Molecular simulation of hydrogen adsorption in organic zeolite

The adsorption of molecular hydrogen on model zeolites has been simulated employing Grand Canonical Monte Carlo (GCMC) procedure. The effects of cation type, available volume, surface area, temperature, pressure and pre-adsorbed organics such as benzene on the hydrogen uptake are analyzed. The hydrogen adsorption can be affected mainly by the available volume and surface area per g-zeolite at the same temperature and pressure. Increase of temperature results in the decrease of sorption intensity and capacity. The adsorption capacity correlates well with the pressure with high linearity at room temperature. Adsorption is lowered by the pre-adsorbed benzene molecule. The orientation and the number of benzene molecule in zeolite affect the adsorption capacity. The organic zeolite with larger available volume shows larger adsorption capacity.     

Prooxidant effects of inorganic chromium compounds in the autoxidation of methyl linoleate

The prooxidant property of inorganic chromium compounds was determined in methyl linoleate free from natural antioxidants and metals. Prooxidant properties of inorganic chromium compounds appeared in order of sodium chromate > chromium (VI)-oxide > chromium chloride > potassium chromate > chromium (III)-oxide > potassium dichomate. In comparison with the control, additions of chromium compounds induced different amounts of autoxidation products derived from methyl linoleate, such as small amounts of hydroperoxides and conjugated dienes and large amounts of hydroxy groups,α,β,γ,δ-unsaturated carbonyls, isolatedtrans double bonds, polymers, and free radicals. From these analytical data, the catalysis of chromium compounds in the autoxidation of methyl linoleate seemed to be based on their abilities of abstracting a hydrogen from methyl linoleate and decomposing hydroperoxides derived from the autoxidation of methyl linoleate.     

Synthesis and physicochemical characterization of amphiphilic block copolymer self‐aggregates formed by poly(ethylene glycol)‐block‐poly(ϵ‐caprolactone)

Diblock copolymers with different poly(ε‐caprolactone) (PCL) block lengths were synthesized by ring‐opening polymerization of ε‐caprolactone in the presence of monomethoxy poly(ethylene glycol) (mPEG‐OH, MW 2000) as initiator. The self‐aggregation behaviors and microscopic characteristics of the diblock copolymer self‐aggregates, prepared by the diafiltration method, were investigated by using ¹H NMR, dynamic light scattering (DLS), and fluorescence spectroscopy. The PEG–PCL block copolymers formed the self‐aggregate in an aqueous environment by intra‐ and/or intermolecular association between hydrophobic PCL chains. The critical aggregation concentrations of the block copolymer self‐aggregate became lower with increasing hydrophobic PCL block length. On the other hand, reverse trends of mean hydrodynamic diameters were measured by DLS owing to the increasing bulkiness of the hydrophobic chains and hydrophobic interaction between the PCL microdomains. The partition equilibrium constants (K_v) of pyrene, measured by fluorescence spectroscopy, revealed that the inner core hydrophobicity of the nanoparticles increased with increasing PCL chain length. The aggregation number of PCL chain per one hydrophobic microdomain, investigated by the fluorescence quenching method using cetylpyridinium chloride as a quencher, revealed that 4–20 block copolymer chains were needed to form a hydrophobic microdomain, depending on PCL block length. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3520–3527, 2006     

Autoxidation of ethyl eicosapentaenoate and docosahexaenoate

The extent of oxidation of ethyl esters of eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) was compared quantitatively with that of ethyl linoleate (Lo) and ethyl linolenate (Ln) by oxygen uptake and formation of conjugated diene, hydroperoxide and secondary oxidation products. EPA and DHA esters were oxidized rapidly even at 5 C in the dark after an induction period of 3–4 days, while the induction periods of Ln and Lo esters were 20 days and more than 60 days, respectively. Oxygen uptake of EPA and DHA esters after the induction period was 5.2 and 8.5 times faster than that of ethyl Ln, respectively. Hydroperoxides of EPA and DHA esters are much less stable than those of ethyl Lo. The peroxide value is not necessarily a good indication of oxidation in these polyenoic acids because a considerable amount of secondary products is formed at the early stage of oxidation. Polymers were found to be major secondary products in these polyenoic esters.     

基于机械臂运动的组合航天器惯性参数在轨辨识

随着空间技术发展,交会对接任务越来越多,服务航天器与目标航天器对接形成组合航天器后惯性参数会发生明显变化。因此,提出一种基于机械臂运动的组合航天器惯性参数在轨辨识方法。该方法可以分为2步:第一步辨识组合航天器的质量和质心;第二步辨识组合航天器的惯性张量。该方法优点是实现了质量、质心与惯性张量等辨识参数的相互解耦,不需要消耗航天器上宝贵的喷气燃料,仅需要测量航天器的速度,而不是加速度和力。仿真结果验证了方法的有效性。     

注气井井筒结垢预测研究

在油田开发过程中,油、气、水和泥浆在地层或管道中流动,当达到一定条件时,油垢、水垢或泥垢便会产生。在实际生产过程中,油垢和泥垢通常伴随着水垢而生成,所以对水垢结垢趋势的预测研究显得至关重要。介绍了Oddo-Tomos饱和指数法的理论预测模型,以及在生产过程中利用Oddo-Tomos饱和指数法预测油田结垢趋势的方法,阐述并分析了油田结垢对油田开采的影响。研究结果可为下一步的生产作业提供理论依据。     

Adaptive interpolation scheme for NURBS curves with the integration of machining dynamics

This paper develops a comprehensive interpolation scheme for non-uniform rational B-spline (NURBS) curves, which does not only simultaneously meet the requirements of both constant feedrate and chord accuracy, but also real-time integrates machining dynamics in the interpolation stage. Although the existing work in this regard has realized the importance to simultaneously consider chord error and machining dynamics, none has really incorporated these in one complete interpolation scheme. In this paper, machining dynamics is considered for three aspects: sharp corners or feedrate sensitive corners on the curves, components with high frequencies or frequencies matching machine natural ones and high jerks. A look-ahead module was developed for detecting and adaptively adjusting the feedrate at the sharp corners. By Fast Fourier Transform (FFT) analysis with a moving window in the interpolation stage identified were some special frequency components such as those containing high frequencies or with frequencies matching machine natural ones. Then, the notch filtering or time spacing method was used to eliminate these components. To more completely reduce feedrate and acceleration fluctuations, the jerk-limited algorithm was also developed. Finally, the interpolated feedrate was further smoothened with B-spline fitting method and the NURBS curves were re-interpolated with the smoothened feedrate. During the interpolation, the chord error was repeatedly checked and confined in the prescribed tolerance. Two NURBS curves were used as examples to test the feasibility of the developed interpolation scheme.     

基于混合参数蚁群算法的移动机器人路径规划北大核心

针对传统蚁群算法因初期信息素分布不均导致算法初期路径选择概率随机性大、搜索速度慢等缺陷,设计一种使用混合参数的蚁群改进算法。在算法开始阶段引入遗传算法,对遗传算法的适应度函数进行改进;设置一个评价点使遗传算法在合适的时机进入蚁群算法,并对算法的信息素挥发因子p采用一种自适应调整方式;对遗传算法的交叉率和变异率以及蚁群算法的信息因子和期望因子采用变异的混合参数,发挥4个参数因子在算法中的优点;在蚁群算法后面设置一个路径进化率的评价点判定是否再次进行遗传变异操作,目的是使蚁群算法跳出局部最优;算法最后引入B样条曲线光滑机制。实验结果表明:改进算法在简单和复杂的环境里找到的路径长度和路径拐点数明显减少,有比其他3种算法更快更准的寻找全局最优能力。     

钨粉表面化学镀铜研究

为了提高钨粉制品的性能,采用正交实验方法,利用SEM、XRD、EDS等分析手段,系统研究了化学镀铜主要工艺参数对钨粉表面化学镀铜的影响规律。结果表明:在温度固定条件下,各因素对镀液稳定性影响的显著性顺序是:硫代硫酸钠加入量>pH值>χ(Tar2-/Cu2 )>甲醛加入量,而对镀速影响的显著性顺序是:χ(Tar2-/Cu2 )>pH值>甲醛加入量>硫代硫酸钠加入量;较佳的钨粉表面化学镀铜工艺为:五水硫酸铜8g/L;酒石酸钾钠28g/L;EDTA0.75g/L;NaOH8.5g/L;硫代硫酸钠10mg/L;甲醛7.5ml/L;pH=12;温度40℃。采用所推荐的工艺,成功的在钨粉上获得了化学镀铜层。     

一种基于蚁群算法的呼叫中心人力需求计算方法

针对呼叫中心人力需求优化这一离散约束问题,基于Dantzig提出的集合覆盖模型,建立了单技能呼叫中心的人力需求计算线性规划模型,并提出一种基于改进蚁群算法的求解方法.在该方法中,对算法的信息素更新规则进行了修改,并基于MATLAB编程针对实例进行仿真分析.选取统计学指标将算法的仿真结果与遗传算法进行对比,结果表明:基于蚁群算法的方法计算复杂度可行;能够节约人力,且话务员匹配度可满足实际运营需求;为智能算法在呼叫中心人力需求计算问题上的应用研究提供了一种新的解决思路.