低剖面紧凑的圆盘加载单极子天线     

侯岳峰  张志军 《南京气象学院学报》2019,11(1):8-12

本文介绍了一种低剖面小型化圆盘加载单极子天线.通过盘加载的方式,在中心频率5.8 GHz处,首先将单极子天线的剖面从大约12.9 mm（0.25λ₀）降低到2 mm（0.039λ₀）,实现了低剖面的特性.加载在单极子天线上方的圆盘,尺寸大概为21 mm（0.41λ₀）,因此天线具有结构紧凑的特点.接着,为了使天线具有良好的匹配,在加载圆盘四周加入4个接地通孔,并且在馈电端口加入集总电感.最终,天线在中心工作频率5.8 GHz处实现了反射系数-15 dB的匹配性能.  相似文献   

Potential Influence of a Developing La Niña on the Sea-Ice Reduction in the Barents–Kara Seas     

Rui Luo  Peng Zhang  Juan Dou 《大气与海洋》2013,51(3):182-194

Abstract

The potential influence of a developing La Niña on Arctic sea-ice annual variability is investigated using both observational data and an atmospheric general circulation model. It is found that during the developing phase of an eastern Pacific (EP) La Niña event in June, July, and August (JJA) and September, October, and November (SON), the sea-ice concentration (SIC) over the Barents–Kara Seas declines more than 15%. The local atmospheric circulation pattern associated with the EP La Niña is characterized as a weak decrease in geopotential height over the Barents–Kara Seas, combined with an anticyclone in the North Atlantic. The corresponding southerly winds push warm waters northward into the key sea-ice reduction region and directly accelerate sea-ice melt. Meanwhile, the abundant moisture contained in the lower troposphere is transported into the Arctic region by winds resulting from the local barotropic structure. The humid atmosphere contributes to both net shortwave and longwave radiation and thus indirectly accelerates the decline in sea ice. Simulations by the European Centre Hamburg Model, version 5.4, are forced by observed sea surface temperature anomalies associated with EP La Niña events. The results of the simulations capture the North Atlantic anticyclone and reproduce the moisture transport, which supports the premise that an EP La Niña plays a crucial role in sea-ice reduction over the Barents–Kara sector from the perspective of atmospheric circulation and net surface heat flux.  相似文献   

Analytical solutions for Euler–Bernoulli beam on visco‐elastic foundation subjected to moving load     

Dipanjan Basu  N. S. V. Kameswara Rao 《国际地质力学数值与分析法杂志》2013,37(8):945-960

Analytical solutions for the steady‐state response of an infinite beam resting on a visco‐elastic foundation and subjected to a concentrated load moving with a constant velocity are developed in this paper. The beam responses investigated are deflection, bending moment, shear force and contact pressure. The mechanical resistance of the foundation is modeled using two parameters k_s and t_s — k_s accounts for soil resistance due to compressive strains in the soil and t_s accounts for the resistance due to shear strains. Since this model represents the ground behavior more accurately than the Winkler spring model, the developed solutions produce beam responses that are closer to reality than those obtained using the existing solutions for Winkler model. The dynamic beam responses depend on the damping present in the system and on the velocity of the moving load. Based on the study, dynamic amplification curves are developed for beam deflection. Such amplification curves for deflection, bending moment, shear force and contact pressure can be developed for any beam‐foundation system and can be used in design. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Evidence for normal and inhomogeneous lowermost mantle and core-mantle boundary structure under the Arctic and northern Canada     

F. Krüger  M. Weber  F. Scherbaum  J. Schlittenhardt 《Geophysical Journal International》1995,122(2):637-657

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作物叶面蒸腾与棵间蒸发分摊系数的计算方法   总被引：13，自引：2，他引：13       下载免费PDF全文

康绍忠  张富仓 《水科学进展》1995,6(4):285-289

依据在冬小麦和玉米冠层表面及冠层内部下方土壤表面的净辐射观测资料,建立了一个能较准确地反映叶面蒸腾与棵间土壤蒸发分摊系数物理变化规律的较实用的计算模式,结果表明,分摊系数(α)随叶面积指数(LAI)增加而增加,且具有明显的日变化,α在中午最小、早、晚稍大,这种日变化受叶气孔调节的影响。  相似文献   

青藏高原地表净辐射的气候学研究   总被引：7，自引：2，他引：7  

翁笃鸣  高建芸 《南京气象学院学报》1993,16(4):464-470

根据作者提出的地表净辐射各分量的气候学计算方法，计算出青藏高原及其周边地区１７３站的净辐射和其各分量的年，月平均通量密度，并分析其地理分布特征。指出高原主体为总辐射，有效辐射的高值区，地表净辐射场在冬，夏季有较大差异。冬季为一弱正值区，相对低中心呈块状散布在祁连山区等几个地区；夏季因夜雨及地表湿润的缘故，高原大部地区的地表净辐射反有加强。各地净辐射年变化基本形式与总辐射相似。有效辐射年变化一般呈双  相似文献   

The effect of sea tides on gravity tidal observations on the Antarctic Ekstrom ice shelf     

Bulent Tezkan  Ugur Yaramanci 《Geophysical Journal International》1993,114(3):561-568

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地球弓激波前的低频磁流体波     

李少峰  孙炜 《地球物理学报》1990,33(2):239-241

一、引言 在地球弓激波前存在着低频磁流体波。这种低频磁流体波是太阳风在地球弓激波上的反射粒子和太阳风粒子之间相互作用产生的。根据人造卫星的观测资料可以得到,在地球弓激波前,Pc3-4脉动频率范围内的低频磁流体波的主频率和行星际磁场强度  相似文献   

激光束光学系统的变焦理论     

何平安  林银森 《武汉大学学报(信息科学版)》1994,(1)

从高斯光束经过光学系统的传输与变换规律出发，借助于高斯括号的性质，研究了激光束光学系统的变焦特性，导出了机械补偿式激光束变焦系统的变焦方程及补偿点位置方程，并给出了计算实例。  相似文献   

用吴氏网法推求震源地方柯氏力的方向          下载免费PDF全文

郭安宁 《地震工程学报》1994,16(2):23-28

本文研究讨论了吴尔夫网（吴氏网）求解地震断层错动时产生的柯里奥利力（简称柯氏力）的方向及其在断层面法线、倾斜方向和走向上分量问题。在空间上用数学方法直接处理柯氏力的方向及分量比较繁琐复杂，且难于表示，而用吴氏网作为工具处理这些问题时就显得快速简便，诸要素都集中于一图上，空间直观性很强。文中还以唐山大地震为例实际处理了唐山地震断层两盘产生的柯氏力方向及在断层面上的各分量方向。  相似文献