不锈钢螺栓连接节点的破坏研究

尽管不锈钢与碳素钢的机械性能有显著的不同,但是现有规范关于不锈钢连接节点的设计规定都基于碳素钢的设计准则。对于不锈钢螺栓连接节点的设计抗力,EN1993-1-4和SCI/EuroInox(美国《科学引文索引》/欧洲不锈钢协会)的不锈钢设计手册基于EN1993-1-8和EN1993-1-3作了一些小修改。研究了厚板和薄板的不锈钢螺栓连接节点的承载性能。提出了一个奥氏体不锈钢和铁素体不锈钢试件的数值分析模型,并证明其正确性。将该模型用于螺栓节点承载力的参数分析,可研究主要变量对其影响。这些参数包括螺栓边距e2,端距e1和板厚t。结果表明,不锈钢螺栓节点的变形性能与碳钢节点存在某种程度的不同。数值模型中最初出现裂纹的部位与试验中观察到的不锈钢节点和碳素钢节点相符,这种相符性被作为定义一种强度失效准则的基础。以参数分析结果为基础的不锈钢螺栓连接节点承载能力极限状态和正常使用极限状态设计法则比现行的EC3法则更加经济和简捷。     

Effect of phosphoric acid on the performance of low antimony grid of Pb‐acid cell under constant current charging and discharging

Effect of phosphoric acid on the performance of Pb‐1.7%Sb grid of lead‐acid cell is studied in 5 M H₂SO₄ by cyclic galvanostatic polarization and impedance spectroscopy. An increase in capacitance to a maximum is recorded during the initial stages of the electro‐reduction of PbO₂ into Pb(II) compounds and attributed to concurrent compositional and dimensional changes. These changes include removal of O₂ bubbles, insertion of large amounts of H₂SO₄ and H₂O. Efficiency of PbO₂ formation decreases, while its rate of self‐discharge increases with increasing the charging current and in the presence of H₃PO₄. The charge capacity increases with increasing the discharging current due to the decrease in the self‐discharge. The charge capacity is lower in the presence of H₃PO₄. On increasing the cycle number, the corrodibility of the grid increases, because more layers of the surface Pb are involved in the self‐discharge. H₃PO₄ significantly retards the effect of cycle number.     

Structure and function of animal fatty acid synthase

Fatty acid synthase (FAS; EC 2.3.1.85) of animal tissues is a complex multifunctional enzyme consisting of two identical monomers. The FAS monomer (approximately 270 kDa) contains six catalytic activities and from the N-terminus the order is beta-ketoacyl synthase (KS), acetyl/malonyl transacylase (AT/MT), beta-hydroxyacyl dehydratase (DH), enoyl reductase (ER), beta-ketoacyl reductase (KR), acyl carrier protein (ACP), and thioesterase (TE). Although the FAS monomer contains all the activities needed for palmitate synthesis, only the dimer form of the synthase is functional. Both the biochemical analyses and the small-angle neutron-scattering analysis determined that in the dimer form of the enzyme the monomers are arranged in a head-to-tail manner generating two centers for palmitate synthesis. Further, these analyses also suggested that the component activities of the monomer are organized in three domains. Domain I contains KS, AT/MT, and DH, domain II contains ER, KR, and ACP, and domain III contains TE. Approximately one fourth of the monomer protein located between domains I and II contains no catalytic activities and is called the interdomain/core region. This region plays an important role in the dimer formation. Electron cryomicrographic analyses of FAS revealed a quaternary structure at approximately 19 A resolution, containing two monomers (180 x 130 x 75 A) that are separated by about 19 A, and arranged in an antiparallel fashion, which is consistent with biochemical and neutron-scattering data. The monomers are connected at the middle by a hinge generating two clefts that may be the two active centers of fatty acid synthesis. Normal mode analysis predicted that the intersubunit hinge region and the intrasubunit hinge located between domains II and III are highly flexible. Analysis of FAS particle images by using a simultaneous multiple model single particle refinement method confirmed that FAS structure exists in various conformational states. Attempts to get higher resolution of the structure are under way.     

Comparison of stochastic filtering methods for 3D tracking

In the recent years, the 3D visual research has gained momentum with publications appearing for all aspects of 3D including visual tracking. This paper presents a review of the literature published for 3D visual tracking over the past five years. The work particularly focuses on stochastic filtering techniques such as particle filter and Kalman filter. These two filters are extensively used for tracking due to their ability to consider uncertainties in the estimation. The improvement in computational power of computers and increasing interest in robust tracking algorithms lead to increase in the use of stochastic filters in visual tracking in general and 3D visual tracking in particular. Stochastic filters are used for numerous applications in the literature such as robot navigation, computer games and behavior analysis. Kalman filter is a linear estimator which approximates system's dynamics with Gaussian model while particle filter approximates system's dynamics using weighted samples. In this paper, we investigate the implementation of Kalman and particle filters in the published work and we provide comparison between these techniques qualitatively as well as quantitatively. The quantitative analysis is in terms of computational time and accuracy. The quantitative analysis has been implemented using four parameters of the tracked object which are object position, velocity, size of bounding ellipse and orientation angle.     

Determination of molecular, atomic, electronic cross-sections and effective atomic number of some boron compounds and TSW

The transmission of gamma-rays of some boron compounds (H₃BO₃, Na₂B₄O₇) and the trommel sieve waste (TSW) have been measured by using an extremely narrow-collimated-beam transmission method in the energy range 15.74-40.93 keV. Molecular, atomic and electronic cross-sections and effective atomic numbers have been determinated on the basis of mixture rule and compared with the results obtained from theory.     

Fabrication and characterization of anisotropic dielectrics for low-loss microwave applications

New magneto-photonic assembly designs for high-gain antennas require dielectrics with a significant anisotropy and low loss at GHz frequencies. This paper describes an approach to fabricate such dielectrics from ceramic laminates. These laminates consist of two ceramics with largely different permittivities and low dielectric losses. Alternating layers of commercially available α-Al₂O₃ and Nd-doped BaTiO₃ were laminated using organic adhesives. Equivalent permittivity tensors and loss tangents were characterized using a resonant cavity-based approach, which was coupled with a finite-element method full-wave solver. Measured permittivity values were in good agreement with mean field predictions; a minimum loss tangent 1.1 × 10^?3 was obtained when using one-component epoxy (Loctite^®-3982) adhesive. Application of two-component epoxy (M-bond 610) adhesive results in a slightly higher loss but better mechanical properties and machinability. These laminates were used to demonstrate high gain in a prototype antenna with 6 misaligned anisotropic dielectric layers.     

Monodisperse fine aerosol generation using fluidized bed

Monodisperse, fine aerosols are needed in many applications: filter testing, experiments for testing models, and aerosol instrument calibration, among others. Usually, monodisperse fine aerosols are generated in very low concentrations, or mass flow rates, in the laboratory scale. In this work, we needed to generate aerosols with higher mass flow rate than typically available by the laboratory-scale methods, such as atomizers, nebulizers, ultrasonic generators, vibrating orifice generators, and condensation generators. Therefore, we constructed a fluidized bed aerosol generator to achieve particle mass flow rates in the range of 15-100 g/h. Monodisperse, spherical SiO₂ particles of two sizes with geometrical diameters of 1.0 and 2.6 µm were used in the aerosol generator. The aerosol generator was used at both atmospheric pressure, and at high pressures up to 5 bar (abs).The particle size, mass concentration and the net average particle charge were measured after mixing the aerosol with nitrogen. The particle size distributions with both particle sizes were monodisperse, and no particle agglomerates were entrained from the fluidized bed. The behavior of the fluidized bed generator was found to be markedly different with the two particle sizes in regard to particle concentration, presumably due to different particle charging inside the generator. After determining the net average charge of the particles, an ion source Kr-85 was used to reduce the charge of the particles. This was found to be effective in neutralizing the particles.     

Vitamin A status of healthy children in Manisa,Turkey

Background  

Vitamin A deficiency is a major public health nutrition problem in the developing world. Even subclinical Vitamin A deficiency is associated with increased childhood mortality. Severe maternal vitamin A deficiency may cause increased mortality in the first months of life. There have been a limited number of studies regarding vitamin A status in Turkey. The aim of this study was to assess vitamin A status of healthy children in Manisa, Turkey.