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Neutron and photon sources have been combined in order to assess the performance of these combinations to discriminate between materials of similar composition. The evaluation has been carried out on the basis of the maximum and minimum ratio values of the relative transmissions of high-energy gamma- or X-ray and neutrons. The number of materials with similar ratio values was used as an indicator of the effectiveness of each source combination. The use of three sources, instead of two, significantly improves the capability of neutron/photon combination to separate similar in composition materials. 相似文献
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Internal waves from a body accelerating in a thermocline 总被引:1,自引:0,他引:1
Many papers study the steady wave system around bodies moving in thermoclines but little attention has been given to unsteady wave systems. This paper concentrates on the unsteady wave systems around accelerating bodies in thermoclines. The wave shapes are calculated using a theory derived from a dispersion relation based on an exp-tanh density profile. All modes of oscillation can be determined and it is shown that for the lowest mode both oblique and transverse waves occur whereas for the higher modes the presence of transverse waves depends on the background conditions and on the speed of the body. Cauchy-Poisson impulsive start waves are included. The theoretical wave shapes compare quite well with those calculated using finite-difference formulations of the full Navier-Stokes equations when a body accelerates from rest.It is also shown how the dispersion relation =N sin together with the WKB approximation can produce the same plan-view wave forms as those obtained using the thermocline wave dispersion relation given by [17, 30]. 相似文献
46.
A three-dimensional ray theory is presented for calculating the phase configuration of internal waves around a moving disturbance
in a flow with arbitrary stratification and background shear. The theory is applied to two-dimensional stratified shear flows
which have been produced in the laboratory and good agreement is shown between the theoretical and experimental phase configurations.
Good agreement is also shown when caustics and critical levels are present. This paper includes the wave systems arising from
a combined translation and oscillatory motion of a source and it shows how distinct systems of waves arise from each, type
of motion under different background conditions. This paper shows that for two-dimensional steady wave systems the critical
level is at a well defined height which is independent of wavenumber but in three dimensions the critical height can in general
vary with wavenumber. 相似文献
47.
A five-step total synthesis of the antibiotic marinopyrrole A (1) is described. The developed synthetic technology enabled the synthesis of several marinopyrrole A analogs whose antibacterial properties against methicillin-resistant Staphylococcus aureus TCH1516 were evaluated. 相似文献
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