Antenna design and implementation for the future space Ultra-Long wavelength radio telescope     

Linjie Chen  Amin Aminaei  Leonid I. Gurvits  Marc Klein Wolt  Hamid Reza Pourshaghaghi  Yihua Yan  Heino Falcke 《Experimental Astronomy》2018,45(2):231-253

In radio astronomy, the Ultra-Long Wavelengths (ULW) regime of longer than 10 m (frequencies below 30 MHz), remains the last virtually unexplored window of the celestial electromagnetic spectrum. The strength of the science case for extending radio astronomy into the ULW window is growing. However, the opaqueness of the Earth’s ionosphere makes ULW observations by ground-based facilities practically impossible. Furthermore, the ULW spectrum is full of anthropogenic radio frequency interference (RFI). The only radical solution for both problems is in placing an ULW astronomy facility in space. We present a concept of a key element of a space-borne ULW array facility, an antenna that addresses radio astronomical specifications. A tripole–type antenna and amplifier are analysed as a solution for ULW implementation. A receiver system with a low power dissipation is discussed as well. The active antenna is optimized to operate at the noise level defined by the celestial emission in the frequency band 1 ? 30 MHz. Field experiments with a prototype tripole antenna enabled estimates of the system noise temperature. They indicated that the proposed concept meets the requirements of a space-borne ULW array facility.  相似文献   

An approximate method for evaluating the shear band thickness in saturated soils     

X. B. Lu  Wang Shuyun  Wang Yihua  Peng Cui 《国际地质力学数值与分析法杂志》2004,28(15):1533-1541

A formula for the thickness of a shear band formed in saturated soils under a simple shear or a combined stress state has been proposed. It is shown that the shear band thickness is dependent on the pore pressure properties of the material and the dilatancy rate, but is independent of the details of the combined stress state. This is in accordance with some separate experimental observations. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

The Magnetic Topological Structure and Energy of the 2B/X2 Flare in NOAA 8100     

Yihua Yan  Yang Liu  Maki Akioka  Fengsi Wei 《Solar physics》2001,201(2):337-355

In this paper, we reconstruct the finite energy force-free magnetic field of the active region NOAA 8100 on 4 November 1997 above the photosphere. In particular, the 3-D magnetic field structures before and after a 2B/X2 flare at 05:58 UT in this region are analyzed. The magnetic field lines were extrapolated in close coincidence with the Yohkoh soft X-ray (SXR) loops accordingly. It is found that the active region is composed of an emerging flux loop, a complex loop system with differential magnetic field shear, and large-scale, or open field lines. Similar magnetic connectivity has been obtained for both instants but apparent changes of the twisting situations of the calculated magnetic field lines can be observed that properly align with the corresponding SXR coronal loops. We conclude that this flare was triggered by the interaction of an emerging flux loop and a large loop system with differential magnetic field shear, as well as large-scale, or open field lines. The onset of the flare was at the common footpoints of several interacting magnetic loops and confined near the footpoints of the emerging flux loop. The sheared configuration remained even after the energetic flare, as demonstrated by calculated values of the twist for the loop system, which means that the active region was relaxed to a lower energy state but not completely to the minimum energy state (two days later another X-class flare occurred in this region).  相似文献   

辽宁菊花岛海域沉积物中某些化学要素分布特征研究     

杨新梅  周义华 《海洋湖沼通报》1991,(1):29-34

菊花岛周围海域38个站表层沉积物的铁、锰、铝、钛、磷、有机质、氮、铜、锌、铅、镉、镍和汞等化学要素含量的Q型因子分析计算表明,本区可划分为三个化学元素沉积区:1.海流悬浮沉积区;2.近岸波浪作用区;3.波浪海流作用区。柱状沉积物中铁等化学元素的迁移、富集受氧化——还原界面的控制。  相似文献   

冲绳海槽北部西坡的古三角洲沉积     

范奉鑫  阎军  陈长安  栾振东  庄丽华 《海洋科学集刊》2007,(48):42-54

自20世纪70年代我国开展东海海洋地质调査以来,在海底经常能发现河流、河口沉积物以及与水道相似的负地形、称为古河道、古三角洲或古河口等(李全兴,1990；金翔龙,1992；石斯器等,1989；秦蕴珊等、1987)第四纪气候频繁波动，造成陆架上尤其是外陆架上陆相地层与海相地层频繁交替,因此有不同时期的古三角洲和古河道保留,沉溺的古河道在我国陆架海底的不少地区均有发现。由于海底沉积作用的不均衡性,埋藏较浅的沉溺河谷从地形特征上依稀可辨,埋藏较深的在海底表面则渺无踪迹,只有借助于高分辦率的地球物理测量,才能发现其踪迹。 晚更新世末期，长江、黄河是否流经东海陆架区进入冲绳海槽,虽有不少作者论述,但终因缺少系统的实测资料而未取得共识。长江、黄河在历史上每年向大海输入巨量泥沙,加快了海淤积和推进速度,但古长江三角洲也应该是体积大、构造特征明显的大型堆积体,然而至今尚未有这方面的报道。 作者对冲绳海槽北部进行大面积高分辨率浅地层剖面分析中,发现在陆架外缘坡折线附近,近海底表面处存在大面积斜层理三角洲沉积结构,这为晚更新世末期以来自我国的大河(黄河/长江)从冲绳海槽入海提供了新的证据。  相似文献   

Variational iteration solving method for El Nio phenomenon atmospheric physics of nonlinear model     

MO Jiaqi  *  WANG Hui  LIN Wantao  LIN Yihua. Anhui Normal University  Wuhu  China. Division of Computional Science  E-Institute of Shanghai Universities  Shanghai Jiaotong University Shanghai  China. Chinese Academy of Meteorological Sciences  Beijing  China. State Laboratory of Numerical Modeling for Atmospheric Sciences  Geophysical Fluid Dynamics  Institute of Atmosheric Physics  Chinese Academy of Sciences  Beijing  China 《海洋学报(英文版)》2005,(5)

1 IntroductionThe El Ni’o atmospheric physics oscillation is anabnormal phenomenon involved in the tropical Pacificocean- atmosphere interactions. Studies on the El Ni(ophenomenon are very attractive (Lin et al., 2000; Linet al., 2001, 2002; Wang, 2001; Feng et al., 2001;Feng et al., 2002; Liu et al., 2002; Wei and Chen,2003; Xie et al., 2002; Zhu et al., 2002; Pu et al.,2003; Gu et al., 2004; Yu and Liu, 2004). Lin and Mo(2004), Mo and Lin (2004) and Mo et al. (2004) alsostudied a s…  相似文献   

开发胶东温泉地热水对环境的影响   总被引：1，自引：0，他引：1  

栾光忠  范德江 《中国海洋大学学报(自然科学版)》1994,(Z3)

根据地热水中阴离子的组分与温泉水类型，指出其中Ⅱ＿１、Ⅱ＿２：型水温高，日采水量大，矿化度高，水质复杂，相应的环境效应明显．提出地热水的大规模开采以及尾水的大量排放，对温泉周边的生态环境、工程环境、土壤及地下水等方面有明显的影响．  相似文献   

黄河三角洲河道沉积规律研究Ⅱ. 建林边滩沉积作用机理     

范德江  陈彰榕  栾光忠 《中国海洋大学学报(自然科学版)》2001,31(2):237-242

通过对建林边滩沉积物粒度分布、粒度参数及水体流变性质的分析，阐述了黄河三角洲上河道水流属于牵引流范畴，与低含沙水流无本质上的差别，并探讨沉积物搬运和沉积的基本特征。  相似文献   

北黄海大鹿岛海域营养盐分布特征     

李淑媛  张风林 《海洋湖沼通报》1995,(3):24-31

根据１９９０年７月辽宁省海岛调查资料，本文讨论了北黄海大鹿岛海水营养盐（ＰＯ４－Ｐ，ＳｉＯ３－Ｓｉ，ＮＯ３－Ｎ，ＮＨ４－Ｎ，ＮＯ２－Ｎ）分布特征，并对海域环境质量作了初步评价。  相似文献   

青岛胶州湾3.2级地震构造背景与控震断裂   总被引：1，自引：0，他引：1  

栾光忠  刘红军  刘冬雁 《中国海洋大学学报(自然科学版)》2002,32(5):763-769

本文应用构造分析的方法 ,对青岛胶州湾 3.2级地震发生的地震地质背景和构造背景进行分析。结果表明 :胶州湾 3.2级地震主要受 NEE向郝官庄断裂和 NNW向大沽河断裂控制 ,并根据现代活动断裂的标志 ,对上述 2组断裂活动性特征作了阐述  相似文献