Late quaternary of the middle Caquetá River area (Colombian Amazonia)     

Thomas Van Der Hammen  Joost F. Duivenvoorden  Johanna M. Lips  Ligia E. Urrego  Nohora Espejo 《第四纪科学杂志》1992,7(1):45-55

The late Quaternary history of the middle Caquetá River area in Colombia, northwestern Amazonia is described, based on observations of river bank sections, radiocarbon dates and palynological analyses of organic layers in floodplain and low terrace sediments of the Caquetá River. It is shown that the Late Pleistocene and Holocene climatic changes that took place in the Andean Cordilleras, were related to the depositional and erosional history of the Caquetá River in the Colombian Amazonian lowlands. The low terrace sediments consist of sandy and gravelly deposits covered by clays that sometimes contain lenses of peaty material. From these organic low terrace sediments, seven finite radiocarbon dates were obtained of Middle Pleniglacial age, between 56 000 and 30 000 yr BP. The coarse textured basal deposits of the low terrace apparently stem from the early part of the Middle Pleniglaciai period, during which the effective rainfall in the Andes was relatively high and the Andean glaciers had a considerable extension. Palynological data from silty sediments with organic remains at one site, show an interval when drier and more open types of vegetation on poor soils must have covered a larger area than today, but Amazonian forest was still the dominating type of vegetation. This interval might correspond to one of the Middle Pleniglacial savanna intervals from eastern Amazonia (Carajas). No organic sediments from the Upper Pleniglacial period were found and hence radiocarbon dates were not obtained. In the Andes this period had a very cold climate with low effective rainfall and in the east Amazonian Carajas area it is characterised by the relative extension of open savanna vegetation. The river run-off and sediment transport must have been much lower than in the Middle Pleniglacial and the Caquetá River cut itself down in its own sediments. Two Late-glacial radiocarbon datings obtained at one site (ca. 12 500 yr BP) indicate the existence of a Late-glacial sedimentation phase, separated from the Holocene sequence by a minor erosional phase. Organic layers in the Holocene floodplain sediments yielded 28 radiocarbon dates between 10 000 and 355 yr BP. Holocene sedimentation started with the rapid deposition of (sandy) clay possibly in a partly permanently inundated Caquetá valley. During the major part of the Holocene (silty) clays were deposited, with a dominant seasonal inundation cycle.  相似文献   

Weak lensing predictions at intermediate scales     

Ludovic Van Waerbeke  Takashi Hamana  †  Román Scoccimarro  Stephane Colombi  Francis Bernardeau 《Monthly notices of the Royal Astronomical Society》2001,322(4):918-926

As pointed out in previous studies, the measurement of the skewness of the convergence field κ will be useful in breaking the degeneracy among the cosmological parameters constrained from weak lensing observations. The combination of shot noise and finite survey volume implies that such a measurement is likely to be performed in a range of intermediate scales (0.5 to 20 arcmin) where neither perturbation theory nor the hierarchical ansatz applies. Here we explore the behaviour of the skewness of κ at these intermediate scales, based on results for the non-linear evolution of the mass bispectrum. We combined different ray-tracing simulations to test our predictions, and we find that our calculations describe accurately the transition from the weakly non-linear to the strongly non-linear regime. We show that the single lens-plane approximation remains accurate even in the non-linear regime, and we explicitly calculate the corrections to this approximation. We also discuss the prospects of measuring the skewness in upcoming weak lensing surveys.  相似文献   

Le volcanisme et sa prévention. H. Tazieff and M. Derruau. Publisher Masson,Paris 1990 (256 pp) FF 206 ISBN 2-225-82122-4     

Jan Van Mourik 《第四纪科学杂志》1995,10(4):402-402

  相似文献   

The Red Supergiant IRAS04553-6825 in the LMC     

Jacco Th. Van Loon 《Astrophysics and Space Science》1997,255(1-2):405-406

  相似文献   

Evolution and Mass Loss of AGB Stars in the Small Magellanic Cloud     

J.A.D.L. Blommaert  N.R. Trams  K. Okumura  M.A.T. Groenewegen  J.Th. Van Loon  L.B.F.M. Waters  M.R. Cioni  H.J. Habing  A.A. Zijlstra  C. Loup 《Astrophysics and Space Science》1997,255(1-2):399-400

  相似文献   

ISO's View on Massive Star Evolution: Neon Abundances in Wolf-Rayet Stars     

P.W. Morris  K.A. Van Der Hucht  A.J. Willis  P.M. Williams 《Astrophysics and Space Science》1997,255(1-2):157-166

  相似文献   

A New Ionosphere Monitoring Technology Based on GPS   总被引：1，自引：0，他引：1  

Claudio Brunini  Amalia Meza  Francisco Azpilicueta  María Andrea Van Zele  Mauricio Gende  Alejandro Díaz 《Astrophysics and Space Science》2004,290(3-4):415-429

Although global positioning system (GPS) was originally planned as a satellite-based radio-navigation system for military purposes, civilian users have significantly increased their access to the system for both, commercial and scientific applications. Almost 400 permanent GPS tracking stations have been stablished around the globe with the main purpose of supporting scientific research. In addition, several GPS receivers on board of low Earth orbit satellites fitted with special antennas that focus on Earth's horizon, are tracking the radio signals broadcasted by the high-orbiting GPS satellites, as they rise and set on Earth horizon. The data of these ground and space-born GPS receivers, readily accessible through Internet in a ‘virtual observatory’ managed by the International GPS Service, are extensively used for many researches and might possibly ignite a revolution in Earth remote sensing. By measuring the changes in the time it takes for the GPS signals to arrive at the receiver as they travel through Earth's atmosphere, scientists can derive a surprising amount of information about the Earth's ionosphere, a turbulent shroud of charged particles that, when stimulated by solar flares, can disrupt communications around the world. This contribution presents a methodology to obtain high temporal resolution images of the ionospheric electron content that lead to two-dimensional vertical total electron content maps and three-dimensional electron density distribution. Some exemplifying results are shown at the end of the paper.  相似文献   

ISO SWS Spectroscopy of WR 146 (WC6+O)     

A.J. Willis  Luc Dessart  P.A. Crowther  P.W. Morris  K.A. Van Der Hucht 《Astrophysics and Space Science》1997,255(1-2):167-168

We have obtained ISO SWS spectroscopy of WR 146 (WC6+O) covering the wavelength range 2.6-20 μm. WC6 wind emission is observed in numerous lines of He II and C IV, as well as in the [Ne III] 15.5 μm line, but not in [Ne II] 12.81 or [Ne V] 14.32 μm. An analysis of these spectra (and complementary radio and optical data) yields for the WC6 star: v∞ = 2700 km s-1; M=2.6×10-5M⊙yr-1; C/He = 0.15; and a neon abundance bound of 3.4×10-3≤Ne/He≤6.8×10-3. The neon abundance is close to that predicted in stellar evolution models of WC stars. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

THE GALATIA,KANSAS, CHONDRITE     

W.R. Van Schmus  Klaus Kei  D.E. Lange  G.H. Conrad 《Meteoritics & planetary science》1978,13(2):267-273

The Galatia meteorite was found in August, 1971, approximately 7 km ENE of Galatia, Barton County, Kansas (98° 53′W., 38° 39.5′N). The single stone weighed 23.9 kg and is partially weathered. Olivine (Fa_24.9) and pyroxene (Fs_20.9) compositions indicate L-group classification, and textural observations indicate that the stone is of petrologic type 6. Galatia is similar in many respects to the Otis L6 chondrite (found 20 km to the west), but it does not have the brecciated structure of Otis and, thus, it is not part of the same fall.  相似文献   

On the equivalence of thomson-haskell matrices and knopoff's method for love waves     

Oldřich Novotný  Reviewer J. Vaněk 《Studia Geophysica et Geodaetica》1974,18(2):120-125

Summary The relation between Thomson-Haskell matrices and Knopoff's method for Love waves is studied. In comparing boths methods one draws on the physical formulation of the problem, used in Thomson-Haskell method.  相似文献