Trace analysis of anions in organic matrices by ion chromatography coupled with a novel reversed-phase column for on-line sample pretreatment

An ion chromatography(IC) system coupled with on-line column-switching technique was used to determine anions ofμg/g levels in organic chemicals of analytical reagent grade.A novel polystyrene-divinylbenzene-carbon nanotube(PS-DVB-CNT) stationary phase was utilized for matrix elimination.A calibration study was conducted by preparing and analyzing eight concentrations(between 10 and 5000μg/L) of eight standards in deionized water.The linearity was between 0.9978 and 1.And the detection limits ranged from 1.54μg/L to 10.02μg/L.A spiking study was performed on two representative organic chemicals.The recoveries were between 84.3%and 119.6%.     

基于LTSPICE的手机充电器电路仿真设计实验

模拟电路的计算机辅助设计是电子类本科生的必备专业技能，本文采用LTSPICE软件对RCC结构手机充电器电路进行设计仿真，通过分析元器件模型及参数选取、电路启振和稳定工作过程，以及外部环境和元器件参数对电路性能的影响，实现了电路的计算机辅助设计和调试。该实验既能使学生理解简易的RCC开关电源的工作原理，又能掌握电路计算机仿真的方法。非常适合于模拟电路类课程实验。     

Thermally assisted switching in FePt single-domain particles with a Gaussian distribution of temperature

Magnetic nanoscale systems,including nanodots,nanofibers,nanowires and nanoparticles,are currently attracting great interest due to their interesting physical and promising applications in various fields,such as magnetic recording,sensors,target drugs and catalysts,as well as others.To achieve ultrahigh recording density,the method of heat assisted magnetic recording(HAMR) has been introduced.In this work,with the help of a Monte Carlo method,the mechanisms of thermally assisted magnetization switching in F...     

On the Implementation and Key Issues of an ATM Multiplexing Equipment

A brief introduction to the first ATM Multiplexing Equipment in China is given, which includes its characteristics, and architecture of hardware and software. Other topics such as the key issues in design and implementation of its parts, and the major techniques already acquired are also discussed. This paper is expected to be helpful for the research and development of the relevant ATM equipment.     

在分组网上开放POS业务

在介绍本地分组交换数据网现状的基础上，对在该网上开放POS业务的好处及有关技术方案进行了讨论。     

Negative differential resistance,rectifying performance and switching behaviour in carbon-chain based molecular devices

Using non equilibrium Green's function formalism coupled with density functional theory, we carry out electronic transport calculation in two types of molecular devices, one constructed by linear monoatomic carbon chain (···C–C–C–C ···) and the other by two carbon chains capped with a phenyl ring (···C–C–Ph–C–C···), sandwiched between two z-shape electrodes, constructed by zigzag-armchair-zigzag (zz-ac-zz) graphene nanoribbons (GNRs). The potential difference between the z-shape contacts can be varied by employing an external d.c. voltage source. Thus, one may observe the variation of conductivity through the channels. The current–voltage (I–V) characteristics of the proposed resistors show N-type negative differential resistance (NDR), within a particular voltage region. The figure of merit or PVR (peak to valley) ratio (I_peak/I_valley) gets significantly increased, on capping the chains with phenyl ring. A higher value of PVR in I–V characteristics enhances the possibility of applications utilizing NDR. The calculated I–V characteristic is asymmetric and the rectification ratio is found to be 7, in case of the linear carbon chain.The rectification ratio R(V) = I(V)/I(−V) is an important parameter which determines, its suitability as rectifying device. It has been demonstrated that on varying the conformation of the phenyl ring with respect to the plane of electrodes, the transport properties of the system can be modulated. Interestingly, I–V characteristics are asymmetric and show dual NDR peaks in perpendicular conformation of the phenyl ring, with respect to the electrodes in the (···C–C–Ph–C–C···) system. The figure of merit is found to be respectively 8 and 51 for the first and second NDR regions. The later value is extremely high, making it an excellent candidate for potential applications. Moreover, the multi peak NDR device may be widely used in multiple-valued logics. Only a limited number of multiple NDR peak molecular-based nano systems have so far been reported, which are quite complex; by contrast the present system seems to be quite simple. The physical phenomenon of NDR was explained in the light of molecular projected self-consistent Hamiltonian (MPSH) and also the evolution of the frontier molecular orbitals (HOMO–LUMO) as well as transmission under various external bias voltages.     

Enhancement of speed of digital operation in bacteriorhodopsin based photonic switch

Nonlinear absorption based photonic switching of probe laser beam transmissions at 640 and 410 nm, respectively, by the nanosecond pump pulses at 570 nm, in bacteriorhodopsin (bR) protein molecules, has been analyzed theoretically using rate equation approach. The speed of digital operation in bR-based photonic switch is shown to be enhanced from earlier reported kHz to MHz. Further, the switching response is shown to be improved by biasing the sample with an additional laser beam at 410 nm. The technique can directly be applied to other rhodopsin proteins with similar photocycle to perform fast switching. Analyses demonstrate the utility of slow photochromic materials, having some energy states with fast relaxation rate, to perform fast photonic switching.     

Diode rectification and negative differential resistance of dipyrimidinyl–diphenyl molecular junctions

Addressable Au/dipyrimidinyl–diphenyl/Au molecular junctions are fabricated using elastic polymer stamp-printing method. To study the charge transport, current–voltage measurements are carried out from 95 up to 295 K in vacuum under both dark and light conditions. Reversible diode rectification and negative differential resistance phenomena are observed. The rectification efficiency dramatically decreases upon temperature increase or light illumination. Theoretical calculations based on the non-equilibrium Green’s function method combined with the density functional theory is performed to elucidate the negative differential resistance behaviors. We show that the different rectification efficiency is caused by the interfacial asymmetry and the dipole effects. The negative differential resistance may be attributed to the variation of the coupling degree between the incident states of the Au electrodes and the molecular orbitals, which depends largely on the S–Au contact geometry. The direct tunneling and Fowler–Nordheim tunneling act as the main transport mechanisms for low and high bias regions, respectively. The barrier height depends largely on the light illumination, substrate temperature, and bias polarity. The distinctly different adsorbing nature of the Au/molecule interface may account for the performances.     

Unipolar resistive switching properties of amorphous Pr0.7Ca0.3MnO3 films grown on a Pt/Ti/SiO2/Si substrate

Amorphous Pr_0.7Ca_0.3MnO₃ (APCMO) films were grown on a Pt/Ti/SiO₂/Si (Pt–Si) substrate at temperatures below 500 °C and the Pt/APCMO/Pt–Si device showed unipolar resistive switching behavior. Conduction behavior of the low resistance state (LRS) of the Pt/APCMO/Pt–Si device followed Ohm's law, and the resistance in LRS was independent of the size of the device, indicating that the conduction behavior in LRS can be explained by the presence of the conductive filaments. On the other hand, the resistance in the high resistance state (HRS) decreased with increasing the device size, and the conduction mechanism in the HRS was explained by Schottky emission.     

光分组交换系统的结构研究

对光分组交换系统的几种结构进行了分类和比较研究,介绍了已研制成功的2.5Gbit/s光ATM交换实验系统的结构,给出了测试波形图,说明了工作机理。