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排序方式: 共有118条查询结果,搜索用时 31 毫秒
21.
给出了一种改善TM01模辐射特性的方法,由不同厚度的扇区组成的介质透镜放置于圆锥喇叭口径处,适当地选择各个扇区的厚度,从而产生圆极化的轴向为极大值的远场方向图。推导出了该天线辐射场的解析公式,解析结果与数值模拟有较好的吻合。当工作频率为5 GHz时,天线的增益达19.6 dB,口径效率31.3%,具有15.8%的带宽(反射系数S11<0.2), 且适合于高功率辐射。 相似文献
22.
Embedding theorems in the Sobolev-Morrey type spaces S
p,a,ℵτ
W
W(G) with dominant mixed derivatives
A. M. Nadzhafov 《Siberian Mathematical Journal》2006,47(3):505-516
We construct Sobolev-Morrey type spaces with dominant mixed derivatives and, using the obtained integral representation, prove some embedding theorems in these spaces. 相似文献
23.
O. V. Besov 《Mathematical Notes》1998,64(3):303-315
We obtain sufficient conditions on a domainG ⊂ ℝn for functions defined onG to be extendable by zero to the entire space ℝn with smoothness preserved in an integral norm.
Translated fromMatematicheskie Zametki, Vol. 64, No. 3, pp. 351–365, September, 1998.
This research was supported by the Russian Foundation for Basic Research under grant No. 96-01-00243 and by program “Leading
Science Schools” under grant No. 96-15-96102. 相似文献
24.
以Ca、Mg、Fe、Zn、Cu、Mn、Co和Pb的含量为评价指标,用多目标决策-理想点法从整体上分析了水牛角、黄牛角与犀角在无机元素组成方面的综合相似性,为寻找理想的犀角代用品提供了科学依据。 相似文献
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27.
牦牛角成分的薄层色谱法分离研究 总被引:2,自引:0,他引:2
牦牛角成分的薄层色谱法分离研究雷根虎,曹永民(西北大学化学系西安710069)关键词薄层色谱法,氨基酸,牦牛角1引言牦牛产于我国的青藏高原,迄今人们已对其乳汁、胆汁、骨、甲状腺、血液等做了系统的分析[1],然而对于其角的分析至今未见报道。为了合理地开... 相似文献
28.
P. Kittara A. Jiralucksanawong G. Yassin S. Wangsuya J. Leech 《International Journal of Infrared and Millimeter Waves》2007,28(12):1103-1114
We describe the design and performance of Potter horns at millimetre and submillimetre wavelength employing a novel software
package that we have developed, using Genetic Algorithm. The horn is easy to fabricate and exhibits excellent beam circularity
and low cross polarization over a 15% bandwidth which is sufficient for many applications. Excitation of the required higher
order modes is done by either a step or a flare discontinuity at the horn throat. In each case we provide design curves that
give the optimum parameters of the horn geometry as a function of frequency and beamwidth. The range of values provided covers
the parameters required for the design of horns for telescope feeds and various other instruments. The design curves show
clearly that the flare-step performance is superior to the traditional groove-step Potter horn. The simulations for designing
these horns were carried out at millimetre and submillimetre wavelengths but the results can be scaled to lower or higher
frequencies. A key component in the design method is the optimization software that searches for the correct magnitude and
location of the flare discontinuities. We have developed a software package based on the combination of modal matching, a
genetic algorithm (GA) and downhill simplex optimization. The genetic code is first used to locate the proximity of the global
minimum. The set of parameters obtained are then used as a starting point for the simplex method, which refines the parameters
to the required accuracy. 相似文献
29.
将TEM喇叭天线密封进填充变压器油的尼龙天线罩中,只要合理设计尼龙天线罩外形,使变压器油形成聚焦透镜,不仅能提高天线的功率容量,还能改善其辐射特性。基于变压器油的缩波效应和椭球的几何性质,借助几何光学理论,设计了一款具有聚焦能力的椭球变压器油透镜。变压器油的缩波效应能够增大TEM喇叭天线电尺寸,使TEM喇叭天线的辐射特性得到初步改善,透镜的聚焦能力使天线的定向性得到进一步改善。为了验证理论分析的正确性,另外设计了一款不具有聚焦能力的球状变压器油透镜作为参照,两款透镜天线仿真结果与理论分析吻合。与大气中的TEM喇叭天线相比,椭球变压器油透镜使TEM喇叭天线主波束变窄,远场电压峰峰值提高56.97%,阻抗带宽低频端从0.28GHz扩展到0.2GHz,功率容量达到18.43GW。 相似文献
30.
A new horn for high displacement amplification is developed. The profile of the horn is a cubic Bézier curve. The ultrasonic actuation of the horn exploits the first longitudinal displacement mode of the horn. A design method of the horn using an optimization scheme and finite element analyses is developed. Prototypes of the horns are manufactured by a numerical control machining process. Performances of the proposed horn have been evaluated by experiments. Experimental results of the harmonic response of the fabricated horn confirm the effectiveness of the design method. The displacement amplification of the proposed horn is 71% higher than that of the traditional catenoidal horn with the same length and end surface diameters. 相似文献