A trinocular vision system for close-range position sensing

A machine vision system for obtaining three-dimensional information from a single camera is presented. Stereo and orthogonal views of the test object are imaged onto a CCD (charge coupled device) camera by using a tri-split lens in conjunction with a mirror arrangement. The calibration procedure involves a direct linear transformation resulting in an overdetermined set of equations that are solved to obtain the three-dimensional coordinate position. The position information obtained from the stereo views is used to locate the object in the orthogonal view, thus improving the accuracy of the position sensor. The relative position of a cylinder-head from a reference point, which is of importance in assembly line applications, was measured using the vision system within an accuracy of 0.3% of full scale value.     

High-pressure Raman study of MgV2O6 synthesized at high pressure and high temperature

A new structural phase of MgV2O6 was obtained by a high-pressure,high-temperature(HPHT) synthesis method.The new phase was investigated by the Rietveld analysis of X-ray powder diffraction data,showing space group Pbcn(No.60) symmetry and a = 13.6113(6) (1 = 0.1 nm),b = 5.5809(1) ,c = 4.8566(3) ,V = 368.93(2) 3(Z = 4).High pressure behavior was studied by Raman spectroscopy at room temperature.Under 22.5 GPa,there was no sign of a structural phase transition in the spectra,demonstrating stability of the HPHT phase up to the highest pressure.     

Fiber optic sensing applications using the entangled states walk-off compensations

This paper presents a new concept of the measurement of the entangled photon states timing walk-off in fiber optic systems. The relationship between the applied physical parameter on fiber optic and timing walk-off compensation can be performed. When polarized light pulse propagates into a fiber optic length, a pair of the entangled photons introduces the change in phase difference, i.e. birefringence, which can be recovered and detected. The potential of use in applications such as quantum interferometer and fiber optic remote sensing is proposed and described. The increase in measurement resolution in terms of the entangled photon walk-off length is analyzed and discussed.     

高温高压下爆轰产物中不同种分子间的相互作用

给出了一种由特殊炸药的爆轰参数确定不同种分子间势函数参数的方法:由基于统计物理的爆轰产物物态方程程序类CHEQ,计算炸药RX-23-AB,HNB和PETN的爆轰参数,反推分子间的相互作用.给出了炸药主要爆轰产物H₂O,CO₂和N₂之间的非理想混合修正系数:K_N2-H2O=1.03,k_N2-CO2=1.035,k_H2O-CO2=0.96,将本文确定的不同种分子间势函数参数用于计算炸药PBX9404的超高压雨贡纽,获得了与实验一致的结果,验证了方法和参数的合理性.     

高温高压下爆轰产物分子间相互作用的研究

给出了一种由分子流体的冲击Hugoniot实验数据确定原分子之间和离解产物分子、原子相互间作用势参数的方法. 在较低压强下,采用Ross硬球微扰理论软球修正模型确定原分子之间的相互作用势参数;在较高压强下,采用基于统计物理的化学平衡方法来确定分子离解后的分子和原子之间的相互作用势参数. 与传统的由对应状态定律确定势函数参数的方法相比,所得到的势函数参数在很大的压强范围内都能较好地描述冲击实验. 关键词： 高温高压 化学平衡 冲击Hugoniot实验     

椭芯光纤干涉型多参量光纤传感技术

本文提出用椭圆纤芯高双折射光纤偏振干涉和双模干涉结合的双技术四参量以及双模干涉多参量同时测量的传感理论和实验原理，对交叉灵敏度作了分析，同时给出了误差分析，并结合理论模型对灵敏度矩阵的状态作了粗略估计。初步结果为：（１）灵敏度矩阵条件数不太大，可以采用迭代改善方法解线性方程组得到较好的解；（２）双模干涉传感器的灵敏度比偏振干涉传感器的灵敏度高两个数量级。     

Steady and transient behavior of perylene under high pressure

Pressure can reduce the distances among atoms, thereby modifying the overall optical characteristics of molecules. In this article, the excited state behavior of perylene is carefully observed under isotropic pressure and non-complexing condition. In a steady state, absorption peak shows red shift and spectral width are broadened with pressure increasing, which is ascribed to the π-electron delocalization between molecules. In a transient state, the transition dynamics presents a wavelike tendency with pressure increasing because the shift of self-tapping exciton state is contrary to that of Y-state with pressure increasing. The results conduce to understanding the influence of inter-molecule interaction on excited state behavior with inter-molecule distance decreasing, which contributes to studying the materials under extreme condition.     

单壁碳纳米管微分电导在高压和强磁场下的实验研究

单壁碳纳米管在高压下会发生结构相变，导致金属型的碳纳米管变成半导体.相变后碳纳米管中电子的库仑关联的表现形式发生变化，从Luttinger liquid行为转变成环境量子涨落行为.同时，相变后电子波函数的相位关联导致弱局域化行为的出现.为了研究库仑关联和相位关联之间是否有相互影响，使用金刚石对顶砧和液压自锁高压包在0—10 GPa准静压范围内测量了单层碳纳米管样品在低温和不同磁场下的微分电导随偏压的依赖关系.实验结果表明，相位关联和库仑关联是两种独立的效应，各自影响着电子的输运行为. 关键词： 单层碳纳米管 高压 微分电导     

In-situ high pressure X-ray diffraction studies of orthoferrite SmFeO_3

The high-pressure behaviors of SmFeO3 are investigated by angle-dispersive synchrotron X-ray powder diffraction under a pressure of up to 40.3 GPa at room temperature. The crystal structure of SmFeO3 remains stable at up to the highest pressure. The different pressure coefficients of the normalized axial compressibility are obtained to be βa = 0.60 × 10-3 GPa-1,βb = 0.79 × 10-3 GPa-1, βc = 1.28 × 10-3 GPa- 1, and the bulk modulus （B0） is determined to be 293（3） GPa by fitting the pressure-volume data using the Birch-Murnaghan equation of state. Furthermore, the larger compressibility of the FeO6 octahedra suggests the evolution of the orthorhombic structure towards higher symmetry configuration at high pressures.     

Evidence of polymorphic transformations of Sn under high pressure

The high-pressure polymorphs and structural transformation of Sn were experimentally investigated using angledispersive synchrotron x-ray diffraction up to 108.9 GPa. The results show that at least at 12.8 GPa β-Sn→bct structure transformation was completed and no two-phase coexistence was found. By using a long-wavelength x-ray, we resolved the diffraction peaks splitting and discovered the formation of a new distorted orthorhombic structure bco from the bct structure at 31.8 GPa. The variation of the lattice parameters and their ratios with pressure further validate the observation of the bco polymorph. The bcc structure appears at 40.9 GPa and coexists with the bco phase throughout a wide pressure range of40.9 GPa–73.1 GPa. Above 73.1 GPa, only the bcc polymorph is observed. The systematically experimental investigation confirms the phase transition sequence of Sn as β-Sn→bct→bco→ bco + bcc→bcc upon compression to 108.9 GPa at room temperature.     

光纤超声传感器及应用研究进展

光纤超声传感器通过检测光纤内传输光的强度、波长、相位、偏振态等参数感知超声波的相关信息.相比于传统的电类超声换能器,光纤超声传感器能够实现宽频带超声波信号的高灵敏探测,且其良好的抗干扰能力和复用性,可有效地提高超声波探测的可靠性和效率,在水下国防安全、生物成像、无损探伤、地震物理模型成像等领域具有巨大的应用潜力.目前,按照传感结构,光纤超声传感器可分为光纤强度调制型、光纤干涉型和光纤光栅型,并在不同方面发挥着各自的优势,均受到关注.本文主要综述了这几种传感器的传感机理、实现方法、发展现状,总结了光纤超声传感器的几个应用领域及面临的科学技术挑战,重点讨论了光纤超声传感器作为一种新技术应用于地震物理模型成像.     

基于路径积分分子动力学与热力学积分方法的高压氢自由能计算

在相图研究中, 严格计算一个真实系统在特定温度、压强下的自由能是近年来该领域理论方法发展的前沿. 自Mermin提出有限温度密度泛函理论后, 在电子结构层面, 弱关联系统中人们就其在对自由能贡献的描述已相对完善, 但在原子核运动的描述上, 热运动与量子运动的非简谐项却总被忽视. 本文将路径积分分子动力学与热力学积分结合, 对300 GPa下氢晶体Cmca 结构中原子核热涨落与量子涨落对自由能的影响进行了分析. 发现在100 K核量子涨落非简谐项的贡献约为15 meV每原子, 远大于不同结构间静态焓的差别. 该研究提醒人们简谐近似在核量子效应描述中可能存在的不准确性(即使在低温下). 同时, 我们采取的方法 也为人们进行自由能的准确计算提供了一个简单有效的手段.     

Superconducting properties of barium in three phases under high pressure from first principles

Electron-phonon coupling (EPC) in the three high-pressure phases of Ba is investigated using a pseudopotential plane-wave method based on density functional perturbation theory. The calculated values of superconducting critical temperature T c of Ba-I and Ba-II under pressure are consistent well with the trends observed experimentally. Moreover, Ba-V is found to be superconducting with a maximum T c exceeding 7.8 K at 45 GPa. With the increase of pressure, the values of T c increase in Ba I and Ba-II but the value of T c decreases in Ba-V. For Ba-I at pressures below 2 GPa, the increases of logarithmic average frequency ω log and electron-phonon coupling parameters λ both contribute to the enhancement of T c . For all the three phases at pressures above 2 GPa, T c is found to be primarily determined by λ . Further investigation reveals that for all the three phases, the change in λ with pressure can be explained mainly by change in the phonon frequency. Thus for Ba-II and Ba-V, although they exhibit completely different superconducting behaviors, their superconductivities have the same origin; the pressure dependence of T c is determined finally by the pressure dependence of phonon frequency.     

Equations of state of MgO at high pressure and temperature

Abstract

A synchrotron X-ray diffraction study on MgO has been done at simultaneous high pressure and temperature. The lattice parameter of MgO has been measured up to a static pressure of 6 GPa and a temperature of 1273 K, using a large volume pressure cell and energy-dispersive synchrotron X-ray powder diffraction. The compression was made following six high-temperature isotherms. A Vinet equation of state was used to fit the experimental P-V-T data. The Vinet's model compares very well with the experimental data above the Debye temperature (760 K) and allows the use of MgO as an alternative internal pressure calibrant for experiments at high temperature.     

Optical current sensing element with single medium layers for high voltage applications

The performance of a Faraday current sensing element with single medium layer coatings with potential for use at high voltage is reported, and the principle and the design parameters of the polarization-preserving, totally reflecting, single medium layer are given. The performance of the sensing element is demonstrated, showing a sensitivity of approximately 90% of the theoretically achievable maximum for an ideal case, a ratio error of 0.33% over a 7 h stability period and a 21 dB EMI immunity. Some of the advantages of this design are considered and discussed.     

Thermal and elastic properties of thorium pnictides under high pressure

Thorium pnictides crystallise in Fm 3 m space group at ambient condition and transform to Pm 3 m space group under pressure. We have investigated the phase transition, elastic and thermophysical properties of thorium pnictides by means of a modified charge-transfer potential model. This model incorporates Coulomb effect modified by Coulomb screening effect due to the delocalisation of the electron of Th-ion (charge-transfer) and covalency along with repulsion extended up to next-nearest neighbours. Present model is capable of explaining the Cauchy's discrepancy correctly. The calculated values of the phase-transition pressure (P _T = 70.6, 29.6, 24.3 and 11.5 GPa) and relative volume collapse (6.37, 11.22, 9.92 and 9.27%) for ThN, ThP, ThAs and ThSb, respectively, are in good agreement with the experimental data. The equation of state has been plotted to obtain phase diagram.     

基于圆环形薄壁截面梁的光纤光栅传感研究

提出将圆环形薄壁截面梁应用于光纤光栅传感，用一个光栅实现了对温度与应力的同时区分测量；对圆环形薄壁截面梁的应变进行了理论与实验分析，结果表明圆环形薄壁截面梁各点应变与该点角度的二倍呈余弦变化关系. 关键词： 光纤光栅传感 圆环形薄壁截面梁 啁啾     

大腔体静高压技术的发展及应用

大腔体静高压技术在现代工业和高压科学研究中具有基础性的重要意义,已被广泛应用于工业和科研领域,如超硬材料的合成、凝聚态物质在高温高压极端条件下的行为与物性研究等。经过逾半个世纪的不懈努力,以国产铰链式六面顶压机为代表的大腔体静高压技术与设备取得了长足的发展和丰硕的成果,改变了长期以来我国大腔体静高压技术落后于国外的局面。文章以四川大学高压科学与技术实验室为例,对我国大腔体静高压技术及装置从起步研制到世界领先的发展历程和技术特点进行了介绍。同时,基于典型大腔体静高压技术、装置及主要应用,展望了我国相关领域的发展前景。     

Structural phase transition in Bi2Te3 under high pressure

Structural change in Bi₂Te₃ under high pressure up to 16.6 GPa has been studied by powder x-ray diffraction. We observed two times of phase transitions at room temperature at the pressures of 8 and 14 GPa, respectively. According to our preliminary result on electrical resistance, it is reasonable to suppose that superconducting transition with T _c =2.8 K at the pressures of 10.2 GPa is observed in phase II. On the other hand, we found anomalies of the pressure dependences of lattice parameters and volume at around 2 GPa, which probably means the change in electrical structure on the Fermi surface.