text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Single-cell genomics is heavily dependent on increasing the copies of DNA found in the cell so there is enough to be sequenced. This has led to the development of strategies for whole genome amplification (WGA). Currently WGA strategies can be grouped into three categories:
* Controlled priming and PCR Amplification: Adapter-Linker PCR WGA
* Random priming and PCR Amplification: DOP-PCR, MALBAC
* Random priming and isothermal amplification: MDA
The Adapter Linker PCR WGA is reported in many comparative studies to be best performing for diploid single cell mutation analysis, thanks to its very low Allelic Dropout effect, and for copy number variation profiling due to its low noise, both with aCGH and with NGS low Pass Sequencing. This method is only applicable to human cells, both fixed and unfixed.
One widely adopted WGA techniques is called degenerate oligonucleotide–primed polymerase chain reaction (DOP-PCR). This method uses the well established DNA amplification method PCR to try and amplify the entire genome using a large set of primers. Although simple, this method has been shown to have very low genome coverage. An improvement on DOP-PCR is Multiple displacement amplification (MDA), which uses random primers and a high fidelity enzyme, usually Φ29 DNA polymerase, to accomplish the amplification of larger fragments and greater genome coverage than DOP-PCR. Despite these improvement MDA still has a sequence dependent bias (certain parts of the genome are amplified more than others because of their sequence). The method shown to largely avoid the bias seen in DOP-PCR and MDA is Multiple Annealing and Looping–Based Amplification Cycles (MALBAC). Bias in this system is reduced by only copying off the original DNA strand instead of making copies of copies. The main draw backs to using MALBA, is it has reduced accuracy compared to DOP-PCR and MDA due to the enzyme used to copy the DNA. Once amplified using any of the above techniques, the DNA can be sequenced using Sanger or next-generation sequencing (NGS). | 1 | Biochemistry |
In the presence of lithium or aluminum amide bases, epoxides may open to give the corresponding allylic alcohols. Removal of a proton adjacent to the epoxide, elimination, and neutralization of the resulting alkoxide lead to synthetically useful allylic alcohol products. In reactions of chiral, non-racemic epoxides, the configuration of the allylic alcohol product matches that of the epoxide substrate at the carbon whose C–O bond does not break (the starred carbon below). Besides β-elimination some other reactions are possible, as metalation of the epoxide ring can take place competitively. Vinylogous eliminations are possible when the epoxide substrate is substituted with vinyl or dienyl groups. Unconstrained systems tend to form trans double bonds, as significant non-bonding interactions are avoided in the transition state for the formation of trans products (see equation (2) below). The strongly basic conditions required for most isomerizations of this type represent the reaction's primary disadvantage. | 0 | Organic Chemistry |
Glutamatergic means "related to glutamate". A glutamatergic agent (or drug) is a chemical that directly modulates the excitatory amino acid (glutamate/aspartate) system in the body or brain. Examples include excitatory amino acid receptor agonists, excitatory amino acid receptor antagonists, and excitatory amino acid reuptake inhibitors. | 1 | Biochemistry |
As previously mentioned 1,3BPG is a metabolic intermediate in the glycolytic pathway. It is created by the exergonic oxidation of the aldehyde in G3P. The result of this oxidation is the conversion of the aldehyde group into a carboxylic acid group which drives the formation of an acyl phosphate bond. This is incidentally the only step in the glycolytic pathway in which NAD is converted into NADH. The formation reaction of 1,3BPG requires the presence of an enzyme called glyceraldehyde-3-phosphate dehydrogenase.
The high-energy acyl phosphate bond of 1,3BPG is important in respiration as it assists in the formation of ATP. The molecule of ATP created during the following reaction is the first molecule produced during respiration. The reaction occurs as follows;
:1,3-bisphosphoglycerate + ADP ⇌ 3-phosphoglycerate + ATP
The transfer of an inorganic phosphate from the carboxyl group on 1,3BPG to ADP to form ATP is reversible due to a low ΔG. This is as a result of one acyl phosphate bond being cleaved whilst another is created. This reaction is not naturally spontaneous and requires the presence of a catalyst. This role is performed by the enzyme phosphoglycerate kinase. During the reaction phosphoglycerate kinase undergoes a substrate induced conformational change similar to another metabolic enzyme called hexokinase.
Because two molecules of glyceraldehyde-3-phosphate are formed during glycolysis from one molecule of glucose, 1,3BPG can be said to be responsible for two of the ten molecules of ATP produced during the entire process. Glycolysis also uses two molecules of ATP in its initial stages as a committed and irreversible step. For this reason glycolysis is not reversible and has a net produce of 2 molecules of ATP and two of NADH. The two molecules of NADH themselves go on to produce approximately 3 molecules of ATP each. | 5 | Photochemistry |
In 1916, Irving Langmuir presented his model for the adsorption of species onto simple surfaces. Langmuir was awarded the Nobel Prize in 1932 for his work concerning surface chemistry. He hypothesized that a given surface has a certain number of equivalent sites to which a species can “stick”, either by physisorption or chemisorption. His theory began when he postulated that gaseous molecules do not rebound elastically from a surface, but are held by it in a similar way to groups of molecules in solid bodies.
Langmuir published two papers that confirmed the assumption that adsorbed films do not exceed one molecule in thickness. The first experiment involved observing electron emission from heated filaments in gases. The second, a more direct evidence, examined and measured the films of liquid onto an adsorbent surface layer. He also noted that generally the attractive strength between the surface and the first layer of adsorbed substance is much greater than the strength between the first and second layer. However, there are instances where the subsequent layers may condense given the right combination of temperature and pressure. | 7 | Physical Chemistry |
Application of the [4+4] photocycloaddition is scarce because of competition with the [[2+2 Photocycloaddition|[2+2] cycloaddition]]. However, when accessible, this method can be used to build 8-membered ring with complex stereocenters and structures in one step, as is seen in proposed syntheses for Taxol and molecules of the fusicoccin family. Additionally, while this reaction first forms fused rings, subsequent cleavages can afford macrocycles.
In this partial synthesis of the BC rings of Taxol, the framework buildup utilized an intramolecule [4+4] photocycloaddition of a relatively linear and simple 2-pyridone derivative, folding it into the desired fused rings with correct stereochemistry at C3, C8, and C15 (compare with Taxol on the right) and two double bonds on the B ring ready to accept trans-addition. Consequent lactam-ring opening and functionalization were expected to give Taxol.
Similarly, molecules of the fusicoccin family, featuring 5-8-5 ring systems, could be constructed rapidly using this reaction. Although the high stereoselectivity of this reaction to form trans-isomers made it unsuitable for the specific target molecules, the general ease to create the four tertiary chiral centers is still noteworthy.
Use of [4+4] photocycloaddition need not be limited to the creation of 8-membered rings. By linking up a network of rings and then breaking the shared bonds, a single macrocycle with built-in stereocenters could be achieved. | 5 | Photochemistry |
Another technique that has been gaining ground for single molecule experiments is the use of optical tweezers for applying mechanical forces on molecules. A strongly focused laser beam has the ability to catch and hold particles (of dielectric material) in a size range from nanometers to micrometers. The trapping action of optical tweezers results from the dipole or optical gradient force on the dielectric sphere. The technique of using a focused laser beam as an atom trap was first applied in 1984 at Bell laboratories. Until then experiments had been carried out using oppositely directed lasers as a means to trap particles. Later experiments, at the same project at Bell laboratories and others since, showed damage-free manipulation on cells using an infrared laser. Thus, the ground was made for biological experiments with optical trapping.
Each technique has its own advantages and disadvantages. For example, AFM cantilevers, can measure angstrom-scale, millisecond events and forces larger than 10 pN. While glass microfibers cannot achieve such fine spatial and temporal resolution, they can measure piconewton forces. Optical tweezers allow the measurement of piconewton forces and nanometer displacements which is an ideal range for many biological experiments. Magnetic tweezers can measure femtonewton forces, and additionally they can also be used to apply torsion. AFS devices allow the statistical analysis of the mechanical properties of biological systems by applying picoNewton forces to hundreds of individual particles in parallel, with sub-millisecond response time. | 7 | Physical Chemistry |
Once mRNA is purified, an oligo-dT primer (a short sequence of deoxy-thymidine nucleotides) is bound to the poly-A tail of the RNA. The primer is required to initiate DNA synthesis by the enzyme reverse transcriptase. This results in the creation of RNA-DNA hybrids where a single strand of complementary DNA is bound to a strand of mRNA. To remove the mRNA, the RNAse H enzyme is used to cleave the backbone of the mRNA and generate free 3-OH groups, which is important for the replacement of mRNA with DNA. DNA polymerase I is then added, the cleaved RNA acts as a primer the DNA polymerase I can identify and initiate replacement of RNA nucleotides with those of DNA. This is provided by the sscDNA itself by coiling on itself at the 3 end, generating a hairpin loop. The polymerase extends the 3-OH end, and later the loop at 3 end is opened by the scissoring action of S nuclease. Restriction endonucleases and DNA ligase are then used to clone the sequences into bacterial plasmids.
The cloned bacteria are then selected, commonly through the use of antibiotic selection. Once selected, stocks of the bacteria are created which can later be grown and sequenced to compile the cDNA library. | 1 | Biochemistry |
Absorption of light and energy transfer (or conversion) involves colored molecules that can transfer electromagnetic energy, commonly in the form of a laser light source, to other molecules in another form of energy, such as thermal or electrical. These laser addressable colorants, also called near-infrared absorbers, are used in thermal energy conversion, photosensitisation of chemical reactions and the selective absorption of light. Applications areas include optical data storage, as organic photoconductors, as sensitisers in photomedicine, such as photodynamic therapy and photothermal therapy in the treatment of cancer, in photodiagnosis and phototheranostics, and in the photoinactivation of microbes, blood and insects. The absorption of natural sunlight by chromic materials/chromophores is exploited in solar cells for the production of electrical energy via solar cells, using both inorganic photovoltaics and organic materials (organic photovoltaics) and dye sensitized solar cells (DSSCs), and also in the production of useful chemicals via artificial photosynthesis. A developing area is the conversion of light into kinetic energy, often described under the generic term of lightdriven molecular machines. | 5 | Photochemistry |
Liquid chromatography is a method of physical separation in which the components of a liquid mixture are distributed between two immiscible phases, i.e., stationary and mobile. The practice of LC can be divided into five categories, i.e., adsorption chromatography, partition chromatography, ion-exchange chromatography, size-exclusion chromatography, and affinity chromatography. Among these, the most widely used variant is the reverse-phase (RP) mode of the partition chromatography technique, which makes use of a nonpolar (hydrophobic) stationary phase and a polar mobile phase. In common applications, the mobile phase is a mixture of water and other polar solvents (e.g., methanol, isopropanol, and acetonitrile), and the stationary matrix is prepared by attaching long-chain alkyl groups (e.g., n-octadecyl or C) to the external and internal surfaces of irregularly or spherically shaped 5 μm diameter porous silica particles.
In HPLC, typically 20 μl of the sample of interest are injected into the mobile phase stream delivered by a high pressure pump. The mobile phase containing the analytes permeates through the stationary phase bed in a definite direction. The components of the mixture are separated depending on their chemical affinity with the mobile and stationary phases. The separation occurs after repeated sorption and desorption steps occurring when the liquid interacts with the stationary bed. The liquid solvent (mobile phase) is delivered under high pressure (up to 400 bar or 5800 psi) into a packed column containing the stationary phase. The high pressure is necessary to achieve a constant flow rate for reproducible chromatography experiments. Depending on the partitioning between the mobile and stationary phases, the components of the sample will flow out of the column at different times. The column is the most important component of the LC system and is designed to withstand the high pressure of the liquid. Conventional LC columns are 100–300 mm long with outer diameter of 6.4 mm (1/4 inch) and internal diameter of 3.0–4.6 mm. For applications involving LC–MS, the length of chromatography columns can be shorter (30–50 mm) with 3–5 μm diameter packing particles. In addition to the conventional model, other LC columns are the narrow bore, microbore, microcapillary, and nano-LC models. These columns have smaller internal diameters, allow for a more efficient separation, and handle liquid flows under 1 ml/min (the conventional flow-rate). In order to improve separation efficiency and peak resolution, ultra performance liquid chromatography (UHPLC) can be used instead of HPLC. This LC variant uses columns packed with smaller silica particles (~1.7 μm diameter) and requires higher operating pressures in the range of 310000 to 775000 torr (6000 to 15000 psi, 400 to 1034 bar). | 3 | Analytical Chemistry |
Non-B DB is a database integrating annotations and analysis of non-B DNA-forming sequence motifs. The database provides alternative DNA structure predictions including Z-DNA motifs, quadruplex-forming motifs, inverted repeats, mirror repeats and direct repeats and their associated subsets of cruciforms, triplex and slipped structures, respectively. | 4 | Stereochemistry |
Global sensitivity measures such as the Hill coefficient do not characterise the local behaviours of the s-shaped curves. Instead, these features are well captured by the response coefficient measure defined as:
In systems biology, such system responses are referred to as control coefficients. Specifically, the concentration control coefficients measure the response of concentrations to changes in a given input. In addition, within the framework of the more general biochemical control analysis, such responses can be described in terms of the individual local responses, called the elasticities. | 1 | Biochemistry |
Each one of the assumptions listed below adds to the complexity of the problems solution. As the density of a gas increases with rising pressure, the intermolecular forces play a more substantial role in gas behavior which results in the ideal gas law no longer providing "reasonable" results. At the upper end of the engine temperature ranges (e.g. combustor sections – 1300 K), the complex fuel particles absorb internal energy by means of rotations and vibrations that cause their specific heats to vary from those of diatomic molecules and noble gases. At more than double that temperature, electronic excitation and dissociation of the gas particles begins to occur causing the pressure to adjust to a greater number of particles (transition from gas to plasma). Finally, all of the thermodynamic processes were presumed to describe uniform gases whose velocities varied according to a fixed distribution. Using a non-equilibrium situation implies the flow field must be characterized in some manner to enable a solution. One of the first attempts to expand the boundaries of the ideal gas law was to include coverage for different thermodynamic processes by adjusting the equation to read pV = constant and then varying the n through different values such as the specific heat ratio, γ'.
Real gas effects include those adjustments made to account for a greater range of gas behavior:
*Compressibility effects (Z allowed to vary from 1.0)
*Variable heat capacity (specific heats vary with temperature)
*Van der Waals forces (related to compressibility, can substitute other equations of state)
*Non-equilibrium thermodynamic effects
*Issues with molecular dissociation and elementary reactions with variable composition.
For most applications, such a detailed analysis is excessive. Examples where real gas effects would have a significant impact would be on the Space Shuttle re-entry where extremely high temperatures and pressures were present or the gases produced during geological events as in the image of the 1990 eruption of Mount Redoubt. | 7 | Physical Chemistry |
The change and degradation in electron backscatter patterns (EBSPs) provide information about the diffracting volume. Pattern degradation (i.e., diffuse quality) can be used to assess the level of plasticity through the pattern/image quality (IQ), where IQ is calculated from the sum of the peaks detected when using the conventional Hough transform. Wilkinson first used the changes in high-order Kikuchi line positions to determine the elastic strains, albeit with low precision (0.3% to 1%); however, this approach cannot be used for characterising residual elastic strain in metals as the elastic strain at the yield point is usually around 0.2%. Measuring strain by tracking the change in the higher-order Kikuchi lines is practical when the strain is small, as the band position is sensitive to changes in lattice parameters. In the early 1990s, Troost et al. and Wilkinson et al. used pattern degradation and change in the zone axis position to measure the residual elastic strains and small lattice rotations with a 0.02% precision. | 7 | Physical Chemistry |
In physics, a bipolaron is a bound pair of two polarons. An electron in a material may cause a distortion in the underlying lattice. The combination of electron and distortion (which may also be understood as a cloud of phonons) is known as a polaron (in part because the interaction between electron and lattice is via a polarization). When two polarons are close together, they can lower their energy by sharing the same distortions, which leads to an effective attraction between the polarons. If the interaction is sufficiently large, then that attraction leads to a bound bipolaron. For strong attraction, bipolarons may be small. Small bipolarons have integer spin and thus share some of the properties of bosons. If many bipolarons form without coming too close, they might be able to form a Bose–Einstein condensate. This has led to a suggestion that bipolarons could be a possible mechanism for high-temperature superconductivity. For example, they can lead to a very direct interpretation of the isotope effect.
Recently, bipolarons were predicted theorethically in a Bose-Einstein condensate. Two polarons interchange sound waves and they attract to each other, forming a bound-state when the strength coupling between the single polarons and the condensate is strong in comparison with the interactions of the host gas. | 7 | Physical Chemistry |
Each phycobiliprotein has a specific absorption and fluorescence emission maximum in the visible range of light. Therefore, their presence and the particular arrangement within the phycobilisomes allow absorption and unidirectional transfer of light energy to chlorophyll a of the photosystem II. In this way, the cells take advantage of the available wavelengths of light (in the 500–650 nm range), which are inaccessible to chlorophyll, and utilize their energy for photosynthesis. This is particularly advantageous deeper in the water column, where light with longer wavelengths is less transmitted and therefore less available directly to chlorophyll.
The geometrical arrangement of a phycobilisome is very elegant in an antenna-like assembly. It results in 95% efficiency of energy transfer. | 5 | Photochemistry |
Adenosinergic means "working on adenosine".
An adenosinergic agent (or drug) is a chemical which functions to directly modulate the adenosine system in the body or brain. Examples include adenosine receptor agonists, adenosine receptor antagonists (such as caffeine), and adenosine reuptake inhibitors. | 1 | Biochemistry |
Bacteria depend on transcription-translation coupling for genome integrity, termination of transcription and control of mRNA stability. Consequently, artificial disruption of transcription-translation coupling impairs the fitness of bacteria. Without coupling, genome integrity is compromised as stalled transcription complexes interfere with DNA replication and induce DNA breaks. Lack of coupling produces premature transcription termination, likely due to increased binding of termination factor Rho. Degradation of prokaryotic mRNAs is accelerated by loss of coupled translation due to increased availability of target sites of RNase E. It has also been suggested that coupling of transcription with translation is an important mechanism of preventing formation of deleterious R-loops. While transcription-translation coupling is likely prevalent across prokaryotic organisms, not all species are dependent on it. Unlike Escherichia coli, in Bacillus subtilis transcription significantly outpaces translation, and coupling consequently does not occur. | 1 | Biochemistry |
A common error in thermocouple construction is related to cold junction compensation. If an error is made on the estimation of , an error will appear in the temperature measurement. For the simplest measurements, thermocouple wires are connected to copper far away from the hot or cold point whose temperature is measured; this reference junction is then assumed to be at room temperature, but that temperature can vary. Because of the nonlinearity in the thermocouple voltage curve, the errors in and are generally unequal values. Some thermocouples, such as Type B, have a relatively flat voltage curve near room temperature, meaning that a large uncertainty in a room-temperature translates to only a small error in .
Junctions should be made in a reliable manner, but there are many possible approaches to accomplish this.
For low temperatures, junctions can be brazed or soldered; however, it may be difficult to find a suitable flux and this may not be suitable at the sensing junction due to the solder's low melting point.
Reference and extension junctions are therefore usually made with screw terminal blocks.
For high temperatures, the most common approach is the spot weld or crimp using a durable material.
One common myth regarding thermocouples is that junctions must be made cleanly without involving a third metal, to avoid unwanted added EMFs.
This may result from another common misunderstanding that the voltage is generated at the junction. In fact, the junctions should in principle have uniform internal temperature; therefore, no voltage is generated at the junction. The voltage is generated in the thermal gradient, along the wire.
A thermocouple produces small signals, often microvolts in magnitude. Precise measurements of this signal require an amplifier with low input offset voltage and with care taken to avoid thermal EMFs from self-heating within the voltmeter itself. If the thermocouple wire has a high resistance for some reason (poor contact at junctions, or very thin wires used for fast thermal response), the measuring instrument should have high input impedance to prevent an offset in the measured voltage. A useful feature in thermocouple instrumentation will simultaneously measure resistance and detect faulty connections in the wiring or at thermocouple junctions. | 8 | Metallurgy |
Model systems consisting of a single phospholipid or a mixture have been studied by physical chemists. Cardiolipin is found mainly in mitochondrial membranes, and calcium ions play an important role in the respiratory processes mediated by the mitochondrion. The forces involved have been postulated to explain this process in terms of nucleation for agglomeration of smaller supramolecular entities or phase changes in the structure of the biomembranes. | 1 | Biochemistry |
Use of cyclooctanone is almost nonexistent drug chemistry with only 2 known exceptions:
#Blonanserin
#Iprindole | 0 | Organic Chemistry |
Vargulin, also called Cypridinid luciferin, Cypridina luciferin, or Vargula luciferin, is the luciferin found in the ostracod Cypridina hilgendorfii, also named Vargula hilgendorfii. These bottom dwelling ostracods emit a light stream into water when disturbed presumably to deter predation. Vargulin is also used by the midshipman fish, Porichthys. | 1 | Biochemistry |
When a protein folds, the titratable amino acids in the protein are transferred from a solution-like environment to an environment determined by the 3-dimensional structure of the protein. For example, in an unfolded protein, an aspartic acid typically is in an environment which exposes the titratable side chain to water. When the protein folds, the aspartic acid could find itself buried deep in the protein interior with no exposure to solvent.
Furthermore, in the folded protein, the aspartic acid will be closer to other titratable groups in the protein and will also interact with permanent charges (e.g. ions) and dipoles in the protein. All of these effects alter the pK value of the amino acid side chain, and pK calculation methods generally calculate the effect of the protein environment on the model pK value of an amino acid side chain.
Typically, the effects of the protein environment on the amino acid pK value are divided into pH-independent effects and pH-dependent effects. The pH-independent effects (desolvation, interactions with permanent charges and dipoles) are added to the model pK value to give the intrinsic pK value. The pH-dependent effects cannot be added in the same straightforward way and have to be accounted for using Boltzmann summation, Tanford–Roxby iterations or other methods.
The interplay of the intrinsic pK values of a system with the electrostatic interaction energies between titratable groups can produce quite spectacular effects such as non-Henderson–Hasselbalch titration curves and even back-titration effects.
The image on the right shows a theoretical system consisting of three acidic residues. One group is displaying a back-titration event (blue group). | 7 | Physical Chemistry |
De Silva et al. constructed an OR molecular logic gate using an aza-crown ether receptor and sodium and potassium ions as the inputs. Either of the two ions could bind to the crown ether, causing the PET to be quenched and the fluorescence to be turned on. Since either of the two ions (input “1”) could turn on the fluorescence (output “1”), the system resembled an OR logic gate. | 6 | Supramolecular Chemistry |
TaqMan probes consist of a fluorophore covalently attached to the 5’-end of the oligonucleotide probe and a quencher at the 3’-end. Several different fluorophores (e.g. 6-carboxyfluorescein, acronym: FAM, or tetrachlorofluorescein, acronym: TET) and quenchers (e.g. tetramethylrhodamine, acronym: TAMRA) are available. The quencher molecule quenches the fluorescence emitted by the fluorophore when excited by the cycler’s light source via Förster resonance energy transfer (FRET). As long as the fluorophore and the quencher are in proximity, quenching inhibits any fluorescence signals.
TaqMan probes are designed such that they anneal within a DNA region amplified by a specific set of primers. (Unlike the diagram, the probe binds to single stranded DNA.) TaqMan probes can be conjugated to a minor groove binder (MGB) moiety, dihydrocyclopyrroloindole tripeptide (DPI), in order to increase its binding affinity to the target sequence; MGB-conjugated probes have a higher melting temperature (T) due to increased stabilization of van der Waals forces. As the Taq polymerase extends the primer and synthesizes the nascent strand (from the single-stranded template), the 5 to 3 exonuclease activity of the Taq polymerase degrades the probe that has annealed to the template. Degradation of the probe releases the fluorophore from it and breaks the proximity to the quencher, thus relieving the quenching effect and allowing fluorescence of the fluorophore. Hence, fluorescence detected in the quantitative PCR thermal cycler is directly proportional to the fluorophore released and the amount of DNA template present in the PCR. | 1 | Biochemistry |
Both aerobic exercise and strength training (resistance exercise) attenuate myostatin expression, and myostatin inactivation potentiates the beneficial effects of endurance exercise on metabolism. | 1 | Biochemistry |
It is thought that early scleraxis-expressing progenitor cells lead to the eventual formation of tendon tissue and other muscle attachments. Scleraxis is involved in mesoderm formation and is expressed in the syndetome (a collection of embryonic tissue that develops into tendon and blood vessels) of developing somites (primitive segments or compartments of embryos). | 1 | Biochemistry |
The Owens/Wendt theory (after D. K. Owens and R. C. Wendt) divides the surface energy into two components: surface energy due to dispersive interactions and surface energy due to polar interactions. This theory is derived from the combination of Youngs relation, which relates the contact angle to the surface energies of the solid and liquid and to the interface tension, and Goods equation (after R. J. Good), which relates the interface tension to the polar and dispersive components of the surface energy. The resulting equation is
Note that this equation has the form of y = mx + b, with
As such, the polar and dispersive components of the solid's surface energy are determined by the slope and intercept of the resulting graph. Of course, the problem at this point is that in order to make that graph, knowing the surface energy of the probe liquid is not enough, as it is necessary to know specifically how it breaks down into its polar and dispersive components as well.
To do this, one can simply reverse the procedure by testing the probe liquid against a standard reference solid that is not capable of polar interactions, such as PTFE. If the contact angle of a sessile drop of the probe liquid is measured on a PTFE surface with
the principle equation reduces to
Since the total surface tension of the liquid is already known, this equation determines the dispersive component, and the difference between the total and dispersive components gives the polar component. | 7 | Physical Chemistry |
K2.3 is found in the central nervous system (CNS), muscle, liver, pituitary, prostate, kidney, pancreas and vascular endothelium tissues. K2.3 is most abundant in regions of the brain, but has also been found to be expressed in significant levels in many other peripheral tissues, particularly those rich in smooth muscle, including the rectum, corpus cavernosum, colon, small intestine and myometrium.
The expression level of KCNN3 is dependent on hormonal regulation, particularly by the sex hormone estrogen. Estrogen not only enhances transcription of the KCNN3 gene, but also affects the activity of K2.3 channels on the cell membrane. In GABAergic preoptic area neurons, estrogen enhanced the ability of α1 adrenergic receptors to inhibit K2.3 activity, increasing cell excitability. Links between hormonal regulation of sex organ function and K2.3 expression have been established. The expression of K2.3 in the corpus cavernosum in patients undergoing estrogen treatment as part of gender reassignment surgery was found to be increased up to 5-fold. The influence of estrogen on K2.3 has also been established in the hypothalamus, uterine and skeletal muscle. | 1 | Biochemistry |
A light-induced fluorescence transient (LIFT) is a device to remotely measure chlorophyll fluorescence in plants in a fast and non-destructive way. By using a series of excitation light pulses, LIFT combines chlorophyll fluorescence data with spectral and RGB information to provide insights into various photosynthetic traits and vegetation indices. LIFT combines the pump-probe method with the principle of laser-induced fluorescence. | 5 | Photochemistry |
RNA polymerase 1 (also known as Pol I) is, in higher eukaryotes, the polymerase that only transcribes ribosomal RNA (but not 5S rRNA, which is synthesized by RNA polymerase III), a type of RNA that accounts for over 50% of the total RNA synthesized in a cell. | 1 | Biochemistry |
Poolman was born in 1959 as the first son of Jelto Poolman and Neeltje Prinsse. In 1983 he married Heleen Stevenson (1959), with whom he has four children. | 0 | Organic Chemistry |
Fluo-4 is used to measure calcium (Ca) concentrations inside living cells, and is often used for high-throughput screening of receptor ligands and calcium permeable ion channels.
The green-fluorescent calcium indicator, Fluo-4, is an improved version of the calcium indicator, Fluo-3. It is commonly used as the non-fluorescent acetoxymethyl ester (Fluo-4 AM) which is cleaved inside the cell to give the free, fluorescent Fluo-4. It loads faster, is brighter at equivalent concentrations and is well-excited by the 488 nm line of the argon-ion laser which is often used in biological research laboratories. Fluo-4 and its cell-permeable AM ester are available from a few commercial vendors. | 1 | Biochemistry |
Of the hundreds of facet arrangements that have been used, the most famous is probably the round brilliant cut, used for diamond and many colored gemstones. This first early version of what would become the modern Brilliant Cut is said to have been devised by an Italian named Peruzzi, sometime in the late 17th century. Later on, the first angles for an "ideal" cut diamond were calculated by Marcel Tolkowsky in 1919. Slight modifications have been made since then, but angles for "ideal" cut diamonds are still similar to Tolkowskys formula. Round brilliants cut before the advent of "ideal" angles are often referred to as "Early round brilliant cut" or "Old European brilliant cut" and are considered poorly cut by todays standards, though there is still interest in them from collectors. Other historic diamond cuts include the "Old Mine Cut" which is similar to early versions of the round brilliant, but has a rectangular outline, and the "Rose Cut" which is a simple cut consisting of a flat, polished back, and varying numbers of angled facets on the crown, producing a faceted dome. Sometimes a 58th facet, called a culet is cut on the bottom of the stone to help prevent chipping of the pavilion point. Earlier brilliant cuts often have very large culets, while modern brilliant cut diamonds generally lack the culet facet, or it may be present in minute size. | 3 | Analytical Chemistry |
The logging system is often simply a personal computer. In initial signal processing, the signal often needs to be amplified and converted for use with the control system. The lines of communication between monochromator, detector output, and computer should be optimized to ensure the desired metrics and features are being used. The commercially available software included with spectroradiometric systems often come stored with useful reference functions for further calculation of measurements, such as CIE color matching functions and the V curve. | 7 | Physical Chemistry |
As described above, contact angle is used to characterize surface wettability. A droplet of solvent, typically water for hydrophobic surfaces, is placed perpendicular to the surface. The droplet is imaged and the angle between the solid/liquid and liquid/vapor interfaces is measured. Samples are considered to be superhydrophobic when the contact angle is greater than 150 degrees. Refer to section on Wenzel and Cassie-Baxter models for information on the different behaviors of droplets on topographical surfaces. For drops to roll effectively on a superhydrophobic surface, Contact angle hysteresis is an important consideration. Low levels of contact angle hysteresis will enhance the self-cleaning effect of a superhydrophobic surface. | 7 | Physical Chemistry |
Many polymers are attacked by UV radiation at vulnerable points in their chain structures. Thus, polypropylene suffers severe cracking in sunlight unless anti-oxidants are added. The point of attack occurs at the tertiary carbon atom present in every repeat unit, causing oxidation and finally chain breakage. Polyethylene is also susceptible to UV degradation, especially those variants that are branched polymers such as low-density polyethylene. The branch points are tertiary carbon atoms, so polymer degradation starts there and results in chain cleavage, and embrittlement. In the example shown at left, carbonyl groups were readily detected by IR spectroscopy from a cast thin film. The product was a road cone that had cracked in service, and many similar cones also failed because an anti-UV additive had not been used. | 7 | Physical Chemistry |
Drospirenone (DRSP) is used by itself as a progestogen-only birth control pill, in combination with the estrogens ethinylestradiol (EE) or estetrol (E4), with or without supplemental folic acid (vitamin B), as a combined birth control pill, and in combination with the estrogen estradiol (E2) for use in menopausal hormone therapy. A birth control pill with low-dose ethinylestradiol is also indicated for the treatment of moderate acne, premenstrual syndrome (PMS), premenstrual dysphoric disorder (PMDD), and dysmenorrhea (painful menstruation). For use in menopausal hormone therapy, E2/DRSP is specifically approved to treat moderate to severe vasomotor symptoms (hot flashes), vaginal atrophy, and postmenopausal osteoporosis. The drospirenone component in this formulation is included specifically to prevent estrogen-induced endometrial hyperplasia. Drospirenone has also been used in combination with an estrogen as a component of hormone therapy for transgender women.
Studies have found that EE/DRSP is superior to placebo in reducing premenstrual emotional and physical symptoms while also improving quality of life. E2/DRSP has been found to increase bone mineral density and to reduce the occurrence of bone fractures in postmenopausal women. In addition, E2/DRSP has a favorable influence on cholesterol and triglyceride levels and decreases blood pressure in women with high blood pressure. Due to its antimineralocorticoid activity, drospirenone opposes estrogen-induced salt and water retention and maintains or slightly reduces body weight. | 4 | Stereochemistry |
In chemistry, a Haworth projection is a common way of writing a structural formula to represent the cyclic structure of monosaccharides with a simple three-dimensional perspective. Haworth projection approximate the shapes of the actual molecules better for furanoses—which are in reality nearly planar—than for pyranoses which exist in solution in the chair conformation. Organic chemistry and especially biochemistry are the areas of chemistry that use the Haworth projection the most.
The Haworth projection was named after the British chemist Sir Norman Haworth.
A Haworth projection has the following characteristics:
* Carbon is the implicit type of atom. In the example on the right, the atoms numbered from 1 to 6 are all carbon atoms. Carbon 1 is known as the anomeric carbon.
* Hydrogen atoms on carbon are implicit. In the example, atoms 1 to 6 have extra hydrogen atoms not depicted.
* A thicker line indicates atoms that are closer to the observer. In the example on the right, atoms 2 and 3 (and their corresponding OH groups) are the closest to the observer. Atoms 1 and 4 are farther from the observer. Atom 5 and the other atoms are the farthest.
*The groups below the plane of the ring in Haworth projections correspond to those on the right-hand side of a Fischer projection. This rule does not apply to the groups on the two ring carbons bonded to the endocyclic oxygen atom. combined with hydrogen. | 4 | Stereochemistry |
Silver nitrate is a salt of silver that is sometimes used by dentists as a caustic material to cauterize mouth sores, and has in the past been used by physicians for treating wounds. It may be an appropriate material to salt the earth after burying a monster that has been killed with silver bullets. | 3 | Analytical Chemistry |
The split gene theory is a theory of the origin of introns, long non-coding sequences in eukaryotic genes between the exons. The theory holds that the randomness of primordial DNA sequences would only permit small (< 600bp) open reading frames (ORFs), and that important intron structures and regulatory sequences are derived from stop codons. In this introns-first framework, the spliceosomal machinery and the nucleus evolved due to the necessity to join these ORFs (now "exons") into larger proteins, and that intronless bacterial genes are less ancestral than the split eukaryotic genes. The theory originated with Periannan Senapathy.
The theory provides solutions to key questions concerning the split gene architecture, including split eukaryotic genes, exons, introns, splice junctions, and branch points, based on the origin of split genes from random genetic sequences. It also provides possible solutions to the origin of the spliceosomal machinery, the nuclear boundary and the eukaryotic cell.
This theory led to the Shapiro–Senapathy algorithm, which provides the methodology for detecting the splice sites, exons and split genes in eukaryotic DNA, and which is the main method for detecting splice site mutations in genes that cause hundreds of diseases.
Split gene theory requires a separate origin of all eukaryotic species. It also requires that the simpler prokaryotes evolved from eukaryotes. This completely contradicts the scientific consensus about the formation of eukaryotic cells by endosymbiosis of bacteria. In 1994, Senapathy wrote a book about this aspect of his theory - The Independent Birth of Organisms. It proposed that all eukaryotic genomes were formed separately in a primordial pool. Dutch biologist Gert Korthoff criticized the theory by posing various problems that cannot be explained by a theory of independent origins. He pointed out that various eukaryotes need nurturing and called this the boot problem, in that even the initial eukaryote needed parental care. Korthoff notes that a large fraction of eukaryotes are parasites. Senapathys theory would require a coincidence to explain their existence. Senapathys theory cannot explain the strong evidence for common descent (homology, universal genetic code, embryology, fossil record.) | 1 | Biochemistry |
Many chloroplast DNAs contain two inverted repeats, which separate a long single copy section (LSC) from a short single copy section (SSC).
While a given pair of inverted repeats are rarely completely identical, they are always very similar to each other, apparently resulting from concerted evolution.
The inverted repeats vary wildly in length, ranging from 4,000 to 25,000 base pairs long each and containing as few as four or as many as over 150 genes. Inverted repeats in plants tend to be at the upper end of this range, each being 20,000–25,000 base pairs long.
The inverted repeat regions are highly conserved among land plants, and accumulate few mutations. Similar inverted repeats exist in the genomes of cyanobacteria and the other two chloroplast lineages (glaucophyta and rhodophyceae), suggesting that they predate the chloroplast, though some chloroplast DNAs have since lost or flipped the inverted repeats (making them direct repeats). It is possible that the inverted repeats help stabilize the rest of the chloroplast genome, as chloroplast DNAs which have lost some of the inverted repeat segments tend to get rearranged more. | 5 | Photochemistry |
Walter McCrone was born in Wilmington, Delaware, but he grew up mostly in New York State. His father was a civil engineer in charge of one of the first DuPont plants to manufacture cellophane. McCrone received a bachelors degree in chemistry from Cornell University in 1938 and a Ph.D. in organic chemistry from the same institution in 1942. From 1942 to 1944 he was a post-doctoral researcher at Cornell. In 1944, McCrone published a detailed study on The Microscopic Examination of High Explosives and Boosters'.
In 1944 McCrone began to work as a microscopist and materials scientist at the Armour Research Foundation, now the Illinois Institute of Technology (IIT) Research Institute. He was also a professor at IIT and served as assistant chairman of its Chemistry and Chemical Engineering Department. In 1948, McCrone and IIT electron microscopist Charles F. Tufts organized the first of the meetings that are now the International Microscopy Conference (Inter/Micro). Among the speakers at the first conference was Nobel laureate Frits Zernike.
In 1956 McCrone left IIT and founded an analytical consulting firm, McCrone Associates, which is now located in Westmont, Illinois. In 1960, he established the McCrone Research Institute, a nonprofit organization for teaching and research in microscopy and crystallography, based in Chicago. In 1979 he retired from McCrone Associates in order to dedicate himself to teaching full time. The proceeds from his work as a consulting chemist allowed McCrone to endow the Émile M. Chamot Professorship of Chemistry at Cornell, named in honor of McCrone's university mentor. According to chemist and forensic scientist John A. Reffner, "during McCrone’s life, he taught microscopy to more students than anyone else in history."
For more than thirty years McCrone edited and published The Microscope, an international quarterly journal of microscopy that had been established in 1937 by the British microscopist Arthur L. E. Barron. McCrone also wrote more than 400 technical articles along with sixteen books or chapters. He is credited with expanding the usefulness of the optical microscopy to chemists, who had previously regarded it as primarily a tool for biologists. One of his publications was the Particle Atlas, first published in 1967, which provided an exhaustive description of small particles and how to identify them with the aid of a microscope. That work became widely used in forensic laboratories. The Particle Atlas, which was written in collaboration with other staff members of McCrone Associates, appeared in a six-volume second edition in 1973. In 1992 it became available in CD-ROM.
Walter McCrone served on the board of directors and as president of the Ada S. McKinley Community Services, a nonprofit social services agency in Chicago. He died of congestive heart failure at his home in Chicago, at the age of 86. From 1957 until his death in 2002, he was married to Lucy B. McCrone, née Beman. The two had met while she was working as an analytical chemist for the management consulting firm Arthur D. Little, in Cambridge, Massachusetts. After their marriage, Lucy McCrone worked as a chemical microanalyst for McCrone Associates in Chicago and was co-founder and director of the McCrone Research Institute until 1984. | 3 | Analytical Chemistry |
A homocycle or homocyclic ring is a ring in which all atoms are of the same chemical element. A heterocycle or heterocyclic ring is a ring containing atoms of at least two different elements, i.e. a non-homocyclic ring. A carbocycle or carbocyclic ring is a homocyclic ring in which all of the atoms are carbon. An important class of carbocycles are alicyclic rings, and an important subclass of these are cycloalkanes. | 4 | Stereochemistry |
In scattering theory, a scattering channel is a quantum state of the colliding system before or after the collision (). The Hilbert space spanned by the states before collision (in states) is equal to the space spanned by the states after collision (out states) which are both Fock spaces if there is a mass gap. This is the reason why the S matrix which maps the in states onto the out states must be unitary. The scattering channel are also called scattering asymptotes. The Møller operators are mapping the scattering channels onto the corresponding states which are solution of the Schrödinger equation taking the interaction Hamiltonian into account. The Møller operators are isometric. | 7 | Physical Chemistry |
One goal of structural genomics is to identify novel protein folds. Experimental methods of protein structure determination require proteins that express and/or crystallize well, which may inherently bias the kinds of proteins folds that this experimental data elucidate. A genomic, modeling-based approach such as ab initio modeling may be better able to identify novel protein folds than the experimental approaches because they are not limited by experimental constraints.
Protein function depends on 3-D structure and these 3-D structures are more highly conserved than sequences. Thus, the high-throughput structure determination methods of structural genomics have the potential to inform our understanding of protein functions. This also has potential implications for drug discovery and protein engineering. Furthermore, every protein that is added to the structural database increases the likelihood that the database will include homologous sequences of other unknown proteins. The Protein Structure Initiative (PSI) is a multifaceted effort funded by the National Institutes of Health with various academic and industrial partners that aims to increase knowledge of protein structure using a structural genomics approach and to improve structure-determination methodology. | 1 | Biochemistry |
Conventional radioisotope thermoelectric generators (RTGs) used to power spacecraft use a radioactive material whose radiation is used to heat a block of material and then converted to electricity using a thermocouple. Thermocouples are very inefficient and their replacement with TPV could offer significant improvements in efficiency and thus require a smaller and lighter RTG for any given mission. Experimental systems developed by Emcore (a multi-junction solar cell provider), Creare, Oak Ridge and NASA's Glenn Research Center demonstrated 15 to 20% efficiency. A similar concept was developed by the University of Houston which reached 30% efficiency, a 3 to 4-fold improvement over existing systems. | 7 | Physical Chemistry |
With deep WGS data of cfDNA from a carcinoma of unknown primary patient with very low ctDNA concentration quantified, they trained a machine learning model using bootstrapping. The results of RNA-sequencing on PBMC runs for the 5 different patients are recorded and the average of 3 of these individuals expression levels is used as a reference for gene expression. The genes are clustered into 10 clusters based on reference gene expression to increase the resolution at the core promoters. Then, genes used as a background value for PFE calculation are removed. Next, all the fragments in extended TSS regions, a region that has the center as TSS regions center and the length of 2000 base pairs, are pooled. The PFE and NDR scores are calculated for the fragments pooled. Further normalization of these scores is done based on their 95th percentile.
Using these two features, they bootstrapped, used in a weighted fashion, 600 expression prediction models developed for WGS data. Among those models, there are 200 univariable standalone NDR, 200 univariable standalone PFE, and 200 NDR-PFE integrated models. | 1 | Biochemistry |
There are several ways to mathematically define quasicrystalline patterns. One definition, the "cut and project" construction, is based on the work of Harald Bohr (mathematician brother of Niels Bohr). The concept of an almost periodic function (also called a quasiperiodic function) was studied by Bohr, including work of Bohl and Escanglon.
He introduced the notion of a superspace. Bohr showed that quasiperiodic functions arise as restrictions of high-dimensional periodic functions to an irrational slice (an intersection with one or more hyperplanes), and discussed their Fourier point spectrum. These functions are not exactly periodic, but they are arbitrarily close in some sense, as well as being a projection of an exactly periodic function.
In order that the quasicrystal itself be aperiodic, this slice must avoid any lattice plane of the higher-dimensional lattice. De Bruijn showed that Penrose tilings can be viewed as two-dimensional slices of five-dimensional hypercubic structures; similarly, icosahedral quasicrystals in three dimensions are projected from a six-dimensional hypercubic lattice, as first described by Peter Kramer and Roberto Neri in 1984. Equivalently, the Fourier transform of such a quasicrystal is nonzero only at a dense set of points spanned by integer multiples of a finite set of basis vectors, which are the projections of the primitive reciprocal lattice vectors of the higher-dimensional lattice.
Classical theory of crystals reduces crystals to point lattices where each point is the center of mass of one of the identical units of the crystal. The structure of crystals can be analyzed by defining an associated group. Quasicrystals, on the other hand, are composed of more than one type of unit, so, instead of lattices, quasilattices must be used. Instead of groups, groupoids, the mathematical generalization of groups in category theory, is the appropriate tool for studying quasicrystals.
Using mathematics for construction and analysis of quasicrystal structures is a difficult task for most experimentalists. Computer modeling, based on the existing theories of quasicrystals, however, greatly facilitated this task. Advanced programs have been developed allowing one to construct, visualize and analyze quasicrystal structures and their diffraction patterns. The aperiodic nature of quasicrystals can also make theoretical studies of physical properties, such as electronic structure, difficult due to the inapplicability of Bloch's theorem. However, spectra of quasicrystals can still be computed with error control.
Study of quasicrystals may shed light on the most basic notions related to the quantum critical point observed in heavy fermion metals. Experimental measurements on an Au–Al–Yb quasicrystal have revealed a quantum critical point defining the divergence of the magnetic susceptibility as temperature tends to zero. It is suggested that the electronic system of some quasicrystals is located at a quantum critical point without tuning, while quasicrystals exhibit the typical scaling behaviour of their thermodynamic properties and belong to the well-known family of heavy fermion metals. | 3 | Analytical Chemistry |
In adults, the primary metabolic pathway for paracetamol is glucuronidation. This yields a relatively non-toxic metabolite, which is excreted into bile and passed out of the body. A small amount of the drug is metabolized via the cytochrome P-450 pathway (to be specific, CYP3A4 and CYP2E1) into NAPQI, which is extremely toxic to liver tissue, as well as being a strong biochemical oxidizer. In an average adult, only a small amount (approximately 10% of a therapeutic paracetamol dose) of NAPQI is produced, which is inactivated by conjugation with glutathione (GSH). The amount of NAPQI produced differs in certain populations.
The minimum dosage at which paracetamol causes toxicity usually is 7.5 to 10g in the average person. The lethal dose is usually between 10 g and 15 g. Concurrent alcohol intake lowers these thresholds significantly. Chronic alcoholics may be more susceptible to adverse effects due to reduced glutathione levels. Other populations may experience effects at lower or higher dosages depending on differences in P-450 enzyme activity and other factors which affect the amount of NAPQI produced. In general, however, the primary concern is accidental or intentional paracetamol overdose.
When a toxic dose of paracetamol is ingested, the normal glucuronide pathway is saturated and large amounts of NAPQI are produced. Liver reserves of glutathione are depleted by conjugation with this excess NAPQI. The mechanism by which toxicity results is complex, but is believed to involve reaction between unconjugated NAPQI and critical proteins as well as increased susceptibility to oxidative stress caused by the depletion of glutathione. | 1 | Biochemistry |
Fraser-Reid was born in Coleyville, Jamaica to William, an elementary school principal, and Laura, a teacher. He had five older siblings. Laura died when Fraser-Reid was only nine months old. He attended Excelsior High School and Clarendon College before moving to Canada to earn BSc (1959) and MSc (1961) at Queen's University in Ontario He went to University of Alberta to earn a PhD in 1964 under the supervision of Raymond Lemieux. He went to Imperial College London to do postdoctoral work for Nobel Laureate Sir Derek Barton from 1964 to 1966. | 0 | Organic Chemistry |
Nucleic acid analogues are compounds which are analogous (structurally similar) to naturally occurring RNA and DNA, used in medicine and in molecular biology research.
Nucleic acids are chains of nucleotides, which are composed of three parts: a phosphate backbone, a pentose sugar, either ribose or deoxyribose, and one of four nucleobases. An analogue may have any of these altered. Typically the analogue nucleobases confer, among other things, different base pairing and base stacking properties. Examples include universal bases, which can pair with all four canonical bases, and phosphate-sugar backbone analogues such as PNA, which affect the properties of the chain (PNA can even form a triple helix).
Nucleic acid analogues are also called xeno nucleic acids and represent one of the main pillars of xenobiology, the design of new-to-nature forms of life based on alternative biochemistries.
Artificial nucleic acids include peptide nucleic acids (PNA), Morpholino and locked nucleic acids (LNA), as well as glycol nucleic acids (GNA), threose nucleic acids (TNA) and hexitol nucleic acids (HNA). Each of these is distinguished from naturally occurring DNA or RNA by changes to the backbone of the molecule. However, the polyelectrolyte theory of the gene proposes that a genetic molecule require a charged backbone to function.
In May 2014, researchers announced that they had successfully introduced two new artificial nucleotides into bacterial DNA, and by including individual artificial nucleotides in the culture media, were able to passage the bacteria 24 times; they did not create mRNA or proteins able to use the artificial nucleotides. The artificial nucleotides featured 2 fused aromatic rings. | 1 | Biochemistry |
The simplest method to measure the electrical resistance of a sample of some material is to place it in an electrical circuit in series with a current source I and measure the resulting voltage V across the sample. The resistance of the sample is given by Ohms law as R = V / I'. If the voltage is zero, this means that the resistance is zero.
Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in MRI machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a lifetime of at least 100,000 years. Theoretical estimates for the lifetime of a persistent current can exceed the estimated lifetime of the universe, depending on the wire geometry and the temperature. In practice, currents injected in superconducting coils have persisted for more than 27 years (as of August 2022) in superconducting [http://www.astro.oma.be/en/world-record-in-the-underground-laboratory-of-membach/ gravimeters]. In such instruments, the measurement is based on the monitoring of the levitation of a superconducting niobium sphere with a mass of 4 grams.
In a normal conductor, an electric current may be visualized as a fluid of electrons moving across a heavy ionic lattice. The electrons are constantly colliding with the ions in the lattice, and during each collision some of the energy carried by the current is absorbed by the lattice and converted into heat, which is essentially the vibrational kinetic energy of the lattice ions. As a result, the energy carried by the current is constantly being dissipated. This is the phenomenon of electrical resistance and Joule heating.
The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons. Instead, it consists of bound pairs of electrons known as Cooper pairs. This pairing is caused by an attractive force between electrons from the exchange of phonons. This pairing is very weak, and small thermal vibrations can fracture the bond. Due to quantum mechanics, the energy spectrum of this Cooper pair fluid possesses an energy gap, meaning there is a minimum amount of energy ΔE that must be supplied in order to excite the fluid. Therefore, if ΔE is larger than the thermal energy of the lattice, given by kT, where k is the Boltzmann constant and T is the temperature, the fluid will not be scattered by the lattice. The Cooper pair fluid is thus a superfluid, meaning it can flow without energy dissipation.
In the class of superconductors known as type II superconductors, including all known high-temperature superconductors, an extremely low but non-zero resistivity appears at temperatures not too far below the nominal superconducting transition when an electric current is applied in conjunction with a strong magnetic field, which may be caused by the electric current. This is due to the motion of magnetic vortices in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is minuscule compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. However, as the temperature decreases far enough below the nominal superconducting transition, these vortices can become frozen into a disordered but stationary phase known as a "vortex glass". Below this vortex glass transition temperature, the resistance of the material becomes truly zero. | 7 | Physical Chemistry |
MiRNA expression profiles are altered in psychiatric conditions, including depression, anxiety, and PTSD. It has been demonstrated that miR-324-5p expression is altered in the brains of suicide victims with depression and in the amygdala, the fear center of the brain, in PTSD. MiRNAs are an underexplored potential biomarker and target for treatment for psychiatric disease. | 1 | Biochemistry |
For an Authority Having Jurisdiction, combustibility is defined by the local code. In the National Building Code of Canada, it is defined as follows:
*Combustible: A material that fails to meet acceptance criteria of [https://web.archive.org/web/20061003193651/http://www.ulc.ca/About_ulc/Publication_Notice_Detail.asp?PN_ID=31 CAN/ULC-S114, Standard Method of Test for Determination of Non-combustibility in Building Materials].
*Non-combustible: means that a material meets the acceptance criteria of [https://web.archive.org/web/20061003193651/http://www.ulc.ca/About_ulc/Publication_Notice_Detail.asp?PN_ID=31 CAN4-S114, "Standard Method of Test for Determination of Non-Combustibility in Building Materials]".
BS 476-4:1970 defines a test for combustibility in which a technician heats three specimens of a material in a furnace. Combustibile materials are those for which any of the three specimens either:
* Makes the temperature reading from either of two thermocouples rise by 50 degrees Celsius or more above the initial furnace temperature
* Flame continuously for 10 seconds or more inside the furnace
Otherwise, the material is classified as non-combustible. | 7 | Physical Chemistry |
Jiří Drahoš (born 20 February 1949; ) is a Czech physical chemist and politician who has been the Senator of Prague 4 since October 2018. Previously, Drahoš served as President of the Czech Academy of Sciences from 2009 to 2017, and was a candidate in the 2018 Czech presidential election.
Born in Český Těšín and raised in nearby Jablunkov, Drahoš studied physical chemistry at the University of Chemistry and Technology in Prague, and joined the Institute of Chemical Process Fundamentals of the Czechoslovak Academy of Sciences in 1973, which he later led from 1995 to 2003. In 2009, he was elected President of the Czech Academy of Sciences. His term as head of the academy ended on 24 March 2017.
In March 2017, Drahoš announced his candidacy for President of the Czech Republic in the 2018 election. He ran on a moderate centrist platform, and is generally pro-European and supportive of NATO and Atlanticism. Drahoš lost the second round of the presidential election to his opponent President Miloš Zeman with 48.6% of the vote, but vowed to remain in public life. In October 2018, he stood for the Czech Senate in the Prague 4 district, winning the election outright in the first round with 52.65% of the vote. | 7 | Physical Chemistry |
The calcium salt of atorvastatin is marketed under the trade name Lipitor for the lowering of blood cholesterol. The first enantioselective medicinal chemistry route to atorvastatin relied on a diastereoselective aldol reaction with a chiral ester to set one of the two alcohol stereocenters. In the commercial route to atorvastatin, this stereocenter is carried forward from the readily available food additive isoascorbic acid. | 4 | Stereochemistry |
The usage of the term canonical sequence to refer to a promoter is often problematic, and can lead to misunderstandings about promoter sequences. Canonical implies perfect, in some sense.
In the case of a transcription factor binding site, there may be a single sequence that binds the protein most strongly under specified cellular conditions. This might be called canonical.
However, natural selection may favor less energetic binding as a way of regulating transcriptional output. In this case, we may call the most common sequence in a population the wild-type sequence. It may not even be the most advantageous sequence to have under prevailing conditions.
Recent evidence also indicates that several genes (including the proto-oncogene c-myc) have G-quadruplex motifs as potential regulatory signals. | 1 | Biochemistry |
PPA is known to have a rigid and brittle backbone which limits its flexibility and usage in some applications. However, it can be easily tuned by adding additives rendering it a soft material. The mechanical properties of cyclic PPA films drop cast using different solvents have recently been investigated. The study showed the polymer to possess a large elastic modulus of 2.5-3 GPa which was also previously reported in another study, in addition to tensile strength values ranging between 25 and 35 MPa and a failure strain of 1-1.5% that is highly dependent of the solvent used. | 7 | Physical Chemistry |
The ocean's chemistry is changing due to the uptake of anthropogenic carbon dioxide (CO). Ocean pH, carbonate ion concentrations ([CO]), and calcium carbonate mineral saturation states (Ω) have been declining as a result of the uptake of approximately 30% of the anthropogenic carbon dioxide emissions over the past 270 years (since around 1750). This process, commonly referred to as "ocean acidification", is making it harder for marine calcifiers to build a shell or skeletal structure, endangering coral reefs and the broader marine ecosystems.
Ocean acidification has been called the "evil twin of global warming" and "the other CO problem". Increased ocean temperatures and oxygen loss act concurrently with ocean acidification and constitute the "deadly trio" of climate change pressures on the marine environment. The impacts of this will be most severe for coral reefs and other shelled marine organisms, as well as those populations that depend on the ecosystem services they provide. | 9 | Geochemistry |
Metal substrates for use in SAMs can be produced through physical vapor deposition techniques, electrodeposition or electroless deposition. Thiol or selenium SAMs produced by adsorption from solution are typically made by immersing a substrate into a dilute solution of alkane thiol in ethanol, though many different solvents can be used besides use of pure liquids. While SAMs are often allowed to form over 12 to 72 hours at room temperature, SAMs of alkanethiolates form within minutes. Special attention is essential in some cases, such as that of dithiol SAMs to avoid problems due to oxidation or photoinduced processes, which can affect terminal groups and lead to disorder and multilayer formation. In this case appropriate choice of solvents, their degassing by inert gasses and preparation in the absence of light is crucial and allows formation of "standing up" SAMs with free –SH groups. Self-assembled monolayers can also be adsorbed from the vapor phase. In some cases when obtaining an ordered assembly is difficult or when different density phases need to be obtained substitutional self-assembly is used. Here one first forms the SAM of a given type of molecules, which give rise to ordered assembly and then a second assembly phase is performed (e.g. by immersion into a different solution). This method has also been used to give information on relative binding strengths of SAMs with different head groups and more generally on self-assembly characteristics. | 6 | Supramolecular Chemistry |
Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode proteins produce messenger RNA (mRNA). Other segments of DNA are transcribed into RNA molecules called non-coding RNAs (ncRNAs).
Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementary language. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript.
In virology, the term transcription may also be used when referring to mRNA synthesis from an RNA molecule (i.e., equivalent to RNA replication). For instance, the genome of a negative-sense single-stranded RNA (ssRNA -) virus may be a template for a positive-sense single-stranded RNA (ssRNA +). This is because the positive-sense strand contains the sequence information needed to translate the viral proteins needed for viral replication. This process is catalyzed by a viral RNA replicase. | 1 | Biochemistry |
Analytical technique is a method used to determine a chemical or physical property of a chemical substance, chemical element, or mixture. There is a wide variety of techniques used for analysis, from simple weighing to advanced techniques using highly specialized instrumentation. | 3 | Analytical Chemistry |
When there is excess glucose, coenzyme A is used in the cytosol for synthesis of fatty acids. This process is implemented by regulation of acetyl-CoA carboxylase, which catalyzes the committed step in fatty acid synthesis. Insulin stimulates acetyl-CoA carboxylase, while epinephrine and glucagon inhibit its activity.
During cell starvation, coenzyme A is synthesized and transports fatty acids in the cytosol to the mitochondria. Here, acetyl-CoA is generated for oxidation and energy production. In the citric acid cycle, coenzyme A works as an allosteric regulator in the stimulation of the enzyme pyruvate dehydrogenase. | 1 | Biochemistry |
*EIF1 aka SUI1
*EIF1AD
*EIF1B
*EIF2A
*EIF2AK1
*EIF2AK3
*EIF2AK4
*EIF2AK1
*EIF2B2
*EIF2B3
*EIF2B4
*EIF2S2
*EIF3A
*EIF3B
*EIF3D formerly EIF3S4
*EIF3G
*EIF3I
*EIF3H
*EIF3J
*EIF3K
*EIF3L
*EIF3M
*EIF3S5
*EIF3S8
*EIF4A1
*EIF4A2
*EIF4A3
*EIF4E2
*EIF4G1
*EIF4G2
*EIF4G3
*EIF4H
*EIF5
*EIF5
*EIF5A
*EIF5AL1
*EIF5B
*EIF6
*TUFM Tu translational elongation factor mitochondrial | 1 | Biochemistry |
Arsenic is a ubiquitous naturally occurring chemical element, and the 20th most common element on Earth. Arsenic levels in the groundwater vary from around 0.5 parts per billion to 5000 parts per billion, depending on an area's geologic features, and possible presence on industrial waste. The highest groundwater arsenic levels have been recorded in Brazil, Cambodia, Afghanistan, Australia, and Bangladesh.
Arsenic is a ubiquitous element present in American drinking water. In the US, the U.S. Geological Survey estimates that the median groundwater concentration is 1 μg/L or less, although some groundwater aquifers, particularly in the western United States, can contain much higher levels. For example, median levels in Nevada were about 8 μg/L but levels of naturally occurring arsenic as high as 1000 μg/L have been measured in the United States in drinking water. Groundwater associated with volcanics in California contain As at concentrations ranging up to 48,000 μg/L, with As-bearing sulfide minerals as the main source. Geothermal waters on Dominica in the Lesser Antilles also contain concentrations of As >50 μg/L. In Wisconsin, As concentrations of water in sandstone and dolomite aquifers were as high as 100 μg/L. Oxidation of pyrite hosted by these formations was the likely source of the As. In the Piedmont of Pennsylvania and New Jersey, groundwater in Mesozoic age aquifers contains elevated levels of As—domestic well waters from Pennsylvania contained up to 65 μg/L, whereas in New Jersey the highest concentration measured recently was 215 μg/L.
Organic arsenic is less harmful than inorganic arsenic. Seafood is a common source of the less toxic organic arsenic in the form of arsenobetaine. Because of its high toxicity, arsenic is seldom used in the Western world, although in Asia it is still a popular pesticide. Arsenic is mainly encountered occupationally in the smelting of zinc and copper ores.
In the United States, Schoof et al. estimated an average adult intake of 3.2 μg/day, with a range of 1–20 μg/day. Estimates for children were similar. Food also contains many organic arsenic compounds. The key organic arsenic compounds that can be routinely found in food (depending on food type) include monomethylarsonic acid (MMAsV), dimethylarsinic acid (DMAsV), arsenobetaine, arsenocholine, arsenosugars, and arsenolipids. DMAsV or MMAsV can be found in various types of fin fish, crabs, and mollusks, but often at very low levels.
Arsenobetaine is the major form of arsenic in marine animals, and is considered nontoxic. Arsenocholine, which is mainly found in shrimp, is chemically similar to arsenobetaine, and is considered to be "essentially nontoxic". Although arsenobetaine is little studied, available information indicates it is not mutagenic, immunotoxic, or embryotoxic. Arsenosugars and arsenolipids have recently been identified. Exposure to these compounds and toxicological implications are currently being studied. Arsenosugars are detected mainly in seaweed but are also found to a lesser extent in marine mollusks. Studies addressing arsenosugar toxicity, however, have largely been limited to in vitro studies, which show that arsenosugars are significantly less toxic than both inorganic arsenic and trivalent methylated arsenic metabolites.
It has been found that rice is particularly susceptible to accumulation of arsenic from soil. Rice grown in the United States has an average 260 ppb of arsenic, according to a study; but U.S. arsenic intake remains far below World Health Organization-recommended limits. China has set a standard for arsenic limits in food (150 ppb), as levels in rice exceed those in water.
The European Commission (2000) reports that levels of arsenic in air range 0–1 ng/m in remote areas, 0.2–1.5 ng/m in rural areas, 0.5–3 ng/m in urban areas, and up to about 50 ng/m in the vicinity of industrial sites. Based on these data, the European Commission (2000) estimated that in relation to food, cigarette smoking, water, and soil, air contributes less than 1% of total arsenic exposure. | 1 | Biochemistry |
In the Gattermann reaction, benzenediazonium chloride is warmed with copper powder and HCl or HBr to produce chlorobenzene and bromobenzene respectively. It is named after the German chemist Ludwig Gattermann. | 0 | Organic Chemistry |
A SPARROW model is a SPAtially-Referenced Regression on Watershed attributes, which helps integrate water quality data with landscape information. More specifically the USGS used this model to display long-term changes within watersheds to further explain in-stream water measurement in relation to upstream sources, water quality, and watershed properties. These models predict data for various spatial scales and integrate streamflow data with water quality at numerous locations across the US. A SPARROW model used by the USGS focused on the nutrients in the Nation's major rivers and estuaries; this model helped create a better understanding of where nutrients come from, where they are transported to while in the water bodies, and where they end up (reservoirs, other estuaries, etc.). | 9 | Geochemistry |
Light-emitting materials that can convert non-emissive triplet states into emissive singlet states are crucial in organic light-emitting diodes (OLEDs) as, statistically, 75% of the excited states formed in an OLED are triplet states. TTA materials are well suited to use in OLEDs due to their low operational voltage, small drop-off in efficiency when increasing brightness, and low cost. However, most TTA materials emit photons that are blue to deep blue, which limits their applications in OLEDs until the colour variety diversifies. | 7 | Physical Chemistry |
The Bunsen–Kirchhoff Award is a prize for "outstanding achievements" in the field of analytical spectroscopy. It has been awarded since 1990 by the German Working Group for Applied Spectroscopy, and is endowed with by PerkinElmer, Germany. The prize is named in honor of chemist Robert Bunsen and physicist Gustav Kirchhoff. | 3 | Analytical Chemistry |
Cefalexin can treat a number of bacterial infections including otitis media, streptococcal pharyngitis, bone and joint infections, pneumonia, cellulitis, and urinary tract infections. It may be used to prevent bacterial endocarditis. It can also be used for the prevention of recurrent urinary-tract infections.
Cefalexin does not treat methicillin-resistant Staphylococcus aureus infections.
Cefalexin is a useful alternative to penicillins in patients with penicillin intolerance. For example, penicillin is the treatment of choice for respiratory tract infections caused by Streptococcus, but cefalexin may be used as an alternative in penicillin-intolerant patients. Caution must be exercised when administering cephalosporin antibiotics to penicillin-sensitive patients, because cross-sensitivity with β-lactam antibiotics has been documented in up to 10% of patients with a documented penicillin allergy. | 4 | Stereochemistry |
A pure stoichiometric mixture may be obtained by water electrolysis, which uses an electric current to dissociate the water molecules:
: Electrolysis:
: Combustion:
William Nicholson was the first to decompose water in this manner in 1800. In theory, the input energy of a closed system always equals the output energy, as the first law of thermodynamics states. However, in practice no systems are perfectly closed, and the energy required to generate the oxyhydrogen always exceeds the energy released by combusting it, even at maximum practical efficiency, as the second law of thermodynamics implies (see Electrolysis of water#Efficiency). | 7 | Physical Chemistry |
Longifolene is the common (or trivial) chemical name of a naturally occurring, oily liquid hydrocarbon found primarily in the high-boiling fraction of certain pine resins. The name is derived from that of a pine species from which the compound was isolated,
Chemically, longifolene is a tricyclic sesquiterpene. This molecule is chiral, and the enantiomer commonly found in pines and other higher plants exhibits a positive optical rotation of +42.73°. The other enantiomer (optical rotation −42.73°) is found in small amounts in certain fungi and liverworts.
Longifolene is also one of two most abundant aroma constituents of lapsang souchong tea, because the tea is smoked over pinewood fires. | 0 | Organic Chemistry |
For an introduction to the theory of electron diffraction, see part 2 of Williams and Carter's Transmission Electron Microscopy text
While it is clear that precession reduces many of the dynamical diffraction effects that plague other forms of electron diffraction, the resulting patterns cannot be considered purely kinematical in general. There are models that attempt to introduce corrections to convert measured PED patterns into true kinematical patterns that can be used for more accurate direct methods calculations, with varying degrees of success. Here, the most basic corrections are discussed. In purely kinematical diffraction, the intensities of various reflections, , are related to the square of the amplitude of the structure factor, by the equation:
where g is the reciprocal space magnitude of the reflection in question and R is the radius of the Laue circle, usually taken to be equal to φ. While this correction accounts for the integration over the excitation error, it takes no account for the dynamical effects that are ever-present in electron diffraction. This has been accounted for using a two-beam correction following the form of the Blackman correction originally developed for powder x-ray diffraction. Combining this with the aforementioned Lorentz correction yields:
where , is the sample thickness, and is the wave-vector of the electron beam. is the Bessel function of zeroeth order.
This form seeks to correct for both geometric and dynamical effects, but is still only an approximation that often fails to significantly improve the kinematic quality of the diffraction pattern (sometimes even worsening it). More complete and accurate treatments of these theoretical correction factors have been shown to adjust measured intensities into better agreement with kinematical patterns. For details, see Chapter 4 of reference.
Only by considering the full dynamical model through multislice calculations can the diffraction patterns generated by PED be simulated. However, this requires the crystal potential to be known, and thus is most valuable in refining the crystal potentials suggested through direct methods approaches. The theory of precession electron diffraction is still an active area of research, and efforts to improve on the ability to correct measured intensities without a priori knowledge are ongoing. | 3 | Analytical Chemistry |
In his 50-year career, Ferrier published 180 papers, reviews and books, and gave 10 invited plenary lectures at international symposia. His reviews were of particular benefit to the chemical community but perhaps of most value was the book "Monosaccharide Chemistry, written with Dr Peter Collins in 1972 and majorly updated as "Monosaccharides: Their chemistry and their roles in natural products in 1995. | 0 | Organic Chemistry |
DSSCs degrade when exposed to light. In 2014 air infiltration of the commonly-used amorphous Spiro-MeOTAD hole-transport layer was identified as the primary cause of the degradation, rather than oxidation. The damage could be avoided by the addition of an appropriate barrier.
The barrier layer may include UV stabilizers and/or UV absorbing luminescent chromophores (which emit at longer wavelengths which may be reabsorbed by the dye) and antioxidants to protect and improve the efficiency of the cell. | 5 | Photochemistry |
There is a pressure difference between the outside air and the air inside the building caused by the difference in temperature between the outside air and the inside air. That pressure difference ( ΔP ) is the driving force for the stack effect and it can be calculated with the equations presented below. The equations apply only to buildings where air is both inside and outside the buildings. For buildings with one or two floors, h is the height of the building. For multi-floor, high-rise buildings, h is the distance from the openings at the neutral pressure level (NPL) of the building to either the topmost openings or the lowest openings. Reference explains how the NPL affects the stack effect in high-rise buildings.
For flue gas stacks and chimneys, where air is on the outside and combustion flue gases are on the inside, the equations will only provide an approximation and h is the height of the flue gas stack or chimney.
:SI units:
:U.S. customary units: | 7 | Physical Chemistry |
Iodic acid can be produced by oxidizing iodine with strong oxidizers such as nitric acid , chlorine , chloric acid or hydrogen peroxide , for example:
Iodic acid is also produced by the reaction of iodine monochloride with water: | 3 | Analytical Chemistry |
The Fischer–Tropsch process involves a series of chemical reactions that produce a variety of hydrocarbons, ideally having the formula (CH). The more useful reactions produce alkanes as follows:
: (2n + 1) H + n CO → CH + n HO
where n is typically 10–20. The formation of methane (n = 1) is unwanted. Most of the alkanes produced tend to be straight-chain, suitable as diesel fuel. In addition to alkane formation, competing reactions give small amounts of alkenes, as well as alcohols and other oxygenated hydrocarbons.
The reaction is a highly exothermic reaction due to a standard reaction enthalpy (ΔH) of −165 kJ/mol CO combined. | 0 | Organic Chemistry |
In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing groups (where R = alkyl, aryl, or just hydrogen). Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly soluble in organic solvents, but soluble in water and common alcohols.
Many commercially important compounds are phosphonates, including glyphosate (the active molecule of the herbicide Roundup), and ethephon, a widely used plant growth regulator. Bisphosphonates are popular drugs for treatment of osteoporosis.
In biochemistry and medicinal chemistry, phosphonate groups are used as stable bioisosteres for phosphate, such as in the antiviral nucleotide analog, Tenofovir, one of the cornerstones of anti-HIV therapy. And there is an indication that phosphonate derivatives are "promising ligands for nuclear medicine." | 0 | Organic Chemistry |
Before the discovery of msDNA in myxobacteria, a group of swarming, soil-dwelling bacteria, it was thought that the enzymes known as reverse transcriptases (RT) existed only in eukaryotes and viruses. The discovery led to an increase in research of the area. As a result, msDNA has been found to be widely distributed among bacteria, including various strains of Escherichia coli and pathogenic bacteria. Further research discovered similarities between HIV-encoded reverse transcriptase and an open reading frame (ORF) found in the msDNA coding region. Tests confirmed the presence of reverse transcriptase activity in crude lysates of retron-containing strains. Although an RNase H domain was tentatively identified in the retron ORF, it was later found that the RNase H activity required for msDNA synthesis is actually supplied by the host. | 1 | Biochemistry |
Near Eastern development of bronze technology spread across Central Asia by way of the Eurasian Steppes, and with it came the knowledge and technology for tin prospection and extraction. By 2000 to 1500 BC Uzbekistan, Afghanistan, and Tajikistan appear to have exploited their sources of tin, carrying the resources east and west along the Silk Road crossing Central Asia. This trade link likely followed an existing trade route of lapis lazuli, a highly prized semi-precious blue gemstone, and chlorite vessels decorated with turquoise from Central Asia that have been found as far west as Egypt and that date to the same period.
In China, early tin was extracted along the Yellow River in Erlitou and Shang times between 2500 and 1800 BC. By Han and later times, China imported its tin from what is today Yunnan province. This has remained China's main source of tin throughout history and into modern times.
It is unlikely that Southeast Asian tin from Indochina was widely traded around the world in ancient times as the area was only opened up to Indian, Muslim, and European traders around 800 AD.
Indo–Roman trade relations are well known from historical texts such as Plinys Natural History' (book VI, 26), and tin is mentioned as one of the resources being exported from Rome to South Arabia, Somaliland, and India. | 8 | Metallurgy |
Expose-R (R stands for its mounting on the Russian module Zvezda) was mounted by Russian cosmonauts extravehicular activity on 11 March 2009 and the exposure to outer space conditions continued for 682 days until 21 January 2011, when it was brought back to Earth by the last Discovery Shuttle flight STS-133 on 9 March 2011. EXPOSE-R was equipped with three trays housing eight experiments and 3 radiation dosimeters. Each tray was loaded with a variety of biological organisms including plant seeds and spores of bacteria, fungi and ferns that were exposed to the harsh space environment for about one and a half years. The ROSE (Response of Organisms to Space Environment) group of experiments are under the coordination of the German Aerospace Center (DLR) and has been composed of scientists from different European countries, from United States and from Japan. In its 8 experiments of biological and chemical content, more than 1200 individual samples were exposed to solar ultraviolet (UV) radiations, vacuum, cosmic rays or extreme temperature variations. In their different experiments, the involved scientists are studying the question of lifes origin on Earth and the results of their experiments are contributing to different aspects of the evolution and distribution of life in the Universe.
The EXPOSE-R experiments are:
* AMINO, study of solar ultraviolet (UV) effects on amino acids and other organic compounds placed in terrestrial orbit.
* ORGANICS, study of the evolution of organic matter placed in outer space.
* ENDO (ROSE-1), study the effects of radiation on endolithic microorganisms (growing within cracks and pore spaces in rocks).
* OSMO (ROSE-2), study of the exposition of osmophilic microorganisms to space environment.
* SPORES (ROSE-3), study of spores placed inside artificial meteorites.
* PHOTO (ROSE-4), study of solar radiation effects on the genetic material of spores.
* SUBTIL (ROSE-5), study of mutagen effect of space environment on bacterial spores (Bacillus subtilis).
* PUR (ROSE-8), study of space environment effect on T7 phage, its DNA and of polycristalline uracil.
* IMBP (Institute of Biomedical Problems), this included bacterial spores, fungal spores, plant seeds, and eggs of lower crustacean and cryptobiotic larvae. | 1 | Biochemistry |
Cyclic α,β-unsaturated ketones are the most commonly employed substrates for vicinal difunctionalization. They tend to be more reactive than acyclic analogues and undergo less direct addition than aldehydes. Amides and esters can be used to encourage conjugate addition in cases when direct addition may be competitive (as in the addition of organolithium compounds).
Because the addition step is highly sensitive to steric effects, β-substituents are likely to slow the reaction. Acetylenic and allenic substrates react to give products with some retained unsaturation. | 0 | Organic Chemistry |
DPPA undergoes pseudohalogen replacement of the azido group by treatment with nucleophilic reagents, such as ammonia and various amines.
This compound is used as a reagent for the synthesis of peptides by virtue of its reactions with carboxylic acids leading to either the urethane or the amide. The formation of the urethane is particularly valuable since it works with carboxylic acids which fail to undergo the Schmidt reaction, and is believed to involve transfer of the azido group to the carboxylic acid.
It is now suggested that this reaction proceeds through the intermediate mixed anhydride, resulting from attack by the nucleophilic carboxylate anion on the phosphorus atom, with expulsion of the azide ion. The latter then attacks the carbonyl carbon atom, to give the acyl azide and loss of the diphenylphosphate anion, known to be a good leaving group. Finally, the acyl azide reacts in the normal manner to give the urethane.
Studies show that DPPA reacts with amines giving the corresponding phosphoramidates; it therefore appears that formation of the amide similarly involves the intermediate anhydride, followed by nucleophilic substitution by the amine.
In the synthesis of NSAIDs, DPPA is able to rearrange a propanoyl group into an isopropanoic acid.
DPPA is also used to prepare an acyl azide for use in the Curtius reaction. | 0 | Organic Chemistry |
For different purposes, different combinations of spectral bands can be used. They are usually represented with red, green, and blue channels. Mapping of bands to colors depends on the purpose of the image and the personal preferences of the analysts. Thermal infrared is often omitted from consideration due to poor spatial resolution, except for special purposes.
* True-color uses only red, green, and blue channels, mapped to their respective colors. As a plain color photograph, it is good for analyzing man-made objects, and is easy to understand for beginner analysts.
* Green-red-infrared, where the blue channel is replaced with near infrared, is used for vegetation, which is highly reflective in near IR; it then shows as blue. This combination is often used to detect vegetation and camouflage.
* Blue-NIR-MIR, where the blue channel uses visible blue, green uses NIR (so vegetation stays green), and MIR is shown as red. Such images allow the water depth, vegetation coverage, soil moisture content, and the presence of fires to be seen, all in a single image.
Many other combinations are in use. NIR is often shown as red, causing vegetation-covered areas to appear red. | 7 | Physical Chemistry |
For a planet around another star, (the incident stellar flux on the planet) is not a readily measurable quantity. To find the equilibrium temperature of such a planet, it may be useful to approximate the host star's radiation as a blackbody as well, such that:
The luminosity () of the star, which can be measured from observations of the star's apparent brightness, can then be written as:
where the flux has been multiplied by the surface area of the star.
To find the incident stellar flux on the planet, , at some orbital distance from the star, , one can divide by the surface area of a sphere with radius :
Plugging this into the general equation for planetary equilibrium temperature gives:
If the luminosity of the star is known from photometric observations, the other remaining variables that must be determined are the Bond albedo and orbital distance of the planet. Bond albedos of exoplanets can be constrained by flux measurements of transiting exoplanets, and may in future be obtainable from direct imaging of exoplanets and a conversion from geometric albedo. Orbital properties of the planet such as the orbital distance can be measured through radial velocity and transit period measurements.
Alternatively, the planetary equilibrium may be written in terms of the temperature and radius of the star: | 7 | Physical Chemistry |
From the mathematical point of view the Lippmann–Schwinger equation in coordinate representation is an integral equation of Fredholm type. It can be solved by discretization. Since it is equivalent to the differential time-independent Schrödinger equation with appropriate boundary conditions, it can also be solved by numerical methods for differential equations. In the case of the spherically symmetric potential it is usually solved by partial wave analysis. For high energies and/or weak potential it can also be solved perturbatively by means of Born series. The method convenient also in the case of many-body physics, like in description of atomic, nuclear or molecular collisions is the method of R-matrix of Wigner and Eisenbud. Another class of methods is based on separable expansion of the potential or Green's operator like the method of continued fractions of Horáček and Sasakawa. Very important class of methods is based on variational principles, for example the Schwinger-Lanczos method combining the variational principle of Schwinger with Lanczos algorithm. | 7 | Physical Chemistry |
The final STQ-77/FET framework classifies temperament traits and their neurochemical biomarkers into 12 components: nine components regulating the formal functional aspects of behaviour (energetic, dynamic and orientational) each assessed in three domains (intellectual, physical and social-verbal); also three components related to emotionality (Neuroticism, Impulsivity and Satisfaction (Self-Confidence)) (see Figure)
The FET framework summarized existing literature showing the nine non-emotionality traits are regulated by the monoamines (MA) (noradrenalin, dopamine, serotonin), acetylcholine and neuropeptide systems, whereas the three emotionality-related traits emerge as a dysregulation of opioid receptors systems that have direct control over MA systems. Importantly, the FET model suggests that there is no one-to-one correspondence between the neurotransmitter systems underlying temperament traits (or mental disorders) but instead specific ensemble relationships between these systems emerge as temperament traits. The FET framework is based only on the strongest consensus points in the research studying the role of neurotransmitter in behavioural regulation and the components of temperament; it doesn't list more controversial links between these multiple systems.
Neurotransmitter systems: 5-HT: serotonin; DA: dopamine; NE: noradrenalin; ACh: acetylcholine; Glu: glutamate; OXY: oxytocin; VSP: vasopressin; NP: Neuropeptides; KOR, MOR, DOR: kappa-, mu- and delta-opioid receptors correspondingly; sANS - sympathetic autonomic nervous system; HPA - hypothalamic–pituitary–adrenal axis.
The FET points out that opioid receptor systems are involved not only in regulation of emotional dispositions but also amplify three non-emotionality aspects of behaviour (KOR for orientation, DOR for integration of actions and MOR of approval-maintenance of behaviour). This involvement was confirmed for MOR systems that bind endorphins: experiments show that MOR overstimulation influences hypothalamic serotonin and Brain-derived neurotrophic factor release and affecting endurance aspects of behaviour. The interplay within hormonal systems and its interaction with serotonin also appeared to be a factor is social emotions, such as shame and guilt | 1 | Biochemistry |
A Luggin capillary (also Luggin probe, Luggin tip, or Luggin-Haber capillary) is a small tube that is used in electrochemistry. The capillary defines a clear sensing point for the reference electrode near the working electrode. This is in contrast to the poorly defined, large reference electrode. | 7 | Physical Chemistry |
During the assay, a fraction of the free receptor is captured by the solid phase ligand and subsequently labeled with a fluorescent secondary molecule (Figure 1). The short contact time with the solid phase does not allow significant dissociation of the pre-formed complexes in the solution. Solution dissociation is thus “kinetically excluded” from contributing to the captured receptor and the resulting signal provides a measure of the free receptor in the solution.
Measuring the free receptor as a function of total ligand in a series of equilibrated solutions enables calculation of the equilibrium dissociation constant (K). Measuring the free receptor with several points before equilibrium enables measurement of the association rate constant (k). The off rate (k) can also be directly measured, however it is usually calculated from the measured K and measured k, (k = K * k).
Kinetic exclusion assays have been used to measure K’s in the nanomolar to femtomolar range. | 1 | Biochemistry |
Even when working with ordinary eukaryotic sequences such as the Yeast genome, it is often desired to be able to use alternative translation tables—namely for translation of the mitochondrial genes. Currently the following translation tables are defined by the NCBI Taxonomy Group for the translation of the sequences in GenBank:
# The standard code
# The vertebrate mitochondrial code
# The yeast mitochondrial code
# The mold, protozoan, and coelenterate mitochondrial code and the mycoplasma/spiroplasma code
# The invertebrate mitochondrial code
# The ciliate, dasycladacean and hexamita nuclear code
# The kinetoplast code
# <li value="9"> The echinoderm and flatworm mitochondrial code
# The euplotid nuclear code
# The bacterial, archaeal and plant plastid code
# The alternative yeast nuclear code
# The ascidian mitochondrial code
# The alternative flatworm mitochondrial code
# The Blepharisma nuclear code
# The chlorophycean mitochondrial code
# <li value="21"> The trematode mitochondrial code
# The Scenedesmus obliquus mitochondrial code
# The Thraustochytrium mitochondrial code
# The Pterobranchia mitochondrial code
# The candidate division SR1 and gracilibacteria code
# The Pachysolen tannophilus nuclear code
# The karyorelict nuclear code
# The Condylostoma nuclear code
# The Mesodinium nuclear code
# The peritrich nuclear code
# The Blastocrithidia nuclear code
# <li value="33"> The Cephalodiscidae mitochondrial code | 1 | Biochemistry |
As expected, the concentration of the unknown will have some error which can be calculated from the formula below. This formula assumes that a linear relationship is observed for all the standards. It is important to note that the error in the concentration will be minimal if the signal from the unknown lies in the middle of the signals of all the standards (the term goes to zero if )
*, is the standard deviation in the residuals
* is the slope of the line
* is the y-intercept of the line
* is the number of standards
* is the number of replicate unknowns
* is the measurement of the unknown
* is the average measurement of the standards
* are the concentrations of the standards
* is the average concentration of the standards | 1 | Biochemistry |
Partition chromatography was one of the first kinds of chromatography that chemists developed, and is barely used these days. The partition coefficient principle has been applied in paper chromatography, thin layer chromatography, gas phase and liquid–liquid separation applications. The 1952 Nobel Prize in chemistry was earned by Archer John Porter Martin and Richard Laurence Millington Synge for their development of the technique, which was used for their separation of amino acids. Partition chromatography uses a retained solvent, on the surface or within the grains or fibers of an "inert" solid supporting matrix as with paper chromatography; or takes advantage of some coulombic and/or hydrogen donor interaction with the stationary phase. Analyte molecules partition between a liquid stationary phase and the eluent. Just as in hydrophilic interaction chromatography (HILIC; a sub-technique within HPLC), this method separates analytes based on differences in their polarity. HILIC most often uses a bonded polar stationary phase and a mobile phase made primarily of acetonitrile with water as the strong component. Partition HPLC has been used historically on unbonded silica or alumina supports. Each works effectively for separating analytes by relative polar differences. HILIC bonded phases have the advantage of separating acidic, basic and neutral solutes in a single chromatographic run.
The polar analytes diffuse into a stationary water layer associated with the polar stationary phase and are thus retained. The stronger the interactions between the polar analyte and the polar stationary phase (relative to the mobile phase) the longer the elution time. The interaction strength depends on the functional groups part of the analyte molecular structure, with more polarized groups (e.g., hydroxyl-) and groups capable of hydrogen bonding inducing more retention. Coulombic (electrostatic) interactions can also increase retention. Use of more polar solvents in the mobile phase will decrease the retention time of the analytes, whereas more hydrophobic solvents tend to increase retention times. | 3 | Analytical Chemistry |
Many proteins are glycosylated on certain residues, which can affect the proteome.
Glycans can interact with receptors, which in turn affect their cellular and subcellular localization. For example, cytokines and the subgroup chemokines are small signaling proteins that are involved in the immune response. Many of the N-linked glycans on these cytokines play an important role in metabolic turnover and by engineering the glycoform and its branching, there can be advantageous physiochemical affects on the immune response.
Furthermore, glycosylated proteins, or glycoproteins, can have increased resistance to degradation by proteases, which will increase the half-life of those proteins. For example, interferon beta has been shown to be important in the treatment of multiple sclerosis. Recombinant versions of interferon beta have been produced in Escherichia coli, with the glycosylated form being more stable and resistant to protease degradation, while the non-glycosylated form is degraded much more quickly. Engineered glycoproteins have also been instrumental in enzyme replacement therapy (ERT). This has been of particular interest in the development of therapeutics for lysosomal storage disease. Proper delivery of these enzymes is highly dependent on the mannose 6-phosphate (M6P) tagging on N-glycans. Thus, engineering of these N-glyans, such as by modification of branching patterns, sialic acid capping, M6P tagging, monosaccharide constituents, and glycosidic bond linkage, there can be increased efficacy of lysosomal targeting and better delivery to the central nervous system through the blood brain barrier.
Additionally, glycoengineering has been utilized with neural stem cell cultures to increase adhesion to the extracellular matrix through the treatment of an N-acetylmannosamine analog. | 1 | Biochemistry |
Immunofluorescence is only limited to fixed (i.e. dead) cells, when studying structures within the cell, as antibodies generally do not penetrate intact cellular or subcellular membranes in living cells, because they are large proteins. To visualize these structures, antigenic material must be fixed firmly on its natural localization inside the cell. To study structures within living cells, in combination with fluorescence, one can utilize recombinant proteins containing fluorescent protein domains, e.g., green fluorescent protein (GFP). The GFP-technique involves altering the genetic information of the cells.
A significant problem with immunofluorescence is photobleaching, the fluorophores permanent loss of ability to emit light. To mitigate the risk of photobleaching one can employ different strategies. By reducing or limiting the intensity, or timespan of light exposure, the absorption-emission cycle of fluorescent light is decreased, thus preserving the fluorophores functionality. One can also increase the concentration of fluorophores, or opt for more robust fluorophores that exhibit resilience against photobleaching such as Alexa Fluors, Seta Fluors, or DyLight Fluors.
Other problems that may arise when using immunofluorescence techniques include autofluorescence, spectral overlap and non-specific staining. Autofluorescence includes the natural fluorescence emitted from the sample tissue or cell itself. Spectral overlap happens when a fluorophore has a broad emission specter, that overlaps with the specter of another fluorophore, thus giving rise to false signals. Non-specific staining occurs when the antibody, containing the fluorophore, binds to unintended proteins because of sufficient similarity in the epitope. This can lead to false positives. | 1 | Biochemistry |
Oxidizing roasting, the most commonly practiced roasting process, involves heating the ore in excess of air or oxygen, to burn out or replace the impurity element, generally sulfur, partly or completely by oxygen. For sulfide roasting, the general reaction can be given by:
:2MS (s) + 3O (g) -> 2MO (s) + 2SO (g)
Roasting the sulfide ore, until almost complete removal of the sulfur from the ore, results in a dead roast. | 8 | Metallurgy |
Increases in the intracellular Ca concentrations are often a result of IP activation. When a ligand binds to a G protein-coupled receptor (GPCR) that is coupled to a Gq heterotrimeric G protein, the α-subunit of Gq can bind to and induce activity in the PLC isozyme PLC-β, which results in the cleavage of PIP into IP and DAG.
If a receptor tyrosine kinase (RTK) is involved in activating the pathway, the isozyme PLC-γ has tyrosine residues that can become phosphorylated upon activation of an RTK, and this will activate PLC-γ and allow it to cleave PIP into DAG and IP. This occurs in cells that are capable of responding to growth factors such as insulin, because the growth factors are the ligands responsible for activating the RTK.
IP (also abbreviated Ins(1,4,5)P is a soluble molecule and is capable of diffusing through the cytoplasm to the ER, or the sarcoplasmic reticulum (SR) in the case of muscle cells, once it has been produced by the action of PLC. Once at the ER, IP is able to bind to the Ins(1,4,5)P receptor Ins(1,4,5)PR which is a ligand-gated Ca channel that is found on the surface of the ER. The binding of IP (the ligand in this case) to Ins(1,4,5)PR triggers the opening of the Ca channel, and thus release of Ca into the cytoplasm. In heart muscle cells this increase in Ca activates the ryanodine receptor-operated channel on the SR, results in further increases in Ca through a process known as calcium-induced calcium release. IP may also activate Ca channels on the cell membrane indirectly, by increasing the intracellular Ca concentration. | 1 | Biochemistry |
The phase change material should possess the following thermodynamic properties:
* Melting temperature in the desired operating temperature range
* High latent heat of fusion per unit volume
* High specific heat, high density, and high thermal conductivity
* Small volume changes on phase transformation and small vapor pressure at operating temperatures to reduce the containment problem
* Congruent melting
Kinetic properties
* High nucleation rate to avoid supercooling of the liquid phase
* High rate of crystal growth, so that the system can meet demands of heat recovery from the storage system
Chemical properties
* Chemical stability
* Complete reversible freeze/melt cycle
* No degradation after a large number of freeze/melt cycle
* Non-corrosiveness, non-toxic, non-flammable and non-explosive materials
Economic properties
* Low cost
* Availability | 7 | Physical Chemistry |
Lakes and oceans appear cyan for several reasons. One is that the surface of the water reflects the color of the sky, which ranges from cyan to light azure. It is a common misconception that this reflection is the sole reason bodies of water appear cyan, though it can contribute. This contribution usually makes the body of water appear more a shade of azure rather than cyan depending on how bright the sky is.
Water in swimming pools with white-painted sides and bottom will appear cyan, even in indoor pools where there is no sky to be reflected. The deeper the pool, the more intense the cyan color becomes.
Some of the light hitting the surface of ocean is reflected but most of it penetrates the water surface, interacting with water molecules and other substances in the water. Water molecules can vibrate in three different modes when they interact with light. The red, orange, and yellow wavelengths of light are absorbed so the remaining light seen is composed of green, cyan, and blue wavelengths. This is the main reason the ocean's color is cyan. The relative contribution of reflected skylight and the light scattered back from the depths is strongly dependent on observation angle.
Scattering from suspended particles also plays an important role in the color of lakes and oceans, causing the water to look greener or bluer in different areas. A few tens of meters of water will absorb all light, so without scattering, all bodies of water would appear black. Because most lakes and oceans contain suspended living matter and mineral particles, light from above is scattered and some of it is reflected upwards. Scattering from suspended particles would normally give a white color, as with snow, but because the light first passes through many meters of cyan-colored liquid, the scattered light appears cyan. In extremely pure water—as is found in mountain lakes, where scattering from particles is very low—the scattering from water molecules themselves also contributes a cyan color.
Diffuse sky radiation due to Rayleigh scattering in the atmosphere along one's line of sight gives distant objects a cyan or light azure tint. This is most commonly noticed with distant mountains, but also contributes to the cyanness of the ocean in the distance. | 3 | Analytical Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.