HIRFL新的束流分配系统

随着CSR的建成和兰州重粒子加速系统(HIRFL)实现质子加速,HIRFL现有的束流传输系统已不能满足越来越多的物理实验对供束时间的要求,为此,对原有的HIRFL的束流输运系统进行了分时供束改造,新的束流分配系统可以在给CSR供束和不供束两种情况下,同时使用SFC和SSC的束流在多个实验终端进行物理实验,介绍了新设计的HIRFL束流分配系统的布局和束流光学计算结果.     

高清晰度电视芯片中视频和音频同步的异步实现

高清晰度电视的传输流采用了MPEG－2系统层标准ISO／IEC 13818－1。阐述了高清晰度电视（HDTV）传送流中时间信息码在视频和音频同步中的作用，分析了信源解码器中视频和音频同步的原理。就实际芯片中系统时钟的恢复，视频和音频的跳帧等机制进行了讨论，并提出了一种非锁相异步全数字视音同步实现方案。该方案采用了直接置数法恢复系统时钟,滞后跳帧法实现视频与系统时钟的同步，数字锁相法控制音频与系统时钟同步，最后，对视频帧率和音频PCM时钟的偏差等问题作了进一步的探讨。     

高功率正交鉴相视放的设计

介绍用于气象雷达中的高功率正交鉴相器的组成，技术要求及设计，分析了影响性能的几个关键因素，由于采用计算机辅助设计，使得本模块达以了比较高的性能指标。     

适于ATM的分层视频编码

ＡＴＭ的统计复用特性，使信道资源得到充分利用；同时又要求其上的业务必须具备抗信元丢失的能力。在视频编码领域，可以通过分层编码减少信元丢失所造成的影响，保证在恶劣条件下实现正常的通信。对一种通用的视频编码器进行了改进，提高了视频编码器的压缩比，并且改善了其信元丢失性能。     

Uncertainty of chemical oxygen demand determination in wastewater samples

 The measurement uncertainty of the result of chemical oxygen demand determination in wastewater was evaluated. The major sources of uncertainty of the result of measurement were identified as the purity of reagents, volumetric operations, gravimetric operations, bias, and the repeatability of the method. Identification and evaluation of uncertainty sources was followed by combined uncertainty calculations. The combined uncertainty was compared to the experimentally determined variation and good agreement was found, indicating that the major uncertainty sources had been identified. The results show that the major sources of uncertainty arose from repeatability at high concentration level and volumetric steps at low concentration level, thus revealing the target operations for reducing the measurement uncertainty of this determination. Received: 5 August 2002 Accepted: 5 November 2002 Acknowledgements This research was supported by the Ministry of Education, Science and Sport of the Republic of Slovenia (Project Z2–3530). Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia Correspondence to A. Drolc     

我国第一辆模拟分量电视转播车

本文简述了几种分量电视方式,着重介绍我国第一辆模拟分量电视转播车的系统设计、技术性能和特色以及经第十一届亚运会的实际运用考验,充分显示出该车系统的优越性,并证明了它与现行彩色电视制式具有良好的兼容牲。     

Statistical multiplexing gain for variable bit rate video codecs in ATM networks

Asynchronous transfer mode (ATM) broadband networks will support variable bit rate video codecs, which are capable of maintaining a constant picture quality. To demonstrate this capability, a prototype hardware video coder has been developed in the Siemens Central Communications Laboratories. The prototype uses interframe coding, combined with a discrete cosine transform, and is able to reproduce the original picture quality, independent of signal sources or picture material used. A gain in transmission efficiency is expected when several video sources share a common ATM channel (‘statistical multiplexing’). This paper reports on a series of measurements that have been performed using this coder for a large variety of video sources to determine the possible gain in transmission efficiency. The main results are: for realistic video phone scenes, up to about three times the number of signals can be transmitted compared to transmision with constant rate and the same picture quality, if the output signal of the coder has been smoothed over a period of one frame. Smoothing over shorter periods reduces the potential gain substantially. The statistical multiplexing gain increases with the duration of the picture sequences due to the criterion of constant picture quality. It varies very little with the acceptable packet loss rate.     

Joint pricing and inventory control with a Markovian demand model

We consider the joint pricing and inventory control problem for a single product over a finite horizon and with periodic review. The demand distribution in each period is determined by an exogenous Markov chain. Pricing and ordering decisions are made at the beginning of each period and all shortages are backlogged. The surplus costs as well as fixed and variable costs are state dependent. We show the existence of an optimal (s, S, p)-type feedback policy for the additive demand model. We extend the model to the case of emergency orders. We compute the optimal policy for a class of Markovian demand and illustrate the benefits of dynamic pricing over fixed pricing through numerical examples. The results indicate that it is more beneficial to implement dynamic pricing in a Markovian demand environment with a high fixed ordering cost or with high demand variability.     

A mild and efficient palladium–triethylsilane system for reduction of olefins and carbon–carbon double bond isomerization

The versatility of palladium(II) acetate and palladium on activated charcoal catalysts with triethylsilane has been investigated in the hydrogenation and the isomerization of carbon–carbon double bond of 1‐alkenes. The reduction of 1‐alkenes was carried out in the presence of triethylsilane, ethanol and a catalytic amount of palladium(II) acetate or palladium on activated charcoal, at room temperature. This facile and efficient method affords high yields for hydrogenation of unsaturated alkenes to the corresponding alkanes. Then the carbon–carbon double bond isomerization of 1‐alkenes was tested using the same catalysts in the absence of solvent. The system palladium(II) acetate‐triethylsilane was found to be more effective compared with palladium on an activated charcoal–triethylsilane system at room temperature, while comparable results were obtained at 50 °C for both catalysts. Copyright © 2006 John Wiley & Sons, Ltd.