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Lipolysis is the metabolic pathway through which lipid triglycerides are hydrolyzed into a glycerol and free fatty acids. It is used to mobilize stored energy during fasting or exercise, and usually occurs in fat adipocytes. The most important regulatory hormone in lipolysis is insulin; lipolysis can only occur when insulin action falls to low levels, as occurs during fasting. Other hormones that affect lipolysis include leptin, glucagon, epinephrine, norepinephrine, growth hormone, atrial natriuretic peptide, brain natriuretic peptide, and cortisol.
1
Biochemistry
Given n genes and k replicates, let the rank of gene g in the i-th replicate. Compute the rank product via the geometric mean:
1
Biochemistry
A synonymous substitution (often called a silent substitution though they are not always silent) is the evolutionary substitution of one base for another in an exon of a gene coding for a protein, such that the produced amino acid sequence is not modified. This is possible because the genetic code is "degenerate", meaning that some amino acids are coded for by more than one three-base-pair codon; since some of the codons for a given amino acid differ by just one base pair from others coding for the same amino acid, a mutation that replaces the "normal" base by one of the alternatives will result in incorporation of the same amino acid into the growing polypeptide chain when the gene is translated. Synonymous substitutions and mutations affecting noncoding DNA are often considered silent mutations; however, it is not always the case that the mutation is silent. Since there are 22 codes for 64 codons, roughly we should expect a random substitution to be synonymous with probability about 22/64 = 34%. The actual value is around 20%. A synonymous mutation can affect transcription, splicing, mRNA transport, and translation, any of which could alter the resulting phenotype, rendering the synonymous mutation non-silent. The substrate specificity of the tRNA to the rare codon can affect the timing of translation, and in turn the co-translational folding of the protein. This is reflected in the codon usage bias that is observed in many species. A nonsynonymous substitution results in a change in amino acid that may be arbitrarily further classified as conservative (a change to an amino acid with similar physiochemical properties), semi-conservative (e.g. negatively to positively charged amino acid), or radical (vastly different amino acid).
1
Biochemistry
The good quantum numbers for a diatomic molecule, as well as good approximations of rotational energy levels, can be obtained by modeling the molecule using Hund's cases.
4
Stereochemistry
Escitalopram is the (S)-enantiomer (left-handed version) of the racemate citalopram, which is responsible for its name: escitalopram.
4
Stereochemistry
The structure of some molecules is sometimes described as a resonance between several apparently different structural isomers. The classical example is 1,2-dimethylbenzene (o-xylene), which is often described as a mix of the two apparently distinct structural isomers: However, neither of these two structures describes a real compound; they are fictions devised as a way to describe (by their "averaging" or "resonance") the actual delocalized bonding of o-xylene, which is the single isomer of with a benzene core and two methyl groups in adjacent positions.
4
Stereochemistry
In biochemistry, the oxygen effect refers to a tendency for increased radiosensitivity of free living cells and organisms in the presence of oxygen than in anoxic or hypoxic conditions, where the oxygen tension is less than 1% of atmospheric pressure (i.e., <1% of 101.3 kPa, 760 mmHg or 760 torr).
1
Biochemistry
The first step in determining the configuration index is to assign a priority number to each coordinating ligand according to the Cahn-Ingold-Prelog priority rules, (CIP rules). The preferred ligand takes the lowest priority number. For example, of the ligands acetonitrile, chloride ion and pyridine thepriority number assigned are chloride, 1; acetonitrile,2; pyridene,3. Each coordination type has a different procedure for specifying the configuration index and these are outlined in below.
4
Stereochemistry
Acid or hydrogen phosphites are called hydrogenphosphonates or acid phosphites. IUPAC recommends the name hydrogenphosphonates). They are anions HP(O)OH. Aypical derivative is the salt [NH][HP(O)OH]. Many related salts are known, e.g., RbHPHO, CsHPHO, TlHPHO. These salts are prepared by treating phosphorous acid with the metal carbonate. These compounds contain a layer polymeric anion consisting of HPO tetrahedra linked by hydrogen bonds. These layers are interleaved by layers of metal cations. Organic esters of hydrogen phosphites are anions with the formula HP(O)OR (R = organic group). One commercial example is the fungicide fosetyl-Al with the formula [CHOP(H)O]Al.
0
Organic Chemistry
The estrogen receptor, as well as the progesterone receptor, have been detected in the skin, including in keratinocytes and fibroblasts. At menopause and thereafter, decreased levels of female sex hormones result in atrophy, thinning, and increased wrinkling of the skin and a reduction in skin elasticity, firmness, and strength. These skin changes constitute an acceleration in skin aging and are the result of decreased collagen content, irregularities in the morphology of epidermal skin cells, decreased ground substance between skin fibers, and reduced capillaries and blood flow. The skin also becomes more dry during menopause, which is due to reduced skin hydration and surface lipids (sebum production). Along with chronological aging and photoaging, estrogen deficiency in menopause is one of the three main factors that predominantly influences skin aging. Hormone replacement therapy, consisting of systemic treatment with estrogen alone or in combination with a progestogen, has well-documented and considerable beneficial effects on the skin of postmenopausal women. These benefits include increased skin collagen content, skin thickness and elasticity, and skin hydration and surface lipids. Topical estrogen has been found to have similar beneficial effects on the skin. In addition, a study has found that topical 2% progesterone cream significantly increases skin elasticity and firmness and observably decreases wrinkles in peri- and postmenopausal women. Skin hydration and surface lipids, on the other hand, did not significantly change with topical progesterone. These findings suggest that progesterone, like estrogen, also has beneficial effects on the skin, and may be independently protective against skin aging.
0
Organic Chemistry
In organic chemistry, a sulfone is a organosulfur compound containing a sulfonyl () functional group attached to two carbon atoms. The central hexavalent sulfur atom is double-bonded to each of two oxygen atoms and has a single bond to each of two carbon atoms, usually in two separate hydrocarbon substituents.
0
Organic Chemistry
Fick's second law is a special case of the convection–diffusion equation in which there is no advective flux and no net volumetric source. It can be derived from the continuity equation: where is the total flux and is a net volumetric source for . The only source of flux in this situation is assumed to be diffusive flux: Plugging the definition of diffusive flux to the continuity equation and assuming there is no source (), we arrive at Fick's second law: If flux were the result of both diffusive flux and advective flux, the convection–diffusion equation is the result.
7
Physical Chemistry
The fundamental interacting force of physisorption is Van der Waals force. Even though the interaction energy is very weak (~10&ndash;100 meV), physisorption plays an important role in nature. For instance, the van der Waals attraction between surfaces and foot-hairs of geckos (see Synthetic setae) provides the remarkable ability to climb up vertical walls. Van der Waals forces originate from the interactions between induced, permanent or transient electric dipoles. In comparison with chemisorption, in which the electronic structure of bonding atoms or molecules is changed and covalent or ionic bonds form, physisorption does not result in changes to the chemical bonding structure. In practice, the categorisation of a particular adsorption as physisorption or chemisorption depends principally on the binding energy of the adsorbate to the substrate, with physisorption being far weaker on a per-atom basis than any type of connection involving a chemical bond.
7
Physical Chemistry
On the cost side of pesticide use there can be costs to the environment and costs to human health. Pesticides safety education and pesticide applicator regulation are designed to protect the public from pesticide misuse, but do not eliminate all misuse. Reducing the use of pesticides and choosing less toxic pesticides may reduce risks placed on society and the environment from pesticide use.
2
Environmental Chemistry
René Marcelin (12 June 1885 – 24 September 1914) was a French physical chemist, who died in World War I at a young age. He was a pupil of Jean Baptiste Perrin at the Faculty of Sciences in Paris and performed theoretical studies in the field of chemical kinetics.
7
Physical Chemistry
* monitoring and assessing aquatic species (incl. plants, animals, and bacteria) * monitoring the behavior of certain aquatic species and assessing any changes in species behavior * analyzing the biochemical make-up of the waterbody, and its potential influence on the species that depend on it.
2
Environmental Chemistry
Azaborane usually refers a borane cluster where BH vertices are replaced by N or NR (R stands typically for H or organic substituent). Like many of the related boranes, these clusters are polyhedra and can be classified as closo-, nido-, arachno-, etc.. Within the context of Wades rules, NR is a 4-electron vertex, and N is a 3-electron vertex. Prominent examples are the charge-neutral nido- (i.e. ) and closo'- (i.e. ). Azaboranes can also refer to simpler compounds including iminoboranes (RB=NR, where R and R stand typically for H or organic substituent) and borazines.
7
Physical Chemistry
An example of a YES logic gate comprises a benzo-crown-ether connected to a cyano-substituted anthracene unit. An output of 1 (fluorescence) is obtained only when sodium ions are present in the solution (indicating an input of 1). Sodium ions are encapsulated by the crown ether, resulting in a quenching of the PET process, and causing the anthracene unit to fluoresce.
6
Supramolecular Chemistry
There are three types of ICP geometries: planar (Fig. 3 (a)), cylindrical (Fig. 3 (b)), and half-toroidal (Fig. 3 (c)). In planar geometry, the electrode is a length of flat metal wound like a spiral (or coil). In cylindrical geometry, it is like a helical spring. In half-toroidal geometry, it is a toroidal solenoid cut along its main diameter to two equal halves. When a time-varying electric current is passed through the coil, it creates a time-varying magnetic field around it, with flux where r is the distance to the center of coil (and of the quartz tube). According to the Faraday–Lenz's law of induction, this creates azimuthal electromotive force in the rarefied gas: which corresponds to electric field strengths of leading to the formation of the electron trajectories providing a plasma generation. The dependence on r suggests that the gas ion motion is most intense in the outer region of the flame, where the temperature is the greatest. In the real torch, the flame is cooled from the outside by the cooling gas, so the hottest outer part is at thermal equilibrium. There temperature reaches 5 000–6 000 K. For more rigorous description, see Hamilton–Jacobi equation in electromagnetic fields. The frequency of alternating current used in the RLC circuit which contains the coil is usually 27–41 MHz. To induce plasma, a spark is produced at the electrodes at the gas outlet. Argon is one example of a commonly used rarefied gas. The high temperature of the plasma allows the determination of many elements, and in addition, for about 60 elements degree of ionization in the torch exceeds 90%. The ICP torch consumes c. 1250–1550 W of power, but this depends on the elemental composition of the sample (due to different ionization energies). The ICPs have two operation modes, called capacitive (E) mode with low plasma density and inductive (H) mode with high plasma density, and E to H heating mode transition occurs with external inputs.
7
Physical Chemistry
Another use of the term occurs in industrial refrigeration, specifically vapor-compression refrigeration. Normally, the economizer concept is applied when a particular design or feature on the refrigeration cycle, allows a reduction either in the amount of energy used from the power grid, in the size of the components (basically the gas compressor's nominal capacity) used to produce refrigeration, or both. For example, for a walk-in freezer that is kept at , the main refrigeration components would include: an evaporator coil (a dense arrangement of pipes containing refrigerant and thin metal fins used to remove heat from inside the freezer), fans to blow air over the coil and around the box, an air-cooled condensing unit sited outdoors, and valves and piping. The condensing unit would include a compressor and a coil and fans to exchange heat with the ambient air. An economizer display takes advantage of the fact that refrigeration systems have increasing efficiencies at increasing pressures and temperatures. The power the gas compressor needs is strongly correlated to both the ratio and the difference, between the discharge and the suction pressures (as well as to other features like the refrigerants heat capacity and the type of compressor). Low temperature systems such as freezers move less fluid in same volumes. That means the compressors pumping is less efficient on low temperature systems. This phenomenon is notorious when taking in account that the evaporation temperature for a walk-in freezer at may be around . Systems with economizers aim to produce part of the refrigeration work on high pressures, condition in which gas compressors are normally more efficient. Depending on the application, this technology either allows smaller compression capacities to be able to supply enough pressure and flow for a system that normally would require bigger compressors, increases the capacity of a system that without economizer would produce less refrigeration, or allows the system to produce the same amount of refrigeration using less power. The economizer concept is linked to subcooling as the condensed liquid line temperature is usually higher than that on the evaporator, making it a good place to apply the notion of increasing efficiencies. Recalling the walk-in freezer example, the normal temperature of the liquid line in that system is around or even higher (it varies depending on the condensing temperature). That condition is by far less hostile to produce refrigeration, than the evaporator at .
7
Physical Chemistry
The rate of this kind of reaction does not depend on the substrate concentration, . Thus the concentration decreases linearly. :The integrated rate law of zero order kinetics is: In order to find the half-life, we have to replace the concentration value for the initial concentration divided by 2: and isolate the time:This formula indicates that the half-life for a zero order reaction depends on the initial concentration and the rate constant.
7
Physical Chemistry
Optical physics is the study of the generation of electromagnetic radiation, the properties of that radiation, and the interaction of that radiation with matter, especially its manipulation and control. It differs from general optics and optical engineering in that it is focused on the discovery and application of new phenomena. There is no strong distinction, however, between optical physics, applied optics, and optical engineering, since the devices of optical engineering and the applications of applied optics are necessary for basic research in optical physics, and that research leads to the development of new devices and applications. Often the same people are involved in both the basic research and the applied technology development, for example the experimental demonstration of electromagnetically induced transparency by S. E. Harris and of slow light by Harris and Lene Vestergaard Hau. Researchers in optical physics use and develop light sources that span the electromagnetic spectrum from microwaves to X-rays. The field includes the generation and detection of light, linear and nonlinear optical processes, and spectroscopy. Lasers and laser spectroscopy have transformed optical science. Major study in optical physics is also devoted to quantum optics and coherence, and to femtosecond optics. In optical physics, support is also provided in areas such as the nonlinear response of isolated atoms to intense, ultra-short electromagnetic fields, the atom-cavity interaction at high fields, and quantum properties of the electromagnetic field. Other important areas of research include the development of novel optical techniques for nano-optical measurements, diffractive optics, low-coherence interferometry, optical coherence tomography, and near-field microscopy. Research in optical physics places an emphasis on ultrafast optical science and technology. The applications of optical physics create advancements in communications, medicine, manufacturing, and even entertainment.
7
Physical Chemistry
Laboratory-scale nitric acid syntheses abound. Most take inspiration from the industrial techniques. A wide variety of nitrate salts metathesize with sulfuric acid () &mdash; for example, sodium nitrate: Distillation at nitric acid's 83 °C boiling point then separates the solid metal salt residue. The resulting acid solution is the 68.5 % azeotrope, and can be further concentrated (as in industry) with either sulfuric acid or magnesium nitrate. Alternatively, thermal decomposition of copper(II) nitrate gives nitrogen dioxide and oxygen gases; these are then passed through water or hydrogen peroxide as in the Ostwald process: :or
3
Analytical Chemistry
These probes are mostly used to monitor corrosion caused by erosion or wear. Generally, the erosion are occurred in gas pipelines where the speed of fluid cause erosion. Here the erosion is more important than corrosion.
8
Metallurgy
The retinal Schiff base accepts a proton from Asp96. In the N state, both Asp96 and the Schiff base are charged.
5
Photochemistry
If the general water speed or the degree of local turbulence in an installation is high, the protective film that would normally be formed on a copper tube as a result of slight initial corrosion, may be torn off the surface locally, permitting further corrosion to take place at that point. If this process continues it can produce deep localised attack of the type known as erosion-corrosion or impingement damage. The actual attack on the metal is by the corrosive action of the water to which it is exposed while the erosive factor is the mechanical removal of the corrosion product from the surface. Impingement attack produces highly characteristic water-swept pits, which are often horseshoe shaped, or it can produce broader areas of attack. The leading edge of the pit is frequently undercut by the swirling action of the water. Usually, the surface of the metal within the pits or areas of attack is smooth and carries no substantial corrosion product. Erosion-corrosion is known to occur in pumped-circulation hot water distribution systems, and even in cold water distribution systems, if the water velocities are too high. The factors influencing the attack include the chemical character of the water passing through the system, the temperature, the average water velocity in the system and the presence of any local features likely to induce turbulence in the water stream. It is unusual for the general water velocity in a system to be so high that impingement attack occurs throughout the whole of the copper pipework. More commonly, the velocity is just sufficiently low for satisfactory protective films to be formed and to remain in position on most of the system, with impingement damage more likely to occur where there is an abrupt change in the direction of water flow giving rise to a high degree of turbulence, such as at tee pieces and elbow fittings. It is not generally realised how great an effect small obstructions can have on the flow pattern of water in a pipe-work system and the extent to which they can induce turbulence and cause corrosion-erosion. For example, it is most important, as far as possible, to ensure that copper tubes cut with a tube cutter are deburred before making the joint. Also a gap between the tube end and the stop in the fitting, due to the tube not having been cut to the correct length and fully inserted into the socket of the fitting, can also induce turbulence in the water stream.
8
Metallurgy
In 1950, a small amount of CoQ was isolated from the lining of a horses gut, a compound initially called substance SA, but later deemed to be quinone found in many animal tissues. In 1957, the same compound was isolated from mitochondrial membranes of beef heart, with research showing that it transported electrons within mitochondria. It was called Q-275 as a quinone. The Q-275/substance SA was later renamed ubiquinone as it was a ubiquitous quinone found in all animal tissues. In 1958, its full chemical structure was reported. Ubiquinone was later called either mitoquinone or coenzyme Q' due to its participation to the mitochondrial electron transport chain. In 1966, a study reported that reduced CoQ was an effective antioxidant in cells.
1
Biochemistry
The most frequent quantitative definition of noise is the coefficient of variation: where is the noise in a quantity , is the mean value of and is the standard deviation of . This measure is dimensionless, allowing a relative comparison of the importance of noise, without necessitating knowledge of the absolute mean. Other quantities often used for mathematical convenience are the Fano factor: and the normalized variance:
1
Biochemistry
Insertion element (also known as an IS, an insertion sequence element, or an IS element) is a short DNA sequence that acts as a simple transposable element. Insertion sequences have two major characteristics: they are small relative to other transposable elements (generally around 700 to 2500 bp in length) and only code for proteins implicated in the transposition activity (they are thus different from other transposons, which also carry accessory genes such as antibiotic resistance genes). These proteins are usually the transposase which catalyses the enzymatic reaction allowing the IS to move, and also one regulatory protein which either stimulates or inhibits the transposition activity. The coding region in an insertion sequence is usually flanked by inverted repeats. For example, the well-known IS911 (1250 bp) is flanked by two 36bp inverted repeat extremities and the coding region has two genes partially overlapping orfA and orfAB, coding the transposase (OrfAB) and a regulatory protein (OrfA). A particular insertion sequence may be named according to the form ISn, where n is a number (e.g. IS1, IS2, IS3, IS10, IS50, IS911, IS26 etc.); this is not the only naming scheme used, however. Although insertion sequences are usually discussed in the context of prokaryotic genomes, certain eukaryotic DNA sequences belonging to the family of Tc1/mariner transposable elements may be considered to be, insertion sequences. In addition to occurring autonomously, insertion sequences may also occur as parts of composite transposons; in a composite transposon, two insertion sequences flank one or more accessory genes, such as an antibiotic resistance gene (e.g. Tn10, Tn5). Nevertheless, there exist another sort of transposons, called unit transposons, that do not carry insertion sequences at their extremities (e.g. Tn7). A complex transposon does not rely on flanking insertion sequences for resolvase. The resolvase is part of the tns genome and cuts at flanking inverted repeats. Transposition frequency of IS elements is dependent of multiple parameters, including culture growth phase, medium composition, oxygen tension, growth scale, and structural conformation of target sites (e.g.: curvature, presence of certain motifs, DNA composition).. Recombination between genomic IS sites can enable bacteria to adapt to new environments, making IS elements an important mechanism for evolution in bacteria.
1
Biochemistry
Although telomeres shorten during the lifetime of an individual, it is telomere shortening-rate rather than telomere length that is associated with the lifespan of a species. Critically short telomeres trigger a DNA damage response and cellular senescence. Mice have much longer telomeres, but a greatly accelerated telomere shortening-rate and greatly reduced lifespan compared to humans and elephants. Telomere shortening is associated with aging, mortality, and aging-related diseases in experimental animals. Although many factors can affect human lifespan, such as smoking, diet, and exercise, as persons approach the upper limit of human life expectancy, longer telomeres may be associated with lifespan.
1
Biochemistry
A 5-step process to synthesise levobupivacaine from N-CBZ (S)-lysine, published in 1996, is depicted in Scheme 1. The key steps in this process include oxidative de-animation and stereospecific ring closure to form the pipecolamide core structure. This method is claimed to be efficient, but showed to be dangerous for mass production due to the high risk of explosion of the diazonium salt intermediates. A more recent patent from 2008, consists of a 3-step process (see Scheme 2) to synthesise levobupivacaine hydrochloride of an optical purity of at least 99%. (S)-2,6-pipecocholxylide (I) is reacted with 1-bromobutane and a base (a), such as potassium carbonate, to obtain a solution of (S)-bupivacaine (II) and its enantiomers. Recrystallisation of this solution with a solvent (b), preferably cyclohexane, can lead to an optical purity of at least 98% levobupivacaine. Lastly, the addition of hydrochloride (c) is possible.
4
Stereochemistry
After World War II he worked in the laboratory of Prof. UG Bijlsma in the area of adrenergic substances and in 1950 both in the field of chemistry and medical doctorate. In 1951, Everhardus Ariëns moved to Nijmegen after there at the Catholic University of the Faculty of Pharmacology was established. From 1954 until his retirement he was employed there as a professor. Based on his dissertation, he developed together with Jacques van Rossum, a method for quantification of pharmacological effects as a result of ligand-receptor interactions. The thesis developed the concepts of receptor affinity and intrinsic activity. With the help of these terms he could describe the behavior of agonists and antagonists as well as the dual agonist / antagonist behavior of partial agonists. An important accomplishment of Ariëns was the establishment of experiments on isolated organs instead of the living animal (ex vivo), which quickly and reproducibly delivered data on the affinity and intrinsic activity of test substances. Everhardus Ariëns was also active in the field of structure-activity relationships (SAR), a branch of medicinal chemistry. With the provocative statement that the then commonly used racemates were drugs with 50% contamination. he triggered a debate among pharmacologists and medicinal chemists and alerted the drug regulators. Everhardus Ariëns was thus the crucial precursor for the targeted development of enantiopure drugs. Another, though less noticed controversy he started by expressing his view that drug metabolism is wasted and called for the development of metabolism-resistant drugs. In addition, he followed in the tradition of Dutch pharmacists to combat quackery.
4
Stereochemistry
1-Arseno-3-phosphoglycerate is a compound produced by the enzyme glyceraldehyde 3-phosphate dehydrogenase, present in high concentrations in many organisms, from glyceraldehyde 3-phosphate and arsenate in the glycolysis pathway. The compound is unstable and hydrolyzes spontaneously to 3-phosphoglycerate, bypassing the energy producing step of glycolysis.
1
Biochemistry
Neurons in the olfactory system are unmyelinated and densely packed and thus the often small effects of ephaptic coupling are more easily seen. A number of studies have shown how inhibition among neurons in the olfactory system work to fine-tune integration of signals in response to odor. This inhibition has been shown to occur from changes in electrical potentials alone. The addition of ephaptic coupling to olfactory neuron models adds further support to the "dedicated-line" model in which each olfactory receptor sends its signal to one neuron. The inhibition due to ephaptic coupling would help account for the integration of signals that gives rise to more nuanced perception of smells.
1
Biochemistry
Many different definitions of standard reference conditions are currently being used by organizations all over the world. The table below lists a few of them, but there are more. Some of these organizations used other standards in the past. For example, IUPAC has, since 1982, defined standard reference conditions as being 0 °C and 100 kPa (1 bar), in contrast to its old standard of 0 °C and 101.325 kPa (1 atm). The new value is the mean atmospheric pressure at an altitude of about 112 metres, which is closer to the worldwide median altitude of human habitation (194 m). Natural gas companies in Europe, Australia, and South America have adopted 15 °C (59 °F) and 101.325 kPa (14.696 psi) as their standard gas volume reference conditions, used as the base values for defining the standard cubic meter. Also, the International Organization for Standardization (ISO), the United States Environmental Protection Agency (EPA) and National Institute of Standards and Technology (NIST) each have more than one definition of standard reference conditions in their various standards and regulations. Abbreviations: * EGIA: Electricity and Gas Inspection Act (of Canada) * SATP: Standard Ambient Temperature and Pressure * SCF: Standard Cubic Foot
7
Physical Chemistry
Testican is a type of proteoglycan. Testican-1 is a highly conserved, multidomain proteoglycan that is most prominently expressed in the thalamus, and is upregulated in activated astroglial cells of the cerebrum. Several functions of this gene product have now been demonstrated in vitro including membrane-type matrix metalloproteinase inhibition, cathepsin L inhibition, and low-affinity calcium binding. The purified gene product has been shown to inhibit cell attachment and neurite extensions in culture. Functions of testican in vivo have yet to be demonstrated in knockout mice or other models. Testican has been shown to carry substantial amounts of chondroitin sulfate as well as other oligosaccharides, but the biological significance of these embellishments is not yet known. In humans there are three testicans: * SPOCK1 (Testican 1) * SPOCK2 (Testican 2) * SPOCK3 (Testican 3) Testican-1 plays a role in lapatinib resistance, which is a drug used to treat HER2-positive gastric cancer. When testican-1 levels are artificially reduced, sensitivity towards lapatinib was once again increased. This shows the potential for future use in combating drug resistance.
1
Biochemistry
In organic chemistry, hyperconjugation (σ-conjugation or no-bond resonance) refers to the delocalization of electrons with the participation of bonds of primarily σ-character. Usually, hyperconjugation involves the interaction of the electrons in a sigma (σ) orbital (e.g. C–H or C–C) with an adjacent unpopulated non-bonding p or antibonding σ* or π* orbitals to give a pair of extended molecular orbitals. However, sometimes, low-lying antibonding σ* orbitals may also interact with filled orbitals of lone pair character (n) in what is termed negative hyperconjugation. Increased electron delocalization associated with hyperconjugation increases the stability of the system. In particular, the new orbital with bonding character is stabilized, resulting in an overall stabilization of the molecule. Only electrons in bonds that are in the β position can have this sort of direct stabilizing effect — donating from a sigma bond on an atom to an orbital in another atom directly attached to it. However, extended versions of hyperconjugation (such as double hyperconjugation) can be important as well. The Baker–Nathan effect, sometimes used synonymously for hyperconjugation, is a specific application of it to certain chemical reactions or types of structures.
7
Physical Chemistry
The Fenton reaction has different implications in biology because it involves the formation of free radicals by chemical species naturally present in the cell under in vivo conditions. Transition-metal ions such as iron and copper can donate or accept free electrons via intracellular reactions and so contribute to the formation, or at the contrary to the scavenging, of free radicals. Superoxide ions and transition metals act in a synergistic way in the appearance of free radical damages. Therefore, although the clinical significance is still unclear, it is one of the viable reasons to avoid iron supplementation in patients with active infections, whereas other reasons include iron-mediated infections.
2
Environmental Chemistry
While absorption and release is always happening as a result of natural processes, the recent rise in levels in the atmosphere is known to be mainly due to human (anthropogenic) activity. Anthropogenic carbon emissions exceed the amount that can be taken up or balanced out by natural sinks. Thus carbon dioxide has gradually accumulated in the atmosphere and, as of May 2022, its concentration is 50% above pre-industrial levels. The extraction and burning of fossil fuels, releasing carbon that has been underground for many millions of years, has increased the atmospheric concentration of . As of year 2019 the extraction and burning of geologic fossil carbon by humans releases over 30 gigatonnes of (9 billion tonnes carbon) each year. This larger disruption to the natural balance is responsible for recent growth in the atmospheric concentration. Currently about half of the carbon dioxide released from the burning of fossil fuels is not absorbed by vegetation and the oceans and remains in the atmosphere. Burning fossil fuels such as coal, petroleum, and natural gas is the leading cause of increased anthropogenic ; deforestation is the second major cause. In 2010, 9.14 gigatonnes of carbon (GtC, equivalent to 33.5 gigatonnes of or about 4.3 ppm in Earth's atmosphere) were released from fossil fuels and cement production worldwide, compared to 6.15 GtC in 1990. In addition, land use change contributed 0.87 GtC in 2010, compared to 1.45 GtC in 1990. In the period 1751 to 1900, about 12 GtC were released as to the atmosphere from burning of fossil fuels, whereas from 1901 to 2013 the figure was about 380 GtC. The International Energy Agency estimates that the top 1% of emitters globally each had carbon footprints of over 50 tonnes of in 2021, more than 1,000 times greater than those of the bottom 1% of emitters. The global average energy-related carbon footprint is around 4.7 tonnes of per person.
2
Environmental Chemistry
The development of stable red color in the surface of the medium indicates sufficient acid production to lower the pH to 4.4 and constitute a positive test. Since other organism may produce lesser quantities of acid from the test substrate, an intermediate orange color between yellow and red may develop. This does not indicate positive test.
3
Analytical Chemistry
Townsend avalanche discharges are fundamental to the operation of gaseous ionisation detectors such as the Geiger–Müller tube and the proportional counter in either detecting ionising radiation or measuring its energy. The incident radiation will ionise atoms or molecules in the gaseous medium to produce ion pairs, but different use is made by each detector type of the resultant avalanche effects. In the case of a GM tube the high electric field strength is sufficient to cause complete ionisation of the fill gas surrounding the anode from the initial creation of just one ion pair. The GM tube output carries information that the event has occurred, but no information about the energy of the incident radiation. In the case of proportional counters, multiple creation of ion pairs occurs in the "ion drift" region near the cathode. The electric field and chamber geometries are selected so that an "avalanche region" is created in the immediate proximity of the anode. A negative ion drifting towards the anode enters this region and creates a localised avalanche that is independent of those from other ion pairs, but which can still provide a multiplication effect. In this way spectroscopic information on the energy of the incident radiation is available by the magnitude of the output pulse from each initiating event. The accompanying plot shows the variation of ionisation current for a co-axial cylinder system. In the ion chamber region, there are no avalanches and the applied voltage only serves to move the ions towards the electrodes to prevent re-combination. In the proportional region, localised avalanches occur in the gas space immediately round the anode which are numerically proportional to the number of original ionising events. Increasing the voltage further increases the number of avalanches until the Geiger region is reached where the full volume of the fill gas around the anodes ionised, and all proportional energy information is lost. Beyond the Geiger region the gas is in continuous discharge owing to the high electric field strength.
7
Physical Chemistry
Supercritical adsorption also referred to as the adsorption of supercritical fluids, is the adsorption at above-critical temperatures. There are different tacit understandings of supercritical fluids. For example, “a fluid is considered to be ‘supercritical’ when its temperature and pressure exceed the temperature and pressure at the critical point”. In the studies of supercritical extraction, however, “supercritical fluid” is applied for a narrow temperature region of 1-1.2 or to +10 K, which is called the supercritical region. ( is the critical temperature)
7
Physical Chemistry
Nucleic acids are generally very large molecules. Indeed, DNA molecules are probably the largest individual molecules known. Well-studied biological nucleic acid molecules range in size from 21 nucleotides (small interfering RNA) to large chromosomes (human chromosome 1 is a single molecule that contains 247 million base pairs). In most cases, naturally occurring DNA molecules are double-stranded and RNA molecules are single-stranded. There are numerous exceptions, however—some viruses have genomes made of double-stranded RNA and other viruses have single-stranded DNA genomes, and, in some circumstances, nucleic acid structures with three or four strands can form. Nucleic acids are linear polymers (chains) of nucleotides. Each nucleotide consists of three components: a purine or pyrimidine nucleobase (sometimes termed nitrogenous base or simply base), a pentose sugar, and a phosphate group which makes the molecule acidic. The substructure consisting of a nucleobase plus sugar is termed a nucleoside. Nucleic acid types differ in the structure of the sugar in their nucleotides–DNA contains 2'-deoxyribose while RNA contains ribose (where the only difference is the presence of a hydroxyl group). Also, the nucleobases found in the two nucleic acid types are different: adenine, cytosine, and guanine are found in both RNA and DNA, while thymine occurs in DNA and uracil occurs in RNA. The sugars and phosphates in nucleic acids are connected to each other in an alternating chain (sugar-phosphate backbone) through phosphodiester linkages. In conventional nomenclature, the carbons to which the phosphate groups attach are the 3-end and the 5-end carbons of the sugar. This gives nucleic acids directionality, and the ends of nucleic acid molecules are referred to as 5-end and 3-end. The nucleobases are joined to the sugars via an N-glycosidic linkage involving a nucleobase ring nitrogen (N-1 for pyrimidines and N-9 for purines) and the 1' carbon of the pentose sugar ring. Non-standard nucleosides are also found in both RNA and DNA and usually arise from modification of the standard nucleosides within the DNA molecule or the primary (initial) RNA transcript. Transfer RNA (tRNA) molecules contain a particularly large number of modified nucleosides.
1
Biochemistry
Crystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. The degree of crystallinity has a big influence on hardness, density, transparency and diffusion. In an ideal gas, the relative positions of the atoms or molecules are completely random. Amorphous materials, such as liquids and glasses, represent an intermediate case, having order over short distances (a few atomic or molecular spacings) but not over longer distances. Many materials, such as glass-ceramics and some polymers, can be prepared in such a way as to produce a mixture of crystalline and amorphous regions. In such cases, crystallinity is usually specified as a percentage of the volume of the material that is crystalline. Even within materials that are completely crystalline, however, the degree of structural perfection can vary. For instance, most metallic alloys are crystalline, but they usually comprise many independent crystalline regions (grains or crystallites) in various orientations separated by grain boundaries; furthermore, they contain other crystallographic defects (notably dislocations) that reduce the degree of structural perfection. The most highly perfect crystals are silicon boules produced for semiconductor electronics; these are large single crystals (so they have no grain boundaries), are nearly free of dislocations, and have precisely controlled concentrations of defect atoms. Crystallinity can be measured using x-ray crystallography, but calorimetric techniques are also commonly used.
7
Physical Chemistry
The filter cloth is washed on both sides with each drum rotation while discharging filter cakes. The products for this mechanism are usually sticky, wet and thin thus, requiring the aid of a discharge roll. Belt discharge is used if slurry with moderate solid concentration is used or if the slurry is easy to filter to produce cake formation or if a longer wear resistance is desired for the separation of the mentioned slurry.....
3
Analytical Chemistry
Quartz fiber filter paper has a high resistance to chemicals, does not absorb NO and SO dioxides, is unaffected by humidity and is easily sterilized. Thus, it is mostly used for air pollution analysis.
3
Analytical Chemistry
Simple alkylcerium reagents are well known. One example is . Although they are described as RCeCl, their structures are far more complex.. Furthermore, the solvent seems to alter the solution structure of the complex, with differences noted between reagents prepared in diethyl ether and tetrahydrofuran. There is evidence that the parent chloride forms a polymeric species in THF solution, of the form [Ce(μ-Cl)(HO)(THF)], but whether this type of polymer exists once the organometallic reagent is formed is unknown.
0
Organic Chemistry
In 1962, Edwards and Pearson (the latter of HSAB theory) introduced the phrase alpha effect for this anomaly. He offered the suggestion that the effect was caused by a transition state (TS) stabilization effect: on entering the TS the free electron pair on the nucleophile moves away from the nucleus, causing a partial positive charge which can be stabilized by an adjacent lone pair as for instance happens in any carbocation.
7
Physical Chemistry
Differences in O solubility and measured concentration (AOU) typically occur when biological activity, ocean circulation, or ocean mixing act to change the ambient concentration of oxygen. For example, primary production liberates oxygen and increases its concentration, while respiration consumes it and decreases its concentration. Consequently, the AOU of a water sample represents the sum of the biological activity that the sample has experienced since it was last in equilibrium with the atmosphere. In shallow water systems (e.g. lakes), the full water column is generally in close contact with the atmosphere, and oxygen concentrations are typically close to saturation, and AOU values are near zero. In deep water systems (e.g. oceans), water can be out of contact with the atmosphere for extremely long periods of time (years, decades, centuries) and large positive AOU values are typical. On occasion, where near-surface primary production has raised oxygen concentrations above saturation, negative AOU values are possible (i.e. oxygen has not been utilized to below saturation concentrations).
9
Geochemistry
Several companies in the United States are now working to commercialize supercritical reactors to destroy hazardous wastes. Widespread commercial application of SCWO technology requires a reactor design capable of resisting fouling and corrosion under supercritical conditions. In Japan a number of commercial SCWO applications exist, among them one unit for treatment of halogenated waste built by Organo. In Korea two commercial size units have been built by Hanwha. In Europe, Chematur Engineering AB of Sweden commercialized the SCWO technology for treatment of spent chemical catalysts to recover the precious metal, the AquaCat process. The unit has been built for Johnson Matthey in the UK. It is the only commercial SCWO unit in Europe and with its capacity of 3000l/h it is the largest SCWO unit in the world. Chematur's Super Critical Fluids technology was acquired by SCFI Group (Cork, Ireland) who are actively commercializing the Aqua Critox SCWO process for treatment of sludge, e.g. de-inking sludge and sewage sludge. Many long duration trials on these applications have been made and thanks to the high destruction efficiency of 99.9%+ the solid residue after the SCWO process is well suited for recycling – in the case of de-inking sludge as paper filler and in the case of sewage sludge as phosphorus and coagulant. SCFI Group operate a 250l/h Aqua Critox demonstration plant in Cork, Ireland. Turbosystems Engineering (California, USA) is actively commercializing their patented transpiring wall SCWO reactor ("TWR") with a focus on renewable energy applications. 374Water Inc. is a company offering commercial SCWO systems that convert organic wastes to clean water, energy and minerals. It is spun out after more than seven years of research and development funded by the Bill & Melinda Gates Foundation to Prof. Deshusses laboratory based at Duke University. The founders of 374Water, Prof. Marc Deshusses and Kobe Nagar, possess the waste processing reactor patent relevant to SCWO. 374Water is actively commercializing its AirSCWO systems for the treatment of biosolids and wastewater sludges, organic chemical wastes, and PFAS wastes including unspent Aqueous Film Forming Foams (AFFFs), rinsates or spent resins and adsorption media. The first commercial sale was announced in February 2022. Aquarden Technologies (Skaevinge, Denmark) provides modular SCWO plants for the destruction of hazardous pollutants such as PFAS, pesticides, and other problematic hydrocarbons in industrial wastestreams. Aquarden is also providing remediation of hazardous energetic wastes and chemical warfare agents with SCWO, where a full-scale SCWO system has been operating for some years in France for the Defense Industry.
7
Physical Chemistry
Most tests employ a monoclonal antibody, which is specific to the β-subunit of hCG (β-hCG). This procedure is employed to ensure that tests do not make false positives by confusing hCG with LH and FSH. (The latter two are always present at varying levels in the body, whereas the presence of hCG almost always indicates pregnancy.) Many hCG immunoassays are based on the sandwich principle, which uses antibodies to hCG labeled with an enzyme or a conventional or luminescent dye. Pregnancy urine dipstick tests are based on the lateral flow technique. * The urine test may be a chromatographic immunoassay or any of several other test formats, home-, physician's office-, or laboratory-based. Published detection thresholds range from 20 to 100 mIU/mL, depending on the brand of test. Early in pregnancy, more accurate results may be obtained by using the first urine of the morning (when urine is most concentrated). When the urine is dilute (specific gravity less than 1.015), the hCG concentration may not be representative of the blood concentration, and the test may be falsely negative. * The serum test, using 2-4 mL of venous blood, is typically a chemiluminescent or fluorimetric immunoassay that can detect βhCG levels as low as 5 mIU/mL and allows quantification of the βhCG concentration.
1
Biochemistry
In April 2005, following the confirmation of asbestos fibres found on tree roots, the council asked developers to provide more detailed information relating to their contaminated land surveys, and placed the application on hold. They also announced that they were considering appointing their own environmental consultants to examine the site. Jason Addy said: "This is what we have been asking for since day one. The information handed in with the planning application was inaccurate, misleading and avoided many issues. As this site begins to reveal more of its murky secrets people are realising just how contaminated it is. We are very concerned about the asbestos contamination on the site. We are very worried about the way this is going, if it wasn't so serious it would be a farce." Rochdale councillor William Hobhouse said: "With no government regulations specifying safe levels of asbestos in soil, it is clear the council, working with outside consultants, will have to formulate what percentage of asbestos in the soil is safe."
2
Environmental Chemistry
The Strep-tag system is a method which allows the purification and detection of proteins by affinity chromatography. The Strep-tag II is a synthetic peptide consisting of eight amino acids (Trp-Ser-His-Pro-Gln-Phe-Glu-Lys). This peptide sequence exhibits intrinsic affinity towards Strep-Tactin, a specifically engineered streptavidin, and can be N- or C- terminally fused to recombinant proteins. By exploiting the highly specific interaction, Strep-tagged proteins can be isolated in one step from crude cell lysates. Because the Strep-tag elutes under gentle, physiological conditions, it is especially suited for the generation of functional proteins.
1
Biochemistry
A polymeric foam is a special foam, in liquid or solidified form, formed from polymers. Examples include: * Ethylene-vinyl acetate (EVA) foam, the copolymers of ethylene and vinyl acetate; also referred to as polyethylene-vinyl acetate (PEVA) * Low-density polyethylene (LDPE) foam, first grade of polyethylene (PE) * Nitrile rubber (NBR) foam, the copolymers of acrylonitrile (ACN) and butadiene * Polychloroprene foam or Neoprene * Polyimide foam * Polypropylene (PP) foam, including expanded polypropylene (EPP) and polypropylene paper (PPP) * Polystyrene (PS) foam, including expanded polystyrene (EPS), extruded polystyrene foam (XPS) and sometimes polystyrene paper (PSP) ** Styrofoam, including extruded polystyrene foam (XPS) and sometimes expanded polystyrene (EPS) * Polyurethane (PU) foam ** LRPu low-resilience polyurethane ** Memory foam ** Sorbothane *Polyurea foam *Polyethylene foam, as used in PEF rod * Polyvinyl chloride (PVC) foam ** Closed-cell PVC foamboard * Silicone foam * Microcellular foam
7
Physical Chemistry
The reaction involves the addition of and cyanide () to the substrate. Usually the substrate is an alkene and the product is a nitrile. The reaction proceeds via the oxidative addition of HCN to a low-valent metal complex to give a hydrido cyanide complex. Subsequent binding of the alkene gives the intermediate , which then undergoes migratory insertion to give an alkylmetal cyanide. The cycle is completed by the reductive elimination of the nitrile. Lewis acids, such as triphenylboron (), induce reductive elimination of the nitrile product, increasing rates. In the case of nickel-based systems, catalyst deactivation involves formation of dicyanonickel(II) species, which are unreactive toward alkenes. The dicyanide arises via two pathways (L = phosphite):
0
Organic Chemistry
Blue flower colour was always associated with something unusual and desired. Blue roses especially were assumed to be a dream that cannot be realised. Blue colour in flower petals is caused by anthocyanins, which are members of flavonoid class metabolites. We can diversify three main classes of anthocyanin pigments: cyaniding type (two hydroxyl groups in the B-ring) responsible for red coloration, pelargonidin type (one hydroxyl group in the B-ring) responsible for orange colour and delphinidin type (three hydroxyl groups in the B-ring) responsible for violet/blue flower and fruits coloration. The main difference in the structure of listed anthocyanins type is the number of hydroxyl groups in the B-ring of the anthocyanin. Nevertheless, in the monomeric state anthocyanins never show blue colour in the weak acidic and neutral pH. The mechanism of blue colour formation are very complicated in most cases, presence of delphinidin type pigments is not sufficient, great role play also the pH and the formation of complexes of anthocyanins with flavones and metal ions.
1
Biochemistry
Polychlorinated biphenyls (PCBs) are various biphenyl based artificial products that are widely used as a dielectric fluid, industrial coolant, and lubricants in the 1960s and 1970s. There is no evidence its synthesis occurs naturally. They are classified as persistent organic pollutants. PCBs share the basic chemical structure of biphenyl and one or more of the hydrogen atoms on the aromatic rings are replaced by chlorine atoms. PCBs is in viscous liquid form at normal temperature and has a poor solubility in water. The aromatic hydrocarbon structure gives PCBs relatively high molecular stability. The chlorine substitution further reinforces its insolubility and chemical stability. Hence, the degradation of PCBs in the natural environment is very slow, which can range from 3 to 37 years depending on the number of chloride substitutions and their positions.
1
Biochemistry
In aeronautics and fluid dynamics the "International Standard Atmosphere" (ISA) is a specification of pressure, temperature, density, and speed of sound at each altitude. The International Standard Atmosphere is representative of atmospheric conditions at mid latitudes. In the US this information is specified the U.S. Standard Atmosphere which is identical to the "International Standard Atmosphere" at all altitudes up to 65,000 feet above sea level.
7
Physical Chemistry
Ionic compounds interact strongly with the solvent medium; therefore, their impact on chemical and biochemical processes involving ions can be significant. Even in the case of simplest ions and solvents, the presence of the former can lead to rearrangement and restructuring of the latter. It is established that ionic reactions are involved in numerous phenomena at the scales of whole galaxies or single living cells. To name a few, in living cells, metal ions bind to metalloenzymes and other proteins therefore modulating their activity; ions are involved in the control of neuronal functioning during sleep – wakefulness cycles; anomalous activity of ion channels results in the development of various disorders, such as Parkinsons and Alzheimers diseases, etc. Thus, despite the problems associated with the studies on properties and activities of ions in various chemical and biological systems, this research field is among the most urgent ones.
1
Biochemistry
COC is commonly extruded with cast or blown film equipment in the manufacture of packaging films. Most often, due to cost, COC is used as a modifier in monolayer or multilayer film to provide properties not delivered by base resins such as polyethylene. Grades of COC based on ethylene show a certain amount of compatibility with polyethylene and can be blended with PE via commercial dry blending equipment. These films are then used in consumer applications including food and healthcare packaging. Key COC enhancements can include thermoformability, shrink, deadfold, easy tear, enhanced stiffness, heat resistance and higher moisture barrier. Common applications include shrink films and labels, twist films, protective or bubble packaging, and forming films. Another noted application which often relies on a high percentage of COC in the end product is pharmaceutical blister packaging.
7
Physical Chemistry
Plants have an array of volatile compounds they can release to signal other plants. By unleashing these cues, plants learn more about their environment and sufficiently respond. However, there are still many factors about plant scents scientists are still trying to understand. Scientists have studied how many of the volatile compounds released by plants are from a floral source. A study concluded that floral cues are as important as other volatile compounds and are pertinent for plant-to-plant communication. Further research found that plants who receive the floral volatiles have higher fitness than other volatile cues because floral cues are the only compounds released by plants that indicate their kind of mating environment. Plants are able to respond to these mating cues and change adjustable floral phenotypes that can affect plant pollination and mating. Floral volatiles can ward off or attract pollinators/mates all at once. Depending on the number of floral signals released by a plant can control the level of attracting/repelling the plant wants. The composition of floral compounds and the rate of their release are the potential factors that control attraction/repellence. These two elements can be in response to ecological cues like high plant density and temperature. For instance, in sexually deceptive orchids, floral scents emitted after pollination reduce the flower's attractiveness to pollinators. This mechanism acts as a signal to pollinators to visit unpollinated flowers. Environmental conditions can affect plant communication and signaling. Signal factors include temperature and plant density. Environmentally high temperatures increase the rate of releasing floral compounds, which can increase the amount of signal released and thus its ability to reach more plants. When plant density increases, plant communication increases as well, since plants would be near each other and have signals reach many neighboring plants. This can also increase the signal's reliability and lowering the chance the signal will degrade before it can reach other plants.
1
Biochemistry
Barium iodate, Ba(IO), has a solubility product K = [Ba][IO] = 1.57 x 10. Its solubility in pure water is 7.32 x 10 M. However in a solution that is 0.0200 M in barium nitrate, Ba(NO), the increase in the common ion barium leads to a decrease in iodate ion concentration. The solubility is therefore reduced to 1.40 x 10 M, about five times smaller.
7
Physical Chemistry
Using the A-values of the hydroxyl and isopropyl subunit, the energetic value of a favorable intramolecular hydrogen bond can be calculated.
4
Stereochemistry
Pharmacometabolomics may be used in a predictive manner to determine the correct course of action in regards to a patient about to undergo some type of drug treatment. This involves determining the metabolic profile of a patient prior to treatment, and correlating metabolic signatures with the outcome of a pharmaceutical treatment course. Analysis of a patient's metabolic profile can reveal factors that may contribute to altered drug metabolism, allowing for predictions of the overall efficacy of a proposed treatment, as well as potential drug toxicity risks that may differ from the general population. This approach has been used to identify novel or previously characterized metabolic biomarkers in patients, which can be used to predict the expected outcome of that patient following treatment with a pharmaceutical compound. One example of the clinical application of pharmacometabolomics are studies that looked to identify a predictive metabolic marker for the treatment of major depressive disorder (MDD)., In a study with antidepressant Sertraline, the Pharmacometabolomics Network illustrated that metabolic profile at baseline of patients with major depression can inform about treatment outcomes. In addition the study illustrated the power of metabolomics for defining response to placebo and compared response to placebo to response to sertraline and showed that several pathways were common to both. In another study with escitalopram citalopram, metabolomic analysis of plasma from patients with MDD revealed that variations in glycine metabolism were negatively associated with patient outcome upon treatment with selective serotonin reuptake inhibitors (SSRIs), an important drug class involved in the treatment of this disease.
1
Biochemistry
The metric tensor is sometimes used for calculations involving the unit cell and is defined (in matrix form) as: In two dimensions, In three dimensions, The distance between two points and in the unit cell can be determined from the relation: The distance from the origin of the unit cell to a point within the unit cell can be determined from the relation: The angle formed from three points , (apex), and within the unit cell can determined from the relation: The volume of the unit cell, can be determined from the relation:
3
Analytical Chemistry
Cannabis Analytical Science Program (CASP) is a forum where the science of hemp and cannabis analysis can be discussed and cannabis standards and methods developed.
3
Analytical Chemistry
* Birchons Dictionary of Metallurgy', London, 1965 * Experimental techniques in low-temperature physics, G. K. White, Oxford University Press, Third Edition
8
Metallurgy
In a simple reaction such as the isomerization: there are two reactions to consider, the forward reaction in which the species A is converted into B and the backward reaction in which B is converted into A. If both reactions are elementary reactions, then the rate of reaction is given by where is the rate constant for the forward reaction and is the rate constant for the backward reaction and the square brackets, , denote concentration. If only A is present at the beginning, time , with a concentration [A], the sum of the two concentrations, [A] and [B], at time , will be equal to [A]. The solution to this differential equation is and is illustrated at the right. As time tends towards infinity, the concentrations [A] and [B] tend towards constant values. Let approach infinity, that is, , in the expression above: In practice, concentration changes will not be measurable after Since the concentrations do not change thereafter, they are, by definition, equilibrium concentrations. Now, the equilibrium constant for the reaction is defined as It follows that the equilibrium constant is numerically equal to the quotient of the rate constants. In general they may be more than one forward reaction and more than one backward reaction. Atkins states that, for a general reaction, the overall equilibrium constant is related to the rate constants of the elementary reactions by
7
Physical Chemistry
Optical depth of a material is also related to its attenuation coefficient by:where *l is the thickness of that material through which the light travels; *α(z) is the attenuation coefficient or Napierian attenuation coefficient of that material at z, and if α(z) is uniform along the path, the attenuation is said to be a linear attenuation and the relation becomes: Sometimes the relation is given using the attenuation cross section of the material, that is its attenuation coefficient divided by its number density:where *σ is the attenuation cross section of that material; *n(z) is the number density of that material at z, and if is uniform along the path, i.e., , the relation becomes:
7
Physical Chemistry
In chemistry, polyvalency (or polyvalence, multivalency) is the property of chemical species (generally atoms or molecules) that exhibit more than one valence by forming multiple chemical bonds (Fig. 1). A bivalent species can form two bonds; a trivalent species can form three bonds; and so on. The principle of polyvalency also applies to larger species, such as antibodies, medical drugs, and even nanoparticles surface-functionalized with ligands, like spherical nucleic acids, which can show enhanced or cooperative binding compared to their monovalent counterparts. Nanoparticles with multiple nucleic acid strands on their surfaces (e.g., DNA) can form multiple bonds with one another by DNA hybridization to form hierarchical assemblies, some of which are highly crystalline in nature.
3
Analytical Chemistry
The absorption of energy followed by the emission of light is often described by the term luminescence. The exact term used is based on the energy source responsible for the luminescence as in color-change phenomena. *Electrical – electroluminescence Galvanoluminescence Sonoluminescence. *Photons (light) – Photoluminescence Fluorescence Phosphorescence Biofluorescence. *Chemical – Chemiluminescence Bioluminescence Electrochemiluminescence. *Thermal – Thermoluminescence Pyroluminescence Candololuminescence. *Electron Beam – Cathodoluminescence Anodoluminescence Radioluminescence. *Mechanical – Triboluminescence Fractoluminescence Mechanoluminescence Crystalloluminescence Lyoluminescence Elasticoluminescence. Many of these phenomena are widely used in consumer products and other important outlets. Cathodoluminescence is used in cathode ray tubes, photoluminescence in fluorescent lighting and plasma display panels, phosphorescence in safety signs and low energy lighting, fluorescence in pigments, inks, optical brighteners, safety clothing, and biological and medicinal analysis and diagnostics, chemoluminescence and bioluminescence in analysis, diagnostics and sensors, and electroluminescence in the burgeoning areas of light-emitting diodes (LEDs/OLEDs), displays and panel lighting. Important new developments are taking place in the areas of quantum dots and metallic nanoparticles.
5
Photochemistry
mTOR signaling intersects with Alzheimer's disease (AD) pathology in several aspects, suggesting its potential role as a contributor to disease progression. In general, findings demonstrate mTOR signaling hyperactivity in AD brains. For example, postmortem studies of human AD brain reveal dysregulation in PTEN, Akt, S6K, and mTOR. mTOR signaling appears to be closely related to the presence of soluble amyloid beta (Aβ) and tau proteins, which aggregate and form two hallmarks of the disease, Aβ plaques and neurofibrillary tangles, respectively. In vitro studies have shown Aβ to be an activator of the PI3K/AKT pathway, which in turn activates mTOR. In addition, applying Aβ to N2K cells increases the expression of p70S6K, a downstream target of mTOR known to have higher expression in neurons that eventually develop neurofibrillary tangles. Chinese hamster ovary cells transfected with the 7PA2 familial AD mutation also exhibit increased mTOR activity compared to controls, and the hyperactivity is blocked using a gamma-secretase inhibitor. These in vitro studies suggest that increasing Aβ concentrations increases mTOR signaling; however, significantly large, cytotoxic Aβ concentrations are thought to decrease mTOR signaling. Consistent with data observed in vitro, mTOR activity and activated p70S6K have been shown to be significantly increased in the cortex and hippocampus of animal models of AD compared to controls. Pharmacologic or genetic removal of the Aβ in animal models of AD eliminates the disruption in normal mTOR activity, pointing to the direct involvement of Aβ in mTOR signaling. In addition, by injecting Aβ oligomers into the hippocampi of normal mice, mTOR hyperactivity is observed. Cognitive impairments characteristic of AD appear to be mediated by the phosphorylation of PRAS-40, which detaches from and allows for the mTOR hyperactivity when it is phosphorylated; inhibiting PRAS-40 phosphorylation prevents Aβ-induced mTOR hyperactivity. Given these findings, the mTOR signaling pathway appears to be one mechanism of Aβ-induced toxicity in AD. The hyperphosphorylation of tau proteins into neurofibrillary tangles is one hallmark of AD. p70S6K activation has been shown to promote tangle formation as well as mTOR hyperactivity through increased phosphorylation and reduced dephosphorylation. It has also been proposed that mTOR contributes to tau pathology by increasing the translation of tau and other proteins. Synaptic plasticity is a key contributor to learning and memory, two processes that are severely impaired in AD patients. Translational control, or the maintenance of protein homeostasis, has been shown to be essential for neural plasticity and is regulated by mTOR. Both protein over- and under-production via mTOR activity seem to contribute to impaired learning and memory. Furthermore, given that deficits resulting from mTOR overactivity can be alleviated through treatment with rapamycin, it is possible that mTOR plays an important role in affecting cognitive functioning through synaptic plasticity. Further evidence for mTOR activity in neurodegeneration comes from recent findings demonstrating that eIF2α-P, an upstream target of the mTOR pathway, mediates cell death in prion diseases through sustained translational inhibition. Some evidence points to mTORs role in reduced Aβ clearance as well. mTOR is a negative regulator of autophagy; therefore, hyperactivity in mTOR signaling should reduce Aβ clearance in the AD brain. Disruptions in autophagy may be a potential source of pathogenesis in protein misfolding diseases, including AD. Studies using mouse models of Huntingtons disease demonstrate that treatment with rapamycin facilitates the clearance of huntingtin aggregates. Perhaps the same treatment may be useful in clearing Aβ deposits as well.
1
Biochemistry
Binding affinity carries a huge importance in medicinal chemistry, as drugs need to bind to the protein effectively within a desired range. However, determining enthalpy changes and optimization of thermodynamic parameters are hugely difficult when designing drugs. ITC troubleshoots this issue easily by deducing the binding affinity, enthalpic/entropic contributions and its binding stoichiometry.
7
Physical Chemistry
Paula Jefferson, head of Beachcroft LLP's Disease Group, said: "Any organisation involved in any activity in the future, where there is the potential for release of harmful substances in to the atmosphere, should ensure that they have taken all necessary steps to identify the potential contamination and to then ensure that they either employ, or have themselves the necessary skills, to deal with that contamination. The principles in the judgment apply not just when there is demolition in progress, but to any activity where there is potential for exposure in to the atmosphere. Where there is any known potential for such exposure, then regard should be had to not just the onsite workforce but also to those living and working in the surrounding area. In the Corby case the area of risk was 4km from the demolition site. The area for potential exposure will clearly vary depending on the circumstances of each case. In essence, the message remains the same - proper risk assessment is key and must include identifying the appropriate people to do the job and not cutting corners, which, as has been proved for Corby Borough Council, is likely to be false economy."
2
Environmental Chemistry
Typically, the open-ring isomers are colorless compounds, whereas the closed-ring isomers have colors dependent on their chemical structure, due to the extended conjugation along the molecular backbone. Therefore, many diarylethenes have photochromic behavior both in solution and in solid state. Moreover, these two isomers differ from one another not only in their absorption spectra but also in various physical and chemical properties, such as their refractive index, dielectric constant, and oxidation-reduction potential. These properties can be readily controlled by reversible isomerization between the open- and closed-ring states using photoirradiation, and thus they have been suggested for use in optical data storage and 3D optical data storage in particular. The closed form has a conjugated path from one end of the molecule to the other, whereas the open form has not. This allows for the electronic communication between functional groups attached to the far ends of the diarylethene to be switched on and off using UV and visible light.
5
Photochemistry
Since SFG is a second-order nonlinear optical phenomenon, one of the main technical concerns in an experimental setup is being able to generate a signal strong enough to detect, with discernible peaks and narrow bandwidths. Picosecond and femtosecond pulse width lasers are often used due to the high peak field intensities. Common sources include Ti:Sapphire lasers, which can easily operate in the femtosecond regime, or Neodymium based lasers, for picosecond operation. Whilst shorter pulses results in higher peak intensities, the spectral bandwidth of the laser pulse is also increased, which can place a limit on the spectral resolution of the output of an experimental setup. This can be compensated for by narrowing the bandwidth of the pump pulse, resulting in a tradeoff for desired properties. In modern experimental setups, the tuneable range of the probe pulse is augmented by optical parametric generation (OPG), optical parametric oscillation (OPO), and optical parametric amplification (OPA) systems. Signal strength can be improved by using special geometries, such as a total internal reflection setup which uses a prism to change the angles so they are close to the critical angles, allowing the SFG signal to be generated at its critical angle, enhancing the signal. Common detector setups utilize a monochromator and a photomultiplier for filtering and detecting.
7
Physical Chemistry
Sickle cell disease can be treated in mice. The mice – which have essentially the same defect that causes human cases – used a viral vector to induce production of fetal hemoglobin (HbF), which normally ceases to be produced shortly after birth. In humans, the use of hydroxyurea to stimulate the production of HbF temporarily alleviates sickle cell symptoms. The researchers demonstrated this treatment to be a more permanent means to increase therapeutic HbF production. A new gene therapy approach repaired errors in messenger RNA derived from defective genes. This technique has the potential to treat thalassaemia, cystic fibrosis and some cancers. Researchers created liposomes 25 nanometers across that can carry therapeutic DNA through pores in the nuclear membrane.
1
Biochemistry
Glycogenin is the initiator of the glycogen biosynthesis. This protein is a glycosyl transferase that have the ability of autoglycosilation using UDP-glucose, which helps in the growth of itself until forming an oligosaccharide made by 8 glucoses. Glycogenin is an oligomer, and it's capable of interacting with several proteins. In recent years, a family of proteins has been identified, the GNIPs (glycogenin-interacting protein), that interacts with glycogenin stimulating its autoglycolsilation activity.
1
Biochemistry
Tumor M2-PK is a synonym for the dimeric form of the pyruvate kinase isoenzyme type M2 (PKM2), a key enzyme within tumor metabolism. Tumor M2-PK can be elevated in many tumor types, rather than being an organ-specific tumor marker such as PSA. Increased stool (fecal) levels are being investigated as a method of screening for colorectal tumors, and EDTA plasma levels are undergoing testing for possible application in the follow-up of various cancers. Sandwich ELISAs based on two monoclonal antibodies which specifically recognize Tumor M2-PK (the dimeric form of M2-PK) are available for the quantification of Tumor M2-PK in stool and EDTA-plasma samples respectively. As a biomarker, the amount of Tumor M2-PK in stool and EDTA-plasma reflects the specific metabolic status of the tumors.
1
Biochemistry
Experimentally it was determined that extent of gas adsorption varies directly with pressure, and then it directly varies with pressure raised to the power until saturation pressure is reached. Beyond that point, the rate of adsorption saturates even after applying higher pressure. Thus, the Freundlich adsorption isotherm fails at higher pressure.
3
Analytical Chemistry
Recycle reactors are PFRs with a recycle loop. Consequently, they behave like a hybrid between PFRs and CSTRs. In all of these equations : is the consumption rate of A, a reactant. This is equal to the rate expression A is involved in. The rate expression is often related to the fractional conversion both through the consumption of A and through any k changes through temperature changes that are dependent on conversion.
9
Geochemistry
The retardation factor, R, is commonly used in paper chromatography and thin layer chromatography for analyzing and comparing different substances. It can be mathematically described by the following ratio: An R value will always be in the range 0 to 1; if the substance moves, it can only move in the direction of the solvent flow, and cannot move faster than the solvent. For example, if particular substance in an unknown mixture travels 2.5 cm and the solvent front travels 5.0 cm, the retardation factor would be 0.50. One can choose a mobile phase with different characteristics (particularly polarity) in order to control how far the substance being investigated migrates. An R value is characteristic for any given compound (provided that the same stationary and mobile phases are used). It can provide corroborative evidence as to the identity of a compound. If the identity of a compound is suspected but not yet proven, an authentic sample of the compound, or standard, is spotted and run on a TLC plate side by side (or on top of each other) with the compound in question. Note that this identity check must be performed on a single plate, because it is difficult to duplicate all the factors which influence R exactly from experiment to experiment.
3
Analytical Chemistry
Agamous (AG) is a homeotic gene and MADS-box transcription factor from Arabidopsis thaliana. The TAIR AGI number is AT4G18960. The identity of a floral organ is determined by particular combinations of homeotic genes, these genes derive from a group of undifferentiated cells known as the floral meristem. The presence of the homeotic gene in Arabidopsis ceases all meristem activity and proceeds to facilitate the development of stamens and carpels.
1
Biochemistry
Benzenesulfonyl chloride is an organosulfur compound with the formula CHSOCl. It is a colourless viscous oil that dissolves in organic solvents, but reacts with compounds containing reactive N-H and O-H bonds. It is mainly used to prepare sulfonamides and sulfonate esters by reactions with amines and alcohols, respectively. The closely related compound toluenesulfonyl chloride is often preferred analogue because it is a solid at room temperature and easier to handle. The compound is prepared by the chlorination of benzenesulfonic acid or its salts with phosphorus oxychloride or, less commonly, by a reaction between benzene and chlorosulfuric acid. The Hinsberg test for amines involves their reaction with benzenesulfonyl chloride.
0
Organic Chemistry
Drinking birds, also known as insatiable birdies, dunking birds, drinky birds, water birds, dipping birds, and “Sippy Chickens” are toy heat engines that mimic the motions of a bird drinking from a water source. They are sometimes incorrectly considered examples of a perpetual motion device.
7
Physical Chemistry
The candidate division SR1 and gracilibacteria code (translation table 25) is used in two groups of (so far) uncultivated bacteria found in marine and fresh-water environments and in the intestines and oral cavities of mammals among others. The difference to the standard and the bacterial code is that UGA represents an additional glycine codon and does not code for termination.
1
Biochemistry
Polyacrylamide gel electrophoresis (PAGE) is used for separating proteins ranging in size from 5 to 2,000 kDa due to the uniform pore size provided by the polyacrylamide gel. Pore size is controlled by modulating the concentrations of acrylamide and bis-acrylamide powder used in creating a gel. Care must be used when creating this type of gel, as acrylamide is a potent neurotoxin in its liquid and powdered forms. Traditional DNA sequencing techniques such as Maxam-Gilbert or Sanger methods used polyacrylamide gels to separate DNA fragments differing by a single base-pair in length so the sequence could be read. Most modern DNA separation methods now use agarose gels, except for particularly small DNA fragments. It is currently most often used in the field of immunology and protein analysis, often used to separate different proteins or isoforms of the same protein into separate bands. These can be transferred onto a nitrocellulose or PVDF membrane to be probed with antibodies and corresponding markers, such as in a western blot. Typically resolving gels are made in 6%, 8%, 10%, 12% or 15%. Stacking gel (5%) is poured on top of the resolving gel and a gel comb (which forms the wells and defines the lanes where proteins, sample buffer, and ladders will be placed) is inserted. The percentage chosen depends on the size of the protein that one wishes to identify or probe in the sample. The smaller the known weight, the higher the percentage that should be used. Changes in the buffer system of the gel can help to further resolve proteins of very small sizes.
1
Biochemistry
myo-Inositol trispyrophosphate (ITPP) is an inositol phosphate, a pyrophosphate, a drug candidate, and a putative performance-enhancing substance, which exerts its biological effects by increasing tissue oxygenation.
1
Biochemistry
In chemistry, a metallofullerene is a molecule composed of a metal atom trapped inside a fullerene cage. Simple metallofullerenes consist of a fullerene cage, typically , with one or two metal atoms trapped inside. Recently, research has produced metallofullerenes that enclose small clusters of atoms, such as , , and . The @ symbol in the formula indicates that the atom(s) are encapsulated inside the cage, rather than being chemically bonded to it. Fullerenes in a variety of sizes have been found to encapsulate metal atoms in this way.
0
Organic Chemistry
Arachidonic acid 5-hydroperoxide (5-hydroperoxyeicosatetraenoic acid, 5-HPETE) is an intermediate in the metabolism of arachidonic acid by the ALOX5 enzyme in humans or Alox5 enzyme in other mammals. The intermediate is then further metabolized to: a) leukotriene A4 which is then metabolized to the chemotactic factor for leukocytes, leukotriene B4, or to contractors of lung airways, leukotriene C4, leukotriene D4, and leukotriene E4; b) the leukocyte chemotactic factors, 5-hydroxyicosatetraenoic acid and 5-oxo-eicosatetraenoic acid; or c) the specialized pro-resolving mediators of inflammation, lipoxin A4 and lipoxin B4.
1
Biochemistry
One recent, successful business endeavor has been the introduction of AFPs into ice cream and yogurt products. This ingredient, labelled ice-structuring protein, has been approved by the Food and Drug Administration. The proteins are isolated from fish and replicated, on a larger scale, in genetically modified yeast. There is concern from organizations opposed to genetically modified organisms (GMOs) who believe that antifreeze proteins may cause inflammation. Intake of AFPs in diet is likely substantial in most northerly and temperate regions already. Given the known historic consumption of AFPs, it is safe to conclude their functional properties do not impart any toxicologic or allergenic effects in humans. As well, the transgenic process of ice structuring proteins production is widely used in society. Insulin and rennet are produced using this technology. The process does not impact the product; it merely makes production more efficient and prevents the death of fish that would otherwise be killed to extract the protein. Currently, Unilever incorporates AFPs into some of its American products, including some Popsicle ice pops and a new line of Breyers Light Double Churned ice cream bars. In ice cream, AFPs allow the production of very creamy, dense, reduced fat ice cream with fewer additives. They control ice crystal growth brought on by thawing on the loading dock or kitchen table, which reduces texture quality. In November 2009, the Proceedings of the National Academy of Sciences published the discovery of a molecule in an Alaskan beetle that behaves like AFPs, but is composed of saccharides and fatty acids. A 2010 study demonstrated the stability of superheated water ice crystals in an AFP solution, showing that while the proteins can inhibit freezing, they can also inhibit melting. In 2021, EPFL and Warwick scientists have found an artificial imitation of antifreeze proteins.
1
Biochemistry
Examples of heterogeneous mixtures are emulsions and foams. In most cases, the mixture consists of two main constituents. For an emulsion, these are immiscible fluids such as water and oil. For a foam, these are a solid and a fluid, or a liquid and a gas. On larger scales both constituents are present in any region of the mixture, and in a well-mixed mixture in the same or only slightly varying concentrations. On a microscopic scale, however, one of the constituents is absent in almost any sufficiently small region. (If such absence is common on macroscopic scales, the combination of the constituents is a dispersed medium, not a mixture.) One can distinguish different characteristics of heterogeneous mixtures by the presence or absence of continuum percolation of their constituents. For a foam, a distinction is made between reticulated foam in which one constituent forms a connected network through which the other can freely percolate, or a closed-cell foam in which one constituent is present as trapped in small cells whose walls are formed by the other constituents. A similar distinction is possible for emulsions. In many emulsions, one constituent is present in the form of isolated regions of typically a globular shape, dispersed throughout the other constituent. However, it is also possible each constituent forms a large, connected network. Such a mixture is then called bicontinuous.
7
Physical Chemistry
According to the kinetic theory of gases, the kinetic energy for a gas at a temperature is where is the mass of one molecule, is the root-mean-square speed of the molecules, and is the Boltzmann constant. The average molecular speed can be calculated from the Maxwell speed distribution as (or, equivalently, ). The rate at which a gas of molar mass effuses (typically expressed as the number of molecules passing through the hole per second) is then Here is the gas pressure difference across the barrier, is the area of the hole, is the Avogadro constant, is the gas constant and is the absolute temperature. Assuming the pressure difference between the two sides of the barrier is much smaller than , the average absolute pressure in the system (i.e. ), it is possible to express effusion flow as a volumetric flow rate as follows: or where is the volumetric flow rate of the gas, is the average pressure on either side of the orifice, and is the hole diameter.
7
Physical Chemistry
The presence of surface active elements such as oxygen and sulfur will have a large impact on the measurements obtained with this technique. Surface active elements will exist in larger concentrations at the surface than in the bulk of the liquid, meaning that the total levels of these elements must be carefully controlled to a very low level. For example, the presence of only 50 ppm sulphur in liquid iron will reduce the surface tension by approximately 20%.
7
Physical Chemistry
In addition to the role of the lactate shuttle in supplying NAD+ substrate for β-oxidation in the peroxisomes, the shuttle also regulates FFA mobilization by controlling plasma lactate levels. Research has demonstrated that lactate functions to inhibit lipolysis in fat cells through activation of an orphan G-protein couple receptor (GPR81) that acts as a lactate sensor, inhibiting lipolysis in response to lactate .
1
Biochemistry
In ionic curing processes, an ionic photoinitiator is used to activate the functional group of the oligomers that are going to participate in cross-linking. Typically photopolymerization is a very selective process and it is crucial that the polymerization takes place only where it is desired to do so. In order to satisfy this, liquid neat oligomer can be doped with either anionic or cationic photoinitiators that will initiate polymerization only when radiated with light. Monomers, or functional groups, employed in cationic photopolymerization include: styrenic compounds, vinyl ethers, N-vinyl carbazoles, lactones, lactams, cyclic ethers, cyclic acetals, and cyclic siloxanes. The majority of ionic photoinitiators fall under the cationic class; anionic photoinitiators are considerably less investigated. There are several classes of cationic initiators, including onium salts, organometallic compounds and pyridinium salts. As mentioned earlier, one of the drawbacks of the photoinitiators used for photopolymerization is that they tend to absorb in the short UV region. Photosensitizers, or chromophores, that absorb in a much longer wavelength region can be employed to excite the photoinitiators through an energy transfer. Other modifications to these types of systems are free radical assisted cationic polymerization. In this case, a free radical is formed from another species in solution that reacts with the photoinitiator in order to start polymerization. Although there are a diverse group of compounds activated by cationic photoinitiators, the compounds that find most industrial uses contain epoxides, oxetanes, and vinyl ethers. One of the advantages to using cationic photopolymerization is that once the polymerization has begun it is no longer sensitive to oxygen and does not require an inert atmosphere to perform well. :::M = Monomer
5
Photochemistry
A material's flash point is a metric of how easy it is to ignite the vapor of the material as it evaporates into the atmosphere. It is defined as the lowest material temperature required for fuel oils in the materials to begin to give off flammable vapors in the quantity high enough to support a flash of fire when ignited by an external source. A lower flash point indicates higher flammability. Materials with flash points below are regulated in the United States by OSHA as potential workplace hazards.
7
Physical Chemistry
When a superconductor is placed in a weak external magnetic field H, and cooled below its transition temperature, the magnetic field is ejected. The Meissner effect does not cause the field to be completely ejected but instead, the field penetrates the superconductor but only to a very small distance, characterized by a parameter λ, called the London penetration depth, decaying exponentially to zero within the bulk of the material. The Meissner effect is a defining characteristic of superconductivity. For most superconductors, the London penetration depth is on the order of 100 nm. The Meissner effect is sometimes confused with the kind of diamagnetism one would expect in a perfect electrical conductor: according to Lenzs law, when a changing' magnetic field is applied to a conductor, it will induce an electric current in the conductor that creates an opposing magnetic field. In a perfect conductor, an arbitrarily large current can be induced, and the resulting magnetic field exactly cancels the applied field. The Meissner effect is distinct from thisit is the spontaneous expulsion that occurs during transition to superconductivity. Suppose we have a material in its normal state, containing a constant internal magnetic field. When the material is cooled below the critical temperature, we would observe the abrupt expulsion of the internal magnetic field, which we would not expect based on Lenz's law. The Meissner effect was given a phenomenological explanation by the brothers Fritz and Heinz London, who showed that the electromagnetic free energy in a superconductor is minimized provided where H is the magnetic field and λ is the London penetration depth. This equation, which is known as the London equation, predicts that the magnetic field in a superconductor decays exponentially from whatever value it possesses at the surface. A superconductor with little or no magnetic field within it is said to be in the Meissner state. The Meissner state breaks down when the applied magnetic field is too large. Superconductors can be divided into two classes according to how this breakdown occurs. In Type I superconductors, superconductivity is abruptly destroyed when the strength of the applied field rises above a critical value H. Depending on the geometry of the sample, one may obtain an intermediate state consisting of a baroque pattern of regions of normal material carrying a magnetic field mixed with regions of superconducting material containing no field. In Type II superconductors, raising the applied field past a critical value H leads to a mixed state (also known as the vortex state) in which an increasing amount of magnetic flux penetrates the material, but there remains no resistance to the flow of electric current as long as the current is not too large. At a second critical field strength H, superconductivity is destroyed. The mixed state is actually caused by vortices in the electronic superfluid, sometimes called fluxons because the flux carried by these vortices is quantized. Most pure elemental superconductors, except niobium and carbon nanotubes, are Type I, while almost all impure and compound superconductors are Type II.
7
Physical Chemistry
Alternatively, Simpson uses: ; Uninervous: Central midrib with no lateral veins (microphyllous), seen in the non-seed bearing tracheophytes, such as horsetails ; Dichotomous: Veins successively branching into equally sized veins from a common point, forming a Y junction, fanning out. Amongst temperate woody plants, Ginkgo biloba is the only species exhibiting dichotomous venation. Also some pteridophytes (ferns). ; Parallel: Primary and secondary veins roughly parallel to each other, running the length of the leaf, often connected by short perpendicular links, rather than form networks. In some species, the parallel veins join at the base and apex, such as needle-type evergreens and grasses. Characteristic of monocotyledons, but exceptions include Arisaema, and as below, under netted. ; Netted (reticulate, pinnate): A prominent midvein with secondary veins branching off along both sides of it. The name derives from the ultimate veinlets which form an interconnecting net like pattern or network. (The primary and secondary venation may be referred to as pinnate, while the net like finer veins are referred to as netted or reticulate); most non-monocot angiosperms, exceptions including Calophyllum. Some monocots have reticulate venation, including Colocasia, Dioscorea and Smilax. However, these simplified systems allow for further division into multiple subtypes. Simpson, (and others) divides parallel and netted (and some use only these two terms for Angiosperms) on the basis of the number of primary veins (costa) as follows; ; Parallel: ; Netted (Reticulate): These complex systems are not used much in morphological descriptions of taxa, but have usefulness in plant identification, although criticized as being unduly burdened with jargon. An older, even simpler system, used in some flora uses only two categories, open and closed. * Open: Higher order veins have free endings among the cells and are more characteristic of non-monocotyledon angiosperms. They are more likely to be associated with leaf shapes that are toothed, lobed or compound. They may be subdivided as; ** Pinnate (feather-veined) leaves, with a main central vein or rib (midrib), from which the remainder of the vein system arises ** Palmate, in which three or more main ribs rise together at the base of the leaf, and diverge upward. ** Dichotomous, as in ferns, where the veins fork repeatedly * Closed: Higher order veins are connected in loops without ending freely among the cells. These tend to be in leaves with smooth outlines, and are characteristic of monocotyledons. ** They may be subdivided into whether the veins run parallel, as in grasses, or have other patterns.
5
Photochemistry
After collection, sperm must be processed for storage. According to the Sperm Bank of California, sperm banks and clinics can use the unwashed or wash method to process sperm samples. The wash method includes removing unwanted particles and adding buffer solutions to preserve viable sperm. However, this approach can contribute to further stress on the sperm cells and decrease the survival of sperm after freezing. The unwashed approach allows for more flexibility to freeze the semen sample and increases the number of sperm survival. One sample can produce 1–20 vials or straws, depending on the quantity of the ejaculate and whether the sample is washed or unwashed. Unwashed samples are used for intracervical insemination (ICI) treatments, and washed samples are used in intrauterine insemination (IUI) and for in-vitro fertilization (IVF) or assisted reproduction technologies (ART) procedures. A cryoprotectant semen extender is conducted if the semen sample is placed in the freezer for storage. Semen extenders play a key factor in protecting sperm sample from freeze and osmotic shock, oxidative stress, and cell injury due to the formation of ice crystal during frozen storage. The collection of semen is preserved by stabilizing the properties of the sperm cells such as the membrane, motility, and DNA integrity in order to create a sustainable viable environment. There are two common forms of medium for sperm cyropreservation, one containing of egg yolk from hens and glycerol, and the other containing just glycerol. One study compared media supplemented with egg yolk and media supplemented with soy lecithin, finding that there was no significance between sperm motility, morphology, chromatin decondensation, or binding between the two, indicating that soy lecithin may be a viable alternative to egg yolk.
1
Biochemistry