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B. F
B is the second letter of the Latin alphabet. B may also refer to: Science, technology, and mathematics Astronomy * Astronomical objects in the Barnard list of dark nebulae (abbreviation B) * Latitude (''b'') in the galactic coordinate system Biology and medicine * Haplogroup B (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup * Haplogroup B (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup * Blood type B * ATC code B ''Blood and blood forming organs'', a section of the Anatomical Therapeutic Chemical Classification System * Vitamin B * Hepatitis B * Berlin Botanical Garden and Botanical Museum, assigned the abbreviation B as a repository of herbarium specimens Computing * B (programming language) * B-Method, for computer software development * B-tree, a data structure * Bit (b) * Byte (B) * , an HTML element denoting bold text Physical and chemical quantities and units * One of the reciprocal lattice vectors (''b*'') * Breadth (''b''); see length * Impact parameter ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Dark Nebulae
This is a list of dark nebulae (absorption nebulae), also called "dark clouds". List * E Nebula ( Barnard 142 and 143) *Barnard 68, possibly the closest to Earth at about 400 light-years. * Bernes 157 (Sandqvist and Lindroos, SL 39-41), another close dark nebula of the Corona Australis Molecular Cloud, which includes NGC 6729 Named absorption nebulae See also the references to names from other cultures at dark cloud constellations: *Coalsack Nebula *Cone Nebula * Dark Doodad Nebula * Dark Horse Nebula * Horsehead Nebula ( Barnard 33) * Pipe Nebula (also see Dark Horse Nebula; includes Barnard 59, 77 and 78) *Snake Nebula (also see Dark Horse Nebula) * Keyhole Nebula Barnard objects See also * Lists of astronomical objects *Nebula *Dark nebula A dark nebula or absorption nebula is a type of interstellar cloud, particularly molecular clouds, that is so dense that it obscures the visible wavelengths of light from objects behind it, such as background stars and emiss ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molality
Molality is a measure of the number of moles of solute in a solution corresponding to 1 kg or 1000 g of solvent. This contrasts with the definition of molarity which is based on a specified volume of solution. A commonly used unit for molality in chemistry is mol/ kg. A solution of concentration 1 mol/kg is also sometimes denoted as ''1 molal''. The unit ''mol/kg'' requires that molar mass be expressed in ''kg/mol'', instead of the usual ''g/mol'' or ''kg/kmol''. Definition The molality (''b''), of a solution is defined as the amount of substance (in moles) of solute, ''n''solute, divided by the mass (in kg) of the solvent, ''m''solvent: :b = \frac In the case of solutions with more than one solvent, molality can be defined for the mixed solvent considered as a pure pseudo-solvent. Instead of mole solute per kilogram solvent as in the binary case, units are defined as mole solute per kilogram mixed solvent. Origin The term ''molality'' is formed in analogy to ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
B Horizon
A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material, i.e. 'coarser' or 'sandier' than the horizons above and below. The identified horizons are indicated with symbols, which are mostly used in a hierarchical way. Master horizons (main horizons) are indicated by capital letters. Suffixes, in form of lowercase letters and figures, further differentiate the master horizons. There are many different systems of horizon symbols in the world. No one system is more correct—as artificial constructs, their utility lies in their ability to accurately describe local conditions in a consistent manner. Due to the different definitions of the horizon sym ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Battery (vacuum Tube)
file:Triode Circuit.svg, A generic triode vacuum tube circuit showing "A", "B" and "C" batteries In the early days of electronics, vacuum tube (called ''valves'' in British contexts) devices (such as radios) were powered by battery (electricity), batteries. Each battery had a different designation depending on which tube element it was associated with. Initially, the only such device was a Diode#Thermionic and gaseous state diodes, diode with only a electrical filament, filament Cathode#Vacuum tubes, (cathode) and a Plate electrode, plate Anode#Vacuum tube anode, (anode). Following the direction of electron flow, these electrodes were identified as "A" and "B", respectively and thus the associated batteries were referred to as the "A" and "B" batteries respectively. Later, when the control grid element was added to create the triode tube, it was logically assigned the letter "C" and supplied from a "C" battery. Subsequent addition of further internal elements to improve the perform ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bulb (photography)
The Bulb setting (abbreviated B) on camera shutters is a momentary-action mode that holds shutters open for as long as a photographer depresses the shutter-release button. The Bulb setting is distinct from shutter's Time (T) setting, which is an alternate-action mode where the shutter opens when the shutter-release button is pressed and released once, and closes when the button is actuated again. History Decades before the first flashbulbs, some box cameras and many view cameras and folding cameras came with a detachable pneumatic shutter release with a rubber bulb on the end; "Bulb" refers to the rubber shutter release bulb. Though mechanically timed exposures could also be triggered by squeezing the shutter release bulb, "Bulb" exposures then had the same momentary action as camera shutters have today, as per this description from Sears Roebuck's 1909 ''Cameras Photographic Supplies'': Around 1894 in Germany, the momentary-action setting on camera shutters made by C. A. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boron
Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the '' boron group'' it has three valence electrons for forming covalent bonds, resulting in many compounds such as boric acid, the mineral sodium borate, and the ultra-hard crystals of boron carbide and boron nitride. Boron is synthesized entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, so it is a low-abundance element in the Solar System and in the Earth's crust. It constitutes about 0.001 percent by weight of Earth's crust. It is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such as borax and kernite. The largest known deposits are in Turkey, the largest producer of boron minerals. Elemental boron is a meta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boolean Domain
In mathematics and abstract algebra, a Boolean domain is a set consisting of exactly two elements whose interpretations include ''false'' and ''true''. In logic, mathematics and theoretical computer science, a Boolean domain is usually written as , or \mathbb. The algebraic structure that naturally builds on a Boolean domain is the Boolean algebra with two elements. The initial object in the category of bounded lattices is a Boolean domain. In computer science, a Boolean variable is a variable that takes values in some Boolean domain. Some programming languages feature reserved words or symbols for the elements of the Boolean domain, for example false and true. However, many programming languages do not have a Boolean datatype in the strict sense. In C or BASIC, for example, falsity is represented by the number 0 and truth is represented by the number 1 or −1, and all variables that can take these values can also take any other numerical values. Generalizations The Boo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modal Logic
Modal logic is a collection of formal systems developed to represent statements about necessity and possibility. It plays a major role in philosophy of language, epistemology, metaphysics, and natural language semantics. Modal logics extend other systems by adding unary operators \Diamond and \Box, representing possibility and necessity respectively. For instance the modal formula \Diamond P can be read as "possibly P" while \Box P can be read as "necessarily P". Modal logics can be used to represent different phenomena depending on what kind of necessity and possibility is under consideration. When \Box is used to represent epistemic necessity, \Box P states that P is epistemically necessary, or in other words that it is known. When \Box is used to represent deontic necessity, \Box P states that P is a moral or legal obligation. In the standard relational semantics for modal logic, formulas are assigned truth values relative to a '' possible world''. A formula's truth value ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decibel
The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 101/10 (approximately ) or root-power ratio of 10 (approximately ). The unit expresses a relative change or an absolute value. In the latter case, the numeric value expresses the ratio of a value to a fixed reference value; when used in this way, the unit symbol is often suffixed with letter codes that indicate the reference value. For example, for the reference value of 1 volt, a common suffix is " V" (e.g., "20 dBV"). Two principal types of scaling of the decibel are in common use. When expressing a power ratio, it is defined as ten times the logarithm in base 10. That is, a change in ''power'' by a factor of 10 corresponds to a 10 dB change in level. When expressing root-power quantities, a change in ''am ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Susceptance
In electrical engineering, susceptance (''B'') is the imaginary part of admittance, where the real part is conductance. The reciprocal of admittance is impedance, where the imaginary part is reactance and the real part is resistance. In SI units, susceptance is measured in siemens. Origin The term was coined by C.P. Steinmetz in a 1894 paper. In some sources Oliver Heaviside is given credit for coining the term, or with introducing the concept under the name ''permittance''. This claim is mistaken according to Steinmetz's biographer. The term ''susceptance'' does not appear anywhere in Heaviside's collected works, and Heaviside used the term ''permittance'' to mean capacitance, not ''susceptance''. Formula The general equation defining admittance is given by Y = G + j B \, where The admittance () is the reciprocal of the impedance (), if the impedance is not zero: Y = \frac = \frac = \left( \frac \right) \left( \frac \right) = \left( \frac \right) + j \left( \frac \r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virial Coefficient
Virial coefficients B_i appear as coefficients in the virial expansion of the pressure of a many-particle system in powers of the density, providing systematic corrections to the ideal gas law. They are characteristic of the interaction potential between the particles and in general depend on the temperature. The second virial coefficient B_2 depends only on the pair interaction between the particles, the third (B_3) depends on 2- and non-additive 3-body interactions, and so on. Derivation The first step in obtaining a closed expression for virial coefficients is a cluster expansion of the grand canonical partition function : \Xi = \sum_ = e^ Here p is the pressure, V is the volume of the vessel containing the particles, k_B is Boltzmann's constant, T is the absolute temperature, \lambda =\exp mu/(k_BT) is the fugacity, with \mu the chemical potential. The quantity Q_n is the canonical partition function of a subsystem of n particles: : Q_n = \operatorname e^ Here H(1,2, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rigid Rotor
In rotordynamics, the rigid rotor is a mechanical model of Rotation, rotating systems. An arbitrary rigid rotor is a 3-dimensional Rigid body, rigid object, such as a top. To orient such an object in space requires three angles, known as Euler angles. A special rigid rotor is the ''linear rotor'' requiring only two angles to describe, for example of a diatomic molecule. More Rotational spectroscopy#Classification of molecular rotors, general molecules are 3-dimensional, such as water (asymmetric rotor), ammonia (symmetric rotor), or methane (spherical rotor). Linear rotor The linear rigid rotor model consists of two point masses located at fixed distances from their center of mass. The fixed distance between the two masses and the values of the masses are the only characteristics of the rigid model. However, for many actual diatomics this model is too restrictive since distances are usually not completely fixed. Corrections on the rigid model can be made to compensate for sma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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