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Geometallurgy relates to the practice of combining geology or geostatistics with metallurgy, or, more specifically, extractive metallurgy, to create a spatially or geologically based predictive model for mineral processing plants. It is used in the hard rock mining industry for risk management and mitigation during mineral processing plant design. It is also used, to a lesser extent, for production planning in more variable ore deposits.
There are four important components or steps to developing a geometallurgical program,:
*the geologically informed selection of a number of ore samples
*laboratory-scale test work to determine the ore's response to mineral processing unit operations
*the distribution of these parameters throughout the orebody using an accepted geostatistical technique
*the application of a mining sequence plan and mineral processing models to generate a prediction of the process plant behavior | 8 | Metallurgy |
A polymeric material can be functionalized by the addition of small moieties, oligomers, and even other polymers (grafting copolymers) onto the surface or interface. | 7 | Physical Chemistry |
At the same temperature, a column of dry air will be denser or heavier than a column of air containing any water vapor, the molar mass of diatomic nitrogen and diatomic oxygen both being greater than the molar mass of water. Thus, any volume of dry air will sink if placed in a larger volume of moist air. Also, a volume of moist air will rise or be buoyant if placed in a larger region of dry air. As the temperature rises the proportion of water vapor in the air increases, and its buoyancy will increase. The increase in buoyancy can have a significant atmospheric impact, giving rise to powerful, moisture rich, upward air currents when the air temperature and sea temperature reaches 25 °C or above. This phenomenon provides a significant driving force for cyclonic and anticyclonic weather systems (typhoons and hurricanes). | 2 | Environmental Chemistry |
* T.F. Fuller, John N. Harb, Electrochemical Engineering, John Wiley & Sons, 2018.
* H. Wright (ed.), Electrochemical Engineering: Emerging Technologies and Applications, Willford Press, 2016.
* D. Stolten, B. Emonts, Fuel Cell Science and Engineering: Materials, Processes, Systems and Technology, John Wiley & Sons, 2012.
* D.D. Macdonald, P. Schmuki (eds.), Electrochemical Engineering, in Encyclopedia of Electrochemistry, Vol. 5, Wiley-VCH, 2007.
* J. Newman, K.E. Thomas-Alyea, Electrochemical Systems, 3rd ed., John Wiley & Sons, Hoboken NJ, 2004. (1st ed. 1973).
* V.M. Schmidt, Elektrochemische Verfahrenstechnik, Wiley-VCH, 2003.
* H. Pütter, Industrial Electroorganic Chemistry, in Organic Electrochemistry, 4th ed., H. Lund, O. Hammerich (eds.), Marcel Dekker, New York, 2001.
* F.C. Walsh, Un Primer Curso de Ingeniería Electroquímica, Editorial Club Universitario, Alicante, España, 2000.
* M.P. Grotheer, Electrochemical Processing, Inorganic, in Kirk-Othmer Encyclopedia of Chemical Technology, 5th ed., Vol. 9, P. 618, John Wiley & Sons, 2000.
* H. Wendt, G. Kreysa, Electrochemical Engineering: Science and Technology in Chemical and Other Industries, Springer, Berlin 1999.
* R.F. Savinell, Tutorials in Electrochemical Engineering - Mathematical Modeling, Pennington, The Electrochemical Society, 1999.
* A. Geoffrey, Electrochemical Engineering Principles, Prentice Hall, 1997.
* F. Goodrige, K. Scott Electrochemical Process Engineering - A Guide to the Design of Electrolytic Plant, Plenum Press, New York & London, 1995.
* J. Newman, R.E. White (eds.), Proceedings of the Douglas N. Bennon Memorial Symposium. Topics in Electrochemical Engineering, The Electrochemical Society, Proceedings Vol. 94-22, 1994.
* F. Lapicque, A. Storck, A.A. Wragg, Electrochemical Engineering and Energy, Springer, 1994.
* F.C. Walsh, A First Course in Electrochemical Engineering, The Electrochemical Consultancy, Romsey UK, 1993.
* F. Coeuret, A. Storck, Eléments de Génie Électrochimique, 2nd ed., Éditions TEC et DOC / Lavoisier, Paris, 1993. (1st ed. 1984)
* F. Coeuret, Introducción a la Ingeniería Electroquímica, Editorial Reverté, Barcelona, 1992.
* K. Scott, Electrochemical Reaction Engineering, Academic Press, London, 1991.
* G. Prentice, Electrochemical Engineering Principles, Prentice Hall, 1991.
* D. Pletcher, F.C. Walsh, Industrial Electrochemistry, 2nd ed., Chapman and Hall, London, 1990.
* J.D. Genders, D. Pletcher, Electrosynthesis - From Laboratory, to Pilot, to Production, The Electrosynthesis Company, New York, 1990.
* M.I. Ismail, Electrochemical Reactors Their Science and Technology - Part A: Fundamentals, Electrolysers, Batteries, and Fuel Cells, Elsevier, Amsterdam, 1989.
* T.R. Beck, Industrial Electrochemical Processes, in Techniques of Electrochemistry, E. Yeager, A.J. Salkind (eds.), Wiley, New York, 1987.
* E. Heitz, G. Kreysa, Principles of Electrochemical Engineering, John Wiley & Sons, 1986.
* I. Roušar, A. Kimla, K. Micka, Electrochemical Engineering, Elsevier, Amsterdam, 1986.
* T.Z. Fahidy, Principles of Electrochemical Reactor Analysis, Elsevier, Amsterdam, 1985.
* F. Hine, Electrode Processes and Electrochemical Engineering, Springer, Boston, 1985.
* R.E. White, (ed.), Electrochemical Cell Design, Springer, 1984.
* P. Horsman, B.E. Conway, S. Sarangapani (eds.), Comprehensive Treatise of Electrochemistry. Vol. 6 Electrodics: Transport, Plenum Press, New York, 1983.
* D. Pletcher, Industrial Electrochemistry, 1st ed., Chapman and Hall, London, 1982.
* J.O’M. Bockris, B.E. Conway, E. Yeager, R.E. White, (eds.) Comprehensive Treatise of Electrochemistry. Vol. 2: Electrochemical Processing, Plenum Press, New York, 1981.
* D.J. Pickett, Electrochemical Reactor Design, 2nd ed., Elsevier, Amsterdam, 1979.
* P. Gallone, Trattato di Ingegneria Elettrochimica, Tamburini, Milan, 1973.
* A. Kuhn, Industrial Electrochemical Processes, Elsevier, Amsterdam, 1971.
* C.L. Mantell, Electrochemical Engineering, 4th ed., McGraw-Hill, New York, 1960.
* C.L. Mantell, Industrial Electrochemistry, 2nd ed., McGraw-Hill, New York, 1940.
* C.F. Burgess, H.B. Pulsifer, B.B. Freud, Applied Electrochemistry and Metallurgy, American Technical Society, Chicago, 1920.
* A.J. Hale, The Manufacture of Chemicals by Electrolysis, Van Nostrand Co., New York, 1919. | 7 | Physical Chemistry |
Time resolved crystallography utilizes X-ray crystallography imaging to visualize reactions in four dimensions (x, y, z and time). This enables the studies of dynamical changes that occur in for example enzymes during their catalysis. The time dimension is incorporated by triggering the reaction of interest in the crystal prior to X-ray exposure, and then collecting the diffraction patterns at different time delays. In order to study these dynamical properties of macromolecules three criteria must be met;
* The macromolecule must be biologically active in the crystalline state
* It must be possible to trigger the reaction in the crystal
* The intermediate of interest must be detectable, i.e. it must have a reasonable amount of concentration in the crystal (preferably over 25%).
This has led to the development of several techniques that can be divided into two groups, the pump-probe method and diffusion-trapping methods. | 3 | Analytical Chemistry |
A prill is a small aggregate or globule of a material, most often a dry sphere, formed from a melted liquid through spray crystallization. Prilled is a term used in mining and manufacturing to refer to a product that has been pelletized. ANFO explosive typically comprises ammonium nitrate prills mixed with #2 fuel oil. The pellets are a neater, simpler form for handling, with reduced dust.
The material to be prilled must be in a solid state at room temperature and a low-viscosity liquid when melted. Prills are formed by allowing drops of the melted prill substance to congeal or freeze in mid-air after being dripped from the top of a tall prilling tower. Certain agrochemicals such as urea are often supplied in prilled form. Fertilizers (ammonium nitrate, urea, NPK fertilizer) and some detergent powders are commonly manufactured as prills. However prilling of ammonium nitrate and urea has in recent years been replaced by fluid bed granulation as this gives strong and more abrasion-resistant granules.
Melted material may also be atomized and then allowed to form smaller prills that are useful in cosmetics, food, and animal feed. | 8 | Metallurgy |
fMRS has several advantages over other functional neuroimaging and brain biochemistry detection techniques.
Unlike push-pull cannula, microdialysis and in vivo voltammetry, fMRS is a non-invasive method for studying dynamics of biochemistry in an activated brain. It is done without exposing subjects to ionizing radiation like it is done in positron emission tomography (PET) or single-photon emission computed tomography (SPECT) studies. fMRS gives a more direct measurement of cellular events occurring during brain activation than BOLD fMRI or PET which rely on hemodynamic responses and show only global neuronal energy uptake during brain activation while fMRS gives also information about underlying metabolic processes that support the working brain.
However, fMRS requires very sophisticated data acquisition, quantification methods and interpretation of results. This is one of the main reasons why in the past it received less attention than other MR techniques, but the availability of stronger magnets and improvements in data acquisition and quantification methods are making fMRS more popular.
Main limitations of fMRS are related to signal sensitivity and the fact that many metabolites of potential interest can not be detected with current fMRS techniques.
Because of limited spatial and temporal resolution fMRS can not provide information about metabolites in different cell types, for example, whether lactate is used by neurons or by astrocytes during brain activation. The smallest volume that can currently be characterized with fMRS is 1 cm, which is too big to measure metabolites in different cell types. To overcome this limitation, mathematical and kinetic modeling is used.
Many brain areas are not suitable for fMRS studies because they are too small (like small nuclei in brainstem) or too close to bone tissue, CSF or extracranial lipids, which could cause inhomogeneity in the voxel and contaminate the spectra. To avoid these difficulties, in most fMRS studies the volume of interest is chosen from the visual cortex – because it is easily stimulated, has high energy metabolisms, and yields good MRS signals. | 7 | Physical Chemistry |
The most popular COF synthesis route is a boron condensation reaction which is a molecular dehydration reaction between boronic acids. In case of COF-1, three boronic acid molecules converge to form a planar six-membered BO (boroxine) ring with the elimination of three water molecules. | 6 | Supramolecular Chemistry |
According to Ostwald's rule, usually less stable polymorphs crystallize before the stable form. The concept hinges on the idea that unstable polymorphs more closely resemble the state in solution, and thus are kinetically advantaged. The founding case of fibrous vs rhombic benzamide illustrates the case. Another example is provided by two polymorphs of titanium dioxide. Nevertheless, there are known systems, such as metacetamol, where only narrow cooling rate favors obtaining metastable form II.
Polymorphs have disparate stabilities. Some convert rapidly at room (or any) temperature. Most polymorphs of organic molecules only differ by a few kJ/mol in lattice energy. Approximately 50% of known polymorph pairs differ by less than 2 kJ/mol and stability differences of more than 10 kJ/mol are rare. Valuable to mention that polymorph stability may change upon temperature or pressure. Important to note that structural and thermodybnamic stability are different. Thermodynamic stability may be studied using experimental or computational methods.
Polymorphism is affected by the details of crystallisation. The solvent in all respects affects the nature of the polymorph, including concentration, other components of the solvent, i.e., species that inhibiting or promote certain growth patterns. A decisive factor is often the temperature of the solvent from which crystallisation is carried out.
Metastable polymorphs are not always reproducibly obtained, leading to cases of "disappearing polymorphs", with usually negative implications on law and business. | 3 | Analytical Chemistry |
Once transferred to the nascent peptide chain, N-linked glycans, in general, undergo extensive processing reactions, whereby the three glucose residues are removed, as well as several mannose residues, depending on the N-linked glycan in question. The removal of the glucose residues is dependent on proper protein folding. These processing reactions occur in the Golgi apparatus. Modification reactions may involve the addition of a phosphate or acetyl group onto the sugars, or the addition of new sugars, such as neuraminic acid. Processing and modification of N-linked glycans within the Golgi does not follow a linear pathway. As a result, many different variations of N-linked glycan structure are possible, depending on enzyme activity in the Golgi. | 0 | Organic Chemistry |
Viral protein interactomes consist of interactions among viral or phage proteins. They were among the first interactome projects as their genomes are small and all proteins can be analyzed with limited resources. Viral interactomes are connected to their host interactomes, forming virus-host interaction networks. Some published virus interactomes include
Bacteriophage
* Escherichia coli bacteriophage lambda
* Escherichia coli bacteriophage T7
* Streptococcus pneumoniae bacteriophage Dp-1
* Streptococcus pneumoniae bacteriophage Cp-1
The lambda and VZV interactomes are not only relevant for the biology of these viruses but also for technical reasons: they were the first interactomes that were mapped with multiple Y2H vectors, proving an improved strategy to investigate interactomes more completely than previous attempts have shown.
Human (mammalian) viruses
* Human varicella zoster virus (VZV)
* Chandipura virus
* Epstein-Barr virus (EBV)
* Hepatitis C virus (HPC), Human-HCV interactions
* Hepatitis E virus (HEV)
* Herpes simplex virus 1 (HSV-1)
* Kaposi's sarcoma-associated herpesvirus (KSHV)
* Murine cytomegalovirus (mCMV) | 1 | Biochemistry |
Togni reagent II (1-trifluoromethyl-1,2-benziodoxol-3(1H)-one) is a chemical compound used in organic synthesis for direct electrophilic trifluoromethylation. | 0 | Organic Chemistry |
Wine, vinegar, cider, perry, brandy, atchara, nata de coco, burong mangga, asinan, pickling, vişinată, chocolate, rakı, aragh sagi, chacha | 1 | Biochemistry |
Mutations in emerin cause X-linked recessive Emery–Dreifuss muscular dystrophy, which is characterized by early contractures in the Achilles tendons, elbows and post-cervical muscles; muscle weakness proximal in the upper limbs and distal in lower limbs; along with cardiac conduction defects that range from sinus bradycardia, PR prolongation to complete heart block. In these patients, immunostaining of emerin is lost in various tissues, including muscle, skin fibroblasts, and leukocytes, however diagnostic protocols involve mutational analysis rather than protein staining. In nearly all cases, mutations result in a complete deletion, or undetectable levels, of emerin protein. Approximately 20% of cases have X chromosomes with an inversion within the Xq28 region.
Moreover, recent research have found that the absence of functional emerin may decrease the infectivity of HIV-1. Thus, it is speculated that patients with Emery–Dreifuss muscular dystrophy may have immunity to or show an irregular infection pattern to HIV-1. | 1 | Biochemistry |
DH5-Alpha Cells are E. coli cells engineered by American biologist Douglas Hanahan to maximize transformation efficiency. They are defined by three mutations: recA1, endA1 which help plasmid insertion and lacZΔM15 which enables blue white screening. The cells are competent and often used with calcium chloride transformation to insert the desired plasmid. A study of four transformation methods and six bacteria strains showed that the most efficient one was the DH5 strain with the Hanahan method. | 1 | Biochemistry |
Environmental analysis is the use of examination and statistical methods to study the chemical and biological factors that determine the quality of an environment. The purpose of this is commonly to monitor and study levels of pollutants in the atmosphere, rivers and other specific settings. Also, to monitor amounts of natural and chemical components. Other environmental analysis techniques include biological surveys or biosurvey<nowiki/>s, soil analysis or soil tests, vegetation surveys, tree identification, and remote sensing which uses satellite imagery to assess the environment on different spatial scales. | 3 | Analytical Chemistry |
Sulfate conjugates are a heterogeneous class of polar, anionic organosulfate compounds containing an ester of sulfuric acid. Sulfate conjugates commonly result from the metabolic conjugation of endogenous and exogenous compounds with sulfate (-OSO).
Biosynthesis of sulfate esters requires an activated sulfate donor, usually adenosine 5-phosphosulfate (APS) or 3-phosphoadenosine-5'-phosphosulfate (PAPS). Sulfate esters may be hydrolyzed by sulfatase enzyme to release the parent alcohol and a sulfate ion.
Steroid sulfation is one of the most common of all forms of steroid conjugation. Except for cholesterol, dehydroepiandrosterone sulfate is the most abundant of all plasma steroids. Estrone sulfate is the most abundant of all the estrogens in the human body. Estrone sulfate is synthesized by the enzyme estrone sulfotransferase. | 1 | Biochemistry |
Though many people conceptualize images and diffraction patterns separately, they contain principally the same information. In the simplest approximation, the two are simply Fourier transforms of one another. Thus, the effects of beam precession on diffraction patterns also have significant effects on the corresponding images in the TEM. Specifically, the reduced dynamical intensity transfer between beams that is associated with PED results in reduced dynamical contrast in images collected during precession of the beam. This includes a reduction in thickness fringes, bend contours, and strain fields. While these features can often provide useful information, their suppression enables a more straightforward interpretation of diffraction contrast and mass contrast in images. | 3 | Analytical Chemistry |
The enzymes trypsin and chymotrypsin were first purified in the 1930s. A serine in each of trypsin and chymotrypsin was identified as the catalytic nucleophile (by diisopropyl fluorophosphate modification) in the 1950s. The structure of chymotrypsin was solved by X-ray crystallography in the 1960s, showing the orientation of the catalytic triad in the active site. Other proteases were sequenced and aligned to reveal a family of related proteases, now called the S1 family. Simultaneously, the structures of the evolutionarily unrelated papain and subtilisin proteases were found to contain analogous triads. The charge-relay mechanism for the activation of the nucleophile by the other triad members was proposed in the late 1960s. As more protease structures were solved by X-ray crystallography in the 1970s and 80s, homologous (such as TEV protease) and analogous (such as papain) triads were found. The MEROPS classification system in the 1990s and 2000s began classing proteases into structurally related enzyme superfamilies and so acts as a database of the convergent evolution of triads in over 20 superfamilies. Understanding how chemical constraints on evolution led to the convergence of so many enzyme families on the same triad geometries has developed in the 2010s.
Since their initial discovery, there have been increasingly detailed investigations of their exact catalytic mechanism. Of particular contention in the 1990s and 2000s was whether low-barrier hydrogen bonding contributed to catalysis, or whether ordinary hydrogen bonding is sufficient to explain the mechanism. The massive body of work on the charge-relay, covalent catalysis used by catalytic triads has led to the mechanism being the best characterised in all of biochemistry. | 1 | Biochemistry |
Silver overlay is an electroplated coating of silver on a non-conductive surface such as porcelain or glass. Most techniques used to create silver overlay involve the use of special flux which contains silver and turpentine oil. This is then painted on the glass ornament as a design. After the painting is complete, the entire ornament is fired under relatively low heat, it is then cleaned after being quenched and cooled, then it is placed in a solution of silver. A low voltage current is run through the solution and the silver binds in the design, creating a permanent fusion of the silver with the glass.
A much older technique of overlay, which was commonly used in the Indian subcontinent since ancient times, involves the use of a silver sheet wrapped around the ornament and then the design beaten onto the sheet or it may be burnished. This technique renders the design silhouetted against a dark backdrop and was commonly called the Aftabi design technique. This technique of overlay predates the technique that is common today, but without the use of electroplating, it was a time consuming and tedious process, which could only be accomplished by skilled artisans. | 8 | Metallurgy |
Carbonyl ylides (RRC=OCRR) can form by ring-opening of epoxides or by reaction of carbonyls with electrophilic carbenes, which are usually prepared from diazo compounds. Oxonium ylides (RR-O-CRR) are formed by the reaction of ethers with electrophilic carbenes. | 0 | Organic Chemistry |
Distinct phases may be described as different states of matter such as gas, liquid, solid, plasma or Bose–Einstein condensate. Useful mesophases between solid and liquid form other states of matter.
Distinct phases may also exist within a given state of matter. As shown in the diagram for iron alloys, several phases exist for both the solid and liquid states. Phases may also be differentiated based on solubility as in polar (hydrophilic) or non-polar (hydrophobic). A mixture of water (a polar liquid) and oil (a non-polar liquid) will spontaneously separate into two phases. Water has a very low solubility (is insoluble) in oil, and oil has a low solubility in water. Solubility is the maximum amount of a solute that can dissolve in a solvent before the solute ceases to dissolve and remains in a separate phase. A mixture can separate into more than two liquid phases and the concept of phase separation extends to solids, i.e., solids can form solid solutions or crystallize into distinct crystal phases. Metal pairs that are mutually soluble can form alloys, whereas metal pairs that are mutually insoluble cannot.
As many as eight immiscible liquid phases have been observed. Mutually immiscible liquid phases are formed from water (aqueous phase), hydrophobic organic solvents, perfluorocarbons (fluorous phase), silicones, several different metals, and also from molten phosphorus. Not all organic solvents are completely miscible, e.g. a mixture of ethylene glycol and toluene may separate into two distinct organic phases.
Phases do not need to macroscopically separate spontaneously. Emulsions and colloids are examples of immiscible phase pair combinations that do not physically separate. | 7 | Physical Chemistry |
Oil extraction is simply the removal of oil from the reservoir (oil pool). There are many methods on extracting the oil from the reservoirs for example; mechanical shaking, water-in-oil emulsion, and specialty chemicals called demulsifiers that separate the oil from water. Oil extraction is costly and often environmentally damaging. Offshore exploration and extraction of oil disturb the surrounding marine environment. | 7 | Physical Chemistry |
After initial sporadic work, archaeometallurgy was more widely institutionalised in the 1960s and 70s, with research groups in Britain (The British Museum, the UCL Institute of Archaeology, the Institute for Archeo-Metallurgical Studies (iams)), Germany (Deutsches Bergbau Museum) and the US (MIT and Harvard).
Specialisations within metallurgical focus on metallography of finished objects, mineralogy of waste products such as slag and manufacturing studies. | 8 | Metallurgy |
The specific conductance of a solution containing one electrolyte depends on the concentration of the electrolyte. Therefore, it is convenient to divide the specific conductance by concentration. This quotient, termed molar conductivity, is denoted by | 7 | Physical Chemistry |
The stopped-flow method depends on the existence of spectroscopic properties that can be used for following the reaction. When that is not the case quenched flow provides an alternative that uses conventional chemical methods for analysis. Instead of a mechanical stopping system the reaction is stopped by quenching, the products being delivered to a recipient that stops the reaction immediately, either by instantaneous freezing or by denaturing the enzyme with a chemical denaturant or exposing the sample to a denaturing light source. As in the continuous-flow method, the time between mixing and quenching can be varied by varying the length of the tube.
The pulsed quenched flow method introduced by Alan Fersht and Ross Jakes overcomes the need for a long tube. The reaction is initiated exactly as in a stopped-flow experiment, but there is a third syringe that brings about quenching a definite and preset time after the initiation.
Quenched flow has both advantages and disadvantages with respect to stopped flow. On the one hand, chemical analysis makes it clear what process is being measured, whereas it may not always be obvious what process a spectroscopic signal represents. On the other hand, quenched flow is much more laborious, as each point along the time course must be determined separately. The image at left for catalysis by nitrogenase from Klebsiella pneumoniae illustrates both of these points: the agreement in half times indicates that the absorbance at 420 nm measured the release of P, but the quenched-flow experiment required 11 data points. | 7 | Physical Chemistry |
abietadiene hydroxylase - acrylamide gels - Act 1 adaptor protein - adenine - adenosine deaminase deficiency - adenovirus - adenylyl-(glutamate—ammonia ligase) hydrolase - agarose gel electrophoresis - agarose gel - akaryocyte - Alagille syndrome - alkaline lysis - allele - amino acids - amino terminus - amp resistance - amplification - amplicon - anchor sequence - animal model - anneal - anthranilate adenylyltransferase - anti-sense strand - antibiotic resistance - antibody - antisense - antisense strand - AP-1 site - apo-beta-carotenoid-14,13-dioxygenase - apoptosis - apovitellenin-1 - archease - arenicin - ArgJ protein family - ascorbate 2,3-dioxygenase - assembled epitope - ataxia-telangiectasia - ATG or AUG - ATP cone - autoimmune lymphoproliferative syndrome - autoradiography - autosomal dominant - autosome - avidin - | 1 | Biochemistry |
The following list provides information and external links to various programs and databases for inverted repeats:
*[https://web.archive.org/web/20131113054733/http://nonb.abcc.ncifcrf.gov/apps/site/default non-B DB] A Database for Integrated Annotations and Analysis of non-B DNA Forming Motifs. This database is provided by The Advanced Biomedical Computing Center (ABCC) at then Frederick National Laboratory for Cancer Research (FNLCR). It covers the A-DNA and Z-DNA conformations otherwise known as "non-B DNAs" because they are not the more common B-DNA form of a right-handed Watson-Crick double-helix. These "non-B DNAs" include left-handed Z-DNA, cruciform, triplex, tetraplex and hairpin structures. Searches can be performed on a variety of "repeat types" (including inverted repeats) and on several species.
*[http://tandem.bu.edu/cgi-bin/irdb/irdb.exe Inverted Repeats Database] Boston University. This database is a web application that allows query and analysis of repeats held in the PUBLIC DATABASE project. Scientists can also analyze their own sequences with the Inverted Repeats Finder algorithm.
*[http://pmite.hzau.edu.cn/django/mite/ P-MITE: a Plant MITE database] — this database for Miniature Inverted-repeat Transposable Elements (MITEs) contains sequences from plant genomes. Sequences may be searched or downloaded from the database.
*EMBOSS is the "European Molecular Biology Open Software Suite" which runs on UNIX and UNIX-like operating systems. Documentation and program source files are available on the [http://emboss.sourceforge.net/news/ EMBOSS website]. Applications specifically related to inverted repeats are listed below:
**[http://emboss.sourceforge.net/apps/cvs/emboss/apps/einverted.html EMBOSS einverted]: Finds inverted repeats in nucleotide sequences. Threshold values can be set to limit the scope of the search.
**[http://emboss.sourceforge.net/apps/cvs/emboss/apps/palindrome.html EMBOSS palindrome]: Finds palindromes such as stem loop regions in nucleotide sequences. The program will find sequences that include sections of mismatches and gaps that may correspond to bulges in a stem loop. | 1 | Biochemistry |
A subgenomic promoter is a promoter added to a virus for a specific heterologous gene, resulting in the formation of mRNA for that gene alone. Many positive-sense RNA viruses produce these subgenomic mRNAs (sgRNA) as one of the common infection techniques used by these viruses and generally transcribe late viral genes. Subgenomic promoters range from 24 nucleotide (Sindbis virus) to over 100 nucleotides (Beet necrotic yellow vein virus) and are usually found upstream of the transcription start. | 1 | Biochemistry |
The etymology of the words valence (plural valences) and valency (plural valencies) traces back to 1425, meaning "extract, preparation", from Latin valentia "strength, capacity", from the earlier valor "worth, value", and the chemical meaning referring to the "combining power of an element" is recorded from 1884, from German Valenz.
The concept of valence was developed in the second half of the 19th century and helped successfully explain the molecular structure of inorganic and organic compounds.
The quest for the underlying causes of valence led to the modern theories of chemical bonding, including the cubical atom (1902), Lewis structures (1916), valence bond theory (1927), molecular orbitals (1928), valence shell electron pair repulsion theory (1958), and all of the advanced methods of quantum chemistry.
In 1789, William Higgins published views on what he called combinations of "ultimate" particles, which foreshadowed the concept of valency bonds. If, for example, according to Higgins, the force between the ultimate particle of oxygen and the ultimate particle of nitrogen were 6, then the strength of the force would be divided accordingly, and likewise for the other combinations of ultimate particles (see illustration).
The exact inception, however, of the theory of chemical valencies can be traced to an 1852 paper by Edward Frankland, in which he combined the older radical theory with thoughts on chemical affinity to show that certain elements have the tendency to combine with other elements to form compounds containing 3, i.e., in the 3-atom groups (e.g., , , , etc.) or 5, i.e., in the 5-atom groups (e.g., , , , etc.), equivalents of the attached elements. According to him, this is the manner in which their affinities are best satisfied, and by following these examples and postulates, he declares how obvious it is that
This "combining power" was afterwards called quantivalence or valency (and valence by American chemists). In 1857 August Kekulé proposed fixed valences for many elements, such as 4 for carbon, and used them to propose structural formulas for many organic molecules, which are still accepted today.
Lothar Meyer in his 1864 book, Die modernen Theorien der Chemie, contained an early version of the periodic table containing 28 elements, for the first time classified elements into six families by their valence. Works on organizing the elements by atomic weight, until then had been stymied by the widespread use of equivalent weights for the elements, rather than atomic weights.
Most 19th-century chemists defined the valence of an element as the number of its bonds without distinguishing different types of valence or of bond. However, in 1893 Alfred Werner described transition metal coordination complexes such as , in which he distinguished principal and subsidiary valences (German: Hauptvalenz and Nebenvalenz), corresponding to the modern concepts of oxidation state and coordination number respectively.
For main-group elements, in 1904 Richard Abegg considered positive and negative valences (maximal and minimal oxidation states), and proposed Abegg's rule to the effect that their difference is often 8.
An alternative definition of valence, developed in the 1920s and having modern proponents, differs in cases where an atoms formal charge is not zero. It defines the valence of a given atom in a covalent molecule as the number of electrons that an atom has used in bonding:
:valence = number of electrons in valence shell of free atom − number of non-bonding electrons on atom in molecule,
or equivalently:
:valence = number of bonds + formal charge.
In this convention, the nitrogen in an ammonium ion bonds to four hydrogen atoms, but it is considered to be pentavalent because all five of nitrogen's valence electrons participate in the bonding. | 3 | Analytical Chemistry |
Anions with the general formula are called sulfonates. They are the conjugate bases of sulfonic acids with formula . As sulfonic acids tend to be strong acids, the corresponding sulfonates are weak bases. Due to the stability of sulfonate anions, the cations of sulfonate salts such as scandium triflate have application as Lewis acids.
A classic preparation of sulfonates is the Strecker sulfite alkylation, in which an alkali sulfite salt displaces a halide, typically in the presence of an iodine catalyst:
An alternative is the condensation of a sulfonyl halide with an alcohol in pyridine: | 0 | Organic Chemistry |
For black body emitters or imperfect selective emitters, filters reflect non-ideal wavelengths back to the emitter. These filters are imperfect. Any light that is absorbed or scattered and not redirected to the emitter or the converter is lost, generally as heat. Conversely, practical filters often reflect a small percentage of light in desired wavelength ranges. Both are inefficiencies. The absorption of suboptimal wavelengths by the photovoltaic device also contributes inefficiency and has the added effect of heating it, which also decreases efficiency. | 7 | Physical Chemistry |
Olefin and alkyne metathesis refers to a carbon–carbon bond forming reaction. In the case of olefin metathesis, the bond forms between two sp-hybridized carbon centers. In alkyne metathesis it forms between two sp-hybridized carbon centers. Ring opening metathesis polymerization (ROMP) can be used in polymerization and macrocycle synthesis. | 6 | Supramolecular Chemistry |
In semiconductors, the Shockley diode equation—the relationship between the flow of electric current and the electrostatic potential across a p–n junction—depends on a characteristic voltage called the thermal voltage, denoted by . The thermal voltage depends on absolute temperature as
where is the magnitude of the electrical charge on the electron with a value Equivalently,
At room temperature , is approximately which can be derived by plugging in the values as follows:
At the standard state temperature of , it is approximately . The thermal voltage is also important in plasmas and electrolyte solutions (e.g. the Nernst equation); in both cases it provides a measure of how much the spatial distribution of electrons or ions is affected by a boundary held at a fixed voltage. | 7 | Physical Chemistry |
A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. They occur especially as proteins, often conjugated. The term was first used by organic chemist Ludwig Brieger (1849–1919) and is derived from the word "toxic".
Toxins can be small molecules, peptides, or proteins that are capable of causing disease on contact with or absorption by body tissues interacting with biological macromolecules such as enzymes or cellular receptors. They vary greatly in their toxicity, ranging from usually minor (such as a bee sting) to potentially fatal even at extremely low doses (such as botulinum toxin). | 1 | Biochemistry |
Phenolphthalein has been used for over a century as a laxative, but is now being removed from over-the-counter laxatives over concerns of carcinogenicity. Laxative products formerly containing phenolphthalein have often been reformulated with alternative active ingredients: Feen-a-Mint switched to bisacodyl, and Ex-Lax was switched to a senna extract.
Thymolphthalein is a related laxative made from thymol.
Despite concerns regarding its carcinogenicity based on rodent studies, the use of phenolphthalein as a laxative is unlikely to cause ovarian cancer. Some studies suggest a weak association with colon cancer, while others show none at all.
Phenolphthalein is described as a stimulant laxative. In addition, it has been found to inhibit human cellular calcium influx via store-operated calcium entry (SOCE, see ) in vivo. This is effected by its inhibiting thrombin and thapsigargin, two activators of SOCE that increase intracellular free calcium.
Phenolphthalein has been added to the European Chemicals Agency's candidate list for substance of very high concern (SVHC). It is on the IARC group 2B list for substances "possibly carcinogenic to humans".
The discovery of phenolphthalein's laxative effect was due to an attempt by the Hungarian government to label genuine local white wine with the substance in 1900. Phenolphthalein did not change the taste of the wine and would change color when a base is added, making it a good label in principle. However, it was found that ingestion of the substance led to diarrhea. Max Kiss, a Hungarian-born pharmacist residing in New York, heard about the news and launched Ex-Lax in 1906. | 3 | Analytical Chemistry |
In chemistry, biochemistry, and pharmacology, a dissociation constant (K) is a specific type of equilibrium constant that measures the propensity of a larger object to separate (dissociate) reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into its component ions. The dissociation constant is the inverse of the association constant. In the special case of salts, the dissociation constant can also be called an ionization constant.
For a general reaction:
in which a complex breaks down into x A subunits and y B subunits, the dissociation constant is defined as
where [A], [B], and [A B] are the equilibrium concentrations of A, B, and the complex A B, respectively.
One reason for the popularity of the dissociation constant in biochemistry and pharmacology is that in the frequently encountered case where x = y = 1, K has a simple physical interpretation: when [A] = K, then [B] = [AB] or, equivalently, . That is, K, which has the dimensions of concentration, equals the concentration of free A at which half of the total molecules of B are associated with A. This simple interpretation does not apply for higher values of x or y. It also presumes the absence of competing reactions, though the derivation can be extended to explicitly allow for and describe competitive binding. It is useful as a quick description of the binding of a substance, in the same way that EC and IC describe the biological activities of substances. | 7 | Physical Chemistry |
Synthesis via the capping method relies strongly upon a thermodynamically driven template effect; that is, the "thread" is held within the "macrocycle" by non-covalent interactions, for example rotaxinations with cyclodextrin macrocycles involve exploitation of the hydrophobic effect. This dynamic complex or pseudorotaxane is then converted to the rotaxane by reacting the ends of the threaded guest with large groups, preventing disassociation. | 6 | Supramolecular Chemistry |
*SNP detection
*Real-time nucleic acid detection
*Real-time PCR quantification
*Allelic discrimination and identification
*Multiplex PCR assays
*Diagnostic clinical assays | 1 | Biochemistry |
Kowalski served as the inaugural director of the Center for Process Analytical Chemistry (CPAC), established in 1984, at the University of Washington. Initially CPAC was a National Science Foundation (NSF) Industry-University Cooperative Research Center (IUCRC). It has since been renamed Center for Process Analysis and Control and has become self-sustaining. Writing for Analytical Chemistry, Alan Newman called CPAC the "brainchild" of Kowalski, who proposed the idea in 1982, and said in the field of analytical chemistry, "CPAC offers a unique model of how chemists can successfully forge bonds with industry, government, and allied academic disciplines to foster new ideas. At the same time, the center establishes a two-way flow of ideas between basic researchers in academia and scientists in industry and government." | 3 | Analytical Chemistry |
ortho-Carborane undergoes 2e- reduction when treated with a solution of lithium in ammonia. The result is the nido cluster 7,9-[CBH]. In the dianion, the carbon vertices are not adjacent. The same cluster is produced by reduction of meta-carborane. Oxidation of the resulting 7,9-[CBH] gives ortho-carborane. | 7 | Physical Chemistry |
Null mutants die at an early gestational age (embryonic day 11.5). By investigating hypomorphic mutants (which can survive 2 days longer), it was found that placental defects were primarily lethal and that there were also defects in cardiac and hepatic development, but many other organs were normal | 1 | Biochemistry |
Survivin has been shown to interact with:
* Aurora B kinase,
* CDCA8,
* Caspase 3,
* Caspase 7,
* Diablo homolog and
* INCENP. | 1 | Biochemistry |
Selective ligands have a tendency to bind to very limited kinds of receptor, whereas non-selective ligands bind to several types of receptors. This plays an important role in pharmacology, where drugs that are non-selective tend to have more adverse effects, because they bind to several other receptors in addition to the one generating the desired effect. | 1 | Biochemistry |
Levobupivacaine (rINN) is a local anaesthetic drug indicated for minor and major surgical anaesthesia and pain management. It is a long-acting amide-type local anaesthetic that blocks nerve impulses by inhibiting sodium ion influx into the nerve cells. Levobupivacaine is the S-enantiomer of racemic bupivacaine and therefore similar in pharmacological effects. The drug typically starts taking effect within 15 minutes and can last up to 16 hours depending on factors such as site of administration and dosage.
Levobupivacaine was designed, in the late 1970s, to be a safer and more effective alternative to bupivacaine, which had been associated with a higher risk of cardiotoxicity. Compared to bupivacaine, levobupivacaine is associated with less vasodilation and has a longer duration of action. It is approximately 13 per cent less potent (by molarity) than racemic bupivacaine and has a longer motor block onset time. Ropivacaine is, next to levobupivacaine, another less cardiotoxic alternative to bupivacaine.
Levobupivacaine hydrochloride is commonly marketed by AbbVie under the trade name Chirocaine. In Europe, Chirocaine is available – prescription only – in concentrations ranging from 0.625 mg/ml to 7.5 mg/mL. | 4 | Stereochemistry |
Leon Francis Phillips (14 July 1935 – 24 September 2023) was a New Zealand physical chemist who specialised in the gas-liquid interface and atmospheric chemistry. | 7 | Physical Chemistry |
The following genes are analogous or homologous between Drosophila melanogaster (in bold) and human TNFR1 signalling:
* Imd: human orthologue = RIP1
* Tak1: human orthologue = Tak1
* TAB2: human orthologue = TAB2
* Dredd: human orthologue = caspase-8
* FADD: human orthologue = FADD
* Key/Ikkγ: human orthologue = NEMO
* Ird5: human orthologue = IKK2
* Relish: human orthologues = p65/p50 and IκB
* Iap2: human orthologue = cIAP2
* UEV1a: human orthologue = UEV1a
* bend: human orthologue = UBC13 | 1 | Biochemistry |
The Gastrin family is a group of peptides evolutionarily similar in structure and function. Commonly synthesized in antroduodenal G-cells. Regulate gastric function along with gastric acid secretion and mucosal growth.
#Gastrin
#<nowiki/>Cholecystokinin (CCK) | 1 | Biochemistry |
Sulfides are sometimes called thioethers, especially in the old literature. The two organic substituents are indicated by the prefixes. (CH)S is called dimethylsulfide. Some sulfides are named by modifying the common name for the corresponding ether. For example, CHSCH is methyl phenyl sulfide, but is more commonly called thioanisole, since its structure is related to that for anisole, CHOCH.
The modern systematic nomenclature in chemistry for the trival name thioether is sulfane. | 0 | Organic Chemistry |
The chemical properties of fumaric acid can be anticipated from its component functional groups. This weak acid forms a diester, it undergoes bromination across the double bond, and it is a good dienophile. | 1 | Biochemistry |
DCP incurs several key disadvantages in comparison to ICP. In addition to the lower sensitivity, spectra generated by DCP generally present fewer spectral lines. DCP samples are often incompletely volatilized due to the relatively short amount of time spent in the hottest region of the plasma. Furthermore, DCP requires more regular upkeep than ICP, because the graphite electrodes wear out after a few hours and must be exchanged
However, DCP is not without a few advantages over ICP. The amount of argon needed for DCP is much less than that needed for ICP. Also, DCP can analyze samples that have a higher percentage of solid in solution than can be handled by ICP. | 3 | Analytical Chemistry |
Precision fermentation is an approach to manufacturing specific functional products which intends to minimise the production of unwanted by-products through the application of synthetic biology, particularly by generating synthetic "cell factories" with engineered genomes and metabolic pathways optimised to produce the desired compounds as efficiently as possible with the available resources. Precision fermentation of genetically modified microorganisms may be used to manufacture proteins needed for cell culture media, providing for serum-free cell culture media in the manufacturing process of cultured meat. A 2021 publication showed that photovoltaic-driven microbial protein production could use 10 times less land for an equivalent amount of protein compared to soybean cultivation. | 1 | Biochemistry |
In organic chemistry, a cycloalkene or cycloolefin is a type of alkene hydrocarbon which contains a closed ring of carbon atoms and either one or more double bonds, but has no aromatic character. Some cycloalkenes, such as cyclobutene and cyclopentene, can be used as monomers to produce polymer chains. Due to geometrical considerations, smaller cycloalkenes are almost always the cis isomers, and the term cis tends to be omitted from the names. Cycloalkenes require considerable p-orbital overlap in the form of a bridge between the carbon-carbon double bond; however, this is not feasible in smaller molecules due to the increase of strain that could break the molecule apart. In greater carbon number cycloalkenes, the addition of substituents decreases strain. trans-Cycloalkenes with 7 or fewer carbons in the ring will not occur under normal conditions because of the large amount of ring strain needed. In larger rings (8 or more atoms), cis–trans isomerism of the double bond may occur. This stability pattern forms part of the origin of Bredts rule, the observation that alkenes do not form at the bridgehead of many types of bridged ring systems because the alkene would necessarily be trans' in one of the rings. | 0 | Organic Chemistry |
The ratio between the surface area and volume of cells and organisms has an enormous impact on their biology, including their physiology and behavior. For example, many aquatic microorganisms have increased surface area to increase their drag in the water. This reduces their rate of sink and allows them to remain near the surface with less energy expenditure.
An increased surface area to volume ratio also means increased exposure to the environment. The finely-branched appendages of filter feeders such as krill provide a large surface area to sift the water for food.
Individual organs like the lung have numerous internal branchings that increase the surface area; in the case of the lung, the large surface supports gas exchange, bringing oxygen into the blood and releasing carbon dioxide from the blood. Similarly, the small intestine has a finely wrinkled internal surface, allowing the body to absorb nutrients efficiently.
Cells can achieve a high surface area to volume ratio with an elaborately convoluted surface, like the microvilli lining the small intestine.
Increased surface area can also lead to biological problems. More contact with the environment through the surface of a cell or an organ (relative to its volume) increases loss of water and dissolved substances. High surface area to volume ratios also present problems of temperature control in unfavorable environments.
The surface to volume ratios of organisms of different sizes also leads to some biological rules such as Allens rule, Bergmanns rule and gigantothermy. | 7 | Physical Chemistry |
Transcription activator-like effector nucleases (TALEN) are restriction enzymes that can be engineered to cut specific sequences of DNA. They are made by fusing a TAL effector DNA-binding domain to a DNA cleavage domain (a nuclease which cuts DNA strands). Transcription activator-like effectors (TALEs) can be engineered to bind to practically any desired DNA sequence, so when combined with a nuclease, DNA can be cut at specific locations. The restriction enzymes can be introduced into cells, for use in gene editing or for genome editing in situ, a technique known as genome editing with engineered nucleases. Alongside zinc finger nucleases and CRISPR/Cas9, TALEN is a prominent tool in the field of genome editing. | 1 | Biochemistry |
Ff phages have been engineered for applications in biological and medical sciences. Many applications build on experiments showing that the DNA sequence determining resistance to the antibiotic kanamycin can be inserted in a functional form into the non-coding intergenic sequence of fd phage DNA. Such modified phage are correspondingly longer that wild-type filamentous fd, because the longer DNA is coated with correspondingly more gene 8 coat proteins, but the phage life-cycle is not otherwise disrupted. The traditional “tadpole” or isometric shaped-phage, on the other hand, which have a limited-sized capsid, cannot be so easily used to encapsidate a larger DNA molecule. The modified phage can be selected by infecting kanamycin-sensitive bacteria with modified phage to introduce resistance to kanamycin, and growing the infected bacteria in media containing an otherwise lethal concentration of kanamycin.
This result was extended by inserting foreign DNA expressing a foreign peptide into fd phage gene 3, rather than into the intergenic sequence, so that the foreign peptide appears on the surface of the phage as a part of the gene 3 adsorption protein. Phage carrying the foreign peptide can then be detected using appropriate antibodies. The reverse of this approach is to insert DNA coding for antibodies into gene 3 and detect their presence by appropriate antigens.
These techniques have been extended over the years in many ways, for instance by inserting foreign DNA into the genes coding for phage coat proteins other than gene 3, and/or duplicating the gene of interest to modify only some of the corresponding gene products. Phage display technology has been widely used for many purposes. | 1 | Biochemistry |
Esketamine is used for similar indications as ketamine. Such uses include induction of anesthesia in high-risk patients such as those with circulatory shock, severe bronchospasm, or as a supplement to regional anesthesia with incomplete nerve blocks. | 4 | Stereochemistry |
2-Furoic acid can be synthesized by the oxidation of either furfuryl alcohol or furfural. This can be achieved either chemically or biocatalytically.
The current industrial route involves the Cannizaro reaction of furfural in an aqueous NaOH solution. This is a disproportionation reaction and produces a 1:1 ratio of 2-furoic acid and furfuryl alcohol (a 50% yield of each). It remains economical because both products have commercial value. The bio-catalytic route involves the microorganism Nocardia corallina. This produces 2-furoic acid in higher yields: 98% from 2-furfuryl alcohol and 88% from 2-furfural, but has yet to be commercialised. | 0 | Organic Chemistry |
Ozone in the troposhere is determined by photochemical production and destruction, dry deposition and cross-tropopause transport of ozone from the stratosphere. In the Arctic troposphere, transport and photochemical reactions involving nitrogen oxides and volatile organic compounds (VOCs) as a result of human emissions also produce ozone resulting in a background mixing ratio of 30 to 50 nmol mol−1 (ppb). Nitrogen oxides play a key role in recycling active free radicals (such as reactive halogens) in the atmosphere and indirectly affect ozone depletion. Ozone depletion events (ODEs) are phenomena associated with the sea ice zone. They are routinely observed at coastal locations when incoming winds have traversed sea ice covered areas. | 2 | Environmental Chemistry |
Lateral flow assays have played a critical role in COVID-19 testing as they have the benefit of delivering a result in 15–30 minutes. The systematic evaluation of lateral flow assays during the COVID-19 pandemic was initiated at Oxford University as part of a UK collaboration with Public Health England. A study that started in June 2020 in the United Kingdom, FALCON-C19, confirmed the sensitivity of some lateral flow devices (LFDs) in this setting. Four out of 64 LFDs tested had desirable performance characteristics according to these early tests; the Innova SARS-CoV-2 Antigen Rapid Qualitative Test performed moderately in viral antigen detection/sensitivity with excellent specificity, although kit failure rates and the impact of training were potential issues. The Innova test's specificity is more widely publicised, but sensitivity in phase 4 trials was 50.1%. This describes a device for which one out of every two patients infected with COVID-19 and tested in real-world conditions would receive a false-negative result. After closure of schools in January 2021, biweekly LFTs were introduced in England for teachers, pupils, and households of pupils when schools re-opened on March 8, 2021 for asymptomatic testing. Biweekly LFT were made universally available to everyone in England on April 9, 2021. LFTs have been used for mass testing for COVID-19 globally and complement other public health measures for COVID-19.
Some scientists outside government expressed serious misgivings in late 2020 about the use of Innova LFDs for screening for Covid. According to Jon Deeks, a professor of biostatistics at the University of Birmingham, England, the Innova test is "entirely unsuitable" for community testing: "as the test may miss up to half of cases, a negative test result indicates a reduced risk of Covid, but does not exclude Covid".
Sensitivity of tests used in 2022 was around 70%. | 1 | Biochemistry |
Using electrophilic aromatic substitution, many functional groups are introduced onto the benzene framework. Sulfonation of benzene involves the use of oleum, a mixture of sulfuric acid with sulfur trioxide. Sulfonated benzene derivatives are useful detergents. In nitration, benzene reacts with nitronium ions (NO), which is a strong electrophile produced by combining sulfuric and nitric acids. Nitrobenzene is the precursor to aniline. Chlorination is achieved with chlorine to give chlorobenzene in the presence of a Lewis acid catalyst such as aluminium tri-chloride. | 2 | Environmental Chemistry |
Plants produce secondary metabolites known as allelochemicals. Rather than participating in basic metabolic processes, they mediate interactions between a plant and its environment, often attracting, repelling, or poisoning insects. They also help produce secondary cell wall components such as those that require amino acid modification.
In a tritrophic system, volatiles, which are released into the air, are superior to surface chemicals in drawing foraging natural enemies from afar. Plants also produce root volatiles which will drive tritrophic interactions between below-ground herbivores and their natural enemies. Some plant volatiles can be smelled by humans and give plants like basil, eucalyptus, and pine their distinctive odors. The mixture and ratios of individual volatiles emitted by a plant under given circumstances (also referred to as synomones in the context of natural enemy attraction) is referred to as a volatile profile. These are highly specific to certain plant species and are detectable meters from the source. Predators and parasitoids exploit the specificity of volatile profiles to navigate the complex infochemical signals presented by plants in their efforts to locate a particular prey species.
The production of volatiles is likely to be beneficial given two conditions: that they are effective in attracting natural enemies and that the natural enemies are effective in removing or impeding herbivores. However, volatile chemicals may not have evolved initially for this purpose; they act in within-plant signaling, attraction of pollinators, or repulsion of herbivores that dislike such odors. | 1 | Biochemistry |
In molecular biology, the term double helix refers to the structure formed by double-stranded molecules of nucleic acids such as DNA. The double helical structure of a nucleic acid complex arises as a consequence of its secondary structure, and is a fundamental component in determining its tertiary structure. The structure was discovered by Rosalind Franklin and her student Raymond Gosling, but the term "double helix" entered popular culture with the publication in 1968 of The Double Helix: A Personal Account of the Discovery of the Structure of DNA by James Watson.
The DNA double helix biopolymer of nucleic acid is held together by nucleotides which base pair together. In B-DNA, the most common double helical structure found in nature, the double helix is right-handed with about 10–10.5 base pairs per turn. The double helix structure of DNA contains a major groove and minor groove. In B-DNA the major groove is wider than the minor groove. Given the difference in widths of the major groove and minor groove, many proteins which bind to B-DNA do so through the wider major groove. | 4 | Stereochemistry |
There are a variety of architectures possible for nonlinear copolymers. Beyond grafted and star polymers discussed below, other common types of branched copolymers include brush copolymers and comb copolymers. | 7 | Physical Chemistry |
Energy-dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) are commonly used techniques to both qualitatively and quantitatively probe the composition of samples in the TEM. A primary challenge in the quantitative accuracy of both techniques is the phenomenon of channelling. Put simply, in a crystalline solid, the probability of interaction between an electron and ion in the lattice depends strongly on the momentum (direction and velocity) of the electron. When probing a sample under diffraction conditions near a zone axis, as is often the case in EDS and EELS applications, channelling can have a large impact on the effective interaction of the incident electrons with specific ions in the crystal structure. In practice, this can lead to erroneous measurements of composition that depend strongly on the orientation and thickness of the sample and the accelerating voltage. Since PED entails an integration over incident directions of the electron probe, and generally does not include beams parallel to the zone axis, the detrimental channeling effects outlined above can be minimized, yielding far more accurate composition measurements in both techniques. | 3 | Analytical Chemistry |
The advances in bisulfite sequencing have led to the possibility of applying them at a genome-wide scale, where, previously, global measure of DNA methylation was feasible only using other techniques, such as Restriction landmark genomic scanning. The mapping of the human epigenome is seen by many scientists as the logical follow-up to the completion of the Human Genome Project. This epigenomic information will be important in understanding how the function of the genetic sequence is implemented and regulated. Since the epigenome is less stable than the genome, it is thought to be important in gene-environment interactions.
Epigenomic mapping is inherently more complex than genome sequencing, however, since the epigenome is much more variable than the genome. One's epigenome varies with age, differs between tissues, is altered by environmental factors, and shows aberrations in diseases. Such rich epigenomic mapping, however, representing different ages, tissue types, and disease states, would yield valuable information on the normal function of epigenetic marks as well as the mechanisms leading to aging and disease.
Direct benefits of epigenomic mapping include probable advances in cloning technology. It is believed that failures to produce cloned animals with normal viability and lifespan result from inappropriate patterns of epigenetic marks. Also, aberrant methylation patterns are well characterized in many cancers. Global hypomethylation results in decreased genomic stability, while local hypermethylation of tumour suppressor gene promoters often accounts for their loss of function. Specific patterns of methylation are indicative of specific cancer types, have prognostic value, and can help to guide the best course of treatment.
Large-scale epigenome mapping efforts are under way around the world and have been organized under the Human Epigenome Project. This is based on a multi-tiered strategy, whereby bisulfite sequencing is used to obtain high-resolution methylation profiles for a limited number of reference epigenomes, while less thorough analysis is performed on a wider spectrum of samples. This approach is intended to maximize the insight gained from a given amount of resources, as high-resolution genome-wide mapping remains a costly undertaking.
Gene-set analysis (for example using tools like DAVID and GoSeq) has been shown to be severely biased when applied to high-throughput methylation data (e.g. genome-wide bisulfite sequencing); it has been suggested that this can be corrected using sample label permutations or using a statistical model to control for differences in the numberes of CpG probes / CpG sites that target each gene. | 1 | Biochemistry |
Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. The goal of hyperspectral imaging is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifying materials, or detecting processes. There are three general types of spectral imagers. There are push broom scanners and the related whisk broom scanners (spatial scanning), which read images over time, band sequential scanners (spectral scanning), which acquire images of an area at different wavelengths, and snapshot hyperspectral imagers, which uses a staring array to generate an image in an instant.
Whereas the human eye sees color of visible light in mostly three bands (long wavelengths, perceived as red; medium wavelengths, perceived as green; and short wavelengths, perceived as blue), spectral imaging divides the spectrum into many more bands. This technique of dividing images into bands can be extended beyond the visible. In hyperspectral imaging, the recorded spectra have fine wavelength resolution and cover a wide range of wavelengths. Hyperspectral imaging measures continuous spectral bands, as opposed to multiband imaging which measures spaced spectral bands.
Engineers build hyperspectral sensors and processing systems for applications in astronomy, agriculture, molecular biology, biomedical imaging, geosciences, physics, and surveillance. Hyperspectral sensors look at objects using a vast portion of the electromagnetic spectrum. Certain objects leave unique fingerprints in the electromagnetic spectrum. Known as spectral signatures, these fingerprints enable identification of the materials that make up a scanned object. For example, a spectral signature for oil helps geologists find new oil fields. | 7 | Physical Chemistry |
Soil-borne nematodes have been shown to transmit viruses. They acquire and transmit them by feeding on infected roots. Viruses can be transmitted both non-persistently and persistently, but there is no evidence of viruses being able to replicate in nematodes. The virions attach to the stylet (feeding organ) or to the gut when they feed on an infected plant and can then detach during later feeding to infect other plants. Nematodes transmit viruses such as tobacco ringspot virus and tobacco rattle virus. | 1 | Biochemistry |
With the current methods, the instrumental error in the measured hairpin length is 1-1.5 nm. The length of a basepair, or 2 extended single-stranded nucleotides, is approximately 0.85 nm. Therefore, the resolution of the system is at a few nucleotides. The sources of noise arise from length-dependent Brownian motion of the bead anchored by the extended hairpin, statistical error in bead position determination, and slow mechanical drifts. However, as mentioned earlier, such resolution is sufficient for the current sequencing method because changes in >4 nm are being measured. | 1 | Biochemistry |
Dispersion is a process by which (in the case of solid dispersing in a liquid) agglomerated particles are separated from each other, and a new interface between the inner surface of the liquid dispersion medium and the surface of the dispersed particles is generated. This process is facilitated by molecular diffusion and convection.
With respect to molecular diffusion, dispersion occurs as a result of an unequal concentration of the introduced material throughout the bulk medium. When the dispersed material is first introduced into the bulk medium, the region at which it is introduced then has a higher concentration of that material than any other point in the bulk. This unequal distribution results in a concentration gradient that drives the dispersion of particles in the medium so that the concentration is constant across the entire bulk. With respect to convection, variations in velocity between flow paths in the bulk facilitate the distribution of the dispersed material into the medium.
Although both transport phenomena contribute to the dispersion of a material into the bulk, the mechanism of dispersion is primarily driven by convection in cases where there is significant turbulent flow in the bulk. Diffusion is the dominant mechanism in the process of dispersion in cases of little to no turbulence in the bulk, where molecular diffusion is able to facilitate dispersion over a long period of time. These phenomena are reflected in common real-world events. The molecules in a drop of food coloring added to water will eventually disperse throughout the entire medium, where the effects of molecular diffusion are more evident. However, stirring the mixture with a spoon will create turbulent flows in the water that accelerate the process of dispersion through convection-dominated dispersion. | 7 | Physical Chemistry |
The inositol-phospholipid signaling pathway is responsible for the generation of IP3 through the cleavage of Phosphatidylinositol 4,5-bisphosphate (PIP2) found in the lipid bi-layer of the plasma membrane by phospholipase C in response to either receptor tyrosine kinase or Gq alpha subunit-G protein-coupled receptor signaling. Soluble inositol trisphosphate (IP3) is able to rapidly diffuse into the cytosol and bind to the inositol trisphosphate receptor (InsP3Rs) calcium channels located in the endoplasmic reticulum. This releases calcium into the cytosol, serving as a rapid and potent signal for various cellular processes.
Further reading: Function of calcium in humans | 1 | Biochemistry |
Historically, aluminium has been used as conductor in integrated circuits, due to its good adherence to substrate, good conductivity, and ability to form ohmic contacts with silicon. However, pure aluminium is susceptible to electromigration. Research shows that adding 2-4% of copper to aluminium increases resistance to electromigration about 50 times. The effect is attributed to the grain boundary segregation of copper, which greatly inhibits the diffusion of aluminium atoms across grain boundaries.
Pure copper wires can withstand approximately five times more current density than aluminum wires while maintaining similar reliability requirements. This is mainly due to the higher electromigration activation energy levels of copper, caused by its superior electrical and thermal conductivity as well as its higher melting point. Further improvements can be achieved by alloying copper with about 1% palladium which inhibits diffusion of copper atoms along grain boundaries in the same way as the addition of copper to aluminium interconnect. | 7 | Physical Chemistry |
To meet the NADPH and ATP demands in the mesophyll and bundle sheath, light needs to be harvested and shared between two distinct electron transfer chains. ATP may be produced in the bundle sheath mainly through cyclic electron flow around Photosystem I, or in the M mainly through linear electron flow depending on the light available in the bundle sheath or in the mesophyll. The relative requirement of ATP and NADPH in each type of cells will depend on the photosynthetic subtype. The apportioning of excitation energy between the two cell types will influence the availability of ATP and NADPH in the mesophyll and bundle sheath. For instance, green light is not strongly adsorbed by mesophyll cells and can preferentially excite bundle sheath cells, or vice versa for blue light. Because bundle sheaths are surrounded by mesophyll, light harvesting in the mesophyll will reduce the light available to reach BS cells. Also, the bundle sheath size limits the amount of light that can be harvested. | 5 | Photochemistry |
In 1831, the East India Company officer William Elliott made a facsimile of the inscription. Based on this facsimile, in 1834, James Prinsep published a lithograph in the Journal of the Royal Asiatic Society of Great Britain and Ireland. However, this lithograph did not represent every single word of the inscription correctly. Some years later, British engineer T. S. Burt made an ink impression of the inscription. Based on this, in 1838, Prinsep published an improved lithograph in the same journal, with his reading of the script and translation of the text.
Decades later, Bhagwan Lal Indraji made another copy of the inscription on a cloth. Based on this copy, Bhau Daji Lad published a revised text and translation in 1875, in Journal of the Bombay Branch of the Royal Asiatic Society. This reading was the first one to correctly mention the kings name as Chandra. In 1888, John Faithfull Fleet published a critical edition of the text in Corpus Inscriptionum Indicarum'.
In 1945, Govardhan Rai Sharma dated the inscription to the first half of the 5th century CE, on paleographic grounds. He observed that its script was similar to the writing on other Gupta-Era inscriptions, including the ones discovered at Bilsad (415 CE), Baigram (449 CE), and Kahanum (449 CE). R. Balasubramaniam (2005) noted that the characters of the Delhi inscription closely resembled the dated inscriptions of Chandragupta II, found at Udayagiri in Madhya Pradesh. | 8 | Metallurgy |
According to a recent investigation by Wong, Liang, Kwon, Bai, Alper and Gropman, TGGE can be utilized to examine the mitochondrial DNA of an individual. According to these authors, TGGE was utilized to determine two novel mutations in the mitochondrial genome: "A 21-year-old woman who has been suspected of mitochondrial cytopathy, but negative for common mitochondrial DNA (mtDNA) point mutations and deletions, was screened for unknown mutations in the entire mitochondrial genome by temperature gradient gel electrophoresis". | 1 | Biochemistry |
Spectral karyotyping is an image of colored chromosomes. Spectral karyotyping involves FISH using multiple forms of many types of probes with the result to see each chromosome labeled through its metaphase stage. This type of karyotyping is used specifically when seeking out chromosome arrangements. | 1 | Biochemistry |
An alternative mechanism to preserve O delivery in the face of low ambient oxygen is to increase the affinity of the blood. The oxygen content of the blood is related to PaO and is illustrated using an oxygen equilibrium curve (OEC). Fish hemoglobins, with the exception of the agnathans, are tetramers that exhibit cooperativity of O binding and have sigmoidal OECs.
The binding affinity of hemoglobin to oxygen is estimated using a measurement called P50 (the partial pressure of oxygen at which hemoglobin is 50% bound with oxygen) and can be extremely variable. If the hemoglobin has a weak affinity for oxygen, it is said to have a high P50 and therefore constrains the environment in which a fish can inhabit to those with relatively high environmental PO. Conversely, fish hemoglobins with a low P50 bind strongly to oxygen and are then of obvious advantage when attempting to extract oxygen from hypoxic or variable PO environments. The use of high affinity (low P50) hemoglobins results in reduced ventillatory and therefore energetic requirements when facing hypoxic insult. The oxygen binding affinity of hemoglobin (Hb-O) is regulated through a suite of allosteric modulators; the principal modulators used for controlling Hb-O affinity under hypoxic insult are:
#Increasing RBC pH
#Reducing inorganic phosphate interactions | 9 | Geochemistry |
Although there are 25 known isotopes of sulfur, only four are stable and of geochemical importance. Of those four, two (S, light and S, heavy) comprise (99.22%) of sulfur on Earth. The vast majority (95.02%) of sulfur occurs as S with only 4.21% in S. The ratio of these two isotopes is fixed in the Solar System and has been since its formation. The bulk Earth sulfur isotopic ratio is thought to be the same as the ratio of 22.22 measured from the Canyon Diablo troilite (CDT), a meteorite. That ratio is accepted as the international standard and is therefore set at δ = 0.00. Deviation from 0.00 is expressed as the δS which is a ratio in per mill (‰). Positive values correlate to increased levels of S, whereas negative values correlate with greater S in a sample.
Formation of sulfur minerals through non-biogenic processes does not substantially differentiate between the light and heavy isotopes, therefore sulfur isotope ratios in gypsum or barite should be the same as the overall isotope ratio in the water column at their time of precipitation. Sulfate reduction through biologic activity strongly differentiates between the two isotopes because of the more rapid enzymic reaction with S. Average present day seawater values of δS are on the order of +21‰.
Prior to 2010s, it was thought that sulfate reduction could fractionate sulfur isotopes up to 46 permil and fractionation larger than 46 permil recorded in sediments must be due to disproportionation of sulfur intermediates in the sediment. This view has changed since the 2010s that sulfate reduction can fractionate to 66 permil. As substrates for disproportionation are limited by the product of sulfate reduction, the isotopic effect of disproportionation should be less than 16 permil in most sedimentary settings.
Throughout geologic history the sulfur cycle and the isotopic ratios have coevolved with the biosphere becoming overall more negative with the increases in biologically driven sulfate reduction, but also show substantial positive excursion. In general positive excursions in the sulfur isotopes mean that there is an excess of pyrite deposition rather than oxidation of sulfide minerals exposed on land. | 9 | Geochemistry |
For hypervalent compounds in which the ligands are more electronegative than the central, hypervalent atom, resonance structures can be drawn with no more than four covalent electron pair bonds and completed with ionic bonds to obey the octet rule. For example, in phosphorus pentafluoride (PF), 5 resonance structures can be generated each with four covalent bonds and one ionic bond with greater weight in the structures placing ionic character in the axial bonds, thus satisfying the octet rule and explaining both the observed trigonal bipyramidal molecular geometry and the fact that the axial bond length (158 pm) is longer than the equatorial (154 pm).
For a hexacoordinate molecule such as sulfur hexafluoride, each of the six bonds is the same length. The rationalization described above can be applied to generate 15 resonance structures each with four covalent bonds and two ionic bonds, such that the ionic character is distributed equally across each of the sulfur-fluorine bonds.
Spin-coupled valence bond theory has been applied to diazomethane and the resulting orbital analysis was interpreted in terms of a chemical structure in which the central nitrogen has five covalent bonds;
This led the authors to the interesting conclusion that "Contrary to what we were all taught as undergraduates, the nitrogen atom does indeed form five covalent linkages and the availability or otherwise of d-orbitals has nothing to do with this state of affairs." | 4 | Stereochemistry |
Constructing a THz-TDS experiment using low temperature grown GaAs (LT-GaAs) based antennas requires a laser whose photon energy exceeds the band gap of the material. Ti:sapphire lasers tuned to around 800 nm, matching the energy gap in LT-GaAs, are ideal as they can generate optical pulses as short as 10 fs. These lasers are available as commercial, turnkey systems. | 7 | Physical Chemistry |
Aza Paternò−Büchi reaction involves an ππ* excited state of alkene reacting with a ground state imine. This strategy was developed by the laboratory Sivaguru and co-workers to overcome the shortcomings involving direct excitation of imines. Traditionally addition of excited imines to carbon-carbon double bonds involves making the imines as part of a carbocycle. | 0 | Organic Chemistry |
Traditionally, the Cohn process incorporating cold ethanol fractionation has been used for albumin purification. However, chromatographic methods for separation started being adopted in the early 1980s. Developments were ongoing in the time period between when Cohn fractionation started being used, in 1946, and when chromatography started being used, in 1983. In 1962, the Kistler & Nistchmann process was created which was a spinoff of the Cohn process. Chromatographic processes began to take shape in 1983. In the 1990s, the Zenalb and the CSL Albumex processes were created which incorporated chromatography with a few variations.
The general approach to using chromatography for plasma fractionation for albumin is: recovery of supernatant I, delipidation, anion exchange chromatography, cation exchange chromatography, and gel filtration chromatography.
The recovered purified material is formulated with combinations of sodium octanoate and sodium N-acetyl tryptophanate and then subjected to viral inactivation procedures, including pasteurisation at 60 °C.
This is a more efficient alternative than the Cohn process for four main reasons:
1) smooth automation and a relatively inexpensive plant was needed,
2) easier to sterilize equipment and maintain a good manufacturing environment,
3) chromatographic processes are less damaging to the albumin protein, and
4) a more successful albumin end result can be achieved.
Compared with the Cohn process, the albumin purity went up from about 95% to 98% using chromatography, and the yield increased from about 65% to 85%. Small percentage increases make a difference in regard to sensitive measurements like purity. There is one big drawback in using chromatography, which has to do with the economics of the process. Although the method was efficient from the processing aspect, acquiring the necessary equipment is a big task. Large machinery is necessary, and for a long time the lack of equipment availability was not conducive to its widespread use. The components are more readily available now but it is still a work in progress and will possibly be ready in the future to help the world. | 3 | Analytical Chemistry |
Strained cyclooctenes and other activated alkenes react with tetrazines in an inverse electron-demand Diels-Alder followed by a retro [4+2] cycloaddition (see figure). Like the other reactions of the trans-cyclooctene, ring strain release is a driving force for this reaction. Thus, three-membered and four-membered cycloalkenes, due to their high ring strain, make ideal alkene substrates.
Similar to other [4+2] cycloadditions, electron-donating substituents on the dienophile and electron-withdrawing substituents on the diene accelerate the inverse-demand Diels-Alder. The diene, the tetrazine, by virtue of having the additional nitrogens, is a good diene for this reaction. The dienophile, the activated alkene, can often be attached to electron-donating alkyl groups on target molecules, thus making the dienophile more suitable for the reaction. | 0 | Organic Chemistry |
After the electrophoresis is complete, the molecules in the gel can be stained to make them visible. DNA may be visualized using ethidium bromide which, when intercalated into DNA, fluoresce under ultraviolet light, while protein may be visualised using silver stain or Coomassie brilliant blue dye. Other methods may also be used to visualize the separation of the mixture's components on the gel. If the molecules to be separated contain radioactivity, for example in a DNA sequencing gel, an autoradiogram can be recorded of the gel. Photographs can be taken of gels, often using a Gel Doc system. Gels are then commonly labelled for presentation and scientific records on the popular figure-creation website, [https://sciugo.com SciUGo]. | 1 | Biochemistry |
In organic chemistry, nitroso refers to a functional group in which the nitric oxide () group is attached to an organic moiety. As such, various nitroso groups can be categorized as C-nitroso compounds (e.g., nitrosoalkanes; ), S-nitroso compounds (nitrosothiols; ), N-nitroso compounds (e.g., nitrosamines, ), and O-nitroso compounds (alkyl nitrites; ). | 0 | Organic Chemistry |
Knowledge of herbivory in geological time comes from three sources: fossilized plants, which may preserve evidence of defense (such as spines) or herbivory-related damage; the observation of plant debris in fossilised animal feces; and the structure of herbivore mouthparts.
Long thought to be a Mesozoic phenomenon, evidence for herbivory is found almost as soon as fossils can show it. As previously discussed, the first land plants emerged around 450 million years ago; however, herbivory, and therefore the need for plant defenses, undoubtedly evolved among aquatic organisms in ancient lakes and oceans. Within 20 million years of the first fossils of sporangia and stems towards the close of the Silurian, around , there is evidence that plants were being consumed. Animals fed on the spores of early Devonian plants, and the Rhynie chert also provides evidence that organisms fed on plants using a "pierce and suck" technique. Many plants of this time are preserved with spine-like enations, which may have performed a defensive role before being co-opted to develop into leaves.
During the ensuing 75 million years, plants evolved a range of more complex organs – from roots to seeds. There was a gap of 50 to 100 million years between each organ's evolution and its being eaten. Hole feeding and skeletonization are recorded in the early Permian, with surface fluid feeding evolving by the end of that period. | 1 | Biochemistry |
Real material systems always incorporate disorder. Examples are structural defects in the lattice or disorder due to variations of the chemical composition. Their treatment is extremely challenging for microscopic theories due to the lack of detailed knowledge about perturbations of the ideal structure. Thus, the influence of the extrinsic effects on the PL is usually addressed phenomenologically. In experiments, disorder can lead to localization of carriers and hence drastically increase the photoluminescence life times as localized carriers cannot as easily find nonradiative recombination centers as can free ones.
Researchers from the King Abdullah University of Science and Technology (KAUST) have studied the photoinduced entropy (i.e. thermodynamic disorder) of InGaN/GaN p-i-n double-heterostructure and AlGaN nanowires using temperature-dependent photoluminescence. They defined the photoinduced entropy as a thermodynamic quantity that represents the unavailability of a system's energy for conversion into useful work due to carrier recombination and photon emission. They have also related the change in entropy generation to the change in photocarrier dynamics in the nanowire active regions using results from time-resolved photoluminescence study. They hypothesized that the amount of generated disorder in the InGaN layers eventually increases as the temperature approaches room temperature because of the thermal activation of surface states, while an insignificant increase was observed in AlGaN nanowires, indicating lower degrees of disorder-induced uncertainty in the wider bandgap semiconductor. To study the photoinduced entropy, the scientists have developed a mathematical model that considers the net energy exchange resulting from photoexcitation and photoluminescence. | 7 | Physical Chemistry |
The family of long non-coding RNAs includes a variety of different kinds of RNA, including, but not limited to, circular RNA (circRNA), nuclear lncRNA, long intergenic non-coding RNA, and enhancer RNA. The development of next-generation sequencing has made the study of lncRNA more accessible (because lncRNA is not very common in the cell relative to other types of RNA).
Editing and modifications to lncRNA have demonstrated to result in changes in RNA expression and rate of mutation. 5-methylcytosine (mC), N-methyladenosine (mA), and pseudouridine are the three most common and most studied modifications occurring in lncRNA. Modifications to the nucleotide structure are likely to impact the structure of lncRNAs and modulate their overall function. The study of the reversibility of these modifications is an active area of research. These modifications impact a variety of different qualities including the lncRNA's function and the initiation of translation. Modifications to lncRNAs have been demonstrated to impact where they localize within the cell and while complicated structures, such as the crucifix of tRNA, are not typically found in lncRNA, modifications may alter their structure and impact the overall function and pathway the lncRNA takes. | 1 | Biochemistry |
The minimum temperature and maximum density of a cloud in a magneto-optical trap is limited by the spontaneously emitted photon in cooling each cycle. While the asymmetry in atom excitation gives cooling and trapping forces, the emission of the spontaneously emitted photon is in a random direction, and therefore contributes to a heating of the atom. Of the two ħk kicks the atom receives in each cooling cycle, the first cools, and the second heats: a simple description of laser cooling which enables us to calculate a point at which these two effects reach equilibrium, and therefore define a lower temperature limit, known as the Doppler cooling limit.
The density is also limited by the spontaneously emitted photon. As the density of the cloud increases, the chance that the spontaneously emitted photon will leave the cloud without interacting with any further atoms tends to zero. The absorption, by a neighboring atom, of a spontaneously emitted photon gives a 2ħk momentum kick between the emitting and absorbing atom which can be seen as a repulsive force, similar to coulomb repulsion, which limits the maximum density of the cloud.
As of 2022 the method has been demonstrated to work up to triatomic molecules. | 7 | Physical Chemistry |
The compound is used as a calibrant in gas chromatography when the analytical technique uses mass spectrometry as a detector to identify and quantify chemical compounds in gases or liquids. When undergoing ionization in the mass spectrometer, the compound decomposes in a repeatable pattern to form fragments of specific masses, which can be used to tune the mass response and accuracy of the mass spectrometer. Most commonly used ions are those with approximate mass of 69, 131, 219, 414 and 502 atomic mass units. | 2 | Environmental Chemistry |
Real-time PCR is carried out in a thermal cycler with the capacity to illuminate each sample with a beam of light of at least one specified wavelength and detect the fluorescence emitted by the excited fluorophore. The thermal cycler is also able to rapidly heat and chill samples, thereby taking advantage of the physicochemical properties of the nucleic acids and DNA polymerase.
The PCR process generally consists of a series of temperature changes that are repeated 25–50 times. These cycles normally consist of three stages: the first, at around 95 °C, allows the separation of the nucleic acid's double chain; the second, at a temperature of around 50–60 °C, allows the binding of the primers with the DNA template; the third, at between 68 and 72 °C, facilitates the polymerization carried out by the DNA polymerase. Due to the small size of the fragments the last step is usually omitted in this type of PCR as the enzyme is able to replicate the DNA amplicon during the change between the alignment stage and the denaturing stage. In addition, in four-step PCR the fluorescence is measured during short temperature phases lasting only a few seconds in each cycle, with a temperature of, for example, 80 °C, in order to reduce the signal caused by the presence of primer dimers when a non-specific dye is used. The temperatures and the timings used for each cycle depend on a wide variety of parameters, such as: the enzyme used to synthesize the DNA, the concentration of divalent ions and deoxyribonucleotide triphosphates (dNTPs) in the reaction and the bonding temperature of the primers. | 1 | Biochemistry |
The steam digester or bone digester (also known as Papin’s digester) is a high-pressure cooker invented by French physicist Denis Papin in 1679. It is a device for extracting fats from bones in a high-pressure steam environment, which also renders them brittle enough to be easily ground into bone meal. It is the forerunner of the autoclave and the domestic pressure cooker.
The steam-release valve, which was invented for Papin's digester following various explosions of the earlier models, inspired the development of the piston-and-cylinder steam engine. | 7 | Physical Chemistry |
Fumaric acid was first prepared from succinic acid. A traditional synthesis involves oxidation of furfural (from the processing of maize) using chlorate in the presence of a vanadium-based catalyst. | 1 | Biochemistry |
The degree of inactivation by ultraviolet radiation is directly related to the UV dose applied to the water. The dosage, a product of UV light intensity and exposure time, is usually measured in microjoules per square centimeter, or equivalently as microwatt seconds per square centimeter (μW·s/cm) = 10 mW·s/m = 0.01 W·s/m, the latter might be better, giving two-digit values for the ones in this article-->. Dosages for a 90% kill of most bacteria and viruses range between 2,000 and 8,000 μW·s/cm. Larger parasites such as Cryptosporidium require a lower dose for inactivation. As a result, US EPA has accepted UV disinfection as a method for drinking water plants to obtain Cryptosporidium, Giardia or virus inactivation credits. For example, for a 90% reduction of Cryptosporidium, a minimum dose of 2,500 μW·s/cm is required based on EPA's 2006 guidance manual. | 5 | Photochemistry |
The evaluation of the performance cannot be considered complete without considering the limit of detection, the range of linear response and the signal reproducibility. EI is known as a low-efficiency ionization technique. Because less than 1/10 000 of the gas-phase sample molecules are ionized, impressive detection limits cannot be expected. However, the efficient interfacing mechanism of this interface allows picogram-level detection limit in selected ion monitoring (SIM) for most substances. On the other hand, soft ionization techniques such as ESI are, in some cases, far more efficient but generate fewer fragment ions. The cost of this attitude is paid in terms of structural information so that a second analyzer to generate MS/MS spectra is an obligation. A typical EI spectrum, in general, has extensive structural information, and a cheaper, single-stage mass spectrometer might be sufficient for analyte characterization or identification. As a rule of the thumb, nanogram-level sensitivity is obtained in full-scan mode for most substances. Linearity and reproducibility are two point of strength of the interface. Up to four orders of magnitude linearity with RSD lower than 10% are common values in many applications. | 3 | Analytical Chemistry |
A refrigeration cycle, also known as heat pump, is a thermodynamic cycle that allows the removal of heat from a low temperature heat source and the rejection of heat into a high temperature heat source, thanks to mechanical power consumption. Traditional refrigeration cycles are subcritical, with the high pressure side (where heat rejection occurs) below the critical pressure.
Innovative transcritical refrigeration cycles, instead, should use a working fluid whose critical temperature is around the ambient temperature. For this reason, carbon dioxide is chosen due to its favourable critical conditions. In fact, the critical point of carbon dioxide is 31°C, reasonably in between the hot source and cold source of traditional refrigeration applications, thus suitable for a transcritical applications.
In transcritical refrigeration cycles the heat is dissipated through a gas cooler instead of a desuperheater and a condenser like in subcritical cycles. This limits the plant components, plant complexity and costs of the power block.
The advantages of using supercritical carbon dioxide as working fluid, instead of traditional refrigerant fluids (like HFC of HFO), in refrigeration cycles is represented both by economic aspects and environmental ones. The cost of carbon dioxide is two order of magnitude lower than the ones of the average refrigerant working fluid and the environmental impact of carbon dioxide is very limited (with a GWP of 1 and an ODP of 0), the fluid is not reactive nor significantly toxic. No other working fluids for refrigeration is able to reach the same environmental favourable characteristics of carbon dioxide. | 7 | Physical Chemistry |
HIV, the retrovirus that causes AIDS in humans, produces a single primary RNA transcript, which is alternatively spliced in multiple ways to produce over 40 different mRNAs. Equilibrium among differentially spliced transcripts provides multiple mRNAs encoding different products that are required for viral multiplication. One of the differentially spliced transcripts contains the tat gene, in which exon 2 is a cassette exon that may be skipped or included. The inclusion of tat exon 2 in the RNA is regulated by competition between the splicing repressor hnRNP A1 and the SR protein SC35. Within exon 2 an exonic splicing silencer sequence (ESS) and an exonic splicing enhancer sequence (ESE) overlap. If A1 repressor protein binds to the ESS, it initiates cooperative binding of multiple A1 molecules, extending into the 5’ donor site upstream of exon 2 and preventing the binding of the core splicing factor U2AF35 to the polypyrimidine tract. If SC35 binds to the ESE, it prevents A1 binding and maintains the 5’ donor site in an accessible state for assembly of the spliceosome. Competition between the activator and repressor ensures that both mRNA types (with and without exon 2) are produced. | 1 | Biochemistry |
More recently, slightly elevated serum GGT has also been found to correlate with cardiovascular diseases and is under active investigation as a cardiovascular risk marker. GGT in fact accumulates in atherosclerotic plaques, suggesting a potential role in pathogenesis of cardiovascular diseases, and circulates in blood in the form of distinct protein aggregates, some of which appear to be related to specific pathologies such as metabolic syndrome, alcohol addiction and chronic liver disease.
Elevated levels of GGT can also be due to congestive heart failure. | 1 | Biochemistry |
The term geochemistry was first used by the Swiss-German chemist Christian Friedrich Schönbein in 1838: "a comparative geochemistry ought to be launched, before geognosy can become geology, and before the mystery of the genesis of our planets and their inorganic matter may be revealed." However, for the rest of the century the more common term was "chemical geology", and there was little contact between geologists and chemists.
Geochemistry emerged as a separate discipline after major laboratories were established, starting with the United States Geological Survey (USGS) in 1884, which began systematic surveys of the chemistry of rocks and minerals. The chief USGS chemist, Frank Wigglesworth Clarke, noted that the elements generally decrease in abundance as their atomic weights increase, and summarized the work on elemental abundance in The Data of Geochemistry.
The composition of meteorites was investigated and compared to terrestrial rocks as early as 1850. In 1901, Oliver C. Farrington hypothesised that, although there were differences, the relative abundances should still be the same. This was the beginnings of the field of cosmochemistry and has contributed much of what we know about the formation of the Earth and the Solar System.
In the early 20th century, Max von Laue and William L. Bragg showed that X-ray scattering could be used to determine the structures of crystals. In the 1920s and 1930s, Victor Goldschmidt and associates at the University of Oslo applied these methods to many common minerals and formulated a set of rules for how elements are grouped. Goldschmidt published this work in the series Geochemische Verteilungsgesetze der Elemente [Geochemical Laws of the Distribution of Elements].
The research of Manfred Schidlowski from the 1960s to around the year 2002 was concerned with the biochemistry of the Early Earth with a focus on isotope-biogeochemistry and the evidence of the earliest life processes in Precambrian. | 9 | Geochemistry |
An increasingly popular method of cleaning windows is the "water-fed pole" system. Instead of washing windows with conventional detergent, they are scrubbed with purified water, typically containing less than 10 ppm dissolved solids, using a brush on the end of a pole wielded from ground level. RO is commonly used to purify the water. | 3 | Analytical Chemistry |
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