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1.
The results of photometric observations of comet/asteroid 2060 Chiron at the Observatório do Pico dos Dias (Brazil-OPD) and the Observatoire de Haute-Provence (France-OHP) during 1994 and 1995 are presented. The analysis of the data shows a decrease of 2060 Chiron brightness from its peak values of 1988–1991. The absolute magnitude, Hv, varies from a maximum of 6.6 in February 1994 up to a minimum of 6.8 in June 1995. Therefore 2060 Chiron is back to a minimum of activity close to that of 1983–1985. The slope parameter G is found to be G = 0.71 ± 0.15. It is suggested that the H-G magnitude system, generally adopted to present 2060 Chiron brightness, is not the most appropriate due to the cometary activity of this object.  相似文献   
2.
We report here on unique post-perihelion (2.3 AU) measurements of Comet Hale-Bopp in the FUV-range (950–1250 Å) by means of the UVSTAR spectrometer from the space shuttle with the main purpose of searching for argon and other FUV emitters. New methods for separating the strong airglow emission at shuttle altitudes are here discussed in detail. Due to our low resolution (15 Å) and S/N ratio the possible rocket-borne detection of argon near perihelion (0.9 AU) could not be confirmed. New species as N2 are suspected but difficult to separate from the strong airglow emission at shuttle altitudes. From the Lyα brightness (1.30± 0.08 kRy) a water production rate Q = 5.9 ± 0.4 × 1029 molecules s?1 could be derived and compared with other post-perihelion observations.  相似文献   
3.
Summary ?Mong Hsu rubies of the “trapiche” type are sporadically seen in the gem market. However, they have never been described in the field. The study of the nature of solid inclusions, the variation of trace-element contents, as well as the cathodoluminescence behaviour of six “trapiche” rubies permit the conclusion that these rubies crystallised in the same geological environment (marble-type deposit) as the normal rubies from Mong Hsu: (1) Cr and V are the main chromophorous elements in both ruby types; they act, together with Ti, as activators or quenchers for cathodoluminescence; (2) calcite, dolomite, rutile, mica, diaspore, apatite, chlorite, and feldspar are solid inclusions found in both ruby types; (3) the presence of bastn?site in trapiche ruby and fluorite in non-trapiche ruby indicates the circulation of F-bearing fluids during ruby deposition; (4) the distribution of trace-element contents in the crystal is similar for both ruby types. In the Cr2O3 vs. Fe2O3 and Cr2O3 vs. Fe2O3/TiO2 diagrams, the population fields of Mong Hsu “trapiche” and non-“trapiche” rubies overlap. They are distinct from those of rubies and sapphires hosted in basalts from South-east Asia. Received October 30, 2001; revised version accepted March 25, 2002  相似文献   
4.
A new updated version of the MSK macroseismic intensity scale has been prepared by a Working Group of the European Seismological Commission and has been published in April 1993 (European Macroseismic Scale 1992: updated MSK scale, 1993, ed. by G. Grünthal, Cahiers du Centre Européen de Geodynamique et de Séismologie, no. 7).  相似文献   
5.
The inception and growth of the active Carpino-Le Piane Basin Fault System (CLPBFS; central-southern Apennines, Italy) was analysed with respect to the neighbouring Isernia and Surrounding (ISFS) and Boiano Basin (BBFS) extensional Fault Systems. 39Ar–40Ar dating showed that the BBFS was already active 649 ± 21 ka bp and that the ISFS was active at least 476 ±10 ka bp , whereas the activity of the CLPBFS started certainly later than 253 ± 22 ka bp , and very probably as recently as <28 ka bp . These ages, combined with structural data (geometry and kinematics of the fault systems), indicate that the inception and development of the CLPBFS could be strictly related to the stress changes caused by earthquakes occurring on the BBFS.  相似文献   
6.
A study of sea surface wave propagation and its energy deformation was carried out using field observations and numerical experiments over a region spanning the midshelf of the South Atlantic Bight (SAB) to the Altamaha River Estuary, GA. Wave heights on the shelf region correlate with the wind observations and directional observations show that most of the wave energy is incident from the easterly direction. Comparing midshelf and inner shelf wave heights during a time when there was no wind and hence no wave development led to an estimation of wave energy dissipation due to bottom friction with corresponding wave dissipation factor of 0.07 for the gently sloping continental shelf of the SAB. After interacting with the shoaling region of the Altamaha River, the wave energy within the estuary becomes periodic in time showing wave energy during flood to high water phase of the tide and very little wave energy during ebb to low water. This periodic modulation inside the estuary is a direct result of enhanced depth and current-induced wave breaking that occurs at the ebb shoaling region surrounding the Altamaha River mouth at longitude 81.23°W. Modelling results with STWAVE showed that depth-induced wave breaking is more important during the low water phase of the tide than current-induced wave breaking during the ebb phase of the tide. During the flood to high water phase of the tide, wave energy propagates into the estuary. Measurements of the significant wave height within the estuary showed a maximum wave height difference of 0.4 m between the slack high water (SHW) and slack low water (SLW). In this shallow environment these wave–current interactions lead to an apparent bottom roughness that is increased from typical hydraulic roughness values, leading to an enhanced bottom friction coefficient.  相似文献   
7.
Dynamics and Variability of Terra Nova Bay Polynya   总被引:1,自引:0,他引:1  
Abstract. We present a process study on the dynamics and variability of the Terra Nova Bay polynya in the western sector of the Ross Sea. The air-sea heat exchange is known to be particularly large in polynya during the winter, when differences between air and sea temperatures are large. We apply a 1-D model (Pease, 1987; Van Woert, 1999a, 1999b), which is modified in the latent heat parameterisation in order to account for time-dependent relative humidity and cloud coverage. Furthermore, the Ice Collection Depth is correlated linearly with a variable wind speed. The model is forced with two different meteorological data sets: the operational analysis of the European Center for Medium Range Weather Forecasts atmospheric data set and the meteorological parameters measured by an Automatic Weather Station located on the coast of Terra Nova Bay. The results are compared in terms of polynya extension, ice, and High Salinity Shelf Water production. According to the two different wind velocities, the results obtained from the different data sets clearly differ. Qualitatively, however, the results are in good agreement.  相似文献   
8.
The structure and functioning of nanoplanktonic assemblages in coastal upwelling areas have usually been overlooked in explorations of the productivity of these areas. As part of a multidisciplinary, time-series station in the coastal area off Concepción, seasonal variations (upwelling and non-upwelling) in the abundance and biomass of these assemblages were investigated. Hydrographic measurements and biological samples were taken monthly over a 2-year period (18 August 2004-28 July 2006). Nanoflagellates dominated the total integrated abundance (3-317 × 109 cells m−2; 0-80 m). Diatoms and dinoflagellates usually contributed to a lesser degree (<20%) but sporadically made important contributions to the total integrated nanoplankton biomass (0.02-10.6 g C m−2). Most of the nanoplankton was concentrated in surface waters (<30 m) during all the samplings and no seasonal differences in abundance or biomass were found in this layer, although the mean values and dispersions around them were highest during the upwelling period along with maximum integrated (0-80 m) chlorophyll-a values, as total or in the <20 μm fraction. Changes in nanoplankton abundance were significantly but weakly (r < 0.4) correlated with changes in the hydrographic variables; the highest correlation values were positive for temperature and oxygen, factors that varied with depth and date. The potential grazing rates of heterotrophic nano-predators (flagellates and dinoflagellates) on prokaryotic prey, estimated with a generic model, ranged from 3 to 242 bacterioplankton predator−1 h−1 and from 0.1 to 14 cyanobacteria predator−1 h−1. Our results imply a small impact of seasonal hydrographic variability on the abundance and biomass of nanoplanktonic assemblages and suggest that grazing by nanoheterotrophs might control the prokaryotic picoplankton populations in the upwelling area off Concepción.  相似文献   
9.
This paper deals with the chronology and the possible correlations among levels of different excavated areas in the Pleistocene vertebrate-bearing deposits at the large San Teodoro Cave (North-Eastern Sicily). Two trenches have been excavated along the eastern side of the cave, located at a distance from the entrance, respectively, of 8 m (α trench) and 28 m (β trench) and at different depths. Lithological features, biometrical data from small mammals and ecological data from molluscs point to similar environmental conditions for the α trench deposits and those located along the eastern wall of the cave in the eastern part of the β trench. The same evidence, and the taphonomic features of large mammals, points to different environmental conditions and perhaps to different ages for the deposits located in the western part of the β trench. The survival of elephants in Sicily up to 32,000 years ago is a new significant result of the 230Th/234U dating carried out from a concretionary stratum from the β trench and represents the youngest elephant survival in the western Mediterranean islands.  相似文献   
10.
The electrical resistivity structure of the crust and upper mantle of the Atlas Mountain System was studied using magnetotelluric and geomagnetic deep soundings. Field experiments were done in eastern Morocco along a traverse from the Anti Atlas to the Rides Rifaines in two campaigns in 1983 and 1988.Zones of very low electrical resistivity could be identified in the various structural settings at different depth ranges, most likely connected directly to the tectonic evolution of the mountain belts. A mid-crustal low resistivity layer with total conductance (thickness-resistivity ratio) of about 2000 Siemens stretches from the southern border of the High Atlas towards the Middle Atlas. This layer seems to characterize the base of crustal detachment, e.g., the plane for large horizontal overthrusting, and supports the idea of thick- and thin-skinned tectonics involved in Atlasic mountain building. In the western Middle Atlas an upper-crustal low resistivity layer (at depth < 10 km) was found in the area where volcanic activity was present, pointing towards a direct relation between low electrical resistivity and volcanic or postvolcanic events. North of the Middle Atlas resistivity structures change totally: The Pre and parts of the Sub-Rif have a highly conductive cover, presumably connected to the molasse basin. Total conductance was calculated to reach 6000 Siemens. No further conductive structures, like, e.g., the ones found beneath the High and Middle Atlas, are seen within the resistive crust, but at much greater depth within the upper mantle.
Zusammenfassung Im marokkanischen Atlas-System wurde der elektrische Widerstand der Kruste und des oberen Mantels mit magnetotellurischen und erdmagnetischen Tiefen-Sondierungen erkundet. Die Feldmessungen wurden in den Jahren 1983 und 1988 im östlichen Marokko entlang einer Traverse vom Anti Atlas bis in das Rif durchgeführt.In den einzelnen strukturellen Einheiten wurden in unterschiedlichen Krustentiefen Schichten sehr kleiner elektrischer Widerstände entdeckt, die direkt mit der tektonischen Entwicklung des Atlasgebirges verknüpft zu sein scheinen. Zwischen dem Südrand des Hohen Atlas und dem Mittleren Atlas im Norden erstreckt sich eine Zone sehr kleiner Widerstände (integrierte Leitfähigkeit etwa 2000 Siemens) in mittleren Krustentiefen. Diese Schicht scheint einen Bereich krustaler Ablösung zu kennzeichnen und kann als Basis einer weitspannigen Überschiebung angenommen werden. Diese Form der »thick- & thin-skinned« Tektonik scheint wesentlich am Prozess der Gebirgsbildung im Atlas beteiligt zu sein. Im westlichen Mittleren Atlas, im Bereich des jungen Vulkanismus, wurde eine gutleitende Zone in der oberen Kruste (Tiefe < 10 km) gefunden. Diese Beobachtung legt einen direkten Zusammenhang zwischen erhöhter elektrischer Leitfähigkeit und vulkanischen bzw. postvulkanischen Ereignissen nahe. Nördlich des Mittleren Atlas ändern sich die Widerstandsstrukturen sehr stark: Im Prä- und teilweise auch noch im Sub-Rif liegt eine sehr gut leitende Deckschicht (integrierte Leitfähigkeit etwa 6000 Siemens) über einem hochohmigen Basement. In der Kruste des Rif werden keine weiteren, tieferliegenden Schichten erhöhter Leitfähigkeit gefunden, wie sie z.B. unter dem Hohen Atlas vorliegen. Dagegen gibt es Hinweise auf Zonen hoher Leitfähigkeit im oberen Mantel.

Résumé Dans l'Atlas marocain la résistivité électrique de la croûte et du manteau supérieur a été étudiée à l'aide des sondages magnétotelluriques et géomagnétiques. Ces travaux ont été effectués le long d'une traverse menant de l'Anti-Atlas jusqu'au Rif durant les années 1983 et 1988.Dans différentes profondeurs de la croûte terrestre des zones de résistances électriques très basses ont pu être découvertes ce qui peut être attribué à l'évolution tectonique de l'Atlas. Une couche de résistances très basses (conductance vers 2000 Siemens) s'étend entre le bord au sud du Haut Atlas et l'Atlas Moyen au nord. Cette couche peut être le signe d'un détachement de l'écorce et d'une poussée très vaste. Cette forme tectonique »thick- & thin-skinned« semble être essentiellement responsable du processus de la formation orogénique de l'Atlas. Une zone de bonne conductance se trouve dans la croûte terrestre supérieure (profondeur < 10 km) dans l'ouest de l'Atlas Moyen aux environs de l'activité volcanique caractérisant une relation directe entre une haute conductance électrique et des événements volcaniques et post-volcaniques. Vers le nord de l'Atlas Moyen les structures de résistance subissent un changement total: Au Pré- et partiellement aussi au Subrif se trouve une bonne couche guide (conductance vers 6000 Siemens). Aucune autre couche de conductance supérieure — comme au-dessous du Haut Atlas — n'a été découverte dans la croûte du Rif. On en décèle, par contre, dans le manteau supérieur.

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