用于GSM系统的低复杂度ML检测的双层LDPC码

为降低最大似然(maximum-likelihood,ML)检测在广义空间调制(generalized spatial modulation,GSM)系统中的复杂度,提出了双层低密度奇偶校验(two-layer low-density parity-check,TL-LDPC)码,并且对TL-LDPC编码的GSM系统和常规低密度奇偶校验(low-density parity-check,LDPC)编码的GSM系统分别做了仿真试验。结果表明,在误码率轻微增高的前提下,TL-LDPC编码的GSM系统中ML检测的复杂度远低于常规LDPC编码的GSM系统。     

基于LDPC的不均等错误保护H.264抗误码算法

从最新的H.264视频压缩标准出发,提出一种基于数据分类和LDPC的不均等错误保护的策略。根据H.264数据分类中信息比特重要性的不同,对其进行不均等错误保护,即对信道中优先级较高的数据,采用码率低,抗误码性能更好的LDPC编码传输,以提高传输效率。仿真结果表明,这种联合的信源信道编码算法在AWGN信道下具有比以前的一般算法(如Turbo码)更好的适应性和更强的健壮性。     

联合LDPC码和网络编码的协作通信技术

结合信道编码和网络编码的思想,提出了一种在两用户协作情况下联合LDPC(low-density parity-check)码和网络编码的协作分集方案,该方案在接收端通过基于整体H矩阵的置信传播算法实现LDPC码和网络编码的联合译码,并对该方案在瑞利慢衰落信道下的性能进行了MATLAB仿真。仿真结果表明:与编码协作和不协作方案相比,所提方案在系统误码率性能上有着明显地改善。     

Tight lower bound of consecutive lengths for QC-LDPC codes with girth at least ten

For an arbitrary (3,L) quasi-cyclic(QC) low-density parity-check (LDPC) code with girth at least ten, a tight lower bound of the consecutive lengths is presented. For an arbitrary length above the bound the corresponding LDPC code necessarily has a girth at least ten, and for the length equal to the bound, the resultant code inevitably has a girth smaller than ten. This new conclusion can be well applied to some important issues, such as the proofs of the existence of large girth QC-LDPC codes, the construction of large girth QC-LDPC codes based on the Chinese remainder theorem, as well as the construction of LDPC codes with the guaranteed error correction capability.     

Molecular pathogenesis of apolipoprotein E-mediated amyloidosis in late-onset Alzheimer’s disease

Apolipoprotein E (apoE) ɛ4 allele is a genetic risk factor for late-onset familial and sporadic Alzheimer’s disease (AD). In the central nervous system, apoE is secreted mainly by astrocytes as a constituent of high-density lipoproteins. A recent study using apoE knockout mice provided strong evidence that apoE promotes cerebral deposition of amyloid β protein (Aβ). However, no clear explanation of the pathogenesis of apoE-induced AD has been provided. Here we discuss two possible mechanisms by which apoE might enhance Aβ deposition. One is the intracellular pathway in which apoE is internalized by neurons and induces lysosomal accumulation of Aβ and amyloidogenic APP (amyloid precursor protein) fragments, leading to neuronal death. The other is the extracellular pathway in which apoE-containing lipoproteins are trapped by Aβ1–42 deposits mobilizing soluble Aβ peptides and consequently enlarge amyloid plaques. These two mechanisms may operate at different stages of AD pathogenesis and suggest a chaperone-like function for the apoE molecule. Received 4 February 1999; received after revision 9 April 1999; accepted 23 April 1999     

Interaction of lipid transfer protein with plasma lipoproteins and cell membranes

Summary The hydrophobic lipid components of lipoproteins, cholesteryl ester and triglyceride, are transferred between all lipoproteins by a specific plasma glycoprotein, termed lipid transfer protein (LTP). LTP facilitates lipid transfer by an exchange process in which cholesteryl ester and triglyceride compete for transfer. Thus, LTP promotes remodeling of the lipoprotein structure, and plays an important role in the intravascular metabolism of these particles and in the lipoprotein-dependent pathways of cholesterol clearance from cells. The properties of LTP, its mechanisms of action, its roles in lipoprotein metabolism, and its modes of regulation are reviewed along with recent data that suggest a possible role for this protein in directly modifying cellular lipid composition.     

Scavenger receptor family proteins: roles for atherosclerosis, host defence and disorders of the central nervous system

In this review, we summarize the structure and function of the scavenger receptor family of proteins including class A (type I and II macrophage scavenger receptors, MARCO), class B (CD36, scavenger receptor class BI), mucinlike (CD68/macrosialin, dSR-CI) and endothelial (LOX-1) receptors. Two motifs have been identified as ligand-binding domains a charged collagen structure of type I and II receptors, and an immunodominant domain of CD36. These structures can recognize a wide range of negatively charged macromolecules, including oxidized low-density lipoproteins, damaged or apoptotic cells, and pathogenic microorganisms. After binding, these ligands can be either internalized by endocytosis or phagocytosis, or remain at the cell surface and mediate adhesion or lipid transfer through caveolae. Under physiological conditions, scavenger receptors serve to scavenge or clean up cellular debris and other related materials, and they play a role in host defence. In pathological states, they mediate the recruitment, activation and transformation of macrophages and other cells which may be related to the development of atherosclerosis and to disorders caused by the accumulation of denatured materials, such as Alzheimer's disease. Received 17 September 1997; received after revision 16 March 1998; accepted 17 March 1998     

中华猕猴桃营养生物学效应研究——Ⅱ.浓缩果汁对家兔血清脂蛋白和高密度脂蛋白胆固醇及其亚组分的效应

采用琼脂糖凝胶电泳分析法和PEG化学沉降分析法,对口服中华猕猴桃浓缩果汁家兔血清脂蛋白组分和高密度脂蛋白胆固醇及其亚组分的动态变化进行实验观察。结果表明,持续30d口服浓缩果汁血清总胆固醇呈明显下降,高密度脂蛋白亚组分胆固醇HDL2-C/HDL3-C比率明显升高。凝胶电泳分析结果,α-脂蛋白与β-脂蛋白的比值明显升高。     

删余LDPC与OFDM联合编码调制算法

为了降低正交频分复用(OFDM)系统中信道的时变导致的高误码平台,提出一种联合编码调制算法。该算法利用低密度校验码(LDPC)对删除信道的优良特性,将LDPC编码删余比特进行预编码,映射为零调制符号,辅助调制解调器减轻子载波间干扰(ICI)自干扰。仿真结果表明:与分离的编码调制相比,在相同传输速率条件下,该方法降低时变信道导致的LDPC误码平台达3个数量级以上。该联合编码调制算法可明显提高宽带无线通信系统在高速移动环境下的性能。     

退火条件对LDPE空间电荷特性的影响研究

使用冷却速率不同的3种退火方法制备了不同微观形态的LDPE薄膜,对薄膜试品进行了显微观测,并运用傅立叶红外分析对3种试品的结晶度进行了比较,同时使用PEA空间电荷测量技术对不同电场下这3种试品的空间电荷分布进行了观测,并基于结晶度和微观形态对LDPE空间电荷特性做了讨论.研究结果表明施加电场撤压后,高速冷却试品比低速冷却试品和正常冷却试品积聚更多的空间电荷,而随着撤压时间的增加,低速冷却试品中积聚的空间电荷衰减得最快.