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91.
Jakob Andres 《International Journal of Earth Sciences》1941,32(1-2):106-132
Ohne Zusammenfassung 相似文献
92.
Norina Andres Fernando Vegas Galdos Waldo Sven Lavado Casimiro Massimiliano Zappa 《水文科学杂志》2013,58(11):2043-2059
AbstractEstimating water resources is important for adequate water management in the future, but suitable data are often scarce. We estimated water resources in the Vilcanota basin (Peru) for the 1998–2009 period with the semi-distributed hydrological model PREVAH using: (a) raingauge measurements; (b) satellite rainfall estimates from the TRMM Multi-satellite Precipitation Analysis (TMPA); and (c) ERA-Interim re-analysis data. Multiplicative shift and quantile mapping were applied to post-process the TMPA estimates and ERA-Interim data. This resulted in improved low-flow simulations. High-flow simulations could only be improved with quantile mapping. Furthermore, we adopted temperature and rainfall anomalies obtained from three GCMs for three future periods to make estimations of climate change impacts (Delta-change approach) on water resources. Our results show more total runoff during the rainy season from January to March, and temporary storages indicate that less water will be available in this Andean region, which has an effect on water supply, especially during dry season.Editor Z.W. Kundzewicz; Associate editor D. Gerten 相似文献
93.
ABSTRACTThe MHD-INPE model was applied in the Ji-Parana Basin, a 30 000 km2 catchment located in the southwest of the Amazon Basin which has lost more than 50% of its forest since the 1980s, to simulate land use and land cover change impacts on runoff generation process and how they are related to basin topography. Simulation results agree with observational studies in the sense that fast response processes are significant in sub-basins with steep slopes while in basins with gentle topography, the impacts are most visible in slow-response hydrological processes. On the other hand, the model is not able to capture the dependence of LUCC impacts on spatial scales. These discrepancies are probably associated with limitations in the spatial representation of heterogeneities within the model, which become more relevant at larger scales. We also tested the hypothesis that secondary forest growth should be able to compensate the decrease in evapotranspiration due to forest–cropland or forest–grassland conversion at a regional scale. Results showed that despite the small fraction of secondary forest estimated on the basin, the higher evapotranspiration efficiency of this type of forest counterbalances a large fraction of the LUCC impacts on evapotranspiration. This result suggests that enhanced transpiration due to secondary forest could explain, at least in part, the lack of clear LUCC signals in discharge series at larger scales.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR T. Wagener 相似文献
94.
Brian Townley Pierrick Roperch Verónica Oliveros Andres Tassara César Arriagada 《Mineralium Deposita》2007,42(7):771-789
In the Carolina de Michilla district, northern Chile, stratabound copper mineralization is hosted by Jurassic volcanic rocks
along the trace of the Atacama fault system. In this study, we present the overall effects of hydrothermal alteration on the
magnetic properties of rocks in this district. Two types of metasomatic alteration associations occur, one of regional extent
and the other of local hydrothermal alteration associated with copper mineralization (e.g., Lince–Estefanía–Susana). Regional
alteration is interpreted as a low-grade “propylitic association” characterized by an epidote–chlorite–smectite–titanite–albite–quartz–calcite
association. The local hydrothermal alteration is characterized broadly by a quartz–albite–epidote–chlorite–calcite mineral
assemblage. The most pervasive alteration mineral is albite, followed by epidote and, locally, actinolite. These minerals
contrast sharply against host rock minerals such as chlorite, calcite, zeolite, prehnite, and pumpellyite, but alteration
is constrained to mineralized bodies as narrow and low contrast alteration halos that go outwards from actinolite–albite to
epidote–albite, to epidote–chlorite, and finally to chlorite. Hydrothermal alteration minerals, compared to regional alteration
minerals, show iron-rich epidotes, a lower chlorite content of the chlorite–smectite series, and a nearly total albite replacement
of plagioclase in the mineralized zones. Opaque minerals associated with regional alteration are magnetite and maghemite,
and those associated to hydrothermal alteration are magnetite, hematite, and copper sulphides. We present paleomagnetic results
from nine sites in the Michilla district and from drill cores from two mines. Local effects of hydrothermal alteration on
the original magnetic mineralogy indicate similar characteristics and mineralogy, except for an increase of hematite that
is spatially associated with the Cu–sulphide breccias with low magnetic susceptibilities. Results indicate that it is impossible
to magnetically differentiate mineralized bodies from unmineralized lavas, except for pyrite-rich hydrothermal breccias. In
conclusion, for stratabound copper deposits of the Michilla type, the overall effect of hydrothermal alteration on the paleomagnetic
properties of rocks is of low contrast, not clearly discernable even at a small scale. From an exploration point of view,
magnetic exploration surveys should not discern mineralized bodies of Cu–sulphide breccias except in detailed ground surveys
due to the small size of contrasting bodies. Unoriented drill cores with primary ore mineralization record a characteristic
remanent magnetization of reverse polarity. Taking into account the azimuth and dip of the drill cores, we were able to compare
the magnetization of the mineralized bodies with the characteristic directions from sites drilled in situ from Late Jurassic–Early
Cretaceous intrusives mostly. The characteristic direction recorded by the Pluton Viera is similar to the magnetization of
the ore bodies of the Estefania mine. If copper mineralization mostly postdates the tilt of the volcanic flows, the low paleomagnetic
inclinations suggest an age for the mineralization near 145 Ma, the time of the lowest paleolatitude for the South American
plate during the Mesozoic. 相似文献
95.
Stephan Margreth Andres Rüggeberg Silvia Spezzaferri 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(12):2216-2234
Cold-water coral ecosystems building cold-water carbonate mounds occur worldwide and are especially developed along the European margin, from northern Norway to the Gulf of Cadiz. A remarkable mound province is documented southwest of Ireland along the Porcupine and Rockall Banks. In this area carbonate mounds are formed in water depths between 500 and 1200 m and are often densely settled by cold-water coral ecosystems offering many ecological niches for benthic foraminifera. We investigated total (unstained) benthic foraminiferal assemblages from surface sediments (0–1 cm, >63 μm size fraction) of this region with the aim to trace their distribution patterns and to test if they can be used as bioindicators for facies characterization in different parts of carbonate mound systems. Our quantitative data were further statistically treated with non-metric multidimensional scaling (nMDS) based on Bray–Curtis similarity matrix to highlight community patterns that were not readily apparent. Our results indicate that different benthic foraminiferal assemblages characterize different facies along cold-water carbonate mounds and are related to the environmental conditions and available substrates. The following facies can be described: (1) the Off-Mound Facies is dominated by uvigerinids and other infaunal species; (2) the Dropstone Facies is characterized by infaunal Globocassidulina subglobosa and attached-epifaunal Cibicidoides sp.; (3) the Dead Coral Facies is characterised by epifaunal species (e.g., Planulina ariminensis, Hanzawaia boueana) and infaunal species (Spiroplectinella wrightii, Angulogerina angulosa, Epistominella vitrea); (4) the Living Coral Facies includes both infaunal and epifaunal species, but is dominated by the epifaunal Discanomalina coronata; and (5) the Sandwave Facies contains high abundances of epifaunal species including D. coronata. Based on this distribution, we propose D. coronata, as an indicator species to identify active mounds and/or living cold-water coral ecosystems. Our results also emphasise the importance of studying the small size fractions that yield many infaunal species. A causal link exists between distribution patterns of benthic foraminifera and cold-water coral facies, thus providing an independent tool to identify and describe the different facies in this setting. 相似文献
96.
Despite two decades of major advances in the field of thermochronological modeling, state-of-the-art numerical implementations still rely mostly on burial and exhumation processes to explain radiometric measurements.Even though such an approach has proved valuable, failing to account for other first-order geological variables has led to misinterpretations and therefore, calls for a refinement.In this study a new version of the Fetkin(finite element temperature kinematics, Ecopetrol) program is presented.Its new algorithm couples time-dependent hydrological and thermal calculations, thus rendering thermochronological ages that, instead of being solely dependent on the kinematical evolution of a system, conditioning by the fluid flow is also present.In contrast with previous thermochronological models, this work considers the influence of effective stress on rock properties(porosity and permeability) and therefore, in thermal conductivity.Sensitivity analyses addressing relevant geological questions show not only the versatility of the code but also, new perspectives on forward low-temperature thermochronological modeling.Groundwater circulation through pure-sandstone settings produce colder thermal architectures than those obtained in impermeable domains.Differences in cooling ages from models with and without fluid circulation are up to 5 Myr.A 4-fold variation in thrusting rates(0.5 km/Myr to 2 km/Myr) produces a 15-Myr difference in cooling ages in models with fluid flow, which contrasts to much lower differences, only 2 Myr, in domains without(or minimal) fluid circulation.2D thermal solutions in fold-bend-fold thrust belts composed of sandstones remain static despite substantial relief development by kinematic folding.A case-study from Western Argentina, in the Andean Precordillera, confirms the plausibility of the numerical algorithm here posed and raises new questions on the first-order thermal controls in settings under deformation. 相似文献
97.
Reinaldo J. Gleiser Andres D. Dagotto Carlos O. Nicasio 《Astrophysics and Space Science》1991,178(2):303-309
We present exact solutions of Einstein's equations that may be interpreted as representing the splitting of a primordial cosmic string imbedded in a perfect fluid Friedmann-Robertson-Walker (FRW) cosmology. The splitting leads to the creation of a bubble whose boundary is given by a gravitational shock wave, expanding from the point of splitting, associated to the motion of the free ends of the string. Inside the bubble we have a perturbed FRW metric. This perturbation is largest near the string ends, producing a sort of wake along the path of the free ends, but decreases rapidly with time and the metric approaches the FRW regime locally everywhere inside the bubble. Similar results are shown to hold also for flat vacuum de Sitter space-times.Supported by a CONICET fellowship.Supported by a CONICOR fellowship. 相似文献
98.
The stratal architecture of the Gulf of Cádiz continental margin (SW Spain) has been analyzed by using single-channel, very
high-resolution seismic reflection profiles. An evolutionary scheme of asymmetrical depositional sequences is proposed that
was governed by the Late Pleistocene–Holocene sea-level fluctuations. Stratigraphic analysis defined 14 seismic units, that
are configured into two major type-1 depositional sequences related to 4th-order eustatic sea level changes (100–110 ka).
Within these sequences, minor asymmetrical depositional sequences have been recognized related to 5th-order eustatic cycles
(22–23 ka) superimposed and modulated by the regressive trends of 4th-order cycles. In 5th-order depositional sequences, the
forced regressive and lowstand deposits are volumetrically dominant. They cause the main progradation of the margin in such
a way that they form the margin structure almost entirely.
Received: 6 April 1995 / Revision received: 8 March 1996 相似文献
99.
Oliver Montenbruck Yago Andres Heike Bock Tom van Helleputte Jose van den Ijssel Marc Loiselet Christian Marquardt Pierluigi Silvestrin Pieter Visser Yoke Yoon 《GPS Solutions》2008,12(4):289-299
The global navigation satellite system receiver for atmospheric sounding (GRAS) on MetOp-A is the first European GPS receiver
providing dual-frequency navigation and occultation measurements from a spaceborne platform on a routine basis. The receiver
is based on ESA’s AGGA-2 correlator chip, which implements a high-quality tracking scheme for semi-codeless P(Y) code tracking
on the L1 and L2 frequency. Data collected with the zenith antenna on MetOp-A have been used to perform an in-flight characterization
of the GRAS instrument with focus on the tracking and navigation performance. Besides an assessment of the receiver noise
and systematic measurement errors, the study addresses the precise orbit determination accuracy achievable with the GRAS receiver.
A consistency on the 5 cm level is demonstrated for reduced dynamics orbit solutions computed independently by four different
agencies and software packages. With purely kinematic solutions, 10 cm accuracy is obtained. As a part of the analysis, an
empirical antenna offset correction and preliminary phase center correction map are derived, which notably reduce the carrier
phase residuals and improve the consistency of kinematic orbit determination results.
相似文献
Oliver MontenbruckEmail: |
100.
Functional diversity of fish and invertebrates in coral and rocky reefs of the Eastern Tropical Pacific 下载免费PDF全文
Georgina Ramírez‐Ortiz Luis E. Calderon‐Aguilera Hector Reyes‐Bonilla Arturo Ayala‐Bocos Luis Hernández Francisco Fernández Rivera‐Melo Andres López‐Pérez Arturo Dominici‐Arosamena 《Marine Ecology》2017,38(4)
To define the functional groups of fish and macroinvertebrates in the Eastern Tropical Pacific (ETP), visual censuses were performed in 18 areas of four biogeographic provinces: Cortés, Mexican, Panamic and Oceanic Islands. A total of 257 fish and macroinvertebrate species were recorded, and from them, 27 morpho‐functional groups (MFGs) were constructed on the basis of trophic level, maximum size, taxonomy and morphology. Biomass, richness, diversity and evenness of MFGs were calculated for each province and compared statistically; a regression analysis between taxonomic and functional diversity was conducted to observe the relationship between these two indicators. There were significant differences in all ecological indices (p < .002), highlighting the high biomass and richness of MFGs in the Cortés and Oceanic Islands provinces (>400 g/m2), associated with the influence of cold currents in the northernmost region and less fishing pressure in protected areas. A decreasing pattern of MFG richness towards the tropics was observed, which demonstrates that in the ETP, the relationship between habitat heterogeneity and species diversity has been translated into functional complexity. The Mexican province was the most functionally diverse (biomass well distributed in the MFG; H′ = 0.46 ± 0.009). Related to this, it is predicted that biomass is biased towards certain functional groups (i.e., large carnivores), which shows that the H′ index of the MFG is not a good indicator of the conservation status of ETP reefs. Finally, regression analysis suggests that functional diversity increases at low species diversity but eventually reaches an asymptote (almost all possible functions are represented). 相似文献