Multiple access interference cancellation in Manchester-coded synchronous optical PPM-CDMA network

A new interference cancellation technique for direct-detection optical code- division multiple-access (OCDMA) network employing pulse-position modulation (PPM) is proposed in this paper. The multiple access interference (MAI) estimation is achieved by pre-reserving one of optical spreading code sequences at the receiver based on the correlation property of padded modified prime codes (PMPC). The estimated interference is then cancelled out after photo-detection process. Additionally, the transmitted signal is Manchester-coded to further improve the system performance. Based on this proposed interference canceller in a shot-noise limited regime, we have obtained an expression for the upper bound of the bit-error probability (BEP) taking into account effects of both MAI and shot-noise. This BEP is compared with that of a PPM-OCDMA without cancellation. Finally, the receiver structure of the proposed optical network unit (ONU) is fairly simple to compare with the conventional cancellation schemes.     

工控系统中实时数据库关键技术研究与实现

文章介绍了在面向工业控制过程的实时监控系统建设中,实时数据库系统的设计。针对实时数据库系统的特点,分析了实时数据库的功能模块、存储结构、事务调度和并发控制等关键技术并给出了具体实现方法。在实现过程中采用了多媒体定时器、内存映射文件、多线程、同步对象等技术,保证了系统的稳定性和强实时性。     

I^2C串行总线存储技术在单片机系统中的应用

介绍I^2C串行总线原理及AT24CXX系列串行EEPROM的特点。着重阐述了利用I^2C串行总线和AT24CXX系列串行EEPROM实现数据存储的技术，并给出了该技术在MCS51系列单片机系统中的实现方法。     

Traffic shaping at the edge node in synchronous optical packet-switched networks

Long-range dependence, short-range dependence and marginal distribution are three key statistical features for incoming traffic, which have a serious impact on network performance. This paper respectively, studies their characteristics during traffic shaping at the edge node in synchronous optical packet-switched networks and highlights the functions of the First-Come-First- Service (FCFS) schedule queue for various offered loads and assembly parameters, including normalized timeout and normalized threshold. Simulation results demonstrate that under light-medium load the FCFS schedule queue works as a low pass filter, i.e., the statistical features before and after the FCFS schedule queue is nearly the same and each of the statistical features approximately follows the same trend. Heavy load drives the FCFS schedule queue into an overload or saturation state and the three statistical features all exhibit different behavior. By adjusting the assembly parameters, the deficiency can be modified.     

广东省黄埔港土壤中铬的价态分析研究

采用化学浸提技术对广东省黄埔港土壤中的铬进行了分析,研究了浸提条件及其对测定结果的影响,并运用GF-AAS法定量分析Cr(Ⅵ).检出限为0.03 μg/L,相对标准偏差(RSD,n=12)为1.52%,加标回收率在95.6%-103.6%.     

Minimal Modules Over Serial Rings

We investigate several model theoretic minimalities in the framework of modules over a given serial ring R.     

Investment optimization on port’s development by fuzzy integer programming

In this research, the main purpose is to formulate a model to determine the optimum investment on port development from national investment prospective; on the other hand, costs and benefits are calculated from consumer and investor’s viewpoint. The formulated model is an integer-programming model. The emphasis is on how to formulate an investment optimization problem where cargo operation, investment costs, cargo-handling capacity, cargo transportation network, and the world maritime fleet constraints are included. Fuzzy numbers are used for cargo forecast study results. The output of the model is the type of design ships and design berths which are needed in each sub period, so that the port planner (the government) will find out the optimum development plan of port in each sub period when there is uncertainty in cargo handling forecast (fuzzy numbers).     

A low-power readout circuit for nanowire based hydrogen sensor

This paper presents a fully integrated lock-in amplifier intended for nanowire gas sensing. The nanowire will change its conductivity according to the concentration of an absorbing gas. To ensure an accurate nanowire impedance measurement, a lock-in technique is implemented to attenuate the low frequency noise and offset by synchronous demodulation or phase-sensitive detection (PSD). The dual-channel lock-in amplifier also provides both resistive and capacitive information of the nanowire in separate channels. Measurement results of test resistors and capacitors show a 2% resolution in the resistance range 10-40 kΩ and a 3% resolution in the capacitance range 0.5-1.8 nF. Moreover, a 28.7-32.1 kΩ impedance variation was measured through the lock-in amplifier for a single palladium nanowire that was exposed to a decreasing hydrogen concentration (10% H₂ in N₂ to air). The chip has been implemented with UMC 0.18 μm CMOS technology and occupies an area of 2 mm². The power consumption of the readout circuit is 2 mW from a 1.8 V supply.     

一种MAC漂移检测功能的实现与应用

提出一种MAC漂移检测功能，该功能对端口间的MAC漂移进行实时统计，并根据统计结果作出适当处理，可以有效解决这一问题，并在多种实用场景中发挥重要作用。     

Pre-emption in resource-constrained project scheduling

The Resource-Constrained Project Scheduling Project (RCPSP), together with some of its extensions, has been widely studied. A fundamental assumption in this basic problem is that activities in progress are non-preemptable. Very little effort has been made to uncover the potential benefits of discrete activity pre-emption, and the papers dealing with this issue have reached the conclusion that it has little effect on project length when constant resource availability levels are defined. In this paper we show how three basic elements of many heuristics for the RCPSP – codification, serial SGS and double justification – can be adapted to deal with interruption. The paper is mainly focussed on problem 1_PRCPSP, a generalization of the RCPSP where a maximum of one interruption per activity is allowed. However, it is also shown how these three elements can be further adapted to deal with more general pre-emptive problems. Computational experiments on the standard j30 and j120 sets support the conclusion that pre-emption does help to decrease project length when compared to the no-interruption case. They also prove the usefulness of the justification in the presence of pre-emption. The justification is a RCPS technique that can be easily incorporated into a wide range of algorithms for the RCPSP, increasing their solution quality – maintaining the number of schedules calculated.