text
stringlengths 105
13.7k
| label
int64 0
1
| label_text
stringclasses 2
values |
|---|---|---|
In this process, the wax and the textile are both replaced by the metal during the casting process, whereby the fabric reinforcement allows for a thinner model, and thus reduces the amount of metal expended in the mould. Evidence of this process is seen by the textile relief on the reverse side of objects and is sometimes referred to as "lost-wax, lost textile". This textile relief is visible on gold ornaments from burial mounds in southern Siberia of the ancient horse riding tribes, such as the distinctive group of openwork gold plaques housed in the Hermitage Museum, Saint Petersburg. The technique may have its origins in the Far East, as indicated by the few Han examples, and the bronze buckle and gold plaques found at the cemetery at Xigou. Such a technique may also have been used to manufacture some Viking Age oval brooches, indicated by numerous examples with fabric imprints such as those of Castletown (Scotland). | 0 | Metallurgy |
Given that DNA and RNA polymerases both carry out template-dependent nucleotide polymerization, it might be expected that the two types of enzymes would be structurally related. However, x-ray crystallographic studies of both types of enzymes reveal that, other than containing a critical Mg ion at the catalytic site, they are virtually unrelated to each other; indeed template-dependent nucleotide polymerizing enzymes seem to have arisen independently twice during the early evolution of cells. One lineage led to the modern DNA polymerases and reverse transcriptases, as well as to a few single-subunit RNA polymerases (ssRNAP) from phages and organelles. The other multi-subunit RNAP lineage formed all of the modern cellular RNA polymerases. | 1 | Gene expression + Signal Transduction |
In eukaryotes, genomic DNA is highly compacted in order to be able to fit it into the nucleus. This is accomplished by winding the DNA around protein octamers called histones, which has consequences for the physical accessibility of parts of the genome at any given time. Significant portions are silenced through histone modifications, and thus are inaccessible to the polymerases or their cofactors. The highest level of transcription regulation occurs through the rearrangement of histones in order to expose or sequester genes, because these processes have the ability to render entire regions of a chromosome inaccessible such as what occurs in imprinting.
Histone rearrangement is facilitated by post-translational modifications to the tails of the core histones. A wide variety of modifications can be made by enzymes such as the histone acetyltransferases (HATs), histone methyltransferases (HMTs), and histone deacetylases (HDACs), among others. These enzymes can add or remove covalent modifications such as methyl groups, acetyl groups, phosphates, and ubiquitin. Histone modifications serve to recruit other proteins which can either increase the compaction of the chromatin and sequester promoter elements, or to increase the spacing between histones and allow the association of transcription factors or polymerase on open DNA. For example, H3K27 trimethylation by the polycomb complex PRC2 causes chromosomal compaction and gene silencing. These histone modifications may be created by the cell, or inherited in an epigenetic fashion from a parent. | 1 | Gene expression + Signal Transduction |
In this process molten metal is poured in the mold and allowed to solidify while the mold is rotating. Metal is poured into the center of the mold at its axis of rotation. Due to inertial force, the liquid metal is thrown out toward the periphery.
Centrifugal casting is both gravity and pressure independent since it creates its own force feed using a temporary sand mold held in a spinning chamber. Lead time varies with the application. Semi- and true-centrifugal processing permit 30–50 pieces/hr-mold to be produced, with a practical limit for batch processing of approximately 9000 kg total mass with a typical per-item limit of 2.3–4.5 kg.
Industrially, the centrifugal casting of railway wheels was an early application of the method developed by the German industrial company Krupp and this capability enabled the rapid growth of the enterprise.
Small art pieces such as jewelry are often cast by this method using the lost wax process, as the forces enable the rather viscous liquid metals to flow through very small passages and into fine details such as leaves and petals. This effect is similar to the benefits from vacuum casting, also applied to jewelry casting. | 0 | Metallurgy |
A receptor antagonist is any given ligand that binds to a receptor in some way without causing any immediate or downstream response, essentially neutralizing the receptor until something with a stronger affinity removes the antagonist or the antagonist itself unbinds. Generally, antagonists can act one of two ways: 1) they can either block the receptors directly, preventing the usual ligand from binding, such as in the case of atropine when it blocks specific acetylcholine receptors to provide important medical benefits. This is competitive antagonism, as they are competing for the same binding sites on the receptor. The other is by binding to a receptor in a site other than the designated receptor site, inducing a conformational change to prevent the usual ligand(s) from binding and activating a downstream cascade. A commonly-seen and used receptor antagonist is naloxone, another opioid competitive antagonist typically used to treat opioid overdoses by blocking receptors outright. Further elaboration can be found in "Orthosteric v. Allosteric Modulators." | 1 | Gene expression + Signal Transduction |
The dominant type in Sweden was the German forge, which had a single hearth that was used for all processes. | 0 | Metallurgy |
A. Cellular T cell response
The first evidence of survivin-specific CTL recognition and killing was shown in an assay wherein cytotoxic T cells (CTLs) induced lysis of B cells transfected to present survivin peptides on its surface. The naive CD8+ T cells were primed with dendritic cells and could therefore recognize the specific peptides of survivin presented on the surface Major Histocompatibility Complex I (MHC I) molecules of the B cells.
B. Humoral antibody response
Taking blood samples from cancer patients, scientists have found antibodies that are specific for survivin. These antibodies were absent in the blood samples of healthy normal patients. Therefore, this shows that survivin is able to elicit a full humoral immune response. This may prove useful, as one could measure the level of survivin-specific antibodies in the patient's blood as a monitor of tumour progression. In acquiring the humoral response to tumour antigens such as survivin, CD4+ T cells are activated to induce B cells to produce antibodies directed against the particular antigens.
The isolation of the antibodies specific for survivin peptides is useful, as one can look at the structure and sequence of the epitope binding groove of the antibody and, therefore, deduce possible epitopes that may fit in that particular antibody groove. Therefore, one can determine the particular peptide portion of the survivin protein that is bound most efficiently and most commonly by humoral antibodies generated against survivin. This will lead to the production of more specific survivin vaccines that contain a specific portion of the survivin protein that is known to elicit a good immune response, generate immune memory, and allow for protection from tumour development. | 1 | Gene expression + Signal Transduction |
It has been suggested that one third of all disease-causing mutations impact on splicing. Common errors include:
*Mutation of a splice site resulting in loss of function of that site. Results in exposure of a premature stop codon, loss of an exon, or inclusion of an intron.
*Mutation of a splice site reducing specificity. May result in variation in the splice location, causing insertion or deletion of amino acids, or most likely, a disruption of the reading frame.
*Displacement of a splice site, leading to inclusion or exclusion of more RNA than expected, resulting in longer or shorter exons.
Although many splicing errors are safeguarded by a cellular quality control mechanism termed nonsense-mediated mRNA decay (NMD), a number of splicing-related diseases also exist, as suggested above.
Allelic differences in mRNA splicing are likely to be a common and important source of phenotypic diversity at the molecular level, in addition to their contribution to genetic disease susceptibility. Indeed, genome-wide studies in humans have identified a range of genes that are subject to allele-specific splicing.
In plants, variation for flooding stress tolerance correlated with stress-induced alternative splicing of transcripts associated with gluconeogenesis and other processes. | 1 | Gene expression + Signal Transduction |
Co-based superalloys depend on carbide precipitation and solid solution strengthening for mechanical properties. While these strengthening mechanisms are inferior to gamma prime (γ') precipitation strengthening, cobalt has a higher melting point than nickel and has superior hot corrosion resistance and thermal fatigue. As a result, carbide-strengthened Co-based superalloys are used in lower stress, higher temperature applications such as stationary vanes in gas turbines.
Cos γ/γ microstructure was rediscovered and published in 2006 by Sato et al. That γ phase was Co(Al, W). Mo, Ti, Nb, V, and Ta partition to the γ phase, while Fe, Mn, and Cr partition to the matrix γ.
The next family of Co-based superalloys was discovered in 2015 by Makineni et al. This family has a similar γ/γ microstructure, but is W-free and has a γ phase of Co(Al,Mo,Nb). Since W is heavy, its elimination makes Co-based alloys increasingly viable in turbines for aircraft, where low density is especially valued.
The most recently discovered family of superalloys was computationally predicted by Nyshadham et al. in 2017, and demonstrated by Reyes Tirado et al. in 2018. This γ' phase is W free and has the composition Co(Nb,V) and Co(Ta,V). | 0 | Metallurgy |
The Wealden iron industry was located in the Weald of south-eastern England. It was formerly an important industry, producing a large proportion of the bar iron made in England in the 16th century and most British cannon until about 1770. Ironmaking in the Weald used ironstone from various clay beds, and was fuelled by charcoal made from trees in the heavily wooded landscape. The industry in the Weald declined when ironmaking began to be fuelled by coke made from coal, which does not occur accessibly in the area. | 0 | Metallurgy |
Parting is a process by which gold is purified to a commercially-tradeable standard, typically ≥99.5%. Removal of silver is of particular interest since the two metals often co-purify. The standard procedure is based on the Miller process. The separation is achieved by passing chlorine gas into a molten alloy. The technique is practiced on a large scale (e.g. 500 kg). The principle of the method exploits the nobility of gold, such that at high temperatures, gold does not react with chlorine, but virtually all contaminating metals do. Thus, at c. 500 °C, as the chlorine gas is passed through molten mixture (again, mainly gold), a low-density slag forms on top, which can be decanted from the liquid gold. Silver chloride and other precious metals can be recovered from this slag. The slag layer is often diluted with a flux like borax to facilitate the separation.
Alternative methods exist for parting gold. Silver can be dissolved selectively by boiling the mixture with 30% nitric acid, a process sometimes called inquartation. Affination is a largely obsolete process of removing silver from gold using concentrated sulfuric acid. Electrolysis using the Wohlwill process is yet another approach. | 0 | Metallurgy |
Stamp sand is a coarse sand left over from the processing of ore in a stamp mill. In the United States, the most well-known deposits of stamp sand are in the Copper Country of northern Michigan, where it is black or dark gray, and may contain hazardous concentrations of trace metals.
In the 19th and early 20th centuries, many metal mines used stamp mills to process ore-bearing rock. The rock was brought to a stamp mill to be crushed. After crushing the material was mechanically separated to extract metals, or chemically treated by acids if the metal could be leached out. The size of the crushed material depended on the nature of the ore found in each mining district. | 0 | Metallurgy |
Other molecules besides ATP undergo dephosphorylation as part of other biological systems. Different compounds produce different free energy changes as a result of dephosphorylation.
Psilocybin also relies on dephosphorylation to be metabolized into psilocin and further eliminated. No information on psilocybin's effect on the change in free energy is currently available. | 1 | Gene expression + Signal Transduction |
The ability of pioneer factors to respond to extracellular signals to differentiate cell type has been studied as a potential component of hormone-dependent cancers. Hormones such as estrogen and IGFI are shown to increase pioneer factor concentration leading to a change in transcription. Known pioneer factors such as FoxA1, PBX1, TLE, AP2, GATA factors 2/3/4, and PU.1 have been associated with hormone-dependent cancer . FoxA1 is necessary for estrogen and androgen mediated hepatocarcinogenesis and is a defining gene for ER luminal breast cancer, as is another pioneer factor GATA3. FOXA1 particularly is expressed in 90% of breast cancer metastases and 89% of metastic prostate cancers. In the breast cancer cell line, MCF-7, it was found that FoxA1 was bound to 50% of estrogen receptor binding sites independent of estrogen presence. High expression of pioneer factors is associated with poor prognosis with the exception of breast cancer where FoxA1 is associated with a stronger outcome.
<br>
The correlation between pioneer factors and cancer has led to prospective therapeutic targeting. In knockdown studies in the MCF-7 breast cancer cell line it was found that decreasing pioneer factors FoxA1 and AP2 decreased ER signalling. Other fork head proteins have been associated with cancer, including FoxO3 and FoxM that repress the cell survival pathways Ras and PPI3K/AKT/IKK. Drugs such as Paclitaxel, Imatinib, and doxorubicin which activate FoxO3a or its targets are being used. Modification to modulate related factors with pioneer activity is a topic of interest in the early stages as knocking down pioneer factors may have toxic effects through alteration of the lineage pathways of healthy cells. | 1 | Gene expression + Signal Transduction |
The BBOC furnace is a cylindrical steel vessel with a protective internal lining of refractory bricks. It is mounted on a tilting frame that allows it to be held at different angles at different stages of its operating cycle (see Figure 2). A hood is fixed over the top of the furnace, providing a seal that prevents lead and other fumes from escaping during the furnace’s operation (see Figure 1).
The key feature of the BBOC is the shrouded lance that passes through the refractory bricks at the bottom of the furnace. This lance allows oxygen to be injected directly into the molten metal contained in the furnace, away from the refractory lining. Doing so allows the region of high reaction rates to be removed from the vicinity of the lining, thus reducing its wear.
By injecting the oxygen directly into the bath, rather than blowing it on top (as in the case of the reverberatory cupellation furnace or top-blown rotary converters), the oxygen transfer efficiency is not impeded by the presence of the slag layer. It results in an oxygen utilization efficiency approaching 100%.
The lack of interference in the oxygen transfer by the slag layer has a couple of key benefits. The first is that the increased certainty in the estimation of oxygen utilization efficiency means that it is easier to calculate the endpoint of the process, making process control much easier. The second is that a thicker slag layer can be tolerated (because the oxygen does not have to pass through it), and this means that the losses of silver to the slag are reduced (because it is the silver at the interface between the metal and slag that becomes entrained during the removal of the slag and the thicker the slag layer, the smaller the silver content of the removed slag). BRM reported a decrease in the silver content of the BBOC slag compared to the reverberatory furnace slag of 50%.
BRM found that the reaction rate of the BBOC was 10–20 times that of its reverberatory cupellation furnace.
Refractory wear in the BBOC is largely confined to the slag line, at the top of the metal, where attack by litharge (lead oxide) is greatest. This is combated by using fused-grain, direct-bonded magnesite-chrome bricks to line the inside of the furnace shell. | 0 | Metallurgy |
Cobalt extraction refers to the techniques used to extract cobalt from its ores and other compound ores. Several methods exist for the separation of cobalt from copper and nickel. They depend on the concentration of cobalt and the exact composition of the ore used. | 0 | Metallurgy |
Similar to liquid metal embrittlement (LME), solid metal-induced embrittlement results in a decrease in fracture strength of a material. In addition, a decrease in tensile ductility over a temperature range is indicative of metal-induced embrittlement. Although SMIE is greatest just below the embrittler’s melting temperature, the range over which SMIE occurs ranges from to T, where T is the melting temperature of the embrittler. The reduction in ductility is caused by formation and propagation of stable, subcritical intergranular cracks. SMIE produces both intergranular and transgranular fracture surfaces in otherwise ductile materials. | 0 | Metallurgy |
Many methods have been developed for the restriction of microbial corrosion. The primary challenge has been finding ways to prevent or stop microbial growth without negatively impacting the surrounding environment. The list below provides an overview of some of the tactics that have been used or that are in development.
* Using biocide (any chemical that inhibits life) to kill microorganisms. Because biofilms are so resistant, a lot of biocide must be used. This is expensive, has negative effects on the surrounding environment, and can actually cause more corrosion of the surface due to its toxicity. Biocides and other chemical treatments against microbes also tend to be dangerous for the people preparing and applying them.
Rao and Mulky developed an extensive list of methods to limit the growth of microbes and therefore microbial corrosion.
* Plant products could aid in restricting microbial growth. These would be biodegradable and safe for the people applying them, but have not yet been widely tested.
* Surfactants, specifically ones generated by organisms as secondary metabolites. They’re useful because they get between the corrosive liquid and the surface and keep them apart.
* Putting a superhydrophobic coating on a surface. This keeps a biofilm from being able to develop, but is sensitive and can easily lose its superhydrophobic qualities.
* Using self-healing surfaces can prevent corrosion in cracks or faults. This could be used with a superhydrophobic surface, to mitigate its sensitivity.
* Using hydrophilic surfaces to create a region that deters the development of proteins into a film covering a surface.
* Using synthetically-created substances that deter corrosion because of their chemical structures. This may have a smaller negative effect on the environment than other options.
* Using biofilms that are grown intentionally to inhibit microbial corrosion. This is done by growing a biofilm on a surface made of a bacteria that can release compounds that kill other microbes and that prevent corrosion.
* Using essential oils. The effectiveness of essential oils against microbial corrosion has not been widely tested.
* Coating a surface with various nanomaterials or ozone to prevent microbial corrosion. | 0 | Metallurgy |
Pelletizing is done in a pellet mill, where feed is normally conditioned and thermal-treated in the fitted conditioners of a pellet mill. The feed is then pushed through the holes and exit the pellet mill as pelleted feed. | 0 | Metallurgy |
The Kirkendall effect was discovered by Ernest Kirkendall and Alice Smigelskas in 1947, in the course of Kirkendalls ongoing research into diffusion in brass. The paper in which he discovered the famous effect was the third in his series of papers on brass diffusion, the first being his thesis. His second paper revealed that zinc diffused more quickly than copper in alpha-brass, which led to the research producing his revolutionary theory. Until this point, substitutional and ring methods were the dominant ideas for diffusional motion. Kirkendalls experiment produced evidence of a vacancy diffusion mechanism, which is the accepted mechanism to this day. At the time it was submitted, the paper and Kirkendalls ideas were rejected from publication by Robert Franklin Mehl, director of the Metals Research Laboratory at Carnegie Institute of Technology (now Carnegie Mellon University). Mehl refused to accept Kirkendalls evidence of this new diffusion mechanism, and denied publication for over six months, only relenting after a conference was held and several other researchers confirmed Kirkendall's results. | 0 | Metallurgy |
Plasma transferred wire arc (PTWA) thermal spraying is a thermal spraying process that deposits a coating on the internal surface of a cylindrical surface, or external surface of any geometry. It is predominantly known for its use in coating the cylinder bores of an internal combustion engine, enabling the construction of aluminium engine blocks without cast iron cylinder sleeves.
The inventors of PTWA received the 2009 IPO National Inventor of the Year award. This technology was initially patented and developed by Flame-Spray Industries, and subsequently improved upon by Flame-Spray and Ford. | 0 | Metallurgy |
The Kidd Metallurgical Site (or Met Site) is a metallurgical facility in Timmins, Ontario, Canada. It was built in 1980 and owned and operated by Xstrata Copper, following their 2006 takeover of Falconbridge Ltd. The site employs approximately 675 hourly employees.
The plant is southeast of the Kidd Mine, and houses a concentrator, copper smelter and refinery, zinc plant, cadmium plant, indium plant and a sulphuric acid plant. The Met Site was built away from the mine because of the muskeg-like terrain surrounding the mine.
The Met Site processes material from the Kidd Mine and outside sources, and employs 875 people. Of the 875 employees 125 work at the concentrator, 205 in the copper operations and 275 in the zinc facilities. The remainder of the employees are support staff.
Xstrata announced its plans to close the Metallurgical Site in May 2010. Only the concentrator will remain as the ore will now be shipped to Québec. The demolition of the rest of the plant started in February 2011. | 0 | Metallurgy |
In the process of transcription (by any polymerase), there are three main stages:
#Initiation: the construction of the RNA polymerase complex on the gene's promoter with the help of transcription factors
#Elongation: the actual transcription of the majority of the gene into a corresponding RNA sequence
#Termination: the cessation of RNA transcription and the disassembly of the RNA polymerase complex. | 1 | Gene expression + Signal Transduction |
In 1993 the silicon carbide was considered a semiconductor in both research and early mass production providing advantages for fast, high-temperature and/or high-voltage devices. The first devices available were Schottky diodes, followed by junction-gate FETs and MOSFETs for high-power switching. Bipolar transistors and thyristors were described.
A major problem for SiC commercialization has been the elimination of defects: edge dislocations, screw dislocations (both hollow and closed core), triangular defects and basal plane dislocations. As a result, devices made of SiC crystals initially displayed poor reverse blocking performance, though researchers have been tentatively finding solutions to improve the breakdown performance.
Apart from crystal quality, problems with the interface of SiC with silicon dioxide have hampered the development of SiC-based power MOSFETs and insulated-gate bipolar transistors. Although the mechanism is still unclear, nitriding has dramatically reduced the defects causing the interface problems.
In 2008, the first commercial JFETs rated at 1200 V were introduced to the market, followed in 2011 by the first commercial MOSFETs rated at 1200 V. JFETs are now available rated 650 V to 1700 V with resistance as low as 25 mΩ. Beside SiC switches and SiC Schottky diodes (also Schottky barrier diode, SBD) in the popular TO-247 and TO-220 packages, companies started even earlier to implement the bare chips into their power electronic modules.
SiC SBD diodes found wide market spread being used in PFC circuits and IGBT power modules.
Conferences such as the International Conference on Integrated Power Electronics Systems (CIPS) report regularly about the technological progress of SiC power devices.
Major challenges for fully unleashing the capabilities of SiC power devices are:
* Gate drive: SiC devices often require gate drive voltage levels that are different from their silicon counterparts and may be even unsymmetric, for example, +20 V and −5 V.
* Packaging: SiC chips may have a higher power density than silicon power devices and are able to handle higher temperatures exceeding the silicon limit of 150 °C. New die attach technologies such as sintering are required to efficiently get the heat out of the devices and ensure a reliable interconnection.
Beginning with Tesla Model 3 the inverters in the drive unit use 24 pairs of silicon carbide (SiC) MOSFET chips rated for 650 volts each. Silicon carbide in this instance gave Tesla a significant advantage over chips made of silicon in terms of size and weight. A number of automobile manufacturers are planning to incorporate silicon carbide into power electronic devices in their products. A significant increase in production of silicon carbide is projected, beginning with a large plant opened 2022 by Wolfspeed in upstate New York. | 0 | Metallurgy |
AC-IV was first reported in the bacterium Aeromonas hydrophila, and the structure of the AC-IV from Yersinia pestis has been reported. These are the smallest of the AC enzyme classes; the AC-IV (CyaB) from Yersinia is a dimer of 19 kDa subunits with no known regulatory components (). AC-IV forms a superfamily with mammalian thiamine-triphosphatase called CYTH (CyaB, thiamine triphosphatase). | 1 | Gene expression + Signal Transduction |
The first known use of silver was in the Near East in Anatolia and Mesopotamia during the 4th and 3rd millennium BC, the Early Bronze Age. Archaeological findings of silver and lead objects together with litharge pieces and slag have been studied in a variety of sites. Although this has been interpreted as silver being extracted from lead ores, it has been also suggested that lead was added to collect silver from visible silver minerals embedded in host rock. In both cases silver would be retrieved from lead metal by cupellation.
During the following Iron Age, cupellation was done by fusing the base metals with a surplus of lead. The bullion or product of this fusion was then heated in a cupellation furnace to separate the noble metals. Mines such as Rio Tinto, near Huelva in Spain, became an important political and economic site around the Mediterranean Sea, as well as Laurion in Greece. Around 500 BC control over the Laurion mines gave Athens political advantage and power in the Mediterranean so that they were able to defeat the Persians.
During the Roman times, the empire needed large quantities of lead to support the Roman civilization over a great territory; they searched for open lead-silver mines in areas they conquered. Silver coinage became the normalised medium of exchange, hence silver production and mine control gave economic and political power. In Roman times it was worth mining lead ores if their content of silver was 0.01% or more.
The origin of the use of cupellation for analysis is not known. One of the earliest written references to cupels is Theophilus Divers Ars in the 12th century AD. The process changed little until the 16th century.
Small-scale cupellation may be considered the most important fire assay developed in history, and perhaps the origin of chemical analysis. Most of the written evidence comes from the Renaissance in the 16th century. Vannoccio Biringuccio, Georg Agricola and Lazarus Ercker, among others, wrote about the art of mining and testing the ores, as well as detailed descriptions of cupellation. Their descriptions and assumptions have been identified in diverse archaeological findings through Medieval and Renaissance Europe. By these times the amount of fire assays increased considerably, mainly because of testing ores in the mines to identify the availability of its exploitation. A primary use of cupellation was related to minting activities, and it was also used in testing jewelry. Since the Renaissance, cupellation became a standardised method of analysis that has changed little, demonstrating its efficiency. Its development touched the spheres of economy, politics, warfare and power in ancient times. | 0 | Metallurgy |
Electric arc guns operate at low voltages (below 45 V dc), but at relatively high currents. They may be safely hand-held. The power supply units are connected to 440 V AC sources, and must be treated with caution. | 0 | Metallurgy |
The sample mass and size distribution requirements are dictated by the kind of mathematical model that will be used to simulate the process plant, and the test work required to provide the appropriate model parameters. Flotation testing usually requires several kg of sample and grinding/hardness testing can required between 2 and 300 kg.
The sample selection procedure is performed to optimize granularity, sample support, and cost. Samples are usually core samples composited over the height of the mining bench. For hardness parameters, the variogram often increases rapidly near the origin and can reach the sill at distances significantly smaller than the typical drill hole collar spacing. For this reason the incremental model precision due to additional test work is often simply a consequence of the central limit theorem, and secondary correlations are sought to increase the precision without incurring additional sampling and testing costs. These secondary correlations can involve multi-variable regression analysis with other, non-metallurgical, ore parameters and/or domaining by rock type, lithology, alteration, mineralogy, or structural domains. | 0 | Metallurgy |
It was excavated between 1968 and 1974 under the direction of German archaeologist Harald Hauptmann as part of the salvage project to document archaeological sites that would be flooded by the construction of the Keban Dam. Excavation of the site focused on three areas: the western slope, the so-called "acropolis" area, and the south terrace. | 0 | Metallurgy |
SLC18A2 is essential for enabling the release of neurotransmitters from the axon terminals of monoamine neurons into the synaptic cleft. If SLC18A2 function is inhibited or compromised, monoamine neurotransmitters such as dopamine cannot be released into the synapse via typical release mechanisms (i.e., exocytosis resulting from action potentials).
Cocaine users display a marked reduction in SLC18A2 immunoreactivity. Those with cocaine-induced mood disorders displayed a significant loss of SLC18A2 immunoreactivity; this might reflect damage to dopamine axon terminals in the striatum. These neuronal changes could play a role in causing disordered mood and motivational processes in more severely addicted users. | 1 | Gene expression + Signal Transduction |
*PRKAG1 Senses energy level and inactivates HMGCoA reductase and Acetyl CoA Carboxylase
*PRKAA1 NM_006251 Catalytic subunit of AMP-activated protein kinase (AMPK), an energy sensor protein kinase that plays a key role in regulating cellular energy metabolism
*PRKAB1 NM_006253 Non-catalytic subunit of AMP-activated protein kinase (AMPK), an energy sensor protein kinase that plays a key role in regulating cellular energy metabolism
*PRKACA NM_002730 Phosphorylates a large number of substrates in the cytoplasm and the nucleus.
*PRKAG1 NM_002733 Homo sapiens protein kinase, AMP-activated, gamma 1 non-catalytic subunit (PRKAG1), mRNA
*PRKAR1A NM_002734 Regulatory subunit of the cAMP-dependent protein kinases involved in cAMP signaling in cells
*PRKRIP1 NM_024653 Binds double-stranded RNA. Inhibits EIF2AK2 kinase activity (By similarity). | 1 | Gene expression + Signal Transduction |
In the early years, people from the surrounding community used the mill tailings as fill dirt in various properties, such as their yards and gardens. A woman who played in such a yard as a child later sued Kerr-McGee over her Hodgkin's disease and settled out of court in 1988.
Radioactive waste from the plant was put in a local landfill that later became a public park called Reed-Keppler Park.
Kress Creek and West Branch Dupage River (including sediments, banks, and floodplains) were contaminated by years of rainwater runoff from REF going into a storm sewer and then into the creek. The floodplain includes people's yards.
The West Chicago Sewage Treatment Plant was contaminated when mill tailings from REF were used as fill dirt there. This also resulted in pollution of the West Branch Dupage River from runoff and erosion.
In 1991, the Illinois Department of Public Health found elevated cancer rates in the community. | 0 | Metallurgy |
TLRs are believed to function as dimers. Though most TLRs appear to function as homodimers, TLR2 forms heterodimers with TLR1 or TLR6, each dimer having a different ligand specificity. TLRs may also depend on other co-receptors for full ligand sensitivity, such as in the case of TLR4's recognition of LPS, which requires MD-2. CD14 and LPS-Binding Protein (LBP) are known to facilitate the presentation of LPS to MD-2.
A set of endosomal TLRs comprising TLR3, TLR7, TLR8 and TLR9 recognize nucleic acid derived from viruses as well as endogenous nucleic acids in context of pathogenic events. Activation of these receptor leads to production of inflammatory cytokines as well as type I interferons (interferon type I) to help fight viral infection.
The adapter proteins and kinases that mediate TLR signaling have also been targeted. In addition, random germline mutagenesis with ENU has been used to decipher the TLR signaling pathways. When activated, TLRs recruit adapter molecules within the cytoplasm of cells to propagate a signal. Four adapter molecules are known to be involved in signaling. These proteins are known as MyD88, TIRAP (also called Mal), TRIF, and TRAM (TRIF-related adaptor molecule).
TLR signaling is divided into two distinct signaling pathways, the MyD88-dependent and TRIF-dependent pathway. | 1 | Gene expression + Signal Transduction |
Cells respond to stress in the form of DNA damage, activated oncogenes, or sub-par growing conditions, and can enter a senescence-like state called "premature senescence". This allows the cell to prevent further replication during periods of damaged DNA or general unfavorable conditions. DNA damage in a cell can induce pRb activation. pRb's role in repressing the transcription of cell cycle progression genes leads to the S phase arrest that prevents replication of damaged DNA. | 1 | Gene expression + Signal Transduction |
Degeneracy or redundancy of codons is the redundancy of the genetic code, exhibited as the multiplicity of three-base pair codon combinations that specify an amino acid. The degeneracy of the genetic code is what accounts for the existence of synonymous mutations. | 1 | Gene expression + Signal Transduction |
There are several differences in the regulation of metabolic control in eukaryotes and in prokaryotes. Prokaryotes vary the numbers of specific enzymes made in their cells in order to regulate gene expression, which is slow metabolic control, and also regulate enzymatic pathways through mechanisms such as feedback inhibition and allosteric regulation, which is rapid metabolic control. The genes of prokaryotes are grouped together based on similar functions into units called operons which consist of a promoter and an operator. The operator is the binding site for the repressor and thus has a function equivalent to the silencer region in Eukaryotic DNA. When a repressor protein is bound to the operator, RNA polymerase cannot bind to the promoter to initiate the transcription of the operon. | 1 | Gene expression + Signal Transduction |
Control of an operon is a type of gene regulation that enables organisms to regulate the expression of various genes depending on environmental conditions. Operon regulation can be either negative or positive by induction or repression.
Negative control involves the binding of a repressor to the operator to prevent transcription.
* In negative inducible operons, a regulatory repressor protein is normally bound to the operator, which prevents the transcription of the genes on the operon. If an inducer molecule is present, it binds to the repressor and changes its conformation so that it is unable to bind to the operator. This allows for expression of the operon. The lac operon is a negatively controlled inducible operon, where the inducer molecule is allolactose.
* In negative repressible operons, transcription of the operon normally takes place. Repressor proteins are produced by a regulator gene, but they are unable to bind to the operator in their normal conformation. However, certain molecules called corepressors are bound by the repressor protein, causing a conformational change to the active site. The activated repressor protein binds to the operator and prevents transcription. The trp operon, involved in the synthesis of tryptophan (which itself acts as the corepressor), is a negatively controlled repressible operon.
Operons can also be positively controlled. With positive control, an activator protein stimulates transcription by binding to DNA (usually at a site other than the operator).
* In positive inducible operons, activator proteins are normally unable to bind to the pertinent DNA. When an inducer is bound by the activator protein, it undergoes a change in conformation so that it can bind to the DNA and activate transcription. Examples of positive inducible operons include the MerR family of transcriptional activators.
* In positive repressible operons, the activator proteins are normally bound to the pertinent DNA segment. However, when an inhibitor is bound by the activator, it is prevented from binding the DNA. This stops activation and transcription of the system. | 1 | Gene expression + Signal Transduction |
The earliest records of bloomery-type furnaces in East Africa are discoveries of smelted iron and carbon in Nubia n ancient Sudan dated at least to the seventh to the sixth century BC. The ancient bloomeries that produced metal tools for the Nubians and Kushites produced a surplus for sale. All traditional sub-Saharan African iron-smelting processes are variants of the bloomery process. There is considerable discussion about the origins of iron metallurgy in Africa. Smelting in bloomery type furnaces in West Africa and forging of tools appeared in the Nok culture of central Nigeria by at least 550 BC and possibly several centuries earlier. Also, evidence indicates iron smelting with bloomery-style furnaces dated to 750 BC in Opi (Augustin Holl 2009) and Lejja dated to 2,000 BC (Pamela Eze-Uzomaka 2009), both sites in the Nsukka region of southeast Nigeria in what is now Igboland. The site of Gbabiri, in the Central African Republic, has also yielded evidence of iron metallurgy, from a reduction furnace and blacksmith workshop, with earliest dates of 896–773 and 907–796 BC, respectively. | 0 | Metallurgy |
One standard increasingly used (e.g. in the United States) is J-STD-004. It is very similar to DIN EN 61190-1-1.
Four characters (two letters, then one letter, and last a number) represent flux composition, flux activity, and whether activators include halides:
* First two letters: Base
** RO: rosin
** RE: resin
** OR: organic
** IN: inorganic
* Third letter: Activity
** L: low
** M: moderate
** H: high
* Number: Halide content
** 0: less than 0.05% in weight (“halide-free”)
** 1: halide content depends on activity:
*** less than 0.5% for low activity
*** 0.5% to 2.0% for moderate activity
*** greater than 2.0% for high activity
Any combination is possible, e.g. ROL0, REM1 or ORH0.
J-STD-004 characterizes the flux by reliability of residue from a surface insulation resistance (SIR) and electromigration standpoint. It includes tests for electromigration and surface insulation resistance (which must be greater than 100 MΩ after 168 hours at elevated temperature and humidity with a DC bias applied). | 0 | Metallurgy |
Recent progress in the field of microfluidics has led to the development of microdroplets, a new drug-delivery system that uses uniform droplets to deliver drugs to specific locations within the body. These microdroplets allow researchers to load drugs during the polymerization step of their formation and provide variations in porosity, which can control the time it takes to release a therapeutic payload. Thus, by using the natural process of chemotaxis, researchers aim to guide these tiny droplets by using chemical gradients released by a specific cell, tissue, or organ within the body. In fact, a few examples of microdroplet systems that use chemotaxis are self-propelling, ionic liquid-based, and synthetic base. These microdroplet-based drug delivery systems offer several advantages over traditional drug delivery methods, which are talked about later in the advantage and limitations subsection of this article. Overall, the development of microdroplet-based drug delivery systems using the phenomenon of chemotaxis is just one of may avenues to potentially revolutionize the field of medicine and targeted drug delivery. | 1 | Gene expression + Signal Transduction |
Electrowinning and electrorefining respectively involve the recovery and purification of metals using electrodeposition of metals at the cathode, and either metal dissolution or a competing oxidation reaction at the anode. | 0 | Metallurgy |
The syndrome primarily affects young males. Preliminary studies suggest that prevalence may be 1.8 per 10,000 live male births. 50% of those affected do not live beyond 25 years of age, with deaths attributed to the impaired immune function. | 1 | Gene expression + Signal Transduction |
High-angle grain boundaries, which have large misorientations between adjacent grains, tend to have higher interfacial energy and are more effective in impeding dislocation motion. In contrast, low-angle grain boundaries with small misorientations and lower interfacial energy may allow for easier dislocation transmission and exhibit weaker grain boundary strengthening effects. | 0 | Metallurgy |
The material was described in NACA-TN-259 of August 1927, as "a new corrosion resistant aluminium product which is markedly superior to the present strong alloys. Its use should result in greatly increased life of a structural part. Alclad is a heat-treated aluminium, copper, manganese, magnesium alloy that has the corrosion resistance of pure metal at the surface and the strength of the strong alloy underneath. Of particular importance is the thorough character of the union between the alloy and the pure aluminium. Preliminary results of salt spray tests (24 weeks of exposure) show changes in tensile strength and elongation of Alclad 17ST, when any occurred, to be so small as to be well within the limits of experimental error." In applications involving aircraft construction, Alclad has proven to have increased resistance to corrosion at the expense of increased weight when compared to sheet aluminium.
As pure aluminium possesses a relatively greater resistance to corrosion over the majority of aluminium alloys, it was soon recognised that a thin coating of pure aluminium over the exterior surface of those alloys would take advantage of the superior qualities of both materials. Thus, a key advantage of Alclad over most aluminium alloys is its high corrosion resistance. However, considerable care must be taken while working on an Alclad-covered exterior surface, such as while cleaning the skin of an aircraft, to avoid scarring the surface to expose the vulnerable alloy underneath and prematurely age those elements.
Due to its relatively shiny natural finish, it is often considered to be cosmetically pleasing when used for external elements, particularly during restoration efforts. It has been observed that some fabrication techniques, such as welding, are not suitable when used in conjunction with Alclad. Mild cleaners with a neutral pH value and finer abrasives are recommended for cleaning and polishing Alclad surfaces. It is common for waterproof wax and other inhibitive coverings to be applied to further reduce corrosion. In the twenty-first century, research and evaluation was underway into new coatings and application techniques. | 0 | Metallurgy |
Translation in plants is tightly regulated as in animals, however, it is not as well understood as transcriptional regulation. There are several levels of regulation including translation initiation, mRNA turnover and ribosome loading. Recent studies have shown that translation is also under the control of the circadian clock. Like transcription, the translation state of numerous mRNAs changes over the diel cycle (day night period). | 1 | Gene expression + Signal Transduction |
Charles M. Schwab (1862–1939) and Eugene Grace (1876–1960) made Bethlehem Steel the second-largest American steel company by the 1920s. Schwab had been the operating head of Carnegie Steel and US Steel. In 1903 he purchased the small firm Bethlehem Steel, and in 1916 made Grace president. Innovation was the keynote at a time when U.S. Steel under Judge Elbert Henry Gary moved slowly. Bethlehem concentrated on government contracts, such as ships and naval armor, and on construction beams, especially for skyscrapers and bridges. Its subsidiary Bethlehem Shipbuilding Corporation operated 15 shipyards in World War II. It produced 1,121 ships, more than any other builder during the war and nearly one-fifth of the U.S. Navy's fleet. Its peak employment was 180,000 workers, out of a company-wide wartime peak of 300,000. After 1945 Bethlehem doubled its steel capacity, a measure of the widespread optimism in the industry. However the company ignored the new technologies then being developed in Europe and Japan. Seeking labor peace in order to avoid strikes, Bethlehem like the other majors agreed to large wage and benefits increases that kept its costs high. After Grace retired the executives concentrated on short term profits and postponed innovations that led to long-term inefficiency. It went bankrupt in 2001. | 0 | Metallurgy |
Plastic deformation happens when stresses flatten, bend, or twist a material until it cannot return to its original shape. This can create cracks in the material and decrease its lifetime. | 0 | Metallurgy |
As it is known that survivin is over-expressed in most cancers, which may be contributing to the cancer cells' resistance to apoptotic stimuli from the environment. The use of antisense survivin therapy hopes to render cancer cells susceptible to apoptosis by eliminating survivin expression in the cancer cells.
Olie et al. developed different 20-mer phosphorothioate antisense oligonucleotides that target different regions in the mRNA of the survivin gene. The antisense function of the oligonucleotides allows binding to surviving mRNA and, depending on the region on which it binds, might inhibit surviving mRNA from being translated into a functional protein. Real-time PCR was used to assess the levels of mRNA present in a lung adenocarcinoma cell line A549 that overexpresses survivin. The best antisense oligonucleotide was identified that effectively down-regulated survivin mRNA levels and resulted in apoptosis of the cells. Survivin's role in cancer development in the context of a signaling pathway is its ability to inhibit activation of downstream caspase-3 and -7 from apoptosis inducing stimuli. The overexpression of survivin in tumors may serve to increase the tumors resistance to apoptosis and, thus, contribute to cell immortality even in the presence of death stimuli. In this experiment, the oligonucleotide 4003 that targets nucleotides 232-251 of survivin mRNA was found to be the most effective at down-regulating the levels of survivin mRNA in the A549 tumour line. The 4003 oligonucleotides were introduced into the tumour cells by transfection. Further experiments were then conducted on 4003. One of the additional experiments involved determining the dose-dependent effect of 4003 on the down-regulation of survivin mRNA levels. It was found that a concentration of 400 nM resulted in a maximum down-regulation of 70% of the initial survivin mRNA present. Another experiment on 4003 involved assessing any biological or cytotoxic effect 4003 down-regulation of survivin mRNA has on A549 cells using the MTT assay. The numbers of A549 cells transfected with 4003 significantly decreased with increasing concentration of 4003 compared to cells transfected either with a mismatch form of the 4003 or lipofectin control. Many physical observations that confirmed the induction of apoptosis by 4003 were made. For example, lysates of the 4003-treated cells showed increased levels of caspase-3-like protease activity; nuclei were observed to be condensed and chromatin was fragmented. | 1 | Gene expression + Signal Transduction |
Sintering is an important cause for loss of catalytic activity, especially on supported metal catalysts. It decreases the surface area of the catalyst and changes the surface structure. For a porous catalytic surface, the pores may collapse due to sintering, resulting in loss of surface area. Sintering is in general an irreversible process.
Small catalyst particles have the highest possible relative surface area and high reaction temperature, both factors that generally increase the reactivity of a catalyst. However, these factors are also the circumstances under which sintering occurs. Specific materials may also increase the rate of sintering. On the other hand, by alloying catalysts with other materials, sintering can be reduced. Rare-earth metals in particular have been shown to reduce sintering of metal catalysts when alloyed.
For many supported metal catalysts, sintering starts to become a significant effect at temperatures over . Catalysts that operate at higher temperatures, such as a car catalyst, use structural improvements to reduce or prevent sintering. These improvements are in general in the form of a support made from an inert and thermally stable material such as silica, carbon or alumina. | 0 | Metallurgy |
There are two main types of kineses, both resulting in aggregations. However, the stimulus does not act to attract or repel individuals.
Orthokinesis: in which the speed of movement of the individual is dependent upon the stimulus intensity. For example, the locomotion of the collembola, Orchesella cincta, in relation to water. With increased water saturation in the soil there is an increase in the direction of its movement towards the aimed place.
Klinokinesis: in which the frequency or rate of turning is proportional to stimulus intensity. For example, the behaviour of the flatworm (Dendrocoelum lacteum) which turns more frequently in response to increasing light thus ensuring that it spends more time in dark areas. | 1 | Gene expression + Signal Transduction |
A screening machine consist of a drive that induces vibration, a screen media that causes particle separation, and a deck which holds the screen media and the drive and is the mode of transport for the vibration.
There are physical factors that makes screening practical. For example, vibration, g force, bed density, and material shape all facilitate the rate or cut. Electrostatic forces can also hinder screening efficiency in way of water attraction causing sticking or plugging, or very dry material generate a charge that causes it to attract to the screen itself.
As with any industrial process there is a group of terms that identify and define what screening is. Terms like blinding, contamination, frequency, amplitude, and others describe the basic characteristics of screening, and those characteristics in turn shape the overall method of dry or wet screening.
In addition, the way a deck is vibrated differentiates screens. Different types of motion have their advantages and disadvantages. In addition media types also have their different properties that lead to advantages and disadvantages.
Finally, there are issues and problems associated with screening. Screen tearing, contamination, blinding, and dampening all affect screening efficiency. | 0 | Metallurgy |
The development of rapamycin as an anticancer agent began again in the 1990s with the discovery of temsirolimus (CCI-779). This novel soluble rapamycin derivative had a favorable toxicological profile in animals. More rapamycin derivatives with improved pharmacokinetics and reduced immunosuppressive effects have since then been developed for the treatment of cancer. These rapalogs include temsirolimus (CCI-779), everolimus (RAD001), and ridaforolimus (AP-23573) which are being evaluated in cancer clinical trials. Rapamycin analogs have similar therapeutic effects as rapamycin. However they have improved hydrophilicity and can be used for oral and intravenous administration. In 2012 National Cancer Institute listed more than 200 clinical trials testing the anticancer activity of rapalogs both as monotherapy or as a part of combination therapy for many cancer types.
Rapalogs, which are the first generation mTOR inhibitors, have proven effective in a range of preclinical models. However, the success in clinical trials is limited to only a few rare cancers. Animal and clinical studies show that rapalogs are primarily cytostatic, and therefore effective as disease stabilizers rather than for regression. The response rate in solid tumors where rapalogs have been used as a single-agent therapy have been modest. Due to partial mTOR inhibition as mentioned before, rapalogs are not sufficient for achieving a broad and robust anticancer effect, at least when used as monotherapy.
Another reason for the limited success is that there is a feedback loop between mTORC1 and AKT in certain tumor cells. It seems that mTORC1 inhibition by rapalogs fails to repress a negative feedback loop that results in phosphorylation and activation of AKT. These limitations have led to the development of the second generation of mTOR inhibitors. | 1 | Gene expression + Signal Transduction |
Panel edge staining is a naturally occurring problem that occurs to anodized aluminium and stainless steel panelling and façades. It is semi-permanent staining that dulls the panel or façade's surface (in particular the edges of the panelling), reducing the natural lustre and shine produced by the anodizing processes used on the aluminium. Panel edge staining may also appear on powder coated aluminium, painted aluminium, stainless steel and titanium surfaces. | 0 | Metallurgy |
The museum has several functional areas, with the main museum building covering over 13,000 square feet. The displays at the main museum building contains iron-industry content as well as a wide variety of archaeological artifacts. In addition, the museum also houses the Walter B. Jones Centre for Industrial Archaeology and includes an exhibit centre, the 1858 May Plantation Cotton Gin House, a 30-seat theatre, as well as a gift shop. The exhibition centre displays preserved Birmingham's iron-and-steel industrial artifacts over the period from 1930s to the 1960s. | 0 | Metallurgy |
TaqMan probes are hydrolysis probes that are designed to increase the specificity of quantitative PCR. The method was first reported in 1991 by researcher Kary Mullis at Cetus Corporation, and the technology was subsequently developed by Hoffmann-La Roche for diagnostic assays and by Applied Biosystems (now part of Thermo Fisher Scientific) for research applications.
The TaqMan probe principle relies on the 5´–3´ exonuclease activity of Taq polymerase to cleave a dual-labeled probe during hybridization to the complementary target sequence and fluorophore-based detection. As in other quantitative PCR methods, the resulting fluorescence signal permits quantitative measurements of the accumulation of the product during the exponential stages of the PCR; however, the TaqMan probe significantly increases the specificity of the detection. TaqMan probes were named after the videogame Pac-Man (Taq Polymerase + PacMan = TaqMan) as its mechanism is based on the Pac-Man principle. | 1 | Gene expression + Signal Transduction |
The expansive force of rusting, which may be called oxide jacking or rust burst, is a phenomenon that can cause damage to structures made of stone, masonry, concrete or ceramics, and reinforced with metal components. A definition is "the displacement of building elements due to the expansion of iron and steel products as the metal rusts and becomes iron oxide". Corrosion of other metals such as aluminum can also cause oxide jacking. | 0 | Metallurgy |
Lead ore (galena) in relatively pure form is present geologically in a number of places in North America. Some native populations mined and used the lead. | 0 | Metallurgy |
Upon binding of LH to the external part of the membrane spanning receptor, a transduction of the signal takes place. This process results in the activation of a heterotrimeric G protein. Binding of LH to the receptor shifts its conformation. The activated receptor promotes the binding of GTP to the G protein and its subsequent activation. After binding GTP, the G protein heterotrimer detaches from the receptor and disassembles. The alpha-subunit Gs binds adenylate cyclase and activates the cAMP system.
It is believed that a receptor molecule exists in a conformational equilibrium between active and inactive states. The binding of LH (or CG) to the receptor shifts the equilibrium towards the active form of the receptor. For a cell to respond to LH only a small percentage (≈1%) of receptor sites need to be activated. | 1 | Gene expression + Signal Transduction |
Whereas Gram-negative bacteria primarily use acylated homoserine lactones, Gram-positive bacteria generally use oligopeptides as autoinducers for quorum sensing. These molecules are often synthesized as larger polypeptides that are cleaved post-translationally to produce “processed” peptides. Unlike AHLs that can freely diffuse across cell membranes, peptide autoinducers usually require specialized transport mechanisms (often ABC transporters). Additionally, they do not freely diffuse back into cells, so bacteria that use them must have mechanisms to detect them in their extracellular environments. Most Gram-positive bacteria use a two-component signaling mechanism in quorum sensing. Secreted peptide autoinducers accumulate as a function of cell density. Once a quorum level of autoinducer is achieved, its interaction with a sensor kinase at the cell membrane initiates a series of phosphorylation events that culminate in the phosphorylation of a regulator protein intracellularly. This regulator protein subsequently functions as a transcription factor and alters gene expression. Similar to Gram-negative bacteria, the autoinduction and quorum sensing system in Gram-positive bacteria is conserved, but again, individual species have tailored specific aspects for surviving and communicating in unique niche environments. | 1 | Gene expression + Signal Transduction |
An example is the trp gene in bacteria. When there is a high level of tryptophan in the region, it is inefficient for the bacterium to synthesize more. When the RNA polymerase binds and transcribes the trp gene, the ribosome will start translating. (This differs from eukaryotic cells, where RNA must exit the nucleus before translation starts.) The attenuator sequence, which is located between the mRNA leader sequence (5' UTR) and trp operon gene sequence, contains four domains, where domain 3 can pair with domain 2 or domain 4.
The attenuator sequence at domain 1 contains instruction for peptide synthesis that requires tryptophans. A high level of tryptophan will permit ribosomes to translate the attenuator sequence domains 1 and 2, allowing domains 3 and 4 to form a hairpin structure, which results in termination of transcription of the trp operon. Since the protein coding genes are not transcribed due to rho independent termination, no tryptophan is synthesised.
In contrast, a low level of tryptophan means that the ribosome will stall at domain 1, causing the domains 2 and 3 to form a different hairpin structure that does not signal termination of transcription. Therefore, the rest of the operon will be transcribed and translated, so that tryptophan can be produced. Thus, domain 4 is an attenuator. Without domain 4, translation can continue regardless of the level of tryptophan. The attenuator sequence has its codons translated into a leader peptide, but is not part of the trp operon gene sequence. The attenuator allows more time for the attenuator sequence domains to form loop structures, but does not produce a protein that is used in later tryptophan synthesis.
Attenuation is a second mechanism of negative feedback in the trp operon. While the TrpR repressor decreases transcription by a factor of 70, attenuation can further decrease it by a factor of 10, thus allowing accumulated repression of about 700-fold. Attenuation is made possible by the fact that in prokaryotes (which have no nucleus), the ribosomes begin translating the mRNA while RNA polymerase is still transcribing the DNA sequence. This allows the process of translation to directly affect transcription of the operon.
At the beginning of the transcribed genes of the trp operon is a sequence of 140 nucleotides termed the leader transcript (trpL). This transcript includes four short sequences designated 1–4. Sequence 1 is partially complementary to sequence 2, which is partially complementary to sequence 3, which is partially complementary to sequence 4. Thus, three distinct secondary structures (hairpins) can form: 1–2, 2–3 or 3–4. The hybridization of strands 1 and 2 to form the 1–2 structure prevents the formation of the 2–3 structure, while the formation of 2-3 prevents the formation of 3–4. The 3–4 structure is a transcription termination sequence, once it forms RNA polymerase will disassociate from the DNA and transcription of the structural genes of the operon will not occur.
Part of the leader transcript codes for a short polypeptide of 14 amino acids, termed the leader peptide. This peptide contains two adjacent tryptophan residues, which is unusual, since tryptophan is a fairly uncommon amino acid (about one in a hundred residues in a typical E. coli protein is tryptophan). If the ribosome attempts to translate this peptide while tryptophan levels in the cell are low, it will stall at either of the two trp codons. While it is stalled, the ribosome physically shields sequence 1 of the transcript, thus preventing it from forming the 1-2 secondary structure. Sequence 2 is then free to hybridize with sequence 3 to form the 2-3 structure, which then prevents the formation of the 3-4 termination hairpin. RNA polymerase is free to continue transcribing the entire operon. If tryptophan levels in the cell are high, the ribosome will translate the entire leader peptide without interruption and will only stall during translation termination at the stop codon. At this point the ribosome physically shields both sequences 1 and 2. Sequences 3 and 4 are thus free to form the 3-4 structure which terminates transcription. The result is that the operon will be transcribed only when tryptophan is unavailable for the ribosome, while the trpL transcript is constitutively expressed.
To ensure that the ribosome binds and begins translation of the leader transcript immediately following its synthesis, a pause site exists in the trpL sequence. Upon reaching this site, RNA polymerase pauses transcription and apparently waits for translation to begin. This mechanism allows for synchronization of transcription and translation, a key element in attenuation.
A similar attenuation mechanism regulates the synthesis of histidine, phenylalanine and threonine. | 1 | Gene expression + Signal Transduction |
It has recently been found that Acinetobacter sp. also show quorum sensing activity. This bacterium, an emerging pathogen, produces AHLs. Acinetobacter sp. shows both quorum sensing and quorum quenching activity. It produces AHLs and can also degrade the AHL molecules. | 1 | Gene expression + Signal Transduction |
*FasR: The Fas receptor (FasR), or CD95, is the most intensely studied member of the death receptor family. The gene is situated on chromosome 10 in humans and 19 in mice. Previous reports have identified as many as eight splice variants, which are translated into seven isoforms of the protein. Many of these isoforms are associated with rare haplotypes that are usually associated with a state of disease. Apoptosis-inducing Fas receptor is dubbed isoform 1 and is a type 1 transmembrane protein. It consists of three cysteine-rich pseudorepeats, a transmembrane domain, and an intracellular death domain.
*DcR3: Decoy receptor 3 (DcR3) is a recently discovered decoy receptor of the tumor necrosis factor superfamily that binds to FasL, LIGHT, and TL1A. DcR3 is a soluble receptor that has no signal transduction capabilities (hence a "decoy") and functions to prevent FasR-FasL interactions by competitively binding to membrane-bound Fas ligand and rendering them inactive. | 1 | Gene expression + Signal Transduction |
The number of two-component systems present in a bacterial genome is highly correlated with genome size as well as ecological niche; bacteria that occupy niches with frequent environmental fluctuations possess more histidine kinases and response regulators. New two-component systems may arise by gene duplication or by lateral gene transfer, and the relative rates of each process vary dramatically across bacterial species. In most cases, response regulator genes are located in the same operon as their cognate histidine kinase; lateral gene transfers are more likely to preserve operon structure than gene duplications. | 1 | Gene expression + Signal Transduction |
Modern day antique collectors have since coined the term "Piloncitos" to describe the small "bead-like" pieces of gold which were used as currency in Precolonial Philippines, comparing the cone-shaped pieces to a pilon of sugar. Early historical descriptions of the term include the Spanish "granitas de oro" (small grains of gold), or simply by whatever local language terms were used to mean "gold" in those times, such as "bulawan." | 0 | Metallurgy |
Antitermination was discovered in bacteriophage infections. A common feature in the control of phage infection is that very few of the phage genes can be transcribed by the bacterial host RNA polymerase. Among these genes, however, are regulators whose products allow the next set of phage genes to be expressed. One of these types of regulator is an antitermination protein. In the absence of the antitermination protein, RNA polymerase terminates at the terminator. When the antitermination protein is present, it continues past the terminator.
The best characterized example of antitermination is provided by lambda phage, in which the phenomenon was discovered. It is used at two stages of phage expression. The antitermination protein produced at each stage is specific for the particular transcription units that are expressed at that stage.
The host RNA polymerase initially transcribes two genes, which are called the immediate early genes (N and cro). The transition to the next stage of expression is controlled by preventing termination at the ends of the immediate early genes, with the result that the delayed early genes are expressed. The antitermination protein pN acts specifically on the immediate early transcription units. Later during infection, another antitermination protein pQ acts specifically on the late transcription unit, to allow its transcription to continue past a termination sequence.
The different specificities on pN and pQ establish an important general principle: RNA polymerase interacts with transcription units in such a way that an ancillary factor can sponsor antitermination specifically for some transcripts. Termination can be controlled with the same sort of precision as initiation.
The antitermination activity of pN is highly specific, but the antitermination event is not determined by the terminators t and t; the recognition site needed for antitermination lies upstream in the transcription unit, that is, at a different place from the terminator site at which the action eventually is accomplished.
The recognition sites required for pN action are called nut (for N utilization). The sites responsible for determining leftward and rightward antitermination are described as nut and nut, respectively.
When pN recognizes the nut site, it forms a persistent antitermination complex in cooperation with a number of E. coli host proteins. These include three host Nus proteins, NusA, B, and C. NusA is an interesting protein. By itself in E. coli, it is part of the transcription termination system. However, when co-opted by N, it participates in antitermination. The complex must act on RNA polymerase to ensure that the enzyme can no longer respond to the terminator. The variable locations of the nut sites indicate that this event is linked neither to initiation nor to termination, but can occur to RNA polymerase as it elongates the RNA chain past the nut site. Phages that are related to lambda have different N genes and different antitermination specificities. The region on the phage genome in which the nut sites lie has a different sequence in each of these phages, and each phage must therefore have characteristic nut sites recognized specifically by its own pN. Each of these pN products must have the same general ability to interact with the transcription apparatus in an antitermination capacity, but each product also has a different specificity for the sequence of DNA that activates the mechanism. | 1 | Gene expression + Signal Transduction |
Viral (as well as some eukaryotic) 5′ UTRs contain internal ribosome entry sites, which is a cap-independent method of translational activation. Instead of building up a complex at the 5′ cap, the IRES allows for direct binding of the ribosomal complexes to the transcript to begin translation. The IRES enables the viral transcript to translate more efficiently due to the lack of needing a preinitation complex, allowing the virus to replicate quickly. | 1 | Gene expression + Signal Transduction |
Yttrium is a chemical element; it has symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals and is never found in nature as a free element. Y is the only stable isotope and the only isotope found in the Earth's crust.
The most important present-day use of yttrium is as a component of phosphors, especially those used in LEDs. Historically, it was once widely used in the red phosphors in television set cathode ray tube displays. Yttrium is also used in the production of electrodes, electrolytes, electronic filters, lasers, superconductors, various medical applications, and tracing various materials to enhance their properties.
Yttrium has no known biological role. Exposure to yttrium compounds can cause lung disease in humans. | 0 | Metallurgy |
It is known that most materials are polycrystalline and contain grain boundaries and that grain boundaries can act as sinks and transport pathways for point defects. However experimentally and theoretically determining what effect point defects have on a system is difficult. Interesting examples of the complications of how point defects behave has been manifested in the temperature dependence of the Seebeck effect. In addition the dielectric and piezoelectric response can be altered by the distribution of point defects near grain boundaries. Mechanical properties can also be significantly influenced with properties such as the bulk modulus and damping being influenced by changes to the distribution of point defects within a material. It has also been found that the Kondo effect within graphene can be tuned due to a complex relationship between grain boundaries and point defects. Recent theoretical calculations have revealed that point defects can be extremely favourable near certain grain boundary types and significantly affect the electronic properties with a reduction in the band gap. | 0 | Metallurgy |
The initial melting of the material to be smelted is usually referred to as the smelting or matte smelting stage. It can be undertaken in a variety of furnaces, including the largely obsolete blast furnaces and reverberatory furnaces, as well as flash furnaces, Isasmelt furnaces, etc. The product of this smelting stage is a mixture of copper, iron and sulfur that is enriched in copper, which is called matte or copper matte. The term matte grade is normally used to refer to the copper content of the matte.
The purpose of the matte smelting stage is to eliminate as much of the unwanted iron, sulfur and gangue minerals (such as silica, magnesia, alumina and limestone) as possible, while minimizing the loss of copper. This is achieved by reacting iron sulfides with oxygen (in air or oxygen enriched air) to produce iron oxides (mainly as FeO, but with some magnetite (FeO)) and sulfur dioxide.
Copper sulfide and iron oxide can mix, but when sufficient silica is added, a separate slag layer is formed. Adding silica also reduces the melting point (or, more properly, the liquidus temperature) of the slag, meaning that the smelting process can be operated at a lower temperature.
The slag forming reaction is:
:FeO + SiO → FeO.SiO
Slag is less dense than matte, so it forms a layer that floats on top of the matte.
Copper can be lost from the matte in three ways: as cuprous oxide (CuO) dissolved in the slag, as sulfide copper dissolved in the slag or as tiny droplets (or prills) of matte suspended in the slag.
The amount of copper lost as oxide copper increases as the oxygen potential of the slag increases. The oxygen potential generally increases as the copper content of the matte is increased. Thus, the loss of copper as oxide increases as the copper content of the matte increases.
On the other hand, the solubility of sulfidic copper in slag decreases as the copper content of the matte increases beyond about 40%. Nagamori calculated that more than half the copper dissolved in slags from mattes containing less than 50% copper is sulfidic copper. Above this figure, oxidic copper begins to dominate.
The loss of copper as prills suspended in the slag depends on the size of the prills, the viscosity of the slag and the settling time available. Rosenqvist suggested that about half the copper losses to slag were due to suspended prills.
The mass of slag generated in the smelting stage depends on the iron content of the material fed into the smelting furnace and the target matte grade. The greater the iron content of the feed, the more iron that will need to be rejected to the slag for a given matte grade. Similarly, increasing the target matte grade requires the rejection of more iron and an increase in the slag volume.
Thus, the two factors that most affect the loss of copper to slag in the smelting stage are:
* matte grade
* mass of slag.
This means that there is a practical limit on how high the matte grade can be if the loss of copper to slag is to be minimized. Therefore, further stages of processing (converting and fire refining) are required.
The following subsections briefly describe some of the processes used in matte smelting. | 0 | Metallurgy |
Permanent mold casting is a metal casting process that employs reusable molds ("permanent molds"), usually made from metal. The most common process uses gravity to fill the mold. However, gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow castings. Common casting metals are aluminum, magnesium, and copper alloys. Other materials include tin, zinc, and lead alloys and iron and steel are also cast in graphite molds. Permanent molds, while lasting more than one casting still have a limited life before wearing out. | 0 | Metallurgy |
Ballast tanks on ships contain the fuels for corrosion. Water is one and air is usually present too and the water can become stagnant. Structural integrity is important for safety and to avoid marine pollution. Coatings have become the solution of choice to reduce the amount of corrosion in ballast tanks. Impressed current cathodic protection has also been used. Likewise sacrificial anode cathodic protection is also used. Since chlorides vastly accelerate corrosion, ballast tanks of marine vessels are particularly susceptible. | 0 | Metallurgy |
It is widely accepted that the synapse plays a key role in the formation of memory. The stability of long-term memory can persist for many years; nevertheless, synapses, the neurological basis of memory, are very dynamic. The formation of synaptic connections significantly depends on activity-dependent synaptic plasticity observed in various synaptic pathways. Indeed, the connection between memory formation and alterations in synaptic efficacy enables the reinforcement of neuronal interactions between neurons. As neurotransmitters activate receptors across the synaptic cleft, the connection between the two neurons is strengthened when both neurons are active at the same time, as a result of the receptor's signaling mechanisms. The strength of two connected neural pathways is thought to result in the storage of information, resulting in memory. This process of synaptic strengthening is known as long-term potentiation (LTP).
By altering the release of neurotransmitters, the plasticity of synapses can be controlled in the presynaptic cell. The postsynaptic cell can be regulated by altering the function and number of its receptors. Changes in postsynaptic signaling are most commonly associated with a N-methyl-d-aspartic acid receptor (NMDAR)-dependent LTP and long-term depression (LTD) due to the influx of calcium into the post-synaptic cell, which are the most analyzed forms of plasticity at excitatory synapses. | 1 | Gene expression + Signal Transduction |
Extracellular binding of cytokines or growth factors induce activation of receptor-associated Janus kinases, which phosphorylate a specific tyrosine residue within the STAT protein promoting dimerization via their SH2 domains. The phosphorylated dimer is then actively transported to the nucleus via an importin α/β ternary complex. Originally, STAT proteins were described as latent cytoplasmic transcription factors as phosphorylation was thought to be required for nuclear retention. However, unphosphorylated STAT proteins also shuttle between the cytosol and nucleus, and play a role in gene expression. Once STAT reaches the nucleus, it binds to a consensus DNA-recognition motif called gamma-activated sites (GAS) in the promoter region of cytokine-inducible genes and activates transcription. The STAT protein can be dephosphorylated by nuclear phosphatases, which leads to inactivation of STAT and subsequent transport out of the nucleus by an exportin-RanGTP complex. | 1 | Gene expression + Signal Transduction |
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, opacity, and luster, but may have properties that differ from those of the pure metals, such as increased strength or hardness. In some cases, an alloy may reduce the overall cost of the material while preserving important properties. In other cases, the mixture imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength.
In an alloy, the atoms are joined by metallic bonding rather than by covalent bonds typically found in chemical compounds. The alloy constituents are usually measured by mass percentage for practical applications, and in atomic fraction for basic science studies. Alloys are usually classified as substitutional or interstitial alloys, depending on the atomic arrangement that forms the alloy. They can be further classified as homogeneous (consisting of a single phase), or heterogeneous (consisting of two or more phases) or intermetallic. An alloy may be a solid solution of metal elements (a single phase, where all metallic grains (crystals) are of the same composition) or a mixture of metallic phases (two or more solutions, forming a microstructure of different crystals within the metal).
Examples of alloys include red gold (gold and copper), white gold (gold and silver), sterling silver (silver and copper), steel or silicon steel (iron with non-metallic carbon or silicon respectively), solder, brass, pewter, duralumin, bronze, and amalgams.
Alloys are used in a wide variety of applications, from the steel alloys, used in everything from buildings to automobiles to surgical tools, to exotic titanium alloys used in the aerospace industry, to beryllium-copper alloys for non-sparking tools. | 0 | Metallurgy |
The InsP3 receptor was first purified from rat cerebellum by neuroscientists Surachai Supattapone and Solomon Snyder at Johns Hopkins University School of Medicine.
The cDNA of the InsP3 receptor was first cloned in the laboratory of Katsuhiko Mikoshiba. The initial sequencing was reported as an unknown protein enriched in the cerebellum called P400. The large size of this open reading frame indicated a molecular weight similar to the protein purified biochemically, and soon thereafter it was confirmed that the protein p400 was in fact the inositol trisphosphate receptor. | 1 | Gene expression + Signal Transduction |
In nuclear polyadenylation, a poly(A) tail is added to an RNA at the end of transcription. On mRNAs, the poly(A) tail protects the mRNA molecule from enzymatic degradation in the cytoplasm and aids in transcription termination, export of the mRNA from the nucleus, and translation. Almost all eukaryotic mRNAs are polyadenylated, with the exception of animal replication-dependent histone mRNAs. These are the only mRNAs in eukaryotes that lack a poly(A) tail, ending instead in a stem-loop structure followed by a purine-rich sequence, termed histone downstream element, that directs where the RNA is cut so that the 3′ end of the histone mRNA is formed.
Many eukaryotic non-coding RNAs are always polyadenylated at the end of transcription. There are small RNAs where the poly(A) tail is seen only in intermediary forms and not in the mature RNA as the ends are removed during processing, the notable ones being microRNAs. But, for many long noncoding RNAs – a seemingly large group of regulatory RNAs that, for example, includes the RNA Xist, which mediates X chromosome inactivation – a poly(A) tail is part of the mature RNA. | 1 | Gene expression + Signal Transduction |
Warm spraying is a novel modification of high velocity oxy-fuel spraying, in which the temperature of combustion gas is lowered by mixing nitrogen with the combustion gas, thus bringing the process closer to the cold spraying. The resulting gas contains much water vapor, unreacted hydrocarbons and oxygen, and thus is dirtier than the cold spraying. However, the coating efficiency is higher. On the other hand, lower temperatures of warm spraying reduce melting and chemical reactions of the feed powder, as compared to HVOF. These advantages are especially important for such coating materials as Ti, plastics, and metallic glasses, which rapidly oxidize or deteriorate at high temperatures. | 0 | Metallurgy |
Poly(ADP-ribose)polymerases (PARPs) can function in DNA repair of single strand breaks as well as double strand breaks. In single-strand break repair (base excision repair) the PARP can either facilitate removal of an oxidized sugar or strand cleavage. PARP1 binds the single-strand breaks and pulls any nearby base excision repair intermediates close. These intermediates include XRCC1 and APLF and they can be recruited directly or through the PBZ domain of the APLF. This leads to the synthesis of poly(ADP-ribose). The PBZ domain is present in many proteins involved in DNA repair and allows for the binding of the PARP and thus ADP-ribosylation which recruits repair factors to interact at the break site. PARP2 is a secondary responder to DNA damage but serves to provide functional redundancy in DNA repair.
There are many mechanisms for the repair of damaged double stranded DNA. PARP1 may function as a synapsis factor in alternative non-homologous end joining. Additionally, it has been proposed that PARP1 is required to slow replication forks following DNA damage and promotes homologous recombination at replication forks that may be dysfunctional. It is possible that PARP1 and PARP3 work together in repair of double-stranded DNA and it has been shown that PARP3 is critical for double-stranded break resolution. There are two hypotheses by which PARP1 and PARP3 coincide. The first hypothesis states that the two (ADP-ribosyl)transferases serve to function for each other's inactivity. If PARP3 is lost, this results in single-strand breaks, and thus the recruitment of PARP1. A second hypothesis suggests that the two enzyme work together; PARP3 catalyzes mono(ADP-ribosyl)ation and short poly(ADP-ribosyl)ation and serves to activate PARP1.
The PARPs have many protein targets at the site of DNA damage. KU protein and DNA-PKcs are both double-stranded break repair components with unknown sites of ADP-ribosylation. Histones are another protein target of the PARPs. All core histones and linker histone H1 are ADP-ribosylated following DNA damage. The function of these modifications is still unknown, but it has been proposed that ADP-ribosylation modulates higher-order chromatin structure in efforts to facilitate more accessible sites for repair factors to migrate to the DNA damage. | 1 | Gene expression + Signal Transduction |
The story is often told of Napoleons men freezing in the bitter Russian Winter, their clothes falling apart as tin pest ate the buttons. This appears to be an urban legend, as there is no evidence of any failing buttons, and thus they cannot have been a contributing factor in the failure of the invasion. Uniform buttons of that era were generally bone for enlisted, and brass for officers. Critics of the theory point out that any tin that might have been used would have been quite impure, and thus more tolerant of low temperatures. Laboratory tests of the time required for unalloyed tin to develop significant tin pest damage at lowered temperatures is about 18 months, which is more than twice the length of the invasion. Nevertheless, some of the regiments in the campaign did have tin buttons and the temperature reached sufficiently low values (below −40 °C or °F). In the event, none of the many survivors tales mention problems with buttons and it has been suggested that the legend is an amalgamation of reports of blocks of Banca tin completely disintegrated in a customs warehouse in St. Petersburg in 1868, and earlier Russian reports that cast-in buttons for military uniforms also disintegrated, and the desperate state of Napoleon's army, having turned soldiers into ragged beggars. | 0 | Metallurgy |
In this situation RNA polymerase is dependent on (lagging) ribosome activity; if the ribosome pauses due to insufficient charged tRNA then the anti-terminator structure is favoured. The canonical attenuator example of the trp operon uses this mechanism in E. coli. Similar regulatory mechanisms have been found in many amino acid biosynthetic operons. | 1 | Gene expression + Signal Transduction |
The physical processes that fall under the designations of recovery, recrystallization and grain growth are often difficult to distinguish in a precise manner. Doherty et al. (1998) stated:
Thus the process can be differentiated from recrystallization and grain growth as both feature extensive movement of high-angle grain boundaries.
If recovery occurs during deformation (a situation that is common in high-temperature processing) then it is referred to as dynamic while recovery that occurs after processing is termed static. The principal difference is that during dynamic recovery, stored energy continues to be introduced even as it is decreased by the recovery process - resulting in a form of dynamic equilibrium. | 0 | Metallurgy |
As the name suggests, hepatocyte nuclear factors are expressed predominantly in the liver. However HNFs are also expressed and play important roles in a number of other tissues so that the name hepatocyte nuclear factor is somewhat misleading. Nevertheless, the liver is the only tissue in which a significant number of different HNFs are expressed at the same time. In addition, there are a number of genes which contain multiple promoter and enhancer regions each regulated by a different HNF. Furthermore, efficient expression of these genes require synergistic activation by multiple HNFs. Hence hepatocyte nuclear factors function to ensure liver specific expression of certain genes.
As is the case with many transcription factors, HNFs regulate the expression of a wide variety of target genes and therefore functions. These functions (and especially functions involving the liver) include development and metabolic homeostasis of the organism. For example, HNFs influence expression of the insulin gene as well as genes involved in glucose transport and metabolism. In embryo development, HNF4α is thought to have an important role in the development of the liver, kidney, and intestines. | 1 | Gene expression + Signal Transduction |
Precious metals are rare, naturally occurring metallic chemical elements of high economic value. Chemically, the precious metals tend to be less reactive than most elements. They include gold and silver, but also the so-called platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum (see precious metals). Extraction of these metals from their corresponding hosting minerals would typically require pyrometallurgy (e.g., roasting), hydrometallurgy (cyanidation), or both as processing routes.
Early studies have demonstrated that gold dissolution rate in Ethaline compares very favourably to the cyanidation method, which is further enhanced by the addition of iodine as an oxidising agent. In an industrial process the iodine has the potential to be employed as an electrocatalyst, whereby it is continuously recovered in situ from the reduced iodide by electrochemical oxidation at the anode of an electrochemical cell. Dissolved metals can be selectively deposited at the cathode by adjusting the electrode potential. The method also allows better selectivity as part of the gangue (e.g., pyrite) tend to be dissolved more slowly.
Sperrylite (PtAs) and moncheite (PtTe), which are typically the more abundant platinum minerals in many orthomagmatic deposits, do not react under the same conditions in Ethaline because they are disulphide (pyrite), diarsenide (sperrylite) or ditellurides (calaverite and moncheite) minerals, which are particularly resistant to iodine oxidation. The reaction mechanism by which dissolution of platinum minerals is taking place is still under investigation. | 0 | Metallurgy |
Enhancer RNAs (eRNAs) represent a class of relatively long non-coding RNA molecules (50-2000 nucleotides) transcribed from the DNA sequence of enhancer regions. They were first detected in 2010 through the use of genome-wide techniques such as RNA-seq and ChIP-seq. eRNAs can be subdivided into two main classes: 1D eRNAs and 2D eRNAs, which differ primarily in terms of their size, polyadenylation state, and transcriptional directionality. The expression of a given eRNA correlates with the activity of its corresponding enhancer in target genes. Increasing evidence suggests that eRNAs actively play a role in transcriptional regulation in cis and in trans, and while their mechanisms of action remain unclear, a few models have been proposed. | 1 | Gene expression + Signal Transduction |
Reverberatory furnaces are widely used to melt secondary aluminium scrap for eventual use by die-casting industries.
The simplest reverberatory furnace is nothing more than a steel box lined with alumina refractory brick with a flue at one end and a vertically lifting door at the other. Conventional oil or gas burners are placed usually on either side of the furnace to heat the brick and the eventual bath of molten metal is then poured into a casting machine to produce ingots. | 0 | Metallurgy |
Caustic ingestion occurs when someone accidentally or deliberately ingests a caustic or corrosive substance. Depending on the nature of the substance, the duration of exposure and other factors it can lead to varying degrees of damage to the oral mucosa, the esophagus, and the lining of the stomach.
The severity of the injury can be determined by endoscopy of the upper digestive tract, although CT scanning may be more useful to determine whether surgery may be required.
During the healing process, strictures of the oesophagus may form, which may require therapeutic dilatation and insertion of a stent. | 0 | Metallurgy |
Silicon carbide is a semiconductor, which can be doped n-type by nitrogen or phosphorus and p-type by beryllium, boron, aluminium, or gallium. Metallic conductivity has been achieved by heavy doping with boron, aluminium or nitrogen.
Superconductivity has been detected in 3C-SiC:Al, 3C-SiC:B and 6H-SiC:B at similar temperatures ~1.5 K. A crucial difference is however observed for the magnetic field behavior between aluminium and boron doping: 3C-SiC:Al is type-II. In contrast, 3C-SiC:B is type-I, as is 6H-SiC:B. Thus the superconducting properties seem to depend more on dopant (B vs. Al) than on polytype (3C- vs 6H-). In an attempt to explain this dependence, it was noted that B substitutes at C sites in SiC, but Al substitutes at Si sites. Therefore, Al and B "see" different environments, in both polytypes. | 0 | Metallurgy |
Increase in the number of dislocations is a quantification of work hardening. Plastic deformation occurs as a consequence of work being done on a material; energy is added to the material. In addition, the energy is almost always applied fast enough and in large enough magnitude to not only move existing dislocations, but also to produce a great number of new dislocations by jarring or working the material sufficiently enough. New dislocations are generated in proximity to a Frank–Read source.
Yield strength is increased in a cold-worked material. Using lattice strain fields, it can be shown that an environment filled with dislocations will hinder the movement of any one dislocation. Because dislocation motion is hindered, plastic deformation cannot occur at normal stresses. Upon application of stresses just beyond the yield strength of the non-cold-worked material, a cold-worked material will continue to deform using the only mechanism available: elastic deformation, the regular scheme of stretching or compressing of electrical bonds (without dislocation motion) continues to occur, and the modulus of elasticity is unchanged. Eventually the stress is great enough to overcome the strain-field interactions and plastic deformation resumes.
However, ductility of a work-hardened material is decreased. Ductility is the extent to which a material can undergo plastic deformation, that is, it is how far a material can be plastically deformed before fracture. A cold-worked material is, in effect, a normal (brittle) material that has already been extended through part of its allowed plastic deformation. If dislocation motion and plastic deformation have been hindered enough by dislocation accumulation, and stretching of electronic bonds and elastic deformation have reached their limit, a third mode of deformation occurs: fracture. | 0 | Metallurgy |
Fretting damage in steel can be identified by the presence of a pitted surface and fine red iron oxide dust resembling cocoa powder. Strictly this debris is not rust as its production requires no water. The particles are much harder than the steel surfaces in contact, so abrasive wear is inevitable; however, particulates are not required to initiate fret. | 0 | Metallurgy |
Usually, but not universally, the numbers indicate:
* the first digit corresponds to the furnace number
* the second digit indicates the year in which the material was melted
* the last three (and sometimes four) indicate the melt number. | 0 | Metallurgy |
A general second messenger system mechanism can be broken down into four steps. First, the agonist activates a membrane-bound receptor. Second, the activated G-protein produces a primary effector. Third, the primary effect stimulates the second messenger synthesis. Fourth, the second messenger activates a certain cellular process.
The G-protein coupled receptors for the PIP messenger system produces two effectors, phospholipase C (PLC) and phosphoinositide 3-kinase (PI3K). PLC as an effector produces two different second messengers, inositol triphosphate (IP) and Diacylglycerol (DAG).
IP is soluble and diffuses freely into the cytoplasm. As a second messenger, it is recognized by the inositol triphosphate receptor (IP3R), a Ca channel in the endoplasmic reticulum (ER) membrane, which stores intracellular Ca. The binding of IP to IP3R releases Ca from the ER into the normally Ca-poor cytoplasm, which then triggers various events of Ca signaling. Specifically in blood vessels, the increase in Ca concentration from IP releases nitric oxide, which then diffuses into the smooth muscle tissue and causes relaxation.
DAG remains bound to the membrane by its fatty acid "tails" where it recruits and activates both conventional and novel members of the protein kinase C family. Thus, both IP and DAG contribute to activation of PKCs.
Phosphoinositide 3-kinase (PI3K) as an effector phosphorylates phosphatidylinositol bisphosphate (PIP) to produce phosphatidylinositol (3,4,5)-trisphosphate (PIP). PIP has been shown to activate protein kinase B, increase binding to extracellular proteins and ultimately enhance cell survival. | 1 | Gene expression + Signal Transduction |
There are two types of VMATs expressed in humans: VMAT1 and VMAT2. VMAT1 is expressed mainly in large dense-core vesicles (LDCVs) of the peripheral nervous system. VMAT1 may be found in neuroendocrine cells, particularly chromaffin and enterochromaffin granules, which are primarily found in the medulla of the adrenal glands.
VMAT2 favors expression in a variety of monoaminergic cells of the central nervous system, such as the brain, sympathetic nervous system, mast cells, It is prevalent in β-cells, expressed in blood platelets, and co-expressed in chromaffin cells. Expression of the two transporters in internal organs seems to differ between species: only VMAT1 is expressed in rat adrenal medulla cells, whereas VMAT2 is the major transporter in bovine adrenal medulla cells. | 1 | Gene expression + Signal Transduction |
Biocorrosion, biofouling and corrosion caused by living organisms are now known to have an electrochemistry foundation. Other marine creatures such as mussels, worms and even sponges have been known to degrade engineering materials. | 0 | Metallurgy |
There are two aspects to surface integrity: topography characteristics and surface layer characteristics. The topography is made up of surface roughness, waviness, errors of form, and flaws. The surface layer characteristics that can change through processing are: plastic deformation, residual stresses, cracks, hardness, overaging, phase changes, recrystallization, intergranular attack, and hydrogen embrittlement. When a traditional manufacturing process is used, such as machining, the surface layer sustains local plastic deformation.
The processes that affect surface integrity can be conveniently broken up into three classes: traditional processes, non-traditional processes, and finishing treatments. Traditional processes are defined as processes where the tool contacts the workpiece surface; for example: grinding, turning, and machining. These processes will only damage the surface integrity if the improper parameters are used, such as dull tools, too high feed speeds, improper coolant or lubrication, or incorrect grinding wheel hardness. Nontraditional processes are defined as processes where the tool does not contact the workpiece; examples of this type of process include EDM, electrochemical machining, and chemical milling. These processes will produce different surface integrity depending on how the processes are controlled; for instance, they can leave a stress-free surface, a remelted surface, or excessive surface roughness. Finishing treatments are defined as processes that negate surface finishes imparted by traditional and non-traditional processes or improve the surface integrity. For example, compressive residual stress can be enhanced via peening or roller burnishing or the recast layer left by EDMing can be removed via chemical milling.
Finishing treatments can affect the workpiece surface in a wide variety of manners. Some clean and/or remove defects, such as scratches, pores, burrs, flash, or blemishes. Other processes improve or modify the surface appearance by improving smoothness, texture, or color. They can also improve corrosion resistance, wear resistance, and/or reduce friction. Coatings are another type of finishing treatment that may be used to plate an expensive or scarce material onto a less expensive base material. | 0 | Metallurgy |
Modern research topics in solid-state physics include:
*High-temperature superconductivity
*Quasicrystals
*Spin glass
*Strongly correlated materials
*Two-dimensional materials
*Nanomaterials | 0 | Metallurgy |
In molecular genetics, the three prime untranslated region (3′-UTR) is the section of messenger RNA (mRNA) that immediately follows the translation termination codon. The 3′-UTR often contains regulatory regions that post-transcriptionally influence gene expression.
During gene expression, an mRNA molecule is transcribed from the DNA sequence and is later translated into a protein. Several regions of the mRNA molecule are not translated into a protein including the 5 cap, 5 untranslated region, 3′ untranslated region and poly(A) tail. Regulatory regions within the 3′-untranslated region can influence polyadenylation, translation efficiency, localization, and stability of the mRNA. The 3′-UTR contains binding sites for both regulatory proteins and microRNAs (miRNAs). By binding to specific sites within the 3′-UTR, miRNAs can decrease gene expression of various mRNAs by either inhibiting translation or directly causing degradation of the transcript. The 3′-UTR also has silencer regions which bind to repressor proteins and will inhibit the expression of the mRNA.
Many 3′-UTRs also contain AU-rich elements (AREs). Proteins bind AREs to affect the stability or decay rate of transcripts in a localized manner or affect translation initiation. Furthermore, the 3′-UTR contains the sequence AAUAAA that directs addition of several hundred adenine residues called the poly(A) tail to the end of the mRNA transcript. Poly(A) binding protein (PABP) binds to this tail, contributing to regulation of mRNA translation, stability, and export. For example, poly(A) tail bound PABP interacts with proteins associated with the 5' end of the transcript, causing a circularization of the mRNA that promotes translation.
The 3′-UTR can also contain sequences that attract proteins to associate the mRNA with the cytoskeleton, transport it to or from the cell nucleus, or perform other types of localization. In addition to sequences within the 3′-UTR, the physical characteristics of the region, including its length and secondary structure, contribute to translation regulation. These diverse mechanisms of gene regulation ensure that the correct genes are expressed in the correct cells at the appropriate times. | 1 | Gene expression + Signal Transduction |
The ISASMELT process is an energy-efficient smelting process that was jointly developed from the 1970s to the 1990s by Mount Isa Mines (a subsidiary of MIM Holdings and now part of Glencore) and the Government of Australia's CSIRO. It has relatively low capital and operating costs for a smelting process.
ISASMELT technology has been applied to lead, copper, and nickel smelting. As of 2021, 22 plants were in operation in eleven countries, along with three demonstration plants located at Mt Isa. The installed capacity of copper/nickel operating plants in 2020 was 9.76 million tonnes per year of feed materials and 750 thousand tonnes per year across lead operating plants.
Smelters based on the copper ISASMELT process are among the lowest-cost copper smelters in the world. | 0 | Metallurgy |
The 3 poly(A) tail is a long sequence of adenine nucleotides (often several hundred) added to the 3 end of the pre-mRNA. This tail promotes export from the nucleus and translation, and protects the mRNA from degradation. | 1 | Gene expression + Signal Transduction |
Retinol (vitamin A) can be metabolized to retinoic acid which activates nuclear receptors such as the RAR to control differentiation and proliferation of many types of cells during development. | 1 | Gene expression + Signal Transduction |
The natural resistance to oxidation exhibited by silicon carbide, as well as the discovery of new ways to synthesize the cubic β-SiC form, with its larger surface area, has led to significant interest in its use as a heterogeneous catalyst support. This form has already been employed as a catalyst support for the oxidation of hydrocarbons, such as n-butane, to maleic anhydride. | 0 | Metallurgy |
Subsets and Splits