2H NMR研究嵌段共聚物溶致液晶相的结构演化与水分子动力学行为

采用2H NMR实验结合谱图线型的理论模拟方法研究了两亲性嵌段共聚物聚氧乙烯一聚氧丙烯一聚氧乙烯／氘代水／对二甲苯三元体系形成的不同液晶相的结构演化和水分子动力学行为．结果表明,对不同组分浓度的样品,2H谱线型发生明显的变化,对应体系从各向同性相、六角相和层状相间的系列结构转变．通过NMR弛豫模型获得了液晶相结构演化中序参数和分子运动相关时间的变化规律,理论模拟获得的自旋．晶格弛豫时间T1、自旋-自旋弛豫时乃等水分子动力学参数与实验测量结果吻合．结果表明：层状相四极劈裂及序参数随嵌段共聚物或二甲苯含量的增加呈现一个极大值,水分子的兀随着嵌段共聚物浓度增加而明显减小,而疋在六角相到层状相的转变中发生了明显的变化．研究表明,通过理论模拟2HNMR实验获得的谱图线型是研究液晶相结构演化和动力学的有力工具．     

Pr_(0.75)Na_(0.25)Mn_(1-x)Fe_xO_3的制备及磁学和输运性质研究

采用溶胶凝胶法通过较低温度、较短的烧结时间制备了单相的多晶钙钛矿Pr0.75Na0.25Mn1-xFexO3(0≤x≤0.3),避免了Na元素的挥发及锰氧化物的析出,使Pr1-xNaxMnO3中Na的最大掺入量由文献报道的0.19提高到0.25,样品单相性得到大幅度提高.系列样品的磁化强度、电阻率随温度的变化关系表明2%的Fe掺杂便能大大减弱低温电荷有序;在x≤0.05时系列样品磁化强度随Fe含量的增加而增加,电阻率随Fe含量的增加而下降,然后二者随Fe含量进一步增加均朝相反的趋势变化.用几何效应(Fe3+的几何尺寸大小)和电子结构的影响两个方面的竞争解释这种现象.     

合金化成分对NiTi合金M_s点影响的正电子湮没研究

用双探头符合系统测量了金属Fe、Co、Ni、Al、Nb、Cu、Ti和NiTi合金的多普勒展宽谱,计算了其S参数和W参数,分析了合金中d-d金属键的作用.结果表明,当用Fe、Co或Al原子加入NiTi合金时,都将使合金中参与形成d-d金属键的d电子减少,从而使金属键减弱;而用Cu或Nb原子加入NiTi合金时,对合金中d-d电子作用的影响很小,合金中共价键的成分变化不大.在NiTi合金中加入合金化元素可以改变其电子结构,进而影响Ms点.     

前驱膜形貌对TFA-MOD技术生长YBCO超导薄膜的影响

本文采用三氟乙酸盐-金属有机沉积(TFA-MOD)技术在LaAlO3(00l)单晶基片上、在不同的低温热处理条件下制备出不同形貌的前驱膜.从金相显微镜(OM)和扫描电镜(SEM)观察可以看出,低温预分解时造成前驱膜的形貌不完整性在高温处理后并没有消除.对高温热处理后的YBCO成相膜用X射线衍射进行了物相定性分析,用Jc-Scan Leipzig系统对超导薄膜进行了超导性能分析.结果表明,前驱膜的形貌不完整性造成高温成相阶段样品杂相出现和超导性能降低.经过对低温热处理条件的优化,得到表面形貌完整的前驱膜,避免了高温成相阶段杂相出现,提高了涂层导体的超导性能,Jc可以超过1.5MA/cm2.     

500GHz超导SIS混频器的设计

超导SIS(Superconductor-Insulator-Superconductor)混频技术是新兴的低噪声检测技术,其卓越的低噪声性能使其成为太赫兹波段理想的接收技术之一.如何提高太赫兹波和SIS超导结之间的信号耦合是设计超导SIS混频器的一个关键问题.本文依据准光耦合技术,研究了两种改善两者间信号的耦合方法:一是设计工作于500GHz波段的对数周期天线,二是设计微带阻抗变换器以实现对数周期天线和SIS超导结之间的阻抗匹配.     

Low birefringence depressed cladding photosensitive fiber

The highly Ge-doped photosensitive fiber （PSF） has been widely used in the fabrication of fiber Bragg gratings （FBGs）. Its birefringence and cladding mode coupling characteristics greatly influence FBG＇s transmission feature in communication application areas. In this work, a new concept of the PSF is introduced which, along with an optimized birefringence design, a precisely controlled fabrication process, and a cladding mode depressed design, results in a written FBG with -25-dB clad mode-depressed ratio and a polarization mode dispersion value less than 0.045 ps.     

Qualification of superpolished substrates for laser-gyro by surface integrated scatter measurement

<正>Integrated scatterometer for qualification of superpolished substrates for laser-gyro by surface scatter loss measurement is constructed.Different from the qualification of substrate by surface roughness,the scatterometer measures the forward surface scatter loss to check whether the mirror made of the substrate will be suitable for the required laser-gyro lock-in specification.The scatterometer utilizes convex lens instead of integrating sphere to collect scatter light.Special sample support and baffle are designed to block unwanted light.The result of stability test is given,which is about 0.4%over 10 h.     

Sudden death of entanglement in the two-mode cavity field

<正>The entanglement dynamics involving the so-called entanglement sudden death of atoms in two-photon Tavis-Cummings model is investigated.Various initial conditions that may have influences on the entanglement evolution of atoms,especially on the appearance of atomic entanglement sudden death,are studied. The appearance of entanglement sudden death is sensitive to the initial conditions of the whole system, i.e.,the concrete type of atomic initial state,the photon number in the cavity field,and the dipole-dipole interaction between atoms.It is shown that the strong dipole-dipole interaction between atoms can weaken the atomic entanglement sudden death.     

Hyperspectral feature recognition based on kernel PCA and relational perspective map

A novel joint kernel principal component analysis （PCA） and relational perspective map （RPM） method called KPmapper is proposed for hyperspectral dimensionality reduction and spectral feature recognition. Kernel PCA is used to analyze hyperspectral data so that the major information corresponding to features can be better extracted. RPM is used to visualize hyperspectral data through two-dimensional （2D） maps, and it is an efficient approach to discover regularities and extract information by partitioning the data into pieces and mapping them onto a 2D space. The experimental results prove that the KPmapper algorithm can effectively obtain the intrinsic features in nonlinear high dimensional data. It is useful and impressing for dimensionality reduction and spectral feature recognition.     

Effects of viscosity on shock-induced damping of an initial sinusoidal disturbance

A lack of reliable data treatment method has been for several decades the bottleneck of viscosity measurement by disturbance amplitude damping method of shock waves.In this work the finite difference method is firstly applied to obtain the numerical solutions for disturbance amplitude damping behavior of sinusoidal shock front in inviscid and viscous flow.When water shocked to 15 GPa is taken as an example,the main results are as follows:(1) For inviscid and lower viscous flows the numerical method gives results in good agreement with the analytic solutions under the condition of small disturbance(a0/λ=0.02);(2) For the flow of viscosity beyond 200 Pa s(η=κ) the analytic solution is found to overestimate obviously the effects of viscosity.It is attributed to the unreal pre-conditions of analytic solution by Miller and Ahrens;(3) The present numerical method provides an effective tool with more confidence to overcome the bottleneck of data treatment when the effects of higher viscosity in experiments of Sakharov and flyer impact are expected to be analyzed,because it can in principle simulate the development of shock waves in flows with larger disturbance amplitude,higher viscosity,and complicated initial flow.