1,828,824 research outputs found
Molecular dynamics study of contact mechanics: contact area and interfacial separation from small to full contact
We report a molecular dynamics study of the contact between a rigid solid
with a randomly rough surface and an elastic block with a flat surface. We
study the contact area and the interfacial separation from small contact (low
load) to full contact (high load). For small load the contact area varies
linearly with the load and the interfacial separation depends logarithmically
on the load. For high load the contact area approaches to the nominal contact
area (i.e., complete contact), and the interfacial separation approaches to
zero. The present results may be very important for soft solids, e.g., rubber,
or for very smooth surfaces, where complete contact can be reached at moderate
high loads without plastic deformation of the solids.Comment: 4 pages,5 figure
Optimal multicopy asymmetric Gaussian cloning of coherent states
We investigate the asymmetric Gaussian cloning of coherent states which
produces M copies from N input replicas, such that the fidelity of all copies
may be different. We show that the optimal asymmetric Gaussian cloning can be
performed with a single phase-insensitive amplifier and an array of beam
splitters. We obtain a simple analytical expression characterizing the set of
optimal asymmetric Gaussian cloning machines.Comment: 7 pages, 2 figures, RevTeX
Ionization of hydrogen atoms by electron impact at 1eV, 0.5eV and 0.3eV above threshold
We present here triple differential cross sections for ionization of hydrogen
atoms by electron impact at 1eV, 0.5eV and 0.3eV energy above threshold,
calculated in the hyperspherical partial wave theory. The results are in very
good agreement with the available semiclassical results of Deb and Crothers
\cite{DC02} for these energies. With this, we are able to demonstrate that the
hyperspherical partial wave theory yields good cross sections from 30 eV
\cite{DPC03} down to near threshold for equal energy sharing kinematics.Comment: 6 pages, 9 figure
Multipartite Asymmetric Quantum Cloning
We investigate the optimal distribution of quantum information over
multipartite systems in asymmetric settings. We introduce cloning
transformations that take identical replicas of a pure state in any
dimension as input, and yield a collection of clones with non-identical
fidelities. As an example, if the clones are partitioned into a set of
clones with fidelity and another set of clones with fidelity ,
the trade-off between these fidelities is analyzed, and particular cases of
optimal cloning machines are exhibited. We also present an
optimal cloning machine, which is the first known example of a
tripartite fully asymmetric cloner. Finally, it is shown how these cloning
machines can be optically realized.Comment: 5 pages, 2 figure
Roll waves in mud
The stability of a viscoplastic fluid film falling down an inclined plane is explored, with the aim of determining the critical Reynolds number for the onset of roll waves. The Herschel–Bulkley constitutive law is adopted and the fluid is assumed two-dimensional and incompressible. The linear stability problem is described for an equilibrium in the form of a uniform sheet flow, when perturbed by introducing an infinitesimal stress perturbation. This flow is stable for very high Reynolds numbers because the rigid plug riding atop the fluid layer cannot be deformed and the free surface remains flat. If the flow is perturbed by allowing arbitrarily small strain rates, on the other hand, the plug is immediately replaced by a weakly yielded ‘pseudo-plug’ that can deform and reshape the free surface. This situation is modelled by lubrication theory at zero Reynolds number, and it is shown how the fluid exhibits free-surface instabilities at order-one Reynolds numbers. Simpler models based on vertical averages of the fluid equations are evaluated, and one particular model is identified that correctly predicts the onset of instability. That model is used to describe nonlinear roll waves
Cloning quantum entanglement in arbitrary dimensions
We have found a quantum cloning machine that optimally duplicates the
entanglement of a pair of -dimensional quantum systems. It maximizes the
entanglement of formation contained in the two copies of any
maximally-entangled input state, while preserving the separability of
unentangled input states. Moreover, it cannot increase the entanglement of
formation of all isotropic states. For large , the entanglement of formation
of each clone tends to one half the entanglement of the input state, which
corresponds to a classical behavior. Finally, we investigate a local
entanglement cloner, which yields entangled clones with one fourth the input
entanglement in the large- limit.Comment: 6 pages, 3 figure
Collective Rotation of Tetrahedral Nuclei in the Cranking Model
The three-dimensional cranking model is used to investigate the microscopic
aspects of the rotation of nuclei with the tetrahedral symmetry. Two classes of
rotation axes are studied corresponding to two different discrete symmetries of
the rotating hamiltonian. Self-consistent Hartree-Fock-Bogoliubov calculations
show that the tetrahedral minimum remains remarkably stable until the first
single-particle crossing.Comment: Proceedings of the XII Nuclear Physics Workshop Pierre and Marie
Curie, October 2005. To be published in IJMP
- …