一个B-B型国际贸易网站的设计与实现

国际贸易是电子商务的重要应用领域。基于对国际贸易作业流程的深刻认识,讨论了互联网平台在国际贸易中的重要作用。给出了一个国际贸易网站的系统功能结构,给出了网站详细的业务流程设计,包括询盘处理、报盘处理、询盘特殊要求处理、回盘处理、合同处理等。最后,给出了系统的详细设计及实现技术。

考虑正压力分配的B-B型涡轮叶片缘板阻尼器系统减振特性研究

为提升涡轮叶片缘板阻尼器设计水平,对比B-G(blade to ground)型阻尼器和切向无约束B-B(blade to blade)型阻尼器结构,提出了一种基于刚度设计的B-B型缘板阻尼器结构。在动力学建模中重点分析了相邻叶片缘板和阻尼器之间总的正压力随阻尼器与左、右叶片缘板间相对运动在左、右缘板间的分配,给出了基于阻尼器运动的正压力分配方法;通过数值仿真分析了正压力分配对系统振动响应的影响,并重点讨论了阻尼器刚度、外激励相位差、正压力以及外激励幅值对系统减振特性的影响。仿真结果表明,在左、右叶片缘板与阻尼器完全粘滞和左、右叶片相对阻尼器对称同步振动的工况下可以将正压力按照平均分配处理;相比于切向无约束的B-B型阻尼器和刚性的B-G型阻尼器,所提出的基于刚度设计的缘板阻尼结构具有更优的减振性能。因此,研究结果提升了涡轮叶片缘板阻尼器接触正压力计算的准确性,拓展了阻尼器设计思路,可为同类阻尼器设计提供理论和工程参考。

基于整体-局部统一滑动模型的叶片缘板阻尼器减振特性分析

文章通过在干摩擦接触面间引入弹性塑料剪切层来模拟摩擦接触,建立了整体-局部统一滑动摩擦模型。根据一次谐波平衡和等效线性化法计算等效刚度和等效阻尼2个干摩擦因子,用弹簧阻尼单元(包含2个干摩擦因子)模拟干摩擦力,建立了更为贴近工程实际的B-B型缘板阻尼叶片有限元模型。最后用谐响应分析及迭代的方法对系统进了求解,得到了缘板阻尼器设计中关键参数对叶片减振效果的影响规律。文中结论为工程中缘板干摩擦阻尼器设计提供了重要参考。

浅谈双面印刷机的类型、特点及常见的问题

我们知道，双面印刷是指一次走纸印刷双面（正反两面），完成印什件的印刷。双面印刷在整个印刷业务中占有相当大的比重，除了部分招贴画、海报、包装彩盒等产品必需进行单面印刷外，像书刊、报纸等产品正反向都包含有各种图文信息，正反面都要进行印刷。

再谈重影

本公司的一台B-B型胶印机ZM200B,出现了一系列的重影故障,通过对故障的分析,有很多体会.

单张纸双面印刷的几种方式

在当今单张纸印刷中双面印刷的业务占90%以上,仅有很少一部分招贴、海报和包装盒等采用单面印刷.双面印刷存在多种方式,总的来说单张纸双面印刷有以下几种方式:

Simulation study on dynamics of A- to B-form transition in aqueous DNA solution:Effect of alkali metal counterions

DNA and its conformational transition can be used to design nanometer-scale structures, nano-tweezers and nanomechanical devices. Experiments and molecular simulations have been used to study the concentration effect on the A-DNA→B-DNA conformational transition, but a systematical investigation on counterion effect on the dynamics of this transition has not been reported up to now. In present work, restrained and unrestrained molecular dynamics （MD） simulations have been performed to characterize the stability of DNA conformations and the dynamics of A-DNA→B-DNA transitions in aqueous solutions with different alkali metal counterions. The DNA duplex d（CGCGAATTCGCG）2, coion Cl- and counterions Li＋, Na＋, K＋, Rb＋ and Cs~ as well as water molecule were considered using the PARM99 force field in the AMBER8 package. It was found that B-form DNA is more stable than A-form DNA in aqueous electrolyte solutions with different alkali metal counterions. In- creasing KCI concentration in solution hinders the A-DNA^B-DNA transition and the transition times for different alkali metal counterions conform to neither the simple sequence related to naked ion size nor to hydrated diameter, but an apparently abnormal sequence of K＋ 〈 Rb＋ 〈 Cs＋ 〈 Na＋ 〈 Li＋. This abnormal sequence can be well understood in terms of an electrostatic model based on the effective cation diameters and the modified mean-spherical approximation （MMSA）. The present results provide valuable information for the design of DNA-based nanomaterials and nanodevices.

Molecular dynamics simulation of the A-DNA to B-DNA transition in aqueous RbCl solution

Unrestrained molecular dynamics （MD） simulations have been carded out to characterize the stability of DNA conformations and the dynamics of A-DNA^B-DNA conformational transitions in aqueous RbC1 solutions. The PARM99 force field in the AMBER8 package was used to investigate the effect of RbC1 concentration on the dynamics of the A^B conformational tran- sition in the DNA duplex d（CGCGAATTCGCG）2. Canonical A- and B-form DNA were assumed for the initial conformation and the final conformation had a length per complete turn that matched the canonical B-DNA. The DNA structure was moni- tored for 3.0 ns and the distances between the C5＇ atoms were obtained from the simulations. It was found that all of the double stranded DNA strands of A-DNA converged to the structure of B-form DNA within 1.0 ns during the unrestrained MD simula- tions. In addition, increasing the RbC1 concentration in aqueous solution hindered the A^B conformational transition and the transition in aqueous RbC1 solution was faster than that in aqueous NaC1 solution for the same electrolyte strength. The effects of the types and concentrations of counterions on the dynamics of the A^B conformational transition can be understood in terms of the variation in water activity and the number of accumulated counterions in the major grooves of A-DNA. The ru- bidium ion distributions around both fixed A-DNA and B-DNA were obtained using the restrained MD simulations to help ex- plain the effect of RbC1 concentration on the dynamics of the A^B conformational transition.

The Global Existence of Small Solutions to the Oldroyd-B Model

The Cauchy problem to the Oldroyd-B model is studied.In particular,it is shown that if the smooth solution （u,τ） to this system blows up at a finite time T～＊,then 0～T～＊u（t） L∞dt = ∞.Furthermore,the global existence of smooth solution to this system is given with small initial data.