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91.
介绍了多道中心式记录强震仪的工作原理,性能及技术指标,给出了仪器的设计方法、理论分析和具体电气功能控制、时间服务系统等结构框图。文中还介绍了强震仪在地震现场观测获取的很有价值的地震记录。 相似文献
92.
David K. Aitken Craig H. Smith Toby J. T. Moore & Patrick F. Roche 《Monthly notices of the Royal Astronomical Society》1998,299(3):743-752
Thermal emission from magnetically aligned dust grains produces the observed mid-infrared polarization in the northern arm and east–west bar of SgrA West; recent arcsecond-resolution imaging polarimetry at 12.5 μm of these ionized filaments is presented, which confirms and extends previous studies. A lower limit ∼2 mG is found for the magnetic field in the northern arm and the IRS16 complex appears to be displaced from the northern arm by ∼ 0.15 pc along the line of sight. It is shown that the physical conditions in the ionized filaments of the central parsec lead to a very uniform grain alignment that is directed along the local magnetic field. The position angle of polarized emission will then be at right angles to the projection of the field direction on the plane of the sky and its amplitude a measure of the component of field along the line of sight; this makes possible a partial reconstruction of the field in three dimensions. We present the first application of the use of polarimetry in this way. This partial reconstruction is compared with the H92α observations of Roberts et al. and the implications are that the northern arm and east–west bar do not define either an orbital path or a spiral arm but rather represent a tidally stretched structure in free fall about SgrA★ with significant deviations from a single plane, and most likely represent the inner ionized rim of a more extended neutral cloud. 相似文献
93.
Gazi Md. Khalil 《Natural Hazards》1990,3(4):379-401
Bangladesh has been experiencing floods more frequently than ever before. Since 1947, she has been hit by extremely devastating floods in 1954, 1955, 1956, 1962, 1963, 1966, 1968, 1969, 1970, 1971, 1974, 1976, 1984, 1987, and 1988. Each year's highest flood record and damage costs have been broken by that of the subsequent year. All means of communication become paralysed. People lose food grains, domestic animals, homesteads, and lives. They remain marooned without food and drinking water until relief arrives. Despite huge spending on flood control, the intensity of the floods has been increasing. Therefore, speculation is naturally rife about the causes.The aim of this paper is to identify the factors which contribute to these devastating floods, and then to recommend an appropriate strategy for effective flood control. The geography, geology, and hydrology of Bangladesh are briefly discussed. The whole of the country is a huge river basin criss-crossed by as many as seven hundred rivers, tributaries, and distributaries, having a total length of 22 155 km.The river-beds are rendered shallow by heavy deposits of alluvial earth each year and tend easily to cause inundations. The quantum of silt carried by the river systems into Bangladesh is estimated to be 2.4 × 109 tonnes/yr.Disciplining the rivers means keeping the rivers navigable all year round, removing excessive deposits of silt where they threaten to block a channel, preventing widening by erosion, contracting the width where the river is excessively wide, and last but not least, preventing construction whose eventual impact might prove harmful.Natural disasters do not respect political frontiers, nothing can stop them, but their adverse impact could be minimised. The author emphasises the need for employing the abundant cheap manpower, local materials, and indigenous technology for flood control projects. 相似文献
94.
一种基于 K-D 树优化的 ICP三维点云配准方法 总被引:1,自引:0,他引:1
为提高三维点云数据配准精度和速度,提出一种基于K-D树优化的ICP三维点云配准方法,首先采用中心重合法实现点云数据的粗配准,然后利用K-D tree快速搜索最近点对改进传统ICP方法,完成三维点云数据精配准,该方法克服传统ICP算法中由于利用欧式距离来判断最近点所引起的工作量大、耗费时间多的缺陷,提高点云的配准速度。在此基础上利用斯坦福不同密度Bunny点云数据进行实验验证,结果表明在采用中心重合法实现三维点云粗配准的基础上,利用K-D tree优化ICP算法,能够提高点云配准的精度、速度和稳定性。 相似文献
95.
Paul H. Whitfield 《水文研究》2013,27(18):2691-2698
The centre of volume (COV), or the hydrograph centroid, is a measure of streamflow timing that is a widely used indicator of the effects of warmer temperatures on the hydrology of snowmelt streams. The COV was originally developed as a measure of land‐use effects, and its response is affected by several factors other than temperature, particularly total run‐off. A ‘toy’ model is used to demonstrate some of these effects, and these effects are also shown for streamflow data from Canada's Reference Hydrologic Basin Network. These deficiencies indicate that COV is neither specific nor robust as an indicator. Although these effects might be overcome by streamflow decomposition, the use of COV as an indicator of snowmelt timing should be avoided. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
96.
晚三叠世鄂尔多斯盆地湖盆沉积中心厚层砂体特征及形成机制分析 总被引:13,自引:2,他引:11
晚三叠世延长组长6、长7油层组沉积期鄂尔多斯盆地湖盆中部深水区稳定发育厚层砂岩,局部地区连续厚度可达上百米。在盆地西南沉积体系,巨型砂带北西—南东向平行于相带界线展布,与三角洲前缘砂体呈现出“断根”的现象;在东北沉积体系,砂带围绕三角洲呈群状、带状分布。厚层砂体成因复杂,总体上可称作深水重力流—牵引流沉积复合体,包括滑塌砂体、砂质碎屑流砂体、浊积砂体、三角洲砂体及底流改造砂体5种成因类型,其中以重力流沉积组合为主,但白豹及其北部主要为三角洲沉积夹重力流沉积。不同成因的砂体纵向叠加,横向复合连片形成了稳定分布、规模宏大的砂带。厚层砂体的形成、展布方向、分布范围主要受控于沉积物的供给速率、湖盆底形及构造活动等因素。 相似文献
97.
Sungho Lee Soojong Pak Christopher J. Davis Robeson M. Herrnstein T. R. Geballe Paul T. P. Ho J. Craig Wheeler 《Monthly notices of the Royal Astronomical Society》2003,341(2):509-516
We have detected the v = 1 → 0 S(1) (λ= 2.1218 μm) and v = 2 → 1 S(1) (λ= 2.2477 μm) lines of H2 in the Galactic Centre, in a 90 × 27 arcsec2 region between the north-eastern boundary of the non-thermal source Sgr A East, and the giant molecular cloud (GMC) M−0.02 − 0.07 . The detected H2 v = 1 → 0 S(1) emission has an intensity of 1.6–21 × 10−18 W m−2 arcsec−2 and is present over most of the region. Along with the high intensity, the large linewidths (FWHM = 40–70 km s−1 ) and the H2 v = 2 → 1 S(1) to v = 1 → 0 S(1) line ratios (0.3–0.5) can be best explained by a combination of C-type shocks and fluorescence. The detection of shocked H2 is clear evidence that Sgr A East is driving material into the surrounding adjacent cool molecular gas. The H2 emission lines have two velocity components at ∼+50 and ∼0 km s−1 , which are also present in the NH3 (3, 3) emission mapped by McGary, Coil & Ho. This two-velocity structure can be explained if Sgr A East is driving C-type shocks into both the GMC M−0.02 − 0.07 and the northern ridge of McGary et al. 相似文献
98.
99.
改革开放以来福建省经济重心格局演变及其空间差异 总被引:2,自引:0,他引:2
引入重心概念,运用经济空间结构重心分析模型和福建省经济发展数据,本文计算出了1989~2008年福建省经济重心点及其移动方向、移动距离;通过GIS技术输出经济重心点的空间变化图,着重从移动方向、移动距离、空间相关性等层面,阐述了福建省20年来经济重心的动态变化及演变规律、进而反映出全省经济发展的空间差异。研究表明:福建... 相似文献
100.
张靖 《成都信息工程学院学报》2007,22(1):76-79
校园数据中心是数字化校园的核心基础,包含了各种网络应用和服务的数据,其安全性关系到各项网络应用系统的安全和稳定运行。参考OSI模型原理和根据现实运行情况,提出了校园数据中心层次性安全防范策略,分级分层部署,保证了校园网络系统应用安全,具有一定的使用价值。 相似文献