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51.
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. 相似文献
52.
In a recent paper [P. Bates, A. Chmaj, A discrete convolution model for phase transition, Arch. Rational Mech. Anal. 150 (1999) 281-305], a discrete convolution model for Ising-like phase transition has been derived, and the existence, uniqueness of traveling waves and stability of stationary solution have been studied. This nonlocal model describes l2-gradient flow for a Helmholts free energy functional with general range interaction. In this paper, by using the comparison principle and the squeezing technique, we prove that the traveling wavefronts with nonzero speed is globally asymptotic stable with phase shift. 相似文献
53.
A.M. Serra 《Talanta》2009,78(3):790-794
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%. 相似文献
54.
The Coherent Gradient Sensor (CGS) is extended to the optical differentiation of specular, diffracted wave fronts leading
to the combined measurement of in- and out-of-plane displacement field gradients. A derivation of the underlying optical interference
principles is presented along with an analysis of the effective instrument sensitivity. In order to demonstrate the capabilities
of the technique, experimental measurements of crack-tip deformation fields were conducted under various loading conditions
corresponding to mode-I, mode-II, and mixed mode near-tip crack fields. The experimental procedures and results of these tests
are presented as validation of the technique. 相似文献
55.
In this paper, we study the diffusive vector disease model with delay. This problem with strong biological background has attracted much research attention. We focus on the existence of traveling wave fronts, and find that there is a moving zone for the transition from the disease-free state to the infective state. To complete the theoretical analysis, we employ the mathematical tools including the monotone iteration technique as well as the upper and lower solution method. 相似文献
56.
The degree of asphericity is estimated by determining the average radius of curvature in different sections, at various points on the surface of a sphere, and the deviation from it. We employ the vectorial shearing interferometer (VSI) as the instrument to determine the radius of curvature from two subapertures of the transparent glass sphere. We incorporate the sphere as a thick lens into the interferometric setup, illuminating it with an expanded beam. The spherical aberration, introduced by the sphere in the wave front, depends on the local sphere radius, on the refraction index of the glass, and on the cone angle of the source. The wave front aberrated by the sphere impinges on the VSI. Here, the wave front is divided in two in amplitude, it is sheared vectorially, and it is superimposed with itself. The fringe pattern is formed in the intersection of the wave fronts. The shape of the resulting fringe pattern is directly related to spherical aberration. We estimate qualitatively the degree of asphericity, comparing the phase gradients in different sections of the sphere. Here, we report on the experimental setup to test the asphericity, the results with different vectorial shearing (magnitude and direction). Finally, we perform a comparison with the theoretical predictions. 相似文献
57.
越南火龙果冷藏现状分析 总被引:1,自引:0,他引:1
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. 相似文献
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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 相似文献