text
stringlengths 105
13.7k
| label
int64 0
1
| label_text
stringclasses 2
values |
|---|---|---|
Development of theoretical models describing grain growth is an active field of research. Many models have been proposed for grain growth, but no theory has yet been put forth that has been independently validated to apply across the full range of conditions and many questions remain open. By no means is the following a comprehensive review. One recent theory of grain growth posits that normal grain growth only occurs in the polycrystalline systems with grain boundaries which have undergone roughening transitions, and abnormal and/or stagnant grain growth can only occur in the polycrystalline systems with non-zero GB (grain boundary) step free energy of grains. Other models explaining grain coarsening assert that disconnections are responsible for the motion of grain boundaries, and provide limited experimental evidence suggesting that they govern grain boundary migration and grain growth behavior. Other models have indicated that triple junctions play an important role in determining the grain growth behavior in many systems. | 0 | Metallurgy |
Transcriptomics is the quantitative science that encompasses the assignment of a list of strings ("reads") to the object ("transcripts" in the genome). To calculate the expression strength, the density of reads corresponding to each object is counted. Initially, transcriptomes were analyzed and studied using expressed sequence tags libraries and serial and cap analysis of gene expression (SAGE).
Currently, the two main transcriptomics techniques include DNA microarrays and RNA-Seq. Both techniques require RNA isolation through RNA extraction techniques, followed by its separation from other cellular components and enrichment of mRNA.
There are two general methods of inferring transcriptome sequences. One approach maps sequence reads onto a reference genome, either of the organism itself (whose transcriptome is being studied) or of a closely related species. The other approach, de novo transcriptome assembly, uses software to infer transcripts directly from short sequence reads and is used in organisms with genomes that are not sequenced. | 1 | Gene expression + Signal Transduction |
Bacterial transcription is the process in which a segment of bacterial DNA is copied into a newly synthesized strand of messenger RNA (mRNA) with use of the enzyme RNA polymerase.
The process occurs in three main steps: initiation, elongation, and termination; and the end result is a strand of mRNA that is complementary to a single strand of DNA. Generally, the transcribed region accounts for more than one gene. In fact, many prokaryotic genes occur in operons, which are a series of genes that work together to code for the same protein or gene product and are controlled by a single promoter. Bacterial RNA polymerase is made up of four subunits and when a fifth subunit attaches, called the sigma factor (σ-factor), the polymerase can recognize specific binding sequences in the DNA, called promoters. The binding of the σ-factor to the promoter is the first step in initiation. Once the σ-factor releases from the polymerase, elongation proceeds. The polymerase continues down the double stranded DNA, unwinding it and synthesizing the new mRNA strand until it reaches a termination site. There are two termination mechanisms that are discussed in further detail below. Termination is required at specific sites for proper gene expression to occur. Gene expression determines how much gene product, such as protein, is made by the gene. Transcription is carried out by RNA polymerase but its specificity is controlled by sequence-specific DNA binding proteins called transcription factors. Transcription factors work to recognize specific DNA sequences and based on the cells needs, promote or inhibit additional transcription. Similar to other taxa, bacteria experience bursts of transcription. The work of the Jones team in Jones et al 2014 explains some of the underlying causes of bursts and other variability, including stability of the resulting mRNA, the strength of promotion encoded in the relevant promoter and the duration of transcription due to strength of the TF binding site. They also found that bacterial TFs linger too briefly for TFs binding characteristics to explain the sustained transcription of bursts.
Bacterial transcription differs from eukaryotic transcription in several ways. In bacteria, transcription and translation can occur simultaneously in the cytoplasm of the cell, whereas in eukaryotes transcription occurs in the nucleus and translation occurs in the cytoplasm. There is only one type of bacterial RNA polymerase whereas eukaryotes have 3 types. Bacteria have a σ-factor that detects and binds to promoter sites but eukaryotes do not need a σ-factor. Instead, eukaryotes have transcription factors that allow the recognition and binding of promoter sites.
Overall, transcription within bacteria is a highly regulated process that is controlled by the integration of many signals at a given time. Bacteria heavily rely on transcription and translation to generate proteins that help them respond specifically to their environment. | 1 | Gene expression + Signal Transduction |
The effluent from the tailings from the mining of sulfidic minerals has been described as "the largest environmental liability of the mining industry". These tailings contain large amounts of pyrite (FeS) and Iron(II) sulfide (FeS), which are rejected from the sought-after ores of copper and nickel, as well as coal. Although harmless underground, these minerals are reactive toward air in the presence of microorganisms, which if not properly managed lead to acid mine drainage. | 0 | Metallurgy |
CMTM7 protein levels are low in the malignant tissues of various cancers such as those of esophagus, stomach, pancreas, liver, lung, cervix, and breast. as compared with its expression in the normal tissues of these organs. Furthermore, the forced overexpression of CMTM7 protein in various cancer immortalized cell lines inhibit their proliferation and motility in culture as well as their ability to form tumors in a nude mouse experimental model of cancer. These findings suggest that the CMTM7 protein acts to inhibit the development and/or progression of these cancers and therefore that the CMTM7 gene acts as tumor suppressor in these cancers. However, further studies are needed to support these suggestion and determine if expression of the CMTM7 can be used as a clinical marker of these cancers severity/prognosis and/or as therapeutic targets for treating them. | 1 | Gene expression + Signal Transduction |
Evolutionary simulations are performed by reproduction-mutation-selection life cycle. Populations are fixed at size and they will not go extinct. Non-overlapping generations are employed. In a typical evolutionary simulation, a single random viable individual that can produce a stable gene expression pattern is chosen as the founder. Cloned individuals are generated to create a population of identical individuals. According to the asexual or sexual reproductive mode, offspring are produced by randomly choosing (with replacement) parent individual(s) from current generation. Mutations can be acquired with probability μ and survive with probability equal to their fitness. This process is repeated until N individuals are produced that go on to found the following generation. | 1 | Gene expression + Signal Transduction |
In 1526 Kamiya Jutei, a wealthy merchant from Hakata, founded the Iwami Ginzan Silver Mine in Ōda. Seeking to increase silver production, In 1533 he introduced a Korean method of silver refining to the mine which became the Hai-Fuki-Ho method. The two technicians, Keiju (慶寿; Korean: 경수; Revised Romanization: Gyeongsu) and Sotan (宗丹; Korean: 종단; Revised Romanization: Jongdan), were invited to Japan to instruct their skills. Historians have compared the Hai-Fuki-Ho method to the Medieval European method of silver smelting.
Under the Hai-Fuki-Ho method, silver-containing copper ore would be cast-smelted with lead, then allowed to dry. The silver in the copper ore would bind to the lead, creating a single mixture. This mixture would then be heated so that the lead melted and separated out of the copper, taking the bonded silver with it. The silver-rich lead would then be treated with an oxidizing airflow to separate the silver. This was akin to a liquation method.
The high-purity silver produced by the Hai-Fuki-Ho method was highly desired by foreign merchants. In addition, the process allowed for greater amounts of the silver to be produced by Japanese mines, which had more efficient refining processes than their competitors. By the 16th century, Japanese mines were producing up to one third of the world's silver.
The Hai-Fuki-Ho method was eventually replaced by more modern methods of silver mining. | 0 | Metallurgy |
Initial treatment can involve placing the object in a desiccating environment. Deprived of water, the reaction cannot continue. However, re-exposure of the object to even atmospheric water can restart the process. Bronze disease remains an active area of research within object conservation. | 0 | Metallurgy |
Non-specific binding of the repressor to DNA plays a crucial role in the repression and induction of the Lac-operon. The specific binding site for the Lac-repressor protein is the operator. The non-specific interaction is mediated mainly by charge-charge interactions while binding to the operator is reinforced by hydrophobic interactions. Additionally, there is an abundance of non-specific DNA sequences to which the repressor can bind. Essentially, any sequence that is not the operator, is considered non-specific. Studies have shown, that without the presence of non-specific binding, induction (or unrepression) of the Lac-operon could not occur even with saturated levels of inducer. It had been demonstrated that, without non-specific binding, the basal level of induction is ten thousand times smaller than observed normally. This is because the non-specific DNA acts as sort of a "sink" for the repressor proteins, distracting them from the operator. The non-specific sequences decrease the amount of available repressor in the cell. This in turn reduces the amount of inducer required to unrepress the system. | 1 | Gene expression + Signal Transduction |
* Ebrey, Walthall, Palais (2006). East Asia: A Cultural, Social, and Political History. Boston: Houghton Mifflin Company.
* Needham, Joseph (1986). Science and Civilization in China: Volume 4, Part 2; Needham, Joseph (1986). Science and Civilization in China: Volume 4, Part 3. | 0 | Metallurgy |
Gamma TiAl has excellent mechanical properties and oxidation and corrosion resistance at elevated temperatures (over 600°C), which makes it a possible replacement for traditional Ni based superalloy components in aircraft turbine engines.
TiAl-based alloys have potential to increase the thrust-to-weight ratio in aircraft engines. This is especially the case with the engine's low-pressure turbine blades and the high-pressure compressor blades. These are traditionally made of Ni-based superalloy, which is nearly twice as dense as TiAl-based alloys. Some gamma titanium aluminide alloys retain strength and oxidation resistance to 1000 °C, which is 400 °C higher than the operating temperature limit of conventional titanium alloys.
General Electric uses gamma TiAl for the low-pressure turbine blades on its GEnx engine, which powers the Boeing 787 and Boeing 747-8 aircraft. This was the first large-scale use of this material on a commercial jet engine when it entered service in 2011. The TiAl LPT blades are cast by Precision Castparts Corp. and Avio s.p.a. Machining of the Stage 6, and Stage 7 LPT blades is performed by Moeller Manufacturing. An alternate pathway for production of the gamma TiAl blades for the GEnx and GE9x engines using additive manufacturing is being explored.
In 2019 a new 55g lightweight version of the Omega Seamaster wristwatch was made, using gamma titanium aluminide for the case, backcase and crown, and a titanium dial and mechanism in Ti 6/4 (grade 5). The retail price of this watch at £37,240 was nine times that of the basic Seamaster and comparable to the top of the range platinum-cased version with a moonphase complication. | 0 | Metallurgy |
isomiRs (from iso- + miR) are miRNA sequences that have variations with respect to the reference sequence. The term was coined by Morin et al in 2008. It has been found that isomiR expression profiles can also exhibit race, population, and gender dependencies.
There are four main variation types:
*5 trimming—the 5 dicing site is upstream or downstream from the reference miRNA sequence
*3 trimming—the 3 dicing site is upstream or downstream from the reference miRNA sequence
*3 nucleotide addition—nucleotides added to the 3 end of the reference miRNA
*nucleotide substitution—nucleotides changes from the miRNA precursor. It is thought that may be similar process than post-transcriptional modifications. | 1 | Gene expression + Signal Transduction |
There are four commonly used types of applications for nitinol:
; Free recovery
: Nitinol is deformed at a low temperature, remains deformed, and then is heated to recover its original shape through the shape memory effect.
; Constrained recovery
: Similar to free recovery, except that recovery is rigidly prevented and thus a stress is generated.
; Work production
: The alloy is allowed to recover, but to do so it must act against a force (thus doing work).
; Superelasticity
: Nitinol acts as a super spring through the superelastic effect.
Superelastic materials undergo stress-induced transformation and are commonly recognized for their "shape-memory" property. Due to its superelasticity, NiTi wires exhibit "elastocaloric" effect, which is stress-triggered heating/cooling. NiTi wires are currently under research as the most promising material for the technology. The process begins with tensile loading on the wire, which causes fluid (within the wire) to flow to HHEX (hot heat exchanger). Simultaneously, heat will be expelled, which can be used to heat the surrounding. In the reverse process, tensile unloading of the wire leads to fluid flowing to CHEX (cold heat exchanger), causing the NiTi wire to absorb heat from the surrounding. Therefore, the temperature of the surrounding can be decreased (cooled).
Elastocaloric devices are often compared with magnetocaloric devices as new methods of efficient heating/cooling. Elastocaloric device made with NiTi wires has an advantage over magnetocaloric device made with gadolinium due to its specific cooling power (at 2 Hz), which is 70X better (7 kWh/kg vs. 0.1 kWh/kg). However, elastocaloric device made with NiTi wires also have limitations, such as its short fatigue life and dependency on large tensile forces (energy consuming).
In 1989 a survey was conducted in the United States and Canada that involved seven organizations. The survey focused on predicting the future technology, market, and applications of SMAs. The companies predicted the following uses of nitinol in a decreasing order of importance: (1) Couplings, (2) Biomedical and medical, (3) Toys, demonstration, novelty items, (4) Actuators, (5) Heat Engines, (6) Sensors, (7) Cryogenically activated die and bubble memory sockets, and finally (8) lifting devices. | 0 | Metallurgy |
In metallurgy, hot working refers to processes where metals are plastically deformed above their recrystallization temperature. Being above the recrystallization temperature allows the material to recrystallize during deformation. This is important because recrystallization keeps the materials from strain hardening, which ultimately keeps the yield strength and hardness low and ductility high. This contrasts with cold working.
Many kinds of working, including rolling, forging, extrusion, and drawing, can be done with hot metal. | 0 | Metallurgy |
Mitogen-activated protein kinase 3 (MAPK3) is also known as extracellular signal-regulated kinase 1 (ERK1). Transgenic gene knockout mice lacking MAPK3 are viable and it is thought that MAPK1 can fulfill some MAPK3 functions in most cells. The main exception is in T cells. Mice lacking MAPK3 have reduced T cell development past the CD4+ and CD8+ stage. | 1 | Gene expression + Signal Transduction |
Oxide dispersion strengthened alloys (ODS) are alloys that consist of a metal matrix with small oxide particles dispersed within it. They have high heat resistance, strength, and ductility. Alloys of nickel are the most common but includes iron aluminum alloys.
Applications include high temperature turbine blades and heat exchanger tubing, while steels are used in nuclear applications. ODS materials are used on spacecraft to protect the vehicle, especially during re-entry. Noble metal ODS alloys, for example, platinum-based alloys, are used in glass production.
When it comes to re-entry at hypersonic speeds, the properties of gases change dramatically. Shock waves that can cause serious damage on any structure are created. At these speeds and temperatures, oxygen becomes aggressive. | 0 | Metallurgy |
The Falcon semi batch centrifugal concentrator is primarily used for the recovery of free (liberated) precious metals such as gold, silver and platinum. The machine generates forces up to 200 times the force of gravity (200 Gs) and makes use of a two-stage rotating bowl for mineral separation. The smooth-walled lower portion is for particle stratification and then a fluidized upper portion is used for the collection of the heavier particles. The machine is stopped periodically to rinse and collect the valuable concentrate from the bowl. The Falcon SB concentrator is used for gold recovery at many mines around the world, including Quadra FNX Minings Robinson mine in the United States, Newcrest's Telfer Gold Mine in Australia and the Sadiola Gold Mine (owned principally by AngloGold Ashanti and Iamgold) in Mali. | 0 | Metallurgy |
TADs are defined as regions whose DNA sequences preferentially contact each other. They were discovered in 2012 using chromosome conformation capture techniques including Hi-C. They have been shown to be present in multiple species, including fruit flies (Drosophila), mouse, plants, fungi and human genomes. In bacteria, they are referred to as Chromosomal Interacting Domains (CIDs). | 1 | Gene expression + Signal Transduction |
Huntington's disease (HD) results from a mutation in the huntingtin gene that causes an excess of CAG repeats. The gene then forms a mutated huntingtin protein with polyglutamine repeats near the amino terminus. This disease is incurable and known to cause motor, cognitive, and behavioral deficits. Researchers have been looking to gene silencing as a potential therapeutic for HD.
Gene silencing can be used to treat HD by targeting the mutant huntingtin protein. The mutant huntingtin protein has been targeted through gene silencing that is allele specific using allele specific oligonucleotides. In this method, the antisense oligonucleotides are used to target single nucleotide polymorphism (SNPs), which are single nucleotide changes in the DNA sequence, since HD patients have been found to share common SNPs that are associated with the mutated huntingtin allele. It has been found that approximately 85% of patients with HD can be covered when three SNPs are targeted. In addition, when antisense oligonucleotides were used to target an HD-associated SNP in mice, there was a 50% decrease in the mutant huntingtin protein.
Non-allele specific gene silencing using siRNA molecules has also been used to silence the mutant huntingtin proteins. Through this approach, instead of targeting SNPs on the mutated protein, all of the normal and mutated huntingtin proteins are targeted. When studied in mice, it was found that siRNA could reduce the normal and mutant huntingtin levels by 75%. At this level, they found that the mice developed improved motor control and a longer survival rate when compared to the controls. Thus, gene silencing methods may prove to be beneficial in treating HD. | 1 | Gene expression + Signal Transduction |
Flotation is one of the unit processes used to separate the bituminous component of oil sands as part of the process of oil extraction. Some of the bitumen is not recovered in the primary separation vessel and reports to the tailings. These tailings are typically retreated in a scavenging operation to try to recover some of the remaining bitumen.
Three industrial-size single downcomer Jameson Cells were sold by Xstrata Technology to Shell Canada in 2007 for a large scale pilot plant project and eight 500 mm downcomers were sold to Syncrude Limited in 2008. In the latter case, the downcomers were used to treat middlings in an existing tertiary oil recovery vessel in a bitumen recovery process patented by Syncrude. | 0 | Metallurgy |
The class IA phospholipid kinase, PI-3 kinase, is activated by the majority of RTKs. Similarly to other SH2 domain-containing proteins, PI-3 kinase forms a complex with PY sites on activated receptors. The main function of PI3K activation is the generation of PIP3, which functions as a second messenger to activate downstream tyrosine kinases Btk and Itk, the Ser/Thr kinases PDK1 and Akt (PKB). The major biological functions of Akt activation can be classified into three categories – survival, proliferation and cell growth. Akt is also known to be implicated in several cancers, particularly breast. PLCγ is immediately recruited by an activated RTK through the binding of its SH2 domains to phosphotyrosine sites of the receptor. After activation, PLCγ hydrolyses its substrate PtdIns(4,5)P2 and forms two second messengers, diacylglycerol and Ins(1,4,5)P3. Ins(1,4,5)P3 stimulates the release of Ca 2+ from intracellular supplies. Ca 2+ then binds to calmodulin, which subsequently activates a family of calmodulindependent protein kinases (CamKs). In addition, both diacylglycerol and Ca 2+ activate members of the PKC family. The second messengers generated by PtdIns(4,5)P2 hydrolysis stimulate a variety of intracellular processes such as proliferation, angiogenesis, cell motility. | 1 | Gene expression + Signal Transduction |
mTORC1 activation is required for myofibrillar muscle protein synthesis and skeletal muscle hypertrophy in humans in response to both physical exercise and ingestion of certain amino acids or amino acid derivatives. Persistent inactivation of mTORC1 signaling in skeletal muscle facilitates the loss of muscle mass and strength during muscle wasting in old age, cancer cachexia, and muscle atrophy from physical inactivity. mTORC2 activation appears to mediate neurite outgrowth in differentiated mouse neuro2a cells. Intermittent mTOR activation in prefrontal neurons by β-hydroxy β-methylbutyrate inhibits age-related cognitive decline associated with dendritic pruning in animals, which is a phenomenon also observed in humans. | 1 | Gene expression + Signal Transduction |
Because of their importance in cell signaling and regulation, co-receptors have been implicated in a number of diseases and disorders. Co-receptor knockout mice are often unable to develop and such knockouts generally result in embryonic or perinatal lethality. In immunology in particular, the term "co-receptor" often describes a secondary receptor used by a pathogen to gain access to the cell, or a receptor that works alongside T cell receptors such as CD4, CD8, or CD28 to bind antigens or regulate T cell activity in some way. | 1 | Gene expression + Signal Transduction |
Pol I requires no TATA box in the promoter, instead relying on an upstream control element (UCE) located between −200 and −107, and a core element located between −45 and +20.
#The dimeric eukaryotic upstream binding factor (UBF) binds the UCE and the core element.
#UBF recruits and binds a protein complex called SL1 in humans (or TIF-IB in mouse), composed of the TATA-binding protein (TBP) and three TBP-associated factors (TAFs).
#The UBF dimer contains several high-mobility-group boxes (HMG-boxes) that introduce loops into the upstream region, allowing the UCE and the core elements to come into contact.
#RRN3/TIF-IA is phosphorylated and binds Pol I.
#Pol I binds to the UBF/SL1 complex via RRN3/TIF-IA, and transcription starts.
Note that this process is variable in different organisms. | 1 | Gene expression + Signal Transduction |
In metallurgy, the Bower–Barff process is a method of coating iron or steel with magnetic iron oxide, such as FeO, in order to minimize atmospheric corrosion.
The articles to be treated are put into a closed retort and a current of superheated steam passed through for twenty minutes followed by a current of producer gas (carbon monoxide), to reduce any higher oxides that may have been formed. | 0 | Metallurgy |
RdRps are highly conserved throughout viruses and are even related to telomerase, though the reason for this is an ongoing question as of 2009. The similarity has led to speculation that viral RdRps are ancestral to human telomerase.
The most famous example of RdRp is that of the polio virus. The viral genome is composed of RNA, which enters the cell through receptor-mediated endocytosis. From there, the RNA is able to act as a template for complementary RNA synthesis, immediately. The complementary strand is then, itself, able to act as a template for the production of new viral genomes that are further packaged and released from the cell ready to infect more host cells. The advantage of this method of replication is that there is no DNA stage; replication is quick and easy. The disadvantage is that there is no back-up DNA copy.
Many RdRps are associated tightly with membranes and are, therefore, difficult to study. The best-known RdRps are polioviral 3Dpol, vesicular stomatitis virus L, and hepatitis C virus NS5B protein.
Many eukaryotes also have RdRps and these are involved in RNA interference: these amplify microRNAs and small temporal RNAs and produce double-stranded RNA using small interfering RNAs as primers. In fact these same RdRps that are used in the defense mechanisms can be usurped by RNA viruses for their benefit. Their evolutionary history has been reviewed. | 1 | Gene expression + Signal Transduction |
The huge amount of Pre-Hispanic silver adornments known especially from Perú, Bolivia and Ecuador raises the question whether the pre-Hispanic civilizations obtained the raw material from native ores or from argentiferous-lead ores. Although native silver may be available in America, it is as rare as in the Old World. From colonial texts it is known that silver mines were open in colonial times by the Spaniards from Mexico to Argentina, the main ones being those of Tasco, Mexico, and Potosí in Bolivia.
Some kind of blast furnaces called huayrachinas were described in colonial texts, as native technology furnaces used in Perú and Bolivia to smelt the ores that come from the silver mines owned by the Spaniards. Although it is not conclusive, it is believed that these kinds of furnaces were used before the Spanish Conquest. Ethnoarchaeological and archaeological work in Porco Municipality, Potosí, Bolivia, has suggested pre-European use of huayrachinas.
There are no specific archaeological accounts about silver smelting or mining in the Andes prior to the Incas. Silver and lead artefacts have been found in the Peruvian central highlands dated in the pre-Inca and Inca periods. From the presence of lead in silver artefacts, archaeologists suggest that cupellation occurred there. | 0 | Metallurgy |
Smooth muscle cells cultured from the myometrium showed no significant induction of SFRP1 mRNA in response to treatment with E2 and/or progesterone. Conversely, cells cultured from leiomyomas showed significant dose-dependent induction of SFRP1 mRNA in response to treatment with E2; however, progesterone had no effect on SFRP1 even when coapplied with E2. | 1 | Gene expression + Signal Transduction |
The American Federation of Labor (AFL) tried and failed to organize the steelworkers in 1919. Although the strike gained widespread middle-class support because of its demand and the 12-hour day, the strike failed and unionization was postponed until the late 1930s. The mills ended the 12-hour day in the early 1920s.
The second surge of unionization came under the auspices of the militant Congress of Industrial Organizations in the late 1930s, when it set up the Steel Workers Organizing Committee. The SWOC focused almost exclusively on the achievement of a signed contract, with "Little Steel" (the major producers except for US Steel). At the grassroots however, women of the steel auxiliaries, workers on the picket line, and middle-class liberals from across Chicago sought to transform the strike into something larger than a showdown over union recognition. In Chicago, the Little Steel strike raised the possibility that steelworkers might embrace the ‘civic unionism’ that animated the left-led unions of the era. The effort failed, and while the strike was won, the resulting powerful United Steelworkers of America union suppressed grassroots opinions. | 0 | Metallurgy |
The lower limit of the hot working temperature is determined by its recrystallization temperature. As a guideline, the lower limit of the hot working temperature of a material is 60% its melting temperature (on an absolute temperature scale). The upper limit for hot working is determined by various factors, such as: excessive oxidation, grain growth, or an undesirable phase transformation. In practice materials are usually heated to the upper limit first to keep forming forces as low as possible and to maximize the amount of time available to hot work the workpiece.
The most important aspect of any hot working process is controlling the temperature of the workpiece. 90% of the energy imparted into the workpiece is converted into heat. Therefore, if the deformation process is quick enough the temperature of the workpiece should rise, however, this does not usually happen in practice. Most of the heat is lost through the surface of the workpiece into the cooler tooling. This causes temperature gradients in the workpiece, usually due to non-uniform cross-sections where the thinner sections are cooler than the thicker sections. Ultimately, this can lead to cracking in the cooler, less ductile surfaces. One way to minimize the problem is to heat the tooling. The hotter the tooling the less heat lost to it, but as the tooling temperature rises, the tool life decreases. Therefore the tooling temperature must be compromised; commonly, hot working tooling is heated to 500–850 °F (325–450 °C). | 0 | Metallurgy |
In order to be functional, STAT5 proteins must first be activated. This activation is carried out by kinases associated with transmembrane receptors:
* Ligands binding to these transmembrane receptors on the outside of the cell activate the kinases;
* The stimulated kinases add a phosphate group to a specific tyrosine residue on the receptor;
* STAT5 then binds to these phosphorylated-tyrosines using their SH2 domain (STAT domains illustrated below);
* The bound STAT5 is then phosphorylated by the kinase, the phosphorylation occurring at particular tyrosine residues on the C-terminus of the protein;
* Phosphorylation causes STAT5 to dissociate from the receptor;
* The phosphorylated STAT5 finally goes on to form either homodimers, STAT5-STAT5, or heterodimers, STAT5-STATX, with other STAT proteins. The SH2 domains of the STAT5 proteins are once again used for this dimerization. STAT5 can also form homo-tetramers, usually in concert with the histone methyltransferase EZH2, and act as a transcriptional repressor.
In the activation pathway illustrated to the left, the ligand involved is a cytokine and the specific kinase taking part in activation is JAK. The dimerized STAT5 represents the active form of the protein, which is ready for translocation into the nucleus.
Once in the nucleus, the dimers bind to STAT5 response elements, inducing transcription of specific sets of genes. Upregulation of gene expression by STAT5 dimers has been observed for genes dealing with:
* Controlled cell growth and division, or cell proliferation
* Programmed cell death, or apoptosis
* Cell specialization, or differentiation and
* Inflammation.
Activated STAT5 dimers are, however, short-lived and the dimers are made to undergo rapid deactivation. Deactivation may be carried out by a direct pathway, removing the phosphate groups using phosphatases like PIAS or SHP-2 for example, or by an indirect pathway, which involves reducing cytokine signalling. | 1 | Gene expression + Signal Transduction |
The microprocessor complex is a protein complex involved in the early stages of processing microRNA (miRNA) and RNA interference (RNAi) in animal cells. The complex is minimally composed of the ribonuclease enzyme Drosha and the dimeric RNA-binding protein DGCR8 (also known as Pasha in non-human animals), and cleaves primary miRNA substrates to pre-miRNA in the cell nucleus. Microprocessor is also the smaller of the two multi-protein complexes that contain human Drosha. | 1 | Gene expression + Signal Transduction |
A transcription bubble is a molecular structure formed during DNA transcription when a limited portion of the DNA double helix is unwound. The size of a transcription bubble ranges from 12 to 14 base pairs. A transcription bubble is formed when the RNA polymerase enzyme binds to a promoter and causes two DNA strands to detach. It presents a region of unpaired DNA, where a short stretch of nucleotides are exposed on each strand of the double helix. | 1 | Gene expression + Signal Transduction |
More advanced direct reduction processes were developed at the beginning of the 20th century, when it became possible to smelt pre-reduced ores using the Martin-Siemens process or the electric arc furnace. Based on this technical and economic model, a number of processes were industrialized before World War II (the Krupp-Renn process adopted by the Shōwa Steel Works, the Chenot process, etc.). They remained confidential, however, and their profitability was generally debated.
Modern direct reduction processes, based on the use of natural gas instead of coal, were studied intensively in the 1950s. On December 5, 1957, the Mexican company Hylsa started up the first industrial production unit of this type in Monterrey, with the pre-reduced ore obtained destined for smelting in an electric arc furnace. As the production of pre-reduced ore with natural gas was economically viable, several plants were built in the late 1960s. As a cheap supply of natural gas was essential to their profitability, most plants were located in countries with gas deposits, in Latin America (where many were developed) and in the Middle East.
In 1970, worldwide production of pre-reduced iron ore reached 790,000 tonnes. The processes then in operation were the HYL process (680,000 tonnes produced), an SL/RN unit, a Purofer unit, and the first plant to use the Midrex process.
Although profitable and innovative, the processes invented did not ultimately prove to be a technological revolution capable of supplanting the traditional blast furnace-based process. However, the quantity of steel produced from pre-reduced materials grew steadily, outstripping world steel production:
* in 1976, installations in service totalled less than 5 Mt;
* in 1985, annual production was 11 Mt for an installed capacity of around 20 Mt, the difference being explained by fluctuations in energy costs;
* in 1991, production reached 20 Mt.
* in 1995, worldwide production of prereducts passed the 30 Mt mark for the first time.
* In 2010, 70 Mt were produced, 14% from HYL processes and 60% from the Midrex process. The latter accounts for most of the growth in natural gas-fired production of pre-reduced products, although since 2005 coal-fired processes have been making a strong comeback, mainly in India.
Packaging of pre-reduced iron ore is evenly divided between sponge iron and briquettes. Sponges are a highly porous metallic product, close to the original ore but highly pyrophoric, which limits their transport. They are therefore often subjected to hot compaction, which improves both product density and handling safety. In 2012, 45% of prereducts were transformed into briquettes in this way. | 0 | Metallurgy |
Transcription factor 4 (TCF-4) also known as immunoglobulin transcription factor 2 (ITF-2) is a protein that in humans is encoded by the TCF4 gene located on chromosome 18q21.2. | 1 | Gene expression + Signal Transduction |
eIF2 is an essential factor for protein synthesis that forms a ternary complex (TC) with GTP and the initiator Met-tRNA. After its formation, the TC binds the 40S ribosomal subunit to form the 43S preinitiation complex (43S PIC). 43S PIC assembly is believed to be stimulated by the initiation factors eIF1, eIF1A, and the eIF3 complex according to in vitro experiments. The 43S PIC then binds mRNA that has previously been unwound by the eIF4F complex. The 43S PIC and the eIF4F proteins form a new 48S complex on the mRNA, which starts searching along the mRNA for the start codon (AUG). Upon base pairing of the AUG-codon with the Met-tRNA, eIF5 (which is a GTPase-activating protein , or GAP) is recruited to the complex and induces eIF2 to hydrolyse its GTP. This causes eIF2-GDP to be released from this 48S complex and translation begins after recruitment of the 60S ribosomal subunit and formation of the 80S initiation complex. Finally, with the help of the guanine nucleotide exchange factor (GEF) eIF2B, the GDP in eIF2 is exchanged for a GTP and the ternary complex reforms for a new round of translation initiation. | 1 | Gene expression + Signal Transduction |
FSP was used to modify a Mg alloy and insert nano-sized SiO. The test was conducted a total four times with the average grain size varying from 0.5–2μm. This nearly doubled the hardness of the Mg and also increased the super-plasticity. At room temperature, the yield stress of the FSP composites was improved in the 1D and in the 2D specimens signifying a larger resistance of the product metal under high stress conditions without deforming. The tensile strength was shown to increase along with the yield stress. | 0 | Metallurgy |
In the 1990s, Southern Peru Copper Corporation ("SPCC") was seeking to modernise its smelter at Ilo in southern Peru as part of 1997 commitment to the Peruvian government to capture at least 91.7% of the sulfur dioxide generated in its smelting operations by January 2007. It initially selected flash smelting technology to replace its reverberatory furnaces, at a cost of almost US$1 billion; however, one of the first actions following Grupo México's acquisition of ASARCO was to review the proposed Ilo smelter modernisation plans. | 0 | Metallurgy |
The upper critical magnetic field H of the superconducting state of CeCoIn is anisotropic, in accordance with the crystal structure and other physical properties. For magnetic fields applied along the [100] direction, H amounts to approximately 11.6 T, and H for fields along the [001] directions to 4.95 T.
The superconducting order parameter has d-wave symmetry, as established by several experiments, such as scanning tunneling microscopy (STM) and spectroscopy (STS).
Detailed studies close to the critical field have been performed on CeCoIn, and indications were found that certain regimes in the phase diagram of this material should be interpreted in terms of the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase.
Subsequently, the neutron-diffraction experiments showed that this regime features a more complex phase that also exhibits incommensurate antiferromagnetic order, a so-called Q phase.
Evidence for a delocalization quantum phase transition without symmetry breaking is presented. | 0 | Metallurgy |
The pipecolate region of rapamycin structure seems necessary for rapamycin-binding to FKBP12. This step is required for further binding of rapamycin to the mTOR kinase, which is the key enzyme in many biological actions of rapamycin.
The high affinity of rapamycin binding to FKBP12 is explained by number of hydrogen bonds through two different hydrophobic binding pockets, and this has been revealed by X-ray crystal structure of the compound bound to the protein. The structural characteristics common to temsirolimus and sirolimus; the pipecolic acid, tricarbonyl region from C13-C15, and lactone functionalities play the key role in binding groups with the FKBP12.
The most important hydrogen bonds are the lactone carbonyl oxygen at C-21 to the backbone NH of Ile56, amide carbonyl at C-15 to the phenolic group on the sidechain of Tyr82, and the hydroxyl proton at the hemiketal carbon, C-13, to the sidechain of Asp37.
Structural changes to the rapamycin structure can affect binding to mTOR. This could include both direct and indirect binding as a part of binding to FKBP12. Interaction of the FKBP12-rapamycin complex with mTOR corresponds with conformational flexibility of the effector domain of rapamycin. This domain consists of molecular regions that make hydrophobic interactions with the FKB domain and triene region from C-1-C-6, methoxy group at C-7, and methyl groups at C-33, C-27 and C-25. All changes of the macrolide ring can have unpredictable effects on binding and therefore, make determination of SAR for rapalogs problematic.
Rapamycin contains no functional groups that ionize in the pH range 1-10 and therefore, are rather insoluble in water. Despite its effectiveness in preclinic cancer models, its poor solubility in water, stability, and the long half-life elimination made its parenteral use difficult, but the development of soluble rapamycin analogs vanquished various barriers.
Nonetheless, the rapamycin analogs that have been approved for human use are modified at C-43 hydroxyl group and show improvement in pharmacokinetic parameters as well as drug properties, for example, solubility.
Rapamycin and temsirolimus have similar chemical structures and bind to FKBP12, though their mechanism of action differs.
Temsirolimus is a dihydroxymethyl propionic acid ester of rapamycin, and its first derivative. Therefore, it is more water-soluble, and due to its water solubility it can be given by intravenous formulation.
Everolimus has O-2 hydroxyethyl chain substitution and deforolimus has a phosphine oxide substitution at position C-43 in the lactone ring of rapamycin.
Deforolimus (Ridaforolimus ) has C43 secondary alcohol moiety of the cyclohexyl group of Rapamycin that was substituted with phosphonate and phosphinate groups, preventing the high-affinity binding to mTOR and FKBP. Computational modelling studies helped the synthesise of the compound. | 1 | Gene expression + Signal Transduction |
Nucleic acid analogues are used in molecular biology for several purposes:
* Investigation of possible scenarios of the origin of life: By testing different analogs, researchers try to answer the question of whether life's use of DNA and RNA was selected over time due to its advantages, or if they were chosen by arbitrary chance;
* As a tool to detect particular sequences: XNA can be used to tag and identify a wide range of DNA and RNA components with high specificity and accuracy;
* As an enzyme acting on DNA, RNA and XNA substrates - XNA has been shown to have the ability to cleave and ligate DNA, RNA and other XNA molecules similar to the actions of RNA ribozymes;
* As a tool with resistance to RNA hydrolysis;
* Investigation of the mechanisms used by enzyme; and
* Investigation of the structural features of nucleic acids. | 1 | Gene expression + Signal Transduction |
Silicon carbide fibers are used to measure gas temperatures in an optical technique called thin-filament pyrometry. It involves the placement of a thin filament in a hot gas stream. Radiative emissions from the filament can be correlated with filament temperature. Filaments are SiC fibers with a diameter of 15 micrometers, about one fifth that of a human hair. Because the fibers are so thin, they do little to disturb the flame and their temperature remains close to that of the local gas. Temperatures of about 800–2500 K can be measured. | 0 | Metallurgy |
Corrosion engineering is an engineering specialty that applies scientific, technical, engineering skills, and knowledge of natural laws and physical resources to design and implement materials, structures, devices, systems, and procedures to manage corrosion.
From a holistic perspective, corrosion is the phenomenon of metals returning to the state they are found in nature. The driving force that causes metals to corrode is a consequence of their temporary existence in metallic form. To produce metals starting from naturally occurring minerals and ores, it is necessary to provide a certain amount of energy, e.g. Iron ore in a blast furnace. It is therefore thermodynamically inevitable that these metals when exposed to various environments would revert to their state found in nature. Corrosion and corrosion engineering thus involves a study of chemical kinetics, thermodynamics, electrochemistry and materials science. | 0 | Metallurgy |
The stereotypic inflammatory response provoked by toll-like receptor activation has prompted speculation that endogenous activators of toll-like receptors might participate in autoimmune diseases. TLRs have been suspected of binding to host molecules including fibrinogen (involved in blood clotting), heat shock proteins (HSPs), HMGB1, extracellular matrix components and self DNA (it is normally degraded by nucleases, but under inflammatory and autoimmune conditions it can form a complex with endogenous proteins, become resistant to these nucleases and gain access to endosomal TLRs as TLR7 or TLR9). These endogenous ligands are usually produced as a result of non-physiological cell death. | 1 | Gene expression + Signal Transduction |
The Teck Cominco smelter, also known as the Teck Cominco Lead-Zinc Smelter, Cominco Smelter, and Trail smelter located in Trail, British Columbia, Canada, is the largest integrated lead-zinc smelter of its kind in the world. It is situated approximately north of the border between British Columbia, Canada and Washington, in the United States, on the Columbia River. It is owned and operated by Vancouver, British Columbia-based Teck Cominco Metals Ltd—renamed Teck Resources.
Since 1896, there has been a copper and gold smelting operation in the area. The original company, Consolidated Mining and Smelting Company of Canada, was founded in 1906 through a merger of several entities then under the control of the Canadian Pacific Railway (CPR). In July 2001, Cominco and Tech Resources merged and in 2008, Teck Cominco renamed itself as Teck. By 2018, the Teck Cominco smelter complex had been in operation for over a century. It provided 1,400 jobs in 2018, making it the largest employer in the small city of Trail, with a population of 7800. In 2017, the smelter produced more than 230,000 tons of zinc, which is used in rustproofing both iron and steel. Teck reported that they had invested CA$525 million in the late 2010s to "improve efficiency and performance at its Trail Operations" and that they intend to invest an added CA$150 million. The Trail Operations contributed CA$169 million to Teck Resources CA$3.3-billion gross profit in 2017. | 0 | Metallurgy |
In addition to LaNi, there are other alloys such as LaNi, LaNi, LaNi, LaNi, LaNi, and LaNi, and nonstoichiometric alloys such as LaNi (tetragonal, space group I4̄2m). The nickel atoms in LaNi can also be replaced by other atoms, such as LaNiCo. | 0 | Metallurgy |
Synapses can be classified by the type of cellular structures serving as the pre- and post-synaptic components. The vast majority of synapses in the mammalian nervous system are classical axo-dendritic synapses (axon synapsing upon a dendrite), however, a variety of other arrangements exist. These include but are not limited to axo-axonic, dendro-dendritic, axo-secretory, axo-ciliary, somato-dendritic, dendro-somatic, and somato-somatic synapses.
In fact, the axon can synapse onto a dendrite, onto a cell body, or onto another axon or axon terminal, as well as into the bloodstream or diffusely into the adjacent nervous tissue. | 1 | Gene expression + Signal Transduction |
Senapathy addressed the origin of the spliceosomal machinery that edits out the introns from RNA transcripts. If the split genes had originated from random DNA, then the introns would have become an unnecessary but integral part of eukaryotic genes along with the splice junctions. The spliceosomal machinery would be required to remove them and to enable the short exons to be linearly spliced together as a contiguously coding mRNA that can be translated into a complete protein. Thus, the split gene theory argues that spliceosomal machinery exists to remove the unnecessary introns.
Blake states, “Work by Senapathy, when applied to RNA, comprehensively explains the origin of the segregated form of RNA into coding and noncoding regions. It also suggests why a splicing mechanism was developed at the start of primordial evolution.” | 1 | Gene expression + Signal Transduction |
Transcription is when RNA is copied from DNA. During transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed. This process differs slightly in eukaryotes and prokaryotes. One notable difference is that prokaryotic RNA polymerase associates with DNA-processing enzymes during transcription so that processing can proceed during transcription. Therefore, this causes the new mRNA strand to become double stranded by producing a complementary strand known as the tRNA strand, which when combined are unable to form structures from base-pairing. Moreover, the template for mRNA is the complementary strand of tRNA, which is identical in sequence to the anticodon sequence that the DNA binds to. The short-lived, unprocessed or partially processed product is termed precursor mRNA, or pre-mRNA; once completely processed, it is termed mature mRNA. | 1 | Gene expression + Signal Transduction |
The SECEM factory in Cordoba was located to the west of the city, next to the route of the Cordoba-Seville and Cordoba-Malaga railway lines, which allowed its production to be transported by rail. For this purpose, an industrial branch and several sidings were set up within the industrial complex. Eventually SECEM acquired two 0-2-0T steam locomotives to take over the shunting and traction work with the freight wagons. One of these engines, acquired in 1963, was the former RENFE 020–0212. It is currently preserved and exhibited in Cordoba. | 0 | Metallurgy |
Eukaryotic messages are subject to surveillance by nonsense-mediated decay (NMD), which checks for the presence of premature stop codons (nonsense codons) in the message. These can arise via incomplete splicing, V(D)J recombination in the adaptive immune system, mutations in DNA, transcription errors, leaky scanning by the ribosome causing a frame shift, and other causes. Detection of a premature stop codon triggers mRNA degradation by 5 decapping, 3 poly(A) tail removal, or endonucleolytic cleavage. | 1 | Gene expression + Signal Transduction |
The Kroll process was invented in 1940 by William J. Kroll in Luxembourg. After moving to the United States, Kroll further developed the method for the production of zirconium.
Many methods had been applied to the production of titanium metal, beginning with a report in 1887 by Nilsen and Pettersen using sodium, which was optimized into the commercial Hunter process. In the 1920s van Arkel had described the thermal decomposition of titanium tetraiodide to give highly pure titanium. Titanium tetrachloride was found to reduce with hydrogen at high temperatures to give hydrides that can be thermally processed to the pure metal. With this background, Kroll developed both new reductants and new apparatus for the reduction of titanium tetrachloride. Its high reactivity toward trace amounts of water and other metal oxides presented challenges. Significant success came with the use of calcium as a reductant, but the resulting mixture still contained significant oxide impurities. Major success using magnesium at 1000 °C using a molybdenum clad reactor, as reported to the Electrochemical Society in Ottawa. Krolls titanium was highly ductile reflecting its high purity. The Kroll process displaced the Hunter process and continues to be the dominant technology for the production of titanium metal, as well as driving the majority of the worlds production of magnesium metal. | 0 | Metallurgy |
Most hormones initiate a cellular response by initially binding to either cell surface receptors or intracellular receptors. A cell may have several different receptors that recognize the same hormone but activate different signal transduction pathways, or a cell may have several different receptors that recognize different hormones and activate the same biochemical pathway.
Receptors for most peptide as well as many eicosanoid hormones are embedded in the cell membrane as cell surface receptors, and the majority of these belong to the G protein-coupled receptor (GPCR) class of seven alpha helix transmembrane proteins. The interaction of hormone and receptor typically triggers a cascade of secondary effects within the cytoplasm of the cell, described as signal transduction, often involving phosphorylation or dephosphorylation of various other cytoplasmic proteins, changes in ion channel permeability, or increased concentrations of intracellular molecules that may act as secondary messengers (e.g., cyclic AMP). Some protein hormones also interact with intracellular receptors located in the cytoplasm or nucleus by an intracrine mechanism.
For steroid or thyroid hormones, their receptors are located inside the cell within the cytoplasm of the target cell. These receptors belong to the nuclear receptor family of ligand-activated transcription factors. To bind their receptors, these hormones must first cross the cell membrane. They can do so because they are lipid-soluble. The combined hormone-receptor complex then moves across the nuclear membrane into the nucleus of the cell, where it binds to specific DNA sequences, regulating the expression of certain genes, and thereby increasing the levels of the proteins encoded by these genes. However, it has been shown that not all steroid receptors are located inside the cell. Some are associated with the plasma membrane. | 1 | Gene expression + Signal Transduction |
The Soviet Union recovered 29 furnaces as war damage, but failed to gain significant profits from them. According to sources, the Red Army's destructive techniques in dismantling German industrial plants proved inappropriate and wasted valuable resources. It was also challenging for Russians to reconstruct these factories within the Soviet Union. Travelers from Berlin to Moscow reported observing German machinery scattered, largely deteriorating, along every meter of track and shoulder, suffering from the harsh climatic conditions. The Russian iron and steel industry did not heavily rely on technological input from the West. Eventually, the Eastern Bloc only maintained this marginal technology to a limited extent in the recently sovietized European countries, where it was eventually abandoned.
Meanwhile large furnaces rebuilt in the 1950s in West Germany operated for approximately ten years before shutting down, due to the low cost of scrap and imported ore. The process then vanished from West Germany, concurrently with Western Europe.
In Japan furnaces also progressed towards increasingly bigger tools. However, the dwindling of local ferruginous sand deposits, along with the low cost of scrap and imported ores, eventually resulted in the gradual discontinuation of the process. The process was steadily improved by the Japanese, who developed it under various names for specialized products including ferroalloys and the recycling of steelmaking by-products. Currently, at the start of the 21st century, the Krupp-Renn process is exclusively used for ferronickel production in Japan.
By 1972 most plants in Czechoslovakia, Japan, and West Germany had ceased operations. The process was widely considered obsolete and no longer garnered the attention of industrialists. | 0 | Metallurgy |
In 1707, Abraham Darby I patented a method of making cast iron pots. His pots were thinner and hence cheaper than those of his rivals. Needing a larger supply of pig iron he leased the blast furnace at Coalbrookdale in 1709. There, he made iron using coke, thus establishing the first successful business in Europe to do so. His products were all of cast iron, though his immediate successors attempted (with little commercial success) to fine this to bar iron.
Bar iron thus continued normally to be made with charcoal pig iron until the mid-1750s. In 1755 Abraham Darby II (with partners) opened a new coke-using furnace at Horsehay in Shropshire, and this was followed by others. These supplied coke pig iron to finery forges of the traditional kind for the production of bar iron. The reason for the delay remains controversial. | 0 | Metallurgy |
In prehistory gold could be found in several areas of Europe; the Carpathian region, Iberia, south-western France, Brittany, Britain and Ireland. The latter in particular had rich gold reserves, and as such has been labelled an "ancient El Dorado". Across the world, and in many cultures, gold has been highly valued as a precious metal, in part because of its rarity and also because of its properties; for instance, unlike copper it is malleable, flexible and homogenous, and can be worked by hammering, rather than having to be worked through casting, annealing or soldering. Any products made from gold do not corrode, but instead have what has been described as an "intrinsic beauty", with many prehistoric peoples probably ascribing gold items a "symbolic as well as a decorative function". | 0 | Metallurgy |
The most basic mechanistic flow for RNA Silencing is as follows:
(For a more detailed explanation of the mechanism, refer to the RNAi:Cellular mechanism article.)
1: RNA with inverted repeats hairpin/panhandle constructs --> 2: dsRNA --> 3: miRNAs/siRNAs --> 4: RISC --> 5: Destruction of target mRNA
# It has been discovered that the best precursor to good RNA silencing is to have single stranded antisense RNA with inverted repeats which, in turn, build small hairpin RNA and panhandle constructs. The hairpin or panhandle constructs exist so that the RNA can remain independent and not anneal with other RNA strands.
# These small hairpin RNAs and/or panhandles then get transported from the nucleus to the cytosol through the nuclear export receptor called exportin-5, and then get transformed into a dsRNA, a double stranded RNA, which, like DNA, is a double stranded series of nucleotides. If the mechanism didn't use dsRNAs, but only single strands, there would be a higher chance for it to hybridize to other "good" mRNAs. As a double strand, it can be kept on call for when it is needed.
# The dsRNA then gets cut up by a Dicer into small (21-28 nt = nucleotides long) strands of miRNAs (microRNAs) or siRNAs (short interfering RNAs.) A Dicer is an endoribonuclease RNase, which is a complex of a protein mixed with strand(s) of RNA.
# Lastly, the double stranded miRNAs/siRNAs separate into single strands; the antisense RNA strand of the two will combine with another endoribonuclease enzyme complex called RISC (RNA-induced silencing complex), which includes the catalytic component Argonaute, and will guide the RISC to break up the "perfectly complementary" target mRNA or viral genomic RNA so that it can be destroyed.
# It means that based on a short sequence specific area, a corresponding mRNA will be cut. To make sure, it will be cut in many other places as well. (If the mechanism only worked with a long stretch, then there would be higher chance that it would not have time to match to its complementary long mRNA.) It has also been shown that the repeated-associated short interference RNAs (rasiRNA) have a role in guiding chromatin modification.
For an animated explanation of the mechanism of RNAi by Nature Reviews, see the External Links section below. | 1 | Gene expression + Signal Transduction |
Cleaning is the preparatory process of ensuring that the surface to be etched is free of contaminants which could negatively impact the quality of the finished part. An improperly cleaned surface could result in poor adhesion of the maskant, causing areas to be etched erroneously, or a non-uniform etch rate which could result in inaccurate final dimensions. The surface must be kept free from oils, grease, primer coatings, markings and other residue from the marking out process, scale (oxidation), and any other foreign contaminants. For most metals, this step can be performed by applying a solvent substance to the surface to be etched, washing away foreign contaminants. The material may also be immersed in alkaline cleaners or specialized de-oxidizing solutions. It is common practice in modern industrial chemical etching facilities that the workpiece never be directly handled after this process, as oils from human skin could easily contaminate the surface. | 0 | Metallurgy |
Sendai virus (family Paramyxoviridae) has a linear, single stranded, negative-sense, nonsegmented RNA genome. The viral RdRp consists of two virus-encoded subunits, a smaller one P and a larger one L. When different inactive RdRp mutants with defects throughout the length of the L subunit where tested in pairwise combinations, restoration of viral RNA synthesis was observed in some combinations. This positive L–L interaction is referred to as intragenic complementation and indicates that the L protein is an oligomer in the viral RNA polymerase complex. | 1 | Gene expression + Signal Transduction |
Hundreds of metal artefacts were found from the Late Bronze Age (second half of 2nd millennium BCE): ca.
200 blade weapons, 140 metal vessels, some working tools, small arrowheads, and decorative objects. All
the blades analyzed were made of tin bronze and most of all the other copper-based objects are either tin bronze alloy or have tin in their metal as impurity.
At this stage, large quantities of copper and tin ingots (i.e., 10 tons of Cu and 3 tons of Sn ingots in one cargo of Uluburun shipwreck from the 14th century BCE) were found all over the coasts of the Mediterranean and in several shipwrecks under the sea, mainly off the southern coast of Turkey. In Canaan at that time, Cypriot, Egyptian, Syrian, and Mesopotamian types of bronze objects were found, besides the local Canaanite metal collection. These were all basically made of tin bronze. The “prestige” objects like sickle blade swords or cast-hilt daggers were alloyed with highquality (11–13% by weight) Sn, whereas the simpler and probably less expensive objects had lower levels of tin in the metal. | 0 | Metallurgy |
The Krupp–Renn process is a direct reduction process that uses a long tubular furnace similar to those found in cement production. The most recent units constructed have a diameter of approximately 4.5 meters and a length of 110 meters. The residence time of the product is influenced by the slope and speed of rotation of the rotary kiln, which is inclined at an angle of roughly 2.5 percent.
Prior to usage, the iron ore is crushed to less than 6 mm in particle size. The iron ore is introduced into the furnace upstream and mixed with a small amount of fuel, typically hard coal. After 6 to 8 hours, it exits the furnace as pre-reduced iron ore at 1,000 °C. The amount of iron recovered ranges from 94% to 97.5% of the initial iron in the ore.
A burner located at the lower end of the furnace provides heat, transforming it into a counter-current reactor. The fuel comprises finely pulverized coal, which, upon high-temperature combustion, generates reducing gas primarily consisting of CO. Once the furnace reaches an optimal temperature, the ore-coal mixture can serve as the primary fuel source.
The fumes exiting the furnace's upper end attain temperatures ranging from 850 to 900 °C and are subsequently cooled and purged of dust by water injection before discharge through the chimney.
The process is efficient in producing ferronickel due to the proximity of its constituent elements. At 800 °C, carbon easily reduces iron and nickel oxides, while the gangue's other oxides are not significantly reduced. Specifically, iron(II) oxide (or wustite), which is the stable iron oxide at 800 °C, has a reducibility similar to that of nickel(II) oxide, making it impossible to reduce one without reducing the other. | 0 | Metallurgy |
Myristoylation is an integral part of apoptosis, or programmed cell death. Apoptosis is necessary for cell homeostasis and occurs when cells are under stress such as hypoxia or DNA damage. Apoptosis can proceed by either mitochondrial or receptor mediated activation. In receptor mediated apoptosis, apoptotic pathways are triggered when the cell binds a death receptor. In one such case, death receptor binding initiates the formation of the death-inducing signaling complex, a complex composed of numerous proteins including several caspases, including caspase 3. Caspase 3 cleaves a number of proteins that are subsequently myristoylated by NMT. The pro-apoptotic BH3-interacting domain death agonist (Bid) is one such protein that once myristoylated, translocates to the mitochondria where it prompts the release of cytochrome c leading to cell death. Actin, gelsolin and p21-activated kinase 2 PAK2 are three other proteins that are myristoylated following cleavage by caspase 3, which leads to either the up-regulation or down-regulation of apoptosis. | 1 | Gene expression + Signal Transduction |
In metallurgy, a shape-memory alloy (SMA) is an alloy that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. It is also known in other names such as memory metal, memory alloy, smart metal, smart alloy, and muscle wire. The "memorized geometry" can be modified by fixating the desired geometry and subjecting it to a thermal treatment, for example a wire can be taught to memorize the shape of a coil spring.
Parts made of shape-memory alloys can be lightweight, solid-state alternatives to conventional actuators such as hydraulic, pneumatic, and motor-based systems. They can also be used to make hermetic joints in metal tubing, and it can also replace a sensor-actuator closed loop to control water temperature by governing hot and cold water flow ratio. | 0 | Metallurgy |
DXZ4 is a variable number tandemly repeated DNA sequence. In humans it is composed of 3kb monomers containing a highly conserved CTCF binding site. CTCF is a transcription factor protein and the main insulator responsible for partitioning of chromatin domains in the vertebrate genome.
In addition to being enriched in CpG-islands, DXZ4 transcribes long non-coding RNAs (lncRNAs) and small RNAs of unknown function. Repeat copy number of DXZ4 is highly polymorphic in human populations (varying between 50 and 100 copies). DXZ4 is one of many large tandem repeat loci defined as macrosatellites. Several macrosatellites have been described in humans and share similar features, such as high GC content, large repeat monomers, and high variability for repeat copy number within populations. DXZ4 plays an important role in the unique structural conformation of the inactive X chromosome (Xi) in female somatic cells by acting as a hinge point between two large “super domains”.
In addition to acting as the primary division between domains, DXZ4 forms long-range interactions with a number of other repeat rich regions along the inactive X chromosome. Knockout of the DXZ4 locus revealed loss of this structural conformation on the Xi with chromosome wide silencing being maintained. | 1 | Gene expression + Signal Transduction |
Ecologically, V. fischeri is known to have symbiotic associations with a number of eukaryotic hosts, including the Hawaiian Bobtail Squid (Euprymna scolopes). In this relationship, the squid host maintains the bacteria in specialized light organs. The host provides a safe, nutrient rich environment for the bacteria and in turn, the bacteria provide light. Although bioluminescence can be used for mating and other purposes, in E. scolopes it is used for counter illumination to avoid predation.
The autoinducer molecule used by V. fischeri is N-(3-oxohexanoyl)-homoserine lactone. This molecule is produced in the cytoplasm by the LuxI synthase enzyme and is secreted through the cell membrane into the extracellular environment. As is true of most autoinducers, the environmental concentration of N-(3-oxohexanoyl)-homoserine lactone is the same as the intracellular concentration within each cell. N-(3-oxohexanoyl)-homoserine lactone eventually diffuses back into cells where it is recognized by LuxR once a threshold concentration (~10 μg/ml) has been reached. LuxR binds the autoinducer and directly activates transcription of the luxICDABE operon. This results in an exponential increase in both the production of autoinducer and in bioluminescence. LuxR bound by autoinducer also inhibits the expression of luxR, which is thought to provide a negative feedback compensatory mechanism to tightly control levels of the bioluminescence genes. | 1 | Gene expression + Signal Transduction |
This reaction accounts for around half of the transformation of wustite FeO into iron, and removes 30% of the total oxygen supplied, mainly in the form of iron oxide FeO. This mode of wustite reduction is highly endothermic, whereas the reduction of iron oxides by CO is slightly exothermic (+155.15 kJ/mol vs. -17.45 kJ/mol), so it is essential to keep it to a minimum.
This reaction concerns all the iron oxides present in a blast furnace, but also manganese(II) oxides (Mno), silica (SiO), chromium, vanadium and titanium, which are partially reduced in blast furnaces. These chemical reactions are described below:
MnO + C → Mn + CO consuming 282,4 kJ/mol à 1 400 °C (begins above 1,000°C and involves half of the manganese present in the charge)
SiO + 2 C → Si + 2 CO consuming 655,5 kJ/mol (begins above 1 500 °C)
Chromium and vanadium behave like manganese, titanium like silicon. As for the other iron oxides, their direct reduction is of negligible importance. This can be written as:
3 FeO + C → 2 FeO + CO consuming 118,821 kJ/mol
FeO + C → 3 FeO + CO consuming 209,256 kJ/mol
In non-steel blast furnaces, dedicated to the production of ferroalloys, direct reduction is fundamental. For example, for ferronickel production, both direct reduction reactions are used:
NiO + C → Ni + CO above 445 °C
FeO + C → Fe + CO above 800 °C
So, although nickel reduces slightly more easily than iron, it cannot be reduced and cast independently of iron. | 0 | Metallurgy |
Grb2 has been shown to interact with:
* ADAM15,
* Abl gene,
* Arachidonate 5-lipoxygenase,
* B-cell linker,
* BCAR1,
* BCR gene,
* Beta-2 adrenergic receptor,
* C-Met,
* CBLB,
* CD117,
* CD22,
* CD28,
* CDKN1B,
* CRK,
* Cbl gene,
* Colony stimulating factor 1 receptor,
* DCTN1,
* DNM1,
* Dock180,
* Dystroglycan,
* EPH receptor A2,
* ETV6,
* Epidermal growth factor receptor,
* Erythropoietin receptor,
* FRS2,
* Fas ligand,
* GAB1,
* GAB2,
* Glycoprotein 130,
* Granulocyte colony-stimulating factor receptor,
* HER2/neu,
* HNRNPC,
* Huntingtin,
* INPP5D,
* IRS1,
* ITK,
* Janus kinase 1,
* Janus kinase 2,
* KHDRBS1,
* Linker of activated T cells,
* Lymphocyte cytosolic protein 2,
* MAP2,
* MAP3K1
* MAP4K1,
* MED28,
* MST1R,
* MUC1,
* Mitogen-activated protein kinase 9,
* NCKIPSD,
* NEU3,
* PDGFRB,
* PIK3R1,
* PLCG1,
* PRKAR1A,
* PTK2,
* PTPN11,
* PTPN12,
* PTPN1,
* PTPN6,
* PTPRA,
* RAPGEF1,
* RET proto-oncogene,
* SH2B1,
* SH3KBP1,
* SHC1,
* SOS1,
* Src,
* Syk,
* TNK2,
* TrkA,
* VAV1,
* VAV2,
* VAV3, and
* Wiskott-Aldrich syndrome protein. | 1 | Gene expression + Signal Transduction |
The Westinghouse Lamp Plant was constructed on Arlington Avenue in 1920 near the Watsessing Station of the rail line in the Watsessing neighborhood that connected Montclair, Glen Ridge and Bloomfield. The population in the area had grown since the time that the Township of Bloomfield was incorporated as a township from portions of Newark Township by an act of the New Jersey Legislature on March 23, 1812 until World War II. The population boom was contributed by the manufacturing jobs at the Westinghouse Lamp Plant along with other manufacturing plants such as General Electric, Lehn and Fink and Schering during the war time.
The Westinghouse Lamp Plant was devoted to lamp manufacturing in its early years. The plant had a research department to find a new suitable material for a light bulb filament. After World War I, the department led by Harvey C. Rentschler, and his deputy, John W. Marden, started looking into uranium to discover whether there was any similarity with tungsten to be used as a filament. The problem at the time was to make uranium into a metal form so that researchers could work with it. Westinghouse failed to establish uranium as a viable filament material, however, the research department continued to experiment with it until they found an electrolysis method to use a fused uranium salt to produce a metal. The metal was pure enough for nuclear research in many university laboratories during the 1930s. By 1941, Westinghouse Lamp Plant had the only practical process for producing pure uranium metal. | 0 | Metallurgy |
She married fellow metallurgist Norman Petch whom she met in Cambridge but they divorced in 1944. She went on to marry metallurgist, Alan Dennis McQuillam in 1947. Her husband died in 1987. McQuillan died in Gloucestershire in 1998. | 0 | Metallurgy |
One of the first DREADDs was based on the human M muscarinic receptor (hM). Only two point mutations of hM were required to achieve a mutant receptor with nanomolar potency for CNO, insensitivity to acetylcholine and low constitutive activity and this DREADD receptor was named hM3Dq. M and M muscarinic receptors have been mutated to create DREADDs hM1Dq and hM5Dq respectively.
The most commonly used inhibitory DREADD is hM4Di, derived from the M muscarinic receptor that couples with the G protein. Another G coupled human muscarinic receptor, M, was also mutated to obtain the DREADD receptor hM2D. Another inhibitory G-DREADD is the kappa-opioid-receptor (KOR) DREADD (KORD) which is selectively activated by salvinorin B (SalB).
G-coupled DREADDs have also been developed. These receptors are also known as GD and are chimeric receptors containing intracellular regions of the turkey erythrocyte β-adrenergic receptor substituted into the rat M DREADD. | 1 | Gene expression + Signal Transduction |
Planar Flow Casting (PFC) is a commonly used melt spinning process for the industrial fabrication of wide metallic glass sheets. In this process, the primary modification is that a much wider nozzle is used to eject the melt from the crucible. As a result, the melt puddle covers a larger area of the drum, which in turn forms a larger area of ribbon. PFC is commonly cast in a vacuum to avoid oxidation of the molten material, which would affect the quality of the resulting product. Ribbons up to 200 mm wide have been industrially achieved using PFC. | 0 | Metallurgy |
Tin-lead (Sn-Pb) solders, also called soft solders, are commercially available with tin concentrations between 5% and 70% by weight. The greater the tin concentration, the greater the solder's tensile and shear strengths. Lead mitigates the formation of tin whiskers, though the precise mechanism for this is unknown. Today, many techniques are used to mitigate the problem, including changes to the annealing process (heating and cooling), addition of elements like copper and nickel, and the application of conformal coatings. Alloys commonly used for electrical soldering are 60/40 Sn-Pb, which melts at , and 63/37 Sn-Pb used principally in electrical/electronic work. The latter mixture is a eutectic alloy of these metals, which:
# has the lowest melting point () of all the tin-lead alloys; and
# the melting point is truly a point — not a range.
In the United States, since 1974, lead is prohibited in solder and flux in plumbing applications for drinking water use, per the Safe Drinking Water Act. Historically, a higher proportion of lead was used, commonly 50/50. This had the advantage of making the alloy solidify more slowly. With the pipes being physically fitted together before soldering, the solder could be wiped over the joint to ensure water tightness. Although lead water pipes were displaced by copper when the significance of lead poisoning began to be fully appreciated, lead solder was still used until the 1980s because it was thought that the amount of lead that could leach into water from the solder was negligible from a properly soldered joint. The electrochemical couple of copper and lead promotes corrosion of the lead and tin. Tin, however, is protected by insoluble oxide. Since even small amounts of lead have been found detrimental to health as a potent neurotoxin, lead in plumbing solder was replaced by silver (food-grade applications) or antimony, with copper often added, and the proportion of tin was increased (see lead-free solder).
The addition of tin—more expensive than lead—improves wetting properties of the alloy; lead itself has poor wetting characteristics. High-tin tin-lead alloys have limited use as the workability range can be provided by a cheaper high-lead alloy.
Lead-tin solders readily dissolve gold plating and form brittle intermetallics.
60/40 Sn-Pb solder oxidizes on the surface, forming a complex 4-layer structure: tin(IV) oxide on the surface, below it a layer of tin(II) oxide with finely dispersed lead, followed by a layer of tin(II) oxide with finely dispersed tin and lead, and the solder alloy itself underneath.
Lead, and to some degree tin, as used in solder contains small but significant amounts of radioisotope impurities. Radioisotopes undergoing alpha decay are a concern due to their tendency to cause soft errors. Polonium-210 is especially troublesome; lead-210 beta decays to bismuth-210 which then beta decays to polonium-210, an intense emitter of alpha particles. Uranium-238 and thorium-232 are other significant contaminants of alloys of lead. | 0 | Metallurgy |
The enhancers determining early segmentation in Drosophila melanogaster embryos are among the best characterized developmental enhancers. In the early fly embryo, the gap gene transcription factors are responsible for activating and repressing a number of segmentation genes, such as the pair rule genes. The gap genes are expressed in blocks along the anterior-posterior axis of the fly along with other maternal effect transcription factors, thus creating zones within which different combinations of transcription factors are expressed. The pair-rule genes are separated from one another by non-expressing cells. Moreover, the stripes of expression for different pair-rule genes are offset by a few cell diameters from one another. Thus, unique combinations of pair-rule gene expression create spatial domains along the anterior-posterior axis to set up each of the 14 individual segments. The 480 bp enhancer responsible for driving the sharp stripe two of the pair-rule gene even-skipped (eve) has been well-characterized. The enhancer contains 12 different binding sites for maternal and gap gene transcription factors. Activating and repressing sites overlap in sequence. Eve is only expressed in a narrow stripe of cells that contain high concentrations of the activators and low concentration of the repressors for this enhancer sequence. Other enhancer regions drive eve expression in 6 other stripes in the embryo. | 1 | Gene expression + Signal Transduction |
It is a method used to obtain aluminium of very high purity. The metal obtained in the Hall–Héroult process is about 99.5% pure, and for most purposes it is taken as pure metal.
However, further purification of aluminium can be carried out by the Hoopes process. This is an electrolytic process. | 0 | Metallurgy |
Temperature dependent loop formations introduce temperature-dependence in the expression of downstream operons. All such elements act in a translation-dependent manner by controlling the accessibility of the Shine-Dalgarno sequence, for example the expression of pathogenicity islands of some bacteria upon entry to a host. Recent data predict the existence of temperature-dependent alternative secondary structures (including Rho-independent terminators) upstream of cold shock proteins in E. coli. | 1 | Gene expression + Signal Transduction |
The introduction of amalgamation to silver refining in the Americas not only ended the mid-sixteenth century crisis in silver production, it also inaugurated a rapid expansion of silver production in New Spain and Peru as miners could now profitably mine lower-grade ores. In addition, places that were rich in ore but too isolated from indigenous populations or forests for the labor- and fuel-intensive smelting method to be profitable, as was the case with Potosí in modern-day Bolivia, were now viable. As a result of this expansion, the Americas became the primary producer of the worlds silver, with Spanish America producing three-fifths of the worlds silver supply prior to 1900.
Increased silver production due to the introduction of mercury amalgamation resulted in an increased demand for labor. In New Spain, mining labor was initially supplied by the encomienda system or by enslaved Indians before transitioning to a repartimiento rotating labor system, but by the early 1600s, the majority of workers were Indian free wage or debt peonage workers. These naboríos were free, unattached Indians who contracted themselves out for sustenance and payment. Spaniards tended to distrust naboríos and accused them of profiteering by stealing ore, taking advances and fleeing, or contracting themselves out to multiple employers at a time. Regardless, the mines in New Spain increasingly relied on naboríos, who constituted over two thirds of mine workers in the region. Repartimiento Indian workers made up roughly seventeen percent of laborers, with another fourteen percent composed of Black slaves. Throughout the Spanish colonies, white men typically took positions as supervisors or mine owners.
The introduction of silver amalgamation allowed for an expansion of silver production in Peru that had profound consequences for Perus native population. From 1571, the year the amalgamation process was introduced to the Andes, to 1575, Perus silver production quintupled. In 1572, in order to provide sufficient labor to accommodate the expansion of silver mining to lower-grade ores, Viceroy Francisco Toledo organized an Indian draft labor system, the mita. This system of forced labor was based on the mita, a rotating, reciprocal labor obligation instituted in pre-Hispanic Andean society. Under this system, thousands of natives were forced to work in silver and mercury mines for less than subsistence-level wages. Thirteen thousand draft laborers per year worked at the largest mine in the Americas, located at Potosí in modern Bolivia. Native attempts to avoid the mita led to the abandonment of many Indian villages throughout Peru as thousands of Indians either moved permanently to Potosí or fled their traditional ayllus' in order to escape the labor draft. Spanish monopolization of refining through amalgamation cut natives out of what had earlier been a native-dominated enterprise. Refining represented the most profitable segment of silver production. In conjunction with the mita, the exclusion of natives from owning refineries contributed to the transformation of Peruvian natives into a poorly paid labor force.
The rapid expansion of silver production and coinage—made possible due to the invention of amalgamation—has often been identified as the primary driver of the price revolution, a period of high inflation lasting from the sixteenth to early seventeenth-century in Europe. Proponents of this theory argue that Spain's reliance on silver coins from the Americas to finance its large balance of payments deficits resulted in a general expansion of the European money supply and corresponding inflation. Critics of the theory, however, argue that inflation was really a result of European government policies and population growth.
While the role of the expansion in silver production in the price revolution may be disputed, this expansion is often acknowledged as a key ingredient in the formation of early-modern world trade. In the 1530s, China decreed that all internal taxation must be paid in silver, driving demand for Spanish American silver and facilitating the development of extensive trade networks linking Europe, Africa, Asia, and the Americas as Europeans sought to gain access to Chinese wares. | 0 | Metallurgy |
Type J (iron–constantan) has a more restricted range (−40 °C to +750 °C) than type K but higher sensitivity of about 50 μV/°C. The Curie point of the iron (770 °C) causes a smooth change in the characteristic, which determines the upper temperature limit. Note, the European/German Type L is a variant of the type J, with a different specification for the EMF output (reference DIN 43712:1985-01). | 0 | Metallurgy |
Heterogeneous nuclear ribonucleoproteins (hnRNPs) are complexes of RNA and protein present in the cell nucleus during gene transcription and subsequent post-transcriptional modification of the newly synthesized RNA (pre-mRNA). The presence of the proteins bound to a pre-mRNA molecule serves as a signal that the pre-mRNA is not yet fully processed and therefore not ready for export to the cytoplasm. Since most mature RNA is exported from the nucleus relatively quickly, most RNA-binding protein in the nucleus exist as heterogeneous ribonucleoprotein particles. After splicing has occurred, the proteins remain bound to spliced introns and target them for degradation.
hnRNPs are also integral to the 40S subunit of the ribosome and therefore important for the translation of mRNA in the cytoplasm. However, hnRNPs also have their own nuclear localization sequences (NLS) and are therefore found mainly in the nucleus. Though it is known that a few hnRNPs shuttle between the cytoplasm and nucleus, immunofluorescence microscopy with hnRNP-specific antibodies shows nucleoplasmic localization of these proteins with little staining in the nucleolus or cytoplasm. This is likely because of its major role in binding to newly transcribed RNAs. High-resolution immunoelectron microscopy has shown that hnRNPs localize predominantly to the border regions of chromatin, where it has access to these nascent RNAs.
The proteins involved in the hnRNP complexes are collectively known as heterogeneous ribonucleoproteins. They include protein K and polypyrimidine tract-binding protein (PTB), which is regulated by phosphorylation catalyzed by protein kinase A and is responsible for suppressing RNA splicing at a particular exon by blocking access of the spliceosome to the polypyrimidine tract. hnRNPs are also responsible for strengthening and inhibiting splice sites by making such sites more or less accessible to the spliceosome. Cooperative interactions between attached hnRNPs may encourage certain splicing combinations while inhibiting others. | 1 | Gene expression + Signal Transduction |
Based on the tetrahedral units, FK crystallographic structures are classified into low and high polyhedral groups denoted by their coordination numbers (CN) referring to the number of atom centering the polyhedron.
Some atoms have an icosahedral structure with low coordination, labeled CN12. Some others have higher coordination numbers of 14, 15 and 16, labeled CN14, CN15, and CN16, respectively. These atoms with higher coordination numbers form uninterrupted networks connected along the directions where the five-fold icosahedral symmetry is replaced by six-fold local symmetry. The sites of 12-coordination are called minor sites and those with more than 12-fold coordination are major sites. | 0 | Metallurgy |
A more complex, specific example of crosstalk between two major signaling pathways can be observed with the interaction of the cAMP and MAPK signaling pathways in the activation of lymphocytes. In this case, components of the cAMP pathway directly and indirectly affect MAPK signaling pathway meant to activate genes involving immunity and lymphocytes.
Newly formed cAMP is released from the membrane and diffuses across the intracellular space where it serves to activate PKA. The catalytic subunit of PKA must bind four molecules of cAMP to be activated, whereupon activation consists of cleavage between the regulatory and catalytic subunits. This cleavage in turn activates PKA by exposing the catalytic sites of the C subunits, which can then phosphorylate an array of proteins in the cell.
In lymphocytes, the intracellular levels of cAMP increase upon antigen-receptor stimulation and even more so in response to prostaglandin E and other immunosuppression agents. In this case, cAMP serves to inhibit immunity players. PKA type I colocalizes with the T-cell and B-cell antigen receptors and causes inhibition of T- and B-cell activation. PKA has even been highlighted as a direct inducer of genes contributing to immunosuppression.
Additionally, the cAMP pathway also interacts with the MAPK pathway in a more indirect manner through its interaction with hematopoietic PTPase (HePTP). HePTP is expressed in all leukocytes. When overexpressed in T-cells, HePTP reduces the transcriptional activation of the interleukin-2 promoter typically induced by the activated T-cell receptor through a MAPK signaling cascade. The way that HePTP effectively inhibits the MAPK signaling is by interacting with the MAP kinases Erk1, Erk2, and p38 through a short sequence in HePTP's non-catalytic N terminus termed the kinase interaction motif (KIM)., The highly-specific binding of Erk and p38 to this subunit of HePTP results in rapid inactivation of the signaling cascade (see figure 3).
Yet, since both HePTP and Erk are cytosolic enzymes, it is reasonable to conclude that there exists a mechanism for the inhibition of Erk by HePTP to cease in order to allow for the translocation of activated Erk to the nucleus. Indeed, like in many other cases of protein-protein interaction, HePTP appears to be phosphorylated by Erk and p38 at the sites Thr45 and Ser72. Importantly though, a third phosphorylation site in the non-catalytic N terminus (the KIM region) of HePTP has been found—one that is phosphorylated to a much higher stoichiometry by the cAMP pathway, in yet another instance of crosstalk between the cAMP and MAPK pathways.
Phosphorylation of this third site by PKAs from the cAMP pathway inhibits binding of MAP kinases to HePTP and thereby upregulates the MAPK/ERK signaling cascade. The MAPK pathway, through Ras, Raf, Mek, and Erk, shows low activity in the presence of unphosphorylated (active) HePTP. However, activation the cAMP pathway stimulates the activation of PKA, which in turn phosphorylates HePTP at Ser23. This prevents HePTP from binding to Erk and frees the MAPK pathway from inhibition, allowing downstream signaling to continue (see figure 4).
Moreover, studies involving smooth muscle cells from the atrium of the heart have shown that PKA can reduce the activation of MAP kinases in response to platelet-derived growth factor (PDGF) by phosphorylating the kinase c-Raf. Thus, it seems plausible that PKA in the cAMP pathway could even be further involved in the regulation of lymphocyte activation not only by inhibiting the antigen-receptor MAPK signal pathway at its final stage, but even further upstream. | 1 | Gene expression + Signal Transduction |
In the field of medicine, pelletization is referred to as the agglomeration process that converts fine powders or granules into more or less spherical pellets. The use of the technology increased because it allows for the controlled release of dosage form, which also lead to a uniform absorption with less mucosal irritation within the gastrointestinal tract. There are different pelletization processes applied in the pharmaceutical industry and these typically vary according to the bonding forces. Some examples of the processes include balling, compression, and spray congealing. Balling is similar to the wet (or green) pelletization used in the iron ore industry. | 0 | Metallurgy |
Forskolin is commonly used as a tool in biochemistry to raise levels of cAMP in the study and research of cell physiology. | 1 | Gene expression + Signal Transduction |
Solid solution strengthening increases yield strength of the material by increasing the shear stress, , to move dislocations:
where c is the concentration of the solute atoms, G is the shear modulus, b is the magnitude of the Burger's vector, and is the lattice strain due to the solute. This is composed of two terms, one describing lattice distortion and the other local modulus change.
Here, the term that captures the local modulus change, a constant dependent on the solute atoms and is the lattice distortion term.
The lattice distortion term can be described as:
, where a is the lattice parameter of the material.
Meanwhile, the local modulus change is captured in the following expression:
, where G is shear modulus of the solute material. | 0 | Metallurgy |
In rolling element bearings fretting may occur when the bearings are operating in an oscillating motion. Examples of applications are blade bearings in wind turbines, helicopter rotor pitch bearings, and bearings in robots. If the bearing movement is limited to small motions the damage caused may be called fretting or false brinelling depending on mechanism encountered. The main difference is that false brinelling occurs under lubricated and fretting under dry contact conditions. Between false brinelling and fretting corrosion, a time-dependent relation has been proposed. | 0 | Metallurgy |
The electrolysis process, also known as the hydrometallurgical process, Roast-Leach-Electrowin (RLE) process, or electrolytic process, is more widely used than the pyrometallurgical processes.
The electrolysis process consists of 4 steps: leaching, purification, electrolysis, and melting and casting. | 0 | Metallurgy |
The dimerization partner, RB-like, E2F and multi-vulval class B (DREAM) complex is a protein complex responsible for the regulation of cell cycle-dependent gene expression. The complex is evolutionarily conserved, although some of its components vary from species to species. In humans, the key proteins in the complex are RBL1 (p107) and RBL2 (p130), both of which are homologs of RB (p105) and bind repressive E2F transcription factors E2F4 and E2F5; DP1, DP2 and DP3, dimerization partners of E2F; and MuvB, which is a complex of LIN9/37/52/54 and RBBP4. | 1 | Gene expression + Signal Transduction |
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:
* no minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium, zirconium, or any other element to be added to obtain a desired alloying effect;
* the specified minimum for copper does not exceed 0.40%;
* or the specified maximum for any of the following elements does not exceed the percentages noted: manganese 1.65%; silicon 0.60%; copper 0.60%.
The term carbon steel may also be used in reference to steel which is not stainless steel; in this use carbon steel may include alloy steels. High carbon steel has many different uses such as milling machines, cutting tools (such as chisels) and high strength wires. These applications require a much finer microstructure, which improves the toughness.
As the carbon content percentage rises, steel has the ability to become harder and stronger through heat treating; however, it becomes less ductile. Regardless of the heat treatment, a higher carbon content reduces weldability. In carbon steels, the higher carbon content lowers the melting point. | 0 | Metallurgy |
The Kfar Monash Hoard is a hoard of metal objects dated to the Early Bronze Age (the third millennium BCE) found in the spring of 1962 by the agriculturalist Zvi Yizhar in Kfar Monash, Israel. Kfar Monash is located 3.3 km south-east of Tel Hefer (Tell Ishbar) in the Plain of Sharon or in modern terms 9 km/6 mi northeast of Netanya, which is roughly located along the Israeli coast between Netanya and Haifa.
The Monash Hoard consists of:
The Crescentic Axehead was found about 5 years later at about 200m distance.
As of June 2006, the Kfar Monash Hoard was on display in the Israel Museum. | 0 | Metallurgy |
The LiMCA method measures the total concentration and size distribution of inclusions present in aluminum alloys. Its measuring principle is based on an objective and user-independent method. The LiMCA CM system can characterize the cleanliness of a melt at time intervals in the order of one minute. It can therefore monitor, in real-time, the evolution of cleanliness along a cast as a function of process parameters and melt-handling practices.
The heart of the LiMCA measuring system consists of a closed glass tube (electrically insulating material) bearing a small orifice at its bottom. The tube is positioned in liquid metal. By creating a vacuum inside the tube, the metal with the suspended inclusions to be detected is forced through the small orifice. Two electrodes are necessary: one inside the tube and the other outside. Both electrodes are immersed in the liquid metal. A constant electric current is applied between the electrodes. The current flows through the
liquid metal by the small orifice in the tube. When an inclusion enters the orifice, it displaces its volume of conducting fluid, temporarily raising the electrical resistance. The increase of resistance generates a voltage pulse. The magnitude of the voltage pulse is a function of the volume of the particle. The duration of the pulse is related to the
transit time of the inclusion. The voltage pulses are amplified and their amplitude measured digitally. The size distribution and total concentration are displayed in real-time on a computer screen. | 0 | Metallurgy |
The Wilfley Table was conceived by Arthur Wilfley, a mining engineer based in Kokomo, Colorado in the United States. As a silver mine operator, Wilfley spent many years refining his separation table design in order to make the extraction of silver more economic. Rather than using heating processes (smelting) to concentrate the ore, Wilfley had been experimenting on mineral separation by use mineral density contrasts.
Wilfley was able to perfect a mechanical solution for the recovery of gold and silver from low-grade ores by means of the Wilfley table. The first Wilfley table was built on a preliminary scale in May 1895. The first full-sized table was used in Wilfley's own mill in Kokomo, in May 1896, while the first table sold for installation was placed in the Puzzle Mill, Breckinridge, Colorado, in August 1896. Patented in 1897, the Wilfley table made mining lower-grade ores profitable. Pulverised ore, suspended in a water solution, was washed across a sloping riffled vibrating table so that metals separated as they drained off.
The Wilfley Table was said to have revolutionised ore dressing worldwide and more than 25,000 were in service by the 1930s. | 0 | Metallurgy |
The industrial revolution at the Ural mining plants consisted of three major stages:
* Early 19th century - 1830s: the appearance of the first steam engines, the development of blast furnace production, and the introduction of rolling mills.
* 1840-1870s: the development and implementation of more progressive methods of obtaining iron: puddling, kontuaz furnaces, and Lancashire hearth.
* 1880-1910s: introduction of open-hearth and Bessemer methods of steel production, and the complete displacement of water wheels by steam and other engines.
The replacement of wooden bellows with cylindrical blowers in the early 19th century reduced coal consumption by up to 20% and doubled the productivity of blast furnaces. Further development of blast furnace technology was associated with increasing the height of the furnaces, optimizing their profile and increasing the power of the blower motors. Cupola furnaces appeared at factories, and the casting of metals became a separate production. In 1808, serf S. I. Badaev invented a method for producing cast steel, later called Badaevskaya, for which he received his freedom and in 1811 was sent to the Votkinsk Plant to organize production. At the Zlatoust plant since 1828, experiments on the production of cast steel were conducted by P. P. Anosov.
Foreign engineers played a significant role in the development of existing plants and the construction of new ones in the Urals. In the 18th century, up to 600 German metallurgists worked at the factories of the Yekaterinburg Department at various times. At the beginning of the 19th century, 140 craftsmen from Europe were invited to the Izhevsk Arms Factory, and 115 German gunsmiths and steelworkers were invited to the Zlatoust Arms Factory. After the end of the contract, many foreigners remained in the factories as freelance workers.
Administrative changes at the beginning of the 19th century were associated with the approval in 1806 of the Mining Charter, compiled by A. F. Deryabin and later included in part in the Code of Laws of 1832, and the formation of the Mining Department, which was transformed in 1811 into the Department of Mining and Salt Affairs.
In the period from 1801 to 1860, 37 new plants were built in the Urals, including 3 copper smelters. Next to the previously built factories, auxiliary plants were built, which used the wastewater of the main factories and were actually their rolling shops. During the same period, 14 Ural copper smelters were closed due to the refusal of mints' coinage and the transition to paper money. To stabilize the situation, the government in 1834 abolished all taxes from factories, except for tithes. At the same time, the level of copper production at the beginning of the century was reached only in 1826. Since the 1850s, due to the appearance of cheap English, and later — Chilean, North American, and Australian copper on the market, the metallurgical industry of the Southern Urals entered a period of long-term crisis. In 1859, the price of Russian copper in comparison with the level of 1854 had decreased by 50%.
Steam engines were introduced and took root in the Urals slowly. The first steam engines appeared in the Ural factories in the last years of the 18th century. From 1800 to the 1810s, machines often failed and consumed a lot of firewood, which caused their slow spread. In the 1830s, the machines became more reliable, there were machine-building enterprises that designed, assembled, and repaired steam engines. In 1834, the Cherepanovs built the first steam locomotive and the first railway with a length of 853.4 m, designed to deliver ore from the Vysokogorsky mine to the Vysky plant. By 1840, the number of steam engines in the Ural factories reached 73 units. Also in the 1840s, hydraulic turbines became widespread in the Urals, replacing low-performance water wheels.
In the 1840s, the introduction of the Kontuaz method of iron production began at the Ural factories. The Yuryuzan-Ivanovsky plant in 1840 and the Simsky plant in 1842 were the first to switch to it. Subsequently, the Kontuaz forges were built at state-owned factories, and later at private ones. By 1861, 364 Kontuaz forges operated at 37 factories in the Urals. In the 1860s and 1870s, when production was already supplanted by steelmaking, Lancashire forges appeared in the Urals. A more productive puddling process was introduced in the Urals in 1817 in a test mode at the Pozhevsky plant, from 1825 to 1830 at the Nizhniy Tagil plant, and in September 1837 the Votkinsky plant completely switched to puddling. By 1861, among 58 factories, there were 201 puddling furnaces, 34 gas puddling, 153 welding, and 23 gas welding furnaces. Before the widespread use of steel-making processes in 1857, P. M. Obukhov invented a cheap method, called Obukhov, of steel production at the Zlatoust plant.
The height of the Ural blast furnaces in the 19th century reached 18 meters, which significantly exceeded the height of European furnaces. This advantage made it possible to carry out the blast furnace process on a cold blast with relatively low costs. This led to the later introduction of hot blast in the Urals, although successful experiments on its use were carried out back in the 1830s and 1840s at the Kushvinsky, Lysvensky, Verkh-Isetsky, and other plants. Thanks to the events of the Industrial Revolution in England, the average productivity of blast furnaces in the Ural factories in the second half of the 19th century was already inferior to those in England. So, in 1800, one blast furnace in the Urals produced an average of 91.6 thousand poods of iron, and in 1860, 137 thousand poods. British furnaces produced respectively 65.5 thousand and 426 thousand poods.
Since the middle of the 19th century, rolling production has developed, and steel and iron casting continued to develop. Castings from the Kasli plant have become world-famous. At large factories, rail rolling production was mastered. In 1859, 12.2 million poods of iron were smelted at the factories of the Urals, which was about 2/3 of all iron smelted in Russia.
During the Patriotic War of 1812, many Ural factories were converted to weapons production facilities. The Kamensk plant issued 87,274 poods of artillery pieces during 1810-1813. During the war years, 47 private factories crossed over to manufacturing shells, some of which had never produced such products. Often, production plans were frustrated, and the cast guns did not withstand testing due to haste and unexploited technologies. The victory in the Patriotic War of 1812 did not allow the authorities to identify these problems. At the same time, the war substantially reduced the demand of the domestic market for metal, which led to inflation and long standstills at factories.
The casting of artillery pieces resumed in 1834. Before the beginning of the Crimean War, from 1834 to 1852, the Ural factories cast 1,542 guns instead of the 3,250 ordered, on average, orders for the production of shells were fulfilled by about 23-25 %. Already during the war, the supply of 60-pounder guns was disrupted due to a gap in testing. During the defense of Sevastopol, 900 Ural guns were unsuitable.
The development of the Ural copper-smelting industry in the 19th century was associated with an increase in the height of furnaces, the use of hot blast and coal. Steam engines began to be used to lift the ore to the surface and pump water out of the mines. Copper production has shifted to the Northern and Southern Urals. In the second half of the 19th century, copper smelting began to decline due to the depletion of deposits and reduced demand from mints.
Since the 1820s, gold and platinum mining has been rapidly developing in the Urals. In 1823, there were 309 mines in the region. 105 poods of gold were mined. In 1842, the largest Ural gold nugget weighing 36.04 kg was found at the Tsarevo-Alexandrovsky mine. Platinum was mined at the mines of the Nizhniy Tagil district of the Demidovs, at the Isov mines of the Verkh-Isetsk district, and at the Krestovozdvizhensk mines. In the 19th century, the Urals produced 93–95% of the world's platinum.
In the 18th century and first half of the 19th century, the use of adolescent and child labor was widespread in the mines and factories of the Urals, sanctioned by a number of legislative acts and reinforced in the Mining Statute of 1842. In the 1850s, children and adolescents accounted for 30 to 50% of all workers in factories, and in mines - from 40 to 85%. At the beginning of the 19th century, women were employed in 17% of factories. In the 1850s, female labor was already more widely used, and the proportion of women was about 10% of the workers.
By the time of the abolition of serfdom, the Ural metallurgy was in a deep crisis, which was facilitated by a sharp increase in grain prices in 1857 due to crop failures, especially significant in the Northern Urals. Of the 41 mining districts, 13 had a total debt of 8.1 million rubles, which increased to 12.4 million rubles by the end of the 1860s. The transition to freelance labor led to a sharp reduction in the number of workers in factories. If in 1860 there were 8,663 workers at the seven Goroblagodatsky factories, in 1861 — 7,030, then in 1862 the number decreased to 4,671 people, in 1863 - to 3,097, and in 1864 - to 2,839 people. During this period, there were 154 metallurgical plants of various specializations and gold crafts in the Urals, including 24 state-owned, 78 possessory, and 52 manorial ones. Of these, 115 enterprises were located within the Perm Governorate, 26 in the Orenburg Governorate, and 13 in the Vyatka Governorate.
In 1824, to support the miners, the government established a State Loan Bank. According to the data of 1849, the State Loan Bank pledged the Kanonikolsky, Beloretsky, Voskresensky, Troitsky, Blagoveshchensky, Yuryuzan-Ivanovsky mining districts a total amount of 1,106,995 rubles in silver. In 1851, the Beloretsk Mining District was re-mortgaged to the bank, and in 1852, the Preobrazhensky Plant was mortgaged to private investors in the amount of 300 thousand rubles with the obligation to pay the debt to the bank. In general, the pre-reform level of production at the Ural factories was reached only in 1870. The Government provided support to mining companies in the form of soft loans secured by metals and orders for the construction of railways. The industry was heavily influenced by commercial banks and wealthy entrepreneurs who bought up entire mountain districts. In the 1880s, mining plants began to be incorporated.
In 1870, at the invitation of the Russian government, the Austrian metallurgist P. von Tunner visited an industrial exhibition in St. Petersburg and inspected the Ural metallurgical plants. As a result of this trip, in 1871, he published a book with a description of the factories, in which he noted the technical and organizational backwardness of the metallurgy of the Urals, and the high cost of production. Von Tunner's book eventually became the first systematic description of the Ural mining plants.
The lack of customs regulation of foreign supplies of metals had a negative impact on the development of Ural metallurgy. European metallurgical companies in the 2nd half of the 19th century actively united in syndicates to regulate market prices and control production volumes. The surplus, as a rule, was exported to the Russian markets and sold at low prices. This led to overstocking of markets and lower prices for metals. The amount of unsold metal at the Nizhny Novgorod Fair was 0.9 million poods in 1883, 1.16 million poods in 1884, 1.84 million poods in 1885, and 1.94 million poods in 1886.
In the 1880s and 1890s, 16 metallurgical plants were built in the Urals, including the large Chusovsky (1883) and Nadezhdinsky plants(1896). The old factories underwent significant modernization, including the introduction of mechanical processing plants, the construction of open-hearth shops, power plants, and air heaters. The introduction of hot blast was promoted in the 1860s and 1870s in the factories of the Urals. Rashet blast furnaces equipped with trapping devices for heating the air were used. Despite these successes, since 1896, the Urals has lost the primacy in the share of metal produced to enterprises in Southern Russia. In 1900, the Ural factories smelted 50.1 million poods of iron. The first open-hearth furnaces in the Urals were built in 1871 at Votkinsky and in 1875 at the Perm Cannon Factory. By 1900, there were a total of 42 of the furnace. Bessemerization in the Urals was first introduced at the Nizhnesaldinsky and Katav-Ivanovsky plants. In 1900, 48.9% of the Ural finished ferrous metal was produced by open-hearth and Bessemer methods.
By the end of the 19th century, with the expansion of factories in the Urals, the problems with the depletion of forest resources and environmental pollution intensified.
In 1899, on behalf of S. Yu. Witte, an expedition of scientists headed by D. I. Mendeleev was sent to the Urals, the main task of which was to find out the causes of stagnation in the metallurgical industry. In his report, Mendeleev called the main reasons for the industrial crisis of the Ural metallurgy, off-road conditions, the preserved serf relations between factory owners and peasants, the use of outdated equipment and technologies, the monopoly of large entrepreneurs on ore and forests, and the arbitrariness of local authorities. As a result of the expedition, a plan was drawn up for the development of Ural metallurgy with an increase in the volume of iron smelting to 300 million poods per year, which did not find the support of the authorities. | 0 | Metallurgy |
Recalescence is an increase in temperature that occurs while cooling metal when a change in structure with an increase in entropy occurs. The heat responsible for the change in temperature is due to the change in entropy. When a structure transformation occurs the Gibbs free energy of both structures are more or less the same. Therefore, the process will be exothermic. The heat provided is the latent heat.
Recalescence also occurs after supercooling, when the supercooled liquid suddenly crystallizes, forming a solid but releasing heat in the process. | 0 | Metallurgy |
Signaling Gateway is a web portal dedicated to signaling pathways powered by the San Diego Supercomputer Center at the University of California, San Diego. It was initiated by a collaboration between the Alliance for Cellular Signaling and Nature. A primary feature is the Molecule Pages database. | 1 | Gene expression + Signal Transduction |
Sodium–potassium alloy, colloquially called NaK (commonly pronounced ), is an alloy of the alkali metals sodium (Na, atomic number 11) and potassium (K, atomic number 19) that is normally liquid at room temperature. Various commercial grades are available. NaK is highly reactive with water (like its constituent elements) and may catch fire when exposed to air, so must be handled with special precautions. | 0 | Metallurgy |
Early hot rolling strip mills did not produce strip suitable for tinning, but in 1929 cold rolling began to be used to reduce the gauge further, which made tinning achievable. The plate was then tinned using the process outlined above. | 0 | Metallurgy |
The use of two wires of iridium/rhodium alloys can provide a thermocouple that can be used up to about 2000 °C in inert atmospheres. | 0 | Metallurgy |
Leaching is a process widely used in extractive metallurgy where ore is treated with chemicals to convert the valuable metals within the ore, into soluble salts while the impurity remains insoluble. These can then be washed out and processed to give the pure metal; the materials left over are commonly known as tailings. Compared to pyrometallurgy, leaching is easier to perform, requires less energy and is potentially less harmful as no gaseous pollution occurs. Drawbacks of leaching include its lower efficiency and the often significant quantities of waste effluent and tailings produced, which are usually either highly acidic or alkali as well as toxic (e.g. bauxite tailings).
There are four types of leaching:
# Cyanide leaching (e.g. gold ore)
# Ammonia leaching (e.g. crushed ore)
# Alkali leaching (e.g. bauxite ore)
# Acid leaching (e.g. sulfide ore)
Leaching is also notable in the extraction of rare earth elements, which consists of lanthanides, yttrium and scandium. | 0 | Metallurgy |
In the nervous system there are primarily two ways of propagating signals. By far the most common method of intracellular signal propagation is the action potential. The dendrites of neurons contain ionotropic (aka ligand-gated ion channel) and metabotropic neurotransmitter receptors that bind chemical neurotransmitters. At ionotropic receptors, these chemical neurotransmitters cause quick changes in ion flux into or out of the cell. The resulting internal voltage change in the dendrites is propagated towards the cell body and axon hillock, where a large concentration of voltage-gated ion channels typically exists. If some voltage threshold is met, voltage gated sodium channels open up, letting in a critical charge of sodium, and the positive current propagates down the axon towards the presynaptic axon terminal. This action potential leads to neurotransmitter vesicular release at in this terminal.
While action potentials are the typical means of signal propagation in the nervous system, some sensory neurons use graded potentials to trigger vesicular release. These cells are typically short enough that regenerative action potentials aren't needed to cause a large enough voltage change at the presynaptic terminal. For example, photoreceptor cells in the eye produce graded potentials in response to light, and these graded potentials can directly lead to neurotransmitter release. | 1 | Gene expression + Signal Transduction |
The word "nitinol" is derived from its composition and its place of discovery: (Nickel Titanium-Naval Ordnance Laboratory). William J. Buehler along with Frederick E. Wang, discovered its properties during research at the Naval Ordnance Laboratory in 1959. Buehler was attempting to make a better missile nose cone, which could resist fatigue, heat and the force of impact. Having found that a 1:1 alloy of nickel and titanium could do the job, in 1961 he presented a sample at a laboratory management meeting. The sample, folded up like an accordion, was passed around and flexed by the participants. One of them applied heat from his pipe lighter to the sample and, to everyone's surprise, the accordion-shaped strip contracted and took its previous shape.
While the potential applications for nitinol were realized immediately, practical efforts to commercialize the alloy did not take place until a decade later. This delay was largely because of the extraordinary difficulty of melting, processing and machining the alloy. Even these efforts encountered financial challenges that were not readily overcome until the 1980s, when these practical difficulties finally began to be resolved.
The discovery of the shape-memory effect in general dates back to 1932, when Swedish chemist Arne Ölander first observed the property in gold–cadmium alloys. The same effect was observed in Cu-Zn (brass) in the early 1950s. | 0 | Metallurgy |
The oldest and most widely used expression systems are cell-based and may be defined as the "combination of an expression vector, its cloned DNA, and the host for the vector that provide a context to allow foreign gene function in a host cell, that is, produce proteins at a high level". Overexpression is an abnormally and excessively high level of gene expression which produces a pronounced gene-related phenotype.
There are many ways to introduce foreign DNA to a cell for expression, and many different host cells may be used for expression — each expression system has distinct advantages and liabilities. Expression systems are normally referred to by the host and the DNA source or the delivery mechanism for the genetic material. For example, common hosts are bacteria (such as E. coli, B. subtilis), yeast (such as S. cerevisiae) or eukaryotic cell lines. Common DNA sources and delivery mechanisms are viruses (such as baculovirus, retrovirus, adenovirus), plasmids, artificial chromosomes and bacteriophage (such as lambda). The best expression system depends on the gene involved, for example the Saccharomyces cerevisiae is often preferred for proteins that require significant posttranslational modification. Insect or mammal cell lines are used when human-like splicing of mRNA is required. Nonetheless, bacterial expression has the advantage of easily producing large amounts of protein, which is required for X-ray crystallography or nuclear magnetic resonance experiments for structure determination.
Because bacteria are prokaryotes, they are not equipped with the full enzymatic machinery to accomplish the required post-translational modifications or molecular folding. Hence, multi-domain eukaryotic proteins expressed in bacteria often are non-functional. Also, many proteins become insoluble as inclusion bodies that are difficult to recover without harsh denaturants and subsequent cumbersome protein-refolding.
To address these concerns, expressions systems using multiple eukaryotic cells were developed for applications requiring the proteins be conformed as in, or closer to eukaryotic organisms: cells of plants (i.e. tobacco), of insects or mammalians (i.e. bovines) are transfected with genes and cultured in suspension and even as tissues or whole organisms, to produce fully folded proteins. Mammalian in vivo expression systems have however low yield and other limitations (time-consuming, toxicity to host cells,..). To combine the high yield/productivity and scalable protein features of bacteria and yeast, and advanced epigenetic features of plants, insects and mammalians systems, other protein production systems are developed using unicellular eukaryotes (i.e. non-pathogenic <nowiki/>Leishmania<nowiki/> cells). | 1 | Gene expression + Signal Transduction |