共查询到20条相似文献，搜索用时 31 毫秒
1.
Rubin VC 《Science (New York, N.Y.)》1980,209(4452):64-71
Our perception of the universe has been altered by recent discoveries in astronomy, discoveries of new objects and of new phenomena, coming from a wide range of observing techniques. By 1990 astronomers expect to know more about the distribution of mass in the universe, the physics of energetic sources, and the intricate interconnections of astrophysical processes on a variety of spatial and temporal scales. 相似文献
2.
Huchra JP 《Science (New York, N.Y.)》1992,256(5055):321-325
The Hubble constant is the constant of proportionality between recession velocity and distance in the expanding universe. It is a fundamental property of cosmology that sets both the scale and the expansion age of the universe. It is determined by measurement of galaxy The Hubble constant is the constant of proportionality between recession velocity and development of new techniques for the measurements of galaxy distances, both calibration uncertainties and debates over systematic errors remain. Current determinations still range over nearly a factor of 2; the higher values favored by most local measurements are not consistent with many theories of the origin of large-scale structure and stellar evolution. 相似文献
3.
Kron RG 《Science (New York, N.Y.)》1982,216(4543):265-269
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. 相似文献
4.
Turner MS 《Science (New York, N.Y.)》1993,262(5135):861-867
The Cosmic Background Explorer satellite has recently made the most accurate measurement of the temperature of the universe, determining it to be 2.726 +/- 0.01 kelvin. In trying to understand why the temperature has this value, one is led to discover the most fundamental features of the universe-an early, radiation-dominated epoch, enormous entropy per nucleon, synthesis of the light elements around 3 minutes after the bang, and a small excess of matter over antimatter-as well as some of the most pressing issues in cosmology today-the development of structure in the universe and the identification of the nature of the ubiquitous dark matter. 相似文献
5.
Simon HA 《Science (New York, N.Y.)》1977,195(4283):1186-1191
From an economic standpoint, the modern computer is simply the most recent of a long line of new technologies that increase productivity and cause a gradual shift from manufacturing to service employment. The empirical evidence provides no support for the claim sometimes made that the computer "mechanizes" and "dehumanizes" work. Perhaps the greatest significance of the computer lies in its impact on Man's view of himself. No longer accepting the geocentric view of the universe, he now begins to learn that mind, too, is a phenomenon of nature, explainable in terms of simple mechanisms. Thus the computer aids him to obey, for the first time, the ancient injunction, "Know thyself." 相似文献
6.
提出了一种基于执行剖面过滤的分割测试方法.该方法通过从大量的执行操作中过滤出包含容易引起错误输出的特殊执行操作的子集,并对子集的执行操作进行回放和检验,从而可以发现软件潜在的错误.从而使引起错误输出的输入元素集中分割在某些子域内,提高了发现错误的概率.实验结果表明,该方法分割错误元素的集中度以及命中错误的概率较高,相同条件下其效果要优于随机测试. 相似文献
7.
Barkana R 《Science (New York, N.Y.)》2006,313(5789):931-934
The earliest generation of stars, far from being a mere novelty, transformed the universe from darkness to light. The first atoms to form after the Big Bang filled the universe with atomic hydrogen and a few light elements. As gravity pulled gas clouds together, the first stars ignited and their radiation turned the surrounding atoms into ions. By looking at gas between us and distant galaxies, we know that this ionization eventually pervaded all space, so that few hydrogen atoms remain today between galaxies. Knowing exactly when and how it did so is a primary goal of cosmologists, because this would tell us when the early stars formed and in what kinds of galaxies. Although this ionization is beginning to be understood by using theoretical models and computer simulations, a new generation of telescopes is being built that will map atomic hydrogen throughout the universe. 相似文献
8.
Dark matter, proposed decades ago as a speculative component of the universe, is now known to be the vital ingredient in the cosmos: six times more abundant than ordinary matter, one-quarter of the total energy density, and the component that has controlled the growth of structure in the universe. Its nature remains a mystery, but assuming that it is composed of weakly interacting subatomic particles, is consistent with large-scale cosmic structure. However, recent analyses of structure on galactic and subgalactic scales have suggested discrepancies and stimulated numerous alternative proposals. We discuss how studies of the density, demography, history, and environment of smaller-scale structures may distinguish among these possibilities and shed new light on the nature of dark matter. 相似文献
9.
Cruz M Turok N Vielva P Martínez-González E Hobson M 《Science (New York, N.Y.)》2007,318(5856):1612-1614
The Cosmic Microwave Background provides our most ancient image of the universe and our best tool for studying its early evolution. Theories of high-energy physics predict the formation of various types of topological defects in the very early universe, including cosmic texture, which would generate hot and cold spots in the Cosmic Microwave Background. We show through a Bayesian statistical analysis that the most prominent 5 degrees -radius cold spot observed in all-sky images, which is otherwise hard to explain, is compatible with having being caused by a texture. From this model, we constrain the fundamental symmetry-breaking energy scale to be (0) approximately 8.7 x 10(15) gigaelectron volts. If confirmed, this detection of a cosmic defect will probe physics at energies exceeding any conceivable terrestrial experiment. 相似文献
10.
《Science (New York, N.Y.)》1983,220(4594):256
In the article "The new inflationary universe" by M. Mitchell Waldrop (Research News, 28 Jan., p. 375), it was stated incorrectly that, in the standard model, the expanding universe cooled below 10(27) degrees Kelvin about 10(35) seconds after the Big Bang. The correct time is 10(-35) second. 相似文献
11.
Gamma-ray bursts (GRBs) are bright flashes of gamma rays coming from the cosmos. They occur roughly once per day, typically last for tens of seconds, and are the most luminous events in the universe. More than three decades after their discovery, and after pioneering advances from space and ground experiments, they still remain mysterious. The launch of the Swift and Fermi satellites in 2004 and 2008 brought in a trove of qualitatively new data. In this Review, we survey the interplay between these recent observations and the theoretical models of the prompt GRB emission and the subsequent afterglow. 相似文献
12.
Stars and gas in galaxies, hot intracluster medium, and intergalactic photo-ionized gas make up at most half of the baryons that are expected to be present in the universe. The majority of baryons are still missing and are expected to be hidden in a web of warm-hot intergalactic medium. This matter was shock-heated during the collapse of density perturbations that led to the formation of the relaxed structures that we see today. Finding the missing baryons and thereby producing a complete inventory of possibly the only detectable component of the energy-mass budget of the universe is crucial to validate or invalidate our standard cosmological model. 相似文献
13.
Glanz J 《Science (New York, N.Y.)》1995,268(5219):1849-1850
Pittsburgh-Most everything in astronomy is big. But the truly outsized features of the universe-vast filaments of galaxies and its great dark voids-were highlighted when 772 researchers gathered here on 11-15 June for the 186th meeting of the American Astronomical Society. Talks included a new explanation for the large-scale "tapestry" of the universe and a new glimpse of what may fill its voids. 相似文献
14.
RC Reis JM Miller MT Reynolds K Gültekin D Maitra AL King TE Strohmayer 《Science (New York, N.Y.)》2012,337(6097):949-951
Supermassive black holes (SMBHs; mass is greater than or approximately 10(5) times that of the Sun) are known to exist at the center of most galaxies with sufficient stellar mass. In the local universe, it is possible to infer their properties from the surrounding stars or gas. However, at high redshifts we require active, continuous accretion to infer the presence of the SMBHs, which often comes in the form of long-term accretion in active galactic nuclei. SMBHs can also capture and tidally disrupt stars orbiting nearby, resulting in bright flares from otherwise quiescent black holes. Here, we report on a ~200-second x-ray quasi-periodicity around a previously dormant SMBH located in the center of a galaxy at redshift z = 0.3534. This result may open the possibility of probing general relativity beyond our local universe. 相似文献
15.
Waxman E 《Science (New York, N.Y.)》2007,315(5808):63-65
In the past four decades a new type of astronomy has emerged, where instead of looking up into the sky, "telescopes" are buried miles underground or deep under water or ice and search not for photons (that is, light), but rather for particles called neutrinos. Neutrinos are nearly massless particles that interact very weakly with matter. The detection of neutrinos emitted by the Sun and by a nearby supernova provided direct tests of the theory of stellar evolution and led to modifications of the standard model describing the properties of elementary particles. At present, several very large neutrino detectors are being constructed, aiming at the detection of the most powerful sources of energy and particles in the universe. The hope is that the detection of neutrinos from these sources, which are extra-Galactic and are most likely powered by mass accretion onto black holes, will not only allow study of the sources, but, much like solar neutrinos, will also provide new information about fundamental properties of matter. 相似文献
16.
Weinberg S 《Science (New York, N.Y.)》1985,230(4721):15-18
The farthest of the galaxies that can be seen through the large ground-based telescopes of modern astronomy, such as those on La Palma in the Canary Islands, are so far away that they appear as they did close to the time of the origin of the universe, perhaps some 10 billion years ago. Much has been learned, and much has still to be learned, about the young universe from optical and radio telescopes, but these instruments cannot be used to look directly at the universe in its first few hundred thousand years. Instead, they are used to search the relatively recent past for relics of much earlier times. Together with experiments planned for the next generation of elementary particle accelerators, astronomical observations should continue to extend what is known about the universe backward in time to the Big Bang and may eventually help to reveal the origins of the physical laws that govern the universe. 相似文献
17.
Olinto AV 《Science (New York, N.Y.)》2007,315(5808):68-70
The origin of the most energetic particles ever observed, cosmic rays, will begin to be revealed in the next few years. Newly constructed ultrahigh-energy cosmic ray observatories together with high-energy gamma-ray and neutrino observatories are well positioned to unveil this mystery before the centenary of their discovery in 2012. Cosmic ray sources are likely to involve the most energetic phenomena ever witnessed in the universe. 相似文献
18.
李冰 《信阳农业高等专科学校学报》2009,19(4)
《紫颜色》成功地描述了一位黑人妇女西丽摆脱父权压迫,追求自我身份和自我价值实现的心路历程。小说中黑人女性的成长和谋求女性解放的斗争告诉人们:黑人女性只有抛弃传统基督教,获得对上帝新的理解———在和大自然的和谐中寻找自己的上帝,以及坚持和弘扬黑人传统文化,才能在苦难中获得新生,并确立自己的社会地位。 相似文献
19.
Light from the brightest supernova in almost 400 years arrived at Earth on 23 February 1987. Although located 160,000 light years away in a satellite galaxy of our own known as the Large Magellanic Cloud, this supernova's relative proximity compared to all others that have been observed in modern times has allowed observations, which were never possible before, to be made from space, from detectors on the ground and carried by balloons and airplanes, and from neutrino detectors deep underground. What emerges is a greater understanding of one of the most violent events in the universe, the death of a massive star. For the most part, theoretical expectations have been borne out, but some major surprises have made the event all the more fascinating. 相似文献
20.
Turner MS 《Science (New York, N.Y.)》2007,315(5808):59-61
Cosmology is in the midst of a period of revolutionary discovery, propelled by bold ideas from particle physics and by technological advances from gigapixel charge-coupled device cameras to peta-scale computing. The basic features of the universe have now been determined: It is 13.7 billion years old, spatially flat, and expanding at an accelerating rate; it is composed of atoms (4%), exotic dark matter (20%), and dark energy (76%); and there is evidence that galaxies and other structures were seeded by quantum fluctuations. Although we know much about the universe, we understand far less. Poised to dramatically advance our understanding of both the universe and the laws that govern it, cosmology is on the verge of a golden age. 相似文献