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Hessdalen Lights
The Hessdalen lights are unidentified lights observed in a stretch of the Hessdalen valley in rural central Norway. Background The Hessdalen lights are of unknown origin. They appear both by day and by night, and seem to float through and above the valley. They are usually bright white, yellow or red and can appear above and below the horizon. The duration of the phenomenon may be a few seconds to well over an hour. Sometimes the lights move with enormous speed; at other times they seem to sway slowly back and forth. On yet other occasions, they hover in mid‑air. Unusual lights have been reported in the region since at least the 1930s. Especially high activity occurred between December 1981 and mid-1984, during which the lights were observed 15–20 times per week, attracting many overnight tourists. , the number of observations had dwindled, with only 10 to 20 sightings yearly. Since 1983, "Project Hessdalen" initiated by UFO-Norge and UFO-Sverige have attempted to investiga ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hessdalen
Hessdalen is a village in the municipality of Holtålen in Trøndelag county, Norway. Hessdalen also refers to the long valley that surrounds the village. Hessdalen is located in the central part of the village, approximately south of the city of Trondheim, approximately north of the mining town of Røros, and about southwest of the village of Renbygda. About 150 people live in the village and surrounding valley. Hessdalen Church is located in the village of Hessdalen and the lake Øyungen lies about southwest of the village. The Hessdalen area is known for the occurrence of unexplained aerial luminous phenomena called the Hessdalen lights. The phenomenon is monitored by the Hessdalen AMS. Name The first element is the name of the local river ''Hesja'' and the last element is the definite form of ''dal'', which means " dale" or "valley A valley is an elongated low area often running between hills or mountains, which will typically contain a river or strea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Japanese Journal Of Applied Physics
The ''Japanese Journal of Applied Physics'' is a peer-reviewed scientific journal that was established in 1962 and is published by the Japan Society of Applied Physics. From 1982 until 2008, the journal was published in two editions, Part 1 and Part 2: * Part 1 was published monthly and was for regular papers, short notes and review papers. * Part 2 was published semi-monthly and was for letters and express letters. In 2008, Part 2 was separated as an independent journal and renamed ''Applied Physics Express''. Part 1 continues to be published as the ''Japanese Journal of Applied Physics''. In June 2013, the Japan Society of Applied Physics signed an agreement with IOP Publishing for its journals to be published by IOP Publishing. inpublishing.co.uk. 6 June 201 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bremsstrahlung
''Bremsstrahlung'' (), from "to brake" and "radiation"; i.e., "braking radiation" or "deceleration radiation", is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic energy, which is converted into radiation (i.e., photons), thus satisfying the law of conservation of energy. The term is also used to refer to the process of producing the radiation. ''Bremsstrahlung'' has a continuous spectrum, which becomes more intense and whose peak intensity shifts toward higher frequencies as the change of the energy of the decelerated particles increases. Broadly speaking, ''bremsstrahlung'' or braking radiation is any radiation produced due to the deceleration (negative acceleration) of a charged particle, which includes synchrotron radiation (i.e., photon emission by a relativistic particle), cyclotron radiation (i.e. photon emission by a non ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Thickness
In physics, optical depth or optical thickness is the natural logarithm of the ratio of incident to ''transmitted'' radiant power through a material. Thus, the larger the optical depth, the smaller the amount of transmitted radiant power through the material. Spectral optical depth or spectral optical thickness is the natural logarithm of the ratio of incident to transmitted spectral radiant power through a material. Optical depth is dimensionless, and in particular is not a length, though it is a monotonically increasing function of optical path length, and approaches zero as the path length approaches zero. The use of the term "optical density" for optical depth is discouraged. In chemistry, a closely related quantity called "absorbance" or "decadic absorbance" is used instead of optical depth: the common logarithm of the ratio of incident to transmitted radiant power through a material, that is the optical depth divided by ln 10. Mathematical definitions Optical depth Op ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Species
A chemical species is a chemical substance or ensemble composed of chemically identical molecular entity, molecular entities that can explore the same set of molecular energy levels on a characteristic or delineated time scale. These energy levels determine the way the chemical species will interact with others (engaging in chemical bonds, etc.). The species can be an atom, molecule, ion, or radical, and it has a specific chemical name and chemical formula. The term is also applied to a set of chemically identical atomic or molecular structural units in a solid array. In supramolecular chemistry, chemical species are those supramolecular structures whose interactions and associations are brought about via intermolecular bonding and debonding actions, and function to form the basis of this branch of chemistry. For instance: * The chemical species argon is an atom, atomic species of formula Ar; * dioxygen and ozone are different molecule, molecular species, of respective formulas O ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Temperature
Plasma parameters define various characteristics of a plasma, an electrically conductive collection of charged particles that responds ''collectively'' to electromagnetic forces. Plasma typically takes the form of neutral gas-like clouds or charged ion beams, but may also include dust and grains. The behaviour of such particle systems can be studied statistically. Fundamental plasma parameters All quantities are in Gaussian ( cgs) units except energy and temperature which are in electronvolts. The ion mass is expressed in units of the proton mass \mu = m_i/m_p and Z the ion charge in units of the elementary charge e (in the case of a fully ionized atom, Z equals to the respective atomic number). The other physical quantities used are the Boltzmann constant (k), speed of light (c), and the Coulomb logarithm (\ln\Lambda). Frequencies Lengths Velocities Dimensionless * number of particles in a Debye sphere *: \left(\frac\right)n\lambda_D^3 \approx 1.72 \times 10^ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dissociative Recombination
Dissociative recombination is a chemical process where a positive polyatomic ion recombines with an electron, and as a result, the neutral molecule dissociates. This reaction is important for extraterrestrial and atmospheric chemistry. On Earth, dissociative recombination rarely occurs naturally, as free electrons react with any molecule (even neutral molecules) they encounter. Even in the best laboratory conditions, dissociative recombination is hard to observe, but is an important reaction in systems that have large populations of ionized molecules, for instance in atmospheric-pressure plasmas. In astrophysics, dissociative recombination is one of the main mechanisms via which molecules are broken down, and other molecules are formed. The existence of dissociative recombination is possible due to the vacuum of the interstellar medium. A typical example of dissociative recombination in astrophysics is: :CH3+ + e- -> CH2 + H See also *Ionization Ionization, or Ionisation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rate Coefficient
In chemical kinetics a reaction rate constant or reaction rate coefficient, ''k'', quantifies the rate and direction of a chemical reaction. For a reaction between reactants A and B to form product C the reaction rate is often found to have the form: r = k(T) mathrmm mathrm Here ''k''(''T'') is the reaction rate constant that depends on temperature, and and are the molar concentrations of substances A and B in moles per unit volume of solution, assuming the reaction is taking place throughout the volume of the solution. (For a reaction taking place at a boundary, one would use moles of A or B per unit area instead.) The exponents ''m'' and ''n'' are called partial orders of reaction and are ''not'' generally equal to the stoichiometric coefficients ''a'' and ''b''. Instead they depend on the reaction mechanism and can be determined experimentally. Elementary steps For an elementary step, there ''is'' a relationship between stoichiometry and rate law, as determined by the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Electronic Transition
Molecular electronic transitions take place when electrons in a molecule are excited from one energy level to a higher energy level. The energy change associated with this transition provides information on the structure of a molecule and determines many molecular properties such as colour. The relationship between the energy involved in the electronic transition and the frequency of radiation is given by Planck's relation. Organic molecules and other molecules The electronic transitions in organic compounds and some other compounds can be determined by ultraviolet–visible spectroscopy, provided that transitions in the ultraviolet (UV) or visible range of the electromagnetic spectrum exist for this compound. Electrons occupying a HOMO of a sigma bond can get excited to the LUMO of that bond. This process is denoted as a σ → σ* transition. Likewise promotion of an electron from a π-bonding orbital to an antibonding π orbital* is denoted as a π → π* transition. Au ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ion-acoustic Waves
In plasma physics, an ion acoustic wave is one type of longitudinal oscillation of the ions and electrons in a plasma, much like acoustic waves traveling in neutral gas. However, because the waves propagate through positively charged ions, ion acoustic waves can interact with their electromagnetic fields, as well as simple collisions. In plasmas, ion acoustic waves are frequently referred to as acoustic waves or even just sound waves. They commonly govern the evolution of mass density, for instance due to pressure gradients, on time scales longer than the frequency corresponding to the relevant length scale. Ion acoustic waves can occur in an unmagnetized plasma or in a magnetized plasma parallel to the magnetic field. For a single ion species plasma and in the long wavelength limit, the waves are dispersionless (\omega=v_sk) with a speed given by (see derivation below) :v_s = \sqrt where k_\text is the Boltzmann constant, M is the mass of the ion, Z is its charge, T_e is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Very Low Frequency
Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave as the wavelengths range from one to ten myriameters (an obsolete metric unit equal to 10 kilometers). Due to its limited bandwidth, audio (voice) transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations (broadcasting time signals to set radio clocks) and for secure military communication. Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for military communication with submarines. Propagation characteristics Because of their long wavelengths, VLF radio waves can diffract around large obstacles and so are not blocked by mountain ranges, and can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiation Pressure
Radiation pressure is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of any wavelength that is absorbed, reflected, or otherwise emitted (e.g. black-body radiation) by matter on any scale (from macroscopic objects to dust particles to gas molecules). The associated force is called the radiation pressure force, or sometimes just the force of light. The forces generated by radiation pressure are generally too small to be noticed under everyday circumstances; however, they are important in some physical processes and technologies. This particularly includes objects in outer space, where it is usually the main force acting on objects besides gravity, and where the net effect of a tiny force may have a large cumulative effect over long periods of time. For example, had the effects of the Sun's radiation pressure on the spacecraft of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
