Search results for "force"
showing 10 items of 3423 documents
Computing bulk and shear viscosities from simulations of fluids with dissipative and stochastic interactions
2016
Exact values for bulk and shear viscosity are important to characterize a fluid and they are a necessary input for a continuum description. Here we present two novel methods to compute bulk viscosities by non-equilibrium molecular dynamics (NEMD) simulations of steady-state systems with periodic boundary conditions -- one based on frequent particle displacements and one based on the application of external bulk forces with an inhomogeneous force profile. In equilibrium simulations, viscosities can be determined from the stress tensor fluctuations via Green-Kubo relations; however, the correct incorporation of random and dissipative forces is not obvious. We discuss different expressions pro…
Three-nucleon forces and the three-nucleon systems
1993
The basic principles and philosophy which have guided the area of few-nucleon physics are motivated and discussed. Recent advances have made it possible to solve accurately the Schrodinger (or Faddeev) equation for many of the configurations of the few-nucleon systems, A brief review is given of some of the results of these calculations, which also Indicate that one-pion exchange plays roughly the same role in binding these systems that it plays in electromagnetic meson-exchange currents. Finally, a qualitative discussion of chiral perturbation theory is presented, which highlights the role that chiral symmetry plays in the nuclear force. Three-body forces from different areas of physics ar…
Systematic study of shell-model effective interaction insdshell
2014
The spin-tensor decomposition method has been used to analyse the shell model effective interactions in sd shell systematically. Almost all the interactions have been studied, including the microscopic interactions and phenomenological ones. It can be noticed that the discrepancies between the central force of microscopic interactions with the ones of empirical interactions are remarkable.
Towards an atomistic understanding of solid friction by computer simulations
2002
Friction between two solid bodies in sliding motion takes place on a large spectrum of length and time scales: From the nanometer/second scale in an atomic force microscope up to the extremely macroscopic scales of tectonic motion. Despite our familiarity with friction, fundamental questions about its atomistic origins remain unanswered. Phenomenological laws that describe the friction in many systems were published more than 300 years ago by Amontons: The frictional force is proportional to the applied load and independent of the apparent area of contact. The atomistic origins of this simple law is still controversial. Many explanations, which seemed to be well-established until recently, …
Vacuum field correlations and three-body Casimir-Polder potential with one excited atom
2004
The three-body Casimir-Polder potential between one excited and two ground-state atoms is evaluated. A physical model based on the dressed field correlations of vacuum fluctuations is used, generalizing a model previously introduced for three ground-state atoms. Although the three-body potential with one excited atom is already known in the literature, our model gives new insights on the nature of non-additive Casimir-Polder forces with one or more excited atoms.
First-principles investigation of the bulk and low-index surfaces ofMoSe2
2014
In the framework of density functional theory, the geometry, electronic structure, and magnetic properties of the bulk and low index surfaces of $\mathrm{Mo}{\mathrm{Se}}_{2}$ have been studied. We have carried out calculations with various exchange-correlation functionals to select one which is able to describe the van der Waals (vdW) interactions and gives the best geometry compared with experiments. The inclusion of the vdW forces, however, does not guarantee a reliable description for the geometry of this compound: some vdW functionals strongly overestimate the interlayer distance, similar to GGA functionals. Our investigation shows that the recently introduced optB86b-vdW functional yi…
High Antiferromagnetic Domain Wall Velocity Induced by Néel Spin-Orbit Torques.
2016
We demonstrate the possibility to drive an antiferromagnetic domain wall at high velocities by fieldlike Neel spin-orbit torques. Such torques arise from current-induced local fields that alternate their orientation on each sublattice of the antiferromagnet and whose orientation depends primarily on the current direction, giving them their fieldlike character. The domain wall velocities that can be achieved by this mechanism are 2 orders of magnitude greater than the ones in ferromagnets. This arises from the efficiency of the staggered spin-orbit fields to couple to the order parameter and from the exchange-enhanced phenomena in antiferromagnetic texture dynamics, which leads to a low doma…
Relaxation and phonons in viscous and glassy orthoterphenyl by neutron scattering
1993
We present an extended set of incoherent neutron scattering measurements on the van der Waals liquido-terphenyl, obtained by time-of-flight and backscattering spectroscopy. In the supercooled liquid regime, data from three instruments are combined and analysed in terms of the selfcorrelationS(Q, t). In the time range 1...100 ps, the crossover from α-to β-relaxation is well described by the masterfunction of mode coupling theory, and fitted parameters are consistent with the previously established critical temperatureT c [Z. Phys. B83, 175 (1991)]. In the glassy regime, vibrations are harmonic and can be described by a density of states. Deviations at lowQ are quantitatively explained by a m…
Refrigeration of an Array of Cylindrical Nanosystems by Flowing Superfluid Helium
2016
We consider the refrigeration of an array of heat-dissipating cylindrical nanosystems as a simplified model of computer refrigeration. We explore the use of He II as cooling fluid, taking into account forced convection and heat conduction. The main conceptual and practical difficulties arise in the calculation of the effective thermal conductivity. Since He II does not follow Fourier’s law, the effective geometry-dependent conductivity must be extracted from a more general equation for heat transfer. Furthermore, we impose the restrictions that the maximum temperature along the array should be less than (Formula presented.) transition temperature and that quantum turbulence is avoided, in o…
The influence of disorder on the exciton spectra in two-dimensional structures
2019
We study the role of disorder in the exciton spectra in two-dimensional (2D) semiconductors. These can be heterostructures, thin films and multilayers (so-called van der Waals structures) of organometallic perovskites, transition metal dichalcogenides and other semiconductors for optoelectronic applications. We model the disorder by introduction of a fractional Laplacian (with Le´vy index m, defining the degree of disorder) to the Scro¨dinger equation with 2D Coulomb potential. Combining analytical and numerical methods, we observe that the exciton exists only for m 4 1, while the point m = 1 (strongest disorder) corresponds to the exciton collapse. We show also that in the fractional (diso…