软件无线电中的A/D技术

Ａ／Ｄ变换器是软件无线电的关键器件,本文首先介绍了软件无线电的概念和原理,然后介绍了Ａ／Ｄ变换器的研究和存在的问题,最后从三个方面讨论了解决的办法。     

块交错方案在移动图像通信系统中的应用

提出了一种适合于卷积码的新的交错方案块交错方案,并对采用块交错方案的(2,1,3)卷积码在移动图像通信系统中的抗干扰性能进行了计算机模拟,且与周期交错方案的结果做了比较.模拟结果表明周期交错方案不适合于卷积码,而采用块交错方案的(2,1,3)卷积码可明显改善图像质量,大大提高了快衰落移动信道环境中图像通信系统的可靠性.     

替代定理的研究

教材中的替代定理存在很大的局限性和不完整性,没有考虑：如果被替换支路是受控源的控制电压或控制电流,将如何替代等问题。本文从被替换支路的特点入手,反替代定理分成三种形式加以论述,从而完善了替代定理。     

Coding of arbitrarily shaped video objects based on SPIHT

A new coding algorithm is proposed for encoding arbitrarily shaped video objects. This algorithm employs an object-based discrete wavelet transform to decompose the video object. The decomposed pyramid is entropy encoded with a modified set partitioning in hierarchical trees (SPIHT) algorithm called partial-SPIHT (P-SPIHT), which only encodes the coefficients belonging to the decomposed video objects. The performance of this algorithm shows that it is a competitive candidate for the standardisation of video object coding     

1030nm高重复频率纳秒脉冲全光纤放大器

采用脉冲调制的单模带尾纤输出的半导体激光器作为种子源,以掺镱光纤为增益介质,采用主振荡功率放大(MOPA)结构,实现了1030nm全光纤脉冲激光放大。脉冲重复频率在50～100kHz范围内可调,在重复频率50kHz时,实现了脉冲宽度为6.53ns,峰值功率为16.08kW的脉冲输出,相应的斜率效率为69%,输出激光的中心波长在1029.49nm。实验还研究了不同重复频率下输出激光脉冲的时域特性。该激光器的输出波长在激光雷达探测器的光谱响应范围内,可作为激光雷达发射光源。     

复数域网络编码中最大似然解码算法的改进

针对复数域网络编码中继网络,提出一种改进的中继处的最大似然解码算法。当传统的最大似然解码算法使用在复数域网络编码中继网络中时,计算复杂度会随着信息星座图映射方式的改变而大大增加。为了降低计算复杂度,在前人研究的基础上提出一种改进的最大似然解码算法,该算法利用无线中继网络通信系统的非对称性,在解码时,先进行预判决,然后进行精确判决,这样可以大大降低计算复杂度,提高了系统性能。     

基于UML的考试管理系统设计

利用计算机实现排考,简化了操作过程,提高了教务管理效率。文中着重解决UML在完成各阶段任务中的应用、分析设计流程等问题,就类图与时序图两者设计次序进行探讨。UML有利于各类人员之间的沟通,提高了系统建模的效率。     

一种军事假目标识别的新方法

通常的侦察手段对于军事假目标的识别能力有限,文中提出了一种新的军事假目标识别方法。在介绍偏振成像机理的基础上,分析了偏振信息检测和强度信息检测在物理含义中的区别。提出了获得偏振度图像的方法,通过理论分析,能够很好地分辨真假目标,证明了文中方法的科学性和可行性,对军事假目标的检测有重要意义。     

红外系统对飞行弹丸探测地点选取的模型方法

红外系统捕获飞行弹丸时,必须保证该系统对飞行弹丸的作用距离大于弹丸到红外系统的距离,分析了传统的红外系统作用距离计算公式,考虑了弹丸在飞行过程中与红外系统之间的距离会随着飞行时间变化,而红外辐射在大气中的衰减随着波长和传输距离不同而变化,因此红外系统接收到的弹丸辐射会在弹丸飞行过程中随着时间而变化;同时考虑到弹丸在飞行中系统接收的红外辐射受天空背景影响和弹丸截面等效面积的辐射影响,从而重新提出了红外系统的作用距离模型。在简单弹道模型的基础上,计算并分析理论飞行距离与系统作用距离相互影响的关系,获得红外系统对弹丸发射过程捕获的最佳位置,为红外系统探测飞行弹丸的地点选取提供理论依据。     

Subpicosecond Domain Switching in Discrete Regions of Pb(Zr0.35Ti0.65)O3 Thick Films

The time dependence of the domain switching current density, J_sw(t), under pulsed voltages on a ferroelectric parallel‐plate capacitor is the consequence of region‐by‐region polarization reversals across the film. As the distributive coercive voltage of domain nucleation increases from zero to the maximum applied voltage during the capacitor charging time, J_sw(t) is proportional to the domain switching speed at each time. By transforming the spatially inhomogeneous domain nucleation distribution into a temporal distribution of coercive fields (E_c), a local lnJ_sw versus E_c^?1 plot is derived for each domain, following the Merz equation. This provides insight into the independent domain switching dynamics at different nucleation sites in Pb(Zr_0.35Ti_0.65)O₃ thick films over a large current range. Although the activation field of the slope of the lnJ_sw(t) versus E_c^?1 plot varies with film area and temperature, all the plots extrapolate to a single point (J₀, E₀) from which the ultimate domain switching current density of J₀ =1.4 × 10⁸ A cm^?2 at the highest field of E₀ = 0.20‐0.25 MV cm^?1 is derived. Unexpectedly, J₀ and E₀ are independent of the film thickness and area, after correction for a small interfacial‐layer effect. This analysis provides rigorous evidence for nucleation rate‐limited domain switching with a subpicosecond nucleation time and the relative unimportance of domain forward‐growth time across film thicknesses between 0.14 and 2 μm. This work paves the way to improve the efficiency of ferroelectric thick‐film functionality in electronic and optoelectronic devices with ultrafast clock rates.