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Attenuators may be classified according to the type of molecule which induces the change in RNA structure. It is likely that transcription-attenuation mechanisms developed early, perhaps prior to the archaea/bacteria separation and have since evolved to use a number of different sensing molecules (the tryptophan biosynthetic operon has been found to use three different mechanisms in different organisms.) | 1 | Biochemistry |
Following its introduction to Europe from the New World in the late 15th century, natural rubber (polyisoprene) was regarded mostly as a fascinating curiosity. Its most useful application was its ability to erase pencil marks on paper by rubbing, hence its name. One of its most peculiar properties is a slight (but detectable) increase in temperature that occurs when a sample of rubber is stretched. If it is allowed to quickly retract, an equal amount of cooling is observed. This phenomenon caught the attention of the English physicist John Gough. In 1805 he published some qualitative observations on this characteristic as well as how the required stretching force increased with temperature.<br>
By the mid nineteenth century, the theory of thermodynamics was being developed and within this framework, the English mathematician and physicist Lord Kelvin showed that the change in mechanical energy required to stretch a rubber sample should be proportional to the increase in temperature. Later, this would be associated with a change in entropy. The connection to thermodynamics was firmly established in 1859 when the English physicist James Joule published the first careful measurements of the temperature increase that occurred as a rubber sample was stretched. This work confirmed the theoretical predictions of Lord Kelvin.<br>
In 1838 the American inventor Charles Goodyear found that natural rubbers elastic properties could be immensely improved by adding a few percent sulphur. The short sulfur chains produced chemical cross-links between adjacent polyisoprene molecules. Before it is cross-linked, the liquid natural rubber consists of very long polymer molecules, containing thousands of isoprene backbone units, connected head-to-tail (commonly referred to as chains). Every chain follows a random, three dimensional path through the polymer liquid and is in contact with thousands of other nearby chains. When heated to about 150C, reactive cross-linker molecules, such as sulfur or dicumyl peroxide, can decompose and the subsequent chemical reactions produce a chemical bond between adjacent chains. A crosslink can be visualized as the letter X' but with some of its arms pointing out of the plane. The result is a three dimensional molecular network. All of the polyisoprene molecules are connected together at multiple points by these chemical bonds (network nodes) resulting in a single giant molecule and all information about the original long polymers is lost. A rubber band is a single molecule, as is a latex glove! The sections of polyisoprene between two adjacent cross-links are called network chains and can contain up to several hundred isoprene units. In natural rubber, each cross-link produces a network node with four chains emanating from it. It is the network that gives rise to the elastic properties.
Because of the enormous economic and technological importance of rubber, predicting how a molecular network responds to mechanical strains has been of enduring interest to scientists and engineers. To understand the elastic properties of rubber, theoretically, it is necessary to know both the physical mechanisms that occur at the molecular level and how the random-walk nature of the polymer chain defines the network. The physical mechanisms that occur within short sections of the polymer chains produce the elastic forces and the network morphology determines how these forces combine to produce the macroscopic stress that we observe when a rubber sample is deformed, e.g. subjected to tensile strain. | 7 | Physical Chemistry |
Chloromethane has been detected in the low-mass Class 0 protostellar binary, IRAS 16293–2422, using the Atacama Large Millimeter Array (ALMA). It was also detected in the comet 67P/Churyumov–Gerasimenko (67P/C-G) using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument on the Rosetta spacecraft. The detections reveal that chloromethane can be formed in star-forming regions before planets or life is formed. | 2 | Environmental Chemistry |
Because of the electronegative nitrogen in the pyridine ring, pyridine enters less readily into electrophilic aromatic substitution reactions than benzene derivatives. Instead, in terms of its reactivity, pyridine resembles nitrobenzene.
Correspondingly pyridine is more prone to nucleophilic substitution, as evidenced by the ease of metalation by strong organometallic bases. The reactivity of pyridine can be distinguished for three chemical groups. With electrophiles, electrophilic substitution takes place where pyridine expresses aromatic properties. With nucleophiles, pyridine reacts at positions 2 and 4 and thus behaves similar to imines and carbonyls. The reaction with many Lewis acids results in the addition to the nitrogen atom of pyridine, which is similar to the reactivity of tertiary amines. The ability of pyridine and its derivatives to oxidize, forming amine oxides (N-oxides), is also a feature of tertiary amines.
The nitrogen center of pyridine features a basic lone pair of electrons. This lone pair does not overlap with the aromatic π-system ring, consequently pyridine is basic, having chemical properties similar to those of tertiary amines. Protonation gives pyridinium, CHNH.The pK of the conjugate acid (the pyridinium cation) is 5.25. The structures of pyridine and pyridinium are almost identical. The pyridinium cation is isoelectronic with benzene. Pyridinium p-toluenesulfonate (PPTS) is an illustrative pyridinium salt; it is produced by treating pyridine with p-toluenesulfonic acid. In addition to protonation, pyridine undergoes N-centred alkylation, acylation, and N-oxidation. Pyridine and poly(4-vinyl) pyridine have been shown to form conducting molecular wires with remarkable polyenimine structure on UV irradiation, a process which accounts for at least some of the visible light absorption by aged pyridine samples. These wires have been theoretically predicted to be both highly efficient electron donors and acceptors, and yet are resistant to air oxidation. | 0 | Organic Chemistry |
The eggs are retrieved from the patient using a transvaginal technique called transvaginal oocyte retrieval, involving an ultrasound-guided needle piercing the vaginal wall to reach the ovaries. Through this needle follicles can be aspirated, and the follicular fluid is passed to an embryologist to identify ova. It is common to remove between ten and thirty eggs. The retrieval process, which lasts approximately 20 to 40 minutes, is performed under conscious sedation or general anesthesia to ensure patient comfort. Following optimal follicular development, the eggs are meticulously retrieved using transvaginal ultrasound guidance with the aid of a specialised ultrasound probe and a fine needle aspiration technique. The follicular fluid, containing the retrieved eggs, is expeditiously transferred to the embryology laboratory for subsequent processing. | 1 | Biochemistry |
In some scientific areas such as polymer physics, one may consider a chain of points and links between consecutive points. If the points are sequentially numbered and located at positions , , , etc. then bond vectors are defined by =−, =−, and =−, more generally. This is the case for kinematic chains or amino acids in a protein structure. In these cases, one is often interested in the half-planes defined by three consecutive points, and the dihedral angle between two consecutive such half-planes. If , and are three consecutive bond vectors, the intersection of the half-planes is oriented, which allows defining a dihedral angle that belongs to the interval . This dihedral angle is defined by
or, using the function atan2,
This dihedral angle does not depend on the orientation of the chain (order in which the point are considered) — reversing this ordering consists of replacing each vector by its opposite vector, and exchanging the indices 1 and 3. Both operations do not change the cosine, but change the sign of the sine. Thus, together, they do not change the angle.
A simpler formula for the same dihedral angle is the following (the proof is given below)
or equivalently,
This can be deduced from previous formulas by using the vector quadruple product formula, and the fact that a scalar triple product is zero if it contains twice the same vector:
Given the definition of the cross product, this means that is the angle in the clockwise direction of the fourth atom compared to the first atom, while looking down the axis from the second atom to the third. Special cases (one may say the usual cases) are , and , which are called the trans, gauche, and gauche conformations. | 4 | Stereochemistry |
The Evelyn effect is defined as the phenomena in which the product ratios in a chemical reaction change as the reaction proceeds. This phenomenon contradicts the fundamental principle in organic chemistry by reactions always go by the lowest energy pathway. The favored product should remain so throughout a reaction run at constant conditions. However, the ratio of alkenes before the synthesis is complete shows that the favored product to is not the favored product. The basic idea here is that the proportions of the various alkene products changes as a function of time with a change in mechanism. | 7 | Physical Chemistry |
The Zisman plot the graphical method of the Zisman theory or the Zisman method for characterizing the wettability of a solid surface [https://www.kruss-scientific.com/services/education-theory/glossary/method-according-to-zisman/], named for the American chemist and geophysicist, William Albert Zisman (1905–1986). It is a prominent Sessile drop technique used for characterizing liquid-surface interactions based on the contact angle of a single drop of liquid sitting on the solid surface. | 7 | Physical Chemistry |
* Lyophilized bovine plasma gamma globulin
* Coomassie brilliant blue 1
* 0.15 M NaCl
* Spectrophotometer and cuvettes or a mobile smartphone camera (RGBradford method).
* Micropipettes | 3 | Analytical Chemistry |
The company collaborates with the Budker Institute of Nuclear Physics. In 2020, Sibelektroterm completed several complicated orders for the research work of this scientific organization. In addition, in November 2020, the company won a tender for the supply of magnetic cores for the Siberian Ring Photon Source (SKIF), which has been under construction in Koltsovo since August 2021.
According to an article published in Kontinent Sibir Online in 2021, 80% of the customers of Sibelektroterm's products were Kazakhstan plants. | 8 | Metallurgy |
The binding constant is a special case of the equilibrium constant . It is associated with the binding and unbinding reaction of receptor (R) and ligand (L) molecules, which is formalized as:
The reaction is characterized by the on-rate constant and the off-rate constant , which have units of 1/(concentration time) and 1/time, respectively. In equilibrium, the forward binding transition should be balanced by the backward unbinding transition . That is,
where , and represent the concentration of unbound free receptors, the concentration of unbound free ligand and the concentration of receptor-ligand complexes. The binding constant, or the association constant is defined by | 7 | Physical Chemistry |
The process of transcription (by any polymerase) involves three main stages:
*Initiation, requiring the construction of the RNA polymerase complex on the gene's promoter
*Elongation, the synthesis of the RNA transcript
*Termination, the finishing of RNA transcription, and disassembly of the RNA polymerase complex | 1 | Biochemistry |
Vanadium tetrachloride is the inorganic compound with the formula VCl. This reddish-brown liquid serves as a useful reagent for the preparation of other vanadium compounds. | 0 | Organic Chemistry |
Prp24 (precursor RNA processing, gene 24) is a protein part of the pre-messenger RNA splicing process and aids the binding of U6 snRNA to U4 snRNA during the formation of spliceosomes. Found in eukaryotes from yeast to E. coli, fungi, and humans, Prp24 was initially discovered to be an important element of RNA splicing in 1989. Mutations in Prp24 were later discovered in 1991 to suppress mutations in U4 that resulted in cold-sensitive strains of yeast, indicating its involvement in the reformation of the U4/U6 duplex after the catalytic steps of splicing. | 1 | Biochemistry |
Surface roughness can also affect the adhesive strength. Surfaces with roughness on the scale of 1–2 micrometres can yield better wetting because they have a larger surface area. Thus, more intermolecular interactions at closer distances can arise, yielding stronger attractions and larger adhesive strength. Once the roughness becomes larger, on the order of 10 micrometres, the coating can no longer wet effectively, resulting in less contact area and a smaller adhesive strength. | 6 | Supramolecular Chemistry |
Control of the wetting contact angle can often be achieved through the deposition or incorporation of various organic and inorganic molecules onto the surface. This is often achieved through the use of specialty silane chemicals which can form a SAM (self-assembled monolayers) layer. With the proper selection of the organic molecules with varying molecular structures and amounts of hydrocarbon and/or perfluorinated terminations, the contact angle of the surface can tune. The deposition of these specialty silanes can be achieved in the gas phase through the use of a specialized vacuum ovens or liquid-phase process. Molecules that can bind more perfluorinated terminations to the surface can results in lowering the surface energy (high water contact angle). | 7 | Physical Chemistry |
The 3′-untranslated region plays a crucial role in gene expression by influencing the localization, stability, export, and translation efficiency of an mRNA. It contains various sequences that are involved in gene expression, including microRNA response elements (MREs), AU-rich elements (AREs), and the poly(A) tail. In addition, the structural characteristics of the 3′-UTR as well as its use of alternative polyadenylation play a role in gene expression. | 1 | Biochemistry |
The steps for naming molecules using the CIP system are often presented as:
# Identification of stereocenters and double bonds;
# Assignment of priorities to the groups attached to each stereocenter or double-bonded atom; and
# Assignment of R/S and E/Z descriptors. | 4 | Stereochemistry |
Many processes contribute to soil acidification. These include:
* Rainfall: Average rainfall has a pH of 5.6 and is moderately acidic due to dissolved atmospheric carbon dioxide () that combines with water to form carbonic acid (). When this water flows through the soil it results in the leaching of basic cations as bicarbonates; this increases the percentage of and relative to other cations.
* Root respiration and decomposition of organic matter by microorganisms release which increases the carbonic acid () concentration and subsequent leaching.
* Plant growth: Plants take up nutrients in the form of ions (e.g. , , , ), and they often take up more cations than anions. However, plants must maintain a neutral charge in their roots. In order to compensate for the extra positive charge, they will release ions from the root. Some plants also exude organic acids into the soil to acidify the zone around their roots to help solubilize metal nutrients that are insoluble at neutral pH, such as iron (Fe).
* Fertilizer use: Ammonium () fertilizers react in the soil by the process of nitrification to form nitrate (), and in the process release ions.
* Acid rain: The burning of fossil fuels releases oxides of sulfur and nitrogen into the atmosphere. These react with water in the atmosphere to form sulfuric and nitric acid in rain.
* Oxidative weathering: Oxidation of some primary minerals, especially sulfides and those containing , generate acidity. This process is often accelerated by human activity:
** Mine spoil: Severely acidic conditions can form in soils near some mine spoils due to the oxidation of pyrite.
** Acid sulfate soils formed naturally in waterlogged coastal and estuarine environments can become highly acidic when drained or excavated. | 9 | Geochemistry |
Many systems are in place to repair DNA and RNA lesions but it is possible for lesions to escape these measures. This may lead to mutations or large genome abnormalities, which can threaten the cell or organism's ability to live. Several cancers are a result of DNA lesions. Even repair mechanisms to heal the damage may end up causing more damage. Mismatch repair defects, for example, cause instability that predisposes to colorectal and endometrial carcinomas.
DNA lesions in neurons may lead to neurodegenerative disorders such as Alzheimers, Huntingtons, and Parkinsons diseases. These come as a result of neurons generally being associated with high mitochondrial respiration and redox species production, which can damage nuclear DNA. Since these cells often cannot be replaced after being damaged, the damage done to them leads to dire consequences. Other disorders stemming from DNA lesions and their association with neurons include but are not limited to Fragile X syndrome, Friedreichs ataxia, and Spinocerebellar ataxias.
During replication, usually DNA polymerases are unable to go past the lesioned area, however, some cells are equipped with special polymerases which allow for translesion synthesis (TLS). TLS polymerases allow for the replication of DNA past lesions and risk generating mutations at a high frequency. Common mutations that occur after undergoing this process are point mutations and frameshift mutations. Several diseases come as a result of this process including several cancers and Xeroderma pigmentosum.
The effect of oxidatively damaged RNA has resulted in a number of human diseases and is especially associated with chronic degeneration. This type of damage has been observed in many neurodegenerative diseases such as Amyotrophic lateral sclerosis, Alzheimers, Parkinsons, dementia with Lewy bodies, and several prion diseases. It is important to note that this list is rapidly growing and data suggests that RNA oxidation occurs early in the development of these diseases, rather than as an effect of cellular decay. RNA and DNA lesions are both associated with the development of diabetes mellitus type 2. | 1 | Biochemistry |
The relative activity of a species , denoted , is defined as:
where is the (molar) chemical potential of the species under the conditions of interest, is the (molar) chemical potential of that species under some defined set of standard conditions, is the gas constant, is the thermodynamic temperature and is the exponential constant.
Alternatively, this equation can be written as:
In general, the activity depends on any factor that alters the chemical potential. Such factors may include: concentration, temperature, pressure, interactions between chemical species, electric fields, etc. Depending on the circumstances, some of these factors, in particular concentration and interactions, may be more important than others.
The activity depends on the choice of standard state such that changing the standard state will also change the activity. This means that activity is a relative term that describes how "active" a compound is compared to when it is under the standard state conditions. In principle, the choice of standard state is arbitrary; however, it is often chosen out of mathematical or experimental convenience. Alternatively, it is also possible to define an "absolute activity" (i.e., the fugacity in statistical mechanics), , which is written as:
Note that this definition corresponds to setting as standard state the solution of , if the latter exists. | 7 | Physical Chemistry |
R-12 was used in most refrigeration and vehicle air conditioning applications prior to 1994 before being replaced by 1,1,1,2-tetrafluoroethane (R-134a), which has an insignificant ozone depletion potential. Automobile manufacturers started using R-134a instead of R-12 in 1992–1994. When older units leak or require repair involving removal of the refrigerant, retrofitment to a refrigerant other than R-12 (most commonly R-134a which has a global warming potential 3,400 times that of carbon dioxide) is required in some jurisdictions. The United States does not require automobile owners to retrofit their systems; however, taxes on ozone-depleting chemicals coupled with the relative scarcity of the original refrigerants on the open market make retrofitting the only economical option. Retrofitment requires a system flush and a new filter/dryer or accumulator, and may also involve the installation of new seals and/or hoses made of materials compatible with the refrigerant being installed. Mineral oil used with R-12 is not compatible with R-134a. Some oils designed for conversion to R-134a are advertised as compatible with residual R-12 mineral oil. Another replacement for R-12 is the highly flammable, but truly drop-in HC-12a, whose flammability has led to injuries and deaths in a bus fire in 2006. | 2 | Environmental Chemistry |
Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula . One of the haloalkanes, it is a colorless, sweet-smelling, flammable gas. Methyl chloride is a crucial reagent in industrial chemistry, although it is rarely present in consumer products, and was formerly utilized as a refrigerant. Most chloromethane is biogenic. | 2 | Environmental Chemistry |
In 2002, a seminal paper on Brownian motors published in the American Institute of Physics magazine Physics Today, "Brownian motors", by Dean Astumian and Peter Hänggi. There, they proposed the then novel concept of Brownian motors and posited that "thermal motion combined with input energy gives rise to a channeling of chance that can be used to exercise control over microscopic systems". Astumian and Hänggi provide in their paper a copy of Wallace Stevens' 1919 poem, The Place of the Solitaries to elegantly illustrate, from an abstract perspective, the ceaseless nature of noise.
A year after the Astumian-Hänggi paper, David Leighs organic chemistry group reported the first artificial molecular Brownian motors. In 2007 the same team reported a Maxwells Demon-inspired molecular information ratchet.
Another important demonstration of nanoengineering and nanotechnology was the building of a practical artificial Brownian motor by IBM in 2018. Specifically, an energy landscape was created by accurately shaping a nanofluidic slit, and alternate potentials and an oscillating electric field were then used to “rock” nanoparticles to produce directed motion. The experiment successfully made the nanoparticles move along a track in the shape of the outline of the IBM logo, and serves as an important milestone in the practical use of Brownian motors and other elements at the nanoscale.Additionally, various institutions around the world, such as the University of Sydney Nano Institute, headquartered at the Sydney Nanoscience Hub (SNH), and the Swiss Nanoscience Institute (SNI) at the University of Basel, are examples of the research activity emerging in the field of nanoscience. Brownian motors remain a central concept in both the understanding of natural molecular motors and the construction of useful nanoscale machines that involve directed motion. | 7 | Physical Chemistry |
Traian V. Chirilă (born 14 February 1948 in Arad, Romania) is a Romanian-Australian polymer and organic chemist who is the inventor of AlphaCor, an artificial cornea in current clinical use throughout the world.
His past and current research has contributed in several areas of biomaterials, polymer science and bioengineering, especially in the understanding of biomaterials and biocompatibility, in the development of polymers, hydrophilic sponges, artificial cornea, artificial vitreous substitutes and in topics such as interaction of laser radiation with polymers, photoresponsive polymers, supramolecular polymers, sustained release of bioactive agents, tissue engineering and the use of polymers in genetic therapies. | 0 | Organic Chemistry |
The role of TLRs in direct recognition of peptidoglycan is controversial. In some studies, has been reported that peptidoglycan is sensed by TLR2. But this TLR2-inducing activity could be due to cell wall lipoproteins and lipoteichoic acids that commonly co-purify with peptidoglycan. Also variation in peptidoglycan structure in bacteria from species to species may contribute to the differing results on this topic. | 1 | Biochemistry |
Beta-2 transferrin is a carbohydrate-free (desialated) isoform of transferrin, which is almost exclusively found in the cerebrospinal fluid. It is not found in blood, mucus or tears, thus making it a specific marker of cerebrospinal fluid, applied as an assay in cases where cerebrospinal fluid leakage is suspected.
Beta-2 transferrin would also be positive in patients with perilymph fluid leaks, as it is also present in inner ear perilymph. Thus, beta-2 transferrin in otorrhea would be suggestive of either a CSF leak or a perilymph leak. | 1 | Biochemistry |
Entomopathogens are another group of organisms that are influenced by plants. The extent of the influence largely depends on the evolutionary history shared between the two and the pathogens' method of infection and survival duration outside of a host. Different insect host plants contain compounds that cause modulate insect mortality when certain entomopathogens are simultaneously injected. Increases in mortality of up to 50-fold have been recorded. However, certain plants influence entomopathogens in negative ways, reducing their efficacy.
It is primarily the leaf surface of the plant that influences the entomopathogen; plants can release various exudates, phytochemicals, and alleolochemicals through their leaves, some of which have the ability to inactivate certain entomopathogens. In contrast, in other plant species, leaf characteristics can increase the efficacy of entomopathogens. For example, the mortality of pea aphids was higher in the group of aphids that were found on plants with fewer wax exudates than in those on plants with more wax exudates. This reduced waxiness increases the transmission of Pandora neoaphidus conidia from the plant to the aphids.
Feeding-induced volatiles emitted by different plants increase the amount of spores released by certain entomopathogenic fungi, increasing the likelihood of infection of some herbivores but not others. Plants can also influence pathogen efficacy indirectly, and this typically occurs either by increasing the susceptibility of the herbivore hosts or by changing their behavior. This influence can often take the form of altered growth rates, herbivore physiology, or feeding habits. Thus, there are various ways that host plant species can influence entomopathogenic interactions.
In one study, brassicas were found to defend themselves by acting as a vector for entomopathogens. Virus-infected aphids feeding on the plants introduce a virus into the phloem. The virus is passively transported in the phloem and carried throughout the plant. This causes aphids feeding apart from the infected aphids to become infected as well. This finding offers the possibility of injecting crops with compatible entomopathogenic viruses to defend against susceptible insect pests. | 1 | Biochemistry |
In physics and thermodynamics, the Redlich–Kwong equation of state is an empirical, algebraic equation that relates temperature, pressure, and volume of gases. It is generally more accurate than the van der Waals equation and the ideal gas equation at temperatures above the critical temperature. It was formulated by Otto Redlich and Joseph Neng Shun Kwong in 1949. It showed that a two-parameter, cubic equation of state could well reflect reality in many situations, standing alongside the much more complicated Beattie–Bridgeman model and Benedict–Webb–Rubin equation that were used at the time. The Redlich–Kwong equation has undergone many revisions and modifications, in order to improve its accuracy in terms of predicting gas-phase properties of more compounds, as well as in better simulating conditions at lower temperatures, including vapor–liquid equilibria. | 7 | Physical Chemistry |
The potential exposure of humans and animals on the ground to the high power microwave beams is a significant concern with these systems. At the Earth's surface, a suggested SPSP microwave beam would have a maximum intensity at its center, of 23 mW/cm. While this is less than 1/4 the solar irradiation constant, microwaves penetrate much deeper into tissue than sunlight, and at this level would exceed the current United States Occupational Safety and Health Act (OSHA) workplace exposure limits for microwaves at 10 mW/cm At 23 mW/cm, studies show humans experience significant deficits in spatial learning and memory. If the diameter of the proposed SPSP array is increased by 2.5x, the energy density increases to 1 W/cm. At this level, the median lethal dose for mice is 30-60 seconds of microwave exposure. While designing an array with 2.5x larger diameter should be avoided, the dual-use military potential of such a system is readily apparent.
With good array sidelobe design, outside the receiver may be less than the OSHA long-term levels as over 95% of the beam energy will fall on the rectenna. However, any accidental or intentional mis-pointing of the satellite could be deadly to life on Earth within the beam.
Exposure to the beam can be minimized in various ways. On the ground, assuming the beam is pointed correctly, physical access must be controllable (e.g., via fencing). Typical aircraft flying through the beam provide passengers with a protective metal shell (i.e., a Faraday Cage), which will intercept the microwaves. Other aircraft (balloons, ultralight, etc.) can avoid exposure by using controlled airspace, as is currently done for military and other controlled airspace. In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Suggestions have been made to locate rectennas offshore, but this presents serious problems, including corrosion, mechanical stresses, and biological contamination.
A commonly proposed approach to ensuring fail-safe beam targeting is to use a retrodirective phased array antenna/rectenna. A "pilot" microwave beam emitted from the center of the rectenna on the ground establishes a phase front at the transmitting antenna. There, circuits in each of the antennas subarrays compare the pilot beams phase front with an internal clock phase to control the phase of the outgoing signal. This forces the transmitted beam to be centered precisely on the rectenna and to have a high degree of phase uniformity; if the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused. Such a system would not focus its power beam very effectively anywhere that did not have a pilot beam transmitter. The long-term effects of beaming power through the ionosphere in the form of microwaves has yet to be studied. | 7 | Physical Chemistry |
High-energy beta emitters, such as phosphorus-32 and yttrium-90 can also be counted in a scintillation counter without the cocktail, instead using an aqueous solution containing no scintillators. This technique, known as Cherenkov counting, relies on Cherenkov radiation being detected directly by the photomultiplier tubes. Cherenkov counting benefits from the use of plastic vials which scatter the emitted light, increasing the potential for light to reach the photomultiplier tube. | 5 | Photochemistry |
Phosphonic esters are prepared using the Michaelis–Arbuzov reaction. For example, methyl iodide catalyses the conversion of trimethylphosphite to the phosphonate ester dimethyl methylphosphonate:
:P(OMe) → MePO(OMe)
These esters can be hydrolysed to the acid (Me = methyl):
:MePO(OMe) + HO → MePO(OH) + 2 MeOH
In the Michaelis–Becker reaction, a hydrogen phosphonate diester is first deprotonated and the resulting anion is alkylated. | 0 | Organic Chemistry |
The reactivity of a methyl group depends on the adjacent substituents. Methyl groups can be quite unreactive. For example, in organic compounds, the methyl group resists attack by even the strongest acids. | 0 | Organic Chemistry |
Parasitic use of chemical mimicry involves the invasion of the nest of a duped species, which may consist of an individual or a colony. By emitting mimics of the chemicals that create the host's familiar odours the invader is able to conceal themselves efficiently within the nest without alerting the host.
One example of a group of insects that uses this method of chemical mimicry would be cuckoo bees (genus: Nomada). Cuckoo bees will parasitize bees of the families Melittidae and Andrenidae. Cuckoo bee males will produce chemicals that are similar in structure to the volatile lipids secreted by host females and these chemicals are transferred to cuckoo females so that they may camouflage their eggs within the host's nest. This would allow the females to pass off the care of her eggs and larvae onto the host, benefiting the parasite and burdening the host. | 1 | Biochemistry |
Mukaiyama had a scientific career spanning over sixty years, during which he published over 900 papers. After its founding in 1972, Mukaiyama only published in the Japanese journal Chemistry Letters, citing a belief that "the results of ones chemistry should be published in journals of ones country." The combination of the high quality of his work and the over 600 papers that he published in Chemistry Letters played an important role in its spread to other nations.
A total of 145 people earned their doctorates under Mukaiyama, with 54 eventually becoming professors in various institutions. | 0 | Organic Chemistry |
Methylene blue has been described as "the first fully synthetic drug used in medicine." Methylene blue was first prepared in 1876 by German chemist Heinrich Caro.
Its use in the treatment of malaria was pioneered by Paul Guttmann and Paul Ehrlich in 1891. During this period before the first World War, researchers like Ehrlich believed that drugs and dyes worked in the same way, by preferentially staining pathogens and possibly harming them. Changing the cell membrane of pathogens is in fact how various drugs work, so the theory was partially correct although far from complete. Methylene blue continued to be used in the second World War, where it was not well liked by soldiers, who observed, "Even at the loo, we see, we pee, navy blue." Antimalarial use of the drug has recently been revived. It was discovered to be an antidote to carbon monoxide poisoning and cyanide poisoning in 1933 by Matilda Brooks.
The blue urine was used to monitor psychiatric patients compliance with medication regimes. This led to interest - from the 1890s to the present day - in the drugs antidepressant and other psychotropic effects. It became the lead compound in research leading to the discovery of chlorpromazine. | 3 | Analytical Chemistry |
Dorothy Martin Simon (September 18 1919 – March 25 2016) was an American physical chemist known for her work with aerospace combustion and development of polymers. She made important contributions while at NACA regarding heat shield construction and improvement of rocket engine designs. Her work with DuPont resulted in the creation of synthetic polymers Dacron and Orlon. | 7 | Physical Chemistry |
Firefly luciferase is thought to be a homolog of long-chain fatty acyl-CoA synthetase because of its ability to synthesize luciferyl-CoA from CoA and dehydroluciferyl-AMP. Inouye tested this hypothesis in 2010 by expressing the cDNA of Photinus pyralis and Lychocoriolaus lateralis luciferses in E. coli through cold shock gene expression. The resulting enzymes were then exposed to long-chain fatty acids, short-chain fatty acids, amino acids, and imino acids. Unsurprisingly, Inouye found that the luciferases only showed adenylation activity when exposed to long-chain fatty acids.
The gene product of CG6178 in Drosophila was also found to have high amino acid sequence similarity with firefly luciferase. While it did show high adenyltation activity when exposed to long-chain fatty acids, there was no luminescence when exposed to oxygen and LH-AMP– further suggesting that luciferase emerged as a long-chain fatty acyl-CoA homolog due to gene duplication. | 1 | Biochemistry |
The rate for a bimolecular gas-phase reaction, A + B → product, predicted by collision theory is
where:
*k is the rate constant in units of (number of molecules)⋅s⋅m.
* n is the number density of A in the gas in units of m.
* n is the number density of B in the gas in units of m. E.g. for a gas mixture with gas A concentration 0.1 mol⋅L and B concentration 0.2 mol⋅L, the number of density of A is 0.1×6.02×10÷10 = 6.02×10 m, the number of density of B is 0.2×6.02×10÷10 = 1.2×10 m
* Z is the collision frequency in units of m⋅s.
* is the steric factor.
* E is the activation energy of the reaction, in units of J⋅mol.
* T is the temperature in units of K.
* R is the gas constant in units of J molK.
The unit of r(T) can be converted to mol⋅L⋅s, after divided by (1000×N), where N is the Avogadro constant.
For a reaction between A and B, the collision frequency calculated with the hard-sphere model with the unit number of collisions per m per second is:
where:
* n is the number density of A in the gas in units of m.
* n is the number density of B in the gas in units of m. E.g. for a gas mixture with gas A concentration 0.1 mol⋅L and B concentration 0.2 mol⋅L, the number of density of A is 0.1×6.02×10÷10 = 6.02×10 m, the number of density of B is 0.2×6.02×10÷10 = 1.2×10 m.
*σ is the reaction cross section (unit m), the area when two molecules collide with each other, simplified to , where r the radius of A and r the radius of B in unit m.
* k is the Boltzmann constant unit J⋅K.
* T is the absolute temperature (unit K).
* μ is the reduced mass of the reactants A and B, (unit kg).
* N is the Avogadro constant.
* [A] is molar concentration of A in unit mol⋅L.
* [B] is molar concentration of B in unit mol⋅L.
* Z can be converted to mole collision per liter per second dividing by 1000N.
If all the units that are related to dimension are converted to dm, i.e. mol⋅dm for [A] and [B], dm for σ, dm⋅kg⋅s⋅K for the Boltzmann constant, then
unit mol⋅dm⋅s. | 7 | Physical Chemistry |
P42 MAP kinase -p53 - pancreatic polypeptide - parathyroid hormone receptor - partial pressure - passive transport - Pauling scale - PCR - peptide - peptide bond - peptide elongation factor - peptide elongation factor tu - peptide fragment - peptide initiation factor - peptide receptor - peptide termination factor - peripheral membrane protein - pesticide - pH - phage display - pharmaceutical - pharmacist - pharmacology - phenol - phenotype - phenyl group - phenylalanine - Philadelphia chromosome - phospholipid - phospholipid bilayer - phosphopeptide - phosphoprotein - phosphorus - phosphorylation - phosphoserine - phosphothreonine - phosphotyrosine - photobiology - photolysis - photophosphorylation - photoreceptor - photorespiration - photosynthesis - photosystem I - photosystem II - phototransduction - phylogenetics - phylogeny - physical chemistry - physiology - phytohaemagglutinin - pituitary hormone receptor - pituitary hormone-regulating hormone receptor - plant protein - plasma membrane - plasmid - plasmin - plasminogen - platelet glycoprotein GPIb-IX complex - platelet membrane glycoprotein - platelet-derived growth factor - platelet-derived growth factor receptor - polymer - polymerase chain reaction - polymerization - polymyxin - polymyxin B - polyomavirus transforming antigen - polypeptide - polysaccharide - porphyrin - Posttranslational modification - potassium - potassium channel - potential energy - pregnancy proteins - primary nutritional groups - primary structure - primer - prion - progesterone receptor - prokaryote - prolactin - prolactin receptor - proline - promoter - prostaglandin e receptor - prostaglandin receptor - protein - protein biosynthesis - Protein Data Bank - protein design - protein expression - protein folding - protein isoform - protein nuclear magnetic resonance spectroscopy - protein P16 - protein P34cdc2 - protein precursor - protein structure prediction - protein subunit - protein synthesis - protein targeting - protein translocation - protein-tyrosine kinase - protein-tyrosine-phosphatase - proteinoid - proteomics - protirelin - proto-oncogene - proto-oncogene proteins - proto-oncogene protein C-kit - proto-oncogene proteins c-abl - proto-oncogene proteins c-bcl-2 - Proto-oncogene proteins c-fos - proto-oncogene proteins c-jun - proto-oncogene proteins c-mo - proto-oncogene proteins c-myc - proto-oncogene proteins c-raf - proton - proton pump - protozoan proteins - purine - purinergic P1 receptor - purinergic P2 receptor - purinergic receptor - pyridine - pyrimidine - pyruvate - pyruvate oxidation | 1 | Biochemistry |
Achiral components may form a chiral arrangement. In this case, chirality is not an intrinsic property of the components, but rather imposed extrinsically by their relative positions and orientations. This concept is typically applied to experimental arrangements, for example, an achiral (meta)material illuminated by a beam of light, where the illumination direction makes the whole experiment different from its mirror image. Extrinsic planar chirality results from illumination of any periodically structured interface for suitable illumination directions. Starting from normal incidence onto a periodically structured interface, extrinsic planar chirality arises from tilting the interface around any axis that does not coincide with a line of mirror symmetry of the interface. In the presence of losses, extrinsic planar chirality can result in circular conversion dichroism, as described above. | 4 | Stereochemistry |
Togni reagent II is used for trifluoromethylation of organic compounds. For phenolates, the substitution takes place preferably in the ortho position. It is possible to obtain a second substitution by using an excess of Togni reagent II.
Reactions with alcohols yield the corresponding trifluoromethyl ethers.
Trifluoromethylation of alkenes is possible under copper catalysis. | 0 | Organic Chemistry |
Tang was educated at Northeastern University (China), where he received his BSc degree in chemistry in 1995. Then he attended the Institute of Metal Research in China and was awarded a MSc degree in inorganic materials in 1998. In 2001, Tang was awarded a PhD in physical chemistry with research on heterogeneous catalytic conversion of NO to N, supervised by Tao Zhang at Dalian Institute of Chemical Physics (DICP), China | 5 | Photochemistry |
The idea that the electrical activity generated by nervous tissue may influence the activity of surrounding nervous tissue is one that dates back to the late 19th century. Early experiments, like those by Emil du Bois-Reymond, demonstrated that the firing of a primary nerve may induce the firing of an adjacent secondary nerve (termed "secondary excitation"). This effect was not quantitatively explored, however, until experiments by Katz and Schmitt in 1940, when the two explored the electric interaction of two adjacent limb nerves of the crab Carcinus maenas. Their work demonstrated that the progression of the action potential in the active axon caused excitability changes in the inactive axon. These changes were attributed to the local currents that form the action potential. For example, the currents that caused the depolarization (excitation) of the active nerve caused a corresponding hyperpolarization (depression) of the adjacent resting fiber. Similarly, the currents that caused repolarization of the active nerve caused slight depolarization in the resting fiber. Katz and Schmitt also observed that stimulation of both nerves could cause interference effects. Simultaneous action potential firing caused interference and resulted in decreased conduction velocity, while slightly offset stimulation resulted in synchronization of the two impulses.
In 1941 Angélique Arvanitaki explored the same topic and proposed the usage of the term "ephapse" (from the Greek and meaning "to touch") to describe this phenomenon and distinguish it from synaptic transmission. Over time the term ephaptic coupling has come to be used not only in cases of electric interaction between adjacent elements, but also more generally to describe the effects induced by any field changes along the cell membrane. | 1 | Biochemistry |
Funded by the European Commission- Horizon 2020 and European Green Deal
Duration: 4 years (October 2021-September 2025)
Objective: SophiA enables African countries to pursue sustainable pathways of development through a low-carbon, climate resilient and green growth trajectory, leapfrogging fossil fuels and high global warming potential refrigerant technologies. | 7 | Physical Chemistry |
Season cracking is a form of stress-corrosion cracking of brass cartridge cases originally reported from British forces in India. During the monsoon season, military activity was temporarily reduced, and ammunition was stored in stables until the dry weather returned. Many brass cartridges were subsequently found to be cracked, especially where the case was crimped to the bullet. It was not until 1921 that the phenomenon was explained by Moor, Beckinsale and Mallinson: ammonia from horse urine, combined with the residual stress in the cold-drawn metal of the cartridges, was responsible for the cracking.
Season cracking is characterised by deep brittle cracks which penetrate into affected components. If the cracks reach a critical size, the component can suddenly fracture, sometimes with disastrous results. However, if the concentration of ammonia is very high, then attack is much more severe, and attack over all exposed surfaces occurs. The problem was solved by annealing the brass cases after forming so as to relieve the residual stresses. | 8 | Metallurgy |
The majority of miRNAs act in the cytoplasm and mediate mRNA degradation or translational arrest. However, some plant miRNAs have been shown to act directly to promote DNA methylation. miRNAs come from hairpin precursors generated by the RNaseIII enzymes Drosha and Dicer. Both miRNA and siRNA form either the RNA-induced silencing complex (RISC) or the nuclear form of RISC known as RNA-induced transcriptional silencing complex (RITS). The volume of literature on miRNA within the framework of RNAi is extensive. | 1 | Biochemistry |
In 1993, Periana et al. reported a synthesis of methyl bisulfate from methane using a mercury catalyst at 180 °C. Mercuric bisulfate activates methane electrophilically to form a methyl-complex, which then reacts with sulfuric acid to produce methyl bisulfate. The resulting mercury complex Hg(OSO) is re-oxidized by sulfuric acid to regenerate the catalyst and restart the catalytic cycle ().
This method of functionalizing methane preceded the 1998 discovery by the same group of the so-called Catalytica system, the most active cycle to date in terms of turnover rate, yields, and selectivity. Performing the reaction in sulfuric acid at 220 °C means that the catalyst must be able to withstand these harsh conditions. A platinum-bipyrimidine complex serves as the catalyst. The mechanism for this system is similar to the one described above, where methane is first activated electrophilically to form a methyl-platinum intermediate. The Pt(II) complex is then oxidized to Pt(IV) as two sulfuric acid groups are added to the complex. The reductive elimination of methyl bisulfate transforms the Pt(IV) species back to Pt(II) to regenerate the catalyst ().
In a hypothetical combined process, the Catalytica system could be used in a net conversion of methane to methanol. The methyl bisulfate produced in the cycle could be converted to methanol by hydrolysis, and the sulfur dioxide generated could be converted back to sulfuric acid. | 0 | Organic Chemistry |
FADH and FADH are reduced forms of FAD. FADH is produced as a prosthetic group in succinate dehydrogenase, an enzyme involved in the citric acid cycle. In oxidative phosphorylation, two molecules of FADH typically yield 1.5 ATP each, or three ATP combined. | 1 | Biochemistry |
Book chapters are cited in short form above and long form below. All other sources are cited above only.
*Coups, Elliot J. and Phillips, L. Alison (2012). "Prevalence and Correlates of Indoor Tanning", in Carolyn J. Heckman, Sharon L. Manne (eds.), Shedding Light on Indoor Tanning. Dordrecht: Springer Science & Business Media, 5–32.
*Hay, Jennifer and Lipsky, Samara (2012), "International Perspectives on Indoor Tanning", in Heckman and Manne (eds)., 179–193.
*Hunt, Yvonne; Augustson, Erik; Rutten, Lila; Moser, Richard; and Yaroch, Amy (2012). "History and Culture of Tanning in the United States", in Heckman and Manne (eds.), 33–68.
*Lessin, Stuart R; Perlis, Clifford S.; Zook, and Matthew B. Zook (2012). "How Ultraviolet Radiation Tans Skin" in Heckman and Manne (eds.), 87–94.
*Lluria-Prevatt, Maria; Dickinson, Sally E.; and Alberts, David S. (2013). "Skin Cancer Prevention", in David Alberts, Lisa M. Hess (eds.). Fundamentals of Cancer Prevention. Heidelberg and Berlin: Springer Verlag, 321–376. | 5 | Photochemistry |
The Wealden iron industry was located in the Weald of south-eastern England. It was formerly an important industry, producing a large proportion of the bar iron made in England in the 16th century and most British cannon until about 1770. Ironmaking in the Weald used ironstone from various clay beds, and was fuelled by charcoal made from trees in the heavily wooded landscape. The industry in the Weald declined when ironmaking began to be fuelled by coke made from coal, which does not occur accessibly in the area. | 8 | Metallurgy |
Convenient generation of a directing group on the nitrogen of indoles is possible through treatment with an organolithium reagent and carbon dioxide. A similar method can be applied for lateral lithiations of ortho-tolyl anilines.
Oxazoles containing two methyl groups exhibit interesting selectivity patterns. In the absence of a directing substituent, the methyl group closer to the more electronegative oxygen atom is selectively metalated. However, in the presence of a directing substituent, the director fully controls the site of lithiation. | 0 | Organic Chemistry |
The Si-V center is a single-hole (spin-1/2) system with ground and excited electronic states located within the diamond bandgap. The ground and excited electronic states have two orbital states split by spin–orbit coupling. Each of these spin–orbit states is doubly degenerate by spin, and this splitting can be affected by lattice strain. Phonons in the diamond lattice drive transitions between these orbital states, causing rapid equilibration of the orbital population at temperatures above ca. 1 K.
All four transitions between the two ground and two excited orbital states are dipole allowed with a sharp zero-phonon line (ZPL) at 738 nm (1.68 eV) and minimal phononic sideband in a roughly 20 nm window around 766 nm. The Si-V center emits much more of its emission into its ZPL, approximately 70% (Debye–Waller factor of 0.7), than most other optical centers in diamond, such as the nitrogen-vacancy center (Debye–Waller factor ~ 0.04). The Si-V center also has higher excited states that relax quickly to the lowest excited states, allowing off-resonant excitation.
The Si-V center has an inversion symmetry, and no static electric dipole moment (to the first order); it is therefore insensitive to the Stark shift that could result from inhomogeneous electric fields within the diamond lattice. This property, together with the weak electron-phonon coupling, results in a narrow ZPL in the Si-V center, which is mostly limited by its intrinsic lifetime. Bright photoluminescence, narrow optical lines, and ease of finding optically indistinguishable Si-V centers favor them for applications in solid-state quantum optics. | 7 | Physical Chemistry |
Signal pheromones cause short-term changes, such as the neurotransmitter release that activates a response. For instance, GnRH molecule functions as a neurotransmitter in rats to elicit lordosis behavior. | 1 | Biochemistry |
* Bacteria: The code is used in Entomoplasmatales and Mycoplasmatales (Bove et al. 1989). The situation in the Acholeplasmatales is unclear. Based on a study of ribosomal protein genes, it had been concluded that UGA does not code for tryptophan in plant-pathogenic mycoplasma-like organisms (MLO) and the Acholeplasmataceae (Lim and Sears, 1992) and there seems to be only a single tRNA-CCA for tryptophan in Acholeplasma laidlawii (Tanaka et al. 1989). In contrast, in a study of codon usage in Phytoplasmas, it was found that 30 out of 78 open reading frames analysed translated better with this code (UGA for tryptophan) than with the bacterial, archaeal and plant plastid code while the remainder showed no differences between the two codes (Melamed et al. 2003). In addition, the coding reassignment of UGA Stop → Trp can be found in an alpha-proteobacterial symbiont of cicadas: Candidatus Hodgkinia cicadicola (McCutcheon et al. 2009). Mycoplasma pneumoniae also uses the codon UGA to code for tryptophan rather than using it as a stop codon.
* Fungi: Emericella nidulans, Neurospora crassa, Podospora anserina, Acremonium (Fox, 1987), Candida parapsilosis (Guelin et al., 1991), Trichophyton rubrum (de Bievre and Dujon, 1992), Dekkera/Brettanomyces, Eeniella (Hoeben et al., 1993), and probably Ascobolus immersus, Aspergillus amstelodami, Claviceps purpureaand Cochliobolus heterostrophus.
* Protists: the red algae of Gigartinales (Boyen et al. 1994), the protozoa Trypanosoma brucei, Leishmania tarentolae, Paramecium tetraurelia, Tetrahymena pyriformis and probably Plasmodium gallinaceum (Aldritt et al., 1989), and the stramenopile Cafileria marina.
* Metazoa: Coelenterata (Ctenophora and Cnidaria).
* Other: this code is also used for the kinetoplast DNA (maxicircles, minicircles). Kinetoplasts are modified mitochondria (or their parts). | 1 | Biochemistry |
NAPQI becomes toxic when GSH is depleted by an overdose of acetaminophen, Glutathione is an essential antidote to overdose. Glutathione conjugates to NAPQI and helps to detoxify it. In this capacity, it protects cellular protein thiol groups, which would otherwise become covalently modified; when all GSH has been spent, NAPQI begins to react with the cellular proteins, killing the cells in the process. The preferred treatment for an overdose of this painkiller is the administration of N-acetyl--cysteine (either via oral or IV administration)), which is processed by cells to -cysteine and used in the de novo synthesis of GSH. | 1 | Biochemistry |
PCBs are technically attractive because of their inertness, which includes their resistance to combustion. Nonetheless, they can be effectively destroyed by incineration at 1000 °C. When combusted at lower temperatures, they convert in part to more hazardous materials, including dibenzofurans and dibenzodioxins. When conducted properly, the combustion products are water, carbon dioxide, and hydrogen chloride. In some cases, the PCBs are combusted as a solution in kerosene. PCBs have also been destroyed by pyrolysis in the presence of alkali metal carbonates.
Thermal desorption is highly effective at removing PCBs from soil. | 2 | Environmental Chemistry |
Amorphous materials in soil strongly influence bulk density, aggregate stability, plasticity, and water holding capacity of soils. The low bulk density and high void ratios are mostly due to glass shards and other porous minerals not becoming compacted. Andisol soils contain the highest amounts of amorphous materials. | 7 | Physical Chemistry |
Osmolarity is distinct from molarity because it measures osmoles of solute particles rather than moles of solute. The distinction arises because some compounds can dissociate in solution, whereas others cannot.
Ionic compounds, such as salts, can dissociate in solution into their constituent ions, so there is not a one-to-one relationship between the molarity and the osmolarity of a solution. For example, sodium chloride (NaCl) dissociates into Na and Cl ions. Thus, for every 1 mole of NaCl in solution, there are 2 osmoles of solute particles (i.e., a 1 mol/L NaCl solution is a 2 osmol/L NaCl solution). Both sodium and chloride ions affect the osmotic pressure of the solution.
Another example is magnesium chloride (MgCl), which dissociates into Mg and 2Cl ions. For every 1 mole of MgCl in the solution, there are 3 osmoles of solute particles.
Nonionic compounds do not dissociate, and form only 1 osmole of solute per 1 mole of solute. For example, a 1 mol/L solution of glucose is 1 osmol/L.
Multiple compounds may contribute to the osmolarity of a solution. For example, a 3 Osm solution might consist of: 3 moles glucose, or 1.5 moles NaCl, or 1 mole glucose + 1 mole NaCl, or 2 moles glucose + 0.5 mole NaCl, or any other such combination. | 3 | Analytical Chemistry |
The earliest metal manipulation was probably hammering (Craddock 1995, 1999), where copper ore was pounded into thin sheets. The ore (if there were large enough pieces of metal separate from mineral) could be beneficiated (made better) before or after melting, where the prills of metal could be hand-picked from the cooled slag. Melting beneficiated metal also allowed early metallurgists to use moulds and casts to form shapes of molten metal (Craddock 1995). Many of the metallurgical skills developed in the Bronze Age were still in use during Roman times. Melting—the process of using heat to separate slag and metal, smelting—using a reduced oxygen heated environment to separate metal oxides into metal and carbon dioxide, roasting—process of using an oxygen rich environment to isolate sulphur oxide from metal oxide which can then be smelted, casting—pouring liquid metal into a mould to make an object, hammering—using blunt force to make a thin sheet which can be annealed or shaped, and cupellation—separating metal alloys to isolate a specific metal—were all techniques which were well understood (Zwicker 1985, Tylecote 1962, Craddock 1995). However, the Romans provided few new technological advances other than the use of iron and the cupellation and granulation in the separation of gold alloys (Tylecote 1962).
While native gold is common, the ore will sometimes contain small amounts of silver and copper. The Romans utilised a sophisticated system to separate these precious metals. The use of cupellation, a process developed before the rise of Rome, would extract copper from gold and silver, or an alloy called electrum. In order to separate the gold and silver, however, the Romans would granulate the alloy by pouring the liquid, molten metal into cold water, and then smelt the granules with salt, separating the gold from the chemically altered silver chloride (Tylecote 1962). They used a similar method to extract silver from lead.
While Roman production became standardised in many ways, the evidence for distinct unity of furnace types is not strong, alluding to a tendency of the peripheries continuing with their own past furnace technologies. In order to complete some of the more complex metallurgical techniques, there is a bare minimum of necessary components for Roman metallurgy: metallic ore, furnace of unspecified type with a form of oxygen source (assumed by Tylecote to be bellows) and a method of restricting said oxygen (a lid or cover), a source of fuel (charcoal from wood or occasionally peat), moulds and/or hammers and anvils for shaping, the use of crucibles for isolating metals (Zwicker 1985), and likewise cupellation hearths (Tylecote 1962). | 8 | Metallurgy |
Iron is an important biological element. It is used in both the ubiquitous iron-sulfur proteins and in vertebrates it is used in hemoglobin which is essential for blood and oxygen transport. | 1 | Biochemistry |
For purposes of theoretical calculations about a thermodynamic system, one can imagine fictive idealized thermodynamic "processes" that occur so slowly that they do not incur friction within or on the surface of system; they can then be regarded as virtually reversible. These fictive processes proceed along paths on geometrical surfaces that are described exactly by a characteristic equation of the thermodynamic system. Those geometrical surfaces are the loci of possible states of thermodynamic equilibrium for the system. Really possible thermodynamic processes, occurring at practical rates, even when they occur only by work assessed in the surroundings as adiabatic, without heat transfer, always incur friction within the system, and so are always irreversible. The paths of such really possible processes always depart from those geometrical characteristic surfaces. Even when they occur only by work assessed in the surroundings as adiabatic, without heat transfer, such departures always entail entropy production. | 7 | Physical Chemistry |
The Small Molecule Pathway Database (SMPDB) is a comprehensive, high-quality, freely accessible, online database containing more than 600 small molecule (i.e. metabolic) pathways found in humans. SMPDB is designed specifically to support pathway elucidation and pathway discovery in metabolomics, transcriptomics, proteomics and systems biology. It is able to do so, in part, by providing colorful, detailed, fully searchable, hyperlinked diagrams of five types of small molecule pathways: 1) general human metabolic pathways; 2) human metabolic disease pathways; 3) human metabolite signaling pathways; 4) drug-action pathways and 5) drug metabolism pathways. SMPDB pathways may be navigated, viewed and zoomed interactively using a Google Maps-like interface. All SMPDB pathways include information on the relevant organs, subcellular compartments, protein cofactors, protein locations, metabolite locations, chemical structures and protein quaternary structures (Fig. 1). Each small molecule in SMPDB is hyperlinked to detailed descriptions contained in the HMDB or DrugBank and each protein or enzyme complex is hyperlinked to UniProt. Additionally, all SMPDB pathways are accompanied with detailed descriptions and references, providing an overview of the pathway, condition or processes depicted in each diagram. Users can browse the SMPDB (Fig. 2) or search its contents by text searching (Fig. 3), sequence searching, or chemical structure searching. More powerful queries are also possible including searching with lists of gene or protein names, drug names, metabolite names, GenBank IDs, Swiss-Prot IDs, Agilent or Affymetrix microarray IDs. These queries will produce lists of matching pathways and highlight the matching molecules on each of the pathway diagrams. Gene, metabolite and protein concentration data can also be visualized through SMPDB's mapping interface.
SMPDB is part of a suite of metabolomics databases that also includes Human Metabolome Database, DrugBank, and the Toxin and Toxin-Target Database (T3DB). While DrugBank includes information on 7000 drugs and >4200 non-redundant drug targets, enzymes, transporters, and carriers, HMDB houses over 40,000 small molecule metabolites found in the human body. The suite is complemented by T3DB with its over 3100 common toxic substances and over 1300 corresponding toxin targets. | 1 | Biochemistry |
Based on the first high frequency, high precision, in situ atmospheric and archived air measurements, sulfuryl fluoride has an atmospheric lifetime of 30–40 years, much longer than the 5 years earlier estimated.
Sulfuryl fluoride has been reported to be a greenhouse gas which is about 4000–5000 times more efficient in trapping infrared radiation (per kg) than carbon dioxide (per kg). The amount of sulfuryl fluoride released into the atmosphere is about 2000 metric tons per year. The most important loss process of sulfuryl fluoride is dissolution of atmospheric sulfuryl fluoride in the ocean followed by hydrolysis. | 2 | Environmental Chemistry |
Although additional research is required to improve the efficiency of prime editing, the technology offers promising scientific improvements over other gene editing tools. The prime editing technology has the potential to correct the vast majority of pathogenic alleles that cause genetic diseases, as it can repair insertions, deletions, and nucleotide substitutions. | 1 | Biochemistry |
Alkali metal and alkaline earth metal acetylides of the general formula MC≡CM are salt-like Zintl phase compounds, containing ions. Evidence for this ionic character can be seen in the ready hydrolysis of these compounds to form acetylene and metal oxides, there is also some evidence for the solubility of ions in liquid ammonia. The ion has a closed shell ground state of Σ, making it isoelectronic to a neutral molecule N, which may afford it some stability.
Analogous acetylides prepared from other metals, particularly transition metals, show covalent character and are invariably associated with their metal centers. This can be seen in their general stability to water (such as silver acetylide, copper acetylide) and radically different chemical applications.
Acetylides of the general formula RC≡CM (where R = H or alkyl) generally show similar properties to their doubly substituted analogues. In the absence of additional ligands, metal acetylides adopt polymeric structures wherein the acetylide groups are bridging ligands. | 0 | Organic Chemistry |
In the RHEED setup, only atoms at the sample surface contribute to the RHEED pattern. The glancing angle of incident electrons allows them to escape the bulk of the sample and to reach the detector. Atoms at the sample surface diffract (scatter) the incident electrons due to the wavelike properties of electrons.
The diffracted electrons interfere constructively at specific angles according to the crystal structure and spacing of the atoms at the sample surface and the wavelength of the incident electrons. Some of the electron waves created by constructive interference collide with the detector, creating specific diffraction patterns according to the surface features of the sample. Users characterize the crystallography of the sample surface through analysis of the diffraction patterns. Figure 2 shows a RHEED pattern. Video 1 depicts a metrology instrument recording the RHEED intensity oscillations and deposition rate for process control and analysis.
Two types of diffraction contribute to RHEED patterns. Some incident electrons undergo a single, elastic scattering event at the crystal surface, a process termed kinematic scattering. Dynamic scattering occurs when electrons undergo multiple diffraction events in the crystal and lose some of their energy due to interactions with the sample. Users extract non-qualitative data from the kinematically diffracted electrons. These electrons account for the high intensity spots or rings common to RHEED patterns. RHEED users also analyze dynamically scattered electrons with complex techniques and models to gather quantitative information from RHEED patterns. | 3 | Analytical Chemistry |
Lipoexpediency refers to the beneficial effects of lipids in a cell or a tissue, primarily lipid-mediated signal transmission events, that may occur even in the setting of excess fatty acids. The term was coined as an antonym to lipotoxicity. | 1 | Biochemistry |
Annulenes may be aromatic (benzene, [6]annulene and [18]annulene), non-aromatic ([8] and [10]annulene), or anti-aromatic (cyclobutadiene, [4]annulene). Cyclobutadiene is the only annulene with considerable antiaromaticity, since planarity is unavoidable. With [8]annulene, the molecule takes on a tub shape that allows it to avoid conjugation of double bonds. [10]Annulene is of the wrong size to achieve a planar structure: in a planar conformation, ring strain due to either steric hindrance of internal hydrogens (when some double bonds are trans) or bond angle distortion (when the double bonds are all cis) is unavoidable. Thus, it does not exhibit appreciable aromaticity.
When the annulene is large enough, [18]annulene for example, there is enough room internally to accommodate hydrogen atoms without significant distortion of bond angles. [18]Annulene possesses several properties that qualify it as aromatic. However, none of the larger annulenes are as stable as benzene, as their reactivity more closely resembles a conjugated polyene than an aromatic hydrocarbon.
In general, charged annulene species of the form [CH] (n = 0, 1, 2, ..., q = 0, ±1, ±2, 4n + 2 + q ≥ 3) are aromatic, provided a planar conformation can be achieved. For instance, CH, CH, and CH are all known aromatic species. | 7 | Physical Chemistry |
When running simulations on a biological model, any simulation software evaluates a set of rules, starting from a specified set of initial conditions, and usually iterating through a series of time steps until a specified end time. One way to classify simulation algorithms is by looking at the level of analysis at which the rules are applied: they can be population-based, single-particle-based or hybrid. | 1 | Biochemistry |
Geochemical Perspectives Letters is a peer-reviewed open access scholarly journal publishing original research in geochemistry. It is published by the European Association for Geochemistry. | 9 | Geochemistry |
To achieve comparability of VOC measurements, reference standards traceable to SI-units are required. For a number of VOCs gaseous reference standards are available from specialty gas suppliers or national metrology institutes, either in the form of cylinders or dynamic generation methods. However, for many VOCs, such as oxygenated VOCs, monoterpenes, or formaldehyde, no standards are available at the appropriate amount of fraction due to the chemical reactivity or adsorption of these molecules. Currently, several national metrology institutes are working on the lacking standard gas mixtures at trace level concentration, minimising adsorption processes, and improving the zero gas. The final scopes are for the traceability and the long-term stability of the standard gases to be in accordance with the data quality objectives (DQO, maximum uncertainty of 20% in this case) required by the WMO/GAW program. | 0 | Organic Chemistry |
Trans-splicing is a form of splicing that removes introns or outrons, and joins two exons that are not within the same RNA transcript. Trans-splicing can occur between two different endogenous pre-mRNAs or between an endogenous and an exogenous (such as from viruses) or artificial RNAs. | 1 | Biochemistry |
Asphalt made with vegetable oil based binders was patented by Colas SA in France in 2004.
A number of homeowners seeking an environmentally friendly alternative to asphalt for paving have experimented with waste vegetable oil as a binder for driveways and parking areas in single-family applications. The earliest known test occurred in 2002 in Ohio, where the homeowner combined waste vegetable oil with dry aggregate to create a low-cost and less polluting paving material for his 200-foot driveway. After five years, he reports the driveway is performing as well or better than petroleum-based materials.
Shell Oil Company paved two public roads in Norway in 2007 with vegetable-oil-based asphalt. Results of this study are still premature.
[http://www.halik.biz HALIK Asphalts LTD] from Israel has been experimenting with recycled and secondary road building since 2003. The company is using various wastes such as vegetable fats & oils, wax and thermoplastic elastomers to build and repair roads. The results reported are so far satisfying.
On October 6, 2010, a bicycle path in Des Moines, Iowa, was paved with bio-oil based asphalt through a partnership between Iowa State University, the City of Des Moines, and [http://www.avellobioenergy.com/ Avello Bioenergy] Inc. Research is being conducted on the asphalt mixture, derived from plants and trees to replace petroleum-based mixes.
Bioasphalt is a registered trademark of Avello Bioenergy Inc.
Dr. Elham H. Fini, at North Carolina A&T University, has been spearheading research that has successfully produced bio asphalt from swine manure.
Since November 2014 the Dutch Wageningen University & Research centre is running a pilot in the Dutch province of Zeeland with bioasphalt in which the binder of bitumen was substituted by lignin.
In 2015, French researchers published their results about the usage of microalgaes as a source of asphalt binding material. | 7 | Physical Chemistry |
Countertop components fabricated out of granite and other natural stones are sometimes reinforced with metal rods inserted into grooves cut into the underside of the stone, and bonded in place with various resins. This procedure is called "rodding" by countertop fabricators. Most commonly, these rods will be placed near sink cutouts to prevent cracking of the brittle stone countertop during transportation and installation. Data published by the Marble Institute of America shows that this technique results in a 600% increase in the deflection strength of the component.
However, if a metal rod subject to oxidation or other forms of corrosion is used, and moisture from a sink or faucet reaches the rod, oxide jacking can crack the countertop directly above the rod. Mild steel and some grades of aluminium rods are known to cause oxide jacking failures in granite countertops. Skilled stone repair professionals can disassemble the cracked stone, remove the metal rod, and reassemble the stone using various resins tinted to match the colors of the stone. This type of problem can be prevented by using reinforcing rods made of stainless steel or fiberglass in the rodding procedure. | 8 | Metallurgy |
The two oil price shocks had many short- and long-term effects on global politics and the global economy. They led to sustained reductions in demand as a result of substitution to other fuels, especially coal and nuclear, and improvements in energy efficiency, facilitated by government policies. High oil prices also induced investment in oil production by non-OPEC countries, including Prudhoe Bay in Alaska, the North Sea offshore fields of the United Kingdom and Norway, the Cantarell offshore field of Mexico, and oil sands in Canada.
About 90 percent of vehicular fuel needs are met by oil. Petroleum also makes up 40 percent of total energy consumption in the United States, but is responsible for only one percent of electricity generation. Petroleums worth as a portable, dense energy source powering the vast majority of vehicles and as the base of many industrial chemicals makes it one of the worlds most important commodities.
The top three oil-producing countries as of 2018 are the United States, Russia, and Saudi Arabia. In 2018, due in part to developments in hydraulic fracturing and horizontal drilling, the United States became the world's largest producer.
About 80 percent of the worlds readily accessible reserves are located in the Middle East, with 62.5 percent coming from the Arab five: Saudi Arabia, United Arab Emirates, Iraq, Qatar, and Kuwait. A large portion of the worlds total oil exists as unconventional sources, such as bitumen in Athabasca oil sands and extra heavy oil in the Orinoco Belt. While significant volumes of oil are extracted from oil sands, particularly in Canada, logistical and technical hurdles remain, as oil extraction requires large amounts of heat and water, making its net energy content quite low relative to conventional crude oil. Thus, Canada's oil sands are not expected to provide more than a few million barrels per day in the foreseeable future. | 7 | Physical Chemistry |
Substrate unbinding is influenced by various factors. Larger ligands generally stay in the active site longer, as do those with more rotatable bonds (although this may be a side effect of size). When the solvent is excluded from the active site, less flexible proteins result in longer residence times. More hydrogen bonds shielded from the solvent also decrease unbinding. | 1 | Biochemistry |
In the 1970s, ferredoxin was demonstrated to contain FeS clusters and later nitrogenase was shown to contain a distinctive MoFeS active site. The Fe-S clusters mainly serve as redox cofactors, but some have a catalytic function. In the area of bioinorganic chemistry, a variety of Fe-S clusters have also been identified that have CO as ligands.
FeMoco, the active site of most nitrogenases, features a FeMoSC cluster. | 7 | Physical Chemistry |
Depending on the ore and plant size, a furnace can daily output 250 to 800 tons of pre-reduced iron ore. The biggest furnaces, up to 5 meters in diameter and 110 meters long, can process 950 to 1,000 tons of ore daily, excluding fuel. A properly operated plant typically runs for around 300 days per year. The internal refractory typically lasts 7 to 8 months in the most exposed part of the furnace and for 2 years elsewhere. In 1960, a Krupp-Renn furnace using low-grade ore yielded 100 kilotons of iron annually, while a contemporaneous modern blast furnace produced ten times as much cast iron.
Direct reduction processes employing rotary furnaces frequently face a significant challenge due to the localized formation of iron and slag rings, which sinter together and gradually obstruct the furnace. Understanding the mechanism of lining formation is a complex process involving mineralogy, chemical reactions, and ore preparation. The formation of the lining ring, which progressively grows and poisons the furnace, is caused by a few elements in minute quantities. To remedy this, increasing the supply of combustion air or interrupting the furnace charging process are effective solutions. Otherwise, it may be necessary to adjust the grain size of the charged ore or the chemical composition of the mineral blend.
In 1958, Krupp constructed a plant that could generate 420,000 tons per year of pre-reduced iron ore (consisting of six furnaces) which had an estimated value of 90 million Deutsche Mark, or 21.4 million dollars. By contrast, the plant erected in Salzgitter-Watenstedt in 1956–1957, which was well-integrated with an existing steelworks, only cost 33 million Deutsche Mark. At that time, a Krupp-Renn plant presented itself as a feasible substitute to the established blast furnace process, considering its investment and operating costs: initial investment cost per ton produced was nearly half and operating costs were roughly two and a half times greater.
The slag, a glassy silica, can be effortlessly employed as an additive for constructing road surfaces or concrete. However, the method does not produce a recoverable gas similar to blast furnace gas, decreasing its profitability in most cases. Nevertheless, it also solves the issue regarding gas recovery. | 8 | Metallurgy |
In physics, The Werthamer–Helfand–Hohenberg (WHH) theory was proposed in 1966 by N. Richard Werthamer, Eugene Helfand and Pierre Hohenberg to go beyond BCS theory of superconductivity and it provides predictions of upper critical field () in type-II superconductors.
The theory predicts the upper critical field () at 0 K from and the slope of at . | 7 | Physical Chemistry |
GC–MS is the main tool used in sports anti-doping laboratories to test athletes' urine samples for prohibited performance-enhancing drugs, for example anabolic steroids. | 3 | Analytical Chemistry |
A molecule in the gas phase is free to rotate relative to a set of mutually orthogonal axes of fixed orientation in space, centered on the center of mass of the molecule. Free rotation is not possible for molecules in liquid or solid phases due to the presence of intermolecular forces. Rotation about each unique axis is associated with a set of quantized energy levels dependent on the moment of inertia about that axis and a quantum number. Thus, for linear molecules the energy levels are described by a single moment of inertia and a single quantum number, , which defines the magnitude of the rotational angular momentum.
For nonlinear molecules which are symmetric rotors (or symmetric tops - see next section), there are two moments of inertia and the energy also depends on a second rotational quantum number, , which defines the vector component of rotational angular momentum along the principal symmetry axis. Analysis of spectroscopic data with the expressions detailed below results in quantitative determination of the value(s) of the moment(s) of inertia. From these precise values of the molecular structure and dimensions may be obtained.
For a linear molecule, analysis of the rotational spectrum provides values for the rotational constant and the moment of inertia of the molecule, and, knowing the atomic masses, can be used to determine the bond length directly. For diatomic molecules this process is straightforward. For linear molecules with more than two atoms it is necessary to measure the spectra of two or more isotopologues, such as OCS and OCS. This allows a set of simultaneous equations to be set up and solved for the bond lengths). A bond length obtained in this way is slightly different from the equilibrium bond length. This is because there is zero-point energy in the vibrational ground state, to which the rotational states refer, whereas the equilibrium bond length is at the minimum in the potential energy curve. The relation between the rotational constants is given by
where v is a vibrational quantum number and α is a vibration-rotation interaction constant which can be calculated if the B values for two different vibrational states can be found.
For other molecules, if the spectra can be resolved and individual transitions assigned both bond lengths and bond angles can be deduced. When this is not possible, as with most asymmetric tops, all that can be done is to fit the spectra to three moments of inertia calculated from an assumed molecular structure. By varying the molecular structure the fit can be improved, giving a qualitative estimate of the structure. Isotopic substitution is invaluable when using this approach to the determination of molecular structure. | 7 | Physical Chemistry |
Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at approximately . This is an endothermic reaction requiring per mole and high temperatures to drive off the carbon monoxide. This method has not changed since its invention in 1892:
:CaO + 3 C → CaC + CO
The high temperature required for this reaction is not practically achievable by traditional combustion, so the reaction is performed in an electric arc furnace with graphite electrodes. The carbide product produced generally contains around 80% calcium carbide by weight. The carbide is crushed to produce small lumps that can range from a few mm up to 50 mm. The impurities are concentrated in the finer fractions. The CaC content of the product is assayed by measuring the amount of acetylene produced on hydrolysis. As an example, the British and German standards for the content of the coarser fractions are 295 L/kg and 300 L/kg respectively (at 101 kPa pressure and temperature). Impurities present in the carbide include calcium phosphide, which produces phosphine when hydrolysed.
This reaction was an important part of the industrial revolution in chemistry, and was made possible in the United States as a result of massive amounts of inexpensive hydroelectric power produced at Niagara Falls before the turn of the 20th century.
The electric arc furnace method was discovered in 1892 by T. L. Willson, and independently in the same year by H. Moissan. In Jajce, Bosnia and Herzegovina, the Austrian industrialist Josef Kranz and his "Bosnische-Elektrizitäts AG" company, whose successor later became "Elektro-Bosna", opened the largest chemical factory for the production of calcium carbide at the time in Europe in 1899. A hydroelectric power station on the Pliva river with an installed capacity of 8 MW was constructed to supply electricity for the factory, the first power station of its kind in Southeast Europe, and became operational on 24 March 1899. | 8 | Metallurgy |
A multivariate optical element (MOE), is the key part of a multivariate optical computer; an alternative to conventional spectrometry for the chemical analysis of materials.
It is helpful to understand how light is processed in a multivariate optical computer, as compared to how it is processed in a spectrometer. For example, if we are studying the composition of a powder mixture using diffuse reflectance, a suitable light source is directed at the powder mixture and light is collected, usually with a lens, after it has scattered from the powder surface. Light entering a spectrometer first strikes a device (either a grating or interferometer) that separates light of different wavelengths to be measured. A series of independent measurements is used to estimate the full spectrum of the mixture, and the spectrometer renders a measurement of the spectral intensity at many wavelengths. Multivariate statistics can then be applied to the spectrum produced.
In contrast, when using multivariate optical computing, the light entering the instrument strikes an application specific multivariate optical element, which is uniquely tuned to the pattern that needs to be measured using multivariate analysis.
This system can produce the same result that multivariate analysis of a spectrum would produce. Thus, it can generally produce the same accuracy as laboratory grade spectroscopic systems, but with the fast speed inherent with a pure, passive, optical computer. The multivariate optical computer makes use of optical computing to realize the performance of a full spectroscopic system using traditional multivariate analysis. A side benefit is that the throughput and efficiency of the system is higher than conventional spectrometers, which increases the speed of analysis by orders of magnitude.
While each chemical problem presents its own unique challenges and opportunities, the design of a system for a specific analysis is complex and requires the assembly of several pieces of a spectroscopic puzzle. The data necessary for a successful design are spectral characteristics of light sources, detectors and a variety of optics to be used in the final assemblage, dispersion characteristics of the materials used in the wavelength range of interest, and a set of calibrated sample spectra for pattern-recognition-based analysis. With these pieces assembled, suitable application specific multivariate optical computer designs can be generated and the performance accurately modeled and predicted. | 7 | Physical Chemistry |
Bond stretch isomerism is confirmed for complexes subject to spin crossover transitions. In some octahedral complexes of d configuration, the depopulation of e orbitals causes significant contractions of the metal-ligand bond distances. The phenomenon is mainly manifested in the solid forms of the compounds.
Although no example of bond stretch isomerism has been established in solution, two isomers have been crystallized for pentamethylcyclopentadienyl ruthenium dichloride dimer ([Cp*RuCl]). One has an Ru-Ru bond (2.93 Å) and the other has a long intermetallic distance of 3.75 Å. The former isomer is thought to be diamagnetic, and the latter is magnetic. | 4 | Stereochemistry |
One example is the reconstruction of thioredoxin enzymes from up to 4 billion year old organisms. Whereas the chemical activity of these reconstructed enzymes were remarkably similar to modern enzymes, their physical properties showed significantly elevated thermal and acidic stability. These results were interpreted as suggesting that ancient life may have evolved in oceans that were much hotter and more acidic than today. | 1 | Biochemistry |
To start with, the raw material must be obtained. Copper can be found in over 160 different minerals, but mining activities are entailed to obtain them in large quantities if a reasonable amount of copper is wanted. Some of the most commonly exploited minerals are cuprite, malachite, azurite, chalcopyrite, chrysocolla and tennantite; e.g. malachite was extracted in Rudna Glava (Serbia), Cabrierés (France) or Chinflón (Riotinto, Spain). In fact, one of the possible explanations about what Ötzi the Iceman, the ancient mummy found in the Alps who lived around 3300 years BCE, was doing at of altitude is that he could have been prospecting for new ores of minerals.
Secondly, the mineral is separated from the gangue. This is only possible by smelting or beneficiation. To do so, it is necessary to use a furnace that is able to reach at least .
Lastly, a wide range of specific tools and resources have to be available, such as furnaces, moulds, crucibles, mauls, etc.
*Stage A: Although native copper nowadays is frequently displayed in museum showcases of mineral collections, it once occurred copiously during prehistoric times. In Cyprus or Crete, collecting the mineral was once as easy as simply picking it up from the ground. In fact, native copper is no longer as easy to find in that state these days. The treatment of this native mineral was also uncomplicated through cold-hammering. This only permitted the production of a limited range of artifacts like awls, pins, or beads. In larger objects, the metal cracks when it is cold-hammered.
*Stage B: Annealing the metal on an open fire ( is hot enough) reduces its hardness considerably and gives in malleability. This permits the manufacture of slightly more sophisticated objects, like bracelets, but is still a rather limited technique.
*Stage C: In the first two steps, the material used was native copper that does not actually need specialized technology. Probably, due to the situation that native copper was increasingly difficult to find, copper ore is used in this third step. This is a very significant development. In fact, this is truly the beginning of the metallurgy, as the mineral has to be smelted to separate the copper from the gangue, requiring technology. | 8 | Metallurgy |
By means of controlling the identity and reactivity of the endcaps, PPA can withstand harsh chemical conditions with no significant changes in its structure. For instance, while functionalizing PPA with an allyl acetate and tert-butyldimethylsilyl ether functional groups can lead to its rapid depolymerization in the presence of Pd(0) and F respectively, a simple change in the nature of the endcaps will preserve the chain even in the presence of both corrosive agents. On a separate note, while PPA is insoluble in aqueous solvents and alcohols, it is highly soluble in organic solvents such as THF, DCM, and DMSO where it can be dissolved for days without triggering depolymerization. | 7 | Physical Chemistry |
The untranslated region is seen in prokaryotes and eukaryotes, although the length and composition may vary. In prokaryotes, the 5 UTR is typically between 3 and 10 nucleotides long. In eukaryotes, the 5 UTR can be hundreds to thousands of nucleotides long. This is consistent with the higher complexity of the genomes of eukaryotes compared to prokaryotes. The 3 UTR varies in length as well. The poly-A tail is essential for keeping the mRNA from being degraded. Although there is variation in lengths of both the 5 and 3 UTR, it has been seen that the 5 UTR length is more highly conserved in evolution than the 3' UTR length. | 1 | Biochemistry |
In 1831, Erhard Friedrich Leuchs (1800–1837) described the hydrolysis of starch by saliva, due to the presence of an enzyme in saliva, "ptyalin", an amylase. it was named after the Ancient Greek name for saliva: - .
The modern history of enzymes began in 1833, when French chemists Anselme Payen and Jean-François Persoz isolated an amylase complex from germinating barley and named it "diastase". It is from this term that all subsequent enzyme names tend to end in the suffix -ase.
In 1862, Russian biochemist (1838–1923) separated pancreatic amylase from trypsin. | 1 | Biochemistry |
Body composition may be analyzed in various ways. This can be done in terms of the chemical elements present, or by molecular structure e.g., water, protein, fats (or lipids), hydroxylapatite (in bones), carbohydrates (such as glycogen and glucose) and DNA. In terms of tissue type, the body may be analyzed into water, fat, connective tissue, muscle, bone, etc. In terms of cell type, the body contains hundreds of different types of cells, but notably, the largest number of cells contained in a human body (though not the largest mass of cells) are not human cells, but bacteria residing in the normal human gastrointestinal tract. | 1 | Biochemistry |
To view a simple video explaining how Kode Technology works, click the following link: https://www.youtube.com/watch?v=TIbjAl5KYpA | 1 | Biochemistry |
As well as circulating coins, where they are generally restricted to high-denomination coins, bi-metallic coins are often used in commemorative issues, often made of precious metals. For example, the only bi-metallic coin issued by the United States is the $10 Library of Congress commemorative, made of a gold ring around a platinum center. They are used primarily as a way of securing against coin counterfeiting. | 8 | Metallurgy |
Like intravenous immunoglobulin therapy, ZMapp contains a mixture of neutralizing antibodies that confer passive immunity to an individual, enhancing the normal immune response, and is designed to be administered after exposure to the Ebola virus. Such antibodies have been used in the treatment and prevention of various infectious diseases and are intended to attack the virus by interfering with its surface and neutralizing it to prevent further damage. | 1 | Biochemistry |
Compressors pump gas for a wide variety of applications each of which has its own flow resistance which the compressor has to meet to keep the gas flowing. A map shows the pumping characteristics for the complete range of flows and pressure requirements for its application. The map may be produced by driving the compressor with an electric motor with the flow resistance selected artificially using a variable area throttle valve. The compressor may also be mapped if it is part of a gas generator with a valve at the turbine exit. Campbell shows a General Electric J79 compressor mapped in this way. | 7 | Physical Chemistry |
Hydrolysis (breaking) of phosphodiester bonds can be promoted in several ways. Phosphodiesterases are enzymes that catalyze the hydrolysis of the phosphodiester bond. These enzymes are involved in repairing DNA and RNA sequences, nucleotide salvage, and in the conversion of cGMP and cAMP to GMP and AMP, respectively. Hydrolysis of the phosphodiester bond also occurs chemically and spontaneously, without the aid of enzymes. For example, simple ribose (in RNA) has one more hydroxyl group than deoxyribose (in DNA), making the former less stable and more susceptible to alkaline hydrolysis, wherein relatively high pH conditions induce the breaking of the phosphodiester linkage between two ribonucleotides. The relative instability of RNA under hydroxyl attack of its phosphodiester bonds makes it inadequate for the storage of genomic information, but contributes to its usefulness in transcription and translation. | 1 | Biochemistry |
The behavior of the chiral twins depends mainly on the nature of the environment (achiral/chiral) in which they are present. An achiral environment does not differentiate the molecular twins whereas a chiral environment does distinguish the left-handed version from the right-handed version. Human body, a classic bio-environment, is inherently handed as it is filled with chiral discriminators like amino acids, enzymes, carbohydrates, lipids, nucleic acids, etc. Hence when a racemic therapeutic gets exposed to biological system the component enantiomers will be acted upon stereoselectively. For drugs, chiral discrimination can take place either in the pharmacokinetic or pharmacodynamic phase. | 4 | Stereochemistry |
Proton beams can be used for writing (proton beam writing) through either the hardening of a polymer (by proton induced cross-linking), or through the degradation of a proton sensitive material. This may have important effects in the field of nanotechnology. | 7 | Physical Chemistry |
Experiments and calculations generally agree that the methenium ion is planar, with threefold symmetry. The carbon atom is a prototypical (and exact) example of sp hybridization. | 7 | Physical Chemistry |
When a molecule of DNA is double stranded, as DNA usually is, the two strands run in opposite directions. Therefore, one end of the molecule will have the 3 end of strand 1 and the 5 end of strand 2, and vice versa in the other end. However, the fact that the molecule is two stranded allows numerous different variations. | 1 | Biochemistry |
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