On shallow-water bottom reverberation frequency dependence     

Cable  P.G. Yudichak  T.W. Dorfman  Y. Knobles  D.P. Renhe Zhang Zhaohui Peng Fenghua Li Zhenglin Li 《Oceanic Engineering, IEEE Journal of》2006,31(1):145-155

Determinations of bottom scattering strength in the decade below 1 kHz under downward refracting conditions have been made using acoustic reverberation and transmission data from the 2001 East China Sea Asian Seas International Acoustic Experiment (ASIAEX). The measurements were performed using explosive sources and receiving hydrophones in ship-suspended vertical-line arrays. The focus of this paper has been the dependence of bottom scattering strength on the frequency and characterization of the uncertainties associated with the extraction of scattering strength from reverberation. The derived bottom scattering strength gradually rises with frequency from 100-300 Hz and then more rapidly above 300 Hz. A potential explanation suggests that the frequency variation results from two scattering mechanisms, rough layer scattering at the low end of the band and sediment near-surface volume scattering at the high end. The spatial extrapolation of these results is explored by comparing them with similarly derived scattering strengths using data obtained under the Navy's Harsh Environments Program at a somewhat separated site (56 km) under environmental conditions similar to those during ASIAEX. In the ASIAEX analysis, it has been found that the largest source of uncertainty in the scattering-strength frequency dependence arises from persistence of finite-amplitude effects associated with the source signal.  相似文献   

Disk Galaxies with Finite Thickness     

Qiu-He Peng  Fang Peng  Chih-Kang Chou  Yi-Hui Lin 《Astrophysics and Space Science》2002,282(3):499-525

The effect of finite thickness on the properties of disk galaxies is calculated on the basis of a rigorous mathematical treatment in terms of Green function and Bessel Fourier transformation. In our approach, the mass of the galactic halo is determined by fitting the observed rotation curve with a five-component model. We not only choose a bulge, a thin disk and a halobut also include a nuclear bulge (i.e. the Galactic Nucleus) and a thick disk. The effect of finite thickness of the disk on both the radial and vertical self-gravity is considered in detail. The vertical dynamics of this three-dimensional system is also investigated.  相似文献   

硫化物吸附金属离子的实验研究──Ⅱ．温度与介质条件的影响     

吴大清  彭金莲  陈国玺 《地球化学》1996,(3)

合成ＰｂＳ和ＺｎＳ对Ａｇ２＋、Ｃｕ２＋、Ｃｄ２＋、Ｆｅ２＋、Ｍｎ２＋、Ｍｇ２＋、Ｓｂ２＋和Ｂｉ３＋等离子吸附量与温度关系的实验研究表明，其遵从Ｋｅｌｖｉｎ公式：在Ａ类吸附，即抗衡离子交换型吸附中，温度上升，其吸附量升降由反应热决定，本实验中Ａ类吸附多为上升型；而大部分Ｂ和Ｃ类吸附，即朗谬尔型及反朗谬尔型的吸附量则随温度上升呈指数下降。例外的仅有ＰｂＳ对Ｂｉ３＋离子的吸附，其吸附量随温度上升有微弱的上升。这可能与Ｂｉ３＋离子和吸附剂ＰｂＳ之间共晶反应和铅的铋硫盐的形成有关。Ａ类吸附的吸附量受介质条件变化影响很少。但对Ｂ和Ｃ类吸附，吸附量受ｐＨ和离子强度变化影响取决于三个因素：①吸附剂ＰｂＳ、ＺｎＳ表面电荷特性；②溶液介质条件变化时吸附离子在溶液中离子态的分布与变化；③被吸附离子在吸附剂中扩散和形成化合物或共晶的能力。因此，当ｐＨ增加时，Ｐｂｓ和ＺｎＳ对金属离子吸附量的变化表现出多样性：增加的有ＰｂＳ对Ｆｅ２＋离子的吸附；下降的有ＰｂＳ对Ｓｂ３＋离子的吸附和ＺｎＳ对Ｆｅ２＋、Ｍｎ２＋离子的吸附；不变的有ＰｂＳ对Ｂｉ３＋、Ｚｎ２＋离子的吸附和ＺｎＳ对Ｍｇ２＋离子的吸附。当溶液中离子强度增加时，由于溶液中自由态离子  相似文献   

Genetic study of Kelp “901” strain     

夏鹏王秀良  李晓捷赵玉山姚琳  段德麟 《中国海洋湖沼学报》2005,23(2):152-157

Based on DNA extraction and optimization of random amplified reaction (RAPD) to the gametophytes and sporophytes of Kelp “901” strain, genetic study on variation was conducted to its parents and offsprings of F6, F7,Fs, and F9 generation. RAPD results have shown that among 30 selected primers for gametophytes, 297 loci ranging from 200 to 3 000 bp were obtained in the average of 9,9 loci for each primer, This indicated a high polymorphic rate with RAPD detection. UPGMA (unweighted pair-group method arithmetic average) analysis showed that each male and female gametophyte of a generation could be clustered into one pair separately. The genetic distances of the Kelp 901 generation were 0.321 2-0.476 7, and the maximum was between F7 and Fs (0.476 7). Identity analysis showed that F6 generation was more close to the female parent (0.659 3), and F7 generation was more close to the male parent (0.5788). To the sporophytes study in 24 selected primers for RAPD amplification, 191 loci ranging from 230-2 800 bp were obtained, in the average to each primer of 8.0 loci. The heterozygosity to six populations were male parent (0.223 9),female parent (0.107 2), F6 (0.216 4), F7 (0.228 6), F8 (0.229 6) and F9 (0.317 2). The nearest genetic distance was 0.083 5 (Fs, F9). Total heterozygosity (HT) ofF6, F7, F8 and F9 generations was 0.318 6, the average heterozygosity (Hs) for F6,F7, F8 and F9 generations was 0.248 0, and deduced coefficient of population differentiation (Gst) was 22.2%. Six sequence characterized amplified regions (SCAR) were preliminary screened through RAPD analysis. It needed to be verified in detail as they are significant for molecular marker assistance in breeding and selecting Laminaria.  相似文献   

RFI Test Observations at a Candidate Ska Site in China     

B. Peng  J. M. Sun  H. Y. Zhang  T. Y. Piao  J. Q. Li  L. Lei  T. Luo  D. H. Li  Y. J. Zheng  R. NAN 《Experimental Astronomy》2004,17(1-3):423-430

Radio frequency interference (RFI) test observations were carried out at one of the candidate Square Kilometre Array (SKA) sites in Guizhou province, following the “RFI Measurement Protocol for Candidate SKA Sites” (hereafter RFI protocol). All data (raw and calibrated) are preserved in some suitable format, such as that set by the international RFI working group of the Site Evaluation and Selection Committee (SESC). An RFI test in December 2003 was performed according to Mode 1 of the RFI Protocol, in order to identify technical difficulties which might arise during a co-ordinated RFI measurement campaign over a period of 1 year. In this paper we describe the current equipment, observational technique and data presentation. The preliminary results demonstrate that the RFI situation at Dawodang depression in Guizhou province makes it quite a promising location for the proposed SKA. Furthermore, the first session of the RFI monitoring program, which was made in May 2004, showed that a complete RFI measurement including both modes 1 and 2 of the RFI Protocol would take about 2 weeks. The possible ways to minimize some limitations of the current equipment are also discussed, which will enable us to meet the RFI protocol.  相似文献   

上海天文台CHAMP掩星资料处理结果的统计分析   总被引：3，自引：0，他引：3  

郭鹏  严豪健  黄珹  洪振杰 《天文学报》2006,47(2):192-201

随着GPS全球定位系统的发展,已经有可能使用GPS掩星技术反演精确的大气温度,压强和湿度剖面．在概要地描述上海天文台(SHAO)开发的GPS掩星数据资料反演地球大气流程模块以后,分析了2002年8月1日至2002年8月17日期间2700多次CHAMP掩星数据资料的结果,并且与欧洲中尺度天气预报分析(ECMWF)资料进行比较和统计分析,讨论了CHAMP掩星数据的质量,并分析了CHAMP掩星数据的观测误差和ECMWF的分析模型误差．提出了一种优化的统计分析方法,它能更客观地反映GPS掩星技术的外部符合．统计分析结果表明GPS掩星数据将有可能成为数值天气预报和长期监测地球气候的非常有价值的数据资料．  相似文献   

A Statistical Model for Predicting the Average Abundance Patterns of Heavier Elements in Metal-Poor Stars     

Bo Zhang  Yan-Xia Zhang  Ji Li  Qiu-He Peng Department of Physics  Hebei Normal University  Shijiazhuang Center of Theoretical Nuclear Physics  National Laboratory of Heavy Ion Accelerator  Lanzhou National Astronomical Observatories  Chinese Academy of Sciences  Beijing Department of Astronomy  Nanjing University  Nanjing 《中国天文和天体物理学报》2002,2(5):429-440

We have collected nearly all the available observed data of the elements from Ba to Dy in halo and disk stars in the metallicity range -4.0 <[Fe/H]< 0.5. Based on the observed data of Ba and Eu, we evaluated the least-squares regressions of [Ba/Fe] on [Fe/H], and [Eu/H] on [Ba/H]. Assuming that the heavy elements (heavier than Ba) are produced by a combination of the main components of s- and r-processes in metal-poor stars, and choosing Ba and Eu as respective representative elements of the main s- and the main r-processes, a statistical model for predicting the Galactic chemical evolution of the heavy elements is presented. With this model, we calculate the mean abundance trends of the heavy elements La, Ce, Pr, Nd, Sm, and Dy with the metallicity. We compare our results with the observed data at various metallicities, showing that the predicted trends are in good agreement with the observed trends, at least for the metallicity range [Fe/H]> -2.5. Finally, we discuss our results and deduce some importa  相似文献   

Ekman层风速随高度分布方程的数值解试验     

刘敏  郭鹏 《中国科学院上海天文台年刊》2005,(1):31-38

根据大气水平运动方程推导出Ekman层风速随高度分布方程,该分布可用二阶线性微分方程表示,用有限差分法求解该二阶线性微分方程的边值问题的数值解,并给出计算程序,输出结果。将结果与经典解析解比较,讨论了经典解的正确性和适用范围。  相似文献   

Grazing of Salpa thompsoni on phytoplankton in summer in the Prydz Bay region, Antarctica     

Li Chaolun  SUN Song  Zhang Guangtao  Ji Peng 《极地研究(英文版)》2001,12(1)

During the CHINARE-Ⅺ cruise in austral summer of 1998/1999, the abundance and feeding activity of Salps thompsoni were investigated in the Prydz Bav region. Salps samples were collected by vertical tows from the depth of 200 m to the surface with a conical net of 330 μm mesh-size. At Ⅵ-3 station, the grazing rates were studied by the gut fluorescence method and culture experiments. S. Thompsoni was mainly distributed in the northern part of the survey area, and its maximum densities reached to 2795 ind. · 1000 m-3. A dramatic decrease in salp stock was observed at the Marginal Ice Zone. The results of the feeding experiments at the Ⅵ-3 show that the gut pigment contents of S. thompsoni ranged from (0. 14 - 1.27) μig ind. -1(average 0. 98 μg ind.-1). The individual ingestion rate is 7. 9 μg ind. -1 · day-1, and the filtration rate is 28 L ind. -1 · day-1 Through the daily grazing rate of S. thompsoni, which takes account of less than 1% of the phytoplankton standing stock, it shows arelatively higher grazing impress on the primary production (72. 2 % ).  相似文献   

低纬子午环绝对测定仪器瞬时方位差方法的改进(Ⅱ)     

彭青玉 《天文研究与技术》1997,(1)

在导出低纬子午环测定一颗星过卯酉、子午圈的记录时刻与瞬时方位差关系式的基础上，结合仪器在卯酉圈测定星对天顶距的方法［１］，提出了既可以绝对测定瞬时方位差，又可以绝对测定定位误差ε的新设想  相似文献