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The concentrations of arsenic, selenium, iodine and bromine in a series of fish, plant and mammalian oils have been determined
by cyclic instrumental neutron activation analysis (CINAA). Crude fish oils contain between 0.047 and 0.151 μg Se g−1, 2.36–14.5 μg As g−1, 2.36–9.63 μg Br g−1 and 0.97–4.76 μgI g−1. Seal oil contains the same four elements, but at levels below the lower end of the fish oil ranges. Iodine, bromine and
arsenic were not detected in rape-seed or soybean oils and the concentration of selenium varied from < 0.010 to 0.042 μg g−1. The levels of selenium, iodine and bromine are reduced markedly by hydrogenation of the menhaden oils. The CINAA method
yielded results which were in agreement with pub-lished values obtained by other methods. The technique was rapid, requiring
minimal sample manipulation, and was essentially free from interferences. 相似文献
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Microwave acid digestion and preconcentration neutron activation analysis of biological and diet samples for iodine 总被引:1,自引:0,他引:1
A simple preconcentration neutron activation analysis (PNAA) method has been developed for the determination of low levels of iodine in biological and nutritional materials. The method involves dissolution of the samples by microwave digestion in the presence of acids in closed Teflon bombs and preconcentration of total iodine, after reduction to iodide with hydrazine sulfate, by coprecipitation with bismuth sulfide. The effects of different factors such as acidity, time for complete precipitation, and concentrations of bismuth, sulfide, and diverse ions on the quantitative recovery of iodide have been studied. The absolute detection limit of the PNAA method is 5 ng of iodine. Precision of measurement, expressed in terms of relative standard deviation, is about 5% at 100 ppb and 10% at 20 ppb levels of iodine. The PNAA method has been applied to several biological reference materials and total diet samples. 相似文献
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The propagation of horizontally polarised shear waves in an internal irregular magnetoelastic self-reinforced stratum which is sandwiched between two semi-infinite magnetoelastic self-reinforced media is studied. Two shapes of irregularities on the interface of layer and lower semi-infinite media are considered, namely rectangular and parabolic. The dispersion equation is obtained in closed form. The combined effects of reinforcement, magnetic field and irregularity are also studied. Some important features of the results are highlighted. It is also observed that the dispersion equation is in agreement with the classical Love-type wave equation for an isotropic layer sandwiched between two isotropic half-spaces in the absence of reinforcement, magnetic field and irregularity. 相似文献
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The present article investigates the characteristic of moving load and effect of irregularity, hydrostatic stress, and magneto-elastic coupling parameter on the stresses developed due to moving load on the surface of an irregular magneto-elastic monoclinic half-space subjected to the friction associated with a rough surface. Boundary conditions are listed for which corresponding analyses can be performed analogously. The expressions for stresses are obtained analytically. Numerical computation of the obtained results are carried out for three different materials with monoclinic symmetry (lithium niobate, lithium tantalate, and quartz); the significant effects of affecting parameters on these relations are distinctly marked by means of graphs. 相似文献
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Amares Singh Teow Sinn Khai Rajkumar Durairaj Amer Ahmed Qassem Saleh 《哈尔滨工业大学学报(英文版)》2022,29(1):57-63
In recent years, intensive studies have been carried out to find an alternative for Tin (Sn)-Lead (Pb) solder alloys with increasing demand over lower temperature solder alloys in current electronic packaging industry. High temperature operational solder alloys seem to produce drawback to other components on the printed circuit board (PCB). Low melting temperature Sn58Bi substrate as a potential replacement was investigated in this paper based on the melting properties, wettability, and shear strength. The Sn58Bi was soldered at a temperature below 200 ℃ on the Cu substrate, and the shear strength and contact angle were calculated. A peak temperature (melting temperature, TM) of 144.83 ℃ was identified. Single lap joint method was performed at a strain rate of 0.1 mm/min and an average shear strength of 23.4 MPa was found from three samples. The contact angle (wettability) was calculated to study the solder joint behaviour at reflow temperature of 170 ℃. The contact angle of the Sn58Bi was found to be 32.4 ° and considered to be desired value since the angle is less than 50 °. The low temperature soldering provides a preliminary result to allow further application on the real PCB. 相似文献
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Rasiah S. Ramakrishna Senerath Palmakumbura Amares Chatt 《Journal of the science of food and agriculture》1987,38(4):331-339
Trace elements, phosphorus, ?catechins’? and caffeine levels in different varieties of Sri Lanka tea have been determined. The range and mean of zinc, copper, iron, lead and cadmium in 73 tea samples were as follows: zinc 22.5–62.5 and 35.0 μug g?1, copper 10.0–25.0 and 17.8 μug g?1, iron 40.0–185.0 and 128.1 μug g?1, lead 0.188–0.561 and 0.426 μug g?1, cadmium 0.156–0.380 and 0.239 μug g?1. Significant differences in zinc, iron, lead and cadmium were observed among tea varieties grown at different elevations in Sri Lanka. These levels were also compared with results obtained with samples from other countries. The phosphorus content in ?black tea’? showed correlations with trace metal levels in the order lead>zinc>iron>copper>cadmium. Positive correlation with levels of ?catechins’? were more significant with zinc and cadmium. Caffeine levels were found to be significantly correlated with lead and zinc in ?black tea’?. Studies of translocation of trace metals from soil have involved analysis of various parts of the tea shoot and supporting soil. 相似文献
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The main qualities of a protocol for multimedia flows transportation are related to the way congestions are handled. This paper addresses the problem of end-to-end congestion control performed in the Internet transport layer. We present a simple protocol called Primo, which determines the appropriate sending rate in order to maximize network resources usage and minimize packets loss. Comparison with existing transport protocols (Tcp Reno, Sack, Vegas andTfrc) are considered, regarding various efficiency criteria such as sending and reception rates stability, loss rate, resources occupancy rate and fairness. 相似文献