621 research outputs found
Probing the origin of the dark material on Iapetus
Among the icy satellites of Saturn, Iapetus shows a striking dichotomy
between its leading and trailing hemispheres, the former being significantly
darker than the latter. Thanks to the VIMS imaging spectrometer on-board
Cassini, it is now possible to investigate the spectral features of the
satellites in Saturn system within a wider spectral range and with an enhanced
accuracy than with previously available data. In this work, we present an
application of the G-mode method to the high resolution, visible and near
infrared data of Phoebe, Iapetus and Hyperion collected by Cassini/VIMS, to
search for compositional correlations. We also present the results of a
dynamical study on the efficiency of Iapetus in capturing dust grains
travelling inward in Saturn system to evaluate the viability of
Poynting-Robertson drag as the physical mechanism transferring the dark
material to the satellite. The results of spectroscopic classification are used
jointly with the ones of the dynamical study to describe a plausible physical
scenario for the origin of Iapetus' dichotomy. Our work shows that mass
transfer from the outer Saturnian system is an efficient mechanism,
particularly for the range of sizes hypothesised for the particles composing
the newly discovered outer ring around Saturn. Both spectral and dynamical data
indicate Phoebe as the main source of the dark material. However, we suggest a
multi-source scenario where now extinct prograde satellites and the disruptive
impacts that generated the putative collisional families played a significant
role in supplying the original amount of dark material.Comment: 20 pages, 4 tables, 11 figures, major revision (manuscript extended
and completed, figures added and corrected, new results added), minor
revision and finalization of author list, moderate revision (update of the
manuscript following reviewer's feedback and discovery of the new Saturnian
outer ring
Merging of the USGS Atlas of Mercury 1:5,000,000 Geologic Series
After 30 years, the planet Mercury is going to give us new information. The NASA MESSENGER [1] already made its first successful flyby on December 2007 while the European Space Agency and the Japanese Space Agency ISAS/JAXA are preparing the upcoming mission BepiColombo [2]. In order to contribute to current and future analyses on the geology of Mercury, we have started to work on the production of a single digital geologic map of Mercury derived from the merging process of the geologic maps of the Atlas of Mercury, produced by the United States Geological Survey, based on Mariner 10 data. The aim of this work is to merge the nine maps so that the final product reflects as much as possible the original work. Herein we describe the data we used, the working environment and the steps made for producing the final map
The effect of the Coriolis force on Kelvin-Helmholtz-driven mixing in protoplanetary disks
We study the stability of proto-planetary disks with vertical velocity
gradients in their equilibrium rotation rates; such gradients are expected to
develop when dust settles into the midplane. Using a linear stability analysis
of a simple three-layer model, we show that the onset of instability occurs at
a larger value of the Richardson number, and therefore for a thicker layer,
when the effects of Coriolis forces are included. This analysis also shows that
even-symmetry (midplane-crossing) modes develop faster than odd-symmetry ones.
These conclusions are corroborated by a large number of nonlinear numerical
simulations with two different parameterized prescriptions for the initial
(continuous) dust distributions. Based on these numerical experiments, the
Richardson number required for marginal stability is more than an order of
magnitude larger than the traditional 1/4 value. The dominant modes that grow
have horizontal wavelengths of several initial dust scale heights, and in
nonlinear stages mix solids fairly homogeneously over a comparable vertical
range. We conclude that gravitational instability may be more difficult to
achieve than previously thought, and that the vertical distribution of matter
within the dust layer is likely globally, rather than locally, determined.Comment: Accepted for publication in Ap
Influência de estresse por déficit hídrico em acessos do gênero Paspalum.
Editado por Ana Rita de araújo Nogueira, Simone Cristina Méo Niciur
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Marco Polo: near Earth object sample return mission
Marco Polo is a joint European-Japanese mission of sample return from a Near Earth Object. The Marco Polo proposal was submitted to ESA on July 2007 in the framework of the Cosmic Vision 2015-2025 context, and on October 2007 passed the first evaluation process. The primary objectives of this mission is to visit a primitive NEO, belonging to a class that cannot be related to known meteorite types, to characterize it at multiple scales, and to bring samples back to Earth. Marco Polo will give us the first opportunity for detailed laboratory study of the most primitive materials that formed the planets. This will allow us to improve our knowledge on the processes which governed the origin and early evolution of the Solar System, and possibly of the life on Earth
Avaliação da tolerância de acesso do gênero Paspalum ao sombreamento.
Editado por Ana Rita de Araújo Nogueira, Simone Cristina Meo Niciura
Vascular endothelial growth factor in node-positive breast cancer patients treated with adjuvant tamoxifen
In 212 postmenopausal women with node-positive oestrogen receptor-positive (ER(LBA)) breast cancer subjected to radical surgery and adjuvant tamoxifen, the risk of 6-year relapse increased with increasing values of intratumoral vascular endothelial growth factor (VEGF) in patients whose tumours had a low/intermediate ER(LBA) content compared to patients with high-ER(LBA) tumours. These findings indicate that tumour progression, activated or sustained by high VEGF levels, may be counteracted in high-ER(LBA) cancers by tamoxifen, which in contrast fails to contrast the metastatic potential in low-ER(LBA) tumours
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