Theoretical investigation of isotopic scrambling mechanisms in 2-chloroethyl methyl sulfide

Ab initio and semiempirical molecular orbital calculations have been applied to study the concerted and stepwise isotopic scrambling mechanisms of 2-chloroethyl methyl sulfide in the gas phase and in aqueous solution. The calculations reveal the structural details of the reactants, transition structures, and intermediates involved in this reaction and provide relative energy estimates. The concerted mechanism is found to be competitive with the stepwise mechanism in the gas phase, but the stepwise mechanism is favored in aqueous solution as no true transition structure for the concerted mechanism could be found using the solvation models. A combined approach of evaluating solvation energies with the generalized-Bom-plus-surface-tensions SM _x solvation models of Cramer and Truhlar at ab initio optimized geometries is found to deliver the best agreement with experimentally determined reaction barriers. Together with the recent experimental results of McManus and co-workers, the present study provides insights into the controlling factors involved in the elementary reaction steps of sulfur mustards and a solid foundation for investigations into more complex reactions of related compounds.     

视频信号行旋转加解扰的实现

采用ｉＳＰＬＳＩ完成了视频加解扰处理，并将视频行内分割点数目增加到８个，使图像加扰效果更佳．同时采用数字补偿技术很好地解决了图像恢复时视频切割点存在裂缝的问题．     

一种基于函数变换的数字图象置乱新方法

本文提出了一种新的置乱度定义，该定义能较明确地衡量置乱图像的均匀与细密程度，并使用它柬衡量本文中的置乱实验的效果；提出了一种基于初等函数变换的图像置乱新方法，具有易于实现、复杂性低、密钥空间大、只需一次运算即可达到很好的置乱效果等特点．     

水印图像的混沌置乱算法

利用混合光学双稳混沌序列的伪随机性和初值敏感性,提出一种用于数字水印中的水印图像置乱算法.该算法针对水印图像,没有使用过多的额外技术,所以算法的复杂度较低;因为混合光学双稳混沌序列的伪随机特性,所以图像置乱的效果比较理想;混沌序列对初值具有敏感性,因此提高了置乱算法的安全性,使水印的安全依赖于密钥,且只需1个密钥,不同于logistic混沌序列需2个密钥.在数字水印技术中使用这种置乱技术,可以有效抵抗例如剪切等集中式攻击,使水印更具鲁棒性.     

基于矩阵变换的数字图像置乱技术

以图像信息安全问题为背景,在Arnold变换的基础上,提出了密钥控制下新的利用矩阵变换对数字图像进行置乱与恢复的技术.结果表明:在图像信息隐藏中,这种技术能达到较好的加密与解密效果,而且易于实现,具有应用价值.     

一种基于DCT域MPEG2的透明加扰算法

提出一种新的在DCT域实现的透明加扰算法，按照特定规律修改Intra帧的DCT系数，再利用帧间预测将加扰效果扩散至所有帧，最终实现视频的无级扰乱。实验结果表明，该算法克服了以往空域加扰算法造成压缩效率下降的不足，具有很好的加扰效果，可广泛应用于DVB、ATSC等基于MPEG2压缩的视频系统中。     

A 31P NMR STUDY OF TERTIARY PHOSPHINE COMPLEXES OF PLATINUM(II) AND PALLADIUM(II)

Complexes of the type NBu ₄ MCl ₃ PR ₃ R=P.Tolyl,Ph,Bu) (M = Pt, Pd) are prepared by the reaction of MCl ₂ or K ₂ [MCl ₄ ] by phosphine ligands. Addition of NBu ₄ Br or NBu ₄ I to these compounds, in dichloromethane results in a redistribution of halogens and formation of all six isomers of the type MBr _{3 ?X}Cl_XPR ₃ X= 0, 1, 2, and 3 which have been identified by ³¹ P- ¹ H NMR spectroscopy. The intensities show that the products are proportional to the statistical distribution.     

The Family of Ferrocene‐Stabilized Silylium Ions: Synthesis, 29Si NMR Characterization,Lewis Acidity,Substituent Scrambling,and Quantum‐Chemical Analyses

The purpose of this systematic experimental and theoretical study is to deeply understand the unique bonding situation in ferrocene‐stabilized silylium ions as a function of the substituents at the silicon atom and to learn about the structure parameters that determine the ²⁹Si NMR chemical shift and electrophilicity of these strong Lewis acids. For this, ten new members of the family of ferrocene‐stabilized silicon cations were prepared by a hydride abstraction reaction from silanes with the trityl cation and characterized by multinuclear ¹H and ²⁹Si NMR spectroscopy. A closer look at the NMR spectra revealed that additional minor sets of signals were not impurities but silylium ions with substitution patterns different from that of the initially formed cation. Careful assignment of these signals furnished experimental proof that sterically less hindered silylium ions are capable of exchanging substituents with unreacted silane precursors. Density functional theory calculations provided mechanistic insight into that substituent transfer in which the migrating group is exchanged between two silicon fragments in a concerted process involving a ferrocene‐bridged intermediate. Moreover, the quantum‐chemical analysis of the ²⁹Si NMR chemical shifts revealed a linear relationship between δ(²⁹Si) values and the Fe???Si distance for subsets of silicon cations. An electron localization function and electron localizability indicator analysis shows a three‐center two‐electron bonding attractor between the iron, silicon, and C′_ipso atoms, clearly distinguishing the silicon cations from the corresponding carbenium ions and boranes. Correlations between ²⁹Si NMR chemical shifts and Lewis acidity, evaluated in terms of fluoride ion affinities, are seen only for subsets of silylium ions, sometimes with non‐intuitive trends, indicating a complicated interplay of steric and electronic effects on the degree of the Fe???Si interaction.     

Dioxygen Activation by Siloxide Complexes of Chromium(II) and Chromium(IV)

The reaction of a tripodal trisilanol with n‐butyllithium and CrCl₂ results in a dinuclear Cr^II complex ( 1 ), which is capable of cleaving O₂ to yield in a unique complex ( 2 ) with an asymmetric diamond core composed of two Cr^IV?O units. Magnetic susceptibility data reveal significant exchange coupling of Cr^II (S=2) in 1 and large zero‐field splitting for Cr^IV (S=1) in 2 owing to strong spin–orbit coupling of the ground state. The Cr^IV?O compound can also be generated using PhIO, and evidence was gathered that although it is the stable product isolated after excessive O₂ treatment, it further activates O₂ to yield an intermediate species that oxidizes THF or Me‐THF. By extensive ¹⁸O labeling studies we were able to show, that in the course of this process ¹⁸O₂ exchanges its label with siloxide O atoms of the ligand via terminal oxido ligands.     

基于图像重组和比特置乱的多图像加密

针对现有多图像加密算法只能同时加密多张同类型同大小的图像,适用范围不广、实用性差等问题,提出一种基于图像重组和比特置乱的多图像加密算法.该算法通过将任意数量、不同大小和不同类型的图像重新组合成新多灰度图,一次完成同时加密,极大提高了加密效率和适用范围.首先,依次提取所有待加密图像像素值重新组合出N张m×n新灰度图,并将其转化成m×n×8N二进制矩阵.然后,采用3D比特置乱方式,对高位页进行行列比特置乱,低位页进行整页比特置乱.最后,进行异或扩散操作,得到密文图像.高低位分开置乱提高了算法的抗噪声能力,最终密文信息熵达到7.999以上,很好地掩盖了明文的统计特性.构造一种新型Logistic与广义三阶Fibonacci级联的混沌系统产生随机序列,增加了初值和控制参数范围,扩大了密钥空间,使其达到8×10^84以上,极大地提高了抗穷举攻击能力.既提高了序列随机性,又同时保留了低维混沌系统的快速性.结合明文哈希值(SHA-256)产生密钥,明文像素值发生微小改变后密文像素值变化率达到0.996以上,极大地提高了的明文敏感性和算法抗选择明文攻击的能力.实验分析表明,提出的多图像加密算法安全性高、实用性强.