Periodic orbits in the gravity field of a fixed homogeneous cube     

Xiaodong Liu  Hexi Baoyin  Xingrui Ma 《Astrophysics and Space Science》2011,334(2):357-364

In the current study, the existence of periodic orbits around a fixed homogeneous cube is investigated, and the results have powerful implications for examining periodic orbits around non-spherical celestial bodies. In the two different types of symmetry planes of the fixed cube, periodic orbits are obtained using the method of the Poincaré surface of section. While in general positions, periodic orbits are found by the homotopy method. The results show that periodic orbits exist extensively in symmetry planes of the fixed cube, and also exist near asymmetry planes that contain the regular Hex cross section. The stability of these periodic orbits is determined on the basis of the eigenvalues of the monodromy matrix. This paper proves that the homotopy method is effective to find periodic orbits in the gravity field of the cube, which provides a new thought of searching for periodic orbits around non-spherical celestial bodies. The investigation of orbits around the cube could be considered as the first step of the complicated cases, and helps to understand the dynamics of orbits around bodies with complicated shapes. The work is an extension of the previous research work about the dynamics of orbits around some simple shaped bodies, including a straight segment, a circular ring, an annulus disk, and simple planar plates.  相似文献   

虚拟天文台数据访问系统(VO-DAS)任务调度设计与实现     

田海俊  刘超  高丹  路勇  杨阳  崔辰州  赵永恒  郑小平 《天文研究与技术》2011,8(1)

为解决异地、异构、海量天文数据无缝透明地统一访问,中国虚拟天文台(China-VO)研究小组自主设计并开发了一套解决方案——虚拟天文台数据访问系统(VO-DAS)。着重从执行流程、设计模式、Session机制、生命周期、资源销毁、异常处理等模块详细阐述了该系统的任务调度设计。为了验证该系统的可行性和性能,最后描述了多个天文科学范例。  相似文献   

南京北郊大气垂直扩散参数特征的测量及其应用     

曹琪敏  邹嘉南  马欣  等. 《气象与环境科学》2018,41(4):56-61

利用平面照相法,以江苏南热发电有限责任公司#Q2号烟囱为研究对象,进行了500次拍摄,通过风向风速、云量、太阳高度角等气象数据,确定了不同稳定度下南京北郊大气扩散参数的特征。与P-G扩散曲线对比发现,在强不稳定A、弱不稳定C、中性D层结中,南京北郊的大气垂直扩散参数在距离排放源200 m范围内更不稳定,而在200—1000 m范围内更稳定。其中,不稳定B层结的扩散曲线与P-G扩散曲线一致,较稳定E、稳定F层结出现于白天的频率很低。对比垂直扩散参数幂函数表达式σ_z=γx~α的系数值γ和α,本研究中α值分别比国家标准增加了28. 6%(A层结)、56. 4%(C层结)、30. 4%(D层结),而B层结的α值却比国家标准减少了22. 9%。此外,通过高斯扩散公式计算得到SO_2和NO_X扩散到观测点的浓度,发现该计算值仅占气象楼污染气体监测平台实测SO_2和NO_X浓度的0. 82%和0. 69%。结合风场发现,SO_2和NO_X实测值受观测点东部工业污染物排放的叠加效应影响较大。其中,NO_X的实测值在受到偏东风和偏南风的影响时具有较大值,且在0. 5～1. 5 m·s~(-1)的较弱风速影响时,NO_X的实测值将达到60μg·m~(-3)以上。  相似文献   

Associations of decimetric type Ⅲ bursts with coronal mass ejections and Hα flares     

Yuan Ma  De-Yu Wang  Jun Lin    Shuo Dai  Xue-Fei Zhang National Astronomical Observatories of China / Yunnan Astronomical Observatory  Chinese Academy of Sciences  Kunming  China Purple Mountain Observatory  Nanjing  China Harvard-Smithsonian Center for Astrophysics  Cambridge  MA  USA 《中国天文和天体物理学报》2010,10(5)

We present a statistical study of decimetric type Ⅲ radio bursts,coronal mass ejections(CMEs),and Hα flares observed in the period from July 2000 to March2005.In total,we investigated 395 decimetric type Ⅲ radio burst events,21% of which showed apparent correlation to CMEs that were associated with Hα flares.We noticed that the Hα flares which were strongly associated with CMEs were gradual events,and82% of them took place before CMEs appeared in the field of view of LASCO C2;that most of the CME-associated radio bursts started in the frequency range around750 MHz with a frequency drifting rate of several hundred MHz s-1,of which both positive and negative ones were recognized; and that the correlation of type Ⅲ radio bursts to CMEs without associated flares is fairly vague,less than 9%.  相似文献   

CCD photometry of five X-ray selected BL Lacertae objects     

L. Ma  G. Z. Xie  T. F. Yi  S. B. Zhou  K. H. Li  X. Zhang  H. Dai 《Astrophysics and Space Science》2010,327(1):35-58

We present the results of the monitoring of a sample of 5 HBLs in the B, V and R bands during 2003–2008. All sources in our monitoring project show significant rapid optical variations, except 1ES 1959+650, however; for 1ES 1959+650, the gamma-ray variability on a timescale of ～7 hours has been observed by Holder et al. (Astrophys. J. 583:L9, 2003). Using these variability timescales, we estimate the black hole masses for each source with the Kerr black hole theory.  相似文献   

福建省兴化湾、九龙江河口和东山湾潮间带沉积物岩心碘研究     

纪丽红  刘广山  李超  陈志刚  黄奕普 《海洋学报》2013,35(5):177-183

用碱熔法处理样品,水沥取,用分光光度法测量了采集自福建省兴化湾、九龙江河口和东山湾3个海湾潮间带沉积物岩心的碘分布。兴化湾、九龙江河口和东山湾3岩心中的碘含量分别为2.5~43.7,17.3~39.6和11.3~29.1 mg/kg。3个沉积物岩心中的碘含量稍高于福建省的土壤的碘含量,与我国海域的沉积物碘含量在同一水平,但明显低于文献报道的开阔海域沉积物的碘含量。兴化湾和东山湾沉积物中的碘与有机碳含量有较好的相关性;在九龙江河口采集的岩心中的碘与有机物碳含量的相关性较差。推测海洋源的沉积物碘与有机碳含量相关性较好,而陆源沉积物的碘与有机碳含量相关性较差。  相似文献   

Growth performance of the clam, Meretrix meretrix, breedingselection populations cultured in different conditions     

WANG Chao  CHAI Xueliang  WANG Hongxi  TANG Baojun  LIU Baozhong 《海洋学报(英文版)》2013,32(10):82-87

A breeding-selection program for the clam,Meretrix meretrix,was conducted since 2004.Two of the selection populations were generated with the shell color pattern as an additional selection criterion and named as SP(purple stripes)population and SB(black dots)population.The third-generation SP and SB populations(08G3SP and 08G3SB,respectively)were cultured at two commercial clam farms and a nursery pond and their shell lengths were compared.08G3SB clams had significantly larger sizes than 08G3SP clams at commercial clam farms(p<0.05),yet 08G3SB individuals were significantly smaller than 08G3SP individuals at the nursery pond(p<0.05).Then,we examined the growth of the fourth-generation SP and SB populations(10G4SP and 10G4SB,respectively)at a commercial farm,and found that the shell lengths of the 10G4SB clams increased at a significantly higher growth rate than the 10G4SP clams(p<0.05)from May to September,when the water temperature was between 24.2–27.5 C,while 10G4SB lost the growth advantage in the other months.These results indicated that SP and SB populations responded differently to environmental factors,so it is beneficial for the clam farmers to select a suitable population according to the culture environment.Furthermore,a diallel mating of the SB and SP populations was designed to investigate whether their hybrid population would show heterosis.However,the heterosis was not shown in this study,which might result from the slight genetic divergence between SB and SP populations.  相似文献   

地面气象站环境变化对气温序列均一性影响   总被引：12，自引：3，他引：9  

吴利红  康丽莉  陈海燕  马仙妹 《气象科技》2007,35(1):152-156

为研究浙江省地面气象站环境变化对气温序列均一性的影响程度,采用测站历史沿革资料,对全省测站环境的时空演变进行了分析。采用距平累加、偏差界限值、F值检验法,对36个代表站的年平均气温序列进行均一性检验,并对非均一性产生的原因进行分析。结果表明:1971~2004年,浙江省测站的地理环境有显著改变;36站中有39%的测站为非均一性,产生非均一性的测站中,迁站原因占57%,环境恶化占36%;测站迁站引起的非均一性多发生在1980年以后;测站迁站时,新旧站址海拔高度差大且地理环境差异显著是造成气温序列非均一性的主要原因,迁站后气温序列较旧址存在偏高或偏低现象,其值对累年平均值有影响。指出了测站在迁移或环境变化过程中应注意的事项,以助于减少气温序列非均一性。  相似文献   

沈阳长白乡-观音阁断裂、抚顺浑河断裂的定位和活动性研究   总被引：3，自引：0，他引：3  

雷清清  王超  赵晓辉  曲乐 《震灾防御技术》2007,2(2):128-136

本文基于对沈阳长白乡-观音阁断裂,以及抚顺浑河断裂开展的1:10000地质地貌填图工作,获得了这两条断裂在最老第四纪地层热释光的测年结果,它们分别为(112±6.7)ka和(150±9.0)ka。长白乡-观音阁断裂为一沿丘陵山地前缘分布的断裂,由2—3条分支断裂组成,最新的断面活动显示为压扭性正断层性质。断裂在晚更新世坡洪积扇堆积形成以来没有活动显示。3条浅层人工地震测线探测结果表明,其上断点均未错断第四系上更新统底界。断裂为中更新世活动断裂,晚更新世以来没有活动。浑河断裂为一沿丘陵山地前缘分布的断裂,由3—4条分支断裂组成,最新的断面活动显示为压扭性正断层性质。断裂在晚更新世坡洪积扇堆积形成以来没有活动显示。5条浅层人工地震测线探测结果表明,其上断点均在第四系上更新统底界以下。断裂为中更新世活动断裂,晚更新世以来没有活动。  相似文献   

Variations of Sr–Nd–Hf isotopic systematics in basalt during intensive weathering     

Jinlong Ma  Gangjian Wei  Yigang Xu  Wenguo Long 《Chemical Geology》2010,269(3-4):376-385

The Sr–Nd–Hf isotopic compositions of both saprolites and parent rocks of a profile of intensively weathered Neogene basalt in Hainan, South China are reported in this paper to investigate changes of isotopic systematics with high masses. The results indicate that all these isotopic systematics show significant changes in saprolites compared to those in corresponding parent rocks. The ⁸⁷Sr/⁸⁶Sr system was more seriously affected by weathering processes than other isotope systems, with ε_Sr drifts 30 to 70 away from those of the parent rocks. In the upper profile (> 2.2 m), the Sr isotopes of the saprolites show an upward increasing trend with ε_Sr changing from ~ 50 at 2.2 m to ~ 70 at 0.5 m, accompanying a upward increasing of Sr concentrations, from ~ 10 μg/g to ~ 25 μg/g. As nearly all the Sr of the parent rock has been removed during intensive weathering in this profile, the upward increasing of Sr concentrations in the upper profile suggests import of extraneous Sr. Rainwater in this region, which enriches in Sr (up to 139 μg/L) from seawater, may be the important extraneous source. Thus, the Sr isotopes of the saprolites in the upper profile may be mainly influenced by import of extraneous materials, and the Sr isotopic characteristics may not be retained. In contrast, the ε_Nd and ε_Hf of the saprolites drift only 0–2.6 and 0–3.7 away from the parent rocks, respectively. The negative drifts of the ε_Nd and ε_Hf are coupled with Nd and Hf losses in the saprolites; i.e., larger proportions of Nd and Hf loss correspond to lower ε_Nd and ε_Hf. Compared with the relative high Nd and Hf concentrations of the saprolites, the contributions of extraneous Nd and Hf both from wet and dry deposits of aeolian input are negligible. Thus, the ε_Nd and ε_Hf changes in the profile are mainly resulted from consecutive removal of the Nd and Hf. Calculation indicates that the ¹⁴³Nd/¹⁴⁴Nd and ¹⁷⁶Hf/¹⁷⁷Hf ratios in saprolites are all significantly lower than their initial values in the parent rock. Simply removing part of the Nd and Hf by incongruent decomposing some of the minerals may not account for this. Fractionation should be happen, which ¹⁴³Nd and ¹⁷⁶Hf may be preferentially removed from the profile relative to ¹⁴⁴Nd and ¹⁷⁷Hf during intensive chemical weathering, resulting in lower ¹⁴³Nd/¹⁴⁴Nd and ¹⁷⁶Hf/¹⁷⁷Hf ratios in saprolites relative to the parent rock, even though details for this process is not known. A positive correlation is observed between the ε_Nd and ε_Hf of the saprolites. Interestingly, the saprolites with a net loss of Nd and Hf in the upper profile show good positive correlation, and the regression line parallels the terrestrial array. By contrast, saprolites with a net gain of Nd and Hf in the lower profile generally show higher ε_Hf values at a given ε_Nd value, and the regression line between these ε_Nd and ε_Hf appears to parallel the seawater array. This supports the hypothesis that the contribution of continental Hf from chemical weathering release is the key to the obliquity of the seawater array away from the terrestrial array of the global ε_Nd and ε_Hf correlation. Our results also indicate that caution is needed when using ε_Sr, ε_Nd, and ε_Hf to trace provenances for sediments and soils.  相似文献