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匹配条件: “Zoltán László” ,找到相关结果约372080条。
Acta Geographica Debrecina. Landscape and Environment Series , 2008,
Abstract: The aim of the study was to rank and classify Hungarian cities and counties according to their environmental quality and level of environmental awareness. Ranking of the Hungarian cities and counties are represented on their Green Cities Index” and Green Counties Index” values. According to the methodology shown in Part 1, cities and counties were grouped on different classification techniques and efficacy of the classification was analysed. However, they did not give acceptable results either for the cities, or for the counties. According to the parameters of the here mentioned three algorithms, reasonable structures were not found in any clustering. Clusters received applying algorithm fanny, though having weak structure, indicate large and definite regions in Hungary, which can be circumscribed by clear geographical objects.
3+1+1 dimensional covariant gravitational dynamics on an asymmetrically embedded brane
Zoltán Keresztes,László á. Gergely
Physics , 2009, DOI: 10.1002/andp.201010421
Abstract: We give the evolution and constraint equations on an asymmetrically embedded brane in the form of average and difference equations.
On the validity of the 5-dimensional Birkhoff theorem: The tale of an exceptional case
Zoltán Keresztes,László á. Gergely
Physics , 2007, DOI: 10.1088/0264-9381/25/16/165016
Abstract: The 5-dimensional (5d) Birkhoff theorem gives the class of 5d vacuum space-times containing spatial hypersurfaces with cosmological symmetries. This theorem is violated by the 5d vacuum Gergely-Maartens (GM) space-time, which is not a representant of the above class, but contains the static Einstein brane as embedded hypersurface. We prove that the 5d Birkhoff theorem is still satisfied in a weaker sense: the GM space-time is related to the degenerated horizon metric of certain black-hole space-times of the allowed class. This result resembles the connection between the Bertotti-Robinson space-time and the horizon region of the extremal Reissner-Nordstrom space-time in general relativity.
Gravitational dynamics in s+1+1 dimensions
László á. Gergely,Zoltán Kovács
Physics , 2005, DOI: 10.1103/PhysRevD.72.064015
Abstract: We present the concomitant decomposition of an (s+2)-dimensional spacetime both with respect to a timelike and a spacelike direction. The formalism we develop is suited for the study of the initial value problem and for canonical gravitational dynamics in brane-world scenarios. The bulk metric is replaced by two sets of variables. The first set consist of one tensorial (the induced metric $g_{ij}$), one vectorial ($M^{i}$) and one scalar ($M$) dynamical quantity, all defined on the s-space. Their time evolutions are related to the second fundamental form (the extrinsic curvature $K_{ij}$), the normal fundamental form ($\mathcal{K}^{i}$) and normal fundamental scalar ($\mathcal{K}$), respectively. The non-dynamical set of variables is given by the lapse function and the shift vector, which however has one component less. The missing component is due to the externally imposed constraint, which states that physical trajectories are confined to the (s+1)-dimensional brane. The pair of dynamical variables ($g_{ij}$, $K_{ij}$), well-known from the ADM-decomposition is supplemented by the pairs ($M^{i}$, $\mathcal{K}^{i}$) and ($M$, $\mathcal{K}$) due to the bulk curvature. We give all projections of the junction condition across the brane and prove that for a perfect fluid brane neither of the dynamical variables has jump across the brane. Finally we complete the set of equations needed for gravitational dynamics by deriving the evolution equations of $K_{ij}$, $\mathcal{K}^{i}$ and $\mathcal{K}$ on a brane with arbitrary matter.
Hamiltonian theory of brane-world gravity
Zoltán Kovács,László á. Gergely
Physics , 2006,
Abstract: A brane-world universe consists of a 4-dimensional brane embedded into a 5-dimensional space-time (bulk). We apply the Arnowitt-Deser-Misner decomposition to the brane-world, which results in a 3+1+1 break-up of the bulk. We present the canonical theory of brane cosmology based on this decomposition. The Hamiltonian equations allow for the study of any physical phenomena in brane gravity. This method gives new prospects for studying the initial value problem, stability analysis, brane black holes, cosmological perturbation theory and canonical quantization in brane-worlds.
Vacuum Kerr-Schild metrics generated by nontwisting congruences
László á. Gergely,Zoltán Perjés
Physics , 2002, DOI: 10.1002/andp.19945060706
Abstract: The Kerr-Schild pencil of metrics $\tilde g_{ab}=g_{ab}+V l_al_b$, with $g_{ab}$ and $\tilde g_{ab}$ satisfying the vacuum Einstein equations, is investigated in the case when the null vector $l$ has vanishing twist. This class of Kerr-Schild metrics contains two solutions: the Kasner metric and a metric wich can be obtained from the Kasner metric by a complex coordinate transformation. Both are limiting cases of the K\'ota-Perj\'es metrics. The base space-time is a pp-wave.
Solution of the vacuum Kerr-Schild problem
László á. Gergely,Zoltán Perjés
Physics , 2002, DOI: 10.1016/0375-9601(93)90385-D
Abstract: The complete solution of the vacuum Kerr-Schild equations in general relativity is presented, including the space-times with a curved background metric. The corresponding result for a flat background has been obtained by Kerr.
Gravitational radiation reaction in compact binary systems: Contribution of the quadrupole-monopole interaction
László á. Gergely,Zoltán Keresztes
Physics , 2002, DOI: 10.1103/PhysRevD.67.024020
Abstract: The radiation reaction in compact spinning binaries on eccentric orbits due to the quadrupole-monopole interaction is studied. This contribution is of second post-Newtonian order. As result of the precession of spins the magnitude $L$ of the orbital angular momentum is not conserved. Therefore a proper characterization of the perturbed radial motion is provided by the energy $E$ and angular average $\bar{L}$. As powerful computing tools, the generalized true and eccentric anomaly parametrizations are introduced. Then the secular losses in energy and magnitude of orbital angular momentum together with the secular evolution of the relative orientations of the orbital angular momentum and spins are found for eccentric orbits by use of the residue theorem. The circular orbit limit of the energy loss agrees with Poisson's earlier result.
Gravitational dynamics in s+1+1 dimensions II. Hamiltonian theory
Zoltán Kovács,László á. Gergely
Physics , 2007, DOI: 10.1103/PhysRevD.77.024003
Abstract: We develop a Hamiltonian formalism of brane-world gravity, which singles out two preferred, mutually orthogonal directions. One is a unit twist-free field of spatial vectors with integral lines intersecting perpendicularly the brane. The other is a temporal vector field with respect to which we perform the Arnowitt-Deser-Misner decomposition of the Einstein-Hilbert Lagrangian. The gravitational variables arise from the projections of the spatial metric and their canonically conjugated momenta as tensorial, vectorial and scalar quantities defined on the family of hypersurfaces containing the brane. They represent the gravitons, a gravi-photon and a gravi-scalar, respectively. From the action we derive the canonical evolution equations and the constraints for these gravitational degrees of freedom both on the brane and outside it. By integrating across the brane, the dynamics also generates the tensorial and scalar projection of the Lanczos equation. The vectorial projection of the Lanczos equation arises in a similar way from the diffeomorphism constraint. Both the graviton and the gravi-scalar are continuous across the brane, however the momentum of the gravi-vector has a jump, related to the energy transport (heat flow) on the brane.
Covariant gravitational dynamics in 3+1+1 dimensions
Zoltán Keresztes,László á. Gergely
Physics , 2009, DOI: 10.1088/0264-9381/27/10/105009
Abstract: We develop a 3+1+1 covariant formalism with cosmological and astrophysical applications. First we give the evolution and constraint equations both on the brane and off-brane in terms of 3-space covariant kinematical, gravito-electro-magnetic (Weyl) and matter variables. We discuss the junction conditions across the brane in terms of the new variables. Then we establish a closure condition for the equations on the brane. We also establish the connection of this formalism with isotropic and anisotropic cosmological brane-worlds. Finally we derive a new brane solution in the framework of our formalism: the tidal charged Taub-NUT-(A)dS brane, which obeys the closure condition.

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