Ulysses observations of cosmic gamma-ray bursts     

K. Hurley  M. Sommer  T. Cline  M. Boer  M. Niel 《Astrophysics and Space Science》1995,231(1-2):227-230

We review the current status of the Ulysses mission and summarize the results to date of the GRB experiment. This instrument detects bursts at the rate of about one every 3.5 days, and the localization data are being disseminated rapidly via the BACO-DINE and NMSU networks. The mission should operate through 2001, and future missions to Mars starting in 1996 will complete the 3rd Interplanetary Network.  相似文献   

Plant–arthropod interaction in the Early Cretaceous (Berriasian) of the Araripe Basin,Brazil     

Etiene Fabbrin Pires  Margot Guerra Sommer 《Journal of South American Earth Sciences》2009,27(1):50-59

Plant–arthropod interactions provide the first relevant data for addressing evidence of phytophagy for an assemblage of coniferous silicified woods from the pre-rift phase in the Araripe Basin, Brazil. A complex system of borings, sometimes filled with small, oval to hexagonal coprolites, allow inferences to be made about the activities of termites (Isoptera). Previous dendrological data indicated that the climate during the Early Cretaceous on the landmasses of the northern Afro-Brazilian Depression was dry and savanna like, where termite borings were common. Features of wood preservation demonstrate that the damage was probably caused by herbivores, not detritivores.  相似文献   

Feeding behaviour of adult Centropages hamatus (Copepoda, Calanoida): Functional response and selective feeding experiments     

Andrea Saage  Olav Vadstein  Ulrich Sommer 《Journal of Sea Research》2009,62(1):16-21

The feeding behaviour of adults of the marine calanoid copepod Centropages hamatus was studied in laboratory experiments with ciliates and phytoplankton as food sources. The ingestion rate of algal (flagellates, diatoms) and ciliate prey (oligotrichs) as a function of prey concentration could be described by a Holling type III functional response, with close to zero ingestion rates at concentrations below 5 µg C l^− 1. In general, ingestion of ciliates was higher than ingestion of algae, and maximum feeding rates by adult males reached were half the feeding rates of adult females at prey concentrations exceeding 50 µg C l^− 1. When diatoms and ciliates were offered together C. hamatus (both sexes) fed exclusively on ciliates as long as they contributed with more than 5% to the mixture. This indicates the capability of active prey selection and switching between suspension feeding and ambush predation. Therefore, the feeding behaviour of adult C. hamatus can be characterised as omnivorous with a preference for larger motile prey. This implies a trophic level above two, if there is a sufficient abundance of protozoan food available.  相似文献   

“Wet” low angle subduction: a possible mechanism below the Tanzania craton 2 Ga ago     

Holger Sommer 《Mineralogy and Petrology》2009,96(1-2):113-120

The hypothesis that much of the lithosphere of the Archaean Tanzania Craton was hydrated, by the dehydration of a buoyant subduction 2 Ga ago is presented in this study. Buoyant subduction is a potential mechanism for thermal erosion and metasomatism of extensive regions of the cold overlying continental lithosphere. This hypothesis could explain why the Tanzania Craton forms an undeformed island within the intensely deformed mobile belts. Furthermore, it would explain the formation of the eclogite and lherzolite bearing kimberlites within the Tanzania Craton far away from the trench. A buoyant, slow subduction is required because this would provide sufficient cooling from the overlying cratonic lithosphere and therefore the dipping slab could retain hydrous minerals such as antigorite in hydrated aureoles in peridotites. To test this hypothesis, the release of water during prograde metamorphism of a flat-subducting plate was modeled. It is shown that water can be transported ～800 km laterally, inboard of the trench, which is close to the north-south extension of the Archaean Tanzania Craton.  相似文献   

The Hilbert Transform on the Two-Sphere: A Spectral Characterization     

Oliver Fleischmann  Lennart Wietzke  Gerald Sommer 《Mathematical Geosciences》2010,42(7):857-876

The local analysis of signals arising on the sphere is a common task in earth sciences. On the real line the analytic signal turned out to be an important representation in local one-dimensional signal processing. Its generalization to two dimensions is the monogenic signal, and the properties of the analytic and the monogenic signal in the Fourier domain are well known. A generalization to the sphere is given by the Hilbert transform on the sphere known from Clifford analysis. To obtain a spectral characterization, the transform has to be decomposed into spherical harmonic functions. In this paper, we derive the spherical harmonic coefficients of the Hilbert transform on the sphere and give a series expansion. This will show that it acts as a differential operator on the spherical harmonic basis functions of the Laplace equation solution, analogously to the Riesz transform in two dimensions. This allows an interpretation of the Hilbert transform suitable for signal processing of signals naturally arising on the two-sphere. We show that the scale space naturally arising is a Poisson scale space in the unit ball. In addition, the obtained interpretation of the Hilbert transform is used for orientation analysis of plane waves. This representation is justified as a novel signal model on the sphere which can be used to construct intensity and rotation-invariant operators for local signal analysis in a scale-space concept.  相似文献   

The Southern Baltic Sea and its coast in transition     

Ulrich Sommer  Peter Frenzel 《Aquatic Sciences - Research Across Boundaries》2005,67(2):129-131

No Abstract.  .  相似文献   

Шестидесятилетие проф. Д-ра микулаша кончека     

Alois Gregor 《Studia Geophysica et Geodaetica》1960,4(4):416-417

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Inversion of the geomagnetic field determined by palaeomagnetic investigations of quaternary sediments     

Alois Kočí 《Studia Geophysica et Geodaetica》1969,13(3):326-331

Résumé Au cours des recherches paléomagnétiques en Tchécoslovaquie, on a constaté und double polarité de la magnétisation rémanente des sédiments quaternaires. Des recherches plus détaillées de la localité Červeny kopec près de Brno, qui représente une région de sédiments avec une suite initerrompue de couches déposées au cours d'un million d'années dernières, datées par la méthode de correlation astronomique, fournissent certains résultats importants sur l'époque au cours de laquelle s'est passé l'inversion du champ géomagnétique. Selon nos recherches de jusqu'à présent, on peut déterminer la fin de l'époque inverse de Matuyama par 0,930 million d'années environ. Après elle succède la pèriode de transition, dont la durée est de 60 000 ans environ, au cours de laquelle se sont passé des changements rapides dans le champ géomagnétique et au cours de laquelle existent des roches possédant une magnétisation avec inclinaison soit positive, soit négative. L'époque de polarité normale de Brunhes commence selon nos constatations autour de 0,870 million d'années.

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Address: Bočni II, Praha 4-Spořilov  相似文献   

Carbon isotopic compositions of Recent planktonic foraminifera of the Indian Ocean     

Douglas F. Williams  Michael A. Sommer  Michael L. Bender 《Earth and Planetary Science Letters》1977,36(3):391-403

Carbon and oxygen isotopic determinations have been made of 29 species of Recent Indian Ocean planktonic foraminifera. Fourteen core-top samples were used and as many as 18 species were chosen from a single core-top sample. The δ¹³C of the foraminifera was compared with that of total dissolved CO₂ (ΣCO₂) and of calcite precipitated in isotopic equilibrium with ΣCO₂. The foraminiferal calcite is always at least 1.2‰ less than the value estimated for equilibrium calcite. This carbon isotopic disequilibrium suggests the partial utilization of¹³C-depleted metabolic CO₂. The calcite tests of several species, however, have δ¹³C values which are similar to the δ¹³C of ΣCO₂ in seawater. This relationship suggests that important paleohydrographic information may be obtained from carbon isotope records based on analyses of several foraminiferal species from single deep-sea sediment samples.  相似文献   

Sixty years since the foundation of the (state) institute of geophysics at the charles university in Prague     

Alois Zátopek 《Studia Geophysica et Geodaetica》1981,25(3):296-312

Conclusion It was the intention of the author to present, on the occassion of the sixtieth anniversary of the foundation of the Institute of Geophysics on Dec. 20th, 1920, a sequence of events and episodes connected with the history of geophysics in Czechoslovakia, in which the most significant role was played by the State Institute of Geophysics and its founder Professor Václav LÁSKA. In many cases LÁSKA's ideas have preserved their vitality up to the present and, perhaps, they will prove to be a new inspiration even to younger generations of Czechoslovak geophysicists.  相似文献