Synonyms containing spontaneous emission

We've found 931 synonyms:

Clean Development Mechanism

Clean Development Mechanism

The Clean Development Mechanism (CDM) is one of the Flexible Mechanisms defined in the Kyoto Protocol (IPCC, 2007) that provides for emissions reduction projects which generate Certified Emission Reduction units (CERs) which may be traded in emissions trading schemes. The market crashed in 2012 when the value of credits collapsed and thousands of projects were left with unclaimed credits. The struggle about what to do with the old credits sank the 2019 COP 25 in Madrid.The CDM, defined in Article 12 of the Protocol, was intended to meet two objectives: (1) to assist parties not included in Annex I in achieving sustainable development and in contributing to the ultimate objective of the United Nations Framework Convention on Climate Change (UNFCCC), which is to prevent dangerous climate change; and (2) to assist parties included in Annex I in achieving compliance with their quantified emission limitation and reduction commitments (greenhouse gas (GHG) emission caps)."Annex I" parties are the countries listed in Annex I of the treaty, the industrialized countries. Non-Annex I parties are developing countries. The CDM addresses the second objective by allowing the Annex I countries to meet part of their emission reduction commitments under the Kyoto Protocol by buying Certified Emission Reduction units from CDM emission reduction projects in developing countries (Carbon Trust, 2009, p. 14). Both the projects and the issue of CERs units are subject to approval to ensure that these emission reductions are real and "additional." The CDM is supervised by the CDM Executive Board (CDM EB) under the guidance of the Conference of the Parties (COP/MOP) of the United Nations Framework Convention on Climate Change (UNFCCC). The CDM allows industrialized countries to buy CERs and to invest in emission reductions where it is cheapest globally (Grubb, 2003, p. 159). Between 2001, which was the first year CDM projects could be registered and 7 September 2012, the CDM issued 1 billion Certified Emission Reduction units. As of 1 June 2013, 57% of all CERs had been issued for projects based on destroying either HFC-23 (38%) or N2O (19%). Carbon capture and storage (CCS) was included in the CDM carbon offsetting scheme in December 2011.However, a number of weaknesses of the CDM have been identified (World Bank, 2010, p. 265-267). Several of these issues were addressed by the new Program of Activities (PoA), which moves to approving 'bundles' of projects instead of accrediting each project individually. In 2012, the report Climate Change, Carbon Markets and the CDM: A Call to Action said governments urgently needed to address the future of the CDM. It suggested the CDM was in danger of collapse because of the low price of carbon and the failure of governments to guarantee its existence into the future. Writing on the website of the Climate & Development Knowledge Network, Yolanda Kakabadse, a member of the investigating panel for the report and founder of Fundación Futuro Latinamericano, said a strong CDM is needed to support the political consensus essential for future climate progress. "Therefore we must do everything in our hands to keep it working," she said.

— Wikipedia

Field electron emission

Field electron emission

Field emission is emission of electrons induced by an electrostatic field. The most common context is FE from a solid surface into vacuum. However, FE can take place from solid or liquid surfaces, into vacuum, air, a fluid, or any non-conducting or weakly conducting dielectric. The field-induced promotion of electrons from the valence to conduction band of semiconductors can also be regarded as a form of FE. The terminology is historical because related phenomena of surface photoeffect, thermionic emission or Richardson-Dushman effect and "cold electronic emission", i.e. the emission of electrons in strong static electric fields, were discovered and studied independently from 1880s to 1930s. When field emission is used without qualifiers it typically means "cold emission." Field emission in pure metals occurs in high electric fields: the gradients are typically higher than 1 gigavolt per metre and strongly dependent upon the work function. Electron sources based on field emission have a number of applications, but it is most commonly an undesirable primary source of vacuum breakdown and electrical discharge phenomena, which engineers work to prevent. Examples of applications for surface field emission include construction of bright electron sources for high-resolution electron microscopes or to discharge spacecraft from induced charges. Devices which eliminate induced charges are termed charge-neutralizers.

— Freebase

Spectral index

Spectral index

In astronomy, the spectral index of a source is a measure of the dependence of radiative flux density (that is, radiative flux per unit of frequency) on frequency. Given frequency ν {\displaystyle \nu } and radiative flux density S ν {\displaystyle S_{\nu }} , the spectral index α {\displaystyle \alpha } is given implicitly by S ν ∝ ν α . {\displaystyle S_{\nu }\propto \nu ^{\alpha }.} Note that if flux does not follow a power law in frequency, the spectral index itself is a function of frequency. Rearranging the above, we see that the spectral index is given by α ( ν ) = ∂ log ⁡ S ν ( ν ) ∂ log ⁡ ν . {\displaystyle \alpha \!\left(\nu \right)={\frac {\partial \log S_{\nu }\!\left(\nu \right)}{\partial \log \nu }}.} Clearly the power law can only apply over a certain range of frequency because otherwise the integral over all frequencies would be infinite. Spectral index is also sometimes defined in terms of wavelength λ {\displaystyle \lambda } . In this case, the spectral index α {\displaystyle \alpha } is given implicitly by S λ ∝ λ α , {\displaystyle S_{\lambda }\propto \lambda ^{\alpha },} and at a given frequency, spectral index may be calculated by taking the derivative α ( λ ) = ∂ log ⁡ S λ ( λ ) ∂ log ⁡ λ . {\displaystyle \alpha \!\left(\lambda \right)={\frac {\partial \log S_{\lambda }\!\left(\lambda \right)}{\partial \log \lambda }}.} The spectral index using the S ν {\displaystyle S_{\nu }} , which we may call α ν , {\displaystyle \alpha _{\nu },} differs from the index α λ {\displaystyle \alpha _{\lambda }} defined using S λ . {\displaystyle S_{\lambda }.} The total flux between two frequencies or wavelengths is S = C 1 ( ν 2 α ν + 1 − ν 1 α ν + 1 ) = C 2 ( λ 2 α λ + 1 − λ 1 α λ + 1 ) = c α λ + 1 C 2 ( ν 2 − α λ − 1 − ν 1 − α λ − 1 ) {\displaystyle S=C_{1}(\nu _{2}^{\alpha _{\nu }+1}-\nu _{1}^{\alpha _{\nu }+1})=C_{2}(\lambda _{2}^{\alpha _{\lambda }+1}-\lambda _{1}^{\alpha _{\lambda }+1})=c^{\alpha _{\lambda }+1}C_{2}(\nu _{2}^{-\alpha _{\lambda }-1}-\nu _{1}^{-\alpha _{\lambda }-1})} which implies that α λ = − α ν − 2. {\displaystyle \alpha _{\lambda }=-\alpha _{\nu }-2.} The opposite sign convention is sometimes employed, in which the spectral index is given by S ν ∝ ν − α . {\displaystyle S_{\nu }\propto \nu ^{-\alpha }.} The spectral index of a source can hint at its properties. For example, using the positive sign convention, the spectral index of the emission from an optically thin thermal plasma is -0.1, whereas for an optically thick plasma it is 2. Therefore, a spectral index of -0.1 to 2 at radio frequencies often indicates thermal emission, while a steep negative spectral index typically indicates synchrotron emission. It is worth noting that the observed emission can be affected by several absorption processes that affect the low-frequency emission the most; the reduction in the observed emission at low frequencies might result in a positive spectral index even if the intrinsic emission has a negative index. Therefore, it is not straightforward to associate positive spectral indices with thermal emission.

— Wikipedia

Thermionic emission

Thermionic emission

Thermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function of the metal. The charge carriers can be electrons or ions, and in older literature are sometimes referred to as "thermions". After emission, a charge will initially be left behind in the emitting region that is equal in magnitude and opposite in sign to the total charge emitted. But if the emitter is connected to a battery, then this charge left behind will be neutralized by charge supplied by the battery, as the emitted charge carriers move away from the emitter, and finally the emitter will be in the same state as it was before emission. The thermionic emission of electrons is also known as thermal electron emission. The classical example of thermionic emission is the emission of electrons from a hot cathode, into a vacuum in a vacuum tube. The hot cathode can be a metal filament, a coated metal filament, or a separate structure of metal or carbides or borides of transition metals. Vacuum emission from metals tends to become significant only for temperatures over 1000 K. The science dealing with this phenomenon has been known as thermionics, but this name seems to be gradually falling into disuse.

— Freebase

Stimulated emission

Stimulated emission

Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron (or other excited molecular state), causing it to drop to a lower energy level. The liberated energy transfers to the electromagnetic field, creating a new photon with a phase, frequency, polarization, and direction of travel that are all identical to the photons of the incident wave. This is in contrast to spontaneous emission, which occurs at random intervals without regard to the ambient electromagnetic field. The process is identical in form to atomic absorption in which the energy of an absorbed photon causes an identical but opposite atomic transition: from the lower level to a higher energy level. In normal media at thermal equilibrium, absorption exceeds stimulated emission because there are more electrons in the lower energy states than in the higher energy states. However, when a population inversion is present, the rate of stimulated emission exceeds that of absorption, and a net optical amplification can be achieved. Such a gain medium, along with an optical resonator, is at the heart of a laser or maser. Lacking a feedback mechanism, laser amplifiers and superluminescent sources also function on the basis of stimulated emission.

— Wikipedia

Beta decay

Beta decay

In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atomic nucleus. Beta decay is a process which allows the atom to obtain the optimal ratio of protons and neutrons. There are two types of beta decay, a decay that is mediated by the weak force: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus, while in the case of a positron emission as beta plus. An example of β− decay is shown when carbon-14 decays into nitrogen-14: Notice how, in electron emission, an electron antineutrino is also emitted. In this form of decay, the original element has decayed into a new element with an unchanged mass number A but an atomic number Z that has increased by one. An example of positron is shown with magnesium-23 decaying into sodium-23: In contrast to electron emission, positron emission is accompanied by the emission of an electron neutrino. Similar to electron emission, positron decay results in nuclear transmutation, changing an atom of a chemical element into an atom of an element with an unchanged mass number. However, in positron decay, the resulting element has an atomic number that has decreased by one.

— Freebase

Spontaneous remission

Spontaneous remission

Spontaneous remission, also called spontaneous healing or spontaneous regression, is an unexpected improvement or cure from a disease that usually progresses. These terms are commonly used for unexpected transient or final improvements in cancer. Spontaneous remissions concern cancers of the haematopoietic system (blood cancer, e.g. leukemia), while spontaneous regressions concern palpable tumors; however, both terms are often used interchangeably.

— Wikipedia

Thermophotovoltaic

Thermophotovoltaic

Thermophotovoltaic (TPV) energy conversion is a direct conversion process from heat to electricity via photons. A basic thermophotovoltaic system consists of a thermal emitter and a photovoltaic diode cell. The temperature of the thermal emitter varies between different systems from about 900 °C to about 1300 °C, although in principle TPV devices can extract energy from any emitter with temperature elevated above that of the photovoltaic device (forming an optical heat engine). The emitter can be a piece of solid material or a specially engineered structure. Thermal emission is the spontaneous emission of photons due to thermal motion of charges in the material. For these TPV temperatures, this radiation is mostly at near infrared and infrared frequencies. The photovoltaic diodes absorbs some of these radiated photons and converts them into electricity. Thermophotovoltaic systems have few to no moving parts and are therefore quiet and require little maintenance. These properties make thermophotovoltaic systems suitable for remote-site and portable electricity-generating applications. Their efficiency-cost properties, however, are often poor compared to other electricity-generating technologies. Current research in the area aims at increasing system efficiencies while keeping the system cost low. TPV systems usually attempt to match the optical properties of thermal emission (wavelength, polarization, direction) with the most efficient absorption characteristics of the photovoltaic cell, since unconverted thermal emission is a major source of inefficiency. Most groups focus on gallium antimonide (GaSb) cells. Germanium (Ge) is also suitable. Much research and development concerns methods for controlling the emitter's properties. TPV cells have been proposed as auxiliary power conversion devices for capture of otherwise lost heat in other power generation systems, such as steam turbine systems or solar cells. A prototype TPV hybrid car was built, the "Viking 29" (TPV) powered automobile, designed and built by the Vehicle Research Institute (VRI) at Western Washington University. TPV research is an active area. Among others, the University of Houston TPV Radioisotope Power Conversion Technology development effort is attempting to combine a thermophotovoltaic cell with thermocouples to provide a 3 to 4-fold improvement in system efficiency over current radioisotope thermoelectric generators. Panels can also be made using thermoradiative cells. In 2020, Professor Jeremy Munday devised panels that would allow the harvest of electricity from the night sky. The panels would be able to generate up to 50 watts of power per square meter, which is a quarter of what conventional panels can generate in the daytime.

— Wikipedia

Emission

Emission

the act of sending or throwing out; the act of sending forth or putting into circulation; issue; as, the emission of light from the sun; the emission of heat from a fire; the emission of bank notes

— Webster Dictionary

Emissivity

Emissivity

tendency to emission; comparative facility of emission, or rate at which emission takes place, as of heat from the surface of a heated body

— Webster Dictionary

Spontaneous emission

Spontaneous emission

Spontaneous emission is the process by which a quantum system such as an atom, molecule, nanocrystal or nucleus in an excited state undergoes a transition to a state with a lower energy and emits quanta of energy. Light or luminescence from an atom is a fundamental process that plays an essential role in many phenomena in nature and forms the basis of many applications, such as fluorescent tubes, older television screens, plasma display panels, lasers, and light emitting diodes. Lasers start by spontaneous emission, and then normal continuous operation works by stimulated emission.

— Freebase

Esophageal rupture

Esophageal rupture

Esophageal rupture is a rupture of the esophageal wall. Iatrogenic causes account for approximately 56% of esophageal perforations, usually due to medical instrumentation such as an endoscopy or paraesophageal surgery. In contrast, the term Boerhaave syndrome is reserved for the 10% of esophageal perforations which occur due to vomiting.Spontaneous perforation of the esophagus most commonly results from a full-thickness tear in the esophageal wall due to a sudden increase in intraesophageal pressure combined with relatively negative intrathoracic pressure caused by straining or vomiting (effort rupture of the esophagus or Boerhaave's syndrome). Other causes of spontaneous perforation include caustic ingestion, pill esophagitis, Barrett's esophagus, infectious ulcers in patients with AIDS, and following dilation of esophageal strictures.In most cases of Boerhaave's syndrome, the tear occurs at the left postero-lateral aspect of the distal esophagus and extends for several centimeters. The condition is associated with high morbidity and mortality and is fatal without treatment. The occasionally nonspecific nature of the symptoms may contribute to a delay in diagnosis and a poor outcome. Spontaneous effort rupture of the cervical esophagus, leading to localized cervical perforation, may be more common than previously recognized and has a generally benign course. Preexisting esophageal disease is not a prerequisite for esophageal perforation but it contributes to increased mortality.This condition was first documented by the 18th-century physician Herman Boerhaave, after whom it is named. A related condition is Mallory-Weiss syndrome which is only a mucosal tear. In case of iatrogenic perforation common site is cervical esophagus just above the upper sphincter whereas spontaneous rupture as seen in Boerhaave's syndrome perforation commonly occurs in the lower (1/3)rd of esophagus.

— Wikipedia

X-ray astronomy

X-ray astronomy

X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray astronomy is the space science related to a type of space telescope that can see farther than standard light-absorption telescopes, such as the Mauna Kea Observatories, via x-ray radiation. X-ray emission is expected from astronomical objects that contain extremely hot gasses at temperatures from about a million kelvin to hundreds of millions of kelvin. Although X-rays have been observed emanating from the Sun since the 1940s, the discovery in 1962 of the first cosmic X-ray source was a surprise. This source is called Scorpius X-1, the first X-ray source found in the constellation Scorpius. The X-ray emission of Scorpius X-1 is 10,000 times greater than its visual emission, whereas that of the Sun is about a million times less. In addition, the energy output in X-rays is 100,000 times greater than the total emission of the Sun in all wavelengths. Based on discoveries in this new field of X-ray astronomy, starting with Scorpius X-1, Riccardo Giacconi received the Nobel Prize in Physics in 2002. It is now known that such X-ray sources as Sco X-1 are compact stars, such as neutron stars or black holes. Material falling into a black hole may emit X-rays, but the black hole itself does not. The energy source for the X-ray emission is gravity. Infalling gas and dust is heated by the strong gravitational fields of these and other celestial objects.

— Freebase

Secondary emission

Secondary emission

Secondary emission in physics is a phenomenon where primary incident particles of sufficient energy, when hitting a surface or passing through some material, induce the emission of secondary particles. The primary particles are often charged particles like electrons or ions. If the secondary particles are electrons, the effect is termed secondary electron emission. In this case, the number of secondary electrons emitted per incident particle is called secondary emission yield. If the secondary particles are ions, the effect is termed secondary ion emission.

— Freebase

Spectrofluorometer

Spectrofluorometer

The spectrofluorometer is an instrument which takes advantage of fluorescent properties of some compounds in order to provide information regarding their concentration and chemical environment in a sample. A certain excitation wavelength is selected, and the emission is observed either at a single wavelength or a scan is performed to record the intensity versus wavelength also called an emission spectra. See Fluorescence spectroscopy Generally spectrofluorometers use high intensity light sources to bombard a sample with as many photons as possible. This allows for the maximum number of molecules to be in the excited state at any one point in time. The light is either passed through a filter, selecting a fixed wavelength, or monochromator, which allows you to select a wavelength of interest to use as the exciting light. The emission is collected at 90 degrees to the exciting light. The emission too is either passed through a filter or a monochromator before being detected by a PMT, photodiode, or CCD detector. The signal can either be processed as a digital or analog output. Systems vary greatly and a few things must be considered when choosing. The first is signal to noise. There are many ways to look at the signal to noise of a given system but the accepted standard is by using water Raman. Sensitivity or detection limit is another spec to look at, that is how little light they can measure. The standard for this would be fluorescein in NaOH, typical values for a high end instrument are in the femtomolar range. Stray light is another big issue in these instruments. Stray light is basically how monochromatic the light is. This matters when you have a highly scattering sample, however one can always use an excitation wavelength further away from the emission band to negate this issue or use a laser or interference filter.

— Freebase

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