共查询到20条相似文献，搜索用时 31 毫秒
1.
A new equivalent map projection called the parallels plane projection is proposed in this paper. The transverse axis of the parallels plane projection is the expansion of the equator and its vertical axis equals half the length of the central meridian. On the parallels plane projection, meridians are projected as sine curves and parallels are a series of straight, parallel lines. No distortion of length occurs along the central meridian or on any parallels of this projection. Angular distortion and the proportion of length along meridians (except the central meridian) introduced by the projection transformation increase with increasing longitude and latitude. A potential application of the parallels plane projection is that it can provide an efficient projection transformation for global discrete grid systems. 相似文献
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Eve L. Kuniansky 《Ground water》2017,55(2):255-260
For regional groundwater flow models (areas greater than 100,000 km2), improper choice of map projection parameters can result in model error for boundary conditions dependent on area (recharge or evapotranspiration simulated by application of a rate using cell area from model discretization) and length (rivers simulated with head‐dependent flux boundary). Smaller model areas can use local map coordinates, such as State Plane (United States) or Universal Transverse Mercator (correct zone) without introducing large errors. Map projections vary in order to preserve one or more of the following properties: area, shape, distance (length), or direction. Numerous map projections are developed for different purposes as all four properties cannot be preserved simultaneously. Preservation of area and length are most critical for groundwater models. The Albers equal‐area conic projection with custom standard parallels, selected by dividing the length north to south by 6 and selecting standard parallels 1/6th above or below the southern and northern extent, preserves both area and length for continental areas in mid latitudes oriented east‐west. Custom map projection parameters can also minimize area and length error in non‐ideal projections. Additionally, one must also use consistent vertical and horizontal datums for all geographic data. The generalized polygon for the Floridan aquifer system study area (306,247.59 km2) is used to provide quantitative examples of the effect of map projections on length and area with different projections and parameter choices. Use of improper map projection is one model construction problem easily avoided. 相似文献
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Dr. Carlo Bernasconi 《Pure and Applied Geophysics》1953,26(1):16-19
Riassunto Quando una membrana elastica ed isotropa che riveste parzialmente una sfera viene distesa su un piano, la rete dei meridiani e paralleli stampata sulla membrana stessa si deforma secondo il principio della minima energia. L'Autore illustra con alcuni esempi la possibilità di ottenere buone proiezioni cartografiche fruendo del principio medesimo.
Summary Whenever an elastic and isotropic diaphragm partially coating a sphere is spread on a plane, the net of the meridians and parallels loses the proper shape according to the principle of the lowest energy. The Author explains through some examples how to get cartographic projections by using the same principle.相似文献
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ZDOAN YILMAZ 《Geophysical Prospecting》1989,37(4):357-382
A conventional velocity-stack gather consists of constant-velocity CMP-stacked traces. It emphasizes the energy associated with the events that follow hyperbolic traveltime trajectories in the CMP gather. Amplitudes along a hyperbola on a CMP gather ideally map onto a point on a velocity-stack gather. Because a CMP gather only includes a cable-length portion of a hyperbolic traveltime trajectory, this mapping is not exact. The finite cable length, discrete sampling along the offset axis and the closeness of hyperbolic summation paths at near-offsets cause smearing of the stacked amplitudes along the velocity axis. Unless this smearing is removed, inverse mapping from velocity space (the plane of stacking velocity versus two-way zero-offset time) back to offset space (the plane of offset versus two-way traveltime) does not reproduce the amplitudes in the original CMP gather. The gather resulting from the inverse mapping can be considered as the model CMP gather that contains only the hyperbolic events from the actual CMP gather. A least-squares minimization of the energy contained in the difference between the actual CMP gather and the model CMP gather removes smearing of amplitudes on the velocity-stack gather and increases velocity resolution. A practical application of this procedure is in separation of multiples from primaries. A method is described to obtain proper velocity-stack gathers with reduced amplitude smearing. The method involves a t2-stretching in the offset space. This stretching maps reflection amplitudes along hyperbolic moveout curves to those along parabolic moveout curves. The CMP gather is Fourier transformed along the stretched axis. Each Fourier component is then used in the least-squares minimization to compute the corresponding Fourier component of the proper velocity-stack gather. Finally, inverse transforming and undoing the stretching yield the proper velocity-stack gather, which can then be inverse mapped back to the offset space. During this inverse mapping, multiples, primaries or all of the hyperbolic events can be modelled. An application of velocity-stack processing to multiple suppression is demonstrated with a field data example. 相似文献
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Z. Y. Yue 《地球物理与天体物理流体动力学》2013,107(1-2):69-110
Abstract The asymptotic solution and the quantum condition of an eigen-value problem which appears in the density wave theory of the spiral galaxy are re-examined from a mathematical point of view. The dependence of the complex eigen-frequency ω on a large parameter λ is carefully discussed. It turns out that, in the expansion ω=∑χ i=o ωj/λj, the first term ωo must be real in order that the radiation condition may be satisfied. A related conclusion is that the quantum condition may be expressed in terms of an integral along the real axis of the complex plane of the independent variable. This form for the complex quantum condition is convenient not only for determining the complex eigen-frequency numerically, but also for drawing some physically interesting conclusions directly. 相似文献
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本文提出一个三维力学模型,对1976年7月28日唐山地震的破裂过程做了进一步的理论分析.结果表明断裂面长轴两端存在一个10左右的角域,在这个角域内断裂面前缘的初始扩展方向是非共面扩展,即在与断裂面本身偏离一个角度(0,0)的面内扩展,而在其它区域断裂面的前缘是沿自身平面扩展的.在邻近长轴端部的点,扩展角0,0=80.5,这和二维分析得到的扩展分支的方向一致.由于主断裂面在长轴端部10角域左右的非共面扩展,大量余震沿此方向发生,断裂面变成扭曲形状. 相似文献
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We present a numerical solution for the momentum equation of the magnetosheath particles that describes the distribution of the pressure anisotropy of the magnetosheath plasma in the midday meridian plane. The pressure anisotropy is a maximum near the magnetopause subsolar point (p⊥/p\Vert\cong10). The pressure anisotropy is caused by two factors: particles with small pitch angles (V\Vert>V⊥) which travel along the magnetic field lines away from the equatorial plane of the magnetosheath; and particles, after crossing the bowshock, which reach the bulk velocity component directed along the magnetic field lines again, away from the magnetosheath equatorial plane. This velocity increases with increasing distance from the subsolar point of the bowshock, and does not permit particles with large pitch angles (V⊥>V\Vert) to move toward the equatorial plane. 相似文献
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The coupling ray theory bridges the gap between the isotropic and anisotropic ray theories, and is considerably more accurate than the anisotropic ray theory. The coupling ray theory is often approximated by various quasi-isotropic approximations.Commonly used quasi-isotropic approximations of the coupling ray theory are discussed. The exact analytical solution for the plane S wave, propagating along the axis of spirality in the 1-D anisotropic oblique twisted crystal model, is then numerically compared with the coupling ray theory and its three quasi-isotropic approximations. The three quasi-isotropic approximations of the coupling ray theory are (a) the quasi-isotropic projection of the Green tensor, (b) the quasi-isotropic approximation of the Christoffel matrix, (c) the quasi-isotropic perturbation of travel times. The comparison is carried out numerically in the frequency domain, comparing the exact analytical solution with the results of the 3-D ray tracing and coupling ray theory software. In the oblique twisted crystal model, the three studied quasi-isotropic approximations considerably increase the error of the coupling ray theory. Since these three quasi-isotropic approximations do not noticeably simplify the numerical implementation of the coupling ray theory, they should deffinitely be avoided. The common ray approximations of the coupling ray theory do not affect the plane wave, propagating along the axis of spirality in the 1-D oblique twisted crystal model, and should be studied in more complex models. 相似文献
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A semi-analytical boundary element method is developed for the efficient time-domain dynamic response analysis of a finitely long cylindrical cavity with an arbitrary cross-section geometry. High computational efficiency is achieved by mapping a complex shape of the cross-section into a circular shape. For this purpose a special coordinate transformation equation is presented. This mapping enables us to discretize the boundary element equation only along the longitudinal axis of the cavity. The versatility and accuracy of the method are amply demonstrated through a number of examples. The transient stresses and displacements are found to be considerably influenced by the slenderness ratio, length over diameter of the cavity and the incidence angle of the incident wave. 相似文献
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<正>Ground motion records are often used to develop ground motion prediction equations(GMPEs) for a randomly oriented horizontal component,and to assess the principal directions of ground motions based on the Arias intensity tensor or the orientation of the major response axis.The former is needed for seismic hazard assessment,whereas the latter can be important for assessing structural responses under multi-directional excitations.However,a comprehensive investigation of the pseudo-spectral acceleration(PSA) and of GMPEs conditioned on different axes is currently lacking.This study investigates the principal directions of strong ground motions and their relation to the orientation of the major response axis, statistics of the PSA along the principal directions on the horizontal plane,and correlation of the PSA along the principal directions on the horizontal plane.For these,three sets of strong ground motion records,including intraplate California earthquakes,inslab Mexican earthquakes,and interface Mexican earthquakes,are used.The results indicate that one of the principal directions could be considered as quasi-vertical.By focusing on seismic excitations on the horizontal plane,the statistics of the angles between the major response axis and the major principal axis are obtained;GMPEs along the principal axes are provided and compared with those obtained for a randomly oriented horizontal component;and statistical analysis of residuals associated with GMPEs along the principal directions is carried out. 相似文献
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不同资料和方法给出的2019年6月17日四川长宁6.0级地震震源机制解存在较大差异,为了找到1个合适的震源机制解来研究此次地震的发震方式,通过数学方法得到了与现有震源机制解差别最小的中心震源机制解,节面I的走向、倾角、滑动角分别为194.78°、52.68°和139.16°,节面Ⅱ的走向、倾角、滑动角分别为312.44°、58.67°和45.22°,根据本次地震余震分布拟合得到的断层面的走向为312.17°,与中心震源机制的节面Ⅱ走向一致,因而推断节面Ⅱ为本次地震的发震断层面。之后,利用此次地震之前震源区地震的震源机制解,反演了震源区的震前构造应力场。结果表明,长宁6.0级地震的中心震源机制解和震源区震前应力场均为逆冲型为主兼走滑分量的类型,震前应力场压轴为NWW—SEE向,中间轴为NNE—SSW向,两轴倾角接近水平,而张轴较陡,表现为逆冲型的应力场。将反演得到的应力场投影到中心震源机制解给出的与余震分布一致的节面上,发现中心震源机制解的滑动角和应力场预测的滑动角差别仅为13.45°,表明此次地震受背景应力场控制而发生在先存的薄弱面上。 相似文献
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D. V. Erofeev 《Geomagnetism and Aeronomy》2013,53(7):822-826
Compressible fluctuations in solar wind plasma are analyzed on the basis of the 1995–2010 WIND and Advanced Composition Explorer (ACE) spacecraft data. In the low-speed solar wind (V 0 < 430 km/s), correlations between fluctuations in the magnetic field direction and plasma density, as well as between velocity fluctuations and plasma density, are found. The covariance functions of these parameters calculated as functions of the local magnetic field direction are axially symmetric relative to the axis, which is oriented nearly along the regular magnetic field of the heliosphere (the Parker spiral). Fluctuations in the magnetic field and velocity are polarized in the plane that is orthogonal to the axis of symmetry. Plasma oscillations of these properties can be caused by fast magnetosonic waves propagating from the Sun along the Parker spiral. 相似文献
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The Arica Elbow region represents that part of Andean South America where the azimuth of the strike of the Peru-Chile trench changes from 150° to 190°. The area under study is roughly bounded by latitudes 17 °S and 23 °S, The shape of the Wadati-Benioff zone was studied in terms of the distribution of ISC hypocentres dated between 1964 and 1993. A system of 22 vertical cross-sections, perpendicular to the trench axis, and a map of epicentres was used to derive the detailed shape of the Wadati-Benioff zone of the presently descending slab. The distribution of earthquake foci indicates a fingerlike shape of the lower part of the Wadati-Benioff zone beneath the aseismic gap. The slab length shows small changes around 350 km in the northern sections, pronounced length oscillations between 350 and 750 km in the neighbouring central sections and a constant value of 650 km in the southern sections. The dip and thickness of the Wadati-Benioff zone are practically constant in all sections. Fault plane solutions, separated spatially into three zones, were used to estimate the state of stress in the slab. 相似文献
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Hisashi Kuno 《Bulletin of Volcanology》1964,27(1):53-59
Subparallel dikes are exposed on a new road-cut along the foot of the southeastern caldera wall of Hakone Volcano. The dikes are concentrated within a zone 1,915 m wide. Altogether 96 dikes trending generally from NW to SE are seen within a total length of the actual outcrops of 855 m measured at right angles to the trend of the dikes. This implies that there are 215 dikes within the zone of the dike swarm. As the average thickness of the dikes is 2.85 m, the zone was stretched for about 650 m in NE-SW direction owing to the intrusion of the dikes. The dikes tend to converge to a small area near the center of the caldera, and also tend to dip steeply toward the central axis of the zone. It is concluded that the dikes intruded along originally vertical fissures radiating from the central vent of the pre-caldera cone, but the zone of the dike swarm was subjected to bulging with the maximum elevation along its central axis owing to successive intrusion of the dikes from below. Stretching and bulging of the flank of a volcanic cone owing to rise of magma along one of radial fissures were observed during the 1940 eruption of Miyake-zima, Izu Islands, Japan. 相似文献
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ＴｈｅｓｔｕｄｙａｎｄａｐｐｌｉｃａｔｉｏｎｏｆＰＴＲａｌｇｏｒｉｔｈｍｏｎｒｅｃｏｇｎｉｚｉｎｇｖａｒｉｏｕｓｓｔｒｕｃｔｕｒｅｓａｍｐｌｅｓＢｉ－ＱｕａｎＷＡＮＧ（王碧泉）；Ｈａｎ－ＭｉｎｇＨＵＡＮＧ（黄汉明）ａｎｄＨｏｎｇ－ＳｈｕｎＦＡＮ（范洪... 相似文献
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带状地形剖面是以高程为纵向参考,以距剖面起始端点的距离为横向参考进行制图表达。由于其可真实地反映地表形态,是新构造和活动构造地貌研究中的基本参考和研究对象。随着数字化基础地理信息成果的普及,很多GIS软件可实现地形剖面的自动化提取。但以往方法的位置信息均是建立在剖面投影平面的基础上,当研究区域范围过大,会引入非构造变形,为消除该影响,提出基于球面坐标系统的带状地形剖面图制作方法。该方法不仅适用于小型地质构造,也适用于喜马拉雅弧形造山带等大型地质构造,可提取出更接近真实地形的地形剖面。 相似文献
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Abstract A nonlinear Stommel model of the ocean circulation on the beta plane, driven by a time periodic wind stress, is investigated in order to study symmetry properties of the observed time-mean ocean gyres. Due to the presence of vorticity advection terms the model will have a steady or rectified response to fluctuating wind fields. In this paper a small inverse Ekman number, “the small beta regime”, is considered. It is demonstrated that for this case all qualitative features of the residual circulation, obtained numerically by Veronis (1970). are reproduced in an analytical way. They include the dipole character of the gyre, its maximum symmetry breaking around the north-south axis for intermediate Reynolds numbers, measuring the ratio of vorticity forcing and dissipation, and the maximum residual response for intermediate forcing frequencies. 相似文献
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M. K. PAUL 《Geophysical Prospecting》1972,20(1):118-129
The interpretation of the gravity anomaly on a horizontal plane over a causative body having circular symmetry about a vertical axis is considered from a rather unconventional approach. As the analytical expression for the gravity effect of a circular body assumes a closed form only on the axis of symmetry, the interpretation in this approach is carried out with the anomaly profile along the axis—which leads to simpler and faster computation. A numerical method is developed for computation of the anomaly profile along the vertical axis from the horizontal radial profile of the symmetric anomaly by upward continuation. Provision is also made for an end correction when the radial profile has only a limited extension. Some simple geometrical shapes are assumed for the causative body. Its parameters are then determined from least squares fitting of its gravity effects to the observed (upward continued) vertical profile (i) by the steepest descent method and (ii) by the Newton-Raphson method. Some applications of these methods are demonstrated. 相似文献