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1.
In a granular gas of rough particles the axis of rotation is shown to be correlated with the translational velocity of the particles. The average relative orientation of angular and linear velocities depends on the parameters which characterize the dissipative nature of the collision. We derive a simple theory for these correlations and validate it with numerical simulations for a wide range of coefficients of normal and tangential restitution. The limit of smooth spheres is shown to be singular: even an arbitrarily small roughness of the particles gives rise to orientational correlations. 相似文献
2.
The oblique impacts of nanoclusters are studied theoretically and by means of molecular dynamics. In simulations we explore two models--Lennard-Jones clusters and particles with covalently bonded atoms. In contrast with the case of macroscopic bodies, the standard definition of the normal restitution coefficient yields for this coefficient negative values for oblique collisions of nanoclusters. We explain this effect and propose a proper definition of the restitution coefficient which is always positive. We develop a theory of an oblique impact based on a continuum model of particles. A surprisingly good agreement between the macroscopic theory and simulations leads to the conclusion that macroscopic concepts of elasticity, bulk viscosity, and surface tension remain valid for nanoparticles of a few hundred atoms. 相似文献
3.
The aim of this study was to measure the shear modulus of the vocal fold in a human hemilarynx, such that the data can be related to direction of applied stress and anatomical context. Dynamic spring rate data were collected using a modified linear skin rheometer using human hemilarynges, and converted to estimated shear modulus via application of a simple shear model. The measurement probe was attached to the epithelial layer of the vocal fold cover using suction. A sinusoidal force of 3g was applied to the epithelium, and the resultant displacement logged at a rate of 1kHz. Force measurement accuracy was 20microg and position measurement accuracy was 4microm. The force was applied in a transverse direction at the midmembranous point between the vocal process and the anterior commissure. The shear modulus of the three female vocal folds ranged from 814 to 1232Pa. The shear modulus of the three male vocal folds ranged from 1021 to 1796Pa. These data demonstrate that it is possible to obtain estimates for the shear modulus of the vocal fold while preserving anatomical context. The modulus values reported here are higher than those reported using parallel plate rheometry. This is to be expected as the tissue is attached to surrounding structures, and is under natural tension. 相似文献
4.
W.T.?Kranz N.V.?Brilliantov T.?P?schel A.?Zippelius 《The European physical journal. Special topics》2009,179(1):91-111
In a granular gas of rough particles the spin of a grain is correlated with its linear velocity. We develop an analytical
theory to account for these correlations and compare its predictions to numerical simulations, using Direct Simulation Monte
Carlo as well as Molecular Dynamics. The system is shown to relax from an arbitrary initial state to a steady-state, which
is characterized by time-independent, finite correlations of spin and linear velocity. The latter are analyzed systematically
for a wide range of system parameters, including the coefficients of tangential and normal restitution as well as the moment
of inertia of the particles. For most parameter values the axis of rotation and the direction of linear momentum are perpendicular
like in a sliced tennis ball, while parallel orientation, like in a rifled bullet, occurs only for a small range of parameters.
The limit of smooth spheres is singular: any arbitrarily small roughness unavoidably causes significant translation-rotation
correlations, whereas for perfectly smooth spheres the rotational degrees of freedom are completely decoupled from the dynamic
evolution of the gas. 相似文献
5.
The evolution of a granular gas of viscoelastic particles in the homogeneous cooling state is studied. The velocity distribution function of granular particles and the time dependence of the mean kinetic energy of particles (granular temperature) are found. The noticeable deviation of the distribution function from the Maxwell distribution and its non-monotonous evolution are established. The perturbation theory with respect to the small dispersion parameter is elaborated and the analytical expressions for the asymptotic time dependence of the velocity distribution function and the granular gas temperature are derived. 相似文献
6.
T. Pöschel T. Schwager N.V. Brilliantov 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):169-174
The resistance against rolling of a rigid cylinder on a flat viscous surface is investigated. We found that the rolling-friction
coefficient reveals strongly non-linear dependence on the cylinder's velocity. For low velocity the rolling-friction coefficient
rises with velocity due to increasing deformation rate of the surface. For larger velocity, however, it decreases with velocity
according to decreasing contact area and deformation of the surface.
Received 24 December 1998 and Received in final form 14 January 1999 相似文献
7.
The thermodynamic properties are studied for the solutions of charged colloidal particles with ionizable surface groups. The microscopic mechanism of microion binding at surface groups is considered. The free energy of the system in the parameter range where the usual theory of such solutions is inadequate (a range of practical interest) is calculated using the method of the thermodynamic perturbation theory. The first-order phase transition of the liquid–liquid type is shown to be possible; in this phase transition, a phase with a high concentration of colloidal particles that have a higher charge coexists with a phase with a lower concentration of particles that have a lower charge. 相似文献
8.
N.V. Brilliantov T. Pöschel 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):299-301
We show that two basic mechanical processes, the collision of particles and rolling motion of a sphere on a plane, are intimately
related. According to our recent findings, the restitution coefficient for colliding spherical particles , which characterizes the energy loss upon collision, is directly related to the rolling friction coefficient for a viscous sphere on a hard plane. We quantify both coefficients in terms of material constants which allows to determine
either of them provided the other is known. This relation between the coefficients may give rise to a novel experimental technique
to determine alternatively the coefficient of restitution or the coefficient of rolling friction.
Received 5 May 1999 相似文献
9.
A force-free granular gas is considered with an impact-velocity-dependent coefficient of restitution as it follows from the model of viscoelastic particles. We analyze structure formation in this system by means of three independent methods: molecular dynamics, numerical solution of the hydrodynamic equations, and linear stability analysis of these equations. All these approaches indicate that structure formation occurs in force-free granular gases only as a transient process. 相似文献
10.
N.V. Brilliantov V.V. Malinin R.R. Netz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):339-345
A continuous liquid flow in a vacuum (a liquid beam) of an aqueous solution of adenine salt containing hydrochloric acid or
sodium hydroxide was irradiated with an intense pulsed IR laser at 3 μm, which is resonant to a vibrational mode related to
the OH stretch vibration of H2O. Neutral species isolated into the vacuum were ionized by a pulsed UV laser at 270 nm, and the product ions were mass-analyzed
by a time-of-flight mass spectrometer. It is found that AH 2
2 + . 2Cl- and [A-iH] i - .
iNa+ (i = 1-3) are isolated in the vacuum from the aqueous acidic and alkaline solutions, respectively, under irradiation of the
IR laser, and undergo four-photon ionization involving decomposition and proton transfer of the intermediate species under
irradiation of the UV laser.
Received 1st May 2002 Published online 13 September 2002 相似文献