基于多模误差切换的变步长盲均衡算法

利用多电平正交幅度调制(MQAM)信号的分布特点,提出了一种适合MQAM教字通信系统的新的基于多模误差切换的变步长盲均衡算法.仿真表明,针对巴西A广播信道和rural信道新算法具有更快的收敛速度和更小的剩余误差.     

基于MODBUS现场总线的滚塑设备控制系统

滚塑生产是塑料制品的主要生产方式。现有的滚塑设备已成为制约企业发展的关键因素。研制以PLC为核心控制元件、基于MODBUS协议的控制系统已迫在眉捷。着重介绍基于MODBUS现场总线的滚塑设备控制系统,它由上位机、PLC、变频器组成一个数字通信网络,可方便地实现对现场各参数的修改,将系统运行中出现的故障进行分级处理,并将各参数进行记录。将现场总线应用到滚塑设备的控制系统之后,既可以提高设备的智能化程度又能提高生产效率,同时增强了设备运行的可靠性、稳定性,使产品质量大大提高。利用现场总线PLC,PLD等现代化数控网络技术对滚塑设备进行革新和改造,显著提高现有设备的智能化程度。     

A Low‐Complexity 128‐Point Mixed‐Radix FFT Processor for MB‐OFDM UWB Systems

In this paper, we present a fast Fourier transform (FFT) processor with four parallel data paths for multiband orthogonal frequency‐division multiplexing ultra‐wideband systems. The proposed 128‐point FFT processor employs both a modified radix‐2⁴ algorithm and a radix‐2³ algorithm to significantly reduce the numbers of complex constant multipliers and complex booth multipliers. It also employs substructure‐sharing multiplication units instead of constant multipliers to efficiently conduct multiplication operations with only addition and shift operations. The proposed FFT processor is implemented and tested using 0.18 µm CMOS technology with a supply voltage of 1.8 V. The hardware‐ efficient 128‐point FFT processor with four data streams can support a data processing rate of up to 1 Gsample/s while consuming 112 mW. The implementation results show that the proposed 128‐point mixed‐radix FFT architecture significantly reduces the hardware cost and power consumption in comparison to existing 128‐point FFT architectures.     

定容燃烧器法热损失影响因素研究

推导了定容燃烧器法工作过程中热损失计算公式,通过实验对影响定容燃烧器法热损失各因素进行定性分析和定量研究.详细研究了推进剂试样的升压速率、燃烧时间、点火方式、燃速等对热损失的影响.研究表明:热损失随着燃烧器内升压速率的增大而减少;随着推进剂的试样燃烧时间减短而减少;合适的点火方式可以减少热损失;推进剂试样的燃速越快则热...     

定应变加速老化条件下HTPB衬层交联密度老化模型

为了对定应变贮存老化条件下端羟基聚丁二烯(HTPB)衬层横向弛豫特性和交联密度的变化规律进行研究,设计了0%、5%、10%、15%定应变水平下HTPB衬层的加速老化试验,采用低场~1H NMR CPMG序列对HTPB衬层的质子横向弛豫衰减曲线进行了测试,并根据修正的单链模型计算得到了HTPB衬层的交联密度,分析了交联密度的变化规律,同时建立了考虑物理拉伸和化学老化因素的交联密度老化模型,对老化模型参数的影响因素和变化规律进行了研究。结果表明,定应变贮存老化条件下HTPB衬层的交联密度呈现先增大后降低的趋势,定应变的存在会导致HTPB衬层的应力松弛时间增加,但是对HTPB衬层的老化反应速率常数没有显著的影响。建立的交联密度老化模型的具体形式为ν_(NMR)(ε,t)=ν_(p0)(ε)τ(ε)[1-exp(-t/τ(ε))]+ν_(ini)-k (ε) t,该模型与试验结果的相关系数R0.9500(5%定应变时相关系数R0.9000),可以用来描述定应变条件下HTPB衬层交联密度的老化规律。     

The influence of high energy electron irradiation on the Schottky barrier height and the Richardson constant of Ni/4H-SiC Schottky diodes

The influence of high energy electron (HEE) irradiation from a Sr-90 radio-nuclide on n-type Ni/4H–SiC samples of doping density 7.1×10¹⁵ cm⁻³ has been investigated over the temperature range 40–300 K. Current–voltage (I–V), capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) were used to characterize the devices before and after irradiation at a fluence of 6×10¹⁴ electrons-cm⁻². For both devices, the I–V characteristics were well described by thermionic emission (TE) in the temperature range 120–300 K, but deviated from TE theory at temperature below 120 K. The current flowing through the interface at a bias of 2.0 V from pure thermionic emission to thermionic field emission within the depletion region with the free carrier concentrations of the devices decreased from 7.8×10¹⁵ to 6.8×10¹⁵ cm⁻³ after HEE irradiation. The modified Richardson constants were determined from the Gaussian distribution of the barrier height across the contact and found to be 133 and 163 A cm⁻² K⁻² for as-deposited and irradiated diodes, respectively. Three new defects with energies 0.22, 0.40 and 0.71 eV appeared after HEE irradiation. Richardson constants were significantly less than the theoretical value which was ascribed to a small active device area.     

甲烷掺混氢气的燃烧特性试验研究

通过在定容燃烧室内研究不同的初始温度、初始压力、燃空当量比、掺氢比下甲烷-氢气-空气混合气的燃烧压力变化规律,得到了上述条件对混合气最大燃烧压力、最大压力升高率、火焰发展期、燃烧持续期以及最大燃烧压力循环变动的影响.研究结果表明:其他初始条件不变时,甲烷-氢气-空气混合气在高温低压时火焰传播的更快;随着甲烷中掺氢比增加...     

MgO含量对微波高Q介电材料电性能与微观结构的影响

借助典型的固相反应烧结机制,研究了MgO含量对微波高品质因数瓷介材料微观结构与介电性能参数影响的规律。结果表明:高温烧结的镁钛系瓷介质中,随着MgO含量增加,Mg2TiO4晶相的含量逐渐降低、瓷体晶粒由尖晶石型演变为氯化钠型结构,对应的微波介电常数出现缓慢降低,在10.10~13.37范围连续可调。当x=16时,在1 525℃/2 h烧成,可获得性能优良的(2+x)MgO-TiO2陶瓷,其ρ=3.49 g·cm–3,εr=10.37,Q·f=118 747 GHz(f=10.47 GHz),τf=–53.35×10–6℃–1。     

Determination of Optical Constant and Thickness for Thin Film by Using Improved FTM

A new method to determine the optical constant and thickness of thin films is proposed. Based on the Fresnel＇s optical expression, the improved flexible tolerance method（FTM） is employed in the case of a digital model of thin film to fit the curve of measured reflectance spectrum. The simulation results show a satisfactory correlation of the optical constant with the thickness of the target film. By taking the influence of nonlinear condition into account as well as more direct and indirect limitation, the precision and value-searching efficiency have been improved. Furthermore, the problem of dimension degradation, which exists in “Downhill Simplex”, has been successfully avoided. No initial input is needed for the procedure of optimization to achieve optical solution, which makes the whole processing of value calculation much more convenient and efficient.     

Spectral Efficiency Evaluation for MRC Diversity Schemes Over Generalized Rician Fading Channels

In this paper, closed-form expressions for the capacities per unit bandwidth for generalized Rician fading channels are derived for power and rate adaptation, constant transmit power, channel inversion with fixed rate, and truncated channel inversion adaptation policies. The closed-form solutions are derived for the single antenna reception (without diversity combining) and maximal-ratio combining (MRC) diversity cases. Truncated channel inversion adaptation policy is the best policy for the single antenna reception case, while the channel inversion with fixed rate policy is the best policy for the MRC diversity case. Constant transmit power policy provides the lowest spectral efficiency as compared to the other policies with and without diversity.