text
stringlengths 105
4.57k
| label
int64 0
1
| label_text
stringclasses 2
values |
|---|---|---|
Historically, this approach was seen through the New England colonies. Virtually every old home is a clapboard structure fitted with shutters applied in this manner. They were likely hung on the casing to allow for the frost heaves and movement of the structures in the harsh New England winters. The shutters simply allowed the house to heave and settle behind them.
A strap hinge with a zero offset and an angle pintle matched to the thickness of the shutter will serve in every case. The shutter is removed from the face of the casing by the thickness of the shutter plus the diameter of the pintle pin leaving the shutter to clear the corner of the casing. | 1 | Applied and Interdisciplinary Chemistry |
Phoslactomycin (PLM) is a natural product from the isolation of Streptomyces species. This is an inhibitor of the protein serine/threonine phosphatase which is the protein phosphate 2A (PP2A). The PP2A involves the growth factor of the cell such as to induce the formation of mitogen-activated protein interaction and playing a role in cell division and signal transduction. Therefore, PLM is used for the drug that prevents the tumor, cancer, or bacteria. There are nowsaday has 7 kinds of different PLM from PLM A to PLM G which differ the post-synthesis from the biosynthesis of PLM.
Phoslactomycin B (PLM B) is the product of the post synthase of the biosynthesis of phoslactomycin and the intermediate to produce the other PLMs. The biosynthesis of phoslactomycin belongs to type I polyketide synthase (PKS). A polyketide is are characterized by a macrocyclic lactone and is produced by bacteria and fungi. From the PLM B, there are many articles wrote about the synthesis of different PLM A through PLM G. | 1 | Applied and Interdisciplinary Chemistry |
Xenon tetroxide is a chemical compound of xenon and oxygen with molecular formula XeO, remarkable for being a relatively stable compound of a noble gas. It is a yellow crystalline solid that is stable below −35.9 °C; above that temperature it is very prone to exploding and decomposing into elemental xenon and oxygen (O).
All eight valence electrons of xenon are involved in the bonds with the oxygen, and the oxidation state of the xenon atom is +8. Oxygen is the only element that can bring xenon up to its highest oxidation state; even fluorine can only give XeF (+6).
Two other short-lived xenon compounds with an oxidation state of +8, XeOF and XeOF, are accessible by the reaction of xenon tetroxide with xenon hexafluoride. XeOF and XeOF can be detected with mass spectrometry. The perxenates are also compounds where xenon has the +8 oxidation state.
__TOC__ | 0 | Theoretical and Fundamental Chemistry |
In 1960, Vogel discovered that 1,2-divinylcyclopropane rearranges to cycloheptan-1,4-diene., After his discovery, a series of intense mechanistic investigations of the reaction followed in the 1960s, as researchers realized it bore resemblance (both structural and mechanistic) to the related rearrangement of vinylcyclopropane to cyclopentene. By the 1970s, the rearrangement had achieved synthetic utility and to this day it continues to be a useful method for the formation of seven-membered rings. Variations incorporating heteroatoms have been reported (see below).
Advantages: Being a rearrangement, the process exhibits ideal atom economy. It often proceeds spontaneously without the need for a catalyst. Competitive pathways are minimal for the all-carbon rearrangement.
Disadvantages: The configuration of the starting materials needs be controlled in many cases—trans-divinylcyclopropanes often require heating to facilitate isomerization before rearrangement will occur. Rearrangements involving heteroatoms can exhibit reduced yields due to the formation of side products. | 0 | Theoretical and Fundamental Chemistry |
Esomeprazole, sold under the brand name Nexium [or Neksium] among others, is a medication which reduces stomach acid. It is used to treat gastroesophageal reflux disease, peptic ulcer disease, and Zollinger–Ellison syndrome. Its effectiveness is similar to that of other proton pump inhibitors (PPIs). It is taken by mouth or injection into a vein.
Common side effects include headache, constipation, dry mouth, and abdominal pain. Serious side effects may include angioedema, Clostridium difficile infection, and pneumonia. Use in pregnancy appears to be safe, while safety during breastfeeding is unclear. Esomeprazole is the (S)-(−)-enantiomer (or less specifically the S-isomer) of omeprazole. It works by blocking H/K-ATPase in the parietal cells of the stomach.
It was patented in 1993 and approved for medical use in 2000. It is available as a generic medication and sold over the counter in a number of countries. In 2021, it was the 125th most commonly prescribed medication in the United States, with more than 4million prescriptions. It is also available in lower dose formulations without a prescription in the United States, the United Kingdom as well as Australia, Canada, and New Zealand. | 0 | Theoretical and Fundamental Chemistry |
Scleroderma, polymyositis, and dermatomyositis elicit little or no CRP response. CRP levels also tend not to be elevated in systemic lupus erythematosus (SLE) unless serositis or synovitis is present. Elevations of CRP in the absence of clinically significant inflammation can occur in kidney failure. CRP level is an independent risk factor for atherosclerotic disease. Patients with high CRP concentrations are more likely to develop stroke, myocardial infarction, and severe peripheral vascular disease. Elevated level of CRP can also be observed in inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis.
High levels of CRP has been associated to point mutation Cys130Arg in the APOE gene, coding for apolipoprotein E, establishing a link between lipid values and inflammatory markers modulation. | 1 | Applied and Interdisciplinary Chemistry |
The protein carbaminohemoglobin plays an important role in the transport of carbon dioxide in the blood, and its biologically important in many functions:
# Transport of Carbon Dioxide: This process allows for the transport of carbon dioxide from the tissues to the lungs. It is essential for maintaining the balance of gases in the bloodstream and to guarantee the removal of waste carbon dioxide from the body.
# Buffering Blood pH: The binding of carbon dioxide to hemoglobin plays a part in the buffering of blood pH. When tissues produce carbon dioxide, the increase in acidity is reduced by the formation of bicarbonate ions. This buffering process helps prevent a decrease in pH and helps maintain a stable environment.
# Facilitation of Gas Exchange: Hemoglobin facilitates the exchange of gases in the lungs and tissues. In the lungs, oxygen binds to hemoglobin and carbon dioxide is released. In the tissues, carbon dioxide binds to form carbaminohemoglobin and oxygen is released. This exchange process is important because tissues need oxygen and the removal of carbon dioxide is also necessary. | 1 | Applied and Interdisciplinary Chemistry |
The hybrid difference scheme of Spalding (1970) is a combination of the central difference scheme and upwind difference scheme. It makes use of the central difference scheme, which is second order accurate, for small Peclet numbers (|Pe| < 2). For large Peclet numbers (|Pe| > 2) it uses the Upwind difference scheme, which first order accurate but takes into account the convection of the fluid.
As it can be seen in figure 4 that for Pe = 0, it is a linear distribution and for high Pe it takes the upstream value depending on the flow direction. For example, the value at the left face, in different circumstances is,
: for ()
: for ()
: for ()
Substituting these values in equation () we get the same equation () with the values of the coefficients as follows, | 1 | Applied and Interdisciplinary Chemistry |
Deprotonation of enolizable ketones, aldehydes, and esters gives enolates. Enolates can be trapped by the addition of electrophiles at oxygen. Silylation gives silyl enol ether. Acylation gives
esters such as vinyl acetate. | 0 | Theoretical and Fundamental Chemistry |
The type III partition system is the most recently discovered partition system. It is composed of tubulin-like GTPase termed TubZ, and the CBP is termed TubR.
Amino-acid sequence identity can go down to 21% for TubZ proteins.
The mechanism is similar to a treadmill mechanism:
# Multiple TubR dimer binds to the centromere-like region stbDRs of the plasmids.
# Contact between TubR and filament of treadmilling TubZ polymer. TubZ subunits are lost from the - end and are added to the + end.
# TubR-plasmid complex is pulled along the growing polymer until it reaches the cell pole.
# Interaction with membrane is likely to trigger the release of the plasmid.
The net result being transport of partition complex to the cell pole. | 1 | Applied and Interdisciplinary Chemistry |
-Malic acid is the naturally occurring form, whereas a mixture of - and -malic acid is produced synthetically.
Malate plays an important role in biochemistry. In the C4 carbon fixation process, malate is a source of CO in the Calvin cycle. In the citric acid cycle, (S)-malate is an intermediate, formed by the addition of an -OH group on the si face of fumarate. It can also be formed from pyruvate via anaplerotic reactions.
Malate is also synthesized by the carboxylation of phosphoenolpyruvate in the guard cells of plant leaves. Malate, as a double anion, often accompanies potassium cations during the uptake of solutes into the guard cells in order to maintain electrical balance in the cell. The accumulation of these solutes within the guard cell decreases the solute potential, allowing water to enter the cell and promote aperture of the stomata. | 1 | Applied and Interdisciplinary Chemistry |
On May 19, 2003, during a conference at the Sandestin Resort in Florida, a group consisting of about 65 chemists, engineers, and government officials met to create a narrowed down set of green principles relating to engineers and engineering. After 4 days of debating and proposals, the Sandestin Declaration was created. This declaration established the 9 Principles of Green Engineering, which narrowed down the focus to processes engineers can abide by, with a focus on designing processes and products with the future in mind. The resulting 9 Principles were later supported and recognized by The U.S. Environmental Protection Agency, National Science Foundation, Department of Energy (Los Alamos National Laboratory), and the ACS Green Chemistry institute. | 1 | Applied and Interdisciplinary Chemistry |
The most common reactions of benzene involve substitution of a proton by other groups. Electrophilic aromatic substitution is a general method of derivatizing benzene. Benzene is sufficiently nucleophilic that it undergoes substitution by acylium ions and alkyl carbocations to give substituted derivatives.
The most widely practiced example of this reaction is the ethylation of benzene.
Approximately 24,700,000 tons were produced in 1999. Highly instructive but of far less industrial significance is the Friedel-Crafts alkylation of benzene (and many other aromatic rings) using an alkyl halide in the presence of a strong Lewis acid catalyst. Similarly, the Friedel-Crafts acylation is a related example of electrophilic aromatic substitution. The reaction involves the acylation of benzene (or many other aromatic rings) with an acyl chloride using a strong Lewis acid catalyst such as aluminium chloride or Iron(III) chloride. | 1 | Applied and Interdisciplinary Chemistry |
PERK (encoded in humans by the gene EIF2AK3) responds mainly to endoplasmic reticulum stress and has two modes of activation. This kinase has a unique luminal domain that plays a role in activation. The classical model of activation states that the luminal domain is normally bound to 78-kDa glucose-regulated protein (GRP78). Once there is a buildup of unfolded proteins, GRP78 dissociates from the luminal domain. This causes PERK to dimerize, leading to autophosphorylation and activation. The activated PERK kinase will then phosphorylate eIF2α, causing a cascade of events. Thus, the activation of this kinase is dependent on the aggregation of unfolded proteins in the endoplasmic reticulum. PERK has also been observed to activate in response to activity of the proto-oncogene MYC. This activation causes ATF4 expression, resulting in tumorigenesis and cellular transformation. | 1 | Applied and Interdisciplinary Chemistry |
In both naturally occurring and synthetic porous structures, the geometry of pores and capillaries is almost never perfectly cylindrical. Often, porous media contain networks of capillaries, much like a sponge. Since pore geometry affects the shape and curvature of an equilibrium meniscus, the Kelvin equation could be represented differently every time the meniscus changes along a "snake-like" capillary. This makes the analysis via the Kelvin equation complicated very quickly. Adsorption isotherm studies utilizing capillary condensation are still the main method for determining pore size and shape. With advancements in synthetic techniques and instrumentation, very well ordered porous structures are now available which circumvent the problem of odd-pore geometries in engineered systems. | 1 | Applied and Interdisciplinary Chemistry |
"Ultraviolet" means "beyond violet" (from Latin ultra, "beyond"), violet being the color of the highest frequencies of visible light. Ultraviolet has a higher frequency (thus a shorter wavelength) than violet light.
UV radiation was discovered in 1801 when the German physicist Johann Wilhelm Ritter observed that invisible rays just beyond the violet end of the visible spectrum darkened silver chloride-soaked paper more quickly than violet light itself. He called them "(de-)oxidizing rays" () to emphasize chemical reactivity and to distinguish them from "heat rays", discovered the previous year at the other end of the visible spectrum. The simpler term "chemical rays" was adopted soon afterwards, and remained popular throughout the 19th century, although some said that this radiation was entirely different from light (notably John William Draper, who named them "tithonic rays"). The terms "chemical rays" and "heat rays" were eventually dropped in favor of ultraviolet and infrared radiation, respectively. In 1878, the sterilizing effect of short-wavelength light by killing bacteria was discovered. By 1903, the most effective wavelengths were known to be around 250 nm. In 1960, the effect of ultraviolet radiation on DNA was established.
The discovery of the ultraviolet radiation with wavelengths below 200 nm, named "vacuum ultraviolet" because it is strongly absorbed by the oxygen in air, was made in 1893 by German physicist Victor Schumann. | 0 | Theoretical and Fundamental Chemistry |
Several synthesis methods exist to produce LAGP in the form of bulk pellets or thin films, depending on the required performances and final applications. The synthesis path significantly affects the microstructure of the LAGP material, which plays a key role in determining its overall conductive properties. Indeed, a compact layer of crystalline LAGP with large and connected grains, and minimal amount of secondary, non-conductive phases ensures the highest conductivity values. On the contrary, an amorphous structure or the presence of small grains and pores tend to hinder the motion of lithium ions, with values of ionic conductivity in the range of 10 - 10 S/cm for glassy LAGP.
In most cases, a post-process thermal treatment is performed to achieve the desired degree of crystallinity. | 0 | Theoretical and Fundamental Chemistry |
MimoDB is a database of peptides that have been selected from random peptide libraries based on their ability to bind small compounds, nucleic acids, proteins, cells, and tissues through phage display. | 1 | Applied and Interdisciplinary Chemistry |
One of the earliest steps towards atomic physics was the recognition that matter was composed of atoms, in modern terms the basic unit of a chemical element. This theory was developed by John Dalton in the 18th century. At this stage, it wasn't clear what atoms were - although they could be described and classified by their observable properties in bulk; summarized by the developing periodic table, by John Newlands and Dmitri Mendeleyev around the mid to late 19th century.
Later, the connection between atomic physics and optical physics became apparent, by the discovery of spectral lines and attempts to describe the phenomenon - notably by Joseph von Fraunhofer, Fresnel, and others in the 19th century.
From that time to the 1920s, physicists were seeking to explain atomic spectra and blackbody radiation. One attempt to explain hydrogen spectral lines was the Bohr atom model.
Experiments including electromagnetic radiation and matter - such as the photoelectric effect, Compton effect, and spectra of sunlight the due to the unknown element of Helium, the limitation of the Bohr model to Hydrogen, and numerous other reasons, lead to an entirely new mathematical model of matter and light: quantum mechanics. | 0 | Theoretical and Fundamental Chemistry |
Topoisomers or topological isomers are molecules with the same chemical formula and stereochemical bond connectivities but different topologies. Examples of molecules for which there exist topoisomers include DNA, which can form knots, and catenanes. Each topoisomer of a given DNA molecule possesses a different linking number associated with it. DNA topoisomers can be interchanged by enzymes called topoisomerases. Using a topoisomerase along with an intercalator, topoisomers with different linking number may be separated on an agarose gel via gel electrophoresis. | 0 | Theoretical and Fundamental Chemistry |
Many permanent bioadhesives (e.g., the oothecal foam of the mantis) are generated by a "mix to activate" process that involves hardening via covalent cross-linking. On non-polar surfaces the adhesive mechanisms may include van der Waals forces, whereas on polar surfaces mechanisms such as hydrogen bonding and binding to (or forming bridges via) metal cations may allow higher sticking forces to be achieved.
* Microorganisms use acidic polysaccharides (molecular mass around 100 000 Da)
* Marine bacteria use carbohydrate exopolymers to achieve bond strengths to glass of up to 500 000 N/m
* Marine invertebrates commonly employ protein-based glues for irreversible attachment. Some mussels achieve 800 000 N/m on polar surfaces and 30 000 N/m on non-polar surfaces these numbers are dependent on the environment, mussels in high predation environments have an increased attachment to substrates. In high predation environments it can require predators 140% more force to dislodge mussels
* Some algae and marine invertebrates use lecproteins that contain L-DOPA to effect adhesion
* Proteins in the oothecal foam of the mantis are cross-linked covalently by small molecules related to L-DOPA via a tanning reaction that is catalysed by catechol oxidase or polyphenol oxidase enzymes.
L-DOPA is a tyrosine residue that bears an additional hydroxyl group. The twin hydroxyl groups in each side-chain compete well with water for binding to surfaces, form polar attachments via hydrogen bonds, and chelate the metals in mineral surfaces. The Fe(L-DOPA) complex can itself account for much cross-linking and cohesion in mussel plaque, but in addition the iron catalyses oxidation of the L-DOPA to reactive quinone free radicals, which go on to form covalent bonds. | 1 | Applied and Interdisciplinary Chemistry |
The methyl red (MR) test can detect whether the mixed acid fermentation pathway occurs in microbes when given glucose. A pH indicator is used that turns the test solution red if the pH drops below 4.4. If the fermentation pathway has taken place, the mixture of acids it has produced will make the solution very acidic and cause a red colour change.
The methyl red test belongs to a group known as the IMViC tests. | 1 | Applied and Interdisciplinary Chemistry |
The Born series can also be written for other scattering quantities like the T-matrix which is closely related to the scattering amplitude.
Iterating Lippmann-Schwinger equation for the T-matrix we get
For the T-matrix stands only for retarded Greens operator . The standing wave Greens operator would give the K-matrix instead. | 0 | Theoretical and Fundamental Chemistry |
Heat engines, refrigeration cycles and heat pumps usually involve a fluid to and from which heat is transferred while undergoing a thermodynamic cycle. This fluid is called the working fluid. Refrigeration and heat pump technologies often refer to working fluids as refrigerants. Most thermodynamic cycles make use of the latent heat (advantages of phase change) of the working fluid. In case of other cycles the working fluid remains in gaseous phase while undergoing all the processes of the cycle. When it comes to heat engines, working fluid generally undergoes a combustion process as well, for example in internal combustion engines or gas turbines. There are also technologies in heat pump and refrigeration, where working fluid does not change phase, such as reverse Brayton or Stirling cycle.
This article summarises the main criteria of selecting working fluids for a thermodynamic cycle, such as heat engines including low grade heat recovery using Organic Rankine Cycle (ORC) for geothermal energy, waste heat, thermal solar energy or biomass and heat pumps and refrigeration cycles. The article addresses how working fluids affect technological applications, where the working fluid undergoes a phase transition and does not remain in its original (mainly gaseous) phase during all the processes of the thermodynamic cycle.
Finding the optimal working fluid for a given purpose – which is essential to achieve higher energy efficiency in the energy conversion systems – has great impact on the technology, namely it does not just influence operational variables of the cycle but also alters the layout and modifies the design of the equipment. Selection criteria of working fluids generally include thermodynamic and physical properties besides economical and environmental factors, but most often all of these criteria are used together. | 0 | Theoretical and Fundamental Chemistry |
Until late in the 20th century the word "radical" was used in chemistry to indicate any connected group of atoms, such as a methyl group or a carboxyl, whether it was part of a larger molecule or a molecule on its own. A radical is often known as an R group. The qualifier "free" was then needed to specify the unbound case. Following recent nomenclature revisions, a part of a larger molecule is now called a functional group or substituent, and "radical" now implies "free". However, the old nomenclature may still appear in some books.
The term radical was already in use when the now obsolete radical theory was developed. Louis-Bernard Guyton de Morveau introduced the phrase "radical" in 1785 and the phrase was employed by Antoine Lavoisier in 1789 in his Traité Élémentaire de Chimie. A radical was then identified as the root base of certain acids (the Latin word "radix" meaning "root"). Historically, the term radical in radical theory was also used for bound parts of the molecule, especially when they remain unchanged in reactions. These are now called functional groups. For example, methyl alcohol was described as consisting of a methyl "radical" and a hydroxyl "radical". Neither are radicals in the modern chemical sense, as they are permanently bound to each other, and have no unpaired, reactive electrons; however, they can be observed as radicals in mass spectrometry when broken apart by irradiation with energetic electrons.
In a modern context the first organic (carbon–containing) radical identified was the triphenylmethyl radical, (CH)C. This species was discovered by Moses Gomberg in 1900. In 1933 Morris S. Kharasch and Frank Mayo proposed that free radicals were responsible for anti-Markovnikov addition of hydrogen bromide to allyl bromide.
In most fields of chemistry, the historical definition of radicals contends that the molecules have nonzero electron spin. However, in fields including spectroscopy and astrochemistry, the definition is slightly different. Gerhard Herzberg, who won the Nobel prize for his research into the electron structure and geometry of radicals, suggested a looser definition of free radicals: "any transient (chemically unstable) species (atom, molecule, or ion)". The main point of his suggestion is that there are many chemically unstable molecules that have zero spin, such as C, C, CH and so on. This definition is more convenient for discussions of transient chemical processes and astrochemistry; therefore researchers in these fields prefer to use this loose definition. | 1 | Applied and Interdisciplinary Chemistry |
In corrosion, spalling occurs when a substance (metal or concrete) sheds tiny particles of corrosion products as the corrosion reaction progresses. Although they are not soluble or permeable, these corrosion products do not adhere to the parent material's surface to form a barrier to further corrosion, as happens in passivation. Spallation happens as the result of a large volume change during the reaction.
In the case of actinide metals (most notably the depleted uranium used in some types of ammunition), the material expands so strongly upon exposure to air that a fine layer of oxide is forcibly expelled from the surface. A slowly oxidised plug of metallic uranium can sometimes resemble an onion subjected to desquamation. The main hazard however arises from the pyrophoric character of actinide metals which can spontaneously ignite when their specific area is high. This property, along with the inherent toxicity and (for some to a lesser extent) radioactivity of these elements, make them dangerous to handle in metallic form under air. Therefore, they are often handled under an inert atmosphere (nitrogen or argon) inside an anaerobic glovebox. | 1 | Applied and Interdisciplinary Chemistry |
A hexagonal structure that is often described as chicken wire-like can also be found in other types of chemical compounds such as:
* Non-aromatic polycyclic hydrocarbons, e.g. steroids like cholesterol
* Flat hexagonal hydrogen bonded trimesic acid (benzene-1,3,5-tricarboxylic acid), boric acid, or melamine-cyanuric acid complexes
* Interwoven molecule chains in the inorganic polymer NaAuS
* Complexes of the protein clathrin | 0 | Theoretical and Fundamental Chemistry |
The phosphaethynolate anion, also referred to as PCO, is the phosphorus-containing analogue of the cyanate anion with the chemical formula or . The anion has a linear geometry and is commonly isolated as a salt. When used as a ligand, the phosphaethynolate anion is ambidentate in nature meaning it forms complexes by coordinating via either the phosphorus or oxygen atoms. This versatile character of the anion has allowed it to be incorporated into many transition metal and actinide complexes but now the focus of the research around phosphaethynolate has turned to utilising the anion as a synthetic building block to organophosphanes. | 0 | Theoretical and Fundamental Chemistry |
With the yeast two-hybrid system, gonococcal Opa proteins were found to interact with PKM2. The results suggest that direct molecular interaction with the host metabolic enzyme PKM2 is required for the acquisition of pyruvate and for gonococcal growth and survival. | 1 | Applied and Interdisciplinary Chemistry |
Gestation lasts 20 to 23 days. Neonates are pink and hairless, with closed eyes and ears. Fur begins to appear by three days, and young are completely furred except for the belly by seven days. Eyes and ears open by eight days. Weaning occurs from 12 to 14 days. Young born in spring and early summer attain adult weight in 12 weeks, but undergo a fall weight loss. Young born in late summer continue growing through the fall and maintain their weight through the winter. Maximum size is reached between two and 10 months.
Typical eastern meadow vole litters consist of four to six young, with extremes of one and 11 young. On average, 2.6 young are successfully weaned per litter. Litter size is not significantly correlated with latitude, elevation, or population density. Fall, winter, and spring litters tend to be smaller than summer litters. Litter size was positively correlated with body size, and is not significantly different in primaparous and multiparous females. Primaparous females had fewer young per litter than multiparous females. Litter size was constant in summer breeding periods at different population densities. Female eastern meadow voles reach reproductive maturity earlier than males; some ovulate and become pregnant as early as three weeks old. Males are usually six to eight weeks old before mature sperm are produced. One captive female produced 17 litters in one year for a total of 83 young. One of her young produced 13 litters (totalling 78 young) before she was a year old.
Patterns of mortality apparently vary among eastern meadow vole populations. The average eastern meadow vole lifespan is less than one month because of high nestling and juvenile mortality. The average time adults are recapturable in a given habitat is about two months, suggesting the average extended lifespan (i.e. how much time adult eastern meadow voles have left) is about two months, not figuring in emigration. Mortality was 88% for the first 30 days after birth. and postnestling juveniles had the highest mortality rate (61%), followed by young adults (58%) and older age groups (53%). Nestlings were estimated to have the lowest mortality rate (50%). Estimated mean longevity ranges from two to 16 months. The maximum lifespan in the wild is 16 months, and few voles live more than two years.
Eastern meadow vole populations fluctuate annually and also tend to reach peak densities at two- to five-year
intervals, with population declines in intervening years. Breeding often ceases in January and starts again in March. Over the course of a year, eastern meadow vole populations tend to be lowest in early spring; the population increases rapidly through summer and fall.
In years of average population sizes, typical eastern meadow vole population density is about 15 to 45 eastern meadow voles per acre in old-field habitat. In peak years, their population densities may reach 150 per acre in marsh habitat (more favorable for eastern meadow voles than old fields). Peak eastern meadow vole abundance can exceed 1,482 eastern meadow voles per hectare (600/acre) in northern prairie wetlands. Eastern meadow voles in optimal habitats in Virginia (old fields with dense vegetation) reached densities of 983/ha (398/ac); populations declined to 67/ha (27/ac) at the lowest point in the cycle. Different factors influencing population density have been assigned primary importance by different authors. Reich listed the following factors as having been suggested by different authors: food quality, predation, climatic events, density-related physiological stress, and the presence of genetically determined behavioral variants among dispersing individuals.
Normal population cycles do not occur when dispersal is prevented; under normal conditions, dispersers have been shown to be behaviorally, genetically, and demographically different from residents. A threshold density of cover is thought to be needed for eastern meadow vole populations to increase. Above the threshold amount, the quantity of cover influences the amplitude and possibly the duration of the population peak. Local patches of dense cover could serve as source populations or reservoirs to colonize less favorable habitats with sparse cover.
Eastern meadow voles form extensive colonies and develop communal latrine areas. They are socially aggressive and agonistic; females dominate males and males fight amongst themselves. | 1 | Applied and Interdisciplinary Chemistry |
Zero electron kinetic energy (ZEKE) spectroscopy was developed with the idea of collecting only the resonance ionization photoelectrons that have extremely low kinetic energy. The technique involves waiting for a period of time after a resonance ionization experiment and then pulsing an electric field to collect the lowest energy photoelectrons in a detector. Typically, ZEKE experiments utilize two different tunable lasers. One laser photon energy is tuned to be resonant with the energy of an intermediate state. (This may be resonant with an excited state at a multiphoton transition.) Another photon energy is tuned to be close to the ionization threshold energy. The technique worked extremely well and demonstrated energy resolution that was significantly better than the laser bandwidth. It turns out that it was not the photoelectrons that were detected in ZEKE. The delay between the laser and the electric field pulse selected the longest lived and most circular Rydberg states closest to the energy of the ion core. The population distribution of surviving long-lived near threshold Rydberg states is close to the laser energy bandwidth. The electric field pulse Stark shifts the near-threshold Rydberg states and vibrational autoionization occurs. ZEKE has provided a significant advance in the study of the vibrational spectroscopy of molecular ions. Schlag, Peatman and Müller-Dethlefs originated ZEKE spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
A Paul trap is a type of quadrupole ion trap that uses static direct current (DC) and radio frequency (RF) oscillating electric fields to trap ions. Paul traps are commonly used as components of a mass spectrometer. The invention of the 3D quadrupole ion trap itself is attributed to Wolfgang Paul who shared the Nobel Prize in Physics in 1989 for this work. The trap consists of two hyperbolic metal electrodes with their foci facing each other and a hyperbolic ring electrode halfway between the other two electrodes. Ions are trapped in the space between these three electrodes by the oscillating and static electric fields. | 0 | Theoretical and Fundamental Chemistry |
Octafluoropropane (CF) is the perfluorocarbon counterpart to the hydrocarbon propane. This non-flammable and non-toxic synthetic substance has applications in semiconductor production and medicine. It is also an extremely potent greenhouse gas. | 1 | Applied and Interdisciplinary Chemistry |
There are a number of AFPs found in insects, including those from Dendroides, Tenebrio and Rhagium beetles, spruce budworm and pale beauty moths, and midges (same order as flies). Insect AFPs share certain similarities, with most having higher activity (i.e. greater thermal hysteresis value, termed hyperactive) and a repetitive structure with a flat ice-binding surface. Those from the closely related Tenebrio and Dendroides beetles are homologous and each 12–13 amino-acid repeat is stabilized by an internal disulfide bond. Isoforms have between 6 and 10 of these repeats that form a coil, or beta-solenoid. One side of the solenoid has a flat ice-binding surface that consists of a double row of threonine residues. Other beetles (genus Rhagium) have longer repeats without internal disulfide bonds that form a compressed beta-solenoid (beta sandwich) with four rows of threonine residus, and this AFP is structurally similar to that modelled for the non-homologous AFP from the pale beauty moth. In contrast, the AFP from the spruce budworm moth is a solenoid that superficially resembles the Tenebrio protein, with a similar ice-binding surface, but it has a triangular cross-section, with longer repeats that lack the internal disulfide bonds. The AFP from midges is structurally similar to those from Tenebrio and Dendroides, but the disulfide-braced beta-solenoid is formed from shorter 10 amino-acids repeats, and instead of threonine, the ice-binding surface consists of a single row of tyrosine residues. Springtails (Collembola) are not insects, but like insects, they are arthropods with six legs. A species found in Canada, which is often called a "snow flea", produces hyperactive AFPs. Although they are also repetitive and have a flat ice-binding surface, the similarity ends there. Around 50% of the residues are glycine (Gly), with repeats of Gly-Gly- X or Gly-X-X, where X is any amino acid. Each 3-amino-acid repeat forms one turn of a polyproline type II helix. The helices then fold together, to form a bundle that is two helices thick, with an ice-binding face dominated by small hydrophobic residues like alanine, rather than threonine. Other insects, such as an Alaskan beetle, produce hyperactive antifreezes that are even less similar, as they are polymers of sugars (xylomannan) rather than polymers of amino acids (proteins). Taken together, this suggests that most of the AFPs and antifreezes arose after the lineages that gave rise to these various insects diverged. The similarities they do share are the result of convergent evolution. | 1 | Applied and Interdisciplinary Chemistry |
Palytoxin was first isolated, named and described from Palythoa toxica by Moore and Scheuer in a study published in 1971. They measured that its molar mass is approximately 3300 g/mol. They also identified it to be the substance that was probably responsible for the toxicity of P. toxica, but it was uncertain at the time if the coral also had other toxic compounds in it. It was then assessed by Walsh and Bowers that the limu-make-o-Hana was not a seaweed but a zoanthid coral, subsequently described as Palythoa toxica. Moore and Scheuer were aware of the study that Walsh and Bowers were writing. | 0 | Theoretical and Fundamental Chemistry |
In this variant the OAA produced by aspartate aminotransferase in the bundle sheath is decarboxylated to PEP by PEPCK. The fate of PEP is still debated. The simplest explanation is that PEP would diffuse back to the mesophyll to serve as a substrate for PEPC. Because PEPCK uses only one ATP molecule, the regeneration of PEP through PEPCK would theoretically increase photosynthetic efficiency of this subtype, however this has never been measured. An increase in relative expression of PEPCK has been observed under low light, and it has been proposed to play a role in facilitating balancing energy requirements between mesophyll and bundle sheath. | 0 | Theoretical and Fundamental Chemistry |
Before being able to use the minor head losses in an equation, the losses in the system due to friction must also be calculated.
Equation for friction losses:
= Frictional head loss
= Downstream velocity
= Gravity of Earth
= Hydraulic radius
=Total length of piping
= Fanning friction factor | 1 | Applied and Interdisciplinary Chemistry |
Thermite reactions have many uses. It is not an explosive; instead, it operates by exposing a very small area to extremely high temperatures. Intense heat focused on a small spot can be used to cut through metal or weld metal components together both by melting metal from the components, and by injecting molten metal from the thermite reaction itself.
Thermite may be used for repair by the welding in-place of thick steel sections such as locomotive axle-frames where the repair can take place without removing the part from its installed location.
Thermite can be used for quickly cutting or welding steel such as rail tracks, without requiring complex or heavy equipment. However, defects such as slag inclusions and voids (holes) are often present in such welded junctions, so great care is needed to operate the process successfully. The numerical analysis of thermite welding of rails has been approached similar to casting cooling analysis. Both this finite element analysis and experimental analysis of thermite rail welds has shown that weld gap is the most influential parameter affecting defect formation. Increasing weld gap has been shown to reduce shrinkage cavity formation and cold lap welding defects, and increasing preheat and thermite temperature further reduces these defects. However, reducing these defects promotes a second form of defect: microporosity. Care must also be taken to ensure that the rails remain straight, without resulting in dipped joints, which can cause wear on high speed and heavy axle load lines.
A thermite reaction, when used to purify the ores of some metals, is called the , or aluminothermic reaction. An adaptation of the reaction, used to obtain pure uranium, was developed as part of the Manhattan Project at Ames Laboratory under the direction of Frank Spedding. It is sometimes called the Ames process.
Copper thermite is used for welding together thick copper wires for the purpose of electrical connections. It is used extensively by the electrical utilities and telecommunications industries (exothermic welded connections). | 0 | Theoretical and Fundamental Chemistry |
Schild regression is a radioligand binding assay. It is used for DNA labelling (5 and 3), leaving the nucleic acids intact. | 0 | Theoretical and Fundamental Chemistry |
On 28 March 2017, Drahoš announced his intention to stand in the 2018 presidential election. On 24 April 2017, he started gathering the signatures required to be registered as a candidate. In July 2017, after meeting with Drahoš, the leaders of Populars and Mayors, Pavel Bělobrádek and Petr Gazdík, announced that they would ask their respective parties members to nominate and endorse Drahošs candidacy. Mayors and Independents endorsed Drahoš on 25 July 2017 while the Christian and Democratic Union – Czechoslovak People's Party (KDU–ČSL) endorsed him on 14 November 2017. Young Social Democrats also endorsed Drahoš on 9 December 2017. Polls in late 2017 showed Drahoš as the second strongest candidate behind Zeman.
Drahoš received campaign donations from several influential businessmen, including Dalibor Dědek, Jiří Grygar and Luděk Sekyra. Drahoš started gathering signatures for his nomination in May 2017. On 19 August 2017, Drahoš announced he had gathered 78,000 signatures. He submitted his nomination on 3 November 2017 with 142,000 signatures.
On 4 November 2017 on Facebook, Drahoš criticized Mirek Topolánek, who had announced his candidacy that day, describing Topolánek as similar to Miloš Zeman and calling his candidacy a bad joke. The two candidates met during a presidential debate at Charles University; Drahoš reflected that the status he posted was "Topolánek-like", to which Topolánek replied that it was written either by "a woman or PR mage".
Drahoš received media attention when he expressed his fear that the election could be influenced by Russia. He met outgoing Prime Minister Bohuslav Sobotka to discuss the matter and stated he would also meet the new Prime Minister Andrej Babiš. The incumbent president Miloš Zeman criticized Drahoš and compared his actions to Hillary Clinton's when she lost to Donald Trump.
Drahoš received criticism when he published a status on social media about Václav Klaus' amnesty, when it was revealed that he had copied a similar status by his fellow presidential candidate Michal Horáček. Drahoš apologised and attributed the mistake to an external member of staff.
The first round was held on 12 and 13 January 2018. Drahoš received 1,369,601 (26.6%) votes, and advanced to the second round against the incumbent president Miloš Zeman. In the second round, held on 26–27 January 2018, Drahoš received 48.63% of the vote and thus lost to Zeman. Drahoš conceded defeat to Zeman, telling a crowd of his supporters that "I would like to congratulate election winner Miloš Zeman". | 0 | Theoretical and Fundamental Chemistry |
Simon retired from AVCO at the age of 65, moving to Pittsboro, North Carolina. She would operate her own consulting firm, Simon Associates, from her home until 1993. After concluding her research career, she served on numerous committees and advisory boards for government agencies, universities, and corporations. The most notable positions include the Department of Commerce Committee for the National Bureau of Standards, and the committee for the National Medal of Science during the Carter administration. Simon served as the first female trustee at Worcester Polytechnic Institute, where she set up the Dorothy M. Simon Endowed Fund for Fire Safety Studies.
Simon died on March 25, 2016, at the age of 96, in her home in Pittsboro, North Carolina. | 0 | Theoretical and Fundamental Chemistry |
The non-fluorescent acetomethoxy derivate of calcein (calcein AM, AM = acetoxymethyl) is used in biology as it can be transported through the cellular membrane into live cells, which makes it useful for testing of cell viability and for short-term labeling of cells. Alternatively, Fura-2 , Furaptra , Indo-1 and aequorin may be used. An acetomethoxy group obscures the part of the molecule that chelates Ca, Mg, Zn and other ions. After transport into the cells, intracellular esterases remove the acetomethoxy group, the molecule gets trapped inside and gives out strong green fluorescence. As dead cells lack active esterases, only live cells are labeled and counted by flow cytometry.
Calcein is now rarely used as a Ca or Mg indicator because its fluorescence is directly sensitive to these ions only at strongly alkaline pH, and thus it is not particularly useful for measuring Ca or Mg in cells. Fluorescence of calcein is quenched strongly by Co, Ni and Cu and appreciably by Fe and Mn at physiological pH. This fluorescence quenching response can be exploited for detecting the opening of the mitochondrial permeability transition pore (mPTP) and for measuring cell volume changes. Calcein is commonly used for cell tracing and in studies of endocytosis, cell migration, and gap junctions.
The acetoxymethyl ester of calcein is also used to detect drug interactions with multidrug resistance proteins (ABC transporters ATP-binding cassette transporter genes) in intact cells as it is an excellent substrate of the multidrug resistance transporter 1 (MDR1) P-glycoprotein and the Multidrug Resistance-Associated Protein (MRP1). The calcein AM assay can be used as a model for drug-drug interactions, for screening transporter substrates and/or inhibitors; and also to determine in vitro drug resistance of cells, including samples from patients.
Calcein is also used for marking freshly hatched fish and for labeling of bones in live animals. | 0 | Theoretical and Fundamental Chemistry |
Magnetic resonance force microscopy (MRFM) is an imaging technique that acquires magnetic resonance images (MRI) at nanometer scales, and possibly at atomic scales in the future. MRFM is potentially able to observe protein structures which cannot be seen using X-ray crystallography and protein nuclear magnetic resonance spectroscopy. Detection of the magnetic spin of a single electron has been demonstrated using this technique. The sensitivity of a current MRFM microscope is 10 billion times greater than a medical MRI used in hospitals. | 0 | Theoretical and Fundamental Chemistry |
The term magnetofection, currently trademarked by the company OZ Biosciences, combines the words magnetic and transfection. Magnetofection uses nucleic acids associated with magnetic nanoparticles. These molecular complexes are then concentrated and transported into cells using an applied magnetic field. | 1 | Applied and Interdisciplinary Chemistry |
The location of substrate attachment to the complex has yet to be elucidated. It is believed that the Fe atoms closest to the interstitial carbon participate in substrate activation, but the terminal molybdenum is also a candidate for nitrogen fixation. X-ray crystallographic studies utilizing MoFe-protein and carbon monoxide (CO), which is isoelectronic to dinitrogen, demonstrated that carbon monoxide is binding to the Fe2-Fe6-edge of FeMoco. Additional studies showed simultaneous binding of two CO-molecules to FeMoco, providing a structural basis for biological Fischer-Tropsch-type chemistry. Se-incorporation studies in combination with time-resolved X-ray crystallography evidenced major structural rearrangements in the FeMoco-structure upon substrate binding events. | 0 | Theoretical and Fundamental Chemistry |
Efficiency was further improved by the development of a multi-stage injector which is powered not by live steam from the boiler but by exhaust steam from the cylinders, thereby making use of the residual energy in the exhaust steam which would otherwise go to waste. However, an exhaust injector also cannot work when the locomotive is stationary; later exhaust injectors could use a supply of live steam if no exhaust steam was available. | 1 | Applied and Interdisciplinary Chemistry |
Although technically speaking, DNA sequence polymorphism has been going on since the use of RFLP in the 1960s, the analysis has changed significantly over the years. DNA sequence polymorphism uses older techniques like RFLP, but on a larger scale. Sequencing is much faster and more efficient. The analysis is automated, as it uses a technique known as shotgun sequencing. This high-throughput method is commonly used in population genetics. | 1 | Applied and Interdisciplinary Chemistry |
Complexometric indicators are water-soluble organic molecules. Some examples are:
* Calcein with EDTA for calcium
* Patton-Reeder Indicator with EDTA for calcium with magnesium
* Curcumin for boron, that forms Rosocyanine, although the red color change of curcumin also occurs for pH > 8.4
* Eriochrome Black T for aluminium, cadmium, zinc, calcium and magnesium
* Fast Sulphon Black with EDTA for copper
* Hematoxylin for copper
* Murexide for calcium and rare earths, but also for copper, nickel, cobalt, and thorium
* Xylenol orange for gallium, indium and scandium | 0 | Theoretical and Fundamental Chemistry |
Frank was elected Fellow of the Royal Society in 1954, delivering the Bakerian Lecture in 1973. He was knighted in 1977. He was also awarded honorary degrees by seven universities.
In 1963 he won the Fernand Holweck Medal and Prize.
In 1967 he was awarded the A. A. Griffith Medal and Prize. He was also a member of the Materials Science Club Awards Sub-Committee which selected the Griffith medallist for 1972 (L. R. G. Treloar).
In 1994 he was awarded the Royal Societys Copley Medal, its highest honour, "in recognition of his fundamental contribution to the theory of crystal morphology, in particular to the source of dislocations and their consequences in interfaces and crystal growth; to fundamental understanding of liquid crystals and the concept of disclination; and to the extension of crystallinity concepts to aperiodic crystals."' | 0 | Theoretical and Fundamental Chemistry |
Fermentation can be simply defined, in this context, as the conversion of sugar molecules into ethanol and carbon dioxide by yeast.
Fermentation practices have led to the discovery of ample microbial and antimicrobial cultures on fermented foods and products. | 1 | Applied and Interdisciplinary Chemistry |
Hydroxyl groups (-OH), found in alcohols, are polar and therefore hydrophilic (water liking) but their carbon chain portion is non-polar which make them hydrophobic. The molecule increasingly becomes overall more nonpolar and therefore less soluble in the polar water as the carbon chain becomes longer. Methanol has the shortest carbon chain of all alcohols (one carbon atom) followed by ethanol (two carbon atoms), and 1-propanol along with its isomer 2-propanol, all being miscible with water. Tert-Butyl alcohol, with four carbon atoms, is the only one among its isomers to be miscible with water. | 0 | Theoretical and Fundamental Chemistry |
Reversed phase liquid chromatography (RPLC) is the most important chromatographic method for measuring solute hydrophobicity. The non polar stationary phase mimics biological membranes. Peptide usage has many advantages because partition is not extended by the terminal charges in RPLC. Also, secondary structures formation is avoided by using short sequence peptides. Derivatization of amino acids is necessary to ease its partition into a C18 bonded phase. Another scale had been developed in 1971 and used peptide retention on hydrophilic gel. 1-butanol and pyridine were used as the mobile phase in this particular scale and glycine was used as the reference value. Pliska and his coworkers used thin layer chromatography to relate mobility values of free amino acids to their hydrophobicities. About a decade ago, another hydrophilicity scale was published, this scale used normal phase liquid chromatography and showed the retention of 121 peptides on an amide-80 column.
The absolute values and relative rankings of hydrophobicity determined by chromatographic methods can be affected by a number of parameters. These parameters include the silica surface area and pore diameter, the choice and pH of aqueous buffer, temperature and the bonding density of stationary phase chains. | 0 | Theoretical and Fundamental Chemistry |
The use of a solvent gradient is very well developed in column chromatography but is less common in CCC. A solvent gradient is produced by increasing (or decreasing) the polarity of the mobile phase during the separation to achieve optimal resolution across a wider range of polarities. For example, a methanol-water mobile phase gradient may be employed using heptane as the stationary phase. This is not possible with all biphasic solvent systems, due to excessive loss of stationary phase created by disruption the equilibrium conditions within the column. Gradients may either be produced in steps, or continuously. | 0 | Theoretical and Fundamental Chemistry |
Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their activities. Photosynthetic organisms use intracellular organic compounds to store the chemical energy they produce in photosynthesis within organic compounds like sugars, glycogen, cellulose and starches. Photosynthesis is usually used to refer to oxygenic photosynthesis, a process that produces oxygen. To use this stored chemical energy, the organisms cells metabolize the organic compounds through another process called cellular respiration. Photosynthesis plays a critical role in producing and maintaining the oxygen content of the Earths atmosphere, and it supplies most of the biological energy necessary for complex life on Earth.
Some bacteria also perform anoxygenic photosynthesis, which uses bacteriochlorophyll to split hydrogen sulfide as a reductant instead of water. This process produces sulfur of oxygen. Archaea such as Halobacterium also perform a type of non-carbon-fixing anoxygenic photosynthesis, where the simpler photopigment retinal and its microbial rhodopsin derivatives are used to absorb green light and power proton pumps to directly synthesize adenosine triphosphate (ATP), the "energy currency" of cells. Such archaeal photosynthesis might have been the earliest form of photosynthesis that evolved on Earth, going back as far as the Paleoarchean, preceding that of cyanobacteria (see Purple Earth hypothesis).
While the details may differ between species, the process always begins when light energy is absorbed by the reaction centers, proteins that contain photosynthetic pigments or chromophores. In plants, these proteins are chlorophylls (a porphyrin derivative that absorbs the red and blue spectrums of light, thus reflecting a green color) held inside chloroplasts, abundant in leaf cells. In bacteria they are embedded in the plasma membrane. In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, producing oxygen gas. The hydrogen freed by the splitting of water is used in the creation of two important molecules that participate in energetic processes: reduced nicotinamide adenine dinucleotide phosphate (NADPH) and ATP.
In plants, algae, and cyanobacteria, sugars are synthesized by a subsequent sequence of reactions called the Calvin cycle. In this process, atmospheric carbon dioxide is incorporated into already existing organic carbon compounds, such as ribulose bisphosphate (RuBP). Using the ATP and NADPH produced by the light-dependent reactions, the resulting compounds are then reduced and removed to form further carbohydrates, such as glucose. In other bacteria, different mechanisms like the reverse Krebs cycle are used to achieve the same end.
The first photosynthetic organisms probably evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen or hydrogen sulfide, rather than water, as sources of electrons. Cyanobacteria appeared later; the excess oxygen they produced contributed directly to the oxygenation of the Earth, which rendered the evolution of complex life possible. Today, the average rate of energy captured by photosynthesis globally is approximately 130 terawatts, which is about eight times the current power consumption of human civilization. Photosynthetic organisms also convert around 100–115 billion tons (91–104 Pg petagrams, or a billion metric tons), of carbon into biomass per year. Photosyntesis was first discovered in 1779 by Jan Ingenhousz; he showed that plants need light, not just air, soil, and water.
Photosynthesis is vital for climate processes, as it captures carbon dioxide from the air and then binds it in plants, harvested products and soil. Cereals alone are estimated to bind 3,825 Tg (teragrams) or 3.825 Pg (petagrams) of carbon dioxide every year, i.e. 3.825 billion metric tons. | 0 | Theoretical and Fundamental Chemistry |
Select filter cloth based on the type filter aid used (refer Filter aid selection), adjust the advancing knife to optimize the knife advance rate per drum revolution. (Detail explained in Advance blade section) | 0 | Theoretical and Fundamental Chemistry |
Most synthetic radioisotopes have a short half-life. Though a health hazard, radioactive materials have many medical and industrial uses. | 0 | Theoretical and Fundamental Chemistry |
Zero-point energy evolved from historical ideas about the vacuum. To Aristotle the vacuum was , "the empty"; i.e., space independent of body. He believed this concept violated basic physical principles and asserted that the elements of fire, air, earth, and water were not made of atoms, but were continuous. To the atomists the concept of emptiness had absolute character: it was the distinction between existence and nonexistence. Debate about the characteristics of the vacuum were largely confined to the realm of philosophy, it was not until much later on with the beginning of the renaissance, that Otto von Guericke invented the first vacuum pump and the first testable scientific ideas began to emerge. It was thought that a totally empty volume of space could be created by simply removing all gases. This was the first generally accepted concept of the vacuum.
Late in the 19th century, however, it became apparent that the evacuated region still contained thermal radiation. The existence of the aether as a substitute for a true void was the most prevalent theory of the time. According to the successful electromagnetic aether theory based upon Maxwell's electrodynamics, this all-encompassing aether was endowed with energy and hence very different from nothingness. The fact that electromagnetic and gravitational phenomena were easily transmitted in empty space indicated that their associated aethers were part of the fabric of space itself. Maxwell himself noted that:
However, the results of the Michelson–Morley experiment in 1887 were the first strong evidence that the then-prevalent aether theories were seriously flawed, and initiated a line of research that eventually led to special relativity, which ruled out the idea of a stationary aether altogether. To scientists of the period, it seemed that a true vacuum in space might be created by cooling and thus eliminating all radiation or energy. From this idea evolved the second concept of achieving a real vacuum: cool a region of space down to absolute zero temperature after evacuation. Absolute zero was technically impossible to achieve in the 19th century, so the debate remained unsolved. | 0 | Theoretical and Fundamental Chemistry |
About 70% of a humans total energy expenditure is due to the basal life processes taking place in the organs of the body (see table). About 20% of ones energy expenditure comes from physical activity and another 10% from thermogenesis, or digestion of food (postprandial thermogenesis). All of these processes require an intake of oxygen along with coenzymes to provide energy for survival (usually from macronutrients like carbohydrates, fats, and proteins) and expel carbon dioxide, due to processing by the Krebs cycle.
For the BMR, most of the energy is consumed in maintaining fluid levels in tissues through osmoregulation, and only about one-tenth is consumed for mechanical work, such as digestion, heartbeat, and breathing.
What enables the Krebs cycle to perform metabolic changes to fats, carbohydrates, and proteins is energy, which can be defined as the ability or capacity to do work. The breakdown of large molecules into smaller molecules—associated with release of energy—is catabolism. The building up process is termed anabolism. The breakdown of proteins into amino acids is an example of catabolism, while the formation of proteins from amino acids is an anabolic process.
Exergonic reactions are energy-releasing reactions and are generally catabolic. Endergonic reactions require energy and include anabolic reactions and the contraction of muscle. Metabolism is the total of all catabolic, exergonic, anabolic, endergonic reactions.
Adenosine triphosphate (ATP) is the intermediate molecule that drives the exergonic transfer of energy to switch to endergonic anabolic reactions used in muscle contraction. This is what causes muscles to work which can require a breakdown, and also to build in the rest period, which occurs during the strengthening phase associated with muscular contraction. ATP is composed of adenine, a nitrogen containing base, ribose, a five carbon sugar (collectively called adenosine), and three phosphate groups. ATP is a high energy molecule because it stores large amounts of energy in the chemical bonds of the two terminal phosphate groups. The breaking of these chemical bonds in the Krebs Cycle provides the energy needed for muscular contraction. | 1 | Applied and Interdisciplinary Chemistry |
There have also been attempts to distill creosote from peat-tar, although mostly unsuccessful due to the problems with winning and drying peat on an industrial scale. Peat tar by itself has in the past been used as a wood preservative. | 0 | Theoretical and Fundamental Chemistry |
The spectral power distribution (SPD) of a source describes how much flux reaches the sensor over a particular wavelength and area. This effectively expresses the per-wavelength contribution to the radiometric quantity being measured. The SPD of a source is commonly shown as an SPD curve. SPD curves provide a visual representation of the color characteristics of a light source, showing the radiant flux emitted by the source at various wavelengths across the visible spectrum It is also a metric by which we can evaluate a light source's ability to render colors, that is, whether a certain color stimulus can be properly rendered under a given illuminant. | 0 | Theoretical and Fundamental Chemistry |
FTLE ridges have proven to be a simple and efficient tool for the visualize hyperbolic LCSs in a number of physical problems, yielding intriguing images of initial positions of hyperbolic LCSs in different applications (see, e.g., Figs. 5a-b). However, FTLE ridges obtained over sliding time windows do not form material surfaces. Thus, ridges of under varying cannot be used to define Lagrangian objects, such as hyperbolic LCSs. Indeed, a locally strongest repelling material surface over will generally not play the same role over and hence its evolving position at time will not be a ridge for . Nonetheless, evolving second-derivative FTLE ridges computed over sliding intervals of the form have been identified by some authors broadly with LCSs. In support of this identification, it is also often argued that the material flux over such sliding-window FTLE ridges should necessarily be small.
The "FTLE ridge=LCS" identification, however, suffers form the following conceptual and mathematical problems:
* Second-derivative FTLE ridges are necessarily straight lines and hence do not exist in physical problems.
* FTLE ridges computed over sliding time windows with a varying are generally not Lagrangian and the flux through them is generally not small.
* In particular, a broadly referenced material flux formula for FTLE ridges is incorrect, even for straight FTLE ridges
* FTLE ridges mark hyperbolic LCS positions, but also highlight surfaces of high shear. A convoluted mixture of both types of surfaces often arises in applications (see Fig. 6 for an example).
* There are several other types LCSs (elliptic and parabolic) beyond the hyperbolic LCSs highlighted by FTLE ridges | 1 | Applied and Interdisciplinary Chemistry |
Fluoroform was first obtained by Maurice Meslans in the violent reaction of iodoform with dry silver fluoride in 1894. The reaction was improved by Otto Ruff by substitution of silver fluoride by a mixture of mercury fluoride and calcium fluoride. The exchange reaction works with iodoform and bromoform, and the exchange of the first two halogen atoms by fluorine is vigorous. By changing to a two step process, first forming a bromodifluoromethane in the reaction of antimony trifluoride with bromoform and finishing the reaction with mercury fluoride the first efficient synthesis method was found by Henne. | 1 | Applied and Interdisciplinary Chemistry |
The Beer–Lambert law can be applied to the analysis of a mixture by spectrophotometry, without the need for extensive pre-processing of the sample. An example is the determination of bilirubin in blood plasma samples. The spectrum of pure bilirubin is known, so the molar attenuation coefficient is known. Measurements of decadic attenuation coefficient are made at one wavelength that is nearly unique for bilirubin and at a second wavelength in order to correct for possible interferences. The amount concentration is then given by
For a more complicated example, consider a mixture in solution containing two species at amount concentrations and . The decadic attenuation coefficient at any wavelength is, given by
Therefore, measurements at two wavelengths yields two equations in two unknowns and will suffice to determine the amount concentrations and as long as the molar attenuation coefficients of the two components, and are known at both wavelengths. This two system equation can be solved using Cramer's rule. In practice it is better to use linear least squares to determine the two amount concentrations from measurements made at more than two wavelengths. Mixtures containing more than two components can be analyzed in the same way, using a minimum of wavelengths for a mixture containing components.
The law is used widely in infra-red spectroscopy and near-infrared spectroscopy for analysis of polymer degradation and oxidation (also in biological tissue) as well as to measure the concentration of various compounds in different food samples. The carbonyl group attenuation at about 6 micrometres can be detected quite easily, and degree of oxidation of the polymer calculated. | 0 | Theoretical and Fundamental Chemistry |
Binding of Ca by the EF-hands causes an opening of the N- and C-domains, which exposes hydrophobic target-binding surfaces. These surfaces interact with complementary nonpolar segments on target proteins, typically consisting of groups of bulky hydrophobic amino acids separated by 10–16 polar and/or basic amino acids. The flexible central domain of calmodulin allows the protein to wrap around its target, although alternate modes of binding are known. "Canonical" targets of calmodulin, such as myosin light-chain kinases and CaMKII, bind only to the Ca-bound protein, whereas some proteins, such as NaV channels and IQ-motif proteins, also bind to calmodulin in the absence of Ca. Binding of calmodulin induces conformational rearrangements in the target protein via "mutually induced fit", leading to changes in the target protein's function.
Calcium binding by calmodulin exhibits considerable cooperativity, making calmodulin an unusual example of a monomeric (single-chain) cooperative binding protein. Furthermore, target binding alters the binding affinity of calmodulin toward Ca ions, which allows for complex allosteric interplay between Ca and target binding interactions. This influence of target binding on Ca affinity is believed to allow for Ca activation of proteins that are constitutively bound to calmodulin, such as small-conductance Ca-activated potassium (SK) channels.
Although calmodulin principally operates as a Ca binding protein, it also coordinates other metal ions. For example, in the presence of typical intracellular concentrations of Mg (0.5–1.0 mM) and resting concentrations of Ca (100 nM), calmodulins Ca binding sites are at least partially saturated by Mg. This Mg is displaced by the higher concentrations of Ca generated by signaling events. Similarly, Ca may itself be displaced by other metal ions, such as the trivalent lanthanides, that associate with calmodulins binding pockets even more strongly than Ca. Though such ions distort calmodulins structure and are generally not physiologically relevant due to their scarcity in vivo', they have nonetheless seen wide scientific use as reporters of calmodulin structure and function. | 1 | Applied and Interdisciplinary Chemistry |
Glucuronidation occurs mainly in the liver, although the enzyme responsible for its catalysis, UDP-glucuronyltransferase, has been found in all major body organs (e.g., intestine, kidneys, brain, adrenal gland, spleen, and thymus). | 0 | Theoretical and Fundamental Chemistry |
In a high-temperature, classical paramagnet phase, the magnetic susceptibility is given by the Curie–Weiss law
Fitting experimental data to this equation determines a phenomenological Curie–Weiss temperature, . There is a second temperature, , where magnetic order in the material begins to develop, as evidenced by a non-analytic feature in . The ratio of these is called the frustration parameter
In a classic antiferromagnet, the two temperatures should coincide and give . An ideal quantum spin liquid would not develop magnetic order at any temperature and so would have a diverging frustration parameter . A large value is therefore a good indication of a possible spin liquid phase. Some frustrated materials with different lattice structures and their Curie–Weiss temperature are listed in the table below. All of them are proposed spin liquid candidates. | 0 | Theoretical and Fundamental Chemistry |
Polyunsaturated aldehydes are oxylipins that are formed from lipids (specifically the fatty acid portion of lipids) when diatoms are exposed to environmental stresses. Stresses can include nutrient limitations, grazing by predators, and wounding.
In particular, damage to diatom cells as a result of grazing by zooplankton invokes a chemical defense mechanism that produces PUA’s as secondary metabolites from fatty acids. The production mechanism is as follows:
# Grazing by predators results in diatom cell membrane disruption.
# Enzymes (lipases) are produced in response to the damaged membranes. These enzymes make contact with newly freed phospholipids (from cell membranes) and catalyze the formation of polyunsaturated fatty acids.
# The enzyme lipoxygenase then catalyzes the reaction of fatty acids to polyunsaturated aldehydes, which are then directly exposed to the grazing zooplankton.
Thalassiosira rotula represents the most well-studied diatom species in terms of polyunsaturated aldehyde production. Wichard et al. determined that only 30% of PUA precursor molecules remain in T. rotula within minutes of cell membrane wounding, indicating a fast rate of response by diatoms to zooplankton grazing. | 1 | Applied and Interdisciplinary Chemistry |
For assembly, a purified amphiphilic polypeptoid of specific sequence is dissolved in aqueous solution. These form a monolayer (Langmuir–Blodgett film) on the air-water interface with their hydrophobic side chains oriented in air and hydrophilic side chains in the water. When this mono-layer is shrunk, it buckles into a bilayer with the hydrophobic groups forming the interior core of the peptoid nanosheet. This method has been standardized in the Zuckermann laboratory by repetitively tilting vials of peptoid solution at 85° before returning the vials to the upright position. This repetitive vial “rocking” motion lessens the interfacial area of the air-water interface inside the vial, compressing the peptoid mono-layer by a factor of four and causing the mono-layer to buckle into peptoid nanosheets. Using this method, nanosheets are produced in high yield, and 95% of the peptoid polymer starting material is efficiently converted into peptoid nanosheets after rocking the vials several hundred times. | 0 | Theoretical and Fundamental Chemistry |
Sinker EDM, also called ram EDM, cavity type EDM or volume EDM, consists of an electrode and workpiece submerged in an insulating liquid such as, more typically, oil or, less frequently, other dielectric fluids. The electrode and workpiece are connected to a suitable power supply. The power supply generates an electrical potential between the two parts. As the electrode approaches the workpiece, dielectric breakdown occurs in the fluid, forming a plasma channel, and a small spark jumps.
These sparks usually strike one at a time, because it is very unlikely that different locations in the inter-electrode space have the identical local electrical characteristics which would enable a spark to occur simultaneously in all such locations. These sparks happen in huge numbers at seemingly random locations between the electrode and the workpiece. As the base metal is eroded, and the spark gap subsequently increased, the electrode is lowered automatically by the machine so that the process can continue uninterrupted. Several hundred thousand sparks occur per second, with the actual duty cycle carefully controlled by the setup parameters. These controlling cycles are sometimes known as "on time" and "off time", which are more formally defined in the literature.
The on time setting determines the length or duration of the spark. Hence, a longer on time produces a deeper cavity from each spark, creating a rougher finish on the workpiece. The reverse is true for a shorter on time. Off time is the period of time between sparks. Although not directly affecting the machining of the part, the off time allows the flushing of dielectric fluid through a nozzle to clean out the eroded debris. Insufficient debris removal can cause repeated strikes in the same location which can lead to a short circuit. Modern controllers monitor the characteristics of the arcs and can alter parameters in microseconds to compensate. The typical part geometry is a complex 3D shape, often with small or odd shaped angles. Vertical, orbital, vectorial, directional, helical, conical, rotational, spin, and indexing machining cycles are also used. | 1 | Applied and Interdisciplinary Chemistry |
Bacteria themselves do not have noticeable effect on concrete. However, sulfate-reducing bacteria (SRB) in untreated sewage water tend to produce hydrogen sulfide (HS), which is then oxidized in sulfuric acid (HSO) by atmospheric oxygen (abiotic reaction) and by aerobic bacteria present in biofilm (biotic reaction) on the concrete surface above the water level. The sulfuric acid dissolves the carbonates in the hardened cement paste (HCP), and also calcium hydroxide (portlandite: Ca(OH)) and calcium silicate hydrate (CaO·SiO·nHO), and causes strength loss, as well as producing sulfates which are harmful to concrete.
:HSO + Ca(OH) → CaSO + 2 HO
:HSO + CaO·SiO·n HO → CaSO + HSiO + n HO
In each case the soft expansive and water-soluble corrosion product of gypsum (CaSO) is formed. Gypsum is easily washed away in wastewater causing a loss of concrete aggregate and exposing fresh material to acid attack.
Concrete floors lying on ground that contains pyrite (iron(II) disulfide) are also at risk.
As a preventive measure sewage may be pretreated to increase pH or oxidize or precipitate the sulfides in order to minimize the activity of sulfide-reducing bacteria.
As bacteria often prefer to adhere to the surfaces of solids than to remain into suspension in water (planktonic bacteria), the biofilms formed by sessile (i.e., fixed) bacteria are often the place where they are the most active. Biofilms made of multiple layers (like an onion) of dead and living bacteria protect the living ones from the harsh conditions often prevailing in water outside biofilm. Biofilms developing on the already exposed surface of metallic elements encased in concrete can also contribute to accelerate their corrosion (differential aeration and formation of anodic zones at the surface of the metal). Sulfides produced by the SRB bacteria can also induce stress corrosion cracking in steel and other metals. | 1 | Applied and Interdisciplinary Chemistry |
Medical use of HPLC typically use mass spectrometer (MS) as the detector, so the technique is called LC-MS or LC-MS/MS for tandem MS, where two types of MS are operated sequentially. When the HPLC instrument is connected to more than one detector, it is called a hyphenated LC system. Pharmaceutical applications are the major users of HPLC, LC-MS and LC-MS/MS. This includes drug development and pharmacology, which is the scientific study of the effects of drugs and chemicals on living organisms, personalized medicine, public health and diagnostics. While urine is the most common medium for analyzing drug concentrations, blood serum is the sample collected for most medical analyses with HPLC. One of the most important roles of LC-MS and LC-MS/MS in the clinical lab is the Newborn Screening (NBS) for metabolic disorders and follow-up diagnostics. The infants' samples come in the shape of dried blood spot (DBS), which is simple to prepare and transport, enabling safe and accessible diagnostics, both locally and globally.
Other methods of detection of molecules that are useful for clinical studies have been tested against HPLC, namely immunoassays. In one example of this, competitive protein binding assays (CPBA) and HPLC were compared for sensitivity in detection of vitamin D. Useful for diagnosing vitamin D deficiencies in children, it was found that sensitivity and specificity of this CPBA reached only 40% and 60%, respectively, of the capacity of HPLC. While an expensive tool, the accuracy of HPLC is nearly unparalleled. | 0 | Theoretical and Fundamental Chemistry |
NpPS is a compound related to Lawessons reagent formed by the reaction of 1-bromonaphthalene with PS, this is a 1,3,2,4-dithiadiphosphetane 2,4-disulfide which has a naphth-1,8-diyl group holding the two phosphorus atoms together. The mechanism by which the NpPS forms is not yet elucidated, but it is thought to occur by a process involving free radicals, and naphthalene has been detected as a side product in its synthesis. In general, NpPS has been found to be less reactive than Lawessons reagent, in agreement with the hypothesis that the dithiophosphine ylides are responsible for the majority of the chemical reactions of the 1,3,2,4-dithiadiphosphetane 2,4-disulfides.
NpPS has been found to react with many hydroxyl compounds, such as methanol, ethylene glycol and a catechol to form species with oxygen atoms bonded to the phosphorus atoms.
NpPS when refluxed in methanol reacts to form a heterocycle CHOPS with one O-methyl and one S-methyl bonded to the two phosphorus atoms. | 0 | Theoretical and Fundamental Chemistry |
The optical reflection in (semi-)conductors happens mostly in the surface region of the material. Therefore, the band structure of this region is extra important. Band structure usually covers bulk material. For deviations from this structure, it is conventional to use a band diagram. In a band diagram the x-axis is changed from wavevector k in band structure diagrams to position x in the preferred direction. Usually, this positional direction is normal to the surface plane.
For semiconductors specifically, the band diagram near the surface of the material is important. When an electric field is present close to, or in the material, this will lead to a potential difference within the semiconductor. Dependent on the electric field, the semiconductor will become n- or p-like in the surface region. From now on we will use that the semiconductor has become n-like at the surface. The bands near the surface will bend under the electrostatic potential of the applied electric field. This bending can be interpreted in the same way as the bending of the valence and conduction bands in a p-n-junction, when equilibrium has been reached. The result of this bending leads to a conduction band that comes close to the Fermi level. Therefore, the conduction band will begin to fill with electrons. This change in band structure leads to a change in optical reflection of the semiconductor. | 0 | Theoretical and Fundamental Chemistry |
In the United States of America, microbial food cultures are regulated under the Food, Drug and Cosmetic Act. Section 409 of the 1958 Food Additives Amendment of the Food, Drug and Cosmetic Act, exempts from the definition of food additives substances generally recognized by experts as safe (GRAS) under conditions of their intended use. These substances do not require premarket approval by the US Food and Drug Administration.
Because there are various ways to obtain GRAS status for microbial food cultures, there is no exhaustive list of microbial food cultures having GRAS status in the US. | 1 | Applied and Interdisciplinary Chemistry |
Diisopropyl fluorophosphate (DIFP) is an irreversible inhibitor that blocks the action of serine protease. When it binds to the enzyme a nucleophilic substitution reaction occurs and releases one hydrogen fluoride molecule. The OH group in the active site acts as a nucleophile to attack the phosphorus in DIFP and form a tetrahedral intermediate and release a proton. Then the P-F bond is broken, one electron is transferred to the F atom and it leaves the intermediate as F anion. It combines with a proton in solution to form one HF molecule. A covalent bond formed between the active site and DIFP, so the serine side chain is no longer available to the substrate. | 1 | Applied and Interdisciplinary Chemistry |
In 1856, William Henry Perkin, then age 18, was given a challenge by his professor, August Wilhelm von Hofmann, to synthesize quinine. In one attempt, Perkin oxidized aniline using potassium dichromate, whose toluidine impurities reacted with the aniline and yielded a black solid, suggesting a "failed" organic synthesis. Cleaning the flask with alcohol, Perkin noticed purple portions of the solution.
Suitable as a dye of silk and other textiles, it was patented by Perkin, who the next year opened a dyeworks mass-producing it at Greenford on the banks of the Grand Union Canal in Middlesex. It was originally called aniline purple. In 1859, it was named mauve in England via the French name for the mallow flower, and chemists later called it mauveine. Between 1859 and 1861, mauve became a fashion must have. The weekly journal All the Year Round described women wearing the colour as "all flying countryward, like so many migrating birds of purple paradise". Punch magazine published cartoons poking fun at the huge popularity of the colour “The Mauve Measles are spreading to so serious an extent that it is high time to consider by what means [they] may be checked.”
By 1870, demand succumbed to newer synthetic colors in the synthetic dye industry launched by mauveine.
In the early 20th century, the U.S. National Association of Confectioners permitted mauveine as a food coloring with a variety of equivalent names: rosolan, violet paste, chrome violet, anilin violet, anilin purple, Perkins violet, indisin, phenamin, purpurin and lydin'.
Laborers in the aniline dye industry were later found to be at increased risk of bladder cancer, specifically transitional cell carcinoma, yet by the 1950s, the synthetic dye industry had helped transform medicine, including cancer treatment. | 0 | Theoretical and Fundamental Chemistry |
The principle intracellular signalling protein is Imd, a death domain-containing protein that binds with FADD and Dredd to form a complex. Dredd is activated following ubiquitination by the Iap2 complex (involving Iap2, UEV1a, bend, and eff), which allows Dredd to cleave the 30 residue N-terminus of Imd, allowing it to also be ubiquitinated by Iap2. Following this, the Tak1/TAB2 complex binds to the activated form of Imd and subsequently activates the IKKγ/Ird5 complex through phosphorylation. This IKKγ complex activates Relish by phosphorylation, leading to cleavage of Relish and thereby producing both N-terminal and C-terminal Relish fragments. The N-terminal Relish fragments dimerize leading to their translocation into the nucleus where these dimers bind to Relish-family NF-κB binding sites. Binding of Relish promotes the transcription of effectors such as antimicrobial peptides.
While Relish is integral for transcription of Imd pathway effectors, there is additional cooperation with other pathways such as Toll and JNK. The TAK1/TAB2 complex is key to propagating intracellular signalling of not only the Imd pathway, but also the JNK pathway. As a result, mutants for JNK signalling have severely reduced expression of Imd pathway antimicrobial peptides. | 1 | Applied and Interdisciplinary Chemistry |
Continuous casting is a refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section. Its primarily used to produce a semi-finished products for further processing. Molten metal is poured into an open-ended, water-cooled mold, which allows a skin' of solid metal to form over the still-liquid center, gradually solidifying the metal from the outside in. After solidification, the strand, as it is sometimes called, is continuously withdrawn from the mold. Predetermined lengths of the strand can be cut off by either mechanical shears or traveling oxyacetylene torches and transferred to further forming processes, or to a stockpile. Cast sizes can range from strip (a few millimeters thick by about five meters wide) to billets (90 to 160 mm square) to slabs (1.25 m wide by 230 mm thick). Sometimes, the strand may undergo an initial hot rolling process before being cut.
Continuous casting is used due to the lower costs associated with continuous production of a standard product, and also increased quality of the final product. Metals such as steel, copper, aluminum and lead are continuously cast, with steel being the metal with the greatest tonnages cast using this method. | 1 | Applied and Interdisciplinary Chemistry |
With the advent of more reactive catalysts, equilibrium RCM is observed quite often which may lead to a greater product distribution. The mechanism can be expanded to include the various competing equilibrium reactions as well as indicate where various side-products are formed along the reaction pathway, such as oligomers.
Although the reaction is still under thermodynamic control, an initial kinetic product, which may be dimerization or oligomerization of the starting material, is formed at the onset of the reaction as a result of higher catalyst reactivity. Increased catalyst activity also allows for the olefin products to reenter the catalytic cycle via non-terminal alkene addition onto the catalyst. Due to additional reactivity in strained olefins, an equilibrium distribution of products is observed; however, this equilibrium can be perturbed through a variety of techniques to overturn the product ratios in favor of the desired RCM product.
Since the probability for reactive groups on the same molecule to encounter each other is inversely proportional to the ring size, the necessary intramolecular cycloaddition becomes increasingly difficult as ring size increases. This relationship means that the RCM of large rings is often performed under high dilution (0.05 - 100 mM) (A) to reduce intermolecular reactions; while the RCM of common rings can be performed at greater concentrations, even neat in rare cases. The equilibrium reaction can be driven to the desired thermodynamic products by increasing temperature (B), to decrease viscosity of the reaction mixture and therefore increase thermal motion, as well as increasing or decreasing reaction time (C).
Catalyst choice (D) has also been shown to be critical in controlling product formation. A few of the catalysts commonly used in ring-closing metathesis are shown below. | 0 | Theoretical and Fundamental Chemistry |
Lohr and coworkers (2001) report that in a comprehensive study of pancreatic secretions of individuals without pancreatic carcinoma, p53 mutations could be found in the pancreatic juices of a small percentage of participants. Because mutations of p53 has been extensively found in pancreatic carcinomas, the researchers for this investigation were attempting to determine if the mutation itself can be linked to the development of pancreatic cancer. While Lohr was able to find p53 mutations via TGGE in a few subjects, none subsequently developed pancreatic carcinoma. Thus, the researchers conclude by noting that the p53 mutation may not be the sole indicator of pancreatic carcinoma oncogenesis. | 1 | Applied and Interdisciplinary Chemistry |
Appointed to a teaching position at Birkbeck College, University of London, Ferrier's focus turned from polysaccharides to monosaccharides. New laboratory tools and methods enabled their reactions and mechanisms to be studied like normal organic compounds, rather than a separate field, and he pioneered this approach. In the early 1960s as a NATO Post Doctoral Fellow, he worked in Professor Melvin Calvin’s group at the University of California, Berkeley. They were exciting times. While Ferrier was there, Calvin was awarded the Nobel Prize for Chemistry, and he also met Carolyn Tompkins, the pair marrying in Edinburgh in 1962.
Arriving in New Zealand in 1970 as Victoria University’s first Chair of Organic Chemistry, Ferrier continued to lead work on the monosaccharides, specialising in their use as starting materials for the synthesis of non-carbohydrate compounds of pharmaceutical interest. He had previously clarified the mechanism of the Fischer glycosidation and discovered an allylic rearrangement reaction of glycals, now known as the Ferrier rearrangement – the first of two reactions that bear his name. Many of Ferrier's best discoveries were made by following up unexpected chemical observations, which often led him into uncharted territory. His second ‘name’ reaction, the Ferrier carbocyclization, was the result of this approach.
He served on the Toxic Substances Board in the 1980s and the leadership of the RSNZ report Lead in the Environment that confirmed the toxic effects of lead and began the phase-out of leaded petrol.
After his retirement from Victoria University in 1998, he became an emeritus professor. Ferrier then entered what he referred to as his supposed retirement, working with the carbohydrate chemists at Industrial Research Ltd. Here he continued to foster the next generation of carbohydrate chemists in New Zealand – his grandchildren, instilling his rigorous approach to chemistry with mentoring and assistance with the group's publications. | 0 | Theoretical and Fundamental Chemistry |
Atkinson friction factor is a measure of the resistance to airflow of a duct. It is widely used in the mine ventilation industry but is rarely referred to outside of it.
Atkinson friction factor is represented by the symbol and has the same units as air density (kilograms per cubic metre in SI units, lbfmin^2/ft^4 in Imperial units). It is related to the more widespread Fanning friction factor by
in which is the density of air in the shaft or roadway under consideration and is Fanning friction factor (dimensionless). It is related to the Darcy friction factor by
in which is the Darcy friction factor (dimensionless).
It was introduced by John J Atkinson in an early mathematical treatment of mine ventilation (1862) and has been known under his name ever since. | 1 | Applied and Interdisciplinary Chemistry |
Ion chromatography (or ion-exchange chromatography) is a form of chromatography that separates ions and ionizable polar molecules based on their affinity to the ion exchanger. It works on almost any kind of charged molecule—including small inorganic anions, large proteins, small nucleotides, and amino acids. However, ion chromatography must be done in conditions that are one pH unit away from the isoelectric point of a protein.
The two types of ion chromatography are anion-exchange and cation-exchange. Cation-exchange chromatography is used when the molecule of interest is positively charged. The molecule is positively charged because the pH for chromatography is less than the pI (also known as pH(I)). In this type of chromatography, the stationary phase is negatively charged and positively charged molecules are loaded to be attracted to it. Anion-exchange chromatography is when the stationary phase is positively charged and negatively charged molecules (meaning that pH for chromatography is greater than the pI) are loaded to be attracted to it. It is often used in protein purification, water analysis, and quality control. The water-soluble and charged molecules such as proteins, amino acids, and peptides bind to moieties which are oppositely charged by forming ionic bonds to the insoluble stationary phase. The equilibrated stationary phase consists of an ionizable functional group where the targeted molecules of a mixture to be separated and quantified can bind while passing through the column—a cationic stationary phase is used to separate anions and an anionic stationary phase is used to separate cations. Cation exchange chromatography is used when the desired molecules to separate are cations and anion exchange chromatography is used to separate anions. The bound molecules then can be eluted and collected using an eluant which contains anions and cations by running a higher concentration of ions through the column or by changing the pH of the column.
One of the primary advantages for the use of ion chromatography is that only one interaction is involved the separation, as opposed to other separation techniques; therefore, ion chromatography may have higher matrix tolerance. Another advantage of ion exchange is the predictability of elution patterns (based on the presence of the ionizable group). For example, when cation exchange chromatography is used, certain cations will elute out first and others later. A local charge balance is always maintained. However, there are also disadvantages involved when performing ion-exchange chromatography, such as constant evolution of the technique which leads to the inconsistency from column to column. A major limitation to this purification technique is that it is limited to ionizable group. | 0 | Theoretical and Fundamental Chemistry |
Isoschizomers are pairs of restriction enzymes specific to the same recognition sequence. For example, SphI (CGTAC/G) and BbuI (CGTAC/G) are isoschizomers of each other. The first enzyme discovered which recognizes a given sequence is known as the prototype; all subsequently identified enzymes that recognize that sequence are isoschizomers. Isoschizomers are isolated from different strains of bacteria and therefore may require different reaction conditions.
In some cases, only one out of a pair of isoschizomers can recognize both the methylated as well as unmethylated forms of restriction sites. In contrast, the other restriction enzyme can recognize only the unmethylated form of the restriction site.
This property of some isoschizomers allows identification of methylation state of the restriction site while isolating it from a bacterial strain.
For example, the restriction enzymes HpaII and MspI are isoschizomers, as they both recognize the sequence 5-CCGG-3 when it is unmethylated. But when the second C of the sequence is methylated, only MspI can recognize it while HpaII cannot.
An enzyme that recognizes the same sequence but cuts it differently is a neoschizomer. Neoschizomers are a specific type (subset) of isoschizomer. For example, SmaI (CCC/GGG) and XmaI (C/CCGGG) are neoschizomers of each other. Similarly KpnI (GGTAC/C) and Acc65I (G/GTACC) are neoschizomers of each other.
An enzyme that recognizes a slightly different sequence, but produces the same ends is an isocaudomer. | 1 | Applied and Interdisciplinary Chemistry |
Carbon-14 goes through radioactive beta decay:
: → + + + 156.5 keV
By emitting an electron and an electron antineutrino, one of the neutrons in the carbon-14 atom decays to a proton and the carbon-14 (half-life of 5,700 ± 30 years) decays into the stable (non-radioactive) isotope nitrogen-14.
As usual with beta decay, almost all the decay energy is carried away by the beta particle and the neutrino. The emitted beta particles have a maximum energy of about 156 keV, while their weighted mean energy is 49 keV. These are relatively low energies; the maximum distance traveled is estimated to be 22 cm in air and 0.27 mm in body tissue. The fraction of the radiation transmitted through the dead skin layer is estimated to be 0.11. Small amounts of carbon-14 are not easily detected by typical Geiger–Müller (G-M) detectors; it is estimated that G-M detectors will not normally detect contamination of less than about 100,000 disintegrations per minute (0.05 µCi). Liquid scintillation counting is the preferred method although more recently, accelerator mass spectrometry has become the method of choice; it counts all the carbon-14 atoms in the sample and not just the few that happen to decay during the measurements; it can therefore be used with much smaller samples (as small as individual plant seeds), and gives results much more quickly. The G-M counting efficiency is estimated to be 3%. The half-distance layer in water is 0.05 mm. | 0 | Theoretical and Fundamental Chemistry |
The reading of data from 3D optical memories has been carried out in many different ways. While some of these rely on the nonlinearity of the light-matter interaction to obtain 3D resolution, others use methods that spatially filter the media's linear response. Reading methods include:
Two photon absorption (resulting in either absorption or fluorescence). This method is essentially two-photon microscopy.
Linear excitation of fluorescence with confocal detection. This method is essentially confocal laser scanning microscopy. It offers excitation with much lower laser powers than does two-photon absorbance, but has some potential problems because the addressing light interacts with many other data points in addition to the one being addressed.
Measurement of small differences in the refractive index between the two data states. This method usually employs a phase-contrast microscope or confocal reflection microscope. No absorption of light is necessary, so there is no risk of damaging data while reading, but the required refractive index mismatch in the disc may limit the thickness (i.e., number of data layers) that the media can reach due to the accumulated random wavefront errors that destroy the focused spot quality.
Second-harmonic generation has been demonstrated as a method to read data written into a poled polymer matrix.
Optical coherence tomography has also been demonstrated as a parallel reading method. | 0 | Theoretical and Fundamental Chemistry |
A disadvantage of AFM compared with the scanning electron microscope (SEM) is the single scan image size. In one pass, the SEM can image an area on the order of square millimeters with a depth of field on the order of millimeters, whereas the AFM can only image a maximum scanning area of about 150×150 micrometers and a maximum height on the order of 10–20 micrometers. One method of improving the scanned area size for AFM is by using parallel probes in a fashion similar to that of millipede data storage.
The scanning speed of an AFM is also a limitation. Traditionally, an AFM cannot scan images as fast as an SEM, requiring several minutes for a typical scan, while an SEM is capable of scanning at near real-time, although at relatively low quality. The relatively slow rate of scanning during AFM imaging often leads to thermal drift in the image making the AFM less suited for measuring accurate distances between topographical features on the image. However, several fast-acting designs were suggested to increase microscope scanning productivity including what is being termed videoAFM (reasonable quality images are being obtained with videoAFM at video rate: faster than the average SEM). To eliminate image distortions induced by thermal drift, several methods have been introduced.
AFM images can also be affected by nonlinearity, hysteresis, and creep of the piezoelectric material and cross-talk between the x, y, z axes that may require software enhancement and filtering. Such filtering could "flatten" out real topographical features. However, newer AFMs utilize real-time correction software (for example, feature-oriented scanning) or closed-loop scanners, which practically eliminate these problems. Some AFMs also use separated orthogonal scanners (as opposed to a single tube), which also serve to eliminate part of the cross-talk problems.
As with any other imaging technique, there is the possibility of image artifacts, which could be induced by an unsuitable tip, a poor operating environment, or even by the sample itself, as depicted on the right. These image artifacts are unavoidable; however, their occurrence and effect on results can be reduced through various methods.
Artifacts resulting from a too-coarse tip can be caused for example by inappropriate handling or de facto collisions with the sample by either scanning too fast or having an unreasonably rough surface, causing actual wearing of the tip.
Due to the nature of AFM probes, they cannot normally measure steep walls or overhangs. Specially made cantilevers and AFMs can be used to modulate the probe sideways as well as up and down (as with dynamic contact and non-contact modes) to measure sidewalls, at the cost of more expensive cantilevers, lower lateral resolution and additional artifacts. | 0 | Theoretical and Fundamental Chemistry |
The procedure involves heating a sample of genomic DNA until it denatures into the single stranded-form, and then slowly cooling it, so the strands can pair back together. While the sample is cooling, measurements are taken of how much of the DNA is base paired at each temperature.
The amount of single and double-stranded DNA is measured by rapidly diluting the sample, which slows reassociation, and then binding the DNA to a hydroxyapatite column. The column is first washed with a low concentration of sodium phosphate buffer, which elutes the single-stranded DNA, and then with high concentrations of phosphate, which elutes the double stranded DNA. The amount of DNA in these two solutions is then measured using a spectrophotometer. | 1 | Applied and Interdisciplinary Chemistry |
Two main subunits of PSI, PsaA and PsaB, are closely related proteins involved in the binding of the vital electron transfer cofactors P, Acc, A, A, and F. PsaA and PsaB are both integral membrane proteins of 730 to 750 amino acids that contain 11 transmembrane segments. A [[4Fe-4S|[4Fe-4S] iron-sulfur cluster]] called F is coordinated by four cysteines; two cysteines are provided each by PsaA and PsaB. The two cysteines in each are proximal and located in a loop between the ninth and tenth transmembrane segments. A leucine zipper motif seems to be present downstream of the cysteines and could contribute to dimerisation of PsaA/PsaB. The terminal electron acceptors F and F, also [4Fe-4S] iron-sulfur clusters, are located in a 9-kDa protein called PsaC that binds to the PsaA/PsaB core near F. | 0 | Theoretical and Fundamental Chemistry |
Phosphaalkenes (IUPAC name: alkylidenephosphanes) are organophosphorus compounds with double bonds between carbon and phosphorus(III) with the formula RC=PR. In the compound phosphorine one carbon atom in benzene is replaced by phosphorus. The reactivity of phosphaalkenes is often compared to that of alkenes and not to that of imines because the HOMO of phosphaalkenes is not the phosphorus lone pair (as in imines the amine lone pair) but the double bond. Therefore like alkenes, phosphaalkenes engage in Wittig reactions, Peterson reactions, Cope rearrangements and Diels-Alder reactions.
The first phosphaalkene discovered was a phosphabenzene, by Mërkl in 1969. The first localized phosphaalkene was reported in 1976 by Gerd Becker as a keto-enol tautomerism akin a Brook rearrangement:
In the same year Harold Kroto established spectroscopically that thermolysis of MePH generates CH=PMe. A general method for the synthesis of phosphaalkenes is by 1,2-elimination of suitable precursors, initiated thermally or by base such as DBU, DABCO or triethylamine:
The Becker method is used in the synthesis of the phosphorus pendant of Poly(p-phenylene vinylene):
The reduction or oxidation of phosphaalynes can produce radical phosphorus ions. | 0 | Theoretical and Fundamental Chemistry |
The expression of genes in the operon is controlled by three differentially regulated promoters, two of which are controlled by RpoS encoded sigma factor σ.
* csiD : is σ-dependent and is activated exclusively upon carbon starvation because cAMP-CRP acts an essential activator for σ containing RNA polymerase at the csiD promoter.
* gabD: is σ -dependent and is induced by multiple stresses.
* gabD: is σ dependent and is controlled by Nac (Nitrogen Assimilation Control) regulatory proteins expressed under nitrogen limitation. | 1 | Applied and Interdisciplinary Chemistry |
The ratio r between the apparent molar volume of a dissolved electrolyte in a concentrated solution and the molar volume of the solvent (water) can be linked to the statistical component of the activity coefficient of the electrolyte and its solvation shell number h:
where ν is the number of ions due to dissociation of the electrolyte, and b is the molality as above. | 0 | Theoretical and Fundamental Chemistry |
On 5 October 2016, Ranga Dias and Isaac F. Silvera of Harvard University released claims of experimental evidence that solid metallic hydrogen had been synthesized in the laboratory at a pressure of around using a diamond anvil cell. This manuscript was available in October 2016, and a revised version was subsequently published in the journal Science in January 2017.
In the preprint version of the paper, Dias and Silvera write:
Silvera stated that they did not repeat their experiment, since more tests could damage or destroy their existing sample, but assured the scientific community that more tests are coming. He also stated that the pressure would eventually be released, in order to find out whether the sample was metastable (i.e., whether it would persist in its metallic state even after the pressure was released).
Shortly after the claim was published in Science, Nature news division published an article stating that some other physicists regarded the result with skepticism. Prominent members of the high pressure research community criticized the claimed results, questioning the claimed pressures or the presence of metallic hydrogen at the pressures claimed.
In February 2017, it was reported that the sample of claimed metallic hydrogen was lost, after the diamond anvils it was contained between broke.
In August 2017, Silvera and Dias issued an erratum to the Science article, regarding corrected reflectance values due to variations between the optical density of stressed natural diamonds and the synthetic diamonds used in their pre-compression diamond anvil cell.
In June 2019 a team at the Commissariat à l'énergie atomique et aux énergies alternatives (French Alternative Energies & Atomic Energy Commission) claimed to have created metallic hydrogen at around 425GPa using a toroidal profile diamond anvil cell produced using electron beam machining.
W. Ferreira et al. (including Dias and Silvera) released a preprint in September 2022 claiming to have repeated the experiment, finding metallisation of hydrogen between 477 and 491 GPa. This time, the pressure was released to assess the question of metastability. They reported that metallic hydrogen was not found to be metastable to zero pressure, and that transformation to the molecular phase likely occurred between 113 and 84 GPa. The authors plan to study the metallisation and metastability of deuterium in the future. | 0 | Theoretical and Fundamental Chemistry |
TCF7L2 is downstream of the WNT/β-catenin pathways. The activation of the WNT/β-catenin pathways have been associated demyelination in multiple sclerosis. TCF7L2 is unregulated during early remyelination, leading scientists to believe that it is involved in remyelination. TCF7L2 could act in dependence or independent of the WNT/β-catenin pathways. | 1 | Applied and Interdisciplinary Chemistry |
The term "eutrophication" comes from the Greek eutrophos, meaning "well-nourished". Water bodies with very low nutrient levels are termed oligotrophic and those with moderate nutrient levels are termed mesotrophic. Advanced eutrophication may also be referred to as dystrophic and hypertrophic conditions. Thus, eutrophication has been defined as "degradation of water quality owing to enrichment by nutrients which results in excessive plant (principally algae) growth and decay."
Eutrophication was recognized as a water pollution problem in European and North American lakes and reservoirs in the mid-20th century. Breakthrough research carried out at the Experimental Lakes Area (ELA) in Ontario, Canada, in the 1970s provided the evidence that freshwater bodies are phosphorus-limited. ELA uses the whole ecosystem approach and long-term, whole-lake investigations of freshwater focusing on cultural eutrophication. | 1 | Applied and Interdisciplinary Chemistry |
Galanin-like peptide (GALP) is a neuropeptide present in humans and other mammals. It is a 60-amino acid polypeptide produced in the arcuate nucleus of the hypothalamus and the posterior pituitary gland. It is involved in the regulation of appetite and may also have other roles such as in inflammation, sex behavior, and stress.
Findings additionally suggest that GALP could play a function in energy metabolism due to its ability to maintain continual activation of the sympathetic nervous system (SNS) via thermogenesis, which refers to the production of heat within living organisms. In addition, the administration of GALP directly into the brain leads to a reduction in the secretion of thyroid-stimulating hormone (TSH), which indicates the involvement of GALP in the neuroendocrine regulation of the hypothalamic-pituitary-thyroid (HPT) axis, and further adding to the evidence of the role of GALP in energy homeostasis. | 1 | Applied and Interdisciplinary Chemistry |
The mass-independent distribution of isotopes in stratospheric ozone can be transferred to carbon dioxide (CO). This anomalous isotopic composition in CO can be used to quantify gross primary production, the uptake of CO by vegetation through photosynthesis. This effect of terrestrial vegetation on the isotopic signature of atmospheric CO was simulated with a global model and confirmed experimentally. | 0 | Theoretical and Fundamental Chemistry |
The removal of phosphorus can in principle remediate eutrophication. Of the several phosphate sorbents, alum (aluminium sulfate) is of practical interest.) Many materials have been investigated. The phosphate sorbent is commonly applied in the surface of the water body and it sinks to the bottom of the lake reducing phosphate, such sorbents have been applied worldwide to manage eutrophication and algal bloom (for example under the commercial name Phoslock). In a large scale study, 114 lakes were monitored for the effectiveness of alum at phosphorus reduction. Across all lakes, alum effectively reduced the phosphorus for 11 years. While there was variety in the longevity (21 years in deep lakes and 5.7 years in shallow lakes), the results express the effectiveness of alum at controlling phosphorus within lakes. Alum treatment is less effective in deep lakes, as well as lakes with substantial external phosphorus loading.
Finnish phosphorus removal measures started in the mid-1970s and have targeted rivers and lakes polluted by industrial and municipal discharges. These efforts have had a 90% removal efficiency. Still, some targeted point sources did not show a decrease in runoff despite reduction efforts. | 1 | Applied and Interdisciplinary Chemistry |
As with other members of the penicillin family, the chemical structure of oxacillin features a 6-aminopenicillanic acid nucleus with a substituent attached to the amino group. The 6-aminopenicillanic acid nucleus consists of a thiazolidine ring attached to a β-lactam ring, which is the active moiety responsible for the antibacterial activity of the penicillin family. The substituent present on oxacillin is thought to impart resistance to degradation via bacterial β-lactamases. | 0 | Theoretical and Fundamental Chemistry |
Most homoleptic complexes of NCS feature isothiocyanate ligands (N-bonded). All first-row metals bind thiocyanate in this way. Octahedral complexes [M(NCS)] include M = Ti(III), Cr(III), Mn(II), Fe(III), Ni(II), Mo(III), Tc(IV), and Ru(III). Four-coordinated tetrakis(isothiocyanate) complexes would be tetrahedral since isothiocyanate is a weak-field ligand. Two examples are the deep blue [Co(NCS)] and the green [Ni(NCS)].
Few homoleptic complexes of NCS feature thiocyanate ligands (S-bonded). Octahedral complexes include [M(SCN)] (M = Rh and Ir) and [Pt(SCN)]. Square planar complexes include [M(SCN)] (M = Pd(II), Pt(II), and Au(III)). Colorless [Hg(SCN)] is tetrahedral.
Some octahedral isothiocyanate complexes undergo redox reactions reversibly. Orange [Os(NCS)] can be oxidized to violet [Os(NCS)]. The Os-N distances in both derivatives are almost identical at 200 picometers. | 0 | Theoretical and Fundamental Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.