水平激励下颗粒物质的有效质量及耗散功率的研究

对颗粒物质的有效质量谱及耗散功率进行了数值研究,发现水平和垂直激励下颗粒体系的共振频率f_g与体积模量k均随压强P呈分段幂律变化,在高压强下遵循fg∝P~(1/6),k∝P~(1/3)的规律,在低压强下遵循fg∝P~(1/4),k∝P~(1/2)的规律.同时,在水平和垂直振动下,颗粒体系品质因子的倒数1/Q随P的变化呈指数衰减.在特定频率和压强下,颗粒体系的平均耗散功率p随振动强度Γ的变化曲线上存在一个特征振动强度Γ*,当ΓΓ*时,颗粒体系表现出类固态行为,平均耗散功率p随振动强度Γ呈幂律标度,p∝Γ~α(2α5);当ΓΓ*时,颗粒体系表现出类液态行为,体系的平均耗散功率p随振动强度Γ呈线性变化.由此得到了水平激励下颗粒体系类固体类流体转变的Γ-P相图.     

磁场对石墨烯中弱耦合极化子性质的影响

研究了磁场作用下石墨烯中电子与表面光学声子弱耦合情况下的极化子的性质。采用线性组合算符和Pekar变分法分别推导出了石墨烯中弱耦合极化子的基态能量E₀、第一激发态能量E₁和跃迁频率ω随磁场强度B和德拜截止波数k_d之间的变化关系。数值计算结果表明,极化子的基态能量E₀随磁场强度B变化的曲线（k_d一定时）和E₀随k_d的变化曲线（B一定时）均会分裂成对称的两条,并且当B一定时E₀的绝对值随k_d的增加而增加。在k_d一定时,极化子的第一激发态能量E₁和跃迁频率ω均为磁场B的增函数;在B一定时,E₁和ω均随k_d的增加而增大。     

垂直振动激发下颗粒物质的能量耗散

本文对垂直振动激发下的铜和玻璃珠两种密集颗粒样品,通过实时测量样品盒的加速度和振台对它的作用力,研究了样品的平均耗散功率.实验发现该耗散功率在给定振动强度下随振动频率的变化曲线是一个峰值在几十赫兹的宽峰结构,在给定频率下随强度的变化具有幂率规律,其幂值小于简谐受迫振动模型的幂值2.这些结果将有助于研究测定颗粒流体和气体的迁移系数,以及它们在不同运动模式下的能耗差异.     

Raman光谱方法研究三氯甲烷与苯分子间的C/H…π相互作用

测量了不同浓度三氯甲烷（CHCl₃）与苯（C₆H₆）二元溶液的Raman光谱,随C₆H₆浓度的增加,受分子间C/H…π相互作用的影响,CHCl₃中C—H键伸缩振动频率向低波数移动;当CHCl₃体积分数小于40%,C—H键伸缩振动频率不变,分子间C/H…π相互作用达到饱和.分别以CHCl₃和C₆H₆体积分数为70%的CHCl₃-C₆H₆混合溶液为研究对象,测量了它们的高压和低温Raman光谱.根据CHCl₃中C—H键伸缩振动频率随压强和温度的变化关系,得出了分子间C/H…π相互作用对压强和温度的扰动表现出不稳定性.     

摩擦颗粒体系各向同性压缩过程中的堵塞行为

利用分子动力学方法,模拟了5000个表面轻微摩擦(μ=1×10^-4)的弹性颗粒组成的体系在各向同性压缩过程中的堵塞(jamming)现象,研究了颗粒体系对边壁压强P和对关联函数第一个峰的高度g₁随体积分数φ的变化规律. 结果表明,当体系的体积分数φ大于临界体积分数φ_c时,P(φ)曲线表现出明显的黏滑(stick-slip)行为,法向的力-力关联函数、切向的力-力关联函数和颗粒的位置-位置关联函数同时发生跳变,说明宏观黏滑现象源自内部的力位形和几何构形的调整. 体系在φ缓慢增大过程中得到了不同的堵塞态,随着颗粒粒径的缓慢减小,体系得以松弛(unjamming),实现松弛过程并得到相应的φ_c. 对于不同堵塞态,其边壁压强P与φ-φ_c遵从幂律标度P∝(φ-φ_c)^0.964. 关键词： 堵塞相图 对关联函数 力-力关联函数 标度规律     

颗粒物质内部滑动摩擦力的非线性振动现象

实验研究了探测棒竖直穿过圆筒中颗粒物质运动时所受的滑动摩擦阻力.研究发现，厚度为容器直径的0.5到2倍之间，粒径为2 mm的颗粒堆，对探测棒的滑动摩擦力在一个平均水平上随时间作非线性振动.当探测棒以小于2×10^-3 m/s的匀速率上升时，滑动摩擦力平均水平超过初始最大静摩擦力F₀的0.2到0.5倍，变化范围可从F₀到2F₀.频率低于1.35 Hz时，各种频率成分的强度随频率增加按幂函数方式衰减，其主要部分的平均周期T与探测棒运动速率v成反比关系. 关键词： 颗粒物质 滑动摩擦力 非线性振动     

自辐射场下UN2分子的光谱研究

对铀原子和氮原子分别使用相对论有效原子实势和6-311+G(d)基组, 采用优选的密度泛函B3P86方法, 研究了铀本身产生自辐射场(-0.005–0.005 a.u.)作用下UN₂基态分子的能隙E_g和谐振频率ν. 结果表明: UN₂分子在自辐射场中反对称伸缩振动频率ν₃(σ_g)和对称伸缩振动频率σ₁(σ_g)与实验值1051.1 cm^-1和1008.3 cm^-1 基本符合; E_g随自辐射场场强的增大而趋于减少, 占据轨道的电子容易被激发至空轨道而形成激发态; UN₂分子在自辐射场中趋于不稳定, N₂, O₂等更容易扩散到表面内层而腐蚀铀表面, 加剧了铀在自辐射场中的腐蚀.     

二维圆盘颗粒体系声学行为的数值研究

数值测量了卸载过程中二维单分散圆盘颗粒系统的横波、纵波声速、声衰减系数、非线性系数随压强的变化以及声衰减系数随频率的变化.结果表明,二维(2D)圆盘颗粒体系的横波、纵波声速均随压强呈分段幂律标度:当压强P10~(-4)时,横波、纵波声速随压强的增大而减小;当P10~(-4)时,有v_t~P~(0.202),v_l~P~(0.338).进一步得到其剪切模量和体积模量的比值G/B也随压强呈幂律标度,G/B~P~(-0.502),暗示在低压强下,与三维(3D)球形颗粒体系类似,2D圆盘颗粒体系也处于L玻璃态.水平激励和垂直激励下2D圆盘颗粒系统的衰减系数随频率变化也呈现分段行为:当频率f0.05时,衰减系数不随f变化;当f0.05时,横波纵波的衰减系数α~f;当f0.35时,横波衰减系数α_T~f~2,纵波衰减系数α_L~f~(1.5).此外,竖直水平激励下的2D圆盘颗粒系统的非线性系数和衰减系数随压强也呈现与声速类似的分段规律:当P10~(-4)时,横波非线性系数β_T~P~(-0.230),其余都不随压强变化.当P10~(-4)时,两者均随压强增大呈幂律减小:β_T~P~(-0.703),β_L~P~(-0.684),α_T~P~(-0.099),α_L~P~(-0.105).进而得到2D圆盘颗粒系统中散射相关的特征长度?~*随压强呈幂律标度,当P10~(-4)时,?~*~P~(-0.595);当P10~(-4)时,?~*~P~(0.236).     

YVO4：Eu3+纳米微粒发射光谱与温度的关系

测量了非选择激发下YVO₄:Eu³⁺纳米微粒中Eu³⁺的⁵D₀→⁷F₂发射光谱随温度的变化.低温下的光谱是很多谱线叠加在一起形成的宽带;而室温下主要是与体材料相似的两条分离谱线.根据选择激发下YVO₄:Eu³⁺的发射光谱研究得到的结论,把发射光谱分解为两部分之和,一部分来自占据靠近纳米微粒中心的格位的Eu³⁺离子发射谱线具有与体材料相近峰值;另一部分来自占据靠近表面位置的Eu离子,发射分布在更大的光谱范围内.这两部分发光的相对强度随温度变化的分析表明,YVO₄:Eu³⁺纳米微粒发射光谱随温度的变化是由于靠近表面的Eu通过表面猝灭中心猝灭而引起的.     

BaF2高压相变行为的第一性原理研究

通过理论计算研究了BaF₂在高压下的晶体结构及物理性质.结果表明,在3.5和18.3 GPa,BaF₂依次经历了Fm■m-Pnma-P6₃/mmc两次结构相变,相变过程伴随着体积的塌缩,均为一级相变.约15 GP时,Pnma相晶轴压缩性出现异常,表现为随压强增大,晶轴b_o轻微增加,a_o略微减小.对其电子态密度进行分析发现,在16 GPa以后,由于F1原子的p_y+p_z与p_x轨道电子离域,导致其带隙随压强增加而降低.在约20 GPa时,Pnma相完全转变为P6₃/mmc相,相变完成.对BaF₂的拉曼峰位随压强变化进行了计算,为其高压拉曼光谱行为提供了相应的理论依据.计算了P6₃/mmc相在不同压强下的声子色散曲线,揭示了其卸压过程中的滞后机制,计算结果还预测该物相至少可以稳定到80 GPa.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.