragastric balloons are an alternative to bariatric surgery (or weight loss surgery), which is not generally offered to patients with a body mass index of less than 35. Gastric balloons are also designed for patients who require weight-loss support but who do not want to commit to surgical interventions.
Intragastric balloons help induce weight loss by increasing satiety, delaying gastric emptying, and reducing the amount of food eaten at each meal. Gastric balloons take up space in the stomach, which limits the amount of food that can be held. This creates an early feeling of fullness and satiety. A reduced intake of food then results in weight loss.
Endoscopic Intragastric Balloons
Most balloons require endoscopy for removal or placement. They are usually placed for up to six months, though some devices are placed for twelve months. The device is then removed, again using endoscopy. Longer placement is not advised because of the danger of damage to the tissue wall and degradation of the balloon. The use of the balloon is complemented with counseling and nutritional support or advice.
Endoscopic placement of the balloon is temporary and reversible without surgical incisions. The gastric balloon for weight loss differs from the Sengstaken-Blakemore balloon used to stop esophageal and gastric bleeding.
Non-Endoscopic Intragastric Balloons
Gastric balloon uptake has until recently been limited due to the need for endoscopy for placement or removal.
Procedureless, or non-endoscopic, intragastric balloons offer a promising alternative to historic endoscopic balloons. Non-endoscopic balloons are also a less invasive alternative to weight-loss surgery.
In 2015, Allurion's Elipse gastric balloon became the world's first non-endoscopic swallowable gastric balloon when it gained approval in Europe. Except under exceptional circumstances, it does not require endoscopy or surgery for placement or removal. The non-endoscopic gastric balloon capsule is swallowed for placement and once in the stomach is filled with saline liquid. After 16 weeks, the non-endoscopic gastric balloon then automatically deflates and passes naturally at the end of placement. A recent meta analysis of 6 studies found the balloon was a safe device offering effective weight loss. Total pooled weight loss at the completion of treatment (4–6 months) was 12.8% and at 12 months was 10.9%.
Adjustable Intragastric Balloons
Adjustable gastric balloons are able to increase or decrease their volume. While non-adjustable gastric balloons have been successfully used for weight loss for the last 30 years, the adjustability function was developed to address the following issues: (1) variability of response and reduced efficacy after 3 months and (2) intolerance necessitating early balloon extraction. Alleviating intolerance with a downward adjustment and renewing weight loss after balloon upward adjustment, are responsible for higher success rates compared with non-adjustable balloons. The Spatz3 adjustable gastric balloon is the first intragastric balloon approved for 1-year implantation (outside of the US), while featuring an adjustability function that provides balloon volume changes as needed.
Results
The device is intended to be used by people with a body mass index of more than 27 kg/m2. or between 30 and 40 kg/m2 and have weight-related co-morbidity. It should not be applied to patients with certain intestinal problems such as inflammatory bowel disease or delayed gastric emptying, who are pregnant, or who are taking blood thinner medications such as Coumadin. Low dose aspirin (100 mg) is permitted.
A 2016 meta analysis of studies showed short term weight loss without any mortality. It was calculated that the weight loss was 1.59 and 1.34 kg/m2 for overall and 3-month body mass index (BMI) loss, respectively, and 4.6 and 4.77 kg for overall and 3-month weight loss, respectively.
Results are influenced by the adherence to nutritional and dietary programs. Long-term studies show promise for patients who combine balloon treatment with exercise and a healthy diet. In a study on the 'Long-Term Efficacy of the Elipse Gastric Balloon System: An International Multicenter Study, Dr. Roberta Ienca and colleagues' report on 509 patients who received the non-endoscopic Elipse balloon and were followed for one year. After 4 months of treatment, patients achieved weight loss of 14.4 kg or 13.9% of total body weight. At one-year follow-up, 95% of this weight loss was maintained by patients included in the study.
Safety and side effects
Gastric balloons are generally considered to be safe and effective in the short term. Existing clinical data shows an acceptable safety profile. One of the largest intragastric balloon studies ever performed, which included 1770 patients, demonstrated an excellent safety profile.
There can be procedure-related side effects due to endoscopy and anesthesia on balloons that require medical intervention for placement or removal. On very rare occasions, the endoscopic placement of a balloon has led to death.
Several studies have demonstrated that the data on both the efficacy and safety for the non-endoscopic Allurion Elipse gastric balloon compares favorably with balloons that require endoscopy. It showed an acceptable safety profile with 0.2% of serious adverse events, which is comparable to the Orbera balloon, which requires endoscopy.
Post-placement side effects of gastric balloons are common and may include nausea, vomiting, reflux and stomach cramps. Other side effects include indigestion, bloating, flatulence and diarrhea. Rare side effects include esophagitis, gastric ulcer formation or gastric perforation. The device can become deflated and slip into the lower intestines. Migration of a balloon can lead to bowel obstruction.
Mechanism
Currently, there are three types of FDA-approved gastric balloons in the USA. These approved devices are placed via the esophagus using endoscopy. This can be done in an outpatient setting under sedation. One further balloon, Allurion's Ellipse, has European CE approval and does not require endoscopy for placement or removal.
Once in place the balloon is filled with saline and remains as a free-floating object in the stomach cavity, too big to pass through the pylorus. In addition to saline, the balloon that is made from silicone may contain some radio-opaque material as a radiographic marker and a dye such as methylene blue to alert the patient if the balloon leaks. Studies have suggested that fluid is superior to air for distending gastric balloons. Inflated balloons reduce the operative volume capacity of the stomach. While the typical gastric volume is about 900 ml, an inflated balloon may take up most of the space, about 700 (+/-100) ml.
Availability and costs
Gastric balloon-type devices have been approved in many countries, among them Australia, Canada, Mexico, India, Guatemala and several European and South American countries. They became available in the United States in 2015 when two different balloon devices were approved by the FDA.
ReShape Integrated Dual Balloon System (ReShape Dual Balloon) is a double balloon device. The double balloon system is supposed to provide a level of safety: when one balloon leaks or ruptures, blue dye in the urine will alert the patient that there is a problem.
Orbera consists of a single balloon device. It has been shown to reduce weight when combined with exercise and diet over six months.
The Obalon balloon system may consist of one, two or three balloon devices. This balloon is swallowed for placement but requires endoscopy for removal.
Europe has given the CE mark to Allurion Elipse gastric balloon, which is the only gastric balloon that does not need an endoscopic procedure for either placement or removal. It is swallowed for placement and passes naturally after around 16 weeks. It is offered as part of a combined package with a healthy lifestyle plan that includes nutritional advice.
Costs for the gastric balloon are surgeon-specific and vary by region. Average cost in the US is US$8,150, and generally less in other countries. Average cost in Europe is around €3,000. Insurance coverage is usually not provided in the US. There are three cost categories for the intragastric balloon: pre-operative (e.g. professional fees, lab work and testing), the procedure itself (e.g. surgeon, surgical assistant, anesthesia and hospital fees) and post-operative (e.g. follow-up physician office visits, vitamins and supplements).
History
The first person to use a gastric balloon for the treatment of obesity was A. Henning 1979. (Inn. Med.6(1979),149) He and his wife used it in a self-experiment.
The use of gastric filling devices to induce weight loss is not new. DeBakey's review in 1938 showed that bezoars led to weight loss. Free floating intragastric balloons were used by Nieben and Harboe in 1982. Percival presented a “balloon diet” in 1984 when he placed inflated mammary implants as gastric balloons. Elipse mide Balonu In 1985 the Garren-Edwards Bubble was introduced as the first FDA-approved device, but the approval was withdrawn seven years later because of complications. Analysis of its problems led to recommendations for safer designs. While a number of further developed devices were used outside of the US, mostly in Europe and South America, the FDA did not approve any new devices until 2015. In October 2017, ReShape Medical, which makes gastric balloons, was acquired by EnteroMedics in $38m cash-and-stock deal.
References
External links
Bariatrics
Medical devices | Gastric balloon | Biology | 2,116 |
41,883,177 | https://en.wikipedia.org/wiki/List%20of%20biophysically%20important%20macromolecular%20crystal%20structures | Crystal structures of protein and nucleic acid molecules and their complexes are central to the practice of most parts of biophysics, and have shaped much of what we understand scientifically at the atomic-detail level of biology. Their importance is underlined by the United Nations declaring 2014 as the International Year of Crystallography, as the 100th anniversary of Max von Laue's 1914 Nobel Prize for discovering the diffraction of X-rays by crystals. This chronological list of biophysically notable protein and nucleic acid structures is loosely based on a review in the Biophysical Journal. The list includes all the first dozen distinct structures, those that broke new ground in subject or method, and those that became model systems for work in future biophysical areas of research.
Myoglobin
1958 Myoglobin was the very first crystal structure of a protein molecule. Myoglobin cradles an iron-containing heme group that reversibly binds oxygen for use in powering muscle fibers, and those first crystals were of myoglobin from the sperm whale, whose muscles need copious oxygen storage for deep dives. The myoglobin 3-dimensional structure is made up of 8 alpha-helices, and the crystal structure showed that their conformation was right-handed and very closely matched the geometry proposed by Linus Pauling, with 3.6 residues per turn and backbone hydrogen bonds from the peptide NH of one residue to the peptide CO of residue i+4. Myoglobin is a model system for many types of biophysical studies, especially involving the binding process of small ligands such as oxygen and carbon monoxide.
Hemoglobin
1960 The hemoglobin crystal structure showed a tetramer of two related chain types and was solved at much lower resolution than the monomeric myoglobin, but it clearly had the same basic 8-helix architecture (now called the "globin fold"). Further hemoglobin crystal structures at higher resolution (PDB 1MHB, 1DHB) soon showed the coupled change of both local and quaternary conformation between the oxy and deoxy states of hemoglobin, which explains the cooperativity of oxygen binding in the blood and the allosteric effect of factors such as pH and DPG. For decades hemoglobin was the primary teaching example for the concept of allostery, as well as being an intensive focus of research and discussion on allostery. In 1909, hemoglobin crystals from >100 species were used to relate taxonomy to molecular properties. That book was cited by Perutz in the 1938 report of horse hemoglobin crystals that began his long saga to solve the crystal structure. Hemoglobin crystals are pleochroic dark red in two directions and pale red in the third because of the orientation of the hemes, and the bright Soret band of the heme porphyrin groups is used in spectroscopic analysis of hemoglobin ligand binding.
Hen-egg-white lysozyme
1965 Hen-egg-white lysozyme (PDB file 1lyz). was the first crystal structure of an enzyme (it cleaves small carbohydrates into simple sugars), used for early studies of enzyme mechanism. It contained beta sheet (antiparallel) as well as helices, and was also the first macromolecular structure to have its atomic coordinates refined (in real space). The starting material for preparation can be bought at the grocery store, and hen-egg lysozyme crystallizes very readily in many different space groups; it is the favorite test case for new crystallographic experiments and instruments. Recent examples are nanocrystals of lysozyme for free-electron laser data collection and microcrystals for micro electron diffraction.
Ribonuclease
1967 Ribonuclease A (PDB file 2RSA) is an RNA-cleaving enzyme stabilized by 4 disulfide bonds. It was used in Anfinsen's seminal research on protein folding which led to the concept that a protein's 3-dimensional structure was determined by its amino-acid sequence. Ribonuclease S, the cleaved, two-component form studied by Fred Richards, was also enzymatically active, had a nearly identical crystal structure (PDB file 1RNS), and was shown to be catalytically active even in the crystal, helping dispel doubts about the relevance of protein crystal structures to biological function.
Serine proteases
1967 The serine proteases are a historically very important group of enzyme structures, because collectively they illuminated catalytic mechanism (in their case, by the Ser-His-Asp "catalytic triad"), the basis of differing substrate specificities, and the activation mechanism by which a controlled enzymatic cleavage buries the new chain end to properly rearrange the active site. The early crystal structures included chymotrypsin (PDB file 2CHA), chymotrypsinogen (PDB file 1CHG), trypsin (PDB file 1PTN), and elastase (PDB file 1EST). They also were the first protein structures that showed two near-identical domains, presumably related by gene duplication. One reason for their wide use as textbook and classroom examples was the insertion-code numbering system, which made Ser195 and His57 consistent and memorable despite the protein-specific sequence differences.
Papain
1968 Papain
Carboxypeptidase
1969 Carboxypeptidase A is a zinc metalloprotease. Its crystal structure (PDB file 1CPA) showed the first parallel beta structure: a large, twisted, central sheet of 8 strands with the active-site Zn located at the C-terminal end of the middle strands and the sheet flanked on both sides with alpha helices. It is an exopeptidase that cleaves peptides or proteins from the carboxy-terminal end rather than internal to the sequence. Later a small protein inhibitor of carboxypeptidase was solved (PDB file 4CPA) that mechanically stops the catalysis by presenting its C-terminal end just sticking out from between a ring of disulfide bonds with tight structure behind it, preventing the enzyme from sucking in the chain past the first residue.
Subtilisin
1969 Subtilisin (PDB file 1sbt ) was a second type of serine protease with a near-identical active site to the trypsin family of enzymes, but with a completely different overall fold. This gave the first view of convergent evolution at the atomic level. Later, an intensive mutational study on subtilisin documented the effects of all 19 other amino acids at each individual position.
Lactate dehydrogenase
1970 Lactate dehydrogenase
Trypsin inhibitor
1970 Basic pancreatic trypsin inhibitor, or BPTI (PDB file 2pti), is a small, very stable protein that has been a highly productive model system for study of super-tight binding, disulfide bond (SS) formation, protein folding, molecular stability by amino-acid mutations or hydrogen-deuterium exchange, and fast local dynamics by NMR. Biologically, BPTI binds and inhibits trypsin while stored in the pancreas, allowing activation of protein digestion only after trypsin is released into the stomach.
Rubredoxin
1970 Rubredoxin (PDB file 2rxn) was the first redox structure solved, a minimalist protein with the iron bound by 4 Cys sidechains from 2 loops at the top of β hairpins. It diffracted to 1.2Å, enabling the first reciprocal-space refinement of a protein (4,5rxn). (NB: note that 4rxn was done without geometry restraints.) Archaeal rubredoxins account for many of the highest-resolution small structures in the PDB.
Insulin
1971 Insulin (PDB file 1INS) is a hormone central to the metabolism of sugar and fat storage, and important in human diseases such as obesity and diabetes. It is biophysically notable for its Zn binding, its equilibrium between monomer, dimer, and hexamer states, its ability to form crystals in vivo, and its synthesis as a longer "pro" form which is then cleaved to fold up as the active 2-chain, SS-linked monomer. Insulin was a success of NASA's crystal-growth program on the Space Shuttle, producing bulk preparations of very uniform tiny crystals for controlled dosage.
Staphylococcal nuclease
1971 Staphylococcal nuclease
Cytochrome C
1971 Cytochrome C
T4 phage lysozyme
1974 T4 phage lysozyme
Immunoglobulins
1974 Immunoglobulins
Superoxide dismutase
1975 Cu,Zn Superoxide dismutase
Transfer RNA
1976 Transfer RNA
Triose phosphate isomerase
1976 Triose phosphate isomerase
Pepsin-like aspartic proteases
1976 Rhizopuspepsin
1976 Endothiapepsin
1976 Penicillopepsin
Later structures (1978 onwards)
1978 Icosahedral virus
1981 Dickerson B-form DNA dodecamer
1981 Crambin
1985 Calmodulin
1985 DNA polymerase
1985 Photosynthetic reaction center: Pairs of bacteriochlorophylls (green) inside the membrane capture energy from sunlight, then traveling by many steps to become available at the heme groups (red) in the cytochrome-C module at the top. This was first crystal structure solved for a membrane protein, a milestone recognized by a Nobel Prize to Hartmut Michel, Hans Deisenhofer, and Robert Huber.
1986 Repressor/DNA interactions
1987 Major histocompatibility complex
1987 Ubiquitin
1987 ROP protein
1989 HIV-1 protease
1990 Bacteriorhodopsin
1991 GCN4 coiled coil
1991 HIV-1 reverse transcriptase
1993 Beta helix of Pectate lyase
1994 Collagen
1994 Barnase/barstar complex
1994 F1 ATPase
1995 Heterotrimeric G proteins
1996 Green fluorescent protein
1996 CDK/cyclin complex
1996 Kinesin motor protein
1997 GroEL/ES chaperone
1997 Nucleosome
1998 Group I self-splicing intron
1998 DNA topoisomerases perform the biologically important and necessary job of untangling DNA strands or helices that get entwined with each other or twisted too tightly during normal cellular processes such as the transcription of genetic information.
1998 Tubulin alpha/beta dimer
1998 Potassium channel
1998 Holliday junction
2000 Ribosomes are a central part of biology and biophysics, which first became accessible structurally in 2000
2000 AAA+ ATPase
2002 Ankyrin repeats
2003 TOP7 protein design
2004 Cyanobacterial Circadian clock proteins
2004 Riboswitch
2006 Human exosome
2007 G-protein-coupled receptor
2009 The vault particle is an intriguing new discovery of a large hollow particle common in cells, with several different suggestions for its possible biological function. The crystal structures (PDB files 2zuo, 2zv4, 2zv5 and 4hl8) show that each half of the vault is made up of 39 copies of a long 12-domain protein that swirl together to form the enclosure. Disorder at the very top and bottom ends suggests openings for possible access to the interior of the vault.
References
Structural biology
Macromolecular crystal structures
Macromolecular crystal structures
Macromolecular crystal structures | List of biophysically important macromolecular crystal structures | Physics,Chemistry,Biology | 2,425 |
6,008,230 | https://en.wikipedia.org/wiki/Solar%20System%20Ambassadors | The Solar System Ambassadors Program is a public outreach program of the Jet Propulsion Laboratory. More than 1400 volunteers in all 50 states as well as Washington DC, Puerto Rico, the US Virgin Islands, and Guam share information about exploration missions and recent discoveries to their local communities. The program is an extension of the original Galileo Ambassadors program created to share information about the Galileo mission.
Ambassadors offer outreach programming free of charge at a variety of venues ranging from classrooms, to talks at museums, planetariums, and television.
See also
NASA Tweetup
References
External links
directory current ambassadors
Jet Propulsion Laboratory | Solar System Ambassadors | Astronomy | 119 |
5,228,037 | https://en.wikipedia.org/wiki/Mycotroph | A mycotroph is a plant that gets all or part of its carbon, water, or nutrient supply through symbiotic association with fungi. The term can refer to plants that engage in either of two distinct symbioses with fungi:
Many mycotrophs have a mutualistic association with fungi in any of several forms of mycorrhiza. The majority of plant species are mycotrophic in this sense. Examples include Burmanniaceae.
Some mycotrophs are parasitic upon fungi in an association known as myco-heterotrophy.
References
Trophic ecology
Mycology
Symbiosis
Parasites of fungi
Parasitic plants
Plant nutrition | Mycotroph | Biology | 136 |
60,260,200 | https://en.wikipedia.org/wiki/Fariborz%20Haghighat | Fariborz Haghighat is an Iranian-Canadian academic, engineer and Distinguished Professor of Building, Civil & Environmental Engineering at Concordia University. Haghighat has a Concordia University Research Chair (Tier I) in Energy and Environment and he was Inducted into the Provost's Circle of Distinction in 2009.
Early life, education and career
He completed his undergraduate degree in chemical engineering at the Aryamehr Technical University of Technology (now called Sharif University of Technology) in 1975. He moved to the United States to continue his M.Sc.Eng. in mechanical engineering at the University of Arizona. In 1983, Haghighat decided to pursue a PhD in Systems Design Engineering at the University of Waterloo. Following his doctoral studies, Haghighat worked as an NSERC Postdoctoral Fellow at the National Research Council.
In 1986, Haghighat started his work as a full-time member of the Centre for Building Studies (CBS) at the Concordia University. He was promoted to Associate Professor in 1993, and became a Full Professor in 1999. In 2019, he was made a Distinguished University Research Professor in the Department of Building, Civil and Environmental Engineering.
In 1992, Haghighat founded the International Conference on Indoor Air Quality, Ventilation and Energy Conservation in Buildings (IAQVEC).
Research
Haghighat serves as a subject matter expert on various national and international committees, and Editor Board member of several international scientific journals. He has authored over 400 papers in the peer-reviewed scientific journals, conference papers, proceedings, books, contributions to books and technical reports.
Haghighat's many accomplishments throughout his career includes:
Editor-in-chief, International Journal of Sustainable Cities and Society (SCS)
Editor-in-chief, International Journal of Energy and Built Environment (EBE)
Operating Agent, International Energy Agency, ECES Annex 31: "Energy storage with Net Zero Energy Buildings and Districts: Optimisation and Automation"
Operating Agent, International Energy Agency, ECES Annex 23: "Applying Energy Storage in Buildings of the Future"
Canadian Representative, International Energy Agency, ECES Annex 53: "Total energy use in buildings: Analysis and evaluation methods"
Member, Editorial Board of the International Journal of Ventilation
Member, Editorial Board of the International Journal of Building Simulation
International Editorial Board, Editorial Board of the International Journal of High-Rise Buildings
Honours
Haghighat is a member of the Professional Engineers of Ontario since 1998.
Since 2002 he has been a member of ISIAQ Academy of Fellows – International Society of Indoor Air Quality and Climate (previously known as IAIAS, the International Academy of Indoor Air Sciences).
He is a Honorary Theme Editor (HTE) for the Theme 1.32 – Technology, Information, and Systems Management to develop the UNESCO's Encyclopedia of Life Support Systems (ELOSS).
He was awarded Fellow, American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) in 2007.
Haghighat received the Thomas C. Keefer Medal (2015) for his paper entitled "Efficient non-hydrostatic modelling of flow and bed shear stress in a pier scour hole", Canadian Journal of Civil Engineering, 2014, 41(5): 450–460.
In 2008, Haghighat and his wife Roya Haghighat established the "Fariborz and Roya Haghighat Entrance Scholarship in Engineering". This entrance scholarship is intended to promote and recognize academic excellence among newly admitted undergraduate students in the Gina Cody School of Engineering and Computer Science.
See also
List of University of Waterloo people
References
External links
Academic staff of Concordia University
Living people
Canadian academics in engineering
21st-century Canadian engineers
Canada Research Chairs
University of Arizona alumni
1951 births
Iranian emigrants to Canada
University of Waterloo alumni
Sharif University of Technology alumni
Iranian expatriates in the United States
Academic journal editors
Fellows of ASHRAE | Fariborz Haghighat | Engineering | 789 |
19,178,886 | https://en.wikipedia.org/wiki/Protist | A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a polyphyletic grouping of several independent clades that evolved from the last eukaryotic common ancestor.
Protists were historically regarded as a separate taxonomic kingdom known as Protista or Protoctista. With the advent of phylogenetic analysis and electron microscopy studies, the use of Protista as a formal taxon was gradually abandoned. In modern classifications, protists are spread across several eukaryotic clades called supergroups, such as Archaeplastida (photoautotrophs that includes land plants), SAR, Obazoa (which includes fungi and animals), Amoebozoa and Excavata.
Protists represent an extremely large genetic and ecological diversity in all environments, including extreme habitats. Their diversity, larger than for all other eukaryotes, has only been discovered in recent decades through the study of environmental DNA and is still in the process of being fully described. They are present in all ecosystems as important components of the biogeochemical cycles and trophic webs. They exist abundantly and ubiquitously in a variety of forms that evolved multiple times independently, such as free-living algae, amoebae and slime moulds, or as important parasites. Together, they compose an amount of biomass that doubles that of animals. They exhibit varied types of nutrition (such as phototrophy, phagotrophy or osmotrophy), sometimes combining them (in mixotrophy). They present unique adaptations not present in multicellular animals, fungi or land plants. The study of protists is termed protistology.
Definition
Protists are a diverse group of eukaryotes (organisms whose cells possess a nucleus) that are primarily single-celled and microscopic but exhibit a wide variety of shapes and life strategies. They have different life cycles, trophic levels, modes of locomotion, and cellular structures. Although most protists are unicellular, there is a considerable range of multicellularity amongst them; some form colonies or multicellular structures visible to the naked eye. The term 'protist' is defined as a paraphyletic group of all eukaryotes that are not animals, plants or fungi, the three traditional eukaryotic kingdoms. Because of this definition by exclusion, the term includes the ancestors of those three kingdoms.
The names of some protists (called ambiregnal protists), because of their mixture of traits similar to both animals and plants or fungi (e.g., slime molds and flagellated algae like euglenids), have been published under either or both of the botanical (ICN) and the zoological (ICZN) codes of nomenclature.
Common types
Protists display a wide range of distinct morphological types that have been used to classify them for practical purposes, although most of these categories do not represent evolutionary cohesive lineages or clades and have instead evolved independently several times. The most recognizable types are:
Amoebae. Characterized by their irregular, flexible shapes, these protists move by extending portions of their cytoplasm, known as pseudopodia, to crawl along surfaces. Many groups of amoebae are naked, but testate amoebae and foraminifera grow a shell around their cell made from digested material or surrounding debris. Some, known as radiolarians and heliozoans, have special spherical shapes with microtubule-supported pseudopodia radiating from the cell. Some amoebae are capable of producing stalked multicellular stages that bear spores, often by aggregating together; these are known as slime molds. The main clades containing amoebae are Amoebozoa (including various slime molds and testate amoebae) and Rhizaria (including famous groups such as foraminifera and radiolarians, as well as a few testate amoebae). Even some individual amoebae can grow to giant sizes visible to the naked eye.
Flagellates. These protists are equipped with one or more whip-like appendages called cilia, undulipodia or eukaryotic flagella, which enable them to swim or glide freely through the environment. Flagellates are found in all lineages, reflecting that the common ancestor of all living eukaryotes was a flagellate. They usually exhibit two cilia (e.g., in Provora, Telonemia, Stramenopiles, Alveolata, Obazoa and most excavates), but there are a number of flagellate groups with a high number of cilia (such as Hemimastigophora and other excavates). Some groups, such as the well-known ciliates and the parasitic opalinids, have a cell surface covered in rows of cilia that beat rhythmically. A few groups of amoebae have retained their flagella, making them amoeboflagellates.
Algae. They are the photosynthetic protists, and can be found in most of the main clades, completely intermingled with heterotrophic protists which are traditionally called protozoa. Algae exhibit the most diverse range of morphologies, from single flagellated or coccoid cells (e.g., cryptophytes, haptophytes, dinoflagellates, chromerids, many green algae, ochrophytes, euglenophytes) to amoeboid cells (chlorarachniophytes) to colonial and multicellular macroscopic forms (e.g., red algae, some green algae, and some ochrophytes such as kelp).
Fungus-like protists. Several clades of protists have evolved an appearance similar to fungi through hyphae-like structures and a saprophytic nutrition. They have evolved multiple times, often very distantly from true fungi (e.g., the oomycetes, labyrinthulomycetes and hyphochytrids, in Stramenopiles; the myxomycetes, in Amoebozoa; the phytomyxeans, in Rhizaria; the perkinsozoans, in Alveolata).
Sporozoa. This category traditionally included parasitic protists that reproduced via spores (the apicomplexans, microsporidians, myxozoans and ascetosporeans). Its current use is restricted to the apicomplexans, such as Plasmodium falciparum, the cause of malaria.
Diversity
The species diversity of protists is severely underestimated by traditional methods that differentiate species based on morphological characteristics. The number of described protist species is very low (ranging from 26,000 to over 76,000) in comparison to the diversity of plants, animals and fungi, which are historically and biologically well-known and studied. The predicted number of species also varies greatly, ranging from 1.4×10 to 1.6×10, and in several groups the number of predicted species is arbitrarily doubled. Most of these predictions are highly subjective. Molecular techniques such as environmental DNA barcoding have revealed a vast diversity of undescribed protists that accounts for the majority of eukaryotic sequences or operational taxonomic units (OTUs), dwarfing those from plants, animals and fungi. As such, it is considered that protists dominate eukaryotic diversity.
The evolutionary relationships of protists have been explained through molecular phylogenetics, the sequencing of entire genomes and transcriptomes, and electron microscopy studies of the flagellar apparatus and cytoskeleton. New major lineages of protists and novel biodiversity continue to be discovered, resulting in dramatic changes to the eukaryotic tree of life. The newest classification systems of eukaryotes do not recognize the formal taxonomic ranks (kingdom, phylum, class, order...) and instead only recognize clades of related organisms, making the classification more stable in the long term and easier to update. In this new cladistic scheme, the protists are divided into various branches informally named supergroups. Most photosynthetic eukaryotes fall under the Diaphoretickes clade, which contains the supergroups Archaeplastida (which includes plants) and TSAR (including Telonemia, Stramenopiles, Alveolata and Rhizaria), as well as the phyla Cryptista and Haptista. The animals and fungi fall into the Amorphea supergroup, which contains the phylum Amoebozoa and several other protist lineages. Various groups of eukaryotes with primitive cell architecture are collectively known as the Excavata.
Excavata
Excavata is a group that encompasses diverse protists, mostly flagellates, ranging from aerobic and anaerobic predators to phototrophs and heterotrophs. The common name 'excavate' refers to the common characteristic of a ventral groove in the cell used for suspension feeding, which is considered to be an ancestral trait present in the last eukaryotic common ancestor. The Excavata is composed of three clades: Discoba, Metamonada and Malawimonadida, each including 'typical excavates' that are free-living phagotrophic flagellates with the characteristic ventral groove. According to most phylogenetic analyses, this group is paraphyletic, with some analyses placing the root of the eukaryote tree within Metamonada.
Discoba includes three major groups: Jakobida, Euglenozoa and Percolozoa. Jakobida are a small group (~20 species) of free-living heterotrophic flagellates, with two cilia, that primarily eat bacteria through suspension feeding; most are aquatic aerobes, with some anaerobic species, found in marine, brackish or fresh water. They are best known for their bacterial-like mitochondrial genomes. Euglenozoa is a rich (>2,000 species) group of flagellates with very different lifestyles, including: the free-living heterotrophic (both osmo- and phagotrophic) and photosynthetic euglenids (e.g., the euglenophytes, with chloroplasts originated from green algae); the free-living and parasitic kinetoplastids (such as Trypanosoma cruzi, the agent of Chagas disease); the deep-sea anaerobic symbiontids; and the elusive diplonemids. Percolozoa (~150 species) are a collection of amoebae, flagellates and amoeboflagellates with complex life cycles, among which are some slime molds (acrasids). The two clades Euglenozoa and Percolozoa are sister taxa, united under the name Discicristata, in reference to their mitochondrial cristae shaped like discs. The species Tsukubamonas globosa is a free-living flagellate whose precise position within Discoba is not yet settled, but is probably more closely related to Discicristata than to Jakobida.
The metamonads (Metamonada) are a phylum of completely anaerobic or microaerophilic protozoa, primarily flagellates. Some are gut symbionts of animals such as termites, others are free-living, and others are parasitic. They include three main clades: Fornicata, Parabasalia and Preaxostyla. Fornicata (>140 species) encompasses the diplomonads, with two nuclei (e.g., Giardia, genus of well-known parasites of humans), and several smaller groups of free-living, commensal and parasitic protists (e.g., Carpediemonas, retortamonads). Parabasalia (>460 species) is a varied group of anaerobic, mostly endobiotic organisms, ranging from small parasites (like Trichomonas vaginalis, another human pathogen) to giant intestinal symbionts with numerous flagella and nuclei found in wood-eating termites and cockroaches. Preaxostyla (~140 species) includes the anaerobic and endobiotic oxymonads, with modified (or completely lost) mitochondria, and two genera of free-living microaerophilic bacterivorous flagellates Trimastix and Paratrimastix, with typical excavate morphology. Two genera of anaerobic flagellates of recent description and unique cell architecture, Barthelona and Skoliomonas, are closely related to the Fornicata.
The malawimonads (Malawimonadida) are a small group (three species) of freshwater or marine suspension-feeding bacterivorous flagellates with typical excavate appearance, closely resembling Jakobida and some metamonads but not phylogenetically close to either in most analyses.
Diaphoretickes
Diaphoretickes includes nearly all photosynthetic eukaryotes. Within this clade, the TSAR supergroup gathers a colossal diversity of protists. The most basal branching member of the TSAR clade is Telonemia, a small (seven species) phylum of obscure phagotrophic predatory flagellates, found in marine and freshwater environments. They share some cellular similarities with the remaining three clades: Rhizaria, Alveolata and stramenopiles, collectively known as the SAR supergroup. Another highly diverse clade within Diaphoretickes is Archaeplastida, which houses land plants and a variety of algae. In addition, two smaller groups, Haptista and Cryptista, also belong to Diaphoretickes.
Stramenopiles
The stramenopiles, also known as Heterokonta, are characterized by the presence of two cilia, one of which bears many short, straw-like hairs (mastigonemes). They include one clade of phototrophs and numerous clades of heterotrophs, present in virtually all habitats. Stramenopiles include two usually well-supported clades, Bigyra and Gyrista, although the monophyly of Bigyra is being questioned. Branching outside both Bigyra and Gyrista is a single species of enigmatic heterotrophic flagellates, Platysulcus tardus. Much of the diversity of heterotrophic stramenopiles is still uncharacterized, known almost entirely from lineages of genetic sequences known as MASTs (MArine STramenopiles), of which only a few species have been described.
The phylum Gyrista includes the photosynthetic Ochrophyta or Heterokontophyta (>23,000 species), which contain chloroplasts originated from a red alga. Among these are many lineages of algae that encompass a wide range of structures and morphologies. The three most diverse ochrophyte classes are: the diatoms, unicellular or colonial organisms encased in silica cell walls (frustules) that exhibit widely different shapes and ornamentations, responsible for a big portion of the oxygen produced worldwide, and comprising much of the marine phytoplankton; the brown algae, filamentous or 'truly' multicellular (with differentiated tissues) macroalgae that constitute the basis of many temperate and cold marine ecosystems, such as kelp forests; and the golden algae, unicellular or colonial flagellates that are mostly present in freshwater habitats. Inside Gyrista, the sister clade to Ochrophyta are the predominantly osmotrophic and filamentous pseudofungi (>1,200 species), which include three distinct lineages: the parasitic oomycetes or water moulds (e.g., Phytophthora infestans, the agent behind the Irish Potato Famine), which encompass most of the pseudofungi species; the less diverse non-parasitic hyphochytrids that maintain a fungus-like lifestyle; and the bigyromonads, a group of bacterivorous or eukaryovorous phagotrophs. A small group of heliozoan-like heterotrophic amoebae, Actinophryida, has an uncertain position, either within or as the sister taxon of Ochrophyta.
The little studied phylum Bigyra is an assemblage of exclusively heterotrophic organisms, most of which are free-living. It includes the labyrinthulomycetes, among which are single-celled amoeboid phagotrophs, mixotrophs, and fungus-like filamentous heterotrophs that create slime networks to move and absorb nutrients, as well as some parasites and a few testate amoebae (Amphitremida). Also included in Bigyra are the bicosoecids, phagotrophic flagellates that consume bacteria, and the closely related Placidozoa, which consists of several groups of heterotrophic flagellates (e.g., the deep-sea halophilic Placididea) as well as the intestinal commensals known as Opalinata (e.g., the human parasite Blastocystis, and the highly unusual opalinids, composed of giant cells with numerous nuclei and cilia, originally misclassified as ciliates).
Alveolata
The alveolates (Alveolata) are characterized by the presence of cortical alveoli, cytoplasmic sacs underlying the cell membrane of unknown physiological function. Among them are three of the most well-known groups of protists: apicomplexans, dinoflagellates and ciliates. The ciliates (Ciliophora) are a highly diverse (>8,000 species) and probably the most thoroughly studied group of protists. They are mostly free-living microbes characterized by large cells covered in rows of cilia and containing two kinds of nuclei, micronucleus and macronucleus (e.g., Paramecium, a model organism). Free-living ciliates are usually the top heterotrophs and predators in microbial food webs, feeding on bacteria and smaller eukaryotes, present in a variety of ecosystems, although a few species are kleptoplastic. Others are parasitic of numerous animals. Ciliates have a basal position in the evolution of alveolates, together with a few species of heterotrophic flagellates with two cilia collectively known as colponemids.
The remaining alveolates are grouped under the clade Myzozoa, whose common ancestor acquired chloroplasts through a secondary endosymbiosis from a red alga. One branch of Myzozoa contains the apicomplexans and their closest relatives, a small clade of flagellates known as Chrompodellida where phototrophic and heterotrophic flagellates, called chromerids and colpodellids respectively, are evolutionarily intermingled. In contrast, the apicomplexans (Apicomplexa) are a large (>6,000 species) and highly specialized group of obligate parasites who have all secondarily lost their photosynthetic ability (e.g., Plasmodium falciparum, cause of malaria). Their adult stages absorb nutrients from the host through the cell membrane, and they reproduce between hosts via sporozoites, which exhibit an organelle complex (the apicoplast) evolved from non-photosynthetic chloroplasts.
The other branch of Myzozoa contains the dinoflagellates and their closest relatives, the perkinsids (Perkinsozoa), a small group (26 species) of aquatic intracellular parasites which have lost their photosynthetic ability similarly to apicomplexans. They reproduce through flagellated spores that infect dinoflagellates, molluscs and fish. In contrast, the dinoflagellates (Dinoflagellata) are a highly diversified (~4,500 species) group of aquatic algae that have mostly retained their chloroplasts, although many lineages have lost their own and instead either live as heterotrophs or reacquire new chloroplasts from other sources, including tertiary endosymbiosis and kleptoplasty. Most dinoflagellates are free-living and compose an important portion of phytoplankton, as well as a major cause of harmful algal blooms due to their toxicity; some live as symbionts of corals, allowing the creation of coral reefs. Dinoflagellates exhibit a diversity of cellular structures, such as complex eyelike ocelli, specialized vacuoles, bioluminescent organelles, and a wall surrounding the cell known as the theca.
Rhizaria
Rhizaria is a lineage of morphologically diverse organisms, composed almost entirely of unicellular heterotrophic amoebae, flagellates and amoeboflagellates, commonly with reticulose (net-like) or filose (thread-like) pseudopodia for feeding and locomotion. It was the last supergroup to be described, because it lacks any defining characteristic and was discovered exclusively through molecular phylogenetics. Three major clades are included, namely the phyla Cercozoa, Endomyxa and Retaria.
Retaria contains the most familiar rhizarians: forams and radiolarians, two groups of large free-living marine amoebae with pseudopodia supported by microtubules, many of which are macroscopic. The radiolarians (Radiolaria) are a diverse group (>1,000 living species) of amoebae, often bearing delicate and intricate siliceous skeletons. The forams (Foraminifera) are also diverse (>6,700 living species), and most of them are encased in multichambered tests constructed from calcium carbonate or agglutinated mineral particles. Both groups have a rich fossil record, with tens of thousands of described fossil species.
Cercozoa (also known as Filosa) is an assemblage of free-living protists with very different morphologies. Cercozoan amoeboflagellates are important predators of other microbes in terrestrial habitats and the plant microbiota (e.g., cercomonads and paracercomonads and glissomonads, collectively known as class Sarcomonadea), and a few can generate slime molds (e.g., Helkesea). Many cercozoans are testate or scale-bearing amoebae, namely the elusive Kraken and the two classes Imbricatea (e.g., the euglyphids) and Thecofilosea. Thecofilosea also contains the Phaeodaria (~400–500 species), a group of skeleton-bearing marine amoebae previously classified as radiolarians, and both classes include some non-scaly naked flagellates (e.g., spongomonads in Imbricatea and thaumatomonads in Thecofilosea). Among the basal-branching cercozoans are the pseudopodia-lacking thecate flagellates of Metromonadea, the heliozoan-like Granofilosea and the photosynthetic chlorarachniophytes, whose chloroplasts originated from a secondary endosymbiosis with a green alga.
Endomyxa contains two major clades of parasitic protists: Ascetosporea are sporozoan-type parasites of marine invertebrates, while Phytomyxea are obligate pathogens of plants and algae, divided into the terrestrial plasmodiophorids and the marine phagomyxids. Also included in Endomyxa are the order of predatory amoebae Vampyrellida (48 species) and two genera of marine amoebae, the thecate Gromia and the naked Filoreta.
Besides these three phyla, Rhizaria includes numerous enigmatic and understudied lineages of uncertain evolutionary position. One such clade is the Gymnosphaerida, which includes heliozoan-type protists. Several clades labeled as Novel Clades (NC) are entirely composed of environmental DNA from uncultured protists, although a few have slowly been resolved over the decades with the description of new taxa (e.g., Tremulida and Aquavolonida, formerly NC11 and NC10 respectively, with a deep-branching position in Rhizaria).
Haptista and Cryptista
Haptista and Cryptista are two similar phyla of single-celled protists previously thought to be closely related, and collectively known as Hacrobia. However, the monophyly of Hacrobia was disproven, as the two groups originated independently. Molecular analyses place Cryptista next to Archaeplastida, forming the hypothesized "CAM" clade, and Haptista next to the TSAR clade.
The phylum Haptista includes two distinct clades with mineralized scales: haptophytes and centrohelids. The haptophytes (Haptophyta) are a group of over 500 living species of flagellated or coccoid algae that have acquired chloroplasts from a secondary endosymbiosis. They are mostly marine, comprise an important portion of oceanic plankton, and include the coccolithophores, whose calcified scales ('coccoliths') contribute to the formation of sedimentary rocks and the biogeochemical cycles of carbon and calcium. Some species are capable of forming toxic blooms. The centrohelids (Centroplasthelida) are a small (~95 species) but widespread group of heterotrophic heliozoan-type amoebae, usually covered in scale-bearng mucous, that form an important component of benthic food webs of aquatic habitats, both marine and freshwater.
The phylum Cryptista is a clade of three distinct groups of unicellular protists: cryptomonads, katablepharids, and the species Palpitomonas bilix. The cryptomonads (>100 species), also known as cryptophytes, are flagellated algae found in aquatic habitats of diverse salinity, characterized by extrusive organelles or extrusomes called ejectisomes. Their chloroplasts, of red algal origin, contain a nucleomorph, a remnant of the eukaryotic nucleus belonging to the endosymbiotic red alga. The katablepharids, the closest relatives of cryptomonads, are heterotrophic flagellates with two cilia, also characterized by ejectisomes. The species Palpitomonas bilix is the most basal-branching member of Cryptista, a marine heterotrophic flagellate with two cilia, but unlike the remaining members it lacks ejectisomes.
Archaeplastida
Archaeplastida is the clade containing those photosynthetic groups whose plastids were likely obtained through a single event of primary endosymbiosis with a cyanobacterium. It contains land plants (Embryophyta) and a big portion of the diversity of algae, most of which are the green algae, from which plants evolved, and the red algae. A third lineage of algae, the glaucophytes (25 species), contains rare and obscure species found in surfaces of freshwater and terrestrial habitats.
The red algae or Rhodophyta (>7,100 species) are a group of diverse morphologies, ranging from single cells to multicellular filaments to giant pseudoparenchymatous thalli, all without flagella. They lack chlorophyll and only harvest light energy through phycobiliproteins. Their life cycles are varied and may include two or three generations. They are present in terrestrial, freshwater and primarily marine habitats, from the intertidal zone to deep waters; some are calcified and are vital components of marine ecosystems such as coral reefs. Closely related to the red algae are two small lineages of non-photosynthetic predatory flagellates: the freshwater and marine Rhodelphidia (3 species), which still retain genetic evidence of relic plastids; and the marine Picozoa (1 species), which lack any remains of plastids. The evolutionary position of Picozoa may indicate that there have been two separate events of primary endosymbiosis, as opposed to one.
The green algae, unlike the monophyletic glaucophytes and rhodophytes, are a paraphyletic group from which land plants evolved. Together they compose the Chloroplastida or Viridiplantae clade. The earliest branching member is the phylum Prasinodermophyta (ten species), whose members are exclusively marine coccoid cells or small macroscopic thalli. The remaining green algae are distributed in two major clades. One clade is the phylum Chlorophyta (>7,900 species), which includes numerous lineages of scaly unicellular flagellate algae known collectively as prasinophytes along with the Prasinodermophyta, but also includes a variety of morphologies such as coccoids, palmelloids, colonies, and macroscopic filamentous, foliose or tubular thalli, present in aquatic and terrestrial habitats. The opposed clade is Streptophyta, which contains the land plants and a paraphyletic group of green algae collectively known as phylum Charophyta, composed of several classes: Zygnematophyceae (>4,300 species), containing unicellular, colonial and filamentous flagella-lacking organisms found almost exclusively in freshwater habitats; Charophyceae (450 living species), also known as stoneworts, consisting of complex multicellular thalli only found in freshwater habitats; Klebsormidiophyceae (52 species), with unbranched filamentous thalli; Coleochaetophyceae (36 species), containing branched filamentous thalli; Mesostigmatophyceae, composed of a single species of scaly flagellates; and Chlorokybophyceae (five species), with sarcinoid forms.
Amorphea
Amorphea is a group of exclusively heterotrophic organisms. It contains the fungi and animals, as well as most slime moulds, many amoebae and some flagellates. Many of its protist members exhibit complex life cycles with different levels of multicellularity. Amorphea is roughly equivalent to the concept of 'unikonts', meaning 'single cilium', although it currently contains several organisms with more cilia. It is defined as the smallest clade containing the groups Amoebozoa (containing mostly slime moulds and amoebae) and Opisthokonta (containing fungi, animals, and their closest relatives). The closest relatives of Opisthokonta are two small lineages of single-celled protists with two cilia: the flagellate Apusomonadida (28 species) and the amoeboflagellate anaerobic Breviatea (four species). Together with opisthokonts, these two groups form the clade Obazoa, the sister clade to Amoebozoa.
Amoebozoa
The phylum Amoebozoa (2,400 species) is a large group of morphologically diverse phagotrophic protists, mostly amoebae. A considerable portion of amoebozoans are lobose amoebae, meaning they produce round, blunt-ended pseudopods. It includes the 'archetypal' amoebae, known as the naked lobose amoebae or 'gymnamoebae' (such as Amoeba itself), among which is a genus of sorocarp-forming slime moulds, Copromyxa. Some gymnamoebae are important pathogens to animals (e.g., Acanthamoeba). Other relevant lobose amoebae are the Arcellinida, a diverse order of testate amoebae and one of the most conspicuous protist groups overall. The remaining, non-lobose amoebozoans include the Eumycetozoa or 'true slime moulds', comprising the sorocarp-producing bacterivorous dictyostelids and the sporocarp-producing omnivorous myxogastrids and protosporangiids. Due to the fungus-like appearance of their fruiting bodies, eumycetozoans are often studied by mycologists. Closely related to the eumycetozoans are two lineages: the Variosea, a heterogeneous assortment of amoeboid, reticulate or flagellated organisms (including some sorocarp-producing organisms); and the anaerobic Archamoebae, some of which live as intestinal symbionts of some animals (e.g., Entamoeba).
Opisthokonta
Opisthokonta includes the animal and fungal kingdoms, as well as their closest protist relatives. The branch leading to the fungi is known as Nucletmycea or Holomycota, while the branch leading to the animals is called Holozoa. The Holomycota includes the closest relatives of fungi, the nucleariids, a small group (~50 species) of free-living naked or scale-bearing phagotrophic amoebae with filose pseudopodia, some of which can aggregate into slime moulds. Within the wider definition of fungi, three groups are studied as protists by some authors: Aphelida (15 species), Rozellida (27 species) and Microsporidia (~1,300 species), collectively known as Opisthosporidia, as opposed to the 'true' or osmotrophic fungi. Both aphelids and rozellids are single-celled phagotrophic flagellates that feed in an endobiotic manner, penetrating the cells of their respective hosts. Microsporidians are obligate intracellular parasites that feed through osmotrophy, much like true fungi. Aphelids and true fungi are closest relatives, and generally feed on cellulose-walled organisms (many algae and plants). Conversely, rozellids and microsporidians form a separate clade, and generally feed on chitin-walled organisms (fungi and animals).
The Holozoa includes various lineages with complex life cycles involving different cell types and associated with the origin of animal multicellularity. The closest relatives to animals are the choanoflagellates (~360 species), free-living flagellates that feed through a collar of microvilli surrounding a larger cilium and often form colonies. The Ichthyosporea (>40 species), otherwise known as mesomycetozoans, are a group of fungus-like pathogenic holozoans specialized in infecting fish and other animals. The Filasterea (six species) are a heterogeneous group of free-living, endosymbiotic, or parasitic amoebae or flagellates. Lastly, the Pluriformea are two species of free-living holozoans with life cycles that include multicellular aggregates. An elusive flagellate species Tunicaraptor unikontum has an uncertain evolutionary position among these holozoan groups.
Orphan groups
Several smaller lineages do not belong to any of the three main supergroups, and instead have a deep-branching "kingdom-level" position in eukaryote evolution. They are usually poorly known groups with limited data and few species, often referred to as "orphan groups". The CRuMs clade, containing the free-swimming Collodictyonidae (seven species) with two to four cilia, the amoeboid Rigifilidae (two species) with filose pseudopodia, and the gliding Mantamonadidae (three species) with two cilia, are the sister clade of Amorphea. The Ancyromonadida (35 species) are aquatic gliding flagellates with two cilia, positioned near Amorphea and CRuMs. The Hemimastigophora (ten species), or hemimastigotes, are predatory flagellates with a distinctive cell morphology and two rows of around a dozen flagella. The Provora (eight species) are predatory flagellates with an unremarkable morphology similar to that of excavates and other flagellates with two cilia. Both Hemimastigophora and Provora were thought to be related to or within Diaphoretickes, although further analyses have placed them in a separate clade along with a mysterious species of predatory protists, Meteora sporadica. This species has a remarkable morphology: they lack flagella, are bilaterally symmetrical, project a pair of lateral "arms" that swing back and forth, and contain a system of motility unlike any other.
There are also many genera of uncertain affiliation among eukaryotes because their DNA has not been sequenced, and consequently their phylogenetic affinities are unknown. One enigmatic heliozoan species is so large that it does not match the description of any known genus, and was consequently transferred to a separate genus Berkeleyaesol with an unclear position, although it probably belongs to Diaphoretickes along with all other heliozoa. The organism Parakaryon is harder to place, as it shares traits from both prokaryotes and eukaryotes.
Biology
In general, protists have typical eukaryotic cells that follow the same principles of biology described for those cells within the "higher" eukaryotes (animals, fungi and plants). However, many have evolved a variety of unique physiological adaptations that do not appear in the remaining eukaryotes, and in fact protists encompass almost all of the broad spectrum of biological characteristics expected in eukaryotes.
Nutrition
Protists display a wide variety of food preferences and feeding mechanisms. According to the source of their nutrients, they can be divided into autotrophs (producers) and heterotrophs (consumers). Autotrophic protists synthesize their own organic compounds from inorganic substrates through the process of photosynthesis, using light as the source of energy; accordingly, they are also known as phototrophs.
Heterotrophic protists obtain organic molecules synthesized by other organisms, and can be further divided according to the size of their nutrients. Those that feed on soluble molecules or macromolecules under 0.5 μm in size are called osmotrophs, and they absorb them by diffusion, ciliary pits, transport proteins of the cell membrane, and a type of endocytosis (i.e., invagination of the cell membrane into vacuoles, called endosomes) known as pinocytosis or fluid-phase endocytosis. Those that feed on organic particles over 0.5 μm in size or entire cells are called phagotrophs, and they ingest them through a type of endocytosis known as phagocytosis. Endocytosis is considered one of the most important adaptations in the origin of eukaryotes because it increased the potential food supply, and phagocytosis allowed the endosymbiosis and development of mitochondria and chloroplasts. In both osmotrophs and phagotrophs, endocytosis is often restricted to a specific region of the cell membrane, known as the cytostome, which may be followed by a cytopharynx, a specialized tract supported by microtubules.
Osmotrophy
Osmotrophic protists acquire soluble nutrients through membrane channels and carriers, but also through different types of pinocytosis. Macropinocytosis involves the folding of membrane into ruffles, which creates large (0.2 to 1.0 μm) vacuoles. Micropinocytosis involves smaller vesicles that are usually formed by clathrin. In both scenarios, the vesicles merge into a digestive vacuole or endosome where digestion takes place. Some osmotrophs, called saprotrophs or lysotrophs, perform external digestion by releasing enzymes into the environment and decomposing organic matter into simpler molecules that can be absorbed. This external digestion has a distinct advantage: it allows greater control over the substances that are allowed to enter the cell, thus minimizing the intake of harmful substances or infection.
Probably all eukaryotes are capable of osmotrophy, but some have no alternative of acquiring nutrients. Obligate osmotrophs and saprotrophs include some euglenids, some green algae, the human parasite Blastocystis, some metamonads, the parasitic trypanosomatids, and the fungus-like oomycetes and hyphochytrids.
Phagotrophy
Phagotrophic feeding consists of two phases: the concentration of food particles in the environment, and the phagocytosis, which encloses the food particle in a vacuole (the phagosome) where digestion takes place. In ciliates and most phagotrophic flagellates, digestion occurs at the oral region or cytostome, which is covered by a single membrane from which vacuoles are formed; the phagosomes then may be shuttled to the interior of the cell along the cytopharynx. In amoebae, phagocytosis takes place anywhere on the cell surface. The average food particle size is around one tenth the size of the protist cell.
Phagotrophic protists can be further classified according to how they approach the nutrients. The filter feeders acquire small, suspended food particles or prokaryotic cells and accumulate them by filtration into the cytostome (e.g., choanoflagellates, some chrysomonads, most ciliates); filter-feeding flagellates accumulate particles by propelling them with a flagellum through a collar of rigid tentacles or pseudopodia that act as a filter, while filter-feeding ciliates generate water currents through cilia and membranelle zones surrounding the cytostome. The raptorial feeders (e.g., bicosoecids, chrysomonads, kinetoplastids, some euglenids, many dinoflagellates and ciliates), instead of retaining all particles in bulk, capture each particle individually. Among raptorial protists, the grazers search and ingest prey from surfaces covered with potential food items such as bacterial lawns, while the predators actively pursue scarce prey. Predators that feed on filamentous algae or fungal hyphae either swallow the filaments entirely or penetrate the cell wall and ingest the cytoplasm (e.g., Viridiraptoridae). Predators may have adaptations to hunt prey, such as 'toxicysts' that immobilize prey cells. Certain ciliates have developed a specialized kind of raptorial feeding called histophagy, where they attack damaged but live animals (e.g., annelids and small crustaceans), enter the wounds, and ingest animal tissue. Large raptorial amoebae enclose their prey in a "food cup" of pseudopodia, prior to the formation of the food vacuole. Lastly, diffusion feeders (e.g., heliozoa, foraminifera and many other amoebae, suctorian ciliates) engulf prey that happen to collide with their pseudopods or, in the case of ciliates, tentacles that carry toxicysts or extrusomes to immobilize the prey.
Consumers of prokaryotes are popularly called bacterivores (e.g., most amoebae), while consumers (including osmotrophic parasites) of eukaryotes are known as eukaryovores. In particular, eukaryovores that feed on unicellular protists are cytotrophs (e.g., colponemids, colpodellids, many amoebae, some ciliates); those that feed on fungi are mycophages or mycotrophs (e.g., the ciliate family Grossglockneriidae of obligate mycophages); those that prey on nematodes are nematophages; and those that feed on algae are phycotrophs (e.g., vampyrellids).
Mixotrophy
Most autotrophic protists are mixotrophs and combine photosynthesis with phagocytosis. They are classified into various functional groups or 'mixotypes'. Constitutive mixotrophs have the innate ability to photosynthesize through already present chloroplasts, and have diverse feeding behaviors, as some require phototrophy, others phagotrophy, and others are obligate mixotrophs (e.g., nanoflagellates such as some haptophytes and dinoflagellates). Non-constitutive mixotrophs acquire the ability to photosynthesize by stealing chloroplasts from their prey, a process known as kleptoplasty. Non-constitutives can be divided into two: generalists, which can steal chloroplasts from a variety of prey (e.g., oligotrich ciliates), or specialists, which can only acquire chloroplasts from a few specific prey (e.g., Rapaza viridis can only steal from Tetraselmis cells). The specialists are further divided into two types: plastidic, which contain differentiated plastids (e.g., Mesodinium, Dinophysis), and endosymbiotic, which contain whole endosymbionts (e.g., mixotrophic Rhizaria such as Foraminifera and Radiolaria, dinoflagellates like Noctiluca).
Among exclusively heterotrophic protists, variation of nutritional modes is also observed. The diplonemids, which inhabit deep waters where photosynthesis is absent, can flexibly switch between osmotrophy and bacterivory depending on the environmental conditions.
Osmoregulation
Many freshwater protists need to osmoregulate (i.e., remove excess water volume to adjust the ion concentrations) because non-saline water enters in excess by osmosis from the environment and by endocytosis when feeding. Osmoregulation is done through active ion transporters of the cell membrane and through contractile vacuoles, specialized organelles that periodically excrete fluid high in potassium and sodium through a cycle of diastole and systole. The cycle stops when the cells are placed in a medium with different salinity, until the cell adapts.
The contractile vacuoles are surrounded by the spongiome, an array of cytoplasmic vesicles or tubes that slowly collect fluid from the cytoplasm into the vacuole. The vacuoles then contract and discharge the fluid outside of the cell through a pore. The contractile mechanism varies depending on the protist: in ciliates, the spongiome is composed of irregular tubules and actin filaments wind around the pore and over the vacuole surface, together with microtubules; in most flagellates and amoebae, the spongiome is composed of both vesicles and tubules; in dinoflagellates, a flagellar rootlet branches to form a contractile sheath around the vacuole (known as pusule). The location and amount also varies: unicellular flagellated algae (cryptomonads, euglenids, prasinophytes, golden algae, haptophytes, etc.) typically have a single contractile vacuole in a fixed position; naked amoebae have numerous small vesicles that fuse into one vacuole and then split again after excretion. Marine or parasitic protists (e.g., metamonads), as well as those with rigid cell walls, lack these vacuoles.
Respiration
The last eukaryotic common ancestor was aerobic, bearing mitochondria for oxidative metabolism. Many lineages of free-living and parasitic protists have independently evolved and adapted to inhabit anaerobic or microaerophilic habitats, by modifying the early mitochondria into hydrogenosomes, organelles that generate ATP anaerobically through fermentation of pyruvate. In a parallel manner, in the microaerophilic trypanosomatid protists, the fermentative glycosome evolved from the peroxisome.
Sensory perception
Many flagellates and probably all motile algae exhibit a positive phototaxis (i.e. they swim or glide toward a source of light). For this purpose, they exhibit three kinds of photoreceptors or "eyespots": (1) receptors with light antennae, found in many green algae, dinoflagellates and cryptophytes; (2) receptors with opaque screens; and (3) complex ocelloids with intracellular lenses, found in one group of predatory dinoflagellates, the Warnowiaceae. Additionally, some ciliates orient themselves in relation to the Earth's gravitational field while moving (geotaxis), and others swim in relation to the concentration of dissolved oxygen in the water.
Endosymbionts
Protists have an accentuated tendency to include endosymbionts in their cells, and these have produced new physiological opportunities. Some associations are more permanent, such as Paramecium bursaria and its endosymbiont Chlorella; others more transient. Many protists contain captured chloroplasts, chloroplast-mitochondrial complexes, and even eyespots from algae. The xenosomes are bacterial endosymbionts found in ciliates, sometimes with a methanogenic role inside anaerobic ciliates.
Life cycle and reproduction
Protists exhibit a large range of life cycles and strategies involving multiple stages of different morphologies which have allowed them to thrive in most environments. Nevertheless, most of the knowledge concerning protist life cycles concerns model organisms and important parasites. Free-living uncultivated protists represent the majority, but knowledge on their life cycles remains fragmentary.
Asexual reproduction
Protists typically reproduce asexually under favorable environmental conditions, allowing for rapid exponential population growth with minimal genetic diversification. This asexual reproduction, occurs through mitosis and has historically been regarded as the primary reproductive mode in protists. This process is also known as vegetative reproduction, as it is only performed by the 'vegetative stage' or individual.
Unicellular protists often multiply via binary fission, similarly to bacteria. They can also divide through budding, similarly to yeasts, or through multiple fissions, a process known as schizogony. In multicellular protists, vegetative reproduction can take the form of fragmentation of body parts, or specialized propagules composed of numerous cells (e.g., in red algae).
Sexual reproduction
While asexual reproduction remains the most common strategy among protists, sexual reproduction is also a fundamental characteristic of eukaryotes. Sexual reproduction involves meiosis (a specialized nuclear division enabling genetic recombination) and syngamy (the fusion of nuclei from two parents). These processes are thought to have been present in the last eukaryotic common ancestor, which likely had the ability to reproduce sexually on a facultative (non-obligate) basis. Even protists that no longer reproduce sexually still retain a core set of meiosis-related genes, reflecting their descent from sexual ancestors. For example, although amoebae are traditionally considered asexual organisms, most asexual amoebae likely arose recently and independently from sexually reproducing amoeboid ancestors. Even in the early 20th century, some researchers interpreted phenomena related to chromidia (chromatin granules free in the cytoplasm) in amoebae as sexual reproduction.
Basic sexual cycles
Every sexual cycle involves the events of syngamy and meiosis, which increase or decrease the ploidy (i.e., number of chromosome sets, represented by the letter n), respectively. Syngamy implies the fusion of two haploid (1n) reproductive cells, known as gametes, which generates a diploid (2n) cell called zygote. The diploid cell then undergoes meiosis to generate haploid cells. Depending on which cells compose the individual or vegetative stage (i.e., the stage that grows by mitosis), there are three distinguishable sexual cycles observed in free-living protists:
In the haploid cycle, the individual is haploid and differentiates into haploid gametes through mitosis. The gametes fuse into a zygote which immediately undergoes meiosis to generate new haploid individuals. This is the case for some green algae (namely Volvocales), many dinoflagellates, some metamonads, and apicomplexans.
In the diploid cycle, the individual is diploid and undergoes meiosis to generate haploid gametes, which in turn fuse with others to form a zygote that develops into a new individual. This is the case for some metamonads, heliozoans, many green algae, diatoms, and ciliates, as well as animals. Instead of generating gametes, ciliates divide their diploid micronucleus into two haploid nuclei, exchange one of them by conjugation with another ciliate, and fuse the two nuclei into a new diploid nucleus.
In the haplo-diploid cycle, there are two alternating generations of individuals. One generation is the diploid 'agamont', which undergoes meiosis to generate haploid cells (spores) that develop into the other generation, the haploid 'gamont'. The gamont then generates gametes by mitosis, which in turn fuse to form the zygote that develops into the agamont. This is the case for many foraminifera and many algae, as well as land plants. There are three modes of this cycle depending on the relative growth and lifespan of one generation compared to the other: haploid-dominant, diploid-dominant, or equally dominant generations. Brown algae exhibit the full range of these modes.
Free-living protists tend to reproduce sexually under stressful conditions, such as starvation or heat shock. Oxidative stress, which leads to DNA damage, also appears to be an important factor in the induction of sex in protists.
Sexual cycles in pathogenic protists
Pathogenic protists tend to have extremely complex life cycles that involve multiple forms of the organism, some of which reproduce sexually and others asexually. The stages that feed and multiply inside the host are generally known as trophozoites (), but the names of each stage vary depending on the protist group. For example:
In apicomplexans, a haploid sporozoite is released into the host, penetrates a host cell, begins the infection and transforms into a meront that grows and asexually divides into numerous merozoites (a schizogony called merogony); each merozoite continues the infection by multiplying. Eventually, the merozoites differentiate (gamogony) into female (macrogametocytes) and male (microgametocytes) that generate gametes, which in turn fuse (sporogony) into a diploid zygote that grows into a sporocyst. The sporocyst then undergoes meiosis to form sporozoites that transmit the infection.
In phytomyxeans, the diploid primary zoospores enter the host, encyst, and penetrate cells as a uninucleate protoplast or plasmodium. Inside the cells, the protoplast grows into a multinucleate zoosporangium, which then divides into secondary zoospores that infect more cells. These multiply into thick-walled resting spores that begin meiosis and divide into binucleate resting spores; one nucleus is lost, and the spores hatch as primary zoospores.
Some protist pathogens undergo asexual reproduction in a wide variety of organisms – which act as secondary or intermediate hosts – but can undergo sexual reproduction only in the primary or definitive host (e.g., Toxoplasma gondii in felids such as domestic cats). Others, such as Leishmania, are capable of performing syngamy in the secondary vector. In apicomplexans, sexual reproduction is obligatory for parasite transmission.
Despite undergoing sexual reproduction, it is unclear how frequently there is genetic exchange between different strains of pathogenic protists, as most populations may be clonal lines that rarely exchange genes with other members of their species.
Ecology
Protists are indispensable to modern ecosystems worldwide. They also have been the only eukaryotic component of all ecosystems for much of Earth's history, which allowed them to evolve a vast functional diversity that explains their critical ecological significance. They are essential as primary producers, as intermediates in multiple trophic levels, as key regulating parasites or parasitoids, and as partners in diverse symbioses.
Habitat diversity
Protists are abundant and diverse in nearly all habitats. They contribute 4 gigatons (Gt) to Earth's biomass—double that of animals (2 Gt), but less than 1% of the total. Combined, protists, animals, archaea (7 Gt), and fungi (12 Gt) make up less than 10% of global biomass, with plants (450 Gt) and bacteria (70 Gt) dominating. Protist diversity, as detected through environmental DNA surveys, is vast in every sampled environment, but it is mostly undescribed. The richest protist communities appear in soils, followed by oceanic and lastly freshwater habitats, mostly as part of the plankton. Freshwater protist communities are characterized by a higher "beta diversity" (i.e. highly heterogeneous between samples) than soil and marine plankton. The high diversity can be a result of the hydrological dynamic of recruiting organisms from different habitats through extreme floods. Soil-dwelling protist communities are ecologically the richest, possibly be due to the complex and highly dynamic distribution of water in the sediment, which creates extremely heterogenous environmental conditions. The constantly changing environment promotes the activity of only one part of the community at a time, while the rest remains inactive; this phenomenon promotes high microbial diversity in prokaryotes as well as protists.
Primary producers
Microscopic phototrophic protists (or microalgae) are the main contributors to the biomass and primary production in nearly all aquatic environments, where they are collectively known as phytoplankton (together with cyanobacteria). In marine phytoplankton, the smallest fractions, the picoplankton (<2 μm) and nanoplankton (2–20 μm), are dominated by several different algae (prymnesiophytes, pelagophytes, prasinophytes); fractions larger than 5 μm are instead dominated by diatoms and dinoflagellates. In freshwater phytoplankton, golden algae, cryptophytes and dinoflagellates are the most abundant groups. Altogether, they are responsible for almost half of the global primary production. They are the main providers of much of the energy and organic matter used by bacteria, archaea, and higher trophic levels (zooplankton and fish), including essential nutrients such as fatty acids. Their abundance in the oceans depends mostly on the availability of inorganic nutrients, rather than temperature or sunlight; they are most abundant in coastal waters that receive nutrient-rich run-off from land, and areas where nutrient-rich deep ocean water reaches the surface, namely the upwelling zones in the arctic oceans and along continental margins. In freshwater habitats, most phototrophic protists are mixotrophic, meaning they also behave as consumers, while strict consumers (heterotrophs) are less abundant.
Macroalgae (namely red algae, green algae and brown algae), unlike phytoplankton, generally require a fixation point, which limits their marine distribution to coastal waters, and particularly to rocky substrates. They support numerous herbivorous animals, especially benthic ones, as both food and refuge from predators. Some communities of seaweeds exist adrift on the ocean surface, serving as a refuge and means of dispersal for associated organisms.
Phototrophic protists are as abundant in soils as their aquatic counterparts. Given the importance of aquatic algae, soil algae may provide a larger contribution to the global carbon cycle than previously thought, but the magnitude of their carbon fixation has yet to be quantified. Most soil algae are stramenopiles (diatoms, xanthophytes and eustigmatophytes) and archaeplastids (green algae). There is also presence of environmental DNA from dinoflagellates and haptophytes in soil, but no living forms have been seen.
Consumers
Phagotrophic protists are the most diverse functional group in all ecosystems, primarily represented by cercozoans (dominant in freshwater and soils), radiolarians (dominant in oceans), non-photosynthetic stramenopiles (with higher abundance in soils than in oceans), and ciliates.
Contrary to the common division between phytoplankton and zooplankton, much of the marine plankton is composed of mixotrophic protists, which pose a largely underestimated importance and abundance (around 12% of all marine environmental DNA sequences). Mixotrophs have varied presence due to seasonal abundance and depending on their specific type of mixotrophy. Constitutive mixotrophs are present in almost the entire range of oceanic conditions, from eutrophic shallow habitats to oligotrophic subtropical waters but mostly dominating the photic zone, and they account for most of the predation of bacteria. They are also responsible for harmful algal blooms. Plastidic and generalist non-constitutive mixotrophs have similar biogeographies and low abundance, mostly found in eutrophic coastal waters, with generalist ciliates dominating up to half of ciliate communities in the photic zone. Lastly, endosymbiotic mixotrophs are by far the most widespread and abundant non-constitutive type, representing over 90% of all mixotroph sequences (mostly radiolarians).
In the trophic webs of soils, protists are the main consumers of both bacteria and fungi, the two main pathways of nutrient flow towards higher trophic levels. Amoeboflagellates like the glissomonads and cercomonads are among the most abundant soil protists: they possess both flagella and pseudopodia, a morphological variability well suited for foraging between soil particles. Testate amoebae are also acclimated to the soil environment, as their shells protect against desiccation. As bacterial grazers, they have a significant role in the foodweb: they excrete nitrogen in the form of NH, making it available to plants and other microbes. Traditionally, protists were considered primarily bacterivorous due to biases in cultivation techniques, but many (e.g., vampyrellids, cercomonads, gymnamoebae, testate amoebae, small flagellates) are omnivores that feed on a wide range of soil eukaryotes, including fungi and even some animals such as nematodes. Bacterivorous and mycophagous protists amount to similar biomasses.
Decomposers
Necrophagy (the degradation of dead biomass) among microbes is mainly attributed to bacteria and fungi, but protists have a still poorly recognized role as decomposers with specialized lytic enzymes. In soils, fungus-like protists and slime molds (e.g., oomycetes, myxomycetes, acrasids) are present abundantly as osmotrophs and saprotrophs. In marine and estuarine environments, the well-studied thraustochytrids (part of labyrinthulomycetes) are relevant saprotrophs that decompose various substrates, including dead plant and animal tissue. Various ciliates and testate amoebae scavenge on dead animals. Some nucleariid amoebae specifically consume the contents of dead or damaged cells, but not healthy cells. However, all these examples are only facultative necrophages that also feed on live prey. In contrast, the algivorous cercozoan family Viridiraptoridae, present in shallow bog waters, are broad-range but sophisticated necrophages that feed on a variety of exclusively dead algae, potentially fulfilling an important role in cleaning up the environment and releasing nutrients for live microbes.
Parasites and pathogens
Parasitic protists occupy around 15–20% of all environmental DNA in marine and soil systems, but only around 5% in freshwater systems, where chytrid fungi likely fill that ecological niche. In oceanic systems, parasitoids (i.e. those which kill their hosts, e.g. Syndiniales) are more abundant. In freshwater ecosystems, parasitoids are mainly Perkinsea and Syndiniales (Alveolata), while true parasites (i.e. those which do not kill their hosts) in freshwater are mostly oomycetes, Apicomplexa and Ichthyosporea. In soil ecosystems, true parasites are primarily animal-hosted apicomplexans and plant-hosted oomycetes and plasmodiophorids. In Neotropical forest soils, apicomplexans dominate eukaryotic diversity and have an important role as parasites of small invertebrates, while oomycetes are very scarce in contrast.
Some protists are significant parasites of animals (e.g.; five species of the parasitic genus Plasmodium cause malaria in humans and many others cause similar diseases in other vertebrates), plants (the oomycete Phytophthora infestans causes late blight in potatoes) or even of other protists. Around 100 protist species can infect humans.
Biogeochemical cycles
Marine protists have a fundamental impact on biogeochemical cycles, particularly the carbon cycle. As phytoplankton, they fix as much carbon as all terrestrial plants combined. Soil protists, particularly testate amoebae, contribute to the silica cycle as much as forest trees through the biomineralization of their shells.
History of protist classification
Early classifications
From the start of the 18th century, the popular term "infusion animals" (later infusoria) referred to protists, bacteria and small invertebrate animals. In the mid-18th century, while Swedish scientist Carl von Linnaeus largely ignored the protists, his Danish contemporary Otto Friedrich Müller was the first to introduce protists to the binomial nomenclature system.
In the early 19th century, German naturalist Georg August Goldfuss introduced Protozoa (meaning 'early animals') as a class within Kingdom Animalia, to refer to four very different groups: Infusoria (ciliates), corals, phytozoa (such as Cryptomonas) and jellyfish. Later, in 1845, Carl Theodor von Siebold was the first to establish Protozoa as a phylum of exclusively unicellular animals consisting of two classes: Infusoria (ciliates) and Rhizopoda (amoebae, foraminifera). Other scientists did not consider all of them part of the animal kingdom, and by the middle of the century they were regarded within the groupings of Protozoa (early animals), Protophyta (early plants), Phytozoa (animal-like plants) and Bacteria (mostly considered plants). Microscopic organisms were increasingly constrained in the plant/animal dichotomy. In 1858, the palaeontolgist Richard Owen was the first to define Protozoa as a separate kingdom of eukaryotic organisms, with "nucleated cells" and the "common organic characters" of plants and animals, although he also included sponges within protozoa.
In 1860, British naturalist John Hogg proposed Protoctista (meaning 'first-created beings') as the name for a fourth kingdom of nature (the other kingdoms being Linnaeus' plant, animal and mineral) which comprised all the lower, primitive organisms, including protophyta, protozoa and sponges, at the merging bases of the plant and animal kingdoms.
In 1866, the 'father of protistology', German scientist Ernst Haeckel, addressed the problem of classifying all these organisms as a mixture of animal and vegetable characters, and proposed Protistenreich (Kingdom Protista) as the third kingdom of life, comprising primitive forms that were "neither animals nor plants". He grouped both bacteria and eukaryotes, both unicellular and multicellular organisms, as Protista. He retained the Infusoria in the animal kingdom, until German zoologist Otto Bütschli demonstrated that they were unicellular. At first, he included sponges and fungi, but in later publications he explicitly restricted Protista to predominantly unicellular organisms or colonies incapable of forming tissues. He clearly separated Protista from true animals on the basis that the defining character of protists was the absence of sexual reproduction, while the defining character of animals was the blastula stage of animal development. He also returned the terms Protozoa and Protophyta as subkingdoms of Protista.
End of the animal-plant dichotomy
Bütschli considered the kingdom to be too polyphyletic and rejected the inclusion of bacteria. He fragmented the kingdom into protozoa (only nucleated, unicellular animal-like organisms), while bacteria and the protophyta were a separate grouping. This strengthened the old dichotomy of protozoa/protophyta from German scientist Carl Theodor von Siebold, and the German naturalists asserted this view over the worldwide scientific community by the turn of the century. However, British biologist C. Clifford Dobell in 1911 brought attention to the fact that protists functioned very differently compared to the animal and vegetable cellular organization, and gave importance to Protista as a group with a different organization that he called "acellularity", shifting away from the dogma of German cell theory. He coined the term protistology and solidified it as a branch of study independent from zoology and botany.
In 1938, American biologist Herbert Copeland resurrected Hogg's label, arguing that Haeckel's term Protista included anucleated microbes such as bacteria, which the term Protoctista (meaning "first established beings") did not. Under his four-kingdom classification (Monera, Protoctista, Plantae, Animalia), the protists and bacteria were finally split apart, recognizing the difference between anucleate (prokaryotic) and nucleate (eukaryotic) organisms. To firmly separate protists from plants, he followed Haeckel's blastular definition of true animals, and proposed defining true plants as those with chlorophyll a and b, carotene, xanthophyll and production of starch. He also was the first to recognize that the unicellular/multicellular dichotomy was invalid. Still, he kept fungi within Protoctista, together with red algae, brown algae and protozoans. This classification was the basis for Whittaker's later definition of Fungi, Animalia, Plantae and Protista as the four kingdoms of life.
In the popular five-kingdom scheme published by American plant ecologist Robert Whittaker in 1969, Protista was defined as eukaryotic "organisms which are unicellular or unicellular-colonial and which form no tissues". Just as the prokaryotic/eukaryotic division was becoming mainstream, Whittaker, after a decade from Copeland's system, recognized the fundamental division of life between the prokaryotic Monera and the eukaryotic kingdoms: Animalia (ingestion), Plantae (photosynthesis), Fungi (absorption) and the remaining Protista.
In the five-kingdom system of American evolutionary biologist Lynn Margulis, the term "protist" was reserved for microscopic organisms, while the more inclusive kingdom Protoctista (or protoctists) included certain large multicellular eukaryotes, such as kelp, red algae, and slime molds. Some use the term protist interchangeably with Margulis' protoctist, to encompass both single-celled and multicellular eukaryotes, including those that form specialized tissues but do not fit into any of the other traditional kingdoms.
Advances in electron microscopy and molecular phylogenetics
The five-kingdom model remained the accepted classification until the development of molecular phylogenetics in the late 20th century, when it became apparent that protists are a paraphyletic group from which animals, fungi and plants evolved, and the three-domain system (Bacteria, Archaea, Eukarya) became prevalent. Today, protists are not treated as a formal taxon, but the term is commonly used for convenience in two ways:
Phylogenetic definition: protists are a paraphyletic group. A protist is any eukaryote that is not an animal, land plant or fungus, thus excluding many unicellular groups like the fungal Microsporidia, Chytridiomycetes and yeasts, and the non-unicellular Myxozoan animals included in Protista in the past.
Functional definition: protists are essentially those eukaryotes that are never multicellular, that either exist as independent cells, or if they occur in colonies, do not show differentiation into tissues. While in popular usage, this definition excludes the variety of non-colonial multicellularity types that protists exhibit, such as aggregative (e.g., choanoflagellates) or complex multicellularity (e.g., brown algae).
There is, however, one classification of protists based on traditional ranks that lasted until the 21st century. The British protozoologist Thomas Cavalier-Smith, since 1998, developed a six-kingdom model: Bacteria, Animalia, Plantae, Fungi, Protozoa and Chromista. In his context, paraphyletic groups take preference over clades: both protist kingdoms Protozoa and Chromista contain paraphyletic phyla such as Apusozoa, Eolouka or Opisthosporidia. Additionally, red and green algae are considered true plants, while the fungal groups Microsporidia, Rozellida and Aphelida are considered protozoans under the phylum Opisthosporidia. This scheme endured until 2021, the year of his last publication.
Fossil record
Paleo- and Mesoproterozoic
Before the existence of plants, animals and fungi, all eukaryotes were protists. Modern or crown-group eukaryotes originated from the last eukaryotic common ancestor (LECA) and emerged between 1600 and 2400 million years ago (Ma), during the Paleoproterozoic and Mesoproterozoic eras. However, the fossil record through this time is scarce and dominated by stem-group eukaryotes, extinct lineages preceding LECA. These lineages displayed early eukaryotic traits like flexible cell membranes and complex cell wall ornamentations, which require a flexible endomembrane system, but they lacked crown-group eukaryotes' advanced sterols (e.g., cholesterol), and instead produced simpler protosterols that require less oxygen during biosynthesis. Examples of these are: Trachyhystrichosphaera and Leiosphaeridia dated at 1100 Ma, Satka dated at 1300 Ma, Tappania and Shuiyousphaeridium dated at 1600 Ma, Grypania dated at 1800–1900 Ma, and Valeria which ranges from 1650 to 700 Ma.
Crown-group eukaryotes achieved significant morphological and ecological diversity before 1000 Ma, with multicellular algae capable of sexual reproduction and unicellular protists exhibiting modern phagocytosis and locomotion. Their advanced but metabolically expensive sterols likely provided numerous evolutionary advantages due to the increased membrane flexibility, including resilience to osmotic shock during dessication and rehydration cycles, extreme temperatures, UV light exposure, and protection against changing oxygen levels. These adaptations allowed crown-group eukaryotes to colonize diverse and harsh environments (e.g., mudflats, rivers, agitated shorelines and land). In contrast, stem-group eukaryotes occupied the low-oxygen marine waters as anaerobes. The oldest definitive crown-group eukaryotic fossils include Rafatazmia and Ramathallus, both putative red algae, dated at 1600 Ma.
Neoproterozoic
As oxygen levels rose during the Tonian period, crown-group eukaryotes outcompeted stem-group eukaryotes, expanding into oxygen-rich marine environments that supported an aerobic metabolism enabled by their mitochondria. Stem-group eukaryotes may have gone extinct due to competition and the extreme climatic changes of the Cryogenian glaciations and subsequent global warming, cementing the dominance of crown-group eukaryotes. Crown-group eukaryotes began to appear abundantly in this era, fueled by the proliferation of red algae. The oldest fossils assigned to modern eukaryotic groups include two photosynthetic protists: the multicellular red alga Bangiomorpha (1047 Ma), and the chlorophyte green alga Proterocladus (1000 Ma). Also included are the oldest fossils of Opisthokonta: Ourasphaira giraldae (1010–890 Ma), interpreted as the earliest fungus, and Bicellum brasieri (1000 Ma), the earliest holozoan, showing traits associated with complex multicellularity.
Abundant fossils of heterotrophic protists appear significantly later, parallel to the emergence of fungi. Vase-shaped microfossils (VSMs), widespread rocks dated at 780–720 Ma (Tonian to Cryogenian), have been described as a variety of organisms across the decades (e.g., algae, chitinozoans, tintinnids), but current scientific consensus relates most VSMs to testate amoebae. As such, VSMs comprise the oldest known fossils of both filose (Cercozoa) and lobose (Amoebozoa) testate amoebae.
After the Gaskiers glaciation of the Late Ediacaran (~579 Ma), fossils of heterotrophic protists undergo diversification. Some fossils similar to VSMs are interpreted as the oldest fossils of Foraminifera dated at 548 Ma (e.g., Protolagena), but their foraminiferal affinity is doubtful. Other microfossils that are possibly foraminifera include some poorly preserved tubular shells from 716–635 Ma rocks.
Phanerozoic
Radiolarian shells appear abundantly in the fossil record since the Middle Cambrian. Definitive radiolarian fossils have been found in rocks as old as the Early Cambrian period (~540 Ma), with records from older Precambrian rocks disregarded due to the lack of reliable fossils. Shortly afterwards, the oldest convincible foraminifera shells appear at around 525 Ma.
See also
Evolution of sexual reproduction
Protist locomotion
Footnotes
References
Bibliography
General
Hausmann, K., N. Hulsmann, R. Radek. Protistology. Schweizerbart'sche Verlagsbuchshandlung, Stuttgart, 2003.
Margulis, L., J.O. Corliss, M. Melkonian, D.J. Chapman. Handbook of Protoctista. Jones and Bartlett Publishers, Boston, 1990.
Margulis, L., K.V. Schwartz. Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth, 3rd ed. New York: W.H. Freeman, 1998.
Margulis, L., L. Olendzenski, H.I. McKhann. Illustrated Glossary of the Protoctista, 1993.
Margulis, L., M.J. Chapman. Kingdoms and Domains: An Illustrated Guide to the Phyla of Life on Earth. Amsterdam: Academic Press/Elsevier, 2009.
Schaechter, M. Eukaryotic microbes. Amsterdam, Academic Press, 2012.
Physiology, ecology and paleontology
Fontaneto, D. Biogeography of Microscopic Organisms. Is Everything Small Everywhere? Cambridge University Press, Cambridge, 2011.
Moore, R. C., and other editors. Treatise on Invertebrate Paleontology. Protista, part B (vol. 1, Charophyta, vol. 2, Chrysomonadida, Coccolithophorida, Charophyta, Diatomacea & Pyrrhophyta), part C (Sarcodina, Chiefly "Thecamoebians" and Foraminiferida) and part D (Chiefly Radiolaria and Tintinnina). Boulder, Colorado: Geological Society of America; & Lawrence, Kansas: University of Kansas Press.
External links
UniEuk Taxonomy App
Tree of Life: Eukaryotes
Tsukii, Y. (1996). Protist Information Server (database of protist images). Laboratory of Biology, Hosei University. Protist Information Server. Updated: March 22, 2016.
Obsolete eukaryote taxa
Paraphyletic groups | Protist | Biology | 17,838 |
1,836,606 | https://en.wikipedia.org/wiki/Allylic%20rearrangement | An allylic rearrangement or allylic shift is an organic chemical reaction in which reaction at a center vicinal to a double bond causes the double bond to shift to an adjacent pair of atoms:
It is encountered in both nucleophilic and electrophilic substitution, although it is usually suppressed relative to non-allylic substitution. For example, reaction of 1-chloro-2-butene with sodium hydroxide gives 2-buten-1-ol and 3-buten-2-ol:
In the similar substitution of 1-chloro-3-methyl-2-butene, the secondary 2-methyl-3-buten-2-ol is produced in a yield of 85%, while that for the primary 3-methyl-2-buten-1-ol is 15%.
Allylic shifts occur because the transition state is an allyl intermediate. In other respects they are similar to classical nucleophilic substitution, and admit both bimolecular and monomolecular mechanisms (respectively the SN2' and SN1'/SNi' substitutions).
Scope
Allylic shifts become the dominant reaction pathway when there is substantial resistance to a normal (non-allylic) substitution. For nucleophilic substitution, such resistance is known when there is substantial steric hindrance at or around the leaving group, or if there is a geminal substituent destabilizing an accumulation of positive charge. The effects of substitution at the vinyl group are less clear.
Although rarer still than SN', allylic shifts can occur vinylogously, as a "butadienylic shift":
SN2' reduction
In SN2' reduction, a hydride allylically displaces a good leaving group in a formal organic reduction, similar to the Whiting diene synthesis. One example occurred in taxol total synthesis (ring C):
The hydride is lithium aluminium hydride and the leaving group a phosphonium salt; the allylic shift causes the exocyclic double bond in the product. Only when the cyclohexane ring is properly substituted will the proton add trans to the adjacent methyl group.
Electrophilic allyl shifts
Allyl shifts can also take place with electrophiles. In the example below the carbonyl group in benzaldehyde is activated by diboronic acid prior to reaction with the allyl alcohol (see: Prins reaction):
The active catalyst system in this reaction is a combination of a palladium pincer compound and p-toluenesulfonic acid, the reaction product is obtained as a single regioisomer and stereoisomer.
Examples
Repeated allylic shifts can "flip-flop" a double-bond between two possible locations:
An SN2' reaction should explain the outcome of the reaction of an aziridine carrying a methylene bromide group with methyllithium:
In this reaction one equivalent of acetylene is lost.
Named reactions
Ferrier rearrangement
Meyer–Schuster rearrangement
References
Rearrangement reactions
Reaction mechanisms | Allylic rearrangement | Chemistry | 648 |
5,062,962 | https://en.wikipedia.org/wiki/Mercury%28II%29%20sulfate | Mercury(II) sulfate, commonly called mercuric sulfate, is the chemical compound HgSO4. It is an odorless salt that forms white granules or crystalline powder. In water, it separates into an insoluble basic sulfate with a yellow color and sulfuric acid.
Structure
The anhydrous compound features Hg2+ in a highly distorted tetrahedral HgO4 environment. Two Hg-O distances are 2.22 Å and the others are 2.28 and 2.42 Å. In the monohydrate, Hg2+ adopts a linear coordination geometry with Hg-O (sulfate) and Hg-O (water) bond lengths of 2.179 and 2.228 Å, respectively. Four weaker bonds are also observed with Hg---O distances >2.5 Å.
History
In 1932, the Japanese chemical company Chisso Corporation began using mercury sulfate as the catalyst for the production of acetaldehyde from acetylene and water. Though it was unknown at the time, methylmercury is formed as side product of this reaction. Exposure and consumption of the mercury waste products, including methylmercury, that were dumped into Minamata Bay by Chisso are believed to be the cause of Minamata disease in Minamata, Japan.
Production
Mercury sulfate can be produced
by treating mercury with hot concentrated sulfuric acid:
Alternatively yellow mercuric oxide reacts also with concentrated sulfuric acid.
Uses
Denigés' reagent
An acidic solution of mercury sulfate is known as Denigés' reagent. It was commonly used throughout the 20th century as a qualitative analysis reagent. If Denigés' reagent is added to a solution containing compounds that have tertiary alcohols, a yellow or red precipitate will form.
Hydration reactions
Mercury compounds such as mercury sulfate and mercury(II) acetate are commonly used as catalysts in oxymercuration-demercuration, a type of electrophilic addition reaction which results in hydration of an unsaturated compound. The hydration of an alkene results in an alcohol that follows the regioselectivity predicted by Markovnikov's rule. For an alkyne, the result is an enol, which tautomerizes to give a ketone. An example is the conversion of 2,5-dimethylhexyne-2,5-diol to 2,2,5,5-tetramethyltetrahydrofuran using aqueous mercury sulfate without the addition of acid.As previously mentioned, HgSO4 was used as the catalyst for the production of acetaldehyde from acetylene and water.
Health issues
Inhalation of HgSO4 can result in acute poisoning: causing tightness in the chest, difficulties breathing, coughing and pain. Exposure of HgSO4 to the eyes can cause ulceration of conjunctiva and cornea. If mercury sulfate is exposed to the skin it may cause sensitization dermatitis. Lastly, ingestion of mercury sulfate will cause necrosis, pain, vomiting, and severe purging. Ingestion can result in death within a few hours due to peripheral vascular collapse.
It was used in the late 19th century to induce vomiting for medical reasons.
References
External links
National Pollutant Inventory – Mercury and compounds Fact Sheet
NIOSH Pocket Guide to Chemical Hazards
Sulfates
Mercury(II) compounds | Mercury(II) sulfate | Chemistry | 720 |
56,398 | https://en.wikipedia.org/wiki/Phase%20diagram | A phase diagram in physical chemistry, engineering, mineralogy, and materials science is a type of chart used to show conditions (pressure, temperature, etc.) at which thermodynamically distinct phases (such as solid, liquid or gaseous states) occur and coexist at equilibrium.
Overview
Common components of a phase diagram are lines of equilibrium or phase boundaries, which refer to lines that mark conditions under which multiple phases can coexist at equilibrium. Phase transitions occur along lines of equilibrium. Metastable phases are not shown in phase diagrams as, despite their common occurrence, they are not equilibrium phases.
Triple points are points on phase diagrams where lines of equilibrium intersect. Triple points mark conditions at which three different phases can coexist. For example, the water phase diagram has a triple point corresponding to the single temperature and pressure at which solid, liquid, and gaseous water can coexist in a stable equilibrium ( and a partial vapor pressure of ). The pressure on a pressure-temperature diagram (such as the water phase diagram shown) is the partial pressure of the substance in question.
The solidus is the temperature below which the substance is stable in the solid state. The liquidus is the temperature above which the substance is stable in a liquid state. There may be a gap between the solidus and liquidus; within the gap, the substance consists of a mixture of crystals and liquid (like a "slurry").
Working fluids are often categorized on the basis of the shape of their phase diagram.
Types
2-dimensional diagrams
Pressure vs temperature
The simplest phase diagrams are pressure–temperature diagrams of a single simple substance, such as water. The axes correspond to the pressure and temperature. The phase diagram shows, in pressure–temperature space, the lines of equilibrium or phase boundaries between the three phases of solid, liquid, and gas.
The curves on the phase diagram show the points where the free energy (and other derived properties) becomes non-analytic: their derivatives with respect to the coordinates (temperature and pressure in this example) change discontinuously (abruptly). For example, the heat capacity of a container filled with ice will change abruptly as the container is heated past the melting point. The open spaces, where the free energy is analytic, correspond to single phase regions. Single phase regions are separated by lines of non-analytical behavior, where phase transitions occur, which are called phase boundaries.
In the diagram on the right, the phase boundary between liquid and gas does not continue indefinitely. Instead, it terminates at a point on the phase diagram called the critical point. This reflects the fact that, at extremely high temperatures and pressures, the liquid and gaseous phases become indistinguishable, in what is known as a supercritical fluid. In water, the critical point occurs at around Tc = , pc = and ρc = 356 kg/m3.
The existence of the liquid–gas critical point reveals a slight ambiguity in labelling the single phase regions. When going from the liquid to the gaseous phase, one usually crosses the phase boundary, but it is possible to choose a path that never crosses the boundary by going to the right of the critical point. Thus, the liquid and gaseous phases can blend continuously into each other. The solid–liquid phase boundary can only end in a critical point if the solid and liquid phases have the same symmetry group.
For most substances, the solid–liquid phase boundary (or fusion curve) in the phase diagram has a positive slope so that the melting point increases with pressure. This is true whenever the solid phase is denser than the liquid phase. The greater the pressure on a given substance, the closer together the molecules of the substance are brought to each other, which increases the effect of the substance's intermolecular forces. Thus, the substance requires a higher temperature for its molecules to have enough energy to break out of the fixed pattern of the solid phase and enter the liquid phase. A similar concept applies to liquid–gas phase changes.
Water is an exception which has a solid-liquid boundary with negative slope so that the melting point decreases with pressure. This occurs because ice (solid water) is less dense than liquid water, as shown by the fact that ice floats on water. At a molecular level, ice is less dense because it has a more extensive network of hydrogen bonding which requires a greater separation of water molecules. Other exceptions include antimony and bismuth.
At very high pressures above 50 GPa (500 000 atm), liquid nitrogen undergoes a liquid-liquid phase transition to a polymeric form and becomes denser than solid nitrogen at the same pressure. Under these conditions therefore, solid nitrogen also floats in its liquid.
The value of the slope dP/dT is given by the Clausius–Clapeyron equation for fusion (melting)
where ΔHfus is the heat of fusion which is always positive, and ΔVfus is the volume change for fusion. For most substances ΔVfus is positive so that the slope is positive. However for water and other exceptions, ΔVfus is negative so that the slope is negative.
Other thermodynamic properties
In addition to temperature and pressure, other thermodynamic properties may be graphed in phase diagrams. Examples of such thermodynamic properties include specific volume, specific enthalpy, or specific entropy. For example, single-component graphs of temperature vs. specific entropy (T vs. s) for water/steam or for a refrigerant are commonly used to illustrate thermodynamic cycles such as a Carnot cycle, Rankine cycle, or vapor-compression refrigeration cycle.
Any two thermodynamic quantities may be shown on the horizontal and vertical axes of a two-dimensional diagram. Additional thermodynamic quantities may each be illustrated in increments as a series of lines—curved, straight, or a combination of curved and straight. Each of these iso-lines represents the thermodynamic quantity at a certain constant value.
3-dimensional diagrams
It is possible to envision three-dimensional (3D) graphs showing three thermodynamic quantities. For example, for a single component, a 3D Cartesian coordinate type graph can show temperature (T) on one axis, pressure (p) on a second axis, and specific volume (v) on a third. Such a 3D graph is sometimes called a p–v–T diagram. The equilibrium conditions are shown as curves on a curved surface in 3D with areas for solid, liquid, and vapor phases and areas where solid and liquid, solid and vapor, or liquid and vapor coexist in equilibrium. A line on the surface called a triple line is where solid, liquid and vapor can all coexist in equilibrium. The critical point remains a point on the surface even on a 3D phase diagram.
An orthographic projection of the 3D p–v–T graph showing pressure and temperature as the vertical and horizontal axes collapses the 3D plot into the standard 2D pressure–temperature diagram. When this is done, the solid–vapor, solid–liquid, and liquid–vapor surfaces collapse into three corresponding curved lines meeting at the triple point, which is the collapsed orthographic projection of the triple line.
Binary mixtures
Other much more complex types of phase diagrams can be constructed, particularly when more than one pure component is present. In that case, concentration becomes an important variable. Phase diagrams with more than two dimensions can be constructed that show the effect of more than two variables on the phase of a substance. Phase diagrams can use other variables in addition to or in place of temperature, pressure and composition, for example the strength of an applied electrical or magnetic field, and they can also involve substances that take on more than just three states of matter.
One type of phase diagram plots temperature against the relative concentrations of two substances in a binary mixture called a binary phase diagram, as shown at right. Such a mixture can be either a solid solution, eutectic or peritectic, among others. These two types of mixtures result in very different graphs. Another type of binary phase diagram is a boiling-point diagram for a mixture of two components, i. e. chemical compounds. For two particular volatile components at a certain pressure such as atmospheric pressure, a boiling-point diagram shows what vapor (gas) compositions are in equilibrium with given liquid compositions depending on temperature. In a typical binary boiling-point diagram, temperature is plotted on a vertical axis and mixture composition on a horizontal axis.
A two component diagram with components A and B in an "ideal" solution is shown. The construction of a liquid vapor phase diagram assumes an ideal liquid solution obeying Raoult's law and an ideal gas mixture obeying Dalton's law of partial pressure. A tie line from the liquid to the gas at constant pressure would indicate the two compositions of the liquid and gas respectively.
A simple example diagram with hypothetical components 1 and 2 in a non-azeotropic mixture is shown at right. The fact that there are two separate curved lines joining the boiling points of the pure components means that the vapor composition is usually not the same as the liquid composition the vapor is in equilibrium with. See Vapor–liquid equilibrium for more information.
In addition to the above-mentioned types of phase diagrams, there are many other possible combinations. Some of the major features of phase diagrams include congruent points, where a solid phase transforms directly into a liquid. There is also the peritectoid, a point where two solid phases combine into one solid phase during cooling. The inverse of this, when one solid phase transforms into two solid phases during cooling, is called the eutectoid.
A complex phase diagram of great technological importance is that of the iron–carbon system for less than 7% carbon (see steel).
The x-axis of such a diagram represents the concentration variable of the mixture. As the mixtures are typically far from dilute and their density as a function of temperature is usually unknown, the preferred concentration measure is mole fraction. A volume-based measure like molarity would be inadvisable.
Ternary phase diagrams
A system with three components is called a ternary system. At constant pressure the maximum number of independent variables is three – the temperature and two concentration values. For a representation of ternary equilibria a three-dimensional phase diagram is required. Often such a diagram is drawn with the composition as a horizontal plane and the temperature on an axis perpendicular to this plane. To represent composition in a ternary system an equilateral triangle is used, called Gibbs triangle (see also Ternary plot).
The temperature scale is plotted on the axis perpendicular to the composition triangle. Thus, the space model of a ternary phase diagram is a right-triangular prism. The prism sides represent corresponding binary systems A-B, B-C, A-C.
However, the most common methods to present phase equilibria in a ternary system are the following:
1) projections on the concentration triangle ABC of the liquidus, solidus, solvus surfaces;
2) isothermal sections;
3) vertical sections.
Crystals
Polymorphic and polyamorphic substances have multiple crystal or amorphous phases, which can be graphed in a similar fashion to solid, liquid, and gas phases.
Mesophases
Some organic materials pass through intermediate states between solid and liquid; these states are called mesophases. Attention has been directed to mesophases because they enable display devices and have become commercially important through the so-called liquid-crystal technology. Phase diagrams are used to describe the occurrence of mesophases.
See also
CALPHAD (method)
Computational thermodynamics
Congruent melting and incongruent melting
Gibbs phase rule
Glass databases
Hamiltonian mechanics
Phase separation
Saturation dome
Schreinemaker's analysis
Simple phase envelope algorithm
References
External links
Iron-Iron Carbide Phase Diagram Example
How to build a phase diagram
Phase Changes: Phase Diagrams: Part 1
Equilibrium Fe-C phase diagram
Phase diagrams for lead free solders
DoITPoMS Phase Diagram Library
DoITPoMS Teaching and Learning Package – "Phase Diagrams and Solidification"
Phase Diagrams: The Beginning of Wisdom – Open Access Journal Article
Binodal curves, tie-lines, lever rule and invariant points – How to read phase diagrams (Video by SciFox on TIB AV-Portal)
The Alloy Phase Diagram International Commission (APDIC)
Periodic table of phase diagrams of the elements (pdf poster)
Diagram
Equilibrium chemistry
Materials science
Metallurgy
Charts
Diagrams
Gases
Chemical engineering thermodynamics | Phase diagram | Physics,Chemistry,Materials_science,Engineering | 2,576 |
52,575,230 | https://en.wikipedia.org/wiki/Coelomomyces%20elegans | Coelomomyces elegans is a species of mosquito parasitic fungi, in the genus Coelomomyces. It has been found in Culex gelidus mosquitoes, in Matara, Sri Lanka.
It is distinguishable from other species of Coelomomycetacea by its resting sporangia, which are ornamented by circular depressed areas with papillae. Other distinct features include prominent vertical striae within ridges and a dehiscence split bordered by papillae.
References
Blastocladiomycota
Fungi described in 1985
Fungi of Sri Lanka
Parasitic fungi
Parasites of Diptera
Fungus species | Coelomomyces elegans | Biology | 130 |
14,798,926 | https://en.wikipedia.org/wiki/HOXA4 | Homeobox A4, also known as HOXA4, is a protein which in humans is encoded by the HOXA4 gene.
Function
In vertebrates, the genes encoding the class of transcription factors called homeobox genes are found in clusters named A, B, C, and D on four separate chromosomes. Expression of these proteins is spatially and temporally regulated during embryonic development. This gene is part of the A cluster on chromosome 7 and encodes a DNA-binding transcription factor which may regulate gene expression, morphogenesis, and differentiation.
See also
Homeobox
References
Further reading
External links
Transcription factors | HOXA4 | Chemistry,Biology | 129 |
23,267,052 | https://en.wikipedia.org/wiki/DC%20block | DC blocks are coaxial components that prevent the flow of audio and direct current (DC) frequencies while offering minimum interference to RF signals. There are three basic forms of DC blocks. "Inner only" models have a capacitor in series with the center conductor, "outer only" models have a capacitor in series with the outer conductor, and "inner/outer" models have capacitors in series with both the inner and outer conductors. The insulation material on the outer models is non-conductive. Applications include ground loop elimination, signal source modulation leakage suppression, system signal-to-noise ratio improvement, test setup isolation and other situations where undesired DC or audio current flows in the system.
DC blocks serve a wide range of practical functions, primarily in systems where undesired DC or audio currents can degrade performance. One of their key applications is in eliminating ground loops, which are common sources of hum and noise in audio and video systems. DC blocks also help suppress signal leakage, such as modulation leakage in signal sources, thereby improving the system’s signal integrity. They can enhance the signal-to-noise ratio (SNR) in sensitive communication systems by preventing the intrusion of unwanted currents. Additionally, DC blocks are used in test setups to isolate different parts of the system and prevent interference, ensuring more accurate measurements and maintaining the quality of the overall signal transmission.
See also
Bias tee
Choke (electronics)
DC-blocking capacitor
External links
What Is a DC Block? // wiseGEEK
DC Blocks & Bias Tees
Electrical components
Electrical wiring | DC block | Physics,Technology,Engineering | 324 |
41,574,964 | https://en.wikipedia.org/wiki/Prorenone | Prorenone (developmental code name SC-23133) is a steroidal antimineralocorticoid of the spirolactone group related to spironolactone that was never marketed. It is the lactonic form of prorenoic acid (prorenoate), and prorenoate potassium (SC-23992), the potassium salt of prorenoic acid, also exists. Prorenoate potassium is about 8 times more potent than spironolactone as an antimineralocorticoid in animals, and it may act as a prodrug to prorenone. In addition to the mineralocorticoid receptor, prorenone also binds to the glucocorticoid, androgen, and progesterone receptors. The antiandrogenic potency of prorenone in vivo in animals is close to that of spironolactone. Similarly to spironolactone, prorenone is also a potent inhibitor of aldosterone biosynthesis.
Chemistry
Synthesis
Prorenone can be synthesized via a Johnson–Corey–Chaykovsky reaction by reaction of canrenone with trimethylsulfoxonium iodide and sodium hydride.
See also
Canrenone
Mexrenone
Prorenoate potassium
Prorenoic acid
Potassium canrenoate
References
Antiandrogens
Antimineralocorticoids
Cyclopropanes
Pregnanes
Progestogens
Spiro compounds
Spirolactones
Steroidal antiandrogens | Prorenone | Chemistry | 327 |
24,417,538 | https://en.wikipedia.org/wiki/Multiscale%20Electrophysiology%20Format | Multiscale Electrophysiology Format (MEF) was developed to handle the large amounts of data produced by large-scale electrophysiology in human and animal subjects. MEF can store any time series data up to 24 bits in length, and employs lossless range encoded difference compression. Subject identifying information in the file header can be encrypted using 128-bit AES encryption in order to comply with HIPAA requirements for patient privacy when transmitting data across an open network.
Compressed data is stored in independent blocks to allow direct access to the data, facilitate parallel processing and limit the effects of potential damage to files. Data fidelity is ensured by a 32-bit cyclic redundancy check in each compressed data block using the Koopman polynomial (0xEB31D82E), which has a Hamming distance of from 4 to 114 kbits.
A formal specification and source code are available online. MEF_import is an EEGLAB plugin to import MEF data into EEGLAB.
See also
Range encoding
AES encryption
CRC-32
MED Format official website
References
Sources
Martin, GNN. Range encoding: an algorithm for removing redundancy from a digitised message. Video & Data Recoding Conference, Southampton, 1979.
Koopman, P. 32-Bit Cyclic Redundancy Codes for Internet Applications. The International Conference on Dependable Systems and Networks (June 2002). 459.
Electrophysiology
Neurophysiology
Neurotechnology
Bioinformatics
Health standards
Computer file formats | Multiscale Electrophysiology Format | Engineering,Biology | 317 |
58,621,816 | https://en.wikipedia.org/wiki/Aspergillus%20neoglaber | Aspergillus neoglaber is a species of fungus in the genus Aspergillus. It is from the Fumigati section. Several fungi from this section produce heat-resistant ascospores, and the isolates from this section are frequently obtained from locations where natural fires have previously occurred. The species was first described in 1989. It has been reported to produce asperpentyn, avenaciolide, glabramycin A, B, C, sartoryglabrin A, B, C, and wortmannins.
Growth and morphology
A. neoglaber has been cultivated on both Czapek yeast extract agar (CYA) plates and Malt Extract Agar Oxoid® (MEAOX) plates. The growth morphology of the colonies can be seen in the pictures below.
References
neoglaber
Fungi described in 1989
Fungus species | Aspergillus neoglaber | Biology | 186 |
61,702,855 | https://en.wikipedia.org/wiki/Child%20Passenger%20Safety%20Week | Child Passenger Safety Week is observed the third week of September as part of Baby Safety Month in the United States. The goal of Child Passenger Safety Week is to make sure every child is in the correct child safety seat, that the seats are properly installed and used, and that seats are registered with their manufacturers to ensure parents and caregivers receive important safety updates.
Child Passenger Safety Week begins with Child Passenger Safety Technician (CPST) Appreciation Day and concludes with National Seat Check Saturday. During the week, CPSTs, child safety seat manufacturers, and nonprofit and governmental organizations share safety advice, conduct seat checks, offer community educational opportunities, and generally collaborate to reduce preventable child injury or death.
See also
Child safety seat
Safe Kids Worldwide
National Highway Traffic Safety Administration (NHTSA)
Transport Canada
National Safety Council
References
September observances
Awareness weeks in the United States
Road safety campaigns | Child Passenger Safety Week | Physics | 176 |
13,525,570 | https://en.wikipedia.org/wiki/Oracle%20WebCenter | Oracle WebCenter is Oracle's portfolio of user engagement software products built on top of the JSF-based Oracle Application Development Framework. There are three main products that make up the WebCenter portfolio, and they can be purchased together as a suite or individually:
Oracle WebCenter Content (includes WebCenter Imaging)
Oracle WebCenter Sites
Oracle WebCenter Portal
Each of these products are in separate but connected markets. WebCenter Content competes in the Enterprise Content Management market. WebCenter Sites competes in the Web Experience Management market, and WebCenter Portal competes in the self-service portal and content delivery market space. Different combinations of these products are frequently used together, so Oracle has bundled them together within the same WebCenter product family.
Oracle WebCenter contains a set of components for building rich web applications, portals, and team collaboration and social sites. Oracle WebCenter is targeted at enterprise and larger accounts that have significant content management requirements and the need to deliver that information with internal or external portals, customer-facing websites or within integrated business applications. Oracle has made a particular effort to integrate WebCenter into its leading business applications such as E-Business Suite, PeopleSoft and JD Edwards so that content can be centrally managed in one location and shared across multiple applications. For the development community and advanced business users, WebCenter provides a development environment that includes WebCenter Framework and WebCenter Services, along with an out-of-the-box application for team collaboration and enterprise social networking. According to Oracle, this is the strategic portal product, eventually replacing Oracle Portal as well as the portal products acquired from BEA.
Versions
WebCenter 12c (12.2.1.4) released Oct 2019
WebCenter 12c (12.2.1.3) released Aug 2017
WebCenter 12c (12.2.1) released Oct 2016
WebCenter 11gR1 PS8 (11.1.1.9.0) released May 2014
WebCenter 11gR1 PS7 (11.1.1.8.0) released Aug 2013
WebCenter 11gR1 PS6 (11.1.1.7.0) released Apr 2013
WebCenter 11gR1 PS5 (11.1.1.6.0) released Feb 2012
WebCenter 11gR1 PS4 (11.1.1.5.0) released May 2011
WebCenter 11gR1 PS3 (11.1.1.4.0) released Jan 2011
WebCenter 11gR1 PS2 (11.1.1.3.0) released Apr 2010
WebCenter 11gR1 PS1 (11.1.1.2.0) released Nov 2009
WebCenter 11gR1 (11.1.1.1.0) released July 2, 2009
WebCenter 10g (10.1.3.2.0) released January 2007
Cost
The product costs $70,000 per CPU for the WebCenter Services, and $125,000 per CPU for WebCenter Suite. In a production installation, users can expect to deploy at least 4 CPUs as a base system, with likely additional CPUs for development and testing. WebCenter includes embedded US licenses of Oracle Secure Enterprise Search, Oracle Universal Content Management, and Oracle BPEL Process Manager. In addition, WebCenter needs a database to store information: any supported and licensed database such as Oracle database, MS SQL Server or IBM Db2 will work.
WebCenter product stack
There are three major products in the WebCenter product stack.
The base WebCenter Framework allows a user to embed portlets, ADF Taskflows and Pages, content, and customizable components in an Oracle ADF application. All Framework pieces are integrated into the Oracle JDeveloper IDE, providing access to these resources.
WebCenter Services are a set of independently deployable collaboration services. It incorporates Web 2.0 components such as content, collaboration, and communication services the full list is provided below. WebCenter Services includes Oracle ADF user interface components (called Taskflows) that can be embedded directly into ADF applications. In addition, APIs can be utilized to create custom UIs and to integrate some of these services into non-ADF applications.
Finally, WebCenter Spaces is a closed source application built on WebCenter Framework and Services that offers a prebuilt project collaboration solution. It can be compared with solutions like Microsoft SharePoint and Atlassian Confluence. There are limited mechanisms to extend this application.
Note that there is a product called WebCenter Interaction which is not built on the core WebCenter stack it is the former Plumtree portal product. Also, all Oracle portal products at Oracle are included in the WebCenter Suite, which is an umbrella of products. Products can be included in the suite regardless of whether they are built on the ADF based WebCenter Framework.
WebCenter comprises furthermore several editions, among others WebCenter Suite Plus, WebCenter Portal, WebCenter Content, WebCenter Sites, WebCenter Sites Satellite Server (a distributed caching mechanism which stores and assembles "pagelets," or elements of output), WebCenter Universal Content Management. Seven WebCenter Adapters and one WCE Management are available.
WebCenter services capabilities
Social Networking Services - Enables users to maximize productivity through collaboration.
People Connection – Enables users to assemble their business networks like linked-in.
Discussions Provides the ability to create and participate in threaded discussion. This is an embedded version of Forums provided by Jive Software.
Announcements Enables users to post, personalize, and manage announcements.
Instant Messaging and Presence (IMP) Provides the ability to observe the online presence status of other authenticated users (whether online, offline, busy, or idle) and to contact them.
Blog Enables blogging functionality within the context of an application.
Wiki Self-service, community, oriented-content publishing and sharing.
Shared Services - Provides features for both social networking and personal productivity.
Documents Provides content management and storage capabilities, including content upload, file and folder creation and management, file check out, versioning, and so on. WebCenter Portal includes a restricted-use license of Oracle's enterprise content management product called WebCenter Content (formerly known as Universal Content Management).
Links Provides the ability to view, access, and associate related information; for example, you can link to a solution document from a discussion thread.
Lists Enables users to create, publish, and manage lists. (Available only in WebCenter Spaces).
Page Provides the ability to create and manage pages at run time.
Tags Provides the ability to assign one or more personally relevant keywords to a given page or document. This feature is similar to the del.cio.us website.
Events Provides group calendars, which users can use to schedule meetings, appointments, and any other type of team get-together. This feature requires deployment of a separate calendaring server, which may be Oracle Beehive or Microsoft Exchange (Available only in WebCenter Spaces).
Personal Productivity Services Focuses on the requirements of an individual, rather than a group.
Mail Provides integration with IMAP and SMTP mail servers to enable users to perform simple mail functions such as viewing, reading, creating, and deleting messages, creating messages with attachments, and replying to or forwarding existing messages.
Notes Provides the ability to "jot down" and retain quick bits of personally relevant information (Available only in WebCenter Spaces).
Recent Activities Provides a summary view of recent changes to documents, discussions, and announcements.
RSS Provides the ability to publish content from WebCenter Web 2.0 Services as news feeds in RSS 2.0 and Atom 1.0 formats.
Search Provides the ability to search tags, services, an application, or an entire site. This makes use of a license limited version of Oracle's Secure Enterprise Search (SES) product.
Worklist Provides a personal, at-a-glance view of business processes that require attention. These can include a request for document review and other types of business process that come directly from enterprise applications.
Official and de facto standards support
WebCenter Framework supports the following standards:
J2EE 1.4 and above (Java EE)
JSR 168 and JSR 286
WSRP 1.0 and 2.0
JCR 1.0
JSF
JSR 116
Release of WebCenter 11g R1 Patch Set 5 (PS5)
On 22 February 2012 Oracle released WebCenter 11g Release 1 Patch Set 5. It includes many bug fixes in addition to several new enhancements. This patch set is mainly targeted at releasing customer bug fixes.
Release of WebCenter 11g R1 Patch Set 3 (PS3)
In January 2011 Oracle released WebCenter 11g Release 1 Patch Set 3. As the converged portal platform, this is a major new release with many features integrated from previously acquired portal products, including a greatly improved and flexible portal framework, improved GUI, personalization server, brand new navigation model, support for hierarchical pages and spaces, JSR 286, improved performance, and more.
WebCenter Framework and Services lacks support for these notable technologies:
Internet Explorer 6.0
Eclipse (software) IDE but Oracle JDeveloper is provided as part of the suite of tools.
Notes
External links
WebCenter Official Home
WebCenter Content
WebCenter Sites
WebCenter Portal
WebCenter Imaging
Oracle WebCenter Official Blog
Oracle Application Server
Oracle WebCenter page on the Oracle Wiki
Oracle software
Java platform
Portal software
Middleware
Content management systems | Oracle WebCenter | Technology,Engineering | 1,989 |
69,638,712 | https://en.wikipedia.org/wiki/Sewellia%20lineolata | Sewellia lineolata, the reticulated hillstream loach, is a species of fish from the provinces of Thua Thien-Hue, Quang Nam, Quang Ngai and Binh Dinh in Vietnam.
Habitat
Sewellia lineotola is found in shallow, fast-flowing, highly oxygenated tributaries and headwaters that contain stretches of riffles broken up by pools or sometimes waterfalls. Inhabited substrates are normally composed of gravel, bedrock and sand among stretches containing boulders, surrounded by well-developed riparian vegetations but with fewer aquatic plants present. The most favorable habitats have oxygen-saturated clear water which, combined with the sun, creates a rich biofilm covering submerged surfaces. During times of high rainfall, some streams can become murky as a result of suspended material caused by larger flow rate and water depth.
Diet
Sewellia lineolata eat benthic algae and associated micro-organisms. Insect larvae may be eaten opportunistically. In the aquarium, fish flakes, mini pellets, and algae wafers can also be added to the diet, along with bloodworms, brine shrimp, daphnia, and tubifex.
Tiger Hillstream Loaches, Sewellia lineolata, have especially developed fins to attach themselves to rocks and flat areas in their naturally fast moving rivers and streams. For them to survive and be happy they need strong currents plus abundant oxygen, numerous rocky hiding places and smooth pebbles and boulders to graze over.
Lighting should be bright to encourage algal growth in the aquarium. Plants are not necessary as the fish do not normally encounter them in the wild. They demand excellent water-quality. Suitable plants for high-flow environments are Anubias and Microsoreum. These will grow on rock-work or driftwood.
Note these fish have smaller mouths than Gastromyzon species which should be a consideration with foodstuffs. Good quality flake, small sinking pellets, algae wafers, thawed frozen Bloodworm, Mysis Shrimp, blanched Spinach, Kale, natural algae are good foods for them.
One part of their habits that differs from Gastromyzon or Beaufortia is that of "gliding" on the current. Those other species will move from a rock quickly to another in short hops, but Sewellia will launch from an elevated rock or other decor and glide on the current for some distance before alighting on another hard surface, or sometimes the substrate.
Also, unlike many other Sucker-bodied Hillstream Loaches, they seem far more at ease when searching for food on the loose surface of sand or fine gravel, and will flutter their fins, disturbing the surface grains. It appears they do this to uncover possible food items.
References
External links
Fish described in 1846
Fish of Vietnam
lineolata
Taxa named by Achille Valenciennes
Vulnerable species | Sewellia lineolata | Biology | 590 |
41,564,872 | https://en.wikipedia.org/wiki/C2H4I2 | {{DISPLAYTITLE:C2H4I2}}
The molecular formula C2H4I2 (molar mass: 281.86 g/mol, exact mass: 281.8402 u) may refer to:
1,1-Diiodoethane
1,2-Diiodoethane | C2H4I2 | Chemistry | 67 |
66,105,482 | https://en.wikipedia.org/wiki/V368%20Aquilae | V368 Aquilae, also known as Nova Aquilae 1936 no. 2 was the second nova which occurred in the constellation of Aquila during 1936 (the first was the fainter V356 Aquilae, which was discovered on 18 September 1936). It was discovered on a photographic plate by Nils Tamm at Kvistaberg Observatory on 7 October 1936. At the time of discovery it was at photographic magnitude 7, and was already fading. Pre-discovery photographs showed that peak brightness occurred around 25 September 1936, at which time it had reached apparent magnitude 5.0, making it visible to the naked eye. The nova was described as being fiery red due to strong Hα emission, and for a time could be seen with binoculars simultaneously with V356 Aquilae, another nova which Nill Tamm had discovered a month earlier.
V368 Aquilae is classified as a "moderately fast nova"; it dropped by three magnitudes in about 42 days.
All novae are binary stars, with a "donor" star orbiting a white dwarf. The two stars are so close to each other that matter is transferred from the donor star to the white dwarf. Because the separation between the stars is comparable to the size of the donor star, these stars are often eclipsing binaries and V368 Aquilae does show eclipses. Marin and Shfter studied these eclipses, which have a depth of about 0.25 magnitudes and a period of 16.57 hours - an unusually long orbital period for a nova.
References
Aquilae 1936, Nova
Aquila (constellation)
Aquilae, V368 | V368 Aquilae | Astronomy | 339 |
10,113,932 | https://en.wikipedia.org/wiki/Talking%20clock | A talking clock (also called a speaking clock and an auditory clock) is a timekeeping device that presents the time as sounds. It may present the time solely as sounds, such as a phone-based time service (see "Speaking clock") or a clock for the visually impaired, or may have a sound feature in addition to an analog or digital face.
History
Although they would not be considered to be speaking, clocks have incorporated noisemakers such as clangs, chimes, gongs, melodies, and the sounds of cuckoos or roosters from almost the beginning of the mechanical clock. Soon after Thomas Edison's invention of the phonograph, the earliest attempts to make a clock that incorporated a voice were made. Around 1878, Frank Lambert invented a machine that used a voice recorded on a lead cylinder to call out the hours. Lambert used lead in place of Edison's soft tinfoil. In 1992, the Guinness Book of World Records recognized this as the oldest known sound recording that was playable (though that status now rests with a phonautogram of Édouard-Léon Scott de Martinville, recorded in 1857). It is on display at the National Watch and Clock Museum in Columbia, Pennsylvania.
Although there have been rumors that other talking clocks may have been produced afterward, it is not until around 1910 that another talking clock was introduced, when Bernhard Hiller created a clock that used a belt with a recording on it to announce the time. However, these belts were often broken by the hand-tightening required, and all attempts to reproduce the celluloid ribbon have so far failed.
In 1933, the first practical use of talking clocks was seen when Ernest Esclangon created a talking telephone time service in Paris, France. On its first day, February 14, 1933, more than 140,000 calls were received. London began a similar service three years later. This type of talking time service is still around, and more than a million calls per year are received for the NIST's Telephone Time-of-Day Service.
In 1954, Ted Duncan, Inc., released the Hickory Dickory Clock, a crank toy intended for children. This clock used a record, needle, and tone arm to produce its sound.
In 1968, the first truly portable talking clock, the Mattel-a-Time Talking Clock, was released.
In 1979, Sharp released the world's first quartz-based talking clock, the Talking Time CT-660E (German version CT-660G). Its silver transistor-radio-like case contained complex LSI circuitry with 3 SMD ICs (likely clock CPU, speech CPU and sound IC), producing a Speak&Spell-like synthetic voice. At the front rim was a small LCD. The alarm spoke the time and also had a melody "Boccherini's Minuet"; after 5 minutes the alarm repeated with the words "Please hurry!". It also had stopwatch and countdown timer modes. The tiny controls to turn off alarm or set functions are hard to reach under a small bottom lid.
In 1984, the Hattori Seiko Co. released their famous pyramid-shaped talking clock, the Pyramid Talk. As a futuristic design object even its LCD was hidden at the bottom, requiring the user to push the clock's top to hear it talk.
Current talking clocks often include many more features than just giving the time; in these, the ability to speak the time is part of a wide range of voice capabilities, such as reading the weather and other information to the user.
Uses and purposes
Teaching timetelling
After the telephone time service, the next practical application of the talking clock was in the teaching of timetelling to children. The first talking clock to be used for this purpose was the Mattel "Mattel-a-Time Talking Clock" of 1968. Several other clocks of this type followed, including one featuring Thomas the Tank Engine. One of the latest ones, the "Talking Clever Clock", includes a quiz button which asks questions such as "What time is it?", "What time will it be in an hour?", and "How much time has passed between 1:00 and 2:30?" Other educational talking clocks come in a kit designed to be assembled by children.
Talking clocks can also be used with children whose learning disabilities may be partially offset by the reinforcement provided by hearing the time as well as seeing it.
Assisting the blind
Talking clocks have found a natural home as an assistive technology for people who are blind or visually impaired. There are over 150 tabletop clocks and 50 types of watches that talk. Manufacturers of such clocks include Sharp, Panasonic, RadioShack, and Reizen. In addition, one manufacturer purportedly produced a clock that would announce the time upon detecting a user's whistling signal.
Branding/Advertising
Many companies have used talking clocks as a novelty item to promote their brand. In 1987, the H. J. Heinz Company released a clock with the figure of "Mr. Aristocrat", a tomato with a motif similar to Mr. Peanut. At alarm time, the clock said, "It's time to get up; get up right away! Wait any longer and it's 'ketchup' all day! Remember, Heinz is the thick rich one." At roughly the same time, Pillsbury created a similar clock with the character of Little Sprout. In recent years, the Coca-Cola polar bear, the Red and Yellow M&M's characters, the Pillsbury Doughboy, a Campbell's Soup girl, and others have at one time appeared on a talking clock. One of the more interesting branded clocks was produced by Energizer and was a soft, battery-shaped clock whose alarm was turned off by punching it or throwing it against a hard surface.
Entertainment/conversation pieces
The inexpensiveness of modern speech technology has allowed manufacturers to include talking clock capabilities into a wide range of products. Many of these are intended as conversation pieces or speak merely for the entertainment of hearing sounds or words spoken by an inanimate object. Such timepieces include Darth Vader clocks, calculators with time features, and even a painting of Leonardo da Vinci's The Last Supper that announces the time on the hour along with a quote from Jesus.
Other themes of talking timepieces include fortune-telling, astrology, clocks with moving lips, animated creatures, sports and athletes, and movies, among others.
Technology
Most modern talking clocks are based on speech-synthesis integrated circuits that generate speech from sampled, stored data. The rapid technological progress of the 1980s enabled today's high-quality talking products. Early talking clocks employed chips that linked phonemes to generate speech. These products could generate unlimited speech, but it was of relatively poor quality that sounded robotic, at worst, unintelligible. Today's higher-quality speech is produced by sampled-data systems that take elements of an actual human voice. Modern voice synthesis technologies can produce synthesized vocabularies that retain the style of the speaker exactly and are not limited to just perfect English, but can be as varied as Scottish accents, Japanese, and even the voice of a young child. Such voices are all generated using tiny, inexpensive voice chips that are readily available.
Almost all of the latest voice-chipped talking clocks incorporate the female human voice to announce the time. Dr. Mark McKinley, the president of the International Society of Talking Clock Collectors, proposes three possible explanations for this phenomenon. The female voice may be considered more soothing psychologically; it may be a relic of the female voice being historically associated with secretarial (Administrative Assistant) functions; or a feminine voice may possibly simply be softer in a less intrusive way.
Many talking clocks include a light sensor or a setting that will automatically silence them between certain hours (usually between 10 p.m. and 8 a.m.).
Ozen Box
Many talking clocks of the 1970s utilized an Ozen box, which is a mechanism similar to a phonograph, in which a needle-like stylus tracks on a 2.25 inch platter similar to a vinyl phonograph record. The Janex Corporation produced most of the clocks which use this device, and they are highly prized among collectors.
Characters
A very large number of popular characters have appeared on talking clocks. The following list is not exhaustive, nor is it intended to be — the International Society of Talking Clocks Collectors (ISTCC) has a Museum collection of over 800 talking clocks.
Mickey Mouse
Several Looney Tunes characters (including Bugs Bunny, Daffy Duck, Tweety, et al.)
The Simpsons
Strawberry Shortcake
Superheroes (including Superman, Spider-Man, The Incredible Hulk, et al.)
Furby
Biz Markie
The Smurfs
SpongeBob SquarePants
Mario
See also
Speaking clock
References
External links
ISTCC Virtual Museum.
Frank Lambert's talking clock.
More on Lambert's clock.
Clocks
Assistive technology
Educational hardware
Novelty items | Talking clock | Physics,Technology,Engineering | 1,840 |
15,094,960 | https://en.wikipedia.org/wiki/Journal%20of%20Combinatorial%20Theory | The Journal of Combinatorial Theory, Series A and Series B, are mathematical journals specializing in combinatorics and related areas. They are published by Elsevier. Series A is concerned primarily with structures, designs, and applications of combinatorics. Series B is concerned primarily with graph and matroid theory. The two series are two of the leading journals in the field and are widely known as JCTA and JCTB.
The journal was founded in 1966 by Frank Harary and Gian-Carlo Rota. Originally there was only one journal, which was split into two parts in 1971 as the field grew rapidly.
In 2020, most of the editorial board of JCTA resigned to form a new, open access journal Combinatorial Theory. The new journal aims to be a continuation of JCTA independently from Elsevier. It published its first issue in December 2021.
Influential articles
Influential articles that appeared in the journal include Katona's elegant proof of the Erdős–Ko–Rado theorem and a series of papers spanning over 500 pages, appearing from 1983 to 2004, by Neil Robertson and Paul D. Seymour on the topic of graph minors, which together constitute the proof of the graph minors theorem. Two articles proving Kneser's conjecture, the first by László Lovász and the other by Imre Bárány, appeared back-to-back in the same issue of the journal.
References
Combinatorics journals
Academic journals established in 1966
Elsevier academic journals
English-language journals | Journal of Combinatorial Theory | Mathematics | 303 |
11,471,465 | https://en.wikipedia.org/wiki/Phomopsis%20ganjae | Phomopsis ganjae is a fungal plant pathogen infecting hemp.
References
External links
USDA ARS Fungal Database
Fungal plant pathogens and diseases
Hemp diseases
ganjae
Fungus species | Phomopsis ganjae | Biology | 41 |
69,188,655 | https://en.wikipedia.org/wiki/Zytek%20ZJ458 | The Zytek ZJ458 engine is a 4.5-litre, normally-aspirated, V8 racing engine, developed and produced by Zytek for sports car racing. The ZJ458's rev-limit was about 10,000 rpm, and produces its power output of @ 9,000 rpm, and peak torque of @ 7,500 rpm.
Applications
Ginetta-Zytek GZ09S
Zytek Z11SN
References
Engines by model
Gasoline engines by model
Zytek engines
V8 engines | Zytek ZJ458 | Technology | 113 |
23,879,584 | https://en.wikipedia.org/wiki/Adjoint%20state%20method | The adjoint state method is a numerical method for efficiently computing the gradient of a function or operator in a numerical optimization problem. It has applications in geophysics, seismic imaging, photonics and more recently in neural networks.
The adjoint state space is chosen to simplify the physical interpretation of equation constraints.
Adjoint state techniques allow the use of integration by parts, resulting in a form which explicitly contains the physically interesting quantity. An adjoint state equation is introduced, including a new unknown variable.
The adjoint method formulates the gradient of a function towards its parameters in a constraint optimization form. By using the dual form of this constraint optimization problem, it can be used to calculate the gradient very fast. A nice property is that the number of computations is independent of the number of parameters for which you want the gradient.
The adjoint method is derived from the dual problem and is used e.g. in the Landweber iteration method.
The name adjoint state method refers to the dual form of the problem, where the adjoint matrix is used.
When the initial problem consists of calculating the product and must satisfy , the dual problem can be realized as calculating the product , where must satisfy .
And
is called the adjoint state vector.
General case
The original adjoint calculation method goes back to Jean Cea, with the use of the Lagrangian of the optimization problem to compute the derivative of a functional with respect to a shape parameter.
For a state variable , an optimization variable , an objective functional is defined. The state variable is often implicitly dependent on through the (direct) state equation (usually the weak form of a partial differential equation), thus the considered objective is . Usually, one would be interested in calculating using the chain rule:
Unfortunately, the term is often very hard to differentiate analytically since the dependance is defined through an implicit equation. The Lagrangian functional can be used as a workaround for this issue. Since the state equation can be considered as a constraint in the minimization of , the problem
has an associate Lagrangian functional defined by
where is a Lagrange multiplier or adjoint state variable and is an inner product on . The method of Lagrange multipliers states that a solution to the problem has to be a stationary point of the lagrangian, namely
where is the Gateaux derivative of with respect to in the direction . The last equation is equivalent to , the state equation, to which the solution is . The first equation is the so-called adjoint state equation,
because the operator involved is the adjoint operator of , . Resolving this equation yields the adjoint state .
The gradient of the quantity of interest with respect to is (the second equation with and ), thus it can be easily identified by subsequently resolving the direct and adjoint state equations. The process is even simpler when the operator is self-adjoint or symmetric since the direct and adjoint state equations differ only by their right-hand side.
Example: Linear case
In a real finite dimensional linear programming context, the objective function could be , for , and , and let the state equation be , with and .
The Lagrangian function of the problem is , where .
The derivative of with respect to yields the state equation as shown before, and the state variable is . The derivative of with respect to is equivalent to the adjoint equation, which is, for every ,
Thus, we can write symbolically . The gradient would be
where is a third-order tensor, is the dyadic product between the direct and adjoint states and denotes a double tensor contraction. It is assumed that has a known analytic expression that can be differentiated easily.
Numerical consideration for the self-adjoint case
If the operator was self-adjoint, , the direct state equation and the adjoint state equation would have the same left-hand side. In the goal of never inverting a matrix, which is a very slow process numerically, a LU decomposition can be used instead to solve the state equation, in operations for the decomposition and operations for the resolution. That same decomposition can then be used to solve the adjoint state equation in only operations since the matrices are the same.
See also
Adjoint equation
Backpropagation
Method of Lagrange multipliers
Shape optimization
References
External links
A well written explanation by Errico: What is an adjoint Model?
Another well written explanation with worked examples, written by Bradley
More technical explanation: A review of the adjoint-state method for computing the gradient of a functional with geophysical applications
MIT course
MIT notes
Numerical analysis | Adjoint state method | Mathematics | 961 |
1,366,384 | https://en.wikipedia.org/wiki/Windows%20for%20Pen%20Computing | Windows for Pen Computing is a software suite for Windows 3.1x, that Microsoft designed to incorporate pen computing capabilities into the Windows operating environment. Windows for Pen Computing was the second major pen computing platform for x86 tablet PCs; GO Corporation released their operating system, PenPoint OS, shortly before Microsoft published Windows for Pen Computing 1.0 in 1992.
The software features of Windows for Pen Computing 1.0 includes an on-screen keyboard, a notepad program for writing with the stylus, and a program for training the system to respond accurately to the user's handwriting. Microsoft included Windows for Pen Computing 1.0 in the Windows SDK, and the operating environment was also bundled with compatible devices.
Microsoft published Windows 95 in 1995, and later released Pen Services for Windows 95, also known as Windows for Pen Computing 2.0, for this new operating system. Windows XP Tablet PC Edition superseded Windows for Pen Computing in 2002. Subsequent Windows versions, such as Windows Vista and Windows 7, supported pen computing intrinsically.
See also
Windows Ink Workspace
References
External links
The Unknown History of Pen Computing contains a history of pen computing, including touch and gesture technology, from approximately 1917 to 1992.
About Tablet Computing Old and New - an article that mentions Windows Pen in passing
Annotated bibliography of references to handwriting recognition and pen computing
Windows für Pen Computer
Windows for Pen Computer (German link above translated by Google)
Notes on the History of Pen-based Computing (YouTube)
1992 software
Handwriting recognition
Pen Computing
Microsoft Tablet PC
Tablet computers | Windows for Pen Computing | Technology | 309 |
3,659,808 | https://en.wikipedia.org/wiki/Hall%20%28concept%29 | The meanings attributed to the word hall have varied over the centuries, as social practices have changed. The word derives from the Old Teutonic (hallâ), where it is associated with the idea of covering or concealing. In modern German it is Halle where it refers to a building but Saal where it refers to a large public room though the distinction is blurred:(Halle (Architektur) (de)). The latter may arise from a genitive form of the former. The French salle is borrowed from the German.
Simple beginnings
The Oxford English Dictionary gives nine meanings of hall relevant to buildings with a root of the word meaning "...to cover, conceal." A hall is, fundamentally, a relatively large space enclosed by a roof such as a market hall. Coming from the Old English language, it was brought into Britain in the fifth century.
A hall is also a large, public or stately room in a building, such as Westminster Hall.
Hall also may refer to a building itself where meetings or events occur such as a Guild hall, a town hall or a concert hall.
Also a dwelling-house with a large, open room (the hall) typically with an open hearth such as the original form of the Wealden hall house.
In 500, such a simple building was the residence of a lord and his retainers. This is the kind of hall which Beowulf knew. Even now, hall is the term used for a country house in midland and northern England.
The concept was more fundamental than referring to just domestic buildings. Though the lord's hall had an administrative aspect, this was more prominent in the town hall and the guild hall. The term might even be applied to a temple, in the same way as a basilica, now an ecclesiastical building, originated as a lordly reception hall with other domestic and other buildings close by in the same compound, just like an Anglo-Saxon moated hall but in a warmer climate. Compare the Basilica in Trier. (picture). Similarly, the French word salle can refer to a large, former church building such as the Salle Stengel de Lorentzen (fr) or to a sports hall (fr) large enough for playing hockey in.
Medieval developments
Later, partitions were set up so that the lord's family could have more privacy, a fairly new concept in northern Europe at the time. The English had come to Britain from a part of Europe which had not been directly exposed to the ways of the Roman Empire. As further time passed, the hall became the largest room of the house, often referred to as the great hall. While the humbler residents still slept there, the lord's family had one or more chambers at one end of the building in what came to be called the solar.
At this stage, we have the hall house in which the central room is the great hall. Off one end is the solar while a partition divides the other end of the hall off as the screens passage. Across the passage lie the pantry and buttery with between them, a passage through to the kitchen. The function of the last had been removed from the hall for the convenience of both cooks and inhabitants but also because roasting fires were a serious fire risk. Kitchens were by this time, built of more fireproof materials in a separate building. These arrangements were well established by the fifteenth century. At some stage, one of these divisions was the parlour, a concept which was in secular use by 1374.
Renaissance domesticity
During the sixteenth the process of subdivision proceeded. Notably, in an increasing number of cases, this was by inserting a floor, dividing the space which would have been occupied by the open hall in two, horizontally. From the early seventeenth century, the hall was usually a space inside the front door, more or less grand, in keeping with the grandeur of the house, in which people were first welcomed before proceeding to one of the partitioned rooms. The Red Hall in Bourne from about 1620 is still called a hall, but is designed not around a great hall but its staircase. Its hall, at the front door, has rather the nature of a passage leading to the featured staircase at the back of the house. The hall has a ceiling as low as any other in the house.
In a modern house, the hall is the space inside the front door from which the rooms are reached. Where this kind of hall is elongated, it may be called a passage, or hallway. The corresponding space upstairs is a landing.
Other aspects
In an early medieval building, as in the round Iron Age houses before them, the hall was where the fire was kept. With time, its functions as dormitory, kitchen, parlour and so on were divided off to separate rooms or, in the case of the kitchen, a separate building.
University halls
On the same principle many buildings at colleges and universities are formally titled "So-and-so Hall". Such a hall is typically named after the person who endowed it, for example, King's Hall, Cambridge. Others, such as Lady Margaret Hall, Oxford, commemorate respected people.
Between these in age, Nassau Hall at Princeton University began as the single building of the then college, showing a continuation of the medieval European pattern in America. The medieval universities had developed from colleges, that is groups of like-minded people living together in halls similar to the lordly ones described above and sleeping in carrels or separate rooms around the great hall.
In many cases, some aspect of this community remains in the modern institution. At colleges in the universities of Oxford, Cambridge and Durham for example, Hall is the dining hall for students, with High Table, on the dais at the high end, for fellows. Typically, at "Formal Hall", gowns are worn for dinner during the evening, whereas for "informal Hall" they are not.
Livery companies
Many Livery Companies such as the Mercers in the City of London, have a Hall which serves as their headquarters and meeting place. In origin, this was just like the lordly hall with its great hall though the peripheral rooms would have their specialist uses as parlours and robing rooms for example.
Public halls
Similarly a hall is also a building consisting largely of a principal room, whether medieval like Westminster Hall or more modern like Carnegie Hall, used for various ceremonial, social or concert events. Most public halls of this sort are available for renting out for meetings and social affairs. It may be privately or government-owned, such as a function hall owned by one company used for weddings and cotillions (organized and run by the same company on a contractual basis) or a community hall available for rent to anyone.
Following a line of similar development:
In office buildings and larger buildings (theatres, cinemas etc.), the entrance hall is generally known as the foyer (the French for fireplace). The atrium, a name sometimes used in public buildings for the entrance hall, was the central courtyard of a Roman house.
Derived from the residential meanings of the word:
Hall is also a surname of people, one of whose ancestors may have lived or worked in a hall as distinct from one such as David M. Cote, whose ancestor was named for a "cote": a much humbler place shared with the livestock.
Association with salt
From a completely separate derivation:
A Hall is a brand of bitter (beer) made in Germany and sold worldwide, mainly across America.
In German speaking areas, Hall (with a short a) can also form part of a town name, like Halle, where the name refers to hall, the Celtic word for salt (compare Welsh halen or Breton holen or Cornish holan). In this connection, Hall is the short form of the name of:
the medieval German town Schwäbisch Hall, where Hall was its whole name prior to 1933
the Austrian town Hall in Tirol near Innsbruck, which used to be called Solbad Hall from 1938 to 1974,
Hallstatt in Austria, which gave its name to the Celtic Hallstatt culture.
Sir Charles Hallé (originally Karl Halle) lent his name to the Hallé Orchestra. His forebears were probably associated with the German town of Halle. The accent was added to his name in order to assist English-speakers in pronouncing the word.
In the ancient world, the Celts were neighbours of the Greeks, whose word for salt was háls (ἅλς). While European science was developing, some branches of it adopted the Greek language as the source of its terminology. English therefore has words like halogen, halide, halotrichite and the hybrid halocarbon.
References
Rooms | Hall (concept) | Engineering | 1,765 |
21,033,863 | https://en.wikipedia.org/wiki/Flow%20assurance | Flow assurance is a relatively new term in oil and gas industry. It refers to ensuring successful and economical flow of hydrocarbon stream from reservoir to the point of sale. The term was coined by Petrobras in the early 1990s ahead of a DeepStar Program meeting, in Portuguese as Garantia do Escoamento (:pt::Garantia do Escoamento), meaning literally “Guarantee of Flow”, or Flow Assurance.
Flow assurance is extremely diverse, encompassing many discrete and specialized subjects and bridging across the full gamut of engineering disciplines. Besides network modeling and transient multiphase simulation, flow assurance involves effectively handling many solid deposits, such as, gas hydrates, asphaltene, wax, scale, and naphthenates. Flow assurance is the most critical task during deep water energy production because of the high pressures and low temperature (~4 degree Celsius) involved. The financial loss from production interruption or asset damage due to flow assurance mishap can be astronomical. What compounds the flow assurance task even further is that these solid deposits can interact with each other, and can cause catastrophic blockage formation in pipelines and result in flow assurance failure.
Flow assurance includes thermal investigation of pipelines, making sure the temperature is above the hydrate's formation temperature. Other important aspects of flow assurance are the estimation of stable production limits, and evaluation of erosion due to sand and corrosion in pipelines and equipment.
References
Petroleum technology
Natural gas technology
Oilfield terminology | Flow assurance | Chemistry,Engineering | 305 |
61,591,895 | https://en.wikipedia.org/wiki/Index%20to%20Organism%20Names | The Index to Organism Names (ION) is an extensive compendium of scientific names of taxa at all ranks in the field of zoology, compiled from the Zoological Record (later supplemented with content from Sherborn's Index Animalium) by its operators as a publicly accessible internet resource. Initially developed by BIOSIS, its ownership then passed to Thomson Reuters and is currently with Clarivate Analytics.
History
ION was initially developed as a freely available, web accessible component of a larger project, "TRITON" (the Taxonomy Resource and Index To Organism Names system) by BIOSIS, the then publishers of the Zoological Record ("ZR") and Biological Abstracts, in approximately 2000. As originally released it covered all animal names (sensu lato) reported in Zoological Record since 1978, along with names from some other groups not covered by the Zoological Record contributed by several partner organizations (the latter were subsequently deprecated in the system). Its initially stated aim was to provide basic nomenclatural and hierarchy information, plus ZR volume occurrence counts (reflecting use in the literature) for animal names, to identify the taxonomic group to which an organism belongs, and to link to further information from ZR (or initially, other collaborating organization).
By 2006, the BIOSIS products had been purchased by Thomson Scientific, subsequently Thomson Reuters, who continued and extended the ION database (example archived search interface here) using the URL www.organismnames.com, where it continues to reside. The Intellectual Property and Science division of Thomson Reuters was subsequently acquired by Clarivate Analytics who continue to make ION available (as at mid 2019).
Included content
In its initial release, the Index contained content from Zoological Record dating back to 1978, which was subsequently extended to the full span of the Zoological Record commencing in 1864. In 2011, Nigel Robinson of Thomson Reuters described an in-progress upgrade of the database to include an additional >200,000 names from a digitised version of Sherborn's Index Animalium, extending the content of ION back to the commencement of official zoological nomenclature in 1758. As at 2019, the Index contained over 2 million newly published names from 1758 onwards (with a small gap around the period 1850-1864 corresponding to the difference between the end of coverage of Index Animalium and the commencement of the "Zoological Record"), out of a total complement of over 5 million name instances, each with an associated unique numeric identifier (ION LSID).
References
External links
ION online search interface
BioNames home page (R. Page enhanced version of the ION dataset)
Zoological nomenclature
Taxonomy (biology)
Online databases
Internet properties established in 2000
Biodiversity databases
Biological databases | Index to Organism Names | Biology,Environmental_science | 548 |
3,163,517 | https://en.wikipedia.org/wiki/Chromium%28II%29%20carbide | Chromium(II) carbide is a ceramic compound that exists in several chemical compositions: Cr3C2, Cr7C3, and Cr23C6. At standard conditions it exists as a gray solid. It is extremely hard and corrosion resistant. It is also a refractory compound, which means that it retains its strength at high temperatures as well. These properties make it useful as an additive to metal alloys. When chromium carbide crystals are integrated into the surface of a metal it improves the wear resistance and corrosion resistance of the metal, and maintains these properties at elevated temperatures. The hardest and most commonly used composition for this purpose is Cr3C2.
The mineral form of the Cr3C2 compound is tongbaite. Isovite, , is a related mineral. Both are extremely rare. Yet another chromium-rich carbide mineral is yarlongite, Cr4Fe4NiC4.
Properties
There are three different crystal structures for chromium carbide corresponding to the three different chemical compositions. Cr23C6 has a cubic crystal structure and a Vickers hardness of 976 kg/mm2. Cr7C3 has a hexagonal crystal structure and a microhardness of 1336 kg/mm2. Cr3C2 is the most durable of the three compositions, and has an orthorhombic crystal structure with a microhardness of 2280 kg/mm2. For this reason Cr3C2 is the primary form of chromium carbide used in surface treatment.
Synthesis
Synthesis of chromium carbide can be achieved through mechanical alloying. In this type of process metallic chromium and pure carbon in the form of graphite are loaded into a ball mill and ground into a fine powder. After the components have been ground they are pressed into a pellet and subjected to hot isostatic pressing. Hot isostatic pressing utilizes an inert gas, primarily argon, in a sealed oven. This pressurized gas applies pressure to the sample from all directions while the oven is heated. The heat and pressure cause the graphite and metallic chromium to react and form chromium carbide. Decreasing the percentage of carbon content in the initial mixture results in an increase in the yield of the Cr7C3, and Cr23C6 forms of chromium carbide.
Another method for the synthesis of chromium carbide utilizes chromium oxide, pure aluminum, and graphite in a self-propagating exothermic reaction that proceeds as follows:
3Cr2O3 + 6Al + 4C → 2Cr3C2 + 3Al2O3
In this method the reactants are ground and blended in a ball mill. The blended powder is then pressed into a pellet and placed under an inert atmosphere of argon. The sample is then heated. A heated wire, a spark, a laser, or an oven may provide the heat. The exothermic reaction is initiated, and the resulting heat propagates the reaction throughout the rest of the sample.
Uses
Chromium carbide is useful in the surface treatment of metal components. Chromium carbide is used to coat the surface of another metal in a technique known as thermal spraying. Cr3C2 powder is mixed with solid nickel-chromium. This mixture is then heated to very high temperatures and sprayed onto the object being coated where it forms a protective layer. This layer is essentially its own metal matrix composite, consisting of hard ceramic Cr3C2 particles embedded in a nickel-chromium matrix. The matrix itself contributes to the corrosion resistance of the coating because both nickel and chromium are corrosion resistant in their metallic form. After over spraying the coating, the coated part must run through a diffusion heat treatment to reach the best results in matter of coupling strength to the base metal and also in matter of hardness.
Another technique utilizes chromium carbide in the form of overlay plates. These are prefabricated chromium carbide-coated steel plates, which are meant to be welded onto existing structures or machinery in order to improve performance.
Chromium carbide is used as an additive in cutting tools made of cemented carbides, in order to improve hardness by preventing the growth of large grains. The primary constituent in most extremely hard cutting tools is tungsten carbide. The tungsten carbide is combined with other carbides such as titanium carbide, niobium carbide, and chromium carbide and sintered together with a cobalt matrix. Cr3C2 prevents large grains from forming in the composite, which results in a fine-grained structure of superior hardness.
Undesired formation of chromium carbides in stainless steel and other alloys can lead to intergranular corrosion.
References
External links
National Pollutant Inventory - Chromium (III) compounds fact sheet
Carbides
Chromium(II) compounds
Refractory materials
Superhard materials | Chromium(II) carbide | Physics | 1,039 |
76,919,299 | https://en.wikipedia.org/wiki/Exidia%20pithya | Exidia pithya is a species of fungus in the family Auriculariaceae. Basidiocarps (fruit bodies) are gelatinous, black, and button-shaped at first, later coalescing and drying to form tar-like patches. The species grows on dead branches of conifers in continental Europe.
Taxonomy
The species was originally found growing on pine in Germany and was described in 1805 by the German mycologists Johannes Baptista von Albertini and Lewis David de Schweinitz.
Description
Exidia pithya forms grey-black to brown-black, gelatinous fruit bodies that are button-shaped at first, coalescing with age and forming effused patches up to 20 cm long. The upper, spore-bearing surface is normally smooth, becoming slightly furrowed, occasionally with a few scattered pegs or warts. The spore print is white.
Microscopic characters
The microscopic characters are typical of the genus Exidia. The basidia are ellipsoid and septate. The spores are cylindrical to weakly allantoid (sausage-shaped), 11 to 15 by 4 to 5 μm.
Similar species
Fruit bodies of Exidia glandulosa and E. nigricans are similarly coloured, but occur on broad leaved trees. Fruit bodies of E. saccharina and E. umbrinella occur on conifers, but are brown to orange-brown.
Habitat and distribution
Exidia pithya is a wood-rotting species, typically found on dead branches. It was originally described from pine (Pinus species), but is more common on spruce (Picea species) and less common on fir and larch (Abies and Larix species). It is widely distributed throughout continental Europe from Scandinavia to Turkey, but is absent from the British Isles.
References
Auriculariales
Fungi described in 1805
Fungi of Europe
Fungus species
Taxa named by Lewis David de Schweinitz
Taxa named by Johannes Baptista von Albertini | Exidia pithya | Biology | 407 |
234,731 | https://en.wikipedia.org/wiki/Virtuosity | Virtuosity is a 1995 American science fiction action film directed by Brett Leonard and starring Denzel Washington and Russell Crowe. Howard W. Koch Jr. served as an executive producer for the film. The film was released in the United States on August 4, 1995. Virtuosity had an estimated budget of $30 million and grossed $37 million worldwide.
Plot
In Los Angeles, Parker Barnes is a former police officer imprisoned for killing political terrorist Matthew Grimes, who killed Parker's wife and daughter. Barnes killed Grimes but also accidentally shot two news reporters in the process and was sentenced to 17 years to life. In the year 1999, Barnes and John Donovan are testing a virtual reality system designed for training police officers. The two are tracking down a serial killer named SID 6.7 at a Japanese sushi restaurant in virtual reality. SID (short for Sadistic, Intelligent, Dangerous, a VR amalgam of the most violent serial killers throughout history) causes Donovan to go into shock, killing him. The director overseeing the project orders the programmer in charge of creating SID, Dr. Darrel Lindenmeyer, to shut down the project with Commissioner Elizabeth Deane and her associate, William Wallace, as his witnesses.
Following a fight with another prisoner, Big Red, Barnes meets with criminal psychologist Dr. Madison Carter. Meanwhile, Lindenmeyer informs SID that he is about to be shut down because Donovan's death was caused when SID disabled the fail-safes. At SID's suggestion, Lindenmeyer convinces another employee, Clyde Reilly, that a sexually-compliant virtual reality model, Sheila 3.2, another project created by Lindenmeyer, can be brought to life in a synthetically grown android body. However, Lindenmeyer replaces the Sheila 3.2 module with the SID 6.7 module. Now processed into the real world, SID 6.7 kills Reilly.
Once word gets out of SID being in the real world, Deane and LAPD Chief William Cochran offer Barnes a deal: if he catches SID and brings him back to virtual reality, he will be pardoned. Barnes agrees, and with help from Carter they discover that Matthew Grimes, the terrorist who killed Barnes's wife and daughter, is a part of SID 6.7's personality profile. After killing a family along with a group of security guards, SID heads over to the Media Zone, a local nightclub, where he takes hostages. Barnes and Carter go to the nightclub to stop him, but SID escapes.
The next day, SID begins a killing spree at the Los Angeles Olympic Auditorium where a UFC match is taking place. Barnes arrives at the Stadium to capture SID, and finds him on a train, where another hostage is being held by SID. Barnes seemingly kills the hostage in front of horrified witnesses and is sent back to prison. Having caught up with Barnes after the incident, Carter tries to prove Barnes's innocence, but Barnes is freed from his prisoner transport by SID, who once again escapes. Wallace and Deane are about to have Barnes terminated via a fail-safe transmitter implanted in his body but Cochran destroys the system after learning from Carter that Barnes didn't kill the hostage on the train.
SID kidnaps Carter's daughter Karin and takes over a television studio. Lindenmeyer, having come out of hiding, sees what SID is doing and is impressed, but is captured by Carter. After a fight on the roof of the studio Barnes ultimately destroys SID's body but is unable to learn where he hid Karin. They place SID back in VR to trick the location out of him which proves to be one of the fan enclosures on the studio roof. When SID discovers that he is back in virtual reality he goes into a rage. Cochran lets Carter out of VR, but Lindenmeyer kills Cochran before he can release Barnes. Barnes starts to go into the same shock that Donovan suffered, but Carter kills Lindenmeyer, and saves Barnes.
Barnes and Carter return to the building that SID took over in the real world and save Karin from a booby trap set up by SID that's similar to the one that killed Barnes' family. After Karin is saved, Barnes destroys the SID 6.7 module.
Cast
Denzel Washington as Lieutenant Parker Barnes, who was imprisoned after killing a man who killed his family
Russell Crowe as SID 6.7, a virtual reality entity who later becomes a regenerating android
Kelly Lynch as Dr. Madison Carter, a criminal psychologist who teams with Barnes to understand SID's behavior
Stephen Spinella as Dr. Darrel Lindenmeyer, who created SID 6.7 and Sheila 3.2
William Forsythe as Chief Billy Cochran
Louise Fletcher as Commissioner Elizabeth Deane
William Fichtner as William Wallace
Costas Mandylor as John Donovan
Kevin J. O'Connor as Clyde Reilly
Kaley Cuoco as Karin Carter, Madison's daughter
Christopher Murray as Matthew Grimes
Mari Morrow as Linda Barnes
Johnny Kim as Lab Tech
Heidi Schanz as Sheila 3.2
Traci Lords as Media Zone singer
Gordon Jennison Noice as 'Big Red'
Michael Buffer as Emcee
Production
Washington restructured much of the story and dialogue during filming, entirely removing a romantic subtext between the Lt. Barnes and Dr. Carter characters from the original script.
Principal photography for the film began on January 25, 1995. Parts of the film were filmed at the abandoned Hughes Aircraft plant in Los Angeles.
Music
The soundtrack was released on MCA imprint Radioactive Records and contained music from Peter Gabriel, The Heads, Tricky and Live, among others.
An album containing the complete score by Christopher Young was released on July 26, 2019 on Intrada Records. A promo CD had previously been released. Producer Gary Lucchesi hired Young after working with him previously on Jennifer 8. Much of Young's score is electronic-influenced while the last third of the film utilizes an orchestra.
Reception
Critical response
The film received mostly mixed to negative reviews. Roger Ebert, however, wrote that the movie was "filled with bright ideas and fresh thinking" and "still finds surprises" despite a somewhat clichéd premise.
The film was nominated for Best Picture at the Sitges Film Festival, losing to Citizen X.
Box office
The film grossed $24 million in the United States and Canada and $37 million worldwide.
Novelization
In 1995, a novelization of the film by author Terry Bisson was published by Pocket.
See also
American Gangster, 2007 film starring Washington and Crowe in switched antagonist/protagonist roles
Simulated reality
References
External links
1995 films
1990s chase films
1990s science fiction action films
American chase films
American science fiction action films
1990s English-language films
Films about computing
Films about telepresence
Films about virtual reality
Films directed by Brett Leonard
Films produced by Gary Lucchesi
Films scored by Christopher Young
Films set in 1999
Films set in California
Films set in Los Angeles
American police detective films
Paramount Pictures films
1990s American films
1995 science fiction films
English-language science fiction action films
English-language action thriller films | Virtuosity | Technology | 1,405 |
72,602,031 | https://en.wikipedia.org/wiki/List%20of%20Argentine%20provinces%20and%20territories%20by%20life%20expectancy | This is a list of provinces of Argentina by life expectancy. Life expectancy is the average number of years of age that a group of infants born in the same year can expect to live, if maintained, from birth. The data is from a 2020 report by the Pacific Disaster Center.
Life expectancy in 2018
See also
List of South American countries by life expectancy
References
Ranked lists of country subdivisions
Argentina | List of Argentine provinces and territories by life expectancy | Biology | 83 |
195,645 | https://en.wikipedia.org/wiki/Alexei%20Leonov | Alexei Arkhipovich Leonov (30 May 1934 – 11 October 2019) was a Soviet and Russian cosmonaut and aviator, Air Force major general, writer, and artist. On 18 March 1965, he became the first person to conduct a spacewalk, exiting the capsule during the Voskhod 2 mission for 12 minutes and 9 seconds. He was also selected to be the first Soviet person to land on the Moon although the project was cancelled.
In July 1975, Leonov commanded the Soyuz capsule in the Apollo–Soyuz mission, which docked in space for two days with an American Apollo capsule.
Leonov was twice Hero of the Soviet Union (1965, 1975), a Major General of Aviation (1975), laureate of the USSR State Prize (1981), and a member of the Supreme Council of the United Russia party (2002–2019).
Early life and military service
Leonov was born on 30 May 1934 in Listvyanka, West Siberian Krai, Russian SFSR, in a Russian family. His grandfather had been forced to relocate to Siberia for his role in the 1905 Russian Revolution. Alexei was the eighth of nine surviving children born to Yevdokia and Arkhip. His father was an electrician and miner.
In 1936, his father was arrested and declared an "enemy of the people". Leonov wrote in his autobiography: "He was not alone: many were being arrested. It was part of a conscientious drive by the authorities to eradicate anyone who showed too much independence or strength of character. These were the years of Stalin's purges. Many disappeared into remote gulags and were never seen again."
The family moved in with one of his married sisters in Kemerovo. His father rejoined the family in Kemerovo after he was released. He was compensated for his wrongful imprisonment. Leonov used art as a way to provide more food for the family. He began his art career by drawing flowers on ovens and later painted landscapes on canvasses.
The Soviet government encouraged its citizens to move to Soviet-occupied Prussia, so in 1948 his family relocated to Kaliningrad. Leonov graduated from secondary school (No. 21) in 1953. He applied to the Academy of Arts in Riga, Latvia, but decided not to attend due to the high tuition costs. Leonov decided to join a Ukrainian preparatory flying school in Kremenchug. He made his first solo flight in May 1955. While indulging in his passion for art by studying part-time in Riga, Leonov started an advanced two-year course to become a fighter pilot at the Chuguev Higher Air Force Pilots School in the Ukrainian SSR.
On 30 October 1957, Leonov graduated with an honours degree and was commissioned a lieutenant in the 113th Parachute Aviation Regiment, part of the 10th Engineering Aviation Division of the 69th Air Army in Kyiv. On 13 December 1959, he married Svetlana Pavlovna Dozenko. The next day he moved to East Germany to his new assignment with the 294th Reconnaissance Regiment of the 24th Air Army.
Soviet space program
He was one of the 20 Soviet Air Forces pilots selected to be part of the first cosmonaut training group in 1960. As with most cosmonauts, Leonov was a member of the Communist Party of the Soviet Union. His walk in space was originally to have taken place on the Voskhod 1 mission, but this was cancelled, and the historic event happened on the Voskhod 2 flight instead. He was outside the spacecraft for 12 minutes and nine seconds on 18 March 1965, connected to the craft by a tether.
At the end of the spacewalk, Leonov's spacesuit had inflated in the vacuum of space to the point where he could not re-enter the airlock. He opened a valve to allow some of the suit's pressure to bleed off and was barely able to get back inside the capsule. While on the mission, Leonov drew a small sketch of an orbital sunrise, the first work of art made in outer space. Leonov had spent eighteen months undergoing weightlessness training for the mission.
In 1968, Leonov was selected to be commander of a circumlunar Soyuz 7K-L1 flight. This was cancelled because of delays in achieving a reliable circumlunar flight (only the later Zond 7 and Zond 8 members of the programme were successful) and the Apollo 8 mission had already achieved that step in the Space Race. He was also selected to be the first Soviet person to land on the Moon, aboard the LOK/N1 spacecraft. This project was also cancelled. (The design required a spacewalk between lunar vehicles, something that contributed to his selection.) Leonov was to have been commander of the 1971 Soyuz 11 mission to Salyut 1, the first crewed space station, but his crew was replaced with the backup after one of the members, cosmonaut Valery Kubasov, was suspected to have contracted tuberculosis (the other member was Pyotr Kolodin).
Leonov was to have commanded the next mission to Salyut 1, but this was scrapped after the deaths of the Soyuz 11 crew members, and the space station was lost. The next two Salyuts (actually the military Almaz station) were lost at launch or failed soon after, and Leonov's crew stood by. By the time Salyut 4 reached orbit, Leonov had been switched to a more prestigious project.
Leonov's second trip into space was as commander of Soyuz 19, the Soviet half of the 1975 Apollo-Soyuz mission—the first joint space mission between the Soviet Union and the United States.
During the project Leonov became lasting friends with the US commander Thomas P. Stafford, with Leonov being the godfather of Stafford's younger children. Stafford gave a eulogy in Russian at Leonov's funeral in October 2019.
From 1976 to 1982, Leonov was the commander of the cosmonaut team ("Chief Cosmonaut") and deputy director of the Yuri Gagarin Cosmonaut Training Center, where he oversaw crew training. He also edited the cosmonaut newsletter Neptune. He retired in 1992.
Later life and death
Leonov was an accomplished artist whose published books include albums of his artistic works and works he did in collaboration with his friend Andrei Sokolov. Leonov took coloured pencils and paper into space, where he sketched the Earth, becoming the first artist in space, and drew portraits of the Apollo astronauts who flew with him during the 1975 Apollo–Soyuz Test Project.
Arthur C. Clarke wrote in his notes to his 1982 novel 2010: Odyssey Two that, after a 1968 screening of 2001: A Space Odyssey, Leonov pointed out to him that the alignment of the Moon, Earth, and Sun shown in the opening is essentially the same as that in Leonov's 1967 painting Near the Moon, although the painting's diagonal framing of the scene was not replicated in the film. Clarke kept an autographed sketch of this painting—which Leonov made after the screening—hanging on his office wall. Clarke dedicated 2010: Odyssey Two to Leonov and Soviet physicist Andrei Sakharov. The fictional spaceship in the book is named Cosmonaut Alexei Leonov.
Together with Valentin Selivanov, Leonov wrote the script for the 1980 science fiction film The Orion Loop.
Leonov was the head of the Banner of Peace in Space project from 1990 until his death.
Leonov retired in 1991 and lived in Moscow. He had been in reserve since March 1992. In 1992–1993, he was director of space programs at Chetek. Leonov was an advisor to the First Deputy Chairman of the Board of Directors of the Moscow-based Alfa-Bank, and in 2001, vice-president of Alfa-Bank. He was a member of the United Russia party since 18 December 2002 and a member of the party's Supreme Council. He received recognition as an artist (he collaborated with Andrei Sokolov), and his works are widely exhibited and published.
In 2004, Leonov and former American astronaut David Scott began work on a dual memoir covering the history of the Space Race between the United States and the Soviet Union. Titled Two Sides of the Moon: Our Story of the Cold War Space Race, it was published in 2006. Neil Armstrong and Tom Hanks both wrote introductions to the book.
Leonov was interviewed by Francis French for the 2007 book Into That Silent Sea by Colin Burgess and French.
Leonov died in Moscow on 11 October 2019 after a long illness. His funeral took place on 15 October. He was 85 and the last living member of the five cosmonauts in the Voskhod programme. He was survived by his wife Svetlana Dozenko, daughter Oksana, and two grandchildren; his other daughter, Viktoria, died in 1996.
Legacy
Worried about the Siberian wildlife, namely bears and wolves, while awaiting pick-up after landing, Alexei Leonov inspired the TP-82 Cosmonaut survival pistol, which was regularly carried by Cosmonaut expeditions from 1986 to 2007.
The Leonov crater, near Mare Moscoviense (Sea of Moscow) on the far side of the Moon, was named after Leonov in 1970.
9533 Aleksejleonov, an asteroid first observed in 1981, was named for him.
In the 1982 book 2010: Odyssey Two by Arthur C. Clarke the Soviet spaceship Alexei Leonov is named after the cosmonaut. The book is dedicated to Leonov and Andrei Sakharov.
Leonov, along with Rusty Schweickart, established the Association of Space Explorers in 1985. Membership is open to all people who have orbited the Earth.
Leonov created the image of Stephen Hawking for the medal, which was established by the Starmus Festival. Since 2015, it has been awarded for works contributing to the promotion of scientific knowledge in various fields, such as music, art, cinema. The portrait of Hawking painted by the astronaut is depicted on the front side of the "scientific Oscar". The reverse depicts Leonov's first spacewalk and Brian May's guitar, symbolizing the two main components of the festival. Leonov created the design for the reverse side in close cooperation with May.
The 2017 film The Age of Pioneers () is based on Leonov's account of the Voskhod 2 mission. Leonov was portrayed by Yevgeny Mironov. He was a technical adviser for the movie; the director cut all scenes featuring Gagarin–about 40 minutes of film–so Leonov could be the focus.
The song "E.V.A." by Public Service Broadcasting on their 2015 album, The Race for Space, references Leonov becoming the first man to undertake extravehicular activity in space.
In the 2019 alternate history television series, For All Mankind, Leonov is portrayed as the first person to walk on the Moon.
Leonov, a 2020 album by BlackWeald, is a dark ambient interpretation of the Voskhod 2 mission.
"Orbital Sunrise," an essay by John Green, focuses in part on the sketch Leonov made during his 1965 mission. It was released on 26 August 2021 as part of Green's podcast, The Anthropocene Reviewed. Later, it was posted separately on the YouTube channel vlogbrothers, and included in the Anthropocene Reviewed book.
At the 2022 on Starmus festival, held for the first time in the post-Soviet space, in Armenia, the premiere of the documentary film "Space Inside" about Alexei Leonov took place. It was introduced by the cosmonaut's daughter, Oksana Leonova. It is based on the last interview of the pioneer.
Soviet/Russian awards and honours
Twice Hero of the Soviet Union (23 March 1965 and 22 July 1975)
Two Orders of Lenin (23 March 1965 and 22 July 1975)
Pilot-Cosmonaut of the USSR (1965)
Merited Master of Sport of the USSR (1965)
Order of the Red Star (1961)
Order for Service to the Homeland in the Armed Forces of the USSR, 3rd class (1975)
Jubilee Medal "Twenty Years of Victory in the Great Patriotic War 1941–1945"
Jubilee Medal "40 Years of the Armed Forces of the USSR"
Jubilee Medal "50 Years of the Armed Forces of the USSR"
Jubilee Medal "60 Years of the Armed Forces of the USSR"
Jubilee Medal "70 Years of the Armed Forces of the USSR"
Medal "Veteran of the Armed Forces of the USSR"
Medals "For Impeccable Service", 1st, 2nd and 3rd classes
Lenin Komsomol Prize (1980)
USSR State Prize (1981)
Order for Merit to the Fatherland, 4th class (2 March 2000)
Order of Friendship (12 April 2011)
Order "For Merit to the Fatherland", 3rd class (22 May 2014)
Order "For Merit to the Fatherland", 1st class (29 May 2019)
Foreign awards
Hero of Socialist Labour (People's Republic of Bulgaria, 1965)
Order of Georgi Dimitrov (People's Republic of Bulgaria, 1965)
(German Democratic Republic, 1965)
Order of Karl Marx (German Democratic Republic, 1965)
Order of the Flag of the Republic of Hungary (1965)
Hero of Labor (Democratic Republic of Vietnam, 1966)
Order of Civil Merit, 1st class (Syria, 1966)
Order of Merit, 3rd class (Ukraine, 2011)
Public organizations
1975 Gold Space Medal from the Fédération Aéronautique Internationale (FAI) in 1976. FAI created an exception which allowed Thomas P. Stafford to be awarded it alongside him; typically the award is restricted to one person per year.
International Space Hall of Fame (1976)
International Air & Space Hall of Fame, inducted in 2001, along with Valeri Kubasov, Vance D. Brand, Deke Slayton, and Thomas P. Stafford
Ludwig Nobel Prize (2007)
Elmer A. Sperry Award (US, 2008), with Konstantin Bushuyev, Thomas P. Stafford, and Glynn Lunney
Order of Saint Constantine the Great (Union of the Golden Knights of the Order of St. Constantine the Great)
Order "Golden Star" (Foundation Heroes of the Soviet Union and Heroes of the Russian Federation)
Order the "Pride of Russia" (Foundation for the "Pride of the Fatherland", 2007)
National Award "To the Glory of the Fatherland" in the "Glory to Russia" class (International Academy of Social Sciences and International Academy of patronage, 2008)
Order of "the Glory of the Fatherland", 2nd class (2008)
2011 co-founder and the member of board of directors of the international festival of science, space and music Starmus together with astrophysicist Garik Israelyan, musician of the band Queen Brian May, scientist-educator Stephen Hawking, a number of astronauts and Nobel laureates.
Other awards and titles
Commander of the Order of Saint Anna III degree (2008), by Grand Duchess Maria Vladimirovna of Russia
Commander of the Order of Saint Anna II degree (2011), by Grand Duchess Maria Vladimirovna of Russia
Honorary member of the Russian Academy of Arts
See also
Attempted assassination of Leonid Brezhnev (Moscow, 1969), in which a gunman fired 14 shots at a limousine carrying Leonov and other cosmonauts.
Notes
References
Sources
Further reading
"Testing of rocket and space technology – the business of my life" Events and facts – A. I. Ostashev, Korolyov, 2001.New Page 1;
"Rockets and people" – B. E. Chertok, M: "mechanical engineering", 1999.
"Bank of the Universe" – edited by Boltenko A. C., Kyiv, 2014., publishing house "Phoenix",
A.I. Ostashev, Sergey Pavlovich Korolyov – The Genius of the 20th Century — 2010 M. of Public Educational Institution of Higher Professional Training MGUL .
S. P. Korolev. Encyclopedia of life and creativity – edited by C. A. Lopota, RSC Energia. S. P. Korolev, 2014
External links
A video of his spacewalk
The Voskhod 2 mission revisited
Science fiction art by Leonov and Sokolov. Extensive gallery, with annotation.
The official website of the city administration Baikonur – Honorary citizens of Baikonur
Alexeï Léonov, the Spacewalker, Vladimir Kozlov's film, France-Russia, 2011
1934 births
2019 deaths
1965 in spaceflight
20th-century Russian painters
21st-century Russian painters
Apollo–Soyuz Test Project
Burials at the Federal Military Memorial Cemetery
Extravehicular activity
Heroes of Socialist Labour
Heroes of the Soviet Union
Honorary members of the Russian Academy of Arts
People from Kemerovo Oblast
Recipients of the Order "For Merit to the Fatherland", 1st class
Recipients of the Lenin Komsomol Prize
Recipients of the Order of Lenin
Recipients of the Order of Merit (Ukraine), 3rd class
Recipients of the USSR State Prize
Russian cosmonauts
20th-century Russian explorers
Russian male painters
Russian speculative fiction artists
Soviet Air Force generals
Soviet major generals
Soviet painters
Space artists
Voskhod program cosmonauts
Spacewalkers
20th-century Russian male artists
21st-century Russian male artists
Deputies of Mossoviet | Alexei Leonov | Astronomy | 3,556 |
33,437,726 | https://en.wikipedia.org/wiki/Anthopleurin | Anthopleurin is a toxin from the venom of the sea anemones Anthopleura xanthogrammica and Anthopleura elegantissima. These anemones use anthopleurin as a pheromone to quickly withdraw their tentacles in the presence of predators. Anthopleurin has four isoforms (Anthopleurin-A, -B, -C, and -Q). Their working mechanism is based on binding to sodium channels, which leads to increased excitation especially in cardiac myocytes.
Function in sea anemones
Anthopleurin functions both as a toxin as well as a pheromone. When a predator approaches the anemone, their reaction is to withdraw their tentacles and oral disc. These are the preferred attack sites for predators, because the concentration of anthopleurin is the lowest in these sites. The body region of the sea-anemone that is exposed to the predator contains the highest concentration of anthopleurin. After consuming the sea-anemone, the predator travels through the water and actually helps to spread the anthopleurin. This functions as an alarm pheromone for the other anemones, so they can hide certain body parts and defend themselves.
Sources
Anthopleura xanthogrammica (Giant green anemone) and Anthopleura elegantissima (Aggregating anemone) are named after the terrestrial anemone flower and are typically found along rocky, tidy shores in the Pacific Ocean.
Molecular structure
Anthopleurins are water-soluble proteins. They are built of four short strands of antiparallel beta-sheets, and contain three disulfide bridges.
Mode of action
Anthopleurins bind to the extracellular site-3 of mammalian sodium channels. Anthopleurins can affect cardiac myocytes by binding to the cardiac isoform of the sodium channel, RT4-B. Anthopleurins slow down inactivation of the sodium channels As a result, they can have positive inotropic effects on the whole heart. Pre-treatment with AP-Q has an effect on hepatocytes in CCl4-induced acute liver injury, decreasing the activity of aspartate transaminase (AST) and alanine transaminase (ALT) in the liver.
Potency
All different forms of anthopleurin are potent toxins. Anthopleurin A and C show effect at concentrations of 50 nM, Anthopleurin B at 3 nM and AP-Q at 30 nM.
Mechanism of toxin action
Anthopleurin can bind to the extracellular site of voltage-gated sodium channels. This results in slower inactivation, which has a positive inotropic effect on the heart. Anthopleurin has no effect on heart rate and blood pressure when given in concentrations of normal range. When the concentration of anthopleurin gets too high, arrhythmia of the heart can occur and this can cause serious damage or even death. Intoxication in humans is very rare.
Therapeutic implications
Cardiac therapeutic implications
Since AP is known to have an excitatory effect on cardiac muscle contractility at very low concentrations, without interfering with heart rate and blood pressure, it has been suggested to be useful as a possible treatment for patients with heart failure. Digoxin (purified cardiac glycoside) has more side-effects and is less potent than AP (which is 200 times more potent in the case of AP-A and AP-C, while AP-B is even more potent). AP-Q is quite similar to vesnarinone, a quinolinone derivative, a medicine that can be given to patients with chronic heart failure. Only lower doses of both AP-Q and vesnarinone have beneficial effects without raising blood pressure or heart rhythm. There is a narrow dose range in which the contractility is improved but also arrhythmias could be induced. AP itself cannot be used for therapeutic admission, because the stability of the molecule after oral transmission is too low and an immunological reaction might occur since the molecule is unfamiliar to the body. However, it may be possible to modify its structure using biological engineering.
Studies have also been performed to investigate the effects of AP-Q in acute liver injury. Given in low doses (3.5–7 microgram/kg) AST and ALT are decreased, whereas high doses of AP-Q (14 microgram) increase these liver enzyme values. AP-Q also increases the delayed outward potassium current thereby increasing the outflow of potassium ions from hepatocytes. This causes a hyperpolarization of its membrane potential. This hyperpolarizing effect could lead to increased uptake of substrates that help in restoring the cellular ATP levels.
References
Neurotoxins
Ion channel toxins
Sea anemone toxins
Protein toxins | Anthopleurin | Chemistry | 1,027 |
70,064,140 | https://en.wikipedia.org/wiki/Cilofexor | Cilofexor (also known as GS-9674) is a nonsteroidal farnesoid X receptor (FXR) agonist in clinical trials for the treatment of non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and primary sclerosing cholangitis (PSC). It is being investigated for use alone or in combination with firsocostat, selonsertib, or semaglutide. In rat models and human clinical trials of NASH it has been shown to reduce fibrosis and steatosis, and in human clinical trials of PSC it improved cholestasis and reduced markers of liver injury.
It is being developed by the pharmaceutical company Gilead Sciences.
References
Pyridines
Chlorobenzene derivatives
Cyclopropyl compounds
Oxazoles
Azetidines
Carboxylic acids
Farnesoid X receptor agonists | Cilofexor | Chemistry | 200 |
20,228,736 | https://en.wikipedia.org/wiki/Regional%20geochemistry | Regional geochemistry is the study of the spatial variation in the chemical composition of materials at the surface of the Earth, on a scale of tens to thousands of kilometres. Important parameters to consider when designing or evaluating a geochemical survey are:
Areal extent of the survey
Sampling density
The type of samples collected (soil, stream water, vegetation, bedrock, etc.)
Post-collection treatment of the samples (e.g. sieving of soil samples into different particle size fractions)
Methodology of chemical analysis
describe how the discipline has evolved from its beginnings in Russia in the 1930s. The first surveys were aimed at mineral exploration. In recent years, many surveys have emphasised a more broad-based environmental mapping approach. Numerous government agencies around the world have initiated multi-year systematic geochemical mapping projects, aimed at producing baseline geochemical maps of very large areas. See, for example, the description by of the British Geological Survey’s G-BASE project.
References
Geochemistry | Regional geochemistry | Chemistry | 199 |
23,716,097 | https://en.wikipedia.org/wiki/Time-lapse%20microscopy | Time-lapse microscopy is time-lapse photography applied to microscopy. Microscope image sequences are recorded and then viewed at a greater speed to give an accelerated view of the microscopic process.
Before the introduction of the video tape recorder in the 1960s, time-lapse microscopy recordings were made on photographic film. During this period, time-lapse microscopy was referred to as microcinematography. With the increasing use of video recorders, the term time-lapse video microscopy was gradually adopted. Today, the term video is increasingly dropped, reflecting that a digital still camera is used to record the individual image frames, instead of a video recorder.
Applications
Time-lapse microscopy can be used to observe any microscopic object over time. However, its main use is within cell biology to observe artificially cultured cells. Depending on the cell culture, different microscopy techniques can be applied to enhance characteristics of the cells as most cells are transparent.
To enhance observations further, cells have therefore traditionally been stained before observation. Unfortunately, the staining process kills the cells. The development of less destructive staining methods and methods to observe unstained cells has led to that cell biologists increasingly observe living cells. This is known as live-cell imaging. A few tools have been developed to identify and analyze single cells during live-cell imaging.
Time-lapse microscopy is the method that extends live-cell imaging from a single observation in time to the observation of cellular dynamics over long periods of time. Time-lapse microscopy is primarily used in research, but is clinically used in IVF clinics as studies has proven it to increase pregnancy rates, lower abortion rates and predict aneuploidy
Modern approaches are further extending time-lapse microscopy observations beyond making movies of cellular dynamics.
Traditionally, cells have been observed in a microscope and measured in a cytometer. Increasingly this boundary is blurred as cytometric techniques are being integrated with imaging techniques for monitoring and measuring dynamic activities of cells and subcellular structures.
History
The Cheese Mites by Martin Duncan from 1903 is one of the earliest microcinematographic films. However, the early development of scientific microcinematography took place in Paris. The first reported time-lapse microscope was assembled in the late 1890s at the Marey Institute, founded by the pioneer of chronophotography, Étienne-Jules Marey. It was, however, Jean Comandon who made the first significant scientific contributions around 1910.
Comandon was a trained microbiologist specializing in syphilis research.
Inspired by Victor Henri's microcinematic work on Brownian motion, he used the newly invented ultramicroscope to study the movements of the syphilis bacteria.
At the time, the ultramicroscope was the only microscope in which the thin spiral shaped bacteria was visible.
Using an enormous cinema camera bolted to the fragile microscope, he demonstrated visually that the
movement of the disease-causing bacteria is uniquely different from the non-disease-causing form.
Comandon's films proved instrumental in teaching doctors how to distinguish the two forms.
Comandon's extensive pioneering work inspired others to adopt microcinematography. Heniz Rosenberger builds a microcinematograph in the mid-1920s. In collerboration with Alexis Carrel, they used the device to further develop Carrel's cell culturing techniques. Similar work was conducted by Warren Lewis.
During World War II, Carl Zeiss AG released the first phase-contrast microscope on the market.
With this new microscope, cellular details could for the first time be observed without using lethal stains.
By setting up some of the first time-lapse experiments with chicken fibroblasts and a phase-contrast microscope,
Michael Abercrombie described the basis of our current understanding of cell migration in 1953.
With the broad introduction of the digital camera at the beginning of this century, time-lapse microscopy has been made dramatically more accessible and is currently experiencing an unrepresented raise in scientific publications.
See also
Live-cell imaging
Live single-cell imaging
Cytometry
Time-lapse photography
References
External links
Introduction to Live-Cell Imaging Techniques by Florida State University
Historic time-lapse microscopy films
1903 – Cheese Mites by Martin Duncan
1909 – Syphilis spirochaeta pallida by Jean Comandon
1939 – Normal and abnormal white blood cells in tissue cultures by Warren Lewis
1943 – The early cell division stage of grasshopper sperm cells shown using phase contrast time-lapse microscopy by Kurt Michel, Carl Zeiss AG
Microscopy
Cell imaging
Microbiology techniques
Laboratory techniques
Laboratory equipment
Biological techniques and tools
Articles containing video clips | Time-lapse microscopy | Chemistry,Biology | 938 |
15,354,706 | https://en.wikipedia.org/wiki/MRPS26 | 28S ribosomal protein S26, mitochondrial is a protein that in humans is encoded by the MRPS26 gene.
Mammalian mitochondrial ribosomal proteins are encoded by nuclear genes and help in protein synthesis within the mitochondrion. Mitochondrial ribosomes (mitoribosomes) consist of a small 28S subunit and a large 39S subunit. They have an estimated 75% protein to rRNA composition compared to prokaryotic ribosomes, where this ratio is reversed. Another difference between mammalian mitoribosomes and prokaryotic ribosomes is that the latter contain a 5S rRNA. Among different species, the proteins comprising the mitoribosome differ greatly in sequence, and sometimes in biochemical properties, which prevents easy recognition by sequence homology. This gene encodes a 28S subunit protein. This gene lies adjacent to and downstream of the gonadotropin-releasing hormone precursor gene.
References
Further reading
External links
Ribosomal proteins | MRPS26 | Chemistry | 199 |
31,555,901 | https://en.wikipedia.org/wiki/Ethernet%20Global%20Data%20Protocol | Ethernet Global Data (EGD) is a protocol that enables producer (server) to share a portion of its memory to all the consumers (clients) at a scheduled periodic rate. This protocol is developed for GE Fanuc PLCs to exchange data between PLCs / Drive Systems / HMI/SCADA systems. The protocol uses UDP over Ethernet layers for exchanging the data. A snapshot of internal reference memory, mediated by an Ethernet interface, is referred to as an exchange. An exchange does not require a reply and is identified by a unique combination of three major identifiers.
The Producer ID (the producer's IP address)
The Exchange ID (the exchange's identifier)
The Adapter Name (the Ethernet interface identifier)
EGD is implemented using classes.
Class 0 - supports configured exchanges only (implemented in most PACSystems CPUs)
Class 1 - supports all class 0 services plus programmed EGD exchanges that can be used to read and write other devices on an ad-hoc basis
Class 2 - supports all class 1 services plus acts as a responder for programmed EGD exchanges (implemented by Ethernet interface module only)
Class 3 - supports all class 2 services plus static configuration from an EGD configuration server
Class 4 - supports all class 3 services plus dynamically bound configuration from an EGD configuration server
External links
Industrial computing
Industrial Ethernet | Ethernet Global Data Protocol | Technology,Engineering | 282 |
61,344,346 | https://en.wikipedia.org/wiki/Borate%20fluoride | The borate fluorides or fluoroborates are compounds containing borate or complex borate ions along with fluoride ions that form salts with cations such as metals. They are in the broader category of mixed anion compounds. They are not to be confused with tetrafluoroborates (BF4) or the fluorooxoborates which have fluorine bonded to boron.
Examples
References
Borates
Fluorides
Mixed anion compounds | Borate fluoride | Physics,Chemistry | 98 |
16,706,608 | https://en.wikipedia.org/wiki/Phase-field%20model | A phase-field model is a mathematical model for solving interfacial problems. It has mainly been applied to solidification dynamics, but it has also been applied to other situations such as viscous fingering, fracture mechanics, hydrogen embrittlement, and vesicle dynamics.
The method substitutes boundary conditions at the interface by a partial differential equation for the evolution of an auxiliary field (the phase field) that takes the role of an order parameter. This phase field takes two distinct values (for instance +1 and −1) in each of the phases, with a smooth change between both values in the zone around the interface, which is then diffuse with a finite width. A discrete location of the interface may be defined as the collection of all points where the phase field takes a certain value (e.g., 0).
A phase-field model is usually constructed in such a way that in the limit of an infinitesimal interface width (the so-called sharp interface limit) the correct interfacial dynamics are recovered. This approach permits to solve the problem by integrating a set of partial differential equations for the whole system, thus avoiding the explicit treatment of the boundary conditions at the interface.
Phase-field models were first introduced by Fix and Langer, and have experienced a growing interest in solidification and other areas. Langer, had handwritten notes where he showed you could use coupled Cahn-Hilliard and Allen-Cahn equations to solve a solidification problem. George Fix worked on programing problem. Langer felt, at the time, that the method was of no practical use since the interface thickness is so small compared to the size of a typical microstructure, so he never bothered publishing them.
Equations of the phase-field model
Phase-field models are usually constructed in order to reproduce a given interfacial dynamics. For instance, in solidification problems the front dynamics is given by a diffusion equation for either concentration or temperature in the bulk and some boundary conditions at the interface (a local equilibrium condition and a conservation law), which constitutes the sharp interface model.
A number of formulations of the phase-field model are based on a free energy function depending on an order parameter (the phase field) and a diffusive field (variational formulations). Equations of the model are then obtained by using general relations of statistical physics. Such a function is constructed from physical considerations, but contains a parameter or combination of parameters related to the interface width. Parameters of the model are then chosen by studying the limit of the model with this width going to zero, in such a way that one can identify this limit with the intended sharp interface model.
Other formulations start by writing directly the phase-field equations, without referring to any thermodynamical functional (non-variational formulations). In this case the only reference is the sharp interface model, in the sense that it should be recovered when performing the small interface width limit of the phase-field model.
Phase-field equations in principle reproduce the interfacial dynamics when the interface width is small compared with the smallest length scale in the problem. In solidification this scale is the capillary length , which is a microscopic scale. From a computational point of view integration of partial differential equations resolving such a small scale is prohibitive. However, Karma and Rappel introduced the thin interface limit, which permitted to relax this condition and has opened the way to practical quantitative simulations with phase-field models.
With the increasing power of computers and the theoretical progress in phase-field modelling, phase-field models have become a useful tool for the numerical simulation of interfacial problems.
Variational formulations
A model for a phase field can be constructed by physical arguments if one has an explicit expression for the free energy of the system. A simple example for solidification problems is the following:
where is the phase field, , is the local enthalpy per unit volume, is a certain polynomial function of , and (where is the latent heat, is the melting temperature, and is the specific heat). The term with corresponds to the interfacial energy. The function is usually taken as a double-well potential describing the free energy density of the bulk of each phase, which themselves correspond to the two minima of the function . The constants and have respectively dimensions of energy per unit length and energy per unit volume. The interface width is then given by .
The phase-field model can then be obtained from the following variational relations:
where D is a diffusion coefficient for the variable , and and are stochastic terms accounting for thermal fluctuations (and whose statistical properties can be obtained from the fluctuation dissipation theorem). The first equation gives an equation for the evolution of the phase field, whereas the second one is a diffusion equation, which usually is rewritten for the temperature or for the concentration (in the case of an alloy). These equations are, scaling space with and times with :
where is the nondimensional interface width, , and , are nondimensionalized noises.
Alternative energy-density functions
The choice of free energy function, , can have a significant effect on the physical behaviour of the interface, and should be selected with care. The double-well function represents an approximation of the Van der Waals equation of state near the critical point, and has historically been used for its simplicity of implementation when the phase-field model is employed solely for interface tracking purposes. But this has led to the frequently observed spontaneous drop shrinkage phenomenon, whereby the high phase miscibility predicted by an Equation of State near the critical point allows significant interpenetration of the phases and can eventually lead to the complete disappearance of a droplet whose radius is below some critical value. Minimizing perceived continuity losses over the duration of a simulation requires limits on the Mobility parameter, resulting in a delicate balance between interfacial smearing due to convection, interfacial reconstruction due to free energy minimization (i.e. mobility-based diffusion), and phase interpenetration, also dependent on the mobility. A recent review of alternative energy density functions for interface tracking applications has proposed a modified form of the double-obstacle function which avoids the spontaneous drop shrinkage phenomena and limits on mobility, with comparative results provide for a number of benchmark simulations using the double-well function and the volume-of-fluid sharp interface technique. The proposed implementation has a computational complexity only slightly greater than that of the double-well function, and may prove useful for interface tracking applications of the phase-field model where the duration/nature of the simulated phenomena introduces phase continuity concerns (i.e. small droplets, extended simulations, multiple interfaces, etc.).
Sharp interface limit of the phase-field equations
A phase-field model can be constructed to purposely reproduce a given interfacial dynamics as represented by a sharp interface model. In such a case the sharp interface limit (i.e. the limit when the interface width goes to zero) of the proposed set of phase-field equations should be performed. This limit is usually taken by asymptotic expansions of the fields of the model in powers of the interface width . These expansions are performed both in the interfacial region (inner expansion) and in the bulk (outer expansion), and then are asymptotically matched order by order. The result gives a partial differential equation for the diffusive field and a series of boundary conditions at the interface, which should correspond to the sharp interface model and whose comparison with it provides the values of the parameters of the phase-field model.
Whereas such expansions were in early phase-field models performed up to the lower order in only, more recent models use higher order asymptotics (thin interface limits) in order to cancel undesired spurious effects or to include new physics in the model. For example, this technique has permitted to cancel kinetic effects, to treat cases with unequal diffusivities in the phases, to model viscous fingering and two-phase Navier–Stokes flows, to include fluctuations in the model, etc.
Multiphase-field models
In multiphase-field models, microstructure is described by set of order parameters, each of which is related to a specific phase or crystallographic orientation. This model is mostly used for solid-state phase transformations where multiple grains evolve (e.g. grain growth, recrystallization or first-order transformation like austenite to ferrite in ferrous alloys). Besides allowing the description of multiple grains in a microstructure, multiphase-field models especially allow for consideration of multiple thermodynamic phases occurring e.g. in technical alloy grades.
Phase-field models on graphs
Many of the results for continuum phase-field models have discrete analogues for graphs, just replacing calculus with calculus on graphs.
Phase Field Modeling in Fracture Mechanics
Fracture in solids is often numerically analyzed within a finite element context using either discrete or diffuse crack representations. Approaches using a finite element representation often make use of strong discontinuities embedded at the intra-element level and often require additional criteria based on, e.g., stresses, strain energy densities or energy release rates or other special treatments such as virtual crack closure techniques and remeshing to determine crack paths. In contrast, approaches using a diffuse crack representation retain the continuity of the displacement field, such as continuum damage models and phase-field fracture theories. The latter traces back to the reformulation of Griffith’s principle in a variational form and has similarities to gradient-enhanced damage-type models. Perhaps the most attractive characteristic of phase-field approaches to fracture is that crack initiation and crack paths are automatically obtained from a minimization problem that couples the elastic and fracture energies. In many situations, crack nucleation can be properly accounted for by following branches of critical points associated with elastic solutions until they lose stability. In particular, phase-field models of fracture can allow nucleation even when the elastic strain energy density is spatially constant.
A limitation of this approach is that nucleation is based on strain energy density and not stress. An alternative view based on introducing a nucleation driving force seeks to address this issue.
Phase Field Models for Collective Cell Migration
A group of biological cells can self-propel in a complex way due to the consumption of Adenosine triphosphate. Interactions between cells like cohesion or several chemical cues can produce movement in a coordinated manner, this phenomenon is called "Collective cell migration". A theoretical model for these phenomena is the phase-field model and incorporates a phase field for each cell species and additional field variables like chemotactic agent concentration. Such a model can be used for phenomena like cancer, cell extrusion, wound healing, morphogenesis and ectoplasm phenomena.
Software
PACE3D – Parallel Algorithms for Crystal Evolution in 3D is a parallelized phase-field simulation package including multi-phase multi-component transformations, large scale grain structures and coupling with fluid flow, elastic, plastic and magnetic interactions. It is developed at the Karlsruhe University of Applied Sciences and Karlsruhe Institute of Technology.
The Mesoscale Microstructure Simulation Project (MMSP) is a collection of C++ classes for grid-based microstructure simulation.
The MICRostructure Evolution Simulation Software (MICRESS) is a multi-component, multiphase-field simulation package coupled to thermodynamic and kinetic databases. It is developed and maintained by ACCESS e.V .
MOOSE massively parallel open source C++ multiphysics finite-element framework with support for phase-field simulations developed at Idaho National Laboratory.
PhasePot is a Windows-based microstructure simulation tool, using a combination of phase-field and Monte Carlo Potts models.
OpenPhase is an open source software for the simulation of microstructure formation in systems undergoing first order phase transformation based on the multiphase field model.
mef90/vDef is an open source variational phase-field fracture simulator based on the theory developed in.
MicroSim is a software stack that consists of phase-field codes that offer flexibility with discretization, models as well as the high-performance computing hardware(CPU/GPU) that they can execute on.
PRISMS-PF is a massively parallel finite element code for conducting phase-field and other related simulations of microstructure evolution. It is based on the deal.II finite element library and developed and maintained by the PRISMS Center at the University of Michigan.
Celadro-3D is a three-dimensional extension of Celadro that utilizes multiphase-field modeling to capture the collective dynamics of active liquid droplets, such as living cells, offering a flexible platform to incorporate physics-based models for active matter.
References
Further reading
a review of phase-field models.
Provatas, Nikolas; Elder, Ken (2010). Phase-Field Methods in Materials Science and Engineering. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. .
Steinbach, I.: "Quantum-Phase-Field Concept of Matter: Emergent Gravity in the Dynamic Universe", Zeitschrift für Naturforschung A 72 1 (2017)
Schmitz, G.J.: "A Combined Entropy/Phase-Field Approach to Gravity", Entropy 2017, 19(4) 151;
Mathematical modeling
Materials science | Phase-field model | Physics,Materials_science,Mathematics,Engineering | 2,760 |
1,055,399 | https://en.wikipedia.org/wiki/Barium%20chloride | Barium chloride is an inorganic compound with the formula . It is one of the most common water-soluble salts of barium. Like most other water-soluble barium salts, it is a white powder, highly toxic, and imparts a yellow-green coloration to a flame. It is also hygroscopic, converting to the dihydrate , which are colourless crystals with a bitter salty taste. It has limited use in the laboratory and industry.
Preparation
On an industrial scale, barium chloride is prepared via a two step process from barite (barium sulfate). The first step requires high temperatures.
The second step requires reaction between barium sulfide and hydrogen chloride:
or between barium sulfide and calcium chloride:
In place of HCl, chlorine can be used. Barium chloride is extracted out from the mixture with water. From water solutions of barium chloride, its dihydrate () can be crystallized as colorless crystals.
Barium chloride can in principle be prepared by the reaction between barium hydroxide or barium carbonate with hydrogen chloride. These basic salts react with hydrochloric acid to give hydrated barium chloride.
Structure and properties
crystallizes in two forms (polymorphs). At room temperature, the compound is stable in the orthorhombic cotunnite () structure, whereas the cubic fluorite structure () is stable between 925 and 963 °C. Both polymorphs accommodate the preference of the large ion for coordination numbers greater than six. The coordination of is 8 in the fluorite structure and 9 in the cotunnite structure. When cotunnite-structure is subjected to pressures of 7–10 GPa, it transforms to a third structure, a monoclinic post-cotunnite phase. The coordination number of increases from 9 to 10.
In aqueous solution behaves as a simple salt; in water it is a 1:2 electrolyte and the solution exhibits a neutral pH. Its solutions react with sulfate ion to produce a thick white solid precipitate of barium sulfate.
This precipitation reaction is used in chlor-alkali plants to control the sulfate concentration in the feed brine for electrolysis.
Oxalate effects a similar reaction:
When it is mixed with sodium hydroxide, it gives barium hydroxide, which is moderately soluble in water.
is stable in the air at room temperature, but loses one water of crystallization above , becoming , and becomes anhydrous above . may be formed by shaking the dihydrate with methanol.
readily forms eutectics with alkali metal chlorides.
Uses
Although inexpensive, barium chloride finds limited applications in the laboratory and industry.
Its main laboratory use is as a reagent for the gravimetric determination of sulfates. The sulfate compound being analyzed is dissolved in water and hydrochloric acid is added. When barium chloride solution is added, the sulfate present precipitates as barium sulfate, which is then filtered through ashless filter paper. The paper is burned off in a muffle furnace, the resulting barium sulfate is weighed, and the purity of the sulfate compound is thus calculated.
In industry, barium chloride is mainly used in the purification of brine solution in caustic chlorine plants and also in the manufacture of heat treatment salts, case hardening of steel. It is also used to make red pigments such as Lithol red and Red Lake C. Its toxicity limits its applicability.
Toxicity
Barium chloride, along with other water-soluble barium salts, is highly toxic. It irritates eyes and skin, causing redness and pain. It damages kidneys. Fatal dose of barium chloride for a human has been reported to be about 0.8-0.9 g. Systemic effects of acute barium chloride toxicity include abdominal pain, diarrhea, nausea, vomiting, cardiac arrhythmia, muscular paralysis, and death. The ions compete with the ions, causing the muscle fibers to be electrically unexcitable, thus causing weakness and paralysis of the body. Sodium sulfate and magnesium sulfate are potential antidotes because they form barium sulfate BaSO4, which is relatively non-toxic because of its insolubility in water.
Barium chloride is not classified as a human carcinogen.
References
External links
International Chemical Safety Card 0614. (anhydrous)
International Chemical Safety Card 0615. (dihydrate)
Barium chloride's use in industry.
ChemSub Online: Barium chloride.
Chlorides
Alkaline earth metal halides
Barium compounds
Inorganic compounds
Pyrotechnic colorants
Fluorite crystal structure | Barium chloride | Chemistry | 979 |
1,912 | https://en.wikipedia.org/wiki/Ampicillin | Ampicillin is an antibiotic belonging to the aminopenicillin class of the penicillin family. The drug is used to prevent and treat several bacterial infections, such as respiratory tract infections, urinary tract infections, meningitis, salmonellosis, and endocarditis. It may also be used to prevent group B streptococcal infection in newborns. It is used by mouth, by injection into a muscle, or intravenously.
Common side effects include rash, nausea, and diarrhea. It should not be used in people who are allergic to penicillin. Serious side effects may include Clostridioides difficile colitis or anaphylaxis. While usable in those with kidney problems, the dose may need to be decreased. Its use during pregnancy and breastfeeding appears to be generally safe.
Ampicillin was discovered in 1958 and came into commercial use in 1961. It is on the World Health Organization's List of Essential Medicines. The World Health Organization classifies ampicillin as critically important for human medicine. It is available as a generic medication.
Medical uses
Diseases
Bacterial meningitis; an aminoglycoside can be added to increase efficacy against gram-negative meningitis bacteria
Endocarditis by enterococcal strains (off-label use); often given with an aminoglycoside
Gastrointestinal infections caused by contaminated water or food (for example, by Salmonella)
Genito-urinary tract infections
Healthcare-associated infections that are related to infections from using urinary catheters and that are unresponsive to other medications
Otitis media (middle ear infection)
Prophylaxis (i.e. to prevent infection) in those who previously had rheumatic heart disease or are undergoing dental procedures, vaginal hysterectomies, or C-sections. It is also used in pregnant woman who are carriers of group B streptococci to prevent early-onset neonatal infections.
Respiratory infections, including bronchitis, pharyngitis
Sinusitis
Sepsis
Whooping cough, to prevent and treat secondary infections
Ampicillin used to also be used to treat gonorrhea, but there are now too many strains resistant to penicillins.
Bacteria
Ampicillin is used to treat infections by many gram-positive and gram-negative bacteria. It was the first "broad spectrum" penicillin with activity against gram-positive bacteria, including Streptococcus pneumoniae, Streptococcus pyogenes, some isolates of Staphylococcus aureus (but not penicillin-resistant or methicillin-resistant strains), Trueperella, and some Enterococcus. It is one of the few antibiotics that works against multidrug resistant Enterococcus faecalis and E. faecium. Activity against gram-negative bacteria includes Neisseria meningitidis, some Haemophilus influenzae, and some of the Enterobacteriaceae (though most Enterobacteriaceae and Pseudomonas are resistant). Its spectrum of activity is enhanced by co-administration of sulbactam, a drug that inhibits beta lactamase, an enzyme produced by bacteria to inactivate ampicillin and related antibiotics. It is sometimes used in combination with other antibiotics that have different mechanisms of action, like vancomycin, linezolid, daptomycin, and tigecycline.
Available forms
Ampicillin can be administered by mouth, an intramuscular injection (shot) or by intravenous infusion. The oral form, available as capsules or oral suspensions, is not given as an initial treatment for severe infections, but rather as a follow-up to an IM or IV injection. For IV and IM injections, ampicillin is kept as a powder that must be reconstituted.
IV injections must be given slowly, as rapid IV injections can lead to convulsive seizures.
Specific populations
Ampicillin is one of the most used drugs in pregnancy, and has been found to be generally harmless both by the Food and Drug Administration in the U.S. (which classified it as category B) and the Therapeutic Goods Administration in Australia (which classified it as category A). It is the drug of choice for treating Listeria monocytogenes in pregnant women, either alone or combined with an aminoglycoside. Pregnancy increases the clearance of ampicillin by up to 50%, and a higher dose is thus needed to reach therapeutic levels.
Ampicillin crosses the placenta and remains in the amniotic fluid at 50–100% of the concentration in maternal plasma; this can lead to high concentrations of ampicillin in the newborn.
While lactating mothers secrete some ampicillin into their breast milk, the amount is minimal.
In newborns, ampicillin has a longer half-life and lower plasma protein binding. The clearance by the kidneys is lower, as kidney function has not fully developed.
Contraindications
Ampicillin is contraindicated in those with a hypersensitivity to penicillins, as they can cause fatal anaphylactic reactions. Hypersensitivity reactions can include frequent skin rashes and hives, exfoliative dermatitis, erythema multiforme, and a temporary decrease in both red and white blood cells.
Ampicillin is not recommended in people with concurrent mononucleosis, as over 40% of patients develop a skin rash.
Side effects
Ampicillin is comparatively less toxic than other antibiotics, and side effects are more likely in those who are sensitive to penicillins and those with a history of asthma or allergies. In very rare cases, it causes severe side effects such as angioedema, anaphylaxis, and C. difficile infection (that can range from mild diarrhea to serious pseudomembranous colitis). Some develop black "furry" tongue. Serious adverse effects also include seizures and serum sickness. The most common side effects, experienced by about 10% of users are diarrhea and rash. Less common side effects can be nausea, vomiting, itching, and blood dyscrasias. The gastrointestinal effects, such as hairy tongue, nausea, vomiting, diarrhea, and colitis, are more common with the oral form of penicillin. Other conditions may develop up several weeks after treatment.
Overdose
Ampicillin overdose can cause behavioral changes, confusion, blackouts, and convulsions, as well as neuromuscular hypersensitivity, electrolyte imbalance, and kidney failure.
Interactions
Ampicillin reacts with probenecid and methotrexate to decrease renal excretion. Large doses of ampicillin can increase the risk of bleeding with concurrent use of warfarin and other oral anticoagulants, possibly by inhibiting platelet aggregation. Ampicillin has been said to make oral contraceptives less effective, but this has been disputed. It can be made less effective by other antibiotic, such as chloramphenicol, erythromycin, cephalosporins, and tetracyclines. For example, tetracyclines inhibit protein synthesis in bacteria, reducing the target against which ampicillin acts. If given at the same time as aminoglycosides, it can bind to it and inactivate it. When administered separately, aminoglycosides and ampicillin can potentiate each other instead.
Ampicillin causes skin rashes more often when given with allopurinol.
Both the live cholera vaccine and live typhoid vaccine can be made ineffective if given with ampicillin. Ampicillin is normally used to treat cholera and typhoid fever, lowering the immunological response that the body has to mount.
Pharmacology
Mechanism of action
Ampicillin is in the penicillin group of beta-lactam antibiotics and is part of the aminopenicillin family. It is roughly equivalent to amoxicillin in terms of activity. Ampicillin is able to penetrate gram-positive and some gram-negative bacteria. It differs from penicillin G, or benzylpenicillin, only by the presence of an amino group. This amino group, present on both ampicillin and amoxicillin, helps these antibiotics pass through the pores of the outer membrane of gram-negative bacteria, such as Escherichia coli, Proteus mirabilis, Salmonella enterica, and Shigella.
Ampicillin acts as an irreversible inhibitor of the enzyme transpeptidase, which is needed by bacteria to make the cell wall. It inhibits the third and final stage of bacterial cell wall synthesis in binary fission, which ultimately leads to cell lysis; therefore, ampicillin is usually bacteriolytic.
Pharmacokinetics
Ampicillin is well-absorbed from the GI tract (though food reduces its absorption), and reaches peak concentrations in one to two hours. The bioavailability is around 62% for parenteral routes. Unlike other penicillins, which usually bind 60–90% to plasma proteins, ampicillin binds to only 15–20%.
Ampicillin is distributed through most tissues, though it is concentrated in the liver and kidneys. It can also be found in the cerebrospinal fluid when the meninges become inflamed (such as, for example, meningitis). Some ampicillin is metabolized by hydrolyzing the beta-lactam ring to penicilloic acid, though most of it is excreted unchanged. In the kidneys, it is filtered out mostly by tubular secretion; some also undergoes glomerular filtration, and the rest is excreted in the feces and bile.
Hetacillin and pivampicillin are ampicillin esters that have been developed to increase bioavailability.
History
Ampicillin has been used extensively to treat bacterial infections since 1961. Until the introduction of ampicillin by the British company Beecham, penicillin therapies had only been effective against gram-positive organisms such as staphylococci and streptococci. Ampicillin (originally branded as "Penbritin") also demonstrated activity against gram-negative organisms such as H. influenzae, coliforms, and Proteus spp.
Society and culture
Economics
Ampicillin is relatively inexpensive. In the United States, it is available as a generic medication.
Veterinary use
In veterinary medicine, ampicillin is used in cats, dogs, and farm animals to treat:
Anal gland infections
Cutaneous infections, such as abscesses, cellulitis, and pustular dermatitis
E. coli and Salmonella infections in cattle, sheep, and goats (oral form). Ampicillin use for this purpose had declined as bacterial resistance has increased.
Mastitis in sows
Mixed aerobic–anaerobic infections, such as from cat bites
Multidrug-resistant Enterococcus faecalis and E. faecium
Prophylactic use in poultry against Salmonella and sepsis from E. coli or Staphylococcus aureus
Respiratory tract infections, including tonsilitis, bovine respiratory disease, shipping fever, bronchopneumonia, and calf and bovine pneumonia
Urinary tract infections in dogs
Horses are generally not treated with oral ampicillin, as they have low bioavailability of beta-lactams.
The half-life in animals is around that same of that in humans (just over an hour). Oral absorption is less than 50% in cats and dogs, and less than 4% in horses.
References
External links
Enantiopure drugs
Penicillins
Phenyl compounds
World Health Organization essential medicines
Wikipedia medicine articles ready to translate | Ampicillin | Chemistry | 2,481 |
65,184 | https://en.wikipedia.org/wiki/QNX | QNX ( or ) is a commercial Unix-like real-time operating system, aimed primarily at the embedded systems market.
The product was originally developed in the early 1980s by Canadian company Quantum Software Systems, founded March 30, 1980, and later renamed QNX Software Systems.
, it is used in a variety of devices including automobiles, medical devices, program logic controllers, automated manufacturing, trains, and more.
History
Gordon Bell and Dan Dodge, both students at the University of Waterloo in 1980, took a course in real-time operating systems, in which the students constructed a basic real-time microkernel and user programs. Both were convinced there was a commercial need for such a system, and moved to the high-tech planned community Kanata, Ontario, to start Quantum Software Systems that year. In 1982, the first version of QUNIX was released for the Intel 8088 CPU. In 1984, Quantum Software Systems renamed QUNIX to QNX in an effort to avoid any trademark infringement challenges.
One of the first widespread uses of the QNX real-time OS (RTOS) was in the nonembedded world when it was selected as the operating system for the Ontario education system's own computer design, the Unisys ICON. Over the years QNX was used mostly for larger projects, as its 44k kernel was too large to fit inside the one-chip computers of the era. The system garnered a reputation for reliability and became used in running machinery in many industrial applications.
In the late-1980s, Quantum realized that the market was rapidly moving towards the Portable Operating System Interface (POSIX) model and decided to rewrite the kernel to be much more compatible at a low level. The result was QNX 4. During this time Patrick Hayden, while working as an intern, along with Robin Burgener (a full-time employee at the time), developed a new windowing system. This patented concept was developed into the embeddable graphical user interface (GUI) named the QNX Photon microGUI. QNX also provided a version of the X Window System.
To demonstrate the OS's capability and relatively small size, in the late 1990s QNX released a demo image that included the POSIX-compliant QNX 4 OS, a full graphical user interface, graphical text editor, TCP/IP networking, web browser and web server that all fit on a bootable 1.44 MB floppy disk for the 386 PC.
Toward the end of the 1990s, the company, then named QNX Software Systems, began work on a new version of QNX, designed from the ground up to be symmetric multiprocessing (SMP) capable, and to support all current POSIX application programming interfaces (APIs) and any new POSIX APIs that could be anticipated while still retaining the microkernel architecture. This resulted in QNX Neutrino, released in 2001.
Along with the Neutrino kernel, QNX Software Systems became a founding member of the Eclipse (integrated development environment) consortium. The company released a suite of Eclipse plug-ins packaged with the Eclipse workbench in 2002, and named QNX Momentics Tool Suite.
In 2004, the company announced it had been sold to Harman International Industries. Before this acquisition, QNX software was already widely used in the automotive industry for telematics systems. Since the purchase by Harman, QNX software has been designed into over 200 different automobile makes and models, in telematics systems, and in infotainment and navigation units. The QNX CAR Application Platform was running in over 20 million vehicles as of mid-2011. The company has since released several middleware products including the QNX Aviage Multimedia Suite, the QNX Aviage Acoustic Processing Suite and the QNX HMI Suite.
The microkernels of Cisco Systems' IOS-XR (ultra high availability IOS, introduced 2004) and IOS Software Modularity (introduced 2006) were based on QNX. IOS Software Modularity never gained traction and was limited only to small run for Catalyst 6500, while IOS XR moved to Linux as of release 6.x.
In September 2007, QNX Software Systems announced the availability of some of its source code.
On April 9, 2010, Research In Motion (later renamed to BlackBerry Limited) announced they would acquire QNX Software Systems from Harman International Industries. On the same day, QNX source code access was restricted from the public and hobbyists.
In September 2010, the company announced a tablet computer, the BlackBerry PlayBook, and a new operating system BlackBerry Tablet OS based on QNX to run on the tablet.
On October 18, 2011, Research In Motion announced "BBX", which was later renamed BlackBerry 10, in December 2011. Blackberry 10 devices build upon the BlackBerry PlayBook QNX based operating system for touch devices, but adapt the user interface for smartphones using the Qt based Cascades Native User-Interface framework.
At the Geneva Motor Show, Apple demonstrated CarPlay which provides an iOS-like user interface to head units in compatible vehicles. Once configured by the automaker, QNX can be programmed to hand off its display and some functions to an Apple CarPlay device.
On December 11, 2014, Ford Motor Company stated that it would replace Microsoft Auto with QNX.
In January 2017, QNX announced the upcoming release of its SDP 7.0, with support for Intel and ARM 32- and 64-bit platforms, and support for C++14. It was released in March 2017.
In December 2023, QNX released QNX SDP 8.0 which is powered by a next generation microkernel with support for the latest Intel and ARM [v8 and v9] 64 bit platforms, GCC12 based toolchain and a QNX toolkit for Visual Studio Code.
On July 17, 2024, QNX launched QNX Containers, providing a standards-based environment for the deployment, execution, and management of container technology on QNX-based devices.
On September 14, 2024, QNX Filesystem for Safety (QFS) was announced. QFS is a POSIX-compliant, ISO 26262 certified, integrity checking filesystem to provide OEMs and other embedded software suppliers an additional layer of validation when building safety-critical systems.
On January 2, 2025, BlackBerry unveiled the strategic relaunch of the QNX brand. Previously named ‘BlackBerry IoT’, the decision to rename the division ‘QNX’ and relaunch the QNX brand is part of a broader strategy to increase visibility and fortify leadership within the automotive and embedded industries.
On January 6, 2025, QNX, Vector, and TTTech Auto announced a multi-year, global undertaking to collaborate, develop and market a foundational vehicle software platform for software integration. This vehicle software platform is pre-integrated, lightweight, and certified to the automotive industry’s highest functional safety (ISO 26262 ASIL D) and security (ISO 21434) standards.
At CES 2025, QNX announced it is collaborating with Microsoft to make it easier for automakers to build, test, and refine software within the cloud, accelerating the development of Software-Defined Vehicles (SDVs). QNX confirmed that its Software Development Platform (SDP) 8.0 would be coming to Microsoft Azure as part of the collaboration.
At CES 2025, QNX launched QNX Cabin, its industry-first automotive software solution designed to accelerate digital cockpit development. QNX Cabin aims to solve the problem of developing in mixed-criticality environments, blending safety-critical features (e.g. Advanced Driver Assistance Systems) running on the safety-certified QNX Operating System (OS) with consumer applications delivered via guest operating systems including Android Automotive and Linux.
QNX also revealed more details of its QNX Everywhere initiative at CES 2025. Intended to nurture and grow QNX’s worldwide developer community by giving free access to QNX Software Development Platform (SDP) 8.0 to students, schools, research organizations, and hobbyists, QNX Everywhere also includes complimentary resources and on-demand training.
Technology
As a microkernel-based OS, QNX is based on the idea of running most of the operating system kernel in the form of a number of small tasks, named Resource Managers. This differs from the more traditional monolithic kernel, in which the operating system kernel is one very large program composed of a huge number of parts, with special abilities. In the case of QNX, the use of a microkernel allows users (developers) to turn off any functions they do not need without having to change the OS. Instead, such services will simply not run.
The QNX kernel, procnto (also name of the binary executable program for the QNX Neutrino ('nto') process ('proc') itself), contains only CPU scheduling, interprocess communication, interrupt redirection and timers. Everything else runs as a user process, including a special process known as proc which performs process creation and memory management by operating in conjunction with the microkernel. This is made possible by two key mechanisms: subroutine-call type interprocess communication, and a boot loader which can load an image containing the kernel and any desired set of user programs and shared libraries. There are no device drivers in the kernel. The network stack is based on NetBSD code. Along with its support for its own, native, device drivers, QNX supports its legacy, io-net manager server, and the network drivers ported from NetBSD.
QNX interprocess communication consists of sending a message from one process to another and waiting for a reply. This is a single operation, called MsgSend. The message is copied, by the kernel, from the address space of the sending process to that of the receiving process. If the receiving process is waiting for the message, control of the CPU is transferred at the same time, without a pass through the CPU scheduler. Thus, sending a message to another process and waiting for a reply does not result in "losing one's turn" for the CPU. This tight integration between message passing and CPU scheduling is one of the key mechanisms that makes QNX message passing broadly usable. Most Unix and Linux interprocess communication mechanisms lack this tight integration, although a user space implementation of QNX-type messaging for Linux does exist. Mishandling of this subtle issue is a primary reason for the disappointing performance of some other microkernel systems such as early versions of Mach. The recipient process need not be on the same physical machine.
All I/O operations, file system operations, and network operations were meant to work through this mechanism, and the data transferred was copied during message passing. Later versions of QNX reduce the number of separate processes and integrate the network stack and other function blocks into single applications for performance reasons.
Message handling is prioritized by thread priority. Since I/O requests are performed using message passing, high priority threads receive I/O service before low priority threads, an essential feature in a hard real-time system.
The boot loader is the other key component of the minimal microkernel system. Because user programs can be built into the boot image, the set of device drivers and support libraries needed for startup need not be, and are not, in the kernel. Even such functions as program loading are not in the kernel, but instead are in shared user-space libraries loaded as part of the boot image. It is possible to put an entire boot image into ROM, which is used for diskless embedded systems.
Neutrino supports symmetric multiprocessing and processor affinity, called bound multiprocessing (BMP) in QNX terminology. BMP is used to improve cache hitting and to ease the migration of non-SMP safe applications to multi-processor computers.
Neutrino supports strict priority-preemptive scheduling and adaptive partition scheduling (APS). APS guarantees minimum CPU percentages to selected groups of threads, even though others may have higher priority. The adaptive partition scheduler is still strictly priority-preemptive when the system is underloaded. It can also be configured to run a selected set of critical threads strictly real time, even when the system is overloaded.
The QNX operating system also contained a web browser known as 'Voyager'.
Due to its microkernel architecture QNX is also a distributed operating system. Dan Dodge and Peter van der Veen hold based on the QNX operating system's distributed processing features known commercially as Transparent Distributed Processing. This allows the QNX kernels on separate devices to access each other's system services using effectively the same communication mechanism as is used to access local services.
Releases
Uses
The BlackBerry PlayBook tablet computer designed by BlackBerry uses a version of QNX as the primary operating system. The BlackBerry 10 operating system is also based on QNX.
QNX is also used in car infotainment systems with many major car makers offering variants that include an embedded QNX architecture. It is supported by popular SSL/TLS libraries such as wolfSSL.
Since the introduction of its "Safe Kernel 1.0" in 2010, QNX was projected and used subsequently in automated drive or ADAS systems for automotive projects that require a functional safety certified RTOS. QNX provides this with its QNX OS for Safety products.
QNX Neutrino (2001) has been ported to a number of platforms and now runs on practically any modern central processing unit (CPU) family that is used in the embedded market. This includes the PowerPC, x86, MIPS, SH-4, and the closely interrelated group of ARM, StrongARM, and XScale.
As of June 26, 2023, QNX software is now embedded in over 235 million vehicles worldwide, including most leading OEMs and Tier 1s, such as BMW, Bosch, Continental, Dongfeng Motor, Geely, Ford, Honda, Mercedes-Benz, Toyota, Volkswagen, Volvo, and more.
Licensing
QNX offers a license for noncommercial and academic users. In January 2024, BlackBerry introduced QNX Everywhere to make QNX more accessible to Hobbyists. QNX Everywhere was made publicly accessible in early 2024.
Community
OpenQNX is a QNX Community Portal established and run independently. An IRC channel and Newsgroups access via web is available. Diverse industries are represented by the developers on the site.
Foundry27 is a web-based QNX community established by the company. It serves as a hub to QNX Neutrino development where developers can register, choose the license, and get the source code and related toolkit of the RTOS.
QNX Board Support Packages
QNX Standard Support is available for a BSP that is listed below as available on QNX Software Center. For other BSPs, alternative forms of support (e.g., custom support plans, etc.) may be available or required from the “BSP Supplier” or “Board Vendor” indicated below.
BlackBerry QNX Partners
BlackBerry QNX has worked with a network of partner organizations to provide complementary technologies. These important relationships have ability to provide the foundational software, middleware, and services behind the world's most critical embedded systems.
See also
Comparison of operating systems
Android Auto
Android Automotive
Automotive Grade Linux
CarPlay
Ford Sync
HarmonyOS NEXT
OpenHarmony
Windows Embedded Automotive
References
Further reading
External links
Development for QNX phones
Foundry27
QNX User Community
Open source applications
GUIdebook > GUIs > QNX
QNX used for Canadian Nuclear Power Plants
QNX demo floppy disk
1980 establishments in Ontario
ARM operating systems
BlackBerry Limited
Computing platforms
Distributed operating systems
Embedded operating systems
Information technology companies of Canada
Lightweight Unix-like systems
Microkernel-based operating systems
Microkernels
Mobile operating systems
Proprietary operating systems
Real-time operating systems
Tablet operating systems
Software companies established in 1980
X86 operating systems
X86-64 operating systems | QNX | Technology | 3,291 |
42,744,533 | https://en.wikipedia.org/wiki/Lauri%20Love | Lauri Love (; born 14 December 1984, United Kingdom) is a British activist who was previously charged by the United States for his alleged activities with the hacker collective Anonymous. Love's case has been cited as precedent in the Julian Assange extradition proceedings.
Early life and education
Love is from Stradishall, Suffolk. His parents, Alexander Love, a prison chaplain at HM Prison Highpoint North, and Sirkka-Liisa Love (a Finnish citizen), who also works at the prison, live in Stradishall. He has dual citizenship of the United Kingdom and Finland.
After dropping out of sixth form college and working in a turkey plant, Love applied for a Finnish passport, and then served in the Finnish Army for six months, became a conscientious objector and finished another six months of his obligation in alternative civilian service.
After that, he applied at the University of Nottingham in England and dropped out in his second term after a physical and mental collapse, then at the University of Glasgow in Scotland, but dropped out in his second year, again for health reasons. He was part of the 2011 Hetherington House Occupation, a student protest at Glasgow University.
United States indictment
In January 2013, the website of the United States Sentencing Commission was replaced with a video protesting the treatment of activist Aaron Swartz who had committed suicide days earlier. The video claimed that those responsible had obtained secrets from the United States Army, Missile Defense Agency, and NASA but they were only ever released in encrypted form. The subsequent investigation named Lauri Love in two indictments (2013 in District of New Jersey, 2014 in Southern District of New York and Eastern District of Virginia) for allegedly "breaching thousands of computer systems in the United States and elsewhere – including the computer networks of federal agencies – to steal massive quantities of confidential data". The United States made an extradition request.
Love's attorney in America was Tor Ekeland.
National Crime Agency arrest
The National Crime Agency (NCA) arrested Love in October 2013. In February 2015, BBC News revealed that Love was taking legal action for the return of computers seized by the NCA when he was arrested.
In May 2016, Judge Nina Tempia of the Westminster Magistrates' Court ruled that Love did not have to tell the NCA what his passwords, or encryption keys, are.
Extradition hearing
During Love's two day extradition hearing on 28 and 29 June 2016 at the Westminster Magistrates' Court in London, his father testified that Lauri Love is autistic and so should not be extradited. Specifically, he testified that his son was not diagnosed autistic until he was an adult serving in the Finnish Army. Psychologist Simon Baron-Cohen, who diagnosed Love as autistic in 2012, testified that Love should not be extradited because of his diagnosed disorders, which also include eczema, psychosis, and depression. Baron-Cohen stated that Love told him that he would commit suicide if extradited.
Love, who lived at home with his parents, testified at his extradition hearing on 29 June 2016. He was supported by the Courage Foundation. Love's barrister for this extradition hearing was Ben Cooper of Doughty Street Chambers. The case was adjourned.
On 16 September 2016, at Westminster Magistrates' Court, a judge ruled that Love could be extradited to the United States. Love's solicitor Karen Todner said that they would appeal, and on 5 February 2018, Lord Chief Justice Lord Burnett and Mr Justice Ouseley, at the High Court, upheld his appeal against extradition because his extradition would be "oppressive by reason of his physical and mental condition".
Popular culture
In January 2018, it was announced that novelist Frederick Forsyth would publish a novel inspired by the Lauri Love and Gary McKinnon stories. The novel, The Fox, was released in Autumn 2018.
Personal life
As of the late 2010s, Love was in a long-term relationship with fashion model Sylvia Mann.
References
External links
1984 births
Alumni of the University of Suffolk
Anonymous (hacker group)
Computer law
English people of Finnish descent
English people of Scottish descent
Finnish people of British descent
Finnish people of Scottish descent
Living people
Hackers
People from the Borough of St Edmundsbury
People with Asperger syndrome
Finnish people with disabilities
English people with disabilities
Alumni of the University of Nottingham | Lauri Love | Technology | 888 |
24,457,768 | https://en.wikipedia.org/wiki/Lower%20Sava%20Statistical%20Region | The Lower Sava Statistical Region (; until December 31, 2014 ) is a statistical region in Slovenia. It has good traffic accessibility and is located in the Sava and Krka Valleys, with hilly areas with vineyards and an abundance of water. It is the second-smallest statistical region in Slovenia. The only nuclear power plant in the country and Čatež spa are located in the region. The region annually spends EUR 22 million on environmental protection. In 2013, the employment rate in the region was 57.5%. The region was characterized by the largest difference between the employment rate for men and for women (for men it was 12 percentage points higher than for women). In 2013 this region also stood out in number of convicted persons per 1,000 population (8.3).
Cities and towns
The Lower Sava Statistical Region includes 5 cities and towns, the largest of which are Krško and Brežice.
Municipalities
The Lower Sava Statistical Region comprises six municipalities:
Bistrica ob Sotli
Brežice
Kostanjevica na Krki
Krško
Radeče
Sevnica
Demographics
The population in 2020 was 70,349. It has a total area of .
Economy
Employment structure: 45.8% services, 50% industry, 4.2% agriculture.
Tourism
It attracts 5.1% of the total number of tourists in Slovenia, most being from Slovenia (53%).
Transportation
Length of motorways:
Length of other roads:
Sources
Slovenian regions in figures 2014
Statistical regions of Slovenia
Lower Sava Valley | Lower Sava Statistical Region | Mathematics | 310 |
1,275,975 | https://en.wikipedia.org/wiki/Disruptive%20selection | In evolutionary biology, disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the population is divided into two distinct groups. In this more individuals acquire peripheral character value at both ends of the distribution curve.
Overview
Natural selection is known to be one of the most important biological processes behind evolution. There are many variations of traits, and some cause greater or lesser reproductive success of the individual. The effect of selection is to promote certain alleles, traits, and individuals that have a higher chance to survive and reproduce in their specific environment. Since the environment has a carrying capacity, nature acts on this mode of selection on individuals to let only the most fit offspring survive and reproduce to their full potential. The more advantageous the trait is the more common it will become in the population. Disruptive selection is a specific type of natural selection that actively selects against the intermediate in a population, favoring both extremes of the spectrum.
Disruptive selection is inferred to oftentimes lead to sympatric speciation through a phyletic gradualism mode of evolution. Disruptive selection can be caused or influenced by multiple factors and also have multiple outcomes, in addition to speciation. Individuals within the same environment can develop a preference for extremes of a trait, against the intermediate. Selection can act on having divergent body morphologies in accessing food, such as beak and dental structure. It is seen that often this is more prevalent in environments where there is not a wide clinal range of resources, causing heterozygote disadvantage or selection favoring homozygotes.
Niche partitioning allows for selection of differential patterns of resource usage, which can drive speciation. To the contrast, niche conservation pulls individuals toward ancestral ecological traits in an evolutionary tug-of-war. Also, nature tends to have a 'jump on the band wagon' perspective when something beneficial is found. This can lead to the opposite occurring with disruptive selection eventually selecting against the average; when everyone starts taking advantage of that resource it will become depleted and the extremes will be favored. Furthermore, gradualism is a more realistic view when looking at speciation as compared to punctuated equilibrium.
Disruptive selection can initially rapidly intensify divergence; this is because it is only manipulating alleles that already exist. Often it is not creating new ones by mutation which takes a long time. Usually complete reproductive isolation does not occur until many generations, but behavioral or morphological differences separate the species from reproducing generally. Furthermore, generally hybrids have reduced fitness which promotes reproductive isolation.
Example
Suppose there is a population of rabbits. The colour of the rabbits is governed by two incompletely dominant traits: black fur, represented by "B", and white fur, represented by "b". A rabbit in this population with a genotype of "BB" would have a phenotype of black fur, a genotype of "Bb" would have grey fur (a display of both black and white), and a genotype of "bb" would have white fur.
If this population of rabbits occurred in an environment that had areas of black rocks as well as areas of white rocks, the rabbits with black fur would be able to hide from predators amongst the black rocks, and the rabbits with white fur likewise amongst the white rocks. The rabbits with grey fur, however, would stand out in all areas of the habitat, and would thereby suffer greater predation.
As a consequence of this type of selective pressure, our hypothetical rabbit population would be disruptively selected for extreme values of the fur colour trait: white or black, but not grey. This is an example of underdominance (heterozygote disadvantage) leading to disruptive selection.
Sympatric speciation
It is believed that disruptive selection is one of the main forces that drive sympatric speciation in natural populations. The pathways that lead from disruptive selection to sympatric speciation seldom are prone to deviation; such speciation is a domino effect that depends on the consistency of each distinct variable. These pathways are the result of disruptive selection in intraspecific competition; it may cause reproductive isolation, and finally culminate in sympatric speciation.
It is important to keep in mind that disruptive selection does not always have to be based on intraspecific competition. It is also important to know that this type of natural selection is similar to the other ones. Where it is not the major factor, intraspecific competition can be discounted in assessing the operative aspects of the course of adaptation. For example, what may drive disruptive selection instead of intraspecific competition might be polymorphisms that lead to reproductive isolation, and thence to speciation.
When disruptive selection is based on intraspecific competition, the resulting selection in turn promotes ecological niche diversification and polymorphisms. If multiple morphs (phenotypic forms) occupy different niches, such separation could be expected to promote reduced competition for resources. Disruptive selection is seen more often in high density populations rather than in low density populations because intraspecific competition tends to be more intense within higher density populations. This is because higher density populations often imply more competition for resources. The resulting competition drives polymorphisms to exploit different niches or changes in niches in order to avoid competition. If one morph has no need for resources used by another morph, then it is likely that neither would experience pressure to compete or interact, thereby supporting the persistence and possibly the intensification of the distinctness of the two morphs within the population. This theory does not necessarily have a lot of supporting evidence in natural populations, but it has been seen many times in experimental situations using existing populations. These experiments further support that, under the right situations (as described above), this theory could prove to be true in nature.
When intraspecific competition is not at work disruptive selection can still lead to sympatric speciation and it does this through maintaining polymorphisms. Once the polymorphisms are maintained in the population, if assortative mating is taking place, then this is one way that disruptive selection can lead in the direction of sympatric speciation. If different morphs have different mating preferences then assortative mating can occur, especially if the polymorphic trait is a "magic trait", meaning a trait that is under ecological selection and in turn has a side effect on reproductive behavior. In a situation where the polymorphic trait is not a magic trait then there has to be some kind of fitness penalty for those individuals who do not mate assortatively and a mechanism that causes assortative mating has to evolve in the population. For example, if a species of butterflies develops two kinds of wing patterns, crucial to mimicry purposes in their preferred habitat, then mating between two butterflies of different wing patterns leads to an unfavorable heterozygote. Therefore, butterflies will tend to mate with others of the same wing pattern promoting increased fitness, eventually eliminating the heterozygote altogether. This unfavorable heterozygote generates pressure for a mechanism that cause assortative mating which will then lead to reproductive isolation due to the production of post-mating barriers. It is actually fairly common to see sympatric speciation when disruptive selection is supporting two morphs, specifically when the phenotypic trait affects fitness rather than mate choice.
In both situations, one where intraspecific competition is at work and the other where it is not, if all these factors are in place, they will lead to reproductive isolation, which can lead to sympatric speciation.
Other outcomes
polymorphism
sexual dimorphism
phenotypic plasticity
Significance
Disruptive selection is of particular significance in the history of evolutionary study, as it is involved in one of evolution's "cardinal cases", namely the finch populations observed by Darwin in the Galápagos.
He observed that the species of finches were similar enough to ostensibly have been descended from a single species. However, they exhibited disruptive variation in beak size. This variation appeared to be adaptively related to the seed size available on the respective islands (big beaks for big seeds, small beaks for small seeds). Medium beaks had difficulty retrieving small seeds and were also not tough enough for the bigger seeds, and were hence maladaptive.
While it is true that disruptive selection can lead to speciation, this is not as quick or straightforward of a process as other types of speciation or evolutionary change. This introduces the topic of gradualism, which is a slow but continuous accumulation of changes over long periods of time. This is largely because the results of disruptive selection are less stable than the results of directional selection (directional selection favors individuals at only one end of the spectrum).
For example, let us take the mathematically straightforward yet biologically improbable case of the rabbits: Suppose directional selection were taking place. The field only has dark rocks in it, so the darker the rabbit, the more effectively it can hide from predators. Eventually there will be a lot of black rabbits in the population (hence many "B" alleles) and a lesser amount of grey rabbits (who contribute 50% chromosomes with "B" allele and 50% chromosomes with "b" allele to the population). There will be few white rabbits (not very many contributors of chromosomes with "b" allele to the population). This could eventually lead to a situation in which chromosomes with "b" allele die out, making black the only possible color for all subsequent rabbits. The reason for this is that there is nothing "boosting" the level of "b" chromosomes in the population. They can only go down, and eventually die out.
Consider now the case of disruptive selection. The result is equal numbers of black and white rabbits, and hence equal numbers of chromosomes with "B" or "b" allele, still floating around in that population. Every time a white rabbit mates with a black one, only gray rabbits results. So, in order for the results to "click", there needs to be a force causing white rabbits to choose other white rabbits, and black rabbits to choose other black ones. In the case of the finches, this "force" was geographic/niche isolation. This leads one to think that disruptive selection cannot happen and is normally because of species being geographically isolated, directional selection or by stabilising selection.
See also
Character displacement
Balancing selection
Directional selection
Negative selection (natural selection)
Stabilizing selection
Sympatric speciation
Fluctuating selection
Selection
References
Selection | Disruptive selection | Biology | 2,201 |
22,431 | https://en.wikipedia.org/wiki/Oracle%20machine | In complexity theory and computability theory, an oracle machine is an abstract machine used to study decision problems. It can be visualized as a Turing machine with a black box, called an oracle, which is able to solve certain problems in a single operation. The problem can be of any complexity class. Even undecidable problems, such as the halting problem, can be used.
Oracles
An oracle machine can be conceived as a Turing machine connected to an oracle. The oracle, in this context, is an entity capable of solving some problem, which for example may be a decision problem or a function problem. The problem does not have to be computable; the oracle is not assumed to be a Turing machine or computer program. The oracle is simply a "black box" that is able to produce a solution for any instance of a given computational problem:
A decision problem is represented as a set A of natural numbers (or strings). An instance of the problem is an arbitrary natural number (or string). The solution to the instance is "YES" if the number (string) is in the set, and "NO" otherwise.
A function problem is represented by a function f from natural numbers (or strings) to natural numbers (or strings). An instance of the problem is an input x for f. The solution is the value f(x).
An oracle machine can perform all of the usual operations of a Turing machine, and can also query the oracle to obtain a solution to any instance of the computational problem for that oracle. For example, if the problem is a decision problem for a set A of natural numbers, the oracle machine supplies the oracle with a natural number, and the oracle responds with "yes" or "no" stating whether that number is an element of A.
Definitions
There are many equivalent definitions of oracle Turing machines, as discussed below. The one presented here is from .
An oracle machine, like a Turing machine, includes:
a work tape: a sequence of cells without beginning or end, each of which may contain a B (for blank) or a symbol from the tape alphabet;
a read/write head, which rests on a single cell of the work tape and can read the data there, write new data, and increment or decrement its position along the tape;
a control mechanism, which can be in one of a finite number of states, and which will perform different actions (reading data, writing data, moving the control mechanism, and changing states) depending on the current state and the data being read.
In addition to these components, an oracle machine also includes:
an oracle tape, which is a semi-infinite tape separate from the work tape. The alphabet for the oracle tape may be different from the alphabet for the work tape.
an oracle head which, like the read/write head, can move left or right along the oracle tape reading and writing symbols;
two special states: the ASK state and the RESPONSE state.
From time to time, the oracle machine may enter the ASK state. When this happens, the following actions are performed in a single computational step:
the contents of the oracle tape are viewed as an instance of the oracle's computational problem;
the oracle is consulted, and the contents of the oracle tape are replaced with the solution to that instance of the problem;
the oracle head is moved to the first square on the oracle tape;
the state of the oracle machine is changed to RESPONSE.
The effect of changing to the ASK state is thus to receive, in a single step, a solution to the problem instance that is written on the oracle tape.
Alternative definitions
There are many alternative definitions to the one presented above. Many of these are specialized for the case where the oracle solves a decision problem. In this case:
Some definitions, instead of writing the answer to the oracle tape, have two special states YES and NO in addition to the ASK state. When the oracle is consulted, the next state is chosen to be YES if the contents of the oracle tape are in the oracle set, and chosen to the NO if the contents are not in the oracle set.
Some definitions eschew the separate oracle tape. When the oracle state is entered, a tape symbol is specified. The oracle is queried with the number of times that this tape symbol appears on the work tape. If that number is in the oracle set, the next state is the YES state; if it is not, the next state is the NO state.
Another alternative definition makes the oracle tape read-only, and eliminates the ASK and RESPONSE states entirely. Before the machine is started, the indicator function of the oracle set is written on the oracle tape using symbols 0 and 1. The machine is then able to query the oracle by scanning to the correct square on the oracle tape and reading the value located there.
These definitions are equivalent from the point of view of Turing computability: a function is oracle-computable from a given oracle under all of these definitions if it is oracle-computable under any of them. The definitions are not equivalent, however, from the point of view of computational complexity. A definition such as the one by van Melkebeek, using an oracle tape which may have its own alphabet, is required in general.
Complexity classes of oracle machines
The complexity class of decision problems solvable by an algorithm in class A with an oracle for a language L is called AL. For example, PSAT is the class of problems solvable in polynomial time by a deterministic Turing machine with an oracle for the Boolean satisfiability problem. The notation AB can be extended to a set of languages B (or a complexity class B), by using the following definition:
When a language L is complete for some class B, then AL=AB provided that machines in A can execute reductions used in the completeness definition of class B. In particular, since SAT is NP-complete with respect to polynomial time reductions, PSAT=PNP. However, if A = DLOGTIME, then ASAT may not equal ANP. (The definition of given above is not completely standard. In some contexts, such as the proof of the time and space hierarchy theorems, it is more useful to assume that the abstract machine defining class only has access to a single oracle for one language. In this context, is not defined if the complexity class does not have any complete problems with respect to the reductions available to .)
It is understood that NP ⊆ PNP, but the question of whether NPNP, PNP, NP, and P are equal remains tentative at best. It is believed they are different, and this leads to the definition of the polynomial hierarchy.
Oracle machines are useful for investigating the relationship between complexity classes P and NP, by considering the relationship between PA and NPA for an oracle A. In particular, it has been shown there exist languages A and B such that PA=NPA and PB≠NPB. The fact the P = NP question relativizes both ways is taken as evidence that answering this question is difficult, because a proof technique that relativizes (i.e., unaffected by the addition of an oracle) will not answer the P = NP question. Most proof techniques relativize.
One may consider the case where an oracle is chosen randomly from among all possible oracles (an infinite set). It has been shown in this case, that with probability 1, PA≠NPA. When a question is true for almost all oracles, it is said to be true for a random oracle. This choice of terminology is justified by the fact that random oracles support a statement with probability 0 or 1 only. (This follows from Kolmogorov's zero–one law.) This is only weak evidence that P≠NP, since a statement may be true for a random oracle but false for ordinary Turing machines; for example, IPA≠PSPACEA for a random oracle A but IP = PSPACE.
Oracles and halting problems
A machine with an oracle for the halting problem can determine whether particular Turing machines will halt on particular inputs, but it cannot determine, in general, whether machines equivalent to itself will halt. This creates a hierarchy of machines, each with a more powerful halting oracle and an even harder halting problem.
This hierarchy of machines can be used to define the arithmetical hierarchy.
Applications to cryptography
In cryptography, oracles are used to make arguments for the security of cryptographic protocols where a hash function is used. A security reduction (proof of security) for the protocol is given in the case where, instead of a hash function, a random oracle answers each query randomly but consistently; the oracle is assumed to be available to all parties including the attacker, as the hash function is. Such a proof shows that unless the attacker solves the hard problem at the heart of the security reduction, they must make use of some interesting property of the hash function to break the protocol; they cannot treat the hash function as a black box (i.e., as a random oracle).
See also
Black box group
Turing reduction
Interactive proof system
Matroid oracle
Demand oracle
Padding oracle attack
References
Footnotes
Sources
Computability theory
Turing machine | Oracle machine | Mathematics | 1,885 |
245,434 | https://en.wikipedia.org/wiki/Proplyd | A proplyd, short for ionized protoplanetary disk, is an externally illuminated photoevaporating protoplanetary disk around a young star. Nearly 180 proplyds have been discovered in the Orion Nebula. Images of proplyds in other star-forming regions are rare, while Orion is the only region with a large known sample due to its relative proximity to Earth.
History
In 1979 observations with the Lallemand electronic camera at the Pic-du-Midi Observatory showed six unresolved high-ionization sources near the Trapezium Cluster. These sources were not interpreted as proplyds, but as partly ionized globules (PIGs). The idea was that these objects are being ionized from the outside by M42. Later observations with the Very Large Array showed solar-system-sized condensations associated with these sources. Here the idea appeared that these objects might be low-mass stars surrounded by an evaporating protostellar accretion disk.
Proplyds were clearly resolved in 1993 using images of the Hubble Space Telescope Wide Field Camera and the term "proplyd" was used.
Characteristics
In the Orion Nebula the proplyds observed are usually one of two types. Some proplyds glow around luminous stars, in cases where the disk is found close to the star, glowing from the star's luminosity. Other proplyds are found at a greater distance from the host star and instead show up as dark silhouettes due to the self-obscuration of cooler dust and gases from the disk itself. Some proplyds show signs of movement from solar irradiance shock waves pushing the proplyds. The Orion Nebula is approximately 1,500 light-years from the Sun with very active star formation. The Orion Nebula and the Sun are in the same spiral arm of the Milky Way galaxy.
A proplyd may form new planets and planetesimal systems. Current models show that the metallicity of the star and proplyd, along with the correct planetary system temperature and distance from the star, are keys to planet and planetesimal formation. To date, the Solar System, with 8 planets, 5 dwarf planets and 5 planetesimal systems, is the largest planetary system found. Most proplyds develop into a system with no planetesimal systems, or into one very large planetesimal system.
Proplyds in other star-forming regions
Photoevaporating proplyds in other star forming regions were found with the Hubble Space Telescope. NGC 1977 currently represents the star-forming region with the largest number of proplyds outside of the Orion Nebula, with 7 confirmed proplyds. It was also the first instance where a B-type star, 42 Orionis is responsible for the photoevaporation. In addition, 4 clear and 4 candidate proplyds were discovered in the very young region NGC 2024, two of which have been photoevaporated by a B star. The NGC 2024 proplyds are significant because they imply that external photoevaporation of protoplanetary disks could compete even with very early planet formation (within the first half a million years).
Another type of photoevaporating proplyd was discovered with the Spitzer Space Telescope. These cometary tails represent dust being pulled away from the disks. Westerhout 5 is a region with many dusty proplyds, especially around HD 17505. These dusty proplyds are depleted of any gas in the outer regions of the disk, but the photoevaporation could leave an inner, more robust, and possibly gas-rich disk component of radius 5-10 astronomical units.
The proplyds in the Orion Nebula and other star-forming regions represent proto-planetary disks around low-mass stars being externally photoevaporated. These low-mass proplyds are usually found within 0.3 parsec (60,000 astronomical units) of the massive OB star and the dusty proplyds have tails with a length of 0.1 to 0.2 parsec (20,000 to 40,000 au). There is a proposed type of intermediate massive counterpart, called proplyd-like objects. Objects in NGC 3603 and later in Cygnus OB2 were proposed as intermediate massive versions of the bright proplyds found in the Orion Nebula. The proplyd-like objects in Cygnus OB2 for example are 6 to 14 parsec distant to a large collection of OB stars and have tail lengths of 0.11 to 0.55 parsec (24,000 to 113,000 au). The nature of proplyd-like objects as intermediate massive proplyds is partly supported by a spectrum for one object, which showed that the mass loss rate is higher than the mass accretion rate. Another object did not show any outflow, but accretion.
List of star-forming regions with proplyds
List is sorted after distance.
Gallery
See also
Formation and evolution of the Solar System
Grand tack hypothesis
Late Heavy Bombardment
Nice model
Photoevaporation
Planetary migration
Wiki commons photos: Bright and dark proplyds in the Orion Nebula
References
Orion (constellation) | Proplyd | Astronomy | 1,065 |
55,569,264 | https://en.wikipedia.org/wiki/Bison%20industrialised%20building%20system | The Bison industrialised building system is a precast concrete building system used in high rise flats, developed by Bison Manufacturing Ltd, Dartford, Kent, England.
History
Bison Manufacturing was founded in 1919 to build military pill-boxes.
The Bison wall-frame construction system was a construction method used in tower block construction. It was launched in 1963 by Concrete Ltd who set up factories across the UK to pre-fabricate the parts it.
It was not a frame structure as such, instead precast concrete panels formed the structure of high rise blocks. It evolved into a rapid construction method.
In tower blocks over 12 storeys in height, all of the walls were loadbearing - external and internal. Whilst there were no partition walls, the internal walls were still thinner at 6 inches in thickness. Two-bedroom flats could be constructed out of 21 pre-cast concrete pieces. The bathroom and toilet elements could be constructed from a similarly few number of pre-fabricated pieces. The lift shaft and staircases could be constructed out of pieces that were 3 storeys high. The method was limited in that it was only really practical for two and three-bedroom flats.
See also
Chelmsley Wood
References
External links
Company heritage page
Contains text from an article on wikia cc-by-sa
Building engineering | Bison industrialised building system | Engineering | 261 |
39,328,460 | https://en.wikipedia.org/wiki/F%C3%A9tizon%20oxidation | Fétizon oxidation is the oxidation of primary and secondary alcohols utilizing the compound silver(I) carbonate absorbed onto the surface of celite also known as Fétizon's reagent first employed by Marcel Fétizon in 1968. It is a mild reagent, suitable for both acid and base sensitive compounds. Its great reactivity with lactols makes the Fétizon oxidation a useful method to obtain lactones from a diol. The reaction is inhibited significantly by polar groups within the reaction system as well as steric hindrance of the α-hydrogen of the alcohol.
Preparation
Fétizon's reagent is typically prepared by adding silver nitrate to an aqueous solution of a carbonate, such as sodium carbonate or potassium bicarbonate, while being vigorously stirred in the presence of purified celite.
Mechanism
A proposed mechanism for the oxidation of an alcohol by Fétizon's reagent involves single electron oxidation of both the alcoholic oxygen and the hydrogen alpha to the alcohol by two atoms of silver(I) within the celite surface. The carbonate ion then proceeds to deprotonate the resulting carbonyl generating bicarbonate which is further protonated by the additionally generated hydrogen cation to cause elimination of water and generation of carbon dioxide.
The rate limiting step of this reaction is proposed to be the initial association of the alcohol to the silver ions. As a result, the presence of even weakly associating ligands to the silver can inhibit the reaction greatly. As a result, even slightly polar solvents of any variety, such as ethyl acetate or methyl ethyl ketone, are avoided when using this reagent as they competitively associate with the reagent. Additional polar functionalities of the reactant should also be avoided whenever possible as even the presence of an alkene can sometimes reduce the reactivity of a substrate 50 fold. Commonly employed solvents such as benzene and xylene are extremely non-polar and further acceleration of the reaction can be achieved through the use of the more non-polar heptane. The solvent is also typically refluxed to drive the reaction with heat and remove the water generated by the reaction through azeotropic distillation.
Steric hindrance of the hydrogen alpha to the alcohol is a major determination of the rate of oxidation as it affects the rate of association. Tertiary alcohols lacking an alpha hydrogen are selected against and generally do not oxidize in the presence of Fétizon's reagent.
Increasing the amount of celite used in the reagent accelerates the rate of the reaction by increasing the surface area available to react. However, increasing the amount of celite past 900 grams per mole of silver(I) carbonate begins to slow the reaction due to dilution effects.
Reactivity
Fétizon's reagent is used primarily in the oxidation of primary or secondary alcohols to aldehydes or ketones with a slight selectivity toward secondary alcohols and unsaturated alcohols. The reaction is typically done in a refluxing dry non-polar organic solvent with copious stirring. The reaction time varies with the structure of the alcohol and is typically completed within three hours. A very attractive property of Fétizon's reagent is its ability to be separated from the reaction product by physically filtering it out and washing with benzene.
The inability of Fétizon's reagent to oxidize tertiary alcohols makes it extremely useful in the monooxidation of a [1,2] diol in which one of the alcohols is tertiary while avoiding cleavage of the carbon-carbon bond.
The mildness and structural sensitivity of the reagent also makes this reagent ideal for the monooxidation of a symmetric diol.
Lactols are extremely sensitive to Fétizon's reagent, being oxidized very quickly to a lactone functionality. This allows for the selective oxidation of lactols in the presence of other alcohols. This also allows for a classic use of Fétizon's reagent to form lactones from a primary diol. By oxidizing one of the alcohols to an aldehyde, the second alcohol equilibrates with the aldehyde to form a lactol which is reacted quickly with more Fétizon's reagent to trap the cyclic intermediate as a lactone. This method allows for the synthesis of seven-member lactones which are traditionally more challenging to synthesize.
Phenol functional groups can be oxidized to their respective quinone forms. These quinones can further couple within solution producing numerous dimerizations depending upon their substituents.
Amines have been shown to oxidize in the presence of Fétizon's reagent to enamines and iminium cations that have been trapped, but can also be selected against in a compound with more easily oxidized alcohol functionalities.
Fétizon's reagent can also being used to facilitate cycloaddition of a 4-hydroxy-2-furoquinilone and an olefin to form dihydrofuroquinolinones.
Protecting groups
Para-methoxybenzyl (PMB) is a commonly used protecting group for alcohols against Fétizon's reagent. As Fétizon's oxidation is a neutral reaction, acid and base sensitive protecting groups are also compatible with the reagent and by products generated.
Sensitive groups
While tertiary alcohols are typically not affected by Fétizon's reagent, tertiary propargylic alcohols have been shown to oxidize under these conditions and results in the fragmentation of the alcohol with an alkyne leaving group.
Halohydrins that possess a trans stereochemistry have been demonstrated to form epoxides and transposed products in the presence of Fétizon's reagent. Halohydrins possessing a cis-stereochemistry seem to perform a typical Fétizon's oxidation to a ketone.
[1,3] diols have a tendency to eliminate water following the monooxidation by Fétizon's reagent to form an enone.
Under differing structural conditions, [1,2] diols can form diketones in the presence of Fétizon's reagent. However, oxidative carbon-carbon bond cleavage may also occur.
Applications
Since its discovery as a useful method of oxidation, Fétizon's reagent has been used in the total synthesis of numerous molecules such as (±)-bukittinggine.
Fétizon's reagent has also been employed extensively in the study of various sugar chemistry, to achieve selective oxidation of tri and tetra methylated aldoses to aldolactones, oxidation of D-xylose and L-arabinose to D-threose and L-erythrose respectively, and oxidation of L-sorbose to afford L-threose among many others.
References
Organic oxidation reactions
Name reactions | Fétizon oxidation | Chemistry | 1,463 |
30,521,203 | https://en.wikipedia.org/wiki/Auriscalpium%20umbella | Auriscalpium umbella is a species of fungus in the family Auriscalpiaceae of the Russulales order. Described by the Dutch mycologist Rudolph Arnold Maas Geesteranus in 1971, it is known from New Zealand.
References
External links
Fungi described in 1971
Fungi of New Zealand
Russulales
Fungus species | Auriscalpium umbella | Biology | 69 |
1,206,990 | https://en.wikipedia.org/wiki/Elevator%20algorithm | The elevator algorithm, or SCAN, is a disk-scheduling algorithm to determine the motion of the disk's arm and head in servicing read and write requests.
This algorithm is named after the behavior of a building elevator, where the elevator continues to travel in its current direction (up or down) until empty, stopping only to let individuals off or to pick up new individuals heading in the same direction.
From an implementation perspective, the drive maintains a buffer of pending read/write requests, along with the associated cylinder number of the request, in which lower cylinder numbers generally indicate that the cylinder is closer to the spindle, and higher numbers indicate the cylinder is farther away.
Description
When a new request arrives while the drive is idle, the initial arm/head movement will be in the direction of the cylinder where the data is stored, either in or out. As additional requests arrive, requests are serviced only in the current direction of arm movement until the arm reaches the edge of the disk. When this happens, the direction of the arm reverses, and the requests that were remaining in the opposite direction are serviced, and so on.
Variations
One variation of this method ensures all requests are serviced in only one direction, that is, once the head has arrived at the outer edge of the disk, it returns to the beginning and services the new requests in this one direction only (or vice versa). This is known as the "Circular Elevator Algorithm" or C-SCAN. Although the time of the return seek is wasted, this results in more equal performance for all head positions, as the expected distance from the head is always half the maximum distance, unlike in the standard elevator algorithm where cylinders in the middle will be serviced as much as twice as often as the innermost or outermost cylinders.
Other variations include:
FSCAN
LOOK
C-LOOK
N-Step-SCAN
Example
The following is an example of how to calculate average disk seek times for both the SCAN and C-SCAN algorithms.
Example list of pending disk requests (listed by track number): 100, 50, 10, 20, 75.
The starting track number for the examples will be 35.
The list will need to be sorted in ascending order: 10, 20, 50, 75, 100.
Both SCAN and C-SCAN behave in the same manner until they reach the last track queued. For the sake of this example let us assume that the SCAN algorithm is currently going from a lower track number to a higher track number (like the C-SCAN is doing). For both methods, one takes the difference in magnitude (i.e. absolute value) between the next track request and the current track.
Seek 1: 50 − 35 = 15
Seek 2: 75 − 50 = 25
Seek 3: 100 − 75 = 25
At this point both have reached the highest (end) track request. SCAN will just reverse direction and service the next closest disk request (in this example, 20) and C-SCAN will always go back to track 0 and start going to higher track requests.
Seek 4 (SCAN): 20 − 100 = 80
Seek 5 (SCAN): 10 − 20 = 10
Total (SCAN): 155
Average (SCAN): 155 ÷ 5 = 31
Seek 4 (C-SCAN): 0 − 100 = 0 head movement as cylinders are treated as a circular list (C-SCAN always goes back to the first track)
Seek 5 (C-SCAN): 10 − 0 = 10
Seek 6 (C-SCAN): 20 − 10 = 10
Total (C-SCAN): 85
Average (C-SCAN): 85 ÷ 5 = 17
Even though six seeks were performed using the C-SCAN algorithm, only five I/Os were actually done.
The scan algorithm (often known as prefix sum algorithm) is commonly used in computer science for problems that involve computing the cumulative sum or the cumulative result of a series of elements in an array or list. It operates by iterating through the list and maintaining an accumulated result up to the current element, and can be used in various scenarios such as parallel computation, reducing operations, or processing large data efficiently.
Here’s a real-world example where the scan algorithm is applied:
Example: Real-Time Data Processing in Stock Market Analysis
Imagine a financial trading application that tracks the price changes of a stock over time and calculates the cumulative value or gain/loss of the stock at any given moment.
Scenario:
You have a list of daily stock price changes (positive or negative values) for a particular stock over a period of days. The scan algorithm can be used to calculate the cumulative gain or loss at each day, showing the total change in stock price from the start up to that day.
Input data: A list of daily stock price changes:
csharp
Copy code
[10, -5, 3, 7, -2]
Where:
10 represents a gain of $10 on day 1,
-5 represents a loss of $5 on day 2,
3 represents a gain of $3 on day 3,
7 represents a gain of $7 on day 4,
-2 represents a loss of $2 on day 5.
Step-by-Step Execution (Scan Algorithm):
Start with an initial cumulative sum of 0.
For each subsequent day, add the day's change to the cumulative sum:
Day 1: 0 + 10 = 10 (Total gain so far: $10)
Day 2: 10 + (-5) = 5 (Total gain so far: $5)
Day 3: 5 + 3 = 8 (Total gain so far: $8)
Day 4: 8 + 7 = 15 (Total gain so far: $15)
Day 5: 15 + (-2) = 13 (Total gain so far: $13)
Output: The cumulative gains after each day:
csharp
Copy code
[10, 5, 8, 15, 13]
This cumulative list shows how the stock has performed in terms of total gain/loss at each day in the period. By using the scan algorithm, you efficiently compute these cumulative results in a single pass over the data.
Parallelism and Optimization:
In a real-world application where the data set is large (e.g., tracking stock prices across thousands of days for multiple stocks), this scan algorithm can be parallelized to run faster. For example, using techniques like parallel prefix sum (where the input array is divided into chunks, processed in parallel, and then merged), large-scale data can be processed much more efficiently.
Use Cases Beyond Stock Market Analysis:
Image Processing: Cumulative operations (like pixel intensities) for tasks such as convolution or blur filters.
Distributed Systems: Aggregating values across multiple nodes to compute cumulative statistics.
Database Systems: Efficiently computing running totals in financial applications or analytics.
The scan algorithm is essential in scenarios where you need to process or aggregate data in a way that builds on prior computations, and its parallel implementation helps in scaling up for larger datasets.
Analysis
For both versions of the elevator algorithm, the arm movement is less than twice the number of total cylinders and produces a smaller variance in response time. The algorithm is also relatively simple.
The elevator algorithm is not always better than shortest seek first, which is slightly closer to optimal, but can result in high variance in response time and even in starvation when new requests continually get serviced prior to existing requests. Anti-starvation techniques can be applied to the shortest seek time first algorithm to guarantee a maximum response time.
See also
FIFO (computing and electronics)
References
Disk scheduling algorithms
Sorting algorithms | Elevator algorithm | Mathematics | 1,536 |
68,132,433 | https://en.wikipedia.org/wiki/Duinviridae | Duinviridae is a family of RNA viruses, which infect prokaryotes.
Taxonomy
Duinviridae contains 6 genera:
Apeevirus
Beshanovirus
Kahshuvirus
Kohmavirus
Samuneavirus
Tehuhdavirus
References
Virus families
Riboviria | Duinviridae | Biology | 60 |
49,223,966 | https://en.wikipedia.org/wiki/International%20Journal%20of%20Behavioral%20Medicine | The International Journal of Behavioral Medicine is a quarterly peer-reviewed medical journal covering behavioral medicine. It was established in 1994 and is published by Springer Science+Business Media on behalf of the International Society of Behavioral Medicine, of which it is the official journal. The editors-in-chief is Michael A. Hoyt. According to the Journal Citation Reports, the journal has a 2017 impact factor of 2.012.
References
External links
Academic journals established in 1994
Quarterly journals
Springer Science+Business Media academic journals
English-language journals
Academic journals associated with learned and professional societies
Behavioral medicine journals | International Journal of Behavioral Medicine | Biology | 117 |
8,422,399 | https://en.wikipedia.org/wiki/Microbial%20food%20web | The microbial food web refers to the combined trophic interactions among microbes in aquatic environments. These microbes include viruses, bacteria, algae, heterotrophic protists (such as ciliates and flagellates). In aquatic ecosystems, microbial food webs are essential because they form the basis for the cycling of nutrients and energy. These webs are vital to the stability and production of ecosystems in a variety of aquatic environments, including lakes, rivers, and oceans. By converting dissolved organic carbon (DOC) and other nutrients into biomass that larger organisms may eat, microbial food webs maintain higher trophic levels. Thus, these webs are crucial for energy flow and nutrient cycling in both freshwater and marine ecosystems.
Role of Different Microbes
In aquatic environments, microbes constitute the base of the food web. Single celled photosynthetic organisms such as diatoms and cyanobacteria are generally the most important primary producers in the open ocean. Many of these cells, especially cyanobacteria, are too small to be captured and consumed by small crustaceans and planktonic larvae. Instead, these cells are consumed by phagotrophic protists which are readily consumed by larger organisms.
Viruses
Aquatic ecosystems are full of viruses, which are essential for managing microbial populations. They release organic matter back into the environment by infecting and lysing planktonic algae (phycoviruses) and bacterial cells (bacteriophages). This mechanism, called the viral shunt, promotes nutrient recycling and aids in the control of microbial populations. Viral particles and dissolved organic carbon (DOC), which can be further used by other microorganisms, are released when bacterial cells are lysed. Viruses can infect and break open bacterial cells and (to a lesser extent), planktonic algae (a.k.a. phytoplankton). Therefore, viruses in the microbial food web act to reduce the population of bacteria and, by lysing bacterial cells, release particulate and dissolved organic carbon (DOC).
Bacteria
In the microbial food web, bacteria play a crucial role in breaking down organic materials and recycling nutrients. They transform DOC into bacterial biomass so that protists and other higher trophic levels can consume it. Additionally, bacteria take part in the nitrogen and carbon cycles, among other biogeochemical cycles.
Algae
In aquatic ecosystems, single-celled photosynthetic organisms like cyanobacteria and diatoms are the main producers. Through the process of photosynthesis, they transform sunlight into chemical energy and create organic matter, which is the foundation of the food chain. Particularly significant in nutrient-poor environments are cyanobacteria because of their capacity to fix atmospheric nitrogen. When vital nutrients like nitrogen and phosphorus are scarce during periods of uneven development, algal cells have the potential to produce DOC. DOC may also be released into the environment by algal cells. One of the reasons phytoplankton release DOC termed "unbalanced growth" is when essential nutrients (e.g. nitrogen and phosphorus) are limiting. Therefore, carbon produced during photosynthesis is not used for the synthesis of proteins (and subsequent cell growth), but is limited due to a lack of the nutrients necessary for macromolecules. Excess photosynthate, or DOC is then released, or exuded.
Heterotrophic Protists
In the microbial food web, protists including ciliates and flagellates are significant consumers. By consuming bacteria, algae, and other tiny particles, they move nutrients and energy up the food chain. Larger creatures like zooplankton feed on these protists in turn.
Microbial Interactions
The food web's microbial interactions are varied and diverse. Predation, rivalry, and symbiotic connections are some of these interactions. For instance, certain bacteria and algae create mutualistic relationships in which the bacteria give the algae vital nutrients, and the algae give the bacteria organic carbon. Microbial communities can be shaped by competition for resources like light and nutrition, which can affect their makeup and functionality.
Environmental Factors
Environmental factors that have a significant impact on microbial food webs include temperature, availability of light, and nutrient concentrations. Microbe development and metabolic rates are influenced by temperature, and photosynthetic organisms are impacted by light availability. The availability of nutrients, especially phosphorus and nitrogen, might restrict the growth and productivity of microorganisms. For instance, during times of nitrogen constraint, phytoplankton may emit DOC, a phenomenon referred to as imbalanced growth.
Human Impact
A major impact of human activity on microbial food webs is eutrophication, pollution, and climate change. The activities of microbial communities can be disturbed by pollutants like pesticides and heavy metals. Microbial growth and dispersal are impacted by temperature and precipitation changes brought about by climate change. The entire aquatic food chain may be impacted by eutrophication, which is brought on by nutrient runoff from cities and farms. Eutrophication can also result in toxic algal blooms and hypoxic conditions.
Technological Advances
Technological developments have completely changed the way that microbial food webs are studied. By analyzing genetic material from environmental samples, researchers can get insights into the diversity and roles of microbial communities using metagenomics. The utilization of remote sensing technology facilitates the large-scale monitoring of environmental variables and microbial activity, consequently augmenting our comprehension of microbial dynamics across various ecosystems.
The Microbial Loop
The microbial loop describes a pathway in the microbial food web where DOC is returned to higher trophic levels via the incorporation into bacterial biomass. This loop makes sure that the DOC created by photosynthetic organisms is used by heterotrophic bacteria and then moves up the food chain, which is crucial for sustaining the flow of nutrients and energy within the ecosystem.
Conclusion
By facilitating the transfer of nutrients and energy, microbial food webs are essential for the health and stability of aquatic ecosystems. It is crucial to comprehend these complex relationships to address environmental issues and advance sustainable management of aquatic resources. Technological developments keep expanding our understanding and illuminating the complex mechanisms that support life in the oceans of our planet.
See also
Microbial cooperation
Microbial intelligence
Microbial population biology
References
Other references
Michaels, A.F. and Silver, M.W. (1988) "Primary production, sinking fluxes and the microbial food web". Deep Sea Research Part A. Oceanographic Research Papers, 35(4): 473–90.
Microbiology | Microbial food web | Chemistry,Biology | 1,364 |
55,684,327 | https://en.wikipedia.org/wiki/Horndeski%27s%20theory | Horndeski's theory is the most general theory of gravity in four dimensions whose Lagrangian is constructed out of the metric tensor and a scalar field and leads to second order equations of motion. The theory was first proposed by Gregory Horndeski in 1974 and has found numerous applications, particularly in the construction of cosmological models of Inflation and dark energy. Horndeski's theory contains many theories of gravity, including General relativity, Brans-Dicke theory, Quintessence, Dilaton, Chameleon and covariant Galileon as special cases.
Action
Horndeski's theory can be written in terms of an action as
with the Lagrangian densities
Here is Newton's constant, represents the matter Lagrangian, to are generic functions of and , are the Ricci scalar and Einstein tensor, is the Jordan frame metric, semicolon indicates covariant derivatives, commas indicate partial derivatives, , and repeated indices are summed over following Einstein's convention.
Constraints on parameters
Many of the free parameters of the theory have been constrained, from the coupling of the scalar field to the top field and via coupling to jets down to low coupling values with proton collisions at the ATLAS experiment. and , are strongly constrained by the direct measurement of the speed of gravitational waves following GW170817.
See also
Classical theories of gravitation
General relativity
Brans–Dicke theory
Dual graviton
Massive gravity
Lovelock theory of gravity
Alternatives to general relativity
References
General relativity | Horndeski's theory | Physics | 316 |
2,729,485 | https://en.wikipedia.org/wiki/Neuromuscular-blocking%20drug | Neuromuscular-blocking drugs, or Neuromuscular blocking agents (NMBAs), block transmission at the neuromuscular junction, causing paralysis of the affected skeletal muscles. This is accomplished via their action on the post-synaptic acetylcholine (Nm) receptors.
In clinical use, neuromuscular block is used adjunctively to anesthesia to produce paralysis, firstly to paralyze the vocal cords, and permit endotracheal intubation, and secondly to optimize the surgical field by inhibiting spontaneous ventilation, and causing relaxation of skeletal muscles. Because the appropriate dose of neuromuscular-blocking drug may paralyze muscles required for breathing (i.e., the diaphragm), mechanical ventilation should be available to maintain adequate respiration.
This class of medications helps to reduce patient movement, breathing, or ventilator dyssynchrony and allows lower insufflation pressures during laparoscopy. It has several indications for use in the intense care unit. It can help reduce hoarseness in voice as well as injury to the vocal cord during intubation. In addition, it plays an important role in facilitating mechanical ventilation in patients with poor lung function.
Patients are still aware of pain even after full conduction block has occurred; hence, general anesthetics and/or analgesics must also be given to prevent anesthesia awareness.
Nomenclature
Neuromuscular blocking drugs are often classified into two broad classes:
Pachycurares, which are bulky molecules with nondepolarizing activity
Leptocurares, which are thin and flexible molecules that tend to have depolarizing activity.
It is also common to classify them based on their chemical structure.
Acetylcholine, suxamethonium, and decamethonium
Suxamethonium was synthesised by connecting two acetylcholine molecules and has the same number of heavy atoms between methonium heads as decamethonium. Just like acetylcholine, succinylcholine, decamethonium and other polymethylene chains, of the appropriate length and with two methonium, heads have small trimethyl onium heads and flexible links. They all exhibit a depolarizing block.
Aminosteroids
Pancuronium, vecuronium, rocuronium, rapacuronium, dacuronium, malouètine, dihydrochandonium, dipyrandium, pipecuronium, chandonium (HS-310), HS-342 and other HS- compounds are aminosteroidal agents. They have in common the steroid structural base, which provides a rigid and bulky body. Most of the agents in this category would also be classified as non-depolarizing.
Tetrahydroisoquinoline derivatives
Compounds based on the tetrahydroisoquinoline moiety such as atracurium, mivacurium, and doxacurium would fall in this category. They have a long and flexible chain between the onium heads, except for the double bond of mivacurium. D-tubocurarine and dimethyltubocurarine are also in this category. Most of the agents in this category would be classified as non-depolarizing.
Gallamine and other chemical classes
Gallamine is a trisquaternary ether with three ethonium heads attached to a phenyl ring through an ether linkage. Many other different structures have been used for their muscle relaxant effect such as alcuronium (alloferin), anatruxonium, diadonium, fazadinium (AH8165) and tropeinium.
Novel NMB agents
In recent years much research has been devoted to new types of quaternary ammonium muscle relaxants. These are asymmetrical diester isoquinolinium compounds and bis-benzyltropinium compounds that are bistropinium salts of various diacids. These classes have been developed to create muscle relaxants that are faster and shorter acting. Both the asymmetric structure of diester isoquinolinium compounds and the acyloxylated benzyl groups on the bisbenzyltropiniums destabilizes them and can lead to spontaneous breakdown and therefore possibly a shorter duration of action.
Classification
These drugs fall into two groups:
Non-depolarizing blocking agents: These agents constitute the majority of the clinically relevant neuromuscular blockers. They act by competitively blocking the binding of ACh to its receptors, and in some cases, they also directly block the ionotropic activity of the ACh receptors.
Depolarizing blocking agents: These agents act by depolarizing the sarcolemma of the skeletal muscle fiber. This persistent depolarization makes the muscle fiber resistant to further stimulation by ACh.
Non-depolarizing blocking agents
A neuromuscular non-depolarizing agent is a form of neuromuscular blocker that does not depolarize the motor end plate.
The quaternary ammonium muscle relaxants belong to this class. Quaternary ammonium muscle relaxants are quaternary ammonium salts used as drugs for muscle relaxation, most commonly in anesthesia. It is necessary to prevent spontaneous movement of muscle during surgical operations. Muscle relaxants inhibit neuron transmission to muscle by blocking the nicotinic acetylcholine receptor. What they have in common, and is necessary for their effect, is the structural presence of quaternary ammonium groups, usually two. Some of them are found in nature and others are synthesized molecules.
Below are some more common agents that act as competitive antagonists against acetylcholine at the site of postsynaptic acetylcholine receptors.
Tubocurarine, found in curare of the South American plant Pareira, Chondrodendron tomentosum, is the prototypical non-depolarizing neuromuscular blocker. It has a slow onset (<5 min) and a long duration of action (30 mins). Side-effects include hypotension, which is partially explained by its effect of increasing histamine release, a vasodilator, as well as its effect of blocking autonomic ganglia. It is excreted in the urine.
This drug needs to block about 70–80% of the ACh receptors for neuromuscular conduction to fail, and hence for effective blockade to occur. At this stage, end-plate potentials (EPPs) can still be detected, but are too small to reach the threshold potential needed for activation of muscle fiber contraction.
The speed of onset depends on the potency of the drug, greater potency is associated with slower onset of block. Rocuronium, with an ED95 of 0.3 mg/kg IV has a more rapid onset than Vecuronium with an ED95 of 0.05mg/kg. Steroidal compounds, such as rocuronium and vecuronium, are intermediate-acting drugs while Pancuronium and pipecuronium are long-acting drugs.
In larger clinical dose, some of the blocking agent can access the pore of the ion channel and cause blockage. This weakens neuromuscular transmission and diminishes the effect of acetylcholinesterase inhibitors (e.g. neostigmine). Nondepolarizing NBAs may also block prejunctional sodium channels which interfere with the mobilization of acetylcholine at the nerve ending.
Depolarizing blocking agents
A depolarizing neuromuscular blocking agent is a form of neuromuscular blocker that depolarizes the motor end plate. An example is succinylcholine. Depolarizing blocking agents work by depolarizing the plasma membrane of the muscle fiber, similar to acetylcholine. However, these agents are more resistant to degradation by acetylcholinesterase, the enzyme responsible for degrading acetylcholine, and can thus more persistently depolarize the muscle fibers. This differs from acetylcholine, which is rapidly degraded and only transiently depolarizes the muscle.
There are two phases to the depolarizing block. During phase I (depolarizing phase), succinylcholine interacts with nicotinic receptor to open the channel and cause depolarization of the end plate, which later spread to and result in depolarization of adjacent membranes. As a result, there is disorganisation of contraction of muscle motor unit. This causes muscular fasciculations (muscle twitches) while they are depolarizing the muscle fibers. Eventually, after sufficient depolarization has occurred, phase II (desensitizing phase) sets in and the muscle is no longer responsive to acetylcholine released by the motoneurons. At this point, full neuromuscular block has been achieved. Phase I block effect can be increased by cholinesterase inhibitors which further delay the action of metabolism and removal by cholinesterase.
Under continuous exposure to succinylcholine, the initial end plate depolarization is reduced, and repolarisation process is initiated. As a result of the widespread sustained depolarization the synapses ultimately begin repolarization. Once repolarized, the membrane is still less susceptible to additional depolarization (phase II block).
The prototypical depolarizing blocking drug is succinylcholine (suxamethonium). It is the only such drug used clinically. It has a rapid onset (30 seconds) but very short duration of action (5–10 minutes) because of hydrolysis by various cholinesterases (such as butyrylcholinesterase in the blood). The patient will experience fasciculation due to the depolarisation of muscle neurone fibres and seconds later, flaccid paralysis will occur. Succinylcholine was originally known as diacetylcholine because structurally it is composed of two acetylcholine molecules joined with a methyl group. Decamethonium is sometimes, but rarely, used in clinical practice.
It is indicated for rapid sequence intubation.
Dosing/onset of action
IV dose 1-1.5mg/kg or 3 to 5 x ED95
Paralysis occurs in one to two minutes.
Clinical duration of action (time from drug administration to recovery of single twich to 25% of baseline) is 7-12 minutes.
If IV access is unavailable, intramuscular administration 3-4mg/kg. Paralysis occurs at 4 minutes.
Use of succinylcholine infusion or repeated bolus administration increase the risk of Phase II block and prolonged paralysis. Phase II block occurs after large doses (>4mg/kg). This occurs when the post-synaptic membrane action potential returns to baseline in spite of the presence of succinylcholine and causes continued activation of nicotinic acetylcholine receptors.
Comparison of drugs
The main difference is in the reversal of these two types of neuromuscular-blocking drugs.
Non-depolarizing blockers are reversed by acetylcholinesterase inhibitor drugs since non-depolarizing blockers are competitive antagonists at the ACh receptor so can be reversed by increases in ACh.
The depolarizing blockers already have ACh-like actions, so these agents have prolonged effect under the influence of acetylcholinesterase inhibitors. Administration of depolarizing blockers initially produces fasciculations (a sudden twitch just before paralysis occurs). This is due to depolarization of the muscle. Also, post-operative pain is associated with depolarizing blockers.
The tetanic fade is the failure of muscles to maintain a fused tetany at sufficiently high frequencies of electrical stimulation.
Non-depolarizing blockers have this effect on patients, probably by an effect on presynaptic receptors.
Depolarizing blockers do not cause the tetanic fade. However, a clinically similar manifestation called Phase II block occurs with repeated doses of suxamethonium.
This discrepancy is diagnostically useful in case of intoxication of an unknown neuromuscular-blocking drug.
Physiology at the Neuromuscular Junction
Neuromuscular blocking agents exert their effect by modulating the signal transmission in skeletal muscles. An action potential is, in other words, a depolarisation in neurone membrane due to a change in membrane potential greater than the threshold potential leads to an electrical impulse generation. The electrical impulse travels along the pre-synaptic neurone axon to synapse with the muscle at the neuromuscular junction (NMJ) to cause muscle contraction.
When the action potential reaches the axon terminal, it triggers the opening of the calcium ion gated channels, which causes the influx of Ca2+. Ca2+ will stimulate the release of neurotransmitter in the neurotransmitter containing vesicles by exocytosis (vesicle fuses with the pre-synpatic membrane).
The neurotransmitter, acetylcholine(ACh) binds to the nicotinic receptors on the motor end plate, which is a specialised area of the muscle fibre's post-synaptic membrane. This binding causes the nicotinic receptor channels to open and allow the influx of Na+ into the muscle fibre.
Fifty percent of the released ACh is hydrolysed by acetylcholinesterase (AChE) and the remaining bind to the nicotinic receptors on the motor end plate. When ACh is degraded by AChE, the receptors are no longer stimulated and the muscle cannot be depolarized.
If enough Na+ enter the muscle fibre, it causes an increase in the membrane potential from its resting potential of -95mV to -50mV (above the threshold potential -55mV) which causes an action potential to spread throughout the fibre. This potential travels along the surface of the sarcolemma. The sarcolemma is an excitable membrane that surrounds the contractile structures known as myofibrils that are located deep in the muscle fibre. For the action potential to reach the myofibrils, the action potential travels along the transverse tubules (T-tubules) that connects the sarcolemma and center of the fibre.
Later, action potential reaches the sarcoplasmic reticulum which stores the Ca2+ needed for muscle contraction and causes Ca2+ to be released from the sarcoplasmic reticulum.
Mechanism of action
Quaternary muscle relaxants bind to the nicotinic acetylcholine receptor and inhibit or interfere with the binding and effect of ACh to the receptor. Each ACh-receptor has two receptive sites and activation of the receptor requires binding to both of them. Each receptor site is located at one of the two α-subunits of the receptor. Each receptive site has two subsites, an anionic site that binds to the cationic ammonium head and a site that binds to the blocking agent by donating a hydrogen bond.
Non-depolarizing agents
A decrease in binding of acetylcholine leads to a decrease in its effect and neuron transmission to the muscle is less likely to occur. It is generally accepted that non-depolarizing agents block by acting as reversible competitive inhibitors. That is, they bind to the receptor as antagonists and that leaves fewer receptors available for acetylcholine to bind.
Depolarizing agents
Depolarizing agents produce their block by binding to and activating the ACh receptor, at first causing muscle contraction, then paralysis. They bind to the receptor and cause depolarization by opening channels just like acetylcholine does. This causes repetitive excitation that lasts longer than a normal acetylcholine excitation and is most likely explained by the resistance of depolarizing agents to the enzyme acetylcholinesterase. The constant depolarization and triggering of the receptors keeps the endplate resistant to activation by acetylcholine. Therefore, a normal neuron transmission to muscle cannot cause contraction of the muscle because the endplate is depolarized and thereby the muscle paralysed.
Binding to the nicotinic receptor
Shorter molecules like acetylcholine need two molecules to activate the receptor, one at each receptive site. Decamethonium congeners, which prefer straight line conformations (their lowest energy state), usually span the two receptive sites with one molecule (binding inter-site). Longer congeners must bend when fitting receptive sites.
The greater energy a molecule needs to bend and fit usually results in lower potency.
Structural and conformational action relationship
Conformational study on neuromuscular blocking drugs is relatively new and developing. Traditional SAR studies do not specify environmental factors on molecules. Computer-based conformational searches assume that the molecules are in vacuo, which is not the case in vivo. Solvation models take into account the effect of a solvent on the conformation of the molecule. However, no system of solvation can mimic the effect of the complex fluid composition of the body.
The division of muscle relaxants to rigid and non-rigid is at most qualitative. The energy required for conformational changes may give a more precise and quantitative picture. Energy required for reducing onium head distance in the longer muscle relaxant chains may quantify their ability to bend and fit its receptive sites. Using computers it is possible to calculate the lowest energy state conformer and thus most populated and best representing the molecule. This state is referred to as the global minimum. The global minimum for some simple molecules can be discovered quite easily with certainty. Such as for decamethonium the straight line conformer is clearly the lowest energy state. Some molecules, on the other hand, have many rotatable bonds and their global minimum can only be approximated.
Molecular length and rigidity
Neuromuscular blocking agents need to fit in a space close to 2 nanometres, which resembles the molecular length of decamethonium. Some molecules of decamethonium congeners may bind only to one receptive site. Flexible molecules have a greater chance of fitting receptive sites. However, the most populated conformation may not be the best-fitted one. Very flexible molecules are, in fact, weak neuromuscular inhibitors with flat dose-response curves. On the other hand, stiff or rigid molecules tend to fit well or not at all. If the lowest-energy conformation fits, the compound has high potency because there is a great concentration of molecules close to the lowest-energy conformation. Molecules can be thin but yet rigid. Decamethonium for example needs relatively high energy to change the N-N distance.
In general, molecular rigidity contributes to potency, while size affects whether a muscle relaxant shows a polarizing or a depolarizing effect. Cations must be able to flow through the trans-membrane tube of the ion-channel to depolarize the endplate. Small molecules may be rigid and potent but unable to occupy or block the area between the receptive sites. Large molecules, on the other hand, may bind to both receptive sites and hinder depolarizing cations independent of whether the ion-channel is open or closed below. Having a lipophilic surface pointed towards the synapse enhances this effect by repelling cations. The importance of this effect varies between different muscle relaxants and classifying depolarizing from non-depolarizing blocks is a complex issue. The onium heads are usually kept small and the chains connecting the heads usually keep the N-N distance at 10 N or O atoms. Keeping the distance in mind the structure of the chain can vary (double bonded, cyclohexyl, benzyl, etc.)
Succinylcholine has a 10-atom distance between its N atoms, like decamethonium. Yet it has been reported that it takes two molecules, as with acetylcholine, to open one nicotinic ion channel. The conformational explanation for this is that each acetylcholine moiety of succinylcholine prefers the gauche (bent, cis) state. The attraction between the N and O atoms is greater than the onium head repulsion. In this most populated state, the N-N distance is shorter than the optimal distance of ten carbon atoms and too short to occupy both receptive sites. This similarity between succinyl- and acetyl-choline also explains its acetylcholine-like side-effects.
Comparing molecular lengths, the pachycurares dimethyltubocurarine and d-tubocurarine both are very rigid and measure close to 1.8 nm in total length. Pancuronium and vecuronium measure 1.9 nm, whereas pipecuronium is 2.1 nm. The potency of these compounds follows the same rank of order as their length. Likewise, the leptocurares prefer a similar length. Decamethonium, which measures 2 nm, is the most potent in its category, whereas C11 is slightly too long. Gallamine despite having low bulk and rigidity is the most potent in its class, and it measures 1.9 nm. Based on this information one can conclude that the optimum length for neuromuscular blocking agents, depolarizing or not, should be 2 to 2.1 nm.
The CAR for long-chain bisquaternary tetrahydroisoquinolines like atracurium, cisatracurium, mivacurium, and doxacurium is hard to determine because of their bulky onium heads and large number of rotatable bonds and groups. These agents must follow the same receptive topology as others, which means that they do not fit between the receptive sites without bending. Mivacurium for example has a molecular length of 3.6 nm when stretched out, far from the 2 to 2.1 nm optimum. Mivacurium, atracurium, and doxacurium have greater N-N distance and molecular length than d-tubocurarine even when bent. To make them fit, they have flexible connections that give their onium heads a chance to position themselves beneficially. This bent N-N scenario probably does not apply to laudexium and decamethylene bisatropium, which prefer a straight conformation.
Beers and Reich's law
It has been concluded that acetylcholine and related compounds must be in the gauche (bent) configuration when bound to the nicotinic receptor. Beers and Reich's studies on cholinergic receptors in 1970 showed a relationship affecting whether a compound was muscarinic or nicotinic. They showed that the distance from the centre of the quaternary N atom to the van der Waals extension of the respective O atom (or an equivalent H-bond acceptor) is a determining factor. If the distance is 0.44 nm, the compound shows muscarinic properties—and if the distance is 0.59 nm, nicotinic properties dominate.)
Rational design
Pancuronium remains one of the few muscle relaxants logically and rationally designed from structure-action / effects relationship data. A steroid skeleton was chosen because of its appropriate size and rigidness. Acetylcholine moieties were inserted to increase receptor affinity. Although having many unwanted side-effects, a slow onset of action and recovery rate it was a big success and at the time the most potent neuromuscular drug available. Pancuronium and some other neuromuscular blocking agents block M2-receptors and therefore affect the vagus nerve, leading to hypotension and tachycardia. This muscarinic blocking effect is related to the acetylcholine moiety on the A ring on pancuronium. Making the N atom on the A ring tertiary, the ring loses its acetylcholine moiety, and the resulting compound, vecuronium, has nearly 100 times less affinity to muscarin receptors while maintaining its nicotinic affinity and a similar duration of action. Vecuronium is, therefore, free from cardiovascular effects. The D ring shows excellent properties validating Beers and Reich's rule with great precision. As a result, vecuronium has the greatest potency and specificity of all mono-quaternary compounds.
Potency
Two functional groups contribute significantly to aminosteroidal neuromuscular blocking potency, it is presumed to enable them to bind the receptor at two points. A bis-quaternary two point arrangement on A and D-ring (binding inter-site) or a D-ring acetylcholine moiety (binding at two points intra-site) are most likely to succeed. A third group can have variable effects. The quaternary and acetyl groups on the A and D ring of pipecuronium prevent it from binding intra-site (binding to two points at the same site). Instead, it must bind as bis-quaternary (inter-site). These structures are very dissimilar from acetylcholine and free pipecuronium from nicotinic or muscarinic side-effects linked to acetylcholine moiety. Also, they protect the molecule from hydrolysis by cholinesterases, which explain its nature of kidney excretion. The four methyl-groups on the quaternary N atoms make it less lipophilic than most aminosteroids. This also affects pipecuroniums metabolism by resisting hepatic uptake, metabolism, and biliary excretion. The length of the molecule (2.1 nm, close to ideal) and its rigidness make pipecuronium the most potent and clean one-bulk bis-quaternary. Even though the N-N distance (1.6 nm) is far away from what is considered ideal, its onium heads are well-exposed, and the quaternary groups help to bring together the onium heads to the anionic centers of the receptors without chirality issues.
Adding more than two onium heads in general does not add to potency. Though the third onium head in gallamine seems to help position the two outside heads near the optimum molecular length, it can interfere unfavorably and gallamine turns out to be a weak muscle relaxant, like all multi-quaternary compounds.
Considering acetylcholine a quaternizing group larger than methyl and an acyl group larger than acetyl would reduce the molecule's potency. The charged N and the carbonyl O atoms are distanced from structures they bind to on receptive sites and, thus, decrease potency. The carbonyl O in vecuronium for example is thrust outward to appose the H-bond donor of the receptive site. This also helps explain why gallamine, rocuronium, and rapacuronium are of relatively low potency.
In general, methyl quaternization is optimal for potency but, opposing this rule, the trimethyl derivatives of gallamine are of lower potency than gallamine. The reason for this is that gallamine has a suboptimal N-N distance. Substituting the ethyl groups with methyl groups would make the molecular length also shorter than optimal. Methoxylation of tetrahydroisoquinolinium agents seems to improve their potency. How methoxylation improves potency is still unclear.
Histamine release is a common attribute of benzylisoquinolinium muscle relaxants. This problem generally decreases with increased potency and smaller doses. The need for larger doses increases the degree of this side-effect. Conformational or structural explanations for histamine release are not clear.
Pharmacokinetics
Metabolism and Hofmann elimination
Deacetylating vecuronium at position 3 results in a very active metabolite. In the case of rapacuronium the 3-deacylated metabolite is even more potent than rapacuronium. As long as the D-ring acetylcholine moiety is unchanged they retain their muscle relaxing effect. Mono-quaternary aminosteroids produced with deacylation in position 17 on the other hand are generally weak muscle relaxants. In the development of atracurium the main idea was to make use of Hofmann elimination of the muscle relaxant in vivo. When working with bisbenzyl-isoquinolinium types of molecules, inserting proper features into the molecule such as an appropriate electron withdrawing group then Hofmann elimination should occur at conditions in vivo. Atracurium, the resulting molecule, breaks down spontaneously in the body to inactive compounds and being especially useful in patients with kidney or liver failure. Cis-atracurium is very similar to atracurium except it is more potent and has a weaker tendency to cause histamine release.
Structure relations to onset time
The effect of structure on the onset of action is not very well known except that the time of onset appears inversely related to potency. In general mono-quaternary aminosteroids are faster than bis-quaternary compounds, which means they are also of lower potency. A possible explanation for this effect is that drug delivery and receptor binding are of a different timescale. Weaker muscle relaxants are given in larger doses so more molecules in the central compartment must diffuse into the effect compartment, which is the space within the mouth of the receptor, of the body. After delivery to the effect compartment then all molecules act quickly. Therapeutically this relationship is very inconvenient because low potency, often meaning low specificity can decrease the safety margin thus increasing the chances of side-effects. In addition, even though low potency usually accelerates onset of action, it does not guaranty a fast onset. Gallamine, for example, is weak and slow. When fast onset is necessary then succinylcholine or rocuronium are usually preferable.
Elimination
Muscle relaxants can have very different metabolic pathways and it is important that the drug does not accumulate if certain elimination pathways are not active, for example in kidney failure.
Medical Use
Endotracheal intubation
Administration of neuromuscular blocking agents (NMBA) during anesthesia can facilitate endotracheal intubation. This can decrease the incidence of postintubation hoarseness and airway injury.
Short-acting neuromuscular blocking agents are chosen for endotracheal intubation for short procedures (< 30minutes), and neuromonitoring is required soon after intubation. Options include succinylcholine, rocuronium or vecuronium if sugammadex is available for rapid reversal block.
Any short or intermediate acting neuromuscular blocking agents can be applied for endotracheal intubation for long procedures (≥ 30 minutes). Options include succinylcholine, rocuronium, vecuronium, mivacurium, atracurium and cisatracurium. The choice among these NMBA depends on availability, cost and patient parameters that affect drug metabolism.
Intraoperative relaxation can be maintained as necessary with additional dose of nondepolarizing NMBA.
Among all NMBA, Succinylcholine establish the most stable and fastest intubating conditions, thus is considered as the preferred NMBA for rapid sequence induction and intubation (RSII). Alternatives for succinylcholine for RSII include high dose rocuronium (1.2mg/kg which is a 4 X ED95 dose), or avoidance of NMBAs with a high dose remifentanil intubation.
Facilitation of surgery
Nondepolarizing NMBAs can be used to induce muscle relaxation that improves surgical conditions, including laparoscopic, robotic, abdominal and thoracic procedures. It can reduce patient movement, muscle tone, breathing or coughing against ventilator and allow lower insufflation pressure during laparoscopy. Administration of NMBAs should be individualized according to patient’s parameters. However, many operations can be performed without the need to apply any NMBAs as adequate anesthesia during surgery can achieve many of the theoretical benefits of neuromuscular blockage.
Adverse effects
Since these drugs may cause paralysis of the diaphragm, mechanical ventilation should be at hand to provide respiration.
In addition, these drugs may exhibit cardiovascular effects, since they are not fully selective for the nicotinic receptor and hence may have effects on muscarinic receptors. If nicotinic receptors of the autonomic ganglia or adrenal medulla are blocked, these drugs may cause autonomic symptoms. Also, neuromuscular blockers may facilitate histamine release, which causes hypotension, flushing, and tachycardia.
Succinylcholine may also trigger malignant hyperthermia in rare cases in patients who may be susceptible.
In depolarizing the musculature, suxamethonium may trigger a transient release of large amounts of potassium from muscle fibers. This puts the patient at risk for life-threatening complications, such as hyperkalemia and cardiac arrhythmias. Other effects include myalgia, increased intragastric pressure, increased intraocular pressure, increased intracranial pressure, cardiac dysrhythmias (bradycardia is the most common type) and allergic reactions. As a result, it is contraindicated for patients with susceptibility to malignant hyperthermia, denervating conditions, major burns after 48 hours, and severe hyperkalemia.
For nondepolarizing NMBAs except vecuronium, pipecuronium, doxacurium, cisatracurium, rocuronium and rapacuronium, they produce certain extent of cardiovascular effect. Moreover, Tubocurarine can produce hypotension effect while Pancuronium can lead to moderate increase in heart rate and small increase in cardiac output with little or no increase in systemic vascular resistance, which is unique in nondeploarizing NMBAs.
Certain drugs such as aminoglycoside antibiotics and polymyxin and some fluoroquinolones also have neuromuscular blocking action as their side-effect.
Interactions
Some drugs enhance or inhibit the response to NMBAs which require the dosage adjustment guided by monitoring.
Combination of NMBAs
In some clinical circumstances, succinylcholine may be administered before and after a nondepolarising NMBA or two different nondepolarising NMBAs are administered in sequence. Combining different NMBAs can result in different degrees of neuromuscular block and management should be guided with the use of a neuromuscular function monitor.
The administration of nondepolarising neuromuscular blocking agent has an antagonistic effect on the subsequent depolarising block induced by succinylcholine. If a nondepolarising NMBA is administered prior to succinycholine, the dose of succinylcholine must be increased.
The administration of succinylcholine on the subsequent administration of a nondepolarising neuromuscular block depends on the drug used. Studies have shown that administration of succinylcholien before a nondepolarising NMBA does not affect the potency of mivacurium or rocuronium. But for vecuronium and cisatracurium, it speeds up the onset, increases the potency and prolongs the duration of action.
Combining two nondepolarising NMBAs of the same chemical class (e.g. rocuronium and vecuronium) produces an additive effect, while combining two nondepolarising NMBAs of different chemical class (e.g. rocuronium and cisatracurium) produces a synergistic response.
Inhaled anesthetics
Inhaled anesthetics inhibit nicotinic acetylcholine receptors (nAChRs) and potentiate neuromuscular blockage with nondepolarising NMBAs. It depends on the type of volatile anesthetic (desflurane > sevoflurane > isoflurane > nitrous oxide), the concentration and the duration of exposure.
Antibiotics
Tetracycline, aminoglycosides, polymyxins and clindamycin potentiate neuromuscular blockage by inhibiting ACh release or desensitisation of post-synpatic nAChRs to ACh. This interaction happens mostly during maintenance of anesthesia. As antibiotics typically are given after a dose of NMBA, this interaction needs to be considered when re-dosing NMBA.
Anti-seizure drugs
Patients receiving chronic treatment are relatively resistance to nondepolarising NMBAs due to the accelerated clearance.
Lithium
Lithium is structurally similar to other cations such as sodium, potassium, magnesium and calcium, this causes lithium to activate potassium channels which inhibit neuromuscular transmission. Patients who take lithium can have a prolonged response to both depolarising and nondepolarising NMBAs.
Antidepressants
Sertraline and amitriptyline inhibit butyrylcholinesterase and cause prolonged paralysis. Mivacurium causes prolonged paralysis for patients chronically taking sertraline.
Local anesthetics (LAs)
LAs may enhance the effects of depolarisation and nondepolarising NMBAs through pre and post-synaptic interactions at the NMJ. It may result in blood levels high enough to potentiate NMBA-induced neuromuscular block. Epidurally administered levobupivacaine and mepivacaine potentiate amino-steroidal NMBAs and delay recovery from neuromuscular blockade.
Estimating effect
Methods for estimating the degree of neuromuscular block include valuation of muscular response to stimuli from surface electrodes, such as in the train-of-four test, wherein four such stimuli are given in rapid succession. With no neuromuscular blockade, the resultant muscle contractions are of equal strength, but gradually decrease in case of neuromuscular blockade. It is recommended during use of continuous-infusion neuromuscular blocking agents in intensive care.
Reversal
The effect of non-depolarizing neuromuscular-blocking drugs may be reversed with acetylcholinesterase inhibitors, neostigmine, and edrophonium, as commonly used examples. Of these, edrophonium has a faster onset of action than neostigmine, but it is unreliable when used to antagonize deep neuromuscular block. Acetylcholinesterase inhibitors increase the amount of acetylcholine in the neuromuscular junction, so a prerequisite for their effect is that the neuromuscular block is not complete, because in case every acetylcholine receptor is blocked then it does not matter how much acetylcholine is present.
Sugammadex is a newer drug for reversing neuromuscular block by rocuronium and vecuronium in general anaesthesia. It is the first selective relaxant binding agent (SRBA).
History
Curare is a crude extract from certain South American plants in the genera Strychnos and Chondrodendron, originally brought to Europe by explorers such as Walter Raleigh Edward Bancroft, a chemist and physician in the 16th century brought samples of crude curare from South America back to the Old-World. The effect of curare was experimented with by Sir Benjamin Brodie when he injected small animals with curare, and found that the animals stopped breathing but could be kept alive by inflating their lungs with bellows. This observation led to the conclusion that curare can paralyse the respiratory muscles. It was also experimented by Charles Waterton in 1814 when he injected three donkeys with curare. The first donkey was injected in the shoulder and died afterward. The second donkey had a tourniquet applied to the foreleg and was injected distal to the tourniquet. The donkey lived while the tourniquet was in place but died after it was removed. The third donkey after injected with curare appeared to be dead but was resuscitated using bellows. Charles Waterton's experiment confirmed the paralytic effect of curare.
It was known in the 19th century to have a paralysing effect, due in part to the studies of scientists like Claude Bernard. D-tubocurarine a mono-quaternary alkaloid was isolated from Chondrodendron tomentosum in 1942, and it was shown to be the major constituent in curare responsible for producing the paralysing effect. At that time, it was known that curare and, therefore, d-tubocurarine worked at the neuromuscular junction. The isolation of tubocurarine and its marketing as the drug Intocostrin led to more research in the field of neuromuscular-blocking drugs. Scientists figured out that the potency of tubocurarine was related to the separation distance between the two quaternary ammonium heads.
Neurologist Walter Freeman learned about curare and suggested to Richard Gill, a patient suffering from multiple sclerosis, that he try using it. Gill brought 25 pounds of raw curare from Ecuador. The raw curare was then given to Squibb and Sons to derive an effective antidote to curare. In 1942, Wintersteiner and Dutcher (two scientists working for Squibb and Sons) isolated the alkaloid d-tubocurarine. Soon after, they developed a preparation of curare called Intocostrin.
At the same time in Montreal, Harold Randall Griffith and his resident Enid Johnson at the Homeopathic Hospital administered curare to a young patient undergoing appendectomy. This was the first use of NMBA as muscle relaxant in anesthesia.
The 1940s, 1950s and 1960s saw the rapid development of several synthetic NMBA. Gallamine was the first synthetic NMBA used clinically. Further research led to the development of synthesized molecules with different curariform effects, depending on the distance between the quaternary ammonium groups. One of the synthesized bis-quaternaries was decamethonium a 10-carbon bis-quaternary compound. Following research with decamethonium, scientists developed suxamethonium, which is a double acetylcholine molecule that was connected at the acetyl end. The discovery and development of suxamethonium lead to a Nobel Prize in medicine in 1957. Suxamethonium showed different blocking effect in that its effect was achieved more quickly and augmented a response in the muscle before block. Also, tubocurarine effects were known to be reversible by acetylcholinesterase inhibitors, whereas decamethonium and suxamethonium block were not reversible.
Another compound malouétine that was a bis-quaternary steroid was isolated from the plant Malouetia bequaertiana and showed curariform activity. This led to the synthetic drug pancuronium, a bis-quaternary steroid, and subsequently other drugs that had better pharmacological properties. Research on these molecules helped improve understanding of the physiology of neurons and receptors.
Outdated treatment
Gallamine triethiodide is originally developed for preventing muscle contractions during surgical procedures. However, it is no longer marketed in the United States according to the FDA orange book.
See also
Ganglionic blocker
Cholinergic blocking drugs
References
External links
Muscle relaxants
Muscular system
Neurochemistry | Neuromuscular-blocking drug | Chemistry,Biology | 9,249 |
44,390,320 | https://en.wikipedia.org/wiki/List%20of%20arbitrary-precision%20arithmetic%20software | This article lists libraries, applications, and other software which enable or support arbitrary-precision arithmetic.
Libraries
Stand-alone application software
Software that supports arbitrary precision computations:
bc the POSIX arbitrary-precision arithmetic language that comes standard on most Unix-like systems.
dc: "Desktop Calculator" arbitrary-precision RPN calculator that comes standard on most Unix-like systems.
KCalc, Linux based scientific calculator
Maxima: a computer algebra system which bignum integers are directly inherited from its implementation language Common Lisp. In addition, it supports arbitrary-precision floating-point numbers, bigfloats.
Maple, Mathematica, and several other computer algebra software include arbitrary-precision arithmetic. Mathematica employs GMP for approximate number computation.
PARI/GP, an open source computer algebra system that supports arbitrary precision.
Qalculate!, an open-source free software arbitrary precision calculator with autocomplete.
SageMath, an open-source computer algebra system
SymPy, a CAS
Symbolic Math toolbox (MATLAB)
Windows Calculator, since Windows 98, uses arbitrary precision for basic operations (addition, subtraction, multiplication, division) and 32 digits of precision for advanced operations (square root, transcendental functions).
SmartXML, a free programming language with integrated development environment (IDE) for mathematical calculations. Variables of BigNumber type can be used, or regular numbers can be converted to big numbers using conversion operator # (e.g., #2.3^2000.1). SmartXML big numbers can have up to 100,000,000 decimal digits and up to 100,000,000 whole digits.
Languages
Programming languages that support arbitrary precision computations, either built-in, or in the standard library of the language:
Ada: the upcoming Ada 202x revision adds the Ada.Numerics.Big_Numbers.Big_Integers and Ada.Numerics.Big_Numbers.Big_Reals packages to the standard library, providing arbitrary precision integers and real numbers.
Agda: the BigInt datatype on Epic backend implements arbitrary-precision arithmetic.
Common Lisp: The ANSI Common Lisp standard supports arbitrary precision integer, ratio, and complex numbers.
C#: System.Numerics.BigInteger, from .NET 5
ColdFusion: the built-in PrecisionEvaluate() function evaluates one or more string expressions, dynamically, from left to right, using BigDecimal precision arithmetic to calculate the values of arbitrary precision arithmetic expressions.
D: standard library module std.bigint
Dart: the built-in int datatype implements arbitrary-precision arithmetic.
Emacs Lisp: supports integers of arbitrary size, starting with Emacs 27.1.
Erlang: the built-in Integer datatype implements arbitrary-precision arithmetic.
Go: the standard library package math/big implements arbitrary-precision integers (Int type), rational numbers (Rat type), and floating-point numbers (Float type)
Guile: the built-in exact numbers are of arbitrary precision. Example: (expt 10 100) produces the expected (large) result. Exact numbers also include rationals, so (/ 3 4) produces 3/4. One of the languages implemented in Guile is Scheme.
Haskell: the built-in Integer datatype implements arbitrary-precision arithmetic and the standard Data.Ratio module implements rational numbers.
Idris: the built-in Integer datatype implements arbitrary-precision arithmetic.
ISLISP: The ISO/IEC 13816:1997(E) ISLISP standard supports arbitrary precision integer numbers.
J: built-in extended precision
Java: Class (integer), Class (decimal)
JavaScript: as of ES2020, BigInt is supported in most browsers; the gwt-math library provides an interface to java.math.BigDecimal, and libraries such as DecimalJS, BigInt and Crunch support arbitrary-precision integers.
Julia: the built-in BigFloat and BigInt types provide arbitrary-precision floating point and integer arithmetic respectively.
newRPL: integers and floats can be of arbitrary precision (up to at least 2000 digits); maximum number of digits configurable (default 32 digits)
Nim: bigints and multiple GMP bindings.
OCaml: The Num library supports arbitrary-precision integers and rationals.
OpenLisp: supports arbitrary precision integer numbers.
Perl: The bignum and bigrat pragmas provide BigNum and BigRational support for Perl.
PHP: The BC Math module provides arbitrary precision mathematics.
PicoLisp: supports arbitrary precision integers.
Pike: the built-in int type will silently change from machine-native integer to arbitrary precision as soon as the value exceeds the former's capacity.
Prolog: ISO standard compatible Prolog systems can check the Prolog flag "bounded". Most of the major Prolog systems support arbitrary precision integer numbers.
Python: the built-in int (3.x) / long (2.x) integer type is of arbitrary precision. The Decimal class in the standard library module decimal has user definable precision and limited mathematical operations (exponentiation, square root, etc. but no trigonometric functions). The Fraction class in the module fractions implements rational numbers. More extensive arbitrary precision floating point arithmetic is available with the third-party "mpmath" and "bigfloat" packages.
Racket: the built-in exact numbers are of arbitrary precision. Example: (expt 10 100) produces the expected (large) result. Exact numbers also include rationals, so (/ 3 4) produces 3/4. Arbitrary precision floating point numbers are included in the standard library math/bigfloat module.
Raku: Rakudo supports Int and FatRat data types that promote to arbitrary-precision integers and rationals.
Rexx: variants including Open Object Rexx and NetRexx
RPL (only on HP 49/50 series in exact mode): calculator treats numbers entered without decimal point as integers rather than floats; integers are of arbitrary precision only limited by the available memory.
Ruby: the built-in Bignum integer type is of arbitrary precision. The BigDecimal class in the standard library module bigdecimal has user definable precision.
Scheme: R5RS encourages, and R6RS requires, that exact integers and exact rationals be of arbitrary precision.
Scala: Class BigInt and Class BigDecimal.
Seed7: bigInteger and bigRational.
Self: arbitrary precision integers are supported by the built-in bigInt type.
Smalltalk: variants including Squeak, Smalltalk/X, GNU Smalltalk, Dolphin Smalltalk, etc.
SmartXML, a free programming language with integrated development environment (IDE) for mathematical calculations. Variables of BigNumber type can be used, or regular numbers can be converted to big numbers using conversion operator # (e.g., #2.3^2000.1). SmartXML big numbers can have up to 100,000,000 decimal digits and up to 100,000,000 whole digits.
Standard ML: The optional built-in IntInf structure implements the INTEGER signature and supports arbitrary-precision integers.
Tcl: As of version 8.5 (2007), integers are arbitrary-precision by default. (Behind the scenes, the language switches to using an arbitrary-precision internal representation for integers too large to fit in a machine word. Bindings from C should use library functions such as Tcl_GetLongFromObj to get values as C-native data types from Tcl integers.)
Wolfram Language, like Mathematica, employs GMP for approximate number computation.
Online calculators
For one-off calculations. Runs on server or in browser. No installation or compilation required.
1. https://www.mathsisfun.com/calculator-precision.html 200 places
2. http://birrell.org/andrew/ratcalc/ arbitrary; select rational or fixed-point and number of places
3. PARI/GP online calculator - https://pari.math.u-bordeaux.fr/gp.html (PARI/GP is a widely used computer algebra system designed for fast computations in number theory (factorizations, algebraic number theory, elliptic curves, modular forms, L functions...), but also contains a large number of other useful functions to compute with mathematical entities such as matrices, polynomials, power series, algebraic numbers etc., and a lot of transcendental functions. PARI is also available as a C library to allow for faster computations.)
4.1. AutoCalcs - allow users to Search, Create, Store and Share multi-step calculations using explicit expressions featuring automated Unit Conversion. It is a platform that allows users to go beyond unit conversion, which in turn brings in significantly improved efficiency. A lot of sample calculations can be found at AutoCalcs Docs site. Calculations created with AutoCalcs can be embedded into 3rd party websites.
4.2. AutoCalcs Docs - considering above mentioned AutoCalcs as the calculation engine, this Docs site is a library with a host of calculations, where each calculation is essentially a web app that can run online, be further customized, and much more. Imaging reading a book with a lot of calculations, then this is the book/manual with all calculations that can be used on the fly. It is worthwhile to mention - when units are involved in the calculations, the unit conversion can be automated.
References
Lists of software
Computer arithmetic | List of arbitrary-precision arithmetic software | Mathematics,Technology | 2,007 |
2,969,710 | https://en.wikipedia.org/wiki/PolyAPTAC | PolyAPTAC, or poly (acrylamido-N-propyltrimethylammonium chloride), is an organic polymer. It is water-soluble, forms gels when cross linked, and acts as a cationic polyelectrolyte. It can be used for ion exchange resins. It can form hydrogels.
PolyMAPTAC, or poly[(3-(methacryloylamino)-propyl] trimethylammonium chloride), is similar.
References
Acrylate polymers
Polyelectrolytes | PolyAPTAC | Chemistry | 121 |
57,019,935 | https://en.wikipedia.org/wiki/Diacetyl%20monoxime | Diacetyl monoxime is a chemical compound described by the formula CH3C(O)C(NOH)CH3. This colourless solid is the monooxime derivative of the diketone butane-2,3-dione (also known as diacetyl and biacetyl). Its biological effects include inhibiting certain ATPases.
Preparation
The compound can be prepared from butanone by reaction with ethyl nitrite. It is an intermediate in the preparation of dimethylglyoxime:
Uses
Diacetyl monoxime can be used with thiosemicarbazide to selectively detect small amounts of urea in the presence of other nitrogen-containing compounds.
References
Ketoximes
Chelating agents | Diacetyl monoxime | Chemistry | 161 |
3,311,548 | https://en.wikipedia.org/wiki/Community%20Plant%20Variety%20Office | The Community Plant Variety Office (CPVO) is an agency of the European Union, located in Angers, France. It was established in 1994. Its task is to administer a system of plant variety rights, also known as plant breeders' rights, a form of intellectual property right relating to plants.
The CPVO manages the largest system of plant variety rights in the world. Since the creation of the CPVO in 1995, the office has received about 78,000 applications, of which over 62,000 were granted, with over 30,000 rights currently in force.
Community plant variety right
Plant variety rights allow plant breeders to protect new varieties or types of plants. The CPVO was created to encourage the creation of new plant varieties in the European Union, through the provision of better intellectual property protection for plant breeders. The Community plant variety right gives to its holder an exclusive right to market the protected variety within the territory of the European Union. The Community PVR is valid for a period of 25 to 30 years.
Breeders' Exemption
The Breeders' Exemption ensures that anyone is allowed to use protected (PVR) varieties as a basis for the creation of new varieties. The Breeders' Exemption exists to ensure that PVR and the need to reward breeders for their work is balanced with the need for new and better varieties to reach and benefit the consumer as quickly as possible. It also ensures the continued production of new varieties as breeders need access to as much genetic resources as possible, including protected varieties, in order to create new varieties.
Application
The CPVO system of PVR protection means that only one application need be made (directly to the CPVO) in order to attain EU-wide protection. Before its introduction, EU-wide protection was only possible through obtaining national plant variety rights from the individual member states. That option still exists today.
As part of the application procedure, each candidate variety is tested by an examination office. The examination offices are based in the member states, where they are operated by national experts. The examination offices determine whether the variety is distinct, uniform and stable – this is called a DUS test. The CPVO does not own any technical infrastructure.
The results of the DUS tests are used by the CPVO when taking the decision to grant or refuse a PVR application.
Organisation
Based in Angers, France the CPVO was created by the Council Regulation 2100/94 and has been operational since the 27 April 1995.
The CPVO is entirely self-financed. It neither takes from nor contributes to the EU budget. The CPVO's budget is principally derived from PVR application fees paid by breeders who wish to protect their creations.
• President. Responsible for the operation of the office, legislative functions and all operational aspects. He is appointed by the Council of the EU.
Current President: Francesco Mattina, appointed in 2021. In the past, he served as Vice President from 2017 to 2021 and joined the office in 2013 as Head of Legal Unit.
• Administrative Council. Supervises the CPVO. It is made up of representatives of the 27 member states, representatives of the European Commission and observer organizations. It is also the budgetary authority of the CPVO and adopts the annual work schedule of responsibilities.
• Exams office. They carry out the DHS studies of the corresponding applications.
References
External links
Community Plant Variety Office
Agencies of the European Union
Patent law organizations
Government agencies established in 1994
1994 establishments in France
Angers
1994 in the European Union
Agricultural organizations based in France | Community Plant Variety Office | Chemistry | 704 |
68,291,716 | https://en.wikipedia.org/wiki/Vida%20Dujmovi%C4%87 | Vida Dujmović is a Canadian computer scientist and mathematician known for her research in graph theory and graph algorithms, and particularly for graph drawing, for the structural theory of graph width parameters including treewidth and queue number, and for the use of these parameters in the parameterized complexity of graph drawing. She is a professor of electrical engineering & computer science at the University of Ottawa, where she holds the University Research Chair in Structural and Algorithmic Graph Theory.
Education
Dujmović studied telecommunications and computer science as an undergraduate at the University of Zagreb, graduating in 1996. She came to McGill University for graduate study in computer science, earning a master's degree in 2000 and completing her Ph.D. in 2004. Her dissertation, Track Layouts of Graphs, was supervised by Sue Whitesides, and won the 2005 NSERC Doctoral Prize of the Natural Sciences and Engineering Research Council.
Career
She was an NSERC Postdoctoral Fellow at Carleton University, a CRM-ISM Postdoctoral Fellow at McGill University, and a postdoctoral researcher again at Carleton University before finally becoming an assistant professor at Carleton University in 2012. She moved to the University of Ottawa in 2013.
Recognition
In 2023 the University of Ottawa gave her the Glinski Award for Excellence in Research and the University Research Chair in Structural and Algorithmic Graph Theory. Vida Dujmović was an invited speaker at the 9th European Congress of Mathematics.
References
External links
Home page
Living people
Canadian computer scientists
Canadian mathematicians
Canadian women computer scientists
Canadian women mathematicians
Academic staff of Carleton University
Yugoslav emigrants to Canada
Graph theorists
McGill University alumni
Researchers in geometric algorithms
Academic staff of the University of Ottawa
University of Zagreb alumni
Year of birth missing (living people) | Vida Dujmović | Mathematics | 340 |
29,006 | https://en.wikipedia.org/wiki/Space%20telescope | A space telescope (also known as space observatory) is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first operational telescopes were the American Orbiting Astronomical Observatory, OAO-2 launched in 1968, and the Soviet Orion 1 ultraviolet telescope aboard space station Salyut 1 in 1971. Space telescopes avoid several problems caused by the atmosphere, including the absorption or scattering of certain wavelengths of light, obstruction by clouds, and distortions due to atmospheric refraction such as twinkling. Space telescopes can also observe dim objects during the daytime, and they avoid light pollution which ground-based observatories encounter. They are divided into two types: Satellites which map the entire sky (astronomical survey), and satellites which focus on selected astronomical objects or parts of the sky and beyond. Space telescopes are distinct from Earth imaging satellites, which point toward Earth for satellite imaging, applied for weather analysis, espionage, and other types of information gathering.
History
In 1946, American theoretical astrophysicist Lyman Spitzer, "father of Hubble" proposed to put a telescope in space. Spitzer's proposal called for a large telescope that would not be hindered by Earth's atmosphere. After lobbying in the 1960s and 70s for such a system to be built, Spitzer's vision ultimately materialized into the Hubble Space Telescope, which was launched on April 24, 1990, by the Space Shuttle Discovery (STS-31). This was launched due to many efforts by Nancy Grace Roman, "mother of Hubble", who was the first Chief of Astronomy and first female executive at NASA. She was a program scientist that worked to convince NASA, Congress, and others that Hubble was "very well worth doing".
The first operational space telescopes were the American Orbiting Astronomical Observatory, OAO-2 launched in 1968, and the Soviet Orion 1 ultraviolet telescope aboard space station Salyut 1 in 1971.
Advantages
Performing astronomy from ground-based observatories on Earth is limited by the filtering and distortion of electromagnetic radiation (scintillation or twinkling) due to the atmosphere. A telescope orbiting Earth outside the atmosphere is subject neither to twinkling nor to light pollution from artificial light sources on Earth. As a result, the angular resolution of space telescopes is often much higher than a ground-based telescope with a similar aperture. Many larger terrestrial telescopes, however, reduce atmospheric effects with adaptive optics.
Space-based astronomy is more important for frequency ranges that are outside the optical window and the radio window, the only two wavelength ranges of the electromagnetic spectrum that are not severely attenuated by the atmosphere. For example, X-ray astronomy is nearly impossible when done from Earth, and has reached its current importance in astronomy only due to orbiting X-ray telescopes such as the Chandra X-ray Observatory and the XMM-Newton observatory. Infrared and ultraviolet are also largely blocked.
Disadvantages
Space telescopes are much more expensive to build than ground-based telescopes. Due to their location, space telescopes are also extremely difficult to maintain. The Hubble Space Telescope was serviced by the Space Shuttle, but most space telescopes cannot be serviced at all.
Future of space observatories
Satellites have been launched and operated by NASA, ISRO, ESA, CNSA, JAXA and the Soviet space program (later succeeded by Roscosmos of Russia). As of 2022, many space observatories have already completed their missions, while others continue operating on extended time. However, the future availability of space telescopes and observatories depends on timely and sufficient funding. While future space observatories are planned by NASA, JAXA and the CNSA, scientists fear that there would be gaps in coverage that would not be covered immediately by future projects and this would affect research in fundamental science.
On 16 January 2023, NASA announced preliminary considerations of several future space telescope programs, including the Great Observatory Technology Maturation Program, Habitable Worlds Observatory, and New Great Observatories.
List of space telescopes
See also
Airborne observatory
Balloon-borne telescope
Earth observation satellite
List of telescope types
Timeline of artificial satellites and space probes
Timeline of telescopes, observatories, and observing technology
Ultraviolet astronomy
X-ray telescope
References
Further reading
Lyman Spitzer, "Astronomical Advantages of an Extra-terrestrial Observatory", 1946
Neil English: Space Telescopes – Capturing the Rays of the Electromagnetic Spectrum. Springer, Cham 2017, .
External links
·
Space telescopes with frequencies, at GSFC.
American inventions
Astronomical observatories
Telescope types
Uncrewed spacecraft | Space telescope | Astronomy | 922 |
36,026,013 | https://en.wikipedia.org/wiki/%C3%87NAEM | The Çekmece Nuclear Research and Training Center (), known as ÇNAEM, is the primary nuclear research and training center of Turkey. The organization was established on March 6, 1958 as a subunit of Turkish Atomic Energy Administration (, TAEK) at Küçükçekmece district in the west of Istanbul. The organization's name was coined on August 12, 1960 in conjunction with its location.
The groundbreaking of the facility at the eastern shore of Lake Küçükçekmece to house the country's first nuclear research reactor was held in 1959. After completion of the construction and the start of the operation of the research reactor, the official opening of the center took place on May 27, 1962 in the presence of President Cemal Gürsel.
The center is directed by Ass. Prof. Dr. Gürsel Karahan.
Organization
The acquired valuable knowledge and experience at the institution led in 2010 to the reorganization of ÇNAEM. The six main service divisions newly established are:
Nuclear Technics Division
Application of nuclear technics in industry, medicine and research such as non-destructive (NDT)tests, radiopharmasotics.
Nuclear Electronics Division
Production and calibration of radiation monitors, radioactive measurement devices etc. Calibration of ionizing radiation gauges and dosimeters in the industry, medicine and security, as well as for scientific purposes.
Nuclear Technology Division
Research and operation of research reactor, reactor materials in compliance with international and national regulations for nuclear safety, particularly IAEA safeguards and subsidiary agreements.
Radioactivity Analysis and Analytics Division
Radioactivity analysis of all food, liquid, construction materials etc. Soil and water analysis for environmental purposes.
Waste Management Division
Operation of Cekmece low level radioactive waste processing and storage facility (CWPSF). R&D activities in low and high level nuclear wastes, processing and shielding materials. Implementation of national waste management programme.
Health Physics Division
Radiation Protection, controlling before licensing and radiobiological application.
Research reactor TR-1
The pool-type reactor having a capacity of 1 MW that was named TR-1, achieved criticality on January 6, 1962 at 19:14 local time.
After serving 15-year long for the production of radioisotopes and the neutronics experiments with the help of beam tubes, the TR-1 was shut down on September 9, 1977 as its capacity became insufficient.
Research reactor TR-2
Due to increased demand in the 1970s on nuclear research and radioisotopes in the country, the installation of a second nuclear research reactor with higher capacity was projected for the production of radioisotopes only. The reactor with an output capacity of 5 MW, called TR-2, went into service in the same building and the existing pool after becoming criticality in December 1981. The reactor started radioisotope production in 1984.
See also
ITU TRIGA Mark-II Training and Research Reactor
References
Nuclear research institutes
Nuclear research reactors
Research institutes in Turkey
Nuclear technology in Turkey
Science and technology in Turkey
Buildings and structures in Istanbul
Organizations based in Istanbul
Organizations established in 1958
Küçükçekmece
1958 establishments in Turkey | ÇNAEM | Engineering | 635 |
17,312,138 | https://en.wikipedia.org/wiki/John%20J.%20Makinen%20Bottle%20House | The John J. Makinen Bottle House (also known as the Kaleva Bottle House, Kaleva Bottle House Museum, and Kaleva Historical Museum) is a house built of bottle wall construction in 1941 by John J. Makinen, Sr. It is located in Kaleva, Michigan near Manistee. Construction uses over 60,000 bottles laid on their sides with the bottoms toward the exterior.
History
Makinen was a native of Finland and moved to northwestern Michigan in 1903. He owned and operated the Northwestern Bottling Works Company in Kaleva. He died just before he and his family were to move into the new bottle house.
Most of the bottles came from his bottling plant as the bottom of the bottles reveal. There is a large variety of bottles that were used for many products, including drinks, wine, beer, and liqueur. The bottles were not only round, but oblong in shape as well. The bottles are arranged with clear bottles and brown color bottles on the front of the house to spell "HAPPY HOME."
Museum
The Kaleva Historical Society bought the house in 1980. The Kaleva Historical Museum then purchased it in 1981 for a museum after it was remodeled. The museum includes 19th- and 20th-century items. It also has information on the local area schools, along with local companies and families. It is listed on the National Register of Historical Sites and the Michigan Register of Historical Sites as the plaques in front of the house show.
Corking
The term "pop", for carbonated soft drinks, originated in northern Michigan. The museum claims that perhaps it came from the Northwestern Bottling Works Company. It turns out in the early bottling techniques the beverage in its bottle with the cork could not withstand the pressure of the carbonation. On occasion then the cork would blow out of the bottle from the pressure and a loud "POP" sound would be produced.
Children
Early in the opening of the Kaleva Bottle House Museum, the children coming through it often just wanted to see the bathroom, as the bathtub had been featured in a Nickelodeon show with a sock puppet.
References
External links
- Kaleva, Michigan
Houses completed in 1941
Houses on the National Register of Historic Places in Michigan
Historic house museums in Michigan
Museums in Manistee County, Michigan
Roadside attractions in Michigan
Finnish-American history
Finnish-American culture in Michigan
Houses in Manistee County, Michigan
National Register of Historic Places in Manistee County, Michigan
Bottle houses | John J. Makinen Bottle House | Engineering | 508 |
33,937,103 | https://en.wikipedia.org/wiki/Niven%27s%20theorem | In mathematics, Niven's theorem, named after Ivan Niven, states that the only rational values of in the interval for which the sine of degrees is also a rational number are:
In radians, one would require that , that be rational, and that be rational. The conclusion is then that the only such values are , , and .
The theorem appears as Corollary 3.12 in Niven's book on irrational numbers.
The theorem extends to the other trigonometric functions as well. For rational values of , the only rational values of the sine or cosine are , , and ; the only rational values of the secant or cosecant are and ; and the only rational values of the tangent or cotangent are and .
History
Niven's proof of his theorem appears in his book Irrational Numbers. Earlier, the theorem had been proven by D. H. Lehmer and J. M. H. Olmstead. In his 1933 paper, Lehmer proved the theorem for the cosine by proving a more general result. Namely, Lehmer showed that for relatively prime integers and with , the number is an algebraic number of degree , where denotes Euler's totient function. Because rational numbers have degree 1, we must have or and therefore the only possibilities are . Next, he proved a corresponding result for the sine using the trigonometric identity . In 1956, Niven extended Lehmer's result to the other trigonometric functions. Other mathematicians have given new proofs in subsequent years.
See also
Pythagorean triples form right triangles where the trigonometric functions will always take rational values, though the acute angles are not rational.
Trigonometric functions
Trigonometric number
References
Further reading
External links
Rational numbers
Trigonometry
Theorems in geometry
Theorems in algebra | Niven's theorem | Mathematics | 385 |
367,835 | https://en.wikipedia.org/wiki/Normal%20good | In economics, a normal good is a type of a good which experiences an increase in demand due to an increase in income, unlike inferior goods, for which the opposite is observed. When there is an increase in a person's income, for example due to a wage rise, a good for which the demand rises due to the wage increase, is referred as a normal good. Conversely, the demand for normal goods declines when the income decreases, for example due to a wage decrease or layoffs.
Analysis
There is a positive correlation between the income and demand for normal goods, that is, the changes income and demand for normal goods moves in the same direction. That is to say, that normal goods have an elastic relationship for the demand of a good with the income of the person consuming the good.
In economics, the concept of elasticity, and specifically income elasticity of demand is key to explain the concept of normal goods. Income elasticity of demand measures the magnitude of the change in demand for a good in response to a change in consumer income. the income elasticity of demand is calculated using the following formula,
Income elasticity of demand= % change in quantity demanded / % change in consumer income.
In mathematical terms, the formula can be written as follows:
, where is the original quantity demanded and is the original income, before any change.
A good is classified as a normal good when the income elasticity of demand is greater than zero and has a value less than one. If we look into a simple hypothetical example, the demand for apples increases by 10% for a 30% increase in income, then the income elasticity for apples would be 0.33 and hence apples are considered to be a normal good. Other types of goods like luxury and inferior goods are also classified using the income elasticity of demand. The income elasticity of demand for luxury goods will have a value of greater than one and inferior goods will have a value of less than one. Luxury goods also have a positive correlation of demand and income, but with luxury goods, a greater proportion of peoples income are spent on a luxury item, for example, a sports car. On the other hand, with inferior or normal goods, people spend a lesser proportion of their income. Practically, a higher income group of people spend more on luxury items and a lower income group of people spend more of their income on inferior or normal goods.
However, the classification of normal and luxury goods vary from person to person. A good that is considered to be a normal good to a lot of people maybe considered to be luxury good to someone. This depends on a lot of factors such as geographical locations, socio economic conditions in a country, local traditions and many more.
Normal goods and consumer behaviour
The demand for normal goods are determined by many types of consumer behaviour. A rise in income leads to a change in consumer behaviour. When income increases, consumers are able to afford goods that they could not consume before an income rise. The purchasing power of consumers increases. In this situation, the demand rises because of the attractiveness to consumers. The goods are attractive to the consumers maybe because they are high in quality and functionality and also the goods may help to maintain a certain socio economic prestige. Individual consumers have unique behavioural characteristics and they have their preferences accordingly.
According to economic theory, there must be at least one normal good in any given bundle of goods (i.e. not all goods can be inferior). Economic theory assumes that a good always provides marginal utility (holding everything else equal). Therefore, if consumption of all goods decrease when income increases, the resulting consumption combination would fall short of the new budget constraint frontier. This would violate the economic rationality assumption.
When the price of a normal good is zero, the demand is infinite.
Examples
A caveat to the table above is that not all goods are strictly normal or inferior across all income levels. For example, average used cars could have a positive income elasticity of demand at low income levels – extra income could be funnelled into replacing public transportation with self-commuting. However, the income elasticity of demand of average used cars could turn negative at higher income levels, where the consumer may elect to purchase new and/or luxury cars instead.
Another potential caveat is brought up by "The Notion of Inferior Good in the Public Economy" by Professor Jurion of University of Liège (published 1978). Public goods such as online news are often considered inferior goods. However, the conventional distinction between inferior and normal goods may be blurry for public goods. (At least, for goods that are non-rival enough that they are conventionally understood as "public goods.") Consumption of many public goods will decrease when a rational consumer's income rises, due to replacement by private goods, e.g. building a private garden to replace use of public parks. But when effective congestion costs to a consumer rises with the consumer's income, even a normal good with a low income elasticity of demand (independent of the congestion costs associated with the non-excludable nature of the good) will exhibit the same effect. This makes it difficult to distinguish inferior public goods from normal ones.
See also
Consumer theory
Superior good
Ordinary good
Giffen good
References
Goods (economics) | Normal good | Physics | 1,068 |
41,162,191 | https://en.wikipedia.org/wiki/Richard%20B.%20Norgaard | Richard B. Norgaard (born August 18, 1943) is a professor emeritus of ecological economics in the Energy and Resources Group at the University of California, Berkeley, the first chair and a continuing member of the independent science board of CALFED (California Bay-Delta Authority), and a founding member and former president of the International Society for Ecological Economics. He received the Kenneth E. Boulding Memorial Award in 2006 for recognition of advancements in research combining social theory and the natural sciences. He is considered one of the founders of and a continuing leader in the field of ecological economics.
Personal life
Norgaard was born on August 18, 1943, in Washington D. C., and raised in Montclair, an East Bay neighborhood in the San Francisco Bay Area of California.
At an early age, he was interested in white water rafting, and was introduced to the sport by a friend, whose father, Lou Elliott, worked for the Sierra Club coordinating river trips. When he was 15 Norgaard started working for H.A.T.C.H River Expeditions as a pot washer, and was based in Vernal, Utah, near the confluence of the Green River (Colorado River) and Yampa Rivers. Norgaard continued in the business of white water rafting, quickly becoming a head boatman, and bounced around many guiding companies including one that Lou Elliott eventually founded after his career at The Sierra Club. His commitment to and involvement in the environmental movement began when he served as a river guide to David Brower, then executive director of the Sierra Club, for the Glen Canyon stretch of the Colorado River in the early 1960s. Norgaard also worked shortly as a professional photographer prior to his career in academics.
Since 2004, following the election of George W. Bush to a second term, Norgaard has been seen wearing only black colored attire, a silent yet visible protest against the folly of American electorate and the rise of anti-government, market fundamentalism, and "know-nothingism". He has four children and is married to Nancy A. Rader, the Executive Director of the California Wind Energy Association (CALWEA). Norgaard continues river rafting every summer with his family.
Academic career
Norgaard received his B.A. in economics from University of California, Berkeley, a M.S. in agricultural economics from Oregon State University, and a Ph.D. in economics from the University of Chicago in 1971. That same year, at the age of 27, he was an advisor for President Richard Nixon as part of the President’s Council on Environmental Quality. During the 1970s Dr. Norgaard was one of the nation's leading experts on the leasing of petroleum rights, especially on the outer continental shelf, as well as a leading expert on the economics of pesticide use and biological control of pests. He published an influential paper in 1975 that showed that farmers who hired an independent pest-control expert had higher profits and used half as much pesticide as those who relied on the advice of agribusiness representatives.
Dr. Norgaard became a Professor at U.C. Berkeley at the age of 27 in the Department of Agricultural and Resource Economics. Thereafter he helped found the field of Ecological Economics, and also helped initiate the interdisciplinary Energy and Resources Group at U.C. Berkeley as a graduate program in the early 1970s; he was later fully integrated as a member of its core faculty in the 1980s. He was a professor at the University of California, Berkeley for over 40 years before his retirement in 2013, most recently having taught courses in ecological economics; history of economics; and the history, science, and politics of California's water. His field experience was primarily in Alaska, Brazil, California, and Vietnam with minor forays in other parts of the globe.
Dr. Norgaard is the author of one book, co-author or editor of three additional books, and has over 100 other publications spanning the fields of environment and development, tropical forestry and agriculture, environmental epistemology, energy economics, and ecological economics. Although his research scholarship has been an eclectic mix of sociology, economics, philosophy, and the natural sciences, and he is well known for his iconoclast perspectives of conventional economics, stemming from a strong commitment to inter-disciplinarity and social justice, Professor Norgaard is also among the 1000 economists in the world most cited by other economists (Millennium Editions of Who's Who in Economics, 2000) and was one of ten American economists interviewed in The Changing Face of Economics: Conversations with Cutting Edge Economists (Colander, Holt, and Rosser, University of Michigan Press, 2004).
He is frequently recognized within the field of economics (Who’s Who in Economics, Millennium Edition, and The Changing Face of Economics: Conversations with Cutting Edge Economists 2004) and the field of ecological economics (Kenneth E. Boulding Award, 2006) for both his critiques of and contributions to economics even while he has dedicated most of his time working across disciplinary ways of understanding. The American Association for the Advancement of Science elected Norgaard to the status of “Fellow” in 2007. His research emphasizes how the resolution of complex socio-environmental problems challenges modern beliefs about science and policy and explores development as a process of coevolution between social and environmental systems. His writing is informed through work on energy, environment, and development issues around the globe with different periods of his efforts emphasizing Alaska, Brazil, and California.
Norgaard is a lead author of the 5th Assessment of the Intergovernmental Panel on Climate Change, and serves on the International Panel on Sustainable Resource Management of the United Nations Environment Programme. In 2006, Norgaard was awarded the Kenneth Boulding Memorial Award for "expanding transdisciplinary approaches to knowledge, promoting pluralism, and forging a coevolutionary approach to economy, society, and the environment in the spirit of the open and inquisitive mind that was the hallmark of Boulding's work." He was selected as a fellow of the American Association for the Advancement of Science in 2007. Norgaard also is continuing to lead the Bay Delta Conservation Plan of the Independent Science Board of CALFED (California Bay-Delta Authority).
Norgaard serves on the board of directors of the New Economics Institute, on scientific advisory boards to Tsinghua and Beijing Normal University, and on the board of EcoEquity. He has also served on the board of directors of the American Institute of Biological Sciences (2000–2009), in the position of treasurer (2003–2009. He served as president of the International Society for Ecological Economics (1998–2001). He served as the founding chair of the board of Redefining Progress (1994–97) and as a member of its board until 2007. Norgaard was a project specialist with the Ford Foundation in Brazil (1978 and 1979), a visiting research fellow at the World Bank (1992). Norgaard also has previously served on the science advisory board of the U.S. EPA (2000–2004), as a member of the U.S. committee of the Scientific Committee on Problems of the Environment (SCOPE), and on numerous panels of the National Research Council and the former Office of Technology Assessment.
Selected publications
Books
Norgaard, Richard B. 1994. Development Betrayed: The End of Progress and a Coevolutionary Revisioning of the Future. London and New York. Routledge.
Costanza, Robert, John Cumberland, Herman Daly, Robert Goodland, and Richard B. Norgaard. 1997. An Introduction to Ecological Economics (intermediate level college text). International Society for Ecological Economics and St. Lucie Press, Florida.
Dryzek, John S., David Schlosberg, and Richard B. Norgaard. (eds). 2011. The Oxford Handbook of Climate Change and Society. Oxford University Press. Oxford.
Dryzek, John S., Richard B. Norgaard, and David Schlosberg. 2013. Climate-Challenged Society. Oxford University Press.
Selected journal articles
Hall, Darwin C., and Richard B. Norgaard. "On the timing and application of pesticides." American Journal of Agricultural Economics 55.2 (1973): 198–201.
Norgaard, Richard B. "Coevolutionary development potential." Land economics 60.2 (1984): 160–173.
Norgaard, Richard B. "Environmental economics: an evolutionary critique and a plea for pluralism." Journal of Environmental Economics and Management 12.4 (1985): 382–394.
Howarth, Richard B., and Richard B. Norgaard. "Intergenerational resource rights, efficiency, and social optimality." Land economics 66.1 (1990): 1–11.
Mcneely, Jeffrey A., and Richard B. Norgaard. "Developed country policies and biological diversity in developing countries." Agriculture, ecosystems & environment 42.1 (1992): 194–204.
Howarth, Richard B., and Richard B. Norgaard. "Environmental valuation under sustainable development." The American economic review 82.2 (1992): 473–477.
Norgaard, R. B. "Ecology, politics, and economics: finding the common ground for decision making in conservation." Principles of conservation biology. Sinauer Associates, Sunderland, Massachusetts, USA (1994): 439–465.
Norgaard, Richard B., and Thomas O. Sikor. "The methodology and practice of agroecology." Agroecology, the Science of Sustainable Agriculture (1995): 53–62.
Lélé, Sharachchandra, and Richard B. Norgaard. "Sustainability and the scientist’s burden." Conservation Biology 10.2 (1996): 354–365.
Lélé, Sharachchandra, and Richard B. Norgaard. "Practicing interdisciplinarity." BioScience 55.11 (2005): 967–975.
Norgaard, Richard B., and Paul Baer. "Collectively seeing complex systems: The nature of the problem." BioScience 55.11 (2005): 953–960.
Norgaard, Richard B., and Paul Baer. "Collectively seeing climate change: The limits of formal models." BioScience 55.11 (2005): 961–966.
Norgaard, Richard B. "Bubbles in a back eddy: a commentary on “the origin, diagnostic attributes and practical application of coevolutionary theory”." Ecological Economics 54.4 (2005): 362–365.
Sneddon, Christopher, Richard B. Howarth, and Richard B. Norgaard. 2006. Sustainable Development in a Post-Brundtland World. Ecological Economics 57(2):253–68.
Norgaard, Richard B. and Xuemei Liu. 2007. Market Governance Failure. Ecological Economics. 60(3):634–641.
Norgaard, Richard B. "Deliberative economics." Ecological Economics 63.2-3 (2007): 375–82.
Norgaard, Richard B. "Finding hope in the millennium ecosystem assessment." Conservation Biology 22.4 (2008): 862–869.
Norgaard, Richard B., and Ling Jin. "Trade and the governance of ecosystem services." Ecological Economics 66.4 (2008): 638–652.
Norgaard, Richard B., Giorgos Kallis, and Michael Kiparsky. "Collectively engaging complex socio-ecological systems: re-envisioning science, governance, and the California Delta." environmental science & policy 12.6 (2009): 644–652.
Norgaard, Richard B. "Ecosystem services: From eye-opening metaphor to complexity blinder." Ecological Economics 69.6 (2010): 1219–1227.
Kallis, Giorgos, and Richard B. Norgaard. "Coevolutionary ecological economics." Ecological Economics 69.4 (2010): 690–699.
Gual, Miguel A., and Richard B. Norgaard. "Bridging ecological and social systems coevolution: A review and proposal." Ecological economics 69.4 (2010): 707–717.
Articles about
1992. The Price of Green. Economics Focus. The Economist (May 9): 87.
1992. Warsh, David. Economics, Ecology: Twin sciences of the 21st century. Economic Principles. The Boston Sunday Globe (May 24): 29–30.
1992. Interview titled: Wirtschaften für unsere Enkelkinder? WEINER BLÆTTER 05/92 pages 19–21.
1992. Interview titled: Richard B. Norgaard. Options International Institute for Applied Systems Analysis. (September):14-15.
2004. “Richard B. Norgaard”. Chapter 8 in The Changing Face of Economics: Conversations with Cutting Edge Economists. Dave Colander, Ric Holt, and J. Barkley Rosser. Ann Arbor. University of Michigan Press.
2005. “Return to a lost world of upside-down mountains”. Barry Bergman. Berkeleyan 34(6):8 (September 22).
1992. Taking Future Generations into Account. Lynn Atwood. Berkeleyan20(12):
2010. “Co-Evolutionary Economics (main originator: Richard Norgaard)”. Chapter 9 in Integral Economics: Releasing the Economic Genius of Society.London. Gower Ashgate.
2011. “Richard Norgaard”. Chapter 6 in The Wildness Within: Remembering David Brower. Kenneth Brower. Berkeley. Heyday Books.
References
American non-fiction environmental writers
Ecological economists
Living people
1943 births
Academics from Washington, D.C.
Environmental social scientists | Richard B. Norgaard | Environmental_science | 2,834 |
715,691 | https://en.wikipedia.org/wiki/Higgsino | In particle physics, for models with N = 1 supersymmetry, a higgsino, symbol , is the superpartner of the Higgs field. A higgsino is a Dirac fermionic field with spin and it refers to a weak isodoublet with hypercharge half under the Standard Model gauge symmetries. After electroweak symmetry breaking higgsino fields linearly mix with U(1) and SU(2) gauginos leading to four neutralinos and two charginos that refer to physical particles. While the two charginos are charged Dirac fermions (plus and minus each), the neutralinos are electrically neutral Majorana fermions. In an R-parity-conserving version of the Minimal Supersymmetric Standard Model, the lightest neutralino typically becomes the lightest supersymmetric particle (LSP). The LSP is a particle physics candidate for the dark matter of the universe since it cannot decay to particles with lighter mass. A neutralino LSP, depending on its composition can be bino, wino or higgsino dominated in nature and can have different zones of mass values in order to satisfy the estimated dark matter relic density. Commonly, a higgsino dominated LSP is often referred as a higgsino, in spite of the fact that a higgsino is not a physical state in the true sense.
In natural scenarios of SUSY, top squarks, bottom squarks, gluinos, and higgsino-enriched neutralinos and charginos are expected to be relatively light, enhancing their production cross sections. Higgsino searches have been performed by both the ATLAS and CMS experiments at the Large Hadron Collider at CERN, where physicists have searched for the direct electroweak pair production of Higgsinos. As of 2017, no experimental evidence for Higgsinos has been reported.
Mass
If dark matter is composed only of Higgsinos, then the Higgsino mass is 1.1 TeV. On the other hand, if dark matter has multiple components, then the Higgsino mass depends on the relevant multiverse distribution functions, making the mass of the Higgsino lighter.
mħ ≈ 1.1 (Ωħ/ΩDM)1/2 TeV
Footnotes
Supersymmetric quantum field theory
Fermions
Hypothetical elementary particles | Higgsino | Physics,Materials_science | 503 |
72,176,057 | https://en.wikipedia.org/wiki/Temptin | Temptin is a protein that acts as a water-borne pheromone in the marine gastropod mollusk Aplysia californica. It is an abundant protein that is synthesized in the albumen gland, and is released in the egg cords during oviposition, along with other proteins called attractin, seductin and enticin. Together, they make up a complex of water-soluble proteins that act together to attract mates for reproduction and induce spawning.
History
Temptin was first described in 2004 in the marine gastropod Aplysia californica. In 2017, the knowledge of temptin as a chemical signal was extended to the freshwater gastropod mollusk Biomphalaria glabrata. In 2019 it was reported as a protein present in the aerial eggs of the freshwater gastropod molluscs Pomacea canaliculata and Pomacea maculata. In 2021 a study of the temptin gene suggests that it is unique to all Lophotrochozoa, and that it is present in all molluscs, except in cephalopods.
Structure
The gene encoding temptin is found the Lophotrochozoa clade. Temptin from Aplysia californica has sequence homology to epidermal growth factor (EGF)-like domains of higher organisms that mediate protein surface contact with cells during fertilization and blood coagulation. The protein has two disulfide bound, that could stabilize it from proteolysis in the extracellular medium where it is released, and a possible calcium binding site.
Function
In addition to its pheromone function, in the freshwater bivalve Hyriopsis cumingii, the protein is expressed in the mantle and it is involved in the biomineralization process. Through gene silencing it was shown that their absence alters the biomineral structure of the mollusc shell.
References
Pheromones | Temptin | Chemistry | 401 |
8,307,294 | https://en.wikipedia.org/wiki/Cell%20culture%20assay | A cell culture assay is any method used to assess the cytotoxicity of a material. This refers to the in vitro assessment of a material to determine whether it releases toxic chemicals in the cell. It also determines if the quantity is sufficient to kill cells, either directly or indirectly, through the inhibition of cell metabolic pathways. Cell culture evaluations are the precursor to whole animal studies and are a way to determine if significant cytotoxicity exists for the given material. Cell culture assays are standardized by ASTM, ISO, and BSI (British Standards Institution.)
See also
Microphysiometry
References
Biotechnology
Cell biology | Cell culture assay | Biology | 130 |
46,531,203 | https://en.wikipedia.org/wiki/Profinite%20integer | In mathematics, a profinite integer is an element of the ring (sometimes pronounced as zee-hat or zed-hat)
where the inverse limit of the quotient rings runs through all natural numbers , partially ordered by divisibility. By definition, this ring is the profinite completion of the integers . By the Chinese remainder theorem, can also be understood as the direct product of rings
where the index runs over all prime numbers, and is the ring of p-adic integers. This group is important because of its relation to Galois theory, étale homotopy theory, and the ring of adeles. In addition, it provides a basic tractable example of a profinite group.
Construction
The profinite integers can be constructed as the set of sequences of residues represented as
such that .
Pointwise addition and multiplication make it a commutative ring.
The ring of integers embeds into the ring of profinite integers by the canonical injection:
where
It is canonical since it satisfies the universal property of profinite groups that, given any profinite group and any group homomorphism , there exists a unique continuous group homomorphism with .
Using Factorial number system
Every integer has a unique representation in the factorial number system as
where for every , and only finitely many of are nonzero.
Its factorial number representation can be written as .
In the same way, a profinite integer can be uniquely represented in the factorial number system as an infinite string , where each is an integer satisfying .
The digits determine the value of the profinite integer mod . More specifically, there is a ring homomorphism sending
The difference of a profinite integer from an integer is that the "finitely many nonzero digits" condition is dropped, allowing for its factorial number representation to have infinitely many nonzero digits.
Using the Chinese Remainder theorem
Another way to understand the construction of the profinite integers is by using the Chinese remainder theorem. Recall that for an integer with prime factorization
of non-repeating primes, there is a ring isomorphism
from the theorem. Moreover, any surjection
will just be a map on the underlying decompositions where there are induced surjections
since we must have . It should be much clearer that under the inverse limit definition of the profinite integers, we have the isomorphism
with the direct product of p-adic integers.
Explicitly, the isomorphism is by
where ranges over all prime-power factors of , that is, for some different prime numbers .
Relations
Topological properties
The set of profinite integers has an induced topology in which it is a compact Hausdorff space, coming from the fact that it can be seen as a closed subset of the infinite direct product
which is compact with its product topology by Tychonoff's theorem. Note the topology on each finite group is given as the discrete topology.
The topology on can be defined by the metric,
Since addition of profinite integers is continuous, is a compact Hausdorff abelian group, and thus its Pontryagin dual must be a discrete abelian group.
In fact, the Pontryagin dual of is the abelian group equipped with the discrete topology (note that it is not the subset topology inherited from , which is not discrete). The Pontryagin dual is explicitly constructed by the function
where is the character of the adele (introduced below) induced by .
Relation with adeles
The tensor product is the ring of finite adeles
of where the symbol means restricted product. That is, an element is a sequence that is integral except at a finite number of places. There is an isomorphism
Applications in Galois theory and étale homotopy theory
For the algebraic closure of a finite field of order q, the Galois group can be computed explicitly. From the fact where the automorphisms are given by the Frobenius endomorphism, the Galois group of the algebraic closure of is given by the inverse limit of the groups , so its Galois group is isomorphic to the group of profinite integers
which gives a computation of the absolute Galois group of a finite field.
Relation with étale fundamental groups of algebraic tori
This construction can be re-interpreted in many ways. One of them is from étale homotopy type which defines the étale fundamental group as the profinite completion of automorphisms
where is an étale cover. Then, the profinite integers are isomorphic to the group
from the earlier computation of the profinite Galois group. In addition, there is an embedding of the profinite integers inside the étale fundamental group of the algebraic torus
since the covering maps come from the polynomial maps
from the map of commutative rings
sending
since . If the algebraic torus is considered over a field , then the étale fundamental group contains an action of as well from the fundamental exact sequence in étale homotopy theory.
Class field theory and the profinite integers
Class field theory is a branch of algebraic number theory studying the abelian field extensions of a field. Given the global field , the abelianization of its absolute Galois group
is intimately related to the associated ring of adeles and the group of profinite integers. In particular, there is a map, called the Artin map
which is an isomorphism. This quotient can be determined explicitly as
giving the desired relation. There is an analogous statement for local class field theory since every finite abelian extension of is induced from a finite field extension .
See also
Ring of adeles
Supernatural number
Notes
References
External links
http://ncatlab.org/nlab/show/profinite+completion+of+the+integers
https://web.archive.org/web/20150401092904/http://www.noncommutative.org/supernatural-numbers-and-adeles/
https://euro-math-soc.eu/system/files/news/Hendrik%20Lenstra_Profinite%20number%20theory.pdf
Algebraic number theory
P-adic numbers
Ring theory | Profinite integer | Mathematics | 1,263 |
68,496,606 | https://en.wikipedia.org/wiki/Weijian%20Zhou | Weijian Zhou is a geologist at the Chinese Academy of Sciences known for her research into environmental changes in the Quaternary era using radiocarbon data.
Education and career
Zhou graduated from Guizhou University in 1976. She earned her Ph.D. in 1995 from North-West University in China in 1995, and her Ph.D. won the “First National Prize for the One Hundred Most Outstanding PhD Theses in China”. In 1999, she became a professor in the Institute of Earth Environment at the Chinese Academy of Sciences in Xi'an, China. In 2006 she began her position as the director of the Xi'an Accelerator Mass Spectrometry Center.
In 2016, she was named a fellow of the American Geophysical Union who cited her "for exceptional contributions to radiocarbon dating and our understanding of East Asian and global environmental changes using radionuclides as tracers".
Research
Weijian Zhou is known for using Accelerator mass spectrometry data to track geochemical tracers such as beryllium-10 in loess and Carbon-14. Through these data streams, Zhou studies to chronostratigraphy in the Quaternary era, the period from 2.9 million years ago to the present. Her research has provided insights into the monsoons in China, and records of ancient rainfall through tracking of beryllium-10 in dust layers. During the COVID-19 pandemic, Zhou's research showed carbon dioxide concentrations were lower than previous years, but this decrease was short-lived because values returned to pre-pandemic levels when lockdown restrictions were lifted.
Selected publications
Awards and honors
Academician, Division of Earth Sciences, Chinese Academy of Sciences (2009)
Elected member, Academy of Sciences for the Developing World (2010)
Fellow, American Geophysical Union (2016)
References
Fellows of the American Geophysical Union
Members of the Chinese Academy of Sciences
Guizhou University alumni
North-West University alumni
Chinese women chemists
21st-century Chinese geologists
Chinese geochemists
Year of birth missing (living people)
Living people
20th-century Chinese chemists
21st-century Chinese chemists
Chinese women geologists | Weijian Zhou | Chemistry | 433 |
537,975 | https://en.wikipedia.org/wiki/Thermoluminescence | Thermoluminescence is a form of luminescence that is exhibited by certain crystalline materials, such as some minerals, when previously absorbed energy from electromagnetic radiation or other ionizing radiation is re-emitted as light upon heating of the material. The phenomenon is distinct from that of black-body radiation.
Physics
High energy radiation creates electronic excited states in crystalline materials. In some materials, these states are trapped, or arrested, for extended periods of time by localized defects, or imperfections, in the lattice interrupting the normal intermolecular or inter-atomic interactions in the crystal lattice. Quantum-mechanically, these states are stationary states which have no formal time dependence; however, they are not stable energetically, as vacuum fluctuations are always "prodding" these states. Heating the material enables the trapped states to interact with phonons, i.e. lattice vibrations, to rapidly decay into lower-energy states, causing the emission of photons in the process.
Use in dating
The amount of luminescence is proportional to the original dose of radiation received. In thermoluminescence dating, this can be used to date buried objects that have been heated in the past, since the ionizing dose received from radioactive elements in the soil or from cosmic rays is proportional to age. This phenomenon has been applied in the thermoluminescent dosimeter, a device to measure the radiation dose received by a chip of suitable material that is carried by a person or placed with an object.
Thermoluminescence is a common geochronology tool for dating pottery or other fired archeological materials, as heat empties or resets the thermoluminescent signature of the material (Figure 1). Subsequent recharging of this material from ambient radiation can then be empirically dated by the equation:
Age = (subsequently accumulated dose of ambient radiation) / (dose accumulated per year)
This technique was modified for use as a passive sand migration analysis tool (Figure 2). The research shows direct consequences resulting from the improper replenishment of starving beaches using fine sands. Beach nourishment is a problem worldwide and receives large amounts of attention due to the millions of dollars spent yearly in order to keep beaches beautified for tourists, e.g. in Waikiki, Hawaii. Sands with sizes 90–150 μm (very fine sand) were found to migrate from the swash zone 67% faster than sand grains of 150-212 μm (fine sand; Figure 3). Furthermore, the technique was shown to provide a passive method of policing sand replenishment and a passive method of observing riverine or other sand inputs along shorelines (Figure 4).
References
Further reading
Thermoluminescence dating by M. J. Aitken,
The Dating Game, Scientific American, June 11, 2001, page 2
External links
Luminescence | Thermoluminescence | Chemistry | 591 |
644,436 | https://en.wikipedia.org/wiki/Juan%20Maldacena | Juan Martín Maldacena (born 10 September 1968) is an Argentine theoretical physicist and the Carl P. Feinberg Professor in the School of Natural Sciences at the Institute for Advanced Study, Princeton. He has made significant contributions to the foundations of string theory and quantum gravity. His most famous discovery is the AdS/CFT correspondence, a realization of the holographic principle in string theory.
Biography
Maldacena obtained his licenciatura (a six-year degree) in 1991 at the Instituto Balseiro, Bariloche, Argentina, under the supervision of Gerardo Aldazábal. He then obtained his Ph.D. in physics at Princeton University after completing a doctoral dissertation titled "Black holes in string theory" under the supervision of Curtis Callan in 1996, and went on to a post-doctoral position at Rutgers University. In 1997, he joined Harvard University as associate professor, being quickly promoted to Professor of Physics in 1999. Since 2001 he has been a professor at the Institute for Advanced Study in Princeton, New Jersey and in 2016 became the first Carl P. Feinberg Professor of Theoretical Physics in the institute's School of Natural Sciences.
Maldacena is a member of the Society of Catholic Scientists.
Contributions to physics
Maldacena has made numerous discoveries in theoretical physics. Leonard Susskind called him "perhaps the greatest physicist of his generation... certainly the greatest theoretical physicist of his generation". His most famous discovery is the most reliable realization of the holographic principle – namely the AdS/CFT correspondence, a conjecture about the equivalence of string theory on Anti-de Sitter (AdS) space, and a conformal field theory defined on the boundary of the AdS space. According to the conjecture, certain theories of quantum gravity are equivalent to other quantum mechanical theories (with no gravitational force) in one fewer spacetime dimensions.
In subsequent works, Maldacena elucidated several aspects of the AdS/CFT correspondence, describing how certain physical observables defined in one theory can be described in the equivalent theory. Shortly after his original work on the AdS/CFT correspondence, Maldacena showed how Wilson lines can be computed in a corresponding string theory by considering the area swept by an evolving fundamental string. Wilson lines are non-local physical observables defined in gauge theory. In 2001, Maldacena proposed that an eternal black hole, an object defined in a gravitational theory, is equivalent to a certain entangled state involving two copies of the corresponding quantum mechanical theory. Ordinary black holes emit Hawking radiation and eventually evaporate. An eternal black hole is a type of black hole that survives forever because it eventually re-absorbs the radiation it emits.
In 2013, Maldacena co-authored an analysis of the 2012 black hole firewall paradox with Leonard Susskind, arguing that the paradox can be resolved if entangled particles are connected by minor wormholes."
Publications
Awards
Maldacena has received these awards:
Alfred P. Sloan Foundation Fellowship, 1998
Packard Fellowship in Science and Engineering, 1998
MacArthur Fellowship, 1999
UNESCO Husein Prize for Young Scientists, 1999
Sackler Prize in Physics, 2000
Xanthopoulos International Award for Research in Gravitational Physics, 2001
Pius XI Medal, 2002
Edward A. Bouchet Award of the American Physical Society, 2004
Member of the American Academy of Arts and Sciences, elected 2007
Dannie Heineman Prize, 2007
Dirac Medal of the ICTP, 2008
Pomeranchuk Prize, 2012
Breakthrough Prize in Fundamental Physics, 2012.
Member of the National Academy of Sciences, elected 2013
Diamond Konex Award as the most important scientist in the last decade in Argentina, 2013
Lorentz Medal, 2018
Albert Einstein Medal, 2018
St. Albert Award, 2018
Galileo Galilei Medal, 2019
Les Houches School of Physics prize 2020
References
External links
Maldacena's web page at the Institute
Maldacena Theme tree
Interview of Juan Maldacena by David Zierler on January 15, 2021, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA
1968 births
Living people
Argentine physicists
Harvard University faculty
Institute for Advanced Study faculty
MacArthur Fellows
National University of Cuyo alumni
Scientists from Buenos Aires
Princeton University alumni
String theorists
Theoretical physicists
Members of the Pontifical Academy of Sciences
Mathematical physicists
Albert Einstein Medal recipients | Juan Maldacena | Physics | 894 |
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