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One cheminformatics study identified 849,574 unique substituents up to 12 non-hydrogen atoms large and containing only carbon, hydrogen, nitrogen, oxygen, sulfur, phosphorus, selenium, and the halogens in a set of 3,043,941 molecules. Fifty substituents can be considered common as they are found in more than 1% of this set, and 438 are found in more than 0.1%. 64% of the substituents are found in only one molecule. The top 5 most common are the methyl, phenyl, chlorine, methoxy, and hydroxyl substituents. The total number of organic substituents in organic chemistry is estimated at 3.1 million, creating a total of 6.7×10 molecules. An infinite number of substituents can be obtained simply by increasing carbon chain length. For instance, the substituents methyl (-CH) and pentyl (-CH). | 0 | Organic Chemistry |
A frigorific mixture is a mixture of two or more phases in a chemical system that, so long as none of the phases are completely consumed during equilibration, reaches an equilibrium temperature that is independent of the starting temperature of the phases before they are mixed. The equilibrium temperature is also independent of the quantities of the phases used as long as sufficient amounts of each are present to reach equilibrium without consuming one or more. | 7 | Physical Chemistry |
Due to their high photoluminescence quantum efficiencies, perovskites may find use in light-emitting diodes (LEDs). Although the stability of perovskite LEDs is not yet as good as III-V or organic LEDs, there is ongoing research to solve this problem, such as incorporating organic molecules or potassium dopants in perovskite LEDs. Perovskite-based printing ink can be used to produce OLED display and quantum dot display panels. | 3 | Analytical Chemistry |
Wastewater pollutants discharged by iron and steel mills includes gasification products such as benzene, naphthalene, anthracene, cyanide, ammonia, phenols and cresols, together with a range of more complex organic compounds known collectively as polycyclic aromatic hydrocarbons (PAH). Treatment technologies include recycling of wastewater; settling basins, clarifiers and filtration systems for solids removal; oil skimmers and filtration; chemical precipitation and filtration for dissolved metals; carbon adsorption and biological oxidation for organic pollutants; and evaporation.
Pollutants generated by other types of smelters varies with the base metal ore. For example, aluminum smelters typically generate fluoride, benzo(a)pyrene, antimony and nickel, as well as aluminum. Copper smelters typically discharge cadmium, lead, zinc, arsenic and nickel, in addition to copper. Lead smelters may discharge antimony, asbestos, cadmium, copper and zinc, in addition to lead. | 8 | Metallurgy |
Gemperline joined the chemistry faculty at East Carolina University (ECU) as an assistant professor in 1982. He was promoted to full professor in 1993. According to The Daily Reflector he had a long and distinguished teaching and research career at ECU with "more than 30 years of research experience in chemometrics involving 38 undergraduate students, 20 master’s students, nine visiting doctoral students and six post-doctoral research assistants" and "more than 60 publications in the field and more than $1.8 million in external grant funds." He also is one of three inventors listed on a licensed patent for designing optical filters for chemical calibration. He received the Helms Award for Outstanding Research from the East Carolina University Chapter of Sigma Xi in 1987, the East Carolina University Distinguished Research Professor of Chemistry (award for 5-year achievement and permanent title) in 1999, and in 2001 was made an East Carolina University College of Arts and Sciences Distinguished Professor of Chemistry, an award for lifetime achievement and permanent title, given in recognition of "outstanding teaching and advising, research and creative productivity, and professional service."
In 2003 Gemperline joined the university administration as associate vice chancellor of research and graduate studies. He became dean of the Graduate School in 2008 and remained in that position until his retirement in 2022. Gemperline served in the positions of president-elect (2009-2010), president (2010-2011), and immediate past president (2011-2012) of the North Carolina Council of Graduate Schools. | 3 | Analytical Chemistry |
An amagat is a practical unit of volumetric number density. Although it can be applied to any substance at any conditions, it is defined as the number of ideal gas molecules per unit volume at 1 atm (101.325 kPa) and 0 °C (273.15 K). It is named after Émile Amagat, who also has Amagat's law named after him. The abbreviated form of amagat is "amg". The abbreviation "Am" has also been used. | 7 | Physical Chemistry |
Thomas Haines was born on August 9, 1933, to Elsie Cubbon Haines (1894–1955) and Charles Haines, who deserted when Haines was two. In 1937, "by reason of the insanity of the mother", a judge placed him at the Graham School, an orphanage in Hastings-on-Hudson, New York. The orphanage, now a social services and foster care agency, was founded in 1806 by Isabella Graham and Elizabeth Hamilton, the recently widowed wife of Alexander Hamilton. Haines remained at the orphanage until high school, when he became a resident houseboy and gardener for a wealthy Hastings family. The story of Haines early life appears as "From the Orphanage to the Lab" in the Story Collider podcast. and in his autobiography with Mindy Lewis, A Curious Life: From Rebel Orphan to Innovative Scientist'.
Haines attended the City College of New York, with a B.S. in chemistry in 1957 and an M.S. in education in 1959. During that time he worked as live-in baby sitter for then-blacklisted American songwriter Jay Gorney (co-writer with Yip Harburg of the Depression era anthem, “Brother, Can You Spare a Dime?”) and his wife Sondra. There Haines came to know many other blacklisted professionals including actors Zero Mostel, Paul Robeson, and Lionel Stander, philosopher Barrows Dunham, and Bella Abzug, then a young lawyer defending blacklisted artists and intellectuals at HUAC hearings. | 1 | Biochemistry |
Other methods of refrigeration include the air cycle machine used in aircraft; the vortex tube used for spot cooling, when compressed air is available; and thermoacoustic refrigeration using sound waves in a pressurized gas to drive heat transfer and heat exchange; steam jet cooling popular in the early 1930s for air conditioning large buildings; thermoelastic cooling using a smart metal alloy stretching and relaxing. Many Stirling cycle heat engines can be run backwards to act as a refrigerator, and therefore these engines have a niche use in cryogenics. In addition, there are other types of cryocoolers such as Gifford-McMahon coolers, Joule-Thomson coolers, pulse-tube refrigerators and, for temperatures between 2 mK and 500 mK, dilution refrigerators. | 7 | Physical Chemistry |
A warm body emitting photons has a monochromatic emission coefficient relating to its temperature and total power radiation. This is sometimes called the second Einstein coefficient, and can be deduced from quantum mechanical theory. | 7 | Physical Chemistry |
Hunter was born on 19 February 1965 in Dunedin, New Zealand. He is the son of John Alexander Hunter and his wife Alice Mary Hunter. He and his family moved to Northern Ireland in 1969. He was educated at Portstewart Primary School and the Coleraine Academical Institution, an all-boys grammar school in Coleraine, County Londonderry. He studied Natural Sciences and then chemistry at the University of Cambridge. He graduated with a Bachelor of Arts (BA) degree in 1986, this was later promoted to Master of Arts (MA Cantab) as per tradition, and with a Doctor of Philosophy (PhD) degree in 1989. | 0 | Organic Chemistry |
Coherent grain boundaries are those in which the crystal lattice of adjacent grains is continuous across the boundary. In other words, the crystallographic orientation of the grains on either side of the boundary is related by a small rotation or translation. Coherent grain boundaries are typically observed in materials with small grain sizes or in highly ordered materials such as single crystals. Because the crystal lattice is continuous across the boundary, there are no defects or dislocations associated with coherent grain boundaries. As a result, they do not act as barriers to the motion of dislocations and have little effect on the strength of a material. However, they can still affect other properties such as diffusion and grain growth.
When solid solutions become supersaturated and precipitation occurs, tiny particles are formed. These particles typically have interphase boundaries that match up with the matrix, despite differences in interatomic spacing between the particle and the matrix. This creates a coherency strain, which causes distortion. Dislocations respond to the stress field of a coherent particle in a way similar to how they interact with solute atoms of different sizes. It is worth noting that the interfacial energy can also influence the kinetics of phase transformations and precipitation processes. For instance, the energy associated with a strained coherent interface can reach a critical level as the precipitate grows, leading to a transition from a coherent to a disordered (non-coherent) interface. This transition occurs when the energy associated with maintaining the coherency becomes too high, and the system seeks a lower energy configuration. This happens when particle dispersion is introduced into a matrix. Dislocations pass through small particles and bow between large particles or particles with disordered interphase boundaries. The predominant slip mechanism determines the contribution to strength, which depends on factors such as particle size and volume fraction. | 8 | Metallurgy |
A pericyclic reaction is an organic reaction that proceeds via a single concerted and cyclic transition state, the geometry of which allows for the continuous overlap of a cycle of (π and/or σ) orbitals.
The terms conrotatory and disrotatory describe the relative sense of bond rotation involved in electrocyclic ring-opening and -closing reactions. In a disrotatory process, the breaking or forming bonds two ends rotate in opposing directions (one clockwise, one counterclockwise); in a conrotatory process, they rotate in the same direction (both clockwise or both counterclockwise), the process is conrotatory'.
Eventually, it was recognized that thermally-promoted pericyclic reactions in general obey a single set of generalized selection rules, depending on the electron count and topology of the orbital interactions. The key concept of orbital topology or faciality was introduced to unify several classes of pericyclic reactions under a single conceptual framework. In short, a set of contiguous atoms and their associated orbitals that react as one unit in a pericyclic reaction is known as a component, and each component is said to be antarafacial or suprafacial depending on whether the orbital lobes that interact during the reaction are on the opposite or same side of the nodal plane, respectively. (The older terms conrotatory and disrotatory, which are applicable to electrocyclic ring opening and closing only, are subsumed by the terms antarafacial and suprafacial, respectively, under this more general classification system.) | 7 | Physical Chemistry |
Recombinant DNA is widely used in biotechnology, medicine and research. Today, recombinant proteins and other products that result from the use of DNA technology are found in essentially every western pharmacy, physician or veterinarian office, medical testing laboratory, and biological research laboratory. In addition, organisms that have been manipulated using recombinant DNA technology, as well as products derived from those organisms, have found their way into many farms, supermarkets, home medicine cabinets, and even pet shops, such as those that sell GloFish and other genetically modified animals.
The most common application of recombinant DNA is in basic research, in which the technology is important to most current work in the biological and biomedical sciences. Recombinant DNA is used to identify, map and sequence genes, and to determine their function. rDNA probes are employed in analyzing gene expression within individual cells, and throughout the tissues of whole organisms. Recombinant proteins are widely used as reagents in laboratory experiments and to generate antibody probes for examining protein synthesis within cells and organisms.
Many additional practical applications of recombinant DNA are found in industry, food production, human and veterinary medicine, agriculture, and bioengineering. Some specific examples are identified below. | 1 | Biochemistry |
As a trivalent transition metal, yttrium forms various inorganic compounds, generally in the oxidation state of +3, by giving up all three of its valence electrons. A good example is yttrium(III) oxide (), also known as yttria, a six-coordinate white solid.
Yttrium forms a water-insoluble fluoride, hydroxide, and oxalate, but its bromide, chloride, iodide, nitrate and sulfate are all soluble in water. The Y ion is colorless in solution because of the absence of electrons in the d and f electron shells.
Water readily reacts with yttrium and its compounds to form . Concentrated nitric and hydrofluoric acids do not rapidly attack yttrium, but other strong acids do.
With halogens, yttrium forms trihalides such as yttrium(III) fluoride (), yttrium(III) chloride (), and yttrium(III) bromide () at temperatures above roughly 200 °C. Similarly, carbon, phosphorus, selenium, silicon and sulfur all form binary compounds with yttrium at elevated temperatures.
Organoyttrium chemistry is the study of compounds containing carbon–yttrium bonds. A few of these are known to have yttrium in the oxidation state 0. (The +2 state has been observed in chloride melts, and +1 in oxide clusters in the gas phase.) Some trimerization reactions were generated with organoyttrium compounds as catalysts. These syntheses use as a starting material, obtained from and concentrated hydrochloric acid and ammonium chloride.
Hapticity is a term to describe the coordination of a group of contiguous atoms of a ligand bound to the central atom; it is indicated by the Greek character eta, η. Yttrium complexes were the first examples of complexes where carboranyl ligands were bound to a d-metal center through a η-hapticity. Vaporization of the graphite intercalation compounds graphite–Y or graphite– leads to the formation of endohedral fullerenes such as Y@C. Electron spin resonance studies indicated the formation of Y and (C) ion pairs. The carbides YC, YC, and YC can be hydrolyzed to form hydrocarbons. | 8 | Metallurgy |
An important physical property characterizing the flow of liquids is viscosity. Intuitively, viscosity describes the resistance of a liquid to flow.
More technically, viscosity measures the resistance of a liquid to deformation at a given rate, such as when it is being sheared at finite velocity. A specific example is a liquid flowing through a
pipe: in this case the liquid undergoes shear deformation since it flows more slowly near the walls of the pipe
than near the center. As a result, it exhibits viscous resistance to flow. In order to maintain flow, an external force must be applied, such as a pressure difference between the ends of the pipe.
The viscosity of liquids decreases with increasing temperature.
Precise control of viscosity is important in many applications, particularly the lubrication industry. One way to achieve such control is by blending two or more liquids of differing viscosities in precise ratios.
In addition, various additives exist which can modulate the temperature-dependence of the
viscosity of lubricating oils. This capability is important since machinery often operate over a range of
temperatures (see also viscosity index).
The viscous behavior of a liquid can be either Newtonian or non-Newtonian. A Newtonian liquid exhibits a linear strain/stress curve, meaning its viscosity is independent of time, shear rate, or shear-rate history. Examples of Newtonian liquids include water, glycerin, motor oil, honey, or mercury. A non-Newtonian liquid is one where the viscosity is not independent of these factors and either thickens (increases in viscosity) or thins (decreases in viscosity) under shear. Examples of non-Newtonian liquids include ketchup, custard, or starch solutions. | 7 | Physical Chemistry |
Steinert provides sorting technologies for recycling and mining industries using a variety of sensors, like X-ray, inductive, NIR and color optical sensors and 3D laser camera, which can be combined for sorting a variety of materials. NIR technology is used in the recycling field. | 3 | Analytical Chemistry |
Commonly referred to as STD (Submarine Tailings Disposal) or DSTD (Deep Sea Tailings Disposal). Tailings can be conveyed using a pipeline then discharged so as to eventually descend into the depths. Practically, it is not an ideal method, as the close proximity to off-shelf depths is rare. When STD is used, the depth of discharge is often what would be considered shallow, and extensive damage to the seafloor can result due to covering by the tailings product. It is also critical to control the density and temperature of the tailings product, to prevent it from travelling long distances, or even floating to the surface.
This method is used by the gold mine on Lihir Island; its waste disposal has been viewed by environmentalists as highly damaging, while the owners claim that it is not harmful. | 8 | Metallurgy |
The possibility has been proposed and studied, both theoretically and experimentally, of implementing an orthogonal system inside cells independent of the cellular genetic material in order to make a completely safe system, with the possible increase in encoding potentials.
Several groups have focused on different aspects:
* Novel backbones and base pairs as discussed above;
* XNA artificial replication and transcription polymerases starting generally from T7 RNA polymerase;
* (16S ribosomal sequences with altered anti-Shine-Dalgarno sequences allowing the translation of only orthogonal mRNA with a matching altered Shine-Dalgarno sequence; and
* Novel tRNA encoding non-natural aminoacids for an expanded genetic code. | 1 | Biochemistry |
Different formulations of efficiency are possible depending on which outputs and inputs are considered. For instance, average quantum efficiency is the ratio between gross assimilation and either absorbed or incident light intensity. Large variability of measured quantum efficiency is reported in the literature between plants grown in different conditions and classified in different subtypes but the underpinnings are still unclear. One of the components of quantum efficiency is the efficiency of dark reactions, biochemical efficiency, which is generally expressed in reciprocal terms as ATP cost of gross assimilation (ATP/GA).
In photosynthesis ATP/GA depends mainly on and O concentration at the carboxylating sites of RuBisCO. When concentration is high and O concentration is low photorespiration is suppressed and assimilation is fast and efficient, with ATP/GA approaching the theoretical minimum of 3.
In photosynthesis concentration at the RuBisCO carboxylating sites is mainly the result of the operation of the concentrating mechanisms, which cost circa an additional 2 ATP/GA but makes efficiency relatively insensitive of external concentration in a broad range of conditions.
Biochemical efficiency depends mainly on the speed of delivery to the bundle sheath, and will generally decrease under low light when PEP carboxylation rate decreases, lowering the ratio of /O concentration at the carboxylating sites of RuBisCO. The key parameter defining how much efficiency will decrease under low light is bundle sheath conductance. Plants with higher bundle sheath conductance will be facilitated in the exchange of metabolites between the mesophyll and bundle sheath and will be capable of high rates of assimilation under high light. However, they will also have high rates of retro-diffusion from the bundle sheath (called leakage) which will increase photorespiration and decrease biochemical efficiency under dim light. This represents an inherent and inevitable trade off in the operation of photosynthesis. plants have an outstanding capacity to attune bundle sheath conductance. Interestingly, bundle sheath conductance is downregulated in plants grown under low light and in plants grown under high light subsequently transferred to low light as it occurs in crop canopies where older leaves are shaded by new growth. | 5 | Photochemistry |
At lower temperatures, more energy (i.e. - larger applied stress) is required to activate some slip systems. This is particularly evident in BCC materials, in which not all 5 independent slip systems are thermally activated at temperatures below the ductile-to-brittle transition temperature, or DBTT, so BCC specimens therefore become brittle. In general BCC metals have higher critical resolved shear stress values compared to FCC. However, the relationship between the CRSS and temperature and strain rate is worth examining further.
To understand the relationship between stress and temperature observed, we first divide the critical resolved shear stress into the sum of two components: an athermal term described as and a thermally dependent term known as where
can be attributed to the stresses involved with dislocation motion while dislocations move in long-range internal stress fields. These long-range stresses arise from the presence of other dislocations. however is attributed to short range internal stress fields that arise from defect atoms or precipitates within the lattice that are obstacles for dislocation glide. With increasing temperature, the dislocations within the material have sufficient energy to overcome these short-range stresses. This explains the trend in region I where stress decreases with temperature. At the boundary between region’s I and II, the term is effectively zero and the critical resolved shear stress is completely described by the athermal term, i.e. long-range internal stress fields are still significant. In the third region, diffusive processes begin to play a significant role in plastic deformation of the material and so the critically resolved shear stress decreases once again with temperature. Within region three, the equation suggested earlier no longer applies. Region I has a temperature upper bound of approximately while region III occurs at values where is the melting temperature of the material. The figure also shows the effect of increased strain rate generally increasing the critical resolved shear stress for a constant temperature as this increases the dislocation density in the material. Note that for intermediate temperatures, i.e. region II, there is a region where the strain rate has no effect on the stress. Increasing the strain rate does shift the graph to the right as more energy is needed to balance the short-term stresses with the resulting increased dislocation density.
The thermal component, can be expressed in the following manner.
Where is the thermal component at 0 K and is the temperature at which the thermal energy is sufficient to overcome the obstacles causing stress, i.e. the temperature at the transition from 1 to 2. The above equation has been verified experimentally. In general, the CRSS increases as the homologous temperature decreases because it becomes energetically more costly to activate the slip systems, although this effect is much less pronounced in FCC.
Solid solution strengthening also increases the CRSS compared to a pure single component material because the solute atoms distort the lattice, preventing the dislocation motion necessary for plasticity. With dislocation motion inhibited, it becomes harder to activate the necessary 5 independent slip systems, so the material becomes stronger and more brittle. | 8 | Metallurgy |
The Cromer cycle is a thermodynamic cycle that uses a desiccant to interact with higher relative humidity air leaving a cold surface. When a system is taken through a series of different states and finally returned to its initial state, a thermodynamic cycle is said to have occurred. The desiccant absorbs moisture from the air leaving the cold surface, releasing heat and drying the air, which can be used in a process requiring dry air. The desiccant is then dried by an air stream at a lower relative humidity, where the desiccant gives up its moisture by evaporation, increasing the air's relative humidity and cooling it. This cooler, moister air can then be presented to the same cold surface as above to take it below its dew point and dry it further, or it can be expunged from the system.
The desiccant undergoes a reversible process whereby in the first part of the cycle, it absorbs or adsorbs moisture from air leaving a cold surface, releasing heat, and then in the second part of the cycle evaporates moisture, absorbing heat and returning the desiccant to its original state to complete the cycle again. The result of the Cromer cycle is that the process air leaving the cycle is dehumidified further (higher latent ratio) than it would be leaving the cold surface without the cycle. The Cromer cycle concept was originally patented in the mid-1980s. Those patents have expired and thus the cycle is free for anyone to use. The cycle was first publicized in 1997 by Popular Mechanics' in its Tech Update section. | 7 | Physical Chemistry |
Many different intermetallic compounds are formed during solidifying of solders and during their reactions with the soldered surfaces. The intermetallics form distinct phases, usually as inclusions in a ductile solid solution matrix, but also can form the matrix itself with metal inclusions or form crystalline matter with different intermetallics. Intermetallics are often hard and brittle. Finely distributed intermetallics in a ductile matrix yield a hard alloy while coarse structure gives a softer alloy. A range of intermetallics often forms between the metal and the solder, with increasing proportion of the metal; e.g. forming a structure of . Layers of intermetallics can form between the solder and the soldered material. These layers may cause mechanical reliability weakening and brittleness, increased electrical resistance, or electromigration and formation of voids. The gold-tin intermetallics layer is responsible for poor mechanical reliability of tin-soldered gold-plated surfaces where the gold plating did not completely dissolve in the solder.
Two processes play a role in a solder joint formation: interaction between the substrate and molten solder, and solid-state growth of intermetallic compounds. The base metal dissolves in the molten solder in an amount depending on its solubility in the solder. The active constituent of the solder reacts with the base metal with a rate dependent on the solubility of the active constituents in the base metal. The solid-state reactions are more complex – the formation of intermetallics can be inhibited by changing the composition of the base metal or the solder alloy, or by using a suitable barrier layer to inhibit diffusion of the metals.
Some example interactions include:
* Gold and palladium readily dissolve in solders. Copper and nickel tend to form intermetallic layers during normal soldering profiles. Indium forms intermetallics as well.
* Indium-gold intermetallics are brittle and occupy about 4 times more volume than the original gold. Bonding wires are especially susceptible to indium attack. Such intermetallic growth, together with thermal cycling, can lead to failure of the bonding wires.
* Copper plated with nickel and gold is often used. The thin gold layer facilitates good solderability of nickel as it protects the nickel from oxidation; the layer has to be thin enough to rapidly and completely dissolve so bare nickel is exposed to the solder.
* Lead-tin solder layers on copper leads can form copper-tin intermetallic layers; the solder alloy is then locally depleted of tin and form a lead-rich layer. The Sn-Cu intermetallics then can get exposed to oxidation, resulting in impaired solderability.
* – common on solder-copper interface, forms preferentially when excess of tin is available; in presence of nickel, compound can be formed
* – common on solder-copper interface, forms preferentially when excess of copper is available, more thermally stable than , often present when higher-temperature soldering occurred
* – common on solder-nickel interface
* – very slow formation
* Sn - at higher concentration of silver (over 3%) in tin forms platelets that can serve as crack initiation sites.
* – β-phase – brittle, forms at excess of tin. Detrimental to properties of tin-based solders to gold-plated layers.
* – forms on the boundary between gold and indium-lead solder, acts as a barrier against further dissolution of gold | 8 | Metallurgy |
Thermocells in which the electrolyte connecting the electrodes is an ionic material have been considered and constructed too. The temperature range is also elevated as compared to liquid electrolytes. Studied systems fall in the 400–900 K. Some solid ionic materials that have been employed to construct thermogalvanic cells are AgI, PbCl and PbBr. | 7 | Physical Chemistry |
In Type I photosensitized reactions, the photosensitizer is excited by a light source into a triplet state. The excited, triplet state photosensitizer then reacts with a substrate molecule which is not molecular oxygen to both form a product and reform the photosensitizer. Type I photosensitized reactions result in the photosensitizer being quenched by a different chemical substrate than molecular oxygen. | 5 | Photochemistry |
While a finite thermal contact conductance is due to voids at the interface, surface waviness, and surface roughness, etc., a finite conductance exists even at near ideal interfaces as well. This conductance, known as thermal boundary conductance, is due to the differences in electronic and vibrational properties between the contacting materials. This conductance is generally much higher than thermal contact conductance, but becomes important in nanoscale material systems. | 7 | Physical Chemistry |
Nicking Enzyme Amplification Reaction (NEAR) is a method for in vitro DNA amplification like the polymerase chain reaction (PCR). NEAR is isothermal, replicating DNA at a constant temperature using a polymerase (and nicking enzyme) to exponentially amplify the DNA at a temperature range of 55 °C to 59 °C.
One disadvantage of PCR is that it consumes time uncoiling the double-stranded DNA with heat into single strands (a process called denaturation) . This leads to amplification times typically thirty minutes or more for significant production of amplified products.
Potential advantages of NEAR over PCR are increased speed and lower energy requirements, characteristics that are shared with other isothermal amplification schemes. A major disadvantage of NEAR relative to PCR is that production of nonspecific amplification products is a common issue with isothermal amplification reactions.
The NEAR reaction uses naturally occurring or engineered endonucleases that introduce a strand break on only one strand of a double-stranded DNA cleavage site. The ability of several of these enzymes to catalyze isothermal DNA amplification was disclosed but not claimed in the patents issued for the enzymes themselves. | 1 | Biochemistry |
According to some serotonin was "named for its source (sero-) and ability to modify smooth muscle tone (tonin)" an effect that may be dependent (some controversy exists) upon serotonylation.
The term serotonylation was created in 2003 by Diego J. Walther and colleagues of the Max Planck Institute for Molecular Genetics in a paper in the journal Cell. | 1 | Biochemistry |
An automated read-across tool called Generalized Read-Across (GenRA) is integrated into The Chemicals Dashboard. GenRA is designed to keep the expert consideration inherent in the read-across method, but automate the chemical selection process to help predict toxicity.
The Dashboard also has the capability to search existing scientific literature sources such as PubMed, via a web-based version of the "Abstract Sifter", Google Scholar and reports from EPA's Provisional Peer Reviewed Toxicity Values ([https://www.epa.gov/pprtv/provisional-peer-reviewed-toxicity-values-pprtvs-assessments PPRTV]) and the EPA Integrated Risk Information System ([https://www.epa.gov/iris IRIS]).
Real-time QSAR prediction for multiple physicochemical property and toxicity endpoints is available through the [https://comptox.epa.gov/dashboard/predictions/index predictions tab]. | 2 | Environmental Chemistry |
Rare-earth oxides such as ytterbium oxide (YbO) and erbium oxide (ErO) are the most commonly used selective emitters. These oxides emit a narrow band of wavelengths in the near-infrared region, allowing the emission spectra to be tailored to better fit the absorbance characteristics of a particular PV material. The peak of the emission spectrum occurs at 1.29 eV for YbO and 0.827 eV for ErO. As a result, YbO can be used a selective emitter for silicon cells and ErO, for GaSb or InGaAs. However, the slight mismatch between the emission peaks and band gap of the absorber costs significant efficiency. Selective emission only becomes significant at 1100 °C and increases with temperature. Below 1700 °C, selective emission of rare-earth oxides is fairly low, further decreasing efficiency. Currently, 13% efficiency has been achieved with YbO and silicon PV cells. In general selective emitters have had limited success. More often filters are used with black body emitters to pass wavelengths matched to the bandgap of the PV and reflect mismatched wavelengths back to the emitter. | 7 | Physical Chemistry |
Zyklon B (; translated Cyclone B) was the trade name of a cyanide-based pesticide invented in Germany in the early 1920s. It consists of hydrogen cyanide (prussic acid), as well as a cautionary eye irritant and one of several adsorbents such as diatomaceous earth. The product is notorious for its use by Nazi Germany during the Holocaust to murder approximately 1.1 million people in gas chambers installed at Auschwitz-Birkenau, Majdanek, and other extermination camps.
Hydrogen cyanide, a poisonous gas that interferes with cellular respiration, was first used as a pesticide in California in the 1880s. Research at Degesch of Germany led to the development of Zyklon (later known as Zyklon A), a pesticide that released hydrogen cyanide upon exposure to water and heat. It was banned after World War I, when Germany used a similar product as a chemical weapon. Degussa purchased Degesch in 1922. Their team of chemists, which included and Bruno Tesch, devised a method of packaging hydrogen cyanide in sealed canisters along with a cautionary eye irritant and one of several adsorbents such as diatomaceous earth. The new product was also named Zyklon, but it became known as Zyklon B to distinguish it from the earlier version. Uses included delousing clothing and fumigating ships, warehouses, and trains.
The Nazis started using Zyklon B in extermination camps in early 1942 to murder prisoners during the Holocaust. Tesch and his deputy executive, Karl Weinbacher, were executed in 1946 for knowingly selling the product to the SS for use on humans. Hydrogen cyanide is now rarely used as a pesticide but still has industrial applications. Firms in several countries continue to produce Zyklon B under alternative brand names, including Detia-Degesch, the successor to Degesch, who renamed the product Cyanosil in 1974. | 1 | Biochemistry |
, about a quarter of annual global greenhouse gas emissions is the carbon dioxide from burning petroleum (plus methane leaks from the industry). Along with the burning of coal, petroleum combustion is the largest contributor to the increase in atmospheric CO. Atmospheric CO has risen over the last 150 years to current levels of over 415 ppmv, from the 180–300 ppmv of the prior 800 thousand years. The rise in Arctic temperature has reduced the minimum Arctic ice pack to , a loss of almost half since satellite measurements started in 1979.
Ocean acidification is the increase in the acidity of the Earth's oceans caused by the uptake of carbon dioxide () from the atmosphere.The saturation state of calcium carbonate decreases with the uptake of carbon dioxide in the ocean. This increase in acidity inhibits all marine life—having a greater effect on smaller organisms as well as shelled organisms (see scallops). | 7 | Physical Chemistry |
A majority of the human genome is made up of non-protein coding DNA. It infers that such sequences are not commonly employed to encode for a protein. However, even though these regions do not code for protein, they have other functions and carry necessary regulatory information.They can be classified based on the size of the ncRNA. Small noncoding RNA is usually categorized as being under 200 bp in length, whereas long noncoding RNA is greater than 200bp. In addition, they can be categorized by their function within the cell; Infrastructural and Regulatory ncRNAs. Infrastructural ncRNAs seem to have a housekeeping role in translation and splicing and include species such as rRNA, tRNA, snRNA.Regulatory ncRNAs are involved in the modification of other RNAs. | 1 | Biochemistry |
If a drop is placed on a smooth, horizontal surface, it is generally not in the equilibrium state. Hence, it spreads until an equilibrium contact radius is reached (partial wetting). While taking into account capillary, gravitational, and viscous contributions, the drop radius as a function of time can be expressed as
For the complete wetting situation, the drop radius at any time during the spreading process is given by
where
:*γ is surface tension of the fluid
:*V is drop volume
:*η is viscosity of the fluid
:*ρ is density of the fluid
:*g is gravitational constant
:*λ is shape factor, 37.1m
:*t is experimental delay time
:*r is drop radius in equilibrium | 7 | Physical Chemistry |
The activation energy for a chemical reaction can be provided when one reactant molecule absorbs light of suitable wavelength and is promoted to an excited state. The study of reactions initiated by light is photochemistry, one prominent example being photosynthesis. | 7 | Physical Chemistry |
Piperacillin is used almost exclusively in combination with the beta lactamase inhibitor tazobactam for the treatment of serious, hospital-acquired infections. This combination is among the most widely used drug therapies in United States non-federal hospitals, accounting for $388M in spending in spite of being a low-cost generic drug.
Piperacillin-tazobactam is recommended as part of a three-drug regimen for the treatment of hospital-acquired pneumonia suspected as being due to infection by multi-drug resistant pathogens. It is also one of several antibacterial drugs recommended for the treatment of infections known to be caused by anaerobic Gram-negative rods.
Piperacillin-tazobactam is recommended by the National Institute for Health and Care Excellence as initial empiric treatment for people with suspected neutropenic sepsis.
Piperacillin is used to treat patients diagnosed with various internal infections such as abdominal, bacteremia, gynecological, respiratory, and urinary, mainly caused by Pseudomonas aeruginosa and other infectious bacteria. They are primarily used in current and former neutropenic patients, and patients with biliary tract infections. Other uses include applications in surgical infection prophylaxis; in biliary surgery, a single dose of piperacillin is administered intravenously to inhibit the development of acute cholangitis and prevent wound infections. The combination of piperacillin and an aminoglycoside is commonly used to treat severe infections, but due to the incompatibilities in drug interaction, they are administered separately. | 4 | Stereochemistry |
Commercially available sea salts on the market today vary widely in their chemical composition. Although the principal component is sodium chloride, the remaining portion can range from less than 0.2 to 10% of other salts. These are mostly calcium, potassium, and magnesium salts of chloride and sulfate with substantially lesser amounts of many trace elements found in natural seawater. Though the composition of commercially available salt may vary, the ionic composition of natural saltwater is relatively constant. | 9 | Geochemistry |
The most common thiolactone, homocysteine thiolactone is produced biochemically from homocysteine and it may play a role in protein damage. The thiolactone functional group is also present in some pharmaceutical drugs such as citiolone and erdosteine. Thiolactone rings can also be found in peptides synthesized by bacteria such as Staphylococcus aureus in order to regulate their quorum-sensing system. | 0 | Organic Chemistry |
Enzymes catalyze chemical reactions at rates that are astounding relative to uncatalyzed chemistry at the same reaction conditions. Each catalytic event requires a minimum of three or often more steps, all of which occur within the few milliseconds that characterize typical enzymatic reactions. According to transition state theory, the smallest fraction of the catalytic cycle is spent in the most important step, that of the transition state. The original proposals of absolute reaction rate theory for chemical reactions defined the transition state as a distinct species in the reaction coordinate that determined the absolute reaction rate. Soon thereafter, Linus Pauling proposed that the powerful catalytic action of enzymes could be explained by specific tight binding to the transition state species Because reaction rate is proportional to the fraction of the reactant in the transition state complex, the enzyme was proposed to increase the concentration of the reactive species.
This proposal was formalized by Wolfenden and coworkers at University of North Carolina at Chapel Hill, who hypothesized that the rate increase imposed by enzymes is proportional to the affinity of the enzyme for the transition state structure relative to the Michaelis complex. Because enzymes typically increase the non-catalyzed reaction rate by factors of 10-10, and Michaelis complexes often have dissociation constants in the range of 10-10 M, it is proposed that transition state complexes are bound with dissociation constants in the range of 10-10 M. As substrate progresses from the Michaelis complex to product, chemistry occurs by enzyme-induced changes in electron distribution in the substrate. Enzymes alter the electronic structure by protonation, proton abstraction, electron transfer, geometric distortion, hydrophobic partitioning, and interaction with Lewis acids and bases. Analogs that resemble the transition state structures should therefore provide the most powerful noncovalent inhibitors known.
All chemical transformations pass through an unstable structure called the transition state, which is poised between the chemical structures of the substrates and products. The transition states for chemical reactions are proposed to have lifetimes near 10 seconds, on the order of the time of a single bond vibration. No physical or spectroscopic method is available to directly observe the structure of the transition state for enzymatic reactions, yet transition state structure is central to understanding enzyme catalysis since enzymes work by lowering the activation energy of a chemical transformation.
It is now accepted that enzymes function to stabilize transition states lying between reactants and products, and that they would therefore be expected to bind strongly any inhibitor that closely resembles such a transition state. Substrates and products often participate in several enzyme catalyzed reactions, whereas the transition state tends to be characteristic of one particular enzyme, so that such an inhibitor tends to be specific for that particular enzyme. The identification of numerous transition state inhibitors supports the transition state stabilization hypothesis for enzymatic catalysis.
Currently there is a large number of enzymes known to interact with transition state analogs, most of which have been designed with the intention of inhibiting the target enzyme. Examples include HIV-1 protease, racemases, β-lactamases, metalloproteinases, cyclooxygenases and many others. | 7 | Physical Chemistry |
Chelate complexes of gadolinium are often used as contrast agents in MRI scans, although iron particle and manganese chelate complexes have also been explored. Bifunctional chelate complexes of zirconium, gallium, fluorine, copper, yttrium, bromine, or iodine are often used for conjugation to monoclonal antibodies for use in antibody-based PET imaging. These chelate complexes often employ the usage of hexadentate ligands such as desferrioxamine B (DFO), according to Meijs et al., and the gadolinium complexes often employ the usage of octadentate ligands such as DTPA, according to Desreux et al. Auranofin, a chelate complex of gold, is used in the treatment of rheumatoid arthritis, and penicillamine, which forms chelate complexes of copper, is used in the treatment of Wilson's disease and cystinuria, as well as refractory rheumatoid arthritis. | 7 | Physical Chemistry |
Drospirenone stimulates the proliferation of MCF-7 breast cancer cells in vitro, an action that is independent of the classical PRs and is instead mediated via the progesterone receptor membrane component-1 (PGRMC1). Certain other progestins act similarly in this assay, whereas progesterone acts neutrally. It is unclear if these findings may explain the different risks of breast cancer observed with progesterone and progestins in clinical studies. | 4 | Stereochemistry |
Recently, it has been shown that trabectedin blocks DNA binding of the oncogenic transcription factor FUS-CHOP and reverses the transcriptional program in myxoid liposarcoma. By reversing the genetic program created by this transcription factor, trabectedin promotes differentiation and reverses the oncogenic phenotype in these cells.
Other than transcriptional interference, the mechanism of action of trabectedin is complex and not completely understood. The compound is known to bind and alkylate DNA at the N2 position of guanine. It is known from in vitro work that this binding occurs in the minor groove, spans approximately three to five base pairs and is most efficient with CGG sequences. Additional favorable binding sequences are TGG, AGC, or GGC. Once bound, this reversible covalent adduct bends DNA toward the major groove, interferes directly with activated transcription, poisons the transcription-coupled nucleotide excision repair complex, promotes degradation of RNA polymerase II, and generates DNA double-strand breaks. | 0 | Organic Chemistry |
The Great Calcite Belt can be defined as an elevated particulate inorganic carbon (PIC) feature occurring alongside seasonally elevated chlorophyll a in austral spring and summer in the Southern Ocean. It plays an important role in climate fluctuations, accounting for over 60% of the Southern Ocean area (30–60° S). The region between 30° and 50° S has the highest uptake of anthropogenic carbon dioxide (CO) alongside the North Atlantic and North Pacific oceans. Knowledge of the impact of interacting environmental influences on phytoplankton distribution in the Southern Ocean is limited. For example, more understanding is needed of how light and iron availability or temperature and pH interact to control phytoplankton biogeography. Hence, if model parameterizations are to improve to provide accurate predictions of biogeochemical change, a multivariate understanding of the full suite of environmental drivers is required.
The Southern Ocean has often been considered as a microplankton-dominated (20–200 µm) system with phytoplankton blooms dominated by large diatoms and Phaeocystis sp. However, since the identification of the Great Calcite Belt (GCB) as a consistent feature and the recognition of picoplankton (< 2 µm) and nanoplankton (2–20 µm) importance in high-nutrient, low-chlorophyll (HNLC) waters, the dynamics of small (bio)mineralizing plankton and their export need to be acknowledged. The two dominant biomineralizing phytoplankton groups in the GCB are coccolithophores and diatoms. Coccolithophores are generally found north of the polar front, though Emiliania huxleyi has been observed as far south as 58° S in the Scotia Sea, at 61° S across Drake Passage, and at 65°S south of Australia.
Diatoms are present throughout the GCB, with the polar front marking a strong divide between different size fractions. North of the polar front, small diatom species, such as Pseudo-nitzschia spp. and Thalassiosira spp., tend to dominate numerically, whereas large diatoms with higher silicic acid requirements (e.g., Fragilariopsis kerguelensis) are generally more abundant south of the polar front. High abundances of nanoplankton (coccolithophores, small diatoms, chrysophytes) have also been observed on the Patagonian Shelf and in the Scotia Sea. Currently, few studies incorporate small biomineralizing phytoplankton to species level. Rather, the focus has often been on the larger and noncalcifying species in the Southern Ocean due to sample preservation issues (i.e., acidified Lugol’s solution dissolves calcite, and light microscopy restricts accurate identification to cells > 10 µm. In the context of climate change and future ecosystem function, the distribution of biomineralizing phytoplankton is important to define when considering phytoplankton interactions with carbonate chemistry, and ocean biogeochemistry.
The Great Calcite Belt spans the major Southern Ocean circumpolar fronts: the Subantarctic front, the polar front, the Southern Antarctic Circumpolar Current front, and occasionally the southern boundary of the Antarctic Circumpolar Current. The subtropical front (at approximately 10 °C) acts as the northern boundary of the GCB and is associated with a sharp increase in PIC southwards. These fronts divide distinct environmental and biogeochemical zones, making the GCB an ideal study area to examine controls on phytoplankton communities in the open ocean. A high PIC concentration observed in the GCB (1 µmol PIC L) compared to the global average (0.2 µmol PIC L) and significant quantities of detached E. huxleyi coccoliths (in concentrations > 20,000 coccoliths mL) both characterize the GCB. The GCB is clearly observed in satellite imagery spanning from the Patagonian Shelf across the Atlantic, Indian, and Pacific oceans and completing Antarctic circumnavigation via the Drake Passage. | 9 | Geochemistry |
With the wealth of data available from monitoring reaction progress over time paired with the power of modern computing methods, it has become reasonably straightforward to numerically evaluate the rate law, mapping the integrated rate laws of simulated reactions paths onto a fit of reaction progress over time. Due to the principles of the propagation of error, rate constants and rate laws can be determined by these differential methods with significantly lower uncertainty than by the construction of graphical rate equations (above.) | 7 | Physical Chemistry |
The gel is prepared by dissolving the agarose powder in an appropriate buffer, such as TAE or TBE, to be used in electrophoresis. The agarose is dispersed in the buffer before heating it to near-boiling point, but avoid boiling. The melted agarose is allowed to cool sufficiently before pouring the solution into a cast as the cast may warp or crack if the agarose solution is too hot. A comb is placed in the cast to create wells for loading sample, and the gel should be completely set before use.
The concentration of gel affects the resolution of DNA separation. The agarose gel is composed of microscopic pores through which the molecules travel, and there is an inverse relationship between the pore size of the agarose gel and the concentration – pore size decreases as the density of agarose fibers increases. High gel concentration improves separation of smaller DNA molecules, while lowering gel concentration permits large DNA molecules to be separated. The process allows fragments ranging from 50 base pairs to several mega bases to be separated depending on the gel concentration used. The concentration is measured in weight of agarose over volume of buffer used (g/ml). For a standard agarose gel electrophoresis, a 0.8% gel gives good separation or resolution of large 5–10kb DNA fragments, while 2% gel gives good resolution for small 0.2–1kb fragments. 1% gels is often used for a standard electrophoresis. High percentage gels are often brittle and may not set evenly, while low percentage gels (0.1-0.2%) are fragile and not easy to handle. Low-melting-point (LMP) agarose gels are also more fragile than normal agarose gel. Low-melting point agarose may be used on its own or simultaneously with standard agarose for the separation and isolation of DNA. PFGE and FIGE are often done with high percentage agarose gels. | 1 | Biochemistry |
The process of singlet fission was first introduced to describe the photophysics of anthracene in 1965. Early studies on the effect of the magnetic field on the fluorescence of crystalline tetracene solidified understanding of singlet fission in polyacenes.
Acenes, Pentacene and Tetracene in particular, are prominent candidates for singlet fission. The energy of the triplet states are smaller than or equal to half of the singlet (S) state energy, thus satisfying the requirement of S ≥ 2T. Singlet fission in functionalized pentacene compounds has been observed experimentally. Intramolecular singlet fission in covalently linked pentacene and tetracene dimers has also been reported.
The detailed mechanism of the process is unknown. Particularly, the role of charge transfer states in the singlet fission process is still debated. Typically, the mechanisms for singlet fission are classified into (a) Direct coupling between the molecules and (b) Step-wise one-electron processes involving the charge-transfer states. Intermolecular interactions and the relative orientation of the molecules within the aggregates are known to critically effect the singlet fission efficiencies.
The limited number and structural similarity of chromophores is believed to be the major obstacle to advancing the field for practical applications. It has been proposed that computational modeling of the diradical character of molecules may serve as a guiding principle for the discovery of new classes of singlet fission chromophores. Computations allowed to identify carbenes as building blocks for engineering singlet fission molecules. | 7 | Physical Chemistry |
A small fraction of metabolism – less than 5% in all tissues except the testes where it accounts for about 33% – is initially catalyzed by leucine aminomutase, producing β-leucine, which is subsequently metabolized into (β-KIC), β-ketoisocaproyl-CoA, and then acetyl-CoA by a series of uncharacterized enzymes. | 1 | Biochemistry |
Silicon isotope biogeochemistry is the study of environmental processes using the relative abundance of Si isotopes. As the relative abundance of Si stable isotopes varies among different natural materials, the differences in abundance can be used to trace the source of Si, and to study biological, geological, and chemical processes. The study of stable isotope biogeochemistry of Si aims to quantify the different Si fluxes in the global biogeochemical silicon cycle, to understand the role of biogenic silica within the global Si cycle, and to investigate the applications and limitations of the sedimentary Si record as an environmental and palaeoceanographic proxy. | 9 | Geochemistry |
Water undergoes electrolysis at high temperatures to form hydrogen gas and oxygen gas. The energy to perform this is extracted from renewable sources such as wind power. Then, the hydrogen is reacted with compressed carbon dioxide captured by direct air capture. The reaction produces blue crude which consists of hydrocarbon. The blue crude is then refined to produce high efficiency E-diesel. This method is, however, still debatable because with the current production capability it can only produce 3,000 liters in a few months, 0.0002% of the daily production of fuel in the US. Furthermore, the thermodynamic and economic feasibility of this technology have been questioned. An article suggests that this technology does not create an alternative to fossil fuel but rather converting renewable energy into liquid fuel. The article also states that the energy return on energy invested using fossil diesel is 18 times higher than that for e-diesel. | 0 | Organic Chemistry |
For a long time, it was normal procedure for a decommissioned blast furnace to be demolished and either be replaced with a newer, improved one, or to have the entire site demolished to make room for follow-up use of the area. In recent decades, several countries have realized the value of blast furnaces as a part of their industrial history. Rather than being demolished, abandoned steel mills were turned into museums or integrated into multi-purpose parks. The largest number of preserved historic blast furnaces exists in Germany; other such sites exist in Spain, France, the Czech Republic, Great Britain. Japan, Luxembourg, Poland, Romania, Mexico, Russia and the United States. | 8 | Metallurgy |
The SBSP concept also has a number of problems:
* The large cost of launching a satellite into space. For 6.5 kg/kW, the cost to place a power satellite in geosynchronous orbit (GEO) cannot exceed $200/kg if the power cost is to be competitive.
* Microwave optic requires gigawatt scale to compensate for Airy disk beam spreading. Typically a 1 km disk in geosynchronous orbit transmitting at 2.45 GHz spreads out to 10 km at Earth distance.
* Inability to constrain power transmission inside tiny beam angles. For example, a beam of 0.002 degrees (7.2 arc seconds) is required to stay within a one kilometer receiving antenna target from geostationary altitude. The most advanced directional wireless power transfer systems as of 2019 spread their half power beam width across at least 0.9 arc degrees.
* Inaccessibility: Maintenance of an earth-based solar panel is relatively simple, but construction and maintenance on a solar panel in space would typically be done telerobotically. In addition to cost, astronauts working in GEO are exposed to unacceptably high radiation dangers and risk and cost about one thousand times more than the same task done telerobotically.
* The space environment is hostile; PV panels (if used) suffer about eight times the degradation they would on Earth (except at orbits that are protected by the magnetosphere).
* Space debris is a major hazard to large objects in space, particularly for large structures such as SBSP systems in transit through the debris below 2000 km. Collision risk is much reduced in GEO since all the satellites are moving in the same direction at very close to the same speed.
* The broadcast frequency of the microwave downlink (if used) would require isolating the SBSP systems away from other satellites. GEO space is already well used and would require coordinating with the ITU-R.
* The large size and corresponding cost of the receiving station on the ground. The cost has been estimated at a billion dollars for 5 GW by SBSP researcher Keith Henson.
* Energy losses during several phases of conversion from photons to electrons to photons back to electrons.
* Waste heat disposal in space power systems is difficult to begin with, but becomes intractable when the entire spacecraft is designed to absorb as much solar radiation as possible. Traditional spacecraft thermal control systems such as radiative vanes may interfere with solar panel occlusion or power transmitters.
* Decommissioning costs: The cost of deorbiting the satellites at the end of their service life to prevent them from exacerbating the orbital space debris problem due to impacts with asteroidal, cometary, and planetary debris is likely to be significant. While the future cost of imparting Delta-V is difficult to estimate, the amount of Delta-V that must be imparted to transfer a satellite from GEO to GTO is 1472 m/s. If, upon reentry, the disintegrating satellite would release hazardous chemicals into the Earth's atmosphere, then the additional expenses of disassembling the satellite and deorbiting the environmentally hazardous components within a space vehicle with downmass capabilities must be factored into the decommissioning costs. | 7 | Physical Chemistry |
A pair of diazonium cations can be coupled to give biaryls. This conversion is illustrated by the coupling of the diazonium salt derived from anthranilic acid to give diphenic acid (). In a related reaction, the same diazonium salt undergoes loss of and to give benzyne. | 0 | Organic Chemistry |
Charles law appears to imply that the volume of a gas will descend to zero at a certain temperature (−266.66 °C according to Gay-Lussacs figures) or −273.15 °C. Gay-Lussac was clear in his description that the law was not applicable at low temperatures:
At absolute zero temperature, the gas possesses zero energy and hence the molecules restrict motion.
Gay-Lussac had no experience of liquid air (first prepared in 1877), although he appears to have believed (as did Dalton) that the "permanent gases" such as air and hydrogen could be liquified. Gay-Lussac had also worked with the vapours of volatile liquids in demonstrating Charles' law, and was aware that the law does not apply just above the boiling point of the liquid:
The first mention of a temperature at which the volume of a gas might descend to zero was by William Thomson (later known as Lord Kelvin) in 1848:
However, the "absolute zero" on the Kelvin temperature scale was originally defined in terms of the second law of thermodynamics, which Thomson himself described in 1852. Thomson did not assume that this was equal to the "zero-volume point" of Charles law, merely said that Charles law provided the minimum temperature which could be attained. The two can be shown to be equivalent by Ludwig Boltzmann's statistical view of entropy (1870).
However, Charles also stated:
:The volume of a fixed mass of dry gas increases or decreases by times the volume at 0 °C for every 1 °C rise or fall in temperature. Thus:
:where is the volume of gas at temperature , is the volume at 0 °C. | 7 | Physical Chemistry |
Electron crystallography is a method to determine the arrangement of atoms in solids using a transmission electron microscope (TEM). It can involve the use of high-resolution transmission electron microscopy images, electron diffraction patterns including convergent-beam electron diffraction or combinations of these. It has been successful in determining some bulk structures, and also surface structures. Two related methods are low-energy electron diffraction which has solved the structure of many surfaces, and reflection high-energy electron diffraction which is used to monitor surfaces often during growth. | 3 | Analytical Chemistry |
A separatory funnel, also known as a separation funnel, separating funnel, or colloquially sep funnel, is a piece of laboratory glassware used in liquid-liquid extractions to separate (partition) the components of a mixture into two immiscible solvent phases of different densities. Typically, one of the phases will be aqueous, and the other a lipophilic organic solvent such as ether, MTBE, dichloromethane, chloroform, or ethyl acetate. All of these solvents form a clear delineation between the two liquids. The more dense liquid, typically the aqueous phase unless the organic phase is halogenated, sinks to the bottom of the funnel and can be drained out through a valve away from the less dense liquid, which remains in the separatory funnel. | 3 | Analytical Chemistry |
A variety of ion channel blockers (inorganic and organic molecules) can modulate ion channel activity and conductance.
Some commonly used blockers include:
* Tetrodotoxin (TTX), used by puffer fish and some types of newts for defense. It blocks sodium channels.
* Saxitoxin is produced by a dinoflagellate also known as "red tide". It blocks voltage-dependent sodium channels.
* Conotoxin is used by cone snails to hunt prey.
* Lidocaine and novocaine belong to a class of local anesthetics which block sodium ion channels.
* Dendrotoxin is produced by mamba snakes, and blocks potassium channels.
* Iberiotoxin is produced by the Hottentotta tamulus (Eastern Indian scorpion) and blocks potassium channels.
* Heteropodatoxin is produced by Heteropoda venatoria (brown huntsman spider or laya) and blocks potassium channels. | 1 | Biochemistry |
An analogous reaction with nitrogen as the heteroatom was described in 1984 for the synthesis of the antibiotic substance streptazolin. | 0 | Organic Chemistry |
AFPs work through an interaction with small ice crystals that is similar to an enzyme-ligand binding mechanism which inhibits recrystallization of ice. This explanation of the interruption of the ice crystal structure by the AFP has come to be known as the adsorption-inhibition hypothesis.
According to this hypothesis, AFPs disrupt the thermodynamically favourable growth of an ice crystal via kinetic inhibition of contact between solid ice and liquid water. In this manner, the nucleation sites of the ice crystal lattice are blocked by the AFP, inhibiting the rapid growth of the crystal that could be fatal for the organism. In physical chemistry terms, the AFPs adsorbed onto the exposed ice crystal force the growth of the ice crystal in a convex fashion as the temperature drops, which elevates the ice vapour pressure at the nucleation sites. Ice vapour pressure continues to increase until it reaches equilibrium with the surrounding solution (water), at which point the growth of the ice crystal stops.
The aforementioned effect of AFPs on ice crystal nucleation is lost at the thermal hysteresis point. At a certain low temperature, the maximum convexity of the ice nucleation site is reached. Any further cooling will actually result in a "spreading" of the nucleation site away from this convex region, causing rapid, uncontrollable nucleation of the ice crystal. The temperature at which this phenomenon occurs is the thermal hysteresis point.<br>
The adsorption-inhibition hypothesis is further supported by the observation that antifreeze activity increases with increasing AFP concentration – the more AFPs adsorb onto the forming ice crystal, the more crowded these proteins become, making ice crystal nucleation less favourable.
In the R. inquisitor beetle, AFPs are found in the haemolymph, a fluid that bathes all the cells of the beetle and fills a cavity called the haemocoel. The presence of AFPs in R. inquisitor allows the tissues and fluids within the beetle to withstand freezing up to -30 °C (the thermal hysteresis point for this AFP). This strategy provides an obvious survival benefit to these beetles, who are endemic to cold climates, such as Scandinavia, Siberia, and Alaska. | 1 | Biochemistry |
The joint gap is the distance between the electrofusion fitting and the pipe material. When no joint gap is present, the resulting joint strength is high but not maximum. As joint gap increases, the joint strength increases to a point, then begins to decline fairly sharply. At larger gaps sufficient pressure cannot build during the fusion time, and the joint strength is low. The effect of joint gap on strength is why the scraping of the pipes before welding is a critical step. Uneven or inconsistent scraping can result in areas where the joint gap is large, leading to low joint strength. | 7 | Physical Chemistry |
The Boltzmann constant is named after its 19th century Austrian discoverer, Ludwig Boltzmann. Although Boltzmann first linked entropy and probability in 1877, the relation was never expressed with a specific constant until Max Planck first introduced , and gave a more precise value for it (, about 2.5% lower than todays figure), in his derivation of the law of black-body radiation in 1900–1901. Before 1900, equations involving Boltzmann factors were not written using the energies per molecule and the Boltzmann constant, but rather using a form of the gas constant , and macroscopic energies for macroscopic quantities of the substance. The iconic terse form of the equation on Boltzmanns tombstone is in fact due to Planck, not Boltzmann. Planck actually introduced it in the same work as his eponymous .
In 1920, Planck wrote in his Nobel Prize lecture:
This "peculiar state of affairs" is illustrated by reference to one of the great scientific debates of the time. There was considerable disagreement in the second half of the nineteenth century as to whether atoms and molecules were real or whether they were simply a heuristic tool for solving problems. There was no agreement whether chemical molecules, as measured by atomic weights, were the same as physical molecules, as measured by kinetic theory. Planck's 1920 lecture continued:
In versions of SI prior to the 2019 redefinition of the SI base units, the Boltzmann constant was a measured quantity rather than a fixed value. Its exact definition also varied over the years due to redefinitions of the kelvin (see ) and other SI base units (see ).
In 2017, the most accurate measures of the Boltzmann constant were obtained by acoustic gas thermometry, which determines the speed of sound of a monatomic gas in a triaxial ellipsoid chamber using microwave and acoustic resonances. This decade-long effort was undertaken with different techniques by several laboratories; it is one of the cornerstones of the 2019 redefinition of SI base units. Based on these measurements, the CODATA recommended to be the final fixed value of the Boltzmann constant to be used for the International System of Units. | 7 | Physical Chemistry |
Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the entire Solar System, and has made important contributions to the understanding of a number of processes including mantle convection, the formation of planets and the origins of granite and basalt. It is an integrated field of chemistry and geology. | 9 | Geochemistry |
Photons have a momentum given by (where is the reduced Planck constant and the photon wavenumber), which is conserved in all atom-photon interactions. Thus, when an atom absorbs a photon, it is given a momentum kick in the direction of the photon before absorption. By detuning a laser beam to a frequency less than the resonant frequency (also known as red detuning), laser light is only absorbed if the light is frequency up-shifted by the Doppler effect, which occurs whenever the atom is moving towards the laser source. This applies a friction force to the atom whenever it moves towards a laser source.
For cooling to occur along all directions, the atom must see this friction force along all three Cartesian axes; this is most easily achieved by illuminating the atom with three orthogonal laser beams, which are then reflected back along the same direction. | 7 | Physical Chemistry |
Although ‘sulphur’, ‘sulphate’ and ‘sulphide’ are standard Australian-English spellings, Australian researchers are encouraged to adopt the US-English spelling of these terms in both domestic and international publications so that, inter alia, spelling is consistent with IUPAC definitions. As such, although ‘acid sulphate soil’ is commonly encountered in Australian literature, ‘acid sulfate soil’ is now the preferred spelling. | 9 | Geochemistry |
Known generalisations include monomers with an arbitrary number of functional group types, crosslinking polymerisation, and complex reaction networks. | 7 | Physical Chemistry |
The Society awards the AAG Gold Medal to recognize a lifetime's achievement in or outstanding contribution to applied geochemistry. It also offers an annual student paper prize to reward student contributors of outstanding papers on geochemistry. | 9 | Geochemistry |
By analyzing the isotopic compositions of stable and radiogenic nuclides in meteorites, Dauphas investigates the timing and processes that lead to the formation of Solar System bodies and the establishment of habitable conditions on Earth and Mars. He used iron isotopes to study how the iron biogeochemical cycle of the Earth changed through time. He established that Mars was formed rapidly, within the first 2~4 million years of the birth of the Solar System, which explains the much smaller size of Mars compared to Earth and Venus. He first identified the mineralogical carrier of the Cr isotopic anomalies in meteorites as Cr-rich nano-sized spinels from supernovae. He constrained the nature of Earths accreting materials through time, using a novel approach that relies on the different affinities of elements with Earths core, and showed that the materials formed Earth are from an isotopically homogeneous reservoir.
Dauphas was part of the preliminary examination team for JAXA's Hayabusa2 mission, which returned a fragment of Ryugu carbonaceous asteroid to Earth for scientific research. He was selected as a member of the Mars Sample Return Campaign Science Group in 2022. | 9 | Geochemistry |
The Rutherford model of the nuclear atom (1911) showed that the exterior of an atom is occupied by electrons, which suggests that electrons are responsible for the interaction of atoms and the formation of chemical bonds. In 1916, Gilbert N. Lewis explained valence and chemical bonding in terms of a tendency of (main-group) atoms to achieve a stable octet of 8 valence-shell electrons. According to Lewis, covalent bonding leads to octets by the sharing of electrons, and ionic bonding leads to octets by the transfer of electrons from one atom to the other. The term covalence is attributed to Irving Langmuir, who stated in 1919 that "the number of pairs of electrons which any given atom shares with the adjacent atoms is called the covalence of that atom". The prefix co- means "together", so that a co-valent bond means that the atoms share a valence. Subsequent to that, it is now more common to speak of covalent bonds rather than valence, which has fallen out of use in higher-level work from the advances in the theory of chemical bonding, but it is still widely used in elementary studies, where it provides a heuristic introduction to the subject.
In the 1930s, Linus Pauling proposed that there are also polar covalent bonds, which are intermediate between covalent and ionic, and that the degree of ionic character depends on the difference of electronegativity of the two bonded atoms.
Pauling also considered hypervalent molecules, in which main-group elements have apparent valences greater than the maximal of 4 allowed by the octet rule. For example, in the sulfur hexafluoride molecule (), Pauling considered that the sulfur forms 6 true two-electron bonds using spd hybrid atomic orbitals, which combine one s, three p and two d orbitals. However more recently, quantum-mechanical calculations on this and similar molecules have shown that the role of d orbitals in the bonding is minimal, and that the molecule should be described as having 6 polar covalent (partly ionic) bonds made from only four orbitals on sulfur (one s and three p) in accordance with the octet rule, together with six orbitals on the fluorines. Similar calculations on transition-metal molecules show that the role of p orbitals is minor, so that one s and five d orbitals on the metal are sufficient to describe the bonding. | 3 | Analytical Chemistry |
Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. It is the main storage form of glucose in the human body.
Glycogen functions as one of three regularly used forms of energy reserves, creatine phosphate being for very short-term, glycogen being for short-term and the triglyceride stores in adipose tissue (i.e., body fat) being for long-term storage. Protein, broken down into amino acids, is seldom used as a main energy source except during starvation and glycolytic crisis (see bioenergetic systems).
In humans, glycogen is made and stored primarily in the cells of the liver and skeletal muscle. In the liver, glycogen can make up 5–6% of the organ's fresh weight: the liver of an adult, weighing 1.5 kg, can store roughly 100–120 grams of glycogen. In skeletal muscle, glycogen is found in a low concentration (1–2% of the muscle mass): the skeletal muscle of an adult weighing 70 kg stores roughly 400 grams of glycogen. Small amounts of glycogen are also found in other tissues and cells, including the kidneys, red blood cells, white blood cells, and glial cells in the brain. The uterus also stores glycogen during pregnancy to nourish the embryo.
The amount of glycogen stored in the body mostly depends on oxidative type 1 fibres, physical training, basal metabolic rate, and eating habits. Different levels of resting muscle glycogen are reached by changing the number of glycogen particles, rather than increasing the size of existing particles though most glycogen particles at rest are smaller than their theoretical maximum.
Approximately 4 grams of glucose are present in the blood of humans at all times; in fasting individuals, blood glucose is maintained constant at this level at the expense of glycogen stores, primarily from the liver (glycogen in skeletal muscle is mainly used as an immediate source of energy for that muscle rather than being used to maintain physiological blood glucose levels). Glycogen stores in skeletal muscle serve as a form of energy storage for the muscle itself; however, the breakdown of muscle glycogen impedes muscle glucose uptake from the blood, thereby increasing the amount of blood glucose available for use in other tissues. Liver glycogen stores serve as a store of glucose for use throughout the body, particularly the central nervous system. The human brain consumes approximately 60% of blood glucose in fasted, sedentary individuals.
Glycogen is an analogue of starch, a glucose polymer that functions as energy storage in plants. It has a structure similar to amylopectin (a component of starch), but is more extensively branched and compact than starch. Both are white powders in their dry state. Glycogen is found in the form of granules in the cytosol/cytoplasm in many cell types, and plays an important role in the glucose cycle. Glycogen forms an energy reserve that can be quickly mobilized to meet a sudden need for glucose, but one that is less compact than the energy reserves of triglycerides (lipids). As such it is also found as storage reserve in many parasitic protozoa. | 1 | Biochemistry |
Scientists Miriam Paredes and Maria Quiles led an investigation on the plant species Rosa Meillandina, and its metabolic response to water deficit. They noted how limited water irrigation can cause a reduction in PS II levels, which then results in the inhibition of photosynthesis. Paredes and Quiles also noticed the increase in chlororespiration activity as a protective mechanism for the lack of photosynthesis.
In the experiment, the plants in water deficit were analysed with fluorescence imaging technique. This form of analysis detected increased levels of PTOX, and NAD(P)H activity within the plant. An increase in these two molecules led to the initiation of chlororespiration.
N-propyl gallate was also added to these water deficit plants. The effect resulted in increased chlorophyll fluorescence levels. Quiles recorded a similar outcome in the same species of plants that went under intense light. This increase in chlorophyll fluorescence is attributed to the influx of NAD(P)H in the thylakoid membrane. Which then led to an increase in the by-product, hydrogen peroxide, inside the thylakoid membrane. | 1 | Biochemistry |
The complete breakdown of glucose releasing its energy is called cellular respiration. The last steps of this process occur in mitochondria. The reduced molecules NADH and FADH are generated by the Krebs cycle, glycolysis, and pyruvate processing. These molecules pass electrons to an electron transport chain, which releases the energy of oxygen to create a proton gradient across the inner mitochondrial membrane. ATP synthase then uses the energy stored in this gradient to make ATP. This process is called oxidative phosphorylation because it uses energy released by the oxidation of NADH and FADH to phosphorylate ADP into ATP. | 1 | Biochemistry |
Fluorescence, chemiluminescence and phosphorescence are 3 different types of luminescence properties, i.e. emission of light from a substance.
Fluorescence is a property where light is absorbed and remitted within a few nanoseconds (approx. 10ns) at a lower energy (=higher wavelength), while bioluminescence is biological chemiluminescence, a property where light is generated by a chemical reaction of an enzyme on a substrate.
Phosphorescence is a property of materials to absorb light and emit the energy several milliseconds or more later (due to forbidden transitions to the ground state of a triplet state, while fluorescence occurs in excited singlet states). Until recently, this was not applicable to life science research due to the size of the inorganic particles. However the boundary between the fluorescence and phosphorescence is not clean cut as transition metal-ligand complexes, which combine a metal and several organic moieties, have long lifetimes, up to several microseconds (as they display mixed singlet-triplet states). | 1 | Biochemistry |
In HR-EBSD analysis, the lattice distortion field is calculated relative to a reference pattern or point (EBSP) per grain in the map, and is dependent on the lattice distortion at the point. The lattice distortion field in each grain is measured with respect to this point; therefore, the absolute lattice distortion at the reference point (relative to the unstrained crystal) is excluded from the HR-EBSD elastic strain and rotation maps. This ‘reference pattern problem’ is similar to the ‘d problem’ in X-ray diffraction, and affects the nominal magnitude of HR-EBSD stress fields. However, selecting the reference pattern (EBSP) plays a key role, as severely deformed EBSP adds phantom lattice distortions to the map values, thus, decreasing the measurement precision.
The local lattice distortion at the EBSP influences the resultant HR-EBSD map, e.g., a reference pattern deformed in tension will directly reduce the HR-EBSD map tensile strain magnitude while indirectly influencing the other component magnitude and the strains spatial distribution. Furthermore, the choice of EBSP slightly affects the GND density distribution and magnitude, and choosing a reference pattern with a higher GND density reduces the cross-correlation quality, changes the spatial distribution and induces more errors than choosing a reference pattern with high lattice distortion. Additionally, there is no apparent connection between EBSP’s IQ and EBSPs local lattice distortion.
The use of simulated reference patterns for absolute strain measurement is still an active area of research and scrutiny as difficulties arise from the variation of inelastic electron scattering with depth which limits the accuracy of dynamical diffraction simulation models, and imprecise determination of the pattern centre which leads to phantom strain components which cancel out when using experimentally acquired reference patterns. Other methods assumed that absolute strain at EBSP can be determined using crystal plasticity finite-element (CPFE) simulations, which then can be then combined with the HR-EBSD data (e.g., using linear ‘top-up’ method or displacement integration) to calculate the absolute lattice distortions.
In addition, GND density estimation is nominally insensitive to (or negligibly dependent upon) EBSP choice, as only neighbour point-to-point differences in the lattice rotation maps are used for GND density calculation. However, this assumes that the absolute lattice distortion of EBSP only changes the relative lattice rotation map components by a constant value which vanishes during derivative operations, i.e., lattice distortion distribution is insensitive to EBSP choice. | 7 | Physical Chemistry |
An intergenic region is a stretch of DNA sequences located between genes. Intergenic regions may contain functional elements and junk DNA. | 1 | Biochemistry |
Tetrabutylammonium is a quaternary ammonium cation with the formula , also denoted (where Bu = butyl group). It is used in the research laboratory to prepare lipophilic salts of inorganic anions. Relative to tetraethylammonium derivatives, tetrabutylammonium salts are more lipophilic but crystallize less readily. | 0 | Organic Chemistry |
Zinc has five stable isotopes, tabulated along with their natural abundances below:
The isotopic composition of Zn is reported in delta notation (in ‰):
where Zn is a Zn isotope other than Zn (commonly either Zn or Zn). Standard reference materials used for Zn isotope measurements are JMC 3-0749C, NIST-SRM 683 or NIST-SRM 682. | 9 | Geochemistry |
The anions of orthophosphoric acid are orthophosphate (commonly called simply "phosphate") , monohydrogen phosphate , and dihydrogen phosphate . | 0 | Organic Chemistry |
Reactions of conjugated double-bond systems can be synthesized into cycloalkenes through electrocyclic reactions. Addition of heat or photolysis causes a reversible reaction that causes one pi bond to become a sigma bond, which closes the ring and creates a cycloalkene. | 0 | Organic Chemistry |
The oldest anodizing process uses chromic acid. It is widely known as the Bengough-Stuart process but, due to the safety regulations regarding air quality control, is not preferred by vendors when the additive material associated with type II doesn't break tolerances. In North America, it is known as Type I because it is so designated by the MIL-A-8625 standard, but it is also covered by AMS 2470 and MIL-A-8625 Type IB. In the UK it is normally specified as Def Stan 03/24 and used in areas that are prone to come into contact with propellants etc. There are also Boeing and Airbus standards. Chromic acid produces thinner, 0.5 μm to 18 μm (0.00002" to 0.0007") more opaque films that are softer, ductile, and to a degree self-healing. They are harder to dye and may be applied as a pretreatment before painting. The method of film formation is different from using sulfuric acid in that the voltage is ramped up through the process cycle. | 8 | Metallurgy |
Precious metals such as gold and platinum, but also many other rare and noble metals, largely originated within neutron star collisions - collisions between exceedingly heavy massive and dense remnants of supernovas. In the final moments of the collision, the physical conditions are so extreme that these heavy rare elements can be formed, and are sprayed into space. Interstellar dust and gas clouds contain some of these elements, as did the dust cloud from which our solar system formed.
Those heavy metals fell to the centre of the molten core of earth, and are no longer accessible. However about 200 million years after Earth formed, a late heavy bombardment of meteors impacted earth. As Earth had already begun to cool and solidify, the material (including heavy metals) in that bombardment became part of earth's crust, rather than falling deep into the core. They became processed and exposed by geological processes over billions of years. It is believed that this represents the origin of many elements, and all heavy metals, that are found on earth today. | 9 | Geochemistry |
Europe has very few sources of tin. Therefore, throughout ancient times it was imported long distances from the known tin mining districts of antiquity. These were the Ore Mountains (Erzgebirge) along the modern border between Germany and the Czech Republic, the Iberian Peninsula, Brittany in modern France, and Cornwall and Devon in southwestern Britain.) There are several smaller sources of tin in the Balkans and another minor source of tin is known to exist at Monte Valerio in Tuscany, Italy. The Tuscan source was exploited by Etruscan miners around 800 BC, but it was not a significant source of tin for the rest of the Mediterranean. Even at that time, the Etruscans themselves had to import additional tin from the northwest of the Iberian Peninsula, and later from Cornwall.
It has been claimed that tin was first mined in Europe around 2500 BC in the Erzgebirge, and knowledge of tin bronze and tin extraction techniques spread from there to Brittany and Cornwall around 2000 BC and from northwestern Europe to northwestern Spain and Portugal around the same time. However, the only Bronze Age object from Central Europe whose tin has been scientifically provenanced is the Nebra sky disk, and its tin (and gold, though not its copper), is shown by tin isotopes to have come from Cornwall. In addition, a rare find of a pure tin ingot in Scandinavia was provenanced to Cornwall. Available evidence, though very limited, thus points to Cornwall as the sole early source of tin in Central and Northern Europe.
Cornwall and Devon were important sources of tin for Europe and the Mediterranean throughout ancient times and may have been the earliest sources of tin in Western Europe, with evidence for trade to the Eastern Mediterranean by the Late Bronze Age. Within recorded history, Cornwall and Devon only dominated the European market for tin from late Roman times, starting around the 3rd century AD, as many Spanish tin mines were exhausted. Cornwall maintained its importance as a source of tin throughout medieval times and into the modern period.
Brittany – opposite Cornwall on the Celtic Sea – has significant sources of tin which show evidence of being extensively exploited after the Roman conquest of Gaul during the 50s BC and onwards. Brittany remained a significant source of tin throughout the medieval period.
A group of 52 bronze artifacts from the late Bronze Age Balkans has been shown to have tin of multiple origins, based on the correlation of tin isotope differences with the different find locations of the artifacts. While the locations of these separate tin sources are uncertain, the larger Serbian group of artifacts is inferred to be derived from tin sources in western Serbia (e.g. Mount Cer), while the smaller group, largely from western Romania, is inferred to have western Romanian origins.
Iberian tin was widely traded across the Mediterranean during the Bronze Age, and extensively exploited during Roman times. But Iberian tin deposits were largely forgotten throughout the medieval period, were not rediscovered until the 18th century, and only re-gained importance during the mid-19th century. | 8 | Metallurgy |
Dai has received several honors and awards, among them:
* 1985: Camille and Henry Dreyfus Foundation New Faculty Award
* 1988: Sloan Fellowship
* 1989: The Camille and Henry Dreyfus Foundation Teacher-Scholar Award
* 1990: Coblentz Award in Spectroscopy
* 1992: Fellowship of the American Physical Society
* 1994: Alexander von Humboldt Award for Senior US Scientists
* 1995: Philadelphia Section Award, American Chemical Society
* 2000: Guggenheim Fellowship
* 2006: Ellis Lippincott Award for Spectroscopy of the Optical Society of America
* 2009: Distinguished Achievement Award, the Institute of Chinese Engineers in the U.S.
* 2010: Fellowship of the American Chemical Society
* 2012: Langmuir Lecturer Award, Division of Colloid and Surface Chemistry, American Chemical Society
* 2013: Michael P. Malone International Leadership Award, Association of Public and Land Grant Universities
* 2017: Knight Order of the Italian Star, Government of Italy
* 2017: Distinguished Alumni Award, National Taiwan University
* 2019: Hai-Lung Dai Festschrift, Journal of Physical Chemistry, American Chemical Society | 7 | Physical Chemistry |
Graphite intercalation compounds have fascinated materials scientists for many years owing to their diverse electronic and electrical properties. | 6 | Supramolecular Chemistry |
Lithotrophic bacteria cannot use, of course, their inorganic energy source as a carbon source for the synthesis of their cells. They choose one of three options:
* Lithoheterotrophs do not have the ability to fix carbon dioxide and must consume additional organic compounds in order to break them apart and use their carbon. Only a few bacteria are fully lithoheterotrophic.
* Lithoautotrophs are able to use carbon dioxide from the air as a carbon source, the same way plants do.
* Mixotrophs will take up and use organic material to complement their carbon dioxide fixation source (mix between autotrophy and heterotrophy). Many lithotrophs are recognized as mixotrophic in regard to their C-metabolism. | 1 | Biochemistry |
Molecular data show that PSI likely evolved from the photosystems of green sulfur bacteria. The photosystems of green sulfur bacteria and those of cyanobacteria, algae, and higher plants are not the same, but there are many analogous functions and similar structures. Three main features are similar between the different photosystems. First, redox potential is negative enough to reduce ferredoxin. Next, the electron-accepting reaction centers include iron–sulfur proteins. Last, redox centres in complexes of both photosystems are constructed upon a protein subunit dimer. The photosystem of green sulfur bacteria even contains all of the same cofactors of the electron transport chain in PSI. The number and degree of similarities between the two photosystems strongly indicates that PSI and the analogous photosystem of green sulfur bacteria evolved from a common ancestral photosystem. | 5 | Photochemistry |
Similar to other -ome based technologies, analysis of the transcriptome allows for an unbiased approach when validating hypotheses experimentally. This approach also allows for the discovery of novel mediators in signaling pathways. As with other -omics based technologies, the transcriptome can be analyzed within the scope of a multiomics approach. It is complementary to metabolomics but contrary to proteomics, a direct association between a transcript and metabolite cannot be established.
There are several -ome fields that can be seen as subcategories of the transcriptome. The exome differs from the transcriptome in that it includes only those RNA molecules found in a specified cell population, and usually includes the amount or concentration of each RNA molecule in addition to the molecular identities. Additionally, the transcritpome also differs from the translatome, which is the set of RNAs undergoing translation.
The term meiome is used in functional genomics to describe the meiotic transcriptome or the set of RNA transcripts produced during the process of meiosis. Meiosis is a key feature of sexually reproducing eukaryotes, and involves the pairing of homologous chromosome, synapse and recombination. Since meiosis in most organisms occurs in a short time period, meiotic transcript profiling is difficult due to the challenge of isolation (or enrichment) of meiotic cells (meiocytes). As with transcriptome analyses, the meiome can be studied at a whole-genome level using large-scale transcriptomic techniques. The meiome has been well-characterized in mammal and yeast systems and somewhat less extensively characterized in plants.
The thanatotranscriptome consists of all RNA transcripts that continue to be expressed or that start getting re-expressed in internal organs of a dead body 24–48 hours following death. Some genes include those that are inhibited after fetal development. If the thanatotranscriptome is related to the process of programmed cell death (apoptosis), it can be referred to as the apoptotic thanatotranscriptome. Analyses of the thanatotranscriptome are used in forensic medicine.
eQTL mapping can be used to complement genomics with transcriptomics; genetic variants at DNA level and gene expression measures at RNA level. | 1 | Biochemistry |
It is part of PHEs Radiation Protection Adviser Services. PHE was the UKs first Radiation Protection Adviser Body, under the Ionising Radiations Regulations (IRR) 17 (which came from the International Commission on Radiological Protection). | 2 | Environmental Chemistry |
An oligoester is an ester oligomer chain containing a small number of repeating ester units (monomers). Oligoesters are short analogs of polymeric polyesters.
An example is oligo-(R)-3-hydroxybutyrate. | 0 | Organic Chemistry |
The endothelium maintains vascular homeostasis through the release of active vasodilators. Although nitric oxide (NO) is recognized as the primary factor at level of arteries, increased evidence for the role of another endothelium-derived vasodilator known as endothelium-derived hyperpolarizing factor (EDHF) has accumulated in the last years. Experiments show that when NO and Prostacyclin (Vasodilators) are inhibited there is still another factor causing the vessels to dilate
Despite the ongoing debate of its intriguingly variable nature and mechanisms of action, the contribution of EDHF to the endothelium-dependent relaxation is currently appreciated as an important feature of “healthy” endothelium. Since EDHF's contribution is greatest at level of small arteries, the changes in the EDHF action are of critical importance for the regulation of organ blood flow, peripheral vascular resistance, and blood pressure, and in particular when production of NO is compromised. Moreover, depending on the type of cardiovascular disorders altered, EDHF responses may contribute to, or compensate for, endothelial abnormalities associated with pathogenesis of certain diseases.
It is widely accepted EDHF plays an important role in vasotone, especially in micro vessels. Its effect varies, depending on the size of the vessel. | 1 | Biochemistry |
Wender Taxol total synthesis in organic chemistry describes a Taxol total synthesis (one of six to date) by the group of Paul Wender at Stanford University published in 1997. This synthesis has much in common with the Holton Taxol total synthesis in that it is a linear synthesis starting from a naturally occurring compound with ring construction in the order A,B,C,D. The Wender effort is shorter by approximately 10 steps.
Raw materials for the preparation of Taxol by this route include verbenone, prenyl bromine, allyl bromide, propiolic acid, Gilman reagent, and Eschenmoser's salt. | 0 | Organic Chemistry |
Common side effects include headache, dizziness, feeling tired, cough, nausea, and rash. Serious side effects may include low blood pressure, liver problems, hyperkalemia, and angioedema. Use is not recommended during the entire duration of pregnancy as it may harm the baby. | 4 | Stereochemistry |
The branching index measures the effect of long-chain branches on the size of a macromolecule in solution. It is defined as g = >/>, where s is the mean square radius of gyration of the branched macromolecule in a given solvent, and s is the mean square radius of gyration of an otherwise identical linear macromolecule in the same solvent at the same temperature. A value greater than 1 indicates an increased radius of gyration due to branching. | 7 | Physical Chemistry |
The glycosylation reaction involves the coupling of a glycosyl donor and a glycosyl acceptor via initiation using an activator under suitable reaction conditions.
* A glycosyl donor is a sugar with a suitable leaving group at the anomeric position. This group, under the reaction conditions, is activated and via the formation of an oxocarbenium is eliminated leaving an electrophilic anomeric carbon.
* A glycosyl acceptor is a sugar with an unprotected nucleophilic hydroxyl group which may attack the carbon of the oxocarbenium ion formed during the reaction and allow for the formation of the glycosidic bond.
An activator is commonly a Lewis acid which enables the leaving group at the anomeric position to leave and results in the formation of the oxocarbenium ion. | 0 | Organic Chemistry |
Mitochondrial ferritin has many roles pertaining to molecular function. It participates in ferroxidase activity, binding, iron ion binding, oxidoreductase activity, ferric iron binding, metal ion binding as well as transition metal binding. Within the realm of biological processes it participates in oxidation-reduction, iron ion transport across membranes and cellular iron ion homeostasis. | 1 | Biochemistry |
The conversion of aldehydes to nitriles via aldoximes is a popular laboratory route. Aldehydes react readily with hydroxylamine salts, sometimes at temperatures as low as ambient, to give aldoximes. These can be dehydrated to nitriles by simple heating, although a wide range of reagents may assist with this, including triethylamine/sulfur dioxide, zeolites, or sulfuryl chloride. The related hydroxylamine-O-sulfonic acid reacts similarly.
In specialised cases the Van Leusen reaction can be used. Biocatalysts such as aliphatic aldoxime dehydratase are also effective. | 0 | Organic Chemistry |
Another application for the magnetic sequencing is using the hairpin end-to-end distance to detect the successive ligation of oligonucleotide. First step of sequencing by ligation is using a primer to extend a DNA fragment. Extension is first attempted with a fragment starting with adenine, which can only be ligated if the next nucleotide on the opposite strand is a thymine. Then fragments starting with cytosine, guanine and thymine are attempted in turn, and the cycle is repeated. The magnetic field is released after each ligation, and then the length of the extended primer is measured. Upon ligation the primer is extended by seven bases, which is resulting in a detectable increase in the hairpin’s end to end distance. RNase cleavage at position 2 is followed by the ligation for the preparation of the next ligation cycle, so that the next ligation is positioned just ahead of the previous one. | 1 | Biochemistry |
DNA–DNA hybridization (DDH) is used as a primary method to distinguish bacterial species as it is difficult to visually classify them accurately. This technique is not widely used on larger organisms where differences in species are easier to identify. In the late 1900s, strains were considered to belong to the same species if they had a DNA–DNA similarity value greater than 70% and their melting temperatures were within 5 °C of each other. In 2014, a threshold of 79% similarity has been suggested to separate bacterial subspecies.
DDH is a common technique for bacteria, but it is labor intensive, error-prone, and technically challenging. In 2004, a new DDH technique was described. This technique utilized microplates and colorimetrically labelled DNA to decrease the time needed and increase the amount of samples that can be processed. This new DDH technique became the standard for bacterial taxonomy. | 1 | Biochemistry |
It is well established that the macromolecular structure of nonviral gene delivery vectors alters their transfection efficacy and cytotoxicity. The cyclized structure has been proven to reduce cytotoxicity and increase circulation time for drug and gene delivery applications. The unique structure of cyclizing chains provides the single chain cyclized polymers a different method of interaction between the polymer and plasmid DNA, and results in a general trend of higher transfection capabilities than branched polymers. Moreover, due to the nature of the single chain structure, this cyclized polymer can “untie” to a linear chain under reducing conditions. Transfection profiles on astrocytes comparing 25 kDa-PEI, SuperFect® and Lipofectamine®2000 and cyclized polymer showed greater efficiency and cell viability whilst maintaining neural cell viability above 80% four days post transfections. | 7 | Physical Chemistry |
Rasagiline is molecularly a propargylamine derivative. The form brought to market by Teva and its partners is the mesylate salt, and was designated chemically as: 1H-Inden-1-amine-2,3-dihydro-N-2-propynyl-(1R)-methanesulfonate. | 4 | Stereochemistry |
Source: [https://www.rsc.org/Membership/Networking/InterestGroups/Electrochemistry/faradaymedal.asp RIC]
* 1977 Veniamin Grigorievich Levich (1917–1987)
* 1981 John O’M. Bockris
* 1983 Jean-Michel Savéant
* 1985 Michel Armand
* 1987 Heinz Gerischer (1919–1994)
* 1991 David A. J. Rand, CSIRO Division of Mineral Chemistry, Port Melbourne
* 1994 Stanley Bruckenstein, University at Buffalo
* 1995 Michael J. Weaver (1947–2002), Purdue University
* 1996 Adam Heller, University of Texas
* 1998 Wolf Vielstich, Universität Bonn
* 1999 Philippe Allongue, CNRS
* 2000 Alan Maxwell Bond (b. 1946), Monash University
* 2001 Michael Grätzel, École polytechnique fédérale de Lausanne
* 2002 Henry S. White, University of Utah
* 2003 (1942–2011), Universität Ulm
* 2004 Daniel A. Scherson, Case Western Reserve University
* 2005 Robert Mark Wightman, University of North Carolina
* 2006 Hubert H. Girault, École polytechnique fédérale de Lausanne
* 2007 Christian Amatore, CNRS
* 2008 Nathan Lewis, California Institute of Technology
* 2009 Reginald M. Penner, University of California, Irvine
* 2011 Héctor D. Abruña, Cornell University
* 2012 Zhong-Qun Tian, Xiamen University
* 2013 Nenad Markovic
* 2014 Masatoshi Osawa, Hokkaido University
* 2015 Richard M. Crooks, University of Texas at Austin
* 2016 Justin Gooding, University of New South Wales, Australia
* 2017 Marc Koper, Leiden University
* 2018 Yang Shao-Horn, MIT
* 2019 Martin Winter, Westfälische Wilhelms-Universität Münster
* 2020 Shirley Meng, University of California, San Diego
* 2021 Peter Strasser, Technical University of Berlin
* 2022 Beatriz Roldán Cuenya, Fritz-Haber-Institute, Berlin | 7 | Physical Chemistry |
High power mercury vapor black light lamps are made in power ratings of 100 to 1,000 watts. These do not use phosphors, but rely on the intensified and slightly broadened 350–375 nm spectral line of mercury from high pressure discharge at between , depending upon the specific type. These lamps use envelopes of Woods glass or similar optical filter coatings to block out all the visible light and also the short wavelength (UVC) lines of mercury at 184.4 and 253.7 nm, which are harmful to the eyes and skin. A few other spectral lines, falling within the pass band of the Woods glass between 300 and 400 nm, contribute to the output.
These lamps are used mainly for theatrical purposes and concert displays. They are more efficient UVA producers per unit of power consumption than fluorescent tubes. | 5 | Photochemistry |
In virology, the term "sense" has a slightly different meaning. The genome of an RNA virus can be said to be either positive-sense, also known as a "plus-strand", or negative-sense, also known as a "minus-strand". In most cases, the terms "sense" and "strand" are used interchangeably, making terms such as "positive-strand" equivalent to "positive-sense", and "plus-strand" equivalent to "plus-sense". Whether a viral genome is positive-sense or negative-sense can be used as a basis for classifying viruses. | 1 | Biochemistry |
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