共查询到20条相似文献，搜索用时 15 毫秒
1.
Peter Bond 《Astronomy& Geophysics》2004,45(3):3.26-3.28
Peter Bond brings a round-up of space news, including X-ray observations of the galactic centre, a new sort of black hole, targets within the expanding solar system, and Hubble's longest, deepest look back in time. 相似文献
2.
Gerry Gilmore 《Astronomy& Geophysics》2001,42(5):5.12-5.19
Great things are expected of the GAIA Observatory, currently expected to launch in 2011. Gerry Gilmore explains how it will provide accurate measurements that will help us understand the formation of the Milky Way and the distribution of dark matter.
The GAIA Observatory, ESA's Cornerstone 6 mission, addresses the origin and evolution of our galaxy, and a host of other scientific challenges. GAIA will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our galaxy and throughout the Local Group, about 1% of the galactic stellar population. Combined with astrophysical information for each star, provided by on-board multicolour photometry, these data will have the precision and depth necessary to address the three key questions which underlie the GAIA science case: l when did the stars in the Milky Way form? l when and how was the Milky Way assembled? l what is the distribution of dark matter in our galaxy? The accurate stellar data acquired for this purpose will also have an enormous impact on all areas of stellar astrophysics, including luminosity calibrations, structural studies, and the cosmic distance scale. Additional scientific products include detection and orbital classification of tens of thousands of extrasolar planetary systems, a comprehensive survey of objects ranging from huge numbers of minor bodies in our solar system, including near-Earth objects, through galaxies in the nearby universe, to some 500 000 distant quasars. GAIA will also provide several stringent new tests of general relativity and cosmology. 相似文献
The GAIA Observatory, ESA's Cornerstone 6 mission, addresses the origin and evolution of our galaxy, and a host of other scientific challenges. GAIA will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our galaxy and throughout the Local Group, about 1% of the galactic stellar population. Combined with astrophysical information for each star, provided by on-board multicolour photometry, these data will have the precision and depth necessary to address the three key questions which underlie the GAIA science case: l when did the stars in the Milky Way form? l when and how was the Milky Way assembled? l what is the distribution of dark matter in our galaxy? The accurate stellar data acquired for this purpose will also have an enormous impact on all areas of stellar astrophysics, including luminosity calibrations, structural studies, and the cosmic distance scale. Additional scientific products include detection and orbital classification of tens of thousands of extrasolar planetary systems, a comprehensive survey of objects ranging from huge numbers of minor bodies in our solar system, including near-Earth objects, through galaxies in the nearby universe, to some 500 000 distant quasars. GAIA will also provide several stringent new tests of general relativity and cosmology. 相似文献
3.
Steve Phillipps 《Astronomy& Geophysics》2004,45(6):6.06-6.09
New telescope technology and major sky surveys are finding more and more dwarf galaxies. Steve Phillipps discusses how this growing population may hold the clues to understanding a range of galaxy collisions and interactions. 相似文献
4.
Chinese loess–palaeosol sequences are well known for their records of monsoonal climatic variations. However, the modern processes of dust accumulation and soil formation remain poorly understood. A high‐resolution investigation on modern soils, including the measurement of magnetic susceptibility, particle‐size distribution, total Fe, total organic carbon, CaCO3 content, and optical stimulated luminescence (OSL) dating was carried out on the Zhouyuan loess tableland in the southern Loess Plateau. The results indicate that modern cinnamon soils (luvisols) have developed on contemporarily accumulated aeolian dust during the Holocene. The aeolian loess accumulated during the Younger Dryas was identi?ed in the top part of the Malan Loess that underlay the modern soil by OSL dating and proxy climatic data. It indicates that the Malan Loess accumulated during the last glaciation (marine isotope stages 2–4) does not serve as the parent material for the modern soils. Pedogenesis of the soils started with the increased precipitation and soil moisture that have occurred on the loess tableland since the early Holocene. Precipitation‐driven pedogenesis and organic activities are responsible for the leaching of CaCO3, decomposition of mineral dust and the production of clay and ferromagnetic minerals. Drier intervals have interrupted soil formation several times, and therefore pro?les with multiple soils have been developed at many sites on the loess tableland. At places where soil erosion was relatively strong, either a single soil or welded soils are preserved in the Holocene pro?les. This does not necessarily mean, however, that modern soils over the plateau have been developed without interruption under a constantly warmer, moister climate. This is signi?cant for understanding the surface processes and climatic variation during the formation of the numerous palaeosols over the Loess Plateau in the Quaternary. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
5.
Richard de Grijs 《Astronomy& Geophysics》2001,42(4):4.12-4.18
Richard de Grijs reviews the picture of starbirth presented in this nearby, prototype starburst galaxy, a well-studied example of processes that must be widespread in the early universe.
The last tidal encounter between M82 and M81, some 500 Myr ago, had a major impact on what was probably an otherwise normal, quiescent disk galaxy. It caused a concentrated burst of star formation in the form of massive star clusters that decreased rapidly, within a few 100 Myr. The current starburst in the centre of the galaxy is likely to arise from large-scale propagating star formation. Alternatively, it may be related to late infall of tidally disrupted debris from M82 itself. Star formation here overall may, in fact, come from a combination of these two mechanisms, in the sense that the star formation in the active core is actively propagating, whilst the overall evolution of the starburst depends on tidal debris raining back onto the disk of the galaxy, giving rise to the present-day starburst. 相似文献
The last tidal encounter between M82 and M81, some 500 Myr ago, had a major impact on what was probably an otherwise normal, quiescent disk galaxy. It caused a concentrated burst of star formation in the form of massive star clusters that decreased rapidly, within a few 100 Myr. The current starburst in the centre of the galaxy is likely to arise from large-scale propagating star formation. Alternatively, it may be related to late infall of tidally disrupted debris from M82 itself. Star formation here overall may, in fact, come from a combination of these two mechanisms, in the sense that the star formation in the active core is actively propagating, whilst the overall evolution of the starburst depends on tidal debris raining back onto the disk of the galaxy, giving rise to the present-day starburst. 相似文献
6.
Victor P. Starr 《Pure and Applied Geophysics》1963,56(1):163-173
Summary Equations for the motions in a galaxy which is controlled by gravitational forces and inertial effects are formulated. It is found that for the motions relative to the rotating system formulae analogous, and of similar form, to the geostrophic wind equations may be written. From these formulae and from the distribution of the relative gravitational potential in the disc of the galaxy, it is found that a spiral tendency in the mass distribution carries the implication of an inward flux of angular momentum by advective processes. This is to be compared with an outward flux through gravitational torques obtained in previous studies in which the writer participated. 相似文献
7.
现代海底热液活动的调查研究方法 总被引：11，自引：0，他引：11
介绍了国外在现代海底热液活动调查研究中使用的方法和技术手段。现代海底热液活动是普遍发育于大洋中活动板块边界及板内火山活动中心的一种在岩圈和大洋之间进行能量和物质交换的过程。其突出的表象是高温的热液从海底流出，并由此造成热液活动区和上限覆水体的物理和化学异常。海底热测量、海底岩石取样、水体的CH4、^3He和Mn异常观测、硅氧异常观测、多波束测量、OBS观测、深潜调查等都是进行现代海底热液活动调查研究的重要手段。其中水体异常的观测是最为快捷有效的，而深潜器直接观测是现代海底热液活动研究必不可少的。 相似文献
8.
Julienne I. Harnett 《地球物理与天体物理流体动力学》2013,107(1-3):35-37
Abstract Observations of the face-on galaxy NGC 6946 are inconsistent with a simple bisymmetric large-scale field structure confined to the galactic plane; the magnetic field must also possess significant three-dimensionality. The edge-on galaxy NGC 4945 has an active nucleus and a radio halo. Linear polarization maxima on each side of the central galactic plane suggest the presence of a strongly ordered poloidal magnetic field there. 相似文献
9.
G. H. A. Cole 《Surveys in Geophysics》2006,27(3):365-382
If intelligent life were common in the Universe, should we not be aware of it on Earth through contact with advanced space ships and automatic probes? Would we not at least expect to intercept communication signals between space travellers? That this is not found has led to much speculation in the past. Recent discoveries of planets around other stars (called here exoplanets) and, separately, recent discoveries in the evolution of life on Earth, including Homo sapiens, allow this question to be considered again but now with more information than before. This is the subject of the present paper. The study involves aspects of physics and chemistry in combination with biological studies. It is concluded here that the places where technologically capable intelligent life might be expected to be found in our Galaxy are so few that any such “centres of civilisation” must be separated by large distances, probably in excess of 50 light years. If true, this would make the different centres essentially isolated and would suggest that each manifestation of advanced intelligent life is a purely local development. This would agree with our experience of aloneness. Nevertheless, the number of centres throughout the Universe would still be astronomically large, even if each galaxy had only one centre. An hypothesis is proposed which could account for the existence of such centres in this form. 相似文献
10.
A variety of studies of magnetised plasma turbulence invoke theories for the advection of a passive scalar by turbulent fluctuations. Examples include modelling the electron density fluctuations in the interstellar medium, understanding the chemical composition of galaxy clusters and the intergalactic medium, and testing the prevailing phenomenological theories of magnetohydrodynamic turbulence. While passive scalar turbulence has been extensively studied in the hydrodynamic case, its counterpart in MHD turbulence is significantly less well understood. Herein we conduct a series of high-resolution direct numerical simulations of incompressible, field-guided, MHD turbulence in order to establish the fundamental properties of passive scalar evolution. We study the scalar anisotropy, establish the scaling relation analogous to Yaglom’s law, and measure the intermittency of the passive scalar statistics. We also assess to what extent the pseudo Alfvén fluctuations in strong MHD turbulence can be modelled as a passive scalar. The results suggest that the dynamics of a passive scalar in MHD turbulence is considerably more complicated than in the hydrodynamic case. 相似文献
11.
Peter Bond 《Astronomy& Geophysics》2002,43(2):2.29-2.32
Peter Bond reports on Mars and Jupiter as never seen before, ghosts in galaxy clusters and some surprising sunspots. 相似文献
12.
《Astronomy& Geophysics》2007,48(5):5.05-5.05
The strange case of spiral galaxy M101 has become stranger with detailed far-infrared data from the Japanese satellite AKARI. 相似文献
13.
Rongshan Fu Jianhua Huang Jun Liu Xiaohua Chang National Geophysical Observatory at Mengcheng Mengcheng China Key Laboratory of Crust-Mantle Materials Environments Chinese Academy of Science Hefei China School of Earth Space Science University of Science Technology of China China 《地震学报(英文版)》2009,(4):323-329
Geodynamic studies have shown that mantle convection is like a giant blender to make the original heterogeneous mantle mixing and homogenizing. However,some models,especially from geochemical data show that the modern mantle may still contain a number of reservoir bodies with different chemical composition. Then,the modern mantle is homogeneous? Authors have defined a box replacement degree of convective mantle mixing and pervasion degree of convective mantle mixing (that equals to initial density of tracin... 相似文献
14.
Gravitational microlensing data combined with statistical analysis suggests that stars with solar systems like our own make up just 15% of the stars in our galaxy. 相似文献
15.
Robert E. Dickinson 《Pure and Applied Geophysics》1964,59(1):155-171
Summary We continue the theoretical investigation of geostrophically balanced motions of a star gas in a rotating galaxy. The method of small perturbations is employed to derive a quasi geostrophic vorticity equation suitable for solving initial value problems for slow galactic eddying motions. The results derived for this simple theoretical model are then generalized to obtain approximate geostrophic forecast equations suitable for study of nonlinear galactic motions over a whole disk galaxy. A simple discussion of the stability of our approximate vorticity equation is presented. It is expected that in the absence of rapid gravitational instabilities, actual eddy motions observed in spiral galaxies will be at least approximately of the type of motion discussed in this paper. The Rossby adjustment problem is investigated in this context. 相似文献
16.
Allen C. Gellis Milan J. Pavich Paul R. Bierman Eric M. Clapp Amy Ellevein Scott Aby 《地球表面变化过程与地形》2004,29(11):1359-1372
An Erratum has been published for this article in Earth Surface Processes and Landforms 29(13) 2004, 1707. In the semi‐arid Arroyo Chavez basin of New Mexico, a 2·28 km2 sub‐basin of the Rio Puerco, we contrasted short‐term rates (3 years) of sediment yield measured with sediment traps and dams with long‐term, geologic rates (～10 000 years) of sediment production measured using 10Be. Examination of erosion rates at different time‐scales provides the opportunity to contrast the human impact on erosion with background or geologic rates of sediment production. Arroyo Chavez is grazed and we were interested in whether differences in erosion rates observed at the two time‐scales are due to grazing. The geologic rate of sediment production, 0·27 kg m?2 a?1 is similar to the modern sediment yields measured for geomorphic surfaces including colluvial slopes, gently sloping hillslopes, and the mesa top which ranged from 0·12 to 1·03 kg m?2 a?1. The differences between modern sediment yield and geologic rates of sediment production were most noticeable for the alluvial valley ?oor, which had modern sediment yields as high as 3·35 kg m?2 a?1. The hydraulic state of the arroyo determines whether the alluvial valley ?oor is aggrading or degrading. Arroyo Chavez is incised and the alluvial valley ?oor is gullied and piped and is a source of sediment. The alluvial valley ?oor is also the portion of the basin most modi?ed by human disturbance including grazing and gas pipeline activity, both of which serve to increase erosion rates. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
17.
Three points raised by Solomon's discussion are clarified, a conservative approach is preferred, using pollen-vegetation relationships based on all taxa potentially involved for a given site. The use of techniques for comparison with modern analogues is defended, provided that appropriate methods such as Standardized Euclidian Distance are used. The model ?FORET’? used by Solomon is based on half hectare plots and is not considered ideal for aggregation to the forty hectare lake site or to the same area for pollen grains entering it. 相似文献
18.
Chris R. Stokes 《地球表面变化过程与地形》2018,43(1):85-123
Ice streams are integral components of an ice sheet's mass balance and directly impact on sea level. Their flow is governed by processes at the ice‐bed interface which create landforms that, in turn, modulate ice stream dynamics through their influence on bed topography and basal shear stresses. Thus, ice stream geomorphology is critical to understanding and modelling ice streams and ice sheet dynamics. This paper reviews developments in our understanding of ice stream geomorphology from a historical perspective, with a focus on the extent to which studies of modern and palaeo‐ice streams have converged to take us from a position of near‐complete ignorance to a detailed understanding of their bed morphology. During the 1970s and 1980s, our knowledge was limited and largely gleaned from geophysical investigations of modern ice stream beds in Antarctica. Very few palaeo‐ice streams had been identified with any confidence. During the 1990s, however, glacial geomorphologists began to recognise their distinctive geomorphology, which included distinct patterns of highly elongated mega‐scale glacial lineations, ice stream shear margin moraines, and major sedimentary depocentres. However, studying relict features could say little about the time‐scales over which this geomorphology evolved and under what glaciological conditions. This began to be addressed in the early 2000s, through continued efforts to scrutinise modern ice stream beds at higher resolution, but our current understanding of how landforms relate to processes remains subject to large uncertainties, particularly in relation to the mechanisms and time‐scales of sediment erosion, transport and deposition, and how these lead to the growth and decay of subglacial bedforms. This represents the next key challenge and will require even closer cooperation between glaciology, glacial geomorphology, sedimentology, and numerical modelling, together with more sophisticated methods to quantify and analyse the anticipated growth of geomorphological data from beneath active ice streams. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
19.
《中国科学:地球科学(英文版)》2015,(11)
Early oceans(520 Ma) were characterized by widespread water-column anoxia, stratification, and limited oxidant availability, which are comparable to the chemical characteristics of modern marine sedimentary pore-waters in productive continental margins. Based on this similarity and our current understanding of the formation mechanism of early Earth ocean chemistry, we propose an idealized chemical zonation model for early oceans that includes the following redox zones(from shallow nearshore to deep offshore regions): oxic, nitrogenous(NO3?-NO2?-enriched), manganous-ferruginous(Mn2+ or Fe2+-enriched), sulfidic(H2S-enriched), methanic(CH4-enriched), and ferruginous(Fe2+-enriched). These zones were dynamically maintained by a combination of processes including surface-water oxygenation by atmospheric free oxygen, nitrate reduction beneath the chemocline, nearshore manganese-iron reduction, sulfate reduction, methanogenesis, and hydrothermal Fe2+ inputs from the deep ocean. Our modified "euxinic wedge" model expands on previous versions of this model, providing a more complete theoretical framework for the chemical zonation of early Earth oceans that helps to explain observations of unusual Mo-S-C isotope patterns. This model may provide a useful foundation for future studies of ocean chemistry evolution and elemental biogeochemical cycles in early Earth history. 相似文献
20.
为深入理解井水位同震响应机理,本文开展了向完整井-松散含水层系统输入由不同频率和振幅（加速度）组成的正弦波荷载的振动台实验。以实验模型为物理模型,建立了振动作用下松散承压含水层中孔隙水压力响应的流固耦合模型和含水层水流与井流的相互作用模型,并运用多物理场耦合模拟软件COMSOL Multiphysics对实验过程进行了数值模拟。实验中观测到的四种典型水位变化形态与野外场地同震井水位变化形态相似。数值模拟结果显示,本研究建立的数学模型能较好地反映松散承压含水层中孔隙水压力和水位的响应情况。本文研究对解释地下水同震响应机制、岩体渗流稳定性和安全问题具有重要意义。 相似文献