Optimal inspection and perfect repair

Models are developed for decision making about monitoring andmaintenance of systems whose performance through time is describedby a general stochastic process. The system is monitored andpreventive and corrective maintenance actions are carried outin response to the observed system state. The decision processis simplified by using the maximum process as a decision variable.The models developed generalize age replacement models and othersimple maintenance strategies. The approach can deal with failuresthat prevent the system functioning further, and also failuresthat are defined by regulation or economic considerations. Attentionis restricted to perfect repair and inspection, but the structureprovides the framework for further developments.     

A theoretical examination of the acid-catalyzed and noncatalyzed ring-opening reaction of an oxirane by nucleophilic addition of acetate. Implications to epoxide hydrolases

Ab initio and density functional calculations have been performed to gain a better understanding of the epoxide ring-opening reaction catalyzed by epoxide hydrolase. The S(N)2 reaction of acetate with 1S,2S-trans-2-methylstyrene oxide to provide the corresponding diol acetate ester was studied with and without general-acid catalysis. MP2 and DFT (B3LYP) calculations predict, for the noncatalyzed reaction, a central barrier of approximately 20-21 kcal/mol separating the reactants from products depending on which carbon center in the epoxide is undergoing attack. From these gas-phase reactions the immediate alkoxide products are not energetically far below their associated transition states such that the reaction is predicted to be endothermic. Inclusion of aqueous solvation effects via a polarizable continuum model predicts the activation barrier to increase by almost 10 kcal/mol due to the solvation of the acetate ion nucleophile. The activation barrier for the epoxide ring-opening reaction is reduced to approximately 10 kcal/mol when phenol, as the general-acid catalyst, is included in the gas-phase calculations. This is due to the immediate product being the neutral ester rather than the corresponding alkoxide. The transition state in the general-acid-catalyzed reaction is earlier than that for the noncatalyzed reaction and the reaction is highly exothermic. Molecular mechanics calculations of 1S,2S-trans-2-methylstyrene oxide in the active site of murine epoxide hydrolase show two possible binding conformations. Both conformers have the epoxide oxygen forming hydrogen bonds with the acidic hydrogens of the catalytic tyrosines (Tyr381 and Tyr465). These two conformations likely lead to different products since the nucleophile (Asp333-CO(2)(-)) is positioned to react with either carbon center in the epoxide.     

Incorporating zosteric acid into silicone coatings to achieve its slow release while reducing fresh water bacterial attachment

Biofouling has posed serious problems in maritime industry including increased fuel consumptions, economic loss from ship-hull maintenances, contamination of drinking water, and serious corrosion for mechanical instruments. Minimizing the attachment of bacteria and formation of biofilm could be advantageous in reducing the early stages of biofouling. Zosteric acid, a natural product present in eelgrass, was found to have ability for preventing the attachment of some bacteria and barnacles. In this study, the antifouling ability of zosteric acid during the early stages of fouling was evaluated using attachment studies of fresh water bacteria. Simultaneously, various methods were sought for incorporating zosteric acid into silicone to prolong the release of the compound. The main results from this study were that zosteric acid exhibited anti-bacterial attachment regardless of whether it dispersed in water or incorporated into a coating. In addition, the release rate of zosteric acid from the incorporated coatings, particularly those where zosteric acid was uniformly dispersed with aggregates size of 4 microm or less, was orders of magnitude slower than those of previous reports. The release results indicate that the service life of our coatings could be far extended even with a small amount of zosteric acid incorporated.     

农残水平测试中数据多态性分析及指定值估计研究

对全国农残水平测试中毒死蜱、氯氰菊酯数据进行统计分析,在数据统计分布特征研究基础上,使用内核密度估计进行数据多态性分析,使用bootstrap模拟取样法对数据样本值重复取样,以获得稳健的水平测试样品待测物含量代表值估计、标准误差及置信区间描述,证明以bootstrap模拟取样法获取的均值与标准偏差作为有限单次样本代表值是合理、有效的,解决了四分位稳健统计方法对非正态多态分布代表值估计不稳定问题及取样理论中取样样本数限制的瓶颈,为能力验证计划指定值的获取提供了一种新方法。     

Initial bacterial attachment in slow flowing systems: effects of cell and substrate surface properties

Bacterial biofilm can have significant effects on the behaviors and/or performance of natural and man-made systems. Understanding the factors governing initial bacterial attachment is critical to biofilm management. In this study, the initial attachment of three bacteria, Pseudomonas aeruginosa, Escherichia coli and Pseudomonas putida, on two substrates, glass and octadecyltrichlorosilane (OTS) modified glass, was examined in flow chambers. The flow chambers were designed and operated to mimic slow moving water bodies and minimize the gravitational settlement of cells. The hydrophobicity of bacterial surface was evaluated by partitioning of cells to the water-hexadecane interface and the liquid contact angles on cell layers collected on filter papers. On the more hydrophilic glass surface, the attachment trend was found to be E. coli>P. putida>P. aeruginosa, while the opposite trend was observed on the hydrophobic, OTS modified surface. The attachment trend on glass could be explained by the magnitude of the negative interaction energy at secondary minima, as predicted by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The much higher attachments of P. aeruginosa and P. putida on the OTS-modified substrate, on the other hand, suggested that these cells could overcome the energy barrier between the primary and secondary minima of interaction energy to become attached to the primary minimum. The extent of primary-minimum attachment appeared to correlate with the scale of the energy barrier, with higher attachments in the bacteria-substrate combinations of lower energy barriers. The study generated important insights into the effects of cell and substrate surface properties on initial bacterial attachment.     

High-performance electron-transporting polymers derived from a heteroaryl bis(trifluoroborate)

In this communication, we report that dipotassium aryl bis(trifluoroborate)s make stable and easy-to-purify yet reactive monomers under Suzuki polycondensation reactions. A bis(trifluoroborate) of 2-alkylbenzotriazole was prepared successfully and copolymerized with dibromobenzothiadiazole in the presence of a Pd catalyst and LiOH, yielding high molecular weight conjugated polymers. This polymer (P1) composed of all electron-accepting units shows excellent electron-transport properties (μ(e) = 0.02 cm(2) V(-1) s(-1)), which proves the value of the aryl bis(trifluoroborate) monomers and suggests that many other types of semiconducting polymers that could not be accessed previously can be synthesized using this approach.     

Ni3(Tix,V1-x)合金系中的长周期结构

本文利用电子衍射及高分辨点阵象实验方法证实了Ni₃(Ti_x,V_1-x)合金系在铸态下存在有9R,10H,16H,20H,21H,44H等长周期结构以及2H结构。它们与体心四方基体相(结构与Ni₃V相同)及六角基体相(结构与Ni₃Ti相同)有固定取向关系:{001}_长周期∥{001}_(Ni3Ti)∥{112}_{Ni3V);〈100〉长周期∥〈100〉(Ni3Ti)∥〈110〉(Ni3V)。样品经长期高温退火处理后其它长周期结构均向9R结构转变。 关键词：}     

离线γ技术测量重离子熔合复合核平均角动量

使用离线γ测量技术在质心系25.0—40.5MeV的能区测量了¹²C+⁹³Nb熔合反应产生的二中子和三中子蒸发道的激发函数。由于在相同的激发能下,蒸发道的相对截面比与复合核的角动量有很强的依赖关系,应用统计蒸发程序(CASCADE),从二中子和三中子蒸发道的截面中提取不同能量下的复合核平均角动量和熔合截面。同时从能很好地拟合熔合激发函数的简单耦合道模型(CCFUS)计算中提取复合核的平均角动量。两种方法得到的复合核平均角动量随入射能量的变化相自洽,表明耦合道模型 关键词：     

Application of solution techniques for rapid growth of organic crystals

Single crystals of a pure hydrocarbon, 1,3,5-triphenylbenzene, with properties suitable for high-energy neutron detection were grown from toluene solutions using slow evaporation and temperature reduction methods with growth rates up to 10 mm/day. Application of the rapid growth technique developed earlier for growth of large water-soluble crystals shows that crystals of aromatic compounds can be successfully grown from solutions in large volumes required for their use as scintillator materials for radiation detection.     

Polymeric microstructure arrays consequence of Marangoni flow-induced water droplets

This paper describes a cost-effective approach to fabricate intricate arrays of polydimethylsiloxane (PDMS) and polymeric microstructures based on porous polystyrene (PS) films generated from arrays of water droplets. To start, a thin layer of ethanol film is exposed to a humid air flow. Upon the evaporation of ethanol and simultaneous condensation of water as the ethanol phase recedes, a Marangoni flow causes the flow of liquid from the ethanol phase into water fingers emerged along the receding contact line, which finally detach to form ordered water droplet arrays behind the receding contact line. The water droplet arrays are subsequently used as templates to generate porous PS films. The porous PS films are then used as sacrificial layers and masters to fabricate various arrays of PDMS dots and PDMS stamps with posts, respectively. The PDMS stamps containing various microstructures are further utilized to create polymer rings, PDMS dots, porous PDMS films, and PDMS aperture rings, and for contact printing of patterns of self-assembled monolayers.