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The antenna-shaped light harvesting complex of cyanobacteria, glaucocystophyta, and red algae is known as the phycobilisome which is composed of linear tetrapyrrole pigments. Pigment-protein complexes referred to as R-phycoerythrin are rod-like in shape and make up the rods and core of the phycobilisome. Little light reaches algae that reside at a depth of one meter or more in seawater, as light is absorbed by seawater. The pigments, such as phycocyanobilin and phycoerythrobilin, are the chromophores that bind through a covalent thioether bond to their apoproteins at cysteins residues. The apoprotein with its chromophore is called phycocyanin, phycoerythrin, and allophycocyanin, respectively. They often occur as hexamers of α and β subunits (αβ). They enhance the amount and spectral window of light absorption and fill the "green gap", which occur in higher Plants.
The geometrical arrangement of a phycobilisome is very elegant and results in 95% efficiency of energy transfer. There is a central core of allophycocyanin, which sits above a photosynthetic reaction center. There are phycocyanin and phycoerythrin subunits that radiate out from this center like thin tubes. This increases the surface area of the absorbing section and helps focus and concentrate light energy down into the reaction center to a Chlorophyll. The energy transfer from excited electrons absorbed by pigments in the phycoerythrin subunits at the periphery of these antennas appears at the reaction center in less than 100 ps. | 0 | Theoretical and Fundamental Chemistry |
Multistep-feedback loop mechanism also leads to ultrasensitivity.
There is paper introducing that engineering synthetic feedback loops using yeast mating mitogen-activated protein (MAP) kinase pathway as a model system.
In Yeast mating pathway: alpha-factor activates receptor, Ste2, and Ste4 and activated Ste4 recruits Ste5 complex to membrane, allowing PAK-like kinase Ste20 (membrane-localized) to activate MAPKKK Ste11. Ste11 and downstream kinases, Ste7 (MAPKK) and Fus3 (MAPK), are colocalized on the scaffold and activation of cascade leads to transcriptional program. They used pathway modulators outside of core cascade, Ste50 promotes activation of Ste11 by Ste20; Msg5 (negative, red) is MAPK phosphatase that deactivates Fus3 (Fig.2A).
What they built was circuit with enhanced ultrasensitive switch behavior by constitutively expressing a negative modulator, Msg5 which is one of MAPK phosphatase and inducibly expressing a positive modulator, Ste50 which is pathway modulators outside of core cascade(Fig.2B).
The success of this recruitment-based engineering strategy suggests that it may be possible to reprogram cellular responses with high precision. | 1 | Applied and Interdisciplinary Chemistry |
Heusler compounds are magnetic intermetallics with face-centered cubic crystal structure and a composition of XYZ (half-Heuslers) or XYZ (full-Heuslers), where X and Y are transition metals and Z is in the p-block. The term derives from the name of German mining engineer and chemist Friedrich Heusler, who studied such a compound (CuMnAl) in 1903. Many of these compounds exhibit properties relevant to spintronics, such as magnetoresistance, variations of the Hall effect, ferro-, antiferro-, and ferrimagnetism, half- and semimetallicity, semiconductivity with spin filter ability, superconductivity, topological band structure and are actively studied as thermoelectric materials. Their magnetism results from a double-exchange mechanism between neighboring magnetic ions. Manganese, which sits at the body centers of the cubic structure, was the magnetic ion in the first Heusler compound discovered. (See the Bethe–Slater curve for details of why this happens.) | 1 | Applied and Interdisciplinary Chemistry |
This was first called the liquid ordered phase by Ipsen et al. (1987). However, it has also been called the LG subgel phase by Huang et al. (1993) and the β phase by Vist and Davis (1990). | 1 | Applied and Interdisciplinary Chemistry |
2-Furoic acid can be the sole source of carbon and energy for the organism Pseudomonas putida. The organism aerobically degrades the compound. | 0 | Theoretical and Fundamental Chemistry |
It is a sequence that suppress both cerebrospinal fluid (CSF) and white matter, and samples the remaining transverse magnetisation in fast spin echo, where the majority of the signals are from the grey matter. Thus, this sequence is useful in detecting small changes on the brain cortex such as focal cortical dysplasia and hippocampal sclerosis in those with epilepsy. These lesions are difficult to detect in other MRI sequences. | 0 | Theoretical and Fundamental Chemistry |
Transition metal amino acid complexes are a large family of coordination complexes containing the conjugate bases of the amino acids, the 2-aminocarboxylates. Amino acids are prevalent in nature, and all of them function as ligands toward the transition metals. Not included in this article are complexes of the amides (including peptide) and ester derivatives of amino acids. Also excluded are the polyamino acids including the chelating agents EDTA and NTA. | 0 | Theoretical and Fundamental Chemistry |
Irène took a nursing course during college to assist her mother, Marie Curie, in the field as her assistant. She began her work as a nurse radiographer on the battlefield alongside her mother, but after a few months she was left to work alone at a radiological facility in Belgium. She taught doctors how to locate shrapnel in bodies using radiology and taught herself how to repair the equipment. She moved throughout facilities and battlegrounds including two bombsites, Furnes and Ypres, and Amiens. She received a military medal for her assistance in X-ray facilities in France and Belgium.
After the war, Irène returned to the Sorbonne in Paris to complete her second baccalaureate degree in mathematics and physics in 1918. Irène then went on to work as her mothers assistant, teaching radiology at the Radium Institute, which had been built by her parents. Her doctoral thesis was concerned with the alpha decay of polonium, the element discovered by her parents (along with radium) and named after Maries country of birth, Poland. Irène became a Doctor of Science in 1925. | 0 | Theoretical and Fundamental Chemistry |
Individual transmembrane adenylyl cyclase isoforms have been linked to numerous physiological functions. Soluble adenylyl cyclase (sAC, AC10) has a critical role in sperm motility. Adenylyl cyclase has been implicated in memory formation, functioning as a coincidence detector. | 1 | Applied and Interdisciplinary Chemistry |
Transition metal alkyl complexes are coordination complexes that contain a bond between a transition metal and an alkyl ligand. Such complexes are not only pervasive but are of practical and theoretical interest. | 0 | Theoretical and Fundamental Chemistry |
SBPase is involved in the regeneration of 5-carbon sugars during the Calvin cycle. Although SBPase has not been emphasized as an important control point in the Calvin cycle historically, it plays a large part in controlling the flux of carbon through the Calvin cycle. Additionally, SBPase activity has been found to have a strong correlation with the amount of photosynthetic carbon fixation. Like many Calvin cycle enzymes, SBPase is activated in the presence of light through a ferredoxin/thioredoxin system. In the light reactions of photosynthesis, light energy powers the transport of electrons to eventually reduce ferredoxin. The enzyme ferredoxin-thioredoxin reductase uses reduced ferredoxin to reduce thioredoxin from the disulfide form to the dithiol. Finally, the reduced thioredoxin is used to reduced a cysteine-cysteine disulfide bond in SBPase to a dithiol, which converts the SBPase into its active form.
SBPase has additional levels of regulation beyond the ferredoxin/thioredoxin system. Mg2+ concentration has a significant impact on the activity of SBPase and the rate of the reactions it catalyzes. SBPase is inhibited by acidic conditions (low pH). This is a large contributor to the overall inhibition of carbon fixation when the pH is low inside the stroma of the chloroplast. Finally, SBPase is subject to negative feedback regulation by sedoheptulose-7-phosphate and inorganic phosphate, the products of the reaction it catalyzes. | 0 | Theoretical and Fundamental Chemistry |
The fractional population distribution of different conformers follows a Boltzmann distribution:
The left hand side is the proportion of conformer i in an equilibrating mixture of M conformers in thermodynamic equilibrium. On the right side, E (k = 1, 2, ..., M) is the energy of conformer k, R is the molar ideal gas constant (approximately equal to 8.314 J/(mol·K) or 1.987 cal/(mol·K)), and T is the absolute temperature. The denominator of the right side is the partition function. | 0 | Theoretical and Fundamental Chemistry |
Biogenic sulfide corrosion is a bacterially mediated process of forming hydrogen sulfide gas and the subsequent conversion to sulfuric acid that attacks concrete and steel within wastewater environments. The hydrogen sulfide gas is biochemically oxidized in the presence of moisture to form sulfuric acid. The effect of sulfuric acid on concrete and steel surfaces exposed to severe wastewater environments can be devastating. In the USA alone, corrosion is causing sewer asset losses estimated at $14 billion per year. This cost is expected to increase as the aging infrastructure continues to fail. | 1 | Applied and Interdisciplinary Chemistry |
Etiocholanedione, also known as 5β-androstanedione or as etiocholane-3,17-dione, is a naturally occurring etiocholane (5β-androstane) steroid and an endogenous metabolite of androgens like testosterone, dihydrotestosterone, dehydroepiandrosterone (DHEA), and androstenedione. It is the C5 epimer of androstanedione (5α-androstanedione). Although devoid of androgenic activity like other 5β-reduced steroids, etiocholanedione has some biological activity of its own. The compound has been found to possess potent haematopoietic effects in a variety of models. In addition, it has been found to promote weight loss in animals and in a double-blind, placebo-controlled clinical study in humans conducted in 1993. These effects are said to be similar to those of DHEA. Unlike DHEA however, etiocholanedione cannot be metabolized further into steroid hormones like androgens and estrogens. | 1 | Applied and Interdisciplinary Chemistry |
This geometry has been applied to black hole thermodynamics, with some physically relevant results. The most physically significant case is for the Kerr black hole in higher dimensions, where the curvature singularity signals thermodynamic instability, as found earlier by conventional methods.
The entropy of a black hole is given by the well-known Bekenstein–Hawking formula
where is Boltzmanns constant, the speed of light, Newtons constant and is the area of the event horizon of the black hole. Calculating the Ruppeiner geometry of the black hole's entropy is, in principle, straightforward, but it is important that the entropy should be written in terms of extensive parameters,
where is ADM mass of the black hole and are the conserved charges and runs from 1 to n. The signature of the metric reflects the sign of the hole's specific heat. For a Reissner-Nordström black hole, the Ruppeiner metric has a Lorentzian signature which corresponds to the negative heat capacity it possess, while for the BTZ black hole, we have a Euclidean signature. This calculation cannot be done for the Schwarzschild black hole, because its entropy is
which renders the metric degenerate. | 0 | Theoretical and Fundamental Chemistry |
Water meniscus forces are highly interesting for AFM measurements in air. Due to the ambient humidity, a thin layer of water is formed between the tip and the sample during air measurements. The resulting capillary force gives rise to a strong attractive force that pulls the tip onto the surface. In fact, the adhesion force measured between tip and sample in ambient air of finite humidity is usually dominated by capillary forces. As a consequence, it is difficult to pull the tip away from the surface. For soft samples including many polymers and in particular biological materials, the strong adhesive capillary force gives rise to sample degradation and destruction upon imaging in contact mode. Historically, these problems were an important motivation for the development of dynamic imaging in air (e.g. "tapping mode"). During tapping mode imaging in air, capillary bridges still form. Yet, for suitable imaging conditions, the capillary bridges are formed and broken in every oscillation cycle of the cantilever normal to the surface, as can be inferred from an analysis of cantilever amplitude and phase vs. distance curves. As a consequence, destructive shear forces are largely reduced and soft samples can be investigated.
In order to quantify the equilibrium capillary force, it is necessary to start from the Laplace equation for pressure:
where γ, is the surface energy and r and r are defined in the figure.
The pressure is applied on an area of
where θ is the angle between the tips surface and the liquids surface while h is the height difference between the surrounding liquid and the top of the miniscus.
The force that pulls together the two surfaces is
The same formula could also be calculated as a function of relative humidity.
Gao calculated formulas for different tip geometries. As an example, the force decreases by 20% for a conical tip with respect to a spherical tip.
When these forces are calculated, a difference must be made between the wet on dry situation and the wet on wet situation.
For a spherical tip, the force is:
: for dry on wet,
:for wet on wet,
where θ is the contact angle of the dry sphere and φ is the immersed angle, as shown in the figure
For a conical tip, the formula becomes:
: for dry on wet
: for wet on wet
where δ is the half cone angle and r and h are parameters of the meniscus profile. | 0 | Theoretical and Fundamental Chemistry |
Together with his longtime collaborator Joseph Chatt, Shaw contributed to the development of organoplatinum chemistry. They reported the first platinum hydride, PtHCl(PEt). This colourless, volatile solid was the first non-organometallic hydride (i.e., lacking a metal-carbon bond).
With an interest in cyclometallation, he discovered one of the first pincer complexes via the orthometalation of 1,3-CH(CHPBu). | 0 | Theoretical and Fundamental Chemistry |
The linear dispersion relation – unaffected by wave amplitude – is for nonlinear waves also correct at the second order of the perturbation theory expansion, with the orders in terms of the wave steepness (where a is wave amplitude). To the third order, and for deep water, the dispersion relation is
: so
This implies that large waves travel faster than small ones of the same frequency. This is only noticeable when the wave steepness is large. | 1 | Applied and Interdisciplinary Chemistry |
Despite the difficulty of theoretical interpretation, measured conductivity is a good indicator of the presence or absence of conductive ions in solution, and measurements are used extensively in many industries. For example, conductivity measurements are used to monitor quality in public water supplies, in hospitals, in boiler water and industries that depend on water quality such as brewing. This type of measurement is not ion-specific; it can sometimes be used to determine the amount of total dissolved solids (TDS) if the composition of the solution and its conductivity behavior are known. Conductivity measurements made to determine water purity will not respond to non conductive contaminants (many organic compounds fall into this category), therefore additional purity tests may be required depending on application.
Applications of TDS measurements are not limited to industrial use; many people use TDS as an indicator of the purity of their drinking water. Additionally, aquarium enthusiasts are concerned with TDS, both for freshwater and salt water aquariums. Many fish and invertebrates require quite narrow parameters for dissolved solids. Especially for successful breeding of some invertebrates normally kept in freshwater aquariums—snails and shrimp primarily—brackish water with higher TDS, specifically higher salinity, water is required. While the adults of a given species may thrive in freshwater, this is not always true for the young and some species will not breed at all in non-brackish water.
Sometimes, conductivity measurements are linked with other methods to increase the sensitivity of detection of specific types of ions. For example, in the boiler water technology, the boiler blowdown is continuously monitored for "cation conductivity", which is the conductivity of the water after it has been passed through a cation exchange resin. This is a sensitive method of monitoring anion impurities in the boiler water in the presence of excess cations (those of the alkalizing agent usually used for water treatment). The sensitivity of this method relies on the high mobility of H in comparison with the mobility of other cations or anions. Beyond cation conductivity, there are analytical instruments designed to measure Degas conductivity, where conductivity is measured after dissolved carbon dioxide has been removed from the sample, either through reboiling or dynamic degassing.
Conductivity detectors are commonly used with ion chromatography. | 0 | Theoretical and Fundamental Chemistry |
Due to the lone pair of electrons, halogen groups are available for donating electrons. Hence they are therefore ortho / para directors. | 0 | Theoretical and Fundamental Chemistry |
* B40.200-2008: Thermometers, Direct Reading and Remotes Reading.
* PTC 19.3-1974(R2004): Performance test code for temperature measurement. | 0 | Theoretical and Fundamental Chemistry |
In combustion, the Karlovitz number is defined as the ratio of chemical time scale to Kolmogorov time scale , named after Béla Karlovitz. The number reads as
In premixed turbulent combustion, the chemical time scale can be defined as , where is the thermal diffusivity and is the laminar flame speed and the flame thickness is given by , in which case,
where is the Kolmogorov scale. The Karlovitz number is related to Damköhler number as
if the Damköhler number is defined with Kolmogorov scale. If , the premixed turbulent flame falls into the category of corrugated flamelets and wrinkled flamelets, otherwise into the thin reaction zone or broken reaction zone flames. | 0 | Theoretical and Fundamental Chemistry |
Langerin is expressed in LCs which are located in the epidermis and in vaginal and oral mucosa. LCs are immune cells closely related to macrophages, but by their function, they are more like conventional dendritic cells (cDCs). Langerin recognizes and binds carbohydrates, such as mannose, fucose and N-acetylglucosamine. Thus, LCs may react against pathogens such as HIV-1, Mycobacterium leprae and Candida albicans. After pathogen binding to langerin, fate of the pathogens is not yet understood It has been proposed that the pathogen is internalised into a cytoplasmatic organelle called Birbeck granule. There, degradation and antigen processing for presentation to T-cells take place. For instance, langerin binds lipoarabinomannans of mycobacteria and inside the Birbeck granules, it contributes to the binding of the antigen to CD1a molecule. In mice, langerin is involved in antigen binding to MHC II glycoproteins and to MHC I glycoproteins during cross-presentation.
It seems an intracellular Src homology domain of langerin is important for the formation of Birbeck granules. These organelles contain Rab11a which is a molecule participating in langerin recycling.
Langerin has similar function and structure as a DCs surface protein DC-SIGN (CD209). Both receptors bind similar antigens via the CRD, for instance Mycobacterium tuberculosis and HIV-1. However, whereas HIV-1 binding to langerin leads to the elimination of the virus, HIV-1 binding to DC-SIGN leads to infection of the cell. | 1 | Applied and Interdisciplinary Chemistry |
Modern puddling was one of several processes developed in the second half of the 18th century in Great Britain for producing bar iron from pig iron without the use of charcoal. It gradually replaced the earlier charcoal-fueled process, conducted in a finery forge. | 1 | Applied and Interdisciplinary Chemistry |
One method of measuring FRET efficiency is to measure the variation in acceptor emission intensity. When the donor and acceptor are in proximity (1–10 nm) due to the interaction of the two molecules, the acceptor emission will increase because of the intermolecular FRET from the donor to the acceptor. For monitoring protein conformational changes, the target protein is labeled with a donor and an acceptor at two loci. When a twist or bend of the protein brings the change in the distance or relative orientation of the donor and acceptor, FRET change is observed. If a molecular interaction or a protein conformational change is dependent on ligand binding, this FRET technique is applicable to fluorescent indicators for the ligand detection. | 1 | Applied and Interdisciplinary Chemistry |
The Tolman cone angle method assumes empirical bond data and defines the perimeter as the maximum possible circumscription of an idealized free-spinning substituent. The metal-ligand bond length in the Tolman model was determined empirically from crystal structures of tetrahedral nickel complexes. In contrast, the solid-angle concept derives both bond length and the perimeter from empirical solid state crystal structures. There are advantages to each system.
If the geometry of a ligand is known, either through crystallography or computations, an exact cone angle (θ) can be calculated. No assumptions about the geometry are made, unlike the Tolman method. | 0 | Theoretical and Fundamental Chemistry |
This equation for gives satisfactory agreement with experimental measurements for low electrolyte concentrations, typically less than 10 mol/L. Deviations from the theory occur at higher concentrations and with electrolytes that produce ions of higher charges, particularly unsymmetrical electrolytes. Essentially these deviations occur because the model is oversimplified, so there is little to be gained making small adjustments to the model. The individual assumptions can be challenged in turn.
*Complete dissociation. Ion association may take place, particularly with ions of higher charge. This was followed up in detail by Niels Bjerrum. The Bjerrum length is the separation at which the electrostatic interaction between two ions is comparable in magnitude to kT.
*Weak electrolytes. A weak electrolyte is one that is not fully dissociated. As such it has a dissociation constant. The dissociation constant can be used to calculate the extent of dissociation and hence, make the necessary correction needed to calculate activity coefficients.
*Ions are spherical, not point charges and are not polarized. Many ions such as the nitrate ion, NO, are not spherical. Polyatomic ions are also polarizable.
*Role of the solvent. The solvent is not a structureless medium but is made up of molecules. The water molecules in aqueous solution are both dipolar and polarizable. Both cations and anions have a strong primary solvation shell and a weaker secondary solvation shell. Ion–solvent interactions are ignored in Debye–Hückel theory.
Moreover, ionic radius is assumed to be negligible, but at higher concentrations, the ionic radius becomes comparable to the radius of the ionic atmosphere.
Most extensions to Debye–Hückel theory are empirical in nature. They usually allow the Debye–Hückel equation to be followed at low concentration and add further terms in some power of the ionic strength to fit experimental observations. The main extensions are the Davies equation, Pitzer equations and specific ion interaction theory. | 0 | Theoretical and Fundamental Chemistry |
PFASs are commonly used in Class B firefighting foams due to their hydrophobic and lipophobic properties, as well as the stability of the chemicals when exposed to high heat.
Research into occupational exposure for firefighters is emergent, though frequently limited by underpowered study designs. A 2011 cross-sectional analysis of the C8 Health Studies found higher levels of PFHxS in firefighters compared to the sample group of the region, with other PFASs at elevated levels, without reaching statistical significance. A 2014 study in Finland studying eight firefighters over three training sessions observed select PFASs (PFHxS and PFNA) increase in blood samples following each training event. Due to this small sample size, a test of significance was not conducted. A 2015 cross-sectional study conducted in Australia found that PFOS and PFHxS accumulation was positively associated with years of occupational AFFF exposure through firefighting.
Due to their use in training and testing, recent studies indicate occupational risk for military members and firefighters, as higher levels of PFASs in exposure were indicated in military members and firefighters when compared to the general population. PFAS exposure is prevalent among firefighters not only due to its use in emergencies, but also because it is used in personal protective equipment. In support of these findings, states like Washington and Colorado have moved to restrict and penalize the use of Class B firefighting foam for firefighter training and testing. | 0 | Theoretical and Fundamental Chemistry |
Ionic interactions involve the attraction of ions or molecules with full permanent charges of opposite signs. For example, sodium fluoride involves the attraction of the positive charge on sodium (Na) with the negative charge on fluoride (F). However, this particular interaction is easily broken upon addition to water, or other highly polar solvents. In water ion pairing is mostly entropy driven; a single salt bridge usually amounts to an attraction value of about ΔG =5 kJ/mol at an intermediate ion strength I, at I close to zero the value increases to about 8 kJ/mol. The ΔG values are usually additive and largely independent of the nature of the participating ions, except for transition metal ions etc.
These interactions can also be seen in molecules with a localized charge on a particular atom. For example, the full negative charge associated with ethoxide, the conjugate base of ethanol, is most commonly accompanied by the positive charge of an alkali metal salt such as the sodium cation (Na). | 0 | Theoretical and Fundamental Chemistry |
Animal products such as meat, fish, shellfish, fowl, eggs, and dairy contain zinc. The concentration of zinc in plants varies with the level in the soil. With adequate zinc in the soil, the food plants that contain the most zinc are wheat (germ and bran) and various seeds, including sesame, poppy, alfalfa, celery, and mustard. Zinc is also found in beans, nuts, almonds, whole grains, pumpkin seeds, sunflower seeds, and blackcurrant.
Other sources include fortified food and dietary supplements in various forms. A 1998 review concluded that zinc oxide, one of the most common supplements in the United States, and zinc carbonate are nearly insoluble and poorly absorbed in the body. This review cited studies that found lower plasma zinc concentrations in the subjects who consumed zinc oxide and zinc carbonate than in those who took zinc acetate and sulfate salts. For fortification, however, a 2003 review recommended cereals (containing zinc oxide) as a cheap, stable source that is as easily absorbed as the more expensive forms. A 2005 study found that various compounds of zinc, including oxide and sulfate, did not show statistically significant differences in absorption when added as fortificants to maize tortillas. | 1 | Applied and Interdisciplinary Chemistry |
The main classes of painkillers are NSAIDs, opioids, and local anesthetics.
For consciousness (anesthetic drugs)
Some anesthetics include benzodiazepines and barbiturates. | 1 | Applied and Interdisciplinary Chemistry |
In humans, dietary starches are composed of glucose units arranged in long chains called amylose, a polysaccharide. During digestion, bonds between glucose molecules are broken by salivary and pancreatic amylase, resulting in progressively smaller chains of glucose. This results in simple sugars glucose and maltose (2 glucose molecules) that can be absorbed by the small intestine.
Lactase is an enzyme that breaks down the disaccharide lactose to its component parts, glucose and galactose. Glucose and galactose can be absorbed by the small intestine. Approximately 65 percent of the adult population produce only small amounts of lactase and are unable to eat unfermented milk-based foods. This is commonly known as lactose intolerance. Lactose intolerance varies widely by genetic heritage; more than 90 percent of peoples of east Asian descent are lactose intolerant, in contrast to about 5 percent of people of northern European descent.
Sucrase is an enzyme that breaks down the disaccharide sucrose, commonly known as table sugar, cane sugar, or beet sugar. Sucrose digestion yields the sugars fructose and glucose which are readily absorbed by the small intestine. | 1 | Applied and Interdisciplinary Chemistry |
Because of the specificity of toll-like receptors (and other innate immune receptors) they cannot easily be changed in the course of evolution, these receptors recognize molecules that are constantly associated with threats (i.e., pathogen or cell stress) and are highly specific to these threats (i.e., cannot be mistaken for self molecules that are normally expressed under physiological conditions). Pathogen-associated molecules that meet this requirement are thought to be critical to the pathogens function and difficult to change through mutation; they are said to be evolutionarily conserved. Somewhat conserved features in pathogens include bacterial cell-surface lipopolysaccharides (LPS), lipoproteins, lipopeptides, and lipoarabinomannan; proteins such as flagellin from bacterial flagella; double-stranded RNA of viruses; or the unmethylated CpG islands of bacterial and viral DNA; and also of the CpG islands found in the promoters of eukaryotic DNA; as well as certain other RNA and DNA molecules. As TLR ligands are present in most pathogens, they may also be present in pathogen-derived vaccines (e.g. MMR, influenza, polio vaccines) most commercially available vaccines have been assessed for their inherent TLR ligands capacity to activate distinct subsets of immune cells. For most of the TLRs, ligand recognition specificity has now been established by gene targeting (also known as "gene knockout"): a technique by which individual genes may be selectively deleted in mice. See the table above for a summary of known TLR ligands. | 1 | Applied and Interdisciplinary Chemistry |
Iodolactonization has been used in the synthesis of many biologically important products such as the tumor growth inhibitors vernolepin and vernomenin, the pancreatic lipase inhibitor vibralactone, and prostaglandins, a lipid found in animals. The following total syntheses all use iodolactonization as a key step in obtaining the desired product.
In 1977, Samuel Danishefsky and coworkers were able to synthesize the tumor growth inhibitors dl-vernolepin and dl-vernomenin via a multistep process in which a lactonization was employed. This synthesis demonstrates the use of iodolactonization to preferentially form a five-membered ring over a four- or six-membered ring, as expected from Baldwin's rules.
In 2006, Zhou and coworkers synthesized another natural product, vibralactone, in which the key step was the formation of a lactone. The stereoselectivity of the iodolactonization sets a critical stereochemical configuration for the target compound.
In 1969, Corey and coworkers synthesized prostaglandin E using an iodolactone intermediate. Again, the stereoselectivity of the iodolactonization plays an integral role in product formation. | 0 | Theoretical and Fundamental Chemistry |
There are two methods for the production of spiropyrans. The first one can be by condensation of methylene bases with o-hydroxy aromatic aldehydes (or the condensation of the precursor of methylene bases). Spiropyrans generally could be obtained by boiling the aldehyde and the respective benzazolium salts in presence of pyridine or piperidine. The general formula of the synthesis of spiropyrans is shown in the Figure 1.
The second way is by condensation of o-hydroxy aromatic aldehydes with the salts of heterocyclic cations which contains active methylene groups and isolation of the intermediate styryl salts. This second procedure is followed by the removal of the elements of the acid from the obtained styryl salt, such as perchloric acid, with organic bases (gaseous ammonia or amines). | 0 | Theoretical and Fundamental Chemistry |
As most electromagnetic fields encountered in everyday situations are those generated by household or industrial appliances, the majority of EMF meters available are calibrated to measure 50 and 60 Hz alternating fields (the frequency of European and US mains electricity). There are other meters which can measure fields alternating at as low as 20 Hz, however these tend to be much more expensive and are only used for specific research purposes. | 1 | Applied and Interdisciplinary Chemistry |
The mass-flux fraction (or Hirschfelder-Curtiss variable or Kármán-Penner variable) is the ratio of mass-flux of a particular chemical species to the total mass flux of a gaseous mixture. It includes both the convectional mass flux and the diffusional mass flux. It was introduced by Joseph O. Hirschfelder and Charles F. Curtiss in 1948 and later by Theodore von Kármán and Sol Penner in 1954. The mass-flux fraction of a species i is defined as
where
* is the mass fraction
* is the mass average velocity of the gaseous mixture
* is the average velocity with which the species i diffuse relative to
* is the density of species i
* is the gas density.
It satisfies the identity
similar to the mass fraction, but the mass-flux fraction can take both positive and negative values. This variable is used in steady, one-dimensional combustion problems in place of the mass fraction. For one-dimensional ( direction) steady flows, the conservation equation for the mass-flux fraction reduces to
where is the mass production rate of species i. | 0 | Theoretical and Fundamental Chemistry |
The C−H bond in general is very strong, so it is relatively unreactive. In several compound classes, collectively called carbon acids, the C−H bond can be sufficiently acidic for proton removal. Unactivated C−H bonds are found in alkanes and are not adjacent to a heteroatom (O, N, Si, etc.). Such bonds usually only participate in radical substitution. Many enzymes are known, however, to effect these reactions.
Although the C−H bond is one of the strongest, it varies over 30% in magnitude for fairly stable organic compounds, even in the absence of heteroatoms. | 0 | Theoretical and Fundamental Chemistry |
When an electric field is applied to a metal or semiconductor, the electronic structure of the material changes. The electrons (and other charged particles) will react to the electric field, by repositioning themselves within the material. Electrons in metals can relatively easily move around and are available in abundance. They will move in such a manner that they try to cancel the external electric field. Since no metal is a perfect conductor, no metal will perfectly cancel the external electric field within the material. In semiconductors the electrons that are available will not be able to move around as easily as electrons in metals. This leads to a weaker response and weaker cancellation of the electric field. This has the effect that the electric field can penetrate deeper into a semiconductor than into a metal.
The optical reflectivity of a (semi-)conductor is based on the band structure of the material close to or at the surface of the material. For reflectivity to occur a photon has to have enough energy to overcome the bandgap of electrons at the Fermi surface. When the photon energy is smaller than the bandgap, the solid will be unable to absorb the energy of the photon by excitation of an electron to a higher energy. This means that the photon will not be re-emitted by the solid and thus not reflected. If the photon energy is large enough to excite an electron from the Fermi surface, the solid will re-emit the photon by decaying the electron back to the original energy. This is not exactly the same photon as the incident photon, as it has for example the opposite direction of the incident photon.
By applying an electric field to the material, the band structure of the solid changes. This change in band structure leads to a different bandgap, which in turn leads to a difference in optical reflectivity. The electric field, generally made by creating a potential difference, leads to an altered Hamiltonian. Using analytical methods available, such as the Tight Binding method, it can be calculated that this altered Hamiltonian leads to a different band structure.
The combination of electron repositioning and the change in band structure due to an external electric field is called the field effect. Since the electric field has more influence on semiconductors than on metals, semiconductors are easier to use to observe the electroreflectance effect. | 0 | Theoretical and Fundamental Chemistry |
In mathematics, especially in geometry, a double lattice in is a discrete subgroup of the group of Euclidean motions that consists only of translations and point reflections and such that the subgroup of translations is a lattice. The orbit of any point under the action of a double lattice is a union of two Bravais lattices, related to each other by a point reflection. A double lattice in two dimensions is a p2 wallpaper group. In three dimensions, a double lattice is a space group of the type , as denoted by international notation. | 0 | Theoretical and Fundamental Chemistry |
NAD is synthesized through two metabolic pathways. It is produced either in a de novo pathway from amino acids or in salvage pathways by recycling preformed components such as nicotinamide back to NAD. Although most tissues synthesize NAD by the salvage pathway in mammals, much more de novo synthesis occurs in the liver from tryptophan, and in the kidney and macrophages from nicotinic acid. | 0 | Theoretical and Fundamental Chemistry |
For example, there are three distinct compounds with the molecular formula :
The first two isomers shown of are propanols, that is, alcohols derived from propane. Both have a chain of three carbon atoms connected by single bonds, with the remaining carbon valences being filled by seven hydrogen atoms and by a hydroxyl group comprising the oxygen atom bound to a hydrogen atom. These two isomers differ on which carbon the hydroxyl is bound to: either to an extremity of the carbon chain propan-1-ol (1-propanol, n-propyl alcohol, n-propanol; I) or to the middle carbon propan-2-ol (2-propanol, isopropyl alcohol, isopropanol; II). These can be described by the condensed structural formulas and .
The third isomer of is the ether methoxyethane (ethyl-methyl-ether; III). Unlike the other two, it has the oxygen atom connected to two carbons, and all eight hydrogens bonded directly to carbons. It can be described by the condensed formula .
The alcohol "3-propanol" is not another isomer, since the difference between it and 1-propanol is not real; it is only the result of an arbitrary choice in the direction of numbering the carbons along the chain. For the same reason, "ethoxymethane" is the same molecule as methoxyethane, not another isomer.
1-Propanol and 2-propanol are examples of positional isomers, which differ by the position at which certain features, such as double bonds or functional groups, occur on a "parent" molecule (propane, in that case). | 0 | Theoretical and Fundamental Chemistry |
It is well known that at low temperature many metals become superconductors. A metal can be viewed in part as a Fermi liquid of electrons, and below a critical temperature, an attractive phonon-mediated interaction between the electrons near the Fermi surface causes them to pair up and form a condensate of Cooper pairs, which via the Anderson–Higgs mechanism makes the photon massive, leading to characteristic behaviors of a superconductor: infinite conductivity and the exclusion of magnetic fields (Meissner effect). The crucial ingredients for this to occur are:
# a liquid of charged fermions.
# an attractive interaction between the fermions
# low temperature (below the critical temperature)
These ingredients are also present in sufficiently dense quark matter, leading physicists to expect that something similar will happen in that context:
# quarks carry both electric charge and color charge;
# the strong interaction between two quarks is powerfully attractive;
# the critical temperature is expected to be given by the QCD scale, which is of order 100 MeV, or 10 kelvins, the temperature of the universe a few minutes after the Big Bang, so quark matter that we may currently observe in compact stars or other natural settings will be below this temperature.
The fact that a Cooper pair of quarks carries a net color charge, as well as a net electric charge, means that some of the gluons (which mediate the strong interaction just as photons mediate electromagnetism) become massive in a phase with a condensate of quark Cooper pairs, so such a phase is called a "color superconductor". Actually, in many color superconducting phases the photon itself does not become massive, but mixes with one of the gluons to yield a new massless "rotated photon". This is an MeV-scale echo of the mixing of the hypercharge and W bosons that originally yielded the photon at the TeV scale of electroweak symmetry breaking. | 0 | Theoretical and Fundamental Chemistry |
* 999.999—six nines fine: The purest gold ever produced. Refined by the Perth Mint in 1957.
* 999.99—five nines fine: The purest type of gold currently produced; the Royal Canadian Mint regularly produces commemorative coins in this fineness, including the world's largest, at 100 kg.
* 999.9—four nines fine: Most popular. E.g. ordinary Canadian Gold Maple Leaf and American Buffalo coins.
* 999—24 karat, also occasionally known as three nines fine: e.g., Chinese Gold Panda coins.
* 995: The minimum allowed in Good Delivery gold bars.
* 990—two nines fine
* 986—Ducat fineness: Formerly used by Venetian and Holy Roman Empire mints; still in use in Austria and Hungary.
* 958.3—23 karat
* 916—22 karat: Crown gold. Historically the most widely used fineness for gold bullion coins, such as the oldest American Eagle denominations from 1795–1833. Currently used for British Sovereigns, South African Krugerrands, and the modern (1986—present) American Gold Eagles.
* 900—one nine fine: American Eagle denominations for 1837–1933; currently used in Latin Monetary Union mintage (e.g. French and Swiss "Napoleon coin" 20 francs).
* 899—American Eagles briefly for 1834—1836.
* 834—20 karat
* 750—18 karat: In Spain oro de primera ley (first law gold).
* 625—15 karat
* 585—14 karat
* 583.3—14 karat: In Spain oro de segunda ley (second law gold).
* 500—12 karat
* 417—10 karat: Lowest legal solid gold karat made in the US prior to the August 2018 revision of the FTC Guides (Now 1 karat is legal).
* 375—9 karat: Minimum standard for gold in some of the Commonwealth realms: Australia, Canada, New Zealand, UK, etc. It is also the minimum in Austria, Ireland, Portugal and France.
* 333—8 karat: Minimum standard for gold in Germany after 1884. It is also the minimum for Denmark, Greece and Mexico.
* 1 karat: Legal minimum for gold in the US since the revision of the FTC Guides of August 2018. | 1 | Applied and Interdisciplinary Chemistry |
Many bacteria use the anaerobic pathway for synthesizing unsaturated fatty acids. This pathway does not utilize oxygen and is dependent on enzymes to insert the double bond before elongation utilizing the normal fatty acid synthesis machinery. In Escherichia coli, this pathway is well understood.
* FabA is a β-hydroxydecanoyl-ACP dehydrase – it is specific for the 10-carbon saturated fatty acid synthesis intermediate (β-hydroxydecanoyl-ACP).
* FabA catalyzes the dehydration of β-hydroxydecanoyl-ACP, causing the release of water and insertion of the double bond between C7 and C8 counting from the methyl end. This creates the trans-2-decenoyl intermediate.
* Either the trans-2-decenoyl intermediate can be shunted to the normal saturated fatty acid synthesis pathway by FabB, where the double bond will be hydrolyzed and the final product will be a saturated fatty acid, or FabA will catalyze the isomerization into the cis-3-decenoyl intermediate.
* FabB is a β-ketoacyl-ACP synthase that elongates and channels intermediates into the mainstream fatty acid synthesis pathway. When FabB reacts with the cis-decenoyl intermediate, the final product after elongation will be an unsaturated fatty acid.
* The two main unsaturated fatty acids made are Palmitoleoyl-ACP (16:1ω7) and cis-vaccenoyl-ACP (18:1ω7).
Most bacteria that undergo anaerobic desaturation contain homologues of FabA and FabB. Clostridia are the main exception; they have a novel enzyme, yet to be identified, that catalyzes the formation of the cis double bond.
;Regulation
This pathway undergoes transcriptional regulation by FadR and FabR. FadR is the more extensively studied protein and has been attributed bifunctional characteristics. It acts as an activator of fabA and fabB transcription and as a repressor for the β-oxidation regulon. In contrast, FabR acts as a repressor for the transcription of fabA and fabB. | 1 | Applied and Interdisciplinary Chemistry |
As early as the 1860s, experiments demonstrated that biologically relevant molecules can be produced from interaction of simple carbon sources with abundant inorganic catalysts. The spontaneous formation of complex polymers from abiotically generated monomers under the conditions posited by the "soup" theory is not straightforward. Besides the necessary basic organic monomers, compounds that would have prohibited the formation of polymers were also formed in high concentration during the Miller–Urey and Joan Oró experiments. Biology uses essentially 20 amino acids for its coded protein enzymes, representing a very small subset of the structurally possible products. Since life tends to use whatever is available, an explanation is needed for why the set used is so small. Formamide is attractive as a medium that potentially provided a source of amino acid derivatives from simple aldehyde and nitrile feedstocks. | 0 | Theoretical and Fundamental Chemistry |
Enantiomers of a chiral drug often interact in an enantioselective way in a chiral environment. This may be offered by different biotic substances (viz. proteins, nucleic acids, phospholipids and oligosaccharides). They are made up of chiral building blocks that are put together in space in handed conformations. These biological targets function as receptors for the drug enantiomers. So, at the binding sites of these receptors, enantiomers will be seen as different chemical species. The three point attachment model (Easson & Stedman model) can be used to see how chiral discrimination works. Figure depicts how the enantiomers of a drug interact with receptors in a way that depends on the drug's shape.
This model was made for chiral drugs with a single stereogenic center. It says that there are three binding sites in the receptor (B, C and D) that match the drugs pharmacophoric groups (B, C, D). A three-point fit (good fit) is possible for the eutomer at BB, CC and DD(Fig. A). Even though the distomer is the wrong enantiomer, it can fit either a one-point interaction (bad fit), or a two-point attachment (CC and DD') with the same receptor site as shown in (Fig. B).
Eutomer is the version that works the way you want it to, and distomer is the version that doesnt work or works in a way you dont want it to. Most of the time, the mirror-image versions have different binding affinities. In the eutomer, the ligands or moiety around a stereogenic element have more binding energy than in the distomer. When the eutomer goes through chiral inversion, it loses its ability to bind to a biological receptor. Because of these enantiospecific interactions, therapeutic and toxicological properties are enantioselective So, the stereo-stability of chiral drugs may have big effects on the process of making new drugs, especially when it comes to how pharmaceutical, pharmacokinetic, and pharmacodynamic information is read and understood. At every stage of designing, making, and testing a drug for safety, chiral inversion must be taken into account. | 0 | Theoretical and Fundamental Chemistry |
Heteroatoms aside from the transition metal are a defining feature of heteropolymetalates. Many different elements can serve as heteroatoms but most common are Phosphate|, Silicate|, and Arsenate|. | 0 | Theoretical and Fundamental Chemistry |
Ion balance is a key factor in plant development to produce yield. Too high salt concentration in soil lowers the water potential in root tissue which becomes toxic; stunting growth and inhibiting flowering by dehydrating the plant. Stomatal closure is also a response to high salinity, leading to lowered sugar production and transpiration rates. Plants respond to high salinity soils by accumulating sodium and chlorine, and reducing uptake of macronutrients and other ions. This accumulation results in inhibition of calcium signaling. In order to combat this type of stress, plants must have strategies and adaptations in place for survival, such as osmotic stress pathways. RNA sequencing and qRT-PCR analysis has made finding these gene expression pathways possible, such as the MAPK, allowing for the scrutiny of candidate genes responsible for greater tolerance to salinity. Candidate genes for this type of stress response have also been found in plant hormone signal transduction pathways. Different species of Cannabis carry unique variations of gene expression, with some having a greater ability to utilize salt tolerance by keeping potassium levels high enough as to deny sodium uptake.
Removing sodium from the cytoplasm by means of sodium or hydrogen anti-porters is another mechanism to resist desiccation from high salinity environments by using the salt overly sensitive (SOS) regulation pathway. The SOS pathway exchanges excess sodium for hydrogen, and it is set into action by calcium signal flux.
Modifying the cytoskeleton or utilizing an osmotic stress pathway are two other physiological defenses plants use to handle salinity. The ability to sense excess salinity is a valuable tool, where excess sodium can trigger an influx of calcium and reactive oxygen species (ROS). Without the ability to notice sodium, calcium wouldn't be triggered into a signaling cascade to flow into the cytosol. This flow notifies the system to block salt ions from entering into the roots by using any available defenses, such as modifying the cell wall. A plant without these sensing and signaling capabilities is considered salt-sensitive, known as a glycophyte. | 1 | Applied and Interdisciplinary Chemistry |
Newtons law of viscosity is not a fundamental law of nature, but rather a constitutive equation (like Hookes law, Ficks law, and Ohms law) which serves to define the viscosity . Its form is motivated by experiments which show that for a wide range of fluids, is independent of strain rate. Such fluids are called Newtonian. Gases, water, and many common liquids can be considered Newtonian in ordinary conditions and contexts. However, there are many non-Newtonian fluids that significantly deviate from this behavior. For example:
* Shear-thickening (dilatant) liquids, whose viscosity increases with the rate of shear strain.
* Shear-thinning liquids, whose viscosity decreases with the rate of shear strain.
* Thixotropic liquids, that become less viscous over time when shaken, agitated, or otherwise stressed.
* Rheopectic liquids, that become more viscous over time when shaken, agitated, or otherwise stressed.
* Bingham plastics that behave as a solid at low stresses but flow as a viscous fluid at high stresses.
Trouton's ratio is the ratio of extensional viscosity to shear viscosity. For a Newtonian fluid, the Trouton ratio is 3. Shear-thinning liquids are very commonly, but misleadingly, described as thixotropic.
Viscosity may also depend on the fluids physical state (temperature and pressure) and other, external', factors. For gases and other compressible fluids, it depends on temperature and varies very slowly with pressure. The viscosity of some fluids may depend on other factors. A magnetorheological fluid, for example, becomes thicker when subjected to a magnetic field, possibly to the point of behaving like a solid. | 1 | Applied and Interdisciplinary Chemistry |
There are two aspects to surface integrity: topography characteristics and surface layer characteristics. The topography is made up of surface roughness, waviness, errors of form, and flaws. The surface layer characteristics that can change through processing are: plastic deformation, residual stresses, cracks, hardness, overaging, phase changes, recrystallization, intergranular attack, and hydrogen embrittlement. When a traditional manufacturing process is used, such as machining, the surface layer sustains local plastic deformation.
The processes that affect surface integrity can be conveniently broken up into three classes: traditional processes, non-traditional processes, and finishing treatments. Traditional processes are defined as processes where the tool contacts the workpiece surface; for example: grinding, turning, and machining. These processes will only damage the surface integrity if the improper parameters are used, such as dull tools, too high feed speeds, improper coolant or lubrication, or incorrect grinding wheel hardness. Nontraditional processes are defined as processes where the tool does not contact the workpiece; examples of this type of process include EDM, electrochemical machining, and chemical milling. These processes will produce different surface integrity depending on how the processes are controlled; for instance, they can leave a stress-free surface, a remelted surface, or excessive surface roughness. Finishing treatments are defined as processes that negate surface finishes imparted by traditional and non-traditional processes or improve the surface integrity. For example, compressive residual stress can be enhanced via peening or roller burnishing or the recast layer left by EDMing can be removed via chemical milling.
Finishing treatments can affect the workpiece surface in a wide variety of manners. Some clean and/or remove defects, such as scratches, pores, burrs, flash, or blemishes. Other processes improve or modify the surface appearance by improving smoothness, texture, or color. They can also improve corrosion resistance, wear resistance, and/or reduce friction. Coatings are another type of finishing treatment that may be used to plate an expensive or scarce material onto a less expensive base material. | 1 | Applied and Interdisciplinary Chemistry |
The flow reversal is primarily caused by adverse pressure gradient imposed on the boundary layer by the outer potential flow. The streamwise momentum equation inside the boundary layer is approximately stated as
where are streamwise and normal coordinates.
An adverse pressure gradient is when , which then can be seen to cause the velocity to decrease along and possibly go to zero if the adverse pressure gradient is strong enough. | 1 | Applied and Interdisciplinary Chemistry |
Machine perfusion (MP) is a technique used in organ transplantation as a means of preserving the organs which are to be transplanted.
Machine perfusion has various forms and can be categorised according to the temperature of the perfusate: cold (4 °C) and warm (37 °C). Machine perfusion has been applied to renal transplantation, liver transplantation and lung transplantation. It is an alternative to static cold storage (SCS). | 1 | Applied and Interdisciplinary Chemistry |
Through a continual process of stretching and folding, much like in a "baker's map,"
tracers advected in chaotic flows will develop into complex fractals.
The fractal dimension of a single contour will be between 1 and 2.
Exponential growth ensures that the contour, in the limit of very
long time integration, becomes fractal.
Fractals composed of a single curve are infinitely long and when
formed iteratively, have an exponential growth rate, just like an
advected contour.
The Koch Snowflake, for instance, grows at a rate of 4/3 per iteration.
The figure below shows the fractal dimension of an advected contour as a function
of time, measured in four different ways. A good method of measuring the
fractal dimension of an advected contour is the uncertainty exponent. | 1 | Applied and Interdisciplinary Chemistry |
The first major contribution of Woodwards career in the early 1940s was a series of papers describing the application of ultraviolet spectroscopy in the elucidation of the structure of natural products. Woodward collected together a large amount of empirical data, and then devised a series of rules later called the Woodwards rules, which could be applied to finding out the structures of new natural substances, as well as non-natural synthesized molecules. The expedient use of newly developed instrumental techniques was a characteristic Woodward exemplified throughout his career, and it marked a radical change from the extremely tedious and long chemical methods of structural elucidation that had been used until then.
In 1944, with his post doctoral researcher, William von Eggers Doering, Woodward reported the synthesis of the alkaloid quinine, used to treat malaria. Although the synthesis was publicized as a breakthrough in procuring the hard to get medicinal compound from Japanese occupied southeast Asia, in reality it was too long and tedious to adopt on a practical scale. Nevertheless, it was a landmark for chemical synthesis. Woodward's particular insight in this synthesis was to realise that the German chemist Paul Rabe had converted a precursor of quinine called quinotoxine to quinine in 1905. Hence, a synthesis of quinotoxine (which Woodward actually synthesized) would establish a route to synthesizing quinine. When Woodward accomplished this feat, organic synthesis was still largely a matter of trial and error, and nobody thought that such complex structures could actually be constructed. Woodward showed that organic synthesis could be made into a rational science, and that synthesis could be aided by well-established principles of reactivity and structure. This synthesis was the first one in a series of exceedingly complicated and elegant syntheses that he would undertake. | 0 | Theoretical and Fundamental Chemistry |
The convection–diffusion equation can only rarely be solved with a pen and paper. More often, computers are used to numerically approximate the solution to the equation, typically using the finite element method. For more details and algorithms see: Numerical solution of the convection–diffusion equation. | 1 | Applied and Interdisciplinary Chemistry |
*ADMS 3 (Atmospheric Dispersion Modelling System) – advanced atmospheric pollution dispersion model for calculating concentrations of atmospheric pollutants emitted both continuously from point, line, volume and area sources, or intermittently from point sources.
*AUSTAL
*AERMOD
*CANARY (By Quest)
*CALPUFF
*DISPERSION21
*FLACS
*ISC3
*MERCURE
*NAME (dispersion model)
*Panache
*PHAST
*PUFF-PLUME
*SIRANE | 1 | Applied and Interdisciplinary Chemistry |
Glass disease, also referred to as sick glass or glass illness, is a degradation process of glass that can result in weeping, crizzling, spalling, cracking and fragmentation.
Glass disease is caused by an inherent instability in the chemical composition of the original glass formula.
Properties of a particular glass will vary with the type and proportions of silica, alkali and alkaline earth in its composition.
Once damage has occurred it is irreversible, but decay processes can be slowed by climate control to regulate surrounding temperature, humidity, and air flow. | 0 | Theoretical and Fundamental Chemistry |
MAGS is an alternative to discrete and composite soil sampling. MAGS, while it does not describe the sample with as much precision as the previously mentioned sampling methods, is more powerful statistically: it represents a larger area of a site which is more useful in determining the presence of a compound. Besides increasing the accuracy in identifying the presence compounds in the soil, MAGS also can quickly and accurately narrow down the location and spread of the compounds after a few trials. Once the location has been determined, more thorough and traditional soil borings can be done in the identified location, instead of sampling a whole site.
HSA found particular success using the technique at solvent-impacted sites that were showing signs of rebound after initial remediation efforts. These rebounds are commonly the result of multiple (relatively small) release areas that had not been previously discovered with discrete soil sampling. MAGS can be useful in detecting how effectively the site had been cleaned up post-remediation. | 1 | Applied and Interdisciplinary Chemistry |
* Data from 2009 found that the global mean concentration was rising at a rate of approximately 2 ppm/year and accelerating.
* The daily average concentration of atmospheric at Mauna Loa Observatory first exceeded 400 ppm on 10 May 2013 although this concentration had already been reached in the Arctic in June 2012. Data from 2013 showed that the concentration of carbon dioxide in the atmosphere is this high "for the first time in 55 years of measurement—and probably more than 3 million years of Earth history."
* As of 2018, concentrations were measured to be 410 ppm. | 1 | Applied and Interdisciplinary Chemistry |
Mechanistically, eukaryotic translation termination matches its prokaryotic counterpart. In this case, termination of the polypeptide chain is achieved through the hydrolytic action of a heterodimer consisting of release factors, eRF1 and eRF3. Translation termination is said to be leaky in some cases as noncoding-tRNAs may compete with release factors to bind stop codons. This is possible due to the matching of 2 out 3 bases within the stop codon by tRNAs that may occasionally outcompete release factor base pairing. An example of regulation at the level of termination is functional translational readthrough of the lactate dehydrogenase gene LDHB. This readthrough provides a peroxisomal targeting signal that localizes the distinct LDHBx to the peroxisome. | 1 | Applied and Interdisciplinary Chemistry |
A neuron's ability to generate and propagate an action potential changes during development. How much the membrane potential of a neuron changes as the result of a current impulse is a function of the membrane input resistance. As a cell grows, more channels are added to the membrane, causing a decrease in input resistance. A mature neuron also undergoes shorter changes in membrane potential in response to synaptic currents. Neurons from a ferret lateral geniculate nucleus have a longer time constant and larger voltage deflection at P0 than they do at P30. One consequence of the decreasing action potential duration is that the fidelity of the signal can be preserved in response to high frequency stimulation. Immature neurons are more prone to synaptic depression than potentiation after high frequency stimulation.
In the early development of many organisms, the action potential is actually initially carried by calcium current rather than sodium current. The opening and closing kinetics of calcium channels during development are slower than those of the voltage-gated sodium channels that will carry the action potential in the mature neurons. The longer opening times for the calcium channels can lead to action potentials that are considerably slower than those of mature neurons. Xenopus neurons initially have action potentials that take 60–90 ms. During development, this time decreases to 1 ms. There are two reasons for this drastic decrease. First, the inward current becomes primarily carried by sodium channels. Second, the delayed rectifier, a potassium channel current, increases to 3.5 times its initial strength.
In order for the transition from a calcium-dependent action potential to a sodium-dependent action potential to proceed new channels must be added to the membrane. If Xenopus neurons are grown in an environment with RNA synthesis or protein synthesis inhibitors that transition is prevented. Even the electrical activity of the cell itself may play a role in channel expression. If action potentials in Xenopus myocytes are blocked, the typical increase in sodium and potassium current density is prevented or delayed.
This maturation of electrical properties is seen across species. Xenopus sodium and potassium currents increase drastically after a neuron goes through its final phase of mitosis. The sodium current density of rat cortical neurons increases by 600% within the first two postnatal weeks. | 0 | Theoretical and Fundamental Chemistry |
The coalescence happens in a brush after removing it from water is an example of elastocapillarity. Elastocapillary wrapping driven by drop impact is another example.
Most of the small scale devices such as microelectromechanical systems (MEMS), magnetic head-disk interface (HDI), and the tip of atomic force microscopy (AFM) for which liquids are present in confined regions during fabrication or during operation can experience elastocapillary phenomena. In these devices, where the spacing between solid structures is small, intermolecular interactions become significant. The liquid can exist in these small scale devices due to contamination, condensation or lubrication. The liquid present in these devices can increase the adhesive forces drastically and cause device failure. | 1 | Applied and Interdisciplinary Chemistry |
N-glycan processing is carried out in endoplasmic reticulum and the Golgi body. Initial trimming of the precursor molecule occurs in the ER and the subsequent processing occurs in the Golgi.
Upon transferring the completed glycan onto the nascent polypeptide, two glucose residues are removed from the structure. Enzymes known as glycosidases remove some sugar residues. These enzymes can break glycosidic linkages by using a water molecule. These enzymes are exoglycosidases as they only work on monosaccharide residues located at the non-reducing end of the glycan. This initial trimming step is thought to act as a quality control step in the ER to monitor protein folding.
Once the protein is folded correctly, two glucose residues are removed by glucosidase I and II. The removal of the final third glucose residue signals that the glycoprotein is ready for transit from the ER to the cis-Golgi. ER mannosidase catalyses the removal of this final glucose. However, if the protein is not folded properly, the glucose residues are not removed and thus the glycoprotein can't leave the endoplasmic reticulum. A chaperone protein (calnexin/calreticulin) binds to the unfolded or partially folded protein to assist protein folding.
The next step involves further addition and removal of sugar residues in the cis-Golgi. These modifications are catalyzed by glycosyltransferases and glycosidases respectively. In the cis-Golgi, a series of mannosidases remove some or all of the four mannose residues in α-1,2 linkages. Whereas in the medial portion of the Golgi, glycosyltransferases add sugar residues to the core glycan structure, giving rise to the three main types of glycans: high mannose, hybrid and complex glycans.
*High-mannose is, in essence, just two N-acetylglucosamines with many mannose residues, often almost as many as are seen in the precursor oligosaccharides before it is attached to the protein.
*Complex oligosaccharides are so named because they can contain almost any number of the other types of saccharides, including more than the original two N-acetylglucosamines.
*Hybrid oligosaccharides contain a mannose residues on one side of the branch, while on the other side a N-acetylglucosamine initiates a complex branch.
The order of addition of sugars to the growing glycan chains is determined by the substrate specificities of the enzymes and their access to the substrate as they move through secretory pathway. Thus, the organization of this machinery within a cell plays an important role in determining which glycans are made. | 0 | Theoretical and Fundamental Chemistry |
Assume a two-stream problem having one portion of the boundary the fuel stream with fuel mass fraction and another portion of the boundary the oxidizer stream with oxidizer mass fraction . For example, if the oxidizer stream is air and the fuel stream contains only the fuel, then and . In addition, assume there is no oxygen in the fuel stream and there is no fuel in the oxidizer stream. Let be the mass of oxygen required to burn unit mass of fuel (for hydrogen gas, and for alkanes, ). Introduce the scaled mass fractions as and . Then the mixture fraction is defined as
where
is the stoichiometry parameter, also known as the overall equivalence ratio. On the fuel-stream boundary, and since there is no oxygen in the fuel stream, and hence . Similarly, on the oxidizer-stream boundary, and so that . Anywhere else in the mixing domain, . The mixture fraction is a function of both the spatial coordinates and the time , i.e.,
Within the mixing domain, there are level surfaces where fuel and oxygen are found to be mixed in stoichiometric proportion. This surface is special in combustion because this is where a diffusion flame resides. Constant level of this surface is identified from the equation , where is called as the stoichiometric mixture fraction which is obtained by setting (since if they were react to consume fuel and oxygen, only on the stoichiometric locations both fuel and oxygen will be consumed completely) in the definition of to obtain | 1 | Applied and Interdisciplinary Chemistry |
NADH-coenzyme Q oxidoreductase, also known as NADH dehydrogenase or complex I, is the first protein in the electron transport chain. Complex I is a giant enzyme with the mammalian complex I having 46 subunits and a molecular mass of about 1,000 kilodaltons (kDa). The structure is known in detail only from a bacterium; in most organisms the complex resembles a boot with a large "ball" poking out from the membrane into the mitochondrion. The genes that encode the individual proteins are contained in both the cell nucleus and the mitochondrial genome, as is the case for many enzymes present in the mitochondrion.
The reaction that is catalyzed by this enzyme is the two electron oxidation of NADH by coenzyme Q10 or ubiquinone (represented as Q in the equation below), a lipid-soluble quinone that is found in the mitochondrion membrane:
The start of the reaction, and indeed of the entire electron chain, is the binding of a NADH molecule to complex I and the donation of two electrons. The electrons enter complex I via a prosthetic group attached to the complex, flavin mononucleotide (FMN). The addition of electrons to FMN converts it to its reduced form, FMNH. The electrons are then transferred through a series of iron–sulfur clusters: the second kind of prosthetic group present in the complex. There are both [2Fe–2S] and [4Fe–4S] iron–sulfur clusters in complex I.
As the electrons pass through this complex, four protons are pumped from the matrix into the intermembrane space. Exactly how this occurs is unclear, but it seems to involve conformational changes in complex I that cause the protein to bind protons on the N-side of the membrane and release them on the P-side of the membrane. Finally, the electrons are transferred from the chain of iron–sulfur clusters to a ubiquinone molecule in the membrane. Reduction of ubiquinone also contributes to the generation of a proton gradient, as two protons are taken up from the matrix as it is reduced to ubiquinol (QH). | 1 | Applied and Interdisciplinary Chemistry |
Dithionite is used in conjunction with complexing agents (for example, citric acid) to reduce iron(III) oxy-hydroxide into soluble iron(II) compounds and to remove amorphous iron(III)-bearing mineral phases in soil analyses (selective extraction).
The decomposition of dithionite produces reduced species of sulfur that can be very aggressive for the corrosion of steel and stainless steel. Thiosulfate () is known to induce pitting corrosion, whereas sulfide (S, HS) is responsible for stress corrosion cracking (SCC). | 1 | Applied and Interdisciplinary Chemistry |
HIV belongs to the class of viruses called retroviruses, which carry genetic information in the form of RNA. HIV infects T cells that carry the CD4 antigen on their surface. When HIV infects its target cell it requires fusion of the viral and cellular membranes. The first step is the interaction between envelope proteins of the virus (gp120, gp41) and specific host-cell surface receptors (e.g. CD4 receptor) on the target cell. Then the virus binds to the chemokine coreceptors CXCR4 or CCR5, resulting in conformational changes in the envelope proteins. This fusion creates a pore through which the viral capsid enters the cell. Following entry into the cell the RNA of the virus is reverse-transcribed to DNA by the first virally encoded enzyme, the reverse transcriptase. The viral DNA enters the nucleus where it is integrated into the genetic material of the cell by the integrase, a second virally encoded enzyme. Activation of the host cell leads to the transcription of the viral DNA into mRNA. The mRNA is then translated into viral proteins and the third virally encoded enzyme, namely HIV protease, is required to cleave a viral polyprotein precursor into individual mature proteins. The viral RNA and viral proteins assemble at the surface of the cell into new virions. The virions bud from the cell and are released to infect other cells. All infected cells are eventually killed because of this extensive cell damage, from the destruction of the host's genetic system to the budding and release of virions. | 1 | Applied and Interdisciplinary Chemistry |
Shaw died on 8 November 2020, aged 90.
A short (18 minute) video of his funeral service, held during covid lockdown, is available [https://www.youtube.com/watch?v=Mx4Y7qu7XTQ here]. | 0 | Theoretical and Fundamental Chemistry |
In a reaction much similar to the enamine alkylation, enamines can be acylated to form a final dicarbonyl product. The enamine starting material undergoes a nucleophilic addition to acyl halides forming the iminium salt intermediate which can hydrolyze in the presence of acid. | 0 | Theoretical and Fundamental Chemistry |
Electrofusion welding is characterized by four distinct stages that occur during the welding process:
# Incubation period
# Joint formation and consolidation
# Plateau region
# Cooling period
During the incubation period, heat is introduced into the joint as current is passed through the coil. Although there is no joint strength at this point, the polymer expands and the joint gap is filled. During joint formation and consolidation, melting begins. Melt pressure has begun to build, and the majority of the joint's strength is developed during this stage. The strength increase is due primarily to the constraint of the increasing molten material by the cold zones in the surrounding fitting. The plateau region signals the stabilization of the joint strength. Despite this, the heat of the joint is still increasing with time during this stage. The cooling period occurs after current is no longer applied to the coils. The molten polymer material solidifies and forms the joint. | 0 | Theoretical and Fundamental Chemistry |
The Van t Hoff equation relates the change in the equilibrium constant, , of a chemical reaction to the change in temperature, T, given the standard enthalpy change, , for the process. The subscript means "reaction" and the superscript means "standard". It was proposed by Dutch chemist Jacobus Henricus van t Hoff in 1884 in his book Études de Dynamique chimique (Studies in Dynamic Chemistry).
The Van t Hoff equation has been widely utilized to explore the changes in state functions in a thermodynamic system. The Van t Hoff plot, which is derived from this equation, is especially effective in estimating the change in enthalpy and entropy of a chemical reaction. | 0 | Theoretical and Fundamental Chemistry |
Depending mostly upon the change in conditions from a previous inspection various improvements may be made to the pipe. It may be cleaned with a rotating root cutting blade on the end of a segmented rotating chain, or a chemical foam may be applied to discourage root growth. If damage is found limited to only a few locations these may be excavated and repaired. Extensive moderate defects may be repaired by lining with a fabric liner that is pulled through the pipe, inflated, and then made rigid through chemical means. Severe damage may require excavation and replacement of the conduit. | 1 | Applied and Interdisciplinary Chemistry |
Diffusing-wave spectroscopy (DWS) is an optical technique derived from dynamic light scattering (DLS) that studies the dynamics of scattered light in the limit of strong multiple scattering. It has been widely used in the past to study colloidal suspensions, emulsions, foams, gels, biological media and other forms of soft matter. If carefully calibrated, DWS allows the quantitative measurement of microscopic motion in a soft material, from which the rheological properties of the complex medium can be extracted via the microrheology approach. | 0 | Theoretical and Fundamental Chemistry |
Between 2000 and 2010, the effects of volumetric muscle loss (VML) were assessed as it pertains to muscle tissue engineering. VML can be caused by a variety of injuries or diseases, including general trauma, postoperative damage, cancer ablation, congenital defects, and degenerative myopathy. Although muscle contains a stem cell population called satellite cells that are capable of regenerating small muscle injuries, muscle damage in VML is so extensive that it overwhelms muscles natural regenerative capabilities. Currently VML is treated through an autologous muscle flap or graft but there are various problems associated with this procedure. Donor site morbidity, lack of donor tissue, and inadequate vascularization all limit the ability of doctors to adequately treat VML. The field of muscle tissue engineering attempts to address this problem through the design of a functional muscle construct that can be used to treat the damaged muscle instead of harvesting an autologous muscle flap from elsewhere on the patients body.
Research conducted between 2000 and 2010 informed the conclusion that functional analysis of a tissue engineered muscle construct is important to illustrate its potential to help regenerate muscle. A variety of assays are generally used to evaluate a tissue engineered muscle construct including immunohistochemistry, RT-PCR, electrical stimulation and resulting peak-to-peak voltage, scanning electron microscope imaging, and in vivo response.
The most recent advances in the field include cultured meat, biorobotic systems, and biohybrid impants in regenerative medicine or disease modeling. | 1 | Applied and Interdisciplinary Chemistry |
In molecular biology, a termination factor is a protein that mediates the termination of RNA transcription by recognizing a transcription terminator and causing the release of the newly made mRNA. This is part of the process that regulates the transcription of RNA to preserve gene expression integrity and are present in both eukaryotes and prokaryotes, although the process in bacteria is more widely understood. The most extensively studied and detailed transcriptional termination factor is the Rho (ρ) protein of E. coli. | 1 | Applied and Interdisciplinary Chemistry |
An isoscape is a geologic map of isotope distribution. It is a spatially explicit prediction of elemental isotope ratios (δ) that is produced by executing process-level models of elemental isotope fractionation or distribution in a geographic information system (GIS).
The word isoscape is derived from isotope landscape and was first coined by Jason B. West.
Isoscapes of hydrogen, carbon, oxygen, nitrogen, strontium and sulfur have been used to answer scientific or forensic questions regarding the sources, partitioning, or provenance of natural and synthetic materials or organisms via their isotopic signatures. These include questions about migration, Earth's element cycles, human water use, climate, archaeological reconstructions, forensic science, and pollution. Isoscapes of hydrogen and oxygen isotopes of precipitation, surface water, groundwater, and tap water have been developed to better understand the water cycle at regional to global scales. | 0 | Theoretical and Fundamental Chemistry |
Just as iron produced by a blast furnace comes out alloyed with other chemical elements as cast iron, copper extracted from ore becomes an alloy with sulfur, iron, etc. called matte. To apply the same purification processes to these two metals is therefore logical. Applying the Bessemer process to copper metallurgy was proposed, and the principle validated in 1866, ten years after Henry Bessemer's invention, by the Russian engineer Semenikow.
The refinement of the alloy in the converter is possible because the combustion of undesirable elements is strongly exothermic: the oxidation of silicon and carbon respectively produce 32.8 and 10.3 kilojoules per kilogram. On the other hand, if a copper matte contains an abundance of iron and sulfur, these elements must first be separated (which consumes 6.8 kilojoules per kilogram of FeS) before their oxidation (which only produces 5.9 and 9.1 kJ/kg respectively) can begin. | 1 | Applied and Interdisciplinary Chemistry |
An orally disintegrating tablet or orodispersible tablet (ODT), is a drug dosage form available for a limited range of over-the-counter (OTC) and prescription medications. | 1 | Applied and Interdisciplinary Chemistry |
Consider the case of a vibrating wire of length (L) vibrating with an amplitude (L). The wire has a linear density (M/L) and is under tension (LM/T), and we want to know the energy (LM/T) in the wire. Let and be two dimensionless products of powers of the variables chosen, given by
The linear density of the wire is not involved. The two groups found can be combined into an equivalent form as an equation
where is some unknown function, or, equivalently as
where is some other unknown function. Here the unknown function implies that our solution is now incomplete, but dimensional analysis has given us something that may not have been obvious: the energy is proportional to the first power of the tension. Barring further analytical analysis, we might proceed to experiments to discover the form for the unknown function . But our experiments are simpler than in the absence of dimensional analysis. We'd perform none to verify that the energy is proportional to the tension. Or perhaps we might guess that the energy is proportional to , and so infer that . The power of dimensional analysis as an aid to experiment and forming hypotheses becomes evident.
The power of dimensional analysis really becomes apparent when it is applied to situations, unlike those given above, that are more complicated, the set of variables involved are not apparent, and the underlying equations hopelessly complex. Consider, for example, a small pebble sitting on the bed of a river. If the river flows fast enough, it will actually raise the pebble and cause it to flow along with the water. At what critical velocity will this occur? Sorting out the guessed variables is not so easy as before. But dimensional analysis can be a powerful aid in understanding problems like this, and is usually the very first tool to be applied to complex problems where the underlying equations and constraints are poorly understood. In such cases, the answer may depend on a dimensionless number such as the Reynolds number, which may be interpreted by dimensional analysis. | 1 | Applied and Interdisciplinary Chemistry |
Unnatural processes are logically conceivable but do not occur in nature. They would decrease the sum of the entropies if they occurred. | 0 | Theoretical and Fundamental Chemistry |
Cells secrete ATP to communicate with other cells in a process called purinergic signalling. ATP serves as a neurotransmitter in many parts of the nervous system, modulates ciliary beating, affects vascular oxygen supply etc. ATP is either secreted directly across the cell membrane through channel proteins or is pumped into vesicles which then fuse with the membrane. Cells detect ATP using the purinergic receptor proteins P2X and P2Y. | 1 | Applied and Interdisciplinary Chemistry |
One method of study attempts to characterize the blinking behavior by studying single crystals or single quantum dots. A powerful microscope is employed along with video equipment. Another method uses ensembles or large quantities of quantum dots and develops statistical information. | 0 | Theoretical and Fundamental Chemistry |
A key consideration of hydroformylation is the "normal" vs. "iso" selectivity. For example, the hydroformylation of propylene can afford two isomeric products, butyraldehyde or isobutyraldehyde:
These isomers reflect the regiochemistry of the insertion of the alkene into the M–H bond. Since both products are not equally desirable (normal is more stable than iso), much research was dedicated to the quest for catalyst that favored the normal isomer. | 0 | Theoretical and Fundamental Chemistry |
Solvent extraction and electrowinning (SX/EW) is a two-stage hydrometallurgical process that first extracts and upgrades copper ions from low-grade leach solutions into a solvent containing a chemical that selectively reacts with and binds the copper in the solvent. The copper is extracted from the solvent with strong aqueous acid which then deposits pure copper onto cathodes using an electrolytic procedure (electrowinning).
SX/EW processing is best known for its use by the copper industry, where it accounts for 20% of worldwide production, but the technology is also successfully applied to a wide range of other metals including cobalt, nickel, zinc and uranium. | 1 | Applied and Interdisciplinary Chemistry |
Lipid droplets bud off the membrane of the endoplasmic reticulum. Initially, a lens is formed by accumulation of TAGs between the two layers of its phospholipid membrane. Nascent lipid droplets may grow by diffusion of fatty acids, endocytosis of sterols, or fusion of smaller lipid droplets through the aid of SNARE proteins. The budding of lipid droplets is promoted by an asymmetric accumulation of phospholipids that decrease surface tension towards the cytosol. Lipid droplets have also been observed to be created by the fission of existing lipid droplets, though this is thought to be less common than de novo formation.
The formation of lipid droplets from the endoplasmic reticulum begins with the synthesis of the neutral lipids to be transported. The manufacture of TAGs from diacylglycerol (by the addition of a fatty acyl chain) is catalyzed by the DGAT proteins, though the extent to which these and other proteins are required depends on cell type. Neither DGAT1 nor DGAT2 is singularly essential for TAG synthesis or droplet formation, though mammalian cells lacking both cannot form lipid droplets and have severely stunted TAG synthesis. DGAT1, which seems to prefer exogenous fatty acid substrates, is not essential for life; DGAT2, which seems to prefer endogenously synthesized fatty acids, is.
In non-adipocytes, lipid storage, lipid droplet synthesis and lipid droplet growth can be induced by various stimuli including growth factors, long-chain unsaturated fatty acids (including oleic acid and arachidonic acid), oxidative stress and inflammatory stimuli such bacterial lipopolysaccharides, various microbial pathogens, platelet-activating factor, eicosanoids, and cytokines.
An example is the endocannabinoids that are unsaturated fatty acid derivatives, which mainly are considered to be synthesised “on demand” from phospholipid precursors residing in the cell membrane, but may also be synthesised and stored in intracellular lipid droplets and released from those stores under appropriate conditions.
It is possible to observe the formation of lipid droplets, live and label-free, using label-free live-cell imaging. | 1 | Applied and Interdisciplinary Chemistry |
The development of models for a better representation of real processes is the core of the further development of the simulation software. Model development is done through the principles of chemical engineering but also control engineering and for the improvement of mathematical simulation techniques. Process simulation is therefore a field where practitioners from chemistry, physics, computer science, mathematics, and engineering work together.
Efforts are made to develop new and improved models for the calculation of properties. This includes for example the description of
* thermophysical properties like vapor pressures, viscosities, caloric data, etc. of pure components and mixtures
* properties of different apparatus like reactors, distillation columns, pumps, etc.
* chemical reactions and kinetics
* environmental and safety-related data
There are two main types of models:
# Simple equations and correlations where parameters are fitted to experimental data.
# Predictive methods where properties are estimated.
The equations and correlations are normally preferred because they describe the property (almost) exactly. To obtain reliable parameters it is necessary to have experimental data which are usually obtained from factual data banks or, if no data are publicly available, from measurements.
Using predictive methods is more cost effective than experimental work and also than data from data banks. Despite this advantage predicted properties are normally only used in early stages of the process development to find first approximate solutions and to exclude false pathways because these estimation methods normally introduce higher errors than correlations obtained from real data.
Process simulation has encouraged the development of mathematical models in the fields of numerics and the solving of complex problems. | 1 | Applied and Interdisciplinary Chemistry |
These principles have been applied in multiple natural product targets containing medium and large rings. The syntheses of cladiell-11-ene-3,6,7-
triol, (±)-periplanone B, eucannabinolide, and neopeltolide are all significant in their usage of macrocyclic stereocontrol en route to obtaining the desired structural targets. | 0 | Theoretical and Fundamental Chemistry |
The company processed about 1,000 pounds of ore daily while in operation, which was dumped on the site. The radon and radiation resulting from the 1,600 tons of material on the abandoned factory resulted in the site's designation as a Superfund site by the United States Environmental Protection Agency in 1983. From 1997 through 2005, the EPA remediated the site in a process that involved the excavation and off-site disposal of radium-contaminated material at the former plant site, and at 250 residential and commercial properties that had been contaminated in the intervening decades. In 2009, the EPA wrapped up their long-running Superfund cleanup effort. | 0 | Theoretical and Fundamental Chemistry |
In a "relaxed" double-helical segment of B-DNA, the two strands twist around the helical axis once every 10.4–10.5 base pairs of sequence. Adding or subtracting twists, as some enzymes do, imposes strain. If a DNA segment under twist strain is closed into a circle by joining its two ends, and then allowed to move freely, it takes on different shape, such as a figure-eight. This shape is referred to as a supercoil. (The noun form "supercoil" is often used when describing DNA topology.)
The DNA of most organisms is usually negatively supercoiled. It becomes temporarily positively supercoiled when it is being replicated or transcribed. These processes are inhibited (regulated) if it is not promptly relaxed. The simplest shape of a supercoil is a figure eight; a circular DNA strand assumes this shape to accommodate more or few helical twists. The two lobes of the figure eight will appear rotated either clockwise or counterclockwise with respect to one another, depending on whether the helix is over- or underwound. For each additional helical twist being accommodated, the lobes will show one more rotation about their axis.
Lobal contortions of a circular DNA, such as the rotation of the figure-eight lobes above, are referred to as writhe. The above example illustrates that twist and writhe are interconvertible. Supercoiling can be represented mathematically by the sum of twist and writhe. The twist is the number of helical turns in the DNA and the writhe is the number of times the double helix crosses over on itself (these are the supercoils). Extra helical twists are positive and lead to positive supercoiling, while subtractive twisting causes negative supercoiling. Many topoisomerase enzymes sense supercoiling and either generate or dissipate it as they change DNA topology.
In part because chromosomes may be very large, segments in the middle may act as if their ends are anchored. As a result, they may be unable to distribute excess twist to the rest of the chromosome or to absorb twist to recover from underwinding—the segments may become supercoiled, in other words. In response to supercoiling, they will assume an amount of writhe, just as if their ends were joined.
Supercoiled DNA forms two structures; a plectoneme or a toroid, or a combination of both. A negatively supercoiled DNA molecule will produce either a one-start left-handed helix, the toroid, or a two-start right-handed helix with terminal loops, the plectoneme. Plectonemes are typically more common in nature, and this is the shape most bacterial plasmids will take. For larger molecules it is common for hybrid structures to form – a loop on a toroid can extend into a plectoneme. If all the loops on a toroid extend then it becomes a branch point in the plectonemic structure. DNA supercoiling is important for DNA packaging within all cells, and seems to also play a role in gene expression. | 1 | Applied and Interdisciplinary Chemistry |
The Membership comprises almost 140 member companies in Europe as well as from the rest of the world. Members are:
* Coil coaters companies
* Paint, film and pre-treatment chemical suppliers
* Service centres/Stockholders
* Raw material suppliers
* Equipment manufacturers
* Technology providers
* Related associations/institutes
Member companies are e.g. Euramax Coated Products, ArcelorMittal, Tata Steel, Novelis, Hydro Aluminium, Becker Industrial Coatings, Akzo Nobel Industrial Finishes, BASF, Shingels, Henkel, Bronx… | 1 | Applied and Interdisciplinary Chemistry |
Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. The related term Aufwuchs (German "surface growth" or "overgrowth", ) refers to the collection of small animals and plants that adhere to open surfaces in aquatic environments, such as parts of rooted plants.
Periphyton serves as an important food source for invertebrates, tadpoles, and some fish. It can also absorb contaminants, removing them from the water column and limiting their movement through the environment. The periphyton is also an important indicator of water quality; responses of this community to pollutants can be measured at a variety of scales representing physiological to community-level changes. Periphyton has often been used as an experimental system in, e.g., pollution-induced community tolerance studies. | 1 | Applied and Interdisciplinary Chemistry |
Mefloquine is useful for the prevention of malaria in all areas except for those where parasites may have resistance to multiple medications, and is one of several anti-malarial medications recommended by the United States Centers for Disease Control and Prevention for this purpose. It is also recommended by the Infectious Disease Society of America for malaria prophylaxis as a first or second-line agent, depending on resistance patterns in the malaria found in the geographic region visited. It is typically taken for one to two weeks before entering an area with malaria. Doxycycline and atovaquone/proguanil provide protection within one to two days and may be better tolerated. If a person becomes ill with malaria despite prophylaxis with mefloquine, the use of halofantrine and quinine for treatment may be ineffective. | 0 | Theoretical and Fundamental Chemistry |
Her menstrual product plus her educational campaign has helped in removing the stigma surrounding menstruation and stopped girls from dropping out of schools due to the stigma. The non profit organization Dignity Period has distributed more than 150,000 free menstrual supplies purchased from Freweni's factory. It was reported that attendance among girls improved by 24% due to this effort. | 1 | Applied and Interdisciplinary Chemistry |
Sirtuin-activating compounds (STAC) are chemical compounds having an effect on sirtuins, a group of enzymes that use NAD+ to remove acetyl groups from proteins. They are caloric restriction mimetic compounds that may be helpful in treating various aging-related diseases. | 1 | Applied and Interdisciplinary Chemistry |
Many compounds are known that can act to inhibit the action of a glycoside hydrolase. Nitrogen-containing, sugar-shaped heterocycles have been found in nature, including deoxynojirimycin, swainsonine, australine and castanospermine. From these natural templates many other inhibitors have been developed, including isofagomine and deoxygalactonojirimycin, and various unsaturated compounds such as PUGNAc. Inhibitors that are in clinical use include the anti-diabetic drugs acarbose and miglitol, and the antiviral drugs oseltamivir and zanamivir. Some proteins have been found to act as glycoside hydrolase inhibitors. | 0 | Theoretical and Fundamental Chemistry |
C12-15 pareth-12 (INCI name) is an emulsifier and surfactant commonly used in cosmetics formulations. It is a polyethylene glycol ether formed by combining synthetic C–C fatty alcohols with 12 moles of ethylene oxide.
According to the INCI, "the term Pareth applies to ethoxylated paraffinic alcohols containing both even- and odd-carbon chain length fractions." | 0 | Theoretical and Fundamental Chemistry |
In 1948, Pauling discovered that many proteins included helical (see alpha helix) shapes. Pauling had deduced this structure from X-ray patterns and from attempts to physically model the structures. (Pauling was also later to suggest an incorrect three chain helical DNA structure based on Astbury's data.) Even in the initial diffraction data from DNA by Maurice Wilkins, it was evident that the structure involved helices. But this insight was only a beginning. There remained the questions of how many strands came together, whether this number was the same for every helix, whether the bases pointed toward the helical axis or away, and ultimately what were the explicit angles and coordinates of all the bonds and atoms. Such questions motivated the modeling efforts of Watson and Crick. | 1 | Applied and Interdisciplinary Chemistry |
In metallurgy, gas flushing removes dissolved gases from the molten metal prior to the material being processed. For example, before casting aluminium alloys, argon bubbles are injected into liquid aluminium using a rotary degasser. The argon bubbles rise to the surface, bringing with them some of the dissolved hydrogen. The degassing step reduces the occurrence of hydrogen gas porosity. In the steel making process, this method is used very commonly for duplex steel and some high reactivity metals. | 1 | Applied and Interdisciplinary Chemistry |
A marsh terrace is an artificially created berm that is built in a wetland to prevent erosion, reduce wave energy, and improve habitat for wildlife. Marsh terracing is most common throughout the upper Gulf Coast of the United States, where it is used to prevent coastal erosion, with 980 linear km (609 mi) having been built in Texas and Louisiana alone in the thirty years to 2020. The terraces catch sediment from rivers which is then colonized by plants to form marshland. | 1 | Applied and Interdisciplinary Chemistry |
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