共查询到20条相似文献，搜索用时 15 毫秒
1.
Relations among fault behavior, subsurface geology, and three-dimensional velocity models 总被引：2，自引：0，他引：2
The development of three-dimensional P-wave velocity models for the regions surrounding five large earthquakes in California has lead to the recognition of relations among fault behavior and the material properties of the rocks that contact the fault at seismogenic depths; regions of high moment release appear to correlate with high seismic velocities whereas rupture initiation or termination may be associated with lower seismic velocities. These relations point toward a physical understanding of why faults are divided into segments that can fail independently, an understanding that could improve our ability to predict earthquakes and strong ground motion. 相似文献
2.
GRACE measurements of mass variability in the Earth system 总被引：39，自引：0，他引：39
Tapley BD Bettadpur S Ries JC Thompson PF Watkins MM 《Science (New York, N.Y.)》2004,305(5683):503-505
Monthly gravity field estimates made by the twin Gravity Recovery and Climate Experiment (GRACE) satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers. The annual cycle in the geoid variations, up to 10 millimeters in some regions, peaked predominantly in the spring and fall seasons. Geoid variations observed over South America that can be largely attributed to surface water and groundwater changes show a clear separation between the large Amazon watershed and the smaller watersheds to the north. Such observations will help hydrologists to connect processes at traditional length scales (tens of kilometers or less) to those at regional and global scales. 相似文献
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Animals evaluate and respond to their social environment with adaptive decisions. Revealing the neural mechanisms of such decisions is a major goal in biology. We analyzed expression profiles for 10 neurochemical genes across 12 brain regions important for decision-making in 88 species representing five vertebrate lineages. We found that behaviorally relevant brain regions are remarkably conserved over 450 million years of evolution. We also find evidence that different brain regions have experienced different selection pressures, because spatial distribution of neuroendocrine ligands are more flexible than their receptors across vertebrates. Our analysis suggests that the diversity of social behavior in vertebrates can be explained, in part, by variations on a theme of conserved neural and gene expression networks. 相似文献
4.
Phillips RJ Sjogren WL Abbott EA Smith JC Wimberly RN Wagner CA 《Science (New York, N.Y.)》1979,205(4401):93-96
The line-of-sight gravity field for Venus has been mapped by tracking the Pioneer Venus spacecraft in the vicinity of periapsis for a 45 degrees swath of longitude eastward of 294 degrees . There are consistent and systematic variations in the gravity signature from orbit to orbit, attesting to the reality of observed anomalies. Orbit 93 passes over a large positive topographic feature, the "northern plateau," for which there is no corresponding gravity signature. If this region has no isostatic compensation, the gravity signal would exceed the noise level by a factor of 7. The results of simulation modeling indicate that the northern plateau must be compensated at depths of about 100 kilometers or less. The long-wavelength anomalies seen in the Venus gravity data have been Fourier-decomposed along the orbital tracks and compared to analogous spectra for Earth. The gross power in the two mean spectra is approximately, the same, but systematic variations among the harmonics suggest differences in dynamic processes or lithospheric behavior, or both, for the two planets. 相似文献
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准确评估农用地基准地价是保障失地农民合法权益的前提.在理论分析区域间的相互作用对农用地基准地价影响的基础上,引入修正的引力模型和区域基准地价影响力模型,对农用地基准地价进行修正,弥补了当前仅从农村内部来评估农用地基准地价所带来的弊端.研究结果表明,区域间的相互作用与农用地基准地价分布成正相关,修正后的农用地基准地价与用传统方法计算的农用地基准地价在空间分布上基本一致. 相似文献
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The first two-dimensional images of the source region of Io's neutral sodium cloud have been acquired by ground-based observation. Observed asymmetries in its spatial brightness distribution provide new evidence that the cloud is supplied by sodium that is ejected nonisotropically from Io or its atmosphere. Complementary, high-time-resolution, calibrated image sequences that give the first comprehensive picture of the variations of the fainter regions of the cloud extending more than 10(5) kilometers from Io were also obtained. These data demonstrate that the cloud exhibits a persistent systematic behavior coupled with Io's orbital position, a distinct "east-west orbital asymmetry," a variety of spatial morphologies, and true temporal changes. The geometric stability of the sodium source is also indicated. Isolation of the cloud's temporal changes constitutes an important milestone toward its utilization as a long-term probe of Io and the inner Jovian magnetosphere. 相似文献
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为开展草食畜牧业产业空间转移与影响因素研究，构建分区新型种养关系。基于1980—2020年中国31个省(市、自治区，统计数据未含港澳台地区)的面板数据，利用标准差椭圆方法，系统分析草食畜牧业的空间分布模式、转移特征及其演化过程；并以产业转移特征为基础，采用空间面板模型解释产业转移的影响因素。研究发现:中国草食畜牧业的空间依赖特征显著，整体趋势自西向东北转移，进一步研究发现产业重心整体上穿越了农牧分界线，总直线位移距离达505.36 km；空间面板模型显示影响产业转移的因素总体受到生产性土地比重、土地生产能力、人均GDP、城镇居民恩格尔系数、农业劳动生产率和机械化水平等6个因素的影响，其中土地生产能力是推动草食畜牧业由牧区向农区转移的关键因素；此外，不同时期又各有侧重，将长时间序列分解为3个时期，发现机械化、城镇化、水资源利用效率等因素是各时期产业布局的主要驱动力。本研究可为构建合理空间布局、优化要素配置，进而为草食畜牧业产业结构调整政策的制定提供依据。 相似文献
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Spreading segments of the Mid-Atlantic Ridge show negative bull's-eye anomalies in the mantle Bouguer gravity field. Seismic refraction results from 33 degrees S indicate that these anomalies can be accounted for by variations in crustal thickness along a segment. The crust is thicker in the center and thinner at the end of the spreading segment, and these changes are attributable to variations in the thickness of layer 3. The results show that accretion is focused at a slow-spreading ridge, that axial valley depth reflects the thickness of the underlying crust, and that along-axis density variations should be considered in the interpretation of gravity data. 相似文献
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The spatial-temporal patterns of grain production and consumption have an important influence on the effective national grain supply on condition of tight balance in the total grain amount in China. In this paper, we analyze the spatial-temporal patterns of grain production, consumption and the driving mechanism for their evolution processes in China. The results indicate that both gravity centers of grain production and consumption in China moved toward the northern and eastern regions, almost in the same direction. The coordination of grain production and consumption increased slightly from 1995 to 2007 but decreased from 2000 to 2007. There is a spatial difference between the major districts of output increase and the strong growth potential in grain consumption, which indicates an increasing difficulty in improving the regional coordination of grain production and consumption. The movement of the gravity center of grain production is significantly correlated with regional differences in grain production policy, different economic development models, and spatial disparity of land and water resource use. For grain consumption, the main driving factors include rapid urbanization, the upgrade of food consumption structure, and distribution of food industries. 相似文献
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白洋淀近30年水质时空变化特征 总被引：8，自引：1，他引：7
运用综合污染指数法、累积距平法、Mann-Kendall检验法、分层聚类法,研究了白洋淀水质时空变化特征。结果表明:白洋淀近30年(1988-2016年)综合污染指数呈现波动变化,2015年水质最差,水质平均污染指数(WQI)达2.229;在年内变化上,综合污染指数7月最高,2月最低,夏季>秋季>春季>冬季,且TN污染指数最高;在空间分布上,南刘庄所在的西北部淀区水质最差,其次是东部和南部的光淀张庄、枣林庄、圈头、端村、采蒲台,北部的王家寨、烧车淀水质较好。 相似文献
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鲐鱼(Scomber japonicus)是中上层经济鱼类,也是我国近海重要的捕捞对象,其资源分布受不同尺度气候和海洋环境变化的显著影响。本文根据2005-2016年7-9月中国远洋渔业数据中心提供的我国东海鲐鱼捕捞数据,结合关键因子海表面温度(sea surface temperature,SST),计算各年鲐鱼渔场经纬度重心,量化鲐鱼渔场重心的时空变化。进一步分析了捕捞努力量在经度、纬度以及SST上的分布规律,并基于聚类法筛选出代表年份评估异常气候事件对鲐鱼渔场内SST及渔场重心时空分布的影响。研究结果显示,鲐鱼渔场重心具有显著的年际和月间变化,7-9月渔场逐渐向东北方向移动,且主要分布在SST为25~28°C范围内。聚类分析将各月份渔场重心分为四类,其中2007和2015年渔场分布具有显著差异。此外,鲐鱼渔场内SST与尼诺指数具有显著的正相关关系,且代表年份2007和2015年分别对应拉尼娜事件和厄尔尼诺事件,当拉尼娜事件发生时,渔场内SST上升,渔场重心逐渐北移;而厄尔尼诺事件发生时,渔场内SST下降,渔场重心主要分布在南部海域。研究表明,中国东海鲐鱼渔场时空分布受到厄尔尼诺和拉尼娜调控的海表温度变化的显著影响。 相似文献
13.
戴美琪 《西南大学学报(自然科学版)》2006,28(4):691-696
旅游流是旅游目的地与客源地之间相互作用的结果。旅游客流空间特性是旅游地理学重要研究内容之一。在大量实地调研和资料基础上,本文研究了中国新型的旅游城市张家界旅游客流市场的空间分布特征;在重力模型的基础上,以航空票价为经济距离指标,建立了基于航空廊道的旅游客流空间潜力模型;分析了张家界市旅游者空间行为特征。认为张家界客源市场空间分布广泛,并用旅游客流空间潜力模型指导旅游目的地的旅游客源市场定位。建议张家界市建立旅游航空票价调节基金来降低飞机票价、降低旅游交通门槛,促进旅游客流量的增加,发展张家界旅游业。 相似文献
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为获得不受粒度分选效应影响的黄土矿物学风化指标,对甘肃西峰和山西吉县黄土-古土壤典型样品分离成9个粒级后进行了X射线衍射测试,分析了不同粒级中钾长石/斜长石比值(K/P比值)的变化规律。研究结果表明,黄土-古土壤中K/P比值受粒度分选效应的影响,细粒级(<1μm,1~2μm)的K/P比值显著高于粗粒级(>2μm);黄土在源区的沉积旋回过程中和沉积区的成壤过程中斜长石都经历了一定程度的化学风化作用,呈现出大陆风化早期阶段特征,并且这种风化作用主要发生在细粒级中,因此,黄土和古土壤(2 um K/P比值能够有效地排除粒度分选效应的影响,直接指示黄土沉积在源区和沉积区风化作用。 相似文献
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We have discovered nonvolcanic tremor activity (i.e., long-duration seismic signals with no clear P or S waves) within a transform plate boundary zone along the San Andreas Fault near Cholame, California, the inferred epicentral region of the 1857 Fort Tejon earthquake (moment magnitude approximately 7.8). The tremors occur between 20 to 40 kilometers' depth, below the seismogenic zone (the upper approximately 15 kilometers of Earth's crust where earthquakes occur), and their activity rates may correlate with variations in local earthquake activity. 相似文献
16.
Viboud C Bjørnstad ON Smith DL Simonsen L Miller MA Grenfell BT 《Science (New York, N.Y.)》2006,312(5772):447-451
Quantifying long-range dissemination of infectious diseases is a key issue in their dynamics and control. Here, we use influenza-related mortality data to analyze the between-state progression of interpandemic influenza in the United States over the past 30 years. Outbreaks show hierarchical spatial spread evidenced by higher pairwise synchrony between more populous states. Seasons with higher influenza mortality are associated with higher disease transmission and more rapid spread than are mild ones. The regional spread of infection correlates more closely with rates of movement of people to and from their workplaces (workflows) than with geographical distance. Workflows are described in turn by a gravity model, with a rapid decay of commuting up to around 100 km and a long tail of rare longer range flow. A simple epidemiological model, based on the gravity formulation, captures the observed increase of influenza spatial synchrony with transmissibility; high transmission allows influenza to spread rapidly beyond local spatial constraints. 相似文献
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收获期因遭受雨害而品质劣变的麦粒 ,在精选过程中如不能得到有效的清除 ,则会影响到整批小麦的使用价值。本文在收获期小麦遭受雨害的情况下 ,针对日本现行小麦精选系统中比重分选机分选出的小麦 ,通过研究其糊化粘度等内部品质指标的变化 ,分析了比重分选机的精选、分级效果。结果表明 ,合理使用比重分选机 ,不仅可以有效地去除劣质麦粒、并按小麦的内部品质进行分级 ,同时可极大地缩短生产周期。 相似文献
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利用四川盆地和重庆地区1980-2012年主汛期(5-9月)基本站小时降水观测资料,分析了短时强降水事件降水量、频次和强度的日变化特征,研究了短时强降水事件日峰值位相和空间分布特征,事件极值降水日变化和持续时间等分布特征,得出以下主要结论:1)川渝盆地短时强降水事件开始时间的日变化上(01:00-24:00时,北京时间,下同),表现为"V"型结构下典型夜间峰值位相特征;结束时间的日变化上,表现为多个峰值型结构分布.强降水事件持续时间的日变化上,频次和降水量均呈双峰型结构,频次极大峰值出现在3h,而强度上随着持续时间的延长,呈现逐渐增加的趋势;2)短时强降水事件极值开始时间空间分布上,极大频次和极大降水量出现在20:00-01:00时内,主要分布在盆地南部和西部大部分地区;日峰值频次结束时间主要发生在20:00-01:00时和08:00-13:00时两个时段内,主要分布于盆地南部、中部和西部大部分地区;3)短时强降水事件极值降水的日变化上,降水量和频次呈现单峰型结构,白天多为短时间(2~4h)强降水事件出现极值,而傍晚开始至第二天清晨,持续2~10h强降水事件出现极值均有发生;强降水事件极值降水持续时间日变化,1~24h内呈单峰型结构,峰值出现在2h. 相似文献
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利用综合指数评价模型、区域重心模型、耦合协调模型、地理探测器等模型和方法,分析安徽2011—2018年各市旅游业与新型城镇化系统的重心时空演化和空间层级演化,定量识别两个系统的耦合协调时空演化及影响因素。结果表明:安徽旅游发展和新型城镇化系统的重心整体上处于合肥市区域内,重心移动轨迹向西北迁移;安徽旅游产业呈现双极领先(黄山市、合肥市)的演化格局,新型城镇化呈现单极独强(合肥)的空间格局;安徽旅游业发展和新型城镇化进程的耦合协调呈现“积聚性”与“两极化”的时空特征;人口集聚、投资水平、财政水平、第三产业发展及消费能力,对于安徽旅游发展和城镇化系统的耦合协调发展具有正向促进作用。 相似文献