Interfering modes and an axial wave in an underwater sound channel

Experiments on long-range propagation of low-frequency sound that were conducted starting from the mid-1980s indicate a complex character of propagation in an underwater sound channel, in which a source and a receiver are located close to the channel axis. A burst of energy propagating along the axis follows early arrivals, which are well described by the formulas of geometrical acoustics, in plots of acoustic intensity as a function of propagation time and hydrophone depth. This energy burst cannot be described using geometrical acoustics because of caustics with caustic beaks located near the channel axis. Very complex interference processes occur near these caustics. As the distance from the source grows, the dimensions of the interference vicinity increase and start to overlap producing a peculiar “axial wave.” For an arbitrary two-dimensional underwater sound channel, the axial wave can be represented as a sum of the first normal modes and a residue. This conclusion is based on the use of two representations for an acoustic field. The first of them includes the sum of ray components and an axial wave. The second representation consists of ray addends, the sum of the first normal modes, and a residue. Numerical results are obtained for a canonical profile of sound velocity at the frequency of 200 Hz for the distances of 1600–1650 km.     

Spin nematic and antinematic states in a spin-3/2 isotropic non-Heisenberg magnet

The ground state phase diagram of a general isotropic spin-3/2 system with nearest-neighbor exchange is shown to contain unconventionally ordered spin nematic and antinematic states, as well as usual ferro- and antiferromagnetic phases. The two nematic phases have spontaneously broken rotational symmetry characterized by the long-range order of the nematic director u, as well as the broken time-reversal symmetry described by the pseudospin vector σ. Nematic phase differs from antinematic one by the type of ordering in σ vectors (uniform versus staggered). The ferromagnet-nematic and antiferromagnet-antinematic phase boundaries exhibit enhanced Sp(4) symmetry and correspond to the recently studied effective theory for spin-3/2 cold gases. We discuss optical properties and topological defects in the nematic phases.     

Using Lorentz’s theorem for studying the propagation wave packets in a nonlinear medium

We obtain integral relationships expressing the amplitude of wave-packet field on the output surface of a layer via the field amplitude on the input surface, the field on the side surface of the layer, and the integral of the nonlinear currents inside the layer at the previous times in the spectral and spatiotemporal forms. These relationships allow one to perform studies and develop numerical simulation algorithms of propagation and interaction of wave packets which have wide frequency and angular spectra, including calculations of excitation of evanescent waves in the case of sharp focusing or formation of supernarrow filaments. Using the obtained relationships, we propose an algorithm that employs a simple iteration of the first order and allows one to significantly speed up the calculations. The possibility of using the fast Fourier transform to develop algorithms for numerical simulation of the boundary-value problems of nonlinear optics is demonstrated.     

A system of metrological assurance of measurement quality for the determination of chemical composition of light alloys and superalloys

 The paper covers the main principles of setting up and the function of the Russian system of metrological assurance of analytical measurements for the production of light alloys and superalloys. Received: 20 October 1998 / Accepted: 9 November 1998     

Floating Electrode Dielectric Barrier Discharge Plasma in Air Promoting Apoptotic Behavior in Melanoma Skin Cancer Cell Lines

Initiation of apoptosis, or programmed cell death, is an important issue in cancer treatment as cancer cells frequently have acquired the ability to block apoptosis and thus are more resistant to chemotherapeutic drugs. Targeted and perhaps selective destruction of cancerous tissue is desirable for many reasons, ranging from the enhancement of or aid to current medical methods to problems currently lacking a solution, i.e., lung cancer. Demonstrated in this publication is the inactivation (killing) of human Melanoma skin cancer cell lines, in vitro, by Floating Electrode Dielectric Barrier Discharge (FE-DBD) plasma. Not only are these cells shown to be killed immediately by high doses of plasma treatment, but low doses are shown to promote apoptotic behavior as detected by TUNEL staining and subsequent flow cytometry. It is shown that plasma acts on the cells directly and not by “poisoning” the solution surrounding the cells, even through a layer of such solution. Potential mechanisms of interaction of plasma with cells are discussed and further steps are proposed to develop an understanding of such systems.     

Upper semicontinuity of automorphism groups

The second author was partially supported by NSF#DMS-9101826     

The region of nonlinear effects for intensive sound pulses in the ocean

The formation of a stationary shock wave is studied in media with an arbitrary power dependence of the damping coefficient on the frequency. The conditions for existence of a stationary shock wave are defined and it is shown that when acoustic signals propagate in the ocean the region of nonlinear effects is limited. For acoustic waves generated by explosive sources a calculation is given of the location of the transition point of the nonlinear wave into a linear one, and the dependence of this point on the charge weight is defined.     

Synthesis and proton conductivity of adsorption-saturated and solvated porous hydroxyethylated cyclam layers on the surface of PVC-coated cellulose fabric

Porous layers of associates of adsorption-saturated and benzene- and hexane-solvated chloride and sulfate of hydroxyethylated cyclams with acid aqua complexes were synthesized on the surface of PVC-coated cellulose fabric. The porous structure of the layers includes a system of internal pores connected with the external pores via the diamine rings of the common walls of the hydroxyethylated cyclam nets; the internal pores are filled with the associates; the solvent molecules are adsorbed on the developed surface of the layers or solvate it. The H⁺ motion rate in a layer placed in solvent vapors or liquid solvents was measured; the layers were found to be nonlinear H⁺ conductors. The potential of H⁺ transition from the acid solution into the layer, the H⁺ mobility constant, and the field variation constant of the H⁺ mobility of the layer depend on the layer composition. The adsorption and solvation are accompanied by the formation of host-guest molecular complexes between the diamine rings of the cyclam nets and the benzene or hexane molecules, affecting the resistance of the associates to the incorporation of H⁺ ions and the H⁺ mobility in the associates.     

Two dimorphs of 5‐methyl­sulfanyl‐1H‐tetrazole

5‐Methyl­sulfanyl‐1H‐tetrazole, C₂H₄N₄S, crystallizes in dimor­phic forms; the α‐form crystallizes at room temperature in the monoclinic crystal system, space group P2₁/m, and the β‐form crystallizes by sublimation at 423 K in the orthorhombic crystal system, space group Pbcm. In both forms, the mol­ecules occupy crystallographic mirror planes and are connected to one another via N—H⋯N hydrogen bonds, the amino H atoms being disordered. The two forms differ from one another in their packing; there are polar layers in the α‐form and non‐polar layers in the β‐form.