Conformational Study of the Structure of dibenzo-18-crown-6. Comparison with 18-crown-6

We report for the first time the conformational analysis of dibenzo-18-crown-6, db18c6. The conformational search was carried out using the CONFLEX conformational search method of cyclic molecules. Energies were calculated for the low-lying predicted conformations at different levels of theory up to the G3MP2 level. At the G3MP2 level, the predicted ground state (GS) conformation was more stable than the experimental conformation by only 1.60 kcal/mol. Strong similarity was found between the GS structure and experimental conformations of db18c6 and 18-crown-6, 18c6. The GS and experimental conformations of db18c6 are non-planar. This allows db18c6 to exist in optically active enantiomers. Similar to 18c6, it was concluded that the db18c6 structure is stabilized by intramolecular hydrogen bond. We also performed the computations for the water and chloroform solution phase, where the same conformation was predicted as the GS conformation.     

Long range molecular dynamics study of interactions of the eukaryotic glucosamine-6-phosphate synthase with fructose-6-phosphate and UDP-GlcNAc

Glucosamine-6-phosphate synthase (EC 2.6.1.16) is responsible for catalysis of the first and practically irreversible step in hexosamine metabolism. The final product of this pathway, uridine 5′ diphospho N-acetyl-d-glucosamine (UDP-GlcNAc), is an essential substrate for assembly of bacterial and fungal cell walls. Moreover, the enzyme is involved in phenomenon of hexosamine induced insulin resistance in type II diabetes, which makes of it a potential target for anti-fungal, anti-bacterial and anti-diabetic therapy.The crystal structure of isomerase domain from human pathogenic fungus Candida albicans has been solved recently but it doesn’t reveal the molecular mechanism details of inhibition taking place under UDP-GlcNAc influence, the unique feature of eukaryotic enzyme. The following study is a continuation of the previous research based on comparative molecular dynamics simulations of the structures with and without the enzyme's physiological inhibitor (UDP-GlcNAc) bound. The models used for this study included fructose-6-phosphate, one of the enzyme's substrates in its binding pocket.The simulation results studies demonstrated differences in mobility of the compared structures. Some amino acid residues were determined, for which flexibility is evidently different between the models. Importantly, it has been confirmed that the most fixed residues are related to the inhibitor binding process and to the catalysis reaction. The obtained results constitute an important step towards understanding of the inhibition that GlcN-6-P synthase is subjected by UDP-GlcNAc molecule.     

IPv6安全性分析研究

IPv6作为下一代互联网协议已经得到了各方的公认,未来互联网的发展离不开IPv6的支持和应用。对比IPv4,IPv6在安全性和功能上均有大幅度的提高。本文就IPv6的安全机制及安全特性作一个较全面的分析与探讨。     

On the equivalence of the invariant subdistribution algorithm and the structure algorithm

The invariant subdistribution algorithm is shown to be equivalent to the Structure Algorithm for the computation of the formal ‘structure at infinity' of a nonlinear system which satisfies an assumption introduced earlier by the author. In addition, the above assumption is proved to be weaker than Hirschorn's condition.     

移动IPv6的流传输研究

移动IPv6技术是建立在下一代Internet协议IPv6的基础上，应用于移动环境中的一种新技术。在移动：IPv6中，移动主机在移动过程中保持通信的连续性并对上层屏蔽地址的变化。为了实现随时随地的连接性，移动主机可能希望在不同条件不同要求下使用不同网络或传输不同的业务流。针对这一情况，介绍了一种基于流的移动IPv6的扩展机制，使移动主机可以同时利用多个接口为不同的流进行通信，从而更好地满足了网络的QoS要求。     

浅析IPv6的安全性

随着IPv4的地址即将分配完毕,IPv6作为下一代互联网络的协议标准,必将广泛的推广和使用,IPv6把IPSec集成到协议内部,体现出了安全性在协议中地位。本文就Ipv6面临的安全性问题以及安全性头AH、ESP和Internet密钥交换IKE做了简单的阐述,并对IPv6相对于IPv4在安全性方面的优势提出了一些个人看法。     

A methodology to model the Dynamic structure of an organization

The Integrated Computer Aided Manufacturing (ICAM) program of the U.S. Air Force identified a need to better communicate and analyze manufacturing for the people involved in improving productivity. To satisfy that need, the ICAM program developed the IDEF (ICAM Definition) method to address particular characteristics of manufacturing. This IDEF Method is equally applicable in analyzing other types of organizations.IDEF comprises of three modeling methodologies: function model methodology (IDEF₀), information model methodology (IDEF₁) and dynamics model methodology (IDEF₂). This paper reports on the dynamics model methodology only. This methodology is used to construct models which help in understanding the Dynamic (time-varying behavior) structure which the functions of an organization exhibit.     

IPV6环境下的分布式P2P流行为分析系统

针对IPV6网络中P2P流量管理的需求,设计了一种基于IPV6的分布式P2P流行为分析系统。该系统的包捕获模块采用分布式部署方式,能实时采集来自于多个网络监测点的流量并进行汇总分析。通过实验对比,系统对HASH模块的输入组合进行优化,解决了IPV6环境下系统建流和维护流状态信息的效率问题。利用该系统在真实IPV6网络环境中对BT流行为特征进行测量,取得了相关实验分析结果。     

6-巯基嘌呤质子转移异构化的量子化学计算研究

采用密度泛函B3LYP方法,在6-311G(d,p)基组水平上对6-巯基嘌呤质子转移引起的硫酮式与硫醇式互变异构反应机理进行了计算研究,获得了互变异构过程的反应焓、活化能、活化吉布斯自由能和质子转移反应的速率常数等参数。计算结果表明,6-巯基嘌呤无论是孤立分子还是一水合物,其硫酮式TP2是最稳定的异构体。计算结果同已有实验结果相符。由硫酮式通过分子内质子转移向硫醇式异构化找到4条反应通道(P1,P2,P3,P4),各通道的活化能分别为114.0,133.9,128.0,95.1 kJ·mol~(-1)。当水分子参与反应以双质子转移机理异构化时,活化能垒显著降低,各通道的活化能依次降为51.2,63.0,70.5,42.8 kJ·mol~(-1),可见,水助催化有利于硫酮式向硫醇式转变。计算结果还表明,氢键的强弱对TP2一水合物的稳定性会有一定的影响。     

6LoWPAN协议在电力物联系统中的应用研究

当前电力物联网系统应用Zigbee协议,该协议不能满足IEE802.15.4的MAC层的Ipv6需求,造成电流传输速率低,且电压越限开关控制失败。为此,采用6LoWPAN协议优化了电力物联系统的网关功能。利用6LoWPAN技术原理、应用规范以及相比于其它物联网的优势,基于IEE802.15.4的网络层协议,提出Zigbee和6LoWPAN共存,协议中间层为双协议栈网关的总体设计方案,实现物联网与Ipv6 Internet的互联和信息交互。设计6LoWPAN适配层,解决IEE802.15.4的MAC层不能满足Ipv6需求问题。仿真结果显示：应用6LoWPAN协议后电力物联系统连通性能以及UDP数据报传输性能均符合实际应用需求;6LoWPAN协议应用后可显著提升数据采集节点的续航时间,降低功耗,增加电流传输速率,提升电压越限开关控制成功率。6LoWPAN协议的应用可有效提升电网的安全运行水平。     

Automatic analysis of geologic structure from dip-strike data

A new technique for structural analysis is described. From dip-strike data, a dip—strike distribution map, structure contour map, and block diagram are automatically prepared on an X-Y plotter by using four computer programs. Three test examples of theoretical data are treated as well as an actual example. The Izumi Group (Upper Cretaceous) is revealed to have a more complicated structure than previously recognized.     

在管理信息系统中树型结构的表示和组件设计

关系型数据库中经常有部分树型结构表示的信息,从树型结构数据处理组件的需求分析出发,提出了通用树型结构组件的结构和设计方案。     

一种便携式SF6气体质量分析仪设计

严格监测与管理气体绝缘封闭组合电器(GIS,gas insulated switchgear)设备中SF6(六氟化硫)气体质量是保证GIS设备安全运行的重要保障.为对SF6气体质量实施监测,设计了一个基于STM32的便携式SF6气体质量分析仪.该仪表采用红外光谱吸收原理检测SF6浓度,以电阻电容法测量微水含量,用电化学原理检测SO2、H2S和CO含量.为提高系统可靠性和满足实时性及多任务调度,移植了μC/OS-Ⅱ操作系统.实验测试了仪表的准确性和重复性.实践证明,该仪表可以完成SF6气体质量分析,为GIS设备安全运行提供了可靠的保障.     

IPV6的技术特征与应用

随着互联网的发展，IPv4定义的有限地址空间将被耗尽。作为下一代的互联网协议IPv6，除了能解决IPv4所面临的地址短缺问题以外，还考虑了IPv4面临的其他一些问题。从IPv6提出的背景出发，阐述了IPv6相对于IPv4的技术特性、应用前号。     

Performance Evaluation of the Impact of QoS Mechanisms in an IPv6 Network for IPv6-Capable Real-Time Applications

This paper describes a Quality of Service (QoS) service on an IPv6 domain that aims to service aggregates of real-time traffic with minimum delay, jitter, and packet loss. It contains results from the tests that were performed in order to configure and evaluate the QoS mechanisms. As an actual example of real-time traffic, we have used the OpenH323 project, an open source H.323 implementation that has been ported to IPv6. The QoS mechanisms in IPv6 networks is still a field that has not been researched adequately, and we therefore present the results from the experiments in our IPv6 network that took advantage of the QoS mechanisms. This QoS service uses the Modular QoS CLI (MQC) mechanism and especially the Low Latency Queue feature (LLQ) in order to treat packets from real-time applications.     

IPV6的技术特征与应用

随着互联网的发展,IPv4定义的有限地址空间将被耗尽。作为下一代的互联网协议IPv6,除了能解决IPv4所面临的地址短缺问题以外,还考虑了IPv4面临的其他一些问题。从IPv6提出的背景出发,阐述了IPv6相对于IPv4的技术特性、应用前景。     

李雅普诺夫稳定性理论中V函数的构造研究

李雅普诺夫稳定性理论,在自动控制等方面有着很重要的作用,李雅普诺夫第二判别方法,可以直接判定微分方程组的稳定性,应用非常广泛,但是如何构造满足特定条件下的李雅诺夫函数V,则是微分方程组稳定性理论要解决的课题。本文通过实例分析总结,研究出了几种实用性强的李雅普诺夫函数V的构造形式和方法。     

Implementation and evaluation of the Shim6 protocol in the Linux kernel

In the changing landscape of the todays Internet, several solutions are under investigation to allow efficient, flexible and scalable multihoming. One of the proposals is shim6, a host-based multihoming solution based on the use of multiple IPv6 addresses on each host. In this work, we first describe the main features of this protocol, then we explain our implementation of shim6, along with the associated security mechanisms in the Linux kernel and, finally, we evaluate its performance. In particular, we analyse the performance impact of the security mechanisms used by shim6 and the impact of shim6 on the performance of end-host systems, especially heavily loaded servers. We conclude by discussing the remaining open issues for a widespread deployment of host-based multihoming techniques such as shim6.     

IPv6与IPv4网络安全分析

本文首先对IPv4和IPv6进行了概要介绍,描述了IPv4的缺点和IPv6的优点。然后对IPv4的安全缺陷进行了分析,探讨了IPv6对这些缺陷的改进方法,最后对IPv6的安全问题也进行了分析。