基于改进混沌扩频序列的多用户混沌扩频通信系统的研究与仿真

提出一种改进混沌扩频序列,并将其应用在多用户混沌扩频通信系统中,给出了多用户混沌扩频通信系统的理论推导和SIMULINK仿真模型。对该系统进行了详细的性能分析,包括信噪比、用户数、改进混沌扩频序列的分形参数和初始值等各自对系统误码率的影响,并比较了改进混沌扩频序列与传统混沌扩频序列的系统误码率随信噪比和用户数的变化情况。结果表明改进混沌扩频序列要好于传统混沌扩频序列的系统误码率,具有较好的抗噪声和抗多址干扰的能力。     

Context dependence of phenotype prediction and diversity in combinatorial mutagenesis

Two different combinatorial mutagenesis experiments on the light-harvestingII (LH2) protein of Rhodobacter capsulatus indicate that heuristicrules relating sequence directly to phenotype are dependenton which sets or groups of residues are mutated simultaneously.Previously reported combinatorial mutagenesis of this chromogenicprotein (based on both phylogenetic and structural models) showedthat substituting amino acids with large molar volumes at Gly^ß31caused the mutated protein to have a spectrum characteristicof light-harvesting I (LH1). The six residues that underwentcombinatorial mutagenesis were modeled to lie on one side ofa transmembrane -helix that binds bacteriochlorophyll. In asecond experiment described here, we have not used structuralmodels or phylogeny in choosing mutagenesis sites. Instead,a set of six contiguous residues was selected for combinatorialmutagenesis. In this latter experiment, the residue substitutedat Gly^ß31 was not a determining factor in whetherLH2 or LH1 spectra were obtained; therefore, we conclude thatthe heuristic rules for phenotype prediction are context dependent.While phenotype prediction is context dependent, the abilityto identify elements of primary structure causing phenotypediversity appears not to be. This strengthens the argument forperforming combinatorial mutagenesis with an arbitrary groupingof residues if structural models are unavailable.     

基于灰度匹配的序列影像的目标跟踪研究与实现研究

为了达到特定目标跟踪的目的,对视频帧进行匹配算法的处理。通过利用灰度匹配的算法在平台上对简单背景下的目标进行跟踪,来显示进行目标基本跟踪过程。对目标坐标系的转换、运算的速度和使用的范围进行讨论。     

Dipole moments of copolymers in relation to the distribution of polar monomer unit sequences

A method for evaluating the dipole moments of copolymers in relation to the distribution of polar unit sequences is proposed. Experimental data on the synthesis and dipole moments of styrene-p-chlorostyrene and styrene-p-methoxystyrene copolymers were used to calculate the effective dipole moment of a polar unit in a copolymer. For this purpose, we assumed the following effective moment values for the corresponding polar unit sequences along the copolymer chains: when both of the nearest neighbours are polar, μ_PP, when one of the nearest neighbours is polar and the other is non-polar, μ_PS, and when both of the nearest neighbours are non-polar, μ_SS. The relative magnitudes of μ_SS, μ_PS and μ_PP calculated for both copolymers reflect the influence of dipole-dipole interactions on the effective dipole moment of a polar unit in a copolymer molecule.     

Transformations and losses of fertilizer nitrogen on no-till and conventional till soils

A field study was conducted in 1982 to measure the effect of no-till (NT) and conventional till (CT) systems on N transformation after surface and subsurface applications of N fertilizers. Urea, urea-ammonium nitrate (UAN) solution, (NH₄)₂SO₄ (AS), and CA(NO₃)₂ were applied to NT and CT plots (5.95 m²) at a rate of 448 kg N ha^–1. A comparison of fertilizer N recovered in soils receiving incorporated or surface applied N was used to estimate NH₃ volatilization while denitrification was estimated from fertilizer N recovered in the presence and absence of nitrapyrin with incorporated N. Immobilization was assessed in microplots (0.37 m²) after surface application of (¹⁵NH₄)₂SO₄ to NT and CT systems at a rate of 220 kg N ha^–1.The results indicate little difference between NT and CT systems on urea hydrolysis rates and immobilization of surface applied fertilizer N. Approximately 50% and 10% of the surface applied N was recovered in the inorganic and organic fractions, respectively, on both tillage systems. The N not recovered was likely lost from plot areas through soil runoff. Incorporation of UAN, urea and AS resulted in 20 to 40% greater inorganic N recovery than from surface application. Nitrification rates were greater under the NT than the CT system. The similarities in concentration in the various N pools observed between the two tillage systems may be partially due to the short length of time that NT was imposed in this field study (<1 year) since other researchers using established tillage systems (>5 y) indicate that NT tends to promote decreased efficiency of fertilizer N.     

Lipase PS-catalyzed transesterification of citronellyl butyrate and geranyl caproate: Effect of reaction parameters

Pseudomonas sp. lipase PS was immobilized by adsorption and tested for its ability to catalyze the synthesis of citronellyl butyrate and geranyl caproate by transesterification in n-hexane. The reaction parameters investigated were: enzyme load, effect of substrate concentration, added water, temperature, time course, organic solvent, pH memory, and enzyme reuse. Yields as high as 96 and 99% were obtained for citronellyl butyrate and geranyl caproate, respectively, with 300 units (approx. 15% w/w of reactants) of lipase PS. Increasing amounts of terpene alcohol inhibited lipase activity, while excess acyl donor (triacylglycerol) concentration enhanced ester production. Optimal yields were obtained at temperatures from 30–50°C after 24-h incubation time. Yields of 90 and 99% were obtained for citronellyl and geranyl esters, respectively, with 2% added water. Solvents with log P values ≥ 2.5 showed the highest conversion yields. pH 7 and 6–8 seemed to be ideal for citronellyl butyrate and geraniol caproate, respectively. The lipase remained active after reusing 12 times.     

炭纤维载体表面快速固着机理研究

采用炭纤维作为生物膜载体材料进行了污水处理实验,对炭纤维载体表面快速固着机理进行了研究。研究发现,炭纤维能够在水中快速且大量的固着活性污泥微生物。采用表面积测定仪、扫描电镜和XPS研究了炭纤维的表面特征。结果显示,炭纤维的表面形貌、表面官能团及表面活性碳原子是影响炭纤维表面微生物快速且大量固着的主要因素。     

大跨双曲混凝土组合扭壳屋盖施工拆模优化分析

由于混凝土抗拉能力较差,双曲组合扭壳抵抗悬垂线方向的主拉应力控制至关重要.如果拆模顺序不当,可能会使壳体结构产生过大的拉应力.为解决此问题,以华工扭壳为例,对平行四边形底面双曲组合扭壳的满堂脚手架施工拆模顺序进行全面优化分析,并与工程实测进行对比,得出较为合理的拆模方式.     

基于视频的人体行走状态分析

提出了一种基于多视角的人体行走状态分析方法.首先,利用基于自适应背景更新的背景差分法检测出运动人体;其次,利用4向链码提取人体上半身质心运动轨迹的周期;最后,通过训练不同运动状态的周期得到对应的模糊集,根据隶属度函数判别慢走、走和跑3种运动状态.实验结果表明,该方法能够准确分析人体运动速度并判断其运动状态,并且对背景噪声、视角变化有良好的鲁棒性.     

基于PSK调制的扩频通信研究

基于PSK调制,以直接序列扩频通信系统为研究对象,在MATLAB仿真环境下分析了直接序列扩频前后的通信系统模型的误码率性能。给出了直接扩频通信系统误码率与信噪比的关系曲线,仿真结果表明,直接序列扩频信号要比不扩频信号,更准确、可靠,因此直扩系统具有更好的性能。