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311.
Lorenzo Iorio Herbert I. M. Lichtenegger Matteo Luca Ruggiero Christian Corda 《Astrophysics and Space Science》2011,331(2):351-395
Recent years have seen increasing efforts to directly measure some aspects of the general relativistic gravitomagnetic interaction
in several astronomical scenarios in the solar system. After briefly overviewing the concept of gravitomagnetism from a theoretical
point of view, we review the performed or proposed attempts to detect the Lense-Thirring effect affecting the orbital motions
of natural and artificial bodies in the gravitational fields of the Sun, Earth, Mars and Jupiter. In particular, we will focus
on the evaluation of the impact of several sources of systematic uncertainties of dynamical origin to realistically elucidate
the present and future perspectives in directly measuring such an elusive relativistic effect. 相似文献
312.
In this study we propose a regression model for the estimation of lunar elemental abundances from spectral features extracted from Clementine multispectral imagery in the visible and near-infrared domain. We extract a set of spectral features, including the continuum slope, the FWHM of the ferrous absorption trough near 1000 nm, and the wavelengths and relative depths of the absorption minima and inflection points present in the trough. As a “ground truth” for the elemental abundances we rely on the Lunar Prospector gamma ray spectrometer (LP GRS) data. With respect to the elemental abundances of the Apollo and Luna landing sites independently derived from returned samples, the best examined regression model is a second-order polynomial. The proposed regression-based approach allows an estimation of the elemental abundances of Ca, Al, Fe, Mg, and O at an accuracy of about 1 wt% and some tenths of a weight percent for Ti. We examine the influence of calibration of the Clementine UVVIS+NIR data and find that its effect on the results obtained with the regression approach is minor. Furthermore, we define a three-endmember model which allows the petrographic mapping of the lunar surface materials in terms of their Fe, Mg, and Al abundances. We examine the global distribution of Mg-rich rocks, the distribution of cryptomaria, and the occurrence of aluminous mare basalts in the Frigoris region. A possible regional compositional anomaly in northwestern Oceanus Procellarum is found, which corresponds to an extended area displaying spectral characteristics consistent with mare basalt containing significant amounts of olivine. On local scales, we examine in terms of our regression model the highland craters Proclus and Tycho, the compositionally anomalous central peaks of the craters Copernicus and Bullialdus, and the pyroclastic deposits on the floor of Alphonsus and on the northern rim of Petavius. As a general result, we show that the regression-based approach allows the detection of the main lunar terrain classes and rock types based on multispectral imagery in the visible and near-infrared domain. 相似文献
313.
Space- and ground-based measurements of sulphur dioxide emissions from Turrialba Volcano (Costa Rica) 总被引:2,自引:0,他引:2
Robin Campion Maria Martinez-Cruz Thomas Lecocq Corentin Caudron Javier Pacheco Gaia Pinardi Christian Hermans Simon Carn Alain Bernard 《Bulletin of Volcanology》2012,74(7):1757-1770
Remotely sensed measurements of sulphur dioxide (SO2) emitted by Turrialba Volcano (Costa Rica) are reported for the period September 2009–January 2011. These measurements were obtained using images from Advanced Spaceborne Thermal Emission and Reflexion radiometer, Ozone Monitoring Instrument and a ground-based UV camera. These three very different instruments provide flux measurements in good agreement with each other, which demonstrate that they can be integrated for monitoring SO2 fluxes. Fluxes from Turrialba increased fourfold in January 2010, following a phreatic explosion that formed a degassing vent in the W crater of Turrialba. Since then, the SO2 flux has remained high (30–50?kg/s) but seems to be showing a slowly decreasing trend. We interpret this evolution as the start of open vent degassing from a recently intruded magma body. The opening of the degassing vent decreased the confining pressure of the magma body and allowed the gases to bypass the hydrothermal system. 相似文献
314.
Stefan?R?sel Anna?Rych?a Christian?Wurzbacher Hans-Peter?GrossartEmail author 《Aquatic Sciences - Research Across Boundaries》2012,74(1):87-99
Nutrient fluxes across terrestrial-aquatic boundaries and their subsequent integration into lake nutrient cycles are currently
a major topic of aquatic research. Although pollen represents a good substrate for microorganisms, it has been neglected as
a terrestrial source of organic matter in lakes. In laboratory experiments, we incubated pollen grains of Pinus sylvestris in water of lakes with different trophy and pH to estimate effects of pollen input and its subsequent microbial degradation
on nutrient dynamics. In this ex situ experiment, we measured concentrations of organic carbon, phosphorus and nitrogen in the surrounding water as well as microbial
dynamics (bacteria and fungal sporangia) at well-controlled conditions. Besides leaching, chemical and microbial decomposition
of pollen was strongest within the first week of incubation. This led to a marked increase of soluble reactive phosphorus
and total dissolved nitrogen (up to 0.04 and 1.5 mg L−1, respectively, after 5 days of incubation) in the ambient water. In parallel, pollen grains were rapidly colonized by heterotrophic
bacteria and aquatic fungi. Leaching and microbial degradation of pollen accounted for ≥80, ≥40, ≥50% for organic C, N and
P, respectively, and did not significantly differ among water samples from the studied lakes. Thus, pollen introduces high
amounts of bio-available terrestrial organic matter and nutrients into surface waters within a short time. A rough calculation
on P input into oligotrophic Lake Stechlin indicates that pollen plays an important ecological role in nutrient cycling of
temperate lakes. This requires further attention in aquatic ecology. 相似文献
315.
?yvind Breivik Tor Christian Bekkvik Cecilie Wettre Atle Ommundsen 《Ocean Dynamics》2012,62(2):239-252
The task of determining the origin of a drifting object after it has been located is highly complex due to the uncertainties
in drift properties and environmental forcing (wind, waves, and surface currents). Usually, the origin is inferred by running
a trajectory model (stochastic or deterministic) in reverse. However, this approach has some severe drawbacks, most notably
the fact that many drifting objects go through nonlinear state changes underway (e.g., evaporating oil or a capsizing lifeboat).
This makes it difficult to naively construct a reverse-time trajectory model which realistically predicts the earliest possible
time the object may have started drifting. We propose instead a different approach where the original (forward) trajectory
model is kept unaltered while an iterative seeding and selection process allows us to retain only those particles that end
up within a certain time–space radius of the observation. An iterative refinement process named BAKTRAK is employed where
those trajectories that do not make it to the goal are rejected, and new trajectories are spawned from successful trajectories.
This allows the model to be run in the forward direction to determine the point of origin of a drifting object. The method
is demonstrated using the leeway stochastic trajectory model for drifting objects due to its relative simplicity and the practical
importance of being able to identify the origin of drifting objects. However, the methodology is general and even more applicable
to oil drift trajectories, drifting ships, and hazardous material that exhibit nonlinear state changes such as evaporation,
chemical weathering, capsizing, or swamping. The backtracking method is tested against the drift trajectory of a life raft
and is shown to predict closely the initial release position of the raft and its subsequent trajectory. 相似文献
316.
Coherent structure dynamics and sediment particle motion around a cylindrical pier in developing scour holes 总被引:1,自引:1,他引:0
Oscar Link Christian González María Maldonado Cristián Escauriaza 《Acta Geophysica》2012,60(6):1689-1719
Recent investigations on the dynamics of the turbulent horseshoe vortex system (THV) around cylindrical piers have shown that the rich coherent dynamics of the vortical structures is dominated by low-frequency bimodal fluctuations of the velocity field. In spite of these advances, many questions remain regarding the changes of the flow and sediment transport dynamics as scour progresses. In this investigation we carry out laboratory experiments to register the development of the scour hole around a cylindrical pier in a fine-sand bed (d 50 = 0.36 mm). We use the bathymetry measured in the experiment to simulate the flow field employing the detached-eddy simulation approach (DES), which has shown to resolve most of the turbulent stresses around surface-mounted obstacles. From these simulations we compare the dynamics of the THV to the flat-bed case, and analyze the effects on particle transport and sediment flux using the Lagrangian particle model of Escauriaza and Sotiropoulos (2011b) to study the impact of the changes of the flow on the sediment dynamics. 相似文献
317.
Lucien von Gunten Oliver Heiri Christian Bigler Jacqueline van Leeuwen Carlo Casty André F. Lotter Michael Sturm 《Journal of Paleolimnology》2008,39(3):283-299
We analysed a 42 cm long sediment record from Lej da la Tscheppa, a high-altitude lake (2,616 m a.s.l.) in the Upper Engadine
valley (Switzerland) for subfossil diatoms, chironomids and pollen. The chronology of the top 21 cm of the record was established
using 210Pb analysis using a constant-rate-of-supply model, and validated with 137Cs measurements and the content of spheroidal carbonaceous particles. A tentative chronology for the lower part of the core
was obtained through extrapolation of the sedimentation rates in the uppermost part of the record. Pollen assemblages in the
record reflect regional changes in forestation and land-use patterns in the Upper Engadine valley and show no evidence of
significant local human activity in the lake’s catchment. Diatom assemblages record a distinct increase in planktonic taxa
since the early 19th century, suggesting a decrease in the duration of ice-cover. In contrast, chironomid assemblages remained
stable during a large part of the record. We applied an established chironomid-based July air temperature transfer function
and a newly developed diatom-based spring air temperature transfer function to reconstruct past seasonal air temperature changes
at Lej da la Tscheppa. The reconstructions indicate a diatom-inferred warming trend in spring temperatures during the past
ca. 400 years, whereas chironomid-inferred summer temperatures suggest a slight cooling trend. These biota-based reconstructions
are in good agreement with the centennial-scale temperature trend in an independent reconstruction of regional temperatures
in the Upper Engadine region based on instrumental records and documentary proxy evidence from the Alps. Our results suggest
that, in high-altitude lakes, independent chironomid- and diatom-based seasonal temperature reconstruction is possible and
can be successfully used to track seasonal temperature trends. 相似文献
318.
Aurélien van Welden Christian Beck Jean-Louis Reyss Salvatore Bushati Rexhep Koci François Jouanne Jean-Louis Mugnier 《Journal of Paleolimnology》2008,40(2):619-633
Lake Shkodra (northern Albania, southern Montenegro) is a large (45 km length, 15 km width) and shallow (5 m mean depth) lake,
developed on a mainly karstic carbonate substratum. Its recent sedimentary fill (mixed calcareous/siliciclastic clayey silts)
was analysed through short gravity cores representing five centuries of environmental archive. A combination of high resolution
texture analysis (particle size), magnetic susceptibility, carbon content, and radionuclide activity profiles (210Pb, 137Cs, 241Am) permitted us to detect and date environmental changes, such as the Little Ice Age and the 1962–1963 catastrophic floods.
Anthropogenic influences on the watershed, such as damming of the Drin River in the late 1970s, also appear to be recorded.
Impacts of known strong earthquakes (1905, 1979), however, could not be clearly detected in the sediment record. The potential
of the Shkodra lacustrine archive for paleoseismic investigations on long time intervals (such as Holocene) is discussed.
This paper is a preliminary contribution to Shkodra Lake’s Holocene paleolimnology. 相似文献
319.
A modified method for biogenic silica determination 总被引:1,自引:0,他引:1
We describe a modified method for the determination of biogenic silica (BSi) in lacustrine sediment samples with BSi concentrations
>0.5% SiO2 (detection limit). To speed up the leaching procedure (48 samples per day), we suggest the use of Teflon autoclaves that
can be left unattended (no stirring of the solution) for 3 h at 100°C in an oven. We suggest a volume correction by Na measurement
to account for volume errors during pipetting off a hot solution. We also propose to carry out a correction for minerogenic
silica by the simultaneous determination of Al in the leachate. Analytical precision and accuracy of the proposed method are
2.4% (relative standard deviation) and 70–110% recovery (relative to the mean of four international reference sediment samples),
respectively. Additionally, we demonstrate that pre-treatment of the samples with H2O2 and/or HCl prior to alkaline leaching is not necessary for all samples. Due to the great diversity of lacustrine and marine
sediments, however, the pre-treatment procedure should be tailored for samples from different sites. 相似文献
320.