The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform
Roman Juszkiewicz - One of the best experts on this subject based on the ideXlab platform.
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Dark Matter Gravitational Clustering With a Long-Range Scalar Interaction
Physical Review D, 2009Co-Authors: Wojciech A. Hellwing, Roman JuszkiewiczAbstract:We explore the possibility of improving the {lambda}CDM model at megaparsec scales by introducing a scalar interaction that increases the Mutual Gravitational Attraction of dark matter particles. Using N-body simulations, we study the spatial distribution of dark matter particles and halos. We measure the effect of modifications in the Newton's gravity on properties of the two-point correlation function, the dark matter power spectrum, the cumulative halo mass function, and density probability distribution functions. The results look promising: the scalar interactions produce desirable features at megaparsec scales without spoiling the {lambda}CDM successes at larger scales.
Barrabés Vera Esther - One of the best experts on this subject based on the ideXlab platform.
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Òrbites de segona espècie del problema espacial de 3 cossos
'Universitat Autonoma de Barcelona', 2001Co-Authors: Barrabés Vera EstherAbstract:Òrbites de segona espècie del problema espacial de 3 cossosEl problema general de tres cossos consisteix en l'estudi del moviment de tres cossos subjectes a les atraccions gravitacionals mútues. Una simplificació d'aquest problema s'obté en considerar que un dels cossos té massa menyspreable (P), de manera que la seva presència no afecta el moviment dels altres dos (anomenats primaris, E i M), els quals es mouen en òrbites circulars al voltant del seu centre de masses. L'estudi del moviment del tercer cos degut a l'atracció dels dos primaris és el que es coneix com a problema restringit de tres cossos, pla o espacial segons que aquest moviment es mantingui en el pla orbital dels primaris o no.En aquest context, es situa l'origen de coordenades en el centre de masses dels dos primaris i es pren un sistema d'eixos giratori (sinòdic) de manera que aquests es trobin fixos sobre un dels eixos. Prenent les unitats adequades, els cossos E i M tenen masses 1-m i m respectivament, on m [0,1]. Poincaré en els Méthodes Nouvelles de la Mechanique Celeste defineix dos tipus de solucions periòdiques del problema restringit: les de primera espècie, que són solucions properes a òrbites keplerianes per valors de m petits, i les de segona espècie, que són properes a arcs d'el·lipse connectats per punts angulosos. Aquestes últimes són òrbites que passen molt a prop del primari de massa petita.Ens centrem en l'estudi de les òrbites p-q ressonants. Són òrbites que surten d'un entorn de centre M i radi ma i que, després d'allunyar-se, tornen a ell al cap d'un cert temps, durant el qual el primari petit a fet aproximadament q voltes al voltant de E i el cos infinitesimal n'ha fet p. Mentre P està fora de l'entorn de M, es veu que la solució del problema restringit (solució exterior) es pot aproximar per la d'un problema de dos cossos i es calcula de quin ordre és l'error que es comet en l'aproximació. Aquesta aproximació ens permetrà calcular la posició i velocitat del tercer cos en l'instant de retorn a l'entorn de M i estudiar quines condicions inicials asseguren que l'òrbita és p-q ressonant.S'estudia també la solució del problema restringit amb les mateixes condicions inicials sobre l'entorn de M de radi ma, però fent anar el temps enrera i passant per dins l'entorn (solució interior). En aquest cas es veu que l'òrbita del tercer cos s'aproxima per una d'hiperbòlica i es calcula l'error que es comet en l'aproximació, la qual ens permetrà donar la posició i velocitat de P en el moment de sortir de l'entorn de M i després d'haver-hi passat per dins. Finalment, s'estudia quines condicions inicials asseguren que les posicions i velocitats de retorn a l'entorn exteriors i interiors coincideixen fins a ordre ma i a més asseguren que l'òrbita és p-q ressonant. La memòria finalitza amb algunes exploracions numèriques que mostren famílies d'òrbites periòdiques espacials trobades a partir d'òrbites crítiques, periòdiques i simètriques de segona espècie planes.Second Species Orbits of the Spatial Three Body ProblemThe three-body problem consists of studying the movement of three bodies subjected to their Mutual Gravitational Attraction. This problem can be simplified considering that the mass of one of the bodies (P) is negligible and has no effect on the movement of the other two bodies (E and M, called primaries), which are moving in circular orbits around their centre of mass. The study of the movement of the massless body is known as the Restricted Three-Body Problem (RTBP). It is called Plane RTBP if the third body keeps within the orbital plane of the primaries and, if not, spatial. The later will be our case.In this context, we take a synodical system, in which the origin of coordinates is at the centre of the masses and the primaries are fixed on the x-axis. The units can be chosen in such a way that E and M have respectively mass 1-m and m, where m [0,1]. Poincaré in Méthodes Nouvelles de la Mechanique Celeste defines two classes of periodic solutions in the restricted problem: first species and second species. The first ones are close to Keplerian circles or ellipses for values of m near zero, and the second ones are closed to arcs of Keplerian ellipses joined by corners. These are orbits which several passages near the small primary.Our study is focused on the p-q resonant orbits. These orbits leave the neighbourhood of centre M and radius ma and return to it, while the small and the infinitesimal bodies do p and q revolutions respectively around the main primary. While the third body is far from the small body, the solution of the restricted problem (called outer solution) can be approximated by a two-body solution (an elliptic orbit) and the error involved in the approximation is calculated. This approximated orbit allows us to calculate the position and the velocity of the third body at the time of its return to the neighbourhood of M and to study which initial conditions ensure that the orbit is p-q resonant. The solution to the restricted problem with the same initial conditions on the ball of centre M and radius ma, but moving back inside the ball (called inner solution) is also studied. In that case the orbit of the third body can be approximated by a hyperbola and the error involved in the approximation can also be calculated. This approximation gives us the position and the velocity at the time the orbit leaves the ball after passing through it. In order to obtain periodic orbits it is necessary that the outer and inner applications match. To give an approximation, the set of initial conditions which ensure that the return positions and the velocities match up to order of ma and the orbit is p-q resonant is studied.Finally there are several numerical explorations that show families of spatial, periodic orbits originating from plane, critical, symmetric, periodic second species orbits
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Òrbites de segona espècie del problema espacial de 3 cossos
Bellaterra : Universitat Autònoma de Barcelona, 2001Co-Authors: Barrabés Vera Esther, Universitat Autònoma De Barcelona. Departament De MatemàtiquesAbstract:Consultable des del TDXTítol obtingut de la portada digitalitzadaÒrbites de segona espècie del problema espacial de 3 cossos El problema general de tres cossos consisteix en l'estudi del moviment de tres cossos subjectes a les atraccions gravitacionals mútues. Una simplificació d'aquest problema s'obté en considerar que un dels cossos té massa menyspreable (P), de manera que la seva presència no afecta el moviment dels altres dos (anomenats primaris, E i M), els quals es mouen en òrbites circulars al voltant del seu centre de masses. L'estudi del moviment del tercer cos degut a l'atracció dels dos primaris és el que es coneix com a problema restringit de tres cossos, pla o espacial segons que aquest moviment es mantingui en el pla orbital dels primaris o no. En aquest context, es situa l'origen de coordenades en el centre de masses dels dos primaris i es pren un sistema d'eixos giratori (sinòdic) de manera que aquests es trobin fixos sobre un dels eixos. Prenent les unitats adequades, els cossos E i M tenen masses 1-m i m respectivament, on mŒ[0,1]. Poincaré en els Méthodes Nouvelles de la Mechanique Celeste defineix dos tipus de solucions periòdiques del problema restringit: les de primera espècie, que són solucions properes a òrbites keplerianes per valors de m petits, i les de segona espècie, que són properes a arcs d'el·lipse connectats per punts angulosos. Aquestes últimes són òrbites que passen molt a prop del primari de massa petita. Ens centrem en l'estudi de les òrbites p-q ressonants. Són òrbites que surten d'un entorn de centre M i radi ma i que, després d'allunyar-se, tornen a ell al cap d'un cert temps, durant el qual el primari petit a fet aproximadament q voltes al voltant de E i el cos infinitesimal n'ha fet p. Mentre P està fora de l'entorn de M, es veu que la solució del problema restringit (solució exterior) es pot aproximar per la d'un problema de dos cossos i es calcula de quin ordre és l'error que es comet en l'aproximació. Aquesta aproximació ens permetrà calcular la posició i velocitat del tercer cos en l'instant de retorn a l'entorn de M i estudiar quines condicions inicials asseguren que l'òrbita és p-q ressonant. S'estudia també la solució del problema restringit amb les mateixes condicions inicials sobre l'entorn de M de radi ma, però fent anar el temps enrera i passant per dins l'entorn (solució interior). En aquest cas es veu que l'òrbita del tercer cos s'aproxima per una d'hiperbòlica i es calcula l'error que es comet en l'aproximació, la qual ens permetrà donar la posició i velocitat de P en el moment de sortir de l'entorn de M i després d'haver-hi passat per dins. Finalment, s'estudia quines condicions inicials asseguren que les posicions i velocitats de retorn a l'entorn exteriors i interiors coincideixen fins a ordre ma i a més asseguren que l'òrbita és p-q ressonant. La memòria finalitza amb algunes exploracions numèriques que mostren famílies d'òrbites periòdiques espacials trobades a partir d'òrbites crítiques, periòdiques i simètriques de segona espècie planes.Second Species Orbits of the Spatial Three Body Problem The three-body problem consists of studying the movement of three bodies subjected to their Mutual Gravitational Attraction. This problem can be simplified considering that the mass of one of the bodies (P) is negligible and has no effect on the movement of the other two bodies (E and M, called primaries), which are moving in circular orbits around their centre of mass. The study of the movement of the massless body is known as the Restricted Three-Body Problem (RTBP). It is called Plane RTBP if the third body keeps within the orbital plane of the primaries and, if not, spatial. The later will be our case. In this context, we take a synodical system, in which the origin of coordinates is at the centre of the masses and the primaries are fixed on the x-axis. The units can be chosen in such a way that E and M have respectively mass 1-m and m, where mŒ[0,1]. Poincaré in Méthodes Nouvelles de la Mechanique Celeste defines two classes of periodic solutions in the restricted problem: first species and second species. The first ones are close to Keplerian circles or ellipses for values of m near zero, and the second ones are closed to arcs of Keplerian ellipses joined by corners. These are orbits which several passages near the small primary. Our study is focused on the p-q resonant orbits. These orbits leave the neighbourhood of centre M and radius ma and return to it, while the small and the infinitesimal bodies do p and q revolutions respectively around the main primary. While the third body is far from the small body, the solution of the restricted problem (called outer solution) can be approximated by a two-body solution (an elliptic orbit) and the error involved in the approximation is calculated. This approximated orbit allows us to calculate the position and the velocity of the third body at the time of its return to the neighbourhood of M and to study which initial conditions ensure that the orbit is p-q resonant. The solution to the restricted problem with the same initial conditions on the ball of centre M and radius ma, but moving back inside the ball (called inner solution) is also studied. In that case the orbit of the third body can be approximated by a hyperbola and the error involved in the approximation can also be calculated. This approximation gives us the position and the velocity at the time the orbit leaves the ball after passing through it. In order to obtain periodic orbits it is necessary that the outer and inner applications match. To give an approximation, the set of initial conditions which ensure that the return positions and the velocities match up to order of ma and the orbit is p-q resonant is studied. Finally there are several numerical explorations that show families of spatial, periodic orbits originating from plane, critical, symmetric, periodic second species orbits
Adam Johnson - One of the best experts on this subject based on the ideXlab platform.
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An Experiment in Using Virtual Worlds for Scientific Visualization of Self-Gravitating Systems
Journal For Virtual Worlds Research, 2009Co-Authors: Will M. Farr, Piet Hut, Jeff Ames, Adam JohnsonAbstract:In virtual worlds objects fall straight down. By replacing a few lines of code to include Newton's gravity in full, virtual world software can become an N-body simulation code with visualization included where objects move under their Mutual Gravitational Attraction as stars in a cluster. We report on our recent experience of adding a Gravitational n-body simulator to the OpenSim virtual world physics engine. OpenSim is an open-source, virtual world server that provides a 3D immersive experience to users who connect using the popular “Second Life” client software from Linden Labs. With the addition of the n-body simulation engine, multiple users can collaboratively create point-mass gravitating objects in the virtual world and then observe the subsequent Gravitational evolution of their “stellar” system. We view this work as an experiment examining the suitability of virtual worlds for scientific visualization, and we report on future work to enhance and expand the prototype we have built.
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An Experiment in Using Virtual Worlds for Scientific Visualization of Self-Gravitating Systems
arXiv: Instrumentation and Methods for Astrophysics, 2009Co-Authors: Will M. Farr, Piet Hut, Jeff Ames, Adam JohnsonAbstract:In virtual worlds, objects fall straight down. By replacing a few lines of code to include Newton's gravity, virtual world software can become an N-body simulation code with visualization included where objects move under their Mutual Gravitational Attraction as stars in a cluster. We report on our recent experience of adding a Gravitational N-body simulator to the OpenSim virtual world physics engine. OpenSim is an open-source, virtual world server that provides a 3D immersive experience to users who connect using the popular "Second Life" client software from Linden Labs. With the addition of the N-body simulation engine, which we are calling NEO, short for N-Body Experiments in OpenSim, multiple users can collaboratively create point-mass gravitating objects in the virtual world and then observe the subsequent Gravitational evolution of their "stellar" system. We view this work as an experiment examining the suitability of virtual worlds for scientific visualization, and we report on future work to enhance and expand the prototype we have built. We also discuss some standardization and technology issues raised by our unusual use of virtual worlds.
Wojciech A. Hellwing - One of the best experts on this subject based on the ideXlab platform.
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Dark Matter Gravitational Clustering With a Long-Range Scalar Interaction
Physical Review D, 2009Co-Authors: Wojciech A. Hellwing, Roman JuszkiewiczAbstract:We explore the possibility of improving the {lambda}CDM model at megaparsec scales by introducing a scalar interaction that increases the Mutual Gravitational Attraction of dark matter particles. Using N-body simulations, we study the spatial distribution of dark matter particles and halos. We measure the effect of modifications in the Newton's gravity on properties of the two-point correlation function, the dark matter power spectrum, the cumulative halo mass function, and density probability distribution functions. The results look promising: the scalar interactions produce desirable features at megaparsec scales without spoiling the {lambda}CDM successes at larger scales.
Rajiv Aggarwal - One of the best experts on this subject based on the ideXlab platform.
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On the Newton–Raphson basins of convergence associated with the libration points in the axisymmetric restricted five-body problem: The concave configuration
International Journal of Non-Linear Mechanics, 2019Co-Authors: Sanam Suraj, Prachi Sachan, Euaggelos E. Zotos, Amit Mittal, Rajiv AggarwalAbstract:Abstract The axisymmetric restricted five-body problem with the concave configuration has been studied numerically to reveal the basins of convergence, by exploring the Newton–Raphson iterative scheme, corresponding to the coplanar libration points (which act as attractors). In addition, four primaries are set in axisymmetric central configurations introduced by Erdi and Czirjak [13] and the motion is governed by Mutual Gravitational Attraction only. The evolution of the positions of libration points is illustrated, as a function of the value of angle parameters. A systematic and rigorous investigation is performed in an effort to unveil how the angle parameters affect the topology of the basins of convergence. In addition, the relation of the domain of basins of convergence with required number of iterations and the corresponding probability distributions are illustrated.
