Molecular mechanics conformational analysis of tylosin

The conformations of the 16-membered macrolide antibiotic tylosin were studied with molecular mechanics (AMBER* force field) including modelling of the effect of the solvent on the conformational preferences (GB/SA). A Monte Carlo conformational search procedure was used for finding the most probable low-energy conformations. The present study provides complementary data to recently reported analysis of the conformations of tylosin based on NMR techniques. A search for the low-energy conformations of protynolide, a 16-membered lactone containing the same aglycone as tylosin, was also carried out, and the results were compared with the observed conformation in the crystal as well as with the most probable conformations of the macrocyclic ring of tylosin. The dependence of the results on force field was also studied by utilizing the MM3 force field. Some particular conformations were computed with the semiempirical molecular orbital methods AM1 and PM3.     

Biased fragment distribution in MC simulation of protein folding

Monte Carlo (MC) methods play an important role in simulations of protein folding. These methods rely on a random sampling of moves on a potential energy surface. To improve the efficiency of the sampling, we propose a new selection of trial moves based on an empirical distribution of three-residue (triplet) conformations. This selection is compared to random combinations of the preferred conformations of the three amino acids, and it is shown that the new trial moves lead to finding structures closer to the native conformation.     

Au-Ni 合金表面聚集的计算机模拟

应用改进分析型EAM模型(MAEAM)结合基于Metropolis 算法的Monte Carlo模拟方法,计算了800 K下Au-Ni 二元合金表面成分和剖面成分分布,包括Au含量在40%、50%、60%时(111)面和(100)面的情况,发现Au在(111)面和(100)面聚集,得到了与实验结果和其它理论结果相一致的结果.     

功能化聚乳酸大分子单体的合成与表征

以辛酸亚锡为催化剂、甲基丙烯酸羟乙酯(HEMA)为共引发剂引发消旋-丙交酯(D,L-LA)开环聚合,制备了末端双键功能化的聚乳酸大分子单体(MC),采用FT-IR、 1H NMR、GPC、拉伸强度和表面接触角测定等方法研究了大分子单体的结构与性能.结果表明,大分子单体中HEMA结构单元的含量与单体投料比中HEMA的含量基本一致;单体投料比对大分子单体的结构与性能有显著影响.     

微机保护开入电路芯片的研究

针对微机保护中开入电路比较复杂且成本高等弊端及MC33884的优良特性，探讨了用MC33884代替原来微机保护装置中的开入电路的方法，试验证明，用MC33884作为开入电路的芯片比原来的光耦实现的开入电路抗干扰能力明显提高。     

图象压缩技术的分析与评价

视频图象压缩是多媒体系统中的关键技术，其原理是通过消除视频信号中的冗余信息来减少信息量。文中首先分析了图象压缩的基本技术，其中包括空间冗余信息的压缩和时间冗余信息的压缩，并对这些压缩方法的理论依据和实用效果加以探讨。以此为基础，还重点分析了通过集成基本压缩技术而建立的以混合编码系统，特别针对现有的图象压缩国际标准如ＪＰＥＧ，ＭＰＥＧ和Ｈ．２６１等作了较为深入的探讨，对其系统结构，适用范围及有效性进行了比较和分析。     

GARCH-M模型在股指预测中的应用

本文用GARCH-M模型模拟波动率的变化趋势,并进行预测,将所得结果带入Black-Scholes公式中,用蒙特卡罗模拟10000次,取其期望,得了较真实的股票指数。     

基于ZigBee技术的低成本无线数传系统的实现

介绍了一种低成本的无线数传系统的设计和研制,该系统采用了一款符合IEEE802.15.4标准的ZigBee无线网络芯片MC13192和廉价的8位51单片机89S51,通过SPI接口实现单片机和ZigBee芯片的通讯,并通过单片机的串口连接到计算机.文中给出了系统的硬件结构和软件流程,并针对开发过程中遇到的技术难点给出了解决方案.     

Particle‐in‐cell/Monte Carlo simulation of electron and ion currents to cylindrical Langmuir probe

Electron and ion currents to a cylindrical Langmuir (electrostatic) probe were calculated using the particle‐in‐cell/Monte Carlo (PIC/MC) self‐consistent simulation for a neutral gas in the pressure range 2–3,000 Pa. The simulation enables us to calculate the probe currents even at high neutral gas pressures when the collisions of collected charged particles with neutral gas particles near the probe are important. The main aim of this paper is the calculation of probe currents at such high gas pressures and the comparison of the results with experimentally measured probe currents. Simulations were performed for two cases: (a) probes with varying radii in a non‐thermal plasma with high electron temperature at low neutral gas pressure of 2 Pa (in order to verify the correctness of our simulations), and (b) probe with the radius of 10 μm in the afterglow plasma with low electron temperature and a higher neutral gas pressure (up to 3,000 Pa). The electron probe currents obtained in case (a) show good agreement with those predicted by the orbital motion limited current (OMLC) theory for probes with radii up to 100 μm for the given plasma conditions. At larger probe radii and/or at higher probe voltages, the OMLC theory incorrectly predicts too high an electron probe current for the plasma parameters studied. Additionally, a formula describing the spatial dependence of the electron density in the presheath in the collisionless case is derived. The simulation at higher neutral gas pressures, i.e. case (b), shows a decrease of the electron probe current with increasing gas pressure and the creation of a large presheath around the probe. The simulated electron probe currents are compared with those of measurements by other authors, and the differences are discussed.