排序方式: 共有109条查询结果,搜索用时 46 毫秒
1.
通过理论研究以及高频仿真相结合的方法分析设计了一款新型Ka波段8路径向波导空间功率分配(合成)器。研发的新结构输入输出段为标准矩形波导结构,代替了传统功率分配(合成)器输入输出段的同轴结构,这种新型全金属结构更加简单紧凑,更易于加工。仿真结果表明:功率分配(合成)器工作带宽达到了34%(12GHz),基本覆盖整个Ka波段;全频带内反射系数S11低于-20dB,各支路的相位差均小于5°。通过在同轴波导渐变段引入切比雪夫渐变结构,在减小了器件尺寸的同时,在整个频带内的网络S参数也不错。这款新型Ka波段8路径向波导功率分配(合成)器将应用于前级固态功率放大器,推动回旋行波管项目研发。 相似文献
2.
P. Thangadurai S. Ramasamy R. Kesavamoorthy 《Journal of Physics and Chemistry of Solids》2005,66(10):1621-1627
Nanocrystalline tin oxide (SnO2) was prepared by chemical precipitation method with different grain sizes. The X-ray diffraction studies showed the structural stability of nanocrystalline SnO2 under high-pressure. Electrical and dielectric properties were studied on these samples using complex impedance spectroscopy under different hydrostatic pressures. Electrical resistivity and dielectric studies showed a transition in nanocrystalline SnO2 when it was subjected to high-pressure. The transition pressures obtained from both the resistivity and dielectric measurements agree with each other. The transition pressures were found to increase considerably with the decrease in grain size. Dielectric constant was found to decrease with the reduction of grain size. In order to find whether the transition with pressure is structure- related or not, Raman spectroscopy was done at normal temperature and pressure (NTP) and as a function of pressure at room temperature. Raman modes at NTP showed lines which correspond to tetragonal rutile structure of SnO2. In situ high-pressure Raman measurements were carried out up to 3.38 GPa. No structural change was found with pressure. 相似文献
3.
S.M. Al-Marzoug 《Optics Communications》2006,265(1):234-240
Designing multilayer optical coatings is a difficult optimization problem because of the huge size of the search space. In the present paper, the Luus-Jaakola (LJ) optimization procedure, a new optimization algorithm, is employed to model multilayer optical coatings in the X-ray domain. With this algorithm it is not necessary to specify initially the number of layers present in a design. Only an upper limit needs to be defined. The algorithm has been used to maximize the reflectivity over a range of incident angles at a fixed wavelength, and over a wavelength range at a fixed incident angle. The results show that the LJ algorithm can be effectively applied to the design of multilayer optical coatings resulting in fewer layers than obtained using alternative optimization methods. 相似文献
4.
Lanthanum doped bismuth titanate thin films (Bi3.25La0.75Ti3O12 - BLT) were produced by the polymeric precursor method and crystallized in a domestic microwave oven and in conventional furnace. Using platinum coated silicon substrates configuration, ferroelectric properties of the films were determined with remanent polarization Pr and a coercive field Ec of 3.9 μC/cm2 and 70 kV/cm for the film annealed in the microwave oven and 20 μC/cm2 and 52 kV/cm for the film annealed in conventional furnace, respectively. The films annealed in conventional furnace exhibited excellent retention-free characteristics at low infant periods indicating that BLT thin films can be a promise material for use in non-volatile memories. On the other hand, the pinning of domains wall causes a strong decay at low infant periods for the films annealed in the microwave furnace which makes undesireable the application for future FeRAMS memories. 相似文献
5.
The diffraction of sound from an edge of a thin chipboard panel was measured in an anechoic chamber, and compared to simulations based on the diffraction formulation developed by Svensson et al. [Svensson UP, Fred RI, Vanderkooy J. An analytic secondary source model of edge diffraction impulse responses. J Acoust Soc Am 1999;106(5):2331-44]. The measurements and simulations were performed for a line of receiver positions below the panel to include cases for which the direct sound had an unobstructed propagation path to the receivers, as well as cases for which the direct sound was occluded by the panel. Comparison of the measured and simulated responses is provided in both the time and frequency-domains, and shows that the differences between them are small over the entire audible frequency range. This case study verifies that the applied diffraction-modeling method gives accurate results, and that the assumptions of ideal source and wedge characteristics inherent in the method do not preclude its use in simulations of realistic scenarios. 相似文献
6.
Zhenghua Wang 《Solid State Communications》2004,130(9):585-589
Monodisperse Cu2O nanocubes are synthesized by reducing freshly prepared Cu(OH)2 with N2H4·H2O in water at room temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that most of these nanocubes are uniform in size, with the average edge length of ∼500 nm. Selected area electron diffraction (SAED) investigation reveals that these nanocubes are single crystalline. Further, Cu2O nanoboxes are obtained by etching Cu2O nanocubes with acetic acid solution at room temperature. The nanoboxes retain the size and external morphology of the nanocubes. 相似文献
7.
M.V. Kossov 《The European Physical Journal A - Hadrons and Nuclei》2002,14(3):377-392
Photonuclear interaction cross-sections from the GEANT4 database are approximated for all nuclei and all energies (from the
hadron production threshold to about 40 TeV). The approximation methods in the giant-dipole resonance region, nucleon resonance
region, and high-energy region are improved with respect to existing approximations. As an application of the approximation
for photonuclear cross-sections, an improved method of calculating electronuclear cross-sections is developed. The interaction
cross-section of virtual photons with nuclei at high Q2 are approximated and a simple algorithm for describing the electronuclear reactions, including high-Q2 scattering, is proposed.
Received: 22 February 2002 / Accepted: 6 May 2002 相似文献
8.
ZnO nanotubes were successfully synthesized by a simple template-free hydrothermal method. X-ray powder diffraction and transmission electron microscopy were used to characterize the as-prepared ZnO nanotubes. The average size of the nanotubes is 200-500 nm in length and 20-30 nm in diameter. In addition, a further investigation of the optimized synthetic conditions has been carried out. 相似文献
9.
R. Eichele W. Kern R. P. Huebener 《Applied Physics A: Materials Science & Processing》1981,25(2):95-103
We have studied the influence of oxygen on the superconducting properties of thin films of lead, indium and tin deposited
on glass or sapphire substrates. In addition, the morphological microstructure was investigated by scanning electron microscopy.
The film thickness was 1.0 μm, and the partial pressure of O2 during the film deposition was raised up to 1×10−4 Torr. In all three materials the development of a granular structure and a strong increase in the residual electric resistivity
was observed due to the O2-treatment. Whereas in the Pb films no change of the critical temperature was found, the In films deposited on glass substrates
showed a slight increase ofT
c due to the oxygen. The strongest increase ofT
c (up to 8%) was observed in the O2-treated Sn films. These results are discussed in terms of the McMillan theory. From our measurements of the critical current
densityj
c we conclude that edge pinning is dominant in the undoped films. All three materials showed a strong increase ofj
c due to the O2-treatment which must be interpreted in terms of bulk pinning. 相似文献
10.
An instantaneous temperature imaging technique for chemically reacting, supersonic flows over bodies is described and demonstrated in a H2/O2/Ar shock tube flow (M=1.3, 0.7 atm, 1760K freestream). Based on a planar fluorescence measurement, the approach uses a two-line rotational population ratio to infer temperature. The measured 2-d temperature profiles qualitatively match the expected flowfield structure around the blunt body, and the temperature increase across the bow shock in a single-shot measurement agrees within 5–10% of the prediction of a 1-d shock analysis. The significant systematic error sources for the technique are detailed, and the random error effects associated with shot-noise-limited fluorescence images are statistically analyzed to identify transitions which minimize the temperature errors for instantaneous and average measurements. Even for average temperature measurements, the analysis predicts errors which can be as large as 5–10% when noisy fluorescence images are used in conjunction with low temperature sensitivity. In general, temperature errors can be reduced by increasing sensitivity, i.e., the energy separation of the two rotational levels, until the fluorescence shot-noise rises to a value of 30–50% within the temperature range of interest. 相似文献