Acousto-optic stabilization of the intensity of a laser beam

A system for stabilization of the intensity of a laser beam based on an acousto-optic modulator is theoretically and experimentally studied. An equation that describes dynamic processes in the system and various working regimes is derived. It is demonstrated that the stabilization coefficient depends on the transfer coefficient of the feedback circuit and the position of the working point on the amplitude characteristic of the acoustooptic interaction. An experimental prototype of the stabilization system is based on a paratellurite acousto-optic cell. The system stabilizes the intensity with a coefficient of 78 in a frequency band of 15–180 Hz.     

An Evaluation of a thermochemical technique for increasing the productivity of oil-bearing beds and reduction of oil-deposit watering based on reactions of binary mixtures

Thermodynamic aspects of an innovative binary-mixture (BM) technology for increasing the productivity of oil-bearing beds that provides a substantial reduction of oil-well watering (compared to conventional steam heating) are discussed. Inorganic and organic ammonium nitrates (NH₄NO₃ and HOCH₂NH ₃ ⁺ NO ₃ ^- respectively) are compared qua heat-producing components of a BM that also contains sodium nitrite as an initiator of nitrate decomposition. Effects of temperature and pressure on the product distribution and heat production in ethanolammonium nitrate decomposition are evaluated. Calculations of parameters in a near-well space taking into account the heat capacity of the surrounding rock layer show that temperature and pressure can exceed their critical values for both water and main oil fractions. As a result, conditions for an intense upward flow of water—oil fluid in an artificial gas-lift regime arise.     

Experimental value of G A/GV from a measurement of both P-odd correlations in free-neutron decay

A new experimental value of the fundamental weak-interaction parameter λ=G _A/G_V (?1.2686±0.0046) is obtained for the first time by an original method that consists in measuring both P-odd correlations in free-neutron decay.     

Real-gas properties of n-alkanes, O2, N2, H2O, CO, CO2, and H2 for diesel engine operation conditions

The objective of the research outlined in this paper was to develop the analytical approximations for calculating real-gas properties (p-v-T data, thermodynamic functions: internal energy, enthalpy, and entropy, and specific heats) of vapor-phase n-alkanes from C₁ (methane) to C₁₄ (normal tetradecane), O₂, N₂, H₂O, CO, CO₂, and H₂ within the range of pressure 0.05 MPa ≤ p ≤ 20 MPa and temperature 280 K ≤ T ≤ 3000 K aimed for implementation into computational fluid dynamics (CFD)-codes simulating the operation process in modern Diesel engines. The analytical approximations have been developed based on available literature data and on the new equation of state for moderately dense gases. The approximations reported are rather simple and therefore can be used directly in CFD codes. Approximations for mixing rules are also provided.     

The effect of screening in an erosion flare on the recoil momentum and on the measurement of the reflection coefficient

Experimental investigations have been carried out to measure the transmission coefficient of laser light through an erosion flare, the coefficient of reflection from the irradiated solid surface, and the recoil momentum of insulating and metal targets in the range of pulsed laser intensities from 10⁶ to 10⁷ W/cm² with variation in the pressure of the surrounding medium from 10⁻² to 10⁵ Pa. An analysis is made of how the screening properties of the erosion flare affect the recoil momentum, and it is found necessary to take into account absorption of the radiation in the flare in determining the coefficient of reflection of the radiation from the surface. Zh. Tekh. Fiz. 67, 58–62 (March 1997)     

Electron-stimulated desorption of potassium and cesium atoms from an oxidized molybdenum surface

The yield and energy distributions of potassium and cesium atoms emitted in electron-stimulated desorption (ESD) from a molybdenum surface, oxidized to different extent and maintained at 300 K, have been measured by the time-of-flight technique with a surface ionization detector. The ESD threshold for potassium and cesium atoms lies around 25 eV, irrespective of molybdenum oxidation state. In the case of molybdenum coated by an oxygen monolayer, secondary thresholds at ∼40 and ∼70 eV have been observed, as well as atomic energy distribution tailing down to very low energies. The most probable kinetic energies of the atoms are a few tenths of one eV. The results are explained within a model involving Auger neutralization of the adsorbed alkali metal ions after the filling of the 2s O, 4s Mo, and 4p Mo core holes. The possibility of ESD of a neutral species as a result of oxide-cation core-level ionization has been demonstrated for the first time. Fiz. Tverd. Tela (St. Petersburg) 39, 758–761 (April 1997)     

Electron-stimulated desorption of cesium atoms from cesium layers deposited on a germanium-coated tungsten surface

The yield and energy distribution of Cs atoms from cesium layers adsorbed on germanium-coated tungsten were measured, using the time-of-flight technique with a surface-ionization-based detector, as a function of the energy of bombarding electrons, germanium film thickness, the amount of adsorbed cesium, and substrate temperature. The threshold for the appearance of Cs atoms is ～30 eV, which correlates well with the germanium 3d-level ionization energy. As the electron energy increases, the Cs atom yield passes through a broad maximum at ～120 eV. For germanium film thicknesses from 0.5 to 2 monolayers, resonance Cs yield peaks were observed at electron energies of 50 and 80 eV, which can be related to the tungsten 5p and 5s core-level ionization energies. As the cesium coverage increases, the Cs atom yield passes through a flat maximum at monolayer coverage. The energy distribution of Cs atoms follows a bell-shaped curve. With increasing cesium coverage, this curve shifts to higher energies for thin germanium films and to lower energies for thick films. The Cs energy distribution measured at a substrate temperature T = 160 K exhibits two bell-shaped peaks, namely, a narrow peak with a maximum at ～0.35 eV, associated with tungsten core-level excitation, and a broad peak with a maximum at ～0.5 eV, deriving from the excitation of the germanium 3d core level. The results obtained can be described within a model of Auger-stimulated desorption.     

Galvanomagnetic study of the quantum-well valence band of germanium in the Ge<Subscript>1−x</Subscript>Si<Subscript>x</Subscript>/Ge/Ge<Subscript>1−x</Subscript>Si<Subscript>x</Subscript> potential well

The structure of the quantum-well valence band in a Ge(111) two-dimensional layer is calculated by the self-consistent method. It is shown that the effective mass characterizing the motion of holes along the germanium layer is almost one order of magnitude smaller than the mass for the motion of heavy holes along the [111] direction in a bulk material (this mass is responsible for the formation of quantum-well levels). This creates a unique situation in which a large number of subbands appear to be populated at moderate values of the layer thickness d _w and the hole concentration p _s . The depopulation of two or more upper subbands in a 38-nm-thick germanium layer at a hole concentration p _s = 5 × 10¹⁵ m^?2 is revealed from the results of measuring the magnetoresistance in a strong magnetic field aligned parallel to the germanium layers. The destruction of the quantum Hall state at a filling factor ν = 1 indicates that the two lower subbands merge together in a self-formed potential profile of the double quantum well. It is demonstrated that, in a quasi-two-dimensional hole gas, the latter effect should be sensitive to the layer strain.     

Search for rare and forbidden decays D+ --> h+/- e+/- e+

Using 0.8 x 10(6) D+ D- pairs collected with the CLEO-c detector at the psi(3770) resonance, we have searched for flavor-changing neutral current and lepton-number-violating decays of D+ mesons to final states with dielectrons. We find no indication of either, obtaining 90% confidence level upper limits of B(D+ --> pi+ e+ e-) < 7.4 x 10(-6), B(D+ --> pi- e+ d+) < 3.6 x 10(-6), B(D+ --> K+ e+ e-) < 6.2 x 10(-6), and B(D+ --> K- e+ e+) < 4.5 x 10(-6).