Showing papers in "Annalen der Physik in 1995"
TL;DR: In this paper, the K-matrix formalism is generalized to the production of two-body channels with final state interactions, and a multi-channel treatment of production of resonances has been worked out in the P-vector approach.
Abstract: A description is given of the K-matrix formalism. The formalism, which is normally applied to two-body scattering processes, is generalized to production of two-body channels with finalstate interactions. A multi-channel treatment of production of resonances has been worked out in the P-vector approach of Aitchison. An alternative approach, derived from the P-vector, gives the production amplitude as a product of the T-matrix for a two-body system and a vector Q specifying its production. This formulation, called Q-vector approach here, has also been worked out. Examples of practical importance are given.
147 citations
TL;DR: In this article, the wave-function Monte Carlo method of Quantum Optics is generalized and promoted to the level of a fundamental process generating all the real events in Nature, and a uniquely defined piecewise deterministic algorithm generating quantum jumps, classical events and histories of single quantum objects.
Abstract: The standard formalism of quantum theory is enhanced and definite meaning is given to the concepts of experiment, measurement and event. Within this approach one obtains a uniquely defined piecewise deterministic algorithm generating quantum jumps, classical events and histories of single quantum objects. The wave-function Monte Carlo method of Quantum Optics is generalized and promoted to the level of a fundamental process generating all the real events in Nature. The already worked out applications include SQUID-tank model and generalized cloud chamber model with GRW spontaneous localization as a particular case. Differences between the present approach and quantum measurement theories based on environment-induced master equations are stressed. Questions: what is classical, what is time, and what observers are addressed. Possible applications of the new approach are suggested, among them connection between the stochastic commutative geometry and Connes' noncommutative formulation of the Standard Model, as well as potential applications to the theory and practice of quantum computers.
69 citations
TL;DR: In this paper, the authors investigated the collapse of laser-induced bubbles in water at high speed photography at framing rates as high as 20 million frames per second and compared the case of a spherical bubble in an unbounded liquid with the Gilmore model.
Abstract: The collapse of laser-induced bubbles in water is investigated by high speed photography at framing rates as high as 20 million frames per second. The case of a spherical bubble in an unbounded liquid is compared with the Gilmore model. Bubbles collapsing in front of a solid wall show a rich dynamics depending on their normalized distance. Unprecedented details are given of the generic sequence of events leading to multiple shock waves and bubble shape metamorphosis upon collapse.
63 citations
TL;DR: In this paper, a 5D Machian generalization of the Kaluza-Klein theory is described, in which the cosmological constant appears as the contribution of the rest of the universe to the gravitational field of an isolated source.
Abstract: A 5D Machian generalization of Einstein's theory of gravitation is described in which the cosmological constant appears as the contribution of the rest of the universe to the gravitational field of an “isolated” source. This work amounts to a Machian interpretation of the Kaluza-Klein theory. The standard cosmological models are derived in this framework, and it is shown that - in conformity with the interpretation presented here - the cosmological constant does not directly contribute to the geometric description of the universe as a whole.
54 citations
TL;DR: In this article, the authors studied the overdamped motion of a particle in a one-dimensional periodic potential driven by a stochastic force and obtained a closed expression for the current as a ratio of two determinants.
Abstract: We study the overdamped motion of a particle in a one-dimensional periodic potential driven by a stochastic force. If the stochastic force is correlated in time (non-white), and if the potential has no inversion symmetry, a current is generated. In the case of a piecewise linear potential we obtain a closed expression for the current as a ratio of two determinants. This allows us to calculate the current as a function of the noise strength, the correlation time and the temperature of the system for several stochastic processes. We examine several limiting situations. Depending on the statistics of the noise process, the direction of the current may change. Two different mechanisms for this effect are discussed.
30 citations
TL;DR: In this article, the authors introduce a new class of experiments which provide graphic insights into the propagation of acoustic waves in anisotropic media, where the data may be viewed as a movie or a series of snapshots.
Abstract: We introduce a new class of experiments which provide graphic insights into the propagation of acoustic waves in anisotropic media. Simply stated, we have devised a means of observing the expanding acoustic wavefront from a point disturbance in a solid. The data may be viewed as a movie or a series of snapshots. The observed wavefronts represent the group-velocity surfaces of acoustic waves, which reflect the basic elastic anisotropy of the solid. The technique has been applied to coherent acoustic waves with frequencies in the megahertz range (at ambient temperatures) and to incoherent heat pulses in the hundred-gigahertz range (at liquid-helium temperatures). In this article, we first provide a pedagogical introduction to wave propagation in elastically anisotropic media, reviewing some early methods for visualizing acoustic waves. Next, we describe the “acoustic wavefront imaging” method and give representative results in crystals and composite materials. Finally, we show how this method relates to recent advances in phonon imaging and internal diffraction of ultrasound.
26 citations
TL;DR: In this article, the instability of the fully polarised ground state (Nagaoka state) on the triangular, honeycomb and kagome lattices has been investigated in the framework of Hartree-Fock theory.
Abstract: In order to analyse the lattice dependence of ferromagnetism in the two-dimensional Hubbard model we investigate the instability of the fully polarised ferromagnetic ground state (Nagaoka state) on the triangular, honeycomb and kagome lattices. We mainly focus on the local instability, applying single spin flip variational wave functions which include majority spin correlation effects. The question of global instability and phase separation is addressed in the framework of Hartree-Fock theory. We find a strong tendency towards Nagaoka ferromagnetism on the non-bipartite lattices (triangular, kagome) for more than half filling. For the triangular lattice we find the Nagaoka state to be unstable above a critical density of n = 1.887 at U = ∞, thereby significantly improving former variational results. For the kagome lattice the region where ferromagnetism prevails in the phase diagram widely exceeds the flat band regime. Our results even allow the stability of the Nagaoka state in a small region below half filling. In the case of the bipartite honeycomb lattice several disconnected regions are left for a possible Nagaoka ground state.
25 citations
TL;DR: In this paper, a microwave oscillator based on Bloch oscillations of electrons in a semiconductor superlattice was presented. Butler et al. showed that the ratio of linewidth to frequency was of the order of 10−4, corresponding to a generator efficiency of 10 −3 for the conversion of electrical power to microwave radiation.
Abstract: We report on a microwave oscillator based on Bloch oscillations of electrons in a semiconductor superlattice. Our GaAs/AlAs superlattice, at room temperature, was coupled electromagnetically by an antenna to a rectangular cavity resonator, and was operated at a current-voltage state of negative differential conductance. We observed generation of microwave radiation at frequencies, depending on the resonator length, between 7 and 30 GHz. Electronic tuning by several percent was possible; the ratio of linewidth to frequency was of the order of 10−4. A radiation power up to 1 μW (at 10 GHz) was obtained, corresponding to a generator efficiency of the order of 10−3 for the conversion of electrical power to microwave radiation.
25 citations
TL;DR: In this article, the authors analyze the quantum fluctuations of vacuum stress tensors and spacetime curvatures, using the framework of linear response theory, and deduce noise spectra for geodesic deviations registered by probe fields which determine ultimate limits in length or time measurements.
Abstract: We analyze the quantum fluctuations of vacuum stress tensors and spacetime curvatures, using the framework of linear response theory which connects these fluctuations to dissipation mechanisms arising when stress tensors and spacetime metric are coupled. Vacuum fluctuations of spacetime curvatures are shown to be a sum of two contributions at lowest orders; the first one corresponds to vacuum gravitational waves and is restricted to light-like wavevectors and vanishing Einstein curvature, while the second one arises from gravity of vacuum stress tensors. From these fluctuations, we deduce noise spectra for geodesic deviations registered by probe fields which determine ultimate limits in length or time measurements. In particular, a relation between noise spectra characterizing spacetime fluctuations and the number of massless neutrino fields is obtained.
18 citations
TL;DR: In this article, the authors studied the phase diagram of the bilinear-biquadratic spin-1 chain and obtained upper bounds for the groundstate energy using so-called matrix-product states.
Abstract: We study the phase diagram of the bilinear-biquadratic spin-1 chain. Using so-called matrix-product (MP) states we obtain upper bounds for the groundstate energy. The advantage of these MP states is their simplicity. Moreover they give an accurate description of the physics, especially in the Haldane phase.
17 citations
TL;DR: In this paper, it was shown that the Feynman integrand for the harmonic oscillator in an external potential is a Hida distribution, which is a generalized white noise function.
Abstract: We review some basic notions and results of White Noise Analysis that are used in the construction of the Feynman integrand as a generalized White Noise functional. We show that the Feynman integrand for the harmonic oscillator in an external potential is a Hida distribution.
TL;DR: In this paper, the authors reported the observation of frequency multiplication of microwave radiation in a GaAs/AlAs semiconductor superlattice at room temperature, for a fundamental frequency of 9 GHz, second and third harmonic generation.
Abstract: We report the observation of frequency multiplication of microwave radiation in a GaAs/AlAs semiconductor superlattice at room temperature. We observed, for a fundamental frequency of 9 GHz, second and third harmonic generation. We associate the harmonic generation with a nonlinear current-voltage characteristic that is determined by Bloch oscillations of electrons propagating along the superlattice axis. Our results suggest for the frequency multiplication an upper limit in the tetrahertz frequency range.
TL;DR: In this article, the authors studied the overdamped motion of a particle in a fluctuating one-dimensional periodic potential, where the amplitude and the direction of the current depend on the details of the noise process that is responsible for the potential fluctuations.
Abstract: We study the overdamped motion of a particle in a fluctuating one-dimensional periodic potential. The potential has no inversion symmetry, and the fluctuations are correlated in time. At finite temperatures, a stationary current is induced. The amplitude and the direction of the current depend on the details of the noise process that is responsible for the potential fluctuations. We discuss several limiting situations for a general case. Furthermore we calculate the current in the case of a piecewise linear potential for different noise processes and parameters. A detailed discussion of the results is given, including a discussion of the mechanism that is responsible for the current reversal. We compare the present results with results for transport in a ratchet-like potential due to a fluctuating force. We also discuss the biological relevance of the present models for molecular motors. We present a model for the motion of molecular motors that explains why similar molecular motors can move in different directions.
TL;DR: In this article, the formation and Kondo effect of local magnetic moments in the Anderson-Hubbard model with off-diagonal disorder were investigated. And the existence of moments at sites weakly coupled to the environment was deduced in effective medium approximation.
Abstract: We consider the formation and the Kondo effect of local magnetic moments in the Anderson-Hubbard model with off-diagonal disorder. The existence of moments at sites weakly coupled to the environment is deduced in effective medium approximation. The distribution of moments is calculated both deep in the metallic phase and near the metal-insulator transition. We discuss the Kondo quenching of the moments and derive a distribution of local Kondo temperatures.
TL;DR: In this article, an eigenvalue equation for the amount of time a particle needs for reflection from an impermeable potential barrier is derived, where the eigenvalues are given by τ2(E) = ℏ, where ρ(E), is the phase shift for stationary reflection at fixed scattering energy E. The method allows for a consistent treatment of the quantum mechanical Goos-Hanchen time delay.
Abstract: Starting with wave packets, an eigenvalue equation is derived for the amount of time a particle needs for reflection from an impermeable potential barrier. The corresponding Hermitian operator TR is linear and diagonal in energy space. The eigenvalues are given by τ2(E) = ℏ , where ρ(E) is the phase shift for stationary reflection at fixed scattering energy E. The quantum mechanical reflection time τR(E) has a well defined WKB-limit. For low scattering energies τR(E) is proportional to if weakly bound states are absent in the reflection region. However, if there is an empty weakly bound state it will transiently trap a slowly moving particle, causing a divergence of the reflection time for E0. We work out and illustrate the theory for various reflecting potentials. The method allows for a consistent treatment of the quantum mechanical Goos-Hanchen time delay.
TL;DR: In this article, two different procedures for the preparation of bimorph structures within nonlinear optical polymer layers are reported, one technique consists of thermally assisted poling above the glass transition temperature followed by photo-induced poling below the glass-transition temperature.
Abstract: Two different procedures for the preparation of bimorph structures within nonlinear optical polymer layers are reported. One technique consists of thermally assisted poling above the glass-transition temperature followed by photo-induced poling below the glass-transition temperature. In this poling scheme, the second step is based on the photoisomerization of the dipole molecules. The other method comprises two consecutive thermally assisted poling steps with opposite field polarity in a double layer of two nonlinear optical polymers with different glass-transition temperatures. Pyroelectric thermal analysis is employed for analyzing the stability of the resulting bimorph structures, while pyroelectric depth profiling allows for a non-destructive qualitative analysis of their polarization distributions.
TL;DR: In this article, a two-dimensional diffraction grating for phonons is described, which scatters thermal phonons strongly when their dominant wavelength is equal to the grating's lattice constant.
Abstract: A two-dimensional diffraction grating for phonons is described. It scatters thermal phonons strongly when their dominant wavelength is equal to the grating's lattice constant. Through measurements of the Kapitza resistance between the silicon crystal carrying the grating and liquid helium, it is shown that the scattering by the grating is predominantly coherent, as expected for phonon diffraction.
TL;DR: In this paper, new field equations of the Projective Unified Field Theory are presented, which avoid potential difficulties of former versions with respect to the equivalence principle. But the physical interpretation of this new version remains unchanged: constancy of the "gravitational constant", electromagnetic polarization of the vacuum, definiteness of the energy of the stationary scalaric field, etc.
Abstract: New field equations of the Projective Unified Field Theory are presented which avoid potential difficulties of former versions with respect to the equivalence principle The physical interpretation of this new version remains unchanged: constancy of the “gravitational constant”, electromagnetic polarization of the vacuum, definiteness of the energy of the stationary scalaric field, etc Furthermore, the Klein-Gordon field and the Dirac field are treated
TL;DR: In this paper, it is shown that ultrasonic absorption in vitreous silica exhibits a prominent maximum, the so-called 50 K-peak, caused by thermally activated relaxation processes as can be inferred from the position of the maximum which shifts from 30 K at a measuring frequency of 1 kHz to above 100 K at Brillouin frequencies.
Abstract: Ultrasonic absorption in vitreous silica (a-SiO2) exhibits a prominent maximum, the so-called 50 K-peak. It is caused by thermally activated relaxation processes as can be inferred from the position of the maximum which shifts from 30 K at a measuring frequency of 1 kHz to above 100 K at Brillouin frequencies. The microscopic nature of the relaxing ‘particles’ is unknown but they are believed to originate intrinsically from the random network of the glass. Nevertheless, in the framework of phenomenological models, like the tunneling model or the soft potential model, it is possible to describe the experiments very well in the full range of measured frequencies and temperatures. Both models are founded on the assumption that the particles reside in double well potentials and that their dynamics are based on tunneling between the two equilibrium positions at low temperatures, whereas thermal activation over the barriers is dominating at temperatures exceeding a few Kelvin [1,2].
TL;DR: In this article, the phase diagram of spinless fermions with repulsive nearest neighbour interaction is calculated analytically on a hypercubic lattice in infinite dimensions.
Abstract: The phase diagram of the model of spinless fermions with repulsive nearest neighbour interaction is calculated analytically on a hypercubic lattice in infinite dimensions (d ∞). In spite of its simplicity the model displays a rich phase diagram depending on the doping δ, the interaction U and the temperature T. The system can be in the homogeneous phase (HOM), the nonsegregated AB charge density wave (AB-CDW), the AB phase separation region (PS-AB/HOM; coexistence of AB-CDW and HOM), the incommensurate phase (IP) or the IP phase separation region (PS-AB/IP; coexistence of AB-CDW and IP). We identify three important values of the interaction UIPL = 0.572 < UIPH = 1.914 < UIP/PS = 4.212 which distinguish four intervals of U. These imply four different types of phase diagrams. In all the three phase diagrams with U below UIP/PS the IP appears. We propose a new general ansatz for the order parameter of this phase. A competition between the IP, the PS-AB/IP and the PS-AB/HOM is found. The relevance of our findings for the phase scenario of the Hubbard model is shown.
TL;DR: In this paper, the annealing behavior of quench condensed H2-, HD- and D2-films has been investigated using acoustic surface waves, and the activation energies for surface self-diffusion as 23 K, 35 K, and 47 K for H2, HD, and D 2, respectively.
Abstract: The annealing behaviour of quench condensed H2-, HD- and D2-films has been investigated using acoustic surface waves. Upon annealing at temperatures far below the triple point we observe drastic changes of sound velocity and attenuation which can be attributed to a considerable rearrangement of the film structure via surface diffusion. These findings are in good agreement with recent experiments using surface plasmons. From the temperature dependence of the speed of the structural changes we deduce the activation energies for surface self-diffusion as 23 K, 35 K, and 47 K for H2, HD, and D2, respectively.
TL;DR: In this paper, the Eliashberg equations were solved for the case of an explicit dependence of the interac-tions, and of the resulting self-energies XI (I?, a), X2(% w).
Abstract: We solve the Eliashberg equations for the case of an explicit dependence of the interac- tions, and of the resulting self-energies XI (I?, a), X2(% w). We consider a strong energy-dependence of the electron-electron scattering-rate r;', which is associated with a strong energy-dependence of the electron-phonon matrix element g(k,k'). We characterize this energy-dependence by a cutoff tl, which is of the order of the phonon frequency Up),. We find that we can account for a large number of unexpected features of the superconductivity of the cuprates by the BCS electron-phonon theory, if we consider very large values of the McMillan coupling constant Aph, and small values of the cutoff C1. Specifically, the Coulomb interaction is found not to depress T,; thejsotope effect is strongly reduced when c1
TL;DR: This paper presents simulation results for single a-thermal chain polymers in finite volumes using a recently proposed recursive implementation of the enrichment method, which allows the simulation of extremely long chains in 3 dimensions.
Abstract: We present simulation results for single a-thermal chain polymers in finite volumes. For this we use a recently proposed recursive implementation of the enrichment method. In 3 dimensions it allows the simulation of extremely long chains (up to N = 300,000). It is much less efficient ford = 2, but we can also there extend considerably the previously accessible range of chain lengths and densities. We verify all tested scaling laws except one, and we point out similarities with complex optimization problems.
TL;DR: The essential properties of folding are captured by showing that the statistical weight is concentrated on a very limited domain of closely-related folding pathways whose biological competence has been established experimentally.
Abstract: By systematically assigning weights to kinetically-controlled folding pathways we introduce a novel scheme of statistical inference. We provide supporting experimental evidence to show that this approach is suitable to explain the expediency and robustness of RNA folding. The statistical scheme is constructed in four stages, the last of which leads to a suitable representation that allows for direct comparison with experiment: a) An appropriate space of folding histories is defined; b) The space is endowed with a measure and in this way an ensemble is defined; c) The ensemble is systematically simplified by coarse-graining each copy or replica of conformation space. This procedure entails lumping together rapidly-interconverting conformations; d) A base-pair probability matrix (BPPM) is introduced by representing all structures contributing to the ensemble at a given instant. Thus, we take a convenient cross-section of the ensemble by taking a fixed instant in time. The BPPM is contrasted vis-a-vis experimental information on biologically-competent conformations. This last procedure is paramount to verify the theory. Moreover, the essential properties of folding are captured by showing that the statistical weight is concentrated on a very limited domain of closely-related folding pathways whose biological competence has been established experimentally.
TL;DR: In this paper, the authors present the results of a computer simulation study of charged-particle interferometry, combining features of both the Aharonov-Bohm and Hanbury Brown-Twiss experiment.
Abstract: We present the results of a computer simulation study of charged-particle interferometry, combining features of both the Aharonov-Bohm and Hanbury Brown-Twiss experiment. In contrast to a previous theoretical analysis of this experiment, we find that the Aharonov-Bohm effect is also present in the cross-correlated two-particle intensity. A simple, time-independent scattering theory that leads to conclusions that are in concert with the simulation data is given.
TL;DR: In this paper, the electronic shell structure resulting from the interference of closed orbital paths is determined for mesoscopic systems like spherical clusters, discs and rings by extending the semiclassical theory of Balian and Bloch.
Abstract: The electronic shell structure resulting from the interference of closed orbital paths is determined for mesoscopic systems like spherical clusters, discs and rings by extending the semiclassical theory of Balian and Bloch. Analytical results for the shell structure in the density of states are obtained. Thus, the dependence of the shell structure on dimension, size and geometry and potential of the mesoscopic system and on an external magnetic field can be studied systematically. Comparison of the semiclassical results and those of quantum mechanical calculations permits analysis of typical quantum mechanical effects and shows the validity of the semiclassical theory. Our results should stimulate new experiments, can be used to calculate oscillations in the binding-energy, ionization-potential, and can be applied to analyze oscillations in the electronic density of states of quantum dot systems like anti-dot lattices.
TL;DR: In this paper, the first measurements of the interaction of non-equilibrium phonons with two-dimensional exciton gases (2DExGs) were reported, and it was shown that the rise in the effective temperature of the 2DExG produced by the phonons depends on the width of the quantum well and the exciton sheet density.
Abstract: We report the first measurements of the interaction of non-equilibrium phonons with two-dimensional exciton gases (2DExGs). The rise in the effective temperature of the 2DExG produced by the phonons depends on the width of the quantum well and the exciton sheet density and hence on the ratio τ−1 (ex-ph)/τ−1 (ex-ex). The dependence of the effective temperature rise on this ratio is attributed to the non-equilibrium frequency distribution of the phonons incident on the 2DExG.
TL;DR: In this paper, it was shown that recourse to Information Theory (IT) concepts allows one to infer the pertinent wave functions (and eigenvalues) without attempting to solve the concomitant differential equation.
Abstract: From the sole knowledge (at a finite number of points) of the numerical values of the potential V(r) corresponding to Schrodinger's radial equation, it is found that recourse to Information Theory (IT) concepts allows one to infer the pertinent wave functions (and eigenvalues) without attempting to solve the concomitant differential equation. Moreover, the underlying IT ideas allow for an analytical treatment that yields exact wave functions of the maximum (quantal) entropy form in a number of cases of interest.
TL;DR: In this article, two spin flip variational wave functions describing spin wave excitations were discussed in order to investigate the instability of the fully polarized ferromagnetic state (Nagaoka state) in the infinite U Hubbard model.
Abstract: We discuss two single spin flip variational wave functions describing spin wave excitations which were proposed earlier by Shastry, Krishnamurthy and Anderson (SKA) and by Basile and Elser (BE), respectively, in order to investigate the instability of the fully polarized ferromagnetic state (Nagaoka state) in the infinite U Hubbard model. We calculate the energy of these variational states for the square lattice and for multiple chains. At the zone boundary in the vicinity of the point (0, π) the spin wave energy is reduced substantially by the binding of the spin up hole to the flipped down spin. For the square lattice this leads to a critical hole density of δcr = 0.407 for the SKA spin wave and of δcr = 0.322 for the BE spin wave which implies remarkable improvements in comparison to the corresponding scattering states investigated previously.
TL;DR: In this paper, the authors used a reflex klystron to feed a planar Hertzian resonator for sound generation, detection and undisturbed transmission to the target.
Abstract: Only the study of absorption and angular dependent scattering of GHz and THz sound can give us detailed information about interaction processes of acoustical phonons. Therefore, the necessary techniques of sound generation, detection and undisturbed transmission to the target must be improved or to a large extent must still be developed. Corresponding attempts at 35 GHz are described. Sound-beam topography allowed to study crystal defects and also showed us where transmission without scattering occurred. For the piezoelectric generation a reflex klystron was used feeding a planar Hertzian resonator. The needle-like sound beams appeared as a double beam, each showing a minimum diameter of 35 μm for longitudinal polarized sound at an acoustic wavelength of 165 nm in X-cut quartz and 320 nm in a-cut sapphire. To obtain the smallest possible beam diameter for high resolution work, model calculations are presented for an excited fundamental Gaussian sound beam in an isotropic medium.