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The sunken Colorado pan is square, 0.92 m (3 ft) on a side and 0.46 m (18 in.) deep and made of unpainted galvanized iron. As the name suggests, it is buried in the ground to within about 5 cm (2 in.) of its rim. Evaporation from a Sunken Colorado Pan can be compared with a Class A pan using conversion constants. The pan coefficient, on an annual basis, is about 0.8. | 1 | Applied and Interdisciplinary Chemistry |
The photopigments used to carry out anaerobic photosynthesis are similar to chlorophyll but differ in molecular detail and peak wavelength of light absorbed. Bacteriochlorophylls a through g absorb electromagnetic radiation maximally in the near-infrared within their natural membrane milieu. This differs from chlorophyll a, the predominant plant and cyanobacteria pigment, which has peak absorption wavelength approximately 100 nanometers shorter (in the red portion of the visible spectrum). | 0 | Theoretical and Fundamental Chemistry |
Mid-infrared (MIR) spectroscopy probes fundamental molecular vibrations, which arise in the spectral range 2,500-25,000 nm. Commercial imaging implementations in the MIR region employ hyperspectral imagers or Fourier Transform Infrared (FT-IR) interferometers, depending on the application. The MIR absorption bands tend to be relatively narrow and well-resolved; direct spectral interpretation is often possible by an experienced spectroscopist. MIR spectroscopy can distinguish subtle changes in chemistry and structure, and is often used for the identification of unknown materials. The absorptions in this spectral range are relatively strong; for this reason, sample presentation is important to limit the amount of material interacting with the incoming radiation in the MIR region. Data can be collected in reflectance, transmission, or emission mode. Water is a very strong absorber of MIR radiation and wet samples often require advanced sampling procedures (such as attenuated total reflectance). Commercial instruments include point and line mapping, and imaging. Mid-infrared chemical imaging can also be performed with nanometer level spatial resolution using atomic force microscope based infrared spectroscopy (AFM-IR). Hyperspectral imaging of the entire bandwidth of the mid-infrared can be achieved within seconds using ultrashort mid-infrared pulses.
For types of MIR microscope, see Microscopy#Infrared microscopy.
Atmospheric windows in the infrared spectrum are also employed to perform chemical imaging remotely. In these spectral regions the atmospheric gases (mainly water and CO) present low absorption and allow infrared viewing over kilometer distances. Target molecules can then be viewed using the selective absorption/emission processes described above. An example of the chemical imaging of a simultaneous release of SF and NH is shown in the image. | 0 | Theoretical and Fundamental Chemistry |
A chemical reaction may undergo different reaction mechanisms at different temperatures.
In this case, a Van t Hoff plot with two or more linear fits may be exploited. Each linear fit has a different slope and intercept, which indicates different changes in enthalpy and entropy for each distinct mechanisms. The Van t Hoff plot can be used to find the enthalpy and entropy change for each mechanism and the favored mechanism under different temperatures.
In the example figure, the reaction undergoes mechanism 1 at high temperature and mechanism 2 at low temperature. | 0 | Theoretical and Fundamental Chemistry |
The milk fat globule is surrounded by a phospholipid trilayer containing associated proteins, carbohydrates, and lipids derived primarily from the membrane of the secreting mammary epithelial cell (lactocyte). This trilayer is collectively known as MFGM. While MFGM makes up only an estimated 2% to 6% of the total milk fat globule, it is an especially rich phospholipid source, accounting for the majority of total milk phospholipids. In contrast, the inner core of the milk fat globule is composed predominantly of triacylglycerols.
The MFGM structure is complex and comprises a variety of phospholipids, glycolipids, proteins, and glycoproteins, along with cholesterol and other lipids. Specific lipids and proteins are localized to different layers of the membrane, with carbohydrate chains of glycoproteins and glycolipids directed toward the outer surface of the milk fat globule; the lipid-to-protein weight ratio in MFGM is approximately 1:1.
However, the nutritional significance of these components is defined not only by their structure or macronutrient category, but also by the physiological role that each nutrient serves. As a quantitatively minor presence within milk, MFGM likely contributes little to energy production, but its constituents may confer structural and functional benefits. Many of these nutrients are known to play important functional roles within the gut, brain, and elsewhere in the body; the functions of other components are still being elucidated. | 1 | Applied and Interdisciplinary Chemistry |
Lilleby smelteverk was a smeltmill located in Lilleby, Trondheim, Sør-Trøndelag county, Norway, next to City Lade. It is well known for having produced the world's cleanest ferrosilicon (an alloy that contains iron and silicon) for NASA. Shut down in December 20th, 2002, the production moved to Mo I Rana.
The building is demolished. | 1 | Applied and Interdisciplinary Chemistry |
One possible model for fusion pore formation is the lipid-line pore theory. In this model, once the membranes have been brought into sufficiently close proximity via the "zipper" mechanism of the SNARE complex, membrane fusion occurs spontaneously. It has been shown that when the two membranes are brought within a critical distance, it is possible for hydrophilic lipid headgroups of one membrane to merge with the opposing membrane. In the lipid-lined fusion pore model, the SNARE complex acts as a scaffold, pulling on the membrane, causing both membranes to pucker so they may reach the critical fusion distance. As the two membranes begin to fuse, a lipid-lined stalk is produced, expanding radially outward as fusion proceeds.
While a lipid-lined pore is possible and can achieve all the same properties observed in early pore formation, sufficient data does not exist to prove it is the sole method of formation. There is not currently a proposed mechanism on inter-cellular regulation for fluctuation of lipid-lined pores, and they would have a substantially more difficult time producing effects such as the "kiss-and-run" when compared with their protein-lined counterparts. Lipid-lined pores effectiveness would also be highly dependent on the composition of both membranes, and its success or failure could vary wildly with changes in elasticity and rigidity. | 1 | Applied and Interdisciplinary Chemistry |
In some centers, the nuclear medicine scans can be superimposed, using software or hybrid cameras, on images from modalities such as CT or MRI to highlight the part of the body in which the radiopharmaceutical is concentrated. This practice is often referred to as image fusion or co-registration, for example SPECT/CT and PET/CT. The fusion imaging technique in nuclear medicine provides information about the anatomy and function, which would otherwise be unavailable or would require a more invasive procedure or surgery. | 1 | Applied and Interdisciplinary Chemistry |
Diffusion-prepared pseudocontinuous ASL (DP-pCASL) is a more recent ASL variant sequence that magnetically labels water molecules and measures their movement across the blood-brain barrier complex, which allows for the calculation of the water exchange rate (kw). kw is used as a surrogate for BBB function and permeability. Water exchange across the BBB is mediated by a number of processes, including passive diffusion, active co-transport through the endothelial membrane, and predominantly by facilitated diffusion through the dedicated water channel aquaporin-4 (AQP4). Several studies have investigated the use of DP-pCASL in cerebrovascular diseases, including acute ischemic stroke, CADASIL, hereditary cerebral small vessel disease as well as in animal models. | 0 | Theoretical and Fundamental Chemistry |
Botrytis–induced kinase 1 (BIK1) is a membrane-anchored enzyme in plants. It is a kinase that provides resistance to necrotrophic and biotrophic pathogens. As its name suggests, BIK1 is only active after being induced by Botrytis infection. When Botrytis cinerea is present, the BIK1 gene is transcribed so that the kinase is present to defend the cell. BIK1 functions to regulate the amount of salicylic acid (SA) present in the cell. When Botrytis cinerea or Alternaria brassicicola or any other necrotrophic pathogen is present, BIK1 is transcribed to regulate the pathogen response mechanisms. When BIK1 is present, SA levels decrease, allowing the nectrotrophic response to take place. When nectrotrophic pathogens are not present, BIK1 is not transcribed and SA levels increase, limiting the necrotrophic resistance pathway. Only the pathogenic defense response that is initiated by BIK1 is dependent on SA levels. Non-pathogenic cellular functions occur independently. In terms of non-pathogenic cellular functions, BIK1 is described as a critical component of ET signaling and PAMP-triggered immunity to pathogens. | 1 | Applied and Interdisciplinary Chemistry |
This is due to the fact that as the fuel expands on heating, the core of the pellet expands more than the rim. Because of the thermal stress thus formed the fuel cracks, the cracks tend to go from the center to the edge in a star shaped pattern. A PhD thesis on the subject has been published by a student at the Royal Institute of Technology in Stockholm (Sweden).
The cracking of the fuel has an effect on the release of radioactivity from fuel both under accident conditions and also when the spent fuel is used as the final disposal form. The cracking increases the surface area of the fuel which increases the rate at which fission products can leave the fuel.
The temperature of the fuel varies as a function of the distance from the center to the rim. At distance x from the center the temperature (T) is described by the equation where ρ is the power density (W m) and K is the thermal conductivity.
T = T + ρ (r² – x²) (4 K)
To explain this for a series of fuel pellets being used with a rim temperature of 200 °C (typical for a BWR) with different diameters and power densities of 250 Wm have been modeled using the above equation. These fuel pellets are rather large; it is normal to use oxide pellets which are about 10 mm in diameter.
To show the effects of different power densities on the centerline temperatures two graphs for 20 mm pellets at different power levels are shown below. It is clear that for all pellets (and most true of uranium dioxide) that for a given sized pellet that a limit must be set on the power density. It is likely that the maths used for these calculations would be used to explain how electrical fuses function and also it could be used to predict the centerline temperature in any system where heat is released throughout a cylinder shaped object. | 0 | Theoretical and Fundamental Chemistry |
The experiment itself involves having a radioactive positron source (often Na) situated near the analyte. Positrons are emitted near-simultaneously with gamma rays. These gamma rays are detected by a nearby scintillator. | 0 | Theoretical and Fundamental Chemistry |
The OCP participates in key protein–protein interactions that are critical to its photoprotective function. The activated OCP form binds to allophycocyanin in the core of the phycobilisome and initiates the OCP-dependent photoprotective quenching mechanism. Another protein, the fluorescence recovery protein (FRP), interacts with the CTD in OCP and catalyzes the reaction which reverts it back to the OCP form. Because OCP cannot bind to the phycobilisome antenna, FRP effectively can detach OCP from the antenna and restore full light-harvesting capacity. | 0 | Theoretical and Fundamental Chemistry |
James Watt's research in pneumatic chemistry involved the use of inflammable (H) and dephlogisticated (O) airs to create water. In 1783, James Watt showed that water was composed of inflammable and dephlogisticated airs, and that the masses of gases before combustion were exactly equal to the mass of water after combustion. Until this point, water was viewed as a fundamental element rather than a compound. James Watt also sought to explore the use of different "factitious airs" such as hydrocarbonate in medicinal treatments as "pneumatic therapy" by collaborating with Dr. Thomas Beddoes and Erasmus Darwin to treat Jessie Watt, his daughter suffering from tuberculosis, using fixed air. | 1 | Applied and Interdisciplinary Chemistry |
Davy seriously injured himself in a laboratory accident with nitrogen trichloride. French chemist Pierre Louis Dulong had first prepared this compound in 1811, and had lost two fingers and an eye in two separate explosions with it. In a letter to John Children, on 16 November 1812, Davy wrote: "It must be used with great caution. It is not safe to experiment upon a globule larger than a pins head. I have been severely wounded by a piece scarcely bigger. My sight, however, I am informed, will not be injured". Davys accident induced him to hire Michael Faraday as a co-worker, particularly for assistance with handwriting and record keeping. He had recovered from his injuries by April 1813. | 1 | Applied and Interdisciplinary Chemistry |
Companion planting was practiced in various forms by the indigenous peoples of the Americas prior to the arrival of Europeans. These peoples domesticated squash 8,000 to 10,000 years ago, then maize, then common beans, forming the Three Sisters agricultural technique. The cornstalk served as a trellis for the beans to climb, the beans fixed nitrogen, benefitting the maize, and the wide leaves of the squash plant provide ample shade for the soil keeping it moist and fertile.
Authors in classical Greece and Rome, around 2000 years ago, were aware that some plants were toxic (allelopathic) to other plants nearby. Theophrastus reported that the bay tree and the cabbage plant enfeebled grapevines. Pliny the Elder wrote that the "shade" of the walnut tree (Juglans regia) poisoned other plants.
In China, mosquito ferns (Azolla spp.) have been used for at least a thousand years as companion plants for rice crops. They host a cyanobacterium (Anabaena azollae) that fixes nitrogen from the atmosphere, and they block light from plants that would compete with the rice. | 1 | Applied and Interdisciplinary Chemistry |
One simplified example of a synexpression group is the genes cdc6, cdc3, cdc46, and swi4 in yeast, which are all co-expressed early in the G-1 stage of the cell cycle., These genes share one common cis-regulatory element, called ECB, which serves as a binding site for the MCM1 trans-acting protein. Although these genes are not spatially clustered, co-regulation seems to be achieved via this common cis and trans control mechanism. Most synexpression groups are more complicated than the ECB group in yeast, involving myriad cis and trans control elements. | 1 | Applied and Interdisciplinary Chemistry |
Antifreeze glycoproteins or AFGPs are found in Antarctic notothenioids and northern cod. They are 2.6-3.3 kD. AFGPs evolved separately in notothenioids and northern cod. In notothenioids, the AFGP gene arose from an ancestral trypsinogen-like serine protease gene.
*Type I AFP is found in winter flounder, longhorn sculpin and shorthorn sculpin. It is the best documented AFP because it was the first to have its three-dimensional structure determined. Type I AFP consists of a single, long, amphipathic alpha helix, about 3.3-4.5 kD in size. There are three faces to the 3D structure: the hydrophobic, hydrophilic, and Thr-Asx face.
**Type I-hyp AFP (where hyp stands for hyperactive) are found in several righteye flounders. It is approximately 32 kD (two 17 kD dimeric molecules). The protein was isolated from the blood plasma of winter flounder. It is considerably better at depressing freezing temperature than most fish AFPs. The ability is partially derived from its many repeats of the Type I ice-binding site.
*Type II AFPs (e.g. ) are found in sea raven, smelt and herring. They are cysteine-rich globular proteins containing five disulfide bonds. Type II AFPs likely evolved from calcium dependent (c-type) lectins. Sea ravens, smelt, and herring are quite divergent lineages of teleost. If the AFP gene were present in the most recent common ancestor of these lineages, it is peculiar that the gene is scattered throughout those lineages, present in some orders and absent in others. It has been suggested that lateral gene transfer could be attributed to this discrepancy, such that the smelt acquired the type II AFP gene from the herring.
*Type III AFPs are found in Antarctic eelpout. They exhibit similar overall hydrophobicity at ice binding surfaces to type I AFPs. They are approximately 6kD in size. Type III AFPs likely evolved from a sialic acid synthase (SAS) gene present in Antarctic eelpout. Through a gene duplication event, this gene—which has been shown to exhibit some ice-binding activity of its own—evolved into an effective AFP gene by loss of the N-terminal part.
*Type IV AFPs () are found in longhorn sculpins. They are alpha helical proteins rich in glutamate and glutamine. This protein is approximately 12KDa in size and consists of a 4-helix bundle. Its only posttranslational modification is a pyroglutamate residue, a cyclized glutamine residue at its N-terminus. | 1 | Applied and Interdisciplinary Chemistry |
RECODE is a database of "programmed" frameshifts, bypassing and codon redefinition used for gene expression. | 1 | Applied and Interdisciplinary Chemistry |
Methods to study interpolymer complexes could be classified into:
:(1) approaches to demonstrate the fact of the complex formation and to determine the composition of IPCs in solutions;
:(2) approaches to study the structure of IPCs formed;
:(3) methods to characterize IPCs in solid state. | 0 | Theoretical and Fundamental Chemistry |
The term "ultra-deep" can sometimes also refer to higher coverage (>100-fold), which allows for detection of sequence variants in mixed populations. In the extreme, error-corrected sequencing approaches such as Maximum-Depth Sequencing can make it so that coverage of a given region approaches the throughput of a sequencing machine, allowing coverages of >10^8. | 1 | Applied and Interdisciplinary Chemistry |
The mode of action through which chromium aided in the regulation of blood glucose levels is poorly understood. Recently, it has been suggested that chromium interacts with the low-molecular weight chromium (LMWCr) binding substance to potentiate the action of insulin. LMWCr has a molecular weight of 1500, and is composed solely of the four amino acid residues of glycine, cysteine, aspartic acid and glutamate. It is a naturally occurring oligopeptide that has been purified from many sources: rabbit liver, porcine kidney and kidney powder, bovine liver, colostrum, dog, rat and mouse liver. Widely distributed in mammals, LMWCr is capable of tightly binding four chromic ions. The binding constant of this oligopeptide for chromium ions is very large, (K ≈ 10 M), suggesting it is strong and tightly binding. LMWCr exists in its inactive or apo form within the cytosol and nucleus of insulin-sensitive cells.
When insulin concentrations within the blood rise, insulin binds to the external subunit of the insulin-receptor proteins, and induces a conformational change. This change results in the autophosphorylation of the tyrosine residue located on the internal ß-subunit of the receptor, thereby activating the receptor's kinase activity. An increase in insulin levels also signals for the movement of transferrin receptors from the vesicles of insulin-sensitive cells to the plasma membrane. Transferrin, the protein responsible for the movement of chromium through the body, binds to these receptors, and becomes internalized via the process of endocytosis. The pH of these vesicles containing the transferrin molecules is then decreased (resulting in increased acidity) by the action of ATP-driven proton pumps, and as a consequence, chromium is released from the transferrin. The free chromium within the cell is then sequestered by LMWCr. The binding of LMWCr to chromium converts it into its holo or active form, and once activated, LMWCr binds to the insulin receptors and aids in maintaining and amplifying the tyrosine kinase activity of the insulin receptors. In one experiment that was performed on bovine liver LMWCr, it was determined that LMWCr could amplify the activity of protein kinase receptors by up to seven-fold in the presence of insulin. Furthermore, evidence suggests that the action of LMWCr is most effective when it is bound to four chromic ions.
When the insulin signaling pathway is turned off, the insulin receptors on the plasma membrane relax and become inactivated. The holo-LMWCr is expelled from the cell and ultimately excreted from the body via urine. LMWCr cannot be converted back into its inactive from due to the high binding affinity of this oligopeptide for its chromium ions. As of currently, the mechanism through which apo-LMWCr is replaced within the body is unknown. | 1 | Applied and Interdisciplinary Chemistry |
Temporary tattoo-based sweat diagnostic tools have been demonstrated by Dr. Joseph Wang's group from University of California, San Diego. Their work includes sweat diagnostics for sodium, lactate, ammonium, pH and biofuel opportunities. | 1 | Applied and Interdisciplinary Chemistry |
In medicine, oxygen saturation refers to oxygenation, or when oxygen molecules () enter the tissues of the body. In this case blood is oxygenated in the lungs, where oxygen molecules travel from the air into the blood. Oxygen saturation (() sats) measures the percentage of hemoglobin binding sites in the bloodstream occupied by oxygen. Fish, invertebrates, plants, and aerobic bacteria all require oxygen. | 0 | Theoretical and Fundamental Chemistry |
Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal since 1893 for use as an abrasive. Grains of silicon carbide can be bonded together by sintering to form very hard ceramics that are widely used in applications requiring high endurance, such as car brakes, car clutches and ceramic plates in bulletproof vests. Large single crystals of silicon carbide can be grown by the Lely method and they can be cut into gems known as synthetic moissanite.
Electronic applications of silicon carbide such as light-emitting diodes (LEDs) and detectors in early radios were first demonstrated around 1907. SiC is used in semiconductor electronics devices that operate at high temperatures or high voltages, or both. | 1 | Applied and Interdisciplinary Chemistry |
Solomon joined British Australian Lead Manufacturers Pty Ltd (BALM, which later became Dulux Australia Ltd) as a trainee chemist in 1946 at the age of 16. It was here that he developed his lifelong interest in polymers, and made important observations that the current theories on polymers did not match with what was actually happening in the industrial processes.
Solomon's strong interest in polymer research drew him to join CSIRO as a senior research scientist in the Division of Applied Mineralogy in 1963. In 1970 Solomon transferred to the Division of Applied Chemistry where he established the Polymer Research Group, before going on to become chief of the Division of Applied Organic Chemistry during a reorganisation in 1974, a position he held for the next 17 years.
In 1990 he accepted an invitation to become the ICI Australia – Masson Professor and head of the School of Chemistry at the University of Melbourne. Here he started the Polymer Science Group, his third internationally acclaimed polymer research group. After ‘retirement’ in 1995 David took up the position of honorary professorial fellow in the Department of Chemical and Biomolecular Engineering at the university, moving the Polymer Science Group, to which he still acts as senior advisor. In 2015 he was awarded the title of professor emeritus at the University of Melbourne.
Solomon is often referred to as the father of polymer research in Australia, having established three internationally acclaimed polymer research groups in industry (Dulux, 1960), in Australia's peak scientific research organisation, CSIRO (1970) and at the University of Melbourne (1990). | 0 | Theoretical and Fundamental Chemistry |
Nanoparticles often develop or receive coatings of other substances, distinct from both the particles material and of the surrounding medium. Even when only a single molecule thick, these coatings can radically change the particles properties, such as and chemical reactivity, catalytic activity, and stability in suspension. | 0 | Theoretical and Fundamental Chemistry |
After the on-line questions, students will take a test about what they have learned while solving the on-line questions. First grade students in high school take this test. The questions are based on basic chemistry. The test can determine how much the students understand basic chemistry. 80 well-ranked students can join the Summer school 1. About one organic chemistry questions appear in the test. All the tests are held in Konkuk University. | 1 | Applied and Interdisciplinary Chemistry |
A Bioelectrochemical reactor is a type of bioreactor where bioelectrochemical processes are used to degrade/produce organic materials using microorganisms. This bioreactor has two compartments: The anode, where the oxidation reaction takes place; And the cathode, where the reduction occurs. At these sites, electrons are passed to and from microbes to power reduction of protons, breakdown of organic waste, or other desired processes. They are used in microbial electrosynthesis, environmental remediation, and electrochemical energy conversion. Examples of bioelectrochemical reactors include microbial electrolysis cells, microbial fuel cells, enzymatic biofuel cells, electrolysis cells, microbial electrosynthesis cells, and biobatteries. | 1 | Applied and Interdisciplinary Chemistry |
Harrison has been married to Tomas Kirchhausen, who is currently a Professor at Harvard Medical School, since 2013. They first met in 1978 at a small dinner hosted by Ada Yonath. In the fall of 1979, Tom moved to Cambridge, MA, to work with Harrison, and the two have been in a relationship ever since. | 1 | Applied and Interdisciplinary Chemistry |
Methylene blue is widely used as a redox indicator in analytical chemistry. Solutions of this substance are blue when in an oxidizing environment, but will turn colorless if exposed to a reducing agent. The redox properties can be seen in a classical demonstration of chemical kinetics in general chemistry, the "blue bottle" experiment. Typically, a solution is made of glucose (dextrose), methylene blue, and sodium hydroxide. Upon shaking the bottle, oxygen oxidizes methylene blue, and the solution turns blue. The dextrose will gradually reduce the methylene blue to its colorless, reduced form. Hence, when the dissolved dextrose is entirely consumed, the solution will turn blue again. The redox midpoint potential E' is +0.01 V. | 0 | Theoretical and Fundamental Chemistry |
The algorithm contains a caveat, which concerns rare cases of transition-metal complexes with a type of ligand that is reversibly bonded as a Lewis acid (as an acceptor of the electron pair from the transition metal); termed a "Z-type" ligand in Green's covalent bond classification method. The caveat originates from the simplifying use of electronegativity instead of the MO-based electron allegiance to decide the ionic sign. One early example is the complex with sulfur dioxide () as the reversibly-bonded acceptor ligand (released upon heating). The Rh−S bond is therefore extrapolated ionic against Allen electronegativities of rhodium and sulfur, yielding oxidation state +1 for rhodium: | 0 | Theoretical and Fundamental Chemistry |
In quantum mechanics, a triplet state, or spin triplet, is the quantum state of an object such as an electron, atom, or molecule, having a quantum spin S = 1. It has three allowed values of the spins projection along a given axis m' = −1, 0, or +1, giving the name "triplet".
Spin, in the context of quantum mechanics, is not a mechanical rotation but a more abstract concept that characterizes a particle's intrinsic angular momentum. It is particularly important for systems at atomic length scales, such as individual atoms, protons, or electrons.
A triplet state occurs in cases where the spins of two unpaired electrons, each having spin s = 1/2, align to give S = 1, in contrast to the more common case of two electrons aligning oppositely to give S = 0, a spin singlet. Most molecules encountered in daily life exist in a singlet state because all of their electrons are paired, but molecular oxygen is an exception. At room temperature, O exists in a triplet state, which can only undergo a chemical reaction by making the forbidden transition into a singlet state. This makes it kinetically nonreactive despite being thermodynamically one of the strongest oxidants. Photochemical or thermal activation can bring it into the singlet state, which makes it kinetically as well as thermodynamically a very strong oxidant.
__TOC__ | 0 | Theoretical and Fundamental Chemistry |
Butyric acid reacts as a typical carboxylic acid: it can form amide, ester, anhydride, and chloride derivatives. The latter, butyryl chloride, is commonly used as the intermediate to obtain the others. | 1 | Applied and Interdisciplinary Chemistry |
The formation of a complex between a metal ion, M, and a ligand, L, is in fact usually a substitution reaction. For example, in aqueous solutions, metal ions will be present as aqua ions, so the reaction for the formation of the first complex could be written as
The equilibrium constant for this reaction is given by
[L] should be read as "the concentration of L" and likewise for the other terms in square brackets. The expression can be greatly simplified by removing those terms which are constant. The number of water molecules attached to each metal ion is constant. In dilute solutions the concentration of water is effectively constant. The expression becomes
Following this simplification a general definition can be given, for the general equilibrium
The definition can easily be extended to include any number of reagents. The reagents need not always be a metal and a ligand but can be any species which form a complex. Stability constants defined in this way, are association constants. This can lead to some confusion as pK values are dissociation constants. In general purpose computer programs it is customary to define all constants as association constants. The relationship between the two types of constant is given in association and dissociation constants. | 0 | Theoretical and Fundamental Chemistry |
If a specimen must be observed at higher magnification, it can be examined with a scanning electron microscope (SEM), or a transmission electron microscope (TEM). When equipped with an energy dispersive spectrometer (EDS), the chemical composition of the microstructural features can be determined. The ability to detect low-atomic number elements, such as carbon, oxygen, and nitrogen, depends upon the nature of the detector used. But, quantification of these elements by EDS is difficult and their minimum detectable limits are higher than when a wavelength-dispersive spectrometer (WDS) is used. But quantification of composition by EDS has improved greatly over time. The WDS system has historically had better sensitivity (ability to detect low amounts of an element) and ability to detect low-atomic weight elements, as well as better quantification of compositions, compared to EDS, but it was slower to use. Again, in recent years, the speed required to perform WDS analysis has improved substantially. Historically, EDS was used with the SEM while WDS was used with the electron microprobe analyzer (EMPA). Today, EDS and WDS is used with both the SEM and the EMPA. However, a dedicated EMPA is not as common as an SEM. | 1 | Applied and Interdisciplinary Chemistry |
Lanthanide probes are a non-invasive analytical tool commonly used for biological and chemical applications. Lanthanides are metal ions which have their 4f energy level filled and generally refer to elements cerium to lutetium in the periodic table. The fluorescence of lanthanide salts is weak because the energy absorption of the metallic ion is low; hence chelated complexes of lanthanides are most commonly used. The term chelate derives from the Greek word for “claw,” and is applied to name ligands, which attach to a metal ion with two or more donor atoms through dative bonds. The fluorescence is most intense when the metal ion has the oxidation state of 3+. Not all lanthanide metals can be used and the most common are: Sm(III), Eu(III), Tb(III), and Dy(III). | 1 | Applied and Interdisciplinary Chemistry |
Spin–lattice relaxation in the rotating frame is the mechanism by which M, the transverse component of the magnetization vector, exponentially decays towards its equilibrium value of zero, under the influence of a radio frequency (RF) field in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). It is characterized by the spin–lattice relaxation time constant in the rotating frame, T. It is named in contrast to T, the spin-lattice relaxation time.
T MRI is an alternative to conventional T and T MRI by its use of a long-duration, low-power radio frequency referred to as spin-lock (SL) pulse applied to the magnetization in the transverse plane. The magnetization is effectively spin-locked around an effective B field created by the vector sum of the applied B and any off-resonant component. The spin-locked magnetization will relax with a time constant T, which is the time it takes for the magnetic resonance signal to reach 37% (1/e) of its initial value, . Hence the relation:
, where t is the duration of the RF field. | 0 | Theoretical and Fundamental Chemistry |
Coatings can be both decorative and have other functions. A pipe carrying water for a fire suppression system can be coated with a red (for identification) anticorrosion paint. Most coatings to some extent protect the substrate, such as maintenance coatings for metals and concrete. A decorative coating can offer a particular reflective property, such as high gloss, satin, matte, or flat appearance.
A major coating application is to protect metal from corrosion. Automotive coatings are used to enhance the appearance and durability of vehicles. These include primers, basecoats, and clearcoats, primarily applied with spray guns and electrostatically.
The body and underbody of automobiles receive some form of underbody coating. Such anticorrosion coatings may use graphene in combination with water-based epoxies.
Coatings are used to seal the surface of concrete, such as seamless polymer/resin flooring, bund wall/containment lining, waterproofing and damp proofing concrete walls, and bridge decks.
Most roof coatings are designed primarily for waterproofing, though sun reflection (to reduce heating and cooling) may also be a consideration. They tend to be elastomeric to allow for movement of the roof without cracking within the coating membrane.
Wood has been a key material in construction since ancient times, so its preservation by coating has received much attention. Efforts to improve the performance of wood coatings continue.
Coatings are used to alter tribological properties and wear characteristics. These include anti-friction, wear and scuffing resistance coatings for rolling-element bearings | 1 | Applied and Interdisciplinary Chemistry |
Doubly-expanded (or naphtho-homologated) nucleobases incorporate a naphthalene spacer instead of a benzene ring, widening the base twice as much with its two-ringed structure. These structures (known as xxDNA and yyDNA) are 4.8Å wider than natural bases and were once again created as a result of Leonard's research on expanded adenine in ATP-dependent enzymes in 1984. No literature was published on these doubly-expanded bases for nearly three decades until 2013 when the first xxG was produced by Sharma, Lait, and Wetmore and incorporated along with xxA into a natural helix. Although very little research has been performed on xxDNA, xx-purine neighbours have already been shown to increase intrastrand stacking energy by up to 119% (as opposed to 62% in x-purines). xx-purine and pyrimidine interactions show an overall decrease in stacking energies, but the overall stability of duplexes including pyrimidines and xx-purines increases by 22%, more than twofold that of pyrimidines and x-purines. | 1 | Applied and Interdisciplinary Chemistry |
THz-TDS measures the electric field of a pulse and not just the power. Thus, THz-TDS measures both the amplitude and phase information of the frequency components it contains. In contrast, measuring only the power at each frequency is essentially a photon counting technique; information regarding the phase of the light is not obtained. Thus, the waveform is not uniquely determined by such a power measurement.
Even when measuring only the power reflected from a sample, the complex optical response constant of the material can be obtained. This is so because the complex nature of an optical constant is not arbitrary. The real and imaginary parts of an optical constant are related by the Kramers–Kronig relations. There is a difficulty in applying the Kramers-Kronig relations as written, because information about the sample (reflected power, for example) must be obtained at all frequencies. In practice, far separated frequency regions do not have significant influence on each other, and reasonable limiting conditions can be applied at high and low frequency, outside of the measured range.
THz-TDS, in contrast, does not require use of Kramers-Kronig relations. By measuring the electric field of a THz pulse in the time-domain, the amplitude and phase of each frequency component of the THz pulse are known (in contrast to the single piece of information known by a power measurement). Thus the real and imaginary parts of an optical constant can be known at every frequency within the usable bandwidth of a THz pulse, without need of frequencies outside the usable bandwidth or Kramers-Kronig relations. | 0 | Theoretical and Fundamental Chemistry |
Pump–probe imaging is ideal for the study and characterization of nanomaterials, such as graphene, nanocubes, nanowires, and a variety of semiconductors, due to their large susceptibilities but weak fluorescence. In particular, single-walled carbon nanotubes have been extensively studied and imaged with submicrometer resolution, providing details about carrier dynamics, photophysical, and photochemical properties. | 0 | Theoretical and Fundamental Chemistry |
In theoretical chemistry, molecular electronic transitions take place when electrons in a molecule are excited from one energy level to a higher energy level. The energy change associated with this transition provides information on the structure of the molecule and determines many of its properties, such as colour. The relationship between the energy involved in the electronic transition and the frequency of radiation is given by Planck's relation. | 0 | Theoretical and Fundamental Chemistry |
Another advantage of duplex sequencing is that it can be used in combination with the majority of NGS platforms without making significant changes to the standard protocols. | 1 | Applied and Interdisciplinary Chemistry |
Fulgurites (), commonly called "fossilized lightning", are natural tubes, clumps, or masses of sintered, vitrified, or fused soil, sand, rock, organic debris and other sediments that sometimes form when lightning discharges into ground. When composed of silica, fulgurites are classified as a variety of the mineraloid lechatelierite.
When ordinary positive polarity cloud-ground lightning charges into a grounding less than 100 volts (100 V) of potential difference may be bridged. Such current may propagate into silica-rich quartzose sand, mixed soil, clay, or other sediments, rapidly vaporizing and melting resistant materials within such a common dissipation regime. This results in the formation of generally hollow and/or vesicular, branching assemblages of glassy tubes, crusts, and clumped masses. Fulgurites have no fixed composition because their chemical composition is determined
Fulgurites are structurally similar to Lichtenberg figures, which are the branching patterns produced on surfaces of insulators during dielectric breakdown by high-voltage discharges, such as lightning. | 0 | Theoretical and Fundamental Chemistry |
In addition to reinitiation, uORFs contribute to translation initiation based on:
* The nucleotides of an uORF may code for a codon that leads to a highly structured mRNA, causing the ribosome to stall.
* cis- and trans- regulation on translation of the main protein coding sequence.
* Interactions with IRES sites. | 1 | Applied and Interdisciplinary Chemistry |
Quantasomes are particles found in the thylakoid membrane of chloroplasts in which photosynthesis takes place. They are embedded in a paracrystalline array on the surface of thylakoid discs in chloroplasts. They are composed of lipids and proteins that include various photosynthetic pigments and redox carriers. For this reason they are considered to be photosynthetic units. They occur in 2 sizes: the smaller quantasome is thought to represent the site of photosystem I, the larger to represent the site of photosystem II. | 0 | Theoretical and Fundamental Chemistry |
Generally, two kinds of reactions occur with xylenes: those involving the methyl groups and those involving the ring C–H bonds. Being benzylic and hence weakened, the C–H bonds of the methyl groups are susceptible to free-radical reactions, including halogenation to the corresponding xylene dichlorides (bis(chloromethyl)benzenes), while mono-bromination yields xylyl bromide, a tear gas agent. Oxidation and ammoxidation also target the methyl groups, affording dicarboxylic acids and the dinitriles. Electrophiles attack the aromatic ring, leading to chloro- and nitroxylenes. | 1 | Applied and Interdisciplinary Chemistry |
Solutes can have different effects on surface tension depending on the nature of the surface and the solute:
* Little or no effect, for example sugar at water|air, most organic compounds at oil/air
* Increase surface tension, most inorganic salts at water|air
* Non-monotonic change, most inorganic acids at water|air
* Decrease surface tension progressively, as with most amphiphiles, e.g., alcohols at water|air
* Decrease surface tension until certain critical concentration, and no effect afterwards: surfactants that form micelles
What complicates the effect is that a solute can exist in a different concentration at the surface of a solvent than in its bulk. This difference varies from one solute–solvent combination to another.
Gibbs isotherm states that:
* is known as surface concentration, it represents excess of solute per unit area of the surface over what would be present if the bulk concentration prevailed all the way to the surface. It has units of mol/m
* is the concentration of the substance in the bulk solution.
* is the gas constant and the temperature
Certain assumptions are taken in its deduction, therefore Gibbs isotherm can only be applied to ideal (very dilute) solutions with two components. | 0 | Theoretical and Fundamental Chemistry |
In this regulatory scheme, every current polluting facility is given or may purchase on an open market an emissions allowance for each unit of a designated pollutant it emits. Operators can then install pollution control equipment, and sell portions of their emissions allowances they no longer need for their own operations, thereby recovering some of the capital cost of their investment in such equipment. The intention is to give operators economic incentives to install pollution controls.
The first emissions trading market was established in the United States by enactment of the Clean Air Act Amendments of 1990. The overall goal of the Acid Rain Program established by the Act is to achieve significant environmental and public health benefits through reductions in emissions of sulfur dioxide (SO) and nitrogen oxides (NO), the primary causes of acid rain. To achieve this goal at the lowest cost to society, the program employs both regulatory and market based approaches for controlling air pollution. | 1 | Applied and Interdisciplinary Chemistry |
Tic56 is also a nuclear encoded protein. The preprotein its gene encodes is 527 amino acids long, weighing close to 62 thousand daltons; the mature form probably undergoes processing that trims it down to something that weighs 56 thousand daltons when it gets imported into the chloroplast. Tic56 is largely embedded inside the 1 million dalton complex.
Tic56 and Tic100 are highly conserved among land plants, but they don't resemble any protein whose function is known. Neither has any transmembrane domains. | 0 | Theoretical and Fundamental Chemistry |
All dynamic energy budget models follow the energy budget of an individual organism throughout its life cycle; by contrast,"static" energy budget models describe a specific life stage or size of an organism. The main advantage of the DEB-theory based model over most other models is its description of energy assimilation and utilization (reserve dynamics) simultaneously with decoupled processes of growth, development/ maturation, and maintenance. Under constant environmental conditions (constant food and temperature) the standard DEB model can be simplified to the von Bertalanffy (or better, Putter's ) growth model, but its mechanistic process-based setup enables incorporating fluctuating environmental conditions, as well as studying reproduction and maturation in parallel to growth.
DEB theory specifies reserves as separate from structure: these are the two state variables that contribute to physical volume, and (in combination with reproduction buffer of adults) fully define the size of an individual. Maturity (also a state variable of the model) tracks how much energy has been invested into maturation, and therefore determines the life stage of the organism relative to maturity levels at which life stage transitions (birth and puberty) occur. Dynamics of the state variables are given by ordinary differential equations which include the major processes of energy uptake and use: assimilation, mobilization, maintenance, growth, maturation, and reproduction.
* Food is transformed into reserve, which fuels all other metabolic processes. The feeding rate is proportional to the surface area; food handling time and the transformation efficiency from food to reserve are independent of food density.
* A fixed fraction (kappa) of mobilized reserve is allocated to somatic maintenance plus growth (soma), the rest on maturity maintenance plus maturation or reproduction. Maintenance has priority over other processes. Somatic maintenance is proportional to structural body volume, and maturity maintenance to maturity. Heating costs for endotherms and osmotic work (for fresh water organisms) are somatic maintenance costs that are proportional to surface area.
* Stage transitions occur if the cumulated investment into maturation exceeds threshold values. Life stages typically are: embryo, juvenile, and adult. Reserve that is allocated to reproduction is first accumulated in a buffer. The rules for converting the buffer to gametes are species-specific (e.g. spawning can be once per season).
Parameters of the model are individual specific, but similarities between individuals of the same species yield species-specific parameter estimations. DEB parameters are estimated from several types of data simultaneously. Routines for data entry and parameter estimation are available as free software package [http://www.bio.vu.nl/thb/deb/deblab/debtool/DEBtool_M/manual/index.html DEBtool] implemented in the MATLAB environment, with the process of model construction explained in a [http://www.debtheory.org/wiki/index.php?title=Add-my-pet_Introduction Wiki-style manual] . Estimated parameters are collected in the online library called the [http://www.bio.vu.nl/thb/deb/deblab/add_my_pet/index.html Add-my-pet project]. | 1 | Applied and Interdisciplinary Chemistry |
Therminol is a synthetic heat transfer fluid produced by Eastman Chemical Company.
Therminol fluids are used in a variety of applications, including:
* Hydrocarbon processing (oil and gas, refining, asphalt, gas-to-liquid, etc.)
* Alternative energy and technologies (concentrated solar power, biofuel, organic Rankine cycle, desalination, etc.)
* Plastics processing
* Chemical processing (pharmaceutical, environmental test chambers, etc.)
* Food and beverage processing
* Heat transfer system maintenance
Prior to 1997, Therminol fluids were sold in Europe under the trade names SantoTherm and GiloTherm. Since 1997, all forms of Therminol fluid have been sold with the Therminol name and extension to define its uses. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural polymers (such as proteins).
In polymer chemistry "cross-linking" usually refers to the use of cross-links to promote a change in the polymers' physical properties.
When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions, as well as other creative cross-linking methodologies.
Although the term is used to refer to the "linking of polymer chains" for both sciences, the extent of crosslinking and specificities of the crosslinking agents vary greatly. | 0 | Theoretical and Fundamental Chemistry |
Beta-2 transferrin is a carbohydrate-free (desialated) isoform of transferrin, which is almost exclusively found in the cerebrospinal fluid. It is not found in blood, mucus or tears, thus making it a specific marker of cerebrospinal fluid, applied as an assay in cases where cerebrospinal fluid leakage is suspected.
Beta-2 transferrin would also be positive in patients with perilymph fluid leaks, as it is also present in inner ear perilymph. Thus, beta-2 transferrin in otorrhea would be suggestive of either a CSF leak or a perilymph leak. | 1 | Applied and Interdisciplinary Chemistry |
Heather D. Willauer (born 1974) is an American analytical chemist and inventor working in Washington, D.C., at the United States Naval Research Laboratory (NRL). Leading a research team, Willauer has patented a method for removing dissolved carbon dioxide (CO) from seawater, in parallel with hydrogen (H) recovered by conventional water electrolysis. Willauer is also searching to improve the catalysts required to enable a continuous Fischer–Tropsch process to recombine carbon monoxide (CO) and hydrogen gases into complex hydrocarbon liquids to synthesize jet fuel for Navy aircraft.
Especially significant for the Navy is the possibility of maintaining naval air operations in remote areas without depending too much on long-distance transport of jet fuel across oceans. The Navy is also studying the feasibility of constructing on-shore facilities capable of synthesizing kerosene from hydrogen and CO, both extracted from seawater constituents. Because of the very high electrical power required by water electrolysis to produce considerable amounts of hydrogen, nuclear power plants or ocean thermal energy conversion (OTEC) are necessary to fuel the industrial installations built on-shore on remote islands close to the sea in strategic locations. | 0 | Theoretical and Fundamental Chemistry |
Depending on circumstances, various hydrological, environmental, ecological, and economic side effects can be realised by the implementation of a tidal inlet closure, including:
* change of tide (amplitude, flows) at the seaward side of the dam
* change in bar and gully topography, outside the dam
* removal of tides on the inner side of the dam
* change in groundwater level in adjoining areas
* alteration of drainage capacity for adjoining areas
* loss of fish and vegetation species
* loss of breeding and feeding areas for water birds
* rotting processes during change in vegetation and fauna
* stratification of water quality in stagnant reservoir
* accumulation of sediments in the reservoir
* impact on facilities for shipping
* impact on recreation and leisure pursuits
* change in professional occupations (fishery, navigation)
* social and cultural impacts. | 1 | Applied and Interdisciplinary Chemistry |
Tesoro was a member of several committees of the National Academy of Sciences and the National Research Council concerning toxic materials and fire safety. Other committees she was a part of include: the Fiber Society (founder/president in 1974), Sigma Xi, a Gordon Research Conference committee, the American Chemical Society, the American Association of Textile Chemists and Colorists, the American Institute of Chemists, and the American Association for the Advancement of Science. In 1963, Tesoro was awarded the Olney Medal of the American Association of Textile Chemists and Colorists. She was the recipient of the Society of Women Engineers’ Achievement Award in 1978. Additionally, Tesoro earned the American Dyestuff Reporter Award. | 0 | Theoretical and Fundamental Chemistry |
Grignard reagents react with a variety of carbonyl derivatives.
The most common application of Grignard reagents is the alkylation of aldehydes and ketones, i.e. the Grignard reaction:
Note that the acetal functional group (a protected carbonyl) does not react.
Such reactions usually involve an aqueous acidic workup, though this step is rarely shown in reaction schemes. In cases where the Grignard reagent is adding to an aldehyde or a prochiral ketone, the Felkin-Anh model or Cram's Rule can usually predict which stereoisomer will be formed. With easily deprotonated 1,3-diketones and related acidic substrates, the Grignard reagent RMgX functions merely as a base, giving the enolate anion and liberating the alkane RH.
Grignard reagents are nucleophiles in nucleophilic aliphatic substitutions for instance with alkyl halides in a key step in industrial Naproxen production:
Grignard reagents also react with many "carbonyl-like" compounds and other electrophiles: | 0 | Theoretical and Fundamental Chemistry |
The Journal of Separation Science is a biweekly peer-reviewed scientific journal covering analytical chemistry. It was established in 1978 as the Journal of High Resolution Chromatography & Chromatography Communications: HRC & CC. In 1989, it was renamed the Journal of High Resolution Chromatography. It obtained its current name in 2001, when it also absorbed the preexisting Journal of Microcolumn Separations, which had been established in 1989. It is an organ of the European Society for Separation Science and the California Separation Science Society. The editor-in-chief is František Švec (Charles University). According to the Journal Citation Reports, the journal has a 2020 impact factor of 3.645, ranking it 25th out of 83 journals in the category "Chemistry, Analytical". | 0 | Theoretical and Fundamental Chemistry |
Original direct converters were designed to extract the energy carried by 100 to 800 keV ions produced by D-T fusion reactions. Those electrostatic converters are not suitable for higher energy product ions above 1 MeV generated by other fusion fuels like the D-He or the p-B aneutronic fusion reactions.
A much shorter device than the Traveling-Wave Direct Energy Converter has been proposed in 1997 and patented by Tri Alpha Energy, Inc. as an Inverse Cyclotron Converter (ICC).
The ICC is able to decelerate the incoming ions based on experiments made in 1950 by Felix Bloch and Carson D. Jeffries, in order to extract their kinetic energy. The converter operates at 5 MHz and requires a magnetic field of only 0.6 tesla. The linear motion of fusion product ions is converted to circular motion by a magnetic cusp. Energy is collected from the charged particles as they spiral past quadrupole electrodes. More classical electrostatic collectors would also be used for particles with energy less than 1 MeV. The Inverse Cyclotron Converter has a maximum projected efficiency of 90%. | 0 | Theoretical and Fundamental Chemistry |
Powder metallurgy is a class of modern processing techniques in which metals are first powdered, and then formed into the desired shape by heating below the melting point. This is in contrast to casting, which occurs with molten metal. Superalloy manufacturing often employs powder metallurgy because of its material efficiency - typically much less waste metal must be machined away from the final product—and its ability to facilitate mechanical alloying. Mechanical alloying is a process by which reinforcing particles are incorporated into the superalloy matrix material by repeated fracture and welding. | 1 | Applied and Interdisciplinary Chemistry |
The Pauly reaction is a chemical test used for detecting the presence of tyrosine or histidine in proteins. It is named after German chemist Hermann Pauly, who first described the reaction. When proteins containing either tyrosine or histidine are reacted with diazotized sulfanilic acid under alkaline conditions, a red color is formed by a coupling reaction. | 0 | Theoretical and Fundamental Chemistry |
The sub-surface drainage can be accomplished through drains or pumped wells.<br>
The subsurface drains are characterized by drain depth and drainage capacity factor . The drains are located in the transition zone. The subsurface drainage facility can be applied to natural or artificial drainage systems. The functioning of an artificial drainage system can be regulated through a drainage control factor.<br>
When no drainage system is present, installing drains with zero capacity offers the opportunity to obtain separate water and salt balances for an upper and lower part of the transition zone.<br>
The pumped wells are located in the aquifer. Their functioning is characterized by the well discharge.<br>
The drain and well water can be used for irrigation through a re-use factor. This may affect the salt balance and the irrigation efficiency or sufficiency. | 0 | Theoretical and Fundamental Chemistry |
When studying urease at about the same time as Michaelis and Menten were studying invertase, Donald Van Slyke and G. E. Cullen made essentially the opposite assumption, treating the first step not as an equilibrium but as an irreversible second-order reaction with rate constant . As their approach is never used today it is sufficient to give their final rate equation:
and to note that it is functionally indistinguishable from the Henri–Michaelis–Menten equation. One cannot tell from inspection of the kinetic behaviour whether is equal to or to or to something else. | 0 | Theoretical and Fundamental Chemistry |
There are many dimensionless numbers in fluid mechanics. The Reynolds number measures the ratio of advection and diffusion effects on structures in the velocity field, and is therefore closely related to Péclet numbers, which measure the ratio of these effects on other fields carried by the flow, for example, temperature and magnetic fields. Replacement of the kinematic viscosity in by the thermal or magnetic diffusivity results in respectively the thermal Péclet number and the magnetic Reynolds number. These are therefore related to by-products with ratios of diffusivities, namely the Prandtl number and magnetic Prandtl number. | 1 | Applied and Interdisciplinary Chemistry |
When applied to existing constructions, the lifetime can be extended considerably. If no macroscopically visible cracks are present, HiFIT is a very suitable remediation tool.
With timely remediation of existing structures there is practically no difference to the life of new treated welds. This gives the potential to use existing constructions far beyond the planned lifetime. The HiFIT-method is used very efficient e.g. at highway bridges in steel hollow box-section design on the fly. Costs for reconstruction are low compared to conventional methods. In the commercial vehicle industry and other industries highly stressed welds on existing and new structures are treated with HiFIT to extend lifetime successfully. | 1 | Applied and Interdisciplinary Chemistry |
In solution, detergents help solubilize a variety of chemical species by dissociating aggregates and unfolding proteins. Popular surfactants in the biochemistry laboratory are sodium lauryl sulfate (SDS) and cetyl trimethylammonium bromide (CTAB). Detergents are key reagents to extract protein by lysis of the cells and tissues: They disorganize the membrane's lipid bilayer (SDS, Triton X-100, X-114, CHAPS, DOC, and NP-40), and solubilize proteins. Milder detergents such as octyl thioglucoside, octyl glucoside or dodecyl maltoside are used to solubilize membrane proteins such as enzymes and receptors without denaturing them. Non-solubilized material is harvested by centrifugation or other means. For electrophoresis, for example, proteins are classically treated with SDS to denature the native tertiary and quaternary structures, allowing the separation of proteins according to their molecular weight.
Detergents have also been used to decellularise organs. This process maintains a matrix of proteins that preserves the structure of the organ and often the microvascular network. The process has been successfully used to prepare organs such as the liver and heart for transplant in rats. Pulmonary surfactants are also naturally secreted by type II cells of the lung alveoli in mammals. | 0 | Theoretical and Fundamental Chemistry |
* The light-protective carotenoid pigments (present in photosynthetic organisms such as plants, algae, cyanobacteria and in some bacteria and archaea) have been classified as high priority targets for biosignature models on Mars due to their stability and easy identification by Raman spectroscopy. In this experiment, the light-protective carotenoids in two organisms (cyanobacterium Nostoc sp. and the green alga cf. Sphaerocystis sp.) were still detectable at relatively high levels after being exposed for 15 months.
* Dried biofilms of three desert strains of Chroococcidiopsis showed overall higher viability and lower amounts of DNA damage when compared to multi-layer films of the planktonic counterpart, and were consistent with ground Mars simulation experiments. The strains tested were CCMEE 029 from the Negev Desert, where they live beneath the surface of rocks (endoliths) and strains CCMEE 057 and CCMEE 064 from the Sinai Desert where they are both endoliths and hypoliths (within rocks or on the ground sheltered beneath rocks).
* Other results are expected to be published in Frontiers in Microbiology under the research topic title: "Habitability Beyond Earth", and in an upcoming special collection of Astrobiology journal.
* In March 2019, scientists reported that life-forms from Earth survived 18 months living in outer space outside the International Space Station (ISS), as part of the BIOMEX studies related to the EXPOSE-R2 mission, suggesting that life could survive, theoretically, on the planet Mars. | 1 | Applied and Interdisciplinary Chemistry |
In glycogen, every 10 to 14 glucose units, a side branch with an additional chain of glucose units occurs. The side chain attaches at carbon atom 6 of a glucose unit, an α-1,6-glycosidic bond. This connection is catalyzed by a branching enzyme, generally given the name α-glucan branching enzyme. A branching enzyme attaches a string of seven glucose units (with some minor variation to this number) to the carbon at the C-6 position on the glucose unit, forming the α-1,6-glycosidic bond. The specific nature of this enzyme means that this chain of 7 carbons is usually attached to a glucose molecule that is in position three from the non-reducing end of another chain. Because the enzyme works with such specificity regarding the number of glucose units transferred and the position to which they are transferred, the enzyme creates the very characteristic, highly branched glycogen molecule. | 1 | Applied and Interdisciplinary Chemistry |
Studies on an AS04-adjuvanted HPV-16/18 vaccine showed a high and sustained immune response to HPV antigens after injection, including in patients receiving subsequent doses. Immune response was enhanced by the MPL component which triggered local NF-kB and cytokine production, leading to increased activation of antigen-presenting cells. Immune response duration was extended by the aluminium hydroxide component. The HPV-16/18 AS04-adjuvanted vaccine showed enhanced efficacy compared to an aluminium salt-adjuvanted formulation, with a higher level of antibodies subsequently detected in the body.
Long-term studies appear to show an adequate efficacy and safety profile. | 1 | Applied and Interdisciplinary Chemistry |
Typical efficiency of a full floor coverage diffused aeration system in clean water is 2%/ft submergence or 6.6%/m submergence. When converted to mass transfer into process or dirty water, it is typically closer to about half of those figures. Manufacturers of fine bubble systems have supported claims that the type, number and size of "pores" have a great effect on efficiency of a diffused aeration system. | 1 | Applied and Interdisciplinary Chemistry |
CPC offers direct scale-up from analytical apparatuses (few milliliters) to industrial apparatuses (several liters) for fast batch-production. CPC seems particularly suited to accommodate aqueous two-phase solvent systems. Generally, CPC instruments can retain solvent systems that are not well-retained in a hydrodynamic instrument due to small differences in density between the phases. It has been very helpful for the development of CPC instrumentation to visualize the flow patterns which give rise to the mixing and settling in the CPC chamber with an asynchronous camera and a stroboscope triggered by the CPC rotor. | 0 | Theoretical and Fundamental Chemistry |
Monopolin is a protein complex that in budding yeast is composed of the four proteins CSM1, HRR25, LRS4, and MAM1. Monopolin is required for the segregation of homologous centromeres to opposite poles of a dividing cell during anaphase I of meiosis. This occurs by bridging DSN1 kinetochore proteins to sister kinetochores within the centromere to physically fuse them and allow for the microtubules to pull each homolog toward opposite mitotic spindles. | 1 | Applied and Interdisciplinary Chemistry |
Synthesis of carbido clusters can be accomplished by hydrolysis, thermolysis of labile ligands, thermal rearrangements, and photolysis. Their synthesis has historically been crudely achieved by serendipitous chance following apparent random molecular organization. One example is the following reaction: | 0 | Theoretical and Fundamental Chemistry |
Although oxygen levels inside processing equipment are usually low, it cannot be fully excluded and thermal-oxidation will usually take place more readily than degradation that is exclusively thermal (i.e. without air). Reactions follow the general autoxidation mechanism, leading to the formation of organic peroxides and carbonyls. The addition of antioxidants may inhibit such processes. | 0 | Theoretical and Fundamental Chemistry |
Another pitch-in-funnel demonstration was begun in 1902 by the Royal Scottish Museum in Edinburgh and is in Edinburgh at the Royal Scottish Museum's successor institution the National Museum of Scotland. The known records of its behaviour are incomplete: it is known to have dripped once at some time between 4 and 6 June 2016 and on at least one occasion in the past, but the time and number of the previous drip or drips is unknown. Furthermore, the June 2016 drip happened shortly after the experiment was taken out of museum storage, and the physical movement may have caused it to drip at that time. | 1 | Applied and Interdisciplinary Chemistry |
Polymorphism is the occurrence of multiple crystalline forms of a material. It is found in many crystalline materials including polymers, minerals, and metals. According to Gibbs' rules of phase equilibria, these unique crystalline phases are dependent on intensive variables such as pressure and temperature. Polymorphism is related to allotropy, which refers to elemental solids. The complete morphology of a material is described by polymorphism and other variables such as crystal habit, amorphous fraction or crystallographic defects. Polymorphs have different stabilities and may spontaneously and irreversibly transform from a metastable form (or thermodynamically unstable form) to the stable form at a particular temperature. They also exhibit different melting points, solubilities, and X-ray diffraction patterns.
One good example of this is the quartz form of silicon dioxide, or SiO. In the vast majority of silicates, the Si atom shows tetrahedral coordination by 4 oxygens. All but one of the crystalline forms involve tetrahedral {SiO} units linked together by shared vertices in different arrangements. In different minerals the tetrahedra show different degrees of networking and polymerization. For example, they occur singly, joined together in pairs, in larger finite clusters including rings, in chains, double chains, sheets, and three-dimensional frameworks. The minerals are classified into groups based on these structures. In each of the 7 thermodynamically stable crystalline forms or polymorphs of crystalline quartz, only 2 out of 4 of each the edges of the {SiO} tetrahedra are shared with others, yielding the net chemical formula for silica: SiO.
Another example is elemental tin (Sn), which is malleable near ambient temperatures but is brittle when cooled. This change in mechanical properties due to existence of its two major allotropes, α- and β-tin. The two allotropes that are encountered at normal pressure and temperature, α-tin and β-tin, are more commonly known as gray tin and white tin respectively. Two more allotropes, γ and σ, exist at temperatures above 161 °C and pressures above several GPa. White tin is metallic, and is the stable crystalline form at or above room temperature. Below 13.2 °C, tin exists in the gray form, which has a diamond cubic crystal structure, similar to diamond, silicon or germanium. Gray tin has no metallic properties at all, is a dull gray powdery material, and has few uses, other than a few specialized semiconductor applications. Although the α–β transformation temperature of tin is nominally 13.2 °C, impurities (e.g. Al, Zn, etc.) lower the transition temperature well below 0 °C, and upon addition of Sb or Bi the transformation may not occur at all. | 0 | Theoretical and Fundamental Chemistry |
Dmitri Ivanovich Mendeleev (sometimes romanized as Mendeleyev, Mendeleiev, or Mendeleef; ; , ; 8 February [<nowiki/>O.S. 27 January] 18342 February [O.S. 20 January] 1907) was a Russian chemist and inventor. He is best known for formulating the Periodic Law and creating a version of the periodic table of elements. He used the Periodic Law not only to correct the then-accepted properties of some known elements, such as the valence and atomic weight of uranium, but also to predict the properties of three elements that were yet to be discovered (germanium, gallium and scandium). | 0 | Theoretical and Fundamental Chemistry |
Accelerated studies have been in use since at least the mid-1950s, at least for biological reference materials. CRMs are typically monitored at a range of temperatures and the results are used to predict the rate of change at a proposed, usually low, storage temperature. Often, the prediction uses a well known degradation model such as an Arrhenius model. The advantage over real-time studies is that results are available sooner and predictions of stability over a much longer period than the stability study can be defended. For some applications, accelerated studies have been described as the only practical approach:
The principal disadvantage of accelerated studies is that reference materials, like any other material, can degrade for unexpected reasons over time, or can degrade following different kinetic models; predictions can then become unreliable. | 0 | Theoretical and Fundamental Chemistry |
The feasibility of Tc production with the 22-MeV-proton bombardment of a Mo target in medical cyclotrons was demonstrated in 1971. The recent shortages of Tc reignited the interest in the production of "instant" 99mTc by proton bombardment of isotopically enriched Mo targets (>99.5%) following the reaction Mo(p,2n)Tc. Canada is commissioning such cyclotrons, designed by Advanced Cyclotron Systems, for Tc production at the University of Alberta and the Université de Sherbrooke, and is planning others at the University of British Columbia, TRIUMF, University of Saskatchewan and Lakehead University.
A particular drawback of cyclotron production via (p,2n) on Mo is the significant co-production of Tc. The preferential in-growth of this nuclide occurs due to the larger reaction cross-section pathway leading to the ground state, which is almost five times higher at the cross-section maximum in comparison with the metastable one at the same energy. Depending on the time required to process the target material and recovery of Tc, the amount of Tc relative to Tc will continue to decrease, in turn reducing the specific activity of Tc available. It has been reported that ingrowth of Tc as well as the presence of other Tc isotopes can negatively affect subsequent labelling and/or imaging; however, the use of high purity Mo targets, specified proton beam energies, and appropriate time of use have shown to be sufficient for yielding Tc from a cyclotron comparable to that from a commercial generator. Liquid metal molybdenum-containing targets have been proposed that would aid in streamlined processing, ensuring better production yields. A particular problem associated with the continued reuse of recycled, enriched Mo targets is unavoidable transmutation of the target as other Mo isotopes are generated during irradiation and cannot be easily removed post-processing. | 0 | Theoretical and Fundamental Chemistry |
Sharpless developed stereoselective oxidation reactions, and showed that the formation of an inhibitor with femtomolar potency can be catalyzed by the enzyme acetylcholinesterase, beginning with an azide and an alkyne. He discovered several chemical reactions which have transformed asymmetric synthesis from science fiction to the relatively routine, including aminohydroxylation, dihydroxylation, and the Sharpless asymmetric epoxidation.
In 2001 he was awarded a half-share of the Nobel Prize in Chemistry for his work on chirally catalyzed oxidation reactions (Sharpless epoxidation, Sharpless asymmetric dihydroxylation, Sharpless oxyamination). The other half of the year's Prize was shared between William S. Knowles and Ryōji Noyori (for their work on stereoselective hydrogenation).
The term "click chemistry" was coined by Sharpless around the year 2000, and was first fully described by Sharpless, Hartmuth Kolb, and M.G. Finn at The Scripps Research Institute in 2001. This involves a set of highly selective, exothermic reactions which occur under mild conditions; the most successful example is the azide alkyne Huisgen cycloaddition to form 1,2,3-triazoles.
, Sharpless has an h-index of 180 according to Google Scholar and of 124 according to Scopus. | 0 | Theoretical and Fundamental Chemistry |
D-arabinitol 2-dehydrogenase - D-arabinose 1-dehydrogenase (NAD(P)+) - database search - degeneracy (biology) - deletion - denaturation - denaturing gel - deoxyribonuclease (DNase) - deoxyribonucleic acid - deoxyribonucleotide - deoxyuridine phosphorylase - diabetes mellitus - dideoxy sequencing - dideoxyribonucleotide - diethyl 2-methyl-3-oxosuccinate reductase - dihydrochelirubine 12-monooxygenase - dimethyl sulfide:cytochrome c2 reductase - diploid - direct repeat - directionality - DNA ligase -DNA Bank - DNA polymerase - DNA replication - DNA sequencing - DNase - dominant - dot blot - double helix - downstream (DNA) - downstream (transduction) - drimenol cyclase- ds - duplex - | 1 | Applied and Interdisciplinary Chemistry |
The surface elevation η and the velocity potential Φ are, according to Stokess second-order theory of surface gravity waves on a fluid layer of mean depth h':
Observe that for finite depth the velocity potential Φ contains a linear drift in time, independent of position (x and z). Both this temporal drift and the double-frequency term (containing sin 2θ) in Φ vanish for deep-water waves. | 1 | Applied and Interdisciplinary Chemistry |
Despite its highly pyrophoric nature, diethylzinc is an important chemical reagent. It is used in organic synthesis as a source of the ethyl carbanion in addition reactions to carbonyl groups. For example, the asymmetric addition of an ethyl group to benzaldehyde and imines.
Additionally, it is commonly used in combination with diiodomethane as a Simmons-Smith reagent to convert alkenes into cyclopropyl groups. It is less nucleophilic than related alkyllithium and Grignard reagents, so it may be used when a "softer" nucleophile is needed.
It is also used extensively in materials science chemistry as a zinc source in the synthesis of nanoparticles. Particularly in the formation of the zinc sulfide shell for core/shell-type quantum dots.
While in polymer chemistry, it can be used as part of the catalyst for a chain shuttling polymerization reaction, whereby it participates in living polymerization.
Diethylzinc is not limited to only being used in chemistry. Because of its high reactivity toward air, it was used in small quantities as a hypergolic or "self igniting" liquid rocket fuel—it ignites on contact with oxidizer, so the rocket motor need only contain a pump, without a spark source for ignition. Diethylzinc was also investigated by the United States Library of Congress as a potential means of mass deacidification of books printed on wood pulp paper. Diethylzinc vapour would, in theory, neutralize acid residues in the paper, leaving slightly alkaline zinc oxide residues. Although initial results were promising, the project was abandoned. A variety of adverse results prevented the method's adoption. Most infamously, the final prototype suffered damage in a series of diethylzinc explosions from trace amounts of water vapor in the chamber. This led the authors of the study to humorously comment:
In microelectronics, diethylzinc is used as a doping agent.
For corrosion protection in nuclear reactors of the light water reactor design, depleted zinc oxide is produced by first passing diethylzinc through an enrichment centrifuge.
The pyrophoricity of diethylzinc can be used to test the inert atmosphere inside a glovebox. An oxygen concentration of only a few parts per million will cause a bottle of diethylzinc to fume when opened. | 0 | Theoretical and Fundamental Chemistry |
The first definitive description of a chloroplast (Chlorophyllkörnen, "grain of chlorophyll") was given by Hugo von Mohl in 1837 as discrete bodies within the green plant cell. In 1883, Andreas Franz Wilhelm Schimper named these bodies as "chloroplastids" (Chloroplastiden). In 1884, Eduard Strasburger adopted the term "chloroplasts" (Chloroplasten). | 0 | Theoretical and Fundamental Chemistry |
The membrane process utilizes biofilm, a naturally occurring substance found in lakes, rivers, rocks, and other natural formations. They are utilized by causing the necessary biomass/organic matter to attach to the desired area. The solid particles are too big to permeate the membrane, so only pure liquid is able to get through. This allows for a high retention rate, therefore allowing the wastewater to be reusable. | 1 | Applied and Interdisciplinary Chemistry |
Since a gyromagnetic factor equal to 2 follows from Diracs equation, it is a frequent misconception to think that a -factor 2 is a consequence of relativity; it is not. The factor 2 can be obtained from the linearization of both the Schrödinger equation and the relativistic Klein–Gordon equation (which leads to Diracs). In both cases a 4-spinor is obtained and for both linearizations the -factor is found to be equal to 2; Therefore, the factor 2 is a consequence of the minimal coupling and of the fact of having the same order of derivatives for space and time.
Physical spin particles which cannot be described by the linear gauged Dirac equation satisfy the gauged Klein–Gordon equation extended by the term according to,
Here, and stand for the Lorentz group generators in the Dirac space, and the electromagnetic tensor respectively, while is the electromagnetic four-potential. An example for such a particle, is the spin companion to spin in the representation space of the Lorentz group. This particle has been shown to be characterized by and consequently to behave as a truly quadratic fermion. | 0 | Theoretical and Fundamental Chemistry |
The most commonly used PCMs are salt hydrates, fatty acids and esters, and various paraffins (such as octadecane). Recently also ionic liquids were investigated as novel PCMs.
As most of the organic solutions are water-free, they can be exposed to air, but all salt based PCM solutions must be encapsulated to prevent water evaporation or uptake. Both types offer certain advantages and disadvantages and if they are correctly applied some of the disadvantages becomes an advantage for certain applications.
They have been used since the late 19th century as a medium for thermal storage applications. They have been used in such diverse applications as refrigerated transportation for rail and road applications and their physical properties are, therefore, well known.
Unlike the ice storage system, however, the PCM systems can be used with any conventional water chiller both for a new or alternatively retrofit application. The positive temperature phase change allows centrifugal and absorption chillers as well as the conventional reciprocating and screw chiller systems or even lower ambient conditions utilizing a cooling tower or dry cooler for charging the TES system.
The temperature range offered by the PCM technology provides a new horizon for the building services and refrigeration engineers regarding medium and high temperature energy storage applications. The scope of this thermal energy application is wide-ranging of solar heating, hot water, heating rejection (i.e., cooling tower), and dry cooler circuitry thermal energy storage applications.
Since PCMs transform between solid–liquid in thermal cycling, encapsulation naturally became the obvious storage choice.
*Encapsulation of PCMs
**Macro-encapsulation: Early development of macro-encapsulation with large volume containment failed due to the poor thermal conductivity of most PCMs. PCMs tend to solidify at the edges of the containers preventing effective heat transfer.
**Micro-encapsulation: Micro-encapsulation on the other hand showed no such problem. It allows the PCMs to be incorporated into construction materials, such as concrete, easily and economically. Micro-encapsulated PCMs also provide a portable heat storage system. By coating a microscopic sized PCM with a protective coating, the particles can be suspended within a continuous phase such as water. This system can be considered a phase change slurry (PCS).
**Molecular-encapsulation is another technology, developed by Dupont de Nemours that allows a very high concentration of PCM within a polymer compound. It allows storage capacity up to 515 kJ/m for a 5 mm board (103 MJ/m). Molecular-encapsulation allows drilling and cutting through the material without any PCM leakage.
As phase change materials perform best in small containers, therefore they are usually divided in cells. The cells are shallow to reduce static head – based on the principle of shallow container geometry. The packaging material should conduct heat well; and it should be durable enough to withstand frequent changes in the storage material's volume as phase changes occur. It should also restrict the passage of water through the walls, so the materials will not dry out (or water-out, if the material is hygroscopic). Packaging must also resist leakage and corrosion. Common packaging materials showing chemical compatibility with room temperature PCMs include stainless steel, polypropylene, and polyolefin.
Nanoparticles such as carbon nanotubes, graphite, graphene, metal and metal oxide can be dispersed in PCM. It is worth noting that inclusion of nanoparticles will not only alter thermal conductivity characteristic of PCM but also other characteristics as well, including latent heat capacity, sub-cooling, phase change temperature and its duration, density and viscosity. The new group of PCMs called NePCM. NePCMs can be added to metal foams to build even higher thermal conductive combination. | 0 | Theoretical and Fundamental Chemistry |
After passage of the Food Quality Protection Act (FQPA) of 1996, the U.S. EPA had established a tolerance level for apples at 10 ppm, and for meat and milk at 0 ppm. The tentative LOAEL was 10 mg/kg/day In 1997 EPA approved the reregistration of diphenylamine, and determined that recommended tolerances met the safety standards under FQPA and that "adequate data indicate that tolerances for residues in milk and meat could be increased from 0.0 ppm and established as separate tolerances set at 0.01 ppm". EPA has not reviewed diphenylamine since then. | 0 | Theoretical and Fundamental Chemistry |
Studies have shown that people who are atopic (sensitive), already have allergies, asthma, or compromised immune systems and occupy damp or moldy buildings are at an increased risk of health problems such as inflammatory responses to mold spores, metabolites such as mycotoxins, and other components. Other problems are respiratory and/or immune system responses including respiratory symptoms, respiratory infections, exacerbation of asthma, and rarely hypersensitivity pneumonitis, allergic alveolitis, chronic rhinosinusitis and allergic fungal sinusitis. A person's reaction to mold depends on their sensitivity and other health conditions, the amount of mold present, length of exposure, and the type of mold or mold products.
Some molds also produce mycotoxins, which, in sufficient quantity, can pose serious health risks to humans and animals. The colloquial term "toxic mold" (or more accurately, toxigenic mold) refers to molds that produce mycotoxins known to harm humans, not to all molds. Exposure to high levels of mycotoxins can lead to neurological problems and, in some cases, death. Prolonged exposure, e.g., daily workplace exposure, can be particularly harmful.
The five most common genera of indoor molds are Cladosporium, Penicillium, Aspergillus, Alternaria, and Trichoderma.
Damp environments that allow mold to grow can also allow the proliferation of bacteria and release volatile organic compounds. | 1 | Applied and Interdisciplinary Chemistry |
Pasteur responded to Liebigs works, often through his own writings, and using results from his own experiments to support his theories. For example, in 1858, Pasteur wrote a paper trying to disprove Liebigs theory that fermentation cannot be caused by the growth of the yeast when it takes place when yeast is added to pure sugar-water. Pasteur thought that in pure sugar-water, yeast was both growing and disintegrating, and developed experiments to support his theories. Liebig, however, was not convinced, and claimed that Pasteur was not solving the questions he had about the decomposition in fermentation.
In 1869, Liebig responded to Pasteurs challenge, which he had made public ten years before. Liebig still held this ground, and mentioned that some of Pasteurs experiments were difficult to replicate and use effectively. Pasteur was furious, and suggested the Royal Academy hire a third scientist who would replicate his experiments and verify his results in order to support his theories. Neither Liebig nor the Academy responded.
Later, Pasteur demanded a meeting with Liebig, but Liebig did not him receive cordially, and refused to discuss the topic of fermentation. | 1 | Applied and Interdisciplinary Chemistry |
TISAB is very commonly applied to fluoride ion analysis such as in fluoride ion selective electrodes.
There are four main constituents to TISAB, namely CDTA (cyclohexylenedinitrilotetraacetate), sodium hydroxide, sodium chloride and acetic acid (ethanoic acid), which are all dissolved in deionised water. Hence, TISAB has a density ~1.0 kg/L, though this can vary to 1.18 kg/L. Each constituent plays an important role in controlling the ionic strength and pH of the analyte solution, which may otherwise cause error and inaccuracy.
The activity of a substance in solution depends on the product of its concentration and the activity coefficient in that solution. The activity coefficient depends on the ionic strength of the solution in which the potentiometric measurements are made. This can be calculated for dilute solutions using the Debye–Hückel equation; for more concentrated solutions other approximations must be used. In most cases, the analyst's goal is simply to make sure that the activity coefficient is constant across a set of solutions, with the assumption that no significant ion pairing exists in the solutions.
Example: An ion-selective electrode might be calibrated using dilute solutions of the analyte in distilled water. If this calibration is used to calculate the concentration of the analyte in sea water (high ionic strength), significant error is introduced by the difference between the activity of the analyte in the dilute solutions and the concentrated sample. This can be avoided by adding a small amount of ionic-strength buffer to the standards, so that the activity coefficients match more closely.
Adding a TISAB buffer to increase the ionic strength of the solution helps to "fix" the ionic strength at a stable level, making a linear correlation between the logarithm of the concentration of analyte and the measured voltage. By also adding the TISAB buffer to the samples from which the potentiometric equipment are calibrated, the linear correlation can be used to calculate the concentration of analyte in the solution.
where is measured voltage, is the gas constant, the temperature measured in kelvins, is the Faraday constant and the charge of the analyte. is the concentration of analyte.
TISAB buffers often include chelators which bind ions that could otherwise interfere with the analyte. | 0 | Theoretical and Fundamental Chemistry |
Blade element momentum theory is a theory that combines both blade element theory and momentum theory. It is used to calculate the local forces on a propeller or wind-turbine blade. Blade element theory is combined with momentum theory to alleviate some of the difficulties in calculating the induced velocities at the rotor.
This article emphasizes application of blade element theory to ground-based wind turbines, but the principles apply as well to propellers. Whereas the streamtube area is reduced by a propeller, it is expanded by a wind turbine. For either application, a highly simplified but useful approximation is the Rankine–Froude "momentum" or "actuator disk" model (1865, 1889). This article explains the application of the "Betz limit" to the efficiency of a ground-based wind turbine.
Froude's blade element theory (1878) is a mathematical process to determine the behavior of propellers, later refined by Glauert (1926). Betz (1921) provided an approximate correction to momentum "Rankine–Froude actuator-disk" theory to account for the sudden rotation imparted to the flow by the actuator disk (NACA TN 83, "The Theory of the Screw Propeller" and NACA TM 491, "Propeller Problems"). In blade element momentum theory, angular momentum is included in the model, meaning that the wake (the air after interaction with the rotor) has angular momentum. That is, the air begins to rotate about the z-axis immediately upon interaction with the rotor (see diagram below). Angular momentum must be taken into account since the rotor, which is the device that extracts the energy from the wind, is rotating as a result of the interaction with the wind. | 1 | Applied and Interdisciplinary Chemistry |
The World Health Organization and the UN Environment Programme estimate that 3 million agricultural workers in the developing world experience severe poisoning from pesticides each year, resulting in 18,000 deaths. According to one study, as many as 25 million workers in developing countries may suffer mild pesticide poisoning yearly. Other occupational exposures besides agricultural workers, including pet groomers, groundskeepers, and fumigators, may also put individuals at risk of health effects from pesticides.
Pesticide use is widespread in Latin America, as around US$3 billion are spent each year in the region. Records indicate an increase in the frequency of pesticide poisonings over the past two decades. The most common incidents of pesticide poisoning is thought to result from exposure to organophosphate and carbamate insecticides. At-home pesticide use, use of unregulated products, and the role of undocumented workers within the agricultural industry makes characterizing true pesticide exposure a challenge. It is estimated that 50–80% of pesticide poisoning cases are unreported.
Underreporting of pesticide poisoning is especially common in areas where agricultural workers are less likely to seek care from a healthcare facility that may be monitoring or tracking the incidence of acute poisoning. The extent of unintentional pesticide poisoning may be much greater than available data suggest, particularly among developing countries. Globally, agriculture and food production remain one of the largest industries. In East Africa, the agricultural industry represents one of the largest sectors of the economy, with nearly 80% of its population relying on agriculture for income. Farmers in these communities rely on pesticide products to maintain high crop yields.
Some East Africa governments are shifting to corporate farming, and opportunities for foreign conglomerates to operate commercial farms have led to more accessible research on pesticide use and exposure among workers. In other areas where large proportions of the population rely on subsistence, small-scale farming, estimating pesticide use and exposure is more difficult. | 1 | Applied and Interdisciplinary Chemistry |
In industrial corona and plasma processes, cost-efficient and rapid analytical methods are required for confirming adequate surface functionality on a given substrate. Measuring the surface energy is an indirect method for confirming the presence of surface functional groups without the need for microscopy or spectroscopy, often expensive and demanding tools. Contact angle measurement (goniometry) can be used to find the surface energy of the treated and non-treated surface. Young's relation can be used to find surface energy assuming the simplification of experimental conditions to a three phase equilibrium (i.e. liquid drop applied to flat rigid solid surface in a controlled atmosphere), yielding
where
denotes the surface energy of the solid–liquid, liquid–gas, or solid–gas interface
is the measured contact angle
A series of solutions with known surface tension (e.g., Dyne solutions) can be used to estimate the surface energy of the polymer substrate qualitatively by observing the wettability of each. These methods are applicable to macroscopic surface oxidation, as in industrial processing. | 0 | Theoretical and Fundamental Chemistry |
In 1763, James Watt was working as instrument maker at the University of Glasgow when he was assigned the job of repairing a model Newcomen engine and noted how inefficient it was.
In 1765, Watt conceived the idea of equipping the engine with a separate condensation chamber, which he called a "condenser". Because the condenser and the working cylinder were separate, condensation occurred without significant loss of heat from the cylinder. The condenser remained cold and below atmospheric pressure at all times, while the cylinder remained hot at all times.
Steam was drawn from the boiler to the cylinder under the piston. When the piston reached the top of the cylinder, the steam inlet valve closed and the valve controlling the passage to the condenser opened. The condenser being at a lower pressure, drew the steam from the cylinder into the condenser where it cooled and condensed from water vapour to liquid water, maintaining a partial vacuum in the condenser that was communicated to the space of the cylinder by the connecting passage. External atmospheric pressure then pushed the piston down the cylinder.
The separation of the cylinder and condenser eliminated the loss of heat that occurred when steam was condensed in the working cylinder of a Newcomen engine. This gave the Watt engine greater efficiency than the Newcomen engine, reducing the amount of coal consumed while doing the same amount of work as a Newcomen engine.
In Watts design, the cold water was injected only into the condensation chamber. This type of condenser is known as a jet condenser'. The condenser is located in a cold water bath below the cylinder. The volume of water entering the condenser as spray absorbed the latent heat of the steam, and was determined as seven times the volume of the condensed steam. The condensate and the injected water was then removed by the air pump, and the surrounding cold water served to absorb the remaining thermal energy to retain a condenser temperature of 30 °C to 45 °C and the equivalent pressure of 0.04 to 0.1 bar
At each stroke the warm condensate was drawn off from the condenser and sent to a hot well by a vacuum pump, which also helped to evacuate the steam from under the power cylinder. The still-warm condensate was recycled as feedwater for the boiler.
Watt's next improvement to the Newcomen design was to seal the top of the cylinder and surround the cylinder with a jacket. Steam was passed through the jacket before being admitted below the piston, keeping the piston and cylinder warm to prevent condensation within it. The second improvement was the utilisation of steam expansion against the vacuum on the other side of the piston. The steam supply was cut during the stroke, and the steam expanded against the vacuum on the other side. This increased the efficiency of the engine, but also created a variable torque on the shaft which was undesirable for many applications, in particular pumping. Watt therefore limited the expansion to a ratio of 1:2 (i.e. the steam supply was cut at half stroke). This increased the theoretical efficiency from 6.4% to 10.6%, with only a small variation in piston pressure. Watt did not use high pressure steam because of safety concerns.
These improvements led to the fully developed version of 1776 that actually went into production. | 0 | Theoretical and Fundamental Chemistry |
Agrominerals allow for nutrients to be added to the soil after a long history of crops depleting it. The agriculture industry is suffering from its high loss rate in arable layers in the soil and ground nutrients compared to the natural replenishment rate. Remineralization looks into the process of taking rock powders and incorporating it into the soil as a way to replenish the nutrients in the ground. With rock powder the plant absorbs only what it needs, and any unused minerals will remain crystalized until it is used. While chemical fertilizers use dissolvable salts to deliver the nutrients to the plant, whatever is not absorb will run off into the nearest groundwater.
Rocks have become a cheap by-product in many industries and so there is a potential for a massive supply of viables rocks for a cheap price. Remineralization using rock powder can provide up to 5 years’ worth of nutrients in a soil. When used in the combination with organic fertilizer, rock powder has proven to be just as effective as chemical fertilizer for a much smaller cost. It has even shown to have higher yields for long term crops. When using rock powder, the plants tended to look healthier, and it was found that the powder helps with holding moisture content. The effectiveness of the remineralization process is dependent on the mineralogy and chemistry of the rock powder, as well as the soil characteristics.
The challenge with rock powders is understanding the solubility rates of the rock powder. Rates are dependent on factors like organic matter, pH levels, secondary clay precipitation. This is a major area of research since their dissolution kinetics are not fully understood. One of the major challenges is recreating the field conditions in the lab, in many cases the solubility rates in the lab are 2-5 magnitudes higher than the ones in the field. It's important to fully understand what the mineralogy and chemical components of a rock. Volcanic rocks were thought to be a good source for rock powder but it was determined that it contains toxic elements as well. Research has been done into phosphate rocks, but these too have the issue of containing heavy and radioactive elements.
The use of rock powder in remineralization has the potential to help mitigate global warming. When nutrients from certain powders are absorbed, cations are released in the soil which reacts to with carbon dioxide to create carbonate minerals, which can serve as a carbon sink for the carbon cycle. With this discovery there has been a push to further look into remineralizations using rocks powders due to its sustainability potential both from a farming side and a global climate change side. | 0 | Theoretical and Fundamental Chemistry |
In oceanography, temperature-salinity diagrams, sometimes called T-S diagrams, are used to identify water masses. In a T-S diagram, rather than plotting each water property as a separate "profile," with pressure or depth as the vertical coordinate, potential temperature (on the vertical axis) is plotted versus salinity (on the horizontal axis). As long as it remains isolated from the surface, where heat or fresh water can be gained or lost, and in the absence of mixing with other water masses, a water parcel's potential temperature and salinity are conserved. Deep water masses thus retain their T-S characteristics for long periods of time, and can be identified readily on a T-S plot.
Temperature and salinity combine to determine the potential density of seawater; contours of constant potential density are often shown in T-S diagrams. | 0 | Theoretical and Fundamental Chemistry |
The protection of food from photodegradation is very important. Some nutrients, for example, are affected by degradation when exposed to sunlight. In the case of beer, UV radiation causes a process that entails the degradation of hop bitter compounds to 3-methyl-2-buten-1-thiol and therefore changes the taste. As amber-colored glass has the ability to absorb UV radiation, beer bottles are often made from such glass to prevent this process. | 0 | Theoretical and Fundamental Chemistry |
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