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221.
通过对潼塘、大西滩、五里牌、坑口、龙家山站流量测次精简引起的误差对新安江三水源预报模型影响的分析,论述了流量测次精简误差对洪水预报的影响,提出了流量测次精简误差与洪水流量预测误差之间的关系。对《水文巡测规范》(SL195-97)的精度指标进行了论证。 相似文献
222.
223.
Summary Fresnel volumes, plane-sectional Fresnel zones and interface Fresnel zones of direct and unconverted reflected waves are studied. Exact analytical expressions for various parameters of Fresnel volumes and Fresnel zones are derived and discussed. Among others, these expressions are related to semi-axes of Fresnel zones, to overshooting and penetration distances, and to the off-ray shifts of Fresnel zones. 相似文献
224.
在新时代的城镇建设中,中国倡导发展具有历史记忆和文化脉络的新型城镇。历史街区是地方历史文化得以延续的载体,其更新改造是落实新型城镇化战略的重要内容。论文以空间生产理论作为理论框架,对广州永庆坊空间重构过程和主体文化实践进行剖析。研究发现:文化是永庆坊改造得以推进的关键因素,其文化价值得到官方认可后,开始在文化保护的框架下开展了更新改造工作。更新改造后的永庆坊由原来的居住空间转变为文化消费空间,本土文化与外来文化的杂糅对外来游客文化体验满意度造成一定负面影响。在永庆坊的更新改造案例中,文化作为重要能动力量参与历史街区多主体的空间生产,这在一定程度上丰富了空间生产的文化维度。从实践层面上看,这一案例对落实新型城镇化战略具有参考意义,在城镇化建设中应构建具有地方历史文化特色的新型城镇。 相似文献
225.
一种基于星形的星图识别算法 总被引:2,自引:0,他引:2
针对卫星自主定姿问题,提出了一种基于星形的星图识别算法.该算法直接以星对角距为匹配特征,先确定影像中亮星为中心星,并以此星与相邻星像点构建辐射状星图,统计所有满足星对角距匹配条件的导航星出现次数,次数最多的即为中心星所对应的导航星.实验表明,该算法构造的导航星表容量小,抗星等干扰,与多边形角距匹配算法相比,具有匹配速度快、识别率高、可靠性好的特点. 相似文献
226.
227.
中国古代输卤技术浅析 总被引:2,自引:0,他引:2
中国人古时候用肩担人抬的办法就近运送卤水熬盐。在汉代出现输卤技术的萌芽。北宋即有“以竹引入泉”的记载。南宋嘉定年间已有管道引卤水过江的“”。到了清代 ,输卤技术已发展成为一种行业 ,输卤管道已成了盐场上四通八达的网络。中国建造输卤管道的材料主要是竹子 ,即用锥形工具把竹节打穿 ,削光后连接起来制成输卤管道。为抬高卤水水位 ,中国人发明了“提水马车” ,为使卤水转向 ,中国人发明了“笕窝 相似文献
228.
229.
Peak rainfalls and peak runoff rates per unit area are comparable over a worldwide spectrum of climates. However, while the magnitude of the external contribution of energy or force in diverse regions is similar, the impact on the landscape varies markedly between regions. Absolute magnitudes of climatic events and absolute time intervals between such events do not provide satisfactory measures of the geomorphic effectiveness of events of different magnitudes and recurrence intervals. Although geomorphic processes are driven by complex sets of interrelated climatic, topographic, lithologic, and biologic factors, the work done by individual extreme events can be scaled as a ratio to mean annual erosion and the effectiveness of such events in forming landscape features can be related to the rate of recovery of channel form or mass wasting scars following alteration by the extreme event. Thus, a time scale for effectiveness may relate the recurrence interval of an event to the time required for a landform to recover the form existing prior to the event. River channels in temperate regions widened by floods of recurrence intervals from 50 to more than 200 years may regain their original width in matters of months or years. In semi-arid regions, recovery of channel form depends not only upon flows but upon climatic determinants of the growth of bottomland vegetation resulting in variable rates of recovery, on the order of decades, depending upon coincidence of average flows and strengthened vegetation. In truly arid regions the absence of vegetation and flow precludes recovery and the width of channels increases in drainage areas up to 100 km2 but remains relatively constant at larger drainage areas. Area as well as time controls the effectiveness of specific events inasmuch as the likelihood of simultaneous peak discharges or rainfalls and large areas is less, particularly in arid regions where events spanning areas of more than several thousand km2 are extremely rare if experienced at all. To some extent a decrease in area in a humid region is comparable with a regional change from humid toward more arid climate reflected in the increase in importance of episodic as contrasted with more continuous processes. Exceedingly rare floods of extreme magnitudes, estimated recurrence intervals of 500 years or longer, may exceed thresholds of competence otherwise unattainable in the ‘normal’ record resulting in ‘irreparable’ transformations of valley landforms. Denudation of hillslopes by mass wasting during relatively rare events can also be related to mean rates of denudation and to recovery of hillslope surfaces after scarring by different kinds of landslides. Measured recovery times described in the literature vary from less than a decade for some tropical regions to decades or more in temperate regions. Recurrence intervals of high magnitude storms which trigger mass wasting range from 1 to 2 years in some tropical areas, to 3 or 4 per hundred years in some areas of seasonal rainfall and to 100 or more years in some temperate regions. The effectiveness of climatic events on both hillslopes and rivers is not separable from gradient, lithology or other variables which control both thresholds of activity and recovery rate. 相似文献
230.
S C Bhatia S V Chalam V K Gaur V I Keilis-Borok V G Kosobokov 《Journal of Earth System Science》1989,98(1):111-123
Seismicity of the Himalayan arc lying within the limits shown in figure 1 and covering the period 1964 to 1987 was scanned
using M8 algorithm with a view to identifying the times of increased probabilities (TIPs) of the occurrence of earthquakes
of magnitude greater than or equal to 7·0, during the period 1970 to 1987. In this period, TIPs occupy 18% of the space time
considered. One of these precedes the only earthquake in this magnitude range which occurred during the period. Two numerical
parameters used in the algorithm, namely the magnitude thresholds, had to be altered for the present study owing to incomplete
data. Further monitoring of TIPs is however warranted, both for testing the predictive capability of this algorithm in the
Himalayan region and for creating a base for the search of short-term precursors. 相似文献