Thermodynamics of alternating copolymer of styrene and CO in the 0—600 K region

The temperature dependence of heat capacity and the temperatures and enthalpies of physical transitions of the alternating copolymer of styrene and CO were studied in the 5—600 K region by the adiabatic vacuum and dynamic calorimetric techniques. The heat of combustion of the copolymer was measured at 298.15 K in a calorimeter with a static bomb and an isothermal shield. The thermodynamic parameters of glass transition and fusion were determined. The thermodynamic functions in the 0—550 K region and thermodynamic characteristics of the formation of the copolymer from simple substances at T = 298.15 K and p = 101.325 kPa were calculated. The thermodynamic parameters of alternating copolymerization in the bulk of styrene and CO were calculated in the 0—350 K region at a standard pressure.     

超大容量语音系统的存贮方法研究

提出了语音合成技术实现时的容量存贮问题,简要介绍了语音参数合成法中较优秀的线性预测编码方法,指出了它在实际应用中存在的困难,介绍了美国TI公司两种改进的预测编码算法MELP和CELP及相应硬件MSP50X3X系列语音合成器的原理,提出了一个应用系统实例,给出了详细的硬件和软件设计。     

A Capacity Analysis for the IEEE 802.11 MAC Protocol

The IEEE 802.11 MAC protocol provides shared access to a wireless channel. This paper uses an analytic model to study the channel capacity – i.e., maximum throughput – when using the basic access (two-way handshaking) method in this protocol. It provides closed-form approximations for the probability of collision p, the maximum throughput S and the limit on the number of stations in a wireless cell.The analysis also shows that: p does not depend on the packet length, the latency in crossing the MAC and physical layers, the acknowledgment timeout, the interframe spaces and the slot size; p and S (and other performance measures) depend on the minimum window size W and the number of stations n only through a gap g=W/(n–1) – consequently, halving W is like doubling n; the maximum contention window size has minimal effect on p and S; the choice of W that maximizes S is proportional to the square root of the packet length; S is maximum when transmission rate (including collisions) equals the reciprocal of transmission time, and this happens when channel wastage due to collisions balances idle bandwidth caused by backoffs.The results suggest guidelines on when and how W can be adjusted to suit measured traffic, thus making the protocol adaptive.     

Calculating thermodynamic properties from perturbation theory: II. An analytic representation for the square-well chain fluid

An analytic representation of thermodynamic properties of the freely jointed square-well chain fluid is developed based on the thermodynamic perturbation theory of Barker–Henderson, Zhang and Weitheim. By using a real function expression for the radial distribution function and incorporating structural information for square-well monomer of TPT1 model, an analytic expression for the Helmholtz energy of square-well chain fluid is expanded from Zhang’s analytic expressions for thermodynamic properties of square-well monomer. The expression leads to good predictions of the compressibility factor, residual internal energy and constant-volume heat capacity for 4-mer, 8-mer and 16-mer square-well fluids when compared with the Monte Carlo (MC) simulation results. The incorporating structural information for square-well dimer of TPT-D model is also calculated. To obtain the constant-volume heat capacity needed, NVT MC simulations were performed.     

球形钴离子模板缩聚物的制备及其吸附性能研究

以钴离子为模板,四乙烯五胺为功能基配体,反相悬浮聚合制备出球形钴离子模板缩聚物。该模板缩聚物对钴离子的吸附性能显著优于相应的非模板缩聚物。说明应用离子模板技术可提高普通吸附树脂的吸附性能。可望在环境、医学等领域获得实际应用。     

Reversed Annealing of Thermal Fractionated Polyethylenes by TMDSC

Polyethylene samples prepared by thermal fractionation (TF) were annealed in several consecutive cycles in a temperature modulated DSC (TMDSC) at a temperatures one °C below the peak temperatures, increased from cycle to cycle relative to these peaks. The transition enthalpy of each cooling cycle was greater or equal to that of the preceding heating cycle. The total heat-flows of each heating cycle corresponded to those of the samples in the reference state up until the vicinity of the annealing temperature. During the annealing, the heat capacities decreased to a lower value over a one minute period. The thermal memory effect caused by the thermal fractionation was eliminated by a small overheating of the material for a short time. The fast disappearance of the thermal memory by a relatively very small degree of heating above their melting temperature denies a long range physical separation of macromolecules by TF. This revised version was published online in July 2006 with corrections to the Cover Date.     

Capacity Analysis for Connection Admission Control in Indoor Multimedia CDMA Wireless Communications

In this paper, the capacity analysis for connection admission control is presented for the reverse-link transmission of a packetized indoor multimedia wireless communication system using direct sequence code division multiple access (DS/CDMA). Since CDMA is interference limited, the signal-to-interference-plus-noise ratio criterion is used to check if there is enough system resources (i.e., the CDMA channels and received signal power) for each new connection request. Taking into account the stochastical nature of multimedia traffic, the effective bit rate is used to characterize the resources required by each mobile user and a linear approximation is then used to find the total resources required by all the mobile users already admitted to the system and the new connection request. Transmission errors due to both base station buffer overflow and wireless channel impairments are considered. The capacity of multimedia traffic is determined in such a way that the utilization of the system resources is maximized and, at the same time, the required transmission bit error rate and transmission delay of all users admitted to the system are guaranteed. Computer simulation results are given to demonstrate the performance of the proposed method for capacity analysis.     

On Maximizing the Coverage of Catastrophic and Parametric Faults

The purpose of this paper is to analyze an optimization method to improve the testability of structural and parametric faults in analog circuits. The approach consists of finding an optimum sub-set of tests which maximizes the fault coverage with minimum cost. The method is based on covering a discrete set of intervals by taking advantage of strategies effectively used in digital synthesis. A simple application example is given to illustrate the proposal by studying the fault coverage obtained using different test sets on the ITC97 benchmark op-amp.     

三种多址蜂窝系统的容量及性能分析

从理论上推导了 FDMA、TDMA、CDMA制式的容量表达式 ,计算了 3种典型系统 AMPS、GSM和 Q- CDMA的容量关系 ,分析比较不同系统的通信性能 ,指出了移动通信系统的发展趋势     

磁性功能化酚醛树脂的合成及对金属离子的吸附性能

磁性功能化酚醛树脂的合成及对金属离子的吸附性能;环氧酚醛树脂;螯合;金属离子;溶胀;吸附容量;吸附动力学