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The discharge theory can be tested by measuring the emptying time or time series of the water level within the cylindrical vessel. In many cases, such experiments do not confirm the presented discharge theory: when comparing the theoretical predictions of the discharge process with measurements, very large differences can be found in such cases. In reality, the tank usually drains much more slowly. Looking at the discharge formula
two quantities could be responsible for this discrepancy: the outflow velocity or the effective outflow cross section.
In 1738 Daniel Bernoulli attributed the discrepancy between the theoretical and the observed outflow behavior to the formation of a vena contracta which reduces the outflow cross-section from the orifice's cross-section to the contracted cross-section and stated that the discharge is:
Actually this is confirmed by state-of-the-art experiments (see ) in which the discharge, the outflow velocity and the cross-section of the vena contracta were measured. Here it was also shown that the outflow velocity is predicted extremely well by Torricelli's law and that no velocity correction (like a "coefficient of velocity") is needed.
The problem remains how to determine the cross-section of the vena contracta. This is normally done by introducing a discharge coefficient which relates the discharge to the orifices cross-section and Torricellis law:
For low viscosity liquids (such as water) flowing out of a round hole in a tank, the discharge coefficient is in the order of 0.65. By discharging through a round tube or hose, the coefficient of discharge can be increased to over 0.9. For rectangular openings, the discharge coefficient can be up to 0.67, depending on the height-width ratio. | 1 | Applied and Interdisciplinary Chemistry |
In contrast to materials with a single ferroic order, domains in multiferroics have additional properties and functionalities. For instance, they are characterized by an assembly of at least two order parameters. The order parameters may be independent (typical yet not mandatory for a Type-I multiferroic) or coupled (mandatory for a Type-II multiferroic).
Many outstanding properties that distinguish domains in multiferroics from those in materials with a single ferroic order are consequences of the coupling between the order parameters.
*The coupling can lead to patterns with a distribution and/or topology of domains that is exclusive to multiferroics.
*The order-parameter coupling is usually homogeneous across a domain, i.e., gradient effects are negligible.
*In some cases the averaged net value of the order parameter for a domain pattern is more relevant for the coupling than the value of the order parameter of an individual domain.
These issues lead to novel functionalities which explain the current interest in these materials. | 0 | Theoretical and Fundamental Chemistry |
* Cryogenics, the study of the production and behaviour of materials at very low temperatures and the study of producing extremely low temperatures
* Cryoelectronics, the study of superconductivity under cryogenic conditions and its applications
* Cryosphere, those portions of Earth's surface where water ice naturally occurs
* Cryotron, a switch that uses superconductivity
* Cryovolcano, a theoretical type of volcano that erupts volatiles instead of molten rock | 1 | Applied and Interdisciplinary Chemistry |
Expanded out, the grand potential is:
All thermodynamic properties can be computed from this potential. The following table lists various thermodynamic quantities calculated in the limit of low temperature and high temperature, and in the limit of infinite particle number. An equal sign (=) indicates an exact result, while an approximation symbol indicates that only the first few terms of a series in is shown.
It is seen that all quantities approach the values for a classical ideal gas in
the limit of large temperature. The above values can be used to calculate other
thermodynamic quantities. For example, the relationship between internal energy and
the product of pressure and volume is the same as that for a classical ideal gas over
all temperatures:
A similar situation holds for the specific heat at constant volume
The entropy is given by:
Note that in the limit of high temperature, we have
which, for α=3/2 is simply a restatement of the Sackur–Tetrode equation. In one dimension bosons with delta interaction behave as fermions, they obey Pauli exclusion principle. In one dimension Bose gas with delta interaction can be solved exactly by Bethe ansatz. The bulk free energy and thermodynamic potentials were calculated by Chen-Ning Yang. In one dimensional case correlation functions also were evaluated. In one dimension Bose gas is equivalent to quantum non-linear Schrödinger equation. | 0 | Theoretical and Fundamental Chemistry |
Historically, aluminium has been used as conductor in integrated circuits, due to its good adherence to substrate, good conductivity, and ability to form ohmic contacts with silicon. However, pure aluminium is susceptible to electromigration. Research shows that adding 2-4% of copper to aluminium increases resistance to electromigration about 50 times. The effect is attributed to the grain boundary segregation of copper, which greatly inhibits the diffusion of aluminium atoms across grain boundaries.
Pure copper wires can withstand approximately five times more current density than aluminum wires while maintaining similar reliability requirements. This is mainly due to the higher electromigration activation energy levels of copper, caused by its superior electrical and thermal conductivity as well as its higher melting point. Further improvements can be achieved by alloying copper with about 1% palladium which inhibits diffusion of copper atoms along grain boundaries in the same way as the addition of copper to aluminium interconnect. | 0 | Theoretical and Fundamental Chemistry |
In this regime, flexibility may or may not improve load-bearing capabilities of the plates. The two characteristics lengths are of comparable dimension, so particular values for each determine whether or not additional fluid displaced through bending exceeds fluid lost through the narrowing of the column. | 1 | Applied and Interdisciplinary Chemistry |
Curare is a crude extract from certain South American plants in the genera Strychnos and Chondrodendron, originally brought to Europe by explorers such as Walter Raleigh Edward Bancroft, a chemist and physician in the 16th century brought samples of crude curare from South America back to the Old-World. The effect of curare was experimented with by Sir Benjamin Brodie when he injected small animals with curare, and found that the animals stopped breathing but could be kept alive by inflating their lungs with bellows. This observation led to the conclusion that curare can paralyse the respiratory muscles. It was also experimented by Charles Waterton in 1814 when he injected three donkeys with curare. The first donkey was injected in the shoulder and died afterward. The second donkey had a tourniquet applied to the foreleg and was injected distal to the tourniquet. The donkey lived while the tourniquet was in place but died after it was removed. The third donkey after injected with curare appeared to be dead but was resuscitated using bellows. Charles Waterton's experiment confirmed the paralytic effect of curare.
It was known in the 19th century to have a paralysing effect, due in part to the studies of scientists like Claude Bernard. D-tubocurarine a mono-quaternary alkaloid was isolated from Chondrodendron tomentosum in 1942, and it was shown to be the major constituent in curare responsible for producing the paralysing effect. At that time, it was known that curare and, therefore, d-tubocurarine worked at the neuromuscular junction. The isolation of tubocurarine and its marketing as the drug Intocostrin led to more research in the field of neuromuscular-blocking drugs. Scientists figured out that the potency of tubocurarine was related to the separation distance between the two quaternary ammonium heads.
Neurologist Walter Freeman learned about curare and suggested to Richard Gill, a patient suffering from multiple sclerosis, that he try using it. Gill brought 25 pounds of raw curare from Ecuador. The raw curare was then given to Squibb and Sons to derive an effective antidote to curare. In 1942, Wintersteiner and Dutcher (two scientists working for Squibb and Sons) isolated the alkaloid d-tubocurarine. Soon after, they developed a preparation of curare called Intocostrin.
At the same time in Montreal, Harold Randall Griffith and his resident Enid Johnson at the Homeopathic Hospital administered curare to a young patient undergoing appendectomy. This was the first use of NMBA as muscle relaxant in anesthesia.
The 1940s, 1950s and 1960s saw the rapid development of several synthetic NMBA. Gallamine was the first synthetic NMBA used clinically. Further research led to the development of synthesized molecules with different curariform effects, depending on the distance between the quaternary ammonium groups. One of the synthesized bis-quaternaries was decamethonium a 10-carbon bis-quaternary compound. Following research with decamethonium, scientists developed suxamethonium, which is a double acetylcholine molecule that was connected at the acetyl end. The discovery and development of suxamethonium lead to a Nobel Prize in medicine in 1957. Suxamethonium showed different blocking effect in that its effect was achieved more quickly and augmented a response in the muscle before block. Also, tubocurarine effects were known to be reversible by acetylcholinesterase inhibitors, whereas decamethonium and suxamethonium block were not reversible.
Another compound malouétine that was a bis-quaternary steroid was isolated from the plant Malouetia bequaertiana and showed curariform activity. This led to the synthetic drug pancuronium, a bis-quaternary steroid, and subsequently other drugs that had better pharmacological properties. Research on these molecules helped improve understanding of the physiology of neurons and receptors. | 1 | Applied and Interdisciplinary Chemistry |
For fully brine saturated porous media, three different mechanisms contribute to the relaxation: bulk fluid relaxation, surface relaxation, and relaxation due to gradients in the magnetic field. In the absence of magnetic field gradients, the equations describing the relaxation are:
: on S
with the initial condition
: and
where is the self-diffusion coefficient. The governing diffusion equation can be solved by a 3D random walk algorithm. Initially, the walkers are launched at random positions in the pore space. At each time step, , they advance from their current position, , to a new position, , by taking steps of fixed length in a randomly chosen direction. The time step is given by:
The new position is given by
The angles and represent the randomly selected direction for each random walker in spherical coordinates. It can be noted that must be distributed uniformly in the range (0,). If a walker encounters a pore-solid interface, it is killed with a finite probability . The killing probability is related to the surface relaxation strength by:
If the walker survives, it simply bounces off the interface and its position does not change. At each time step, the fraction of the initial walkers that are still alive is recorded. Since the walkers move with equal probability in all directions, the above algorithm is valid as long as there is no magnetic gradient in the system.
When protons are diffusing, the sequence of spin echo amplitudes is affected by inhomogeneities in the permanent magnetic field. This results in an additional decay of the spin echo amplitudes that depends on the echo spacing . In the simple case of a uniform spatial gradient , the additional decay can be expressed as a multiplicative factor:
where is the ratio of the Larmor frequency to the magnetic field intensity. The total magnetization amplitude as a function of time is then given as: | 0 | Theoretical and Fundamental Chemistry |
No single method can assess impact of contamination-induced degradation of sediment across aquatic communities. Methods of each component of the triad should be selected for efficacy and relevance in lab and field tests. Application of the SQT is typically location-specific and can be used to compare differences in sediment quality temporally or across regions (Chapman, 1997). | 1 | Applied and Interdisciplinary Chemistry |
The discovery of PKM2 began with laboratory observations made by Otto Heinrich Warburg, a German physiologist and Nobel Laureate in Physiology or Medicine in 1931. Warburg's experiments show that the cells exhibit dependence on glucose and are capable of fermentation, even under aerobic conditions. These observations are known as the Warburg effect. Subsequent research on the metabolic demands of cancer cells, studies have been directed towards the investigation of specific subtypes of pyruvate kinase, notably M1 and M2. | 1 | Applied and Interdisciplinary Chemistry |
The nuclear neutron scattering process involves the coherent neutron scattering length, often described by . | 0 | Theoretical and Fundamental Chemistry |
1,3-Propanedithiol is mainly used for the protection of aldehydes and ketones via their reversible formation of dithianes. A prototypical reaction is its formation of 1,3-dithiane from formaldehyde. The reactivity of this dithiane illustrates the concept of umpolung. Alkylation gives thioethers, e.g. 1,5-dithiacyclooctane.
The unpleasant odour of 1,3-propanedithiol has encouraged the development of alternative reagents that generate similar derivatives.
1,3-Propanedithiol is used in the synthesis of tiapamil. | 0 | Theoretical and Fundamental Chemistry |
A transition metal carbene complex is an organometallic compound featuring a divalent carbon ligand, itself also called a carbene. Carbene complexes have been synthesized from most transition metals and f-block metals, using many different synthetic routes such as nucleophilic addition and alpha-hydrogen abstraction. The term carbene ligand is a formalism since many are not directly derived from carbenes and most are much less reactive than lone carbenes. Described often as , carbene ligands are intermediate between alkyls and carbynes . Many different carbene-based reagents such as Tebbe's reagent are used in synthesis. They also feature in catalytic reactions, especially alkene metathesis, and are of value in both industrial heterogeneous and in homogeneous catalysis for laboratory- and industrial-scale preparation of fine chemicals. | 0 | Theoretical and Fundamental Chemistry |
The lower flammability limit or lower explosive limit (LFL/LEL) represents the lowest air to fuel vapor concentration required for combustion to take place when ignited by an external source, for any particular chemical. Any concentration lower than this could not produce a flame or result in combustion. The upper flammability limit or upper explosive limit (UFL/UEL) represents the highest air to fuel vapor concentration at which combustion can take place when ignited by an external source. Any fuel-air mixture higher than this would be too concentrated to result in combustion. The values existing between these two limits represent the flammable or explosive range. Within this threshold, give an external ignition source, combustion of the particular fuel would likely happen. | 0 | Theoretical and Fundamental Chemistry |
Yulia Sister and her family repatriated to Israel in 1990. In 1992–1993 she served as a senior researcher of the Department of Inorganic and Analytical Chemistry at the Hebrew University of Jerusalem, and then she was engaged in the topics related to the analysis of biological objects at the Tel Aviv University. During these years, along with her career in chemistry, Yulia Sister became deeply interested in the study of Russian-Jewish culture.
In 1991 Sister began to write for the Shorter Jewish Encyclopedia (SJE) as a non-staff editor. She served as a research fellow covering the field of history of science and wrote about 90 articles for the encyclopedia. Yulia is the author of the articles "Chemistry" (jointly with P. Smorodnitsky), "Veniamin Levich", "Frederick Reines", "Moise Haissinsky", "Yuri Golfand" and many others.
Yulia Sister's activities in the House of Scientists and Experts of Rehovot started in 1991. Within this forum she organizes lectures, seminars and scientific conferences. She leads the scientific seminars of the House of Scientists that are regularly held at the Weizmann Institute of Science. In 2008, and then in 2014 she organized conferences devoted to the Bilu movement and to the First Aliyah. She also maintains friendly contacts with foreign colleagues, such as the Club of Russian-speaking scientists of Massachusetts.
In 1997 Mikhail Parkhomovsky initiated creation of the Research Center for Russian Jewry Abroad, which aimed to collect and publish information on Jews, who emigrated from the Russian Empire, Soviet Union or Post-Soviet states and made a contribution to world civilization. Parkhomovsky became the Scientific Director and Chief Editor and Yulia Sister Director General of the Center. From 2012 the Center changed its name to Research Centre for Russian Jews abroad and in Israel (Erzi). The collection, processing and publication of materials related to Russian Jewry are organized by Sister. By 2015 the Center published about 30 volumes of collections, including books devoted to Jews in England, France, U.S., Israel and other countries. In addition to her executive functions, Sister is a frequent editor and author of the Center's collective monographs. She is the editor of the 17th volume ("Let Us Build the Walls of Jerusalem. Book 3"), a coeditor of the 11th volume ("Let Us Build the Walls of Jerusalem. Book 1") and of the monograph "Israel, Russian Roots", and a participant in the editing of the 10th volume.
Sister's activities include the organization of seminars and conferences. The following examples are a small sampling of the events organized by the Director General of the Center. In 1999 she was the coordinator of the conference dedicated to the 50th anniversary of the Weizmann Institute in Rehovot. Together with Prof. Aron Cherniak she published a detailed report on the conference and some of its materials in the 8th volume of the "Russian Jewry Abroad" series. In 2003 Sister led a conference in Kiryat Ekron, in which she introduced the contribution of the Russian Aliyah to Israeli science, culture and education. More than 200 scientists from all over the country participated at the tenth-anniversary of the Center conference in 2007. The 2012 conference was devoted to the 130th anniversary of the First Aliyah and the event was covered by the House of Scientists of Rehovot.
Yulia Sister lives with her family in Kiryat Ekron. Her husband, Boris (Bezalel) Iosifovich Gendler, is a physician with an extensive experience in medical practice and education. After his repatriation from Kishinev Bezalel Gendler worked as a doctor in one of the Israeli hospitals and published several articles, some of them in collaboration with Yulia. | 0 | Theoretical and Fundamental Chemistry |
In general, the Fokker–Planck equations are a special case to the general Kolmogorov forward equation
where the linear operator is the Hermitian adjoint to the infinitesimal generator for the Markov process. | 1 | Applied and Interdisciplinary Chemistry |
When generating THz radiation via a photoconductive emitter, an ultrafast pulse (typically 100 femtoseconds or shorter) creates charge carriers (electron-hole pairs) in a semiconductor material. This incident laser pulse abruptly changes the antenna from an insulating state into a conducting state. Due to an electric bias applied across the antenna, a sudden electric current transmits across the antenna. This changing current lasts for about a picosecond, and thus emits terahertz radiation since the Fourier transform of a picosecond length signal will contain THz components.
Typically the two antenna electrodes are patterned on a low temperature gallium arsenide (LT-GaAs), semi-insulating gallium arsenide (SI-GaAs), or other semiconductor (such as InP) substrate.
In a commonly used scheme, the electrodes are formed into the shape of a simple dipole antenna with a gap of a few micrometers and have a bias voltage up to 40 V between them. The ultrafast laser pulse must have a wavelength that is short enough to excite electrons across the bandgap of the semiconductor substrate. This scheme is suitable for illumination with a Ti:sapphire oscillator laser with photon energies of 1.55 eV and pulse energies of about 10 nJ. For use with amplified Ti:sapphire lasers with pulse energies of about 1 mJ, the electrode gap can be increased to several centimeters with a bias voltage of up to 200 kV.
More recent advances towards cost-efficient and compact THz-TDS systems are based on mode-locked fiber laser sources emitting at a center wavelength of 1550 nm. Therefore, the photoconductive emitters must be based on semiconductor materials with smaller band gaps of approximately 0.74 eV such as Fe-doped indium gallium arsenide or indium gallium arsenide/indium aluminum arsenide heterostructures.
The short duration of THz pulses generated (typically ~2 ps) are primarily due to the rapid rise of the photo-induced current in the semiconductor and short carrier lifetime semiconductor materials (e.g., LT-GaAs). This current may persist for only a few hundred femtoseconds to several nanoseconds depending on the substrate material. This is not the only means of generation but is currently () the most common.
Pulses produced by this method have average power levels on the order of several tens of microwatts. The peak power during pulses can be many orders of magnitude higher due to the low duty cycle of mostly >1%, which is dependent on the repetition rate of the laser source. The maximum bandwidth of the resulting THz pulse is primarily limited by the duration of the laser pulse, while the frequency position of the maximum of the Fourier spectrum is determined by the carrier lifetime of the semiconductor. | 0 | Theoretical and Fundamental Chemistry |
Crystallographic data are primarily extracted from published scientific articles and supplementary material. Newer versions of crystallographic databases are built on the relational database model, which enables efficient cross-referencing of tables. Cross-referencing serves to derive additional data or enhance the search capacity of the database.
Data exchange among crystallographic databases, structure visualization software, and structure refinement programs has been facilitated by the emergence of the Crystallographic Information File (CIF) format. The CIF format is the standard file format for the exchange and archiving of crystallographic data.
It was adopted by the International Union of Crystallography (IUCr), who also provides full specifications of the format. It is supported by all major crystallographic databases.
The increasing automation of the crystal structure determination process has resulted in ever higher publishing rates of new crystal structures and, consequentially, new publishing models. Minimalistic articles contain only crystal structure tables, structure images, and, possibly, abstract-like structure description. They tend to be published in author-financed or subsidized open-access journals. Acta Crystallographica Section E and Zeitschrift für Kristallographie belong in this category. More elaborate contributions may go to traditional subscriber-financed journals. Hybrid journals, on the other hand, embed individual author-financed open-access articles among subscriber-financed ones. Publishers may also make scientific articles available online, as Portable Document Format (PDF) files.
Crystal structure data in CIF format are linked to scientific articles as supplementary material. CIFs may be accessible directly from the publisher's website, crystallographic databases, or both. In recent years, many publishers of crystallographic journals have come to interpret CIFs as formatted versions of open data, i.e. representing non-copyrightable facts, and therefore tend to make them freely available online, independent of the accessibility status of linked scientific articles. | 0 | Theoretical and Fundamental Chemistry |
Vibrating-sample magnetometers (VSMs) detect the dipole moment of a sample by mechanically vibrating the sample inside of an inductive pickup coil or inside of a SQUID coil. Induced current or changing flux in the coil is measured. The vibration is typically created by a motor or a piezoelectric actuator. Typically the VSM technique is about an order of magnitude less sensitive than SQUID magnetometry. VSMs can be combined with SQUIDs to create a system that is more sensitive than either one alone. Heat due to the sample vibration can limit the base temperature of a VSM, typically to 2 kelvin. VSM is also impractical for measuring a fragile sample that is sensitive to rapid acceleration. | 0 | Theoretical and Fundamental Chemistry |
In electrochemistry, the electrochemical potential (ECP), , is a thermodynamic measure of chemical potential that does not omit the energy contribution of electrostatics. Electrochemical potential is expressed in the unit of J/mol. | 0 | Theoretical and Fundamental Chemistry |
The master regulator concept has been criticized for being a "simplified paradigm" that fails to account for the multifactorial influences on some cell fates. | 1 | Applied and Interdisciplinary Chemistry |
In the expansion step of the working fluid in transcritical cycles, as in subcritical ones, the working fluid can be discharged either in wet or dry conditions.
Typical dry expansions are those involving organic or other unconventional working fluids, which are characterized by non-negligible molecular complexities and high molecular weights.
The expansion step occurs in turbines: depending on the application and on the nameplate power produced by the power plant, both axial turbines and radial turbines can be exploited during fluid expansion. Axial turbines favour lower rotational speed and higher power production, while radial turbines are suitable for limited powers produced and high rotational speed.
Organic cycles are appropriate choices for low enthalpy applications and are characterized by higher average densities across the expanders than those occurring in transcritical steam cycles: for this reason a low blade height is normally designed and the volumetric flow rate is kept limited to relatively small values. On the other hand in large scale application scenarios the expander blades typically show heights that exceed one meter and that are exploited in the steam cycles. Here, in fact, the fluid density at the outlet of the last expansion stage is significantly low.
In general, the specific work of the cycle is expressed as:
Even though the specific work of any cycle is strongly dependent on the actual working fluid considered in the cycle, transcritical cycles are expected to exhibit higher specific works than the corresponding subcritical and supercritical counterparts (i.e., that exploit the same working fluid). For this reason, at fixed boundary conditions, power produced and working fluid, a lower mass flow rate is expected in transcritical cycles than in other configurations. | 0 | Theoretical and Fundamental Chemistry |
One of the challenges of 3D printing organs is to recreate the vasculature required to keep the organs alive. Designing a correct vasculature is necessary for the transport of nutrients, oxygen, and waste. Blood vessels, especially capillaries, are difficult due to the small diameter. Progress has been made in this area at Rice University, where researchers designed a 3D printer to make vessels in biocompatible hydrogels and designed a model of lungs that can oxygenate blood. However, accompanied with this technique is the challenge of replicating the other minute details of organs. It is difficult to replicate the entangled networks of airways, blood vessels, and bile ducts and complex geometry of organs.
The challenges faced in the organ printing field extends beyond the research and development of techniques to solve the issues of multivascularization and difficult geometries. Before organ printing can become widely available, a source for sustainable cell sources must be found and large-scale manufacturing processes need to be developed. Additional challenges include designing clinical trials to test the long-term viability and biocompatibility of synthetic organs. While many developments have been made in the field of organ printing, more research must be conducted. | 1 | Applied and Interdisciplinary Chemistry |
Young and colleagues proposed Youngs model of wetting that relates the contact angle of a water droplet on a flat surface to the surface energies of the water, the surface, and the surrounding air. This model is typically an oversimplification of a water droplet on an ideally flat surface. This model has been expanded upon to consider surface roughness as a factor in predicting water contact angle on a surface. Youngs model is described by the following equation:
= Contact angle of water on the surface
= Surface energy of the surface-air interface
= Surface energy of surface-liquid interface
= Surface energy of liquid-air interface | 0 | Theoretical and Fundamental Chemistry |
The Cativa process is a method for the production of acetic acid by the carbonylation of methanol. The technology, which is similar to the Monsanto process, was developed by BP Chemicals and is under license by BP Plc. The process is based on an iridium-containing catalyst, such as the complex [Ir(CO)I] (1).
The Cativa and Monsanto processes are sufficiently similar that they can use the same chemical plant. Initial studies by Monsanto had shown iridium to be less active than rhodium for the carbonylation of methanol. Subsequent research, however, showed that the iridium catalyst could be promoted by ruthenium, and this combination leads to a catalyst that is superior to the rhodium-based systems. The switch from rhodium to iridium also allows the use of less water in the reaction mixture. This change reduces the number of drying columns necessary, decreases formation of by-products, such as propionic acid, and suppresses the water gas shift reaction.
The catalytic cycle for the Cativa process, shown above, begins with the reaction of methyl iodide with the square planar active catalyst species (1) to form the octahedral iridium(III) species (2), the fac-isomer of [Ir(CO)(CH)I]. This oxidative addition reaction involves the formal insertion of the iridium(I) centre into the carbon-iodine bond of methyl iodide. After ligand exchange (iodide for carbon monoxide), the migratory insertion of carbon monoxide into the iridium-carbon bond, step (3) to (4), results in the formation of a square pyramidal species with a bound acetyl ligand. The active catalyst species (1) is regenerated by the reductive elimination of acetyl iodide from (4), a de-insertion reaction. The acetyl iodide is hydrolysed to produce the acetic acid product, in the process generating hydroiodic acid which is in turn used to convert the starting material (methanol) to the methyl iodide used in the first step. | 0 | Theoretical and Fundamental Chemistry |
In 1959 Ernst Freese coined the terms "transitions" or "transversions" to categorize different types of point mutations. Transitions are replacement of a purine base with another purine or replacement of a pyrimidine with another pyrimidine. Transversions are replacement of a purine with a pyrimidine or vice versa. There is a systematic difference in mutation rates for transitions (Alpha) and transversions (Beta). Transition mutations are about ten times more common than transversions. | 1 | Applied and Interdisciplinary Chemistry |
Ionic bipolar transistors can be made from two conical channels with the smallest opening in nano-scaled dimension. By introducing opposite surface charges at each side, it is able to rectify ionic current as an ionic diode. An ionic bipolar transistor is built by combining two ionic diodes and forming a PNP junction along the inner surface of the channel. While the ionic current is from emitter end to collector end, the strength of the current can be modulated by the base electrode. The surface charge at the channel wall can be modified using chemical methods, by changing the electrolyte concentration or pH value. | 0 | Theoretical and Fundamental Chemistry |
Insulin stimulates the activity of pyruvate dehydrogenase phosphatase. The phosphatase removes the phosphate from pyruvate dehydrogenase activating it and allowing for conversion of pyruvate to acetyl-CoA. This mechanism leads to the increased rate of catalysis of this enzyme, so increases the levels of acetyl-CoA. Increased levels of acetyl-CoA will increase the flux through not only the fat synthesis pathway but also the citric acid cycle. | 1 | Applied and Interdisciplinary Chemistry |
It is challenging to identify rare variants accurately using standard NGS methods with a mutation rate of (10 to 10). Errors that happen early during sample preparation can be detected as rare variants. An example of such errors is C>A/G>T transversion, detected in low frequencies using deep sequencing or targeted capture data and arising due to DNA oxidation during sample preparation. These types of false-positive variants are filtered out by the duplex sequencing method since mutations need to be accurately matched in both strands of DNA to be validated as true mutations. Duplex sequencing can theoretically detect mutations with frequencies as low as 10 compared to the 10 rate of standard NGS methods. | 1 | Applied and Interdisciplinary Chemistry |
* m-Phenylene ethynylene oligomers are driven to fold into a helical conformation by solvophobic forces and aromatic stacking interactions.
* β-peptides are composed of amino acids containing an additional unit between the amine and carboxylic acid. They are more stable to enzymatic degradation and have been demonstrated to have antimicrobial activity.
* Peptoids are N-substituted polyglycines that utilize steric interactions to fold into polyproline type-I-like helical structures.
* Aedamers that fold in aqueous solutions driven by hydrophobic and aromatic stacking interactions.
* Aromatic oligoamide foldamers. These examples are some of the largest and best structurally characterized foldamers.
* Arylamide foldamers, such as brilacidin. | 0 | Theoretical and Fundamental Chemistry |
Corrosion loop(s) are systematized analysis "loops" used during Risk-based inspection analysis.
Both terms “RBI Corrosion loops” or “RBI corrosion circuits” are generic terms used to indicate the systematization of piping systems into usable and understandable parts associated with corrosion.
Systematized piping loops or circuits are systems used in Risk Based Inspection analysis to assess the likelihood and consequence of failure.
Other systematization may also prove useful, such as, i.e. inspection, consequence, materials of construction and chemistry.
The system (or sub systems) maybe used to identify, pressure / temperature, subsequent failure mechanism and possible failure rate.
They may be based upon Construction drawings, Process Flow diagrams or Piping & Instrument diagrams as required. Each loop or circuit maybe identified using a unique code, with description about; process, material & degradation mode, material, cladding, C.A, specs.
See system model comes under the general heading of system analysis the terms analysis and synthesis come from Greek where they mean respectively "to take apart" and "to put together". See also systems theory:
Note the exact definition of the systematized risk analysis " loop" is left to the reader and their requirements of the system analysis required, however to ensure consistency and that the expected results is produced, this should be defined before they are constructed.
It is suggested that a “true” corrosion loop should be a grouping were the degradation mechanism is "likely" to be the same i.e.
*Material of Construction,
*Process fluid (similar stream properties),
*Temperature (roughly, or at least within the damage mechanisms susceptibility thresholds),
*Pressure (if the damage mechanism/s of concern is/are reliant upon pressure), and
*Velocity (again (if the damage mechanism of concern is reliant upon velocity).
By defining the barrier limits of Damage Susceptible Areas, the susceptibility of any part is similar to that of the whole. | 1 | Applied and Interdisciplinary Chemistry |
Hydrogen forms whenever molten aluminium comes into contact with water vapor, and easily dissolves into the melt. The gas tends to come out of the solution and forms bubbles when the melt solidifies.
The detrimental effects arising from the presence of an excess of dissolved hydrogen in aluminium are numerous. Hydrogen causes porosity in aluminum products leading to many casting defects, reduced mechanical properties like fatigue and lower corrosion resistance. Several methods are used to reduce the amount of dissolved hydrogen from the melt, such as furnace fluxing prior to the casting process or using in-line degassing equipment during the casting process. | 1 | Applied and Interdisciplinary Chemistry |
In imperfect Batesian mimicry, the mimics do not exactly resemble their models. An example of this is the fly Spilomyia longicornis, which mimics vespid wasps. However, it is not a perfect mimic. Wasps have long black antennae and this fly does not. Instead, they wave their front legs above their heads to look like the antennae on the wasps. Many reasons have been suggested for imperfect mimicry.
Imperfect mimics may simply be evolving towards perfection.
They may gain advantage from resembling multiple models at once.
Humans may evaluate mimics differently from actual predators.
Mimics may confuse predators by resembling both model and nonmimic at the same time (satyric mimicry).
Kin selection may enforce poor mimicry.
The selective advantage of better mimicry may not outweigh the advantages of other strategies like thermoregulation or camouflage.
Only certain traits may be required to deceive predators; for example, tests on the sympatry/allopatry border (where the two are in the same area, and where they are not) of the mimic Lampropeltis elapsoides and the model Micrurus fulvius showed that color proportions in these snakes were important in deceiving predators but that the order of the colored rings was not. | 1 | Applied and Interdisciplinary Chemistry |
According to the rule, a casting with a larger surface area and smaller volume will cool more quickly than a casting with a smaller surface area and a larger volume under otherwise comparable conditions. The relationship can be mathematically expressed as:
Where is the solidification time, is the volume of the casting, is the surface area of the casting that contacts the mold, is a constant, and is the mold constant.
This relationship can be expressed more simply as:
Where the modulus is the ratio of the casting's volume to its surface area:
The mold constant depends on the properties of the metal, such as density, heat capacity, heat of fusion and superheat, and the mold, such as initial temperature, density, thermal conductivity, heat capacity and wall thickness. | 1 | Applied and Interdisciplinary Chemistry |
Hot blast refers to the preheating of air blown into a blast furnace or other metallurgical process. As this considerably reduced the fuel consumed, hot blast was one of the most important technologies developed during the Industrial Revolution.
Hot blast also allowed higher furnace temperatures, which increased the capacity of furnaces.
As first developed, it worked by alternately storing heat from the furnace flue gas in a firebrick-lined vessel with multiple chambers, then blowing combustion air through the hot chamber. This is known as regenerative heating. Hot blast was invented and patented for iron furnaces by James Beaumont Neilson in 1828 at Wilsontown Ironworks in Scotland, but was later applied in other contexts, including late bloomeries. Later the carbon monoxide in the flue gas was burned to provide additional heat. | 1 | Applied and Interdisciplinary Chemistry |
To minimize degradation by solvents, reactions involving tert-butyllithium are often conducted at very low temperatures in special solvents, such as the Trapp solvent mixture.
More so than other alkyllithium compounds, tert-butyllithium reacts with ethers. In diethyl ether, the half-life of tert-butyllithium is about 60 minutes at 0 °C. It is even more reactive toward tetrahydrofuran (THF); the half-life in THF solutions is about 40 minutes at −20 °C. In dimethoxyethane, the half-life is about 11 minutes at −70 °C
In this example, the reaction of tert-butyllithium with (THF) is shown: | 0 | Theoretical and Fundamental Chemistry |
As a society, there are certain steps we can take to ensure the minimization of eutrophication, thereby reducing its harmful effects on humans and other living organisms in order to sustain a healthy norm of living, some of which are as follows: | 1 | Applied and Interdisciplinary Chemistry |
Salbutamol is the international nonproprietary name (INN) while albuterol is the United States Adopted Name (USAN). The drug is usually manufactured and distributed as the sulfate salt (salbutamol sulfate).
It was first sold by Allen & Hanburys (UK) under the brand name Ventolin, and has been used for the treatment of asthma ever since. The drug is marketed under many names worldwide. | 0 | Theoretical and Fundamental Chemistry |
FPIA has emerged as a viable technique for quantification of small molecules in mixtures, including: pesticides, mycotoxins in food, pharmaceutical compounds in wastewater, metabolites in urine and serum indicative of drug use (cannabinoids, amphetamines, barbiturates, cocaine, benzodiazepines, methadone, opiates, and PCP), and various small molecule toxins. As well as with the analysis of hormone-receptor interactions. | 1 | Applied and Interdisciplinary Chemistry |
The empirical formula for benzene was long known, but its highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. Archibald Scott Couper in 1858 and Johann Josef Loschmidt in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but in these years very little was known about aromatic chemistry, and so chemists were unable to adduce appropriate evidence to favor any particular formula.
But many chemists had begun to work on aromatic substances, especially in Germany, and relevant data was coming fast. In 1865, the German chemist Friedrich August Kekulé published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds. The next year he published a much longer paper in German on the same subject. Kekulé used evidence that had accumulated in the intervening years—namely, that there always appeared to be only one isomer of any monoderivative of benzene, and that there always appeared to be exactly three isomers of every disubstituted derivative—now understood to correspond to the ortho, meta, and para patterns of arene substitution—to argue in support of his proposed structure. Kekulés symmetrical ring could explain these curious facts, as well as benzenes 1:1 carbon-hydrogen ratio.
The new understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulés honor, celebrating the twenty-fifth anniversary of his first benzene paper. Here Kekulé spoke of the creation of the theory. He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake biting its own tail (a symbol in ancient cultures known as the ouroboros). This vision, he said, came to him after years of studying the nature of carbon-carbon bonds. This was seven years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time. Curiously, a similar, humorous depiction of benzene had appeared in 1886 in a pamphlet entitled Berichte der Durstigen Chemischen Gesellschaft (Journal of the Thirsty Chemical Society), a parody of the Berichte der Deutschen Chemischen Gesellschaft, only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulés anecdote. Some historians have suggested that the parody was a lampoon of the snake anecdote, possibly already well known through oral transmission even if it had not yet appeared in print. Kekulé's 1890 speech in which this anecdote appeared has been translated into English. If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862.
In 1929, the cyclic nature of benzene was finally confirmed by the crystallographer Kathleen Lonsdale using X-ray diffraction methods. Using large crystals of hexamethylbenzene, a benzene derivative with the same core of six carbon atoms, Lonsdale obtained diffraction patterns. Through calculating more than thirty parameters, Lonsdale demonstrated that the benzene ring could not be anything but a flat hexagon, and provided accurate distances for all carbon-carbon bonds in the molecule. | 1 | Applied and Interdisciplinary Chemistry |
In fluid mechanics, the Roshko number (Ro) is a dimensionless number describing oscillating flow mechanisms. It is named after the American Professor of Aeronautics Anatol Roshko. It is defined as
where
* St is the dimensionless Strouhal number;
* Re is the Reynolds number;
* U is mean stream velocity;
* f is the frequency of vortex shedding;
* L is the characteristic length (for example hydraulic diameter);
* ν is the kinematic viscosity of the fluid. | 1 | Applied and Interdisciplinary Chemistry |
Source:
Fretting also occurs on virtually all electrical connectors subject to motion (e.g. a printed circuit board connector plugged into a backplane, i.e. SOSA/VPX). Commonly most board to board (B2B) electrical connectors are especially vulnerable if there is any relative motion present between the mating connectors. A mechanically rigid connection system is required to hold both halves of a B2B motionless (often impossible). Wire to board (W2B) connectors tend to be immune to fretting because the wire half of the connector acts as a spring absorbing relative motion that would otherwise transfer to the contact surfaces of the W2B connector. Very few exotic B2B connectors exist that address fretting by: 1) incorporating springs into the individual contacts or 2) using a Chinese finger trap design to greatly increase the contact area. A connector design that contacts all 4-sides of a square pin instead of just one or 1 or 2 can delay the inevitable fretting some amount. Keeping contacts clean and lubricated also offers some longevity.
Contact fretting can change the impedance of a B2B connector from milliohms to ohms in just minutes when vibration is present. The relatively soft and thin gold plating used on most high quality electrical connectors is quickly worn through exposing the underlying alloy metals and with fretting debris the impedance rapidly increases. Somewhat counterintuitively, high contact forces on the mated connector pair (thought to help lower impedance and increase reliability) can actually make the rate of fretting even worse. | 1 | Applied and Interdisciplinary Chemistry |
Barium nitrite is a chemical compound, the nitrous acid salt of barium. It has the chemical formula Ba(NO). It is a water-soluble yellow powder. It is used to prepare other metal nitrites, such as lithium nitrite.
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Stereoscopic PIV utilises two cameras with separate viewing angles to extract the z-axis displacement. Both cameras must be focused on the same spot in the flow and must be properly calibrated to have the same point in focus.
In fundamental fluid mechanics, displacement within a unit time in the X, Y and Z directions are commonly defined by the variables U, V and W. As was previously described, basic PIV extracts the U and V displacements as functions of the in-plane X and Y directions. This enables calculations of the , , and velocity gradients. However, the other 5 terms of the velocity gradient tensor are unable to be found from this information. The stereoscopic PIV analysis also grants the Z-axis displacement component, W, within that plane. Not only does this grant the Z-axis velocity of the fluid at the plane of interest, but two more velocity gradient terms can be determined: and . The velocity gradient components , , and can not be determined.
The velocity gradient components form the tensor: | 1 | Applied and Interdisciplinary Chemistry |
Magnetic sequencing is a single-molecule sequencing method in development. A DNA hairpin, containing the sequence of interest, is bound between a magnetic bead and a glass surface. A magnetic field is applied to stretch the hairpin open into single strands, and the hairpin refolds after decreasing of the magnetic field. The hairpin length can be determined by direct imaging of the diffraction rings of the magnetic beads using a simple microscope. The DNA sequences are determined by measuring the changes in the hairpin length following successful hybridization of complementary nucleotides. | 1 | Applied and Interdisciplinary Chemistry |
Much effort has been placed on understanding iron–carbon alloy system, which includes steels and cast irons. Plain carbon steels (those that contain essentially only carbon as an alloying element) are used in low-cost, high-strength applications, where neither weight nor corrosion are a major concern. Cast irons, including ductile iron, are also part of the iron-carbon system. Iron-Manganese-Chromium alloys (Hadfield-type steels) are also used in non-magnetic applications such as directional drilling.
Other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. These metals are most often used as alloys with the noted exception of silicon, which is not a metal. Other forms include:
* Stainless steel, particularly Austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important.
* Aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications.
* Copper-nickel alloys (such as Monel) are used in highly corrosive environments and for non-magnetic applications.
* Nickel-based superalloys like Inconel are used in high-temperature applications such as gas turbines, turbochargers, pressure vessels, and heat exchangers.
* For extremely high temperatures, single crystal alloys are used to minimize creep. In modern electronics, high purity single crystal silicon is essential for metal-oxide-silicon transistors (MOS) and integrated circuits. | 1 | Applied and Interdisciplinary Chemistry |
Most LOM observations are conducted using bright-field (BF) illumination, where the image of any flat feature perpendicular to the incident light path is bright, or appears to be white. But, other illumination methods can be used and, in some cases, may provide superior images with greater detail. Dark-field microscopy (DF), is an alternative method of observation that provides high-contrast images and actually greater resolution than bright-field. In dark-field illumination, the light from features perpendicular to the optical axis is blocked and appears dark while the light from features inclined to the surface, which look dark in BF, appear bright, or "self-luminous" in DF. Grain boundaries, for example, are more vivid in DF than BF. | 1 | Applied and Interdisciplinary Chemistry |
In the causal theory of waves, permittivity is a complex quantity. The imaginary part corresponds to a phase shift of the polarization relative to and leads to the attenuation of electromagnetic waves passing through the medium. By definition, the linear relative permittivity of vacuum is equal to 1, that is , although there are theoretical nonlinear quantum effects in vacuum that become non-negligible at high field strengths.
The following table gives some typical values.
The relative low frequency permittivity of ice is ~96 at −10.8 °C, falling to 3.15 at high frequency, which is independent of temperature. It remains in the range 3.12–3.19 for frequencies between about 1 MHz and the far infrared region. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, equivalent weight (also known as gram equivalent or equivalent mass) is the mass of one equivalent, that is the mass of a given substance which will combine with or displace a fixed quantity of another substance. The equivalent weight of an element is the mass which combines with or displaces 1.008 gram of hydrogen or 15.99 grams of oxygen or 35.5 grams of chlorine. These values correspond to the atomic weight divided by the usual valence; for oxygen gas as example that is 31.98 g.
For acid–base reactions, the equivalent weight of an acid or base is the mass which supplies or reacts with one mole of hydrogen cations (). For redox reactions, the equivalent weight of each reactant supplies or reacts with one mole of electrons (e) in a redox reaction.
Equivalent weight has the units of mass, unlike atomic weight, which is now used as a synonym for relative atomic mass and is dimensionless. Equivalent weights were originally determined by experiment, but (insofar as they are still used) are now derived from molar masses. The equivalent weight of a compound can also be calculated by dividing the molecular mass by the number of positive or negative electrical charges that result from the dissolution of the compound. | 0 | Theoretical and Fundamental Chemistry |
In the laboratory, for ICSI treatments, the identified eggs are stripped of surrounding cells (also known as cumulus cells) and prepared for fertilisation. An oocyte selection may be performed prior to fertilisation to select eggs that can be fertilised, as it is required they are in metaphase II. There are cases in which if oocytes are in the metaphase I stage, they can be kept being cultured so as to undergo a posterior sperm injection. In the meantime, semen is prepared for fertilisation by removing inactive cells and seminal fluid in a process called sperm washing. If semen is being provided by a sperm donor, it will usually have been prepared for treatment before being frozen and quarantined, and it will be thawed ready for use. | 1 | Applied and Interdisciplinary Chemistry |
Hemoglobin deficiency can be caused either by a decreased amount of hemoglobin molecules, as in anemia, or by decreased ability of each molecule to bind oxygen at the same partial pressure of oxygen. Hemoglobinopathies (genetic defects resulting in abnormal structure of the hemoglobin molecule) may cause both. In any case, hemoglobin deficiency decreases blood oxygen-carrying capacity. Hemoglobin deficiency is, in general, strictly distinguished from hypoxemia, defined as decreased partial pressure of oxygen in blood, although both are causes of hypoxia (insufficient oxygen supply to tissues).
Other common causes of low hemoglobin include loss of blood, nutritional deficiency, bone marrow problems, chemotherapy, kidney failure, or abnormal hemoglobin (such as that of sickle-cell disease).
The ability of each hemoglobin molecule to carry oxygen is normally modified by altered blood pH or CO, causing an altered oxygen–hemoglobin dissociation curve. However, it can also be pathologically altered in, e.g., carbon monoxide poisoning.
Decrease of hemoglobin, with or without an absolute decrease of red blood cells, leads to symptoms of anemia. Anemia has many different causes, although iron deficiency and its resultant iron deficiency anemia are the most common causes in the Western world. As absence of iron decreases heme synthesis, red blood cells in iron deficiency anemia are hypochromic (lacking the red hemoglobin pigment) and microcytic (smaller than normal). Other anemias are rarer. In hemolysis (accelerated breakdown of red blood cells), associated jaundice is caused by the hemoglobin metabolite bilirubin, and the circulating hemoglobin can cause kidney failure.
Some mutations in the globin chain are associated with the hemoglobinopathies, such as sickle-cell disease and thalassemia. Other mutations, as discussed at the beginning of the article, are benign and are referred to merely as hemoglobin variants.
There is a group of genetic disorders, known as the porphyrias that are characterized by errors in metabolic pathways of heme synthesis. King George III of the United Kingdom was probably the most famous porphyria sufferer.
To a small extent, hemoglobin A slowly combines with glucose at the terminal valine (an alpha aminoacid) of each β chain. The resulting molecule is often referred to as Hb A, a glycated hemoglobin. The binding of glucose to amino acids in the hemoglobin takes place spontaneously (without the help of an enzyme) in many proteins, and is not known to serve a useful purpose. However, as the concentration of glucose in the blood increases, the percentage of Hb A that turns into Hb A increases. In diabetics whose glucose usually runs high, the percent Hb A also runs high. Because of the slow rate of Hb A combination with glucose, the Hb A percentage reflects a weighted average of blood glucose levels over the lifetime of red cells, which is approximately 120 days. The levels of glycated hemoglobin are therefore measured in order to monitor the long-term control of the chronic disease of type 2 diabetes mellitus (T2DM). Poor control of T2DM results in high levels of glycated hemoglobin in the red blood cells. The normal reference range is approximately 4.0–5.9%. Though difficult to obtain, values less than 7% are recommended for people with T2DM. Levels greater than 9% are associated with poor control of the glycated hemoglobin, and levels greater than 12% are associated with very poor control. Diabetics who keep their glycated hemoglobin levels close to 7% have a much better chance of avoiding the complications that may accompany diabetes (than those whose levels are 8% or higher). In addition, increased glycated of hemoglobin increases its affinity for oxygen, therefore preventing its release at the tissue and inducing a level of hypoxia in extreme cases.
Elevated levels of hemoglobin are associated with increased numbers or sizes of red blood cells, called polycythemia. This elevation may be caused by congenital heart disease, cor pulmonale, pulmonary fibrosis, too much erythropoietin, or polycythemia vera. High hemoglobin levels may also be caused by exposure to high altitudes, smoking, dehydration (artificially by concentrating Hb), advanced lung disease and certain tumors.
A recent study done in Pondicherry, India, shows its importance in coronary artery disease. | 0 | Theoretical and Fundamental Chemistry |
During anoxia, provision of ATP by substrate-level phosphorylation in the matrix is important not only as a mere means of energy, but also to prevent mitochondria from straining glycolytic ATP reserves by maintaining the adenine nucleotide translocator in ‘forward mode’ carrying ATP towards the cytosol. | 1 | Applied and Interdisciplinary Chemistry |
A drinking bird consists of two glass bulbs joined by a glass tube (the bird's neck/body). The tube extends nearly all the way into the bottom bulb, and attaches to the top bulb but does not extend into it.
The space inside the bird contains a fluid, usually colored for visibility. (This dye might fade when exposed to light, with the rate depending on the dye/color).
The fluid is typically dichloromethane (DCM), also known as methylene chloride.
Earlier versions contained trichlorofluoromethane.
Miles V. Sullivan's 1945 patent suggested ether, alcohol, carbon tetrachloride, or chloroform.
Air is removed from the apparatus during manufacture, so the space inside the body is filled by vapor evaporated from the fluid. The upper bulb has a "beak" attached which, along with the head, is covered in a felt-like material. The bird is typically decorated with paper eyes, a plastic top hat, and one or more tail feathers. The whole device pivots on a crosspiece attached to the body. | 0 | Theoretical and Fundamental Chemistry |
Using tiled arrays, ChIP-on-chip allows for high resolution of genome-wide maps. These maps can determine the binding sites of many DNA-binding proteins like transcription factors and also chromatin modifications.
Although ChIP-on-chip can be a powerful technique in the area of genomics, it is very expensive. Most published studies using ChIP-on-chip repeat their experiments at least three times to ensure biologically meaningful maps. The cost of the DNA microarrays is often a limiting factor to whether a laboratory should proceed with a ChIP-on-chip experiment. Another limitation is the size of DNA fragments that can be achieved. Most ChIP-on-chip protocols utilize sonication as a method of breaking up DNA into small pieces. However, sonication is limited to a minimal fragment size of 200 bp. For higher resolution maps, this limitation should be overcome to achieve smaller fragments, preferably to single nucleosome resolution. As mentioned previously, the statistical analysis of the huge amount of data generated from arrays is a challenge and normalization procedures should aim to minimize artifacts and determine what is really biologically significant. So far, application to mammalian genomes has been a major limitation, for example, due to the significant percentage of the genome that is occupied by repeats. However, as ChIP-on-chip technology advances, high resolution whole mammalian genome maps should become achievable.
Antibodies used for ChIP-on-chip can be an important limiting factor. ChIP-on-chip requires highly specific antibodies that must recognize its epitope in free solution and also under fixed conditions. If it is demonstrated to successfully immunoprecipitate cross-linked chromatin, it is termed "ChIP-grade". Companies that provide ChIP-grade antibodies include Abcam, Cell Signaling Technology, Santa Cruz, and Upstate. To overcome the problem of specificity, the protein of interest can be fused to a tag like FLAG or HA that are recognized by antibodies. An alternative to ChIP-on-chip that does not require antibodies is DamID.
Also available are antibodies against a specific histone modification like H3 tri methyl K4. As mentioned before, the combination of these antibodies and ChIP-on-chip has become extremely powerful in determining whole genome analysis of histone modification patterns and will contribute tremendously to our understanding of the histone code and epigenetics.
A study demonstrating the non-specific nature of DNA binding proteins has been published in PLoS Biology. This indicates that alternate confirmation of functional relevancy is a necessary step in any ChIP-chip experiment. | 1 | Applied and Interdisciplinary Chemistry |
Coined by Herbert J. Webber, the term clone derives from the Ancient Greek word (), twig, which is the process whereby a new plant is created from a twig. In botany, the term lusus was used. In horticulture, the spelling clon was used until the early twentieth century; the final e came into use to indicate the vowel is a "long o" instead of a "short o". Since the term entered the popular lexicon in a more general context, the spelling clone has been used exclusively. | 1 | Applied and Interdisciplinary Chemistry |
The E-C model accommodates the failure of single parameter descriptions of acids and bases. In 1965 Russell S. Drago and Bradford Wayland published the two term equation such that each acid and each base is described by two parameters. Each acid is characterized by an E and a C. Each base is likewise characterized by its own E and C. The E and C parameters refer, respectively, to the electrostatic and covalent contributions to the strength of the bonds that the acid and base will form. These parameters have been empirically obtained by using enthalpies for adducts that form only σ bonds between the acid and base as well as adducts that have no steric repulsion between the acid and base.
This equation reproduces and predicts the enthalpy, ΔH, of a reaction between many acids and bases. ΔH is a measure of strength of the bond between the acid and the base, both in the gas phase and in weakly solvating media. Entropy effects are ignored. A matrix presentation of the equation enhances its utility.
Four values, two E and two C were assigned as references. E and C of I were chosen as standards. Since I has little tendency to undergo electrostatic bonding, the E parameter was assigned a small value, 0.5, while the value of C for the covalent property was set at 2.0. For the two base parameters, E for CHC(O)N(CH) (DMA) was set at 2.35 and C for (CH)S, diethyl sulfide, was set at 3.92. Fixing the parameters in this way imposed the covalent-electrostatic model on the data set by fixing the EE and CC products of the DMA and (CH)S adducts with iodine, and these four values ensured that none of the parameters had negative values. Due to increasing enthalpy data that became available since the EC equation was first proposed the parameters have been improved. Mixing E and C numbers from the improved set of parameters with older parameters will result in incorrect calculations and is to be avoided. A select set of the improved E and C numbers is found in this article and the complete set is available in the literature.
E and C parameters for phosphines that can be used in combination with the improved parameters for oxygen, nitrogen, and sulfur donors to measure σ-basicity have been reported. | 0 | Theoretical and Fundamental Chemistry |
In vivo ultrasound mediated drug delivery was first reported in 1991 and many other preclinical studies involving sonoporation have followed. This method is being used to deliver therapeutic drugs or genes to treat a variety of diseases including: Stroke, Cancer, Parkinsons, Alzheimers... The preclinical utility of sonoporation is well illustrated through past tumor radiation treatments which have reported a more than 10-fold cellular destruction when ionizing radiation is coupled with ultrasound-mediated microbubble vascular disruption. This increase in delivery efficiency could allow for the appropriate reduction in therapeutic dosing. | 1 | Applied and Interdisciplinary Chemistry |
In contrast with gases, there is no simple yet accurate picture for the molecular origins of viscosity in liquids.
At the simplest level of description, the relative motion of adjacent layers in a liquid is opposed primarily by attractive molecular forces
acting across the layer boundary. In this picture, one (correctly) expects viscosity to decrease with increasing temperature. This is because
increasing temperature increases the random thermal motion of the molecules, which makes it easier for them to overcome their attractive interactions.
Building on this visualization, a simple theory can be constructed in analogy with the discrete structure of a solid: groups of molecules in a liquid
are visualized as forming "cages" which surround and enclose single molecules. These cages can be occupied or unoccupied, and
stronger molecular attraction corresponds to stronger cages.
Due to random thermal motion, a molecule "hops" between cages at a rate which varies inversely with the strength of molecular attractions. In equilibrium these "hops" are not biased in any direction.
On the other hand, in order for two adjacent layers to move relative to each other, the "hops" must be biased in the direction
of the relative motion. The force required to sustain this directed motion can be estimated for a given shear rate, leading to
where is the Avogadro constant, is the Planck constant, is the volume of a mole of liquid, and is the normal boiling point. This result has the same form as the well-known empirical relation
where and are constants fit from data. On the other hand, several authors express caution with respect to this model.
Errors as large as 30% can be encountered using equation (), compared with fitting equation () to experimental data. More fundamentally, the physical assumptions underlying equation () have been criticized. It has also been argued that the exponential dependence in equation () does not necessarily describe experimental observations more accurately than simpler, non-exponential expressions.
In light of these shortcomings, the development of a less ad hoc model is a matter of practical interest. Foregoing simplicity in favor of precision, it is possible to write rigorous expressions for viscosity starting from the fundamental equations of motion for molecules. A classic example of this approach is Irving–Kirkwood theory. On the other hand, such expressions are given as averages over multiparticle correlation functions and are therefore difficult to apply in practice.
In general, empirically derived expressions (based on existing viscosity measurements) appear to be the only consistently reliable means of calculating viscosity in liquids.
Local atomic structure changes observed in undercooled liquids on cooling below the equilibrium melting temperature either in terms of radial distribution function g(r) or structure factor S(Q) are found to be directly responsible for the liquid fragility: deviation of the temperature dependence of viscosity of the undercooled liquid from the Arrhenius equation (2) through modification of the activation energy for viscous flow. At the same time equilibrium liquids follow the Arrhenius equation. | 1 | Applied and Interdisciplinary Chemistry |
Entropy of activation determines the preexponential factor of the Arrhenius equation for temperature dependence of reaction rates. The relationship depends on the molecularity of the reaction:
* for reactions in solution and unimolecular gas reactions
* while for bimolecular gas reactions
In these equations is the base of natural logarithms, is the Planck constant, is the Boltzmann constant and the absolute temperature. ' is the ideal gas constant in units of (bar·L)/(mol·K). The factor is needed because of the pressure dependence of the reaction rate. (bar·L)/(mol·K).
The value of provides clues about the molecularity of the rate determining step in a reaction, i.e. the number of molecules that enter this step. Positive values suggest that entropy increases upon achieving the transition state, which often indicates a dissociative mechanism in which the activated complex is loosely bound and about to dissociate. Negative values for indicate that entropy decreases on forming the transition state, which often indicates an associative mechanism in which two reaction partners form a single activated complex. | 0 | Theoretical and Fundamental Chemistry |
Cholamine chloride hydrochloride is one of Good's buffers with a pH in the physiological range. Its pKa at 20°C is 7.10, making it useful in cell culture work. Its ΔpKa/°C is -0.027 and it has a solubility in water at 0°C of 4.2M. | 1 | Applied and Interdisciplinary Chemistry |
In the earliest stage of glass disease, it may be possible to wash the glass to remove the surface alkali. The Corning Museum of Glass recommends washing with tap water (tepid, not hot) and a mild (non-ionic) conservation detergent. This should be followed by rinsing with de-ionized or distilled water, and careful drying to remove moisture. Careful washing can remove surface deposits, restore the appearance of clearness to the glass, and help to slow further deterioration.
Ethanol has also been suggested for cleaning, particularly for glass beads, depending on the surrounding materials that may be affected.
Once more serious damage has occurred, it cannot be reversed. Climate control of humidity and temperature is a possible intervention. Because crizzling results from the reaction of components of the glass with water vapour, controlling humidity and temperature can slow its occurrence. At the Corning Museum of Glass, items in the collection are kept at stable levels of relative humidity, between 40 and 55 percent.
Fans may be used within a case to encourage the movement of air and minimize adsorption of moisture on the glass surface. Deterioration is more likely to occur in areas with restricted air-flow which allow moisture to remain on the glass. Chemical methods for retarding corrosion rates and stabilizing surfaces are being investigated.
When a composite object contains a variety of materials, one of which is sick glass, the considerations involved in conserving and displaying the object become more complicated. For example, the British Museum chose to conserve and display a Siberian shamanic apron made of leather, glass and other materials. They weighed the likelihood that it would decay more quickly if shown against the desirability of making a unique object visible and the inevitability of its eventual degradation. "Its conservation and display ensures that access to this beautiful and unique object is maximized before the pale yellow beads, which are intrinsic to the object, are inevitably lost beyond repair." | 0 | Theoretical and Fundamental Chemistry |
Proteins are composed of carbon, hydrogen, oxygen, and nitrogen arranged in a variety of ways to form a large combination of amino acids. Unlike fat the body has no storage deposits of protein. All of it is contained in the body as important parts of tissues, blood hormones, and enzymes. The structural components of the body that contain these amino acids are continually undergoing a process of breakdown and replacement. The respiratory quotient for protein metabolism can be demonstrated by the chemical equation for oxidation of albumin:
The R.Q. for albumin is 0.818:
The reason this is important in the process of understanding protein metabolism is that the body can blend the three macronutrients and based on the mitochondrial density, a preferred ratio can be established which determines how much fuel is utilized in which packets for work accomplished by the muscles. Protein catabolism (breakdown) has been estimated to supply 10% to 15% of the total energy requirement during a two-hour aerobic training session. This process could severely degrade the protein structures needed to maintain survival such as contractile properties of proteins in the heart, cellular mitochondria, myoglobin storage, and metabolic enzymes within muscles.
The oxidative system (aerobic) is the primary source of ATP supplied to the body at rest and during low intensity activities and uses primarily carbohydrates and fats as substrates. Protein is not normally metabolized significantly, except during long term starvation and long bouts of exercise (greater than 90 minutes.) At rest approximately 70% of the ATP produced is derived from fats and 30% from carbohydrates. Following the onset of activity, as the intensity of the exercise increases, there is a shift in substrate preference from fats to carbohydrates. During high intensity aerobic exercise, almost 100% of the energy is derived from carbohydrates, if an adequate supply is available. | 1 | Applied and Interdisciplinary Chemistry |
Parker graduated from Senn High School in Chicago. She went on to receive a B.A. from Northwestern University (1966). While in college she won an award from the student chapter of the American Institute of Chemists for her essay "Chemistry as a Profession" making her the first woman to receive this award. She earned her Ph.D. from Stanford University in 1970. Following her Ph.D. she was a postdoctoral research at Columbia University. From 1973 until 2001 Parker was in the chemistry department at Brown University. In 2001 she moved to Stony Brook University, and in 2017 she was named a distinguished professor at Stony Brook University. | 0 | Theoretical and Fundamental Chemistry |
With a 0.1-0.7 mm thick mucus layer, the oral cavity serves as an important route of administration for mucoadhesive dosages. Permeation sites can be separated into two groups: sublingual and buccal, in which the former is much more permeable than the latter. However, the sublingual mucosa also produces more saliva, resulting in relatively low retention rates. Thus, sublingual mucosa is preferable for rapid onset and short duration treatments, while the buccal mucosa is more appropriate for longer dosage and onset times. Because of this dichotomy, the oral cavity is suitable for both local and systemic administration. Some common dosage forms for the oral cavity include gels, ointments, patches, and tablets. Depending on the dosage form, some drug loss can occur due to swallowing of saliva. This can be minimized by layering the side of the dosage facing the oral cavity with an impermeable coating(,) commonly seen in patches. | 1 | Applied and Interdisciplinary Chemistry |
In contrast, in Gram-positive bacteria (e.g. Bacillus stearothermophilus) and eukaryotes the central PDC core contains 60 E2 molecules arranged into an icosahedron. This E2 subunit “core” coordinates to 30 subunits of E1 and 12 copies of E3.
Eukaryotes also contain 12 copies of an additional core protein, E3 binding protein (E3BP) which bind the E3 subunits to the E2 core. The exact location of E3BP is not completely clear. Cryo-electron microscopy has established that E3BP binds to each of the icosahedral faces in yeast. However, it has been suggested that it replaces an equivalent number of E2 molecules in the bovine PDC core.
Up to 60 E1 or E3 molecules can associate with the E2 core from Gram-positive bacteria - binding is mutually exclusive. In eukaryotes E1 is specifically bound by E2, while E3 associates with E3BP. It is thought that up to 30 E1 and 6 E3 enzymes are present, although the exact number of molecules can vary in vivo and often reflects the metabolic requirements of the tissue in question. | 1 | Applied and Interdisciplinary Chemistry |
A RHEED system requires an electron source (gun), photoluminescent detector screen and a sample with a clean surface, although modern RHEED systems have additional parts to optimize the technique. The electron gun generates a beam of electrons which strike the sample at a very small angle relative to the sample surface. Incident electrons diffract from atoms at the surface of the sample, and a small fraction of the diffracted electrons interfere constructively at specific angles and form regular patterns on the detector. The electrons interfere according to the position of atoms on the sample surface, so the diffraction pattern at the detector is a function of the sample surface. Figure 1 shows the most basic setup of a RHEED system. | 0 | Theoretical and Fundamental Chemistry |
While the high-selectivity and tight-binding of RNA aptamers have generated interest in their use as pharmaceuticals, there are many problems which have prevented them from being successful in vivo. For one, without modifications RNA aptamers are degraded after being introduced into the body by nucleases in the span of a few minutes. Also, due to their small size, RNA aptamers can be removed from the bloodstream by the renal system. Because of their negative charge, RNA aptamers are additionally known to bind proteins in the bloodstream, leading to non-target tissue delivery and toxicity. Care must also be taken when isolating the RNA aptamers, as aptamers which contain repeated Cytosine-Phosphate-Guanine (CpG) sequences will cause immune system activation through the Toll-like receptor pathway.
In order to combat some of the in vivo limitations of RNA aptamers, various modifications can be added to the nucleotides to aid in efficacy of the aptamer. For instance, a polyethylene glycol (PEG) moiety can be attached to increase the size of the aptamer, thereby preventing its removal from the bloodstream by the renal glomerulus. However, PEG has been implicated in allergic reactions during in vivo testing. Furthermore, modifications can be added to prevent nuclease degradation, such as a 2’ fluoro or amino group as well as a 3’ inverted thymidine. Additionally, the aptamer can be synthesized so that the ribose sugar is in the L-form instead of the D-form, further preventing nuclease recognition. Such aptamers are known as Spiegelmers. In order to prevent Toll-like receptor pathway activation, the cytosine nucleobases within the aptamer can be methylated. Nevertheless, despite these potential solutions to reduced in vivo efficacy, it is possible that chemically modifying the aptamer may weaken its binding affinity towards its target. | 1 | Applied and Interdisciplinary Chemistry |
Physiological concentrations (ppb-range) of Fe, Cu, Zn, Ni, Mo, Pd, Co, Mn, Pt, Cr, Cd and other metal cofactor species can be identified and absolutely quantified in an aliquot of a fraction by inductively coupled plasma mass spectrometry (ICP-MS) or total reflection X-ray fluorescence (TXRF), for example. In case of ICP-MS the structural information of the associated metallobiomolecules is irreversibly lost due to ionization of the sample with plasma. Another established high sensitive detection method for the determination of trace elements in biological samples is graphite furnace atomic absorption spectrometry (GF-AAS) (cf. fig. Electropherogram). Because of high purity and optimized concentration of the separated metalloproteins, for example, therapeutic recombinant plant-made pharmaceuticals such as copper chaperone for superoxide dismutase (CCS) from medicinal plants, in a few specific PAGE fractions, the related structures of these bioactive analytes can be elucidated quantitatively by using solution NMR spectroscopy under non-denaturing conditions. | 0 | Theoretical and Fundamental Chemistry |
Some low molecular weight alcohols of industrial importance are produced by the addition of water to alkenes. Ethanol, isopropanol, 2-butanol, and tert-butanol are produced by this general method. Two implementations are employed, the direct and indirect methods. The direct method avoids the formation of stable intermediates, typically using acid catalysts. In the indirect method, the alkene is converted to the sulfate ester, which is subsequently hydrolyzed. The direct hydration using ethylene (ethylene hydration) or other alkenes from cracking of fractions of distilled crude oil.
Hydration is also used industrially to produce the diol ethylene glycol from ethylene oxide. | 0 | Theoretical and Fundamental Chemistry |
The skeletal formula, line-angle formula, or shorthand formula of an organic compound is a type of molecular structural formula that serves as a shorthand representation of a molecule's bonding and some details of its molecular geometry. A skeletal formula shows the skeletal structure or skeleton of a molecule, which is composed of the skeletal atoms that make up the molecule. It is represented in two dimensions, as on a piece of paper. It employs certain conventions to represent carbon and hydrogen atoms, which are the most common in organic chemistry.
An early form of this representation was first developed by organic chemist August Kekulé, while the modern form is closely related to and influenced by the Lewis structure of molecules and their valence electrons. Hence they are sometimes termed Kekulé structures or Lewis–Kekulé structures. Skeletal formulae have become ubiquitous in organic chemistry, partly because they are relatively quick and simple to draw, and also because the curved arrow notation used for discussions of reaction mechanisms and electron delocalization can be readily superimposed.
Several other ways of depicting chemical structures are also commonly used in organic chemistry (though less frequently than skeletal formulae). For example, conformational structures look similar to skeletal formulae and are used to depict the approximate positions of atoms in 3D space, as a perspective drawing. Other types of representation, such as Newman projection, Haworth projection or Fischer projection, also look somewhat similar to skeletal formulae. However, there are slight differences in the conventions used, and the reader needs to be aware of them in order to understand the structural details encoded in the depiction. While skeletal and conformational structures are also used in organometallic and inorganic chemistry, the conventions employed also differ somewhat. | 0 | Theoretical and Fundamental Chemistry |
A phylloquinone, sometimes called vitamin K, is the next early electron acceptor in PSI. It oxidizes A in order to receive the electron and in turn is re-oxidized by F, from which the electron is passed to F and F. The reduction of F appears to be the rate-limiting step. | 0 | Theoretical and Fundamental Chemistry |
Consider two lattice points A and B separated by a translation vector r. Consider an angle α such that a rotation of angle α about any lattice point is a symmetry of the lattice. Rotating about point B by α maps point A to a new point A. Similarly, rotating about point A by α maps B to a point B. Since both rotations mentioned are symmetry operations, A and B must both be lattice points. Due to periodicity of the crystal, the new vector r which connects them must be equal to an integer multiple of r':
with integer. The four translation vectors, three of length and one, connecting A and B, of length , form a trapezium. Therefore, the length of r' is also given by:
Combining the two equations gives:
where is also an integer. Bearing in mind that we have allowed integers . Solving for possible values of reveals that the only values in the 0° to 180° range are 0°, 60°, 90°, 120°, and 180°. In radians, the only allowed rotations consistent with lattice periodicity are given by 2π/n, where n = 1, 2, 3, 4, 6. This corresponds to 1-, 2-, 3-, 4-, and 6-fold symmetry, respectively, and therefore excludes the possibility of 5-fold or greater than 6-fold symmetry. | 0 | Theoretical and Fundamental Chemistry |
In active noise control, a microphone is used to pick up the sound that is then analyzed by a computer; then, sound waves with opposite polarity (180° phase at all frequencies) are output through a speaker, causing destructive interference and canceling much of the noise. | 1 | Applied and Interdisciplinary Chemistry |
Consecutively, the probe is incubated in a SAM to make the surface of the probe that is unoccupied unreactive to target or further aptamer binding. The optimized SAM thickness is thick enough for the surface to be passivated against target binding and thin enough to transfer electrons from the redox reporter to the electrode. SAM thickness can be measured as length. It has been reported that cocaine E-AB sensors generate more signal when the SAM is thinner and therefore more conductive. However, reducing the SAM from 6 carbons to 2 carbons decreases signal, and peak current is generated using a 6-carbon SAM. | 0 | Theoretical and Fundamental Chemistry |
ATP (adenosine triphosphate), the main source of energy in cells, must be bound to a magnesium ion in order to be biologically active. What is called ATP is often actually Mg-ATP. | 1 | Applied and Interdisciplinary Chemistry |
On 13 August 1894, John William Strutt, 3rd Baron Rayleigh and William Ramsay announced the detection of a new gas in the atmosphere. On 31 January 1895 they made a full report to the Royal Society on the new gas, argon. In addition, William Crookes, who had been asked to examine a sample, presented on the spectra of argon, reported that argon displayed two distinct spectra. In this way, Crookes identified the first known sample of terrestrial helium and established its correspondence to observations of solar helium. The discovery of argon and of helium led to identification of the noble gases and the reorganization of the periodic system.
Crookes himself suggested a design for a Periodic table in the style of a space lemniscate in 1898.
Crookes was knighted in 1897.
Crookes was named president of the British Association for the Advancement of Science in 1898. In his inaugural address, he outlined in detail a coming catastrophe: The wheat-eating peoples of the world were going to start running out of food in the 1930s. The reason, he said, was a dearth of nitrogen fertilizer available from natural sources. Crookes called on chemists to develop new ways of making fertilizer from the enormous stock of nitrogen in the atmosphere (which is roughly 80 percent nitrogen). His remarks on the coming famine achieved wide distribution in the press and were turned into a popular book. Scientists addressing the problem in the first years of the twentieth century included Kristian Birkeland, whose technology helped found Norsk Hydro, and Fritz Haber and Carl Bosch, whose Haber–Bosch process forms the foundation of today's nitrogen fertilizer industry.
In 1903, Crookes turned his attention to the newly discovered phenomenon of radioactivity, achieving the separation from uranium of its active transformation product, uranium-X (later established to be protactinium). Crookes observed the gradual decay of the separated transformation product, and the simultaneous reproduction of a fresh supply in the original uranium. At about the same time as this important discovery, he observed that when "p-particles", ejected from radio-active substances, impinge upon zinc sulfide, each impact is accompanied by a minute scintillation, an observation which forms the basis of one of the most useful methods in the detection of radioactivity.
In 1913, Crookes created an ultraviolet blocking lens made from glass containing cerium, but only lightly tinted. They were an unintended by-product of Crookess research to find a lens glass formulation that would protect glass workers from cataracts. Crookes tested more than 300 formulations, each numbered and labelled. Crookes Glass 246 was the tint recommended for glassworkers. The best-known Crookes tints are A (withdrawn due to its uranium), A1, B, and B2, which absorb all ultraviolet below 350 nm while darkening visual light. Crookess samples were made by Whitefriars, London, stained glass makers, and Chance Brothers, Birmingham. | 1 | Applied and Interdisciplinary Chemistry |
When a surface is exposed to a multi-protein solution, adsorption of certain protein molecules are favored over the others. Protein molecules approaching the surface compete for binding sites. In multi-protein system attraction between molecules can occur, whereas in single-protein solutions intermolecular repulsive interactions dominate. In addition, there is a time-dependent protein spreading, where protein molecules initially make contact with minimal binding sites on the surface. With the increase in protein's residence time on the surface, the protein may unfold for interaction with additional binding sites. This results in a time-dependent increase in the contact points between protein and surface. This further makes desorption less likely. | 1 | Applied and Interdisciplinary Chemistry |
In some scientific areas such as polymer physics, one may consider a chain of points and links between consecutive points. If the points are sequentially numbered and located at positions , , , etc. then bond vectors are defined by =−, =−, and =−, more generally. This is the case for kinematic chains or amino acids in a protein structure. In these cases, one is often interested in the half-planes defined by three consecutive points, and the dihedral angle between two consecutive such half-planes. If , and are three consecutive bond vectors, the intersection of the half-planes is oriented, which allows defining a dihedral angle that belongs to the interval . This dihedral angle is defined by
or, using the function atan2,
This dihedral angle does not depend on the orientation of the chain (order in which the point are considered) — reversing this ordering consists of replacing each vector by its opposite vector, and exchanging the indices 1 and 3. Both operations do not change the cosine, but change the sign of the sine. Thus, together, they do not change the angle.
A simpler formula for the same dihedral angle is the following (the proof is given below)
or equivalently,
This can be deduced from previous formulas by using the vector quadruple product formula, and the fact that a scalar triple product is zero if it contains twice the same vector:
Given the definition of the cross product, this means that is the angle in the clockwise direction of the fourth atom compared to the first atom, while looking down the axis from the second atom to the third. Special cases (one may say the usual cases) are , and , which are called the trans, gauche, and gauche conformations. | 0 | Theoretical and Fundamental Chemistry |
Gene targeting (GT), or homology-directed repair (HDR), is used routinely in plant genome engineering to insert specific sequences, with the first published example of GT in plants in the 1980s. However, gene targeting is particularly challenging in higher plants due to the low rates of Homologous Recombination, or Homology Directed Repair, in higher plants and the low rate of transformation (DNA uptake) by many plant species. However, there has been much effort to increase the frequencies of gene targeting in plants in the past decades, as it is very useful to be able to introduce specific sequences in the plant genome for plant genome engineering. The most significant improvement to gene targeting frequencies in plants was the induction of double-strand-breaks through site specific nucleases such as CRISPR, as described above. Other strategies include in planta gene targeting, whereby the homology repair template is embedded within the plant genome and then liberated using CRISPR cutting; upregulation of genes involved in the homologous recombination pathway; downregulation of the competing Non-Homologous-End-Joining pathway; increasing copy numbers of the homologous repair template; and engineering Cas variants to be optimised for plant tissue culture. Some of these approaches have also been used to improve gene targeting efficiencies in mammalian cells.
Plants that have been gene-targeted include Arabidopsis thaliana (the most commonly used model plant), rice, tomato, maize, tobacco and wheat. | 1 | Applied and Interdisciplinary Chemistry |
Magnetic-activated cell sorting (MACS) is a method for separation of various cell populations depending on their surface antigens (CD molecules) invented by Miltenyi Biotec. The name MACS is a registered trademark of the company.
The method was developed with Miltenyi Biotec's MACS system, which uses superparamagnetic nanoparticles and columns. The superparamagnetic nanoparticles are of the order of 100 nm. They are used to tag the targeted cells in order to capture them inside the column. The column is placed between permanent magnets so that when the magnetic particle-cell complex passes through it, the tagged cells can be captured. The column consists of steel wool which increases the magnetic field gradient to maximize separation efficiency when the column is placed between the permanent magnets.
Magnetic-activated cell sorting is a commonly used method in areas like immunology, cancer research, neuroscience, and stem cell research. Miltenyi sells microbeads which are magnetic nanoparticles conjugated to antibodies which can be used to target specific cells. | 1 | Applied and Interdisciplinary Chemistry |
Typical adsorbents proposed for carbon capture and storage are zeolites and MOFs. The customization of adsorbents makes them a potentially attractive alternative to absorption. Because adsorbents can be regenerated by temperature or pressure swing, this step can be less energy intensive than absorption regeneration methods. Major problems that are present with adsorption cost in carbon capture are: regenerating the adsorbent, mass ratio, solvent/MOF, cost of adsorbent, production of the adsorbent, lifetime of adsorbent.
In sorption enhanced water gas shift (SEWGS) technology a pre-combustion carbon capture process, based on solid adsorption, is combined with the water gas shift reaction (WGS) in order to produce a high pressure hydrogen stream. The CO stream produced can be stored or used for other industrial processes. | 0 | Theoretical and Fundamental Chemistry |
Absorption bands in the radio frequency range are found in NMR spectroscopy. The frequency ranges and intensities are determined by the magnetic moment of the nuclei that are observed, the applied magnetic field and temperature occupation number differences of the magnetic states. | 0 | Theoretical and Fundamental Chemistry |
In polymer chemistry, a structural unit is a building block of a polymer chain. It is the result of a monomer which has been polymerized into a long chain.
There may be more than one structural unit in the repeat unit. When different monomers are polymerized, a copolymer is formed. It is a routine way of developing new properties for new materials. | 0 | Theoretical and Fundamental Chemistry |
De Novo biosynthesis of a pyrimidine is catalyzed by three gene products CAD, DHODH and UMPS. The first three enzymes of the process are all coded by the same gene in CAD which consists of carbamoyl phosphate synthetase II, aspartate carbamoyltransferase and dihydroorotase. Dihydroorotate dehydrogenase (DHODH) unlike CAD and UMPS is a mono-functional enzyme and is localized in the mitochondria. UMPS is a bifunctional enzyme consisting of orotate phosphoribosyltransferase (OPRT) and orotidine monophosphate decarboxylase (OMPDC). Both, CAD and UMPS are localized around the mitochondria, in the cytosol. In Fungi, a similar protein exists but lacks the dihydroorotase function: another protein catalyzes the second step.
In other organisms (Bacteria, Archaea and the other Eukaryota), the first three steps are done by three different enzymes. | 1 | Applied and Interdisciplinary Chemistry |
Primary reference materials define the scales on which isotopic ratios are reported. This can mean a material that historically defined an isotopic scale, such as Vienna Standard Mean Ocean Water (VSMOW) for hydrogen isotopes, even if that material is not currently in use. Alternatively, it can mean a material that only ever existed theoretically but is used to define an isotopic scale, such as VCDT for sulfur isotope ratios. | 0 | Theoretical and Fundamental Chemistry |
Various theories of ore genesis explain how the various types of mineral deposits form within Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined.
Ore-genesis theories generally involve three components: source, transport or conduit, and trap. (This also applies to the petroleum industry: petroleum geologists originated this analysis.)
*Source is required because metal must come from somewhere, and be liberated by some process.
*Transport is required first to move the metal-bearing fluids or solid minerals into their current position, and refers to the act of physically moving the metal, as well as to chemical or physical phenomena which encourage movement.
*Trapping is required to concentrate the metal via some physical, chemical, or geological mechanism into a concentration which forms mineable ore.
The biggest deposits form when the source is large, the transport mechanism is efficient, and the trap is active and ready at the right time. | 0 | Theoretical and Fundamental Chemistry |
Since the Fleischmann and Pons announcement, the Italian national agency for new technologies, energy and sustainable economic development (ENEA) has funded Franco Scaramuzzi's research into whether excess heat can be measured from metals loaded with deuterium gas. Such research is distributed across ENEA departments, CNR laboratories, INFN, universities and industrial laboratories in Italy, where the group continues to try to achieve reliable reproducibility (i.e. getting the phenomenon to happen in every cell, and inside a certain frame of time). In 2006–2007, the ENEA started a research program which claimed to have found excess power of up to 500 percent, and in 2009, ENEA hosted the 15th cold fusion conference. | 0 | Theoretical and Fundamental Chemistry |
In 2007, an MIT team successfully laser-cooled a macro-scale (1 gram) object to 0.8 K. In 2011, a team from the California Institute of Technology and the University of Vienna became the first to laser-cool a (10 μm x 1 μm) mechanical object to its quantum ground state. | 0 | Theoretical and Fundamental Chemistry |
Energy transmission with a rotating shaft is very common in engineering practice. Often the torque T applied to the shaft is constant which means that the force F applied is constant. For a specified constant torque, the work done during n revolutions is determined as follows: A force F acting through a moment arm r generates a torque T
This force acts through a distance s, which is related to the radius r by
The shaft work is then determined from:
The power transmitted through the shaft is the shaft work done per unit time, which is expressed as | 0 | Theoretical and Fundamental Chemistry |
With the 2006 adoption of the Restriction of Hazardous Substances Directive (RoHS) regulations in the European Union, California banning most uses of lead, and similar regulations elsewhere, the problem of tin pest has returned, since some manufacturers which previously used tin/lead alloys now use predominately tin-based alloys. For example, the leads of some electrical and electronic components are plated with pure tin. In cold environments, this can change to α-modification grey tin, which is not electrically conductive, and falls off the leads. After reheating, it changes back to β-modification white tin, which is electrically conductive. This cycle can cause electrical short circuits and failure of equipment. Such problems can be intermittent as the powdered particles of tin move around. Tin pest can be avoided by alloying with small amounts of electropositive metals or semimetals soluble in tin's solid phase, e.g. antimony or bismuth, which prevent the phase change. | 1 | Applied and Interdisciplinary Chemistry |
This method, also known as transdifferentiation or direct conversion, consists in overexpressing one or several factors, usually transcription factors, introduced in the cells. The starting material can be either pluripotent stem cells (PSCs), or either differentiated cell type such as fibroblasts. The principle was first demonstrated in 1987 with the myogenic factors MyoD.
A drawback of this approach is the introduction of foreign nucleic acid in the cells and the forced expression of transcription factors which effects are not fully understood. | 1 | Applied and Interdisciplinary Chemistry |
Despite the occasional use in pharmaceuticals, the nitro group is associated with mutagenicity and genotoxicity and therefore is often regarded as a liability in the drug discovery process. | 0 | Theoretical and Fundamental Chemistry |
The epoxidation of asymmetric alkenes has also been studied as an example of Curtin–Hammett kinetics. In a computational study of the diastereoselective epoxidation of chiral allylic alcohols by titanium peroxy complexes, the computed difference in transition state energies between the two conformers was 1.43 kcal/mol. Experimentally, the observed product ratio was 91:9 in favor of the product derived from the lower-energy transition state. This product ratio is consistent with the computed difference in transition state energies. This is an example in which the conformer favored in the ground state, which experiences reduced A(1,3) strain, reacts through a lower-energy transition state to form the major product. | 0 | Theoretical and Fundamental Chemistry |
*The complexity of sugars: regarding their structures, they are not linear instead they are highly branched. Moreover, glycans can be modified (modified sugars), this increases its complexity.
*Complex biosynthetic pathways for glycans.
*Usually glycans are found either bound to protein (glycoprotein) or conjugated with lipids (glycolipids).
*Unlike genomes, glycans are highly dynamic.
This area of research has to deal with an inherent level of complexity not seen in other areas of applied biology. 68 building blocks (molecules for DNA, RNA and proteins; categories for lipids; types of sugar linkages for saccharides) provide the structural basis for the molecular choreography that constitutes the entire life of a cell. DNA and RNA have four building blocks each (the nucleosides or nucleotides). Lipids are divided into eight categories based on ketoacyl and isoprene. Proteins have 20 (the amino acids). Saccharides have 32 types of sugar linkages. While these building blocks can be attached only linearly for proteins and genes, they can be arranged in a branched array for saccharides, further increasing the degree of complexity.
Add to this the complexity of the numerous proteins involved, not only as carriers of carbohydrate, the glycoproteins, but proteins specifically involved in binding and reacting with carbohydrate:
*Carbohydrate-specific enzymes for synthesis, modulation, and degradation
*Lectins, carbohydrate-binding proteins of all sorts
*Receptors, circulating or membrane-bound carbohydrate-binding receptors | 0 | Theoretical and Fundamental Chemistry |
Arterial spin labeling (ASL), also known as arterial spin tagging, is a magnetic resonance imaging technique used to quantify cerebral blood perfusion by labelling blood water as it flows throughout the brain. ASL specifically refers to magnetic labeling of arterial blood below or in the imaging slab, without the need of gadolinium contrast. A number of ASL schemes are possible, the simplest being flow alternating inversion recovery (FAIR) which requires two acquisitions of identical parameters with the exception of the out-of-slice saturation; the difference in the two images is theoretically only from inflowing spins, and may be considered a perfusion map.
The ASL technique was developed by Alan P. Koretsky, Donald S. Williams, John A. Detre and John S. Leigh Jr in 1992. | 0 | Theoretical and Fundamental Chemistry |
Wiesner made remarkable contributions to the structural and synthetic chemistry of complex polysubstituted polycyclic natural products. In the 1950s, prior to the development of nuclear magnetic resonance spectroscopy, he determined the structure of several diterpene alkaloids including veatchine, atisine, annotinine, delphinine, aconitine, and songorine. After returning to New Brunswick from Ayerst in 1964, he began a successful program to synthesize these compounds, culminating in the total synthesis of chasmanine and napelline. Towards the end of the 1970s Wiesner turned his attention to digitalis derivatives, with the goal of finding cardiac glycosides with safer therapeutic ratios. In the last decade of his career he succeeded in demonstrating the separation of the inotropic and toxic properties of this group of compounds, elucidated the underlying chemical mechanism, and finally achieved the total synthesis of digitoxin and other cardioactive steroids. | 0 | Theoretical and Fundamental Chemistry |
Home aquaria and inland commercial aquariums are a form of RAS where the water quality is very carefully controlled and the stocking density of fish is relatively low. In these systems the goal is to display the fish rather than producing food. However, biofilters and other forms of water treatment are still used to reduce the need to exchange water and to maintain water clarity. Just like in traditional RAS water must be removed periodically to prevent nitrate and other toxic chemicals from building up in the system. Coastal aquariums often have high rates of water exchange and are typically not operated as a RAS due to their proximity to a large body of clean water. | 1 | Applied and Interdisciplinary Chemistry |
Two research groups reported trifluoromethylations of diazonium salts in 2013. Goossen reported the preparation of a complex from CuSCN, , and . In contrast, Fu reported the trifluoromethylation using Umemotos reagent (S'-trifluoromethyldibenzothiophenium tetrafluoroborate) and Cu powder (Gattermann-type conditions). They can be described by the following equation:
The bracket indicates that other ligands on copper are likely present but are omitted. | 0 | Theoretical and Fundamental Chemistry |
FAM227B is located at 15q21.2 and contains 24 exons. The current size determined for FAM227B is 293,961 base pairs (NCBI). Neighbors of FAM227B on chromosome fifteen include: “ribosomal protein L15 pseudogene”, “galactokinase 2”, “RNA, 7SL, cytoplasmic 307, pseudogene”, “signal peptide peptidase like 2A pseudogene”, “fibroblast growth factor 7”, “uncharacterized LOC105370811”, “DTW domain containing 1”, and “ring finger protein, LIM domain interacting pseudogene 3”. | 1 | Applied and Interdisciplinary Chemistry |
Sickle-cell anemia is caused by a point mutation in the β-globin chain of hemoglobin, causing the hydrophilic amino acid glutamic acid to be replaced with the hydrophobic amino acid valine at the sixth position.
The β-globin gene is found on the short arm of chromosome 11. The association of two wild-type α-globin subunits with two mutant β-globin subunits forms hemoglobin S (HbS). Under low-oxygen conditions (being at high altitude, for example), the absence of a polar amino acid at position six of the β-globin chain promotes the non-covalent polymerisation (aggregation) of hemoglobin, which distorts red blood cells into a sickle shape and decreases their elasticity.
Hemoglobin is a protein found in red blood cells, and is responsible for the transportation of oxygen through the body. There are two subunits that make up the hemoglobin protein: beta-globins and alpha-globins.
Beta-hemoglobin is created from the genetic information on the HBB, or "hemoglobin, beta" gene found on chromosome 11p15.5. A single point mutation in this polypeptide chain, which is 147 amino acids long, results in the disease known as Sickle Cell Anemia.
Sickle-cell anemia is an autosomal recessive disorder that affects 1 in 500 African Americans, and is one of the most common blood disorders in the United States. The single replacement of the sixth amino acid in the beta-globin, glutamic acid, with valine results in deformed red blood cells. These sickle-shaped cells cannot carry nearly as much oxygen as normal red blood cells and they get caught more easily in the capillaries, cutting off blood supply to vital organs. The single nucleotide change in the beta-globin means that even the smallest of exertions on the part of the carrier results in severe pain and even heart attack. Below is a chart depicting the first thirteen amino acids in the normal and abnormal sickle cell polypeptide chain. | 1 | Applied and Interdisciplinary Chemistry |
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