摘要:

The first observations 30 years ago of molecular clustering via quantum diffusion in solidH2in nuclear magnetic resonance (NMR) and pressure experiments are described. A previous review on quantum diffusion and tunneling up to 1986 is updated to reflect progress in the last ten years. In particular I review the effect of clustering on heat capacity in solidD2and on the thermal conductivity in solidH2.The configurational relaxation time observed inD2at 1.75 K is found to scale with that inH2at the same temperature in terms of the predictions of ortho–para resonant conversion-induced hopping. The relaxation times measured simultaneously on the same sample in NMR and conductivity experiments reflect different configurational processes. The theory of molecular hopping and pairing in solidH2is outlined and compared with experiments. The tunneling frequency of HD in solidH2deduced from transverse and longitudinal NMR relaxation experiments between 0.03 and 14 K is discussed. The hopping of ortho-H2,invoked as a mechanism in the enhanced ortho–para conversion in presence ofO2impurities, is mentioned. Finally, recent tunneling results for H, D andH2−anions in solidH2during the studies of low temperature reaction dynamics are also briefly described. In the Appendix, the hopping frequency determination in HD from NMR transverse relaxation time measurements is reviewed. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593606

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A universal phenomenological approach to studying macroscopic fluctuations is proposed and general kinetic equations for long-wave fluctuations in a normal Fermi liquid are derived. These kinetic equations form the basis of the theory of quasi-linear relaxation for zero-point sound in a normal Fermi liquid in the paired fluctuation approximation. The conditions for the existence of the quasi-linear approximation are considered. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593607

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The influence of high-density current pulses on the structure and superconducting properties of HTSC ceramicsYBa2Cu3Oxis studied at room temperature. A gradual increase in the pulsed current density causes appreciable structural changes: when a certain threshold value is reached, the melting of large grains occurs and is accompanied by partial breaking of intergranular contacts resulting in degradation of superconductivity. A further increase in the current density leads to the recovery of superconducting properties, which is probably due to the formation of superconducting bridges between grains aligned along the current flow. The superconducting transition temperature remains unchanged in such samples, but subsequent thermal treatment leads to an increase in the superconducting transition temperature. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593608

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The energy balance technique is used for contactless measuring of integral electrical characteristics of annular samples of Y–Ba–Cu–O ceramics. Dependences of the loss resistance and internal inductance of HTSC samples on transport current are obtained. The critical and resistive states of samples are studied at various frequencies of transport current as functions of the applied constant magnetic field. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593609

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The dependence of the superconducting transition temperature on the thickness of films of niobium, VN, TaN, andYBa2Cu3O7−xare determined experimentally. It is shown that, in addition to the proximity effect, the fluctuations of the electromagnetic field and order parameter of the superconducting phase may also play a significant role in superconductors with a small coherence length. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593610

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The evolution of an arbitrary initial nonequilibrium distribution of electrons and electric fields is investigated in a structure consisting of semiconfined media, viz., plasma and insulator (vacuum). The comprehensive spectrum of potential oscillations of electric fields is obtained. It is shown that the set of frequency eigenvalues is determined by the properties of the electron distribution function in equilibrium and perturbed states. In a cold plasma, volume and surface oscillations with the Langmuir frequency can propagate along with surface plasmons, while only a surface plasmon field exists in the insulator. In the presence of spatial dispersion, all types of volume and surface oscillations emerging in the plasma are emitted to the insulator. In addition to the field of intrinsic oscillations, an electric field of anomalous penetration associated with the effects of ballistic transport of conduction electrons at low temperatures also exists in the plasma. For a cold plasma, delay effects are taken into account, and the spatial and time distributions of the fields in the insulator are found. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593611

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A two-dimensional model generalizing the Peierls model to the case of coupled fields of magnetization and elastic displacement distribution is proposed for describing the structure of a complex magnetoelastic topological defect which has the form of the bound state of a dislocation and a magnetic disclination in an antiferromagnet. The obtained system of nonlinear one-dimensional integro-differential equations has solutions for magnetic vortices and for magnetic disclinations connected with dislocations and having regular asymptotic forms at large distances and no singularities at the core of the topological defect. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593612

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An analysis of the absorption and luminescence spectra of aY2SiO5:Pr3+crystal has revealed the existence of twoPr3+optical centers associated with the presence of impurity ions at nonequivalent cation sites. It is found that energy is transported nonradiatively between the nonequivalentPr3+optical centers. and a preliminary analysis of the transport mechanism is carried out. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593613

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The longitudinal and transverse magnetoresistances are studied in solid solutions ofn-CdxHg1−xTewithx=0.19and 0.226 at hydrogen and helium temperatures. Effective masses at the bottom of the conduction band are determined from an analysis of oscillation amplitudes at helium temperatures. The values ofg-factors are determined from the splitting of the first magnetoresistance peak. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593614

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This research is devoted to an analysis of continuous luminescence spectra of argon and neon crystals in the ranges 4–7 and 9–17 eV, respectively. The experimental results of this research are compared comprehensively with the data on the gaseous phase and with the luminescence of exciplexes of inert-gas halogenides. It is proposed on the basis of the detailed comparison of different experimental data that the continuum with a peak at 6.2 eV can be identified with radiation decay of the excimer complexAr2+O−.The formation of a similar exciplexNe2+O−with charge transfer is observed in the neon matrix doped strongly with oxygen. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593615

出版商:AIP    

年代:1998

数据来源: AIP