THE ACOUSTOELECTRIC EFFECT IN α-LiIO_3 CRYSTAL

In α-LiIO_3 crystal,the attenuation coefficient of longitudinal wave is increased by the action of anelectrostatic field,if the direction of wave propagating and the field are along the same c-axis of the crystal.The change of the attenuation coefficient with time possesses a relaxation character.We believe that thisphenomenon may be caused by the interaction between the longitudinal wave and the unilaterally moving     

Attenuation characteristics of a light attenuator combined by polarizers with different extinction ratios

This paper deals with a systematical analysis and an algorithm of attenuation characteristics of a light attenuator combined by n pieces of polarizers (n-LACP) whose extinction ratios are different from each other.The attenuation ratio expression of a two-LACP is deduced.We find that the monotonic attenuation interval depends on the first polarizer and that the attenuation range depends on the second one.For the three-LACP,a method for obtaining a monotonic attenuation interval is proposed.Moreover,the attenuation ratio expression is demonstrated.Analysis and experiment show that when the initial status of the three-LACP is at the maximum output,if the second or third polarizer rotates alone,the minimum attenuation ratios can reach K-1 2 and K-1 3,respectively,and if the first polarizer rotates,a minimum attenuation ratio of K-1 2 K-1 3 can be obtained (K 1,K 2 and K 3 represent the extinction ratios of the three polarizers in turn).Furthermore,the attenuation ratio expression of n-LACP and the relevant attenuation characteristics are proposed.The minimum attenuation ratio of an n-LACP is (K 2 K 3 ··· K n)-1.     

Structure of the Semi—decoupled π 1／2[411] Band in Odd Proton Nucleus ^169Ta

High spin states of the odd proton-nucleus ^169Ta have been populated in the reaction ^155Gd(^19F,5n) with beam energies of 97MeV,Rotational band based on d3/2 proton 1/2[411]Nilsson state has been pushed up to 39/2^ in the α=1/2 decay sequence.Its signature partner,the α=-1/2 decay sequence with four link transitions has been established and 1/2[411] band in ^169Ta was reassigned to be a semi-decoupled band.The systematics of the signature splitting in the K=1/2 bands in the rear-earth region and the accidental degeneracy conclusion given by the angular projection shell model were discussed.     

Room-temperature epitaxial growth of V2O3 films

Herein we report the room-temperature epitaxial growth of V2O3 films by laser molecule beam epitaxy. X-ray diffraction profiles show the room-temperature epitaxial V2O3 films orient in the [110] direction on α-Al2O3(0001) substrates. Atomic force microscopy measurements reveal that the ultra-smooth surfaces with root-mean-square surface roughness of 0.11 nm and 0.28 nm for 10-nm-thick and 35-nm-thick V+2O3 film, respectively. X-ray photoelectron spectroscopy results indicate the V3 oxidation state in the films. Typical metal-insulator transition is observed in films at about 135 K. The resistivities at 300 K are approximately 0.8 mΩ cm and 0.5 mΩ cm for 10-nm-thick and 35-nm-thick V2O3 film, respectively.     

MEASUREMENTS OF ACOUSTIC ABSORPTION ATTENUATION FOR FREQUENCY RANGE OF 0.2-2 kHz IN SANDY SEDIMENTS OF YELLOW RIVER(HUANGHE)

The measurements of the sound attenuation in sandy sediment of Yellow River(Huanghe)have been made in situ by explosive sources.The attenuation coefficients are determined for thefreqency range of 0.2-2kHz.The experimental results show that the attenuation coefficient α(dB/m)increases approximately as the square of frequency for the frequency range of 0.2-2kHz.Theexperimental results is in agreement with the theoretical results.In addition the sound velocity,density,porosity and grain size distribution of the sediment are given in this paper.     

Predictions of pressure-induced structural transition, mechanical and thermodynamic properties of α-and β-Si3N4 ceramics: ab initio and quasi-harmonic Debye modeling

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4.The ground-state parameters accord quite well with the experimental data.Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K.The α→β phase transformation would not occur in a pressure range of 0-40 GPa and a temperature range of 0-300 K.Actually,the α→β transition occurs at 1600 K and 7.98 GPa.For α-and β-Si3N4,the c axes are slightly more incompressible than the a axes.We conclude that β-Si3N4 is a hard material and ductile in nature.On the other hand,β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0-10 GPa.Besides,the thermodynamic properties such as entropy,heat capacity,and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures.Significant features in these properties are observed at high temperature.The calculated results are in good agreement with available experimental data and previous theoretical values.Many fundamental solid-state properties are reported at high pressure and high temperature.Therefore,our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.     

Predictions of pressure-induced structural transition,mechanical and thermodynamic properties of α-and β-Si₃N₄ ceramics:ab initio and quasi-harmonic Debye modeling

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4.The ground-state parameters accord quite well with the experimental data.Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K.The α→β phase transformation would not occur in a pressure range of 0-40 GPa and a temperature range of 0-300 K.Actually,the α→β transition occurs at 1600 K and 7.98 GPa.For α-and β-Si3N4,the c axes are slightly more incompressible than the a axes.We conclude that β-Si3N4 is a hard material and ductile in nature.On the other hand,β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0-10 GPa.Besides,the thermodynamic properties such as entropy,heat capacity,and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures.Significant features in these properties are observed at high temperature.The calculated results are in good agreement with available experimental data and previous theoretical values.Many fundamental solid-state properties are reported at high pressure and high temperature.Therefore,our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.     

Biot／Squirt Model in Viscoelastic Porous Media

Viscoelastic wave equations are derived for both the Biot flow and squirt-flow involved.The relationship between phase velocity or attenuation of viscoelastic wave and macro parameters of the reservoir is clarified in a porous extensive dilatancy anisotropy medium.Numerical models clearly demonstrate that the viscoelastic property of rocks,not the squirt-flow,causes the dispersion and attenuation in the low-frequency range.The attenuation of the quasi SV-wave,SH-wave and the quasi P-wave depend strongly on the directions of permeabilities.Furthermore,the trends of attenuation of the quasi P-wave fast and the quasi SV-wave are inversed in both the high-frequency and low-frequency ranges.Our numerical result is in agreement with the experimental result that was carried out for the Biot/Squirt model by Jorge [Geophys.65(2000)202].     

Large and anisotropic linear magnetoresistance in bulk stoichiometric Cd3As2 crystals

Cd3As2 was recently identified as a novel three-dimensional(3D)topological semimetal hosting the long-pursuing 3D Dirac Fermion.Crystals of Cd3As2 grown preferentially along the[100]and[112]directions were obtained through the modified chemical vapor transfer growth method,thus allowing the examination of transport anisotropy.The resistivity and magnetoresistance(MR)are basically linear with respect to magnetic field(H)in the measured temperature range of 2–300 K irrespective of the directions.The linear resistivity and MR are significantly anisotropic not only along[100]and[112]directions but also with respect to tilt angle between the growth directions and H,thus providing transport signatures of the 3D Dirac Fermion as well as the possible linear and anisotropic change of Weyl Fermi surface in H.Very large MR along the[100]direction is observed,even approaching 3100%at 2 K and 14 k Oe(1 Oe=79.5775 A m-1).The results would be helpful in renewing interest in studying emergent phenomena arising from bulk 3D Dirac Fermion as well as in paving the way for Cd3As2 to be used in magnetoelectronic sensors.     

Calculation of the elastic scattering properties for cold and ultracold 39K atoms in a triplet state

The elastic scattering properties for collisions between cold and ultracold 39K atoms in a triplet state are investigated. Based on the recent theoretical and experimental results, the improved hybrid potential is presented for a triplet α3∑u^＋ ground state of K2. Our calculated value of the s-wave scattering length a by using the Numerov method for the triplet state is 79.578α0 and found to be in good agreement with the previous ones. The numbers of bound states are supported by the molecular potential. Pronounced shape resonances appear for the l = 3 partial waves for the α3∑u^＋ state. Furthermore, the s-wave scattering cross section, the total cross section and energy positions of shape resonances for the α3∑u^＋ state are calculated.     

mechanical and thermodynamic properties of α-and β-Si3N4 ceramics： ab initio and quasi-harmonic Debye modeling

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4. The ground-state parameters accord quite well with the experimental data. Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K. The α → β phase transformation would not occur in a pressure range of 0-40 （3Pa and a temperature range of 0 300 K. Actually, the α → β transition occurs at 1600 K and 7.98 GPa. For α-and β-Si3N4, the c axes are slightly more incompressible than the a axes. We conclude that β-Si3N4 is a hard material and ductile in nature. On the other hand, β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0 - 010 GPa. Besides, the thermodynamic properties such as entropy, heat capacity, and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures. Significant features in these properties are observed at high temperature. The calculated results are in good agreement with available experimental data and previous theoretical values. Many fundamental solid-state properties are reported at high pressure and high temperature. Therefore, our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.     

ULTRASONIC ATTENUATION OF SHEAR WAVES IN AMORPHOUS PdSiAg ALLOY

With the pulse-echo technique the ultrasonic attenuation of shear waves in amorphous PdSiAgalloy has been measured as a function of frequency and temperature.At room temperature an ap-proximate f-squared frequency dependence is obtained between 10 and 240 MHz.Below 150K,at fixed frequency there is a slow increase of attenuation with decreasing temperature and a smallultrasonic absorption peak at 35K.The linear dependence of the relative variation of the soundvelocity is observed from 35 to 300K;the temperature coefficient of sound velocity is—1.58×10~(-4)/K.Below 35K,the relative varation of the sound velocity begins to deviate from the linear dependence.     

Specific heat of the non-centrosymmetric superconductor Re3W

The alloys of non-centrosymmetric superconductor, Re 3 W, which were reported to have an α-Mn structure [P. Greenfield and P. A. Beck, J. Metals, N. Y. 8, 265 (1959)] with T c = 9 K, are prepared by arc melting. The values of ac susceptibility and the low-temperature specific heat of these alloys are measured. It is found that there are two superconducting phases coexisting in the samples with T c1 ≈ 9 K and T c2 ≈ 7 K, which are both non-centrosymmetric in structure as reported previously. By analysing the specific heat data measured in various magnetic fields down to a temperature of 1.8 K, we find that the absence of the inversion symmetry does not lead to an obvious deviation from an s-wave pairing symmetry in Re 3 W.     

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.     

Influences of Temperature on Proton Conductivity in the Hydrogen-Bond Molecular Systems with Damping

Influences of temperature of medium on proton conductivity in hydrogen-bonded systems exposed in an electricfield are numerically studied by the fourth-order Runge-Kutta method with our model. The results obtained show that the proton soliton is very robust against thermal perturbation and damping of medium, and is thermally stable in the temperature range T ≤ 273 K. From the simulation we find out that the mobility （or velocity） of proton conduction in ice crystal is a nonmonotonic function of temperature in the temperature range 170-273 K： i.e., it increases initially, reaches a maximum at about 191 K, subsequently decreases to a minimum at about 211 K, and then increases again. This changed rule of mobility is qualitatively consistent with its experimental data in ice in the same temperature range. This result provides an evidence for existence of solitons in the hydrogen-bonded systems.     

Dielectric evidence for possible type-Ⅱmultiferroicity in α-RuCl_3

正The Kitaev model in a honeycomb lattice,which has an exactly solvable spin liquid as the ground state[1],has attracted a lot of research interests.Recently,Kitaev-type interactions were discovered in several quasi-2D,honeycomb lattice compounds,such as A_2IrO_3(A=Li,Na)[2-7]and α-RuCl_3[8-15].In these compounds,both the spin-orbit coupling and electron correlations play an essential role in the emergent Mott insulator behaviors[2,16-19].Although the     

ATTENUATION AND GROUP VELOCITY OF NORMAL MODE IN AN ISO-VELOCITY SHALLOW WATER

Proceeding from the eigenvalue equation of the normal mode in homogeneous shallow water,wederive several formulae calculating the mode attenuation and group velocity,and compare their accu-racy by means of numerical results.The paper especially discusses the attenuation and the group ve-locity of critical mode in a Pekeris channel and shows that in general,the attenuation and the groupvelocity of the critical mode respectively are less than the absorption and the sound speed in the bot-tom.Therefore.the Kornhauser,Raney,Weston Tindle‘s conclusions are modified that theattenuation and the group velocity of the critical mode are exactly equal to the absorption and thesound speed in the bottom,respectively.     

Thermoluminescence and optically stimulated luminescence disadvantages of α-Al2O3:C crystal grown by the temperature gradient technique

Recently, α-Al₂O₃:C crystal with highly sensitive thermoluminescence (TL) and optically stimulated luminescence (OSL) has been successfully grown by the temperature gradient technique. This paper investigates the heating rate dependence of TL sensitivity, light-induced fading of TL signals and thermal stability of OSL of α-Al₂O₃:C crystals. As the heating rate increases, the integral TL response decreases and the dosimetric glow peak shifts to higher temperatures in α-Al₂O₃:C crystals. Light-induced fading of TL increases with the irradiation dose, and TL response decreases as the exposure time increases, especially in the first 15 minutes. With the increasing intensity of the exposure light, the TL fading of α-Al₂O₃:C crystal increases sharply. The OSL response of as-grown α-Al₂O₃:C crystal is quite stable below 373 K and decreases sharply for higher temperatures.     

Directional Plasmon Filtering in a Two-Dimensional Electron Gas Embedded in High-Index Crystallographic Planes

We study theoretically the plasmon excitations in a two-dimensional electron gas （2DEG） with spin-orbit interactions （SOIs） embedded in a （11n） crystallographic plane. We demonstrate that the energy spectra and dielectric functions between the 2DEGs embedded in different crystallographic planes can be related by a unitary transformation. Using the unitary transformation, we find that the anisotropy of plasmon excitations and the directional plasmon filtering （DPF） can be tuned by changing the strengths of SOIs in the high-index planes. There are two advantageous directions [110] and [nn2] for plasmon propagation. Moreover, the anisotropy and the DPF can be smeared out by tuning the strength ratio α/β between the Rashba SOI and the Dresselhaus SOI.     

Dendrite growth characteristics within liquid Fe-Sb alloy

Bulk samples and small droplets of liquid Fe-10%Sb alloys are undercooled up to 429 K (0.24TL) and 568 K (0.32TL), respectively, with glass fluxing and free fall techniques. The high undercooling does not change the phase constitution, and only the αFe solid solution is found in the rapidly solidified alloy. The experimental results show that when the undercooling is below 296 K, the growth velocity of αFe dendrite rises exponentially with the increase of undercooling and reaches a maximum value 1.38 m/s. S...