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61.
Visualization experiments in upward forced convective nucleate boiling flows were carried out. The bubble growth and collapse have been measured using high-speed photography technique with distilled water under atmospheric pressure. The experiments show that the bubbles depart from nucleating sites shortly after nucleation and slide along the heater surface. The bubbles grow while sliding, attain a maximum size, then lift from the surface sometime during condensation, and quickly vanish in the bulk liquid. Parametric studies show that bubble diameter and departure frequency increases with an increase in heat flux, a decrease in subcooling, and a decrease in mass flux. 相似文献
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The up-conversion processes were investigated in highly doped Er3+-Yb3+ silica fiber pumped by CW or mode-locked Ti:Sapphire laser at 800 nm band. The mechanism is different from that at 980 nm pumped band. The pumping wavelength and power dependences of green, blue and red fluorescence emission were obtained. The up-conversion efficiencies of different doped concentration were investigated. The strong infrared emissions, which limit the efficiency of up-conversion were observed. 相似文献
65.
The paper is concerned with the eigenvalue problems for piezoelectric bodies with voids in contact with massive rigid plane punches and coved by the system of open-circuited and short-circuited electrodes. The linear theory of piezoelectric materials with voids for porosity change properties according to Cowin–Nunziato model is used. The generalized statements for eigenvalue problem are obtained in the extended and reduced forms. A variational principle is constructed which has the properties of minimality, similar to the well-known variational principle for problems with pure elastic media. The discreteness of the spectrum and completeness of the eigenfunctions are proved. The orthogonality relations for eigenvectors are obtained in different forms. As a consequence of variational principles, the properties of an increase or a decrease in the natural frequencies, when the mechanical, electric and “porous” boundary conditions and the moduli of piezoelectric solid with voids change, are established. 相似文献
66.
Richard A. Stern Richard W. Babbitt John Borowick Gerald Mikucki William Bayha 《International Journal of Infrared and Millimeter Waves》1985,6(10):999-1016
This paper describes the theoretical and experimental results of a novel leaky-wave antenna incorporating a homogeneous dielectric transmission line and radiating aperture into a single structure. The primary objective of this investigation is to demonstrate the ability to control aperture radiation by simply cutting slots into a metal-free dielectric transmission line. Experimental line source antennas with identical periodic slots were designed to operate in the 35 GHz frequency region. The successful performance of these antennas resulted in the design of a dielectric line source antenna with a symmetrical amplitude taper which provided a lower sidelobe level. The design represents a significant breakthrough in achieving affordable, low-loss, lightweight antennas in the millimeter wave region. The most significant applications for this type of antenna include radar surveillance and tactical missile-seeker terminal guidance. 相似文献
67.
This paper revisits the popular Rayleigh integral approximation and also considers a second approximation, the high frequency boundary element method, which is similar to the Rayleigh integral. The Rayleigh integral approximation under consideration is enhanced so that only the elements visible to a particular point in the field are used to calculate the sound pressure at that point. It is demonstrated how both the Rayleigh integral and high frequency boundary element method are approximations to the boundary integral equation so that similarities between the two methods are recognized. Several test cases were conducted in order to assess and compare both methods. The first set of test cases was the pulsating and oscillating sphere. Both methods were then compared on more applied examples including a running engine, construction cab, and transmission housing. It was concluded that though both methods can reliably predict the sound power for some problems, the high frequency boundary element method is the more robust. 相似文献
68.
We investigate transverse electromagnetic waves propagating in a plasma influenced by the gravitational field of the Reissner–Nordström black hole. Applying 3+1 spacetime split we reformulate the relativistic two-fluid equations to take account of gravitational effects due to the event horizon and describe the set of simultaneous linear equations for the perturbations. Using a local approximation we investigate the one-dimensional radial propagation of Alfvén and high frequency electromagnetic waves. We derive the dispersion relation for these waves and solve it for the wave number k numerically. 相似文献
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At least two bunchers are needed in the 3 MeV H- Medium Energy Beam Transport(MEBT)line located between RFQ and DTL for the CSNS(China Spallation Neutron Source).A nose-cone geometry has been adopted as the type of buncher cavity for its simplicity,higher impedance and lower risk of multipacting.By making use of the results got from the simulations on the buncher with two-dimension code SUPERFISH,the thermal and structural analyses have been carried out,the process and results to determine the resulting frequency shift due to thermal and structural distortion of the cavity are presented,the water-cooling channel position and the optimum cooling water temperature as well as the tuning method by adjusting the cooling water temperature when the cavity is out of resonance are also determined through the analyses. 相似文献