Late Weichselian glacial maximum on Andøya, North Norway     

JOKOB J. MØLLER  TOR K. DANIELSEN  ARNE FJALSTAD 《Boreas: An International Journal of Quaternary Research》1992,21(1):1-13

Morphological, seismic and lithostratigraphic investigations of a moraine deposit at Bleik (the Bleik moraine), northern Andøya, show short-distance transported till overlying long-distance transported predominantly glaciofluvial ice-marginal deposits. Consolidated glaciomarine sediments from a core at present sea-level, c . 400 m distally to the moraine complex, contain 31 species of foraminifera, among which Cassidulina reniforme, Islandiella helenae and Trifarina fluens dominate, and fragments of the molluscs Mya truncata and Astarte sp. and the echinoid Strongylocentrotus sp. Amino acid analyses of the foraminifera Cibicides lobatulus and the mollusc Mya truncata indicate ages between 22,000 and 16,000 BP. Radiocarbon dating of fragments of Mya truncata from the upper part of the core gave an age of 17,940 ± 245 BP, while a dating of unidentified shell fragments from the lower part gave an infinite age (>40,000 BP). The sediment was probably disturbed by icebergs beyond the end moraine zone, and the radiocarbon and amino acid dating of Mya truncata therefore represent a maximum age for this process. This new evidence indicates two phases with a higher relative sea-level than at present at Bleik, c . 18,000 and >40,000 BP. The Bleik moraine probably represents the early Late Weichselian glacial maximum ( c . 22,000 BP), while the underlying deglaciation deposit and associated beach-ridge (Bruvollen) is of pre-Late Weichselian age. Moraine ridges 3–4 km to the south of Bleik probably indicate advances of local glaciers between 22,000 and 18,000 BP.  相似文献   

Isolation of resonance in acoustic backscatter from elastic targetsusing adaptive estimation schemes     

Azimi-Sadjadi  M.R. Wilbur  J. Dobeck  G.J. 《Oceanic Engineering, IEEE Journal of》1995,20(4):346-353

It has been shown that at certain frequencies the acoustic backscatter from elastic targets exhibits certain resonance behavior which closely relates to the physical properties of the target such as dimension, thickness, and composition. The purpose of this paper is to develop an automated approach for identifying the presence of resonance in the acoustic backscatter from an unknown underwater target by isolating the resonance part from the specular contribution. An adaptive transversal filter structure is used to estimate the specular part of the backscatter and consequently the error signal would provide an estimate of the resonance part. An important aspect of this scheme lies in the fact that it does not require an underlying model for the elastic return. The adaptation rule is based upon fast recursive least squares (RLS) learning. The approach taken in this paper is general in the sense that it can be applied to targets of unknown geometry and thickness and, further, does not require any a priori information about the target and/or the environment. Test results on acoustic data are presented which indicate the effectiveness of the proposed approach  相似文献   

Are extrusive rhyolites produced from permeable foam eruptions?     

J. C. Eichelberger 《Bulletin of Volcanology》1989,51(1):72-75

This work was sponsored at Sandia National Laboratories (contract DE-AC04-76DP00789) by the US Department of Energy, Office of Basic Energy Sciences, as part of the Continental Scientific Drilling Program  相似文献   

Radial velocity searches for other planetary systems:Current status and future prospects     

W. D. Cochran  A. P. Hatzes 《Astrophysics and Space Science》1996,241(1):43-60

Measurement of variations in the radial velocities of stars due to the reflex orbital motion of the star around the planetary-system barycenter constitutes a powerful method of searching for substellar or planetary mass companions. After several years of patient data acquisition, radial-velocity searches for planetary systems around other stars are now beginning to bear fruit. In late 1995 and early 1996, three candidate systems were announced with Jovian-mass planets around solar-type stars. The current paradigm for low-mass star formation suggests that planetary systems should be able to form in the circumstellar disks surrounding young stellar objects. These newly discovered systems, and other discoveries which will soon follow them, will test critically our understanding of the processes of star- and planet-formation. We review the techniques used in these radial-velocity searches and their results to date. We then discuss planned improvements in the surveys, and the prospects for the next 20 years.  相似文献   

An expansion of the Voigt function     

H. A. Harutyunian 《Astrophysics》1996,39(4):370-374

The Voigt function and its derivatives are represented by means of series in Hermite polynomials. The equations obtained can be used both for numerical calculations of these functions and for analytical research.Translated from Astrofizika, Vol. 39, No. 4, pp. 619–625, October–December, 1996.  相似文献   

On the relationship between the Apollo 16 ancient regolith breccias and feldspathic fragmental breccias,and the composition of the prebasin crust in the Central Highlands of the Moon     

Randy L. Korotev 《Meteoritics & planetary science》1996,31(3):403-412

Abstract Two types of texturally and compositionally similar breccias that consist largely of fragmental debris from meteorite impacts occur at the Apollo 16 lunar site: Feldspathic fragmental breccias (FFBs) and ancient regolith breccias (ARBs). Both types of breccia are composed of a suite of mostly feldspathic components derived from the early crust of the Moon and mafic impact-melt breccias produced during the time of basin formation. The ARBs also contain components, such as agglutinates and glass spherules, indicating that the material of which they are composed occurred at the surface of the Moon as fine-grained regolith prior to lithification of the breccias. These components are absent from the FFBs, suggesting that the FFBs might be the protolith of the ARBs. However, several compositional differences exist between the two types of breccia, making any simple genetic relationship implausible. First, clasts of mafic impact-melt breccia occurring in the FFBs are of a different composition than those in the ARBs. Also the feldspathic “prebasin” components of the FFBs have a lower average Mg/Fe ratio than the corresponding components of the ARBs; the average composition of the plagioclase in the FFBs is more sodic than that of the ARBs; and there are differences in relative abundances of rare earth elements. The two breccia types also have different provenances: the FFBs occur primarily in ejecta from North Ray crater and presumably derive from the Descartes Formation, while the ARBs are restricted to the Cayley plains. Together these observations suggest that although some type of fragmental breccia may have been a precursor to the ARBs, the FFBs of North Ray crater are not a significant component of the ARBs and, by inference, the Cayley plains. The average compositions of the prebasin components of the two types of fragmental breccia are generally similar to the composition of the feldspathic lunar meteorites. With 30–31% Al₂O₃, however, they are slightly richer in plagioclase than the most feldspathic lunar meteorites (～29% Al₂O₃), implying that the crust of the early central nearside of the Moon contained a higher abundance of highly feldspathic anorthosite than typical lunar highlands, as inferred from the lunar meteorites. The ancient regolith breccias, as well as the current surface regolith of the Cayley plains, are more mafic than (1) prebasin regoliths in the Central Highlands and (2) regions of highlands presently distant from nearside basins because they contain a high abundance (～30%) of mafic impact-melt breccias produced during the time of basin formation that is absent from other regoliths.  相似文献   

Boundary Conditions and Efficient Solution Algorithms For the Potential Function Formulation of the 3-D Viscous Flow Equations     

G. A. Houseman 《Geophysical Journal International》1990,100(1):33-38

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Palaeointensity In the Pelagic Realm: Marine Sediment Data Compared With Archaeomagnetic and Lake Sediment Records     

C. G. Constable  L. Tauxe† 《Geophysical Journal International》1987,90(1):43-59

Summary. Four box cores collected from the Ontong—Java plateau during the Eurydice expedition have been used to make relative geomagnetic palaeo-intensity measurements. Rock magnetic measurements on the sediments show that they are characterized by a uniform magnetic mineralogy, and that they are suitable for relative intensity estimates. These are obtained by normalizing the NRM by an ARM imparted in a low DC bias field. the palaeoceanographic event known as the preservation spike is used to establish a crude time-scale for the record so that it may be compared with other data from the same region, and also with global palaeointensity estimates. the marine sediment data are quite similar to Australian intensity data from lake sediments and archaeomagnetic sources, but as might be expected exhibit some obvious differences from the global record.  相似文献   

Collisionless analogs of Riemann S ellipsoids with halo     

M. G. Abramyan 《Astrophysics》1986,25(2):563-569

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Cluster lensing of quasars as a probe of ΛCDM and dark energy cosmologies     

Ana M. Lopes  Lance Miller 《Monthly notices of the Royal Astronomical Society》2004,348(2):519-528

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