RECONSTRUCTIONS OF PHASE SPECTRUM AND TRANSIENT RESPONSES OF SPHERICAL PIEZOELECTRIC TRANSDUCER

In this paper,a simple method deriving the transfer function of a spherical piezoelectric transducerhas been given.Transient responses have been obtained from the analytical expression of transferfunction by using FFT.Calculated results show that the impulse response of the spherical piezoelectrictransducer also exhibits the minimum phase behaviour and so the phase spectrum of its transfer func-tion can be reconstructed from the amplitude spectrum by using the Hilbert transform,the reconstruct-ed phase spectrum is in good agreement with that calculated from the analytical expression of transferfunction directly. Based on above-mentioned results,the phase spectrum of transfer function of a F42-c spherical pic-zoelectric transducer has been reconstructed from the measured values of its amplitude spectrum for thefirst time.The reconstructed phase spectrum is basically consistent with the measured values of phasespectrum. In addition,the impulse response and step response of F42-c spherical piezoelectric tra     

ECHO STRUCTURE OF SOUND SCATTERING BY A FINITE ELASTIC CYLINDER IN WATER

In this paper the echo structure of short pulse from finite solid elastic circular cylinder is investigated.Itis emphasized that in the case of oblique incidence the echoes still include two kinds of scattering wave:(1).Geometrical scattering waves,namely corner waves.(2).Elastic scattering waves,i.e.waves related with theelasticity of cylinder.The geometrical scattering waves are the waves reflected form the discontinuities ofcylinder,and essentially independent of the material of cylind.Using Kirchhoff approximation therepresentation of corner waves from rigid cylinder has been derived.In the case of oblique incidence theelastic scattering waves differ from the circumferential waves for an infinite cylinder.Two sorts of echoescaused by the reradiation of elastic surface wave have been obeerved in experiments;the radial surfacebackscattering wave and the longitudinal surface backscattering wave,They can be identified according to the arriving time and appearing angle,and the results of a comparable obse     

SCATTERING OF A GRAZING LONGITUDINAL WAVE PULSE BY A RIBBON-TYPE CRACK—EXPERIMENTAL VERIFICATION BY THE PHOTOELASTIC METHOD

By using the dynamic photoelastic method and our technique of fabricating an internal crack in solid,the scattered waves of incident grazing longitudinal ultrasonic wave pulse by a ribbon-type crack are ob-served and analyzed.In particular,the distribution of the intensity of the scattered head wave is measuredquantitatively.The experimental results fairly agree with the theoretical ones given in ref.[1].     

SCATTERING OF BG WAVE BY A GROOVE ON THE SURFACE OF A 6 mm CRYSTAL

With the aid of the surface perturbation technique,the problem of the scattering of the BG wave bya groove on the surface of a 6mm crystal is converted into a generalized Lamb problem:not only anequivalent mechanical source distribution,but also an equivalent electrical source distribution exist onthe crystal surface. The analytical solution and some characteristics of the feflected surface Wave and the scatteredbulk wave are obtained for both metallized and free surfaces. From the results it can be seen that for materials with strong electromechanical coupling and highpermittivity,e.g.the PZT piezoelectric ceramics,the reflection coefficient is very large for the metal-lized surface and very small for the free one.     

REFLECTION OF SOUND PULSE BY PLANE INTERFACE BETWEEN AIR AND POROUS MEDIUM

This paper presents a theoretical analysis of the reflection of a sound pulse by the plane interfacebetween air and ideal porous medium.A general expression of impulse response for a pulsed pointsource is derived.The detailed analysis is presented for three special cases:1)source and receiverlocated on a line perpendicular to the interface,semi-infinite media;2)a layer of porous medium;3)semi-infinite media,grazing incidence.In the second case,the problem is solved by consideringthe multi-reflections in the layer of porous medium.Experimental results are compared with the-oretical calculations for a kind of porous material.     

ELASTIC SCATTERING OF K± MESONS BY 40—48Ca AND THE ANALYSIS OF NEUTRON DISTRIBUTIONS

The differential cross sections of the elastic scattering of K^±on ^40—48Ca are calculated in the framework of eikonal approximation. The theoretical values obtained by using different parameters are compared. Through adjusting the parameters of the neutron distribution, the improvement of the coincidence between the theoretical values and the experimental data is arrived. The result shows that the r.m.s radius of the neutron distribution of ⁴⁰Ca is smaller than that of the proton. (about 0.15fm smaller) and the surface thickness of the neutron distribution of ⁴⁰Ca is thinner than that of proton. This is consistent with the results of computation made by H.F. method and agrees with the analysis of elastic scaatering of protons in the mediate energy on ⁴⁰Ca by other authors.     

APPLICATION OF CORRELATION—POLARIZA TION POTENTIAL TO THE LOW—ENERGY ELECTRON SCATTERING WITH ATOMS AND MOLECULES

Applicability of the correlation potential,which is currently used in the local density functional theory,to the low-energy electron-atom and molecule scattering is investigated with some examples of scattering processes.     

INVESTIGATION ON THE VALEN CE STATE OF Ce ATOM IN BULK AND nANOCRYSTAL CeO2 BY X—RAY ABSORPTION AND PHOTOEMISSION

Valence band photoemission spectra(PES) for both bulk and nanocrystal CeO2 have been masured on and off resonance of Ce 4d-4f absorption edge.The PES show that the bulk and nanocrystal CeO2 of diameter ranging from 8nm to 50nm exhibit a peak near Fermi edge with binding energy of abiyt 1.8eV peak shows a strong dependence on excitation energy,although it looks like the contribution of Ce^3 ion following the data reported in literatures.However,According to the results of resonance photoemission and X-ray absorption spectra at O 1s edge,this electronic structure may be associated to the intermediate state charge transfer effcets.     

A STUDY OF RAMAN SCATTERING AND INFRARED ABSORPTION SPECTRUM IN A NEW SERIES OF MERCURY-BASED HIGH-Tc SUPERCONDUCTOR (Hg,Mo)Sr2(Y1-xCax)Cu2O6+δ

Lattice vibrations of the (Hg,Mo)Sr₂(Y_1-xCa_x)Cu₂O_6+δ—a new series of mercury-based high-T_c superconductor are analyzed with the aid ofgroup theory. The vibrations of species are given. They are 4A_1g+ B_1g+ 5E_g+ 7A_2u + B_2u+ 8E_u. The 4A_1g, B_1g and 5E_g modes are Ramma active, the 6A_2u and 7E_u are infrared active. Phonon vibration characteristics of the samples are studied using Raman scattering and infrared absorption spectra. The experimental results show that the typical phonon vibrational modes appear mainly at 145, 320, 440, 578, 592 and 645cm^-1, The intensities of the 145, 320, 440, 578 and 645 peaks decrease with increasing Ca content x and the position of 645 peak moves to higher wavenumber slightly. In this article, the phonan modes are assigned and their variation behavior with increasing Ca content x are discussed.     

STATICAL SPHEROSYMMETRICAL SOURCELESS SOLUTION OF SU(2) GAUGE FIELD——THE SELFDUALITY,UNIQUENESS AND THE SELF INDUCED CHARGE CURRENT

It is shown that the statical spherosymmetrical sourceless solutions of SU(2) guagefield,which satisfy a physical boundary condition,must be selfdual.Then from theselfdual condition,we solve the equation explicitily,hence show the uniqueness analy-tically.By gauge transforming the Lagrangian by a local generator of synchrono-symmetry,we get a corresponding local charge current density,which is both gaugeinvariant and conserved.The total values of either electric or magnetic charge arequantized,but the charge distributions in space are continuous and not restrictedby quantization.Finally we discuss a mechanism of spontaneous symmetry break-down.Contrary to ordinary magnetic flux string,now the ordered phase is surround-ed by the normal phase,the ordered phase repels electric fields,and electric fieldsdestory the ordered phase.