The structure and function of platelet-activating factor acetylhydrolases

Platelet-activating factor acetylhydrolases (PAF-AHs, EC 3.1.1.47) constitute a unique and biologically important family of phospholipase A2s. They are related to neither the well-characterized secretory nor cytosolic PLA2s, and unlike them do not require Ca2+ for catalytic activity. The distinguishing property of PAF-AHs is their unique substrate specificity: they act on the phospholipid platelet-activating factor (PAF), and in some cases on proinflammatory polar phospholipids, from which they remove a short acyl moiety--acetyl in the case of PAF--located at the sn-2 position. Because PAF is found both in the plasma and in the cytosol of many tissues, PAF-acetylhydrolases are equally widely distributed in an animal organism. Recent crystallographic studies shed new light on the complex structure-function relationships in PAF-AHs.     

THE SINGLE PELLET DIFFUSION REACTOR: THEORY AND APPLICATIONS

Most heterogeneous catalysts are either supported on some kind of porous material or the catalyst itself is porous. To satisfy practical constraints such as pressure drop, handling, and separation from products, these catalysts are generally pelletized. Very often the overall chemical reaction rates within these catalyst pellets are determined by a complicated interaction of internal and external transport effects with the intrinsic kinetic rate at the active surface.     

有限精度时间自动机的可达性检测

为了缓解状态空间爆炸问题,减小模型检测过程中生成的状态空间,加快模型检测速度,引入有限精度时间自动机(finite precision timed automata,简称FPTA)作为实时系统的形式模型,并提出了一种数据结构SDS(series of delay sequence)符号化表示状态空间中的状态集.FPTA只记录时钟变量的整数值及时钟变化的先后次序,从而减小生成的状态空间.在一定的时间约束下,Alur与Dill提出的时间自动机的可达性检测可简化为FPTA的可达性检测.举例描述了状态空间的生成过程和表示方法.最后,列出部分初步的实验结果,分析了SDS的特点及不足.     

Photovoltaics as a demand-side management technology: An analysis of peak-shaving and direct load control options

For photovoltaic (PV) technology to play an increasing role in the utility sector at its present price, the technology needs to be developed in a manner that is consistent with, and takes advantage of, the economics of the demand-side management (DSM) market. High-value applications in this direction are for photovoltaics to perform a DSM function either as a direct load control (DLC) device or as a peak-shaving option, which has the effect of raising the end-use efficiency of customers' electrical equipment. This paper describes two PV-DSM applications involving a water heater and an air conditioner studied at a residential PV test facility, Solar One House, located on the campus of the University of Delaware. A single 55-W PV module directly connected to an electric water heater was found to offset standby and mixing losses, resulting in a 2°C increase in water temperature at the end of the afternoon compared to the standard DLC (grid-disconnected) case. A conservatively sized PV array without storage could meet the house air-conditioning load over 97% of the time from noon to 3 p.m., but only 69% from 3 p.m. to 6 p.m. If a PV system is combined with an air-conditioning cycling program, success rates for supply of an air-conditioning load are greatly increased, meeting almost 100% of the load between noon and 3 p.m. and 85% during 3 p.m. to 6 p.m. Furthermore, our results suggest that a modest-size PV array with storage could significantly shave peak air-conditioning loads during 3 p.m. to 6 p.m., thus reducing the peak demand faced by a utility. Preliminary analyses support the economic compatibility of a PV system as a DLC device or a peak-shaving tool.     

Low sideband guided-mode resonant filter

A guided-mode resonant filter with low sideband reflections is proposed. It is shown that, for serious reduction of out-of band reflectance, the combination of waveguide-grating filter design with conventional antireflective stack design methods is not adequate. To achieve symmetrical low sideband reflectances, independent control of various layer thicknesses is necessary. At a given illumination angle with appropriate control of the waveguide thickness, a specific resonant grating filter is designed whose out-of-band reflectance on both sides of the resonant peak is well below 10(-4). Even 50 nm away from the peak, on both sides, the out-of-band reflectance remains below 10(-3). Analysis of the variation in the main manufacturing parameters indicates that such filters can be reliably produced with present-day technologies.     

3D reconstruction based on hard tissue microtome cross-section pictures in dentistry

The aim of this study was to examine the accuracy of the computerized 3D surface analyzing and volume measuring method in dentistry. Two different types of test objects were used in the first part of the measurements. Each sample of the two groups was cross-sectioned using a hard tissue microtome. The sections were photographed on both sides and were projected on a graphical tablet and analyzed using a computer program. The measured and calculated parameters were compared. In the second part, 200 microm thick horizontal sections were prepared from 11 human incisor roots using the hard tissue microtome. This way, five sections were prepared from the apical 2 mm of each root. The effects of section thickness and number were modeled by decreasing the inclusion rate of the obtained number of sections from 10 to 2 and its influence on the calculated results was determined. This method was suitable for the approximation and analysis of 3D parameters. The results indicated that using 200-300 microm section thickness, the measured values were approximately 8-21% lower than the real parameters.     

Dyslipidemias and autoimmune diseases

The paper summarizes the results of over 30-year studies dealt with dyslipidemias and autoimmune diseases. The teaching of the antiphospholipid syndrome (APS) has aroused interest in the problem. The experience gained shows changes in the blood cholesterol transport system. Patients with systemic lupus erythematosus (SLE) have higher levels of low density lipoprotein cholesterol and lower concentrations of high density lipoprotein (HDL) cholesterol, apolipoprotein A than the controls. The quantitative and qualitative changes in particles result in decreased acceptance of cholesterol from the membrane of a cell and tissues, which promotes the development of vascular diseases. Lipoprotein (a) may be an additional risk factor for thrombosis chiefly of coronary arteries, in patients with SLE and APS. Increased levels of oxidized low density proteins having atherogenic activity were found mainly in patients with SLE. The use of corticosteroids causes the changes in the spectrum of blood lipids, which together with other factors (thrombosis, vasculopathy, thrombocytopenia, etc.) create good conditions for the development of atherosclerosis, which determines the necessity of correcting the parameters of blood lipid transport not only to prevent vascular disorders but to improve the general life prognosis in SLE patients.     

A Novel Catalyst Geometry for Automobile Emission Control

The catalytic control of automobile exhaust pollutants (hydrocarbons, carbon monoxide, nitrogen oxides) is now a common practice in the United States and Japan, and there are strong indications that the technology may be introduced in other parts of the world in the coming years. The simultaneous conversion of all three of the above pollutants is achieved by the near-stoichiometric operation of noble metal catalysts which are supported either on alumina particles or on alumina-washcoated cordierite monoliths, A summary of the developments which lead to this technology can be found, e. g., in Hegedus and Gumbleton [1] and references therein.