基于准正交空时分组码的高速率码字设计

为了适应通信系统对高速率大容量的需求,设计了码率为2及1.5的非正交空时分组码。在此基础上,采用简化了的条件最大似然译码方法,可以大大降低译码复杂度。仿真结果表明,该编码设计具有接近实际信道容量的特点,并且其误比特率性能优于正交及准正交编码设计。     

Multi-Gbit/s 60 GHz Transceiver Analysis Using FDM Architecture and Six-Port Circuit

This paper presents an analysis and validation by advanced system simulation of compact and low-cost six-port transceivers for future wireless local area networks （WLANs） operating at millimeter-wave frequencies. To obtain realistic simulation results, a six-port model based on the measurement results of a fabricated V-band hybrid coupler, the core component, is used. A frequency-division multiplexing scheme is used by introducing four quadrature phase-shift keying （QPSK） channels in the wireless communication link. The data rate achieved is about 4 Gbit/s. The operating frequency is in the 60-64 GHz unlicensed band. Bit error rate （BER） results are presented, and a comparison is made between single-carrier and multicarrier architectures. The proposed wireless system can be considered an efficient candidate for millimeter-wave communication systems operating at quasi-optical data rates.     

分类器的分类性能评价指标

通过具体应用实例,指出目前普遍使用的正确率和错误率评价指标在不平衡数据集、语义相关多分、不同错分代价等分类问题中评价分类器性能时存在的缺陷。为了解决这一问题,根据具体问题的不同,提出了综合使用查准率、查全率、漏检率、误检率、F-measure和分类代价矩阵、损失函数等新的分类器性能评价指标。通过实验证明,新的分类评价指标确实能很好的适应不平衡数据集、语义相关多分、不同错分代价等分类问题的分类器性能评价。     

超音速喷嘴涡流管气体分离性能的数值模拟与实验

 建立了超音速喷嘴涡流管的简化几何模型,利用描述两相双组分超音速冷凝流动的 Eulerian 双流体三维湍流模型,以含湿空气为介质对装置内部的自发凝结过程进行数值模拟。设计制造相应的装置,建立实验平台,对装置的含湿气体分离性能进行实验研究。通过模拟和实验2种手段研究了影响超音速喷嘴涡流管气体分离性能的参数及其影响规律。结果表明,气流在喷嘴内部达到超音速流动,使得水蒸气自发凝结成液滴,为混合气体分离提供了先决条件;热端管内气体自旋产生的离心加速度可以达到重力加速度的6×10⁵倍,为气、液分离提供了必要条件;降低进出口压力之比和冷流率,增大入口相对湿度和长径比可以提高装置的气体分离性能,安装阻涡器对性能有不利影响。因此,采用超音速喷嘴涡流管实现混合气体中重组分的脱除是可行的。     

稠油冷采泡沫油中气泡成核生长机理研究

在加拿大、委内瑞拉以及中国的一些稠油油藏开发过程中,显示出异常的"泡沫油"开发特征。国内外已提出一些理论来解释这种异常现象,但很少从微观角度来分析其形成的深层原因。在研究油相中气泡成核、生长规律的基础上,建立并求解了在水动力和扩散力综合作用下稠油油相中单气泡生长的数学模型,描述了稠油和稀油中所表现出的不同气泡生长现象,解释了产生稳定泡沫油现象的原因。     

塔里木盆地大涝坝凝析气处理装置的参数优化

塔里木盆地大涝坝凝析气处理装置的天然气设计处理量为25×10⁴ m³/d,而目前该装置的天然气实际处理量增至40×10⁴ m³/d,原料气的组成也有所变化,天然气变富,进气压力降低且生产装置的运行参数也与设计参数有一定偏差,导致装置的C₃及C₃⁺回收率仅为70%和81%。为此,借助模拟软件HYSYS分析了天然气经膨胀机组膨胀后的压力、低温分离器温度、脱乙烷塔理论塔板数、脱乙烷塔底重沸器温度、脱乙烷塔的进料位置和脱乙烷塔的进料温度对C₃及C₃⁺回收率的影响,并论述了在现有装置条件下对上述参数进行优化的可行性。优化结果表明：在优化条件下C₃及C₃⁺回收率分别得到大幅提高,C₃的回收率由原来的70%提高到现在的85%,增加了15%;C₃⁺的回收率也由原来的81%提高到现在的91%,增加了10%。     

高温高压下金刚石成核机制的研究

本文以国产六面顶压机作为人造金刚石的合成设备,采用金属粉末触媒技术,进行了金刚石晶体的合成.实验中,通过对生长工艺的调整,考察了金刚石在合成区间内的不同合成习性.实验结果表明:金刚石的合成区间可以根据能否自发成核而分为成核区与生长区.在生长区内,金刚石不能自发成核,但金刚石晶种可以在此区间稳定存在并长大.在生长区内金刚...     

Experimental determination of grain density function of AZ91/SiC composite with different mass fractions of SiC and undercoolings using heterogeneous nucleation model

The grain density,Nv,in the solid state after solidification of AZ91/SiC composite is a function of maximum undercooling,ΔT,of a liquid alloy.This type of function depends on the characteristics of heterogeneous nucleation sites and number of SiC present in the alloy.The aim of this paper was selection of parameters for the model describing the relationship between the grain density of primary phase and undercooling.This model in connection with model of crystallisation,which is based on chemical elements diffusion and grain interface kinetics,can be used to predict casting quality and its microstructure.Nucleation models have parameters,which exact values are usually not known and sometimes even their physical meaning is under discussion.Those parameters can be obtained after mathematical analysis of the experimental data.The composites with 0,1,2,3 and 4wt.% of SiC particles were prepared.The AZ91 alloy was a matrix of the composite reinforcement SiC particles.This composite was cast to prepare four different thickness plates.They were taken from the region near to the thermocouple,to analyze the undercooling for different composites and thickness plates and its influence on the grain size.The microstructure and thermal analysis gave set of values that connect mass fraction of SiC particles,and undercooling with grain size.These values were used to approximate nucleation model adjustment parameters.Obtained model can be very useful in modelling composites microstructure.     

Effects of novel self-inoculation method on microstructure of AM60 alloy

A novel cast processing method,self-inoculation method (SIM),was proposed.The process involves the addition of self-inoculant to melt,then pouring the melt to a mould through a multi-stream mixing cooling channel.In this paper,the process parameters were investigated.Results indicate that the melt treatment temperature,the amount of self-inoculant added,and the slope angle of the cooling channel are the key factors for SIM process.The optimized parameters are that the melt treatment temperature is between 680 and 700°C;the addition of self-inoculant is between 5wt.% and 7wt.%;and the slope angle of the cooling channel is between 30° and 45°.Further analysis reveals that SIM changes the solidification microstructure of slurry by controlling the nucleation and growth of the primary phase in the melt.     

Application of ultrasound for start‐up of evaporative batch crystallization of ammonium sulfate in a 75‐L crystallizer

A positive effect of ultrasound on crystallization has been shown for many applications especially on small scale. Predictable scale‐up of sonocrystallization is a challenge due to the inherent dependency of ultrasound on scale. The presented research discusses the experimental application of ultrasound to induce nucleation at low supersaturation for start‐up of evaporative batch‐wise crystallization of ammonium sulfate in a 75‐L draft tube (DT) crystallizer. A comparison is made with a conventional start‐up procedure using primary nucleation or seeding. Ultrasound is applied in two geometrically different vessels of 1.2‐L connected to a 75‐L DT crystallizer. Application of ultrasound for start‐up of a 75‐L DT crystallizer shows that an optimum amount of ground seeds is better capable to suppress nucleation. A challenge for future research is to improve the efficiency of ultrasound to produce a large number of nuclei for start‐up of batch crystallization at larger scale. © 2011 American Institute of Chemical Engineers AIChE J, 2011