Stereocomplementary Routes to Hydroxylated Nitrogen Heterocycles: Total Syntheses of Casuarine,Australine, and 7‐epi‐Australine

Addition of lithiated 1‐benzyloxyallene to a D ‐arabinose‐derived cyclic nitrone occurred with perfect diastereoselectivity furnishing a bicyclic 1,2‐oxazine derivative, which is an excellent precursor for pyrrolizidine alkaloids hydroxylated at C‐7 with optional configuration at this stereogenic center. Depending on the stage of the N? O bond cleavage and ring re‐closure, 7‐hydroxypyrrolizidines with 7R or 7S configuration were obtained, as a result of completely selective addition reactions occurring complementarily at the bottom or top face of the endocyclic C? C double bond in six‐ and five‐membered B rings, respectively. Applicability of these stereodivergent routes to obtain polyhydroxy pyrrolizidine alkaloids is demonstrated by the efficient syntheses of casuarine and australine as examples of the two classes of diversely configured 7‐hydroxypyrrolizidine alkaloids. An alternative synthesis of australine and two strategies for the preparation of 7‐epi‐australine are also reported, which demonstrate that the stereoselectivity of hydride reduction of an exocyclic C? O double bond is independent of the ring size, occurring preferentially from the top face either in a six‐ or five‐membered ring.     

Investigation of damaged interior walls using synchrotron‐based XPS and XANES

Evidence of internal sulfate attack in field exposure was demonstrated by the damaged interior wall of a three‐year‐old house situated in Nakhon Ratchasima Province, Thailand. Partial distension of the mortar was clearly observed together with an expansion of a black substance. Removal of the black substance revealed a dense black layer. This layer was only found in the vicinity of the damaged area, suggesting that this black material is possibly involved in the wall cracking. By employing synchrotron‐based X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption near‐edge structure (XANES) techniques, the unknown sample was chemically identified. The S 2p and O 1s XPS results mutually indicated the existence of sulfate species in the materials collected from the damaged area. The XANES results indicated the presence of ferrous (II) sulfate, confirming sulfate‐induced expansion and cracking. The sulfate attack in the present case appeared to physically affect the structure whereas the chemical integrity at the molecular level of the calcium silicate hydrate phase was retained since there was a lack of spectroscopic evidence for calcium sulfate. It was speculated that internal sulfate probably originated from the contaminated aggregates used during the construction. The current findings would be beneficial for understanding the sulfate‐attack mechanism as well as for future prevention against sulfate attack during construction.     

Functionalization of a cyclo‐P5 Ligand by Main‐Group Element Nucleophiles

Unprecedented functionalized products with an η⁴‐P₅ ring are obtained by the reaction of [Cp*Fe(η⁵‐P₅)] ( 1 ; Cp*=η⁵‐C₅Me₅) with different nucleophiles. With LiCH₂SiMe₃ and LiNMe₂, the monoanionic products [Cp*Fe(η⁴‐P₅CH₂SiMe₃)]^? and [Cp*Fe(η⁴‐P₅NMe₂)]^?, respectively, are formed. The reaction of 1 with NaNH₂ leads to the formation of the trianionic compound [{Cp*Fe(η⁴‐P₅)}₂N]^3?, whereas the reaction with LiPH₂ yields [Cp*Fe(η⁴‐P₅PH₂)]^? as the main product, with {[Cp*Fe(η⁴‐P₅)]₂PH}^2? as a byproduct. The calculated energy profile of the reactions provides a rationale for the formation of the different products.     

基于动态概率攻击图的云环境攻击场景构建方法

针对复杂多步攻击检测问题,研究面向云计算环境的攻击场景构建方法.首先,构建了动态概率攻击图模型,设计了概率攻击图更新算法,使之能够随着时空的推移而周期性更新,从而适应弹性、动态性的云计算环境.其次,设计了攻击意图推断算法和最大概率攻击路径推断算法,解决了误报、漏报导致的攻击场景错误、断裂等不确定性问题,保证了攻击场景的...     

空对空多目标攻击载机攻击航线求解逻辑

介绍了空对空多目标攻击载机攻击航线的基本要求、航线选择和求解方法,以及载机航线、瞄准偏差、操纵指令的计算逻辑图.同时还介绍了多目标攻击"可能攻击扇形区"交集的概念和在载机航线求解中的应用等问题.     

基于运动矢量统计的同步视频水印算法

通过分析运动矢量的数据统计特性,提出一种基于统计的抗同步攻击视频水印算法.该算法水印信息表示空间与数据特性紧密联系,具有物理空间、时间不可划分性,克服了传统水印算法的检测器对水印同步的依赖性.实验表明,该算法具有很好的鲁棒性和不可感知性,能够抵抗帧删除等同步攻击以及基于视频内容的攻击;在帧删除率小于18%时,水印正确率大于80%.     

Improved Side‐Channel Attack on DES with the First Four Rounds Masked

This letter describes an improved side‐channel attack on DES with the first four rounds masked. Our improvement is based on truncated differentials and power traces which provide knowledge of Hamming weights for the intermediate data computed during the enciphering of plaintexts. Our results support the claim that masking several outer rounds rather than all rounds is not sufficient for the ciphers to be resistant to side‐channel attacks.     

基于攻击树的协同入侵攻击建模

由于现代入侵方法从单步入侵转变到协同入侵,文章在传统攻击树基础上,提出了分层次攻击树,并用模块化的方法为协同攻击建模,以IP-spoofing攻击为例说明了建模方法。     

VDS在网络中的应用

VDS是专门解决复杂系统网络安全问题的。它率先解决了网络环境下难以高速准确检测病毒的全球性难题，以旁路方式接入网络，能够实时监测网络环境中的病毒疫情，全高检测各种网络病毒的扫描、传输、攻击等行为，定位病毒的来源，测量病毒产生的网络压力。并准确提供病毒类别、病毒名称、病毒变种、病毒危害级别等全面信息，形成网络病毒的全局视图。     

Synthesis and reactivity of tricarbonyl(1-methoxycarbonyl-5-phenylpentadienyl)iron(1+) cation

Tricarbonyl(1-methoxycarbonyl-5-phenylpentadienyl)iron(1+) hexafluorophosphate (7) was prepared in two steps from tricarbonyl(methyl 6-oxo-2,4-hexadienoate)iron. While addition of carbon and heteroatom nucleophiles to 7 generally occurs at the phenyl-substituted dienyl carbon to afford (2,4-dienoate)iron products, the addition of phthalimide proceeded at C2 to afford a (pentenediyl)iron product (18). Complex 18 was structurally characterized by X-ray diffraction analysis.