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Miura et al. reported the cross coupling of vinyl bromides with an alkenyl carboxylic acid using a palladium catalyst. Some of the conjugated dienes prepared were reported to exhibit solid state fluorescence. | 0 | Organic Chemistry |
Although the sulfide content in sample can be determined straight forwardly as described for sulfites, the results are often poor and inaccurate. A better, alternative method with higher accuracy is available, which involves the addition of excess but known volume of standard sodium arsenite solution to the sample, during which arsenic trisulfide is precipitated:
The excess arsenic trioxide is then determined by titrating against standard iodine solution using starch indicator. Note that for the best results, the sulfide solution must be dilute with the sulfide concentration not greater than 0.01 M. | 3 | Analytical Chemistry |
In DNA, regulation of gene expression normally happens at the level of RNA biosynthesis (transcription). It is accomplished through the sequence-specific binding of proteins (transcription factors) that activate or inhibit transcription. Transcription factors may act as activators, repressors, or both. Repressors often act by preventing RNA polymerase from forming a productive complex with the transcriptional initiation region (promoter), while activators facilitate formation of a productive complex. Furthermore, DNA motifs have been shown to be predictive of epigenomic modifications, suggesting that transcription factors play a role in regulating the epigenome.
In RNA, regulation may occur at the level of protein biosynthesis (translation), RNA cleavage, RNA splicing, or transcriptional termination. Regulatory sequences are frequently associated with messenger RNA (mRNA) molecules, where they are used to control mRNA biogenesis or translation. A variety of biological molecules may bind to the RNA to accomplish this regulation, including proteins (e.g., translational repressors and splicing factors), other RNA molecules (e.g., miRNA) and small molecules, in the case of riboswitches. | 1 | Biochemistry |
This scan uses reverse-geometry (BE-type) instruments. These instruments use a front-end magnetic sector that allows for exclusive mass selection of the precursor ion. The fragmentation region is in-between the two analyzers. The electric sector scan gives the product-ion spectrum. MIKES can also be used for direct measurement of kinetic-energy release values. | 7 | Physical Chemistry |
Destabilization can be accomplished by different methods:
*Removal of the electrostatic barrier that prevents aggregation of the particles. This can be accomplished by the addition of salt to a suspension to reduce the Debye screening length (the width of the electrical double layer) of the particles. It is also accomplished by changing the pH of a suspension to effectively neutralise the surface charge of the particles in suspension. This removes the repulsive forces that keep colloidal particles separate and allows for aggregation due to van der Waals forces. Minor changes in pH can manifest in significant alteration to the zeta potential. When the magnitude of the zeta potential lies below a certain threshold, typically around ± 5mV, rapid coagulation or aggregation tends to occur.
*Addition of a charged polymer flocculant. Polymer flocculants can bridge individual colloidal particles by attractive electrostatic interactions. For example, negatively charged colloidal silica or clay particles can be flocculated by the addition of a positively charged polymer.
*Addition of non-adsorbed polymers called depletants that cause aggregation due to entropic effects.
Unstable colloidal suspensions of low-volume fraction form clustered liquid suspensions, wherein individual clusters of particles sediment if they are more dense than the suspension medium, or cream if they are less dense. However, colloidal suspensions of higher-volume fraction form colloidal gels with viscoelastic properties. Viscoelastic colloidal gels, such as bentonite and toothpaste, flow like liquids under shear, but maintain their shape when shear is removed. It is for this reason that toothpaste can be squeezed from a toothpaste tube, but stays on the toothbrush after it is applied. | 7 | Physical Chemistry |
One of the most widely used tools for probing glycan-protein interactions is glycan arrays. A glycan array usually is an NHS- or epoxy-activated glass slides on which various glycans were printed using robotic printing. These commercially available arrays may contain up to 600 different glycans, specificity of which has been extensively studied.
Glycan-protein interactions may be detected by testing proteins of interest (or libraries of those) that bear fluorescent tags. The structure of the glycan-binding protein may be deciphered by several analytical methods based on mass-spectrometry, including MALDI-MS, LC-MS, tandem MS-MS, and/or 2D NMR. | 1 | Biochemistry |
Like other enzymes, the activity of FF ATP synthase is reversible. Large-enough quantities of ATP cause it to create a transmembrane proton gradient, this is used by fermenting bacteria that do not have an electron transport chain, but rather hydrolyze ATP to make a proton gradient, which they use to drive flagella and the transport of nutrients into the cell.
In respiring bacteria under physiological conditions, ATP synthase, in general, runs in the opposite direction, creating ATP while using the proton motive force created by the electron transport chain as a source of energy. The overall process of creating energy in this fashion is termed oxidative phosphorylation.
The same process takes place in the mitochondria, where ATP synthase is located in the inner mitochondrial membrane and the F-part projects into the mitochondrial matrix. By pumping proton cations into the matrix, the ATP-synthase converts ADP into ATP. | 5 | Photochemistry |
* Georges Friedel (1904) "Étude sur les groupements cristallins", Extrait du Bulletin de la Société de lIndustrie minérale', Quatrième série, Tomes III e IV. Saint-Étienne, Société de l’Imprimerie Théolier J. Thomas et C., 485 pp.
* Georges Friedel (1920) "Contribution à létude géométrique des macles", Bulletin de la Société française de Minéralogie' 43: 246-295.
* Georges Friedel (1926) Leçons de Cristallographie, Berger-Levrault, Nancy, Paris, Strasbourg XIX+602 pp.
* Georges Friedel (1933) "Sur un nouveau type de macles", Bulletin de la Société française de Minéralogie 56: 262-274.
* J.D.H. Donnay (1940) "Width of Albite-Twinning Lamellae", Am. Mineral., 25: 578-586. | 3 | Analytical Chemistry |
First, a cell lysate is generated by glass beads beating, pressure homogenisation or chemical or physical lysis methods that do not denature the protein(s) of interest. (Optionally for targeted analysis) a protein of interest is purified out of this lysate by affinity methods based on intrinsically disordered tags or other suitable purification strategies, often involving several orthogonal chromatographic steps.
This (total or purified) protein solution is aliquoted into several tubes of a PCR strip. All aliquots are exposed in parallel in a thermal gradient PCR cycler to different maximal temperatures in presence of the thermostable protease thermolysin (see figure).
Automated temperature control is achieved in a thermal gradient cycler (commonly used for PCRs). Reaction products can be separated by SDS-PAGE or western blot. The protease thermolysin can be fully inactivated by EDTA. This feature of thermolysin makes FASTpp compatible with subsequent trypsin digestion e.g. for mass spectrometry. | 1 | Biochemistry |
The exchange current density depends critically on the nature of the electrode, not only its structure, but also physical parameters such as surface roughness. Of course, factors that change the composition of the electrode, including passivating oxides and adsorbed species on the surface, also influence the electron transfer. The nature of the electroactive species (the analyte) in the solution also critically affects the exchange current densities, both the reduced and oxidized form.
Less important but still relevant are the environment of the solution including the solvent, nature of other electrolytes, and temperature. For the concentration dependence of the exchange current density, the following expression is given for a one-electron reaction:
where:
* : the concentration of the oxidized species
*: the concentration of the reduced species
* : a symmetry factor
* : Faraday constant
* : reaction rate constant | 7 | Physical Chemistry |
Restriction sites, or restriction recognition sites, are located on a DNA molecule containing specific (4-8 base pairs in length) sequences of nucleotides, which are recognized by restriction enzymes. These are generally palindromic sequences (because restriction enzymes usually bind as homodimers), and a particular restriction enzyme may cut the sequence between two nucleotides within its recognition site, or somewhere nearby. | 1 | Biochemistry |
In 1999, NASA initiated its Space Solar Power Exploratory Research and Technology program (SERT) for the following purposes:
* Perform design studies of selected flight demonstration concepts.
* Evaluate studies of the general feasibility, design, and requirements.
* Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications.
* Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative.
* Construct technology development and demonstration roadmaps for critical space solar power (SSP) elements.
SERT went about developing a solar power satellite (SPS) concept for a future gigawatt space power system, to provide electrical power by converting the Suns energy and beaming it to Earths surface, and provided a conceptual development path that would utilize current technologies. SERT proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar heat engines to convert sunlight into electricity. The program looked both at systems in Sun-synchronous orbit and geosynchronous orbit. Some of SERT's conclusions:
* The increasing global energy demand is likely to continue for many decades resulting in new power plants of all sizes being built.
* The environmental impact of those plants and their impact on world energy supplies and geopolitical relationships can be problematic.
* Renewable energy is a compelling approach, both philosophically and in engineering terms.
* Many renewable energy sources are limited in their ability to affordably provide the base load power required for global industrial development and prosperity, because of inherent land and water requirements.
* Based on their Concept Definition Study, space solar power concepts may be ready to reenter the discussion.
* Solar power satellites should no longer be envisioned as requiring unimaginably large initial investments in fixed infrastructure before the emplacement of productive power plants can begin.
* Space solar power systems appear to possess many significant environmental advantages when compared to alternative approaches.
* The economic viability of space solar power systems depends on many factors and the successful development of various new technologies (not least of which is the availability of much lower cost access to space than has been available); however, the same can be said of many other advanced power technologies options.
* Space solar power may well emerge as a serious candidate among the options for meeting the energy demands of the 21st century.
* Launch costs in the range of $100–$200 per kilogram of payload from low Earth orbit to Geosynchronous orbit are needed if SPS is to be economically viable. | 7 | Physical Chemistry |
Frémys salt is a chemical compound with the formula (K[ON(SO)]), sometimes written as (K[NO(SO)]). It is a bright yellowish-brown solid, but its aqueous solutions are bright violet. The related sodium salt, disodium nitrosodisulfonate (NDS, NaON(SO), CAS 29554-37-8) is also referred to as Frémys salt.
Regardless of the cations, the salts are distinctive because aqueous solutions contain the radical [ON(SO)]. | 0 | Organic Chemistry |
The structure of tetrakis(dimethylamino)ethylene (TDAE) is highly distorted. The dihedral angle for the two NC ends is 28º although the C=C distance is normal 135 pm. The nearly isostructural tetraisopropylethylene also has a C=C distance of 135 pm, but its C core is planar. | 0 | Organic Chemistry |
Dissimilatory sulfate reduction is a relatively energetically poor process used by many Gram-negative bacteria found within the Thermodesulfobacteriota, Gram-positive organisms relating to Desulfotomaculum or the archaeon Archaeoglobus. Hydrogen sulfide () is produced as a metabolic end product. For sulfate reduction electron donors and energy are needed. | 1 | Biochemistry |
The differential cross section may be integrated to find the total cross section.
In the low energy limit there is no energy dependence and we recover the Thomson cross section (~66.5 fm): | 7 | Physical Chemistry |
For isotopes occurring at extremely low levels, accelerator mass spectrometry (AMS) can be used. For example, the decay rate of the radioisotope C is widely used to date organic materials, but this approach was once limited to relatively large samples no more than a few thousand years old. AMS extended the range of C dating to about 60,000 years BP, and is about 10 times more sensitive than conventional IRMS.
AMS works by accelerating negative ions through a large (mega-volt) potential, followed by charge exchange and acceleration back to ground. During charge exchange, interfering species can be effectively removed. In addition, the high energy of the beam allows the use of energy-loss detectors, that can distinguish between species with the same mass/charge ratio. Together, these processes allow the analysis of extreme isotope ratios above 10. | 9 | Geochemistry |
Although the PED technique was initially developed for its improved diffraction applications, the advantageous properties of the technique have been found to enhance many other investigative techniques in the TEM. These include bright field and dark field imaging, electron tomography, and composition-probing techniques like energy-dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). | 3 | Analytical Chemistry |
Consider a particle under a force field that has a velocity parallel to the field direction and a speed proportional to the square of the magnitude of the electric field (any other non-linearity can be employed):
The effective mobility of the particle (the relationship between small changes in drift velocity with respect to small changes in electric field ) can be expressed in Cartesian coordinates as:
Combining (5), (6) and (7) we get:
Further consider the field E is applied in a plane and it rotates counter-clockwise at angular frequency , such that the field components are:
Substituting (10) and (11) in (8) and (9) and simplifying using trigonometric identities results in a sum of constant terms, sine and cosine, at angular frequency . The next calculations will be performed such that only the cosine terms at angular frequency will yield non-zero net drift velocity - therefore we need only evaluate these terms, which will be abbreviated and . The following is obtained:
Let and take the form of a small quadrupole field of intensity that varies in a sinusoidal manner proportional to such that:
Substituting (14) and (15) into (12) and (13) and taking the time average we obtain:
which can be summarized in vector notation to:
Equation (18) shows that for all positions the time averaged velocity is in the direction toward the origin (concentrating the particles towards the origin), with speed proportional to the mobility coefficient k, the strength of the rotating field E and the strength of the perturbing quadrupole field . | 1 | Biochemistry |
Some miRNAs target the messenger RNAs for DNA methyltransferase genes DNMT1, DNMT3A and DNMT3B, whose gene products are needed for initiating and stabilizing promoter methylations. As summarized in three reviews, miRNAs miR-29a, miR-29b and miR-29c target DNMT3A and DNMT3B; miR-148a and miR-148b target DNMT3B; and miR-152 and miR-301 target DNMT1. In addition, miR-34b targets DNMT1 and the promoter of miR-34b itself is hypermethylated and under-expressed in the majority of prostate cancers. When expression of these microRNAs is altered, they may also be a source of the hyper/hypo-methylation of the promoters of protein-coding genes in cancers. | 1 | Biochemistry |
The Urbach tail is an exponential part in the energy spectrum of the absorption coefficient. This tail appears near the optical band edge in amorphous, disordered and crystalline materials. | 3 | Analytical Chemistry |
Most of the reactivity of thioacetic acid arises from the conjugate base, thioacetate. Salts of this anion, e.g. potassium thioacetate, are used to generate thioacetate esters. Thioacetate esters undergo hydrolysis to give thiols. A typical method for preparing a thiol from an alkyl halide using thioacetic acid proceeds in four discrete steps, some of which can be conducted sequentially in the same flask:
:, where X = Cl, Br, I
In an application that illustrates the use of its radical behavior, thioacetic acid is used with AIBN in a free radical mediated nucleophilic addition to an exocyclic alkene forming a thioester: | 0 | Organic Chemistry |
Mass spectrometry is a way to quantify RNA modifications. More often than not, modifications cause an increase in mass for a given nucleoside. This gives a characteristic readout for the nucleoside and the modified counterpart. Moreover, mass spectrometry allows the investigation of modification dynamics by labelling RNA molecules with stable (non-radioactive) heavy isotopes in vivo. Due to the defined mass increase of heavy isotope labeled nucleosides they can be distinguished from their respective unlabelled isotopomeres by mass spectrometry. This method, called NAIL-MS (nucleic acid isotope labelling coupled mass spectrometry), enables a variety of approaches to investigate RNA modification dynamics. | 1 | Biochemistry |
Acid catalysis can be applied to hydrolyses. For example, in the conversion of cellulose or starch to glucose. For the case of ester hydrolysis and amides, it can be defined as an acid catalyzed nucleophilic acyl substitution reaction. Carboxylic acids can be produced from acid hydrolysis of esters.
Acids catalyze hydrolysis of nitriles to amides. Acid hydrolysis does not usually refer to the acid catalyzed addition of the elements of water to double or triple bonds by electrophilic addition as may originate from a hydration reaction. Acid hydrolysis is used to prepare monosaccharide with the help of mineral acids but formic acid and trifluoroacetic acid have been used.
Acid hydrolysis can be utilized in the pretreatment of cellulosic material, so as to cut the interchain linkages in hemicellulose and cellulose. | 7 | Physical Chemistry |
As coral reefs decay, their residents will have to adapt or find new habitats on which to rely. Ocean acidification threatens the fundamental chemical balance of our oceans, creating conditions that eat away at essential minerals like calcium carbonate. A lack of aragonite and decreasing pH levels in ocean water makes it harder for calcifying organisms such as oysters, clams, lobsters, shrimp and coral reefs to build their shells and exoskeletons. Organisms have been found to be more sensitive to the effects of ocean acidification in early, larval or planktonic stages. Larval health and settlement of both calcifying and non-calcifying organisms can be harmed by ocean acidification.
A study published in the journal Global Change Biology developed a model for predicting the vulnerability of sharks and sting rays to climate change in the Great Barrier Reef. It was found that 30 of the 133 species were identified as moderately or highly vulnerable to climate change with the most vulnerable species being the freshwater whipray, porcupine ray, speartooth shark, and sawfish. Increasing temperature is also affecting the behavior and fitness of may reef species such as the common coral trout, a very important fish in sustaining the health of coral reefs. Not only can ocean acidification affect habitat and development, but it can also affect how organisms view predators and conspecifics. Studies on the effects of ocean acidification have not been performed on long enough time scales to see if organisms can adapt to these conditions. However, ocean acidification is predicted to occur at a rate that evolution cannot match. | 9 | Geochemistry |
The gas giants have much greater internal heating than terrestrial planets, due to their greater mass and greater compressibility making more energy available from gravitational contraction. Jupiter, the most massive planet in the Solar System, has the most internal heating, with core temperature estimated to be 36,000 K. For the outer planets of the Solar System, internal heating powers the weather and wind instead of sunlight that powers the weather for terrestrial planets. The internal heating within gas giant planets raise temperatures higher than effective temperatures, as in the case of Jupiter, this makes 40 K warmer than given effective temperature. A combination of external and internal heating (which may be a combination of tidal heating and electromagnetic heating) is thought to make giant planets that orbit very close to their stars (hot Jupiters) into "puffy planets" (external heating is not thought to be sufficient by itself). | 7 | Physical Chemistry |
The standard enthalpy of reaction (denoted ) for a chemical reaction is the difference between total product and total reactant molar enthalpies, calculated for substances in their standard states. The value can be approximately interpreted in terms of the total of the chemical bond energies for bonds broken and bonds formed.
For a generic chemical reaction
the standard enthalpy of reaction is related to the standard enthalpy of formation values of the reactants and products by the following equation:
In this equation, are the stoichiometric coefficients of each product and reactant. The standard enthalpy of formation, which has been determined for a vast number of substances, is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states.
Standard states can be defined at any temperature and pressure, so both the standard temperature and pressure must always be specified. Most values of standard thermochemical data are tabulated at either (25°C, 1 bar) or (25°C, 1 atm).
For ions in aqueous solution, the standard state is often chosen such that the aqueous H ion at a concentration of exactly 1 mole/liter has a standard enthalpy of formation equal to zero, which makes possible the tabulation of standard enthalpies for cations and anions at the same standard concentration. This convention is consistent with the use of the standard hydrogen electrode in the field of electrochemistry. However, there are other common choices in certain fields, including a standard concentration for H of exactly 1 mole/(kg solvent) (widely used in chemical engineering) and mole/L (used in the field of biochemistry). For this reason it is important to note which standard concentration value is being used when consulting tables of enthalpies of formation. | 7 | Physical Chemistry |
Monosaccharide nomenclature is the naming system of the building blocks of carbohydrates, the monosaccharides, which may be monomers or part of a larger polymer. Monosaccharides are subunits that cannot be further hydrolysed in to simpler units. Depending on the number of carbon atom they are further classified into trioses, tetroses, pentoses, hexoses etc., which is further classified in to aldoses and ketoses depending on the type of functional group present in them. | 0 | Organic Chemistry |
For binary solutions, the thermodynamic criterion which defines the spinodal curve is that the second derivative of free energy with respect to density or some composition variable is zero. | 7 | Physical Chemistry |
Initial studies on carboxypeptidases focused on pancreatic carboxypeptidases A1, A2, and B in the digestion of food. Most carboxypeptidases are not, however, involved in catabolism. Instead they help to mature proteins, for example Post-translational modification. They also regulate biological processes, such as the biosynthesis of neuroendocrine peptides such as insulin requires a carboxypeptidase. Carboxypeptidases also function in blood clotting, growth factor production, wound healing, reproduction, and many other processes. | 1 | Biochemistry |
Cyclic alkenes are subject to strain resulting from distortion of the sp-hybridized carbon centers. Illustrative is C where the carbon centres are pyramidalized. This distortion enhances the reactivity of this molecule. Angle strain also is the basis of Bredt's rule which dictates that bridgehead carbon centers are not incorporated in alkenes because the resulting alkene would be subject to extreme angle strain.
Small trans-cycloalkenes have so much ring strain they cannot exist for extended periods of time. For instance, the smallest trans-cycloalkane that has been isolated is trans-cyclooctene. Trans-cycloheptene has been detected via spectrophotometry for minute time periods, and trans-cyclohexene is thought to be an intermediate in some reactions. No smaller trans-cycloalkenes are known. On the contrary, while small cis-cycloalkenes do have ring strain, they have much less ring strain than small trans-cycloalkenes.
In general, the increased levels of unsaturation in alkenes leads to higher ring strain. Increasing unsaturation leads to greater ring strain in cyclopropene. Therefore, cyclopropene is an alkene that has the most ring strain between the two mentioned. The differing hybridizations and geometries between cyclopropene and cyclopropane contribute to the increased ring strain. Cyclopropene also has an increased angle strain, which also contributes to the greater ring strain. However, this trend does not always work for every alkane and alkene. | 7 | Physical Chemistry |
Passive daytime radiative cooling surfaces can be integrated with solar energy plants, referred to as solar energy–radiative cooling (SE–RC), to improve functionality and performance by preventing solar cells from overheating and thus degrading. Since solar cells have a maximum efficiency of 33.7% (with the average commercial PV panel having a conversion rate around 20%), the majority of absorbed power produces excess heat and increases the operating temperature of the system. Solar cell efficiency declines 0.4-0.5% for every 1ᵒC increase in temperature.
Passive daytime radiative cooling can extend the life of solar cells by lowering the operating temperature of the system. Integrating PDRCs into solar energy systems is also relatively simple, given that "most solar energy harvesting systems have a sky-facing flat plate structural design, which is similar to radiative cooling systems." Integration has been shown to "produce a higher energy gain per unit area" while also increasing the "total useful working time." Integrated systems can mitigate issues of "limited working time and low energy gain" and are "a current research hotspot," as per Ahmed et al.
Methods have been proposed to potentially enhance cooling performance. Lu et al. proposes using a "full-spectrum synergetic management (FSSM) strategy to cool solar cells, which combines radiative cooling and spectral splitting to enhance radiative heat dissipation and reduce the waste heat generated by the absorption of sub-BG photons."
Outdoor tests using various PDRC materials, some more scalable than others, have demonstrated various degrees of cooling power:
* Wang et al. (2021), a periodic pyramid-textured polydimethylsiloxane (PDMS) radiative film, cooled commercial silicon solar cells by over 2 °C.
* Lee et al. (2021), a visibly clear PDRC designed "using a rational design to deploy an optical modulator (n-hexadecane) in aerogel microparticles within a silicone elastomer matrix," cooled commercial silicon solar cells by 7.7 °C on average.
* Tang et al. (2022), nanoporous anodic aluminum oxide film, flatpanel solar cell relative efficiency improvement of ~2.72%, concentrated solar cell relative efficiency improvement of ~16.02%, described as "a high-performance and scalable radiative cooler."
* Zhao et al. (2022), a silica micro-grating photonic cooler, cooled commercial silicon cells by 3.6 °C under solar intensity of 830 W m to 990 W m. | 7 | Physical Chemistry |
Polymers such as PMMA and HEMA:MMA are used as matrices in the gain medium of solid-state dye lasers, also known as solid-state dye-doped polymer lasers. These polymers have a high surface quality and are also highly transparent so that the laser properties are dominated by the laser dye used to dope the polymer matrix. These type of lasers, that also belong to the class of organic lasers, are known to yield very narrow linewidths which is useful for spectroscopy and analytical applications. An important optical parameter in the polymer used in laser applications is the change in refractive index with temperature
also known as dn/dT. For the polymers mentioned here the (dn/dT) ~ −1.4 × 10 in units of K in the 297 ≤ T ≤ 337 K range. | 7 | Physical Chemistry |
The Thomson Medal and Prize is an award which has been made, originally only biennially in even-numbered years, since 2008 by the British Institute of Physics for "distinguished research in atomic (including quantum optics) or molecular physics". It is named after Nobel prizewinner Sir J. J. Thomson, the British physicist who demonstrated the existence of electrons, and comprises a silver medal and a prize of £1000.
Not to be confused with the J. J. Thomson IET Achievement Medal for electronics. | 7 | Physical Chemistry |
On January 21, 2015, Nick Goldman from the European Bioinformatics Institute (EBI), one of the original authors of the 2013 Nature paper, announced the Davos Bitcoin Challenge at the World Economic Forum annual meeting in Davos. During his presentation, DNA tubes were handed out to the audience, with the message that each tube contained the private key of exactly one bitcoin, all coded in DNA. The first one to sequence and decode the DNA could claim the bitcoin and win the challenge. The challenge was set for three years and would close if nobody claimed the prize before January 21, 2018.
Almost three years later on January 19, 2018, the EBI announced that a Belgian PhD student, Sander Wuyts, of the University of Antwerp and Vrije Universiteit Brussel, was the first one to complete the challenge. Next to the instructions on how to claim the bitcoin (stored as a plain text and PDF file), the logo of the EBI, the logo of the company that printed the DNA (CustomArray), and a sketch of James Joyce were retrieved from the DNA. | 1 | Biochemistry |
Heap leaching dates back to the second century BC in China, where iron was combined with copper sulfate. By the time of the Northern Song Dynasty, a copper alloy was able to be recovered by leaching.
Leaching can also be traced back to alchemy. Early examples of leaching performed by alchemists resembled mixing iron with copper sulfate, yielding a layer of metallic copper. In the 8th century, Jabir Ibn Hayyan, an Arab alchemist, discovered a substance he coined "aqua regia". Aqua regia, a combination of hydrochloric acid and nitric acid, was found to be effective in dissolving gold, which was previously thought to be insoluble. | 8 | Metallurgy |
Lake metabolism represents a lake's balance between carbon fixation (gross primary production) and biological carbon oxidation (ecosystem respiration). Whole-lake metabolism includes the carbon fixation and oxidation from all organism within the lake, from bacteria to fishes, and is typically estimated by measuring changes in dissolved oxygen or carbon dioxide throughout the day.
Ecosystem respiration in excess of gross primary production indicates the lake receives organic material from the surrounding catchment, such as through stream or groundwater inflows or litterfall. Lake metabolism often controls the carbon dioxide emissions from or influx to lakes, but it does not account for all carbon dioxide dynamics since inputs of inorganic carbon from the surrounding catchment also influence carbon dioxide within lakes. | 1 | Biochemistry |
Alkynes are named using the same system, with the suffix "-yne" indicating a triple bond: ethyne (acetylene), propyne (methylacetylene). | 0 | Organic Chemistry |
The 5 UTR of prokaryotes consists of the Shine–Dalgarno sequence (5-AGGAGGU-3'). This sequence is found 3-10 base pairs upstream from the initiation codon. The initiation codon is the start site of translation into protein. | 1 | Biochemistry |
PELP1 is a proto-oncogene that provides cancer cells with a distinct growth and survival advantage. PELP1 overexpression has been reported in many cancers. PELP1 expression is an independent prognostic predictor of shorter breast cancer–specific survival and disease free interval. Patients whose tumors had high levels of cytoplasmic PELP1 exhibited a tendency to respond poorly to tamoxifen and PELP1 deregulated tumors respond to Src kinase and mTOR inhibitors. Treatment of breast and ovarian cancer xenografts with liposomal PELP1–siRNA–DOPC formulations revealed that knockdown of PELP1 significantly reduce the tumor growth. These results provided initial proof that PELP1 is a bonafide therapeutic target. Emerging data support a central role for PELP1 and its direct protein–protein interactions in cancer progression. Since PELP1 lacks known enzymatic activity, drugs that target PELP1 interactions with other proteins should have clinical utility. Recent studies described an inhibitor (D2) that block PELP1 interactions with AR. Since PELP1 interacts with histone modifications and epigenetic enzymes, drugs targeting epigenetic modifier enzymes may be useful in targeting PELP1 deregulated tumors. | 1 | Biochemistry |
The Hydrogen bond is relevant to drug design. According to Lipinski's rule of five the majority of orally active drugs have no more than five hydrogen bond donors and fewer than ten hydrogen bond acceptors. These interactions exist between nitrogen–hydrogen and oxygen–hydrogen centers. Many drugs do not, however, obey these "rules". | 6 | Supramolecular Chemistry |
Dyneins are microtubule motors capable of a retrograde sliding movement. Dynein complexes are much larger and more complex than kinesin and myosin motors. Dyneins are composed of two or three heavy chains and a large and variable number of associated light chains. Dyneins drive intracellular transport toward the minus end of microtubules which lies in the microtubule organizing center near the nucleus. The dynein family has two major branches. Axonemal dyneins facilitate the beating of cilia and flagella by rapid and efficient sliding movements of microtubules. Another branch is cytoplasmic dyneins which facilitate the transport of intracellular cargos. Compared to 15 types of axonemal dynein, only two cytoplasmic forms are known.
Genomic representation of dynein motors:
* Fungi (yeast): 1
* Plants (Arabidopsis thaliana): 0
* Insects (Drosophila melanogaster): 13
* Mammals (human): 14-15 | 6 | Supramolecular Chemistry |
Quantities of liquids are measured in units of volume. These include the SI unit cubic metre (m) and its divisions, in particular the cubic decimeter, more commonly called the litre (1 dm = 1 L = 0.001 m), and the cubic centimetre, also called millilitre (1 cm = 1 mL = 0.001 L = 10 m).
The volume of a quantity of liquid is fixed by its temperature and pressure. Liquids generally expand when heated, and contract when cooled. Water between 0 °C and 4 °C is a notable exception.
On the other hand, liquids have little compressibility. Water, for example, will compress by only 46.4 parts per million for every unit increase in atmospheric pressure (bar). At around 4000 bar (400 megapascals or 58,000 psi) of pressure at room temperature water experiences only an 11% decrease in volume. Incompressibility makes liquids suitable for transmitting hydraulic power, because a change in pressure at one point in a liquid is transmitted undiminished to every other part of the liquid and very little energy is lost in the form of compression.
However, the negligible compressibility does lead to other phenomena. The banging of pipes, called water hammer, occurs when a valve is suddenly closed, creating a huge pressure-spike at the valve that travels backward through the system at just under the speed of sound. Another phenomenon caused by liquid's incompressibility is cavitation. Because liquids have little elasticity they can literally be pulled apart in areas of high turbulence or dramatic change in direction, such as the trailing edge of a boat propeller or a sharp corner in a pipe. A liquid in an area of low pressure (vacuum) vaporizes and forms bubbles, which then collapse as they enter high pressure areas. This causes liquid to fill the cavities left by the bubbles with tremendous localized force, eroding any adjacent solid surface. | 7 | Physical Chemistry |
Concentration of in the blood and tissues is so low that they feel weak and are unable to think properly, a condition called hypoxia. | 7 | Physical Chemistry |
5-methylcytidine, m5C, is abundantly found in mRNA and ncRNAs, especially tRNA and rRNAs. In tRNAs, this modification stabilizes the secondary structure and influences anticodon stem-loop conformation. In rRNAs, m5C affects translational fidelity.
Two principles have been used to develop m5C sequencing methods. The first one is antibody-based approach (bisuphite sequencing and m5C-RIP), similar to m6C sequencing. The second is detecting targets of m5C RNA methyltransferases by covalently linking the enzyme to its target, and then using IP specific to the target enzyme to enrich for RNA molecules containing the mark (Aza-IP and miCLIP). | 1 | Biochemistry |
The Eyring equation, another Arrhenius-like expression, appears in the "transition state theory" of chemical reactions, formulated by Eugene Wigner, Henry Eyring, Michael Polanyi and M. G. Evans in the 1930s. The Eyring equation can be written:
where is the Gibbs energy of activation, is the entropy of activation, is the enthalpy of activation, is the Boltzmann constant, and is Planck's constant.
At first sight this looks like an exponential multiplied by a factor that is linear in temperature. However, free energy is itself a temperature dependent quantity. The free energy of activation is the difference of an enthalpy term and an entropy term multiplied by the absolute temperature. The pre-exponential factor depends primarily on the entropy of activation. The overall expression again takes the form of an Arrhenius exponential (of enthalpy rather than energy) multiplied by a slowly varying function of T. The precise form of the temperature dependence depends upon the reaction, and can be calculated using formulas from statistical mechanics involving the partition functions of the reactants and of the activated complex. | 7 | Physical Chemistry |
The range of recorded sinking velocities of particles in the oceans spans from negative (particles float toward the surface) to several km per day (as with salp fecal pellets) When considering the sinking velocity of an individual particle, a first approximation can be obtained from Stokes law (originally derived for spherical, non-porous particles and laminar flow) combined with Whites approximation, which suggest that sinking velocity increases linearly with excess density (the difference from the water density) and the square of particle diameter (i.e., linearly with the particle area). Building on these expectations, many studies have tried to relate sinking velocity primarily to size, which has been shown to be a useful predictor for particles generated in controlled environments (e.g., roller tanks. However, strong relationships were only observed when all particles were generated using the same water/plankton community. When particles were made by different plankton communities, size alone was a bad predictor (e.g., Diercks and Asper, 1997) strongly supporting notions that particle densities and shapes vary widely depending on the source material.
Packaging and porosity contribute appreciably to determining sinking velocities. On the one hand, adding ballasting materials, such as diatom frustules, to aggregates may lead to an increase in sinking velocities owing to the increase in excess density. On the other hand, the addition of ballasting mineral particles to marine particle populations frequently leads to smaller more densely packed aggregates that sink slower because of their smaller size. Mucous-rich particles have been shown to float despite relatively large sizes, whereas oil- or plastic-containing aggregates have been shown to sink rapidly despite the presence of substances with an excess density smaller than seawater. In natural environments, particles are formed through different mechanisms, by different organisms, and under varying environmental conditions that affect aggregation (e.g., salinity, pH, minerals), ballasting (e.g., dust deposition, sediment load; van der Jagt et al., 2018) and sinking behaviour (e.g., viscosity;). A universal conversion of size-to-sinking velocity is hence impracticable. | 9 | Geochemistry |
The hydroboration reaction is a useful reaction to functionalize alkenes to alcohols. In the reaction the trimethylsilyl (TMS) group fulfill 2 roles in directing the stereoselectivity of the reaction. First, the bulky size of TMS helped the molecule to preferably adopt a conformation where the TMS is not close to the methyl group on the alkene. Second, the TMS group conferred a stereoelectronic effect on the molecule by adopting an anti conformation to the directing orbitals of the alkene. For the regioselectivity of the reaction, the TMS group can stabilize the developing partial positive charge on the secondary carbon a lot better than a methyl group. | 4 | Stereochemistry |
Differences in the abundance of stable isotopes among natural materials are usually very small (natural differences in the ratio of rare to common isotope are almost always below 0.1%, and sometimes much smaller). Nevertheless, these very small differences can record meaningful biological and geological processes. To facilitate comparison of these small but meaningful differences, isotope abundances in natural materials are often reported relative to isotope abundances in designated standards. The convention for reporting the measured difference between a sample and a standard is called "delta notation." For example, imagine an element X for which we wish to compare the rare, heavy stable isotope with atomic mass A (X) to the light, common isotope with atomic mass B (X). The abundance of X and X in any given material is reported with the notation δX. δX for the sample material is calculated as follows:
:R = (total amount of X)/(total amount of X)
:δX = (R − R)/R
δ values are most commonly reported in parts per thousand, commonly referred to in isotope chemistry as per mille and represented by the symbol ‰. To report δ values in per mille, the δ value as calculated above should be multiplied by 1000:
:δX (‰) = ((R − R)/R) * 1000 | 9 | Geochemistry |
CK is often determined routinely in a medical laboratory. It used to be determined specifically in patients with chest pain, but this test has been replaced by troponin. Normal values at rest are usually between 60 and 400 IU/L, where one unit is enzyme activity, more specifically the amount of enzyme that will catalyze 1 μmol of substrate per minute under specified conditions (temperature, pH, substrate concentrations and activators.) This test is not specific for the type of CK that is elevated.
Creatine kinase in the blood may be high in health and disease. Exercise increases the outflow of creatine kinase to the blood stream for up to a week, and this is the most common cause of high CK in blood. Furthermore, high CK in the blood may be related to high intracellular CK such as in persons of African descent.
Finally, high CK in the blood may be an indication of damage to CK-rich tissue, such as in rhabdomyolysis, myocardial infarction, myositis and myocarditis. This means creatine kinase in blood may be elevated in a wide range of clinical conditions including the use of medication such as statins; endocrine disorders such as hypothyroidism; and skeletal muscle diseases and disorders including malignant hyperthermia, and neuroleptic malignant syndrome.
Furthermore, the isoenzyme determination has in the past been used extensively as an indication for myocardial damage in heart attacks. Troponin measurement has largely replaced this in many hospitals, although some centers still rely on CK-MB. | 1 | Biochemistry |
As the name suggests, surge margin provides a measure of how close an operating point is to surge. Unfortunately, there are a number of different definitions of surge margin. A popular one in use is defined as follows:
where:
is the mass flow at the operating point, be it steady state or transient
is the mass flow at surge, at same corrected speed as | 7 | Physical Chemistry |
The formulae for rokushō are not published widely or freely, but passed on in the Japanese craft tradition. However, some scholars have analysed samples of the material.
Premixed rokushō can be purchased outside Japan through specialty jewelry suppliers. Additionally, several different formulas have been proposed to replicate the traditional product for those who prefer to make their own:
* In a container made of glass, porcelain, or copper, dissolve 6g copper acetate, 2g calcium carbonate, and 2g sodium hydroxide in 150ml water. After a week, siphon or decant the clear liquid from the top; just before use, add another 2g copper sulfate.
* Dissolve 4g copper acetate, 1g copper nitrate, 1g cupric chloride, and 4g copper sulfate in 1 liter of distilled water.
* Dissolve 60g copper acetate and 60g copper sulfate in a 2-liter solution of white vinegar diluted 5-12% with water.
Rokusho is not used alone, but mixed with one or more other chemicals. Further, metal to be processed is cleaned in advance of treatment, using a mild acid bath (oxalic or sulfuric acids are frequently used), scrubbing with daikon radish or pumice, and/or a surface abrasive, and often treated after patination also. | 8 | Metallurgy |
Partially inelastic collisions are the most common form of collisions in the real world. In this type of collision, the objects involved in the collisions do not stick, but some kinetic energy is still lost. Friction, sound and heat are some ways the kinetic energy can be lost through partial inelastic collisions. | 7 | Physical Chemistry |
Eukaryotic promoters are diverse and can be difficult to characterize, however, recent studies show that they are divided in more than 10 classes.
Gene promoters are typically located upstream of the gene and can have regulatory elements several kilobases away from the transcriptional start site (enhancers). In eukaryotes, the transcriptional complex can cause the DNA to bend back on itself, which allows for placement of regulatory sequences far from the actual site of transcription. Eukaryotic RNA-polymerase-II-dependent promoters can contain a TATA box (consensus sequence TATAAA), which is recognized by the general transcription factor TATA-binding protein (TBP); and a B recognition element (BRE), which is recognized by the general transcription factor TFIIB. The TATA element and BRE typically are located close to the transcriptional start site (typically within 30 to 40 base pairs).
Eukaryotic promoter regulatory sequences typically bind proteins called transcription factors that are involved in the formation of the transcriptional complex. An example is the E-box (sequence CACGTG), which binds transcription factors in the basic helix-loop-helix (bHLH) family (e.g. BMAL1-Clock, cMyc). Some promoters that are targeted by multiple transcription factors might achieve a hyperactive state, leading to increased transcriptional activity.
* Core promoter – the minimal portion of the promoter required to properly initiate transcription
** Includes the transcription start site (TSS) and elements directly upstream
** A binding site for RNA polymerase
*** RNA polymerase I: transcribes genes encoding 18S, 5.8S and 28S ribosomal RNAs
*** RNA polymerase II: transcribes genes encoding messenger RNA and certain small nuclear RNAs and microRNA
*** RNA polymerase III: transcribes genes encoding transfer RNA, 5s ribosomal RNAs and other small RNAs
** General transcription factor binding sites, e.g. TATA box, B recognition element.
** Many other elements/motifs may be present. There is no such thing as a set of "universal elements" found in every core promoter.
* Proximal promoter – the proximal sequence upstream of the gene that tends to contain primary regulatory elements
** Approximately 250 base pairs upstream of the start site
** Specific transcription factor binding sites
* Distal promoter – the distal sequence upstream of the gene that may contain additional regulatory elements, often with a weaker influence than the proximal promoter
** Anything further upstream (but not an enhancer or other regulatory region whose influence is positional/orientation independent)
** Specific transcription factor binding sites | 1 | Biochemistry |
In condensed matter physics and physical chemistry, the Lifshitz theory of van der Waals forces, sometimes called the macroscopic theory of van der Waals forces, is a method proposed by Evgeny Mikhailovich Lifshitz in 1954 for treating van der Waals forces between bodies which does not assume pairwise additivity of the individual intermolecular forces; that is to say, the theory takes into account the influence of neighboring molecules on the interaction between every pair of molecules located in the two bodies, rather than treating each pair independently. | 7 | Physical Chemistry |
The function of the C-terminal domain has been experimentally determined as being important for cytoplasmic localisation. The residues are scattered along the C-terminal domain sequence however once the protein folds, they position themselves closely together. | 1 | Biochemistry |
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend the definition to include substances like aerosols and gels. The term colloidal suspension refers unambiguously to the overall mixture (although a narrower sense of the word suspension is distinguished from colloids by larger particle size). A colloid has a dispersed phase (the suspended particles) and a continuous phase (the medium of suspension). The dispersed phase particles have a diameter of approximately 1 nanometre to 1 micrometre.
Some colloids are translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid. Other colloids may be opaque or have a slight color.
Colloidal suspensions are the subject of interface and colloid science. This field of study began in 1845 by Francesco Selmi, who called them pseudosolutions, and expanded by Michael Faraday and Thomas Graham, who coined the term colloid in 1861. | 7 | Physical Chemistry |
Cell–cell fusogens are glycoproteins that facilitate the fusion of cell to cell membranes. Cell–cell fusion is critical for the merging of gamete genomes and the development of organs in multicellular organisms. Cell-cell fusion occurs when both actin cytoskeleton and fusogenic proteins properly rearrange across the cell membrane. This process is led by actin-propelled membrane protrusions. | 1 | Biochemistry |
Deep-level transient spectroscopy (DLTS) is an experimental tool for studying electrically active defects (known as charge carrier traps) in semiconductors. DLTS establishes fundamental defect parameters and measures their concentration in the material. Some of the parameters are considered as defect "finger prints" used for their identifications and analysis.
DLTS investigates defects present in a space charge (depletion) region of a simple electronic device. The most commonly used are Schottky diodes or p-n junctions. In the measurement process the steady-state diode reverse polarization voltage is disturbed by a voltage pulse. This voltage pulse reduces the electric field in the space charge region and allows free carriers from the semiconductor bulk to penetrate this region and recharge the defects causing their non-equilibrium charge state. After the pulse, when the voltage returns to its steady-state value, the defects start to emit trapped carriers due to the thermal emission process. The technique observes the device space charge region capacitance where the defect charge state recovery causes the capacitance transient. The voltage pulse followed by the defect charge state recovery are cycled allowing an application of different signal processing methods for defect recharging process analysis.
The DLTS technique has a higher sensitivity than almost any other semiconductor diagnostic technique. For example, in silicon it can detect impurities and defects at a concentration of one part in 10 of the material host atoms. This feature together with a technical simplicity of its design made it very popular in research labs and semiconductor material production factories.
The DLTS technique was pioneered by David Vern Lang at Bell Laboratories in 1974. A US Patent was awarded to Lang in 1975. | 7 | Physical Chemistry |
In chemistry, the rate equation (also known as the rate law or empirical differential rate equation) is an empirical differential mathematical expression for the reaction rate of a given reaction in terms of concentrations of chemical species and constant parameters (normally rate coefficients and partial orders of reaction) only. For many reactions, the initial rate is given by a power law such as
where and are the molar concentrations of the species and usually in moles per liter (molarity, ). The exponents and are the partial orders of reaction for and and the overall reaction order is the sum of the exponents. These are often positive integers, but they may also be zero, fractional, or negative. The order of reaction is a number which quantifies the degree to which the rate of a chemical reaction depends on concentrations of the reactants. In other words, the order of reaction is the exponent to which the concentration of a particular reactant is raised. The constant is the reaction rate constant or rate coefficient and at very few places velocity constant or specific rate of reaction. Its value may depend on conditions such as temperature, ionic strength, surface area of an adsorbent, or light irradiation. If the reaction goes to completion, the rate equation for the reaction rate applies throughout the course of the reaction.
Elementary (single-step) reactions and reaction steps have reaction orders equal to the stoichiometric coefficients for each reactant. The overall reaction order, i.e. the sum of stoichiometric coefficients of reactants, is always equal to the molecularity of the elementary reaction. However, complex (multi-step) reactions may or may not have reaction orders equal to their stoichiometric coefficients. This implies that the order and the rate equation of a given reaction cannot be reliably deduced from the stoichiometry and must be determined experimentally, since an unknown reaction mechanism could be either elementary or complex. When the experimental rate equation has been determined, it is often of use for deduction of the reaction mechanism.
The rate equation of a reaction with an assumed multi-step mechanism can often be derived theoretically using quasi-steady state assumptions from the underlying elementary reactions, and compared with the experimental rate equation as a test of the assumed mechanism. The equation may involve a fractional order, and may depend on the concentration of an intermediate species.
A reaction can also have an undefined reaction order with respect to a reactant if the rate is not simply proportional to some power of the concentration of that reactant; for example, one cannot talk about reaction order in the rate equation for a bimolecular reaction between adsorbed molecules: | 7 | Physical Chemistry |
The dystrophin-associated protein complex includes dystrophin. Dystrophin binds to actin of the cytoskeleton, and also to proteins in the extracellular matrix.
The dystrophin-associated protein complex also contains dystrophin-associated proteins. This includes a four subunit sarcoglycan complex, which is fixed to dystrophin in muscle cells.
In the epithelia of the kidney, dystrophin may be replaced with utrophin.
Aquaporin 4 may be connected to the dystrophin-associated protein complex. | 1 | Biochemistry |
A significant indentation on the middle section of the pillar, approximately from the current courtyard ground level, has been shown to be the result of a cannonball fired at close range. The impact caused horizontal fissuring of the column in the area diametrically opposite to the indentation site, but the column itself remained intact. While no contemporaneous records, inscriptions, or documents describing the event are known to exist, historians generally agree that Nadir Shah is likely to have ordered the pillar's destruction during his invasion of Delhi in 1739, as he would have considered a Hindu temple monument undesirable within an Islamic mosque complex. Alternatively, he may have sought to dislodge the decorative top portion of the pillar in search of hidden precious stones or other items of value.
No additional damage attributable to cannon fire has been found on the pillar, suggesting that no further shots were taken. Historians have speculated that ricocheting fragments of the cannonball may have damaged the nearby Quwwat-ul-Islam mosque, which suffered damage to its southwestern portion during the same period, and the assault on the pillar might have been abandoned as a result. | 8 | Metallurgy |
In environmental chemistry, the chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution which in SI units is milligrams per litre (mg/L). A COD test can be used to easily quantify the amount of organics in water. The most common application of COD is in quantifying the amount of oxidizable pollutants found in surface water (e.g. lakes and rivers) or wastewater. COD is useful in terms of water quality by providing a metric to determine the effect an effluent will have on the receiving body, much like biochemical oxygen demand (BOD). | 9 | Geochemistry |
Type R (87%Pt/13%Rh–Pt, by weight) thermocouples are used 0 to 1600 °C. Type R Thermocouples are quite stable and capable of long operating life when used in clean, favorable conditions. When used above 1100 °C ( 2000 °F), these thermocouples must be protected from exposure to metallic and non-metallic vapors. Type R is not suitable for direct insertion into metallic protecting tubes. Long term high temperature exposure causes grain growth which can lead to mechanical failure and a negative calibration drift caused by Rhodium diffusion to pure platinum leg as well as from Rhodium volatilization. This type has the same uses as type S, but is not interchangeable with it. | 8 | Metallurgy |
The palladacycles could also be classified by the donor atoms. For example, the Herrmann’s catalyst discussed before is a phosphine-derived palladacycle. Other types of palladacycles such as phosphite palladacycle, imine palladacycle, oxime palladacycle, CS-/CO-palladacycles are also effective in catalytic reactions. Palladacycles derived from 2-aminobiphenyl have been used in a variety of cross-coupling reactions. | 0 | Organic Chemistry |
The Avrami equation was applied in cancer biophysics in two aspects. First aspect is connected with tumor growth and cancer cells kinetics, which can be described by the sigmoidal curve. In this context the Avrami function was discussed as an alternative to the widely used Gompertz curve. In the second aspect the Avrami nucleation and growth theory was used together with multi-hit theory of carcinogenesis to show how the cancer cell is created. The number of oncogenic mutations in cellular DNA can be treated as nucleation particles which can transform whole DNA molecule into cancerous one (neoplastic transformation). This model was applied to clinical data of gastric cancer, and shows that Avramis constant n is between 4 and 5 which suggest the fractal geometry of carcinogenic dynamics. Similar findings were published for breast and ovarian cancers, where n'=5.3. | 3 | Analytical Chemistry |
The coefficient lies always in range values equal to 0 or 1), value 1 indicates ideal equal-spreading of the spots, for example (0.25,0.5,0.75) for three solutes, or (0.2,0.4,0.6,0.8) for four solutes.
This coefficient was proposed as an alternative to earlier approaches, such as delta-Rf, delta-Rf product or MRF (Multispot Response Function). Besides its stable range, the advantage is a stable distribution as a random variable, regardless of compounds investigated.
In contrast to the similar concept called Retention uniformity, R is sensitive to R values close to 0 or 1, or close to themselves. If two values are not separated, it is equal to 0. For example, the R values (0,0.2,0.2,0.3) (two compounds not separated at 0.2 and one at the start ) result in R equal to 0, but R equal to 0.3609. When some distance from 0 and spots occurs, the value is larger, for example R values (0.1,0.2,0.25,0.3) give R = 0.4835, R = 0.4066. | 3 | Analytical Chemistry |
For a general time-dependent wavefunction satisfying the time-dependent Schrödinger equation, the Hellmann–Feynman theorem is not valid.
However, the following identity holds:
For | 6 | Supramolecular Chemistry |
COFs have been studied as non-metallic electrocatalysts for energy-related catalysis, including carbon dioxide electro-reduction and water splitting reaction. However, such researches are still in the very early stage. Most of the efforts have been focusing on solving the key issues, such as conductivity, stability in electrochemical processes. | 6 | Supramolecular Chemistry |
Throughout this sub-section, as in the previous one, the two ends of the polymer are attached to a micro-manipulation device. This time, however, the device does not maintain the two ends of the ideal chain in a fixed position, but rather it maintains a constant pulling force on the ideal chain. In this case the two ends of the polymer fluctuate around a mean position . The ideal chain reacts with a constant opposite force .
For an ideal chain exchanging length with a reservoir, a macro-state of the system is characterized by the vector .
The change between an ideal chain of fixed length and an ideal chain in contact with a length reservoir is very much akin to the change between the micro-canonical ensemble and the canonical ensemble (see the Statistical mechanics article about this). The change is from a state where a fixed value is imposed on a certain parameter, to a state where the system is left free to exchange this parameter with the outside. The parameter in question is energy for the microcanonical and canonical descriptions, whereas in the case of the ideal chain the parameter is the length of the ideal chain.
As in the micro-canonical and canonical ensembles, the two descriptions of the ideal chain differ only in the way they treat the system's fluctuations. They are thus equivalent at the thermodynamic limit. The equation of state of the ideal chain remains the same, except that is now subject to fluctuations: | 7 | Physical Chemistry |
Shape-memory alloys are applied in medicine, for example, as fixation devices for osteotomies in orthopaedic surgery, as the actuator in surgical tools; active steerable surgical needles for minimally invasive percutaneous cancer interventions in the surgical procedures such as biopsy and brachytherapy, in dental braces to exert constant tooth-moving forces on the teeth, in Capsule Endoscopy they can be used as a trigger for biopsy action.
The late 1980s saw the commercial introduction of Nitinol as an enabling technology in a number of minimally invasive endovascular medical applications. While more costly than stainless steel, the self expanding properties of Nitinol alloys manufactured to BTR (Body Temperature Response), have provided an attractive alternative to balloon expandable devices in stent grafts where it gives the ability to adapt to the shape of certain blood vessels when exposed to body temperature. On average, of all peripheral vascular stents currently available on the worldwide market are manufactured with Nitinol. | 8 | Metallurgy |
p-Dimethylaminobenzaldehyde reacts with hydrazine to form p-Dimethylaminobenzalazine azo-dye which has a distinct yellow color. It is therefore used for spectrophotometric determination of hydrazine in aqueous solutions at 457 nm. | 3 | Analytical Chemistry |
Several databases exist for restriction sites and enzymes, of which the largest noncommercial database is REBASE. Recently, it has been shown that statistically significant nullomers (i.e. short absent motifs which are highly expected to exist) in virus genomes are restriction sites indicating that viruses have probably got rid of these motifs to facilitate invasion of bacterial hosts. [https://www.nullomers.org/ Nullomers Database] contains a comprehensive catalogue of minimal absent motifs many of which might potentially be not-yet-known restriction motifs. | 1 | Biochemistry |
The glucose fatty acid cycle is also observed in the fed state after a high-fat meal or during exercise. This is when plasma concentrations of fatty acids or ketone bodies are increased. The glucose that is not oxidized is then rerouted to glycogen. This rerouting to glycogen explains the rapid resynthesis of muscle glycogen after exercise as well as the increased glycogen content in muscles found in starvation or diabetes. This mechanism replenishes the intermediates of the citric acid cycle. | 1 | Biochemistry |
* Charlesby A. Atomic Radiation and Polymers. Pergamon Press, Oxford, pp. 198–257 (1960).
* Gall, K; Dunn, M; Liu, Y. Internal stress storage in shape shape-memory polymer nanocomposites. Applied physical letters. 85, (Jul-2004).
* Jeong, Han Mo; Song H, Chi W. Shape-shape-memory effect of poly (methylene-1,3-cyclopentane) and its copolymer with polyethylene. Polymer International, 51:275-280 (2002).
* Kawate, K. Creep Recovery of Acrylate Urethane Oligomer/Acrylate Networks. Creep recovery, shape shape-memory. Journal of polymer science. 35.
* Kim B K, Lee S Y, Xu M. Polyurethanes having shape-shape-memory effects. Polymer 37: 5781–93, (1998).
* Langer, R; Tirrell, D. A. Designing materials for biology and medicine. Nature 428: (Apr-2004).
* Lendlein, A; Kelch, S; Kratz, K. Shape-shape-memory Polymers. Encyclopedia of Materials: Science and Technology. 1–9. (2005).
* Lendlein, A; Langer, R. Biodegradable, elastic shape-shape-memory polymers for potential biomedical applications. Science. 296, 1673–1676 (2002).
* Lendlein, A; Kelch, S. Shape-Memory Polymers. Angew. Chemie. Chem. Int. 41: 2034 – 2057. (2002).
* Lendlein, A; Schmidt, A M; Langer R, AB-polymer networks based on oligo(ε-caprolactone) segments showing shape-shape-memory properties. Proc. Natl. Acad. Sci. USA. 98(3): 842–7 (2001).
* Li F, Chen Y, Zhu W, Zhang X, Xu M. Shape shape-memory effects of polyethylene/nylon 6 graft copolymers. Polymer 39(26):6929–6934 (1998).
* Liu, Chun, Mather. Chemically Cross-Linked Polycyclooctene: Synthesis, Characterization, and Shape Memory Behavior. Macromolecules, 35: 9868-9874 (2002).
* Nakasima A, Hu J, Ichinosa M, Shimada H. Potential application of shape-shape-memory plastic as elastic material in clinical orthodontics. (1991) Eur. J. Orthodontics 13:179–86.
* Ortega, Alicia M; Gall, Ken. The Effect of Crosslink Density on the Thermo-Mechanical Response of Shape Memory Polymers.
* Peng P; Wang, W; Xuesi C; and Jing X. Poly(ε-caprolactone) Polyurethane and Its Shape-Memory Property. Biomacromolecules 6:587-592 (2005).
* Wang, M; Zhang, L. Recovery as a Measure of Oriented Crystalline Structure in Poly (ether ester) s Based on Poly (ethylene oxide) and poly(ethylene terephthalate) Used as Shape Memory Polymers. Journal of Polymer Science: Part B: Polymer Physics, 37: 101–112 (1999).
* Yiping C. Ying G; Juan D; Juan L; Yuxing P; Albert S. Hydrogen-bonded polymer network—poly (ethylene glycol) complexes with shape shape-memory effect. Journal of Materials Chemistry. 12: 2957–2960 (2002).
* Katime I, Katime O, Katime D "Los materiales inteligentes de este Milenio: los hidrogeles polímeros". Editorial de la Universidad del País Vasco, Bilbao 2004. ISBN 84-8373-637-3.
* Katime I, Katime O y Katime D."Introducción a la Ciencia de los materiales polímeros: Síntesis y caracterización". Servicio Editorial de la Universidad del País Vasco, Bilbao 2010. ISBN 978-84-9860-356-9 | 7 | Physical Chemistry |
Giovanni Aldini is claimed to have applied Galvanic principles (application of electricity to biological organisms) in successfully alleviating the symptoms of "several cases of insanity", and with "complete success". Today, electroconvulsive therapy is used as a treatment option for severely depressed pregnant mothers (as it is the least harmful for the developing fetus) and people suffering treatment-resistant major depressive disorder. It is found to be effective for half of those who receive treatment while the other half may relapse within 12 months.
The modern application of electricity to the human body for medical diagnostics and treatments is practiced under the term electrophysiology. This includes the monitoring of the electric activity of the heart, muscles, and even the brain, respectively termed electrocardiography, electromyography, and electrocorticography. | 7 | Physical Chemistry |
Alkene ligands lose much of their unsaturated character upon complexation. Most famously, the alkene ligand undergoes migratory insertion, wherein it is attacked intramolecularly by alkyl and hydride ligands to form new alkyl complexes. Cationic alkene complexes are susceptible to attack by nucleophiles. | 0 | Organic Chemistry |
Methanosarcina acetivorans is a versatile methane producing microbe which is found in such diverse environments as oil wells, trash dumps, deep-sea hydrothermal vents, and oxygen-depleted sediments beneath kelp beds. Only M. acetivorans and microbes in the genus Methanosarcina use all three known metabolic pathways for methanogenesis. Methanosarcinides, including M. acetivorans, are also the only archaea capable of forming multicellular colonies, and even show cellular differentiation. The genome of M. acetivorans is one of the largest archaeal genomes ever sequenced. Furthermore, one strain of M. acetivorans, M. a. C2A, has been identified to possess an F-type ATPase (unusual for archaea, but common for bacteria, mitochondria and chloroplasts) along with an A-type ATPase. | 1 | Biochemistry |
Theoretical oxygen demand (ThOD) is the calculated amount of oxygen required to oxidize a compound to its final oxidation products. However, there are some differences between standard methods that can influence the results obtained: for example, some calculations assume that nitrogen released from organic compounds is generated as ammonia, whereas others allow for ammonia oxidation to nitrate. Therefore, in expressing results, the calculation assumptions should always be stated.
In order to determine the ThOD for glycine (CH(NH)COOH) using the following assumptions:
#In the first step, the organic carbon and nitrogen are converted to carbon dioxide (CO) and ammonia (NH), respectively.
#In the second and third steps, the ammonia is oxidized sequentially to nitrite and nitrate.
#The ThOD is the sum of the oxygen required for all three steps.
We can calculate by following steps:
#Write balanced reaction for the carbonaceous oxygen demand.(NH)COOH + 1.5O → NH + 2CO + HO
#Write balanced reactions for the nitrogenous oxygen demand. + 1.5O → HNO + HO + 0.5O → HNO + 2O → HNO + HO
#Determine the ThOD./mol glycine/mol glycine × 32 g/mol O / 75 g/mol glycine/g glycine
The theoretical oxygen demand represents the worst-case scenario. The actual oxygen demand of any compound depends on the biodegradability of the compound and the specific organism metabolizing the compound. The actual oxygen demand can be measured experimentally and is called the biochemical oxygen demand (BOD). | 2 | Environmental Chemistry |
Sensor-based sorting has been introduced by Wotruba and Harbeck as an umbrella term for all applications where particles are singularly detected by a sensor technique and then rejected by an amplified mechanical, hydraulic or pneumatic process. | 3 | Analytical Chemistry |
The term methylation in organic chemistry refers to the alkylation process used to describe the delivery of a group. | 0 | Organic Chemistry |
The amg unit for number density can be converted to the SI unit mol/m by the formula
where ≘ indicates correspondence, since the SI unit is of molar concentration and not number density.
The conversion factor (44.615...) is the Loschmidt number divided by the Avogadro constant.
The number density of an ideal gas at pressure p and temperature T can be calculated as
where T = 273.15 K, and p = 101.325 kPa (STP before 1982). | 7 | Physical Chemistry |
When oxygen binds to the iron complex, it causes the iron atom to move back toward the center of the plane of the porphyrin ring (see moving diagram). At the same time, the imidazole side-chain of the histidine residue interacting at the other pole of the iron is pulled toward the porphyrin ring. This interaction forces the plane of the ring sideways toward the outside of the tetramer, and also induces a strain in the protein helix containing the histidine as it moves nearer to the iron atom. This strain is transmitted to the remaining three monomers in the tetramer, where it induces a similar conformational change in the other heme sites such that binding of oxygen to these sites becomes easier.
As oxygen binds to one monomer of hemoglobin, the tetramers conformation shifts from the T (tense) state to the R (relaxed) state. This shift promotes the binding of oxygen to the remaining three monomers heme groups, thus saturating the hemoglobin molecule with oxygen.
In the tetrameric form of normal adult hemoglobin, the binding of oxygen is, thus, a cooperative process. The binding affinity of hemoglobin for oxygen is increased by the oxygen saturation of the molecule, with the first molecules of oxygen bound influencing the shape of the binding sites for the next ones, in a way favorable for binding. This positive cooperative binding is achieved through steric conformational changes of the hemoglobin protein complex as discussed above; i.e., when one subunit protein in hemoglobin becomes oxygenated, a conformational or structural change in the whole complex is initiated, causing the other subunits to gain an increased affinity for oxygen. As a consequence, the oxygen binding curve of hemoglobin is sigmoidal, or S-shaped, as opposed to the normal hyperbolic curve associated with noncooperative binding.
The dynamic mechanism of the cooperativity in hemoglobin and its relation with low-frequency resonance has been discussed. | 7 | Physical Chemistry |
Mevalonate synthesis begins with the beta-ketothiolase-catalyzed Claisen condensation of two molecules of acetyl-CoA to produce acetoacetyl CoA. The following reaction involves the joining of acetyl-CoA and acetoacetyl-CoA to form HMG-CoA, a process catalyzed by HMG-CoA synthase.
In the final step of mevalonate biosynthesis, HMG-CoA reductase, an NADPH-dependent oxidoreductase, catalyzes the conversion of HMG-CoA into mevalonate, which is the primary regulatory point in this pathway. Mevalonate serves as the precursor to isoprenoid groups that are incorporated into a wide variety of end-products, including cholesterol in humans. | 1 | Biochemistry |
* Ebrey, Walthall, Palais (2006). East Asia: A Cultural, Social, and Political History. Boston: Houghton Mifflin Company.
* Needham, Joseph (1986). Science and Civilization in China: Volume 4, Part 2; Needham, Joseph (1986). Science and Civilization in China: Volume 4, Part 3. | 8 | Metallurgy |
Photosensitizers can be placed into 3 generalized domains based on their molecular structure. These three domains are organometallic photosensitizers, organic photosensitizers, and nanomaterial photosensitizers. | 5 | Photochemistry |
The main subprocesses of sensor-based sorting are material conditioning, material presentation, detection, data processing and separation.
* Material conditioning includes all operations which prepare the particles for being detected by the sensor. All optical sensors need clean material to be able to detect optical characteristics. Conditioning includes screening and cleaning of the feed material.
* The aim of the material presentation is the isolation of the particles by creating a single particle layer with the densest surface cover possible without particles touching each other and enough distance to each other allowing for a selective detection and rejection of each single particle.
There are two types of sensor-based sorters: the chute type and the belt type. For both types the first step in acceleration is spreading out the particles by a vibrating feeder followed by either a fast belt or a chute. On the belt type the sensor usually detects the particles horizontally while they pass it on the belt. For the chute type the material detection is usually done vertically while the material passes the sensor in a free fall. The data processing is done in real time by a computer. The computer transfers the result of the data processing to an ultra fast ejection unit which, depending on the sorting decision, ejects a particle or lets it pass. | 3 | Analytical Chemistry |
(a) Cloning: RM systems can be cloned into plasmids and selected because of the resistance provided by the methylation enzyme. Once the plasmid begins to replicate, the methylation enzyme will be produced and methylate the plasmid DNA, protecting it from a specific restriction enzyme.
(b) Restriction fragment length polymorphisms: Restriction enzymes are also used to analyse the composition of DNA in regard to presence or absence of mutations that affect the REase cleavage specificity. When wild-type and mutants are analysed by digestion with different REases, the gel-electrophoretic products vary in length, largely because mutant genes will not be cleaved in a similar pattern as wild-type for presence of mutations that render the REases non-specific to the mutant sequence. | 1 | Biochemistry |
Mechanical stimulation to spines on the arm can cause Amphiura filiformis to bioluminesce in the blue range. The species has been found to possess a luciferase compound. The luciferase has been isolated to clusters of photocytes that exist at the tip off the arms and around the spines. What are believed to be photocytes based on evidence have been found around the spine nerve plexus, mucus cells, and what are believed to be pigment cells. It has been found that luminescence is controlled by the animal's nervous system. Acetylcholine is able to stimulate the cells through nicotinic receptors. | 1 | Biochemistry |
Unlike simple dehydration in plants and animals, lichens may experience a complete loss of body water in dry periods. Lichens are capable of surviving extremely low levels of water content (poikilohydric). They quickly absorb water when it becomes available again, becoming soft and fleshy.
In tests, lichen survived and showed remarkable results on the adaptation capacity of photosynthetic activity within the simulation time of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the German Aerospace Center (DLR).
The European Space Agency has discovered that lichens can survive unprotected in space. In an experiment led by Leopoldo Sancho from the Complutense University of Madrid, two species of lichen—Rhizocarpon geographicum and Rusavskia elegans—were sealed in a capsule and launched on a Russian Soyuz rocket 31 May 2005. Once in orbit, the capsules were opened and the lichens were directly exposed to the vacuum of space with its widely fluctuating temperatures and cosmic radiation. After 15 days, the lichens were brought back to earth and were found to be unchanged in their ability to photosynthesize. | 2 | Environmental Chemistry |
The "inner" bremsstrahlung (also known as "internal bremsstrahlung") arises from the creation of the electron and its loss of energy (due to the strong electric field in the region of the nucleus undergoing decay) as it leaves the nucleus. Such radiation is a feature of beta decay in nuclei, but it is occasionally (less commonly) seen in the beta decay of free neutrons to protons, where it is created as the beta electron leaves the proton.
In electron and positron emission by beta decay the photon's energy comes from the electron-nucleon pair, with the spectrum of the bremsstrahlung decreasing continuously with increasing energy of the beta particle. In electron capture, the energy comes at the expense of the neutrino, and the spectrum is greatest at about one third of the normal neutrino energy, decreasing to zero electromagnetic energy at normal neutrino energy. Note that in the case of electron capture, bremsstrahlung is emitted even though no charged particle is emitted. Instead, the bremsstrahlung radiation may be thought of as being created as the captured electron is accelerated toward being absorbed. Such radiation may be at frequencies that are the same as soft gamma radiation, but it exhibits none of the sharp spectral lines of gamma decay, and thus is not technically gamma radiation.
The internal process is to be contrasted with the "outer" bremsstrahlung due to the impingement on the nucleus of electrons coming from the outside (i.e., emitted by another nucleus), as discussed above. | 7 | Physical Chemistry |
Glycolysis is a metabolic pathway that takes place in the cytosol of cells in all living organisms. Glycolysis can be literally translated as "sugar splitting", and occurs regardless of oxygen's presence or absence. In aerobic conditions, the process converts one molecule of glucose into two molecules of pyruvate (pyruvic acid), generating energy in the form of two net molecules of ATP. Four molecules of ATP per glucose are actually produced, but two are consumed as part of the preparatory phase. The initial phosphorylation of glucose is required to increase the reactivity (decrease its stability) in order for the molecule to be cleaved into two pyruvate molecules by the enzyme aldolase. During the pay-off phase of glycolysis, four phosphate groups are transferred to four ADP by substrate-level phosphorylation to make four ATP, and two NADH are produced when the pyruvate is oxidized. The overall reaction can be expressed this way:
:Glucose + 2 NAD + 2 P + 2 ADP → 2 pyruvate + 2 H + 2 NADH + 2 ATP + 2 H + 2 HO + energy
Starting with glucose, 1 ATP is used to donate a phosphate to glucose to produce glucose 6-phosphate. Glycogen can be converted into glucose 6-phosphate as well with the help of glycogen phosphorylase. During energy metabolism, glucose 6-phosphate becomes fructose 6-phosphate. An additional ATP is used to phosphorylate fructose 6-phosphate into fructose 1,6-bisphosphate by the help of phosphofructokinase. Fructose 1,6-biphosphate then splits into two phosphorylated molecules with three carbon chains which later degrades into pyruvate. | 1 | Biochemistry |
In commerce, the term "polysulfide" usually refers to a class of polymers with alternating chains of several sulfur atoms and hydrocarbons. They have the formula . In this formula n indicates the number of sulfur atoms (or "rank"). Polysulfide polymers can be synthesized by condensation polymerization reactions between organic dihalides and alkali metal salts of polysulfide anions:
Dihalides used in this condensation polymerization are dichloroalkanes (such as 1,2-dichloroethane, bis-(2-chloroethyl)formal (), and 1,3-dichloropropane). The polymers are called thiokols. In some cases, polysulfide polymers can be formed by ring-opening polymerization reactions.
Polysulfide polymers are also prepared by the addition of polysulfanes to alkenes. An idealized equation is:
In reality, homogeneous samples of are difficult to prepare.
Polysulfide polymers are insoluble in water, oils, and many other organic solvents. Because of their solvent resistance, these materials find use as sealants to fill the joints in pavement, automotive window glass, and aircraft structures.
Polymers containing one or two sulfur atoms separated by hydrocarbon sequences are usually not classified polysulfides, e.g. poly(p-phenylene) sulfide . | 8 | Metallurgy |
In Bertrand's persistent carbenes, the unsaturated carbon is bonded to a phosphorus and a silicon. However, these compounds seem to exhibit some alkynic properties, and when published the exact carbenic nature of these red oils was in debate. | 0 | Organic Chemistry |
Andrée Marquet studied engineering at the École nationale supérieure de chimie de Paris, then defended a thesis prepared at the Collège de France under the direction of Jean Jacques (1961), followed by a post-doctoral internship at the ETH in Zurich with Professor Duilio Arigoni. After a career at the CNRS, she was appointed professor at the Pierre-et-Marie-Curie University (1978) and founded the organic biological chemistry laboratory there. She contributed, with a few others, to the development of this interface sub-discipline at the national level, which was still in its infancy, and created at UPMC adapted teaching courses where chemists and biochemists could meet.
In addition to her work as a teacher-researcher, she has held various positions of general interest.
Between 1984 and 1986, she chaired the organic chemistry division of the Société chimique de France, and from 1987 to 1991, the Société Franco-japonaise de chimie fine et thérapeutique. She chaired section 20 of the CNRS National Committee (1991-1995) and was a member of the CNRS Scientific Council from 1992 to 1997. In 1998, she became Scientific Director of the Chemistry Department at the Research Department of the MENRT. Between 1999 and 2003, she was a member of the Board of Directors of the Palais de la Découverte, and between 2007 and 2008, she was a member of the Board of Directors of the MENRT.
2011, member of the Ethics Committee of the CNRS. In 2002, she founded the "Chemistry and Society" Commission, within the Fondation de la Maison de la Chimie, of which she remains president until 2011. This commission seeks to analyse the origin of the misunderstanding that has developed between chemistry and society, and to contribute to the search for solutions by organising actions resolutely directed towards the general public. | 0 | Organic Chemistry |
Although the classification of tumor suppressor genes into these categories is helpful to the scientific community, the potential role of many genes cannot be reliably identified as the functions of many genes are rather ill-defined. In some contexts, genes exhibit discrete caretaker function while in other situations gatekeeper characteristics are recognized. An example of one such gene is p53. Patients with Li-Fraumeni syndrome, for example, have mutations in the p53 gene that suggest caretaker function. p53 has an identified role, however, in regulating the cell cycle as well, which is an essential gatekeeper function. | 1 | Biochemistry |
The techniques observed in all of them are quite similar. Basically they used the thermic alteration or firesetting (Mohen 1992, Craddock 1995, Eiroa et al. 1996, Timberlake 2003). This consists of applying fire to the rock and then pouring water over it: the rapid changes of temperature will cause cracks within the rocks that can be totally broken with the help of mauls and picks. Then the useful masses were selected, crushed and transported to the production centre that could be in the surrounding area (Mitterberg) or far away (Rudna Glava).
The mines were exploited in extremely efficient and clever ways, according to the technology available (Jovanovic 1980, Craddock 1995, Timberlake 2003). The entire convenient mineral was collected and the abandoned shafts carefully refilled with gangue and rocks (Mohen 1992; 85). For example, at Mount Gabriel, it was estimated that they extracted the astonishing number of of rock, gangue and ore. The usable amount of copper was 162.85 tonnes and the final smelting finished metal was 146.56 tonnes (Jackson 1980; 24). The entire process was thoroughly described in 1744 by Lewis Morris, Crown Mineral Agent for Cardiganshire, and, incidentally, antiquarian.
The tools employed are mainly presented in Lewis' observations, but other ones have been recovered in archaeological context:
*Stone tools: The most frequent find are the stone hammers, normally made of hard rocks accessible to the mine, beach or river pebbles. There is no standardization of these mauls but is common a system of hafting, usually a groove carved in the middle for where a rope was tied to the handle, like the twisted hazel recovered in Copa Hill.
* Antler and bone tools: Picks and scrapes made of bone and antlers have been found in the majority of the mines.
* Wood: Evidence of wooden tools are more infrequent. Nevertheless in places like Ai Bunar or Mount Gabriel were recovered shovels and wedges. A rudimentary system of stairs or scaffoldings can be supposed (Mohen 1992).
* Metal: The use of any metallic tool is rather strange and extraordinary. It seems that the copper was not used for the miners' tools. However copper chisels and discarded axes could be utilized as wedges.
* Other evidence: The presence of coal and charcoal, crucial for the firing (fire-setting) and furnace (fuel), is habitual. Leather sacks (at Ai Bunar) and shoulder baskets (at Copa Hill) were used to transport the crushed mineral. | 8 | Metallurgy |
The light attenuation coefficient – often shortened to “light attenuation” – describes the decrease in solar irradiance with depth. To calculate this coefficient, light energy is measured at a series of depths from the surface to the depth of 1% illumination. Then, the exponential decline in light is calculated using Beer’s Law with the equation:
where k is the light attenuation coefficient, I is the intensity of light at depth z, and I is the intensity of light at the ocean surface.
Which translates to:
This measurement can be done for specific colors of light or more broadly for all visible light. The light attenuation coefficient of photosynthetically active radiation (PAR) refers to the decrease in all visible light (400-700 nm) with depth. Light attenuation can be measured as the decrease in downwelling light (Kd) or the decrease in scalar light (Ko) with depth. Light attenuation is most useful as a measure of the total underwater light energy available to plants, such as phytoplankton and submerged aquatic vegetation. | 3 | Analytical Chemistry |
Transcription is the process by which the information contained in a section of DNA is replicated in the form of a newly assembled piece of messenger RNA (mRNA). Enzymes facilitating the process include RNA polymerase and transcription factors. In eukaryotic cells the primary transcript is pre-mRNA. Pre-mRNA must be processed for translation to proceed. Processing includes the addition of a 5' cap and a poly-A tail to the pre-mRNA chain, followed by splicing. Alternative splicing occurs when appropriate, increasing the diversity of the proteins that any single mRNA can produce. The product of the entire transcription process (that began with the production of the pre-mRNA chain) is a mature mRNA chain. | 1 | Biochemistry |
*Quantum yields of reaction (and to a lesser extent, absorption cross sections) are usually temperature and environment-dependent to some extent, and the photostationary state may therefore depend slightly on temperature and solvent as well as on the excitation.
*If thermodynamic interconversion of A and B can take place on a similar timescale to the photochemical reaction, it can complicate experimental measurements. This phenomenon can be important, for example in photochromatic eyeglasses. | 5 | Photochemistry |
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