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In physical organic chemistry, a kinetic isotope effect (KIE) is the change in the reaction rate of a chemical reaction when one of the atoms in the reactants is replaced by one of its isotopes. Formally, it is the ratio of rate constants for the reactions involving the light (k) and the heavy (k) isotopically substituted reactants (isotopologues):
This change in reaction rate is a quantum mechanical effect that primarily results from heavier isotopologues having lower vibrational frequencies compared to their lighter counterparts. In most cases, this implies a greater energetic input needed for heavier isotopologues to reach the transition state (or, in rare cases, the dissociation limit), and consequently, a slower reaction rate. The study of kinetic isotope effects can help the elucidation of the reaction mechanism of certain chemical reactions and is occasionally exploited in drug development to improve unfavorable pharmacokinetics by protecting metabolically vulnerable C-H bonds. | 7 | Physical Chemistry |
Two chemists generally expressed the composition of a mixture in terms of numerical values relating the amount of the product to describe the equilibrium state.
Cato Maximilian Guldberg and Peter Waage, building on Claude Louis Berthollet's ideas about reversible chemical reactions, proposed the law of mass action in 1864. These papers, in Danish, went largely unnoticed, as did the later publication (in French) of 1867 which contained a modified law and the experimental data on which that law was based.
In 1877 van t Hoff independently came to similar conclusions, but was unaware of the earlier work, which prompted Guldberg and Waage to give a fuller and further developed account of their work, in German, in 1879. Van t Hoff then accepted their priority. | 7 | Physical Chemistry |
PT is known to dissociate into two parts in the endoplasmic reticulum (ER): the enzymatically active A subunit (S1) and the cell-binding B subunit. The two subunits are separated by proteolic cleavage. The B subunit will undergo ubiquitin-dependent degradation by the 26S proteasome. However, the A subunit lacks lysine residues, which are essential for ubiquitin-dependent degradation. Therefore, PT subunit A will not be metabolized like most other proteins.
PT is heat-stable and protease-resistant, but once the A and B are separated, these properties change. The B subunit will stay heat-stable at temperatures up to 60 °C, but it is susceptible to protein degradation. PT subunit A, on the other hand, is less susceptible to ubiquitin-dependent degradation, but is unstable at temperature of 37 °C. This facilitates unfolding of the protein in the ER and tricks the cell into transporting the A subunit to the cytosol, where normally unfolded proteins will be marked for degradation. So, the unfolded conformation will stimulate the ERAD-mediated translocation of PT A into the cytosol. Once in the cytosol, it can bind to NAD and form a stable, folded protein again. Being thermally unstable is also the Achilles heel of PT subunit A. As always, there is an equilibrium between the folded and unfolded states. When the protein is unfolded, it is susceptible to degradation by the 20S proteasome, which can degrade only unfolded proteins. | 1 | Biochemistry |
The thermally induced unidirectional shape-shape-memory effect is an effect classified within the new so-called smart materials. Polymers with thermally induced shape-memory effect are new materials, whose applications are recently being studied in different fields of science (e.g., medicine), communications and entertainment.
There are currently reported and commercially used systems. However, the possibility of programming other polymers is present, due to the number of copolymers that can be designed: the possibilities are almost endless. | 7 | Physical Chemistry |
The amination of phosphorus trihalides occur sequentially, with each amination proceeding more slowly than the preceding:
:PCl + 2 HNMe → MeNPCl + [HNMe]Cl
:MeNPCl + 2 HNMe → (MeN)PCl + [HNMe]Cl
With bulky amines like diisopropylamine, the selectivity for the monosubstitution improves.
Commercially available aminophosphine chlorides include dimethylaminophosphorus dichloride and bis(dimethylamino)phosphorus chloride.
Related aminophosphine fluorides compounds are available from trifluorophosphine. The diphosphine MeN(PF) is prepared from methylamine:
:2 PF + 3 MeNH → MeN(PF) + 2 [MeNH]F
Me(PF) is used as a bridging ligand in organometallic chemistry.
Substituted aminophosphines are generally prepared from organophosphorus chlorides and amines. The method is used to prepare ligands for homogeneous catalysis. Chlorodiphenylphosphine and diethylamine react to give an aminophosphine:
:PhPCl + 2 HNEt → PhPNEt + [HNEt]Cl
Primary amines react with phosphorus(III) chlorides give aminophosphines with acidic α-NH centers:
:PhPCl + 2 HNR → PhPN(H)R + [HNR]Cl | 0 | Organic Chemistry |
Some aldehydes are substrates for aldehyde dehydrogenase enzymes which metabolize aldehydes in the body. There are toxicities associated with some aldehydes that are related to neurodegenerative disease, heart disease, and some types of cancer. | 0 | Organic Chemistry |
In size-exclusion chromatography, such as gel permeation chromatography, the intrinsic viscosity of a polymer is directly related to the elution volume of the polymer. Therefore, by running several monodisperse samples of polymer in a gel permeation chromatograph (GPC), the values of and can be determined graphically using a line of best fit. Then the molecular weight and intrinsic viscosity relationship is defined.
Also, the molecular weights of two different polymers in a particular solvent can be related using the Mark–Houwink equation when the polymer-solvent systems have the same intrinsic viscosity:
Knowing the Mark–Houwink parameters and the molecular weight of one of the polymers allows one to find the molecular weight of the other polymer using a GPC. The GPC sorts the polymer chains by volume and as intrinsic viscosity is related to the volume of the polymer chain, the GPC data is the same for the two different polymers. For example, if the GPC calibration curve is known for polystyrene in toluene, polyethylene in toluene can be run in a GPC and the molecular weight of polyethylene can be found according to the polystyrene calibration curve via the above equation. | 7 | Physical Chemistry |
An important factor influencing a substance's volatility is the strength of the interactions between its molecules. Attractive forces between molecules are what holds materials together, and materials with stronger intermolecular forces, such as most solids, are typically not very volatile. Ethanol and dimethyl ether, two chemicals with the same formula (CHO), have different volatilities due to the different interactions that occur between their molecules in the liquid phase: ethanol molecules are capable of hydrogen bonding while dimethyl ether molecules are not. The result in an overall stronger attractive force between the ethanol molecules, making it the less volatile substance of the two. | 7 | Physical Chemistry |
It can complement X-ray crystallography for studies of very small crystals (<0.1 micrometers), both inorganic, organic, and proteins, such as membrane proteins, that cannot easily form the large 3-dimensional crystals required for that process. Protein structures are usually determined from either 2-dimensional crystals (sheets or helices), polyhedrons such as viral capsids, or dispersed individual proteins. Electrons can be used in these situations, whereas X-rays cannot, because electrons interact more strongly with atoms than X-rays do. Thus, X-rays will travel through a thin 2-dimensional crystal without diffracting significantly, whereas electrons can be used to form an image. Conversely, the strong interaction between electrons and protons makes thick (e.g. 3-dimensional > 1 micrometer) crystals impervious to electrons, which only penetrate short distances.
One of the main difficulties in X-ray crystallography is determining phases in the diffraction pattern. Because of the complexity of X-ray lenses, it is difficult to form an image of the crystal being diffracted, and hence phase information is lost. Fortunately, electron microscopes can resolve atomic structure in real space and the crystallographic structure factor phase information can be experimentally determined from an image's Fourier transform. The Fourier transform of an atomic resolution image is similar, but different, to a diffraction pattern—with reciprocal lattice spots reflecting the symmetry and spacing of a crystal. Aaron Klug was the first to realize that the phase information could be read out directly from the Fourier transform of an electron microscopy image that had been scanned into a computer, already in 1968. For this, and his studies on virus structures and transfer-RNA, Klug received the Nobel Prize for chemistry in 1982. | 3 | Analytical Chemistry |
* NSCLC (48% of investigated cell lines)
* SCLC (38% of investigated cell lines)
* Bladder cancers (38%)
* Breast cancers (46%)
* Malignant mesotheliomas (48%)
* Colorectal cancers (76%) | 1 | Biochemistry |
Since its adoption into the International System of Units in 1971, numerous criticisms of the concept of the mole as a unit like the metre or the second have arisen:
* the number of molecules, etc. in a given amount of material is a fixed dimensionless quantity that can be expressed simply as a number, not requiring a distinct base unit;
* The SI thermodynamic mole is irrelevant to analytical chemistry and could cause avoidable costs to advanced economies
* The mole is not a true metric (i.e. measuring) unit, rather it is a parametric unit, and amount of substance is a parametric base quantity
* the SI defines numbers of entities as quantities of dimension one, and thus ignores the ontological distinction between entities and units of continuous quantities
In chemistry, it has been known since Prousts law of definite proportions (1794) that knowledge of the mass of each of the components in a chemical system is not sufficient to define the system. Amount of substance can be described as mass divided by Prousts "definite proportions", and contains information that is missing from the measurement of mass alone. As demonstrated by Dalton's law of partial pressures (1803), a measurement of mass is not even necessary to measure the amount of substance (although in practice it is usual). There are many physical relationships between amount of substance and other physical quantities, the most notable one being the ideal gas law (where the relationship was first demonstrated in 1857). The term "mole" was first used in a textbook describing these colligative properties. | 3 | Analytical Chemistry |
When calculating a thermal transmittance it is helpful to consider the building's construction in terms of its different layers. For instance a cavity wall might be described as in the following table:
In this example the total insulance is 1.64 K⋅m/W. The thermal transmittance of the structure is the reciprocal of the total thermal insulance. The thermal transmittance of this structure is therefore 0.61 W/(m⋅K).
(Note that this example is simplified as it does not take into account any metal connectors, air gaps interrupting the insulation or mortar joints between the bricks and concrete blocks.)
It is possible to allow for mortar joints in calculating the thermal transmittance of a wall, as in the following table. Since the mortar joints allow heat to pass more easily than the light concrete blocks, the mortar is said to "bridge" the light concrete blocks.
The average thermal insulance of the "bridged" layer depends upon the fraction of the area taken up by the mortar in comparison with the fraction of the area taken up by the light concrete blocks. To calculate thermal transmittance when there are "bridging" mortar joints it is necessary to calculate two quantities, known as R and R.
R can be thought of as the total thermal insulance obtained if it is assumed that there is no lateral flow of heat and R can be thought of as the total thermal insulance obtained if it is assumed that there is no resistance to the lateral flow of heat.
The U-value of the above construction is approximately equal to 2 / (R + R)
Further information about how to deal with "bridging" is given in ISO 6946. | 7 | Physical Chemistry |
When a substituent group is located ortho position to the carboxyl group in a substituted benzoic acid compound, the compound becomes more acidic surpassing the unmodified benzoic acid.
Generally ortho-substituted benzoic acids are stronger acids than their meta and para isomers. | 4 | Stereochemistry |
Translation is the process by which a mature mRNA molecule is used as a template for synthesizing a new protein. Translation is carried out by ribosomes, large complexes of RNA and protein responsible for carrying out the chemical reactions to add new amino acids to a growing polypeptide chain by the formation of peptide bonds. The genetic code is read three nucleotides at a time, in units called codons, via interactions with specialized RNA molecules called transfer RNA (tRNA). Each tRNA has three unpaired bases known as the anticodon that are complementary to the codon it reads on the mRNA. The tRNA is also covalently attached to the amino acid specified by the complementary codon. When the tRNA binds to its complementary codon in an mRNA strand, the ribosome attaches its amino acid cargo to the new polypeptide chain, which is synthesized from amino terminus to carboxyl terminus. During and after synthesis, most new proteins must fold to their active three-dimensional structure before they can carry out their cellular functions. | 1 | Biochemistry |
RNA-Binding Proteins (RBPs) are dynamic assemblages between mRNAs and different proteins that form messenger ribonucleoprotein complexes (mRNPs). These complexes are essential for the regulation of gene expression to ensure that all the steps are performed correctly throughout the whole process. Therefore, they are important control factors for protein levels and cell phenotypes. Moreover, they affect mRNA stability by regulating its conformation due to the environment, stress or extracellular signals. However, their ability to bind and control such a wide variety of RNA targets allows them to form complex regulatory networks (PTRNs).These networks represent a challenge to study each RNA-binding protein individually. Thankfully, due to new methodological advances, the identification of RBPs is slowly expanding, which demonstrates that they are contained in broad families of proteins. RBPs can significantly impact multiple biological processes, and have to be very accurately expressed. Overexpression can change the mRNA target rate, binding to low-affinity RNA sites and causing deleterious results on cellular fitness. Not being able to synthesize at the right level is also problematic because it can lead to cell death. Therefore, RBPs are regulated via auto-regulation, so they are in control of their own actions. Furthermore, they use both negative feedback, to maintain homeostasis, and positive feedback, to create binary genetic changes in the cell.
In metazoans and bacteria, many genes involved in post-post transcriptional regulation are regulated post transcriptionally. For Drosophila RBPs associated with splicing or nonsense mediated decay, analyses of protein-protein and protein-RNA interaction profiles have revealed ubiquitous interactions with RNA and protein products of the same gene. It remains unclear whether these observations are driven by ribosome proximal or ribosome mediated contacts, or if some protein complexes, particularly RNPs, undergo co-translational assembly. | 1 | Biochemistry |
The results showed that global warming potential and acidification potential were the most significant environmental impacts. On average producing a tonne of steel emits 1.8 tonnes of . However, a steel mill using a top gas recycling blast furnace (TGRBF) producing a tonne of steel will emit 0.8 to 1.3 tonnes of depending upon the recycle rate of the TGRBF. | 8 | Metallurgy |
Hot tin-dipping is the process of immersing a part into a bath of pure molten tin at a temperature greater than 450 °F or 232 °C.
Tinplate made via hot-dipped tin plating is made by cold rolling steel or iron, pickling to remove any scale, annealing to remove any strain hardening, and then coating it with a thin layer of tin. Originally this was done by producing individual or small packs of plates, which became known as the pack mill process. In the late 1920s strip mills began to replace pack mills, because they could produce the raw plates in larger quantities and more economically. | 8 | Metallurgy |
In environmental chemistry, the term "contamination" is in some cases virtually equivalent to pollution, where the main interest is the harm done on a large scale to humans, organisms, or environments. An environmental contaminant may be chemical in nature, though it may also be a biological (pathogenic bacteria, virus, invasive species) or physical (energy) agent. Environmental monitoring is one mechanism available to scientists to detect contamination activities early before they become too detrimental. | 9 | Geochemistry |
There are five main methodologies to create coordination cages. In directional bonding, also called edge-directed self-assembly, polyhedra are designed using a stoichiometric ratio of ligand to metal precursor. The symmetry interaction method involves combining naked metal ions with multibranched chelating ligands. This results in highly symmetric cages. The molecular paneling method, also called the face-directed method, was the method developed by Fujita.
Here, rigid ligands act as panels and coordination complexes join them together to create the shape. In the figure at left, the yellow triangles represent panel ligands, and the blue dots are metal complexes. The ligands of the complex itself helps enforce the final geometry.
In the weak link method, a hemilabile ligand is used: a weak metal-heteroatom bond is the weak link. The formation of the complexes is driven by favorable π-π interactions between the spacers and the ligands, as well as the chelation of the metal. The metals used in the assembly must be available to perform further in the final structure, without compromising the cage structure. The initial structure is referred to as condensed. In the condensed structure, the weak M-X bond can be selectively replaced by introducing an ancillary ligand with a higher binding affinity, leading to an open cage structure. In the figure to the right, the M is the metal, the orange ellipses are ligands, and the A is the ancillary ligand. For the dimetallic building block method, two pieces are needed: the metal dimer and its nonlinking ligands, and linking ligands. The nonlinking ligands need to be relatively nonlabile, and not too bulky; amidinates, for instance, work well. The linking ligands are either equatorial or axial: equatorial ligands are small polycarboxylato anions, and axial linkers are usually rigid aromatic structures. Axial and equatorial ligands may be used separately or in combination, depending on the desired cage structure. | 6 | Supramolecular Chemistry |
For the solvent isotope effects to be measurable, a finite fraction of the solvent must have a different isotopic composition than the rest. Therefore, large amounts of the less common isotopic species must be available, limiting observable solvent isotope effects to isotopic substitutions involving hydrogen. Detectable kinetic isotope effects occur only when solutes exchange hydrogen with the solvent or when there is a specific solute-solvent interaction near the reaction site. Both such phenomena are common for protic solvents, in which the hydrogen is exchangeable, and they may form dipole-dipole interactions or hydrogen bonds with polar molecules. | 7 | Physical Chemistry |
More recently, Evans presented a different model for nonchelate 1,3-inductions. In the proposed transition state, the β-stereocenter is oriented anti- to the incoming nucleophile, as seen in the Felkin–Anh model. The polar X group at the β-stereocenter is placed anti- to the carbonyl to reduce dipole interactions, and Rβ is placed anti- to the aldehyde group to minimize the steric hindrance. Consequently, the 1,3-anti-diol would be predicted as the major product. | 4 | Stereochemistry |
In 2002, Tang was awarded a Japan Society for the Promotion of Science (JSPS) search Fellowship and NIMS Researcher, enable to expand his research in photocatalysis in the National Institute for Materials Science (NIMS), Japan. In 2005, he was appointed as a senior research associate in the Department of Chemistry at Imperial College London, UK.
In 2009, Tang was appointed as a lecturer in energy (permanent position) in Department of Chemical Engineering at University College London, then promoted to a senior lecturer in 2011, a readership in 2014 and finally a full professor of materials chemistry and engineering in 2017. During this period, he was also appointed as the director of University Materials Hub. In 2022, Tang moved from UCL to Tsinghua University.
Tang is a member of the Academy of Europe / Academia Europaea, a Royal Society Leverhulme Trust Senior Research Fellow, a Fellow of European Academy of Sciences, a Fellow of Royal Society of Chemistry. He also sits on the editorial board of four international journals, e.g. editor of Applied Catalysis B : Environmental, editor-in-chief of Journal of Advanced Chemical Engineering, associate editor of Asia-Pacific Journal of Chemical Engineering and associate editor of Chin Journal of Catalysis, as well as a member of the committees of the RSC Chemical Nanoscience & Nanotechnology. He also sits on the panel of a few counties’ National Science Foundations. | 5 | Photochemistry |
Under a standard set of conditions, the melting point of a substance is a characteristic property. The melting point is often equal to the freezing point. However, under carefully created conditions, supercooling, or superheating past the melting or freezing point can occur. Water on a very clean glass surface will often supercool several degrees below the freezing point without freezing. Fine emulsions of pure water have been cooled to −38 °C without nucleation to form ice. Nucleation occurs due to fluctuations in the properties of the material. If the material is kept still there is often nothing (such as physical vibration) to trigger this change, and supercooling (or superheating) may occur. Thermodynamically, the supercooled liquid is in the metastable state with respect to the crystalline phase, and it is likely to crystallize suddenly. | 7 | Physical Chemistry |
The first Empowering Women in Organic Chemistry Conference took place on Friday, June 28, 2019, at the University of Pennsylvania, Philadelphia, PA.
2019 Career Panel featured Sarah Wengryniuk (Temple University), Emily McLaughlin (Bard College), Nikki Goodwin (GlaxoSmithKline), Jamie McCabe Dunn (Merck), Zhenzhen Dong (Adesis), Nicole Camasso (JACS). | 0 | Organic Chemistry |
A number of lines, generally 7-30, with interesting properties, such as yield or baking quality, are selected and all possible crosses of them are done. If many lines of different genetic background are used, a huge amount of genetic diversity will be present. | 1 | Biochemistry |
Activation of the ERK1/2 pathway by aberrant RAS/RAF signalling, DNA damage, and oxidative stress leads to cellular senescence. Low doses of DNA damage resulting from cancer therapy cause ERK1/2 to induce senescence, whereas higher doses of DNA damage fail to activate ERK1/2, and thus induce cell death by apoptosis. | 1 | Biochemistry |
The diamond cubic crystal structure occurs for example diamond (carbon), tin, and most semiconductors. There are 8 atoms in the cubic unit cell. We can consider the structure as a simple cubic with a basis of 8 atoms, at positions
But comparing this to the FCC above, we see that it is simpler to describe the structure as FCC with a basis of two atoms at (0, 0, 0) and (1/4, 1/4, 1/4). For this basis, Equation () becomes:
And then the structure factor for the diamond cubic structure is the product of this and the structure factor for FCC above, (only including the atomic form factor once)
with the result
* If h, k, ℓ are of mixed parity (odd and even values combined) the first (FCC) term is zero, so
* If h, k, ℓ are all even or all odd then the first (FCC) term is 4
** if h+k+ℓ is odd then
** if h+k+ℓ is even and exactly divisible by 4 () then
** if h+k+ℓ is even but not exactly divisible by 4 () the second term is zero and
These points are encapsulated by the following equations:
where is an integer. | 3 | Analytical Chemistry |
Although artificial pyroelectric materials have been engineered, the effect was first discovered in minerals such as tourmaline. The pyroelectric effect is also present in bone and tendon.
The most important example is gallium nitride, a semiconductor. The large electric fields in this material are detrimental in light emitting diodes (LEDs), but useful for the production of power transistors.
Progress has been made in creating artificial pyroelectric materials, usually in the form of a thin film, using gallium nitride (GaN), caesium nitrate (CsNO), polyvinyl fluorides, derivatives of phenylpyridine, and cobalt phthalocyanine. Lithium tantalate (LiTaO) is a crystal exhibiting both piezoelectric and pyroelectric properties, which has been used to create small-scale nuclear fusion ("pyroelectric fusion"). Recently, pyroelectric and piezoelectric properties have been discovered in doped hafnium oxide (HfO), which is a standard material in CMOS manufacturing. | 7 | Physical Chemistry |
The dynamics of the MPI can be described by finding the time evolution of the state of the atom which is described by the Schrödinger equation. The form of this equation in the electric field gauge, assuming the single active electron (SAE) approximation and using dipole approximation, is the following
where is the electric field of the laser and is the static Coulomb potential of the atomic core at the position of the active electron. By finding the exact solution of equation (1) for a potential ( the magnitude of the ionization potential of the atom), the probability current is calculated. Then, the total MPI rate from short-range potential for linear polarization, , is found from
where is the frequency of the laser, which is assumed to be polarized in the direction of the axis. The effect of the ionic potential, which behaves like ( is the charge of atomic or ionic core) at a long distance from the nucleus, is calculated through first order correction on the semiclassical action. The result is that the effect of ionic potential is to increase the rate of MPI by a factor of
Where and is the peak electric field of laser. Thus, the total rate of MPI from a state with quantum numbers and in a laser field for linear polarization is calculated to be
where is the Keldysh's adiabaticity parameter and . The coefficients , and are given by
The coefficient is given by
where
The ADK model is the limit of the PPT model when approaches zero (quasi-static limit). In this case, which is known as quasi-static tunnelling (QST), the ionization rate is given by
In practice, the limit for the QST regime is . This is justified by the following consideration. Referring to the figure, the ease or difficulty of tunneling can be expressed as the ratio between the equivalent classical time it takes for the electron to tunnel out the potential barrier while the potential is bent down. This ratio is indeed , since the potential is bent down during half a cycle of the field oscillation and the ratio can be expressed as
where is the tunneling time (classical time of flight of an electron through a potential barrier, and is the period of laser field oscillation. | 7 | Physical Chemistry |
Some subfields of geochemistry are:
*Aqueous geochemistry studies the role of various elements in watersheds, including copper, sulfur, mercury, and how elemental fluxes are exchanged through atmospheric-terrestrial-aquatic interactions.
*Biogeochemistry is the field of study focusing on the effect of life on the chemistry of the Earth.
*Cosmochemistry includes the analysis of the distribution of elements and their isotopes in the cosmos.
*Isotope geochemistry involves the determination of the relative and absolute concentrations of the elements and their isotopes in the Earth and on Earth's surface.
*Organic geochemistry, the study of the role of processes and compounds that are derived from living or once-living organisms.
*Photogeochemistry is the study of light-induced chemical reactions that occur or may occur among natural components of the Earth's surface.
*Regional geochemistry includes applications to environmental, hydrological and mineral exploration studies. | 9 | Geochemistry |
There are three stages in the post-Soviet history of Ural metallurgy:
* 1991-1994 - adaptation to market conditions, search for sources of raw materials and sales markets, accumulation of working capital.
* 1994-2003 - formation of vertically integrated companies and their development.
* since 2003 - modernization of enterprises within vertically integrated companies.
Restructuring and the transition to market conditions led to a 2-fold reduction in production at the Ural metallurgical enterprises. The Nizhniy Tagil and Orsko-Khalilovsky plants went bankrupt. Some enterprises went through bankruptcy proceedings several times. The privatization and corporatization of the enterprises of the Ural metallurgy were completed in 1992-1994. In the late 1990s - early 2000s, vertically integrated structures began to form around large enterprises, including all stages of a closed technological cycle. In addition to the Magnitogorsk Metallurgical Combine, the MMK Group includes: the Magnitogorsk Hardware, Metallurgical, and Calibration Plants; the Mechel group united the Chelyabinsk Metallurgical Plant, Yuzhuralnickel, Beloretsk Metallurgical Plant, Izhstal, and Korshunovsky Mining and Processing Plant; NTMK and Kachkanarsky Mining and Processing Plant, together with the West Siberian and Kuznetsk metallurgical plants, entered Evraz-holding; Chelyabinsk Pipe Rolling Plant and Pervouralsk Novotrubny Plants were merged into the ChTPZ Group; copper smelters became part of UMMC and Russian Copper Company; aluminum - Rusal and SUAL, united in 2007.
The main directions of development of ferrous metallurgy in the Urals in the market conditions were the reconstruction of blast furnaces with optimization of the profile and process control systems, the replacement of open-hearth furnaces with oxygen converters and electric furnaces, the widespread introduction of out-of-furnace steel processing, evacuation of steel before casting, as well as an increase in the share of continuous casting of steel. From 1985 to 2000, the share of the Ural steel smelted by the open-hearth method decreased from 78.2% to 46.9%; the share of converter steel in the same period increased from 15% to 46.9%, the share of continuously cast steel - from 1.2% to 33.1%. The share of electric steel in the same period remained at the level of about 6-7%.
After the reconstruction and launch of new capacities, about 85% of the Ural steel was produced at the 4 largest metallurgical plants: MMK (39.1% of the total steel volume in 2006), NTMK (17.6%), Mechel (15.2% ), and Ural steel (11.4%).
In the late 20th - early 21st century, the Ural metallurgical plants are developing taking into account the interests of holding structures. The main directions of development are the automation of production and the minimization of costs. Key investment development projects are the reconstruction of the converter shop and the construction of a pulverized coal injection unit at NTMK in 2010-2012, the launch in 2010 of the "Vysota 239" large-diameter pipe production shop at ChTPZ, as well as the launch in 2009 of Mill-5000 at MMK, which supplies workpieces including for the new ChelPipe workshop. By 2014, the share of Ural steel processed by the out-of-furnace method and poured at the continuous casting machine was brought to 100%.
In 2008, the Ural plants produced 43.1% of all-Russian pig iron, 43.4% of steel, 43.4% of rolled products, 46.4% of pipes, 47.9% of hardware, 72.8% of ferroalloys, about 80% of bauxite, 60% of alumina, 36% of refined copper, 100% of titanium and magnesium alloys, 64% of zinc, 15% of lead, and 8% of aluminum. The largest contribution to the metallurgy of the region is made by enterprises of the Chelyabinsk and Sverdlovsk Oblasts. As of 2013, the contribution of the Ural enterprises was estimated at 38% of steel and rolled products and about 50% of steel pipes. | 8 | Metallurgy |
A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. After invading a host cells cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, the reverse of the usual pattern, thus retro (backwards). The new DNA is then incorporated into the host cell genome by an integrase enzyme, at which point the retroviral DNA is referred to as a provirus. The host cell then treats the viral DNA as part of its own genome, transcribing and translating the viral genes along with the cells own genes, producing the proteins required to assemble new copies of the virus. Many retroviruses cause serious diseases in humans, other mammals, and birds.
Retroviruses have many subfamilies in three basic groups.
* Oncoretroviruses (cancer-causing retroviruses) include human T-lymphotropic virus (HTLV) causing a type of leukemia in humans, and murine leukemia viruses (MLVs) in mice.
* Lentiviruses (slow viruses) include HIV-1 and HIV-2, the cause of acquired immune deficiency syndrome (AIDS) in humans.
* Spumaviruses (foamy viruses) are benign and not linked to any disease in humans or animals.
The specialized DNA-infiltration enzymes in retroviruses make them valuable research tools in molecular biology, and they have been used successfully in gene delivery systems.
Evidence from endogenous retroviruses (inherited provirus DNA in animal genomes) suggests that retroviruses have been infecting vertebrates for at least 450 million years. | 1 | Biochemistry |
With hard water, soap solutions form a white precipitate (soap scum) instead of producing lather, because the 2+ ions destroy the surfactant properties of the soap by forming a solid precipitate (the soap scum). A major component of such scum is calcium stearate, which arises from sodium stearate, the main component of soap:
:2 CHCOO (aq) + Ca (aq) → (CHCOO)Ca (s)
Hardness can thus be defined as the soap-consuming capacity of a water sample, or the capacity of precipitation of soap as a characteristic property of water that prevents the lathering of soap. Synthetic detergents do not form such scums.
Because soft water has few calcium ions, there is no inhibition of the lathering action of soaps and no soap scum is formed in normal washing. Similarly, soft water produces no calcium deposits in water heating systems.
Hard water also forms deposits that clog plumbing. These deposits, called "scale", are composed mainly of calcium carbonate (CaCO), magnesium hydroxide (Mg(OH)), and calcium sulfate (CaSO). Calcium and magnesium carbonates tend to be deposited as off-white solids on the inside surfaces of pipes and heat exchangers. This precipitation (formation of an insoluble solid) is principally caused by thermal decomposition of bicarbonate ions but also happens in cases where the carbonate ion is at saturation concentration. The resulting build-up of scale restricts the flow of water in pipes. In boilers, the deposits impair the flow of heat into water, reducing the heating efficiency and allowing the metal boiler components to overheat. In a pressurized system, this overheating can lead to the failure of the boiler. The damage caused by calcium carbonate deposits varies on the crystalline form, for example, calcite or aragonite.
The presence of ions in an electrolyte, in this case, hard water, can also lead to galvanic corrosion, in which one metal will preferentially corrode when in contact with another type of metal when both are in contact with an electrolyte. The softening of hard water by ion exchange does not increase its corrosivity per se. Similarly, where lead plumbing is in use, softened water does not substantially increase plumbo-solvency.
In swimming pools, hard water is manifested by a turbid, or cloudy (milky), appearance to the water. Calcium and magnesium hydroxides are both soluble in water. The solubility of the hydroxides of the alkaline-earth metals to which calcium and magnesium belong (group 2 of the periodic table) increases moving down the column. Aqueous solutions of these metal hydroxides absorb carbon dioxide from the air, forming insoluble carbonates, and giving rise to turbidity. This often results from the pH being excessively high (pH > 7.6). Hence, a common solution to the problem is, while maintaining the chlorine concentration at the proper level, to lower the pH by the addition of hydrochloric acid, the optimum value is in the range of 7.2 to 7.6. | 3 | Analytical Chemistry |
As a "non-contact" process, the effect differs from traditional electrochemical processes where carrier flow through the surface is achieved by connection to a current source with highly conductive materials such as copper wire. It is well known that materials contacted to an anode can be modified in a variety of ways including anodizing and electropolishing. Electrochemistry was quickly recognized as an important related field in the popular press once the first synthetic diamonds were made. However, the use of an induced field created by remote electrodes allows discontinuous areas on an insulating substrate to be cleaned, modified, or etched (similar to electroetching), greatly expanding the role of electrochemical methods.
The mechanism is presumed to be due to the induced field but little in the way of exhaustive analysis has been done, as the actual processes do not appear to differ from traditional approaches. For example, "identified as the ‘Marchywka Effect’ in the literature. The etching may be due to the galvanic coupling of diamond and non-diamond carbon". The applied field apparently creates directed surface modifications on polished diamond surfaces with little or no actual removal of material. This may be desirable for making various devices, or simply studying the properties of the diamond surface. The induced field deposits or replaces a single layer of some molecule and this could be thought of as a monolayer electroplating method. It has been elucidated in more fully in many works. | 7 | Physical Chemistry |
Micro-incineration or microincineration is a technique to determine the manner and distribution of mineral elements in biological cells, biological tissues and organs. Slide preparation of tissues can be used. Examples include calcium (Ca), potassium (K), sodium (Na), magnesium (Mg), iron (Fe), and silicon (Si).
The organic matter is vaporised by heating. The nature and position of the mineral ash is determined microscopically. Aqueous or cryo-EM fixed tissue materials can also be examined under transmission and scanning electron microscopy (TEM & SEM).
The ashing procedure produces cellular oxidised-residues rich in NaO, CaO, MgO, FeO, SiO, Ca(PO), Mg(PO), etc., which are detected by X-ray microanalysis with 2-4 times sensitivity gained after incineration of sample, due to increased mineral concentration and reduced nonspecific background radiation. | 1 | Biochemistry |
Corrosion monitoring is the use of a corrator (corrosion meter) or set of methods and equipment to provide offline or online information about corrosion rate expressed in mpy (mill per year). - for better care and to take or improve preventive measures to combat and protect against corrosion. In this article, the difference between corrosion monitoring and corrosion protection, its difference with corrosion inspection and also the relationship between them, as well as online corrosion monitoring methods, equipment used and applications of each of them, are presented. | 8 | Metallurgy |
Alkali metal nitrates are relatively low melting and thermally stable. The least stable, lithium nitrate| (m.p. 255 °C) decomposes only at 474 °C. At the other extreme, cesium nitrate melts at 414 °C and decomposes at 584 °C.
*60:40 mixture of sodium nitrate and potassium nitrate is a liquid between 260-550 °C. It has a heat of fusion of 161 J/g, and a heat capacity of 1.53 J/(g·K).
*1:1 mixture :, m.p. 125 °C.
*40:7:53 ::, m. p. 142 °C, stable to 600 °C. | 8 | Metallurgy |
Photosensitizers have existed within natural systems for as long as chlorophyll and other light sensitive molecules have been a part of plant life, but studies of photosensitizers began as early as the 1900s, where scientists observed photosensitization in biological substrates and in the treatment of cancer. Mechanistic studies related to photosensitizers began with scientists analyzing the results of chemical reactions where photosensitizers photo-oxidized molecular oxygen into peroxide species. The results were understood by calculating quantum efficiencies and fluorescent yields at varying wavelengths of light and comparing these results with the yield of reactive oxygen species. However, it was not until the 1960s that the electron donating mechanism was confirmed through various spectroscopic methods including reaction-intermediate studies and luminescence studies.
The term photosensitizer does not appear in scientific literature until the 1960s. Instead, scientists would refer to photosensitizers as sensitizers used in photo-oxidation or photo-oxygenation processes. Studies during this time period involving photosensitizers utilized organic photosensitizers, consisting of aromatic hydrocarbon molecules, which could facilitate synthetic chemistry reactions. However, by the 1970s and 1980s, photosensitizers gained attraction in the scientific community for their role within biologic processes and enzymatic processes. Currently, photosensitizers are studied for their contributions to fields such as energy harvesting, photoredox catalysis in synthetic chemistry, and cancer treatment. | 5 | Photochemistry |
CPT requires specialized chimeric probes, making CPT assays more expensive than PCR. Because CPT probes are so specific, a new probe must be designed for each unique assay, further increasing cost. Clinical implementation is hampered financially, but it is also limited by the possibility of samples containing nonspecific RNases other than RNase H. | 1 | Biochemistry |
Not all amino acid replacements have the same effect on function or structure of protein. The magnitude of this process may vary depending on how similar or dissimilar the replaced amino acids are, as well as on their position in the sequence or the structure. Similarity between amino acids can be calculated based on substitution matrices, physico-chemical distance, or simple properties such as amino acid size or charge (see also amino acid chemical properties). Usually amino acids are thus classified into two types:
* Conservative replacement - an amino acid is exchanged into another that has similar properties. This type of replacement is expected to rarely result in dysfunction in the corresponding protein .
* Radical replacement - an amino acid is exchanged into another with different properties. This can lead to changes in protein structure or function, which can cause potentially lead to changes in phenotype, sometimes pathogenic. A well known example in humans is sickle cell anemia, due to a mutation in beta globin where at position 6 glutamic acid (negatively charged) is exchanged with valine (not charged). | 1 | Biochemistry |
), gives a system of four non-linear ordinary differential equations that define the rate of change of reactants with time
In this mechanism, the enzyme E is a catalyst, which only facilitates the reaction, so that its total concentration, free plus combined, is a constant (i.e. ). This conservation law can also be observed by adding the first and third equations above.--> | 7 | Physical Chemistry |
*5.A.1 The Disulfide Bond Oxidoreductase D (DsbD) Family
*5.A.2 The Disulfide Bond Oxidoreductase B (DsbB) Family
*5.A.3 The Prokaryotic Molybdopterin-containing Oxidoreductase (PMO) Family | 1 | Biochemistry |
There has been controversy over energy-balance messages that downplay energy intake being promoted by food industry groups. | 1 | Biochemistry |
Proteins are functional macromolecules responsible for catalysing the biochemical reactions that sustain life. Proteins carry out all functions of an organism, for example photosynthesis, neural function, vision, and movement.
The single-stranded nature of protein molecules, together with their composition of 20 or more different amino acid building blocks, allows them to fold in to a vast number of different three-dimensional shapes, while providing binding pockets through which they can specifically interact with all manner of molecules. In addition, the chemical diversity of the different amino acids, together with different chemical environments afforded by local 3D structure, enables many proteins to act as enzymes, catalyzing a wide range of specific biochemical transformations within cells. In addition, proteins have evolved the ability to bind a wide range of cofactors and coenzymes, smaller molecules that can endow the protein with specific activities beyond those associated with the polypeptide chain alone. | 7 | Physical Chemistry |
In the recent past the problem of removing the deleterious iron particles from a process stream had a few alternatives. Magnetic separation was typically limited and moderately effective. Magnetic separators that used permanent magnets could generate fields of low intensity only. These worked well in removing ferrous tramp but not fine paramagnetic particles. Thus high-intensity magnetic separators that were effective in collecting paramagnetic particles came into existence. These focus on the separation of very fine particles that are paramagnetic.
The current is passed through the coil, which creates a magnetic field, which magnetizes the expanded steel matrix ring. The paramagnetic matrix material behaves like a magnet in the magnetic field and thereby attracts the fines. The ring is rinsed when it is in the magnetic field and all the non-magnetic particles are carried with the rinse water. Next as the ring leaves the magnetic zone the ring is flushed and a vacuum of about – 0.3 bars is applied to remove the magnetic particles attached to the matrix ring. | 3 | Analytical Chemistry |
Pathogenic bacteria and fungi have developed the means of survival in animal tissue. They may invade the gastro-intestinal tract (Escherichia, Shigella and Salmonella), the lung (Pseudomonas, Bordetella, Streptococcus and Corynebacterium), skin (Staphylococcus) or the urinary tract (Escherichia and Pseudomonas). Such bacteria may colonise wounds (Vibrio and Staphylococcus) and be responsible for septicaemia (Yersinia and Bacillus). Some bacteria survive for long periods of time in intracellular organelles, for instance Mycobacterium. (see table). Because of this continual risk of bacterial and fungal invasion, animals have developed a number of lines of defence based on immunological strategies, the complement system, the production of iron–siderophore binding proteins and the general "withdrawal" of iron.
There are two major types of iron-binding proteins present in most animals that provide protection against microbial invasion – extracellular protection is achieved by the transferrin family of proteins and intracellular protection is achieved by ferritin. Transferrin is present in the serum at approximately 30 μM, and contains two iron-binding sites, each with an extremely high affinity for iron. Under normal conditions it is about 25–40% saturated, which means that any freely available iron in the serum will be immediately scavenged – thus preventing microbial growth. Most siderophores are unable to remove iron from transferrin. Mammals also produce lactoferrin, which is similar to serum transferrin but possesses an even higher affinity for iron. Lactoferrin is present in secretory fluids, such as sweat, tears and milk, thereby minimising bacterial infection.
Ferritin is present in the cytoplasm of cells and limits the intracellular iron level to approximately 1 μM. Ferritin is a much larger protein than transferrin and is capable of binding several thousand iron atoms in a nontoxic form. Siderophores are unable to directly mobilise iron from ferritin.
In addition to these two classes of iron-binding proteins, a hormone, hepcidin, is involved in controlling the release of iron from absorptive enterocytes, iron-storing hepatocytes and macrophages. Infection leads to inflammation and the release of interleukin-6 (IL-6 ) which stimulates hepcidin expression. In humans, IL-6 production results in low serum iron, making it difficult for invading pathogens to infect. Such iron depletion has been demonstrated to limit bacterial growth in both extracellular and intracellular locations.
In addition to "iron withdrawal" tactics, mammals produce an iron –siderophore binding protein, siderochelin. Siderochelin is a member of the lipocalin family of proteins, which while diverse in sequence, displays a highly conserved structural fold, an 8-stranded antiparallel β-barrel that forms a binding site with several adjacent β-strands. Siderocalin (lipocalin 2) has 3 positively charged residues also located in the hydrophobic pocket, and these create a high affinity binding site for iron(III)–enterobactin. Siderocalin is a potent bacteriostatic agent against E. coli. As a result of infection it is secreted by both macrophages and hepatocytes, enterobactin being scavenged from the extracellular space. | 1 | Biochemistry |
In theoretical physics, the electroweak model breaks parity maximally. All its fermions are chiral Weyl fermions, which means that the charged weak gauge bosons W and W only couple to left-handed quarks and leptons.
Some theorists found this objectionable, and so conjectured a GUT extension of the weak force which has new, high energy W′ and Z′ bosons, which do couple with right handed quarks and leptons:
to
Here, (pronounced " left") is from above, while is the baryon number minus the lepton number. The electric charge formula in this model is given by
where and are the left and right weak isospin values of the fields in the theory.
There is also the chromodynamic . The idea was to restore parity by introducing a left-right symmetry. This is a group extension of (the left-right symmetry) by
to the semidirect product
This has two connected components where acts as an automorphism, which is the composition of an involutive outer automorphism of with the interchange of the left and right copies of with the reversal of . It was shown by Mohapatra & Senjanovic (1975) that left-right symmetry can be spontaneously broken to give a chiral low energy theory, which is the Standard Model of Glashow, Weinberg, and Salam, and also connects the small observed neutrino masses to the breaking of left-right symmetry via the seesaw mechanism.
In this setting, the chiral quarks
and
are unified into an irreducible representation ("irrep")
The leptons are also unified into an irreducible representation
The Higgs bosons needed to implement the breaking of left-right symmetry down to the Standard Model are
This then provides three sterile neutrinos which are perfectly consistent with neutrino oscillation data. Within the seesaw mechanism, the sterile neutrinos become superheavy without affecting physics at low energies.
Because the left–right symmetry is spontaneously broken, left–right models predict domain walls. This left-right symmetry idea first appeared in the Pati–Salam model (1974) and Mohapatra–Pati models (1975). | 4 | Stereochemistry |
Under the molecular orbital formalism, a typical ground-state molecule has electrons in the lowest possible energy levels. According to the Pauli principle, at most two electrons can occupy a given orbital, and if an orbital contains two electrons they must be in opposite spin states. The highest occupied molecular orbital is called the HOMO and the lowest unoccupied molecular orbital is called the LUMO; the energy gap between these two states is known as the HOMO–LUMO gap. If the molecule absorbs light whose energy is equal to this gap, an electron in the HOMO may be excited to the LUMO. This is called the molecule's excited state.
Excimers are only formed when one of the dimer components is in the excited state. When the excimer returns to the ground state, its components dissociate and often repel each other. The wavelength of an excimers emission is longer (smaller energy) than that of the excited monomers emission. An excimer can thus be measured by fluorescent emissions.
Because excimer formation is dependent on a bimolecular interaction, it is promoted by high monomer density. Low-density conditions produce excited monomers that decay to the ground state before they interact with an unexcited monomer to form an excimer. | 5 | Photochemistry |
*Erosion corrosion
*Pitting corrosion Oxygen pitting
*Hydrogen embrittlement
*Hydrogen-induced cracking (ASM term)
*Corrosion embrittlement (ASM term)
*Hydrogen disintegration (NACE term)
*Hydrogen-assisted cracking (ASM term)
*Hydrogen blistering
*Corrosion | 8 | Metallurgy |
In the case of concrete, curing entails the formation of silicate crosslinks. The process is not induced by additives.
In many cases, the resin is provided as a solution or mixture with a thermally-activated catalyst, which induces crosslinking but only upon heating. For example, some acrylate-based resins are formulated with dibenzoyl peroxide. Upon heating the mixture, the peroxide converts to a free radical, which adds to an acrylate, initiating crosslinking.
Some organic resins are cured with heat. As heat is applied, the viscosity of the resin drops before the onset of crosslinking, whereupon it increases as the constituent oligomers interconnect. This process continues until a tridimensional network of oligomer chains is created – this stage is termed gelation. In terms of processability of the resin this marks an important stage: before gelation the system is relatively mobile, after it the mobility is very limited, the micro-structure of the resin and the composite material is fixed and severe diffusion limitations to further cure are created. Thus, in order to achieve vitrification in the resin, it is usually necessary to increase the process temperature after gelation.
When catalysts are activated by ultraviolet radiation, the process is called UV cure. | 7 | Physical Chemistry |
Epoxy and modified epoxy are standard coatings used to provide protective barriers to corrosion in ballast tanks. Exposed, unprotected steel will corrode much more rapidly than steel covered with this protective layer. Many ships also use sacrificial anodes or an impressed current for additional protection. Empty ballast tanks will corrode faster than areas fully immersed due to the thin - and electo conducting - moisture film covering them.
The main factors influencing the rate of corrosion are diffusion, temperature, Conductivity, type of ions, pH, and
electrochemical corrosion potential. | 8 | Metallurgy |
Retinitis pigmentosa is an inherited disease which leads to progressive night blindness and loss of peripheral vision as a result of photoreceptor cell death. Most people who suffer from RP are born with rod cells that are either dead or dysfunctional, so they are effectively blind at nighttime, since these are the cells responsible for vision in low levels of light. What follows often is the death of cone cells, responsible for color vision and acuity, at light levels present during the day. Loss of cones leads to full blindness as early as five years old, but may not onset until many years later. There have been multiple hypotheses about how the lack of rod cells can lead to the death of cone cells. Pinpointing a mechanism for RP is difficult because there are more than 39 genetic loci and genes correlated with this disease. In an effort to find the cause of RP, there have been different gene therapy techniques applied to address each of the hypotheses.
Different types of inheritance can attribute to this disease; autosomal recessive, autosomal dominant, X-linked type, etc. The main function of rhodopsin is initiating the phototransduction cascade. The opsin proteins are made in the photoreceptor inner segments, then transported to the outer segment, and eventually phagocytized by the RPE cells. When mutations occur in the rhodopsin the directional protein movement is affected because the mutations can affect protein folding, stability, and intracellular trafficking. One approach is introducing AAV-delivered ribozymes designed to target and destroy a mutant mRNA.
The way this system operates was shown in animal model that have a mutant rhodopsin gene. The injected AAV-ribozymes were optimized in vitro and used to cleave the mutant mRNA transcript of P23H (where most mutation occur) in vivo.
Another mutation in the rhodopsin structural protein, specifically peripherin 2 which is a membrane glycoprotein involved in the formation of photoreceptor outersegment disk, can lead to recessive RP and macular degeneration in human (19). In a mouse experiment, AAV2 carrying a wild-type peripherin 2 gene driven by a rhodopsin promoter was delivered to the mice by subretinal injection. The result showed improvement in photoreceptor structure and function which was detected by ERG (electroretinogram). The result showed improvement of photoreceptor structure and function which was detected by ERG. Also peripherin 2 was detected at the outer segment layer of the retina 2 weeks after injection and therapeutic effects were noted as soon as 3 weeks after injection. A well-defined outer segment containing both peripherin2 and rhodopsin was present 9-month after injection.
Since apoptosis can be the cause of photoreceptor death in most of the retinal dystrophies. It has been known that survival factors and antiapoptoic reagents can be an alternative treatment if the mutation is unknown for gene replacement therapy. Some scientists have experimented with treating this issue by injecting substitute trophic factors into the eye. One group of researchers injected the rod derived cone viability factor (RdCVF) protein (encoded for by the Nxnl1 (Txnl6) gene) into the eye of the most commonly occurring dominant RP mutation rat models. This treatment demonstrated success in promoting the survival of cone activity, but the treatment served even more significantly to prevent progression of the disease by increasing the actual function of the cones. Experiments were also carried out to study whether supplying AAV2 vectors with cDNA for glial cell line-derived neurotrophic factor (GDNF) can have an anti-apoptosis effect on the rod cells.
In looking at an animal model, the opsin transgene contains a truncated protein lacking the last 15 amino acids of the C terminus, which causes alteration in rhodopsin transport to the outer segment and leads to retinal degeneration. When the AAV2-CBA-GDNF vector is administered to the subretinal space, photoreceptor stabilized and rod photoreceptors increased and this was seen in the improved function of the ERG analysis. Successful experiments in animals have also been carried out using ciliary neurotrophic factor (CNTF), and CNTF is currently being used as a treatment in human clinical trials. | 1 | Biochemistry |
The Born series is the expansion of different scattering quantities in quantum scattering theory in the powers of the interaction potential (more precisely in powers of where is the free particle Green's operator). It is closely related to Born approximation, which is the first order term of the Born series. The series can formally be understood as power series introducing the coupling constant by substitution . The speed of convergence and radius of convergence of the Born series are related to eigenvalues of the operator . In general the first few terms of the Born series are good approximation to the expanded quantity for "weak" interaction
and large collision energy. | 7 | Physical Chemistry |
The typical workflow of metabolomics studies is shown in the figure. First, samples are collected from tissue, plasma, urine, saliva, cells, etc. Next, metabolites extracted often with the addition of internal standards and derivatization. During sample analysis, metabolites are quantified (liquid chromatography or gas chromatography coupled with MS and/or NMR spectroscopy). The raw output data can be used for metabolite feature extraction and further processed before statistical analysis (such as principal component analysis, PCA). Many bioinformatic tools and software are available to identify associations with disease states and outcomes, determine significant correlations, and characterize metabolic signatures with existing biological knowledge. | 1 | Biochemistry |
Le Bail analysis fits parameters using a steepest descent minimization process. Specifically, the method is least squares analysis, which is an iterative process that is discussed later in this article. The parameters being fitted include the unit-cell parameters, the instrumental zero error, peak width parameters, and peak shape parameters. First, the Le Bail method defines an arbitrary starting value for the intensities (I). This value is ordinarily set to one, but other values may be used. While peak positions are constrained by the unit cell parameters, intensities are unconstrained. The equation to calculate intensities is:
In the equation, I is the intensity observed at a particular step and y(obs) is the observed profile point. y(calc) is the A single intensity value may contain more than one peak. Other peaks may be calculated similarly. The final intensity for a peak is calculated as y(calc) = y(1) + y(2). The summation is carried out over all contributing profile points for a particular 2-theta bin. The summation process is known as profile intensity partitioning, and it works over any number of peaks. Le Bail technique works especially well with overlapping intensities since in this method the intensity is allotted based on the multiplicity of the intensities that contribute to a particular peak.
The somewhat arbitrary choice of starting values produces a bias in the calculated values. The refinement process continues by setting the new calculated structure factor to the observed structure factor value. The process is then repeated with the new structure factor estimate. At this point, the unit cell, background, peak widths, peak shape, and resolution function are refined, and the parameters are improved. The structure factor is then reset to the new structure factor value, and the process begins again. Structural refinement can continue with whole profile fitting techniques or further treatment of peak overlap. Probabilistic approaches may also be used to treat peak overlap. | 3 | Analytical Chemistry |
A chiral auxiliary is an organic compound which couples to the starting material to form a new compound which can then undergo diastereoselective reactions via intramolecular asymmetric induction. At the end of the reaction the auxiliary is removed, under conditions that will not cause racemization of the product. It is typically then recovered for future use.
Chiral auxiliaries must be used in stoichiometric amounts to be effective and require additional synthetic steps to append and remove the auxiliary. However, in some cases the only available stereoselective methodology relies on chiral auxiliaries and these reactions tend to be versatile and very well-studied, allowing the most time-efficient access to enantiomerically pure products. Additionally, the products of auxiliary-directed reactions are diastereomers, which enables their facile separation by methods such as column chromatography or crystallization. | 4 | Stereochemistry |
A few advantages of ATM over other related microspectroscopy techniques include the orientation of the THz electric field at the sample and the ability to readily measure materials that are sensitive to environmental conditions like hydration, cryo-cooling, and evacuation. | 7 | Physical Chemistry |
High-Mobility Group or HMG is a group of chromosomal proteins that are involved in the regulation of DNA-dependent processes such as
transcription, replication, recombination, and DNA repair. | 1 | Biochemistry |
*1979 Can Test Award by the Chemical Institute of Canada
*1983 Science & Engineering Research Council Senior Fellowship
*1983 Co-recipient of an IR-100 Award
*1984 Meggers Award by the Society for Applied Spectroscopy
*1984 Lester W. Strock Award by the Society for Applied Spectroscopy
*1984 Anachem Award
*1985 Chemical Instrumentation Award by the American Chemical Society
*1986 Pittsburgh Analytical Chemistry Award from the Royal Society of Chemistry
*1986 Theophilus Redwood Award from the Royal Society of Chemistry
*1987 American Chemical Society Award in Analytical Chemistry
*1987 Tracy M. Sonneborn Teacher-Scholar Award from Indiana University
*1987 Elected to Fellowship in the American Association for the Advancement of Science
*1988 R&D 100 Award by Research & Development Magazine
*1989 ACS Award in Spectrochemical Analysis from the Analytical Chemistry Division of the American Chemical Society
*1989 Indiana Academy of Science, Fellow
*1991 Received the Gold Medal of the Quality Control Academy of the Upjohn Company
*1991 Pergamon/Spectrochimica Acta Atomic Spectroscopy Award
*1992 Eastern Analytical Symposium Award for Outstanding Achievements in the Fields of Analytical Chemistry
*1992 Awarded a second Lester W. Strock Award
*1993 Distinguished Faculty Award from the College of Arts and Sciences alumni of Indiana University
*1993 Golden Key National Honor Society, Honorary Member
*1995 Honorary Professor of Jilin University, Jilin, China
*1996 Humboldt Research Award for Senior U.S. Scientists
*1996 Meggers Award from the Society for Applied Spectroscopy
*1998 ACS-Analytical Division Award for Excellence in Teaching
*1999 Awarded Honorary Membership in the Society for Applied Spectroscopy
*1999-00 Director of the Linda and Jack Gill Center for Instrumentation and Measurement Science at Indiana University
*2000 Appointed to the Robert and Marjorie Mann Chair of Chemistry
*2000-01 Indiana Academy of Science Speaker of the Year
*2001 Pittsburgh Spectroscopy Award
*2002 Trustees Teaching Award at Indiana University
*2004 New York Section of the Society for Applied Spectroscopy Gold Medal Award
*2004 Monie A. Ferst Award (Sigma Xi)
*2004 Society for Applied Spectroscopy, Fellow
*2005 Royal Society of Chemistry, Fellow
*2007 CSI XXXV Award, sponsored by Wiley
*2009 Maurice Hasler Award
*2010 USP Award for an Outstanding Contribution to the Standard-Setting Process
*2010 Robert Boyle Prize for Analytical Science
*2011 American Chemical Society (ACS) Fellow
*2011 R&D 100 Award by Research and Development Magazine
*2012 Distinguished Service Award by the American Chemical Society-Analytical Division
*2012 Ralph and Helen Oesper Award by the University of Cincinnati
*2020 Bicentennial Medal | 3 | Analytical Chemistry |
This is the most common use for galvanized metal, and hundreds of thousands of tons of steel products are galvanized annually worldwide. In developed countries most larger cities have several galvanizing factories, and many items of steel manufacture are galvanized for protection. Typically these include: street furniture, building frameworks, balconies, verandahs, staircases, ladders, walkways, and more. Hot dip galvanized steel is also used for making steel frames as a basic construction material for steel frame buildings. | 8 | Metallurgy |
R-410A was invented and patented by Allied Signal (now Honeywell) in 1991. Other producers around the world have been licensed to manufacture and sell R-410A, but Honeywell continues to be the leader in capacity and sales. R-410A was successfully commercialized in the air conditioning segment by a combined effort of Carrier Corporation, Emerson Climate Technologies, Inc., Copeland Scroll Compressors (a division of Emerson Electric Company), and Allied Signal. Carrier Corporation was the first company to introduce an R-410A-based residential air conditioning unit into the market in 1996 and holds the trademark "Puron". | 2 | Environmental Chemistry |
ADP-ribosylation can affect gene expression at nearly every level of regulation, including chromatin organization, transcription factor recruitment and binding, and mRNA processing.
The organization of nucleosomes is key to regulation of gene expression: the spacing and organization of nucleosomes changes what regions of DNA are available for transcription machinery to bind and transcribe DNA. PARP1, a poly-ADP ribose polymerase, has been shown to affect chromatin structure and promote changes in the organization of nucleosomes through modification of histones.
PARPs have been shown to affect transcription factor structure and cause recruitment of many transcription factors to form complexes at DNA and elicit transcription. Mono(ADP-ribosyl)transferases are also shown to affect transcription factor binding at promoters. For example, PARP14, a mono (ADP-ribosyl)transferase, has been shown to affect STAT transcription factor binding.
Other (ADP-ribosyl)transferases have been shown to modify proteins that bind mRNA, which can cause silencing of that gene transcript. | 1 | Biochemistry |
Strange matter (or strange quark matter) is quark matter containing strange quarks. In extreme environments, strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtometers (strangelets) to kilometers, as in the hypothetical strange stars. At high enough density, strange matter is expected to be color superconducting.
Ordinary matter, also referred to as atomic matter, is composed of atoms, with nearly all matter concentrated in the atomic nuclei. Nuclear matter is a liquid composed of neutrons and protons, and they are themselves composed of up and down quarks. Quark matter is a condensed form of matter composed entirely of quarks. When quark matter does not contain strange quarks, it is sometimes referred to as non-strange quark matter. | 7 | Physical Chemistry |
Particular disadvantages of the powder technology include:
# 100% sintered (iron ore) cannot be charged in the blast furnace
# sintering cannot create uniform sizes
# micro- and nanostructures produced before sintering are often destroyed. | 8 | Metallurgy |
Digital genetic sequences may be analyzed using the tools of bioinformatics to attempt to determine its function. | 1 | Biochemistry |
His academic career began in 1948 with a teaching position at Iowa State College; he served as Assistant Professor of Chemistry. In his capacity there he published his eponymous postulate which is now widely known as the most important publication in the field of organic photochemistry. He moved to the University of Oxford and University of Basel as a Guggenheim Fellow and National Science Foundation Fellow, respectively. In 1958, he moved to the California Institute of Technology as a Professor of Organic Chemistry. Later he was appointed the Arthur Amos Noyes Professor of Chemistry and subsequently went on to lead the Departments of Chemistry and Chemical Engineering. After 14 years teaching and serving as an academic administrator at Caltech he moved in 1972 to the University of California Santa Cruz. At University of California Santa Cruz he served as both a professor and the Chancellor of the natural sciences. | 7 | Physical Chemistry |
There are two main classes of chemoreceptor: direct and distance.
* Examples of distance chemoreceptors are:
**olfactory receptor neurons in the olfactory system: Olfaction involves the ability to detect chemicals in the gaseous state. In vertebrates, the olfactory system detects odors and pheromones in the nasal cavity. Within the olfactory system there are two anatomically distinct organs: the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). It was initially thought that the MOE is responsible for the detection of odorants, while the VNO detects pheromones. The current view, however, is that both systems can detect odorants and pheromones. Olfaction in invertebrates differs from olfaction in vertebrates. For example, in insects, olfactory sensilla are present on their antennae.
* Examples of direct chemoreceptors include:
** Taste receptors in the gustatory system: The primary use of gustation as a type of chemoreception is for the detection of tasteants. Aqueous chemical compounds come into contact with chemoreceptors in the mouth, such as taste buds on the tongue, and trigger responses. These chemical compounds can either trigger an appetitive response for nutrients, or a defensive response against toxins depending on which receptors fire. Fish and crustaceans, who are constantly in an aqueous environment, use their gustatory system to identify certain chemicals in the mixture for the purpose of localization and ingestion of food.
**Insects use contact chemoreception to recognize certain chemicals such as cuticular hydrocarbons and chemicals specific to host plants. Contact chemoreception is more commonly seen in insects but is also involved in the mating behavior of some vertebrates. The contact chemoreceptor is specific to one type of chemical. | 3 | Analytical Chemistry |
A polymer brush is the name given to a surface coating consisting of polymers tethered to a surface. The brush may be either in a solvated state, where the tethered polymer layer consists of polymer and solvent, or in a melt state, where the tethered chains completely fill up the space available. These polymer layers can be tethered to flat substrates such as silicon wafers, or highly curved substrates such as nanoparticles. Also, polymers can be tethered in high density to another single polymer chain, although this arrangement is normally named a bottle brush. Additionally, there is a separate class of polyelectrolyte brushes, when the polymer chains themselves carry an electrostatic charge.
The brushes are often characterized by the high density of grafted chains. The limited space then leads to a strong extension of the chains. Brushes can be used to stabilize colloids, reduce friction between surfaces, and to provide lubrication in artificial joints.
Polymer brushes have been modeled with Molecular Dynamics, Monte Carlo methods, Brownian dynamics simulations, and molecular theories. | 7 | Physical Chemistry |
Subtractive hybridization is a technology that allows for PCR-based amplification of only cDNA fragments that differ between a control (driver) and experimental transcriptome. cDNA is produced from mRNA. Differences in relative abundance of transcripts are highlighted, as are genetic differences between species. The technique relies on the removal of dsDNA formed by hybridization between a control and test sample, thus eliminating cDNAs or gDNAs of similar abundance, and retaining differentially expressed, or variable in sequence, transcripts or genomic sequences.
Suppression subtractive hybridization has also been successfully used to identify strain- or species-specific DNA sequences in a variety of bacteria including Vibrio species (Metagenomics). | 1 | Biochemistry |
Electron transfer reactions are central to myriad processes and properties in soils, and redox potential, quantified as Eh (platinum electrode potential (voltage) relative to the standard hydrogen electrode) or pe (analogous to pH as -log electron activity), is a master variable, along with pH, that controls and is governed by chemical reactions and biological processes. Early theoretical research with applications to flooded soils and paddy rice production was seminal for subsequent work on thermodynamic aspects of redox and plant root growth in soils. Later work built on this foundation, and expanded it for understanding redox reactions related to heavy metal oxidation state changes, pedogenesis and morphology, organic compound degradation and formation, free radical chemistry, wetland delineation, soil remediation, and various methodological approaches for characterizing the redox status of soils. | 9 | Geochemistry |
Base calling is the process of assigning nucleobases to chromatogram peaks, light intensity signals, or electrical current changes resulting from nucleotides passing through a nanopore. One computer program for accomplishing this job is Phred, which is a widely used base calling software program by both academic and commercial DNA sequencing laboratories because of its high base calling accuracy.
Base callers for Nanopore sequencing use neural networks trained on current signals obtained from accurate sequencing data. | 1 | Biochemistry |
Because ELPs are protein-based biopolymers, synthesis involves manipulation of genes to continually express the monomeric repeat unit. Various techniques have been employed in the production of ELPs of various sizes, including unidirectional ligation or concatemerization, overlap extension polymerase chain reaction (OEPCR), and recursive directional ligation (RDL). Also, ELPs can be experimentally modified through conjugation with other polymers or through SpyTag/SpyCatcher reaction, allowing for the synthesis of copolymers with unique morphology. | 7 | Physical Chemistry |
The Wohlwill process is an industrial-scale chemical procedure used to refine gold to the highest degree of purity (99.999%). The process was invented in 1874 by Emil Wohlwill. This electrochemical process involves using a cast gold ingot, often called a doré bar, of 95%+ gold to serve as an anode. Lower percentages of gold in the anode will interfere with the reaction, especially when the contaminating metal is silver or one of the platinum group elements. The cathodes for this reaction are small sheets of pure (24k) gold sheeting or stainless steel. Current is applied to the system, and electricity travels through the electrolyte of chloroauric acid. Gold and other metals are dissolved at the anode, and pure gold (coming through the chloroauric acid by ion transfer) is plated onto the gold cathode. When the anode is dissolved, the cathode is removed and melted or otherwise processed in the manner required for sale or use. The resulting gold is 99.999% pure, and of higher purity than gold produced by the other common refining method, the Miller process, which produces gold of 99.5% purity.
For industrial gold production the Wohlwill process is necessary for highest purity gold applications. When lower purity gold is required, refiners often utilize the Miller process for its relative ease and quicker turnaround times and because it does not require a large inventory of gold, in the form of chloroauric acid. | 8 | Metallurgy |
However, if the detector is shot noise dominated (which is typically the case for a photomultiplier tube), noise will be proportional to the square root of the power, so that for a broad flat spectrum the noise will be proportional to the square root of m, where m is the number of sample points comprising the spectrum, thus this disadvantage precisely offsets the Fellgett advantage. Shot noise is the main reason Fourier transform spectroscopy has never been popular for UV and visible light spectrometry. | 7 | Physical Chemistry |
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter.
The smallest group of particles in the material that constitutes this repeating pattern is the unit cell of the structure. The unit cell completely reflects the symmetry and structure of the entire crystal, which is built up by repetitive translation of the unit cell along its principal axes. The translation vectors define the nodes of the Bravais lattice.
The lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called lattice parameters or cell parameters. The symmetry properties of the crystal are described by the concept of space groups. All possible symmetric arrangements of particles in three-dimensional space may be described by the 230 space groups.
The crystal structure and symmetry play a critical role in determining many physical properties, such as cleavage, electronic band structure, and optical transparency. | 3 | Analytical Chemistry |
In stereochemistry, an asymmetric carbon is a carbon atom that is bonded to four different types of atoms or groups of atoms. The four atoms and/or groups attached to the carbon atom can be arranged in space in two different ways that are mirror images of each other, and which lead to so-called left-handed and right-handed versions (stereoisomers) of the same molecule. Molecules that cannot be superimposed on their own mirror image are said to be chiral; as the asymmetric carbon is the center of this chirality, it is also known as a chiral carbon.
As an example, malic acid () has 4 carbon atoms but just one of them is asymmetric. The asymmetric carbon atom, bolded in the formula, is the one attached to two carbon atoms, an oxygen atom, and a hydrogen atom. One may initially be inclined to think this atom is not asymmetric because it is attached to two carbon atoms, but because those two carbon atoms are not attached to exactly the same things, there are two different groups of atoms that the carbon atom in question is attached to, therefore making it an asymmetric carbon atom:
Knowing the number of asymmetric carbon atoms, one can calculate the maximum possible number of stereoisomers for any given molecule as follows:
: If is the number of asymmetric carbon atoms then the maximum number of isomers = (Le Bel-van't Hoff rule)
This is a corollary of Le Bel and vant Hoffs simultaneously announced conclusions, in 1874, that the most probable orientation of the bonds of a carbon atom linked to four groups or atoms is toward the apexes of a tetrahedron, and that this accounted for all then-known phenomena of molecular asymmetry (which involved a carbon atom bearing four different atoms or groups).
A tetrose with 2 asymmetric carbon atoms has 2 = 4 stereoisomers:
An aldopentose with 3 asymmetric carbon atoms has 2 = 8 stereoisomers:
An aldohexose with 4 asymmetric carbon atoms has 2 = 16 stereoisomers: | 4 | Stereochemistry |
Orotidine 5'-monophosphate (OMP), also known as orotidylic acid, is a pyrimidine nucleotide which is the last intermediate in the biosynthesis of uridine monophosphate. OMP is formed from orotate and phosphoribosyl pyrophosphate by the enzyme orotate phosphoribosyltransferase.
In humans, the enzyme UMP synthase converts OMP into uridine 5'- monophosphate. If UMP synthase is defective, orotic aciduria can result. | 1 | Biochemistry |
It carried out work on reactors for the British civil and military (submarine fleet) nuclear energy programmes, investigating metallurgy. In the first ten years, it carried out research on materials for fast breeder reactors; it was the first time that niobium had been part of a fast breeder reactor. The site investigated fracture mechanics, nuclear reactor physics and hydraulics.
Work on irradiation of metals was also carried out with the School of Materials, University of Manchester and the Department of Materials Science and Metallurgy, University of Cambridge. | 8 | Metallurgy |
In the Arrhenius equation, the term activation energy (E) is used to describe the energy required to reach the transition state, and the exponential relationship holds. In transition state theory, a more sophisticated model of the relationship between reaction rates and the transition state, a superficially similar mathematical relationship, the Eyring equation, is used to describe the rate constant of a reaction: . However, instead of modeling the temperature dependence of reaction rate phenomenologically, the Eyring equation models individual elementary steps of a reaction. Thus, for a multistep process, there is no straightforward relationship between the two models. Nevertheless, the functional forms of the Arrhenius and Eyring equations are similar, and for a one-step process, simple and chemically meaningful correspondences can be drawn between Arrhenius and Eyring parameters.
Instead of also using E, the Eyring equation uses the concept of Gibbs energy and the symbol ΔG to denote the Gibbs energy of activation to achieve the transition state. In the equation, k and h are the Boltzmann and Planck constants, respectively. Although the equations look similar, it is important to note that the Gibbs energy contains an entropic term in addition to the enthalpic one. In the Arrhenius equation, this entropic term is accounted for by the pre-exponential factor A. More specifically, we can write the Gibbs free energy of activation in terms of enthalpy and entropy of activation: . Then, for a unimolecular, one-step reaction, the approximate relationships and hold. Note, however, that in Arrhenius theory proper, A is temperature independent, while here, there is a linear dependence on T. For a one-step unimolecular process whose half-life at room temperature is about 2 hours, ΔG is approximately 23 kcal/mol. This is also the roughly the magnitude of E for a reaction that proceeds over several hours at room temperature. Due to the relatively small magnitude of TΔS and RT at ordinary temperatures for most reactions, in sloppy discourse, E, ΔG, and ΔH are often conflated and all referred to as the "activation energy".
The enthalpy, entropy and Gibbs energy of activation are more correctly written as ΔH, ΔS and ΔG respectively, where the o indicates a quantity evaluated between standard states. However, some authors omit the o in order to simplify the notation.
The total free energy change of a reaction is independent of the activation energy however. Physical and chemical reactions can be either exergonic or endergonic, but the activation energy is not related to the spontaneity of a reaction. The overall reaction energy change is not altered by the activation energy. | 7 | Physical Chemistry |
The developers of Ion Torrent semiconductor sequencing have marketed it as a rapid, compact and economical sequencer that can be utilized in a large number of laboratories as a bench top machine. The company hopes that their system will take sequencing outside of specialized centers and into the reach of hospitals and smaller laboratories. A January 2011 New York Times article, [https://www.nytimes.com/2011/01/05/health/05gene.html?pagewanted=1&_r=1&ref=hospitals "Taking DNA Sequencing to the Masses"], underlines these ambitions.
Due to the ability of alternative sequencing methods to achieve a greater read length (and therefore being more suited to whole genome analysis) this technology may be best suited to small scale applications such as microbial genome sequencing, microbial transcriptome sequencing, targeted sequencing, amplicon sequencing, or for quality testing of sequencing libraries. | 1 | Biochemistry |
In common use, the research definition, including post-transition metals and metalloids, is extended to include compounds such as cementite, FeC. These compounds, sometimes termed interstitial compounds, can be stoichiometric, and share similar properties to the intermetallic compounds defined above. | 8 | Metallurgy |
The planets of the Solar System are divided into two groups: the four inner planets are the terrestrial planets (Mercury, Venus, Earth and Mars), with relatively small sizes and rocky surfaces. The four outer planets are the giant planets, which are dominated by hydrogen and helium and have lower mean densities. These can be further subdivided into the gas giants (Jupiter and Saturn) and the ice giants (Uranus and Neptune) that have large icy cores.
Most of our direct information on the composition of the giant planets is from spectroscopy. Since the 1930s, Jupiter was known to contain hydrogen, methane and ammonium. In the 1960s, interferometry greatly increased the resolution and sensitivity of spectral analysis, allowing the identification of a much greater collection of molecules including ethane, acetylene, water and carbon monoxide. However, Earth-based spectroscopy becomes increasingly difficult with more remote planets, since the reflected light of the Sun is much dimmer; and spectroscopic analysis of light from the planets can only be used to detect vibrations of molecules, which are in the infrared frequency range. This constrains the abundances of the elements H, C and N. Two other elements are detected: phosphorus in the gas phosphine (PH) and germanium in germane (GeH).
The helium atom has vibrations in the ultraviolet range, which is strongly absorbed by the atmospheres of the outer planets and Earth. Thus, despite its abundance, helium was only detected once spacecraft were sent to the outer planets, and then only indirectly through collision-induced absorption in hydrogen molecules. Further information on Jupiter was obtained from the Galileo probe when it was sent into the atmosphere in 1995; and the final mission of the Cassini probe in 2017 was to enter the atmosphere of Saturn. In the atmosphere of Jupiter, He was found to be depleted by a factor of 2 compared to solar composition and Ne by a factor of 10, a surprising result since the other noble gases and the elements C, N and S were enhanced by factors of 2 to 4 (oxygen was also depleted but this was attributed to the unusually dry region that Galileo sampled).
Spectroscopic methods only penetrate the atmospheres of Jupiter and Saturn to depths where the pressure is about equal to 1 bar, approximately Earth's atmospheric pressure at sea level. The Galileo probe penetrated to 22 bars. This is a small fraction of the planet, which is expected to reach pressures of over 40 Mbar. To constrain the composition in the interior, thermodynamic models are constructed using the information on temperature from infrared emission spectra and equations of state for the likely compositions. High-pressure experiments predict that hydrogen will be a metallic liquid in the interior of Jupiter and Saturn, while in Uranus and Neptune it remains in the molecular state. Estimates also depend on models for the formation of the planets. Condensation of the presolar nebula would result in a gaseous planet with the same composition as the Sun, but the planets could also have formed when a solid core captured nebular gas.
In current models, the four giant planets have cores of rock and ice that are roughly the same size, but the proportion of hydrogen and helium decreases from about 300 Earth masses in Jupiter to 75 in Saturn and just a few in Uranus and Neptune. Thus, while the gas giants are primarily composed of hydrogen and helium, the ice giants are primarily composed of heavier elements (O, C, N, S), primarily in the form of water, methane, and ammonia. The surfaces are cold enough for molecular hydrogen to be liquid, so much of each planet is likely a hydrogen ocean overlaying one of heavier compounds. Outside the core, Jupiter has a mantle of liquid metallic hydrogen and an atmosphere of molecular hydrogen and helium. Metallic hydrogen does not mix well with helium, and in Saturn, it may form a separate layer below the metallic hydrogen. | 9 | Geochemistry |
The analysis of line intensity ratios is an important tool to obtain information about laboratory and space plasmas. In emission spectroscopy, the intensity of spectral lines can provide various information about the plasma (or gas) condition. It might be used to determine the temperature or density of the plasma. Since the measurement of an absolute intensity in an experiment can be challenging, the ratio of different spectral line intensities can be used to achieve information about the plasma, as well. | 7 | Physical Chemistry |
In the case of oxidizing treatments, spectra taken from treated surfaces will indicate the presence of functionalities in carbonyl and hydroxyl regions according to the Infrared spectroscopy correlation table. | 7 | Physical Chemistry |
Aside from total synthesis, a potentially useful application of hydrogen-bond catalysis is the bulk synthesis of difficult-to-access chiral small molecules. A notable example is the gram-scale Strecker synthesis of unnatural amino acids using thiourea catalysis, reported in the journal Nature in 2009. The catalyst, whether polymer-bound or homogeneous, is derived from natural tert-leucine and can catalyze (4 mol% catalyst loading) the formation of the Strecker product from benzhydryl amines and aqueous HCN. Hydrolysis of the nitrile and deprotections produces pure unnatural tert-leucine in 84% overall yield and 99% ee. | 0 | Organic Chemistry |
Arsenic is highly detrimental to the innate and the adaptive immune system of the body. When the amount of unfolded and misfolded proteins in endoplasmic reticulum stress is excessive, the unfolded protein response (UPR) is activated to increase the activity of several receptors that are responsible the restoration of homeostasis. The inositol-requiring enzyme-1 (IRE1) and protein kinase RNA-like endoplasmic reticulum kinase (PERK) are two receptors that restrict the rate of translation. On the other hand, the unfolded proteins are corrected by the production of chaperones, which are induced by the activating transcription factor 6 (ATF6). If the number of erroneous proteins elevates, further mechanism is active which triggers apoptosis. Arsenic has evidentially shown to increase the activity of these protein sensors. | 1 | Biochemistry |
β-Hydroxybutyryl-CoA (or 3-hydroxybutyryl-coenzyme A) is an intermediate in the fermentation of butyric acid, and in the metabolism of lysine and tryptophan. The L-3-hydroxybutyl-CoA (or (S)-3-hydroxybutanoyl-CoA) enantiomer is also the second to last intermediate in beta oxidation of even-numbered, straight chain, and saturated fatty acids. | 1 | Biochemistry |
As the compound contains the peroxydisulfate ion as the counter anion, this compound should be treated as an explosive even though its explosive properties were not well established. The complex also releases tiny amounts of pyridine vapor which is a possible carcinogen. | 0 | Organic Chemistry |
A potential socioeconomic drawback associated with solar energy conversion is a disruption to the electric utility business model. In America, the economic viability of regional “monopoly” utilities is based on the large aggregation of local customers who balance out each other's variable load. Therefore, the widespread installation of rooftop solar systems that are not connected to the grid poses a threat to the stability of the utility market. This phenomenon is known as Grid Defection. The pressure on electric utilities is exacerbated by an aging grid infrastructure that has yet to adapt to the new challenges posed by renewable energy (mainly regarding inertia, reverse power flow and relay protection schemes). However, some analysts make the case that with the steady increase in natural disasters (which destroy vital grid infrastructure), solar microgrid installation may be necessary to ensure emergency energy access. This emphasis on contingency preparation has expanded the off-grid energy market dramatically in recent years, especially in areas prone to natural disasters. | 7 | Physical Chemistry |
The ionizing effect of radiation on a gas is extensively used for the detection of radiation such as alpha, beta, gamma, and X-rays. The original ionization event in these instruments results in the formation of an "ion pair"; a positive ion and a free electron, by ion impact by the radiation on the gas molecules. The ionization chamber is the simplest of these detectors, and collects all the charges created by direct ionization within the gas through the application of an electric field.
The Geiger–Müller tube and the proportional counter both use a phenomenon known as a Townsend avalanche to multiply the effect of the original ionizing event by means of a cascade effect whereby the free electrons are given sufficient energy by the electric field to release further electrons by ion impact. | 7 | Physical Chemistry |
Hansen solubility parameters were developed by Charles M. Hansen in his Ph.D thesis in 1967 as a way of predicting if one material will dissolve in another and form a solution. They are based on the idea that like dissolves like where one molecule is defined as being like another if it bonds to itself in a similar way.
Specifically, each molecule is given three Hansen parameters, each generally measured in MPa:
* The energy from dispersion forces between molecules
* The energy from dipolar intermolecular forces between molecules
* The energy from hydrogen bonds between molecules.
These three parameters can be treated as co-ordinates for a point in three dimensions also known as the Hansen space. The nearer two molecules are in this three-dimensional space, the more likely they are to dissolve into each other. To determine if the parameters of two molecules (usually a solvent and a polymer) are within range, a value called interaction radius () is given to the substance being dissolved. This value determines the radius of the sphere in Hansen space and its center is the three Hansen parameters. To calculate the distance () between Hansen parameters in Hansen space the following formula is used:
Combining this with the interaction radius gives the relative energy difference (RED) of the system:
* If the molecules are alike and will dissolve
* If the system will partially dissolve
* If the system will not dissolve | 7 | Physical Chemistry |
A new synthetic approach, called nanofiber seeding, was developed to control the bulk morphology of chemically synthesized electronic organic polymers. Bulk quantities of nanofibers of conducting polymers such as polyaniline, can be synthesized in one step without the need for conventional templates, surfactants, polymers, or organic solvents.
Conventional oxidative polymerization approaches to nanostructured conducting polymers include the use of hard template zeolites, opals, and controlled pore-size membranes, or soft template such as polymers and surfactants. A “template-free” approach has also been described in which the use of large organic anions results in polyaniline nanofibers and nanotubes having average diameters in the 650-80 nm range.
Standard synthesis of polyaniline yields granular morphology. However, if the conventional reaction is seeded by 1-4 mg (seed quantities) of added pre-synthesized polyaniline nanofibers, (nanofiber seeds could be prepared from interfacial polymerization) the bulk morphology changes dramatically from granular to nano-fibrillar. Furthermore, increased capacitance values were observed in polyaniline nanofibers synthesized by the nanofiber seeding approach. Oxidative polymerization can be also seeded by other nanostructure materials such as vanadium pentoxide nanofibers, where V2O5 nanofibers (i) Rapidly initiate fibrillar polymer growth (ii) Slowly dissolve in aq. 1.0 M HCl, which eliminates template removal steps. Hence only catalytic amounts (4mg) V2O5 nanofibers are needed prior to onset of polymerization, which significantly change the bulk morphology of the polymer precipitate. Moreover, single-walled carbon nanotube and nano fibrous hexapeptide can be also used as templating seeds. This method can be extended to all major classes of conducting polymers, including polypyrrole, PEDOT and other polythiophenes etc.
Nanofiber seeding is a convenient approach to obtain thin, substrate-supported, transparent films of nanofibers of conducting polymers without requiring any bulk processing steps. | 7 | Physical Chemistry |
Galactolysis refers to the catabolism of galactose.
In the liver, galactose is converted through the Leloir pathway to glucose 6-phosphate in the following reactions:
galacto- uridyl phosphogluco-
kinase transferase mutase
gal --------> gal 1 P ------------------> glc 1 P -----------> glc 6 P
/ v
UDP-glc UDP-gal
epimerase | 1 | Biochemistry |
In most theories of this state, it is supposed that vacancies – empty sites normally occupied by particles in an ideal crystal – lead to supersolidity. These vacancies are caused by zero-point energy, which also causes them to move from site to site as waves. Because vacancies are bosons, if such clouds of vacancies can exist at very low temperatures, then a Bose–Einstein condensation of vacancies could occur at temperatures less than a few tenths of a Kelvin. A coherent flow of vacancies is equivalent to a "superflow" (frictionless flow) of particles in the opposite direction. Despite the presence of the gas of vacancies, the ordered structure of a crystal is maintained, although with less than one particle on each lattice site on average. Alternatively, a supersolid can also emerge from a superfluid. In this situation, which is realised in the experiments with atomic Bose–Einstein condensates, the spatially ordered structure is a modulation on top of the superfluid density distribution. | 7 | Physical Chemistry |
In 2008, the submission was announced of a registration dossier to the European Medicines Agency and the FDA for Yondelis when administered in combination with pegylated liposomal doxorubicin (Doxil, Caelyx) for the treatment of women with relapsed ovarian cancer. In 2011, Johnson & Johnson voluntarily withdrew the submission in the United States following a request by the FDA for an additional phase III study to be done in support of the submission.
Trabectedin is also in phase II trials for prostate, breast, and paediatric cancers. | 0 | Organic Chemistry |
Strained alkenes also utilize strain-relief as a driving force that allows for their participation in click reactions. Trans-cycloalkenes (usually cyclooctenes) and other strained alkenes such as oxanorbornadiene react in click reactions with a number of partners including azides, tetrazines and tetrazoles. These reaction partners can interact specifically with the strained alkene, staying bioorthogonal to endogenous alkenes found in lipids, fatty acids, cofactors and other natural products. | 0 | Organic Chemistry |
In middle and late transition metal complexes, there is larger thermodynamic preference for β-H elimination over β-alkyl elimination, where the difference is usually >15 kcal/mol. Examples involved middle and late transition metal complexes are either absent of β-hydrogens or use ring strain relief and aromaticity as driving forces to favor β-alkyl elimination over β-hydride elimination. | 0 | Organic Chemistry |
The earliest reports of tip enhanced Raman spectroscopy typically used a Raman microscope coupled with an atomic force microscope. Tip-enhanced Raman spectroscopy coupled with a scanning tunneling microscope (STM-TERS) has also become a reliable technique, since it utilizes the gap mode plasmon between the metallic probe and the metallic substrate. | 7 | Physical Chemistry |
The Zeeman effect can be demonstrated by placing a sodium vapor source in a powerful electromagnet and viewing a sodium vapor lamp through the magnet opening (see diagram). With magnet off, the sodium vapor source will block the lamp light; when the magnet is turned on the lamp light will be visible through the vapor.
The sodium vapor can be created by sealing sodium metal in an evacuated glass tube and heating it while the tube is in the magnet.
Alternatively, salt (sodium chloride) on a ceramic stick can be placed in the flame of Bunsen burner as the sodium vapor source. When the magnetic field is energized, the lamp image will be brighter. However, the magnetic field also affects the flame, making the observation depend upon more than just the Zeeman effect. These issues also plagued Zeeman's original work; he devoted considerable effort to ensure his observations were truly an effect of magnetism on light emission.
When salt is added to the Bunsen burner, it dissociates to give sodium and chloride. The sodium atoms get excited due to photons from the sodium vapour lamp, with electrons excited from 3s to 3p states, absorbing light in the process. The sodium vapour lamp emits light at 589nm, which has precisely the energy to excite an electron of a sodium atom. If it was an atom of another element, like chlorine, shadow will not be formed. When a magnetic field is applied, due to the Zeeman effect the spectral line of sodium gets split into several components. This means the energy difference between the 3s and 3p atomic orbitals will change. As the sodium vapour lamp dont precisely deliver the right frequency any more, light doesnt get absorbed and passes through, resulting in the shadow dimming. As the magnetic field strength is increased, the shift in the spectral lines increases and lamp light is transmitted. | 7 | Physical Chemistry |
They include a number of transmembrane cytochrome b-like proteins including coenzyme Q - cytochrome c reductase (cytochrome bc1 ); cytochrome b6f complex; formate dehydrogenase, respiratory nitrate reductase; succinate - coenzyme Q reductase (fumarate reductase); and succinate dehydrogenase. See electron transport chain.
*3.D.1 The H or Na-translocating NADH Dehydrogenase ("complex I") family
*3.D.2 The Proton-translocating Transhydrogenase (PTH) Family
*3.D.3 The Proton-translocating Quinol:Cytochrome c Reductase) Superfamily
*3.D.4 Proton-translocating Cytochrome Oxidase (COX) Superfamily
*3.D.5 The Na-translocating NADH:Quinone Dehydrogenase (Na-NDH or NQR) Family
*3.D.6 The Putative Ion (H or Na)-translocating NADH:Ferredoxin Oxidoreductase (NFO or RNF) Family
*3.D.7 The H:Heterodisulfide Oxidoreductase (HHO) Family
*3.D.8 The Na- or H-Pumping Formyl Methanofuran Dehydrogenase (FMF-DH) Family
*3.D.9 The H-translocating F420H2 Dehydrogenase (F420H2DH) Family
*3.D.10 The Prokaryotic Succinate Dehydrogenase (SDH) Family | 1 | Biochemistry |
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