共查询到20条相似文献，搜索用时 31 毫秒
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Gravitational attraction of a vertical right circular cylinder 总被引：1，自引：0，他引：1
Shri Krishna singh 《Geophysical Journal International》1977,50(1):243-246
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Summary. We propose a simplified method for the calculation of near field accelerograms. It is based upon the hypothesis that, in the course of dynamic faulting, the dominating part of the seismic radiation is emitted by the rupture front. As the rupture moves smoothly it radiates continuously, generating the low-frequency part of the field. High-frequency waves are produced by jumps in the rupture velocity and abrupt changes in the stress intensity factor. The wave-front discontinuities created in this fashion are evaluated by asymptotic methods and may be propagated away from the source by ray theoretical methods. We apply our technique to the evaluation of asymptotic near field accelerograms for a circular fault buried in a half-space. The agreement with numerical accelerograms calculated by full-wave theory is very satisfactory. Two problems are given particular emphasis: (1) the phase shifts introduced by focusing and (2) a simpler method, based on dislocation theory, is proposed for the calculation of the radiation coefficients from a discontinuously moving rupture front. 相似文献
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运用能值理论与分析方法,从能值流量、社会经济发展、资源循环利用、资源环境安全和综合指数5个方面构建了循环经济能值评价指标体系,对2000-2010年陕北资源型城市榆林的循环经济发展状况进行了深入分析.结果表明:榆林自然资源丰富,能值自给率达99％以上,属于资源输出型区域;经济的高速发展建立在大量消耗本地不可更新资源的基础上,仍沿袭着高资源消耗、粗放型的经济发展模式;虽然系统的资源循环利用率(RRR)逐年增长,但可持续发展指数(ESI)、改进的可持续发展指数(SDI)、循环经济能值指数(EREI)、生态效率指数(UEI)逐年下降.基于循环经济的“3+1”模式,今后榆林实现可持续发展的关键是:加大引入外界能值力度,促进能值的合理流动;依托技术创新和技术转型,提高输入能值利用效率和废弃物资源化效率;进一步开发可更新资源,促使区域产业系统的生态化转向. 相似文献
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Summary. Synthetic seismograms based upon first-order perturbation theory are analysed to test the validity of assumptions which form the basis of current velocity inversion procedures. It is found that the lowest order geometrical optics approximation, namely that measured normal mode eigen-frequencies reflect the average structure underlying the source–receiver great circle path, becomes less valid near nodes in the source radiation pattern and near the surface wave foci at the source and its antipode. These failures are a consequence of singlet interference within an isolated normal mode multiplet. The technique of determing frequency by fitting a single resonance peak to a multiplet yields results which agree well with the first-order theory for slow and fast paths where excitation is dominated by one pair of singlets but on intermediate paths where singlet interference is more of a problem, agreement is not as good. Inversion of small data sets is particularly sensitive to frequency fluctuations near radiation nodes, while larger sets are influenced more by antipodal deviations from geometrical optics. The latter leads to inversions which fail to recover the short wavelength structure of the starting model. Basing inversions directly upon first-order theory shows promise of improving recovery of short wavelengths. 相似文献
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以循环经济理论为指导,在充分分析宁县产业发展现状的基础上,依托国家推行循环经济示范县行动,探讨了宁县在创建循环经济示范县过程中存在的生态脆弱、环境承载力不足、工业基础薄弱、基础设施落后等问题,并结合运用SWOT-PEST矩阵分析,根据规划目标,从循环型工业体系、循环型现代农业体系、服务业循环经济体系、创建示范建设平台等方面提出发展循环经济的对策建议。 相似文献
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Antonio García-Jerez Francisco Luzón Manuel Navarro 《Geophysical Journal International》2008,173(3):844-858
A method for the computation of phase velocities of surface waves from microtremor waveforms is shown. The technique starts from simultaneous three-component records obtained in a circular array without a central station. Then, Fourier spectra of vertical, radial and tangential components of motion are calculated for each station and considered as complex-valuated functions of the azimuthal coordinate. A couple of intermediate real physical quantities, B and C , can be defined from the 0- and ±1-order coefficients of the Fourier series expansion of such functions. Finally, phase velocities of Rayleigh and Love waves can be retrieved from B and C by solving respective one-unknown equations. The basic assumption is the possibility of expanding the wavefield as a sum of plane surface waves with Rayleigh and Love wavenumbers being univocal functions of the circular frequency. The method is tested in synthetic ambient noise wavefields confirming its reliability and robustness for passive seismic surveying. 相似文献
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基于循环经济的黑龙江省耕地利用集约度时空差异 总被引：8，自引：0，他引：8
为准确把握耕地集约利用水平及时空变化特征,基于循环经济"减量化、再利用、资源化"的基本原则,从投入强度、重复利用、综合效益和持续状态入手构建耕地集约利用评价指标体系,采用熵值法和变异系数法对1986-2008年黑龙江省耕地利用集约度进行评价,并通过秩相关系数模型和聚类分析法分析黑龙江省各地耕地集约利用空间差异特征。结果表明:1研究期间黑龙江省耕地集约利用水平明显提高,但1994-1998年呈波动下降趋势;2除持续状态呈下降趋势外,其余准则层均表现为上升态势,耕地利用协调度处于高度协调状态;3黑龙江省东北部地区耕地利用集约度明显下降,其余地区耕地利用集约度的上升或下降幅度均不明显;4黑龙江省各地耕地利用集约度差异比较显著。 相似文献
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Attia A. Ashour 《Geophysical Journal International》1985,83(1):127-142
Summary. The electrical system of currents excited by a uniform electric field of arbitrary direction in an infinite plane sheet of uniform conductivity except for two non-overlapping circular areas is obtained analytically. Using the method introduced by Ashour, the magnetic field of the system is also obtained. The components of this additional field are expressed as line integrals which are suitable for computation. The results reduce, in the special case of one insertion, to those obtained earlier by Ashour & Chapman.
As an illustration, numerical results are obtained for the special case of two equal insertions of zero conductivity.
The analysis and results obtained are useful in estimating the modification of the currents flowing in an ocean and their magnetic field by two islands. 相似文献
As an illustration, numerical results are obtained for the special case of two equal insertions of zero conductivity.
The analysis and results obtained are useful in estimating the modification of the currents flowing in an ocean and their magnetic field by two islands. 相似文献
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《The Journal of geography》2012,111(3):150-156
Abstract The geography of Black America represents a legitimate and a distinctive sub-field of the discipline. While research time and attention is being focused increasingly on Black America much remains to be done to incorporate its study into introductory courses at both the secondary and college levels. Since many existing geography courses are inadequately structured to accommodate a meaningful analysis of Black America, it will be necessary to restructure them so that they become relevant not only to Black America but to emerging world-wide cultural patterns as well. The most logical and efficacious framework for such courses is one focused on the geography of cities. Courses dealing with urban topics can be devised so that major concepts of city structure can be presented as concomitants to topics dealing with the role and the contribution of the Negro in the city. 相似文献
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Borders are often portrayed in stark terms, perhaps as national‐scale threats, or as sites of suffering, or conversely as hosts to socio‐cultural symbiosis. Yet borders are many things all at once. In this paper, we use the comparative context of the US–Mexico border and the Mexico‐Guatemala border to critique what we call the ‘border as hegemony’, a borderscape constructed through obstructions, punitive policing and reinforcing the limits of state control. Instead, we propose a model of the ‘border as discord’. In our heuristic framework, diverse mobilities are embraced, interests of borderlanders are acknowledged and prioritized, and borders are interpreted not as a security threat but as a resource for change. 相似文献