A Novel Approach to Correct Diffraction Effect in Measurment of ultrasonic Velocity and Attenuation at High Frequencies

A novel method to correct diffraction effect in measurement of ultrasonic velocity and attenuation at high frequencies is developed by using the superposition technique of Gaussian beams.To examine the validity of this numerical approach,the amplitude loss and phase advance due to the diffraction effect for an SiO2 specimen are numerically calculated in 30-240MHz,and the results are in good agreement with those by the Papadakis method.     

The parametric source method for measuring characteristics of underwater acoustic materials in a pressure vessel

A truncated broadband parametric array with a primary frequency of 500 kHz and difference frequency range of 1 kHz to 30 kHz was designed as a sound source of the underwater acoustic material measurement system.By analyzing the theoretical calculation and actual measurement results in array directivity of the truncated broadband parametric source at typical frequencies,we observed that the curves of the two results were basically consistent,which proved that the calculation model was correct.Application of bell-shaped short-duration pulse to achieve broadband measurement for characteristics of underwater acoustic materials was beneficial to reduce the effects of diffraction from the panel edges.The measurement system was established for measuring the sound pressure reflection coefficients,sound pressure transmission coefficients and absorption coefficients of the large panel sample in the pressure vessel.The size of this tank is φ4 m×12 m,the maximum hydrostatic pressure is 4.5 MPa,and the corresponding measuring frequency range is from 1 kHz to 30 kHz.The measured curves had a good agreement with theoretical curves,which verified that the parametric source measurement method was feasible.Then,the sound absorption properties of the rubber plate sample were measured under different hydrostatic pressures.The studying results could show that the parametric source measurement method had the potential application in the limited space water,such as the pressure vessel.     

Synthesis and magnetic properties of carbon-coated Ni/SiO_2 core/shell nanocomposites

A simple method for the synthesis of carbon-coated Ni/SiO2 core/shell nanocomposites is reported. The Ni nanoparticles were coated with silica layers via a combined procedure of sol-gel fabrication and hydrogen reduction prior to carbon coating via acetylene decomposition at an appropriate temperature. It was found that the anti-acid ability of the Ni/SiO2 composites was greatly enhanced after carbon coating. The results of magnetization measurement show that the real part (μ′) of complex permeability of the as-obtained sample is almost independent of frequency, and the imaginary part (μ″) stays small up to a frequency of 1 GHz. The encapsulation of Ni particles with SiO2 results in the rise of Ni nanoparticles resistivity. The outcome is the reduction in effect of eddy current at high frequency, making the real part μ′ almost constant and the imaginary part μ″ very small. Thus, this simple method may be effective for preparing composites of soft magnetic properties, especially in the high-frequency range.     

A STUDY ON THE ACOUSTIC NONLINEAR PARAMETER IN BIOLOGICAL MEDIA WITH HIGR ATTENUATION

Using the comparative method with the corrections of the diffraction and attenuation,we measured thenonlinear parameter B/A of several biological media with high attenuation.The acoustic nonlinear parameterB/A of biological media such as heart,liver,spleen,kidney,and muscle is about 7,that of bile and urine about6,and about 9.6 for fat.The nonlinear parameter of the fat is more than others mainly due to high lipid contentin it.Ichida‘s result about the fat is discussed.     

PULSE ECHO OVERLAP METHOD USING ELECTROSTATIC TRANSDUCERS

The pulse echo overlap method using electrostaic transducers for accurate measurement ofultrasonic velocity in solid media is discussed in this paper.Owing to the advantage of non-contactfor electrostatic transducers,the correction for coupling layer can be eliminated and the correct cyclicoverlap can be easily achieved,thus the performance of the echo measuring system is significanitlyimproved.In this paper the diffraction correction is calculated for the echo measuring system usingelectrostatic transducers,and an ultrasonic velocity measuring instrument and its transducers arealso described.The measuring results for several specimens of glass and aluminium show that themeasuring accuracy of transmission time in this system reaches 1/500 of RF period,that means themeasnring accuracy reaches 0.2 ns at 10 MHz.     

Nonlinear effect of the structured light profilometry in the phase-shifting method and error correction

Digital structured light （SL） profilometry is increasingly used in three-dimensional （3D） measurement technology. However, the nonlinearity of the off-the-shelf projectors and cameras seriously reduces the measurement accuracy. In this paper, first, we review the nonlinear effects of the projector-camera system in the phase-shifting structured light depth measurement method. We show that high order harmonic wave components lead to phase error in the phase-shifting method. Then a practical method based on frequency domain filtering is proposed for nonlinear error reduction. By using this method, the nonlinear calibration of the SL system is not required. Moreover, both the nonlinear effects of the projector and the camera can be effectively reduced. The simulations and experiments have verified our nonlinear correction method.     

Improving the precision of fluorescence lifetime measurement using a streak camera

Streak camera has high temporal resolution and high sensitivity, and is a powerful tool in biomedical study to measure fluorescence lifetime and perform fluorescence lifetime imaging. However, nonuniformity of the gain in the streak tube and nonlinearity of the sweeping speed limit the precision of fluorescence lifetime measurement, particularly when fluorescence lifetimes are short. We have constructed a two-photon excitation fluorescence lifetime measurement system that is based on a synchroscan streak camera and have developed accordingly a method to correct the effect of gain nonuniformity and nonlinearity of sweeping speed on the measurement precision. A continuous-wave laser of high stability is used to calibrate the gain of the streak camera, and a Fabry-Perot etalon is used to calibrate the nonlinearity of the sweeping speed. Fitting algorithms are used to correct the gain of the streak camera and nonlinearity of the sweeping speed respectively, which significantly improves the measurement precision of the system, as characterized through the fluorescence lifetime of the short-lived fluorescence dye, Rose Bengal. Experimental results show that the measurement fluctuation of the lifetime has been improved from more than 10% to 2% after correcting the effects of gain nonuniformity and sweeping speed nonlinearity.     

Theory of Z-scan technique using Gaussian-Bessel beams with a phase object

This paper reports the theoretical study of combining Z-scan technique with Gauss-Bessel (GB) beams beside a phase object (PO) to measure the third-order nonlinear susceptibility components.By using this method,the sign of refractive index which depends on the shape of the close aperture Z-scan curve can be easily determined.Meanwhile,the magnitude of nonlinear coefficients can also be deduced by theoretical fit.The proposed method is advantageous for high sensitivity and imposes a lower stress in the cases of fragile materials,since small pulse energy is enough for the measurement of nonlinear coefficients.Predictions of the models are compared with Gaussian Z-scan measurement and GB Z-scan measurement.By using GB beams with a PO,the sensitivity of Z-scan measurements is found to be a factor of over 60 times greater than for Gaussian beams and 2 times greater than for Gaussian-Bessel beams.     

Evaluation of threading dislocation density of strained Ge epitaxial layer by high resolution x-ray diffraction

The analysis of threading dislocation density(TDD)in Ge-on-Si layer is critical for developing lasers,light emitting diodes(LEDs),photodetectors(PDs),modulators,waveguides,metal oxide semiconductor field effect transistors(MOS-FETs),and also the integration of Si-based monolithic photonics.The TDD of Ge epitaxial layer is analyzed by etching or transmission electron microscope(TEM).However,high-resolution x-ray diffraction(HR-XRD)rocking curve provides an optional method to analyze the TDD in Ge layer.The theory model of TDD measurement from rocking curves was first used in zinc-blende semiconductors.In this paper,this method is extended to the case of strained Ge-on-Si layers.The HR-XRD 2θ/ωscan is measured and Ge(004)single crystal rocking curve is utilized to calculate the TDD in strained Ge epitaxial layer.The rocking curve full width at half maximum(FWHM)broadening by incident beam divergence of the instrument,crystal size,and curvature of the crystal specimen is subtracted.The TDDs of samples A and B are calculated to be 1.41×10~8cm~(-2)and 6.47×10~8cm~(-2),respectively.In addition,we believe the TDDs calculated by this method to be the averaged dislocation density in the Ge epitaxial layer.     

A Super High Resolution Distance Measurement Method Based on Phase Comparison

Phase comparison method can enhance the measurement resolution to 10^-13/T in time domain. This method can also be used in distance measurement in the navigation and positioning. We propose a super high-resolution distance measurement based on linear phase comparison method. A high resolution scheme is put forward on the basis of the research of major factors concerning the phase comparison in the distance measurement. Conversion of a high-linearity phase difference to voltage and high-resolution voltage meter make it possible to obtain a very high phase measurement resolution. When the purpose is to measure distance, the phase noise of frequency source used in the measurement can be reduced partly. Thus this method is favourable for high resolution distance measurement. The precision of the distance measurement can reach 0.1c ps with c being the velocity of light in vacuum.     

Accurate measurement of ultrasonic velocity by eliminating the diffraction effect

The accurate measurement method of ultrasonic velocity by the pulse interference method with eliminating the diffraction effect has been investigated in VHF range experimen-tally. Two silicate glasses were taken as the specimens, their frequency dependences of longitu-dinal velocities were measured in the frequency range 50-350 MHz, and the phase advances of ultrasonic signals caused by diffraction effect were calculated using A. O. Williams‘ theoreticalexpression. For the frequency dependences of longitudinal velocities, the measurement resultswere in good agreement with the simulation ones in which the phase advances were included.It has been shown that the velocity error due to diffraction effect can be corrected very well bythis method.     

Characterization of tissue cells by full information from spectral interferogram

A new method for characterizing living tissue cells is demonstrated using both phase and amplitude information derived from the spectrally resolved interferogram in a single measurement.The effect of the light source spectral distribution can be cancelled out with the help of the zero order spectrum of the Fourier transform of the interferogram.The ratio of amplitudes between the two interference beams is acquired without this effect.The group delay,the first and second order dispersions,and the absorption,etc.,for the full wavelength range can be measured.The results of the culture medium and the HeLa living cells are given.In addition,the measured values of d2 n/dλ2 and absorption of the distilled water are also provided for comparison.     

DETERMINATION OF REFLECTION TIME DELAY AND CRITERION OF CORRECT OVERLAP IN ULTRASONIC WAVE VELOCITY MEASUREMENT WITH PEO METHOD

The Pulse-Echo-Overlap method(PEO method)has now been considered as the most adequatemethod for accurate measurement of the absolute value of ultrasonic velocity.For this accurate timemeasurement,it is essential to find the time delay and implement its corrections,e.g.the correction ofreflection time delay,the correction of diffraction time delay,etc.To overcome the inconvenience of thewidely used in practice method of reflection time delay calculation,and its imperfection in theory,a newcalculation procedure of the reflection time delay correction is worked out in this paper,and an experimentaldetermination method for its value by means of double crystal is suggested.This paper further suggests aparameter of the period increment of zero phase shift Δτ_r,and considers it as an experimental constant,whose value is about 1.7 ns in practical applications. Furthermore,this paper suggests a criterion of correct overlap.If the echoes are correctly overlapped,the slope of the curve of the ultrasonic wave tri     

Determination of human skin optical properties in vivo from reflectance spectroscopic measurements

A novel approach has been proved to quickly and non-invasively determine the optical properties of human skin in vivo. It is based on the diffuse reflectance approximation model and subjected to the well established library of absorption spectra of water and hemoglobin. Under the nonlinear least-square algorithm, fitting the measured spectra in the range of 400-1000 nm to the diffusion approximation model, the reduced scattering coefficient and absorption coefficient of skin tissue can be quickly determined in vivo. The results show that this method is convenient and suitable for the real-time clinical application.     

Dynamics of entanglement under decoherence in noninertial frames

In this paper,we investigate the entanglement dynamics of a two-qubit entangled state coupled with its noisy environment,and plan to utilize weak measurement and quantum reversal measurement to study the entanglement dynamics under different decoherence channels in noninertial frames.Through the calculations and analyses,it is shown that the weak measurement can prevent entanglement from coupling to the amplitude damping channel,while the system is under the phase damping and flip channels.This protection protocol cannot prevent entanglement but will accelerate the death of entanglement.In addition,if the system is in the noninertial reference frame,then the effect of weak measurement will be weakened for the amplitude damping channel.Nevertheless,for other decoherence channels,the Unruh effect does not affect the quantum weak measurement,the only exception is that the maximum value of entanglement is reduced to√2/2of the original value in the inertial frames.     

GROWTH TECHNIQUE OF MOLECULAR CRYSTAL OF NAPHTHALENE

A furnace for growing single crystal naphthalene of diameter 1-1.3cm and length up to15cm has been constructed by the Bridgman method in combination with zone-melting technique.The furnace is simple in its construction,convenient in its operation and convenient for the observa-tion of the crystal growth process.The effect of the shape of crystal growth container on crystalgrowth is discussed and the experiment in vapor growth of small naphthalene flakes is described.The preparation procedure of naphthalene samples for ultrasonic measurement,which may be alsouseful for preparation of other soft crystals,is given.     

A three-step system calibration procedure with error compensation for 3D shape measurement

System calibration, which usually involves complicated and time-consuming procedures, is crucial for any three-dimensional （3D） shape measurement system based on vision. A novel improved method is proposed for accurate calibration of such a measurement system. The system accuracy is improved with considering the nonlinear measurement error created by the difference between the system model and real measurement environment. We use Levenberg-Marquardt optimization algorithm to compensate the error and get a good result. The improved method has a 50% improvement of re-projection accuracy compared with our previous method. The measurement accuracy is maintained well within 1.5% of the overall measurement depth range.     

Application of Extended Projective Riccati Equation Method to （2＋1）-Dimensional Broer-Kaup-Kupershmidt System

In this paper, extended projective Riccati equation method is presented for constructing more new exact solutions of nonlinear differential equations in mathematical physics, which is direct and more powerful than projective Riccati equation method. In order to illustrate the effect of the method, Broer Kaup Kupershmidt system is employed and Jacobi doubly periodic solutions are obtained. This algorithm can also be applied to other nonlinear differential equations.     

PARAMETRIC EFFECT AND NONLINEARITY PARAMETER IN BIOLOGICAL FLUIDS

Based on the Fenlon‘s theory the parametric effects in fluids due to the nonlinear interaction of a lowfrequency pumping wave and a high frequency probing wave are analysed.The expressions of pressureamplitude of sum or difference frequency sideband and the fromula of nonlinearity parameter B/A forlossy medium are derived.Theoretical calculation demonstrated,that the sideband componentsincrease linearly with pump signal.Therefore,a method for determination of B/A is provided and the val-ues for several biological fluids and mixtures are measured.     

Experimental Study of Capillary Effect in Porous Silicon Using Micro-Raman Spectroscopy and X-Ray Diffraction

We investigate the capillary effect and the residual stress evolution in the wetting, drying and rewetting stages of porous silicon using x-ray diffraction and micro-Raman spectroscopy. A reversible capillary effect and an irreversible oxidation effect are the driving forces for the residual stress evolution. The lattice expansion of the porous-silicon layer is observed to decrease slightly by x-ray diffraction and the tensile residual stress increases rapidly by micro-Raman spectroscopy, with the change of about 82 MPa for the oxidation effect and the change of 2.78 GPa (enough for cracking) for the capillary effect. Therefore, the capillary effect plays a major role in the residual stress evolution in the stages. A simple microscopic liquid-bridge model is introduced to explain the capillary effect and its reversibility. The capillary emergence has a close relation with a great deal of the micro-pore structure of porous silicon.