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We evaluate the exposure during nadir observations with JEM-EUSO, the Extreme Universe Space Observatory, on-board the Japanese Experiment Module of the International Space Station. Designed as a mission to explore the extreme energy Universe from space, JEM-EUSO will monitor the Earth’s nighttime atmosphere to record the ultraviolet light from tracks generated by extensive air showers initiated by ultra-high energy cosmic rays. In the present work, we discuss the particularities of space-based observation and we compute the annual exposure in nadir observation. The results are based on studies of the expected trigger aperture and observational duty cycle, as well as, on the investigations of the effects of clouds and different types of background light. We show that the annual exposure is about one order of magnitude higher than those of the presently operating ground-based observatories.  相似文献   
2.
<正>Objective The Gaoligongshan oblique collisional orogen is located in the southern section of the Hengduan Mountains,and belongs to one of the main Late Yanshanian-Himalayan oblique collisional orogens in the Sanjiang area.Many researchers have studied the geology,geochemistry and geophysics of this region,and many research achievements have been obtained from deep geophysical exploration of the region,especially using the magnetotelluric(MT)sounding technique.However,detailed understanding  相似文献   
3.
Debris flow susceptibility assessment is the premise of risk assessment. In this paper, Sichuan Province is chosen as a study area, where debris flow disasters happen frequently. Information value model is applied to calculate the information values of seven environmental factors, namely elevation, slope, aspect, flow accumulation, vegetation coverage, soil type and land-use type. Geographic information system technology is used to analyze the comprehensive information values so as to determine the debris flow susceptibility. The results show that the northeast, the central and the south of Sichuan are the most hazardous regions, which display a zonal distribution feature from the southeast to the south. From the validation results, 7.53 % of the total area suffers from high susceptibility and 19.97 % suffers from very high susceptibility. However, 80 % of the debris flows are concentrated in two regions. The actual occurrence ratios of debris flows of the high-susceptibility and very high-susceptibility areas are 4.95 and 2.14, respectively.  相似文献   
4.
Concern for the increasing impact of human activities on Earth's ecosystems has generated a growing effort to monitor those impacts and measure the success, if any, of mitigation measures. This contribution argues that ecological impact assessments that tend to rely primarily on the volume of natural resources produced and subsequently consumed overlook the degree to which ecological impact can vary significantly independently of production volumes, due to the varying impact that results from production effort. Production effort, in turn, is directly linked to the quality of raw materials, which inevitably tends to decrease over time. As a result, unless technological improvements were able to compensate for the resource quality decline indefinitely, we face a future of increasing marginal ecological impact over time. This is demonstrated here based on three resource extraction systems, coal mining in the UK, grain production in China, and global marine fisheries.  相似文献   
5.
Environmental factors account for the occurrence of debris flow, as well as different weights of subareas with different risk levels. Considering the relationship between debris flow and rainfall (including the intraday rainfall and the effective rainfall of the previous 10 days), seven environmental factors, including elevation, slope, aspect, flow accumulation, vegetation coverage, soil, and land use, were added in this study. The whole area of Sichuan Province was divided into subareas according to different risk levels. Debris flow prediction models were then established by using a logistic regression model. Results showed that the prediction accuracy was decreased approximately by 3 % after the environmental factors were introduced to the entire study area. The prediction accuracy of the prediction models that comprised the introduced environmental factors was increased by 22.2, 9.7, and 14.3 % in different susceptible areas (moderately susceptible, highly susceptible, very highly susceptible), respectively, compared with that of the prediction models in which rainfall was only considered. Therefore, the research method that introduced the environmental factors may be used to improve the accuracy of debris flow prediction models based on susceptible area classification.  相似文献   
6.
Supervised classification of quad-polarimetric SAR images is often constrained by the availability of reliable training samples. Active learning (AL) provides a unique capability at selecting samples with high representation quality and low redundancy. The most important part of AL is the criterion for selecting the most informative candidates (pixels) by ranking. In this paper, class supports based on the posterior probability function are approximated by ensemble learning and majority voting. This approximation is statistically meaningful when a large enough classifier ensemble is exploited. In this work, we propose to use extreme learning machines and apply AL to quad-polarimetric SAR image classification. Extreme learning machines are ideal because of their fast operation, straightforward solution and strong generalization. As inputs to the so-called active extreme learning machines, both polarimetric and spatial features (morphological profiles) are considered. In order to validate the proposed method, results and performance are compared with random sampling and state-of-the-art AL methods, such as margin sampling, normalized entropy query-by-bagging and multiclass level uncertainty. Experimental results for four quad-polarimetric SAR images collected by RADARSAT-2, AirSAR and EMISAR indicate that the proposed method achieves promising results in different scenarios. Moreover, the proposed method is faster than existing techniques in both the learning and the classification phases.  相似文献   
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考虑到梯级水电站水库联合优化调度模型的高非线性、强约束特点,提出了分形分割与混沌嵌套搜索算法的求解方法。该算法利用嵌套结构把确定性搜索和随机搜索有机结合起来,按照自身的运动规律,直接在优化区间内通过逐步的插值映射来对被优化问题进行优化搜索。通过在南桠河梯级水电站联合优化运行中的成功应用,显示该算法具有参数配置简单、普适性强、稳定性高、全局优化和易于编程等特点,并取得了与POA算法一致的收敛精度且计算速度有优势,从而为求解诸如水库优化调度等具有复杂约束条件的非线性优化问题提供了新的探索。  相似文献   
8.
It is known that sedimentary rocks demonstrate velocity dispersion in the acoustic log frequency range. In this paper we have calculated the waveforms of sonic log for a borehole located in a viscoelastic medium. The acoustic field in the borehole has been obtained for acoustic multipole sources. To describe the viscoelastic properties of a rock we used the Cole–Cole model. This model describes the dispersion of acoustic wave velocities and quality factors in a wide frequency range. To solve the acoustic log direct problem we have applied the double integral Fourier transform (RAI method). The results obtained have shown the feasibility of S-wave velocity dispersion estimation from acoustic dipole waveform processing.  相似文献   
9.
激光诱导荧光(LIF)是一种主动光学探测技术,该技术已在海面未乳化溢油油种鉴别及油膜厚度评估方面取得了一定的研究成果,但乳化溢油的监测理论基础和探测方法尚未成熟。溢油乳化物的量化会直接影响溢油污染的应急处理和灾害评估,但目前对溢油乳化液溢油量的计算尚未有研究报道。本文以水包油乳化液为研究对象,基于等效思想,根据油量相等建立了水包油乳化液与油膜的荧光检测等效模型,并依据光的辐射传输机理推导出等效油膜厚度的估算公式,最后采用仿真实例对估算方法的适用性和有效性进行了验证。实验结果表明,当水包油乳化液含油率小于12×10-6,厚度小于5.98 cm时,利用所提出的等效方法能有效计算出水包油实际溢油厚度。该方法可为海面乳化溢油量的估算提供一种创新性的方法,具有良好的借鉴意义和实际应用价值。  相似文献   
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