排序方式： 共有56条查询结果，搜索用时 15 毫秒
31.
32.
33.
一种利用Cloude-Pottier分解和极化白化滤波的全极化SAR图像分类算法 总被引：6，自引：2，他引：4
提出了一种新的基于Cloude-Pottier分解和极化白化滤波(PWF)的全极化SAR数据分类算法。该算法利用PWF的结果来代替反熵A对复WishartH/α分类结果进行进一步细化,按PWF的值将复WishartH/α分类结果由8类分为16类,然后再次进行Wishart迭代分类。实验结果表明,该算法能有效地提高分类精度,分类结果明显优于常规的复WishartH/α分类结果和复WishartH/α/A分类结果。 相似文献
34.
锦州油田无碱二元复合驱实验研究 总被引：1，自引：0，他引：1
针对锦州油田的条件及开采现状，进行了α烯烃磺酸盐类表面活性剂HDS及SNF聚合物组成的二元复合体系（SIP）提高采收率的室内研究。考查了HDS表面活性剂的界面张力特性以及吸附特征；进行了二元复合体系的界面张力、表观黏度及岩心驱替等实验。结果表明：HDS表面活性剂油水平衡界面张力可以降低到超低数量级（10mN／m），吸附损失小（0．2％浓度HDS≤2．0mg／g）；二元复合体系油水平衡界面张力也能达到超低；黏度保持率高（≥90％），配伍性好，相对水驱提高采收率20％以上。故HDS表面活性剂是性能优良的表面活性剂，HDS与SNF聚合物组成的无碱二元复合体系能大大提高锦州油田的采收率，无碱二元复合驱是适合锦州油田开发的新技术。 相似文献
35.
In this paper, the mα-tangent method is implemented in conjunction with elastic modulus adjustment procedure (EMAP) and an algorithm has been proposed for limit load estimation. This technique is applied to a number of ship structure components possessing different kinematic redundancies. Specifying spatial variations in the elastic modulus, numerous sets of statically admissible and kinematically admissible stress and strain distributions are generated, and both lower and upper bound limit load multipliers are obtained. Utilizing the lower and upper bound multipliers, accurate limit loads of ship structure components are then determined using the mα-tangent method. Results are compared with the inelastic finite element results and the available analytical solutions. 相似文献
36.
2012年7月27日陕北佳县特大暴雨天气的成因 总被引：1，自引：0，他引：1
利用常规高低空气象观测资料、地面逐小时降水、物理量、NCEP再分析资料和卫星云图,对2012年7月27日发生在陕北佳县的一次特大暴雨天气进行诊断分析,结果表明：暴雨前期副热带高压较强,当西风带的冷空气与副热带高压西北侧的西南暖湿气流交汇时,触发对流产生;低层700 hPa西南气流、850 hPa东南气流为特大暴雨提供了比较充沛的水汽;大气低层存在大量不稳定能量;高空200 hPa陕西北部位于浅槽的前部、急流入口区的右侧,存在正涡度平流,这一区域有强烈的辐散,提供了较强的上升运动,是特大暴雨产生的主要机制;在卫星云图上表现为一个水平尺度为200~400km、云顶亮温最低为-60℃,生命史为14 h的中-α尺度对流云团。 相似文献
37.
Recently emerged indications imply that particular concentrations and qualities of dissolved organic carbon (DOC) have the potential to reduce species diversity in zooplankton. In this contribution, we tested the impact of a major component of DOC, the dissolved humic substances (HSs), on two life history traits of a clone of Daphnia magna, namely lifespan and reproduction. We chose reproduction as a variable since it guarantees the persistence of the population in its habitat, and lifespan was selected as the most integrative individual variable. We found that lifespan was extended by exposure to HSs, but lifetime reproduction was clearly reduced. On the other hand, the mineral and biochemical composition of food also significantly modulated these life history traits. By feeding coccal green algae that contained linolenic acid, arginine (Arg), and histidine (His), but that lacked polyunsaturated fatty acids (PUFAs) with C-back bones >18, we examined how short-chained PUFAs, either alone or in concert with Arg and His, are able to modulate life history traits. Our expectation was that the additional challenge by HSs would shift the energy allocation in favor of reproduction. We found that the carbon and amino acid content may account for longevity, even when challenged by HSs. Reproduction appeared to be triggered by the C:P and N:P ratios of the food, particularly given the rather low P-content, which was within the range of severe growth limitation. Consequently, exposure to HSs reduced offspring numbers. Resting eggs without males occurred only in Desmodesmus armatus fed Daphnia that were simultaneously exposed to HSs. Under these conditions, the total amino acid (AA) content seemed to trigger reproduction. In summary, exposure to HSs appeared to have the potential to change the competitive ability of zooplankters by modulating the energy allocation between body maintenance and reproduction. 相似文献
38.
39.
Abstract A spherical α2-dynamo is presented as an expansion in the free decay modes of the magnetic field. In the limit of vanishing viscosity the momentum equation yields various asymptotic expansions for the flow, depending on the precise form of the dissipation and boundary conditions applied. A new form for the dissipation is introduced that greatly simplifies this asymptotic expansion. When these expansions are substituted back into the induction equation, a set of modal amplitude equations is derived, and solved for various distributions of the α-effect. For all choices of α the solutions approach the Taylor state, but the manner in which this occurs can vary, as previously found by Soward and Jones (1983). Furthermore, as hypothesized by Malkus and Proctor (1975), but not previously demonstrated, the post-Taylor equilibration is indeed independent of the viscosity in the asymptotic limit, and depending on the choice of a may be either steady-state or oscillatory. 相似文献
40.
Rainer Hollerbach 《地球物理与天体物理流体动力学》2013,107(1-4):245-260
Abstract The modal α2-dynamo of Hollerbach and Ierley (1991) is extended to include both parities, dipolar and quadrupolar. Two choices of α are considered. As before, the solutions approach the Taylor state, and the subsequent equilibration is independent of the viscosity in the asymptotic limit. The first choice of α yields stable steady-state pure-parity solutions of either type, and may yield some insight into the question of parity selection. The second choice of α yields rather complex time-dependent mixed-parity solutions, and demonstrates the extent to which parity coupling can affect the evolution of time-dependent solutions. 相似文献