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In some cases, the stereochemistry of the starting material can prevent the formation of the Zaytsev product. For example, when menthyl chloride is treated with sodium ethoxide, the Hofmann product is formed exclusively, but in very low yield:
This result is due to the stereochemistry of the starting material. E2 eliminations require anti-periplanar geometry, in which the proton and leaving group lie on opposite sides of the C-C bond, but in the same plane. When menthyl chloride is drawn in the chair conformation, it is easy to explain the unusual product distribution.
Formation of the Zaytsev product requires elimination at the 2-position, but the isopropyl group – not the proton – is anti-periplanar to the chloride leaving group; this makes elimination at the 2-position impossible. In order for the Hofmann product to form, elimination must occur at the 6-position. Because the proton at this position has the correct orientation relative to the leaving group, elimination can and does occur. As a result, this particular reaction produces only the Hofmann product. | 7 | Physical Chemistry |
The Wnt signaling pathways are critical in cell-cell signaling during normal development and embryogenesis and required for maintenance of adult tissue, therefore it is not difficult to understand why disruption in Wnt signaling pathways can promote human degenerative disease and cancer.
The Wnt signaling pathways are complex, involving many different elements, and therefore have many targets for misregulation. Mutations that cause constitutive activation of the Wnt signaling pathway lead to tumor formation and cancer. Aberrant activation of the Wnt pathway can lead to increase cell proliferation. Current research is focused on the action of the Wnt signaling pathway the regulation of stem cell choice to proliferate and self renew. This action of Wnt signaling in the possible control and maintenance of stem cells, may provide a possible treatment in cancers exhibiting aberrant Wnt signaling. | 1 | Biochemistry |
Flocculation is used in biotechnology applications in conjunction with microfiltration to improve the efficiency of biological feeds. The addition of synthetic flocculants to the bioreactor can increase the average particle size making microfiltration more efficient. When flocculants are not added, cakes form and accumulate causing low cell viability. Positively charged flocculants work better than negatively charged ones since the cells are generally negatively charged. | 8 | Metallurgy |
In a bacterium without the proper mutation(s) in rpoB rifampicin binds to a site near the fork in the β subunit and prevents the polymerase from transcribing more than two or three base pairs of any RNA sequence and stopping production of proteins within the cell. Bacteria with mutations in the proper loci along the rpoB gene are resistant to this effect.
Initial studies were done by Jin and Gross to generate rpoB mutations in E. coli that conferred resistance to rifampicin. Three clusters of mutations were identified, cluster I at codons 507-533, cluster II at codons 563-572, and cluster III at codon 687. The majority of these mutations are located within an 81 base pair(bp) region in cluster I dubbed the "Rifampicin Resistance Determining Region (RRDR)". This resistance is typically associated with a mutation wherein a base in the DNA is substituted for another one and the new sequence codes for an amino acid with a large side chain that inhibits the rifampicin molecules from binding to the polymerase.
There are additional mutations which can occur in the β subunit of the polymerase which are located away from the rifampicin binding site that can also result in mild resistance. Potentially indicating that the shape of these areas may affect the formation of the rifampicin binding site.
Nucleic acid probes can detect mutations in rpoB that confer rifampicin resistance. For Mycobacterium tuberculosis, the rifamycin-resistant mutations most commonly encountered involve codons 516, 526, and 531 (numbered, by convention, as in Escherichia coli rpoB). These mutations result in high rifampicin resistance with a relatively low loss of fitness. For Staphylococcus aureus, the rifamycin-resistant mutation most commonly encountered involves codon 526.
In addition to imparting resistance to rifampicin, certain rpoB mutations have been identified in 70% of Vancomycin Intermediate S. aureus (VISA) strains. | 1 | Biochemistry |
The minimum total potential energy principle is a fundamental concept used in physics and engineering. It dictates that at low temperatures a structure or body shall deform or displace to a position that (locally) minimizes the total potential energy, with the lost potential energy being converted into kinetic energy (specifically heat). | 7 | Physical Chemistry |
From 1943 on, Booth started working on the determination of crystal structures using X-ray diffraction data. The computations involved were extremely tedious and there was ample incentive for automating the process and he developed an analogue computer to compute the reciprocal spacings of the diffraction pattern.
In 1947, along with his collaborator and future spouse Kathleen Britten, he spent a few months with von Neumann's team, which was the leading edge in computer research at the time. | 3 | Analytical Chemistry |
Boronic acids are used in organic chemistry in the Suzuki reaction. In this reaction the boron atom exchanges its aryl group with an alkoxy group from palladium. | 0 | Organic Chemistry |
MODOMICS is a comprehensive database that contains information about RNA modifications. MODOMICS provides the following information: the chemical structure of the modified RNAs, the RNA modifying pathways, the location of the modifications in the RNA sequences, the enzymes responsible for the modifications and liquid chromatography/mass spectrometry(LC/MS) data of the modified RNAs. As of November 2017, the database contained 163 different RNA modifications, as well as 340 different enzymes and cofactors involved in the modifications. This database classifies RNA modifying pathways according to their starting point. The LC/MS data has been very useful in determining the specific mass of the modified RNAs, which facilitates the identification of the modification. | 1 | Biochemistry |
The term typically applies in electrochemistry, when electrical energy in the form of an applied voltage is used to modulate the thermodynamic favorability of a chemical reaction. In a battery, an electrochemical potential arising from the movement of ions balances the reaction energy of the electrodes. The maximum voltage that a battery reaction can produce is sometimes called the standard electrochemical potential of that reaction. | 7 | Physical Chemistry |
Histamine N-methyltransferase belongs to methyltransferases, a superfamily of enzymes present in every life form, including archaeans.
These enzymes catalyze methylation, which is a chemical process that involves the addition of a methyl group to a molecule, which can affect its biological function.
To facilitate methylation, methyltransferases transfer a methyl group (-CH) from a cosubstrate (donor) to a substrate molecule (acceptor), leading to the formation of a methylated molecule. Most methyltransferases use S-adenosyl--methionine (SAM-e) as a donor, converting it into S-adenosyl--homocysteine (SAH). In various species, members of the methyltransferase superfamily of enzymes methylate a wide range of molecules, including small molecules, proteins, nucleic acids, and lipids. These enzymes are involved in numerous cellular processes such as signaling, protein repair, chromatin regulation, and gene regulation. More than 230 families of methyltransferases have been described in various species.
This specific protein, histamine N-methyltransferase, is found in vertebrates, including mammals, birds, reptiles, amphibians, and fishes, but not in invertebrates and plants.
The complementary DNA (cDNA) of Hnmt was initially cloned from a rat kidney and has since been cloned from human, mouse, and guinea pig sources. Human HNMT shares 55.37% similarity with that of zebrafish, 86.76% with that of mouse, 90.53% with that of dog, and 99.54% with that of chimpanzee. Moreover, expressed sequence tags from cow, pig, and gorilla, as well as genome survey sequences from pufferfish, also exhibit strong similarity to human HNMT, suggesting that it is a highly conserved protein among vertebrates. To understand the role of histamine N-methyltransferase in brain function, researchers have studied Hnmt-deficient (knockout) mice, that were genetically modified to have the Hnmt gene "knocked out", i.e., deactivated. Scientists discovered that disrupting the gene led to a significant rise in histamine levels in the mouse brain that highlighted the role of the gene in the brains histamine system and suggested that HNMT' genetic variations in humans could be linked to brain disorders. | 1 | Biochemistry |
Phosgene reacts with water to release hydrogen chloride and carbon dioxide:
Analogously, upon contact with ammonia, it converts to urea:
Halide exchange with nitrogen trifluoride and aluminium tribromide gives carbonyl fluoride| and carbonyl bromide|, respectively. | 0 | Organic Chemistry |
The concept of saturation can be described using various naming systems, formulas, and analytical tests. For instance, IUPAC nomenclature is a system of naming conventions used to describe the type and location of unsaturation within organic compounds. The "degree of unsaturation" is a formula used to summarize and diagram the amount of hydrogen that a compound can bind. Unsaturation can be determined by NMR, mass spectrometry, and IR spectroscopy, or by determining a compound's bromine number or iodine number. | 0 | Organic Chemistry |
The ocean is an extensive network of particle transport. Thorium isotopes can help researchers decipher the vertical and horizontal movement of matter. Th has a constant, well-defined production rate in the ocean and a half-life of 24 days. This naturally occurring isotope has been shown to vary linearly with depth. Therefore, any changes in this linear pattern can be attributed to the transport of Th on particles. For example, low isotopic ratios in surface water with very high values a few meters down would indicate a vertical flux in the downward direction. Furthermore, the thorium isotope may be traced within a specific depth to decipher the lateral transport of particles. | 7 | Physical Chemistry |
Tryptophan tryptophylquinone (TTQ) is an enzyme cofactor, generated by posttranslational modification of amino acids within the protein. Methylamine dehydrogenase (MADH), an amine dehydrogenase, requires TTQ for its catalytic function. | 1 | Biochemistry |
A way to experimentally determine wetting is to look at the contact angle (), which is the angle connecting the solid–liquid interface and the liquid–gas interface (as in the figure).
: If , the liquid completely wets the substrate.
: If , high wetting occurs.
: If , low wetting occurs.
: If , the liquid does not wet the substrate at all.
The Young equation relates the contact angle to interfacial energy:
where is the interfacial energy between the solid and gas phases, the interfacial energy between the substrate and the liquid, is the interfacial energy between the liquid and gas phases, and is the contact angle between the solid–liquid and the liquid–gas interface. | 7 | Physical Chemistry |
Venton joined the Department of Chemistry at University of Virginia as an assistant professor in 2005, received tenure and was promoted to an associate professor in 2011, and was promoted to full professor in 2016. Venton develops analytical tools such as carbon-fiber microelectrodes for sensing molecules in the brain to achieve real-time monitoring of neurotransmitters to help understand the brain functions both under normal physiological conditions and in neurological disorders. | 3 | Analytical Chemistry |
Recrystallization is defined as the process in which grains of a crystal structure come in a new structure or new crystal shape.
A precise definition of recrystallization is difficult to state as the process is strongly related to several other processes, most notably recovery and grain growth. In some cases it is difficult to precisely define the point at which one process begins and another ends. Doherty et al. defined recrystallization as:
Thus the process can be differentiated from recovery (where high angle grain boundaries do not migrate) and grain growth (where the driving force is only due to the reduction in boundary area).
Recrystallization may occur during or after deformation (during cooling or subsequent heat treatment, for example). The former is termed dynamic while the latter is termed static. In addition, recrystallization may occur in a discontinuous manner, where distinct new grains form and grow, or a continuous manner, where the microstructure gradually evolves into a recrystallized microstructure. The different mechanisms by which recrystallization and recovery occur are complex and in many cases remain controversial. The following description is primarily applicable to static discontinuous recrystallization, which is the most classical variety and probably the most understood. Additional mechanisms include (geometric) dynamic recrystallization and strain induced boundary migration.
Secondary recrystallization occurs when a certain very small number of {110}<001> (Goss) grains grow selectively, about one in 106 primary grains, at the expense of many other primary recrystallized grains. This results in abnormal grain growth, which may be beneficial or detrimental for product material properties. The mechanism of secondary recrystallization is a small and uniform primary grain size, achieved through the inhibition of normal grain growth by fine precipitates called inhibitors. Goss grains are named in honor of Norman P. Goss, the inventor of grain-oriented electrical steel circa 1934. | 8 | Metallurgy |
Where the helix is unwound, the coding strand consists of unpaired bases, while the template strand consists of an RNA:DNA composite, followed by a number of unpaired bases at the rear. This hybrid consists of the most recently added nucleotides of the RNA transcript, complementary base-paired to the template strand. The number of base-pairs in the hybrid is under investigation, but it has been suggested that the hybrid is formed from the last 10 nucleotides added. | 1 | Biochemistry |
In 2019, the discovery of potent, and selective antagonists of the Luteinizing Hormone Receptor (BAY-298 and BAY-899) were reported which were able to reduce sex hormone levels in vivo. The latter fulfils the quality criteria for a Donated Chemical Probe as defined by the Structural Genomics Consortium.
A series of thienopyr(im)idine-based compounds leading to optimized Org 43553 were described as the first Luteinizing Hormone Receptor agonists. | 1 | Biochemistry |
Optical reflectivity and the Brillouin zones are closely linked, since the band gap energy in the Brillouin zone determines if a photon is absorbed or reflected. If the band gap energy in the Brillouin zone is smaller than the photon energy, the photon will be absorbed, while the photon will be transmitted/reflected if the band gap energy is larger than the photon energy. For example, the photon energies of visible light lie in a range between 1.8 eV (red light) and 3.1 eV (violet light), So if the band gap energy is larger than 3.2 eV, photons of visible light will not be absorbed, but reflected/transmitted: the material appears transparent. This is the case for diamond, quartz etc. But if the band gap is roughly 2.6 eV (this is the case for cadmium sulfide) only blue and violet light is absorbed, while red and green light are transmitted, resulting in a reddish looking material.
When an electric field is added to a (semi)conductor, the material will try to cancel this field by inducing an electric field at its surface. Because of this electric field, the optical properties of the surface layer will change, due to the change in size of critical band gaps, and hence changing its energy. Since the change in band gap only occurs on the surface of the (semi)conductor, optical properties will not change in the core of bulk materials, but for very thin films, where almost all particles can be found at the surface, the optical properties can change: absorption or transmittance of certain wavelengths depending on the strength of the electric field. This can result in more accurate measurements in case there are multiple compounds in the semiconductor, practically canceling the background noise of data.
Commonly, the band gaps are smallest close to, or at the Brillouin zone boundary. Adding an electric field will alter the whole band structure of the material where the electric field penetrates, but the effect will be especially noticeable at the Brillouin zone boundary. When the smallest band gap changes in size, this alters the optical reflectivity of the material more than the change in an already larger band gap. This can be explained by noticing that the smallest band gap determines a lot of the reflectivity, as lower energy photons cannot be absorbed and re-emitted. | 7 | Physical Chemistry |
The structure of etheniums ground state was in dispute for many years, but it was eventually agreed to be a non-classical structure, with the two carbon atoms and one of the hydrogen atoms forming a three-center two-electron bond. Calculations have shown that higher homologues, like the propyl and n-'butyl cations also have bridged structures. Generally speaking, bridging appears to be a common means by which 1° alkyl carbocations achieve additional stabilization. Consequently, true 1° carbocations (with a classical structure) may be rare or nonexistent. | 7 | Physical Chemistry |
Cobalt carbonyl and rhodium complexes catalyse the hydroformylation of formaldehyde and ethylene oxide to give hydroxyacetaldehyde and 3-hydroxypropanal, which can then be hydrogenated to ethylene glycol and propane-1,3-diol, respectively. The reactions work best when the solvent is basic (such as pyridine).
In the case of dicobalt octacarbonyl or Co(CO) as a catalyst, pentan-3-one can arise from ethene and CO, in the absence of hydrogen. A proposed intermediate is the ethylene-propionyl species [CHC(O)Co(CO)(ethene)] which undergoes a migratory insertion to form [CHCOCHCHCo(CO)]. The required hydrogen arises from the water shift reaction. For details, see
If the water shift reaction is not operative, the reaction affords a polymer containing alternating carbon monoxide and ethylene units. Such aliphatic polyketones are more conventionally prepared using palladium catalysts.
Functionalized olefins such as allyl alcohol can be hydroformylated. The target product 1,4-butanediol and its isomer is obtained with isomerization free catalysts such as rhodium-triphenylphosphine complexes. The use of the cobalt complex leads by isomerization of the double bond to n-propanal. The hydroformylation of alkenyl ethers and alkenyl esters occurs usually in the α-position to the ether or ester function.
The hydroformylation of acrylic acid and methacrylic acid in the rhodium-catalyzed process leads to the Markovnikov product in the first step. By variation of the reaction conditions the reaction can be directed to different products. A high reaction temperature and low carbon monoxide pressure favors the isomerization of the Markovnikov product to the thermodynamically more stable β-isomer, which leads to the n-aldehyde. Low temperatures and high carbon monoxide pressure and an excess of phosphine, which blocks free coordination sites, can lead to faster hydroformylation in the α-position to the ester group and suppress the isomerization. | 0 | Organic Chemistry |
PAVA is approved for police and prison service use in the United Kingdom. British police forces had traditionally used CS gas spray, but with the more widespread carriage of tasers, PAVA has now entirely replaced its predecessor due to its non-flammable nature.
Both PAVA and CS are prohibited under Section 5 of the Firearms Act 1968 as a "weapon of whatever description designed or adapted for the discharge of any noxious liquid, gas or other thing", meaning that it is unlawful for a member of the public to possess them. Police officers, prison officers and other servants of the Crown have lawful exemption to possess and use PAVA. They are therefore exempt from prosecution under this act and section. | 1 | Biochemistry |
Recently, chloroplasts have caught attention by developers of genetically modified crops. Since, in most flowering plants, chloroplasts are not inherited from the male parent, transgenes in these plastids cannot be disseminated by pollen. This makes plastid transformation a valuable tool for the creation and cultivation of genetically modified plants that are biologically contained, thus posing significantly lower environmental risks. This biological containment strategy is therefore suitable for establishing the coexistence of conventional and organic agriculture. While the reliability of this mechanism has not yet been studied for all relevant crop species, recent results in tobacco plants are promising, showing a failed containment rate of transplastomic plants at 3 in 1,000,000. | 5 | Photochemistry |
In 2002 he received the State Prize of the Russian Federation in the field of science and technology. In 2011 he was awarded the Prize of the Government of the Russian Federation in the field of science and technology. He also received the Orders of the Red Banner of Labour (1986), Honour (1999) and Friendship (2009).
The Royal Society of Chemistry awarded Moiseev the Centenary Prize for 2006/7. In 2012, he was awarded the Demidov Prize for his contribution to the chemistry of organoelement compounds, petrochemistry, and carbene chemistry, and the RAS Chugaev Prize for his work on coordination compounds in industrially important redox reactions. In 2013 he received the RAS Mendeleev Medal for outstanding work in the field of catalysis and energy-saving technologies.
He became a corresponding member of the Academy of Sciences of the Soviet Union in 1990, and an academician of the Russian Academy of Sciences in 1992. He was a full member of the Academy of Sciences, Arts and Literature in Paris, the European Academy of Sciences and Arts, and the Academia Europaea. | 7 | Physical Chemistry |
Many maritime accidents have been caused by corrosion, and this has led to stringent regulations concerning protective coatings for ballast tanks. The Coating Performance Standard for Ballast Tank Coatings (PSPC), became effective in 2008. It specifies how protective coatings should be applied during vessel construction with the intention of giving a coating a 15-year service life. Additional regulations, such as those established by The International Convention for the Control and Management of Ships Ballast Water & Sediments (SBWS) sought to avoid introducing invasive species throughout the world through ship's ballast tanks. The methods used to avoid having these invasive species surviving in ballast tanks however greatly increased the rate of corrosion. Therefore ongoing research attempts to find water treatment systems that kill invasive species, while not having a destructive effect on the ballast tank coatings. As double-hulled tankers were introduced it meant that there was more ballast tank area had to be coated and therefore a greater capital investment for ship owners. With the onset of the OPA 90 and later the amendments to MARPOL annex 1, single hull tankers (without alternative method) have basically phased out.
Modern double hull tankers, with their fully "segregated ballast tanks" propose another problem. Empty tanks act as insulation from the cold sea and allow the warm cargo areas to retain their heat longer. Corrosion rates increase with differences in temperature. Consequently, the cargo side of the ballast tank corrodes more quickly than it did with single hull tankers. | 8 | Metallurgy |
The first attempts at developing an odor-based form of crowd control began in Israel in 2004 by Rafael. The IDF reconsidered at the time a change in its open fire procedures, and adopting other crowd dispersal methods after an Israeli demonstrator, Gil Na'amati (21), was shot during a protest over the separation barrier, near the West Bank village of Mas-ha in late 2003. It reportedly does not wash off easily and may linger on clothes for up to five years. The development of Skunk followed numerous accusations against Israeli forces that they often employ disproportionate force in clashes with Palestinian protestors (e.g. using rubber bullets or tear gas), which has led them to seek new, non-lethal but effective methods of crowd control.
Skunk was first reported to be used for crowd control in August 2008 in the Palestinian village of Nilin where daily protests had been taking place in response to the construction of a security barrier. Spraying the liquid has developed into one of the preferred measures adopted by the IDF to meet the challenge of civil disobedience and demonstrations by Palestinians. The tactic was devised to tamp down organized civilian protests in the West Bank. It has been used regularly against the villagers of Bilin, Ni'lin, Kafr Qaddum, and Nabi Salih, where weekly protests against the occupation are practiced.
In Hebron it was used on the 26 February 2012 to disperse a crowd of an estimated 1,000 people which clashed with Israeli soldiers during a protest described as commemorating the anniversary of the Cave of the Patriarchs Massacre or as pressing for the reopening of the zone of Shuhada Street. A funeral procession waiting for the riots to be dispersed were also doused with the liquid. It has been used during clashes with "Palestinian protesters calling for the release of Palestinian hunger striker Mohammad Allan near Barzilai Medical Center" in the Israeli city of Ashkelon.
In 2017, Israeli forces began using Skunk against ultra-Orthodox Jewish protesters.
In January 2024, students at a pro-Palestine demonstration at Columbia University were allegedly attacked with Skunk by individuals disguised as fellow protesters. One victim, who claimed that Palestinian friends recognized the odor as Skunk, described it as having the smell of "poop mixed with decaying animal." Victims of the attack reported difficulty removing the odor from their clothes and other possessions, and that the effects of the spray including its odor, skin irritation, nausea, and dizziness continue days after the attack despite efforts to remove it. The incident is currently being investigated by the New York City Police Department as a potential hate crime. | 1 | Biochemistry |
Interstitial hydrides most commonly exist within metals or alloys. They are traditionally termed "compounds" even though they do not strictly conform to the definition of a compound, more closely resembling common alloys such as steel. In such hydrides, hydrogen can exist as either atomic or diatomic entities. Mechanical or thermal processing, such as bending, striking, or annealing, may cause the hydrogen to precipitate out of solution by degassing. Their bonding is generally considered metallic. Such bulk transition metals form interstitial binary hydrides when exposed to hydrogen. These systems are usually non-stoichiometric, with variable amounts of hydrogen atoms in the lattice. In materials engineering, the phenomenon of hydrogen embrittlement results from the formation of interstitial hydrides. Hydrides of this type form according to either one of two main mechanisms. The first mechanism involves the adsorption of dihydrogen, succeeded by the cleaving of the H-H bond, the delocalisation of the hydrogen's electrons, and finally the diffusion of the protons into the metal lattice. The other main mechanism involves the electrolytic reduction of ionised hydrogen on the surface of the metal lattice, also followed by the diffusion of the protons into the lattice. The second mechanism is responsible for the observed temporary volume expansion of certain electrodes used in electrolytic experiments.
Palladium absorbs up to 900 times its own volume of hydrogen at room temperatures, forming palladium hydride. This material has been discussed as a means to carry hydrogen for vehicular fuel cells. Interstitial hydrides show certain promise as a way for safe hydrogen storage. Neutron diffraction studies have shown that hydrogen atoms randomly occupy the octahedral interstices in the metal lattice (in an fcc lattice there is one octahedral hole per metal atom). The limit of absorption at normal pressures is PdH0.7, indicating that approximately 70% of the octahedral holes are occupied.
Many interstitial hydrides have been developed that readily absorb and discharge hydrogen at room temperature and atmospheric pressure. They are usually based on intermetallic compounds and solid-solution alloys. However, their application is still limited, as they are capable of storing only about 2 weight percent of hydrogen, insufficient for automotive applications. | 0 | Organic Chemistry |
In both the FCC and HCP arrangements each sphere has twelve neighbors. For every sphere there is one gap surrounded by six spheres (octahedral) and two smaller gaps surrounded by four spheres (tetrahedral). The distances to the centers of these gaps from the centers of the surrounding spheres is for the tetrahedral, and for the octahedral, when the sphere radius is 1.
Relative to a reference layer with positioning A, two more positionings B and C are possible. Every sequence of A, B, and C without immediate repetition of the same one is possible and gives an equally dense packing for spheres of a given radius.
The most regular ones are
*FCC = ABC ABC ABC... (every third layer is the same)
*HCP = AB AB AB AB... (every other layer is the same).
There is an uncountably infinite number of disordered arrangements of planes (e.g. ABCACBABABAC...) that are sometimes collectively referred to as "Barlow packings", after crystallographer William Barlow.
In close-packing, the center-to-center spacing of spheres in the xy plane is a simple honeycomb-like tessellation with a pitch (distance between sphere centers) of one sphere diameter. The distance between sphere centers, projected on the z (vertical) axis, is:
where d is the diameter of a sphere; this follows from the tetrahedral arrangement of close-packed spheres.
The coordination number of HCP and FCC is 12 and their atomic packing factors (APFs) are equal to the number mentioned above, 0.74. | 3 | Analytical Chemistry |
Molecular cloning refers to the process of making multiple molecules. Cloning is commonly used to amplify DNA fragments containing whole genes, but it can also be used to amplify any DNA sequence such as promoters, non-coding sequences and randomly fragmented DNA. It is used in a wide array of biological experiments and practical applications ranging from genetic fingerprinting to large scale protein production. Occasionally, the term cloning is misleadingly used to refer to the identification of the chromosomal location of a gene associated with a particular phenotype of interest, such as in positional cloning. In practice, localization of the gene to a chromosome or genomic region does not necessarily enable one to isolate or amplify the relevant genomic sequence. To amplify any DNA sequence in a living organism, that sequence must be linked to an origin of replication, which is a sequence of DNA capable of directing the propagation of itself and any linked sequence. However, a number of other features are needed, and a variety of specialised cloning vectors (small piece of DNA into which a foreign DNA fragment can be inserted) exist that allow protein production, affinity tagging, single-stranded RNA or DNA production and a host of other molecular biology tools.
Cloning of any DNA fragment essentially involves four steps
# fragmentation - breaking apart a strand of DNA
# ligation – gluing together pieces of DNA in a desired sequence
# transfection – inserting the newly formed pieces of DNA into cells
# screening/selection – selecting out the cells that were successfully transfected with the new DNA
Although these steps are invariable among cloning procedures a number of alternative routes can be selected; these are summarized as a cloning strategy.
Initially, the DNA of interest needs to be isolated to provide a DNA segment of suitable size. Subsequently, a ligation procedure is used where the amplified fragment is inserted into a vector (piece of DNA). The vector (which is frequently circular) is linearised using restriction enzymes, and incubated with the fragment of interest under appropriate conditions with an enzyme called DNA ligase. Following ligation, the vector with the insert of interest is transfected into cells. A number of alternative techniques are available, such as chemical sensitisation of cells, electroporation, optical injection and biolistics. Finally, the transfected cells are cultured. As the aforementioned procedures are of particularly low efficiency, there is a need to identify the cells that have been successfully transfected with the vector construct containing the desired insertion sequence in the required orientation. Modern cloning vectors include selectable antibiotic resistance markers, which allow only cells in which the vector has been transfected, to grow. Additionally, the cloning vectors may contain colour selection markers, which provide blue/white screening (alpha-factor complementation) on X-gal medium. Nevertheless, these selection steps do not absolutely guarantee that the DNA insert is present in the cells obtained. Further investigation of the resulting colonies must be required to confirm that cloning was successful. This may be accomplished by means of PCR, restriction fragment analysis and/or DNA sequencing. | 1 | Biochemistry |
The near-absence of genetic recombination in mitochondrial DNA makes it a useful source of information for studying population genetics and evolutionary biology. Because all the mitochondrial DNA is inherited as a single unit, or haplotype, the relationships between mitochondrial DNA from different individuals can be represented as a gene tree. Patterns in these gene trees can be used to infer the evolutionary history of populations. The classic example of this is in human evolutionary genetics, where the molecular clock can be used to provide a recent date for mitochondrial Eve. This is often interpreted as strong support for a recent modern human expansion out of Africa. Another human example is the sequencing of mitochondrial DNA from Neanderthal bones. The relatively large evolutionary distance between the mitochondrial DNA sequences of Neanderthals and living humans has been interpreted as evidence for the lack of interbreeding between Neanderthals and modern humans.
However, mitochondrial DNA reflects only the history of the females in a population. This can be partially overcome by the use of paternal genetic sequences, such as the non-recombining region of the Y-chromosome.
Recent measurements of the molecular clock for mitochondrial DNA reported a value of 1 mutation every 7884 years dating back to the most recent common ancestor of humans and apes, which is consistent with estimates of mutation rates of autosomal DNA (10 per base per generation). | 1 | Biochemistry |
The side effects of flutamide are sex-dependent. In men, a variety of side effects related to androgen deprivation may occur, the most common being gynecomastia and breast tenderness. Others include hot flashes, decreased muscle mass, decreased bone mass and an associated increased risk of fractures, depression, and sexual dysfunction including reduced libido and erectile dysfunction. In women, flutamide is, generally, relatively well tolerated, and does not interfere with ovulation. The only common side effect of flutamide in women is dry skin (75%), which can be attributed to a reduction of androgen-mediated sebum production. General side effects that may occur in either sex include dizziness, lack of appetite, gastrointestinal side effects such as nausea, vomiting, and diarrhea, a greenish-bluish discoloration of the urine, and hepatic changes. Because flutamide is a pure antiandrogen, unlike steroidal antiandrogens like cyproterone acetate and megestrol acetate (which additionally possess progestogenic activity), it does not appear to have a risk of cardiovascular side effects (e.g., thromboembolism) or fluid retention. | 4 | Stereochemistry |
Triphosgene (bis(trichloromethyl) carbonate (BTC) is a chemical compound with the formula OC(OCCl). It is used as a solid substitute for phosgene, which is a gas and diphosgene, which is a liquid. Triphosgene is stable up to 200 °C. Triphosgene is used in a variety of halogenation reactions. | 0 | Organic Chemistry |
* ATRX-syndrome (α-thalassemia X-linked mental retardation) and α-thalassemia myelodysplasia syndrome are caused by mutations in ATRX, a SNF2-related ATPase with a PHD finger domain.
* CHARGE syndrome, an autosomal dominant disorder, has been linked recently to haploinsufficiency of CHD7, which encodes the CHD family ATPase CHD7. | 1 | Biochemistry |
Peak copper is the point in time at which the maximum global copper production rate is reached. Since copper is a finite resource, at some point in the future new production from mining will diminish, and at some earlier time production will reach a maximum. When this will occur is a matter of dispute. Unlike fossil fuels, copper is scrapped and reused, and it has been estimated that at least 80% of all copper ever mined is still available (having been repeatedly recycled).
Copper is among the most important industrial metals, ranking third after iron and aluminium in terms of quantity used. It is valued for its heat and electrical conductivities, ductility, malleability and resistance to corrosion. Electrical uses account for about three quarters of total copper consumption, including power cables, data cables and electrical equipment. It is also used in cooling and refrigeration tubing, heat exchangers, water pipes and consumer products.
Copper has been used by humans for at least 10,000 years. More than 97% of all copper ever mined and smelted has been extracted since 1900. The increased demand for copper due to the growing Indian and Chinese economies since 2006 has led to increased prices and an increase in copper theft. | 8 | Metallurgy |
Congo red is an organic compound, the sodium salt of 3,3′-([1,1′-biphenyl]-4,4′-diyl)bis(4-aminonaphthalene-1-sulfonic acid). It is an azo dye. Congo red is water-soluble, yielding a red colloidal solution; its solubility is greater in organic solvents. The use of Congo red in the textile industry has long been abandoned, primarily because of its carcinogenic properties, but it is still used for histological staining. | 3 | Analytical Chemistry |
The pulse-induction method is based on electromagnetic pulse induction technology to detect rebars. Coils in the probe are periodically charged by current pulses and thus generate a magnetic field. On the surface of any electrically conductive material which is in the magnetic field eddy currents are produced. They induce a magnetic field in opposite directions. The resulting change in voltage can be utilized for the measurement. Rebars that are closer to the probe or of larger size produce a stronger magnetic field.
Modern rebar detectors use different coil arrangements to generate several magnetic fields. Advanced signal processing supports not only the localization of rebars but also the determination of the cover and the estimation of the bar diameter. This method is unaffected by all non conductive materials such as concrete, wood, plastics, bricks, etc. However any kind of conductive materials within the magnetic field will have an influence on the measurement.
Advantages of the pulse induction method:
* high accuracy
* not influenced by moisture and heterogeneities of the concrete
* unaffected by environmental influences
* low costs
Disadvantage of the pulse induction method:
* Limited detection range
* Minimum bar spacing depends on cover depths | 8 | Metallurgy |
Interpretation of carbon isotope effects are usually complicated by simultaneously forming and breaking bonds to carbon. Even reactions that involve only bond cleavage from the carbon, such as S1 reactions, involve strengthening of the remaining bonds to carbon. In many such reactions, leaving group isotope effects tend to be easier to interpret. For example, substitution and elimination reactions in which chlorine act as a leaving group are convenient to interpret, especially since chlorine acts as a monatomic species with no internal bonding to complicate the reaction coordinate, and it has two stable isotopes, Cl and Cl, both with high abundance. The major challenge to the interpretation of such isotope affects is the solvation of the leaving group.
Owing to experimental uncertainties, measurement of isotope effect may entail significant uncertainty. Often isotope effects are determined through complementary studies on a series of isotopomers. Accordingly, it is quite useful to combine hydrogen isotope effects with heavy-atom isotope effects. For instance, determining nitrogen isotope effect along with hydrogen isotope effect was used to show that the reaction of 2-phenylethyltrimethylammonium ion with ethoxide in ethanol at 40 °C follows an E2 mechanism, as opposed to alternative non-concerted mechanisms. This conclusion was reached upon showing that this reaction yields a nitrogen isotope effect, k/k, of 1.0133±0.0002 along with a hydrogen kinetic isotope effect of 3.2 at the leaving hydrogen.
Similarly, combining nitrogen and hydrogen isotope effects was used to show that syn eliminations of simple ammonium salts also follow a concerted mechanism, which was a question of debate before. In the following two reactions of 2-phenylcyclopentyltrimethylammonium ion with ethoxide, both of which yield 1-phenylcyclopentene, both isomers exhibited a nitrogen isotope effect k/k at 60 °C. Although the reaction of the trans isomer, which follows syn elimination, has a smaller nitrogen kinetic isotope effect (1.0064) compared to the cis isomer which undergoes anti elimination (1.0108), both results are large enough to be indicative of weakening of the C-N bond in the transition state that would occur in a concerted process. | 7 | Physical Chemistry |
A topogenic sequence is a collective term used for a peptide sequence present at nascent proteins essential for their insertion and orienting in cellular membranes. The sequences are also used to translocate proteins across various intracellular membranes, and ensure they are transported to the correct organelle after synthesis. The position of the sequence may be at the end, e.g. N-terminal signal sequence, or in mid parts of the nascent protein, e.g. stop-transfer anchor sequences and signal-anchor sequences. If the sequence is at the end of the polypeptide, it is cleaved off after entering the ER-lumen (via a translocon) by a signal peptidase, and subsequently degraded.
As an example, the vast majority of all known complex plastid preproteins (an unactivated protein) encoded in the nucleus possess a topogenic sequence. | 1 | Biochemistry |
* The asteroid discovered by S.J. Bus on March 2, 1981, initially called "1981 EO42", was named "(5047) Zanda" in her honor. | 9 | Geochemistry |
Psychrophiles include bacteria, lichens, snow algae, phytoplankton, fungi, and insects.
Among the bacteria that can tolerate extreme cold are Arthrobacter sp., Psychrobacter sp. and members of the genera Halomonas, Pseudomonas, Hyphomonas, and Sphingomonas. Another example is Chryseobacterium greenlandensis, a psychrophile that was found in 120,000-year-old ice.
Umbilicaria antarctica and Xanthoria elegans are lichens that have been recorded photosynthesizing at temperatures ranging down to −24 °C, and they can grow down to around −10 °C. Some multicellular eukaryotes can also be metabolically active at sub-zero temperatures, such as some conifers; those in the Chironomidae family are still active at −16 °C.
Microalgae that live in snow and ice include green, brown, and red algae. Snow algae species such as Chloromonas sp., Chlamydomonas sp., and Chlorella sp. are found in polar environments.
Some phytoplankton can tolerate extremely cold temperatures and high salinities that occur in brine channels when sea ice forms in polar oceans. Some examples are diatoms like Fragilariopsis cylindrus, Nitzchia lecointeii, Entomoneis kjellmanii, Nitzchia stellata, Thalassiosira australis, Berkelaya adeliense, and Navicula glaciei.
Penicillium is a genus of fungi found in a wide range of environments including extreme cold.
Among the psychrophile insects, the Grylloblattidae or ice crawlers, found on mountaintops, have optimal temperatures between 1–4 °C. The wingless midge (Chironomidae) Belgica antarctica can tolerate salt, being frozen and strong ultraviolet, and has the smallest known genome of any insect. The small genome, of 99 million base pairs, is thought to be adaptive to extreme environments. | 1 | Biochemistry |
Ocean-atmospheric exchanges rates of CO depend on the concentration of carbon dioxide already present in both the atmosphere and the ocean, temperature, salinity, and wind speed. This exchange rate can be approximated by Henry's law and can be calculated as S = kP, where the solubility (S) of the carbon dioxide gas is proportional to the amount of gas in the atmosphere, or its partial pressure. | 9 | Geochemistry |
Phenylboronic acid is soluble in most polar organic solvents and is poorly soluble in hexanes and carbon tetrachloride. This planar compound has idealized C molecular symmetry. The boron atom is sp-hybridized and contains an empty p-orbital. The orthorhombic crystals use hydrogen bonding to form units made up of two molecules. These dimeric units are combined to give an extended hydrogen-bonded network. The molecule is planar with a minor bend around the C-B bond of 6.6° and 21.4° for the two PhB(OH) molecules. | 0 | Organic Chemistry |
For the special case where the incident radiation is normal (perpendicular) to a surface and the absorption is negligible, the intensity of the reflected and transmitted beams can be calculated from the refractive indices η and η of the two media, where is the fraction of the incident light reflected, and is the fraction of the transmitted light:
, , with the fraction absorbed taken as zero ( = 0 ). | 7 | Physical Chemistry |
The characteristics capable of supporting Type 1 pits were determined empirically by Lucey after examining the compositions of waters in which the pitting behaviour was known. They should be cold, less than 30°C, hard or moderately hard, 170 to 300 mg/L carbonate hardness, and organically pure. Organically pure waters usually originate from deep wells, or boreholes. Surface waters from rivers or lakes contain naturally occurring organic compounds that inhibit the formation of Type 1 pits, unless a deflocculation treatment has been carried out that removes organic material. Type 1 pitting is relatively uncommon in North America and this may be a result of the lower population density allowing a significant proportion of the potable water to be obtained from surface derived sources. In addition to being cold hard and organically pure, the water needs a specific chemistry. The effect of the water chemistry can be empirically determined though use of the Pitting Propensity Rating (PPR) a number that takes into account the sulfate, chloride, nitrate and sodium ion concentrations of the water as well as its acidity or pH. A water with a positive PPR has been shown to be capable of propagating Type 1 pits. | 8 | Metallurgy |
Anion exchange membranes are used in electrolytic cells and fuel cells to separate reactants present around the two electrodes while transporting the anions essential for the cell operation. An important example is the hydroxide anion exchange membrane used to separate the electrodes of a direct methanol fuel cell (DMFC) or direct-ethanol fuel cell (DEFC).
Poly(fluorenyl-co-aryl piperidinium) (PFAP)-based anion exchange materials (electrolyte membrane and electrode binder) with high ion conductivity and durability under alkaline conditions has been demonstrated for use to extract hydrogen from water. Performance was 7.68 A/cm at 2 V, some 6x the performance of existing materials. Its yield is about 1.2 times that of commercial proton-exchange membrane technology (6 A/cm2), and it does not require the use of expensive rare-earth elements. The system works by increasing the specific surface area. | 7 | Physical Chemistry |
Theoretically, any biomass can be converted into bio-oil using hydrothermal liquefaction regardless of water content, and various different biomasses have been tested, from forestry and agriculture residues, sewage sludges, food process wastes, to emerging non-food biomass such as algae. The composition of cellulose, hemicellulose, protein, and lignin in the feedstock influence the yield and quality of the oil from the process.
Zhang et al., at the University of Illinois, report on a hydrous pyrolysis process in which swine manure is converted to oil by heating the swine manure and water in the presence of carbon monoxide in a closed container. For that process they report that a temperatures of at least is required to convert the swine manure to oil, and temperatures above about reduces the amount of oil produced. The Zhang et al. process produces pressures of about 7 to 18 Mpa (1000 to 2600 psi - 69 to 178 atm), with higher temperatures producing higher pressures. Zhang et al. used a retention time of 120 minutes for the reported study, but report at higher temperatures a time of less than 30 minutes results in significant production of oil.
A commercialized process using hydrous pyrolysis (see the article Thermal depolymerization) used by Changing World Technologies, Inc. (CWT) and its subsidiary Renewable Environmental Solutions, LLC (RES) to convert turkey offal. As a two-stage process, the first stage to convert the turkey offal to hydrocarbons at a temperature of and a second stage to crack the oil into light hydrocarbons at a temperature of near . Adams et al. report only that the first stage heating is "under pressure"; Lemley, in a non-technical article on the CWT process, reports that for the first stage (for conversion) a temperature of about and a pressure of about 600 psi, with a time for the conversion of "usually about 15 minutes". For the second stage (cracking), Lemley reports a temperature of about . | 0 | Organic Chemistry |
RNA-Seq experiments generate a large volume of raw sequence reads which have to be processed to yield useful information. Data analysis usually requires a combination of bioinformatics software tools (see also List of RNA-Seq bioinformatics tools) that vary according to the experimental design and goals. The process can be broken down into four stages: quality control, alignment, quantification, and differential expression. Most popular RNA-Seq programs are run from a command-line interface, either in a Unix environment or within the R/Bioconductor statistical environment. | 1 | Biochemistry |
For the reversible reaction A⇌B, the forward step A→B has a rate constant and the backwards step B→A has a rate constant . The concentration of A obeys the following differential equation:
If we consider that the concentration of product B at anytime is equal to the concentration of reactants at time zero minus the concentration of reactants at time , we can set up the following equation:
Combining and , we can write
Separation of variables is possible and using an initial value , we obtain:
and after some algebra we arrive at the final kinetic expression:
The concentration of A and B at infinite time has a behavior as follows:
Thus, the formula can be linearized in order to determine :
To find the individual constants and , the following formula is required: | 7 | Physical Chemistry |
ATP is a molecule found in and around living cells, and as such it gives a direct measure of biological concentration and health. ATP is quantified by measuring the light produced through its reaction with the naturally occurring firefly enzyme luciferase using a luminometer. The amount of light produced is directly proportional to the amount of ATP present in the sample.
ATP tests can be used to:
* Control biological treatment reactors
* Guide biocide dosing programs
* Determine drinking water cleanliness
* Manage fermentation processes
* Assess soil activity
* Determine corrosion / deposit process type
* Measure equipment or product sanitation | 2 | Environmental Chemistry |
Since the molecule has a hydroxyl (-OH) group, it is frequently bound to other lipids including fatty acids; most analytical methods, therefore, utilise a strong alkali (KOH or NaOH) to saponify the ester linkages. Typical extraction solvents include 6% KOH in methanol. The free sterols and stanols (saturated sterols) are then separated from the polar lipids by partitioning into a less polar solvent such as hexane. Prior to analysis, the hydroxyl group is frequently derivatised with BSTFA (bis-trimethyl silyl trifluoroacetamide) to replace the hydrogen with the less exchangeable trimethylsilyl (TMS) group. Instrumental analysis is frequently conducted on gas chromatograph (GC) with either a flame ionisation detector (FID) or mass spectrometer (MS). The mass spectrum for 5β-coprostanol - TMS ether can be seen in the figure. Alternatively, liquid-chromatography mass spectrometry (LC-MS) techniques that employ atmospheric pressure chemical ionization (APCI) may also be employed to detect coprostanol under positive mode.<br /> | 2 | Environmental Chemistry |
Oxidation of phosphinites gives phosphinates:
:2 P(OR)R + O → 2 OP(OR)R
Phosphinites are ligands, giving derivatives similar to metal phosphine complexes. They are stronger pi-acceptors than typical phosphine ligands. | 0 | Organic Chemistry |
Janice Musfeldt is a professor at University of Tennessee, Knoxville in physical and materials chemistry and experimental physics. She received her B.S. degree in chemical engineering from the University of Illinois in 1987 and a Ph.D. in physical chemistry from the University of Florida in 1992. She served as a post-doctoral research associate at the Departement de Physique, Universite de Sherbrooke in 1993-1994. She received the 2001 Creativity award from the Division of Materials Research, National Science Foundation and the 2010 Chancellor's award for research and creative achievement at the University of Tennessee. She has served on the user committee of the National High Magnetic Field Laboratory between 2010 and 2013 and between 2018 and the present and was elected its chair in 2010. In 2014 she founded the biannual Gordon Research Conference on Multiferroics and Magnetoelectric materials. In 2017, she was elected as a Fellow of the American Physical Society for her contribution to the spectroscopy of quantum materials with an emphasis on high magnetic field effects in multiferroics, quantum magnets, and nanomaterials. | 7 | Physical Chemistry |
Alpha-cleavage (α-cleavage) in organic chemistry refers to the act of breaking the carbon-carbon bond adjacent to the carbon bearing a specified functional group. | 0 | Organic Chemistry |
Radical disproportionation is often thought of as occurring in a linear fashion with the donor radical, the acceptor radical, and the atom being accepted all along the same axis. In fact, most disproportionation reactions do not require linear orientations in space. Molecules that are more sterically hindered require arrangements that are more linear, and thus react more slowly. Steric effects play a significant role in disproportionation with ethyl radicals acting as more effective acceptors than tert-butyl radicals. Tert-butyl radicals have many hydrogens on adjacent carbons to donate and steric effects often prevent tert-butyl radicals from getting close to abstracting hydrogens. | 0 | Organic Chemistry |
Gustav Heinrich Johann Apollon Tammann ( – 17 December 1938) was a prominent Baltic German chemist-physicist who made important contributions in the fields of glassy and solid solutions, heterogeneous equilibria, crystallization, and metallurgy. | 7 | Physical Chemistry |
If the gene in question is the wildtype a superscript + sign is used:
*leuA
If a gene is mutant, it is signified by a superscript -:
*leuA
By convention, if neither is used, it is considered to be mutant.
There are additional superscripts and subscripts which provide more information about the mutation:
* = temperature sensitive (leuA)
* = cold sensitive (leuA)
* = amber mutation (leuA)
* = umber (opal) mutation (leuA)
* = ochre mutation (leuA)
* = resistant (Rif)
Other modifiers:
*Δ = deletion (ΔleuA)
*- = fusion (leuA-lacZ)
* = fusion (leuA:lacZ)
* = insertion (leuA::Tn10)
*Ω = a genetic construct introduced by a two-point crossover (ΩleuA)
*Δdeleted gene::replacing gene = deletion with replacement (ΔleuA::nptII(Kan) indicates that the leuA gene has been deleted and replaced with the gene for neomycin phosphotransferase, which confers kanamycin-resistance, as oftentimes parenthetically noted for drug-resistance markers) | 1 | Biochemistry |
*[http://tomcat.cs.rhul.ac.uk/home/mxba001/ Web-based Structural Analysis tool for any uploaded PDB file, producing Ramachandran plots, computing dihedral angles and extracting sequence from PDB]
*[https://web.archive.org/web/20090726062008/http://www.fos.su.se/~pdbdna/input_Raman.html Web-based tool showing Ramachandran plot of any PDB entry]
*[http://molprobity.biochem.duke.edu MolProbity web service that produces Ramachandran plots and other validation of any PDB-format file]
*[http://services.mbi.ucla.edu/SAVES SAVES] (Structure Analysis and Verification) — uses WHATCHECK, PROCHECK, and does its own internal Ramachandran Plot
*STING
*Pymol with the DynoPlot extension
*VMD, distributed with dynamic Ramachandran plot plugin
*WHAT CHECK, the stand-alone validation routines from the WHAT IF software
*UCSF Chimera, found under the Model Panel.
*Sirius
*[https://spdbv.vital-it.ch/ Swiss PDB Viewer]
*[http://spin.niddk.nih.gov/NMRPipe/talos/ TALOS]
*[http://www.al-nasir.com/www/Jamie/Zeus/ Zeus molecular viewer] — found under "Tools" menu, high quality plots with regional contours
*[http://www.ebi.ac.uk/thornton-srv/software/PROCHECK/ Procheck]
*[http://dunbrack.fccc.edu/ndrd Neighbor-Dependent and Neighbor-Independent Ramachandran Probability Distributions]
*See also PDB for a list of similar software. | 1 | Biochemistry |
In both marine and freshwater environments, algae – particularly green algae and diatoms – make up the dominant component of surface growth communities. Small crustaceans, rotifers, and protozoans are also commonly found in fresh water and the sea, but insect larvae, oligochaetes and tardigrades are peculiar to freshwater aufwuchs faunas. | 2 | Environmental Chemistry |
By sequence similarity, most sigma factors are σ-like (). They have four main regions (domains) that are generally conserved:
N-terminus --------------------- C-terminus
The regions are further subdivided. For example, region 2 includes 1.2 and 2.1 through 2.4.
Domain 1.1 is found only in "primary sigma factors" (RpoD, RpoS in E.coli; "Group 1"). It is involved in ensuring the sigma factor will only bind the promoter when it is complexed with the RNA polymerase. Domains 2-4 each interact with specific promoter elements and with RNAP. Region 2.4 recognizes and binds to the promoter −10 element (called the "Pribnow box"). Region 4.2 recognizes and binds to the promoter −35 element.
Not every sigma factor of the σ family contains all the domains. Group 2, which includes RpoS, is very similar to Group 1 but lacks domain 1. Group 3 also lacks domain 1, and includes σ. Group 4, also known as the Extracytoplasmic Function (ECF) group, lack both σ1.1 and σ3. RpoE is a member.
Other known sigma factors are of the σ/RpoN () type. They are functional sigma factors, but they have significantly different primary amino acid sequences. | 1 | Biochemistry |
Inclusions are usually other minerals or rocks, but may also be water, gas or petroleum. Liquid or vapor inclusions are known as fluid inclusions. In the case of amber it is possible to find insects and plants as inclusions.
The analysis of atmospheric gas bubbles as inclusions in ice cores is an important tool in the study of climate change.
A xenolith is a pre-existing rock which has been picked up by a lava flow. Melt inclusions form when bits of melt become trapped inside crystals as they form in the melt. | 8 | Metallurgy |
Training & Education program offers scientific, regulatory, and professional development training courses in person at the Annual Meeting and Midyear Meeting and as online courses and webinars. | 3 | Analytical Chemistry |
A close packed unit cell, both face-centered cubic and hexagonal close packed, can form two different shaped holes. Looking at the three green spheres in the hexagonal packing illustration at the top of the page, they form a triangle-shaped hole. If an atom is arranged on top of this triangular hole it forms a tetrahedral interstitial hole. If the three atoms in the layer above are rotated and their triangular hole sits on top of this one, it forms an octahedral interstitial hole. In a close-packed structure there are 4 atoms per unit cell and it will have 4 octahedral voids (1:1 ratio) and 8 tetrahedral voids (1:2 ratio) per unit cell. The tetrahedral void is smaller in size and could fit an atom with a radius 0.225 times the size of the atoms making up the lattice. An octahedral void could fit an atom with a radius 0.414 times the size of the atoms making up the lattice. An atom that fills this empty space could be larger than this ideal radius ratio, which would lead to a distorted lattice due to pushing out the surrounding atoms, but it cannot be smaller than this ratio. | 3 | Analytical Chemistry |
It is possible to obtain entropy of activation using Eyring equation. This equation is of the form where:
* = reaction rate constant
* = absolute temperature
* = enthalpy of activation
* = gas constant
* = transmission coefficient
* = Boltzmann constant = R/N, N = Avogadro constant
* = Planck's constant
* = entropy of activation
This equation can be turned into the formThe plot of versus gives a straight line with slope from which the enthalpy of activation can be derived and with intercept from which the entropy of activation is derived. | 7 | Physical Chemistry |
SeaSeep is a combination of 2D seismic data (a group of seismic lines acquired individually, as opposed to multiple closely space lines), high resolution multibeam sonar which is an evolutionary advanced form of side-scan sonar, navigated piston coring (one of the more common sea floor sampling methods), heat flow sampling (which serve a critical purpose in oil exploration and production) and possibly gravity and magnetic data (refer to Dick Gibson's Primer on Gravity and Magnetics).
The term SeaSeep originally belonged to Black Gold Energy LLC and refers to a dataset that combines all of the available data into one integrated package that can be used in hydrocarbon exploration. With the acquisition of Black Gold Energy LLC by Niko Resources Ltd. in December 2009 the term now belongs to Niko Resources
The concept of a SeaSeep dataset is the modern day offshore derivative of how many oil fields were found in the late 19th and early 20th century; by finding a large anticline structure with an associated oil seep. In the United States, many of the first commercial fields in California were found using this method including the Newhall Field discovered in 1876 and the Kern River Field discovered in 1899. Seeps have also been used to find offshore fields including the Cantarell Field in Mexico in 1976; the largest oil field in Mexico and one of the largest in the world. The field is named after a fisherman, Rudesindo Cantarell, who complained to PEMEX about his fishing nets being stained by oil seeps in the Bay of Campeche.
The biological and geochemical manifestations of seepage leads to distinct bathymetrical features including positive relief mounds, pinnacles, mud volcanoes and negative relief pockmarks. These features can be detected by multibeam sonar and then sampled by navigated piston coring. Spec and proprietary multibeam seep mapping and core geochemistry by Texas A&M University's Geochemical & Environmental Research Group and later TDI Brooks demonstrated thermogenic charge in deepwater Angola and deepwater Nigeria leading to an aggressive exploration program by a number of oil companies and subsequent discoveries. The emphasis on, and marketplace acceptance of, multibeam mapping combined with navigated coring as an improvement over grid-based approaches to geochemical exploration is attributed to AOA Geophysics Inc. | 9 | Geochemistry |
Genetic engineering could be used to cure diseases, but also to change physical appearance, metabolism, and even improve physical capabilities and mental faculties such as memory and intelligence. Ethical claims about germline engineering include beliefs that every fetus has a right to remain genetically unmodified, that parents hold the right to genetically modify their offspring, and that every child has the right to be born free of preventable diseases. For parents, genetic engineering could be seen as another child enhancement technique to add to diet, exercise, education, training, cosmetics, and plastic surgery. Another theorist claims that moral concerns limit but do not prohibit germline engineering.
A 2020 issue of the journal Bioethics was devoted to moral issues surrounding germline genetic engineering in people.
Possible regulatory schemes include a complete ban, provision to everyone, or professional self-regulation. The American Medical Association's Council on Ethical and Judicial Affairs stated that "genetic interventions to enhance traits should be considered permissible only in severely restricted situations: (1) clear and meaningful benefits to the fetus or child; (2) no trade-off with other characteristics or traits; and (3) equal access to the genetic technology, irrespective of income or other socioeconomic characteristics."
As early in the history of biotechnology as 1990, there have been scientists opposed to attempts to modify the human germline using these new tools, and such concerns have continued as technology progressed. With the advent of new techniques like CRISPR, in March 2015 a group of scientists urged a worldwide moratorium on clinical use of gene editing technologies to edit the human genome in a way that can be inherited. In April 2015, researchers sparked controversy when they reported results of basic research to edit the DNA of non-viable human embryos using CRISPR. A committee of the American National Academy of Sciences and National Academy of Medicine gave qualified support to human genome editing in 2017 once answers have been found to safety and efficiency problems "but only for serious conditions under stringent oversight." | 1 | Biochemistry |
Plant transformation vectors are plasmids that have been specifically designed to facilitate the generation of transgenic plants. The most commonly used plant transformation vectors are T-DNA binary vectors and are often replicated in both E. coli, a common lab bacterium, and Agrobacterium tumefaciens, a plant-virulent bacterium used to insert the recombinant DNA into plants.
Plant transformation vectors contain three key elements:
* Plasmids Selection (creating a custom circular strand of DNA)
* Plasmids Replication (so that it can be easily worked with)
* Transfer DNA (T-DNA) region (inserting the DNA into the agrobacteria) | 1 | Biochemistry |
Arylsulfonyl chlorides are made industrially in a two-step, one-pot reaction from an arene (in this case, benzene) and chlorosulfuric acid:
The intermediate benzenesulfonic acid can be chlorinated with thionyl chloride as well. Benzenesulfonyl chloride, the most important sulfonyl halide, can also be produced by treating sodium benzenesulfonate with phosphorus pentachlorides.
Benzenediazonium chloride reacts with sulfur dioxide and hydrochloric acid to give the sulfonyl chloride:
For alkylsulfonyl chlorides, one synthetic procedure is the Reed reaction: | 0 | Organic Chemistry |
The European Council directive 1999/13/EC defines volatile organic compounds (VOCs) as “any organic compound having at 293.15 K a vapor pressure of 0.01 kPa or more, or having a corresponding volatility under the particular conditions of use”.
In our daily life, these molecules are notably responsible of the flavor of food products, as well as of the fragrance of essential oils used in the cosmetics industry.
In nature, these molecules are produced by bacteria and fungi.
They are also synthesized by plants (flowers, fruits, leaves and roots) and animals (humans, insects, etc.).
The profiling of VOCs emitted by living organisms takes an increasing importance in various scientific domains like in medicine, in food sciences or in chemical ecology.
For instance, in medicine, non-invasive diagnosis techniques of cancer based on the profiling of VOCs from the exhaled breath have been developed. To this end, a variety of novel sensing approaches and nanomaterial based sensors are being used in volatolomics research.
In the field of chemical ecology, gas chromatography coupled to mass spectrometry (GC-MS) is often used to characterize the volatile semiochemicals involved in the biotic interactions taking place aboveground and belowground between plants, insects and phytopathogens. | 0 | Organic Chemistry |
The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existence of this stage.
Alexander Rich first proposed the concept of the RNA world in 1962, and Walter Gilbert coined the term in 1986. Alternative chemical paths to life have been proposed, and RNA-based life may not have been the first life to exist. Even so, the evidence for an RNA world is strong enough that the hypothesis has gained wide acceptance. The concurrent formation of all four RNA building blocks further strengthened the hypothesis. Regardless of its plausibility in a prebiotic scenario, the RNA world can serve as a model system for studying the origin of life.
* Like DNA, RNA can store and replicate genetic information.
* Like protein enzymes, RNA enzymes (ribozymes) can catalyze (start or accelerate) chemical reactions that are critical for life.
One of the most critical components of cells, the ribosome, is composed primarily of RNA. Ribonucleotide moieties in many coenzymes, such as acetyl-CoA, NADH, FADH, and F420, may be surviving remnants of covalently bound coenzymes in an RNA world.
Although RNA is fragile, some ancient RNAs may have evolved the ability to methylate other RNAs to protect them.
If the RNA world existed, it was probably followed by an age characterized by the evolution of ribonucleoproteins (RNP world), which in turn ushered in the era of DNA and longer proteins. DNA has greater stability and durability than RNA; this may explain why it became the predominant information storage molecule. Protein enzymes may have come to replace RNA-based ribozymes as biocatalysts because their greater abundance and diversity of monomers makes them more versatile. As some cofactors contain both nucleotide and amino-acid characteristics, it may be that amino acids, peptides and finally proteins initially were cofactors for ribozymes. | 9 | Geochemistry |
Passive daytime radiative cooling has "the potential to simultaneously alleviate the two major problems of energy crisis and global warming" while being an "environmental protection refrigeration technology." PDRCs thereby have an array of potential applications, but are now most often applied to various aspects of the built environment, such as building envelopes, cool pavements, and other surfaces to decrease energy demand, costs, and emissions. PDRC has been tested and applied for indoor space cooling, outdoor urban cooling, solar cell efficiency, power plant condenser cooling, among other applications. For outdoor applications, the lifetime of PDRCs should be adequately estimated, both for high humidity and heat as well as for UV stability. | 7 | Physical Chemistry |
This resonant process occurs in a neutral atom when the electric field displaces the electron density relative to the nucleus it surrounds.
This displacement occurs due to the equilibrium between restoration and electric forces.
Electronic polarization may be understood by assuming an atom as a point nucleus surrounded by spherical electron cloud of uniform charge density. | 7 | Physical Chemistry |
The expert conference “Sensor-Based Sorting” is addressing new developments and applications in the field of automatic sensor separation techniques for primary and secondary raw materials. The conference provides a platform for plant operators, manufacturers, developers and scientists to exchange know-how and experiences.
The congress is hosted by the Department of Processing and Recycling and the Unit for Mineral Processing (AMR) of RWTH Aachen University in cooperation with the GDMB Society of Metallurgists and Miners, Clausthal. Scientific supervisors are Professor Thomas Pretz and Professor Hermann Wotruba. | 3 | Analytical Chemistry |
Cold spraying (or gas dynamic cold spraying) was introduced to the market in the 1990s. The method was originally developed in the Soviet Union – while experimenting with the erosion of the target, which was exposed to a two-phase high-velocity flow of fine powder in a wind tunnel, scientists observed accidental rapid formation of coatings.
In cold spraying, particles are accelerated to very high speeds by the carrier gas forced through a converging–diverging de Laval type nozzle. Upon impact, solid particles with sufficient kinetic energy deform plastically and bond mechanically to the substrate to form a coating. The critical velocity needed to form bonding depends on the material's properties, powder size and temperature. Metals, polymers, ceramics, composite materials and nanocrystalline powders can be deposited using cold spraying.
Soft metals such as Cu and Al are best suited for cold spraying, but coating of other materials (W, Ta, Ti, MCrAlY, WC–Co, etc.) by cold spraying has been reported.
The deposition efficiency is typically low for alloy powders, and the window of process parameters and suitable powder sizes is narrow. To accelerate powders to higher velocity, finer powders (<20 micrometers) are used. It is possible to accelerate powder particles to much higher velocity using a processing gas having high speed of sound (helium instead of nitrogen).
However, helium is costly and its flow rate, and thus consumption, is higher. To improve acceleration capability, nitrogen gas is heated up to about 900 °C. As a result, deposition efficiency and tensile strength of deposits increase. | 8 | Metallurgy |
The research that appeared to spark an onslaught of modified applications was a gel permeation chromatography technique of fixing poly(isopropyl acrylate) (PIPA) strands to glass beads and separating a mixture of dextrans, which was developed by Gewehr et al. They found that between the temperatures of 25–32 °C, the elution time of dextrans at different molecular weights exhibited a dependence on the temperature. Dextrans of the highest molecular weight eluted first since the PIPA chains exhibit hydrophilicity at temperatures below the LCST. As the temperature of the elution increased, when the chains behave in a more hydrophobic manner, the elution times increased for each of the analytes for the given range. The trend generally applies over the entire temperature range, but there is a flattening of the curve before 25 °C and after 32 °C (the approximate LCST for this experiment). It is important to note that above the LCST, the PIPA acts as a typical nonpolar stationary phase that would be used in reverse-phased chromatography. There are also instances of the elution times increasing below 15 °C, which most likely can be attributed to the lower temperatures’ effects on mass transfer playing a more significant role on retention than the stationary phase behavior. This study showed that the resolution could essentially be tuned by adjusting the operating temperature. The scope of this study was limited to isothermal conditions and attaching polymer chains to glass beads. The results, however, were satisfying enough to inspire other investigations and modifications to create a more versatile stationary phase for the advancement of chromatography. | 3 | Analytical Chemistry |
12-Phosphotungstic acid, the compound James F. Keggin used to determine the structure, can be purchased commercially. Other compounds that contain the α-Keggin anion such as silicotungstic acid and phosphomolybdic acid are also commercially available at Aldrich Chemicals, Fisher Chemicals, Alfa Aesar, VWR Chemical, American Elements, and others. | 7 | Physical Chemistry |
The theory can be applied also to dilute solutions of mixed electrolytes. Freezing point depression measurements has been used to this purpose. | 7 | Physical Chemistry |
The Stark effect originates from the interaction between a charge distribution (atom or molecule) and an external electric field.
The interaction energy of a continuous charge distribution , confined within a finite volume , with an external electrostatic potential is
This expression is valid classically and quantum-mechanically alike.
If the potential varies weakly over the charge distribution, the multipole expansion converges fast, so only a few first terms give an accurate approximation. Namely, keeping only the zero- and first-order terms,
where we introduced the electric field and assumed the origin 0 to be somewhere within .
Therefore, the interaction becomes
where and are, respectively, the total charge (zero moment) and the dipole moment of the charge distribution.
Classical macroscopic objects are usually neutral or quasi-neutral (), so the first, monopole, term in the expression above is identically zero. This is also the case for a neutral atom or molecule. However, for an ion this is no longer true. Nevertheless, it is often justified to omit it in this case, too. Indeed, the Stark effect is observed in spectral lines, which are emitted when an electron "jumps" between two bound states. Since such a transition only alters the internal degrees of freedom of the radiator but not its charge, the effects of the monopole interaction on the initial and final states exactly cancel each other. | 7 | Physical Chemistry |
A third mission, called EXPOSE-R2, was launched on 24 July 2014 aboard the Russian Progress M-24M, carrying 46 species of bacteria, fungi and arthropods, in 758 different samples that were exposed to different conditions, under different filters, and for various time periods. It was attached on 18 August 2014 to the exterior of the ISS on the Russian module Zvezda, and exposure was finished on 3 February 2016, and were stored inside the ISS until their return to Earth on 18 June 2016. Two main experiments (BIOMEX and BOSS) tested a desert strain of cyanobacterium called Chroococcidiopsis and Deinococcus geothermalis, as well as bacteria, yeast (including Kombucha culture,) archaea, algae, fungi, lichens and mosses, while the Biochip experiment will test affinity receptors to biomolecules. The organisms and organic compounds were exposed to partial and full space conditions for 12 to 18 months, and were returned to Earth in early 2016 for analyses.
* The Biology and Mars Experiment (BIOMEX). Its objective is to measure to what extent biomolecules, such as biological pigments, cellular components, and biofilms are resistant to and able to maintain their stability under space and Mars-like conditions. The results of BIOMEX will be relevant for space-proven biosignature definition and for building a biosignature data base.
:The secondary scientific objective of BIOMEX is to analyze to what extent selected terrestrial extremophiles are able to survive in space and to determine which interactions between biological samples and selected minerals (including terrestrial, Moon and Mars analogs) can be observed under space and Mars-like conditions. BIOMEX contains numerous chambers that are filled with biomolecules and organisms that include bacteria, archaea, algae, fungi, lichens and mosses. The samples will spend up to one and a half years outside the space station, and the organisms will be monitored with temperature sensors and dosimeters, which monitor radiation exposure. Scientists will continuously monitor the survival of the organisms and the stability of important cellular components like membrane lipids, pigments, proteins, and DNA. These investigations could thus enhance the chances of detecting organic traces of life on Mars. At the completion of the experiment, BIOMEX samples will be returned to Earth for study. BIOMEX is led by Jean-Pierre de Vera, from the German Aerospace Center (DLR), together with a team from 27 institutes in 12 countries.
* The second major experiment is called Biofilm Organisms Surfing Space (BOSS). The hypothesis to be tested is that "microorganisms grown as biofilms, hence embedded in self-produced extracellular polymeric substances, are more tolerant to space and Martian conditions compared to their planktonic counterparts." Two of the organisms being exposed are Deinococcus geothermalis and Chroococcidiopsis.
* The Biochip experiment will study the resistance of various biochip models to space constraints, especially cosmic radiation and extreme changes of temperature. Their detection principle is based on the recognition of a target molecule by affinity receptors (antibodies and aptamers) fixed on a solid surface. It is hoped it will eventually be deployed in planetary missions to help the search for biomolecules of past or present extraterrestrial life.
* The BIODIVERSITY experiment was provided by Russia. | 1 | Biochemistry |
The segments resulting from circularization during constructing jumping library are cleaved, and DNA fragments with markers will be enriched and subjected to paired-end sequencing.
These DNA fragments are sequenced from both ends and generate pairs of reads. The genomic distance between the reads in each pair is approximately known and used for the assembly process.
For example, a DNA clone generated by random fragmentation is about 200 bp, and a read from each end is around 180 bp, overlapping each other.
This should be distinguished from mate-pair sequencing, which is basically a combination of next generation sequencing with jumping libraries. | 1 | Biochemistry |
Many photosynthetic life forms (plants, algae, phototrophic and chemoautotrophic bacteria, and archaea) require a way to utilize carbon into their metabolic pathways. This usually occurs in pathways that fix carbon from carbon dioxide (CO). In the 3-hydroxypropionate bicycle, photosynthetic organisms like Chloroflexus aurantiacus, fix CO and bicarbonate (HCO ) as part of their metabolic processes. | 1 | Biochemistry |
Soil contaminated with heavy metals including radionuclides is mitigated primarily using chelating resins.
Chelating polymers (ion-exchange resins) were proposed for maintenance therapy of pathologies accompanied by iron accumulation, such as hereditary hemochromatosis (iron overload) or Wilson's disease (copper overload), by chelating the metal ions in GIT and thus limiting its biological availability. | 3 | Analytical Chemistry |
The transamination of oxaloacetate to aspartate is achieved through the use of glutamate. Glutamate is transported with aspartate via antiporter, thus as one aspartate leaves the cell, a glutamate enters. Glutamate in the matrix is converted into an a-ketoglutarate which is transported in an antiporter with malate. In the cytoplasmic side a-ketoglutarate is converted back into glutamate when aspartate is converted back to oxaloacetate. | 1 | Biochemistry |
Cells can metabolize DHA to products that possess an oxo (i.e. ketone) residue. These products include 13-oxo-DHA (termed EFOXD6) and 17-oxo-DHA (termed 18-EFOXD6). Both oxo metabolites possess anti-inflammatory activity as assesses in in vitro systems (see ). | 1 | Biochemistry |
Firefly luciferase bioluminescence color can vary between yellow-green (λ = 550 nm) to red (λ = 620). There are currently several different mechanisms describing how the structure of luciferase affects the emission spectrum of the photon and effectively the color of light emitted.
One mechanism proposes that the color of the emitted light depends on whether the product is in the keto or enol form. The mechanism suggests that red light is emitted from the keto form of oxyluciferin, while green light is emitted from the enol form of oxyluciferin. However, 5,5-dimethyloxyluciferin emits green light even though it is constricted to the keto form because it cannot tautomerize.
Another mechanism proposes that twisting the angle between benzothiazole and thiazole rings in oxyluciferin determines the color of bioluminescence. This explanation proposes that a planar form with an angle of 0° between the two rings corresponds to a higher energy state and emits a higher-energy green light, whereas an angle of 90° puts the structure in a lower energy state and emits a lower-energy red light.
The most recent explanation for the bioluminescence color examines the microenvironment of the excited oxyluciferin. Studies suggest that the interactions between the excited state product and nearby residues can force the oxyluciferin into an even higher energy form, which results in the emission of green light. For example, Arg 218 has electrostatic interactions with other nearby residues, restricting oxyluciferin from tautomerizing to the enol form. Similarly, other results have indicated that the microenvironment of luciferase can force oxyluciferin into a more rigid, high-energy structure, forcing it to emit a high-energy green light. | 1 | Biochemistry |
It is known that Middle Minoan bronze work flourished as an independent native art. To the very beginning of this epoch belongs the largest sword of the age, found in the palace of Malia. It is a flat blade, 79 cm long, with a broad base and a sharp point; there is a gold and crystal hilt but no ornament on the blade. A dagger of somewhat later date, now in the Metropolitan Museum of New York is the earliest piece of decorated bronze from Crete. Both sides of the blade are engraved with drawings: bulls fighting and a man hunting boars in a thicket. Slightly later again (MM III) are a series of blades from mainland Greece, which must be attributed to Cretan craftsmen, with ornament in relief, or incised, or inlaid with gold, silver and niello. The most elaborate inlays, pictures of men hunting lions and cats hunting birds, are on daggers from the shaftgraves of Mycenae. These large designs cover the whole of the flat blade except its edge, but on swords, best represented by finds at Knossos, the ornament is restricted to the high midribs which are an essential feature of the longer blades. The type belongs to the beginning of the Late Minoan (Mycenaean) age. The hilt is made in one piece with the blade; it has a horned guard, a flanged edge for holding grip-scales, and a tang for a pommel. The scales were ivory or some other perishable substance and were fixed with bronze rivets; the pommels were often made of crystal. A rapier from Zapher Papoura (Knossos) is 91.3 cm long; its midrib and hilt-flange are engraved with bands of spiral coils, and its rivet-heads (originally gold-cased) with whorls. Ordinary Mycenaean blades are enriched with narrow mouldings, parallel to the midribs of swords and daggers, or to the curved backs of one-edged knives. The spearheads have hammered sockets. Other tools and implements are oval two-edged knives, square-ended razors, cleavers, chisels, hammers, axes, mattocks, ploughshares and saws. Cycladic and mainland Greek (Helladic) weapons show no ornament but include some novel types. A tanged spearhead has a slit (Cycladic) or slipped (Helladic) blade for securing the shaft; and the halberd, a west European weapon, was in use in the Middle Helladic Greece. There are few remains of Mycenaean metal armour; a plain cheek-piece from a helmet comes from Ialysos in Rhodes, and a pair of greaves from Enkomi in Cyprus. One of the greaves has wire riveted to its edge for fastening. | 8 | Metallurgy |
The mathematical models that describe chemical reaction kinetics provide chemists and chemical engineers with tools to better understand and describe chemical processes such as food decomposition, microorganism growth, stratospheric ozone decomposition, and the chemistry of biological systems. These models can also be used in the design or modification of chemical reactors to optimize product yield, more efficiently separate products, and eliminate environmentally harmful by-products. When performing catalytic cracking of heavy hydrocarbons into gasoline and light gas, for example, kinetic models can be used to find the temperature and pressure at which the highest yield of heavy hydrocarbons into gasoline will occur.
Chemical Kinetics is frequently validated and explored through modeling in specialized packages as a function of ordinary differential equation-solving (ODE-solving) and curve-fitting. | 7 | Physical Chemistry |
The elements of the space group fixing a point of space are the identity element, reflections, rotations and improper rotations, including inversion points. | 4 | Stereochemistry |
In most of today's smelting, aluminum ore, also known as bauxite, is first smelted into alumina through the Bayer Process. This step could be replaced by the Pedersen process -- either result in alumina. Unlike the smelting processes of iron and coal into steel or copper and tin into bronze, which require thermal energy, alumina must be smelted with electrical energy. This is done through the Hall–Héroult process, producing 99.5–99.8% pure aluminum. | 8 | Metallurgy |
Eyeglass frames made from titanium-containing SMAs are marketed under the trademarks Flexon and TITANflex. These frames are usually made out of shape-memory alloys that have their transition temperature set below the expected room temperature. This allows the frames to undergo large deformation under stress, yet regain their intended shape once the metal is unloaded again. The very large apparently elastic strains are due to the stress-induced martensitic effect, where the crystal structure can transform under loading, allowing the shape to change temporarily under load. This means that eyeglasses made of shape-memory alloys are more robust against being accidentally damaged. | 8 | Metallurgy |
The presence of only one of the above derangements is called a simple acid–base disorder. In a mixed disorder, more than one is occurring at the same time. Mixed disorders may feature an acidosis and alkosis at the same time that partially counteract each other, or there can be two different conditions affecting the pH in the same direction. The phrase "mixed acidosis", for example, refers to metabolic acidosis in conjunction with respiratory acidosis. Any combination is possible, as metabolic acidosis and alkalosis can co exist together. | 7 | Physical Chemistry |
In contrast to purple bacteria and other bacteria performing anoxygenic photosynthesis, thylakoid membranes of cyanobacteria are not continuous with the plasma membrane but are separate compartments. The photosynthetic machinery is embedded in the thylakoid membranes, with phycobilisomes acting as light-harvesting antennae attached to the membrane, giving the green pigmentation observed (with wavelengths from 450 nm to 660 nm) in most cyanobacteria.
While most of the high-energy electrons derived from water are used by the cyanobacterial cells for their own needs, a fraction of these electrons may be donated to the external environment via electrogenic activity. | 5 | Photochemistry |
The Wnt signaling pathway can be divided in canonical and non-canonical. The canonical signaling involves binding of Wnt to Frizzled and LRP5 co-receptor, leading to GSK3 phosphorylation and inhibition of β-catenin degradation, resulting in its accumulation and translocation to the nucleus, where it acts as a transcription factor. The non-canonical Wnt signaling can be divided in planar cell polarity (PCP) pathway and Wnt/calcium pathway. It is characterized by binding of Wnt to Frizzled and activation of G proteins and to an increase of intracellular levels of calcium through mechanisms involving PKC 50. The Wnt signaling pathway plays a significant role in osteoblastogenesis and bone formation, inducing the differentiation of mesenquimal pluripotent cells in osteoblasts and inhibiting the RANKL/RANK pathway and osteoclastogenesis. | 7 | Physical Chemistry |
RNA splicing is a process in molecular biology where a newly-made precursor messenger RNA (pre-mRNA) transcript is transformed into a mature messenger RNA (mRNA). It works by removing all the introns (non-coding regions of RNA) and splicing back together exons (coding regions). For nuclear-encoded genes, splicing occurs in the nucleus either during or immediately after transcription. For those eukaryotic genes that contain introns, splicing is usually needed to create an mRNA molecule that can be translated into protein. For many eukaryotic introns, splicing occurs in a series of reactions which are catalyzed by the spliceosome, a complex of small nuclear ribonucleoproteins (snRNPs). There exist self-splicing introns, that is, ribozymes that can catalyze their own excision from their parent RNA molecule. The process of transcription, splicing and translation is called gene expression, the central dogma of molecular biology. | 1 | Biochemistry |
The inorganic carbon species include carbon dioxide, carbonic acid, bicarbonate anion, and carbonate. It is customary to express carbon dioxide and carbonic acid simultaneously as . C is a key parameter when making measurements related to the pH of natural aqueous systems, and carbon dioxide flux estimates.
where,
* C is the total inorganic carbon
* is the sum of carbon dioxide and carbonic acid concentrations ()
* is the bicarbonate concentration
* is the carbonate concentration
Each of these species are related by the following pH-driven chemical equilibria:
The concentrations of the different species of DIC (and which species is dominant) depends on the pH of the solution, as shown by a Bjerrum plot.
Total inorganic carbon is typically measured by the acidification of the sample which drives the equilibria to . This gas is then sparged from solution and trapped, and the quantity trapped is then measured, usually by infrared spectroscopy. | 9 | Geochemistry |
The Chalcolithic occupation at Norşuntepe can be divided in 3 phases. The oldest Phase I dates to the Middle Chalcolithic and included Ubaid-type pottery. Phase II represents the Late Chalcolithic and during its final levels, more complex architecture appeared in the excavated area. | 8 | Metallurgy |
According to IUPAC, the functionality of a monomer is defined as the number of bonds that a monomers repeating unit forms in a polymer with other monomers. Thus in the case of a functionality of f = 2 a linear polymer is formed by polymerizing (a thermoplastic). Monomers with a functionality f' ≥ 3 lead to a branching point, which can lead to cross-linked polymers (a thermosetting polymer). Monofunctional monomers do not exist as such molecules lead to a chain termination.
From the average functionality of the used monomers the reaching of the gel point can be calculated as a function of reaction progress. Side reactions may increase or decrease the functionality.
However, IUPAC definition and the use of the term in organic chemistry differ with respect to the functionality of a double bond. In polymer chemistry, a double bond possesses a functionality of two (because two points of contact for further polymer chains are present, on each of the two adjacent carbon atoms), while in organic chemistry the double bond is a functional group and thus has a functionality of one. | 0 | Organic Chemistry |
The terminus of the double bond in enols is nucleophilic. Its reactions with electrophilic organic compounds is important in biochemistry as well as synthetic organic chemistry. In the former area, the fixation of carbon dioxide involves addition of CO to an enol. | 0 | Organic Chemistry |
Nines are used in a similar manner to describe computer system availability. In this context, a "one nine" (90%) uptime indicates a system that is available 90% of the time or, as is more commonly described, unavailable 10% of the time – about 72 hours per month. A "five nines" (99.999%) uptime describes a system that is unavailable for at most 26 seconds per month. | 8 | Metallurgy |
While the mechanical behavior of ceramics is often dominated by flaws, i.e. porosity, instead of grain size, grain-size strengthening is also observed in high-density ceramic specimens. Additionally, nanocrystalline ceramics have been shown to sinter more rapidly than bulk ceramics, leading to higher densities and improved mechanical properties, although extended exposure to the high pressures and elevated temperatures required to sinter the part to full density can result in coarsening of the nanostructure.
The large volume fraction of grain boundaries associated with nanocrystalline materials causes interesting behavior in ceramic systems, such as superplasticity in otherwise brittle ceramics. The large volume fraction of grain boundaries allows for a significant diffusional flow of atoms via Coble creep, analogous to the grain boundary sliding deformation mechanism in nanocrystalline metals. Because the diffusional creep rate scales as and linearly with the grain boundary diffusivity, refining the grain size from 10 μm to 10 nm can increase the diffusional creep rate by approximately 11 orders of magnitude. This superplasticity could prove invaluable for the processing of ceramic components, as the material may be converted back into a conventional, coarse-grained material via additional thermal treatment after forming. | 8 | Metallurgy |
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