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NEMO (Stellar Dynamics Toolbox)
NEMO (Not Everybody Must Observe) is a toolkit for stellar dynamics. At its core it manipulates an ''n''-body system (snapshot), but can also derive or compute orbits, derive images and extract tables to take to other analysis systems. Architecture NEMO was developed on Sun workstations, but ports to most Unix-like systems. At its core NEMO defines a series of objects (SnapShot, Orbit, Image) and associated header files and libraries to operate on them, and these mirror the stored data in a portable binary-named and type-tagged XML-like format dubbed ''structured file''. The program tsf in NEMO will show the contents of such a file in a human readable way. Another feature of NEMO is that all its data can be piped from one task into the next, thus creating whole simulations in a simple Unix pipe. For example, mkplummer - 1000 , snapscale - - vscale=0.5 , hackcode1 - - tstop=10 , snaptrim - - times=10 , snapgrid - - , ccdfits - final.fits would create a 1000 particle Pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stellar Dynamics
Stellar dynamics is the branch of astrophysics which describes in a statistical way the collective motions of stars subject to their mutual gravity. The essential difference from celestial mechanics is that the number of body N \gg 10. Typical galaxies have upwards of millions of macroscopic gravitating bodies and countless number of neutrinos and perhaps other dark microscopic bodies. Also each star contributes more or less equally to the total gravitational field, whereas in celestial mechanics the pull of a massive body dominates any satellite orbits. Connection with fluid dynamics Stellar dynamics also has connections to the field of plasma physics. The two fields underwent significant development during a similar time period in the early 20th century, and both borrow mathematical formalism originally developed in the field of fluid mechanics. In accretion disks and stellar surfaces, the dense plasma or gas particles collide very frequently, and collisions result in equ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plummer Model
The Plummer model or Plummer sphere is a density law that was first used by H. C. Plummer to fit observations of globular clusters. It is now often used as toy model in N-body simulations of stellar systems. Description of the model The Plummer 3-dimensional density profile is given by : \rho_P(r) = \frac \left(1 + \frac\right)^, where ''M_0'' is the total mass of the cluster, and ''a'' is the Plummer radius, a scale parameter that sets the size of the cluster core. The corresponding potential is : \Phi_P(r) = -\frac, where ''G'' is Newton's gravitational constant. The velocity dispersion is : \sigma_P^2(r) = \frac. The distribution function is : f(\vec, \vec) = \frac \frac (-E(\vec, \vec))^, if E < 0, and otherwise, where is the .
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Astronomy Software
Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole. Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Babylonians, Greeks, Indians, Egyptians, Chinese, Maya, and many ancient indigenous peoples of the Americas. In the past, astronomy included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars. Nowadays, professiona ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomical Imaging
Astrophotography, also known as astronomical imaging, is the photography or imaging of astronomical objects, celestial events, or areas of the night sky. The first photograph of an astronomical object (the Moon) was taken in 1840, but it was not until the late 19th century that advances in technology allowed for detailed stellar photography. Besides being able to record the details of extended objects such as the Moon, Sun, and planets, modern astrophotography has the ability to image objects invisible to the human eye such as dim stars, nebulae, and galaxies. This is done by long time exposure since both film and digital cameras can accumulate and sum photons over these long periods of time. Photography using extended exposure-times revolutionized the field of professional astronomical research, recording hundreds of thousands of new stars, and nebulae invisible to the human eye. Specialized and ever-larger optical telescopes were constructed as essentially big cameras to rec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barnes–Hut Simulation
The Barnes–Hut simulation (named after Josh Barnes and Piet Hut) is an approximation algorithm for performing an ''n''-body simulation. It is notable for having order O(''n'' log ''n'') compared to a direct-sum algorithm which would be O(''n''2). The simulation volume is usually divided up into cubic cells via an octree (in a three-dimensional space), so that only particles from nearby cells need to be treated individually, and particles in distant cells can be treated as a single large particle centered at the cell's center of mass (or as a low-order multipole expansion). This can dramatically reduce the number of particle pair interactions that must be computed. Some of the most demanding high-performance computing projects do computational astrophysics using the Barnes–Hut treecode algorithm, such as DEGIMA. Algorithm The Barnes–Hut tree In a three-dimensional ''n''-body simulation, the Barnes–Hut algorithm recursively divides the ''n'' bodies into ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Institute For Advanced Study
The Institute for Advanced Study (IAS), located in Princeton, New Jersey, in the United States, is an independent center for theoretical research and intellectual inquiry. It has served as the academic home of internationally preeminent scholars, including J. Robert Oppenheimer, Albert Einstein, Hermann Weyl, John von Neumann, and Kurt Gödel, many of whom had emigrated from Europe to the United States. It was founded in 1930 by American educator Abraham Flexner, together with philanthropists Louis Bamberger and Caroline Bamberger Fuld. Despite collaborative ties and neighboring geographic location, the institute, being independent, has "no formal links" with Princeton University. The institute does not charge tuition or fees. Flexner's guiding principle in founding the institute was the pursuit of knowledge for its own sake.Jogalekar. The faculty have no classes to teach. There are no degree programs or experimental facilities at the institute. Research is never contracted or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Piet Hut
Piet Hut (born September 26, 1952) is a Dutch-American astrophysicist, who divides his time between research in computer simulations of dense stellar systems and broadly interdisciplinary collaborations, ranging from other fields in natural science to computer science, cognitive psychology and philosophy. He is currently the Head of the Program in Interdisciplinary Studies at the Institute for Advanced Study (IAS) in Princeton, New Jersey, USA. Asteroid 17031 Piethut is named after him, in honor of his work in planetary dynamics and for co-founding the B612 Foundation, which focuses on prevention of asteroid impacts on Earth. Career In the Netherlands, Hut did a double PhD program, at Utrecht University, in particle physics under Martinus Veltman and in Amsterdam in astrophysics under Ed van den Heuvel, resulting in a PhD at the University of Amsterdam. Previously an assistant professor at the University of California, Berkeley, Hut was in 1985, at the age of 32, appointed as a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
FITS
Flexible Image Transport System (FITS) is an open standard defining a digital file format useful for storage, transmission and processing of data: formatted as multi-dimensional arrays (for example a 2D image), or tables. FITS is the most commonly used digital file format in astronomy. The FITS standard was designed specifically for astronomical data, and includes provisions such as describing photometric and spatial calibration information, together with image origin metadata. The FITS format was first standardized in 1981; it has evolved gradually since then, and the most recent version (4.0) was standardized in 2016. FITS was designed with an eye towards long-term archival storage, and the maxim ''once FITS, always FITS'' represents the requirement that developments to the format must be backward compatible. Image metadata is stored in a human-readable ASCII header. The information in this header is designed to calculate the byte offset of some information in the subse ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Integral
In mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ..., an integral assigns numbers to functions in a way that describes Displacement (geometry), displacement, area, volume, and other concepts that arise by combining infinitesimal data. The process of finding integrals is called integration. Along with Derivative, differentiation, integration is a fundamental, essential operation of calculus,Integral calculus is a very well established mathematical discipline for which there are many sources. See and , for example. and serves as a tool to solve problems in mathematics and physics involving the area of an arbitrary shape, the length of a curve, and the volume of a solid, among others. The integrals enumerated here are those termed definite integrals, which can be int ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virial Theorem
In mechanics, the virial theorem provides a general equation that relates the average over time of the total kinetic energy of a stable system of discrete particles, bound by potential forces, with that of the total potential energy of the system. Mathematically, the theorem states \left\langle T \right\rangle = -\frac12\,\sum_^N \bigl\langle \mathbf_k \cdot \mathbf_k \bigr\rangle where is the total kinetic energy of the particles, represents the force on the th particle, which is located at position , and angle brackets represent the average over time of the enclosed quantity. The word virial for the right-hand side of the equation derives from ''vis'', the Latin word for "force" or "energy", and was given its technical definition by Rudolf Clausius in 1870. The significance of the virial theorem is that it allows the average total kinetic energy to be calculated even for very complicated systems that defy an exact solution, such as those considered in statistical mechanics; thi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Velocity
Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of bodies. Velocity is a physical vector quantity; both magnitude and direction are needed to define it. The scalar absolute value (magnitude) of velocity is called , being a coherent derived unit whose quantity is measured in the SI (metric system) as metres per second (m/s or m⋅s−1). For example, "5 metres per second" is a scalar, whereas "5 metres per second east" is a vector. If there is a change in speed, direction or both, then the object is said to be undergoing an ''acceleration''. Constant velocity vs acceleration To have a ''constant velocity'', an object must have a constant speed in a constant direction. Constant direction cons ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pipeline (Unix)
In Unix-like computer operating systems, a pipeline is a mechanism for inter-process communication using message passing. A pipeline is a set of processes chained together by their standard streams, so that the output text of each process (''stdout'') is passed directly as input (''stdin'') to the next one. The second process is started as the first process is still executing, and they are executed concurrently. The concept of pipelines was championed by Douglas McIlroy at Unix's ancestral home of Bell Labs, during the development of Unix, shaping its toolbox philosophy. It is named by analogy to a physical pipeline. A key feature of these pipelines is their "hiding of internals" (Ritchie & Thompson, 1974). This in turn allows for more clarity and simplicity in the system. This article is about anonymous pipes, where data written by one process is buffered by the operating system until it is read by the next process, and this uni-directional channel disappears when the processes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
