Analysis of triglycerides by capillary gas chromatography with programmed-temperature injection

The capillary gas chromatographic analysis of complex naturally occurring and food-product triglyceride mixtures is accomplished qualitatively and quantitatively on columns coated with methyl and methyl-phenyl (65%) silicones using programmed-temperature split/splitless and on-column injection. Faster analysis times are achieved using elevated initial column oven temperatures with cold initial injector temperatures.     

利用VB实现焊接方法的优化设计

对于某种母材和接头形式，当有多种焊接方法可实现焊接时，依据优化设计的思想．建立评价函数．用计算机对焊接方法进行优化设计．本文采用VB编制程序．当用户输入焊缝基本情况和对焊接质量、焊接效率及生产成本的要求时．即可得到最优、次优的几种焊接方法以供用户选择．并可选择打印某方法的焊接工艺卡片．     

An MSFIA system for mercury speciation based on an anion-exchange membrane

A new methodology for the in-line preconcentration, clean-up and speciation of mercury by use of an anion-exchange membrane is proposed. The speciation of mercury is based on retention of its tetrachloro complex onto the membrane while organic mercury flows freely through it. A multisyringe is used as a liquid driver and a cold vapour atomic fluorescence detector is employed to ensure a high sensitivity. Organic mercury is decomposed into to inorganic mercury by using a UV lamp. The carrier and reductant streams consist of 1.5% (m/v) hydrochloric acid and 2% (m/v) tin chloride, respectively. Certified reference material DORM-2 was digested with 37% hydrochloric acid and analysed directly without the need for extraction. The proposed system is more environmental friendly than the classical liquid-liquid extraction procedure. Mercury recoveries from spiked samples and the reference material were all close to 100%. An LOD of 14 and 16 ng/L was obtained for total and organic mercury, respectively, both with an RSD less than 1.3%.     

Mechanism of wave formation at the interface in explosive welding

Some of the main progress on the investigation of the mechanism of the wave formation in explosive welding at the Institute of Mechanics is summarized and others' previous works are reviewed. Our systematic experiments and analysis do not substantiate the theory of wave formation based on Karman vortex-street analogy or Helmholtz instability. On the contrary, they show that material strength insensitive to strain rate plays an important role. A simple hydro-plastic model is presented to explain the main features regarding the interfacial wave formation and to estimate the magnitude of wave length. The result is in broad agreement with experiment.     

Analysis of temperature and stress field in Al alloy’s twin wire welding

By analyzing the shape of twin wire welding’s arcs and the track of droplets’ transition, the phenomenon that the twin wire welding’s fore arc and rear arc all deflect to the middle of the two arcs is found. Based on this the double ellipsoid heat source model is amended, and a heat source model which can apply to calculate the twin wire welding’s temperature field is put forward. This model is testified by actual experiment of temperature sampling. By comparing the temperature field of twin wire welding and single wire welding, the results show that twin wire welding has slender weld pool the end part of which is ellipsoid, and its HAZ is narrower than that of single wire welding. So, twin wire welding can not only reduce the Al alloy generating hot crack, but can also weaken the “overaging” softened phenomenon of heat treated strengthening Al alloy. In the end, the evolving rules of 2219 Al alloy’s longitudinal and transverse stress when welded with twin wire welding are analyzed.     

越南火龙果冷藏现状分析

随着全球化经济的快速发展,食品冷藏技术日益重要.文中综述了越南火龙果的现有冷藏技术及其存在的问题,并提出解决方案.     

冷绝缘高温超导电缆绝缘设计的研究

目前随着国内外高压输电系统的不断发展,许多研究机构一直试图开发高电压等级的高温超导电缆系统,这就要求设计的HTS电缆要有可靠的绝缘性能和优化的绝缘设计技术.根据超导电缆的结构特点和高温超导电缆系统的运行特点,对Nomex和PPLP进行了交流耐压、雷电冲击、局部放电(PD)起始电压和热循环等高压绝缘特性试验.根据不同厚度...     

Numerical investigation of hypersonic step-flows

Hypersonic aerospace vehicles are exposed to extreme flight conditions with heavy contour loads during their mission. Especially at ridges and sharp corners, the wall heat flux and pressure may cause serious damage to the body. Sometimes, the surface material cannot resist the high loading and fails completely. In this work the laminar hypersonic flow over forward and backward facing steps is investigated by CFD techniques and the results are compared with experimental data. The selected flow conditions correspond to cold hypersonic flow according to the availability of experimental data. The Navier-Stokes equations in the high temperature gas approximation of a thermally perfect gas in local equilibrium serve as the model for the physical problem. A multiblock finite-volume method is used to discretize consistently all spatial derivatives appearing in the balance equations. A second order in space Godunov-type method is utilized for the non-diffusive part of the governing equations whereas centered differences are used for the diffusive part. Time integration is performed by a second order implicit scheme. In each time step, the resulting nonlinear system of equations is solved by Newton's method employing a relaxation scheme based on conjugate gradients for the linear equation system. The results obtained permit a close insight into the physics of the flow problems under consideration and by this provide valuable information for construction concepts of hypersonic vehicles. Besides a careful comparison of the numerical results with experimental data, numerical aspects like the grid influence are addressed. Received 9 November 1998 / Accepted 2 December 1999     

Trace elements in bovine muscle: an ongoing project for a new certified reference material

In the framework of the activities of the Community Reference Laboratory (CRL) for residues at the Istituto Superiore di Sanità (ISS) of Rome, a number of proficiency tests were performed in order to assess and improve, wherever necessary, the quality of regulatory residue analysis within the EU. In this context, a pilot study was undertaken with the purpose of ascertaining the feasibility of a project for the certification of a new reference material for trace elements in bovine muscle. On behalf of the ISS, approximately 70 kg of bovine muscle, collected at a slaughterhouse in Geel (Belgium), were freeze-dried, homogenized, stabilized and bottled under argon atmosphere by the Institute for Reference Materials and Measurements, Joint Research Centre, European Commission (IRMM-JRC-EC). Preliminary analyses were carried out with Quadrupole (Q) and High Resolution (HR) Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to evaluate the content of As, Cd, Cu and Pb, whereas the Flow Injection Mercury System (FIMS) was used to quantify Hg. Digestion of the matrix was achieved by acid-assisted microwave irradiation. The mean values of experimentally obtained data were the following (in nanograms per gram): As, 24.2±1.2; Cd, 5.48±0.29; Cu, 4765±95; Hg, 3.37±0.73; and Pb, 184±7. Subsequently, 16 National Reference Laboratories (NRLs) for residues in the Member States plus the Norwegian one and eight Italian public laboratories were accepted to participate in the project and received one bottle of the freeze-dried bovine muscle. The laboratories were requested to perform three different analytical runs (in three different days), each consisting of three individual measurements. Preliminary results showed good agreement and fair evidence for homogeneity of the entire mass, thus setting the stage for the future certification of this candidate CRM.