光衍射数值模拟中不同抽样方法的适用性分析

基于标量衍射理论和快速傅里叶变换,分析了光衍射的数值模拟时可以采用的不同抽样方法及其适用性。理论分析表明,按照抽样对象的不同,存在三种适用范围不同的算法:传递函数抽样法、点扩展函数抽样法和加权函数抽样法。其适用范围分别为衍射距离小于、大于和等于特征距离的情况。在Matlab软件环境下给出了三种算法的模拟计算实例,并与相应的实验结果进行了比较,证明了理论分析的正确性。最后还给出了一种无需改变抽样点数和抽样间隔就可计算任意距离衍射过程的自适应抽样算法及其在数字全息再现中的应用实例。     

基于周期极化铌酸锂波导的软件同步光采样

随着大于40 Gb/s高速光通信系统的出现, 为了保证光信号传输质量, 需要对光信号进行监测。对于带宽超过传统光电探测器和示波器可测量带宽的高比特率数据光信号, 光采样技术是进行时域测量的重要手段。采用固定频差的方法可以用百兆速率的采样脉冲对高速光信号进行采样, 降低了对采样后电数据处理系统带宽的要求。在对基于周期极化铌酸锂(PPLN)波导中和频效应的采样过程进行建模仿真的基础上, 实现了对Optsim获得的光传输线内10 Gb/s的非归零码(NRZ)和归零码(RZ)信号的采样。采用软件同步算法对采样数据进行处理, 获得信号的眼图, 这一方法可使采样系统对硬件的要求降到最低。与理想与门获得的采样结果进行比较, 对PPLN波导的光采样特性和采样质量进行了分析。     

Online data quality monitoring system at BESⅢ

The online Data Quality Monitoring (DQM) tool plays an important role in the data recording process of HEP experiments. The BESⅢ DQM collects data from the online data flow, reconstructs them with offline reconstruction software and automatically analyzes the reconstructed data with user-defined algorithms. The DQM software is a scalable distributed system. The monitored results are gathered and displayed in various formats, which provides the shifter with current run information that can be used to identify problems quickly. This paper gives an overview of the DQM system at BESⅢ.     

采用树脂透镜的掌纹图像采集光学系统设计

为了获得高分辨率、高对比度和低畸变的掌纹图像,同时实现系统的轻量化和高性价比,本文基于全反射原理,采用树脂材料设计了一款由6片镜构成双远心光路的掌纹采集光学系统。树脂材料的选用减轻了光学系统的总重量;基于光的全反射原理的系统设计增强了掌纹图像的对比度;选择双远心光学结构,便于对倾斜物面所产生的梯形畸变进行矫正。对所设计光学系统的成像质量分析表明,该系统所有视场的光学传递函数（MTF）在Nyquist频率228 lp/mm处均达0.55以上,畸变〈0.14%。设计的光学系统可以采集120 mm×160 mm的手掌区域,实际手掌面上的分辨率达到500dpi,采集的掌纹图像分辨率达到8.0×106 pixel,满足了实际采集的要求。     

A Control Simulation Method of High-Speed Trains on Railway Network with Irregular Influence

Based on the discrete time method, an effective movement control model is designed for a group of high-speed trains on a rail network. The purpose of the model is to investigate the specific traffic characteristics of high-speed trains under the interruption of stochastic irregular events. In the model, the high-speed rail traffic system is supposed to be equipped with the moving-block signalling system to guarantee maximum traversing capacity of the railway. To keep the safety of trains' movements, some operational strategies are proposed to control the movements of trains in the model, including traction operation, braking operation, and entering-station operation. The numerical simulations show that the designed model can well describe the
movements of high-speed trains on the rail network. The research results can provide the useful information not only for investigating the propagation features of relevant delays under the irregular disturbance but also for rerouting and rescheduling trains on the rail network.     

高速线性光采样用被动锁模光纤激光器重复频率优化

线性光采样是一种测量基于先进调制码型的高速光信号的有效手段, 而被动锁模光纤激光器是其实施所需的关键组件. 本文在介绍线性光采样工作原理的基础上, 首次分析得到被动锁模光纤激光器重复频率与待测信号光线宽的约束关系, 对于正交相移键控(QPSK)信号, 当信号光线宽与采样光脉冲重复频率的比值小于1.5×10^-3 时, 高速信号的相位噪声对线性光采样带来的损伤可以忽略不计. 利用95.984 MHz重复频率的被动锁模光纤激光器对线宽为100 kHz速率为28 Gbaud的QPSK信号开展相关实验, 通过标准数字相干接收算法可以得到与传统高速示波器相同的星座图, 理论分析与实验结果完全符合. 这一研究结果有助于线性光采样用被动锁模光纤激光器的优化设计.     

双通道高速数据采集处理平台的设计与实现

为满足数字式测向接收机对高速数据采集和处理的需求,研制了高速数据采集处理平台,该平台基于ADC12D1800RF模数转换器实现了两路1.35GHz中频信号的带通采样,以Xilinx公司V7系列FPGA为数据处理器,采用高速DDR3作为存储设备解决了海量数据存储问题,并通过高速串行接口（GTX/SRIO）实现了大容量数据的实时传输。该平台的测试结果为：1.8GHz采样率时有效位数大于8bit,DDR3存储器的工作主频可达1333MHz,GTX接口在10Gbps速率下工作时,其误码率小于10-9,上述测试结果表明该平台可以高速、准确地实现信号采集、数据传输、存储和处理,达到了预期设计目标。     

Generalised expressions for the association and dissociation rate constants of molecules with multiple binding sites

ABSTRACT

Many proteins exhibit multiple binding patches. A patch may harbour a key chemical modification site, but may also simply act as a trap for the binding to another site. Here we consider the scenario in which one molecule (enzyme) binds another molecule (substrate) which contains two sites. We present microscopic expressions for the rate at which the enzyme binds to a particular site on the substrate, both for the scenario in which the enzyme directly binds the site without first visiting the other site, and for the case in which it may visit the other site an arbitrary number of times before binding to the site of interest. We also present the expressions for the corresponding dissociation reactions. These expressions can be used to compute in a single rare-event simulation of the dissociation pathway not only both the intrinsic and effective dissociation rate constants but also both association rate constants.     

Neutral Community Theory: How Stochasticity and Dispersal-Limitation Can Explain Species Coexistence

Neutral community theory explains biodiversity, i.e. the coexistence of several species, as the result of a stochastic balance between immigration and extinction on a local level, and between speciation and extinction on a regional level. The most popular model, presented by Hubbell in 2001, has seen many analytical developments in recent years, which can be used in model analysis, model testing and model comparison. We review these developments here, and present alternative derivations and shine previously unnoticed lights on them.     

Multichannel sampling theorem for bandpass signals in the linear canonical transform domain

The linear canonical transform (LCT) describes the effect of first-order quadratic phase optical system on a wave field. The classical multichannel sampling theorem for common bandlimited signals has been extended differently to bandlimited signals associated with LCT. However, a practical issue associated with the reconstruction of the original bandpass signal from multichannel samples in LCT domain still remains unresolved. The purpose of this paper is to introduce a practical multichannel sampling theorem for bandpass signals in LCT domain. The sampling expansion which is constructed by the ordinary convolution in the time domain can reduce the effect of spectral leakage and is easy to implement. The classical multichannel sampling theorem and the well-known sampling theorems for the LCT are shown to be special cases of it. Some potential applications of the multichannel sampling are also presented to show the advantage of the theory.