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Traditionally, the recognition of protein-protein interactions was carried out through chemical cross-linking, that involved the use of moderately reactive bifunctional reagent, commonly attached to free amino groups. However, photochemical cross-linking is much more specific due to the short lifetime of the excited intermediates. In addition, photochemical cross-linking does not interfere with the antibodies recognition whilst the former does.
But photo-leucines advantages go further, because in addition to having a lot of advantages, it doesnt have negative effects. For example, although unnatural amino acids are in general toxic to cells, photo-leucine has been proved not to have any substantial effect to cell viability. Those results have been corroborate by many experiments. For example, an essay with Escherichia coli-galactosidase showed that the addition of either of the three photo-amino acids or of a mixture of them had no effect on enzyme activity. That helps to conclude that photo-amino acids are nontoxic to cultivated mammalian cells and can, at least partially, functionally replace their natural forms.
However, currently photo-reactive amino acids are used in combination with chemical cross-linkers in order to achieve the most reliable results possible within protein-protein interaction studies. | 5 | Photochemistry |
Chirality timeline presents a timeline of landmark events that unfold the developments happened in the field of chirality.
Many molecules come in two forms that are mirror images of each other, just like our hands. This type of molecule is called chiral. In nature, one of these forms is usually more common than the other. In our cells, one of these mirror images of a molecule fits "like a glove," while the other may be harmful.
In nature, molecules with chirality include hormones, DNA, antibodies, and enzymes. For example, (R)-limonene smells like oranges, while (S)-limonene smells like lemons. Both molecules have the same chemical formula, but their spatial orientations are different, which makes a big difference in their biological properties. Chiral molecules in the receptors in our noses can tell the difference between these things. Chirality affects biochemical reactions, and the way a drug works depends on what kind of enantiomer it is. Many drugs are chiral and it is important that the shape of the drug matches the shape of the cell receptor it is meant to affect. Mismatching will make the drug less effective, which could be a matter of life and death, as happened with thalidomide in the 1960s.
It has long been known that structural factors, particularly chirality and stereochemistry, have a big impact on pharmacological efficacy and pharmacokinetic behavior. Since more than a century ago, pertinent information pertaining to chirality has been accumulating in numerous fields, in particular, physics, chemistry and biology, at an accelerated rate, giving rise to more comprehensive and in-depth reasoning, conceptions, and ideas. This page offers a chronology of significant contributions that have been made in the journey of chirality [1809 to 2021]. | 4 | Stereochemistry |
The magnitude of sensory impairment may vary in people of differing weights. The NIAAA defines the term "binge drinking" as a pattern of drinking that brings a person's blood alcohol concentration (BAC) to 0.08 grams percent or above. | 1 | Biochemistry |
Aquatic phytoplankton and zooplankton that died and sedimented in large quantities under anoxic conditions millions of years ago began forming petroleum and natural gas as a result of anaerobic decomposition (by contrast, terrestrial plants tended to form coal and methane). Over geological time this organic matter, mixed with mud, became buried under further heavy layers of inorganic sediment. The resulting high temperature and pressure caused the organic matter to chemically alter, first into a waxy material known as kerogen, which is found in oil shales, and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis.
Such organisms and their resulting fossil fuels typically have an age of millions of years, and sometimes more than 650 million years, the energy released in combustion is still photosynthetic in origin. | 9 | Geochemistry |
Carbenes add to double bonds to form cyclopropanes, and, in the presence of a copper catalyst, to alkynes to give cyclopropenes. Addition reactions are commonly very fast and exothermic, and carbene generation limits reaction rate.
In Simmons-Smith cyclopropanation, the iodomethylzinc iodide typically complexes to any allylic hydroxy groups such that addition is syn to the hydroxy group. | 0 | Organic Chemistry |
Double-stranded DNA is sheared using one of these methods: sonication, enzymatic digestion, or nebulization. Fragments are size selected using Ampure XP beads. Gel-based size selection is not recommended since it can cause melting of DNA double strands and DNA damage due to UV exposure. The size of selected fragments of DNA are subjected to 3’-end-dA-tailing. | 1 | Biochemistry |
Tramadol may be used to treat post-operative, injury-related, and chronic (e.g., cancer-related) pain in dogs and cats as well as rabbits, coatis, many small mammals including rats and flying squirrels, guinea pigs, ferrets, and raccoons. | 4 | Stereochemistry |
Under the brand names Fortekor (Novartis) and VetACE (Jurox Animal Health), benazepril is used to treat congestive heart failure in dogs and chronic kidney failure in cats and dogs. | 4 | Stereochemistry |
Although nonsense-mediated mRNA decay reduces nonsense codons, mutations can occur that lead to various health problems and diseases in humans. A dominant-negative or deleterious gain-of-function mutation can occur if premature terminating (nonsense) codons are translated. NMD is becoming increasingly evident in the way it modifies phenotypic consequences because of the broad way it controls gene expression. For instance, the blood disorder Beta thalassemia is inherited and caused by mutations within the upstream region of the β-globin gene. An individual carrying only one affected allele will have no or extremely low levels of the mutant β-globin mRNA. An even more severe form of the disease can occur called thalassemia intermedia or ‘inclusion body’ thalassemia. Instead of decreased mRNA levels, a mutant transcript produces truncated β chains, which in turn leads to a clinical phenotype in the heterozygote.
Nonsense-mediated decay mutations can also contribute to Marfan syndrome. This disorder is caused by mutations in the fibrillin 1 (FBN1) gene and is resulted from a dominant negative interaction between mutant and wild-type fibrillin-1 gene. | 1 | Biochemistry |
Anthocyanins have been used in organic solar cells because of their ability to convert light energy into electrical energy. The many benefits to using dye-sensitized solar cells instead of traditional p-n junction silicon cells, include lower purity requirements and abundance of component materials, as well as the fact that they may be produced on flexible substrates, making them amenable to roll-to-roll printing processes. | 3 | Analytical Chemistry |
Today, many different types of technologies exist in which splice sites can be located and analyzed for more information. The [http://www.umd.be/HSF3/ Human Splicing Finder] is an online database stemming from the Human Genome Project data. The genome database identifies thousands of mutations related to medical and health fields, as well as providing critical research information regarding splice site mutations. The tool specifically searches for pre-mRNA splicing errors, the calculation of potential splice sites using complex algorithms, and correlation with several other online genomic databases, such as the [http://www.ensembl.org/index.html Ensembl] genome browser. | 1 | Biochemistry |
Steric approach control is common in conjugate addition reactions. Thus, in cyclic substrates, a trans relationship between substituents on the α- and β-carbons is common. The configuration at the α-position is less predictable, especially in cases when epimerization can occur. On the basis of steric approach control, the new α-substituent is predicted to be trans to the new β-substituent, and this is observed in a number of cases. | 0 | Organic Chemistry |
Although menopause is a natural barrier to further conception, IVF has allowed people to be pregnant in their fifties and sixties. People whose uteruses have been appropriately prepared receive embryos that originated from an egg donor. Therefore, although they do not have a genetic link with the child, they have a physical link through pregnancy and childbirth. Even after menopause, the uterus is fully capable of carrying out a pregnancy. | 1 | Biochemistry |
*Coal and oil are possible examples of constituents which may have undergone changes over geologic time periods.
*Chalk and limestone are examples of secretions (marine animal shells) which are of geologic age.
*grass and wood are biogenic constituents of contemporary origin.
*Pearls, silk and ambergris are examples of secretions of contemporary origin.
*Biogenic neurotransmitters. | 0 | Organic Chemistry |
Industrial science attempts to minimize the hazards of isocyanates through multiple techniques. The EPA has sponsored ongoing research on polyurethane production without isocyanates. Where isocyanates are unavoidable but interchangeable, substituting a less hazardous isocyanate may control hazards. Ventilation and automation can also minimizes worker exposure to the isocyanates used.
If human workers must enter isocyanate-contaminated regions, personal protective equipment (PPE) can reduce their intake. In general, workers wear eye protection and gloves and coveralls to reduce dermal exposure For some autobody paint and clear-coat spraying applications, a full-face mask is required.
The US Occupational Safety and Health Administration (OSHA) requires frequent training to ensure isocyanate hazards are appropriately minimized. Moreover, OSHA requires standardized isocyanate concentration measurements to avoid violating occupational exposure limits. In the case of MDI, OSHA expects sampling with glass-fiber filters at standard air flow rates, and then liquid chromatography.
Combined industrial hygiene and medical surveillance can significantly reduce occupational asthma incidence. Biological tests exist to identify isocyanate exposure; the US Navy uses regular pulmonary function testing and screening questionnaires.
Emergency management is a complex process of preparation and should be considered in a setting where a release of bulk chemicals may threaten the well-being of the public. In the Bhopal disaster, an uncontrolled MIC release killed thousands, affected hundreds of thousands more, and spurred the development of modern disaster preparation. | 0 | Organic Chemistry |
In vertebrates the bc complex, or Complex III, contains 11 subunits: 3 respiratory subunits, 2 core proteins and 6 low-molecular weight proteins. Proteobacterial complexes may contain as few as three subunits. | 1 | Biochemistry |
What makes this magnesium blockade of the NMDAR channel particularly significant in terms of LTP induction is that the block is membrane voltage-dependent. The basis of this voltage dependence is relatively straightforward. The NMDAR channel is a transmembrane protein; that is, it spans the cell membrane. As such, it also spans the electric field generated by the membrane potential. The magnesium binding site within the NMDAR channel is physically located within this electric field. Magnesium ions carrying a double positive charge can be acted upon by the field. When the cell is hyperpolarized, magnesium is stabilized inside the channel (i.e. the two positive charges on the magnesium ion are attracted toward the negative pole of the electric field, which points toward the inside of the cell). As a cell is depolarized, the field effect on the magnesium ion weakens, and the dwell time of magnesium ions within the channel decreases. Thus, the kinetics of the binding reaction between magnesium and the NMDAR channel are such that magnesium periodically unbinds and leaves the channel, only to be replaced by another magnesium ion. During the (very brief) time that the magnesium is absent from the open channel, other ions (such as sodium and calcium) can flow through the channel. However, when the cell is more hyperpolarized, the bound state of magnesium is stabilized and it leaves the channel less often and for a shorter period of time (on average). When the cell is less hyperpolarized, the magnesium leaves the channel more often and stays away for longer (on average). Hence, the magnesium blockade of the open NMDAR channel is membrane voltage-dependent.
While the NMDAR channel itself displays little or no voltage dependence (its open channel I/V curve is more or less linear), the voltage dependence of the magnesium block effectively, if indirectly, confers voltage dependence to this channel. Thus, in effect, the NMDAR channel is both a ligand-gated and voltage-gated channel at the same time. This fact is critical to the function of the NMDAR as a Hebbian coincidence detector. More strictly speaking, inward cationic current (sodium or calcium) through the open unblocked NMDAR does decrease with depolarization (because of the decreased electrochemical "driving force"), but the voltage-dependent unblocking seems to outweigh this decrease in driving force, so the calcium influx into the spine caused by a pair of appropriately timed pre- and postsynaptic spikes significantly exceeds the sum of the influxes due to the individual spikes alone. This extra, or "nonlinear", calcium entry triggers the strength change. | 1 | Biochemistry |
Both free and protein-bound flavins are photoreducible, that is, able to be reduced by light, in a mechanism mediated by several organic compounds, such as some amino acids, carboxylic acids and amines. This property of flavins is exploited by various light-sensitive proteins. For example, the LOV domain, found in many species of plant, fungi and bacteria, undergoes a reversible, light-dependent structural change which involves the formation of a bond between a cysteine residue in its peptide sequence and a bound FMN. | 1 | Biochemistry |
The HSQC experiment is a highly sensitive 2D-NMR experiment and was first described in a H—N system, but is also applicable to other nuclei such as H—C and H—P. The basic scheme of this experiment involves the transfer of magnetization on the proton to the second nucleus, which may be N, C or P, via an INEPT (Insensitive nuclei enhanced by polarization transfer) step. After a time delay (t), the magnetization is transferred back to the proton via a retro-INEPT step and the signal is then recorded. In HSQC, a series of experiments is recorded where the time delay t is incremented. The H signal is detected in the directly measured dimension in each experiment, while the chemical shift of N or C is recorded in the indirect dimension which is formed from the series of experiments. | 7 | Physical Chemistry |
Mercury lamps are the most common source of UV radiation due to their high efficiency. However, the use of mercury in these lamps poses disposal and environmental problems. On the contrary, excimer lamps based on rare gases are absolutely non-hazardous and excimer lamps containing halogen are more environmentally benign than mercury ones. | 5 | Photochemistry |
Typical titrations require titrant and analyte to be in a liquid (solution) form. Though solids are usually dissolved into an aqueous solution, other solvents such as glacial acetic acid or ethanol are used for special purposes (as in petrochemistry, which specializes in petroleum.) Concentrated analytes are often diluted to improve accuracy.
Many non-acid–base titrations require a constant pH during the reaction. Therefore, a buffer solution may be added to the titration chamber to maintain the pH.
In instances where two reactants in a sample may react with the titrant and only one is the desired analyte, a separate masking solution may be added to the reaction chamber which eliminates the effect of the unwanted ion.
Some reduction-oxidation (redox) reactions may require heating the sample solution and titrating while the solution is still hot to increase the reaction rate. For instance, the oxidation of some oxalate solutions requires heating to to maintain a reasonable rate of reaction. | 3 | Analytical Chemistry |
Sewer network structures are prone to biodeterioration of materials due to the action of some microorganisms associated to the sulfur cycle. It can be a severely damaging phenomenon which was firstly described by Olmstead and Hamlin in 1900 for a brick sewer located in Los Angeles. Jointed mortar between the bricks disintegrated and ironwork was heavily rusted. The mortar joint had ballooned to two to three times its original volume, leading to the destruction or the loosening of some bricks.
Around 9% of damages described in sewer networks can be ascribed to the successive action of two kinds of microorganisms. Sulfate-reducing bacteria (SRB) can grow in relatively thick layers of sedimentary sludge and sand (typically 1 mm thick) accumulating at the bottom of the pipes and characterized by anoxic conditions. They can grow using oxidized sulfur compounds present in the effluent as electron acceptor and excrete hydrogen sulfide (HS). This gas is then emitted in the aerial part of the pipe and can impact the structure in two ways: either directly by reacting with the material and leading to a decrease in pH, or indirectly through its use as a nutrient by sulfur-oxidizing bacteria (SOB), growing in oxic conditions, which produce biogenic sulfuric acid. The structure is then submitted to a biogenic sulfuric acid attack. Materials like calcium aluminate cements, PVC or vitrified clay pipe may be substituted for ordinary concrete or steel sewers that are not resistant in these environments.
Mild steel corrosion reduction in water by uptake of dissolved oxygen is carried out by Rhodotorula mucilaginosa(7). | 8 | Metallurgy |
Here is a summary of the sequence of events that take place in synaptic transmission from a presynaptic neuron to a postsynaptic cell. Each step is explained in more detail below. Note that with the exception of the final step, the entire process may run only a few hundred microseconds, in the fastest synapses.
#The process begins with a wave of electrochemical excitation called an action potential traveling along the membrane of the presynaptic cell, until it reaches the synapse.
#The electrical depolarization of the membrane at the synapse causes channels to open that are permeable to calcium ions.
#Calcium ions flow through the presynaptic membrane, rapidly increasing the calcium concentration in the interior.
#The high calcium concentration activates a set of calcium-sensitive proteins attached to vesicles that contain a neurotransmitter chemical.
#These proteins change shape, causing the membranes of some "docked" vesicles to fuse with the membrane of the presynaptic cell, thereby opening the vesicles and dumping their neurotransmitter contents into the synaptic cleft, the narrow space between the membranes of the pre- and postsynaptic cells.
#The neurotransmitter diffuses within the cleft. Some of it escapes, but some of it binds to chemical receptor molecules located on the membrane of the postsynaptic cell.
#The binding of neurotransmitter causes the receptor molecule to be activated in some way. Several types of activation are possible, as described in more detail below. In any case, this is the key step by which the synaptic process affects the behavior of the postsynaptic cell.
#Due to thermal vibration, the motion of atoms, vibrating about their equilibrium positions in a crystalline solid, neurotransmitter molecules eventually break loose from the receptors and drift away.
#The neurotransmitter is either reabsorbed by the presynaptic cell, and then repackaged for future release, or else it is broken down metabolically. | 1 | Biochemistry |
Dynamic energy budget theory presents a quantitative framework of metabolic organization common to all life forms, which could help to understand evolution of metabolic organization since the origin of life. As such, it has a common aim with the other widely used metabolic theory: the West-Brown-Enquist (WBE) metabolic theory of ecology, which prompted side-by-side analysis of the two approaches. Though the two theories can be regarded as complementary to an extent, they were built on different assumptions and have different scope of applicability. In addition to a more general applicability, the DEB theory does not suffer from consistency issues pointed out for the WBE theory. | 1 | Biochemistry |
Proteins are complex, high-molecular weight biopolymers. They are inherently chiral being composed of L-amino acids and possess ordered 3D-structure. They are known to bind/interact stereoselectively with small molecules reversibly, making them extremely versatile CSPs for chiral separation of drug molecules. Hermansson made use of this property to develop number of CSPs by immobilizing proteins on to silica surface. They operate under reverse phase mode (phosphate buffer and organic modifiers).
Protein polymer remains in twisted form because of the different intramolecular bonding. These bonding create different type of chiral loops/grooves present in the protein molecule. Separation mechanism of proteins depends on unique combination of hydrophobic and polar interactions by which the analytes are oriented to chiral surfaces. H-bonding and charge transfer may also contribute to enantioselectivity. The mechanism of chiral distinction by proteins is mostly not well established due to their complex nature. Several proteins based CSP have been employed for chiral drug analysis including α-acid glycoprotein (enantiopac; chiral-AGP), ovomucoid protein (Ultron ES DVM), human serum albumin (HSA). α-AGP CSP (chiral AGP), has been employed for the quantification of atenolol enantiomers in biological matrices, for pharmacokinetic investigation of racemic metoprolol. The major weakness of protein based CSPs include low loading capacity, protein phases are expensive, extremely fragile, delicate to handle, very low column efficiency, cannot invert elution order. | 4 | Stereochemistry |
tert-Butyl hydroperoxide is used for epoxidation and hydroxylation reagents in conjunction with metal catalysts. | 0 | Organic Chemistry |
In aquatic toxicology, the sediment quality triad (SQT) approach has been used as an assessment tool to evaluate the extent of sediment degradation resulting from contaminants released due to human activity present in aquatic environments (Chapman, 1990). This evaluation focuses on three main components: 1.) sediment chemistry, 2.) sediment toxicity tests using aquatic organisms, and 3.) the field effects on the benthic organisms (Chapman, 1990). Often used in risk assessment, the combination of three lines of evidence can lead to a comprehensive understanding of the possible effects to the aquatic community (Chapman, 1997). Although the SQT approach does not provide a cause-and-effect relationship linking concentrations of individual chemicals to adverse biological effects, it does provide an assessment of sediment quality commonly used to explain sediment characteristics quantitatively. The information provided by each portion of the SQT is unique and complementary, and the combination of these portions is necessary because no single characteristic provides comprehensive information regarding a specific site (Chapman, 1997) | 2 | Environmental Chemistry |
A system akin to the Bessemer process has existed since the 11th century in East Asia. Economic historian Robert Hartwell writes that the Chinese of the Song Dynasty (960–1279 CE) innovated a "partial decarbonization" method of repeated forging of cast iron under a cold blast. Sinologist Joseph Needham and historian of metallurgy Theodore A. Wertime have described the method as a predecessor to the Bessemer process of making steel. This process was first described by the prolific scholar and polymath government official Shen Kuo (1031–1095) in 1075, when he visited Cizhou. Hartwell states that perhaps the earliest center where this was practiced was the great iron-production district along the Henan–Hebei border during the 11th century. | 8 | Metallurgy |
Lipolysis can be regulated through cAMPs binding and activation of protein kinase A (PKA). PKA can phosphorylate lipases, perilipin 1A, and CGI-58 to increase the rate of lipolysis. Catecholamines bind to 7TM receptors (G protein-coupled receptors) on the adipocyte cell membrane, which activate adenylate cyclase. This results in increased production of cAMP, which activates PKA and leads to an increased rate of lipolysis. Despite glucagons lipolytic activity (which stimulates PKA as well) in vitro, the role of glucagon in lipolysis in vivo is disputed.
Insulin counter-regulates this increase in lipolysis when it binds to insulin receptors on the adipocyte cell membrane. Insulin receptors activate insulin-like receptor substrates. These substrates activate phosphoinositide 3-kinases (PI-3K) which then phosphorylate protein kinase B (PKB) (a.k.a. Akt). PKB subsequently phosphorylates phosphodiesterase 3B (PD3B), which then converts the cAMP produced by adenylate cyclase into 5'AMP. The resulting insulin induced reduction in cAMP levels decreases the lipolysis rate.
Insulin also acts in the brain at the mediobasal hypothalamus. There, it suppresses lipolysis and decreases sympathetic nervous outflow to the fatty part of the brain matter. The regulation of this process involves interactions between insulin receptors and gangliosides present in the neuronal cell membrane. | 1 | Biochemistry |
The thermo-dielectric effect is the production of electric currents and charge separation during phase transition.
This interesting effect was discovered by Joaquim da Costa Ribeiro in 1944. The Brazilian physicist observed that solidification and melting of many dielectrics are accompanied by charge separation. A thermo-dielectric effect was demonstrated with carnauba wax, naphthalene and paraffin. Charge separation in ice was also expected. This effect was observed during water freezing period, electrical storm effects can be caused by this strange phenomenon. Effect was measured by many researches - Bernhard Gross, Armando Dias Tavares, Sergio Mascarenhas etc. César Lattes (co-discoverer of the pion) supposed that this was the only effect ever to be discovered entirely in Brasil. | 7 | Physical Chemistry |
After determining the transition state structures using either KIE or computation simulations, the inhibitor can be designed according to the determined transition state structures or intermediates. The following three examples illustrate how the inhibitors mimic the transition state structure by changing functional groups correspond to the geometry and electrostatic distribution of the transition state structures. | 1 | Biochemistry |
Eutrophication can occur naturally, during the late stage of the natural ecological succession that accompanies the infilling of a lake. It then develops slowly, over thousands of years. It develops within only a few decades when triggered by cropland fertilization, industrial contamination, or urban development. Deforestation, land fertilization, urbanization and industrialization in the catchment of lake Chichoj are all thought to have contributed in a way or the other to the massive lake contamination and eutrophication of the lake that has taken place since the 1950s. Degradation of its ecosystem motivated environmental studies starting in the 1970s. They aimed at documenting the eutrophication process, and at identifying its causes. Most concluded that the main source of eutrophication is the absence of treatment of city waste waters, rather than agriculture.
The most visible consequence of eutrophication is the massive development of large floating rafts of the water hyacinth (Eichhornia crassipes), which is untiringly harvested to prevent complete invasion of the lake open waters. The enormous amount of hyacinth removed from the lake is then composted to produce a horticultural fertilizer.
Many local witnesses have reported that the extensive marshes that surround the lake were open waters in the 1950s. The presence of a well marked shoreline 1.0 ± 0.1 to 1.4 ± 0.1 m above the average current lake level and surrounding the marshes supports these testimonies. Because eutrophication leads to rapid infilling of lakes by plant debris, and conversion of open waters to marshland, it has been hypothesized that eutrophication is responsible for the reduction in the lake surface.
Due to its location halfway between the Atlantic and Pacific Ocean, the lake ecosystem is normally influenced by the Pacific El Niño Oscillation (ENSO) and the North Atlantic Oscillation. Studies are under way to determine the sensitivity of the lake hydrology to these oscillations over the past millennium. | 2 | Environmental Chemistry |
The herpes simplex virus is a human neurotropic virus. This is mostly examined for gene transfer in the nervous system. The wild type HSV-1 virus is able to infect neurons and evade the host immune response, but may still become reactivated and produce a lytic cycle of viral replication. Therefore, it is typical to use mutant strains of HSV-1 that are deficient in their ability to replicate. Though the latent virus is not transcriptionally apparent, it does possess neuron specific promoters that can continue to function normally. Antibodies to HSV-1 are common in humans, however complications due to herpes infection are somewhat rare. Caution for rare cases of encephalitis must be taken and this provides some rationale to using HSV-2 as a viral vector as it generally has tropism for neuronal cells innervating the urogenital area of the body and could then spare the host of severe pathology in the brain. | 1 | Biochemistry |
Exposure studies in the copper smelting industry are much more extensive and have established definitive links between arsenic, a by-product of copper smelting, and lung cancer via inhalation. Dermal and neurological effects were also increased in some of these studies. Although as time went on, occupational controls became more stringent and workers were exposed to reduced arsenic concentrations, the arsenic exposures measured from these studies ranged from about 0.05 to 0.3 mg/m and are significantly higher than airborne environmental exposures to arsenic (which range from 0 to 0.000003 mg/m). | 1 | Biochemistry |
Like the two-hybrid system, phage display is used for the high-throughput screening of protein interactions. In the case of M13 filamentous phage display, the DNA encoding the protein or peptide of interest is ligated into the pIII or pVIII gene, encoding either the minor or major coat protein, respectively. Multiple cloning sites are sometimes used to ensure that the fragments are inserted in all three possible reading frames so that the cDNA fragment is translated in the proper frame. The phage gene and insert DNA hybrid is then inserted (a process known as "transduction") into E. coli bacterial cells such as TG1, SS320, ER2738, or XL1-Blue E. coli. If a "phagemid" vector is used (a simplified display construct vector) phage particles will not be released from the E. coli cells until they are infected with helper phage, which enables packaging of the phage DNA and assembly of the mature virions with the relevant protein fragment as part of their outer coat on either the minor (pIII) or major (pVIII) coat protein.
By immobilizing a relevant DNA or protein target(s) to the surface of a microtiter plate well, a phage that displays a protein that binds to one of those targets on its surface will remain while others are removed by washing. Those that remain can be eluted, used to produce more phage (by bacterial infection with helper phage) and to produce a phage mixture that is enriched with relevant (i.e. binding) phage. The repeated cycling of these steps is referred to as panning, in reference to the enrichment of a sample of gold by removing undesirable materials.
Phage eluted in the final step can be used to infect a suitable bacterial host, from which the phagemids can be collected and the relevant DNA sequence excised and sequenced to identify the relevant, interacting proteins or protein fragments.
The use of a helper phage can be eliminated by using bacterial packaging cell line technology.
Elution can be done combining low-pH elution buffer with sonification, which, in addition to loosening the peptide-target interaction, also serves to detach the target molecule from the immobilization surface. This ultrasound-based method enables single-step selection of a high-affinity peptide. | 1 | Biochemistry |
Unlike the reaction of amines with alcohols the reaction of amines and ammonia with alkyl halides is used for synthesis in the laboratory:
In such reactions, which are more useful for alkyl iodides and bromides, the degree of alkylation is difficult to control such that one obtains mixtures of primary, secondary, and tertiary amines, as well as quaternary ammonium salts.
Selectivity can be improved via the Delépine reaction, although this is rarely employed on an industrial scale. Selectivity is also assured in the Gabriel synthesis, which involves organohalide reacting with potassium phthalimide.
Aryl halides are much less reactive toward amines and for that reason are more controllable. A popular way to prepare aryl amines is the Buchwald-Hartwig reaction. | 0 | Organic Chemistry |
Proteins are also known to contain [FeS] centres, which feature one iron less than the more common [FeS] cores. Three sulfide ions bridge two iron ions each, while the fourth sulfide bridges three iron ions. Their formal oxidation states may vary from [FeS] (all-Fe form) to [FeS] (all-Fe form). In a number of iron–sulfur proteins, the [FeS] cluster can be reversibly converted by oxidation and loss of one iron ion to a [FeS] cluster. E.g., the inactive form of aconitase possesses an [FeS] and is activated by addition of Fe and reductant. | 7 | Physical Chemistry |
The adsorption of a very weakly basic or acidic probe molecule can serve to give a picture of Brønsted and Lewis acid–base sites. Infrared spectroscopy of surface sites and adsorbed molecules can then be used to monitor the change in the vibrational frequencies upon adsorption. A very weakly acidic probe molecule can be used to minimize disturbing neighboring sites so that a more accurate measure of surface acidity or basicity can be obtained. A variety of probe molecules can be used including: ammonia, pyridine, acetonitrile, carbon monoxide, and carbon dioxide. | 7 | Physical Chemistry |
The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of extant cyanobacteria (formerly called blue-green algae). The geological record indicates that this transforming event took place early in Earths history, at least 2450–2320 million years ago (Ma), and, it is speculated, much earlier. Because the Earths atmosphere contained almost no oxygen during the estimated development of photosynthesis, it is believed that the first photosynthetic cyanobacteria did not generate oxygen. Available evidence from geobiological studies of Archean (>2500 Ma) sedimentary rocks indicates that life existed 3500 Ma, but the question of when oxygenic photosynthesis evolved is still unanswered. A clear paleontological window on cyanobacterial evolution opened about 2000 Ma, revealing an already-diverse biota of cyanobacteria. Cyanobacteria remained the principal primary producers of oxygen throughout the Proterozoic Eon (2500–543 Ma), in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation. Green algae joined cyanobacteria as the major primary producers of oxygen on continental shelves near the end of the Proterozoic, but only with the Mesozoic (251–66 Ma) radiations of dinoflagellates, coccolithophorids, and diatoms did the primary production of oxygen in marine shelf waters take modern form. Cyanobacteria remain critical to marine ecosystems as primary producers of oxygen in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae. | 5 | Photochemistry |
The Reststrahlen effect is used to investigate the properties of semiconductors, it is also used in geophysics and meteorology. | 7 | Physical Chemistry |
A boundary can be described by the orientation of the boundary to the two grains and the 3-D rotation required to bring the grains into coincidence. Thus a boundary has 5 macroscopic degrees of freedom. However, it is common to describe a boundary only as the orientation relationship of the neighbouring grains. Generally, the convenience of ignoring the boundary plane orientation, which is very difficult to determine, outweighs the reduced information.
The relative orientation of the two grains is described using the rotation matrix:
Using this system the rotation angle θ is:
while the direction [uvw] of the rotation axis is:
The nature of the crystallography involved limits the misorientation of the boundary. A completely random polycrystal, with no texture, thus has a characteristic distribution of boundary misorientations (see figure). However, such cases are rare and most materials will deviate from this ideal to a greater or lesser degree. | 8 | Metallurgy |
The physical process of sedimentation (the act of depositing sediment) has applications in water treatment, whereby gravity acts to remove suspended solids from water. Solid particles entrained by the turbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans. Settling basins are ponds constructed for the purpose of removing entrained solids by sedimentation. Clarifiers are tanks built with mechanical means for continuous removal of solids being deposited by sedimentation; however, clarification does not remove dissolved solids. | 3 | Analytical Chemistry |
Molten salts (fluoride, chloride, and nitrate) can be used as heat transfer fluids as well as for thermal storage. This thermal storage is used in concentrated solar power plants.
Molten-salt reactors are a type of nuclear reactor that uses molten salt(s) as a coolant or as a solvent in which the fissile material is dissolved. Experimental salts using lithium can be formed that have a melting point of 116 °C while still having a heat capacity of 1.54 J/(g·K). | 8 | Metallurgy |
After he went to Germany from Estonia in 1941 he began his studies of chemistry in 1949 at the University of Tübingen until 1951. He became Dr. rer. nat. in 1954 at the Ludwig Maximilian University of Munich. He did his habilitation 1960 at the same university. After a short but very successful career in industry at Bayer from 1962 until 1968 when he joined the University of Southern California at Los Angeles.
From 1971 he worked at the Technical University of Munich, and was an emeritus from 1999 until his death in 2005. | 0 | Organic Chemistry |
DeepVelo is a neural network–based ordinary differential equation that can model complex transcriptome dynamics by describing continuous-time gene expression changes within individual cells. DeepVelo has been applied to public datasets from different sequencing platforms to (i) formulate transcriptome dynamics on different time scales, (ii) measure the instability of cell states, and (iii) identify developmental driver genes via perturbation analysis. | 1 | Biochemistry |
Amoxicillin is susceptible to degradation by β-lactamase-producing bacteria, which are resistant to most β-lactam antibiotics, such as penicillin. For this reason, it may be combined with clavulanic acid, a β-lactamase inhibitor. This drug combination is commonly called co-amoxiclav. | 4 | Stereochemistry |
Input
Protein structures in PDB format, and a probe radius.
Searching
Users can either search for pre-computed result by 4-letter PDB ID, or upload their own PDB file for customized computation. The core algorithm helps in finding the pocket or cavity with capability of housing a solvent, with a default or adjusted diameter.
Output
CASTp identifies all surface pockets, interior cavities and cross channels, provides detailed delineation of all atoms participating in their formation, including the area and volume of pocket or void as well as measurement of numbers of mouth opening of a particular pocket ID by solvent accessible surface model (Richards' surface) and by molecular surface model (Connolly surface), all calculated analytically. The core algorithm helps in finding the pocket or cavity with capability of housing a solvent with a diameter of 1.4 Å. This online tool also supports PyMOL and UCSF Chimera plugin for molecular visualization. | 1 | Biochemistry |
Proteins are classified into the chemokine family based on their structural characteristics, not just their ability to attract cells. All chemokines are small, with a molecular mass of between 8 and 10 kDa. They are approximately 20-50% identical to each other; that is, they share gene sequence and amino acid sequence homology. They all also possess conserved amino acids that are important for creating their 3-dimensional or tertiary structure, such as (in most cases) four cysteines that interact with each other in pairs to create a Greek key shape that is a characteristic of chemokines. Intramolecular disulfide bonds typically join the first to third, and the second to fourth cysteine residues, numbered as they appear in the protein sequence of the chemokine. Typical chemokine proteins are produced as pro-peptides, beginning with a signal peptide of approximately 20 amino acids that gets cleaved from the active (mature) portion of the molecule during the process of its secretion from the cell. The first two cysteines, in a chemokine, are situated close together near the N-terminal end of the mature protein, with the third cysteine residing in the centre of the molecule and the fourth close to the C-terminal end. A loop of approximately ten amino acids follows the first two cysteines and is known as the N-loop. This is followed by a single-turn helix, called a 3-helix, three β-strands and a C-terminal α-helix. These helices and strands are connected by turns called 30s, 40s and 50s loops; the third and fourth cysteines are located in the 30s and 50s loops. | 1 | Biochemistry |
The project generated widespread media attention and a discussion of appropriate uses of biotechnology. As a result of the controversy, Kickstarter decided to prohibit genetically modified organisms as rewards to project backers.
Though the Animal and Plant Health Inspection Service (APHIS) has shown no regulatory concerns about the project, some synthetic biologists and policy researchers have questioned the project's feasibility and impact on future oversight or public opinion of synthetic biology. In particular, if the company were to encourage backers to use a genetic DIY kit themselves, additional regulatory oversight would likely occur. | 1 | Biochemistry |
In 1787, the French physicist and balloon pioneer, Jacques Charles, found that oxygen, nitrogen, hydrogen, carbon dioxide, and air expand to the same extent over the same 80 kelvin interval. He noted that, for an ideal gas at constant pressure, the volume is directly proportional to its temperature: | 7 | Physical Chemistry |
Adding elements is usually helpful because of solid solution strengthening, but can result in unwanted precipitation. Precipitates can be classified as geometrically close-packed (GCP), topologically close-packed (TCP), or carbides. GCP phases usually benefit mechanical properties, but TCP phases are often deleterious. Because TCP phases are not truly close packed, they have few slip systems and are brittle. Also they "scavenge" elements from GCP phases. Many elements that are good for forming γ' or have great solid solution strengthening may precipitate TCPs. The proper balance promotes GCPs while avoiding TCPs.
TCP phase formation areas are weak because they:
* have inherently poor mechanical properties
* are incoherent with the γ matrix
* are surrounded by a "depletion zone" where there is no γ'
* usually form sharp plate or needle-like morphologies which nucleate cracks
The main GCP phase is γ. Almost all superalloys are Ni-based because of this phase. γ is an ordered L1 (pronounced L-one-two), which means it has a certain atom on the face of the unit cell, and a certain atom on the corners of the unit cell. Ni-based superalloys usually present Ni on the faces and Ti or Al on the corners.
Another "good" GCP phase is γ. It is also coherent with γ, but it dissolves at high temperatures. | 8 | Metallurgy |
The biosynthetic route is based on the alkylation of the amino acid tryptophan with dimethylallyl diphosphate (isoprene derived from 3R-mevalonic acid) giving 4-dimethylallyl--tryptophan which is N-methylated with S-adenosyl--methionine. Oxidative ring closure followed by decarboxylation, reduction, cyclization, oxidation, and allylic isomerization yields -(+)-lysergic acid. The biosynthetic pathway has been reconsituted in transgenic baker's yeast. | 0 | Organic Chemistry |
Total viable count (TVC), gives a quantitative estimate of the concentration of microorganisms such as bacteria, yeast or mould spores in a sample. The count represents the number of colony forming units (cfu) per g (or per ml) of the sample.
A TVC is achieved by plating serial tenfold dilutions of the sample until between 30 and 300 colonies can be counted on a single plate. The reported count is the number of colonies counted multiplied by the dilution used for the counted plate
A high TVC count indicates a high concentration of micro-organisms which may indicate poor quality for drinking water or foodstuff.
In food microbiology it is used as a benchmark for the evaluation of the shelf-life of foodstuffs | 3 | Analytical Chemistry |
Photooxygenation of indolizines (heterocyclic aromatic derivates of indole) has been investigated in both mechanistic and synthetic contexts. Rather than proceeding through a Type I or Type II photooxygenation mechanism, some investigators have chosen to use 9,10-dicyanoanthracene (DCA) as a photosensitizer, leading to the reaction of an indolizine derivative with the superoxide anion radical. Note that the reaction proceeds through an indolizine radical cation intermediate that has not been isolated (and thus is not depicted): | 5 | Photochemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), Valine (Val, V) | 1 | Biochemistry |
Lysergic acid is a chiral compound with two stereocenters. The isomer with inverted configuration at carbon atom 8 close to the carboxyl group is called isolysergic acid. Inversion at carbon 5 close to the nitrogen atom leads to -lysergic acid and -isolysergic acid, respectively. | 0 | Organic Chemistry |
As stated, the quadratic Stark effect is described by second-order perturbation theory. The zeroth-order eigenproblem
is assumed to be solved. The perturbation theory gives
with the components of the polarizability tensor α defined by
The energy E gives the quadratic Stark effect.
Neglecting the hyperfine structure (which is often justified — unless extremely weak electric fields are considered), the polarizability tensor of atoms is isotropic,
For some molecules this expression is a reasonable approximation, too.
For the ground state is always positive, i.e., the quadratic Stark shift is always negative. | 7 | Physical Chemistry |
In 1978, Hoffmann reported the first asymmetric carbonyl allylation using a chiral allylmetal reagent, an allylborane derived from camphor. Such methods utilize preformed allyl metal reagents. The approach is well developed using allyl boranes
As illustrated by the Keck allylation, catalytic enantioselective additions of achiral allylmetal reagents to carbonyl compounds also are possible by organostannane additions.
Allylic boronate and -borane reagents have also been developed for enantioselective addition to carbonyls—in this class of reactions, the allylic boron reagent confers stereochemical control | 0 | Organic Chemistry |
Decantation can be used to separate immiscible liquids that have different densities. For example, when a mixture of water and oil is present in a beaker, after some time a distinct layer between the two liquids is formed, with the oil layer floating on top of the water layer. This separation can be done by pouring oil out of the container, leaving water behind. Generally, this technique gives an incomplete separation as it is difficult to pour off all of the top layer without pouring out some parts of the bottom layer.
A separatory funnel is an alternative apparatus for separating liquid layers. It has a valve at the bottom to allow draining off the bottom layer. It can give better separation between the two liquids. | 3 | Analytical Chemistry |
Prickle is also known as REST/NRSF-interacting LIM domain protein, which is a putative nuclear translocation receptor. Prickle is part of the non-canonical Wnt signaling pathway that establishes planar cell polarity. A gain or loss of function of Prickle1 causes defects in the convergent extension movements of gastrulation. In epithelial cells, Prickle2 establishes and maintains cell apical/basal polarity. Prickle1 plays an important role in the development of the nervous system by regulating the movement of nerve cells.
The first prickle protein was identified in Drosophila as a planar cell polarity protein. Vertebrate prickle-1 was first found as a rat protein that binds to a transcription factor, neuron-restrictive silencer factor (NRSF). It was then recognized that other vertebrates including mice and humans have two genes that are related to Drosophila prickle. Mouse prickle-2 was found to be expressed in mature neurons of the brain along with mouse homologs of Drosophila planar polarity genes flamingo and dischevelled. Prickle interacts with flamingo to regulate sensory axon advance at the transition between the peripheral nervous system and the central nervous system. Also, Prickle1 interacts with RE1-silencing transcription factor (REST) by transporting REST out of the nucleus. REST turns off several critical genes in neurons by binding to particular regions of DNA in the nucleus.
Prickle is recruited to the cell surface membrane by strabismus, another planar cell polarity protein. In the developing Drosophila wing, prickle becomes concentrated at the proximal side of cells. Prickle can compete with the ankyrin-repeat protein Diego for a binding site on Dishevelled.
In Drosophila, prickle is present inside cells in multiple forms due to alternative splicing of the prickle mRNA. The relative levels of the alternate forms may be regulated and involved in the normal control of planar cell polarity.
Mutations in Prickle genes can cause epilepsy in humans by perturbing Prickle function. One mutation in Prickle1 gene can result in Prickle1-Related Progressive Myoclonus Epilepsy-Ataxia Syndrome. This mutation disrupts the interaction between prickle-like 1 and REST, which results in the inability to suppress REST. Gene knockdown of Prickle1 by shRNA or dominant-negative constructs results in decreased axonal and dendritic extension in neurons in the hippocampus. Prickle1 gene knockdown in neonatal retina causes defects in axon terminals of photoreceptors and in inner and outer segments. | 1 | Biochemistry |
A PPO inhibitor may inhibit two unrelated enzymes abbreviated "PPO". They are:
* Protoporphyrinogen oxidase inhibitors Used as herbicides
* Polyphenol oxidase inhibitors | 1 | Biochemistry |
In 2013, OH near-infrared spectra were observed in the night glow in the polar winter atmosphere of Mars by use of the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). | 0 | Organic Chemistry |
Phosphate esters have the general structure P(=O)(OR) feature P(V). Such species are of technological importance as flame retardant agents, and plasticizers. Lacking a P−C bond, these compounds are in the technical sense not organophosphorus compounds but esters of phosphoric acid. Many derivatives are found in nature, such as phosphatidylcholine. Phosphate ester are synthesized by alcoholysis of phosphorus oxychloride. A variety of mixed amido-alkoxo derivatives are known, one medically significant example being the anti-cancer drug cyclophosphamide. Also derivatives containing the thiophosphoryl group (P=S) include the pesticide malathion. The organophosphates prepared on the largest scale are the zinc dithiophosphates, as additives for motor oil. Several million kilograms of this coordination complex are produced annually by the reaction of phosphorus pentasulfide with alcohols.
In the environment, these compounds break down via hydrolysis to eventually afford phosphate and the organic alcohol or amine from which they are derived. | 0 | Organic Chemistry |
In Gross-Pitaevskii mean field theory, one replaces the field operators with c-number functions:
. To find the mean-field
ground states, one then minimises the resulting energy with respect to these c-number functions.
For a spatially uniform system spin-one system, there are two possible mean-field ground states.
When , the ground state is
while for the ground state is
The former expression is referred to as the polar state while the latter is the
ferromagnetic state.
Both states are unique up to overall spin rotations. Importantly,
cannot be rotated into .
The Majorana stellar representation
provides a particularly insightful description of the mean-field phases of spinor
condensates with larger spin. | 7 | Physical Chemistry |
In chemistry, molecularity is the number of molecules that come together to react in an elementary (single-step) reaction and is equal to the sum of stoichiometric coefficients of reactants in the elementary reaction with effective collision (sufficient energy) and correct orientation.
Depending on how many molecules come together, a reaction can be unimolecular, bimolecular or even trimolecular.
The kinetic order of any elementary reaction or reaction step is equal to its molecularity, and the rate equation of an elementary reaction can therefore be determined by inspection, from the molecularity.
The kinetic order of a complex (multistep) reaction, however, is not necessarily equal to the number of molecules involved. The concept of molecularity is only useful to describe elementary reactions or steps. | 7 | Physical Chemistry |
:Direct methods in crystallography are a collection of mathematical techniques that seek to determine crystal structure based on measurements of diffraction patterns and potentially other a priori knowledge (constraints). The central challenge of inverting measured diffraction intensities (i.e. applying an inverse Fourier Transform) to determine the original crystal potential is that phase information is lost in general since intensity is a measurement of the square of the modulus of the amplitude of any given diffracted beam. This is known as the phase problem of crystallography.
:If the diffraction can be considered kinematical, constraints may be used to probabilistically relate the phases of the reflections to their amplitudes, and the original structure can be solved via direct methods (see Sayre equation as an example). Kinematical diffraction is often the case in x-ray diffraction, and is one of the primary reasons that technique has been so successful at solving crystal structures. However, in electron diffraction, the probing wave interacts much more strongly with the electrostatic crystal potential, and complex dynamical diffraction effects can dominate the measured diffraction patterns. This makes application of direct methods much more challenging without a priori knowledge of the structure in question. | 3 | Analytical Chemistry |
During the Deep water Horizon oil spill, an estimated 1.84 million gallons of Corexit was used in an attempt to increase the amount of surface oil and mitigate the damage to coastal habitat. BP purchased all of the world's supply of Corexit soon after the spill began. Nearly half (771,000 gallons) of the dispersants were applied directly at the wellhead. The primary dispersant used were Corexit 9527 and 9500, which were controversial due to toxicity.
In 2012, a study found that Corexit made the oil up to 52 times more toxic than oil alone, and that the dispersant's emulsifying effect makes oil droplets more bio-available to plankton. The Georgia Institute of Technology found that "Mixing oil with dispersant increased toxicity to ecosystems" and made the gulf oil spill worse.
In 2013, in response to the growing body of laboratory-derived toxicity data, some researchers address the scrutiny that should be used when evaluating laboratory test results that have been extrapolated using procedures that are not fully reliable for environmental assessments. Since then, guidance has been published that improves the comparability and relevance of oil toxicity tests. | 2 | Environmental Chemistry |
Advances to the discovery of LB and LM films began with Benjamin Franklin in 1773 when he dropped about a teaspoon of oil onto a pond. Franklin noticed that the waves were calmed almost instantly and that the calming of the waves spread for about half an acre. What Franklin did not realize was that the oil had formed a monolayer on top of the pond surface. Over a century later, Lord Rayleigh quantified what Benjamin Franklin had seen. Knowing that the oil, oleic acid, had spread evenly over the water, Rayleigh calculated that the thickness of the film was 1.6 nm by knowing the volume of oil dropped and the area of coverage.
With the help of her kitchen sink, Agnes Pockels showed that area of films can be controlled with barriers. She added that surface tension varies with contamination of water. She used different oils to deduce that surface pressure would not change until area was confined to about 0.2 nm. This work was originally written as a letter to Lord Rayleigh who then helped Agnes Pockels become published in the journal, Nature, in 1891.
Agnes Pockels’ work set the stage for Irving Langmuir who continued to work and confirmed Pockels’ results. Using Pockels’ idea, he developed the Langmuir (or Langmuir–Blodgett) trough. His observations indicated that chain length did not impact the affected area since the organic molecules were arranged vertically.
Langmuir’s breakthrough did not occur until he hired Katherine Blodgett as his assistant. Blodgett initially went to seek for a job at General Electric (GE) with Langmuir during her Christmas break of her senior year at Bryn Mawr College, where she received a BA in Physics. Langmuir advised to Blodgett that she should continue her education before working for him. She thereafter attended University of Chicago for her MA in Chemistry. Upon her completion of her Master's, Langmuir hired her as his assistant. However, breakthroughs in surface chemistry happened after she received her PhD degree in 1926 from Cambridge University.
While working for GE, Langmuir and Blodgett discovered that when a solid surface is inserted into an aqueous solution containing organic moieties, the organic molecules will deposit a monolayer homogeneously over the surface. This is the Langmuir–Blodgett film deposition process. Through this work in surface chemistry and with the help of Blodgett, Langmuir was awarded the Nobel Prize in 1932. In addition, Blodgett used Langmuir–Blodgett film to create 99% transparent anti-reflective glass by coating glass with fluorinated organic compounds, forming a simple anti-reflective coating. | 7 | Physical Chemistry |
The linked-read sequencing is microfluidic-based, and only needs nanograms of input DNA. One nanogram of DNA can be distributed across more than 100,000 droplet partitions, where DNA fragments are barcoded and subjected to polymerase chain reactions (PCR). As a result, DNA fragments (or reads) that share the same barcode can be grouped as coming from one single long input DNA sequence. And, long range information can be assembled from short reads.
Steps of Linked-read sequencing:
# Sample Preparation: DNA is extracted from a sample (e.g., blood) and cut into fragments of 50 to 200 kilo base-pairs long.
# Barcode Sequencing: each DNA fragment is labelled with a unique barcode through a process known as "Gel Bead-In Emulsion" (GEM).
# Library Preparation: barcoded DNA fragments are amplified with PCR to generate sequencing libraries.
# Sequencing: with Illumina next-generation sequencing technology, generate millions to billions of short sequence reads that represent fragments of the original DNA molecules.
# Barcode Processing: group short reads to longer fragments based on barcodes.
# Downstream Analysis: processed reads are aligned to a reference genome, or used for de novo assembly of complex genomes, haplotype phasing, or identification of structural variations. | 1 | Biochemistry |
Some cyanobacteria can produce neurotoxins, cytotoxins, endotoxins, and hepatotoxins (e.g., the microcystin-producing bacteria genus microcystis), which are collectively known as cyanotoxins.
Specific toxins include anatoxin-a, guanitoxin, aplysiatoxin, cyanopeptolin, cylindrospermopsin, domoic acid, nodularin R (from Nodularia), neosaxitoxin, and saxitoxin. Cyanobacteria reproduce explosively under certain conditions. This results in algal blooms which can become harmful to other species and pose a danger to humans and animals if the cyanobacteria involved produce toxins. Several cases of human poisoning have been documented, but a lack of knowledge prevents an accurate assessment of the risks, and research by Linda Lawton, FRSE at Robert Gordon University, Aberdeen and collaborators has 30 years of examining the phenomenon and methods of improving water safety.
Recent studies suggest that significant exposure to high levels of cyanobacteria producing toxins such as BMAA can cause amyotrophic lateral sclerosis (ALS). People living within half a mile of cyanobacterially contaminated lakes have had a 2.3 times greater risk of developing ALS than the rest of the population; people around New Hampshire's Lake Mascoma had an up to 25 times greater risk of ALS than the expected incidence. BMAA from desert crusts found throughout Qatar might have contributed to higher rates of ALS in Gulf War veterans. | 5 | Photochemistry |
In neurons, action potentials induce neurotransmitter release at axon terminals by opening voltage-gated Ca channels, allowing for Ca influx. As a result, GCaMP is commonly used to measure increases in intracellular Ca in neurons as a proxy for neuronal activity in multiple animal models, including Caenorhabditis elegans, zebrafish, Drosophila, and mice. Recently, genetically encoded voltage indicators (GEVIs) have been developed alongside GECIs to more directly probe neuronal activity at the cellular level in these animal models.
GCaMP has played a vital role in establishing large-scale neural recordings in animals to investigate how activity patterns in neuronal networks influence behavior. For example, Nguyen et al. (2016) used GCaMP in whole-brain imaging during free movement of C. elegans to identify neurons and groups of neurons whose activity correlated with specific locomotor behaviors.
Muto et al. (2003) expressed GCaMP in zebrafish embryos to measure and map the coordinated activity of spinal motor neurons to different parts of the brain during the onset, propagation, and recovery of seizures induced by pentylenetetrazol. GCaMP expression in zebrafish brains has also been used to study activation of neural circuits in cognitive processes like prey capture, impulse control, and attention.
Additionally, researchers have used GCaMP to observe neuronal activity in mice by expressing it under control of the Thy1 promoter, which is found in excitatory pyramidal neurons. For instance, integration of neurons into circuits during motor learning has been tracked by using GCaMP to observe synchronized fluctuation patterns in Ca levels. GCaMP has also been used to observe Ca dynamics in subcellular compartments of mouse neurons: Cichon and Gan (2015) used GCaMP to show that neurons in the mouse motor cortex exhibit NMDA-driven increases in Ca that are independent for each dendritic spine, thus showing that individual dendritic spines regulate synaptic plasticity. Finally, GCaMP has been used to identify activity patterns in specific regions of the mouse brain. For instance, Jones et al. (2018) used GCaMP6 in mice to measure neuronal activity in the suprachiasmatic nucleus (SCN), the mammalian circadian pacemaker, and showed that SCN neurons that produced vasoactive intestinal peptide (VIP) exhibited daily activity rhythms in vivo that correlated with VIP release.
GCaMP has also been combined with fiber photometry to measure population-level Ca changes within subpopulations of neurons in freely moving animals. For instance, Clarkson et al. (2017) used this method to show that neurons in the arcuate nucleus of the hypothalamus synchronize to increases in Ca immediately prior to pulses of luteinizing hormone (LH). While GCaMP imaging with fiber photometry cannot track changes in Ca levels within individual neurons, it provides greater temporal resolution for large-scale changes. | 1 | Biochemistry |
A native of Lahore, Qureshi subsequently attended the Punjab University to study chemistry where he graduated with BSc in chemistry. For his higher studies, he went to United Kingdom to attend Imperial College London. He earned MSc in Chemical Technology and worked towards gaining the DIC in physical metallurgy. At the Imperial College, he joined the doctoral group led by Thomas West and David Craig. He earned his PhD in physical chemistry under the supervision of David Craig, writing his thesis on Physico-chemical studies of the vapour deposition of AlO, in 1972. | 7 | Physical Chemistry |
A magnetic field can also be used to focus charged particles. The Lorentz force acting on the electron is perpendicular to both the direction of motion and to the direction of the magnetic field (vxB). A homogeneous field deflects charged particles, but does not focus them. The simplest magnetic lens is a donut-shaped coil through which the beam passes, preferably along the axis of the coil. To generate the magnetic field, an electric current is passed through the coil. The magnetic field is strongest in the plane of the coil and gets weaker moving away from it. In the plane of the coil, the field gets stronger as we move away from the axis. Thus, a charged particle further from the axis experiences a stronger Lorentz force than a particle closer to the axis (assuming that they have the same velocity). This gives rise to the focusing action. Unlike the paths in an electrostatic lens, the paths in a magnetic lens contain a spiraling component, i.e. the charged particles spiral around the optical axis. As a consequence, the image formed by a magnetic lens is rotated relative to the object. This rotation is absent for an electrostatic lens.
The spatial extent of the magnetic field can be controlled by using an iron (or other magnetically soft material) magnetic circuit. This makes it possible to design and build more compact magnetic lenses with well defined optical properties. The vast majority of electron microscopes in use today use magnetic lenses due to their superior imaging properties and the absence of the high voltages that are required for electrostatic lenses. | 7 | Physical Chemistry |
The LDR is being studied as a byproduct of a concept using a fluid stream for momentum transfer between an approaching spacecraft and another spacecraft, station or Moon base. This method could reduce spacecraft mass while increasing space flight efficiency.
A Liquid Sheet Radiator (LRS), adapted for planetary surfaces, is essentially a fountain enclosed in a transparent envelope. The liquid flows down on the inside of this envelope. The liquid sheet radiator concept is exceptionally stable and does not require special machining of the orifice to achieve its performance. | 7 | Physical Chemistry |
The theoretical description of contact angle arises from the consideration of a thermodynamic equilibrium between the three phases: the liquid phase (L), the solid phase (S), and the gas or vapor phase (G) (which could be a mixture of ambient atmosphere and an equilibrium concentration of the liquid vapor). (The "gaseous" phase could be replaced by another immiscible liquid phase.) If the solid–vapor interfacial energy is denoted by , the solid–liquid interfacial energy by , and the liquid–vapor interfacial energy (i.e. the surface tension) by , then the equilibrium contact angle is determined from these quantities by the Young equation:
The contact angle can also be related to the work of adhesion via the Young–Dupré equation:
where is the solid – liquid adhesion energy per unit area when in the medium G. | 7 | Physical Chemistry |
The most widely practiced reactions convert carboxylic acids into esters, amides, carboxylate salts, acid chlorides, and alcohols. Carboxylic acids react with bases to form carboxylate salts, in which the hydrogen of the hydroxyl (–OH) group is replaced with a metal cation. For example, acetic acid found in vinegar reacts with sodium bicarbonate (baking soda) to form sodium acetate, carbon dioxide, and water:
Carboxylic acids also react with alcohols to give esters. This process is widely used, e.g. in the production of polyesters. Likewise, carboxylic acids are converted into amides, but this conversion typically does not occur by direct reaction of the carboxylic acid and the amine. Instead esters are typical precursors to amides. The conversion of amino acids into peptides is a significant biochemical process that requires ATP.
The hydroxyl group on carboxylic acids may be replaced with a chlorine atom using thionyl chloride to give acyl chlorides. In nature, carboxylic acids are converted to thioesters. | 0 | Organic Chemistry |
The polymerase chain reaction (PCR) is a biochemistry and molecular biology technique for isolating and exponentially amplifying a fragment of DNA, via enzymatic replication, without using a living organism. It enables the detection of specific strands of DNA by making millions of copies of a target genetic sequence. The target sequence is essentially photocopied at an exponential rate, and simple visualisation techniques can make the millions of copies easy to see.
The method works by pairing the targeted genetic sequence with custom designed complementary bits of DNA called primers. In the presence of the target sequence, the primers match with it and trigger a chain reaction. DNA replication enzymes use the primers as docking points and start doubling the target sequences. The process is repeated over and over again by sequential heating and cooling until doubling and redoubling has multiplied the target sequence several million-fold. The millions of identical fragments are then purified in a slab of gel, dyed, and can be seen with UV light. It is not prone to contamination. Irrespective of the variety of methods used for DNA analysis, only PCR in its different formats has been widely applied in GMO detection/analysis and generally accepted for regulatory compliance purposes. Detection methods based on DNA rely on the complementarity of two strands of DNA double helix that hybridize in a sequence-specific manner. The DNA of GMO consists of several elements that govern its functioning. The elements are promoter sequence, structural gene and stop sequence for the gene. | 1 | Biochemistry |
The nodes of Ranvier Na+/Ca2+ exchangers and high density of voltage-gated Na+ channels that generate action potentials. A sodium channel consists of a pore-forming α subunit and two accessory β subunits, which anchor the channel to extra-cellular and intra-cellular components. The nodes of Ranvier in the central and peripheral nervous systems mostly consist of αNaV1.6 and β1 subunits. The extra-cellular region of β subunits can associate with itself and other proteins, such as tenascin R and the cell-adhesion molecules neurofascin and contactin. Contactin is also present at nodes in the CNS and interaction with this molecule enhances the surface expression of Na+ channels.
Ankyrin has been found to be bounded to βIV spectrin, a spectrin isoform enriched at nodes of Ranvier and axon initial segments. The PNS nodes are surrounded by Schwann cell microvilli, which contain ERMs and EBP50 that may provide a connection to actin microfilaments. Several extracellular matrix proteins are enriched at nodes of Ranvier, including tenascin-R, Bral-1, and proteoglycan NG2, as well as phosphacan and versican V2. At CNS nodes, the axonal proteins also include contactin; however, Schwann cell microvilli are replaced by astrocyte perinodal extensions. | 1 | Biochemistry |
HABs contain dense concentrations of organisms and appear as discolored water, often reddish-brown in color. It is a natural phenomenon, but the exact cause or combination of factors that result in a HAB event are not necessarily known. However, three key natural factors are thought to play an important role in a bloom - salinity, temperature, and wind. HABs cause economic harm, so outbreaks are carefully monitored. For example, the Florida Fish and Wildlife Conservation Commission provides an up-to-date status report on HABs in Florida. The Texas Parks and Wildlife Department also provides a status report. While no particular cause of HABs has been found, many different factors can contribute to their presence. These factors can include water pollution, which originates from sources such as human sewage and agricultural runoff.
The occurrence of HABs in some locations appears to be entirely natural (algal blooms are a seasonal occurrence resulting from coastal upwelling, a natural result of the movement of certain ocean currents) while in others they appear to be a result of increased nutrient pollution from human activities. The growth of marine phytoplankton is generally limited by the availability of nitrates and phosphates, which can be abundant in agricultural run-off as well as coastal upwelling zones. Other factors such as iron-rich dust influx from large desert areas such as the Sahara Desert are thought to play a major role in causing HAB events. Some algal blooms on the Pacific Coast have also been linked to occurrences of large-scale climatic oscillations such as El Niño events. | 3 | Analytical Chemistry |
Zinc smelting is the process of converting zinc concentrates (ores that contain zinc) into pure zinc. Zinc smelting has historically been more difficult than the smelting of other metals, e.g. iron, because in contrast, zinc has a low boiling point. At temperatures typically used for smelting metals, zinc is a gas that will escape from a furnace with the flue gas and be lost, unless specific measures are taken to prevent it.
The most common zinc concentrate processed is zinc sulfide, which is obtained by concentrating sphalerite using the froth flotation method. Secondary (recycled) zinc material, such as zinc oxide, is also processed with the zinc sulfide. Approximately 30% of all zinc produced is from recycled sources. | 8 | Metallurgy |
HTIR-TC offers a breakthrough in measuring high-temperature processes. Its characteristics are: durable and reliable at high temperatures, up to at least 1700 °C; resistant to irradiation; moderately priced; available in a variety of configurations - adaptable to each application; easily installed. Originally developed for use in nuclear test reactors, HTIR-TC may enhance the safety of operations in future reactors. This thermocouple was developed by researchers at the Idaho National Laboratory (INL). | 8 | Metallurgy |
During the thirteenth century, Mosul, Iraq became home to a school of luxury metalwork which rose to international renown. Artifacts classified as Mosul are some of the most intricately designed and revered pieces of the Middle Ages. | 8 | Metallurgy |
Phylogenetic footprinting is a technique that utilizes multiple sequence alignments to determine locations of conserved sequences such as regulatory elements. Along with multiple sequence alignments, phylogenetic footprinting also requires statistical rates of conserved and non-conserved sequences. Using the information provided by multiple sequence alignments and statistical rates, one can identify the best conserved motifs in the orthologous regions of interest. | 1 | Biochemistry |
BC200 RNA is expressed in the dendrites as ribonucleoprotein particles. Protein synthesis at the synapses of neurons contribute to neuronal plasticity and help prevent neuronal degradation. Small, non-coding RNAs such as BC200 RNA work to repress translation by inhibiting its initiation. During eukaryotic translation, the preinitiation complex binds mRNA and scans the coding strand for a start codon. This step is often subject to the control of a family of initiation factors and these factors are often a target for translational regulators. Poly(A)-binding protein (PABP) has been shown to bind to BC200 RNA further confirming their role as regulators of protein biosynthesis in synapses.
BC200 RNA targets an ATP-dependent RNA helicase called eukaryotic initiation factor 4A (eIF4A). eIF4A requires energy from ATP hydrolysis to unwind the double helix and initiate translation. However, BC200 RNA interferes with the transmission of energy after hydrolysis by changing the conformation of eIF4A, and thus the energy needed to unwind the double helix is never appropriately supplied and initiation of translation is inhibited.
This highly localized uncoupling of the ATPase activity, and subsequently the unwinding of the RNA duplex is proposed to have evolved as a result of the growing complexity of postsynaptic neurons and neuronal activities. Non-coding RNA molecules evolve at a much faster rate than gene-encoding proteins; thus, the sustained conservation of the BC200 RNA transcript indicates its importance for nervous system function. | 1 | Biochemistry |
Stomata are holes in the leaf by which pathogens can enter unchallenged. However, stomata can sense the presence of some, if not all, pathogens. However, pathogenic bacteria applied to Arabidopsis plant leaves can release the chemical coronatine, which induce the stomata to reopen. | 5 | Photochemistry |
Transcriptional regulation is one of the most common ways for an organism to alter gene expression. The use of activation and coactivation allows for greater control over when, where and how much of a protein is produced. This enables each cell to be able to quickly respond to environmental or physiological changes and helps to mitigate any damage that may occur if it were otherwise unregulated. | 1 | Biochemistry |
Solar cells degrade over time and lose their efficiency. Solar cells in extreme climates, such as desert or polar, are more prone to degradation due to exposure to harsh UV light and snow loads respectively. Usually, solar panels are given a lifespan of 25–30 years before they get decommissioned.
The International Renewable Energy Agency estimated that the amount of solar panel electronic waste generated in 2016 was 43,500–250,000 metric tons. This number is estimated to increase substantially by 2030, reaching an estimated waste volume of 60–78 million metric tons in 2050. | 7 | Physical Chemistry |
Ekimov was awarded the 1975 USSR State Prize in Science and Engineering for work on electron spin orientation in semiconductors. He is co-recipient of the 2006 R. W. Wood Prize of the Optical Society of America for "discovery of nanocrystal quantum dots and pioneering studies of their electronic and optical properties" shared with Alexander Efros and Louis E. Brus.
Ekimov, Brus and Moungi Bawendi were the recipients of the 2023 Nobel Prize in Chemistry "for the discovery and synthesis of quantum dots". | 7 | Physical Chemistry |
Metal recovery is the final step in a hydrometallurgical process, in which metals suitable for sale as raw materials are produced. Sometimes, however, further refining is needed to produce ultra-high purity metals. The main types of metal recovery processes are electrolysis, gaseous reduction, and precipitation. For example, a major target of hydrometallurgy is copper, which is conveniently obtained by electrolysis. Cu ions are reduced to Cu metal at low potentials, leaving behind contaminating metal ions such as Fe and Zn. | 8 | Metallurgy |
Approaches for delivering unaltered natural products using polymeric carriers is of widespread interest. Dendrimers have been explored for the encapsulation of hydrophobic compounds and for the delivery of anticancer drugs. The physical characteristics of dendrimers, including their monodispersity, water solubility, encapsulation ability, and large number of functionalizable peripheral groups make these macromolecules appropriate candidates for drug delivery vehicles. | 6 | Supramolecular Chemistry |
When inactive, the PKA apoenzyme exists as a tetramer which consists of two regulatory subunits and two catalytic subunits. The catalytic subunit contains the active site, a series of canonical residues found in protein kinases that bind and hydrolyse ATP, and a domain to bind the regulatory subunit. The regulatory subunit has domains to bind to cyclic AMP, a domain that interacts with catalytic subunit, and an auto inhibitory domain. There are two major forms of regulatory subunit; RI and RII.
Mammalian cells have at least two types of PKAs: type I is mainly in the cytosol, whereas type II is bound via its regulatory subunits and special anchoring proteins, described in the anchorage section, to the plasma membrane, nuclear membrane, mitochondrial outer membrane, and microtubules. In both types, once the catalytic subunits are freed and active, they can migrate into the nucleus (where they can phosphorylate transcription regulatory proteins), while the regulatory subunits remain in the cytoplasm.
The following human genes encode PKA subunits:
* catalytic subunit – PRKACA, PRKACB, PRKACG
* regulatory subunit type I - PRKAR1A, PRKAR1B
* regulatory subunit type II - PRKAR2A, PRKAR2B | 1 | Biochemistry |
This table lists the gas–liquid–solid triple points of several substances. Unless otherwise noted, the data come from the U.S. National Bureau of Standards (now NIST, National Institute of Standards and Technology).
Notes:
* For comparison, typical atmospheric pressure is 101.325 kPa (1 atm).
* Before the new definition of SI units, water's triple point, 273.16 K, was an exact number. | 7 | Physical Chemistry |
Water clarity is a descriptive term for how deeply visible light penetrates through water. In addition to light penetration, the term water clarity is also often used to describe underwater visibility. Water clarity is one way that humans measure water quality, along with oxygen concentration and the presence or absence of pollutants and algal blooms.
Water clarity governs the health of underwater ecosystems because it impacts the amount of light reaching the plants and animals living underwater. For plants, light is needed for photosynthesis. The clarity of the underwater environment determines the depth ranges where aquatic plants can live. Water clarity also impacts how well visual animals like fish can see their prey. Clarity affects the aquatic plants and animals living in all kinds of water bodies, including rivers, ponds, lakes, reservoirs, estuaries, coastal lagoons, and the open ocean.
Water clarity also affects how humans interact with water, from recreation and property values to mapping, defense, and security. Water clarity influences human perceptions of water quality, recreational safety, aesthetic appeal, and overall environmental health. Tourists visiting the Great Barrier Reef were willing to pay to improve the water clarity conditions for recreational satisfaction. Water clarity also influences waterfront property values. In the United States, a 1% improvement in water clarity increased property values by up to 10%. Water clarity is needed to visualize targets underwater, either from above or in water. These applications include mapping and military operations. To map shallow-water features such as oyster reefs and seagrass beds, the water must be clear enough for those features to be visible to a drone, airplane, or satellite. Water clarity is also needed to detect underwater objects such as submarines using visible light. | 3 | Analytical Chemistry |
Some antibacterial drugs such as penicillin interfere with the production of peptidoglycan by binding to bacterial enzymes known as penicillin-binding proteins or DD-transpeptidases. Penicillin-binding proteins form the bonds between oligopeptide crosslinks in peptidoglycan. For a bacterial cell to reproduce through binary fission, more than a million peptidoglycan subunits (NAM-NAG+oligopeptide) must be attached to existing subunits. Mutations in genes coding for transpeptidases that lead to reduced interactions with an antibiotic are a significant source of emerging antibiotic resistance. Since peptidoglycan is also lacking in L-form bacteria and in mycoplasmas, both are resistant against penicillin.
Other steps of peptidoglycan synthesis can also be targeted. The topical antibiotic bacitracin targets the utilization of C55-isoprenyl pyrophosphate. Lantibiotics, which includes the food preservative nisin, attack lipid II.
Lysozyme, which is found in tears and constitutes part of the body's innate immune system exerts its antibacterial effect by breaking the β-(1,4)-glycosidic bonds in peptidoglycan (see above). Lysozyme is more effective in acting against Gram-positive bacteria, in which the peptidoglycan cell wall is exposed, than against Gram-negative bacteria, which have an outer layer of LPS covering the peptidoglycan layer. Several bacterial peptidoglycan modifications can result in resistance to degradation by lysozyme. Susceptibility of bacteria to degradation is also considerably affected by exposure to antibiotics. Exposed bacteria synthesize peptidoglycan that contains shorter sugar chains that are poorly crosslinked and this peptidoglycan is then more easily degraded by lysozyme. | 1 | Biochemistry |
High precision iron isotope measurements are obtained either via thermal ionization mass spectrometry (TIMS) or multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). | 9 | Geochemistry |
In space plasmas where the electron density is relatively low, the Debye length may reach macroscopic values, such as in the magnetosphere, solar wind, interstellar medium and intergalactic medium. See the table here below: | 7 | Physical Chemistry |
Alkalinity measures the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate, defined as pH 4.5 for many oceanographic/limnological studies. The alkalinity is equal to the stoichiometric sum of the bases in solution. In most Earth surface waters carbonate alkalinity tends to make up most of the total alkalinity due to the common occurrence and dissolution of carbonate rocks and other geological weathering processes that produce carbonate anions. Other common natural components that can contribute to alkalinity include borate, hydroxide, phosphate, silicate, dissolved ammonia, and the conjugate bases of organic acids (e.g., acetate). Solutions produced in a laboratory may contain a virtually limitless number of species that contribute to alkalinity. Alkalinity is frequently given as molar equivalents per liter of solution or per kilogram of solvent. In commercial (e.g. the swimming pool industry) and regulatory contexts, alkalinity might also be given in parts per million of equivalent calcium carbonate (ppm CaCO). Alkalinity is sometimes incorrectly used interchangeably with basicity. For example, the addition of CO lowers the pH of a solution, thus reducing basicity while alkalinity remains unchanged (see example below).
A variety of titrants, endpoints, and indicators are specified for various alkalinity measurement methods. Hydrochloric and sulfuric acids are common acid titrants, while phenolpthalein, methyl red, and bromocresol green are common indicators. | 9 | Geochemistry |
It has been shown that PMCA is capable of detecting as little as a single molecule of oligomeric infectious PrP. PMCA possesses the ability to generate millions infectious units, starting with the equivalent to one PrP oligomer; well below the infectivity threshold. This data demonstrates that PMCA has a similar power of amplification as PCR techniques used to amplify DNA. It opens a great promise for development of a highly sensitive detection of PrP, and for understanding the molecular basis of prion replication. Indeed, PMCA has been used by various groups to PrP in blood of animals experimentally infected with prions during both the symptomatic and pre-symptomatic phases as well as in urine. | 1 | Biochemistry |
While passive radiative cooling technologies have proven successful in mid-latitude regions of Earth, to reach the same level of performance has faced more difficulties in tropical climates. This has primarily been attributed to the higher solar irradiance and atmospheric radiation of these zones, particularly humidity and cloud cover. The average cooling potential of hot and humid climates varies between 10 and 40 W/m2, which is significantly lower than hot and dry climates.
For example, the cooling potential of most of southeast Asia and the Indian subcontinent is significantly diminished in the summer due to a dramatic increase in humidity, dropping as low as 10–30 W/m2. Other similar zones, such as tropical savannah areas in Africa, see a more modest decline during summer, dropping to 20–40 W/m2. However, tropical regions generally have a higher albedo or radiative forcing due to sustained cloud cover and thus their land surface contributes less to planetary albedo.
A study by Han et al. determined criteria for a PDRC surface in tropical climates to have a solar reflectance of at least 97% and an infrared emittance of at least 80% to achieve sub-ambient temperatures in tropical climates. The researchers used a Barium sulphate|-Potassium sulphate| coating with a "solar reflectance and infrared emittance (8–13 μm) of 98.4% and 95% respectively" in the tropical climate of Singapore and achieved a "sustained daytime sub-ambient temperature of 2°C" under direct solar intensity of 1000 W/m2. | 7 | Physical Chemistry |
When the primary beam consists of accelerated electrons, the probe is termed an electron microprobe, when the primary beam consists of accelerated ions, the term ion microprobe is used. The term microprobe may also be applied to optical analytical techniques, when the instrument is set up to analyse micro samples or micro areas of larger specimens. Such techniques include micro Raman spectroscopy, micro infrared spectroscopy and micro LIBS. All of these techniques involve modified optical microscopes to locate the area to be analysed, direct the probe beam and collect the analytical signal.
A laser microprobe is a mass spectrometer that uses ionization by a pulsed laser and subsequent mass analysis of the generated ions. | 7 | Physical Chemistry |
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