共查询到20条相似文献，搜索用时 406 毫秒
1.
The avalanche model of Lu and coworkers successfully reproduces important qualitative features of the flare-energy distribution. We test the prediction of the avalanche model that all active regions share a common power-law exponent by using it to derive a local flare-energy distribution from SXR GOES data, then using the convolution proposed by Wheatland and Sturrock to compare it with the global distribution. The local distribution we derive is not consistent with the global distribution, so it appears that active regions do not share a common power-law distribution. 相似文献
2.
本文利用几种典型的银河系宇宙线分布律和星际氢分布律计算单漏模式和双漏模式中的弥散宇宙γ射线谱。结果表明,几种典型的宇宙线分布中,李惕碚的分布律优于其他作者的分布律;星际氢分子数量的取值应当比Gordon值除以1.7更小;只要适当地选择宇宙线分布和氢分布就可得到与观测γ谱相近的理论谱,宇宙线分布和氢分布均可在一定范围里选取。 相似文献
3.
A simple kinematic method for determining the particle velocity distribution of a model solar wind for which the spatial distribution of particles is given as a function of particle travel time has been developed by Hakamada and Akasofu (1982). Here we formalize their method mathematically and derive an inverse procedure for determining the particle distribution from a given velocity distribution. This inverse procedure is then applied to a simulated velocity distribution obtained from an MHD finite difference code. 相似文献
4.
D. Basu 《Astrophysics and Space Science》1980,70(2):527-529
A gap in a distribution is the interval between two consecutive values. Analysis of gaps in the absorption line redshift distribution (241 values) of QSOs shows a definite trend in the distribution of gaps. The trend indicates that the absorption line distribution is not random, but does not suggest any periodicity. 相似文献
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S. Basilakos M. Plionis S. J. Maddox 《Monthly notices of the Royal Astronomical Society》2000,316(4):779-785
We estimate the distribution of intrinsic shapes of APM galaxy clusters from the distribution of their apparent shapes. We measure the projected cluster ellipticities using two alternative methods. The first method is based on moments of the discrete galaxy distribution while the second is based on moments of the smoothed galaxy distribution. We study the performance of both methods using Monte Carlo cluster simulations covering the range of APM cluster distances and including a random distribution of background galaxies. We find that the first method suffers from severe systematic biases, whereas the second is more reliable. After excluding clusters dominated by substructure and quantifying the systematic biases in our estimated shape parameters, we recover a corrected distribution of projected ellipticities. We use the non-parametric kernel method to estimate the smooth apparent ellipticity distribution, and numerically invert a set of integral equations to recover the corresponding distribution of intrinsic ellipticities under the assumption that the clusters are either oblate or prolate spheroids. The prolate spheroidal model fits the APM cluster data best. 相似文献
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Kuiper带天体的轨道分布特性 总被引：3，自引：1，他引：2
1992年9月,夏威夷大学的D.Jewitt和加利福尼亚大学的J.Lun发现了海王星外绕太阳运行的第一个小天体1992QB1[1],开创了人类对于海王星外天体的实际观测的研究.近10年的接连不断发现,已经证实了海王星轨道外面存在着一个由大量的环绕太阳运动的小天体组成的环带[2].由于G.P.Kuiper曾在1951年的文章中提出过在冥王星的外边可能存在小天体的问题,因此人们一般把这个环带称为Kuiper带,你这些天体为“KuiperBelt Objects”(KBOs),或从逻辑上称它们为“Trans-NeptunianObjects”(TNOs)[3] 相似文献
9.
Ewa Rydzyńska 《Astrophysics and Space Science》1987,133(1):183-187
The axial ratio distribution for a sample of SBc galaxies deviates from a flat distribution in ways that are consistent with predictions of the projection effect model for barred spiral galaxies. The axial ratio distribution for a corresponding sample of non-barred Sc galaxies is shown to have, bin for bin, a reciprocal set of deviations from a flat distribution. When the two samples are combined, the deviations counterbalance each other and a nearly flat axial ratio distribution is recovered. This latter result is also consistent with predictions of the projection effect model. 相似文献
10.
宇宙学的基本假设之一是宇宙在大尺度上均匀各向同性.为了验证星系分布在大尺度上的均匀性,分别计算观测样本和观测空间几何体的分形维数,得到SDSS-DR4中星系分布的分形维数.观测空间几何体的分形维数用随机样本来确定.样本中的星系红移z的范围为0.01-0.26.当尺度持续增加至几十个Mpc时,星系分布的分形维数一致地趋向于3.所有的样本均显示了明显的转变尺度,当尺度大于此转变尺度时,星系分布的分形维数D<,G>～3,星系的分布转变为均匀分布.结果支持了宇宙学的基本原理关于宇宙大尺度均匀的假设.样本的转变尺度随着样本的光度增强而变大,说明小尺度上星系的分布不是简单的分形分布,而是多维分形分布.高光度星系的转变尺度非常大,直到100h-1Mpc左右才变得均匀. 相似文献
11.
Data on the positions of gamma-ray bursts (GRBs) in galaxies are used to construct the radial distributions of their surface density. The gradient in GRB surface density is shown to decrease sharply at a galactocentric distance equal to the effective galactic radius. In central galactic regions, the GRB density distribution agrees with the galactic surface-brightness distribution; in outer regions, the GRB density decreases more slowly than does the surface brightness. Based on improved statistics, we analyze the radial distribution of type Ib/c supernovae. We show that it differs insignificantly from the distributions of other types of supernova and exhibits a much closer similarity to the distribution of star-forming regions than do GRBs. Although the statistics for GRBs is poor, the deviation of their distribution from the distribution of active star-forming regions in nearby galaxies seems to have been firmly established. A correlation of GRBs with the distribution of dark matter in outer galactic regions is not ruled out. 相似文献
12.
Gong Zhi-yuan 《Chinese Astronomy and Astrophysics》2010,34(1):23-29
One of the basic assumptions in cosmology is that the universe is homogeneous and isotropic on large scales. This assumption is the most important keystone of modern cosmology. In order to verify the homogeneity of galaxy distribution on large scales, we have computed the fractal dimensionality of the galaxy distribution in SDSS-DR4. The fractal dimensionality of the observed spatial geometric bodies is determined with random samples. The redshifts of sample galaxies are in the range 0.01～0.26. When the scale grows continuously to dozens of Mpc, the fractal dimensionality of the galaxy distribution approaches to 3 consistently. All the 6 samples exhibit obviously a transition scale. For scales larger than the transition scale, the fractal dimensionality DG of the galaxy distribution is very close to 3, the galaxy distribution is homogeneous. This result supports the assumption that the universe is homogeneous on large scales. The transition scale of the sample increases with the luminosity of the sample. This means that the galaxy distribution on small scales is not a of simple fractal distribution, but a multi-fractal distribution. The transition scale of high-luminosity galaxies is very large, the distribution will not become homogeneous till about 100 h?1Mpc. 相似文献
13.
The velocity distribution function of ionospheric electrons is calculated in the low-energy (< 8·7 eV) region. This is the first realistic model calculation for studying the transition of the distribution function from the nonthermal to the thermal part without assuming the Maxwellian distribution for the latter. The calculation is made for four altitudes between 120 and 250 km. All the relevant atomic collision processes are taken into account. Contributions of each individual process to determining the distribution function are discussed. The calculation shows that the deviation of the thermal energy part of the distribution function from Maxwellian in the region around the mean kinetic energy is within several percent. A much larger deviation is found at other portions of the function (still within the thermal part) especially at lower altitudes. In the Appendix, some features of the distribution function at higher energy regions are discussed. 相似文献
14.
自适应Lp估计及其在照相天体测量中的应用 总被引：2，自引：0，他引：2
Ｐ范分布是一个广义的测量误差分布族．众所周知的正态分布只是其ｐ＝２时的一个特例．因此，与正态分布和最小二乘估计相比，Ｐ范分布和相应的Ｌｐ估计（最小ｐ范估计）可描述和处理类型更广泛的测量误差．针对具体的测量数据，推断其实际误差之Ｐ范分布的Ｐ值，然后依此进行最或然估计，此即自适应Ｌｐ估计．本文介绍了Ｌｐ估计的性质．较为详细地讨了Ｌｐ估计的效率和自适应Ｐ值的具体求解方法；并且还针对鬼星团照相天体测量数据的归算，给出了一个实际应用的例子．结果表明，所处理的观测误差并不服从正态分布；此时自适应Ｌｐ估计的引入将带来显著优于最小二乘估计的结果． 相似文献
15.
Vasily E. Tarasov 《Celestial Mechanics and Dynamical Astronomy》2006,94(1):1-15
In this paper we consider the gravitational field of fractal distribution of particles. To describe fractal distribution,
we use the fractional integrals. The fractional integrals are considered as approximations of integrals on fractals. Using
the fractional generalization of the Gauss’s law, we consider the simple examples of the fields of homogeneous fractal distribution.
The examples of gravitational moments for fractal distribution are considered. 相似文献
16.
Using a kappa velocity distribution function for the electrons of the background plasma, the dynamics of a beam of hot electrons
streaming through the plasma and the generation of Langmuir waves are investigated in the frame work of quasilinear theory.
It is shown that the Langmuir waves are strongly damped by high energy tail of the Kappa distribution function. The spatial
expansion of the beam is reduced and the spectral density of Langmuir waves becomes narrower. The height of the plateau in
the beam distribution function increases at small velocities and the average velocity of beam is larger than that of a Maxwellian
distribution. The influence of Kappa velocity distribution function on the gasdynamical parameters is investigated. It is
found that, the height of plateau in the beam distribution function, and its lower velocity boundary are enhanced while, the
local beam width in velocity space decreases. 相似文献
17.
A. A. Akopian 《Astrophysics》2003,46(1):58-66
A new method is proposed for determining the frequency distribution of bursts from randomly flashing objects based on fitting Pearson distributions by the method of moments. This method is applied to flare stars in the Pleiades cluster and the Orion association. The desired frequency distribution of the bursts from flare stars can be approximated by a gamma distribution. The burst frequency distribution describes the observed statistical picture fairly well. The result is compared with other methods. 相似文献
18.
N. Ograpishvili 《Solar physics》1994,149(1):93-104
Statistical properties of solar active regions (AR) have been studied. In particular, (1) the distribution of ARs by their areas and importances using normal and lognormal distribution laws; (2) it was checked whether the distribution of the ARs' birth sites satisfies the Poisson distribution law (the so-called ‘law of rare events’). Observational data of 1979–1982 have been used and our conclusions are as follows:
- As regards the areas, the distribution of the ARs that emerged near or on the borders of the large-scale background fields is normal or lognormal.
- As regards the importances, the distribution of all ARs is lognormal.
- The distribution of ARs that emerged far from background field borders is not normal.
- ARs are not casual or rare events on the Sun.
19.
《天文和天体物理学研究(英文版)》2016,(10)
The power-law frequency distributions of the peak flux of solar flare X-ray emission have been studied extensively and attributed to a system having self-organized criticality(SOC).In this paper,we first show that,so long as the shape of the normalized light curve is not correlated with the peak flux,the flux histogram of solar flares also follows a power-law distribution with the same spectral index as the powerlaw frequency distribution of the peak flux,which may partially explain why power-law distributions are ubiquitous in the Universe.We then show that the spectral indexes of the histograms of soft X-ray fluxes observed by GOES satellites in two different energy channels are different:the higher energy channel has a harder distribution than the lower energy channel,which challenges the universal power-law distribution predicted by SOC models and implies a very soft distribution of thermal energy content of plasmas probed by the GOES satellites.The temperature(T) distribution,on the other hand,approaches a power-law distribution with an index of 2 for high values of T.Hence the application of SOC models to the statistical properties of solar flares needs to be revisited. 相似文献
20.
It was recently pointed out that the distribution of times between solar flares (the flare waiting-time distribution) follows a power law for long waiting times. Based on 25 years of soft X-ray flares observed by Geostationary Operational Environmental Satellite instruments, it is shown that (1) the waiting-time distribution of flares is consistent with a time-dependent Poisson process and (2) the fraction of time the Sun spends with different flaring rates approximately follows an exponential distribution. The second result is a new phenomenological law for flares. It is shown analytically how the observed power-law behavior of the waiting times originates in the exponential distribution of flaring rates. These results are argued to be consistent with a nonstationary avalanche model for flares. 相似文献