On the periodical structures in populations of galaxies and of clusters of galaxies

Analysing the distribution of the redshift of clusters of galaxies, obtained from the catalogue of SCHMIDT (1986), two already known periodical structures were confirmed and both periods were extended by a number of periods — approximately by two times (We elucidated 5 new periods in the first structure and 4 in the second.). The statistical significance of these structures was estimated to 0.01 in the first case and to 0.02 in the second one. Particularly, the second structure may be the largest known object in the Universe (about 900 Mpc at H = 75 km s^-1 Mpc^-1). These results agree with the predictions of the axion-dominated early Universe. In addition, we discovered periodical structures of an another type — in luminosity functions of galaxies, which are members of rich clusters. Bei der Analyse des Katalogs von SCHMIDT (1986) wurden zwei periodische Strukturen in den Verteilungen der Rotverschiebungen von Galaxienhaufen festgestellt. In den beiden Strukturen wurden 5 bzw. 4 neue Perioden beobachtet, weshalb sich die Periodenzahl in jeder der beiden Strukturen etwa verdoppelt hat. Die statistische Signifikanzen dieser Strukturen wurden zu 0.01 und 0.02 abgeschätzt. Möglicherweise entspricht die zweite Struktur dem größten bekannten Objekt des Weltalls (etwa 900 Mpc bei H = 75 km s^-1 Mpc^-1). Diese Resultate stützen die Theorie eines axiondominierten frühen Universums. Außerdem wurden weitere periodische Strukturen in der Leuchtkraftfunktion von Galaxien aus reichen Galaxien-haufen entdeckt.     

Molecular clouds and the formation of open clusters

Using analytical approximations of the mass spectra of molecular clouds and stellar systems including open clusters and associations a relation between the final star formation efficiency (final SFE) and the initial cloud mass is derived. The dependence of the SFE on cloud mass is estimated for two cases of molecular cloud destruction by stellar winds in spherical geometry. The result of growing SFE with rising cloud mass does not agree with current observations and the above relation. A decrease of the SFE is expected if the fraction of high-mass stars grows with increasing mass of the cloud.     

球状星团NGC4147的绝对自行和颜色星等图

本文以上海天文台佘山40厘米折射望远镜于1958年拍摄的3张照相底片为第一期,印度Kavalur的234米VainuBappu望远镜于1996年用CCD拍摄的4幅图像为第二期,使用Brosche等1985年发表的球状星团NGC4147天区42颗恒星的位置和绝对自行作为参考架,用中心重叠法进行天体测量归算,得到了这个星团中心附近11'×11'天区内到B＝17.6为止115颗恒星的位置和绝对自行,利用这些自行对成员概率作了估计.本文还给出了用VainuBappu望远镜CCD测光结果得到的这个星因水平文和巨星支恒星V与B-V．V－R和V－I颜色星等图,并对这些颜色星等图和团自行作了讨论,得到这个星团的赤经方向绝对自行为-2.82±0.49mas／yr,赤纬方向绝对自行为2.37±0.43mas／yr.     

双差定位法在地震丛集精确定位中的应用

应用双差定位方法(hypodd)对北美Loma Prieta 地区的分属于3个地震丛集的47个地震进行了精确定位.采用交叉谱法精确求取信号的走时差;同时采用人机联做方式在时域调整、修正按自动方式无法准确提取时差的信号,确保每个事件对的走时差精度.重定位后,在几百米的范围内,原来相互重叠的震源位置聚集为三个明显分离的丛集;水平方向的相对位置平均误差为8.5米,震源深度方向的平均误差为23.4 m.     

Determining the size of spatial clusters in focused tests: Comparing two methods by means of simulation in a GIS

 Based on a four-point evaluation system consisting of accuracy, consistency, power, and chance to commit type I errors, this study compares Tango's minimum p (MinP) and Stone's maximum relative risk (MaxRR) methods for detecting focused cluster size through simulations in GIS. It reveals that the MinP method is more effective than the MaxRR method. The MinP method exhibits higher levels of accuracy and consistency; and its power and chance to commit type I errors are similar to the MinP method. The MaxRR method has a tendency to underestimate the cluster size, while the MinP method tends to overestimate the cluster size, particularly when the clusters are relatively big and have high relative risk levels. In addition, the MinP method seems to be most effective in revealing the size of clusters when clusters are neither too strong nor too weak. The lowest detection rates for clustering occur when the clustering signal is relatively weak, which is easily understandable. In practice, it might be useful to use both the methods to estimate a range of possible cluster sizes, where the MaxRR method indicates the lower estimate, while the MinP method gives the higher estimate of the cluster size. Received: 24 August 2002 / Accepted: 20 December 2002     

东莞PC相关制造业地方产业群的发展演变

从地方产业群理论出发，探讨全球联系和本地联系对地方产业群内部企业网络发展的影响，并结合对东莞3镇的PC相关制造业的实地考察，指出随着中国沿海改革开放的不断深入，逐渐形成一些外向型制造业地方产业群，其发展过程中，本地生产网络与全球生产网络格局已经发生了转变，原来为“三来一补”的出口加工贸易服务的制度设计在实践中逐渐变成了地方产业群进一步发展的制度瓶颈。区域持续发展有赖于不断的制度创新，以充分发挥本地已经形成的产业集聚优势。     

Three‐dimensional flow structure around small‐scale bedforms in a simulated gravel‐bed environment

Pebble clusters are common small‐scale morphological features in gravel‐bed rivers, occupying as much as 10 per cent of the bed surface. Important links exist between the presence of pebble clusters and the development of flow structures. These links are poorly understood at the three‐dimensional level. Particularly neglected has been the effect of clusters on the lateral flow characteristics. A laboratory study was conducted using a hydraulic flume, within which simulated pebble clusters were superimposed onto a plane bed of gravel material. High‐resolution three‐dimensional flow data were collected above the bed at two different flow depths using an acoustic Doppler velocimeter. The results present evidence of the importance of lateral flow in the development of turbulent flow structure. Narrow regions of high lateral and downstream turbulence intensity exist to both sides of clusters and in a three‐dimensional separation zone in their lee. This may indicate the presence of horseshoe‐type vortical structures analogous to those identified in less hydraulically rough environments. However, it is likely that these structures are more complicated given the mutual interference of the surrounding medium. The lateral flow was also identified as a key component in the upwelling identified by other authors in the lee of pebble clusters. The results of the vertical flow analysis confirm the hypothesis that six regions with distinct vertical flow characteristics exist above clusters: flow acceleration up the stoss‐side of the cluster; recirculation behind the cluster in the wake region; vortex shedding from the pebble crest and shear layer; flow reattachment downstream of the cluster; upwelling of flow downstream of the point of reattachment; and recovery of flow. Copyright © 2001 John Wiley & Sons, Ltd.     

A unified theory of the formation of galactic bars

We give arguments for a basically unified formation mechanism of slow (Lynden-Bell) and fast (common) galactic bars. This mechanism is based on an instability that is akin to the well-known instability of radial orbits and is produced by the mutual attraction and alignment of precessing stellar orbits (so far, only the formation of slow bars has been explained in this way). We present a general theory of the low-frequency modes in a disk that consists of orbits precessing at different angular velocities. The problem of determining these modes is reduced to integral equations of moderately complex structure. The characteristic pattern angular velocities Ω_p of the low-frequency modes are of the order of the mean orbital precession angular velocity \(\bar \Omega _{pr}\). Bar modes are also among the low-frequency modes; while \(\Omega _p \approx \bar \Omega _{pr}\) for slow bars, Ω_p for fast bars can appreciably exceed even the maximum orbital precession angular velocity in the disk Ω _pr ^max (however, it remains of the order of these precession angular velocities). The possibility of such an excess of Ω_p over Ω _pr ^max is associated with the effect of “repelling” orbits. The latter tend to move in a direction opposite to the direction in which they are pushed. We analyze the pattern of orbital precession in potentials typical of galactic disks. We note that the maximum radius of an “attracting” circular orbit r_c can serve as a reasonable estimate of the bar length l_b. Such an estimate is in good agreement with the available results of N-body simulations.     

A possible shock wave in the intergalactic medium of the cluster of galaxies A754

The cluster of galaxies A754 is undergoing a merger of several large structural units. X-ray observations show the nonequilibrium state of the central part of the cluster, in which a cloud of cold plasma ～500 kpc in size was identified amid the hotter cluster gas. The X-ray image of A754 exhibits a brightness discontinuity, which can be interpreted as a shock wave in front of a moving cloud of dense gas. The shock parameters are determined from the jump in intergalactic gas density using the ROSAT image. The estimated Mach number is M₁ = 1.71 _?0.24 ^+0.45 at a 68% confidence level.