摘要:

AbstractA careful study of the supersymmetric version of Pruisken's nonlinear σ model for the integer quantum Hall effect is presented. The lattice regularized model is cast in Hamiltonian form by taking the anisotropic limit and interpreting the topological density as an alternating sum of Wess Zumino terms. It is argued that the relevant large‐scale physics of the model is preserved by projection of the quantum Hamiltonian on its sector of degenerate strong‐coupling ground states. For values of the Hall conductivity close toe2/2h(mode2/h), where a delocalization transition occurs, this yields the Hamiltonian of a quantum superspin chain which is closely related to an anisotropic version of the Chalker‐Coddington model. The relation implies that the ratio of magnetic length over potential correlation length is an irrelevant parameter at the transition. The superspin chain resembles a 1disotropic antiferromagnet with spin 1/2. It has an alternating structure which however permits an invariance under translation by one site. The conductance coefficients of a quantum Hall system withNsmall contacts translate intoN‐superspin correlation functions which are governed by conformal invariance. The superspin formalism provides a framework for studying the crossover from classical to quantum percolation. It does not however encompass the frequency‐dependent correlations of wave amplitudes at c

ISSN:0003-3804    

DOI:10.1002/andp.19945060702

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe dielectric constant of ferroelectric ceramics shows strong Debye‐like relaxation at GHz frequencies. This relaxation is caused by sound generation inside the crystallites. The ferroelastic domain walls which vibrate in the electric ac field are very effective shear wave transducers. The shear wave emission has a maximum when the wavelength of the sound wave is comparable to the width of the domains. Above this frequency the domain walls can no longer vibrate due to inertia and do not contribute to the dielectric constant. The observed dependence of the microwave dispersion on temperature, doping and grain size of the ferroelectric ceramic is in good agreement with the proposed mechanism of the emission of acoustic shear wave

ISSN:0003-3804    

DOI:10.1002/andp.19945060703

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractCantilevers of atomic force microscopes usually have spring constants of less than 1 N/m and fundamental resonance frequencies for free vibration between 10 and 100 kHz. If, however, the tip is in contact with the surface of a sample vibrating at MHz frequencies, we have observed that the cantilever can be forced to vibrate also at these high frequencies with high amplitude. For the detection of the high frequency vibrations of the cantilever we added in our experiment a fast optical knife‐edge detector to a commercial Atomic Force Microscope. Ultrasonic pulses were excited by a piezoelectric transducer bonded to the sample and the ultrasonic signals transmitted to the cantilever were recorded. Furthermore, the vibrational amplitude of the cantilever was measured locally along the cantilever. For comparison we also measured the absolute surface amplitude by a Michelson‐heterodyne interferometer. The spectral components of the cantilever vibration were examined and discussed theoretica

ISSN:0003-3804    

DOI:10.1002/andp.19945060704

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractStarting from the Enskog equation we derive an analytical equation for the relaxation time necessary for the equilibration between translational energies of the components in a dense binary mixture of hard spheres. Also we give an expression for the collision number describing the average number of collisions of one particle during the relaxation time. The analytical expressions are verified by molecular dynamics simulations for various values of the packing fraction. The results are shown to be valid even for very dense systems, i.e. for liquids in the ranges of density corresponding to the freezing point.

ISSN:0003-3804    

DOI:10.1002/andp.19945060705

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Kerr‐Schild pencil of metrics gab= gab+Vlalb, withgaband gabsatisfying the vacuum Einstein equations, is investigated in the case when the null vectorlhas vanishing twist. This class of Kerr‐Schild metrics contains two solutions: the Kasner metric and a metric which can be obtained from the Kasner metric by a complex coordinate transformation. Both are limiting cases of the Kóta‐Perjés metrics. The base space‐time is

ISSN:0003-3804    

DOI:10.1002/andp.19945060706

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19945060707

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19945060701

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY