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  • 11
    ISSN: 1063-7826
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The influence of low-temperature annealing on the photoluminescence of GaAs/AlGaAs single-quantum-well structures treated in a low-energy CF4 plasma is investigated. It is established that annealing at 160–300 °C causes a decrease of the photoluminescence intensity of the quantum wells located in the near-surface region, while annealing at 350–450 °C leads to partial restoration of their photoluminescence. The activation energy for the diffusion of plasma-produced point defects and the activation energy for the annealing of these defects are determined. These energies are equal to 150 and 540 meV, respectively. It is discovered that the photoluminescence of the quantum wells near the substrate, which had a low intensity in the as-grown sample, increases after treatment in the plasma and decreases after subsequent annealing monotonically with increasing annealing temperature. Repeated treatment in a CF4 plasma leads to a repeated increase in the photoluminescence intensity of these quantum wells. It is theorized that the defects induced by the CF4 plasma form complexes with defects introduced during growth and that these complexes are not recombination centers. After low-temperature annealing, the complexes dissociate, and the nonradiative recombination centers are recreated.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 40 (1998), S. 1169-1174 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The aim of this study is to find universal critical values of the effective dimensionless coupling constant g 6 and refined universal values g 4 for Heisenberg ferromagnets with n-component order parameters. These constants appear in the equation of state and determine the nonlinear susceptibilities χ 4 and χ 6 in the critical region. Calculations are made of the first three terms of the expansion of g 6 in powers of g 4 in the limits of O(n) symmetry three-dimensional λϕ 4 theory, the resultant series is resummed by the Padé-Borel method, and then by substituting the fixed point coordinates g 4 * in the resultant expression, numerical values of g 6 * are obtained for different n. These numbers g 4 * for n〉3 were determined from a six-loop expansion for the β-function resummed using the Padé-Borel-Leroy technique. An analysis of the accuracy of these g 6 * values showed that they may differ from the true values by no more than 1.6%. These values of g 6 * were compared with those obtained by the 1/n expansion method which allowed the level of accuracy of this method to be assessed.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 40 (1998), S. 1467-1469 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study is made of the dynamics of self-consistent motion and growth of spherical new-phase nuclei from a eutectic melt. The growth rate of nuclei is shown to be proportional to supersaturation in both components. Motion of a single nucleus in a concentration-gradient field and of a pair of nuclei in a self-consistent concentration field is investigated. The velocity of motion of the nucleus as a whole has been established to depend on the key parameters of the problem, namely, supersaturation, radii of the nuclei, and their separation. The force of mutual attraction between nuclei is estimated, and it is shown to be inversely proportional to the fifth power of their separation.
    Type of Medium: Electronic Resource
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  • 14
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The magnetic properties of the intermetallic compounds Gd1−x YxMn2Ge2 (0≤x≤0.5) (tetragonal crystal structure of the type ThCr2Ge2) have been measured in fields up to 40 T in the temperature range 4.2–120 K on free powders (whose particles are free to rotate in a magnetic field), fixed powders, and polycrystalline bulk samples. The temperature dependence of the crystal structure parameters of some of these intermetallic compounds was determined from x-ray diffraction measurements. It was found that the temperatures of magnetic disordering of the gadolinium magnetic subsystem and the transition of the manganese subsystem from the ferromagnetic to the antiferromagnetic state decrease as the gadolinium content is decreased, so that in compositions with x〈0.3 this transition is a first-order phase transition, and with further decrease of the gadolinium content it becomes second-order. In intermetallic compounds of this system with x=0.3 and 0.4 another spontaneous first-order transition is observed at lower temperatures. In a magnetic field the magnetization of all the investigated intermetallic compounds except for the composition x=0.5 undergo a metamagnetic transition. The T-x, H-x, and H-T magnetic phase diagrams are constructed. The experimental data are interpreted with allowance for the fact that according to the results of previous studies, the Mn-Mn exchange interaction is antiferromagnetic, and thus the examined intermetallic compounds are two-sublattice ferrimagnets with negative exchange interaction in one of the sublattices. Calculations performed within the framework of this model in the Yafet-Kittel approximation, which assumes that the sublattice with negative exchange can be divided into two sub-sublattices, permit a quantitative description of the experimental results in most cases.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Power technology and engineering 30 (1996), S. 257-266 
    ISSN: 1570-1468
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Conclusions 1. The proposed mathematical model of phytoplankton primary production and destruction permits estimating the dynamics of production and destruction processes both in operating and planned reservoirs as applied to the problem of calculating (predicting) the water quality and oxygen regime of these reservoirs. 2. A necessary condition of the practical use of this model is a preliminary determination of a number of its parameters on an operating reservoir-analog, the selection of which is not limited by any certain conditions related to its size, level of pollution, and trophic state, although, of course, it is advisable that it be close in these indices to the reservoir for which it serves as an analog. 3. The result of using this model for calculating phytoplankton primary production and destruction on an operating reservoir show that it reflects with less accuracy the dynamics of production and destruction during the growing season and with greater accuracy their annual values. 4. When using the given model for predicting phytoplankton primary production and destruction on operating or planned reservoirs it is advisable to calculate them in several variants with the use of various approaches to a determination of various parameters of the model so that the most preferable of the variants is selected in accordance with the purposes and tasks of predicting the water quality and oxygen regime of these reservoirs.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Power technology and engineering 30 (1996), S. 392-399 
    ISSN: 1570-1468
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Conclusions 1. The developed dynamic model of the oxygen regime of the reservoir is in essence the next modification of the classical steady-state Streeter-Phelps model proposed for describing the interaction between dissolved oxygen and BOD on the river stretch. 2. Underlying the given modification is the use, in the Streeter-Phelps model, of a dynamic ideal mixer model for describing the process of movement of water in the reservoir, unlike a river stretch, on a steady-state ideal displacement model and consideration of certain additional oxygen sources and sinks having a determining effect on the oxygen regime of the reservoir and related mainly to the production and destruction (mineralization) of phytoplankton as well as to the inflow of river and wastewaters and oxygen consumption by bottom deposits. 3. The proposed dynamic model includes the main (numerical) and simplified (analytical) methods of calculating the oxygen regime of a reservoir, the practical use of which for calculating and predicting this regime in particular operating and planned reservoirs showed that they give similar results and, consequently, can be used jointly or independently of one another.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Power technology and engineering 32 (1998), S. 618-624 
    ISSN: 1570-1468
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Conclusions A mathematical model is proposed for the oxygen regime of a stratified reservoir. A model is based on representation of the reservoir on the whole or its layers individually as an ideal mixer. The thermal regime of a stratified reservoir is schematized by a two-layer model-epilimnion and hypolimnion, which provide the plane with a pronounced variation in water temperature (thermocline). In calculating the oxygen regime, the epilimnion and hypolimnion are considered individual reservoirs with their own water balance, which is linked, however, to the water balance of the reservoir on the whole. Characteristic features of the aeration and reaeration of the epilimnion and hypolimnion, and also the selectivity of water intake from the reservoir are considered here. Practical use of the model is illustrated in an example of the calculation of the oxygen regime of a hypothetical stratified reservoir, the characteristics of which are determined on the basis of field data derived from observations on the water bodies of the Zagorsk water-storage power plant. The proposed model can be used to predict the oxygen regime of stratified reservoirs and the ecological feasibility of nature-conserving measures directed toward improving the quality of their water and conserving fauna.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Power technology and engineering 3 (1969), S. 256-262 
    ISSN: 1570-1468
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    Power technology and engineering 30 (1996), S. 222-228 
    ISSN: 1570-1468
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Conclusions 1. The results of using the model of an ideal mixer for calculating one of the integral hydrochemical indices of water quality — the annual BOD5 dynamics observed on reservoirs of the Zagorsk PSS in 1989 — permit concluding the correspondence of this mode to the on-site observation data. 2. The methods of calculating the water self-purification coefficients developed on the basis of the model of an ideal mixer permit determining these coefficients by solving the inverse problem on the basis of the data of on-site observations of the actual water, hydrochemical, and hydrobiological regimes of an operating reservoir-analog (for conditions of a steady regime) and recalculating them theoretically for any given regime (steady and transient) of an operating or planned reservoir. 3. An evaluation of the accuracy of various methods of calculating the self-purification coefficients and water quality in a reservoir (main and simplified) for the example of calculating the actual annual BOD5 dynamics of the Zagorsk PSS reservoirs during 1989 showed that they give results close among themselves and to the observed BOD5. This permits recommending both methods for practical use jointly or independently of one another.
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    Springer
    Power technology and engineering 29 (1995), S. 483-489 
    ISSN: 1570-1468
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Conclusions 1. During the physical modeling of the hydrothermal regime of cooling basins, processes of diffusion transfer may play a major role in shaping the temperature distribution. Estimation of the turbulent- and convective-diffusion coefficients under model and field conditions therefore assumes critical significant for determination of the quality, of the modeling. 2. For the actual conditions under which laboratory experiments are conducted, distortion of geometric scales of the hydrothermal model may be necessary both to ensure a turbulent flow regime, and to fulfill the self-similarity condition with respect to the thermal criterion-heat-exchange parameter. 3. Forcing of the flow of water in the model within limits established by corresponding standard documents, as well as a certain deviation in the difference between the densities of the cold, and hot water and the Chezy coefficient from those calculated from similitude conditions (in the example under consideration, by a factor of four and two, respectively), have virtually no reflection in the results of the modeling. The conclusions drawn may not lay claim to universality, since we examined only one of the characteristic schemes for which cooling basins are used. In addition to this, the example that we cited for calculating the hydrothermal regime of a cooling basin under model and field conditions illustrates greater potential use of mathematical models in estimating the effect of parameters of the physical model and the results of modeling. In the future, it is proposed to continue a series of numerical experiments dealing with study of problems associated with the hydrothermal modeling of cooling basins. In that case, it is submitted that basic attention be focused on the modeling of weather conditions, which are some of the basic factors defining the temperature regime.
    Type of Medium: Electronic Resource
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