浙江山地滑坡现状及其成因

在考察浙西、浙南山地滑坡灾害点的基础上,结合地质、土壤、土地背景资料确定了庆元、青田、龙泉等１５个县（市）为滑坡集中分布区;中小型基岩风化残坡积土层滑坡是浙江主要滑坡类型。山高坡陡的地貌特征、软硬互层的地层岩性、多组断珐交叉的区域地质构造和发育深厚的土壤类型,是滑坡形成的地学基础;人为切坡、流水蚀坡、水耕梯田、植被破坏和集中降雨,是滑坡的诱发因子。     

Galaxy destruction and diffuse light in clusters

Deep images of the Centaurus and Coma clusters reveal two spectacular arcs of diffuse light that stretch for over 100 kpc, yet are just a few kiloparsecs wide. At a surface brightness of m _b ∼27–28 mag arcsec⁻² , the Centaurus arc is the most striking example known of structure in the diffuse light component of a rich galaxy cluster. We use numerical simulations to show that the Centaurus feature can be reproduced by the tidal debris of a spiral galaxy that has been tidally disrupted by the gravitational potential of NGC 4709. The surface brightness and narrow dimensions of the diffuse light suggest that the disc was corotating with its orbital path past pericentre. Features this prominent in clusters will be relatively rare, although at fainter surface brightness levels the diffuse light will reveal a wealth of structure. Deeper imaging surveys may be able to trace this feature for several times its presently observed extent, and somewhere along the tidal debris, a fraction of the original stellar component of the disc will remain bound, but transformed into a faint spheroidal galaxy. It should be possible to confirm the galactic origin of the Centaurus arc by observing planetary nebulae along its length with redshifts close to that of NGC 4709.     

Radiation–hydrodynamical collapse of pre-galactic clouds in the ultraviolet background

To explain the effects of the ultraviolet (UV) background radiation on the collapse of pre-galactic clouds, we implement a radiation–hydrodynamical calculation, combining one-dimensional spherical hydrodynamics with an accurate treatment of the radiative transfer of ionizing photons. Both absorption and scattering of UV photons are explicitly taken into account. It turns out that a gas cloud contracting within the dark matter potential does not settle into hydrostatic equilibrium, but undergoes run-away collapse even under the presence of the external UV field. The cloud centre is shown to become self-shielded against ionizing photons by radiative transfer effects before shrinking to the rotation barrier. Based on our simulation results, we further discuss the possibility of H₂ cooling and subsequent star formation in a run-away collapsing core. The present results are closely relevant to the survival of subgalactic Population III objects as well as to metal injection into intergalactic space.     

A population of very young brown dwarfs and free-floating planets in Orion

We describe the results of a very deep imaging survey of the Trapezium cluster in the IJH bands, using the UKIRT high-resolution camera UFTI. Approximately 32 per cent of the 515 point sources detected are brown dwarf candidates, including several free-floating objects with masses below the deuterium-burning (planetary) threshold at 0.013 M_⊙, which are detectable because of their extreme youth. We have confidence that almost all the sources detected are cluster members, since foreground contamination is minimal in the 33-arcmin² area surveyed, and the dense backdrop of OMC-1 obscures all background stars at these wavelengths. Extinction is calculated from the ( J − H ) colours, permitting accurate luminosity estimates, and temperatures are derived from the dereddened ( I − J ) colours. There is some evidence for a cut-off in the luminosity function below the level corresponding to several Jupiter masses, which may represent the bottom end of the initial mass function . Since star formation is complete in the Trapezium, this limit could have wide significance, if confirmed. However, it could well be an effect of the dispersal of the molecular cloud by the central O-type stars, a process for which the time-scale will vary between star formation regions.     

Non-parametric star formation histories for four dwarf spheroidal galaxies of the Local Group

We use recent Hubble Space Telescope colour–magnitude diagrams of the resolved stellar populations of a sample of local dSph galaxies (Carina, Leo I, Leo II and Ursa Minor) to infer the star formation histories of these systems, SFR ( t ). Applying a new variational calculus maximum likelihood method, which includes a full Bayesian analysis and allows a non-parametric estimate of the function one is solving for, we infer the star formation histories of the systems studied. This method has the advantage of yielding an objective answer, as one need not assume a priori the form of the function one is trying to recover. The results are checked independently using Saha's W statistic. The total luminosities of the systems are used to normalize the results into physical units and derive SN type II rates. We derive the luminosity-weighted mean star formation history of this sample of galaxies.     

Core formation in giant gaseous protoplanets

Sedimentation rates of silicate grains in gas giant protoplanets formed by disk instability are calculated for protoplanetary masses between 1 MSaturn to 10 MJupiter. Giant protoplanets with masses of 5 MJupiter or larger are found to be too hot for grain sedimentation to form a silicate core. Smaller protoplanets are cold enough to allow grain settling and core formation. Grain sedimentation and core formation occur in the low mass protoplanets because of their slow contraction rate and low internal temperature. It is predicted that massive giant planets will not have cores, while smaller planets will have small rocky cores whose masses depend on the planetary mass, the amount of solids within the body, and the disk environment. The protoplanets are found to be too hot to allow the existence of icy grains, and therefore the cores are predicted not to contain any ices. It is suggested that the atmospheres of low mass giant planets are depleted in refractory elements compared with the atmospheres of more massive planets. These predictions provide a test of the disk instability model of gas giant planet formation. The core masses of Jupiter and Saturn were found to be ∼0.25 M_⊕ and ∼0.5 M_⊕, respectively. The core masses of Jupiter and Saturn can be substantially larger if planetesimal accretion is included. The final core mass will depend on planetesimal size, the time at which planetesimals are formed, and the size distribution of the material added to the protoplanet. Jupiter's core mass can vary from 2 to 12 M_⊕. Saturn's core mass is found to be ∼8 M_⊕.     

地理国情普查工作报表的特性与作用研究

地理国情普查工作报表是地理国情普查项目管理的基本措施和途径,本文对地理国情普查工作报表的特性和作用进行了论述,以期对从事地理国情普查的生产单位和管理单位起到指导作用。     

我国岩石地层单位“段”的命名及问题

段是重要的岩石地层单位。段的划分和命名在大比例尺区域地质填图、油气勘查和精细地层划分对比等方面有重要意义。"地层指南"中规定段的名称可采用正式名称或非正式名称。正式段名的建立方法必须符合"地层指南"的要求,是相对规范和稳定的命名方法;非正式命名法使用比较方便,但命名方法多种多样,将其归纳为岩性命名、"地理专名+岩性"命名、位置命名、数字命名和字母命名五种。不论正式名称还是非正式名称,使用时均会由于文献或使用者的原因而产生问题。段名使用中的可能存在如下4个问题:1)能清楚地划分对比、具正式名称的段被非正式名称所代替; 2)在相邻省标准剖面距离较远的情况下,位于省界的剖面组内各段的命名问题; 3)同一组段的划分方法基本相同,但采用不同的非正式名称; 4)使用段的数字名称时不了解或未注意数字顺序的差异而产生错误。针对这些问题,除加强"地层规范"的制定和推广外,还要注意名称溯源的严谨性,使段名成为能够规范地追溯和合理应用的地层名称。