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991.
Svetlana A. Suleymanova Vera A. Izvekova Joanna M. Rankin N. Rathnasree 《Journal of Astrophysics and Astronomy》1998,19(1-2):1-18
The characteristics of the “burst” (B) mode and “quiescent” (Q) mode pulse sequences–long known from studies at or below 103
MHz–are identified at 430 MHz for the first time. An 18-minute, Polarimetrie observation begins with a long Bmode sequence,
which has a higher average intensity, regular drifting subpulses, and a preponderance of primary polarisationmode radiation.
An abrupt transition to a Q-mode sequence is then marked by a) weaker average intensity, but occasional very bright individual
subpulses, b) a complete cessation of drifting subpulses, with disorganized subpulses now being emitted over a much wider
longitude interval, and c) near parity between the primary and secondary polarisation modes, resulting in pronounced depolarisation,
both of individual pulses and the average profile.
Careful study, however, of profile changes before and after this mode change reveals slower variations which both anticipate
the abrupt transition and respond to it. A slow attenuation of the intensity level of the dominant component is observed throughout
the duration of the B-mode sequence, which then accelerates with the onset of the Q-mode sequence. This slow variation appears
to represent a “preswitching transition” process; and the combination of effects on slow and abrupt time scales are finally
responsible for the formation of the characteristic B and Q-mode average profiles. 相似文献
992.
地球物理科学计算可视化应用系统的开发 总被引:6,自引:2,他引:4
本文介绍了以Windows95为i平台进行开发的用于地球物理数据处理的应用系统,它为地球物理数据提供提供了一种新的手段。 相似文献
993.
首先分析了磁悬浮球绕组磁力线扭曲特性,构建了含轴向和水平两自由度的磁悬浮球运动模型,采用模型转换,将系统中的匹配性和非匹配性干扰统一重构为匹配性干扰,建立新的系统状态空间方程;其次,针对悬浮气隙中气隙速度与加速度难以获取、干扰实时性观测困难的问题,提出了含干扰重构的气隙速度、加速度滑模观测器,并基于此观测器设计了滑模跟踪控制器;最后搭建含干扰重构的滑模状态观测和跟踪协同控制仿真平台,结果表明所提控制策略在动态响应速度、跟踪误差和抗干扰能力性能方面优于传统PID控制. 相似文献
994.
为提高投资效益,本文针对传统投资组合模型的缺陷,结合经验模态分解(EMD)去噪法和多重分形消除趋势交叉相关分析法(MF-DCCA),提出经验模态分解去噪下的多重分形投资组合模型(简称EMD-Mean-MF-DCCA).将新模型应用于极具投机性的加密货币投资组合,结合滚动窗口技术进行样本外检验和分析,实证结果显示:无论加密货币价格处于上升还是下降趋势,EMD-Mean-MF-DCCA相对于其他传统投资组合模型及未去噪的分形投资组合模型,均在盈利能力和夏普比率方面具有明显优化效果,且当加密货币价格大幅下跌时,基于新模型的组合投资策略也具有较好的抵抗风险能力. 相似文献
995.
基于风云三号(FY-3)气象卫星的积雪产品数据(snow cover),提出了基于经验模态分解的趋势提取方法,探讨了2010—2019年中国积雪时空动态变化趋势。结果表明:1)中国积雪覆盖频率(Snow Cover Frequency,SCF)具有显著的季节性特征,呈现先增加后减少的特点,每年2月、3月SCF达到当年最大;东北的SCF呈显著下降的年际变化趋势,其他地区变化不大。2)中国整体的积雪覆盖率(Snow Cover Rate,SCR)下降了约1.2%,内蒙古和西藏的SCR下降了约1.5%,其他地区的SCR变化不显著;主要积雪覆盖区的SCR均在2016年发生由增加到减少的转变。 相似文献
996.
It is well accepted that there is a transition of failure mode from ductile to brittle with increasing depth of cut during rock cutting process. Rock failure modes affect cutting efficiency, and knowledge of the failure transition is essential to the determination of optimum cutting parameters. The critical transition depth can be linked with rock properties. In this study, an attempt was made to model rock cutting process and to check the dependence of the critical failure mode transition depth on the brittleness of rock. For this purpose, dimensional analysis was first performed to establish the correlations between rock macro‐properties and micro‐parameters for discrete element simulations. Following the specimen calibration procedure, two types of synthetic rocks having approximately the same uniaxial compressive strength were generated as the synthetic specimens for simulating the rock cutting process. The first specimen was created using conventional model construction method with identical bond strengths between particles, giving rise to undesirably high indirect tensile strength. The second specimen was created using a proposed clustering algorithm such that the ratio between the tensile and compressive strength matches reasonably well with that of real rocks. The results of rock cutting simulations demonstrate that failure mode transition took place in both models, but for the clustered model the transition emerged at a shallower cutting depth. A further exploration was made to derive the critical depth for this transition based on the simulations performed on the clustered models. The derived relationship indicates that the critical transition depth decreases as strength ratio or brittleness of the rock increases. This provides a very useful tool for predicting the critical depth which can be used to help cutting tool design and cutting parameter optimisations. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
997.
Abstract Strong decay bounds are obtained for linearized perturbations to an unbounded, plane Couette flow in a parallel magnetic field. Finite conductivity and molecular viscosity are found to be stabilizing. Those modes decaying most slowly have the form of rolls aligned with the shear flow. The non-aligned rolls decay at an enhanced rate. Stability bounds at finite amplitude are obtained for flows bounded in one direction using energy methods. 相似文献
998.
为了解海底热液活动对沉积物元素赋存状态的影响,对东太平洋海隆(EPR)13°N和赤道附近表层沉积物样品17A-EPR-TVG1、17A-EPR-TVG5做了全样及顺序提取分析,探讨了Al、Ca、Fe、Mn、Ti、Ba、Zn、Cu、Sr、V、Mo、U及稀土元素赋存状态。XRD结果显示,17A-EPR-TVG1沉积物的主要矿物形态为黄铁矿,17A-EPR-TVG5沉积物样品主要矿物为方解石。受热液影响明显的17A-EPR-TVG1沉积物中,除Ca、Sr外,其余元素主要赋存于铁锰氧化物与残留相中。正常深海沉积物17A-EPR-TVG5中,除Al、Ba、Ti外,其余元素主要赋存于碳酸盐相及铁锰氧化物相中。稀土元素的顺序提取结果显示,17A-EPR-TVG1沉积物4个相态稀土元素北美页岩配分曲线中均有Eu正异常,17A-EPR-TVG5沉积物4个相态稀土元素北美页岩配分曲线中均出现Ce负异常,分别指示了二者形成过程中热液与海水的加入。 相似文献
999.
In a cracked material, the stress intensity factors (SIFs) at the crack tips, which govern the crack propagation and are associated with the strength of the material, are strongly affected by the crack inclination angle and the orientation with respect to the principal direction of anisotropy. In this paper, a formulation of the boundary element method (BEM), based on the relative displacements of the crack tip, is used to determine the mixed‐mode SIFs of isotropic and anisotropic rocks. Numerical examples of the application of the formulation for different crack inclination angles, crack lengths, and degree of material anisotropy are presented. Furthermore, the BEM formulation combined with the maximum circumferential stress criterion is adopted to predict the crack initiation angles and simulate the crack propagation paths. The propagation path in cracked straight through Brazilian disc specimen is numerically predicted and the results of numerical and experimental data compared with the actual laboratory observations. Good agreement is found between the two approaches. The proposed BEM formulation is therefore suitable to simulate the process of crack propagation. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
1000.
陡峻边坡崩塌主要受控于岩体节理裂隙和结构面的组合,是西南地区频发的地质灾害之一。基于对李家屋脊崩塌区的工程地质条件的调查,阐述了崩塌危岩体的变形特征,进而对其成因机制和破坏模式进行了分析,对危岩体的稳定性进行了评价,对其治理给出了防治措施建议。 相似文献