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121.
Ana I. Gómez?de?Castro Jesús Maíz Pablo Rodriguez Maite Gómez Juan A. Larruquert José A. Méndez Tomas Belenguer Victor Rodrigo-Gudiel Fátima López-Martínez Paola Sestito 《Astrophysics and Space Science》2011,335(1):283-289
ISSIS is the Imaging and Slitless Spectroscopy Instrument for the World Space Observatory-Ultraviolet (WSO-UV) mission. ISSIS
is a multipurpose instrument designed to carry out high resolution (<0.1 arcsec) imaging in the far UV with fields of view
≥2×2 arcmin2. ISSIS has two acquisition channels: the High Sensitivity Channel (HSC) and the Channel for Surveys (CfS). The HSC is equipped
with an MCP-type detector to guarantee high sensitivity in the 1150–1750 ? range and high rejection of lower energy radiation.
The CfS is equipped with a large CCD detector (4k×4k) to obtain images from the far UV to the red (1150–8500 ?); the CfS is
implemented to allow observing UV bright sources such as reflection nebulae or nearby massive star forming regions. The design
drivers and the current status of the instrument are described in this contribution. 相似文献
122.
Maria Castro César De Santos-Berbel 《International journal of geographical information science》2013,27(12):2061-2074
Because of the high number of crashes occurring on highways, it is necessary to intensify the search for new tools that help in understanding their causes. This research explores the use of a geographic information system (GIS) for an integrated analysis, taking into account two accident-related factors: design consistency (DC) (based on vehicle speed) and available sight distance (ASD) (based on visibility). Both factors require specific GIS software add-ins, which are explained. Digital terrain models (DTMs), vehicle paths, road centerlines, a speed prediction model, and crash data are integrated in the GIS. The usefulness of this approach has been assessed through a study of more than 500 crashes. From a regularly spaced grid, the terrain (bare ground) has been modeled through a triangulated irregular network (TIN). The length of the roads analyzed is greater than 100 km. Results have shown that DC and ASD could be related to crashes in approximately 4% of cases. In order to illustrate the potential of GIS, two crashes are fully analyzed: a car rollover after running off road on the right side and a rear-end collision of two moving vehicles. Although this procedure uses two software add-ins that are available only for ArcGIS, the study gives a practical demonstration of the suitability of GIS for conducting integrated studies of road safety. 相似文献
123.
Jacob B. Lowenstern Heather Bleick Jorge A. Vazquez Jonathan M. Castro Peter B. Larson 《Bulletin of Volcanology》2012,74(10):2303-2319
We investigated the distribution of Cl, F, Li, and Be in pumices, obsidians, and crystallized dome rocks at Chaitén volcano in 2008?C2009 in order to explore the behavior of these elements during explosive and effusive volcanic activity. Electron and ion microprobe analyses of matrix and inclusion glasses from pumice, obsidian, and microlite-rich dome rock indicate that Cl and other elements were lost primarily during crystallization of the rhyolitic dome after it had approached the surface. Glass in pumice and microlite-free obsidian has 888?±?121?ppm Cl, whereas residual glass in evolved microlite-rich dome rock generally retains less Cl (as low as <100?ppm). Estimated Cl losses were likely >0.7?Mt Cl, with a potential maximum of 1.8?Mt for the entire 0.8-km3 dome. Elemental variations reflect an integrated bulk distribution ratio for Cl?>?1.7 (1.7 times more Cl was degassed or incorporated into crystals than remained in the melt). Because Cl is lost dominantly as the very last H2O is degassed, and Cl is minimally (if at all) partitioned into microlites, the integrated vapor/melt distribution ratio for Cl exceeds 200 (200 times more Cl in the evolved vapor than in the melt). Cl is likely lost as HCl, which is readily partitioned into magmatic vapor at low pressure. Cl loss is accelerated by the change in the composition of the residual melt due to microlite growth. Cl loss also may be affected by open-system gas fluxing. Integrated vapor-melt distribution ratios for Li, F, and Be all exceed 1,000. On degassing, an unknown fraction of these volatiles could be immediately dissolved in rainwater. 相似文献
124.
Impact of stress and disturbance factors on the phytoplankton communities in Northeastern Brazil reservoir 总被引:1,自引:1,他引:0
Naithirithi T. Chellappa Thiago Chellappa Fabiana R.A. Cmara Odete Rocha Sathyabama Chellappa 《Limnologica》2009,39(4):273-282
The ecology of phytoplankton reservoir communities plays a pivotal role in their management and in the development of inland fisheries in the water scarce semi-arid regions of Rio Grande do Norte State, Brazil. The hydrological conditions characterizing these reservoirs include infrequent rainfall and high evaporative loses. The phytoplankton assemblages in tropical climate are structured primarily on dry and wet cycles, not the annual temperature and light regime. The purpose of the current study was to investigate the ecological aspects of phytoplankton communities from three reservoirs during the period of July 2003–June 2004, which include atypical summer rainfall and reservoir overflow. The environmental data broadly divided into two categories, stress factors and disturbance factors. The stress factors deals with the impact of high particulate organic matter and low dissolved oxygen concentrations and disturbance factors, linked to water level fluctuation through flushing and reservoir drawdown, and these events are associated with the phytoplankton assemblages. Results indicated that the three distinct hydroperiods determined the structure of phytoplankton and chlorophyll levels and limited the presence and relative abundance of cyanobacterial species. Phytoplankton succession accompanied changes in clear and turbid water phase represented by the alternate dominance between diatoms and chlorophytes. Inundation and complete filling of reservoir stimulated “s” and “r” strategists species (<20 um) of unicellular and some colonial members of chlorophytes and cryptomonads in highly turbid water environment, and “c” strategist species in rest of the wet period following disturbance gradients. Statistical analysis elicited a significant relationship between particulate organic matter and relative abundance of smaller chlorophytes, which was deemed as stress factor. The flushing and reservoir drawdown indicate disturbance gradient and as a consequence high diversity. Furthermore, a substantial reduction in chlorophyll levels was registered in turbid water phase is related to the reduction of light penetration and re-suspension of sediments. Considering these results, it can be suggested that the well-managed reservoir drawdown can possibly maintain an environment free of eutrophication and cyanobacterial dominance. 相似文献
125.
Above-ground biomass and productivity in the Montado: From herbaceous to shrub dominated communities
Our study was focused on the effect of abandonment on above-ground biomass and net primary productivity (ANPP) in a Montado in Southern Portugal. The Montado has a long history of human management and control of invasion by shrubs is achieved by clearing, ploughing and grazing. When these cease, it is invaded by Mediterranean matorral species. We hypothesized that the change in life form dominance would affect both biomass and productivity, but while the total biomass was expected to increase, the effects on ANPP were less clear. We tested our hypothesis by determining above-ground biomass and ANPP along a gradient of decreasing land use intensity, ranging from extensive grazing to 20 years of abandonment.Above-ground biomass increased with abandonment, which was related with the increase in shrub cover. In addition, we found a decrease in herbaceous ANPP that was more than compensated by an increase in shrub ANPP in plots abandoned for longer time, resulting in a significant increase in total ANPP. This increase was strongly related with the increase in the cover of Cistus ladanifer, a pioneer species that colonises degraded areas and forms one of the first stages of succession of woody communities. 相似文献
126.
S. Branca P. Del Carlo M. D. Lo Castro E. De Beni J. Wijbrans 《Bulletin of Volcanology》2009,71(1):79-94
Geological surveys, tephrostratigraphic study, and 40Ar/39Ar age determinations have allowed us to chronologically constrain the geological evolution of the lower NW flank of Etna
volcano and to reconstruct the eruptive style of the Mt Barca flank eruption. This peripheral sector of the Mt Etna edifice,
corresponding to the upper Simeto valley, was invaded by the Ellittico volcano lava flows between 41 and 29 ka ago when the
Mt Barca eruption occurred. The vent of this flank eruption is located at about 15 km away from the summit craters, close
to the town of Bronte. The Mt Barca eruption was characterized by a vigorous explosive activity that produced pyroclastic
deposits dispersed eastward and minor effusive activity with the emission of a 1.1-km-long lava flow. Explosive activity was
characterized by a phreatomagmatic phase followed by a magmatic one. The geological setting of this peripheral sector of the
volcano favors the interaction between the rising magma and the shallow groundwater hosted in the volcanic pile resting on
the impermeable sedimentary basement. This process produced phreatomagmatic activity in the first phase of the eruption, forming
a pyroclastic fall deposit made of high-density, poorly vesicular scoria lapilli and lithic clasts. Conversely, during the
second phase, a typical strombolian fall deposit formed. In terms of hazard assessment, the possible occurrence of this type
of highly explosive flank eruption, at lower elevation in the densely inhabited areas, increases the volcanic risk in the
Etnean region and widens the already known hazard scenario. 相似文献
127.
Phillipe Mota Machado Marjorie Cremonez Suciu Leonardo Lopes Costa Davi Castro Tavares Ilana Rosental Zalmon 《Marine Ecology》2017,38(4)
This study evaluated the effect of human trampling on the benthic macrofauna of two beaches in Southeast Brazil with different levels of intensity of tourism, Grussaí (more impacted) and Manguinhos (less impacted), during periods of high and low tourism activity. The macrofauna of urbanized (U) and non‐urbanized (NU) sectors of the inter‐tidal zone was sampled and the number of visitors was recorded. General linear models revealed a decreasing in abundance of macrofauna species in the urbanized sectors of analyzed beaches, which are exposed to higher trampling impact than in non‐urbanized areas. At Manguinhos Beach, trampling did not affect the macrofauna (<1 visitors ? m?²), except for the polychaete Scolelepis sp., which was less abundant in the U sector. Considering the benthic community, Atlantorchestoidea brasiliensis, Hemipodia californiensis and Scolelepis sp. were more sensitive to human trampling pressure and may be used as potential bioindicators of tourism impact. Management plans should consider mitigation of the effects of tourism, such as the control of the visitor number and their decentralization. 相似文献
128.
M.J. Orgeira L.N. Castro G.A. Goldmann C.B. Prezzi E. Sileo D.R. Vega C. Franzosi R.D. Acevedo O. Martínez J. Rabassa J.F. Ponce O.R. Tófalo 《地学前缘(英文版)》2017,8(1):137-149
The Quaternary infilling of a circular structure located in Bajada del Diablo, Chubut Province, Argentina has been proposed as a crater strewn field in previous studies. Here we report the finding of about 65 microspherules collected in a trench excavated in the center of the structure. The majority of hand-picked specimens are single, but some of them exhibit compound forms. The single specimens are spherical with a mean size of 137 μm, whereas the more complex samples show peduncles and drop shapes. Dendritic crystal growth is recognized in the internal structure of some broken microspherules. Preliminary chemical composition from the surface and center of microspherules was determined by energy dispersive spectrometry employing EDS. Quantitative EMPA and XRD analysis indicate that the microspherules are mainly composed of Fe and O with magnetite, Fe0 with subordinate wüstite. Following consideration of possible anthropogenic and volcanic origins, these spherulites are ascribed to an extraterrestrial input. An accumulation rate of 47 microspherules per m2/yr is estimated for the studied sediments. This value is two orders of magnitude higher than the reference flux for cosmic dust estimated for the last 1 Ma in the Transantarctic Mountains. The microspherules might have been generated as a byproduct of asteroid entry in the atmosphere. 相似文献
129.
A study was carried out on a rural catchment located in northwest Spain to examine the sediment yield from the catchment by measuring suspended sediments during rainfall events. Within the catchment regular surveys were conducted to obtain data on the suspended sediment sources. Important variations in sediment load were detected at event scale (0·3–21·0 Mg); some of these can be explained in terms of event size, antecedent conditions, rainfall distribution and soil surface erosion. To study the variables controlling suspended sediment yield during the events in the catchment, several event and pre‐event variables were calculated for all events. The sediment load is strongly influenced by discharge variables. During the events discharge–suspended sediments were also analysed. When the soil surface was unprotected, the formation of rills and ephemeral gullies on agricultural land at the catchment head was an important source of suspended sediments in the catchment. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
130.
C.?Ian?SchipperEmail author Jonathan?M.?Castro Hugh?Tuffen Fabian?B.?Wadsworth Debra?Chappell Andres?E.?Pantoja Mark?P.?Simpson Eric?C.?Le Ru 《Bulletin of Volcanology》2015,77(5):34
Cristobalite is a low-pressure high-temperature polymorph of SiO2 found in many volcanic rocks. Its volcanogenic formation has received attention because (1) pure particulate cristobalite can be toxic when inhaled, and its dispersal in volcanic ash is therefore a potential hazard; and (2) its nominal stability field is at temperatures higher than those of magmatic systems, making it an interesting example of metastable crystallization. We present analyses (by XRD, SEM, EPMA, Laser Raman, and synchrotron μ-cT) of representative rhyolitic pyroclasts and of samples from different facies of the compound lava flow from the 2011–2012 eruption of Cordón Caulle (Chile). Cristobalite was not detected in pyroclasts, negating any concern for respiratory hazards, but it makes up 0–23 wt% of lava samples, occurring as prismatic vapour-deposited crystals in vesicles and/or as a groundmass phase in microcrystalline samples. Textures of lava collected near the vent, which best represent those generated in the conduit, indicate that pore isolation promotes vapour deposition of cristobalite. Mass balance shows that the SiO2 deposited in isolated pore space can have originated from corrosion of the adjacent groundmass. Textures of lava collected down-flow were modified during transport in the insulated interior of the flow, where protracted cooling, additional vesiculation events, and shearing overprint original textures. In the most slowly cooled and intensely sheared samples from the core of the flow, nearly all original pore space is lost, and vapour-deposited cristobalite crystals are crushed and incorporated into the groundmass as the vesicles in which they formed collapse by strain and compaction of the surrounding matrix. Holocrystalline lava from the core of the flow achieves high mass concentrations of cristobalite as slow cooling allows extensive microlite crystallization and devitrification to form groundmass cristobalite. Vapour deposition and devitrification act concurrently but semi-independently. Both are promoted by slow cooling, and it is ultimately devitrification that most strongly contributes to total cristobalite content in a given flow facies. Our findings provide a new field context in which to address questions that have arisen from the study of cristobalite in dome eruptions, with insight afforded by the fundamentally different emplacement geometries of flows and domes. 相似文献