共查询到19条相似文献，搜索用时 406 毫秒
1.
对一数据涨落服从泊松概率分布的实验数据组进行拟合,如果拟合函数是非线性的,常常只能采用某些近似方法。近似性之一,表现在将拟合函数线性化,或者采用某种参数寻优的方法。近似性之二,则是将泊松问题近似地看作高斯分布问题。本文从最大或然法出发,对两类不同概率分布情况下的曲线拟合进行了比较,给出了对泊松分布问题更严格的求解途径。对于特殊的非线性拟合函数y(x)=ae~(bx~N),直接给出了迭代解。本文对曲线拟合的“面积亏损”问题,也进行了讨论。 相似文献
2.
唐泽眉 《中国天文和天体物理学报》1981,(2)
本文从二维气体动力学和泊松方程出发,研究星际气体激波和线性恒星密度波自洽的密度波理论,求出准稳、紧卷、双臂的线性恒星密度波和星际气体激波的总合自洽解。所得结果表明,在采用不完全的流体力学线性方程组及全局的引力方程的条件下,得到的是收敛的自洽解,该解给出了与局部渐近解相同的色散关系、非谐波形式的总密度分布及总引力分布,所得结果还表明,若采用完全的流体力学线性化方程组,将得出不稳定的线性恒星密度波。 相似文献
3.
4.
5.
根据大气水平运动方程推导出Ekman层风速随高度分布方程,该分布可用二阶线性微分方程表示,用有限差分法求解该二阶线性微分方程的边值问题的数值解,并给出计算程序,输出结果。将结果与经典解析解比较,讨论了经典解的正确性和适用范围。 相似文献
6.
7.
电离层的掩星分离假设反演法 总被引：1，自引：0，他引：1
该文首先简要介绍了无线电掩星探测技术及其发展现状和传统Abel变换方法面临的问题.为改进传统Abel变换反演方法,利用电子密度廓线的分离假设,引进了分离假设反演法.随后利用国际电离层参考模式IBI2007给出1000个掩星事件截面的模拟数据及COSMIC卫星星座的一天实测数据,进行比较计算,并对结果进行了分析,验证了分离假设反演法的有效性.文中还给出了垂直电子总量VTEC(Vertical Total Electron Content)先验场的获取途径.最后,对分离假设反演法的进一步研究的方向进行了探讨. 相似文献
8.
本文给出了Vinti型中间轨道根数a,e,s,M_s,ψ_s,Ω_s的摄动方程,结果准到二阶,并消除了方程中的泊松项。 相似文献
9.
李焱 《中国天文和天体物理学报》1989,(4)
本文发展了一种解恒星线性非绝热非径向脉动问题的退耦化方法。这个方法把非绝热非径向脉动问题的六阶线性微分方程,分解为由一个代数方程联系起来的一个四阶线性微分方程和另一个二阶线性微分方程进行数值求解。这样的一个退耦处理,有利于克服以前在数值解这类问题时常常遇到的收敛域小和收敛速度慢等困难,并且为数值解方程时所采用的Henyey方法提供了一个自然和方便的初始猜测解。 相似文献
10.
《天文研究与技术》2016,(3)
时域脉冲机制雷达广泛应用于地球探测、月球与深空探测等领域,研究雷达的探测深度有利于分析目标是否在雷达探测范围内。传统的计算方法大多基于经典雷达传输方程,在实际计算时,需要对地下介质结构以及介质特性做先验性假设,进而给出理论的穿透深度。为了克服传统计算探测深度方法的局限性,给出了一种新的计算方法,该方法不需要对探测介质做先验假设,直接从雷达实测数据出发,通过计算雷达数据间的相关性,给出雷达的探测深度。给出了两种具体的计算方法,一种为结合子波形式,另一种是利用道相关形式。分别对两种方法进行了介绍,并通过仿真验证了两种方法在计算雷达穿透深度时的有效性,同时分析了两种计算方法存在的局限性,该研究为后期处理时域脉冲雷达穿透深度问题提供了解决方法。 相似文献
11.
In Einstein gravity, for an inhomogeneous phantom energy distribution having linear equation of state (but anisotropic), there exists simple exact solution for spherically symmetric space time describing a wormhole. At infinity, the space time is not asymptotically flat and possesses a regular cosmological Killing horizon with an infinite area. In this work, we have shown that, this wormhole solution is also possible in brane world for various matter distribution, which are not necessarily phantom in nature. 相似文献
12.
Recently new calculations for the probability field distribution in plasma generating a new expression for the Debye screening fields was carried out by Martin and Perez (1996). This field is a very accurate solution of the Poisson equation for a point test charge in a plasma described by a uniform charge density at Boltzmann thermal equilibrium. The method that we here present is based mainly on the introduction of this adequate field considering the dependence of the potential with the magnitude of the test charge in the calculus of the distribution. First we find the spectral function F(k) carrying out the Fourier transform of the field which is numerically calculated for each representative value of the variable in k space and then fitting these data in order to get F(k). Thus, after the usual numerical integration on the wave number space d3k, the field strength distribution is achieved. This approximation recovers the Holtsmark distribution in the limit of high temperature, and/or, small densities as also these where 0. As in previous works (Ecker, 1972; Spatschek, 1990) the most probable value of the field decreases as the temperature is reduced, and/or, the density increased. 相似文献
13.
Robert L. Wildey 《Earth, Moon, and Planets》1988,41(3):223-240
A method is derived for determining the dependence of radar backscatter on incidence angle that is applicable to the region corresponding to a particular radar image. The method is based on enforcing mathematical consistency between the frequency distribution of the image's pixel signals (histogram of DN values with suitable normalizations) and a one-dimensional frequency distribution of slope component, as might be obtained from a radar or laser altimetry profile in or near the area imaged. In order to achieve a unique solution, the auxiliary assumption is made that the two-dimensional frequency distribution of slope is isotropic. The backscatter is not derived in absolute units. The method is developed in such a way as to separate the reflectance function from the pixel-signal transfer characteristic. However, these two sources of variation are distinguishable only on the basis of a weak dependence on the azimuthal component of slope; therefore such an approach can be expected to be ill-conditioned unless the revision of the transfer characteristic is limited to the determination of an additive instrumental background level. The altimetry profile does not have to be registered in the image, and the statistical nature of the approach minimizes pixel noise effects and the effects of a disparity between the resolutions of the image and the altimetry profile, except in the wings of the distribution where low-number statistics preclude accuracy anyway. The problem of dealing with unknown slope components perpendicular to the profiling traverse, which besets the one-to-one comparison between individual slope components and pixel-signal values, disappears in the present approach.In order to test the resulting algorithm, an artificial radar image was generated from the digitized topographic map of the Lake Champlain West quadrangle in the Adirondack Mountains, U.S.A., using an arbitrarily selected reflectance function. From the same map, a one-dimensional frequency distribution of slope component was extracted. The algorithm recaptured the original reflectance function to the degree that, for the central 90% of the data, the discrepancy translates to a RMS slope error of 0.1 . For the central 99% of the data, the maximum error translates to 1 ; at the absolute extremes of the data the error grows to 6 . 相似文献
14.
María del Carmen Martínez Juan F. Navarro José Manuel Ferrándiz 《Celestial Mechanics and Dynamical Astronomy》2007,99(1):59-68
The efficiency in the computation of circular functions, such as cos(u) or sin(u), where u is a Poisson series, is important to derive accurate solutions of many problems of Celestial Mechanics, for instance, the
orbital or rotational perturbed motion of natural or artificial bodies, since expansions in terms of Legendre functions and
multiple Fourier series appear almost everywhere. Therefore, it is worth searching for alternative algorithms with lower computational
cost. In this article, we propose a method based on the idea of elimination, which was originally applied to solve numerical
problems, mainly in the case of matrix functions. Our comparisons with the traditional Taylor expansion prove that this new method can be more efficient when applied to compute the sine and cosine of a Poisson series. 相似文献
15.
M. S. Wheatland 《Solar physics》2007,245(2):251-262
Improvements to an existing method for calculating nonlinear force-free magnetic fields (Wheatland, Solar Phys. 238, 29, 2006) are described. In particular a solution of the 3-D Poisson equation using 2-D Fourier transforms is presented. The improved
nonlinear force-free method is demonstrated in application to linear force-free test cases with localized nonzero values of
the normal component of the field in the boundary. These fields provide suitable test cases for nonlinear force-free calculations
because the boundary conditions involve localized nonzero values of the normal components of the field and of the current
density, and because (being linear force-free fields) they have more direct numerical solutions. Despite their simplicity,
fields of this kind have not been recognized as test cases for nonlinear methods before. The examples illustrate the treatment
of the boundary conditions on current in the nonlinear force-free method, and in particular the limitations imposed by field
lines that connect outside of the boundary region. 相似文献
16.
原子钟噪声的蒙特卡络模拟方法 总被引：1，自引：0，他引：1
讨论了原子钟噪声的蒙特卡络模拟方法．具体过程是：先产生模拟所需的正态分布随机数，从实际钟的阿仑方差估算出噪声电平，然后用１组递点函数产生高质量的模拟钟时差的随机序列．在对１台商品铯钟进行具体模拟后，给出了真实数据与模拟值的阿仑方差之问的相符程度，最后对实际问题进行了分析． 相似文献
17.
We present a method to include stereoscopic information about the three-dimensional structure of flux tubes into the reconstruction of the coronal magnetic field. Due to the low plasma beta in the corona we can assume a force-free magnetic field, with the current density parallel to the magnetic field lines. Here we use linear force-free fields for simplicity. The method uses the line-of-sight magnetic field on the photosphere as observational input. The value of is determined iteratively by comparing the reconstructed magnetic field with the observed structures. The final configuration is the optimal linear force-free solution constrained by both the photospheric magnetogram and the observed plasma structures. As an example we apply our method to SOHO MDI/EIT data of an active region. In the future it is planned to apply the method to analyse data from the SECCHI instrument aboard the STEREO mission. 相似文献
18.
We propose the Ptolemaic transformation: a canonical change of variables reducing the Keplerian motion to the form of a perturbed Hamiltonian problem. As a solution of the unperturbed case, the Ptolemaic variables define an intermediary orbit, accurate up to the first power of eccentricity, like in the kinematic model of Claudius Ptolemy. In order to normalize the perturbed Hamiltonian we modify the recurrent Lie series algorithm of HoriuuMersman. The modified algorithm accounts for the loss of a term's order during the evaluation of a Poisson bracket, and thus can be also applied in resonance problems. The normalized Hamiltonian consists of a single Keplerian term; the mean Ptolemaic variables occur to be trivial, linear functions of the Delaunay actions and angles. The generator of the transformation may serve to expand various functions in Poisson series of eccentricity and mean anomaly. 相似文献
19.
A. D. Crouch 《Solar physics》2013,282(1):107-131
We investigate how the azimuthal ambiguity in solar vector magnetogram data can be resolved by using the divergence-free property of magnetic fields. In a previous article, by Crouch, Barnes, and Leka?(Solar Phys. 260, 271, 2009), error-free synthetic data were used to test several methods that each make a different assumption about how the divergence-free property can be used to resolve the ambiguity. In this paper this testing is continued with an examination of the effects of Poisson photon noise and limited instrumental spatial resolution. We find that all currently available methods based on the divergence-free property can produce undesirable results when photon noise or unresolved structure is present in the data. We perform a series of experiments aimed at improving the performance of the global minimisation method, which is the most promising of the methods. We present a two-step approach that produces reasonable results in tests using synthetic data. The first step of this approach involves the global minimisation of a combination of the absolute value of the approximation for the divergence and a smoothness constraint, which is designed to minimise the difference between the magnetic field in neighbouring pixels. In the second step, pixels with measurements known to be strongly affected by photon noise are revisited with a smoothing algorithm that also seeks to minimise the difference between the magnetic field in neighbouring pixels. 相似文献