New light on disordered ensembles: ab initio structure determination of one particle from scattering fluctuations of many copies

We report on the first experimental ab?initio reconstruction of an image of a single particle from fluctuations in the scattering from an ensemble of copies, randomly oriented about an axis. The method is applicable to identical particles frozen in space or time (as by snapshot diffraction from an x-ray free electron laser). These fluctuations enhance information obtainable from an experiment such as conventional small angle x-ray scattering.     

Interaction of acoustic waves with polycrystals

We analyze theoretically the structure of the field created in a semi-infinite polycrystal by an acoustic wave, coming from an isotropic homogeneous medium and incident normally onto its surface. The elastic anisotropy of the polycrystal is supposed to be small, and the perturbation theory is applied. It is shown that the effective medium approach is not valid. In addition to the transmitted wave propagating in the polycrystal with an effective sound speed, there is one more bulk wave, whose amplitude decreases at a distance of the order of the mean size of the grain from the interface. The structure of the reflected wave is the same as when reflecting from an isotropic solid. However, the relation between the amplitudes of reflected and transmitted waves differs from that in an isotropic solid.     

Large scale data acquisition of simultaneous MRI and speech

We describe an arrangement for simultaneous recording of speech and vocal tract geometry in patients undergoing surgery involving this area. Experimental design is considered from an articulatory phonetic point of view. The speech signals are recorded with an acoustic-electrical arrangement. The vocal tract is simultaneously imaged with MRI. A MATLAB-based system controls the timing of speech recording and MR image acquisition. The speech signals are cleaned from acoustic MRI noise by an adaptive signal processing algorithm. Finally, a vowel data set from pilot experiments is qualitatively compared both with validation data from the anechoic chamber and with Helmholtz resonances of the vocal tract volume, obtained using FEM.     

New electrostatic cylindrical energy analyzer

The focusing properties of an ideal cylindrical field in full relativistic field have been investigated for charged particles originating from an extended source and an analytical solution for the equations of motion has been provided. This focusing system can be used for production of electrostatic energy analyzer provided surface analysis from an extended area.     

A comparison between microscopic and empirical estimates of the density dependence of effective interactions

The effective interaction W which was recently deduced empirically from saturation considerations as an addition to the Sussex matrix elements is compared with earlier estimates of corrections arising from an assumed short-range repulsion and from the tensor force in second order.     

Common-path achromatic interferometer-coronagraph: nulling of polychromatic light

A three-dimensional common-path interferometer is proposed, which can achromatically null out an on-axis source while it maintains the detectability of an off-axis source. A geometric phase in the three-dimensional interferometer introduces an achromatic pi-phase shift to the light from the on-axis source, such that destructive interference nulls out the axial light at one of the ports of the interferometer. Light from the off-axis source, which is exempt from the pi-phase shift, comes out from both ports with equal intensity. The common-path scheme makes the system highly immune to environmental disturbances.     

Temperature characterization of Raman scattering in an AlGaN/GaN heterostructure

Raman scattering from an AlGaN/GaN heterostructure was performed in the temperature range from 77 to 773 K. The first- and second-order Raman scattering of the A₁ longitudinal-optical phonon–plasmon coupled mode from an AlGaN/GaN interface as well as the Raman scattering from the GaN layer were observed. All the modes downshift, and their intensities weaken with increasing temperature. The free-carrier concentration estimated by the frequency of the coupled mode from an AlGaN/GaN interface is 7.5 times as high as that of n-AlGaN, indicating mass free-carrier transfer from the AlGaN barrier to the GaN well. Moreover, the temperature dependence of the phonon frequency is well described by an empirical formula. PACS 78.30.Fs; 63.20.Ls; 61.82.Fk; 68.60.Dv; 81.15.Gh     

Bound entangled states invariant under Ux

This paper obtains an entangled condition for isotropic-like states by using an atomic map. It constructs a class of bound entangled states from the entangled condition and shows that the partial transposition of the state from the constructed bound entangled class is an edge bound entangled state by using range criterion.     

铷原子初通道─末通道辐射跃迁矩阵元研究

在相对论性自洽场理论基础上，把量子亏损理论的一个初态到一个末通道的跃迁过程进行了推广：具有相同角动量特征的初态形成所谓的初通道，通过定义重整化矩阵元，统一处理了一个初通道激发到一个末通道的无数个光跃迁过程．作为例子，计算了你原子“s_1/2—p_1/2”，“p_1/2—d_3/2”，“d_3/2—f_5/2”通道之间的光吸收过程．     

Propagation in an elastic wedge using the virtual source technique

The virtual source technique, which is based on the boundary integral method, provides the means to impose boundary conditions on arbitrarily shaped boundaries by replacing them by a collection of sources whose amplitudes are determined from the boundary conditions. In this paper the virtual source technique is used to model propagation of waves in a range-dependent ocean overlying an elastic bottom with arbitrarily shaped ocean-bottom interface. The method is applied to propagation in an elastic Pekeris waveguide, an acoustic wedge, and an elastic wedge. In the case of propagation in an elastic Pekeris waveguide, the results agree very well with those obtained from the wavenumber integral technique, as they do with the solution of the parabolic equation (PE) technique in the case of propagation in an acoustic wedge. The results for propagation in an elastic wedge qualitatively agree with those obtained from an elastic PE solution.     

Thermodynamics and cosmology

A new type of cosmological history which includes large-scale entropy production is proposed. These cosmologies are based on a reinterpretation of the matter-energy stress tensor in Einstein's equations. This modifies the usual adiabatic energy conservation laws, thereby leading to a possible irreversible matter creation. This creation corresponds to an irreversible energy flow from the gravitational field to the created matter constituents. This new point of view results from the consideration of thermodynamics of open systems in the framework of cosmology. It appears that the usual initial singularity is structurally unstable with respect to irreversible matter creation. The corresponding cosmological history therefore starts from an instability of the vacuum rather than from a singularity. The universe evolves through an inflationary phase. This appears to be an attractor independent of the initial vacuum fluctuation.This essay received the fifth award from the Gravity Research Foundation for the year 1988.-Ed.     

Anisotropic Short-Wavelength Friedel Oscillation with Adjustable Envelope in Graphene

We investigate theoretically the intervalley charge density oscillation and the screened ionic potential in graphene caused by the intervalley scattering. We demonstrate that the contribution from the intervalley scattering is comparable with that from the intravalley scattering, and oscillation rather than decaying dominates at a large distance away from the external impurity. We show that the intervalley oscillation is strongly anisotropic because of the inequivalency between neighboring valleys. The anisotropic oscillation consists of an anisotropic short-wavelength oscillation with an anisotropic fixed wavelength and an isotropic long-wavelength envelop with an isotropic wavelength modulated by doping, making an adjustable-widthed wave-packet propagation. One weakens the screening and gets anisotropic short-wavelength oscillation by introducing short-range mechanism in graphene and graphene-like materials.     

Simple cases of spontaneous emission from an atom-photon cluster localized in a microcavity

The spontaneous emission from an atomic ensemble localized in a microcavity with the participation of microcavity photons and an external broadband quantized electromagnetic field at the Raman resonance of photons with an optically forbidden (two-photon) atomic transition has been studied. The average spontaneous decay intensity has been calculated for simple cases. It is shown that the dynamics of spontaneous emission from this atomic ensemble differs generally from the conventional superradiance (spontaneous emission of an atomic ensemble at a one-photon optically allowed transition from excited to the ground state. When the atomic ensemble is strongly excited, the delay times and the emission pulse shape differ significantly. The parameter ranges where the spontaneous emission from the atomic ensemble under consideration at a two-photon Raman transition can be described as conventional superradiance with renormalized parameters are found. In the case of single excitation the photon emission probability depends on the number of photons and atoms in the microcavity.     

Amplitude and Phase Retrieval of Ultrashort Optical Pulse Using Optical Spectrogram Scope

We demonstrate the retrieval of the amplitude and phase of an ultrashort optical pulse from an optical spectrogram obtained by optical spectrogram scope (OSS). OSS is an interferometric method of obtaining a single-shot optical spectrogram without nonlinear optical effects. Since the optical spectrogram obtained by OSS retains information on the amplitude and phase of a signal pulse, we can retrieve this information without an iterative inversion algorithm from the spectrogram. In our demonstration, we retrieved the quadratic variation of a spectral phase of a linear chirped ultrashort laser pulse from a mode-locked Ti: sapphire laser.     

Obtaining spatial information from an extremely unresolved source

A means to extract spatial information from an extremely unresolved source of light using a single element detector is demonstrated by use of an optical vortex coronagraph. Applications may range from astronomy to microscopy. For example, the centroid and angular extent of an unresolved collection of incoherent point sources is revealed.     

Application, à un cristal de béryl,d'une nouvelle méthode d'étude par réflexion

The vibrational frequencies of beryl are determined from a measurement of the optical constants with a method utilizing reflexion from samples with and without an evaporated layer of an optically known substance.     

Anisotropic Short-Wavelength Friedel Oscillation with Adjustable Envelope in Graphene

We investigate theoretically the intervalley charge density oscillation and the screened ionic potential in graphene caused by the intervalley scattering. We demonstrate that the contribution from the intervalley scattering is comparable with that from the intravalley scattering, and oscillation rather than decaying dominates at a large distance away from the external impurity. We show that the intervalley oscillation is strongly anisotropic because of the inequivalency between neighboring valleys. The anisotropic oscillation consists of an anisotropic short-wavelength oscillation with an anisotropic fixed wavelength and an isotropic long-wavelength envelop with an isotropic wavelength modulated by doping, making an adjustable-widthed wave-packet propagation. One weakens the screening and gets anisotropic short-wavelength oscillation by introducing short-range mechanism in graphene and graphene-like materials.     

Control over the instability wave in terms of the two-dimensional model of a nozzle edge

The problem of generation of an instability wave leaving the edge of a half-plane that separates an immobile medium from a moving medium is considered. It is assumed that the instability wave is initiated by an acoustic wave arriving from the moving medium. The possibility of suppressing the instability wave by another acoustic wave incident from the nonflowing medium is considered. It is shown that the suppression is always possible by adjusting the amplitude and phase of the control perturbation to the parameters of the instability wave.     

Analytic theory of correlation energy and spin polarization in the 2D electron gas

We present an analytic theory of the pair distribution function and the ground-state energy in a two-dimensional (2D) electron gas with an arbitrary degree of spin polarization. Our approach involves the solution of a zero-energy scattering Schrödinger equation with an effective potential which includes a Fermi term from exchange and kinetic energy and a Bose-like term from Jastrow-Feenberg correlations. The form of the latter is assessed from an analysis of data on a 2D gas of charged bosons. We obtain excellent agreement with data from quantum Monte Carlo studies of the 2D electron gas. In particular, our results for the correlation energy show a quantum phase transition occurring at coupling strength r_s≈24 from the paramagnetic to the fully spin-polarized fluid.     

Density matrix for particle production processes in an external field

The general problem of finding the density matrices of particles and antiparticles produced by an external electromagnetic field fron an arbitrary initial state is solved. Expressions are obtained for the density matrices of particles and antiparticles produced from a state with given number of initial particles and from a state described by an initial grand canonical ensemble.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fiz., No. 6, pp. 77–81, June, 1980.