Calculation of the relative change in binding free energy of a protein-inhibitor complex

By means of a thermodynamic perturbation method implemented with molecular dynamics, the relative free energy of binding was calculated for the enzyme thermolysin complexed with a pair of phosphonamidate and phosphonate ester inhibitors. The calculated difference in free energy of binding was 4.21 +/- 0.54 kilocalories per mole. This compares well with the experimental value of 4.1 kilocalories per mole. The method is general and can be used to determine a change or "mutation" in any system that can be suitably represented. It is likely to prove useful for protein and drug design.     

长输热油管道水力和热力计算

对于长输热油管道的工艺计算，国内常采用的是平均温度法，并把全线的总传热系数Ｋ作为定值，其缺点是计算精度低，计算结果与工程实际往往存在较大差异。介绍了根据分段计算方法有理有据的长距离加热输油管道水力和热力计算的算法。该算法是将有关参数如所输油品的密度、粘度、热容、土壤的导热系数和总传热系数Ｋ作为变量，根据不同管段内的流态和油品物性，分别采用不同的计算公式，并且计入摩擦生势对油流轴向温降的影响。与前者     

Linking models of polymerization and dynamics to predict branched polymer structure and flow

We present a predictive scheme connecting the topological structure of highly branched entangled polymers, with industrial-level complexity, to the emergent viscoelasticity of the polymer melt. The scheme is able to calculate the linear and nonlinear viscoelasticity of a stochastically branched "high-pressure free radical" polymer melt as a function of the chemical kinetics of its formation. The method combines numerical simulation of polymerization with the tube/entanglement physics of polymer dynamics extended to fully nonlinear response. We compare calculations for a series of low-density polyethylenes with experiments on structural and viscoelastic properties. The method provides a window onto the molecular processes responsible for the optimized rheology of these melts, connecting fundamental science to process in complex flow, and opens up the in silico design of new materials.     

BWRS方程在天然气物性计算中的应用

在输气管道的水力、热力计算中需要计算许多热物性参数，详细地介绍了应用BWRS方程求解各参数的方法、过程以及物性计算程序编制方法，给出了相应的计算实例。通过分析、实例计算和比较得出结论，应用BWRS方程计算天然气物性，其计算精度高，适用范围广。     

Bacterial Methanogenesis and Growth from CO2 with Elemental Iron as the Sole Source of Electrons

Previous studies of anaerobic biocorrosion have suggested that microbial sulfur and phosphorus products as well as cathodic hydrogen consumption may accelerate anaerobic metal oxidation. Methanogenic bacteria, which normally use molecular hydrogen (H(2)) and carbon dioxide (CO(2)) to produce methane (CH(4)) and which are major inhabitants of most anaerobic ecosystems, use either pure elemental iron (Fe(0)) or iron in mild steel as a source of electrons in the reduction of CO(2) to CH(4). These bacteria use Fe(0) oxidation for energy generation and growth. The mechanism of Fe(0) oxidation is cathodic depolarization, in which electrons from Fe(0) and H(+) from water produce H(2), which is then released for use by the methanogens; thermodynamic calculations show that significant Fe(0) oxidation will not occur in the absence of H(2) consumption by the methanogens. The data suggest that methanogens can be significant contributors to the corrosion of iron-containing materials in anaerobic environments.     

长距离输油管道设计计算软件的开发

在对长距离输油管道设计计算过程分析的基础上,依据现行的管道设计规范及管道输送理论,开发完成了基于Ｗｉｎｄｏｗｓ９５／９８操作平台的长距离输油管道设计计算软件ＬＯＰＤＣ。该软件可完成最优管径比选、输油站站址确定和调整、主要设备选型、设计方案经济评价、水击过程模拟、给定管段的热力和水力计算、强度计算和穿跨越计算等工作,并可绘制布站图,敏感性分析图及水击压力图。软件功能完善,操作方便,计算结果可靠,可满     

稠油管道不稳定工作特性的极点流量计算

对稠油管道进行了水力和热力计算,采用黄金分割法对稠油管道不稳定工作状态的极值点进行了求解,计算结果可以为稠油管道工艺参数的设计提供依据.给出了稠油管道的工作特点及确定输油温度和管道工作范围的原则.     

The response of electrons to structural changes

The properties of a molecule are determined by the distribution of its electrons. This distribution can be described by the charge density, which is readily obtained from the wave functions derived by ab initio molecular orbital calculations. The charge density may be analyzed in a number of different fashions to give information about the effects of substituents, structural changes, and electronic excitation on the properties of molecules; one common procedure makes use of projection density or charge difference plots. Charge density also may be partitioned among atoms, and by numerical integration over appropriate volume elements one may obtain atomic charges, dipoles, kinetic energies, and other properties of the atoms in a molecule. Many chemical phenomena have been analyzed in terms of charge densities.     

人工纳米材料吸附放射性核素的机理研究

人工纳米材料因其优异的理化性能以及独特的微观结构,被广泛应用于航空航天、放射医疗、建筑、农业等多个领域,尤其在放射性环境污染治理方面有着巨大的应用价值和潜力。通过综述人工纳米材料对废水中的放射性核素[U(Ⅵ)、Eu(Ⅲ)、Co(Ⅱ)等]富集、去除等方面的研究,系统讨论吸附行为和作用机理,借助吸附动力学、吸附热力学、光谱分析技术、表面络合模型和理论计算等方法,对纳米材料吸附放射性核素机理进行了深入分析,表明纳米材料对放射性核素具有强吸附能力而在放射性废水处理领域有着良好的应用前景,认为在科学研究和实际应用过程中,还需开展更多的研究工作,重点应放在低成本、高选择性的功能性纳米材料的绿色环保制备和应用。通过对前期研究结果的总结,期望能对放射性废物处理以及人工纳米材料应用等研究提供一些帮助。     

The use of graft copolymers to bind immiscible blends

Computer simulations and experimental studies were combined to design copolymers that enhance the strength of polymer composites. These copolymers contain side chains that associate across the boundary between phase-separated regions to form a "molecular velcro" that effectively binds the regions together. This behavior significantly improves the structural integrity and mechanical properties of the material. Because the side chains can be fabricated from a large class of compounds, the technique greatly increases the variety of copolymers that can be used in forming high-strength polymer blends.     

埋地热油管道启输热力数值模拟

在综合考虑预热介质，管道，管道覆盖层以及半无穷大土壤的情况下，提出了埋地热油管道启输传热的数学模型，并在该模型中，将土壤物性参九视为随温度变化的函数，应用保角变换将半无究大土壤区域变换成有限矩形区域。由Keller盒式积分法构造出了问题的差分格式，采用广义阻尼牛顿－拉夫逊法求解非线性差分方程组，得到了问题的数值解，并由算例验证了所述方法的正确性。     

油气管道的锚固法兰结构设计与有限元分析

锚固法兰按照常规计算方法得到的各部位尺寸较为保守,重要部位的结构尺寸往往不合理,局部应力过大,缺少必要的分析优化过程.以某规格高压、大口径锚固法兰为例,采用理论计算与有限元分析方法相结合进行设计计算.结果表明:在法兰的圆角处和管颈处有最大的应力强度分布,其余位置的各应力分量均较小,强度校核满足要求,结构设计合理.因此,锚固法兰设计计算结合有限元分析方法,可确保设计质量,满足不同工程项目锚固的技术要求.     

Band-gap engineering: from physics and materials to new semiconductor devices

Band-gap engineering is a powerful technique for the design of new semiconductor materials and devices. Heterojunctions and modern growth techniques, such as molecular beam epitaxy, allow band diagrams with nearly arbitrary and continuous band-gap variations to be made. The transport properties of electrons and holes can be independently and continuously tuned for a given application. A new generation of devices with unique capabilities, ranging from solid-state photomultipliers to resonant tunneling transistors, is emerging from this approach.     

Helix-rod host-guest complexes with shuttling rates much faster than disassembly

Dynamic assembly is a powerful fabrication method of complex, functionally diverse molecular architectures, but its use in synthetic nanomachines has been hampered by the difficulty of avoiding reversible attachments that result in the premature breaking apart of loosely held moving parts. We show that molecular motion can be controlled in dynamically assembled systems through segregation of the disassembly process and internal translation to time scales that differ by four orders of magnitude. Helical molecular tapes were designed to slowly wind around rod-like guests and then to rapidly slide along them. The winding process requires helix unfolding and refolding, as well as a strict match between helix length and anchor points on the rods. This modular design and dynamic assembly open up promising capabilities in molecular machinery.     

In situ determination of the nanoscale chemistry and behavior of solid-liquid systems

Many fundamental questions in crystal-growth behavior remain unanswered because of the difficulties encountered in simultaneously observing phases and determining elemental concentrations and redistributions while crystals nucleate and grow at the nanoscale. We show that these obstacles can be overcome by performing energy-dispersive x-ray spectroscopy on partially molten Al-Si-Cu-Mg alloy particles during in situ heating in a transmission electron microscope. Using this technique, we were able to (i) determine that the aluminum and silicon concentrations change in a complementary and symmetric manner about the solid-liquid interface as a function of temperature; (ii) directly measure the solid- and liquid-phase compositions at equilibrium and in highly undercooled conditions for quantitative comparison with thermodynamic calculations of the liquidus and solidus phase boundaries; and (iii) provide direct evidence for homogeneous nucleation of the aluminum-rich solid.     

CO2长输管道设计的相关问题

CO2在管道输送工况的温度、压力范围内会呈现出不同的相态，使得CO2输送管道不同于油气输送管道。为此，从CO2管道设计的角度出发，分析了CO2管道工艺系统的相关技术，包括CO2流的物理性质及相态、管道水力热力计算、站场工艺系统以及设备选取等。研究指出：相态控制是CO2管道设计的重要内容之一；CO2管道站场工艺系统设计应根据CO2的含水量考虑脱水工艺，而脱水工艺与CO2的压缩工艺相结合形成一个系统；CO2管道输送设备具有其特殊性，如压缩机、输送用泵、脱水装置、放空系统等，需要根据CO2管道的特点选取和设计。相关结论可为CO2长输管道的设计与建设提供参考。（图6，表1，参7）     

转向梯形的模糊优化设计

运用模糊数学和优化设计理论,提出了转向梯形的模糊优化设计新方法,并建立了半增广优化数学模型。该模型对清晰,模糊约束并存的优化问题求解较为有效。通过几例优化计算表明,新方法在不修改约束条件的情况下,能方便地获得实用优化解。     

液化石油气的储存方式及选择

液化石油气的储存方式是液化石油气储存设计中必须首先考虑的问题。综述了国内外液化石油气的储存方式及相关技术,同时,对影响储存方式的诸多因素,如储存液体的体积(或质量)、进液速度、液化石油气的接收频率、进液和输出手段、储存液体的物理性质和热力性质、投资和每种系统的运行费用等进行了讨论。     

几个吸附等温模型热力学参数的计算方法

从资源平衡与效率、资源限定与时空拓展等方面对农业资源的可持续利用进行了理论探讨。在概念上对资源生产效率、资源利用效率、资源效益等进行了明确的界定。以农产品增长量为判断标准,提出资源生产效益同时取决于资源生产效率和资源投入规模的观点,为我国继续增加农业资源投入规模提供了理论依据。根据农业资源在生产过程中相互联系规律和作用特点,确定了不同农业资源类型的运作策略及可持续利用的时空拓展途径与开发方向。     

基于TIN模型的土方量计算方法研究及应用

土方量计算是工程项目中经常遇到的问题,快速准确高效地计算土方量对于合理安排工程进度、工程量大小计算和投资预算等具有非常重要的意义.该文介绍了利用GPS接收器获取三维地形点数据,基于TIN模型,运用三棱柱法在ARCGIS中计算填挖土方量的工作方法,并以渑池县红花窝土地开发整理项目为例对计算进行进一步验证.将填挖土方量的计算结果与实际结果相比较,挖方误差约为-4.7％,填方误差约为-1％.研究表明该方法计算土方量是可行的,具有较高的精度和可视化效果,可作为工程土方计算的主要方法.