移动荷载作用下离散支承曲线轨道振动特性分析

针对地铁隧道中曲线轨道的振动问题, 将整体式轨道视为单层离散支承Euler梁, 利用振型叠加法和Runger-Kutta法得到了移动荷载作用下曲线梁径向、竖向和轴向挠度以及扭转位移的时程响应解答, 通过参数敏感性分析, 揭示了不同工况下曲线轨道的空间振动特性. 计算结果表明: 在目前列车速度下, 列车移动荷载近似于准静态荷载作用, 轨道梁的位移曲线呈对称分 布; 钢轨扣件间距对位移影响较小, 扣件支承刚度是影响钢轨位移的主要因素; 随着速度的增 加, 横向荷载作用方向发生改变, 径向位移和扭转变形先减小后增大, 存在一个理想车速; 曲线半径对径向位移和扭转变形影响较大, 对竖向位移影响不明显, 在曲线半径增加情况下, 可以适当增加超高角以减小径向位移和扭转变形.     

机械合金化La0.7Ca0.3MnO3的晶化动力学及磁电阻研究

通过机械合金化方法制备了单相La_0.7Ca_0.3MnO₃化合物.球磨形成的非晶态结构在920K退火时转变为钙钛矿型相结构.根据质量作用定律,讨论了非晶晶化动力学行为,其晶化转变激活能约为265kJ/mol.同时研究了化合物的电阻特性,发现低温下样品的电阻ρ与温度T的关系为ρ∝T²,随退火温度的升高,ρ-T²曲线斜率下降.在远离居里温度处的低温磁电阻可用Δρ/ρ₀=p₁-p₂T^3/2-p₃T描述. 关键词：     

多孔TiC陶瓷的制备、性能及机理研究

以TiO2和炭黑为反应物,TiC为添加物,通过反应烧结法制备出多孔TiC陶瓷.研究了TiC的添加量对晶粒大小、孔径尺寸、开气孔率及抗弯强度的影响.研究结果表明:随着TiC的添加量从0;增大到100;,反应生成TiC的粒径从0.17μm增大到0.71μm,孔径尺寸从0.15μm增大到1.51μm,开气孔率从78;持续降到38;,抗弯强度先增加后减小,添加量为80;时最高(86 MPa).TiC生长机理主要是由于添加的TiC使TiO2周围的碳含量减少,从而导致反应生成TiC的熔点降低,扩散能力提高,晶粒粒径增大.     

弯曲振动薄圆盘的共振频率和等效电路参数研究

机电等效电路是分析复合换能器常用的一种解析方法, 但对薄圆盘而言, 由于弯曲振动的复杂性, 其等效集中参数很难获得, 该方法很少被应用. 本文从分布参数系统与集中参数系统等效角度, 根据动能相等原则和势能相等原则, 给出了弯曲振动薄圆盘的集中参数: 等效质量和等效弹性系数, 得到了共振频率方程, 并用ATILA软件模拟了其振动分布情况, 可以看出解析结果与数值结果趋于一致. 最后给出了分析复合振动系统时薄圆盘集中参数模型的等效电路. 本文的结果对弯曲振动复合换能器的设计提供了理论参考.     

Josephson vortices and intrinsic Josephson junctions in the layered iron-based superconductor Ca10(Pt3As8)((Fe0.9Pt0.1)2As2)5

Modulated electronic state due to the layered crystal structures brings about moderate anisotropy of superconductivity in the iron-based superconductors and thus Abrikosov vortices are expected in the mixed state. However, based on the angular and temperature dependent transport measurements in iron-based superconductor Ca$_{10}$(Pt$_3$As$_8$)((Fe$_{0.9}$Pt$_{0.1}$)$_2$As$_2$)$_5$ with $T_{\rm c} \simeq 12$ K, we find clear evidences of a crossover from Abrikosov vortices to Josephson vortices at a crossover temperature $T^{\star} \simeq 7 $ K, when the applied magnetic field is parallel to the superconducting FeAs layers, i.e., the angle between the magnetic field and the FeAs layers $\theta = 0^\circ$. This crossover to Josephson vortices is demonstrated by an abnormal decrease (increase) of the critical current (flux-flow resistance) below $T^{\star}$, in contrast to the increase (decrease) of the critical current (flux-flow resistance) above $T^{\star}$ expected for Abrikosov vortices. Furthermore, when $\theta$ is larger than $0.5^\circ$, the flux-flow resistance and critical current have no anomalous behaviors across $T^{\star}$. These anomalous behaviors can be understood in terms of the distinct transition from the well-pinned Abrikosov vortices to the weakly-pinned Josephson vortices upon cooling, when the coherent length perpendicular to the FeAs layers $\xi_\bot$ becomes shorter than half of the interlayer distance $d/2$. These experimental findings indicate the existence of intrinsic Josephson junctions below $T^{\star}$ and thus quasi-two-dimensional superconductivity in Ca$_{10}$(Pt$_3$As$_8$)((Fe$_{0.9}$Pt$_{0.1}$)$_2$As$_2$)$_5$, similar to those in the cuprate superconductors.     

Passive round-robin differential-quadrature-phase-shift quantum key distribution scheme with untrusted detectors

In this paper, we proposed the scheme for a passive round-robin differential-phase-shift quantum key distribution(RRDPS-QKD) set-up based on the principle of Hong–Ou–Mandel interference. Our scheme requires two legitimate parties to prepare their signal state with two different non-orthogonal bases instead of single in original protocol. Incorporating this characteristic, we establish the level of security of our protocol under the intercept-resend attack and demonstrate its detector-flaw-immune feature. Furthermore, we show that our scheme not only inherits the merit of better tolerance of bit errors and finite-sized-key effects but can be implemented using hardware similar to the measurement device independent QKD(MDI-QKD). This ensures good compatibility with the current commonly used quantum system.     

An Alternating-Current Voltage Modulated Thermal Probe Technique for Local Seebeck Coefficient Characterization

Nanostructured and nanocomposite thermoelec- tric materials have recently attracted a great deal of attention due to the optimization of thermal and electrical transports for high thermoelectric performance The initial ideas for the applica- tions of nano-structures in thermoelectric materials are that the lattice thermal conductivity can be de- pressed by the scattering of nano-particles or nano- boundaries as well as the enhanced electron density of states at the Fermi level. The latter is expected to enhance Seebeck coefficients due to the fact that the low energy carriers can be filtered by nano-sized grain boundaries. Lowered thermal conductivity and enhanced thermoelectric figure of merit have been ob- served in lots of bulk materials with nanostructures or nano-impurities. However, the thermal and electrical transports in these nano-materials are usually mea- sured by normal commercial systems, in which only the statistical values of the transports are obtained. The characterization of local thermoelectric parame- ters still remains a challenging task at the submicro, even nanometer level as a powerful tool for Scanning probe microscopy nanostructure imaging and local properties characterization, has become a promis- ing technique for measuring local thermal and electri- cal properties, like scanning tunneling microscopy, scanning thermal microscopy, and scanning Joule expansion microscopy. Recent work has demon- strated simultaneously determined the thermal con- ductivity and Seebeek coefficient of Bi2Se3 thin film by a microprobe technique.     

入口加旋转速度对ADS无窗散裂靶回流区高度的影响

在已有的加速器驱动次临界堆无窗散裂靶的设计中,回流区内流体流速较低,散裂反应产生的热量无法被有效带走,不利于整个系统的安全运行。本文围绕这一核心问题,在散裂靶入口加入旋转速度,实现对回流区的优化。首先,通过数值模拟与实验结果的瞬态流型比较,验证了数值方法的正确性。紧接着,在入口逐步加入旋转速度,回流区高度逐渐减小且形成一个新的气蚀区,当旋转速度到达较大数值时,回流区消失,通过流体力学分析上述物理过程得到了解释。在加入更大旋转速度后,新的气蚀区与上方的蒸汽区充分联结,形成了一个"V"字形的蒸汽区域。上述物理结果对我国加速器驱动次临界堆无窗散裂靶的设计优化具有一定参考价值。