Olfactory Responses to Aphid and Host Plant Volatile Releases: (E)-β-Farnesene an Effective Kairomone for the Predator Adalia bipunctata

The volatiles released from several aphid and host plant species, alone or associated, were studied for their infochemical role in prey location. Using a four-arm olfactometer, the attraction of several combinations of three aphid (Myzus persicae, Acyrthosiphon pisum, and Brevicoryne brassicae) and three plant (Vicia faba, Brassica napus, and Sinapis alba) species toward Adalia bipunctata larvae and adults was observed. Both predatory larvae and adults were attracted only by A. pisum and M. persicae when they were crushed, whatever the host plant. (E)-beta-farnesene, the aphid alarm pheromone, was the effective kairomone for the ladybird. Plant leaves alone (V. faba, B. napus, and S. alba) or in association with nonstressed whole aphids (the three species) did not have any attraction for the predator. The B. brassicae specialist aphid is the only prey that was not attracted to A. bipunctata larvae and adults, even if they were crushed. Release of B. brassicae molecules similar to the host plant allelochemicals was demonstrated by GC-MS analysis. The lack of behavioral response of the ladybird at short distance toward the cruciferous specialist aphid was related only to the absence of (E)-beta-farnesene in the aphid prey volatile pattern.     

纳米多孔二氧化硅薄膜的制备及其光学性质研究

以正硅酸乙酯(TEOS)为先驱体，采用溶胶-凝胶法，结合旋转涂胶和超临界干燥等工艺，在硅片上制备了纳米多孔SiO2薄膜。XRD和AFM表明该SiO2薄膜为无定形态，具有多孔网络结构，表面均匀平整，其SiO2基本粒子和孔隙的直径为30～40nm。利用椭偏光谱仪测量了SiO2薄膜在波长245～1650nm的椭偏光谱，采用Si／cauchy／rough结构模型对该光谱进行了拟合，获得了SiO2薄膜的厚度和光学常数。SiO2薄膜的厚度为500～1100nm；折射率为1．13～1．21；孔隙率为56％～70％；介电常数为1．9～2．3。     

Re-estimation of absolute gamma ray intensities of ^56Mn using k0-standardization

The thermal neutron capture gamma ray facility at Pakistan Research Reactor （PARR-1） is being used for the re-estimation of various properties like capture cross-sections, resonance integral, absolute gamma intensities, etc. of different isotopes. The data for gamma ray transitions from the capture of thermal neutrons by ^55Mn are not in good agreement specifically below 2 MeV. So there is a need to re-estimate its intensities with better accuracy. Analytical grade MnCl2 powder and high purity Mn metal pieces were used in this study. Standard ^152Eu and ^60Co radioactive sources as well as thermal neutron capture γ-rays in chlorine were chosen for efficiency calibration. The k0 standardization technique was applied for these measurements to eliminate systematic errors in efficiencies. Chlorine also acted as a comparator in k0-factor calculations. The results have been tabulated for the main gamma rays from ^56Mn in the low as well as in the medium energy regions. The absolute intensities are in good agreement with most of the reported values.     

Correlation between structural and electrical properties of ZnO thin films

Thin ZnO films were deposited by radio frequency (r.f.) and direct current (d.c.) magnetron sputtering techniques onto glass substrates. Microstructural and electrical properties of ZnO films were studied using X-ray diffractometer (XRD), scanning electron microscope (SEM) and resistivity measurements. It was found that the size of the crystallites in the d.c. deposited films increased with increasing film thickness, while the crystallite size of r.f. deposited films remained unchanged. The d.c. deposited grains also had much stronger orientation related to the substrate than the r.f. films. XRD data indicated that the thin films with d<350 nm for r.f. and <750 nm for d.c. films have a very high degree of ZnO nonstoichiometry. This agreed well with the conductivity measurements and R(T) behaviour of the films with different resistance R. It was also found that the electrical resistivity of the samples increased exponentially with the thickness of films.     

抗几何攻击的小波变换域图像水印算法

综述了抗几何攻击的水印技术的研究现状,并提出了一个基于小波变换的有意义图像水印算法.该算法具有如下特点:(1)应用BCH编码和二维交织技术,具有纠正随机错误和突发错误的能力;(2)应用图像配准技术,能够抵抗旋转、缩放和平移(RST);(3)在512×512×8bits的图像中隐藏高达536bits的信息.实验结果表明:该算法所隐藏的水印不但可以对抗一般的信号处理,还可以抵抗RST、改变长宽比、小尺寸裁剪、随机去行去列和伴随裁剪的旋转等几何攻击.相对于目前的一些水印算法,本文算法具有隐藏数据量大和更好的特别是对抗几何攻击的稳健性等优点.     

Orlicz空间的单k点

给出了Ｏｒｌｉｃｚ空间中单ｋ点的判据，进而推出了ｘ１→Ｋ（ｘ）为单值的充分必要条件。     

第k条最大可用带宽路径算法

该文提出了无环路的第k条最大可用带宽路径算法．由于具有凹性的带宽和具有加性的代价存在本质区别，第k条最大可用带宽路径算法不能通过简单修改第k条最短路径算法得到．该文结合两个新定义的路径操作和修改的二重扫除算法完成第k条最大可用带宽路径算法，并证明其正确性、无环性和具有多项式复杂性，最后给出实例并讨论算法实际应用．该文解决了基于带宽度量的路由算法中一类很基本的问题；因算法采用能反映网络实时特性的可用带宽作为路由度量，能直接保证网络带宽资源的最优利用．     

一类k阶拟Bent函数密码性质的矩阵特征

由于非线性组合函数的密码性质通常可以由函数的Walsh谱和自相关函数来刻划，因而对函数的密码性质的分析通常要计算大量的Walsh循环谱值和自相关函数值来验证，该文利用一类k阶拟Bent函数的特殊性质，把对这类函数的密码性质的研究转化为对矩阵性质的研究，如平衡性、相关免疫性、扩散性、最高代数次数等，这种转化避开了大量的计算，同时为构造密码性质好的k阶拟Bent函数提供了一种更为简洁且易于实现的方法。     

基于密度的kNN文本分类器训练样本裁剪方法

随着WWW的迅猛发展，文本分类成为处理和组织大量文档数据的关键技术。kNN方法作为一种简单、有效、非参数的分类方法，在文本分类中得到广泛的应用。但是这种方法计算量大，而且训练样本的分布不均匀会造成分类准确率的下降。针对kNN方法存在的这两个问题，提出了一种基于密度的kNN分类器训练样本裁剪方法，这种方法不仅降低了kNN方法的计算量，而且使训练样本的分布密度趋于均匀，减少了边界点处测试样本的误判。实验结果显示，这种方法具有很好的性能。     

基于kNN的快速WEB文档分类

根据测试文档在各个样本类中的分布情况，发现了基于kNN分类的两个有助于减少大量计算的重要性质，在此基础上提出了两个重要算法：排类算法和归类算法，从而构建了一个基于kNN的快速Web文档分类方法．理论与实验表明，这种方法可以在不影响原有准确率的条件下，可提高文档的分类速度．