利用FFT技术计算大地水准面高若干问题研究   总被引：5，自引：1，他引：4  

黄谟涛  翟国君  管铮  凌勇  欧阳永忠 《测绘学报》2000,29(2):124-131

本文首先从普通二维 FFT算法的基本定义和要求出发 ,深入分析和比较了大地水准面二维平面和二维球面 FFT算法的特点和差异 ,找出了影响二维球面 FFT计算精度的主要误差源 ,并给出了二维球面 FFT计算公式的改进形式。在此基础上 ,本文详细分析讨论了参考场选取、积分球冠半径确定以及核函数改化对大地水准面计算结果的作用和影响。最后 ,本文利用全国 5′× 5′实测重力异常对我国海陆大地水准面进行了试算 ,并将计算结果分别同陆上GPS水准和海上卫星测高观测值作了比较。  相似文献   

对常用分裂剪切波识别方法之间的相关性和误差定量评估方法的研究   总被引：3，自引：0，他引：3  

刘希强  周蕙兰  李红  盖殿广 《中国地震》2000,16(1):60-68

根据剪切波在各向异性介质中传播特性的理论研究结果,对几种分裂剪切波震相识别方法的相关性进行了理论探讨。在假定噪声和有用信号数据的方差近似于服从正态分布的前提下,给出了客观估计分裂剪切波震相及其可信度的方法。为了说明方法的有效性,列举了一个含噪声的模拟信号,给出了一定信度水平上的识别结果及误差。  相似文献   

土的周期加载实验的研究     

杨作升  杨少丽  Rolf Sandven 《中国海洋大学学报(自然科学版)》2000,30(4):655-667

作者对室内土的周期加载实验进行了较全面的综述。包括实验设备、方法、结果及分析模型 ,并对以后的研究提出建议。随着海上石油的开发及海岸构筑物的建设 ,迫切需要对海底土动力学特性进行研究。掌握目前世界在这一领域的研究现状有助于在高超点上开展创新工作和解关键问题。  相似文献   

Clustering of galaxy clusters in cold dark matter universes     

J. M. Colberg  S. D. M. White  N. Yoshida  T. J. MacFarland  A. Jenkins  †  C. S. Frenk  F. R. Pearce  A. E. Evrard  H. M. P. Couchman  G. Efstathiou  J. A. Peacock  P. A. Thomas 《Monthly notices of the Royal Astronomical Society》2000,319(1):209-214

We use very large cosmological N -body simulations to obtain accurate predictions for the two-point correlations and power spectra of mass-limited samples of galaxy clusters. We consider two currently popular cold dark matter (CDM) cosmogonies, a critical density model ( τ CDM) and a flat low density model with a cosmological constant (ΛCDM). Our simulations each use 10⁹ particles to follow the mass distribution within cubes of side 2  h ⁻¹ Gpc ( τ CDM) and 3  h ⁻¹ Gpc (ΛCDM) with a force resolution better than 10⁻⁴ of the cube side. We investigate how the predicted cluster correlations increase for samples of increasing mass and decreasing abundance. Very similar behaviour is found in the two cases. The correlation length increases from     for samples with mean separation     to     for samples with     The lower value here corresponds to τ CDM and the upper to ΛCDM. The power spectra of these cluster samples are accurately parallel to those of the mass over more than a decade in scale. Both correlation lengths and power spectrum biases can be predicted to better than 10 per cent using the simple model of Sheth, Mo & Tormen. This prediction requires only the linear mass power spectrum and has no adjustable parameters. We compare our predictions with published results for the automated plate measurement (APM) cluster sample. The observed variation of correlation length with richness agrees well with the models, particularly for ΛCDM. The observed power spectrum (for a cluster sample of mean separation     ) lies significantly above the predictions of both models.  相似文献   

On measuring low-degree p-mode frequency splitting with full-disc integrated data     

T. Appourchaux  H.-Y. Chang  D. O. Gough  T. Sekii 《Monthly notices of the Royal Astronomical Society》2000,319(2):365-376

The standard method of measuring rotational splitting from solar full-disc oscillation data, based on maximum-likelihood fitting of multi-Lorentzian profiles to oscillation power spectra, systematically overestimates the splitting. One of the reasons is that the maximum likelihood estimators (MLE) become unbiased only asymptotically as the number of data tends to infinity; for a finite data set they are often biased, inducing a systematic error. In this paper we assess by Monte Carlo simulations the amount of systematic error in the splitting measurement, using artificially generated power spectra. The simulations are carried out for multiplets of degree     2 and 3 with various signal-to-noise ratios, linewidths and observing times. We address the possible use of non-MLE estimators that could provide a smaller or negligible systematic error. The implication for asteroseismology is also discussed.  相似文献   

Large-scale cosmic homogeneity from a multifractal analysis of the PSCz catalogue     

Jun Pan  Peter Coles 《Monthly notices of the Royal Astronomical Society》2000,318(4):L51-L54

We investigate the behaviour of galaxy clustering on large scales using the PSC z catalogue. In particular, we ask whether there is any evidence of large-scale fractal behaviour in this catalogue. We find the correlation dimension in this survey varies with scale, consistent with other analyses. For example, our results on small and intermediate scales are consistent those obtained from the QDOT sample, but the larger PSC z sample allows us to extend the analysis out to much larger scales. We find firm evidence that the sample becomes homogeneous at large scales; the correlation dimension of the sample is D ₂=2.992±0.003 for r >30  h ⁻¹ Mpc. This provides strong evidence in favour of a universe that obeys the cosmological principle.  相似文献   

Relativistic anisotropic pair plasmas     

Estelle Asseo  Alain Riazuelo 《Monthly notices of the Royal Astronomical Society》2000,318(4):983-1004

The properties of waves able to propagate in a relativistic pair plasma are at the basis of the interpretation of several astrophysical observations. For instance, they are invoked in relation to radio emission processes in pulsar magnetospheres and to radiation mechanisms for relativistic radio jets. In such physical environments, pair plasma particles probably have relativistic, or even ultrarelativistic, temperatures. Besides, the presence of an extremely strong magnetic field in the emission region constrains the particles to one-dimensional motion: all the charged particles strictly move along magnetic field lines.
We take anisotropic effects and relativistic effects into account by choosing one-dimensional relativistic Jűttner–Synge distribution functions to characterize the distribution of electrons and/or positrons in a relativistic, anisotropic pair plasma. The dielectric tensor, from which the dispersion relation associated with plane wave perturbations of such a pair plasma is derived, involves specific coefficients that depend on the distribution function of particles. A precise determination of these coefficients, using the relativistic one-dimensional Jűttner–Synge distribution function, allows us to obtain the appropriate dispersion relation. The properties of waves able to propagate in anisotropic relativistic pair plasmas are deduced from this dispersion relation. The conditions in which a beam and a plasma, both ultrarelativistic, may interact and trigger off a two-stream instability are obtained from this same dispersion relation. Two astrophysical applications are discussed.  相似文献   

Smoothed Particle Hydrodynamics in cosmology: a comparative study of implementations     

R. J. Thacker  †  E. R. Tittley  ‡  F. R. Pearce  H. M. P. Couchman §  P. A. Thomas 《Monthly notices of the Royal Astronomical Society》2000,319(2):619-648

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Time evolution of galactic warps in prolate haloes     

M. Ideta  S. Hozumi  T. Tsuchiya  M. Takizawa 《Monthly notices of the Royal Astronomical Society》2000,311(4):733-740

A recent observation with the Hipparcos satellite and some numerical simulations imply that the interaction between an oblate halo and a disc is inappropriate for the persistence of galactic warps. Following on from this , we have compared the time evolution of galactic warps in a prolate halo with that in an oblate halo. The haloes were approximated as fixed potentials, while the discs were represented by N -body particles. We have found that the warping in the oblate halo continues to wind up, and finally disappears. On the other hand, for the prolate halo model, the precession rate of the outer disc increases when the precession of the outer disc recedes from that of the inner disc, and vice versa. Consequently, the warping in the prolate halo persisted to the end of the simulation by retaining the alignment of the line of nodes of the warped disc. Therefore, our results suggest that prolate haloes could sustain galactic warps. The physical mechanism of the persistence of warp is discussed on the basis of the torque between a halo and a disc and that between the inner and outer regions of the disc.  相似文献   

Large-scale structure, the cosmic microwave background and primordial non-Gaussianity     

Licia Verde  Limin Wang  Alan F. Heavens  Marc Kamionkowski 《Monthly notices of the Royal Astronomical Society》2000,313(1):141-147

Cosmic microwave background and large-scale structure data will shortly improve dramatically with the Microwave Anisotropy Probe and Planck Surveyor , and the Anglo-Australian 2-Degree Field and Sloan Digital Sky Survey. It is therefore timely to ask which of the microwave background and large-scale structure will provide a better probe of primordial non-Gaussianity. In this paper we consider this question, using the bispectrum as a discriminating statistic. We consider several non-Gaussian models and find that in each case the microwave background will provide a better probe of primordial non-Gaussianity. Our results suggest that if microwave background maps appear Gaussian, then apparent deviations from Gaussian initial conditions in galaxy surveys can be attributed with confidence to the effects of biasing. We demonstrate this precisely for the spatial bispectrum induced by local non-linear biasing.  相似文献