Aromatization of n-butane over new LD-HBS catalysts. Effect of the gallium oxide support

It is shown that even pure quartz, other silicas or aluminas can enhance the aromatization activity of a ZSM-5 zeolite. Incorporation of gallium oxide onto these supports increases further the production of aromatics. The use of supported gallium oxide co-catalyst obtained by co-evaporation of a colloidal silica and a Ga salt has led to extremely high aromatization performance for the hybrid catalyst.     

A surrogate-based optimization method with RBF neural network enhanced by linear interpolation and hybrid infill strategy

In engineering, it is computationally prohibitive to directly employ costly models in optimization. Therefore, surrogate-based optimization is developed to replace the accurate models with cheap surrogates during optimization for efficiency. The two key issues of surrogate-based optimization are how to improve the surrogate accuracy by making the most of the available training samples, and how to sequentially augment the training set with certain infill strategy so as to gradually improve the surrogate accuracy and guarantee the convergence to the real global optimum of the accurate model. To address these two issues, a radial basis function neural network (RBFNN) based optimization method is proposed in this paper. First, a linear interpolation (LI) based RBFNN modelling method, LI-RBFNN, is developed, which can enhance the RBFNN accuracy by enforcing the gradient match between the surrogate and the trend observed from the training samples. Second, a hybrid infill strategy is proposed, which uses the surrogate prediction error based surrogate lower bound as the optimization objective to locate the promising region and meanwhile employs a linear interpolation-based sequential sampling approach to improve the surrogate accuracy globally. Finally, extensive tests are investigated and the effectiveness and efficiency of the proposed methods are demonstrated.     

A two‐station embossing process for rapid fabrication of surface microstructures on thermoplastic polymers

An embossing strategy involving a hot station and a cold station for sequentially heating and cooling the embossing tool was investigated to reduce cycle times in hot embossing polymer microstructures. Experimental studies showed that aluminum stamps with a thickness of 1.4 mm can be rapidly heated from room temperature to 200°C in 3 s using contact heating against a hot station at 250°C. Microchannels and microlenses were successfully embossed onto high‐density polyethylene and acrylonitrile–butadiene–styrene substrates using a heating time less than 3 s and a total cycle time around 10 s. The two‐station embossing process for the microlens was also numerically studied. The simulated filling behavior agreed with the experimental observation and the predicted thermal and deformation history of the polymer offered a good explanation on the experimentally observed process characteristics. POLYM. ENG. SCI., 47:530–539, 2007. © 2007 Society of Plastics Engineers.     

Photoinitiated crosslinking of ethylene‐vinyl acetate copolymers and characterization of related properties

Photoinitiated crosslinking of EVA in the presence of benzophenone (BP) as photoinitiator and triallyl isocyanurate (TAIC) as crosslinker and characterization of the related properties have been studied by gel determination, heat extension, DSC, DMTA, TGA, and mechanical measurements. The photoinitiated crosslinking efficiency of the EVA‐BP‐TAIC system and various factors affecting the crosslinking process, such as photoinitiator and crosslinker and their concentrations, irradiation temperature, and irradiation atmosphere were studied in detail and optimized by comparison of gel contents. The results show that the EVA samples with a thickness of 1 mm are readily crosslinked to a gel content of above 80% with 5 s UV‐irradiation under optimum conditions. The data from the heat extension and DSC show that the crosslinking density of photocrosslinked EVA increase and their crystallinities decrease with increasing the UV‐irradiation time. At the same time, photocrosslinking of EVA leads to a lowering of the melt temperature and a decrease of heat of fusion. The DMTA results show that photocrosslinking increases the amorphous phase and storage modulus of the crosslinked EVA, but does not change the glass transition temperature. The data from TGA and mechanical tests give evidence that the thermal stability and mechanical properties of photocrosslinked EVA samples are much better than those of the uncrosslinked EVA. POLYM. ENG. SCI., 47:1761–1767, 2007. © 2007 Society of Plastics Engineers     

通用突变控制方法及其在潜艇中的应用

运用非线性动力学和突变理论,研究了高维系统建立具有理想特性突变的控制方法.引入冲失滤波器保证系统平衡点不变,并利用隐式判据、中心流形定理以及规范形法确定控制增益.以潜艇空间运动为例,阐述计算的全过程.该控制方法简便、快捷,可广泛应用到实际控制系统的设计中.     

云计算中的信息安全风险评估

云计算具有快速灵活、随需求而变、按使用付费、可扩展能力强等特点,其应用愈来愈广泛,如何评价云计算服务的安全风险是信息安全领域面临的新问题.由于云计算服务具有传统意义上的信息系统特点,结合云计算架构的三个服务层次:基础设施即服务、平台即服务和软件即服务.以信息系统安全风险评估的规范性动作为基本流程,从客户端和服务端两个角度,对如何实施信息安全风险评估加以阐述,为人们分析云计算服务中可能存在的安全风险和评价云计算的安全性提供参考.     

基于遗传二进制粒子群混合算法的测试点决策研究

测试点选择是测试性分析和设计的前提。通过对测试问题的分析,建立了数学模型和构造了衡量测试集优劣程度的启发式函数,提出了一种遗传-二进制粒子群混合算法求解满足测试性指标要求的最小完备子集。应用实例表明,该算法能够有效的克服单一算法陷入局部最优和早熟收敛等不足,提高了搜索效率,能够有效快速的获得全局最优解。     

A model for studying LCAT reaction: In vitro cholesterol esterification in pig ovarian follicular fluid

Phosphatidylcholine acyltransferase (lecithin:cholesterol acyltransferase or LCAT; EC 2.3.1.43) activity was found to be present in pig ovarian follicular fluid (POFF), in addition to pig serum (PS). The cholesterol esterification rate in both POFF and PS is linear with incubation time up to 2 hr. The mean absolute rate of POFF-cholesterol esterification was 8.1±0.4 nmoles per ml per hr approximately one-fourth of that in PS. However, the fractional rate (percent of labeled cholesterol esterified per hr) of POFF-cholesterol esterification was similar to that observed in PS. There was little variation of absolute rate of cholesterol esterification in the fluid obtained from different sizes of follicles. Fatty acid or triacylglycerol did not participate in the reaction of cholesterol esterification in POFF. No appreciable change in enzymatic activity was found from storing POFF at 4 C for periods of time up to 24 hr or at −70 C up to 2 months, but activity was lost thereafter. On the other hand, PS showed a much longer period of stability (5 days at 4 C and 9 months at −70 C). A discrepancy between the fatty acid composition of cholesteryl esters formed by the LCAT reaction and the fatty acid composition at the C-2 position of phosphatidylcholine led us to propose a two-step mechanism for the LCAT reaction. It is concluded that the LCAT of POFF, as well as that of plasma, is specific for individual fatty acids rather than for the fatty acid composition of phosphatidylcholine. The fatty acid concentration of lysophosphatidylcholine decreased during prolonged incubation times (6 to 21 hr) suggesting that the increased lysophosphatidylcholine formed as a product of the LCAT reaction may be reused as substrate for the LCAT reaction or for hydrolysis by lysophosphatidylcholine hydrolase. Presented at the AOCS Meeting, New York, May 1977.     

多媒体定时器方法中MFC跨线程传递窗口类消息的实现

为实现高频数据采集,采用多媒体定时器的方法实现上位机精确定时,同时研究实现了MFC中跨线程窗口类消息传递问题的解决方案。实验表明,定时精度高,达到10毫秒精确定时,不会出现数据丢失,运行良好。     

Coupled oscillations of H2/O2/CO on silica supported rhodium catalyst

Self-sustained oscillations obtained during the catalytic oxidation of CO and H₂ were studied over Rh/SiO₂ by an FTIR-mass spectrometric technique. An average oscillatory period of 7.1±0.5 minutes was obtained for the CO/O₂ reaction at 348 K. For the H₂/O₂ oscillatory reaction the period was observed to be 1.3±0.8 minutes. When the oscillations were coupled at the same temperature, the period for both the CO/O₂ and the H₂/O₂ reactions was observed to be 7.9±0.8 minutes. The kinetic coupling of the reaction rates is explained by considering the periodic fluctuations in surface temperature which occur as a result of the more exothermic CO/O₂ reaction.