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The photons of a light beam have a characteristic energy, called photon energy, which is proportional to the frequency of the light. In the photoemission process, when an electron within some material absorbs the energy of a photon and acquires more energy than its binding energy, it is likely to be ejected. If the photon energy is too low, the electron is unable to escape the material. Since an increase in the intensity of low-frequency light will only increase the number of low-energy photons, this change in intensity will not create any single photon with enough energy to dislodge an electron. Moreover, the energy of the emitted electrons will not depend on the intensity of the incoming light of a given frequency, but only on the energy of the individual photons.
While free electrons can absorb any energy when irradiated as long as this is followed by an immediate re-emission, like in the Compton effect, in quantum systems all of the energy from one photon is absorbed—if the process is allowed by quantum mechanics—or none at all. Part of the acquired energy is used to liberate the electron from its atomic binding, and the rest contributes to the electron's kinetic energy as a free particle. Because electrons in a material occupy many different quantum states with different binding energies, and because they can sustain energy losses on their way out of the material, the emitted electrons will have a range of kinetic energies. The electrons from the highest occupied states will have the highest kinetic energy. In metals, those electrons will be emitted from the Fermi level.
When the photoelectron is emitted into a solid rather than into a vacuum, the term internal photoemission is often used, and emission into a vacuum is distinguished as external photoemission. | 0 | Theoretical and Fundamental Chemistry |
The idea of a quantum harmonic oscillator and its associated energy can apply to either an atom or a subatomic particle. In ordinary atomic physics, the zero-point energy is the energy associated with the ground state of the system. The professional physics literature tends to measure frequency, as denoted by above, using angular frequency, denoted with and defined by . This leads to a convention of writing the Planck constant with a bar through its top () to denote the quantity . In these terms, the most famous such example of zero-point energy is the above associated with the ground state of the quantum harmonic oscillator. In quantum mechanical terms, the zero-point energy is the expectation value of the Hamiltonian of the system in the ground state.
If more than one ground state exists, they are said to be degenerate. Many systems have degenerate ground states. Degeneracy occurs whenever there exists a unitary operator which acts non-trivially on a ground state and commutes with the Hamiltonian of the system.
According to the third law of thermodynamics, a system at absolute zero temperature exists in its ground state; thus, its entropy is determined by the degeneracy of the ground state. Many systems, such as a perfect crystal lattice, have a unique ground state and therefore have zero entropy at absolute zero. It is also possible for the highest excited state to have absolute zero temperature for systems that exhibit negative temperature.
The wave function of the ground state of a particle in a one-dimensional well is a half-period sine wave which goes to zero at the two edges of the well. The energy of the particle is given by:
where is the Planck constant, is the mass of the particle, is the energy state ( corresponds to the ground-state energy), and is the width of the well. | 0 | Theoretical and Fundamental Chemistry |
Frohring's father, William, a railroad engineer, was born in Bavaria and immigrated to the United States at 1 years old, while his mother, Martha, was born in Ohio to German emigrants. He was married to the former Gertrude Lewis, and had four children. He died of a heart attack at his home on Munn Road in Newbury, Ohio. | 0 | Theoretical and Fundamental Chemistry |
Hydroxylamine is a source of nitric oxide anion via a disproportionation:
: K[Ni(CN)] + 2NHOH + KOH → K[Ni(CN))NO] + NH + 2HO + KCN | 0 | Theoretical and Fundamental Chemistry |
Based on the Maxwellian behavior of the hydrogel and observations of erosion via surface plasmon resonance (SPR), the following data results for 3 common R-PEG types at their specified concentrations:
XKCY denotes X thousand daltons of molecular mass and Y carbon atoms.
These values can give us information on the degree of entanglement (or degree of cross linking, depending on what polymer is being considered). In general, higher degrees of entanglement leads to higher time required for the polymer to return to the undeformed state or relaxation times. | 0 | Theoretical and Fundamental Chemistry |
Carnobacterium pleistocenium is a recently discovered bacterium from the arctic part of Alaska. It was found in permafrost, seemingly frozen there for 32,000 years. Melting the ice, however, brought these extremophiles back to life. This is the first case of an organism "coming back to life" from ancient ice. These bacterial cells were discovered in a tunnel dug by the Army Corps of Engineers in the 1960s to allow scientists to study the permafrost in preparation for the construction of the Trans-Alaska pipeline system.
The discovery of this bacterium is of particular interest for NASA, for it may be possible for such life to exist in the permafrost of Mars or on the surface of Europa. It is also of interest for scientists investigating the potential for cryogenically freezing life forms to reduce the transportation costs (in terms of life support systems) that would be associated with long-duration space travel. | 1 | Applied and Interdisciplinary Chemistry |
Drying of hydrogels under controlled circumstances may yield xerogels and aerogels. A xerogel is a solid that retains significant porosity (15-50%) with a very small pore size (1–10 nm). In an aerogel, the porosity is somewhat higher and the pores are more than an order of magnitude larger, resulting in an ultra-low-density material with a low thermal conductivity and an almost translucent, smoke-like appearance. | 0 | Theoretical and Fundamental Chemistry |
In a laminar boundary layer, if the initial disturbance spectrum is nearly infinitesimal and random (with no discrete frequency peaks), the initial instability will occur as two-dimensional Tollmien–Schlichting waves, travelling in the mean flow direction if compressibility is not important. However, three-dimensionality soon appears as the Tollmien–Schlichting waves rather quickly begin to show variations.
There are known to be many paths from Tollmien–Schlichting waves to turbulence, and many of them are explained by the non-linear theories of flow instability. | 1 | Applied and Interdisciplinary Chemistry |
Protein synthesis within chloroplasts relies on an RNA polymerase coded by the chloroplasts own genome, which is related to RNA polymerases found in bacteria. Chloroplasts also contain a mysterious second RNA polymerase that is encoded by the plants nuclear genome. The two RNA polymerases may recognize and bind to different kinds of promoters within the chloroplast genome. The ribosomes in chloroplasts are similar to bacterial ribosomes. | 0 | Theoretical and Fundamental Chemistry |
Bronchodilators, antitussives, mucolytics, decongestants, inhaled and systemic corticosteroids, beta2-adrenergic agonists, anticholinergics, mast cell stabilizers, leukotriene antagonists. | 1 | Applied and Interdisciplinary Chemistry |
The denaturing of proteins by an aqueous solution containing many types of ions is more complicated as all the ions can act, according to their Hofmeister activity, i.e., a fractional number specifying the position of the ion in the series (given previously) in terms of its relative efficiency in denaturing a reference protein.
At high salt concentrations lysozyme protein aggregation obeys the Hofmeister series originally observed by Hofmeister in the 1870s, but at low salt concentrations electrostatic interactions rather than ion dispersion forces affect protein stability resulting in the series being reversed. However, at high concentrations of salt, the solubility of the proteins drop sharply and proteins can precipitate out, referred to as "salting out".
Ion binding to carbolylic surface groups of macromolecules can either follow the Hofmeister series or the reversed Hofmeister series depending on the pH.
The concept of Hofmeister ionicity I has been invoked by Dharma-wardana et al. where it is proposed to define I as a sum over all ionic species, of the product of the ionic concentration (mole fraction) and a fractional number specifying the "Hofmeister strength" of the ion in denaturing a given reference protein. The concept of ionicity (as a measure of the Hofmeister strength) used here has to be distinguished from ionic strength as used in electrochemistry, and also from its use in the theory of solid semiconductors.
The stability of metal ion protein binding, which affects the properties of metal cofactor-containing proteins in solution, is reflected by the Irving-Williams series. | 0 | Theoretical and Fundamental Chemistry |
Beta radiation consists of particles (high-speed electrons) given off by some fallout. Most beta particles cannot penetrate more than about of air or about of water, wood, or human body tissue; or a sheet of aluminum foil. Avoiding direct exposure with fallout particles will prevent most injuries from beta radiation.
The primary dangers associated with beta radiation are internal exposure from ingested fallout particles and beta burns from fallout particles no more than a few days old. Beta burns can result from contact with highly radioactive particles on bare skin; ordinary clothing separating fresh fallout particles from the skin can provide significant shielding. | 0 | Theoretical and Fundamental Chemistry |
The thermodynamic equilibrium constant, K, for the equilibrium
can be defined as
where {ML} is the activity of the chemical species ML etc. K is dimensionless since activity is dimensionless. Activities of the products are placed in the numerator, activities of the reactants are placed in the denominator. See activity coefficient for a derivation of this expression.
Since activity is the product of concentration and activity coefficient (γ) the definition could also be written as
where [ML] represents the concentration of ML and Γ is a quotient of activity coefficients. This expression can be generalized as
To avoid the complications involved in using activities, stability constants are determined, where possible, in a medium consisting of a solution of a background electrolyte at high ionic strength, that is, under conditions in which Γ can be assumed to be always constant. For example, the medium might be a solution of 0.1 mol dm sodium nitrate or 3 mol dm sodium perchlorate. When Γ is constant it may be ignored and the general expression in theory, above, is obtained.
All published stability constant values refer to the specific ionic medium used in their determination and different values are obtained with different conditions, as illustrated for the complex CuL (L = glycinate). Furthermore, stability constant values depend on the specific electrolyte used as the value of Γ is different for different electrolytes, even at the same ionic strength. There does not need to be any chemical interaction between the species in equilibrium and the background electrolyte, but such interactions might occur in particular cases. For example, phosphates form weak complexes with alkali metals, so, when determining stability constants involving phosphates, such as ATP, the background electrolyte used will be, for example, a tetralkylammonium salt. Another example involves iron(III) which forms weak complexes with halide and other anions, but not with perchlorate ions.
When published constants refer to an ionic strength other than the one required for a particular application, they may be adjusted by means of specific ion theory (SIT) and other theories. | 0 | Theoretical and Fundamental Chemistry |
There are a number of software tools that can directly compute elasticities and control coefficients:
* COPASI (GUI)
* PySCeS (Python)
* SBW (GUI)
* libroadrunner (Python)
* VCell | 1 | Applied and Interdisciplinary Chemistry |
Abundances of a particular isotope in a substance are usually given relative to some reference material, as a delta in parts per thousand (‰) from the reference. For example, the ratio of deuterium (H) to hydrogen-1 in a substance x may be given as
where denotes the absolute concentration in x.
In 1961, pursuing a standard for measuring and reporting deuterium and oxygen-18 concentrations, Harmon Craig of the Scripps Institution of Oceanography in San Diego, California, proposed an abstract water standard. He based the proportions on his measurements of samples taken by of ocean waters around the world. Approximating an average of their measurements, Craig defined his "standard mean ocean water" (SMOW) relative to a water sample held in the United States' National Bureau of Standards called NBS-1 (sampled from the Potomac River). In particular, SMOW had the following parameters relative to NBS-1:
* δ H = 50‰, i.e., an enrichment of 5%;
* δ O = 8‰, i.e., an enrichment of 0.8%.
Later, researchers at the California Institute of Technology defined another abstract reference, also called "SMOW", for oxygen-18 concentrations, such that a sample of Potsdam Sandstone in their possession satisfied .
To resolve the confusion, November 1966 meeting of the Vienna-based International Atomic Energy Agency (IAEA) recommended the preparation of two water isotopic standards: Vienna SMOW (VSMOW; initially just "SMOW" but later disambiguated) and Standard Light Antarctic Precipitation (SLAP). Craig prepared VSMOW by mixing distilled Pacific Ocean water with small amounts of other waters. VSMOW was intended to match the SMOW standard as closely as possible. Craig's measurements found an identical O concentration and a 0.2‰ lower H concentration. The SLAP standard was created from a melted firn sample from Plateau Station in Antarctica. A standard with oxygen-18 and deuterium concentrations between that of VSMOW and SLAP, called Greenland Ice Sheet Precipitation (GISP), was also prepared. The IAEA began distributing samples in 1968, and compiled analyses of VSMOW and SLAP from 45 laboratories around the world. The VSMOW sample was stored in a stainless-steel container under nitrogen and was transferred to glass ampoules in 1977.
The deuterium and oxygen-18 concentrations in VSMOW are close to the upper end of naturally occurring materials, and the concentrations in SLAP are close to the lower end. Due to confusion over multiple water standards, the Commission on Isotopic Abundances and Atomic Weights recommended in 1994 that all future isotopic measurements of oxygen-18 (O) and deuterium (H) be reported relative to VSMOW, on a scale such that the of SLAP is −55.5‰ and the of SLAP is −428‰, relative to VSMOW. Therefore, SLAP is defined to contain 94.45% the oxygen-18 concentration and 57.2% the deuterium concentration of VSMOW. Using a scale with two defined samples improves comparison of results between laboratories.
In December 1996, because of a dwindling supply of VSMOW, the IAEA decided to create a replacement standard, VSMOW2. Published in 1999, it contains a nearly identical isotopic mixture. About 300 liters was prepared from a mixture of distilled waters, from Lake Bracciano in Italy, the Sea of Galilee in Israel, and a well in Egypt, in proportions chosen to reach VSMOW isotopic ratios. The IAEA also published a successor to SLAP, called SLAP2, derived from melted water from four Antarctic drilling sites. Deviations of O, and O in the new standards from the old standards are zero within the error of measurement. There is a small but measurable deviation of H concentration in SLAP2 from SLAP— is defined to be −427.5‰ instead of −428‰—but not in VSMOW2 from VSMOW. The IAEA recommends that measurements still be reported on the VSMOW–SLAP scale.
The older two standards are now kept at the IAEA and no longer sold. | 0 | Theoretical and Fundamental Chemistry |
A multidimensional population translation experiment was utilized to determine the detection limits of an ARS device, Populations with small multidimensional separation, in this case aspirin and ibuprofen, were used to determine that tablets with a 0.08 mm difference in thickness, 0.0046 g mass difference, and a difference in density of 0.01658 g/mL were not separable by ARS. Using vitamin C and acetaminophen for the largest multidimensional separation, tablets with a thickness difference of 0.27 mm, 0.0756 g mass difference, and 0.01157 g/mL density difference in density were inseparable. Experimentally the dynamic range of ARS is a factor of ten. | 0 | Theoretical and Fundamental Chemistry |
The logarithmic law of the wall is a self similar solution for the mean velocity parallel to the wall, and is valid for flows at high Reynolds numbers — in an overlap region with approximately constant shear stress and far enough from the wall for (direct) viscous effects to be negligible:
: with and
where
From experiments, the von Kármán constant is found to be and for a smooth wall.
With dimensions, the logarithmic law of the wall can be written as:
where y is the distance from the boundary at which the idealized velocity given by the law of the wall goes to zero. This is necessarily nonzero because the turbulent velocity profile defined by the law of the wall does not apply to the laminar sublayer. The distance from the wall at which it reaches zero is determined by comparing the thickness of the laminar sublayer with the roughness of the surface over which it is flowing. For a near-wall laminar sublayer of thickness and a characteristic roughness length-scale ,
Intuitively, this means that if the roughness elements are hidden within the laminar sublayer, they have a much different effect on the turbulent law of the wall velocity profile than if they are sticking out into the main part of the flow.
This is also often more formally formulated in terms of a boundary Reynolds number, , where
The flow is hydraulically smooth for , hydraulically rough for , and transitional for intermediate values.
Values for are given by:
Intermediate values are generally given by the empirically derived Nikuradse diagram, though analytical methods for solving for this range have also been proposed.
For channels with a granular boundary, such as natural river systems,
where is the average diameter of the 84th largest percentile of the grains of the bed material. | 1 | Applied and Interdisciplinary Chemistry |
In spectroscopy, an isosbestic point is a specific wavelength, wavenumber or frequency at which the total absorbance of a sample does not change during a chemical reaction or a physical change of the sample. The word derives from two Greek words: "iso", meaning "equal", and "sbestos", meaning "extinguishable". | 0 | Theoretical and Fundamental Chemistry |
Nuclei are bound together by the residual strong force (nuclear force). The residual strong force is a minor residuum of the strong interaction which binds quarks together to form protons and neutrons. This force is much weaker between neutrons and protons because it is mostly neutralized within them, in the same way that electromagnetic forces between neutral atoms (such as van der Waals forces that act between two inert gas atoms) are much weaker than the electromagnetic forces that hold the parts of the atoms together internally (for example, the forces that hold the electrons in an inert gas atom bound to its nucleus).
The nuclear force is highly attractive at the distance of typical nucleon separation, and this overwhelms the repulsion between protons due to the electromagnetic force, thus allowing nuclei to exist. However, the residual strong force has a limited range because it decays quickly with distance (see Yukawa potential); thus only nuclei smaller than a certain size can be completely stable. The largest known completely stable nucleus (i.e. stable to alpha, beta, and gamma decay) is lead-208 which contains a total of 208 nucleons (126 neutrons and 82 protons). Nuclei larger than this maximum are unstable and tend to be increasingly short-lived with larger numbers of nucleons. However, bismuth-209 is also stable to beta decay and has the longest half-life to alpha decay of any known isotope, estimated at a billion times longer than the age of the universe.
The residual strong force is effective over a very short range (usually only a few femtometres (fm); roughly one or two nucleon diameters) and causes an attraction between any pair of nucleons. For example, between a proton and a neutron to form a deuteron [NP], and also between protons and protons, and neutrons and neutrons. | 0 | Theoretical and Fundamental Chemistry |
The alpha effect refers to the increased nucleophilicity of an atom due to the presence of an adjacent (alpha) atom with lone pair electrons. This first atom does not necessarily exhibit increased basicity compared with a similar atom without an adjacent electron-donating atom, resulting in a deviation from the classical Brønsted-type reactivity-basicity relationship. In other words, the alpha effect refers to nucleophiles presenting higher nucleophilicity than the predicted value obtained from the Brønsted basicity. The representative examples would be high nucleophilicities of hydroperoxide (HO) and hydrazine (NH). The effect is now well established with numerous examples and became an important concept in mechanistic chemistry and biochemistry. However, the origin of the effect is still controversial without a clear winner. | 0 | Theoretical and Fundamental Chemistry |
When a crystal is composed of crystallites with varying lattice orientation, topographic contrast arises: In plane-wave topography, only selected crystallites will be in diffracting position, thus yielding diffracted intensity only in some parts of the image. Upon sample rotation, these will disappear, and other crystallites will appear in the new topograph as strongly diffracting. In white-beam topography, all misoriented crystallites will be diffracting simultaneously (each at a different wavelength). However, the exit angles of the respective diffracted beams will differ, leading to overlapping regions of enhanced intensity as well as to shadows in the image, thus again giving rise to contrast.
While in the case of tilted crystallites, domain walls, grain boundaries etc. orientation contrast occurs on a macroscopic scale, it can also be generated more locally around defects, e.g. due to curved lattice planes around a dislocation core. | 0 | Theoretical and Fundamental Chemistry |
Sensitizers absorb light to give redox-active excited states. For many metal-based sensitizers, excitation is realized as a metal-to-ligand charge transfer, whereby an electron moves from the metal (e.g., a d orbital) to an orbital localized on the ligands (e.g. the π* orbital of an aromatic ligand). The initial excited electronic state relaxes to the lowest energy singlet excited state through internal conversion, a process where energy is dissipated as vibrational energy rather than as electromagnetic radiation. This singlet excited state can relax further by two distinct processes: the catalyst may fluoresce, radiating a photon and returning to the singlet ground state, or it can move to the lowest energy triplet excited state (a state where two unpaired electrons have the same spin) by a second non-radiative process termed intersystem crossing.
Direct relaxation of the excited triplet to the ground state, termed phosphorescence, requires both emission of a photon and inversion of the spin of the excited electron. This pathway is slow because it is spin-forbidden so the triplet excited state has a substantial average lifetime. For the common photosensitizer, tris-(2,2’-bipyridyl)ruthenium (abbreviated as [Ru(bipy)] or [Ru(bpy)]), the lifetime of the triplet excited state is approximately 1100 ns. This lifetime is sufficient for other relaxation pathways (specifically, electron-transfer pathways) to occur before decay of the catalyst to its ground state.
The long-lived triplet excited state accessible by photoexcitation is both a more potent reducing agent and a more potent oxidizing agent than the ground state of the catalyst. Since sensitizer is coordinatively saturated, electron transfer must occur by an outer sphere process, where the electron tunnels between the catalyst and the substrate. | 0 | Theoretical and Fundamental Chemistry |
Aerosol partitioning theory governs condensation on and evaporation from an aerosol surface, respectively. Condensation of mass causes the mode of the particle-size distributions of the aerosol to increase; conversely, evaporation causes the mode to decrease. Nucleation is the process of forming aerosol mass from the condensation of a gaseous precursor, specifically a vapor. Net condensation of the vapor requires supersaturation, a partial pressure greater than its vapor pressure. This can happen for three reasons:
# Lowering the temperature of the system lowers the vapor pressure.
# Chemical reactions may increase the partial pressure of a gas or lower its vapor pressure.
# The addition of additional vapor to the system may lower the equilibrium vapor pressure according to Raoult's law.
There are two types of nucleation processes. Gases preferentially condense onto surfaces of pre-existing aerosol particles, known as heterogeneous nucleation. This process causes the diameter at the mode of particle-size distribution to increase with constant number concentration. With sufficiently high supersaturation and no suitable surfaces, particles may condense in the absence of a pre-existing surface, known as homogeneous nucleation. This results in the addition of very small, rapidly growing particles to the particle-size distribution. | 0 | Theoretical and Fundamental Chemistry |
Saturated vapor pressure, <br>
Actual vapor pressure,
: here e[T] is vapor pressure as a function of temperature, T.
::T = the dewpoint temperature at which water condenses.
::T = the temperature of a wet thermometer bulb from which water can evaporate to air.
::T = the temperature of a dry thermometer bulb in air. | 0 | Theoretical and Fundamental Chemistry |
Exposure to pyridine would normally lead to its inhalation and absorption in the lungs and gastrointestinal tract, where it either remains unchanged or is metabolized. The major products of pyridine metabolism are N-methylpyridiniumhydroxide, which are formed by N-methyltransferases (e.g., pyridine N-methyltransferase), as well as pyridine N-oxide, and 2-, 3-, and 4-hydroxypyridine, which are generated by the action of monooxygenase. In humans, pyridine is metabolized only into N-methylpyridiniumhydroxide. | 0 | Theoretical and Fundamental Chemistry |
Sulfate may be rapidly and easily titrated thermometrically using standard solutions of Ba as titrant. Industrially, the procedure has been applied to the determination of sulfate in brine (including electrolysis brines), in nickel refining solutions and particularly for sulfate in wet process phosphoric acid, where it has proven to be quite popular. The procedure can also be used to assist in the analysis of complex acid mixtures containing sulfuric acid where resorting to titration in non-aqueous media is not feasible.
The reaction enthalpy for the formation of barium sulfate is a modest −18.8 kJ/mol. This can place a restriction on the lower limit of sulfate in a sample which can be analyzed. | 0 | Theoretical and Fundamental Chemistry |
Typical therapeutic doses of I-131 are between 2220 and 7400 megabecquerels (MBq). Because of this high radioactivity and because the exposure of stomach tissue to beta radiation would be high near an undissolved capsule, I-131 is sometimes administered to human patients in a small amount of liquid. Administration of this liquid form is usually by straw which is used to slowly and carefully suck up the liquid from a shielded container. For administration to animals (for example, cats with hyperthyroidism), for practical reasons the isotope must be administered by injection. European guidelines recommend administration of a capsule, due to "greater ease to the patient and the superior radiation protection for caregivers". | 0 | Theoretical and Fundamental Chemistry |
Again, define and to be conjugate pairs, and the to be the natural variables of some potential . We may take the "cross differentials" of the state equations, which obey the following relationship:
From these we get the Maxwell relations. There will be of them for each potential giving a total of equations in all. If we restrict ourselves the , , ,
Using the equations of state involving the chemical potential we get equations such as:
and using the other potentials we can get equations such as: | 0 | Theoretical and Fundamental Chemistry |
Commercially available salts thiamine chloride and thiamine nitrate are produced at scales of thousands of tons annually by chemistry-based manufacturing processes in Europe and Asia. These salts are supplied for formulations for supplementation of human diet and as feed additives for cattle, swine, poultry and fish.
Research for potential biotechnology-based production of thiamine has resulted in patent applications claiming fermentation using recombinant microorganisms modified to deregulate feedback inhibition and allow release of thiamine forms to the media as demonstrated at small scale.
Thiamine forms and their bio-precursors are produced at very large scale in biological matrices such as yeast, grains, plants and meats widely consumed as food and feed. Research into genetic modification of plants. has led to higher levels of thiamine in foodstuffs, such as rice. Use of thiamine forms and their bio-precursors by various means such as seed coating or soil and foliar fertilization to improve plant growth and properties are being investigated. | 1 | Applied and Interdisciplinary Chemistry |
While several experiments yielded negative results, in the 1980s, John Goodkind discovered the first anomaly in a solid by using ultrasound. Inspired by his observation, in 2004 Eun-Seong Kim and Moses Chan at Pennsylvania State University saw phenomena which were interpreted as supersolid behavior. Specifically, they observed a non-classical rotational moment of inertia of a torsional oscillator. This observation could not be explained by classical models but was consistent with superfluid-like behavior of a small percentage of the helium atoms contained within the oscillator.
This observation triggered a large number of follow-up studies to reveal the role played by crystal defects or helium-3 impurities. Further experimentation has cast some doubt on the existence of a true supersolid in helium. Most importantly, it was shown that the observed phenomena could be largely explained due to changes in the elastic properties of the helium. In 2012, Chan repeated his original experiments with a new apparatus that was designed to eliminate any such contributions. In this experiment, Chan and his coauthors found no evidence of supersolidity. | 0 | Theoretical and Fundamental Chemistry |
Inosine monophosphate is synthesized on a pre-existing ribose-phosphate through a complex pathway (as shown in the figure on the right). The source of the carbon and nitrogen atoms of the purine ring, 5 and 4 respectively, come from multiple sources. The amino acid glycine contributes all its carbon (2) and nitrogen (1) atoms, with additional nitrogen atoms from glutamine (2) and aspartic acid (1), and additional carbon atoms from formyl groups (2), which are transferred from the coenzyme tetrahydrofolate as 10-formyltetrahydrofolate, and a carbon atom from bicarbonate (1). Formyl groups build carbon-2 and carbon-8 in the purine ring system, which are the ones acting as bridges between two nitrogen atoms.
A key regulatory step is the production of 5-phospho-α--ribosyl 1-pyrophosphate (PRPP) by ribose phosphate pyrophosphokinase, which is activated by inorganic phosphate and inactivated by purine ribonucleotides. It is not the committed step to purine synthesis because PRPP is also used in pyrimidine synthesis and salvage pathways.
The first committed step is the reaction of PRPP, glutamine and water to 5'-phosphoribosylamine (PRA), glutamate, and pyrophosphate - catalyzed by amidophosphoribosyltransferase, which is activated by PRPP and inhibited by AMP, GMP and IMP.
:PRPP + L-Glutamine + HO → PRA + L-Glutamate + PPi
In the second step react PRA, glycine and ATP to create GAR, ADP, and pyrophosphate - catalyzed by phosphoribosylamine—glycine ligase (GAR synthetase). Due to the chemical lability of PRA, which has a half-life of 38 seconds at PH 7.5 and 37 °C, researchers have suggested that the compound is channeled from amidophosphoribosyltransferase to GAR synthetase in vivo.
:PRA + Glycine + ATP → GAR + ADP + Pi
The third is catalyzed by phosphoribosylglycinamide formyltransferase.
:GAR + fTHF → fGAR + THF
The fourth is catalyzed by phosphoribosylformylglycinamidine synthase.
:fGAR + L-Glutamine + ATP → fGAM + L-Glutamate + ADP + Pi
The fifth is catalyzed by AIR synthetase (FGAM cyclase).
:fGAM + ATP → AIR + ADP + Pi + HO
The sixth is catalyzed by phosphoribosylaminoimidazole carboxylase.
:AIR + CO → CAIR + 2H+
The seventh is catalyzed by phosphoribosylaminoimidazolesuccinocarboxamide synthase.
:CAIR + L-Aspartate + ATP → SAICAR + ADP + Pi
The eight is catalyzed by adenylosuccinate lyase.
:SAICAR → AICAR + Fumarate
The products AICAR and fumarate move on to two different pathways. AICAR serves as the reactant for the ninth step, while fumarate is transported to the citric acid cycle which can then skip the carbon dioxide evolution steps to produce malate. The conversion of fumarate to malate is catalyzed by fumarase. In this way, fumarate connects purine synthesis to the citric acid cycle.
The ninth is catalyzed by phosphoribosylaminoimidazolecarboxamide formyltransferase.
:AICAR + fTHF → FAICAR + THF
The last step is catalyzed by Inosine monophosphate synthase.
:FAICAR → IMP + HO
In eukaryotes the second, third, and fifth step are catalyzed by trifunctional purine biosynthetic protein adenosine-3, which is encoded by the GART gene.
Both ninth and tenth step are accomplished by a single protein named Bifunctional purine biosynthesis protein PURH, encoded by the ATIC gene. | 1 | Applied and Interdisciplinary Chemistry |
The MEMO model (version 6.2) is a Eulerian non-hydrostatic prognostic mesoscale model for wind-flow simulation. It was developed by the Aristotle University of Thessaloniki in collaboration with the Universität Karlsruhe. The MEMO Model together with the photochemical dispersion model MARS are the two core models of the European zooming model (EZM). This model belongs to the family of models designed for describing atmospheric transport phenomena in the local-to-regional scale, frequently referred to as mesoscale air pollution models. | 1 | Applied and Interdisciplinary Chemistry |
Peroxins (or peroxisomal/peroxisome biogenesis factors) represent several protein families found in peroxisomes. Deficiencies are associated with several peroxisomal disorders. Peroxins serve several functions including the recognition of cytoplasmic proteins that contain peroxisomal targeting signals (PTS) that tag them for transport by peroxisomal proteins to the peroxisome. Peroxins are structurally diverse and have been classified to different protein families. Some of them were predicted to be single-pass transmembrane proteins, for example Peroxisomal biogenesis factor 11. | 1 | Applied and Interdisciplinary Chemistry |
Practically speaking, diverse methods may be used to reference chemical shifts in an NMR experiment, which can be subdivided into indirect and direct referencing methods. Indirect referencing uses a channel other than the one of interest to adjust chemical shift scale correctly, i.e. the solvent signal in the deuterium (lock) channel can be used to reference the a H NMR spectrum. Both indirect and direct referencing can be done as three different procedures:
# Internal referencing, where the reference compound is added directly to the system under study." In this common practice, users adjust residual solvent signals of H or C NMR spectra with calibrated spectral tables. If substances other than the solvent itself are used for internal referencing, the sample has to be combined with the reference compound, which may affect the chemical shifts.
# External referencing, involving sample and reference contained separately in coaxial cylindrical tubes." With this procedure, the reference signal is still visible in the spectrum of interest, although the reference and the sample are physically separated by a glass wall. Magnetic susceptibility differences between the sample and the reference phase need to be corrected theoretically, which lowers the practicality of this procedure.
# Substitution method: The use of separate cylindrical tubes for the sample and the reference compound, with (in principle) spectra recorded individually for each." Similar to external referencing, this method allows referencing without sample contamination. If field/frequency locking via the H signal of the deuterated solvent is used and the solvents of reference and analyte are the same, the use of this methods is straightforward. Problems may arise if different solvents are used for the reference compound and the sample as (just like for external referencing) magnetic susceptibility differences need to be corrected theoretically. If this method is used without field/frequency locking, shimming procedures between the sample and the reference need to be avoided as they change the applied magnetic field (and thereby influence the chemical shift).
Modern NMR spectrometers commonly make use of the absolute scale, which defines the H signal of TMS as 0 ppm in proton NMR and the center frequencies of all other nuclei as percentage of the TMS resonance frequency:
The use of the deuterium (lock) channel, so the H signal of the deuterated solvent, and the Ξ value of the absolute scale is a form of internal referencing and is particularly useful in heteronuclear NMR spectroscopy as local reference compounds may not be always be available or easily used (i.e. liquid NH for N NMR spectroscopy). This system, however, relies on accurately determined H NMR chemical shifts enlisted in the spectrometer software and correctly determined Ξ values by IUPAC. A recent study for F NMR spectroscopy revealed that the use of the absolute scale and lock-based internal referencing led to errors in chemical shifts. These may be negated by inclusion of calibrated reference compounds. | 0 | Theoretical and Fundamental Chemistry |
Until recently, the antibacterial activity of essential oils has been primarily evaluated through direct contact methods between the pathogen and the antimicrobial agent through diffusion and dilution methods, however the role of essential oils in the vapour phase as antimicrobial agents is gaining increasing significance.
This method was developed on the premise that essential oil vapours exert critical biological activity. These methods offer rapid screening protocols for the antimicrobial assessment of plant essential oils. It has been suggested that essential oils in the vapour phase possess the greatest degree of antimicrobial activity since the active constituents are highly volatile in nature and thus, the vapour is therefore the contributing attribute for its biological activity. Each individual constituent has differing volatility, therefore when the mixtures are introduced into a free, non-saturated state in a closed micro-environment; the volatile constituents begin to disperse at differing rates in the vapour phase within the headspace according to their degree of volatility until they reach equilibrium.
Preliminary research involving the essential oils of citronella yielded promising results when tested against a selection of Gram-positive bacteria and Gram-negative bacteria. The use of such extracts can be explored especially in the development of cost-effective treatments of respiratory illness, specifically of those caused by bacterial or fungal infection. Preliminary tests exhibit complete inhibition of the growth of certain bacterial strains. | 1 | Applied and Interdisciplinary Chemistry |
In acid catalysis and base catalysis, a chemical reaction is catalyzed by an acid or a base. By Brønsted–Lowry acid–base theory, the acid is the proton (hydrogen ion, H) donor and the base is the proton acceptor. Typical reactions catalyzed by proton transfer are esterifications and aldol reactions. In these reactions, the conjugate acid of the carbonyl group is a better electrophile than the neutral carbonyl group itself. Depending on the chemical species that act as the acid or base, catalytic mechanisms can be classified as either specific catalysis and general catalysis. Many enzymes operate by general catalysis. | 0 | Theoretical and Fundamental Chemistry |
*Vorobiev E., Lebovka N., (2008). Electrotechnologies for Extraction from Food Plants and Biomaterials, . | 0 | Theoretical and Fundamental Chemistry |
Assuming a three-dimensional Bravais lattice and labelling each lattice vector (a vector indicating a lattice point) by the subscript as 3-tuple of integers,
: where
where is the set of integers and is a primitive translation vector or shortly primitive vector. Taking a function where is a position vector from the origin to any position, if follows the periodicity of this lattice, e.g. the function describing the electronic density in an atomic crystal, it is useful to write as a multi-dimensional Fourier series
where now the subscript , so this is a triple sum.
As follows the periodicity of the lattice, translating by any lattice vector we get the same value, hence
Expressing the above instead in terms of their Fourier series we have
Because equality of two Fourier series implies equality of their coefficients, , which only holds when
: where
Mathematically, the reciprocal lattice is the set of all vectors , that are wavevectors of plane waves in the Fourier series of a spatial function whose periodicity is the same as that of a direct lattice as the set of all direct lattice point position vectors , and satisfy this equality for all . Each plane wave in the Fourier series has the same phase (actually can be differed by a multiple of ) at all the lattice point .
As shown in the section multi-dimensional Fourier series, can be chosen in the form of where . With this form, the reciprocal lattice as the set of all wavevectors for the Fourier series of a spatial function which periodicity follows , is itself a Bravais lattice as it is formed by integer combinations of its own primitive translation vectors , and the reciprocal of the reciprocal lattice is the original lattice, which reveals the Pontryagin duality of their respective vector spaces. (There may be other form of . Any valid form of results in the same reciprocal lattice.) | 0 | Theoretical and Fundamental Chemistry |
Single stranded breaks (SSBs) can severely threaten genetic stability and cell survival if not quickly and properly repaired, so cells have developed fast and efficient SSB repair (SSBR) mechanisms. While global SSBR systems extract SSBs throughout the genome and during interphase, S-phase specific SSBR processes work together with homologous recombination at the replication forks. | 1 | Applied and Interdisciplinary Chemistry |
Following hit confirmation, several compound clusters will be chosen according to their characteristics in the previously defined tests. An Ideal compound cluster will contain members that possess:
* high affinity towards the target (less than 1 μM)
* selectivity versus other targets
* significant efficacy in a cellular assay
* druglikeness (moderate molecular weight and lipophilicity usually estimated as ClogP). Affinity, molecular weight and lipophilicity can be linked in single parameter such as ligand efficiency and lipophilic efficiency.
* low to moderate binding to human serum albumin
* low interference with P450 enzymes and P-glycoproteins
* low cytotoxicity
* metabolic stability
* high cell membrane permeability
* sufficient water solubility (above 10 μM)
* chemical stability
* synthetic tractability
* patentability
The project team will usually select between three and six compound series to be further explored. The next step will allow the testing of analogous compounds to determine a quantitative structure-activity relationship (QSAR). Analogs can be quickly selected from an internal library or purchased from commercially available sources ("SAR by catalog" or "SAR by purchase"). Medicinal chemists will also start synthesizing related compounds using different methods such as combinatorial chemistry, high-throughput chemistry, or more classical organic chemistry synthesis. | 1 | Applied and Interdisciplinary Chemistry |
All atoms that are not carbon or hydrogen are signified by their chemical symbol, for instance Cl for chlorine, O for oxygen, Na for sodium, and so forth. In the context of organic chemistry, these atoms are commonly known as heteroatoms (the prefix hetero- comes from Greek ἕτερος héteros, meaning "other").
Any hydrogen atoms bonded to heteroatoms are drawn explicitly. In ethanol, CHOH, for instance, the hydrogen atom bonded to oxygen is denoted by the symbol H, whereas the hydrogen atoms which are bonded to carbon atoms are not shown directly.
Lines representing heteroatom-hydrogen bonds are usually omitted for clarity and compactness, so a functional group like the hydroxyl group is most often written −OH instead of −O−H. These bonds are sometimes drawn out in full in order to accentuate their presence when they participate in reaction mechanisms.
Shown below for comparison are a skeletal formula (top), its Lewis structure (middle) and its ball-and-stick model (bottom) of the actual 3D structure of the ethanol molecule in the gas phase, as determined by microwave spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
Özergin completed a B.S. (1987) and M.S. (1989) in chemical engineering at Boğaziçi University. She earned a Ph.D. in chemical engineering at University of Manchester in 1992. Özergin researched Streptomyces coelicolor antibiotic production and bioreactors. Her dissertation was titled Study of antibiotic synthesis by free and immobilised streptomyces coelicolor a3(2). Özergin's doctoral advisor was . | 1 | Applied and Interdisciplinary Chemistry |
Pheromones are used in the detection of oestrus in sows. Boar pheromones are sprayed into the sty, and those sows that exhibit sexual arousal are known to be currently available for breeding. | 1 | Applied and Interdisciplinary Chemistry |
After the molecules travel the length of the column, pass through the transfer line and enter into the mass spectrometer they are ionized by various methods with typically only one method being used at any given time. Once the sample is fragmented it will then be detected, usually by an electron multiplier, which essentially turns the ionized mass fragment into an electrical signal that is then detected.
The ionization technique chosen is independent of using full scan or SIM. | 0 | Theoretical and Fundamental Chemistry |
Beauty standards varied by tribes. Cosmetics was typically describing an individuals social class. These tribes tend to have the product on their bodies in addition to their face. In Colombia, cosmetic products used oil or petroleum with various colors for the face and vermillion for the body. More color indicates the woman of higher class. For Nicaragua, the arms were painted on the arm with a mixture consisting of wool and the individuals blood. Like the Colombian women, the petroleum is used with the exception of the breasts to prevent interference with child development.
The Maya utilized the color red to represent social class and also used the color in funeral processes. The pigment was produced with mercury, lead, and arsenic. Other products to make the red color includes animals and plants. These items helped create more variety of reds with various tones, intensity, and sheen. Different shades of red determine a persons social status as red was represented luxury. Other colors in Maya society were blue and green made with Indigofera', malachite, azurite, veszelyite, and copper-containing minerals. Similar to red, the colors were also used in funerals and used to represent royalty. Orange and yellow were used with the same purpose of prestige being produced with hematite, goethite, and limonite.
The body was considered as their portrait to the Maya with various images of plants, animals, and humans being common images. Other designs include personal designs using geometry.
The Chinchorro culture in northern Chile followed the same principle as the Mayans regarding the significance of the color red with it being found in mummies. | 1 | Applied and Interdisciplinary Chemistry |
Keblinski et al. had named four main possible mechanisms for the anomalous increase in nanofluids heat transfer which are : | 0 | Theoretical and Fundamental Chemistry |
Nucleotide (abbreviated "nt") is a common unit of length for single-stranded nucleic acids, similar to how base pair is a unit of length for double-stranded nucleic acids. | 1 | Applied and Interdisciplinary Chemistry |
Relatively effective polymer solar cells are built by thermal annealing of caesium carbonate. Caesium carbonate increases the energy effectiveness of the power conversion of solar cells and enhances the life times of the equipment. The studies done on UPS and XPS reveal that the system will do less work due to the thermal annealing of the layer. Caesium carbonate breaks down into Caesium monoxide| and Caesium peroxide| by thermal evaporation. It was suggested that, when combines with they produce n-type dopes that supplies additional conducting electrons to the host devices. This produces a highly efficient inverted cell that can be used to further improve the efficiency of polymer solar cells or to design adequate multijunction photovoltaic cells.
The nanostructure layers of can be used as cathodes for organic electronic materials due to its capacity to increase the kinetic energy of the electrons. The nanostructure layers of caesium carbonate had been probed for various fields using different techniques. The fields include such as photovoltaic studies, current-voltage measurements, UV photoelectron spectroscopy, X-ray photoelectron spectroscopy, and impedance spectroscopy. The n-type semiconductor produced by thermal evaporation of reacts intensively with metals like Al, and Ca in the cathode. This reaction will cut down the work the cathode metals. Polymer solar cells based on solution process are under extensive studies due to their advantage in producing low cost solar cells. Lithium fluoride has been used to raise the power conversion efficiency of polymer solar cells. However, it requires high temperatures (> 500 degree), and high vacuum states raise the cost of production. The devices with layers have produced equivalent power conversion efficiency compared with the devices that use lithium fluoride. Placing a layer in between the cathode and the light-emitting polymer improves the efficiency of the white OLED. | 0 | Theoretical and Fundamental Chemistry |
The elongation phase starts once assembly of the elongation complex has been completed, and progresses until a termination sequence is encountered. The post-initiation movement of RNA polymerase is the target of another class of important regulatory mechanisms. For example, the transcriptional activator Tat affects elongation rather than initiation during its regulation of HIV transcription. In fact, many eukaryotic genes are regulated by releasing a block to transcription elongation called promoter-proximal pausing. Pausing can influence chromatin structure at promoters to facilitate gene activity and lead to rapid or synchronous transcriptional responses when cells are exposed to an activation signal. Pausing is associated with the binding of two negative elongation factors, DSIF (SPT4/SPT5) and NELF, to the elongation complex. Other factors can also influence the stability and duration of the paused polymerase. Pause release is triggered by the recruitment of the P-TEFb kinase.
Transcription termination has also emerged as an important area of transcriptional regulation. Termination is coupled with the efficient recycling of polymerase. The factors associated with transcription termination can also mediate gene looping and thereby determine the efficiency of re-initiation. | 1 | Applied and Interdisciplinary Chemistry |
* Molecular Imaging and Biology (Editor-in-Chief)
* Journal of Nuclear Medicine (Associate Editor)
* ACS Bioconjugate Chemistry (Editorial Advisory Board)
* Nuclear Medicine and Biology (Associate Editor-in-Chief) | 0 | Theoretical and Fundamental Chemistry |
While this polymerization technique did not typically gain fame and popularity until 2010, it was also reported by Aso and Tagami in 1969. In general, LAP involves the usage of a strong nucleophile to initiate polymerization in addition to the employment of an electrophile as a terminator to endcap the polymer chain. In Tagamis article, PPA was prepared by utilizing tert'-butyllithium as an initiator and acetic anhydride as a terminator. However, the drawbacks faced when utilizing LCP (low polydispersity index (PDI), low yield, and no control over molecular weight) were also encountered in this polymerization technique. | 0 | Theoretical and Fundamental Chemistry |
In beads-based extraction, addition of a mixture containing magnetic beads commonly made of iron ions binds to plasmid DNA, separating them from unwanted compounds by a magnetic rod or stand. The plasmid-bound beads are then released by removal of the magnetic field and extracted in an elution solution for down-stream experiments such as transformation or restriction digestion. This form of miniprep can also be automated, which increases the conveniency while reducing mechanical error. | 1 | Applied and Interdisciplinary Chemistry |
*Fluorosulfonic acid, FSOOH, is a related strong acid with a diminished tendency to evolve hydrogen fluoride.
*Bromosulfonic acid, BrSOOH, is unstable, decomposing at its melting point of 8 °C to give bromine, sulfur dioxide, and sulfuric acid.
*Iodosulfonic acid is not known to occur. | 0 | Theoretical and Fundamental Chemistry |
Sodium hydroxide is used to detect the presence of flavonoids. About 5 mg of a compound is dissolved in water, warmed, and filtered. 10% aqueous sodium hydroxide is added to 2 ml of this solution. This produces a yellow coloration. A change in color from yellow to colorless on addition of dilute hydrochloric acid is an indication for the presence of flavonoids. | 0 | Theoretical and Fundamental Chemistry |
A way to identify aglycone is proposed to extract it from Agave spp. by using H-NMR and Heteronuclear multiple bond correlation (HMBC) experiments. The HMBC experiment can be combined with other techniques such as mass spectrometry to further examine the structure and the function of aglycone.
Samples of glycones and glycosides from limonoids can be simultaneously quantified through a high performance liquid chromatography (HPLC) method, where a binary solvent system and a diode array detector separate and detect them at a sensitivity of 0.25-0.50 μg. | 0 | Theoretical and Fundamental Chemistry |
Cyclobutadiene is a classic textbook example of an antiaromatic compound. It is conventionally understood to be planar, cyclic, and have 4 π electrons (4n for n=1) in a conjugated system.
However, it has long been questioned if cyclobutadiene is genuinely antiaromatic and recent discoveries have suggested that it may not be. Cyclobutadiene is particularly destabilized and this was originally attributed to antiaromaticity. However, cyclobutadiene adopts more double bond character in two of its parallel bonds than others and the π electrons are not delocalized between the two double-bond-like bonds, giving it a rectangular shape as opposed to a regular square. As such, cyclobutadiene behaves like two discrete alkenes joined by two single bonds, and is therefore non-aromatic rather than antiaromatic.
Despite the lack of this π-antiaromatic destabilization effect, none of its 4n π-electron relatives (cyclooctatetraene, etc.) had even close to as much destabilization, suggesting there was something more going on in the case of cyclobutadiene. It was found that a combination of angle strain, torsional strain, and Pauli repulsion leads to the extreme destabilization experienced in this molecule.
This discovery is awkward in that it contradicts basic teachings of antiaromaticity. At this point of time, it is presumed that cyclobutadiene will continue to be used to introduce the concept of antiaromaticity in textbooks as a matter of convenience, even though classifying it as antiaromatic technically may not be accurate. | 0 | Theoretical and Fundamental Chemistry |
As with any material implanted in the body, it is important to minimize or eliminate foreign body response and maximize effectual integration. Neural implants have the potential to increase the quality of life for patients with such disabilities as Alzheimers, Parkinsons, epilepsy, depression, and migraines. With the complexity of interfaces between a neural implant and brain tissue, adverse reactions such as fibrous tissue encapsulation that hinder the functionality, occur. Surface modifications to these implants can help improve the tissue-implant interface, increasing the lifetime and effectiveness of the implant. | 0 | Theoretical and Fundamental Chemistry |
HNMT is a cytoplasmic protein, meaning that it operates within the cytoplasm of a cell. The cytoplasm fills the space between the outer cell membrane (also known as the cellular plasma membrane) and the nuclear membrane (which surrounds the cell's nucleus). HNMT helps regulate histamine levels by degrading histamine within the cytoplasm, ensuring proper cellular function.
Proteins consist of amino acid residues and form a three-dimensional structure. The crystallographic structure to depict the three-dimensional structure of human HNMT protein was first described in 2001 as a monomeric protein that has a mass of 33 kilodaltons and consists of two structural domains.
The first domain, called the "MTase domain", contains the active site where methylation occurs. It has a classic fold found in many other methyltransferases and consists of a seven-stranded beta-sheet surrounded by three helices on each side. This domain binds to its cofactor, S-adenosyl--methionine (SAM-e), which provides the methyl group for N-methylation reactions.
The second domain, called the "substrate binding domain", interacts with histamine, contributing to its binding to the enzyme molecule. This domain is connected to the MTase domain and forms a separate region. It includes an anti-parallel beta sheet along with additional alpha helices and 310 helices. | 1 | Applied and Interdisciplinary Chemistry |
The Kroll process is a pyrometallurgical industrial process used to produce metallic titanium from titanium tetrachloride. The Kroll process replaced the Hunter process for almost all commercial production. | 1 | Applied and Interdisciplinary Chemistry |
The most promising results come from recellularized rat hearts. After only 8 days of maturation, the heart models were stimulated with an electrical signal to provide pacing. The heart models showed a unified contraction with a force equivalent to ~2% of a normal rat heart or ~25% of that of a 16-week-old human heart.
Although far from use in a clinical setting, there have been great advances in the field of bioartificial heart generation. The use of decellularization and recellularization processes, has led to the production of a three dimensional matrix that promotes cellular growth; the repopulation of the matrix containing appropriate cell composition; and the bioengineering of organs demonstrating functionality (limited) and responsiveness to stimuli. This area shows immense promise and with future research may redefine treatment of end stage heart failure. | 1 | Applied and Interdisciplinary Chemistry |
General scenario The Le Chatelier–Braun principle analyzes the qualitative behaviour of a thermodynamic system when a particular one of its externally controlled state variables, say changes by an amount the driving change, causing a change the response of prime interest, in its conjugate state variable all other externally controlled state variables remaining constant. The response illustrates moderation in ways evident in two related thermodynamic equilibria. Obviously, one of has to be intensive, the other extensive. Also as a necessary part of the scenario, there is some particular auxiliary moderating state variable , with its conjugate state variable For this to be of interest, the moderating variable must undergo a change or in some part of the experimental protocol; this can be either by imposition of a change , or with the holding of constant, written For the principle to hold with full generality, must be extensive or intensive accordingly as is so. Obviously, to give this scenario physical meaning, the driving variable and the moderating variable must be subject to separate independent experimental controls and measurements. | 0 | Theoretical and Fundamental Chemistry |
The structure has full tetrahedral symmetry and is composed of one heteroatom surrounded by four oxygen atoms to form a tetrahedron. The heteroatom is located centrally and caged by 12 octahedral units linked to one another by the neighboring oxygen atoms. There are a total of 24 bridging oxygen atoms that link the 12 addenda atoms. The metal centres in the 12 octahedra are arranged on a sphere almost equidistant from each other, in four units, giving the complete structure an overall tetrahedral symmetry. The bond length between atoms varies depending on the heteroatom (X) and the addenda atoms (M). For the 12–phosphotungstic acid, Keggin determined the bond length between the heteroatom and each the four central oxygen atoms to be 1.5 Å. The bond length form the central oxygen to the addenda atoms is 2.43 Å. The bond length between the addenda atoms and each of the bridging oxygen is 1.9 Å. The remaining 12 oxygen atoms that are each double bonded to an addenda atom have a bond length of 1.70 Å. The octahedra are therefore distorted. This structure allows the molecule to hydrate and dehydrate without significant structural changes and the molecule is thermally stable in the solid state for use in vapor phase reactions at high temperatures (400−500 °C). | 0 | Theoretical and Fundamental Chemistry |
Consider a system of localized, non-interacting absorbing centers. Based on the semi-classical radiation absorption theory within the electric dipole approximation, the electric vector of the circularly polarized waves propagates along the +z direction. In this system, is the angular frequency, and = n – ik is the complex refractive index. As the light travels, the attenuation of the beam is expressed as
where is the intensity of light at position , is the absorption coefficient of the medium in the direction, and is the speed of light. Circular dichroism (CD) is then defined by the difference between left () and right () circularly polarized light, , following the sign convention of natural optical activity. In the presence of a static, uniform external magnetic field applied parallel to the direction of propagation of light, the Hamiltonian for the absorbing center takes the form for describing the system in the external magnetic field and describing the applied electromagnetic radiation. The absorption coefficient for a transition between two eigenstates of , and , can be described using the electric dipole transition operator as
The term is a frequency-independent correction factor allowing for the effect of the medium on the light wave electric field, composed of the permittivity and the real refractive index . | 0 | Theoretical and Fundamental Chemistry |
Precession electron diffraction (PED), invented by Roger Vincent and Paul Midgley in 1994, is a method to collect electron diffraction patterns in a transmission electron microscope (TEM). The technique involves rotating (precessing) a tilted incident electron beam around the central axis of the microscope, compensating for the tilt after the sample so a spot diffraction pattern is formed, similar to a SAED pattern. However, a PED pattern is an integration over a collection of diffraction conditions, see Figure 19. This integration produces a quasi-kinematical diffraction pattern that is more suitable as input into direct methods algorithms using electrons to determine the crystal structure of the sample. Because it avoids many dynamical effects it can also be used to better identify crystallographic phases. | 0 | Theoretical and Fundamental Chemistry |
Reoxygenating the system water is a crucial part to obtaining high production densities. Fish require oxygen to metabolize food and grow, as do bacteria communities in the biofilter. Dissolved oxygen levels can be increased through two methods, aeration and oxygenation. In aeration air is pumped through an air stone or similar device that creates small bubbles in the water column, this results in a high surface area where oxygen can dissolve into the water. In general due to slow gas dissolution rates and the high air pressure needed to create small bubbles this method is considered inefficient and the water is instead oxygenated by pumping in pure oxygen. Various methods are used to ensure that during oxygenation all of the oxygen dissolves into the water column. Careful calculation and consideration must be given to the oxygen demand of a given system, and that demand must be met with either oxygenation or aeration equipment. | 1 | Applied and Interdisciplinary Chemistry |
Diazirines are widely used in receptor labeling studies. This is because diazirine-containing analogs of various ligands can be synthesized and incubated with their respective receptors, and then subsequently exposed to light to produce reactive carbenes. The carbene will covalently bond to residues in the binding site of the receptor. The carbene compound may include a bioorthogonal tag or handle by which the protein of interest can be isolated. The protein can then be digested and sequenced by mass spectrometry in order to identify which residues the carbene containing ligand is bound to, and hence the identity of the binding site in the receptor.
Examples of diazirines used in receptor labeling studies include:
* The discovery of a brassinosteroid receptor for brassinosteroid plant hormones by Kinoshita et al. Researchers used a plant hormone analog with a diazirine crosslinking moiety and a biotin tag for isolation to identity the new receptor. This study led to a number of similar studies conducted with regards to other plant hormones.
* The discovery of novel non-CB1/CB2 cannabinoid receptors using anandamide analog probes containing a diazirine group by Balas et al.
* The binding cavity of the hypnotic agent propofol in the GABA receptor using a diazirine containing propofol analog. | 0 | Theoretical and Fundamental Chemistry |
The carbonation step is characterized by a fast initial reaction rate abruptly followed by a slow reaction rate (Figure 2). The carrying capacity of the sorbent is defined as the number of moles of CO reacted in the period of fast reaction rate with respect to that of the reaction stoichiometry for complete conversion of CaO to CaCO. As seen in Figure 2, while mass after calcination remains constant, the mass change upon carbonation- the carrying capacity- reduces with a large number of cycles. In calcination, porous CaO (molar volume = ) is formed in place of CaCO (.). On the other hand, in carbonation, the CaCO formed on the surface of a CaO particle occupies a larger molar volume. As a result, once a layer of carbonate has formed on the surface (including on the large internal surface of porous CaO), it impedes further CO capture. This product layer grows over the pores and seals them off, forcing carbonation to follow a slower, diffusion dependent mechanism. | 1 | Applied and Interdisciplinary Chemistry |
1,1,1,2-Tetrafluoroethane is a non-flammable gas used primarily as a "high-temperature" refrigerant for domestic refrigeration and automobile air conditioners. These devices began using 1,1,1,2-tetrafluoroethane in the early 1990s as a replacement for the more environmentally harmful R-12. Retrofit kits are available to convert units that were originally R-12-equipped.
Other common uses include plastic foam blowing, as a cleaning solvent, a propellant for the delivery of pharmaceuticals (e.g. bronchodilators), wine cork removers, gas dusters ("canned air"), and in air driers for removing the moisture from compressed air. 1,1,1,2-Tetrafluoroethane has also been used to cool computers in some overclocking attempts. It is the refrigerant used in plumbing pipe freeze kits. It is also commonly used as a propellant for airsoft airguns. The gas is often mixed with a silicone-based lubricant. | 1 | Applied and Interdisciplinary Chemistry |
Lead(II) azide is an inorganic compound. More so than other azides, it is explosive. It is used in detonators to initiate secondary explosives. In a commercially usable form, it is a white to buff powder. | 0 | Theoretical and Fundamental Chemistry |
Exothermic refers to a transformation in which a closed system releases energy (heat) to the surroundings, expressed by
When the transformation occurs at constant pressure and without exchange of electrical energy, heat is equal to the enthalpy change, i.e.
while at constant volume, according to the first law of thermodynamics it equals internal energy () change, i.e.
In an adiabatic system (i.e. a system that does not exchange heat with the surroundings), an otherwise exothermic process results in an increase in temperature of the system.
In exothermic chemical reactions, the heat that is released by the reaction takes the form of electromagnetic energy or kinetic energy of molecules. The transition of electrons from one quantum energy level to another causes light to be released. This light is equivalent in energy to some of the stabilization energy of the energy for the chemical reaction, i.e. the bond energy. This light that is released can be absorbed by other molecules in solution to give rise to molecular translations and rotations, which gives rise to the classical understanding of heat. In an exothermic reaction, the activation energy (energy needed to start the reaction) is less than the energy that is subsequently released, so there is a net release of energy. | 0 | Theoretical and Fundamental Chemistry |
The structural changes that occur during 72-hour hypothermic storage of previously uninjured kidneys have been described by Mackay who showed how there was progressive vacuolation of the cytoplasm of the cells which particularly affected the proximal tubules. On electron microscopy the mitochondria were seen to become swollen with early separation of the internal cristal membranes and later loss of all internal structure. Lysosomal integrity was well preserved until late, and the destruction of the cell did not appear to be caused by lytic enzymes because there was no more injury immediately adjacent to the lysosomes than in the rest of the cell.
Woods and Liu – when describing successful 5 and 7 day kidney storage - described the light microscopic changes seen at the end of perfusion and at post mortem, but found few gross abnormalities apart from some infiltration with lymphocytes and occasional tubular atrophy.
The changes during short perfusions of human kidneys prior to reimplantation have been described by Hill who also performed biopsies 1 hour after reimplantation. On electron microscopy Hill found endothelial damage which correlated with the severity of the fibrin deposition after reimplantation. The changes that Hill saw in the glomeruli on light microscopy were occasional fibrin thrombi and infiltration with polymorphs. Hill suspected that these changes were an immunologically induced lesion, but found that there was no correlation between the severity of the histological lesion and the presence or absence of immunoglobulin deposits.
There are several reports of the analysis of urine produced by kidneys during perfusion storage. Kastagir analysed urine produced during 24-hour perfusion and found it to be an ultrafiltrate of the perfusate, Scott found a trace of protein in the urine during 24-hour storage, and Pederson found only a trace of protein after 36 hours perfusion storage. Pederson mentioned that he had found heavy proteinuria during earlier experiments. Woods noted protein casts in the tubules of viable kidneys after 5 day storage, but he did not analyse the urine produced during perfusion. In Cohen's study there was a progressive increase in urinary protein concentration during 8 day preservation until the protein content of the urine equalled that of the perfusate. This may have been related to the swelling of the glomerular basement membranes and the progressive fusion of epithelial cell foot processes that was also observed during the same period of perfusion storage. | 1 | Applied and Interdisciplinary Chemistry |
The Irving–Williams series refers to the relative stabilities of complexes formed by transition metals. In 1953 Harry Irving and Robert Williams observed that the stability of complexes formed by divalent first-row transition metal ions generally increase across the period to a maximum stability at copper: Mn(II) < Fe(II) < Co(II) < Ni(II) < Cu(II) > Zn(II).
Specifically, the Irving–Williams series refers to the exchange of aqua (HO) ligands for any other ligand (L) within a metal complex. In other words, the Irving–Williams series is almost exclusively independent of the nature of the incoming ligand, L.
The main application of the series is to empirically suggest an order of stability within first row transition metal complexes (where the transition metal is in oxidation state II).
Another application of the Irving–Williams series is to use it as a correlation "ruler" in comparing the first stability constant for replacement of water in the aqueous ion by a ligand. | 0 | Theoretical and Fundamental Chemistry |
Palladacycles with ring-sizes range from 3 to 10 have been synthesized and characterized, whereas only 5-/6-membered ones are commonly used. Palladacycles of 3-/4-/>6-membered ring-sizes are usually unstable due to their ring strains. | 0 | Theoretical and Fundamental Chemistry |
In his 1960 novel Trouble with Lichen, John Wyndham gives the name Lichenin to a biochemical extract of lichen used to extend life expectancy beyond 300 years. | 1 | Applied and Interdisciplinary Chemistry |
In geophysics, a common assumption is that the rock formations of the crust are locally polar anisotropic (transversely isotropic); this is the simplest case of geophysical interest. Backus upscaling is often used to determine the effective transversely isotropic elastic constants of layered media for long wavelength seismic waves.
Assumptions that are made in the Backus approximation are:
* All materials are linearly elastic
* No sources of intrinsic energy dissipation (e.g. friction)
* Valid in the infinite wavelength limit, hence good results only if layer thickness is much smaller than wavelength
* The statistics of distribution of layer elastic properties are stationary, i.e., there is no correlated trend in these properties.
For shorter wavelengths, the behavior of seismic waves is described using the superposition of plane waves. Transversely isotropic media support three types of elastic plane waves:
* a quasi-P wave (polarization direction almost equal to propagation direction)
* a quasi-S wave
* a S-wave (polarized orthogonal to the quasi-S wave, to the symmetry axis, and to the direction of propagation).
Solutions to wave propagation problems in such media may be constructed from these plane waves, using Fourier synthesis. | 0 | Theoretical and Fundamental Chemistry |
The bead test is a traditional part of qualitative inorganic analysis to test for the presence of certain metals. The oldest one is the borax bead test or blister test. It was introduced by Berzelius in 1812. Since then other salts were used as fluxing agents, such as sodium carbonate or sodium fluoride. The most important one after borax is microcosmic salt, which is the basis of the microcosmic salt bead test. | 0 | Theoretical and Fundamental Chemistry |
In general, when scientists determine the amount of a substance that may be hazardous for humans, animals and/or the environment they determine the amount of the substance likely to trigger effects and if possible establish a safe level. In Europe, the European Food Safety Authority produced risk assessments for more than 4,000 substances in over 1,600 scientific opinions and they provide open access summaries of human health, animal health and ecological hazard assessments in their OpenFoodTox database. The OpenFoodTox database can be used to screen potential new foods for toxicity.
The Toxicology and Environmental Health Information Program (TEHIP) at the United States National Library of Medicine (NLM) maintains a comprehensive toxicology and environmental health web site that includes access to toxins-related resources produced by TEHIP and by other government agencies and organizations. This web site includes links to databases, bibliographies, tutorials, and other scientific and consumer-oriented resources. TEHIP also is responsible for the Toxicology Data Network (TOXNET), an integrated system of toxicology and environmental health databases that are available free of charge on the web.
TOXMAP is a Geographic Information System (GIS) that is part of TOXNET. TOXMAP uses maps of the United States to help users visually explore data from the United States Environmental Protection Agency's (EPA) Toxics Release Inventory and Superfund Basic Research Programs. | 1 | Applied and Interdisciplinary Chemistry |
Before choosing a formula it is worth knowing that in the paper on the Moody chart, Moody stated the accuracy is about ±5% for smooth pipes and ±10% for rough pipes. If more than one formula is applicable in the flow regime under consideration, the choice of formula may be influenced by one or more of the following:
*Required accuracy
*Speed of computation required
*Available computational technology:
**calculator (minimize keystrokes)
**spreadsheet (single-cell formula)
**programming/scripting language (subroutine). | 1 | Applied and Interdisciplinary Chemistry |
Generally, levosalbutamol is well tolerated. Common mild side-effects include an elevated heart rate, muscle cramps, and gastric upset (including heartburn and diarrhea).
Symptoms of overdose in particular include: collapse into a seizure; chest pain (possible precursor of a heart attack); fast, pounding heartbeat, which may cause raised blood pressure (hypertension); irregular heartbeat (cardiac arrhythmia), which may cause paradoxical lowered blood pressure (hypotension); nervousness and tremor; headache; dizziness and nausea/vomiting; weakness or exhaustion (medical fatigue); dry mouth; and insomnia.
Rarer side effects may indicate a dangerous allergic reaction. These include: paradoxical bronchospasm (shortness of breath and difficulty breathing); skin itching, rash, or hives (urticaria); swelling (angioedema) of any part of the face or throat (which can lead to voice hoarseness), or swelling of the extremities. | 0 | Theoretical and Fundamental Chemistry |
* Au/MCr2O4 (M = Co, Mn, Fe) catalysts in the oxidations of CO, C2, and C3 hydrocarbons (Reaction Kinetics, Mechanisms and Catalysis, 2012, v105, pp69–78).
* Oxidation of CO and propane on Pt-Au/Al2O3 catalysts (Polish Journal of Chemistry, 2008, v82, pp1991-1997).
* Oxidative Dehydrogenation of Isobutane on VOx/oxide Support Catalysts: Effect of the Potassium Additive (Polish Journal of Chemistry, 2007, v81, pp1345-1354).
* RNano-Au/oxide support catalysts in oxidation reactions: Provenance of active oxygen species (Catalysis today, 2006, v112, Issues 1–4, pp3-7).
* Effect of additives on the physicochemical and catalytic properties of oxide catalysts in selective oxidation reactions (Topics in catalysis, 2002, v21, pp35–46).
* 8 Catalysis (Royal Society of Chemistry Annual Reports Section "C" (Physical Chemistry), 2000, v96, pp297-334).
* Thirty years in selective oxidation on oxides: what have we learned? (Topics in Catalysis, 2000, v11, pp23–42).
* Active centres on vanadia-based catalysts for selective oxidation of hydrocarbons (Applied Catalysis A: General, 1997, v157, Issues 1–2, pp409-420). | 0 | Theoretical and Fundamental Chemistry |
Diffusion-type cloud chambers will be discussed here. A simple cloud chamber consists of the sealed environment, a warm top plate and a cold bottom plate (See Fig. 3). It requires a source of liquid alcohol at the warm side of the chamber where the liquid evaporates, forming a vapor that cools as it falls through the gas and condenses on the cold bottom plate. Some sort of ionizing radiation is needed.
Isopropanol, methanol, or other alcohol vapor saturates the chamber. The alcohol falls as it cools down and the cold condenser provides a steep temperature gradient. The result is a supersaturated environment. As energetic charged particles pass through the gas they leave ionization trails. The alcohol vapor condenses around gaseous ion trails left behind by the ionizing particles. This occurs because alcohol and water molecules are polar, resulting in a net attractive force toward a nearby free charge (See Fig. 4). The result is a misty cloud-like formation, seen by the presence of droplets falling down to the condenser. When the tracks are emitted from a source, their point of origin can easily be determined. Fig. 5 shows an example of an alpha particle from a Pb-210 pin-type source undergoing Rutherford scattering.
Just above the cold condenser plate there is a volume of the chamber which is sensitive to ionization tracks. The ion trail left by the radioactive particles provides an optimal trigger for condensation and cloud formation. This sensitive volume is increased in height by employing a steep temperature gradient, and stable conditions. A strong electric field is often used to draw cloud tracks down to the sensitive region of the chamber and increase the sensitivity of the chamber. The electric field can also serve to prevent large amounts of background "rain" from obscuring the sensitive region of the chamber, caused by condensation forming above the sensitive volume of the chamber, thereby obscuring tracks by constant precipitation. A black background makes it easier to observe cloud tracks, and typically a tangential light source is needed to illuminate the white droplets against the black background. Often the tracks are not apparent until a shallow pool of alcohol is formed at the condenser plate.
If a magnetic field is applied across the cloud chamber, positively and negatively charged particles will curve in opposite directions, according to the Lorentz force law; strong-enough fields are difficult to achieve, however, with small hobbyist setups. This method was also used to prove the existence of the Positron in 1932, in accordance with Paul Dirac's theoretical proof, published in 1928. | 0 | Theoretical and Fundamental Chemistry |
Each POCIS disk will sample a certain volume of water per day. The volume of water sampled varies from chemical to chemical and is dependent on the physical and chemical properties of the compound as well as the duration of sampling. The sampling rate of POCIS can vary with changes in the water flow, turbulence, temperature, and the buildup of solids on the sampler’s surface. The accumulation of contaminants into a POCIS device is the result of three successive process occurring at the same time. First, the contaminants have to diffuse across the water boundary layer. The thickness of this layer is dependent on water flow and turbulence around the sampler and can significantly alter sampling rates. Second, the contaminant must transport across the membrane either through the water-filled pores or through the membrane itself. Finally, contaminants transfer from the membrane into the sorbent material mainly through adsorption. These last two steps make the modeling, understanding, and prediction of accumulation by a POCIS device challenging. To date, a limited number of chemical sampling rates have been determined.
Accumulation of chemicals by a POCIS device generally follows first order kinetics. The kinetics are characterized by an initial integrative phase, followed by an equilibrium partitioning phase. During the integrative phase of uptake, a passive sampling device accumulates residues linearly relative to time, assuming constant exposure concentrations. Based on current results, the POCIS sampler remains in a linear phase for at least 30 days, and has been observed up to 56 days. Therefore, both laboratory and field data justify the use of a linear uptake model for the calculation of sample rates. In order to estimate the ambient water concentration of contaminants sampled by a POCIS device, there must be available calibration data applicable for in situ conditions regarding the target compound. Currently, this information is limited. | 0 | Theoretical and Fundamental Chemistry |
Epitaxy is used in nanotechnology and in semiconductor fabrication. Indeed, epitaxy is the only affordable method of high quality crystal growth for many semiconductor materials. In surface science, epitaxy is used to create and study monolayer and multilayer films of adsorbed organic molecules on single crystalline surfaces via scanning tunnelling microscopy. | 0 | Theoretical and Fundamental Chemistry |
Homologous series are not unique to organic chemistry. Titanium, vanadium, and molybdenum oxides all form homologous series (e.g. VO for 2 H (with n up to 8) that are analogous to the alkanes, CH. | 0 | Theoretical and Fundamental Chemistry |
Quinapril inhibits angiotensin converting enzyme, an enzyme which catalyses the formation of angiotensin II from its precursor, angiotensin I. Angiotensin II is a powerful vasoconstrictor and increases blood pressure through a variety of mechanisms. Due to reduced angiotensin production, plasma concentrations of aldosterone are also reduced, resulting in increased excretion of sodium in the urine and increased concentrations of potassium in the blood. | 0 | Theoretical and Fundamental Chemistry |
Cloning, or more precisely, the reconstruction of functional DNA from extinct species has, for decades, been a dream. Possible implications of this were dramatized in the 1984 novel Carnosaur and the 1990 novel Jurassic Park. The best current cloning techniques have an average success rate of 9.4 percent (and as high as 25 percent) when working with familiar species such as mice, while cloning wild animals is usually less than 1 percent successful. | 1 | Applied and Interdisciplinary Chemistry |
The energy of a nucleon in a nucleus is its rest mass energy minus a binding energy. In addition to this, there is an energy due to degeneracy: for instance, a nucleon with energy E will be forced to a higher energy E if all the lower energy states are filled. This is because nucleons are fermions and obey Fermi–Dirac statistics. The work done in putting this nucleon to a higher energy level results in a pressure, which is the degeneracy pressure. When the effective binding energy, or Fermi energy, reaches zero, adding a nucleon of the same isospin to the nucleus is not possible, as the new nucleon would have a negative effective binding energy — i.e. it is more energetically favourable (system will have lowest overall energy) for the nucleon to be created outside the nucleus. This defines the particle drip point for that species. | 0 | Theoretical and Fundamental Chemistry |
The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural thorium contains only trace amounts of fissile material (such as ), which are insufficient to initiate a nuclear chain reaction. Additional fissile material or another neutron source is necessary to initiate the fuel cycle. In a thorium-fuelled reactor, absorbs neutrons to produce . This parallels the process in uranium breeder reactors whereby fertile absorbs neutrons to form fissile . Depending on the design of the reactor and fuel cycle, the generated either fissions in situ or is chemically separated from the used nuclear fuel and formed into new nuclear fuel.
The thorium fuel cycle has several potential advantages over a uranium fuel cycle, including thorium's greater abundance, superior physical and nuclear properties, reduced plutonium and actinide production, and better resistance to nuclear weapons proliferation when used in a traditional light water reactor though not in a molten salt reactor. | 0 | Theoretical and Fundamental Chemistry |
Single photon detector used in time-domain diffuse optics require not only a high photon detection efficiency in the wavelength range of optical window, but also a large active area as well as large numerical aperture (N.A.) to maximize the overall light collection efficiency. They also require narrow timing response and a low noise background.
Traditionally, fiber coupled photomultiplier tubes (PMT) have been the detector of choice for diffuse optical measurements, thanks mainly due to the large active area, low dark count and excellent timing resolution. However, they are intrinsically bulky, prone to electromagnetic disturbances and they have a quite limited spectral sensitivity. Moreover, they require a high biasing voltage and they are quite expensive. Single photon avalanche diodes have emerged as an alternative to PMTS. They are low cost, compact and can be placed in contact, while needing a much lower biasing voltage. Also, they offer a wider spectral sensitivity and they are more robust to bursts of light. However, they have a much lower active area and hence a lower photon collection efficiency and a larger dark count. Silicon photomultipliers (SiPM) are an arrays of SPADs with a global anode and a global cathode and hence have a larger active area while maintaining all the advantages offered by SPADs. However, they suffer from a larger dark count and a broader timing response. | 0 | Theoretical and Fundamental Chemistry |
Mucoadhesion describes the attractive forces between a biological material and mucus or mucous membrane. Mucous membranes adhere to epithelial surfaces such as the gastrointestinal tract (GI-tract), the vagina, the lung, the eye, etc. They are generally hydrophilic as they contain many hydrogen macromolecules due to the large amount of water (approximately 95%) within its composition. However, mucin also contains glycoproteins that enable the formation of a gel-like substance. Understanding the hydrophilic bonding and adhesion mechanisms of mucus to biological material is of utmost importance in order to produce the most efficient applications. For example, in drug delivery systems, the mucus layer must be penetrated in order to effectively transport micro- or nanosized drug particles into the body. Bioadhesion is the mechanism by which two biological materials are held together by interfacial forces. The mucoadhesive properties of polymers can be evaluated via rheological synergism studies with freshly isolated mucus, tensile studies and mucosal residence time studies. Results obtained with these in vitro methods show a high correlation with results obtained in humans. | 1 | Applied and Interdisciplinary Chemistry |
The activated sludge process was discovered in 1913 in the United Kingdom by two engineers, Edward Ardern and W.T. Lockett, who were conducting research for the Manchester Corporation Rivers Department at Davyhulme Sewage Works. In 1912, Gilbert Fowler, a scientist at the University of Manchester, observed experiments being conducted at the Lawrence Experiment Station at Massachusetts involving the aeration of sewage in a bottle that had been coated with algae. Fowlers engineering colleagues, Ardern and Lockett, experimented on treating sewage in a draw-and-fill reactor, which produced a highly treated effluent. They aerated the waste-water continuously for about a month and were able to achieve a complete nitrification of the sample material. Believing that the sludge had been activated (in a similar manner to activated carbon) the process was named activated sludge'. Not until much later was it realized that what had actually occurred was a means to concentrate biological organisms, decoupling the liquid retention time (ideally, low, for a compact treatment system) from the solids retention time (ideally, fairly high, for an effluent low in BOD and ammonia.)
Their results were published in their seminal 1914 paper, and the first full-scale continuous-flow system was installed at Worcester two years later. In the aftermath of the First World War the new treatment method spread rapidly, especially to the US, Denmark, Germany and Canada. By the late 1930s, the activated sludge treatment became a well-known biological wastewater treatment process in those countries where sewer systems and sewage treatment plants were common. | 1 | Applied and Interdisciplinary Chemistry |
It had long been thought that the sigma factor obligatorily leaves the core enzyme once it has initiated transcription, allowing it to link to another core enzyme and initiate transcription at another site. Thus, the sigma factor would cycle from one core to another.
However, fluorescence resonance energy transfer was used to show that the sigma factor does not obligatorily leave the core. Instead, it changes its binding with the core during initiation and elongation. Therefore, the sigma factor cycles between a strongly bound state during initiation and a weakly bound state during elongation. | 1 | Applied and Interdisciplinary Chemistry |
Asakura and Oosawa described the second case as consisting of two plates in a solution of rod like macromolecules. The rod like macromolecules are described as having a length, , where , the area of the plates. As the length of the rods increases, the concentration of the rods between the plates is decreased as it becomes more difficult for the rods to enter between the plates due to steric hindrances. As a result, the force acting on the plates increases with the length of the rods until it becomes equal to the osmotic pressure. In this context, it is worth mentioning that even the isotropic-nematic transition of lyotropic liquid crystals, as first explained in Onsager's theory, can in itself be considered a special case of depletion forces. | 0 | Theoretical and Fundamental Chemistry |
Multiphoton excitation is a way of focusing the viewing plane of the microscope by taking advantage of the phenomenon where two simultaneous low energy photons are absorbed by a fluorescent moiety which normally absorbs one photon with double their individual energy: say two NIR photons (800 nm) to excite a UV dye (400 nm). | 1 | Applied and Interdisciplinary Chemistry |
Aza Paternò−Büchi reaction involves an ππ* excited state of alkene reacting with a ground state imine. This strategy was developed by the laboratory Sivaguru and co-workers to overcome the shortcomings involving direct excitation of imines. Traditionally addition of excited imines to carbon-carbon double bonds involves making the imines as part of a carbocycle. | 0 | Theoretical and Fundamental Chemistry |
Known generalisations include monomers with an arbitrary number of functional group types, crosslinking polymerisation, and complex reaction networks. | 0 | Theoretical and Fundamental Chemistry |
Physicists overwhelmingly reject any possibility that the zero-point energy field can be exploited to obtain useful energy (work) or uncompensated momentum; such efforts are seen as tantamount to perpetual motion machines.
Nevertheless, the allure of free energy has motivated such research, usually falling in the category of fringe science. As long ago as 1889 (before quantum theory or discovery of the zero point energy) Nikola Tesla proposed that useful energy could be obtained from free space, or what was assumed at that time to be an all-pervasive aether. Others have since claimed to exploit zero-point or vacuum energy with a large amount of pseudoscientific literature causing ridicule around the subject. Despite rejection by the scientific community, harnessing zero-point energy remains an interest of research, particularly in the US where it has attracted the attention of major aerospace/defence contractors and the U.S. Department of Defense as well as in China, Germany, Russia and Brazil. | 0 | Theoretical and Fundamental Chemistry |
Crop rotation can help restore tilth in compacted soils. Two processes contribute to this gain. First, accelerated organic matter decomposition from tillage ends under the sod crop. Another way to achieve this is via no-till farming. Second, grass and legume sods develop extensive root systems that continually grow and die off. The dead roots supply a source of active organic matter, which feeds soil organisms that create aggregation – the soil carbon sponge. Beneficial organisms need continual supplies of organic matter to sustain themselves and they deposit the digested materials on soil aggregates and thereby stabilize them. Also, the living roots and symbiotic microorganisms (for example, mycorrhizal fungi) can exude organic materials that nourish soil organisms and help with aggregation. Grass and legume sod crops therefore deposit more organic matter in the soil than most other crops.
Some annual rotation crops such as buckwheat also have dense, fibrous, root systems and can improve tilth. Crop mixtures with different rooting systems can be beneficial. For example, red clover seeded into winter wheat provide additional roots and a more protein-rich soil organic matter.
Other rotation crops are more valuable for improving subsoils. Perennial crops such as alfalfa have strong, deep, penetrating tap roots that can push through hard layers, especially during wet periods when the soil is soft. These deep roots establish pathways for water and future plant roots, and produce soil organic matter.
Crops rotation can extend the period of active growth compared to conventional row crops, leaving more organic material behind. For example, in a corn-soybean rotation, active growth occurs 32% of the time, while a dry bean–winter wheat–corn rotation is active 72% of the time. Crops such as rye, wheat, oat, barley, pea and cool-season grasses grow actively in the late fall and early spring when other crops are inactive. They are beneficial both as rotation and cover crops, although intensive tillage can negate their effects. | 0 | Theoretical and Fundamental Chemistry |
In their first paper, Guldberg and Waage suggested that in a reaction such as
the "chemical affinity" or "reaction force" between A and B did not just depend on the chemical nature of the reactants, as had previously been supposed, but also depended on the amount of each reactant in a reaction mixture. Thus the law of mass action was first stated as follows:
:When two reactants, A and B, react together at a given temperature in a "substitution reaction," the affinity, or chemical force between them, is proportional to the active masses, [A] and [B], each raised to a particular power
In this context a substitution reaction was one such as . Active mass was defined in the 1879 paper as "the amount of substance in the sphere of action". For species in solution active mass is equal to concentration. For solids, active mass is taken as a constant. , a and b were regarded as empirical constants, to be determined by experiment.
At equilibrium, the chemical force driving the forward reaction must be equal to the chemical force driving the reverse reaction. Writing the initial active masses of A,B, A and B as p, q, p and q and the dissociated active mass at equilibrium as , this equality is represented by
represents the amount of reagents A and B that has been converted into A and B. Calculations based on this equation are reported in the second paper. | 0 | Theoretical and Fundamental Chemistry |
The total synthesis of bottromycin was accomplished in 2009. The synthesis was achieved in 17 steps. Although bottromycin is a peptide-based natural product, it contains an unusual macrocycle and thiazole heterocycle, so that the total synthesis could not be accomplished using traditional solid-phase peptide synthesis. The synthesis was accomplished using a combination of peptide coupling and other methods. To obtain the primary thia-β-Ala-OMe intermediate, a sequence of condensation, Mannich reaction, and palladium-catalyzed decarboxylation steps were performed. This intermediate was prepared stereoselectively. To obtain the amidine linkage, a tripeptide intermediate was coupled to a phthaloyl-protected thioamide via mercury-mediated condensation using mercury (II) trifluoromethanesulfonate () to yield a branched amidine intermediate. To obtain the final product macrocycle, macrolactamization of the amidine-containing intermediate was required. Macrolactamization was performed with 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDCI) and yielded the final product, bottromycin A2. To confirm that the synthesized bottromycin A2 had the same stereochemistry as natural bottromycin A2, the product was studied by optical rotation, H and C NMR, IR, and HRMS. The data was found to match that of isolated bottromycin A2. Further, the synthetic sample of bottromycin was also found to have antibacterial activity against both MRSA and VRE, although quantitative data was not reported. A full rendering of the synthetic scheme may be seen under the collapsed synthetic scheme link.
In 2012, an alternative synthesis of the bottromycin macrocyclic ring system and amidine linkage was reported. The synthesis was achieved in 10 steps. Unlike the previous synthesis, Ackerman and colleagues synthesized a linear peptide and achieved intramolecular amidine formation using an S-methylated endothiopeptide. The endothiopeptide was obtained by a thio-Ugi reaction. The resulting macrocycle was obtained as a racemic mixture at the amidine linkage. The full synthetic scheme may be viewed under the collapsed synthetic scheme link. | 0 | Theoretical and Fundamental Chemistry |
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