Coherent and Incoherent Contributions to the Damping of Cyclotron Magnetoplasma Resonance for Two-Dimensional Electrons

The spectrum of resonant microwave absorption for a two-dimensional electron disk is studied by the optical detection technique. The dependence of the width of cyclotron magnetoplasma resonance on the electron density and on the size of the two-dimensional electron system is analyzed. The contributions of the coherent radiative and incoherent collision mechanisms to the relaxation of magnetoplasma excitations are measured. It is demonstrated that the ratio of the length of the electromagnetic wave and the lateral size of the twodimensional electron system is an important parameter determining the width of the resonance.     

Gamma-ray bursts from evaporating primordial black holes

It is believed that the detection of gamma-ray bursts from evaporating primordial black holes is highly improbable in the near future since the expected photon flux, consisting mainly of photons with energies ≳ GeV, is too low. Contrary to this point of view, we show that a large fraction of the black hole power at the final stage of evaporation (the last 10³ s) can be liberated as a burst of soft γ-ray emission of duration 10⁻¹–10³ s and luminosity 10²⁸–10³¹ erg/s in the energy range 0.1–1 MeV. According to our calculations of the black hole evaporation rate (within the Standard Model of elementary particles), when the black hole temperature exceeds approximately 10 GeV, the charged particle outflow from a black hole forms a well-defined plasma and can be described in the hydrodynamic approximation. In this case more than half of the rest energy of a black hole can be converted into soft gamma-rays due to the presence of the magnetic field with energy density comparable to that of charged particles. We consider various mechanisms leading to such transformation and estimate their efficiency. It is shown that, at least, some of the gamma-ray bursts detected by BATSE can be associated with evaporating black holes. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 1, pp. 36–45, January, 1998.     

Simulating dynamic modes of polymer synthesis,based on the method of moments for multimodal distributions

Aspects of using the method of moments to simulate processes of the synthesis of polymers by means of gel chromatography are considered. Problems of modeling multimodal molecular weight distributions and their evolution as a function of conversion are discussed.     

Efficient Procedure for Preparing Salicyl Alcohols

A new convenient procedure was developed for selective ortho-hydroxymethylation of phenols by reaction of paraformaldehyde with a mixture of phenol and orthoboric acid. The method is general for phenols containing no strong electron-withdrawing substituents; it allows preparation of o-hydroxybenzyl alcohols of high purity in a high yield.     

Study of interband cascade lasers with tunneling transition

Two-frequency lasing in a new class of heterolasers (interband cascade lasers with tunneling transition that separates two active regions of quantum wells located in a single waveguide) is realized and studied. The laser scheme weakens the competition between the quantum wells upon the simultaneous generation of the long-and short-wavelength modes.     

Nonlinear optics with quantum cascade lasers

We discuss new approaches to monolithic integration of quantum cascade lasers with resonant intersubband nonlinearities. We show that the proposed approaches can greatly enhance the performance of quantum cascade lasers and give rise to new functionalities. Examples considered include extreme frequency up-or down-conversion and wide-range electric tuning.     

Difference-frequency pulse generation in quantum well heterolasers

It is shown that mid-to far-infrared (IR) and terahertz (THz) pulse generation via difference-frequency mixing in quantum well (QW) dual-wavelength heterolasers can be rather efficient under the modelocking regime for one or both lasing fields even at room temperature. In such a device, the long-wavelength field is produced in the process of intracavity difference-frequency mixing of two optical fields: continuous wave (CW) and pulsed (or both pulsed), due to the resonant intersubband quantum coherence in QWs, as well as due to the nonresonant second-order semiconductor bulk nonlinearity. The mode-locking regime of the optical generation allows one to significantly enhance the pulsed driving fields in comparison with those under CW operation and, therefore, substantially increase the output difference-frequency power. Within a simple model, an explicit formula for the intensity and shape of the generated IR or THz pulse is derived. It is shown that this method is capable of producing picosecond pulses at a ∼ 1-GHz repetition rate with a peak power of the order of 1 W and ≲0.2 mW at 10 and 50 μm wavelengths, respectively. Original Text ? Astro, Ltd., 2007.     

Method of computing the chemically nonequilibrium gas flow in a heated tube in almost equilibrium or frozen states

The solution of equations describing turbulent isobaric flow of a chemically reacting gas in a heated tube is investigated analytically. Solutions of the ordinary nonlinear differential equations are obtained for almost frozen flow by the perturbation method, and for almost equilibrium flow by an asymptotic method taking account of the zero and first approximations, Linear differential equations in variations are written down to find the subsequent approximations.Translated from Izvestiya Akademiya Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 8–14, July–August, 1973.