A NICMOS imaging study of high-z quasar host galaxies     

Marek J. Kukula  James S. Dunlop  Ross J. McLure  Lance Miller  Will J. Percival  Stefi A. Baum  Christopher P. O'Dea 《Monthly notices of the Royal Astronomical Society》2001,326(4):1533-1546

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Numerical solution to the oblique derivative boundary value problem on non-uniform grids above the Earth topography     

Matej Medl’a  Karol Mikula  Róbert Čunderlík  Marek Macák 《Journal of Geodesy》2018,92(1):1-19

The paper presents a numerical solution of the oblique derivative boundary value problem on and above the Earth’s topography using the finite volume method (FVM). It introduces a novel method for constructing non-uniform hexahedron 3D grids above the Earth’s surface. It is based on an evolution of a surface, which approximates the Earth’s topography, by mean curvature. To obtain optimal shapes of non-uniform 3D grid, the proposed evolution is accompanied by a tangential redistribution of grid nodes. Afterwards, the Laplace equation is discretized using FVM developed for such a non-uniform grid. The oblique derivative boundary condition is treated as a stationary advection equation, and we derive a new upwind type discretization suitable for non-uniform 3D grids. The discretization of the Laplace equation together with the discretization of the oblique derivative boundary condition leads to a linear system of equations. The solution of this system gives the disturbing potential in the whole computational domain including the Earth’s surface. Numerical experiments aim to show properties and demonstrate efficiency of the developed FVM approach. The first experiments study an experimental order of convergence of the method. Then, a reconstruction of the harmonic function on the Earth’s topography, which is generated from the EGM2008 or EIGEN-6C4 global geopotential model, is presented. The obtained FVM solutions show that refining of the computational grid leads to more precise results. The last experiment deals with local gravity field modelling in Slovakia using terrestrial gravity data. The GNSS-levelling test shows accuracy of the obtained local quasigeoid model.  相似文献   

Optimization routine for identification of model parameters in soil plasticity     

Hans Mattsson  Marek Klisinski  Kennet Axelsson 《国际地质力学数值与分析法杂志》2001,25(5):435-472

The paper presents an optimization routine especially developed for the identification of model parameters in soil plasticity on the basis of different soil tests. Main focus is put on the mathematical aspects and the experience from application of this optimization routine. Mathematically, for the optimization, an objective function and a search strategy are needed. Some alternative expressions for the objective function are formulated. They capture the overall soil behaviour and can be used in a simultaneous optimization against several laboratory tests. Two different search strategies, Rosenbrock's method and the Simplex method, both belonging to the category of direct search methods, are utilized in the routine. Direct search methods have generally proved to be reliable and their relative simplicity make them quite easy to program into workable codes. The Rosenbrock and simplex methods are modified to make the search strategies as efficient and user‐friendly as possible for the type of optimization problem addressed here. Since these search strategies are of a heuristic nature, which makes it difficult (or even impossible) to analyse their performance in a theoretical way, representative optimization examples against both simulated experimental results as well as performed triaxial tests are presented to show the efficiency of the optimization routine. From these examples, it has been concluded that the optimization routine is able to locate a minimum with a good accuracy, fast enough to be a very useful tool for identification of model parameters in soil plasticity. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Black hole spin in GRS 1915+105   总被引：2，自引：0，他引：2  

Matthew Middleton  Chris Done  Marek Gierli&#;ski  Shane W. Davis 《Monthly notices of the Royal Astronomical Society》2006,373(3):1004-1012

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The International Conference on ＂Geoheritage for Sustainable Development＂ Druskininkai, Lithuania, May 27-30, 2006     

Barry Thomas Jonas Satkunas Marek Graniczny 《《幕》》2006,29(4):303-304

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GRS 1915+105: the brightest Galactic black hole     

Chris Done  Grzegorz Wardzi&#;ski  Marek Gierli&#;ski 《Monthly notices of the Royal Astronomical Society》2004,349(2):393-403

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Discovery of powerful millisecond flares from Cygnus X-1     

Marek Gierli&#;ski  Andrzej A. Zdziarski 《Monthly notices of the Royal Astronomical Society》2003,343(3):L84-L88

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A structure and energy dissipation efficiency of relativistic reconfinement shocks     

Krzysztof Nalewajko  Marek Sikora 《Monthly notices of the Royal Astronomical Society》2009,392(3):1205-1210

We present a semi-analytical hydrodynamical model for the structure of reconfinement shocks formed in astrophysical relativistic jets interacting with external medium. We take into account exact conservation laws, both across the shock front and in the zone of the shocked matter, and exact angular relations. Our results confirm a good accuracy of the approximate formulae derived by Komissarov & Falle. However, including the transverse pressure gradient in the shocked jet, we predict an absolute size of the shock to be about twice larger. We calculate the efficiency of the kinetic energy dissipation in the shock and show a strong dependence on both the bulk Lorentz factor and opening angle of the jet.  相似文献   

High-frequency X-ray variability as a mass estimator of stellar and supermassive black holes     

Marek Gierli&#;ski  Marek Niko&#;ajuk  Bo&#;ena Czerny 《Monthly notices of the Royal Astronomical Society》2008,383(2):741-749

There is increasing evidence that supermassive black holes in active galactic nuclei (AGN) are scaled-up versions of Galactic black holes. We show that the amplitude of high-frequency X-ray variability in the hard spectral state is inversely proportional to the black hole mass over eight orders of magnitude. We have analysed all available hard-state data from RXTE of seven Galactic black holes. Their power density spectra change dramatically from observation to observation, except for the high-frequency (≳10 Hz) tail, which seems to have a universal shape, roughly represented by a power law of index −2. The amplitude of the tail,   C _M   (extrapolated to 1 Hz), remains approximately constant for a given source, regardless of the luminosity, unlike the break or quasi-periodic oscillation frequencies, which are usually strongly correlated with luminosity. Comparison with a moderate-luminosity sample of AGN shows that the amplitude of the tail is a simple function of black hole mass,   C _M = C / M   , where   C ≈ 1.25 M_⊙ Hz⁻¹  . This makes   C _M   a robust estimator of the black hole mass which is easy to apply to low- to moderate-luminosity supermassive black holes. The high-frequency tail with its universal shape is an invariant feature of a black hole and, possibly, an imprint of the last stable orbit.  相似文献   

Spacetime is not just space and time     

Marek A. Abramowicz   《New Astronomy Reviews》2008,51(10-12):799

Our physical intuition usually separates space from time, ignoring the spacetime character of the physical reality. In strongly curved spacetimes this may lead to confusion and paradoxes. I present here two examples: (1) in the non-static cosmological spacetimes with flat space sections, the cosmological expansion of space is a true physical effect. Contrary to what the intuition imagines, it cannot be explained as a motion of matter in a non-expanding flat space. (2) Contrary to intuition, for static spacetimes the mathematically simplest 3+1 split is not given by the direct projection as in the standard ADM scheme. The simplest split is defined by a counter intuitive “optical geometry” that redshifts both space and time by the same conformal factor.  相似文献