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901.
We applied an image correlation method to Japanese Earth Resources Satellite-1 (JERS-1) synthetic aperture radar (SAR) data obtained from 1996 to 1998 to examine flow velocity within Shirase Glacier, Antarctica. From the grounding line to the downstream region of the glacier, the obtained ice-flow velocity was systematically higher on the western streamline than the eastern. The differences between the two streamlines were 0.31 km/a in 1996 and 0.37 km/a in 1998, significantly larger than the error estimate of 0.03 km/a. The direction of ice flow was about 312° at the grounding line and changed to 327° at 10 km, 346° at 20 km and 2° at 30 km downstream from the grounding line. The total accumulated deflection is 50° to the east. Under the assumption of the conservation of ice mass across the glacier, the observed eastward change in flow direction can be explained by an asymmetric deepening of bedrock topography, that is, across the 8 km width of the glacier, the eastern side is 50 m (10%) deeper than the western side. This eastward turning of flow direction appears to be accelerated by tributary inlets, that flow to the north and northeast at 60–75% of the velocity of inlets on the western streamline. 相似文献
902.
On the migration of a system of protoplanets 总被引:1,自引:0,他引:1
W. Kley † 《Monthly notices of the Royal Astronomical Society》2000,313(4):L47-L51
The evolution of a system consisting of a protoplanetary disc with two embedded Jupiter-sized planets is studied numerically. The disc is assumed to be flat and non-self-gravitating; this is modelled by the planar (two-dimensional) Navier–Stokes equations. The mutual gravitational interaction of the planets and the star, and the gravitational torques of the disc acting on the planets and the central star are included. The planets have an initial mass of one Jupiter mass M Jup each, and the radial distances from the star are one and two semimajor axes of Jupiter, respectively.
During the evolution a joint wide annular gap is created by the planets. Both planets increase their mass owing to accretion of gas from the disc: after about 2500 orbital periods of the inner planet it has reached a mass of 2.3 MJup , while the outer planet has reached a mass of 3.2 M Jup . The net gravitational torques exerted by the disc on the planets result in an inward migration of the outer planet on time-scales comparable to the viscous evolution time of the disc. The semimajor axis of the inner planet remains constant as there is very little gas left in its vicinity to induce any migration. When the distance of close approach eventually becomes smaller than the mutual Hill radius, the eccentricities increase strongly and the system may become unstable.
If disc depletion occurs rapidly enough before the planets come too close to each other, a stable system similar to our own Solar system may remain. Otherwise the orbits may become unstable and produce systems like υ And. 相似文献
During the evolution a joint wide annular gap is created by the planets. Both planets increase their mass owing to accretion of gas from the disc: after about 2500 orbital periods of the inner planet it has reached a mass of 2.3 M
If disc depletion occurs rapidly enough before the planets come too close to each other, a stable system similar to our own Solar system may remain. Otherwise the orbits may become unstable and produce systems like υ And. 相似文献
903.
本文采用NewMap Server将基础地理信息数据和旅游专题数据发布为地图服务和要素服务,通过数据库引擎连接Oracle 11g并建立服务器端的旅游空间信息数据库,将地图空间数据和属性数据进行存储与管理,并结合NewMap Server JSAPI,在Web GIS、物联网等技术的基础上,设计并完成了B/S架构的"数字洛阳旅游信息服务系统",实现了旅游信息资源的空间查询和分析、景区在线实时监控、旅游APP下载等诸多功能,为旅游管理部门和社会大众提供了直观、便捷的空间信息服务,从而方便用户掌握当地旅游资源、了解旅游即时动态、制定个性化的旅游计划。 相似文献
904.
为研究真盐生植物矿质营养特征,以北疆荒漠囊果碱蓬群落为对象,通过土壤及植株调查,分析其矿质元素特征。结果显示:(1)囊果碱蓬的生长增加了0~30cm土壤的pH值、水分及盐份含量,并使盐分在土层重新分布。(2)根系相对于土壤,具有优先吸收K+、Mg2+ 养分离子的特点;叶片相对于根系,具有优先运输Cl-、Na+、SO42- 盐分离子的特点,同一离子在吸收和运输的选择不一致,与其在整株的功能相关。(3)Cl-、Na+、SO42- 积累于叶片,含量远大于K+、Mg2+、Ca2+ ,Cl- 和Na+ 可能相伴向上运输,K+、Ca2+、Mg2+ 在根、茎、叶保持基本不变的比例。(4)囊果碱蓬属于SO4 -Cl 盐积累植物,而背景土壤为Cl-SO4 型盐土。 相似文献
905.
一种双向测距与时间同步系统的设计与分析 总被引:1,自引:0,他引:1
在研究双向单程伪距测量原理的基础上,设计了双向测距与时间同步(DRTS)终端系统总体构架,阐述了在系统中使用的技术,并搭建了基于DSP+FPGA的双向测距与时间同步系统软硬件平台。实验结果表明,此系统的码速率为5MHz、中心频率为15MI-Iz时,测距和时间同步的分辨率可达0.15cm和5ps(@1S),采用不同频率源时测距和时间同步的精度分别为1.038m和3.46ns,采用相同频率源时分别为0.28cm和9.43ps(参考频率稳定度1×10^-10/d量级)。与国外同类产品相比具有测量精度优势,但考虑通用性,此系统的硬件仍需进一步优化,软件上需要做到码速率可调。 相似文献
906.
Medicinal plants and fungi play important roles in the health of Maliseet people of northern Maine, USA. A critical aspect of exercising choice in health care for this community is the ability to locate and have access to these plants. Habitat suitability modeling is a form of geospatial technology that can enhance health sovereignty by identifying locations in which populations of medicinal plants can be conserved or established. However, use of this technology within indigenous communities has been limited. Focusing on the medicinal plant muskrat root, Acorus americanus (Raf.) Raf., we generate a habitat suitability model for eastern Aroostook County, Maine (1,055,653.659 ha) that also takes community needs into consideration. Drawing on participatory ethnographic data as well as environmental characteristics, our model combines ecological and sociocultural parameters to identify previously unknown populations of A. americanus that are accessible to tribal elders. Our model successfully predicted 95% of A. americanus locations in our field validation data set of ∼71,000 ha. Results suggest that approximately 0.6% of our study area contains suitable habitat to plant muskrat root that could also meet tribal members' gathering needs for the future. Increasing the number of potential collection sites gives communities options for gathering, thereby enhancing health sovereignty. Broadly, our work suggests that, when done in partnership with communities, different forms of geospatial technology can be beneficial tools for efforts to promote health sovereignty. 相似文献
907.
Xiang-Jun Lai Yan Li National Astronomical Observatories/ Yunnan Observatory Chinese Academy of Sciences Kunming China Key Laboratory for the Structure Evolution of Celestial Objects China Graduate University of Chinese Academy of Sciences Beijing China. 《中国天文和天体物理学报》2011,(10)
Based on the turbulent convection model (TCM) of Li & Yang, we have studied the characteristics of turbulent convection in the envelopes of 2 and 5M⊙ stars at the red giant branch and asymptotic giant branch phases. The TCM has been successfully applied over the entire convective envelopes, including the convective unstable zone and the overshooting regions. We find that the convective motions become progressively stronger when the stellar models are located farther up along the Hayashi line. In the convect... 相似文献
908.
确定卫星的位置和速度是GPS定位导航的基础,以二体问题为基础,介绍了卫星运动状态的计算方法,建立了计算卫星实时位置、速度的数学模型,并运用C 语言实现了算法,证实了算法的正确性。 相似文献
909.
《Urban geography》2013,34(7):662-682
Complementary and alternative medical approaches such as chiropractic, massage, acupuncture, holistic, and naturopathic therapies act as complements to, and in some cases replacements for, conventional medical techniques. The growing acceptance of the benefits of "traditional" medicine in the Canadian province of Ontario continues to provide complementary and alternative medicine (CAM) practitioners with business opportunities, but to date little attention has been directed toward the spatial patterns exhibited by these operations. A province-wide database of 4,599 records, containing addresses and selected characteristics (e.g., sales, employment) of CAM offices, is utilized to describe the geographic pattern across Ontario. An additional database allows for the assessment of four intermediate-sized census metropolitan areas (CMAs) in Ontario (Kingston, Guelph, Thunder Bay, and Greater Sudbury), and it is determined (using a general nearest neighbor analysis and a nearest neighbor hierarchical clustering procedure) that CAM offices are significantly clustered in specific portions of each CMA. The results from a survey administered to CAM practitioners suggests that the benefits of urbanization economies are biasing location decisions within these CMAs, and that localization economies advantages appear to be influencing complementary and alternative healthcare specialists to share offices. 相似文献
910.