强磁场对金属离子掺杂CaTiO_3结构和光学性能的影响

研究了800℃条件下不同制备磁场强度(最高12 T)对Ca Ti O3及其浸渍掺杂样品在结构和光学性能方面的影响.研究表明:样品吸光性能随浸渍掺杂的离子浓度的增大而提升,且发生红移现象;相同掺杂浓度下,磁场下制备样品的吸光性能均较非磁场下制备的样品有所提高,但不同磁场强度下所制备样品的吸光曲线彼此差异不大;此外,磁制备纯Ca Ti O3晶体粉末的X-射线衍射曲线峰左移,紫外-可见漫反射光谱吸收截止波长增长,这表明强磁场可使Ca Ti O3晶面间距和晶格常数增大、禁带宽度减小.     

偶极子在径向非均匀介质中的电磁场分布

提出了柱状多层介质中的磁偶极子在任意介质层中的电磁场的递推算法，给出了磁偶极子产生的电磁波在柱状多层介质中的反射、透射系数和广义反射系数，从而得到了任意介质层中满足各层界面边界条件的电磁场解析表达式．     

Variable temperature system using vortex tube cooling and fiber optic temperature measurement for low temperature magic angle spinning NMR

We describe the construction and operation of a variable temperature (VT) system for a high field fast magic angle spinning (MAS) probe. The probe is used in NMR investigations of biological macromolecules, where stable setting and continuous measurement of the temperature over periods of several days are required in order to prevent sample overheating and degradation. The VT system described is used at and below room temperature. A vortex tube is used to provide cooling in the temperature range of -20 to 20 degrees C, while a liquid nitrogen-cooled heat exchanger is used below -20 degrees C. Using this arrangement, the lowest temperature that is practically achievable is -140 degrees C. Measurement of the air temperature near the spinning rotor is accomplished using a fiber optic thermometer that utilizes the temperature dependence of the absorption edge of GaAs. The absorption edge of GaAs also has a magnetic field dependence that we have measured and corrected for. This dependence was calibrated at several field strengths using the well-known temperature dependence of the (1)H chemical shift difference of the protons in methanol.     

The Effect of Pea Chloroplast Alignment and Variation of Excitation Wavelength on the Circularly Polarized Chlorophyll Luminescence

Circularly polarized luminescence (CPL) is a powerful technique to study the macroorganization of photosynthetic light-harvesting apparatus in vivo and in vitro. It is particularly useful for monitoring environmental stress induced molecular re-organization of thylakoid membranes in green leaves. The current study focuses on two questions which are important to perform and interpret such experiments: how does CPL depend on the excitation wavelength and how on the orientation of the granal thylakoids. CPL and circular dichroism (CD) of pea chloroplasts were complementarily applied when chloroplasts were either in suspension or trapped in a polyacrylamide gel (PAAG) after alignment in a magnetic field. In contrast to the CD spectrum, the CPL signal was found to be independent of the excitation wavelength in both the Soret and the Qy absorption region for chloroplasts in both suspension and PAAG. The improved resolution of luminescence measurements revealed a relatively small negative CPL band in addition to the previously described large positive band. No effect of photoselection upon excitation on the CPL spectra was detected. The CPL intensity at 690 nm at the edge of the granal thylakoids was found to be higher than at the face of the grana suggesting the CPL anisotropy.     

物质抗磁性的经典统计解释

介绍一种解释物质抗磁性的经典统计方法.     

Three-dimensional linearised Euler model simulations of sound propagation in idealised urban situations with wind effects

A three-dimensional numerical time-domain model based on the linearised Euler equation is applied to idealised urban situations with elongated, isolated buildings beside a straight street with sound emissions. The paper aims at the investigation of principle relationships between the source-receiver geometry (street and building facades) and sound propagation under the consideration of ground and wind. By applying cyclic lateral boundary conditions for either one or both horizontal co-ordinates, two different idealised urban environments were considered: a single street and parallel streets. Numerical experiments were performed to elaborate the effects of different roof types, ground properties, wind flow, and turbulence in both urban environments with the focus on the back facades (‘quiet’ sides) of the buildings. As a result it was found that the back facades of flat-roof buildings are quieter than those of hip roof buildings despite equal cross-cut areas. The wind effect (resulting in quieter upwind and louder downwind facades) is more pronounced for hip-roof buildings. In the case of parallel streets upwind facades are slightly louder than downwind facades because they are simultaneously exposed to downwind propagating sound from the next parallel street.     

Spin–orbit stiffness of the spin‐polarized electron gas

In a spin‐polarized electron gas, Coulomb interaction couples the spin and motion degrees of freedom to build propagating spin waves. The spin wave stiffness S_sw quantifies the energy cost to trigger such excitation by perturbing the kinetic energy of the electron gas (i.e. putting it in motion). Here we introduce the concept of spin–orbit stiffness, S_so, as the energy necessary to excite a spin wave with a spin polarization induced by spin–orbit coupling. This quantity governs the Coulombic enhancement of the spin–orbit field acting of the spin wave. First‐principles calculations and electronic Raman scattering experiments carried out on a model spin‐polarized electron gas, embedded in a CdMnTe quantum well, demonstrate that S_so = S_sw. Through optical gating of the structure, we demonstrate the reproducible tuning of S_so by a factor of 3, highlighting the great potential of spin–orbit control of spin waves in view of spintronics applications. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Spin-Dependent Transport and Densities of States in Non-collinear Magnetic Barriers

The spin-dependent transport properties in the non-collinear pattern of series of δ-magnetic barriers are studied by using scattering theory and Green＇s function methods. The Green＇s function is obtained by using distorted wave approach and the scattering matrix is related by Fisher-Lee relationship. In addition to reproducing the results of Papp＇s and Xu＇s in parallel and antiparallel configurations, we also obtain further results, where arbitrary orientations of the magnetic barriers and arbitrary number of barriers are included. The main finding of our results is that the signs of polarizations can be switched around some ＂geometric unpolarized windows＂. The well-known antiparallel configuration has no such characteristics. Furthermore, we discuss spin-related partial densities of states in both polarized and unpolarized structures.     

快脉冲直线变压器驱动源模块的原理及实验

 介绍了直线型变压器驱动源（LTD）产生快脉冲的基本原理及技术优势,阐述了快脉冲LTD模块设计的要点,设计了输出脉冲上升时间小于100 ns的快脉冲LTD模块,并进行了初步的实验研究。实验得到该LTD模块充电±16 kV时,短路放电的电流峰值为23.7 kA,电流振荡1/4周期为69.6 ns;充电±50 kV驱动0.85 Ω负载时,电流峰值为41.4 kA,上升时间为36.8 ns（10%~90%）和60.8 ns（0~100%）。     

Rigid Motions in the Presence of a Magnetic Field

It is shown that, in the standard framework of non-relativistic quantum mechanics, the presence of a magnetic field implies that there are no operators representing those translations or rotations that do not leave invariant the magnetic field, and the corresponding components of the linear or angular momentum are undefined. Pacs: 03.65.-w. 02.20.-a