A theoretical characterization of the structure formation enthalpy,and fluzional behaviour of B2H6 and AlBH6

Summary A comprehensive study of the binary association complexes B₂H₆ and AlBH₆ has been performed by ab initio molecular orbital theory. Reliable formation enthalpies can be computed only be extended basis sets and a reasonably complete account of correlation. The greater stability towards neutral dissociation of AlBH₆ with respect to B₂H₆ obtained at the Hartree-Fock level employing the 6-21G^* basis set ( 10 kcal/mol) is reduced to only 2 kcal/mol when the basis set is sufficiently saturated and correlation energy properly included. The value of the activation energy for hydrogen scrambling in AlBH₆ is much less sensitive to the method used, although correlation still plays a significant rôle reducing the potential energy barrier from 11.4 to 7.7 kcal/mol.     

基于HVS的小波域信息隐藏方法

为了提高信息隐藏的不可感知性和鲁棒性,结合人眼视觉系统(HVS)的相关知识,提出了一种新的小波域信息隐藏算法。将载体图像的中等亮度区域设为不可用区域,不在该区域隐藏信息,同时选择在载体图像小波变换的高频系数细节子图隐藏信息,并优先选择在对角高频系数细节子图中隐藏。计算局部子块的方差值作为隐藏信息的嵌入系数,并通过计算高频子图的噪声敏感模型ωθ(i,j)决定隐藏信息的位置。充分考虑了人眼的各种视觉掩蔽效应,使得隐藏信息后的结果图像相比隐藏之前没有出现明显的降质。实验结果表明该方法能够有效提高信息隐藏的不可知性,达到了很好的隐藏效果,同时能够有效地抗击噪声、裁剪和压缩等攻击影响,具有很好的鲁棒性,在信息安全领域有较好的应用前景。     

Double image encryption by using Arnold transform and discrete fractional angular transform

Based on Arnold transform and discrete fractional angular transform, a double image encryption algorithm is designed. Two original images are regarded as the amplitude and phase of a complex function. Arnold transform is introduced for scrambling the pixels at a local area of the complex function. Subsequently the changed complex function is converted by discrete fractional angular transform. The operations mentioned will be performed many times. The amplitude of final output complex function is the encrypted image and its phase is regarded as the key of encryption algorithm. The parameters of the two transforms serve as the additional keys for enhancing the security. Some numerical simulations have been done to validate the performance of this encryption scheme.     

Simple route to meso-substituted trans-A2B2-porphyrins bearing pyridyl units

We have developed a methodology that affords regioisomerically pure trans-A₂B₂-porphyrins bearing pyridyl substituents. The optimal conditions for their synthesis were identified by the modification of known conditions for the reaction of dipyrromethanes with aromatic aldehydes. A total of five new porphyrins were synthesized.     

Specific Processes and Scrambling in the Dehydrogenation of Ethane and the Degenerate Hydrogen Exchange in the Gas‐Phase Ion Chemistry of the Ni(C,H3,O)+/C2H6 Couple

A mechanistically unprecedented situation characterizes the gas‐phase ion chemistry of Ni(C,H₃,O)⁺ when reacted under thermal, single‐collision conditions with ethane. A dehydrogenation channel leading to Ni(C₃,H₇,O)⁺ is to 90% preceded by a complete loss of positional identity of all nine H‐atoms of the encounter complex (‘scrambling’), whereas ca. 10% of the reaction exhibit a selective C? H bond activation of the alkane. In addition, a degenerate H exchange between ethane and the (C,H₃,O) unit occurs as a side reaction, the mechanistic details of which remain unknown for the time being.     

Quantum Information Scrambling in Non-Markovian Open Quantum System

In this paper, we investigate the dynamics of a spin chain whose two end spins interact with two independent non-Markovian baths by using the non-Markovian quantum state diffusion (QSD) equation approach. Specifically, two issues about information scrambling in an open quantum system are addressed. The first issue is that tripartite mutual information (TMI) can quantify information scrambling properly via its negative value in a closed system, whether it is still suitable to indicate information scrambling in an open quantum system. We find that negative TMI is not a suitable quantifier of information scrambling in an open quantum system in some cases, while negative tripartite logarithmic negativity (TLN) is an appropriate one. The second one is that up to now almost all information scrambling in open quantum systems reported were focus on a Markovian environment, while the effect of a non-Markovian environment on information scrambling is still elusive. Our results show that the memory effect of an environment will be beneficial to information scrambling. Moreover, it is found that the environment is generally detrimental for information scrambling in the long-term, while in some cases it will be helpful for information scrambling in the short-term.     

基于混沌与位平面的图像置乱方法

根据混沌序列良好的随机性及灰度图像可分成若干位平面二值图的特点,提出了将混沌二值序列与位平面图像异或运算进行置乱,将置乱后的位平面图重新组合成灰度图,以此达到灰度图像置乱的效果。仿真结果表明,基于混沌与位平面的图像置乱方法可有效地使图像灰度值均匀化。     

基于像素置乱技术的多重双随机相位加密法

提出一种基于像素置乱技术的多重双随机相位加密法,对该加密法中像素置乱操作的原理进行了阐述,并且提出在光学上实现像素置乱操作和解置乱操作的途径.在计算机上模拟实现了该加密法,并且得到很好的加密解密结果.仿真结果证实仅用部分加密图像来解密也能够得到原图像,并且得到随着待解密的加密图像像素的增加,解密图像的信号能量、噪声以及信噪比的变化曲线.最后分析比较了该加密法与双随机相位加密法,得到该加密法与双随机相位加密法相比具有更高的保密性,而且解密图像的信噪比也不会因为引入像素置乱操作而降低.     

High-resolution H/D exchange studies on the HET-s218-295 prion protein

In a search for improved resolution of hydrogen/deuterium (H/D) exchange experiments analyzed by mass spectrometry (HXMS), we evaluated two methodologies for a detailed structural study of solvent accessibility in the case of the HET-s(218-295) prion protein. For the first approach, after incubation in the deuterated solvent, aggregated HET-s(218-295) was digested with pepsin and the generated peptides were analyzed by nanospray mass spectrometry in an ion trap, with and without collision-induced dissociation (CID). We compared deuterium incorporation in peptides as determined on peptide pseudomolecular ions and on b and y fragments produced by longer peptides under CID conditions. For both b and y fragment ions, an extensive H/D scrambling phenomenon was observed, in contrast with previous studies comparing CID-MS experiments and (1)H NMR data. Thus, the spatial resolution of HXMS experiments could not be improved by means of MS/MS data generated by an ion trap mass spectrometer. In a second approach, the incorporation of deuterium was analyzed by MS for 76 peptides of the HET-s(218-289) peptide mass fingerprint, and the use of shared boundaries among peptic peptides allowed us to determine deuteration levels of small regions ranging from one to four amino acids. This methodology led to evidence of highly protected regions along the HET-s(218-295) sequence.