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Corrosion is an electrochemical process, which reveals itself as rust or tarnish on metals like iron or copper and their respective alloys, steel and brass. | 0 | Theoretical and Fundamental Chemistry |
HDXsite is an online websever which includes some applications such as HDX modeller increasing the resolution of experimental HDX data and modeling protection factors for individual residues. | 0 | Theoretical and Fundamental Chemistry |
Sulfamoyl fluorides can be made by treating secondary amines with sulfuryl fluoride (SOF) or sulfuryl chloride fluoride (SOClF). Cyclic secondary amines work as well, provided they are not aromatic.
Sulfamoyl fluorides can also be made from sulfamoyl chlorides, by reacting with a substance that can supply the fluoride ion, such as NaF, KF, HF, or SbF.
Sulfonamides can undergo a Hofmann rearrangement when treated with a difluoro-λ-bromane to yield a singly substituted N-sulfamoyl fluoride. | 0 | Theoretical and Fundamental Chemistry |
Polymers are chainlike molecules that are made of the same repetition unit. With a few exceptions such as proteins, a polymer consists of a mix of molecules with different chain lengths. Therefore, average values are given for the molecular weight like the number average, the weight average or the viscosity average molar mass. A measure for the width of the molecular weight distribution is the polydispersity index. The targeted manipulation of the molecular weight distribution of a polymer by removing short and/or long chain material is called polymer fractionation. | 0 | Theoretical and Fundamental Chemistry |
In the finery, a workman known as the "finer" remelted pig iron so as to oxidise the carbon (and silicon). This produced a lump of iron (with some slag) known as a bloom. This was consolidated using a water-powered hammer (see trip hammer) and returned to the finery.
The next stages were undertaken by the "hammerman", who in some iron-making areas such as South Yorkshire was also known as the "stringsmith", who heated his iron in a string-furnace. Because the bloom is highly porous, and its open spaces are full of slag, the hammermans or stringsmiths tasks were to beat (work) the heated bloom with a hammer to drive the molten slag out of it, and then to draw the product out into a bar to produce what was known as anconies or bar iron. In order to do this, he had to reheat the iron, for which he used the chafery. The fuel used in the finery had to be charcoal (later coke), as impurities in any mineral fuel would affect the quality of the iron. | 1 | Applied and Interdisciplinary Chemistry |
Chemical shift is usually expressed in parts per million (ppm) by frequency, because it is calculated from:
where is the absolute resonance frequency of the sample and is the absolute resonance frequency of a standard reference compound, measured in the same applied magnetic field . Since the numerator is usually expressed in hertz, and the denominator in megahertz, is expressed in ppm.
The detected frequencies (in Hz) for H, C, and Si nuclei are usually referenced against TMS (tetramethylsilane), TSP (Trimethylsilylpropanoic acid), or DSS, which by the definition above have a chemical shift of zero if chosen as the reference. Other standard materials are used for setting the chemical shift for other nuclei.
Thus, an NMR signal observed at a frequency 300 Hz higher than the signal from TMS, where the TMS resonance frequency is 300 MHz, has a chemical shift of:
Although the absolute resonance frequency depends on the applied magnetic field, the chemical shift is independent of external magnetic field strength. On the other hand, the resolution of NMR will increase with applied magnetic field. | 0 | Theoretical and Fundamental Chemistry |
The electrons around a nucleus will circulate in a magnetic field and create a secondary induced magnetic field. This field opposes the applied field as stipulated by Lenzs law and atoms with higher induced fields (i.e., higher electron density) are therefore called shielded, relative to those with lower electron density. Electron-donating alkyl groups, for example, lead to increased shielding whereas electron-withdrawing substituents such as nitro groups lead to deshielding of the nucleus. Not only substituents cause local induced fields. Bonding electrons can also lead to shielding and deshielding effects. A striking example of this is the pi bonds in benzene. Circular current through the hyperconjugated system causes a shielding effect at the molecules center and a deshielding effect at its edges. Trends in chemical shift are explained based on the degree of shielding or deshielding.
Nuclei are found to resonate in a wide range to the left (or more rare to the right) of the internal standard. When a signal is found with a higher chemical shift:
* the applied effective magnetic field is lower, if the resonance frequency is fixed (as in old traditional CW spectrometers)
* the frequency is higher, when the applied magnetic field is static (normal case in FT spectrometers)
* the nucleus is more deshielded
* the signal or shift is downfield or at low field or paramagnetic
Conversely a lower chemical shift is called a diamagnetic shift, and is upfield and more shielded. | 0 | Theoretical and Fundamental Chemistry |
No applications have been found thus far, although physicist Andreas Hermann states that if the state of matter could be recreated in other materials, it could have many different applications. | 0 | Theoretical and Fundamental Chemistry |
Dendrimer drug delivery has also shown major promise as a potential solution for many traditionally difficult drug delivery problems. In the case of drug delivery to the brain, dendrimers are able to take advantage of the EPR effect and blood-brain barrier (BBB) impairment to cross the BBB effectively in vivo. For example, hydroxyl-terminated PAMAM dendrimers possess an intrinsic targeting ability to inflamed macrophages in the brain, verified using fluorescently labeled neutral generation dendrimers in a rabbit model of cerebral palsy. This intrinsic targeting has enabled drug delivery in a variety of conditions, ranging from cerebral palsy and other neuroinflammatory disorders to traumatic brain injury and hypothermic circulatory arrest, across a variety of animal models ranging from mice and rabbits to canines. Dendrimer uptake into the brain correlates with severity of inflammation and BBB impairment and it is believed that the BBB impairment is the key driving factor allowing dendrimer penetration. Localization is heavily skewed towards activated microglia. Dendrimer-conjugated N-acetyl cysteine has shown efficacy in vivo as an anti-inflammatory at more than 1000-fold lower dose than free drug on a drug basis, reversing the phenotype of cerebral palsy, Rett syndrome, macular degeneration and other inflammatory diseases. | 0 | Theoretical and Fundamental Chemistry |
Proteinase K is commonly used in molecular biology to digest protein and remove contamination from preparations of nucleic acid. Addition of Proteinase K to nucleic acid preparations rapidly inactivates nucleases that might otherwise degrade the DNA or RNA during purification. It is highly suited to this application since the enzyme is active in the presence of chemicals that denature proteins, such as SDS and urea, chelating agents such as EDTA, sulfhydryl reagents, as well as trypsin or chymotrypsin inhibitors.
Proteinase K is used for the destruction of proteins in cell lysates (tissue, cell culture cells) and for the release of nucleic acids, since it very effectively inactivates DNases and RNases. Some examples for applications:
Proteinase K is very useful in the isolation of highly native, undamaged DNAs or RNAs, since most microbial or mammalian DNases and RNases are rapidly inactivated by the enzyme, particularly in the presence of 0.5–1% SDS.
The enzyme's activity towards native proteins is stimulated by denaturants such as SDS. In contrast, when measured using peptide substrates, denaturants inhibit the enzyme. The reason for this result is that the denaturing agents unfold the protein substrates and make them more accessible to the protease. | 1 | Applied and Interdisciplinary Chemistry |
Today, most trichloroethylene is produced from ethylene. First, ethylene is chlorinated over a ferric chloride catalyst to produce 1,2-dichloroethane:
:CH=CH + Cl → ClCHCHCl
When heated to around 400 °C with additional chlorine, 1,2-dichloroethane is converted to trichloroethylene:
:ClCHCHCl + 2 Cl → ClCH=CCl + 3 HCl
This reaction can be catalyzed by a variety of substances. The most commonly used catalyst is a mixture of potassium chloride and aluminum chloride. However, various forms of porous carbon can also be used. This reaction produces tetrachloroethylene as a byproduct and depending on the amount of chlorine fed to the reaction, tetrachloroethylene can even be the major product. Typically, trichloroethylene and tetrachloroethylene are collected together and then separated by distillation.
Prior to the early 1970s, however, most trichloroethylene was produced in a two-step process from acetylene. First, acetylene was treated with chlorine using a ferric chloride catalyst at 90 °C to produce 1,1,2,2-tetrachloroethane according to the chemical equation:
:HC≡CH + 2 Cl → ClCHCHCl
The 1,1,2,2-tetrachloroethane is then dehydrochlorinated to give trichloroethylene. This can be accomplished either with an aqueous solution of calcium hydroxide:
:2 ClCHCHCl + Ca(OH) → 2 ClCH=CCl + CaCl + 2 HO
or in the vapor phase by heating it to 300–500 °C on a barium chloride or calcium chloride catalyst:
:ClCHCHCl → ClCH=CCl + HCl
Common impurities in reagent and technical grade TCE are methyl chloroform, carbon tetrachloride, ethylene dichloride, tetrachloroethanes, benzene and phenol. However, these compounds are present in very small amounts and do not possess any risk. | 1 | Applied and Interdisciplinary Chemistry |
Signal transducing histidine kinases are the key elements in two-component signal transduction systems. Examples of histidine kinases are EnvZ, which plays a central role in osmoregulation, and CheA, which plays a central role in the chemotaxis system. Histidine kinases usually have an N-terminal ligand-binding domain and a C-terminal kinase domain, but other domains may also be present. The kinase domain is responsible for the autophosphorylation of the histidine with ATP, the phosphotransfer from the kinase to an aspartate of the response regulator, and (with bifunctional enzymes) the phosphotransfer from aspartyl phosphate to water. The kinase core has a unique fold, distinct from that of the Ser/Thr/Tyr kinase superfamily.
HKs can be roughly divided into two classes: orthodox and hybrid kinases. Most orthodox HKs, typified by the E. coli EnvZ protein, function as periplasmic membrane receptors and have a signal peptide and transmembrane segment(s) that separate the protein into a periplasmic N-terminal sensing domain and a highly conserved cytoplasmic C-terminal kinase core. Members of this family, however, have an integral membrane sensor domain. Not all orthodox kinases are membrane bound, e.g., the nitrogen regulatory kinase NtrB (GlnL) is a soluble cytoplasmic HK. Hybrid kinases contain multiple phosphodonor and phosphoacceptor sites and use multi-step phospho-relay schemes instead of promoting a single phosphoryl transfer. In addition to the sensor domain and kinase core, they contain a CheY-like receiver domain and a His-containing phosphotransfer (HPt) domain. | 1 | Applied and Interdisciplinary Chemistry |
Sulfolipids are a class of lipids which possess a sulfur-containing functional group. An abundant sulfolipid is sulfoquinovosyl diacylglycerol, which is composed of a glycoside of sulfoquinovose and diacylglycerol. In plants, sulfoquinovosyl diacylglycerides (SQDG) are important members of the sulfur cycle. Other important sulfolipids include sulfatide and seminolipid, each of which are sulfated glycolipids. Sulfolipids have been implicated in the functions of two of the core components of the photosynthetic electron transport chain and while not necessarily essential, might have a protective function when the photosynthetic apparatus is under stress. | 1 | Applied and Interdisciplinary Chemistry |
The objective of this drug discovery phase is to synthesize lead compounds, new analogs with improved potency, reduced off-target activities, and physiochemical/metabolic properties suggestive of reasonable in vivo pharmacokinetics. This optimization is accomplished through chemical modification of the hit structure, with modifications chosen by employing knowledge of the structure–activity relationship (SAR) as well as structure-based design if structural information about the target is available.
Lead optimization is concerned with experimental testing and confirmation of the compound based on animal efficacy models and ADMET (in vitro and in situ) tools that may be followed by target identification and target validation. | 1 | Applied and Interdisciplinary Chemistry |
Heparin and heparan sulfate (HS) are mammalian glycosaminoglycans with the highest negative charge density of known biological macromolecules. They bind by ionic interactions with a variety of proteins. Heparin is widely used as an injectable anticoagulant. SFRP1 are heparin-binding proteins, with the heparin-binding domain within the C-terminal region of the SFRP1 protein. In vitro studies show that SFRP1 is stabilized by heparin, suggesting that heparin or endogenous heparan-sulfate proteoglycan (HSPG) has the potential to promote SFRP1/Wnt binding by serving as a scaffold to facilitate interaction between SFRP1 and Wnt proteins. Lowering HSPG levels in tissue have been shown to impair Wnt signaling in vivo, supporting the idea that HSPG plays an important role in Wnt signaling regulation. Furthermore, SFRP1 is tyrosine-sulfated at two N-terminal tyrosines; this modification is, however, inhibited by heparin. Tyrosine sulfation could partially destabilize the SFRP1 protein, which is supported by previous studies showing that SFRP1 is susceptible to degradation in the absence of heparin. The finding that heparin can inhibit intracellular post-translational modification of SFRP1 was surprising. This indicates that heparin may inhibit the process of tyrosine sulfation, for example, by tyrosyl-protein sulfotransferases enzymes or sulfate donor pathways. Since heparin is highly negatively charged and cannot permeate the membrane, it must activate a signal transduction pathway to carry out its effect. It is well known that fibroblast growth factors (FGFs) bind heparin with relatively high affinity. HSPGs have also been shown to be involved in FGF cell signaling. Zhong et al. revealed a specificity of FGFs and FGF receptors on SFRP1 accumulation, demonstrating that FGF and their receptors are involved in post-translational modification of SFRP1. As stated above, SFRP1 has been shown to attenuate the malignant phenotype and decrease the growth of tumors. Thus, Heparin is a potential drug that could be used to stabilize and accumulate SFRP1 in cancer cells. | 1 | Applied and Interdisciplinary Chemistry |
Carbohydrates have four major functions within the body:
# Energy supply, particularly for the brain in the form of glucose
# Avoiding the breakdown of amino acids for energy
# Avoiding ketosis from the breakdown of fatty acids
# Cellular and protein recognition | 0 | Theoretical and Fundamental Chemistry |
The PoDFA method provides information on the composition and concentration of the inclusions in molten aluminum. PoDFA is widely used for process characterization and optimization, as well as product improvement. It allows to quickly and accurately assess the effects of various operating practices on metal cleanliness or identify filtration efficiency.
The PoDFA method was developed by Rio Tinto Alcan in the 70s. The metallographic analysis method has been optimized for over the years on a wide variety of alloys.
The measurement principle is the following: A predetermined quantity of liquid aluminum is filtered under controlled conditions using a very fine porosity filter. Inclusions in the melt are concentrated at the filter surface by a factor of about 10,000. The filter, along with the residual metal, is then cut, mounted and polished before being analyzed under an optical microscope by a trained PoDFA metallographer. | 1 | Applied and Interdisciplinary Chemistry |
Laser diffraction analysis is originally based on the Fraunhofer diffraction theory, stating that the intensity of light scattered by a particle is directly proportional to the particle size. The angle of the laser beam and particle size have an inversely proportional relationship, where the laser beam angle increases as particle size decreases and vice versa. The Mie scattering model, or Mie theory, is used as alternative to the Fraunhofer theory since the 1990s.
Commercial laser diffraction analyzers leave to the user the choice of using either Fraunhofer or Mie theory for data analysis, hence the importance of understanding the strengths and limitations of both models. Fraunhofer theory only takes into account the diffraction phenomena occurring at the contour of the particle. Its main advantage is that it does not require any knowledge of the optical properties (complex refractive index) of the particle’s material. Hence is it typically applied to samples of unknown optical properties, or to mixtures of different materials. For samples of known optical properties, Fraunhofer theory should only be applied for particles of an expected diameter at least 10 times larger than the light source’s wavelength, and/or to opaque particles.
The Mie theory is based on measuring the scattering of electromagnetic waves on spherical particles. Hence, it is taking into account not only the diffraction at the particle’s contour, but also the refraction, reflection and absorption phenomena within the particle and at its surface. Thus, this theory is better suited than the Fraunhofer theory for particles that are not significantly larger than the wavelength of the light source, and to transparent particles. The model’s main limitation is that it requires precise knowledge of the complex refractive index (including the absorption coefficient) of the particle’s material. The lower theoretical detection limit of laser diffraction, using the Mie theory, is generally thought to lie around 10 nm. | 0 | Theoretical and Fundamental Chemistry |
Cisplatin has been studied with Auger therapy to increase the therapeutic effects of cisplatin, without increasing normal tissue toxicities. However, due to significant side effects, the search for structurally novel Pt(II) and Pd(II) compounds exhibiting antineoplastic activity is extremely important and aims to develop more effective and less toxic drugs. Metal complexes comprising cisplatin-like molecules ([PtCl(NH)] or [Pt(NH)Cl]) linked by variable length alkandiamine chains have attracted great interest in the last few years as next-generation alternatives drugs in cancer chemotherapy. | 1 | Applied and Interdisciplinary Chemistry |
Since the outer conductor layer is low-impedance copper, and only the center is higher impedance steel, the skin effect gives RF transmission lines with heavy copper-cladding a low impedance at high frequencies, equivalent to that of a solid copper wire.
Tensile strength of copper-clad steel conductors is greater than that of ordinary copper conductors permitting greater span lengths than with copper.
Another advantage is that smaller diameter copper-clad steel conductors may be used in coaxial cables, permitting higher impedance and smaller cable diameter than with copper conductors of similar strength.
Due to the inseparable union of the two metals and the low amount of the more costly one, it deters theft since copper recovery is impractical and thus has very little scrap value.
Installations with copper-clad steel conductors are generally accepted as fulfilling the legal specifications for a good electrical ground. For this reason its use is preferred by industrial companies and utilities when cost is a concern. | 1 | Applied and Interdisciplinary Chemistry |
Unlike spin-echo sequence, a gradient echo sequence does not use a 180 degrees RF pulse to make the spins of particles coherent. Instead, the gradient echo uses magnetic gradients to manipulate the spins, allowing the spins to dephase and rephase when required. After an excitation pulse (usually less than 90 degrees), the spins are dephased after a period of time (due to free induction decay) and also by applying a reversed magnetic gradient to decay the spins. No signal is produced because the spins are not coherent. When the spins are rephased via a magnetic gradient, they become coherent, and thus signal (or "echo") is generated to form images. Unlike spin echo, gradient echo does not need to wait for transverse magnetisation to decay completely before initiating another sequence, thus it requires very short repetition times (TR), and therefore to acquire images in a short time.
After echo is formed, some transverse magnetisations remains because of short TR. Manipulating gradients during this time will produce images with different contrast. There are three main methods of manipulating contrast at this stage, namely steady-state free-precession (SSFP) that does not spoil the remaining transverse magnetisation, but attempts to recover them in subsequent RF pulses (thus producing T2-weighted images); the sequence with spoiler gradient that averages the transverse magnetisations in subsequent RF pulses by rotating residual transverse magnetisation into longitudinal plane and longitudinal magnetisation into transverse planes (thus producing mixed T1 and T2-weighted images), and RF spoiler that vary the phases of RF pulse to eliminates the transverse magnetisation, thus producing pure T1-weighted images.
Gradient echo uses a flip angle smaller than 90 degrees, thus longitudinal magnetisation is not eliminated while flipping the spins. The larger the flip angle, the higher the T1 weighing of the tissue because more longitudinal magnetisation most recover to produce a difference in signals between the tissues. | 0 | Theoretical and Fundamental Chemistry |
There are limited examples of small molecules that target RNA and are approved drugs for the treatment of human disease. Ribavirin was approved in 2002 to treat Hepatitis C and viral hemorrhagic fever. As a nucleoside inhibitor, the guanosine analog prodrug is used to stop viral RNA synthesis and viral mRNA capping by incorporating into RNA and pairing to uracil or cytosine. Branaplam is currently in phase I/II clinical trial for the treatment of Spinal Muscular Atrophy (SMA). This molecule is from a class of pyridazine small molecules and enhances the inclusion of exon 7, resulting in a full-length and functional protein product.
Branaplam represents the first mechanistic study of splicing modulation using a sequence-selective small molecule. The drug stabilizes the transient double-stranded RNA (dsRNA) structure formed between the SMN2 pre-mRNA and U1 snRNP complex, a key component of the splicesome. Further, this compound acts by increasing the binding affinity of U1 snRNP to the 5’ splice site (5’ss) in a sequence-selective manner that is discrete from constitutive recognition. Ataluren is in clinical trials for the treatment of Duchenne Muscular Dystrophy (DMD). It is believed that Ataluren acts by promoting insertion of near-cognate tRNAs at the site of the nonsense codon without affecting transcription, mRNA processing, mRNA stability, or protein stability to give nonsense suppression. This drug would be effective for ~10% of patients with DMD who have a single mutation in the DMD gene causing a stop codon to appear prematurely (nonsense mutation). | 1 | Applied and Interdisciplinary Chemistry |
Mandarino, in his review of the Gladstone–Dale relationship in minerals proposed the concept of the Compatibility Index in comparing the physical and optical properties of minerals. This compatibility index is a required calculation for approval as a new mineral species (see IMA guidelines).
The compatibility index (CI) is defined as follows:
Where, KP = Gladstone-Dale Constant derived from physical properties. | 1 | Applied and Interdisciplinary Chemistry |
Valves are found in virtually every industrial process, including water and sewage processing, mining, power generation, processing of oil, gas and petroleum, food manufacturing, chemical and plastic manufacturing and many other fields.
People in developed nations use valves in their daily lives, including plumbing valves, such as taps for tap water, gas control valves on cookers, small valves fitted to washing machines and dishwashers, safety devices fitted to hot water systems, and poppet valves in car engines.
In nature, there are valves, for example one-way valves in veins controlling the blood circulation, and heart valves controlling the flow of blood in the chambers of the heart and maintaining the correct pumping action.
Valves may be operated manually, either by a handle or grip, lever, pedal or wheel. Valves may also be automatic, driven by changes in pressure, temperature, or flow. These changes may act upon a diaphragm or a piston which in turn activates the valve, examples of this type of valve found commonly are safety valves fitted to hot water systems or boilers.
More complex control systems using valves requiring automatic control based on an external input (i.e., regulating flow through a pipe to a changing set point) require an actuator. An actuator will stroke the valve depending on its input and set-up, allowing the valve to be positioned accurately, and allowing control over a variety of requirements. | 1 | Applied and Interdisciplinary Chemistry |
There are several techniques to prove the existence of a liquid layer on a well-ordered surface. Basically it is all about showing that there is a phase on top of the solid which has hardly any order (quasi-liquid, see fig. order parameter). One possibility was done by Frenken and van der Veen using proton scattering on a lead (Pb) single crystal (110) surface. First the surface was atomically cleaned in [UHV], because one obviously has to have a very well ordered surface for such experiments. Then they did proton shadowing and blocking measurements. An ideal shadowing and blocking measurements results in an energy spectrum of the scattered protons that shows only a peak for the first surface layer and nothing else. Due to the non ideality of the experiment the spectrum also shows effects of the underlying layers. That means the spectrum is not one well defined peak but has a tail to lower energies due to protons scattered on deeper layers which results in losing energies because of stopping.
This is different for a liquid film on the surface: This film does hardly (to the meaning of hardly see Landau theory) have any order. So the effects of shadowing and blocking vanish what means all the liquid film contributes the same amount of scattered electrons to the signal. Therefore, the peak does not only have a tail, but also becomes broadened.
During their measurements Frenken and van der Veen raised the temperature to the melting point and hence could show that with increasing temperature a disordered film formed on the surface in equilibrium with a still well ordered Pb crystal. | 0 | Theoretical and Fundamental Chemistry |
Amplitude modulation was one of the original modes of operation introduced by Binnig and Quate in their seminal 1986 AFM paper, in this mode the sensor is excited just off resonance. By exciting the sensor just above its resonant frequency, it is possible to detect forces which change the resonant frequency by monitoring the amplitude of oscillation. An attractive force on the probe causes a decrease in the sensors resonant frequency, thus the driving frequency is further from resonance and the amplitude decreases, the opposite is true for a repulsive force. The microscopes control electronics can then use amplitude as the SPM reference channel, either in feedback mode, or it can be recorded directly in constant height mode.
Amplitude modulation can fail if the non-conservative forces (damping) change during the experiment, as this changes the amplitude of the resonance peak itself, which will be interpreted as a change in resonant frequency. Another potential problem with amplitude modulation is that a sudden change to a more repulsive (less attractive) force can shift the resonance past the drive frequency causing it to decrease again. In constant height mode this will just lead to an image artefact, but in feedback mode the feedback will read this as a stronger attractive force, causing positive feedback until the feedback saturates.
An advantage of amplitude modulation is that there is only one feedback loop (the topography feedback loop) compared to three in frequency modulation (the phase/frequency loop, the amplitude loop, and the topography loop), making both operation and implementation much easier. Amplitude modulation, however, is rarely used in vacuum as the Q of the sensor is usually so high that the sensor oscillates many times before the amplitude settles to its new value, thus slowing down operation. | 0 | Theoretical and Fundamental Chemistry |
A number of software products are available for calculating cut and fill. A simple approach involves defining different earthworks features in a computer program and then adjusting elevations manually to calculate the optimal cut and fill. More sophisticated software is able to automatically balance cut and fill while also considering the materials. Software that can do this falls under the broad category of earthworks estimation software. | 1 | Applied and Interdisciplinary Chemistry |
There are several research groups around the world currently working on ways to use NQR to detect explosives. Units designed to detect landmines and explosives concealed in luggage have been tested. A detection system consists of a radio frequency (RF) power source, a coil to produce the magnetic excitation field and a detector circuit which monitors for a RF NQR response coming from the explosive component of the object.
A fake device known as the ADE 651 claimed to exploit NQR to detect explosives but in fact could do no such thing. Nonetheless, the device was successfully sold for millions to dozens of countries, including the government of Iraq.
Another practical use for NQR is measuring the water/gas/oil coming out of an oil well in realtime.
This particular technique allows local or remote monitoring of the extraction process, calculation of the well's remaining capacity and the water/detergents ratio the input pump must send to efficiently extract oil.
Due to the strong temperature dependence of the NQR frequency, it can be used as a precise temperature sensor with resolution on the order of 10 °C. | 0 | Theoretical and Fundamental Chemistry |
Grinding uses an abrasive process to remove material from the workpiece. A grinding machine is a machine tool used for producing very fine finishes, making very light cuts, or high precision forms using an abrasive wheel as the cutting device. This wheel can be made up of various sizes and types of stones, diamonds or inorganic materials.
The simplest grinder is a bench grinder or a hand-held angle grinder, for deburring parts or cutting metal with a zip-disc.
Grinders have increased in size and complexity with advances in time and technology. From the old days of a manual toolroom grinder sharpening endmills for a production shop, to today's 30000 RPM CNC auto-loading manufacturing cell producing jet turbines, grinding processes vary greatly.
Grinders need to be very rigid machines to produce the required finish. Some grinders are even used to produce glass scales for positioning CNC machine axis. The common rule is the machines used to produce scales be 10 times more accurate than the machines the parts are produced for.
In the past grinders were used for finishing operations only because of limitations of tooling. Modern grinding wheel materials and the use of industrial diamonds or other man-made coatings (cubic boron nitride) on wheel forms have allowed grinders to achieve excellent results in production environments instead of being relegated to the back of the shop.
Modern technology has advanced grinding operations to include CNC controls, high material removal rates with high precision, lending itself well to aerospace applications and high volume production runs of precision components. | 1 | Applied and Interdisciplinary Chemistry |
Gene symbols generally are italicised, with only the first letter in uppercase and the remaining letters in lowercase (Shh). Italics are not required on web pages. Protein designations are the same as the gene symbol, but are not italicised and all are upper case (SHH). | 1 | Applied and Interdisciplinary Chemistry |
Many risks and challenges must still be addressed and explored before tissue engineered heart valves can fully be clinically implemented:
* Contamination – Particular source materials can foster a microbiological environment that is conducive to the susceptibility of viruses and infectious diseases. Anytime an external scaffold is implanted within the human body, contamination, while inevitable, can be diminished through the enforcement of sterile technique.
* Scaffold Interactions - There are many risks associated with the interactions between cells and the implanted scaffold as specific biocompatibility requirements are still largely unknown with current research. The response to these interactions are also highly individualistic, dependent on the specific patient's biological environment; therefore, animal models researched prior may not accurately portray outcomes in the human body. Due to the highly interactive nature between the scaffold and surrounding tissue, properties such as biodegradability, biocompatibility, and immunogenicity must all be carefully considered as they are key factors in the performance of the final product.
* Structural complexity – Heart valves with their heterogeneous structure are very complex and dynamic, thus posing a challenge for tissue engineered valves to mimic. The new valves must have high durability while also meeting the anatomical shape and mechanical functions of the native valve. | 1 | Applied and Interdisciplinary Chemistry |
The theoretical heat (the standard enthalpy) of reaction required to make high-calcium lime is around 3.15 MJ per kg of lime, so the batch kilns were only around 20% efficient. The key to development in efficiency was the invention of continuous kilns, avoiding the wasteful heat-up and cool-down cycles of the batch kilns. The first were simple shaft kilns, similar in construction to blast furnaces. These are counter-current shaft kilns. Modern variants include regenerative and annular kilns. Output is usually in the range 100–500 tonnes per day. | 1 | Applied and Interdisciplinary Chemistry |
In all of the typical emulsions, there are tiny particles (discrete phase) suspended in a liquid (continuous phase). In an oil-in-water emulsion, oil is the discrete phase, while water is the continuous phase.
What the Bancroft rule states is that contrary to common sense, what makes an emulsion oil-in-water or water-in-oil is not the relative percentages of oil or water, but which phase the emulsifier is more soluble in. So even though there may be a formula that's 60% oil and 40% water, if the emulsifier chosen is more soluble in water, it will create an oil-in-water system.
There are some exceptions to Bancrofts rule, but its a very useful rule of thumb for most systems.
The hydrophilic-lipophilic balance (HLB) of a surfactant can be used in order to determine whether it's a good choice for the desired emulsion or not.
*In oil-in-water emulsions – use emulsifying agents that are more soluble in water than in oil (High HLB surfactants).
*In water-in-oil emulsions – use emulsifying agents that are more soluble in oil than in water (Low HLB surfactants).
Bancroft's rule suggests that the type of emulsion is dictated by the emulsifier and that the emulsifier should be soluble in the continuous phase. This empirical observation can be rationalized by considering the interfacial tension at the oil-surfactant and water-surfactant interfaces. | 0 | Theoretical and Fundamental Chemistry |
Clinical trials are closely supervised by appropriate regulatory authorities. All studies involving a medical or therapeutic intervention on patients must be approved by a supervising ethics committee before permission is granted to run the trial. The local ethics committee has discretion on how it will supervise noninterventional studies (observational studies or those using already collected data). In the US, this body is called the Institutional Review Board (IRB); in the EU, they are called Ethics committees. Most IRBs are located at the local investigator's hospital or institution, but some sponsors allow the use of a central (independent/for profit) IRB for investigators who work at smaller institutions.
To be ethical, researchers must obtain the full and informed consent of participating human subjects. (One of the IRBs main functions is to ensure potential patients are adequately informed about the clinical trial.) If the patient is unable to consent for him/herself, researchers can seek consent from the patients legally authorized representative. In addition, the clinical trial participants must be made aware that they can withdraw from the clinical trial at any time without any adverse action taken against them. In California, the state has prioritized the individuals who can serve as the legally authorized representative.
In some US locations, the local IRB must certify researchers and their staff before they can conduct clinical trials. They must understand the federal patient privacy (HIPAA) law and good clinical practice. The International Conference of Harmonisation Guidelines for Good Clinical Practice is a set of standards used internationally for the conduct of clinical trials. The guidelines aim to ensure the "rights, safety and well being of trial subjects are protected".
The notion of informed consent of participating human subjects exists in many countries but its precise definition may still vary.
Informed consent is clearly a necessary condition for ethical conduct but does not ensure ethical conduct. In compassionate use trials the latter becomes a particularly difficult problem. The final objective is to serve the community of patients or future patients in a best-possible and most responsible way. See also Expanded access. However, it may be hard to turn this objective into a well-defined, quantified, objective function. In some cases this can be done, however, for instance, for questions of when to stop sequential treatments (see Odds algorithm), and then quantified methods may play an important role.
Additional ethical concerns are present when conducting clinical trials on children (pediatrics), and in emergency or epidemic situations.
Ethically balancing the rights of multiple stakeholders may be difficult. For example, when drug trials fail, the sponsors may have a duty to tell current and potential investors immediately, which means both the research staff and the enrolled participants may first hear about the end of a trial through public business news. | 1 | Applied and Interdisciplinary Chemistry |
The induction of NMDA receptor-dependent long-term potentiation (LTP) in chemical synapses in the brain occurs via a fairly straightforward mechanism. A substantial and rapid rise in calcium ion concentration inside the postsynaptic cell (or more specifically, within the dendritic spine) is most possibly all that is required to induce LTP. But the mechanism of calcium delivery to the postsynaptic cell in inducing LTP is more complicated. | 1 | Applied and Interdisciplinary Chemistry |
*Weaknesses of ERH include heat losses on small sites. Treatment volumes that have a large surface area but are thin with respect to depth will have significant heat losses which makes ERH less efficient. The minimum treatment interval for efficient ERH remediation is approximately 10 vertical feet.
*Co-contaminants like oil or grease make remediation more difficult. Oil and grease cause a Raoult’s Law effect which requires more energy to remove the contaminants.
*Peat or high organic carbon in the subsurface will preferentially adsorb VOCs due to van der Waals forces. This preferential adsorption will increase the amount of energy required to remove the VOCs from the subsurface.
*Fuel sites are less-commonly treated by ERH because other less-expensive remediation technologies are available and because fuel sites are usually thin (resulting in significant heat losses).
*Sites within landfills are also challenging because metallic debris can distort the electric current paths. ERH is more uniform in natural soil or rock. | 1 | Applied and Interdisciplinary Chemistry |
The entropy is given by the entropic equation of state:
Using as before, and integrating the second term using we obtain simply
This is the entropic equation of state for a perfect vdW fluid, or in reduced form | 0 | Theoretical and Fundamental Chemistry |
In fluid dynamics, the Taylor–Green vortex is an unsteady flow of a decaying vortex, which has an exact closed form solution of the incompressible Navier–Stokes equations in Cartesian coordinates. It is named after the British physicist and mathematician Geoffrey Ingram Taylor and his collaborator A. E. Green. | 1 | Applied and Interdisciplinary Chemistry |
* Robert Burns Woodward: Architect and Artist in the World of Molecules; Otto Theodor Benfey, Peter J. T. Morris, Chemical Heritage Foundation, April 2001.
* Robert Burns Woodward and the Art of Organic Synthesis: To Accompany an Exhibit by the Beckman Center for the History of Chemistry (Publication / Beckman Center for the History of Chemistry); Mary E. Bowden; Chemical Heritage Foundation, March 1992
*[https://web.archive.org/web/20060516234558/http://www.ch.ic.ac.uk/video/index.rss Video podcast of Robert Burns Woodward talking about cephalosporin]
*[http://www.sigmaaldrich.com/etc/medialib/docs/Aldrich/Acta/al_acta_10_01.Par.0001.File.tmp/al_acta_10_01.pdf Robert Burns Woodward: Three Score Years and Then?] David Dolphin, Aldrichimica Acta, 1977, 10(1), 3–9.
*[http://www.patentgenius.com/inventor/WoodwardRobertBurns.html Robert Burns Woodward Patents] | 0 | Theoretical and Fundamental Chemistry |
The optical properties of materials are determined by their electronic structure and band gap. The energy gap between the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO/LUMO) varies with the size and composition of a nanocluster. Thus, the optical properties of nanoclusters change. Furthermore, the gaps can be modified by coating the nanoclusters with different ligands or surfactants. It is also possible to design nanoclusters with tailored band gaps and thus tailor optical properties by simply tuning the size and coating layer of the nanocluster. | 0 | Theoretical and Fundamental Chemistry |
Cobalt sensors have been made that capitalize on the breaking of C-O bonds by Co(II) in a fluorescent probe known as Cobalt Probe 1 (CP1). | 0 | Theoretical and Fundamental Chemistry |
Neutrophil apoptosis, or programmed cell death, is vital in controlling the duration of the early inflammatory response, thus restricting damage to tissues by the neutrophils. ANCA may be developed either via ineffective apoptosis or ineffective removal of apoptotic cell fragments, leading to the exposure of the immune system to molecules normally sequestered inside the cells. This theory solves the paradox of how it could be possible for antibodies to be raised against the intracellular antigenic targets of ANCA. | 1 | Applied and Interdisciplinary Chemistry |
Mono Lake is a highly alkaline lake, or soda lake. Alkalinity is a measure of how many bases are in a solution, and how well the solution can neutralize acids. Carbonate (CO) and bicarbonate (HCO) are both bases. Hence, Mono Lake has a very high content of dissolved inorganic carbon. Through supply of calcium ions (Ca), the water will precipitate carbonate-minerals such as calcite (CaCO). Subsurface waters enter the bottom of Mono Lake through small springs. High concentrations of dissolved calcium ions in these subsurface waters cause huge amounts of calcite to precipitate around the spring orifices.
The tufa originally formed at the bottom of the lake. It took many decades or even centuries to form the well-recognized tufa towers. When lake levels fell, the tufa towers came to rise above the water surface and stand as the pillars seen today (see Lake Level History for more information). | 1 | Applied and Interdisciplinary Chemistry |
The primary reference document for safety pharmacology is ICH S7A, followed by many key regulatory documents which either focus on or mention safety pharmacology:
* ICH S7A: Safety pharmacology studies for human pharmaceuticals. [http://www.ich.org/fileadmin/Public_Web_Site/ICH_Products/Guidelines/Safety/S7A/Step4/S7A_Guideline.pdf].
* ICH S7B: Nonclinical evaluation of the potential for delayed ventricular repolarization (QT interval prolongation) by human pharmaceuticals. [http://www.ich.org/fileadmin/Public_Web_Site/ICH_Products/Guidelines/Safety/S7B/Step4/S7B_Guideline.pdf].
* ICH S6(R1): Preclinical safety evaluation of biotechnology-derived pharmaceuticals. [http://www.ich.org/fileadmin/Public_Web_Site/ICH_Products/Guidelines/Safety/S6_R1/Step4/S6_R1_Guideline.pdf].
* ICH S9: Nonclinical evaluation for anticancer pharmaceuticals. [http://www.ich.org/fileadmin/Public_Web_Site/ICH_Products/Guidelines/Safety/S9/Step4/S9_Step4_Guideline.pdf].
* ICH M3(R2): Guidance on nonclinical safety studies for the conduct of human clinical trials and marketing authorisation for pharmaceuticals. [http://www.ich.org/fileadmin/Public_Web_Site/ICH_Products/Guidelines/Multidisciplinary/M3_R2/Step4/M3_R2__Guideline.pdf].
* ICH E14: Clinical evaluation of QT/QTc interval and proarrhythmic potential for non-antiarrhythmic drugs. [http://www.ich.org/fileadmin/Public_Web_Site/ICH_Products/Guidelines/Efficacy/E14/E14_Guideline.pdf].
* EMEA/CHMP/SWP/94227/2004. Adopted by CHMP. Guideline on the Non-Clinical Investigation of the Dependence Potential of Medicinal Products. [http://cpdd.org/Pages/Index/Index_PDFs/EMEAGuidelinesOnTheNonClinicalInvestigationOfTheDependencePotentialOfMedicinalProducts.pdf].
* FDA U.S. Department of Health and Human Services Food and Drug Administration - Center for Drug Evaluation and Research (CDER). Guidance for Industry. Assessment of abuse potential of drugs. Final Guidance. [https://www.fda.gov/downloads/drugs/guidances/ucm198650.pdf].
* FDA U.S. Department of Health and Human Services Food and Drug Administration - Center for Drug Evaluation and Research (CDER). Guidance for Industry. Exploratory IND studies. [https://www.fda.gov/downloads/drugs/guidancecomplianceregulatoryinformation/guidances/ucm078933.pdf]. | 1 | Applied and Interdisciplinary Chemistry |
If the thickness of the diffusion layer is known, the finite-length Warburg element is defined as:
where
where is the thickness of the diffusion layer and is the diffusion coefficient.
There are two special conditions of finite-length Warburg elements: the Warburg Short () for a transmissive boundary, and the Warburg Open () for a reflective boundary. | 0 | Theoretical and Fundamental Chemistry |
Site-specific recombination, also known as conservative site-specific recombination, is a type of genetic recombination in which DNA strand exchange takes place between segments possessing at least a certain degree of sequence homology. Enzymes known as site-specific recombinases (SSRs) perform rearrangements of DNA segments by recognizing and binding to short, specific DNA sequences (sites), at which they cleave the DNA backbone, exchange the two DNA helices involved, and rejoin the DNA strands. In some cases the presence of a recombinase enzyme and the recombination sites is sufficient for the reaction to proceed; in other systems a number of accessory proteins and/or accessory sites are required. Many different genome modification strategies, among these recombinase-mediated cassette exchange (RMCE), an advanced approach for the targeted introduction of transcription units into predetermined genomic loci, rely on SSRs.
Site-specific recombination systems are highly specific, fast, and efficient, even when faced with complex eukaryotic genomes. They are employed naturally in a variety of cellular processes, including bacterial genome replication, differentiation and pathogenesis, and movement of mobile genetic elements. For the same reasons, they present a potential basis for the development of genetic engineering tools.
Recombination sites are typically between 30 and 200 nucleotides in length and consist of two motifs with a partial inverted-repeat symmetry, to which the recombinase binds, and which flank a central crossover sequence at which the recombination takes place. The pairs of sites between which the recombination occurs are usually identical, but there are exceptions (e.g. attP and attB of λ integrase). | 1 | Applied and Interdisciplinary Chemistry |
Prehydrated electrons are free electrons that occur in water under irradiation. Usually they form complexes with water molecules and become hydrated electrons. They can also react with the bases of the nucleotides dGMP and dTMP in aqueous solution. This suggests they may also react with the bases of the DNA double helix, ultimately breaking molecular bonds and causing DNA damage. This mechanism is hypothesized to be a cause of radiation damage to DNA. | 0 | Theoretical and Fundamental Chemistry |
Born and raised in New Orleans, Louisiana, to a professional musician-father and a housewife-mother, Ted Ellis earliest hints of artistic talent began to show at five-years-old. Ellis first attempt at art was a third-grade freehand sketch of a dog from Archie Comics, which he drew so accurately that friends and family believed it had been traced. Growing up, one of his favorite characters to draw was Wile E. Coyote, and as an adult he continues to enjoy comic books as "refreshing".
When he was old enough, Ted would ride the bus alone to downtown New Orleans so as to be exposed to and spend time with the area artists. He and his friends would in their spare time compete with one another to see who could draw the best designs, and Ted continued developing his art skills throughout primary school despite only receiving "satisfactory" marks in art class. In elementary school he attended a summer program at the New Orleans Center for Creative Arts, and later attended an after-school program at Lawless High School. Ellis says that he knew he wanted to be an artist in the seventh grade, and credits his teacher in that class for keeping him focused.
Ted worked for a time with charcoal and pastel before settling on oil and acrylic. He took art classes during high school and enrolled in four months of private art lessons, but is otherwise self-taught. Ellis followed advice from Anna Torregano, his mentor, friend and high school art teacher, and his parents, all of whom advised him to pursue an academic career so as not to become a "starving artist".
His mother especially stressed university and earning a professional degree.
Ted Ellis earned a B.Sc. in chemistry at Dillard University on a United States Army ROTC scholarship as well as academic scholarship, and went on to be commissioned a second lieutenant in the United States Army's Field Artillery Branch. Ellis spent the next ten years working in the field of chemistry, eight years of which were as an environmental chemist at Rollins Engineering Services.
Ellis has lived in Louisiana and California, and currently resides in Friendswood, Texas with his wife, Erania. They have a daughter, Chaney, and a son, Tanner.
Chaney is an aspiring rap artist and has produced a positive, parent-friendly CD about school and drugs titled Off the Chain. | 0 | Theoretical and Fundamental Chemistry |
The most studied is neurturin’s role in neurodegenerative disease like Parkinsons disease and Huntingtons, where several rat studies have implicated neurturin’s role in rescuing neurons. However, these results have never been observed in humans. Hirschsprung disease, a autosomal dominant genetic disorder, is characterized by complete absence of neuronal ganglion cells from the intestinal tract. Previous studies indicate a role of NRTN gene mutations in the disease. One study showed evidence that a mutation in the NRTN gene was not enough alone to cause onset of the disease, however when coupled with a mutation in the RET gene, disease was present in family members as well as the individual. A more recent study showed NRTN variants present in individuals with Hirschsprung disease. However, RET associated mutations were not found and in one variant, RET phosphorylation levels were reduced, which has the potential to have downstream effects on the proliferation and differentiation of neuronal crests. Also, high levels of expression of neurturin were found to be associated with nephroblastoma indicating the possible that the growth factor could be influencing differentiation. Lastly, a study also associated neurturin deficiency in mice with keratoconjunctivitis and dry eye. | 1 | Applied and Interdisciplinary Chemistry |
The FLC operon is a conserved eukaryotic locus that is negatively associated with flowering via repression of genes needed for the development of the meristem to switch to a floral state in the plant species Arabidopsis thaliana. FLC expression has been shown be regulated by the presence of [https://www.uniprot.org/uniprot/P0DH90 FRIGIDA], and negatively correlates with decreases in temperature resulting in the prevention of vernalization. The degree to which expression decreases depends on the temperature and exposure time as seasons progress. After the downregulation of FLC expression, the potential for flowering is enabled. The regulation of FLC expression involves both genetic and epigenetic factors such as histone methylation and DNA methylation. Furthermore, a number of genes are cofactors act as negative transcription factors for FLC genes. FLC genes also have a large number of homologues across species that allow for specific adaptations in a range of climates. | 1 | Applied and Interdisciplinary Chemistry |
In 1707, Abraham Darby I patented a method of making cast iron pots. His pots were thinner and hence cheaper than those of his rivals. Needing a larger supply of pig iron he leased the blast furnace at Coalbrookdale in 1709. There, he made iron using coke, thus establishing the first successful business in Europe to do so. His products were all of cast iron, though his immediate successors attempted (with little commercial success) to fine this to bar iron.
Bar iron thus continued normally to be made with charcoal pig iron until the mid-1750s. In 1755 Abraham Darby II (with partners) opened a new coke-using furnace at Horsehay in Shropshire, and this was followed by others. These supplied coke pig iron to finery forges of the traditional kind for the production of bar iron. The reason for the delay remains controversial. | 1 | Applied and Interdisciplinary Chemistry |
He carried out his doctoral studies at Yale University in New Haven, Connecticut, United States, obtaining his Ph.D. in 1961 under the tutorship of Prof. F.M. Richards. He did post doctoral work with Prof. Fritz Lipmann at Rockefeller University and with Marshall Warren Nirenberg at NIH.
During the 1960s, his research was focused on protein synthesis, a field in which he made crucial contributions. In the 1970s he was a pioneer in studying the mechanism of hormonal induction of oocyte maturation. His later research is focused in two ubiquitous protein kinases, CK1 and CK2, involved in the phosphorylation of key cellular proteins.
He devoted much of his life to organizing activities for the scientific integration in Latin America especially through organizing series of training courses in molecular biology techniques, and through the creation of the Latin American Network of Biological Sciences.
In recent years, Doctor Allende has been an promoter of science education through his personal commitment in several projects, like the Science Education Inquiry Based program, funded by the University of Chile, and through his participation in the Allende-Connelly Foundation, founded by him and his wife.
Though he retired from active science in 2009, he remains a professor at the Faculty of Medicine. He was also Research Vice President of the University of Chile.
He published his autobiography in 2010. | 1 | Applied and Interdisciplinary Chemistry |
* "Deposition" is said to occur when the drop spreads on the surface at impact and remains attached to the surface during the entire impact process without breaking up. This outcome is representative of impact of small, low-velocity drops onto smooth wetting surfaces.
* The "prompt splash" outcome occurs when the drop strikes a rough surface, and is characterized by the generation of droplets at the contact line (where solid, gas, and liquid meet) at the beginning of the process of spreading of the drop on the surface, when the liquid has a high outward velocity.
* At reduced surface tension, the liquid layer can detach from the wall, resulting in a "corona splash".
* On a wetting surface, "receding breakup" can occur as the liquid retracts from its maximum spreading radius, due to the fact that the contact angle decreases during retraction, causing some drops to be left behind by the receding drop. On superhydrophobic surfaces, the retracting drop can break up into a number of fingers which are each capable of further breakup, likely due to capillary instability. Such satellite droplets have been observed to break off from the impacting drop both during the spreading and retracting phases.
* "Rebound" and "partial rebound" outcomes can occur when a drop recedes after impact. As the drop recedes to the impact point, the kinetic energy of the collapsing drop causes the liquid to squeeze upward, forming a vertical liquid column. The case where drop stays partially on the surface but launches one or more drops at its top is known as partial rebound, whereas the case where the entire drop leaves the solid surface due to this upward motion is known as complete rebound. The difference between rebound and partial rebound is caused by the receding contact angle of the drop on the surface. For low values a partial rebound occurs, while for high values a complete rebound occurs (assuming that the drop recedes with enough kinetic energy). Addition of polymers like xanthan into water alters its rheological properties, transitioning it from a Newtonian fluid to a viscoelastic one. Consequently, this modification affects the shape of the droplet upon rebounding from a solid surface. | 1 | Applied and Interdisciplinary Chemistry |
The fermentation reaction only involves two steps. Pyruvate is converted to acetaldehyde by Pdc and then acetaldehyde is converted to ethanol by alcohol dehydrogenase (Adh). There is no significant increase in the number of Pdc genes in Crabtree-positive compared to Crabtree-negative species and no correlation between number of Pdc genes and efficiency of fermentation. There are five Adh genes in S. cerevisiae. Adh1 is the major enzyme responsible for catalyzing the fermentation step from acetaldehyde to ethanol. Adh2 catalyzes the reverse reaction, consuming ethanol and converting it to acetaldehyde. The ancestral, or original, Adh had a similar function as Adh1 and after a duplication in this gene, Adh2 evolved a lower K for ethanol. Adh2 is believed to have increased yeast species tolerance for ethanol and allowed Crabtree-positive species to consume the ethanol they produced after depleting sugars. However, Adh2 and consumption of ethanol is not essential for aerobic fermentation. Sch. pombe and other Crabtree positive species do not have the ADH2' gene and consumes ethanol very poorly. | 1 | Applied and Interdisciplinary Chemistry |
When depositing a droplet on a solid surface with contact angle θ, horizontal force balance is described by Young's equation. However, there is a vertical force balance which while often ignored can be written as:
Where
is the force per unit length in the vertical direction
is the surface tension of a liquid
is the Young's modulus of a substrate
is deformation of the substrate
This gives length scale δ~ γ/E sin θ for the deformation of bulk materials caused by the surface tension force.
For example, if a water ( ~ 72 mN/m) droplet is deposited on the glass ( ~ 700 GPa), this gives ~10m which is typically negligible. However, if a water droplet is deposited on the PDMS ( ~ 300 kPa), this causes the deformation to be ~10m, which is in micron scale. This can have great impact on micro/nanotechnology applications where length scale is comparable and "soft" photoresists are used. | 1 | Applied and Interdisciplinary Chemistry |
The relationship between fractional and Cartesian coordinates can be described by the matrix transformation :
Similarly, the Cartesian coordinates can be converted back to fractional coordinates using the matrix transformation : | 0 | Theoretical and Fundamental Chemistry |
High intensity ultrashort pulse lasers can create ATI features with 20 or more peaks. The photoelectron spectrum of electron energies is continuous since actual light sources contain a spread of energies. | 0 | Theoretical and Fundamental Chemistry |
During the same period, Santorio Santorio came up with one of the earliest thermoscopes. In 1612 he published his results on the heating effects from the Sun, and attempts to measure heat from the Moon.
Earlier 1589, Giambattista della Porta reported on the heat resented by his face, emitted by a remote candle and facilitated by a concave metallic mirror. He also reported the cooling felt from a solid ice block Della Porta experiment would be replicated many times with increasing accuracy. It was replicated by astronomers Giovanni Antonio Magini and Christopher Heydon in 1603, and supplied instructions for Rudolf II, Holy Roman Emperor who performed it in 1611. In 1660, della Porta experiment was updated by the Accademia del Cimento using a thermometer invented by Ferdinand II, Grand Duke of Tuscany. | 0 | Theoretical and Fundamental Chemistry |
The toxicity of PCBs varies considerably among congeners. The coplanar PCBs, known as nonortho PCBs because they are not substituted at the ring positions ortho to (next to) the other ring, (such as PCBs 77, 126 and 169), tend to have dioxin-like properties, and generally are among the most toxic congeners. Because PCBs are almost invariably found in complex mixtures, the concept of toxic equivalency factors (TEFs) has been developed to facilitate risk assessment and regulation, where more toxic PCB congeners are assigned higher TEF values on a scale from 0 to 1. One of the most toxic compounds known, [[2,3,7,8-tetrachlorodibenzodioxin|2,3,7,8-tetrachlorodibenzo[p]dioxin]], a PCDD, is assigned a TEF of 1. In June 2020, State Impact of Pennsylvania stated that "In 1979, the EPA banned the use of PCBs, but they still exist in some products produced before 1979. They persist in the environment because they bind to sediments and soils. High exposure to PCBs can cause birth defects, developmental delays, and liver changes." | 1 | Applied and Interdisciplinary Chemistry |
Most plant pathogens reprogram host gene expression patterns to directly benefit the pathogen. Reprogrammed genes required for pathogen survival and proliferation can be thought of as “disease-susceptibility genes.” Recessive resistance genes are disease-susceptibility candidates. For example, a mutation disabled an Arabidopsis gene encoding pectate lyase (involved in cell wall degradation), conferring resistance to the powdery mildew pathogen Golovinomyces cichoracearum. Similarly, the Barley MLO gene and spontaneously mutated pea and tomato MLO orthologs also confer powdery mildew resistance.
Lr34 is a gene that provides partial resistance to leaf and yellow rusts and powdery mildew in wheat. Lr34 encodes an adenosine triphosphate (ATP)–binding cassette (ABC) transporter. The dominant allele that provides disease resistance was recently found in cultivated wheat (not in wild strains) and, like MLO provides broad-spectrum resistance in barley.
Natural alleles of host translation elongation initiation factors eif4e and eif4g are also recessive viral-resistance genes. Some have been deployed to control potyviruses in barley, rice, tomato, pepper, pea, lettuce and melon. The discovery prompted a successful mutant screen for chemically induced eif4e alleles in tomato.
Natural promoter variation can lead to the evolution of recessive disease-resistance alleles. For example, the recessive resistance gene xa13 in rice is an allele of Os-8N3. Os-8N3 is transcriptionally activated byXanthomonas oryzae pv. oryzae strains that express the TAL effector PthXo1. The xa13 gene has a mutated effector-binding element in its promoter that eliminates PthXo1 binding and renders these lines resistant to strains that rely on PthXo1. This finding also demonstrated that Os-8N3 is required for susceptibility.
Xa13/Os-8N3 is required for pollen development, showing that such mutant alleles can be problematic should the disease-susceptibility phenotype alter function in other processes. However, mutations in the Os11N3 (OsSWEET14) TAL effector–binding element were made by fusing TAL effectors to nucleases (TALENs). Genome-edited rice plants with altered Os11N3 binding sites remained resistant to Xanthomonas oryzae pv. oryzae, but still provided normal development function. | 1 | Applied and Interdisciplinary Chemistry |
at the Pharmacological Institute in Berlin published a survey of literature on antibiotics in the 7 August 1943 issue of Klinische Wochenschrift that included the Oxford team's publications. A copy was acquired by the Japanese embassy in Berlin and taken to Japan on the , which docked at Kure, Hiroshima, on 21 December 1943. The article was translated into Japanese, and production of penicillin was underway by 1 February 1944. By mid-May, a research team under Hamao Umezawa had tested 750 different strains of mould and found that 75 exhibited antibiotic activity. Experiments were conducted on mice to determine efficacy and toxicity. The Morinaga Milk company had a small penicillin production plant in operation in Mishima, Shizuoka, by the end of the year, and the opened a small plant in Okazaki, Aichi, in January 1945. The penicillin was called "Hekiso" after its blue colour. By 1948 Japan had become the third country, after the US and UK, to become self-sufficient in penicillin, and exports to China and Korea began the following year. | 1 | Applied and Interdisciplinary Chemistry |
Sit Kim Ping is a Singaporean biochemist and an Emeritus Professor at the Department of Biochemistry at the National University of Singapore. She was the Head of the Department of Biochemistry (part of the Yong Loo Lin School of Medicine) from 1996 to 2000. | 1 | Applied and Interdisciplinary Chemistry |
The latest efforts in integrating nanotechnology and biological research have been successful and show much promise for the future, including in fields such as nanobiomechanics. Since nanoparticles are a potential vehicle of drug delivery, the biological responses of cells to these nanoparticles are continuously being explored to optimize their efficacy and how their design could be improved. Pyrgiotakis et al. were able to study the interaction between CeO and FeO engineered nanoparticles and cells by attaching the engineered nanoparticles to the AFM tip. Studies have taken advantage of AFM to obtain further information on the behavior of live cells in biological media. Real-time atomic force spectroscopy (or nanoscopy) and dynamic atomic force spectroscopy have been used to study live cells and membrane proteins and their dynamic behavior at high resolution, on the nanoscale. Imaging and obtaining information on the topography and the properties of the cells has also given insight into chemical processes and mechanisms that occur through cell-cell interaction and interactions with other signaling molecules (ex. ligands). Evans and Calderwood used single cell force microscopy to study cell adhesion forces, bond kinetics/dynamic bond strength and its role in chemical processes such as cell signaling.
Scheuring, Lévy, and Rigaud reviewed studies in which AFM to explore the crystal structure of membrane proteins of photosynthetic bacteria.
Alsteen et al. have used AFM-based nanoscopy to perform a real-time analysis of the interaction between live mycobacteria and antimycobacterial drugs (specifically isoniazid, ethionamide, ethambutol, and streptomycine), which serves as an example of the more in-depth analysis of pathogen-drug interactions that can be done through AFM. | 0 | Theoretical and Fundamental Chemistry |
Artificial chromosomes are manufactured chromosomes in the context of yeast artificial chromosomes (YACs), bacterial artificial chromosomes (BACs), or human artificial chromosomes (HACs). An artificial chromosome can carry a much larger DNA fragment than other vectors. YACs and BACs can carry a DNA fragment up to 300,000 nucleotides long. Three structural necessities of an artificial chromosome include an origin of replication, a centromere, and telomeric end sequences. | 1 | Applied and Interdisciplinary Chemistry |
The subgroup structure suggests another way to compose an arbitrary isometry:
: Pick a fixed point, and a mirror through it.
# If the isometry is odd, use the mirror; otherwise do not.
# If necessary, rotate around the fixed point.
# If necessary, translate.
This works because translations are a normal subgroup of the full group of isometries, with quotient the orthogonal group; and rotations about a fixed point are a normal subgroup of the orthogonal group, with quotient a single reflection. | 0 | Theoretical and Fundamental Chemistry |
The thermite () reaction was discovered in 1893 and patented in 1895 by German chemist Hans Goldschmidt. Consequently, the reaction is sometimes called the "Goldschmidt reaction" or "Goldschmidt process". Goldschmidt was originally interested in producing very pure metals by avoiding the use of carbon in smelting, but he soon discovered the value of thermite in welding.
The first commercial application of thermite was the welding of tram tracks in Essen in 1899. | 0 | Theoretical and Fundamental Chemistry |
LSAT was originally developed as a substrate for the growth of high T cuprate superconductors thin films, mostly of yttrium barium copper oxide (YBCO), for microwave device applications. The motivation for its development was to create a lattice-matched substrate with a similar thermal expansion coefficient and no structural phase transition over a wide temperature range, spanning from the high temperatures used for the growth of cuprates, to the cryogenic temperatures where they are superconducting. | 0 | Theoretical and Fundamental Chemistry |
While the first reports of its use dated to 1980, it was a further two decades before the technique of SRCD took off largely due to the work of Bonnie Wallace at Birkbeck College, University of London. From around 2000, her aims in the field focused on both enhancing the collection of quality data through technical improvements, and on demonstrating "proof-of-principle" application studies, illustrating the novel information that SRCD offers. The construction on the Synchrotron Radiation Source (SRS) of the CD12 beamline at Daresbury Laboratory, opened in 2005 under the auspices of the Centre for Protein and Membrane Structure and Dynamics (CPMSD) of which Wallace was the Director, represented the first of the new, dedicated, second-generation SRCD beamlines. It was quickly identified that the high photon flux from CD12 was causing denaturation of the protein sample but that this was resolvable by reducing the sample area being irradiated. Later studies have identified the flux threshold limits that induce SRCD protein denaturation. The input from the Wallace lab to the early years of SRCD development also included the introduction of calibration and standardization of SRCD and cCD spectrophotometers, the creation of software to process the spectral data using CDtool, and CDtoolX, and to analyse the data using DichroWeb, and the generation of reference data sets of proteins to support these data analyses. Additionally, her lab produced sample cells with reduced pathlengths, and using material, (CaF), transparent to VUV radiation which significantly enhanced the collection of data into the SRCD lower wavelength regions.
New SRCD beamlines were constructed on various synchrotrons around the world. ring, in the Department of Physics and Astronomy of Aarhus University in Denmark, became a dedicated second-generation synchrotron in 2005. Ultimately this ring had two SRCD beamlines, [https://www.isa.au.dk/facilities/astrid/beamlines/uv1/uv1.asp UV1] and [https://www.isa.au.dk/facilities/astrid/beamlines/cd1/cd1.asp CD1], which migrated to the new third-generation ring, ASTRID2, in 2013/14, as [https://www.isa.au.dk/facilities/astrid2/beamlines/AU-uv/AU-uv.asp AU-UV] and [https://www.isa.au.dk/facilities/astrid2/beamlines/AU-cd/AU-cd.asp AU-CD]. SOLEIL synchrotron, near Paris, France, commissioned a dedicated SRCD beamline, [https://www.synchrotron-soleil.fr/en/beamlines/disco DISCO], around 2005. At Hiroshima Synchrotron Radiation Center, also known as HiSOR, a VUVCD beamline was constructed over the same period, while a little later in 2009, an SRCD beamline was commissioned in Beijing, China. This particular beamline is unique in that the synchrotron which acts as its light source is also the electron carrying ring of the Beijing Electron Positron Collider. The SRS closed in 2008 being superseded in the UK by the Diamond Light Source on which an SRCD beamline opened for use in 2010. With the SRS closure the CD12 SRCD beamline was moved to, and installed on, the ANKA Synchrotron Radiation Facility, (now called [https://www.ibpt.kit.edu/kara.php KARA]), part of Karlsruhe Institute of Technology (KIT), in Karlsruhe, Germany. This beamline opened for users in 2011 but was closed in 2021. Currently under construction (as of June 2023) on the Sirius synchrotron light source in Campinas, Brazil, is a new SRCD beamline, CEDRO. | 0 | Theoretical and Fundamental Chemistry |
Hattori presented evidence in her Nature paper that, resolved the long-standing debate regarding the timing of the change in ancient Earths surface oxidation. Her findings demonstrated that atmospheric oxygen levels were still low around 2.4 billion years ago, during the early Proterozoic, based on detailed sulfur isotope analysis of sedimentary rocks on the north shore of Lake Huron. In her subsequent work published in Science', she revealed that atmospheric oxygen levels sharply rose within the sedimentary sequence at about 2.3 billion years.
Hattori also highlighted the role of volcanic processes in shaping the surface redox condition, challenging the previously held belief that increased photosynthesis was solely responsible for the oxidation of Earth's surface environment. Subsequent work provided further confirmation of the crystallization of oxidized magmatic sulfates during igneous crystallization, as well as the presence of such sulfate minerals in ancient (2.6 billion years old) igneous rocks. | 0 | Theoretical and Fundamental Chemistry |
Long-chain hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency is a mitochondrial effect of impaired enzyme function.
LCHAD performs the dehydrogenation of hydroxyacyl-CoA derivatives, facilitating the removal of hydrogen and the formation of a keto group. This reaction is essential for the subsequent steps in beta oxidation that lead to the production of acetyl-CoA, NADH, and FADH2, which are important for generating ATP, the energy currency of the cell.
Long-chain hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency is a condition that affects mitochondrial function due to enzyme impairments. LCHAD deficiency is specifically caused by a shortfall in the enzyme long-chain 3-hydroxyacyl-CoA dehydrogenase. This leads to the body's inability to transform specific fats into energy, especially during fasting periods.
* Severe Phenotype: symptoms appear soon after birth and include hypoglycemia, hepatomegaly, brain dysfunction (encephalopathy) and often cardiomyopathy
* Intermediate Phenotype: characterized by hypoketotic hypoglycemia and is triggered by infection or fasting during infancy
* Mild (Late-Onset) Phenotype: presents as muscle weakness (myopathy) and nerve disease (neuropathy)
* Long-Term Complications: can include peripheral neuropathy and eye damage (retinopathy)
* Regular feeding to avoid fasting
* Use of medium-chain triglyceride (MCT) or triheptanoin supplements and carnitine supplements
* Low-fat diet
* Hospitalization with intravenous fluids containing at least 10% dextrose
* Bicarbonate therapy for severe metabolic acidosis
* Management of high ammonia levels and muscle breakdown
* Cardiomyopathy management
* Regular monitoring of nutrition, blood and liver tests with annual fatty acid profile
* Growth, development, heart and neurological assessments and eye evaluations | 1 | Applied and Interdisciplinary Chemistry |
Many cross-couplings entail forming carbon–heteroatom bonds (heteroatom = S, N, O). A popular method is the Buchwald–Hartwig reaction: | 0 | Theoretical and Fundamental Chemistry |
A sperm bank will aim to provide donor sperm which is safe by checking and screening donors and of their semen. A sperm donor must generally meet specific requirements regarding age and medical history. Requirements for sperm donors are strictly enforced, as in a study of 24,040 potential sperm donors, only 5620, or 23.38% were eligible to donate their sperm.
Sperm banks typically screen potential donors for a range of diseases and disorders, including genetic diseases, chromosomal abnormalities and sexually transmitted infections that may be transmitted through sperm. The screening procedure generally also includes a quarantine period, in which the samples are frozen and stored for at least six months after which the donor will be re-tested for the STIs. This is to ensure no new infections have been acquired or have developed during the period of donation. Providing the result is negative, the sperm samples can be released from quarantine and used in treatments. Common reasons for sperm rejection include suboptimal semen quality and STDs. Chromosomal abnormalities are also a cause for semen rejection, but are less common. Children conceived through sperm donation have a birth defect rate of almost a fifth compared with the general population.
A sperm bank takes a number of steps to ensure the health and quality of the sperm which it supplies and it will inform customers of the checks which it undertakes, providing relevant information about individual donors. A sperm bank will usually guarantee the quality and number of motile sperm available in a sample after thawing. They will try to select men as donors who are particularly fertile and whose sperm will survive the freezing and thawing process. Samples are often sold as containing a particular number of motile sperm per milliliter, and different types of samples may be sold by a sperm bank for differing types of use, e.g. ICI or IUI.
The sperm will be checked to ensure its fecundity and also to ensure that motile sperm will survive the freezing process. If a man is accepted onto the sperm banks program as a sperm donor, his sperm will be constantly monitored, the donor will be regularly checked for infectious diseases, and samples of his blood will be taken at regular intervals. A sperm bank may provide a donor with dietary supplements containing herbal or mineral substances such as maca, zinc, vitamin E and arginine which are designed to improve the quality and quantity of the donors semen, as well as reducing the refractory time (i.e. the time between viable ejaculations). All sperm is frozen in straws or vials and stored for as long as the sperm donor may and can maintain it.
Donors are subject to tests for infectious diseases such as human immunoviruses HIV (HIV-1 and HIV-2), human T-cell lymphotropic viruses (HTLV-1 and HTLV-2), syphilis, chlamydia, gonorrhea, hepatitis B virus, hepatitis C virus, cytomegalovirus (CMV), Trypanosoma cruzi and malaria as well as hereditary diseases such as cystic fibrosis, Sickle cell anemia, Familial Mediterranean fever, Gauchers disease, thalassaemia, Tay–Sachs disease, Canavans disease, familial dysautonomia, congenital adrenal hyperplasia, carnitine transporter deficiency and Karyotyping 46XY. Karyotyping is not a requirement in either EU or the US but some sperm banks choose to test donors as an extra service to the customer.
A sperm donor may also be required to produce their medical records and those of their family, often for several generations. A sperm sample is usually tested micro-biologically at the sperm bank before it is prepared for freezing and subsequent use. A sperm donor's blood group may also be registered to ensure compatibility with the recipient.
Some sperm banks may disallow sexually active gay men from donating sperm due to the population's increased risk of HIV and hepatitis B. Modern sperm banks have also been known to screen out potential donors based on genetic conditions and family medical history. | 1 | Applied and Interdisciplinary Chemistry |
In nuclear transitions governed by strong and electromagnetic interactions (which are invariant under parity), the physical laws would be the same if the interaction was reflected in a mirror. Hence the sum of a vector and a pseudovector is not meaningful. However, the weak force, which governs beta decay and the corresponding nuclear transitions, does depend on the chirality of the interaction, and in this case pseudovectors and vectors are added.
The Gamow–Teller transition is a pseudovector transition, that is, the selection rules for beta decay caused by such a transition involve no parity change of the nuclear state. The spin of the parent nucleus can either remain unchanged or change by ±1. However, unlike the Fermi transition, transitions from spin 0 to spin 0 are excluded.
In terms of total nuclear angular momentum, the Gamow–Teller transition () is
:;Examples
:: also parity is conserved: the final Li 1 state has and the state has states that couple to an even parity state. | 0 | Theoretical and Fundamental Chemistry |
Pol III has three classes of initiation, which start with different factors recognizing different control elements but all converging on TFIIIB (similar to TFIIB-TBP; consists of TBP/TRF, a TFIIB-related factor, and a B″ unit) recruiting the Pol III preinitiation complex. The overall architecture resembles that of Pol II. Only TFIIIB needs to remain attached during elongation. | 1 | Applied and Interdisciplinary Chemistry |
In the most simplified quorum sensing systems, bacteria only need two components to make use of autoinducers. They need a way to produce a signal and a way to respond to that signal. These cellular processes are often tightly coordinated and involve changes in gene expression. The production of autoinducers generally increases as bacterial cell densities increase. Most signals are produced intracellularly and are subsequently secreted in the extracellular environment. Detection of autoinducers often involves diffusion back into cells and binding to specific receptors. Usually, binding of autoinducers to receptors does not occur until a threshold concentration of autoinducers is achieved. Once this has occurred, bound receptors alter gene expression either directly or indirectly. Some receptors are transcription factors themselves, while others relay signals to downstream transcription factors. In many cases, autoinducers participate in forward feedback loops, whereby a small initial concentration of an autoinducer amplifies the production of that same chemical signal to much higher levels. | 1 | Applied and Interdisciplinary Chemistry |
Bacteria proteins, also known as effectors, have been shown to use AMPylation. Effectors such as VopS, IbpA, and DrrA, have been shown to AMPylate host GTPases and cause actin cytoskeleton changes. GTPases are common targets of AMPylators. Rho, Rab, and Arf GTPase families are involved in actin cytoskeleton dynamics and vesicular trafficking. They also play roles in cellular control mechanisms such as phagocytosis in the host cell.
The pathogen enhances or prevents its internalization by either inducing or inhibiting host cell phagocytosis. Vibrio parahaemolyticus is a Gram-negative bacterium that causes food poisoning as a result of raw or undercooked seafood consumption in humans. VopS, a type III effector found in Vibrio parahaemolyticus, contains a Fic domain that has a conserved HPFx(D/E)GN(G/K)R motif that contains a histidine residue essential for AMPylation. VopS blocks actin assembly by modifying threonine residue in the switch 1 region of Rho GTPases. The transfer of an AMP moiety using ATP to the threonine residue results in steric hindrance, and thus prevents Rho GTPases from interacting with downstream effectors. VopS also adenylates RhoA and cell division cycle 42 (CDC42), leading to a disaggregation of the actin filament network. As a result, the host cell's actin cytoskeleton control is disabled, leading to cell rounding.
IbpA is secreted into eukaryotic cells from H. somni, a Gram-negative bacterium in cattle that causes respiratory epithelium infection. This effector contains two Fic domains at the C-terminal region. AMPylation of the IbpA Fic domain of Rho family GTPases is responsible for its cytotoxicity. Both Fic domains have similar effects on host cells' cytoskeleton as VopS. The AMPylation on a tyrosine residue of the switch 1 region blocks the interaction of the GTPases with downstream substrates such as PAK.
DrrA is the Dot/Icm type IV translocation system substrate DrrA from Legionella pneumophila. It is the effector secreted by L. pneumophila to modify GTPases of the host cells. This modification increases the survival of bacteria in host cells. DrrA is composed of Rab1b specific guanine nucleotide exchange factor (GEF) domain, a C-terminal lipid binding domain and an N-terminal domain with unclear cytotoxic properties. Research works show that N-terminal and full-length DrrA shows AMPylators activity toward hosts Rab1b protein (Ras related protein), which is also the substrate of Rab1b GEF domain. Rab1b protein is the GTPase Rab to regulate vesicle transportation and membrane fusion. The adenylation by bacteria AMPylators prolong GTP-bound state of Rab1b. Thus, the role of effector DrrA is connected toward the benefits of bacterias vacuoles for their replication during the infection. | 1 | Applied and Interdisciplinary Chemistry |
The CEEES has three major Technical Advisory Boards:
*Mechanical Environments: The aim of this board is to advance methodologies and technologies for quantifying, describing and simulating mechanical environmental conditions experienced by mechanical equipment during its useful life.
*Climatic and Atmospheric Pollution Effects: The aim of this board is the study of the climatic and atmospheric pollution effects on materials and mechanical equipment.
*Reliability and Environmental Stress Screening: The aim of this board is the study how the environmental effects the reliability of equipment. | 1 | Applied and Interdisciplinary Chemistry |
In addition to the role of the lactate shuttle in supplying NAD+ substrate for β-oxidation in the peroxisomes, the shuttle also regulates FFA mobilization by controlling plasma lactate levels. Research has demonstrated that lactate functions to inhibit lipolysis in fat cells through activation of an orphan G-protein couple receptor (GPR81) that acts as a lactate sensor, inhibiting lipolysis in response to lactate . | 1 | Applied and Interdisciplinary Chemistry |
The internal cavity of a carcerand can be as large as 1700 Å (1.7 nm) when six hemicarcerands form a single octahedral compound. This is accomplished by dynamic covalent chemistry in a one-pot condensation of 6 equivalents of a and 12 equivalents of ethylene diamine with trifluoroacetic acid catalyst in chloroform at room temperature followed by reduction of the imine bonds with sodium borohydride. | 0 | Theoretical and Fundamental Chemistry |
The local variational theory of elliptic LCSs targets material surfaces that locally maximize material shear over the finite time interval of interest. This means that at initial point each point of an elliptic LCS , the tangent space is the plane along which the local Lagrangian shear is maximal (cf. Fig 7).
Introducing the two-dimensional shear vector field
and the three-dimensional shear normal vector field
the criteria for two- and three-dimensional elliptic LCSs can be summarized as follows:
For 3D flows, as in the case of hyperbolic LCSs, solving the Frobenius PDE can be avoided. Instead, one can construct intersections of a tubular elliptic LCS with select 2D planes, and fit a surface numerically to a large number of these intersection curves. As for hyperbolic LCSs above, let us denote the unit normal of a 2D plane by . Again, the intersection curves of elliptic LCSs with the plane are normal to both and to the unit normal of the LCS. As a consequence, an intersection curve satisfies the reduced shear ODE
whose trajectories we refer to as reduced shear lines. (Strictly speaking, the reduced shear ODE is not an ordinary differential equation, given that its right-hand side is not a vector field, but a direction field, which is generally not globally orientable). Intersections of tubular elliptic LCSs with are limit cycles of the reduced shear ODE. Determining such limit cycles in a smooth family of nearby planes, then fitting a surface to the limit cycle family yields a numerical approximation for 2D shear surface. A three-dimensional example of this local variational computation of an elliptic LCS is shown in Fig. 11. | 1 | Applied and Interdisciplinary Chemistry |
The historical background is divided into several subsections. The first is the general background to electrons in vacuum and the technological developments that led to cathode-ray tubes as well as vacuum tubes that dominated early television and electronics; the second is how these led to the development of electron microscopes; the last is work on the nature of electron beams and the fundamentals of how electrons behave, a key component of quantum mechanics and the explanation of electron diffraction. | 0 | Theoretical and Fundamental Chemistry |
An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O), creating toxic, euxinic (anoxic and sulfidic) waters. Although anoxic events have not happened for millions of years, the geologic record shows that they happened many times in the past. Anoxic events coincided with several mass extinctions and may have contributed to them. These mass extinctions include some that geobiologists use as time markers in biostratigraphic dating. On the other hand, there are widespread, various black-shale beds from the mid-Cretaceous which indicate anoxic events but are not associated with mass extinctions. Many geologists believe oceanic anoxic events are strongly linked to the slowing of ocean circulation, climatic warming, and elevated levels of greenhouse gases. Researchers have proposed enhanced volcanism (the release of CO) as the "central external trigger for euxinia."
Human activities in the Holocene epoch, such as the release of nutrients from farms and sewage, cause relatively small-scale dead zones around the world. British oceanologist and atmospheric scientist Andrew Watson says full-scale ocean anoxia would take "thousands of years to develop." The idea that modern climate change could lead to such an event is also referred to as Kump's hypothesis, | 0 | Theoretical and Fundamental Chemistry |
Unlike other isotopic dating methods, the "daughter" in fission track dating is an effect in the crystal rather than a daughter isotope. Uranium-238 undergoes spontaneous fission decay at a known rate, and it is the only isotope with a decay rate that is relevant to the significant production of natural fission tracks; other isotopes have fission decay rates too slow to be of consequence. The fragments emitted by this fission process
leave trails of damage (fossil tracks or ion tracks) in the crystal structure of the mineral that contains the uranium. The process of track production is essentially the same by which swift heavy ions produce ion tracks.
Chemical etching of polished internal surfaces of these minerals reveals spontaneous fission tracks, and the track density can be determined. Because etched tracks are relatively large (in the range 1 to 15 micrometres), counting can be done by optical microscopy, although other imaging techniques are used. The density of fossil tracks correlates with the cooling age of the sample and with uranium content, which needs to be determined independently.
To determine the uranium content, several methods have been used. One method is by neutron irradiation, where the sample is irradiated with thermal neutrons in a nuclear reactor, with an external detector, such as mica, affixed to the grain surface. The neutron irradiation induces fission of uranium-235 in the sample, and the resulting induced tracks are used to determine the uranium content of the sample because the U:U ratio is well known and assumed constant in nature. However, it is not always constant. To determine the number of induced fission events that occurred during neutron irradiation an external detector is attached to the sample and both sample and detector are simultaneously irradiated by thermal neutrons. The external detector is typically a low-uranium mica flake, but plastics such as CR-39 have also been used. The resulting induced fission of the uranium-235 in the sample creates induced tracks in the overlying external detector, which are later revealed by chemical etching. The ratio of spontaneous to induced tracks is proportional to the age.
Another method of determining uranium concentration is through LA-ICPMS, a technique where the crystal is hit with a laser beam and ablated, and then the material is passed through a mass spectrometer. | 0 | Theoretical and Fundamental Chemistry |
Apart from the original evidence provided by Männig and Nöth, the total synthesis of (+)-ptilocaulin also demonstrates selective hydroboration of a terminal alkene in the presence of a ketone.
In terms of regioselectivity, the catalyzed hydroboration differs from the uncatalyzed parallel. Depending on the ligands and the alkene, either Markovnikov or anti-Markovnikov product result. The difference in regioselectivity is more pronounced in the hydroboration of vinylarenes with HBcat. Wilkinson's catalyst or the cation Rh(COD) (in the presence of PPh) produces the Markovnikov product. The anti-Markovnikov product is produced in the absence of a catalyst. It is worth noticing that the use of RhCl·nH2O produces selectively the anti-Markovnikov product. To account for the high regioselectivity of catalyzed hydroboration, Hayashi proposed a mechanism involving a η-benzylrhodium complex.
Catalyzed hydroboration-oxidation of substituted alkenes can be rendered enantioselective. In 1990, Brown and co-workers achieved asymmetric hydroboration using an achiral catalyst and chiral borane sources derived from ephedrine and pseudoephedrine. In most cases, the regioselectivity was poor although the ee values can be close to 90%.
Use of a chiral catalyst and an achiral borane source is more common, e.g. chiral diphosphines such as BINAP.
Styrene or its simple derivatives are usually the prochiral substrate.
Enantioselectivity tends to be lowered with ortho-substituents on the aromatic ring, as well as further substitution on the olefin. Successful results have also been obtained on other reactants. The second class of ligands is phosphinamine ligands. In 1993, Brown first reported the successful use of QUINAP in asymmetric alkene hydroboration. QUINAP improve upon the intolerance of substitution on the aromatic ring as observed for diphosphine ligands. Reactions using styrene and derivatives with electron-donating groups on the para position still gave high ee values. Similar results were also obtained on cyclic vinyl arenes. Such results expand the scope of asymmetric hydroboration to more sterically demanding alkenes. Several new ligands of this class have also been developed. Some recent results are summarized below.
The studies above have all utilized oxidation of the boronate esters to produce alcohols, which is a severe limitation to the synthetic scope of such species, especially when they can be made enantioselectively. Another important class of compounds that can be derived from boronate esters is α-substituted benzylamines, some of which are commercially useful. The synthesis of such chiral amines via catalytic hydroboration involves conversion of the catecholboronate ester to trialkylborane by diethyl zinc or methylmagnesium chloride. Reaction of the trialkylborane with hydroxylamine-O-sulfonic acid produces primary benzylamines. Secondary amines can also be prepared by in situ formation of N-chloramines. | 0 | Theoretical and Fundamental Chemistry |
Monophosphine-type ligands were among the first to appear in asymmetric hydrogenation, e.g., the ligand CAMP. Continued research into these types of ligands has explored both P-alkyl and P-heteroatom bonded ligands, with P-heteroatom ligands like the phosphites and phosphoramidites generally achieving more impressive results. Structural classes of ligands that have been successful include those based on the binapthyl structure of MonoPHOS or the spiro ring system of SiPHOS. Notably, these monodentate ligands can be used in combination with each other to achieve a synergistic improvement in enantioselectivity; something that is not possible with the diphosphine ligands. | 0 | Theoretical and Fundamental Chemistry |
hnRNP has been shown to regulate CD44, a cell-surface glycoprotein, through splicing mechanisms. CD44 is involved in cell-cell interactions and has roles in cell adhesion and migration. Splicing of CD44 and the functions of the resulting isoforms are different in breast cancer cells, and when knocked down, hnRNP reduced both cell viability and invasiveness. | 1 | Applied and Interdisciplinary Chemistry |
The disulfide bonds are strong, with a typical bond dissociation energy of 60 kcal/mol (251 kJ mol). However, being about 40% weaker than and bonds, the disulfide bond is often the "weak link" in many molecules. Furthermore, reflecting the polarizability of divalent sulfur, the bond is susceptible to scission by polar reagents, both electrophiles and especially nucleophiles (Nu):
The disulfide bond is about 2.05 Å in length, about 0.5 Å longer than a bond. Rotation about the axis is subject to a low barrier. Disulfides show a distinct preference for dihedral angles approaching 90°. When the angle approaches 0° or 180°, then the disulfide is a significantly better oxidant.
Disulfides where the two R groups are the same are called symmetric, examples being diphenyl disulfide and dimethyl disulfide. When the two R groups are not identical, the compound is said to be an asymmetric or mixed disulfide.
Although the hydrogenation of disulfides is usually not practical, the equilibrium constant for the reaction provides a measure of the standard redox potential for disulfides:
This value is about −250 mV versus the standard hydrogen electrode (pH = 7). By comparison, the standard reduction potential for ferrodoxins is about −430 mV. | 0 | Theoretical and Fundamental Chemistry |
Single-strand breaks (SSBs) occur when one strand of the DNA double helix experiences breakage of a single nucleotide accompanied by damaged 5’- and/or 3’-termini at this point. One common source of SSBs is due to oxidative attack by physiological reactive oxygen species (ROS) such as hydrogen peroxide. HO causes SSBs three times more frequently than double-strand breaks (DSBs). Alternative methods of SSB acquisition include direct disintegration of the oxidized sugar or through DNA base-excision repair (BER) of damaged bases. Additionally, cellular enzymes may perform erroneous activity leading to SSBs or DSBs by a variety of mechanisms. One such example would be when the cleavage complex formed by DNA topoisomerase 1 (TOP1) relaxes DNA during transcription and replication through the transient formation of a nick. While TOP1 normally reseals this nick shortly after, these cleavage complexes may collide with RNA or DNA polymerases or be proximal to other lesions, leading to TOP1-linked SSBs or TOP1-linked DSBs. | 1 | Applied and Interdisciplinary Chemistry |
Mercapturic acids are condensation products formed from the coupling of cysteine with aromatic compounds. They are formed as conjugates in the liver and are excreted in the urine.
Glutathione adducts lose glutamate and glycine portions, and are acetylated to form mercapturic acids, which are excreted.
Levels of mercapturic acids in urine may be used as an indicator of exposure to, e.g., ethylene dibromide, acrylamide, and terbuthylazine. | 1 | Applied and Interdisciplinary Chemistry |
Due to its progestogenic activity, levonorgestrel has antigonadotropic effects and is able to suppress the secretion of the gonadotropins, luteinizing hormone and follicle-stimulating hormone, from the pituitary gland. This in turn, results in suppression of gonadal activity, including reduction of fertility and gonadal sex hormone production in both women and men. The ovulation-inhibiting dose of levonorgestrel in premenopausal women is 50 to 60μg/day.
In men, levonorgestrel causes marked suppression of circulating testosterone levels secondary to its antigonadotropic effects. In healthy young men, levonorgestrel alone at a dose of 120 to 240 μg/day orally for 2 weeks suppressed testosterone levels from ~450 ng/dL to ~248 ng/dL (–45%). Because of its effects on testosterone levels, and due to its androgenic activity being only weak and hence insufficient for purposes of androgen replacement in males, levonorgestrel has potent functional antiandrogenic effects in men. Consequently, it is able to produce adverse effects like decreased libido and erectile dysfunction, among others. In relation to this, levonorgestrel has been combined with an androgen like testosterone or dihydrotestosterone when it has been studied as a hormonal contraceptive in men. | 0 | Theoretical and Fundamental Chemistry |
Thirteen people were exposed to caesium-137 in May 2019 at the Research and Training building in the Harborview Medical Center complex. A contract crew was transferring the caesium from the lab to a truck when the powder was spilled. Five people were decontaminated and released, but 8 who were more directly exposed were taken to the hospital while the research building was evacuated. | 0 | Theoretical and Fundamental Chemistry |
where is the velocity of the fluid along a streamline far upstream, and is the velocity of the fluid just prior to the rotor. Written in cylindrical polar co-ordinates, we have the following expression:
where and are the z-components of the velocity far upstream and just prior to the rotor respectively. This is exactly the same as the upstream equation from the Betz model.
As can be seen from the figure above, the flow expands as it approaches the rotor, a consequence of the increase in static pressure and the conservation of mass. This would imply that upstream. However, for the purpose of this analysis, that effect will be neglected. | 1 | Applied and Interdisciplinary Chemistry |
Digital polymerase chain reaction (digital PCR, DigitalPCR, dPCR, or dePCR) is a biotechnological refinement of conventional polymerase chain reaction methods that can be used to directly quantify and clonally amplify nucleic acids strands including DNA, cDNA, or RNA. The key difference between dPCR and traditional PCR lies in the method of measuring nucleic acids amounts, with the former being a more precise method than PCR, though also more prone to error in the hands of inexperienced users. A "digital" measurement quantitatively and discretely measures a certain variable, whereas an “analog” measurement extrapolates certain measurements based on measured patterns. PCR carries out one reaction per single sample. dPCR also carries out a single reaction within a sample, however the sample is separated into a large number of partitions and the reaction is carried out in each partition individually. This separation allows a more reliable collection and sensitive measurement of nucleic acid amounts. The method has been demonstrated as useful for studying variations in gene sequences — such as copy number variants and point mutations — and it is routinely used for clonal amplification of samples for next-generation sequencing. | 1 | Applied and Interdisciplinary Chemistry |
A pair of forward and reverse reactions may occur simultaneously with comparable speeds. For example, A and B react into products P and Q and vice versa (a, b, p, and q are the stoichiometric coefficients):
The reaction rate expression for the above reactions (assuming each one is elementary) can be written as:
where: k is the rate coefficient for the reaction that consumes A and B; k is the rate coefficient for the backwards reaction, which consumes P and Q and produces A and B.
The constants k and k are related to the equilibrium coefficient for the reaction (K) by the following relationship (set v=0 in balance): | 0 | Theoretical and Fundamental Chemistry |
The priming effect is characterized by intense changes in the natural process of soil organic matter (SOM) turnover, resulting from relatively moderate intervention with the soil. The phenomenon is generally caused by either pulsed or continuous changes to inputs of fresh organic matter (FOM). Priming effects usually result in an acceleration of mineralization due to a trigger such as the FOM inputs. The cause of this increase in decomposition has often been attributed to an increase in microbial activity resulting from higher energy and nutrient availability released from the FOM. After the input of FOM, specialized microorganisms are believed to grow quickly and only decompose this newly added organic matter. The turnover rate of SOM in these areas is at least one order of magnitude higher than the bulk soil.
Other soil treatments, besides organic matter inputs, which lead to this short-term change in turnover rates, include "input of mineral fertilizer, exudation of organic substances by roots, mere mechanical treatment of soil or its drying and rewetting."
Priming effects can be either positive or negative depending on the reaction of the soil with the added substance. A positive priming effect results in the acceleration of mineralization while a negative priming effect results in immobilization, leading to N unavailability. Although most changes have been documented in C and N pools, the priming effect can also be found in phosphorus and sulfur, as well as other nutrients.
Löhnis was the first to discover the priming effect phenomenon in 1926 through his studies of green manure decomposition and its effects on legume plants in soil. He noticed that when adding fresh organic residues to the soil, it resulted in intensified mineralization by the humus N. It was not until 1953, though, that the term priming effect was given by Bingeman in his paper titled, The effect of the addition of organic material on the decomposition of an organic soil. Several other terms had been used before priming effect was coined, including priming action, added nitrogen interaction (ANI), extra N and additional N. Despite these early contributions, the concept of the priming effect was widely disregarded until about the 1980s-1990s.
The priming effect has been found in many different studies and is regarded as a common occurrence, appearing in most plant soil systems. However, the mechanisms which lead to the priming effect are more complex then originally thought, and still remain generally misunderstood.
Although there is a lot of uncertainty surrounding the reason for the priming effect, a few undisputed facts have emerged from the collection of recent research:
# The priming effect can arise either instantaneously or very shortly (potentially days or weeks) after the addition of a substance is made to the soil.
# The priming effect is larger in soils that are rich in C and N as compared to those poor in these nutrients.
# Real priming effects have not been observed in sterile environments.
# The size of the priming effect increases as the amount of added treatment to the soil increases.
Recent findings suggest that the same priming effect mechanisms acting in soil systems may also be present in aquatic environments, which suggests a need for broader considerations of this phenomenon in the future. | 0 | Theoretical and Fundamental Chemistry |
There is varying impact on local corrosion noted from biofilms formed of diverse microbial communities. For instance, when isolating a sample of biofilm from a pipe within the first week of growth, the corrosion of the pipe accelerated, yet by the end of a month, the same biofilm began to act as a protective layer for the pipe. Variation between corrosion in similar environments might be attributed to the local bacterial communities. Biofilms further mediate corrosion by altering the electrochemical processes at the interface of the underlying substrate. | 1 | Applied and Interdisciplinary Chemistry |
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Uranium tailings are waste by-product materials left over from the rough processing of uranium-bearing ore. They are not significantly radioactive. Mill tailings are sometimes referred to as 11(e)2 wastes, from the section of the Atomic Energy Act of 1946 that defines them. Uranium mill tailings typically also contain chemically hazardous heavy metal such as lead and arsenic. Vast mounds of uranium mill tailings are left at many old mining sites, especially in Colorado, New Mexico, and Utah.
Although mill tailings are not very radioactive, they have long half-lives. Mill tailings often contain radium, thorium and trace amounts of uranium. | 0 | Theoretical and Fundamental Chemistry |
Mikael Kubista (born 13 August 1961) is Czech-born Swedish chemist and entrepreneur who works in the field of molecular diagnostics. Since 2007, he is serving as a Professor of Chemistry and Head of the Department of Gene Expression Profiling at the Biotechnology Institute, Czech Academy of Sciences in the Czech Republic.
Kubista has contributed to the field of quantitative real-time PCR (qPCR), with his work recognized as part of the early research in this area.
Kubista was a member of the research team at Astra Hässle, where they focused on investigating Omeprazole, an inhibitor of K+/H+-ATPase. The drug is now marketed under the trade names Losec and Nexium, widely prescribed medications for the treatment of gastric ulcer. Additionally, Kubista is the Chairman of the Board of MultiD Analyses AB and the founder of TATAA Biocenter. | 1 | Applied and Interdisciplinary Chemistry |
The first two steps in an oxidation reaction involving N-tert-butylbenzenesulfinimidoyl chloride are similar to a nucleophilic acyl substitution reaction. A nucleophile, such as an alkoxide (1), attacks the S=N bond in 2. The resulting intermediate (3) collapses and ejects chloride ion, which is a good leaving group. The resulting sulfimide has two resonance forms - 4a and 4b. Because of this, the nitrogen is basic, and via a five-membered ring transition state, it can abstract the hydrogen adjacent to the oxygen. This forms a new C=O bond and ejects a neutral sulfenamide (5), giving ketone 6 as the product. N-tert-Butylbenzenesulfinimidoyl chloride reacts with enolates, amides, and primary alkoxides by the same general mechanism.
The Swern oxidation, which converts primary and secondary alcohols to aldehydes and ketones, respectively, also uses a sulfur-containing compound (DMSO) as the oxidant and proceeds by a similar mechanism. In the Swern oxidation, elimination also occurs via a five-membered ring transition state, but the basic species is a sulfur ylide instead of a negatively charged nitrogen. Several other oxidation reactions also make use of DMSO as the oxidant and pass through a similar transition state (see #See also). | 0 | Theoretical and Fundamental Chemistry |
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