Single-phase and multiphase effective models describing periodic media

In this work wave propagation processes are investigated in media obtained by averaging periodic layered systems with fluid, elastic-fluid, and elastic with contact-slippage conditions on the boundaries.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 140, pp. 105–122, 1984.     

Investigation of the tangency of front sets of two transversal waves in transversely isotropic elastic media

A special case of a transversely isotropic elastic medium is considered. This medium is excited by a point force perpendicular to the anisotropy axis. The wave field in this medium is constructed and investigated. The front sets of SV and SH waves are in contact with one another at a point. In order to investigate a neighborhood of this point, we derive simpler expressions for the wave field and establish a special function describing the tangency of two front sets. Bibliography: 8 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 342, 2007, pp. 206–216.     

Quantum bit commitment in a channel with noise

Under rather general assumptions about the properties of a quantum channel with noise, a quantum protocol providing implementation of secret bit commitment with the probability as close to unity as is wished is proposed.     

On the vulnerability of the swiss system of coherent quantum cryptography to an attack with repeated measurements

It has been shown that the coherent quantum cryptography protocol (Coherent One Way) and, correspondingly, fiber optic systems involving this protocol for quantum key distribution, are vulnerable to an attack with repeated measurements and do not guarantee the security of distributed keys in a communication channel with losses. The coherent quantum cryptography system is used in Switzerland as one of the key distribution channels in the framework of the network project SECOQC (SEcure COmmunications based on Quantum Cryptography). A critical attack with repeated measurements was missed when the cryptographic strength of this protocol was analyzed. The critical length of the communication channel has been determined; this is a value above which secure key distribution is certainly impossible. Beginning with the critical length, an eavesdropper knows the entire distributed key, does not introduce errors at the receiver end, and remains undetected. For typical parameters in a real system (the average photon number μ = 0.5 and the quantum efficiency of avalanche detectors η = 0.1, see N. Gisin, G. Ribordy, H. Zbinden, et al., arXiv:quant-ph/0411022 and D. Stucki, C. Barreiro, S. Fasel, et al., arXiv:quant-ph/08095264), the security of keys cannot be guaranteed even for a communication channel whose length is as small as wished.     

Dusty plasma induced by solar radiation under microgravitational conditions: An experiment on board the Mir orbiting space station

The dynamics of the formation of ordered structures of macroparticles charged by photoemission under the action of solar radiation under microgravitational conditions without the use of electrostatic traps to confine the particles is studied experimentally and theoretically. The working conditions needed for the formation of structures of charged macroparticles are chosen as a result of a numerical solution of the problem posed, the particle charges and the interparticle interaction parameter are determined, and the characteristic times specifying the dynamics of the formation of an ordered system of macroparticles are calculated. The behavior of an ensemble of macroparticles under the effect of solar radiation is observed experimentally on board the Mir space station. An analysis and comparison of the results of the experimental and theoretical investigations permit drawing a conclusion regarding the possibility of the existences of extended ordered formations of macroparticles charged by photoemission under microgravitational conditions. Zh. éksp. Teor. Fiz. 114, 2004–2021 (December 1998)     

Combined phase-time encoding method in quantum cryptography

A new combined phase-time encoding method is proposed for fiber optic quantum cryptography systems. Preliminary estimates are given for the probability of the critical error to which cryptographic key distribution is possible.     

The tube wave generated by a point source located outside a borehole

The excitation of the tube wave by a point source situated inside an elastic medium is considered. The amplitude of the tube wave as a function of the radial distance is given for media with high and low velocies. Two models of sources are considered: a point vertical source and a point horizontal source. It is shown that the radial source is an efficient tool for excitation of a tube wave in high-and low-velocity media. Bibliography: 17 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 332, 2006, pp. 99–122.     

The dynamics of macroparticles in a direct current glow discharge plasma under microgravitation conditions

The dynamics of large-sized (70-180 μm) spherical bronze particles in a direct current glow discharge plasma was studied experimentally under microgravitation conditions. The temperatures, velocities, pair correlation functions, and self-diffusion coefficients of macroparticles were measured at various discharge currents. The charges of dust particles (on the order of 10⁶ e) corresponded to high surface potentials of about 30–40 V. The experimental data were in close agreement with the simulation data on Yukawa systems with weak screening of dust charges. The influence of macroparticles on equilibrium ionization in a dense dust cloud was considered.     

Nonstationary-states quantum cryptography

A quantum cryptosystem is proposed in which a pair of nonstationary states differing in their times of preparation is used as the information carriers. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 11, 742–745 (10 December 1997)     

Possibility of observing magnetic macroscopic quantum tunneling using a scanning tunneling microscope

A theory describing the detection of magnetic macroscopic quantum tunneling on the basis of current fluctuations in a scanning tunneling microscope is proposed. Zh. éksp. Teor. Fiz. 112, 1011–1020 (September 1997)