On the Moyal Formulation of Quantum Identical Particles

Wigner functions of permutation operators are obtained and are used as a basis for a phase space formulation of quantum identical particles. Non-spin systems as well as 1/2 spin systems are considered. The general results are applied to a couple of examples.     

Acoustic cavitation series: part five rectified diffusion

A general review is given of the mechanism of rectified diffusion. The equations that describe the threshold acoustic pressure amplitude as well as the growth rate are presented. Simplified versions of the complicated threshold equation are also obtained for two regions that are of particular interest. Graphical representations of the equations for a variety of physical parameters are given as well as a comparison between the available measurements and the theoretical predictions. Finally, some suggested areas of future research in this area are presented.     

Interaction of electromagnetic waves with anisotropic collisional plasma half space

Interaction of electromagnetic waves penetrating into anisotropic semi-infinite collisional plasma embedded in a uniform external magnetic field is studied using half range Fourier transforms. General field equations are developed for fractionally accommodating boundary and a particular case of specular reflection is discussed both for right handed as well as left handed circularly polarized modes. Anisotropy effects are found to be more prominent in the continuum mode of field component. Anisotropy as well as collisions make the field to attain a constant value at a shorter distance. Left handed polarized modes are found to be more penetrating than right handed modes. Surface impedance is calculated and effects of collisions as well as anisotropy are discussed.     

Design of a Compact Millimeter-Wave Microstrip Antenna with Wide Bandwidth and Broad Beamwidth

Design of a novel compact millimeter-wave microstrip antenna with wide bandwidth and broad beamwidth is presented. In the structure, multiple layers and a parasitic element as well as a coupling aperture are used to achieve wideband, while a conducting cylinder and the coupling aperture are used to obtain broad beamwidth. Finally, phased array with eight present elements has been designed as an example. Compared to traditional microstrip antennas and arrays, present antenna and array are of smaller dimension and broader beamwidth as well as wider bandwidth.     

Structure and dynamics of graphite-supported bimetallic nanoclusters

Molecular dynamics simulations are used to analyze the structure and dynamics of isolated bimetallic nanoclusters of 343 (Cu-Ni) and 1000 atoms (Cu-Ni and Pt-Au) deposited on a graphite substrate. The metal-metal interactions are modeled with the many-body Sutton-Chen potential, and a Lennard-Jones potential is used to describe the metal-carbon interactions. The nanocluster melting temperature is determined from caloric and heat capacity curves, and the atomic distribution is studied layer-by-layer as a function of temperature in a direction perpendicular to the substrate plane. Changes in the nanocluster shape as temperature increases are monitored through deformation parameters that show clear evidence of structural and melting transitions as well as of atomic surface diffusion in the cluster. Dynamic properties such as atomic and whole-cluster diffusion, and the motion of the metal atoms at the interface metal/graphite are characterized as a function of temperature.     

Plasma synthesis and liquid-phase surface passivation of brightly luminescent Si nanocrystals

While silicon's optical properties are improved at the nanoscale, they also become highly sensitive to the properties of the surfaces and interfaces of silicon nanostructures. For instance, while reported quantum yields for photoluminescence of silicon quantum dots covered by a native oxide are often in the few percent range, quantum yields as high as 30% have been found in quantum dots whose surfaces were passivated by covalently bonded organic molecules. In this paper, we describe an approach that is based on the gas phase synthesis of silicon quantum dots in a nonthermal plasma, and the subsequent organic surface passivation in the liquid phase. Nanocrystals are formed within a few milliseconds with a high mass yield in a nonthermal plasma. Various organic ligands such as octadecene, dodecence, and styrene are grafted onto the nanocrystal surfaces in a reaction known as hydrosilylation. Materials are characterized through transmission electron microscopy, atomic force microscopy, and fluorescence measurements. The particle size distributions are found to be relatively monodisperse and are well controllable through the plasma process parameters. Photoluminescence quantum yields as high as 60-70% have been achieved for particles luminescing in the red range of the visible spectrum.     

Microscopic particle-vibrator model: A new fermion-boson expansion

The elements for a microscopic foundation of the particle-vibrator model are derived in the form of a new fermion-boson expansion in which valence particles or holes added to a closed shell are treated essentially as fermion degrees of freedom, while particle-hole excitations of the closed shell itself are treated as bosons. The Pauli principle is completely fulfilled without redundancy. The generalizations of both the non-unitary Dyson and the unitary Holstein-Primak off representations are given, as well as an equivalent intermediate unitary representation.     

Velocity measurements in jets with application to noise source modeling

This paper describes an experimental investigation of the statistical properties of turbulent velocity fluctuations in an axisymmetric jet. The focus is on those properties that are relevant to the prediction of noise. Measurements are performed using two single hot-wire anemometers as well as a two-component anemometer. Two-point cross correlations of the axial velocity fluctuations and of the fluctuations in the square of the axial velocity fluctuations are presented. Several reference locations in the jet are used including points on the jet lip and centerline. The scales of the turbulence and the convection velocity are determined, both in an overall sense as well as a function of frequency. The relationship between the second and fourth order correlations is developed and compared with the experimental data. The implications of the use of dimensional as well as non-dimensional correlations are considered. Finally, a comparison is made between the length scales deduced from the flow measurements and a RANS CFD calculation.     

High-resolution diode-laser spectroscopy of calcium

Saturated-absorption signals on the calcium 657 nm transition are observed by direct absorption using diode lasers and a high flux atomic-beam cell. Line-widths as narrow as 65 kHz are observed with a high signal-to-noise ratio. Prospects for using this system as a compact wavelength/frequency reference are considered.     

Characterisation of valves as sound sources: Structure-borne sound

Taps and other valves are major sound sources in piping systems and can cause unacceptable noise levels in buildings. The noise results from the fluid-, structure- and air-borne sound emission. At present the acoustic emission of water appliances is tested according to a European standard, the shortcomings of which are apparent as a result of a round robin test of different European laboratories. As a result, there are currently neither acceptable measurement methods for water appliances available nor input data for prediction models. This paper considers methods of characterizing water appliances as sources of structure-borne sound. The concepts of mobility and free velocity are employed for a source characterisation based on power. Taps are considered alone and also in combination with a basin, where again the mobility and free velocity are used. A reception plate method is assessed as an alternative. The two methods each provide an independent characterisation of a structure-borne sound source as a single value. The values are on a power basis and provide input data suitable for prediction of the installed structure-borne power and thence the resultant sound pressure in adjacent rooms. Measured and predicted values of sound pressure level, caused by a wash-basin installed in an adjacent room, are compared.     

Discrete, Amorphous Physical Models

Discrete models of physical phenomena are an attractive alternative to continuous models such as partial differential equations. In discrete models, such as cellular automata, space is treated as having finitely many locations per unit volume, and physical processes are modelled by rules that depend on a small number of nearby locations. Such models depend critically on a regular (crystalline) lattice, as well as the global synchronization of all sites. We should ask, on the grounds of minimalism, whether the global synchronization and crystalline lattice are inherent in any discrete formulation. Is it possible to do without these conditions and still have a useful physical model? Or are they somehow fundamental? We will answer this question by presenting a class of models that are “extremely local” in the sense that the update rule does not depend on synchronization with the other sites, or on knowledge of the lattice geometry. All interactions involve only a single pair of sites. The models have the further advantage that they exactly conserved the analog of quantities such as momentum and energy which are conserved in physics. An example model of waves is given, and evidence is given that it agrees well qualitatively and quantitatively with continuous differential equations.     

Models of the Classical Electron after a Century

The point charge and the extended charge as models of the classical electron are studied. The problems inherent to each model with respect to self-interaction are disclosed and the possible solutions are analysed. The possible relation between these models is also discussed. We argue that a totally electromagnetic electron, as well as a point electron, is beyond the scope of classical electrodynamics. This work is intended as a complement to F. Rohrlich's recent account in the sense that it points at challenges still present in the way to a deeper understanding of the electron.     

Group analysis of masses and spins in curved space-time: Cosmological and experimental consequences

Recent developments in spontaneously broken gauge theories as well as in group analysis of masses and spins in curved space-time indicate that rest masses may change as a function of cosmic time. Such as effect is incompatible with standard cosmological models. A set of cosmological models that incorporate mass variation is introduced. These cosmological models are shown to be fully compatible with the group analysis, yielding exactly the same formula; they are used therefore as a theoretical testing ground for the hypothesis of mass variation. The following consequences of this hypothesis are obtained: (1) Cosmological red-shifts are shown to correspond to a contracting, rather than expanding, universe. (2) The effects of mass variation on planetary orbits are calculated; they are not precluded by the data. Conclusive experimental evidence is expected within a few years.     

Characterization of soft ferromagnetic materials by inductance spectroscopy and magnetoimpedance

Inductance spectroscopy and magnetoimpedance are extremely sensitive to a wide variety of intrinsic and extrinsic magnetic properties of soft magnetic materials; as a result, they can be used as a characterization tool. In this paper, the basic principles underpinning these magnetic phenomena are briefly discussed. The use of equivalent circuits is presented, as well as the correlations between the elements of such circuits and the relevant physical parameters of materials. Some specific cases are discussed.     

Moiré alignment and positioning using a synthetic Fresnel zone plate

A new method for optical alignment and positioning is proposed. The actual position and shape of a spherical wavefront emerging from an optical system to be aligned are interferometrically encoded as “live” fringes similar to a Fresnel zone plate (FZP). Any in-plane misalignment and inaccurate positioning are detected in real-time as a unique moiré pattern by overlapping the “live” fringes and a synthetic interferometric FZP which is regarded as a reference grating. Experimental data are presented and future applications are suggested.     

Double-exposed Gabor holograms: a new approach to storage of information

The interface patterns obtained using doubly-exposed Gabor holograms of rough objects undergoing small axial displacement are investigated by treating the resulting speckle patterns as a system such as an array of slits. The reconstructed images, which are related to each other as separate identical diffusers that are correlated, give rise to an interference phenomenon in their Fourier plane. The resultant intensity is modulated by a ring system, the geometrical characteristics of which are dependent on the geometry of the arrangement. New formulae are obtained and their validity is substantiated by experiments.     

Decay vertex reconstruction and 3-dimensional lifetime determination at BESⅢ

This paper focuses mainly on the vertex reconstruction of resonance particles with a relatively long lifetime such as KSO, A, as well as on lifetime measurements using a 3-dimensional fit. The kinematic constraints between the production and decay vertices and the decay vertex fitting algorithm based on the least squares method are both presented. Reconstruction efficiencies including experimental resolutions are discussed. The results and systematic errors are calculated based on a Monte Carlo simulation.     

Ultrasound fields in attenuating media

For medical ultrasonic imaging and for nondestructive testing, the attenuation of pressure waves and the resulting shift in wave velocity are important features in commonly used transmission media such as biological tissue. An algorithm for the numerical evaluation of pressure field distributions generated by ultrasonic transducers is presented. The attenuation and dispersion of the sound transmission medium are taken into consideration. The sound fields are computed numerically for continuous wave as well as pulse excitation. The transducer has plane or gently curved geometry and is embedded in a plane rigid baffle. The numerically determined pressure fields are presented as 3D plots, as gray-scale images for a fixed time stamp (like a snapshot), or as isobars regarding the maximum values over time for each local point in the area under investigation. The algorithm described here can be utilized as a tool for design of ultrasound transducers, especially array antennas.