Microwave transmission properties of metamaterials with double sets of square holes

The transmission property of microwave through a kind of metamaterial is investigated experimentally. Such metamaterials are fabricated with a structure of double sets of square holes: subwavelength ones, and small ones whose sizes and spacing are smaller at least one order of magnitude than those of the subwavelength holes. The experimental results show that the peak power of the measured transmission spectra is dependent on the structure parameters of the small holes. The physical origin to create this phenomenon is that the designer surface plasmons sustained by the small holes affect on the transmission property of the microwave passing through the subwavelength holes. The results are promising for proposing some techniques for optoelectronic devices in terahertz and microwave regime.     

Eocene high grade metamorphism and crustal anatexis in the North Himalaya Gneiss Domes,Southern Tibet

Determination of the timing and geochemical nature of early metamorphic and anatectic events in the Himalayan orogen may provide key insights into the physical and chemical behavior of lower crustal materials during the early stage of tectonic evolution in large-scale collisional belts.The Yardoi gneiss dome is the easternmost dome of the North Himalayan Gneiss Domes(NHGD),and contains three types of amphibolites with distinct mineral assemblage,elemental and radiogenic isotope geochemistry,as well as various types of gneisses.SHRIMP zircon U/Pb analyses on the garnet amphibolite and garnet-bearing biotite granitic gneiss yield ages of nearly peak metamorphism at 45.0±1.0 Ma and 47.6±1.8 Ma,respectively,which are 2 to 4 Ma older than the age for partial melting in migmatitic garnet amphibolite(43.5±1.3 Ma).Available data have demonstrated that ultra-high pressure metamorphism in the Tethyan Himalaya occurred at ～55 Ma,and high amphibolite facies to granulite facies metamorphism at 45 to 47 Ma.In addition,partial melting at thickened crustal conditions occurred at 43.5±1.3 Ma,which led to the formation of high Sr/Y ratios two-mica granites.The high-grade metamorphic rocks in the NHGD may represent the subducted front of the Indian continental lithosphere.In large collisional belts,fertile components in crustal materials could melt and form granitic melts with relatively high Na/K and Sr/Y ratios under thickened crustal conditions,significantly different from those formed by decompressional melting during rapid exhumation.     

Episodic crustal anatexis and the formation of Paiku composite leucogranitic pluton in the Malashan Gneiss Dome, Southern Tibet

The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite, two-mica granite and garnet-bearing leucogranite. Zircon U-Pb dating yields that (1) tourmaline leucogranite formed at 28.2±0.5 Ma and its source rock experienced simultaneous metamorphism and anatexis at 33.6±0.6 Ma; (2) two-mica granite formed at 19.8±0.5 Ma; (3) both types of leucogranite contain inherited zircon grains with an age peak at ～480 Ma. These leucogranites show distinct geochemistry in major and trace elements as well as in Sr-Nd-Hf isotope compositions. As compared to the two-mica granites, the tourmaline ones have higher initial Sr and zircon Hf isotope compositions, indicating that they were derived from different source rocks combined with different melting reactions. Combined with available literature data, it is suggested that anatexis at ～35 Ma along the Himalayan orogenic belt might have triggered the initial movement of the Southern Tibetan Detachment System (STDS), and led to the tectonic transition from compressive shortening to extension. Such a tectonic transition could be a dominant factor that initiates large scale decompressional melting of fertile high-grade metapelites along the Himalayan orogenic belt. Crustal anatexis at ～28 Ma and ～20 Ma represent large-scale melting reactions associated with the movement of the STDS.     

Numerical study of threshold gain behavior for a THz random laser in a two-dimensional active disordered medium with a three-level atomic system

By numerically solving Maxwell’s equations and rate equations in a two-dimensional (2D) active random media made of ruby grains with a three-level atomic system, the threshold gain behavior for a THz random laser is investigated. The spectral intensity variation with the pumping rate is calculated for both the transverse magnetic (TM) field and the transverse electric (TE) field. The computed results show that THz random lasing could occur in a 2D disordered medium for both the TM and TE cases. Further analysis reveals that the THz lasing threshold for TM fields is lower than that for TE fields.     

一种基于Gabor小波和颜色参数模型的阴影检测算法

本文提出了一种基于Gabor小波纹理特征分析和阴影参数模型颜色分析的阴影检测算法.首先,建立背景的混合高斯分布模型,通过对特定帧的颜色分析建立阴影参数模型.对图像序列中的每一帧,首先通过差分法提取出前景区域,然后通过Gabor小波滤波的方法,对背景和前景图中的相同小区域进行纹理特征分析,比较特征向量的距离,以判断潜在的阴影点.然后,通过阴影参数模型对这些潜在的阴影点进行颜色分析,并通过连通区域标记,形态学运算,FPR(去除假阴影)分析等方法,找出真正的阴影区域.实验结果表明,本算法具有较高的阴影检测率和物体检测率,可以满足实时检测的需要.     

Polarization-dependent difference of the power spectra from two-dimensional random media with different shapes

Polarization-dependent difference of the power spectra from a set of two-dimensional （2D） passive random media is investigated by simultaneously solving Maxwell＇s equations for both transverse magnetic （TM） and transverse electric （TE） fields. The random media have the same random constitution but different shapes. Results show that both two polarized states are morphology dependent, and the variety of the shapes has more influence on the selection of TM polarized modes than that of TE polarized modes. Such polarization-dependent difference of morphology property presents a new modeselecting technique for random lasers.     

Early Oligocene anatexis in the Yardoi gneiss dome, southern Tibet and geological implications

The Yardoi gneiss dome is located to the easternmost of the North Himalayan Gneiss Dome (NHGD), southern Tibet. It consists of metapelite, garnet amphibolite, granite and leucogranite, and is a key subject to constrain the formation and tectonic evolution of NHGD. SHRIMP zircon U/Pb data on the leucogranite yield an age of 35.3±1.1 Ma, which is substantially older than that of the similar leucogranites to the west. Sr and Nd isotope systematics indicate that this leucogranite was derived from partial melting of the mixed garnet amphibolite and metapelite. Our data suggest that (1) during the early stage of Himalayan magmatism, amphibolite dehydration melting overwhelmed that of the metapelite; and (2) such a melting at middle-lower crust might be a major factor that initiated the movement along the Southern Tibetan Detachment System (STDS). Supported by National Natural Science Foundation of China (Grant No. 40673027), the Outlay Research Fund of Chinese Academy of Geological Sciences (Grant No. 20071120101125), and the Hundred Talent Program of Chinese Academy of Sciences