text stringlengths 105 4.57k | label int64 0 1 | label_text stringclasses 2 values |
|---|---|---|
In a 2022 study by Chaudhary et al., aquasomes were explored for delivery of the drug dithranol, which is a treatment for psoriasis. A limitation of the practical application of free dithranol in the treatment of psoriasis is its degradation when encountering oxygen, light, alkaline pH, and heavy metallic elements, leading to the exploration of aquasomes as a delivery system for dithranol to overcome these limitations. Aquasomes displayed a 72% drug entrapment efficiency for dithranol, and drug release studies showed 55% release within 12 hours in vitro and good deposition of the drug ex vivo, indicating a strong controlled release profile for dithranol-loaded aquasomes. This study indicates support for aquasomes as a drug delivery system due to their ability to stabilize easily degradable drugs such as dithranol, while also providing controlled drug release profiles.
In a 2019 study by Kutlehria et al., aquasomes were explored for the oral delivery of the drug bromelain, which inhibits platelet aggregation and modulates anti-inflammatory cytokines, and has shown anti-tumor activity. A challenge in the administration of bromelain has been its limited ability to reach the site of therapeutic action before it degrades. The water-absorbent nature of aquasomes allows for the aqueous transfer of bromelain. The Kutlehria et al. study demonstrated desirable drug-carrying properties for bromelain-loaded aquasomes, such as a drug entrapment efficiency of 72% to 79% and sustained release in vitro, showing promise as an oral delivery mechanism to increase the bioavailability of bromelain. Such applications may be useful for the transport and targeting of poorly soluble drugs, enabled by the structure and polysaccharide coating of aquasomes.
Dual drug delivery is another application of aquasomes enabled by their structure. Dual drug delivery systems can deliver two drugs simultaneously, and aim to enhance the therapeutic efficiency and reduce the side effects of the drugs delivered. Such systems can be useful in treating patients suffering from multiple diseases. Challenges in dual drug delivery include independently controlling release rates of each of the drugs loaded in the system. In a 2019 study by Damera et al., aquasomes were used to deliver bovine serum albumin (BSA) in combination with one of three therapeutic drugs (C153, WAR, and IBU), allowing release of a bioactive molecule and a hydrophobic drug simultaneously. Damera et al. suggested that dual drug delivery was enabled by the bioactive molecule layer of the aquasome being BSA. This BSA layer interacted with the hydrophobic therapeutic drugs, and the strength of the binding interactions was shown to affect the release behaviors of the drugs. Dual drug delivery with aquasomes thus shows promise for treatment of patients with coexisting diseases alongside hypoalbuminemia, as the albumin from BSA can treat the hypoalbuminemia while the additional drug treats the disease. | 0 | Theoretical and Fundamental Chemistry |
For many years mutations of the seipin gene were associated with a loss of function, such as in CGL (see above). However, recent studies show that mutations such as N88S and S90L seem to have a gain-of-toxic-function which may result in autosomal dominant motor neuron diseases and distal hereditary motor neuropathy, such as Silver syndrome and distal hereditary motor neuropathy type V.
Owing to the wide clinical spectrum of these mutations, it has been proposed to collectively refer to seipin-related motor neuron diseases as seipinopathies.
Symptoms can vary and include: developmental regression of motor and cognitive skills in the first years of life leading to death (encephalopathy), muscle weakness and spasticity in lower limbs (spastic paraplegia type XVII), weakness of distal muscles of upper limbs (distal hereditary motor neuropathy type V) as well as wasting of the hand muscles (in both cases). Complex forms of seipinopathies may include deafness, dementia or mental retardation. | 1 | Applied and Interdisciplinary Chemistry |
The concept of natural product, which initially based on organic compounds that could be isolated from plants, was extended to include animal material in the middle of the 19th century by the German Justus von Liebig. Hermann Emil Fischer in 1884, turned his attention to the study of carbohydrates and purines, work for which he was awarded the Nobel Prize in 1902. He also succeeded to make synthetically in the laboratory in a variety of carbohydrates, including glucose and mannose. After the discovery of penicillin by Alexander Fleming in 1928, fungi and other micro-organisms were added to the arsenal of sources of natural products. | 1 | Applied and Interdisciplinary Chemistry |
Technetium-99ms short half-life of 6 hours makes storage impossible and would make transport very expensive. Instead, its parent nuclide Mo is supplied to hospitals after its extraction from the neutron-irradiated uranium targets and its purification in dedicated processing facilities. It is shipped by specialised radiopharmaceutical companies in the form of technetium-99m generators worldwide or directly distributed to the local market. The generators, colloquially known as moly cows, are devices designed to provide radiation shielding for transport and to minimize the extraction work done at the medical facility. A typical dose rate at 1 metre from the Tc generator is 20-50 μSv/h during transport. These generators output declines with time and must be replaced weekly, since the half-life of Mo is still only 66 hours.
Molybdenum-99 spontaneously decays to excited states of Tc through beta decay. Over 87% of the decays lead to the excited state of Tc. A electron and a electron antineutrino are emitted in the process (Mo → Tc + + ). The electrons are easily shielded for transport, and Tc generators are only minor radiation hazards, mostly due to secondary X-rays produced by the electrons (also known as Bremsstrahlung).
At the hospital, the Tc that forms through Mo decay is chemically extracted from the technetium-99m generator. Most commercial Mo/Tc generators use column chromatography, in which Mo in the form of water-soluble molybdate, MoO is adsorbed onto acid alumina (AlO). When the Mo decays, it forms pertechnetate TcO, which, because of its single charge, is less tightly bound to the alumina. Pulling normal saline solution through the column of immobilized MoO elutes the soluble TcO, resulting in a saline solution containing the Tc as the dissolved sodium salt of the pertechnetate. One technetium-99m generator, holding only a few micrograms of Mo, can potentially diagnose 10,000 patients because it will be producing Tc strongly for over a week. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, an active ester is an ester functional group that is highly susceptible toward nucleophilic attack. Activation can be imparted by modifications of the acyl or the alkoxy components of a normal ester, say ethyl acetate. Typical modifications call for electronegative substituents. Active esters are employed in both synthetic and biological chemistry. | 0 | Theoretical and Fundamental Chemistry |
* Till early 1970s, it was often recommended for use in victims of rape in order to avoid pregnancy. The idea stemmed from the fact that, in the laboratory, Lugols iodine appeared to kill sperm cells even in such great dilutions as 1:32. Thus it was thought that an intrauterine application of Lugols iodine, immediately after the event, would help avoid pregnancy. | 0 | Theoretical and Fundamental Chemistry |
A non-Newtonian fluid is a fluid that does not follow Newton's law of viscosity, that is, it has variable viscosity dependent on stress. In particular, the viscosity of non-Newtonian fluids can change when subjected to force. Ketchup, for example, becomes runnier when shaken and is thus a non-Newtonian fluid. Many salt solutions and molten polymers are , as are many commonly found substances such as custard, toothpaste, starch suspensions, corn starch, paint, blood, melted butter, and shampoo.
Most commonly, the viscosity (the gradual deformation by shear or tensile stresses) of non-Newtonian fluids is dependent on shear rate or shear rate history. Some non-Newtonian fluids with shear-independent viscosity, however, still exhibit normal stress-differences or other non-Newtonian behavior. In a Newtonian fluid, the relation between the shear stress and the shear rate is linear, passing through the origin, the constant of proportionality being the coefficient of viscosity. In a non-Newtonian fluid, the relation between the shear stress and the shear rate is different. The fluid can even exhibit time-dependent viscosity. Therefore, a constant coefficient of viscosity cannot be defined.
Although the concept of viscosity is commonly used in fluid mechanics to characterize the shear properties of a fluid, it can be inadequate to describe non-Newtonian fluids. They are best studied through several other rheological properties that relate stress and strain rate tensors under many different flow conditions—such as oscillatory shear or extensional flow—which are measured using different devices or rheometers. The properties are better studied using tensor-valued constitutive equations, which are common in the field of continuum mechanics. | 1 | Applied and Interdisciplinary Chemistry |
The coordination numbers are well defined for atoms in the interior of a crystal lattice: one counts the nearest neighbors in all directions. The number of neighbors of an interior atom is termed the bulk coordination number. For surfaces, the number of neighbors is more limited, so the surface coordination number is smaller than the bulk coordination number. Often the surface coordination number is unknown or variable. The surface coordination number is also dependent on the Miller indices of the surface. In a body-centered cubic (BCC) crystal, the bulk coordination number is 8, whereas, for the (100) surface, the surface coordination number is 4. | 0 | Theoretical and Fundamental Chemistry |
Using the stream function, one can express the velocity in terms of the vector potential
where , and is the unit vector pointing in the positive direction. This can also be written as the vector cross product
where we've used the vector calculus identity
Noting that , and defining , one can express the velocity field as
This form shows that the level surfaces of and the level surfaces of (i.e., horizontal planes) form a system of orthogonal stream surfaces. | 1 | Applied and Interdisciplinary Chemistry |
A compound may be labeled as dextrorotary by using the "(+)-" or "d-" prefix. Likewise, a laevorotary compound may be labeled using the "(−)-" or "l-" prefix. The lowercase "d-" and "l-" prefixes are obsolete, and are distinct from the "-" and "-" prefixes. The "-" and "-" prefixes are used to specify the enantiomer of chiral organic compounds in biochemistry and are based on the compound's absolute configuration relative to (+)-glyceraldehyde, which is the -form by definition. The prefix used to indicate absolute configuration is not directly related to the (+) or (−) prefix used to indicate optical rotation in the same molecule. For example, nine of the nineteen -amino acids naturally occurring in proteins are, despite the - prefix, actually dextrorotary (at a wavelength of 589 nm), and -fructose is sometimes called "laevulose" because it is laevorotary.
The - and - prefixes describe the molecule as a whole, as do the (+) and (−) prefixes for optical rotation. In contrast, the (R)- and (S)- prefixes from the Cahn–Ingold–Prelog priority rules characterize the absolute configuration of each specific chiral stereocenter with the molecule, rather than a property of the molecule as a whole. A molecule having exactly one chiral stereocenter (usually an asymmetric carbon atom) can be labeled (R) or (S), but a molecule having multiple stereocenters needs more than one label. For example, the essential amino acid -threonine contains two chiral stereocenters and is written (2S,3S)-threonine. There is no strict relationship between the R/S, the /, and (+)/(−) designations, although some correlations exist. For example, of the naturally occurring amino acids, all are , and most are (S). For some molecules the (R)-enantiomer is the dextrorotary (+) enantiomer, and in other cases it is the laevorotary (−) enantiomer. The relationship must be determined on a case-by-case basis with experimental measurements or detailed computer modeling. | 0 | Theoretical and Fundamental Chemistry |
Plastics exist in huge variety, however several types of commodity polymer dominate global production: polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET, PETE), polystyrene (PS), polycarbonate (PC), and poly(methyl methacrylate) (PMMA). The degradation of these materials is of primary importance as they account for most plastic waste.
These plastics are all thermoplastics and are more susceptible to degradation than equivalent thermosets, as those are more thoroughly cross-linked. The majority (PP, PE, PVC, PS and PMMA) are addition polymers with all-carbon backbones that are more resistant to most types of degradation. PET and PC are condensation polymers which contain carbonyl groups more susceptible to hydrolysis and UV-attack. | 0 | Theoretical and Fundamental Chemistry |
An example of a nucleogenic nuclide is neon-21 produced from neon-20 that absorbs a thermal neutron (though some neon-21 is also primordial). Other nucleogenic reactions that produce heavy neon isotopes are (fast neutron capture, alpha emission) reactions, starting with magnesium-24 and magnesium-25, respectively. The source of the neutrons in these reactions is often secondary neutrons produced by alpha radiation from natural uranium and thorium in rock. | 0 | Theoretical and Fundamental Chemistry |
La confusion sexuelle or mating disruption, was first discussed by the Institut national de la recherche agronomique in 1974 in Bordeaux, France.
Winemakers in France, Switzerland, Spain, Germany, and Italy were the first to use the method to treat vines against the larvae of the moth genus Cochylis. | 1 | Applied and Interdisciplinary Chemistry |
The first uncoupling protein discovered, UCP1, was discovered in the brown adipose tissues of hibernators and small rodents, which provide non-shivering heat to these animals. These brown adipose tissues are essential to maintaining the body temperature of small rodents, and studies with (UCP1)-knockout mice show that these tissues do not function correctly without functioning uncoupling proteins. In fact, these studies revealed that cold-acclimation is not possible for these knockout mice, indicating that UCP1 is an essential driver of heat production in these brown adipose tissues.
Elsewhere in the body, uncoupling protein activities are known to affect the temperature in micro-environments. This is believed to affect other proteins' activity in these regions, though work is still required to determine the true consequences of uncoupling-induced temperature gradients within cells.
The structure of human uncoupling protein 1 UCP1 has been solved by cryogenic-electron microscopy. The structure has the typical fold of a member of the SLC25 family. UCP1 is locked in a cytoplasmic-open state by guanosine triphosphate in a pH-dependent manner. | 1 | Applied and Interdisciplinary Chemistry |
A germicidal lamp (also known as disinfection lamp or sterilizer lamp) is an electric light that produces ultraviolet C (UVC) light. This short-wave ultraviolet light disrupts DNA base pairing, causing formation of pyrimidine dimers, and leads to the inactivation of bacteria, viruses, and protozoans. It can also be used to produce ozone for water disinfection. They are used in ultraviolet germicidal irradiation (UVGI).
There are four common types available:
* Low-pressure mercury lamps
* High-pressure mercury lamps
* Excimer lamps
* LEDs | 0 | Theoretical and Fundamental Chemistry |
New was born in Sydney in 1984. She represented Australia at the International Chemistry Olympiad in 2000 and 2001, winning bronze and gold medals respectively, and graduated from James Ruse Agricultural High School with a UAI of 100. She earned a bachelors degree in chemistry at the University of Sydney in 2005, where she completed her masters degree in 2006 with Professor Trevor Hambley. During her graduate studies she worked on fluorescent tags to monitor the cellular uptake and metabolism of anti-tumor complexes. New completed her doctoral studies at Durham University working with David Parker, graduating in 2010. Her work looked at the cellular behaviour of lanthanide complexes. | 0 | Theoretical and Fundamental Chemistry |
Pyridines and pyrimidines have shown good complexation properties for palladium and have been employed in the formation of catalysts suitable for Sonogashira couplings. The dipyrimidyl-palladium complex shown below has been employed in the copper-free coupling of iodo-, bromo-, and chlorobenzene with phenylacetylene using N-butylamine as base in THF solvent at 65 °C. Furthermore, all structural features of this complex have been characterized by extensive X-ray analysis, verifying the observed reactivity.
More recently, the dipyridylpalladium complex has been obtained and has been used in the copper-free Sonogashira coupling reaction of aryl iodides and bromides in N-methylpyrrolidinone (NMP) using tetra-n-butylammonium acetate (TBAA) as base at room temperature. This complex has also been used for the coupling of aryl iodides and bromides in refluxing water as solvent and in the presence of air, using pyrrolidine as base and TBAB as additive, although its efficiency was higher in N-methylpyrrolidinone (NMP) as solvent. | 0 | Theoretical and Fundamental Chemistry |
Biofiltration is used to treat wastewater from a wide range of sources, with varying organic compositions and concentrations. Many examples of biofiltration applications are described in the literature. Bespoke biofilters have been developed and commercialized for the treatment of animal wastes, landfill leachates, dairy wastewater, domestic wastewater.
This process is versatile as it can be adapted to small flows (< 1 m3/d), such as onsite sewage as well as to flows generated by a municipality (> 240 000 m3/d). For decentralized domestic wastewater production, such as for isolated dwellings, it has been demonstrated that there are important daily, weekly and yearly fluctuations of hydraulic and organic production rates related to modern families' lifestyle. In this context, a biofilter located after a septic tank constitutes a robust process able to sustain the variability observed without compromising the treatment performance.
In anaerobic wastewater treatment facilities, biogas is fed through a bio-scrubber and “scrubbed” with activated sludge liquid from an aeration tank. [Removal of hydrogen sulfide from an anaerobic biogas using a bio-scrubber - ScienceDirect] Most commonly found in wastewater treatment is the trickling filter process (TFs) [Chaudhary, 2003]. Trickling filters are an aerobic treatment that uses microorganisms on attached medium to remove organic matter from wastewater.
In primary wastewater treatment, biofiltration is used to control levels of biochemical oxygen, demand, chemical oxygen demand, and suspended solids. In tertiary treatment processes, biofiltration is used to control levels of organic carbon [ Carlson, 1998]. | 1 | Applied and Interdisciplinary Chemistry |
The Mayo-Lewis method uses a form of the copolymer equation relating to :
For each different monomer composition, a line is generated using arbitrary values. The intersection of these lines is the , for the system. More frequently, the lines do not intersect in a single point and the area in which most lines intersect can be given as a range of , and values. | 0 | Theoretical and Fundamental Chemistry |
The AMPA receptor (AMPAR) is the engine that drives excitatory postsynaptic potentials (EPSPs). While some forms of the AMPAR can conduct calcium, most AMPARs found in the neocortex do not. The AMPAR, upon binding two glutamate molecules, undergoes a conformational change that resembles the opening of a clam shell. This conformational change opens an ion channel within the AMPAR protein structure that allows sodium ions to flow into the cell and potassium ions to flow out (i.e. it is a mixed cation-conducting channel). The Na and K permeabilities of the AMPAR channel are roughly equal, so when this channel is open the resulting change in membrane potential tends towards zero (a bit more than halfway between the equilibrium potentials E and E). This balance point is reached at around 0 mV (i.e. the reversal potential of the EPSP current is roughly 0 mV). However, the postsynaptic membrane potential will not change by more than a few millivolts from resting potential with a single presynaptic release of glutamate, because not many AMPAR channels open. The lifetime of the glutamate in the synaptic cleft is too short to allow more than a brief opening of the AMPAR channel, thus causing only a small depolarization. The open AMPAR channel is often considered to be non-calcium permeable, but this is only an approximation as AMPARs with certain subunit compositions will allow calcium through, albeit at different levels and frequency to NMDARs.
Historically, the most widely used experimental means of inducing LTP has been to deliver a tetanic stimulation to the presynaptic axon of a synapse or group of synapses. The frequency of this tetanus is typically 100 Hz, and the duration typically 1 s. A single AMPAR-mediated EPSP has a rise time-to-peak of approximately 2–5 ms and a duration of approximately 30 ms. If a synapse is being stimulated at 100 Hz, the presynaptic neuron will be attempting to release glutamate once every 10 ms. An EPSP occurring only 10 ms after a previous EPSP will arrive at a time when that previous EPSP is at its peak amplitude. Thus, during a 100 Hz stimulus train, each EPSP will add to the membrane depolarization caused by the previous EPSPs. This synaptic summation drives the membrane potential toward values that could not be reached with single synaptic stimuli. As the EPSPs summate, they will exceed the spike threshold. | 1 | Applied and Interdisciplinary Chemistry |
In this oxidation scheme, ultraviolet light alone oxidizes the carbon within the sample to produce CO. The UV oxidation method offers the most reliable, low maintenance method of analyzing TOC in ultra-pure waters. | 0 | Theoretical and Fundamental Chemistry |
In aqueous solution the concentration of the hydroxide ion is related to the concentration of the hydrogen ion by
The first step in metal ion hydrolysis can be expressed in two different ways
It follows that . Hydrolysis constants are usually reported in the β form and therefore often have values much less than 1. For example, if and so that β = 10. In general when the hydrolysis product contains n hydroxide groups | 0 | Theoretical and Fundamental Chemistry |
* Diffusion constant, relates the flux of particles with the negative gradient of the concentration (see Fick's laws of diffusion)
* Thermal conductivity (see Fourier's law)
* Ionic conductivity
* Mass transport coefficient
* Shear viscosity , where is the viscous stress tensor (see Newtonian fluid)
* Electrical conductivity | 0 | Theoretical and Fundamental Chemistry |
Benzene is used mainly as an intermediate to make other chemicals, above all ethylbenzene (and other alkylbenzenes), cumene, cyclohexane, and nitrobenzene. In 1988 it was reported that two-thirds of all chemicals on the American Chemical Societys lists contained at least one benzene ring. More than half of the entire benzene production is processed into ethylbenzene, a precursor to styrene, which is used to make polymers and plastics like polystyrene. Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. Cyclohexane consumes around 10% of the worlds benzene production; it is primarily used in the manufacture of nylon fibers, which are processed into textiles and engineering plastics. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides. In 2013, the biggest consumer country of benzene was China, followed by the USA. Benzene production is currently expanding in the Middle East and in Africa, whereas production capacities in Western Europe and North America are stagnating.
Toluene is now often used as a substitute for benzene, for instance as a fuel additive. The solvent-properties of the two are similar, but toluene is less toxic and has a wider liquid range. Toluene is also processed into benzene. | 1 | Applied and Interdisciplinary Chemistry |
Bromothymol blue is synthesized by addition of elemental bromine to thymol blue in a solution in glacial acetic acid.
To prepare a solution for use as pH indicator, dissolve 0.10 g in 8.0 cm N/50 (a.k.a. 0.02 Normal) NaOH and dilute with water to 250 cm. To prepare a solution for use as indicator in volumetric work, dissolve 0.1 g in 100 cm of 50% (v/v) ethanol. | 0 | Theoretical and Fundamental Chemistry |
If , where (say, the Reynolds number) is a constant, then we have
In the limit , the limiting behaviour isa diffusional spreading of a source and therefore is given by
On the other hand, In the limit , the solution approaches that of the aforementioned Chandrasekhars shock-wave solution of the inviscid Burgers equation and is given by
The shock wave location and its speed are given by and | 1 | Applied and Interdisciplinary Chemistry |
Capsaicin is not soluble in water, and even large volumes of water will not wash it off, only dilute it. In general, victims are encouraged to blink vigorously in order to encourage tears, which will help flush the irritant from the eyes.
A study of five often-recommended treatments for skin pain (Maalox, 2% lidocaine gel, baby shampoo, milk, or water) concluded that: "...there was no significant difference in pain relief provided by five different treatment regimens. Time after exposure appeared to be the best predictor for a decrease in pain...".
Many ambulance services and emergency departments carry saline to remove the spray. Some of the OC and CS will remain in the respiratory system, but a recovery of vision and the coordination of the eyes can be expected within 7 to 15 minutes.
Some "triple-action" pepper sprays also contain "tear gas" (CS gas), which can be neutralized with sodium metabisulfite (Campden tablets), though it is not for use on a person, only for area clean up. | 1 | Applied and Interdisciplinary Chemistry |
A significant question remains unanswered. If the insidious dangers of alchemical elixir poisoning were common knowledge, why did people continue to consume them for centuries? Joseph Needham and his collaborators suggested three hypothetical explanations, and Michel Strickmann proposed another. | 1 | Applied and Interdisciplinary Chemistry |
*https://pubs.aip.org/aip/adv/article/9/7/075112/22584/Reactor-Monte-Carlo-RMC-model-validation-and
*[https://web.archive.org/web/20080703183328/http://nuclear.inl.gov/52reactors.shtml List of reactors at INL and picture of ATR core]
*[https://web.archive.org/web/20051108154456/http://teton.if.uidaho.edu/drying.html ATR plate fuel] | 0 | Theoretical and Fundamental Chemistry |
Source: [https://www.nace.org/membership/member-resources/awards/frank-newman-speller-award NACE International]
*1947 - Frank Newman Speller
*1948 - John M. Pearson
*1949 - Francis L. LaQue
*1950 - O.C. Mudd
*1951 - Kirk H. Logan
*1952 - Starr Thayer
*1953 - Scott P. Ewing
*1954 - E.H. Dix, Jr.
*1955 - Gordon N. Scott
*1956 - Mars G. Fontana
*1957 - Walter F. Rogers
*1958 - Robert J. Kuhn
*1959 - A. Wachter
*1960 - J.C. Hudson
*1961 - K.G. Compton
*1962 - C.P. Larrabee
*1963 - Thomas P. May
*1964 - Hugh P. Godard
*1965 - F.W. Wink
*1966 - Richard S. Treseder
*1967 - John D. Sudbury
*1968 - Lee P. Sudrabin
*1969 - Charles G. Munger
*1970 - Arland W. Peabody
*1971 - Andrew Dravnieks
*1972 - No recipient
*1973 - Fred M. Reinhart
*1974 - K.N. Barnard
*1975 - Bernard Husock
*1976 - E.H. Phelps
*1977 - Walter K. Boyd
*1978 - Joseph B. Cotton
*1979 - M.C. Miller
*1980 - H. Spahn
*1981 - J.H. Morgan
*1982 - Richard F. Stratful
*1983 - Ernest W. Haycock
*1984 - Warren E. Berry
*1985 - Stanley L. Lopata
*1986 - R.N. Miller
*1987 - Einar Mattsson
*1988 - Robert A. Baboian
*1989 - A.J. Sedricks
*1990 - M.E. Indig
*1991 - Sheldon W. Dean
*1993 - Bryan E. Wilde
*1994 - S. Evans
*1995 - P.R. Rhodes
*1996 - Peter L. Andresen
*1997 - Jacques-Philippe Berge
*1998 - H. Okada
*1999 - Herbert E. Townsend
*2000 - Peter M. Scott
*2001 - G. Schick
*2002 - G.M. Gordon
*2003 - R.W. Schutz
*2004 - Boris A. Miksic
*2005 - D. Knotkova-Cermakova
*2006 - Masakatsu Ueda
*2007 - Jorge A. González
*2008 - David C. Silverman
*2009 - Bruce Hinton
*2010 - Andrew Garner
*2011 - Pierre Combrade
*2012 - William Hartt
*2013 - John Beavers
*2014 - Shunichi Suzuki
*2015 - Jeffrey Gorman
*2016 - David Shifler
*2017 - Narasi Sridhar
*2018 - Robert Tapping
*2019 - U. Kamachi Mudali
*2020 - Roy Johnsen | 1 | Applied and Interdisciplinary Chemistry |
Phosphine gas is denser than air and hence may collect in low-lying areas. It can form explosive mixtures with air, and may also self-ignite. | 0 | Theoretical and Fundamental Chemistry |
Lithuanias first peat moss cultivation trial was in 2011, in Aukštumala Moor in Nemunas Delta Regional Park. Researchers from Vilnius Institute of Botany transplanted sections of Sphagnum' from a neighbouring degraded raised bog to the exposed peat surface. They found that 94% of the patches survived and expanded to the exposed peat.
The ongoing "DESIRE" project is investigating peatland restoration and paludiculture in the Neman River catchment area to reduce nutrient run-off into the Baltic. | 1 | Applied and Interdisciplinary Chemistry |
The stability class can be defined also by using the
* Temperature gradient
* fluctuations in wind direction
* Richardson number
* Bulk Richardson number
* Monin–Obukhov length | 1 | Applied and Interdisciplinary Chemistry |
In the last years, in silico medicine turned out to be promising, aiding scientists and clinicians to prevent and adequately cure several diseases. Computational modeling aid in understanding complex phenomena, allowing scientists to vary parameters aiming to measure variables that otherwise could have not been investigated.
In the field of electrophysiology, the pharmacological cardiotoxicity assessment can be carried out leveraging specific computational models. According to the type and parameters to be investigated in the research, it is possible to analyze the pharmacological effect on the atria and ventricles separately.
Since the two cardiac chambers are very different each other and play a key role both on a functional and anatomical basis, suitable computational models have to be accounted for to describe their different behaviour. During the years, several models have been developed o best characterize and replicate the cellular action potential behaviour of the most relevant anatomical region of the heart, such as Courtemanche model for atria or O'Hara model for ventricles. | 1 | Applied and Interdisciplinary Chemistry |
Propionyl-CoA accumulation can prove toxic to different organisms. Since different cycles have been proposed regarding how propionyl-CoA is transformed into pyruvate, one studied mechanism is the methylcitrate cycle. The initial reaction is beta-oxidation to form the propionyl-CoA which is further broken down by the cycle. This pathway involves the enzymes both related to the methylcitrate cycle as well as the citric acid cycle. These all contribute to the overall reaction to detoxify the bacteria from harmful propionyl-CoA. It is also attributed as a resulting pathway due to the catabolism of fatty acids in mycobacteria. In order to proceed, the prpC gene codes for methylcitrate synthase, and if not present, the methylcitrate cycle will not occur. Instead, catabolism proceeds through propionyl-CoA carboxylase. This mechanism is shown below to the left along with the participating reactants, products, intermediates, and enzymes. | 1 | Applied and Interdisciplinary Chemistry |
Many reef aquarium keepers use RO systems to make fish-friendly seawater. Ordinary tap water can contain excessive chlorine, chloramines, copper, nitrates, nitrites, phosphates, silicates, or other chemicals detrimental to marine organisms. Contaminants such as nitrogen and phosphates can lead to unwanted algae growth. An effective combination of both RO and deionization is popular among reef aquarium keepers, and is preferred above other water purification processes due to the low cost of ownership and operating costs. Where chlorine and chloramines are found in the water, carbon filtration is needed before RO, as common residential membranes do not address these compounds.
Freshwater aquarists also use RO to duplicate the soft waters found in many tropical waters. While many tropical fish can survive in treated tap water, breeding can be impossible. Many aquatic shops sell containers of RO water for this purpose. | 0 | Theoretical and Fundamental Chemistry |
The fixed carbon content of the coal is the carbon found in the material which is left after volatile materials are driven off. This differs from the ultimate carbon content of the coal because some carbon is lost in hydrocarbons with the volatiles. Fixed carbon is used as an estimate of the amount of coke that will be yielded from a sample of coal. Fixed carbon is determined by removing the mass of volatiles determined by the volatility test, above, from the original mass of the coal sample. | 0 | Theoretical and Fundamental Chemistry |
Although most consider the French physicist Nicolas Sadi Carnot to be the first true thermodynamicist, the term thermodynamics itself wasnt coined until 1849 by Lord Kelvin in his publication An Account of Carnots Theory of the Motive Power of Heat.
The first thermodynamic textbook was written in 1859 by William Rankine, a civil and mechanical engineering professor at the University of Glasgow. | 0 | Theoretical and Fundamental Chemistry |
In 1933, Prelog married Kamila Vitek. The couple had a son Jan (born 1949).
An intellectual with a wide cultural background, Prelog was one of the 109 Nobel Prize winners who signed the peace appeal for Croatia in 1991.
Vladimir Prelog died in Zürich, at the age of 91. An urn containing Prelog's ashes was ceremoniously interred at the Mirogoj cemetery in Zagreb on 27 September 2001. In 2008, a memorial to Prelog was unveiled in Prague. | 0 | Theoretical and Fundamental Chemistry |
The species was formerly grouped with the western meadow vole (M. drummondii) and the Florida salt marsh vole (M. dukecampbelli) as a single species with a very large range, but genetic evidence indicates that these are all distinct species. | 1 | Applied and Interdisciplinary Chemistry |
The Tabula Affinitatum is a table of chemical affinities between substances.
Commissioned around 1766 by the pharmacist Hubert Franz Hoefer for the apothecarys shop of the Grand Duke of Florence, this large table of chemical substances was designed to guide the preparer of pharmaceutical remedies in identifying the compounds most likely to combine with one another. The table is modeled on Étienne-François Geoffroys Table des différents Rapports observés entre différentes substances (Paris, 1718), from which it differs by adding a seventeenth column. The substances are identified by traditional alchemical symbols and the symbolic language in use in the seventeenth and early eighteenth centuries. The Florentine table does not, however, include the symbol of air. This means that it was compiled in a period when there was not yet a full awareness of the function of air as a chemically active substance, hence capable of combining with solids and liquids. A similar table is found among the plates of Diderot and dAlemberts Grande Encyclopédie.
The oil painting is 1540 × 1300 mm and is displayed in the Museo Galileo, Florence. | 1 | Applied and Interdisciplinary Chemistry |
HDAC3 has been found to be most closely related to HDAC8. HDAC3 contains a non-conserved region in the C-terminal region that was found to be required for transcriptional repression as well as its deacetylase activity. It also contains two regions, one called a Nuclear Localization Signal (NLS) as well as a Nuclear Export Signal (NES). The NLS functions as a signal for nuclear action while an NES functions with HDACs that perform work outside of the nucleus. A presence of both signals for HDAC3 suggests it travels between the nucleus and the cytoplasm. HDAC3 has even been found to interact with the plasma membrane. Silencing Mediator for Retinoic Acid and Thyroid Hormone (SMRT) receptors and Nuclear Receptor Co-Repressor (N-CoR) factors must be utilized by HDAC3 in order to activate it. Upon doing so, it gains the ability to co-precipitate with HDACs 4, 5, and 7. HDAC3 can also be found complexed together with HDAC-related protein (HDRP). HDACs 1 and 3 have been found to mediate Rb-RbAp48 interactions which suggests that it functions in cell cycle progression. HDAC3 also shows involvement in stem cell self-renewal and a transcription independent role in mitosis. | 0 | Theoretical and Fundamental Chemistry |
The genetic code was once believed to be universal: a codon would code for the same amino acid regardless of the organism or source. However, it is now agreed that the genetic code evolves, resulting in discrepancies in how a codon is translated depending on the genetic source. For example, in 1981, it was discovered that the use of codons AUA, UGA, AGA and AGG by the coding system in mammalian mitochondria differed from the universal code. Stop codons can also be affected: in ciliated protozoa, the universal stop codons UAA and UAG code for glutamine. The following table displays these alternative codons. | 1 | Applied and Interdisciplinary Chemistry |
In 2017, the Systems Thinking Into Chemistry Education (STICE) project proposed a systems thinking approach for (post)-secondary education in general chemistry education. Chemistry education has largely relied on a reductionist approach, which involves studying a complex topic as the sum of its parts. A reductionist approach is beneficial in increasing our knowledge of the natural world, however, it is insufficient in tackling global issues—sustainability, climate change, pollution, poverty, etc. Due to the limitations of a reductionist approach, researchers are suggesting a complementary systems thinking approach in chemistry education. A systems thinking approach involves learning concepts with a holistic perspective, allowing chemistry students to think critically about how chemistry relates to larger, societal issues. Researchers believe that a reductionist approach, complemented by a systems thinking approach, can produce global-minded chemists. | 1 | Applied and Interdisciplinary Chemistry |
As a result of the growing need to manage waste throughout greater Hamburg, the first commercially operating ATR facility – the Müllverwertung Rugenberger Damm (MVR) in Hamburg, Germany – was commissioned in 1999. The German Green Party has endorsed the specific features of the MVR facility in its "Concept 2020" initiative to cease all landfilling of waste by 2020 as an essential part of an integrated waste management system achieving the highest standards in the EfW industry. No landfilling of unprocessed waste has been allowed in Germany since 2005. | 1 | Applied and Interdisciplinary Chemistry |
In asymmetric addition of dialkylzinc compounds to aldehydes dialkyl zinc compounds can be used to perform asymmetric additions to aldehydes, generating substituted alcohols as products (See Barbier reaction). Chiral alcohols are prevalent in many natural products, drugs, and other important organic molecules. Dimethyl zinc is often used with an asymmetric amino alcohol, amino thiol, or other ligand to affect enantioselective additions to aldehydes and ketones. One of the first examples of this process, reported by Noyori and colleagues, features the use of the amino alcohol ligand (−)-3-exo-dimethylaminoisobornenol along with dimethylzinc to add a methyl group asymmetrically to benzaldehyde (see figure). Many ligands have been developed for binding zinc during addition reactions. TADDOLs (tetraaryl-1,3-dioxolane-4,5-dimethanols), which are derived from chiral tartaric acid, are a class of diol ligands often used to bind titanium, but have been adopted for zinc addition chemistry. These ligands require relatively low catalyst loadings, and can achieve up to 99% ee in dialkylzinc additions to aromatic and aliphatic aldehydes. Martens and colleagues have used azetidine alcohols as ligands for asymmetric zinc additions. The researchers found that when paired with catalytic n-butyllithium, diethylzinc can add to aromatic aldehydes with ee in the range of 94-100%.
Many studies have shown that in zinc addition reactions, the enantioselectivity is not linearly correlated with catalyst enantiomeric purity. Researchers propose that this is because the kinetics of the reaction are controlled by the relative concentrations of hetero and homodimeric catalytic complexes; that is, the system displays autocatalysis because the product alcohol itself acts as an asymmetric ligand on zinc. | 0 | Theoretical and Fundamental Chemistry |
Pressurized water reactor (PWR) fuel consists of cylindrical rods put into bundles. A uranium oxide ceramic is formed into pellets and inserted into Zircaloy tubes that are bundled together. The Zircaloy tubes are about in diameter, and the fuel cladding gap is filled with helium gas to improve heat conduction from the fuel to the cladding. There are about 179–264 fuel rods per fuel bundle and about 121 to 193 fuel bundles are loaded into a reactor core. Generally, the fuel bundles consist of fuel rods bundled 14×14 to 17×17. PWR fuel bundles are about long. In PWR fuel bundles, control rods are inserted through the top directly into the fuel bundle. The fuel bundles usually are enriched several percent in U. The uranium oxide is dried before inserting into the tubes to try to eliminate moisture in the ceramic fuel that can lead to corrosion and hydrogen embrittlement. The Zircaloy tubes are pressurized with helium to try to minimize pellet-cladding interaction which can lead to fuel rod failure over long periods. | 0 | Theoretical and Fundamental Chemistry |
Ibuprofen was derived from propionic acid by the research arm of Boots Group during the 1960s. The name is derived from the 3 functional groups: isobutyl (ibu) propionic acid (pro) phenyl (fen). Its discovery was the result of research during the 1950s and 1960s to find a safer alternative to aspirin. The molecule was discovered and synthesized by a team led by Stewart Adams, with a patent application filed in 1961. Adams initially tested the drug as treatment for his hangover. In 1985, Boots' worldwide patent for ibuprofen expired and generic products were launched.
The medication was launched as a treatment for rheumatoid arthritis in the United Kingdom in 1969, and in the United States in 1974. Later, in 1983 and 1984, it became the first NSAID (other than aspirin) to be available over the counter (OTC) in these two countries. Boots was awarded the Queen's Award for Technical Achievement in 1985 for the development of the drug.
In November 2013, work on ibuprofen was recognized by the erection of a Royal Society of Chemistry blue plaque at Boots' Beeston Factory site in Nottingham, which reads:
and another at BioCity Nottingham, the site of the original laboratory, which reads: | 0 | Theoretical and Fundamental Chemistry |
In male dominated Japan, Okamoto had to fight against sexism. She had a supervisor sympathetic to women in science during the early stages of her career.
However she and a coworker were asked to leave a pediatric conference, because the event was not for "women and children" (onna kodomo), a term she said in a 2012 interview she had never heard before.
After she had presented her research for the first time, the male audience members ridiculed her by asking if she was going to dance for them.
In the video interview, Okamoto said: "Men are always aware of the fundamental differences between men and women, and so cannot help but think of themselves as superior. So I used that to my advantage by stroking their egos. [...] Until [I had a child] I could compensate for the disadvantages of being a woman by working longer hours—10 hours per day instead of the 8 that the men worked." At Keio University, she could not find day care for her daughter and brought her to the laboratory, "[hoping] that she would behave herself". She carried her on her back as an infant while working in the lab. | 1 | Applied and Interdisciplinary Chemistry |
Hammond married Ellen Sarah Sophia Clarke (1833–1905), the sister-in-law of Samuel Warren, in 1874. Hammond survived her by three years upon her death in 1905.
Along with New York architect Alexander Twombly, who was the engineer and draftsman of Forest Paper Company, Hammond designed what is today known as Camp Hammond, set back from Yarmouths Main Street and from which Hammond could see his mill. Twombly also designed several buildings in Boston. Frederick Law Olmsted, who designed Central Park in New York City, designed the gardens of the property. With the Hammonds splitting their time between Boston and Yarmouth, the property became known as the Camp'.
The Hammonds also formed the Antiquarian Society in order to facilitate the 1890 purchase of the North Yarmouth and Freeport Baptist Meetinghouse on Yarmouth's Hillside Street. It became a library and museum, known as the Hillside Library.
Among the many roles Hammond took on without payment was as president of the Yarmouth Water Committee, established in 1895, which sourced its water supply from Hammond Spring on the property of Forest Paper Company. Hammond donated Forest Paper Company land for the 1903 construction of Merrill Memorial Library, on Main Street, which was designed by Alexander Longfellow, a nephew of the poet Henry Wadsworth Longfellow.
Hammond served in the Maine Legislature between 1868 and 1870, was on the Maine Board of Agriculture and the board of trustees of North Yarmouth Academy, was a member of the American Association for the Advancement of Science, the Society of Chemical Industry, the American Institute of Mining, Metallurgical, and Petroleum Engineers, The Society of Arts and Crafts of Boston, the Massachusetts Historical Society, the New England Historic Genealogical Society (from January 1876), The Bostonian Society and the Franklin Institute. He was also a Freemason.
A member of the American Horticultural Society, he was a keen arborist, and his knowledge of trees and plants earned him a place on the Overseers Committee at Harvard Universitys Gray Herbarium between 1888 and the time of his death.
The Hammonds were members of Yarmouths First Parish Congregational Church and Bostons Trinity Church. | 1 | Applied and Interdisciplinary Chemistry |
In many areas of science, Braggs law, Wulff–Braggs condition, or Laue–Bragg interference are a special case of Laue diffraction, giving the angles for coherent scattering of waves from a large crystal lattice. It describes how the superposition of wave fronts scattered by lattice planes leads to a strict relation between the wavelength and scattering angle. This law was initially formulated for X-rays, but it also applies to all types of matter waves including neutron and electron waves if there are a large number of atoms, as well as visible light with artificial periodic microscale lattices. | 0 | Theoretical and Fundamental Chemistry |
In an ideal system, the emitter is surrounded by converters so no light is lost. Realistically, geometries must accommodate the input energy (fuel injection or input light) used to heat the emitter. Additionally, costs have prohibited surrounding the filter with converters. When the emitter reemits light, anything that does not travel to the converters is lost. Mirrors can be used to redirect some of this light back to the emitter; however, the mirrors may have their own losses. | 0 | Theoretical and Fundamental Chemistry |
Caustic embrittlement is the phenomenon in which the material of a boiler becomes brittle due to the accumulation of caustic substances. | 1 | Applied and Interdisciplinary Chemistry |
Spin column-based nucleic acid purification is a solid phase extraction method to quickly purify nucleic acids. This method relies on the fact that nucleic acid will bind to the solid phase of silica under certain conditions. | 1 | Applied and Interdisciplinary Chemistry |
Intravenous dexmedetomidine exhibits linear pharmacokinetics with a rapid distribution half-life of approximately 6 minutes in healthy volunteers, and a longer and more variable distribution half-life in ICU patients. The terminal elimination half-life of intravenous dexmedetomidine ranged 2.1 to 3.1 hours in healthy adults and 2.2 to 3.7 hours in ICU patients. Plasma protein binding of dexmedetomidine is about 94% (mostly albumin).
Dexmedetomidine is metabolized by the liver, largely by glucuronidation (34%) as well as by oxidation via CYP2A6 and other Cytochrome P450 enzymes. As such, it should be used with caution in people with liver disease.
The majority of metabolized dexmedetomidine is excreted in the urine (~95%).
It can be absorbed sublingually. | 0 | Theoretical and Fundamental Chemistry |
The onset of the Iron Age in most parts of the world coincides with the first widespread use of the bloomery. While earlier examples of iron are found, their high nickel content indicates that this is meteoric iron. Other early samples of iron may have been produced by accidental introduction of iron ore in copper-smelting operations. Iron appears to have been smelted in the Middle East as early as 3000 BC, but coppersmiths, not being familiar with iron, did not put it to use until much later. In the West, iron began to be used around 1200 BC. | 1 | Applied and Interdisciplinary Chemistry |
Adiabatic electron-transfer is a type of oxidation-reduction processes. The mechanism is ubiquitous in nature in both the inorganic and biological spheres. Adiabatic electron-transfers proceed without making or breaking chemical bonds. Adiabatic electron-transfer can occur by either optical or thermal mechanisms. Electron transfer during a collision between an oxidant and a reductant occurs adiabatically on a continuous potential-energy surface. | 0 | Theoretical and Fundamental Chemistry |
Carbon added to sedimentary rocks can take the form of carbonates, or organic carbon compounds. In order of source quantity the organic carbon comes from phytoplankton, plants, bacteria and zooplankton. However terrestrial sediments may be mostly from higher plants, and some oxygen deficient sediments from water may be mostly bacteria. Fungi and other animals make insignificant contributions. On the oceans the main contributor of organic matter to sediments is plankton, either dead fragments or faecal pellets termed marine snow. Bacteria degrade this matter in the water column, and the amount surviving to the ocean floor is inversely proportional to the depth. This is accompanied by biominerals consisting of silicates and carbonates. The particulate organic matter in sediments is about 20% of known molecules 80% of material that cannot be analysed. Detritivores consume some of the fallen organic materials. Aerobic bacteria and fungi also consume organic matter in the oxic surface parts of the sediment. Coarse-grained sediments are oxygenated to about half a meter, but fine grained clays may only have a couple of millimetres exposed to oxygen. The organic matter in the oxygenated zone will become completely mineralized if it stays there long enough.
Deeper in sediments where oxygen is exhausted, anaerobic biological processes continue at a slower rate. These include anaerobic mineralization making ammonium, phosphate and sulfide ions; fermentation making short chain alcohols, acids or methyl amines; acetogenesis making acetic acid; methanogenesis making methane, and sulfate, nitrite and nitrate reduction. Carbon dioxide and hydrogen are also outputs. Under freshwater, sulfate is usually very low, so methanogenesis is more important. Yet other bacteria can convert methane, back into living matter, by oxidising with other substrates. Bacteria can reside at great depths in sediments. However sedimentary organic matter accumulates the indigestible components.
Deep bacteria may be lithotrophes, using hydrogen, and carbon dioxide as a carbon source.
In the oceans and other waters there is much dissolved organic materials. These are several thousand years old on average, and are called gelbstoff (yellow substance) particularly in fresh waters. Much of this is tannins. The nitrogen containing materials here appear to be amides, perhaps from peptidoglycans from bacteria. Microorganisms have trouble consuming the high molecular weight dissolved substances, but quickly consume small molecules.
From terrestrial sources black carbon produced by charring is an important component. Fungi are important decomposers in soil. | 0 | Theoretical and Fundamental Chemistry |
N-Methylmorpholine is the organic compound with the formula O(CHCH)NCH. It is a colorless liquid. It is a cyclic tertiary amine. It is used as a base catalyst for generation of polyurethanes and other reactions. It is produced by the reaction of methylamine and diethylene glycol as well as by the hydrogenolysis of N-formylmorpholine. It is the precursor to N-methylmorpholine N-oxide, a commercially important oxidant. | 0 | Theoretical and Fundamental Chemistry |
The spin angular momentum of an electron precesses counter-clockwise about the direction of the magnetic field. An electron has a negative charge, so the direction of its magnetic moment is opposite to that of its spin. | 0 | Theoretical and Fundamental Chemistry |
Hypopituitarism commonly develops after radiation therapy for sellar and parasellar neoplasms, extrasellar brain tumors, head and neck tumors, and following whole body irradiation for systemic malignancies. 40–50% of children treated for childhood cancer develop some endocrine side effect. Radiation-induced hypopituitarism mainly affects growth hormone and gonadal hormones. In contrast, adrenocorticotrophic hormone (ACTH) and thyroid stimulating hormone (TSH) deficiencies are the least common among people with radiation-induced hypopituitarism. Changes in prolactin-secretion is usually mild, and vasopressin deficiency appears to be very rare as a consequence of radiation. | 0 | Theoretical and Fundamental Chemistry |
The Wigner–Seitz cell always has the same point symmetry as the underlying Bravais lattice. For example, the cube, truncated octahedron, and rhombic dodecahedron have point symmetry O, since the respective Bravais lattices used to generate them all belong to the cubic lattice system, which has O point symmetry. | 0 | Theoretical and Fundamental Chemistry |
In the United States the EPA mandates certain treatment processes designed to significantly decrease levels of certain so-called indicator organisms, in biosolids. These include, "...operational standards for fecal coliforms, Salmonella sp. bacteria, enteric viruses, and viable helminth ova."
However, the US-based Water Environment Research Foundation has shown that some pathogens do survive sewage sludge treatment.
EPA regulations allow only biosolids with no detectable pathogens to be widely applied; those with remaining pathogens are restricted in use. | 1 | Applied and Interdisciplinary Chemistry |
Chloroplasts are a special type of a plant cell organelle called a plastid, though the two terms are sometimes used interchangeably. There are many other types of plastids, which carry out various functions. All chloroplasts in a plant are descended from undifferentiated proplastids found in the zygote, or fertilized egg. Proplastids are commonly found in an adult plant's apical meristems. Chloroplasts do not normally develop from proplastids in root tip meristems—instead, the formation of starch-storing amyloplasts is more common.
In shoots, proplastids from shoot apical meristems can gradually develop into chloroplasts in photosynthetic leaf tissues as the leaf matures, if exposed to the required light. This process involves invaginations of the inner plastid membrane, forming sheets of membrane that project into the internal stroma. These membrane sheets then fold to form thylakoids and grana.
If angiosperm shoots are not exposed to the required light for chloroplast formation, proplastids may develop into an etioplast stage before becoming chloroplasts. An etioplast is a plastid that lacks chlorophyll, and has inner membrane invaginations that form a lattice of tubes in their stroma, called a prolamellar body. While etioplasts lack chlorophyll, they have a yellow chlorophyll precursor stocked. Within a few minutes of light exposure, the prolamellar body begins to reorganize into stacks of thylakoids, and chlorophyll starts to be produced. This process, where the etioplast becomes a chloroplast, takes several hours. Gymnosperms do not require light to form chloroplasts.
Light, however, does not guarantee that a proplastid will develop into a chloroplast. Whether a proplastid develops into a chloroplast some other kind of plastid is mostly controlled by the nucleus and is largely influenced by the kind of cell it resides in. | 0 | Theoretical and Fundamental Chemistry |
Alternative means of assimilating iron are surface reduction, lowering of pH, utilization of heme, or extraction of protein-complexed metal. Recent data suggest that iron-chelating molecules with similar properties to siderophores, were produced by marine bacteria under phosphate limiting growth condition. In nature phosphate binds to different type of iron minerals, and therefore it was hypothesized that bacteria can use siderophore-like molecules to dissolve such complex in order to access the phosphate. | 1 | Applied and Interdisciplinary Chemistry |
Laser Doppler velocimetry, also known as laser Doppler anemometry, is the technique of using the Doppler shift in a laser beam to measure the velocity in transparent or semi-transparent fluid flows or the linear or vibratory motion of opaque, reflecting surfaces. The measurement with laser Doppler anemometry is absolute and linear with velocity and requires no pre-calibration. | 1 | Applied and Interdisciplinary Chemistry |
To suppress competing isomerization of the alkene, the rate of migratory insertion of the carbonyl into the carbon-metal bond of the alkyl must be relatively fast. The rate of insertion of the carbonyl carbon into the C-M bond is likely to be greater than the rate of beta-hydride elimination. | 0 | Theoretical and Fundamental Chemistry |
Imidapril, sold under the brand name Tanatril among others, is an ACE inhibitor used as an antihypertensive drug and for the treatment of chronic heart failure.
It was patented in 1982 and approved for medical use in 1993. | 0 | Theoretical and Fundamental Chemistry |
The tool called gpaGUI provides an interactive interface for geometric phase analysis. It allows to generate 2D maps of various crystallographic quantities using high-resolution images.
Since the geometric phase analysis is performed in frequency domain, the high-resolution image needs to be transformed into frequential representation using Fourier transform. Mathematically, the frequential image is a complex matrix with the size equal to the original image. Crystallographically, it can be seen as an artificial diffraction pattern of the original image depicting intensity peaks corresponding to the crystallographic planes present in the original image. After performing desired calculations, the frequential representation can be transformed back to the original spatial domain using inverse Fourier transform.
Various crystallographic analyses can be performed using the frequential image. If it is filtered so that only the information from a region close to a particular diffraction spot is used (the rest is set to zero), a filtered direct image obtained by inverse Fourier transform then depicts only the planes corresponding to the selected diffraction spot. Moreover, due to its complex nature, the frequential image can be used to calculate amplitude and phase. Together with a vector of one crystallographic plane depicted in the image, they can be used to generate a 2D map interplanar distance of given plane. If two vectors of non-parallel planes are known, the method can be used to generate maps of strain and displacement.
Graphical user interface of gpaGUI is vertically divided into two halves, each of which contains:
* Diffractogram preview allowing to select one diffraction spot corresponding to a crystallographic plane.
* Visualization of a selected quantity (input image, filtered image or one of the maps mentioned above) allowing to select point of interest or region of interest for further analysis.
* Results of detailed analysis of point or region of interest. The point analysis allows the user to select any pixel of the visualized map to see exact values of the particular pixel and its closest neighbourhood. If analysis of broader area is needed, a polygonal region can be outlined in the map allowing to enumerate its statistical details: mean, standard deviation, median, minimum, maximum and total area of the polygon.
Since each half of the interface allows to specify one crystallographic plane, gpaGUI allows to calculate all the aforementioned crystallographic quantities including those which require two vectors. Precision and repeatability of the whole analysis relies on accuracy of the diffraction peak localization. To overcome inaccuracy of manual peak localization (with a mouse click), gpaGUI provides a possibility to process the input image with in order to accurately localize and index the peaks. | 0 | Theoretical and Fundamental Chemistry |
In astrophysics, mass transfer is the process by which matter gravitationally bound to a body, usually a star, fills its Roche lobe and becomes gravitationally bound to a second body, usually a compact object (white dwarf, neutron star or black hole), and is eventually accreted onto it. It is a common phenomenon in binary systems, and may play an important role in some types of supernovae and pulsars. | 1 | Applied and Interdisciplinary Chemistry |
In condensed matter physics, second sound is a quantum mechanical phenomenon in which heat transfer occurs by wave-like motion, rather than by the more usual mechanism of diffusion. Its presence leads to a very high thermal conductivity. It is known as "second sound" because the wave motion of entropy and temperature is similar to the propagation of pressure waves in air (sound). The phenomenon of second sound was first described by Lev Landau in 1941. | 0 | Theoretical and Fundamental Chemistry |
Thermodynamically, proton coupled multiple-electron reduction of CO is easier than single electron reduction. But to manage multiple proton coupled multiple-electron processes is a huge challenge kinetically. This leads to a high overpotential for electrochemical heterogeneous reduction of CO to hydrocarbons and alcohols. Even further heterogeneous reduction of singly reduced CO radical anion is difficult because of repulsive interaction between negatively biased electrode and negatively charged anion.
Figure 2 shows that in case of a p-type semiconductor/liquid junction photo generated electrons are available at the semiconductor/liquid interface under illumination. The reduction of redox species happens at less negative potential on illuminated p-type semiconductor compared to metal electrode due to the band bending at semiconductor/liquid interface. Figure 3 shows that thermodynamically, some of the proton-coupled multi-electron CO reductions are within semiconductors band gap. This makes it feasible to photo-reduce CO on p-type semiconductors. Various p-type semiconductors have been successfully employed for CO photo reduction including p-GaP, p-CdTe, p-Si, p-GaAs, p-InP, and p-SiC. Kinetically, however, these reactions are extremely slow on given semiconductor surfaces; this leads to significant overpotential for CO reduction on these semiconductor surfaces. Apart from high overpotential; these systems have a few advantages including sustainability (nothing is consumed in this system apart from light energy), direct conversion of solar energy to chemical energy, utilization of renewable energy resource for energy intensive process, stability of the process (semiconductors are really stable under illumination) etc. A different approach for photo-reduction of CO involves molecular catalysts, photosensitizers and sacrificial electron donors. In this process sacrificial electron donors are consumed during the process and photosensitizers degrade under long exposure to illumination. | 0 | Theoretical and Fundamental Chemistry |
The discovery of msDNA has led to broader questions regarding where reverse transcriptase originated, as genes encoding for reverse transcriptase (not necessarily associated with msDNA) have been found in prokaryotes, eukaryotes, viruses and even archaea. After a DNA fragment coding for the production of msDNA in E. coli was discovered, it was conjectured that bacteriophages might have been responsible for the introduction of the RT gene into E. coli. These discoveries suggest that reverse transcriptase played a role in the evolution of viruses from bacteria, with one hypothesis stating that, with the help of reverse transcriptase, viruses may have arisen as a breakaway msDNA gene that acquired a protein coat. Since nearly all RT genes function in retrovirus replication and/or the movement of transposable elements, it is reasonable to imagine that retrons might be mobile genetic elements, but there has been little supporting evidence for such a hypothesis, save for the observed fact that msDNA is widely yet sporadically dispersed among bacterial species in a manner suggestive of both horizontal and vertical transfer. Since it is not known whether retron sequences per se represent mobile elements, retrons are functionally defined by their ability to produce msDNA while deliberately avoiding speculation about other possible activities. | 1 | Applied and Interdisciplinary Chemistry |
In the early years, people from the surrounding community used the mill tailings as fill dirt in various properties, such as their yards and gardens. A woman who played in such a yard as a child later sued Kerr-McGee over her Hodgkin's disease and settled out of court in 1988.
Radioactive waste from the plant was put in a local landfill that later became a public park called Reed-Keppler Park.
Kress Creek and West Branch Dupage River (including sediments, banks, and floodplains) were contaminated by years of rainwater runoff from REF going into a storm sewer and then into the creek. The floodplain includes people's yards.
The West Chicago Sewage Treatment Plant was contaminated when mill tailings from REF were used as fill dirt there. This also resulted in pollution of the West Branch Dupage River from runoff and erosion.
In 1991, the Illinois Department of Public Health found elevated cancer rates in the community. | 1 | Applied and Interdisciplinary Chemistry |
Vancomycin is a glycopeptide antibiotic medication used to treat a number of bacterial infections. It is used intravenously (injection into a vein) as a treatment for complicated skin infections, bloodstream infections, endocarditis, bone and joint infections, and meningitis caused by methicillin-resistant Staphylococcus aureus. Blood levels may be measured to determine the correct dose. Vancomycin is also taken orally (by mouth) as a treatment for severe Clostridium difficile colitis. When taken orally it is poorly absorbed.
Common side effects include pain in the area of injection and allergic reactions. Occasionally, hearing loss, low blood pressure, or bone marrow suppression occur. Safety in pregnancy is not clear, but no evidence of harm has been found, and it is likely safe for use when breastfeeding. It is a type of glycopeptide antibiotic and works by blocking the construction of a cell wall.
Vancomycin was approved for medical use in the United States in 1958. It is on the World Health Organizations List of Essential Medicines. The World Health Organization classifies vancomycin as critically important for human medicine. It is available as a generic medication. Vancomycin is made by the soil bacterium Amycolatopsis orientalis'. | 0 | Theoretical and Fundamental Chemistry |
The South African company Rand Refinery Limited rebuilt its smelter in 1986, incorporating two 1.5 t TBRCs and a small static reverberatory furnace for cupellation to produce doré bullion containing gold and silver. The original concept was to produce doré bullion directly from the TBRCs, but this proved impossible, as it was found impossible to take the oxidation stage to completion while maintaining temperatures at which the doré would remain molten. Consequently, the reverberatory cupellation furnace was necessary to complete the process.
In January 1993, the management team of Rand Refinery decided to review alternate technologies to replace the TBRC–reverberatory furnace circuit, with the objective of having cupellation undertaken in a single stage. After evaluating the possibility of modifying the existing TBRCs by replacing the existing lance–burner combination with a separate lance and burner, and considering complete replacement of the TBRCs with an Ausmelt top-submerged lance furnace, Rand Refinery decided to replace one of the TBRC with a 4 t BBOC. The remaining TBRC is used to treat litharge slag to recover the lead for sale.
The Rand Refinery BBOC was commissioned in 1994. The operators reported a 28% reduction in the operating costs when the BBOC’s costs were compared with those of the TBRC–reverberatory furnace combination. This included a 45% reduction in bulk oxygen costs and halving the number of operators required to run the plant. The BBOC’s refractory life was 13 weeks, compared to an average refractory life of 2 weeks for the TBRCs. Other maintenance costs also fell. | 1 | Applied and Interdisciplinary Chemistry |
The institute also contributes to the undergraduate programs and university studies as well as continuing vocational trainings. Academic staff is involved in several master programs and coordinates two of them. The institute is also engaged in an Erasmus Mundus master, «EACH» (Excellence in Analytical Chemistry), and the «pNMR Marie Curie Initial network». Regarding vocational training, the institute provides several trainings in a wide range of analytical techniques. | 0 | Theoretical and Fundamental Chemistry |
Insulators have two main functions:
# Enhancer-blocking insulators prevent distal enhancers from acting on the promoter of neighbouring genes
# Barrier insulators prevent silencing of euchromatin by the spread of neighbouring heterochromatin
While enhancer-blocking is classified as an inter-chromosomal interaction, acting as a barrier is classified as an intra-chromosomal interaction. The need for insulators arises where two adjacent genes on a chromosome have very different transcription patterns; it is critical that the inducing or repressing mechanisms of one do not interfere with the neighbouring gene. Insulators have also been found to cluster at the boundaries of topologically associating domains (TADs) and may have a role in partitioning the genome into "chromosome neighborhoods" - genomic regions within which regulation occurs.
Some insulators can act as both enhancer blocker and barriers, and some just have one of the two functions. Some examples of different insulators are:
* Drosophila melanogaster insulators gypsy and scs scs are both enhancer-blocking insulators
* Gallus gallus have insulators, Lys 5 A that have both enhancer-blocking and barrier activity, as well as HS4' that have only enhancer-blocking activity
* Saccharomyces cerevisiae insulators STAR and UAS are both barrier insulators
* Homo sapiens HS5 insulator acts as an enhancer-blocker | 1 | Applied and Interdisciplinary Chemistry |
The diphosphine ligands have received considerably more attention than the monophosphines and, perhaps as a consequence, have a much longer list of achievement. This class includes the first ligand to achieve high selectivity (DIOP), the first ligand to be used in industrial asymmetric synthesis (DIPAMP) and what is likely the best known chiral ligand (BINAP). Chiral diphosphine ligands are now ubiquitous in asymmetric hydrogenation.
<br /> | 0 | Theoretical and Fundamental Chemistry |
Example phases are:
*β-MgAl: 1168 atoms per unit cell, face-centred cubic, atoms arranged in Friauf polyhedra.
*ξ'–AlPdMn: 318 atoms per unit cell, face-centred orthorhombic, atoms arranged in Mackay-type clusters.
* (Bergman phase): 163 atoms per unit cell, body centred cubic, atoms arranged in Bergman clusters.
* (Taylor phase): 204 atoms per unit cell, face-centred orthorhombic, atoms arranged in Mackay-type clusters. | 1 | Applied and Interdisciplinary Chemistry |
Each piston is mechanically or magnetically operated to fill a cylinder with the fluid and then discharge the fluid. Each stroke represents a finite measurement of the fluid (can be a single or multi-piston device). | 1 | Applied and Interdisciplinary Chemistry |
An aquatic system lacking dissolved oxygen (0% saturation) is termed anaerobic, reducing, or anoxic.
In water, oxygen levels are approximately 7 ppm or 0.0007% in good quality water, but fluctuate.
Many organisms require hypoxic conditions. Oxygen is poisonous to anaerobic bacteria for example.
Oxygen depletion is typically expressed as a percentage of the oxygen that would dissolve in the water at the prevailing temperature and salinity. A system with low concentration—in the range between 1 and 30% saturation—is called hypoxic or dysoxic. Most fish cannot live below 30% saturation since they rely on oxygen to derive energy from their nutrients. Hypoxia leads to impaired reproduction of remaining fish via endocrine disruption. A "healthy" aquatic environment should seldom experience less than 80% saturation. The exaerobic zone is found at the boundary of anoxic and hypoxic zones.
Hypoxia can occur throughout the water column and also at high altitudes as well as near sediments on the bottom. It usually extends throughout 20-50% of the water column, but depends on the water depth and location of pycnoclines (rapid changes in water density with depth). It can occur in 10-80% of the water column. For example, in a 10-meter water column, it can reach up to 2 meters below the surface. In a 20-meter water column, it can extend up to 8 meters below the surface. | 0 | Theoretical and Fundamental Chemistry |
Generally this topic is discussed when covering tandem mass spectrometry fragmentation and occurs generally by the same mechanisms.
For example, of a mechanism of alpha-cleavage, an electron is knocked off an atom (usually by electron collision) to form a radical cation. Electron removal generally happens in the following order: 1) lone pair electrons, 2) pi bond electrons, 3) sigma bond electrons.
One of the lone pair electrons moves down to form a pi bond with an electron from an adjacent (alpha) bond. The other electron from the bond moves to an adjacent atom (not one adjacent to the lone pair atom) creating a radical. This creates a double bond adjacent to the lone pair atom (oxygen is a good example) and breaks/cleaves the bond from which the two electrons were removed.
In molecules containing carbonyl groups, alpha-cleavage often competes with McLafferty rearrangement. | 0 | Theoretical and Fundamental Chemistry |
When used in the context of the Boussinesq approximation the densimetric Froude number is defined as
where is the reduced gravity:
The densimetric Froude number is usually preferred by modellers who wish to nondimensionalize a speed preference to the Richardson number which is more commonly encountered when considering stratified shear layers. For example, the leading edge of a gravity current moves with a front Froude number of about unity. | 1 | Applied and Interdisciplinary Chemistry |
RNA interference(RNAi) is a process that occurs naturally within the cytoplasm inhibiting gene expression at specific sequences. Regulation of gene expression through RNAi is possible by introducing small interfering RNAs(siRNAs), which effectively silence expression of a targeted gene. RNAi activates the RNA-induced silencing complex(RISC) containing siRNA, siRNA derived from cleaved dsRNA. The siRNA guides the RISC complex to a specific sequence on the mRNA that is cleaved by RISC and, consequently, silences those genes.
However, without modifications to the RNA backbone or inclusion of inverted bases at either end, siRNA instability in the plasma makes it extremely difficult to apply this technique in vivo. Pattern recognition receptors(PRRs), which can be grouped as endocytic PRRs or signaling PRRs, are expressed in all cells of the innate immune system. Signaling PRRs, in particular, include Toll-like receptors(TLRs) and are involved primarily with identifying pathogen-associated molecular patterns(PAMPs). For example, TLRs can recognize specific regions conserved in various pathogens, recognition stimulating an immune response with potentially devastating effects to the organism. In particular, TLR 3 recognizes both dsRNA characteristic of viral replication and siRNA, which is also double-stranded. In addition to this instability, another limitation of siRNA therapy concerns the inability to target a tissue with any specificity.
SNALPs, though, may provide the stability and specificity required for this mode of RNAi therapy to be effective. Consisting of a lipid bilayer, SNALPs are able to provide stability to siRNAs by protecting them from nucleases within the plasma that would degrade them. In addition, delivery of siRNAs is subject to endosomal trafficking, potentially exposing them to TLR3 and TLR7, and can lead to activation of interferons and proinflammatory cytokines. However, SNALPs allow siRNA uptake into the endosome without activating Toll-like receptors and consequently stimulating an impeding immune response, thus enabling siRNA escape from the endosome. | 1 | Applied and Interdisciplinary Chemistry |
The Fischer–Tropsch process involves a series of chemical reactions that produce a variety of hydrocarbons, ideally having the formula (CH). The more useful reactions produce alkanes as follows:
: (2n + 1) H + n CO → CH + n HO
where n is typically 10–20. The formation of methane (n = 1) is unwanted. Most of the alkanes produced tend to be straight-chain, suitable as diesel fuel. In addition to alkane formation, competing reactions give small amounts of alkenes, as well as alcohols and other oxygenated hydrocarbons.
The reaction is a highly exothermic reaction due to a standard reaction enthalpy (ΔH) of −165 kJ/mol CO combined. | 0 | Theoretical and Fundamental Chemistry |
In crystallography, atomic packing factor (APF), packing efficiency, or packing fraction is the fraction of volume in a crystal structure that is occupied by constituent particles. It is a dimensionless quantity and always less than unity. In atomic systems, by convention, the APF is determined by assuming that atoms are rigid spheres. The radius of the spheres is taken to be the maximum value such that the atoms do not overlap. For one-component crystals (those that contain only one type of particle), the packing fraction is represented mathematically by
where N is the number of particles in the unit cell, V is the volume of each particle, and V is the volume occupied by the unit cell. It can be proven mathematically that for one-component structures, the most dense arrangement of atoms has an APF of about 0.74 (see Kepler conjecture), obtained by the close-packed structures. For multiple-component structures (such as with interstitial alloys), the APF can exceed 0.74.
The atomic packing factor of a unit cell is relevant to the study of materials science, where it explains many properties of materials. For example, metals with a high atomic packing factor will have a higher "workability" (malleability or ductility), similar to how a road is smoother when the stones are closer together, allowing metal atoms to slide past one another more easily. | 0 | Theoretical and Fundamental Chemistry |
In Bronze Age Britain, gold objects were prestigious items, and archaeologists believe that those who owned them, or were buried with them, had a high status in society. Archaeologist George Eogan noted that gold reflected "ostentation in society, a society that has divisions along rank." | 1 | Applied and Interdisciplinary Chemistry |
Guderley–Landau–Stanyukovich problem describes the time evolution of converging shock waves. The problem was discussed by G. Guderley in 1942 and independently by Lev Landau and K. P. Stanyukovich in 1944, where the later authors' analysis was published in 1955. | 1 | Applied and Interdisciplinary Chemistry |
A classic example of transition metal-assisted dearomatization is the Buchner ring expansion. Catalytic asymmetric dearomatization reactions (CADA) are used in enantioselective synthesis. | 0 | Theoretical and Fundamental Chemistry |
On May 19, 2003, Paul Anastas along with his future wife, Julie Zimmerman created the 12 Principles of Green Engineering. This expanded upon the 12 Principles of Green Chemistry to not only include the guidelines for what an environmentally conscious chemical should be in theory, but also what steps should be followed to create an environmentally conscious alternative to the chemical. Environmentally conscious thought can be applied to engineering disciplines such as civil and mechanical engineers when considering practices with negative environmental impacts, such as concrete hydration. These principles still were centered around chemical processes, with about half pertaining to engineers. There are many ways that both the 12 Principles of Green Chemistry and 12 Principles of Green Engineering interact, referred to by Tse-Lun Chen et al. as "cross connections". Every one Principle of Green Engineering has one or more corresponding "cross connections" to Principles of Green Chemistry. For example, principle 1 of green engineering is "Inherent Rather than Circumstantial", which has cross connections to principles 1, 3, and 8 of green chemistry. | 1 | Applied and Interdisciplinary Chemistry |
*ISO.15730:2000 Metallic and other Inorganic Coatings - Electropolishing as a Means of Smoothing and Passivating Stainless Steel
*ASME BPE Standards for Electropolishing Bioprocessing Equipment
*SEMI F19, Electropolishing Specifications for Semiconductor Applications
*ASTM B 912-02 (2008), Passivation of Stainless Steels Using Electropolishing
*ASTM E1558, Standard Guide for Electrolytic Polishing of Metallographic Specimens | 1 | Applied and Interdisciplinary Chemistry |
Treatment with RO is limited, resulting in low recoveries on high concentration (measured with electrical conductivity) and membrane fouling. RO applicability is limited by conductivity, organics, and scaling inorganic elements such as CaSO, Si, Fe and Ba. Low organic scaling can use two different technologies: spiral wound membrane, and (for high organic scaling, high conductivity and higher pressure (up to 90 bars)), disc tube modules with RO membranes can be used. Disc tube modules were redesigned for landfill leachate purification that is usually contaminated with organic material. Due to the cross-flow, it is given a flow booster pump that recirculates the flow over the membrane between 1.5 and 3 times before it is released as a concentrate. High velocity protects against membrane scaling and allows membrane cleaning. | 0 | Theoretical and Fundamental Chemistry |
Compared to other integration-based techniques that compute field lines of the input vector field, LIC has the advantage that all structural features of the vector field are displayed, without the need to adapt the start and end points of field lines to the specific vector field. In other words, it shows the topology of the vector field.
In user testing, LIC was found to be particularly good for identifying critical points. | 1 | Applied and Interdisciplinary Chemistry |
In some instances, differentiation between species may be problematic when using 16S rRNA sequences due to similarity. In such instances, 23S rRNA may be a better alternative. The global standard library of rRNA sequences is constantly becoming larger and continuously being updated, and thus the possibility of a random hybridization event between a specifically-designed probe (based on complete and current data from a range of test organisms) and an undesired/unknown target organism cannot be easily dismissed. On the contrary, it is plausible that there exist microorganisms, yet to be identified, which are phylogenetically members of a probe target group, but have partial or near-perfect target sites, usually applies when designing group-specific probes.
Probably the greatest practical limitation to this technique is the lack of available automation. | 1 | Applied and Interdisciplinary Chemistry |
A solution of a chemical compound in a liquid will become supersaturated when the temperature of the saturated solution is changed. In most cases solubility decreases with decreasing temperature; in such cases the excess of solute will rapidly separate from the solution as crystals or an amorphous powder.
In a few cases the opposite effect occurs. The example of sodium sulfate in water is well-known and this was why it was used in early studies of solubility.
Recrystallization is a process used to purify chemical compounds. A mixture of the impure compound and solvent is heated until the compound has dissolved. If there is some solid impurity remaining it is removed by filtration. When the temperature of the solution is subsequently lowered it briefly becomes supersaturated and then the compound crystallizes out until chemical equilibrium at the lower temperature is achieved. Impurities remain in the supernatant liquid. In some cases crystals do not form quickly and the solution remains supersaturated after cooling. This is because there is a thermodynamic barrier to the formation of a crystal in a liquid medium. Commonly this is overcome by adding a tiny crystal of the solute compound to the supersaturated solution, a process known as "seeding". Another process in common use is to rub a rod on the side of a glass vessel containing the solution to release microscopic glass particles which can act as nucleation centres. In industry, centrifugation is used to separate the crystals from the supernatant liquid.
Some compounds and mixtures of compounds can form long-living supersaturated solutions. Carbohydrates are a class of such compounds; The thermodynamic barrier to formation of crystals is rather high because of extensive and irregular hydrogen bonding with the solvent, water. For example, although sucrose can be recrystallised easily, its hydrolysis product, known as "invert sugar" or "golden syrup" is a mixture of glucose and fructose that exists as a viscous, supersaturated, liquid. Clear honey contains carbohydrates which may crystallize over a period of weeks.
Supersaturation may be encountered when attempting to crystallize a protein. | 0 | Theoretical and Fundamental Chemistry |
In September 2011, three NASA investigators claimed that they identified tin whiskers on the accelerator position sensors of sampled Toyota Camry models that could contribute to the "stuck accelerator" crashes affecting certain Toyota models during 2005–2010. This contradicted an earlier 10-month joint investigation by the National Highway Traffic Safety Administration (NHTSA) and a large group of other NASA researchers that found no electronic defects.
In 2012, NHTSA maintained: "We do not believe that tin whiskers are a plausible explanation for these incidents...[the likely cause was] pedal misapplication."
Toyota also maintains that tin whiskers were not the cause of any stuck accelerator issues: "In the words of U.S. Transportation Secretary Ray LaHood, 'The verdict is in. There is no electronic-based cause for unintended high-speed acceleration in Toyotas. Period. According to a Toyota press release, "no data indicates that tin whiskers are more prone to occur in Toyota vehicles than any other vehicle in the marketplace." Toyota also states that "their systems are designed to reduce the risk that tin whiskers will form in the first place." | 1 | Applied and Interdisciplinary Chemistry |
Stripping works on the basis of mass transfer. The idea is to make the conditions favorable for the component, A, in the liquid phase to transfer to the vapor phase. This involves a gas–liquid interface that A must cross. The total amount of A that has moved across this boundary can be defined as the flux of A, N. | 0 | Theoretical and Fundamental Chemistry |
Tc remained a scientific curiosity until the 1950s when Powell Richards realized the potential of technetium-99m as a medical radiotracer and promoted its use among the medical community. While Richards was in charge of the radioisotope production at the Hot Lab Division of the Brookhaven National Laboratory, Walter Tucker and Margaret Greene were working on how to improve the separation process purity of the short-lived eluted daughter product iodine-132 from tellurium-132, its 3.2-days parent, produced in the Brookhaven Graphite Research Reactor. They detected a trace contaminant which proved to be Tc, which was coming from Mo and was following tellurium in the chemistry of the separation process for other fission products. Based on the similarities between the chemistry of the tellurium-iodine parent-daughter pair, Tucker and Greene developed the first technetium-99m generator in 1958. It was not until 1960 that Richards became the first to suggest the idea of using technetium as a medical tracer. | 0 | Theoretical and Fundamental Chemistry |
The presence of radioactive waste in the environment may cause long-term effects due to the activity and half-life of the radionuclides, leading their impact to grow with time. These particles exist in various oxidation states and are found as oxides, coprecipitates, or as organic or inorganic complexes, according to their origin and ways of liberation. Most commonly they are found in oxidized form, which makes them more soluble in water and thus more mobile. Unlike organic contaminants, however, they cannot be destroyed and must be converted into a stable form or extracted from the environment.
The sources of radioactivity are not exclusive of human activity. Natural radioactivity does not come from human sources: it covers up to three fourths of the total radioactivity in the world and has its origins in the interaction of terrestrial elements with high energy cosmic rays (cosmogenic radionuclides) or in the existing materials on Earth since its formation (primordial radionuclides). In this regard, there are differences in the levels of radioactivity throughout the Earth's crust. India and mountains like the Alps are among the areas with the highest level of natural radioactivity due to their composition of rocks and sand.
The most frequent radionuclides in soils are naturally radium-226 (Ra), radon-222 (Rn), thorium-232 (Th), uranium-238 (U) and potassium-40 (K). Potassium-40 (up to 88% of total activity), carbon-14 (C), radium-226, uranium-238 and rubidium-87 (Rb) are found in ocean waters. Moreover, in groundwater abound radius radioisotopes such as radium-226 and radium-228 (Ra). They are also habitual in building materials radionuclides of uranium, thorium and potassium (the latter common to wood).
At the same time, anthropogenic radionuclides (caused by humans) are due to thermonuclear reactions resulting from explosions and nuclear weapons tests, discharges from nuclear facilities, accidents deriving from the reprocessing of commercial fuel, waste storage from these processes and to a lesser extent, nuclear medicine. Some polluted sites by these radionuclides are the US DOE facilities (like Hanford Site), the Chernobyl and Fukushima exclusion zones and the affected area of Chelyabinsk Oblast due to the Kyshtym disaster.
In ocean waters, the presence of tritium (H), cesium-137 (Cs), strontium-90 (Sr), plutonium-239 (Pu) and plutonium-240 (Pu) has significantly increased due to anthropogenic causes. In soils, technetium-99 (Tc), carbon-14, strontium-90, cobalt-60 (Co), iodine-129 (I), iodine-131 (I), americium-241 (Am), neptunium-237 (Np) and various forms of radioactive plutonium and uranium are the most common radionuclides.
The classification of radioactive waste established by the International Atomic Energy Agency (IAEA) distinguishes six levels according to equivalent dose, specific activity, heat released and half-life of the radionuclides:
*Exempt waste (EW): Waste that meets the criteria for exclusion from regulatory control for radiation protection purposes.
*Very short lived waste (VSLW): Waste with very short half-lives (often used for research and medical purposes) that can be stored over a limited period of up to a few years and subsequently cleared from regulatory control.
*Very low level waste (VLLW): Waste like soil and rubble (with low levels of activity concentration) that may also contain other hazardous waste.
*Low level waste (LLW): Waste that is above clearance levels and requires robust isolation and containment for periods of up to a few hundred years and is suitable for disposal in engineered near surface facilities. LLW include short lived radionuclides at higher levels of activity concentration and also long lived radionuclides, but only at relatively low levels of activity concentration.
*Intermediate level waste (ILW): Waste with long lived radionuclides that requires a greater degree of containment and isolation at greater depths.
*High level waste (HLW): Waste with large amounts of long lived radionuclides that need to be stored in deep, stable geological formations usually several hundred metres or more below the surface. | 1 | Applied and Interdisciplinary Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.