Dynamics of particles in the steady flows of an inviscid fluid

Advection of small particles with inertia in two-dimensional ideal flows is studied both numerically and analytically. It is assumed that the flow disturbance around the particle corresponds to a potential dipole, so that the motion is driven by pressure gradient, inertial, and added-mass forces. It is found that in general the motion is nonintegrable, but particular exact solutions can be obtained. The problem is then studied for the cases of axisymmetric flow, when the motion proves to be completely integrable, and of a cellular flow, for which both regular and stochastic (bounded and unbounded) trajectories are calculated. In the latter case, the unbounded stochastic motion is of Brownian-like character, and the results derived show that the particle dispersion process is generally anomalous.     

Nonlinear Dynamics of Rock: Hysteretic Behavior

We discuss the dynamics of media with hysteretic stress-strain properties. First, experimental evidence of the hysteretic behavior of rock is presented. This evidence leads to a pattern of unifying behavior whose origin is within the bond system of the material, which includes small cracks, intergrain contacts and, the cement that holds the grains in place. Nonlinear response is evident over a large frequency interval (dc to several MHz at least), and it is significant from strains of plasticity down to the smallest measurable strains (order 10^-8-10^-9). Second, some models related to such a behavior are outlined. Finally, oscillations and waves in hysteretic media are discussed.     

The role of an initial Na(3p) state alignment in 1 keV H++Na(3p)→H(2p)+Na+ collisions

Charge exchange in 1 keV H⁺+Na→H(2p)+Na⁺ is studied in a Lyman-α scattered particle coincidence experiment. An initial Na(3p) state is prepared by laser-optical pumping; its alignment is controlled by the laser light polarization. The results are compared to a 34 coupled-channels calculation (R. Shingal), and discussed on the basis of an asymptotic model of the charge exchange process.     

Optical solitons: Perspectives and applications

This article serves as an introduction to the focus issue on optical solitons. After a short review of the history of solitons and the field of integrable systems, a brief overview of the development of nonlinear optics and optical solitons is provided. Next, the various contributions to this focus issue are presented, and a few separate remarks are devoted to optical communications, where solitons promise to play a decisive role in the next generation of commercial systems. (c) 2000 American Institute of Physics.     

Conductivity of carbon nanotubes in a longitudinal magnetic field

Multiwall carbon nanotubes exhibit oscillations of magnetoresistance with the period Φ₀=hc/2e [A. Bachtold, C. Strunk, J.-P. Salvetat, et al., Nature 397, 673 (1999)]. This effect is analogous to the Sharvin effect for a normal metal [D. Yu. Sharvin and Yu. V. Sharvin, Pis’ma Zh. Éksp. Teor. Fiz. 34, 285 (1981)]. It is shown that, along with the magnetoresistance peaks corresponding to the flux values that are multiples of Φ ₀, additional peaks with a period three times shorter can be observed in carbon nanotubes.     

The structure of LC-continuous functions

A function f is LC-continuous if the inverse image of any open set is a locally closed set; i.e., an intersection of an open set and a closed set. The aim of this paper is to prove the following theorem: Let f: X→Y be an LC-continuous function onto a separable metric space Y. Then X can be covered by countably many subsets T _n ⊂X such that each restriction f∣T _n is continuous at all points of T _n .