Search results for "LOCI"
showing 10 items of 1277 documents
A Frozen-Flow Approximation to the Evolution of Large-Scale Structures in the Universe
1992
A new approximation to the evolution of large-scale structures in the Universe is proposed which is based on neglecting the role of particle inertia compared to the damping implied by the Hubble drag. We call this approximation frozen flow because particles move by updating at each step their velocity to the local value of the peculiar velocity field, here approximated by its growing linear mode: stream-lines are then frozen to their initial shape. The situation is quite different from that of the Zel'dovich algorithm, where the velocity is kept constant along each particle trajectory
Colloidal crystal motion in electric fields
2003
Abstract We report on the short and long time flow behaviour of colloidal crystals subjected to a homogeneous electrical square wave a.c.-field in closed cells of rectangular cross section. Local velocities are determined from Laser Doppler velocimetry, sample structure and morphology were observed by time resolved polarisation microscopy. We observe a complex time dependence of the flow behaviour. After each field reversal we find a transition from an initial parabola-like flow to a final plug-like flow. On the time scale of minutes to hours channel narrowing occurs, i.e. flow initially restricted by the cell walls becomes restricted to the cell centre by wall based stationary crystals. Wi…
Stability of a Tensioned Axially Moving Plate Subjected to Cross-Direction Potential Flow
2015
We analyze the stability of an axially moving Kirchhoff plate, subjected to an axial potential flow perpendicular to the direction of motion. The dimensionality of the problem is reduced by considering a cross-directional cross-section of the plate, approximating the axial response with the solution of the corresponding problem of a moving plate in vacuum. The flow component is handled via a Green’s function solution. The stability of the cross-section is investigated via the classical Euler type static linear stability analysis method. The resulting eigenvalue problem is solved numerically using Hermite type finite elements. As a result, the critical velocity and the corresponding eigenfun…
HD 50975: a yellow supergiant in a spectroscopic binary system
2014
Context. Recent detection of a yellow supergiant star as a possible progenitor of a supernova has posed serious questions about our understanding of the evolution of massive stars. Aims. The spectroscopic binary star HD 50975 with an unseen hot secondary was studied in detail with the main goal of estimating fundamental parameters of both components and the binary system. Methods. A comprehensive analysis and modeling of collected long-term radial velocity measurements, photometric data, and spectra was performed to calculate orbital elements, atmospheric parameters, abundances, and luminosities. The spectrum in an ultraviolet region was studied to clarify the nature of an unseen companion …
Absolute parameters for binary systems
1997
New high-quality light curves of the late-type binary system BH Vir have been obtained during a 6 year photometric uvby and monitoring program of low mass eclipsing binaries (Clement et al. 1997), hereafter Papers I and II. This paper presents detailed analysis of this binary based on the four light curves obtained within our program. The activity wave superimposed on the eclipse-modulated light curves has been adjusted and removed by using a new iterative application of the standard EBOP code together with truncated Fourier Series fittings. Combining the recent radial velocity curves (Popper 1995) with the geometrical elements deduced from the "clean" photometric light curves, the absolute…
Absolute parameters for binary systems
1997
New light curves of the late-type binary sys- tem ZZ UMa were obtained during a uvby and H mon- itoring program on low mass eclipsing binaries, that has been carried out in a six year photometric observational program (Clement et al. 1997a, Paper I). The main goal of the program is to obtain accurate absolute parameters for stars in the low and intermediate mass range, in order to improve the Mass-Luminosity Relationship (MLR) at the end of the main sequence. This paper presents a complete analysis of the rst uvby light curves of the late-type detached eclipsing binary ZZ UMa. This binary system has been observed during eight campaigns at the Calar Alto Observatory (Almeria, Spain). The act…
Kinematic relative velocity with respect to stationary observers in Schwarzschild spacetime
2013
We study the kinematic relative velocity of general test particles with respect to stationary observers (using spherical coordinates) in Schwarzschild spacetime, obtaining that its modulus does not depend on the observer, unlike Fermi, spectroscopic and astrometric relative velocities. We study some fundamental particular cases, generalizing some results given in other work about stationary and radial free-falling test particles. Moreover, we give a new result about test particles with circular geodesic orbits: the modulus of their kinematic relative velocity with respect to any stationary observer depends only on the radius of the circular orbit, and so, it remains constant.
Numerical simulations of the internal shock model in magnetized relativistic jets of blazars
2015
The internal shocks scenario in relativistic jets is used to explain the variability of the blazar emission. Recent studies have shown that the magnetic field significantly alters the shell collision dynamics, producing a variety of spectral energy distributions and light-curves patterns. However, the role played by magnetization in such emission processes is still not entirely understood. In this work we numerically solve the magnetohydodynamic evolution of the magnetized shells collision, and determine the influence of the magnetization on the observed radiation. Our procedure consists in systematically varying the shell Lorentz factor, relative velocity, and viewing angle. The calculatio…
The structure of steady, relativistic, magnetised jets with rotation
2015
We present equilibrium models of relativistic magnetised, infinite, axisymmetric jets with rotation propagating through an homogeneous, unmagnetised ambient medium at rest. The jet models are characterised by six functions defining the radial profiles of density, pressure, and the toroidal and axial components of velocity and magnetic field. Fixing the ambient pressure and the jet rest-mass density and axial components of the flow velocity and magnetic field, we analyze the influence of the toroidal magnetic field and several rotation laws on the structure of the equilibrium models. Our approach excludes by construction the analysis of the self-consistently magnetically launched jet models …
The termination region of high-mass microquasar jets
2011
The environment of high-mass X-ray binaries can be characterized either by the SNR that forms these systems, or by the wind from the companion massive star. These regions should be tenuous but very hot, and surrounded by a dense and cold shocked ISM shell. The interaction between the jet and such a complex medium, also affected by the system proper motion, can lead to very different jet termination structures. The evolution of the jet termination regions during the life of a high-mass microquasar is simulated to improve the present understanding of these structures. Also, the evolving emission characteristics are modeled to inform potential observational campaigns for this class of object. …