17,745 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
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
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.
CLIC Drive Beam and LHC Based Fel-Nucleus Collider
The feasibility of a CLIC-LHC based FEL-nucleus collider is investigated. It
is shown that the proposed scheme satisfies all requirements of an ideal photon
source for the Nuclear Resonance Fluorescence method. The physics potential of
the proposed collider is illustrated for a beam of Pb nuclei.Comment: Presented at PAC05, 16-20 May 2005, Knoxville, TN, US
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Intra- and interuniversity competition and cooperation within the Berlin region
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