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排序方式: 共有72条查询结果,搜索用时 15 毫秒
1.
Faith Vilas David J. Tholen Larry A. Lebofsky Humberto Campins Glenn J. Veeder Richard P. Binzel Alan T. Tokunaga 《Icarus》1985,63(2):201-205
Visual and infrared observations were made of Amor asteroid 1982 DV during its discovery apparition. Broadband visual and near-infrared photometry shows that it is an S-class asteroid. Narrowband spectrophotometry shows an absorption feature due to olivine or pyroxene or both centered at 0.93 μm. Applying a nonrotating thermal model to 10-μm photometry, the geometric albedo is calculated to be approximately 0.27. The geometric albedo for a slowly rotating, rocky surface was calculated for 1 night to be 0.15, consistent with S-class asteroid albedos. Thus, 1982 DV is either one of the most reflective S-class asteroids known, or a significant amount of bare rock is exposed on the asteroid's surface. For the nonrotating model, ellipsoidal dimensions for 1982 DV are 3.5 × 1.4 × 1.4 km. 相似文献
2.
Carmen E. Morales Humberto E. González Gabriel Yuras Leonardo R. Castro 《Progress in Oceanography》2007,75(3):452-469
The oceanographic setting and the planktonic distribution in the coastal transition zone off Concepción (∼35-38°S, ∼73-77°W), an area characterized by its high biological production, were assessed during two different seasons: austral spring with equatorward upwelling favorable winds and austral winter with predominately northerly winds. Oceanographic and biological data (total chlorophyll-a, particulate organic carbon, microplankton, large mesozooplankton >500 μm as potential consumers of microplankton) were obtained during two cruises (October 1998, July 1999) together with satellite imagery for wind stress, geostrophic flow, surface temperature, and chlorophyll-a data. The physical environment during the spring sampling was typical of the upwelling period in this region, with a well-defined density front in the shelf-break area and high concentrations of surface chlorophyll-a (>5 mg m−3) on the shelf over the Itata terrace. During the winter sampling, highly variable though weakly upwelling-favorable winds were observed along with lower surface chlorophyll-a values (<2 mg m−3) on the shelf. In the oceanic area (>100 km from the coast), cyclonic and anti-cyclonic eddies were evident in the flow field during both periods, the former coinciding with higher chlorophyll-a contents (∼1 mg m−3) than in the surrounding waters. Also, a cold, chlorophyll-a rich filament was well defined during the spring sampling, extending from the shelf out to 350-400 km offshore. Along a cross-shelf transect, the micro- and meso-planktonic assemblages displayed higher coastal abundances during the spring cruise but secondary peaks appeared in the oceanic area during the winter cruise, coinciding with the distribution of the eddies. These results suggest that the mesoscale features in this region, in combination with upwelling, play a role in potentially increasing the biological productivity of the coastal transition zone off Concepción. 相似文献
3.
Seasonal and inter-annual variation of mesozooplankton in the coastal upwelling zone off central-southern Chile 总被引:1,自引:0,他引:1
Ruben Escribano Pamela Hidalgo Humberto González Ricardo Giesecke Ramiro Riquelme-Bugueño Karen Manríquez 《Progress in Oceanography》2007,75(3):470-485
Zooplankton sampling at Station 18 off Concepción (36°30′S and 73°07′W), on an average frequency of 30 days (August 2002 to December 2005), allowed the assessment of seasonal and inter-annual variation in zooplankton biomass, its C and N content, and the community structure in relation to upwelling variability. Copepods contributed 79% of the total zooplankton community and were mostly represented by Paracalanus parvus, Oithona similis, Oithona nana, Calanus chilensis, and Rhincalanus nasutus. Other copepod species, euphausiids (mainly Euphausia mucronata), gelatinous zooplankton, and crustacean larvae comprised the rest of the community. Changes in the depth of the upper boundary of the oxygen minimum zone indicated the strongly seasonal upwelling pattern. The bulk of zooplankton biomass and total copepod abundance were both strongly and positively associated with a shallow (<20 m) oxygen minimum zone; these values increased in spring/summer, when upwelling prevailed. Gelatinous zooplankton showed positive abundance anomalies in the spring and winter, whereas euphausiids had no seasonal pattern and a positive anomaly in the fall. The C content and the C/N ratio of zooplankton biomass significantly increased during the spring when chlorophyll-a was high (>5 mg m−3). No major changes in zooplankton biomass and species were found from one year to the next. We concluded that upwelling is the key process modulating variability in zooplankton biomass and its community structure in this zone. The spring/summer increase in zooplankton may be largely the result of the aggregation of dominant copepods within the upwelling region; these may reproduce throughout the year, increasing their C content and C/N ratios given high diatom concentrations. 相似文献
4.
Seasonal variations in diversity and biomass of diatoms, tintinnids, and dinoflagellates and the contribution of microplankton and faecal material to the vertical flux of particulates were investigated at one time series station T (station 18) between 2002 and 2005 and at a grid of stations during November 2004 in the coastal and oceanic area off Concepción (36°S), Chile. The variations were analysed in relation to water column temperature, dissolved oxygen, nutrient concentration, offshore Ekman transport, and chlorophyll-a concentration. Abundance was estimated as cell numbers per litre and biomass in terms of biovolume and carbon units.A sharp decrease with depth was observed in the abundance of both phytoplankton and microzooplankton during the whole annual cycle; over 70% of their abundance was concentrated in the upper 10 m of the water column. Also, a clear seasonality in microplankton distribution was observed at station T, with maxima for diatoms, tintinnids, and dinoflagellates every summer (centred on January) from 2002 to 2005.On the grid of stations, the maximum integrated (0-50 m) micro-phytoplankton abundances (>1 × 109 cells m−2) occurred at the coastal stations, an area directly influenced by upwelling. A similar spatial distribution was observed for the integrated (0-200 m) faecal carbon (with values up to 632 mg C m−2). Tintinnids were distributed in all the first 300 miles from the coast and dinoflagellates were more abundant in oceanic waters.At station T, the average POC export production (below 50 m depth) was 16.6% (SD = 17%; range 2-67%; n = 16). The biological-mediated fluxes of carbon between the upper productive layer and the sediments of the continental shelf off Concepción depend upon key groups of phytoplankton (Thalassiosira spp., Chaetoceros spp.) and zooplankton (euphausiids) through the export of either cells or faecal material, respectively. 相似文献
5.
Till Czypionka Cristian A. Vargas Nelson Silva Giovanni Daneri Humberto E. González José Luis Iriarte 《Continental Shelf Research》2011,31(3-4):216-224
Mixotrophy, the combination of autotrophic and heterotrophic nutrition in the same organism, is widespread in planktonic algae. Several reports from temperate and high-latitude fjords in Scandinavia suggest the occurrence of a niche in late summer and autumn during post-bloom conditions in which mixotrophic algae can become important grazers in pelagic ecosystems, accessing the nutrients bound in their prey to overcome nutrient limitation. Here, we experimentally determined the trophic modes and bacterivory rates for the nanoplankton community (2–20 μm) in Aysén Fjord located in the Chilean Northern Patagonia during two contrasting seasons: winter and spring. While mixotrophic nanoplankton was virtually absent from the system in spring, in winter at occasions it even constituted the dominant trophic group of the nanoplankton with abundances of >900 cells mL?1. This indicates a second niche for mixotrophs in winter, when mixotrophy allows overcoming light limitation. 相似文献
6.
7.
Wolf-Rainer Abraham Alexandre José Macedo Luiz Humberto Gomes Flavio C. A. Tavares 《洁净——土壤、空气、水》2007,35(4):339-347
The load of pathogenic bacteria, their fate and their dangerousness in the Tietê River were assessed along 100 km starting from the city of São Paulo, Brazil. The data were compared with those from two German rivers. High loads of pathogens were found in the Tietê River near the city of São Paulo (Escherichia coli O157:H7, Shigella flexneri, and Shigella boydii), which were absent 30 km downstream of São Paulo. The antibiotic resistances observed in the Tietê river were rather low and decreased after the major input in São Paulo to significantly lower levels about 30 km downstream. While the Brazilian isolates were more susceptible for ampicillin than the German ones, the reverse was observed for gentamycin. For optimal control of infections in humans critical areas where these bacteria survived longer and their elimination mechanisms should be identified as well as the extent and the origin of antibiotic resistance should be determined. 相似文献
8.
We present an analysis of OH, CN, and C2 jets observed in thecoma of Comet Hale–Bopp on UT April 22, 23, and 25, 1997. Monte Carlomodels designed to simulate the
gas jets were employed to analyze thenuclear active areas responsible for the observed coma gas jets. Ourresults indicate
that four active areas are necessary to reproduce theCN and C2 jets while five active areas are required to simulatethe OH jets. The additional OH active area must produce significantlevels
of OH, but cannot emit measurable quantities of either carbonradical. This difference suggests that the nucleus of Comet Hale–Boppis
chemically heterogeneous. 相似文献
9.
Chaulagain Hemchandra Rodrigues Hugo Silva Vitor Spacone Enrico Varum Humberto 《Natural Hazards》2015,78(1):583-602
Natural Hazards - Seismic risk in the form of impending disaster has been seen from past records that moderate-to-large earthquakes have caused the loss of life and property in all parts of Nepal.... 相似文献
10.
Julie Ziffer Humberto Campins Javier Licandro Noemi Pinilla-Alonso Yanga Fernandez Schelte J. Bus 《Earth, Moon, and Planets》2005,97(3-4):203-212
We present near infrared reflectance spectra from 0.8 to 2.5 μm of two asteroids with low Tisserand invariant, 1373 Cincinnati and 2906 Caltech. We compare our spectra with cometary nuclei and other asteroids in their class. Asteroids Cincinnati and Caltech have Tisserand invariant values of 2.72 and 2.97, respectively, values less than 3 are considered suggestive of cometary origin. The observed spectral slopes in the near-infrared are consistent with both the spectra of cometary nuclei and of primitive asteroids. However, both asteroids have features in the near-infrared that are not seen in cometary nuclei, but are present in other X-type asteroids. 1373 Cincinnati has a sharp slope change between 0.75 and 1.0 μm and 2906 Caltech has a broad and shallow absorption between 1.35 and 2.2 μm. Our attempts to model the visible and near-infrared spectrum of these two objects, with the components successfully used by Emery and Brown (2004, Icarus
164, 104–121) to fit Trojan asteroids, did not yield acceptable fits.Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract to the National Aeronautics and Space Administration. 相似文献