New Cholesteric and Nematic Lyotropic Mesophases from Di-Sodium N-Lauroyl-Aspartate

Lyotropic liquid crystals are prepared from racemic and optically active di-sodium N-lauroyl aspartate (SNLA). The optically active levo enantiomer is a suitable amphiphile for obtaining cholesteric lyotropic mesophases. In the present work, different types of mesophases, including cholesteric and nematic, were prepared and their type I or II magnetic behavior characterized by deuterium and ²³Na NMR. The polarizing microscope textures were investigated, particularly with regards to magnetic field effects upon the samples. The usual chevron pattern was obtained for particular sample orientations and several characteristic effects were observed for the type I cholesteric lyomesophase in the first few minutes following removal of the sample from the magnetic field. Although the head group of di-sodium N-lauroyl aspartate possesses two negative charges, compositions are not too different from those reported for other amphiphile lyotropic systems.     

Energy calibration issues in nuclear resonant vibrational spectroscopy: observing small spectral shifts and making fast calibrations

The conventional energy calibration for nuclear resonant vibrational spectroscopy (NRVS) is usually long. Meanwhile, taking NRVS samples out of the cryostat increases the chance of sample damage, which makes it impossible to carry out an energy calibration during one NRVS measurement. In this study, by manipulating the 14.4 keV beam through the main measurement chamber without moving out the NRVS sample, two alternative calibration procedures have been proposed and established: (i) an in situ calibration procedure, which measures the main NRVS sample at stage A and the calibration sample at stage B simultaneously, and calibrates the energies for observing extremely small spectral shifts; for example, the 0.3 meV energy shift between the 100%‐⁵⁷Fe‐enriched [Fe₄S₄Cl₄]⁼ and 10%‐⁵⁷Fe and 90%‐⁵⁴Fe labeled [Fe₄S₄Cl₄]⁼ has been well resolved; (ii) a quick‐switching energy calibration procedure, which reduces each calibration time from 3–4 h to about 30 min. Although the quick‐switching calibration is not in situ, it is suitable for normal NRVS measurements.     

类锂离子双电子复合过程中辐射光子角分布和极化特性的理论研究

基于多组态Dirac-Fock 方法和密度矩阵理论,本文详细计算了高电荷态类锂离子（26 ≤ Z ≤ 92）KLL 双电子复合过程中,自由电子被共振俘获到中间双激发态1s2s²2p_3/2J = 1 的磁子能级截面以及该双激发态的取向参数,进而得到了此激发态向基态电偶极辐射跃迁1s2s²2p_3/2J = 1→1s²2s²J = 0 所发出光子的角分布和极化度,重点讨论了Breit 相互作用对相关物理量的影响. 研究表明,Breit 相互作用极大地改变了中间双激发态1s2s²2p_3/2J = 1 不同磁子能级的截面,从而导致了随后退激发放出光子的角分布和极化特性的显著变化. 关键词： 角分布和极化特性 多组态Dirac-Fock方法 密度矩阵理论     

Influence of molecular orientation on the photodissociation process of LiH molecules

Regulation of photodissociation dynamics of oriented LiH molecules in different dissociation channels is proposed based on time dependent quantum wave packet theory. The enhancement of molecular orientation on the photodissociation of LiH is obvious with our theoretical scheme. The results show that the molecular orientation in the ground state has a great effect on the angular distributions of wave packets. By using the proper laser pulses and controlling the polarization direction of the laser pulses, the enhancement of the photodissociation could be realized. After the molecular orientation, an optimal dissociation channel is observed with an improved dissociation probability. Compared with the results without molecular orientation, the maximal dissociation probability is increased by 8.1% in the indirect dissociation channel and 30.7% in the direct dissociation channel. The enhancement effect is more obvious in the direct dissociation channel, which provides a possible method to manipulate the dissociation of LiH molecules experimentally. Additionally, the photodissociation process of LiH also relies on the electric intensity and delay time of two pump pulses.     

主动雷达导引头射频干扰技术研究

主动雷达导引头具有较高的抗干扰性能,以PD体制导引头为例,分析了导引头单脉冲角跟踪的工作原理,在此基础上分析了同步闪烁干扰和交叉眼干扰这两种能够有效进行角度欺骗的干扰手段,并对干扰性能做出了仿真。     

Mixing greedy and predictive approaches to improve geographic routing for VANET

In recent years, thanks to the development and popularization of wireless network technologies, the issue of vehicular ad hoc network (VANET) has received great attention, and more and more VANET‐related researches have been brought up. Generally speaking, the biggest difference between VANET and traditional ad hoc network is the velocity of carriers because in VANET, the velocity of vehicles, the carriers, is much higher than those in traditional ad hoc. Therefore, it would be a great challenge to forward data efficiently in VANETs and many researches proposed have focused on the development of routing protocols. The current proposed routing protocols are all assumed to simulate in a distributed and ideal environment. As for the complex geographic environments, such as urban scenarios, extra amendments must be needed to improve the efficiency of the routing protocols. Thus, the main purpose of this paper is to design a suitable routing protocol for urban scenarios with better performance and adaptability. For this reason, greedy on straight roads and predictive at the intersections (GSPI) routing protocol is proposed to use greedy mode on straight roads and to use predictive mode at the intersections. In greedy mode, we choose the next hop according to the weight value that combines the distances and multi‐rate. In predictive mode, we predict the directions of the vehicles to determine the next hop. The simulation results reveal that our proposed algorithm indeed proves its feasibility. Copyright © 2010 John Wiley & Sons, Ltd.     

开关磁阻电机变角度电压斩波控制实现方法研究

电压斩波、变角度控制,是开关磁阻电机两种基本的控制方式。变角度电压斩波控制结合了两种控制方式的优点,可优化开关磁阻电机调速系统的效率。角度位置传感器的安装是实现角度位置控制及电机四象限运行的关键,并提出了角度细分软件设计方法。提出了变角度与模糊电压斩波控制相结合的原理及实现方法,最终在dsPIC单片机上实现,验证了该方法的有效性。     

一种基于RS码和MPPM的新型大气激光通信系统

为了进一步改善大气激光通信系统的性能,将具有强纠错能力的RS码和具有更强的传信能力和更高的带宽利用率的三脉冲的多脉冲位置调制(MPPM)技术引入了系统。实现了一种新型的大气激光通信系统,即基于RS码和MPPM的大气激光通信系统。实验结果表明,用FPGA实现的这种新型系统能够正确地完成二进制信息的传送。     

机动雷达大惯量天线定位控制策略

由于机动雷达大惯量天线的加速度受限,所以在加速度无法提高的前提下,如何减少大惯量天线的转动中定位时间尤为重要.文中提出了一种特殊的机动雷达大惯量天线转动中定位控制策略-分区域定位控制策略,比较了这种控制策略与常规控制方法的优劣,且基于以驱动器为速度内环的控制系统,给出了采用单片机控制的位置环控制电路,并简述了控制软件的实现方法.以实际控制模型为依托、以改善的定位时间为支撑、以简化的定位控制策略为主线,详细介绍了这种新型控制策略的工程运用.     

受光阑限制的部分相干光通过湍流大气传输的方向性

基于广义惠更斯菲涅耳原理,并利用Rytov相位结构函数二次近似的方法,推导出了受光阑限制的高斯谢尔模型(GSM)光束通过湍流大气传输的二阶矩宽度及扩展角解析表达式。以未受光阑限制的GSM光束为参照光束,分别利用扩展角和归一化远场平均光强分布研究了受光阑限制的GSM光通过湍流大气传输的方向性。研究表明,若以扩展角表征光束的方向性,则在一定条件下,截断参数δ不同的受光阑限制的GSM光束能够与相应的未受光阑限制的GSM光束在自由空间及湍流大气中具有相同的方向性;若以归一化远场平均光强分布表征光束的方向性,则即使扩展角一致,δ不同的受光阑限制的GSM光束与相应的未受光阑限制的GSM光束在自由空间中的方向性也并不相同,但在湍流中则一致。