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  • 11
    Electronic Resource
    Electronic Resource
    Multi-gas assessment of the Kyoto Protocol (1999)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 401 (1999), S. 549-555 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Kyoto Protocol allows reductions in emissions of several ‘greenhouse’ gases to be credited against a CO2-equivalent emissions limit, calculated using ‘global warming potential’ indices for each gas. Using an integrated global-systems model, it is shown that a ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/44069
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  • 12
    Electronic Resource
    Electronic Resource
    Transformation of nonradiative recombination centers in GaAs/AlGaAs quantum well structures upon treatment in a CF4 plasma followed by low-temperature annealing (1998)
    Springer
    Semiconductors 32 (1998), S. 1293-1298 
    Details
    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
    URL: http://dx.doi.org/10.1134/1.1187617
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  • 13
    Electronic Resource
    Electronic Resource
    Linear low-temperature dependence of the surface impedance of a Ba0.6K0.4BiO3 single crystal (1996)
    Springer
    JETP letters 64 (1996), S. 832-838 
    Details
    ISSN: 1090-6487
    Keywords: 84.37.+q ; 74.72.Yg ; 74.72.Bk ; 74.72.Hs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The temperature dependences of the real part R s and the imaginary part X s of the surface impedance Z s =R s +iX s of the superconductor Ba0.6K0.4BiO3 (T c ≃30 K) are measured at a frequency of 9.4 GHz. Its temperature dependence Z s (T) and that of the complex conductivity σ s (T) can be described on the basis of a two-fluid model under two assumptions: The density of superconducting carriers increases linearly, and the relaxation time increases as a power law (∝1/T 5), with decreasing temperature T〈T c . This model also describes well the curves Z s (T) and σs (T) recently measured for YBa2Cu3O6.95 and Bi2Sr2CaCu2O8 single crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567255
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  • 14
    Electronic Resource
    Electronic Resource
    Universal effective coupling constants for the generalized Heisenberg model (1998)
    Springer
    Physics of the solid state 40 (1998), S. 1169-1174 
    Details
    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
    URL: http://dx.doi.org/10.1134/1.1130512
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  • 15
    Electronic Resource
    Electronic Resource
    Self-consistent diffusion-controlled growth of nuclei from eutectic solutions (1998)
    Springer
    Physics of the solid state 40 (1998), S. 1467-1469 
    Details
    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
    URL: http://dx.doi.org/10.1134/1.1130577
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  • 16
    Electronic Resource
    Electronic Resource
    Microwave impedance of Ba0.6K0.4BiO3 crystals: Comparison with Nb (1997)
    Springer
    Journal of experimental and theoretical physics 84 (1997), S. 383-387 
    Details
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The surface impedance Z s=R s+iX s of samples of Ba0.6K0.4BiO3 in the temperature range 4〈T〈50 K is measured at 9.42 GHz. The BCS theory completely describes the electrodynamic properties of Nb in the dirty limit, and its application to Ba0.6K0.4BiO3 allows determination of the London penetration depth λ L(0)=3100±100 Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.558127
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  • 17
    Electronic Resource
    Electronic Resource
    Temperature dependence of surface impedance of Tl2Ba2CaCu2O8−δ and YBa2Cu3O6.95 single crystals measured in the microwave band (1997)
    Springer
    Journal of experimental and theoretical physics 85 (1997), S. 1211-1217 
    Details
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The real part R s and the imaginary part X s of the surface impedance Z s=R s+ iX s of Tl2Ba2CaCu2O8−δ and YBa2Cu3O6.95 single crystals have been measured with high precision at frequency ω/2π=9.4 GHz in the temperature range 0〈T〈140 K. In the Tl2Ba2CaCu2O8−δ crystal a linear temperature dependence R s(T) has been found for T⩽50 K, and the magnetic field penetration depth λ(4.2 K)=X s(4.2 K)/ω μ 0≈3760 Å has been measured. Along with well known features of the function Z s(T) in high-quality YBa2Cu3O6.95 single crystals, such as the linearity of λ(T) and R s(T) for T〈T c/3 and a maximum of R s(T) at T∼T c/2, the linearity range of λ(T) extends to T≃50 K, and this curve has a plateau in the range 60〈T〈85 K. The curve of R s(T) in both the superconducting and normal states of YBa2Cu3O6.95 is well described by a two-fluid model with the electron-phonon mechanism of quasiparticle relaxation. A formula describing the curve of λ 2(0)/λ 2(T) throughout the studied temperature range is also given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.558395
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  • 18
    Electronic Resource
    Electronic Resource
    Spontaneous and field-induced magnetic phase transitions in the intermetallic compounds (Gd1−x Y x )Mn2Ge2 (1999)
    Springer
    Journal of experimental and theoretical physics 89 (1999), S. 723-733 
    Details
    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
    URL: http://dx.doi.org/10.1134/1.559034
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  • 19
    Electronic Resource
    Electronic Resource
    A flexible climate model for use in integrated assessments (1998)
    Springer
    Climate dynamics 14 (1998), S. 291-303 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  Because of significant uncertainty in the behavior of the climate system, evaluations of the possible impact of an increase in greenhouse gas concentrations in the atmosphere require a large number of long-term climate simulations. Studies of this kind are impossible to carry out with coupled atmosphere ocean general circulation models (AOGCMs) because of their tremendous computer resource requirements. Here we describe a two dimensional (zonally averaged) atmospheric model coupled with a diffusive ocean model developed for use in the integrated framework of the Massachusetts Institute of Technology (MIT) Joint Program on the Science and Policy of Global Change. The 2-D model has been developed from the Goddard Institute for Space Studies (GISS) GCM and includes parametrizations of all the main physical processes. This allows it to reproduce many of the nonlinear interactions occurring in simulations with GCMs. Comparisons of the results of present-day climate simulations with observations show that the model reasonably reproduces the main features of the zonally averaged atmospheric structure and circulation. The model’s sensitivity can be varied by changing the magnitude of an inserted additional cloud feedback. Equilibrium responses of different versions of the 2-D model to an instantaneous doubling of atmospheric CO2 are compared with results of similar simulations with different AGCMs. It is shown that the additional cloud feedback does not lead to any physically inconsistent results. On the contrary, changes in climate variables such as precipitation and evaporation, and their dependencies on surface warming produced by different versions of the MIT 2-D model are similar to those shown by GCMs. By choosing appropriate values of the deep ocean diffusion coefficients, the transient behavior of different AOGCMs can be matched in simulations with the 2-D model, with a unique choice of diffusion coefficients allowing one to match the performance of a given AOGCM for a variety of transient forcing scenarios. Both surface warming and sea level rise due to thermal expansion of the deep ocean in response to a gradually increasing forcing are reasonably reproduced on time scales of 100–150 y. However a wide range of diffusion coefficients is needed to match the behavior of different AOGCMs. We use results of simulations with the 2-D model to show that the impact on climate change of the implied uncertainty in the rate of heat penetration into the deep ocean is comparable with that of other significant uncertainties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050224
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  • 20
    Electronic Resource
    Electronic Resource
    Application of technetium-99m hexamethylpropylene amine oxime single-photon emission tomography to neurologic prognosis in patients undergoing urgent carotid surgery (1995)
    Springer
    European journal of nuclear medicine 22 (1995), S. 132-138 
    Details
    ISSN: 1619-7089
    Keywords: Acute cerebral ischaemia ; Carotid endarterectomy ; Technetium-99m hexamethylpropylene amine oxime ; Single-photon emission tomography ; Discriminant analysis ; Prognosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In this study we aimed to work out a quantitative prognostic index for preoperative assessment of brain technetium-99m hexamethylpropylene amine oxime (HMPAO) single-photon emission tomography (SPET) in patients referred for urgent carotid endarterectomy due to acute obstructive disease of the internal carotid artery (ICA) and neurological deficit. To this end we compared data from preoperative SPET studies with the postinterventional changes in neurological status in 20 patients (17 males, three females; mean age 53 years, SD 4 years) with acute ischaemic cerebral disorders induced by obstruction of the ICA. Carotid obstruction was diagnosed by ultrasound B-mode study. All patients underwent urgent carotid endarterectomy from the ICA. Patients were divided into two groups in accordance with the results of postoperative follow-up: group A comprised patients with significant (more than 3 points) postoperative improvement in neurological condition as quantified by the Canadian Neurological Scale (11 patients); group B consisted of patients with minimal improvement or deterioration (nine, three of whom died). All patients were studied preoperatively by99mTc-HMPAO SPET. The volume of nonperfused tissue (VS, cm3) was quantified using the Mountz technique. Hypoperfused volume (V hypoperf, cm3) in the affected hemisphere was calculated as the total volume of voxels with99mTc-HMPAO uptake 〈90% of the contralateral symmetric voxels. Discriminant prognostic function was calculated by discriminant analysis as:PF = 0.072×VS + 29.46×(VS/V hypoperf). Patients with preoperativePF values 〈8.20 demonstrated postoperative improvement in neurological status, while the group withPF〉8.90 comprised patients who demonstrated minimal improvement or deterioration. PF values in the range 8.20–8.90 carried an indefinite prognosis. We conclude that the preoperative99mTc-HMPAO SPET can be used for the selection of patients in whom improvement in neurological status may be expected after urgent surgical correction of acute extracranial obstruction of the ICA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00838943
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