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Fluorescence cross-correlation spectroscopy (FCCS) is a spectroscopic technique that examines the interactions of fluorescent particles of different colours as they randomly diffuse through a microscopic detection volume over time, under steady conditions. | 7 | Physical Chemistry |
Ultracold atoms have a variety of applications owing to their unique quantum properties and the great experimental control available in such systems. For instance, ultracold atoms have been proposed as a platform for quantum computation and quantum simulation, accompanied by very active experimental research to achieve these goals.
Quantum simulation is of great interest in the context of condensed matter physics, where it may provide valuable insights into the properties of interacting quantum systems. The ultracold atoms are used to implement an analogue of the condensed matter system of interest, which can then be explored using the tools available in the particular implementation. Since these tools may differ greatly from those available in the actual condensed matter system, one can thus experimentally probe otherwise inaccessible quantities. Furthermore, ultracold atoms may even allow to create exotic states of matter, which cannot otherwise be observed in nature.
All atoms are identical, making ensembles of atoms ideal for universal timekeeping. In 1967, the SI definition of the second was changed to reference a hyperfine transition frequency in Cesium atoms. Atomic clocks based on alkaline earth atoms or alkaline earth like ions (such as Al) have now been developed making use of narrow-line optical transitions. To achieve high numbers of non-interacting atoms, which assists in the precision of these clocks, neutral atoms can be trapped in optical lattices. On the other hand, ion traps permit long interrogation times.
Ultracold atoms are also used in experiments for precision measurements enabled by the low thermal noise and, in some cases, by exploiting quantum mechanics to exceed the standard quantum limit. In addition to potential technical applications, such precision measurements may serve as tests of our current understanding of physics. | 7 | Physical Chemistry |
Thermodynamic adiabatic processes have no entropy change. Typically, an external control modifies
the state. A quantum version of an adiabatic process can be modeled by an externally controlled time dependent
Hamiltonian . If the system is isolated, the dynamics are unitary, and therefore, is
a constant. A quantum adiabatic process is defined by the energy entropy being constant.
The quantum adiabatic
condition is therefore equivalent to no net change in the population of the instantaneous energy levels.
This implies that the Hamiltonian should commute with itself at different times: .
When the adiabatic conditions are not fulfilled, additional work is required to reach the final control
value. For an isolated system, this work is recoverable, since the dynamics is unitary and can be reversed. In this case, quantum friction can be suppressed using shortcuts to adiabaticity as demonstrated in the laboratory using a unitary Fermi gas in a time-dependent trap.
The coherence stored in the off-diagonal elements of the density operator carry the required information
to recover the extra energy cost and reverse the dynamics. Typically, this energy is not recoverable, due
to interaction with a bath that causes energy dephasing. The bath, in this case, acts like a measuring
apparatus of energy. This lost energy is the quantum version of friction. | 7 | Physical Chemistry |
Galvanic cells are extensions of spontaneous redox reactions, but have been merely designed to harness the energy produced from said reaction. For example, when one immerses a strip of zinc metal (Zn) in an aqueous solution of copper sulfate (CuSO), dark-colored solid deposits will collect on the surface of the zinc metal and the blue color characteristic of the Cu ion disappears from the solution. The depositions on the surface of the zinc metal consist of copper metal, and the solution now contains zinc ions. This reaction is represented by
: Zn (s) + Cu (aq) → Zn (aq) + Cu (s)
In this redox reaction, Zn is oxidized to Zn and Cu is reduced to Cu. When electrons are transferred directly from Zn to Cu , the enthalpy of reaction is lost to the surroundings as heat. However, the same reaction can be carried out in a galvanic cell, allowing some of the chemical energy released to be converted into electrical energy. In its simplest form, a half-cell consists of a solid metal (called an electrode) that is submerged in a solution; the solution contains cations (+) of the electrode metal and anions (−) to balance the charge of the cations. The full cell consists of two half-cells, usually connected by a semi-permeable membrane or by a salt bridge that prevents the ions of the more noble metal from plating out at the other electrode.
A specific example is the Daniell cell (see figure), with a zinc (Zn) half-cell containing a solution of ZnSO (zinc sulfate) and a copper (Cu) half-cell containing a solution of CuSO (copper sulfate). A salt bridge is used here to complete the electric circuit.
If an external electrical conductor connects the copper and zinc electrodes, zinc from the zinc electrode dissolves into the solution as Zn ions (oxidation), releasing electrons that enter the external conductor. To compensate for the increased zinc ion concentration, via the salt bridge zinc ions leave and anions enter the zinc half-cell. In the copper half-cell, the copper ions plate onto the copper electrode (reduction), taking up electrons that leave the external conductor. Since the Cu ions (cations) plate onto the copper electrode, the latter is called the cathode. Correspondingly the zinc electrode is the anode. The electrochemical reaction is
This is the same reaction as given in the previous example. In addition, electrons flow through the external conductor, which is the primary application of the galvanic cell.
As discussed under cell voltage, the electromotive force of the cell is the difference of the half-cell potentials, a measure of the relative ease of dissolution of the two electrodes into the electrolyte. The emf depends on both the electrodes and on the electrolyte, an indication that the emf is chemical in nature. | 8 | Metallurgy |
Several different structural and compositional motifs can be prepared using the Stöber process by the addition of chemical compounds to the reaction mixture. These additives can interact with the silica through chemical and/or physical means either during or after the reaction, leading to substantial changes in morphology of the silica particles. | 7 | Physical Chemistry |
The source of adhesive forces, according to the dispersive adhesion mechanism, is the weak interactions that occur between molecules close together. These interactions include London dispersion forces, Keesom forces, Debye forces and hydrogen bonds. Individually, these attractions are not very strong, but when summed over the bulk of a material, they can become significant. | 6 | Supramolecular Chemistry |
In addition to distinct physical mechanisms by which lichens break down raw stone, studies indicate lichens attack stone chemically, entering newly chelated minerals into the ecology. The substances exuded by lichens, known for their strong ability to bind and sequester metals, along with the common formation of new minerals, especially metal oxalates, and the traits of the substrates they alter, all highlight the important role lichens play in the process of chemical weathering. Over time, this activity creates new fertile soil from stone.
Lichens may be important in contributing nitrogen to soils in some deserts through being eaten, along with their rock substrate, by snails, which then defecate, putting the nitrogen into the soils. Lichens help bind and stabilize soil sand in dunes. In deserts and semi-arid areas, lichens are part of extensive, living biological soil crusts, essential for maintaining the soil structure. | 2 | Environmental Chemistry |
Josette Garnier is a French biogeochemist. She is research director at the French National Centre for Scientific Research (CNRS). She won the 2016 Ruth Patrick Award. | 9 | Geochemistry |
Reductions with diimide are a chemical reactions that convert unsaturated organic compounds to reduced alkane products. In the process, diimide () is oxidized to dinitrogen. | 0 | Organic Chemistry |
The Denigés' reagent is a reagent used for qualitative analysis. It was developed in 1898 by Georges Denigés (December 25, 1859–February 20, 1951), a French biochemist. | 3 | Analytical Chemistry |
A linear combination of atomic orbitals or LCAO is a quantum superposition of atomic orbitals and a technique for calculating molecular orbitals in quantum chemistry. In quantum mechanics, electron configurations of atoms are described as wavefunctions. In a mathematical sense, these wave functions are the basis set of functions, the basis functions, which describe the electrons of a given atom. In chemical reactions, orbital wavefunctions are modified, i.e. the electron cloud shape is changed, according to the type of atoms participating in the chemical bond.
It was introduced in 1929 by Sir John Lennard-Jones with the description of bonding in the diatomic molecules of the first main row of the periodic table, but had been used earlier by Linus Pauling for H. | 7 | Physical Chemistry |
The Boulet Asphyxiant was a rumoured Russian chemical weapon during the Crimean War. The rumour was first found in the French newspaper Atlas before spreading to English-language publications.
According to the rumour, the Asphyxiant was developed by a French chemical researcher, M. Fortier, in 1839. He approached the Minister of Marine, who refused to accept the design, noting "the great number of means for the destruction of human life already existing", and the proposal ended there. The same proposal was made again in 1842, this time by a M. Champion, and again rejected, ending the matter until Champion "repaired his broken fortunes in Russia".
Fortiers Asphyxiant was then allegedly discovered during the Crimean War after the Battle of Sinop; those Turkish sailors who escaped reported that the Russians were using Greek fire. This was treated as humour until a French engineer examined the destroyed ships and found that the weapons used against them were new and unknown, sending fragments to his commander, who served with an officer who had been on the Council of the Marine when Fortier made his initial proposal. The Asphyxiant, according to the rumour, was a liquid fire that exploded under the waters surface, producing a gas that suffocated anyone on the surface. The rumour was countered by allegations amongst British forces that they had invented a secret device of their own, MacIntosh's Portable Buoyant Wave Repressor, which suppressed waves. | 1 | Biochemistry |
In the field of molecular biology, transrepression is a process whereby one protein represses (i.e., inhibits) the activity of a second protein through a protein-protein interaction. Since this repression occurs between two different protein molecules (intermolecular), it is referred to as a trans-acting process.
The protein that is repressed is usually a transcription factor whose function is to up-regulate (i.e., increase) the rate of gene transcription. Hence the net result of transrepression is down regulation of gene transcription.
An example of transrepression is the ability of the glucocorticoid receptor to inhibit the transcriptional promoting activity of the AP-1 and NF-κB transcription factors. In addition to transactivation, transrepression is an important pathway for the anti-inflammatory effects of glucocorticoids. Other nuclear receptors such as LXR and PPAR have been demonstrated to also have the ability to transrepress the activity of other proteins. | 1 | Biochemistry |
TFB is a single polypeptide, around 280 to 300 amino acids in length and 34 kDa in mass, that is required for the recruitment of RNA polymerase (RNAP) to begin transcription, and it may also affect the transcription complexs structure during changes that occur before transcription, though specific mechanisms are unknown. TFBs structure consists of an amino-terminal region (TFB) with conserved sequences and complex structures, linked to a larger, globular carboxyl-terminal region (TFB). While the N-terminal domain mediates the RNAP interactions, the C-terminal domain mediates interactions with complex formed of the TATA box and TBP, a DNA sequence and polypeptide involved with translation initiation. The degree of conservation of TFB's sequence throughout Archaea ranges from 50% to 60%. In respect to its eukaryotic equivalent, TFB shows "high levels of structural and functional conservation." The interactions between TBP and a sequence upstream of the TATA box governs transcription polarity, "yields an archaeal preinitiation complex," and orients the complex in the direction in which the target gene should be transcribed. The TBP shows an inverted orientation compared to the eukaryotic TFIIB.
TFB makes up approximately one third of the protein and contains both a B-finger motif (homologous to the TFIIB B-finger) and a zinc-finger motif, the latter of which is located at amino acids 2-34. The N-terminal domain size varies from 100 to 120 amino acids in length. Crosslinking experiments have shown this domain is located close to the transcription start site. The zinc-finger interacts with the RNAP dock domain, and the B-finger may affect RNAP-promoter interactions. TFB contains motifs which interact with the TATA binding protein (TBP), the TFB-recognition elements (BRE) upstream of the TATA box, and sequences of DNA downstream of the TATA. Its size is approximately 180 amino acids, which is made up of two repeats of a 90-amino acid sequence. The C-terminal domain specifically may be what influences the direction of the preinitiation complex. Since TFB binds the RNAP and TFB binds the TBP-TATA complex, TBP connects the two. | 1 | Biochemistry |
In crystallography, atomic packing factor (APF), packing efficiency, or packing fraction is the fraction of volume in a crystal structure that is occupied by constituent particles. It is a dimensionless quantity and always less than unity. In atomic systems, by convention, the APF is determined by assuming that atoms are rigid spheres. The radius of the spheres is taken to be the maximum value such that the atoms do not overlap. For one-component crystals (those that contain only one type of particle), the packing fraction is represented mathematically by
where N is the number of particles in the unit cell, V is the volume of each particle, and V is the volume occupied by the unit cell. It can be proven mathematically that for one-component structures, the most dense arrangement of atoms has an APF of about 0.74 (see Kepler conjecture), obtained by the close-packed structures. For multiple-component structures (such as with interstitial alloys), the APF can exceed 0.74.
The atomic packing factor of a unit cell is relevant to the study of materials science, where it explains many properties of materials. For example, metals with a high atomic packing factor will have a higher "workability" (malleability or ductility), similar to how a road is smoother when the stones are closer together, allowing metal atoms to slide past one another more easily. | 3 | Analytical Chemistry |
Measuring nonlinear optical interactions requires a high level of instantaneous power and very precise timing. In order to achieve the high number of photons needed to generate these interactions while avoiding damage of delicate specimens, these microscopes require a modelocked laser. These lasers can achieve very high photon counts on the femtosecond timescale and maintain a low average power. Most systems use a Ti:Sapph gain medium due to the wide range of wavelengths that it can access.
Typically, the same source is used to generate the pump and the probe. An optical parametric oscillator (OPO) is used to convert the probe beam to the desired wavelength. The probe wavelength can be tuned over a large range for spectroscopic applications.
However, for certain types of two-photon interactions, it is possible to use separate pulsed sources. This is only possible with interactions such as excited-state absorption, in which the electrons remain in the excited state for several picoseconds. However, it is more common to use a single femtosecond source with two separate beam paths of different lengths to modulate timing between the pump and probe beams.
The pump beam amplitude is modulated using an acousto-optic or electro-optic modulator on the order of 10 Hz. The pump and probe beams are then recombined using a dichroic beamsplitter and scanned using galvanometric mirrors for point-by-point image generation before being focused onto the sample. | 7 | Physical Chemistry |
Anodizing can be performed in combination with chromate conversion coating. Each process provides corrosion resistance, with anodizing offering a significant advantage when it comes to ruggedness or physical wear resistance. The reason for combining the processes can vary, however, the significant difference between anodizing and chromate conversion coating is the electrical conductivity of the films produced. Although both stable compounds, chromate conversion coating has a greatly increased electrical conductivity. Applications where this may be useful are varied, however the issue of grounding components as part of a larger system is an obvious one.
The dual finishing process uses the best each process has to offer, anodizing with its hard wear resistance and chromate conversion coating with its electrical conductivity.
The process steps can typically involve chromate conversion coating the entire component, followed by a masking of the surface in areas where the chromate coating must remain intact. Beyond that, the chromate coating is then dissolved in unmasked areas. The component can then be anodized, with anodizing taking to the unmasked areas. The exact process will vary dependent on service provider, component geometry and required outcome. It helps to protect aluminium article. | 8 | Metallurgy |
*Wax, used in the packaging of frozen foods, among others, Paraffin wax, derived from petroleum oil.
* Sulfur and its derivative sulfuric acid. Hydrogen sulfide is a product of sulfur removal from petroleum fraction. It is oxidized to elemental sulfur and then to sulfuric acid.
* Bulk tar and Asphalt
* Petroleum coke, used in speciality carbon products or as solid fuel | 7 | Physical Chemistry |
In acute toxicity, people have primarily gastrointestinal symptoms such as vomiting and diarrhea, which may result in volume depletion. During acute toxicity, lithium distributes later into the central nervous system causing dizziness and other mild neurological symptoms. | 1 | Biochemistry |
Energy carriers are energy forms which have been transformed from primary energy sources. Electricity is one of the most common energy carriers, being transformed from various primary energy sources such as coal, oil, natural gas, and wind. Electricity is particularly useful since it has low entropy (is highly ordered) and so can be converted into other forms of energy very efficiently. District heating is another example of secondary energy.
According to the laws of thermodynamics, primary energy sources cannot be produced. They must be available to society to enable the production of energy carriers.
Conversion efficiency varies. For thermal energy, electricity and mechanical energy production is limited by Carnots theorem, and generates a lot of waste heat. Other non-thermal conversions can be more efficient. For example, while wind turbines do not capture all of the winds energy, they have a high conversion efficiency and generate very little waste heat since wind energy is low entropy. In principle solar photovoltaic conversions could be very efficient, but current conversion can only be done well for narrow ranges of wavelength, whereas solar thermal is also subject to Carnot efficiency limits. Hydroelectric power is also very ordered, and converted very efficiently. The amount of usable energy is the exergy of a system. | 7 | Physical Chemistry |
A Frost diagram or Frost–Ebsworth diagram is a type of graph used by inorganic chemists in electrochemistry to illustrate the relative stability of a number of different oxidation states of a particular substance. The graph illustrates the free energy vs oxidation state of a chemical species. This effect is dependent on pH, so this parameter also must be included. The free energy is determined by the oxidation–reduction half-reactions. The Frost diagram allows easier comprehension of these reduction potentials than the earlier-designed Latimer diagram, because the “lack of additivity of potentials” was confusing. The free energy ΔG° is related to the reduction potential E shown in the graph by the formula: or , where n is the number of transferred electrons, and F is the Faraday constant ). The Frost diagram is named after , who originally invented it as a way to "show both free energy and oxidation potential data conveniently" in a 1951 paper. | 7 | Physical Chemistry |
In medicine, oxygen saturation refers to oxygenation, or when oxygen molecules () enter the tissues of the body. In this case blood is oxygenated in the lungs, where oxygen molecules travel from the air into the blood. Oxygen saturation (() sats) measures the percentage of hemoglobin binding sites in the bloodstream occupied by oxygen. Fish, invertebrates, plants, and aerobic bacteria all require oxygen. | 3 | Analytical Chemistry |
In order to associate with the inner leaflet of the plasma membrane, many G proteins and small GTPases are lipidated, that is, covalently modified with lipid extensions. They may be myristoylated, palmitoylated or prenylated. | 1 | Biochemistry |
In organic chemistry, two molecules are valence isomers when they are constitutional isomers that can interconvert through pericyclic reactions. | 4 | Stereochemistry |
Genomic editing takes place by transfecting cells with the pegRNA and the fusion protein. Transfection is often accomplished by introducing vectors into a cell. Once internalized, the fusion protein nicks the target DNA sequence, exposing a 3’-hydroxyl group that can be used to initiate (prime) the reverse transcription of the RT template portion of the pegRNA. This results in a branched intermediate that contains two DNA flaps: a 3’ flap that contains the newly synthesized (edited) sequence, and a 5’ flap that contains the dispensable, unedited DNA sequence. The 5’ flap is then cleaved by structure-specific endonucleases or 5’ exonucleases. This process allows 3’ flap ligation, and creates a heteroduplex DNA composed of one edited strand and one unedited strand. The reannealed double stranded DNA contains nucleotide mismatches at the location where editing took place. In order to correct the mismatches, the cells exploit the intrinsic mismatch repair mechanism, with two possible outcomes: (i) the information in the edited strand is copied into the complementary strand, permanently installing the edit; (ii) the original nucleotides are re-incorporated into the edited strand, excluding the edit. | 1 | Biochemistry |
APCI generally suffers less ion suppression than ESI, as discussed previously. Where possible, if ion suppression is unavoidable it may be advisable to switch from ESI to APCI. If this is not possible, it may be useful to switch the ESI ionisation mode from positive to negative. Since fewer compounds are ionisable in negative ionisation mode, it is entirely possible that the ion suppressing species may be removed from the analysis. However, it should also be considered that the analyte of interest may not be ionised effectively in negative mode either, rendering this approach useless. | 3 | Analytical Chemistry |
From a practical view, low-melting alloys can be divided into the following categories:
*Mercury-containing alloys
*Only alkali metal-containing alloys
*Gallium-containing alloys (but neither alkali metal nor mercury)
*Only bismuth, lead, tin, cadmium, zinc, indium, and sometimes thallium-containing alloys
*Other alloys (rarely used)
Some reasonably well-known fusible alloys are Woods metal, Fields metal, Rose metal, Galinstan, and NaK. | 8 | Metallurgy |
Application of BNAs include small RNA research; design and synthesis of RNA aptamers; siRNA; antisense probes; diagnostics; isolation; microarray analysis; Northern blotting; real-time PCR; in situ hybridization; functional analysis; SNP detection and use as antigens and many others nucleotide base applications. | 1 | Biochemistry |
The most recent and most clear cut example of enzyme evolution is the rise of bioremediating enzymes in the past 60 years. Due to the very low number of amino acid changes, these provide an excellent model to investigate enzyme evolution in nature. However, using extant enzymes to determine how the family of enzymes evolved has the drawback that the newly evolved enzyme is compared to paralogues without knowing the true identity of the ancestor before the two genes diverged. This issue can be resolved thanks to ancestral reconstruction.
First proposed in 1963 by Linus Pauling and Emile Zuckerkandl, ancestral reconstruction is the inference and synthesis of a gene from the ancestral form of a group of genes, which has had a recent revival thanks to improved inference techniques and low-cost artificial gene synthesis, resulting in several ancestral enzymes—dubbed "stemzymes" by some—to be studied.
Evidence gained from reconstructed enzyme suggests that the order of the events where the novel activity is improved and the gene is duplication is not clear cut, unlike what the theoretical models of gene evolution suggest.
One study showed that the ancestral gene of the immune defence protease family in mammals had a broader specificity and a higher catalytic efficiency than the contemporary family of paralogues, whereas another study showed that the ancestral steroid receptor of vertebrates was an oestrogen receptor with slight substrate ambiguity for other hormones—indicating that these probably were not synthesised at the time.
This variability in ancestral specificity has not only been observed between different genes, but also within the same gene family.
In light of the large number of paralogous fungal α-glucosidase genes with a number of specific maltose-like (maltose, turanose, maltotriose, maltulose and sucrose) and isomaltose-like (isomaltose and palatinose) substrates, a study reconstructed all key ancestors and found that the last common ancestor of the paralogues was mainly active on maltose-like substrates with only trace activity for isomaltose-like sugars, despite leading to a lineage of iso-maltose glucosidases and a lineage that further split into maltose glucosidases and iso-maltose glucosidases. Antithetically, the ancestor before the latter split had a more pronounced isomaltose-like glucosidase activity. | 1 | Biochemistry |
Melted fusible alloys can be used as coolants as they are stable under heating and can give much higher thermal conductivity than most other coolants; particularly with alloys made with a high thermal conductivity metal such as indium or sodium. Metals with low neutron cross-section are used for cooling nuclear reactors.
Such alloys are used for making the fusible plugs inserted in the furnace crowns of steam boilers, as a safeguard in the event of the water level being allowed to fall too low. When this happens the plug, being no longer covered with water, is heated to such a temperature that it melts and allows the contents of the boiler to escape into the furnace. In automatic fire sprinklers the orifices of each sprinkler is closed with a plug that is held in place by fusible metal, which melts and liberates the water when, owing to an outbreak of fire in the room, the temperature rises above a predetermined limit.
Bismuth on solidification expands by about 3.3% by volume. Alloys with at least half of bismuth display this property too. This can be used for mounting of small parts, e.g. for machining, as they will be tightly held. | 8 | Metallurgy |
The result of a T-RFLP profiling is a graph called electropherogram which is an intensity plot representation of an electrophoresis experiment (gel or capillary). In an electropherogram the X-axis marks the sizes of the fragments while the Y-axis marks the fluorescence intensity of each fragment. Thus, what appears on an electrophoresis gel as a band appears as a peak on the electropherogram whose integral is its total fluorescence. In a T–RFLP profile each peak assumingly corresponds to one genetic variant in the original sample while its height or area corresponds to its relative abundance in the specific community. Both assumptions listed above, however, are not always met. Often, several different bacteria in a population might give a single peak on the electropherogram due to the presence of a restriction site for the particular restriction enzyme used in the experiment at the same position. To overcome this problem and to increase the resolving power of this technique a single sample can be digested in parallel by several enzymes (often three) resulting in three T-RFLP profiles per sample each resolving some variants while missing others. Another modification which is sometimes used is to fluorescently label the reverse primer as well using a different dye, again resulting in two parallel profiles per sample each resolving a different number of variants.
In addition to convergence of two distinct genetic variants into a single peak artifacts might also appear, mainly in the form of false peaks. False peaks are generally of two types: background “noises” and “pseudo” TRFs. Background (noise) peaks are peaks resulting from the sensitivity of the detector in use. These peaks are often small in their intensity and usually form a problem in case the total intensity of the profile is low (i.e. low concentration of DNA). Because these peaks result from background noise they are normally irreproducible in replicate profiles, thus the problem can be tackled by producing a consensus profile from several replicates or by eliminating peaks below a certain threshold. Several other computational techniques were also introduced in order to deal with this problem. Pseudo TRFs, on the other hand, are reproducible peaks and are linear to the amount of DNA loaded. These peaks are thought to be the result of ssDNA annealing on to itself and creating double stranded random restriction sites which are later recognized by the restriction enzyme resulting in a terminal fragment which does not represent any genuine genetic variant. It has been suggested that applying a DNA exonuclease such as the Mung bean exonuclease prior to the digestion stage might eliminate such artifact. | 1 | Biochemistry |
* Singer and songwriter Tom Wisner recorded several albums, often about the Chesapeake Bay. The Boston Globe wrote that Wisner "always tried to capture the voice of the water and the sky, of the rocks and the trees, of the fish and the birds, of the gods of nature he believed still watched over it all." He was known as the Bard of the Chesapeake Bay.
* The Chesapeake Bay is referenced in the hit musical Hamilton, in the song "Yorktown (The World Turned Upside Down)." It describes the famous Battle of Yorktown, the last battle in the Revolutionary War. When describing the US army's plan for attack, Hamilton sings: "When we finally drive the British away, Lafayette is there waiting in Chesapeake Bay!" | 2 | Environmental Chemistry |
Pharmacokinetic data of enalapril:
* Onset of action: about 1 hour
* Peak effect: 4–6 hours
* Duration: 12–24 hours
* Absorption: ~60%
* Metabolism: prodrug, undergoes biotransformation to enalaprilat | 4 | Stereochemistry |
High photon intensity experiments can involve multiphoton processes with the absorption of integer multiples of the photon energy. In experiments that involve a multiphoton resonance, the intermediate is often a Rydberg state, and the final state is often an ion. The initial state of the system, photon energy, angular momentum and other selection rules can help in determining the nature of the intermediate state. This approach is exploited in resonance enhanced multiphoton ionization spectroscopy (REMPI). An advantage of this spectroscopic technique is that the ions can be detected with almost complete efficiency and even resolved for their mass. It is also possible to gain additional information by performing experiments to look at the energy of the liberated photoelectron in these experiments. (Compton and Johnson pioneered the development of REMPI) | 7 | Physical Chemistry |
The p75 neurotrophin receptor (p75NTR) was first identified in 1973 as the low-affinity nerve growth factor receptor (LNGFR) before discovery that p75NTR bound other neurotrophins equally well as nerve growth factor. p75NTR is a neurotrophic factor receptor. Neurotrophic factor receptors bind Neurotrophins including Nerve growth factor, Neurotrophin-3, Brain-derived neurotrophic factor, and Neurotrophin-4. All neurotrophins bind to p75NTR. This also includes the immature pro-neurotrophin forms. Neurotrophic factor receptors, including p75NTR, are responsible for ensuring a proper density to target ratio of developing neurons, refining broader maps in development into precise connections. p75NTR is involved in pathways that promote neuronal survival and neuronal death. | 1 | Biochemistry |
* Switzerland: Swiss Nano Dragster, University of Basel
* France: Toulouse nanomobile club, Paul Sabatier University
* Austria/United States: NanoPrix Team University of Graz / Rice University
* Germany: Nano-windmill Company Technical University of Dresden (TU Dresden)
* Japan: Nano-Vehicle NIMS-MANA National Institute for Materials Science
* United States: Ohio Bobcat Nano-Wagon, Ohio University | 6 | Supramolecular Chemistry |
In chemistry, an ester is a compound derived from an acid (organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (). Analogues derived from oxygen replaced by other chalcogens belong to the ester category as well. According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well (e.g. amides), but not according to the IUPAC.
Glycerides are fatty acid esters of glycerol; they are important in biology, being one of the main classes of lipids and comprising the bulk of animal fats and vegetable oils. Lactones are cyclic carboxylic esters; naturally occurring lactones are mainly 5- and 6-membered ring lactones. Lactones contribute to the aroma of fruits, butter, cheese, vegetables like celery and other foods.
Esters can be formed from oxoacids (e.g. esters of acetic acid, carbonic acid, sulfuric acid, phosphoric acid, nitric acid, xanthic acid), but also from acids that do not contain oxygen (e.g. esters of thiocyanic acid and trithiocarbonic acid). An example of an ester formation is the substitution reaction between a carboxylic acid () and an alcohol (), forming an ester (), where R stands for any group (typically hydrogen or organyl) and R stands for organyl group.
Organyl esters of carboxylic acids typically have a pleasant smell; those of low molecular weight are commonly used as fragrances and are found in essential oils and pheromones. They perform as high-grade solvents for a broad array of plastics, plasticizers, resins, and lacquers, and are one of the largest classes of synthetic lubricants on the commercial market. Polyesters are important plastics, with monomers linked by ester moieties. Esters of phosphoric acid form the backbone of DNA molecules. Esters of nitric acid, such as nitroglycerin, are known for their explosive properties.
There are compounds in which an acidic hydrogen of acids mentioned in this article are not replaced by an organyl, but by some other group. According to some authors, those compounds are esters as well, especially when the first carbon atom of the organyl group replacing acidic hydrogen, is replaced by another atom from the group 14 elements (Si, Ge, Sn, Pb); for example, according to them, trimethylstannyl acetate (or trimethyltin acetate) is a trimethylstannyl ester of acetic acid, and dibutyltin dilaurate is a dibutylstannylene ester of lauric acid, and the Phillips catalyst is a trimethoxysilyl ester of chromic acid (). | 0 | Organic Chemistry |
The Corby toxic waste case was a court case decided by The Hon. Mr. Justice Akenhead at the High Court of Justice, London, on 29 July 2009 in the case of Corby Group Litigation v. Corby Borough Council [2009] EWHC 1944 (TCC). The judge found Corby Borough Council liable in negligence, public nuisance and a breach of statutory duty for its reclamation of a Corby Steelworks in the town of Corby, Northamptonshire, between 1985 and 1997. The landmark decision was historically significant as the first in the world to establish a link between atmospheric toxic waste and birth defects - all previous cases have involved water pollution - and held implications for other council reclamation programs and the methods of conducting reclamation in England and Wales.
The case has been described as "the British Erin Brockovich". | 2 | Environmental Chemistry |
Diffusion hardening can be done in many different ways to achieve different hardnesses and different surface finishes on metal parts. Some of the different diffusion hardening operations include: Carburizing, Nitriding, Carbonitriding, Nitrocarburizing, Boriding, Titanium-carbon diffusion, and Toyota diffusion. While diffusion hardening is performed mainly on steel parts and carbon is mainly the element used for diffusion, diffusion hardening can also be performed with other diffusion elements and with other metals. In nitriding, nitrogen is diffused into the surface of steel, but can also be used with metals such as Aluminum, Chromium, Molybdenum, and Vanadium. Besides metals and diffusion elements used, diffusion hardening processes differ in the temperature required for diffusion, the phase of the diffusion element, and additional treatments such as quenching and tempering. These different factors greatly affect surface finish and dimensional accuracy of a part. A quenched and tempered part does not have the same dimensional accuracy as a part that has not undergone such a process. Also, they can affect the efficiency of the overall process. In carburizing, the carbon can be in any of the solid, liquid, or gas phases. Although using carbon in the solid phase is usually the safest and easiest of these to work with, the process is difficult to control and the heating is inefficient. All these things must come into consideration when choosing a diffusion hardening process. | 8 | Metallurgy |
Müllerian mimicry was discovered and has mainly been researched in insects. However, there is no reason why the mechanisms evolutionary advantages should not be exploited in other groups. There is some evidence that birds in the New Guinea genus Pitohui are Müllerian mimics. Pitohui dichrous and Pitohui kirhocephalus' "share a nearly identical colour pattern" where their geographic ranges overlap, but differ elsewhere; they are conspicuous; and they are chemically defended by a powerful neurotoxic alkaloid, batrachotoxin, in their feathers and skin. This combination of facts implies that the populations in these zones of overlap have converged to share honest warning signals.
Many species of flowers resemble each other but actual mimicry has not been demonstrated. It has been proposed that spiny plants such as Cactaceae and Agave in the Americas, Aloe, Euphorbia, white-thorned Acacia in Africa and spiny Asteraceae of the Mediterranean may form Müllerian mimicry rings, as they are strongly defended, are generally agreed to be aposematic, have similar conspicuous patterns and coloration, and are found in overlapping territories.
Aposematic mammals in the families Mustelidae, Viverridae, and Herpestidae have independently evolved conspicuous black-and-white coloration, suggesting that Müllerian mimicry may be involved. | 1 | Biochemistry |
The x-ray beam used for topography is generated by an x-ray source, typically either a laboratory x-ray tube (fixed or rotating) or a synchrotron source. The latter offers advantages due to its higher beam intensity, lower divergence, and its continuous wavelength spectrum. X-ray tubes are still useful, however, due to easier access and continuous availability, and are often used for initial screening of samples and/or training of new staff.
For white beam topography, not much more is required: most often, a set of slits to precisely define the beam shape and a (well polished) vacuum exit window will suffice. For those topography techniques requiring a monochromatic x-ray beam, an additional crystal monochromator is mandatory. A typical configuration at synchrotron sources is a combination of two Silicon crystals, both with surfaces oriented parallel to [111]-lattice planes, in geometrically opposite orientation. This guarantees relatively high intensity, good wavelength selectivity (about 1 part in 10000) and the possibility to change the target wavelength without having to change the beam position ("fixed exit"). | 3 | Analytical Chemistry |
One of the defining features of polymer surfaces and coatings is the chemical regularity of the surface. While many materials can be irregular mixtures of different components, polymer surfaces tend to be chemically uniform, with the same distribution of different functional groups across all areas of the surface. Because of this, adsorption of molecules onto polymer surfaces can be easily modeled by the Langmuir or Frumkin Isotherms. The Langmuir equation states that for the adsorption of a molecule of adsorbate A onto a surface binding site S, a single binding site is used, and each free binding site is equally likely to accept a molecule of adsorbate:
where:
: is the adsorbate
: is the surface binding site
: is the bound adsorbate/binding site pair
The equilibrium constant for this reaction is then defined as:
The equilibrium constant is related to the equilibrium surface coverage , which is given by:
where:
:' is the surface coverage (fraction, 0 is empty, 1 is fully covered)
: is the adsorption equilibrium constant | 7 | Physical Chemistry |
Since the discovery of Ste5 in yeast, scientists were on the hunt to discover similar non-enzymatic scaffolding pathway elements in mammals. There are indeed a number of proteins involved in ERK signaling, that can bind to multiple elements of the pathway: MP1 binds both MKK1/2 and ERK1/2, KSR1 and KSR2 can bind B-Raf or c-Raf, MKK1/2 and ERK1/2. Analogous proteins were also discovered for the JNK pathway: the JIP1/JIP2 and the JIP3/JIP4 families of proteins were all shown to bind MLKs, MKK7 and any JNK kinase. Unfortunately, unlike the yeast Ste5, the mechanisms by which they regulate MAPK activation are considerably less understood. While Ste5 actually forms a ternary complex with Ste7 and Fus3 to promote phosphorylation of the latter, known mammalian scaffold proteins appear to work by very different mechanisms. For example, KSR1 and KSR2 are actually MAP3 kinases and related to the Raf proteins. Although KSRs alone display negligible MAP3 kinase activity, KSR proteins can still participate in the activation of Raf kinases by forming side-to-side heterodimers with them, providing an allosteric pair to turn on each enzymes. JIPs on the other hand, are apparently transport proteins, responsible for enrichment of MAPK signaling components in certain compartments of polarized cells. In this context, JNK-dependent phosphorylation of JIP1 (and possibly JIP2) provides a signal for JIPs to release the JIP-bound and inactive upstream pathway components, thus driving a strong local positive feedback loop. This sophisticated mechanism couples kinesin-dependent transport to local JNK activation, not only in mammals, but also in the fruitfly Drosophila melanogaster. | 1 | Biochemistry |
Other much more complex types of phase diagrams can be constructed, particularly when more than one pure component is present. In that case, concentration becomes an important variable. Phase diagrams with more than two dimensions can be constructed that show the effect of more than two variables on the phase of a substance. Phase diagrams can use other variables in addition to or in place of temperature, pressure and composition, for example the strength of an applied electrical or magnetic field, and they can also involve substances that take on more than just three states of matter.
One type of phase diagram plots temperature against the relative concentrations of two substances in a binary mixture called a binary phase diagram, as shown at right. Such a mixture can be either a solid solution, eutectic or peritectic, among others. These two types of mixtures result in very different graphs. Another type of binary phase diagram is a boiling-point diagram for a mixture of two components, i. e. chemical compounds. For two particular volatile components at a certain pressure such as atmospheric pressure, a boiling-point diagram shows what vapor (gas) compositions are in equilibrium with given liquid compositions depending on temperature. In a typical binary boiling-point diagram, temperature is plotted on a vertical axis and mixture composition on a horizontal axis.
A two component diagram with components A and B in an "ideal" solution is shown. The construction of a liquid vapor phase diagram assumes an ideal liquid solution obeying Raoults law and an ideal gas mixture obeying Daltons law of partial pressure. A tie line from the liquid to the gas at constant pressure would indicate the two compositions of the liquid and gas respectively.
A simple example diagram with hypothetical components 1 and 2 in a non-azeotropic mixture is shown at right. The fact that there are two separate curved lines joining the boiling points of the pure components means that the vapor composition is usually not the same as the liquid composition the vapor is in equilibrium with. See Vapor–liquid equilibrium for more information.
In addition to the above-mentioned types of phase diagrams, there are many other possible combinations. Some of the major features of phase diagrams include congruent points, where a solid phase transforms directly into a liquid. There is also the peritectoid, a point where two solid phases combine into one solid phase during cooling. The inverse of this, when one solid phase transforms into two solid phases during cooling, is called the eutectoid.
A complex phase diagram of great technological importance is that of the iron–carbon system for less than 7% carbon (see steel).
The x-axis of such a diagram represents the concentration variable of the mixture. As the mixtures are typically far from dilute and their density as a function of temperature is usually unknown, the preferred concentration measure is mole fraction. A volume-based measure like molarity would be inadvisable. | 7 | Physical Chemistry |
For many substances, the formation reaction may be considered as the sum of a number of simpler reactions, either real or fictitious. The enthalpy of reaction can then be analyzed by applying Hesss Law, which states that the sum' of the enthalpy changes for a number of individual reaction steps equals the enthalpy change of the overall reaction. This is true because enthalpy is a state function, whose value for an overall process depends only on the initial and final states and not on any intermediate states. Examples are given in the following sections. | 7 | Physical Chemistry |
The simplest kind of magnetic phase is a paramagnet, where each individual spin behaves independently of the rest, just like atoms in an ideal gas. This highly disordered phase is the generic state of magnets at high temperatures, where thermal fluctuations dominate. Upon cooling, the spins will often enter a ferromagnet (or antiferromagnet) phase. In this phase, interactions between the spins cause them to align into large-scale patterns, such as domains, stripes, or checkerboards. These long-range patterns are referred to as "magnetic order," and are analogous to the regular crystal structure formed by many solids.
Quantum spin liquids offer a dramatic alternative to this typical behavior. One intuitive description of this state is as a "liquid" of disordered spins, in comparison to a ferromagnetic spin state, much in the way liquid water is in a disordered state compared to crystalline ice. However, unlike other disordered states, a quantum spin liquid state preserves its disorder to very low temperatures. A more modern characterization of quantum spin liquids involves their topological order, long-range quantum entanglement properties, and anyon excitations. | 7 | Physical Chemistry |
Chromosome walking can be used for the purpose of cloning a gene. It does this by using the known gene’s markers that are closest and can therefore be used in techniques like isolating DNA sequences and aiding in the sequencing and cloning of the DNA of organisms. Chromosome walking is also useful when it comes to filling in the gaps that may be present in genomes by locating clones that overlap with a library clone end. This means that for chromosome walking to be carried out, it requires a clone library of a genomic format. This is why Vectorette PCR is one of the methods that can be used to create this library for chromosome walking to occur. Vectorette PCR comes in handy when it is necessary to obtain the regions that are both upstream and downstream and flank a sequence that is already known. By obtaining these regions, it provides the library of a genomic format that chromosome walking requires. | 1 | Biochemistry |
MAD1L1 is a component of the mitotic spindle-assembly checkpoint that prevents the onset of anaphase until all chromosome are properly aligned at the metaphase plate. MAD1L1 functions as a homodimer and interacts with MAD2L1. MAD1L1 may play a role in cell cycle control and tumor suppression. Some studies indicate associations of MAD1L1 with psychiatric disorders, including schizophrenia, bipolar disorder, and depression. Three transcript variants encoding the same protein have been found for this gene. | 1 | Biochemistry |
The Anti-apoptotic Ras signaling cascade is an intracellular signal transduction cascade
that involves the Ras protein and inhibits apoptosis. It is the target of the cancer drug gefitinib.
It may refer to the PI3K/AKT pathway.
It may refer to the MAPK/ERK pathway which involves ras and can affect apoptosis.
The anti-apoptotic STAT pathway does not involve Ras. | 1 | Biochemistry |
Thermal contact conductance is a complicated phenomenon, influenced by many factors. Experience shows that the most important ones are as follows: | 7 | Physical Chemistry |
Topologically close pack (TCP) phases, also known as Frank-Kasper (FK) phases, are one of the largest groups of intermetallic compounds, known for their complex crystallographic structure and physical properties. Owing to their combination of periodic and aperiodic structure, some TCP phases belong to the class of quasicrystals. Applications of TCP phases as high-temperature structural and superconducting materials have been highlighted; however, they have not yet been sufficiently investigated for details of their physical properties. Also, their complex and often non-stoichiometric structure makes them good subjects for theoretical calculations. | 8 | Metallurgy |
Progesterone is the most important progestogen in the body. As a potent agonist of the nuclear progesterone receptor (nPR) (with an affinity of K = 1 nM) the resulting effects on ribosomal transcription plays a major role in regulation of female reproduction. In addition, progesterone is an agonist of the more recently discovered membrane progesterone receptors (mPRs), of which the expression has regulation effects in reproduction function (oocyte maturation, labor, and sperm motility) and cancer although additional research is required to further define the roles. It also functions as a ligand of the PGRMC1 (progesterone receptor membrane component 1) which impacts tumor progression, metabolic regulation, and viability control of nerve cells. Moreover, progesterone is also known to be an antagonist of the sigma σ receptor, a negative allosteric modulator of nicotinic acetylcholine receptors, and a potent antagonist of the mineralocorticoid receptor (MR). Progesterone prevents MR activation by binding to this receptor with an affinity exceeding even those of aldosterone and glucocorticoids such as cortisol and corticosterone, and produces antimineralocorticoid effects, such as natriuresis, at physiological concentrations. In addition, progesterone binds to and behaves as a partial agonist of the glucocorticoid receptor (GR), albeit with very low potency (EC >100-fold less relative to cortisol).
Progesterone, through its neurosteroid active metabolites such as 5α-dihydroprogesterone and allopregnanolone, acts indirectly as a positive allosteric modulator of the GABA receptor.
Progesterone and some of its metabolites, such as 5β-dihydroprogesterone, are agonists of the pregnane X receptor (PXR), albeit weakly so (EC >10 μM). In accordance, progesterone induces several hepatic cytochrome P450 enzymes, such as CYP3A4, especially during pregnancy when concentrations are much higher than usual. Perimenopausal women have been found to have greater CYP3A4 activity relative to men and postmenopausal women, and it has been inferred that this may be due to the higher progesterone levels present in perimenopausal women.
Progesterone modulates the activity of CatSper (cation channels of sperm) voltage-gated Ca channels. Since eggs release progesterone, sperm may use progesterone as a homing signal to swim toward eggs (chemotaxis). As a result, it has been suggested that substances that block the progesterone binding site on CatSper channels could potentially be used in male contraception. | 0 | Organic Chemistry |
A longitudinal facial crack is a specialized type of defect that only occurs in continuous casting processes. This defect is caused by uneven cooling, both primary cooling and secondary cooling, and includes molten steel qualities, such as the chemical composition being out of specification, cleanliness of the material, and homogeneity. | 8 | Metallurgy |
Interleukin-15 stimulates fat oxidation, glucose uptake, mitochondrial biogenesis and myogenesis in skeletal muscle and adipose tissue. In humans, basal concentrations of IL-15 and its alpha receptor (IL-15Rα) in blood have been inversely associated with physical inactivity and fat mass, particularly trunk fat mass. Moreover, in response to a single session of resistance exercise the IL-15/IL-15Rα complex has been related to myofibrillar protein synthesis (hypertrophy). | 1 | Biochemistry |
In most stability studies, real-time or accelerated, a few units of the reference material are tested at intervals. If the measurement system used for testing the materials is not perfectly stable, this can generate imprecise data or can be mistaken for instability of the material. To overcome these difficulties, it is often possible to move RM units, at intervals, to some reference temperature where they remain stable, and then test all the accumulated units - which have undergone different exposure times - at the same time. This is referred to as an isochronous study. This strategy has the advantage of improving the precision of data used in assessing stability at the cost of delaying results until the end of the stability study period. | 3 | Analytical Chemistry |
It has been found that the F number linearly correlates with the log k' value (logarithm of the retention factor) in aqueous reversed-phase liquid chromatography. This relationship can be used to understand the significance of different aspects of molecular architecture on their separation using different stationary phases. This size analysis is complementary to the length-to-breadth (L/B) ratio, which classifies molecules according to their "rodlike" or "squarelike" shape. | 3 | Analytical Chemistry |
In this technique the cells are lysed in alkaline conditions. The DNA in the mixture is denatured (strands separated) by disrupting the hydrogen bonds between the two strands. The large genomic DNA is subject to tangling and staying denatured when the pH is lowered during the neutralization. In other words, the strands come back together in a disordered fashion, basepairing randomly. The circular supercoiled plasmids' strands will stay relatively closely aligned and will renature correctly. Therefore, the genomic DNA will form an insoluble aggregate and the supercoiled plasmids will be left in solution. This can be followed by phenol extraction to remove proteins and other molecules. Then the DNA can be subjected to ethanol precipitation to concentrate the sample. | 1 | Biochemistry |
FRET (Förster resonance energy transfer) is a property in which the energy of the excited electron of one fluorphore, called the donor, is passed on to a nearby acceptor dye, either a dark quencher or another fluorophore, which has an excitation spectrum which overlaps with the emission spectrum of the donor dye resulting in a reduced fluorescence.
This can be used to:
* detect if two labelled protein or nucleic acids come into contact or a doubly labelled single molecules is hydrolysed;
* detect changes in conformation;
* measure concentration by a competitive binding assay. | 1 | Biochemistry |
In 1949, Saul Winstein observed that 2-exo-norbornyl brosylate (p-bromobenzenesulfonate) and 2-endo-norbornyl tosylate (p-toluenesulfonate) gave a racemic mixture of the same product, 2-exo-norbornyl acetate, upon acetolysis (see Figure 6). Since tosylates and brosylates work equally well as leaving groups, he concluded that both the 2-endo and 2-exo substituted norbornane must be going through a common cationic intermediate with a dominant exo reactivity. He reported that this intermediate was most likely a symmetric, delocalized 2-norbornyl cation. It was later shown via vapor phase chromatography that the amount of the endo epimer of product produced was less than 0.02%, proving the high stereoselectivity of the reaction.
When a single enantiomer of 2-exo-norbornyl brosylate undergoes acetolysis, no optical activity is seen in the resulting 2-exo-norbornyl acetate (see Figure 7). Under the non-classical description of the 2-norbornyl cation, the plane of symmetry present (running through carbons 4, 5, and 6) allow equal access to both enantiomers of the product, resulting in the observed racemic mixture.
It was also observed that the 2-exo-substituted norbornanes reacted 350 times faster than the corresponding endo isomers. Anchimeric assistance of the sigma bond between carbons 1 and 6 was rationalized as the explanation for this kinetic effect. Importantly, the invoked anchimeric assistance led many chemists to postulate that the energetic stability of the 2-norbornyl cation was directly due to the symmetric, bridged structure invoked in the non-classical explanation. However, some other authors offered alternative explanations for the high stability without invoking a non-classical structure.
In 1951, it was first suggested that the 2-norbornyl cation could actually be better described when viewed as a nortricyclonium ion. It has been shown that the major product formed from an elimination reaction of the 2-norbornyl cation is nortricyclene (not norbornene), but this has been claimed to support both non-classical ion postulates. | 7 | Physical Chemistry |
Prairie restoration is a conservation effort to restore prairie lands that were destroyed due to industrial, agricultural, commercial, or residential development. The primary aim is to return areas and ecosystems to their previous state before their depletion. The mass of SOC able to be stored in these restored plots is typically greater than the previous crop, acting as a more effective carbon sink. | 5 | Photochemistry |
A reducing sugar is any sugar that is capable of acting as a reducing agent. In an alkaline solution, a reducing sugar forms some aldehyde or ketone, which allows it to act as a reducing agent, for example in Benedict's reagent. In such a reaction, the sugar becomes a carboxylic acid.
All monosaccharides are reducing sugars, along with some disaccharides, some oligosaccharides, and some polysaccharides. The monosaccharides can be divided into two groups: the aldoses, which have an aldehyde group, and the ketoses, which have a ketone group. Ketoses must first tautomerize to aldoses before they can act as reducing sugars. The common dietary monosaccharides galactose, glucose and fructose are all reducing sugars.
Disaccharides are formed from two monosaccharides and can be classified as either reducing or nonreducing. Nonreducing disaccharides like sucrose and trehalose have glycosidic bonds between their anomeric carbons and thus cannot convert to an open-chain form with an aldehyde group; they are stuck in the cyclic form. Reducing disaccharides like lactose and maltose have only one of their two anomeric carbons involved in the glycosidic bond, while the other is free and can convert to an open-chain form with an aldehyde group.
The aldehyde functional group allows the sugar to act as a reducing agent, for example, in the Tollens test or Benedicts test. The cyclic hemiacetal forms of aldoses can open to reveal an aldehyde, and certain ketoses can undergo tautomerization to become aldoses. However, acetals, including those found in polysaccharide linkages, cannot easily become free aldehydes.
Reducing sugars react with amino acids in the Maillard reaction, a series of reactions that occurs while cooking food at high temperatures and that is important in determining the flavor of food. Also, the levels of reducing sugars in wine, juice, and sugarcane are indicative of the quality of these food products. | 0 | Organic Chemistry |
Tetramethyl­ammonium fluoride is the quaternary ammonium salt with the formula (CH)NF. This hygroscopic white solid is a source of “naked fluoride": fluoride ions not complexed with a metal atom. Most other soluble salts of fluoride are in fact bifluorides, HF. Historically, there have been two main approaches to prepare tetramethyl­ammonium fluoride: hydrofluoric acid neutralization of tetramethyl­ammonium hydroxide, and salt metathesis between different ammonium salts and inorganic fluoride sources, such as KF or CsF. Because the fluoride anion is extremely basic, the salt slowly reacts with acetonitrile, inducing dimerization to CHC(NH)=CHCN, which co-crystallizes. | 0 | Organic Chemistry |
The society recognizes members for outstanding technical achievement in electrochemical and solid-state science and technology at various career levels, and recognizes exceptional service to the Society, through the ECS Honors & Awards Program—the international awards, medals, and prizes administered by the Society.
Starting in 1919, Honorary Membership was bestowed for outstanding contributions to the Society. ECS's most prestigious award, the Edward Goodrich Acheson Award, established in 1928, is presented in even-numbered years for "conspicuous contribution to the advancement of the objectives, purposes, and activities of the society".
Supporting students and early career scientists has been a long-held goal of The Electrochemical Society. The Norman Hackerman Young Author Award —established in 1928—is one of the first awards created by the Society. It is given for the best paper published in the Journal of The Electrochemical Society that year by a young author or co-authors. Recipients must be under 31 years of age. Among the significant talents recognized at an early age by this award is Nobel laureate, M. Stanley Whittingham, who received it in 1970.
The Olin Palladium Award (formerly the Palladium Medal Award), established in 1950, is presented in odd-numbered years to recognize "distinguished contributions to the field of electrochemical or corrosion science."
ECS honors members with the designation, Fellow of The Electrochemical Society for having made significant accomplishments to the fields of electrochemistry and solid state science and technology, and to the Society.
The Vittorio de Nora Award was established in 1971 to recognize distinguished contributions to the field of electrochemical engineering and technology. | 7 | Physical Chemistry |
Manufacturing processes have five main variables: the workpiece, the tool, the machine tool, the environment, and process variables. All of these variables can affect the surface integrity of the workpiece by producing:
*High temperatures involved in various machining processes
*Plastic deformation in the workpiece (residual stresses)
*Surface geometry (roughness, cracks, distortion)
*Chemical reactions, especially between the tool and the workpiece | 8 | Metallurgy |
Silyl enol ethers of esters () or carboxylic acids () are called silyl ketene acetals and have the general structure . These compounds are more nucleophilic than the silyl enol ethers of ketones (). | 0 | Organic Chemistry |
The main advantages of using nanoelectrodes and arrays of nanoelectrodes include enhanced mass transport, lower capacitance, ability to work in smaller volumes and smaller overall device footprints.
The electrical current generated at an electrode is proportional to the electrode's geometric area. A disadvantage of using a single nanoelectrode is that it generates a small current output, which puts pressure on the instrumentation, and in turn, the reliability of the measurements recorded. One way to overcome this is the use an array of nanoelectrodes. The arrays produce a current, which is proportional with the number of electrodes in the array. This method has been used extensively in electroanalysis. Through the careful and accurate fabrication of arrays of nanoelectrodes, the electrochemical instrumentation is more reliable for sensitive measurement that enables implementation of a range of electroanalytical techniques.
There are two main types of arrangements; nanoelectrode arrays (NEAs) where the nanoelectrodes are spaced in an ordered arrangement and nanoelectrode ensembles (NEEs), where the individual nanoelectrodes are distributed randomly. | 7 | Physical Chemistry |
Heat is not to be confused with internal energy or synonymously thermal energy. While intimately connected to heat, they are distinct physical quantities.
As a heating technology, Joule heating has a coefficient of performance of 1.0, meaning that every joule of electrical energy supplied produces one joule of heat. In contrast, a heat pump can have a coefficient of more than 1.0 since it moves additional thermal energy from the environment to the heated item.
The definition of the efficiency of a heating process requires defining the boundaries of the system to be considered. When heating a building, the overall efficiency is different when considering heating effect per unit of electric energy delivered on the customer's side of the meter, compared to the overall efficiency when also considering the losses in the power plant and transmission of power. | 7 | Physical Chemistry |
The amount of alcohol on the breath can be measured, without requiring drawing blood, by blowing into a breathalyzer, resulting in a breath alcohol content (BrAC). The BrAC specifically correlates with the concentration of alcohol in arterial blood, satisfying the equation . Its correlation with the standard BAC found by drawing venous blood is less strong. Jurisdictions vary in the statutory conversion factor from BrAC to BAC, from 2000 to 2400. Many factors may affect the accuracy of a breathalyzer test, but they are the most common method for measuring alcohol concentrations in most jurisdictions. | 1 | Biochemistry |
There are various methods of adequately identifying and monitoring hydrogen damage, including ultrasonic echo attenuation method, amplitude-based backscatter, velocity ratio, creeping waves/time-of-flight measurement, pitch-catch mode shear wave velocity, advanced ultrasonic backscatter techniques (AUBT), time of flight diffraction (TOFD), thickness mapping and in-situ metallography – replicas. For hydrogen damage, the backscatter technique is used to detect affected areas in the material. To cross-check and confirm the findings of the backscatter measurement, the velocity ratio measurement technique is used. For the detection of micro and macro cracks, time of flight diffraction is a suitable method to use. | 8 | Metallurgy |
A carbazone is a partially oxidized carbazide with the general formula R=NNH(C=O)NH-NHR. The sulfur analog is called a thiocarbazone, of which dithizone is an example. | 0 | Organic Chemistry |
* Phosphorous acid (or phosphonic acid), (or ), a diprotic acid (with only two acidic hydrogens). Its salts and esters are called phosphites or phosphonates. | 0 | Organic Chemistry |
Sumner has presented lectures to public and school groups, and she has participated in videos and films on exploring Mars. These have included presentations at Sierra College, a Northern California Rotary Club, and Sacramento State University's Science in the River City. She appeared in several videos on Mars exploration, including ones hosted by UC Davis and in the Finnish documentary film “The Other Side of Mars”.
Dawn Sumner's research has been covered in local and national media outlets, including Popular Science, Wired Magazine, KPCC public radio, the television series Take Part, and the BBC. | 9 | Geochemistry |
FG-7142 (ZK-31906) is a drug which acts as a partial inverse agonist at the benzodiazepine allosteric site of the GABA receptor. It has anorectic, anxiogenic and pro-convulsant effects. It also increases release of acetylcholine and noradrenaline, and improves memory retention in animal studies. | 1 | Biochemistry |
In photosynthetic bacteria, the proteins that gather light for photosynthesis are embedded in cell membranes. In its simplest form, this involves the membrane surrounding the cell itself. However, the membrane may be tightly folded into cylindrical sheets called thylakoids, or bunched up into round vesicles called intracytoplasmic membranes. These structures can fill most of the interior of a cell, giving the membrane a very large surface area and therefore increasing the amount of light that the bacteria can absorb.
In plants and algae, photosynthesis takes place in organelles called chloroplasts. A typical plant cell contains about 10 to 100 chloroplasts. The chloroplast is enclosed by a membrane. This membrane is composed of a phospholipid inner membrane, a phospholipid outer membrane, and an intermembrane space. Enclosed by the membrane is an aqueous fluid called the stroma. Embedded within the stroma are stacks of thylakoids (grana), which are the site of photosynthesis. The thylakoids appear as flattened disks. The thylakoid itself is enclosed by the thylakoid membrane, and within the enclosed volume is a lumen or thylakoid space. Embedded in the thylakoid membrane are integral and peripheral membrane protein complexes of the photosynthetic system.
Plants absorb light primarily using the pigment chlorophyll. The green part of the light spectrum is not absorbed but is reflected which is the reason that most plants have a green color. Besides chlorophyll, plants also use pigments such as carotenes and xanthophylls. Algae also use chlorophyll, but various other pigments are present, such as phycocyanin, carotenes, and xanthophylls in green algae, phycoerythrin in red algae (rhodophytes) and fucoxanthin in brown algae and diatoms resulting in a wide variety of colors.
These pigments are embedded in plants and algae in complexes called antenna proteins. In such proteins, the pigments are arranged to work together. Such a combination of proteins is also called a light-harvesting complex.
Although all cells in the green parts of a plant have chloroplasts, the majority of those are found in specially adapted structures called leaves. Certain species adapted to conditions of strong sunlight and aridity, such as many Euphorbia and cactus species, have their main photosynthetic organs in their stems. The cells in the interior tissues of a leaf, called the mesophyll, can contain between 450,000 and 800,000 chloroplasts for every square millimeter of leaf. The surface of the leaf is coated with a water-resistant waxy cuticle that protects the leaf from excessive evaporation of water and decreases the absorption of ultraviolet or blue light to minimize heating. The transparent epidermis layer allows light to pass through to the palisade mesophyll cells where most of the photosynthesis takes place. | 5 | Photochemistry |
He has published over 222 papers (200 indexed publications) coedited four books, 9 book chapters and 3 patents. H impact factor= 41 (Web of Science), H= 42 Scopus and H= 48 (Google Scholar) with more 7460 citations in Google. He has created three patents with the Chilean Navy on electrode materials for energy conversion. He has presented more than 300 papers in national and international meetings, including some plenary and invited lectures and keynotes worldwide. He has been a guest editor for the Journal of Applied Electrochemistry, The International Journal of Electrochemistry and recently in Current Opinion in Electrochemistry | 7 | Physical Chemistry |
When there is no equilibrium between phases or chemical compounds, kinetic fractionation can occur. For example, at interfaces between liquid water and air, the forward reaction is enhanced if the humidity of the air is less than 100% or the water vapor is moved by a wind. Kinetic fractionation generally is enhanced compared to equilibrium fractionation and depends on factors such as reaction rate, reaction pathway and bond energy. Since lighter isotopes generally have weaker bonds, they tend to react faster and enrich the reaction products.
Biological fractionation is a form of kinetic fractionation since reactions tend to be in one direction. Biological organisms prefer lighter isotopes because there is a lower energy cost in breaking energy bonds. In addition to the previously mentioned factors, the environment and species of the organism can have a large effect on the fractionation. | 9 | Geochemistry |
Epoxidation of a substituted cyclohexene affords a product where the R group resides in the pseudo-equatorial position. Nucleophilic ring-opening of this class of epoxides can occur by an attack at either the C1 or C2-position. It is well known that nucleophilic ring-opening reactions of these substrates can proceed with excellent regioselectivity. The Fürst-Plattner rule attributes this regiochemical control to a large preference for the reaction pathway that follows the more stable chair-like transition state (attack at the C1-position) compared to the one proceeding through the unfavored twist boat-like transition state (attack at the C2-position). The attack at the C1-position follows a substantially lower reaction barrier of around 5 kcal mol depending on the specific conditions. Similarly, the Fürst-Plattner rule applies to nucleophilic additions to imines and halonium ions. | 4 | Stereochemistry |
Rif is a small (~21 kDa) signaling G protein (more specifically a GTPase), and is a member of the Rho family of GTPases. It is primarily active in the brain and plays a physiological role in the formation of neuronal dendritic spine. This process is regulated by FARP1, a type of activator for RhoA GTPases. Alternatively, Rif can induce the formation of actin stress fibers in epithelial cells, which is dependent on the activity levels of ROCK proteins since the absence of ROCK activity would mean Rif would be unable to stimulate the growth of stress fibers.
Rif is also seen expressed in diverse amount of human tissues such as in the colon and stomach due to Rhos use of actin dynamics to absorb intestinal epithelial cells. Rif is one way of generating filopodia (Rif-induced filopodia) through its interaction with mDia2. Specifically, the interaction is between the GTP from Rif and the GTPase binding domain (GBD) of mDia2. Rifs function in forming filopodia has a relation to the function of platelets. But in mice, Rif is not necessary for platelets to function. The co-expression of Rif with Rac or Cdc42, other GTPases that also participate in regulating cell structure and morphology, can give rise to new filopodial structures that differ from the filopodia arrangements stimulated by each of these GTPases functioning separately. | 1 | Biochemistry |
The loss on ignition is reported as part of an elemental or oxide analysis of a mineral. The volatile materials lost usually consist of combined water (hydrates and labile hydroxy-compounds) and carbon dioxide from carbonates. It may be used as a quality test, commonly carried out for minerals such as iron ore. For example, the loss on ignition of fly ash is composed of contaminants and unburnt fuel.
In pyroprocessing industries such as lime,calcined bauxite, refractories or cement manufacture, the loss on ignition of the raw material is roughly equivalent to the mass loss it will experience in a kiln. Likewise, in minerals, the loss on ignition indicates the material actually lost during smelting or refining in a furnace or smelter. The loss on ignition of the product indicates the extent to which the pyroprocessing was incomplete. ASTM tests are defined for limestone and lime and cement among others. | 3 | Analytical Chemistry |
The cycling of and excretion of urea by the kidneys is a vital part of mammalian metabolism. Besides its role as carrier of waste nitrogen, urea also plays a role in the countercurrent exchange system of the nephrons, that allows for reabsorption of water and critical ions from the excreted urine. Urea is reabsorbed in the inner medullary collecting ducts of the nephrons, thus raising the osmolarity in the medullary interstitium surrounding the thin descending limb of the loop of Henle, which makes the water reabsorb.
By action of the urea transporter 2, some of this reabsorbed urea eventually flows back into the thin descending limb of the tubule, through the collecting ducts, and into the excreted urine. The body uses this mechanism, which is controlled by the antidiuretic hormone, to create hyperosmotic urine — i.e., urine with a higher concentration of dissolved substances than the blood plasma. This mechanism is important to prevent the loss of water, maintain blood pressure, and maintain a suitable concentration of sodium ions in the blood plasma.
The equivalent nitrogen content (in grams) of urea (in mmol) can be estimated by the conversion factor 0.028 g/mmol. Furthermore, 1 gram of nitrogen is roughly equivalent to 6.25 grams of protein, and 1 gram of protein is roughly equivalent to 5 grams of muscle tissue. In situations such as muscle wasting, 1 mmol of excessive urea in the urine (as measured by urine volume in litres multiplied by urea concentration in mmol/L) roughly corresponds to a muscle loss of 0.67 gram. | 0 | Organic Chemistry |
The first commercial primary-lead ISASMELT furnace was installed at the Yunnan Chihong Zinc and Germanium Company Limited (YCZG) greenfield zinc and lead smelting complex at Qujing in Yunnan Province in China. This furnace was part of a plant consisting of the ISASMELT furnace and a blast furnace specially designed to treat high-lead ISASMELT slag. The ISASMELT furnace was designed to produce both the slag and lead bullion, with about 40% of the lead in the concentrate being converted to lead bullion in the ISASMELT furnace.
The ISASMELT–blast furnace combination was designed to treat 160,000 t/y of lead concentrate.
The second commercial primary-lead ISASMELT furnace was commissioned at Kazzinc's smelting complex at Ust-Kamenogorsk in Kazakhstan in 2012. It is designed to treat 300,000 t/y of lead concentrate, again using an ISASMELT–blast furnace combination.
YCZG is constructing another lead ISASMELT at a new greenfield smelter in Huize in China, and this is due to be commissioned in 2013.
In June 2017, Glencore announced that Nyrstar NV had acquired an Isasmelt licence for its new Ausmelt furnace in Port Pirie. As part of the agreement, Nyrstar engaged training and ramp-up support services for the Ausmelt furnace and blast furnace by personnel from Glencore's Kazzinc operations in Kazakhstan. This involved training Nyrstar personnel at Ust-Kamenogorsk operations and site support by Kazzinc personnel during the commissioning and ramp-up stages of the Ausmelt plant. | 8 | Metallurgy |
Viel received a PhD in molecular and cellular biology of development in 1990 from Pierre and Marie Curie University in Paris, France (Paris VI) for a thesis "Les particules ribonucleoproteiques dans le oocytes de xenopus laevis. mise en place du systeme de synthese proteique" and did postdoctoral work at Harvard University. | 1 | Biochemistry |
The S−H bond in thiols is weak compared to the O−H bond in alcohols. For CHX−H, the bond enthalpies are for X = S and for X = O. Hydrogen-atom abstraction from a thiol gives a thiyl radical with the formula RS, where R = alkyl or aryl. | 0 | Organic Chemistry |
A reducing atmosphere is an atmospheric condition in which oxidation is prevented by absence of oxygen and other oxidizing gases or vapours, and which may contain actively reductant gases such as hydrogen, carbon monoxide, methane and hydrogen sulfide that would be readily oxidized to remove any free oxygen. Although Early Earth had had a reducing prebiotic atmosphere prior to the Proterozoic eon, starting at about 2.5 billion years ago in the late Neoarchaean period, the Earth's atmosphere experienced a significant rise in oxygen transitioned to an oxidizing atmosphere with a surplus of molecular oxygen (dioxygen, O) as the primary oxidizing agent. | 8 | Metallurgy |
Phosphine ligands, such as triphenylphosphine or the Trost ligand, have been used to greatly expand the scope of the Tsuji–Trost reaction. These ligands can modulate the properties of the palladium catalyst such as steric bulk as well as the electronic properties. Importantly, these ligands can also instill chirality to the final product, making it possible for these reactions to be carried out asymmetrically as shown below. | 0 | Organic Chemistry |
In the Maxwell Garnett approximation, the effective medium consists of a matrix medium with and inclusions with . Maxwell Garnett was the son of physicist William Garnett, and was named after Garnett's friend, James Clerk Maxwell. He proposed his formula to explain colored pictures that are observed in glasses doped with metal nanoparticles. His formula has a form
where is effective relative complex permittivity of the mixture, is relative complex permittivity of the background medium containing small spherical inclusions of relative permittivity with volume fraction of . This formula is based on the equality
where is the absolute permittivity of free space and is electric dipole moment of a single inclusion induced by the external electric field . However this equality is good only for homogeneous medium and . Moreover, the formula (1) ignores the interaction between single inclusions. Because of these circumstances, formula (1) gives too narrow and too high resonant curve for plasmon excitations in metal nanoparticles of the mixture. | 7 | Physical Chemistry |
Cyclization reactions, or intramolecular addition reactions, can be used to form cycloalkenes. These reactions primarily form cyclopentenones, a cycloalkene that contains two functional groups: the cyclopentene and a ketone group. However, other cycloalkenes, such as Cyclooctatetraene, can be formed as a result of this reaction. | 0 | Organic Chemistry |
The fundamental properties of currents mediated by ion channels were analyzed by the British biophysicists Alan Hodgkin and Andrew Huxley as part of their Nobel Prize-winning research on the action potential, published in 1952. They built on the work of other physiologists, such as Cole and Bakers research into voltage-gated membrane pores from 1941. The existence of ion channels was confirmed in the 1970s by Bernard Katz and Ricardo Miledi using noise analysis . It was then shown more directly with an electrical recording technique known as the "patch clamp", which led to a Nobel Prize to Erwin Neher and Bert Sakmann, the techniques inventors. Hundreds if not thousands of researchers continue to pursue a more detailed understanding of how these proteins work. In recent years the development of automated patch clamp devices helped to increase significantly the throughput in ion channel screening.
The Nobel Prize in Chemistry for 2003 was awarded to Roderick MacKinnon for his studies on the physico-chemical properties of ion channel structure and function, including x-ray crystallographic structure studies. | 1 | Biochemistry |
RNA primers are used by living organisms in the initiation of synthesizing a strand of DNA. A class of enzymes called primases add a complementary RNA primer to the reading template de novo on both the leading and lagging strands. Starting from the free 3’-OH of the primer, known as the primer terminus, a DNA polymerase can extend a newly synthesized strand. The leading strand in DNA replication is synthesized in one continuous piece moving with the replication fork, requiring only an initial RNA primer to begin synthesis. In the lagging strand, the template DNA runs in the 5′→3′ direction. Since DNA polymerase cannot add bases in the 3′→5′ direction complementary to the template strand, DNA is synthesized ‘backward’ in short fragments moving away from the replication fork, known as Okazaki fragments. Unlike in the leading strand, this method results in the repeated starting and stopping of DNA synthesis, requiring multiple RNA primers. Along the DNA template, primase intersperses RNA primers that DNA polymerase uses to synthesize DNA from in the 5′→3′ direction.
Another example of primers being used to enable DNA synthesis is reverse transcription. Reverse transcriptase is an enzyme that uses a template strand of RNA to synthesize a complementary strand of DNA. The DNA polymerase component of reverse transcriptase requires an existing 3' end to begin synthesis. | 1 | Biochemistry |
Once the stimuli have reached the cell body, the nerve must integrate the various stimuli before the nerve can respond. The stimuli that have traveled down the dendrites converge at the axon hillock, where they are summed to determine the neuronal response. If the sum of the stimuli reaches a certain voltage, known as the threshold potential, depolarization continues from the axon hillock down the axon. | 7 | Physical Chemistry |
Rivers can also transport organic carbon to the ocean through weathering or erosion of aluminosilicate (equation 7) and carbonate rocks (equation 8) on land,
or by the decomposition of life (equation 5, e.g. plant and soil material). Rivers contribute roughly equal amounts (~0.4 GtC/yr) of DIC and DOC to the oceans. It is estimated that approximately 0.8 GtC (DIC + DOC) is transported annually from the rivers to the ocean. The rivers that flow into Chesapeake Bay (Susquehanna, Potomac, and James rivers) input approximately 0.004 Gt (6.5 x 10 moles) DIC per year. The total carbon transport of rivers represents approximately 0.02% of the total carbon in the atmosphere. Though it seems small, over long time scales (1000 to 10,000 years) the carbon that enters rivers (and therefore does not enter the atmosphere) serves as a stabilizing feedback for greenhouse warming. | 9 | Geochemistry |
For an open system, the first law of thermodynamics admits three forms of energy transfer, as work, as heat, and as energy associated with matter that is transferred. The latter cannot be split uniquely into heat and work components.
One-way convection of internal energy is a form a transport of energy but is not, as sometimes mistakenly supposed (a relic of the caloric theory of heat), transfer of energy as heat, because one-way convection is transfer of matter; nor is it transfer of energy as work. Nevertheless, if the wall between the system and its surroundings is thick and contains fluid, in the presence of a gravitational field, convective circulation within the wall can be considered as indirectly mediating transfer of energy as heat between the system and its surroundings, though the source and destination of the transferred energy are not in direct contact. | 7 | Physical Chemistry |
DHA can be converted non-enzymatically by free radical-mediated peroxidation to 8 different neurofuran regioisomers termed neuroprostanes and neurofuranes including 4-, 7-, 10-, 11-, 13-, 14-, 17-, and 20-series neurofurans/neuroporstanes for a total of 128 different racemic compounds. The most studied DHA-derived of these products are members of the 4-series, neurofuran 4-Fneuroprostane and 4(RS)-ST-Δ6-8-neurofurane. These metabolites have been used mainly as biomarkers of oxidative stress that are formed in nerve tissues of the central nervous system. | 1 | Biochemistry |
Forging temperature is the temperature at which a metal becomes substantially more soft, but is lower than the melting temperature, such that it can be reshaped by forging. Bringing a metal to its forging temperature allows the metal's shape to be changed by applying a relatively small force, without creating cracks. For most metals, forging temperature is approximately 70% of the absolute temperature (usually measured in kelvins) of its melting point.
Selecting the maximum forging temperature allows metals to be forged more easily, lowering the forging pressure and thus the wear on metal-forming dies. The temperature at which a metal is forged can affect the homogeneity in microstructure and mechanical properties of forged products, which can highly affect the performance of products used in manufacturing. | 7 | Physical Chemistry |
When we have a set of possible events, coming from the distribution , we can encode them (with a lossless data compression) using entropy encoding. This compresses the data by replacing each fixed-length input symbol with a corresponding unique, variable-length, prefix-free code (e.g.: the events (A, B, C) with probabilities p = (1/2, 1/4, 1/4) can be encoded as the bits (0, 10, 11)). If we know the distribution in advance, we can devise an encoding that would be optimal (e.g.: using Huffman coding). Meaning the messages we encode will have the shortest length on average (assuming the encoded events are sampled from ), which will be equal to Shannon's Entropy of (denoted as ). However, if we use a different probability distribution () when creating the entropy encoding scheme, then a larger number of bits will be used (on average) to identify an event from a set of possibilities. This new (larger) number is measured by the cross entropy between and .
The cross entropy between two probability distributions ( and ) measures the average number of bits needed to identify an event from a set of possibilities, if a coding scheme is used based on a given probability distribution , rather than the "true" distribution . The cross entropy for two distributions and over the same probability space is thus defined as follows.
For explicit derivation of this, see the Motivation section above.
Under this scenario, relative entropies (kl-divergence) can be interpreted as the extra number of bits, on average, that are needed (beyond ) for encoding the events because of using for constructing the encoding scheme instead of . | 7 | Physical Chemistry |
The unique interaction between the oligosaccharide chains have different applications. First, it aids in quality control by identifying misfolded proteins. The oligosaccharide chains also change the solubility and polarity of the proteins that they are bonded to. For example, if the oligosaccharide chains are negatively charged, with enough density around the protein, they can repulse proteolytic enzymes away from the bonded protein. The diversity in interactions lends itself to different types of glycoproteins with different structures and functions.
One example of glycoproteins found in the body is mucins, which are secreted in the mucus of the respiratory and digestive tracts. The sugars when attached to mucins give them considerable water-holding capacity and also make them resistant to proteolysis by digestive enzymes.
Glycoproteins are important for white blood cell recognition. Examples of glycoproteins in the immune system are:
* molecules such as antibodies (immunoglobulins), which interact directly with antigens.
* molecules of the major histocompatibility complex (or MHC), which are expressed on the surface of cells and interact with T cells as part of the adaptive immune response.
*sialyl Lewis X antigen on the surface of leukocytes.
H antigen of the ABO blood compatibility antigens.
Other examples of glycoproteins include:
* gonadotropins (luteinizing hormone and follicle-stimulating hormone)
* glycoprotein IIb/IIIa, an integrin found on platelets that is required for normal platelet aggregation and adherence to the endothelium.
* components of the zona pellucida, which surrounds the oocyte, and is important for sperm-egg interaction.
* structural glycoproteins, which occur in connective tissue. These help bind together the fibers, cells, and ground substance of connective tissue. They may also help components of the tissue bind to inorganic substances, such as calcium in bone.
* Glycoprotein-41 (gp41) and glycoprotein-120 (gp120) are HIV viral coat proteins.
Soluble glycoproteins often show a high viscosity, for example, in egg white and blood plasma.
* Miraculin, is a glycoprotein extracted from Synsepalum dulcificum a berry which alters human tongue receptors to recognize sour foods as sweet.
Variable surface glycoproteins allow the sleeping sickness Trypanosoma parasite to escape the immune response of the host.
The viral spike of the human immunodeficiency virus is heavily glycosylated. Approximately half the mass of the spike is glycosylation and the glycans act to limit antibody recognition as the glycans are assembled by the host cell and so are largely self. Over time, some patients can evolve antibodies to recognise the HIV glycans and almost all so-called 'broadly neutralising antibodies (bnAbs) recognise some glycans. This is possible mainly because the unusually high density of glycans hinders normal glycan maturation and they are therefore trapped in the premature, high-mannose, state. This provides a window for immune recognition. In addition, as these glycans are much less variable than the underlying protein, they have emerged as promising targets for vaccine design.
P-glycoproteins are critical for antitumor research due to its ability block the effects of antitumor drugs. P-glycoprotein, or multidrug transporter (MDR1), is a type of ABC transporter that transports compounds out of cells. This transportation of compounds out of cells includes drugs made to be delivered to the cell, causing a decrease in drug effectiveness. Therefore, being able to inhibit this behavior would decrease P-glycoprotein interference in drug delivery, making this an important topic in drug discovery. For example, P-Glycoprotein causes a decrease in anti-cancer drug accumulation within tumor cells, limiting the effectiveness of chemotherapies used to treat cancer. | 0 | Organic Chemistry |
Andrew Carnegie, a Scottish immigrant, advanced the cheap and efficient mass production of steel rails for railroad lines, by adopting the Bessemer process. After an early career in railroads, Carnegie foresaw the potential for steel to amass vast profits. He asked his cousin, George Lauder to join him in America from Scotland. Lauder was a leading mechanical engineer who had studied under Lord Kelvin. Lauder devised several new systems for the Carnegie Steel Company including the process for washing and coking dross from coal mines, which resulted in a significant increase in scale, profits, and enterprise value.
Lauder would go on to lead the development of the use of steel in armor and armaments for the Carnegie Steel Company, spending significant time at the Krupp factory in Germany in 1886 before returning to build the massive armor plate mill at the Homestead Steel Works that would revolutionize naval warfare.
Carnegies first mill was the Edgar Thomson Works in Braddock, PA, just outside of Pittsburgh. In 1888, he bought the rival Homestead Steel Works, which included an extensive plant served by tributary coal and iron fields, a 425-mile (685 km) long railway, and a line of lake steamships. He would also add the Duquesne Works to his empire. These three mills on the Monongahela River would make Pittsburgh the steel capital of the world. In the late 1880s, the Carnegie Steel Company was the largest manufacturer of pig iron, steel rails, and coke in the world, with a capacity to produce approximately 2,000 tons of pig iron per day. A consolidation of Carnegies assets and those of his associates occurred in 1892 with the launching of the Carnegie Steel Company.
Lauder would go on to lead the development of the use of steel in armor and armaments for the Carnegie Steel Company, spending significant time at the Krupp factory in Germany in 1886 before returning to build the massive armor plate mill at the Homestead Steel Works that would revolutionize naval warfare.
By 1889, the U.S. output of steel exceeded that of Britain, and Andrew Carnegie owned a large part of it. By 1900, the profits of Carnegie Bros. & Company alone stood at $480,000,000 with $225,000,000 being Carnegie's share.
Carnegie, through Keystone, supplied the steel for and owned shares in the landmark Eads Bridge project across the Mississippi River in St. Louis, Missouri (completed 1874). This project was an important proof-of-concept for steel technology which marked the opening of a new steel market.
The Homestead Strike was a violent labor dispute in 1892 that involved an attack by strikers against private security guards. The governor called in the National Guard. The strike failed and the union collapsed. The dispute took place at Carnegie's Homestead Steel Works between the Amalgamated Association of Iron and Steel Workers and the Carnegie Steel Company. The final result was a major defeat for the union and a setback for efforts to unionize steelworkers.
Carnegie sold all his steel holdings in 1901; they were merged into U.S. Steel and it was non-union until the late 1930s. | 8 | Metallurgy |
The following are synthetic gemstones that were developed by Tairus scientists; they are alternately referred to as Tairus stones (e.g. "Tairus Ruby").
*Floating zone ruby, synthesized in 1991 (no longer in production)
*Hydrothermal ruby, synthesized in 1992 by Alexander Dokukin.
*Hydrothermal aquamarine, synthesized in 1993.
*Hydrothermal sapphires, in pink, green, orange, and blue.
*Colombian color emerald, developed in 2004. | 3 | Analytical Chemistry |
In biology, quorum sensing or quorum signaling (QS) is the ability to detect and respond to cell population density by gene regulation. Quorum sensing is a type of cellular signaling, and more specifically can be considered a type of paracrine signaling. However, it also contains traits of both autocrine signaling: a cell produces both the autoinducer molecule and the receptor for the autoinducer. As one example, QS enables bacteria to restrict the expression of specific genes to the high cell densities at which the resulting phenotypes will be most beneficial, especially for phenotypes that would be ineffective at low cell densities and therefore too energetically costly to express. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population. In a similar fashion, some social insects use quorum sensing to determine where to nest. Quorum sensing in pathogenic bacteria activates host immune signaling and prolongs host survival, by limiting the bacterial intake of nutrients, such as tryptophan, which further is converted to serotonin. As such, quorum sensing allows a commensal interaction between host and pathogenic bacteria. Quorum sensing may also be useful for cancer cell communications.
In addition to its function in biological systems, quorum sensing has several useful applications for computing and robotics. In general, quorum sensing can function as a decision-making process in any decentralized system in which the components have: (a) a means of assessing the number of other components they interact with and (b) a standard response once a threshold number of components is detected. | 1 | Biochemistry |
Cycloalkenes follow a similar nomenclature system to alkenes, but the carbons are numbered starting at a carbon on the double bond and then through the double bond and around the ring. This method is used to keep the index numbers small. | 0 | Organic Chemistry |
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