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31.
预警的概念及相关物理问题 总被引:2,自引:0,他引:2
预警是现代社会减轻自然灾害的工作中最重要的物理概念之一,也是在预测/预报的物理问题没有得到解决的情况下最具实际意义的技术之一.文章介绍了与预警有关的概念和物理问题,包括预报和预警的概念,现地预警和异地预警,讨论了不同领域的预警技术中共同的物理问题,包括“有限传播”原理、“连锁效应”原理、“相似放大”原理,以及实际工作对预警系统的主要技术要求. 相似文献
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Yuan J Mei CS Madore B McDannold NJ Panych LP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,210(1):38-43
The purpose of this study is to develop a fast and accurate temperature mapping method capable of both fat suppression and reduced field-of-view (rFOV) imaging, using a two-dimensional spatially-selective RF (2DRF) pulse. Temperature measurement errors caused by fat signals were assessed, through simulations. An 11×1140μs echo-planar 2DRF pulse was developed and incorporated into a gradient-echo sequence. Temperature measurements were obtained during focused ultrasound (FUS) heating of a fat-water phantom. Experiments both with and without the use of a 2DRF pulse were performed at 3T, and the accuracy of the resulting temperature measurements were compared over a range of TE values. Significant inconsistencies in terms of measured temperature values were observed when using a regular slice-selective RF excitation pulse. In contrast, the proposed 2DRF excitation pulse suppressed fat signals by more than 90%, allowing good temperature consistency regardless of TE settings. Temporal resolution was also improved, from 12 frames per minute (fpm) with the regular pulse to 28 frames per minute with the rFOV excitation. This technique appears promising toward the MR monitoring of temperature in moving adipose organs, during thermal therapies. 相似文献
34.
Li-Wen Cheng Yang Sheng Chang-Sheng Xia Wei Lu Michel Lestrade Zhan-Ming Li 《Optical and Quantum Electronics》2011,42(11-13):739-745
In this paper, we introduce a full 3D simulation for light power distribution of an InGaN/GaN MQW LED with a textured surface. Device simulation was performed with the APSYS software to get power distribution of light sources inside the LED. Based on this, ray tracing simulation was carried out to get light power distribution outside the LED. During the process of ray tracing, the textured surface was treated as a special material interface whose reflectivity, transmittance and refraction angle are obtained with a Finite-Difference Time-Domain (FDTD) method instead of using the usual Fresnel formulas for normal material interfaces. By comparing the ray tracing results with and without the textured surface, we found that the textured surface yields a smoother transmitted power distribution and greatly improved power extraction efficiency, which are comparable to experiment. These effects may be further improved by optimizing the texture geometry. 相似文献
35.
以2,2′-二硫代二苯甲酸、2,2′-联吡啶、咪唑、硝酸锌和硝酸锰为原料,使用水热方法合成了配合物[Zn(EBLA)(2,2′-bipy)(H2O)](EBLA=2,2′-二苯甲酸硫醚)(2,2′-bipy=2,2′-联吡啶)(1),自然挥发法制备了配合物[Mn(EBSA)(im)2(H2O)]n(EBSA=2,2′-二硫代二苯甲酸)(im=咪唑)(2)。利用元素分析、红外和热重分析对其进行了表征。利用X-射线单晶衍射对结构进行了测定,并研究了配合物1的荧光性质。配合物1中,2,2′-二苯甲酸硫醚是通过水热方法由2,2′-二硫代二苯甲酸发生原位反应制备,Zn2+离子是五配位的四角锥双核结构;配合物2中,Mn2+离子是六配位的变形八面体一维链状结构。配合物中存在氢键和π-π堆积等弱的分子间作用力。 相似文献
36.
利用圆二色光谱, 核磁, 等温滴定量热法和化学滴定方法研究单-6-马来二氰二硫代酸钠-β-环糊精在水溶液中的自包合性质。化学滴定实验结果表明十二烷基硫酸钠(SDS), Cu2+和Co2+可以改变单-6-马来二氰二硫代酸钠-β-环糊精的构象, 并且得出单-6-马来二氰二硫代酸钠-β-环糊精在水溶液中的存在形式是自包合的结论;Cu2+可以作为打开单-6-马来二氰二硫代酸钠-β-环糊精自包合结构的"钥匙", 使其构象改变后可以与中性红(NR)发生包合作用;加入EDTA与Cu2+配位后, 单-6-马来二氰二硫代酸钠-β-环糊精恢复自包合结构, 同时释放中性红客体分子。 相似文献
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使用密度泛函理论(DFT)B3LYP/6-31G(d)方法优化得到了3(5)-(9-蒽基)吡唑及其衍生物的基态(S0)分子结构, 使用单激发组态相互作用(CIS)/6-31G(d)方法优化得到这些分子的第一单重激发态(S1)的几何结构, 并使用含时密度泛函理论(TD-DFT)B3LYP/6-311++G(d,p)方法计算了它们的吸收和发射光谱. 计算结果表明, 与3(5)-(9-蒽基)吡唑相比, 无论取代基是吸电子基团还是供电子基团, 衍生物的吸收和发射峰均发生红移, 并且当取代基―R=―BH2, ―CCl3, ―CHO, ―NH2时衍生物有较长的吸收波长和发射波长. 相似文献
39.
Liling Sun Arthur L. Ruoff Chang-Sheng Zha 《Journal of Physics and Chemistry of Solids》2006,67(12):2603-2608
Optical properties of solid methane (CH4) were studied at high pressure and room temperature using a diamond anvil cell. Reflectivity and transmission measurements were used to measure the refractive index to 288 GPa. Fabry-Perot interferometery was used to measure the sample thickness to 172 GPa. This data was fitted to the derived expression of thickness vs. pressure that was then used to calculate the thickness to 288 GPa. This in turn was combined with optical absorption experiments to obtain the absorption coefficient and hence the extinction coefficient k*. From combined reflection and absorption experiments the refractive index n=ns+ik* was obtained. The index of refraction and the ratio of molar refraction to molar volume showed a large increase between 208 and 288 GPa. This behavior indicated that a phase transformation of insulator-semiconductor might have occurred in solid CH4 by 288 GPa. 相似文献
40.
The carbides of NdDy0.2Fe12-yMoyC0.6 (y = 1.5, 2) crystallized in the ThMn12-type structure have been successfully synthesized by arc melting method, followed by a heat treatment. The magnetic properties are strongly enhanced with the addition of carbon. Upon the carbonation the saturation magnetization Ms is increased by about 20emu/g and the Curie temperature Tc is enhanced by 40-70K. The spin reorientation (SR) temperature decreases from 125 K for NdDy0.2Fe10Mo2 to 55 K for NdDy0.2Fe10MO2C0.6 indicating the change of magnetocrystalline anisotropy in the Nd sublattice. It is found that the intrinsic magnetic properties of the carbides can be improved by further nitrogenation, The composite carbon-nitrogen compounds show a Tc - 560K, M8 - 105 emu/g and Ha (anisotropy field) - 86kOe for NdDy0.2Fe10Mo2Co.6Nz and a Tc- 628K, M8 - 119 emu/g and Ha - 115kOe for NdDy0.2Fe10.5Mo1.5C0.6Nz. These magnetic properties are even better than those of simple nitrides, suggesting that these compounds can be considered as a good candidate for permanent magnet applications. 相似文献