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The rough timeline of events during the putrefaction stage is as follows:
*1–2 days: Pallor mortis, algor mortis, rigor mortis, and livor mortis are the first steps in the process of decomposition before the process of putrefaction.
*2–3 days: Discoloration appears on the skin of the abdomen. The abdomen begins to swell due to gas formation.
*3–4 days: The discoloration spreads and discolored veins become visible.
*5–6 days: The abdomen swells noticeably and the skin blisters.
*10–20 days: Black putrefaction occurs, which is when noxious odors are released from the body and the parts of the body undergo a black discoloration.
*2 weeks: The abdomen is bloated; internal gas pressure nears maximum capacity.
*3 weeks: Tissues have softened. Organs and cavities are bursting. The nails and hair fall off.
*4 weeks: Soft tissues such as the internal organs begin to liquefy and the face becomes unrecognizable. The skin, muscles, tendons and ligaments degrade exposing the skeleton.
Order of organs' decomposition in the body:
#Larynx and trachea
#Infant brain
#Stomach
#Intestines
#Spleen
#Omentum and mesentery
#Liver
#Adult brain
#Heart
#Lungs
#Kidneys
#Bladder
#Esophagus
#Pancreas
#Diaphragm
#Blood vessels
#Uterus
The rate of putrefaction is greatest in air, followed by water, soil, and earth. The exact rate of putrefaction is dependent upon many factors such as weather, exposure and location. Thus, refrigeration at a morgue or funeral home can retard the process, allowing for burial in three days or so following death without embalming. The rate increases dramatically in tropical climates. The first external sign of putrefaction in a body lying in air is usually a greenish discoloration of the skin over the region of the cecum, which appears in 12–24 hours. The first internal sign is usually a greenish discoloration on the undersurface of the liver. | 1 | Biochemistry |
Optical tweezers (originally called single-beam gradient force trap) are scientific instruments that use a highly focused laser beam to hold and move microscopic and sub-microscopic objects like atoms, nanoparticles and droplets, in a manner similar to tweezers. If the object is held in air or vacuum without additional support, it can be called optical levitation.
The laser light provides an attractive or repulsive force (typically on the order of piconewtons), depending on the relative refractive index between particle and surrounding medium. Levitation is possible if the force of the light counters the force of gravity. The trapped particles are usually micron-sized, or even smaller. Dielectric and absorbing particles can be trapped, too.
Optical tweezers are used in biology and medicine (for example to grab and hold a single bacterium, a cell like a sperm cell or a blood cell, or a molecule like DNA), nanoengineering and nanochemistry (to study and build materials from single molecules), quantum optics and quantum optomechanics (to study the interaction of single particles with light). The development of optical tweezing by Arthur Ashkin was lauded with the 2018 Nobel Prize in Physics. | 1 | Biochemistry |
Eastern meadow voles eat most available species of grasses, sedges, and forbs, including many agricultural plant species. In summer and fall, grasses are cut into match-length sections to reach the succulent portions of the leaves and seedheads. Leaves, flowers, and fruits of forbs are also typical components of the summer diet. Fungi, primarily endogones (Endogone spp.), have been reported in eastern meadow vole diets. They occasionally consume insects and snails, and occasionally scavenge on animal remains; cannibalism is frequent in periods of high population density. Eastern meadow voles may damage woody vegetation by girdling when population density is high.
In winter, eastern meadow voles consume green basal portions of grass plants, often hidden under snow. Other winter diet components include seeds, roots, and bulbs. They occasionally strip the bark from woody plants. Seeds and tubers are stored in nests and burrows. Evidence of coprophagy is sparse, but thought to occur.
In an old-field community in Quebec, plants preferred by eastern meadow voles included quackgrass (Elytrigia repens), sedges, fescues (Festuca spp.), wild strawberry (Fragaria virginiana), timothy (Phleum pratense), bluegrasses (Poa spp.), and bird vetch (Vicia cracca). | 2 | Environmental Chemistry |
Tokita completed BS degree at Tokyo University in 1948, and his Ph.D. in physics and chemistry in 1957 at the University of Hokkaido. | 7 | Physical Chemistry |
The Clausius–Clapeyron relation leads to another equation also attributed to Kelvin, as the Kelvin equation. It explains why, because of surface tension, the vapor pressure for small droplets of liquid in suspension is greater than standard vapor pressure of that same liquid when the interface is flat. That is to say that when a liquid is forming small droplets, the equilibrium concentration of its vapor in its surroundings is greater. This arises because the pressure inside the droplet is greater than outside.
* is the standard vapor pressure for that liquid at that temperature and pressure.
* is the molar volume.
* is the gas constant
* is the Kelvin radius, the radius of the droplets.
The effect explains supersaturation of vapors. In the absence of nucleation sites, tiny droplets must form before they can evolve into larger droplets. This requires a vapor pressure many times the vapor pressure at the phase transition point.
This equation is also used in catalyst chemistry to assess mesoporosity for solids.
The effect can be viewed in terms of the average number of molecular neighbors of surface molecules (see diagram).
The table shows some calculated values of this effect for water at different drop sizes:
The effect becomes clear for very small drop sizes, as a drop of 1 nm radius has about 100 molecules inside, which is a quantity small enough to require a quantum mechanics analysis. | 6 | Supramolecular Chemistry |
Because most gases are difficult to observe directly, they are described through the use of four physical properties or macroscopic characteristics: pressure, volume, number of particles (chemists group them by moles) and temperature. These four characteristics were repeatedly observed by scientists such as Robert Boyle, Jacques Charles, John Dalton, Joseph Gay-Lussac and Amedeo Avogadro for a variety of gases in various settings. Their detailed studies ultimately led to a mathematical relationship among these properties expressed by the ideal gas law (see section below).
Gas particles are widely separated from one another, and consequently, have weaker intermolecular bonds than liquids or solids. These intermolecular forces result from electrostatic interactions between gas particles. Like-charged areas of different gas particles repel, while oppositely charged regions of different gas particles attract one another; gases that contain permanently charged ions are known as plasmas. Gaseous compounds with polar covalent bonds contain permanent charge imbalances and so experience relatively strong intermolecular forces, although the compounds net charge remains neutral. Transient, randomly induced charges exist across non-polar covalent bonds of molecules and electrostatic interactions caused by them are referred to as Van der Waals forces. The interaction of these intermolecular forces varies within a substance which determines many of the physical properties unique to each gas. A comparison of boiling points' for compounds formed by ionic and covalent bonds leads us to this conclusion.
Compared to the other states of matter, gases have low density and viscosity. Pressure and temperature influence the particles within a certain volume. This variation in particle separation and speed is referred to as compressibility. This particle separation and size influences optical properties of gases as can be found in the following list of refractive indices. Finally, gas particles spread apart or diffuse in order to homogeneously distribute themselves throughout any container. | 7 | Physical Chemistry |
Nucleotides are the monomers which polymerize into nucleic acids. All nucleotides contain a sugar, a phosphate, and a nitrogenous base. The bases found in nucleic acids are either purines or pyrimidines. In the more complex multicellular animals, they are both primarily produced in the liver but the two different groups are synthesized in different ways. However, all nucleotide synthesis requires the use of phosphoribosyl pyrophosphate (PRPP) which donates the ribose and phosphate necessary to create a nucleotide. | 1 | Biochemistry |
In bacteria, trans-translation, a highly conserved mechanism, acts as a direct counter to the accumulation of non-stop RNA, inducing decay and liberating the misregulated ribosome. Originally discovered in Escherichia coli, the process of trans-translation is made possible by the interactions between transfer-messenger RNA (tmRNA) and the cofactor protein SmpB, which allows for the stable binding of the tmRNA to the stalled ribosome. The current tmRNA model states that tmRNA and SmpB interact together in order to mimic tRNA. The SmpB protein recognizes the point of stalling, and directs the tmRNA to bind to the ribosomal A site. Once bound, SmpB engages in a transpeptidation reaction with the improperly functioning polypeptide chain through the donation of charged alanine. Through this process, the stalled and defective mRNA sequence is replaced with the SmpB RNA sequence, which encodes for the addition of an 11 amino acid tag on the C-terminus of the mRNA, which promotes degradation. The modified portion of RNA, along with the amino acid tag, are translated, and demonstrate incomplete characteristics, alerting and allowing for intracellular proteases to remove these harmful protein fragments, causing stalled ribosomes on damaged mRNA to resume function. | 1 | Biochemistry |
There are four major pools of phosphorus in freshwater ecosystems: dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), particulate inorganic phosphorus (PIP) and particulate organic phosphorus (POP). Dissolved material is defined as substances that pass through a 0.45 μm filter. DIP consists mainly of orthophosphate (PO) and polyphosphate, while DOP consists of DNA and phosphoproteins. Particulate matter are the substances that get caught on a 0.45 μm filter and do not pass through. POP consists of both living and dead organisms, while PIP mainly consists of hydroxyapatite, Ca(PO)OH . Inorganic phosphorus comes in the form of readily soluble orthophosphate. Particulate organic phosphorus occurs in suspension in living and dead protoplasm and is insoluble. Dissolved organic phosphorus is derived from the particulate organic phosphorus by excretion and decomposition and is soluble. | 9 | Geochemistry |
Pretreatment is important when working nanofiltration membranes due to their spiral-wound design. The material is engineered to allow one-way flow. The design does not allow for backpulsing with water or air agitation to scour its surface and remove accumulated solids. Since material cannot be removed from the membrane surface, it is susceptible to fouling (loss of production capacity). Therefore, pretreatment is a necessity for any RO or nanofiltration system. Pretreatment has four major components:
* Screening solids: Solids must be removed and the water treated to prevent membrane fouling by particle or biological growth, and reduce the risk of damage to high-pressure components.
* Cartridge filtration: String-wound polypropylene filters are typically used to remove particles of 1–5 µm diameter.
* Dosing: Oxidizing biocides, such as chlorine, are added to kill bacteria, followed by bisulfite dosing to deactivate the chlorine that can destroy a thin-film composite membrane. Biofouling inhibitors do not kill bacteria, while preventing them from growing slime on the membrane surface and plant walls.
* Prefiltration pH adjustment: If the pH, hardness and the alkalinity in the feedwater result in scaling while concentrated in the reject stream, acid is dosed to maintain carbonates in their soluble carbonic acid form.
:CO + HO = HCO + HO
:HCO + HO = HCO + HO
* Carbonic acid cannot combine with calcium to form calcium carbonate scale. Calcium carbonate scaling tendency is estimated using the Langelier saturation index. Adding too much sulfuric acid to control carbonate scales may result in calcium sulfate, barium sulfate, or strontium sulfate scale formation on the membrane.
* Prefiltration antiscalants: Scale inhibitors (also known as antiscalants) prevent formation of more scales than acid, which can only prevent formation of calcium carbonate and calcium phosphate scales. In addition to inhibiting carbonate and phosphate scales, antiscalants inhibit sulfate and fluoride scales and disperse colloids and metal oxides. Despite claims that antiscalants can inhibit silica formation, no concrete evidence proves that silica polymerization is inhibited by antiscalants. Antiscalants can control acid-soluble scales at a fraction of the dosage required to control the same scale using sulfuric acid.
* Some small-scale desalination units use beach wells. These are usually drilled on the seashore. These intake facilities are relatively simple to build and the seawater they collect is pretreated via slow filtration through subsurface sand/seabed formations. Raw seawater collected using beach wells is often of better quality in terms of solids, silt, oil, grease, organic contamination, and microorganisms, compared to open seawater intakes. Beach intakes may also yield source water of lower salinity. | 3 | Analytical Chemistry |
Diffuse correlation spectrometry is an extension of single-scattering dynamic light scattering (DLS). Single-scattering theory becomes inadequate as multiple scattering effects take place in biological thick tissues. Therefore, each scattering event contributes to the decay of the correlation function. The fields from individual photon paths are assumed to be uncorrelated; therefore, the total field autocorrelation function can be expressed as the weighted sum of the field autocorrelation function from each photon path.
The physical effect that makes the blood flow measurement possible is the temporal electric field autocorrelation function, shown in equation 1, diffuses through tissue in a manner that is similar to the light fluence rate.
In a highly scattering media, the photon fluence rate obeys the time-dependent diffusion equation, shown in equation 2. Optical imaging variables used in these equation are [https://imgur.com/a/5TDR72u here].
The blood flow measurement can be governed by the diffusion equation. Many tissue optical properties that affect diffusion such as tissue absorption and tissue reduced scattering coefficient are the same for temporal autocorrelation.
Using the same set of approximations, the temporal field autocorrelation function obeys a formally similar diffusion equation, shown in equation 3.
The mean-square particle displacement has been found to be reasonably well approximated as an “effective” Brownian motion, i.e., D represents the effective diffusion coefficient of the moving scatterers. In order to estimate relative blood flow from DCS data, we fit the measured intensity autocorrelation functions to solutions of the equation in equation 3. Currently, there is no evidence explaining why Brownian-motion correlation curves work effectively. This is the current empirical approach. The unit of αD (cm/s) has been found to correlate well with other blood flow measurement modalities and is used to measure blood flow. Therefore, is the blood flow index (BFI). To calculate the relative blood flow (rBF), the equation is shown in equation 4 where BFI is the DCS blood flow measurement at a baseline. | 7 | Physical Chemistry |
In the 19th century new developments such as the discovery of photography, Rowlands invention of the concave diffraction grating, and Schumanns works on discovery of vacuum ultraviolet (fluorite for prisms and lenses, low-gelatin photographic plates and absorption of UV in air below 185 nm) made advance to shorter wavelengths very fast. At the same time Dewar observed series in alkali spectra, Hartley found constant wave-number differences, Balmer discovered a relation connecting wavelengths in the visible hydrogen spectrum, and finally Rydberg derived a formula for wave-numbers of spectral series. Meanwhile, the substantial summary of past experiments performed by Maxwell (1873), resulted in his equations of electromagnetic waves.
In 1895, the German physicist Wilhelm Conrad Röntgen discovered and extensively studied X-rays, which were later used in X-ray spectroscopy. One year later, in 1896, French physicist Antoine Henri Becquerel discovered radioactivity, and Dutch physicist Pieter Zeeman observed spectral lines being split by a magnetic field.
In 1897, theoretical physicist, Joseph Larmor explained the splitting of the spectral lines in a magnetic field by the oscillation of electrons.
Physicist, Joseph Larmor, created the first solar system model of the atom in 1897. He also postulated the proton, calling it a “positive electron.” He said the destruction of this type of atom making up matter “is an occurrence of infinitely small probability.” | 7 | Physical Chemistry |
In high-energy nuclear physics, strangeness production in relativistic heavy-ion collisions is a signature and diagnostic tool of quark–gluon plasma (QGP) formation and properties. Unlike up and down quarks, from which everyday matter is made, heavier quark flavors such as strange and charm typically approach chemical equilibrium in a dynamic evolution process. QGP (also known as quark matter) is an interacting localized assembly of quarks and gluons at thermal (kinetic) and not necessarily chemical (abundance) equilibrium. The word plasma signals that color charged particles (quarks and/or gluons) are able to move in the volume occupied by the plasma. The abundance of strange quarks is formed in pair-production processes in collisions between constituents of the plasma, creating the chemical abundance equilibrium. The dominant mechanism of production involves gluons only present when matter has become a quark–gluon plasma. When quark–gluon plasma disassembles into hadrons in a breakup process, the high availability of strange antiquarks helps to produce antimatter containing multiple strange quarks, which is otherwise rarely made. Similar considerations are at present made for the heavier charm flavor, which is made at the beginning of the collision process in the first interactions and is only abundant in the high-energy environments of CERN's Large Hadron Collider. | 7 | Physical Chemistry |
*Fractional crystallization: separates ore and non-ore minerals according to their crystallization temperature. As early crystallizing minerals form from magma, they incorporate certain elements, some of which are metals. These crystals may settle onto the bottom of the intrusion, concentrating ore minerals there. Chromite and magnetite are ore minerals that form in this way.
*Liquid immiscibility: sulfide ores containing copper, nickel, or platinum may form from this process. As a magma changes, parts of it may separate from the main body of magma. Two liquids that will not mix are called immiscible; oil and water are an example. In magmas, sulfides may separate and sink below the silicate-rich part of the intrusion or be injected into the rock surrounding it. These deposits are found in mafic and ultramafic rocks. | 9 | Geochemistry |
They find use in coatings, adhesives, sealants and elastomers. Specific uses include industrial coatings, UV coating resins, floor coatings, hygiene coatings, wood coatings, adhesives, concrete coatings, automotive coatings, clear coatings and anticorrosive applications. They are also used in the design and manufacture of medical devices such as the polyurethane dressing, a liquid bandage based on polyurethane dispersion. To improve their functionality in flame retardant applications, products are being developed which have this feature built into the polymer molecule. They have also found use in general textile applications such as coating nonwovens. Leather coatings with antibacterial properties have also been synthesized using PUDs and silver nanoparticles. On a similar theme, recent (post 2020) innovations have included producing a waterborne polyurethane that has embedded silver particles to combat COVID. | 7 | Physical Chemistry |
Ribosomal frameshifting, also known as translational frameshifting or translational recoding, is a biological phenomenon that occurs during translation that results in the production of multiple, unique proteins from a single mRNA. The process can be programmed by the nucleotide sequence of the mRNA and is sometimes affected by the secondary, 3-dimensional mRNA structure. It has been described mainly in viruses (especially retroviruses), retrotransposons and bacterial insertion elements, and also in some cellular genes.
Small molecules, proteins, and nucleic acids have also been found to stimulate levels of frameshifting. In December 2023, it was reported that in vitro-transcribed (IVT) mRNAs in response to BNT162b2 (Pfizer–BioNTech) anti-COVID-19 vaccine caused ribosomal frameshifting. | 1 | Biochemistry |
Rhodium-catalyzed C-C bondactivation of strained spiropentanes leads to a cyclopentenones. In terms of mechanism, the reaction proceeds by apparent oxidative addition of the 4-5 carbon-carbon bond, leading to a rhodacyclobutane intermediate. In the presence of carbon monoxide, migratory insertion of CO into one of the carbon-rhodium bonds gives a rhodacyclopentanone intermediate. Beta-carbon elimination to form an alkene from the other carbon-rhodium bond leads to a rhodacyclohexanone intermediate with an exocyclic double bond. Reductive elimination of the two carbon-rhodium bonds followed by isomerization of the exocyclic double bond leads to the desired beta-substituted cyclopentenone product. This reaction was applied to the total synthesis of (±)-β-cuparenone.
Using the same rhodium(I) catalyst and C-C bond activation strategy one can access compounds with fused rings. Once again the reaction involves oxidative addition to give a rhodacyclobutane eventually affording a rhodacycloheptene intermediate. Insertion of carbon monoxide into one of the carbon-rhodium bonds form a rhodacyclooctenone intermediate that can reductively eliminate to yield a 6,7-fused ring system. The authors propose that the regioselectivity of the initial oxidative addition is controlled by coordination of the endocyclic double bond to the rhodium catalyst. | 0 | Organic 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 | Organic Chemistry |
Two missense mutations, H391Y and K422R, of PKM2 were found in cells from Bloom syndrome patients prone to developing cancer. Results show that, despite the presence of mutations in the inter-subunit contact domain, the K422R and H391Y mutant proteins maintained their homotetrameric structure, similar to the wild-type protein, but showed a loss of activity of 75 and 20%, respectively. H391Y showed a 6-fold increase in affinity for its substrate phosphoenolpyruvate and behaved like a non-allosteric protein with compromised cooperative binding. However, the affinity for phosphoenolpyruvate was lost significantly in K422R. Unlike K422R, H391Y showed enhanced thermal stability, stability over a range of pH values, a lesser effect of the allosteric inhibitor Phe, and resistance toward structural alteration upon binding of the activator (fructose 1,6-bisphosphate) and inhibitor (Phe). Both mutants showed a slight shift in the pH optimum from 7.4 to 7.0. The co-expression of homotetrameric wild type and mutant PKM2 in the cellular milieu resulting in the interaction between the two at the monomer level was substantiated further by in vitro experiments. The cross-monomer interaction significantly altered the oligomeric state of PKM2 by favoring dimerisation and heterotetramerization. In silico study provided an added support in showing that hetero-oligomerization was energetically favorable. The hetero-oligomeric populations of PKM2 showed altered activity and affinity, and their expression resulted in an increased growth rate of Escherichia coli as well as mammalian cells, along with an increased rate of polyploidy. These features are known to be essential to tumor progression.
Further, cells stably expressing exogenous wild- or mutant-PKM2 (K422R or H391Y) or co-expressing both wild and mutant (PKM2-K422R or PKM2-H391Y), were assessed for cancer metabolism and tumorigenic potential. Cells co-expressing PKM2 and mutant (K422R or H391Y) showed significantly aggressive cancer metabolism, compared to cells expressing either wild or mutant PKM2 independently. A similar trend was observed for oxidative endurance, tumorigenic potential, cellular proliferation and tumor growth. These observations signify the dominant negative nature of these mutations. Remarkably, PKM2-H391Y co-expressed cells showed a maximal effect on all the studied parameters. Such a dominant negative impaired function of PKM2 in tumor development is not known; also evidencing for the first time the possible predisposition of BS patients with impaired PKM2 activity to cancer, and the importance of studying genetic variations in PKM2 in future to understand their relevance in cancer in general. | 1 | Biochemistry |
The rate of reductive elimination is greatly influenced by the geometry of the metal complex. In octahedral complexes, reductive elimination can be very slow from the coordinatively saturated center, and often, reductive elimination only proceeds via a dissociative mechanism, where a ligand must initially dissociate to make a five-coordinate complex. This complex adopts a Y-type distorted trigonal bipyramidal structure where a π-donor ligand is at the basal position and the two groups to be eliminated are brought very close together. After elimination, a T-shaped three-coordinate complex is formed, which will associate with a ligand to form the square planar four-coordinate complex. | 0 | Organic Chemistry |
For substances in solution, the isoelectric point (pI) is defined as the pH at which the sum, weighted by charge value, of concentrations of positively charged species is equal to the weighted sum of concentrations of negatively charged species. In the case that there is one species of each type, the isoelectric point can be obtained directly from the pK values. Take the example of glycine, defined as AH. There are two dissociation equilibria to consider.
Substitute the expression for [AH] from the second equation into the first equation
At the isoelectric point the concentration of the positively charged species, , is equal to the concentration of the negatively charged species, , so
Therefore, taking cologarithms, the pH is given by
pI values for amino acids are listed at proteinogenic amino acid. When more than two charged species are in equilibrium with each other a full speciation calculation may be needed. | 7 | Physical Chemistry |
Pseudouridine, or Ψ, the overall most abundant post-translational RNA modification, is created when a uridine base is isomerised. In eukaryotes, this can occur by either of two distinct mechanisms; it is sometimes referred to as the ‘fifth RNA nucleotide’. It is incorporated into stable non-coding RNAs such as tRNA, rRNA, and snRNA, with roles in ribosomal ligand binding and translational fidelity in tRNA, and in fine-tuning branching events and splicing events in snRNAs. Pseudouridine has one more hydrogen bond donor from an imino group and a more stable C–C bond, since a C-glycosidic linkage has replaced the N-glycosidic linkage found in its counterpart (regular uridine). As neither of these changes affect its base-pairing properties, both will have the same output when directly sequenced; therefore methods for its detection involve prior biochemical modification. | 1 | Biochemistry |
The method combines a standard and efficient technique of mutagenesis using a chemical mutagen such as ethyl methanesulfonate (EMS) with a sensitive DNA screening-technique that identifies single base mutations (also called point mutations) in a target gene. The TILLING method relies on the formation of DNA heteroduplexes that are formed when multiple alleles are amplified by PCR and are then heated and slowly cooled. A “bubble” forms at the mismatch of the two DNA strands, which is then cleaved by a single stranded nuclease. The products are then separated by size on several different platforms (see below).
Mismatches may be due to induced mutation, heterozygosity within an individual, or natural variation between individuals.
EcoTILLING is a method that uses TILLING techniques to look for natural mutations in individuals, usually for population genetics analysis. DEcoTILLING is a modification of TILLING and EcoTILLING which uses an inexpensive method to identify fragments. Since the advent of NGS sequencing technologies, TILLING-by-sequencing has been developed based on Illumina sequencing of target genes amplified from multidimensionally pooled templates to identify possible single-nucleotide changes. | 1 | Biochemistry |
Hydrolysis of the terminal phosphoanhydridic bond is a highly exergonic process. The amount of released energy depends on the conditions in a particular cell. Specifically, the energy released is dependent on concentrations of ATP, ADP and P. As the concentrations of these molecules deviate from values at equilibrium, the value of Gibbs free energy change (ΔG) will be increasingly different. In standard conditions (ATP, ADP and P concentrations are equal to 1M, water concentration is equal to 55 M) the value of ΔG is between -28 and -34 kJ/mol.
The range of the ΔG value exists because this reaction is dependent on the concentration of Mg cations, which stabilize the ATP molecule. The cellular environment also contributes to differences in the ΔG value since ATP hydrolysis is dependent not only on the studied cell, but also on the surrounding tissue and even the compartment within the cell. Variability in the ΔG values is therefore to be expected.
The relationship between the standard Gibbs free energy change ΔG and chemical equilibrium is revealing. This relationship is defined by the equation ΔG = -RT ln(K), where K is the equilibrium constant, which is equal to the reaction quotient Q in equilibrium. The standard value of ΔG for this reaction is, as mentioned, between -28 and -34 kJ/mol; however, experimentally determined concentrations of the involved molecules reveal that the reaction is not at equilibrium. Given this fact, a comparison between the equilibrium constant, K, and the reaction quotient, Q, provides insight. K takes into consideration reactions taking place in standard conditions, but in the cellular environment the concentrations of the involved molecules (namely, ATP, ADP, and P) are far from the standard 1 M. In fact, the concentrations are more appropriately measured in mM, which is smaller than M by three orders of magnitude. Using these nonstandard concentrations, the calculated value of Q is much less than one. By relating Q to ΔG using the equation ΔG = ΔG + RT ln(Q), where ΔG is the standard change in Gibbs free energy for the hydrolysis of ATP, it is found that the magnitude of ΔG is much greater than the standard value. The nonstandard conditions of the cell actually result in a more favorable reaction.
In one particular study, to determine ΔG in vivo in humans, the concentration of ATP, ADP, and P was measured using nuclear magnetic resonance. In human muscle cells at rest, the concentration of ATP was found to be around 4 mM and the concentration of ADP was around 9 μM. Inputing these values into the above equations yields ΔG = -64 kJ/mol. After ischemia, when the muscle is recovering from exercise, the concentration of ATP is as low as 1 mM and the concentration of ADP is around 7 μM. Therefore, the absolute ΔG would be as high as -69 kJ/mol.
By comparing the standard value of ΔG and the experimental value of ΔG, one can see that the energy released from the hydrolysis of ATP, as measured in humans, is almost twice as much as the energy produced under standard conditions. | 1 | Biochemistry |
Elsa Lundanes (born 22 May 1953) is a Norwegian chemist.
She was born in Ålesund and took her cand.real. degree in 1978. After two years at Texas University she took the dr.scient. degree in 1986. She worked in the pharmaceutical industry for Nycomed before she was employed by the University of Oslo in 1988. Her specialty is analytical chemistry. She became professor in 1999 and a member of the Norwegian Academy of Science and Letters in 2009. | 3 | Analytical Chemistry |
From 2002 to 2014, plants appear to have gone into overdrive, starting to pull more CO out of the air than they have done before. The result was that the rate at which CO accumulates in the atmosphere did not increase during this time period, although previously, it had grown considerably in concert with growing greenhouse gas emissions.
A 1993 review of scientific greenhouse studies found that a doubling of concentration would stimulate the growth of 156 different plant species by an average of 37%. Response varied significantly by species, with some showing much greater gains and a few showing a loss. For example, a 1979 greenhouse study found that with doubled concentration the dry weight of 40-day-old cotton plants doubled, but the dry weight of 30-day-old maize plants increased by only 20%.
In addition to greenhouse studies, field and satellite measurements attempt to understand the effect of increased in more natural environments. In free-air carbon dioxide enrichment (FACE) experiments plants are grown in field plots and the concentration of the surrounding air is artificially elevated. These experiments generally use lower levels than the greenhouse studies. They show lower gains in growth than greenhouse studies, with the gains depending heavily on the species under study. A 2005 review of 12 experiments at 475–600 ppm showed an average gain of 17% in crop yield, with legumes typically showing a greater response than other species and C4 plants generally showing less. The review also stated that the experiments have their own limitations. The studied levels were lower, and most of the experiments were carried out in temperate regions. Satellite measurements found increasing leaf area index for 25% to 50% of Earth's vegetated area over the past 35 years (i.e., a greening of the planet), providing evidence for a positive CO fertilization effect.
Depending on environment, there are differential responses to elevated atmospheric CO between major functional types of plant, such as C3 plant| and C4 carbon fixation| plants, or more or less woody species; which has the potential among other things to alter competition between these groups. Increased CO can also lead to increased Carbon : Nitrogen ratios in the leaves of plants or in other aspects of leaf chemistry, possibly changing herbivore nutrition. Studies show that doubled concentrations of CO will show an increase in photosynthesis in C3 plants but not in C4 plants. However, it is also shown that plants are able to persist in drought better than the plants. | 2 | Environmental Chemistry |
Chlorosulfuric acid (IUPAC name: sulfurochloridic acid) is the inorganic compound with the formula HSOCl. It is also known as chlorosulfonic acid, being the sulfonic acid of chlorine. It is a distillable, colorless liquid which is hygroscopic and a powerful lachrymator. Commercial samples usually are pale brown or straw colored.
Salts and esters of chlorosulfuric acid are known as chlorosulfates. | 0 | Organic Chemistry |
Due to the hydrophilic property of sucrose and the lipophilic property of fatty acids, the overall hydrophilicity of sucrose esters can be tuned by the number of hydroxyl groups that are reacted with fatty acids and the identity of the fatty acids. The fewer free hydroxyl groups and the more lipophilic fatty acids, the less hydrophilic the resulting sucrose ester becomes. Sucrose esters' HLB values can range from 1-16. Low HLB (3.5-6.0) sucrose esters act as a water-in-oil emulsifier while high HLB (8-18) sucrose esters act as an oil-in-water emulsifier. | 0 | Organic Chemistry |
The first to mention premelting might have been Michael Faraday in 1842 for ice surfaces. He compared the effect which holds a snowball together to that which makes buildings from moistured sand stable. Another interesting thing he mentioned is that two blocks of ice can freeze together. Later Tammann (1910) and Stranski (1942) suggested that all crystals might, due to the reduction of surface energy, start melting at their surfaces. Frenkel strengthened this by noting that, in contrast to liquids, no overheating can be found for solids. After extensive studies on many materials, it can be concluded that it is a common attribute of the solid state that the melting process begins at the surface. | 7 | Physical Chemistry |
In 1988, the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances introduced detailed provisions and requirements relating the control of precursors used to produce drugs of abuse.
In Europe the Regulation (EC) No. 273/2004 of the European Parliament and of the Council on drug precursors was adopted on 11 February 2004. (European law on drug precursors) | 1 | Biochemistry |
In organometallic chemistry, a transition metal formyl complex is a metal complex containing one (usually) or more formyl (CHO) ligand. A subset of transition metal acyl complexes, formyl complexes can be viewed as metalla-aldehydes. A representative example is (CO)ReCHO. The formyl is viewed as an X (pseudohalide) ligand. Metal formyls are proposed as intermediates in the hydrogenation of carbon monoxide, as occurs in the Fischer-Tropsch process. | 0 | Organic Chemistry |
If the β phase is replaced by a flat rigid surface, as shown in Figure 5, then β = π, and the second net force equation simplifies to the Young equation,
which relates the surface tensions between the three phases: solid, liquid and gas. Subsequently, this predicts the contact angle of a liquid droplet on a solid surface from knowledge of the three surface energies involved. This equation also applies if the "gas" phase is another liquid, immiscible with the droplet of the first "liquid" phase. | 7 | Physical Chemistry |
The bioanalyst deals with complex biological samples containing the analyte alongside a diverse range of chemicals that can have an adverse impact on the accurate and precise quantification of the analyte. As such, a wide range of techniques are applied to extract the analyte from its matrix. These include:
*Protein precipitation
*Liquid–liquid extraction
*Solid phase extraction
Bioanalytical laboratories often deal with large numbers of samples, for example resulting from clinical trials. As such, automated sample preparation methods and liquid-handling robots are commonly employed to increase efficiency and reduce costs. | 3 | Analytical Chemistry |
The gas-diffusion electrocrystallization process was invented in 2014 by Xochitl Dominguez Benetton at the Flemish Institute for Technological Research, in Belgium. The patent for the process granted in Europe was filed in 2015 and its expiration is anticipated in 2036. | 7 | Physical Chemistry |
Plasma spraying offers versatility of usable coatings, and high-temperature performance. Plasma spraying can accommodate a wide range of materials, versus other techniques. As long as the difference between melting and decomposition temperatures is greater than 300 K, plasma spraying is viable. | 8 | Metallurgy |
In the late 1930s August Pfund used a triple-pass cell like the one shown above for atmospheric study. The cell, which became known as the Pfund cell, is constructed using two identical spherical mirrors, each having a hole carefully machined into its center. The separation distance between the mirrors is equal to the mirror focal length. A source enters from a hole in either mirror, is redirected twice at two reflection points, and then exits the cell through the other mirror on the third pass. The Pfund cell was one of the earliest examples of this type of spectroscopic technique and is noted for having used multiple passes. | 7 | Physical Chemistry |
The salt marsh plant Batis maritima contains the enzyme methyl chloride transferase that catalyzes the synthesis of CHCl from S-adenosine-L-methionine and chloride. This protein has been purified and expressed in E. coli, and seems to be present in other organisms such as white rot fungi (Phellinus pomaceus), red algae (Endocladia muricata), and the ice plant (Mesembryanthemum crystallinum), each of which is a known CHCl producer. | 2 | Environmental Chemistry |
A major limitation of classical omic studies is the isolation of only one level of biological complexity. For example, transcriptomic studies may provide information at the transcript level, but many different entities contribute to the biological state of the sample (genomic variants, post-translational modifications, metabolic products, interacting organisms, among others). With the advent of high-throughput biology, it is becoming increasingly affordable to make multiple measurements, allowing transdomain (e.g. RNA and protein levels) correlations and inferences. These correlations aid the construction or more complete biological networks, filling gaps in our knowledge.
Integration of data, however, is not an easy task. To facilitate the process, groups have curated database and pipelines to systematically explore multiomic data:
*Multi-Omics Profiling Expression Database (MOPED), integrating diverse animal models,
* The Pancreatic Expression Database, integrating data related to pancreatic tissue,
* [http://www.linkedomics.org/ LinkedOmics], connecting data from TCGA cancer datasets,
* OASIS, a web-based resource for general cancer studies,
* BCIP, a platform for breast cancer studies,
* C/VDdb, connecting data from several cardiovascular disease studies,
* ZikaVR, a multiomic resource for Zika virus data
* Ecomics, a normalized multi-omic database for Escherichia coli data,
* GourdBase, integrating data from studies with gourd,
* MODEM, a database for multilevel maize data,
* SoyKB, a database for multilevel soybean data,
*[https://www.proteomicsdb.org/ ProteomicsDB], a multi-omics and multi-organism resource for life science research | 1 | Biochemistry |
Triplet-triplet annihilation (TTA) is an energy transfer mechanism where two molecules in their triplet excited states interact to form a ground state molecule and an excited molecule in its singlet state. This mechanism is example of Dexter energy transfer mechanism. In triplet-triplet annihilation, one molecule transfers its excited state energy to the second molecule, resulting in the first molecule returning to its ground state and the second molecule being promoted to a higher excited singlet state.
Triplet-triplet annihilation was first discovered in the 1960s to explain the observation of delayed fluorescence in anthracene derivatives. | 7 | Physical Chemistry |
Diatomic molecules are normally in their lowest or ground state, which conventionally is also known as the state. When a gas of diatomic molecules is bombarded by energetic electrons, some of the molecules may be excited to higher electronic states, as occurs, for example, in the natural aurora; high-altitude nuclear explosions; and rocket-borne electron gun experiments. Such excitation can also occur when the gas absorbs light or other electromagnetic radiation. The excited states are unstable and naturally relax back to the ground state. Over various short time scales after the excitation (typically a fraction of a second, or sometimes longer than a second if the excited state is metastable), transitions occur from higher to lower electronic states and ultimately to the ground state, and in each transition results a photon is emitted. This emission is known as fluorescence. Successively higher electronic states are conventionally named , , , etc. (but this convention is not always followed, and sometimes lower case letters and alphabetically out-of-sequence letters are used, as in the example given below). The excitation energy must be greater than or equal to the energy of the electronic state in order for the excitation to occur.
In quantum theory, an electronic state of a diatomic molecule is represented by the molecular term symbol
where is the total electronic spin quantum number, is the total electronic angular momentum quantum number along the internuclear axis, and is the vibrational quantum number. takes on values 0, 1, 2, ..., which are represented by the electronic state symbols , , ,....
For example, the following table lists the common electronic states (without vibrational quantum numbers) along with the energy of the lowest vibrational level () of diatomic nitrogen (N), the most abundant gas in the Earth's atmosphere.
The subscripts and superscripts after give additional quantum mechanical details about the electronic state. The superscript or determines whether reflection in a plane containing the internuclear axis introduces a sign change in the wavefunction. The sub-script or applies to molecules of identical atoms, and when reflecting the state along a plane perpendicualr to the molecular axis, states that does not change are labelled (gerade), and states that change sign are labelled (ungerade).
The aforementioned fluorescence occurs in distinct regions of the electromagnetic spectrum, called "emission bands": each band corresponds to a particular transition from a higher electronic state and vibrational level to a lower electronic state and vibrational level (typically, many vibrational levels are involved in an excited gas of diatomic molecules). For example, N - emission bands (a.k.a. Vegard-Kaplan bands) are present in the spectral range from 0.14 to 1.45 μm (micrometres). A given band can be spread out over several nanometers in electromagnetic wavelength space, owing to the various transitions that occur in the molecules rotational quantum number, . These are classified into distinct sub-band branches, depending on the change in . The branch corresponds to , the branch to , and the branch to . Bands are spread out even further by the limited spectral resolution of the spectrometer that is used to measure the spectrum. The spectral resolution depends on the instruments point spread function. | 4 | Stereochemistry |
Mark S. Workentin is a professor of organic chemistry at the University of Western Ontario. The primary interests of the Workentin research group are materials chemistry, organic electrochemistry, organic photochemistry, physical organic chemistry and physical materials organic electrophotochemistry. | 0 | Organic Chemistry |
In the old days of traditional manufacturing, steel and other metals arrived at factories in an untreated and unpainted state. Companies would fabricate and paint or treat the metal components of their product before assembly. This was costly, time-consuming, and environmentally harmful. The coil coating process was pioneered in the 1930s for painting, coating and pre-treating large coils of metals before they arrived at a manufacturing facility. The venetian blind industry was the first to utilize pre-painted metal. | 8 | Metallurgy |
Polymer degradation is a change in the properties—tensile strength, color, shape, or molecular weight—of a polymer or polymer-based product under the influence of one or more environmental factors, such as heat, light, and the presence of certain chemicals, oxygen, and enzymes. This change in properties is often the result of bond breaking in the polymer backbone (chain scission) which may occur at the chain ends or at random positions in the chain.
Although such changes are frequently undesirable, in some cases, such as biodegradation and recycling, they may be intended to prevent environmental pollution. Degradation can also be useful in biomedical settings. For example, a copolymer of polylactic acid and polyglycolic acid is employed in hydrolysable stitches that slowly degrade after they are applied to a wound.
The susceptibility of a polymer to degradation depends on its structure. Epoxies and chains containing aromatic functionalities are especially susceptible to UV degradation while polyesters are susceptible to degradation by hydrolysis. Polymers containing an unsaturated backbone degrade via ozone cracking. Carbon based polymers are more susceptible to thermal degradation than inorganic polymers such as polydimethylsiloxane and are therefore not ideal for most high-temperature applications.
The degradation of polyethylene occurs by random scission—a random breakage of the bonds that hold the atoms of the polymer together. When heated above 450 °C, polyethylene degrades to form a mixture of hydrocarbons. In the case of chain-end scission, monomers are released and this process is referred to as unzipping or depolymerization. Which mechanism dominates will depend on the type of polymer and temperature; in general, polymers with no or a single small substituent in the repeat unit will decompose via random-chain scission.
The sorting of polymer waste for recycling purposes may be facilitated by the use of the resin identification codes developed by the Society of the Plastics Industry to identify the type of plastic. | 7 | Physical Chemistry |
Ramesh Jasti is a professor of organic chemistry at the University of Oregon. He was the first person to synthesize the elusive cycloparaphenylene in 2008 during post doctoral work in the laboratory of Professor Carolyn Bertozzi. He started his laboratory at Boston University where he was the recipient of the NSF CAREER award. His early lab repeatedly broke the record for the synthesis of the smallest cycloparaphenylene known. In 2014, he moved his laboratory to the University of Oregon where he expanded his focus to apply the molecules he discovered in the areas of organic materials, mechanically interlocked molecules, and biology. He is the Associate Director of the Materials Science Institute at the University of Oregon. | 0 | Organic Chemistry |
Captopril blocks the conversion of angiotensin I to angiotensin II and prevents the degradation of vasodilatory prostaglandins, thereby inhibiting vasoconstriction and promoting systemic vasodilation. | 4 | Stereochemistry |
Forming acyliminium ions from α-hydroxyamides can be done using methanesulfonyl chloride and a base, typically triethylamine. | 0 | Organic Chemistry |
August 2023 research, drawing from 176 flux stations globally, reveals a climate trade-off: increased carbon uptake from afforestation results in reduced albedo. Initially, this reduction may lead to moderate global warming over a span of approximately 20 years, but it is expected to transition into significant cooling thereafter. | 5 | Photochemistry |
There are polyols based on renewable sources such as plant-based materials including castor oil and cottonseed oil. Vegetable oils and biomass are also potential renewable polyol raw materials. Seed oil can even be used to produce polyester polyols. | 7 | Physical Chemistry |
There are two types of electrolytes: strong and weak. Strong electrolytes usually undergo complete ionization, and therefore they have higher conductivity than weak electrolytes, which undergo only partial ionization. For strong electrolytes, such as salts, strong acids and strong bases, the molar conductivity depends only weakly on concentration. On dilution there is a regular increase in the molar conductivity of strong electrolyte, due to the decrease in solute–solute interaction. Based on experimental data Friedrich Kohlrausch (around the year 1900) proposed the non-linear law for strong electrolytes:
where
: Λ is the molar conductivity at infinite dilution (or limiting molar conductivity), which can be determined by extrapolation of Λ as a function of ,
: K is the Kohlrausch coefficient, which depends mainly on the stoichiometry of the specific salt in solution,
: α is the dissociation degree even for strong concentrated electrolytes,
: f is the lambda factor for concentrated solutions.
This law is valid for low electrolyte concentrations only; it fits into the Debye–Hückel–Onsager equation.
For weak electrolytes (i.e. incompletely dissociated electrolytes), however, the molar conductivity strongly depends on concentration: The more dilute a solution, the greater its molar conductivity, due to increased ionic dissociation. For example, acetic acid has a higher molar conductivity in dilute aqueous acetic acid than in concentrated acetic acid. | 7 | Physical Chemistry |
A kairomone is a semiochemical, emitted by an organism, which mediates interspecific interactions in a way that benefits an individual of another species which receives it, without benefitting the emitter. Two main ecological cues are provided by kairomones; they generally either indicate a food source for the receiver, or give warning of the presence of a predator. Often a pheromone may be utilized as a kairomone by a predator or parasitoid to locate the emitting organism. | 1 | Biochemistry |
Jai Pal Mittal was born on 21 September 1940 in Meerut in the Indian state of Uttar Pradesh. He completed his graduate (BSc) and master's studies (MSc) in chemistry from the Agra University and migrated to Mumbai in 1959, looking for career opportunities. He joined the Training School of Atomic Energy Establishment, erstwhile Bhabha Atomic Research Centre and did a one-year course after which he moved to USA to join the Department of Radiation Chemistry of the University of Notre Dame, Indiana. He completed his doctoral studies (PhD) in 1967, under the guidance of A. A. Lamola and W. H. Hamill. Receiving an invitation from Willard Libby, the 1960 Nobel laureate in Chemistry, to assist him, Mittal did his post doctoral research, for over a year, at the Radiation and Nuclear Chemistry laboratory of the University of California.
In 1969, Mittal returned to India to start his career as a Pool Officer at the Bhabha Atomic Research Centre (BARC) and started working in the field of photochemistry. Two years later, in 1971, he got an opportunity to work with Professor E. Hayon at the United States Army Natick Soldier Research, Development and Engineering Center and worked there for one year. On his return to India in 1972, he formed a research group at BARC for research in photochemistry and radiation chemistry. During this period, he organized the first national symposium in Thiruvananthapuram, National Symposium on Fast Reaction Chemistry and Techniques.
Mittal continued at BARC to become the Director of Chemistry and Isotope Group and the DAE Raja Ramanna Fellow of the institution. He also holds the position of M. N. Saha Distinguished Professor of the National Academy of Sciences, India and the post of a Distinguished Professor at the University of Pune and the Indian Institute of Technology, Mumbai. During his tenure at BARC, he is known to have contributed for the establishment of a nanosecond LINAC based pulse radiolysis system at BARC and promoted the nano, pico and femtosecond pump and probe techniques to study the chemical dynamics. He is reported to have initiated a new school of research in Radiation Chemistry and Photochemistry in India and his group was successful in isotopic enrichment of hydrogen, carbon and uranium isotopes. His research findings have been recorded by way of over 300 scientific papers, published in peer reviewed journals and ResearchGate, an online scientific data repository, have listed 250 of them. He has also mentored many students in their doctoral studies.
Mittal has been associated with the Board of Research in Nuclear Sciences as a chairman of many of its basic sciences committees. He is a former president of the Indian Society of Radiation and Photochem Sciences (1997-2001), the National Academy of Sciences, India (2003–04) and the Asian Photochemistry Association (2003- 2008). He has also served the Indian National Science Academy as a council member (1998-2000) and as an additional member (2005–06). He serves as the president of the Asian and Oceanian Photochemistry Association and is a member of the education council of the University of Allahabad. He is a life member of the Indian Chemical Society where has also been a past president.
Mittal lives in Navi Mumbai in Maharashtra and continues attending seminars and conferences to deliver keynote addresses. | 5 | Photochemistry |
The shockwave generated coldwork (plastic strain) in the workpiece material creates compressive and tensile residual stresses to maintain an equilibrium state of the material. These residual stresses are compressive at the workpiece surface and gradually fade into low tensile stresses below and surrounding the laser peened area. The cold work also work hardens the surface layer. The compressive residual stresses, and to a lesser extent, the cold work, from laser peening have been shown to prevent and mitigate high cycle fatigue (HCF), low cycle fatigue (LCF), stress corrosion cracking, fretting fatigue, and, to some degree, wear and corrosion pitting. It is outstanding at mitigating foreign object damage in turbine blades.
The plastic strain introduced by laser peening is much lower than that introduced by other impact peening technologies. As a result, the residual plastic strain has much greater thermal stability than the more heavily cold worked microstructures. This enables the laser peened compressive stresses to be retained at higher operating temperatures during long exposures than is the case for the other technologies. Among the applications benefiting from this are gas turbine fan and compressor blades and nuclear plant components.
By enhancing material performance, laser peening enables more-efficient designs that reduce weight, extend component lifetimes, and increase performance. In the future, it is anticipated that laser peening will be incorporated into the design of fatigue critical components to achieve longer life, lighter weight, and perhaps a simpler design to manufacture. | 8 | Metallurgy |
The acronym prefix "R.A." is sometimes pronounced as the one syllable word "ray" because of the plot's strong resemblance to a geometric ray. This characteristic arrow-like shape derives from two key features: on the right at the vector origin, a long asymptotic tail, and on the left (forming the arrow head) two (often dense) patches of condition-unique points. | 1 | Biochemistry |
In his ruling, Mr Justice Akenhead said it was clear that the council had permitted toxic waste to disperse into the atmosphere. He also said that there was a "statistically significant" cluster of birth defects between 1989 and 1999, and that, "toxicologically, there were present on and from the Corby Borough Council sites, over the whole period from 1985 (and possibly before) until 1997, the types of contaminants which could cause the birth defects complained of."
"There was an extended period between 1983 and August 1997 in which Corby Borough Council was extensively negligent in its control and management of the sites which they acquired from British Steel and otherwise used. That negligence and, as from April 1, 1992, breach of statutory duty on the part of CBC permitted and led to the extensive dispersal of contaminated mud and dust over public areas of Corby and into and over private homes, with the result that the contaminants could realistically have caused the types of birth defects of which complaint has been made by the claimants (save in limited respects)... Corby Borough Council is liable in public nuisance, negligence and breach of statutory duty, obviously subject to it being established in later proceedings by individual claimants that their particular conditions were actually caused by the defaults identified in this judgment."
The two youngest claimants, nine-year-old India Harrison and ten-year-old Ashleigh Jane Custance, were unable at that time to proceed with their cases, however, because of the ruling that there were no breaches of duty after August 1997. Their parents indicated that they would appeal this cut-off date. | 2 | Environmental Chemistry |
Different average values can be defined, depending on the statistical method applied. In practice, four averages are used, representing the weighted mean taken with the mole fraction, the weight fraction, and two other functions which can be related to measured quantities:
*Number average molar mass (), also loosely referred to as number average molecular weight (NAMW).
*Mass average molar mass (), where stands for weight; also commonly referred to as weight average or weight average molecular weight (WAMW).
*Z-average molar mass (), where stands for centrifugation ().
*Viscosity average molar mass ().
Here, is the exponent in the Mark–Houwink equation that relates the intrinsic viscosity to molar mass. | 7 | Physical Chemistry |
The Hofmeister series or lyotropic series is a classification of ions in order of their lyotrophic properties, which is the ability to salt out or salt in proteins. The effects of these changes were first worked out by Franz Hofmeister, who studied the effects of cations and anions on the solubility of proteins. | 7 | Physical Chemistry |
When overheating, the temperature of the part rises above the operating temperature. Overheating can take place:
*if heat is produced in more than expected amount (such as in cases of short-circuits, or applying more voltage than rated), or
*if heat dissipation is poor, so that normally produced waste heat does not drain away properly.
Overheating may be caused from any accidental fault of the circuit (such as short-circuit or spark-gap), or may be caused from a wrong design or manufacture (such as the lack of a proper heat dissipation system).
Due to accumulation of heat, the system reaches an equilibrium of heat accumulation vs. dissipation at a much higher temperature than expected. | 7 | Physical Chemistry |
Heavy water, DO, self-ionizes less than normal water, HO;
:DO + DO DO + OD
This is due to the equilibrium isotope effect, a quantum mechanical effect attributed to oxygen forming a slightly stronger bond to deuterium because the larger mass of deuterium results in a lower zero-point energy.
Expressed with activities a, instead of concentrations, the thermodynamic equilibrium constant for the heavy water ionization reaction is:
Assuming the activity of the DO to be 1, and assuming that the activities of the DO and OD are closely approximated by their concentrations
The following table compares the values of pK for HO and DO. | 7 | Physical Chemistry |
Acid solutions exhibit proton-conductivity, while pure proton conductors are usually dry solids. Typical materials are polymers or ceramic. Typically, the pores in practical materials are small such that protons dominate direct current and transport of cations or bulk solvent is prevented. Water ice is a common example of a pure proton conductor, albeit a relatively poor one. A special form of water ice, superionic water, has been shown to conduct much more efficiently than normal water ice.
Solid-phase proton conduction was first suggested by Alfred Rene Jean Paul Ubbelohde and S. E. Rogers. in 1950, although electrolyte proton currents have been recognized since 1806.
Proton conduction has also been observed in the new type of proton conductors for fuel cells – protic organic ionic plastic crystals (POIPCs), such as 1,2,4-triazolium perfluorobutanesulfonate and imidazolium methanesulfonate. In particular, a high ionic conductivity of 10 mS/cm is reached at 185 °C in the plastic phase of imidazolium methanesulfonate.
When in the form of thin membranes, proton conductors are an essential part of small, inexpensive fuel cells. The polymer nafion is a typical proton conductor in fuel cells. A jelly-like substance similar to Nafion residing in the ampullae of Lorenzini of sharks has proton conductivity only slightly lower than nafion.
High proton conductivity has been reported among alkaline-earth cerates and zirconate based perovskite materials such as acceptor doped SrCeO, BaCeO and BaZrO. Relatively high proton conductivity has also been found in rare-earth ortho-niobates and ortho-tantalates as well as rare-earth tungstates. | 7 | Physical Chemistry |
The quality of an SKP measurement is affected by a number of factors. This includes the diameter of the SKP probe, the probe to sample distance, and the material of the SKP probe. The probe diameter is important in the SKP measurement because it affects the overall resolution of the measurement, with smaller probes leading to improved resolution. On the other hand, reducing the size of the probe causes an increase in fringing effects which reduces the sensitivity of the measurement by increasing the measurement of stray capacitances. The material used in the construction of the SKP probe is important to the quality of the SKP measurement. This occurs for a number of reasons. Different materials have different work function values which will affect the contact potential measured. Different materials have different sensitivity to humidity changes. The material can also affect the resulting lateral resolution of the SKP measurement. In commercial probes tungsten is used, though probes of platinum, copper, gold, and NiCr has been used. The probe to sample distance affects the final SKP measurement, with smaller probe to sample distances improving the lateral resolution and the signal-to-noise ratio of the measurement. Furthermore, reducing the SKP probe to sample distance increases the intensity of the measurement, where the intensity of the measurement is proportional to 1/d, where d is the probe to sample distance. The effects of changing probe to sample distance on the measurement can be counteracted by using SKP in constant distance mode. | 7 | Physical Chemistry |
Oil-tar creosote is derived from the tar that forms when using petroleum or shale oil in the manufacturing of gas. The distillation of the tar from the oil occurs at very high temperatures; around 980 °C. The tar forms at the same time as the gas, and once processed for creosotes contains a high percentage of cyclic hydrocarbons, a very low amount of tar acids and tar bases, and no true anthracenes have been identified. Historically, this has mainly been produced in the United States on the Pacific coast, where petroleum has been more abundant than coal. Limited quantities have been used industrially, either alone, mixed with coal-tar creosote, or fortified with pentachlorophenol. | 7 | Physical Chemistry |
Fretting in Aluminium causes black debris to be present in the contact area due to the fine oxide particles. | 8 | Metallurgy |
Exometabolomics, or "metabolic footprinting", is the study of extracellular metabolites. It uses many techniques from other subfields of metabolomics, and has applications in biofuel development, bioprocessing, determining drugs' mechanism of action, and studying intercellular interactions. | 1 | Biochemistry |
Mathews was raised on a dairy farm near the unincorporated community of Auroraville, Wisconsin in Waushara County, Wisconsin. As a youth, he had little interest in farm life or in the cheese factory operated by his older brother. His parents sent Joseph to public school in nearby Berlin, a city that straddles the boundary between Waushara and Green Lake counties. He graduated from Omro High School (Omro, Winnebago County). Mathews studied briefly at Ripon College in Ripon, Wisconsin, and then transferred to the University of Wisconsin. Mathews earned the B.S. in chemistry in 1903, writing a senior thesis on nitrosyl selenic acid, based on research under the supervision of Victor Lenher (1873–1927). | 7 | Physical Chemistry |
The count rates observed from a given astronomical radiation source have no simple relationship to the flux from that source, such as might be incident at the top of the Earth's atmosphere. This lack of a simple relationship is due in no small part to the complex properties of radiation detectors.
These detector properties can be divided into
*those that merely attenuate the beam, including
*#residual atmosphere between source and detector,
*#absorption in the detector window when present,
*#quantum efficiency of the detecting medium,
*those that redistribute the beam in detected energy, such as
*#fluorescent photon escape phenomena,
*#inherent energy resolution of the detector. | 7 | Physical Chemistry |
Measurement of diel changes in dissolved gases within the lake, also known as the "free-water" method, has quickly become the most common method of estimating lake metabolism since the wide adoption of autonomous sensors used to measure dissolved oxygen and carbon dioxide in water. The free-water method is particularly popular since many daily estimates of lake metabolism can be collected relatively cheaply and can give insights into metabolic regimes during difficult-to-observe time periods, such as during storm events. Measured changes in dissolved oxygen and carbon dioxide within a lake represents the sum of all organismal metabolism from bacteria to fishes, after accounting for abiotic changes in dissolved gases. Abiotic changes in dissolved gases include exchanges of dissolved gases between the atmosphere and lake surface, vertical or horizontal entrainment of water with differing concentrations (e.g. low-oxygen water below a lake's thermocline), or import and export of dissolved gases from inflowing streams or a lake outlet. Abiotic changes in dissolved gases can dominate changes of dissolved gases if the lake has a low metabolic rate (e.g. oligotrophic lake, cloudy day), or if there is a large event that causes abiotic factors to exceed biotic (e.g. wind event causing mixing and entrainment of low-oxygenated water). Biotic signals in dissolved gases are most evident when the sun is shining and photosynthesis is occurring, resulting in the production of dissolved oxygen and consumption of carbon dioxide. The conversion of solar energy to chemical energy is termed gross primary production (GPP) and the dissipation of this energy through biological carbon oxidation is termed ecosystem respiration (ER). High-frequency (e.g. 10 minute interval) measurements of dissolved oxygen or carbon dioxide can be translated into estimates of GPP, ER, and the difference between the two termed Net Ecosystem Production (NEP), by fitting the high-frequency data to models of lake metabolism. The governing equation for estimating lake metabolism from a single sensor located in the upper mixed layer measuring dissolved oxygen is:
DO/t = GPP-ER+F
Where F is the flux of gases between the lake and the atmosphere. Additional terms of abiotic gas flux can be added if those abiotic fluxes are deemed significant for a lake (e.g. mixing events, inflowing stream gases). Atmospheric gas exchange (F) is rarely directly measured and typically modeled by estimating lake surface turbulence from wind-driven and convective mixing. Most often, F is estimated from measurements of wind speed and atmospheric pressure, and different models for estimating F can result in significantly different estimates of lake metabolic rates depending on the study lake. Gross primary production is assumed to be zero during the night due to low or no light, and thus ER can be estimated from nighttime changes in dissolved oxygen (or carbon dioxide) after accounting for abiotic changes in dissolved oxygen. Gross primary production can be estimated assuming that ER is equal during the day and night and accounting for dissolved oxygen changes during the day, however, this assumption may not be valid in every lake.
Extracting a high signal-to-noise ratio is key to obtaining good estimates of lake metabolism from the free-water technique, and there are choices that a researcher needs to make prior to collection data and during data analyses to ensure accurate estimates. Location of dissolved gas collection (typically in the surface mixed layer), number of sensors vertically and horizontally, frequency and duration of data collection, and modeling methods need to be considered. | 1 | Biochemistry |
Below is the sequence of events that are followed in phage display screening to identify polypeptides that bind with high affinity to desired target protein or DNA sequence:
# Target proteins or DNA sequences are immobilized to the wells of a microtiter plate.
# Many genetic sequences are expressed in a bacteriophage library in the form of fusions with the bacteriophage coat protein, so that they are displayed on the surface of the viral particle. The protein displayed corresponds to the genetic sequence within the phage.
# This phage-display library is added to the dish and after allowing the phage time to bind, the dish is washed.
# Phage-displaying proteins that interact with the target molecules remain attached to the dish, while all others are washed away.
# Attached phage may be eluted and used to create more phage by infection of suitable bacterial hosts. The new phage constitutes an enriched mixture, containing considerably less irrelevant phage (i.e. non-binding) than were present in the initial mixture.
# Steps 3 to 5 are optionally repeated one or more times, further enriching the phage library in binding proteins.
# Following further bacterial-based amplification, the DNA within the interacting phage is sequenced to identify the interacting proteins or protein fragments. | 1 | Biochemistry |
All elements aside from argon, neon, and helium form fluorides by direct reaction with fluorine. Chlorine is slightly more selective, but still reacts with most metals and heavier nonmetals. Following the usual trend, bromine is less reactive and iodine least of all. Of the many reactions possible, illustrative is the formation of gold(III) chloride by the chlorination of gold. The chlorination of metals is usually not very important industrially since the chlorides are more easily made from the oxides and hydrogen chloride. Where chlorination of inorganic compounds is practiced on a relatively large scale is for the production of phosphorus trichloride and disulfur dichloride. | 0 | Organic Chemistry |
Aminoacyl-tRNA synthetase enzymes consume ATP in the attachment tRNA to amino acids, forming aminoacyl-tRNA complexes. Aminoacyl transferase binds AMP-amino acid to tRNA. The coupling reaction proceeds in two steps:
# aa + ATP ⟶ aa-AMP + PP
# aa-AMP + tRNA ⟶ aa-tRNA + AMP
The amino acid is coupled to the penultimate nucleotide at the 3′-end of the tRNA (the A in the sequence CCA) via an ester bond (roll over in illustration). | 1 | Biochemistry |
Eicosapentaenoic acid (EPA), the active metabolite of ethyl eicosapentaenoic acid (E-EPA), like other omega-3 fatty acid based drugs, appears to reduce production of triglycerides in the liver and to enhance clearance of triglycerides from circulating very low-density lipoprotein (VLDL) particles. The way it does that is not clear, but potential mechanisms include increased breakdown of fatty acids; inhibition of diglyceride acyltransferase, which is involved in biosynthesis of triglycerides in the liver; and increased activity of lipoprotein lipase in blood. | 1 | Biochemistry |
The enzyme is important for carotenoid biosynthesis during chloroplast biogenesis. In developing plastids, its activity prevents the over-reduction of the plastoquinone pool. Knockout plants for PTOX exhibit phenotypes of variegated leaves with white patches. Without the enzyme, the carotenoid synthesis pathway slows down due to the lack of oxidized plastoquinone with which to oxidize phytoene, a carotenoid intermediate. The colorless compound phytoene accumulates in the leaves, resulting in white patches of cells. PTOX is also thought to determine the redox poise of the developing photosynthetic apparatus and without it, plants fail to assemble organized internal membrane structures in chloroplasts when exposed to high light during early development. | 5 | Photochemistry |
Brain tissue swelling, known as cerebral oedema, results from brain injury and other traumatic head injuries that can increase intracranial pressure (ICP). Negatively charged molecules within cells create a fixed charge density, which increases intracranial pressure through the Donnan effect. ATP pumps maintain a negative membrane potential even though negative charges leak across the membrane; this action establishes a chemical and electrical gradient.
The negative charge in the cell and ions outside the cell creates a thermodynamic potential; if damage occurs to the brain and cells lose their membrane integrity, ions will rush into the cell to balance chemical and electrical gradients that were previously established. The membrane voltage will become zero, but the chemical gradient will still exist. To neutralize the negative charges within the cell, cations flow in, which increases the osmotic pressure inside relative to the outside of the cell. The increased osmotic pressure forces water to flow into the cell and tissue swelling occurs. | 7 | Physical Chemistry |
The equation relating thermal energy to thermal mass is:
where Q is the thermal energy transferred, C is the thermal mass of the body, and ΔT is the change in temperature.
For example, if 250 J of heat energy is added to a copper gear with a thermal mass of 38.46 J/°C, its temperature will rise by 6.50 °C.
If the body consists of a homogeneous material with sufficiently known physical properties, the thermal mass is simply the mass of material present times the specific heat capacity of that material. For bodies made of many materials, the sum of heat capacities for their pure components may be used in the calculation, or in some cases (as for a whole animal, for example) the number may simply be measured for the entire body in question, directly.
As an extensive property, heat capacity is characteristic of an object; its corresponding intensive property is specific heat capacity, expressed in terms of a measure of the amount of material such as mass or number of moles, which must be multiplied by similar units to give the heat capacity of the entire body of material. Thus the heat capacity can be equivalently calculated as the product of the mass m of the body and the specific heat capacity c for the material, or the product of the number of moles of molecules present n and the molar specific heat capacity . For discussion of why the thermal energy storage abilities of pure substances vary, see factors that affect specific heat capacity.
For a body of uniform composition, can be approximated by
where is the mass of the body and is the isobaric specific heat capacity of the material averaged over temperature range in question. For bodies composed of numerous different materials, the thermal masses for the different components can just be added together. | 7 | Physical Chemistry |
The efficiency of duplex sequencing depends on the final number of DCSs which is directly related to the number of reads in each family (family size). If the family size is too small then the DCS can not be assembled and if too many reads are sharing the same tag, the data yield will be low. Family size is determined by the amount of DNA template needed for PCR amplification and the dedicated sequencing lane fraction. The optimal tag family size is between 6 and 12 members. To obtain the optimal family size, the amounts of DNA template and the dedicated sequencing lane fraction need to be adjusted. The following formula takes into account the most important variables that can affect depth of coverage (N=40DG÷R) where "N" is the number of reads, "D" is the desired depth of coverage, "G" is the size of DNA target in base pair, and "R" is final read length. | 1 | Biochemistry |
Hydrazine, organohydrazines, and 1,1-diorganohydrazines react with aldehydes and ketones to give hydrazones.
Phenylhydrazine reacts with reducing sugars to form hydrazones known as osazones, which was developed by German chemist Emil Fischer as a test to differentiate monosaccharides. | 0 | Organic Chemistry |
Mercury has been smelted from cinnabar for thousands of years. Mercury dissolves many metals, such as gold, silver, and tin, to form amalgams (an alloy in a soft paste or liquid form at ambient temperature). Amalgams have been used since 200 BC in China for gilding objects such as armor and mirrors with precious metals. The ancient Romans often used mercury-tin amalgams for gilding their armor. The amalgam was applied as a paste and then heated until the mercury vaporized, leaving the gold, silver, or tin behind. Mercury was often used in mining, to extract precious metals like gold and silver from their ores. | 8 | Metallurgy |
Most molecular carbido complexes are clusters, usually featuring carbide as a six-fold bridging ligand. Examples include [C(CO)], and [C(CO)]. Though exceptions exist, such as the nonanuclear Ruthenium cluster (μ-C)Ru(CO) (μ-η: η:η-CH) containing a tripped trigonal prism geometry around the carbide.
The iron carbonyl carbides exist not only in the encapsulated carbon ([C(CO)]) but also with exposed carbon centres as in FeC(CO) and FeC(CO)
Bimetallic and exotic clusters such as metal carbide clusterfullerenes (MCCF's) have also been able to be prepared. | 0 | Organic Chemistry |
Mitogen-activated protein kinase 3 (MAPK3) is also known as extracellular signal-regulated kinase 1 (ERK1). Transgenic gene knockout mice lacking MAPK3 are viable and it is thought that MAPK1 can fulfill some MAPK3 functions in most cells. The main exception is in T cells. Mice lacking MAPK3 have reduced T cell development past the CD4+ and CD8+ stage. | 1 | Biochemistry |
The oceanic carbon cycle (or marine carbon cycle) is composed of processes that exchange carbon between various pools within the ocean as well as between the atmosphere, Earth interior, and the seafloor. The carbon cycle is a result of many interacting forces across multiple time and space scales that circulates carbon around the planet, ensuring that carbon is available globally. The Oceanic carbon cycle is a central process to the global carbon cycle and contains both inorganic carbon (carbon not associated with a living thing, such as carbon dioxide) and organic carbon (carbon that is, or has been, incorporated into a living thing). Part of the marine carbon cycle transforms carbon between non-living and living matter.
Three main processes (or pumps) that make up the marine carbon cycle bring atmospheric carbon dioxide (CO) into the ocean interior and distribute it through the oceans. These three pumps are: (1) the solubility pump, (2) the carbonate pump, and (3) the biological pump. The total active pool of carbon at the Earth's surface for durations of less than 10,000 years is roughly 40,000 gigatons C (Gt C, a gigaton is one billion tons, or the weight of approximately 6 million blue whales), and about 95% (~38,000 Gt C) is stored in the ocean, mostly as dissolved inorganic carbon. The speciation of dissolved inorganic carbon in the marine carbon cycle is a primary controller of acid-base chemistry in the oceans.
Earth's plants and algae (primary producers) are responsible for the largest annual carbon fluxes. Although the amount of carbon stored in marine biota (~3 Gt C) is very small compared with terrestrial vegetation (~610 GtC), the amount of carbon exchanged (the flux) by these groups is nearly equal – about 50 GtC each. Marine organisms link the carbon and oxygen cycles through processes such as photosynthesis. The marine carbon cycle is also biologically tied to the nitrogen and phosphorus cycles by a near-constant stoichiometric ratio C:N:P of 106:16:1, also known as the Redfield Ketchum Richards (RKR) ratio, which states that organisms tend to take up nitrogen and phosphorus incorporating new organic carbon. Likewise, organic matter decomposed by bacteria releases phosphorus and nitrogen.
Based on the publications of NASA, World Meteorological Association, IPCC, and International Council for the Exploration of the Sea, as well as scientists from NOAA, Woods Hole Oceanographic Institution, Scripps Institution of Oceanography, CSIRO, and Oak Ridge National Laboratory, the human impacts on the marine carbon cycle are significant. Before the Industrial Revolution, the ocean was a net source of CO to the atmosphere whereas now the majority of the carbon that enters the ocean comes from atmospheric carbon dioxide (CO). The burning of fossil fuels and production of cement have changed the balance of carbon dioxide between the atmosphere and oceans, causing acidification of the oceans. Climate change, a result of excess CO in the atmosphere, has increased the temperature of the ocean and atmosphere (global warming). The slowed rate of global warming occurring from 2000–2010 may be attributed to an observed increase in upper ocean heat content. | 9 | Geochemistry |
Copy number variation was initially thought to occupy an extremely small and negligible portion of the genome through cytogenetic observations. Copy number variations were generally associated only with small tandem repeats or specific genetic disorders, therefore, copy number variations were initially only examined in terms of specific loci. However, technological developments led to an increasing number of highly accurate ways of identifying and studying copy number variations. Copy number variations were originally studied by cytogenetic techniques, which are techniques that allow one to observe the physical structure of the chromosome. One of these techniques is fluorescent in situ hybridization (FISH) which involves inserting fluorescent probes that require a high degree of complementarity in the genome for binding. Comparative genomic hybridization was also commonly used to detect copy number variations by fluorophore visualization and then comparing the length of the chromosomes. One major drawback of these early techniques is that the genomic resolution is relatively low and only large repeats such as whole gene repeats can be detected.
Recent advances in genomics technologies gave rise to many important methods that are of extremely high genomic resolution and as a result, an increasing number of copy number variations in the genome have been reported. Initially these advances involved using bacterial artificial chromosome (BAC) array with around 1 megabase of intervals throughout the entire gene, BACs can also detect copy number variations in rearrangement hotspots allowing for the detection of 119 novel copy number variations. High throughput genomic sequencing has revolutionized the field of human genomics and in silico studies have been performed to detect copy number variations in the genome. Reference sequences have been compared to other sequences of interest using fosmids by strictly controlling the fosmid clones to be 40kb. Sequencing end reads would provide adequate information to align the reference sequence to the sequence of interest, and any misalignments are easily noticeable thus concluded to be copy number variations within that region of the clone. This type of detection technique offers a high genomic resolution and precise location of the repeat in the genome, and it can also detect other types of structural variation such as inversions.
In addition, another way of detecting copy number variation is using single nucleotide polymorphisms (SNPs). Due to the abundance of the human SNP data, the direction of detecting copy number variation has changed to utilize these SNPs. Relying on the fact that human recombination is relatively rare and that many recombination events occur in specific regions of the genome known as recombination hotspots, linkage disequilibrium can be used to identify copy number variations. Efforts have been made in associating copy number variations with specific haplotype SNPs by analyzing the linkage disequilibrium, using these associations, one is able to recognize copy number variations in the genome using SNPs as markers. Next-generation sequencing techniques including short and long read sequencing are nowadays increasingly used and have begun to replace array-based techniques to detect copy number variations. In contrast to array-based techniques, sequencing-based detection methods readily identify other classes of structural variation such as inversions and translocations. | 1 | Biochemistry |
The solubility product for the hydroxide of a metal ion, M, is usually defined, as follows:
However, general-purpose computer programs are designed to use hydrogen ion concentrations with the alternative definitions.
For hydroxides, solubility products are often given in a modified form, K*, using hydrogen ion concentration in place of hydroxide ion concentration. The two values are related by the self-ionization constant for water, K.
For example, at ambient temperature, for calcium hydroxide, Ca(OH), lg K is ca. −5 and lg K* ≈ −5 + 2 × 14 ≈ 23. | 7 | Physical Chemistry |
Relative inductive effects have been experimentally measured through the resulting s of a nearby carboxylic acid group (see ). In increasing order of -I effect or decreasing order of +I effect, common functional groups are:
Hydrogen subsituents also exhibit an isotope effect: relative to the same order,
where H is hydrogen, D deuterium, and T tritium.
The strength of inductive effect is also dependent on the distance between the substituent group and the main group that react; the longer the distance, the weaker the effect.
Inductive effects can be expressed quantitatively through the Hammett equation, which describes the relationship between reaction rates and equilibrium constants with respect to substituent. | 7 | Physical Chemistry |
Lineatin was first isolated in 1977 by MacConnell. The absolute configuration of the biologically active form was later determined as (+)-(1R,4S,5R,7R)-3,3,7-trimethyl-2,9- dioxatricyclo[3.3.1.0]nonane, whereas other enatinomers process no biological attraction activity. | 0 | Organic Chemistry |
Blacklights are a common tool for rock-hunting and identification of minerals by their fluorescence. The most common minerals and rocks that glow under UV light are fluorite, calcite, aragonite, opal, apatite, chalcedony, corundum (ruby and sapphire), scheelite, selenite, smithsonite, sphalerite, sodalite. The first person to observe fluorescence in minerals was George Stokes in 1852. He noted the ability of fluorite to produce a blue glow when illuminated with ultraviolet light and called this phenomenon “fluorescence” after the mineral fluorite. Lamps used to visualise seams of fluorite and other fluorescent minerals are commonly used in mines but they tend to be on an industrial scale. The lamps need to be short wavelength to be useful for this purpose and of scientific grade. UVP range of hand held UV lamps are ideal for this purpose and are used by Geologists to identify the best sources of fluorite in mines or potential new mines. Some transparent selenite crystals exhibit an “hourglass” pattern under UV light that is not visible in natural light. These crystals are also phosphorescent. Limestone, marble, and travertine can glow because of calcite presence. Granite, syenite, and granitic pegmatite rocks can also glow. | 5 | Photochemistry |
The movement of adatoms across a surface can be described by the Burton, Cabrera and Frank (CBF) model. The model treats adatoms as a 2D gas on top of the surface. The adatoms diffuse with a diffusion constant D; they are desorbed back to the medium above with a rate of per atom and adsorbed with flux F.
The diffusion constant can be, when the concentration of particles is small, expressed as:
Where a is the hopping distance for the atom. E is the energy needed to pass the diffusion barrier. ν is the attempt frequency.
The CBF model obeys the following continuity equation:
Combining the steady states () with the following boundary conditions can lead to an expression for the velocity of the adatoms at each adsorption site.
The boundary conditions:
And: | 7 | Physical Chemistry |
Although technically speaking, DNA sequence polymorphism has been going on since the use of RFLP in the 1960s, the analysis has changed significantly over the years. DNA sequence polymorphism uses older techniques like RFLP, but on a larger scale. Sequencing is much faster and more efficient. The analysis is automated, as it uses a technique known as shotgun sequencing. This high-throughput method is commonly used in population genetics. | 1 | Biochemistry |
There are several types of glycosylation, although the first two are the most common.
* In N-glycosylation, sugars are attached to nitrogen, typically on the amide side-chain of asparagine.
* In O-glycosylation, sugars are attached to oxygen, typically on serine or threonine, but also on tyrosine or non-canonical amino acids such as hydroxylysine and hydroxyproline.
* In P-glycosylation, sugars are attached to phosphorus on a phosphoserine.
* In C-glycosylation, sugars are attached directly to carbon, such as in the addition of mannose to tryptophan.
* In S-glycosylation, a beta-GlcNAc is attached to the sulfur atom of a cysteine residue.
* In glypiation, a GPI glycolipid is attached to the C-terminus of a polypeptide, serving as a membrane anchor.
* In glycation, also known as non-enzymatic glycosylation, sugars are covalently bonded to a protein or lipid molecule, without the controlling action of an enzyme, but through a Maillard reaction. | 0 | Organic Chemistry |
The anomeric effect is taken into consideration synthetically. Due to its discovery in sugars, sugar and carbohydrate chemistry is one of the more common synthetic uses of the anomeric effect. For instance, the Koenigs-Knorr glycosidation installs an α-OR or β-OR group in high diastereoselectivity which is effected by the anomeric effect. Sophorolipid lactone, (+)-Lepicidin A, and (−)-Lithospermoside are a few of the products synthesized via the Koenigs-Knorr Glycosidation overcoming the anomeric effect. | 7 | Physical Chemistry |
There is an additional multiplex advantage for emission lines of atomic and molecular spectra. At the peak of the emission line, a monochromator measurement will be noisy, since the noise is proportional to the square root of the signal. For the same reason, the measurement will be less noisy at the baseline of the spectrum. In a multiplexed measurement, however, the noise in a given measurement is spread more or less evenly across the spectrum, regardless of the local signal intensity. Thus, multiplexed measurements can achieve higher SNR at the emission line peaks. There is a corresponding multiplex disadvantage, however. When the signals of interest are absorption lines in the spectrum, then the same principle will produce increased noise at the valleys of the absorption lines relative to the noise of a scanning monochromator. | 7 | Physical Chemistry |
A different, but related, mechanism is Dexter electron transfer.
An alternative method to detecting protein–protein proximity is the bimolecular fluorescence complementation (BiFC), where two parts of a fluorescent protein are each fused to other proteins. When these two parts meet, they form a fluorophore on a timescale of minutes or hours. | 1 | Biochemistry |
There are various mechanisms for glycosylation, although most share several common features:
*Glycosylation, unlike glycation, is an enzymatic process. Indeed, glycosylation is thought to be the most complex post-translational modification, because of the large number of enzymatic steps involved.
*The donor molecule is often an activated nucleotide sugar.
*The process is non-templated (unlike DNA transcription or protein translation); instead, the cell relies on segregating enzymes into different cellular compartments (e.g., endoplasmic reticulum, cisternae in Golgi apparatus). Therefore, glycosylation is a site-specific modification. | 0 | Organic Chemistry |
A kinetic scheme is a network (a directed graph) of distinct states (although repetition of states may occur and this depends on the system), where each pair of states i and j are associated with directional rates, (and ). It is described with a master equation: a first-order differential equation for the probability of a system to occupy each one its states at time t (element i represents state i). Written in a matrix form, this states: , where is the matrix of connections (rates) .
In a Markovian kinetic scheme the connections are constant with respect to time (and any jumping time probability density function for state i is an exponential, with a rate equal the value of all the exiting connections).
When detailed balance exists in a system, the relation holds for every connected states i and j. The result represents the fact that any closed loop in a Markovian network in equilibrium does not have a net flow.
Matrix can also represent birth and death, meaning that probability is injected (birth) or taken from (death) the system, where then, the process is not in equilibrium. These terms are different than a birth–death process, where there is simply a linear kinetic scheme. | 7 | Physical Chemistry |
While radon presents the aforementioned risks in adults, exposure in children leads to a unique set of health hazards that are still being researched. The physical composition of children leads to faster rates of exposure through inhalation given that their respiratory rate is higher than that of adults, resulting in more gas exchange and more potential opportunities for radon to be inhaled.
The resulting health effects in children are similar to those of adults, predominantly including lung cancer and respiratory illnesses such as asthma, bronchitis, and pneumonia. While there have been numerous studies assessing the link between radon exposure and childhood leukemia, the results are largely varied. Many ecological studies show a positive association between radon exposure and childhood leukemia; however, most case control studies have produced a weak correlation. Genotoxicity has been noted in children exposed to high levels of radon, specifically a significant increase of frequency of aberrant cells was noted, as well as an "increase in the frequencies of single and double fragments, chromosome interchanges, [and] number of aberrations chromatid and chromosome type". | 2 | Environmental Chemistry |
SIR2 is an NAD-dependent lysine deacetylase. It was the first-discovered member of the Sirtuin protein family and it is highly conserved, with homologs found in organisms ranging from humans to bacteria and archaea. It interacts with a variety of protein substrates, but does not exhibit strong affinity for DNA, chromatin, or other silencer-binding factors. Instead, it relies on other SIR proteins to find its appropriate silencing target.
In the SIR protein complex, SIR2 removes acetyl groups from the lysine on histone tails H3 and H4, priming the nucleosome for chromatin packaging by the SIR3 component of the complex. | 1 | Biochemistry |
Rosenthals reagent is a metallocene bis(trimethylsilyl)acetylene complex with zirconium (CpZr) or titanium (CpTi) used as central atom of the metallocene fragment CpM. Additional ligands such as pyridine or THF are commonly used as well. With zirconium as central atom and pyridine as ligand, a dark purple to black solid with a melting point of 125–126 °C is obtained. Synthesizing Rosenthals reagent of a titanocene source yields golden-yellow crystals of the titanocene bis(trimethylsilyl)acetylene complex with a melting point of 81–82 °C. This reagent enables the generation of the themselves unstable titanocene and zirconocene under mild conditions.
The reagent is named after the German chemist (born 1950) and was first synthesized by him and his co-workers in 1995. | 0 | Organic Chemistry |
In its anionic form, the green chromophore has an absorption maxima at 506 nm and an emission maxima at 516 nm. It is formed autocatalytically from amino acids His-62, Tyr-63 and Gly-64. Immediately surrounding the chromophore there is a cluster of charged or polar amino acids as well as structural water molecules. Above the plane of the chromophore, there is a network of hydrogen bond interactions between Glu-144, His-194, Glu-212 and Gln-38. Arg-66 and Arg-91 participate in hydrogen bonding with the carbonyl oxygen of green Eos's imidazolinone moiety. The His-62 side chain lies in an unpolar environment. Conversion from the green to red form depends on the presence of a histidine in the first position of the tripeptide HYG that forms the chromophore. When this histidine residue is substituted with M, S, T or L, Eos only emits bright green light and no longer acts as a photoconvertible fluorescent protein. | 1 | Biochemistry |
* A kinetic scheme with time dependent rates: When the connections depend on the actual time (i.e. matrix depends on the time, ), the process is not Markovian, and the master equation obeys, . The reason for a time dependent rates is, for example, a time dependent external field applied on a Markovian kinetic scheme (thus making the process a not Markovian one).
* A semi-Markovian kinetic scheme: When the connections represent multi exponential jumping time probability density functions, the process is semi-Markovian, and the equation of motion is an integro-differential equation termed the generalized master equation: .
An example for such a process is a reduced dimensions form.
* The Fokker Planck equation: when expanding the master equation of the kinetic scheme in a continuous space coordinate, one finds the Fokker Planck equation. | 7 | Physical Chemistry |
Sandra Pizzarello was born in Venice, Italy in 1933. In 1955, she graduated summa cum laude from the University of Padua earning her Doctor of Biological Sciences degree under her adviser Professor Roncato. Pizzarello went on to work as a research associate developing tranquilizers for Farmitalia Research Laboratories in the Department of Neuropharmacology. Over the course of several years, Pizzarello transitioned from research to raising a family. Following a career opportunity for her husband, an aeronautical engineer and computer scientist, she moved her family to Phoenix, Arizona in 1970.
Once Pizzarello's youngest of four children finished primary school, her focus returned to her career after a decade away from scientific research. She audited a graduate biochemistry seminar course at ASU where she met Professor John Cronin, future co-discoverer of amino acid enantiomeric excess in meteorites. Due to her outstanding performance in the course, she was offered a job to work with Cronin at the university as a research professor in analyzing the recently recovered Murchison meteorite.
Sandra Pizzarello died on October 24, 2021. | 1 | Biochemistry |
Cyclobutadiene is a classic textbook example of an antiaromatic compound. It is conventionally understood to be planar, cyclic, and have 4 π electrons (4n for n=1) in a conjugated system.
However, it has long been questioned if cyclobutadiene is genuinely antiaromatic and recent discoveries have suggested that it may not be. Cyclobutadiene is particularly destabilized and this was originally attributed to antiaromaticity. However, cyclobutadiene adopts more double bond character in two of its parallel bonds than others and the π electrons are not delocalized between the two double-bond-like bonds, giving it a rectangular shape as opposed to a regular square. As such, cyclobutadiene behaves like two discrete alkenes joined by two single bonds, and is therefore non-aromatic rather than antiaromatic.
Despite the lack of this π-antiaromatic destabilization effect, none of its 4n π-electron relatives (cyclooctatetraene, etc.) had even close to as much destabilization, suggesting there was something more going on in the case of cyclobutadiene. It was found that a combination of angle strain, torsional strain, and Pauli repulsion leads to the extreme destabilization experienced in this molecule.
This discovery is awkward in that it contradicts basic teachings of antiaromaticity. At this point of time, it is presumed that cyclobutadiene will continue to be used to introduce the concept of antiaromaticity in textbooks as a matter of convenience, even though classifying it as antiaromatic technically may not be accurate. | 7 | Physical Chemistry |
Alison Sarah Tomlin is a British physical chemist and applied mathematician whose research involves building detailed mathematical models of combustion, including uncertainty quantification for those models. She is a professor in the School of Chemical and Process Engineering at the University of Leeds, where she heads the Clean Combustion Research Group. | 7 | Physical Chemistry |
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