text stringlengths 105 4.57k | label int64 0 1 | label_text stringclasses 2
values |
|---|---|---|
Normally, the Wnt signaling pathway leads to stabilization of β-catenin through inactivation of a protein complex containing the tumor suppressors APC and Axin. This destruction complex normally triggers β-catenin phosphorylation, inducing its degradation. De-regulation of the autocrine Wnt signaling pathway via mutations in APC and Axin have been linked to activation of various types of human cancer. Genetic alterations that lead to de-regulation of the autocrine Wnt pathway result in transactivation of epidermal growth factor receptor (EGFR) and other pathways, in turn contributing to proliferation of tumor cells. In colorectal cancer, for example, mutations in APC, axin, or β-catenin promote β-catenin stabilization and transcription of genes encoding cancer-associated proteins. Furthermore, in human breast cancer, interference with the de-regulated Wnt signaling pathway reduces proliferation and survival of cancer. These findings suggest that interference with Wnt signaling at the ligand-receptor level may improve the effectiveness of cancer therapies. | 1 | Applied and Interdisciplinary Chemistry |
Robert Stirlings innovative contribution to the design of hot air engines of 1816 was what he called the Economiser'. Now known as the regenerator, it stored heat from the hot portion of the engine as the air passed to the cold side, and released heat to the cooled air as it returned to the hot side. This innovation improved the efficiency of the Stirling engine enough to make it commercially successful in particular applications, and has since been a component of every air engine that is called a Stirling engine. | 0 | Theoretical and Fundamental Chemistry |
A theoretical plate in many separation processes is a hypothetical zone or stage in which two phases, such as the liquid and vapor phases of a substance, establish an equilibrium with each other. Such equilibrium stages may also be referred to as an equilibrium stage, ideal stage, or a theoretical tray. The performance of many separation processes depends on having series of equilibrium stages and is enhanced by providing more such stages. In other words, having more theoretical plates increases the efficiency of the separation process be it either a distillation, absorption, chromatographic, adsorption or similar process. | 1 | Applied and Interdisciplinary Chemistry |
On an industrial scale, barium chloride is prepared via a two step process from barite (barium sulfate). The first step requires high temperatures.
The second step requires reaction between barium sulfide and hydrogen chloride:
or between barium sulfide and calcium chloride:
In place of HCl, chlorine can be used. Barium chloride is extracted out from the mixture with water. From water solutions of barium chloride, its dihydrate () can be crystallized as colorless crystals.
Barium chloride can in principle be prepared by the reaction between barium hydroxide or barium carbonate with hydrogen chloride. These basic salts react with hydrochloric acid to give hydrated barium chloride. | 0 | Theoretical and Fundamental Chemistry |
Many of the advantages of cell-free protein array technology address the limitations of cell-based expression system used in traditional methods of protein microarray production. | 1 | Applied and Interdisciplinary Chemistry |
Oxidation and reduction reactions are not common in organic chemistry as few organic molecules can act as oxidizing or reducing agents. Iron(II), on the other hand, can easily be oxidized to iron(III). This functionality is used in cytochromes, which function as electron-transfer vectors. The presence of the metal ion allows metalloenzymes to perform functions such as redox reactions that cannot easily be performed by the limited set of functional groups found in amino acids. The iron atom in most cytochromes is contained in a heme group. The differences between those cytochromes lies in the different side-chains. For instance cytochrome a has a heme a prosthetic group and cytochrome b has a heme b prosthetic group. These differences result in different Fe/Fe redox potentials such that various cytochromes are involved in the mitochondrial electron transport chain.
Cytochrome P450 enzymes perform the function of inserting an oxygen atom into a C−H bond, an oxidation reaction. | 1 | Applied and Interdisciplinary Chemistry |
Photoproteins do not display typical enzyme kinetics as seen in luciferases. Instead, when mixed with luciferin, they display luminescence proportional to the amount of the photoprotein. For example, the photoprotein aequorin produces a flash of light when luciferin and calcium are added, rather than the prolonged glow that is seen for luciferases when luciferin is added. In this respect, it may appear that photoproteins are not enzymes, when in fact they do catalyze their bioluminescence reactions. This is due to a fast catalytic step, which produces the light, and a slow regeneration step, where the oxyluciferin is freed and another molecule of luciferin is then enabled to bind to the enzyme. Because of the kinetically slow step, each aequorin molecule must "recharge" with another molecule of luciferin before it can emit light again, and this makes it appear as though it is not behaving as a typical enzyme.
Photoproteins form a stable luciferin-photoprotein complex, often until the addition of another required factor such as Ca in the case of aequorin. | 1 | Applied and Interdisciplinary Chemistry |
Following is a summary table for the list of 989 nuclides with half-lives greater than one hour. A total of 251 nuclides have never been observed to decay, and are classically considered stable. Of these, 90 are believed to be absolutely stable except to proton decay (which has never been observed), while the rest are "observationally stable" and theoretically can undergo radioactive decay with extremely long half-lives.
The remaining tabulated radionuclides have half-lives longer than 1 hour, and are well-characterized (see list of nuclides for a complete tabulation). They include 30 nuclides with measured half-lives longer than the estimated age of the universe (13.8 billion years), and another four nuclides with half-lives long enough (> 100 million years) that they are radioactive primordial nuclides, and may be detected on Earth, having survived from their presence in interstellar dust since before the formation of the Solar System, about 4.6 billion years ago. Another 60+ short-lived nuclides can be detected naturally as daughters of longer-lived nuclides or cosmic-ray products. The remaining known nuclides are known solely from artificial nuclear transmutation.
Numbers are not exact, and may change slightly in the future, as "stable nuclides" are observed to be radioactive with very long half-lives.
This is a summary table for the 989 nuclides with half-lives longer than one hour (including those that are stable), given in list of nuclides. | 0 | Theoretical and Fundamental Chemistry |
The College Board recommends successful completion of high school chemistry and algebra 2; however, requirement of this may differ from school to school. AP Chemistry usually requires knowledge of algebra 2; however, some schools allow students to take the course concurrently with this class. The requirement of regular or honors level high school chemistry may also be waived, but usually requires completion of a special assignment or exam, or completion of high school chemistry alongside AP Chemistry. | 1 | Applied and Interdisciplinary Chemistry |
Different form of the stationary principle for T-matrix reads
The wave functions and must satisfy the same Lippmann-Schwinger equations to get the stationary value. | 0 | Theoretical and Fundamental Chemistry |
Everyday examples of heat engines include the thermal power station, internal combustion engine, firearms, refrigerators and heat pumps. Power stations are examples of heat engines run in a forward direction in which heat flows from a hot reservoir and flows into a cool reservoir to produce work as the desired product. Refrigerators, air conditioners and heat pumps are examples of heat engines that are run in reverse, i.e. they use work to take heat energy at a low temperature and raise its temperature in a more efficient way than the simple conversion of work into heat (either through friction or electrical resistance). Refrigerators remove heat from within a thermally sealed chamber at low temperature and vent waste heat at a higher temperature to the environment and heat pumps take heat from the low temperature environment and vent it into a thermally sealed chamber (a house) at higher temperature.
In general heat engines exploit the thermal properties associated with the expansion and compression of gases according to the gas laws or the properties associated with phase changes between gas and liquid states. | 0 | Theoretical and Fundamental Chemistry |
This piece is the smaller part of the fragment broken during Bahadur Shah's reign. Henry Cousens (1902–03) measured its length as . The part with the square cross-section measured , while the part with the octagonal section measured . Klaus Roessler (1995) found this piece to be long. Roessler estimated its weight at .
The piece was removed from the Lat Masjid site at an unknown time. In February 1903, Henry Cousens of ASI found it in Anand High School, where a museum had been set up in 1902. The museum was relocated to another site between the years 1922 and 1942. When this happened, the pillar was brought back to the Lat Masjid and placed horizontally on the ground. | 1 | Applied and Interdisciplinary Chemistry |
Klein-Seetharaman moved to the University of Pittsburgh as an assistant professor in 2002 and was promoted to associate professor in 2009. She joined the Warwick Medical School as a professor in medicine in 2013. She returned to the[United States in 2017, first as a professor at the Colorado School of Mines and then as a professor at the Arizona State University in 2021. Her research looks to uncover the structure-property relationships of membrane proteins. | 1 | Applied and Interdisciplinary Chemistry |
In biochemistry, a glycolytic oscillation is the repetitive fluctuation of in the concentrations of metabolites, classically observed experimentally in yeast and muscle. The first observations of oscillatory behaviour in glycolysis were made by Duysens and Amesz in 1957.
The problem of modelling glycolytic oscillation has been studied in control theory and dynamical systems since the 1960s since the behaviour depends on the rate of substrate injection.
Early models used two variables, but the most complex behaviour they could demonstrate was period oscillations due to the Poincaré–Bendixson theorem, so later models introduced further variables. | 1 | Applied and Interdisciplinary Chemistry |
Phase transitions (phase changes) that help describe polymorphism include polymorphic transitions as well as melting and vaporization transitions. According to IUPAC, a polymorphic transition is "A reversible transition of a solid crystalline phase at a certain temperature and pressure (the inversion point) to another phase of the same chemical composition with a different crystal structure." Additionally, Walter McCrone described the phases in polymorphic matter as "different in crystal structure but identical in the liquid or vapor states." McCrone also defines a polymorph as “a crystalline phase of a given compound resulting from the possibility of at least two different arrangements of the molecules of that compound in the solid state.” These defining facts imply that polymorphism involves changes in physical properties but cannot include chemical change. Some early definitions do not make this distinction.
Eliminating chemical change from those changes permissible during a polymorphic transition delineates polymorphism. For example, isomerization can often lead to polymorphic transitions. However, tautomerism (dynamic isomerization) leads to chemical change, not polymorphism. As well, allotropy of elements and polymorphism have been linked historically. However, allotropes of an element are not always polymorphs. A common example is the allotropes of carbon, which include graphite, diamond, and londsdaleite. While all three forms are allotropes, graphite is not a polymorph of diamond and londsdaleite. The reason is that graphite is chemically distinct, having sp hybridized bonding, while diamond, and londsdaleite are chemically identical, both having sp hybridized bonding. Diamond and londsdaleite differ in their crystal structures but do not differ chemically. Isomerization and allotropy are only two of the phenomena linked to polymorphism. For additional information about identifying polymorphism and distinguishing it from other phenomena, see the review by Brog et al.
Polymorphism is of practical relevance to pharmaceuticals, agrochemicals, pigments, dyestuffs, foods, and explosives. | 0 | Theoretical and Fundamental Chemistry |
Molecular beacons, or molecular beacon probes, are oligonucleotide hybridization probes that can report the presence of specific nucleic acids in homogenous solutions. Molecular beacons are hairpin-shaped molecules with an internally quenched fluorophore whose fluorescence is restored when they bind to a target nucleic acid sequence. This is a novel non-radioactive method for detecting specific sequences of nucleic acids. They are useful in situations where it is either not possible or desirable to isolate the probe-target hybrids from an excess of the hybridization probes. | 1 | Applied and Interdisciplinary Chemistry |
Spectroscopy is a sufficiently broad field that many sub-disciplines exist, each with numerous implementations of specific spectroscopic techniques. The various implementations and techniques can be classified in several ways. | 0 | Theoretical and Fundamental Chemistry |
The slow-reacting substance of anaphylaxis or SRS-A is a mixture of the leukotrienes LTC4, LTD4 and LTE4. Mast cells secrete it during the anaphylactic reaction, inducing inflammation. It can be found in basophils.
It induces prolonged, slow contraction of smooth muscle and has a major bronchoconstrictor role in asthma. Compared to histamine, it is approximately 1000 times more potent and has a slower onset but longer duration of action. | 1 | Applied and Interdisciplinary Chemistry |
Bioanalysis is a sub-discipline of analytical chemistry covering the quantitative measurement of xenobiotics (drugs and their metabolites, and biological molecules in unnatural locations or concentrations) and biotics (macromolecules, proteins, DNA, large molecule drugs, metabolites) in biological systems. | 0 | Theoretical and Fundamental Chemistry |
For self-diffusion in gases at two different pressures (but the same temperature), the following empirical equation has been suggested:
where
* D is the diffusion coefficient,
* ρ is the gas mass density,
* P and P are the corresponding pressures. | 1 | Applied and Interdisciplinary Chemistry |
Though the principle equation is essentially identical to that of Owens and Wendt, the Fowkes theory in a larger sense has slightly different applications. Because it is derived from different principles than Owens/Wendt, the rest of the information that Fowkes theory is concerned with is related to adhesion. As such, it is more applicable to situations where adhesion occurs, and in general works better than does the Owens/Wendt theory when dealing with higher surface energies.
In addition, there is an extended Fowkes theory, rooted in the same principles, but dividing the total surface energy into a sum of three rather than two components: surface energy due to dispersive interactions, polar interactions, and hydrogen bonding. | 0 | Theoretical and Fundamental Chemistry |
Coal contains a small amount of radioactive uranium, barium, thorium, and potassium, but, in the case of pure coal, this is significantly less than the average concentration of those elements in the Earths crust. The surrounding strata, if shale or mudstone, often contain slightly more than average and this may also be reflected in the ash content of dirty' coals. The more active ash minerals become concentrated in the fly ash precisely because they do not burn well. The radioactivity of fly ash is about the same as black shale and is less than phosphate rocks, but is more of a concern because a small amount of the fly ash ends up in the atmosphere where it can be inhaled. According to U.S. National Council on Radiation Protection and Measurements (NCRP) reports, population exposure from 1000-MWe power plants amounts to 490 person-rem/year for coal power plants, 100 times as great as nuclear power plants (4.8 person-rem/year). The exposure from the complete nuclear fuel cycle from mining to waste disposal is 136 person-rem/year; the corresponding value for coal use from mining to waste disposal is "probably unknown". | 0 | Theoretical and Fundamental Chemistry |
The Fas receptor, also known as Fas, FasR, apoptosis antigen 1 (APO-1 or APT), cluster of differentiation 95 (CD95) or tumor necrosis factor receptor superfamily member 6 (TNFRSF6), is a protein that in humans is encoded by the FAS gene. Fas was first identified using a monoclonal antibody generated by immunizing mice with the FS-7 cell line. Thus, the name Fas is derived from FS-7-associated surface antigen.
The Fas receptor is a death receptor on the surface of cells that leads to programmed cell death (apoptosis) if it binds its ligand, Fas ligand (FasL). It is one of two apoptosis pathways, the other being the mitochondrial pathway. | 1 | Applied and Interdisciplinary Chemistry |
Thermophysical properties of matter and the kinetics of interaction and energy exchange among the principal carriers are based on the atomic-level configuration and interaction. Transport properties such as thermal conductivity are calculated from these atomic-level properties using classical and quantum physics. Quantum states of principal carriers (e.g.. momentum, energy) are derived from the Schrödinger equation (called first principle or ab initio) and the interaction rates (for kinetics) are calculated using the quantum states and the quantum perturbation theory (formulated as the Fermi golden rule). Variety of ab initio (Latin for from the beginning) solvers (software) exist (e.g., ABINIT, CASTEP, Gaussian, Q-Chem, Quantum ESPRESSO, SIESTA, VASP, WIEN2k). Electrons in the inner shells (core) are not involved in heat transfer, and calculations are greatly reduced by proper approximations about the inner-shells electrons.
The quantum treatments, including equilibrium and nonequilibrium ab initio molecular dynamics (MD), involving larger lengths and times are limited by the computation resources, so various alternate treatments with simplifying assumptions have been used and kinetics. In classical (Newtonian) MD, the motion of atom or molecule (particles) is based on the empirical or effective interaction potentials, which in turn can be based on curve-fit of ab initio calculations or curve-fit to thermophysical properties. From the ensembles of simulated particles, static or dynamics thermal properties or scattering rates are derived.
At yet larger length scales (mesoscale, involving many mean free paths), the Boltzmann transport equation (BTE) which is based on the classical Hamiltonian-statistical mechanics is applied. BTE considers particle states in terms of position and momentum vectors (x, p) and this is represented as the state occupation probability. The occupation has equilibrium distributions (the known boson, fermion, and Maxwell–Boltzmann particles) and transport of energy (heat) is due to nonequilibrium (cause by a driving force or potential). Central to the transport is the role of scattering which turn the distribution toward equilibrium. The scattering is presented by the relations time or the mean free path. The relaxation time (or its inverse which is the interaction rate) is found from other calculations (ab initio or MD) or empirically. BTE can be numerically solved with Monte Carlo method, etc.
Depending on the length and time scale, the proper level of treatment (ab initio, MD, or BTE) is selected. Heat transfer physics analyses may involve multiple scales (e.g., BTE using interaction rate from ab initio or classical MD) with states and kinetic related to thermal energy storage, transport and transformation.
So, heat transfer physics covers the four principal energy carries and their kinetics from classical and quantum mechanical perspectives. This enables multiscale (ab initio, MD, BTE and macroscale) analyses, including low-dimensionality and size effects. | 0 | Theoretical and Fundamental Chemistry |
Symmetries in nature lead directly to conservation laws, something which is precisely formulated by Noether's theorem.
The basic idea of time-translation symmetry is that a translation in time has no effect on physical laws, i.e. that the laws of nature that apply today were the same in the past and will be the same in the future. This symmetry implies the conservation of energy. | 0 | Theoretical and Fundamental Chemistry |
The atomic mass (m) of an isotope (nuclide) is determined mainly by its mass number (i.e. number of nucleons in its nucleus). Small corrections are due to the binding energy of the nucleus (see mass defect), the slight difference in mass between proton and neutron, and the mass of the electrons associated with the atom, the latter because the electron:nucleon ratio differs among isotopes.
The mass number is a dimensionless quantity. The atomic mass, on the other hand, is measured using the atomic mass unit based on the mass of the carbon-12 atom. It is denoted with symbols "u" (for unified atomic mass unit) or "Da" (for dalton).
The atomic masses of naturally occurring isotopes of an element determine the standard atomic weight of the element. When the element contains N isotopes, the expression below is applied for the average atomic mass :
where m, m, ..., m are the atomic masses of each individual isotope, and x, ..., x are the relative abundances of these isotopes. | 0 | Theoretical and Fundamental Chemistry |
Bacterial and mammalian SCSs are made up of α and β subunits. In E. coli two αβ heterodimers link together to form an αβ heterotetrameric structure. However, mammalian mitochondrial SCSs are active as αβ dimers and do not form a heterotetramer.
The E. coli SCS heterotetramer has been crystallized and characterized in great detail. As can be seen in Image 2, the two α subunits (pink and green) reside on opposite sides of the structure and the two β subunits (yellow and blue) interact in the middle region of the protein. The two α subunits only interact with a single β unit, whereas the β units interact with a single α unit (to form the αβ dimer) and the β subunit of the other αβ dimer. A short amino acid chain links the two β subunits which gives rise to the tetrameric structure.
The crystal structure of Succinyl-CoA synthetase alpha subunit (succinyl-CoA-binding isoform) was determined by Joyce et al. to a resolution of 2.10 A, with PDB code 1CQJ. [http://www.rcsb.org/pdb/explore.do?structureId=1CQJ]. | 1 | Applied and Interdisciplinary Chemistry |
A particularly interesting property of many catenanes is the ability of the rings to rotate with respect to one another. This motion can often be detected and measured by NMR spectroscopy, among other methods. When molecular recognition motifs exist in the finished catenane (usually those that were used to synthesize the catenane), the catenane can have one or more thermodynamically preferred positions of the rings with respect to each other (recognition sites). In the case where one recognition site is a switchable moiety, a mechanical molecular switch results. When a catenane is synthesized by coordination of the macrocycles around a metal ion, then removal and re-insertion of the metal ion can switch the free motion of the rings on and off.
If there are more than one recognition sites it is possible to observe different colors depending on the recognition site the ring occupies and thus it is possible to change the color of the catenane solution by changing the preferred recognition site. Switching between the two sites may be achieved by the use of chemical, electrochemical or even visible light based methods.
Catenanes have been synthesized incorporating many functional units, including redox-active groups (e.g. viologen, TTF=tetrathiafulvalene), photoisomerizable groups (e.g. azobenzene), fluorescent groups and chiral groups. Some such units have been used to create molecular switches as described above, as well as for the fabrication of molecular electronic devices and molecular sensors. | 0 | Theoretical and Fundamental Chemistry |
While environmental controversy surrounding use of this fuel is wide and varied, the greatest supported evidence of toxicity comes from the presence of dioxins and furans in the flue gases. Zinc has also been found to dissolve into storm water, from shredded rubber, at acutely toxic levels for aquatic life and plants.
A study of dioxin and furan content of stack gasses at a variety of cement mills, paper mills, boilers, and power plants conducted in the 1990s shows a wide and inconsistent variation in dioxin and furan output when fueled partially by TDF as compared to the same facilities powered by only coal. Some facilities added as little as 4% TDF and experienced as much as a 4,140% increase in dioxin and furan emissions. Other facilities added as much as 30% TDF and experienced dioxin and furan emissions increases of only as much as 58%. Still other facilities used as much as 8% TDF and experienced a decrease of as much as 83% of dioxin and furan emissions. One facility conducted four tests with two tests resulting in decreased emissions and two resulting in increased emissions. Another facility also conducted four tests and had widely varying increases in emissions.
A 2004 study showed that huge polyaromatic emissions are generated from combustion of tire rubber, at a minimum, 2 orders of magnitude higher than coal alone. The study concludes with, "atmospheric contamination dramatically increases when tire rubber is used as the fuel. Other different combustion variables compared to the ones used for coal combustion should be used to avoid atmospheric contamination by toxic, mutagenic, and carcinogenic pollutants, as well as hot-gas cleaning systems and COx capture systems." | 1 | Applied and Interdisciplinary Chemistry |
Levofenfluramine (INN), or (−)-3-trifluoromethyl-N-ethylamphetamine, also known as (−)-fenfluramine or (R)-fenfluramine, is a drug of the amphetamine family that, itself (i.e., in enantiopure form), was never marketed. It is the levorotatory enantiomer of fenfluramine, the racemic form of the compound, whereas the dextrorotatory enantiomer is dexfenfluramine. Both fenfluramine and dexfenfluramine are anorectic agents that have been used clinically in the treatment of obesity (and hence, levofenfluramine has been as well since it is a component of fenfluramine). However, they have since been discontinued due to reports of causing cardiovascular conditions such as valvular heart disease and pulmonary hypertension, adverse effects that are likely to be caused by excessive stimulation of 5-HT receptors expressed on heart valves.
Dexfenfluramine is believed to be solely responsible for the appetite suppressant properties of fenfluramine, of which it has been demonstrated to mediate predominantly via activation of postsynaptic 5-HT and 5-HT receptors through a combination of indirect serotonin releasing agent and direct serotonin receptor agonist activities (the latter of which are mediated fully by its active metabolite dexnorfenfluramine). Contrarily, levofenfluramine is thought to contribute only to unwanted side effects. Paradoxically, however, it has been shown that levofenfluramine too acts as a relatively potent releaser of serotonin, though with approximately 1/3 of the efficacy of dexfenfluramine. As such, it would be expected to possess some degree of appetite suppressant properties as well, yet it does not. A potential explanation as to why levofenfluramine is not similarly an effective anorectic is that it has also been found to behave as a dopamine receptor antagonist, which, as dopamine antagonists like atypical antipsychotics are associated with causing increased appetite and weight gain—effects that their actions on dopamine receptors have been implicated in playing a role in the development of, is an action that could in theory cancel out the hypothetical serotonergically-mediated appetite suppressant effects of the compound. However, this is speculation and has not been proven.
Levonorfenfluramine, an active metabolite of levofenfluramine, is also a fairly potent serotonin releasing agent (with a potency of approximately 1/2 that of norfenfluramine and 1/6 that of dexfenfluramine) and, similarly to dexnorfenfluramine, is a 5-HT and 5-HT receptor agonist, as well as a somewhat less potent norepinephrine reuptake inhibitor (about 1/2 that of its efficacy as a serotonin releaser). As such, it likely contributes significantly to the biological activity—though not necessarily appetite suppressant effects—of not only levofenfluramine but of racemic fenfluramine as well. In contrast to levonorfenfluramine, levofenfluramine is virtually inactive as a reuptake inhibitor or releaser of norepinephrine, and neither compound has any effect on dopamine reuptake or release. | 0 | Theoretical and Fundamental Chemistry |
The GC-O analysis is carried out by a panel of 6–12 assessors to count the number of participants who perceive an odour at each retention time. This frequency is then used to represent the relative importance of an odorant in the extract. It is also presumed to relate to the intensity of the odorant at the particular concentration, based on the assumption that individual detection thresholds are normally distributed.
Two different kinds of data can be reported by this method depending on the data collected. First, if only frequency data is available, it is reported as the nasal impact frequency (NIF) or the peak height of the olfactometric signal. It is zero if no assessor senses the odour and added with one each time an assessor senses an odour. Second, if both frequency of detection and duration of odour are collected, the surface of NIF (SNIF) or the peak area corresponding to the product of frequency of detection (%) and duration of odour (s) can be interpreted. SNIF allows further interpretation of odour compounds other than just peak height.
The detection frequency method benefits from its simplicity and lack of requirement for trained assessors, as the signal recorded is binary (presence/absence of odour). On the other hand, a drawback of this method is the limitation to the assumption of the relationship between frequency and perceived odour intensity. Odour-active compounds in food samples are often present at concentrations above their detection thresholds. This means that a compound may be detected by all assessors and therefore reach the limit of 100% detection in spite of increases in intensity. | 0 | Theoretical and Fundamental Chemistry |
In the design of fluid bearings, the Sommerfeld number (S) is a dimensionless quantity used extensively in hydrodynamic lubrication analysis. The Sommerfeld number is very important in lubrication analysis because it contains all the variables normally specified by the designer.
The Sommerfeld number is named after Arnold Sommerfeld (1868–1951). | 1 | Applied and Interdisciplinary Chemistry |
Exopolysaccharides can facilitate the attachment of nitrogen-fixing bacteria to plant roots and soil particles, which mediates a symbiotic relationship. This is important for colonization of roots and the rhizosphere, which is a key component of soil food webs and nutrient cycling in ecosystems. It also allows for successful invasion and infection of the host plant. Bacterial extracellular polymeric substances can aid in bioremediation of heavy metals as they have the capacity to adsorb metal cations, among other dissolved substances. This can be useful in the treatment of wastewater systems, as biofilms are able to bind to and remove metals such as copper, lead, nickel, and cadmium. The binding affinity and metal specificity of EPSs varies, depending on polymer composition as well as factors such as concentration and pH. In a geomicrobiological context, EPSs have been observed to affect precipitation of minerals, particularly carbonates. EPS may also bind to and trap particles in biofilm suspensions, which can restrict dispersion and element cycling. Sediment stability can be increased by EPS, as it influences cohesion, permeability, and erosion of the sediment. There is evidence that the adhesion and metal-binding ability of EPS affects mineral leaching rates in both environmental and industrial contexts. These interactions between EPS and the abiotic environment allow for EPS to have a large impact on biogeochemical cycling. Predator-prey interactions between biofilms and bacterivores, such as the soil-dwelling nematode Caenorhabditis elegans, had been extensively studied. Via the production of sticky matrix and formation of aggregates, Yersinia pestis biofilms can prevent feeding by obstructing the mouth of C. elegans. Moreover, Pseudomonas aeruginosa biofilms can impede the slithering motility of C. elegans, termed as quagmire phenotype, resulting in trapping of C. elegans within the biofilms and preventing the exploration of nematodes to feed on susceptible biofilms. This significantly reduced the ability of predator to feed and reproduce, thereby promoting the survival of biofilms. | 1 | Applied and Interdisciplinary Chemistry |
If different phases of the same pure substance are present in a multiphase system, interphase heat transfer will result in a change of phase, which is always accompanied by interphase mass transfer. The combination of heat transfer with mass transfer during phase change makes multiphase systems distinctly more challenging than simpler systems. Based on the phases that are involved in the system, phase change problems can be classified as: (1) solid–liquid phase change (melting and solidification), (2) solid–vapor phase change (sublimation and deposition), and (3) liquid–vapor phase change (boiling/evaporation and condensation). Melting and sublimation are also referred to as fluidification because both liquid and vapor are regarded as fluids. | 1 | Applied and Interdisciplinary Chemistry |
The height of the liquid column in the tube is constrained by the hydrostatic pressure and by the surface tension. The following derivation is for a liquid that rises in the tube; for the opposite case when the liquid is below the reference level, the derivation is analogous but pressure differences may change sign. | 1 | Applied and Interdisciplinary Chemistry |
The Energy Independence and Security Act of 2007 calls for the production of of renewable fuels by 2022, including of corn-based ethanol, a tripling of current production that would require a similar increase in corn production. Unfortunately, the plan poses a new problem; the increase in demand for corn production results in a proportional increase in nitrogen runoff. Although nitrogen, which makes up 78% of the Earth's atmosphere, is an inert gas, it has more reactive forms, two of which (nitrate and ammonia) are used to make fertilizer.
According to , a professor of crop physiology at the University of Illinois at Urbana-Champaign, corn requires more nitrogen-based fertilizer because it produces a higher grain per unit area than other crops and, unlike other crops, corn is completely dependent on available nitrogen in soil. The results, reported March 18, 2008, in Proceedings of the National Academy of Sciences, showed that scaling up corn production to meet the goal would increase nitrogen loading in the Dead Zone by 10–18%. This would boost nitrogen levels to twice the level recommended by the Mississippi Basin/Gulf of Mexico Water Nutrient Task Force (Mississippi River Watershed Conservation Programs), a coalition of federal, state, and tribal agencies that have monitored the dead zone since 1997. The task force says a 30% reduction of nitrogen runoff is needed if the dead zone is to shrink. | 0 | Theoretical and Fundamental Chemistry |
There are typically two different ways of mathematically describing how an electromagnetic wave interacts with the elements within an ellipsometer (including the sample): the Jones matrix and the Mueller matrix formalisms. In the Jones matrix formalism, the electromagnetic wave is described by a Jones vector with two orthogonal complex-valued entries for the electric field (typically and ), and the effect that an optical element (or sample) has on it is described by the complex-valued 2×2 Jones matrix. In the Mueller matrix formalism, the electromagnetic wave is described by Stokes vectors with four real-valued entries, and their transformation is described by the real-valued 4x4 Mueller matrix. When no depolarization occurs both formalisms are fully consistent. Therefore, for non-depolarizing samples, the simpler Jones matrix formalism is sufficient. If the sample is depolarizing the Mueller matrix formalism should be used, because it also gives the amount of depolarization. Reasons for depolarization are, for instance, thickness non-uniformity or backside-reflections from a transparent substrate. | 0 | Theoretical and Fundamental Chemistry |
The rate of change of temperature with respect to pressure in a Joule–Thomson process (that is, at constant enthalpy ) is the Joule–Thomson (Kelvin) coefficient . This coefficient can be expressed in terms of the gas's specific volume , its heat capacity at constant pressure , and its coefficient of thermal expansion as:
See the below for the proof of this relation. The value of is typically expressed in °C/bar (SI units: K/Pa) and depends on the type of gas and on the temperature and pressure of the gas before expansion. Its pressure dependence is usually only a few percent for pressures up to 100 bar.
All real gases have an inversion point at which the value of changes sign. The temperature of this point, the Joule–Thomson inversion temperature, depends on the pressure of the gas before expansion.
In a gas expansion the pressure decreases, so the sign of is negative by definition. With that in mind, the following table explains when the Joule–Thomson effect cools or warms a real gas:
Helium and hydrogen are two gases whose Joule–Thomson inversion temperatures at a pressure of one atmosphere are very low (e.g., about 40 K, −233 °C for helium). Thus, helium and hydrogen warm when expanded at constant enthalpy at typical room temperatures. On the other hand, nitrogen and oxygen, the two most abundant gases in air, have inversion temperatures of 621 K (348 °C) and 764 K (491 °C) respectively: these gases can be cooled from room temperature by the Joule–Thomson effect.
For an ideal gas, is always equal to zero: ideal gases neither warm nor cool upon being expanded at constant enthalpy. | 0 | Theoretical and Fundamental Chemistry |
Turbo-Grignards are Grignard reagents modified with lithium chloride. Compared to conventional Grignard reagents, Turbo-Grignards are more chemoselective; esters, amides, and nitriles do not react with the Turbo-Grignard reagent. | 0 | Theoretical and Fundamental Chemistry |
Coffee Joulies are small, stainless-steel capsules containing a phase-change material; the capsules were designed to be placed in a cup of coffee in order to cool coffee that is too hot then slowly release the heat to keep the coffee warm. The company was founded by Dave Petrillo and Dave Jackson, mechanical engineers from Pennington, New Jersey.
They made prototypes in their basement, then in 2011 started refining and producing them in rented space at Sherrill Manufacturing in Sherrill, New York, a former Oneida silverware factory that had changed its business model to hosting startups and small companies in 2010, after Oneida had moved most of its manufacturing overseas in 2004 but had left a small amount of business with the factory under contract. The company received help on manufacturing costs from Sherrill and raised money on Kickstarter in 2011. The team decided to continue with production in the United States, rather than moving to Mexico, as was their initial plan.
A similar concept using phase change materials, but integrated into the walls and bottom of a cup, had been invented by the Fraunhofer Institute for Building Physics in 2009.
Some reviews show Joulies work while others have expressed doubts over the product's effectiveness. After doing some tests, they reported that the product does not work very well if at all.
Specifically it is stated that the promised effect, while existing, is "barely noticeable", especially when compared to adding other objects of similar heat capacity, thus being far from the creators' claims that the drink “will be ready to drink three times sooner and will remain hot twice as long.”
In 2013 the founders were contestants on Shark Tank and raised $150,000. | 0 | Theoretical and Fundamental Chemistry |
Many cancers can raise LDH levels, so LDH may be used as a tumor marker, but at the same time, it is not useful in identifying a specific kind of cancer. Measuring LDH levels can be helpful in monitoring treatment for cancer. Noncancerous conditions that can raise LDH levels include heart failure, hypothyroidism, anemia, pre-eclampsia, meningitis, encephalitis, acute pancreatitis, HIV and lung or liver disease.
Tissue breakdown releases LDH, and therefore, LDH can be measured as a surrogate for tissue breakdown (e.g., hemolysis). LDH is measured by the lactate dehydrogenase (LDH) test (also known as the LDH test or lactic acid dehydrogenase test). Comparison of the measured LDH values with the normal range help guide diagnosis. | 1 | Applied and Interdisciplinary Chemistry |
Glycogen synthesis is, unlike its breakdown, endergonic—it requires the input of energy. Energy for glycogen synthesis comes from uridine triphosphate (UTP), which reacts with glucose-1-phosphate, forming UDP-glucose, in a reaction catalysed by UTP—glucose-1-phosphate uridylyltransferase. Glycogen is synthesized from monomers of UDP-glucose initially by the protein glycogenin, which has two tyrosine anchors for the reducing end of glycogen, since glycogenin is a homodimer. After about eight glucose molecules have been added to a tyrosine residue, the enzyme glycogen synthase progressively lengthens the glycogen chain using UDP-glucose, adding α(1→4)-bonded glucose to the nonreducing end of the glycogen chain.
The glycogen branching enzyme catalyzes the transfer of a terminal fragment of six or seven glucose residues from a nonreducing end to the C-6 hydroxyl group of a glucose residue deeper into the interior of the glycogen molecule. The branching enzyme can act upon only a branch having at least 11 residues, and the enzyme may transfer to the same glucose chain or adjacent glucose chains. | 1 | Applied and Interdisciplinary Chemistry |
According to the structure and function study on the antifreeze protein from Pseudopleuronectes americanus, the antifreeze mechanism of the type-I AFP molecule was shown to be due to the binding to an ice nucleation structure in a zipper-like fashion through hydrogen bonding of the hydroxyl groups of its four Thr residues to the oxygens along the direction in ice lattice, subsequently stopping or retarding the growth of ice pyramidal planes so as to depress the freeze point.
The above mechanism can be used to elucidate the structure-function relationship of other antifreeze proteins with the following two common features:
# recurrence of a Thr residue (or any other polar amino acid residue whose side-chain can form a hydrogen bond with water) in an 11-amino-acid period along the sequence concerned, and
# a high percentage of an Ala residue component therein. | 1 | Applied and Interdisciplinary Chemistry |
Because gas molecules diffract electrons and affect the quality of the electron gun, RHEED experiments are performed under vacuum. The RHEED system must operate at a pressure low enough to prevent significant scattering of the electron beams by gas molecules in the chamber. At electron energies of 10keV, a chamber pressure of 10 mbar or lower is necessary to prevent significant scattering of electrons by the background gas. In practice, RHEED systems are operated under ultra high vacuums. The chamber pressure is minimized as much as possible in order to optimize the process. The vacuum conditions limit the types of materials and processes that can be monitored in situ with RHEED. | 0 | Theoretical and Fundamental Chemistry |
OFM is routinely applied in pharmaceutical research in preclinical (e.g. mice, rats, pigs, primates) and in clinical studies in humans (Figure 3). OFM-related procedures such as probe insertions or prolonged sampling with numerous probes are well tolerated by the subjects. | 1 | Applied and Interdisciplinary Chemistry |
Plasmin-α2-antiplasmin complex (PAP) is a 1:1 irreversibly formed inactive complex of the enzyme plasmin and its inhibitor α-antiplasmin. It is a marker of the activity of the fibrinolytic system and a marker of net activation of fibrinolysis.
PAP levels are increased with pregnancy and by ethinylestradiol-containing combined birth control pills. Conversely, levels of PAP do not appear to be affected with menopausal hormone therapy. PAP levels have been reported to be elevated in men with prostate cancer. | 1 | Applied and Interdisciplinary Chemistry |
Debierne studied at the elite École supérieure de physique et de chimie industrielles de la ville de Paris (ESPCI ParisTech).
He was a student of Charles Friedel, was a close friend of Pierre and Marie Curie and was associated with their work. In 1899, he discovered the radioactive element actinium, as a result of continuing the work with pitchblende that the Curies had initiated.
After the death of Pierre Curie in 1906, Debierne helped Marie Curie carry on and worked with her in teaching and research.
In 1911, he and Marie Curie prepared radium in metallic form in visible amounts. They did not keep it metallic, however. Having demonstrated the metal's existence as a matter of scientific curiosity, they reconverted it into compounds with which they might continue their researches. | 1 | Applied and Interdisciplinary Chemistry |
A viral titer is the lowest concentration of a virus that still infects cells. To determine the titer, several dilutions are prepared, such as 10, 10, 10, ... 10.
The titer of a fat is the temperature, in degrees Celsius, at which it solidifies. The higher the titer, the harder the fat. This titer is used in determining whether an animal fat is considered tallow (titer higher than 40 °C) or a grease (titer below 40 °C). | 1 | Applied and Interdisciplinary Chemistry |
A kairomone (a coinage using the Greek καιρός opportune moment, paralleling pheromone) is a semiochemical, emitted by an organism, which mediates interspecific interactions in a way that benefits an individual of another species which receives it and harms the emitter. This "eavesdropping" is often disadvantageous to the producer (though other benefits of producing the substance may outweigh this cost, hence its persistence over evolutionary time). The kairomone improves the fitness of the recipient and in this respect differs from an allomone (which is the opposite: it benefits the producer and harms the receiver) and a synomone (which benefits both parties). The term is mostly used in the field of entomology (the study of insects). Two main ecological cues are provided by kairomones; they generally either indicate a food source for the receiver, or the presence of a predator, the latter of which is less common or at least less studied. | 1 | Applied and Interdisciplinary Chemistry |
In chemical physics and physical chemistry, chemical affinity is the electronic property by which dissimilar chemical species are capable of forming chemical compounds. Chemical affinity can also refer to the tendency of an atom or compound to combine by chemical reaction with atoms or compounds of unlike composition. | 0 | Theoretical and Fundamental Chemistry |
After a WGD, one of the duplicated gene pair is often lost through fractionation; less than 10% of WGD gene pairs have remained in S. cerevisiae genome. A little over half of WGD gene pairs in the glycolysis reaction pathway were retained in post-WGD species, significantly higher than the overall retention rate. This has been associated with an increased ability to metabolize glucose into pyruvate, or higher rate of glycolysis. After glycolysis, pyruvate can either be further broken down by pyruvate decarboxylase (Pdc) or pyruvate dehydrogenase (Pdh). The kinetics of the enzymes are such that when pyruvate concentrations are high, due to a high rate of glycolysis, there is increased flux through Pdc and thus the fermentation pathway. The WGD is believed to have played a beneficial role in the evolution of the Crabtree effect in post-WGD species partially due to this increase in copy number of glycolysis genes. | 1 | Applied and Interdisciplinary Chemistry |
* Microsoft and Running Tide signed Two-Year agreement in 2023 to remove up to 12,000 tons of carbon through an ocean-based carbon removal system.
* In Canada, a North Atlantic Carbon Observatory (NACO) project is underway to establish an accurate measurement of the ocean's ability to continue to absorb carbon with particular emphasis on deep blue capacity.
* In Denmark, the "Greensand" project is underway to capture carbon at source and deposit it in the deep blue regions of the North Sea, creating a CO graveyard. The project is expected to store up to eight million tonnes of CO per year by 2030.
* A restoration project in South Australia will cover of mangroves, salt marsh and sea grasses extending in the St Vincents Gulf and Spencer Gulf in South Australia. The project will also look at various possibilities of insuring the huge expanse of existing blue carbon ecosystems.
* In South Korea, macroalgae have been utilized as part of a climate change mitigation program. The country has established the Coastal CO Removal Belt (CCRB) which is composed of artificial and natural ecosystems. The goal is to capture carbon using large areas of kelp forest.
* Marine permaculture also fixes carbon in seaweed forest projects offshore in Tasmania and the Philippines, with potential use from the tropics to temperate oceans. | 0 | Theoretical and Fundamental Chemistry |
There are many examples of ancestral proteins that have been computationally reconstructed, expressed in living cell lines, and – in many cases – purified and biochemically studied.
* The Thornton lab notably resurrected several ancestral hormone receptors (from about 500Ma) and collaborated with the Stevens lab to resurrect ancient V-ATPase subunits from yeast (800Ma).
* The [https://zebra.berkeley.edu/ Marqusee] lab has recently published several studies concerning the evolutionary biophysical history of E. coli Ribonuclease H1.
Some other examples are ancestral visual pigments in vertebrates, enzymes in yeast that break down sugars (800Ma); enzymes in bacteria that provide resistance to antibiotics (2 – 3Ga); the ribonucleases involved in ruminant digestion; the alcohol dehydrogenases (Adhs) involved in yeast fermentation(~85Ma); and RuBisCO in Solanaceae.
The age of a reconstructed sequence is determined using a molecular clock model, and often several are employed. This dating technique is often calibrated using geological time-points (such as ancient ocean constituents or BIFs) and while these clocks offer the only method of inferring a very ancient proteins age, they have sweeping error margins and are diffuclt to defend against contrary data. To this end, ASR age' should really be only used as an indicative feature and is often surpassed altogether for a measurement of the number of substitutions between the ancestral and the modern sequences (the fundiment on which the clock is calculated). That being said, the use of a clock allows one to compare observed biophysical data of an ASR protein to the geological or ecological environment at the time. For example, ASR studies on bacterial EF-Tus (proteins involved in translation, that are likely rarely subject to HGT and typically exhibit Tms ~2C greater than Tenv) indicate a hotter Precambrian Earth which fits very closely with geological data on ancient earth ocean temperatures based on Oxygen-18 isotopic levels. ASR studies of yeast Adhs reveal that the emergence of subfunctionalized Adhs for ethanol metabolism (not just waste excretion) arose at a time similar to the dawn of fleshy fruit in the Cambrian Period and that before this emergence, Adh served to excrete ethanol as a byproduct of excess pyruvate. The use of a clock also perhaps indicates that the origin of life occurred before the earliest molecular fossils indicate (>4.1Ga), but given the debatable reliability of molecular clocks, such observations should be taken with caution. | 1 | Applied and Interdisciplinary Chemistry |
* Facilitate the acceptance and implementation of modular, miniature and automated (smart) sample system technology using the mechanical design based on the ANSI/ISA SP76.00.02-2002 standard.
* Provide the mechanical, electrical and software infrastructure needed to accelerate the use of microanalytical sensors within the process industries.
* Move the analytical systems out of the analyzer houses by promoting the use of field-mounted analytical systems (similar to pressure transmitters) which are close-coupled to the major process equipment. (NeSSI refers to this concept as By-Line analysis)
* Lay the groundwork for the adoption of an open communication standard(s) for process analytical. This includes communication between sample system components such as flow sensors, actuators, and microanalytical sensors, as well as communication to a Distributed Control System (DCS).
Comparison of Current Technology vs. NeSSI Technology (Extractive Systems) | 1 | Applied and Interdisciplinary Chemistry |
A variant basin design called an extended detention dry basin can limit downstream erosion and control of some pollutants such as suspended solids. This basin type differs from a retention basin, also known as a "wet pond," which includes a permanent pool of water, and which is typically designed to protect water quality.
While basic detention ponds are often designed to empty within 6 to 12 hours after a storm, extended detention (ED) dry basins improve on the basic detention design by lengthening the storage time, for example, to 24 or 48 hours. Longer storage times tend to result in improved water quality because additional suspended solids are removed. | 1 | Applied and Interdisciplinary Chemistry |
The Wnt signaling pathway can be divided in canonical and non-canonical. The canonical signaling involves binding of Wnt to Frizzled and LRP5 co-receptor, leading to GSK3 phosphorylation and inhibition of β-catenin degradation, resulting in its accumulation and translocation to the nucleus, where it acts as a transcription factor. The non-canonical Wnt signaling can be divided in planar cell polarity (PCP) pathway and Wnt/calcium pathway. It is characterized by binding of Wnt to Frizzled and activation of G proteins and to an increase of intracellular levels of calcium through mechanisms involving PKC 50. The Wnt signaling pathway plays a significant role in osteoblastogenesis and bone formation, inducing the differentiation of mesenquimal pluripotent cells in osteoblasts and inhibiting the RANKL/RANK pathway and osteoclastogenesis. | 0 | Theoretical and Fundamental Chemistry |
Studies have shown that Zn, Pb, Cd, Sn and In can embrittle steel at temperature below each embrittler’s melting point.
*Cadmium can embrittle titanium at temperatures below its melting point.
*Hg can embrittle zinc at temperatures below its melting point.
*Hg can embrittle copper at temperatures below its melting point. | 1 | Applied and Interdisciplinary Chemistry |
The chemical structure of the materials involved in a given adhesive system plays a large role in the adhesion of the system as a whole because the structure determines the type and strength of the intermolecular interactions present. All things equal, larger molecules, which experience higher dispersion forces, will have a larger adhesive strength than smaller molecules of the same basic chemical fingerprint. Similarly, polar molecules will have Keesom and Debye forces not experienced by nonpolar molecules of similar size. Compounds which can hydrogen bond across the adhesive interface will have even greater adhesive strength. | 0 | Theoretical and Fundamental Chemistry |
The Chemistry Quality Eurolabels or European Quality Labels in Chemistry (Labels européens de Qualité en Chimie) is a marketing scheme for chemistry degrees at institutions located within the 45 countries involved in the Bologna process. Labels are awarded to qualifying institutions under the names are Eurobachelor and Euromaster, as well as the proposed Eurodoctorate. Label Committee not only prepares for the ECTN Administrative Council proposals to award the Eurolabels but also judge the quality of chemical education programmes at HEIs. ECTN and its Label Committee closely collaborates with EuCheMS and American Chemical Society.
It is a framework which is supported by EuCheMS, and the labels are awarded by ECTN. The project is supported by the European Commission (EC) through its SOCRATES programme. The purpose of the framework is to "promote recognition of first, second cycle degrees, and third cycle degrees not only within the 45 countries involved in the Bologna process". | 1 | Applied and Interdisciplinary Chemistry |
Several formats for citing radiocarbon results have been used since the first samples were dated. As of 2019, the standard format required by the journal Radiocarbon is as follows.
Uncalibrated dates should be reported as ": ± BP", where:
* identifies the laboratory that tested the sample, and the sample ID
* is the laboratory's determination of the age of the sample, in radiocarbon years
* is the laboratory's estimate of the error in the age, at 1σ confidence.
* BP stands for "before present", referring to a reference date of 1950, so that "500 BP" means the year AD 1450.
For example, the uncalibrated date "UtC-2020: 3510 ± 60 BP" indicates that the sample was tested by the Utrecht van der Graaff Laboratorium ("UtC"), where it has a sample number of "2020", and that the uncalibrated age is 3510 years before present, ± 60 years. Related forms are sometimes used: for example, "2.3 ka BP" means 2,300 radiocarbon years before present (i.e. 350 BC), and " yr BP" might be used to distinguish the uncalibrated date from a date derived from another dating method such as thermoluminescence.
Calibrated dates are frequently reported as "cal BP", "cal BC", or "cal AD", again with BP referring to the year 1950 as the zero date. Radiocarbon gives two options for reporting calibrated dates. A common format is "cal ", where:
* is the range of dates corresponding to the given confidence level
* indicates the confidence level for the given date range.
For example, "cal 1220–1281 AD (1σ)" means a calibrated date for which the true date lies between AD 1220 and AD 1281, with a confidence level of 1 sigma, or approximately 68%. Calibrated dates can also be expressed as "BP" instead of using "BC" and "AD". The curve used to calibrate the results should be the latest available IntCal curve. Calibrated dates should also identify any programs, such as OxCal, used to perform the calibration. In addition, an article in Radiocarbon in 2014 about radiocarbon date reporting conventions recommends that information should be provided about sample treatment, including the sample material, pretreatment methods, and quality control measurements; that the citation to the software used for calibration should specify the version number and any options or models used; and that the calibrated date should be given with the associated probabilities for each range. | 0 | Theoretical and Fundamental Chemistry |
# Steam-jet agglomeration: A continuous process wherein fine powders are exposed to steam to provide the necessary adhesion properties. Agglomeration is controlled by particle size distribution in the raw materials, gas and steam flow conditions and the adhesion forces between the particles. After the steam section the particles are exposed to warm air flowing upwards and countercurrent to the particles, which solidifies the liquid bridges formed between the particles. Advantages: used for many years in the food industry, a continuous process
#Spray drying: Spray drying starts with a liquid raw material which is sprayed as fine droplets into heated air which causes the droplets to dry into fine particles. To agglomerate, fully dried particles (collected from the dry air outlet) are re-introduced at the point where the particles are partly dried and still sticky, to collide and create porous agglomerates. Spray drying agglomeration creates irregularly shaped, highly porous particles with excellent instant properties.
#Fluid bed agglomeration uses an air stream to both agitate the particles and to dry the agglomerates. Fluidized bed dryers are hot-air driers in which the air is forced up through a layer of product. The air is evenly distributed along the chamber to maintain a uniform velocity and prevent areas of higher velocities. These dryers can either be batch or continuous. Batch processing methods tend to have more uniform moisture content throughout the product after drying whereas continuous driers vary more throughout the process and may require a finishing set. When used for agglomeration, fluidized bed dryers have spray nozzles located at various heights within the chamber, allowing a spray of water or a solution of other ingredients (the binding solution) to be sprayed on the particles as they are fluidized. This encourages the particles to stick together, and can impart other properties to the finished product. Examples of binding solutions are a water/sugar solution, or lecithin. In this method, particle wetting, growth, consolidation, erosion and drying all occur at the same time. | 1 | Applied and Interdisciplinary Chemistry |
The resonance condition of any -type Raman process requires that the difference in the two photon energies match the difference in energy between the states at the "legs" of the , here the ground states identified above. In experimental settings, this condition is realized when the detunings of the cycling and repumper frequencies in respect to the and transition frequencies, respectively, are equal.
Unlike most Doppler cooling techniques, light in the gray molasses must be blue-detuned from its resonant transition; the resulting Doppler heating is offset by polarization-gradient cooling. Qualitatively, this is because the choice of means that the AC Stark shifts of the three levels are the same sign at any given position. Selecting the potential energy maxima as the sites of optical pumping to the dark state requires the overall light to be blue-detuned; in doing so, the atoms in the bright state traverse the maximum potential energy difference and thus dissipate the most kinetic energy. A full quantitative explanation of the molasses force with respect to detuning can be found in Hänschs paper. | 0 | Theoretical and Fundamental Chemistry |
In order to isolate noble-metalliferous materials, pyrolysis and/or hydrolysis procedures are used. In pyrolysis, the noble-metalliferous products are released from the other materials by solidifying in a melt to become cinder and then poured off or oxidized. In hydrolysis, the noble-metalliferous products are dissolved either in aqua regia (consisting of hydrochloric acid and nitric acid) or in hydrochloric acid and chlorine gas in solution. Subsequently, certain metals can be precipitated or reduced directly with a salt, gas, organic, and/or nitro hydrate connection. Afterwards, they go through cleaning stages or are recrystallized. The precious metals are separated from the metal salt by calcination. The noble-metalliferous materials are hydrolyzed first and thermally prepared (pyrolysed) thereafter. The processes are better yielding when using catalysts that may sometimes contain precious metals themselves. When using catalysts, the recycling product is removed in each case and driven several times through the cycle. | 1 | Applied and Interdisciplinary Chemistry |
A promiscuous activity is a non-native activity the enzyme did not evolve to do, but arises due to an accommodating conformation of the active site. However, the main activity of the enzyme is a result not only of selection towards a high catalytic rate towards a particular substrate to produce a particular product, but also to avoid the production of toxic or unnecessary products. For example, if a tRNA syntheses loaded an incorrect amino acid onto a tRNA, the resulting peptide would have unexpectedly altered properties, consequently to enhance fidelity several additional domains are present. Similar in reaction to tRNA syntheses, the first subunit of tyrocidine synthetase (tyrA) from Bacillus brevis adenylates a molecule of phenylalanine in order to use the adenyl moiety as a handle to produce tyrocidine, a cyclic non-ribosomal peptide. When the specificity of enzyme was probed, it was found that it was highly selective against natural amino acids that were not phenylalanine, but was much more tolerant towards unnatural amino acids. Specifically, most amino acids were not catalysed, whereas the next most catalysed native amino acid was the structurally similar tyrosine, but at a thousandth as much as phenylalanine, whereas several unnatural amino acids where catalysed better than tyrosine, namely D-phenylalanine, β-cyclohexyl-L-alanine, 4-amino-L-phenylalanine and L-norleucine.
One peculiar case of selected secondary activity are polymerases and restriction endonucleases, where incorrect activity is actually a result of a compromise between fidelity and evolvability. For example, for restriction endonucleases incorrect activity (star activity) is often lethal for the organism, but a small amount allows new functions to evolve against new pathogens. | 1 | Applied and Interdisciplinary Chemistry |
Magnetically assisted slip casting is a manufacturing technique that uses anisotropic stiff nanoparticle platelets in a ceramic, metal or polymer functional matrix to produce layered objects that can mimic natural objects such as nacre. Each layer of platelets is oriented in a different direction, giving the resulting object greater strength. The inventors claimed that the process is 10x faster than commercial 3D printing. The magnetisation and orientation of the ceramic platelets has been patented. | 0 | Theoretical and Fundamental Chemistry |
* Allègre C.J., 2008. Isotope Geology (Cambridge University Press).
* Faure G., Mensing T.M. (2004), Isotopes: Principles and Applications (John Wiley & Sons).
* Hoefs J., 2004. Stable Isotope Geochemistry (Springer Verlag).
* Sharp Z., 2006. Principles of Stable Isotope Geochemistry (Prentice Hall). | 0 | Theoretical and Fundamental Chemistry |
EU legislation has been approved banning the use of highly toxic pesticides including those that are carcinogenic, mutagenic or toxic to reproduction, those that are endocrine-disrupting, and those that are persistent, bioaccumulative and toxic (PBT) or very persistent and very bioaccumulative (vPvB) and measures have been approved to improve the general safety of pesticides across all EU member states.
In 2023 The Environment Committee of European Parliament approved a decision aiming to reduce pesticide use by 50% (the most hazardous by 65%) by the year 2030 and ensure sustainable use of pesticides (for example use them only as a last resort). The decision also includes measures for providing farmers with alternatives. | 1 | Applied and Interdisciplinary Chemistry |
While some isocyanides (e.g., cyclohexyl isocyanide) are toxic, others "exhibit no appreciable toxicity for mammals". Referring to ethyl isocyanide, toxicological studies in the 1960s at Bayer showed that "oral and subcutaneous doses of 500-5000 mg/kg can be tolerated by mice". | 0 | Theoretical and Fundamental Chemistry |
Manganese deficiency in humans results in a number of medical problems. Manganese is a vital element of nutrition in very small quantities (adult male daily intake 2.3 milligrams). However poisoning may occur when greater amounts are ingested. | 1 | Applied and Interdisciplinary Chemistry |
Indirect enantiomer separation involves the interaction between the chiral analyte (CA) of interest and the suitable reactive CS (in this case it is an enantiopure chiral derivatizing agent, CDA) leading to the formation of a covalent diastereomeric complex that can be separated with an achiral chromatographic technique. Therapeutic agents often contain reactive functional groups (amino, hydroxyl, epoxy, carbonyl and carboxylic acid, etc.) in their structures. They are converted into covalently bonded diastereomeric derivatives using enantiomerically pure chiral derivatizing agent. The diastereomers thus formed unlike enantiomers, exhibit different physicochemical properties in an achiral environment and are eventually separated as a result of differential retention time on a stationary phase. The success of this approach depends on the availability of stable enantiopure chiral derivatizing agent (CDA) and on the presence of a suitable reactive functional group in the chiral drug molecule for covalent formation of diastereomeric derivative. The reaction of a racemic, (R,S)- Drug with a chirally and chemically pure chiral derivatizing agent, (R’)-CDA, will afford diastereomeric products, (R)-Drug-(R')-CDA + (S)-Drug-(R’)- CDA. The chiral derivatization reaction scheme is illustrated in the box on the right hand side.
In contrast to enantiomers, diastereomers have different physicochemical properties that make them separable on regular achiral stationary phases. The major benefit of the indirect methodology is that conventional achiral stationary phase/mobile phase system may be used for the separation of the generated diastereomers. Thus, considerable flexibility in chromatographic conditions is available to achieve the desired separation and to eliminate interferences from metabolites and endogenous substances. Moreover, the sensitivity of the method can be enhanced by sensible choice of the CDA and the chromatographic detection system. But this indirect approach to enantiomeric analysis has some potential problems. These include availability of a suitable functional group on the enantiomer for derivatization, enantiomeric purity of the CDA, racemization of the CDA during derivatization, and racemization of the analyte during the derivatization. Currently, however, the application of indirect analytical approaches is in decline. | 0 | Theoretical and Fundamental Chemistry |
Proponents of aerobic granular sludge technology claim "it will play an important role as an innovative technology alternative to the present activated sludge process in industrial and municipal wastewater treatment in the near future" and that it "can be readily established and profitably used in activated sludge plants". However, in 2011 it was characterised as "not yet established as a large-scale application ... with limited and unpublished full-scale applications for municipal wastewater treatment." | 1 | Applied and Interdisciplinary Chemistry |
The oxidase catalyzes the transfer of four electrons from reduced plastoquinone to molecular oxygen to form water . The net reaction is written below:
2 QH + O → 2 Q + 2 HO
Analysis of substrate specificity revealed that the enzyme almost exclusively catalyzes the reduction of plastoquinone over other quinones such as ubiquinone and duroquinone. Additionally, iron is essential for the catalytic function of the enzyme and cannot be substituted by another metal cation like Cu, Zn, or Mn at the catalytic center.
It is unlikely that four electrons could be transferred at once in a single iron cluster, so all of the proposed mechanisms involve two separate two-electron transfers from reduced plastoquinone to the di-iron center. In the first step common to all proposed mechanisms, one plastoquinone is oxidized and both irons are reduced from iron(III) to iron(II). Four different mechanisms are proposed for the next step, oxygen capture. One mechanism proposes a peroxide intermediate, after which one oxygen atom is used to create water and another is left bound in a diferryl configuration. Upon one more plastoquinone oxidation, a second water molecule is formed and the irons return to a +3 oxidation state. The other mechanisms involve the formation of Fe(III)-OH or Fe(IV)-OH and a tyrosine radical. These radical-based mechanisms could explain why over-expression of the PTOX gene causes increased generation of reactive oxygen species. | 0 | Theoretical and Fundamental Chemistry |
4D scanning transmission electron microscopy (4D STEM) is a subset of scanning transmission electron microscopy (STEM) methods which uses a pixelated electron detector to capture a convergent beam electron diffraction (CBED) pattern at each scan location; see the main page for further information. This technique captures a 2 dimensional reciprocal space image associated with each scan point as the beam rasters across a 2 dimensional region in real space, hence the name 4D STEM. Its development was enabled by better STEM detectors and improvements in computational power. The technique has applications in diffraction contrast imaging, phase orientation and identification, strain mapping, and atomic resolution imaging among others; it has become very popular and rapidly evolving from about 2020 onwards.
The name 4D STEM is common in literature, however it is known by other names: 4D STEM EELS, ND STEM (N- since the number of dimensions could be higher than 4), position resolved diffraction (PRD), spatial resolved diffractometry, momentum-resolved STEM, "nanobeam precision electron diffraction", scanning electron nano diffraction, nanobeam electron diffraction, or pixelated STEM. Most of these are the same, although there are instances such as momentum-resolved STEM where the emphasis can be very different. | 0 | Theoretical and Fundamental Chemistry |
Complementarity is achieved by distinct interactions between nucleobases: adenine, thymine (uracil in RNA), guanine and cytosine. Adenine and guanine are purines, while thymine, cytosine and uracil are pyrimidines. Purines are larger than pyrimidines. Both types of molecules complement each other and can only base pair with the opposing type of nucleobase. In nucleic acid, nucleobases are held together by hydrogen bonding, which only works efficiently between adenine and thymine and between guanine and cytosine. The base complement A = T shares two hydrogen bonds, while the base pair G ≡ C has three hydrogen bonds. All other configurations between nucleobases would hinder double helix formation. DNA strands are oriented in opposite directions, they are said to be antiparallel.
A complementary strand of DNA or RNA may be constructed based on nucleobase complementarity. Each base pair, A = T vs. G ≡ C, takes up roughly the same space, thereby enabling a twisted DNA double helix formation without any spatial distortions. Hydrogen bonding between the nucleobases also stabilizes the DNA double helix.
Complementarity of DNA strands in a double helix make it possible to use one strand as a template to construct the other. This principle plays an important role in DNA replication, setting the foundation of heredity by explaining how genetic information can be passed down to the next generation. Complementarity is also utilized in DNA transcription, which generates an RNA strand from a DNA template. In addition, human immunodeficiency virus, a single-stranded RNA virus, encodes an RNA-dependent DNA polymerase (reverse transcriptase) that uses complementarity to catalyze genome replication. The reverse transcriptase can switch between two parental RNA genomes by copy-choice recombination during replication.
DNA repair mechanisms such as proof reading are complementarity based and allow for error correction during DNA replication by removing mismatched nucleobases. In general, damages in one strand of DNA can be repaired by removal of the damaged section and its replacement by using complementarity to copy information from the other strand, as occurs in the processes of mismatch repair, nucleotide excision repair and base excision repair.
Nucleic acids strands may also form hybrids in which single stranded DNA may readily anneal with complementary DNA or RNA. This principle is the basis of commonly performed laboratory techniques such as the polymerase chain reaction, PCR.
Two strands of complementary sequence are referred to as sense and anti-sense. The sense strand is, generally, the transcribed sequence of DNA or the RNA that was generated in transcription, while the anti-sense strand is the strand that is complementary to the sense sequence. | 1 | Applied and Interdisciplinary Chemistry |
The McKendrick–von Foerster equation is a linear first-order partial differential equation encountered in several areas of mathematical biology – for example, demography and cell proliferation modeling; it is applied when age structure is an important feature in the mathematical model. It was first presented by Anderson Gray McKendrick in 1926 as a deterministic limit of lattice models applied to epidemiology, and subsequently independently in 1959 by biophysics professor Heinz von Foerster for describing cell cycles. | 1 | Applied and Interdisciplinary Chemistry |
Lichens cover about 7% of the planet's surface and grow on and in a wide range of substrates and habitats, including some of the most extreme conditions on earth. They are abundant growing on bark, leaves, and hanging from epiphyte branches in rain forests and in temperate woodland. They grow on bare rock, walls, gravestones, roofs, and exposed soil surfaces. They can survive in some of the most extreme environments on Earth: arctic tundra, hot dry deserts, rocky coasts, and toxic slag heaps. They can live inside solid rock, growing between the grains, and in the soil as part of a biological soil crust in arid habitats such as deserts. Some lichens do not grow on anything, living out their lives blowing about the environment.
When growing on mineral surfaces, some lichens slowly decompose their substrate by chemically degrading and physically disrupting the minerals, contributing to the process of weathering by which rocks are gradually turned into soil. While this contribution to weathering is usually benign, it can cause problems for artificial stone structures. For example, there is an ongoing lichen growth problem on Mount Rushmore National Memorial that requires the employment of mountain-climbing conservators to clean the monument.
Lichens are not parasites on the plants they grow on, but only use them as a substrate. The fungi of some lichen species may "take over" the algae of other lichen species. Lichens make their own food from their photosynthetic parts and by absorbing minerals from the environment. Lichens growing on leaves may have the appearance of being parasites on the leaves, but they are not. Some lichens in Diploschistes parasitise other lichens. Diploschistes muscorum starts its development in the tissue of a host Cladonia species.
In the arctic tundra, lichens, together with mosses and liverworts, make up the majority of the ground cover, which helps insulate the ground and may provide forage for grazing animals. An example is "reindeer moss", which is a lichen, not a moss.
There are only two species of known permanently submerged lichens; Hydrothyria venosa is found in fresh water environments, and Verrucaria serpuloides is found in marine environments.
A crustose lichen that grows on rock is called a saxicolous lichen. Crustose lichens that grow on the rock are epilithic, and those that grow immersed inside rock, growing between the crystals with only their fruiting bodies exposed to the air, are called endolithic lichens. A crustose lichen that grows on bark is called a corticolous lichen. A lichen that grows on wood from which the bark has been stripped is called a lignicolous lichen. Lichens that grow immersed inside plant tissues are called endophloidic lichens or endophloidal lichens. Lichens that use leaves as substrates, whether the leaf is still on the tree or on the ground, are called epiphyllous or foliicolous. A terricolous lichen grows on the soil as a substrate. Many squamulous lichens are terricolous. Umbilicate lichens are foliose lichens that are attached to the substrate at only one point. A vagrant lichen is not attached to a substrate at all, and lives its life being blown around by the wind. | 1 | Applied and Interdisciplinary Chemistry |
A common form for the rate equation is a power law:
The constant is called the rate constant. The exponents, which can be fractional, are called partial orders of reaction and their sum is the overall order of reaction.
In a dilute solution, an elementary reaction (one having a single step with a single transition state) is empirically found to obey the law of mass action. This predicts that the rate depends only on the concentrations of the reactants, raised to the powers of their stoichiometric coefficients.
The differential rate equation for an elementary reaction using product notation is:
Where:
* is the rate of change of reactant concentration with respect to time.
*k is the rate constant of the reaction.
* represents the concentrations of the reactants, raised to the powers of their stoichiometric coefficients and multiplied together. | 0 | Theoretical and Fundamental Chemistry |
In Tiraspol, in the house in which Zelinsky spent his childhood, there is a memorial house-museum of the academician, and on the building of school No. 6 (now the humanitarian and mathematical gymnasium), where he studied, a memorial plaque was erected, a monument was erected in front of the building; in the Kirovsky district of Tiraspol there is a street named after Zelinsky. In Chisinau, a street in the Botanica sector is named after him. | 0 | Theoretical and Fundamental Chemistry |
The Hydraulic Engineering Circular Manual No. 23 (HEC-23) contains general design guidelines as scour countermeasures that are applicable to piers and abutments. The numbering in the following table indicates the HEC-23 design guideline section:
Bend way weirs, spurs and guide banks can help to align the upstream flow while riprap, gabions, articulated concrete blocks and grout-filled mattresses can mechanically stabilize the pier and abutment slopes. Riprap remains the most common countermeasure used to prevent scour at bridge abutments. A number of physical additions to the abutments of bridges can help prevent scour, such as the installation of gabions and stone pitching upstream from the foundation. The addition of sheet piles or interlocking prefabricated concrete blocks can also offer protection. These countermeasures do not change the scouring flow and are temporary since the components are known to move or be washed away in a flood. The Federal Highway Administration (FHWA) recommends design criteria in HEC-18 and 23, such as avoiding unfavourable flow patterns, streamlining the abutments, and designing pier foundations resistant to scour without depending upon the use of riprap or other countermeasures.
Trapezoidal-shaped channels through a bridge can significantly decrease local scour depths compared to vertical wall abutments, as they provide a smoother transition through a bridge opening. This eliminates abrupt corners that cause turbulent areas. Spur dykes, barbs, groynes, and vanes are river training structures that change stream hydraulics to mitigate undesirable erosion or deposits. They are usually used on unstable stream channels to help redirect stream flow to more desirable locations through the bridge. The insertion of piles or deeper footings is also used to help strengthen bridges. | 1 | Applied and Interdisciplinary Chemistry |
Researchers began questioning the nature of "tail states" in disordered semiconductors in the 1950s. It was found that such tails arise from the strains sufficient to push local states past the band edges.
In 1953, the Austrian-American physicist Franz Urbach (1902–1969) found that such tails decay exponentially into the gap. Later, photoemission experiments delivered absorption models revealing temperature dependence of the tail.
A variety of amorphous crystalline solids expose exponential band edges via optical absorption. The universality of this feature suggested a common cause. Several attempts were made to explain the phenomenon, but these could not connect specific topological units to the electronic structure. | 0 | Theoretical and Fundamental Chemistry |
For most fluids and some homogenous solid materials, like gels, diffusion is the same in all directions and characterized by the same diffusion coefficient number. This property is called isotropicity which gives cubosomes the ability to be used in biological tissues which are highly structured and typically have different diffusion coefficients along different directions (anisotropic). Because of advantages such as the unique structure of the cubic phase and its resemblance to biological membranes as well as biodegradability of lipids, cubosomes are a great tool for drug delivery system. In addition, the bicontinuous cubic liquid crystalline phase (cubic phase)’s tortuosity is useful for slowing down diffusion as shown by Higuchi’s square root of time release kinetics. Capability to encapsulate hydrophilic, hydrophobic, and amphiphilic substance, being simple to prepare, and all the aforementioned qualities give cubosomes a property that can be used in controlled transport applications as drug delivery vehicles. | 0 | Theoretical and Fundamental Chemistry |
Adina Paytan is a research professor at the Institute of Marine Sciences at the University of California, Santa Cruz. known for research into biogeochemical cycling in the present and the past. She has over 270 scientific publications in journals such as Science, Nature, Proceedings of the National Academy of Sciences, and Geophysical Research Letters. | 0 | Theoretical and Fundamental Chemistry |
The bonnet provides a leakproof closure for the valve body. The threaded section of the stem goes through a hole with matching threads in the bonnet. Globe valves may have a screw-in, union, or bolted bonnet. Screw-in bonnet is the simplest bonnet, offering a durable, pressure-tight seal. Union bonnet is suitable for applications | 1 | Applied and Interdisciplinary Chemistry |
Magnetometers have a very diverse range of applications, including locating objects such as submarines, sunken ships, hazards for tunnel boring machines, hazards in coal mines, unexploded ordnance, toxic waste drums, as well as a wide range of mineral deposits and geological structures. They also have applications in heart beat monitors, weapon systems positioning, sensors in anti-locking brakes, weather prediction (via solar cycles), steel pylons, drill guidance systems, archaeology, plate tectonics and radio wave propagation and planetary exploration. Laboratory magnetometers determine the magnetic dipole moment of a magnetic sample, typically as a function of temperature, magnetic field, or other parameter. This helps to reveal its magnetic properties such as ferromagnetism, antiferromagnetism, superconductivity, or other properties that affect magnetism.
Depending on the application, magnetometers can be deployed in spacecraft, aeroplanes (fixed wing magnetometers), helicopters (stinger and bird), on the ground (backpack), towed at a distance behind quad bikes(ATVs) on a (sled or trailer), lowered into boreholes (tool, probe or sonde) and towed behind boats (tow fish). | 0 | Theoretical and Fundamental Chemistry |
The FT-IR spectra were recorded using a Nicolet 170SX or a JASCO FT/IR-410 spectrometer. For spectra recorded in the Nicolet spectrometer, the data were stored at intervals of 0.5 cm in the 4,000 – 2,000 cm region and of 0.25 cm in the 2,000 – 400 cm region and the spectral resolution was 0.25 cm. For spectra recorded in the JASCO spectrometer, the resolution as well as the intervals was 0.5 cm. Samples from solids were prepared using the KBr disc or the Nujol paste methods, samples from liquids were prepared with the liquid film method. This collections contains ca 54,100 spectra and is being updated. | 0 | Theoretical and Fundamental Chemistry |
George William Scott Blair (23 July 1902 – 30 September 1987) was British chemist noted for his contributions to rheology. In fact he has been called "the first rheologist" | 0 | Theoretical and Fundamental Chemistry |
Renal cells and nephrons have already been simulated by microfluidic devices. "Such cell cultures can lead to new insights into cell and organ function and be used for drug screening". A kidney-on-a-chip device has the potential to accelerate research encompassing artificial replacement for lost kidney function. Nowadays, dialysis requires patients to go to a clinic up to three times per week. A more transportable and accessible form of treatment would not only increase the patient's overall health (by increasing frequency of treatment), but the whole process would become more efficient and tolerable. Artificial kidney research is striving to bring transportability, wearability and perhaps implantation capability to the devices through innovative disciplines: microfluidics, miniaturization and nanotechnology.
The nephron is the functional unit of the kidney and is composed of a glomerulus and a tubular component. Researchers at MIT claim to have designed a bioartificial device that replicates the function of the nephron's glomerulus, proximal convoluted tubule and loop of Henle.
Each part of the device has its unique design, generally consisting of two microfabricated layers separated by a membrane. The only inlet to the microfluidic device is designed for the entering blood sample. In the glomerulus section of the nephron, the membrane allows certain blood particles through its wall of capillary cells, composed by the endothelium, basement membrane and the epithelial podocytes. The fluid that is filtered from the capillary blood into Bowmans space is called filtrate or primary urine.
In the tubules, some substances are added to the filtrate as part of the urine formation, and some substances reabsorbed out of the filtrate and back into the blood. The first segment of these tubules is the proximal convoluted tubule. This is where the almost complete absorption of nutritionally important substances takes place. In the device, this section is merely a straight channel, but blood particles going to the filtrate have to cross the previously mentioned membrane and a layer of renal proximal tubule cells. The second segment of the tubules is the loop of Henle where the reabsorption of water and ions from the urine takes place. The device's looping channels strives to simulate the countercurrent mechanism of the loop of Henle. Likewise, the loop of Henle requires a number of different cell types because each cell type has distinct transport properties and characteristics. These include the descending limb cells, thin ascending limb cells, thick ascending limb cells, cortical collecting duct cells and medullary collecting duct cells.
One step towards validating the microfluidic devices simulation of the full filtration and reabsorption behavior of a physiological nephron would include demonstrating that the transport properties between blood and filtrate are identical with regards to where they occur and what is being let in by the membrane. For example, the large majority of passive transport of water occurs in the proximal tubule and the descending thin limb, or the active transport of NaCl largely occurs in the proximal tubule and the thick ascending limb. The devices design requirements would require the filtration fraction in the glomerulus to vary between 15–20%, or the filtration reabsorption in the proximal convoluted tubule to vary between 65–70%, and finally the urea concentration in urine (collected at one of the two outlets of the device) to vary between 200–400 mM.
One recent report illustrates a biomimic nephron on hydrogel microfluidic devices with establishing the function of passive diffusion. The complex physiological function of nephron is achieved on the basis of interactions between vessels and tubules (both are hollow channels). However, conventional laboratory techniques usually focus on 2D structures, such as petri-dish that lacks capability to recapitulate real physiology that occurs in 3D. Therefore, the authors developed a new method to fabricate functional, cell-lining and perfusable microchannels inside 3D hydrogel. The vessel endothelial and renal epithelial cells are cultured inside hydrogel microchannel and form cellular coverage to mimic vessels and tubules, respectively. They employed confocal microscope to examine the passive diffusion of one small organic molecule (usually drugs) between the vessels and tubules in hydrogel. The study demonstrates the beneficial potential to mimic renal physiology for regenerative medicine and drug screening. | 1 | Applied and Interdisciplinary Chemistry |
Gold extraction is the extraction of gold from dilute ores using a combination of chemical processes. Gold mining produces about 3600 tons annually, and another 300 tons is produced from recycling.
Since the 20th century, gold has been principally extracted in a cyanide process by leaching the ore with cyanide solution. The gold may then be further refined by gold parting, which removes other metals (principally silver) by blowing chlorine gas through the molten metal. Historically, small particles of gold were amalgamated with mercury, and then concentrated by boiling away the mercury. The mercury method is still used in some small operations. | 1 | Applied and Interdisciplinary Chemistry |
Rwanda and Burundi, former Belgian colonies in Central Africa, are RHT but are considering switching to LHT like neighbouring members of the East African Community (EAC). A survey in 2009 found that 54% of Rwandans favoured the switch. Reasons cited were the perceived lower costs of RHD vehicles, easier maintenance and the political benefit of harmonising traffic regulations with other EAC countries. The survey indicated that RHD cars were 16% to 49% cheaper than their LHD counterparts. In 2014, an internal report by consultants to the Ministry of Infrastructure recommended a switch to LHT. In 2015, the ban on RHD vehicles was lifted; RHD trucks from neighbouring countries cost $1,000 less than LHD models imported from Europe. | 0 | Theoretical and Fundamental Chemistry |
The lysocline is the depth in the ocean dependent upon the carbonate compensation depth (CCD), usually around 5 km, below which the rate of dissolution of calcite increases dramatically because of a pressure effect. While the lysocline is the upper bound of this transition zone of calcite saturation, the CCD is the lower bound of this zone.
CaCO content in sediment varies with different depths of the ocean, spanned by levels of separation known as the transition zone. In the mid-depth area of the ocean, sediments are rich in CaCO, content values reaching 85–95%. This area is then spanned hundreds of meters by the transition zone, ending in the abyssal depths with 0% concentration. The lysocline is the upper bound of the transition zone, where amounts of CaCO content begins to noticeably drop from the mid-depth 85–95% sediment. The CaCO content drops to 0% concentration at the lower bound, known as the calcite compensation depth.
Shallow marine waters are generally supersaturated in calcite, CaCO, because as marine organisms (which often have shells made of calcite or its polymorph, aragonite) die, they tend to fall downwards without dissolving. As depth and pressure increases within the water column, calcite solubility increases, causing supersaturated water above the saturation depth, allowing for preservation and burial of CaCO on the seafloor. However, this creates undersaturated seawater below the saturation depth, preventing CaCO burial on the sea floor as the shells start to dissolve.
The equation Ω = [Ca] X [CO]/K' expresses the CaCO saturation state of seawater. The calcite saturation horizon is where Ω =1; dissolution proceeds slowly below this depth. The lysocline is the depth that this dissolution impacts is again notable, also known as the inflection point with sedimentary CaCO versus various water depths. | 0 | Theoretical and Fundamental Chemistry |
Water can be converted to its component elemental gases, H and O, through the application of an external voltage. Water does not decompose into hydrogen and oxygen spontaneously as the Gibbs free energy change for the process at standard conditions is very positive, about 474.4 kJ. The decomposition of water into hydrogen and oxygen can be performed in an electrolytic cell. In it, a pair of inert electrodes usually made of platinum immersed in water act as anode and cathode in the electrolytic process. The electrolysis starts with the application of an external voltage between the electrodes. This process will not occur except at extremely high voltages without an electrolyte such as sodium chloride or sulfuric acid (most used 0.1 M).
Bubbles from the gases will be seen near both electrodes. The following half reactions describe the process mentioned above:
:Anode (oxidation): 2 HO → O + 4 H + 4 e
:Cathode (reduction): 2 HO + 2 e → H + 2 OH
:Overall reaction: 2 HO → 2 H + O
Although strong acids may be used in the apparatus, the reaction will not net consume the acid. While this reaction will work at any conductive electrode at a sufficiently large potential, platinum catalyzes both hydrogen and oxygen formation, allowing for relatively low voltages (~2 V depending on the pH). | 0 | Theoretical and Fundamental Chemistry |
The result of the nuclear medicine imaging process is a dataset comprising one or more images. In multi-image datasets the array of images may represent a time sequence (i.e. cine or movie) often called a "dynamic" dataset, a cardiac gated time sequence, or a spatial sequence where the gamma-camera is moved relative to the patient. SPECT (single photon emission computed tomography) is the process by which images acquired from a rotating gamma-camera are reconstructed to produce an image of a "slice" through the patient at a particular position. A collection of parallel slices form a slice-stack, a three-dimensional representation of the distribution of radionuclide in the patient.
The nuclear medicine computer may require millions of lines of source code to provide quantitative analysis packages for each of the specific imaging techniques available in nuclear medicine.
Time sequences can be further analysed using kinetic models such as multi-compartment models or a Patlak plot. | 1 | Applied and Interdisciplinary Chemistry |
A multichannel analyzer (MCA) is an instrument used in laboratory and field applications to analyze an input signal consisting of voltage pulses. MCAs are used extensively in digitizing various spectroscopy measurements, especially those related to nuclear physics, including various types of spectroscopy (alpha-, beta-, and gamma spectroscopy). | 0 | Theoretical and Fundamental Chemistry |
In general, patches consist of three separate layers that contribute and control the release of medicine. The outer impermeable backing layer controls the direction of release and reduces drug loss away from the site of contact. It also protects the other layers and acts as a mechanical support. The middle reservoir layer holds the drug and is tailored to provide the specified dosage. The final inner layer consists of the mucoadhesive, allowing the patch to adhere to the specified mucosa. | 1 | Applied and Interdisciplinary Chemistry |
The shape of the zero-phonon line is Lorentzian with a width determined by the excited state lifetime T according to the Heisenberg uncertainty principle. Without the influence of the lattice, the natural line width (full width at half maximum) of the chromophore is γ = 1/T . The lattice reduces the lifetime of the excited state by introducing radiationless decay mechanisms. At absolute zero the lifetime of the excited state influenced by the lattice is T. Above absolute zero, thermal motions will introduce random perturbations to the chromophores local environment. These perturbations shift the energy of the electronic transition, introducing a temperature dependent broadening of the line width. The measured width of a single chromophores zero phonon line, the homogeneous line width, is then γ(T) ≥ 1/T' .
The line shape of the phonon side band is that of a Poisson distribution as it expresses a discrete number of events, electronic transitions with phonons, during a period of time. At higher temperatures, or when the chromophore interacts strongly with the matrix, the probability of multiphonon is high and the phonon side band approximates a Gaussian distribution.
The distribution of intensity between the zero-phonon line and the phonon sideband is characterized by the Debye-Waller factor α. | 0 | Theoretical and Fundamental Chemistry |
The process of organohalide respiration, uses reductive dehalogenation to produce energy that can be used by the respiring microorganism to carry out its growth and metabolism. Halogenated organic compounds are used as the terminal electron acceptor, which results in their dehalogenation. Reductive dehalogenation is the process by which this occurs. It involves the reduction of halogenated compounds by removing the halogen substituents, while simultaneously adding electrons to the compound. Hydrogenolysis and vicinal reduction are the two known processes of this mechanism that have been identified. In both processes, the removed halogen substituents are released as anions. Reductive dehalogenation is catalyzed by reductive dehalogenases, which are membrane-associated enzymes. A number of not only membrane-associated but also cytoplasmic hydrogenases, in some cases as part of the protein complexes, are predicted to play roles in the organohalide respiration process. Most of these enzymes contain iron-sulfur (Fe-S) clusters, and a corrinoid cofactor at their active sites. Although the exact mechanism is unknown, research suggests that these two components of the enzyme may be involved in the reduction. | 0 | Theoretical and Fundamental Chemistry |
LaNi has a calcium pentacopper (CaCu) type crystal structure, with a hexagonal lattice, space group is P6/mmm (No. 191), with lanthanum atom is located at coordinate origin 1a (0,0,0), two nickel atoms are located at 2c (1/ 3,2/3,0) and (2/3,1/3,0), the other three at 3g (1/2,0,1/2), (0,1/2,1/2), (1/2,1/2,1/2), with a=511pm, c=397pm. The unit cell contains 1 LaNi atom, the volume is 90×10 cm, the LaNi unit cell contains a larger The six deformed tetrahedral voids can be used to fill in hydrogen atoms. | 1 | Applied and Interdisciplinary Chemistry |
The proposed mechanism of how this mRNA secondary structure and the trp leader peptide could regulate transcription of the trp biosynthetic enzymes includes the following.
*RNAP initiates transcription of the trp promoter.
*RNAP pauses at about nucleotide 90 at a secondary structure (?the first one shown above?).
*Ribosomes engage this nascent mRNA and initiate translation of the leader peptide.
**RNAP is then "released" from its pause and continues transcription.
*When RNAP reaches the region of the potential terminator, whether it continues or not is dependent on the position of the ribosome "trailing behind".
**If the ribosome stalls at the tandem Trp codons, waiting for the appropriate tRNA, region 1 is sequestered within the ribosome and thus cannot base pair with region 2. This means that region 2 and 3 become based paired before region 4 can be transcribed. This forces region 4 when it is made to be single stranded, preventing the formation of the region 3/4 terminator structure. Transcription will then continue.
**If the ribosome translates the leader peptide with no hesitation, it then covers a portion of region 2 preventing it from base pairing with region 3. Then when region 4 is transcribed, it forms a stem and loop with region 3 and transcription is terminated, generating a ca. 140 base transcript.
*This mechanism of control measures the amount of available, charged Trp-tRNA.
The location of ribosomes determines which alternate secondary structures form. | 1 | Applied and Interdisciplinary Chemistry |
Advances to the discovery of LB and LM films began with Benjamin Franklin in 1773 when he dropped about a teaspoon of oil onto a pond. Franklin noticed that the waves were calmed almost instantly and that the calming of the waves spread for about half an acre. What Franklin did not realize was that the oil had formed a monolayer on top of the pond surface. Over a century later, Lord Rayleigh quantified what Benjamin Franklin had seen. Knowing that the oil, oleic acid, had spread evenly over the water, Rayleigh calculated that the thickness of the film was 1.6 nm by knowing the volume of oil dropped and the area of coverage.
With the help of her kitchen sink, Agnes Pockels showed that area of films can be controlled with barriers. She added that surface tension varies with contamination of water. She used different oils to deduce that surface pressure would not change until area was confined to about 0.2 nm. This work was originally written as a letter to Lord Rayleigh who then helped Agnes Pockels become published in the journal, Nature, in 1891.
Agnes Pockels’ work set the stage for Irving Langmuir who continued to work and confirmed Pockels’ results. Using Pockels’ idea, he developed the Langmuir (or Langmuir–Blodgett) trough. His observations indicated that chain length did not impact the affected area since the organic molecules were arranged vertically.
Langmuir’s breakthrough did not occur until he hired Katherine Blodgett as his assistant. Blodgett initially went to seek for a job at General Electric (GE) with Langmuir during her Christmas break of her senior year at Bryn Mawr College, where she received a BA in Physics. Langmuir advised to Blodgett that she should continue her education before working for him. She thereafter attended University of Chicago for her MA in Chemistry. Upon her completion of her Master's, Langmuir hired her as his assistant. However, breakthroughs in surface chemistry happened after she received her PhD degree in 1926 from Cambridge University.
While working for GE, Langmuir and Blodgett discovered that when a solid surface is inserted into an aqueous solution containing organic moieties, the organic molecules will deposit a monolayer homogeneously over the surface. This is the Langmuir–Blodgett film deposition process. Through this work in surface chemistry and with the help of Blodgett, Langmuir was awarded the Nobel Prize in 1932. In addition, Blodgett used Langmuir–Blodgett film to create 99% transparent anti-reflective glass by coating glass with fluorinated organic compounds, forming a simple anti-reflective coating. | 0 | Theoretical and Fundamental Chemistry |
Interstitial hydrides most commonly exist within metals or alloys. They are traditionally termed "compounds" even though they do not strictly conform to the definition of a compound, more closely resembling common alloys such as steel. In such hydrides, hydrogen can exist as either atomic or diatomic entities. Mechanical or thermal processing, such as bending, striking, or annealing, may cause the hydrogen to precipitate out of solution by degassing. Their bonding is generally considered metallic. Such bulk transition metals form interstitial binary hydrides when exposed to hydrogen. These systems are usually non-stoichiometric, with variable amounts of hydrogen atoms in the lattice. In materials engineering, the phenomenon of hydrogen embrittlement results from the formation of interstitial hydrides. Hydrides of this type form according to either one of two main mechanisms. The first mechanism involves the adsorption of dihydrogen, succeeded by the cleaving of the H-H bond, the delocalisation of the hydrogen's electrons, and finally the diffusion of the protons into the metal lattice. The other main mechanism involves the electrolytic reduction of ionised hydrogen on the surface of the metal lattice, also followed by the diffusion of the protons into the lattice. The second mechanism is responsible for the observed temporary volume expansion of certain electrodes used in electrolytic experiments.
Palladium absorbs up to 900 times its own volume of hydrogen at room temperatures, forming palladium hydride. This material has been discussed as a means to carry hydrogen for vehicular fuel cells. Interstitial hydrides show certain promise as a way for safe hydrogen storage. Neutron diffraction studies have shown that hydrogen atoms randomly occupy the octahedral interstices in the metal lattice (in an fcc lattice there is one octahedral hole per metal atom). The limit of absorption at normal pressures is PdH0.7, indicating that approximately 70% of the octahedral holes are occupied.
Many interstitial hydrides have been developed that readily absorb and discharge hydrogen at room temperature and atmospheric pressure. They are usually based on intermetallic compounds and solid-solution alloys. However, their application is still limited, as they are capable of storing only about 2 weight percent of hydrogen, insufficient for automotive applications. | 0 | Theoretical and Fundamental Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.