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65,240,283 | https://en.wikipedia.org/wiki/Fault%20zone%20hydrogeology | Fault zone hydrogeology is the study of how brittlely deformed rocks alter fluid flows in different lithological settings, such as clastic, igneous and carbonate rocks. Fluid movements, that can be quantified as permeability, can be facilitated or impeded due to the existence of a fault zone. This is because different mechanisms that deform rocks can alter porosity and permeability within a fault zone. Fluids involved in a fault system generally are groundwater (fresh and marine waters) and hydrocarbons (Oil and Gas).
Take notice that permeability (k) and hydraulic conductivity (K) are used interchangeably in this article for simplified understanding
Architecture
A fault zone can be generally subdivided into two major sections, including a Fault Core (FC) and a Damage Zone (DZ) (Figure 1).
The fault core is surrounded by the damage zone. It has a measurable thickness which increases with fault throw and displacement, i.e. increasing deformations.
The damage zone envelopes the fault core irregularly in a 3D manner which can be meters to few hundred meters wide (perpendicular to the fault zone). Within a large fault system, multiple fault cores and damage zones can be found. Younger fault cores and damage zones can overlap the older ones.
Different processes can alter the permeability of the fault zone in the fault core and the damage zone will be discussed respectively in the next section. In general, the permeability of a damage zone is several orders of magnitude higher than that of a fault core as damage zones typically act as conduits (will be discussed in section 3). Within a damage zone, permeability decreases further away from a fault core.
Permeability classification
There are many classifications to group fault zones based on their permeability patterns. Some terms are interchangeable; while some have different subgroups. Most of expressions are listed in the following table for comparison. Dickerson's categorisation is commonly used and easier to understand in a broad range of studies.
The classification of a fault zone can change spatially and temporally. The fault core and damage zone can behave differently to accommodate the deformations. Moreover, the fault zone can be dynamic through time. Thus, the permeability patterns can change for short-term and long-term effects.
*K = Permeability/ Hydraulic Conductivity
*fz = fault zone
*hr = host rock = Undeformed rock surrounds the fault zones
Mechanisms (permeability)
Fault zone results from brittle deformation. Numerous mechanisms can vary the permeability of a fault zone. Some processes affect the permeability temporarily. These processes enhance the permeability for a certain period, and then reduce it later on: in this case, like seismic events, the permeability is not constant through time. Physical and chemical reactions are the major types of mechanisms. Different mechanisms can occur different in fault core and damage zone since the intensities of deformation they experience are different (Table 3).
*+ = more likely to occur at
Enhancing fault zone permeability
Deformation bands
The formation of a dilation band, in unconsolidated material, is the early result of applying extensional forces. Disaggregation of mineral fabric occurs along with the band, yet no offset is accommodated by the movement of grains (Figure 3). Further deformation causes offsets of mineral grains by rotation and sliding. This is called a shear band. The pore network is rearranged by granular movements (also called particulate flow), hence moderately enhance permeability. However, continuing deformation leads to the cataclasis of mineral grains which will further reduce permeability later on (section 3.2.3) (Figure 4).
Brecciation
Brecciation refers to the formation of angular, coarse-grained fragments embedded in a fine-grained matrix. As breccia (the rock experienced brecciation) is often non-cohesive, thus, permeability can be increased up to four or five orders of magnitude. However, the void space enlarged by brecciation will lead to further displacement along the fault zone by cementation, resulting in a strong permeability reduction (Figure 5).
Fracturing
Fractures propagate along a fault zone in direction responding to the stress applied. The enhancement of permeability is controlled by the density, orientation, length distribution, aperture, and connectivity of fractures. Even fracture with aperture of a 100-250 μm can still greatly influence fluid movement (Figure 6).
Reducing fault zone permeability
Sediment mixing
Sediments, typically from distinct formations, with different grain sizes, are mixed physically by deformation, resulting in a more poorly-sorted mixture. The pore space is filled by smaller grains, increasing tortuosity (mineral scale in this case) of fluid flow across the fault system.
Clay smears
Clay minerals are phyllo-silicate, in other words, with sheet-like structure. They are effective agents that block fluid flows across a fault zone. Clay smears, deformed layers of clay, that are developed along fault zone can act as a seal of hydrocarbon reservoir i.e. extremely low permeability that nearly prohibits all fluid flows (Figure 7).
Cataclasis
Cataclasis refers to pervasive brittle fracturing and comminution of grains. This mechanism becomes dominant at depth, greater than 1 km, and with larger grains. With increasing intensity of cataclasis, fault gouge, often with the presence of clay, is formed. The largest reduction occurs on the flows that are perpendicular to the band.
Enhancing and reducing fault zone permeability successively
Compaction and cementation
Compactions and cementation generally lead to permeability reduction by losing porosity. When a large region, which consist a fault zone, experience compaction and cementation, porosity loss in host rock (undeformed rock surrounding the fault zone) can be greater than that of fault zone rock. Hence, fluids are forced to flow through a fault zone.
Dissolution and precipitation
Solute carried by fluids can either enhance or reduce permeability by dissolution or precipitation (cementation). Which process takes place depends on geochemical conditions like rock composition, solute concentration, temperature, and so on. The changes in porosity dominantly control whether the fluid-rock interaction continues or slows down as a strong feedback reaction.
For example, minerals like carbonates, quartz, and feldspars are dissolved by the fluid-rock interactions due to enhanced permeability. Further introduction of fluids can either continuously dissolve or otherwise re-precipitate minerals in the fault core, and thus alters the permeability. Therefore, whether the feedback is positive or negative heavily depends on the geochemical conditions.
Seismic event
Earthquakes can either increase or decrease permeability along fault zones, depending on the hydrogeological settings. Recorded hot spring discharges show seismic waves dominantly enhance permeability, but reductions in discharge may also result occasionally. The timescale of the changes can be up to thousands of years. Hydraulic fracturing (fracking) requires increasing the interconnectedness of the pore space (in other words, permeability) of shale to allow the gas to flow through the rock, and very small deliberately induced seismic activity of magnitudes smaller than 1 are applied to enhance rock permeability.
Taking the Chile earthquake in 2017 as an example, the discharge of streamflow temporally increased six times indicates a sixfold enhancement in permeability along the fault zone. Yet, seismic-induced effects are temporary that normally last for months, for Chile's case, it lasted for one and a half months which gradually decreased back to original discharge.
Mechanisms (porosity)
Porosity (φ) directly reflects the specific storage of rock. And brittle formation alters the pores by different mechanisms. If the pores are deformed and connected together, the permeability of rock enhances. On the other hand, if the deformed pores disconnect with each other, the permeability of rock in this case reduces.
Pore types
Enhancing porosity
Dissolution
The mineral grains can be dissolved when there is fluid flow. The spaces originally occupied by the minerals will be spare as voids, increasing the porosity of rock. The minerals that are usually dissolved are feldspar, calcite and quartz. Grain dissolution pores results from this process can enhance porosity.
Reducing porosity
Cataclasis, fracturing and brecciation
The mineral grains are broken up into smaller pieces by faulting event. Those smaller fragments will re-organise and further be compacted to form smaller pore spaces. These processes create intragranular fracture pores and transgranular fracture pores.
Important to be aware is that reducing porosity does not equal to reduction in permeability. Fracturing, bracciation and initial stage of cataclasis can connect pore spaces by cracks and dilation bands, increasing permeability.
Precipitation
The mineral grains can be precipitated when there is fluid flow. The voids in the rocks can be occupied by precipitation of mineral grains. The minerals fill the voids and hence, reducing the porosity. Overgrowth, precipitation around an existing mineral grain, of quartz are common. And overgrown minerals infill pre-existing pores, reducing porosity.
Clay deposition
Clay minerals are phyllo-silicate, in other words, with sheet-like structure. They are effective agents that block fluid flows. Kaolinite which is altered from potassium feldspar with the presence of water is a common mineral that fills pore spaces. Precipitation and infiltration only affect materials on shallow depth, hence, more clay materials infill pore spaces when they are closer to the surface. Yet, development of a fault zone introduces fluid to flow deeper. Thus, this facilitates clay deposition at depth, reducing porosity.
Lithological effects
Lithology has a dominant effect on controlling which mechanisms would take place along a fault zone, hence, changing the porosity and permeability.
*↑ = mechanism that enhance permeability
*↓ = mechanism that reduce permeability
Fault type effects
All faults can be classified into three types. They are normal fault, reverse fault (thrust fault) and strike-slip fault. These different faulting behaviours accommodate the displacement in distinct structural ways.
The differences in faulting motions might favour or disfavour certain permeability altering mechanisms to occur. However, the main controlling factor of the permeability is the rock type. Since the characteristics of rock control how a fault zone can be developed and how fluids can move. For instance, sandstone generally has a higher porosity than that of shale. A deformed sandstone in three different faulting systems should have a higher specific storage, hence permeability, than that of shale. Similar example like the strength (resistance to deform) also significantly depends on rock types instead of fault types. Thus, the geological features of rock involved in a fault zone is a more dominated factor.
On the other hand, the type of fault might not be a dominant factor but the intensity of deformation is. The higher intensity of stresses applied to the rock, the more intense the rock will be deformed. The rock will experience a greater permeability changing event. Thus, the amount of stress applied matters.
Equally important is that identifying the permeability category of the fault zones (barriers, barrier-conduits and conduits) is the main scope of study. In other words, how the fault zones behave when there are fluids pass through.
Studying approaches and methods
Surface and subsurface test
The studies of fault zones are recognised in the discipline of Structural Geology as it involves how rocks were deformed; while investigations of fluid movements are grouped in the field of Hydrology. There are mainly two types of methods used to examine the fault zone by structural geologists and hydrologists (Figure 7).
In situ test includes obtaining data from boreholes, drill cores, and tunnel projects. Normally the existence of a fault zone is found as different hydraulic properties are measured across it as fault zones are rarely drilled through (except for tunnel projects) (Figure 8).
The hydraulic properties of rocks are either obtained directly from outcrop samples or shallow probe holes/ trial pits, then the predictions of fault structure are made for the rocks at depth (Figure 8).
Example of a subsurface test
An example of a large-scale aquifer test conducted by Hadley (2020), the author used 5 wells aligned perpendicular to the Sandwich Fault Zone in the US, and the drawdowns as well as the recovery rates of water levels in every well were observed. From the evidence that the recovery rates are slower for the wells closer to the fault zone, it is suggested that the fault zone acts as a barrier for northward groundwater movement, affecting freshwater supply in the north.
Example of a surface test
From an outcrop study of the Zuccale Fault in Italy by Musumeci (2015), the surface outcrop findings and cross-cutting relationship are used to determine the number and mechanism of deformational events happened in the region. Moreover, the presences of breccias and cataclasites, that formed under brittle deformation, suggest that there was an initial stage of permeability increase, promoting an influx of -rich hydrous fluids. The fluids triggered low-grade metamorphism and dissolution-and-precipitation (i.e. pressure-solution) in mineral scale that shaped a foliated fault core, hence, enhancing the sealing effect significantly.
Other methods
Geophysics
Underground fluids, particularly groundwater, create anomalies for superconducting gravity data which help study the fault zone at depth. The method combines gravitational data and groundwater conditions to determine not only the permeability of a fault zone but also whether the fault zone is active or not.
Geochemistry
The geochemistry conditions of mineral fluids, water or gases, can be used to determine the existence of a fault zone by comparing the geochemistry of fluids' source, given that the conditions of aquifers are known. The fluids can be categorized by the concentrations of common solutes like total dissolved solids (TDS), Mg-Ca-Na/K phase, SO4-HCO3-Cl phase, and other dissolved trace elements.
Existing biases
The selection of an appropriate studying approach(es) is essential as there are biases existed when determining the fault zone permeability structure.
In crystalline rocks, the subsurface-focused investigations favor the discoveries of a conduit fault zone pattern; while the surface methods favor a combined barrier-conduit fault zone structure. The same biases, to a lesser extend, exist in sedimentary rock as well.
The biases can be related to the differences in studying scale. For structural geologists, it is very difficult to conduct outcrop study over a vast region; likewise, for hydrologists, it is expensive and ineffective to shorten borehole intervals for testing.
Economic geology
It is economically worth studying the complex system, especially for arid/ semi-arid regions, where freshwater resources are limited, and potential areas with hydrocarbon storages. Further research on the fault zone, the result of deformation, gave insights on the interactions between earthquakes and hydrothermal fluids along fault zone. Moreover, hydrothermal fluids associated with the fault zone also provide information on how ore deposits accumulated.
Artificial hydrocarbon reservoirs
Carbon sequestration is a modern method dealing with atmospheric carbon. One of the methods is pumping atmospheric carbon to specific depleted oil and gas reservoirs at depth. However, the presence of a fault zone act as either a seal or a conduit, affecting the efficiency of hydrocarbon formation.
Micro-fractures that cut along the sealing unit and the reservoir rock can greatly affect the hydrocarbon migration. The deformation band blocks the lateral (horizontal) flow of and the sealing unit keeps the from vertical migration (Gif 1). The propagation of a micro-fracture that cuts through a sealing unit, instead of having a deformation band within the sealing unit, facilitates upward migration (Gif 2). This allows fluid migrations from one reservoir to another. In this case, the deformation band still does not facilitate lateral (horizontal) fluid flow. This might lead to the loss of injected atmospheric carbon, lowering the efficiency of carbon sequestration.
A fault zone that displaces sealing units and reservoir rocks can act as a conduit for hydrocarbon migration. The fault zone itself has higher storage capacity (specific capacity) than that of the reservoir rocks, therefore, before the migration to other units, the fault zone has to be fully filled (Gif 3). This can slower and concentrate the fluid migration. The fault zone facilitates vertical downwards movement of due to its buoyancy and piezometric head differences, i.e. pressure/ hydraulic head is greater at a higher elevation, which helps store at depth.
Seismic-induced ore deposits
Regions that are or were seismic active and with the presence of fault zones might indicate there are ore deposits.
A case study in Nevada, US by Howald (2015) studied how seismic-induced fluids accumulate mineral deposits, namely sinter and gold, along spaces provided by a fault zone. Two separate seismic events were identified and dated by oxygen isotopic concentrations, followed by episodes of the upward hydrothermal fluid migrations through permeable normal fault zone. Mineralization started to take place when these hot silica-rich hydrothermal fluids met the cool meteoric water infiltrated along the fault zone until the convective flow system was shut down. In order to deposit minerals, seismic events that bring hydrothermal fluids are not the only dominant factor, the permeability of the fault zone also has to be sufficient for permitting fluid flows.
Another example taken from Sheldon (2005) also shows that development of fault zone, in this case by strike-slip faulting, facilitates mineralization. Sudden dilation happened along with strike-slip events increases the porosity and permeability along the fault zone. Larger displacement will lead to greater increase in porosity. If the faulting event cut through a sealing unit which seals a confined aquifer of over-pressured fluids, the fluids can rise through the fault zone. Then mineralization will take place along the fault zone by pressure solution, reducing the porosity of the fault zone. The fluid flow channel along the fault zone will be shut down when the pores are almost occupied by newly precipitated ore minerals. Multiple seismic events have to be occurred to form these economic ore deposit with vein structure.
See also
Carbon sequestration
Fault (geology)
Fault breccia
Fault gouge
Hydraulic conductivity
Hydrocarbons
Hydrology
Hydrogeology
Petroleum
Permeability
Structural geology
References
Hydrogeology
Faults (geology)
Porous media
Soil mechanics | Fault zone hydrogeology | [
"Physics",
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"Porous media",
"Soil mechanics",
"Materials science",
"Hydrogeology"
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65,243,377 | https://en.wikipedia.org/wiki/Allotropes%20of%20arsenic | Arsenic in the solid state can be found as gray, black, or yellow allotropes. These various forms feature diverse structural motifs, with yellow arsenic enabling the widest range of reactivity. In particular, reaction of yellow arsenic with main group and transition metal elements results in compounds with wide-ranging structural motifs, with butterfly, sandwich and realgar-type moieties featuring most prominently.
Gray arsenic
Gray arsenic, also called grey arsenic or metallic arsenic, is the most stable allotrope of the element at room temperature, and as such is its most common form. This soft, brittle allotrope of arsenic has a steel gray, metallic color, and is a good conductor. The rhombohedral form of this allotrope is analogous to the phosphorus allotrope black phosphorus. In its α-form, As6 rings in chair confirmations are condensed into packed layers lying perpendicular to the crystallographic c axis. Within each layer, the vicinal As-As bond distances are 2.517 Å, while the layer-to-layer As-As bond distances are 3.120 Å. The overall structure displays a distorted octahedral geometry, resulting in the largely metallic properties of this allotrope. Upon sublimation at 616 °C, the gas phase arsenic molecules lose this packing arrangement and form small clusters of As4, As2, and As, though As4 is by far the most abundant in this phase. If these vapors are condensed swiftly onto a cold surface (<200 K), solid yellow arsenic (As4) results due to the lack of energy required to form the rhombohedral gray arsenic lattice. Conversely, condensation of arsenic vapors onto a heated surface generates amorphous black arsenic. The crystalline form of black arsenic can also be isolated, and the amorphous form can be annealed to return to the metallic gray arsenic form. Yellow arsenic can also be returned to the gray allotrope in a facile manner through application of light or by returning the molecule to room temperature.
Reactivity
Relatively few in-situ reactions have been reported involving gray arsenic due to its low solubility, although it reacts in air to form gaseous As2O3 . Two examples of the reactivity of gray arsenic towards transition metals are known. In these reactions, cyclopentadienyl complexes of molybdenum, tungsten and chromium proceed via loss of carbon monoxide to react with gray arsenic and form mono-, di-, and triarsenic compounds.
Black arsenic
Black, or amorphous arsenic (chemical formula Asn) is synthesized first through the sublimation of gray arsenic followed by condensation onto a heated surface. This structure is thought to be the arsenic analogue of red phosphorus. The structure of black arsenic in its crystalline phase, while not synthesized in its pure form, is by extension analogous to black phosphorus, and takes on an orthorhombic structure built from As6 rings. Black arsenic has as-yet been synthesized only in the presence of atomic impurities including mercury,
phosphorus, and oxygen, though a pure form of black arsenic was found in the Copiapó region of Chile. Mechanical exfoliation of the mineral found in Chilean caves, arsenolamprite, revealed a molecular structure with high in-phase anisotropy and potential as a semiconducting material.
Yellow arsenic
Rapid condensation of arsenic vapors on to a cold surface results in the formation of yellow arsenic (As4), consisting of four arsenic atoms arranged in a tetrahedral geometry analogous to white phosphorus. Though it is the only soluble form of arsenic known, yellow arsenic is metastable: at room temperature, or in the presence of light, the structure quickly decomposes to adopt the lower-energy configuration of gray arsenic. For this reason, extensive care is required to maintain yellow arsenic in a state suitable for reaction, including rigorous exclusion of light and maintenance of temperatures below −80 °C. Yellow arsenic is the allotrope most suited for reactivity studies, due to its solubility (low, but comparatively large relative to the metallic allotrope) and molecular nature. In comparison to its lighter congener, phosphorus, the reactivity of arsenic is relatively underexplored. Research investigating reactions with arsenic are primarily concerned with the activation of main group and transition metal compounds; in the case of transition metal complexes, As4 has demonstrated competent reactivity across the d-block of the periodic table.
Reactivity towards main group compounds
The first activation of a main group compound by yellow arsenic was reported in 1992 by West and coworkers, involving the reaction of As4 with a disilene compound, tetramesityldisilene, to generate a mixture of compounds including a butterfly structural motif of bridging arsenic atoms. Notably, the product mixture obtained in this reaction differs from the analogous reaction with P4 that produces the butterfly compound alone, highlighting that the reactivity of yellow arsenic and white phosphorus cannot be considered identical. The first organo-substituted As4 compound was produced by Scheer and coworkers in 2016 via reaction with the CpPEt radical. Analogous to the butterfly compound obtained by the West group, the product obtained in this reaction featured a bridging As4 motif that reversibly returned As4 and the parent radical in the presence of light or heat. This characteristic makes the CpPEt2As4 complex a uniquely suitable "storage" molecule for yellow arsenic, as it is stable when stored at room temperature in the dark, but can release As4 in thermal or photochemical solutions.
Other reactions of main group compounds with yellow arsenic have been shown to involve units of arsenic with more than four atoms. In reaction with the silylene compound [PhC(NtBu)2SiN(SiMe3)2], an aggregation of As4 was observed to form a cage compound of ten arsenic atoms, including a seven-membered arsenic ring at its center.
Reactivity towards transition metal compounds
Group 4 and 5 metals
Among the early (group 4 and 5) transition metal elements, few examples of arsenic activation has been reported to date. Carbon monoxide complexes of zirconium with derivatized cyclopentadienyl ligands were shown to react with yellow arsenic in boiling xylene to release CO and bind the As4 moiety in η1:1-fashion. Trace amounts of a zirconium dimer bridged by a (μ,η2:2:1-As5)-moiety were also reported in this study, which described the complexes as possible reagents for As4 transfer. In group 5, arsenic activation has been more widely explored, with complexes of both niobium and tantalum known. Investigation of the electron density topology in a phosphorus/arsenic/niobium-containing system demonstrated the unique η2-bonding configuration in these complexes, in which an arsenic-phosphorus double bond binds side-on to a niobium center.
Group 6 metals
Reactions of yellow arsenic with the group 6 transition metals largely proceed through thermolytic carbon monoxide elimination in chromium and molybdenum carbonyl complexes. Notable examples include the formation of triple-decker complexes [(CpRMo)2(μ,η6-As6)] and [{CpRCr}2(μ,η5-As5)] via reaction of the corresponding molybdenum and chromium dimers with yellow arsenic. These remarkable structures feature three planar-rings arranged in parallel fashion to result in an idealized D5h point group for the chromium complex. Both of these reactions necessitate harsh reaction conditions like boiling xylene to overcome the high barriers to activation of As4. Conversely, utilization of more sterically demanding ligands on the metal center enabled reactions in milder conditions with molybdenum and chromium. Cummins' Mo(N(tBu)Ar)3 catalyst, also known to split the N-N triple bond in dinitrogen, reacts with yellow arsenic to form a terminal arsenic moiety triple-bonded to the metal center - one of only several compounds known to contain a terminal arsenic atom. Complexes with metal-metal multiple bonds also enable mild As4 activation parameter. A chromium-chromium quintuply-bonded species reported by Kempe reacts with yellow arsenic to form a crown complex in which the four arsenic atoms form an approximately tetrahedral structure, with each chromium atom bonding to three arsenic atoms.
Group 8 and 9 metals
The metals of groups 8 and 9 feature the most extensive library of reactivity with yellow arsenic documented in the scientific literature, with particular focus on reactions of iron and cobalt complexes with As4. Much like the chromium and molybdenum sandwich complexes, (CpRFe(CO)2]2 complexes of iron react with yellow arsenic to produce analogous bimetallic products featuring "triple-decker" geometry. These reports also detail the isolation of a key intermediate, pentaarsaferrocene ([CpRFe(μ5-As5)]). This intermediate, isolobal to ferrocene, replaces one of the cyclopentadienyl ligands with a cyclic As5 ligand that features As-As bond lengths of 2.312 Å (in line with delocalized As-As double bonds). This "sandwich-forming" reactivity can be meaningfully tuned by introducing bulkier ligands. Modifying the cyclopentadienyl groups with much bulkier derivatives produces a vastly different set of products. First, a butterfly complex with a central As4 unit is formed. Irradiation with light leads to further CO elimination and the formation of a bridged butterfly complex, which then rearranges into a unique complex featuring a central As8 moiety. This ligand, formally tetraanionic, forms an eight-membered ring bridging four iron atoms in total.
Much of the same reactivity, including formation of butterfly and sandwich compounds, has been described for cobalt complexes in the presence of yellow arsenic. Beyond these compounds, the history of reactivity of cobalt and yellow arsenic dates back to 1978, when Sacconi and coworkers reported the reaction of cobalt tetrafluoroborate and yellow arsenic in the presence of 1,1,1-tris(diphenylphosphinomethyl)ethane. The resulting complex features a cyclic As3 moiety bridging two cobalt centers, of which the former is assigned formally as a 3π-electron system. The reaction of [Cp*Co(CO)]2 dimer with yellow arsenic was shown by Scherer et al. to produce a wide variety of isolable products, featuring a mixture of linking arsenic moieties including cyclobutane-like and butterfly type complexes. Analogous reactions with rhodium complexes are also known.
Group 10 and 11 metals
Among the group 10 and 11 elements, nickel and copper feature most prominently in literature reactions with yellow arsenic. Nickel tetrafluoroborate salts react analogously to cobalt complexes in the presence of triphos to form a sandwich structure with a central cyclic As3 moiety. Much like iron, the reaction of nickel cyclopentadienyl carbonyl complexes with As4 yields a variety of bi- and multi-metallic products depending on the size of the attending ligands, though the nature and geometric structure of these compounds differ from those observed with iron. These include trimers with bridging As4 and As5 moieties in cubane structural arrangements when smaller Cp ligands are employed, and distorted hexagonal prism complexes with two nickel fragments and four arsenic atoms when bulkier Cp groups are introduced.
The reaction of the copper complex [L2Cu(NCMe)] (L2 = [{N(C6H3iPr2-2,6)C(Me)}2CH]) with yellow arsenic yields the As4-bridged dimer [{L2Cu}2- (μ,η2:2-As4)]. The four-atom arsenic moiety in this complex was deemed to be "intact" yellow arsenic through the use of density functional theory calculations determining the change in bond critical points between the free and bound arsenic molecules. Specifically, only a small shift was observed in the bond critical points between arsenic atoms involved in binding to copper; the remaining bond critical points were very similar to free yellow arsenic.
See also
Allotropes of phosphorus
References
Arsenic
Arsenic | Allotropes of arsenic | [
"Physics",
"Chemistry"
] | 2,599 | [
"Periodic table",
"Properties of chemical elements",
"Allotropes",
"Materials",
"Matter"
] |
61,486,154 | https://en.wikipedia.org/wiki/C16H14N2O2 | {{DISPLAYTITLE:C16H14N2O2}}
The molecular formula C16H14N2O2 (molar mass: 266.295 g/mol) may refer to:
Doliracetam
Methoxyqualone
Miroprofen
URB754
Molecular formulas | C16H14N2O2 | [
"Physics",
"Chemistry"
] | 65 | [
"Molecules",
"Set index articles on molecular formulas",
"Isomerism",
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61,486,848 | https://en.wikipedia.org/wiki/Rock%20analogs%20for%20structural%20geology | This is a compilation of the properties of different analog materials used to simulate deformational processes in structural geology. Such experiments are often called analog or analogue models. The organization of this page follows the review of rock analog materials in structural geology and tectonics of Reber et al. 2020.
Materials used to simulate upper crustal deformation
These materials need to exhibit brittle deformation upon failure as well as elastic and viscous deformation before failure.
Materials that simulate upper crustal deformation
Dry granular materials
Materials used to simulate deformation of the lower crust and mantle
Various fluids are used to simulate deformation of the lower crust and mantle, such as: linear, non-linear, and yield stress fluids.
Materials used to simulate deformation of the middle crust
Composite Model Materials
Composite materials combine phases with different physical properties. A common composite mixture contains dry granular materials and fluids. These analog materials have been used:
Sediment transport (Parker et al., 1982) using low viscosity fluids
Dynamics in the middle crust (Mookerjee et al., 2017; Reber et al., 2014) employing high viscosity fluids
Stick-slip dynamics (Higashi and Sumita, 2009; Reber et al., 2014)
Strain softening and hardening processes (Panien et al., 2006)
The most commonly used granular materials in composite mixtures are:
Sand
Glass beads
Acrylic discs
Common fluids used in composite mixtures are:
Carbopol
Silicone
Wax, which can behave as a brittle or viscous material depending on the melting temperature (Mookerjee et al., 2017)
Visco-elasto-plastic model materials
Visco-elasto-plastic deformation exhibits a combination of elastic, viscous, and plastic deformation at the same time. Various asphalts and bituminous materials demonstrate visco-elasto-plastic deformation but they are rarely as modeling materials (McBirney and Best, 1961).Common modeling materials demonstrating complex rheology are;
Carbopol (Piau, 2007; Shafiei et al., 2018)
Kaolinite clay (Cooke and van der Elst, 2012)
References
Structural geology
Earth sciences
Deformation (mechanics) | Rock analogs for structural geology | [
"Materials_science",
"Engineering"
] | 446 | [
"Deformation (mechanics)",
"Materials science"
] |
61,491,450 | https://en.wikipedia.org/wiki/Perovskite%20nanocrystal | Perovskite nanocrystals are a class of semiconductor nanocrystals, which exhibit unique characteristics that separate them from traditional quantum dots. Perovskite nanocrystals have an ABX3 composition where A = cesium, methylammonium (MA), or formamidinium (FA); B = lead or tin; and X = chloride, bromide, or iodide.
Their unique qualities largely involve their unusual band-structure which renders these materials effectively defect tolerant or able to emit brightly without surface passivation. This is in contrast to other quantum dots such as CdSe which must be passivated with an epitaxially matched shell to be bright emitters. In addition to this, lead-halide perovskite nanocrystals remain bright emitters when the size of the nanocrystal imposes only weak quantum confinement. This enables the production of nanocrystals that exhibit narrow emission linewidths regardless of their polydispersity.
The combination of these attributes and their easy-to-perform synthesis has resulted in numerous articles demonstrating the use of perovskite nanocrystals as both classical and quantum light sources with considerable commercial interest. Perovskite nanocrystals have been applied to numerous other optoelectronic applications such as light emitting diodes, lasers, visible communication, scintillators, solar cells, and photodetectors.
Physical properties
Perovskite nanocrystals possess numerous unique attributes: defect tolerance, high quantum yield, fast rates of radiative decay and narrow emission line width in weak confinement, which make them ideal candidates for a variety of optoelectronic applications.
Bulk vs. nano
The intriguing optoelectronic properties of lead halide perovskites were first studied in single crystals and thin films.: From these reports, it was discovered that these materials possess high carrier mobility, long carrier lifetimes, long carrier diffusion lengths, and small effective carrier masses. Unlike their nanocrystal counterparts, bulk ABX3 materials are non-luminescent at room temperature, but they do exhibit bright photoluminescence once cooled to cryogenic temperatures.
Defect-tolerance
Contrary to the characteristics of other colloidal quantum dots such as CdSe, ABX3 QDs are shown to be bright, high quantum yield (above 80%) and stable emitters with narrow linewidths without surface passivation. In II-VI systems, the presence of dangling bonds on the surface results in photoluminescence quenching and photoluminescent intermittence or blinking. The lack of sensitivity to the surface can be rationalized from the electronic band structure and density of states calculations for these materials. Unlike conventional II-VI semiconductors where the band gap is formed by bonding and antibonding orbitals, the frontier orbitals in ABX3 QDs are formed by antibonding orbitals composed of Pb 6s 6p and X np orbitals (n is the principle quantum number for the corresponding halogen atom). As a result, dangling bonds (under-coordinated atoms) result in intraband states or shallow traps instead of deep mid-gap states (e.g. d in CdSe QDs. This observation was corroborated by computational studies which demonstrated that the electronic structure of CsPbX3 materials exhibits a trap-free band gap. Furthermore, band structure calculations performed by various groups have demonstrated that these are direct band gap materials at their R-point (a critical point of the Brillouin zone) with a composition dependent band gaps.
Photoluminescence
It was discovered in 2015 that the photoluminescence of perovskite nanocrystals can be post-synthetically tuned across the visible spectral range through halide substitution to obtain , , , , and ; there was no evidence of . The change in band-gap with composition can be described by Vegard's Law, which describes the change in lattice parameter as a function of the change in composition for a solid solution. However, the change in lattice parameter can be rewritten to describe the change in band gap for many semiconductors. The change in band gap directly affects the energy or wavelength of light that can be absorbed by the material and therefore its color. Furthermore, this directly alters the energy of emitted light according to the Stokes shift of the material. This quick, post-synthetic anion-tunability is in contrast to other quantum dot systems where emission wavelength is primarily tuned through particle size by altering the degree of quantum confinement.
Aside from tuning the absorption edge and emission wavelength by anion substitution, it was also observed that the A-site cation also affects both properties. This occurs as a result of the distortion of the perovskite structure and the tilting of octahedra due to the size of the A-cation. Cs, which yields a Goldschmidt tolerance factor of less than one, results in a distorted, orthorhombic structure at room temperature. This results in reduced orbital overlap between the halide and lead atoms and blue shifts the absorption and emission spectra. On the other hand, FA yields a cubic structure and results in FAPbX3 having red shifted absorption and emission spectra as compared to both Cs and MA. Of these three cations, MA is intermediate size between Cs and FA and therefore results in absorption and emission spectra intermediate between those of Cs and FA. Through the combination of both anionic and cationic tuning, the whole spectrum ranging from near-UV to near-IR can be covered.
Absorption Coefficient
Recent studies have demonstrated that CsPbBr3 nanocrystals have an absorption coefficient of 2x105 cm−1 at 335 nm and 8x104 cm−1 at 400 nm.
Single Dot Spectroscopy of Perovskite Nanocrystals
Blinking and Spectral diffusion
Spectroscopic studies of individual nanocrystals have revealed blinking-free emission and very low spectral diffusion without a passivating shell around the NCs. Studies have also demonstrated blinking-free emission at room temperature with a strongly reduced Auger recombination rate at room temperature (CsPbI3 NCs).
Exciton fine-structure and the Rashba effect
It was observed that emission from perovskite nanocrystals may be the result of a bright (optically active) triplet state. Several effects have been suggested to play a role on the exciton fine structure such as electron-hole exchange interactions, crystal field and shape anisotropy, as well as the Rashba effect. Recent reports have described the presence of the Rashba effect within bulk- and nano- and . While it has been reported that the Rashba effect contributes to the existence of a lowest energy triplet state , recent work on has indicated the presence of a lower lying dark state, which can be activated with the application of a magnetic field.
Coherent emission
Numerous quantum optical technologies require coherent light sources. Perovskite nanocrystals have been demonstrated as sources of such light as well as suitable materials for the generation of single photons with high coherence.
Self-assembly and Superfluorescence
Monodisperse perovskite nanocrystals can be assembled into cubic superlattices, which can range from a few hundreds of nanometers to tens of microns in size and show tunable photoluminescence by changing nanocrystal composition via anion exchange (for example, from green-emitting CsPbBr3 nanocrystal superlattices to yellow and orange emitting nanocrystal superlattices to red-emitting CsPbI3 ones). These superlattices have been reported to exhibit very high degree of structural order and unusual optical phenomena such as superfluorescence. In the case of these superlattices, it was reported that the dipoles of the individual nanocrystals can become aligned and then simultaneously emit several pulses of light.
Chemical properties
Synthesis
Early attempts were made to prepare MAPbX3 perovskites as nanocrystals in 2014 by non-template synthesis. It was not until 2015 that CsPbX3 nanocrystals were prepared by the Kovalenko research group at ETH Zurich. by a hot-injection synthesis. Since then numerous other synthetic routes towards the successful preparation of ABX3 NCs have been demonstrated.
Hot-injection
The majority of papers reporting on ABX3 NCs make use of a hot injection procedure in which one of the reagents is swiftly injected into a hot solution containing the other reagents and ligands. The combination of high temperature and rapid addition of the reagent result in a rapid reaction that results in supersaturation and nucleation occurring over a very short period of time with a large number of nuclei. After a short period of time, the reaction is quenched by quickly cooling to room temperature. Since 2015, several articles detailing improvements to this approach with zwitterionic ligands, branched ligands and post-synthetic treatments have been reported. Recently, soy-lecithin was demonstrated to be a ligand system for these nanocrystals that could stabilize concentrations from several ng/mL up to 400 mg/mL.
Co-precipitation
A second, popular method for the preparation of ABX3 NCs relies on the ionic nature of APbX3 materials. Briefly, a polar, aprotic solvent such as DMF or DMSO is used to dissolve the starting reagents such as PbBr2, CsBr, oleic acid, and an amine. The subsequent addition of this solution into a non-polar solvent reduces the polarity of the solution and causes precipitation of the ABX3 phase.
Microfluidics
Microfluidics have been also used to synthesize CsPbX3 NCs and to screen and study synthetic parameters. Recently, a modular microfluidic platform has been developed at North Carolina State University to further optimize the synthesis and composition of these materials.
Other routes
Outside of the traditional synthetic routes, several papers have reported that CsPbX3 NCs could be prepared on supports or within porous structures even without ligands. Dirin et al. first demonstrated that bright NCs of CsPbX3 could be prepared without organic ligands within the pores of mesoporous silica. By using mesoporous silica as a template, the size of CsPbX3 nanodomains is restricted to the pore size. This allows for greater control over emission wavelength via quantum confinement and illustrates the defect tolerant nature of these materials. This concept was later extended to the preparation of ligand-free APbX3 NCs on alkali-halide supports that could be shelled with NaBr without deteriorating their optical properties and protecting the nanocrystals against a number of polar solvents.
As a result of the low melting point and ionic nature of ABX3 materials, several studies have demonstrated that bright ABX3 nanocrystals can also be prepared by ball-milling.
With NCs, the composition can be tuned via ion exchange i.e. the ability to post-synthetically exchange the ions in the lattice for those added. This has been shown to be possible for both anions and cations.
Anion exchange
The anions in the lead halide perovskites are highly mobile. The mobility arises from the diffusion of halide vacancies throughout the lattice, with an activation barrier of 0.29 eV and 0.25 eV for CsPbCl3 and CsPbBr3 respectively. (see: physical properties). This was used by Nedelcu et al. and Akkerman et al., to demonstrate that the composition of cesium lead halide perovskite nanocrystals could be tuned continuously from CsPbCl3 to CsPbBr3 and from CsPbBr3 to CsPbI3 to obtain emission across the entire visible spectrum. While this was first observed in a colloidal suspension, this was also shown in solid pellets of alkali halide salts pressed with previously synthesized nanocrystals. This same phenomenon has also been observed for MAPbX3 and FAPbX3 NCs. The anion exchange reaction has been investigated at the single nanocrystal level. In quantum-confined nanocrystals, the anion exchange leads to a uniform bandgap energy across the nanocrystal due to the quantum confinement effect. However, in nanocrystals larger than the Bohr diameter, multiple emission sites form, resulting in iodide- or bromide-rich regions.
Cation exchange and doping
Although several reports showed that CsPbX3 NCs could be doped with Mn2+, they accomplished this through the addition of the Mn precursor during the synthesis, and not through cation exchange. Cation exchange can be used to partially exchange Pb2+ with Sn2+, Zn2+, or Cd2+ over the course of several hours. In addition to these cations, gold was also shown to be a suitable candidate for cation exchange yielding a mixed-valent, and distorted, perovskite with the composition Cs2Au(I)Au(III)Br6. A-site cation exchange has also been shown to be a viable route for the transformation of CsPbBr3 to MAPbBr3 and from CsPbI3 to FAPbI3.
Ligand-assisted reprecipitation (LARP)
Ligand-assisted reprecipitation method is dedicated for the preparation of perovskite nanoplatelets (NPls). In this method, the precursors in different solvents whether polar like Dimethylformamide and Dimethyl sulfoxide or non-polar like toluene and hexane are added in the presence of the ligands to form the perovskite NPls theough supersaturation. The NPls thickness obtained from this method depends on the concentration of the ligands as well as the chain length of the organic ligands. Therefore, the thickness can be controlled by ratio between A-cation-oleate and lead-halide precursors in the reaction medium. By adjusting the toluene and acetone during the synthesis, the NPls are crystallized and precipitated at room temperature with these two solvents, respectively.
Morphology
Nanomaterials can be prepared with various morphologies that range from spherical particles/quantum wells (0D) to wires (1D) and platelets or sheets (2D), and this has been previously demonstrated for QDs such as CdSe. While the initial report of lead halide perovskite NCs covered cubic particles, subsequent reports demonstrated that these materials could also be prepared as both platelets (2D) and wires (1D). Due to the varying degrees of quantum confinement present in these different shapes, the optical properties (emission spectrum and mean lifetime) change. As an example of the effect of morphology, cubic nanocrystals of CsPbBr3 can emit from 470 nm to 520 nm based on their size (470 nm emission requires nanocrystals with an average diameter of less than 4 nm). Within this same composition (CsPbBr3), nanoplatelets exhibit emission that is blue shifted from that of cubes with the wavelength depending on the number of monolayers contained within the platelet (from 440 nm for three monolayers to 460 nm for 5 monolayers). Nanowires of CsPbBr3, on the other hand, emit from 473 nm to 524 nm depending on the width of the wire prepared with lifetimes also in the range of 2.5 ns – 20.6 ns.
Similarly to CsPbBr3, MAPbBr3 NCs also exhibit morphologically dependent optical properties with nanocrystals of MAPbBr3 emitting from 475 nm to 520 nm and exhibiting average lifetimes on the order of 240 ns depending on their composition. Nanoplatelets and nanowires have been reported to emit at 465 nm and 532 nm, respectively.
Structure and composition
Perovskite nanocrystal all have the general composition ABX3 in which A is a large, central cation (typically MA, FA, or Cs) that sits in a cavity surrounded by corner-sharing BX6 octahedra (B = Pb, Sn; X = Cl, Br, I). Depending on the composition, the crystal structure can vary from orthorhombic to cubic, and the stability of a given composition can be qualitatively predicted by its goldschmidt tolerance factor
where t is the calculated tolerance factor and r is the ionic radius of the A, B, and X ions, respectively. Structures with tolerance factors between 0.8 and 1 are expected to have cubic symmetry and form three dimensional perovskite structures such as those observed in CaTiO3. Furthermore, tolerance factors of t > 1 yield hexagonal structures (CsNiBr3 type), and t < 0.8 result in NH4CdCl3 type structures. If the A-site cation is too large (t >1), but packs efficiently, 2D perovskites can be formed.
Distortions and Phase transitions
The corner-sharing BX6 octahedra form a three-dimensional framework through bridging halides. The angle (Φ) formed by B-X-B (metal-halide-metal) can be used to judge the closeness of a given structure to that of an ideal perovskite. Although these octahedra are interconnected and form a framework, the individual octahedra are able to tilt with respect to one another. This tilting is affected by the size of the "A" cation as well as external stimuli such as temperature or pressure.
If the B-X-B angle deviates too far from 180°, phase transitions towards non-luminescent or all-together non-perovskite phases can occur. If the B-X-B angle does not deviate very far from 180°, the overall structure of the perovskite remains as a 3D network of interconnected octahedra, but the optical properties may change. This distortion increases the band gap of the material as the overlap between Pb and X based orbitals is reduced. For example, changing the A cation from Cs to MA or FA alters the tolerance factor and decreases the band gap as the B-X-B bond angle approaches 180° and the orbital overlap between the lead and halide atoms increases. These distortions can further manifest themselves as deviations in the band gap from that expected by Vegard's Law for solid solutions.
Crystal structure and twinning in nanocrystals
The room temperature crystal structures of the various bulk lead-halide perovskites have been extensively studied and have been reported for the APbX3 perovskites. The average crystal structures of the nanocrystals tend to agree with those of the bulk. Studies have, however, shown that these structures are dynamic and deviate from the predicted structures due to the presence of twinned nanodomains.
Surface chemistry
Calculations as well as empirical observations have demonstrated that perovskite nanocrystals are defect-tolerant semiconductor materials. As a result, they do not require epitaxial shelling or surface passivation since they are insensitive to surface defect states. In general, the perovskite nanocrystal surface is considered to be both ionic and highly dynamic. However, the ionic properties caused the instability of perovskite nanocrystals in humid condition and the degradation process can be accelerated by photoirradiation, which can alter the electronic properties of nanocrystals. Initial reports utilized dynamically bound oleylammonium and oleate ligands that exhibited an equilibrium between bound and unbound states. This resulted in severe instability with respect to purification and washing, which was improved in 2018 with the introduction of zwitterionic ligands. The stability and quality of these colloidal materials was further improved in 2019 when it was demonstrated that deep traps could be generated by the partial destruction of the lead-halide octahedra, and that they could also be subsequently repaired to restore the quantum yield of nanocrystals.
Applications and Devices
Light-emitting Diodes
Perovskite NCs are promising materials for the emitting layer of light-emitting diodes (LEDs) as they offer potential advantages over organic LEDs (OLEDs) such as the elimination of precious metals (Ir, Pt) and simpler syntheses. The first report of green electroluminescence (EL) was from MAPbBr3 NCs although no efficiency values were reported. It was later observed that MAPbBr3 NCs could form in a polymer matrix when the precursors for MAPbBr3 thin films were mixed with an aromatic polyidmide precursor. The authors of this study obtained green EL with an external quantum efficiency (EQE) of up to 1.2%.
The first LEDs based on colloidal CsPbX3 NCs demonstrated blue, green and orange EL with sub-1% EQE. Since then, efficiencies have reached above 8% for green LEDs (CsPbBr3 NCs), above 7% for red LEDs (CsPbI3 NCs), and above 1% for blue LEDs ).
Lasers
Perovskite MAPbX3 thin films have been shown to be promising materials for optical gain applications such as lasers and optical amplifiers. Afterwards, the lasing properties of colloidal perovskite NCs such as CsPbX3 nanocubes, MAPbBr3 nanoplatelets and FAPbX3 nanocubes were also demonstrated. Thresholds as low as 2 uJ cm−2 have been reported for colloidal NCs (CsPbX3) and 220 nJ cm−2 for MAPbI3 nanowires. Interestingly, perovskite NCs show efficient optical gain properties not only under resonant excitation, but also under two-photon excitation where the excitation light falls into the transparent range of the active material. While the nature of optical gain in perovskites is not yet clearly understood, the dominant hypothesis is that the population inversion of excited states required for gain appears to be due to bi-excitonic states in the perovskite.
Photocatalysis
Perovskite nanocrystals have also been investigated as potential photocatalysts.
Security
Perovskite nanocrystals doped with large cations such as ethylene diamine (en) were demonstrated to exhibit hypsochromaticity concomitantly with lengthened photoluminescence lifetimes relative to their undoped counterparts. This phenomenon was utilized by researchers to generate single color luminescent QR codes that could only be deciphered by measuring the photoluminescence lifetime. The lifetime measurements were carried out utilizing both time correlated single photon counting equipment as well as a prototype time-of-flight fluorescence imaging device developed by CSEM.
Other phases
Ternary cesium lead halides have multiple stable phases that can be formed; these include CsPbX3 (perovskite), Cs4PbX6 (so called "zero-dimensional" phase due to disconnected [PbX6]4- octahedra), and CsPb2X5. All three phases have been prepared colloidally either by a direct synthesis or via nanocrystal transformations.
A rising research interest in these compounds created a disagreement within the community around the zero-dimensional Cs4PbBr6 phase. Two contradicting claims exist regarding the optical properties of this material: i) the phase exhibits high photoluminescent quantum yield emission at 510-530 nm and ii) the phase is non-luminescent in the visible spectrum. It was later demonstrated that pure, Cs4PbBr6 NCs were non-luminescent, and that these could be converted to luminescent CsPbX3 NCs and vice versa.
A similar debate had occurred regarding the CsPb2Br5 phase, which was also reported as being strongly luminescent. This phase, like the Cs4PbBr6 phase, is a wide gap semiconductor (~3.1 eV), but it is also an indirect-semiconductor and is non-luminescent. The non-luminescent nature of this phase was further demonstrated in NH4Pb2Br5.
Lead-free perovskite nanocrystals
Given the toxicity of lead, there is ongoing research into the discovery of lead-free perovskites for optoelectronics. Several lead-free perovskites have been prepared colloidally: Cs3Bi2I9, Cs2PdX6, CsSnX3. CsSnX3 NCs, although the closest lead-free analogue to the highly luminescent CsPbX3 NCs, do not exhibit high quantum yields (<1% PLQY) CsSnX3 NCs are also sensitive towards O2 which causes oxidation of Sn(II) to Sn(IV) and renders the NCs non-luminescent.
Another approach to this problem relies on the replacement of the Pb(II) cation with the combination of a monovalent and a trivalent cation i.e. B(II) replaced with B(I) and B(III). Double perovskite nanocrystals such as Cs2AgBiX6 (X = Cl, Br, I), Cs2AgInCl6 (including Mn-doped variant), and Cs2AgInxBi1−xCl6 (including Na-doped variant) have been studied as potential alternatives to lead-halide perovskites, although none exhibit narrow, high PLQY emission.
See also
Quantum Dots
Perovskites
Perovskite (structure)
Light-emitting diode (LED)
Methylammonium lead halide
nanomaterials
Semiconductors
Optoelectronics
References
Materials science
Nanomaterials
Perovskites | Perovskite nanocrystal | [
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72,382,129 | https://en.wikipedia.org/wiki/L%27%C3%AEle%20du%20Sud | L'île du Sud (South Island, l'île Boisées) is an island located in the St. Brandon archipelago. It is one of the three islands (the others being Île Raphael and L'Île Coco) used as a base of operations for fishing activities by Raphael Fishing Company, the only resident fishing company in the Cargados Carajos shoals under a 1901 contract with the government of Mauritius.
Shipwrecks
On 1 February 2015, the fishing vessel, Kha Yang, with of fuel in its tanks, ran aground on the reef off L'île du Sud. Twenty crew were rescued shortly after its grounding, and a salvage operation pumped the fuel from its tanks a few weeks later.
On 5 December 2022, the Taiwanese fishing vessel, 41 FV YU FENG 67, ran aground off L'île du Sud. Its crew of 20 were later rescued by the local commercial fishing boats of Raphael Fishing Company, in the presence of the National Coast Guard. The vessel is now an effective shipwreck, and more than 20 tons of diesel were spilled into the fragile lagoon, affecting coral life and associated flora and fauna.
See also
St. Brandon
Île Raphael
Raphaël Fishing Company
Avocaré Island
L'île du Gouvernement
Île Verronge
Casting (fishing)
Fishing tournament
Fly Casting Analyzer
Constitution of Mauritius
permanent grant
Mauritian Wildlife Foundation
References
External links
Australian Bureau of Meteorology - Understanding tropical cyclone categories
Regional specialized meteorological centres
India Meteorological Department – Bay of Bengal and the Arabian Sea
Météo-France – La Reunion – South Indian Ocean from 30°E to 90°E
Tropical cyclone warning centres
Australian Bureau of Meteorology . – South Indian Ocean & South Pacific Ocean from 90°E to 160°E, south of 10°S
Islands of St. Brandon
Outer Islands of Mauritius
Reefs of the Indian Ocean
Fishing areas of the Indian Ocean
Atolls of the Indian Ocean
Marine conservation
Protected areas
Oceanography
Fisheries science
Fisheries law
2022 disasters in Africa
Maritime incidents in 2022 | L'île du Sud | [
"Physics",
"Environmental_science"
] | 404 | [
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72,383,834 | https://en.wikipedia.org/wiki/Silicon%20carbide%20color%20centers | Silicon carbide color centers are point defects in the crystal lattice of silicon carbide, which are known as color centers. These color centers have multiple uses, some of which are in photonics, semiconductors, and quantum applications like metrology and quantum communication. Defects in materials have a plethora of applications, but the reason defects, or color centers in silicon carbide are significant is due to many important properties of these color centers. Silicon carbide as a material has second-order nonlinearity, as well as optical transparency and low two-photon absorption. This makes silicon carbide viable to be an alternate platform for many things, including but not limited to nanofabrication, integrated quantum photonics, and quantum systems in large-scale wafers.
Fabrication
There are mainly three methods for fabricating silicon carbide color centers. The three methods are electronic irradiation, ion injection, and femtosecond laser writing.
Electronic irradiation
This technique works by exposing the material to an electron beam that is highly ionizing. This knocks off electrons in the material itself, which generates color centers (or defects). This process however, requires a large amount of energy, having 9MeV normally being the lower limit of energy in most materials.
Ion injection
Ion injection is normally used to dope semiconductors, but it can also be used to create color centers. An ion is first accelerated to a certain energy, normally in the MeV range. This ion is then accelerated into the material, which then implants the ion into the material, changing the material composition, which can create a color center.
Femtosecond laser writing
Utilizing a nonlinear laser writing process, along with the appropriate aberration correction, defects can be generated at any depth in the crystal. This process preserves spin and optical coherence properties. The way it works is from multiphoton ionization from the femtosecond laser process. This method of fabricating defects does not only work for silicon carbide, but can also work for other materials.
Other types of fabrication for defects are neutron irradiation, proton irradiation, and focused Si beams.
Currently, new methods of fabrication are also being experimented with to try and reduce the energy used, or the complication of the process. One of the new methods is a new method of utilizing a laser writing method with a nanosecond laser.
Types of defects
There are multiple types of defects in silicon carbide, some of which are listed below:
Vsi(-) (TV1-TV3)
VsiVC(0)
DV(0)
Ky5
CAV (Carbon anti-site-vacancy pair)
SiC(D1)
NCVSi(-)
Transition metal color centers:
TI(0)
Cr3+
V(-), V(0)
Mo(0)
Er3+
Studies have been done on TV1 as a qubit, which provided a better spin-photon interface than TV2. Recently however, the role of Vsi(-) as a qubit has been full identified.
Applications
Photonics
Recently, these color centers in silicon carbide have shown promise in becoming one of the best single-photon emitters for non-classical light sources. Traditionally, attenuated lasers have been the substitute for single-photon sources. This works for quantum cryptography, but they are a partial substitute, and in the end this was not a substitute for single-photon sources as they do not produce single photons. Normally, there are two main methods of generating single photons: spontaneous parametric down-conversion and epitaxial quantum dots.
In spontaneous parametric down-conversion, single photons can be produced up to a rate of 106 photons per second. The drawback to this approach is that there is no way to generate single photons on demand. This makes this type of generation hard to use practically.
Epitaxial quantum dots are shown to generate single photons exceptionally when put under electrical pumping. This however works under very low temperatures, which also makes these applications harder to do practically in experiments.
Color centers in silicon carbide, diamonds, and other related materials would be more practical that the two other traditional approaches due to the higher temperature that they can operate at when under optical and electrical pumping.
Semiconductors
Silicon carbide is currently being used in the semiconductor industry already, due to the fact that it belongs to a family of materials called complementary metal–oxide–semiconductor compatible materials, as well as its reliability in fabrication of high-quality single crystal wafers. Since semiconductors by definition already have point defects, some may be used for purposes like single-photon sources.
Quantum properties of silicon carbide color centers
When studied at the single defect level, single emitters could be isolated. As a result of this, silicon carbide color centers can be used for applications in quantum cryptography protocols. One example of this was a study on nitrogen-vacancy centers in diamonds in 2014, which are similar to color centers in silicon carbide, that showcased novel results on how in diamonds, the nitrogen-vacancy were color centers, which also are fluorescent impurities that have many applications
Quantum entanglement between the electron spin state and the single photon quantum state occurs when two conditions are met:
The quantum state of a single photon can be correlated to the electron spin state of the silicon carbide color centers
This correlation is able to be stored in nearby nuclear spins in the color centers
This quantum entanglement allows the creation of quantum networks, which leads to quantum communications, quantum memory, and metrology.
Quantum sensing
When the color centers are first brought to an excited state, a photon can be emitted from the decay from the excited state to the ground states. This photon can then interact with other sources of static and variable magnetic fields. As a result of this, the spin transition frequency and the coherence time are altered, which then this effect is used in quantum sensing.
Comparison to diamond color centers
Much of the color center research was originally performed using diamond instead of silicon carbide. For comparison, the nitrogen-vacancy in diamond has similar quantum properties to the divacancy in silicon carbide. Diamond's vacancy potentially has better quantum properties than silicon carbide's, but one of the major benefits of silicon carbide and its color centers is increased scalability and greater ease of manufacture when compared to diamond. Additionally, silicon carbide does not suffer from complications in production such as graphitization during irradiation which is possible during diamond color center manufacture.
References
Wikipedia Student Program
Crystallographic defects | Silicon carbide color centers | [
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72,387,477 | https://en.wikipedia.org/wiki/Prigogine%27s%20theorem | Prigogine's theorem is a theorem of non-equilibrium thermodynamics, originally formulated by Ilya Prigogine.
The formulation of Prigogine's theorem is:
According to this theorem, the stationary state of a linear non-equilibrium system (under conditions that prevent the achievement of an equilibrium state) corresponds to the minimum entropy production. If there are no such obstacles, then the production of entropy reaches its absolute minimum - zero. A linear system means the fulfillment of linear phenomenological relationships between thermodynamic flows and driving forces. The coefficients of proportionality in the relationships between flows and driving forces are called phenomenological coefficients.
The theorem was proved by Prigogine in 1947 from the Onsager relations. Prigogine's theorem is valid if the kinetic coefficients in the Onsager relations are constant (do not depend on driving forces and flows); for real systems, it is valid only approximately, so the minimum entropy production for a stationary state is not such a general principle as the maximum entropy for an equilibrium state. It has been experimentally established that Onsager's linear relations are valid in a fairly wide range of parameters for heat conduction and diffusion processes (for example, Fourier's law, Fick's law). For chemical reactions, the linear assumption is valid in a narrow region near the state of chemical equilibrium. The principle is also violated for systems odd with respect to time reversal.
References
External links
1977 Nobel Prize lecture by Ilya Prigogine
Attribution note: early versions of this article were translated from the Russian-language Wikipedia article on this topic.
Theorems
Thermodynamics | Prigogine's theorem | [
"Physics",
"Chemistry",
"Mathematics"
] | 350 | [
"Thermodynamics stubs",
"Physical chemistry stubs",
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75,180,389 | https://en.wikipedia.org/wiki/Ezio%20Todini | Ezio Todini (born 5 June 1943) is an Italian academic, hydrologist and civil engineer.
Early life and education
Ezio Todini born in Lucca, Italy on 5 June 1943, spent most of his early life and youth in Cairo, Egypt. In 1969, he was awarded the degree of Doctor in Hydraulic Engineering by the University of Pisa and joined the then just inaugurated IBM Pisa Scientific Centre in 1971.
Career
In 1973, he became professor of applied hydromechanics at the University of Pisa. In 1979, he was appointed professor of water resources planning at the University of Florence. Since 1980, he has held the chair of hydrology at the University of Bologna. He retired as professor in 2010. In 2009, he was the founding president of the Italian Hydrological Society. Currently he has research collaborations with several universities and serves as water resources expert for international bodies and in particular for the World Bank.
Todini is a leading scientist in the development of hydrological modeling approaches for water resources management and planning. Since the mid-1970s, he pioneered the systems approach to hydrology and crafted a direction which guided hydrologic sciences into a new level of distributed hydrologic modelling, uncertainty quantification, and optimal parameter estimation via Kalman filtering. His Mutually Interactive State Parameter (MISP) algorithm based on an approach conceptually similar to the Gibbs sampler, introduced a novel methodology to the joint estimation of state and parameters in Kalman Filters, and served not only the hydrologic community at large but other fields of communications and environmental sciences.
In hydraulics, Todini largely contributed to the enhancement of design and simulation methods for flow in looped water distribution networks (WDN). In this context he authored the global gradient algorithm for the analysis of WDN. The algorithm is at the core of the worldwide used WDN analysis freeware EPANET. Moreover, in 2000 he introduced the resilience index, as the basis for implementing multi-objective Pareto design to WDN.
Todini initiated his research career dealing with hydrological models. Initially he proposed a quadratic programming alternative to the constrained estimation of unit hydrographs as an alternative to the linear programming approach proposed by Eagleson. The work was based on the seminal work of Norbert Wiener and Norman Levinson. This gave rise to the constrained linear systems (CLS) model, which favorably compared to the existing well known hydrological models at the WMO Project on Intercomparison of Conceptual Models Used for Hydrological Forecasting.
He also developed the ARNO hydrological model. ARNO was the first soil moisture accounting model to be included into a general circulation models (GCM) such as ECHAM GCM (Hamburg climate model). As distributed precipitation evolved, Todini developed the land surface model TOPKAPI. The model is structured around grids that capture soil and precipitation variably. He used Bayesian inference to determine flood risk based on long-term TOPKAPI simulations. The use of Bayesian inference in hydrological modelling allowed to separate out parameter and input uncertainty in operational river flow forecasting.
A major contribution to hydrology is the explanation for mass losses in flow computations on mild river bed slopes using the Muskingum-Cunge routing method and the proposition of a corrective approach for making the method mass conservative.
Another important contribution are his works on the quantification of forecasting uncertainty using multiple streamflow models through meta-Gaussian correlation-based ensemble averaging, an approach known as Model-Conditional Processor (MCP).
A major component of Todini's work has been the continuous transfer of the developed scientific approaches into operational tools to be used in the solution of real-world problems. The hydrological models, the flood routing models and the uncertainty post processors were thus integrated into operational real time flood forecasting packages installed on several rivers all around the world, such as the Po, the Arno and the Tiber in Italy, the Han Jang, the Yellow river, and the Fuchun river in China, the Duero, the Tajo, the Jucar and the Segura rivers in Spain.
He also contributed to the reference Handbook of Applied Hydrology.
Between 1984 and 1991, Todini served as vice-president of the IAHS International Commission on Water Resources Systems (ICWRS), and from 1991 to 1994 as vice-president of the IAHS. Between 2009 and 2016 he served as president the Società Idrologica Italiana – Italian Hydrological Society. From 2017 he has become the honorary president of SII-IHS.
currently he acts as Honorary President of the Italian Hydrological Society and is a member of the scientific community of the World Wildlife Fund (WWF) Italy.
References
External links
Research Gate
Living people
Hydrology
Water resources management
Decision support systems
University of Bologna
Italian engineers
1943 births | Ezio Todini | [
"Chemistry",
"Technology",
"Engineering",
"Environmental_science"
] | 982 | [
"Information systems",
"Hydrology",
"Decision support systems",
"Environmental engineering"
] |
75,182,170 | https://en.wikipedia.org/wiki/Sponge%20bomb | A sponge bomb is a specialized device designed to seal the end of a tunnel. Small enough that it can be set by a single person, it is a non-explosive, chemical bomb that releases a burst of expanding foam that quickly hardens.
Development
The sponge bomb was developed by the Israel Defense Forces (IDF) to address the use of tunnels by Hamas in Gaza.
Design
Housed in a plastic container, the bomb has a metal partition that separates two liquid reagents. Once the partition is removed, the liquids mix and react, causing them to rapidly expand and then solidify, creating a physical barrier blocking the tunnel. The device is either set at its target by an individual or thrown.
In 2021, testing of sponge bombs was reportedly conducted by IDF in simulated tunnels.
During initial testing of these bombs, the liquid emulsion was found to be hazardous to work with when mishandled – some Israeli soldiers lost their eyesight.
Historical perspective
This is not the first time that sticky foam has been used by a military force. Reportedly, the U.S. Marine Corps and the U.S. Army have used streams of foam as non-lethal tools for crowd control or restraint of hostile combatants.
References
External links
Military use of non-lethal foam (at 20 seconds into video)
Bombs of Israel
Foams
Tunnel warfare
Tunnels in Palestine
Israel–Hamas war
Israeli inventions | Sponge bomb | [
"Chemistry",
"Engineering"
] | 276 | [
"Foams",
"Military engineering",
"Tunnel warfare"
] |
75,184,216 | https://en.wikipedia.org/wiki/291%20%28number%29 | 291 is the natural number following 290 and preceding 292.
In mathematics
291 is an odd composite number with two prime factors.
291 is a semiprime number meaning that it has 2 prime factors.
291 can be written as the sum of the nth prime plus n. It is the 52nd prime (239) plus 52.
291 is one of the positions of “c” in the tribonacci word abacabaab… defined by a->ab, b->ac, c->a.
291 is the sum of six 4th powers. It is the sum of 4⁴+2⁴+2⁴+1⁴+1⁴+1⁴.
References
Integers | 291 (number) | [
"Mathematics"
] | 140 | [
"Elementary mathematics",
"Integers",
"Mathematical objects",
"Numbers"
] |
75,184,637 | https://en.wikipedia.org/wiki/Cobalt%28II%29%20azide | Cobalt(II) azide is an inorganic chemical compound with the formula . It can be formed through the reaction between dicobalt octacarbonyl and iodine azide.
Properties
Aqueous solutions of cobalt(II) azide change in color when introduced to suitable organic solvents, from pink-violet to a blue shade. Like most azides, it is explosive.
References
azide
cobalt | Cobalt(II) azide | [
"Chemistry"
] | 85 | [
"Explosive chemicals",
"Azides",
"Inorganic compounds",
"Inorganic compound stubs"
] |
75,185,099 | https://en.wikipedia.org/wiki/Chromium%20azide | Chromium azide is an inorganic chemical compound with the formula .
Properties
Chromium azide formation has been investigated from chromium salts and sodium azide. It was separated in 1922 through the evaporation of a dry crystalline chromium(III) nitrate solution in absolute alcohol with sodium azide. Through a spectrophotometric study, it was shown that the chromium(III) nitrate solution's green color was due to the mono-azido-chromium(III) complex. Two absorbency maxima were located at 442 and 605 nm. Chromium azide has luminescence properties from its optically active Cr3+ ions.
References
azide
chromium | Chromium azide | [
"Chemistry"
] | 151 | [
"Explosive chemicals",
"Azides",
"Inorganic compounds",
"Inorganic compound stubs"
] |
75,187,709 | https://en.wikipedia.org/wiki/Cagrilintide | Cagrilintide is a long-acting analogue of amylin. It is being tested to treat obesity and type 2 diabetes by itself and in combination with semaglutide as cagrilintide/semaglutide.
Research
A systematic review and metanalysis of cagrisema, published in 2024, found that cagrisema may provide weight loss benefits.
References
Amylin receptor agonists
Experimental diabetes drugs
Cyclic peptides | Cagrilintide | [
"Chemistry"
] | 96 | [
"Pharmacology",
"Pharmacology stubs",
"Medicinal chemistry stubs"
] |
75,187,722 | https://en.wikipedia.org/wiki/Cagrilintide/semaglutide | Cagrilintide/semaglutide, marketed as CagriSema, is a combination of cagrilintide, a dual amylin and calcitonin receptor agonist, and semaglutide, a GLP-1 agonist. It is injected once weekly and is being tested in type 2 diabetes and obesity. Preliminary trial results found a greater weight loss compared to either medication alone. HbA1c was significantly improved compared to cagrilintide alone and non-significantly better than semaglutide alone. In a Phase II trial, weight loss averaged -15.6 percent after 32 weeks, making CagriSema comparable in efficacy to tirzepatide. A future trial sponsored by Novo Nordisk is comparing tirzepatide and CagriSema head-to-head.
CagriSema entered Phase III clinical trials in 2023. In December 2024, Novo Nordisk announced the results of REDEFINE 1, one of their series of Phase III trials, testing weekly cagrilintide 2.4 mg and semaglutide 2.4 mg individually and together versus placebo in obese or overweight subjects with one or more comorbidities. In the intention-to-treat analysis, people treated with CagriSema lost 20.4% of their body weight over 68 weeks, versus 11.5% with cagrilintide 2.4 mg alone, 14.9% with semaglutide 2.4 mg alone, and 3.0% with placebo.
References
GLP-1 receptor agonists
Experimental diabetes drugs
Peptide therapeutics
Amylin receptor agonists
Combination diabetes drugs
Combination anti-obesity drugs | Cagrilintide/semaglutide | [
"Chemistry"
] | 358 | [
"Pharmacology",
"Pharmacology stubs",
"Medicinal chemistry stubs"
] |
70,885,459 | https://en.wikipedia.org/wiki/PhyCV | PhyCV is the first computer vision library which utilizes algorithms directly derived from the equations of physics governing physical phenomena. The algorithms appearing in the first release emulate the propagation of light through a physical medium with natural and engineered diffractive properties followed by coherent detection. Unlike traditional algorithms that are a sequence of hand-crafted empirical rules, physics-inspired algorithms leverage physical laws of nature as blueprints. In addition, these algorithms can, in principle, be implemented in real physical devices for fast and efficient computation in the form of analog computing. Currently PhyCV has three algorithms, Phase-Stretch Transform (PST) and Phase-Stretch Adaptive Gradient-Field Extractor (PAGE), and Vision Enhancement via Virtual diffraction and coherent Detection (VEViD). All algorithms have CPU and GPU versions. PhyCV is now available on GitHub and can be installed from pip.
History
Algorithms in PhyCV are inspired by the physics of the photonic time stretch (a hardware technique for ultrafast and single-shot data acquisition). PST is an edge detection algorithm that was open-sourced in 2016 and has 800+ stars and 200+ forks on GitHub. PAGE is a directional edge detection algorithm that was open-sourced in February, 2022. PhyCV was originally developed and open-sourced by Jalali-Lab @ UCLA in May 2022. In the initial release of PhyCV, the original open-sourced code of PST and PAGE is significantly refactored and improved to be modular, more efficient, GPU-accelerated and object-oriented. VEViD is a low-light and color enhancement algorithm that was added to PhyCV in November 2022.
Background
Phase-Stretch Transform (PST)
Phase-Stretch Transform (PST) is a computationally efficient edge and texture detection algorithm with exceptional performance in visually impaired images. The algorithm transforms the image by emulating propagation of light through a device with engineered diffractive property followed by coherent detection. It has been applied in improving the resolution of MRI image, extracting blood vessels in retina images, dolphin identification, and waste water treatment, single molecule biological imaging, and classification of UAV using micro Doppler imaging.
Phase-Stretch Adaptive Gradient-Field Extractor (PAGE)
Phase-Stretch Adaptive Gradient-Field Extractor (PAGE) is a physics-inspired algorithm for detecting edges and their orientations in digital images at various scales. The algorithm is based on the diffraction equations of optics. Metaphorically speaking, PAGE emulates the physics of birefringent (orientation-dependent) diffractive propagation through a physical device with a specific diffractive structure. The propagation converts a real-valued image into a complex function. Related information is contained in the real and imaginary components of the output. The output represents the phase of the complex function.
Vision Enhancement via Virtual diffraction and coherent Detection (VEViD)
Vision Enhancement via Virtual diffraction and coherent Detection (VEViD) a efficient and interpretable low-light and color enhancement algorithm that reimagines a digital image as a spatially varying metaphoric light field and then subjects the field to the physical processes akin to diffraction and coherent detection. The term “Virtual” captures the deviation from the physical world. The light field is pixelated and the propagation imparts a phase with an arbitrary dependence on frequency which can be different from the quadratic behavior of physical diffraction. VEViD can be further accelerated through mathematical approximations that reduce the computation time without appreciable sacrifice in image quality. A closed-form approximation for VEViD which we call VEViD-lite can achieve up to 200 FPS for 4K video enhancement.
PhyCV on the Edge
Featuring low-dimensionality and high-efficiency, PhyCV is ideal for edge computing applications. In this section, we demonstrate running PhyCV on NVIDIA Jetson Nano in real-time.
NVIDIA Jetson Nano Developer Kit
NVIDIA Jetson Nano Developer Kit is a small- sized and power-efficient platform for edge computing applications. It is equipped with an NVIDIA Maxwell architecture GPU with 128 CUDA cores, a quad-core ARM Cortex-A57 CPU, 4GB 64-bit LPDDR4 RAM, and supports video encoding and decoding up to 4K resolution. Jetson Nano also offers a variety of interfaces for connectivity and expansion, making it ideal for a wide range of AI and IoT applications. In our setup, we connect a USB camera to the Jetson Nano to acquire videos and demonstrate using PhyCV to process the videos in real-time.
Real-time PhyCV on Jetson Nano
We use the Jetson Nano (4GB) with NVIDIA JetPack SDK version 4.6.1, which comes with pre- installed Python 3.6, CUDA 10.2, and OpenCV 4.1.1. We further install PyTorch 1.10 to enable the GPU accelerated PhyCV. We demonstrate the results and metrics of running PhyCV on Jetson Nano in real-time for edge detection and low-light enhancement tasks. For 480p videos, both operations achieve beyond 38 FPS, which is sufficient for most cameras that capture videos at 30 FPS. For 720p videos, PhyCV low-light enhancement can operate at 24 FPS and PhyCV edge detection can operate at 17 FPS.
Highlights
Modular Code Architecture
The code in PhyCV has a modular design which faithfully follows the physical process from which the algorithm was originated. Both PST and PAGE modules in the PhyCV library emulate the propagation of the input signal (original digital image) through a device with engineered diffractive property followed by coherent (phase) detection. The dispersive propagation applies a phase kernel to the frequency domain of the original image. This process has three steps in general, loading the image, initializing the kernel and applying the kernel. In the implementation of PhyCV, each algorithm is represented as a class in Python and each class has methods that simulate the steps described above. The modular code architecture follows the physics behind the algorithm. Please refer to the source code on GitHub for more details.
GPU Acceleration
PhyCV supports GPU acceleration. The GPU versions of PST and PAGE are built on PyTorch accelerated by the CUDA toolkit. The acceleration is beneficial for applying the algorithms in real-time image video processing and other deep learning tasks. The running time per frame of PhyCV algorithms on CPU (Intel i9-9900K) and GPU (NVIDIA TITAN RTX) for videos at different resolutions are shown below. Note that the PhyCV low-light enhancement operates in the HSV color space, so the running time also includes RGB to HSV conversion. However, for all running times using GPUs, we ignore the time of moving data from CPUs to GPUs and count the algorithm operation time only.
Installation and Examples
Please refer to the GitHub README file for a detailed technical documentation.
Current Limitations
I/O (Input/Output) Bottleneck for Real-time Video Processing
When dealing with real-time video streams from cameras, the frames are captured and buffered in CPU and have to be moved to GPU to run the GPU-accelerated PhyCV algorithms. This process is time-consuming and it is a common bottleneck for real-time video-processing algorithms.
Lack of Parameter Adaptivity for Different Images
Currently, the parameters of PhyCV algorithms have to be manually tuned for different images. Although a set of pre-selected parameters work relatively well for a wide range of images, the lack of parameter adaptivity for different images remains a limitation for now.
See also
Edge detection
Feature detection (computer vision)
Time stretch analog-to-digital converter
Time stretch dispersive Fourier transform
Phase stretch transform
References
Computer vision software
Computer vision | PhyCV | [
"Engineering"
] | 1,663 | [
"Artificial intelligence engineering",
"Packaging machinery",
"Computer vision"
] |
70,887,546 | https://en.wikipedia.org/wiki/Arsenite%20bromides | The arsenite bromides are mixed anion compounds containing both arsenite and bromide ions. Similar compounds include arsenate bromides, arsenite chlorides, antimonite bromides, antimonite chlorides, and ...
They are in the category of halide oxidoarsenates(III)
List
References
Arsenites
Bromides
Mixed anion compounds | Arsenite bromides | [
"Physics",
"Chemistry"
] | 85 | [
"Matter",
"Mixed anion compounds",
"Salts",
"Bromides",
"Ions"
] |
70,888,472 | https://en.wikipedia.org/wiki/Antimonide%20iodide | Antimonide iodides or iodide antimonides are compounds containing anions composed of iodide (I−) and antimonide (Sb3−). They can be considered as mixed anion compounds. They are in the category of pnictide halides. Related compounds include the antimonide chlorides, antimonide bromides, phosphide iodides, and arsenide iodides.
List
References
Antimonides
Iodides
Mixed anion compounds | Antimonide iodide | [
"Physics",
"Chemistry"
] | 107 | [
"Ions",
"Matter",
"Mixed anion compounds"
] |
70,891,828 | https://en.wikipedia.org/wiki/Tammann%20and%20H%C3%BCttig%20temperatures | The Tammann temperature (also spelled Tamman temperature) and the Hüttig temperature of a given solid material are approximations to the absolute temperatures at which atoms in a bulk crystal lattice (Tammann) or on the surface (Hüttig) of the solid material become sufficiently mobile to diffuse readily, and are consequently more chemically reactive and susceptible to recrystallization, agglomeration or sintering. These temperatures are equal to one-half (Tammann) or one-third (Hüttig) of the absolute temperature of the compound's melting point. The absolute temperatures are usually measured in Kelvin.
Tammann and Hüttig temperatures are important for considerations in catalytic activity, segregation and sintering of solid materials. The Tammann temperature is important for reactive compounds like explosives and fuel oxiders, such as potassium chlorate (, TTammann = 42 °C), potassium nitrate (, TTammann = 31 °C), and sodium nitrate (NaNO3, TTammann = 17 °C), which may unexpectedly react at much lower temperatures than their melting or decomposition temperatures.
The bulk compounds should be contrasted with nanoparticles which exhibit melting-point depression, meaning that they have significantly lower melting points than the bulk material, and correspondingly lower Tammann and Hüttig temperatures. For instance, 2 nm gold nanoparticles melt at only about 327 °C, in contrast to 1065 °C for a bulk gold.
History
Tammann temperature was pioneered by German astronomer, solid-state chemistry, and physics professor Gustav Tammann in the first half of the 20th century. He had considered a lattice motion very important for the reactivity of matter and quantified his theory by calculating a ratio of the given material temperatures at solid-liquid phases at absolute temperatures. The division of a solid's temperature by a melting point would yield a Tammann temperature. The value is usually measured in Kelvins (K):
where is a constant dimensionless number.
The threshold temperature for activation and diffusion of atoms at surfaces was studied by :de:Gustav Franz Hüttig, physical chemist on the faculty of Graz University of Technology, who wrote in 1948 (translated from German):
Description
The Hüttig temperature for a given material is
where is the absolute temperature of the material's bulk melting point (usually specified in Kelvin units) and is a unitless constant that is independent of the material, having the value according to some sources, or according to other sources. It is an approximation to the temperature necessary for a metal or metal oxide surfaces to show significant atomic diffusion along the surface, sintering, and surface recrystallization. Desorption of adsorbed gasses and chemical reactivity of the surface often increase markedly as the temperature is increases above the Hüttig temperature.
The Tammann temperature for a given material is
where is a unitless constant usually taken to be , regardless of the material. It is an approximation to the temperature necessary for mobility and diffusion of atoms, ions, and defects within a bulk crystal. Bulk chemical reactivity often increase markedly as the temperature is increased above the Tammann temperature.
Examples
The following table gives an example Tammann and Hüttig temperatures calculated from each compound's melting point Tmp according to:
TTammann = 0.5 × Tmp
THüttig = 0.3 × Tmp
See also
Notes
References
Heat_transfer
Thermodynamic properties | Tammann and Hüttig temperatures | [
"Physics",
"Chemistry",
"Mathematics"
] | 698 | [
"Transport phenomena",
"Physical phenomena",
"Heat transfer",
"Thermodynamic properties",
"Physical quantities",
"Quantity",
"Thermodynamics"
] |
68,003,141 | https://en.wikipedia.org/wiki/Paired%20receptors | Paired receptors are pairs or clusters of receptor proteins that bind to extracellular ligands but have opposing activating and inhibitory signaling effects. Traditionally, paired receptors are defined as homologous pairs with similar extracellular domains and different cytoplasmic regions, whose genes are located together in the genome as part of the same gene cluster and which evolved through gene duplication. Homologous paired receptors often, but not always, have a shared ligand in common. More broadly, pairs of receptors have been identified that exhibit paired functional behavior - responding to a shared ligand with opposing intracellular signals - but are not closely homologous or co-located in the genome. Paired receptors are highly expressed in the cells of the immune system, especially natural killer (NK) and myeloid cells, and are involved in immune regulation.
Structure
Paired receptors are membrane proteins with extracellular domains that interact with extracellular ligands. The extracellular region may contain multiple repeating protein domains and may be members of either the immunoglobulin or C-type lectin families. The extracellular domains of homologous paired receptors are typically very similar in sequence but have different binding affinity for their shared ligands, with the inhibitory member of the pair binding more tightly.
Homologous paired receptors have characteristic differences in their transmembrane and cytoplasmic regions that distinguish the activating and inhibiting members of the pair. Inhibitory receptors have a cytoplasmic sequence typically containing at least one immunoreceptor tyrosine-based inhibitory motif (ITIM). Activating receptors have a truncated cytoplasmic sequence compared to their corresponding inhibitory receptor and feature a positively charged amino acid residue in their transmembrane domain, enabling protein-protein interaction with an adaptor protein that possesses a immunoreceptor tyrosine-based activation motif (ITAM).
Genetics and evolution
Homologous paired receptors are located in the same gene cluster and are thought to have evolved through gene duplication. Sequence features such as the presence of an ITIM-like sequence in the 3' untranslated region of some activating receptors imply that the activating members of the pair likely evolved from the inhibitory members. A number of pathogens interact with the inhibitory member of a pair as a means of immune evasion or viral entry, suggesting that activating members with similar binding competencies may be an evolutionary response to this mechanism. This hypothesis is known as the "counterbalance theory" and these evolutionary dynamics represent an evolutionary arms race between pathogens and the host immune system. The evolutionary pressures on some paired-receptor families have been described as examples of the "Red Queen" effect.
Including non-paired examples, over 300 potential immune inhibitory receptors have been identified in the human genome. There are strong indications that paired receptors are rapidly and recently evolving. These genetic regions have high levels of gene polymorphism, and the gene repertoires found in the genomes of closely related lineages vary significantly. The selective pressure experienced by the host from pathogens is thought to underlie this rapid evolution.
Although paired receptors are best characterized as part of the human and mouse immune systems, they have also been studied in other organisms. The chicken (Gallus gallus domesticus) genome contains a number of examples including a very large family, the chicken Ig-like receptors (CHIR) with over 100 members. Paired receptor evolution has also been studied in Xenopus (clawed frog) species. The adaptive immune system is unique to jawed vertebrates, but an example of a paired receptor family has been identified in a jawless vertebrate, termed agnathan paired receptors resembling Ag receptors (APAR) in the hagfish.
Expression
Expression of paired receptors is common in many types of leukocytes, especially myeloid cells and natural killer (NK) cells. Activation of NK cells is a complex regulatory process modulated by a number of different paired receptor families coexpressed in this cell type. In some cases, only one member of the pair is expressed in a cell type. Expression of the paired members in a single cell type may vary with time, or the proteins may differ in subcellular localization, resulting in variations in signaling. Expression in NK cells can be stochastic, resulting in unique variations in receptor repertoire.
Some paired receptors are expressed outside the immune system, for example in neurons, endothelium, and epithelium but in many examples, wide tissue distribution can be observed.
Function
Paired receptors transduce extracellular signals through opposing intracellular signaling pathways. Canonically, inhibitory receptors recruit phosphatases through their ITIM motifs, inhibiting the function of cells in which they are expressed. By contrast, activating receptors interact with adaptor proteins such as DAP-12 bearing an ITAM motif, which in turn recruit kinases such as Syk and ZAP70.
Ligands for paired receptors can be very diverse. They are often proteins; the best-characterized are the MHC class I molecules, but a number of other endogenous molecules have been described as ligands for at least one family of paired receptors, and in a few cases in the LILR family, even intact bacteria or viruses can serve as ligands. Lipids such as phosphatidylethanolamine and phosphatidylserine, sugars and sialylated glycans, and nucleic acids can all serve as ligands for some paired receptors.
The binding affinity of paired receptors' extracellular domains for their ligands is generally fairly weak, with dissociation constants (Kd) in the micromolar (μM) range. However, the inhibitory member of a pair usually binds with higher affinity than the activating member. This can produce a competitive inhibition effect, in which the inhibitory member of the pair out-competes its activating counterpart for ligand binding; other mechanisms of interference with activation, such as disrupting dimerization, have also been described. Thus the net baseline signal from the pair is usually inhibitory, but may be modulated through differences in expression, surface density, subcellular localization, or other factors.
In NK cells, ligands for inhibitory receptors are often MHC class I (MHC-I) molecules, while those for activating receptors may include signals of abnormality or infection such as proteins from pathogens or tumors, or molecules associated with cell stress. Endogenous ligands for inhibitory receptors are better characterized than those for activating receptors. Paired receptor signaling may represent maintenance of homeostasis such that immune responses to normal host cells are inhibited, while responses to abnormal or pathogenic molecules in the environment are activating. NK activation in the absence of inhibitory receptor signals from endogenous ligands is a molecular mechanism for the missing-self hypothesis of NK activation.
Interaction with pathogens
A number of examples of molecular mimicry by pathogens, emulating natural endogenous ligands of paired receptors for immune evasion, have been described in the literature. Such interactions are particularly common with the inhibitory members of receptor pairs, bolstering the hypothesis that activating partners are a later evolutionary response to this immune escape strategy.
The first described interaction between a paired receptor and a viral protein identified ILT-2 and ILR-4 (LILRB1 and LILRB2) as targets for herpes simplex virus UL18 protein, which resembles an MHC-I molecule. Variations in susceptibility to mouse cytomegalovirus infection due to differences in Ly49-family paired receptors among mouse strains are well-characterized, and are attributed to the structural resemblance between the viral protein m157 and MHC-I molecules. The pathogenic bacterium Escherichia coli K1 exposes surface polysialic acid molecules that serve as a molecular mimic for the native ligand of the inhibitory receptor Siglec-11, but induces an opposing response through interactions with the paired activating receptor Siglec-16, exemplifying the benefit of activating receptors as defense mechanisms against molecular mimicry by pathogens.
Paired receptors are also used as viral entry receptors by a number of viruses and occasionally as entry mechanisms for other pathogens. Sialylation is common among mammalian cell-surface proteins and a number of pathogens use sialic acid - either self-synthesized or obtained from the host cell - to evade host immunity, including by interacting with inhibitory siglec receptors.
Families
There are two main groups of paired receptors, distinguished by extracellular regions containing immunoglobulin or C-type lectin domains. Nomenclature within these families is complex and has changed over time as new members were identified. In general, the example of the LILR family applies; genes designated A represent the inhibitory receptor and genes designated B represent the activating receptor.
Immunoglobulin-like receptors
Immunoglobulin-like receptors are members of the immunoglobulin superfamily and have one or more 70-110 residue immunoglobulin domains (Ig) in their extracellular region, typically multiple such domains in tandem. Many of the genes encoding these proteins occur in the leukocyte receptor complex (LRC), a large gene cluster on human chromosome 19. Members of this group found in the human genome include:
The killer-cell immunoglobulin-like receptor (KIR) family contains proteins with 2-3 extracellular Ig domains and long (inhibitory) or short (activating) cytoplasmic regions. Typically expressed in NK and some T cells, they interact with MHC class I. This gene family located in the LRC is highly polymorphic and there is individual variation in both alleles and copy number, as well as in alternative splicing. This family has undergone significant diversification in primate lineages.
The leukocyte immunoglobulin-like receptors (LILR) family contains 13 genes, including two pseudogenes. They have 2-4 Ig domains. One member, LILRA3, lacks a transmembrane region and is a soluble protein; others may be expressed in soluble form through alternative splicing. Like the similar KIR family, LILR genes are found in the LRC and are polymorphic, though less so than KIR. LILR proteins are broadly expressed in immune cells and have very diverse ligands.
The paired type 2 immunoglobulin like receptor (PILR) family contains two genes, PILRA (inhibiting) and PILRB (activating). They have a single extracellular Ig domain with a siglec-like structure.
The signal regulatory protein (SIRP) family contains three genes, SIRPA (inhibiting), SIRPB1 (activating), and SIRPG (non-signaling), with the more distantly related SIRPD and SIRPB2 not yet well characterized. SIRPA interacts with CD47, a regulator of phagocytosis. This family also interacts with surfactant protein D.
The carcinoembryonic antigen-related cell adhesion (CEACAM) family contains 12 genes with one or more Ig domains. They are expressed broadly, especially in endothelium and epithelium and have roles in cell-cell recognition. They have been extensively studied for their role in cancer and have been used as cancer biomarkers.
The siglec family contains 15 genes divided into two evolutionarily related groups. This family has three members with activating motifs, Siglec-14, Siglec-15, and Siglec-16. These proteins bind sialic acids, and are often targeted by pathogens.
TIGIT (T cell immunoreceptor with Ig and ITIM domains) is an inhibitory receptor that forms a nonhomologous but functional pair with DNAM1 (CD226).
C-type lectin-like receptors
C-type lectin-like receptors (CLRs) contain one or more C-type lectin (Ca2+ dependent carbohydrate-binding lectin) domains. Example pairs include:
CD94/NKG2, expressed in NK and some T cells and interacts with the ligand HLA-E.
Dendritic cell immunoreceptor (DCIR)/dendritic cell immunoactivating receptor (DCAR), characterized as a pair in mice, though no human DCAR has been identified.
NKR-P1 (CD161) is a member of a paired receptor group in rodents, but the human genome contains only one, inhibitory receptor, NKRP1A (KLRB1).
The Ly49 family in mice has been extensively studied for its role in NK activation using laboratory mice as a model organism, but has no homologous gene cluster in the human genome. The KIR family is the functional equivalent.
References
Immune receptors
Signal transduction | Paired receptors | [
"Chemistry",
"Biology"
] | 2,691 | [
"Biochemistry",
"Neurochemistry",
"Signal transduction"
] |
68,004,457 | https://en.wikipedia.org/wiki/Merafloxacin | Merafloxacin is a fluoroquinolone antibacterial that inhibits the pseudoknot formation which is necessary for the frameshift in the SARS-CoV-2 genome. It is a promising drug candidate for SARS-CoV-2.
References
Beta-Amino acids
Fluoroquinolone antibiotics
COVID-19 drug development
Secondary amino acids
Pyrrolidines | Merafloxacin | [
"Chemistry"
] | 85 | [
"COVID-19 drug development",
"Drug discovery"
] |
63,687,736 | https://en.wikipedia.org/wiki/Embelin | Embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone) is a naturally occurring para-benzoquinone isolated from dried berries of Embelia ribes plants. Several studies have reported antidiabetic activity of embelin.
References
Antioxidants
Anti-aging substances
1,4-Benzoquinones
Hydroquinones | Embelin | [
"Chemistry",
"Biology"
] | 86 | [
"Senescence",
"Anti-aging substances"
] |
63,687,901 | https://en.wikipedia.org/wiki/Thermogravitational%20cycle | A thermogravitational cycle is a reversible thermodynamic cycle using the gravitational works of weight and buoyancy to respectively compress and expand a working fluid.
Theoretical framework
Consider a column filled with a transporting medium and a balloon filled with a working fluid. Due to the hydrostatic pressure of the transporting medium, the pressure inside the column increases along the z axis (see figure). Initially, the balloon is inflated by the working fluid at temperature TC and pressure P0 and located on top of the column. A thermogravitational cycle is decomposed into four ideal steps:
1→2: Descent of the balloon towards the bottom of the column. The working fluid undergoes adiabatic compression with its temperature increasing and its pressure reaching value Ph at the bottom (Ph>P0).
2→3: While the ballon lays at the bottom, the working fluid receives heat from the hot source at temperature TH and undergoes isobaric expansion at pressure Ph.
3→4: The balloon rises towards the column top. The working fluid undergoes adiabatic expansion with a drop in temperature and reaches pressure P0 after expansion when the balloon is on top.
4→1: Once arrived on top, the working fluid supplies heat to the cold source at temperature TC while undergoing isobaric compression at pressure P0.
For a thermogravitational cycle to occur, the balloon has to be denser than the transporting medium during 1→2 step and less dense during 3→4 step. If these conditions are not naturally satisfied by the working fluid, a weight can be attached to the balloon to increase its effective mass density.
Applications and examples
An experimental device working according to thermogravitational cycle principle was developed in a laboratory of the University of Bordeaux and patented in France. Such thermogravitational electric generator is based on inflation and deflation cycles of an elastic bag made of nitrile elastomer cut from a glove finger. The bag is filled with a volatile working fluid that has low chemical affinity for the elastomer such as perfluorohexane (C6F14). It is attached to a strong NdFeB spherical magnet that acts both as a weight and for transducing the mechanical energy into voltage. The glass cylinder is filled with water acting as transporting fluid. It is heated at the bottom by a hot circulating water-jacket, and cooled down at the top by a cold water bath. Due to its low boiling point temperature (56 °C), the perfluorohexane drop contained in the bag vaporizes and inflates the balloon. Once its density is lower than the water density, the balloon raises according to Archimedes’ principle. Cooled down at the column top, the balloon deflates partially until its gets effectively denser than water and starts to fall down. As seen from the videos, the cyclic motion has a period of several seconds. These oscillations can last for several hours and their duration is limited only by leaks of the working fluid through the rubbery membrane. Each time the magnet goes through the coil produces a variation in the magnetic flux. An electromotive force is created and detected through an oscilloscope. It has been estimated that the average power of this machine is 7 μW and its efficiency is 4.8 x 10−6. Although these values are very small, this experiment brings a proof of principle of renewable energy device for harvesting electricity from a weak waste heat source without need of other external energy supply, e.g. for a compressor in a regular heat engine. The experiment was successfully reproduced by undergraduate students in preparatory classes of the Lycée Hoche in Versailles.
Several other applications based on the thermogravitational cycles could be found in the literature. For example:
In solar balloons, heat from the sun is absorbed which causes a balloon filled with air to rise and convert its movement in an electric signal.
In a gravity driven organic Rankine cycle, gravity is used instead of a pump to pressurize a working fluid. In literature, different authors have studied the working fluid characteristics best suited to optimize their efficiency for gravity-driven ORC devices.
In a version of a magnetic fluid generator, a refrigerant fluid is vaporized at the bottom of a column by an external heat source, and its bubbles move across a magnetized ferrofluid, thereby producing electric voltage via a linear generator.
In a conceptual hybrid of several patents, solar or geothermal energy is harnessed by means of a modified organic Rankine cycle with high columns of water below ground
Cycle efficiency
The efficiency η of a thermogravitational cycle depends on the thermodynamic processes the working fluid goes through during each step of the cycle. Below some examples:
If the heat exchanges at the bottom and top of the column with a hot source and cold source respectively, occur at constant pressure and temperature, the efficiency would be equal to the efficiency of a Carnot cycle:
If the working fluid stays at the liquid stage during the compression stage 1→2, the efficiency would be equal to the Rankine cycle efficiency. By noting h1, h2, h3 and h4 the specific enthalpies of the working fluid at stages 1,2,3 and 4 respectively:
If the working fluid remains a gas during all the steps of a thermogravitational cycle, the efficiency would be equal to the Brayton cycle efficiency. By noting γ the heat capacity ratio:
References
Thermodynamic cycles
Equilibrium chemistry
Thermodynamic processes
Thermodynamic systems | Thermogravitational cycle | [
"Physics",
"Chemistry",
"Mathematics"
] | 1,163 | [
"Thermodynamic systems",
"Thermodynamic processes",
"Physical systems",
"Equilibrium chemistry",
"Thermodynamics",
"Dynamical systems"
] |
63,694,205 | https://en.wikipedia.org/wiki/Inductive%20tensor%20product | The finest locally convex topological vector space (TVS) topology on the tensor product of two locally convex TVSs, making the canonical map (defined by sending to ) continuous is called the inductive topology or the -topology. When is endowed with this topology then it is denoted by and called the inductive tensor product of and
Preliminaries
Throughout let and be locally convex topological vector spaces and be a linear map.
is a topological homomorphism or homomorphism, if it is linear, continuous, and is an open map, where the image of has the subspace topology induced by
If is a subspace of then both the quotient map and the canonical injection are homomorphisms. In particular, any linear map can be canonically decomposed as follows: where defines a bijection.
The set of continuous linear maps (resp. continuous bilinear maps ) will be denoted by (resp. ) where if is the scalar field then we may instead write (resp. ).
We will denote the continuous dual space of by and the algebraic dual space (which is the vector space of all linear functionals on whether continuous or not) by
To increase the clarity of the exposition, we use the common convention of writing elements of with a prime following the symbol (e.g. denotes an element of and not, say, a derivative and the variables and need not be related in any way).
A linear map from a Hilbert space into itself is called positive if for every In this case, there is a unique positive map called the square-root of such that
If is any continuous linear map between Hilbert spaces, then is always positive. Now let denote its positive square-root, which is called the absolute value of Define first on by setting for and extending continuously to and then define on by setting for and extend this map linearly to all of The map is a surjective isometry and
A linear map is called compact or completely continuous if there is a neighborhood of the origin in such that is precompact in
In a Hilbert space, positive compact linear operators, say have a simple spectral decomposition discovered at the beginning of the 20th century by Fredholm and F. Riesz:
There is a sequence of positive numbers, decreasing and either finite or else converging to 0, and a sequence of nonzero finite dimensional subspaces of () with the following properties: (1) the subspaces are pairwise orthogonal; (2) for every and every ; and (3) the orthogonal of the subspace spanned by is equal to the kernel of
Notation for topologies
denotes the coarsest topology on making every map in continuous and or denotes endowed with this topology.
denotes weak-* topology on and or denotes endowed with this topology.
Every induces a map defined by is the coarsest topology on making all such maps continuous.
denotes the topology of bounded convergence on and or denotes endowed with this topology.
denotes the topology of bounded convergence on or the strong dual topology on and or denotes endowed with this topology.
As usual, if is considered as a topological vector space but it has not been made clear what topology it is endowed with, then the topology will be assumed to be
Universal property
Suppose that is a locally convex space and that is the canonical map from the space of all bilinear mappings of the form going into the space of all linear mappings of
Then when the domain of is restricted to (the space of separately continuous bilinear maps) then the range of this restriction is the space of continuous linear operators
In particular, the continuous dual space of is canonically isomorphic to the space the space of separately continuous bilinear forms on
If is a locally convex TVS topology on ( with this topology will be denoted by ), then is equal to the inductive tensor product topology if and only if it has the following property:
For every locally convex TVS if is the canonical map from the space of all bilinear mappings of the form going into the space of all linear mappings of then when the domain of is restricted to (space of separately continuous bilinear maps) then the range of this restriction is the space of continuous linear operators
See also
References
Bibliography
External links
Nuclear space at ncatlab
Functional analysis
Topological vector spaces
Topology
Topological tensor products | Inductive tensor product | [
"Physics",
"Mathematics",
"Engineering"
] | 878 | [
"Functions and mappings",
"Tensors",
"Functional analysis",
"Vector spaces",
"Mathematical objects",
"Space (mathematics)",
"Topological vector spaces",
"Topology",
"Space",
"Mathematical relations",
"Geometry",
"Spacetime",
"Topological tensor products"
] |
73,837,085 | https://en.wikipedia.org/wiki/Nzambici | Nzambici (also called Nzambi) is the eternal God of Essence, as well as Moon, Earth and Sky Mother in Bakongo religion. She is also the female counterpart of the Kongo creator god, Nzambi Mpungu.
History
By the 17th century, Nzambici's importance seems to have diminished. Oral tradition from the period states that Nzambi Mpungu was surrounded by lesser spirits, including Nzambici. There is consensus among historians that this reduction of nature spirits to lesser spirits was due to the Portuguese influence of monotheism and their shunning of "idols." Whereas Nzambici and Nzambi Mpungu were once "the marvel of marvels," Nzambi Mpungu began to exist independently of Nzambici, and was seen as a supreme Creator God, similar to the Christian God of Portuguese colonizers.
Kongo cosmology
Oral tradition states that in the beginning, time, place and space did not exist. There was only a circular void, called mbûngi. One day, the "Sovereign Master" Nzambi Mpungu summoned a spark of fire, called kalûnga, which gained energy and burned until its flames filled mbungi. When it became too hot, it hurled pieces of debris outside of the circle. Those pieces traveled far and wide in all directions until they came to stop. When they cooled off, they were stars and planets, which formed the universe. Nzambi Mpungu then became Kalûnga, the god of fire and change.
Nzambici and Nzambi Mpungu
Wanting to expand his creation, some oral traditions say that Nzambi Mpungu crafted his female counterpart named Nzambici, the god of essence. Other oral traditions say Nzambici always existed alongside Nzambi Mpungu as an eternal goddess in her own right.
Nevertheless, they lived as one, watching over all they had made. That was until Nzambici stole some of his fire, or kalûnga, and gained power of her own. To punish her, Nzambi Mpungu is said to have created the earth and sent her there. But unable to stay away from her for too long, he returned to earth and married Nzambici. On earth, they created the waters, the land and the animals. She subsequently became "the god on earth, the great princess, the mother of all the animals, the one who promises her daughter to the animal who shall bring her the fire from heaven."
Nzambici and Nzambi then created the first Kongo person, or muntu. Nzambici also became the great mystery of the earth, "the mother of a beautiful daughter, gives mankind all laws, ordinances, arts, games, and musical instruments." She "settles quarrels between animals, and in the stories giving her decision is embedded an immense amount of Fjort law." To guide man, Nzambici and Nzambi Mpungu created nature spiritssimbi, nkisi, nkita, and kilunduand separated the physical world, called Nseke, from the spiritual world, called Mpémba, with a boundary of water, called the kalûnga line. A mystical forest, mfinda, ran between the worlds, where nature spirits and the ancestors could travel from one world to the other and advise the living. Nzambici and Nzambi Mpungu withdrew from the earth and took their place in the heavens, choosing to no longer interact with man. Man knew Nzambici as the earth and moon and Nzambi Mpungu as the sun. Because of the duality of Nzambici and Nzambi, the Kongo people believed that the right side of the body was male, while the left side was believed to be female.
See also
Bunzi
Kongo cosmogram
Kongo religion
Lunar deity
Simbi
Sky deity
References
African deities
African goddesses
Animal goddesses
Bantu deities
Bantu religion
Creator deities
Creator goddesses
Earth deities
Earth goddesses
Kongo culture
Lunar deities
Lunar goddesses
Sky and weather deities
Sky and weather goddesses
Traditional African religions
Tutelary deities
Tutelary goddesses
Kongo religion | Nzambici | [
"Physics"
] | 884 | [
"Weather",
"Sky and weather deities",
"Physical phenomena"
] |
73,837,678 | https://en.wikipedia.org/wiki/Mono-N-protected%20amino%20acids | Mono-N-protected amino acid (MPAA) is a bifunctional ligand that plays a key role in C–H functionalizations by accelerating the reaction rate and imparting specified chirality into the product. Amino acids are ideal building blocks for chiral ligand synthesis due to the cost, accessibility, large variety, solubility, and inherent chirality. Naturally occurring amino acids are transformed into chiral MPAA ligands that, upon coordination to metal complexes, allow reactions to occur that are otherwise energetically unfavorable. Great strides in the development of MPAA ligands over the past two decades have led to the integral role that enantioselective catalysis now plays in complex organic synthesis.
History and development
In the past century, there has been much research into the development of effective chiral catalysts due to its great potential in organic synthesis. In the 1960s, cyclometalation reactions including C(sp2)–H and C(sp3)–H cleavage were pioneered by Kleiman, Dubeck, Cope, and Siekman. A decade later, Shaw discovered that inorganic acetate salts promoted otherwise difficult cyclopalladations. To build off of this work, Sokolov focused on developing chiral, enantioenriched metallacyles and proposed the concerted metal-deprotonation (CMD) mechanism.
Despite this foundation of discoveries, enantioselective catalysis for C–H functionalization continued to lack in efficiency oand selectivity for desired chiral product formation. In 2008, Jin-Quan Yu reported the first MPAA ligands, showcasing their use in enantioselective activation of C(sp2)–H and C(sp3)–H bonds. Initial synthesis occurred by reacting the nucleophilic amino acid in base with a highly electrophilic acyl chloride resulting in one new amide bond formation. Upon addition of acyl chloride, most resulting groups off of the nitrogen were common protecting groups used in organic synthesis, hence mono-N-protected. Taking advantage of the weak coordination of amides and carboxylates with Pd-complexes, this enantioselective catalysis requires the MPAA ligand to allow the reaction to proceed and determine the product chirality, minimizing side reactions that may occur without the ligand. Since the initial discovery, Yu has continued to pioneer the field by expanding the substrate scope, increasing functional group tolerance, and developing ligand variations.
Mechanism
After iterative computational and experimental studies, the internal amidate mechanism was proposed in collaboration of Wu, Yu, and Houk. In the proposed mechanism, the trimeric Pd-precatalyst converts to the mono-Pd complex with coordination to solvent and the bidentate MPAA ligand. Mass spectrometry results reveal this active catalyst which forms favorably with the stabilizing dianionic MPAA ligand as computations suggest.
The key intermediate step of these cyclometalation reactions involves the metal-mediated cleavage of the C–H bond and simultaneous formation of the metal–C bond of the substrate. Upon addition of substrate, the N-acyl motif acts as an internal proton acceptor in the concerted metal-deprotonation (CMD) of the transition state for this inner-sphere process. According to this model, the rate and selectivity of the C–H functionalization are impacted by the basicity of the MPAA ligand. The resulting experimental data of steric and electronic alteration of the MPAA ligands align with this model. In 2023, the first experimental observations to support the proposed mechanism were reported, which were previously unattainable due to the lack of well-defined isolated palladium-MPAA complexes.
Ligand variations
Since the initial MPAA ligand report, many variations of bifunctional ligands derived from amino acids have been developed. Bidentate MPAQ (mono-protected amino quinoline) ligands were introduced in the application of β-methylene C–H bonds in aliphatic amides. The highly successful MPAO (mono-protected amino oxazoline) ligand allowed for C(sp3)–H functionalization via arylation of α-methyls, borylation of cyclobutyl carboxylic amides, and boronic cross coupling of alkyl amines. MPAAM (mono-protected aminoalkyl amine) ligands were used in enantioselective C(sp3)–H arylations of free aliphatic acids without the need for exogenous directing groups. Variations of the MPAAThio (mono-protected aminoalkyl thioether) ligands have been use in olefination of free carboxylic acids and arylation, carbonylation, and olefination of free aliphatic amines.
Expanding the reaction substrate scope to non-directed C(sp2)–H bonds, pyridone ligands were developed to functionalize arenes and heteroarenes which proved to be particularly useful in late-state derivatization of bioactive compounds such as estrone, caffeine, and camptothecin. Many analogues of the pyridine-pyridone (azine-pyridone) ligands were developed and used in the C(sp2)–H hydroxylation of (hetero)arenes and the dehydrogenation of methylene C(sp3)–H bonds on alkyl free acids.
Applications in total synthesis
The development of MPAA ligands enabled and improved the synthesis of many complex natural products. Examples include Arnottin 1, Aspercylide B, Berkelic Acid, Boletopsin 11, Danshenspiroketallactone, Delavatine A, Herbindole B/cis-Trikentrin A, Hongoquercin A, Incarviatone A, Indoxamycin, Kedarcidin/Neocarzinostatin, Kinamycin
, Lithospermic Acid, M1 PAMs, and VS-548. In the formation of indoxamycin cores, MPAA ligand assisted C–H functionalization introduces high complexity via intramolecular ortho olefination.
The use of C–H functionalization in the synthesis of lithospheric acid exemplifies the site- and stereoselective capabilities of using MPAA ligands in these reactions. As the penultimate step, the intermolecular C–H olefination introduces almost double the complexity into the compound enabling the highly convergent synthesis.
References
Ligands
Amino acids | Mono-N-protected amino acids | [
"Chemistry"
] | 1,391 | [
"Amino acids",
"Biomolecules by chemical classification",
"Ligands",
"Coordination chemistry"
] |
73,842,156 | https://en.wikipedia.org/wiki/Pentaoxygen%20difluoride | Pentaoxygen difluoride is a binary inorganic compound of fluorine and oxygen with the chemical formula . The compound is one of many known oxygen fluorides.
Synthesis
The compound can be prepared by electric discharges through the — mixture of the certain molar ratio at 60 to 77K. The ratio is predicted to be 5:2.
Physical properties
Pentaoxygen difluoride is an oxidizing agent. At 90K, the compound looks like a reddish-brown liquid and as an oil at 77 K.
At 77K, the compound is insoluble in liquid , soluble in liquid and . At 65K, it is soluble in liquid .
References
Oxygen fluorides
Nonmetal halides
Oxidizing agents | Pentaoxygen difluoride | [
"Chemistry"
] | 155 | [
"Oxygen fluorides",
"Redox",
"Inorganic compounds",
"Oxidizing agents",
"Inorganic compound stubs"
] |
73,842,665 | https://en.wikipedia.org/wiki/Stewartson%20layer | In fluid dynamics, a Stewartson layer is a thin cylindrical shear layer that connects two differentially rotating regions in the radial direction, namely the inside and outside the cylinder. The Stewartson layer, typically, also connects different Ekman boundary layers in the axial direction. The layer was first identified by Ian Proudman and was first described by Keith Stewartson. This layer should be compared with the Ekman layer which occurs near solid boundaries.
Structure
The Stewartson layer is not elementary but possesses a complex structure and emerges when the relevant Ekman number is ; here is the kinematic viscosity, and are the characteristic scales for the angular speed and length. The fundamental balance that occurs in the Stewartson shear layer is between Coriolis forces and viscous forces.
Spherical geometry
For simplicity, consider the example of two concentric spheres that rotate about a common axis with slightly different angular velocity. The fluid domain corresponds to the annular region. In this problem, the Stewartson layer emerges as a cylinder circumscribing the inner sphere with its generators lying parallel to the rotation axis. Outside , the fluid rotates as a solid body with a speed that of the outer sphere. Inside (in the annular region), again the fluid rotates as a solid body, except near the inner and outer sphere walls, where Ekman boundary layers of thickness are set up that help adjusting the flow to transition from uniform rotation to their respective rotating values on the solid walls. Across , there is a jump in the azimuthal velocity and on , there is an axial flow connecting the two Ekman layers. The structure of is the Stewartson layer.
The Stewartson layer consists of two outer layers, one on the inner side of with a thicknesses and one on the outer side of with a thickness ; these outer layers flank a thin inner layer of thickness . The differential rotation between inside and outside is smoothed out in the outer layers (primarily in the outer layer lying on the outer side of ). The adjustment of azimuthal motion in the outer layers induces secondary axial flow. The inner layer becomes necessary partly to accommodate this induced axial motion and partly to accommodate the transport of flow between one Ekman boundary layer to the other one (from the Ekman layer on the faster-rotating sphere to the slower one). Note that the thickness of the Ekman layer is , which is much smaller than the inner Stewartson layer. In the inner layer, change in the azimuthal velocity is very small, because the outer layers are already smoothed out jump in the azimuthal velocity. In addition, the outer layers (again primarily in the outler layer lying outer side of the cylinder) also transport axially flow from the fast rotating sphere to slower one.
Cylindrical geometry
In cylindrical geometries, the thickness of both the two outer layers is and the thickness of inner layer is .
See also
Ekman layer
References
Flow regimes
Fluid dynamics | Stewartson layer | [
"Chemistry",
"Engineering"
] | 598 | [
"Piping",
"Chemical engineering",
"Flow regimes",
"Fluid dynamics"
] |
73,847,522 | https://en.wikipedia.org/wiki/SN%202023ixf | SN 2023ixf is a type II-L (core collapse) supernova located in the Pinwheel Galaxy. It was first observed on 19 May 2023 by Kōichi Itagaki and immediately classified as a type II supernova. Initial magnitude at discovery was 14.9. After discovery, the Zwicky Transient Facility project found a precovery image of the supernova at magnitude 15.87 two days before discovery. The supernova was about 21 million light-years from Earth and is expected to have left behind either a neutron star or black hole, based on current stellar evolution models.
The supernova is located near a prominent HII region, NGC 5461, in an outer spiral arm of the bright galaxy.
By 22 May 2023, SN 2023ixf had brightened to about magnitude 11. It could be seen in telescopes as small as and remained visible with backyard telescopes for several months. The supernova started to fade around 10 June 2023.
The last supernova that close to Earth occurred 9 years previously: SN 2014J in Messier 82, roughly 12 million light-years from Earth.
Before becoming a supernova, the progenitor star is believed to have been a supergiant with an absolute magnitude in the near-infrared (814nm) of MF814W = –4.66.
Image gallery
References
See also
SN 1987A
External links
Supernova Discovered in Nearby Spiral Galaxy M101, Astronomy Picture of the Day (NASA)
AAVSO: magnitude plot
Supernovae
Astronomical objects discovered in 2023
Discoveries by Koichi Itagaki
Ursa Major
2023 in outer space | SN 2023ixf | [
"Chemistry",
"Astronomy"
] | 339 | [
"Supernovae",
"Ursa Major",
"Astronomical events",
"Constellations",
"Explosions"
] |
69,392,090 | https://en.wikipedia.org/wiki/Transition%20metal%20nitrate%20complex | A transition metal nitrate complex is a coordination compound containing one or more nitrate ligands. Such complexes are common starting reagents for the preparation of other compounds.
Ligand properties
Being the conjugate base of a strong acid (nitric acid, pKa = -1.4), nitrate has modest Lewis basicity. Two coordination modes are common: unidentate and bidentate. Often, bidentate nitrate, denoted κ2-NO3, is bound unsymmetrically in the sense that one M-O distance is clearly bonding and the other is more weakly interacting. The MO-N distances for the coordinated oxygen are longer by about 10 picometers longer than the N-Oterminal bonds. This observation suggests that the terminal N-O bonds have double bond character. Nitrate is isostructural with but less basic than carbonate. Both exhibit comparable coordination geometries. The nitrogen center of nitrate does not form bonds to metals.
Coordination complexes
With three terminal oxide groups, nitrate can in principle bind metals through many geometries. Even though the ligand is written as MNO3, the oxygen atoms are invariably coordinated. Thus, monodentate nitrate is illustrated by [Co(NH3)5NO3]2+, which could also be written as [Co(NH3)5ONO2]2+. Homoleptic metal nitrate complexes generally have O,O'-bidentate nitrate ligands.
Hydrates
Typical metal nitrates are hydrated. Some of these salts crystallize with one or more nitrate ligands, but most are assumed to dissolve in water to give aquo complexes, often of the stoichiometry [M(H2O)6]n+.
Cr(NO3)3(H2O)6
Mn(NO3)2(H2O)4
Fe(NO3)3(H2O)9
Co(NO3)2(H2O)2
Ni(NO3)2(H2O)4
Pd(NO3)2(H2O)2
Cu(NO3)2(H2O)x
Zn(NO3)2(H2O)4
Hg2(NO3)2(H2O)2
Synthesis
Metal nitrate complexes are often prepared by treating metal oxides or metal carbonates with nitric acid. The main complication with dissolving metals in nitric acid arises from redox reactions, which can afford either nitric oxide or nitrogen dioxide.
Anhydrous nitrates can be prepared by the oxidation of metals with dinitrogen tetroxide (often as a mixture with nitrogen dioxide, with which it interconverts). N2O4 undergoes molecular autoionization to give [NO+] [NO3−], with the former nitrosonium ion being a strong oxidant. The method is illustrated by the route to β-Cu(NO3)2:
Cu + 2N2O4 → Cu(NO3)2 + 2NO
Many metals, metal halides, and metal carbonyls undergo similar reactions, but the product formulas can be deceptive. For example from chromium one obtains Cr(NO3)3(N2O4)2, which was shown to be the salt (NO+)2[Cr(NO3)5]2-. Nitrogen oxides readily interconvert between various forms, some of which may act as completing ligands. The redox reaction of nitrosonium and the metal can give rise to nitrogen oxide which forms strong metal nitrosyl complexes; nitronium ions (NO2+) are similarly observed.
In some cases, nitrate complexes are produced from the reaction of nitrogen dioxide with a metal dioxygen complex:
(PPh3 = triphenylphosphine)
Reactions
Given nitrate's low basicity, the tendency of metal nitrate complexes toward hydrolysis is expected. Thus copper(II) nitrate readily dissociates in aqueous solution to give the aqua complex:
Cu(NO3)2 + 6 H2O → [Cu(H2O)6](NO3)2
Pyrolysis of metal nitrates yields oxides.
Ni(NO3)2 → NiO + NO2 + 0.5O2
This reaction is used to impregnate oxide supports with nickel oxides.
Nitrate reductase enzymes convert nitrate to nitrite. The mechanism involves the intermediacy of Mo-ONO2 complexes.
References
Nitrates | Transition metal nitrate complex | [
"Chemistry"
] | 942 | [
"Oxidizing agents",
"Nitrates",
"Salts"
] |
69,392,210 | https://en.wikipedia.org/wiki/Neuroecology | Neuroecology studies ways in which the structure and function of the brain results from adaptations to a specific habitat and niche.
It integrates the multiple disciplines of neuroscience, which examines the biological basis of cognitive and emotional processes, such as perception, memory, and decision-making, with the field of ecology, which studies the relationship between living organisms and their physical environment.
In biology, the term 'adaptation' signifies the way evolutionary processes enhance an organism's fitness to survive within a specific ecological context. This fitness includes the development of physical, cognitive, and emotional adaptations specifically suited to the environmental conditions in which the organism or phenotype lives, and in which its species or genotype evolves.
Neuroecology concentrates specifically on neurological adaptations, particularly those of the brain. The purview of this study encompasses two areas. Firstly, neuroecology studies how the physical structure and functional activity of neural networks in a phenotype is influenced by characteristics of the environmental context. This includes the way social stressors, interpersonal relationships, and physical conditions precipitate persistent alterations in the individual brain, providing the neural correlates of cognitive and emotional responses. Secondly, neuroecology studies how neural structure and activity common to a genotype is determined by natural selection of traits that benefit survival and reproduction in a specific environment.
See also
Evolutionary ecology
Evolutionary psychology
References
External links
Cognitive Neuroecology Lab at the FMRIB Centre of the University of Oxford (UK) and Donders Institute in Nijmegen (Netherlands)
Behavioral neuroscience
Evolutionary biology
Ecology terminology
Ecology | Neuroecology | [
"Biology"
] | 322 | [
"Evolutionary biology",
"Ecology terminology",
"Behavior",
"Behavioral neuroscience",
"Ecology",
"Behavioural sciences"
] |
69,395,571 | https://en.wikipedia.org/wiki/Dispersion%20stabilized%20molecules | Dispersion stabilized molecules are molecules where the London dispersion force (LDF), a non-covalent attractive force between atoms and molecules, plays a significant role in promoting the molecule's stability. Distinct from steric hindrance, dispersion stabilization has only recently been considered in depth by organic and inorganic chemists after earlier gaining prominence in protein science and supramolecular chemistry. Although usually weaker than covalent bonding and other forms of non-covalent interactions like hydrogen bonding, dispersion forces are known to be a significant if not dominating stabilizing force in certain organic, inorganic, and main group molecules, stabilizing otherwise reactive moieties and exotic bonding.
Stabilization through dispersion
Dispersion interactions are a stabilizing force arising from quantum mechanical electron correlation. Although quantum mechanical in nature, the energy of dispersion interactions can be approximated classically, showing a R−6 dependence on the distance between two atoms. This distance dependence helps make dispersion interactions weak for individual atoms and has led to dispersion effects being historically neglected in molecular chemistry. However, in larger molecules dispersion effects can become significant. Dispersion forces in molecular chemistry are most apparent in molecules with large, bulky functional groups. Dispersion stabilization is often signified by atomic contacts below their van der Waals radii in a molecule's crystal structure. Especially for H•••H contacts between bulky, rigid, polarizable groups, short contacts may indicate that a dispersion force is overcoming the Pauli repulsion present between the two H atoms.
Dispersion forces stabilizing a reactive moiety within a molecule is distinct from using steric bulk to protect that reactive moiety. Adding "steric hindrance" to a molecule's reactive site through bulky groups is a common strategy in molecular chemistry to stabilize reactive moieties within a molecule. In this case bulky ligands like terphenyls, bulky alkoxides, aryl-substituted NHCs, etc. serve as a protective wrapper on the molecule. Under the steric hindrance model, the filled orbitals of a bulky group repel other molecules and/or functional groups through Pauli repulsion. These bulky groups inhibit the approach to a molecule's reactive site, kinetically stabilizing the molecule. By contrast dispersion stabilization occurs when these bulky ligands form energetically favorable non-covalent interactions. In molecules where dispersion forces are a dominant factor, the attractive interactions between bulky groups is greater than repulsive interactions between the groups, providing overall thermodynamic stability to the molecule. Although dispersion stabilization and steric hindrance are distinct, dispersion stabilized molecules frequently benefit from steric protection of the molecule's reactive moiety.
Molecular dispersion in computational chemistry
Advances in quantum computational chemistry methods have allowed for faster theoretical examination of dispersion effects in molecular chemistry. Standard density functional theory (DFT) does not account well for dispersion effects, but corrections like the popular -D3 correction can be used with DFT to provide efficient dispersion energy corrections. The -D3 correction is a force field type correction that does not take into account electronic structure, but nonetheless the popular correction works with many functionals and produces values that often fall within 5-10% of more sophisticated calculations. The "gold standard" computational method are coupled-cluster methods like CCSD(T) that account for the electron correlation origin of dispersion interactions.
Richard Bader's theory of Atoms in Molecules (AIM) has also been invoked to computationally identify dispersion interactions. Bader proposed that a bond critical point, or a critical point in the electron density, between two electronically similar, closed-shell hydrogen atoms is evidence for a stabilizing dispersion interaction between those two atoms. Although there is controversy about accepting bond critical points as evidence for net attractive interactions, AIM analysis has been invoked by different research groups to show dispersion effects in a variety of molecules.
Alternative computational analysis methods include Yang's electron density based non-covalent interaction (NCI) analysis, and the local energy decomposition (LED) analysis to produce a dispersion interaction density (DID) plot.
Example molecules
Organic chemistry
Dispersion stabilization explains the reactivity patterns of bulky hydrocarbon radicals. •CPh3 radicals have been known since 1900. In the mid-1960s, the dimer form of the radical was observed, and instead of forming the expected Ph3CCPh3 product, the radical instead undergoes head to tail addition. By contrast, adding two tBu groups to the meta positions on the phenyl rings causes the radical to readily dimerize to (3,5-tBu2H3C6)3C–C(C6H3-3,5-tBu2)3. Initially this discovery puzzled researchers because •CPh3 head-to-tail addition seemed to suggest steric repulsion disfavored direct addition; however, the more sterically crowded molecule underwent head-to-head addition. More recently, computational analysis has shown the formation of the tBu substituted dimer to be stabilized through dispersion interactions. The study suggests that dispersion interactions between tBu groups provide ~60kcal/mol of stabilization to the molecule, enough to overcome the unfavorable steric interactions from the additional tBu groups. Further, the dimer contains a 1.67Å C-C single bond, much longer than the canonical 1.54Å C-C single bond. Despite the long C-C bond, the molecule remains stable at room temperature through dispersion based stability.
Beyond just the tBu substituted hexaphenylethane, Schriener and coworkers have synthesized new molecules with "dispersion energy donors" to form both long C-C bonds and short H•••H contacts. The effect of dispersion stabilization was further probed with a series of meta-substituted hexaphenylethane molecules substituted with Me, iPr, tBu, Cy, and adamantyl groups. Of these molecules, only the tBu and adamantyl analogs were observed to form the head-to-head dimer, showing the sensitivity of dispersion stabilization to rigid, polarizable substituents. Dispersion stabilization has additionally been used to stabilize intermolecular contacts. When the (3,5-tBu2H3C6)3CH molecule dimerizes to form [(3,5-tBu2H3C6)3CH]2, stabilizing interactions between tBu groups bring the central pair of hydrogens to a contact distance of 1.566Å as determined by neutron diffraction. This distance is well within the combined van der Waals radii of the two H atoms, and at the time was the shortest reported H•••H contact.Researchers have posited that the stability of the bulky hydrocarbon tetra(tert-butyl)tetrahedrane is in part from dispersion forces. Originally, the molecule's thermal stability in air up to 135 °C was attributed to the corset effect, wherein any stability gained by elongating a C-C bond to release ring strain would be countered by increased repulsion between the remaining tBu groups. Although the corset effect is the dominant force driving stability, this explanation has been recently supplemented with calculations that show the tBu groups provide 3.1 kcal/mol of stability to the molecule.
Inorganic chemistry
Dispersion forces can stabilize reactive organometallic molecules by using bulky ligands in metal complexes. The first two-coordinate linear Cu(II) complex, Cu{N(SiMe3)Dipp}2 (Dipp = C6H5-2,6iPr2), was prepared by combining a 1:1 ratio of LiN(SiMe3)Dipp and CuCl. The mechanism of this reaction is unknown, but the net result is Cu disproportionation to form the Cu(II) complex and Cu metal. The authors suggest that a dispersion stabilization of about 25 kcal/mol from the bulky ligands assists in the initial disproportionation reaction and that this stabilization prevents crystals of the complex from decomposing via further disproportionation to DippN=NDipp, N-(SiMe3)2Dipp, and Cu metal. The complex's eclipsed ligand conformation further suggests that dispersion stabilizes the low coordinate complex.
Metal tetranorbornyls, M(nor)4 (1-nor = 4bicyclo[2.2.1]hept-1-yl, M = Fe, Co), benefit from stability imparted by dispersion. The compounds display high stability for a formally 4+ oxidation state metal center, which has traditionally been attributed to unfavorable β-elimination. Computational work has determined that the close norbornyl contacts are worth -45.9 kcal/mol of energy, providing significant stabilization to the molecule.
Main group chemistry
Researches have used dispersion stabilization to promote unusual main group bonding. Dispersion forces have been shown to stabilize a cyclic silylated plumbylene dimer, which shows different Pb-Pb bonding than in the parent parent diplumbene (Pb2H4). The crystal structure of the silylated plumbylene dimer has different geometries about each Pb atom, indicating that the molecule forms a singular donor-acceptor interaction. By contrast, the Pb atoms in Pb2H4 participate in a double donor-acceptor interaction giving the molecule a trans-bent structure. Computational investigations reveal that the silylated dimer has roughly twice the bond dissociation energy of parent diplumbene Pb2H4 despite the parent diplumbene having a higher Wiberg Bond Index. The authors suggest through DFT calculations that dispersion forces between bulky trimethylsilyl groups determine the dimer's conformation.Dispersion has been implicated in stabilizing a Ga-substituted doubly bonded dipnictenes of the form [L(X)Ga]2E2 where E = As, Sb, Bi and L = C[C(Me)N(2,6-iPr2-C6H3). Researchers synthesized the As version of the molecule and computationally analyzed the full series. By calculating the energy of the molecules with and without dispersion, it was determined that dispersion nearly doubles the dimer's enthalpic stabilization when formed from the monomer. In this case, dispersion couples with electronics to provide stability to the molecule.
The thermal stability of an extended Si-Si bond in tBu3SiSitBu3, or superdisilane, has also been attributed to dispersion interactions. Superdisilane has a Si-Si bond length of 2.697Å in the solid state, significantly extended compared to the gas phase Si-Si bond length of 2.331Å in the parent disilane H3SiSiH3. Despite the long bond length, superdisilane exhibits thermal stability up to 323K. Dispersion forces keep the molecule inert even while its core Si-Si bond lengthens. Similarly, the longest known Ge-Ge bond is found in tBu3GeGetBu3 and is also facilitated by dispersion stabilization.
Dispersion stabilization has also been invoked for (tBuC)3P, a main group analog of a hydrocarbon tetrahedrane. Monophosphatetrahedrane, (tBuC)3P, displays greater thermal stability than diphosphatetrahedrane, (tBuCP)2, which decomposes at just -32 °C. The additional stability has been attributed to dispersion interactions between the adjacent, bulky tBu groups. Through computational analysis, the authors identified 9 H-H interactions that each provide -0.7 kcal/mol of energy, overcoming the steric penalty of bringing the tBu groups together. Geometry optimizations with tBu groups swapped for less bulky hydrogens cause significant molecule shape change, indicating that dispersion plays a significant role in stabilizing the molecule's structure.
Applications
Dispersion stabilized molecules are an active area of research. Presently dispersion interactions have mostly been examined after the synthesis of molecules, but molecular design with dispersion effects in mind has generated some excitement for potential future applications. The dispersion interaction effect has been compared to the emerging work on frustrated Lewis pairs, and there is speculation that dispersion could be useful in future catalysis.
References
Van der Waals molecules | Dispersion stabilized molecules | [
"Physics",
"Chemistry"
] | 2,659 | [
"Molecules",
"Matter",
"Van der Waals molecules"
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69,396,356 | https://en.wikipedia.org/wiki/Friction%20Acoustics | Solid bodies in contact that undergo shear relative motion (friction) radiate energy. Part of this energy is radiated directly into the surrounding fluid media, and another part radiates throughout the solid bides and the connecting boundary conditions. The coupling of structural vibration and acoustic radiation takes is rooted in the mechanism of atomic oscillations, by which kinetic energy is translated to thermal energy.
This field involves principles of acoustics, solid mechanics, contact dynamics, and tribology.
Coupling and Stick-Slip
Vibrational energy induced by either kinetic or breakaway friction can cause modal excitation of a subset of the contacting bodies or the vibratory coupling of the multiple bodies, depending on the strength of coupling.
Friction noise can be the product of multiple distinct dynamic processes, sliding and stick-slip. Sliding generally leads to stick-slip under a decreasing friction-velocity relation, or other unstable oscillations.
Weak Contact
When normal forces are low, the solid bodies vibratory modes are weakly excited. The resulting noise generated is known as roughness noise. This noise is largely broad-band near the surface, and radiation efficiency and material geometry dictates which frequency content is radiated into the far field.
Surfaces that are relatively smooth, or well-lubricated, low normal forces, and low relative velocities are prone to set conditions for this regime, and avoid stick-slip.
Strong Contact
Under some conditions, the radiated energy is high at the mechanical eigenmodes of the coupled system. This conditions is more likely under higher roughness, higher normal loads, and higher relative sliding velocities.
Empirical Relationships
A review of observed relationships between sound pressure due to friction and parameters such as normal force, roughness, and sliding velocity is provided by Feng et al.
References
Friction
Acoustics | Friction Acoustics | [
"Physics",
"Chemistry"
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69,401,249 | https://en.wikipedia.org/wiki/Acoustic%20angiography | A specific branch of contrast-enhanced ultrasound, acoustic angiography is a minimally invasive and non-ionizing medical imaging technique used to visualize vasculature. Acoustic angiography was first developed by the Dayton Laboratory at North Carolina State University and provides a safe, portable, and inexpensive alternative to the most common methods of angiography such as Magnetic Resonance Angiography and Computed Tomography Angiography. Although ultrasound does not traditionally exhibit the high resolution of MRI or CT, high-frequency ultrasound (HFU) achieves relatively high resolution by sacrificing some penetration depth. HFU typically uses waves between 20 and 100 MHz and achieves resolution of 16-80μm at depths of 3-12mm. Although HFU has exhibited adequate resolution to monitor things like tumor growth in the skin layers, on its own it lacks the depth and contrast necessary for imaging blood vessels. Acoustic angiography overcomes the weaknesses of HFU by combining contrast-enhanced ultrasound with the use of a dual-element ultrasound transducer to achieve high resolution visualization of blood vessels at relatively deep penetration levels.
Acoustic angiography is performed by first injecting specially designed microbubbles with a low resonant frequency into the vessels. Next, a low-frequency transducer element with good depth penetration is used to send ultrasound waves into the sample at the resonant frequency of the microbubbles. This will generate a response from the microbubbles consisting of subharmonic, fundamental, and super-harmonic frequencies, as well as a response from the surrounding tissue consisting of only the fundamental and second-harmonic frequencies. Finally, a high-frequency transducer with high resolution is used to measure the super-harmonic frequencies, effectively removing any background signal from the microbubble signal, and allowing the vessels to be visualized
Background
Angiography, or the examination of blood vessels, is essential in many areas of research and clinical practice. In particular, angiography is needed to monitor angiogenesis, which is the growth and development of new blood vessels. Angiogenesis is an essential process which is most often observed in organ growth in fetuses and children, the development of the placenta in adults, and wound healing. However, excessive angiogenesis has been observed in dozens of disorders, including diabetes, endometriosis, autoimmune disease, and asthma. Angiography has been used in the research, diagnosis, and treatment of many of these disorders. Perhaps the most important application of angiography for monitoring angiogenesis is in tumor growth. Tumors can exist for months or even years in a non-angiogeneic stage of development and only begin rapid growth once the angiogenic phenotype is expressed. Thus, angiogenesis has become a target for certain cancer therapies. Some therapies aim to promote organized development of blood vessels in tumor regions, which allows for more homogenous and effective distribution of chemotherapy. Other methods aim to block the start or progression of angiogenesis altogether. In both cases, angiography is essential for measuring the growth, recession, or shape of blood vessels in-vivo over time during these treatments and related research
Currently, the most common techniques used for angiography are X-ray CT and MRI. However, many other methods are used for performing angiography in special circumstances, such as the use of optical coherence tomography for performing angiography during retinal exams. MRI angiography provides the highest resolution of the current angiographic methods and can often be performed without the use of contrast agents by modifying the pulse sequence to visualize aspects of the vessels such as blood flow. On the other hand, x-ray CT angiography requires the use of a contrast agent, but still maintains relatively high resolution. Despite the high quality images produced by both of these techniques, there remain significant drawbacks. Both are relatively slow and require expensive equipment, while x-ray CT also exposes patients to potentially harmful ionizing radiation. Thus, there is still a need for an inexpensive, portable, and safe candidate for angiography. Acoustic angiography is able to fill this need. By using microbubbles as a contrast agent and a dual-element transducer for signal identification, acoustic angiography achieves depth, vessel contrast, and resolution not possible with other ultrasound techniques.
Ultrasound contrast agents
Ultrasound contrast agents are particles used in ultrasound scans to improve image contrast. The first reported use of an ultrasound contrast agent was by Dr. Raymond Gramiak and Pravin Shah in 1968, when they injected saline into the aortic root of the heart and observed increased contrast. They hypothesized that the increase in contrast was a result of "mini bubbles produced by the rapid injection rate or possibly included in the contrast medium". Although most ultrasound contrast agents take the form of microbubbles, other types exist, such as perfluorocarbon nanoparticles or echogenic liposomes.
Components
Microbubble contrast agents generally have three main components:
Inner Gas: The gas inside the microbubble is generally air or a perfluorocarbon.
Lipid Shell: This shell serves to enclose the gas within it and is always made of lipids due to their hydrophobic property
Ligands: In the case of actively targeted microbubbles, ligands are attached to the outer surface of the lipid shell. These ligands are specific to membrane receptors in the body, and can be used to target certain physiological processes (such as inflammation) or organs. In the case of passively targeted microbubbles, no ligands are attached to the outer shell, and instead the microbubbles rely on factors such as surface charge in order to adhere to the endothelium.
Mechanism of contrast
Microbubbles work as contrast agents in ultrasound for two main reasons: The large difference in acoustic impedance between body tissues and the microbubbles and their quality of having a resonant frequency generally under 10 MHz. Due to the larger mismatch in acoustic impedances, the microbubbles are near-perfect reflectors of ultrasound waves in the body. This allows them to be point-sources of acoustic waves. Furthermore, at their resonant frequency, the microbubbles have a relatively large-magnitude broadband frequency response, which is picked up by the ultrasound transducer.
Microbubble signal identification
In classical contrast-enhanced ultrasound, many methods exist for separating signal reflected by the microbubbles and signal reflected by surrounding body tissues. Most of these methods utilize the subharmonic and super harmonic response of the microbubbles, as well as the microbubbles nonlinear response to ultrasound waves, as opposed to body tissues linear response to ultrasound waves. Some of the more common filtering methods are listed below.
Subharmonic filtering: This works by filtering out all signals but the subharmonic signals. Since tissue generally does not have a subharmonic response, only the microbubble signal remains. However, since this filters for the low-frequency signals, the resolution is slightly degraded as spatial resolution in ultrasound is dependent on the acoustic frequency.
Super harmonic filtering: Similar to subharmonic filtering, this works by filtering all but the super harmonic frequencies, which are mostly emitted by the microbubbles and not surrounding tissue. Unlike subharmonic filtering, the resolution is actually improved since only the high-frequency response is received. However, most clinical transducers do not have the wide bandwidth necessary to be able to accomplish this.
Phase inversion: This filtering method utilizes the characteristically nonlinear response of the microbubbles to ultrasound waves. Here, nonlinear response means that the phase and magnitude of the acoustic wave reflected by the microbubble do not have a linear relationship with the phase and magnitude of the excitatory acoustic wave. In this method, two pulses with opposite phase are emitted by the transducer. The linear response of tissue will cause mostly destructive interference of the opposite-phased waves, while the nonlinear response of microbubbles will allow some signal to pass through.
With the creation of a dual-element transducer, these filtering methods are no longer critical. This is what distinguishes acoustic angiography from the more generic contrast-enhanced ultrasound. An element centered at a low frequency serves to excite the microbubbles at their resonant frequency, while an element centered at a high frequency receives the super harmonic response of the microbubbles. Since the tissue is excited by the low frequency input and does not produce a high frequency response, the only response received by the dual-element transducer is that originating from the microbubbles. Thus, little to no signal processing is necessary to remove tissue signal from the acquired data.
Because the inner element is receive only while the outer element is transmit only, special materials can be chosen to optimize the efficiency and sensitivity of this process. Lead Zirconate Titanate (PZT) works well as a material choice for the transmitting element because it has a high transmitting constant (d = 300 x 10^-12 m/V) while Polyvinylidene Fluoride (PVDF) works well as a material for the receiving element because it has a high receiving constant (g = 14 x 10^-2 Vm/N). Generally, PVDF is not a good choice for an ultrasound transducer because it has a relatively poor transmitting constant, however, since acoustic angiography separates the transmitting and receiving elements, this is no longer an issue.
Image formation
Data acquisition
As acoustic angiography uses a dual-element ultrasonic transducer in the format of a focused ultrasound probe, it is not feasible to form an array of transducers as can be done in other forms of ultrasound imagining. Thus acoustic angiography images are formed by combining multiple a-mode images where each a-mode is a one-dimensional image identifying the acoustic boundaries along a vector originating at the transducer.
In order to form two or three dimensional images, the position and angle of the transducer and the resulting a-mode image must be mechanically manipulated. Two common configurations used to acquire these a-mode images include the wobbler configuration and mechanical sweep configuration.
In the wobbler configuration, the probe is rotated back and forth about a central axis in one plane so that the a-scans are radially oriented and the field of view, or region that is able to be imaged, is a cone. This allows for very quick acquisition of a-scans, but has nonhomogeneous resolution as the distance between each point on neighboring a-scans increases with depth.
In the linear sweep configuration, the ultrasound probe is mechanically moved, either by an external mechanism or hand, in a direction orthogonal to the direction of the a-scan. This configuration allows relatively consistent resolution as a function of depth as each point on neighboring a-scans is equidistant.
Once data has been collected as described above, it can be processed to form a variety of image types including projections and volumetric reconstruction.
Projection
Projection images in ultrasound are similar in concept to projection radiography. However, instead of projecting the degree of absorbance of X-ray photons along a given path, projection images in ultrasound generally project the mismatch of acoustic impedance and the location along a given boundary in tissue.
Maximum amplitude projection
The maximum amplitude projection or the maximum intensity projection is an image processing technique used to project three dimensional data onto a two dimensional image. This is a valuable tool as it allows the complex data to be formed into more readily understandable images that include the perception of depth.
In many forms of ultrasound imaging and photoacoustic imaging, the maximum amplitude of the signal along a given a-scan is used as the value for a pixel associated with that a-scan. As acoustic wave experience distance-dependent acoustic attenuation, the amplitude of a given signal along a given a-scan also encodes the distance to the object that generated that signal.
This simple image reconstruction technique allows for easily formed and interpretable projection images formed from acoustic signals.
Volumetric renderings
Volumetric renderings convert volumetric data into projection images. Most methods use data acquired in lower dimensions to generate voxels, volumetric pixels, that can form 3D images when combined.
Volumetric reconstruction
Volume reconstruction techniques are used to convert multiple 1D or 2D images into 3D volumes. Common volume reconstruction techniques include pixel-nearest-neighbors, voxel-nearest-neighbors, distance-weighted voxels, and function based methods used to statistically infer the value of a given voxel.
Applications
As acoustic angiography is currently under development, this specific branch of contrast-enhanced ultrasound is not currently used in clinical settings. The majority of the previous work using acoustic angiography has studied angiogenesis in animal models for research purposes.
Though the FDA has only approved contrast-enhanced ultrasound use in one clinical application in the United States, echocardiography, the broader technique has been used throughout Europe and Asia to great success in a variety of clinical applications. To learn more, see the current applications of contrast enhanced ultrasound.
Currently investigated clinical uses
The only use of acoustic angiography that has been investigated in clinical settings to date studied angiogenesis in the peripheral vasculature of human breast tissue. This study investigated if acoustic angiography could be used to reduce the need for biopsy of breast tissue when diagnosing if lesions in breast tissue were cancerous or not.
Using acoustic angiography, the authors collected and reconstructed the 3D volumes associated with vasculature surrounding lesions in the breast. These reconstructed volumes were then analyzed for vascular density and tortuosity. This information is useful for diagnosis as it has been shown that when these two factors increase in the vasculature surrounding a lesion, there is an increased risk that the lesion is cancerous.
References
Acoustics
Medical ultrasonography | Acoustic angiography | [
"Physics"
] | 2,852 | [
"Classical mechanics",
"Acoustics"
] |
69,402,060 | https://en.wikipedia.org/wiki/Prenylthiol | Prenylthiol or 3-methyl-2-butene-1-thiol is a chemical compound. It is one of a group of chemicals that give cannabis its characteristic "skunk-like" aroma. It is also present in lightstruck or "skunky" beer.
References
Thiols | Prenylthiol | [
"Chemistry"
] | 66 | [
"Organic compounds",
"Thiols",
"Organic compound stubs",
"Organic chemistry stubs"
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61,495,667 | https://en.wikipedia.org/wiki/C6334H9792N1700O2000S42 | {{DISPLAYTITLE:C6334H9792N1700O2000S42}}
The molecular formula C6334H9792N1700O2000S42 (molar mass: 143.1 kg/mol) may refer to:
Drozitumab
Enavatuzumab
Molecular formulas | C6334H9792N1700O2000S42 | [
"Physics",
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61,495,684 | https://en.wikipedia.org/wiki/C24H29FO4 | {{DISPLAYTITLE:C24H29FO4}}
The molecular formula C24H29FO4 (molar mass: 400.49 g/mol) may refer to:
DU-41164
DU-41165, or 6-fluoro-16-methylene-17α-acetoxy-δ6-retroprogesterone
Molecular formulas | C24H29FO4 | [
"Physics",
"Chemistry"
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"Molecules",
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61,502,277 | https://en.wikipedia.org/wiki/Coate%E2%80%93Loury%20model | The Coate–Loury model of affirmative action was developed by Stephen Coate and Glenn Loury in 1993. The model seeks to answer the question of whether, by mandating expanded opportunities for minorities in the present, these policies are rendered unnecessary in the future. Affirmative action may lead to one of two outcomes:
By improving employers’ perceptions of minorities or improving minorities’ skills, or both, affirmative action policies would eventually cause employers to want to hire minorities regardless of the presence of affirmative action policies.
By dampening incentives for minorities, affirmative action policies would reduce minority skill investment, thus leading to an equilibrium where employers correctly believe minorities to be less productive than majorities, thus perpetuating the need for affirmative action in order to achieve parity in the labor market.
Coate and Loury concluded that either equilibrium is possible under certain assumptions.
Model framework
The exposition of the Coate–Loury model follows the notes of David Autor. The authors make three assumptions as a starting point for their model:
The underlying skill distributions of minorities and non-minorities are the same. This skill distribution is modeled as a distribution of costs of obtaining a qualification.
Employers cannot observe qualifications but do observe noisy signals that are correlated with it.
Employers have rational expectations about worker qualifications and workers have rational expectations about employer screening. Thus, in equilibrium, employers beliefs about worker qualifications will be confirmed. And, similarly, workers will make investments consistent with the returns they will receive in the labor market for those investments.
Employers are able to observe worker's identity , where the fraction of the population that is is , and a noisy signal of the worker's qualification level . Employers can assign workers to either Task 0 or Task 1, with only qualified workers being successful at Task 1. Employers get a net return from assigning a worker to Task 1 of the form:The ratio of net gain to loss .
The distribution of depends on whether or not the worker is qualified, which is assumed to not differ between and . Let be the probability that the signal does not exceed , given that the worker is qualified; is the probability that the signal does not exceed , given that the worker is unqualified. The corresponding probability density functions are and . Let be the likelihood ratio, and assume that it is non-increasing on . This implies that:Therefore, higher values of the signal are more likely if the worker is qualified. This implies that has the monotone likelihood ratio (MLR) property.
Employers' decision rule
For a worker from group or , the fraction of qualified workers in the group is . Using Bayes' rule, the employer’s posterior probability that the worker is qualified, given the worker’s signal, is:
The expected benefit of assigning a worker to Task 1 is:Then the employer will assign a worker to Task 1 if the return is positive, which implies that:Based on the MLR assumption, there exists a threshold standard that depends on group membership, so that workers with are placed in Task 1:This implies that a higher qualification rate of a group will lead to a lower threshold hiring standard .
Workers' investment decision
The expected gross benefit to obtaining appropriate qualification for a worker is:where is gross benefit of being assigned to Task 1 and is the passing standard. Given the assumption that employers have rational expectations, only the true probability that a worker is qualified should matter - not the employer's beliefs about the probability.
Note that is a single-peaked function with , since there would be no point to investing if all workers were assigned to Task 1 or no workers were assigned to Task 1. This implies that the gross benefit to investing will rise so long as the marginal probability of being assigned to Task 1 is increasing in . To see this, note that the derivative of the gross benefit with respect to is:This is only positive if . Since the boundary points are equal to zero, it follows that must sometimes be above 1 and sometimes below 1 in the interval.
Workers will invest if , so the share of workers investing will be . If is continuous and , it will have the property that when the gross benefit is rising in , the net benefit should also be rising.
Equilibrium
An equilibrium is a fixed point of the aforementioned hiring and investment policies where beliefs are self-confirming, such that:A discriminatory equilibrium can occur whenever the equilibrium equation has multiple solutions. In this case, it is possible that employers will believe that members of are less qualified than members of , which will be confirmed by the investment behavior of members of .
Proposition 1 (p. 1226) proves that, under reasonable conditions, if a solution exists to the equilibrium condition, then at least two solutions will exist. At this point, there are several observations that can be made:
Group identity conveys information only because employers expect it to.
Stereotypes are inefficient sources of information.
No single employer could break the discriminatory equilibrium.
The employer's expected benefit from hiring a worker exceeds that of hiring a worker.
Affirmative action
Under the assumption that a discriminatory equilibrium exists, with the further assumption of no differences in skill distributions, an affirmative action policy can be easily rationalized. Coate and Loury consider the policy where the rate of assignment for and workers to Task 1 is equalized. Let be the proportion of in the population.
Let be the ex ante probability that a worker is assigned to Task 1:And let be the expected payoff from hiring this worker:Under affirmative action, the employers' optimization problem is to solve:where the equality constraint on the ex ante probabilities is the affirmative action constraint. The equivalent Lagrangian is:where is the Lagrange multiplier. Proposition 2 (p. 1229) develops a condition for the existence of a nondiscriminatory equilibrium under affirmative action. In particular, if any group of workers facing standard invest so that the fraction is qualified, then all equilibria are self-confirming:In this case, the affirmative action policy would equate employers' beliefs about members of each group.
Patronizing equilibrium
However, it is not in general true that affirmative action under the model's assumptions leads to the nondiscriminatory equilibrium. If at the employer lowered the threshold , then the fraction of workers investing would fall, and the employers' beliefs about the fraction who are qualified would not be satisfied. Therefore, a policy that lowered would not be self-enforcing.
Coate and Loury define an equilibrium where affirmative action constraint is permanently binding as a patronizing equilibrium, where employers are compelled to lower their hiring standards for members of , relative to a member of . Therefore, the following conditions hold in a patronizing equilibrium:There are several possible negative effects on members of from being trapped in a patronizing equilibrium:
Due to a lower standard, members of find it optimal to invest less in skills acquisition, which then confirms employers' negative views
Despite being initially identical, reduced investment leads to a divergence between groups and the development of a negative stereotype
Recalling the Lagrangian that was developed earlier, we may consider the first-order optimality conditions. Computing and rearranging terms gives us:where the ratios of net gain to loss for each group are:Given a shadow price of equality , employers act as if they must pay the tax of for each assigned to Task 1 instead of Task 0, while receiving the subsidy for each put into Task 1 rather than Task 0. Therefore, employers generally respond to the affirmative action constraint by lowering the standard for and raising it for .
Proposition 4 (p. 1234) shows that, under reasonable assumptions, the marginal productivity of and hires is not equated.
See also
Labour economics
Law and economics
Mathematical economics
Statistical discrimination (economics)
References
Further reading
Fryer Jr., Roland G.; Loury, Glenn C. (2005). "Affirmative Action and Its Mythology". Journal of Economic Perspectives 19 (3): 147-162.
Affirmative action
Labour economics
Law and economics
Mathematical economics | Coate–Loury model | [
"Mathematics"
] | 1,622 | [
"Applied mathematics",
"Mathematical economics"
] |
61,503,585 | https://en.wikipedia.org/wiki/Greenhouse%20gas%20emissions%20from%20agriculture | The amount of greenhouse gas emissions from agriculture is significant: The agriculture, forestry and land use sectors contribute between 13% and 21% of global greenhouse gas emissions. Emissions come from direct greenhouse gas emissions (for example from rice production and livestock farming). And from indirect emissions. With regards to direct emissions, nitrous oxide and methane makeup over half of total greenhouse gas emissions from agriculture. Indirect emissions on the other hand come from the conversion of non-agricultural land such as forests into agricultural land. Furthermore, there is also fossil fuel consumption for transport and fertilizer production. For example, the manufacture and use of nitrogen fertilizer contributes around 5% of all global greenhouse gas emissions. Livestock farming is a major source of greenhouse gas emissions. At the same time, livestock farming is affected by climate change.
Farm animals' digestive systems can be put into two categories: monogastric and ruminant. Ruminant cattle for beef and dairy rank high in greenhouse gas emissions. In comparison, monogastric, or pigs and poultry-related foods, are lower. The consumption of the monogastric types may yield less emissions. Monogastric animals have a higher feed-conversion efficiency and also do not produce as much methane. Non-ruminant livestock, such as poultry, emit far fewer greenhouse gases.
There are many strategies to reduce greenhouse gas emissions from agriculture (this is one of the goals of climate-smart agriculture). Mitigation measures in the food system can be divided into four categories. These are demand-side changes, ecosystem protections, mitigation on farms, and mitigation in supply chains. On the demand side, limiting food waste is an effective way to reduce food emissions. Changes to a diet less reliant on animal products such as plant-based diets are also effective. This could include milk substitutes and meat alternatives. Several methods are also under investigation to reduce the greenhouse gas emissions from livestock farming. These include genetic selection, introduction of methanotrophic bacteria into the rumen, vaccines, feeds, diet modification and grazing management.
Global estimates
Total emissions from agrifood systems in 2022 amounted to 16.2 billion tonnes of carbon dioxide equivalent (Gt CO2eq) of GHG released into the atmosphere, an increase of 10%, or 1.5 Gt CO2eq compared with 2000.
In 2020, it was estimated that the food system as a whole contributed 37% of total greenhouse gas emissions and that this figure was on course to increase by 30–40% by 2050 due to population growth and dietary change.
Between 2010 and 2019, agriculture, forestry and land use contributed between 13% and 21% to global greenhouse gas emissions. Nitrous oxide and methane make up over half of total greenhouse gas emissions from agriculture.
Older estimates
In 2010, agriculture, forestry and land-use change were estimated to contribute 20–25% of global annual emissions.
Emissions by type of activity
Land use changes
Agriculture contributes to greenhouse gas increases through land use in four main ways:
CO2 releases linked to deforestation
Methane releases from rice cultivation
Methane releases from enteric fermentation in cattle
Nitrous oxide releases from fertilizer application
Together, these agricultural processes comprise 54% of methane emissions, roughly 80% of nitrous oxide emissions, and virtually all carbon dioxide emissions tied to land use.
Land cover has changed majorly since 1750, as humans have deforested temperate regions. When forests and woodlands are cleared to make room for fields and pastures, the albedo of the affected area increases, which can result in either warming or cooling effects depending on local conditions. Deforestation also affects regional carbon reuptake, which can result in increased concentrations of CO2, the dominant greenhouse gas. Land-clearing methods such as slash and burn compound these effects, as the burning of biomatter directly releases greenhouse gases and particulate matter such as soot into the air. Land clearing can destroy the soil carbon sponge.
Livestock
Livestock produces the majority of greenhouse gas emissions from agriculture and demands around 30% of agricultural freshwater needs, while only supplying 18% of the global calorie intake. Animal-derived food plays a larger role in meeting human protein needs, yet is still a minority of supply at 39%, with crops providing the rest.
Out of the Shared Socioeconomic Pathways used by the Intergovernmental Panel on Climate Change, only SSP1 offers any realistic possibility of meeting the target. Together with measures like a massive deployment of green technology, this pathway assumes animal-derived food will play a lower role in global diets relative to now. As a result, there have been calls for phasing out subsidies currently offered to livestock farmers in many places worldwide, and net zero transition plans now involve limits on total livestock headcounts, including substantial reductions of existing stocks in some countries with extensive animal agriculture sectors like Ireland. Yet, an outright end to human consumption of meat and/or animal products is not currently considered a realistic goal. Therefore, any comprehensive plan of adaptation to the effects of climate change, particularly the present and future effects of climate change on agriculture, must also consider livestock.
Livestock activities also contribute disproportionately to land-use effects, since crops such as corn and alfalfa are cultivated to feed the animals.
In 2010, enteric fermentation accounted for 43% of the total greenhouse gas emissions from all agricultural activity in the world. The meat from ruminants has a higher carbon equivalent footprint than other meats or vegetarian sources of protein based on a global meta-analysis of lifecycle assessment studies. Small ruminants such as sheep and goats contribute approximately 475 million tons of carbon dioxide equivalent to GHG emissions, which constitutes around 6.5% of world agriculture sector emissions. Methane production by animals, principally ruminants, makes up an estimated 15-20% of global production of methane.
Worldwide, livestock production occupies 70% of all land used for agriculture or 30% of the land surface of the Earth. The global food system is responsible for one-third of the global anthropogenic GHG emissions, of which meat accounts for nearly 60%.
Cows, sheep and other ruminants digest their food by enteric fermentation, and their burps are the main methane emissions from land use, land-use change, and forestry: together with methane and nitrous oxide from manure, this makes livestock the main source of greenhouse gas emissions from agriculture.
The IPCC Sixth Assessment Report in 2022 stated that: "Diets high in plant protein and low in meat and dairy are associated with lower GHG emissions. [...] Where appropriate, a shift to diets with a higher share of plant protein, moderate intake of animal-source foods and reduced intake of saturated fats could lead to substantial decreases in GHG emissions. Benefits would also include reduced land occupation and nutrient losses to the surrounding environment, while at the same time providing health benefits and reducing mortality from diet-related non-communicable diseases."According to a 2022 study quickly stopping animal agriculture would provide half the GHG emission reduction needed to meet the Paris Agreement goal of limiting global warming to 2 °C. There are calls to phase out livestock subsidies as part of a just transition.
In the context of global GHG emissions, food production within the global food system accounts for approximately 26%. Breaking it down, livestock and fisheries contribute 31%, whereas crop production, land use, and supply chains add 27%, 24%, and 18% respectively to the emissions.
A 2023 study found that a vegan diet reduced emissions by 75%.
Research in New Zealand estimated that switching agricultural production towards a healthier diet while reducing greenhouse gas emissions would cost approximately 1% of the agricultural sector's export revenue for New Zealand, which is an order of magnitude less than the estimated health system savings from a healthier diet.
Research continues on the use of various seaweed species, in particular Asparegopsis armata, as a food additive that helps reduce methane production in ruminants.
Fertilizer production
Crop growth
is re-emitted into the atmosphere by plant and soil respiration in the later stages of crop growth, causing more greenhouse gas emissions.
Rice production
Emissions by type of greenhouse gas
Agricultural activities emit the greenhouse gases carbon dioxide, methane and nitrous oxide.
Carbon dioxide emissions
Activities such as tilling of fields, planting of crops, and shipment of products cause carbon dioxide emissions. Agriculture-related emissions of carbon dioxide account for around 11% of global greenhouse gas emissions. Farm practices such as reducing tillage, decreasing empty land, returning biomass residue of crops to the soil, and increasing the use of cover crops can reduce carbon emissions.
Methane emissions
Methane emissions from livestock are the number one contributor to agricultural greenhouse gases globally. Livestock are responsible for 14.5% of total anthropogenic greenhouse gas emissions. One cow alone will emit 220 pounds of methane per year. While the residence time of methane is much shorter than that of carbon dioxide, it is 28 times more capable of trapping heat. Not only do livestock contribute to harmful emissions, but they also require a lot of land and may overgraze, which leads to unhealthy soil quality and reduced species diversity. A few ways to reduce methane emissions include switching to plant-rich diets with less meat, feeding the cattle more nutritious food, manure management, and composting.
Traditional rice cultivation is the second biggest agricultural methane source after livestock, with a near-term warming impact equivalent to the carbon dioxide emissions from all aviation. Government involvement in agricultural policy is limited due to the high demand for agricultural products like corn, wheat, and milk. The United States Agency for International Development's (USAID) global hunger and food security initiative, the Feed the Future project, is addressing food loss and waste. By addressing food loss and waste, greenhouse gas emission mitigation is also addressed. By only focusing on dairy systems of 20 value chains in 12 countries, food loss and waste could be reduced by 4-10%. These numbers are impactful and would mitigate greenhouse gas emissions while still feeding the population.
Nitrous oxide emissions
Nitrous oxide emission comes from the increased use of synthetic and organic fertilizers. Fertilizers increase crop yield production and allow the crops to grow at a faster rate. Agricultural emissions of nitrous oxide make up 6% of the United States' greenhouse gas emissions; they have increased in concentration by 30% since 1980. While 6% may appear to be a small contribution, nitrous oxide is 300 times more effective at trapping heat per pound than carbon dioxide and has a residence time of around 120 years. Different management practices such as conserving water through drip irrigation, monitoring soil nutrients to avoid overfertilization, and using cover crops in place of fertilizer application may help in reducing nitrous oxide emissions.
Reducing emissions
Agriculture is often not included in government emissions reduction plans. For example, the agricultural sector is exempt from the EU emissions trading scheme which covers around 40% of the EU greenhouse gas emissions.
See also
Agroecology
Effects of climate change on agriculture
Effects of climate change on livestock
Environmental issues with agriculture
References
External links
Climate change on the Food and Agriculture Organization of the United Nations website.
Report on the relationship between climate change, agriculture and food security by the International Food Policy Research Institute
Climate Change, Rice and Asian Agriculture: 12 Things to Know Asian Development Bank
Greenhouse gas emissions | Greenhouse gas emissions from agriculture | [
"Chemistry"
] | 2,347 | [
"Greenhouse gases",
"Greenhouse gas emissions"
] |
61,504,024 | https://en.wikipedia.org/wiki/C20H28FN3O3 | {{DISPLAYTITLE:C20H28FN3O3}}
The molecular formula C20H28FN3O3 (molar mass: 377.453 g/mol, exact mass: 377.2115 u) may refer to:
5F-ADB
5F-EMB-PINACA
Molecular formulas | C20H28FN3O3 | [
"Physics",
"Chemistry"
] | 75 | [
"Molecules",
"Set index articles on molecular formulas",
"Isomerism",
"Molecular formulas",
"Matter"
] |
61,504,407 | https://en.wikipedia.org/wiki/Crepuscular%20rays | Crepuscular rays, sometimes colloquially referred to as god rays, are sunbeams that originate when the Sun appears to be just above or below a layer of clouds, during the twilight period. Crepuscular rays are noticeable when the contrast between light and dark is most obvious. Crepuscular comes from the Latin word , meaning "twilight". Crepuscular rays usually appear orange because the path through the atmosphere at dawn and dusk passes through up to 40 times as much air as rays from a high Sun at noon. Particles in the air scatter short-wavelength light (blue and green) through Rayleigh scattering much more strongly than longer-wavelength yellow and red light.
Loosely, the term crepuscular rays is sometimes extended to the general phenomenon of rays of sunlight that appear to converge at a point in the sky, irrespective of time of day.
A rare related phenomena are anticrepuscular rays which can appear at the same time (and coloration) as crepuscular rays but in the opposite direction of the setting sun (east rather than west).
Gallery
See also
References
External links
Atmospheric optical phenomena
Sun | Crepuscular rays | [
"Physics"
] | 235 | [
"Optical phenomena",
"Physical phenomena",
"Atmospheric optical phenomena",
"Earth phenomena"
] |
61,505,702 | https://en.wikipedia.org/wiki/C22H26FN3O | {{DISPLAYTITLE:C22H26FN3O}}
The molecular formula C22H26FN3O (molar mass: 367.460 g/mol, exact mass: 367.2060 u) may refer to:
5F-CUMYL-P7AICA
5F-CUMYL-PINACA (SGT-25)
Molecular formulas | C22H26FN3O | [
"Physics",
"Chemistry"
] | 82 | [
"Molecules",
"Set index articles on molecular formulas",
"Isomerism",
"Molecular formulas",
"Matter"
] |
78,171,013 | https://en.wikipedia.org/wiki/Pseudonajatoxin%20b | Pseudonajatoxin b, or Pt-b, is a highly potent and lethal long-chain α-neurotoxin found in the venom of the eastern brown snake (Pseudonaja textilis). While the pharmacodynamics of pseudonajatoxin b are currently undocumented, α-neurotoxins are known to cause neuromuscular paralysis by blocking cholinergic neurotransmission.
Source
Pseudonajatoxin b is present in the venom of the highly lethal eastern brown snake, Pseudonaja textilis, which is the leading cause of snakebites in Australia. The concentration of pseudonajatoxin b in venom of South Australian specimens is up to a hundred times higher than in those from Queensland.
Chemistry
Structure and homology
Pseudonajatoxin b is composed of a single polypeptide chain of 71 amino acids and features five disulphide bridges. It exhibits 61-73% sequence homology with other long neurotoxins. Distinctive characteristics of pseudonajatoxin b include a high occurrence of proline residues, particularly at positions 49 and 54, where valines are usually present. Moreover, it contains an additional amino acid in the loop between Cys-46 and Cys-58.
Protein family
Pseudonajatoxin b is a type of three-finger toxin, which are characterized by a structure of three loops that emerge from a hydrophobic core. Specifically, it falls within the long-chain subfamily of the α-neurotoxin group.
Target and mechanism of action
Although the pharmacodynamics of pseudonajatoxin b have not been documented, α-neurotoxins generally exhibit some common traits.
Long-chain α-neurotoxins have been shown to bind with high affinity to both muscular and neuronal nicotinic acetylcholine receptors. These receptors serve as the primary mediator of muscle contraction in response to nerve impulses. Additionally, they are present in the central nervous system, where they play an important role in autonomic processes, including the regulation of heart rate and respiration.
By acting as competitive antagonists to acetylcholine, α-neurotoxins block acetylcholine from binding and subsequently prevent the activation of ion channels. This disruption in neurotransmission effectively leads to neuromuscular paralysis. Importantly, since the activation of nicotinic acetylcholine receptors requires the binding of two acetylcholine molecules, the blockage of just one binding site by an α-neurotoxin is sufficient to prevent channel opening. Furthermore, long-chain α-neurotoxins typically bind tightly and irreversibly to nicotinic receptors, resulting in permanent channel inactivation once they are bound.
Toxicity and treatment
Pseudonajatoxin b is a highly potent toxin, with a median lethal dose (LD50) of 15 pg/kg in mice. Although the specific lethal mechanisms of pseudonajatoxin b remain unknown, it is well established that both α-neurotoxins and the venom of P. textilis induce paralysis, leading to death through asphyxiation.
Currently, no treatment specific for pseudonajatoxin b has been documented. However, envenomation from Pseudonaja textilis can be treated with snake antivenom made from antibodies, specifically horse immuno-globulins. Despite this, studies have shown that brown snake antivenom has low efficacy against Pseudonaja textilis venom.
References
Snake toxins
Peptides
Neurotoxins | Pseudonajatoxin b | [
"Chemistry"
] | 751 | [
"Biomolecules by chemical classification",
"Molecular biology",
"Neurochemistry",
"Neurotoxins",
"Peptides"
] |
78,173,887 | https://en.wikipedia.org/wiki/Butralin | Butralin is a preemergent herbicide used to control suckers on tobacco in the United States, Australia, Mozambique and, for food crops also, China. It is a dinitroaniline, first registered in the US in 1976. It was used in the EU until a ban in 2009 due to its ecotoxicity.
Mode of action and effects
Butralin works by the HRAC mode of action Group D / K1 / 3, (Australian, Global, Numeric respectively), which involves inhibition of microtubule formation, by binding to tubulin, halting growth, and causing depolymerization.
In ryegrass meristems, butralin-treated roots show reduced elongation, but greater diameter. The cells' rate of mitosis lowers 36% after one hour, and they develop multiple nuclei. Butralin's effect is more similar to carbamate herbicides such as chlorpropham rather than other dinitroanilines.
Usage
Butralin is sold in Mozambique as "Tobralin 36% EC", made in South Africa. Users are instructed to pour 10 mL on each tobacco plant by hand, and not to unclog nozzles with their mouths.
In China, over 100 tons per year are used, as of 2022, on garlic, soybean, tomato, rice, peanut, pepper, cotton, eggplant, and watermelon. The maximum residue limit is 0.02 to 0.1 mg/kg. The growing Chinese market sells it in 36% or 48% emulsifiable concentrates, and in development as of 2012, a 41% wettable powder. The powder claims to be environmentally friendly, as it lacks the volatile organic molecules such as toluene and xylene used as solvent in EC formulations. The powder is recommended to be applied at 2100 g/Ha (active ingredient).
Health
Butralin is of low acute toxicity. There is no association with lung cancer.
It is very toxic to Daphnia.
In soil
Butralin is likely to be moderately persistent to persistent and relatively immobile in terrestrial environments. Butralin is stable to abiotic hydrolysis and photodegradation on soil. Its characteristics are unlike those of chemicals that leach to groundwater. Butralin's major soil metabolite is 4-tert-butyl-2,6-dinitroaniline. Other major metabolites see the loss of more or all of the carbons and hydrogen over the nitrogen, or loss of oxygen from the nitro groups. The principle residue in crops, however, is the parent butralin.
References
Links
Preemergent herbicides
Nitrotoluene derivatives
Anilines
Herbicides
Products introduced in 1976
Sec-Butyl compounds
Tert-butyl compounds | Butralin | [
"Biology"
] | 587 | [
"Herbicides",
"Biocides"
] |
78,184,192 | https://en.wikipedia.org/wiki/KIC%209970396 | KIC 9970396 is an eclipsing binary system located in the northern constellation of Cygnus about distant. The system consists of a red-giant branch star and an F-type main-sequence star. The two stars orbit each other every at a mean distance of ( AU), almost the same as Earth's distance from the Sun.
The system was given the Kepler Object of Interest designation KOI-7606 as a planetary candidate, but has been marked a false positive since the dips in the light curve are caused by an eclipsing stellar companion rather than a transiting exoplanet.
Stellar components
KIC 9970396A
KIC 9970396A is a pulsating red giant currently in the red-giant branch, past the first dredge-up event and approaching the red giant bump. The star displays solar-like oscillations caused by turbulent convection near the surface. Since the star has used up all of its hydrogen within its core, the core now consists mostly of helium, with a mass of 0.229 , that is 19% of the star's entire mass, and a radius of 0.03055 . Its age is estimated at billion years, about 1.5 billion years older than the Solar System (4.568 Gyr).
KIC 9970396B
KIC 9970396B is a late F-type star almost identical in mass to the Sun but slightly larger and hotter. Its mass is slightly smaller than the red giant primary, thus a possible scenario for the system is that the two stars formed together and the more massive primary star evolved past the main sequence first.
Its stellar parameters, alongside those of the red giant, were precisely measured using a combination of Kepler photometry and spectroscopic observations.
References
Cygnus (constellation)
Kepler objects of interest
J19545035+4649589
Kepler Input Catalog
Eclipsing binaries
Red giants
F-type main-sequence stars | KIC 9970396 | [
"Astronomy"
] | 410 | [
"Cygnus (constellation)",
"Constellations"
] |
65,249,333 | https://en.wikipedia.org/wiki/Wirthbacteria | Candidatus Wirthbacteria is a proposed bacterial phylum containing only one known sample from the Crystal Geyser aquifer, Ca. Wirthibacter wanneri. This bacterium stands out in a basal position in some trees of life as it is closely related to Candidate phyla radiation but is not considered part of that clade.
See also
List of bacteria genera
List of bacterial orders
References
Bacteria described in the 21st century
Candidatus taxa
Bacteria phyla | Wirthbacteria | [
"Biology"
] | 98 | [
"Bacteria stubs",
"Bacteria"
] |
65,249,555 | https://en.wikipedia.org/wiki/SB-228357 | SB-228357 is a drug which acts as a selective antagonist of the serotonin 5-HT2B and 5-HT2C receptors.
It has antidepressant and anxiolytic effects in animal models and inhibits 5-HT2B mediated proliferation of cardiac fibroblasts. It has also been found to reverse meta-chlorophenylpiperazine (mCPP)-induced hypolocomotion and to attenuate haloperidol-induced catalepsy.
The drug was under development by GlaxoSmithKline for the treatment of major depressive disorder and anxiety disorders. It reached the preclinical research phase of development. However, development of the drug was discontinued.
See also
RS-102221
SB-242084
SB-243213
References
5-HT2C antagonists
Abandoned drugs
Indoles
3-Pyridyl compounds
Ureas | SB-228357 | [
"Chemistry"
] | 200 | [
"Pharmacology",
"Drug safety",
"Medicinal chemistry stubs",
"Organic compounds",
"Pharmacology stubs",
"Abandoned drugs",
"Ureas"
] |
65,253,869 | https://en.wikipedia.org/wiki/New%20Towns%20for%20Old | "New Towns for Old" is a 1942 British promotional short film promoting the clearance of old historic "slum towns" and replacement with "new towns". It promotes the then new concept of town planning. It was directed by John Eldridge and scripted by the poet Dylan Thomas. The film was produced by the Ministry of Information and was one of the few wartime documentary to focus on a topic unrelated to the war.
The title alludes to a line from Aladdin: New Lamps for Old.
Synopsis
Two civil servants wander around various vantage points looking at the fictional town of Smokedale. One with a bowler hat and carrying an umbrella has a refined London accent; the other in a trilby and smoking a pipe has a Yorkshire accent.
The footage itself is largely in and around Sheffield and Manchester and the civic functions discussed are in Manchester Town Hall. They proudly look at the new housing completed so far.
The film discusses true figures from the replanning of the Manchester slums from 1922 onward: 26,000 condemned; 14,000 demolished (plus "some help from Hitler"); 30,000 new houses planned. It stresses the need for a Green Belt around each town. Schools, hospitals and play areas are to be part of the plan. Old industries are discussed (and were in truth the hardest issue to address). The solution for relocating industries is not fully explained, and simply states that new areas will be zoned for industrial use - away from the housing.
It explains how war has delayed the plan.
It states "we've got to rebuild all our big towns".
The men then point to the camera and address the viewer, saying it is up to You. Remember it's your town.
Later Recognition
The title was repeated in the 1962 guide to town planning "New Towns for Old" by J. B. Cullingworth.
References
External links
New Towns for Old at Screenonline
1942 films
British short documentary films
Urban planning
Films directed by John Eldridge
1940s British films | New Towns for Old | [
"Engineering"
] | 406 | [
"Urban planning",
"Architecture"
] |
65,254,591 | https://en.wikipedia.org/wiki/Guillermo%20Rein | Guillermo Rein (born May 1975) is a professor of fire science in the Department of Mechanical Engineering at Imperial College London. His research is focused on fire, combustion, and heat transfer. He is the editor-in-chief of the journal Fire Technology and Fellow of the Combustion Institute.
Rein is best known for his contributions to smouldering combustion research in the field of fire science.
Biography
Rein obtained his Industrial Engineering degree at the ICAI School of Engineering in 1999. He studied mechanical engineering at the University of California, Berkeley, and obtained an MSc in 2003 and a PhD. in 2005. He taught at the School of Engineering of the University of Edinburgh (2006–2012), where he was a senior lecturer before moving to Imperial College in 2012.
Research
His research meanly focus on heat transfer, combustion, fire and wildfire. He is best known in three areas: polymer and wood ignition; design of fire-resistant structures; and wildfire spread and mitigation.
Rein, together with his research group and collaborators, has edited two books, published six book chapters and over 200 journal publications. His current h-index is above 60 and citation count is over 12,000 on Google Scholar.
Rein has been editor-in-chief of the journal Fire Technology since 2012. He was associate editor of Proceedings of the Combustion Institute from 2013 to 2019; associate editor of Thermal and Mass Transport (Frontiers of Mechanical Engineering) from 2016; and is on the editorial board of Safety Science and the advisory board of International Journal of Wildland Fire since 2016. He was also on the editorial board of Fire Safety Journal from 2014 to 2017.
Selected awards
2009 Hinshelwood Prize
2016 SFPE Lund Award
2017 The Engineer Collaborate-to-Innovate Prize
2017 Sugden Award
2018 Arthur B. Guise Medal
2020 Research Excellence Award
References
External links
Imperial Hazelab's webpage
Mechanical engineers
Living people
University of California, Berkeley alumni
Academics of Imperial College London
Combustion engineering
Fellows of the Combustion Institute
Academics of the University of Edinburgh
Fire
Science communicators
21st-century British scientists
21st-century Spanish scientists
21st-century British educators
21st-century British engineers
1975 births | Guillermo Rein | [
"Chemistry",
"Engineering"
] | 436 | [
"Mechanical engineers",
"Combustion engineering",
"Industrial engineering",
"Fellows of the Combustion Institute",
"Combustion",
"Mechanical engineering",
"Fire"
] |
66,479,755 | https://en.wikipedia.org/wiki/Grammatophora%20%28alga%29 | Grammatophora is a genus of Chromista belonging to the family Grammatophoraceae.
The genus was first described by C. G. Ehrenberg in 1840.
Species:
Grammatophora marina
Grammatophora oceanica
References
Diatoms
Diatom genera | Grammatophora (alga) | [
"Biology"
] | 59 | [
"Diatoms",
"Algae"
] |
66,482,576 | https://en.wikipedia.org/wiki/Corey%E2%80%93Nicolaou%20macrolactonization | Corey–Nicolaou macrolactonization is a named reaction of organic chemistry, for the synthesis of lactones from hydroxy acids, found in 1974. The reaction uses 2,2'-dipyridyldisulfide and triphenylphosphine as reagents and runs in polar aprotic solvent under mild conditions.
Mechanism
The hydroxy acid first reacts with the 2,2'-Dipyridyldisulfide to form the corresponding 2-pyridinethiol ester, and after a proton transfer, the alkoxide attacks the carbonyl carbon, forming a tetrahedral transition state, before resolving back to the desired lactone and 2-pyridinethione.
Variants
Other heterocyclic disulfides have been used in place of 2,2'-dipyridyldisulfide.
See also
Shiina macrolactonization
Ružička reaction
References | Corey–Nicolaou macrolactonization | [
"Chemistry"
] | 191 | [
"Name reactions"
] |
66,490,111 | https://en.wikipedia.org/wiki/Geiringer%E2%80%93Laman%20theorem | The Geiringer–Laman theorem gives a combinatorial characterization of generically rigid graphs in -dimensional Euclidean space, with respect to bar-joint frameworks. This theorem was first proved by Hilda Pollaczek-Geiringer in 1927, and later by Gerard Laman in 1970. An efficient algorithm called the pebble game is used to identify this class of graphs. This theorem has been the inspiration for many Geiringer-Laman type results for other types of frameworks with generalized pebble games.
Statement of the theorem
This theorem relies on definitions of genericity that can be found on the structural rigidity page. Let denote the vertex set of a set of edges .
Geiringer-Laman Theorem. A graph is generically rigid in -dimensions with respect to bar-joint frameworks if and only if has a spanning subgraph such that
for all subsets , .
The spanning subgraph satisfying the conditions of the theorem is called a Geiringer-Laman, or minimally rigid, graph. Graphs satisfying the second condition form the independent sets of a sparsity matroid, and are called -sparse. A graph satisfying both conditions is also called a -tight graph. The direction of the theorem which states that a generically rigid graph is -tight is called the Maxwell direction, because James Clerk Maxwell gave an analogous necessary condition of -sparsity for a graph to be independent in the -dimensional generic rigidity matroid. The other direction of the theorem is the more difficult direction to prove. For dimensions , a graph that is -tight is not necessarily generically minimally rigid, i.e., the converse of the Maxwell Direction is not true.
Example. Consider the graphs in Figure 1. The graph in (c) is generically minimally rigid, but it is not infinitesimally rigid. The red velocity vectors depict a non-trivial infinitesimal flex. Removing the red edge in (a) yields a generically minimally rigid spanning graph. Adding the dashed red edge in (b) makes the graph generically minimally rigid.
Theorem. Let be a graph. The following statements are equivalent:
is a generically minimally rigid;
is -tight; and
contains three edge-disjoint spanning trees and such that (i) each vertex of is contained in exactly two of these spanning trees and (ii) distinct subtrees of these spanning trees do not have the same vertex set.
The equivalence of the first and second statements is the Geiringer-Laman theorem. The equivalence of the first and third statements was first proved by Crapo via the Geiringer-Laman theorem, and later by Tay via a more direct approach.
Outline of proof
The proof of the Geiringer-Laman theorem given below is based on Laman's proof. Furthermore, the details of the proofs below are based on lecture notes found here
Consider a bar-joint system and a framework of this system, where is a map that places the vertices of in the plane such that the distance constraints are satisfied. For convenience, we refer to as a framework of . The proof of the Geiringer-Laman theorem follows the outline below.
A graph is generically rigid if and only if it is generically infinitesimally rigid.
Infinitesimal rigidity is a generic property of graphs.
Rigidity is a generic property of graphs.
If a framework is infinitesimally rigid, then it is rigid.
If a framework is generic with respect to infinitesimally rigidity and rigid, then it is infinitesimally rigid.
If a graph has a generic infinitesimally rigid framework, then is a Geiringer-Laman graph.
A graph is a Geiringer-Laman graph if and only if has a Henneberg construction.
If a graph has a Henneberg construction, then has a generic infinitesimally rigid framework.
Step 1 sets up the generic setting of rigidity so that we can focus on generic infinitesimal rigidity rather than generic rigidity. This is an easier approach, because infinitesimal rigidity involves a system of linear equations, rather than quadratic in the case of regular rigidity. In particular, we can prove structural properties about the rigidity matrix of a generic framework. These results were first proved by Asimow and Roth, see Combinatorial characterizations of generically rigid graphs. Note that in Step 1.4 the framework must be generic with respect to infinitesimal rigidity. In particular, a framework that is rigid and generic with respect to rigidity is not necessarily infinitesimally rigid. Step 2 is the Maxwell Direction of the proof, which follows from simple counting arguments on the rigidity matrix. Step 3 shows that generically minimally rigid graphs are exactly the graphs that can be constructed starting from a single edge using two simple operations, which are defined below. Step 4 shows that graphs with this type of construction are generically infinitesimally rigid. Finally, once Step 1 is proved, Steps 2-3 prove the Geiringer-Laman theorem.
Equivalence of generic rigidity and generic infinitesimal rigidity
Let be a graph. First, we show that generic frameworks with respect to infinitesimal rigidity form an open and dense set in . One necessary and sufficient condition for a framework of to be infinitesimally rigid is for its rigidity matrix to have max rank over all frameworks of .
Proposition 1. For any framework of and any neighborhood , there exists a framework in such that the rigidity matrix has max rank.
Proof. If the rigidity matrix does not have max rank, then it has a set of dependent rows corresponding to a subset of edges such that for some other rigidity matrix , the rows corresponding to are independent. Let be the set of frameworks such that the rows corresponding to in their rigidity matrices are dependent. In other words, is the set of frameworks such that the minor of the rows corresponding to in is . Hence, is a curve in , because a minor is a polynomial in the entries of a matrix. Let be the union of these curves over all subsets of edges of . If a framework does not have max rank for some framework , then is contained in . Finally, since is a finite set of curves, the proposition is proved.
Proposition 2. Infinitesimal rigidity is a generic property of graphs.
Proof. We show that if one generic framework with respect to infinitesimal rigidity is infinitesimally rigid, then all generic frameworks are infinitesimally rigid. If a framework of a graph is infinitesimally rigid, then has max rank. Note that the kernel of the rigidity matrix is the space of infinitesimal motions of a framework, which has dimension for infinitesimally rigid frameworks. Hence, by the Rank–nullity theorem, if one generic framework is infinitesimally rigid then all generic frameworks are infinitesimal rigidity have rigid.
Proposition 3. If a framework of a graph is infinitesimally rigid, then it is rigid.
Proof. Assume that is not rigid, so there exists a framework in a neighborhood such that and is cannot be obtained via a trivial motion of . Since is in , there exists a and such that . Applying some algebra yields:
Hence,
We can choose a sequence of such that and . This causes and . Hence,
The first and last expressions in the equations above state that is an infinitesimal motion of the framework . Since there is no trivial motion between and , is not a trivial infinitesimal motion. Thus, is not infinitesimally rigid.
Proposition 4. If a framework of a graph is rigid and generic with respect to infinitesimal rigidity, then is infinitesimally rigid.
Proof. This follows from the implicit function theorem. First, we will factor out all trivial motions of . Since has max rank, no points of are colinear. Hence, we can pin points of to factor out trivial motions: one point at the origin and another along the -axis at a distance from the origin consistent with all constraints. This yields a pinned framework that lives in . This can be done for all frameworks in a neighborhood of to obtain a neighborhood of of pinned frameworks. The set of such frameworks is still a smooth manifold, so the rigidity map and rigidity matrix can be redefined on the new domain. Specifically, the rigidity matrix of a pinned framework has columns and rank equal to , where is the unpinned framework corresponding to . In this pinned setting, a framework is rigid if it is the only nearby solution to the rigidity map.
Now, assume an unpinned framework is not infinitesimally rigid, so that . Then the , where is the pinned version of . We now set up to apply the implicit function theorem. Our continuously differentiable function is the rigidity map . The Jacobian of is the rigidity matrix. Consider the subset of edges corresponding to the independent rows of , yielding the submatrix . We can find independent columns of . Denote the entries in these columns by the vectors . Denote the entries of the remaining columns by the vectors . The submatrix of induced the is invertible, so by the implicit function theorem, there exists a continuously differentiable function such that and . Hence, the framework of the subgraph is not rigid, and since the rows of span the row space of , is also not rigid. This contradicts our assumption, so is infinitesimally rigid.
Proposition 5. Rigidity is a generic property of graphs.
Proof. Let be a rigid framework of that is generic with respect to rigidity. By definition, there is a neighborhood of rigid frameworks of . By Proposition 1, there is a framework in that is generic with respect to infinitesimal rigidity, so by Proposition 4, is infinitesimally rigid. Hence, by Proposition 2, all frameworks that are generic with respect to infinitesimal rigidity are infinitesimally rigid, and by Proposition 3 they are also rigid. Finally, every neighborhood of every framework that is generic with respect to rigidity contains a framework that is generic with respect to infinitesimal rigidity, by Proposition 1. Thus, if is rigid then is rigid.
Theorem 1. A graph is generically rigid if and only if it is generically infinitesimally rigid.
Proof. The proof follows a similar argument to the proof of Proposition 5. If is generically rigid, then there exists a generic framework with respect to rigidity that is rigid by definition. By Propositions 1 and 4, in any neighborhood of there is a framework that is generic with respect to infinitesimal rigidity and infinitesimally rigid. Hence, by Proposition 2, is generically infinitesimally rigid.
For the other direction, assume to the contrary that is generically infinitesimally rigid, but not generically rigid. Then there exists a generic framework with respect to rigidity that is not rigid by definition. By Proposition 1, in any neighborhood of there is a framework that is generic with respect to infinitesimal rigidity. By assumption is infinitesimally rigid, and by Proposition 3, is also rigid. Thus, must be rigid and, by Proposition 5, all frameworks that are generic with respect to rigidity are rigid. This contradicts our assumption that is not generically rigid.
Maxwell direction
The Maxwell Direction of the Geiringer-Laman theorem follows from a simple counting argument on the rigidity matrix.
Maxwell Direction. If a graph has a generic infinitesimally rigid framework, then has a Geiringer-Laman subgraph.
Proof. Let be a generic infinitesimally rigid framework of . By definition, has max rank, i.e., . In particular, has independent rows. Each row of corresponds to an edge of , so the submatrix with just the independent rows corresponds to a subgraph such that . Furthermore, any subgraph of corresponds to a submatrix of . Since the rows of are independent, so are the rows of . Hence, , which clearly satisfies .
Equivalence of generic infinitesimal rigidity and Henneberg constructions
Now we begin the proof of the other direction of the Geiringer-Laman theorem by first showing that a generically minimally rigid graph has a Henneberg construction. A Henneberg graph has the following recursive definition:
is a single edge or
can be obtained from a Henneberg graph via one of the following operations
add a vertex to and connect it to distinct vertices of
For an edge and a vertex of , add a vertex to , connect it to and , and then remove .
The two operations above are called a -extension and a -extension respectively.
The following propositions are proved in:
Proposition 6. A generically minimally rigid graph has no vertex with degree and at least one vertex with degree less than
Proposition 7. If is a generically minimally rigid graph with a vertex of degree , connected to vertices and , then for at least one pair of the neighbors of , without loss of generality say , there is no subgraph of that contains and and satisfies .
Theorem 2. A generically minimally rigid graph with at least vertices has a Henneberg construction.
Proof. We proceed by induction on the number of vertices . The base case of is the base case Henneberg graph. Assume has a Henneberg construction when and we will prove it for . When , has a vertex with degree or , by Proposition 6.
Case 1: has degree 2.
Let be the subgraph of obtained by removing , so and . Since is minimally rigid, we have
Furthermore, any subgraph of is also a subgraph of , so by assumption. Hence, is minimally rigid, by the Maxwell Direction, and has a Henneberg construction by the inductive hypothesis. Now simply notice that can be obtained from via a -extension.
Case 2: has degree 3.
Let the edges incident to be and . By Proposition 7, for one pair of the neighbors of , without loss of generality say , there is no subgraph of that contains and and satisfies . Note that cannot be an edge, or else the subgraph on just that edge satisfies the previous equality. Consider the graph obtained by removing from and adding the edge . We have
.
Furthermore, as with Case 1, any subgraph of that does not contain satisfies the second condition for minimal rigidity by assumption. For a subgraph of that does contain , removing this edge yields a subgraph of . By Proposition 7, , so . Hence, is minimally rigid, and has a Henneberg construction by the inductive hypothesis. Finally, notice that can be obtained from via a -extension.
Combining Cases 1 and 2 proves the theorem by induction.
It is also easy to the converse of Theorem 2 by induction.
Proposition 8. A graph with a Henneberg construction is generically minimally rigid.
Henneberg constructible graphs are generically infinitesimally rigid
To complete the proof of the Geringer-Laman theorem, we show that if a graph has a Henneberg construction then it is generically infinitesimmaly rigid. The proof of this result relies on the following proposition from.
Proposition 9. If are three non-colinear -dimensional points and are three -dimensional vectors, then the following statements are equivalent:
for all
The function
vanishes at every point .
Theorem 3. If a graph with at least vertices has a Henneberg construction, then is generically infinitesimally rigid.
Proof. We proceed by induction on the number of vertices . The graph in the base case is a triangle, which is generically infinitesimally rigid. Assume that when is generically infinitesimally rigid and we will prove it for . For , consider the graph that was obtained from via - or -extension. By the inductive hypothesis, is generically infinitesimally rigid. Hence, has a generic infinitesimally rigid framework such that the kernel of has dimension . Let be the vertex added to to obtain . We must choose a placement in -dimensions such that is a generic infinitesimally rigid framework of .
Case 1: is obtained from via a -extension.
Choosing such a placement for is equivalent to adding rows corresponding to the equations
to the rigidity matrix , where and are the neighbors of after the -extension and is the velocity assigned to by an infinitesimal motion. Our goal is to choose such the dimension of the space of infinitesimal motions of is the same as that of . We can choose such that it is not colinear to and , which ensures that there is only one solution to these equations. Hence, the kernel of has dimension , so is a generic infinitesimally rigid framework of .
Case 2: is obtained from via a -extension.
Let the neighbors of after the -extension be the edges , and , and let be the edge that was removed. Removing the edge from yields the subgraph . Let be the framework of that is equivalent to , except for the removed edge. The rigidity matrix can be obtained from by removing the row corresponding to the removed edge. By Proposition 8, is generically minimally rigid, so the rows of are independent. Hence, the rows of are independent and its kernel has dimension . Let be a basis vector for the space of infinitesimal motions of such that is a basis for the space of trivial infinitesimal motions. Then, any infinitesimal motion of can be written as a linear combination of these basis vectors. Choosing a placement for that results in a generic infinitesimally rigid framework of is equivalent to adding rows corresponding to the equations
to the rigidity matrix . Our goal is to choose such the dimension of the space of infinitesimal motions of is less than that of . After rearranging, these equations have a solution if and only if
Note that can be written as , for constants . Furthermore, we can move the summation outside of the determinant to obtain
Since form a basis for the trivial infinitesimal motions, the first three terms in the summation are , leaving only
Solutions to this equation form a curve in -dimensions. We can choose not along this curve so that , which ensures that there is only one solution to this equation. Hence, by Proposition 9, the kernel of has dimension , so is a generic infinitesimally rigid framework of .
Combining Cases 1 and 2 proves the theorem by induction.
See also
Laman graph
References
Theorems in graph theory | Geiringer–Laman theorem | [
"Physics",
"Mathematics"
] | 3,816 | [
"Theorems in graph theory",
"Mathematics of rigidity",
"Mechanics",
"Theorems in discrete mathematics"
] |
66,491,048 | https://en.wikipedia.org/wiki/Arvid%20Reuterdahl | Arvid Reuterdahl (February 15, 1876 – January 13, 1933) was a Swedish-American engineer, scientist and educator.
Biography
Reuterdahl was born at Karlstad on February 15, 1876. He moved to the United States as a child in 1882. He graduated Sc.B. from Brown University in 1897 and was a mathematics and physics instructor at the Technical High School in Providence. Reuterdahl worked as an engineer in Spokane, Washington for five years and as an assistant city engineer, water commissioner and President of the board of public works. He designed bridges for the city. He was an consulting engineer of Boise, Idaho (1910–1913) and Kansas City, Missouri (1913–1918).
He was professor of theoretical and applied mechanics at Kansas City Polytechnic Institute (1915–1918) and was the first Dean of the Department of Engineering and Architecture at the College of St. Thomas (1918–1922). He was President of the Ramsey Institute of Technology, Saint Paul, Minnesota (1922-1926).
He was a Fellow of the American Association for the Advancement of Science. He married Elinor Morrison on June 16, 1902. They had one son, Norman Morrison Reuterdahl.
Opposition to the theory of relativity
Reuterdahl was a noted opponent of Albert Einstein's theory of relativity. He considered Einstein's theory to be largely "bunk" and accused him of plagiarism. Reuterdahl argued that Einstein's theory of relativity was plagiarized from a mechanical gravitation theory of Scottish engineer Robert Stevenson (pseudonym Kinertia). He argued that Stevenson's papers were sent to the Prussian Academy of Sciences in 1903 and that Einstein, a member of the Academy secretly made use of the papers.
Reuterdahl communicated with other anti-relativists such as Ernst Gehrcke. He was science editor for Henry Ford's journal the Dearborn Independent.
Selected publications
Scientific Theism Versus Materialism: The Space-time Potential (1920)
Einstein and the New Science (1921)
"Kinertia" Versus Einstein (1921)
A Synthesis of Number, Space-Time and Energy (1923)
The God of Science (1928)
Einsteinism: Its Fallacies and Frauds (1931)
References
1876 births
1933 deaths
20th-century American engineers
Brown University alumni
Fellows of the American Association for the Advancement of Science
People from Karlstad
Relativity critics
Swedish emigrants to the United States
University of St. Thomas (Minnesota) faculty | Arvid Reuterdahl | [
"Physics"
] | 509 | [
"Relativity critics",
"Theory of relativity"
] |
76,816,751 | https://en.wikipedia.org/wiki/LMC%20X-1 | LMC X-1 is the first X-ray source detected in the Large Magellanic Cloud. It was discovered in 1969, using data from an instrument carried by a Sandia Terrier-Sandhawk sounding rocket, launched from the Johnston Atoll on October 29, 1968. LMC X-1 is a persistently luminous X-ray binary.
In the 80s Hutchings et al. performed spectroscopic follow-up observations of the optical counterpart and found an orbital period of about 4 days and a secondary mass of about 6 , making the secondary a stellar mass black hole. The orbital period later turned out to be shorter at around 3.9 days. The optical counterpart is also called "star 32". The black hole has a mass of around 11 and the star has a mass of around 32 and a radius of 17 . With this radius the star nearly fills its Roche lobe and it is predicted that it will encounter its Roche lobe in a few hundred thousand years. Once it reaches its Roche lobe, it will begin rapid and possibly unstable mass transfer to its companion.
The X-ray source is surrounded by a nebula, which is the only nebula energized by an X-ray binary. It is suspected that the nebula is a bow shock nebula. The nebula is also detected in radio wavelengths with ATCA imaging. A possible origin of LMC X-1 is the star cluster [NKN2005] N159-O1. Other possible origins are NGC 2077, NGC 2080, NGC 2085 and NGC 2086. In the scenario of N159-O1 being the origin, the progenitor to the black hole would have a mass of about 60 , meaning it was the most massive member of this star cluster.
See also
M33 X-7 is a stellar mass black hole in the Triangulum Galaxy
Cyg X-1 another x-ray binary with a stellar black hole and a massive star
Gaia BH1 first dormant black hole
References
Stellar black holes
O-type stars
X-ray binaries
Dorado
Astronomical objects discovered in 1969 | LMC X-1 | [
"Physics",
"Astronomy"
] | 426 | [
"Black holes",
"Stellar black holes",
"Dorado",
"Unsolved problems in physics",
"Constellations"
] |
76,817,562 | https://en.wikipedia.org/wiki/Levonadifloxacin | Levonadifloxacin (trade name Emrok) is an antibiotic drug of the fluoroquinolone class. Chemically, it is the (S)-enantiomer of the racemic drug nadifloxacin.
It is approved in India for the treatment of skin and soft tissue infections of Gram-positive bacteria. It is also being studied for potential use against resistant strains of bacteria including Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, and Moraxella catarrhalis.
Levonadifloxacin has poor oral bioavailability. A prodrug of levonadifloxacin with high oral bioavailability, alalevonadifloxacin, has been developed to mitigate this problem.
References
Fluoroquinolone antibiotics
Enantiopure drugs
Piperidines
Carboxylic acids
Heterocyclic compounds with 3 rings | Levonadifloxacin | [
"Chemistry"
] | 206 | [
"Carboxylic acids",
"Stereochemistry",
"Functional groups",
"Enantiopure drugs"
] |
72,406,120 | https://en.wikipedia.org/wiki/Foucault%27s%20gyroscope | The Foucault gyroscope was a gyroscope created by French physicist Léon Foucault in 1852, conceived as a follow-up experiment to his pendulum in order to further demonstrate the Earth's rotation.
Foucault felt that the results of his famous pendulum experiment had been misunderstood. He therefore endeavored to create an apparatus with a "body freely suspended by its center of gravity and rotating around one of its principal axes", allowing the study of a plane with "absolute directional stability". The mechanical precision of Foucault's gyroscope allowed this to be proven clearly to the scientific establishment, and the gyroscope became a widely popular instrument.
Design
Together with Paul-Gustave Froment, Foucault built an apparatus in which the inner gimbal was balanced on knife edge bearings on the outer gimbal and the outer gimbal was suspended by a fine, torsion-free thread in such a manner that the lower pivot point carried almost no weight.
The gyro was spun to 9,000–12,000 revolutions per minute with an arrangement of gears before being placed into position, which was sufficient time to balance the gyroscope and carry out 10 minutes of experimentation. The instrument could be observed either with a microscope viewing a tenth of a degree scale or by a long pointer.
Publications
Foucault published two papers in 1852, one focused on astronomy with the weight free to move on all three axes (On a new experimental demonstration of the motion of the Earth, based on the fixity of the plane of rotation) and the other on mechanics with the weight free to move on only two axes (On the orientation phenomena of rotating bodies driven by a fixed axis on the Earth's surface. New sensitive signs of daily movement).
In the paper on mechanics, Foucault explained that if one axis of rotation is fixed in line with the surface of the Earth, the other two axes of rotation tend to the same direction, similar to "a magnetic needle", making it possible to use the instrument to highlight a directing force.
Naming
Foucault coined the name "gyroscope" in the 1852 publication of his experiment:
This apparatus specially designed to highlight and approximate the deviation of a freely rotating body can also be used to produce and observe the phenomena of orientation that I have just stated and described. As all these phenomena depend on the movement of the Earth and are its varied manifestations, I propose to name the sole instrument which has served me to observe them gyroscope.
Copies
At least three more copies of a Foucault's gyroscope were made in convenient travelling and demonstration boxes, and copies survive in the UK, France, and the US. The original was given to the Collège de France and was lost, there are no known photographs of the original suggesting it was lost a few decades after the College received it.
The Foucault gyroscope became a challenge and source of inspiration for skilled science hobbyists such as David B. Adamson.
Gallery
Citations
References
Gyroscopes
Physics experiments
French inventions | Foucault's gyroscope | [
"Physics"
] | 644 | [
"Experimental physics",
"Physics experiments"
] |
72,406,363 | https://en.wikipedia.org/wiki/Gurzadyan%20theorem | In cosmology, the Gurzadyan theorem, proved by Vahe Gurzadyan, states the most general functional form for the force satisfying the condition of identity of the gravity of the sphere and of a point mass located in the sphere's center. This theorem thus refers to the first statement of Isaac Newton’s shell theorem (the identity mentioned above) but not the second one, namely, the absence of gravitational force inside a shell.
The theorem had entered and its importance for cosmology outlined in several papers as well as in shell theorem.
The formula and the cosmological constant
The formula for the force derived in has the form
where and are constants. The first term is the familiar law of universal gravitation, the second one corresponds to the cosmological constant term in general relativity and McCrea-Milne cosmology.
Then the field is force-free only in the center of a shell but the confinement (oscillator) term does not change the initial symmetry of the Newtonian field. Also, this field corresponds to the only field possessing the property of the Newtonian one: the closing of orbits at any negative value of energy, i.e. the coincidence of the period of variation of the value of the radius vector with that of its revolution by (resonance principle) .
Consequences: cosmological constant as a physical constant
Einstein named the cosmological constant as a universal constant, introducing it to define the static cosmological model. Einstein has stated: “I should have initially set in Newton's sense. But the new considerations speak for a non-zero , which strives to bring about a non-zero mean density of matter.” This theorem solves that contradiction between “non-zero ” and Newton's law.
From this theorem the cosmological constant emerges as additional constant of gravity along with the Newton's gravitational constant . Then, the cosmological constant is dimension independent and matter-uncoupled and hence can be considered even more universal than Newton's gravitational constant.
For joining the set of fundamental constants , the gravitational
Newton's constant, the speed of light and the Planck constant, yields
and a dimensionless quantity emerges for the 4-constant set
where is a real number. Note, no dimensionless quantity is possible to construct from the 3 constants .
This within a numerical factor, , coincides with the information (or entropy) of de Sitter event horizon
and the Bekenstein Bound
Rescaling of physical constants
Within the Conformal Cyclic Cosmology this theorem implies that, in each aeon of an initial value of , the values of the 3 physical constants will be eligible for rescaling fulfilling the dimensionless ratio of invariants with respect to the conformal transformation
Then the ratio yields
for all physical quantities in Planck (initial) and de Sitter (final) eras of the aeons, remaining invariant under conformal transformations.
Inhomogeneous Fredholm equation
This theorem, in the context of nonlocal effects in a system of gravitating particles, leads to the inhomogeneous Dirichlet boundary problem for the Poisson equation
where is the radius of the region,
.
Its solution can be expressed in terms of the double layer potential, which leads to an inhomogeneous nonlinear Hammerstein integral equation for the gravitational potential
This leads to a linear inhomogeneous 2nd kind Fredholm equation
Its solution can be expressed in terms of the resolvent of the integral kernel and the non-linear (repulsive) term
Observational indications
The dynamics of groups and clusters of galaxies are claimed to fit the theorem, see also.
The possibility of two Hubble flows, a local one, determined by that formula, and a global one, described by Friedmannian cosmological equations was stated in.
References
Eponymous theorems of physics
Gravity
Mathematical theorems | Gurzadyan theorem | [
"Physics",
"Mathematics"
] | 788 | [
"Equations of physics",
"Eponymous theorems of physics",
"nan",
"Mathematical problems",
"Mathematical theorems",
"Physics theorems"
] |
72,408,552 | https://en.wikipedia.org/wiki/Hyperpolarized%20gas%20MRI | Hyperpolarized gas MRI, also known as hyperpolarized helium-3 MRI or HPHe-3 MRI, is a medical imaging technique that uses hyperpolarized gases to improve the sensitivity and spatial resolution of magnetic resonance imaging (MRI). This technique has many potential applications in medicine, including the imaging of the lungs and other areas of the body with low tissue density.
The current standard for diagnosing and monitoring treatment of pulmonary diseases is spirometric pulmonary function testing (PFTs). However, these tests only assess the lung on a global basis and are generally not sensitive enough to detect functional changes in the small airways and gas exchange regions. This lack of sensitivity has led these regions to be known as the "silent zone." Additionally, PFT metrics largely rely on the effort of the subject, leading to significant measurement uncertainty and variability. As a result, current therapy is largely based on patients' symptoms and survival. Given the high burden on the healthcare system and the increasing prevalence of pulmonary disease, there is a need for improved diagnostic tools and quantitative metrics to better diagnose and quantify pulmonary disease progression and accurately measure response to therapy.
The basic principle of hyperpolarized gas MRI is similar to that of conventional MRI, which uses powerful magnetic fields and radio waves to create detailed images of the body's internal structures. In conventional MRI, the magnetic moments of hydrogen atoms (protons) in the body's water and fat molecules are aligned with the magnetic field and then subjected to a radiofrequency pulse. This causes the protons to absorb energy and become excited, and when the radiofrequency pulse is turned off, the protons relax and release their energy in the form of a detectable signal. This signal is used to construct an image of the body's tissues.
Overcoming challenges of traditional MRI
Traditional MR imaging of the lungs is difficult because conventional scanners are designed to excite hydrogen protons, which are present in water molecules. However, the lungs have only a very low density of hydrogen protons compared to other structures, and their long relaxation time means that the signal available for imaging is minimal. In addition, the inhomogeneous magnetic environment of the lungs introduces susceptibility artifacts that further complicate MR acquisitions. These challenges are not faced by external gaseous contrast media like 3He or 129Xe, which image the airways and airspaces within the lungs rather than the surrounding tissues. This greatly reduces the problems of unfavorable longitudinal and transverse relaxation times faced by hydrogen MRIs in the lung. However, MR imaging of a gas is challenging because its density is typically about 4 orders of magnitude lower than that of protons. To overcome this limitation, a process called hyperpolarization is used to increase the magnetization of these gases by about 5 orders of magnitude. This makes MR-based imaging of inhaled gases feasible within a single breath hold.
To improve the ability to detect early lung disease, it is necessary to use imaging techniques that provide regional information. Hyperpolarized gas magnetic resonance imaging (HP gas MRI) is a non-invasive, radiation-free method that can image the structure and function of the lungs. While 3He was originally used extensively in HP gas MRI, its recent scarcity and increase in price has led to a shift towards the cheaper and more abundant 129Xe. The advantage of using 129Xe is that it is soluble in pulmonary tissues, providing two additional signal sources in addition to the xenon in the airspaces. These three 129Xe resonances can provide quantitative regional information about the fundamental function of the lungs: gas exchange.
History and safety
In 1994, the first studies on hyperpolarized (HP) gas magnetic resonance imaging (MRI) were carried out using the noble gas isotope 129-Xenon (129Xe). In 1997, Mugler and colleagues used 129Xe to conduct the first studies in humans. However, these studies were limited by relatively low 129Xe polarizations (1-2%), which resulted in low signal intensities. This issue led to a shift in research interest to helium (3He), which has a larger gyromagnetic ratio than 129Xe and offers a simpler and more mature polarization technology (30%) and corresponding larger signal intensities. 3He also does not have any physiological side effects, making it a better starting point for clinical imaging.
In 1996, 3He MR imaging entered clinical research and expanded to multi-center clinical studies. The results of the ventilation studies showed a significant correlation to conventional pulmonary function tests in patients with chronic obstructive pulmonary disease, asthma, and cystic fibrosis. The main problem with 3He HP MR imaging is the limited supply of 3He, which comes from the decay of tritium, a byproduct of nuclear weapons production. This has driven up costs significantly to around $800–2000 per liter depending on academic versus commercial use. Due to these higher costs and lower availability, 3He HP MR imaging is not economically sustainable.
Recent advances in 129Xe polarization technology have led to the reintroduction of 129Xe MR imaging in humans. Xenon has a long history of safe use as a contrast agent in computed tomography lung imaging studies, which was confirmed in safety studies on inhaling hyperpolarized 129Xe. With the development of more efficient polarizers, resulting in improved 129Xe polarization, it is expected that better image quality can be achieved with a lower volume of xenon. A second safety study showed that inhalation of only 0.5-liter volumes caused subjects to experience few or no symptoms.
Physics of hyperpolarization
The basic principle of hyperpolarized gas MRI is similar to that of conventional MRI, which uses powerful magnetic fields and radio waves to create detailed images of the body's internal structures. In conventional MRI, the magnetic moments of hydrogen atoms (protons) in the body's water and fat molecules are aligned with the magnetic field and then subjected to a radiofrequency pulse. This causes the protons to absorb energy and become excited, and when the radiofrequency pulse is turned off, the protons relax and release their energy in the form of a detectable signal. This signal is used to construct an image of the body's tissues.
In hyperpolarized gas MRI, the gases used are noble gases, such as 3He or 129Xe, which have large nuclear magnetic moments but low natural abundance and therefore produce very weak signals. To increase the nuclear spin polarization of either 3He or 129Xe, two processes are involved: 1) optical pumping and 2) spin exchange.
Hyperpolarized gas MRI is a technique that uses the alignment of nuclear spins in certain gases, such as 3He or 129Xe, to create detailed images of the body's internal structures. In order for the nuclear spins to be used for imaging, they must be aligned in the same direction, or polarized. Under normal conditions, the nuclear spins within the gas volume are randomly aligned, leading to a zero signal.
Once the nuclear spins have been polarized, they can be placed in a large magnetic field, such as that of a 1.5T or 3.0T scanner. This will cause slightly more spins to align with the field than against it. However, this difference is not sufficient for imaging dilute gases like 3He or 129Xe. Therefore, hyperpolarization techniques are used to add angular momentum to the system and align all of the nuclear spins in the same direction, resulting in a strong signal that can be used to create detailed images of the body's tissues.
Optical pumping
Hyperpolarization is the process of aligning the nuclear spins in a gas, such as 3He or 129Xe, in the same direction to create a strong signal for imaging. To accomplish this, angular momentum is added to the system through the use of circularly polarized laser light. Since nuclei cannot directly absorb laser light, an intermediary is used to absorb the light and transfer its angular momentum to the nuclei.
This intermediary is typically an alkali metal atom, such as rubidium, whose outer-shell valence electron is aligned by the laser light. Only atoms with electron spins that are down can absorb the light, so illuminating the alkali vapor with circularly polarized resonant light will convert the entire sample to the spin up direction. Once a valence electron spin has been flipped up, it remains aligned until collisions cause it to depolarize. However, it can simply absorb another photon and return to the aligned state. This process, known as optical pumping, allows for the efficient alignment of nuclear spins in the gas.
Spin exchange
The alignment of the valence electron is then transferred to the noble-gas nuclei through collisions with polarized electron spins of the rubidium. This process is called spin exchange. The rubidium electrons are then aligned again by absorbing additional laser light and continue to build polarization in the noble-gas nuclei. Current techniques using optical pumping and spin exchange can achieve polarizations of around 40-80% for 3He and 10-40% for 129Xe. Recently, very high peak polarization levels for 129Xe have been demonstrated in diluted mixtures.
Mechanism of hyperpolarization
The process of optical pumping uses rubidium (Rb) contained in a glass optical cell. This cell is placed in an oven with two Helmholtz coils that generate a small, but homogenous 20 G magnetic field. The Rb is heated to around 150 °C to produce a vapor pressure of about 1ppm of the total gas density in the cell. Circularly polarized laser light is then directed at the cell, which is tuned to the D1 transition of rubidium. This light is absorbed by the Rb vapor, polarizing the valence electron spins on the Rb atoms.
Spin exchange is a process that begins when a mixture of 1% 129Xe, 89% 4He and 10% N2 is directed to flow through an optical cell that contains optically pumped Rubidium (Rb) atoms. The buffer gases, helium and nitrogen, serve to broaden the Rb absorption cross section, allowing a large fraction of laser light to be absorbed and used to polarize the valence electron spins of the Rb atoms. Through a combination of binary collisions and the formation of transient Van der Waals complexes, the electron spin polarization is transferred to the 129Xe nuclei. The gas flow rate is regulated to ensure that the 129Xe emerges from the cell with a high level of polarization. To separate the 129Xe from the helium and nitrogen, it is cryogenically accumulated in a cold finger immersed in liquid nitrogen. Since xenon has a higher freezing point than the other gases, it is frozen out and separated from them. Once a sufficient amount of xenon has been accumulated, it is thawed and dispensed into a perfluoropolymer bag. The xenon polarization is then measured using a low-field NMR-based system and delivered to the patient for use in MRI imaging. Commercially available systems can produce liters of xenon polarized to 10-15% within an hour. Advances in polarization physics are expected to improve both the production rate and polarization of 129Xe in the future.
In order to obtain images of the subject's lung tissue, the polarized xenon gas is inhaled through a tube connected to a mouthpiece. The subject is instructed to take a deep breath and exhale fully twice before inhaling the gas. The typical scan uses a mixture of 200-1000 ml of 129Xe and a buffer gas such as helium or nitrogen. This mixture is inhaled by the subject and used to create detailed images of the lung tissue.
Applications
Ventilation imaging
HP 3He gas MR imaging of the lungs has been confirmed to be effective in multiple clinical studies since 1997. This technique is mainly used to create images of gas distribution in the lungs, allowing for the identification of ventilation defects. These defects can be caused by blocked airways or destruction of lung tissue. The MR signal intensities in the ventilation images can be grouped into four clusters for analysis. Low or absent signal within the lungs corresponds well with ventilation defects and allows for the detection and quantification of functional ventilation impairment in conditions such as asthma, COPD, and cystic fibrosis. Data acquisition for this technique is completed in a single breath-hold, providing static ventilation information. Dynamic ventilation properties, such as gas flow, are more difficult to measure but progress has been made in this area.
Traditionally, HP 3He provided better image quality due to its larger polarization compared to 129Xe. However, recent improvements in polarization technology and MR acquisition have allowed 129Xe to produce images of similar quality to 3He. In terms of detecting ventilation defects, 129Xe has a lower signal-to-noise ratio but is more sensitive to defects due to its higher density and lower diffusivity. Currently, using a larger volume of 129Xe (up to 1 liter per scan) can compensate for its decreased signal-to-noise ratio compared to 3He (usually 0.1-0.3 liters per scan).
Diffusion weighted imaging
Diffusion-weighted MRI has been proven effective and is commonly used with hyperpolarized gases to calculate the apparent diffusion coefficient (ADC) of the gas. This is done by taking gas images with and without diffusion sensitizing gradients. The usefulness of this contrast comes from the fact that the diffusion of gases is limited by the structure of healthy lungs. In diseases like emphysema, where the airspaces are larger, the gases are free to diffuse more easily. This allows diffusion-weighting to differentiate normal airspaces from enlarged ones based on the degree of signal attenuation. The signal intensities in the weighted and non-weighted images are then used to calculate the ADC on a voxel-by-voxel basis. ADC maps show low values in healthy lung tissue, but in emphysematous lungs, elevated ADC values are often seen. In addition to showing emphysema, 3He or 129Xe ADC values have been found to be sensitive to early changes in the lung tissue of smokers and people exposed to second-hand smoke. ADC MRI has also been shown to be sensitive to age-related changes in alveolar size in healthy individuals. Comparisons to CT densitometry have shown that ADC strongly correlates with DLCO and may be able to detect early emphysema before it is visible on CT scans. While most ADC imaging has used 3He MRI, it has recently been shown that 129Xe can also be used for this purpose.
Future direction
129Xe dissolving imaging
Xenon has a lower gyromagnetic ratio and lower SNR in images than helium. However, it has the useful property of being moderately soluble in lung tissue. This allows it to diffuse into the capillaries and blood stream, where it experiences shifts in frequency that provide information about gas exchange in the lungs. These shifts can be used to study ventilatory distribution and diffusive gas exchange.
Imaging the dissolved-phase of gases in the lungs can be difficult. The signal intensity in this phase is only 2% of the gas-phase, and its T2* is very fast at 2 ms. Additionally, the dissolved-phase resonances are 200 ppm from the gas-phase on a 1.5T scanner, so RF excitation pulses must be carefully tuned to avoid exciting the gas-phase.
Early attempts at imaging the dissolved-phase used indirect methods like Xenon Polarization Transfer Contrast (XTC). This method used RF pulses applied to the dissolved-phase to slightly attenuate the gas-phase signal, allowing for the indirect mapping of the dissolved-phase distribution. As polarization and pulse sequence technology improved, direct imaging of dissolved 129Xe became possible. By using frequency-selective RF pulses and a 3D radial pulse sequence, the first direct images of the dissolved-phase in humans were acquired in 2010. These images were lower resolution due to the small signal intensity of dissolved-phase 129Xe, but still showed interesting aspects of lung function. Soon after this technique was introduced, Mugler et al. showed the value of acquiring the gas-phase distribution in the same breath, allowing for the quantification of the dissolved-phase distribution. This was later extended to a radial acquisition strategy, which allowed for the analysis of the effects of posture on gas transfer.
It is important to be able to separately detect the transfer of 129Xe to red blood cells (RBCs) because the pathway xenon follows to reach RBCs is the same as that of oxygen. Recently, spectra of 129Xe in the dissolved phase were acquired in subjects with idiopathic pulmonary fibrosis and showed greatly reduced 129Xe transfer to RBCs compared to healthy volunteers. This work showed that separating the dissolved 129Xe resonances is critical for detecting diffusion limitation caused by lung tissue thickening. 129Xe measurements correlated strongly with DLCO and showed that the frequency of the 129Xe RBC resonance may be a sensitive measure of blood oxygenation at the capillary level. This work also emphasized the need for imaging to separately detect xenon uptake in barrier tissues and RBCs.
Separately imaging 129Xe in barrier tissues and RBCs is similar to separating fat and water in 1H MRI. The two resonances are similarly spaced, so fat-water separation algorithms can be used. Qing et al. used the Hierarchical IDEAL algorithm to image all three resonances of xenon in a single breath. The 1-point Dixon strategy has also been successful and may be more robust against the short T2* of the dissolved-phase 129Xe signal. This technique was also recently used to image all three resonances of xenon in a single breath.
See also
Xenon gas MRI
References
Magnetic resonance imaging | Hyperpolarized gas MRI | [
"Chemistry"
] | 3,730 | [
"Nuclear magnetic resonance",
"Magnetic resonance imaging"
] |
63,703,274 | https://en.wikipedia.org/wiki/DF-space | In the mathematical field of functional analysis, DF-spaces, also written (DF)-spaces are locally convex topological vector space having a property that is shared by locally convex metrizable topological vector spaces. They play a considerable part in the theory of topological tensor products.
DF-spaces were first defined by Alexander Grothendieck and studied in detail by him in .
Grothendieck was led to introduce these spaces by the following property of strong duals of metrizable spaces: If is a metrizable locally convex space and is a sequence of convex 0-neighborhoods in such that absorbs every strongly bounded set, then is a 0-neighborhood in (where is the continuous dual space of endowed with the strong dual topology).
Definition
A locally convex topological vector space (TVS) is a DF-space, also written (DF)-space, if
is a countably quasi-barrelled space (i.e. every strongly bounded countable union of equicontinuous subsets of is equicontinuous), and
possesses a fundamental sequence of bounded (i.e. there exists a countable sequence of bounded subsets such that every bounded subset of is contained in some ).
Properties
Let be a DF-space and let be a convex balanced subset of Then is a neighborhood of the origin if and only if for every convex, balanced, bounded subset is a neighborhood of the origin in Consequently, a linear map from a DF-space into a locally convex space is continuous if its restriction to each bounded subset of the domain is continuous.
The strong dual space of a DF-space is a Fréchet space.
Every infinite-dimensional Montel DF-space is a sequential space but a Fréchet–Urysohn space.
Suppose is either a DF-space or an LM-space. If is a sequential space then it is either metrizable or else a Montel space DF-space.
Every quasi-complete DF-space is complete.
If is a complete nuclear DF-space then is a Montel space.
Sufficient conditions
The strong dual space of a Fréchet space is a DF-space.
The strong dual of a metrizable locally convex space is a DF-space but the convers is in general not true (the converse being the statement that every DF-space is the strong dual of some metrizable locally convex space). From this it follows:
Every normed space is a DF-space.
Every Banach space is a DF-space.
Every infrabarreled space possessing a fundamental sequence of bounded sets is a DF-space.
Every Hausdorff quotient of a DF-space is a DF-space.
The completion of a DF-space is a DF-space.
The locally convex sum of a sequence of DF-spaces is a DF-space.
An inductive limit of a sequence of DF-spaces is a DF-space.
<li>Suppose that and are DF-spaces. Then the projective tensor product, as well as its completion, of these spaces is a DF-space.<li>
However,
An infinite product of non-trivial DF-spaces (i.e. all factors have non-0 dimension) is a DF-space.
A closed vector subspace of a DF-space is not necessarily a DF-space.
There exist complete DF-spaces that are not TVS-isomorphic to the strong dual of a metrizable locally convex TVS.
Examples
There exist complete DF-spaces that are not TVS-isomorphic with the strong dual of a metrizable locally convex space.
There exist DF-spaces having closed vector subspaces that are not DF-spaces.
See also
Citations
Bibliography
External links
DF-space at ncatlab
Topology
Topological vector spaces
Functional analysis | DF-space | [
"Physics",
"Mathematics"
] | 817 | [
"Functions and mappings",
"Functional analysis",
"Vector spaces",
"Mathematical objects",
"Space (mathematics)",
"Topological vector spaces",
"Topology",
"Space",
"Mathematical relations",
"Geometry",
"Spacetime"
] |
63,703,703 | https://en.wikipedia.org/wiki/Statistical%20Physics%20of%20Particles | Statistical Physics of Particles and Statistical Physics of Fields are a two-volume series of textbooks by Mehran Kardar. Each book is based on a semester-long course taught by Kardar at the Massachusetts Institute of Technology. They cover statistical physics and thermodynamics at the graduate level.
Editions
External links
Statistical Mechanics I at MIT OpenCourseWare
Statistical Mechanics II at MIT OpenCourseWare
Publisher's website for Particles
Publisher's website for Fields
References
2007 non-fiction books
Physics textbooks
Statistical mechanics | Statistical Physics of Particles | [
"Physics"
] | 107 | [
"Statistical mechanics stubs",
"Statistical mechanics"
] |
78,184,948 | https://en.wikipedia.org/wiki/Tityus%20stigmurus%20toxin%201 | Tityus stigmurus toxin 1 (Tst1) is a neurotoxin found in the venom of the Brazilian scorpion, Tityus stigmurus. It acts on voltage-gated sodium channels (Navs), altering opening and inactivation voltages, recovery from inactivation, and overall current flow.
Etymology and source
Tst1 (alternatively PT-Mice-beta* NaTx6.3, Tst-gamma, toxin gamma-like of Tityus stigmurus) is a neurotoxic peptide which can be purified from the venom of the Brazilian scorpion, Tityus stigmurus.
The toxin name is derived from the name of the scorpion, with ‘Tst’ standing for Tityus stigmurus toxin. The ‘1’ was initially used by Becerril et al. to indicate that the toxin is 𝛾-like, however, Tst1 has since been found to be a β-toxin.
Chemistry
Tst1 consists of 61 amino acid residues, with an average molecular mass of 6981.8 Da. Tst1 has 96.7% identity with Ts1 and 93.4% with Tt1g, which are from Tityus serrulatus and Tityus trivittatus scorpions, respectively and both of which are also β-toxins.
Tst1 is part of the NaScTx family, which are neurotoxins that specifically target Nav channels. The 3D structure of the toxin has not yet been solved, however it can be predicted using Alphafold. The prediction suggests that the peptide is a cysteine-stabilised alpha/beta fold protein consisting of two α - helices and three β-sheets, with the last cysteine in the amino acid sequence being a cysteine amide.
Target and mode of action
Tst1 is a β-toxin, meaning that it interacts with the voltage sensing domains of Navs. Tst1 affects the activation voltage, inactivation voltage and recovery, and the overall current flow through the channels, with the largest effects being observed in Nav 1.3. Tst1 shifts the activation voltage of the channel towards more hyperpolarized potentials, with a shift of approximately -35 mV in Nav 1.3. It also shifts the steady-state inactivation potential by approximately -21 mV and delays recovery from inactivation by 10.69 ms. Finally, Tst1 reduces the current flow through these channels by 85.23%, in a dosage-dependent manner, with an IC50 of 8.79 nM. While Nav 1.3 is the most sensitive to Tst1, it is not the only isoform affected. Nav 1.2 and 1.4 were also significantly affected in all the parameters mentioned above, demonstrating that Tst1 activity is not specific to one isoform.
Toxicity
T. stigmurus is one of the most medically relevant species in its genus, particularly in the northeast region of Brazil. Symptoms of a T. stigmurus sting are variable, including localised pain, edema, erythema, paresthesia, headache, vomiting, and, in more severe cases, cardiac arrhythmias and shock. The effects of isolated Tst1 have not been determined, however, sodium channel toxins are the peptides mainly responsible for the neurotoxic symptoms of human envenomation, and so it is expected that Tst1 contributes to the neurotoxic symptoms in these cases.
References
Ion channel toxins
Peptides
Scorpion toxins | Tityus stigmurus toxin 1 | [
"Chemistry"
] | 753 | [
"Biomolecules by chemical classification",
"Peptides",
"Molecular biology"
] |
78,190,572 | https://en.wikipedia.org/wiki/Optical%20chemical%20structure%20recognition | Optical chemical structure recognition (OCSR) is the translation of images that depict chemical structure information into machine-readable formats. It addresses the challenge of translating chemical structures from graphical representations into their corresponding chemical formulas.
In scientific publications, documents, and textbooks, molecular structures are typically represented through images and annotated text. These structural formulas are depicted as chemical graphs, where the vertices represent atoms, and the edges signify bonds between them. However, much of the data from older publications remains undigitised, both in image and descriptive formats. This lack of digitisation makes extracting useful information a time-consuming, manual process. OSCR can also translate digital images of molecules available online and scanned pages of chemical documents.
The development of the first OCSR systems faced limitations due to the computational resources available and the early stages of Computer Vision and machine learning algorithms. These initial systems primarily relied on heuristic and rule-based approaches, supported by classic Artificial Intelligence (AI) and optical character recognition techniques.
However, advancements in hardware, cloud computing, and deep neural networks have revolutionised OCSR. Modern systems now employ attention-based and context-aware image classification models, eliminating the need for separate pre-processing steps like noise removal or image restoration.
References
Machine vision | Optical chemical structure recognition | [
"Engineering"
] | 262 | [
"Machine vision",
"Robotics engineering"
] |
78,191,707 | https://en.wikipedia.org/wiki/Parker%20theorem | Parker theorem, or the fundamental magnetostatic theorem, was formulated by physicist Eugene Parker in 1972. Parker's theorem describes how magnetic fields behave in perfectly conducting fluids, particularly in space plasmas. The theorem states that three-dimensional magnetic fields naturally form infinitesimally thin current sheets – regions where the magnetic field direction changes abruptly. These sheets arise from the fundamental interaction between magnetic fields that are "frozen" into the conducting fluid.
When different magnetic field regions come into contact, they cannot smoothly merge due to the perfect conductivity of the fluid. Instead, they form sharp boundaries where electric currents flow. This process is analogous to how non-mixing fluids like oil and water form distinct boundaries rather than mixing. The theorem's central claim is that such discontinuities are not exceptional but are the standard feature of magnetic field equilibria in perfectly conducting fluids.
Further reading
References
Plasma theory and modeling
Eponymous theorems of physics | Parker theorem | [
"Physics"
] | 190 | [
"Equations of physics",
"Plasma physics",
"Eponymous theorems of physics",
"Plasma theory and modeling",
"Physics theorems"
] |
78,191,798 | https://en.wikipedia.org/wiki/Alpiropride | Alpiropride (; brand name Revistel, Rivistel, or Rivestel) is a dopamine D2 receptor antagonist of the benzamide group related to sulpiride. It is described as an antihypertensive agent and has been marketed for use as an antimigraine medication in Portugal. The drug was first described by 1980 and was introduced for medical use by 1989. It remained marketed in Portugal as late as 2000.
References
Abandoned drugs
Amines
Antihypertensive agents
Antimigraine drugs
Benzamides
D2 antagonists
Methoxy compounds
Pyrrolidines
Sulfonamides | Alpiropride | [
"Chemistry"
] | 133 | [
"Drug safety",
"Functional groups",
"Amines",
"Bases (chemistry)",
"Abandoned drugs"
] |
78,193,931 | https://en.wikipedia.org/wiki/ENX-105 | ENX-105 is an investigational new drug being developed by Engrail Therapeutics for the treatment of post-traumatic stress disorder (PTSD). It is currently in the preclinical stage, trailing behind a closely related Engrail compound, ENX-104, which is focused on depression and anhedonia.
The drug is described as a dopamine D2 and D3 receptor antagonist and serotonin 5-HT1A and 5-HT2A receptor agonist. In terms of its serotonin 5-HT2A receptor agonism, it is said to not produce the head-twitch response in animals and hence to be putatively non-hallucinogenic.
As with ENX-104, ENX-105 is a deuterated enantiomer of nemonapride.
References
Amines
Benzamides
Benzyl compounds
Chlorobenzene derivatives
D2 antagonists
D3 antagonists
Deuterated compounds
Experimental antidepressants
Experimental non-hallucinogens
Methoxy compounds
Non-hallucinogenic 5-HT2A receptor agonists
Pyrrolidines | ENX-105 | [
"Chemistry"
] | 239 | [
"Amines",
"Bases (chemistry)",
"Functional groups"
] |
78,194,677 | https://en.wikipedia.org/wiki/Three-term%20recurrence%20relation | In mathematics, and especially in numerical analysis, a homogeneous linear three-term recurrence relation (TTRR, the qualifiers "homogeneous linear" are usually taken for granted) is a recurrence relation of the form
for
where the sequences and , together with the initial values govern the evolution of the sequence .
Applications
If the and are constant and independent of the step index n, then the TTRR is a Linear recurrence with constant coefficients of order 2. Arguably the simplest, and most prominent, example for this case is the Fibonacci sequence, which has constant coefficients .
Orthogonal polynomials Pn all have a TTRR with respect to degree n,
where An is not 0. Conversely, Favard's theorem states that a sequence of polynomials satisfying a TTRR is a sequence of orthogonal polynomials.
Also many other special functions have TTRRs. For example, the solution to
is given by the Bessel function . TTRRs are an important tool for the numeric computation of special functions.
TTRRs are closely related to continuous fractions.
Solution
Solutions of a TTRR, like those of a linear ordinary differential equation, form a two-dimensional vector space: any solution can be written as the linear combination of any two linear independent solutions. A unique solution is specified through the initial values .
See also
Miller's recurrence algorithm
Literature
Walter Gautschi. Computational Aspects of Three-Term Recurrence Relations. SIAM Review, 9:24–80 (1967).
Walter Gautschi. Minimal Solutions of Three-Term Recurrence Relation and Orthogonal Polynomials. Mathematics of Computation, 36:547–554 (1981).
Amparo Gil, Javier Segura, and Nico M. Temme. Numerical Methods for Special Functions. siam (2007)
J. Wimp, Computation with recurrence relations, London: Pitman (1984)
References
Numerical analysis | Three-term recurrence relation | [
"Mathematics"
] | 386 | [
"Computational mathematics",
"Mathematical relations",
"Approximations",
"Numerical analysis"
] |
68,011,960 | https://en.wikipedia.org/wiki/Condensed%20mathematics | Condensed mathematics is a theory developed by Dustin Clausen and Peter Scholze which replaces a topological space by a certain sheaf of sets, in order to solve some technical problems of doing homological algebra on topological groups.
According to some, the theory aims to unify various mathematical subfields, including topology, complex geometry, and algebraic geometry.
Idea
The fundamental idea in the development of the theory is given by replacing topological spaces by condensed sets, defined below. The category of condensed sets, as well as related categories such as that of condensed abelian groups, are much better behaved than the category of topological spaces. In particular, unlike the category of topological abelian groups, the category of condensed abelian groups is an abelian category, which allows for the use of tools from homological algebra in the study of those structures.
The framework of condensed mathematics turns out to be general enough that, by considering various "spaces" with sheaves valued in condensed algebras, one might expect to be able to incorporate algebraic geometry, p-adic analytic geometry and complex analytic geometry.
Liquid vector space
In condensed mathematics, liquid vector spaces are alternatives to topological vector spaces.
Definition
A condensed set is a sheaf of sets on the site of profinite sets, with the Grothendieck topology given by finite, jointly surjective collections of maps. Similarly, a condensed group, condensed ring, etc. is defined as a sheaf of groups, rings etc. on this site.
To any topological space one can associate a condensed set, customarily denoted , which to any profinite set associates the set of continuous maps . If is a topological group or ring, then is a condensed group or ring.
History
In 2013, Bhargav Bhatt and Peter Scholze introduced a general notion of pro-étale site associated to an arbitrary scheme. In 2018, Dustin Clausen and Scholze arrived at the conclusion that the pro-étale site of a single point, which is isomorphic to the site of profinite sets introduced above, already has rich enough structure to realize large classes of topological spaces as sheaves on it. Further developments have led to a theory of condensed sets and solid abelian groups, through which one is able to incorporate non-Archimedean geometry into the theory.
In 2020 Scholze completed a proof of their results which would enable the incorporation of functional analysis as well as complex geometry into the condensed mathematics framework, using the notion of liquid vector spaces. The argument has turned out to be quite subtle, and to get rid of any doubts about the validity of the result, he asked other mathematicians to provide a formalized and verified proof. Over a 6-month period, a group led by Johan Commelin verified the central part of the proof using the proof assistant Lean. As of 14 July 2022, the proof has been completed.
Coincidentally, in 2019 Barwick and Haine introduced a similar theory of pyknotic objects. This theory is very closely related to that of condensed sets, with the main differences being set-theoretic in nature: pyknotic theory depends on a choice of Grothendieck universes, whereas condensed mathematics can be developed strictly within ZFC.
See also
Liquid vector space
Pyknotic set
References
Further reading
https://mathoverflow.net/questions/441838/condensed-vs-pyknotic-vs-consequential
https://mathoverflow.net/questions/tagged/condensed-mathematics
https://math.stackexchange.com/questions/4044728/examples-of-the-difference-between-topological-spaces-and-condensed-sets
External links
Topology
Algebraic geometry
Analytic geometry
Functional analysis | Condensed mathematics | [
"Physics",
"Mathematics"
] | 770 | [
"Functions and mappings",
"Functional analysis",
"Mathematical objects",
"Fields of abstract algebra",
"Topology",
"Space",
"Mathematical relations",
"Geometry",
"Algebraic geometry",
"Spacetime"
] |
68,013,481 | https://en.wikipedia.org/wiki/Gallium%20palladide | Gallium palladide (GaPd or PdGa) is an intermetallic combination of gallium and palladium. It has the iron monosilicide crystal structure. The compound has been suggested as an improved catalyst for hydrogenation reactions. In principle, gallium palladide can be a more selective catalyst since unlike substituted compounds, the palladium atoms are spaced out in a regular crystal structure rather than randomly.
References
Intermetallics
Palladium compounds
Gallium compounds
Iron monosilicide structure type | Gallium palladide | [
"Physics",
"Chemistry",
"Materials_science"
] | 107 | [
"Inorganic compounds",
"Metallurgy",
"Inorganic compound stubs",
"Intermetallics",
"Condensed matter physics",
"Alloys"
] |
75,190,377 | https://en.wikipedia.org/wiki/Ji-Ping%20Huang | Ji-Ping Huang (alternative spelling forms: J. P. Huang or Jiping Huang; simplified Chinese: 黄吉平；born 8 January 1977) is a Chinese theoretical physicist known for his invention of the concept of diffusion metamaterials.
Education
Huang obtained a BSc and MSc from the Department of Physics at Soochow University, China, in 1998 and 2000, respectively. He earned his PhD from the Department of Physics at the Chinese University of Hong Kong, China, in 2003.
Career
Huang was a postdoctoral researcher at the Max Planck Institute for Polymer Research, Germany, from 2003 to 2004. He then held the position of a Humboldt Research Fellow at the same institute from 2004 to 2005. In 2005, he assumed the role of a professor in the Department of Physics at Fudan University, China.
Research
His research area encompasses thermodynamics, statistical physics, and complex systems, with a particular emphasis on transformation thermotics and its extended theories, thermal metamaterials and their engineering applications, diffusionics, diffusion metamaterials, and diffusion control.
Thermal cloak, thermal metamaterials, and diffusion metamaterials
In 2008, Huang introduced the concept of a thermal cloak. During that period, he formulated the steady-state transformation thermotics theory, drawing inspiration from the transformation optics theory. He introduced the novel idea of a thermal cloak, drawing parallels with optical and electromagnetic cloaks. The term "thermal cloak" refers to a protective shell enveloping an object, enabling the unobstructed passage of heat while preserving the temperature and heat flow patterns in the surrounding background.
Subsequently, the concept of the thermal cloak underwent significant extensions. First, it evolved from the thermal cloak to thermal metamaterials. Second, it further advanced from thermal metamaterials to diffusion metamaterials. The description of diffusion metamaterials employs transformation theory and extended theories, a field referred to as diffusionics. According to the categorization of governing equations, diffusion metamaterials constitute the third branch of metamaterials to emerge, setting themselves apart from the two previously established branches: electromagnetic/optical (transverse) wave metamaterials pioneered by Sir John Brian Pendry, and other (longitudinal/transverse) wave metamaterials pioneered by Ping Sheng. Currently, these three branches represent the comprehensive framework of the thriving field of metamaterials. For diffusion metamaterials that regulate diverse diffusion processes, the characteristic length coincides with the diffusion length, which is dependent on time but independent of frequency. Conversely, for wave metamaterials that manipulate various wave propagation modes, the characteristic length corresponds to the wavelength of incident waves, which is independent of time but dependent on frequency. In essence, the characteristic length of diffusion metamaterials stands in contrast to that of wave metamaterials, exhibiting a complementary relationship.
For more in-depth information, please consult Section I.B of Ref.
References
Living people
1977 births
Theoretical physicists
Chinese physicists
Soochow University (Suzhou) alumni | Ji-Ping Huang | [
"Physics",
"Materials_science"
] | 623 | [
"Metamaterials scientists",
"Theoretical physics",
"Theoretical physicists",
"Metamaterials"
] |
75,192,485 | https://en.wikipedia.org/wiki/Amylin%20receptor | The amylin receptors (AMYRs) are heterodimers of the calcitonin receptor that are bound to by amylin with high affinity and consist of AMY1, AMY2, and AMY3. Amylin mimetics that are agonists at the amylin receptors are being developed as therapies for diabetes and obesity, and one, pramlintide, has been FDA approved. The AMY1 receptor may be activated by both amylin and the calcitonin gene-related peptide (CGRP) and could play a role in the effects of CGRP receptor antagonists developed for migraine. Dual agonists of the amylin and calcitonin receptors (DACRAs) are under development for obesity. Amylin and its receptors are believed to play a role in Alzheimer's disease.
References
Receptor heteromers | Amylin receptor | [
"Chemistry"
] | 179 | [
"Pharmacology",
"Pharmacology stubs",
"Medicinal chemistry stubs"
] |
75,192,529 | https://en.wikipedia.org/wiki/Dual%20amylin%20and%20calcitonin%20receptor%20agonists | Dual amylin and calcitonin receptor agonists (DACRAs) are a class of drugs that act as agonists at the amylin receptor and calcitonin receptor that are under development as therapies for obesity and type 2 diabetes. Examples are cagrilintide, Petrelintide, ACCG-2671 and the KBP family derived from salmon calcitonin, including KBP‐042, KBP-066A, KBP-089, and KBP-336.
References
Amylin receptor agonists
Experimental diabetes drugs | Dual amylin and calcitonin receptor agonists | [
"Chemistry"
] | 123 | [
"Pharmacology",
"Pharmacology stubs",
"Medicinal chemistry stubs"
] |
75,193,454 | https://en.wikipedia.org/wiki/Chain-melted%20state | The chain-melted state is a state of matter in which a substance, typically a metal, notably potassium, behaves both in the liquid and solid state at the same time. This is done by applying extreme pressure and temperature, causing the metal to become solid and molten simultaneously. It was confirmed to be a state of matter in 2019 by a group of researchers at the University of Edinburgh using artificial intelligence to analyse the results of subjecting potassium to high temperatures and pressure, when the potassium began exhibiting properties where it was apparently both solid and liquid. The phenomenon was observed by a group of other researchers in 2014; however, it was only thought to be a transitioning state. The chain-melted state has also been observed in other elements, such as sodium and rubidium. Some other elements, like bismuth, are also capable of being in the chain-melted state.
Properties
Substances in the chain-melted state display properties of both a solid and a liquid. The co-author of a study regarding the chain-melted state, Andreas Hermann, stated that if the matter were hypothetically to be handled by a person, it would be like holding a wet sponge that is leaking water, while the sponge itself is actually made of water. Described more formally, the potassium metal developed two internal structures, a chain-like lattice that dissolved, and a stronger Bravais lattice that remained in a solid state. This is a type of host–guest chemistry where, in this case, the host lattice of metal atoms remains solid while some of the material binds weakly and resembles a liquid.
Real world examples
Metals in Earth's inner core could possibly be in the chain-melted state, as suggested by several simulations, where metals such as titanium and iron displayed partially molten states, or quasi-solid properties. It is also possible that Earth's mantle may contain metals like potassium in the chain-melted state; however, potassium is usually not found in pure form.
These suggestions may also possibly be proven by the Kola superdeep borehole, where according to declassified documents, the rock at the bottom of the borehole was found to be in a texture between solid and liquid.
Applications
No applications have been found thus far, although physicist Andreas Hermann states that if the state of matter could be recreated in other materials, it could have many different applications.
References
Phases of matter | Chain-melted state | [
"Physics",
"Chemistry"
] | 480 | [
"Phases of matter",
"Matter"
] |
69,404,632 | https://en.wikipedia.org/wiki/Dipole%20glass | A dipole glass is an analog of a glass where the dipoles are frozen below a given freezing temperature Tf introducing randomness thus resulting in a lack of long-range ferroelectric order. A dipole glass is very similar to the concept of a spin glass where the atomic spins don't all align in the same direction (like in a ferromagnetic material) and thus result in a net-zero magnetization. The randomness of dipoles in a dipole glass creates local fields resulting in short-range order but no long-range order.
The dipole glass like state was first observed in Alkali halide crystal-type dielectrics containing dipole impurities. The dipole impurities in these materials result in off-center ions which results in anomalies in certain properties like specific heat, thermal conductivity as well as some spectroscopic properties. Other materials which show a dipolar glass phase include Rb(1-x)(NH4)xH2PO4 (RADP) and Rb(1-x)(ND4)xD2PO4 (DRADP). In materials like DRADP the dipole moment is introduced due to the deuteron O-D--O bond. Dipole glass like behavior is also observed in materials like ceramics, 3D water framework and perovskites.
Random-bond-random-field Ising model (RBRF)
The model describing the pseudo-spins (dipole moments) is given by the Hamiltonian as:
,
where is the Ising dipole moments. The refers to the random bond interactions which are described by a gaussian probability distribution with mean and variance . The second term provides a description of the interactions of the pseudo-spins in presence of random local fields where are represented by an independent gaussian distribution with zero mean and variance . The final term denotes the interaction in presence of an external electric field .
The replica method is used to obtain the glass order parameter:
.
where is the gaussian measure and under the assumption that the free energy is given by:
.
where and with .
The term is zero in case of magnetic spin glasses and with no presence of an external electric field this model reduces to the Edwards–Anderson model which is used to describe spin glasses. This model has been used to give quantitative description of DRADP type systems.
References
Electromagnetism
Electromagnetic compatibility
Types of magnets | Dipole glass | [
"Physics",
"Engineering"
] | 501 | [
"Electromagnetic compatibility",
"Electromagnetism",
"Physical phenomena",
"Radio electronics",
"Fundamental interactions",
"Electrical engineering"
] |
69,412,864 | https://en.wikipedia.org/wiki/Bottom%20simulating%20reflector | Bottom simulating reflectors (BSRs) are, on seismic reflection profiles, shallow seismic reflection events, characterized by their reflection geometry similar to seafloor bathymetry.
. They have, however, the opposite reflection polarity to the seabed reflection, and frequently intersect the primary reflections.
Cause of Reflection
Seismic reflection is a sound wave bounced back from subsurface at the interface between media with different acoustic properties (density and wave velocity). In geology, the reflections normally occur at the contacts between different rocks, for example, between layers of sedimentary rocks (stratification). The acoustic properties of sedimentary rocks are influenced by their rock materials, pore space and fluid content. Reflections are generally parallel to sedimentary layering or bedding surfaces. Fluid content in pore space, however, sometimes becomes the dominant influence factor for the acoustic properties, therefore, reflections in such case, may not be parallel to bedding surfaces. BSRs are such a case of crossing bedding surfaces.
Drilling results show BSRs approximately marking the base of gas hydrated sediments below the seafloor and the reflection is primarily caused by the free gas contained in sediments below the gas hydrated section. Gas presence in sediments is well known for its drastically lowering the sediment acoustic impedance and hence, generates high amplitude reflection at the interface of gas bearing formation. Formation of gas hydrate in deep sea sediments depends on its ambient pressure and temperature, both which are largely influenced by the depth below seafloor. This is the primary reason for BSRs grossly parallel to the seafloor reflection on seismic profiles.
Formation and Occurrence
Gas hydrates are made of molecules of natural gas, mostly biogenic or thermogenic methane, contained in solid water molecule lattice. They are formed by combining methane with water under elevated pressures and at relatively low temperatures. Hence BSRs are widespread in arctic permafrost regions and in shallow sedimentary columns below seabed in deepwater continental margins
Application
Geological hazard studies
Identification of natural gas hydrate in deep sea sediments is crucial for offshore petroleum exploration. Without adequate equipment installed prior to drilling, blowout may occur if penetrating the gas hydrate sediments. Furthermore, presence of gas hydrates in marine sediments may alter sea floor stability, and induce submarine slumping.
Alternative energy resource
Although current production technology has not been proven to be commercially viable, gas hydrates’ global occurrence in deep sea sediments, have still been considered as a potential alternative energy resource. It should be pointed out that areal distribution of BSRs alone is not adequate to properly estimate the potential reserve, since other techniques are needed to address the thickness of sedimentary columns which contain the hydrates. In addition, seismic acquisition parameters and acoustic properties of sediments with free gas in pores may all influence acoustic impedance contrast, which inevitably affects the reflection amplitude. This would cause the uncertainty of the relationship between BSRs and the presence of gas hydrate.
Climatic impact
Because gas hydrates are only stable in a range of low temperatures and moderate pressures, atmospheric and ocean warming may trigger the hydrates instability and release significant amounts of methane from both permafrost and marine sediments. This could aggravate the greenhouse effect on the earth climate.
References
Geophysics | Bottom simulating reflector | [
"Physics"
] | 648 | [
"Applied and interdisciplinary physics",
"Geophysics"
] |
73,851,558 | https://en.wikipedia.org/wiki/Lov%C3%A1sz%E2%80%93Woodall%20conjecture | In graph theory, the Lovász–Woodall conjecture is a long-standing problem on cycles in graphs. It says:
If is a -connected graph and is a set of independent edges in , then has a cycle containing , unless is odd and is an edge cut.
It was proposed independently by László Lovász in 1974 and by D. R. Woodall in 1977.
Background and motivation
Many results in graph theory, starting with Menger's theorem, guarantee the existence of paths or cycles in a -connected graph. For 2-connected graphs, Menger's theorem is equivalent to the statement that any two vertices lie on a common cycle. A theorem of G. A. Dirac generalizes this claim: if a graph is -connected for , then for every set of vertices in the graph there is a cycle that passes through all the vertices in the set.
Another corollary of Menger's theorem is that in 2-connected graphs, any two edges lie on a common cycle. The proof, however, does not generalize to the corresponding statement for edges in a -connected graph; rather, Menger's theorem can be used to show that in a -connected graph, given any 2 edges and vertices, there is a cycle passing through all of them.
There is one obstacle to the stronger claim that in a -connected graph , given any set of edges, there should be a cycle containing . Suppose that the edges in form an edge cut: the vertices of can be separated into two sets and such that the edges in all join a vertex in to a vertex in , and are the only edges to do so. Then any cycle in can only use an even number of edges of : it must cross from to and from back to an equal number of times. If is odd, this means that no cycle can contain all of .
The Lovász–Woodall conjecture states that this is the only obstacle: given any set of edges, there is a cycle containing , except in the case that is odd and is an edge cut.
Woodall proposed the conjecture as one of several possible statements that would imply a conjecture made by Claude Berge: given a -connected graph with independence number , and any subgraph of with at most edges whose components are all paths, has a Hamiltonian cycle containing . In 1982, Roland Häggkvist and Carsten Thomassen proved Berge's conjecture by proving one of the weaker statements proposed by Woodall.
Partial results
As mentioned above, the case of the Lovász–Woodall conjecture follows from Menger's theorem. The case was given as an exercise by Lovász. After the conjecture was made, it was proven for by Péter L. Erdős and E. Győri and independently by Michael V. Lomonosov., and for by Daniel P. Sanders.
Other partial progress toward the conjecture has included versions of the result with a stronger assumption on connectivity. Woodall's paper included a proof that the conclusion of the conjecture holds if is -connected, and in 1977, Thomassen proved that the conjecture holds if is -connected. In 1982, Häggkvist and Thomassen proved that the conjecture holds if is -connected.
In 2002, Ken-ichi Kawarabayashi proved that under the hypotheses of the conjecture, is either contained in a cycle of or in two disjoint cycles.
Current status
In two publications in 2002 and 2008, Kawarabayashi claimed to have a proof on the conjecture, giving an outline for the proof and leaving several steps to future publications, but the full proof has not been published since.
References
Conjectures
Unsolved problems in graph theory | Lovász–Woodall conjecture | [
"Mathematics"
] | 757 | [
"Unsolved problems in mathematics",
"Mathematical problems",
"Conjectures",
"Unsolved problems in graph theory"
] |
73,864,495 | https://en.wikipedia.org/wiki/Lidia%20Gall | Lidia Nikolaevna Gall (; ; 1 September 1934 – 21 October 2023) was a Russian mass spectrometrist, credited as one of the inventors for electrospray ionization source and high-performance mass analyzers.
Life and career
Gall studied physical electronics at Leningrad Polytechnic Institute and graduated in 1957. After graduation, she conducted research at the Leningrad Special Design Department. She received her PhD in 1973 from Leningrad Polytechnic Institute.
Gall developed ERIAD, an ionization method of liquid samples at atmospheric pressure for mass spectrometry, which is an analogue of electrospray ionization. She researched on a number of high-performance mass analyzers: static mass spectrometers, orbital trapping (Gall, L. N.; Golikov, Y. K.; Aleksandrov, M. L.; Pechalina, Y. E.; Holin, N. A. USSR Inventor’s Certificate 1247973, 1986), MTI-350 series of mass spectrometers; and worked on theoretical calculations of ion trajectories.
Gall was a professor at the Institute of Analytical Instrumentation of the Russian Academy of Sciences.
Lidia Gall died on 21 October 2023, at the age of 89.
Awards
For her contribution to mass spectrometry, Gall was awarded the Thomson Medal by the International Mass Spectrometry Foundation in 2022. In the same year, she was awarded the Manuel Riveros Medal by the Brazilian Society of Mass Spectrometry.
References
1934 births
2023 deaths
Scientists from Saint Petersburg
Peter the Great St. Petersburg Polytechnic University alumni
Russian Academy of Sciences
Recipients of the Order of the Badge of Honour
Mass spectrometrists
Russian women physicists
Soviet women physicists | Lidia Gall | [
"Physics",
"Chemistry"
] | 358 | [
"Biochemists",
"Mass spectrometry",
"Spectrum (physical sciences)",
"Mass spectrometrists"
] |
58,507,168 | https://en.wikipedia.org/wiki/C18H19NO | {{DISPLAYTITLE:C18H19NO}}
The molecular formula C18H19NO (molar mass: 265.356 g/mol) may refer to:
Nordoxepin
HP-505
Molecular formulas | C18H19NO | [
"Physics",
"Chemistry"
] | 49 | [
"Molecules",
"Set index articles on molecular formulas",
"Isomerism",
"Molecular formulas",
"Matter"
] |
58,507,200 | https://en.wikipedia.org/wiki/Gearspace | Gearspace is a website and forum dedicated to audio engineering. Gearspace is one of the largest resources for pro audio information, with over 1.6 million monthly visitors from 218 countries. Originally established in 2002 as Gearslutz, the site rebranded in March 2021.
History
In 2002, Julian Standen and Meg Lee Chin, both musicians and audio engineers, created the site, which is widely regarded as a top online resource for music production knowledge and discussion. The site has been described as the "best place … for help with your interface, DAW, signal path, or just about anything else."
In 2018, the website was ranked by Alexa.com as the 7,360th most popular website in the world. In 2020, it had over 1.6 million monthly visitors from 218 countries.
Behringer Lawsuit
In mid-2017, Music Tribe, the parent company of music equipment manufacturer Behringer, pursued legal action against synthesizer manufacturer Dave Smith Instruments (DSI) and a number of the website's forum participants, including a DSI employee, for defamation over various statements made in forum discussions that alleged that Behringer copies other companies' products and exhibits other questionable business practices.
Name change
On January 6, 2021, a forum user started an online petition at Change.org encouraging the website to change its name from Gearslutz. Site co-founder Standen announced later the same month that the site would be undergoing a name change, stating "the word-play pun in the name has gotten old and it is now time to move forward".
On March 29, 2021, Standen confirmed that the site would be renamed "Gearspace.com".
References
British music websites
Audio engineering | Gearspace | [
"Engineering"
] | 346 | [
"Electrical engineering",
"Audio engineering"
] |
58,507,539 | https://en.wikipedia.org/wiki/Feldman%E2%80%93H%C3%A1jek%20theorem | In probability theory, the Feldman–Hájek theorem or Feldman–Hájek dichotomy is a fundamental result in the theory of Gaussian measures. It states that two Gaussian measures and on a locally convex space are either equivalent measures or else mutually singular: there is no possibility of an intermediate situation in which, for example, has a density with respect to but not vice versa. In the special case that is a Hilbert space, it is possible to give an explicit description of the circumstances under which and are equivalent: writing and for the means of and and and for their covariance operators, equivalence of and holds if and only if
and have the same Cameron–Martin space ;
the difference in their means lies in this common Cameron–Martin space, i.e. ; and
the operator is a Hilbert–Schmidt operator on
A simple consequence of the Feldman–Hájek theorem is that dilating a Gaussian measure on an infinite-dimensional Hilbert space (i.e. taking for some scale factor ) always yields two mutually singular Gaussian measures, except for the trivial dilation with since is Hilbert–Schmidt only when
See also
References
Probability theorems
Theorems in measure theory | Feldman–Hájek theorem | [
"Mathematics"
] | 246 | [
"Theorems in mathematical analysis",
"Theorems in measure theory",
"Theorems in probability theory",
"Mathematical problems",
"Mathematical theorems"
] |
58,513,265 | https://en.wikipedia.org/wiki/Silica%20cycle | The silica cycle is the biogeochemical cycle in which biogenic silica is transported between the Earth's systems. Silicon is considered a bioessential element and is one of the most abundant elements on Earth. The silica cycle has significant overlap with the carbon cycle (see carbonate–silicate cycle) and plays an important role in the sequestration of carbon through continental weathering, biogenic export and burial as oozes on geologic timescales.
Overview
Silicon is the eighth most abundant element in the universe and the second most abundant element in the Earth's crust (the most abundant is oxygen). The weathering of the Earth's crust by rainwater rich in carbon dioxide is a key process in the control of atmospheric carbon dioxide. It results in the generation of silicic acid in aqueous environments. Silicic acid, Si(OH)4, is a hydrated form of silica found only as an unstable solution in water, yet it plays a central role in the silica cycle.
Silicifiers are organisms that use silicic acid to precipitate biogenic silica, SiO2. Biogenic silica, also referred to as opal, is precipitated by silicifiers as internal structures and/or external structures. Silicifiers are among the most important aquatic organisms. They include micro-organisms such as diatoms, rhizarians, silicoflagellates and several species of choanoflagellates, as well as macro-organisms such as siliceous sponges. Phototrophic silicifiers, such as diatoms, globally consume vast amounts of silicon along with nitrogen (N), phosphorus (P), and inorganic carbon (C), connecting the biogeochemistry of these elements and contributing to the sequestration of atmospheric carbon dioxide in the ocean. Heterotrophic organisms like rhizarians, choanoflagellates, and sponges produce biogenic silica independently of the photoautotrophic processing of C and N.
The diatoms dominate the fixation and export of particulate matter in the contemporary marine silica cycle. This includes the export of organic carbon from the euphotic zone to the deep ocean via the biological carbon pump. As a result, diatoms, and other silica-secreting organisms play crucial roles in the global carbon cycle by sequestering carbon in the ocean. The connection between biogenic silica and organic carbon, together with the significantly higher preservation potential of biogenic siliceous compounds compared to organic carbon makes opal accumulation records of interest in paleoceanography and paleoclimatology.
Understanding the silica cycle is important for understanding the functioning of marine food webs, biogeochemical cycles, and the biological pump. Silicic acid is delivered to the ocean through six pathways as illustrated in the diagram above, which all ultimately derive from the weathering of the Earth's crust.
Terrestrial silica cycling
Silica is an important nutrient utilized by plants, trees, and grasses in the terrestrial biosphere. Silicate is transported by rivers and can be deposited in soils in the form of various siliceous polymorphs. Plants can readily uptake silicate in the form of H4SiO4 for the formation of phytoliths. Phytoliths are tiny rigid structures found within plant cells that aid in the structural integrity of the plant. Phytoliths also serve to protect the plants from consumption by herbivores who are unable to consume and digest silica-rich plants efficiently. Silica release from phytolith degradation or dissolution is estimated to occur at a rate double that of global silicate mineral weathering. Considering biogeochemical cycling within ecosystems, the import and export of silica to and from terrestrial ecosystems is small.
Weathering
Silicate minerals are abundant in rock formations all over the planet, comprising approximately 90% of the Earth's crust. The primary source of silicate to the terrestrial biosphere is weathering. The process and rate of weathering is variable, depending on rainfall, runoff, vegetation, lithology, and topography.
Given sufficient time, rainwater can dissolve even a highly resistant silicate-based mineral such as quartz. Water breaks the bonds between atoms in the crystal:
The overall reaction for the dissolution of quartz results in silicic acid
Another example of a silicate-based mineral is enstatite (MgSiO3). Rainwater weathers this to silicic acid as follows:
MgSiO3(s) + 2CO2(g) + H2O(l) = Mg2+(aq) + 2HCO3- (aq) + SiO2(aq)
Reverse weathering
In recent years, the effect of reverse weathering on biogenic silica has been of interest in quantifying the silica cycle. During weathering, dissolved silica is delivered to oceans through glacial runoff and riverine inputs. This dissolved silica is taken up by a multitude of marine organisms, such as diatoms, and is used to create protective shells. When these organisms die, they sink through the water column. Without active production of biogenic SiO2, the mineral begins diagenesis. Conversion of this dissolved silica into authigenic silicate clays through the process of reverse weathering constitutes a removal of 20-25% of silicon input.
Reverse weathering is often found in river deltas as these systems have high sediment accumulation rates and are observed to undergo rapid diagenesis. The formation of silicate clays removes reactive silica from the pore waters of sediment, increasing the concentration of silica found in the rocks that form in these locations.
Silicate weathering also appears to be a dominant process in deeper methanogenic sediments, whereas reverse weathering is more common in surface sediments, but still occurs at a lower rate.
Sinks
The major sink of the terrestrial silica cycle is export to the ocean by rivers. Silica that is stored in plant matter or dissolved can be exported to the ocean by rivers. The rate of this transport is approximately 6 Tmol Si yr−1. This is the major sink of the terrestrial silica cycle, as well as the largest source of the marine silica cycle. A minor sink for terrestrial silica is silicate that is deposited in terrestrial sediments and eventually exported to the Earth's crust.
Marine inputs
Riverine
As of 2021, the best estimate of the total riverine input of silicic acid is 6.2 (±1.8) Tmol Si yr−1. This is based on data representing 60% of the world river discharge and a discharge-weighted average silicic acid riverine concentration of 158 μM−Si. However, silicic acid is not the only way silicon can be transferred from terrestrial to riverine systems, since particulate silicon can also be mobilised in crystallised or amorphous forms. According to Saccone and others in 2007, the term "amorphous silica" includes biogenic silica (from phytoliths, freshwater diatoms, sponge spicules), altered biogenic silica, and pedogenic silicates, the three of which can have similar high solubilities and reactivities. Delivery of amorphous silica to the fluvial system has been reviewed by Frings and others in 2016, who suggested a value of 1.9(±1.0) Tmol Si yr−1. Therefore, the total riverine input is 8.1(±2.0) Tmol Si yr−1.
Aeolian
No progress has been made regarding aeolian dust deposition into the ocean and subsequent release of silicic acid via dust dissolution in seawater since 2013, when Tréguer and De La Rocha summed the flux of particulate dissolvable silica and wet deposition of silicic acid through precipitation. Thus, the best estimate for the aeolian flux of silicic acid, FA, remains 0.5(±0.5) Tmol Si yr−1.
Sandy beaches
A 2019 study has proposed that, in the surf zone of beaches, wave action disturbed abiotic sand grains and dissolved them over time. To test this, the researchers placed sand samples in closed containers with different kinds of water and rotated the containers to simulate wave action. They discovered that the higher the rock/water ratio within the container, and the faster the container spun, the more silica dissolved into solution. After analyzing and upscaling their results, they estimated that anywhere from 3.2 ± 1.0 – 5.0 ± 2.0 Tmol Si yr−1 of lithogenic DSi could enter the ocean from sandy beaches, a massive increase from a previous estimate of 0.3 Tmol Si yr−1. If confirmed, this represents a significant input of dissolved LSi that was previously ignored.
Marine silica cycling
Siliceous organisms in the ocean, such as diatoms and radiolaria, are the primary sink of dissolved silicic acid into opal silica. Only 3% of the Si molecules dissolved in the ocean are exported and permanently deposited in marine sediments on the seafloor each year, demonstrating that silicon recycling is a dominant process in the oceans. This rapid recycling is dependent on the dissolution of silica in organic matter in the water column, followed by biological uptake in the photic zone. The estimated residence time of the silica biological reservoir is about 400 years. Opal silica is predominately undersaturated in the world's oceans. This undersaturation promotes rapid dissolution as a result of constant recycling and long residence times. The estimated turnover time of Si is 1.5x104 years. The total net inputs and outputs of silica in the ocean are 9.4 ± 4.7 Tmol Si yr−1 and 9.9 ± 7.3 Tmol Si yr−1, respectively.
Biogenic silica production in the photic zone is estimated to be 240 ± 40 Tmol Si year −1. Dissolution in the surface removes roughly 135 Tmol Si year−1, while the remaining Si is exported to the deep ocean within sinking particles. In the deep ocean, another 26.2 Tmol Si Year−1 is dissolved before being deposited to the sediments as opal rain. Over 90% of the silica here is dissolved, recycled and eventually upwelled for use again in the euphotic zone.
Sources
The major sources of marine silica include rivers, groundwater flux, seafloor weathering inputs, hydrothermal vents, and atmospheric deposition (aeolian flux). Rivers are by far the largest source of silica to the marine environment, accounting for up to 90% of all the silica delivered to the ocean. A source of silica to the marine biological silica cycle is silica that has been recycled by upwelling from the deep ocean and seafloor.
The diagram on low-temperature processes shows how these can control the dissolution of (either amorphous or crystallized) siliceous minerals in seawater in and to the coastal zone and in the deep ocean, feeding submarine groundwater (FGW) and dissolved silicon in seawater and sediments (FW). These processes correspond to both low and medium energy flux dissipated per volume of a given siliceous particle in the coastal zone, in the continental margins, and in the abysses and to high-energy flux dissipated in the surf zone.
Sinks
Rapid dissolution in the surface removes roughly 135 Tmol opal Si year−1, converting it back to soluble silicic acid that can be used again for biomineralization. The remaining opal silica is exported to the deep ocean in sinking particles. In the deep ocean, another 26.2 Tmol Si Year−1 is dissolved before being deposited to the sediments as opal silica. At the sediment water interface, over 90% of the silica is recycled and upwelled for use again in the photic zone. Biogenic silica production in the photic zone is estimated to be 240 ± 40 Tmol si year −1. The residence time on a biological timescale is estimated to be about 400 years, with each molecule of silica recycled 25 times before sediment burial.
Deep seafloor deposition is the largest long-term sink of the marine silica cycle (6.3 ± 3.6 Tmol Si year−1), and is roughly balanced by the sources of silica to the ocean. The silica deposited in the deep ocean is primarily in the form of siliceous ooze. When opal silica accumulates faster than it dissolves, it is buried and can provide a diagenetic environment for marine chert formation. The processes leading to chert formation have been observed in the Southern Ocean, where siliceous ooze accumulation is the fastest. Chert formation however can take tens of millions of years. Skeleton fragments from siliceous organisms are subject to recrystallization and cementation. Chert is the main fate of buried siliceous ooze and permanently removes silica from the oceanic silica cycle.
The siliceous ooze is eventually subducted under the crust and metamorphosed in the upper mantle. Under the mantle, silicate minerals are formed in oozes and eventually uplifted to the surface. At the surface, silica can enter the cycle again through weathering. This process can take tens of millions of years. The only other major sink of silica in the ocean is burial along continental margins (3.6 ± 3.7 Tmol Si year −1), primarily in the form of siliceous sponges. Due to the high degrees of uncertainty in source and sink estimations, it's difficult to conclude if the marine silica cycle is in equilibrium. The residence time of silica in the oceans is estimated to be about 10,000 years. Silica can also be removed from the cycle by becoming chert and being permanently buried.
Anthropogenic influences
The rise in agriculture of the past 400 years has increased the exposure rocks and soils, which has resulted in increased rates of silicate weathering. In turn, the leaching of amorphous silica stocks from soils has also increased, delivering higher concentrations of dissolved silica in rivers. Conversely, increased damming has led to a reduction in silica supply to the ocean due to uptake by freshwater diatoms behind dams. The dominance of non-siliceous phytoplankton due to anthropogenic nitrogen and phosphorus loading and enhanced silica dissolution in warmer waters has the potential to limit silicon ocean sediment export in the future.
In 2019 a group of scientists suggested acidification is reducing diatom silica production in the Southern Ocean.
Role in climate regulation
The silica cycle plays an important role in long term global climate regulation. The global silica cycle also has large effects on the global carbon cycle through the carbonate-silicate cycle. The process of silicate mineral weathering transfers atmospheric CO2 to the hydrologic cycle through the chemical reaction displayed above. Over geologic timescales, the rates of weathering change due to tectonic activity. During a time of high uplift rate, silicate weathering increases which results in high CO2 uptake rates, offsetting increased volcanic CO2 emissions associated with the geologic activity. This balance of weathering and volcanoes is part of what controls the greenhouse effect and ocean pH over geologic time scales.
Biogenic silica accumulation on the sea floor contains lot of information about where in the ocean export production has occurred on time scales ranging from hundreds to millions of years. For this reason, opal deposition records provide valuable information regarding large-scale oceanographic reorganizations in the geological past, as well as paleoproductivity. The mean oceanic residence time for silicate is approximately 10,000–15,000 yr. This relative short residence time, makes oceanic silicate concentrations and fluxes sensitive to glacial/interglacial perturbations, and thus an excellent proxy for evaluating climate changes.
Isotope ratios of oxygen (O18:O16) and silicon (Si30:Si28) are analysed from biogenic silica preserved in lake and marine sediments to derive records of past climate change and nutrient cycling (De La Rocha, 2006; Leng and Barker, 2006). This is a particularly valuable approach considering the role of diatoms in global carbon cycling. In addition, isotope analyses from BSi are useful for tracing past climate changes in regions such as in the Southern Ocean, where few biogenic carbonates are preserved.
The silicon isotope compositions in fossil sponge spicules (δ30Si) are being increasingly often used to estimate the level of silicic acid in marine settings throughout the geological history, which enables the reconstruction of past silica cycles.
See also
Carbon cycle
Lithogenic silica
Oxygen cycle
Silicification
Silicon isotope biogeochemistry
References
Biogeochemical cycle
Silicon | Silica cycle | [
"Chemistry"
] | 3,564 | [
"Biogeochemical cycle",
"Biogeochemistry"
] |
65,266,320 | https://en.wikipedia.org/wiki/Fertiliser%20use%20in%20Nepal | Agriculture is the main GDP contributor for the economy of Nepal and fertilisers play a vital role. The annual average fertiliser requirement in Nepal to replenish the soil nutrition is 310 kg per hectare but only 29 kg of fertiliser is added to the soil. Fifty per cent of nutrient loss from the soil occurs during the early monsoon.
The use of fertiliser is relatively new to Nepal. Up to the 1950s, chemical fertilisers were not used in Nepal and all fertilizers were organic, produced locally. Currently, both organic and chemical fertilisers are used.
Organic fertilisers
Organic fertilisers are produced locally by recycling agricultural waste and animal waste. In hilly farms, compost and farm yard manure are the traditional source of fertiliser.
Government supports the use of organic fertiliser. It has adopted a policy to promote organic fertilisers. The Ministry of Agriculture provides a subsidy to the farmers purchasing the organic fertilisers at a rate of NPR 10 per kg or 50% of the sales price whichever is low. Similarly, the organic fertilisers production plant is also subsidised by providing 50% of the cost.
There are 25 centres that produce organic fertilisers with the total annual capacity of 100,600 MT (2015 AD). Some of the major ones are listed in the table. Besides, some portion of inorganic fertilizer is imported from abroad.
Chemical fertilisers
The use of chemical fertiliser is relatively new in Nepal. In the 50s, a small quantity of ammonium sulphate used to be imported from India. It was followed by importing from Russia by the National Trading Limited (a government agency) up to the mid-sixties To facilitate the import and distribution of fertilisers, Agriculture Inputs Corporation (AIC) was established under the Ministry of Agriculture in 1966.
In 1974, the government subsidized the fertiliser to some selected high hills and mid-hills districts due to price rise in the international market. However, the local price was still set 15-20% higher than the neighbouring country (India) to discourage outflow of fertilisers from Nepal. Germany, Canada, Japan and Finland in the late 60s started providing chemical fertiliser to Nepal in the form of aid. However, this did not continue long. By the 1990s only a few countries were providing the fertilizer aid.
In 1997, the government started deregulating the subsidy on fertilisers. By 1999, the subsidy was completely removed from all kinds of fertilisers. This removed the monopoly of AIC and the private sector started to compete in the fertiliser market. To institutionalize the deregulation policy, and to regulate the business under the policy, the government promulgated Fertiliser Control Order in 1999. In 2002, a National Fertiliser Policy was formulated and AIC was divided into two new organization viz. Agriculture Inputs Company Limited (AICL) responsible for fertiliser business and 2) National Seed Company Limited (NSCL). The fertiliser policy was considered to focus on supplying high-quality and affordable fertiliser to farmers.
In November 2008 the government again started to subsidise fertilisers (both organic and chemical) and it was endorsed on 25 March 2009.
Production and import
As of 2020, chemical fertilisers are not produced in Nepal. They are imported mostly from or through India. In the 1980s, there were plans to build the plant and feasibility study were carried out, but the plans have not been implemented. The import of chemical fertilisers (in MT) is shown in the bar-chart.
Types of chemical fertilisers
Mainly seven types of chemical fertilisers are used in Nepal. These are Urea, Diammonium Phosphate (DAP), Murate of Potash (MOP), Ammonium Sulphate (AS), Single Super Phosphate (SSP), Ammonium Phosphate Sulphate (APS) and NPK. The use of chemical fertilisers has an increaseing trend. Among them, Urea and DAP is the most used ones.
Quality
The fertiliser supplied by informal and illegal sources (mainly from India) is considered to have poor quality. Some private traders were found to repack the low-quality imported fertilisers into popular brands.
See also
Agriculture in Nepal
References
Agriculture in Nepal
Fertilizers | Fertiliser use in Nepal | [
"Chemistry"
] | 937 | [
"Fertilizers",
"Soil chemistry"
] |
65,266,916 | https://en.wikipedia.org/wiki/Lark%20Health | Lark Health is an American digital health company based in Mountain View, California. It provides a 24/7 nursing platform for chronic conditions, powered by artificial intelligence (AI) and has a text-messaging type interface. Lark also provides AI nurses for type 2 diabetes care, hypertension care, tobacco cessation, stress management, obesity, and more for 1.5 million patients.
Lark is notable for being preloaded on all Samsung Galaxy S5 phones by 2014.
History
Lark was founded by Julia Hu and Jeff Zira. It first produced a sleep health monitor worn on a person's wrist. It was designed to wake up the individual wearing the device without disturbing anyone else who might be sleeping nearby. The product was soon sold in all Apple stores globally.
Lark eventually focused more on artificial intelligence and less on hardware. By 2014, Lark was preloaded on all Samsung Galaxy S5 phones.
The Lark apps focus on common chronic conditions such as obesity, diabetes prevention, diabetes, and hypertension. Lark Diabetes Prevention Program (DPP) is officially recognized by the Centers for Disease Control and Prevention (CDC) as an online DPP.
Lark's efficacy has been evaluated by a study published in the Journal of Medical Internet Research Diabetes,
Products and services
Lark has specialized health plans focusing on patients with diabetes, hypertension, prediabetes or at high risk for type 2 diabetes, and overall health. Lark's services are delivered and automatically syncs with certain bluetooth-enabled health monitors devices such as home blood pressure monitors, glucometers, activity trackers, and body weight scales. Some programs allow for both the app and one or more connected devices to be used.
References
External links
Companies based in Mountain View, California
Health informatics
Telehealth | Lark Health | [
"Biology"
] | 360 | [
"Health informatics",
"Medical technology"
] |
65,269,943 | https://en.wikipedia.org/wiki/Animal%20models%20of%20Parkinson%27s%20disease | Animal models of Parkinson's disease are essential in the research field and widely used to study Parkinson's disease. Parkinson's disease is a neurodegenerative disorder, characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The loss of the dopamine neurons in the brain, results in motor dysfunction, ultimately causing the four cardinal symptoms of PD: tremor, rigidity, postural instability, and bradykinesia. It is the second most prevalent neurodegenerative disease, following Alzheimer's disease. It is estimated that nearly one million people could be living with PD in the United States.
There are a variety of models that can be utilized to be able to address important aspects of Parkinson's disease. Researchers can consider disease progression, cell death, behavioral characteristics, and more PD phenotypes. Parkinson's disease animal models are divided into two categories: neurotoxin models and genetic models. Neurotoxin models include chemically induced toxicity in the brain; whereas, genetic models include genes that are mutated and induce PD phenotypes.
Neurotoxin models
6-OHDA
6-Hydroxydopamine, better known as 6-OHDA, is a widely used neurotoxin in PD models. It is structurally similar to dopamine, only differentiating by an additional hydroxyl group in the 6-OHDA structure (Figure 1 & Figure 2). Through scientific studies, this neurotoxin has been used in rodents (rats and mice), guinea pigs, cats, dogs, and monkeys. 6-OHDA does not cross the blood-brain-barrier (BBB) making the chemical more selective for dopaminergic neurons. This model requires injecting the 6-OHDA directly into the nigrostriatal pathway, targeting the dopamine transporter (DAT).This can be performed through stereotaxic injections (both unilateral and bilateral are experimentally permissible) and will eventually cause loss of dopamine neurons in the SNpc and loss of dopamine terminals in the striatum since the nigrostriatal pathway is being affected. The neurotoxin can be injected has been shown to be injected into the striatum and the substantia nigra. However, injections into the SNpc is estimated to degrade about 60% of tyrosine hydroxylase (TH+) neurons as well as loss of TH positive terminals in the striatum. A limitation to using 6-OHDA is that the potency of the neurotoxin causes rapid apoptosis, which makes it difficult to study Parkinson's disease progression.
The mechanism of action of 6-OHDA occurs through the aggregation of toxins and the conversion into catecholaminergic neurons. Since the structures of both dopamine and 6-OHDA are similar, the dopamine transporter takes up the 6-OHDA and induces toxicity. This toxicity emerges from the production of free radicals from the additional hydroxyl group in the neurotoxin's structure. There is also oxidative stress occurring mediated through the inhibition of the cell's mitochondrial complex I, producing ROS (reactive oxygen species), which causes a decrease or loss in respiratory activity. In addition, there is also the proposed mechanism of oxidative stress inducing neuroinflammation (Figure 3).
MPTP
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a widely used neurotoxin in Parkinson's disease research (Figure 4). In contrast to 6-OHDA, MPTP crosses the BBB which making the neurotoxin even more selective for dopaminergic neurons. Due to the ability to cross the blood-brain-barrier, MPTP is administered peripherally, subcutaneously. This neurotoxin is known to replicate oxidative stress, ROS, energy failure, and inflammation; which are all hallmarks in Parkinson's disease. However, it does not produce Lewy body pathology. The mechanism of action of MPTP is due to its conversion to 1-methyl-4-phenylpyridinium (MPP+) caused by the interaction of MPTP with monoamine oxidase B (MAO-B). (Figure5). MPTP enters astrocytes and is metabolized to MPP+ before being released. Once released into the extracellular space, MPP+ is taken up into the neuron by DAT and is stored in vesicles by the up take of vesicular monoamine transporter (VMAT2). In the neuron, MPP+ inhibits the function of complex 1 of electron transport chain, which decreases ATP production and releases ROS.
Herbicides (rotenone and paraquat)
Rotenone is a chemical compound (Figure 6) that can be derived from the plants: Derris elliptica, D mallaccensis, Lonchocarpus utilis, and L urucu. It is a known neurotoxin that is selective to dopaminergic neurons when administered to rodents via stereotaxic injections. However, it targets the striatum and not the substantia nigra. Moreover, rotenone can cross the BBB and spread through the central nervous system. Since rotenone can cross the blood-brain-barrier, it can be administered peripherally as well. Although, peripheral injections can lead to system toxicity. The exact mechanism of action of rotenone is still unclear, but one aspect that is known is that the herbicide accumulates and clusters in the neuron in organelles like the mitochondria, which disrupts the oxidative phosphorylation mechanism in the cell and inhibits the respiratory chain complex I. Limitations of using rotenone is the lack of reproducibility of results throughout experiments and the quantity of aggregates and lesion. In addition, there is an elevated mortality rate in the animals induced with rotenone.Paraquat
1,1'-dimethyl-4-4'-bipyridinium dichloride (Paraquat) is a nonselective herbicide (Figure 7). Human exposure to this chemical is highly toxic. Its chemical structure is very similar to MPP+, therefore, it was thought to act as a neurotoxin as well. Paraquat has the capability to cross the BBB and is selective to dopamine neurons when injected via stereotaxic injections in the brain. Similar to rotenone, paraquat can also be administered peripherally, however, this can lead to systemic toxicity. It is found to decrease dopamine concentration and produce parkinsonian phenotypes (both physically and behaviorally). Mechanistically, paraquat targets the dopamine transporter to be transported into dopaminergic neurons and ends up in the striatum. It lingers in the midbrain for approximately four weeks. However, since it is capable to cross the BBB, the toxin can be found in other regions such as the pineal gland, cerebral ventricles, olfactory bulb, hypothalamus, and the area postrema. Several studies have demonstrated the relationship between paraquat and oxidative stress indicating that this may be another mechanism of paraquat induced neurodegeneration. In addition, the herbicide is accumulated in the lungs and kidney, resulting high toxicity; as well, as death.
Genetic models
alpha-synuclein
Alpha-synuclein (α-synuclein) is an endogenous protein that is encoded by the SNCA gene and known as the pathological hallmark of Parkinson's disease. It is found in distinct regions of the body, but in PD, alpha-synuclein accumulation in the brain is of main importance. This protein misfolds and accumulates creating insoluble aggregates in the brain known as Lewy bodies (found in the soma) and Lewy neurites (found in the neuropil)(Figure 8). This pathology is well known as synucleinopathies. The inclusions/aggregates lead to dopamine neuronal depletion in the SNpc as well as dopamine terminal loss in the striatum from the projection of SNpc neurons through the nigrostriatal pathway. In addition, studies have shown that there is progressive formation of α-synuclein inclusions in distinct brain areas like the hippocampus, the cortex, and amygdala. However, according to the Braak staging, α-synuclein aggregates initially develop in the olfactory bulb and the lower brainstem; propagating towards the higher brainstem and the substantia nigra; reaching the mesocortex and the thalamus; and, ultimately covering the neocortex. Braak staging is a widely used method to measure the stage of pathology (stage 1 being the lowest level of pathology and stage 4 being the highest) of Parkinson's disease; used both in basic research and clinically.
There are proposed mechanisms by which α-synuclein acts, in terms of pathology, one being the inhibition of the autophagy-lysosome pathway. This pathway is highly important as it is responsible for intracellular degradation. Therefore, as α-synuclein fibrils inhibits the function of autophagy impairing the removal of aggregated protein, there is the production of more α-synuclein inclusions since it cannot be degraded. Other pathological mechanisms include the oxidative stress, dysfunction of the mitochondria, and neuroinflammation.
Alpha-synuclein preformed fibrils
The pre-formed fibril model was developed as a way to study the propagation of α-synuclein. This model consists of injecting extracellular α-synuclein fibrils via stereotaxic injections to induce intracellular α-synuclein aggregation. Consequently, this will induce parkinsonian phenotypes.
The α-synuclein pre-formed fibrils (PFFs) are made in vitro utilizing recombinant α-synuclein monomers which will aggregate and form fibrils. The fibrils can then be manipulated to form different conformations like being sonicated to form short fibrils or form heterogenous mixes of fibrils with oligomers and monomers. Once the fibrils are generated, they can be injected into the brain, where hyperphosphorylation of endogenous α- synuclein (pα-syn) will occur and induce aggregation, forming cytoplasmic Lewy body and Lewy neurite inclusions. This method can be injected in brain regions like the SNpc and the cortex, however, the most common region to inject PFFs is into the striatum. Moreover, the spread of α-synuclein PFFs to brain regions occur through the uptake of the fibrils by dopamine neuron terminals that make their way up to the soma in the SNpc (Figure 9). A limitation to the pre-formed fibril model is that although it is a widely used model, it lacks overt neurodegeneration.
Alpha-synuclein viral vector mediated overexpression
The different synuclein models that have been widely used have also faced challenges of targeting the fibrils to the SNpc, thus, lacking abundant neurodegeneration. Through the viral vector-mediated delivery of alpha-synuclein, the vectors can target the dopaminergic neurons directly. Vectors like lentivirus and adeno-associated virus have been used in this method. This method allows for targeting of nigrostriatal neurons, where α-synuclein protein can be overexpressed and there can be a production of alpha-synuclein- leading to accumulated phosphorylated α-synuclein in the SNpc, and overt dopaminergic neurodegeneration, including loss of dopamine terminals in the striatum. Moreover, the use of the viral vectors, allows for a longer lasting expression of α-synuclein. Delivery of the α-synuclein through the viral vector is conducted through stereotaxic injections into the brain similar to the injections of α-synuclein pre-formed fibrils. In addition, the optimal pα-synuclein expression in this method is around week 4 post-injection.
In contrast to the PFF model, the α-synuclein inclusions are nuclear and demonstrates an anterograde transport in which the pα-syn travels from the soma of the neuron to the terminals, where expression are maintained within medium spiny neurons.
LRRK-2
Leucine-rich repeat kinase (LRRK2) is a protein, that when mutated, is implicated in PD pathology. It is associated with both familial (most prevalent causes of familial PD) and sporadic PD. There are key mutations of the LRRK2 protein, like G2019s which is the most common missense mutation and R1441C/G. Most studies have been conducted on C.elegans, Drosophila, and rodents (mice and rats). It is still unclear as to the mechanism of action of LRRK2, however, the kinase activity is of importance and its ability to function as a GTPase is also a factor in its neurotoxicity. Unlike the other Parkinson's disease genetic models, LRRK2 can exhibit both Lewy body pathology and tau pathology, but it is also unclear as to its relationship. On the other hand, results from LRRK2 mutation studies have demonstrated deficits in dopamine transmission, as well as axonal degeneration. Similar to other genetic animal models, LRRK2 mutations also produce dopaminergic neuron loss in the substantia nigra and Lewy body pathology. LRRK2 knockout models have also been studied and show the increase of protein aggregation and accumulation which also includes α-synuclein; but, it does not decrease degeneration of nigrostriatal neurons. A limitation to the LRRK2 animal model is that although there is a loss in dopaminergic neurons, neurodegeneration is very low.
PINK1
Pten-Induced Kinase 1 (PINK1) mutations are associated with autosomal recessive parkinsonism. It is a neuroprotective kinase predominantly found in the mitochondria and cytoplasmic areas of the cell. PINK1 is also a serine/threonine protein kinase and is associated with the mitochondria. PINK1, in research studies, is generally used as a knockout (KO) model. The mechanism of action of this gene involves the recruitment of the Parkin gene from the cytoplasm to the mitochondria. Once recruited, this leads to augmented ubiquitin activity and therefore induces mitophagy. Mitophagy is a pathway in which the mitochondria is degraded. Both PINK1 and Parkin share functions in the same pathway, therefore, their activities are similar. Some studies have demonstrated expression of the PINK1 mutation in rodents, inducing dopaminergic neuron loss and motor defects. Other studies are more associated with PINK1 KO. PINK1 knockouts show reduction in dopamine levels in the striatum. They express very low levels of dopaminergic neuron loss and do not present the formation of Lewy bodies. However, the KO models demonstrate mitochondria dysfunction and oxidative stress. On the other hand, studies are demonstrating loss of dopaminergic neurons and showing motor deficits in rats.
DJ-1
Protein Deglycase (DJ-1) mutations are associated with recessive forms of familial parkinsonism. It is a molecular chaperone that undergoes reduction-oxidation (redox) reaction and plays a major role in the inhibition of alpha synuclein aggregate formation. It is believed that this is possible due to DJ-1 antioxidant properties, therefore, inhibiting oxidative stress in the cell which is what induces pathological phenotypes. To demonstrate the proposed neuroprotective properties of DJ-1, knockout studies of this gene have shown motor deficits in mice, less dopamine levels in the striatum, and no evidence of Lewy body aggregation. In addition to the knockout model, DJ-1 is very sensitive to neurotoxins (MPTP, 6-OHDA, etc.). Studies have demonstrated that under those conditions, DJ-1 expresses dopaminergic neuron loss in the SNpc and motor defects.
Summary
Table 1 represents a summary of the PD animal models and details regarding their mechanisms of action, pathogenesis, and limitations.
References
Parkinson's disease
Animal models | Animal models of Parkinson's disease | [
"Biology"
] | 3,614 | [
"Model organisms",
"Animal models"
] |
70,904,996 | https://en.wikipedia.org/wiki/Rio%20scale | The Rio scale was proposed in 2000 as a means of quantifying the significance of a SETI detection. The scale was designed by Iván Almár and Jill Tarter to help tell policy-makers how likely, from 0 to 10, it is that an extraterrestrial radio signal has been produced by an intelligent civilization.
The scale is inspired by the Torino scale, which is used to determine the impact risk associated with near-Earth objects. Just as the Torino scale takes into account how significant an object's impact on the planet would be, the Rio scale takes into account how much a public announcement of the discovery of extraterrestrial intelligence would probably impact society.
The IAA SETI Permanent Study Group officially adopted the Rio scale as a way of bringing perspective to claims of extraterrestrial intelligence (ETI) detection, and as an acknowledgement that even false ETI detections may have disastrous consequences.
The scale was modified in 2011 to include a consideration of whether contact was achieved through an interstellar message or a physical extraterrestrial artifact, including all indications of intelligent extraterrestrial life such as technosignatures. A 2.0 version of the scale was proposed in 2018.
Calculation
In its 2.0 version, the Rio Scale, R, of a given event is calculated as the product of two terms.
The first term, Q, is the significance of the consequences of an event. It is determined considering three factors: the estimated distance to the source of the signal (a value between 0 and 4), the prospects for communicating with the source (a value between 0 and 4) and how likely is that the sender is aware of humanity (a value between -1 and 2). The value of each factor is determined by answering a question and Q is calculated by summing the three values.
The second term, δ, is the probability that the event actually occurred. Its value is determined by first calculating a term, J, based on three factors: the probability that the signal is real, the probability that it is not instrumental, and the probability that it is not natural or human-made. The values for these factors are determined by answering a questionnaire and J is calculated by summing them. δ is then calculated using the formula .
The final R value, going from 0 to 10, is the likelihood that the observed event was produced by an intelligent civilization.
Rating scale
See also
Quiet and loud aliens
San Marino Scale
References
Search for extraterrestrial intelligence
Extraterrestrial life
Interstellar messages | Rio scale | [
"Astronomy",
"Biology"
] | 516 | [
"Astrobiology stubs",
"Hypothetical life forms",
"Extraterrestrial life",
"Astronomy stubs",
"Astronomical controversies",
"Biological hypotheses"
] |
70,911,322 | https://en.wikipedia.org/wiki/Rubicon%20homology%20domain | The Rubicon homology domain (also known as RH domain) is an evolutionarily conserved protein domain of approximately 250 amino acids that mediates protein–protein interaction. RH domains are present in several human proteins involved in regulation of autophagy and endosomal trafficking. While not all RH domains have been characterized, those of human Rubicon and PLEKHM1 mediate interaction with the small GTPase Rab7, which is found on late endosomes and autophagosomes.
RH domains contain 16 conserved cysteine and histidine residues that bind zinc atoms and form at least 4 zinc finger motifs. Amino acid residues toward the C-terminus of the RH domain of Rubicon have been shown to be essential for interaction with Rab7.
Structure
The 3D atomic structure of the Rubicon RH domain in complex with Rab7 has been determined by X-ray crystallography. The structure of the RH domain has an "L" shape, with the base of the "L" making contact with the switch regions of Rab7. The structure is predominantly alpha helical, with short beta strand regions present in the vicinity of zinc finger motifs. The N-terminal region of the Rubicon RH domain resembles a FYVE domain, however the basic residues required for canonical FYVE domain binding of PI3P are not present.
Proteins containing an RH domain
RH domains are found in a number of proteins, including (in humans):
Rubicon, the defining member of the RH domain-containing family of proteins and a negative regulator of autophagy
PLEKHM1, a protein implicated in osteopetrosis
Pacer, a positive regulator of autophagy
DEF8, a regulator of lysosome peripheral distribution
PLEKHM3, involved in skeletal muscle differentiation
References
Protein domains
Protein structure | Rubicon homology domain | [
"Chemistry",
"Biology"
] | 384 | [
"Protein structure",
"Protein domains",
"Structural biology",
"Protein classification"
] |
61,509,971 | https://en.wikipedia.org/wiki/Cromer%20cycle | The Cromer cycle is a thermodynamic cycle that uses a desiccant to interact with higher relative humidity air leaving a cold surface. When a system is taken through a series of different states and finally returned to its initial state, a thermodynamic cycle is said to have occurred. The desiccant absorbs moisture from the air leaving the cold surface, releasing heat and drying the air, which can be used in a process requiring dry air. The desiccant is then dried by an air stream at a lower relative humidity, where the desiccant gives up its moisture by evaporation, increasing the air's relative humidity and cooling it. This cooler, moister air can then be presented to the same cold surface as above to take it below its dew point and dry it further, or it can be expunged from the system.
The desiccant undergoes a reversible process whereby in the first part of the cycle, it absorbs or adsorbs moisture from air leaving a cold surface, releasing heat, and then in the second part of the cycle evaporates moisture, absorbing heat and returning the desiccant to its original state to complete the cycle again. The result of the Cromer cycle is that the process air leaving the cycle is dehumidified further (higher latent ratio) than it would be leaving the cold surface without the cycle. The Cromer cycle concept was originally patented in the mid-1980's. Those patents have expired and thus the cycle is free for anyone to use. The cycle was first publicized in 1997 by Popular Mechanics in its Tech Update section.
Psychrometrics
The Cromer cycle is primarily used in air conditioning and drying applications. The cold surface portion of the cycle is most often a result of a reversed Carnot or refrigeration cycle. For the Cromer cycle to operate, a desiccant must be exposed to two air streams, one with higher humidity from a cold surface, and one with lower humidity to dry it. This is most easily accomplished by moving the desiccant. Any cycling mechanism can be used, such as pumping a liquid desiccant, however an easy mechanical application is a rotating wheel, loaded with desiccant, through which the different air streams pass. This is shown in Figure 1 where a desiccant wheel has been applied to a standard air conditioning set-up.
The psychrometric process of the air passing through the system with four state points is shown on the psychrometric chart of Figure 2 as 1, 2, 3 and 4. The state points of the air are also depicted in Figure 1. In this application, the air returning from the space, typically around 50% relative humidity (RH), is presented to the desiccant wheel and dries the desiccant. The air picks up moisture and cools in process 1 to 2. The moist air is now presented to the cooling surface (cooling coil of the air conditioner), which cools it below its dew point and dries the air in process 2 to 3. This represents the work done by the cold coil. In the meantime, the dried desiccant from below is rotated to the upper air stream. The saturated air leaving the coil, typically 93–98% RH, is presented to the desiccant at 3, where the air is dried further in process 3 to 4, where it is presented to the space as supply air. The desiccant, now loaded with moisture, rotates to the return air, where the cycle repeats.
Typical cooling and drying by the cold coil without the Cromer cycle is depicted on the psychrometric chart and is also shown in Figure 2. State point 1 is the air that returns from the space to the system (return air). For a typical air conditioning system, this air at state point 1 enters the cooling coil and leaves at about state point 4' after cooling and drying. State point 4' represents the temperature and moisture content of the air that leaves the typical unit, about and 95–98% RH.
Changes to a standard AC system by the Cromer cycle
The psychrometric chart depicts the changes of the cycle to the standard air conditioning cycle. First, the end state point 4 for air from the wheel represents a latent ratio increase (moisture removal) to about 45%, as opposed to the 25% of the typical coil shown. Secondly, the air quality delivered by the cycle is much dryer, about 55% RH (state point 4), rather than 98% with the standard coil (state point 4'). Third, this is accomplished with a higher average evaporator temperature. Compare the midpoint of the evaporator's temperature, line 1 to 4’, to the midpoint of the Cromer cycle's evaporator's temperature, line 2 to 3. These lines represent the work done by the coil on the air stream (its change in enthalpy). This is significant because, given a constant condenser temperature and equivalent change in enthalpy, the higher the evaporator coil temperature, the more efficient is the Carnot refrigeration cycle and the greater the energy efficiency a particular system can deliver.
Common dehumidification strategies include: reheating (electric or hot-gas bypass), where sensible heat is added to the air leaving the equipment; recuperative heat (run-around coils or heat pipes), where sensible heat is transferred from the return air to the supply air; or the Cromer cycle, where the latent heat of moisture sorption and evaporation is transferred from the return air to the supply air. These various strategies were compared in an ASHRAE Journal article that found that "the Cromer cycle produces similar enhanced dehumidification performance as is obtained with recuperative configurations."
Desiccants used
To operate in this cycle, the desiccant is required to absorb moisture from air coming off of the coil that is colder and about 98% RH and to desorb moisture to air that is warmer and at a lower RH. The desiccant is regenerated by the vapor pressure differential inherent in the RH differences rather than heat or temperature difference. Desiccants that have a moisture sorption isotherm of the type shown in Figure 3 (Type III) are common, such as many formulations of silica gel. Type III desiccants absorb little moisture below 70% RH but many will take up more than their own weight in water from the air when presented with over 90% RH. The absorption isotherm is very steep between 90 and 100% RH. Desiccants of Type III have plenty of potential for the cycling of moisture from the air off of the coil, around 98% RH, over to the return air stream, typically around 50% RH.
Field tests
In 2011, Khalifa, Al-Omran, and Mohammed reported on a monitored study of a 2-ton capacity air conditioner unit while exchanging out a silica gel wheel and a wheel made of activated carbon to determine if it would reduce the relative humidity in a small room in Baghdad when compared to the unit without the Cromer cycle added. They found that the "Cromer cycle can reduce the indoor relative humidity from 80% to about 60% using active carbon of 5 cm wheel thickness."
Incorporating fresh air exchange
To maintain indoor air quality, it may be desirable to expunge return air from the conditioned space and replace it with fresh outdoor air, sometimes called "make-up air." The optimal location to expunge return air from a Cromer cycle system is just after the desiccant (location 2 on Figure 1). At this point, the return air has been loaded with moisture from the desiccant, and expunging it removes additional moisture from the space. Furthermore, this expunge air is cooled below the return air condition by the desiccant's evaporation of the moisture into it. Location 2 (but before the fan) is also the ideal place to bring outdoor air into the system, as the coil can then reduce its temperature and moisture before it enters the space. Also, if heat exchange is provided between the expunged air and the outdoor air, the incoming air can be cooled and brought near to or at saturation before it enters the cooling coil for process 2 to 3, enhancing its dehumidification.
Dehumidifier
When the process needed is more dehumidification or drying, the Cromer cycle can be enhanced by using the free heat available from the condensing side of the reverse Carnot refrigeration cycle. This heat, sometimes called "hot gas bypass" can be added before the desiccant wheel to enhance the drying of the wheel at location 1 of Figure 1 (but after the filter), called pre-heat. Hot gas bypass heat can also be added to the process at location 4, called reheat, which delivers warmer but even lower RH supply air. Either one or both hot gas bypass locations can be used. When a Cromer cycle air conditioning system is enhanced with hot gas bypass, it is typically referred to as "active" Cromer cycle air-conditioning. When the cycle is used as equipment designed for dehumidification or drying, it is typically called a Cromer cycle dehumidifier or Cromer cycle dryer.
R&D magazine recognized the Cromer cycle in 2006 with an R&D 100 Award in the mechanical/materials category, recognizing the year's 100 most significant technological innovations.
References
Thermodynamics
Desiccants | Cromer cycle | [
"Physics",
"Chemistry",
"Mathematics"
] | 2,039 | [
"Desiccants",
"Materials",
"Thermodynamics",
"Matter",
"Dynamical systems"
] |
61,510,140 | https://en.wikipedia.org/wiki/C15H23N5O2S | {{DISPLAYTITLE:C15H23N5O2S}}
The molecular formula C15H23N5O2S (molar mass: 337.440 g/mol, exact mass: 337.1572 u) may refer to:
GS-39783
Oclacitinib
Molecular formulas | C15H23N5O2S | [
"Physics",
"Chemistry"
] | 71 | [
"Molecules",
"Set index articles on molecular formulas",
"Isomerism",
"Molecular formulas",
"Matter"
] |
61,513,349 | https://en.wikipedia.org/wiki/CONUS-Experiment | CONUS (COherent Neutrino nUcleus Scattering) Experiment is a research project at the commercial nuclear power plant in Brokdorf, Germany (see Figure 1). The CONUS project is sponsored by the Max-Planck-Institut für Kernphysik and Preussen Elektra GmbH.
The CONUS project is searching for the fundamental process of coherent elastic scattering of neutrinos off atomic nuclei. The primary goal is to confirm the existence of this process and to use this interaction type to investigate further neutrino properties within and beyond the standard model of elementary particle physics.
Science Principles and Motivation - Coherent Elastic Neutrino Nucleus Scattering
As electrically neutral leptons, neutrinos only interact via the weak force with other particles. Due to this fact, neutrino detectors are generally very large and filled with several (kilo)tons of target material.
There are basically two possibilities to detect neutrinos: First, they can interact with the electrons in the atomic shell of a target atom, and second they can interact with the protons and neutrons of an atomic nucleus. Interactions between neutrinos and electrons as well as neutrinos and nuclear constituents have already been well studied.
However, at low energies up to a maximum of a few tens of mega-electronvolt (MeV), neutrinos can interact coherently with the nucleus as a whole (see Figure 2). This process was predicted in 1974 and is known as coherent elastic neutrino nucleus scattering (CEυNS, pronounced "sevens"). Although its cross section is several magnitudes larger than the cross section of the conventionally used interaction channels (see Figure 3), the tiny recoil of the struck nucleus leads to a very low energy release, making the process very hard to detect. Therefore, experiments investigating this process need detectors with an extremely low energy threshold, i.e., below 1 kilo-electronvolt (keV). On the other hand, since the CEυNS interaction cross sections is enhanced, a few kilogram of detector material can already be enough to detect the interaction.
As the first experiment worldwide, the COHERENT experiment was able to experimentally prove the existence of coherent elastic neutrino nucleus scattering in 2017. Herein, it used a relatively high energy neutrino beam in comparison with reactor neutrinos. Further complementary studies at lower energies in the fully coherent regime are yet to come. Examining this low energy neutrino region is the main goal of the CONUS project.
Detector
Site
The detection as well as detailed investigations of the properties of CEυNS utilizing neutrinos from a nuclear reactor require the detector to be located as close as possible to the reactor core to guarantee a maximized neutrino flux. To achieve this, the CONUS detector is located at a distance of 17 m from the reactor core inside the nuclear reactor facility at Brokdorf, see Figure 4. This is only possible due to the selected detector technology such that it can be placed inside the facility without interfering with the operation of the reactor.
The Brokdoft reactor runs at a maximum thermal power of 3.9 GW, making it one of the most powerful in the world. On average, about 7.2 neutrinos are produced per nuclear fission (6 from fission products and 1.2 due to decays after neutron captures on Uranium-238). At the detector site this results in a flux of about 23 trillion neutrinos per second and square centimeter.
Detectors and Measurement
The CONUS Collaboration is using four highly pure germanium semiconductor detectors, each weighing 1 kg (see Figure 5).
If a neutrino originating from the reactor core scatters off a germanium nucleus, the small recoil energy of the nucleus is partially converted into ionization energy and partially into dissipation heat. Only the first energy part contributes to electrical signal formation in the ionisation detectors as used in CONUS. The dissipation phenomenon is known as quenching and is typically described by the Lindhard theory. Thus, a precise knowledge of this quenching factor is crucial, since its uncertainty is one of the main systematics of the experiment. To detect coherent elastic neutrino nucleus scattering, CONUS is collecting reactor-on and reactor-off data. By comparing these data, an excess of events in the expected energy window during reactor-on time can reveal the existence of CEυNS. In addition, measurements during reactor-off times allow for a precise determination of the background rate and its components. CONUS started collecting data on April 1, 2018, and has been continuously operated since then.
Shield
Although CEυNS is the neutrino interaction with the highest cross section, it still is a rare process. Moreover, since it comes with a very small energy and momentum transfer (<1 keV), a suitable detector needs to be shielded from any additional background. The three main background types and their mitigation strategies applied in CONUS are summarized here:
The relevant backgrounds can be put into 3 different categories:
Cosmic Radiation: Cosmic muons and muon-induced showers can interact with the target material of the detector in large quantities. Thus, cosmic radiation is one of the most relevant backgrounds. To suppress this type of background, many low background experiments are located deep underground. This is however not possible for CONUS; here the reactor building offers a modest overburden leading to a reduction of the muon flux by a factor of 2-3 only. To achieve an even better suppression of the muonic background, the CONUS detector is surrounded by an active muon veto system (see Figure 5). It consists of scintillator layers that can detect incoming muons crossing the detector setup. This way, the muon-induced background can be reduced approximately by a factor of 100.
Local Background: Besides cosmic radiation, there is also background coming from the direct surroundings. The most important contributions to the local background are naturally occurring radioactivity in the surroundings and neutrons radiated from the reactor core. To shield the detectors against this background, they are covered with several layers of lead (25 cm in total) as well as boron-doped polyethylene plates (see Figure 5). Another important background source that experiments (especially those located in a closed environment) have to deal with is the radioactive decay of airborne radon. Radon is an inert gas and can therefore leak through tiniest gaps of the shield layers and decay close to the detectors. To solve this problem, the detector chamber is continuously flushed with radon-free air from compressed air bottles.
Intrinsic Radioactivity: The detectors also contain small concentrations of radioactive isotopes. Hence, it is necessary to minimize the amount of radioactive impurities inside the detector. To achieve this goal, the materials used to build the detector were carefully analyzed with the help of the GIOVE detector at the underground laboratory of the Max-Planck-Institut für Kernphysik and selected correspondingly.
Despite the small volume of the CONUS setup of 1.6m^3, the massive high-density shield leads to a total mass of 11 tons.
Results
January 2021
In 2020, The CONUS project published first results on CEυNS using 3.73 kg of active detector material after almost 70 days of effective measurement time with the reactor turned on and about 16 days with the reactor turned off. With these data the until now most precise upper limit for the existence of the CEυNS process in the fully coherent regime could be determined. This limit constitutes valuable information for basic neutrino research, since it allows one to test predictions for the strength of CEυNS in the standard model theory or in variations of it. The unique performance of the CONUS detectors with their very low energy thresholds, ultra-low background levels and long-term stability is highlighted in Ref.
With additional data collected until and beyond the end of the reactor operation in late 2021, additional improvements of the data acquisition systems and a better understanding of the quenching factor in germanium, the sensitivity of the experiment is expected to improve significantly in the next few years.
January 20245
On January 9, 2025, a paper was published on the pre-print server Arχiv, announcing the possible first measurement of Coherent Elastic Neutrino-Nucleus Scattering (CEνNS) from reactor antineutrinos, which would be the first observation of the interaction in the full coherence regime. The paper only claims a statistical significance of 3.7σ (5σ is considered the standard for discovery in physics), and has not been peer-reviewed as of January 22, 2025.
Applications
Understanding the process of coherent elastic neutrino nucleus scattering may offer some possibilities in other areas, too.
It is generally expected that the coherent elastic neutrino nucleus scattering process plays a significant role in the dynamics of Core-Collapse Supernovae. Investigating this process will therefore help to better understand the dynamics of such stellar explosions. Furthermore a detailed study of coherent elastic neutrino nucleus scattering could potentially reveal some new physics beyond the standard model of particle physics. For instance, it could be used to study electromagnetic properties of neutrinos (e.g. neutrino magnetic moment), to investigate potential deviations of the weak mixing angle at low energies or to study possible non-standard interactions in the neutrino-quark sector.
Besides its fundamental importance for basic science, the detection of neutrinos via CEυNS offers some practical applications. One example is the possibility to use CONUS-like detectors for reactor monitoring.
External links
MPIK Division Lindner: CONUS
PreussenElektra GmbH: Brokdorf NPP
References
Particle physics facilities
Experimental particle physics
Research institutes in Germany | CONUS-Experiment | [
"Physics"
] | 2,002 | [
"Experimental physics",
"Particle physics",
"Experimental particle physics"
] |
61,514,499 | https://en.wikipedia.org/wiki/C23H32O4S | {{DISPLAYTITLE:C23H32O4S}}
The molecular formula C23H32O4S (molar mass: 404.563 g/mol) may refer to:
6β-Hydroxy-7α-thiomethylspironolactone
7α-Thiomethylspironolactone sulfoxide
Molecular formulas | C23H32O4S | [
"Physics",
"Chemistry"
] | 82 | [
"Molecules",
"Set index articles on molecular formulas",
"Isomerism",
"Molecular formulas",
"Matter"
] |
61,514,597 | https://en.wikipedia.org/wiki/C19H28O6S | {{DISPLAYTITLE:C19H28O6S}}
The molecular formula C19H28O6S (molar mass: 384.487 g/mol, exact mass: 384.1607 u) may refer to:
15α-Hydroxy-DHEA sulfate
16α-Hydroxy-DHEA sulfate
Molecular formulas | C19H28O6S | [
"Physics",
"Chemistry"
] | 76 | [
"Molecules",
"Set index articles on molecular formulas",
"Isomerism",
"Molecular formulas",
"Matter"
] |
61,515,200 | https://en.wikipedia.org/wiki/C18H20INO4 | {{DISPLAYTITLE:C18H20INO4}}
The molecular formula C18H20INO4 (molar mass: 441.260 g/mol, exact mass: 441.0437 u) may refer to:
25I-NB34MD (NB34MD-2C-I)
25I-NBMD
Molecular formulas | C18H20INO4 | [
"Physics",
"Chemistry"
] | 77 | [
"Molecules",
"Set index articles on molecular formulas",
"Isomerism",
"Molecular formulas",
"Matter"
] |
61,515,664 | https://en.wikipedia.org/wiki/C860H1353N227O255S9 | {{DISPLAYTITLE:C860H1353N227O255S9}}
The molecular formula C860H1353N227O255S9 (molar mass: 19240.898 g/mol) may refer to:
Interferon alfacon-1
Peginterferon alfa-2a
Molecular formulas | C860H1353N227O255S9 | [
"Physics",
"Chemistry"
] | 77 | [
"Molecules",
"Set index articles on molecular formulas",
"Isomerism",
"Molecular formulas",
"Matter"
] |
61,516,900 | https://en.wikipedia.org/wiki/Gurzhi%20effect | The Gurzhi effect was theoretically predicted by Radii Gurzhi in 1963, and it consists of decreasing of electric resistance of a finite size conductor with increasing of its temperature (i.e. the situation for some temperature interval). Gurzhi effect usually being considered as the evidence of electron hydrodynamic transport in conducting media. The mechanism of Gurzhi effect is the following. The value of the resistance of the conductor is inverse to the — a mean free path corresponding to the momentum loss from the electrons+phonons systemwhere is the average distance which electron pass between two consecutive interactions with a boundary, and is a mean free path corresponding to other possibilities of momentum loss. The electron reflection from the boundary is assumed to be diffusive.
When temperature is low we have ballistic transport with , , where is a width of the conductor, is a mean free path corresponding to effective normal electron-electron collisions (i.e. collisions without total electrons+phonons momentum loss). For low temperatures phonon emitted by electron quickly interacts with another electron without loss of total electron+phonons momentum and , where is a mean free path corresponding to the electron-phonon collisions. Also we assume . Thus the resistance for lowest temperatures is a constant (see the picture). The Gurzhi effect appears when the temperature is increased to have . In this regime the electron diffusive length between two consecutive interactions with the boundary can be considered as momentum loss free path: , and the resistance is proportional to , and thus we have a negative derivative . Therefore, Gurzhi effect can be observed when .
Gurzhi effect corresponds to unusual situation when electrical resistance depends on a frequency of normal collisions. As one can see this effect appears due to the presence of a boundaries with finite characteristic size . Later Gurzhi's group discovered a special role of electron hydrodynamics in a spin transport. In such a case magnetic inhomogeneity plays role of a "boundary" with spin-diffusion length as a characteristic size instead of as before. This magnetic inhomogeneity stops electrons of the one spin component which becomes an effective scatterers for electrons of another spin component. In this case magnetoresistance of a conductor depends on the frequency of normal electron-electron collisions as well as in the Gurzhi effect.
References
Electric current | Gurzhi effect | [
"Physics"
] | 490 | [
"Electric current",
"Wikipedia categories named after physical quantities",
"Physical quantities"
] |
61,519,578 | https://en.wikipedia.org/wiki/AptarGroup | AptarGroup, Inc., also known as Aptar, is a United States–based global manufacturer of consumer dispensing packaging and drug delivery devices. The group has manufacturing operations in 18 countries.
History
The company began as Werner Die & Stamping in Cary, Illinois, in 1946 and later incorporated as AptarGroup in 1992. Aptar originally developed spray valves and pumps for consumer and household products. The company later began producing nasal administration and pulmonary drug delivery devices such as nasal spray systems and metered-dose inhaler valves. Biotech and pharmaceutical companies use Aptar's different Unidose and Bidose devices for the single or two-shot intranasal delivery of different medicines.
In 2016, Aptar announced that it provided the delivery system for Adapt Pharma's Narcan. Narcan is a naloxone hydrochloride nasal spray used as an emergency treatment for opioid overdoses. Aptar's liquid spray drug delivery technology platform works as a ready-to-use, single-shot, unit-dose system for Narcan. It was the first FDA approved nasally administered, ready-to-use medication used to reverse the effects of an opioid overdose. Narcan does not require any assembly, medical training, or needle injection.
In 2016, Aptar entered into an agreement with Becton Dickinson & Company to develop new self-injection devices.
Aptar entered into an agreement in 2016 with Propeller Health Partners to develop a digitally connected medication inhaler. The company made an investment in Propeller Health Partners (now part of Resmed) in 2018.
In July 2019, the FDA-approved Aptar Pharma's Unidose Powder System as the first intranasally-delivered, needle-free rescue treatment for severe hypoglycemia.
In 2020, during the COVID-19 pandemic, Aptar invested in new tools to accelerate its molding equipment and assembly machines for pumps, but it still wasn't enough to keep up with demand.
Acquisitions
In 2012, Aptar acquired Stelmi, a manufacturer of elastomer primary packaging components. In 2016, Aptar acquired Mega Airless, a manufacturer of airless packaging solutions. In 2018, Aptar acquired CSP Technologies, a material science company that manufactures active packaging solutions.
In June 2019, Aptar acquired two companies, Nanopharm and Gateway Analytical. In November 2019, the company acquired Noble International, which specializes in training devices and patient onboarding. In February 2020, Aptar acquired FusionPKG, a makeup packaging company.
In November 2020, the company acquired the digital respiratory health company Cohero Health.
In July 2021 Aptar acquired the digital therapeutics company, Voluntis (ENXTPA: ALVTX), and 80% of the equity interests of Weihai Hengyu Medical Products Co., Ltd., a Chinese manufacturer of elastomeric and plastic components used in injectable drug delivery.
Sustainability
Aptar was named to Barron's list of the Top 100 Most Sustainable U.S. Companies in 2019, 2020, 2021, and 2022. At the end of 2020, 85% of the company’s global electricity use came from renewable sources. It was also named by Newsweek as one of America's Most Responsible Companies in 2021, 2022, and 2023 and received an A score for climate change from the Climate Disclosure Project.
In September 2019, the company announced a partnership with Loop, a shopping platform from TerraCycle that delivers products in reusable containers. The company made the Forbes Green Growth 50 List in 2021.
References
1992 establishments in Illinois
Drug delivery devices
Packaging companies
Manufacturing
Pumps
Sustainable communities
Companies listed on the New York Stock Exchange
Packaging companies of the United States
Manufacturing companies established in 1992
Companies listed on the Nasdaq
Companies in the S&P 400 | AptarGroup | [
"Physics",
"Chemistry",
"Engineering"
] | 796 | [
"Pumps",
"Pharmacology",
"Turbomachinery",
"Drug delivery devices",
"Manufacturing",
"Physical systems",
"Hydraulics",
"Mechanical engineering"
] |
66,494,088 | https://en.wikipedia.org/wiki/Glossary%20of%20power%20electronics | This glossary of power electronics is a list of definitions of terms and concepts related to power electronics in general and power electronic capacitors in particular. For more definitions in electric engineering, see Glossary of electrical and electronics engineering. For terms related to engineering in general, see Glossary of engineering.
The glossary terms fit in the following categories in power electronics:
Electronic power converters; converters, rectifiers, inverters, filters.
Electronic power switches and electronic AC power converters; switches and controllers.
Essential components of electric power equipment; device, stack, assembly, reactor, capacitor, transformer, AC filter, DC filter, snubber circuit.
Circuits and circuit elements of power electronic equipment; arms and connections.
Operations within power electronic equipment; commutations, quenchings, controls, angles, factors, states, directions, intervals, periods, frequencies, voltages, breakthroughs and failures, breakdowns, blocking and flows.
Properties of power electronic equipment
Characteristic curves of power electronic equipment
Power supplies
A
B
C
D
E
F
H
I
J
L
M
N
O
P
Q
R
S
T
U
V
Overview of electronic power converters
See also
Glossary of engineering
Glossary of civil engineering
Glossary of mechanical engineering
Glossary of structural engineering
Notes
References
Attribution
External links
Websites
Online Electrotechnical Vocabulary
A Glossary of Electrical Terms
Electronic Terminology
Electronics Glossary
Glossary / Dictionary of Electronics Terms
PDFs
Pictorial Glossary
Electrical Engineering Dictionary
Electrical engineering
Electronic engineering
Power electronics
Power electronics
Power electronics
Wikipedia glossaries using description lists | Glossary of power electronics | [
"Technology",
"Engineering"
] | 314 | [
"Electrical engineering",
"Electronic engineering",
"Computer engineering",
"Power electronics"
] |
66,494,982 | https://en.wikipedia.org/wiki/Flat%20band%20potential | In semiconductor physics, the flat band potential of a semiconductor defines the potential at which there is no depletion layer at the junction between a semiconductor and an electrolyte or p-n-junction. This is a consequence of the condition that the redox Fermi level of the electrolyte must be equal to the Fermi level of the semiconductor and therefore preventing any band bending of the conduction and valence band. An application of the flat band potential can be found in the determining the width of the space charge region in a semiconductor-electrolyte junction. Furthermore, it is used in the Mott-Schottky equation to determine the capacitance of the semiconductor-electrolyte junction and plays a role in the photocurrent of a photoelectrochemical cell. The value of the flat band potential depends on many factors, such as the material, pH and crystal structure of the material
Background semiconductor physics
In semiconductors, valence electrons are located in energy bands. According to band theory, the electrons are either located in the valence band (lower energy) or the conduction band (higher energy), which are separated by an energy gap. In general, electrons will occupy different energy levels following the Fermi-Dirac distribution; for energy levels higher than the Fermi energy Ef, the occupation will be minimal. Electrons in lower levels can be excited into the higher levels through thermal or photoelectric excitations, leaving a positively-charged hole in the band they left. Due to conservation of net charge, the concentration of electrons (n) and of protons or holes (p) in a (pure) semiconductor must always be equal. Semiconductors can be doped to increase these concentrations: n-doping increases the concentration of electrons while p-doping increases the concentration of holes. This also affects the Fermi energy of the electrons: n-doped means a higher Fermi energy, while p-doped means a lower energy. At the interface between a n-doped and p-doped region in a semiconductor, band bending will occur. Due to the different charge distributions in the regions, an electric field will be induced, creating a so-called depletion region at the interface. Similar interfaces also appear at junctions between (doped) semiconductors and other materials, such as metals/electrolytes. A way to counteract this band bending is by applying a potential to the system. This potential would have to be the flat band potential and is defined to be the applied potential at which the conduction and valence bands become flat
References
Electronic band structures
Semiconductors | Flat band potential | [
"Physics",
"Chemistry",
"Materials_science",
"Engineering"
] | 538 | [
"Electron",
"Matter",
"Physical quantities",
"Semiconductors",
"Electronic band structures",
"Materials",
"Electronic engineering",
"Condensed matter physics",
"Solid state engineering",
"Electrical resistance and conductance"
] |
66,501,922 | https://en.wikipedia.org/wiki/Minimal%20polynomial%20of%202cos%282pi/n%29 | In number theory, the real parts of the roots of unity are related to one-another by means of the minimal polynomial of The roots of the minimal polynomial are twice the real part of the roots of unity, where the real part of a root of unity is just with coprime with
Formal definition
For an integer , the minimal polynomial of is the non-zero monic polynomial of smallest degree for which .
For every , the polynomial is monic, has integer coefficients, and is irreducible over the integers and the rational numbers. All its roots are real; they are the real numbers with coprime with and either or These roots are twice the real parts of the primitive th roots of unity. The number of integers relatively prime to is given by Euler's totient function it follows that the degree of is for and for
The first two polynomials are and
The polynomials are typical examples of irreducible polynomials whose roots are all real and which have a cyclic Galois group.
Examples
The first few polynomials are
Explicit form if n is odd
If is an odd prime, the polynomial can be written in terms of binomial coefficients following a "zigzag path" through Pascal's triangle:
Putting and
then we have for primes .
If is odd but not a prime, the same polynomial , as can be expected, is reducible and, corresponding to the structure of the cyclotomic polynomials reflected by the formula , turns out to be just the product of all for the divisors of , including itself:
This means that the are exactly the irreducible factors of , which allows to easily obtain for any odd , knowing its degree . For example,
Explicit form if n is even
From the below formula in terms of Chebyshev polynomials and the product formula for odd above, we can derive for even
Independently of this, if is an even prime power, we have for the recursion (see )
,
starting with .
Roots
The roots of are given by , where and . Since is monic, we have
Combining this result with the fact that the function is even, we find that is an algebraic integer for any positive integer and any integer .
Relation to the cyclotomic polynomials
For a positive integer , let , a primitive -th root of unity. Then the minimal polynomial of is given by the -th cyclotomic polynomial . Since , the relation between and is given by . This relation can be exhibited in the following identity proved by Lehmer, which holds for any non-zero complex number :
Relation to Chebyshev polynomials
In 1993, Watkins and Zeitlin established the following relation between and Chebyshev polynomials of the first kind.
If is odd, then
and if is even, then
If is a power of , we have moreover directly
Absolute value of the constant coefficient
The absolute value of the constant coefficient of can be determined as follows:
Generated algebraic number field
The algebraic number field is the maximal real subfield of a cyclotomic field . If denotes the ring of integers of , then . In other words, the set is an integral basis of . In view of this, the discriminant of the algebraic number field is equal to the discriminant of the polynomial , that is
References
Number theory
Polynomials
Trigonometry | Minimal polynomial of 2cos(2pi/n) | [
"Mathematics"
] | 671 | [
"Algebra",
"Discrete mathematics",
"Number theory",
"Polynomials"
] |
66,504,202 | https://en.wikipedia.org/wiki/Dan%20Burghelea | Dan Burghelea (born July 30, 1943) is a Romanian-American mathematician, academic, and researcher. He is an Emeritus Professor of Mathematics at Ohio State University.
Burghelea has contributed to a number of mathematical domains such as geometric and algebraic topology (including differential topology, algebraic K-theory, cyclic homology), global and geometric analysis (including topology of infinite dimensional manifolds, spectral geometry, dynamical systems), and applied topology (including computational topology).
Early life and education
Burghelea was born in Râmnicu Vâlcea, Romania, in 1943, where he attended Alexandru Lahovari National College (at that time lyceum Nicolae Bălcescu). He attended the University of Bucharest and graduated in mathematics in 1965, with a diploma-thesis in algebraic topology. He obtained his Ph.D. in 1968 from the Institute of Mathematics of the Romanian Academy (IMAR) with a thesis on Hilbert manifolds.
In 1972, Burghelea was awarded the title of Doctor Docent in sciences by the University of Bucharest, making him the youngest recipient of the highest academic degree in Romania.
Career
After a brief military service, Burghelea started his career in 1966 as a junior researcher at IMAR. He was promoted to Researcher in 1968, and to Senior Researcher in 1970. After the dissolution of IMAR, he was employed by the Institute of Nuclear Physics (IFA-Bucharest) and National Institute for Scientific Creation (INCREST) from 1975 until 1977. Burghelea left Romania for the United States in 1977, and in 1979 he joined the Ohio State University as a professor of mathematics. He retired in 2015, and remains associated with this university as an Emeritus Professor.
During his career he has been a visiting professor at numerous universities from Europe and the United States, including the University of Paris, the University of Bonn, ETH Zurich, the University of Chicago, and research institutions including the Institute for Advanced Study, Institut des Hautes Études Scientifiques, Max Planck Institute for Mathematics, Mathematical Sciences Research Institute; and invited speaker to many conferences in Europe, North and South America, and Asia and organized/co-organized workshops and conferences in Topology and Applications in Europe and the United States. He has significantly influenced the orientation of the geometry-topology research in Romania.
Research
Burghelea has worked in algebraic, differential, geometrical topology, differential and complex geometry, commutative algebra, global and geometric analysis, and applied topology.
His most significant contributions are on Topology of infinite dimensional manifolds; Homotopy type of the space of homeomorphisms and diffeomorphisms of compact smooth manifolds; Algebraic K-theory and cyclic homology of topological spaces, groups (including simplicial groups) and commutative algebras (including differential graded commutative algebras); Zeta-regularized determinants of elliptic operators and implications to torsion invariants for Riemannian manifolds.
Burghelea has also proposed and studied a computer friendly alternative to Morse–Novikov theory which makes the results of Morse–Novikov theory a powerful tool in topology, applicable outside topology in situations of interest in fields like physics and data analysis. He was the first to generate concepts of semisimple degree of symmetry and BFK-gluing formula.
He has authored several books including Groups of Automorphisms of Manifolds and New Topological Invariants for Real- and Angle-valued Maps: An Alternative to Morse-Novikov Theory.
He has advised several Ph.D. students.
Awards and honors
1966 – Simion Stoilow Prize, the Romanian Academy
1995 – Doctor Honoris-Causa, West University of Timișoara
2003 – National Order of Faithful Service, Commander rank
2005 – Honorary membership, IMAR, Romania
2009 – Distinction Academic Merit, Romanian Academy of Sciences
2019 – Medal of Honor, the Romanian Mathematical Society
Personal life
Dan Burghelea married Ana Burghelea, in 1965. They have a daughter, Gabriela Tomescu.
Bibliography
Burghelea's books include:
The concordance-homotopy groups of geometric automorphism groups (1971)
Introducere în topologia diferențială (1973)
New Topological Invariants For Real- And Angle-valued Maps: An Alternative To Morse-Novikov Theory, World Scientific (2017)
References
External links
Living people
1943 births
People from Râmnicu Vâlcea
Romanian emigrants to the United States
University of Bucharest alumni
Ohio State University faculty
Topologists
20th-century Romanian mathematicians
21st-century Romanian mathematicians
20th-century American mathematicians
21st-century American mathematicians
Recipients of the National Order of Faithful Service
Institute for Advanced Study visiting scholars | Dan Burghelea | [
"Mathematics"
] | 961 | [
"Topologists",
"Topology"
] |
63,711,218 | https://en.wikipedia.org/wiki/European%20Bank%20for%20induced%20pluripotent%20Stem%20Cells | The European Bank for induced pluripotent Stem Cells (EBiSC) is a non-profit induced pluripotent stem cell (iPSC) biorepository and service provider with central facilities in Germany and the United Kingdom.
EBiSC was set up between 2014 and 2017 by a consortium that represented researchers, clinicians and industry stakeholders. A second phase of the project runs between 2019 and 2022 with the aim of consolidating EBiSC as a not-for-profit, self-sustainable iPSC bank and service provider. The initiative is funded by the European Commission and the European Federation of Pharmaceutical Industries and Associations under the Innovative Medicines Initiative.
The European Bank for induced pluripotent Stem Cells performs collection, banking, quality control and distribution of iPSC lines for research purposes. EBiSC's stated goal is to supply academic, non-profit and commercial researchers with quality-controlled, disease-relevant iPSC lines, data and other services. It also seeks to promote the international standardisation of iPSC banking practices and to act as a central hub that ensures the sustainability and accessibility of iPSC lines generated by different research organisations. IPSC lines generated externally can be deposited into EBiSC for storage, banking, quality control and distribution.
Catalogue and facilities
In February 2020, the EBiSC catalogue contained iPSC lines representing diseases and conditions such as Alzheimer's disease, Frontotemporal Dementia, Parkinson's disease, Huntington's disease, Dravet syndrome, Bardet-Biedl syndrome, depression and pain, diabetes mellitus, eye diseases and heart disease. These iPSC lines have been deposited into EBiSC by academic institutions and non-profit and commercial organisations internationally. This includes lines generated within research projects such as StemBANCC, HipSci, IMI-ADAPTED, CRACK IT BadIPS and CRACK IT UnTangle.
The EBiSC Bank is run by two central facilities: the main distributor of EBiSC cell lines, the European Collection of Authenticated Cell Cultures in the UK, and the 'mirror bank' storing duplicates of all deposited lines long-term, established by the Fraunhofer Institute for Biomedical Engineering (IBMT) in Germany.
All EBiSC lines are distributed by the European Collection of Authenticated Cell Cultures operated by Public Health England.
References
Stem cell research
South Cambridgeshire District
Science and technology in Cambridgeshire
Wellcome Trust
Biorepositories | European Bank for induced pluripotent Stem Cells | [
"Chemistry",
"Biology"
] | 500 | [
"Stem cell research",
"Bioinformatics",
"Translational medicine",
"Tissue engineering",
"Biorepositories"
] |
63,717,070 | https://en.wikipedia.org/wiki/Ministry%20of%20Energy%20%28Kazakhstan%29 | The Ministry of Energy of the Republic of Kazakhstan (ME RK, , ҚР ЭМ; , МЭ РК) is an executive body of the Government of Kazakhstan, which carries out state administration in the field of energy. The Ministry was created during the reorganization of the government on 6 August 2014. The Ministry's functions and powers was from the Ministry of Oil and Gas, Ministry of Industry and New Technologies and the Ministry of Environment and Water.
Background
In 2014, Kazakhstan's energy sector turned to the country's Prime Minister Karim Massimov with a request to create a Ministry of Energy, as the situation in the republic with a lack of coordination in the activities of various government bodies in the electric power industry has developed. Prior to the creation of the ministry, various departments dealt with energy issues, which could not cope with their duties.
Structure
Departments
Department of Strategic and Information Development;
Department of Subsoil Use;
Department of Oil Industry Development;
Department of Gas and Oil;
Department of State Control in the Spheres of Hydrocarbons and Subsoil Use;
Department of Public Policy in the field of electric power industry;
Department of Atomic Energy and Industry;
Department of Renewable Energy Sources;
Department of Environmental Policy and Sustainable Development;
Department of Climate Policy and Green Technologies;
Department of Public Policy in Waste Management;
Department of Internal Audit;
Department of Budget and Financial Procedures;
Department of International Cooperation;
Department of Legal Service;
Department of Administrative Work;
Department of Digitalization and Informatization.
Administrations
Administration of Staff Development;
Administration of Mobilization Preparation and Civil Defense;
Administration of Protection of Public Secrets;
Administration of Information Security.
Committees
Committee of Atomic and Energy Supervision and Control of the Ministry of Energy of the Republic of Kazakhstan;
Committee of Environmental Regulation and Control of the Ministry of Energy of the Republic of Kazakhstan (transferred to the new ministry).
Interregional Department of State Inspection
Western Interregional State Inspection in the oil and gas complex;
Southern Interregional Office of the State Inspection in the oil and gas complex.
References
Energy
Kazakhstan
2014 establishments in Kazakhstan
Ministries established in 2014 | Ministry of Energy (Kazakhstan) | [
"Engineering"
] | 419 | [
"Energy organizations",
"Energy ministries"
] |
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