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991.
洪涝灾害是长江中游地区最为严重的自然灾害.本文叙述了以遥感和地理信息的应用为基础,将多元资料复合^[1],快速、准确与全天候的对长江中游地区水灾进行监测的方法.介绍了RS和GIS支持下建立起来的监测系统的目标、技术路线、结构流程等,并进行了应用分析.以期利用高新技术手段为长江中游地区有关部门快速了解灾情、指定救灾方案和灾后重建提供决策支持. 相似文献
992.
DING Bin WANG Hongmei YI Long CHENG Peng LI Licun ZHAI Yuping LIAO Daizheng YAN Shiping & JIANG Zonghui Department of Chemistry Nankai University Tianjin China Correspondence should be addressed to Cheng Peng or Liao Daizheng 《科学通报(英文版)》2003,48(22):2446-2449
Spin-crossover complexes are of great interest to the scientists because of their potential application in molecular-based electronic devices. Some octahedral metal compounds with 3dn (4 ≤ n ≤ 7) configuration can induce a spin state conversion through a fine tuning condition (temperature, pressure, light irradiation, etc.). If the conversion occurs reversibly with a hystersis loop and color change, it will make the system possessing memory effect. The memory effect can be magnified and the … 相似文献
993.
R. G. Vishwakarma 《General Relativity and Gravitation》2001,33(11):1973-1984
Models with a dynamic cosmological term (t) are becoming popular as they solve the cosmological constant problem in a natural way. Instead of considering any ad-hoc assumption for the variation of , we consider a particular symmetry, the contracted Ricci-collineation along the fluid flow, in Einstein's theory. We show that apart from having interesting properties, this symmetry does demand to be a function of the scale factor of the Robertson-Walker metric. In order to test the consistency of the resulting model with observations, we study the magnitude-redshift relation for the type Ia supernovae data from Perlmutter et al. The data fit the model very well and require a positive non-zero and a negative deceleration parameter. The best-fitting flat model is obtained as 0 0.5 with q
0 –0.2. 相似文献
994.
Traversa Enrico Di Vona Maria Luisa Licoccia Silvia Sacerdoti Michele Carotta Maria Cristina Gallana Massimiliano Martinelli Giuliano 《Journal of Sol-Gel Science and Technology》2000,19(1-3):193-196
Pure, 5 at%, and 10 at% Ta- or Nb-doped TiO2 nanosized powders were prepared by the sol-gel method. The powders heated to 400°C have the crystalline anatase structure. While the pure TiO2 powder heated to 850°C has the rutile structure, the addition of Ta and Nb inhibited the anatase-to-rutile phase transformation at this temperature. Ta was soluble in the titania lattice up to the concentration of 10 at%, while the solubility of Nb was 5 at%. Thick films were fabricated with these powders by screen printing technology and then fired at 650°C and 850°C for 1 h. SEM observations showed that the anatase-to-rutile phase transformation induces a grain growth of about one order of magnitude for pure TiO2. The addition of Ta and Nb is effective to keep the TiO2 grain size at the nanometric level even at 850°C. Conductance measurements showed that a good gas response is observed only for the nanostructured titania-based films. The CO response of these materials is only slightly affected by humidity. 相似文献
995.
Probability Density Function Estimation Using Gamma Kernels 总被引:6,自引:0,他引:6
Song Xi Chen 《Annals of the Institute of Statistical Mathematics》2000,52(3):471-480
We consider estimating density functions which have support on [0, ) using some gamma probability densities as kernels to replace the fixed and symmetric kernel used in the standard kernel density estimator. The gamma kernels are non-negative and have naturally varying shape. The gamma kernel estimators are free of boundary bias, non-negative and achieve the optimal rate of convergence for the mean integrated squared error. The variance of the gamma kernel estimators at a distance x away from the origin is O(n
–4/5
x
–1/2) indicating a smaller variance as x increases. Finite sample comparisons with other boundary bias free kernel estimators are made via simulation to evaluate the performance of the gamma kernel estimators. 相似文献
996.
Cosmologies with variable G and are developed in this paper from an action principle, and some exact cosmological models are presented. These models indicate that the era of variable G and must have occurred, if at all, prior to other possible eras like radiation and dust. 相似文献
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