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Passive blue roof systems control the rate at which water drains from a rooftop through non-mechanical means. Unlike active systems which inhibit water flow through drainage pipes, passive systems temporarily detain water on the surface of the roof by lengthening the path the water must take in order to reach outlet drains. Blue roofs can include open water surfaces, storage within or beneath a porous media or modular surface, or below a raised decking surface or cover.
* Roof‐integrated passive blue roof designs are built to retain water directly on a roof's surface, protected by a waterproof membrane, for extended periods of time. This ponding of water can be done either within a porous media, such as gravel, or free standing on the roof surface. The release rate of the stored water is controlled by weirs on the roof drain. Roof-integrated designs are most effective in new construction as achievable storage volume on existing flat roofs is often quite limited.
*Modular tray designs allow existing roofs to be retrofitted for stormwater retention capabilities with the addition of plastic or metal trays. Similarly to roof-integrated designs, water collected in the trays can either be ponded within a porous media or free standing within the tray. Modular tray blue roofs allow for more flexibility in the size and location of detention areas on a rooftop than a roof-integrated design. This selective placement of trays makes avoiding roof areas which cannot support the additional structural load, as well as any roof obstructions easier than other blue roof designs. Trays also have the added advantage of not using the roof material itself as a component of the detention structure and thus decrease instead of increase the hydraulic head on the underlying roofing membrane. As the water drains from the trays, it is released onto the roof surface itself and drains normally.
*Roof‐dams or roof‐checks physically interrupt the flow path of the water as it travels towards the roof drain. Similar to roof-integrated designs, the roof surface is the primary location of water detention with these impermeable or slow-releasing dams forcing water to pond behind them. The height of the dam and the size of weep holes can be used to control the detention time of the structures.
*Blue-green roof designs are aesthetically similar to green roofs in that they are vegetative roofs, but functionally different in that they have additional water storage capacity beneath the growing media to facilitate in stormwater retention. | 1 | Applied and Interdisciplinary Chemistry |
In this class it is worthwhile to highlight the small non-peptide molecules LM22A-24 and LM11A-31 developed by Longo and Massa. Through the modulation of p75NTR activity, these compounds downregulate degenerative and upregulate trophic signaling. In particular, LM11A-31 was found to inhibit several pathophysiological mechanisms involved in AD and related to p75NTR. Oral administration in AD mice models reduces degeneration of cholinergic neurites. Furthermore, by a direct activation of p75NTR signaling and inhibition of apoptotic pathway, it improves motor function in a spinal cord injury (SCI) mice model and leads to an antiapoptotic effect in mice after traumatic brain injury (TBI). In February 2017, a phase 2 clinical trial started focusing on the evaluation of the safety of LM11A-31 in mild to moderate AD (NCT03069014). This study was completed in June 2020, but the results have not been published yet.
Another drug belonging to the class of p75NTR antagonists is THX-B, which inhibits NGF-p75NTR binding and prevents the death of RGCs in axotomy and glaucoma. In addition, in combination with LM22A-24, THX-B delays the loss of retinal structure, prevents RGC degeneration and preserves ganglion cell layer-inner plexiform layer thickness with a better efficacy compared to LM22A-24. Finally, a p75NTR antagonist, EVT901, was able to improve functional outcomes in two models of traumatic brain injury. Furthermore it was found to reduce inflammation in vivo in the TGFAD344 rat model of AD. | 1 | Applied and Interdisciplinary Chemistry |
The use of iron isotopes may also have applications when studying potential evidence for life on other planets. The ability of microbes to utilize iron in their metabolisms makes it possible for organisms to survive in anoxic, iron-rich environments, such as Mars. Thus, the continual improvement of knowledge regarding the biological fractionations of iron observed on Earth can have applications when studying extraterrestrial samples in the future. While this field of research is still developing, this could provide evidence regarding whether a sample was generated as a result of biologic or abiologic processes depending on the isotopic fractionation. For example, it has been hypothesized that magnetite crystals found in Martian meteorites may have formed biologically as a result of their striking similarity to magnetite crystals produced by magnetotactic bacteria on Earth. Iron isotopes could be used to study the origin of the proposed "magnetofossils" and other rock formations on Mars. | 0 | Theoretical and Fundamental Chemistry |
Studies performed seeded scaffolds made of polymers with various cell lines in vitro, in which the scaffolds degraded over time while leaving behind a cellular matrix and proteins. The first study on tissue engineering of heart valves was published in 1995. During 1995 and 1996, Shinoka used a scaffold made of polyglycolic acid (PGA), approved by the FDA for human implantation, and seeded it with sheep endothelial cells and fibroblasts with the goal of replacing a sheeps pulmonary valve leaflet. What resulted from Shinokas study was an engineered heart valve that was much thicker and more rigid, which prompted Hoerstrup to conduct a study to replace all three pulmonary valve leaflets in a sheep using a poly-4-hydroxybutyrate (P4HB) coated PGA scaffold and sheep endothelial cells and myofibroblast. | 1 | Applied and Interdisciplinary Chemistry |
Household RO units use a lot of water because they have low back pressure. Household RO water purifiers typically produce one liter of usable water and 3-25 liters of wastewater. The remainder is discharged, usually into the drain. Because wastewater carries the rejected contaminants, recovering this water is not practical for household systems. Wastewater is typically delivered to house drains. A RO unit delivering of treated water per day also discharge between . This led India's National Green Tribunal to propose a ban on RO water purification systems in areas where the total dissolved solids (TDS) measure in water is less than 500 mg/liter. In Delhi, large-scale use of household RO devices has increased the total water demand of the already water-parched National Capital Territory of India. | 0 | Theoretical and Fundamental Chemistry |
FDA hydrolysis is often used to measure activity in soil and compost samples; however, it may not give an accurate reading if microbes with lower activity phases, such as esterases, cleave the fluorescein first.
It is also used in combination with propidium iodide (PI) to determine viability in eukaryotic cells. Living cells will actively convert the non-fluorescent FDA into the green fluorescent compound fluorescein, a sign of viability; while nucleus of membrane-compromised cells will fluoresce red, a sign of cell death. Currently FDA/PI staining is the standard assessment of human pancreatic islet viability with suitability for transplantation when viability score is above 70%. | 1 | Applied and Interdisciplinary Chemistry |
The product scope of this reaction is extremely broad with the use of different substrates; however development of different functionalities has required accompanied studies to determine the proper catalyst system. The most typical class of reactions involves coupling between C–COOH and C–X bonds, however C–COOH and C–M cross-coupling, homo-coupling of carboxylic acids, heck coupling, and dehydrogenative cross-coupling can also be including in this class as they release CO. Heteroatom cross coupling reactions involving formation of C–N, C–S, C–P, and C–X bonds have also been demonstrated. | 0 | Theoretical and Fundamental Chemistry |
* Therapeutic antibody discovery
* Cell-receptor monoclonal antibody development
* In vivo animal study-grade antibodies development
* Molecular modeling
* Antibody sequencing
* Anti-idiotype antibody production
* Anti-protein antibodies for pharmacokinetics studies
* Immunogenicity assays for reagents and controls
* Immunoassay development
* Ligand-binding assay analysis
* Drug potency assay analysis
* Cell bank storage
* Full technical and project management | 1 | Applied and Interdisciplinary Chemistry |
The process of water sampling introduces two significant problems:
* The first problem is the extent to which the sample may be representative of the water source of interest. Water sources vary with time and with location. The measurement of interest may vary seasonally or from day to night or in response to some activity of man or natural populations of aquatic plants and animals. The measurement of interest may vary with distances from the water boundary with overlying atmosphere and underlying or confining soil. The sampler must determine if a single time and location meets the needs of the investigation, or if the water use of interest can be satisfactorily assessed by averaged values of sampling over time and location, or if critical maxima and minima require individual measurements over a range of times, locations or events. The sample collection procedure must assure correct weighting of individual sampling times and locations where averaging is appropriate. Where critical maximum or minimum values exist, statistical methods must be applied to observed variation to determine an adequate number of samples to assess the probability of exceeding those critical values.
* The second problem occurs as the sample is removed from the water source and begins to establish chemical equilibrium with its new surroundings – the sample container. Sample containers must be made of materials with minimal reactivity with substances to be measured; pre-cleaning of sample containers is important. The water sample may dissolve part of the sample container and any residue on that container, and chemicals dissolved in the water sample may sorb onto the sample container and remain there when the water is poured out for analysis. Similar physical and chemical interactions may take place with any pumps, piping, or intermediate devices used to transfer the water sample into the sample container. Water collected from depths below the surface will normally be held at the reduced pressure of the atmosphere; so gas dissolved in the water will collect at the top of the container. Atmospheric gas above the water may also dissolve into the water sample. Other chemical reaction equilibria may change if the water sample changes temperature. Finely divided solid particles formerly suspended by water turbulence may settle to the bottom of the sample container, or a solid phase may form from biological growth or chemical precipitation. Microorganisms within the water sample may biochemically alter concentrations of oxygen, carbon dioxide, and organic compounds. Changing carbon dioxide concentrations may alter pH and change solubility of chemicals of interest. These problems are of special concern during measurement of chemicals assumed to be significant at very low concentrations.
Sample preservation may partially resolve the second problem. A common procedure is keeping samples cold to slow the rate of chemical reactions and phase change, and analyzing the sample as soon as possible; but this merely minimizes the changes rather than preventing them. A useful procedure for determining influence of sample containers during delay between sample collection and analysis involves preparation for two artificial samples in advance of the sampling event. One sample container is filled with water known from previous analysis to contain no detectable amount of the chemical of interest. This sample, called a "blank", is opened for exposure to the atmosphere when the sample of interest is collected, then resealed and transported to the laboratory with the sample for analysis to determine if sample collection or holding procedures introduced any measurable amount of the chemical of interest. The second artificial sample is collected with the sample of interest, but then "spiked" with a measured additional amount of the chemical of interest at the time of collection. The blank (negative control) and spiked sample (positive control) are carried with the sample of interest and analyzed by the same methods at the same times to determine any changes indicating gains or losses during the elapsed time between collection and analysis. | 0 | Theoretical and Fundamental Chemistry |
Type II rearrangements often involve double hydrogen migration in a carbon skeleton. This reaction type can be found in certain transfer hydrogenations. An example is hydrogen transfer in syn-sesquinorbornene
disulfones. | 0 | Theoretical and Fundamental Chemistry |
Atomic physics is the subfield of AMO that studies atoms as an isolated system of electrons and an atomic nucleus, while molecular physics is the study of the physical properties of molecules. The term atomic physics is often associated with nuclear power and nuclear bombs, due to the synonymous use of atomic and nuclear in standard English. However, physicists distinguish between atomic physics — which deals with the atom as a system consisting of a nucleus and electrons — and nuclear physics, which considers atomic nuclei alone. The important experimental techniques are the various types of spectroscopy. Molecular physics, while closely related to atomic physics, also overlaps greatly with theoretical chemistry, physical chemistry and chemical physics.
Both subfields are primarily concerned with electronic structure and the dynamical processes by which these arrangements change. Generally this work involves using quantum mechanics. For molecular physics, this approach is known as quantum chemistry. One important aspect of molecular physics is that the essential atomic orbital theory in the field of atomic physics expands to the molecular orbital theory. Molecular physics is concerned with atomic processes in molecules, but it is additionally concerned with effects due to the molecular structure. Additionally to the electronic excitation states which are known from atoms, molecules are able to rotate and to vibrate. These rotations and vibrations are quantized; there are discrete energy levels. The smallest energy differences exist between different rotational states, therefore pure rotational spectra are in the far infrared region (about 30 - 150 µm wavelength) of the electromagnetic spectrum. Vibrational spectra are in the near infrared (about 1 - 5 µm) and spectra resulting from electronic transitions are mostly in the visible and ultraviolet regions. From measuring rotational and vibrational spectra properties of molecules like the distance between the nuclei can be calculated.
As with many scientific fields, strict delineation can be highly contrived and atomic physics is often considered in the wider context of atomic, molecular, and optical physics. Physics research groups are usually so classified. | 0 | Theoretical and Fundamental Chemistry |
Corrosion under insulation (CUI) is a severe form of localized external corrosion that occurs in carbon and low alloy steel equipment that has been insulated. This form of corrosion occurs when water is absorbed by or collected in the insulation. The equipment begins to corrode as it is exposed to water and oxygen. CUI is common in refineries and process plants that typically operate equipment at high temperatures.
Corrosion occurs where there is thermal cycling. In this instance the moist condenses back on to the core material until it is flashed off when the plant is brought back into operation.
It also occurs in carbon and low alloy steels at temperatures between 10°F and 350°F (-12°C and 175°C), and in austenitic stainless steels and duplex stainless steels at temperatures between 140°F and 400°F (60°C and 205°C) | 1 | Applied and Interdisciplinary Chemistry |
Kinetic resolution is a possible method for irreversibly differentiating a pair of enantiomers due to (potentially) different activation energies. While both enantiomers are at the same Gibbs free energy level by definition, and the products of the reaction with both enantiomers are also at equal levels, the , or transition state energy, can differ. In the image below, the R enantiomer has a lower and would thus react faster than the S enantiomer.
The ideal kinetic resolution is that in which only one enantiomer reacts, i.e. k>>k. The selectivity (s) of a kinetic resolution is related to the rate constants of the reaction of the R and S enantiomers, k and k respectively, by s=k/k, for k>k. This selectivity can also be referred to as the relative rates of reaction. This can be written in terms of the free energy difference between the high- and low-energy transitions states, .
The selectivity can also be expressed in terms of ee of the recovered starting material and conversion (c), if first-order kinetics (in substrate) are assumed.
If it is assumed that the S enantiomer of the starting material racemate will be recovered in excess, it is possible to express the concentrations (mole fractions) of the S and R enantiomers as
where ee is the ee of the starting material. Note that for c=0, which signifies the beginning of the reaction, , where these signify the initial concentrations of the enantiomers. Then, for stoichiometric chiral resolving agent B*,
Note that, if the resolving agent is stoichiometric and achiral, with a chiral catalyst, the [B*] term does not appear. Regardless, with a similar expression for R, we can express s as
If we wish to express this in terms of the enantiomeric excess of the product, ee", we must make use of the fact that, for products R and S from R and S, respectively
From here, we see that
which gives us
which, when we plug into our expression for s derived above, yield
The conversion (c) and selectivity factor (s) can be expressed in terms of starting material and product enantiomeric excesses (ee and ee, respectively) only:
Additionally, the expressions for c and ee can be parametrized to give explicit expressions for C and ee in terms of t. First, solving explicitly for [S] and [R] as functions of t yields
which, plugged into expressions for ee and c, gives
Without loss of generality, we can allow k=1, which gives k=s, simplifying the above expressions. Similarly, an expression for ee″ as a function of t can be derived
Thus, plots of ee and ee″ vs. c can be generated with t as the parameter and different values of s generating different curves, as shown below.
As can be seen, high enantiomeric excesses are much more readily attainable for the unreacted starting material. There is however a tradeoff between ee and conversion, with higher ee (of the recovered substrate) obtained at higher conversion, and therefore lower isolated yield. For example, with a selectivity factor of just 10, 99% ee is possible with approximately 70% conversion, resulting in a yield of about 30%. In contrast, in order to get good ee's and yield of the product, very high selectivity factors are necessary. For example, with a selectivity factor of 10, ee″ above approximately 80% is unattainable, and significantly lower ee″ values are obtained for more realistic conversions. A selectivity in excess of 50 is required for highly enantioenriched product, in reasonable yield.
This is a simplified version of the true kinetics of kinetic resolution. The assumption that the reaction is first order in substrate is limiting, and it is possible that the dependence on substrate may depend on conversion, resulting in a much more complicated picture. As a result, a common approach is to measure and report only yields and ee's, as the formula for k only applies to an idealized kinetic resolution. It is simple to consider an initial substrate-catalyst complex forming, which could negate the first-order kinetics. However, the general conclusions drawn are still helpful to understand the effect of selectivity and conversion on ee. | 0 | Theoretical and Fundamental Chemistry |
In a 1998 study, tritium concentrations in surface seawater and atmospheric water vapor (10 meters above the surface) were sampled at the following locations: the Sulu Sea, the Fremantle Bay, the Bay of Bengal, the Penang Bay, and the Strait of Malacca. Results indicated that the tritium concentration in surface seawater was highest at the Fremantle Bay (approximately 0.40 Bq/liter), which could be accredited to the mixing of runoff of freshwater from nearby lands due to large amounts found in coastal waters. Typically, lower concentrations were found between 35 and 45 degrees south latitude and near the equator. Results also indicated that (in general) tritium has decreased over the years (up to 1997) due to the physical decay of bomb tritium in the Indian Ocean. As for water vapor, the tritium concentration was approximately one order of magnitude greater than surface seawater concentrations (ranging from 0.46 to 1.15 Bq/liter). Therefore, the water vapor tritium is not affected by the surface seawater concentration; thus, the high tritium concentrations in the vapor were concluded to be a direct consequence of the downward movement of natural tritium from the stratosphere to the troposphere (therefore, the ocean air showed a dependence on latitudinal change).
In the North Pacific Ocean, the tritium (introduced as bomb tritium in the Northern Hemisphere) spread in three dimensions. There were subsurface maxima in the middle and low latitude regions, which is indicative of lateral mixing (advection) and diffusion processes along lines of constant potential density (isopycnals) in the upper ocean. Some of these maxima even correlate well with salinity extrema. In order to obtain the structure for ocean circulation, the tritium concentrations were mapped on 3 surfaces of constant potential density (23.90, 26.02, and 26.81). Results indicated that the tritium was well-mixed (at 6 to 7 TU) on the 26.81 isopycnal in the subarctic cyclonic gyre and there appeared to be a slow exchange of tritium (relative to shallower isopycnals) between this gyre and the anticyclonic gyre to the south; also, the tritium on the 23.90 and 26.02 surfaces appeared to be exchanged at a slower rate between the central gyre of the North Pacific and the equatorial regions.
The depth penetration of bomb tritium can be separated into three distinct layers:
;Layer 1: Layer 1 is the shallowest layer and includes the deepest, ventilated layer in winter; it has received tritium via radioactive fallout and lost some due to advection and/or vertical diffusion and contains approximately 28% of the total amount of tritium.
;Layer 2: Layer 2 is below the first layer but above the 26.81 isopycnal and is no longer part of the mixed layer. Its two sources are diffusion downward from the mixed layer and lateral expansions outcropping strata (poleward); it contains about 58% of the total tritium.
;Layer 3: Layer 3 is representative of waters that are deeper than the outcrop isopycnal and can only receive tritium via vertical diffusion; it contains the remaining 14% of the total tritium. | 0 | Theoretical and Fundamental Chemistry |
Considering the limitations of the dose-response concept, a novel Abstract Drug Toxicity Index (DTI) has been proposed recently. DTI redefines drug toxicity, identifies hepatotoxic drugs, gives mechanistic insights, predicts clinical outcomes and has potential as a screening tool. | 1 | Applied and Interdisciplinary Chemistry |
* Morphine is the prototype of opioid analgesics
* Propranolol is the prototype of the beta blockers
* Chlorpromazine is the prototypical phenothiazine antipsychotic
* Imipramine is the prototypical tricyclic antidepressant, and itself a derivative of chlorpromazine
* Diazepam is the prototype of the benzodiazepine
* Diphenhydramine (Benadryl) is the prototype ethanolamine antihistamine
* Nifedipine is the prototype dihydropyridine calcium channel blocker
* Chloroquine is the prototypical antimalarial agent
* Acyclovir is the prototype antiviral agent that is activated by viral thymidine kinase
* Aspirin is the prototype NSAID | 1 | Applied and Interdisciplinary Chemistry |
β-receptors are membrane-bound receptors coupled to G-proteins. Three types of β-receptors have been identified by molecular pharmacology. β receptors make up to 75% of all beta receptors and are predominantly located in the heart. β receptors are found in vascular and bronchial smooth muscle. β receptors, which are presumed to be involved in fatty acid metabolism, are located in the adipocytes.
G-protein coupled receptors consist of single polypeptide chains of 300-600 amino acids and span the plasma membrane seven times. There are three extracellular loops, one of them being the amino-terminus, and three intracellular loops with a carboxy-terminus. The hydrophilic pocket is formed within the membrane by the seven alpha-helical transmembrane domains. The ligand binds to the hydrophilic pocket in the receptor protein and activates the receptor, giving rise to the cellular effect.
When the β-agonist binds and activates the β-adrenoreceptor intracellular signaling becomes largely affected through cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA). The coupling of the β-receptor to adenylate cyclase is affected through a trimeric Gs protein, as shown in figure 2, consisting of an α-subunit (which stimulates adenylate cyclase) and βγ-subunits (which transduce other signals). Adenylate cyclase catalyzes the conversion of adenosine triphosphate into cAMP, which is a second messenger, thereby increasing the intracellular cAMP levels, resulting in relaxation of smooth muscles. cAMP levels are regulated through the activity of phosphodiesterase isozymes/isoforms, which degrades it to 5′-AMP.
The mechanism by which cAMP induces relaxation in airway smooth muscle cells is not fully understood. It is believed that cAMP catalyzes the activation of PKA, which in turn phosphorylates key regulatory proteins involved in the control of muscle tone. cAMP also has a role in inhibition of calcium ion (Ca) release from intracellular stores, sequestration of intracellular Ca, and reduction of membrane Ca entry, leading to relaxation of the airway smooth muscle.
The binding of norephinephrine to the binding site consists of one ionic bond, three hydrogen bonds and van der Waals interaction in two places. Ionic bonding forms between the protonated amine and Asp-113 in helix 3. Hydrogen bonds are formed from the hydroxyl groups, linked to the catechol ring, to Ser-204 and Ser-207 in helix 5. This binding limits configurational and rotational freedom. Van der Waals forces between aromatic catechol ring and Phe-290 in helix 6 residue and Val-114 in helix 3 residue reinforce the binding. It is believed that the N-alkyl substituents fit into a hydrophobic pocket formed between residues in helix 6 and 7. The beta-carbon is chiral and must have the R-configuration so that the beta-hydroxyl group is oriented towards the Asn-293 residue in helix 6 to form a hydrogen bond essential to binding to the beta-2 receptor. | 1 | Applied and Interdisciplinary Chemistry |
Hydrogen bonding plays an important role in determining the three-dimensional structures and the properties adopted by many proteins. Compared to the , , and bonds that comprise most polymers, hydrogen bonds are far weaker, perhaps 5%. Thus, hydrogen bonds can be broken by chemical or mechanical means while retaining the basic structure of the polymer backbone. This hierarchy of bond strengths (covalent bonds being stronger than hydrogen-bonds being stronger than van der Waals forces) is relevant in the properties of many materials. | 0 | Theoretical and Fundamental Chemistry |
Friedrich Wilhelm Strassmann (; 22 February 1902 – 22 April 1980) was a German chemist who, with Otto Hahn in December 1938, identified the element barium as a product of the bombardment of uranium with neutrons. Their observation was the key piece of evidence necessary to identify the previously unknown phenomenon of nuclear fission, as was subsequently recognized and published by Lise Meitner and Otto Frisch. In their second publication on nuclear fission in February 1939, Strassmann and Hahn predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction. | 0 | Theoretical and Fundamental Chemistry |
Martin Schröder was born in Taplow, Buckinghamshire of Estonian refugee parents in 1954, and was educated at Montem Primary School and Slough Grammar School. He is first in family to attend university, and was awarded a Bachelor of Science degree in chemistry from the University of Sheffield in 1975 and a PhD from Imperial College London in 1978 where his research on oxo complexes of osmium and ruthenium was supervised by William P. Griffith. | 0 | Theoretical and Fundamental Chemistry |
Glass-ceramics are used in medical applications due to their unique interaction, or lack thereof, with human body tissue. Bioceramics are typically placed into the following groups based on their biocompatibility: biopassive (bioinert), bioactive, or resorbable ceramics.
Biopassive (bioinert) ceramics are, as the name suggests, characterized by the limited interaction the material has with the surrounding biological tissue. Historically, these were the "first generation" biomaterials used as replacements for missing or damaged tissues. One problem resulting from using inert biomaterials was the body's reaction to the foreign object; it was found that a phenomenon known as "fibrous encapsulation" would occur, where tissues would grow around the implant in an attempt to isolate the object from the rest of the body. This occasionally caused a variety of problems such as necrosis or sequestration of the implant. Two commonly used bioinert materials are alumina (Al2O3) and zirconia (ZrO2).
Bioactive materials have the ability to form bonds and interfaces with natural tissues. In the case of bone implants, two properties known as osteoconduction and osteoinduction play an important role in the success and longevity of the implant. Osteoconduction refers to a material's ability to permit bone growth on the surface and into the pores and channels of the material. Osteoinduction is a term used when a material stimulates existing cells to proliferate, causing new bone to grow independently of the implant. In general, the bioactivity of a material is a result of a chemical reaction, typically dissolution of the implanted material. Calcium phosphate ceramics and bioactive glasses are commonly used as bioactive materials as they exhibit this dissolution behavior when introduced to living body tissue. One engineering goal relating to these materials is that the dissolution rate of the implant be closely matched to the growth rate of new tissue, leading to a state of dynamic equilibrium.
Resorbable ceramics are similar to bioactive ceramics in their interaction with the body, but the main difference lies in the extent to which the dissolution occurs. Resorbable ceramics are intended to gradually dissolve entirely, all the while new tissue grows in its stead. The architecture of these materials has become quite complex, with foam-like scaffolds being introduced to maximize the interfacial area between the implant and body tissue. One issue that arises from using highly porous materials for bioactive/resorbable implants is the low mechanical strength, especially in load-bearing areas such as the bones in the legs. An example of a resorbable material that has seen some success is tricalcium phosphate (TCP), however, it too falls short in terms of mechanical strength when used in high-stress areas. | 0 | Theoretical and Fundamental Chemistry |
Aircraft engines with a fixed exhaust nozzle area have a single steady-state operating or running line which is fixed by fuel flow from idle to maximum speed. Variable vane angles and flow areas (bleed valves) in the compressor don't change the running line at a particular operating point because the angles and valve positions are unique for a corrected speed, that is they are controlled according to a schedule against corrected speed. Over or under-fuelling compared to the fuel flow required for constant-speed running moves the line up or down while the engine is changing speed to a new requirement. | 0 | Theoretical and Fundamental Chemistry |
All equilibrium constants vary with temperature according to the van 't Hoff equation
is the gas constant and is the absolute temperature. Thus, for exothermic reactions, the standard enthalpy change, , is negative and K decreases with temperature. For endothermic reactions, is positive and K increases with temperature.
The standard enthalpy change for a reaction is itself a function of temperature, according to Kirchhoff's law of thermochemistry:
where is the heat capacity change at constant pressure. In practice may be taken to be constant over a small temperature range. | 0 | Theoretical and Fundamental Chemistry |
The soils and sediments most prone to becoming acid sulfate soils formed within the last 10,000 years, after the last major sea level rise. When the sea level rose and inundated the land, sulfate in the seawater mixed with land sediments containing iron oxides and organic matter. Under these anaerobic conditions, lithotrophic bacteria such as Desulfovibrio desulfuricans obtain oxygen for respiration through the reduction of sulfate ions in sea or groundwater, producing hydrogen sulfide. This in turn reacts with dissolved ferrous iron, forming very fine grained and highly reactive framboid crystals of iron sulfides such as (pyrite). Up to a point, warmer temperatures are more favourable conditions for these bacteria, creating a greater potential for formation of iron sulfides. Tropical waterlogged environments, such as mangrove swamps or estuaries, may contain higher levels of pyrite than those formed in more temperate climates.
The pyrite is stable until exposed to air, at which point the pyrite rapidly oxidises and produces sulfuric acid. The impacts of acid sulfate soil leachate may persist over a long time, and/or peak seasonally (after dry periods with the first rains). In some areas of Australia, acid sulfate soils that drained 100 years ago are still releasing acid (e.g., Gillman wetlands, South Australia). | 0 | Theoretical and Fundamental Chemistry |
It is important to note that A-values do not predict the physical size of a molecule, only the steric effect. For example, the tert-butyl group (A-value=4.9) has a larger A-value than the trimethylsilyl group (A-value=2.5), yet the tert-butyl group actually occupies less space. This difference can be attributed to the longer length of the carbon–silicon bond as compared to the carbon–carbon bond of the tert-butyl group. The longer bond allows for less interactions with neighboring substituents, which effectively makes the trimethylsilyl group less sterically hindering, thus, lowering its A-value. This can also be seen when comparing the halogens. Bromine, iodine, and chlorine all have similar A-values even though their atomic radii differ. A-values then, predict the apparent size of a substituent, and the relative apparent sizes determine the differences in steric effects between compounds. Thus, A-values are useful tools in determining compound reactivity in chemical reactions. | 0 | Theoretical and Fundamental Chemistry |
Beatriz Roldán Cuenya (born 1976 in Oviedo) is a Spanish physicist working in surface science and catalysis. Since 2017 she has been director of the Department of Interface Science at the Fritz Haber Institute of the Max Planck Society in Berlin, Germany. Since April 2023, she has also been interim director of the Department of Inorganic Chemistry, also at the Fritz Haber Institute. | 0 | Theoretical and Fundamental Chemistry |
Electron-withdrawing groups exert an "inductive" or "electron-pulling" effect on covalent bonds. The strength of the electron-withdrawing group is inversely proportional to the pKa of the carboxylic acid.
The inductive effect is cumulative: trichloroacetic acid is 1000x stronger than chloroacetic acid.
The impact of the EWG group on pKa decreases with distances from the carboxylic group.
For benzoic acids, the effect is quantified by the Hammett equation:
where
: = Reference constant
: = Substituent constant
: = Reaction rate constant | 0 | Theoretical and Fundamental Chemistry |
The gas-diffusion electrocrystallization process was invented in 2014 by Xochitl Dominguez Benetton at the Flemish Institute for Technological Research, in Belgium. The patent for the process granted in Europe was filed in 2015 and its expiration is anticipated in 2036. | 0 | Theoretical and Fundamental Chemistry |
Initially in the process of degradation, fatty acids are stored in adipocytes. The breakdown of this fat is known as lipolysis. The products of lipolysis, free fatty acids, are released into the bloodstream and circulate throughout the body. During the breakdown of triacylglycerols into fatty acids, more than 75% of the fatty acids are converted back into triacylglycerol, a natural mechanism to conserve energy, even in cases of starvation and exercise. | 1 | Applied and Interdisciplinary Chemistry |
In the human genome, CCL7 is encoded by the CCL7 gene which is one of the several chemokine genes clustered on chromosome 17q11.2-q12. This region contains the gene for the MCP subset of CC chemokines. The CCL7 gene has been given the locus symbol SCYA7.
The gene consists of three exons and two introns. The first exon contains a 5′-untranslated region (5′-UTR), the information for the signal sequence (23 amino acids), and the mature protein's first two amino acids. The second exon encodes amino acids 3–42 of the mature proteins. The third exon is composed of the C-terminal region of the protein, a 3′-UTR containing one or more destabilizing AU-rich sequences and a polyadenylation signal. | 1 | Applied and Interdisciplinary Chemistry |
A microcoil is a tiny electrical conductor such as a wire in the shape of a spiral or helix which could be a solenoid or a planar structure. | 0 | Theoretical and Fundamental Chemistry |
After the entire sample is loaded, the feed is switched to the displacer, chosen to have higher affinity than any sample component. The displacer forms a sharp-edged zone at the head of the column, pushing the other components downstream. Each sample component now acts as a displacer for the lower-affinity solutes, and the solutes sort themselves out into a series of contiguous bands (a "displacement train"), all moving downstream at the rate set by the displacer. The size and loading of the column are chosen to let this sorting process reach completion before the components reach the bottom of the column. The solutes appear at the bottom of the column as a series of contiguous zones, each consisting of one purified component, with the concentration within each individual zone effectively uniform. | 0 | Theoretical and Fundamental Chemistry |
In alchemy, cadmia (Latin for cadmium) is an oxide of zinc (tutty; from tutiya, via Persian, from Sanskrit तुत्थ tuttha) which collects on the sides of furnaces where copper or brass was smelted, and zinc sublimed. The term is also applied to an ore of cobalt.
For the cadmium produced in furnaces, there were five identified kinds: the first called botrytis, as being in the form of a bunch of grapes; the second, ostracitis, as resembling a sea shell; the third, placitis, for resembling a crust; the fourth, capnitis; and the fifth, calamitis, which hung around certain iron rods that were used to stir material in the furnace; being shaken off, the cadmium resembled the figure of a quill, called in the Latin, calamus. The cadmia botrytis was found in the middle of the furnace; the ostrytis at the bottom; the placitis at the top; and the capnitis at the mouth of the furnace.
In pre-modern medicine, cadmium was used as a desiccative and detersive, in moist stinking ulcers, causing the area to become healed by the formation of scar tissue. The botrytis and placitis were also used for diseases of the eyes.
The term cadmia was formerly applied to the mineral cadmium, or lapis calaminaris. | 1 | Applied and Interdisciplinary Chemistry |
Plaster casting is similar to sand casting except that plaster of paris is used instead of sand as a mold material. Generally, the form takes less than a week to prepare, after which a production rate of 1–10 units/hr-mold is achieved, with items as massive as and as small as with very good surface finish and close tolerances. Plaster casting is an inexpensive alternative to other molding processes for complex parts due to the low cost of the plaster and its ability to produce near net shape castings. The biggest disadvantage is that it can only be used with low melting point non-ferrous materials, such as aluminium, copper, magnesium, and zinc. | 1 | Applied and Interdisciplinary Chemistry |
Oblique shocks are often preferable in engineering applications when compared to normal shocks. This can be attributed to the fact that using one or a combination of oblique shock waves results in more favourable post-shock conditions (smaller increase in entropy, less stagnation pressure loss, etc.) when compared to utilizing a single normal shock. An example of this technique can be seen in the design of supersonic aircraft engine intakes or supersonic inlets. A type of these inlets is wedge-shaped to compress air flow into the combustion chamber while minimizing thermodynamic losses. Early supersonic aircraft jet engine intakes were designed using compression from a single normal shock, but this approach caps the maximum achievable Mach number to roughly 1.6. Concorde (which first flew in 1969) used variable geometry wedge-shaped intakes to achieve a maximum speed of Mach 2.2. A similar design was used on the F-14 Tomcat (the F-14D was first delivered in 1994) and achieved a maximum speed of Mach 2.34.
Many supersonic aircraft wings are designed around a thin diamond shape. Placing a diamond-shaped object at an angle of attack relative to the supersonic flow streamlines will result in two oblique shocks propagating from the front tip over the top and bottom of the wing, with Prandtl-Meyer expansion fans created at the two corners of the diamond closest to the front tip. When correctly designed, this generates lift. | 1 | Applied and Interdisciplinary Chemistry |
Cnidarians such as Hydra have become attractive model organisms to study the evolution of immunity. However, despite long-term efforts, stably transgenic animals could not be generated, severely limiting the functional analysis of genes. For analytical purposes, therefore, an important technical breakthrough in the field was the development of a transgenic procedure for generation of stably transgenic lines by embryo microinjection. | 1 | Applied and Interdisciplinary Chemistry |
Reynolds number interpretation has been extended into the area of arbitrary complex systems. Such as financial flows, nonlinear networks, etc. In the latter case, an artificial viscosity is reduced to a nonlinear mechanism of energy distribution in complex network media. Reynolds number then represents a basic control parameter that expresses a balance between injected and dissipated energy flows for an open boundary system. It has been shown that Reynolds critical regime separates two types of phase space motion: accelerator (attractor) and decelerator. High Reynolds number leads to a chaotic regime transition only in frame of strange attractor model. | 1 | Applied and Interdisciplinary Chemistry |
C-MORE: SUPER HI-CAT (Center for Microbial Oceanography- Research and Education: Survey of Underwater Plastic Ecosystem Response Hawaii to California Transit)
The SUPER HI-CAT research cruise was the first effort to study the microbial communities and the biogeochemistry associated with the Great Pacific Garbage Patch.[1] The study was conducted aboard the RV Kilo Moana (T-AGOR-26) between August 25, 2008 and September 5, 2008 by researchers from University of Hawaiʻi at Mānoa, Oregon State University, and the Algalita Marine Research Foundation.
Previous research on the Plastic Patch had mostly focused on the effects of the plastic pieces on jellyfish, fish, sea turtles, and seabirds. Relatively little was known about how this type of marine debris would affect the microbial communities that make up 98% of the biomass in the ocean and control oceanic biogeochemistry. During this cruise, 30 sites were sampled. At 15 of these sites, a modified surface net called a manta trawl was used to collect plastic pieces, while water samples were collected from the upper 200 meters of the ocean. At the other 15 stations, only the surface waters were sampled. This study will allow researchers to begin to determine whether biofilms are forming on the plastic particles, whether the microbes living on the particles are different from the free-living planktonic organisms, and what effect these communities might have on the oceanic carbon cycle and nitrogen cycle. | 0 | Theoretical and Fundamental Chemistry |
The unidirectional shape-shape-memory effect was first observed by Chand and Read in 1951 in a Gold-Cadmium alloy and in 1963 Buehler described this effect for nitinol, which is an equiatomic Nickel-Titanium alloy.
This effect in metals and ceramics is based on a change in the crystal structure, called martensitic phase transition. The disadvantage of these materials is that it is an equiatomic alloy and deviations of 1% in the composition modify the transition temperature by approximately 100 K.
Some metals and ceramics present the effect bidirectionally, which means that at a certain temperature there is a shape and this can be changed by changing the temperature, but if the first temperature is recovered, also the first shape is recovered. This is achieved by training the material for each shape at each temperature.
Metals and ceramics with thermally induced bidirectional shape-memory effect have had great application in medical implants, sensors, transducers, etc. Many present a risk however due to their high toxicity. | 0 | Theoretical and Fundamental Chemistry |
Soret held the chairs of chemistry (1873-1887) and medical physics (1887-1890) at the University of Geneva.
Soret determined the chemical composition and density of ozone and the conditions for its production. He described it correctly as being composed of three oxygen atoms bound together.
Soret also developed optical instruments. He climbed Mont Blanc, where he was the first scientist to make actinometric measurements of solar radiation. These observations were published in the Philosophical Magazine in 1867.
In 1878, he and Marc Delafontaine were the first to spectroscopically observe the element later named holmium, which they identified simply as an "earth X" derived from "erbia". Independently, Per Teodor Cleve separated it chemically from thulium and erbium in 1879. All three researchers are given credit for the element's discovery.
The Soret peak or Soret band, a strong absorption band at approximately 420 nm in the absorption spectra of hemoglobin, is also named after him. | 1 | Applied and Interdisciplinary Chemistry |
Samarium–neodymium is an isotope system which can be utilised to provide a date as well as isotopic fingerprints of geological materials, and various other materials including archaeological finds (pots, ceramics).
Sm decays to produce Nd with a half life of 1.06x10 years.
Dating is achieved usually by trying to produce an isochron of several minerals within a rock specimen. The initial Nd/Nd ratio is determined.
This initial ratio is modelled relative to CHUR (the Chondritic Uniform Reservoir), which is an approximation of the chondritic material which formed the solar system. CHUR was determined by analysing chondrite and achondrite meteorites.
The difference in the ratio of the sample relative to CHUR can give information on a model age of extraction from the mantle (for which an assumed evolution has been calculated relative to CHUR) and to whether this was extracted from a granitic source (depleted in radiogenic Nd), the mantle, or an enriched source. | 0 | Theoretical and Fundamental Chemistry |
Compounds that contain phosphorus exhibit unique chemistry due to the ability of phosphorus to form more bonds than nitrogen, its lighter analogue on the periodic table. | 0 | Theoretical and Fundamental Chemistry |
René Roy uses carbohydrate chemistry to develop neoglycoconjugates and polymers to treat disease related to glycoproteins such as bacterial infections and cancers. His synthesis of new glycan structures, among which glycopolymers, glycodendrimers, and glycodendrimersomes (terms that he first developed) enabled progress in the area of multivalent molecular recognition mechanisms.
He is known for his work on semi-synthetic glycoconjugate vaccines. He has designed a breast cancer vaccine prototype.
René Roy has authored more than 370 scientific articles and 2 books on vaccines and glycomimetics. He has 5 patents to his credit, of which two ended in commercial products | 0 | Theoretical and Fundamental Chemistry |
A Grotrian diagram, or term diagram, shows the allowed electronic transitions between the energy levels of atoms. They can be used for one-electron and multi-electron atoms. They take into account the specific selection rules related to changes in angular momentum of the electron. The diagrams are named after Walter Grotrian, who introduced them in his 1928 book Graphische Darstellung der Spektren von Atomen und Ionen mit ein, zwei und drei Valenzelektronen ("Graphical representation of the spectra of atoms and ions with one, two and three valence electrons"). | 0 | Theoretical and Fundamental Chemistry |
Modification of human genes in order to treat genetic diseases is referred to as gene therapy. Gene therapy is a medical procedure that involves inserting genetic material into a patients cells to repair or fix a malfunctioning gene in order to treat hereditary illnesses. Between 1989 and December 2018, over 2,900 clinical trials of gene therapies were conducted, with more than half of them in phase I. Since that time, many gene therapy based drugs became available, such as Zolgensma and Patisiran. Most of these approaches utilize viral vectors, such as adeno-associated viruses (AAVs), adenoviruses (AV) and lentiviruses (LV), for inserting or replacing transgenes in vivo or ex vivo'.
In 2023, nanoparticles that act similarly to viral vectors were created. These nanoparticles, called bioorthgonal engineered virus-like recombinant biosomes, display strong and rapid binding capabilities to LDL receptors on cell surfaces, allowing them to enter cells efficiently and deliver genes to specific target areas, such as tumor and arthritic tissues.
RNA interference-based agents, such as zilebesiran, contain siRNA which binds with mRNA of the target cells, modifying gene expression. | 1 | Applied and Interdisciplinary Chemistry |
As of 2013, eighteen cases of overdoses had been reported with doses of up to 14.4 grams, none of them fatal. No specific antidote for overdose exists and treatment is purely supportive. | 0 | Theoretical and Fundamental Chemistry |
Despite being larger and heavier than other bioaerosols, some studies show that pollen can be transported thousands of kilometers. They are a major source of wind-dispersed allergens, coming particularly from seasonal releases from grasses and trees. Tracking distance, transport, resources, and deposition of pollen to terrestrial and marine environments are useful for interpreting pollen records. | 0 | Theoretical and Fundamental Chemistry |
In molecular biology, protein catabolism is the breakdown of proteins into smaller peptides and ultimately into amino acids. Protein catabolism is a key function of digestion process. Protein catabolism often begins with pepsin, which converts proteins into polypeptides. These polypeptides are then further degraded. In humans, the pancreatic proteases include trypsin, chymotrypsin, and other enzymes. In the intestine, the small peptides are broken down into amino acids that can be absorbed into the bloodstream. These absorbed amino acids can then undergo amino acid catabolism, where they are utilized as an energy source or as precursors to new proteins.
The amino acids produced by catabolism may be directly recycled to form new proteins, converted into different amino acids, or can undergo amino acid catabolism to be converted to other compounds via the Krebs cycle. | 1 | Applied and Interdisciplinary Chemistry |
AMOC is driven by ocean temperature and salinity differences. The major possible mechanism causing the cold ocean surface temperature anomaly is based on the fact that freshwater decreases ocean water salinity, and through this process prevents colder waters sinking. Observed freshwater increase originates probably from Greenland ice melt. | 0 | Theoretical and Fundamental Chemistry |
Modafinil has been used non-medically as a "smart drug" by various groups, including students, office workers, transhumanists, and professionals in various sectors. Its use is attributed by these individuals to its potential for enhancing attention, cognitive capabilities, and alertness.
The effectiveness of modafinil as cognitive enhancer is still debated. Some studies suggest significant increases in cognitive abilities, while others indicate mild to non existent cognitive improvements. In some cases, it has even been associated with impairments in certain cognitive functions. It has been shown that modafinil's positive impact on cognitive abilities is more noticeable on sleep deprived individuals. Therefore, in people who are not sleep-deprived, the potential of modafinil as a cognitive enhancer may be limited. | 0 | Theoretical and Fundamental Chemistry |
Transition metal complexes of aldehydes and ketones describes coordination complexes with aldehyde (RCHO) and ketone ligands. Because aldehydes and ketones are common, the area is of fundamental interest. Some reactions that are useful in organic chemistry involve such complexes. | 0 | Theoretical and Fundamental Chemistry |
Carbon dioxide, like other gases, is soluble in water. However, unlike many other gases (oxygen for instance), it reacts with water and forms a balance of several ionic and non-ionic species (collectively known as dissolved inorganic carbon, or DIC). These are dissolved free carbon dioxide (CO ), carbonic acid (HCO), bicarbonate (HCO) and carbonate (CO), and they interact with water as follows :
The balance of these carbonate species (which ultimately affects the solubility of carbon dioxide), is dependent on factors such as pH, as shown in a Bjerrum plot. In seawater this is regulated by the charge balance of a number of positive (e.g. Na, K, Mg, Ca) and negative (e.g. CO itself, Cl, SO, Br) ions. Normally, the balance of these species leaves a net positive charge. With respect to the carbonate system, this excess positive charge shifts the balance of carbonate species towards negative ions to compensate. The result of which is a reduced concentration of the free carbon dioxide and carbonic acid species, which in turn leads to an oceanic uptake of carbon dioxide from the atmosphere to restore balance. Thus, the greater the positive charge imbalance, the greater the solubility of carbon dioxide. In carbonate chemistry terms, this imbalance is referred to as alkalinity.
In terms of measurement, four basic parameters are of key importance: Total inorganic carbon (TIC, T or C), Total alkalinity (T or A), pH, and pCO. Measuring any two of these parameters allows for the determination of a wide range of pH-dependent species (including the above-mentioned species). This balance can be changed by a number of processes. For example, the air-sea flux of CO, the dissolution/precipitation of CaCO, or biological activity such as photosynthesis/respiration. Each of these has different effects on each of the four basic parameters, and together they exert strong influences on global cycles. The net and local charge of the oceans remains neutral during any chemical process. | 0 | Theoretical and Fundamental Chemistry |
There are a number of disorders which disrupt normal functioning of ion channels and have disastrous consequences for the organism. Genetic and autoimmune disorders of ion channels and their modifiers are known as channelopathies. See :Category:Channelopathies for a full list.
* Shaker gene mutations cause a defect in the voltage gated ion channels, slowing down the repolarization of the cell.
* Equine hyperkalaemic periodic paralysis as well as human hyperkalaemic periodic paralysis (HyperPP) are caused by a defect in voltage-dependent sodium channels.
* Paramyotonia congenita (PC) and potassium-aggravated myotonias (PAM)
* Generalized epilepsy with febrile seizures plus (GEFS+)
* Episodic ataxia (EA), characterized by sporadic bouts of severe discoordination with or without myokymia, and can be provoked by stress, startle, or heavy exertion such as exercise.
* Familial hemiplegic migraine (FHM)
* Spinocerebellar ataxia type 13
* Long QT syndrome is a ventricular arrhythmia syndrome caused by mutations in one or more of presently ten different genes, most of which are potassium channels and all of which affect cardiac repolarization.
* Brugada syndrome is another ventricular arrhythmia caused by voltage-gated sodium channel gene mutations.
* Polymicrogyria is a developmental brain malformation caused by voltage-gated sodium channel and NMDA receptor gene mutations.
* Cystic fibrosis is caused by mutations in the CFTR gene, which is a chloride channel.
* Mucolipidosis type IV is caused by mutations in the gene encoding the TRPML1 channel
* Mutations in and overexpression of ion channels are important events in cancer cells. In Glioblastoma multiforme, upregulation of gBK potassium channels and ClC-3 chloride channels enables glioblastoma cells to migrate within the brain, which may lead to the diffuse growth patterns of these tumors. | 1 | Applied and Interdisciplinary Chemistry |
Stacking of the nucleotides in a double helix is a major determinant of the helixs stability. With the added surface area and hydrogen available for bonding, stacking potential for the nucleobases increases with the addition of a benzene spacer. By increasing the separation between the nitrogenous bases and either sugar-phosphate backbone, the helixs stacking energy is less variable and therefore more stable. The energies for natural nucleobase pairs vary from 18 to 52 kJ/mol. This variance is only 14–40 kJ/mol for xDNA.
Due to an increased overlap between and expanded strand of DNA and its neighbouring strand, there are greater interstrand interactions in expanded and mixed helices, resulting in a significant increase in the helixs stability. xDNA has enhanced stacking abilities resultant from changes in inter- and intrastrand hydrogen bonding that arise from the addition of a benzene spacer, but expanding the bases does not alter hydrogens contribution to the stability of the duplex. These stacking abilities are exploited by helices consisting of both xDNA and B-DNA in order to optimize the strength of the helix. Increased stacking is seen most prominently in strands consisting only of A and xA and T and xT, as T-xA has stronger stacking interactions than T-A.
The energy resultant from pyrimidines ranges from 30 to 49 kJ/mol. The range for purines is between 40-58kJ/mol. By replacing one nucleotide in a double-helix with an expanded nucleotide, the strength of the stacking interactions increases by 50%. Expanding both nucleotides results in a 90% increase in stacking strength. While xG has an overall negative effect on the binding strength of the helix, the other three expanded bases outweigh this with their positive effects. The change in energy caused by expanding the bases is mostly dependent on the rotation of the bond about the nucleobases' centers of mass, and center of mass stacking interactions improve the stacking potential of the helix. Because the size-expanded bases widen the helix, it is more thermally stable with a higher melting temperature. | 1 | Applied and Interdisciplinary Chemistry |
* NASA (1969), [http://www.dept.aoe.vt.edu/~cdhall/courses/aoe4065/NASADesignSPs/sp8031.pdf Slosh suppression] , May 1969, PDF, 36p
* NASA (1966), [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670006555.pdf Dynamic behavior of liquids in moving containers with applications to propellants in space vehicle fuel tanks], Jan 1, 1966, PDF, 464 p | 1 | Applied and Interdisciplinary Chemistry |
Single-sized aggregate without any binder, e.g. loose gravel, stone-chippings, is another alternative. Although it can only be safely used in walkways and very low-speed, low-traffic settings, e.g. car-parks and drives, its potential cumulative area is great. | 1 | Applied and Interdisciplinary Chemistry |
An attractant is any chemical that attracts an organism, e.g. i) synthetic lures; ii) aggregation and sex pheromones (intraspecific interactions); and iii) synomone (interspecific interactions) | 1 | Applied and Interdisciplinary Chemistry |
During capping, a 7-methylguanosine residue is attached to the 5-terminal end of the primary transcripts.This is otherwise known as the GTP or 5 cap. The 5 cap is used to increase mRNA stability. Further, the 5 cap is used as an attachment point for ribosomes. Beyond this, the 5' cap has also been shown to have a role in exporting the mature mRNA from the nucleus and into the cytoplasm. | 1 | Applied and Interdisciplinary Chemistry |
Factors governing organic reactions are essentially the same as that of any chemical reaction. Factors specific to organic reactions are those that determine the stability of reactants and products such as conjugation, hyperconjugation and aromaticity and the presence and stability of reactive intermediates such as free radicals, carbocations and carbanions.
An organic compound may consist of many isomers. Selectivity in terms of regioselectivity, diastereoselectivity and enantioselectivity is therefore an important criterion for many organic reactions. The stereochemistry of pericyclic reactions is governed by the Woodward–Hoffmann rules and that of many elimination reactions by Zaitsev's rule.
Organic reactions are important in the production of pharmaceuticals. In a 2006 review, it was estimated that 20% of chemical conversions involved alkylations on nitrogen and oxygen atoms, another 20% involved placement and removal of protective groups, 11% involved formation of new carbon–carbon bond and 10% involved functional group interconversions. | 0 | Theoretical and Fundamental Chemistry |
Radiation emitted from a surface can propagate in any direction from the surface. Irradiation can also be incident upon a surface from any direction. The amount of irradiation on a surface is therefore dependent on the relative orientation of both the emitter and the receiver. The parameter radiation intensity, is used to quantify how much radiation makes it from one surface to another.
Radiation intensity is often modeled using a spherical coordinate system. | 0 | Theoretical and Fundamental Chemistry |
Benzene undergoes electrophilic aromatic substitution with sulfuric acid to give the corresponding sulfonic acids: | 0 | Theoretical and Fundamental Chemistry |
The department consists of thirteen (13) research laboratories in different fields of chemical engineering and allied fields, and also hosts the Chemical Engineering Analytical Laboratory (CEAL), which offers analytical services to the university and industry.
CEAL houses a Scanning Electron Microscope (SEM), a Fourier-Transform Infrared (FTIR) Spectroscope, a Universal Testing Machine (UTM); gas chromatographs (FID, TCD, MS), Ion Chromatographs, and high-performance liquid chromatograph (HPLC); the Department also has a Kjeldahl apparatus, a Karl Fischer apparatus, and an atomic absorption spectrophotometer (AAS). There is a real-time PCR, and digital gradient electrophoresis, shaking incubators and refrigerated incubators for biological studies.
The thirteen (13) research laboratories are the following:
* Advanced Materials and Organic Synthesis Laboratory
* Bioprocess Engineering Laboratory
* Catalysis Research Laboratory
* Chemical Engineering Intelligence Learning Laboratory
* Environmental Process Engineering Laboratory
* Fuels, Energy and Thermal Systems Laboratory
* Green Materials Laboratory
* Inorganic Synthesis Laboratory
* Laboratory of Electrochemical Engineering
* Molecular Modelling Laboratory
* Nanotechnology Research Laboratory
* Process Systems Engineering Laboratory
* Sustainable Production & Responsible Consumption Laboratory | 1 | Applied and Interdisciplinary Chemistry |
Some techniques commonly used in bioanalytical studies include:
*Hyphenated techniques
**LC–MS (liquid chromatography–mass spectrometry)
**GC–MS (gas chromatography–mass spectrometry)
**LC–DAD (liquid chromatography–diode array detection)
**CE–MS (capillary electrophoresis–mass spectrometry)
*Chromatographic methods
**HPLC (high performance liquid chromatography)
**GC (gas chromatography)
**UPLC (ultra performance liquid chromatography)
**Supercritical fluid chromatography
*Electrophoresis
*Ligand binding assays
**Dual polarisation interferometry
**ELISA (Enzyme-linked immunosorbent assay)
**MIA (magnetic immunoassay)
**RIA (radioimmunoassay)
*Mass spectrometry
*Nuclear magnetic resonance
The most frequently used techniques are: liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) for small molecules and enzyme-linked immunosorbent assay (ELISA) for macromolecules. | 0 | Theoretical and Fundamental Chemistry |
PDE inhibitors have been identified as new potential therapeutics in areas such as pulmonary arterial hypertension, coronary heart disease, dementia, depression, asthma, COPD, protozoal infections (including malaria) and schizophrenia.
PDE also are important in seizure incidence. For example, PDE compromised the antiepileptic activity of adenosine. In addition, using of a PDE inhibitor (pentoxifylline) in pentylenetetrazole-induced seizure indicated the antiepileptic effect by increasing the time latency to seizure incidence and decreasing the seizure duration in vivo.
Cilostazol (Pletal) inhibits PDE3. This inhibition allows red blood cells to be more able to bend. This is useful in conditions such as intermittent claudication, as the cells can maneuver through constricted veins and arteries more easily.
Dipyridamole inhibits PDE-3 and PDE-5. This leads to intraplatelet accumulation of cAMP and/or cGMP, inhibiting platelet aggregation.
Zaprinast inhibits the growth of asexual blood-stage malaria parasites (Plasmodium falciparum) in vitro with an ED value of 35 μM, and inhibits PfPDE1, a P. falciparum cGMP-specific phosphodiesterase, with an IC value of 3.8 μM.
Xanthines such as caffeine and theobromine are cAMP-phosphodiesterase inhibitors. However, the inhibitory effect of xanthines on phosphodiesterases are only seen at dosages higher than what people normally consume.
Sildenafil, Tadalafil and Vardenafil are PDE-5 inhibitors and are widely used in the treatment of erectile dysfunction. | 1 | Applied and Interdisciplinary Chemistry |
EPE foams are low density, semi-rigid, closed cell foam that are generally somewhere in stiffness/compliance between Expanded polystyrene and Polyurethane. Production of EPE foams is similar to that of expanded polystyrene, but starting with PE beads. Typical densities are with the lower figure being common. Densities as low as can be produced.
Base polymer for EPE foams range from Low-density polyethylene (LDPE) to High-density polyethylene (HDPE). | 0 | Theoretical and Fundamental Chemistry |
Helium accumulates in the cores of stars as a result of the proton–proton chain reaction and the carbon–nitrogen–oxygen cycle.
Nuclear fusion reaction of two helium-4 nuclei produces beryllium-8, which is highly unstable, and decays back into smaller nuclei with a half-life of , unless within that time a third alpha particle fuses with the beryllium-8 nucleus to produce an excited resonance state of carbon-12, called the Hoyle state, which nearly always decays back into three alpha particles, but once in about 2421.3 times releases energy and changes into the stable base form of carbon-12. When a star runs out of hydrogen to fuse in its core, it begins to contract and heat up. If the central temperature rises to 10 K, six times hotter than the Sun's core, alpha particles can fuse fast enough to get past the beryllium-8 barrier and produce significant amounts of stable carbon-12.
The net energy release of the process is 7.275 MeV.
As a side effect of the process, some carbon nuclei fuse with additional helium to produce a stable isotope of oxygen and energy:
: + → + (+7.162 MeV)
Nuclear fusion reactions of helium with hydrogen produces lithium-5, which also is highly unstable, and decays back into smaller nuclei with a half-life of .
Fusing with additional helium nuclei can create heavier elements in a chain of stellar nucleosynthesis known as the alpha process, but these reactions are only significant at higher temperatures and pressures than in cores undergoing the triple-alpha process. This creates a situation in which stellar nucleosynthesis produces large amounts of carbon and oxygen, but only a small fraction of those elements are converted into neon and heavier elements. Oxygen and carbon are the main "ash" of helium-4 burning. | 0 | Theoretical and Fundamental Chemistry |
Flow injection analysis (FIA), was introduced in 1975 by Ruzicka and Hansen, The first generation of FIA technology, termed flow injection (FI), was inspired by the AutoAnalyzer technique invented by Skeggs in early 1950s. While Skeggs' AutoAnalyzer uses air segmentation to separate a flowing stream into numerous discrete segments to establish a long train of individual samples moving through a flow channel, FIA systems separate each sample from subsequent sample with a carrier reagent. While the AutoAnalyzer mixes sample homogeneously with reagents, in all FIA techniques sample and reagents are merged to form a concentration gradient that yields analysis results.
FIA methods can be used for both fast reactions as well as slow reactions. For slow reactions, a heater is often utilized. The reaction does not need to reach completion since all samples and standards are given the same period to react. For typical assays commonly measured with FIA (e.g., nitrite, nitrate, ammonia, phosphate) it is not uncommon to have a throughput of 60-120 samples per hour.
FIA methods are limited by the amount of time necessary to obtain a measurable signal since travel time through the tubing tends to broaden peaks to the point where samples can merge with each other. As a general rule, FIA methods should not be used if an adequate signal cannot be obtained within two minutes, and preferably less than one. Reactions that need longer reaction times should be segmented. However, considering the number of FIA publications and wide variety of uses of FIA for serial assays, the "one minute" time limitation does not seem to be a serious limitation for most real life assays. Yet, assays based on slow chemical reactions have to be carried either in stopped flow mode ( SIA) or by segmenting the flow.
OI Analytical, in its gas diffusion amperometric total cyanide method, uses a segmented flow injection analysis technique that allows reaction times of up to 10 minutes by flow injection analysis.
Technicon experimented with FIA long before it was championed by Ruzicka and Hansen. Andres Ferrari reported that analysis was possible without bubbles if flow rates were increased and tubing diameters decreased. In fact, Skegg's first attempts at the auto analyzer did not segment. Technicon chose to not pursue FIA because it increased reagent consumption and the cost of analysis.
The second generation of the FIA technique, called sequential injection analysis (SIA), was conceived in 1990 by Ruzicka and Marshal, and has been further developed and miniaturized over the course of the following decade. It uses flow programming instead of the continuous flow regime (as used by CFA and FIA), that allows the flow rate and flow direction to be tailored to the need of individual steps of analytical protocol. Reactants are mixed by flow reversals and a measurement is carried out while the reaction mixture is arrested within the detector by stopping the flow. Microminiaturized chromatography is carried out on microcolumns that are automatically renewed by microfluidic manipulations. The discrete pumping and metering of microliter sample and reagent volumes used in SI only generates waste per each sample injection. The enormous volume of FI and SI literature documents the versatility of FI and SI and their usefulness for routine assays (in soil, water, environmental, biochemical and biotechnological assays) has demonstrated their potential to be used as a versatile research tool. | 0 | Theoretical and Fundamental Chemistry |
Theoretically, the ATP yield for each oxidation cycle where two carbons are broken down at a time is 17, as each NADH produces 3 ATP, FADH produces 2 ATP and a full rotation of Acetyl-CoA in citric acid cycle produces 12 ATP. In practice, it is closer to 14 ATP for a full oxidation cycle as 2.5 ATP per NADH molecule is produced, 1.5 ATP per each FADH molecule is produced and Acetyl-CoA produces 10 ATP per rotation of the citric acid cycle (according to the P/O ratio). This breakdown is as follows:
For an even-numbered saturated fat (C), 0.5 * n - 1 oxidations are necessary, and the final process yields an additional acetyl CoA. In addition, two equivalents of ATP are lost during the activation of the fatty acid. Therefore, the total ATP yield can be stated as:
or
For instance, the ATP yield of palmitate (C, n = 16) is:
Represented in table form: | 1 | Applied and Interdisciplinary Chemistry |
Selegiline has been limitedly studied in the treatment of attention deficit hyperactivity disorder (ADHD) in both children/adolescents and adults. In a small randomized trial of selegiline for treatment of ADHD in children, there were improvements in attention, hyperactivity, and learning/memory performance but not in impulsivity. A small clinical randomized trial compared selegiline to methylphenidate, a first line treatment for ADHD, and reported equivalent efficacy as assessed by parent and teacher ratings. In another small randomized controlled trial of selegiline for the treatment of adult ADHD, a high dose of the medication for 6 weeks was not significantly more effective than placebo in improving symptoms. | 0 | Theoretical and Fundamental Chemistry |
Activated protein C–protein C inhibitor (APC-PCI) is a complex of activated protein C (APC) and protein C inhibitor (PCI). It has been measured in coagulation testing to evaluate coagulation, thrombosis, and other cardiovascular complications. It is a marker of thrombin generation and indicates hypercoagulability. The half-life of APC-PCI is either 40 minutes or 140minutes.
Ethinylestradiol-containing birth control pills have been found to increase levels of APC-PCI to a similar degree as thrombin–antithrombin complex (TAT) and to a greater extent than D-dimer. However, only APC-PCI was able to differentiate between a second- and third-generation birth control pill.
Another complex related to APC-PCI is the activated protein C–α-antitrypsin (APCAT) complex. | 1 | Applied and Interdisciplinary Chemistry |
Water is particularly common solvent to be found in crystals because it is small and polar. But all solvents can be found in some host crystals. Water is noteworthy because it is reactive, whereas other solvents such as benzene are considered to be chemically innocuous. Occasionally more than one solvent is found in a crystal, and often the stoichiometry is variable, reflected in the crystallographic concept of "partial occupancy". It is common and conventional for a chemist to "dry" a sample with a combination of vacuum and heat "to constant weight".
For other solvents of crystallization, analysis is conveniently accomplished by dissolving the sample in a deuterated solvent and analyzing the sample for solvent signals by NMR spectroscopy. Single crystal X-ray crystallography is often able to detect the presence of these solvents of crystallization as well. Other methods may be currently available. | 0 | Theoretical and Fundamental Chemistry |
It was set up to allow interdisciplinary communication between environmental scientists around the world. It was founded in 1979 in North America. | 1 | Applied and Interdisciplinary Chemistry |
PT is released from B. pertussis in an inactive form. Following PT binding to a cell membrane receptor, it is taken up in an endosome, after which it undergoes retrograde transport to the trans-Golgi network and endoplasmic reticulum. At some point during this transport, the A subunit (or protomer) becomes activated, perhaps through the action of glutathione and ATP. PT catalyzes the ADP-ribosylation of the α subunits of the heterotrimeric G protein. This prevents the G proteins from interacting with G protein-coupled receptors on the cell membrane, thus interfering with intracellular communication. The Gi subunits remain locked in their GDP-bound, inactive state, thus unable to inhibit adenylate cyclase activity, leading to increased cellular concentrations of cAMP.
Increased intracellular cAMP affects normal biological signaling. The toxin causes several systemic effects, among which is an increased release of insulin, causing hypoglycemia. Whether the effects of pertussis toxin are responsible for the paroxysmal cough remains unknown.
As a result of this unique mechanism, PT has also become widely used as a biochemical tool to ADP-ribosylate GTP-binding proteins in the study of signal transduction. It has also become an essential component of new acellular vaccines. | 1 | Applied and Interdisciplinary Chemistry |
The Hammett acidity function, H, can replace the pH in concentrated solutions. It is defined using an equation analogous to the Henderson–Hasselbalch equation:
where log(x) is the common logarithm of x, and pK, which is the conjugate acid of a very weak base B, with a very negative pK</sub>. In this way, it is rather as if the pH scale has been extended to very negative values. Hammett originally used a series of anilines with electron-withdrawing groups for the bases.
Hammett also pointed out the equivalent form
where is the activity, and the γ are thermodynamic activity coefficients. In dilute aqueous solution (pH 0–14) the predominant acid species is HO and the activity coefficients are close to unity, so H is approximately equal to the pH. However, beyond this pH range, the effective hydrogen-ion activity changes much more rapidly than the concentration. This is often due to changes in the nature of the acid species; for example in concentrated sulfuric acid, the predominant acid species ("H") is not HO but rather HSO, which is a much stronger acid. The value H = -12 for pure sulfuric acid must not be interpreted as pH = −12 (which would imply an impossibly high HO concentration of 10 mol/L in ideal solution). Instead it means that the acid species present (HSO) has a protonating ability equivalent to HO at a fictitious (ideal) concentration of 10 mol/L, as measured by its ability to protonate weak bases.
Although the Hammett acidity function is the best known acidity function, other acidity functions have been developed by authors such as Arnett, Cox, Katrizky, Yates, and Stevens. | 0 | Theoretical and Fundamental Chemistry |
Iodate is part of a series of oxyacids in which iodine can assume oxidation states of −1, +1, +3, +5, or +7. A number of neutral iodine oxides are also known. | 0 | Theoretical and Fundamental Chemistry |
The advantages of the method include:
* uniquely wide field of view (because translation complexes of any type, including scanning small ribosomal subunits, are captured for the first time);
* potentially more natural representation of complex dynamics (because all, and not only selected, translation processes are arrested by formaldehyde fixation);
* possibly more faithful and/or sensitive detection of translation complexes locations (as covalent fixation prevents detachment of the fragments from the ribosomes or their subunits).
The disadvantages include:
* higher overall complexity of the experimental procedure (due to requirement of the initial isolation of translated mRNA and preparative sedimentation to separate ribosomes and ribosomal subunits);
* higher contamination of the useful sequencing read depth with the undesired fragments of the ribosomal RNA (inherited from the wide size selection window used for protected RNA fragments);
* a pre-requirement for optimization of the formaldehyde fixation procedure for each new cell or sample type (as optimal formaldehyde fixation timings strongly depend on sample morphology and both over- and under-fixation will compromise the results). | 1 | Applied and Interdisciplinary Chemistry |
A component is any part of a molecule or molecules that function as a unit in a pericyclic reaction. A component consists of one or more atoms and any of the following types of associated orbitals:
* An isolated p- or sp-orbital (unfilled or filled, symbol ω)
* A conjugated π system (symbol π)
* A σ bond (symbol σ)
The electron count of a component is the number of electrons in the orbital(s) of the component:
* The electron count of an unfilled ω orbital (i.e., an empty p orbital) is 0, while that of a filled ω orbital (i.e., a lone pair) is 2.
* The electron count of a conjugated π system with n double bonds is 2n (or 2n + 2, if a (formal) lone pair from a heteroatom or carbanion is conjugated thereto).
* The electron count of a σ bond is 2.
The bond topology of a component can be suprafacial and antarafacial:
* The relationship is suprafacial (symbol: s) when the interactions with the π system or p orbital occur on the same side of the nodal plane (think syn). For a σ bond, it corresponds to interactions occurring on the two "interior" lobes or two "exterior" lobes of the bond.
* The relationship is antarafacial (symbol: a) when the interactions with the π system or p orbital occur on opposite sides of the nodal plane (think anti). For a σ bond, it corresponds to interactions occurring on one "interior" lobe and one "exterior" lobe of the bond.
Using this notation, all pericyclic reactions can be assigned a descriptor, consisting of a series of symbols N, connected by + signs and enclosed in brackets, describing, in order, the type of orbital(s), number of electrons, and bond topology involved for each component. Some illustrative examples follow:
* The Diels-Alder reaction (a (4+2)-cycloaddition) is [4 + 2].
* The 1,3-dipolar cycloaddition of ozone and an olefin in the first step of ozonolysis (a (3+2)-cycloaddition) is [4 + 2].
* The cheletropic addition of sulfur dioxide to 1,3-butadiene (a (4+1)-cheletropic addition) is [0 + 4] + [2 + 4].
* The Cope rearrangement (a [3,3]-sigmatropic shift) is [2 + 2 + 2] or [2 + 2 + 2].
* The [1,3]-alkyl migration with inversion at carbon discovered by Berson (a [1,3]-sigmatropic shift) is [2 + 2].
* The conrotatory electrocyclic ring closing of 1,3-butadiene (a 4π-electrocyclization) is [4].
* The conrotatory electrocyclic ring opening of cyclobutene (a reverse 4π-electrocyclization) is [2 + 2] or [2 + 2].
* The disrotatory electrocyclic ring closing of 1,3-cyclooctadien-5-ide anion (a 6π-electrocyclization) is [6].
* A Wagner-Meerwein shift of a carbocation (a [1,2]-sigmatropic shift) is [0 + 2].
Antarafacial and suprafacial are associated with (conrotation or inversion) and (disrotation or retention), respectively. A single descriptor may correspond to two pericyclic processes that are chemically distinct, that a reaction and its microscopic reverse are often described with two different descriptors, and that a single process may have more than a one correct descriptor. One can verify, using the pericyclic selection rule given below, that all of these reactions are allowed processes. | 0 | Theoretical and Fundamental Chemistry |
The Orbiting Carbon Observatory (OCO) is a NASA satellite mission intended to provide global space-based observations of atmospheric carbon dioxide (). The original spacecraft was lost in a launch failure on 24 February 2009, when the payload fairing of the Taurus rocket which was carrying it failed to separate during ascent. The added mass of the fairing prevented the satellite from reaching orbit. It subsequently re-entered the atmosphere and crashed into the Indian Ocean near Antarctica. The replacement satellite, Orbiting Carbon Observatory-2, was launched 2 July 2014 aboard a Delta II rocket. The Orbiting Carbon Observatory-3, a stand-alone payload built from the spare OCO-2 flight instrument, was installed on the International Space Station Kibō Exposed Facility in May 2019. | 1 | Applied and Interdisciplinary Chemistry |
A bifidus factor (bifidogenic factor) is a compound that specifically enhances the growth of bifidobacteria in either a product or in the intestines of humans and/or animals. Several products have been marketed as bifidogenic factors, such as several prebiotics and methyl-N-acetyl D-glucosamine in human milk. | 1 | Applied and Interdisciplinary Chemistry |
A nephelometer or aerosol photometer is an instrument for measuring the concentration of suspended particulates in a liquid or gas colloid. A nephelometer measures suspended particulates by employing a light beam (source beam) and a light detector set to one side (often 90°) of the source beam. Particle density is then a function of the light reflected into the detector from the particles. To some extent, how much light reflects for a given density of particles is dependent upon properties of the particles such as their shape, color, and reflectivity. Nephelometers are calibrated to a known particulate, then use environmental factors (k-factors) to compensate lighter or darker colored dusts accordingly. K-factor is determined by the user by running the nephelometer next to an air sampling pump and comparing results. There are a wide variety of research-grade nephelometers on the market as well as open source varieties. | 0 | Theoretical and Fundamental Chemistry |
Magic numbers are connected with the number of metal atoms in those thiolate-protected clusters which display an outstanding stability. Such clusters can be synthesized monodispersely and are end products of the etching procedure after an addition of excess thiols does not lead to further metal dissolution. Some important clusters with magic numbers are (SG:Glutathione): Au(SG), Au(SG), Au(SG), Au(SG), Au(SG), Au(SG), Au(SG), Au(SG), and Au(SG).
Au(SCHPh) is also well-known. It was greater than representatives Au(p-MBA) with the para-mercaptobenzoice (para-mercapto-benzoic acid, p-MBA) produced ligand. | 0 | Theoretical and Fundamental Chemistry |
According to the Japanese mathematical physicist Ryogo Kubo, the spacing of energy levels can be predicted by
</blockquote>
where E is Fermi energy and N is the number of atoms. For quantum confinement 𝛿 can be estimated to be equal to the thermal energy (), where k is Boltzmanns constant and T' is temperature. | 0 | Theoretical and Fundamental Chemistry |
Nearly all animals have more than one kind of Hb present in the RBC. Multiple Hb isoforms (see isoforms) are particularly common in ectotherms, but especially in fish that are required to cope with both fluctuating temperature and oxygen availability. Hbs isolated from the European eel can be separated into anodic and cathodic isoforms. The anodic isoforms have low oxygen affinities (high P50) and marked Bohr effects, while the cathodic lack significant pH effects and are therefore thought to confer hypoxia tolerance. Several species of African cichlids raised from early stage development under either hypoxic or normoxic conditions were contrasted in an attempt to compare Hb isoforms. They demonstrated there were Hb isoforms specific to the hypoxia-raised individuals. | 0 | Theoretical and Fundamental Chemistry |
alkB is an iron-dependent oxidoreductase, and it is associated with DNA repair because this gene is able to repair lesions in phage DNA prior to infection. It has been also demonstrated that alkB is required for reactivation of MMS-treated (methylating agent methyl methanesulfonate) single-stranded phage and since there are no lesions to be removed, it has been suggested that alkBB is involved in replication of damaged template DNA. Also, the fact that alkB can confer resistance to a methylating agent it suggests that it functions by itself. | 1 | Applied and Interdisciplinary Chemistry |
Homogeneity testing for a candidate reference material typically involves replicated measurements on multiple units or subsamples of the material.
Homogeneity tests for CRMs follow planned experimental designs. Because the experiment is intended to test for (or estimate the size of) variation in value between different CRM units, the designs are chosen to allow separation of variation in results due to random measurement error and variation due to differences between units of the CRM. Among the simplest designs recommended for this purpose is a simple balanced nested design (see schematic). Typically 10-30 CRM units are taken from the batch at random; stratified random sampling is recommended so that the selected units are spread across the batch. An equal number of subsamples (usually two or three) is then taken from each CRM unit and measured. Subsamples are measured in random order. Other designs, such as randomized block designs, have also been used for CRM certification.
Data processing for homogeneity tests usually involves a statistical significance test for evidence of differences between units of the candidate CRM. For the simple balanced design above, this typically uses an F test following ANOVA. A check for trends with production order is also recommended.
This approach is not taken in ISO Guide 35:2017; rather, emphasis is placed on deciding whether the between-unit standard deviation is sufficiently small for the intended end use. If statistical tests are used, however, the homogeneity experiment should be capable of detecting important heterogeneity, ISO Guide 35:2017 in turn requiring a sufficient combination of precision of the measurement procedure, number of RM units and number of replicates per unit. Statistical power calculations can assist in ensuring a sufficiently effective test .
In extreme cases, such as microanalysis, materials must be checked for homogeneity on sub-micron scales; this may involve much larger numbers of observations and adjustments to statistical analysis. | 0 | Theoretical and Fundamental Chemistry |
For example, ammonia (NH) is soluble in both water (aq) and the organic solvent trichloromethane (CHCl) - two immiscible solvents. If ammonia is first dissolved in water, and then an equal volume of trichloromethane is added, and the two liquids shaken together, the following equilibrium is established:
:K = [NH ]/[NH] (where K is the equilibrium constant)
The equilibrium concentrations of ammonia in each layer can be established by titration with standard acid solution. It can thus be determined that K remains constant, with a value of 0.4 in this case. | 0 | Theoretical and Fundamental Chemistry |
*Prince, Leon M., Microemulsions in Theory and Practice Academic Press (1977) .
*Rosano, Henri L and Clausse, Marc, eds., Microemulsion Systems (Surfactant Science Series) Marcel Dekker, Inc. (1987) | 0 | Theoretical and Fundamental Chemistry |
At 17, he discussed the question of the materiality of heat with his Quaker friend and mentor Robert Dunkin. Dunkin remarked: I tell thee what, Humphry, thou art the most quibbling hand at a dispute I ever met with in my life. One winter day he took Davy to the Lariggan River to show him that rubbing two plates of ice together developed sufficient energy by motion to melt them, and that after the motion was suspended, the pieces were united by regelation. It was a crude form of analogous experiment exhibited by Davy in the lecture-room of the Royal Institution that elicited considerable attention. As professor at the Royal Institution, Davy repeated many of the ingenious experiments he learnt from Dunkin. | 1 | Applied and Interdisciplinary Chemistry |
The Zwikker reagent is used as a simple spot-test to presumptively identify barbiturates. It is composed of a mixture of two solutions. Part A is 0.5 g of copper (II) sulfate in 100 ml of distilled water. Part B consists of 5% pyridine (v/v) in chloroform. One drop of each is added to the substance to be tested and any change in colour is observed.
The test turns phenobarbital, pentobarbital and secobarbital light purple. Tea and tobacco turn yellow-green.
The test's lack of specificity and tendency to produce false positives means it is not widely used for presumptive drug testing, although it does still play a role as a thin layer chromatography stain.
It is named after the Dutch scientist Cornelis Zwikker. | 0 | Theoretical and Fundamental Chemistry |
In this book, Jung argues for a reevaluation of the symbolism of Alchemy as being intimately related to the psychoanalytical process. Using a cycle of dreams of one of his patients he shows how the symbols used by the Alchemists occur in the psyche as part of the reservoir of mythological images drawn upon by the individual in their dream states. Jung draws an analogy between the Great Work of the Alchemists and the process of reintegration and individuation of the psyche in the modern psychiatric patient.
In drawing these parallels Jung reinforces the universal nature of his theory of the archetype and makes an impassioned argument for the importance of spirituality in the psychic health of the modern man. Lavishly illustrated with images, drawings and paintings from Alchemy and other mythological sources including Christianity the book is another example of Jung's immense erudition and fascination with the eso- and exoteric expressions of spirituality and the psyche in religion and mysticism.
Influenced by pioneering work by Ethan Allen Hitchcock and Herbert Silberer (who was in turn influenced by Jung), Psychology and Alchemy is a seminal work of reevaluation of a forgotten system of thought which did much to revitalise interest in Alchemy as a serious force in Western philosophical and esoteric culture.
Also interesting about this book is that the patient whose dreams are being analyzed in the second section is the physicist Wolfgang Pauli, who would go on to collaborate with Jung on such ideas as the acausal connecting principle of synchronicity. The dreams are interpreted as a series to elucidate the meanings of recurring motifs and symbols, with the series culminating in the vision of a world clock, which is actually several clocks on different planes operating on different scales and colours as a symbol of Paulis unconscious apprehension of some grand cosmic order. Three of the best of these dreams were also mentioned by Jung in his Terry lectures Psychology of Religion'. | 1 | Applied and Interdisciplinary Chemistry |
The ionization rate of a hydrogen atom in an alternating electric field, like that of a laser, can be treated, in the appropriate limit, as the DC ionization rate averaged over a single period of the electric field's oscillation. Multiphoton and tunnel ionization of an atom or a molecule describes the same process by which a bounded electron, through the absorption of more than one photon from the laser field, is ionized. The difference between them is a matter of definition under different conditions. They can henceforth be called multiphoton ionization (MPI) whenever the distinction is not necessary. The dynamics of the MPI can be described by finding the time evolution of the state of the atom which is described by the Schrödinger equation.
When the intensity of the laser is strong, the lowest-order perturbation theory is not sufficient to describe the MPI process. In this case, the laser field on larger distances from the nucleus is more important than the Coulomb potential and the dynamic of the electron in the field should be properly taken into account. The first work in this category was published by Leonid Keldysh. He modeled the MPI process as a transition of the electron from the ground state of the atom to the Volkov states (the state of a free electron in the electromagnetic field). In this model, the perturbation of the ground state by the laser field is neglected and the details of atomic structure in determining the ionization probability are not taken into account. The major difficulty with Keldyshs model was its neglect of the effects of Coulomb interaction on the final state of the electron. As is observed from the figure, the Coulomb field is not very small in magnitude compared to the potential of the laser at larger distances from the nucleus. This is in contrast to the approximation made by neglecting the potential of the laser at regions near the nucleus. A. M. Perelomov, V. S. Popov and M. V. Terentev included the Coulomb interaction at larger internuclear distances. Their model (which is called the PPT model after their initials) was derived for short-range potential and includes the effect of the long-range Coulomb interaction through the first-order correction in the quasi-classical action. In the quasi-static limit, the PPT model approaches the ADK model by M. V. Ammosov, N. B. Delone, and V. P. Krainov.
Many experiments have been carried out on the MPI of rare gas atoms using strong laser pulses, through measuring both the total ion yield and the kinetic energy of the electrons. Here, one only considers the experiments designed to measure the total ion yield. Among these experiments are those by S. L. Chin et al., S. Augst et al. and T. Auguste et al. Chin et al. used a 10.6 μm CO laser in their experiment. Due to the very small frequency of the laser, the tunneling is strictly quasi-static, a characteristic that is not easily attainable using pulses in the near infrared or visible region of frequencies. These findings weakened the suspicion on the applicability of models basically founded on the assumption of a structureless atom. S. Larochelle et al. have compared the theoretically predicted ion versus intensity curves of rare gas atoms interacting with a :Ti:sapphire laser with experimental measurement. They have shown that the total ionization rate predicted by the PPT model fits very well the experimental ion yields for all rare gases in the intermediate regime of Keldysh parameter. | 0 | Theoretical and Fundamental Chemistry |
The title, Mappae clavicula, is absurd, translating approximately as the little key to the small cloth. The best explanation is that it is a mis-translation from a Greek original, in which χειρόκμητον kheirókmēton (knack or trick of the trade) was mis-read as χειρόμακτρον kheirómaktron (hand-towel). This is consistent with the observation that certain recipes derive from the Greek technical papyri, the Leyden papyrus X and the Stockholm papyrus. | 1 | Applied and Interdisciplinary Chemistry |
Hot baths of sodium hydroxide (NaOH), nitrates such as sodium nitrate (), and/or nitrites such as sodium nitrite (NaNO) at are used to convert the surface of the material into magnetite (FeO). Water must be periodically added to the bath, with proper controls to prevent a steam explosion.
Hot blackening involves dipping the part into various tanks. The workpiece is usually dipped by automated part carriers for transportation between tanks. These tanks contain, in order, alkaline detergent, water, sodium hydroxide at (the blackening compound), and finally the sealant, which is usually oil.
The NaOH (caustic soda) and elevated temperature cause FeO (black oxide) to form on the surface of the metal instead of FeO (red oxide; rust). While it is physically denser than red oxide, the fresh black oxide is porous, so oil is then applied as post treatment to the heated part, which seals it by "sinking" into it. The combination prevents corrosion of the workpiece. There are many advantages of blackening, including:
* Blackening can be done in large batches, which is ideal for small parts.
* There is no significant dimensional impact. The blacking process creates a layer about 1μm thick.
* It is far cheaper than similar corrosion protection systems, such as paint and electroplating.
The oldest and most widely used specification for hot black oxide is MIL-DTL-13924, which covers four classes of processes for different substrates. Alternate specifications include AMS 2485, ASTM D769, and ISO 11408.
Iron(III) chloride (FeCl) may also be used for steel blackening by dipping a piece of steel into a hot bath of 50% FeCl solution and then into a hot boiling water. The process is usually repeated several times. | 0 | Theoretical and Fundamental Chemistry |
Stereochemistry has important applications in the field of medicine, particularly pharmaceuticals. An often cited example of the importance of stereochemistry relates to the thalidomide disaster. Thalidomide is a pharmaceutical drug, first prepared in 1957 in Germany, prescribed for treating morning sickness in pregnant women. The drug was discovered to be teratogenic, causing serious genetic damage to early embryonic growth and development, leading to limb deformation in babies. Some of the several proposed mechanisms of teratogenicity involve a different biological function for the (R)- and the (S)-thalidomide enantiomers. In the human body however, thalidomide undergoes racemization: even if only one of the two enantiomers is administered as a drug, the other enantiomer is produced as a result of metabolism. Accordingly, it is incorrect to state that one stereoisomer is safe while the other is teratogenic. Thalidomide is currently used for the treatment of other diseases, notably cancer and leprosy. Strict regulations and controls have been enabled to avoid its use by pregnant women and prevent developmental deformations. This disaster was a driving force behind requiring strict testing of drugs before making them available to the public. | 0 | Theoretical and Fundamental Chemistry |
Before performing any kind of immobilization techniques, some factors should be in mind. It is necessary to understand the chemical and physical effects on an enzyme following immobilization. Enzyme stability and kinetic characteristics can be altered due to changes in the microenvironment conditions of the enzyme after entrapment, support material attachment, or products of enzymatic actions for instance. Additionally, it is important to consider maintaining the tertiary structure of an enzyme prior to immobilizing to have a functional enzyme. Similarly, another crucial site for the functionality of an enzyme is the active-site, which should also be maintained while enzyme is being attached to a surface for immobilization, it is a must to have a selective method for the attachment of surface/material to not end up with an immobilized, but dysfunctional enzyme. Consequently, there are three foundational factors to be thought of for the production of functional immobilized enzymes: immobilization supports selection, conditions and methods of immobilization. | 0 | Theoretical and Fundamental Chemistry |
Various aromatic alkynes can be employed to yield desired disubstituted products with satisfactory yields. Aliphatic alkynes are generally less reactive. | 0 | Theoretical and Fundamental Chemistry |
The Society traces its origins back to an organization of young Parisian chemists who began meeting in May 1857 under the name Société Chimique, with the goal of self-study and mutual education. In 1858 the established chemist Adolphe Wurtz joined the society, now named the Société Chimique de Paris, and immediately transformed it into a learned society modeled after the Chemical Society of London, which was the precursor of the Royal Society of Chemistry. Like its British counterpart, the French association sought to foster the communication of new ideas and facts throughout France and across international borders. In 1906, the society changed its name from Société Chimique de Paris to Société Chimique de France; in 1983 it became the Société Française de Chimie; and in 2009 it returned to the name Société Chimique de France. | 1 | Applied and Interdisciplinary Chemistry |
* The advantages of an oxidation-reduction reactor in gas chromatography include
* The reactor ensures uniform sensitivity to most organic molecules, leading to consistent and reliable detection across a wide range of analytes.
* By eliminating the need for multiple calibrations and standards, the reactor increases the accuracy of quantification, reducing errors and enhancing the reliability of analytical results.
* Reduction in calibration requirements decreases the cost of ownership and saves time, making the analytical process more efficient.
* The reactor enables the quantification of complex mixtures even when standards are not available, provided retention times are known or can be estimated, thereby expanding the applicability of gas chromatography.
* Unlike traditional methanizers, which primarily convert CO and CO2, oxidation-reduction reactors can convert a broader range of organic compounds to methane, leading to a more comprehensive response and improved sensitivity for a wide variety of analytes.
* These reactors are more resistant to poisoning by compounds containing nitrogen and oxygen, ensuring consistent performance even in the presence of interfering substances.
* Compared to packed column versions of methanizers, oxidation-reduction reactors typically produce sharper peaks, enhancing resolution and improving the quality of chromatographic separation. | 0 | Theoretical and Fundamental Chemistry |
KREEP, an acronym built from the letters K (the atomic symbol for potassium), REE (rare-earth elements) and P (for phosphorus), is a geochemical component of some lunar impact breccia and basaltic rocks. Its most significant feature is somewhat enhanced concentration of a majority of so-called "incompatible" elements (those that are concentrated in the liquid phase during magma crystallization) and the heat-producing elements, namely radioactive uranium, thorium, and potassium (due to presence of the radioactive K). | 0 | Theoretical and Fundamental Chemistry |
The absorbance of a material that has only one absorbing species also depends on the pathlength and the concentration of the species, according to the Beer–Lambert law
where
* is the molar absorption coefficient of that material;
* is the molar concentration of those species;
* is the path length.
Different disciplines have different conventions as to whether absorbance is decadic (10-based) or Napierian (e-based), i.e., defined with respect to the transmission via common logarithm (log) or a natural logarithm (ln). The molar absorption coefficient is usually decadic. When ambiguity exists, it is important to indicate which one applies.
When there are N absorbing species in a solution, the overall absorbance is the sum of the absorbances for each individual species i:
The composition of a mixture of N absorbing species can be found by measuring the absorbance at N wavelengths (the values of the molar absorption coefficient for each species at these wavelengths must also be known). The wavelengths chosen are usually the wavelengths of maximum absorption (absorbance maxima) for the individual species. None of the wavelengths may be an isosbestic point for a pair of species. The set of the following simultaneous equations can be solved to find the concentrations of each absorbing species:
The molar absorption coefficient (in units of cm) is directly related to the attenuation cross section via the Avogadro constant N: | 0 | Theoretical and Fundamental Chemistry |
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