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排序方式: 共有224条查询结果,搜索用时 23 毫秒
91.
Riccardo Campana Mauro Orlandini Ettore Del Monte Marco Feroci Filippo Frontera 《Experimental Astronomy》2014,37(3):599-613
Low-inclination, low altitude Earth orbits (LEO) are of increasing importance for astrophysical satellites, due to their low background environment. Here, the South Atlantic Anomaly (SAA) is the region with the highest amount of radiation. We study the radiation environment in a LEO (500–600 km altitude, 4° inclination) through the particle background measured by the Particle Monitor (PM) experiment onboard the BeppoSAX satellite, between 1996 and 2002. Using time series of particle count rates measured by PM we construct intensity maps and derive SAA passage times and fluences. The low-latitude SAA regions are found to have an intensity strongly decreasing with altitude and dependent on the magnetic rigidity. The SAA extent, westward drift and strength vs altitude is shown. 相似文献
92.
Bartolini F Cimò F Fusi M Dahdouh-Guebas F Lopes GP Cannicci S 《Marine environmental research》2011,71(1):53-61
A number of studies have suggested that mangrove forests and their faunal components may be pre-adapted to the impact of organic waste discharge, making them possible natural wastewater treatment wetlands. However, the results from recent research are contradictory. Some studies have shown that negative effects, sometimes subtle and difficult to observe, can be detected on specific biotic components of forests subjected to organic pollution. Therefore, the aim of the present study was to investigate possible alterations in the ecosystem engineering activities of a fiddler crab community dominating the landward belts of Kenyan mangrove forests. The total processed sediment produced by burrowing and foraging activities in a population from a peri-urban mangrove area receiving untreated domestic sewage was compared with that from a forest not affected by urban wastewater. The results showed how the peri-urban site hosted a higher biomass of crabs, which produced a significantly lower amount of processed sediment compared with the pristine site, resulting in a lower total top sediment mixing activity of the crabs. Thus, the present study showed a link between sewage exposure and top sediment reworking by crabs, which is potentially beneficial for mangrove growth and ecosystem functioning. This represents a possible example of cryptic ecological degradation in mangal systems. 相似文献
93.
94.
We compared regional biases and transient doubled CO2 sensitivities of nine coupled atmosphere-ocean general circulation models (GCMs) from six international climate modeling
groups. We evaluated biases and responses in winter and summer surface air temperatures and precipitation for seven subcontinental
regions, including those in the 1990 Intergovernmental Panel on Climate Change (IPCC) Scientific Assessment. Regional biases
were large and exceeded the variance among four climatological datasets, indicating that model biases were not primarily due
to uncertainty in observations. Model responses to altered greenhouse forcing were substantial (average temperature change=2.7±0.9 °C, range of precipitation change =−35 to +120% of control). While coupled models include more climate system feedbacks than
earlier GCMs implemented with mixed-layer ocean models, inclusion of a dynamic ocean alone did not improve simulation of long-term
mean climatology nor increase convergence among model responses to altered greenhouse gas forcing. On the other hand, features
of some of the coupled models including flux adjustment (which may have simply masked simulation errors), high horizontal
resolution, and estimation of screen height temperature contributed to improved simulation of long-term surface climate. The
large range of model responses was partly accounted for by inconsistencies in forcing scenarios and transient-simulation averaging
periods. Nonetheless, the models generally had greater agreement in their sensitivities than their controls did with observations.
This suggests that consistent, large-scale response features from an ensemble of model sensitivity experiments may not depend
on details of their representation of present-day climate.
Received: 9 September 1996 / Revised: 31 July 1997 相似文献
95.
Testing of a new single-frequency GNSS carrier phase attitude determination method: land,ship and aircraft experiments 总被引:4,自引:1,他引:3
Global navigation satellite system (GNSS) ambiguity resolution is the process of resolving the unknown cycle ambiguities of
the carrier phase data as integers. The sole purpose of ambiguity resolution is to use the integer ambiguity constraints as
a means of improving significantly on the precision of the remaining GNSS model parameters. In this contribution, we consider
the problem of ambiguity resolution for GNSS attitude determination. We analyse the performance of a new ambiguity resolution
method for GNSS attitude determination. As it will be shown, this method provides a numerically efficient, highly reliable
and robust solution of the nonlinearly constrained integer least-squares GNSS compass estimators. The analyses have been done
by means of a unique set of extensive experimental tests, using simulated as well as actual GNSS data and using receivers
of different manufacturers and type as well as different platforms. The executed field tests cover two static land experiments,
one in the Netherlands and one in Australia, and two dynamic experiments, a low-dynamics vessel experiment and high-dynamics
aircraft experiment. In our analyses, we focus on stand-alone, unaided, single-frequency, single-epoch attitude determination,
as this is the most challenging case of GNSS compass processing. 相似文献
96.
97.
Adriano Ribolini Monica Bini Ilaria Consoloni Ilaria Isola Marta Pappalardo Giovanni Zanchetta Enrique Fucks Laura Panzeri Marco Martini Filippo Terrasi 《Geografiska Annaler: Series A, Physical Geography》2014,96(2):161-176
This paper investigates several wedge structures formed in continental deposits covering marine sediments deposited during MIS 5 along the central Patagonian coast of Argentina. The size and surface microtexture characteristics of the infilling sediments are consistent with a depositional environment dominated by aeolian transport. Fragments of Andean volcanic rocks (glass shards) in the wedge‐fill suggest long‐distance transport via a westerly component of wind direction. The wedges are interpreted as products of deep seasonal frost action in frozen ground, which produced open cracks that filled rapidly with partially non‐local aeolian sediments. Many wedges cross cut carbonate crusts that formed under permafrost conditions in coastal Patagonia. The radiocarbon dating of carbonate crusts yielded an age of 25–27 kyr bp , while wedge‐fill sediments are OSL dated to 14 670 ± 750 yr bp . This indicates that ground wedge formation occurred during a cold event (the Antarctic Cold Reversal period) that interrupted the permafrost degradation following the Last Glacial Maximum. 相似文献
98.
99.
Ettore Cardarelli Michele Cercato Antonio Cerreto Gerardina Di Filippo 《Geophysical Prospecting》2010,58(4):685-695
Near‐surface cavities can pose serious hazards to human safety, especially in highly urbanized town centres. The location of subsurface voids, the estimation of their size and the evaluation of the overburden thickness are necessary to assess the risk of collapse. In this study, electrical resistivity tomography (ERT) and seismic refraction tomography data are integrated in a joint interpretation process for cavity location in the city of Rome. ERT is a well established and widely employed method for cavity detection. However, additional information provided by seismic refraction tomography is capable of eliminating some potential pitfalls in resistivity data interpretation. We propose that the structure of the cavities defined by ERT can be used as a base to optimize seismic refraction tomography investigations within the framework of a joint interpretation process. Data integration and the insertion of a priori information are key issues for reducing the uncertainties associated with the inversion process and for optimizing both acquisition procedures and computation time. Herein, the two geophysical methods are tested on both synthetic and real data and the integration of the results is found to be successful in detecting isolated cavities and in assessing their geometrical characteristics. The cavity location inferred by geophysical non‐invasive methods has been subsequently confirmed by direct inspection. 相似文献
100.
Renzo Sancisi Filippo Fraternali Tom Oosterloo Thijs van der Hulst 《Astronomy and Astrophysics Review》2008,15(3):189-223
Evidence for the accretion of cold gas in galaxies has been rapidly accumulating in the past years. HI observations of galaxies and their environment have brought to light new facts and phenomena which are evidence of ongoing
or recent accretion: (1) A large number of galaxies are accompanied by gas-rich dwarfs or are surrounded by HI cloud complexes, tails and filaments. This suggests ongoing minor mergers and recent arrival of external gas. It may be regarded,
therefore, as direct evidence of cold gas accretion in the local universe. It is probably the same kind of phenomenon of material
infall as the stellar streams observed in the halos of our galaxy and M 31. (2) Considerable amounts of extra-planar HI have been found in nearby spiral galaxies. While a large fraction of this gas is undoubtedly produced by galactic fountains,
it is likely that a part of it is of extragalactic origin. Also the Milky Way has extra-planar gas complexes: the Intermediate-
and High-Velocity Clouds (IVCs and HVCs). (3) Spirals are known to have extended and warped outer layers of HI. It is not clear how these have formed, and how and for how long the warps can be sustained. Gas infall has been proposed
as the origin. (4) The majority of galactic disks are lopsided in their morphology as well as in their kinematics. Also here
recent accretion has been advocated as a possible cause. In our view, accretion takes place both through the arrival and merging
of gas-rich satellites and through gas infall from the intergalactic medium (IGM). The new gas could be added to the halo
or be deposited in the outer parts of galaxies and form reservoirs for replenishing the inner parts and feeding star formation.
The infall may have observable effects on the disk such as bursts of star formation and lopsidedness. We infer a mean “visible”
accretion rate of cold gas in galaxies of at least . In order to reach the accretion rates needed to sustain the observed star formation (), additional infall of large amounts of gas from the IGM seems to be required. 相似文献