The origin of galaxies and clusters of galaxies

Debate on how galaxies and clusters of galaxies formed has reached an interesting stage at which one can find arguments for quite different scenarios. The galaxy distribution has a complex "frothy" character that could be the fossil of a network of protoclusters or pancakes that produced galaxies. However, there are galaxies like our own that seem never to have been in a protocluster but are physically similar to the galaxies in dense clusters. Some clues to be assessed in resolving this dilemma are the possible existence of galaxy filaments, the relative ages of galaxies and clusters of galaxies, and the continuity between cluster and field galaxies and between galaxies and clusters of galaxies.     

A theory of diversity equilibrium and morphological evolution

If the world can only support a finite amount of biomass, species might be added over time, with a decrease in population size of an average species. Population sizes of species will decrease to the extent that stochastic events eliminate species as fast as others appear, yielding an equilibrium. A resource diversity control of niche subdivision is therefore not needed to generate an equilibrium number of species. Morphological evolution may decelerate over time for similar reasons.     

The rotation of spiral galaxies

There is accumulating evidence that as much as 90 percent of the mass of the universe is nonluminous and is clumped, halo-like, around individual galaxies. The gravitational force of this dark matter is presumed to be responsible for the high rotational velocities of stars and gas in the disks of spiral galaxie. At present, the form of the dark matter is unknown. Possible candidates span a range in mass of 10(70), from non-zero-mass neutrinos to massive black holes.     

The most distant known galaxies

Ever since the proposal of the idea of an expanding universe more than 50 years ago, each generation of investigators has found that some current theory could be (marginally) tested by the properties of the most distant known galaxies. There has consequently been a continuing effort to identify very remote objects, especially to confront theories of the evolution of galaxies (since galaxies are seen as they were at prior epochs) and to confront cosmological theories (which make predictions about the overall dynamics of the expansion of the universe). These theories have yet to be definitively tested, but a new generation of optical telescopes and detectors provides hope for significant progress during this decade.     

Climate-driven range expansion and morphological evolution in a marine gastropod

Little is known about the phenotypic consequences of global climate change, despite the excellent Pleistocene fossil record of many taxa. We used morphological measurements from extant and Pleistocene populations of a marine gastropod (Acanthinucella spirata) in conjunction with mitochondrial DNA sequence variation from living populations to determine how populations responded phenotypically to Pleistocene climatic changes. Northern populations show little sequence variation as compared to southern populations, a pattern consistent with a recent northward range expansion. These recently recolonized northern populations also contain shell morphologies that are absent in extant southern populations and throughout the Pleistocene fossil record. Thus, contrary to traditional expectations that morphological evolution should occur largely within Pleistocene refugia, our data show that geographical range shifts in response to climatic change can lead to significant morphological evolution.     

Percolation and galaxies

A theory is presented in which much of the structure of spiral galaxies arises from a percolation phase transition that underlies the phenomenon of propagating star formation. According to this view, the appearance of spiral arms is a consequence of the differential rotation of the galaxy and the characteristic divergence of correlation lengths for continuous phase transitions. Other structural properties of spiral galaxies, such as the distribution of the gaseous components and the luminosity, arise directly from a feedback mechanism that pins the star formation rate close to the critical point of the phase transition. The approach taken in this article differs from traditional dynamical views. The argument is presented that, at least for some galaxies, morphological and other features are already fixed by general properties of phase transitions, irrespective of detailed dynamic or other considerations.     

Dynamics of elliptical galaxies

Elliptical galaxies were once thought to be similar in their structure and dynamics to rotationally flattened bodies like stars. The discovery that elliptical galaxies rotate much more slowly than a fluid body with the same shape has led to a qualitative change in our understanding of the dynamics of these systems. It is now believed that elliptical galaxies are fully triaxial in shape. Self-consistent triaxial equilibria have been constructed and appear to be long-lived; they are made possible by the existence of conserved quantities, or integrals of motion, for galactic potentials without rotational symmetry. Many self-consistent equilibria are unstable; the nonexistence of elliptical galaxies with axis ratios more extreme than 3:1 is probably the result of such an instability. There is evidence for strong central mass concentrations, perhaps massive black holes, at the centers of some nearby galaxies. Recent observations suggest that many elliptical galaxies formed through the merger of two or more spiral galaxies.     

The detection of a population of submillimeter-bright, strongly lensed galaxies

Gravitational lensing is a powerful astrophysical and cosmological probe and is particularly valuable at submillimeter wavelengths for the study of the statistical and individual properties of dusty star-forming galaxies. However, the identification of gravitational lenses is often time-intensive, involving the sifting of large volumes of imaging or spectroscopic data to find few candidates. We used early data from the Herschel Astrophysical Terahertz Large Area Survey to demonstrate that wide-area submillimeter surveys can simply and easily detect strong gravitational lensing events, with close to 100% efficiency.     

Colliding and merging galaxies

Aided by advances in computer technology and observations from space, astronomers have begun to unravel the mysteries of galaxy formation and evolution. Galaxies evolve by interacting with their environment and especially with each other. During brief but often fierce galactic encounters, gravitational forces generate strong tides that survive as telltale signatures for billions of years. Because these so-called collisions dissipate orbital energy, galaxies on bound orbits may eventually merge. Collisions and mergers are responsible for a great variety of phenomena, including the triggering of widespread star formation in galaxies and the fueling of nuclear activity in quasars. Evidence is accumulating that not all galaxies formed shortly after the Big Bang. A sizable fraction of them may have formed later, and many are still experiencing significant dynamical evolution.     

Convergent morphological evolution detected by studying proteins of tree frogs in the Hyla eximia species group

Protein studies have uncovered an apparent case of convergent evolution among North American tree frogs. The species Hyla eximia and Hyla regilla are so similar in external morphology that the "wrightorum" subspecies is assigned by some authorities to H. eximia and by others to H. regilla. Yet microcomplement fixation experiments show that "wrightorum" albumin, though virtually indistinguishable from authentic H. eximia albumin, differs as much from H. regilla albumin as from albumins of species outside the genus Hyla, such as Acris crepitans. The morphological resemblance of "wrightorum" to H. regilla is thus probably due to convergence.     

栽培黄精的植物学形态特征

中药黄精是百合科Liliaceae黄精属Polygonatum多种植物根茎的总称,我国有30多种。中国药典将黄精P．sibiricum Redoute．、多花黄精P．cyrtonemaHua及滇黄精P．kingianum Coll．et Hemsl．3种定为原生药。作为常用药材,黄精不仅具有提高免疫力、降血糖、降血脂、抗菌、抗病毒、抗肿瘤等作用,而且在研制新药和开发保健品等方面具有广阔的发展前景。近年来,随着黄精市场需求量的不断增加和野生资源的不断减少,黄精人工栽培已成为市场供求之主体,规范化种植势在必行。而研究栽培黄精植物学形态特征,是进行黄精规范化种植的基本要求,目前在这方面的研究报道较少。本试验对贵州省凤冈县西山黄精GAP试验示范基地的栽培滇黄精和多花黄精生长发育过程实行系统定点观察,研究其植物学形态特征,以期为黄精规范化种植提供理论依据;同时也为西山基地黄精品种（Culti-varietas）的申报工作提供资料。