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All-trans-retinal is also an essential component of microbial opsins such as bacteriorhodopsin, channelrhodopsin, and halorhodopsin, which are important in bacterial and archaeal anoxygenic photosynthesis. In these molecules, light causes the all-trans-retinal to become 13-cis retinal, which then cycles back to all-trans-retinal in the dark state. These proteins are not evolutionarily related to animal opsins and are not GPCRs; the fact that they both use retinal is a result of convergent evolution. | 1 | Biochemistry |
A kodecyte (ko•de•cyte) is a living cell that has been modified (koded) by the incorporation of one or more function-spacer-lipid constructs (FSL constructs) to gain a new or novel biological, chemical or technological function. The cell is modified by the lipid tail of the FSL construct incorporating into the bilipid membrane of the cell.
All kodecytes retain their normal vitality and functionality while gaining the new function of the inserted FSL constructs. The combination of dispersibility in biocompatible media, spontaneous incorporation into cell membranes, and apparent low toxicity, makes FSL constructs suitable as research tools and for the development of new diagnostic and therapeutic applications. | 1 | Biochemistry |
Magnesium is anodized primarily as a primer for paint. A thin (5 μm) film is sufficient for this. Thicker coatings of 25 μm and up can provide mild corrosion resistance when sealed with oil, wax, or sodium silicate. Standards for magnesium anodizing are given in AMS 2466, AMS 2478, AMS 2479, and ASTM B893. | 8 | Metallurgy |
During mitosis, mitotic spindle orientation is essential for determining the site of cleavage furrowing and position of daughter cells for subsequent cell fate determination. This orientation is achieved by polarizing cortical factors and rapid alignment of the spindle with the polarity axis. In fruit flies, three cortical factors have been found to regulate the position of the spindle: heterotrimeric G protein α subunit (Gαi), Partner of Inscuteable (Pins), and Mushroom body defect (Mud). Gαi localizes at apical cortex to recruit Pins. Upon binding to GDP-bound Gαi, Pins is activated and recruits Mud to achieve polarized distribution of cortical factors. N-terminal tetratricopeptide repeats (TPRs) in Pins is the binding region for Mud, but is autoinhibited by intrinsic C-terminal GoLoco domains (GLs) in the absence of Gαi. Activation of Pins by Gαi binding to GLs is highly ultrasensitive and is achieved through the following decoy mechanism: GLs 1 and 2 act as a decoy domains, competing with the regulatory domain, GL3, for Gαi inputs. This intramolecular decoy mechanism allows Pins to establish its threshold and steepness in response to distinct Gαi concentration. At low Gαi inputs, the decoy GLs 1 and 2 are preferentially bound. At intermediate Gαi concentration, the decoys are nearly saturated, and GL3 begins to be populated. At higher Gαi concentration, the decoys are fully saturated and Gαi binds to GL3, leading to Pins activation. Ultrasensitivity of Pins in response to Gαi ensures that Pins is activated only at the apical cortex where Gαi concentration is above the threshold, allowing for maximal Mud recruitment. | 1 | Biochemistry |
Cystinosis is a condition where cystine precipitates as a solid in various organs. This accumulation interferes with bodily function and can be fatal. This disorder can be resolved by treatment with cysteamine. Cysteamine acts to solubilize the cystine by (1) forming the mixed disulfide cysteine-cysteamine, which is more soluble and exportable, and (2) reducing cystine to cysteine. | 0 | Organic Chemistry |
He graduated from the Chinese University of Hong Kong with a B.Sc. in 1977, and obtained his Ph.D. in biochemistry and cell biology at the University of Newcastle, Australia, in 1981. He came to New York as a Population Council post-doctoral trainee in 1981, studying in the laboratory of Drs. Wayne Bardin, Neal Musto, and Glen Gunsalus and was appointed as a research investigator in December 1982.
Cheng's research focuses on the development of a novel contraceptive for human males. These studies currently are supported by grants from the National Institutes of Health, the CONRAD Program, and the Andrew Mellon Foundation. | 1 | Biochemistry |
Squalene is an organic compound. It is a triterpene with the formula CH. It is a colourless oil, although impure samples appear yellow. It was originally obtained from shark liver oil (hence its name, as Squalus is a genus of sharks). An estimated 12% of bodily squalene in humans is found in sebum. Squalene has a role in topical skin lubrication and protection.
Most plants, fungi, and animals produce squalene as biochemical precursor in sterol biosynthesis, including cholesterol and steroid hormones in the human body. It is also an intermediate in the biosynthesis of hopanoids in many bacteria.
Squalene is an important ingredient in some vaccine adjuvants: The Novartis and GlaxoSmithKline adjuvants are called MF59 and AS03, respectively. | 1 | Biochemistry |
Supercritical liquid–gas boundaries are lines in the pressure-temperature (pT) diagram that delimit more liquid-like and more gas-like states of a supercritical fluid. They comprise the Fisher–Widom line, the Widom line, and the Frenkel line. | 7 | Physical Chemistry |
Chemical imaging (as quantitative – chemical mapping) is the analytical capability to create a visual image of components distribution from simultaneous measurement of spectra and spatial, time information. Hyperspectral imaging measures contiguous spectral bands, as opposed to multispectral imaging which measures spaced spectral bands.
The main idea - for chemical imaging, the analyst may choose to take as many data spectrum measured at a particular chemical component in spatial location at time; this is useful for chemical identification and quantification. Alternatively, selecting an image plane at a particular data spectrum (PCA - multivariable data of wavelength, spatial location at time) can map the spatial distribution of sample components, provided that their spectral signatures are different at the selected data spectrum.
Software for chemical imaging is most specific and distinguished from chemical methods such as chemometrics.
Imaging instrumentation has three components: a radiation source to illuminate the sample, a spectrally selective element, and usually a detector array (the camera) to collect the images. The data format is called a hypercube. The data set may be visualized as a data cube, a three-dimensional block of data spanning two spatial dimensions (x and y), with a series of wavelengths (lambda) making up the third (spectral) axis. The hypercube can be visually and mathematically treated as a series of spectrally resolved images (each image plane corresponding to the image at one wavelength) or a series of spatially resolved spectra. | 7 | Physical Chemistry |
Time to obtain the test result is a key driver for these products. Tests results can be available in as little as a few minutes. Generally there is a trade off between time and sensitivity: more sensitive tests may take longer to develop. The other key advantage of this format of test compared to other immunoassays is the simplicity of the test, by typically requiring little or no sample or reagent preparation. | 1 | Biochemistry |
Tamejiro Hiyama (born August 24, 1946) is a Japanese organic chemist. He is best known for his work in developing the Nozaki-Hiyama-Kishi reaction and the Hiyama coupling. He is currently a professor at the Chuo University Research and Development Initiative, and a Professor Emeritus of Kyoto University. | 0 | Organic Chemistry |
Polymers, which are not fully saturated, are vulnerable to attack by ozone. This gas exists naturally in the atmosphere but is also formed by nitrogen oxides released in vehicle exhaust pollution. Many common elastomers (rubbers) are affected, with natural rubber, polybutadiene, styrene-butadiene rubber and NBR being most sensitive to degradation. The ozonolysis reaction results in immediate chain scission. Ozone cracks in products under tension are always oriented at right angles to the strain axis, so will form around the circumference in a rubber tube bent over. Such cracks are dangerous when they occur in fuel pipes because the cracks will grow from the outside exposed surfaces into the bore of the pipe, and fuel leakage and fire may follow. The problem of ozone cracking can be prevented by adding antiozonants. | 7 | Physical Chemistry |
Heat engines have been known since antiquity but were only made into useful devices at the time of the industrial revolution in the 18th century. They continue to be developed today. | 7 | Physical Chemistry |
Sit studied detoxification, namely the process of conjugation by which metabolic by-products are made soluble prior to excretion. She also studied metabolism within cancer cells and found aerobic respiration within mitochondria in cancer cells, which contradicts the Warburg hypothesis. | 1 | Biochemistry |
Enthalpy (H) is the transfer of energy in a reaction (for chemical reactions, it is in the form of heat) and ΔH is the change in enthalpy. ΔH is a state function, meaning that ΔH is independent of processes occurring between initial and final states. In other words, it does not matter which steps are taken to get from initial reactants to final products, as ΔH will always be the same. ΔHrxn, or the change in enthalpy of a reaction, has the same value of ΔH as in a thermochemical equation; however, ΔHrxn is measured in units of kJ/mol, meaning that it is the enthalpy change per moles of any particular substance in an equation. Values of ΔH are determined experimentally under standard conditions of 1 atm and 25 °C (298.15K).
As discussed earlier, ΔH can have a positive or negative sign. If ΔH has a positive sign, the system uses heat and is endothermic; if ΔH is negative, then heat is produced and the system is exothermic.
Endothermic: A + B + Heat → C, ΔH > 0
Exothermic: A + B → C + Heat, ΔH < 0
Since enthalpy is a state function, the ΔH given for a particular reaction is only true for that exact reaction. Physical states of reactants and products matter, as do molar concentrations.
Since ΔH is dependent on the physical state and molar concentrations in reactions, thermochemical equations must be stoichiometrically correct. If one agent of an equation is changed through multiplication, then all agents must be proportionally changed, including ΔH.
The multiplicative property of thermochemical equations is mainly due to the first law of thermodynamics, which says that energy can neither be created nor destroyed; this concept is commonly known as the conservation of energy. It holds true on a physical or molecular scale. | 7 | Physical Chemistry |
Generally related to metallurgy or materials science, corrosion engineering also relates to non-metallics including ceramics, cement, composite material, and conductive materials such as carbon and graphite. Corrosion engineers often manage other not-strictly-corrosion processes including (but not restricted to) cracking, brittle fracture, crazing, fretting, erosion, and more typically categorized as Infrastructure asset management. In the 1990s, Imperial College London even offered a Master of Science degree entitled "The Corrosion of Engineering Materials". UMIST – University of Manchester Institute of Science and Technology and now part of the University of Manchester also offered a similar course. Corrosion Engineering master's degree courses are available worldwide and the curricula contain study material about the control and understanding of corrosion. Ohio State University has a corrosion center named after one of the more well known corrosion engineers Mars G Fontana. | 8 | Metallurgy |
* Cell wall reinforcement (cellulose, lignin, suberin, callose, cell wall proteins)
* Antimicrobial chemicals, including reactive oxygen species such as hydrogen peroxide or peroxynitrite, or more complex phytoalexins such as genistein or camalexin
* Antimicrobial proteins such as defensins, thionins, or PR-1
* Antimicrobial enzymes such as chitinases, beta-glucanases, or peroxidases
* Hypersensitive response – a rapid host cell death response associated with defence induction. | 1 | Biochemistry |
Particles and small organisms floating through the water column can become trapped within aggregates. Marine snow aggregates are porous, however, and some particles are able to pass through them. | 9 | Geochemistry |
Sumner was born near Seattle, Washington, and spent part of her childhood on the Yakama Indian Reservation in the Pacific Northwest. From there, she earned a B.S. with Honors in geology from the California Institute of Technology (Caltech), then attended the Massachusetts Institute of Technology for her Ph.D. which she completed in 1995. Sumner then returned Caltech for postdoctoral research, supported by an O.K. Earl Postdoctoral Fellowship. | 9 | Geochemistry |
Oligonucleotidase (, oligoribonuclease) is an exoribonuclease derived from Flammulina velutipes. This enzyme catalyses the following chemical reaction
: 3'-end directed exonucleolytic cleavage of viral RNA-DNA hybrid | 1 | Biochemistry |
In 1960, Vogel discovered that 1,2-divinylcyclopropane rearranges to cycloheptan-1,4-diene., After his discovery, a series of intense mechanistic investigations of the reaction followed in the 1960s, as researchers realized it bore resemblance (both structural and mechanistic) to the related rearrangement of vinylcyclopropane to cyclopentene. By the 1970s, the rearrangement had achieved synthetic utility and to this day it continues to be a useful method for the formation of seven-membered rings. Variations incorporating heteroatoms have been reported (see below).
Advantages: Being a rearrangement, the process exhibits ideal atom economy. It often proceeds spontaneously without the need for a catalyst. Competitive pathways are minimal for the all-carbon rearrangement.
Disadvantages: The configuration of the starting materials needs be controlled in many cases—trans-divinylcyclopropanes often require heating to facilitate isomerization before rearrangement will occur. Rearrangements involving heteroatoms can exhibit reduced yields due to the formation of side products. | 0 | Organic Chemistry |
RNA-Seq refers to the combination of a high-throughput sequencing methodology with computational methods to capture and quantify transcripts present in an RNA extract. The nucleotide sequences generated are typically around 100 bp in length, but can range from 30 bp to over 10,000 bp depending on the sequencing method used. RNA-Seq leverages deep sampling of the transcriptome with many short fragments from a transcriptome to allow computational reconstruction of the original RNA transcript by aligning reads to a reference genome or to each other (de novo assembly). Both low-abundance and high-abundance RNAs can be quantified in an RNA-Seq experiment (dynamic range of 5 orders of magnitude)—a key advantage over microarray transcriptomes. In addition, input RNA amounts are much lower for RNA-Seq (nanogram quantity) compared to microarrays (microgram quantity), which allow examination of the transcriptome even at a single-cell resolution when combined with amplification of cDNA. Theoretically, there is no upper limit of quantification in RNA-Seq, and background noise is very low for 100 bp reads in non-repetitive regions.
RNA-Seq may be used to identify genes within a genome, or identify which genes are active at a particular point in time, and read counts can be used to accurately model the relative gene expression level. RNA-Seq methodology has constantly improved, primarily through the development of DNA sequencing technologies to increase throughput, accuracy, and read length. Since the first descriptions in 2006 and 2008, RNA-Seq has been rapidly adopted and overtook microarrays as the dominant transcriptomics technique in 2015.
The quest for transcriptome data at the level of individual cells has driven advances in RNA-Seq library preparation methods, resulting in dramatic advances in sensitivity. Single-cell transcriptomes are now well described and have even been extended to in situ RNA-Seq where transcriptomes of individual cells are directly interrogated in fixed tissues. | 1 | Biochemistry |
Chromosome territories are spheroid with diameters on the order of one to few micrometers.
Nuclear compartments devoid of DNA called interchromatin compartments have been reported to tunnel into chromosome territories to facilitate molecular diffusion into the otherwise tightly packed chromosome-occupied regions. | 1 | Biochemistry |
Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). If the sugar is ribose, the polymer is RNA; if the sugar is deoxyribose, a variant of ribose, the polymer is DNA.
Nucleic acids are chemical compounds that are found in nature. They carry information in cells and make up genetic material. These acids are very common in all living things, where they create, encode, and store information in every living cell of every life-form on Earth. In turn, they send and express that information inside and outside the cell nucleus. From the inner workings of the cell to the young of a living thing, they contain and provide information via the nucleic acid sequence. This gives the RNA and DNA their unmistakable ladder-step order of nucleotides within their molecules. Both play a crucial role in directing protein synthesis.
Strings of nucleotides are bonded to form spiraling backbones and assembled into chains of bases or base-pairs selected from the five primary, or canonical, nucleobases. RNA usually forms a chain of single bases, whereas DNA forms a chain of base pairs. The bases found in RNA and DNA are: adenine, cytosine, guanine, thymine, and uracil. Thymine occurs only in DNA and uracil only in RNA. Using amino acids and protein synthesis, the specific sequence in DNA of these nucleobase-pairs helps to keep and send coded instructions as genes. In RNA, base-pair sequencing helps to make new proteins that determine most chemical processes of all life forms. | 1 | Biochemistry |
A geminal diol has two hydroxyl groups bonded to the same atom. These species arise by hydration of the carbonyl compounds. The hydration is usually unfavorable, but a notable exception is formaldehyde which, in water, exists in equilibrium with methanediol HC(OH). Another example is (FC)C(OH), the hydrated form of hexafluoroacetone. Many gem-diols undergo further condensation to give dimeric and oligomeric derivatives. This reaction applies to glyoxal and related aldehydes. | 0 | Organic Chemistry |
In free radical polymerization, branching occurs when a chain curls back and bonds to an earlier part of the chain. When this curl breaks, it leaves small chains sprouting from the main carbon backbone. Branched carbon chains cannot line up as close to each other as unbranched chains can. This causes less contact between atoms of different chains, and fewer opportunities for induced or permanent dipoles to occur. A low density results from the chains being further apart. Lower melting points and tensile strengths are evident, because the intermolecular bonds are weaker and require less energy to break.
The problem of branching occurs during propagation, when a chain curls back on itself and breaks - leaving irregular chains sprouting from the main carbon backbone. Branching makes the polymers less dense and results in low tensile strength and melting points. Developed by Karl Ziegler and Giulio Natta in the 1950s, Ziegler–Natta catalysts (triethylaluminium in the presence of a metal(IV) chloride) largely solved this problem. Instead of a free radical reaction, the initial ethene monomer inserts between the aluminium atom and one of the ethyl groups in the catalyst. The polymer is then able to grow out from the aluminium atom and results in almost totally unbranched chains. With the new catalysts, the tacticity of the polypropene chain, the alignment of alkyl groups, was also able to be controlled. Different metal chlorides allowed the selective production of each form i.e., syndiotactic, isotactic and atactic polymer chains could be selectively created.
However, there were further complications to be solved. If the Ziegler–Natta catalyst was poisoned or damaged then the chain stopped growing. Also, Ziegler–Natta monomers have to be small, and it was still impossible to control the molecular mass of the polymer chains. Again new catalysts, the metallocenes, were developed to tackle these problems. Due to their structure they have less premature chain termination and branching. | 7 | Physical Chemistry |
Clarke was born in Harrow in England. His father was Joseph Thacher Clarke, an archeologist. His older sister was the composer and violist Rebecca Clarke. Hans Clarke attended University College London School, and went on to enter the University as a student of chemistry, where he studied under William Ramsay, J. Norman Collie, and Samuel Smiles. He received a degree (Bachelor of Science) in 1908, and continued performing research at the University directed by Smiles and Stewart. In 1911 he was awarded an 1851 Exhibition Scholarship, which allowed him to study for three semesters in Berlin under Emil Fischer, and one semester with A. W. Stewart at Queen's College, Belfast. On his return he was granted the D.Sc. from London University in 1913. | 0 | Organic Chemistry |
A 2006 project at University of California, Berkeley produced a design for inexpensive water disinfection in resource deprived settings. The project was designed to produce an open source design that could be adapted to meet local conditions. In a somewhat similar proposal in 2014, Australian students designed a system using potato chip (crisp) packet foil to reflect solar UV radiation into a glass tube that disinfects water without power. | 5 | Photochemistry |
In biochemistry, paucimannosylation is an enzymatic post-translational modification involving the attachment of relatively simple mannose (Man) and N-Acetylglucosamine (GlcNAc) containing carbohydrates (glycans) to proteins. The paucimannosidic glycans may also be modified with other types of monosaccharides including fucose (Fuc) and xylose (Xyl) depending on the species, tissue and cell origin.
Paucimannosylation forms a separate sub-type in the asparagine N-linked glycosylation system. The short paucimannosidic glycans neither structurally nor functionally fit into the three well-established N-glycan classes i.e. oligomannosidic-, hybrid- and complex-type N-glycans.
Paucimannosylation has traditionally been referred to as a N-glycosylation type of "lower organisms", mostly documented in insects, worms and plants. Recent findings have, however, added nuances to this view, by showing their presence and roles in mammals in the areas of immunity, cellular development, pathogen infection and cancer. To this end, paucimannosylation is therefore now considered to be a distinct type of N-glycosylation that adds diversity to the highly heterogeneous glycoproteome across the eukaryotic domain. | 1 | Biochemistry |
Iodic acid is a relatively strong acid with a pK of 0.75. It is strongly oxidizing in acidic solution, less so in basic solution. When iodic acid acts as oxidizer, then the product of the reaction is either iodine, or iodide ion. Under some special conditions (very low pH and high concentration of chloride ions, such as in concentrated hydrochloric acid), iodic acid is reduced to iodine trichloride, a golden yellow compound in solution and no further reduction occurs. In the absence of chloride ions, when there is an excess amount of reductant, then all iodate is converted to iodide ion. When there is an excess amount of iodate, then part of the iodate is converted to iodine. It may be used in preparation of ionization to form alkyl halides. | 3 | Analytical Chemistry |
In 1850, Clausius, responding to Joule's experimental demonstrations of heat production by friction, rejected the caloric doctrine of conservation of heat, writing:
:::::If we assume that heat, like matter, cannot be lessened in quantity, we must also assume that it cannot be increased; but it is almost impossible to explain the ascension of temperature brought about by friction otherwise than by assuming an actual increase of heat. The careful experiments of Joule, who developed heat in various ways by the application of mechanical force, establish almost to a certainty, not only the possibility of increasing the quantity of heat, but also the fact that the newly-produced heat is proportional to the work expended in its production. It may be remarked further, that many facts have lately transpired which tend to overthrow the hypothesis that heat is itself a body, and to prove that it consists in a motion of the ultimate particles of bodies.
The process function was introduced by Rudolf Clausius in 1850.
Clausius described it with the German compound Wärmemenge, translated as "amount of heat". | 7 | Physical Chemistry |
The elasticities for a reversible uni-uni enzyme catalyzed reaction was previously given by:
An interesting result can be obtained by evaluating the sum . This can be shown to equal:
Two extremes can be considered. At high saturation (), the right-hand term tends to zero so that:
That is the absolute magnitudes of the substrate and product elasticities tends to equal each other. However, it is unlikely that a given enzyme will have both substrate and product concentrations much greater than their respective Kms. A more plausible scenario is when the enzyme is working under sub-saturating conditions (). Under these conditions we obtain the simpler result:
Expressed in a different way we can state:
That is, the absolute value for the substrate elasticity will be greater than the absolute value for the product elasticity. This means that a substrate will have a great influence over the forward reaction rate than the corresponding product.
This result has important implications for the distribution of flux control in a pathway with sub-saturated reaction steps. In general, a perturbation near the start of a pathway will have more influence over the steady state flux than steps downstream. This is because a perturbation that travels downstream is determined by all the substrate elasticities, whereas a perturbation downstream that has to travel upstream if determined by the product elasticities. Since we have seen that the substrate elasticities tends to be larger than the product elasticities, it means that perturbations traveling downstream will be less attenuated than perturbations traveling upstream. The net effect is that flux control tends to be more concentrated at upstream steps compared to downstream steps.
The table below summarizes the extreme values for the elasticities given a reversible Michaelis-Menten rate law. Following Westerhoff et al. the table is split into four cases that include one reversible type, and three irreversible types. | 7 | Physical Chemistry |
A Lorentzian line shape function can be represented as
where L signifies a Lorentzian function standardized, for spectroscopic purposes, to a maximum value of 1; is a subsidiary variable defined as
where is the position of the maximum (corresponding to the transition energy E), p is a position, and w is the full width at half maximum (FWHM), the width of the curve when the intensity is half the maximum intensity (this occurs at the points ). The unit of , and is typically wavenumber or frequency. The variable x is dimensionless and is zero at . | 7 | Physical Chemistry |
Healey and Woodall were not able to analyze any sediments underneath more than one meter (3.3 ft) of water because the particles were too fine for the Ekman dredge sifter that they used. In 2013 Sarah Shenstone-Harris, a University of Toronto undergraduate interning at the schools Centre for Global Climate Science, was able to analyze the sediments. She looked to the diatoms in them to try to see if climate change had played a role in the lakes decline. If so, she also asked, when did that change occur, and was it possible to restore the lake to a level of water quality comparable to what it had been prior to the establishment of Yellowknife?
Shenstone-Harris started from the observation that subarctic lakes generally had shown great sensitivity to climate change because of shifts in the amount of ice cover. Those stresses could be exacerbated for subarctic lakes in an urban area facing higher levels of pollution from a number of different sources, such as Frame. Her inquiry was a paleolimnological one, focusing on the algae species present in the lake at various times in the recent past. She took core samples of the sediment down to and dated them by the lead-210 levels. Once their age was established, she looked at the diatom remains, since the species of algae in the water can reflect environmental changes, and counted the ratio of chrysophyte stomatocysts to establish nutrient levels in the water at that time.
Due to diatom dissolution at the lowest level of the sediments taken, Shenstone-Harris was unable to establish data for any years earlier than 1943, making it impossible to set the desired baseline for a pre-settlement Frame Lake. However, she was able to establish that the lake had always been at a high trophic state, even before it became fully eutrophied by the mid- to late-1990s. That was preceded by a rapid replacement of epiphytic species with benthic ones around 1990.
It was not clear to Shenstone-Harris that that event had been the result of climate change. From 1956 to 1992, the last year records were kept, ice cover on the lake remained relatively stable throughout the winter, yet the amount of Cyclotella and Fragliaria, two genera whose species have been shown to be responsive to changing ice cover and warming climates, varied considerably. This suggested to her that while climate change may be a factor in the lakes decline, it is not the only one. Instead, the change in species around 1990 pointed to a change in littoral zone microhabitat, a loss of macrophytes and mosses, as bearing the primary responsibility for tipping the lake to its present eutrophic state. However, the lack of data on ice cover since 1992 and her inability to determine the lakes status prior to the establishment of Yellowknife qualified that conclusion. "Alternatively", she wrote, "Frame Lake may be a subarctic anomaly and was always high in nutrients".
In 2015 the Carleton team was able to examine the sediments. They found that the period between the late 1940s and 1970 added a half-meter () of sediment to the bottom of the lake, the most of any lake in the region. Above it, the of sediment postdating the causeway was "black, sulfurous smelling and characterized by very high levels of metals, particularly arsenic". These are consistent with the patches of sediment Mallon recalled from his youthful recreation on the lake in his 2015 article, noting that "I can still vividly feel the stuff's gloopy embrace on my feet" (although an accompanying sidebar by another reporter suggested that the sediments may be the result of sewage back-flushed from Niven Lake). | 2 | Environmental Chemistry |
TrkB agonists have received extensive interest from the scientific community resulting in the synthesis and biological evaluation of a large number of mimetics. Deoxygedunin, with a selective TrkB activity, is able to promote axon regeneration in topical treatments. Furthermore, it shows efficacy in two Parkinsons disease (PD) animal models, leading to the protection of locomotor function and the reduction of neuronal death in dopaminergic neurons. A number of studies corroborated that the flavonoid 7,8-Dihydroxyflavone (7,8-DHF) shows neuroprotection in PD and Huntingtons disease (HD) models together with antioxidant activity and enhancement of motor neuronal survival, motor function and spine density in amyotrophic lateral sclerosis (ALS) model. The benzothiazole riluzole exerts neuroprotective effects by increasing BDNF and GDNF levels with improvement of motor neuron survival. It has been approved for the treatment of ALS and delays the onset of ventilator-dependence or tracheostomy in some people and may increase survival by two to three months. Furthermore, several combinations of riluzole with other drugs are in clinical trials (NCT02588677, NCT03127267).
Brimonidine exerts neuroprotective effects in retinal ganglion cells (RGCs) through up-regulation of the expression of BDNF in these cells. It is used in the treatment of glaucoma as eye drops to reduce intraocular pressure (IOP) under the brand name Lumify®. Different drugs, used against PD also behave as neurotrophin mimetics such as rotigotine, selegiline, rasagiline, memantine and levodopa interacting with TrkB and increasing BDNF expression. Furthermore, of particular note, the groups of F. Longo and S. Massa discovered small molecule neurotrophic mimetics exhibiting specificity for TrkB at nanomolar concentrations. In particular, LM22A-4, prevents neuronal death in in vitro models of AD, HD and PD.
Among the peptidomimetic TrkB agonists, the dimeric dipeptide GSB-106 showed neurotrophic and neuroprotective effects by specific activation of TrkB and its signaling pathways. Furthermore, the tricyclic dimeric peptide TDP6 acts as a TrkB agonist mimicking BDNF and induces autophosphorylation of TrkB in primary oligodendrocyte cultures, leading to oligodendrocyte myelination. Regarding DHEA derivatives, the C17-spiroepoxy analogue, BNN-20, binds with high affinity to TrkB, showing antiapoptotic activity in vitro. Its neuroprotective activity was analyzed in the Weaver mouse genetic model of PD in which long term administration of BNN-20 protects the dopaminergic neurons by mimicking BDNF and induces antiapoptotic, antioxidant and anti-inflammatory effects. | 1 | Biochemistry |
The Pacific Proving Grounds was the name used to describe a number of sites in the Marshall Islands and a few other sites in the Pacific Ocean, used by the United States to conduct nuclear testing at various times between 1946 and 1962. In July 1947, after the first atomic weapons testing at Bikini Atoll, the United States entered into an agreement with the United Nations to govern the Trust Territory of the Pacific Islands as a strategic trusteeship territory. The Trust Territory is composed of 2,000 islands spread over of the North Pacific Ocean. On July 23, 1947, the United States Atomic Energy Commission announced the establishment of the Pacific Proving Grounds.
105 atmospheric (i.e., not underground) nuclear tests were conducted there, many of which were of extremely high yield. While the Marshall Islands testing composed 14% of all U.S. tests, it composed nearly 80% of the total yields of those detonated by the U.S., with an estimated total yield of around 210 megatons, with the largest being the 15 Mt Castle Bravo shot of 1954 which spread considerable nuclear fallout on many of the islands, including several which were inhabited, and some that had not been evacuated.
Many of the islands which were part of the Pacific Proving Grounds continue to be contaminated by nuclear fallout, and many of those who were living on the islands at the time of testing has suffered from an increased incidence of various health problems. Through the Radiation Exposure Compensation Act of 1990, at least $759 million has been paid to Marshall Islanders as compensation for their exposure to U.S. nuclear testing. Following the Castle Bravo accident, $15.3 million was paid to Japan. | 2 | Environmental Chemistry |
Amylolytic process or amylolysis is the conversion of starch into sugar by the action of acids or enzymes such as amylase.
Starch begins to pile up inside the leaves of plants during times of light when starch is able to be produced by photosynthetic processes. This ability to make starch disappears in the dark due to the lack of illumination; there is insufficient amount of light produced during the dark needed to carry this reaction forward. Turning starch into sugar is done by the enzyme amylase. | 0 | Organic Chemistry |
The Severinghaus electrode is an electrode that measures carbon dioxide (CO). It was developed by Dr. John W. Severinghaus and his technician A. Freeman Bradley in 1958.
It utilizes a CO-sensitive glass electrode in a surrounding film of bicarbonate solution covered by a thin plastic carbon dioxide permeable membrane, but impermeable to water and electrolytic solutes. The carbon dioxide pressure of a sample gas or liquid equilibrates through the membrane and the glass electrode measures the resulting pH of the bicarbonate solution.
Clark, galvanic, and paramagnetic electrodes measure oxygen. Severinghaus electrode measures . Sanz electrode measures pH. | 3 | Analytical Chemistry |
According to a few oral traditions from San Cristóbal Verapaz, the lake would have formed catastrophically by ground collapse during an earthquake in the early 16th Century, soon after the arrival of the Dominican friars (around 1525 CE), engulfing a church and its surrounding Maya settlement. The cataclysm has been explained as a divine punishment imparted to the inhabitants of San Cristóbal Caccoh, following the expulsion of a Dominican friar and the refusal of the inhabitants to submit to the Christian faith. This tradition is echoed in a book published in 1648 CE by the Irish Dominican friar Thomas Gage: "The English-American, or a New Survey of the West Indies". Gage's book suffers many exaggerations, casting doubt on the validity of his testimony. However, an independent report by Spanish Dominicans also mentions the sudden formation of a lake near San Cristóbal, by cave collapse, during an earthquake in 1590 CE. The parochial church suffered little damage during that earthquake. The most serious report therefore suggests that the purported event would have taken place far enough from the city for the church not to be damaged, but still would have been large enough to be deemed to reported. The event did not affect the western part of the lake, which was already in existence since at least the 8th Century. Montero de Miranda wrote about the lake that by 1575 (UNAM, 1982: 223–248) it was a "very large, long and very deep lake". | 2 | Environmental Chemistry |
Taken over all species and experiments, high light does not affect the organic nitrogen concentration, but decreases the concentration of chlorophyll and minerals. It increases the concentration of starch and sugars, soluble phenolics, and also the xanthophyll/chlorophyll ratio and the chlorophyll a/b ratio. | 5 | Photochemistry |
A stink bomb that could be launched with arrows was invented by Leonardo da Vinci.
The 1972 U.S. presidential campaign of Edmund Muskie was disrupted at least four times in Florida in 1972 with the use of stink bombs during the Florida presidential primary. Stink bombs were set off at campaign picnics in Miami and Tampa, at the Muskie campaign headquarters in Tampa and at offices in Tampa where the campaign's telephone bank was located. The stink bomb plantings served to disrupt the picnics and campaign operations, and was deemed by the U.S. Select Committee on Presidential Campaign Activities of the U.S. Senate to have "disrupted, confused, and unnecessarily interfered with a campaign for the office of the Presidency".
In 2004, it was reported that the Israeli weapons research and development directorate had created a liquid stink bomb, dubbed the "skunk bomb", with an odor that lingers for five years on clothing. It is a synthetic stink bomb based upon the chemistry of the spray that is emitted from the anal glands of the skunk. It was designed as a crowd control tool to be used as a deterrent that causes people to scatter, such as at a protest. It has been described as a less than lethal weapon. | 1 | Biochemistry |
ScBCSi (x = 0.030, y = 0.36 and z = 0.026) has a cubic crystal structure with space group F3m (No. 216) and lattice constant a = 2.03085(5) nm. This compound was initially identified as ScBC (phase I in the Sc-B-C phase diagram of figure 17). A small amount of Si was added into the floating zone crystal growth and thus this phase is a quaternary compound. Its rare cubic structure has 26 sites in the unit cell: three Sc sites, two Si sites, one C site and 20 B sites; 4 out of 20 B sites are boron-carbon mixed-occupancy sites. Atomic coordinates, site occupancies and isotropic displacement factors are listed in table VIII.
In the unit cell, there are three independent icosahedra, I1, I2 and I3, and a B polyhedron which are formed by the B1–B4, B5–B8, B9–B13 and B14–B17 sites, respectively. The B polyhedron has not been observed previously and it is shown in figure 23. The icosahedron I2 has a boron-carbon mixed-occupancy site B,C6 whose occupancy is B/C=0.58/0.42. Remaining 3 boron-carbon mixed-occupancy sites are bridge sites; C and Si sites are also bridge sites.
More than 1000 atoms are available in the unit cell, which is built up by large structure units such as two supertetrahedra T(1) and T(2) and one superoctahedron O(1). As shown in figure 24a, T(1) consists of 4 icosahedra I(1) which have no direct bonding but are bridged by four B and C20 atoms. These atoms also form tetrahedron centered by the Si2 sites. The supertetrahedron T(2) that consists of 4 icosahedra I(2) is the same as shown in figure 18b; its mixed-occupancy sites B and C6 directly bond with each other. The superoctahedron O(1) consists of 6 icosahedra I(3) and bridge sites B, C18, C1 and Si1; here Si1 and C1 exhibit a tetrahedral arrangement at the center of O(1). The B polyhedra also arrange octahedrally, without the central atom, as shown in figure 24c where the B and C19 atoms bridge the B polyhedra to form the octahedral supercluster of the B polyhedra.
Using these large polyhedra, the crystal structure of ScBCSi can be described as shown in figure 25. Owing to the crystal symmetry, the tetrahedral coordination between these superstructure units is again a key factor. The supertetrahedron T(1) lies at the body center and at the edge center of the unit cell. The superoctahedra O(1) locate at the body center (0.25, 0.25, 0.25) of the quarter of the unit cell. They coordinate tetrahedrally around T(1) forming a giant tetrahedron. The supertetrahedra T(2) are located at the symmetry-related positions (0.25, 0.25, 0.75); they also form a giant tetrahedron surrounding T(1). Edges of both giant tetrahedra orthogonally cross each other at their centers; at those edge centers, each B polyhedron bridges all the super-structure clusters T(1), T(2) and O(1). The superoctahedron built of B polyhedra is located at each cubic face center.
Scandium atoms reside in the voids of the boron framework. Four Sc1 atoms form a tetrahedral arrangement inside the B polyhedron-based superoctahedron. Sc2 atoms sit between the B polyhedron-based superoctahedron and the O(1) superoctahedron. Three Sc3 atoms form a triangle and are surrounded by three B polyhedra, a supertetrahedron T(1) and a superoctahedron O(1). | 3 | Analytical Chemistry |
Though the terms equivalence point and endpoint are often used interchangeably, they are different terms. Equivalence point is the theoretical completion of the reaction: the volume of added titrant at which the number of moles of titrant is equal to the number of moles of analyte, or some multiple thereof (as in polyprotic acids). Endpoint is what is actually measured, a physical change in the solution as determined by an indicator or an instrument mentioned above.
There is a slight difference between the endpoint and the equivalence point of the titration. This error is referred to as an indicator error, and it is indeterminate. | 3 | Analytical Chemistry |
Tilth is a physical condition of soil, especially in relation to its suitability for planting or growing a crop. Factors that determine tilth include the formation and stability of aggregated soil particles, moisture content, degree of aeration, soil biota, rate of water infiltration and drainage. Tilth can change rapidly, depending on environmental factors such as changes in moisture, tillage and soil amendments. The objective of tillage (mechanical manipulation of the soil) is to improve tilth, thereby increasing crop production; in the long term, however, conventional tillage, especially plowing, often has the opposite effect, causing the soil carbon sponge to oxidize, break down and become compacted.
Soil with good tilth is spongy with large pore spaces for air infiltration and water movement. Roots only grow where the soil tilth allows for adequate levels of soil oxygen. Such soil also holds a reasonable supply of water and nutrients.
Tillage, organic matter amendments, fertilization and irrigation can each improve tilth, but when used excessively, can have the opposite effect. Crop rotation and cover crops can rebuild the soil carbon sponge and positively impact tilth. A combined approach can produce the greatest improvement. | 9 | Geochemistry |
In natural systems, secondary minerals may form as a byproduct of bacterial metal reduction. Commonly observed secondary minerals produced during experimental bio-reduction by dissimilatory metal reducers include magnetite, siderite, green rust, vivianite, and hydrous Fe(II)-carbonate. | 1 | Biochemistry |
He subsequently joined the MRC Laboratory of Molecular Biology (LMB) in Cambridge to pursue post-doctoral research with Jan Löwe using cryo-EM to study proteins within bacterial cells. After his post-doctoral appointment concluded, he was recruited to the Sir William Dunn School of Pathology, University of Oxford as a Wellcome Trust and Royal Society Sir Henry Dale Fellow. After obtaining tenure at Oxford, he moved back to the LMB as a programme leader in 2022. His research investigates how bacteria and archaea use their surface molecules to form multicellular communities. For instance, during human infections bacteria form biofilms that help them evade antibiotics. The group also use electron tomography. | 1 | Biochemistry |
The Shelby Gem Factory was the production facility of ICT Incorporated, a company in Shelby, Michigan, United States, that manufactured artificial gemstones through proprietary processes. ICT began operations in 1970 and closed in December 2019. | 7 | Physical Chemistry |
* Relatively low array size: Although it has the potential to use an increased amount of dyes to generate millions of different array elements, the current generation of commercially available microsphere arrays (from Luminex xMAP technology) only uses two sets of dyes and therefore can only detect ~100 targets per experiment.
* Hybridization between different sets of probes and target sequences requires a specific annealing temperature, which is affected by length and sequence of the oligonucleotide probe. Therefore, for every experiment, only one possible annealing temperature can be used. Thus, all probes used in given experiment must be designed to hybridize to the target at the same temperature. Although introducing base pair mismatch in some sets of the probes could minimize annealing temperature differences between each set of probes, the hybridization problem is still significant if more than 10-20 targets are tested in one reaction. | 1 | Biochemistry |
In common as well as medical usage, virilization often refers to the process of normal male puberty. These effects include growth of the penis and the testes, accelerated growth, development of pubic hair, and other androgenic hair of face, torso, and limbs, deepening of the voice, increased musculature, thickening of the jaw, prominence of the neck cartilage, and broadening of the shoulders. | 1 | Biochemistry |
The ERK1/2 pathway of mammals is probably the best-characterized MAPK system. The most important upstream activators of this pathway are the Raf proteins (A-Raf, B-Raf or c-Raf), the key mediators of response to growth factors (EGF, FGF, PDGF, etc.); but other MAP3Ks such as c-Mos and Tpl2/Cot can also play the same role. All these enzymes phosphorylate and thus activate the MKK1 and/or MKK2 kinases, that are highly specific activators for ERK1 and ERK2. The latter phosphorylate a number of substrates important for cell proliferation, cell cycle progression, cell division and differentiation (RSK kinases, Elk-1 transcription factor, etc.)
In contrast to the relatively well-insulated ERK1/2 pathway, mammalian p38 and JNK kinases have most of their activators shared at the MAP3K level (MEKK1, MEKK4, ASK1, TAK1, MLK3, TAOK1, etc.). In addition, some MAP2K enzymes may activate both p38 and JNK (MKK4), while others are more specific for either JNK (MKK7) or p38 (MKK3 and MKK6). Due to these interlocks, there are very few if any stimuli that can elicit JNK activation without simultaneously activating p38 or reversed. Both JNK and p38 signaling pathways are responsive to stress stimuli, such as cytokines, ultraviolet irradiation, heat shock, and osmotic shock, and are involved in adaptation to stress, apoptosis or cell differentiation. JNKs have a number of dedicated substrates that only they can phosphorylate (c-Jun, NFAT4, etc.), while p38s also have some unique targets (e.g. the MAPKAP kinases MK2 and MK3), ensuring the need for both in order to respond to stressful stimuli.
ERK5 is part of a fairly well-separated pathway in mammals. Its sole specific upstream activator MKK5 is turned on in response to the MAP3 kinases MEKK2 and MEKK3. The specificity of these interactions are provided by the unique architecture of MKK5 and MEKK2/3, both containing N-terminal PB1 domains, enabling direct heterodimerisation with each other. The PB1 domain of MKK5 also contributes to the ERK5-MKK5 interaction: it provides a special interface (in addition to the D-motif found in MKK5) through which MKK5 can specifically recognize its substrate ERK5. Although the molecular-level details are poorly known, MEKK2 and MEKK3 respond to certain developmental cues to direct endothel formation and cardiac morphogenesis. While also implicated in brain development, the embryonic lethality of ERK5 inactivation due to cardiac abnormalities underlines its central role in mammalian vasculogenesis. It is notable, that conditional knockout of ERK5 in adult animals is also lethal, due to the widespread disruption of endothelial barriers. Mutations in the upstream components of the ERK5 pathway (the CCM complex) are thought to underlie cerebral cavernous malformations in humans. | 1 | Biochemistry |
Addition of a Grignard reagent to a tert-butanesulfinyl aldimine or ketimine results in asymmetric addition to give the branched sulfinamide. The observed stereoselectivity can be rationalized by a six-membered ring transition structure, wherein both oxygen and nitrogen of the sulfinyl imine coordinate magnesium.
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It has four units in Birmingham, Cardiff, Edinburgh and Newcastle. It is a member of the European Association of Poisons Centres and Clinical Toxicologists.
* NPIS Birmingham Unit (West Midlands Poisons Unit), City Hospital, Birmingham - Dr Sally Bradberry
* NPIS Cardiff Unit, Llandough Hospital - Dr Laurence Gray
* NPIS Edinburgh Unit (Scottish Poisons Information Bureau), Royal Infirmary of Edinburgh - Dr. Euan Sandilands.
* NPIS Newcastle Unit, Regional Drug and Therapeutics Centre, Newcastle University - Professor Simon Thomas
NPIS Birmingham has the NPIS Product Data Centre, provided by manufacturer's information, and deals with around 2,300 companies.
NPIS supports (24 hours) NHS Direct (for England and Wales) and (24 hours) NHS 24 for Scotland. Northern Ireland has its Northern Ireland Regional Medicines and Poisons Information Service in Belfast, and NPIS is used when this is not available. The Republic of Ireland uses the service, via the TOXBASE database, which is used by the country's National Poisons Information Centre.
Of all UK nations, Wales has the highest proportionate number of enquiries to the service, with Northern Ireland the fewest. Within England, there is a distribution of higher number of enquiries to the service in the north than the south, with NHS North East having the highest and NHS South of England having the least proportionate number of enquiries. The vast majority (95%) of enquiries come from A&E departments. Around 65% of poisoning is from pharmaceuticals (paracetamol, ibuprofen, citalopram, diazepam and zopiclone) and 15% from household chemicals (detergents, bleach, and isopropanol). There are very dangerous chemicals stored in most UK kitchens.
Wednesday is the busiest day of the week for enquiries, with the fewest at the weekend. | 1 | Biochemistry |
The surface of photocathodes can be characterized by various surface sensitive techniques like scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy. | 7 | Physical Chemistry |
Here are listed and discussed some of the most common techniques and approaches pursued in attosecond research centers. | 7 | Physical Chemistry |
Diacylglycerol has been shown to exert some of its excitatory actions on vesicle release through interactions with the presynaptic priming protein family Munc13. Binding of DAG to the C1 domain of Munc13 increases the fusion competence of synaptic vesicles resulting in potentiated release.
Diacylglycerol can be mimicked by the tumor-promoting compounds phorbol esters. | 1 | Biochemistry |
β-Leucine (beta-leucine) is a beta amino acid and positional isomer of -leucine which is naturally produced in humans via the metabolism of -leucine by the enzyme leucine 2,3-aminomutase. In cobalamin (vitamin B) deficient individuals, plasma concentrations of β-leucine are elevated. | 1 | Biochemistry |
An extreme case of intercalation is the complete separation of the layers of the material. This process is called exfoliation. Typically aggressive conditions are required involving highly polar solvents and aggressive reagents. | 6 | Supramolecular Chemistry |
After the creation of and successful research surrounding xDNA, more forms of expanded nucleotides were investigated. yDNA is a second, similar system of nucleotides which uses a benzene ring to expand the four natural bases. xxDNA and yyDNA use naphthalene, a polycyclic molecule consisting of two hydrocarbon rings. The two rings expand the base even wider, further altering its chemical properties. | 1 | Biochemistry |
The hydrophobic interaction is mostly an entropic effect originating from the disruption of the highly dynamic hydrogen bonds between molecules of liquid water by the nonpolar solute, causing the water to form a clathrate-like structure around the non-polar molecules. This structure formed is more highly ordered than free water molecules due to the water molecules arranging themselves to interact as much as possible with themselves, and thus results in a higher entropic state which causes non-polar molecules to clump together to reduce the surface area exposed to water and decrease the entropy of the system. Thus, the two immiscible phases (hydrophilic vs. hydrophobic) will change so that their corresponding interfacial area will be minimal. This effect can be visualized in the phenomenon called phase separation. | 6 | Supramolecular Chemistry |
Permanent gas is a term used for a gas which has a critical temperature below the range of normal human-habitable temperatures and therefore cannot be liquefied by pressure within this range. Historically such gases were thought to be impossible to liquefy and would therefore permanently remain in the gaseous state. The term is relevant to ambient temperature storage and transport of gases at high pressure. | 7 | Physical Chemistry |
Lithium is present in biological systems in trace amounts; its functions are uncertain. Lithium salts have proven to be useful as a mood stabilizer and antidepressant in the treatment of mental illness such as bipolar disorder. | 1 | Biochemistry |
Scrutiny of the land includes examination of potential soil contamination, groundwater quality, surface water quality, vapor intrusion, and sometimes issues related to hazardous substance uptake by biota. The examination of a site may include: definition of any chemical residues within structures; identification of possible asbestos containing building materials; inventory of hazardous substances stored or used on site; assessment of mold and mildew; and evaluation of other indoor air quality parameters.
Depending upon precise protocols utilized, there are a number of variations in the scope of a Phase I study. The tasks listed here are common to almost all Phase I ESAs:
* Performance of an on-site visit to view present conditions (chemical spill residue, die-back of vegetation, etc.); hazardous substances or petroleum products usage (presence of above ground or underground storage tanks, storage of acids, etc.); and evaluate any likely environmentally hazardous site history.
*Evaluation of risks of neighboring properties upon the subject property
*Review of Federal, State, Local and Tribal Records out to distances specified by the ASTM 1528 and AAI Standards (ranging from 1/8 to 1 mile depending on the database)
* Interview of persons knowledgeable regarding the property history (past owners, present owner, key site manager, present tenants, neighbors).
*Examine municipal or county planning files to check prior land usage and permits granted.
*Conduct file searches with public agencies (State water board, fire department, county health department, etc.) having oversight relative to water quality and soil contamination issues.
*Examine historical aerial photography of the vicinity.
*Examine current USGS maps to scrutinize drainage patterns and topography.
*Examine chain-of-title for Environmental Liens and/or Activity and Land Use Limitations (AULs).
In most cases, the public file searches, historical research and chain-of-title examinations are outsourced to information services that specialize in such activities. Non-Scope Items in a Phase I Environmental Site Assessment can include visual inspections or records review searches for:
*Asbestos Containing Building Materials (ACBM)
*Lead-Based Paint
*Lead in Drinking Water
*Mold
*Radon
*Wetlands
*Threatened and Endangered Species
*Mercury poisoning
*Debris flow
*Earthquake Hazard
*Vapor intrusion
*Emerging contaminants
Observations of Non-scope Items can be reported as "findings" if requested by the report user, however, these items do not constitute recognized environmental conditions. | 2 | Environmental Chemistry |
The first spectrum analyzers, in the 1960s, were swept-tuned instruments.
Following the discovery of the fast Fourier transform (FFT) in 1965, the first FFT-based analyzers were introduced in 1967.
Today, there are three basic types of analyzer: the swept-tuned spectrum analyzer, the vector signal analyzer, and the real-time spectrum analyzer. | 7 | Physical Chemistry |
Factors which influence this include the atmospheric abundance of the two gases, the supply of the gases to the site of fixation (i.e. in land plants: whether the stomata are open or closed), the length of the liquid phase (how far these gases have to diffuse through water in order to reach the reaction site). For example, when the stomata are closed to prevent water loss during drought: this limits the supply, while production within the leaf will continue. In algae (and plants which photosynthesise underwater); gases have to diffuse significant distances through water, which results in a decrease in the availability of relative to . It has been predicted that the increase in ambient concentrations predicted over the next 100 years may lower the rate of photorespiration in most plants by around 50%. However, at temperatures higher than the photosynthetic thermal optimum, the increases in turnover rate are not translated into increased assimilation because of the decreased affinity of Rubisco for . | 5 | Photochemistry |
The RFU peak height depends on the amount of DNA being analyzed. When the amount of DNA is very low, then
it can be difficult to separate a true low-level RFU peak from signal noise or other technical artifacts. As a result, many forensic DNA laboratories have set minimum RFU peak-height levels in "scoring" the analysis of alleles.
There are no firm industry-wide rules for establishing minimum RFU threshold values. Each laboratory, in general, has established its own threshold levels as one aspect of its particular validation procedure. Many laboratories have established both lower and upper thresholds for data interpretation, as a window of minimum and maximum readings.
Some threshold levels can be derived experimentally based on the equipment's known signal-to-noise ratios, or a threshold can be defined to match published data or the manufacturer specifications. The company which sells the most widely used equipment for STR typing, Applied Biosystems, Inc. (ABI), has recommended a peak-height minimum of 150 RFU, advising how peaks below that level should be judged with caution. However, many forensic laboratories which have ABI systems have defined lower thresholds, often only 50 to 100 RFU, as determined by their own studies.
Many different factors can affect a laboratory's choice of thresholds. For instance, there might be regulatory guidelines in specific jurisdictions. Also, different kinds of instruments vary in sensitivity (such as slab gel instruments being less sensitive than capillary electrophoresis (CE) instruments). Individual instruments, of a particular model type, have also been known to differ in performance (e.g. differences among various ABI 310 units, all of the same model). Capillary electrophoresis instruments generally provide better resolution compared gel-based systems, as well having better sensitivity. In addition, some laboratories have set different threshold standards depending on which instruments in the lab are used for an analysis.
Setting an upper maximum threshold is critical when analyzing DNA data within high quantity samples. Samples with large amounts of amplified DNA will report high RFU levels that might oversaturate an instrument's sensitivity to measure the results. In such cases, an accurate measurement of the relative peak heights and/or areas might be unattainable. Oversaturation can be a problem when analyzing mixed samples. | 1 | Biochemistry |
Flutamide, as a monotherapy, causes gynecomastia in 30 to 79% of men, and also produces breast tenderness. However, more than 90% of cases of gynecomastia with NSAAs including flutamide are mild to moderate. Tamoxifen, a selective estrogen receptor modulator (SERM) with predominantly antiestrogenic actions, can counteract flutamide-induced gynecomastia and breast pain in men. | 4 | Stereochemistry |
Fas ligand has been shown to interact with:
* CASP8,
* EZR,
* FADD,
* FNBP1,
* FYN,
* FAS,
* Grb2,
* PACSIN2, and
* TNFRSF6B. | 1 | Biochemistry |
Armodafinil is currently FDA-approved to treat excessive daytime sleepiness associated with obstructive sleep apnea, narcolepsy, and shift work disorder. It is commonly used off-label to treat attention deficit hyperactivity disorder, chronic fatigue syndrome, and major depressive disorder, and has been repurposed as an adjunctive treatment for bipolar disorder. It has been shown to improve vigilance in air traffic controllers, however in the United States, sleep prevention medications such as modafinil (Provigil) and armodafinil (Nuvigil) are not approved by the FAA for civilian controllers or pilots. | 4 | Stereochemistry |
CDP's funding comes from a combination of government and philanthropic grants (44.4%) and a mixture of membership fees, administrative fees, sponsorships and data licensing. In Europe, CDP is around 30% funded by the LIFE programme of the European Commission. | 2 | Environmental Chemistry |
A GeneRIF or Gene Reference Into Function is a short (255 characters or fewer) statement about the function of a gene. GeneRIFs provide a simple mechanism for allowing scientists to add to the functional annotation of genes described in the Entrez Gene database. In practice, function is constructed quite broadly. For example, there are GeneRIFs that discuss the role of a gene in a disease, GeneRIFs that point the viewer towards a review article about the gene, and GeneRIFs that discuss the structure of a gene. However, the stated intent is for GeneRIFs to be about gene function. Currently over half a million geneRIFs have been created for genes from almost 1000 different species.
GeneRIFs are always associated with specific entries in the Entrez Gene database. Each GeneRIF has a pointer to the PubMed ID (a type of document identifier) of a scientific publication that provides evidence for the statement made by the GeneRIF. GeneRIFs are often extracted directly from the document that is identified by the PubMed ID, very frequently from its title or from its final sentence.
GeneRIFs are usually produced by NCBI indexers, but anyone may submit a GeneRIF.
To be processed, a valid Gene ID must exist for the specific gene, or the Gene staff must have assigned an overall Gene ID to the species. The latter case is implemented via records in Gene with the symbol NEWENTRY. Once the Gene ID is identified, only three types of information are required to complete a submission:
# a concise phrase describing a function or functions (less than 255 characters in length, preferably more than a restatement of the title of the paper);
# a published paper describing that function, implemented by supplying the PubMed ID of a citation in PubMed;
# a valid e-mail address (which will remain confidential). | 1 | Biochemistry |
This comparison is approximate. The actual relative strengths will vary depending on the molecules involved. For instance, the presence of water creates competing interactions that greatly weaken the strength of both ionic and hydrogen bonds. We may consider that for static systems, Ionic bonding and covalent bonding will always be stronger than intermolecular forces in any given substance. But it is not so for big moving systems like enzyme molecules interacting with substrate molecules. Here the numerous intramolecular (most often - hydrogen bonds) bonds form an active intermediate state where the intermolecular bonds cause some of the covalent bond to be broken, while the others are formed, in this way proceeding the thousands of enzymatic reactions, so important for living organisms. | 6 | Supramolecular Chemistry |
Tic20 is an integral protein thought to have four transmembrane α-helices. It is found in the 1 million dalton TIC complex. Because it is similar to bacterial amino acid transporters and the mitochondrial import protein Tim17 (translocase on the inner mitochondrial membrane), it has been proposed to be part of the TIC import channel. There is no in vitro evidence for this though. In Arabidopsis thaliana, it is known that for about every five Toc75 proteins in the outer chloroplast membrane, there are two Tic20 I proteins (the main form of Tic20 in Arabidopsis) in the inner chloroplast membrane.
Unlike Tic214, Tic100, or Tic56, Tic20 has homologous relatives in cyanobacteria and nearly all chloroplast lineages, suggesting it evolved before the first chloroplast endosymbiosis. Tic214, Tic100, and Tic56 are unique to chloroplastidan chloroplasts, suggesting that they evolved later. | 5 | Photochemistry |
The theory of bimodal AFM operation encompasses several aspects. Among them, the approximations to express the Euler-Bernoulli equation of a continuous cantilever beam in terms of the equations of the excited modes, the type of interaction forces acting on the tip, the theory of demodulation methods or the introduction of finite-size effects.
In a nutshell, the tip displacement in AFM is approximated by a point-mass model,
where , , , , , and are, respectively, the driving frequency, the free resonant frequency, the quality factor, the stiffness, the driving force of the i-th mode, and the tip–sample interaction force. In bimodal AFM, the vertical motion of the tip (deflection) has two components, one for each mode,
with , , , as the static, the first, and the second mode deflections; , and are, respectively, the amplitude, frequency and phase shift of mode i.
The theory that transforms bimodal AFM observables into material properties is based on applying the virial and energy dissipation theorems to the equations of motion of the excited modes. The following equations were derived
where is a time where the oscillation of both modes are periodic; the quality factor of mode i. Bimodal AFM operation might be involve any pair of eigenmodes. However, experiments are commonly performed by exciting the first two eigenmodes.
The theory of bimodal AFM provides analytical expressions to link material properties with microscope observables. For example, for a paraboloid probe (radius ) and a tip-sample force given by the linear viscoelastic Kelvin-Voigt model, the effective elastic modulus of the sample, viscous coefficient of compressibility , loss tangent or retardation time are expressed by
For an elastic material, the second term of equation to calculate disappears because which gives . The elastic modulus is obtained from the equation above. Other analytical expressions were proposed for the determination of the Hamaker constant and the magnetic parameters of a ferromagnetic sample. | 6 | Supramolecular Chemistry |
The first polar FOCE (antFOCE) experiment was awarded funding in November 2012, followed by design and concept studies initiated in 2013. Installation and initial science experiments are planned for 2014. antFOCE is a collaborative effort between the University of Tasmania, Australian Antarctic Division, Antarctic Climate & Ecosystems Cooperative Research Centre, Monterey Bay Aquarium Research Institute and specialist ocean acidification policy advisors from the International Ocean Acidification Reference Users Group (IOA-RUG). The IOA-RUG will take the lead in communicating the outcomes of the FOCE experiment to global climate and ocean policy related organizations. | 9 | Geochemistry |
Applications of phage display technology include determination of interaction partners of a protein (which would be used as the immobilised phage "bait" with a DNA library consisting of all coding sequences of a cell, tissue or organism) so that the function or the mechanism of the function of that protein may be determined. Phage display is also a widely used method for in vitro protein evolution (also called protein engineering). As such, phage display is a useful tool in drug discovery. It is used for finding new ligands (enzyme inhibitors, receptor agonists and antagonists) to target proteins. The technique is also used to determine tumour antigens (for use in diagnosis and therapeutic targeting) and in searching for protein-DNA interactions using specially-constructed DNA libraries with randomised segments. Recently, phage display has also been used in the context of cancer treatments - such as the adoptive cell transfer approach. In these cases, phage display is used to create and select synthetic antibodies that target tumour surface proteins. These are made into synthetic receptors for T-Cells collected from the patient that are used to combat the disease.
Competing methods for in vitro protein evolution include yeast display, bacterial display, ribosome display, and mRNA display. | 1 | Biochemistry |
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, thus, prefer other neutral molecules and nonpolar solvents. Because water molecules are polar, hydrophobes do not dissolve well among them. Hydrophobic molecules in water often cluster together, forming micelles. Water on hydrophobic surfaces will exhibit a high contact angle.
Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar substances from polar compounds.
Hydrophobic is often used interchangeably with lipophilic, "fat-loving". However, the two terms are not synonymous. While hydrophobic substances are usually lipophilic, there are exceptions, such as the silicones and fluorocarbons.
The term hydrophobe comes from the Ancient Greek (), "having a fear of water", constructed . | 6 | Supramolecular Chemistry |
Butyrate is produced by several fermentation processes performed by obligate anaerobic bacteria. This fermentation pathway was discovered by Louis Pasteur in 1861. Examples of butyrate-producing species of bacteria:
*Clostridium butyricum
*Clostridium kluyveri
*Clostridium pasteurianum
*Faecalibacterium prausnitzii
*Fusobacterium nucleatum
*Butyrivibrio fibrisolvens
*Eubacterium limosum
The pathway starts with the glycolytic cleavage of glucose to two molecules of pyruvate, as happens in most organisms. Pyruvate is oxidized into acetyl coenzyme A catalyzed by pyruvate:ferredoxin oxidoreductase. Two molecules of carbon dioxide () and two molecules of hydrogen () are formed as waste products. Subsequently, is produced in the last step of the fermentation. Three molecules of ATP are produced for each glucose molecule, a relatively high yield. The balanced equation for this fermentation is
Other pathways to butyrate include succinate reduction and crotonate disproportionation.
Several species form acetone and n-butanol in an alternative pathway, which starts as butyrate fermentation. Some of these species are:
*Clostridium acetobutylicum, the most prominent acetone and butanol producer, used also in industry
*Clostridium beijerinckii
*Clostridium tetanomorphum
*Clostridium aurantibutyricum
These bacteria begin with butyrate fermentation, as described above, but, when the pH drops below 5, they switch into butanol and acetone production to prevent further lowering of the pH. Two molecules of butanol are formed for each molecule of acetone.
The change in the pathway occurs after acetoacetyl CoA formation. This intermediate then takes two possible pathways:
*acetoacetyl CoA → acetoacetate → acetone
*acetoacetyl CoA → butyryl CoA → butyraldehyde → butanol
For commercial purposes Clostridium species are used preferably for butyric acid or butanol production.
The most common species used for probiotics is the Clostridium butyricum. | 1 | Biochemistry |
The second generation, the Qubit 2.0 Fluorometer, was released in 2010, and the 3rd generation as Qubit 3.0 in 2014. The newest version is the 4th generation Qubit 4, introduced in 2017. | 7 | Physical Chemistry |
The White catalyst was originally developed for use in a branched allylic acetoxylation reaction. An enantioselective version of this reaction was subsequently reported, using chromium(III) salen fluoride as a chiral cocatalyst. A macrolactonization reaction based on the branched allylic esterification was developed for the preparation of 14- to 19-membered macrolides. This method was applied to the total synthesis of 6-deoxyerythronolide B. In addition to acetate, a wide variety of carboxylic acids may be employed as nucleophiles in the branch allylic esterification reaction. As the first step in an esterification/Heck sequence, aliphatic and aromatic carboxylates were demonstrated, including amino acids. | 0 | Organic Chemistry |
If the liquid and vapor are pure, in that they consist of only one molecular component and no impurities, then the equilibrium state between the two phases is described by the following equations:
:; and
where and are the pressures within the liquid and vapor, and are the temperatures within the liquid and vapor, and and are the molar Gibbs free energies (units of energy per amount of substance) within the liquid and vapor, respectively. In other words, the temperature, pressure and molar Gibbs free energy are the same between the two phases when they are at equilibrium.
An equivalent, more common way to express the vapor–liquid equilibrium condition in a pure system is by using the concept of fugacity. Under this view, equilibrium is described by the following equation:
where and are the fugacities of the liquid and vapor, respectively, at the system temperature and pressure . It is often convenient to use the quantity , the dimensionless fugacity coefficient, which is 1 for an ideal gas. | 7 | Physical Chemistry |
Benzoyl chloride is produced from benzotrichloride using either water or benzoic acid:
As with other acyl chlorides, it can be generated from the parent acid and other chlorinating agents phosphorus pentachloride or thionyl chloride.
Representative laboratory routes to aromatic acyl halides are comparable to those for aliphatic acyl halides. For example, chloroformylation, a specific type of Friedel-Crafts acylation which uses formaldehyde as a reagent, or by the direct chlorination of benzaldehyde derivatives. | 0 | Organic Chemistry |
ATP synthase is an enzyme that catalyzes the formation of the energy storage molecule adenosine triphosphate (ATP) using adenosine diphosphate (ADP) and inorganic phosphate (P). ATP synthase is a molecular machine. The overall reaction catalyzed by ATP synthase is:
* ADP + P + 2H ATP + HO + 2H
ATP synthase lies across a cellular membrane and forms an aperture that protons can cross from areas of high concentration to areas of low concentration, imparting energy for the synthesis of ATP. This electrochemical gradient is generated by the electron transport chain and allows cells to store energy in ATP for later use. In prokaryotic cells ATP synthase lies across the plasma membrane, while in eukaryotic cells it lies across the inner mitochondrial membrane. Organisms capable of photosynthesis also have ATP synthase across the thylakoid membrane, which in plants is located in the chloroplast and in cyanobacteria is located in the cytoplasm.
Eukaryotic ATP synthases are F-ATPases, running "in reverse" for an ATPase. This article deals mainly with this type. An F-ATPase consists of two main subunits, F and F, which has a rotational motor mechanism allowing for ATP production. | 5 | Photochemistry |
In his 1803 publication about the quantity of gases absorbed by water, William Henry described the results of his experiments:
Charles Coulston Gillispie states that John Dalton "supposed that the separation of gas particles one from another in the vapor phase bears the ratio of a small whole number to their interatomic distance in solution. Henry's law follows as a consequence if this ratio is a constant for each gas at a given temperature." | 7 | Physical Chemistry |
MIRO Analytical is a spin-off of Empa, a Swiss research institute of the ETH domain. It has know-how in laser spectroscopy and in particular, in the combination of several quantum-cascade lasers (QCLs) into compact laser-based gas analyzers.
The company's first instrument was a nine gas analyzer MGA-9 in 2018. By 2019 the MGA-10 a ten gas analyzer was introduced which measures greenhouse gases and air pollutants. | 7 | Physical Chemistry |
Small GTPases function as monomers and have a molecular weight of about 21 kilodaltons that consists primarily of the GTPase domain. They are also called small or monomeric guanine nucleotide-binding regulatory proteins, small or monomeric GTP-binding proteins, or small or monomeric G-proteins, and because they have significant homology with the first-identified such protein, named Ras, they are also referred to as Ras superfamily GTPases. Small GTPases generally serve as molecular switches and signal transducers for a wide variety of cellular signaling events, often involving membranes, vesicles or cytoskeleton. According to their primary amino acid sequences and biochemical properties, the many Ras superfamily small GTPases are further divided into five subfamilies with distinct functions: Ras, Rho ("Ras-homology"), Rab, Arf and Ran. While many small GTPases are activated by their GEFs in response to intracellular signals emanating from cell surface receptors (particularly growth factor receptors), regulatory GEFs for many other small GTPases are activated in response to intrinsic cell signals, not cell surface (external) signals. | 1 | Biochemistry |
First a strongly hydrophobic essential oil such as trans-anethole is dissolved in a water-miscible solvent, such as ethanol, and the ethanol itself forms a solution (a homogenous mixture) with water.
If then the concentration of ethanol is lowered by addition of more water the hydrophobic substance precipitates from the solution and forms an emulsion with the remaining ethanol-water-mixture. The tiny droplets of the substance in the emulsion scatter light and thus make the mixture appear white.
Oil-in-water emulsions are not normally stable. Oil droplets coalesce until complete phase separation is achieved at macroscopic levels. Addition of a small amount of surfactant or the application of high shear rates (strong stirring) can stabilize the oil droplets.
In a water-rich ouzo mixture the droplet coalescence is dramatically slowed without mechanical agitation, dispersing agents, or surfactants. It forms a stable homogeneous fluid dispersion by liquid–liquid nucleation. The size of the droplets when measured by small-angle neutron scattering was found to be on the order of a micron.
Using dynamic light scattering, Sitnikova et al. showed that the droplets of oil in the emulsion grow by Ostwald ripening, and that droplets do not coalesce. The Ostwald ripening rate is observed to diminish with increasing ethanol concentrations until the droplets stabilize in size with an average diameter of .
Based on thermodynamic considerations of the multi-component mixture, the emulsion derives its stability from trapping between the binodal and spinodal curves in the phase diagram. However, the microscopic mechanisms responsible for the observed slowing of Ostwald ripening rates at increasing ethanol concentrations appear not fully understood. | 7 | Physical Chemistry |
The Warburg diffusion element () is a constant phase element (CPE), with a constant phase of 45° (phase independent of frequency) and with a magnitude inversely proportional to the square root of the frequency by:
where
* is the Warburg coefficient (or Warburg constant);
* is the imaginary unit;
* is the angular frequency.
This equation assumes semi-infinite linear diffusion, that is, unrestricted diffusion to a large planar electrode. | 7 | Physical Chemistry |
Single-strand conformation polymorphism (SSCP), or single-strand chain polymorphism, is defined as a conformational difference of single-stranded nucleotide sequences of identical length as induced by differences in the sequences under certain experimental conditions. This property allows sequences to be distinguished by means of gel electrophoresis, which separates fragments according to their different conformations. | 1 | Biochemistry |
The first recorded attempt to make copper clad steel wire took place in the early 1860s. Although for over 100 years people had been suggesting various ways of uniting copper and steel, it was not until the period mentioned that Farmer and Milliken tried wrapping a strip of copper about a steel wire. American engineers in 1883 and again in the 1890s made attempts to produce a copper-steel wire, in one instance at least, by electroplating copper on steel.
The Duplex Metals Co. traces its beginning to John Ferreol Monnot between 1900 and 1905. He had been very interested in the work of Mr. Martin in Paris.
:"After several years devoted to experimenting, [he] organized the Duplex Metals Company. Prior to his discovery of the process under which this company operates in producing its copper clad, probably almost every other possible way of welding copper and steel together had been tried by Mr. Monnot, but found useless for the purpose." | 8 | Metallurgy |
Sintering occurs by diffusion of atoms through the microstructure. This diffusion is caused by a gradient of chemical potential – atoms move from an area of higher chemical potential to an area of lower chemical potential. The different paths the atoms take to get from one spot to another are the "sintering mechanisms" or "matter transport mechanisms".
In solid state sintering, the six common mechanisms are:
# surface diffusion – diffusion of atoms along the surface of a particle
# vapor transport – evaporation of atoms which condense on a different surface
# lattice diffusion from surface – atoms from surface diffuse through lattice
# lattice diffusion from grain boundary – atom from grain boundary diffuses through lattice
# grain boundary diffusion – atoms diffuse along grain boundary
# plastic deformation – dislocation motion causes flow of matter.
Mechanisms 1–3 above are non-densifying (i.e. do not cause the pores and the overall ceramic body to shrink) but can still increase the area of the bond or "neck" between grains; they take atoms from the surface and rearrange them onto another surface or part of the same surface. Mechanisms 4–6 are densifying – atoms are moved from the bulk material or the grain boundaries to the surface of pores, thereby eliminating porosity and increasing the density of the sample. | 8 | Metallurgy |
A complexometric indicator is an ionochromic dye that undergoes a definite color change in presence of specific metal ions. It forms a weak complex with the ions present in the solution, which has a significantly different color from the form existing outside the complex.
Complexometric indicators are also known as pM indicators. | 3 | Analytical Chemistry |
MTBE is used as a fuel component in fuel for gasoline engines. It is one of a group of chemicals commonly known as oxygenates because they raise the oxygen content of gasoline. | 2 | Environmental Chemistry |
There are three classes of SMADs:
# Receptor-regulated SMAD (R-SMAD)
# Common-mediator SMAD (Co-SMAD)
# Inhibitory SMAD (I-SMAD)
Examples of SMADs in each class:
The TGF-β superfamily activates members of the SMAD family, which function as transcription factors. Specifically, the type I receptor, activated by the type II receptor, phosphorylates R-SMADs that then bind to the co-SMAD, SMAD4. The R-SMAD/Co-SMAD forms a complex with importin and enters the nucleus, where they act as transcription factors and either up-regulate or down-regulate in the expression of a target gene.
Specific TGF-β ligands will result in the activation of either the SMAD2/3 or the SMAD1/5 R-SMADs. For instance, when activin, Nodal, or TGF-β ligand binds to the receptors, the phosphorylated receptor complex can activate SMAD2 and SMAD3 through phosphorylation. However, when a BMP ligand binds to the receptors, the phosphorylated receptor complex activates SMAD1 and SMAD5. Then, the Smad2/3 or the Smad1/5 complexes form a dimer complex with SMAD4 and become transcription factors. Though there are many R-SMADs involved in the pathway, there is only one co-SMAD, SMAD4. | 1 | Biochemistry |
A backdraft (North American English) or backdraught (British English) is the abrupt burning of superheated gases in a fire caused when oxygen rapidly enters a hot, oxygen-depleted environment; for example, when a window or door to an enclosed space is opened or broken. Backdrafts are typically seen as a blast of smoke and/or flame out of an opening of a building. Backdrafts present a serious threat to firefighters. There is some debate concerning whether backdrafts should be considered a type of flashover. | 7 | Physical Chemistry |
Two very similar expressions for are in wide use in hydrology. Both have the form ‰ (‰ = permil or parts per thousand) where s and a are the relative abundances of N in respectively the sample and the atmosphere. The difference is whether the relative abundance is with respect to all the nitrogen, i.e. N plus N, or just to N. Since the atmosphere is 99.6337% N and 0.3663% N, a is 0.003663 in the former case and 0.003663/0.996337 = 0.003676 in the latter. However s varies similarly; for example if in the sample N is 0.385% and N is 99.615%, s is 0.003850 in the former case and 0.00385/0.99615 = 0.003865 in the latter. The value of is then 51.05‰ in the former case and 51.38‰ in the latter, an insignificant difference in practice given the typical range of -20 to 80 for . | 9 | Geochemistry |
PCBs are toxic to bacterial communities above 1000 mg/kg. However, if the concentration is too low (lower than 50 mg/kg), the degradation slows down significantly, for there is not enough material to stimulate the expression of required genes and support the growth of competent microorganisms. PCBs includes various different compounds with slightly different structures. Those slight differences make big differences in metabolic rate. Generally speaking, the more chlorines in a PCB molecule, the harder for it to be degraded. In particular, microorganisms cannot degrade di- and tetra-ortho substituted well. It is possible that those structures prevent enzymes from accessing reaction sites. | 1 | Biochemistry |
Hyperconjugation is also found in acyclic molecules containing heteroatoms, another form of the anomeric effect. If a molecule has an atom with a lone pair of electrons and the adjacent atom is able to accept electrons into the σ* orbital, hyperconjugation occurs, stabilizing the molecule. This forms a "no bond" resonance form. For this orbital overlap to occur, the trans, trans conformation is preferred for most heteroatoms, however for the stabilization to occur in dimethoxymethane, the gauche, gauche conformation is about 3–5 kcal/mol lower in energy (more stable) than the trans,trans conformation—this is about two times as big as the effect in sugars because there are two rotatable bonds (hence it is trans around both bonds or gauche around both) that are affected. | 7 | Physical Chemistry |
Thermoplastic polymers (be they virgin or recycled) must be heated until molten to be formed into their final shapes, with processing temperatures anywhere between 150-320 °C (300–600 °F) depending on the polymer. Polymers will oxidise under these conditions, but even in the absence of air, these temperatures are sufficient to cause thermal degradation in some materials. The molten polymer also experiences significant shear stress during extrusion and moulding, which is sufficient to snap the polymer chains. Unlike many other forms of degradation, the effects of melt-processing degrades the entire bulk of the polymer, rather than just the surface layers. This degradation introduces chemical weak points into the polymer, particularly in the form of hydroperoxides, which become initiation sites for further degradation during the object's lifetime.
Polymers are often subject to more than one round of melt-processing, which can cumulatively advance degradation. Virgin plastic typically undergoes compounding to introduce additives such as dyes, pigments and stabilisers. Pelletised material prepared in this may also be pre-dried in an oven to remove trace moisture prior to its final melting and moulding into plastic items. Plastic which is recycled by simple re‑melting (mechanical recycling) will usually display more degradation than fresh material and may have poorer properties as a result. | 7 | Physical Chemistry |
Several transition metal dithiocarbamate complexes are useful in industry. Zinc dithiocarbamates are used to modify the crosslinking of certain polyolefins with sulfur, a process called vulcanization. They are used as ligands for chelating metals.
Some dithiocarbamates, specifically ethylene bisdithiocarbamates (), in the form of complexes with manganese (maneb), zinc (zineb) or a combination of manganese and zinc (mancozeb), have been used extensively as fungicides in agriculture since the 1940s. In the United States they began to be registered for use in the late 1950s and early 1960s and were quickly put to work on sooty blotch and flyspeck. Many growers switched from captan to EBDCs for the longer residual period. Both captan and EBDCs were the primary treatments for SBFS in that country until the early 1990s when the US Environmental Protection Agency banned EBDCs within 77 days to harvest. This effectively made summer use impossible, reduced EBDC use overall, and radically increased SBFS. | 0 | Organic Chemistry |
In chemistry, a diamino acid, also called a diamino carboxylic acid, is a molecule including a carboxylic acid and two amine functional groups. Diamino acids belong to the class of amino acids. | 1 | Biochemistry |
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