Finitely generated simple algebras: A question of B. I. Plotkin

In his recent series of lectures, Prof. B. I. Plotkin discussed geometrical properties of the variety of associativeK-algebras. In particular, he studied geometrically noetherian and logically noetherian algebras and, in this connection, he asked whether there exist uncountably many simpleK-algebras with a fixed finite number of generators. We answer this question in the affirmative using both crossed product constructions and HNN extensions of division rings. Specifically, we show that there exist uncountably many nonisomorphic 4-generator simple Ore domains, and also uncountably many nonisomorphic division algebras having 2 generators as a division algebra. The first author is grateful to Professor B. I. Plotkin for communicating this problem to him and for stimulating conversations.     

Development of the mechanics of underground and special structures in Kazakhstan over the last 40 years

Some results on underground structures obtained by Kazakh mechanicians are reviewed. The review covers a period of the last forty years. Also results on the mechanics of special objects are discussed.Translated from Prikladnaya Mekhanika, Vol. 40, No. 10, pp. 3–36, October 2004.     

Nonreciprocity of losses and shift of the zero point in a laser gyroscope

Results of calculations of intensities, losses, and frequencies of counterpropagating waves in a ring resonator containing a weakly nonlinear active medium and an aperture are given. It is shown that inequalities of frequencies and intensities of generation of counterpropagating waves occur in such a resonator. The behavior of these inequalities is determined by the nonreciprocity of frequency-dependent losses of the counterpropagating waves.     

A stable dual-wavelength fiber laser with tunable wavelength spacing using a polarization-maintaining linear cavity

We propose and experimentally demonstrate a stable dual-wavelength erbium-doped polarization-maintaining (PM) fiber laser with tunable wavelength spacing using an all-PM linear cavity that makes use of two reflection peaks from the PM fiber Bragg grating (PM-FBG). Experimental results show stable dual lasing lines with a wavelength separation of ∼0.22 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. By applying axial strain to the PM-FBG, the center wavelengths of the two lasing lines can be tuned over several nanometers and the wavelength separation between the lasing lines can also be tuned to as small as 0.05 nm, which, to our knowledge, is the smallest wavelength spacing ever obtained from a stable room-temperature dual-wavelength fiber laser. The proposed laser configuration has the advantages of simple structure, low loss, stable dual-wavelength operation and a very small lasing linewidth of ∼5 kHz . PACS 42.55.Wd; 42.81.-i; 42.81.Gs     

Hydrogen generation in nitric acid solutions of plutonium

Summary Literature data on the radiolytic generation of hydrogen in nitric acid solutions of plutonium are used to construct a model that predicts G(H₂) as a function of the nitric acid and plutonium concentrations. The model indicates that G(H₂) decreases with increasing concentration of nitric acid, in agreement with most experimental observations. The effect of the plutonium concentration on G(H₂) is secondary to the effect of the acid concentration. An equation for interpolating Gvalues for total gas is included.     

Results from GRACE/SUSY at one-loop

We report the recent development on the SUSY calculations with the help of GRACE system. GRACE/SUSY/1LOOP is the computer code which can generate Feynman diagrams in the MSSM automatically and compute one-loop amplitudes in the numerical way. We present new results of various two-body decay widths and chargino pair production at ILC (international linear collider) at one-loop level.      

Some applications of polarized inelastic neutron scattering in magnetism

A brief account of applications of polarized inelastic neutron scattering in condensed matter research is given. We show that full polarization analysis is the only tool allowing to discriminate unambiguously between different magnetic modes in various magnetic materials. We show by means of recent results in the Heisenberg ferromagnet EuS that the effects of dipolar interactions can be studied on a microscopic scale. Moreover, we have found for the first time indications for the divergence of the longitudinal fluctuations belowT _c. In the itinerant antiferromagnet chromium we demonstrate that the dynamics of the longitudinal and transverse excitations are very different, resolving a long standing puzzle concerning the slope of their dispersion. Finally, we show that a measurement of the polarization-dependent part of the cross section of non-centrosymmetric MnSi proves directly that the chirality of the magnetic fluctuations is left-handed.     

Two-photon interference spectra at the sum-frequency generation of a bichromatic field interacting with a three-level atom

We have calculated the spectral functions for a number of induced excitations near the sum-frequency generation of a bichromatic field interacting with a three-level atom in the cascade configuration. Although the two-photon spontaneous emission is electric dipole forbidden, there are induced peaks whose subnatural line widths and spectral heights depend on the intensities of the bichromatic field. At low intensities of both laser fields, the maximum heights of the induced peaks take positive, zero, and negative values, indicating that the physical processes of absorption (attenuation), dark resonance (nonabsorbing state), and stimulated emission (amplification) are likely to occur at the sum-frequency generation of the two laser fields, respectively. The derived results are graphically presented and discussed. PACS 32.80.-t; 42.50.Hz     

The mechanism of emission in the red photoluminescence band of porous silicon

Porous silicon (PS) exhibits several photoluminescence (PL) bands, whose spectral position and intensity depend strongly on the actual conditions of preparation of PS, its treatment, and subsequent use. The PS PL band peaking at about 1.8 eV and usually assigned to the intrinsic emission of silicon nanocrystals was studied. It was shown that the temperature-induced variation of the PL kinetics in the 80 to 300-K interval follows a complex pattern and depends noticeably on the actual point on the band profile. The temperature behavior of PL decay in the 1.8-eV band is determined by the electron-hole recombination rate within a nanocrystal and the cascade carrier transitions from small to large nanocrystals, with an attendant decrease in energy.