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The computation modules of Khimera allow one to calculate the kinetic parameters of elementary processes and thermodynamic and transport properties from the data on the molecular structures and properties obtained from quantum-chemical calculations or from an experiment. The molecular properties and the parameters of molecular interactions can be calculated using quantum-chemical software (Gaussian, GAMESS, Jaguar, ADF) and directly imported into Khimera in an automatic mode. The results of calculations can be presented visually and exported for the further use in kinetic modeling and CFD packages. | 0 | Theoretical and Fundamental Chemistry |
In condensed matter physics, a Bose–Einstein condensate (BEC) is a state of matter that is typically formed when a gas of bosons at very low densities is cooled to temperatures very close to absolute zero (−273.15 °C or −459.67 °F). Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which microscopic quantum-mechanical phenomena, particularly wavefunction interference, become apparent macroscopically.
More generally, condensation refers to the appearance of macroscopic occupation of one or several states: for example, in BCS theory, a superconductor is a condensate of Cooper pairs. As such, condensation can be associated with phase transition, and the macroscopic occupation of the state is the order parameter.
Bose–Einstein condensate was first predicted, generally, in 1924–1925 by Albert Einstein, crediting a pioneering paper by Satyendra Nath Bose on the new field now known as quantum statistics. In 1995, the Bose–Einstein condensate was created by Eric Cornell and Carl Wieman of the University of Colorado Boulder using rubidium atoms; later that year, Wolfgang Ketterle of MIT produced a BEC using sodium atoms. In 2001 Cornell, Wieman, and Ketterle shared the Nobel Prize in Physics "for the achievement of Bose–Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates". | 0 | Theoretical and Fundamental Chemistry |
Enterococcus faecalis is an opportunistic, Gram-positive bacteria that forms biofilm in glass. This process is also known as forming a biofilm in vitro. The presence of (Esp), a certain cell surface protein, aids the formation of a biofilm by Enterococcus faecalis. | 1 | Applied and Interdisciplinary Chemistry |
In pre-modern medicine, diascordium (medical Lat diascordium, for diascordiōn, from Gr , [a preparation] of scordium, , "a strong-smelling plant mentioned by Dioscorides", possibly Teucrium scordium), or diascord, is a kind of electuary, or opiate, first described by Jerome Frascata, and denominated from the dried leaves of scordium, which is an ingredient therein. The other ingredients are red roses, bole, storax, cinnamon, cassia lignea (coarse bark of Cinnamomum cassia), dittany, tormentil roots, bistort, gentian, galbanum, amber, terra sigillata, opium, long pepper, ginger, mel rosatum, and malmsey. It was used against malignant fevers, the plague, worms, colic, to promote sleep, and resist putrefaction. In 1746, diascordium was offered in two forms: with or without opium.
In 1654, Nicholas Culpeper wrote in his London Dispensatorie about the mixture: "It is a well composed Electuary, a something appropriate to the nature of women, for it Provokes the Terms, hastens their Labor, helps their usual sickness at the time of their Lying-in, I know nothing better."
Over the years, the composition of diascordium was modified, until it gradually changed into what became known as pulvis catechu compositus ("compound powder of catechu"). | 1 | Applied and Interdisciplinary Chemistry |
The logging system is often simply a personal computer. In initial signal processing, the signal often needs to be amplified and converted for use with the control system. The lines of communication between monochromator, detector output, and computer should be optimized to ensure the desired metrics and features are being used. The commercially available software included with spectroradiometric systems often come stored with useful reference functions for further calculation of measurements, such as CIE color matching functions and the V curve. | 0 | Theoretical and Fundamental Chemistry |
In the early 1990s, at least thirty separate groups were working on the total synthesis of the chemotherapy medicine paclitaxel (Taxol), culminating with the groups of Robert A. Holton and K. C. Nicolaou publishing nearly simultaneously in 1994. By then, Mukaiyama had retired from the University of Tokyo after reaching the mandatory age of 60 and set up an academic lab at the Tokyo University of Science. The Mukaiyama taxol total synthesis was published between the years of 1997 and 1999 after five years of research, making the Mukaiyama lab the sixth group to report results.
This total synthesis is largely a linear synthesis which forms the four rings of taxol in the order C, B, A, D. It is differentiated from the others from its use of L-serine as a starting material and for being the only total synthesis not to use the Ojima lactam to create the amide tail. Instead, the tail is created from scratch by converting benzyloxyacetic acid into a silyl enol ether, joining it with benzaldehyde with a Mukaiyama aldol addition, and creating the amide from the alcohol via a Mitsunobu reaction followed by benzoylation.
The synthesis also made use of three Swern oxidations during the synthesis of the C ring. This reaction is typically performed at very low temperatures (< -50 °C) to stabilize its activated DMSO intermediate and constantly evolves the strong-smelling DMS, making it very difficult to work with at large scales. The difficulties encountered during their total synthesis prompted Mukaiyama to pursue an alternative method, and in 2001 a room-temperature oxidation involving N-chlorosuccinimide and a catalytic amount of N-t-butylbenzenesulfenamide was developed. The more electronegative nitrogen adjacent to the sulfur in the sulfenamide increased the stability of the intermediate relative to that formed from the sulfur-carbon bond of DMSO and was inspired by his earlier work with sulfenamides while still at the Tokyo Institute of Technology. | 0 | Theoretical and Fundamental Chemistry |
According to Archimedes principle, the weight of an immersed object is reduced by the weight of fluid it displaces. This holds for a fluid parcel of density surrounded by an ambient fluid of density . Its weight per unit volume is , in which is the acceleration of gravity. Dividing by a characteristic density, , gives the definition of the reduced gravity:
If , is positive though generally much smaller than . Because water is much more dense than air, the displacement of water by air from a surface gravity wave feels nearly the full force of gravity (). The displacement of the thermocline of a lake, which separates warmer surface from cooler deep water, feels the buoyancy force expressed through the reduced gravity. For example, the density difference between ice water and room temperature water is 0.002 the characteristic density of water. So the reduced gravity is 0.2% that of gravity. It is for this reason that internal waves move in slow-motion relative to surface waves.
Whereas the reduced gravity is the key variable describing buoyancy for interfacial internal waves, a different quantity is used to describe buoyancy in continuously stratified fluid whose density varies with height as . Suppose a water column is in hydrostatic equilibrium and a small parcel of fluid with density is displaced vertically by a small distance . The buoyant restoring force results in a vertical acceleration, given by
This is the spring equation whose solution predicts oscillatory vertical displacement about in time about with frequency given by the buoyancy frequency:
The above argument can be generalized to predict the frequency, , of a fluid parcel that oscillates along a line at an angle to the vertical:
This is one way to write the dispersion relation for internal waves whose lines of constant phase lie at an angle to the vertical. In particular, this shows that the buoyancy frequency is an upper limit of allowed internal wave frequencies. | 1 | Applied and Interdisciplinary Chemistry |
Mahdi was born on 1 January 1970. He received his Bachelors degree in chemical engineering from University of Toronto, Canada, and his Masters in the same field from the Illinois Institute of Technology, USA. Mahdi received his PhD in chemical engineering from Northwestern University, USA, where he specialized on applications of statistical mechanics on complex thermodynamic systems working with Professor Monica Olvera de la Cruz research group. | 1 | Applied and Interdisciplinary Chemistry |
Sericitic alteration or sericitization is a process of mineral alteration caused by hydrothermal fluids invading permeable country rock. Plagioclase feldspar within the rock is converted to sericite (sericite is not a mineral; it is a term that is used to describe any fine-grained white phyllosilicate when a distinction cannot be determined), which typically consists of fine-grained white mica and related minerals. Sericitic alteration occurs within the phyllic alteration zone. | 0 | Theoretical and Fundamental Chemistry |
LNGFR also activates a caspase-dependent signaling pathway that promotes developmental axon pruning, and axon degeneration in neurodegenerative disease.
In the apoptosis pathway, members of the TNF receptor superfamily assemble a death-inducing signaling complex (DISC) in which TRADD or FADD bind directly to the receptor's death domain, thereby allowing aggregation and activation of Caspase 8 and subsequent activation of the Caspase cascade. However, Caspase 8 induction does not appear to be involved in p75NTR-mediated apoptosis, but Caspase 9 is activated during p75NTR-mediated killing. | 1 | Applied and Interdisciplinary Chemistry |
For reversible dissociations in a chemical equilibrium
the dissociation constant K is the ratio of dissociated to undissociated compound
where the brackets denote the equilibrium concentrations of the species. | 0 | Theoretical and Fundamental Chemistry |
Poly(p-phenylene) (PPP) is made of repeating p-phenylene units, which act as the precursor to a conducting polymer of the rigid-rod polymer family. The synthesis of PPP has proven challenging, but has been accomplished through excess polycondensation with the Suzuki coupling method.
Early efforts typically produced black, insoluble powders that were difficult to characterize. For example, a 1962 paper reports "The solid glowed red-hot in a Bunsen flame, with no evidence of flame formation, and disappeared only slowly." (J. Polym. Sci. (1960), 47, 45) Initially, the chemical and thermal stability of the material drove interest in its synthesis. It was used in rocket nozzles and some fabrics requiring high thermal stability.
Oxidation or the use of dopants is used to convert the non-conductive form to a semiconductor. | 0 | Theoretical and Fundamental Chemistry |
:V10AX01 Phosphorus (P) chromicphosphate colloid
:V10AX02 Samarium (Sm) hydroxyapatite colloid
:V10AX03 Dysprosium (Dy) colloid
:V10AX04 Erbium (Er) citrate colloid
:V10AX05 Rhenium (Re) sulfide colloid
:V10AX06 Gold (Au) colloidal | 1 | Applied and Interdisciplinary Chemistry |
By local transformations, the weld toe plastically deformed and solidified.
The depth of the aftertreatment track should be between 0.2 and 0.35 mm.
The undercut at the weld toe is no longer recognizable. | 1 | Applied and Interdisciplinary Chemistry |
Vicinal difunctionalization refers to a chemical reaction involving transformations at two adjacent centers (most commonly carbons). This transformation can be accomplished in α,β-unsaturated carbonyl compounds via the conjugate addition of a nucleophile to the β-position followed by trapping of the resulting enolate with an electrophile at the α-position. When the nucleophile is an enolate and the electrophile a proton, the reaction is called Michael addition. | 0 | Theoretical and Fundamental Chemistry |
Molecular cloning refers to the process of making multiple molecules. Cloning is commonly used to amplify DNA fragments containing whole genes, but it can also be used to amplify any DNA sequence such as promoters, non-coding sequences and randomly fragmented DNA. It is used in a wide array of biological experiments and practical applications ranging from genetic fingerprinting to large scale protein production. Occasionally, the term cloning is misleadingly used to refer to the identification of the chromosomal location of a gene associated with a particular phenotype of interest, such as in positional cloning. In practice, localization of the gene to a chromosome or genomic region does not necessarily enable one to isolate or amplify the relevant genomic sequence. To amplify any DNA sequence in a living organism, that sequence must be linked to an origin of replication, which is a sequence of DNA capable of directing the propagation of itself and any linked sequence. However, a number of other features are needed, and a variety of specialised cloning vectors (small piece of DNA into which a foreign DNA fragment can be inserted) exist that allow protein production, affinity tagging, single-stranded RNA or DNA production and a host of other molecular biology tools.
Cloning of any DNA fragment essentially involves four steps
# fragmentation - breaking apart a strand of DNA
# ligation – gluing together pieces of DNA in a desired sequence
# transfection – inserting the newly formed pieces of DNA into cells
# screening/selection – selecting out the cells that were successfully transfected with the new DNA
Although these steps are invariable among cloning procedures a number of alternative routes can be selected; these are summarized as a cloning strategy.
Initially, the DNA of interest needs to be isolated to provide a DNA segment of suitable size. Subsequently, a ligation procedure is used where the amplified fragment is inserted into a vector (piece of DNA). The vector (which is frequently circular) is linearised using restriction enzymes, and incubated with the fragment of interest under appropriate conditions with an enzyme called DNA ligase. Following ligation, the vector with the insert of interest is transfected into cells. A number of alternative techniques are available, such as chemical sensitisation of cells, electroporation, optical injection and biolistics. Finally, the transfected cells are cultured. As the aforementioned procedures are of particularly low efficiency, there is a need to identify the cells that have been successfully transfected with the vector construct containing the desired insertion sequence in the required orientation. Modern cloning vectors include selectable antibiotic resistance markers, which allow only cells in which the vector has been transfected, to grow. Additionally, the cloning vectors may contain colour selection markers, which provide blue/white screening (alpha-factor complementation) on X-gal medium. Nevertheless, these selection steps do not absolutely guarantee that the DNA insert is present in the cells obtained. Further investigation of the resulting colonies must be required to confirm that cloning was successful. This may be accomplished by means of PCR, restriction fragment analysis and/or DNA sequencing. | 1 | Applied and Interdisciplinary Chemistry |
In MRI and NMR spectroscopy, an observable nuclear spin polarization (magnetization) is created by a homogeneous magnetic field. This field makes the magnetic dipole moments of the sample precess at the resonance (Larmor) frequency of the nuclei. At thermal equilibrium, nuclear spins precess randomly about the direction of the applied field. They become abruptly phase coherent when they are hit by radiofrequency (RF) pulses at the resonant frequency, created orthogonal to the field. The RF pulses cause the population of spin-states to be perturbed from their thermal equilibrium value. The generated transverse magnetization can then induce a signal in an RF coil that can be detected and amplified by an RF receiver. The return of the longitudinal component of the magnetization to its equilibrium value is termed spin-lattice relaxation while the loss of phase-coherence of the spins is termed spin-spin relaxation, which is manifest as an observed free induction decay (FID).
For spin=½ nuclei (such as H), the polarization due to spins oriented with the field N relative to the spins oriented against the field N is given by the Boltzmann distribution:
where ΔE is the energy level difference between the two populations of spins, k is the Boltzmann constant, and T is the sample temperature. At room temperature, the number of spins in the lower energy level, N−, slightly outnumbers the number in the upper level, N+. The energy gap between the spin-up and spin-down states in NMR is minute by atomic emission standards at magnetic fields conventionally used in MRI and NMR spectroscopy. Energy emission in NMR must be induced through a direct interaction of a nucleus with its external environment rather than by spontaneous emission. This interaction may be through the electrical or magnetic fields generated by other nuclei, electrons, or molecules. Spontaneous emission of energy is a radiative process involving the release of a photon and typified by phenomena such as fluorescence and phosphorescence. As stated by Abragam, the probability per unit time of the nuclear spin-1/2 transition from the + into the
- state through spontaneous emission of a photon is a negligible phenomenon.
Rather, the return to equilibrium is a much slower thermal process induced by the fluctuating local magnetic fields due to molecular or electron (free radical) rotational motions that return the excess energy in the form of heat to the surroundings. | 0 | Theoretical and Fundamental Chemistry |
Since the seminal work of P. Orlandi, the Lamb–Chaplygin vortex model has been a popular choice for numerical studies on vortex-environment interactions. The fact that it does not deform make it a prime candidate for consistent flow initialization. A less favorable property is that the second derivative of the flow field at the dipole's edge is not continuous. Further, it serves a framework for stability analysis on dipolar-vortex structures. | 1 | Applied and Interdisciplinary Chemistry |
This element describes the impedance of a finite-length diffusion with reflective boundary. It is described by the following equation: | 0 | Theoretical and Fundamental Chemistry |
In many cases, it is preferable to use a slightly modified version of the Gouy-Stodola theorem in work form, where is replaced by some effective temperature. When this is done, it often enlarges the scope of the theorem, and adapts it to be applicable to more systems or situations. For example, the corrections elaborated below are only necessary when the system exchanges heat with more than one reservoir - if it exchanges heat only at the environmental temperature , the simple form above holds true. Additionally, modifications may change the reversible process to which the real process is compared in calculating .
The modified theorem then readswhere is the effective temperature.
For a flow process, let denote the specific entropy (entropy per unit mass) at the inlet, where mass flows in, and the specific entropy at the outlet, where mass flows out. Similarly, denote the specific enthalpies by and . The inlet and outlet, in this case, function as initial and final states a process: mass enters the system at an initial state (the inlet, indexed "1"), undergoes some process, and then leaves at a final state (the outlet, indexed "2").
This process is then compared to a reversible process, with the same initial state, but with a (possibly) different final state. The theoretical specific entropy and enthalpy after this ideal, isentropic process are given by and , respectively. When the actual process is compared to this theoretical reversible process and is evaluated, the proper effective temperature is given byIn general, lies somewhere in between the final temperature in the actual process and the final temperature in the theoretical reversible process .
This equation above can sometimes be simplified. If both the pressure and the specific heat capacity remain constant, then the changes in enthalpy and entropy can be written in terms of the temperatures, andHowever, it is important to note that this version of the theorem doesn't relate the exact values which the original theorem does. Specifically, in comparing the actual process to a reversible one, the modified version allows the final state to be different between the two. This is in contrast to the original version, wherein reversible process is constructed to match so that the final states are the same. | 0 | Theoretical and Fundamental Chemistry |
Substituting for f the Metropolis function defined above (which satisfies the detailed balance condition), and setting C to zero, gives
The advantage of this formulation (apart from its simplicity) is that it can be computed without performing two simulations, one in each specific ensemble. Indeed, it is possible to define an extra kind of "potential switching" Metropolis trial move (taken every fixed number of steps), such that the single sampling from the "mixed" ensemble suffices for the computation. | 0 | Theoretical and Fundamental Chemistry |
Confluences are studied in a variety of sciences. Hydrology studies the characteristic flow patterns of confluences and how they give rise to patterns of erosion, bars, and scour pools. The water flows and their consequences are often studied with mathematical models. Confluences are relevant to the distribution of living organisms (i.e., ecology) as well; "the general pattern [downstream of confluences] of increasing stream flow and decreasing slopes drives a corresponding shift in habitat characteristics."
Another science relevant to the study of confluences is chemistry, because sometimes the mixing of the waters of two streams triggers a chemical reaction, particularly in a polluted stream. The United States Geological Survey gives an example: "chemical changes occur when a stream contaminated with acid mine drainage combines with a stream with near-neutral pH water; these reactions happen very rapidly and influence the subsequent transport of metals downstream of the mixing zone."
A natural phenomenon at confluences that is obvious even to casual observers is a difference in color between the two streams; see images in this article for several examples. According to Lynch, "the color of each river is determined by many things: type and amount of vegetation in the watershed, geological properties, dissolved chemicals, sediments and biologic content – usually algae." Lynch also notes that color differences can persist for miles downstream before they finally blend completely. | 1 | Applied and Interdisciplinary Chemistry |
The mechanical properties of materials describe characteristics such as their strength and resistance to deformation. For example, steel beams are used in construction because of their high strength, meaning that they neither break nor bend significantly under the applied load.
Mechanical properties include elasticity, plasticity, tensile strength, compressive strength, shear strength, fracture toughness, ductility (low in brittle materials) and indentation hardness. Solid mechanics is the study of the behavior of solid matter under external actions such as external forces and temperature changes.
A solid does not exhibit macroscopic flow, as fluids do. Any degree of departure from its original shape is called deformation. The proportion of deformation to original size is called strain. If the applied stress is sufficiently low, almost all solid materials behave in such a way that the strain is directly proportional to the stress (Hookes law). The coefficient of the proportion is called the modulus of elasticity or Youngs modulus. This region of deformation is known as the linearly elastic region. Three models can describe how a solid responds to an applied stress:
*Elasticity – When an applied stress is removed, the material returns to its undeformed state.
*Viscoelasticity – These are materials that behave elastically, but also have damping. When the applied stress is removed, work has to be done against the damping effects and is converted to heat within the material. This results in a hysteresis loop in the stress–strain curve. This implies that the mechanical response has a time-dependence.
*Plasticity – Materials that behave elastically generally do so when the applied stress is less than a yield value. When the stress is greater than the yield stress, the material behaves plastically and does not return to its previous state. That is, irreversible plastic deformation (or viscous flow) occurs after yield that is permanent.
Many materials become weaker at high temperatures. Materials that retain their strength at high temperatures, called refractory materials, are useful for many purposes. For example, glass-ceramics have become extremely useful for countertop cooking, as they exhibit excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C.
In the aerospace industry, high performance materials used in the design of aircraft and/or spacecraft exteriors must have a high resistance to thermal shock. Thus, synthetic fibers spun out of organic polymers and polymer/ceramic/metal composite materials and fiber-reinforced polymers are now being designed with this purpose in mind. | 0 | Theoretical and Fundamental Chemistry |
Quark matter or QCD matter (quantum chromodynamic) refers to any of a number of hypothetical phases of matter whose degrees of freedom include quarks and gluons, of which the prominent example is quark-gluon plasma. Several series of conferences in 2019, 2020, and 2021 were devoted to this topic.
Quarks are liberated into quark matter at extremely high temperatures and/or densities, and some of them are still only theoretical as they require conditions so extreme that they cannot be produced in any laboratory, especially not at equilibrium conditions. Under these extreme conditions, the familiar structure of matter, where the basic constituents are nuclei (consisting of nucleons which are bound states of quarks) and electrons, is disrupted. In quark matter it is more appropriate to treat the quarks themselves as the basic degrees of freedom.
In the standard model of particle physics, the strong force is described by the theory of QCD. At ordinary temperatures or densities this force just confines the quarks into composite particles (hadrons) of size around 10 m = 1 femtometer = 1 fm (corresponding to the QCD energy scale Λ ≈ 200 MeV) and its effects are not noticeable at longer distances.
However, when the temperature reaches the QCD energy scale (T of order 10 kelvins) or the density rises to the point where the average inter-quark separation is less than 1 fm (quark chemical potential μ around 400 MeV), the hadrons are melted into their constituent quarks, and the strong interaction becomes the dominant feature of the physics. Such phases are called quark matter or QCD matter.
The strength of the color force makes the properties of quark matter unlike gas or plasma, instead leading to a state of matter more reminiscent of a liquid. At high densities, quark matter is a Fermi liquid, but is predicted to exhibit color superconductivity at high densities and temperatures below 10 K. | 0 | Theoretical and Fundamental Chemistry |
Mathematically, the pressure of a mixture of non-reactive gases can be defined as the summation:
where , , ..., represent the partial pressures of each component.
where is the mole fraction of the ith component in the total mixture of n components . | 0 | Theoretical and Fundamental Chemistry |
Changes in land use, the combustion of fossil fuels, and the production of cement have led to an increase in CO concentration in the atmosphere. At present, about one third (approximately 2 Pg C y = 2 × 10 grams of carbon per year) of anthropogenic emissions of CO may be entering the ocean, but this is quite uncertain. Some research suggests that a link between elevated CO and marine primary production exists.
Climate change may affect the biological pump in the future by warming and stratifying the surface ocean. It is believed that this could decrease the supply of nutrients to the euphotic zone, reducing primary production there. Also, changes in the ecological success of calcifying organisms caused by ocean acidification may affect the biological pump by altering the strength of the hard tissues pump. This may then have a "knock-on" effect on the soft tissues pump because calcium carbonate acts to ballast sinking organic material.
The second diagram on the right shows some possible effects of sea ice decline and permafrost thaw on Arctic carbon fluxes. On land, plants take up carbon while microorganisms in the soil produce methane and respire CO. Lakes are net emitters of methane, and organic and inorganic carbon (dissolved and particulate) flow into the ocean through freshwater systems. In the ocean, methane can be released from thawing subsea permafrost, and CO is absorbed due to an undersaturation of CO in the water compared with the atmosphere. In addition, multiple fluxes are closely associated to sea ice. Current best estimates of atmospheric fluxes are given in Tg C year, where available. Note that the emission estimate for lakes is for the area North of ~50º N rather than the narrower definition of arctic tundra for the other terrestrial fluxes. When available, uncertainty ranges are shown in brackets. The arrows do not represent the size of each flux.
The biological pump is thought to have played significant roles in atmospheric CO fluctuations during past glacial-interglacial periods. However, it is not yet clear how the biological pump will respond to future climate change. For such predictions to be reasonable, it is important to first decipher the response of phytoplankton, one of the key components of the biological pump to future changes in atmospheric CO. Due to their phylogenetic diversity, different phytoplankton taxa will likely respond to climate change in different ways. For instance, a decrease in the abundance of diatom is expected due to increased stratification in the future ocean. Diatoms are highly efficient in transporting carbon to depths by forming large, rapidly sinking aggregates and their reduced numbers could in turn lead to decreased carbon export.
Further, decreased ocean pH due to ocean acidification may thwart the ability of coccolithophores to generate calcareous plates, potentially affecting the biological pump; however, it appears that some species are more sensitive than others. Thus, future changes in the relative abundance of these or other phytoplankton taxa could have a marked impact on total ocean productivity, subsequently affecting ocean biogeochemistry and carbon storage.
A 2015 study determined that coccolithophore concentrations in the North Atlantic have increased by an order of magnitude since the 1960s and an increase in absorbed CO, as well as temperature, were modeled to be the most likely cause of this increase.
In a 2017 study, scientists used species distribution modelling (SDM) to predict the future global distribution of two phytoplankton species important to the biological pump: the diatom Chaetoceros diadema and the coccolithophore Emiliania huxleyi. They employed environmental data described in the IPCC Representative Concentration Pathways scenario 8.5, which predicts radiative forcing in the year 2100 relative to pre-industrial values. Their modelling results predicted that the total ocean area covered by C. diadema and E. huxleyi would decline by 8% and 16%, respectively, under the examined climate scenario. They predicted changes in the range and distribution of these two phytoplankton species under these future ocean conditions, if realized, might result in reduced contribution to carbon sequestration via the biological pump. In 2019, a study indicated that at current rates of seawater acidification, we could see Antarctic phytoplanktons smaller and less effective at storing carbon before the end of the century. | 0 | Theoretical and Fundamental Chemistry |
Arsenic interferes with cellular longevity by allosteric inhibition of an essential metabolic enzyme pyruvate dehydrogenase complex, which catalyzes the oxidation of pyruvate to acetyl-CoA by NAD. With the enzyme inhibited, the energy system of the cell is disrupted resulting in cellular apoptosis. Biochemically, arsenic prevents use of thiamine resulting in a clinical picture resembling thiamine deficiency. Poisoning with arsenic can raise lactate levels and lead to lactic acidosis. Low potassium levels in the cells increases the risk of experiencing a life-threatening heart rhythm problem from arsenic trioxide.
Arsenic in cells clearly stimulates the production of hydrogen peroxide (HO). When the HO reacts with certain metals such as iron or manganese it produces a highly reactive hydroxyl radical. Inorganic arsenic trioxide found in ground water particularly affects voltage-gated potassium channels,
disrupting cellular electrolytic function resulting in neurological disturbances, cardiovascular episodes such as prolonged QT interval, neutropenia, high blood pressure,
central nervous system dysfunction, anemia, and death.
Arsenic has also been shown to induce cardiac hypertrophy by activating certain transcription factors involved in pathologically remodeling the heart. Tissue culture studies have shown that arsenic compounds block both IKr and Iks channels and, at the same time, activate IK-ATP channels. Arsenic compounds also disrupt ATP production through several mechanisms. At the level of the citric acid cycle, arsenic inhibits pyruvate dehydrogenase and by competing with phosphate it uncouples oxidative phosphorylation, thus inhibiting energy-linked reduction of NAD+, mitochondrial respiration, and ATP synthesis. Hydrogen peroxide production is also increased, which might form reactive oxygen species and oxidative stress. These metabolic interferences lead to death from multi-system organ failure, probably from necrotic cell death, not apoptosis. A post mortem reveals brick red colored mucosa, due to severe hemorrhage. Although arsenic causes toxicity, it can also play a protective role. | 1 | Applied and Interdisciplinary Chemistry |
Iron is an important biological element. It is used in both the ubiquitous iron-sulfur proteins and in vertebrates it is used in hemoglobin which is essential for blood and oxygen transport. | 1 | Applied and Interdisciplinary Chemistry |
Arteriviruses are small, enveloped, animal viruses with an icosahedral core containing a positive-sense RNA genome. The family includes equine arteritis virus (EAV), porcine reproductive and respiratory syndrome virus (PRRSV), lactate dehydrogenase elevating virus (LDV) of mice and simian haemorrhagic fever virus (SHFV). | 1 | Applied and Interdisciplinary Chemistry |
Dianium was the proposed name for a new element found by the mineralogist and poet Wolfgang Franz von Kobell in 1860. The name derived from the Roman goddess Diana. During the analysis of the mineral tantalite and niobite, he concluded that it does contain an element similar to niobium and tantalum. The symbol was Di.
Following the rediscovery of niobium in 1846 by the German chemist Heinrich Rose, Friedrich Wöhler, Heinrich Rose, R. Hermann and Kobell analysed the minerals tantalite and columbite to better understand the chemistry of niobium and tantalum. The similar reactivity of niobium and tantalum hindered preparation of pure samples and therefore several new elements were proposed, which were later found to be mixtures of niobium and tantalum. Rose discovered pelopium in 1846, while Hermann announced the discovery of ilmenium in 1847. In 1860, Kobell published the results on the tantalite from a quarry near Kimito a village in Finland and columbite from Bodenmais a village in Germany. He concluded that the element he found was different from tantalum, niobium, pelopium and ilmenium.
The differences between tantalum and niobium and the fact that no other similar element was present were unequivocally demonstrated in 1864 by Christian Wilhelm Blomstrand, and Henri Etienne Sainte-Claire Deville, as well as by Louis J. Troost, who determined the formulas of some of the compounds in 1865 and finally by the Swiss chemist Jean Charles Galissard de Marignac.
Both tantalum and niobium react with chlorine and traces of oxygen, including atmospheric concentrations, with niobium forming two compounds: the white volatile niobium pentachloride (NbCl) and the non-volatile niobium oxychloride (NbOCl). The claimed new elements pelopium, ilmenium and dianium were in fact identical to niobium or mixtures of niobium and tantalum. | 1 | Applied and Interdisciplinary Chemistry |
Vacuum arc remelting (VAR) is a secondary remelting process for vacuum refining and manufacturing of ingots with improved chemical and mechanical homogeneity.
In critical military and commercial aerospace applications, material engineers commonly specify VIM-VAR steels. VIM means vacuum induction melted and VAR means vacuum arc remelted. VIM-VAR steels become bearings for jet engines, rotor shafts for military helicopters, flap actuators for fighter jets, gears in jet or helicopter transmissions, mounts or fasteners for jet engines, jet tail hooks and other demanding applications.
Most grades of steel are melted once and are then cast or teemed into a solid form prior to extensive forging or rolling to a metallurgically-sound form. In contrast, VIM-VAR steels go through two more highly purifying melts under vacuum. After melting in an electric arc furnace and alloying in an argon oxygen decarburization vessel, steels destined for vacuum remelting are cast into ingot molds. The solidified ingots then head for a vacuum induction melting furnace. This vacuum remelting process rids the steel of inclusions and unwanted gases while optimizing the chemical composition.
The VIM operation returns these solid ingots to the molten state in the contaminant-free void of a vacuum. This tightly controlled melt often requires up to 24 hours. Still enveloped by the vacuum, the hot metal flows from the VIM furnace crucible into giant electrode molds. A typical electrode is about 15 feet (5 m) tall and will be in various diameters. The electrodes solidify under vacuum.
For VIM-VAR steels, the surface of the cooled electrodes must be ground to remove surface irregularities and impurities before the next vacuum remelt. Then the ground electrode is placed in a VAR furnace. In a VAR furnace, the steel gradually melts drop-by-drop in the vacuum-sealed chamber. Vacuum arc remelting further removes lingering inclusions to provide superior steel cleanliness and remove gases like oxygen, nitrogen and hydrogen. Controlling the rate at which these droplets form and solidify ensures a consistency of chemistry and microstructure throughout the entire VIM-VAR ingot, making the steel more resistant to fracture or fatigue. This refinement process is essential to meet the performance characteristics of parts like a helicopter rotor shaft, a flap actuator on a military jet, or a bearing in a jet engine.
For some commercial or military applications, steel alloys may go through only one vacuum remelt, namely the VAR. For example, steels for solid rocket cases, landing gears, or torsion bars for fighting vehicles typically involve one vacuum remelt.
Vacuum arc remelting is also used in production of titanium and other metals which are reactive or in which high purity is required. | 1 | Applied and Interdisciplinary Chemistry |
In inorganic chemistry, the cis effect is defined as the labilization (or destabilization) of CO ligands that are cis to other ligands. CO is a well-known strong pi-accepting ligand in organometallic chemistry that will labilize in the cis position when adjacent to ligands due to steric and electronic effects. The system most often studied for the cis effect is an octahedral complex where X is the ligand that will labilize a CO ligand cis to it. Unlike the trans effect, which is most often observed in 4-coordinate square planar complexes, the cis effect is observed in 6-coordinate octahedral transition metal complexes. It has been determined that ligands that are weak sigma donors and non-pi acceptors seem to have the strongest cis-labilizing effects. Therefore, the cis effect has the opposite trend of the trans-effect, which effectively labilizes ligands that are trans to strong pi accepting and sigma donating ligands. | 0 | Theoretical and Fundamental Chemistry |
Some carbon removal techniques add alkalinity to the ocean and therefore immediately buffer pH changes which might help the organisms in the region that the extra alkalinity is added to. The two technologies that fall into this category are ocean alkalinity enhancement and electrochemical methods. Eventually, due to diffusion, that alkalinity addition will be quite small to distant waters. This is why the term local ocean acidification mitigation is used. Both of these technologies have the potential to operate on a large scale and to be efficient at removing carbon dioxide. However, they are expensive, have many risks and side effects and currently have a low technology readiness level. | 0 | Theoretical and Fundamental Chemistry |
After Wilhelm Röntgen discovered X-rays in 1895, many scientists began to work on ionizing radiation. One of these was Henri Becquerel, who investigated the relationship between phosphorescence and the blackening of photographic plates. When Becquerel (working in France) discovered that, with no external source of energy, the uranium generated rays which could blacken (or fog) the photographic plate, radioactivity was discovered. Marie Skłodowska-Curie (working in Paris) and her husband Pierre Curie isolated two new radioactive elements from uranium ore. They used radiometric methods to identify which stream the radioactivity was in after each chemical separation; they separated the uranium ore into each of the different chemical elements that were known at the time, and measured the radioactivity of each fraction. They then attempted to separate these radioactive fractions further, to isolate a smaller fraction with a higher specific activity (radioactivity divided by mass). In this way, they isolated polonium and radium. It was noticed in about 1901 that high doses of radiation could cause an injury in humans. Henri Becquerel had carried a sample of radium in his pocket and as a result he suffered a highly localized dose which resulted in a radiation burn. This injury resulted in the biological properties of radiation being investigated, which in time resulted in the development of medical treatment.
Ernest Rutherford, working in Canada and England, showed that radioactive decay can be described by a simple equation (a linear first degree derivative equation, now called first order kinetics), implying that a given radioactive substance has a characteristic "half-life" (the time taken for the amount of radioactivity present in a source to diminish by half). He also coined the terms alpha, beta and gamma rays, he converted nitrogen into oxygen, and most importantly he supervised the students who conducted the Geiger–Marsden experiment (gold foil experiment) which showed that the plum pudding model of the atom was wrong. In the plum pudding model, proposed by J. J. Thomson in 1904, the atom is composed of electrons surrounded by a cloud of positive charge to balance the electrons' negative charge. To Rutherford, the gold foil experiment implied that the positive charge was confined to a very small nucleus leading first to the Rutherford model, and eventually to the Bohr model of the atom, where the positive nucleus is surrounded by the negative electrons.
In 1934, Marie Curie's daughter (Irène Joliot-Curie) and son-in-law (Frédéric Joliot-Curie) were the first to create artificial radioactivity: they bombarded boron with alpha particles to make the neutron-poor isotope nitrogen-13; this isotope emitted positrons. In addition, they bombarded aluminium and magnesium with neutrons to make new radioisotopes.
In the early 1920s Otto Hahn created a new line of research. Using the "emanation method", which he had recently developed, and the "emanation ability", he founded what became known as "applied radiochemistry" for the researching of general chemical and physical-chemical questions. In 1936 Cornell University Press published a book in English (and later in Russian) titled Applied Radiochemistry, which contained the lectures given by Hahn when he was a visiting professor at Cornell University in Ithaca, New York, in 1933. This important publication had a major influence on almost all nuclear chemists and physicists in the United States, the United Kingdom, France, and the Soviet Union during the 1930s and 1940s, laying the foundation for modern nuclear chemistry.
Hahn and Lise Meitner discovered radioactive isotopes of radium, thorium, protactinium and uranium. He also discovered the phenomena of radioactive recoil and nuclear isomerism, and pioneered rubidium–strontium dating. In 1938, Hahn, Lise Meitner and Fritz Strassmann discovered nuclear fission, for which Hahn received the 1944 Nobel Prize for Chemistry. Nuclear fission was the basis for nuclear reactors and nuclear weapons. Hahn is referred to as the father of nuclear chemistry and godfather of nuclear fission. | 0 | Theoretical and Fundamental Chemistry |
Organismal metabolic rate, or the rate at which organisms assimilate, transform, and expend energy, is influenced by a few key constituents, namely light, nutrients, temperature, and organic matter. The influence of these constituents on organismal metabolism ultimately governs metabolism at the whole-lake scale and can dictate whether a lake is a net source or sink of carbon. In the following section, we describe the relationship between these key constituents and organismal and ecosystem-level metabolism. Although relationships between organisms and constituents described here are well-established, interacting effects of constituents on metabolic rates from organisms to lake ecosystems makes predicting changes in metabolism across lakes or within lakes through time difficult. Many of these complex interacting effects will be discussed in the spatial and temporal variability section. | 1 | Applied and Interdisciplinary Chemistry |
Photoredox catalysis exploits [Ru(bpy)] as a sensitizer as a strategy for organic synthesis. Many analogues of [Ru(bpy)] are employed as well. These transformations exploit the redox properties of [Ru(bpy)]* and its reductively quenched derivative [Ru(bpy)]. | 0 | Theoretical and Fundamental Chemistry |
Consider the simpler case where there are two binding sites. See the scheme shown below. Each site is assumed to bind either molecule of substrate S or product P. The catalytic reaction is shown by the two reactions at the base of the scheme triangle, that is S to P and P to S. The model assumes the binding steps are always at equilibrium. The reaction rate is given by:
Invoking the rapid-equilibrium assumption we can write the various complexes in terms of equilibrium constants to give:
where . The and <math>
\pi and and
Using the author's own notation, if an enzyme has sites that can bind ligand, the form, in the general case, can be shown to be:
The non-cooperative reversible Michaelis-Menten equation can be seen to emerge when we set the Hill coefficient to one.
If the enzyme is irreversible the equation turns into the simple Michaelis-Menten equation that is irreversible. When setting the equilibrium constant to infinity, the equation can be seen to revert to the simpler case where the product inhibits the reverse step.
A comparison has been made between the MWC and reversible Hill equation.
A modification of the reversible Hill equation was published by Westermark et al where modifiers affected the catalytic properties instead. This variant was shown to provide a much better fit for describing the kinetics of muscle phosphofructokinase. | 0 | Theoretical and Fundamental Chemistry |
Lauri Vaska (May 7, 1925 – November 15, 2015) was an Estonian-American chemist who has made noteworthy contributions to organometallic chemistry.
Vaska was born in Rakvere, Estonia. He was educated at the Baltic University in Hamburg, Germany (1946) and subsequently at the University of Göttingen (1946–1949), where he received his Vordiplom (equivalent to the American B.S. degree). He emigrated to the United States in 1952 and pursued his Ph.D. in inorganic chemistry at the University of Texas (1952–1956). He was a postdoctoral fellow at Northwestern University (1956–1957) where he conducted research on magnetochemistry. In 1957 he took a position as Fellow at the Mellon Institute in Pittsburgh, where he remained until 1964. During that time, the Mellon Institute housed a number of future chemists, including Paul Lauterbur and R. Bruce King. Vaska moved as an associate professor to Clarkson University in Potsdam, New York, where, from 1990 to his death, he was professor emeritus of chemistry. His brother is a philosopher. He died in Basking Ridge, New Jersey in 2015, aged 90. | 0 | Theoretical and Fundamental Chemistry |
The use of fibrin hydrogel in gene delivery (transfection) is studied to address essential factors controlling the delivery process such as fibrinogen and pDNA concentration in addition to significance of cell-mediated fibrin degradation for pursuing the potential of cell-transfection microarray engineering or in vivo gene transfer. Gene transfer is more successful in-gel than on-gel probably because of proximity of lipoplexes and target cells. Less cytotoxicity is observed due to less use of transfection agents like lipofectamine and steady degradation of fibrin. Consequently, each cell type requires optimization of fibrinogen and pDNA concentrations for higher transfection yields and studies towards high-throughput transfection microarray experiments are promising. | 1 | Applied and Interdisciplinary Chemistry |
Ružička was the recipient of eight honorary doctorates and the 1938 Marcel Benoist Prize. He was listed as author on 583 scientific papers. In 1965, he became an honorary member of the Polish Chemical Society, and he was an honorary member of the American Academy of Arts and Sciences. After the war he acquired a taste for Dutch masterpieces, which he later lodged in the Kunsthaus Zürich as the Ružička collection. He militated against nuclear weapons.
In 1970, Ružička delivered to the Nobel Laureate Conferences in Lindau a lecture entitled "Nobel Prizes and the chemistry of life".
In later years, he served as consultant to Sandoz A. G. of Basel.
Ružička dedicated significant efforts to the problems of education. He insisted on a better organization of academic education and scientific work in the new Yugoslavia, and established the Swiss-Yugoslav Society. Ružička became an honorary academician at the then Yugoslav Academy of Sciences and Arts in Zagreb.
In 1974 he was awarded the Order of the Yugoslav Flag with Golden Wreath.
At ETH Zurich, the Ružička Award was established in 1957 on the occasion of his retirement, for young chemists working in Switzerland.
In his native Vukovar, a museum was opened in his honour in 1977.
Ružička's archives are kept at ETH Zurich.
The Ružička reaction is named after him. | 0 | Theoretical and Fundamental Chemistry |
Other lipase inhibitors have been recognized, e.g. from different plant products. These include alkaloids, carotenoids, glycosides, polyphenols, polysaccharides, saponins and terpenoids. However, none of these have been used clinically as lipase inhibitors. More active lipase inhibitors are the lipophilic compounds from microbial sources.
Lipase inhibitors from microbial source can be divided into two classes based on their structure. Those who have a β-lactone ring are lipstatin, valilactone, percyquinin, panclicin A-E, ebelactone A and B, vibralactone and esterastin. Those who do not have a β-lactone ring are (E)-4-amino styryl acetate, ε–polylysine and caulerpenyne.
Lipase inhibitors have also been made synthetically, e.g. cetilistat, based on the structure of triglycerides and other natural lipase substrates. However, the synthetic lipase inhibitors differ in structure and some of them lack the β-lactone ring. | 1 | Applied and Interdisciplinary Chemistry |
The Shelby Gem Factory was the production facility of ICT Incorporated, a company in Shelby, Michigan, United States, that manufactured artificial gemstones through proprietary processes. ICT began operations in 1970 and closed in December 2019. | 0 | Theoretical and Fundamental Chemistry |
Jiří Hála claims in his textbook "Radioactivity, Ionizing Radiation and Nuclear Energy" that cattle only pass a minority of the strontium, caesium, plutonium and americium they ingest to the humans who consume milk and meat. Using milk as an example, if the cow has a daily intake of 1000 Bq of the preceding isotopes then the milk will have the following activities.
* Sr, 2 Bq/L
* Cs, 5 Bq/L
* Pu, 0.001 Bq/L
* Am, 0.001 Bq/L | 0 | Theoretical and Fundamental Chemistry |
Butter yellow was synthesized by Peter Griess in the 1860s at the Royal College of Chemistry in London. The dye was used to dye butter in Germany and other parts of the world during the latter half of the 19th century and the beginning of the 20th before being phased out in the 1930s and 40s. It was in the 1930s that research led by Riojun Kinosita showed the link between several azo dyes and cancer, linking butter yellow to liver cancer in rats after two to three months exposure. In 1939, the International Congress for Cancer Research issued a recommendation for the banning of cancer-causing food dyes (including butter yellow) from food production.
In 2014, dried tofu products (a.k.a. dougan 豆乾) from Taiwan were found to have been adulterated with methyl yellow, used as a coloring agent. | 0 | Theoretical and Fundamental Chemistry |
The most direct way of measuring the activity of a volatile species is to measure its equilibrium partial vapor pressure. For water as solvent, the water activity a is the equilibrated relative humidity. For non-volatile components, such as sucrose or sodium chloride, this approach will not work since they do not have measurable vapor pressures at most temperatures. However, in such cases it is possible to measure the vapor pressure of the solvent instead. Using the Gibbs–Duhem relation it is possible to translate the change in solvent vapor pressures with concentration into activities for the solute.
The simplest way of determining how the activity of a component depends on pressure is by measurement of densities of solution, knowing that real solutions have deviations from the additivity of (molar) volumes of pure components compared to the (molar) volume of the solution. This involves the use of partial molar volumes, which measure the change in chemical potential with respect to pressure.
Another way to determine the activity of a species is through the manipulation of colligative properties, specifically freezing point depression. Using freezing point depression techniques, it is possible to calculate the activity of a weak acid from the relation,
where is the total equilibrium molality of solute determined by any colligative property measurement (in this case ), is the nominal molality obtained from titration and is the activity of the species.
There are also electrochemical methods that allow the determination of activity and its coefficient.
The value of the mean ionic activity coefficient of ions in solution can also be estimated with the Debye–Hückel equation, the Davies equation or the Pitzer equations. | 0 | Theoretical and Fundamental Chemistry |
Single-step carbon sequestration and storage is a saline water-based mineralization technology extracting carbon dioxide from seawater and storing it in the form of solid minerals. | 0 | Theoretical and Fundamental Chemistry |
Freeze–thaw weathering is caused by moisture freezing inside cracks in rock. Upon freezing its volume expands, causing large forces which cracks spall off the outer surface. As this cycle repeats the outer surface repeatedly undergoes spalling, resulting in weathering.
Some stone and masonry surfaces used as building surfaces will absorb moisture at their surface. If exposed to severe freezing conditions, the surface may flake off due to the expansion of the water. This effect can also be seen in terracotta surfaces (even if glazed) if there is an entrance for water at the edges. | 1 | Applied and Interdisciplinary Chemistry |
Chvorinov's rule is a physical relationship that relates the solidification time for a simple casting to the volume and surface area of the casting. It was first expressed by Czech engineer Nicolas Chvorinov in 1940. | 1 | Applied and Interdisciplinary Chemistry |
xDNA (also known as expanded DNA or benzo-homologated DNA) is a size-expanded nucleotide system synthesized from the fusion of a benzene ring and one of the four natural bases: adenine, guanine, cytosine, and thymine. This size expansion produces an 8 letter alphabet which has a larger information storage capacity than natural DNA's (often referred to as B-DNA in literature) 4 letter alphabet. As with normal base-pairing, A pairs with xT, C pairs with xG, G pairs with xC, and T pairs with xA. The double helix is thus 2.4Å wider than a natural double helix. While similar in structure to B-DNA, xDNA has unique absorption, fluorescence, and stacking properties.
Initially synthesized as an enzyme probe by Nelson J. Leonards group, benzo-homologated adenine was the first base synthesized. Later, Eric T. Kools group finished synthesizing the remaining three expanded bases, eventually followed by yDNA ("wide" DNA), another benzo-homologated nucleotide system, and naphtho-homologated xxDNA and yyDNA. xDNA is more stable when compared to regular DNA when subjected to higher temperature, and while entire strands of xDNA, yDNA, xxDNA and yyDNA exist, they are currently difficult to synthesize and maintain. Experiments with xDNA provide new insight into the behavior of natural B-DNA. The extended bases xA, xC, xG, and xT are naturally fluorescent, and single strands composed of only extended bases can recognize and bind to single strands of natural DNA, making them useful tools for studying biological systems. xDNA is most commonly formed with base pairs between a natural and expanded nucleobase, however x-nucleobases can also be paired together. Current research supports xDNA as a viable genetic encoding system in the near future. | 1 | Applied and Interdisciplinary Chemistry |
RopB transcriptional regulator, also known as RopB/Rgg transcriptional regulator is a transcriptional regulator protein that regulates expression of the extracellularly secreted cysteine protease streptococcal pyrogenic exotoxin B (speB) [See Also: erythrogenic toxins] which is an important virulence factor of Streptococcus pyogenes and is responsible for the dissemination of a host of infectious diseases including strep throat, impetigo, streptococcal toxic shock syndrome, necrotizing fasciitis, and scarlet fever. Functional studies suggest that the ropB multigene regulon is responsible for not only global regulation of virulence but also a wide range of functions from stress response, metabolic function, and two-component signaling. Structural studies implicate ropB's regulatory action being reliant on a complex interaction involving quorum sensing with the leaderless peptide signal speB-inducing peptide (SIP) acting in conjunction with a pH sensitive histidine switch.
See Photo: | 1 | Applied and Interdisciplinary Chemistry |
Chromatin assembly factor-1 (CAF-1) is a protein complex — including Chaf1a (p150), Chaf1b (p60), and p48 subunits in humans, or Cac1, Cac2, and Cac3, respectively, in yeast— that assembles histone tetramers onto replicating DNA during the S phase of the cell cycle. | 1 | Applied and Interdisciplinary Chemistry |
Suppose that for a change in time and change in age , the population density is:That is, during a time period the population density decreases by a percentage . Taking a Taylor series expansion to order gives us that:We know that , since the change of age with time is 1. Therefore, after collecting terms, we must have that: | 1 | Applied and Interdisciplinary Chemistry |
The Kfar Monash Hoard is a hoard of metal objects dated to the Early Bronze Age (the third millennium BCE) found in the spring of 1962 by the agriculturalist Zvi Yizhar in Kfar Monash, Israel. Kfar Monash is located 3.3 km south-east of Tel Hefer (Tell Ishbar) in the Plain of Sharon or in modern terms 9 km/6 mi northeast of Netanya, which is roughly located along the Israeli coast between Netanya and Haifa.
The Monash Hoard consists of:
The Crescentic Axehead was found about 5 years later at about 200m distance.
As of June 2006, the Kfar Monash Hoard was on display in the Israel Museum. | 1 | Applied and Interdisciplinary Chemistry |
In thermal power stations, mechanical power is produced by a heat engine that transforms thermal energy, often from combustion of a fuel, into rotational energy. Most thermal power stations produce steam, so they are sometimes called steam power stations. Not all thermal energy can be transformed into mechanical power, according to the second law of thermodynamics; therefore, there is always heat lost to the environment. If this loss is employed as useful heat, for industrial processes or district heating, the power plant is referred to as a cogeneration power plant or CHP (combined heat-and-power) plant. In countries where district heating is common, there are dedicated heat plants called heat-only boiler stations. An important class of power stations in the Middle East uses by-product heat for the desalination of water.
The efficiency of a thermal power cycle is limited by the maximum working fluid temperature produced. The efficiency is not directly a function of the fuel used. For the same steam conditions, coal-, nuclear- and gas power plants all have the same theoretical efficiency. Overall, if a system is on constantly (base load) it will be more efficient than one that is used intermittently (peak load). Steam turbines generally operate at higher efficiency when operated at full capacity.
Besides use of reject heat for process or district heating, one way to improve overall efficiency of a power plant is to combine two different thermodynamic cycles in a combined cycle plant. Most commonly, exhaust gases from a gas turbine are used to generate steam for a boiler and a steam turbine. The combination of a "top" cycle and a "bottom" cycle produces higher overall efficiency than either cycle can attain alone.
In 2018, Inter RAO UES and [https://g.esgcc.com.cn/ State Grid] planned to build an 8-GW thermal power plant, which's the largest coal-fired power plant construction project in Russia. | 1 | Applied and Interdisciplinary Chemistry |
Lavoisiers chemical research between 1772 and 1778 was largely concerned with developing his own new theory of combustion. In 1783 he read to the academy his paper entitled Réflexions sur le phlogistique (Reflections on Phlogiston), a full-scale attack on the current phlogiston theory of combustion. That year Lavoisier also began a series of experiments on the composition of water which were to prove an important capstone to his combustion theory and win many converts to it. Many investigators had been experimenting with the combination of Henry Cavendishs inflammable air, now known as hydrogen, with "dephlogisticated air" (air in the process of combustion, now known to be oxygen) by electrically sparking mixtures of the gases. All of the researchers noted Cavendishs production of pure water by burning hydrogen in oxygen, but they interpreted the reaction in varying ways within the framework of phlogiston theory. Lavoisier learned of Cavendishs experiment in June 1783 via Charles Blagden (before the results were published in 1784), and immediately recognized water as the oxide of a hydroelectric gas.
In cooperation with Laplace, Lavoisier synthesized water by burning jets of hydrogen and oxygen in a bell jar over mercury. The quantitative results were good enough to support the contention that water was not an element, as had been thought for over 2,000 years, but a compound of two gases, hydrogen and oxygen. The interpretation of water as a compound explained the inflammable air generated from dissolving metals in acids (hydrogen produced when water decomposes) and the reduction of calces by inflammable air (a combination of gas from calx with oxygen to form water).
Despite these experiments, Lavoisiers antiphlogistic approach remained unaccepted by many other chemists. Lavoisier labored to provide definitive proof of the composition of water, attempting to use this in support of his theory. Working with Jean-Baptiste Meusnier, Lavoisier passed water through a red-hot iron gun barrel, allowing the oxygen to form an oxide with the iron and the hydrogen to emerge from the end of the pipe. He submitted his findings of the composition of water to the Académie des Sciences in April 1784, reporting his figures to eight decimal places. Opposition responded to this further experimentation by stating that Lavoisier continued to draw the incorrect conclusions and that his experiment demonstrated the displacement of phlogiston from iron by the combination of water with the metal. Lavoisier developed a new apparatus which used a pneumatic trough, a set of balances, a thermometer, and a barometer, all calibrated carefully. Thirty savants were invited to witness the decomposition and synthesis of water using this apparatus, convincing many who attended of the correctness of Lavoisiers theories. This demonstration established water as a compound of oxygen and hydrogen with great certainty for those who viewed it. The dissemination of the experiment, however, proved subpar, as it lacked the details to properly display the amount of precision taken in the measurements. The paper ended with a hasty statement that the experiment was "more than sufficient to lay hold of the certainty of the proposition" of the composition of water and stated that the methods used in the experiment would unite chemistry with the other physical sciences and advance discoveries. | 1 | Applied and Interdisciplinary Chemistry |
For females:
* 0 to 5 years: < 0.1 mg/24 hours
* 6 to 9 years: < 0.3 mg/24 hours
* 10 to 15 years: 0.1 to 0.6 mg/24 hours
* 16 years and older: 0 to 1.4 mg/ 24 hours.
For males:
* 0 to 5 years: < 0.1 mg/24 hours
* 6 to 9 years: < 0.3 mg/24 hours
* 10 to 15 years: 0.2 to 0.6 mg/24 hours
* 16 years and older: 0.2 to 2 mg/ 24 hours | 1 | Applied and Interdisciplinary Chemistry |
* Chapter: Molecular Spectroscopy 2.
* Chapter 4: Fundamentals of Fluorescence and Fluorescence Microscopy | 0 | Theoretical and Fundamental Chemistry |
Silyl enol ethers of esters () or carboxylic acids () are called silyl ketene acetals and have the general structure . These compounds are more nucleophilic than the silyl enol ethers of ketones (). | 0 | Theoretical and Fundamental Chemistry |
The Nernst–Planck equation is a continuity equation for the time-dependent concentration of a chemical species:
where is the flux. It is assumed that the total flux is composed of three elements: diffusion, advection, and electromigration. This implies that the concentration is affected by an ionic concentration gradient , flow velocity , and an electric field :
where is the diffusivity of the chemical species, is the valence of ionic species, is the elementary charge, is the Boltzmann constant, and is the absolute temperature. The electric field may be further decomposed as:
where is the electric potential and is the magnetic vector potential. Therefore, the Nernst–Planck equation is given by: | 0 | Theoretical and Fundamental Chemistry |
IIR Section E co-ordinates the work of the both Commissions E1 Air-Conditioning and E2 Heat Pumps and Heat Recovery.
The core activities and interests of both Commissions are strongly connected resulting in tight collaborate and jointly organised conferences.
Air-conditioning is a subject that is now more frequently addressed due to both better comfort in an increasing number of countries and the effects of global warming. Now, even countries where demand for air-conditioning during summer months was limited, due to a cooler climate, require the operation of an air-conditioning plant for longer periods. The demand of heating is nevertheless significant and the most efficient system to provide heating is undoubtedly the heat pump. No other technology can provide net primary energy savings, economic benefits to users and reduced climate impact at the same time.
Also providing a cooling effect, the heat pump is expected to be the most common solution in the future for all year round operations. The combination of these technologies, with heat recovery capable buildings or industrial plants, cooling and heating requirements can be meet in the most efficient, reliable, cost-effective and environmentally friendly way.
* Commission E1 Air Conditioning
Commission E1 on Air Conditioning often collaborates with Commission E2 on Heat pumps and Energy Recovery as they have at least one common aspect, the compressor. Both Commissions frequently work with the same equipment which is adapted according to the seasons, alternating between air conditioners and heat pumps.
The commission is involved in various aspects of air conditioning from equipment to systems. In the last years it developed a particular focus on energy saving and sustainability, whilst maintaining good conditions of thermal comfort ranging from topics such as free cooling, solar cooling or long term energy storage. The general importance of the themes addressed by the Commission results in relevant International Conferences.
The expertise of the Commission members on the use of new refrigerants in air conditioning systems, annual comparative studies of innovative and renewable energy systems, opportunities of part load operation on air conditioning systems to limit penalties or even to gain efficiency, and on other up-to-date research fields, is valuable, not only to the scientific community but also to the multitude of air conditioning users.
*Commission E2: Heat pumps and Energy Recovery
Commission members are proposed by member countries then appointed by the STC following proposals from Presidents of commissions. These commission members comprise industry, university, and research-centre specialists or refrigeration practitioners.
The aim of commission E2 on Heat Pumps, Energy Recovery is to promote and enhance scientific and technological knowledge in heat pump and energy recovery fields thanks to various activities such as the organization or co-sponsoring of international conferences, or the publication of books and Informatory Notes. | 0 | Theoretical and Fundamental Chemistry |
Effectene Reagent is used in conjunction with the enhancer and the DNA condensation buffer (Buffer EC) to achieve high transfection efficiency. In the first step of Effectene–DNA complex formation, the DNA is condensed by interaction with the enhancer in a defined-buffer system. Effectene Reagent is then added to the condensed DNA to produce condensed Effectene–DNA complexes. The Effectene–DNA complexes are mixed with the medium and directly added to the cells.
Effectene Reagent spontaneously forms micelle structures exhibiting no size or batch variation (as may be found with pre-formulated liposome reagents). This feature ensures reproducibility of transfection-complex formation. The process of highly condensing DNA molecules and then coating them with Effectene Reagent is an effective way to transfer DNA into eukaryotic cells. | 1 | Applied and Interdisciplinary Chemistry |
Water has an unusually high surface tension of 71.99 mN/m at 25 °C which is caused by the strength of the hydrogen bonding between water molecules. This allows insects to walk on water. | 1 | Applied and Interdisciplinary Chemistry |
Weakly dissociated acids yield sharp thermometric endpoints when titrated with a strong base. For instance, bicarbonate can be unequivocally determined in the company of carbonate by titrating with hydroxyl (ΔH=-40.9 kJ/mol). | 0 | Theoretical and Fundamental Chemistry |
Bismuthyl — inorganic oxygen-containing radical, a singly charged ion with the chemical formula BiO, is an oxycation of bismuth in the +3 oxidation state. Most often it is formed during the hydrolysis of trivalent bismuth salts, primarily nitrate, chloride and other halides. In chemical compounds, bismuthyl plays the role of a monovalent cation.
In inorganic chemistry bismuthyl has been used to describe compounds such as BiOCl which were assumed to contain the diatomic bismuthyl, BiO, cation, that was also presumed to exist in aqueous solution.
This diatomic ion is not now believed to exist. Unlike other inorganic radicals such as hydroxyl, carbonyl, chromyl, uranyl or vanadyl, according to the current IUPAC rules, names such as bismuthyl and antimonyl (stibil) for BiO and SbO are not recommended, since individual molecules of these groups do not actually contain, and their presence in compounds preferably referred to as oxides. However, the latter position remains controversial. For example, to this day the Russian school of inorganic chemistry still operates with bismuthyl and stibil (antimonyl) cations as actually existing radicals. | 1 | Applied and Interdisciplinary Chemistry |
Carbonyl ylides (RRC=OCRR) can form by ring-opening of epoxides or by reaction of carbonyls with electrophilic carbenes, which are usually prepared from diazo compounds. Oxonium ylides (RR-O-CRR) are formed by the reaction of ethers with electrophilic carbenes. | 0 | Theoretical and Fundamental Chemistry |
The HR-EBSD method can achieve a precision of ±10 in components of the displacement gradient tensors (i.e., variations in lattice strain and lattice rotation in radians) by measuring the shifts of zone axes within the pattern image with a resolution of ±0.05 pixels. It was limited to small strains and rotations (>1.5°) until Britton and Wilkinson and Maurice et al. raised the rotation limit to ~11° by using a re-mapping technique that recalculated the strain after transforming the patterns with a rotation matrix () calculated from the first cross-correlation iteration.
However, further lattice rotation, typically caused by severe plastic deformations, produced errors in the elastic strain calculations. To address this problem, Ruggles et al. improved the HR-EBSD precision, even at 12° of lattice rotation, using the inverse compositional Gauss–Newton-based (ICGN) method instead of cross-correlation. For simulated patterns, Vermeij and Hoefnagels also established a method that achieves a precision of ±10 in the displacement gradient components using a full-field integrated digital image correlation (IDIC) framework instead of dividing the EBSPs into small ROIs. Patterns in IDIC are distortion-corrected to negate the need for re-mapping up to ~14°.
These measurements do not provide information about the hydrostatic or volumetric strains, because there is no change in the orientations of lattice planes (crystallographic directions), but only changes in the position and width of the Kikuchi bands. | 0 | Theoretical and Fundamental Chemistry |
Diverted total synthesis in chemistry is a strategy in drug discovery aiming at organic synthesis of natural product analogues rather than the natural product itself. The target can be the modification of a natural product or the modification of an intermediate. In this sense it differs from other strategies such as total synthesis and semisynthesis. The purpose can be gaining a scientific understanding of the biological activity of the original natural product or the discovery of new drugs with the same biological activity but simpler to produce. The concept was introduced by Samuel J. Danishefsky in 2006. Notable examples of this strategy are the potential drug ixabepilone which is an analogue of the natural product epothilone B and carfilzomib which is derived from epoxomicin and eravacycline derived from tetracycline. Cabergoline is derived from a number of ergot alkaloids one of which is lysergic acid and Simvastatin is based on Lovastatin.
Diverted total synthesis is a topic in academic research. | 0 | Theoretical and Fundamental Chemistry |
CrysTBox offers tools for automated processing of diffraction patterns and high-resolution transmission electron microscope images. Since the tools employ algorithms of artificial intelligence and computer vision, they are designed to require minimal operator effort providing higher accuracy compared to manual evaluation. Four analytical tools can be used to index diffraction patterns, measure lattice constants (distances and angles), sample thickness etc. Despite the high level of automation, the user is able to control the whole process and perform individual steps manually if needed. | 0 | Theoretical and Fundamental Chemistry |
A variety of other compounds are added to optimize the separation process, these additives are called modifiers. Modifying reagents react either with the mineral surfaces or with collectors and other ions in the flotation pulp, resulting in a modified and controlled flotation response.
* pH modifiers include lime (used as quicklime CaO, or more commonly as slaked lime, a slurry of Ca(OH)), Soda ash (NaCO), Caustic soda (NaOH), sulfuric and hydrochloric acid (HSO, HCl).
, Ca, Cu, Pb, Zn, Ag-->
* Anionic modifiers include phosphates, silicates, and carbonates.
* Organic modifiers include the thickeners dextrin, starch, glue, and CMC. | 1 | Applied and Interdisciplinary Chemistry |
The viscosity of a shear thickeningi.e. dilatant fluid appears to increase when the shear rate increases. Corn starch suspended in water ("oobleck", see below) is a common example: when stirred slowly it looks milky, when stirred vigorously it feels like a very viscous liquid. | 1 | Applied and Interdisciplinary Chemistry |
The Knudsen number of the particle define three different dynamical regimes that govern the behaviour of an aerosol:
where is the mean free path of the suspending gas and is the diameter of the particle. For particles in the free molecular regime, K >> 1; particles small compared to the mean free path of the suspending gas. In this regime, particles interact with the suspending gas through a series of "ballistic" collisions with gas molecules. As such, they behave similarly to gas molecules, tending to follow streamlines and diffusing rapidly through Brownian motion. The mass flux equation in the free molecular regime is:
where a is the particle radius, P and P are the pressures far from the droplet and at the surface of the droplet respectively, k is the Boltzmann constant, T is the temperature, C is mean thermal velocity and α is mass accommodation coefficient. The derivation of this equation assumes constant pressure and constant diffusion coefficient.
Particles are in the continuum regime when K << 1. In this regime, the particles are big compared to the mean free path of the suspending gas, meaning that the suspending gas acts as a continuous fluid flowing round the particle. The molecular flux in this regime is:
where a is the radius of the particle A, M is the molecular mass of the particle A, D is the diffusion coefficient between particles A and B, R is the ideal gas constant, T is the temperature (in absolute units like kelvin), and P and P are the pressures at infinite and at the surface respectively.
The transition regime contains all the particles in between the free molecular and continuum regimes or K ≈ 1. The forces experienced by a particle are a complex combination of interactions with individual gas molecules and macroscopic interactions. The semi-empirical equation describing mass flux is:
where I is the mass flux in the continuum regime. This formula is called the Fuchs-Sutugin interpolation formula. These equations do not take into account the heat release effect. | 0 | Theoretical and Fundamental Chemistry |
The oligodynamic effect (from Greek oligos, "few", and dynamis, "force") is a biocidal effect of metals, especially heavy metals, that occurs even in low concentrations. This effect is attributed to the antibacterial behavior of metal ions, which are absorbed by bacteria upon contact and damage their cell membranes.
In modern times, the effect was observed by Carl Nägeli, although he did not identify the cause. Brass doorknobs and silverware both exhibit this effect to an extent. | 1 | Applied and Interdisciplinary Chemistry |
Countercurrent exchange is used extensively in biological systems for a wide variety of purposes. For example, fish use it in their gills to transfer oxygen from the surrounding water into their blood, and birds use a countercurrent heat exchanger between blood vessels in their legs to keep heat concentrated within their bodies. In vertebrates, this type of organ is referred to as a rete mirabile (originally the name of the organ in the fish gills). Mammalian kidneys use countercurrent exchange to remove water from urine so the body can retain water used to move the nitrogenous waste products (see countercurrent multiplier). | 1 | Applied and Interdisciplinary Chemistry |
The biological pump is accompanied by a physico-chemical counterpart known as the solubility pump. This pump transports significant amounts of carbon in the form of dissolved inorganic carbon (DIC) from the ocean's surface to its interior. It involves physical and chemical processes only, and does not involve biological processes.
The solubility pump is driven by the coincidence of two processes in the ocean:
* The solubility of carbon dioxide is a strong inverse function of seawater temperature (i.e. solubility is greater in cooler water)
* The thermohaline circulation is driven by the formation of deep water at high latitudes where seawater is usually cooler and denser
Since deep water (that is, seawater in the oceans interior) is formed under the same surface conditions that promote carbon dioxide solubility, it contains a higher concentration of dissolved inorganic carbon than might be expected from average surface concentrations. Consequently, these two processes act together to pump carbon from the atmosphere into the oceans interior. One consequence of this is that when deep water upwells in warmer, equatorial latitudes, it strongly outgasses carbon dioxide to the atmosphere because of the reduced solubility of the gas. | 0 | Theoretical and Fundamental Chemistry |
The fucoxanthin dinophyte lineages (including Karlodinium and Karenia) lost their original red algal derived chloroplast, and replaced it with a new chloroplast derived from a haptophyte endosymbiont. Karlodinium and Karenia probably took up different heterokontophytes. Because the haptophyte chloroplast has four membranes, tertiary endosymbiosis would be expected to create a six membraned chloroplast, adding the haptophytes cell membrane and the dinophytes phagosomal vacuole. However, the haptophyte was heavily reduced, stripped of a few membranes and its nucleus, leaving only its chloroplast (with its original double membrane), and possibly one or two additional membranes around it.
Fucoxanthin-containing chloroplasts are characterized by having the pigment fucoxanthin (actually 19′-hexanoyloxy-fucoxanthin and/or 19′-butanoyloxy-fucoxanthin) and no peridinin. Fucoxanthin is also found in haptophyte chloroplasts, providing evidence of ancestry. | 0 | Theoretical and Fundamental Chemistry |
Developments in mass spectrometry led to the adoption of oxygen-16 as the standard substance, in lieu of natural oxygen.
The oxygen-16 definition was replaced with one based on carbon-12 during the 1960s. The mole was defined by International Bureau of Weights and Measures as "the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12." Thus, by that definition, one mole of pure C had a mass of exactly 12 g. The four different definitions were equivalent to within 1%.
Because a dalton, a unit commonly used to measure atomic mass, is exactly 1/12 of the mass of a carbon-12 atom, this definition of the mole entailed that the mass of one mole of a compound or element in grams was numerically equal to the average mass of one molecule or atom of the substance in daltons, and that the number of daltons in a gram was equal to the number of elementary entities in a mole. Because the mass of a nucleon (i.e. a proton or neutron) is approximately 1 dalton and the nucleons in an atom's nucleus make up the overwhelming majority of its mass, this definition also entailed that the mass of one mole of a substance was roughly equivalent to the number of nucleons in one atom or molecule of that substance.
Since the definition of the gram was not mathematically tied to that of the dalton, the number of molecules per mole N (the Avogadro constant) had to be determined experimentally. The experimental value adopted by CODATA in 2010 is .
In 2011 the measurement was refined to .
The mole was made the seventh SI base unit in 1971 by the 14th CGPM. | 0 | Theoretical and Fundamental Chemistry |
The derivation of Avogadro's law follows directly from the ideal gas law, i.e.
where R is the gas constant, T is the Kelvin temperature, and P is the pressure (in pascals).
Solving for V/n, we thus obtain
Compare that to
which is a constant for a fixed pressure and a fixed temperature.
An equivalent formulation of the ideal gas law can be written using Boltzmann constant k, as
where N is the number of particles in the gas, and the ratio of R over k is equal to the Avogadro constant.
In this form, for V/N is a constant, we have
If T and P are taken at standard conditions for temperature and pressure (STP), then k′ = 1/n, where n is the Loschmidt constant. | 0 | Theoretical and Fundamental Chemistry |
The words "paracrystallinity" and "paracrystal" were coined by the late Friedrich Rinne in the year 1933. Their German equivalents, e.g. "Parakristall", appeared in print one year earlier.
A general theory of paracrystals has been formulated in a basic textbook, and then further developed/refined by various authors.
Rolf Hosemann's definition of an ideal paracrystal is: "The electron density distribution of any material is equivalent to that of a paracrystal when there is for every building block one ideal point so that the distance statistics to other ideal points are identical for all of these points. The electron configuration of each building block around its ideal point is statistically independent of its counterpart in neighboring building blocks. A building block corresponds then to the material content of a cell of this "blurred" space lattice, which is to be considered a paracrystal." | 0 | Theoretical and Fundamental Chemistry |
FTIR is an analytical method which uses an infrared laser focused on a spot on the glass phase of the melt inclusion to determine an absorption (or extinction) coefficient for either HO and CO associated with wavelengths for each species depending on the parent lithology that contained the melt inclusion. | 0 | Theoretical and Fundamental Chemistry |
At Three Mile Island a recently SCRAMed core was starved of cooling water, as a result of the decay heat the core dried out and the fuel was damaged. Attempts were made to recool the core using water. According to the International Atomic Energy Agency for a 3,000 MW (t) PWR the normal coolant radioactivity levels are shown below in the table, and the coolant activities for reactors which have been allowed to dry out (and over heat) before being recovered with water. In a gap release the activity in the fuel/cladding gap has been released while in the core melt release the core was melted before being recovered by water. | 0 | Theoretical and Fundamental Chemistry |
In the nervous system there are primarily two ways of propagating signals. By far the most common method of intracellular signal propagation is the action potential. The dendrites of neurons contain ionotropic (aka ligand-gated ion channel) and metabotropic neurotransmitter receptors that bind chemical neurotransmitters. At ionotropic receptors, these chemical neurotransmitters cause quick changes in ion flux into or out of the cell. The resulting internal voltage change in the dendrites is propagated towards the cell body and axon hillock, where a large concentration of voltage-gated ion channels typically exists. If some voltage threshold is met, voltage gated sodium channels open up, letting in a critical charge of sodium, and the positive current propagates down the axon towards the presynaptic axon terminal. This action potential leads to neurotransmitter vesicular release at in this terminal.
While action potentials are the typical means of signal propagation in the nervous system, some sensory neurons use graded potentials to trigger vesicular release. These cells are typically short enough that regenerative action potentials aren't needed to cause a large enough voltage change at the presynaptic terminal. For example, photoreceptor cells in the eye produce graded potentials in response to light, and these graded potentials can directly lead to neurotransmitter release. | 1 | Applied and Interdisciplinary Chemistry |
Retrograde extrapolation is the mathematical process by which someone's blood alcohol concentration at the time of driving is estimated by projecting backwards from a later chemical test. This involves estimating the absorption and elimination of alcohol in the interim between driving and testing. The rate of elimination in the average person is commonly estimated at 0.015 to 0.020 grams per deciliter per hour (g/dL/h), although again this can vary from person to person and in a given person from one moment to another. Metabolism can be affected by numerous factors, including such things as body temperature, the type of alcoholic beverage consumed, and the amount and type of food consumed.
In an increasing number of states, laws have been enacted to facilitate this speculative task: the blood alcohol content at the time of driving is legally presumed to be the same as when later tested. There are usually time limits put on this presumption, commonly two or three hours, and the defendant is permitted to offer evidence to rebut this presumption.
Forward extrapolation can also be attempted. If the amount of alcohol consumed is known, along with such variables as the weight and sex of the subject and period and rate of consumption, the blood alcohol level can be estimated by extrapolating forward. Although subject to the same infirmities as retrograde extrapolation—guessing based upon averages and unknown variables—this can be relevant in estimating BAC when driving and/or corroborating or contradicting the results of a later chemical test. | 1 | Applied and Interdisciplinary Chemistry |
The paramagnetic ring current resulting from the electron delocalization in antiaromatic compounds can be observed by NMR. This ring current leads to a deshielding (downfield shift) of nuclei inside the ring and a shielding (upfield shift) of nuclei outside the ring. [[Cyclododecahexaene|[12]annulene]] is an antiaromatic hydrocarbon that is large enough to have protons both inside and outside of the ring. The chemical shift for the protons outside its ring is 5.91 ppm and that for the protons inside the ring is 7.86 ppm, compared to the normal range of 4.5-6.5 ppm for nonaromatic alkenes. This effect is of a smaller magnitude than the corresponding shifts in aromatic compounds.
Many aromatic and antiaromatic compounds (benzene and cyclobutadiene) are too small to have protons inside of the ring, where shielding and deshielding effects can be more diagnostically useful in determining if a compound is aromatic, antiaromatic, or nonaromatic. Nucleus Independent Chemical Shift (NICS) analysis is a method of computing the ring shielding (or deshielding) at the center of a ring system to predict aromaticity or antiaromaticity. A negative NICS value is indicative of aromaticity and a positive value is indicative of antiaromaticity. | 0 | Theoretical and Fundamental Chemistry |
The study of the tumor metabolism, also known as tumor metabolome describes the different characteristic metabolic changes in tumor cells. The characteristic attributes of the tumor metabolome are high glycolytic enzyme activities, the expression of the pyruvate kinase isoenzyme type M2, increased channeling of glucose carbons into synthetic processes, such as nucleic acid, amino acid and phospholipid synthesis, a high rate of pyrimidine and purine de novo synthesis, a low ratio of Adenosine triphosphate and Guanosine triphosphate to Cytidine triphosphate and Uridine triphosphate, low Adenosine monophosphate levels, high glutaminolytic capacities, release of immunosuppressive substances and dependency on methionine.
Although the link between the cancer and metabolism was observed in the early days of cancer research by Otto Heinrich Warburg, which is also known as Warburg hypothesis, not much substantial research was carried out until the late 1990s because of the lack of in vitro tumor models and the difficulty in creating environments that lack oxygen. Recent research has revealed that metabolic reprogramming occurs as a consequence of mutations in cancer genes and alterations in cellular signaling. Therefore, the alteration of cellular and energy metabolism has been suggested as one of The Hallmarks of Cancer. | 1 | Applied and Interdisciplinary Chemistry |
ASHRAE standard 62 states that air removed from an area with environmental tobacco smoke shall not be recirculated into ETS-free air. A space with ETS requires more ventilation to achieve similar perceived air quality to that of a non-smoking environment.
The amount of ventilation in an ETS area is equal to the amount of an ETS-free area plus the amount V, where:
V = DSD × VA × A/60E
*V = recommended extra flow rate in CFM (L/s)
*DSD = design smoking density (estimated number of cigarettes smoked per hour per unit area)
*VA = volume of ventilation air per cigarette for the room being designed (ft/cig)
*E = contaminant removal effectiveness | 1 | Applied and Interdisciplinary Chemistry |
Hydrogen is produced by hydrogenases and nitrogenases enzymes in many microorganisms, some of which are being studied for their potential for biofuel production. These H-metabolizing enzymes are found in all three domains of life, and out of known genomes over 30% of microbial taxa contain hydrogenase genes. Fermentation produces H from organic matter as part of the anaerobic microbial food chain via light-dependent or light-independent pathways. | 1 | Applied and Interdisciplinary Chemistry |
It was announced in 2022 that a burning plasma had been achieved at the National Ignition Facility, a large laser-based inertial confinement fusion research device, located at the Lawrence Livermore National Laboratory in Livermore, California. The burning plasma created was sustained for approximately 100 trillionths of a second, and the process consumed more energy than it created by a factor of approximately ten. NIF achieved ignition on December 5, 2022, net energy release from a burning plasma fusion reaction. | 0 | Theoretical and Fundamental Chemistry |
In clearance, or the rate at which a substance is removed or cleared from the body, it has been found that the cellular proteolysis of AGEs—the breakdown of proteins—produces AGE peptides and "AGE free adducts" (AGE adducts bound to single amino acids). These latter, after being released into the plasma, can be excreted in the urine.
Nevertheless, the resistance of extracellular matrix proteins to proteolysis renders their advanced glycation end products less conducive to being eliminated. While the AGE free adducts are released directly into the urine, AGE peptides are endocytosed by the epithelial cells of the proximal tubule and then degraded by the endolysosomal system to produce AGE amino acids. It is thought that these acids are then returned to the kidney's inside space, or lumen, for excretion.
AGE free adducts are the major form through which AGEs are excreted in urine, with AGE-peptides occurring to a lesser extent but accumulating in the plasma of patients with chronic kidney failure.
Larger, extracellularly derived AGE proteins cannot pass through the basement membrane of the renal corpuscle and must first be degraded into AGE peptides and AGE free adducts. Peripheral macrophage as well as liver sinusoidal endothelial cells and Kupffer cells
have been implicated in this process, although the real-life involvement of the liver has been disputed.
Large AGE proteins unable to enter the Bowman's capsule are capable of binding to receptors on endothelial and mesangial cells and to the mesangial matrix. Activation of RAGE induces production of a variety of cytokines, including TNFβ, which mediates an inhibition of metalloproteinase and increases production of mesangial matrix, leading to glomerulosclerosis and decreasing kidney function in patients with unusually high AGE levels.
Although the only form suitable for urinary excretion, the breakdown products of AGE—that is, peptides and free adducts—are more aggressive than the AGE proteins from which they are derived, and they can perpetuate related pathology in diabetic patients, even after hyperglycemia has been brought under control.
Some AGEs have an innate catalytic oxidative capacity, while activation of NAD(P)H oxidase through activation of RAGE and damage to mitochondrial proteins leading to mitochondrial dysfunction can also induce oxidative stress. A 2007 study found that AGEs could significantly increase expression of TGF-β1, CTGF, Fn mRNA in NRK-49F cells through enhancement of oxidative stress, and suggested that inhibition of oxidative stress might underlie the effect of ginkgo biloba extract in diabetic nephropathy. The authors suggested that antioxidant therapy might help prevent the accumulation of AGEs and induced damage. In the end, effective clearance is necessary, and those suffering AGE increases because of kidney dysfunction might require a kidney transplant.
In diabetics who have an increased production of an AGE, kidney damage reduces the subsequent urinary removal of AGEs, forming a positive feedback loop that increases the rate of damage. In a 1997 study, diabetic and healthy subjects were given a single meal of egg white (56 g protein), cooked with or without 100 g of fructose; there was a greater than 200-fold increase in AGE immunoreactivity from the meal with fructose. | 1 | Applied and Interdisciplinary Chemistry |
One approach is the collision theory of chemical reactions, developed by Max Trautz and William Lewis in the years 1916–18. In this theory, molecules are supposed to react if they collide with a relative kinetic energy along their line of centers that exceeds E. The number of binary collisions between two unlike molecules per second per unit volume is found to be
where N is the Avogadro constant, d is the average diameter of A and B, T is the temperature which is multiplied by the Boltzmann constant k to convert to energy, and μ is the reduced mass.
The rate constant is then calculated as , so that the collision theory predicts that the pre-exponential factor is equal to the collision number z. However for many reactions this agrees poorly with experiment, so the rate constant is written instead as . Here is an empirical steric factor, often much less than 1.00, which is interpreted as the fraction of sufficiently energetic collisions in which the two molecules have the correct mutual orientation to react. | 0 | Theoretical and Fundamental Chemistry |
The interconversion of chair conformers is called ring flipping or chair-flipping. Carbon–hydrogen bonds that are axial in one configuration become equatorial in the other, and vice versa. At room temperature the two chair conformations rapidly equilibrate. The proton NMR spectrum of cyclohexane is a singlet at room temperature, with no separation into separate signals for axial and equatorial hydrogens.
In one chair form, the dihedral angle of the chain of carbon atoms (1,2,3,4) is positive whereas that of the chain (1,6,5,4) is negative, but in the other chair form, the situation is the opposite. So both these chains have to undergo a reversal of dihedral angle. When one of these two four-atom chains flattens to a dihedral angle of zero, we have the half-chair conformation, at a maximum energy along the conversion path. When the dihedral angle of this chain then becomes equal (in sign as well as magnitude) to that of the other four-atom chain, the molecule has reached the continuum of conformations, including the twist boat and the boat, where the bond angles and lengths can all be at their normal values and the energy is therefore relatively low. After that, the other four-carbon chain has to switch the sign of its dihedral angle in order to attain the target chair form, so again the molecule has to pass through the half-chair as the dihedral angle of this chain goes through zero. Switching the signs of the two chains sequentially in this way minimizes the maximum energy state along the way (at the half-chair state) — having the dihedral angles of both four-atom chains switch sign simultaneously would mean going through a conformation of even higher energy due to angle strain at carbons 1 and 4.
The detailed mechanism of the chair-to-chair interconversion has been the subject of much study and debate. The half-chair state (D, in figure below) is the key transition state in the interconversion between the chair and twist-boat conformations. The half-chair has C symmetry. The interconversion between the two chair conformations involves the following sequence: chair → half-chair → twist-boat → half-chair′ → chair′. | 0 | Theoretical and Fundamental Chemistry |
The Integrated Carbon Observation System (ICOS) is a research infrastructure to quantify the greenhouse gas balance of Europe and adjacent regions. In November 2015 it received the international legal status of ERIC (European Research Infrastructure Consortium) by decision of the European Commission. It is recognized by The European Strategy Forum on Research Infrastructures (ESFRI) as a landmark European research infrastructure. It consists of a harmonized network of almost 150 long-term observation sites for the domains of atmosphere, ecosystems and ocean. The network is coordinated through its Head Office, the central data portal and central facilities including an atmosphere, ecosystem and ocean thematic center, and central analytical laboratories.
ICOS provides the essential long-term observations required to understand the present state and predict future behavior of the global carbon cycle and greenhouse gas emissions. It monitors and assesses the effectiveness of carbon sequestration and/or greenhouse gases emission reduction activities on global atmospheric composition levels, including attribution of sources and sinks by region and sector.
The highly standardized network offers improved access to data and enables the development of flux products for research and political application. ICOS is a state-of-the-art facility for the European research community. It contributes to the European share of global greenhouse gas observations under Group on Earth Observations (GEO), World Meteorological Organization GAW and GCOS programs. | 1 | Applied and Interdisciplinary Chemistry |
Threading bases structural modeling on fold similarities rather than sequence identity. This method may help identify distantly related proteins and can be used to infer molecular functions. | 1 | Applied and Interdisciplinary Chemistry |
* Contamination by phenol, which is commonly used in nucleic acid purification, can significantly throw off quantification estimates. Phenol absorbs with a peak at 270 nm and a A of 1.2. Nucleic acid preparations uncontaminated by phenol should have a A of around 2. Contamination by phenol can significantly contribute to overestimation of DNA concentration.
* Absorption at 230 nm can be caused by contamination by phenolate ion, thiocyanates, and other organic compounds. For a pure RNA sample, the A should be around 1:2:1, and for a pure DNA sample, the A should be around 1:1.8:1.
* Absorption at 330 nm and higher indicates particulates contaminating the solution, causing scattering of light in the visible range. The value in a pure nucleic acid sample should be zero.
* Negative values could result if an incorrect solution was used as blank. Alternatively, these values could arise due to fluorescence of a dye in the solution. | 0 | Theoretical and Fundamental Chemistry |
Opioids (also known as narcotics) such as morphine and heroin attach to opioid receptors in the brain. These substances have long been known to inhibit sexual behavior.
Similar to the effects of psycho-stimulants, both men and women who use heroin report engaging in high-risk sexual practices.
Subjects typically report having several sexual partners, using condoms seldom or not at all, and having a high frequency of STI diagnosis.
While small doses of heroin may enhance sexual desire and performance, chronic opiate use, including methadone and buprenorphine, synthetic and semi-synthetic opiates prescribed for opiate addiction treatment, results in decreased sexual desire, response, and orgasms for both men and women, as well as erectile, ejaculatory dysfunction, and vaginismus. | 1 | Applied and Interdisciplinary Chemistry |
Phosphate esters have the general structure P(=O)(OR) feature P(V). Such species are of technological importance as flame retardant agents, and plasticizers. Lacking a P−C bond, these compounds are in the technical sense not organophosphorus compounds but esters of phosphoric acid. Many derivatives are found in nature, such as phosphatidylcholine. Phosphate ester are synthesized by alcoholysis of phosphorus oxychloride. A variety of mixed amido-alkoxo derivatives are known, one medically significant example being the anti-cancer drug cyclophosphamide. Also derivatives containing the thiophosphoryl group (P=S) include the pesticide malathion. The organophosphates prepared on the largest scale are the zinc dithiophosphates, as additives for motor oil. Several million kilograms of this coordination complex are produced annually by the reaction of phosphorus pentasulfide with alcohols.
In the environment, these compounds break down via hydrolysis to eventually afford phosphate and the organic alcohol or amine from which they are derived. | 0 | Theoretical and Fundamental Chemistry |
In reinforced concrete, the chemical reaction between carbon dioxide
In the air and calcium hydroxide and hydrated calcium silicate in the concrete is known as neutralisation. The similar reaction in which calcium hydroxide from cement reacts with carbon dioxide and forms insoluble calcium carbonate is carbonatation. | 0 | Theoretical and Fundamental Chemistry |
Diffusion hardening is a process used in manufacturing that increases the hardness of steels. In diffusion hardening, diffusion occurs between a steel with a low carbon content and a carbon-rich environment to increase the carbon content of the steel and ultimately harden the workpiece. Diffusion only happens through a small thickness of a piece of steel (about 2.5 μm to 1.5 mm), so only the surface is hardened while the core maintains its original mechanical properties. Heat treating may be performed on a diffusion hardened part to increase the hardness of the core as desired, but in most cases in which diffusion hardening is performed, it is desirable to have parts with a hard outer shell and a more ductile inside. Heat treating and quenching is a more efficient process if hardness is desired throughout the whole part. In the case of manufacturing parts subject to large amounts of wear, such as gears, the non-uniform properties acquired through diffusion hardening are desired. Through this process, gears obtain a hard wear-resistant outer shell but maintain their softer and more impact-resistant core. | 1 | Applied and Interdisciplinary Chemistry |
Friedel's law, named after Georges Friedel, is a property of Fourier transforms of real functions.
Given a real function , its Fourier transform
has the following properties.
where is the complex conjugate of .
Centrosymmetric points are called Friedel's pairs.
The squared amplitude () is centrosymmetric:
The phase of is antisymmetric:
Friedels law is used in X-ray diffraction, crystallography and scattering from real potential within the Born approximation. Note that a [http://reference.iucr.org/dictionary/Twin_operation twin operation] ( Opération de maclage) is equivalent to an inversion centre and the intensities from the individuals are equivalent under Friedels law. | 0 | Theoretical and Fundamental Chemistry |
Reactivity of sterically demanding lithium (fluorosilyl)silylphosphanides with GeI yields green, cubic crystals in moderate yield. The identity of this species was investigated using only multinuclear NMR, elemental analysis, and UV-vis. Computational calculations (at the CIS level with the ab initio Los Alamos pseudopotential method (LAN L 1 DZ)) of the diphosphagermylene electronic structure was in agreement experimentally-derived electronic transition values. Due to disorder, the crystal structure of the diphosphagermylene could not be investigated. | 0 | Theoretical and Fundamental Chemistry |
Coward was born on 2 July 1885 in Blackburn, Lancashire. She studied Botany and graduated M.Sc. from University of Manchester. After a few years, she joined University College London to study biochemistry and perform research under J. C. Drummond on Vitamin A, paving the way for her to be nominated to the Fellow of the Chemical Society in 1923. | 0 | Theoretical and Fundamental Chemistry |
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