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排序方式: 共有423条查询结果,搜索用时 31 毫秒
81.
Francesco Di Benedetto Daniele Borrini Andrea Caneschi Gabriele Fornaciai Massimo Innocenti Alessandro Lavacchi Carlo Andrea Massa Giordano Montegrossi Werner Oberhauser Luca A. Pardi Maurizio Romanelli 《Physics and Chemistry of Minerals》2011,38(6):483-490
An extensive characterisation of the magnetic properties of synthetic powders of kuramite, with formal composition Cu3SnS4, was performed. Powders were investigated through superconducting quantum interference device (SQUID) magnetometry, electron paramagnetic resonance (EPR) spectroscopy, X-ray powder diffraction (XRPD), scanning and transmission electron microscopies (SEM and TEM) and microanalysis. SEM and TEM reveal the presence of nanodimensioned particles. XRPD clearly shows that Cu3SnS4 crystallised in a cubic sphalerite-type structural model, in spite of the stannite-type tetragonal structure described for the natural phase. This difference arises from a full random distribution of cations. Synthetic kuramite nanopowders exhibit a marked paramagnetism, originated by the presence of Cu(II), definitely assessed by EPR measurements. Moreover, the overall magnetic behaviour of the sample cannot be simply ascribed to diluted paramagnetism, and this suggests the presence of strong superexchange interactions among Cu(II) ions even at room temperature. The main consequences of these results are the definitive assessment of the chemical formula Cu(I)2Cu(II)SnS4 and of a random distribution of Cu(II), Cu(I) and Sn(IV) ions within the available tetrahedral sites. 相似文献
82.
Marco Cuffaro Federica Riguzzi Davide Scrocca Carlo Doglioni 《International Journal of Earth Sciences》2011,100(8):1915-1924
We performed geodetic strain rate analyses in southern Italy, using new GPS velocities. Two-dimensional strain and rotation
rate fields were estimated and results show that most of the shortening is distributed in the northern Sicily offshore. Extension
becomes more evident and comparable with shortening on the eastern side of the same margin, and greater in the eastern Sicily
offshore. Principal shortening and extension rate axes are consistent with long-term geological features: seismic reflection
profiles show both active compressive and extensional faults affecting Pleistocene strata. We show evidence for contemporaneous
extension and transtension in the Cefalù Basin. Combining geodetic data and geological features point to the coexistence of
independent geodynamic processes, i.e., the active E–W backarc spreading in the hangingwall of the Apennines subduction zone
and shortening along the southern margin of the Tyrrhenian backarc basin operated by the NNW-motion of Africa relative to
Eurasia. 相似文献
83.
Patrick Drupp Eric Heinen De Carlo Fred T. Mackenzie Paul Bienfang Christopher L. Sabine 《Aquatic Geochemistry》2011,17(4-5):473-498
The marine shelf areas in subtropical and tropical regions represent only 35% of the total shelf areas globally, but receive a disproportionately large amount of water (65%) and sediment (58%) discharges that enter such environments. Small rivers and/or streams that drain the mountainous areas in these climatic zones deliver the majority of the sediment and nutrient inputs to these narrow shelf environments; such inputs often occur as discrete, episodic introductions associated with storm events. To gain insight into the linked biogeochemical behavior of subtropical/tropical mountainous watershed-coastal ocean ecosystems, this work describes the use of a buoy system to monitor autonomously water quality responses to land-derived nutrient inputs and physical forcing associated with local storm events in the coastal ocean of southern Kaneohe Bay, Oahu, Hawaii, USA. The data represent 2.5 years of near-real time observations at a fixed station, collected concurrently with spatially distributed synoptic sampling over larger sections of Kaneohe Bay. Storm events cause most of the fluvial nutrient, particulate, and dissolved organic carbon inputs to Kaneohe Bay. Nutrient loadings from direct rainfall and/or terrestrial runoff produce an immediate increase in the N:P ratio of bay waters up to values of 48 and drive phytoplankton biomass growth. Rapid uptake of such nutrient subsidies by phytoplankton causes rapid declines of N levels, return to N-limited conditions, and subsequent decline of phytoplankton biomass over timescales ranging from a few days to several weeks, depending on conditions and proximity to the sources of runoff. The enhanced productivity may promote the drawing down of pCO2 and lowering of surface water column carbonate saturation states, and in some events, a temporary shift from N to P limitation. The productivity-driven CO2 drawdown may temporarily lead to air-to-sea transfer of atmospheric CO2 in a system that is on an annual basis a source of CO2 to the atmosphere due to calcification and perhaps heterotrophy. Storms may also strongly affect proximal coastal zone pCO2 and hence carbonate saturation state due to river runoff flushing out high pCO2 soil and ground waters. Mixing of the CO2-charged water with seawater causes a salting out effect that releases CO2 to the atmosphere. Many subtropical and tropical systems throughout the Pacific region are similar to Kaneohe Bay, and our work provides an important indication of the variability and range of CO2 dynamics that are likely to exist elsewhere. Such variability must be taken into account in any analysis of the direction and magnitude of the air?Csea CO2 exchange for the integrated coastal ocean, proximal and distal. It cannot be overemphasized that this research illustrates several examples of how high frequency sampling by a moored autonomous system can provide details about ecosystem responses to stochastic atmospheric forcing that are commonly missed by traditional synoptic observational approaches. Finally, the work exemplifies the utility of combining synoptic sampling and real-time autonomous observations to elucidate the biogeochemical and physical responses of coastal subtropical/tropical coral reef ecosystems to climatic perturbations. 相似文献
84.
Ghislain Dubois Benjamin Sovacool Carlo Aall Maria Nilsson Carine Barbier Alina Herrmann Sébastien Bruyère Camilla Andersson Bore Skold Franck Nadaud Florian Dorner Karen Richardsen Moberg Jean Paul Ceron Helen Fischer Dorothee Amelung Marta Baltruszewicz Jeremy Fischer Françoise Benevise Rainer Sauerborn 《Chemie der Erde / Geochemistry》2013
Through their consumption behavior, households are responsible for 72% of global greenhouse gas emissions. Thus, they are key actors in reaching the 1.5 °C goal under the Paris Agreement. However, the possible contribution and position of households in climate policies is neither well understood, nor do households receive sufficiently high priority in current climate policy strategies. This paper investigates how behavioral change can achieve a substantial reduction in greenhouse gas emissions in European high-income countries. It uses theoretical thinking and some core results from the HOPE research project, which investigated household preferences for reducing emissions in four European cities in France, Germany, Norway and Sweden. The paper makes five major points: First, car and plane mobility, meat and dairy consumption, as well as heating are the most dominant components of household footprints. Second, household living situations (demographics, size of home) greatly influence the household potential to reduce their footprint, even more than country or city location. Third, household decisions can be sequential and temporally dynamic, shifting through different phases such as childhood, adulthood, and illness. Fourth, short term voluntary efforts will not be sufficient by themselves to reach the drastic reductions needed to achieve the 1.5 °C goal; instead, households need a regulatory framework supporting their behavioral changes. Fifth, there is a mismatch between the roles and responsibilities conveyed by current climate policies and household perceptions of responsibility. We then conclude with further recommendations for research and policy. 相似文献
85.
Angelo Gavezzotti Francesco Demartin Carlo Castellano Italo Campostrini 《Physics and Chemistry of Minerals》2013,40(2):175-182
An accurate structure refinement, using single-crystal X-ray diffraction data, on natural α- and β-dimorphites collected at Solfatara di Pozzuoli, in the Phlegraean Fields, near Naples and at Vesuvius (Italy) is reported. Theoretical calculations at various levels of sophistication have been used to calculate molecular vibrational frequencies and gas-phase specific heats, to analyze the crystal packing, and to estimate lattice energies of both phases. All computational methods contribute to demonstrate that the β-phase is the thermodynamically stable one at room temperature. 相似文献
86.
Jhan Carlo Espinoza Villar Jean Loup Guyot Josyane Ronchail Grard Cochonneau Naziano Filizola Pascal Fraizy David Labat Eurides de Oliveira Juan Julio Ordoez Philippe Vauchel 《Journal of Hydrology》2009,375(3-4):297-311
Former hydrological studies in the Amazon Basin generally describe annual discharge variability on the main stem. However, the downstream Amazon River only represents the mean state of the Amazonian hydrological system. This study therefore uses a new data set including daily discharge in 18 sub-basins to analyze the variability of regional extremes in the Amazon basin, after recalling the diversity of the hydrological annual cycles within the Amazon basin. Several statistical tests are applied in order to detect trends and breaks in the time series. We show that during the 1974–2004 period, the stability of the mean discharge on the main stem in Óbidos is explained by opposite regional features that principally involve Andean rivers: a decrease in the low stage runoff, particularly important in the southern regions, and an increase in the high stage runoff in the northwestern region. Both features are observed from the beginning of the nineties. These features are also observed in smaller meridian sub-basins in Peru and Bolivia. Moreover we show that the changes in discharge extremes are related to the regional pluriannual rainfall variability and the associated atmospheric circulation as well as to tropical large-scale climatic indicators. 相似文献
87.
Carlo Laj Herv Guillou Nadia Szeremeta Robert Coe 《Earth and Planetary Science Letters》1999,170(4):191-376
We have sampled a sequence of 107 lava flows in the Waianae series on Oahu, Hawaii, in two separate stretches. The first (51 flows) at Kaena Point extends from sea level to an altitude of 190 m, and the second (56 flows) follows the Satellite Tracking Station road from 218 m to 360 m above sea level. Thermal and af demagnetization yield very similar results, and reveal only normal polarities. K/Ar dating at five different horizons combined with the paleomagnetic results indicate that the sequence was emplaced entirely in the normal polarity interval between the Upper Mammoth and the Lower Kaena polarity transitions (3.22–3.11 Ma). Some of the flows are serially correlated. Filtering does not, however, drastically affect the final results. Inclinations are shallower than those expected from a centered dipole field. Although large (13°), the inclination anomaly is consistent with results from other sites at the same latitude. The scatter of the VGPs about the geographic pole is consistent with available data from other regions at similar latitudes. The scatter of the directions is also consistent with the predictions of recent statistical models of paleosecular variation. Therefore, these results do not support the hypothesis of a Pacific dipole window. 相似文献
88.
Raphael Di Carlo Silva dos Santos João Carlos Ribeiro Cruz Manuel de Jesus dos Santos Costa 《Geophysical Prospecting》2020,68(7):2046-2063
Recently, the interest in PS-converted waves has increased for several applications, such as sub-basalt layer imaging, impedance estimates and amplitude-versus-offset analysis. In this study, we consider the problem of separation of PP- and PS-waves from pre-stacked multicomponent seismic data in two-dimensional isotropic medium. We aim to demonstrate that the finite-offset common-reflection-surface traveltime approximation is a good alternative for separating PP- and PS-converted waves in common-offset and common shot configurations by considering a two-dimensional isotropic medium. The five parameters of the finite-offset common-reflection-surface are firstly estimated through the inversion methodology called very fast simulated annealing, which estimates all parameters simultaneously. Next, the emergence angle, one of the inverted parameters, is used to build an analytical separation function of PP and PS reflection separation based on the wave polarization equations. Once the PP- and PS-converted waves were separated, the sections are stacked to increase the signal-to-noise ratio using the special curves derived from finite-offset common-reflection-surface approximation. We applied this methodology to a synthetic dataset from simple-layered to complex-structured media. The numerical results showed that the inverted parameters of the finite offset common-reflection-surface and the separation function yield good results for separating PP- and PS-converted waves in noisy common-offset and common shot gathers. 相似文献
89.
Alessandro Simoni Martino Bernard Matteo Berti Mauro Boreggio Stefano Lanzoni Laura Maria Stancanelli Carlo Gregoretti 《地球表面变化过程与地形》2020,45(14):3556-3571
In the Dolomitic region, abundant coarse hillslope sediment is commonly found at the toe of rocky cliffs. Ephemeral channels originate where lower permeability bedrock surfaces concentrate surface runoff. Debris flows initiate along such channels following intense rainfall and determine the progressive erosion and deepening of the channels. Sediment recharge mechanisms include rock fall, dry ravel processes and channel-bank failures. Here we document debris flow activity that took place in an active debris flow basin during the year 2015. The Cancia basin is located on the southwestern slope of Mount Antelao (3264 m a.s.l.) in the dolomitic region of the eastern Italian Alps. The 2.5 km2 basin is incised in dolomitic limestone rocks. The data consist of repeated topographic surveys, distributed rainfall measurements, time-lapse (2 s) videos of two events and pore pressure measurements in the channel bed. During July and August 2015, two debris flow events occurred, following similarly intense rainstorms. We compared rainfall data to existing rainfall triggering thresholds and simulated the hydrological response of the headwater catchment with a distributed model in order to estimate the total and peak water discharge. Our data clearly illustrate how debris entrainment along the channel is the main contributor to the overall mobilized volume and that erosion is dominant when the channel slope exceeds 16°. Further downstream, sediment accumulation and depletion occurred alternately for the two successive events, indicating that sediment availability along the channel also influences the flow behaviour along the prevailing-transport reach. The comparison between monitoring data, topographical analysis and hydrological simulation allows the estimation of the average solid concentration of the two events and suggests that debris availability has a significant influence on the debris flow volume. © 2020 John Wiley & Sons, Ltd. 相似文献
90.
Carlo Doglioni 《地学学报》1992,4(2):152-164
It is useful to differentiate between thrust belts that are related to east(E)-dipping or west(W)-dipping subduction. More precisely, these either follow or resist the overall ‘eastward’ mantle flow detected by the hot-spot reference frame. Because of the overall ‘westward’ drift of the lithosphere we find in E-dipping subduction that the basal decollement underlying the eastern plate reaches the surface and involves deep crustal rocks. With W-dipping subduction, however, we find that the basal decollement of the eastern plate is warped as well as subducted. Consequently thrust belts related to E- (or NE-) dipping subduction show conspicuous structural and morphologic relief, involve deep crustal rocks, and are associated with shallow foredeeps. On the other hand, thrust belts related to W- (or SW-) dipping subduction show relatively low structural and morphological relief, involve only shallow upper crustal rocks and are associated with deep foredeeps as well as back-arc extension. The accretionary wedge-foredeep-back-arc basin association is visualized as an overall eastward propagating tectonic wave. The accretionary wedge forms in the frontal parts and generally below sea-level. This is followed by forward migrating extension that cuts the earlier accretionary wedge. Typically such a system occurs in the context of overall W-dipping subduction and is characterized by an arcuate shape (e.g. Carpathians, Apennines, Barbados, etc.). Along the branches of the arc external transpression and internal transtension co-exist but with different sense (i.e. sinistral transpression contrasting with dextral transtension). We also observe that with W-dipping subduction the tangent to a pre- deformation marker is descending into the foredeep at an angle in the range of 1–10° while with E-(or NE-)dipping subduction the same marker would rise towards the hinterland with typical angles of about 5–10°. Foredeep subsidence is mainly controlled by the load of the thrust sheets in thrust belts due to E-(or NE-)dipping subduction and by the roll-back of the subduction hinge in accretionary wedges due to W-dipping subduction. Subsidence or uplift rates in the foredeeps and accretionary wedges related to the two different types of subduction are very different, providing different P-T-t paths in the two geodynamic realms. The present shape and structure of the thrust belts belonging to one of these two general types may help us in reconstructing the location of thinned lithosphere and basin evolution in the past. 相似文献