Frequency Dependences of Sound Attenuation and Phase Velocity in Suspensions Containing Encapsulated Microbubbles

Frequency dependences of the sound attenuation and phase velocity in an encapsulated bubbly liquid, such as ultrasound contrast agent or Levovist suspensions, at three different concentrations are studied over a bandwidth 1.5-4.5MHz by using an ultrasonic spectroscopy technique. Measurement of acoustic attenuation spectra demonstrates that the resonant frequency of the Levovist suspension is nearly 2.3-2.5MHz, and the sound attenuation enhances with the increasing concentration. With the measured sound attenuation spectra, the shear modulus and the shear viscosity are estimated to be 80 Mpa and 1.3 Pa s, respectively. The phase velocity exhibits a rapid rise with frequency smaller than 3.0 MHz, then appears to approach a frequency-independent limit above 3.0 MHz, and the change of the phase velocity over the measured frequency range is also proportional to the concentration.     

ULTRASONIC ATTENUATION AND VELOCITY IN FRESH PIG SOFT TISSUES IN VITRO

Ultrasonic attenuation and velocity were measured for six fresh pig tissues:blood vessel,brain,heart,liver,spleen and kidney by using the pulse insertion method. Frequency dependence of attenuation has been found to be nearly linear,with the power rangingfrom 0.96 to 1.39 over the 1—13 MHz at 37℃. Velocity dispersion has been observed for all of the six tissues and the average value was 0.11—O.38 m/s.MHz for frequency range from 5 to 13 MHz at 37℃. Temperature effect over the 7—37℃ range for brain was also studied.Velocity at 1 MHz wasfound to be of positive temperature coefficient with average value 1.3m/s·℃and attenuation at 1,3,5MHz decreased with increasing temperature. Velocity for six tissues studied was an approximately linear function of their whole protein content.Every unit protein percentage concentration raises velocity by about 2.9m/s at 5 MHz and 37℃.     

Ultrasonic attenuation investigation of liquid hydrogen

Ultrasonic attenuation in liquid hydrogen has been messured withthe pulse-echo technique as a function of temperature from 13.84K to 20.50K,at 45MHz.The results indicate that the temperature dependence ofultrasonic attenuation in liquid hydrogen is mainly determined by volumeviscosity effect.Ultrasonic attenuatin due to volume viscosity is gettingmore and more with cooling.The ratio between volume viscous coefficientand shear viscous coefficient is from 1.4 to 4.2 within the measured tempera-ture region.     

The nonlinear propagation of acoustic waves in a viscoelastic medium containing cylindrical micropores

Based on an equivalent medium approach,this paper presents a model describing the nonlinear propagation of acoustic waves in a viscoelastic medium containing cylindrical micropores.The influences of pores’ nonlinear oscillations on sound attenuation,sound dispersion and an equivalent acoustic nonlinearity parameter are discussed.The calculated results show that the attenuation increases with an increasing volume fraction of micropores.The peak of sound velocity and attenuation occurs at the resonant frequency of the micropores while the peak of the equivalent acoustic nonlinearity parameter occurs at the half of the resonant frequency of the micropores.Furthermore,multiple scattering has been taken into account,which leads to a modification to the effective wave number in the equivalent medium approach.We find that these linear and nonlinear acoustic parameters need to be corrected when the volume fraction of micropores is larger than 0.1%.     

ACOUSTICAL METHOD FOR CLASSIFICATION OF SEAFLOOR SEDIMENTS

This paper discusses the classification of seabed sediments using normally incident,high frequecysound pulse.A number of investigators used the reflectivity of sound on the sea bottom and some otherquantities as features for classifying the sediment types.We suggest a new feature which is independentof the reflectivity and roughness of the seabed.Our feature is extracted from relative form of echoenvelope,and is closely correlated to the attenuation of sound in sediments.The attenuation in differ-ent sediments varies in the range of about tenfold,and can be a good feature for classification.Weused a high frequency signal of 120 KHz to get greater difference in attenuation of different sediments.In order to avoid the influence of seabottom roughness,we use a directional transducer and put it nearto the bottom.In the laboratory,a Bayes classifier is implemented by computer,and a fairly highsuccess rate is achieved.     

Mobile Rayleigh Doppler wind lidar based on double-edge technique

<正>We describe a mobile molecular Doppler wind lidar(DWL) based on double-edge technique for wind measurement of altitudes ranging from 10 to 40 km.A triple Fabry-Perot etalon is employed as a frequency discriminator to determine the Doppler shift proportional to the wind velocity.The lidar operates at 355 nm with a 45-cm-aperture telescope and a matching azimuth-over-elevation scanner that provides full hemispherical pointing.To guarantee wind accuracy,a single servo loop is used to monitor the outgoing laser frequency to remove inaccuracies due to the frequency drift of the laser or the etalon.The standard deviation of the outgoing laser frequency drift is 6.18 MHz and the corresponding velocity error is 1.11 m/s.The wind profiles measured by the DWL are in good agreement with the results of the wind profile radar(WPR).Evaluation is achieved by comparing at altitudes from 2 to 8 km.The relative error of horizontal wind speed is from 0.8 to 1.8 m/s in the compared ranges.The wind accuracy is less than 6 m/s at 40 km and 3 m/s at 10 km.     

A Direct Comparison between Static and Dynamic Melting Temperature Determinations below 100 GPa

A preliminary experiment of sound velocity measurements for porous iron with initial average density of 6.275 g/cm^3 has been performed at pressures below 100 CPa, in order to clarify a long-standing problem that the static melting temperature Tin, mostly below 100CPa due to its technical limitations, is notably lower than the extrapolated melting data inferred from the shock wave experiments made above 200 CPa, for the sake of making a direct comparison between the experimental static and dynamic melting temperatures in the same pressure region. With the lately proposed Hugoniot sound velocity data analysis technique [Chin. Phys. Left. 22 (2005) 863], the results deduced from this Hugoniot sound velocity measurement is Tm = 3200 K at 87 CPa and Tm = 3080 K at 80 GPa, which are in good agreement with the two latest static data of Tm = 3510 K at 105 GPa and Tm = 2750 K at 58 GPa, which utilized modern improved double-side laser heating and in situ accurate x-ray diffraction techniques in experiments. It can be concluded that consensus Tm data would be obtained from static and shock wave experiments in the case that the recently improved techniques are adopted in investigations.     

Carrier Dynamics Determined by Carrier-Phonon Coupling in InGaN/GaN Multiple Quantum Well Blue Light Emitting Diodes

Phonon sidebands in the electrolumiescence(EL) spectra of InGaN/GaN multiple quantum well blue light emitting diodes are investigated. S-shaped injection current dependence of the energy spacing(ES) between the zero-phonon and first-order phonon-assisted luminescence lines is observed in a temperature range of 100–150 K.The S-shape is suppressed with increasing temperature from 100 to 150 K, and vanishes at temperature above200 K. The S-shaped injection dependence of ES at low temperatures could be explained by the three stages of carrier dynamics related to localization states:(i) carrier relaxation from shallow into deep localization states,(ii) band filling of shallow and deep localization states, and(iii) carrier overflow from deep to shallow localization states and to higher energy states. The three stages show strong temperature dependence. It is proposed that the fast change of the carrier lifetime with temperature is responsible for the suppression of S-shaped feature.The proposed mechanisms reveal carrier recombination dynamics in the EL of InGaN/GaN MQWs at various injection current densities and temperatures.     

Hopping Conductivity in a Single-Walled Carbon Nanotube Network

We investigate the resistance and magnetoresistance （MR） of an entangled single-walled carbon nanotube （SWNT） network. The temperature dependence of conductance is fitted by formula G（T） = Go exp[-（To/T）^1/2] with To = 15.8 K at a wide temperature range from 4 K to 300K. The MR defined by [R（T, H） - R（T, 0）]/ R（T, 0） as a function of temperature and magnetic field perpendicular to the tube axis is negative at low temperatures. The MR amplitude increases as the temperature decreases at relative high temperature, but becomes decrease when temperature below 4 K. The results are explained in terms of the coherent hopping of carriers in the presence of a Coulomb gap at low temperature.     

Concrete damage diagnosed by using non-classical nonlinear acoustic method

<正>It is known that the strength of concrete is seriously affected by damage and cracking.In this paper,six concrete samples under different damage levels are studied.The experimental results show a linear dependence of the resonance frequency shift on strain amplitude at the fundamental frequency,and approximate quadratic dependence of the amplitudes of the second and third harmonics on strain amplitude at the fundamental frequency as well.In addition,the amplitude of the third harmonics is shown to increase with the increase of damage level,which is even higher than that of the second harmonics in samples with higher damage levels.These are three properties of non-classical nonlinear acoustics.The nonlinear parameters increase from 10~6 to 10~8 with damage level,and are more sensitive to the damage level of the concrete than the linear parameters obtained by using traditional acoustics methods.So,this method based on non-classical nonlinear acoustics may provide a better means of non-destructive testing(NDT) of concrete and other porous materials.