15,685 research outputs found
Dependence of boundary lubrication on the misfit angle between the sliding surfaces
Using molecular dynamics based on Langevin equations with a coordinate- and
velocity-dependent damping coefficient, we study the frictional properties of a
thin layer of "soft" lubricant (where the interaction within the lubricant is
weaker than the lubricant-substrate interaction) confined between two solids.
At low driving velocities the system demonstrates stick-slip motion. The
lubricant may or may not be melted during sliding, thus exhibiting either the
"liquid sliding" (LS) or the "layer over layer sliding" (LoLS) regimes. The
LoLS regime mainly operates at low sliding velocities. We investigate the
dependence of friction properties on the misfit angle between the sliding
surfaces and calculate the distribution of static frictional thresholds for a
contact of polycrystalline surfaces.Comment: 8 pages, 11 figure
Crystalline misfit-angle implications for solid sliding
For the contact of two finite portions of interacting rigid crystalline
surfaces, we compute the dependence of the pinning energy barrier on the misfit
angle and contact area. The resulting data are used to investigate the
distribution of static frictional thresholds for a contact of polycrystal
surfaces, as occurs at the touching points of dry or even lubricated friction.
The simplicity of the model allows us to investigate a broad contact-size and
angular range, thus obtaining the statistical properties of the energy barriers
opposing sliding for a single asperity. These statistical properties are used
as the input of a master-equation model to predict the sliding properties of
two macroscopic surfaces in contact. The model is consistent with the
well-established result that low temperature should generally favor stick-slip
motion, while at high temperature sliding should be smooth.Comment: 11 pages, including 7 figure
coupling constant in light cone QCD sum rules
We employ the light cone QCD sum rules to calculate coupling
constant by studying the two point correlation function between the vacuum and
the pion state. Our result is consistent with the traditional QCD sum rules
calculations and it is in agreement with the experimental value.Comment: 8 pages, latex, 2 figure
Solitonic-exchange mechanism of surface~diffusion
We study surface diffusion in the framework of a generalized
Frenkel-Kontorova model with a nonconvex transverse degree of freedom. The
model describes a lattice of atoms with a given concentration interacting by
Morse-type forces, the lattice being subjected to a two-dimensional substrate
potential which is periodic in one direction and nonconvex (Morse) in the
transverse direction. The results are used to describe the complicated
exchange-mediated diffusion mechanism recently observed in MD simulations [J.E.
Black and Zeng-Ju Tian, Phys. Rev. Lett. {\bf 71}, 2445-2448(1993)].Comment: 22 Revtex pages, 9 figures to appear in Phys. Rev.
Dynamical phase diagram of the dc-driven underdamped Frenkel-Kontorova chain
Multistep dynamical phase transition from the locked to the running state of
atoms in response to a dc external force is studied by MD simulations of the
generalized Frenkel-Kontorova model in the underdamped limit. We show that the
hierarchy of transition recently reported [Braun et al, Phys. Rev. Lett. 78,
1295 (1997)] strongly depends on the value of the friction constant. A simple
phenomenological explanation for the friction dependence of the various
critical forces separating intermediate regimes is given.Comment: 12 Revtex Pages, 4 EPS figure
Periodically driven stochastic un- and refolding transitions of biopolymers
Mechanical single molecule experiments probe the energy profile of
biomolecules. We show that in the case of a profile with two minima (like
folded/unfolded) periodic driving leads to a stochastic resonance-like
phenomenon. We demonstrate that the analysis of such data can be used to
extract four basic parameters of such a transition and discuss the statistical
requirements of the data acquisition. As advantages of the proposed scheme, a
polymeric linker is explicitly included and thermal fluctuations within each
well need not to be resolved.Comment: 7 pages, 5 figures, submitted to EP
Structural lubricity: Role of dimension and symmetry
When two chemically passivated solids are brought into contact, interfacial
interactions between the solids compete with intrabulk elastic forces. The
relative importance of these interactions, which are length-scale dependent,
will be estimated using scaling arguments. If elastic interactions dominate on
all length scales, solids will move as essentially rigid objects. This would
imply superlow kinetic friction in UHV, provided wear was absent. The results
of the scaling study depend on the symmetry of the surfaces and the
dimensionalities of interface and solids. Some examples are discussed
explicitly such as contacts between disordered three-dimensional solids and
linear bearings realized from multiwall carbon nanotubes.Comment: 7 pages, 1 figur
Creation of Entanglement by Interaction with a Common Heat Bath
I show that entanglement between two qubits can be generated if the two
qubits interact with a common heat bath in thermal equilibrium, but do not
interact directly with each other. In most situations the entanglement is
created for a very short time after the interaction with the heat bath is
switched on, but depending on system, coupling, and heat bath, the entanglement
may persist for arbitrarily long times. This mechanism sheds new light on the
creation of entanglement. A particular example of two quantum dots in a closed
cavity is discussed, where the heat bath is given by the blackbody radiation.Comment: 4 revtex pages, 1 eps figure; replaced with published version; short
discussion on entanglement distillation adde
Dynamical transitions in correlated driven diffusion in a periodic potential
The diffusion of a two-dimensional array of particles driven by a constant
force in the presence of a periodic external potential exhibits a hierarchy of
dynamical phase transitions when the driving force is varied. This behavior can
be explained by a simple phenomenological approach which reduces the system of
strongly interacting particles to weakly interacting quasi-particles (kinks).
The richness of the strongly coupled system is however not lost because,
contrary to a single-Brownian particle, the array shows an hysteretic behavior
even at non-zero temperature. The present investigation can be viewed as a
first step toward understanding nanotribology.Comment: 4 pages, 3 pictures, revtex to appear in Phys Rev. Let
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