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Oded Regev (physicist)
Oded Regev (born 1946) is a physicist and astrophysicist, professor emeritus of the Technion, Israel Institute of Technology. He is best known for his theoretical application of fluid dynamics and dynamical systems theory to astrophysics. Career Regev was born in Poland and emigrated to Israel in 1958. His academic career was mainly in Israel. He studied physics and mathematics at the Hebrew University of Jerusalem, with graduate studies and a Ph.D. at Tel Aviv University, and became a faculty member at the Technion – Israel Institute of Technology. During his studies he served four years in the Israel Defense Forces and continued to serve in the reserve units, reaching the rank of major. In 2002 he moved to the US. Contributions His early numerical calculations (with G. Shaviv) of a rotating gas sphere gravitational collapse (1980) were the first to show that a central object (a star) is formed surrounded by a protoplanetary disk-like nebula, provided turbulent viscosity i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wałbrzych
Wałbrzych (; german: Waldenburg; szl, Wałbrzich; sli, label= Lower Silesian, Walmbrig or ''Walmbrich''; cs, Valbřich or ) is a city located in the Lower Silesian Voivodeship, in southwestern Poland. From 1975–1998 it was the capital of Wałbrzych Voivodeship; it is now the seat of Wałbrzych County. Wałbrzych lies approximately southwest of the voivodeship capital Wrocław and about from the Czech border. Wałbrzych has the status of municipality. Its administrative borders encompass an area of with 110,000 inhabitants, making it the second-largest city in the voivodeship and the 33rd largest in the country. Wałbrzych was once a major coal mining and industrial center alongside most of Silesia. The city was left undamaged after World War II and possesses rich historical architecture; among the most recognizable landmarks is the Książ Castle, the largest castle of Lower Silesia and the third-largest in Poland. In 2015 Wałbrzych became widely known due to the searc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Israel Defense Forces
The Israel Defense Forces (IDF; he, צְבָא הַהֲגָנָה לְיִשְׂרָאֵל , ), alternatively referred to by the Hebrew-language acronym (), is the national military of the Israel, State of Israel. It consists of three service branches: the Israeli Ground Forces, the Israeli Air Force, and the Israeli Navy. It is the sole military wing of the Israeli security forces, Israeli security apparatus, and has no civilian jurisdiction within Israel. The IDF is headed by the Chief of the General Staff (Israel), Chief of the General Staff, who is subordinate to the Ministry of Defense (Israel), Israeli Defense Minister. On the orders of David Ben-Gurion, the IDF was formed on 26 May 1948 and began to operate as a Conscription in Israel, conscript military, drawing its initial recruits from the already-existing paramilitaries of the Yishuv—namely Haganah, the Irgun, and Lehi (militant group), Lehi. Since its formation shortly after the Israeli Declaration of Independen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Living People
Related categories * :Year of birth missing (living people) / :Year of birth unknown * :Date of birth missing (living people) / :Date of birth unknown * :Place of birth missing (living people) / :Place of birth unknown * :Year of death missing / :Year of death unknown * :Date of death missing / :Date of death unknown * :Place of death missing / :Place of death unknown * :Missing middle or first names See also * :Dead people * :Template:L, which generates this category or death years, and birth year and sort keys. : {{DEFAULTSORT:Living people 21st-century people People by status ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1946 Births
Events January * January 6 - The 1946 North Vietnamese parliamentary election, first general election ever in Vietnam is held. * January 7 – The Allies recognize the Austrian republic with its 1937 borders, and divide the country into four Allied-occupied Austria, occupation zones. * January 10 ** The first meeting of the United Nations is held, at Methodist Central Hall Westminster in London. ** ''Project Diana'' bounces radar waves off the Moon, measuring the exact distance between the Earth and the Moon, and proves that communication is possible between Earth and outer space, effectively opening the Space Age. * January 11 - Enver Hoxha declares the People's Republic of Albania, with himself as prime minister of Albania, prime minister. * January 16 – Charles de Gaulle resigns as head of the Provisional Government of the French Republic, French provisional government. * January 17 - The United Nations Security Council holds its first session, at Church House, Westmin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prandtl Number
The Prandtl number (Pr) or Prandtl group is a dimensionless number, named after the German physicist Ludwig Prandtl, defined as the ratio of momentum diffusivity to thermal diffusivity. The Prandtl number is given as: : \mathrm = \frac = \frac = \frac = \frac where: * \nu : momentum diffusivity (kinematic viscosity), \nu = \mu/\rho, ( SI units: m2/s) * \alpha : thermal diffusivity, \alpha = k/(\rho c_p), (SI units: m2/s) * \mu : dynamic viscosity, (SI units: Pa s = N s/m2) * k : thermal conductivity, (SI units: W/(m·K)) * c_p : specific heat, (SI units: J/(kg·K)) * \rho : density, (SI units: kg/m3). Note that whereas the Reynolds number and Grashof number are subscripted with a scale variable, the Prandtl number contains no such length scale and is dependent only on the fluid and the fluid state. The Prandtl number is often found in property tables alongside other properties such as viscosity and thermal conductivity. The mass transfer analog of the Prandtl number is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Black Holes
A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. Although it has a great effect on the fate and circumstances of an object crossing it, it has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly. Objects whose gravitational fields are too strong for light to escape were first ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Accretion Disks
An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other forces induce instabilities causing orbiting material in the disk to spiral inward towards the central body. Gravitational and frictional forces compress and raise the temperature of the material, causing the emission of electromagnetic radiation. The frequency range of that radiation depends on the central object's mass. Accretion disks of young stars and protostars radiate in the infrared; those around neutron stars and black holes in the X-ray part of the Electromagnetic spectrum, spectrum. The study of oscillation modes in accretion disks is referred to as diskoseismology. Manifestations Accretion disks are a ubiquitous phenomenon in astrophysics; active galactic nuclei, protoplanetary disks, and gamma ray bursts all involve accretio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Accretion (astrophysics)
In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, in an accretion disk. Most astronomical objects, such as galaxies, stars, and planets, are formed by accretion processes. Overview The accretion model that Earth and the other terrestrial planets formed from meteoric material was proposed in 1944 by Otto Schmidt, followed by the ''protoplanet theory'' of William McCrea (1960) and finally the ''capture theory'' of Michael Woolfson. For details of Kant's position, see In 1978, Andrew Prentice resurrected the initial Laplacian ideas about planet formation and developed the ''modern Laplacian theory''. None of these models proved completely successful, and many of the proposed theories were descriptive. The 1944 accretion model by Otto Schmidt was further developed in a quantitative way in 1969 by Viktor Safronov. He calculated, in detail, the different stages of terrestrial plane ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the internal frictional force between adjacent layers of fluid that are in relative motion. For instance, when a viscous fluid is forced through a tube, it flows more quickly near the tube's axis than near its walls. Experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion. For a tube with a constant rate of flow, the strength of the compensating force is proportional to the fluid's viscosity. In general, viscosity depends on a fluid's state, such as its temperature, pressure, and rate of deformation. However, the dependence on some of these properties is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turbulent
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between those layers. Turbulence is commonly observed in everyday phenomena such as surf, fast flowing rivers, billowing storm clouds, or smoke from a chimney, and most fluid flows occurring in nature or created in engineering applications are turbulent. Turbulence is caused by excessive kinetic energy in parts of a fluid flow, which overcomes the damping effect of the fluid's viscosity. For this reason turbulence is commonly realized in low viscosity fluids. In general terms, in turbulent flow, unsteady vortices appear of many sizes which interact with each other, consequently drag due to friction effects increases. This increases the energy needed to pump fluid through a pipe. The onset of turbulence can be predicted by the dimensionless Reyno ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravitational Collapse
Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of gravity. Gravitational collapse is a fundamental mechanism for structure formation in the universe. Over time an initial, relatively smooth distribution of matter will collapse to form pockets of higher density, typically creating a hierarchy of condensed structures such as clusters of galaxies, stellar groups, stars and planets. A star is born through the gradual gravitational collapse of a cloud of interstellar matter. The compression caused by the collapse raises the temperature until thermonuclear fusion occurs at the center of the star, at which point the collapse gradually comes to a halt as the outward thermal pressure balances the gravitational forces. The star then exists in a state of dynamic equilibrium. Once all its energy sources are exhausted, a star will again collapse until it reaches a new equilibrium ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Technion – Israel Institute Of Technology
The Technion – Israel Institute of Technology ( he, הטכניון – מכון טכנולוגי לישראל) is a public research university located in Haifa, Israel. Established in 1912 under the dominion of the Ottoman Empire, the Technion is the oldest university in the country. The Technion is ranked as one of the top universities in both Israel and the Middle East, and in the world's top 100 universities in the 2022 Academic Ranking of World Universities. The university offers degrees in science and engineering, and related fields such as architecture, medicine, industrial management, and education. It has 19 academic departments, 60 research centers, and 12 affiliated teaching hospitals. Since its founding, it has awarded more than 123,000 degrees and its graduates are cited for providing the skills and education behind the creation and protection of the State of Israel. Technion's 565 faculty members include three Nobel Laureates in chemistry. Four Nobel Laureates ha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
