宇宙大尺度分形结构的一阶Kohmoto熵

已有观测证据表明宇宙大尺度结构是自相似或自仿射的分形分布，并已求出表征这两类分形的结构分数维。多分形热力学中提出的Ｋｏｈｍｏｔｏ熵函数建立了多重分形和热力学的形式类比。本文在三维球对称坐标系中求取了无标度区间ｒｏ≤ｒ≤Ｒ范围内宇宙大尺度自相似分形分布的一阶Ｋｏｈｍｏｔｏ熵函数，它对应于信息论中的信息底从热力学角度看，宇宙大尺度结构代表了某种有序结构，耗散自组织过程也许是导致这一有序结构的直接原因。     

由SLOAN观测数据测试大尺度结构的均匀性

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.     

宇宙大尺度结构对星系形成和空间排列的影响

星系的空间排列以及指向并非随机的.星系的主轴和角动量与物质的大尺度分布存在一定的指向相关.这一方向的研究将可以促进我们对结构形成机制的认识,并提供一个独立的视角去检验星系形成过程中的环境效应.本文就相关问题做了详细的探讨.     

宇宙大尺度分形结构的上限

本文给出了用几种达到不同极限星等的星系表确定宇宙分形结构上限截止尺度的公式.利用Zwicky星系表、Shane-Wirtanen星系表和Jagellonian天区的星系表的数据,可以估计这一截止尺度R_c至少为60—70Mpc,且R_c随着自相似分布所占比例f的减小而增大,或可大到约270Mpc的尺度.     

从准一维红移巡天样本分析大尺度结构

通过分析由五个笔形天区的完备红移巡天和九个1/3采样红移巡天得到的样本,研究了星系分布中的大尺度结构。用一种改进过的方法计算了该分布的分维。结果表明星系分布确实具有3—4.5h~(-1)Mpc的典型尺度,这与Shanks等的结果一致。     

Large Scale Jets in Microquasars

Relativistic jets are now believed to be a fairly ubiquitous property of accreting compact objects, and are intimately coupled with the accretion history. Associated with rapid changes in the accretion states of the binary systems, ejections of relativistic plasma can be observed at radio frequencies on timescale of weeks before becoming undetectable. However, recent observations point to long-term effects of these ejecta on the interstellar medium with the formation of large-scale relativistic jets around binary systems. In this paper, we review the observations of these large-scale structures in microquasars, highlighting their contributions at high energies.     

星系大尺度本动速度

本文从高斯型的初始质量密度扰动出发,采用球对称演化模型计算了星系大尺度本动速度随尺度的分布。采用这样一种模型可以避免通常流体模型中线性增长以及窗函数的假设,对不同的宇宙物质主导成分的讨论表明,在各种情况下本动速度的期待值v_p在大尺度上的分布是随着尺度的增大而逐渐减小,这与流体模型以及宇宙弦模型下的趋势是一致的,但对所有参数的可能取值所作的计算表明,理论结果很难解释Dressler等人在r～60h~(-1)Mpc的尺度上观测到的大的本动速度,这很可能是由于在本星系群(LG)之外r 60h~(-1)Mpc的远处存在着一个大质量的物质凝聚区域。     

Jets and Large Scale Outflows: Theory Confronts the Observations

This article summarizes recent theoretical, numerical and observational progress on the nature of jets and outflows in regions of star formation. The emphasis is placed on the role of hydromagnetic phenonmena in understanding these new results. The confluence of sophisticated 3D numerical MHD simulations and the recent observations of rotating jets makes it possible, for the first time, to rigorously test jet models.     

Clumpy Structure and Polarization in NGC 1068

The polarization map from the HST archival data of the imaging polarimetry for NGC 1068 is analyzed. In the HST images, the central few arcsecond region seems to consist of several clumps, and if we extract the polarization of the clumps separately, the viewing angle of each clump can be determined. This enables us to have a three-dimensional view of this central region. This revised version was published online in July 2006 with corrections to the Cover Date.     

Linear Polarization Features in the Quiet-Sun Photosphere: Structure and Dynamics

We present detailed characteristics of linear polarization features (LPFs) in the quiet-Sun photosphere from high-resolution observations obtained with Sunrise/IMaX. We explore differently treated data with various noise levels in linear polarization signals, from which structure and dynamics of the LPFs are studied. Physical properties of the detected LPFs are also obtained from the results of Stokes inversions. The number of LPFs and their sizes and polarization signals are found to be strongly dependent on the noise level and on the spatial resolution. While the linear polarization with a signal-to-noise ratio \(\geq4.5\) covers about 26% of the entire area in the least noisy data in our study (with a noise level of \(1.7\times10^{-4}\) in the unit of Stokes \(I\) continuum), the detected (spatially resolved) LPFs cover about 10% of the area at any given time, with an occurrence rate on the order of \(8\times10^{-3}\mbox{ s}^{-1}\)?arcsec^?2. The LPFs were found to be short lived (in the range of 30?–?300 s), relatively small structures (radii of \(\approx0.1\)?–?1.5 arcsec), highly inclined, posing hG fields, and they move with an average horizontal speed of 1.2 km?s^?1. The LPFs were observed (almost) equally on both upflow and downflow regions, with an intensity contrast always larger than that of the average quiet Sun.     

A Large Scale Energy Source For Feeding: ISM Turbulence in Spiral Galaxies

One of the important consequences of a newly discovered secular dynamical evolution process of spiral galaxies (Zhang, 1996, 1998, 1999) is that the orbiting disk matter receives energy injection each time it crosses the spiral density wave crest. This energy injection has been shown to be able to quantitatively explain the observed age-velocity-dispersion relation of the solar neighborhood stars. We demostrate in this paper that similar energy injection into the interstellar medium could serve as the large-scale energy source to continuously power the observed interstellar turbulence and to offset its downward cascade tendency. This revised version was published online in September 2006 with corrections to the Cover Date.     

The Sub-surface Structure of a Large Sample of Active Regions

We employ ring-diagram analysis to study the sub-surface thermal structure of active regions. We present results using a large number of active regions over the course of Solar Cycle 23. We present both traditional inversions of ring-diagram frequency differences, with a total sample size of 264, and a statistical study using Principal Component Analysis. We confirm earlier results on smaller samples that sound speed and adiabatic index are changed below regions of strong magnetic field. We find that sound speed is decreased in the region between approximately r=0.99?R _⊙ and r=0.995?R _⊙ (depths of 3 Mm to 7 Mm) and increased in the region between r=0.97?R _⊙ and r=0.985?R _⊙ (depths of 11 Mm to 21 Mm). The adiabatic index [Γ₁] is enhanced in the same deeper layers where sound-speed enhancement is seen. A weak decrease in adiabatic index is seen in the shallower layers in many active regions. We find that the magnitudes of these perturbations depend on the strength of the surface magnetic field, but we find a great deal of scatter in this relation, implying that other factors may be relevant.     

星系形成与宇宙大尺度结构

宇宙大尺度结构的形成与星系形成密切相关,前者的研究把星系基本上视为一质点,而星系形成研究涉及到其内部结构,宇宙大尺度结构形成有两种模式,由小到大与由大到小,这两种模式被交替使用（当然不同简单的重复）很重要的一个原因是星系形成研究的推动。     

大尺度质量扰动和速度场的计算

本文在宇宙弦模型中,计算了各种暗物质主导宇宙的大尺度均方质量扰动和速度场。我们的计算结果表明,如果冷暗物质和重子主导字苗在8Mpch~(-1)处引力成团达到非线性或者中微子主导宇宙在z～3时出现Pancake碎裂,则相应的宇宙弦线密度μ均应满足关系式:Gμ>10~(-5),而这样的弦密度将导致宇宙微波背景较大的各向异性并违反大爆炸核合成理论。对大尺度速度场的计算,我们得到了它随距离增大比通常宇宙模型下降得更慢的结果,但它仍不足以解释Collins等最近报告的在50h~(-1)Mpc处v_p=970±300km·s~(-1)的固有速度。因此我们的计算表明,由单一的弦扰动形成观测到的大尺度结构是困难的。双扰动模型有可能是解决困难的一种途径。     

M 87大尺度喷流的多波段研究

射电星系M87的大尺度喷流在射电、光学和X波段都已经具备高分辨率的成像观测和频谱观测。其各个节点的宽波段连续谱目前被认为是同步辐射主导的。文章采用相对论性电子同步辐射的Kardashev-Pacholczyk模型,对各节点的多波段连续谱进行了独立的最佳拟和,从而得到相应的多普勒因子。此外进一步结合各节点的视超光速运动的观测数据,导出了不同节点整体运动的Lorentz因子和对观测者的视角。计算结果表明,M87的大尺度喷流具有一定程度的弯曲,其整体动力学行为是减速的。     

光学亮星系大尺度分布中的多级结构

本文在Wen等人工作的基础上,对CfA红移巡天样本中银道以北和以南天区中星系的大尺度分布分别进行了分维计算并比较其所得结果。分析表明,这两个区域内星系的大尺度分布存在显著差异。说明CfA样本还不能构成代表宇宙大尺度结构的好样本。另一方面,两个区域中样本分析结果又存在着一些明显的共同点:它们都表现出明显的多级分形特征。结合对IRAS星系红移巡天样本和星系分立小天区红移巡天样本的分析结果。我们认为,多级分形很可能是宇宙大尺度结构的一个普遍和重要的特征。本文对这一特征的含义也作了简略的讨论。     

Structure of a Large low-Latitude Coronal Hole

Coronal holes on the Sun are the source of high-speed solar wind streams that produce magnetic disturbances at the Earth. A series of multi-wavelength, multi-instrument observations obtained during the 1996 Whole Sun Month campaign examined a large coronal hole in greater detail than ever before. It appeared on the Sun in August, and extended from the north pole to a large active region in the southern hemisphere. Its physical and magnetic structure and subsequent evolution are described.     

The Polarization Characteristics of Mercury-like Exoplanets

This paper aimed at studying the polarization characteristics of Mercury-like exoplanets via the polarimetric phase curve of the unresolvable Mercury. We utilized the Bayesian non-linear ?tting method to get the photo- metric phase curve and the polarimetric phase curve of Mercury. From these two kinds of curves, we obtained further the polarimetric phase curve of the unresolvable Mercury. The results derived from this curve are as follows: ?rst, in the visible light waveband the order of magnitude of the polarization degree is 10−12; second, the maximum degree of polarization parallel to the scattering plane is comparable to that vertical to the scattering plane, but their corre- sponding phase angles have changed evidently in comparison with the case of the resolvable Mercury; third, when the phase angle is greater than 158°, the polarization degree of the unresolvable Mercury is almost reduced to zero.