Search results for "Computational physics"

GPU Based Molecular Dynamics Simulations of Polymer Rings in Concentrated Solution: Structure and Scaling

2011

We report on equilibrium properties of a concentrated solution of non-concatenated ring polymers by Molecular dynamics simulations using HooMD-blue, a fast implementation on graphics processor units (GPUs). We are able to identify the intermediate scaling regime for the radius of gyration Rg ∝ N as well as indication for a crossover to Rg ∝ N for rings with chain length N in our fully flexible off-lattice polymer model. This crossover takes place between a ring size of 2500 and 7500 monomers for monomer density ρ = 0.5. Our results are in agreement with recent studies for lattice and stiff off-lattice models and show once again that this scaling is not model dependent at all. Furthermore th…

1982

The molecular weight distribution (MWD) of a high polymer is calculated from a weakly perturbed Zimm-plot of the classical light scattering on dilute solutions of Gaussian polymer coils (theta state). A typical Zimm-plot is simulated corresponding to the measurements of high accuracy as would be obtained by using the laser photometer described by Hack and Meyerhoff. The accuracy as published by these authors for small dissymmetries is used. Two inversion procedures are described in detail and tested, both of them avoiding the use of an empirical formula for the Laplace image of the calculated MWD. A complete numerical analysis of the results is given. The results are compared with those of …

Applications of “Forced Rayleigh Scattering” and “Photon Correlation Spectroscopy” for the examination of transport properties in polymer melts

2007

The importance of optical techniques for the characterization of the dynamics in polymers has increased in the last 10 years. This was caused by the rapid development in optics and microelectronics which has made these techniques easily available and extremely precise. However, in case of the examination of transport properties in bulk polymers, new difficulties arise due to the comparably slow dynamics underlying these phenomena. The topic of this paper is a small survey of two optical techniques which can be applied to solve the arising problems and a presentation of some results of our working group concerning slow translational transport processes in polymers. In a first part, the techn…

GPU accelerated Monte Carlo simulations of lattice spin models

2011

We consider Monte Carlo simulations of classical spin models of statistical mechanics using the massively parallel architecture provided by graphics processing units (GPUs). We discuss simulations of models with discrete and continuous variables, and using an array of algorithms ranging from single-spin flip Metropolis updates over cluster algorithms to multicanonical and Wang-Landau techniques to judge the scope and limitations of GPU accelerated computation in this field. For most simulations discussed, we find significant speed-ups by two to three orders of magnitude as compared to single-threaded CPU implementations.

Time-domain effective-one-body gravitational waveforms for coalescing compact binaries with nonprecessing spins, tides and self-spin effects

2018

We present TEOBResumS, a new effective-one-body (EOB) waveform model for nonprecessing (spin-aligned) and tidally interacting compact binaries.Spin-orbit and spin-spin effects are blended together by making use of the concept of centrifugal EOB radius. The point-mass sector through merger and ringdown is informed by numerical relativity (NR) simulations of binary black holes (BBH) computed with the SpEC and BAM codes. An improved, NR-based phenomenological description of the postmerger waveform is developed.The tidal sector of TEOBResumS describes the dynamics of neutron star binaries up to merger and incorporates a resummed attractive potential motivated by recent advances in the post-Newt…

Multipactor radiation analysis within a waveguide region based on a frequency-domain representation of the dynamics of charged particles

2009

[EN] A technique for the accurate computation of the electromagnetic fields radiated by a charged particle moving within a parallel-plate waveguide is presented. Based on a transformation of the time-varying current density of the particle into a time-harmonic current density, this technique allows the evaluation of the radiated electromagnetic fields both in the frequency and time domains, as well as in the near- and far-field regions. For this purpose, several accelerated versions of the parallel-plate Green's function in the frequency domain have been considered. The theory has been successfully applied to the multipactor discharge occurring within a two metal-plates region. The proposed…

Characterizing Cavities in Model Inclusion Fullerenes: A Comparative Study

2001

Abstract: The fullerene-82 cavity is selected as a model system in order to test several methods for characterizing inclusion molecules. The methods are based on different technical foundations such as a square and triangular tessellation of the molecular surface, spherical tessellation of the molecular surface, numerical integration of the atomic volumes and surfaces, triangular tessellation of the molecular surface, and cubic lattice approach to the molecular volume. Accurate measures of the molecular volume and surface area have been performed with the pseudorandom Monte Carlo (MCVS) and uniform Monte Carlo (UMCVS) methods. These calculations serve as a reference for the rest of the meth…

Механика композитных материалов, 2022, Т. 58, No 1, Январь-февраль

2022

Modeling friction between shearing brittle surfaces with a discrete element method

2018

Hauraiden materiaalien murtuminen on eräs materiaalifysiikan peruskysymyksistä. Sille ei ole vieläkään olemassa täydellistä teoreettista selitystä, joten ennusteiden tekeminen nojaa vahvasti kokeisiin ja niihin perustuviin numeerisiin malleihin. Tässä työssä suunnittelemme ja toteutamme diskreettielementtimenetelmän sellaisen fysikaalisen systeemin tutkimiseen, jossa kaksi haurasta pintaa leikkaavat toisiaan. Keskitymme erityisesti siihen kuinka erilaiset voimamallit sisäiselle kitkalle vaikuttavat materiaalin ulkoiseen kitkaan. Käyttämällä graniittia koemateriaalina huomaamme, että sen ulkoinen kitka riippuu voimakkaasti sen sisäisestä kitkasta, kun ulkoinen paine on lähellä materiaalin pu…

SPI/INTEGRAL in-flight performance

2003

The SPI instrument has been launched on-board the INTEGRAL observatory on October 17, 2002. SPI is a spectrometer devoted to the sky observation in the 20 keV-8 MeV energy range using 19 germanium detectors. The performance of the cryogenic system is nominal and allows to cool the 19 kg of germanium down to 85 K with a comfortable margin. The energy resolution of the whole camera is 2.5 keV at 1.1 MeV. This resolution degrades with time due to particle irradiation in space. We show that the annealing process allows the recovery of the initial performance. The anticoincidence shield works as expected, with a low threshold at 75 keV, reducing the GeD background by a factor of 20. The digital …