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Oil refinery For example, benzene has been shown to have a relationship with leukemia, however studies examining benzene exposure and resultant leukemia specifically in the context of oil refinery workers have come to opposing conclusions. Asbestos-related mesothelioma is another particular cancer-carcinogen relationsh... | https://en.wikipedia.org/wiki?curid=195137 |
Oil refinery Exposure can also occur through ingestion via contaminated water, but this is unlikely in an occupational setting. Dermal exposure and absorption is also possible, but is again less likely in an occupational setting where appropriate personal protective equipment is in place. OSHA, NIOSH, and ACGIH have al... | https://en.wikipedia.org/wiki?curid=195137 |
Oil refinery However, Bureau of Labor (BLS) statistical reports indicate that petroleum refinery workers have a significantly lower rate of occupational injury (0.7 OSHA-recordable cases per 100 full-time workers) than all industries (3.1), oil and gas extraction (1.0), and petroleum manufacturing in general (1.6). Hea... | https://en.wikipedia.org/wiki?curid=195137 |
Oil refinery While not specific to the industry, oil refinery workers may also be at risk for hazards such as vehicle-related accidents, machinery-associated injuries, work in a confined space, explosions/fires, ergonomic hazards, shift-work related sleep disorders, and falls. The theory of hierarchy of controls can be... | https://en.wikipedia.org/wiki?curid=195137 |
Oil refinery These occur when many of the engineering controls are shut down or suppressed, and may be especially dangerous to workers. Detailed coordination is necessary to ensure that maintenance of one part of the facility will not cause dangerous exposures to those performing the maintenance, or to workers in other... | https://en.wikipedia.org/wiki?curid=195137 |
Oil refinery Below is a list of the most common regulations referenced in petroleum refinery safety citations issued by OSHA: Corrosion of metallic components is a major factor of inefficiency in the refining process. Because it leads to equipment failure, it is a primary driver for the refinery maintenance schedule. C... | https://en.wikipedia.org/wiki?curid=195137 |
Oil refinery Monitoring methods include both offline checks taken during maintenance and online monitoring. Offline checks measure corrosion after it has occurred, telling the engineer when equipment must be replaced based on the historical information they have collected. This is referred to as preventative management... | https://en.wikipedia.org/wiki?curid=195137 |
Oil refinery In areas of minimal corrosion, cheap materials are preferable, but when bad corrosion can occur, more expensive but longer lasting materials should be used. Other materials methods come in the form of protective barriers between corrosive substances and the equipment metals. These can be either a lining of... | https://en.wikipedia.org/wiki?curid=195137 |
Berylliosis Berylliosis, or chronic beryllium disease (CBD), is a chronic allergic-type lung response and chronic lung disease caused by exposure to beryllium and its compounds, a form of beryllium poisoning. It is distinct from acute beryllium poisoning, which became rare following occupational exposure limits establi... | https://en.wikipedia.org/wiki?curid=195514 |
Berylliosis Other symptoms include chest pain, joint aches, weight loss, and fever. Rarely, one can get granulomas in other organs including the liver. The onset of symptoms can range from weeks up to tens of years from the initial exposure. In some individuals, a single exposure to beryllium can cause berylliosis. In ... | https://en.wikipedia.org/wiki?curid=195514 |
Berylliosis Definitive diagnosis of berylliosis is based on history of beryllium exposures, documented beryllium sensitivity and granulomatous inflammation on lung biopsy. Given the invasive nature of a lung biopsy diagnosis can also be based on clinical history consistent with berylliosis, abnormal chest x-ray or CT s... | https://en.wikipedia.org/wiki?curid=195514 |
Berylliosis One study found that ground-glass opacities were more commonly seen on CT scan in berylliosis than in sarcoidosis. In later stages hilar lymphadenopathy, interstitial pulmonary fibrosis and pleural thickening. is an occupational disease. Relevant occupations are those where beryllium is mined, processed or ... | https://en.wikipedia.org/wiki?curid=195514 |
Berylliosis The American Conference of Governmental Industrial Hygienists (ACGIH), which is an independent organization of experts in the field of occupational health, has proposed a threshold limit value (TLV) of in a 2006 Notice of Intended Change (NIC). This TLV is 40 times lower than the current OSHA permissible ex... | https://en.wikipedia.org/wiki?curid=195514 |
Berylliosis There is no cure for berylliosis; the goals of treatment are to reduce symptoms and slow the progression of disease. Although the evidence that stopping exposure to beryllium decreases progression of the disease is limited, it is still considered to be an accepted approach to treatment in any stage of disea... | https://en.wikipedia.org/wiki?curid=195514 |
Berylliosis Stopping exposure to beryllium in those sensitized has not been definitively shown to stop the progression to CBD. The overall prevalence of CBD among workers exposed to beryllium has ranged from 1 – 5% depending on industry and time period of study. The general population is unlikely to develop acute or ch... | https://en.wikipedia.org/wiki?curid=195514 |
Berylliosis Beryllium sensitivity testing was first performed as a cutaneous beryllium patch test in the early 1950s, but was discontinued due to the test stimulating sensitization or aggravating existing chronic beryllium disease. In the 1990s, the DOE began screening employees using the BeLPT test in facilities where... | https://en.wikipedia.org/wiki?curid=195514 |
Legionella The genus is a pathogenic group of Gram-negative bacteria that includes the species "L. pneumophila", causing legionellosis (all illnesses caused by "Legionella") including a pneumonia-type illness called Legionnaires' disease and a mild flu-like illness called Pontiac fever. "Legionella" may be visualized w... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella war veterans, occurring in the same city as—and within days of the 200th anniversary of—the signing of the Declaration of Independence, was widely publicized and caused great concern in the United States. On January 18, 1977, the causative agent was identified as a previously unknown bacterium subsequently n... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella Although the plating method is quite specific for most species of "Legionella", one study has shown that a coculture method that accounts for the close relationship with amoebae may be more sensitive since it can detect the presence of the bacteria even when masked by their presence inside the amoeba. Conseq... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella In the natural environment, "Legionella" lives within amoebae such as "Acanthamoeba" spp., "Naegleria" spp., and "Vermamoeba vermiformis", or other protozoa such as "Tetrahymena pyriformis". Upon inhalation, the bacteria can infect alveolar macrophages, where the bacteria can replicate. This results in Legio... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella According to "Infection Control and Hospital Epidemiology", hospital-acquired "Legionella" pneumonia has a fatality rate of 28%, and the source is the water distribution system. "Legionella" species typically exist in nature at low concentrations, in groundwater, lakes, and streams. They reproduce after ente... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella It was previously believed that transmission of the bacterium was restricted to much shorter distances. A team of French scientists reviewed the details of an epidemic of Legionnaires' disease that took place in Pas-de-Calais, northern France, in 2003–2004. Of 86 confirmed cases during the outbreak, 18 resul... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella The high cost incurred with this method arises from the extensive retrofitting required for existing complex distribution systems in large facilities and the energy cost of chilling or heating the water and maintaining the required temperatures at all times and at all distal points within the system. Tempera... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella Copper and silver ion concentrations must be maintained at optimal levels, taking into account both water flow and overall water usage, to control "Legionella". The disinfection function within all of a facility's water distribution network occurs within 30 to 45 days. Key engineering features such as 10 amp... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella Furthermore, tolytriazole, a common additive in cooling water treatment, could bind the copper making it ineffective. Ionization became the first such hospital disinfection process to have fulfilled a proposed four-step modality evaluation; by then, it had been adopted by over 100 hospitals. Additional studi... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella Like chlorine and chlorine dioxide, monochloramine is approved by the Environmental Protection Agency as a primary potable water disinfectant. Environmental Protection Agency registration requires a biocide label which lists toxicity and other data required for all registered biocides. If the product is bein... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella An employer or property owner must follow an Approved Code of Practice, or achieve the same result. Failure to show monitoring records to at least this standard has resulted in several high-profile prosecutions, e.g. Nalco + Bulmers – neither could prove a sufficient scheme to be in place whilst investigatin... | https://en.wikipedia.org/wiki?curid=195768 |
Legionella A former Soviet bioengineer, Sergei Popov, stated in 2000 that his team experimented with genetically enhanced bioweapons, including "Legionella". Popov worked as a lead researcher at the Vector Institute from 1976 to 1986, then at Obolensk until 1992, when he defected to the West. He later divulged much of ... | https://en.wikipedia.org/wiki?curid=195768 |
List of chemical engineers This is a list of notable chemical engineers, people who studied or practiced chemical engineering. The main list is those who achieved status in chemical engineering or a closely related field such as management or science. At the foot of the page is a list of people with chemical engineerin... | https://en.wikipedia.org/wiki?curid=195833 |
Anaerobic glycolysis is the transformation of glucose to lactate when limited amounts of oxygen (O) are available. is only an effective means of energy production during short, intense exercise, providing energy for a period ranging from 10 seconds to 2 minutes. The anaerobic glycolysis (lactic acid) system is dominant... | https://en.wikipedia.org/wiki?curid=195939 |
Uncle Tungsten Uncle Tungsten: Memories of a Chemical Boyhood is a memoir by Oliver Sacks about his childhood published in 2001. The book is named after Sacks's Uncle Dave, whom Oliver nicknamed because he was secretary of a business named Tungstalite, which made incandescent lightbulbs with a tungsten filament. was fa... | https://en.wikipedia.org/wiki?curid=195961 |
Nanocrystalline silicon (nc-Si), sometimes also known as microcrystalline silicon (μc-Si), is a form of porous silicon. It is an allotropic form of silicon with paracrystalline structure—is similar to amorphous silicon (a-Si), in that it has an amorphous phase. Where they differ, however, is that nc-Si has small grains... | https://en.wikipedia.org/wiki?curid=197129 |
Nanocrystalline silicon Although it currently cannot attain the mobility that poly-Si can, it has the advantage over poly-Si that it is easier to fabricate, as it can be deposited using conventional low temperature a-Si deposition techniques, such as PECVD, as opposed to laser annealing or high temperature CVD processe... | https://en.wikipedia.org/wiki?curid=197129 |
Lead styphnate (lead 2,4,6-trinitroresorcinate, CHNOPb ), whose name is derived from styphnic acid, is an explosive used as a component in primer and detonator mixtures for less sensitive secondary explosives. is only slightly soluble in water and methanol. Samples of lead styphnate vary in color from yellow to gold, o... | https://en.wikipedia.org/wiki?curid=197213 |
Lead styphnate The water molecule is coordinated to the metal and is also hydrogen-bonded to the anion. Many of the Pb-O distances are short, indicating some degree of covalency. The styphnate ions lie in approximately parallel planes linked by Pb atoms. Lead styphnate's heat of formation is −835 kJ mol. The loss of wa... | https://en.wikipedia.org/wiki?curid=197213 |
Delay line memory is a form of computer memory, now obsolete, that was used on some of the earliest digital computers. Like many modern forms of electronic computer memory, delay line memory was a refreshable memory, but as opposed to modern random-access memory, delay line memory was sequential-access. Analog delay li... | https://en.wikipedia.org/wiki?curid=197673 |
Delay line memory Eckert and John Mauchly applied for a patent for a delay line memory system on October 31, 1947; the patent was issued in 1953. This patent focused on mercury delay lines, but it also discussed delay lines made of strings of inductors and capacitors, magnetostrictive delay lines, and delay lines built... | https://en.wikipedia.org/wiki?curid=197673 |
Delay line memory This was not an ideal situation; it required careful aiming which was difficult for smaller mobile radars, and did not remove other sources of clutter-like reflections from features like prominent hills, and in the worst case would allow low-flying enemy aircraft to literally fly "under the radar". To... | https://en.wikipedia.org/wiki?curid=197673 |
Delay line memory The Japanese deployed a system consisting of a quartz element with a powdered glass coating that reduced surface waves that interfered with proper reception. The United States Naval Research Laboratory used steel rods wrapped into a helix, but this was useful only for low frequencies under 1 MHz. Rayt... | https://en.wikipedia.org/wiki?curid=197673 |
Delay line memory One problem with practical development was the lack of a suitable memory device, and Eckert's work on the radar delays gave him a major advantage over other researchers in this regard. For a computer application the timing was still critical, but for a different reason. Conventional computers have a n... | https://en.wikipedia.org/wiki?curid=197673 |
Delay line memory The system heated the mercury to a uniform above-room temperature setting of 40 °C (104 °F), which made servicing the tubes hot and uncomfortable work. (Alan Turing proposed the use of gin as an ultrasonic delay medium, claiming that it had the necessary acoustic properties.) A considerable amount of ... | https://en.wikipedia.org/wiki?curid=197673 |
Delay line memory In the UNIVAC I the capacity of an individual delay line was smaller, each column stored 120 bits (although the term "bit" was not in popular use at the time), requiring seven large memory units with 18 columns each to make up a 1000-word store. Combined with their support circuitry and amplifiers, th... | https://en.wikipedia.org/wiki?curid=197673 |
Delay line memory Unlike the compressive wave, however, the torsional waves are considerably more resistant to problems caused by mechanical imperfections, so much so that the wires could be wound into a loose coil and pinned to a board. Due to their ability to be coiled, the wire-based systems could be built as "long"... | https://en.wikipedia.org/wiki?curid=197673 |
Delay line memory A similar solution to the magnetostrictive system was to use delay lines made entirely of a piezo material, typically quartz. Current fed into one end of the crystal would generate a compressive wave that would flow to the other end, where it could be read. In effect, piezoelectric delays simply repla... | https://en.wikipedia.org/wiki?curid=197673 |
Delay line memory Electric delay lines are used for shorter delay times (ns to several µs). They consist of a long electric line or are made of discrete inductors and capacitors, which are arranged in a chain. To shorten the total length of the line it can be wound around a metal tube, getting some more capacitance aga... | https://en.wikipedia.org/wiki?curid=197673 |
Delay line memory This approach also reduces interference to nearby circuits. | https://en.wikipedia.org/wiki?curid=197673 |
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha decay, bet... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay The energy of an excited nucleus may be emitted as a gamma ray in a process called gamma decay, or that energy may be lost when the nucleus interacts with an orbital electron causing its ejection from the atom, in a process called internal conversion. Another type of radioactive decay results in produ... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Well-known examples are uranium and thorium, but also included are naturally occurring long-lived radioisotopes, such as potassium-40. Another 50 or so shorter-lived radionuclides, such as radium-226 and radon-222, found on Earth, are the products of decay chains that began with the primordial nuclide... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay It became clear from these experiments that there was a form of invisible radiation that could pass through paper and was causing the plate to react as if exposed to light. At first, it seemed as though the new radiation was similar to the then recently discovered X-rays. Further research by Becquerel... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Their research on the penetrating rays in uranium and the discovery of radium launched an era of using radium for the treatment of cancer. Their exploration of radium could be seen as the first peaceful use of nuclear energy and the start of modern nuclear medicine. The dangers of ionizing radiation d... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Despite this, there were some early systematic hazard investigations, and as early as 1902 William Herbert Rollins wrote almost despairingly that his warnings about the dangers involved in the careless use of X-rays were not being heeded, either by industry or by his colleagues. By this time, Rollins ... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Only a year after Röntgen's discovery of X rays, the American engineer Wolfram Fuchs (1896) gave what is probably the first protection advice, but it was not until 1925 that the first International Congress of Radiology (ICR) was held and considered establishing international protection standards. The... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay The International System of Units (SI) unit of radioactive activity is the becquerel (Bq), named in honor of the scientist Henri Becquerel. One Bq is defined as one transformation (or decay or disintegration) per second. An older unit of radioactivity is the curie, Ci, which was originally defined as ... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay is seen in all isotopes of all elements of atomic number 83 (bismuth) or greater. Bismuth-209, however, is only very slightly radioactive, with a half-life greater than the age of the universe; radioisotopes with extremely long half-lives are considered effectively stable for practical purposes. In an... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Gamma decay as a separate phenomenon, with its own half-life (now termed isomeric transition), was found in natural radioactivity to be a result of the gamma decay of excited metastable nuclear isomers, which were in turn created from other types of decay. Although alpha, beta, and gamma radiations we... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Isolated proton emission was eventually observed in some elements. It was also found that some heavy elements may undergo spontaneous fission into products that vary in composition. In a phenomenon called cluster decay, specific combinations of neutrons and protons other than alpha particles (helium n... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay In this process, beta electron-decay of the parent nuclide is not accompanied by beta electron emission, because the beta particle has been captured into the K-shell of the emitting atom. An antineutrino is emitted, as in all negative beta decays. Radionuclides can undergo a number of different reacti... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay More common in heavy nuclides is competition between alpha and beta decay. The daughter nuclides will then normally decay through beta or alpha, respectively, to end up in the same place. results in a reduction of summed rest mass, once the released energy (the "disintegration energy") has escaped in ... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Thus, while the sum of the rest masses of the particles is not conserved in radioactive decay, the "system" mass and system invariant mass (and also the system total energy) is conserved throughout any decay process. This is a restatement of the equivalent laws of conservation of energy and conservati... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay However, whatever the probability is, it does not change along time. This is in marked contrast to complex objects which do show aging, such as automobiles and humans. These aging systems do have a chance of breakdown per unit of time that increases from the moment they begin their existence. Aggregat... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Therefore, given a sample of a particular radioisotope, the number of decay events expected to occur in a small interval of time is proportional to the number of atoms present , that is Particular radionuclides decay at different rates, so each has its own decay constant . The expected decay is propor... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay In other words, the number of second generation nuclei increases as a result of the first generation nuclei decay of , and decreases as a result of its own decay into the third generation nuclei . The sum of these two terms gives the law for a decay chain for two nuclides: The rate of change of , that... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Consider the case of one initial nuclide that can decay into either of two products, that is ' and ' in parallel. For example, in a sample of potassium-40, 89.3% of the nuclei decay to calcium-40 and 10.7% to argon-40. We have for all time : which is constant, since the total number of nuclides remain... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Each atom "lives" for a finite amount of time before it decays, and it may be shown that this mean lifetime is the arithmetic mean of all the atoms' lifetimes, and that it is , which again is related to the decay constant as follows: This form is also true for two-decay processes simultaneously ", ins... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay The following equation can be shown to be valid: Since radioactive decay is exponential with a constant probability, each process could as easily be described with a different constant time period that (for example) gave its "(1/3)-life" (how long until only 1/3 is left) or "(1/10)-life" (a time perio... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay For example, chemical bonds can affect the rate of electron capture to a small degree (in general, less than 1%) depending on the proximity of electrons to the nucleus. In Be, a difference of 0.9% has been observed between half-lives in metallic and insulating environments. This relatively large effec... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Comparison of laboratory experiments over the last century, studies of the Oklo natural nuclear reactor (which exemplified the effects of thermal neutrons on nuclear decay), and astrophysical observations of the luminosity decays of distant supernovae (which occurred far away so the light has taken a ... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay An unexpected series of experimental results for the rate of decay of heavy highly charged radioactive ions circulating in a storage ring has provoked theoretical activity in an effort to find a convincing explanation. The rates of weak decay of two radioactive species with half lives of about 40 s an... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay These rearrangements and transformations may be hindered energetically, so that they do not occur immediately. In certain cases, random quantum vacuum fluctuations are theorized to promote relaxation to a lower energy state (the "decay") in a phenomenon known as quantum tunneling. half-life of nuclide... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Such a collapse (a gamma-ray "decay event") requires a specific activation energy. For a snow avalanche, this energy comes as a disturbance from outside the system, although such disturbances can be arbitrarily small. In the case of an excited atomic nucleus decaying by gamma radiation in a spontaneou... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Thus, all radioactive nuclei are, therefore, relatively young with respect to the birth of the universe, having formed later in various other types of nucleosynthesis in stars (in particular, supernovae), and also during ongoing interactions between stable isotopes and energetic particles. For example... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Because the process is not thought to vary significantly in mechanism over time, it is also a valuable tool in estimating the absolute ages of certain materials. For geological materials, the radioisotopes and some of their decay products become trapped when a rock solidifies, and can then later be us... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay This effect can be used to separate isotopes by chemical means. The Szilard–Chalmers effect was discovered in 1934 by [Leó Szilárd]] and Thomas A. Chalmers. They observed that after bombardment by neutrons, the breaking of a bond in liquid ethyl iodide allowed radioactive iodine to be removed. Radioac... | https://en.wikipedia.org/wiki?curid=197767 |
Radioactive decay Any decay daughters that are the result of an alpha decay will also result in helium atoms being created. An example is the natural decay chain of U: Some radionuclides may have several different paths of decay. For example, approximately 36% of bismuth-212 decays, through alpha-emission, to thallium-... | https://en.wikipedia.org/wiki?curid=197767 |
Decay chain In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay directly to a stable state, but rather undergo a series of decays until... | https://en.wikipedia.org/wiki?curid=197774 |
Decay chain These can range from nearly instantaneous (less than 10 seconds) to more than 10 years. The intermediate stages each emit the same amount of radioactivity as the original radioisotope (i.e. there is a one-to-one relationship between the numbers of decays in successive stages) but each stage releases a diffe... | https://en.wikipedia.org/wiki?curid=197774 |
Decay chain All the elements and isotopes found on Earth, with the exceptions of hydrogen, deuterium, helium, helium-3, and perhaps trace amounts of stable lithium and beryllium isotopes which were created in the Big Bang, were created by the s-process or the r-process in stars, and for those to be today a part of the ... | https://en.wikipedia.org/wiki?curid=197774 |
Decay chain The heaviest elements such as lead have close to 1.5 neutrons per proton(e.g. 1.536 in lead-208). No nuclide heavier than lead-208 is stable; these heavier elements have to shed mass to achieve stability, most usually as alpha decay. The other common decay method for isotopes with a high neutron to proton r... | https://en.wikipedia.org/wiki?curid=197774 |
Decay chain There are other decay modes, but they invariably occur at a lower probability than alpha or beta decay. (It should not be supposed that these chains have no branches: the diagram below shows a few branches of chains, and in reality there are many more, because there are many more isotopes possible than are ... | https://en.wikipedia.org/wiki?curid=197774 |
Decay chain Near the end of that chain is bismuth-209, which was long thought to be stable. Recently, however, bismuth-209 was found to be unstable with a half-life of 19 billion billion years; it is the last step before stable thallium-205. In the distant past, around the time that the solar system formed, there were ... | https://en.wikipedia.org/wiki?curid=197774 |
Decay chain All four chains also produce helium-4 (alpha particles are helium-4 nuclei). Three main decay chains (or families) are observed in nature, commonly called the thorium series, the radium or uranium series, and the actinium series, representing three of these four classes, and ending in three different, stabl... | https://en.wikipedia.org/wiki?curid=197774 |
Decay chain Since 1945, the testing and use of nuclear weapons has also released numerous radioactive fission products. Almost all such isotopes decay by either β or β decay modes, changing from one element to another without changing atomic mass. These later daughter products, being closer to stability, generally have... | https://en.wikipedia.org/wiki?curid=197774 |
Decay chain All these isotopes are stable and are also present in nature as primordial nuclides, but their excess amounts in comparison with lead-204 (which has only a primordial origin) can be used in the technique of uranium-lead dating to date rocks. The 4n chain of Th-232 is commonly called the "thorium series" or ... | https://en.wikipedia.org/wiki?curid=197774 |
Decay chain Since this series was only discovered and studied in 1947–1948, its nuclides do not have historic names. One unique trait of this decay chain is that the noble gas radon is only produced in a rare branch and not the main decay sequence; thus, it does not migrate through rock nearly as much as the other thre... | https://en.wikipedia.org/wiki?curid=197774 |
Decay chain The total energy released from uranium-235 to lead-207, including the energy lost to neutrinos, is 46.4 MeV. | https://en.wikipedia.org/wiki?curid=197774 |
Electron affinity The electron affinity ("E") of an atom or molecule is defined as the amount of energy "released" when an electron is attached to a neutral atom or molecule in the gaseous state to form a negative ion. Note that this is not the same as the enthalpy change of electron capture ionization, which is define... | https://en.wikipedia.org/wiki?curid=197964 |
Electron affinity For any reaction that "releases" energy, the "change" Δ"E" in total energy has a negative value and the reaction is called an exothermic process. Electron capture for almost all non-noble gas atoms involves the release of energy and thus are exothermic. The positive values that are listed in tables of... | https://en.wikipedia.org/wiki?curid=197964 |
Electron affinity the energy change for the process If the same table is employed for the forward and reverse reactions, "without switching signs", care must be taken to apply the correct definition to the corresponding direction, attachment (release) or detachment (require). Since almost all detachments "(require +)" ... | https://en.wikipedia.org/wiki?curid=197964 |
Electron affinity The following data are quoted in kJ/mol. The electron affinity of molecules is a complicated function of their electronic structure. For instance the electron affinity for benzene is negative, as is that of naphthalene, while those of anthracene, phenanthrene and pyrene are positive. "In silico" exper... | https://en.wikipedia.org/wiki?curid=197964 |
Electron affinity 05 eV, whereas an isolated silicon atom has electron affinity 1.39 eV. The electron affinity of a surface is closely related to, but distinct from, its work function. The work function is the thermodynamic work that can be obtained by reversibly, isothermally moving an electron from the vacuum to the ... | https://en.wikipedia.org/wiki?curid=197964 |
Electron affinity For one illustration of the apparent effect of surface termination on electron emission, see Figure 3 in Marchywka Effect. | https://en.wikipedia.org/wiki?curid=197964 |
Molecular dynamics (MD) is a computer simulation method for analyzing the physical movements of atoms and molecules. The atoms and molecules are allowed to interact for a fixed period of time, giving a view of the dynamic "evolution" of the system. In the most common version, the trajectories of atoms and molecules are... | https://en.wikipedia.org/wiki?curid=198608 |
Molecular dynamics MD has also been termed "statistical mechanics by numbers" and "Laplace's vision of Newtonian mechanics" of predicting the future by animating nature's forces and allowing insight into molecular motion on an atomic scale. MD was originally developed in the early 1950s, following the earlier successes... | https://en.wikipedia.org/wiki?curid=198608 |
Molecular dynamics The aim was to arrange them in such as way as to replicate the structure of a liquid and use this to examine its behavior. J.D. Bernal said, in 1962: ""... I took a number of rubber balls and stuck them together with rods of a selection of different lengths ranging from 2.75 to 4 inches. I tried to d... | https://en.wikipedia.org/wiki?curid=198608 |
Molecular dynamics In 1964, Rahman published simulations of liquid argon that used a Lennard-Jones potential; calculations of system properties, such as the coefficient of self-diffusion, compared well with experimental data. First used in theoretical physics, the MD method gained popularity in materials science soon a... | https://en.wikipedia.org/wiki?curid=198608 |
Molecular dynamics MD-derived structure predictions can be tested through community-wide experiments in Critical Assessment of protein Structure Prediction (CASP), although the method has historically had limited success in this area. Michael Levitt, who shared the Nobel Prize partly for the application of MD to protei... | https://en.wikipedia.org/wiki?curid=198608 |
Molecular dynamics Another important factor are intramolecular hydrogen bonds, which are not explicitly included in modern force fields, but described as Coulomb interactions of atomic point charges. This is a crude approximation because hydrogen bonds have a partially quantum mechanical and chemical nature. Furthermor... | https://en.wikipedia.org/wiki?curid=198608 |
Molecular dynamics However, the simulations should be long enough to be relevant to the time scales of the natural processes being studied. To make statistically valid conclusions from the simulations, the time span simulated should match the kinetics of the natural process. Otherwise, it is analogous to making conclus... | https://en.wikipedia.org/wiki?curid=198608 |
Molecular dynamics The timestep must be chosen small enough to avoid discretization errors (i.e., smaller than the period related to fastest vibrational frequency in the system). Typical timesteps for classical MD are in the order of 1 femtosecond (10 s). This value may be extended by using algorithms such as the SHAKE... | https://en.wikipedia.org/wiki?curid=198608 |
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