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No abstract available

No abstract available

[en] The theory on Coulomb collisions in plasmas has been previously presented [K. Nanbu, Phys. Rev. E 55, 4642 (1997)]. The theory is based on the relaxation equation for the scattering angle and the model equation for the probability density function of the scattering angle. The validity of both equations was ascertained by numerical simulations in the above paper. It is shown that the first equation, which describes the relaxation of the momentum of a particle, can be derived analytically. copyright 1997 The American Physical Society

[en] In the presence of a small heat current and appropriate boundary conditions, ⁴He will reach the superfluid critical point without fine tuning the temperature. This provides a physical example of self-organized criticality via the mechanism of singular diffusion proposed by Carlson et al. [Phys. Rev. Lett. 65, 2547 (1990)]

[en] We present a statistical field theory to describe large length scale effects induced by solutes in a cold and otherwise placid liquid. The theory divides space into a cubic grid of cells. The side length of the cells is of the order of the bulk correlation length of the bulk liquid. Large length scale states of the cells are specified with an Ising variable. Finer length scales effects are described with a Gaussian field, with mean and variance affected by both the large length scale field and by the constraints imposed by solutes. In the absence of solutes and corresponding restraints, integration over the Gaussian field yields an effective lattice-gas Hamiltonian. We identify these terms analytically. They can provoke large length scale effects, such as the formation of interfaces and depletion layers. We apply our theory to compute the reversible work to form a bubble in liquid water, as a function of the bubble radius. Comparison with molecular simulation results for the same function indicates that the theory is reasonably accurate. Importantly, simulating the large length scale field involves binary arithmetic only. It thus provides a computationally convenient scheme to incorporate explicit solvent dynamics and structure in simulation studies of large molecular assemblies

No abstract available

No abstract available

[en] We report on strong nonuniformities in target heating with intense, laser-produced proton beams. The observed inhomogeneity in energy deposition can strongly perturb equation of state (EOS) measurements with laser-accelerated ions which are planned in several laboratories. Interferometric measurements of the target expansion show different expansion velocities on the front and rear surfaces, indicating a strong difference in local temperature. The nonuniformity indicates at an additional heating mechanism, which seems to originate from electrons in the keV range

[en] We consider stochastic excitable units with three discrete states. Each state is characterized by a waiting time density function. This approach allows for a non-Markovian description of the dynamics of separate excitable units and of ensembles of such units. We discuss the emergence of oscillations in a globally coupled ensemble with excitatory coupling. In the limit of a large ensemble we derive the non-Markovian mean-field equations: nonlinear integral equations for the populations of the three states. We analyze the stability of their steady solutions. Collective oscillations are shown to persist in a large parameter region beyond supercritical and subcritical Hopf bifurcations. We compare the results with simulations of discrete units as well as of coupled FitzHugh-Nagumo systems