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排序方式: 共有500条查询结果,搜索用时 15 毫秒
341.
Peter von Ballmoos Jose Alvarez Nicolas Barrière Steve Boggs Andrei Bykov Juan Manuel Del Cura Velayos Filippo Frontera Lorraine Hanlon Margarita Hernanz Emmanuel Hinglais Jordi Isern Pierre Jean Jürgen Kn?dlseder Lucien Kuiper Mark Leising Beno?t Pirard Jean-Pierre Prost Rui M. Curado da Silva Tadayuki Takahashi John Tomsick Roland Walter Andreas Zoglauer 《Experimental Astronomy》2012,34(2):583-622
DUAL will study the origin and evolution of the elements and explores new frontiers of physics: extreme energies that drive powerful stellar explosions and accelerate particles to macroscopic energies; extreme densities that modify the laws of physics around the most compact objects known; and extreme fields that influence matter in a way that is unknown on Earth. The variability of these extreme objects requires continuous all-sky coverage, while detailed study demands an improvement in sensitivity over previous technologies by at least an order of magnitude. The DUAL payload is composed of an All-Sky Compton Imager (ASCI), and two optical modules, the Laue-Lens Optic (LLO) and the Coded-Mask Optic (CMO). The ASCI serves dual roles simultaneously, both as an optimal focal-plane sensor for deep observations with the optical modules and as a sensitive true all-sky telescope in its own right for all-sky surveys and monitoring. While the optical modules are located on the main satellite, the All-Sky Compton Imager is situated on a deployable structure at a distance of 30?m from the satellite. This configuration not only permits to maintain the less massive payload at the focal distance, it also greatly reduces the spacecraft-induced detector background, and, above all it provides ASCI with a continuous all-sky exposure. 相似文献
342.
Here we report on two separate ongoing, multi-year investigations on the dependence of the dissolution rate (R) of albite feldspar on fluid saturation state, as defined by the Gibbs free energy of reaction (ΔGr) for dissolution. The investigations are based on dissolution at pH 9.2, 150 °C and pH 3.3, 100 °C. Both studies reveal that the R–ΔGr relation is highly non-linear and sigmoidal. The kinetic data from the first study, being the most complete, can be fitted with a sigmoidal rate curve that is composed of two separate, parallel rate laws that represent distinct mechanisms of dissolution. The switch between one dominant mechanism and the other may be controlled by a critical free energy. The fact that in both studies the same type of sigmoidal R–ΔGr relation exists for dissolution at different pH and temperature condition suggests that this behavior may be universal for albite and other feldspars. Moreover, the experimental data contradict the commonly used R–ΔGr relation that is loosely based on transition state theory (TST). This has important implications with respect to the accuracy of geochemical codes that model water–rock interactions at near-equilibrium conditions. 相似文献
343.
Measurements of the concentration and vertical distribution of dissolved aluminium and silica, and of pH. in interstitial waters of recent marine sediments from the North Sea and the Mediterranean Sea were performed to evaluate the behaviour of aluminium during early diagenesis. The results suggest that thermodynamic equilibria alone do not control the concentrations of dissolved species in the system Al-Si-O2-H2O during early diagenesis. Rather, these concentrations are governed by dynamic factors involving mineral dissolution-precipitation reactions and diffusion. 相似文献
344.
Roland Vanderspek Hans A. Krimm George R. Ricker 《Astrophysics and Space Science》1995,231(1-2):259-262
The Explosive Transient Camera (ETC) has been performing automatic observations of the night sky since 1990. Since the launch of the Compton Gamma-Ray Observatory, the times and localizations of-ray bursts detected by the Burst and Transient Source Experiment (BATSE) have been compared with ETC observations to determine whether the ETC had observed a -ray burst in progress. To date, six temporal and spatial correlations have been found, but no new optical radiation has been detected. In this paper, we present current results of ETC/BATSE correlated observations and describe plans for future observations. 相似文献
345.
Tuna Eken Jaroslava Plomerová Roland Roberts Ludek Vecsey Vladislav Babuška Hossein Shomali Reynir Bodvarsson 《Tectonophysics》2010,480(1-4):241-258
Body-wave analysis — shear-wave splitting and P travel time residuals — detect anisotropic structure of the upper mantle beneath the Swedish part of Fennoscandia. Geographic variations of both the splitting measurements and the P-residual spheres map regions of different fabrics of the mantle lithosphere. The fabric of individual mantle domains is internally consistent, usually with sudden changes at their boundaries. Distinct backazimuth dependence of SKS splitting excludes single-layer anisotropy models with horizontal symmetry axes for the whole region. Based upon joint inversion of body-wave anisotropic parameters, we instead propose 3D self-consistent anisotropic models of well-defined mantle lithosphere domains with differently oriented fabrics approximated by hexagonal aggregates with plunging symmetry axes. The domain-like structure of the Precambrian mantle lithosphere, most probably retaining fossil fabric since the domains' origin, supports the idea of the existence of an early form of plate tectonics during the formation of continental cratons already in the Archean. Similarly to different geochemical and geological constraints, the 3D anisotropy modelling and mapping of fabrics of the lithosphere domains contribute to tracking plate tectonics regimes back in time. 相似文献
346.
Roland Schmidt Monika Roth Richard Tessadri Kaarina Weckström 《Journal of Paleolimnology》2008,40(1):453-469
Major and trace elements, minerals and grain-size were analysed from a sediment core covering the last 4,000 years of an Austrian
Alpine lake (Oberer Landschitzsee, ObLAN, 2,076 m a.s.l.). These analyses were combined with autumn and spring temperature
anomalies and ice-cover estimated from a diatom and chrysophyte cyst, thermistor-based regional calibration dataset and selected
pollen markers published previously. Diatom-inferred pH (Di-pH) and DOC (Di-DOC) completed the multi-proxy approach, which,
together with ordination techniques (PCA and RDA), helped (1) to confirm proposed climatic patterns and hypotheses, and (2)
to disentangle the complex interactions between climatic and anthropogenic impacts. Shifts in chemical and physical weathering,
erosion, production, lake stratification, redox potentials and air pollution were the major processes that have affected Oberer
Landschitzsee in relation to climate, lake/catchment interactions, and human impact. Geochemistry supported the finding that
the four waves of high-altitude land use (Early to Middle Bronze, ca. 1,800–1,300 B.C.; Late Bronze to Hallstatt, ca. 1,000–500
B.C.; Celtic to Roman, ca. 300 B.C.–400 A.D.; and Medieval, ca. 1,000–1,600 A.D.) were coupled mainly with warm periods. Increased
production, onset of lake stratification, and the deterioration of hypolimnetic oxygen conditions were the major changes governing
in-lake processes during climate warming. They resulted in specific element assemblages associated with organic matter accumulation
(Br), oxygen depletion (As, Ga, Cu, S), and changes in redox (Fe/Mn). The Se/Di-DOC ratio was introduced to track shifts between
in-lake production and allochthonous sources. Nutrient loading from pastures, coupled with climate warming, could explain
that in-lake production was highest during Roman and Medieval land use. Lithogenic elements mainly originated from chemical
weathering of silicate bedrock and they increased when intense land-use was coupled with climate deterioration and/or increased
humidity. These perturbations were highest during a High Medieval climate fluctuation around 1,000 A.D. The association of
sand with LOI and C/N and the decoupling of sand from quartz and feldspar separates erosion from physical weathering. Di-DOC,
S, and C/N showed hybrid characters in relation to climate and human impact. The mineral proportions indicated gradients in
relation to weathering, snow-cover and running waters, as well as vegetation. Air pollution by metallurgic industries, starting
during the High Medieval and culminating during the Late Medieval, caused lead accumulation and could have contributed to
As and S enrichment. Corresponding features in the distribution of selected elements and pollen tracers, as well as changes
in mineral proportions, supported the hypotheses of shifts in seasonal climate and an overall trend towards more continental
climate conditions since Medieval times. 相似文献
347.
This study evaluates the potential of using chironomid assemblages to estimate past temperature changes by comparing chironomid-inferred temperatures to meteorological data for the last 87 years. This comparison is made using high-resolution (i.e., sub-decadally resolved) short cores of four lakes along a gradient of altitude (Lake Njulla, 999 m a.s.l., Lake 850, 850 m a.s.l., Lake Alanen Laanijavri, 365 m a.s.l. and Lake Vuoskkujavri, 348 m a.s.l.), vegetation (pine forest to alpine tundra vegetation) and temperature (mean July temperature of 12.4 to 8.1°C). Patterns of chironomid-inferred changes in mean July air temperature were highly comparable to changes in the meteorological data. Moreover, instrumental data were almost always within the specific errors of the quantitative estimates using chironomids. These results indicate that chironomids can be used as a powerful tool to reconstruct temperatures and that chironomids are sensitive enough to record temperature changes of low magnitude such as those recorded during the Holocene. Although this relationship between temperature and chironomid community is strong for the last 87 years, we cannot assume that other environmental factors such as organic matter, changes of lake water depth or oxygen availability were not more significant over longer temporal scales of the Holocene, or longer. 相似文献
348.
Zofia Ecaterina Taranu Dörte Köster Roland I. Hall Theo Charette Francine Forrest Les C. Cwynar Irene Gregory-Eaves 《Aquatic Sciences - Research Across Boundaries》2010,72(1):97-115
Although comparative analyses between dimictic and polymictic lakes have noted the key role of mixing regime in governing
water quality, limnologists have historically focused on dimictic lakes, leaving polymictic lakes relatively understudied.
In this study, we investigated whether the effects of agricultural development on water quality differed between dimictic
and polymictic lakes in a naturally nutrient-rich region of Alberta, Canada. Through a spatial limnological analysis of 36
sites, we found that the relationship between surface water total phosphorus concentration and the percent of agriculture
(% Agr) in the catchments differed between dimictic and polymictic lakes, where the proportion of variance explained was much
more pronounced in the dimictic (79% explained) than in the polymictic systems (7% explained). Paleolimnological analyses
of subfossil chironomids in surface sediment samples (0–1 cm) from 18 of the 36 study lakes, and in sediment core profiles
from the dimictic and polymictic basins of a eutrophic lake, showed that water quality differed between mixis groups. We found
that the surface sediment chironomid assemblages differed significantly between polymictic and dimictic lakes. Detailed analyses
of the sediment cores demonstrated that the two basin types differed in their responses to land-use change through time, as
only the dimictic basin showed a parallel increase in anoxia with increasing agricultural development. We suggest that in
naturally-fertile landscapes, external nutrient loading exerts a more notable effect on dimictic lakes, whereas internal nutrient
loading is more important in polymictic systems. 相似文献
349.
350.