1,045 research outputs found
Theoretical models of planetary system formation. II. Post-formation evolution
We extend the results of planetary formation synthesis by computing the
long-term evolution of synthetic systems from the clearing of the gas disk into
the dynamical evolution phase. We use the symplectic integrator SyMBA to
numerically integrate the orbits of planets for 100 Ma, using populations from
previous studies as initial conditions.We show that within the populations
studied, mass and semi-major axis distributions experience only minor changes
from post-formation evolution. We also show that, depending upon their initial
distribution, planetary eccentricities can statistically increase or decrease
as a result of gravitational interactions. We find that planetary masses and
orbital spacings provided by planet formation models do not result in
eccentricity distributions comparable to observed exoplanet eccentricities,
requiring other phenomena such as e.g. stellar fly-bys to account for observed
eccentricities
Theoretical models of planetary system formation: mass vs semi-major axis
Planet formation models have been developed during the last years in order to
try to reproduce the observations of both the solar system, and the extrasolar
planets. Some of these models have partially succeeded, focussing however on
massive planets, and for the sake of simplicity excluding planets belonging to
planetary systems. However, more and more planets are now found in planetary
systems. This tendency, which is a result of both radial velocity, transit and
direct imaging surveys, seems to be even more pronounced for low mass planets.
These new observations require the improvement of planet formation models,
including new physics, and considering the formation of systems. In a recent
series of papers, we have presented some improvements in the physics of our
models, focussing in particular on the internal structure of forming planets,
and on the computation of the excitation state of planetesimals, and their
resulting accretion rate. In this paper, we focus on the concurrent effect of
the formation of more than one planet in the same protoplanetary disc, and show
the effect, in terms of global architecture and composition of this
multiplicity. We use a N-body calculation including collision detection to
compute the orbital evolution of a planetary system. Moreover, we describe the
effect of competition for accretion of gas and solids, as well as the effect of
gravitational interactions between planets. We show that the masses and
semi-major axis of planets are modified by both the effect of competition and
gravitational interactions. We also present the effect of the assumed number of
forming planets in the same system (a free parameter of the model), as well as
the effect of the inclination and eccentricity damping.Comment: accepted in Astronomy and Astrophysic
Discontinuous symplectic capacities
We show that the spherical capacity is discontinuous on a smooth family of
ellipsoidal shells. Moreover, we prove that the shell capacity is discontinuous
on a family of open sets with smooth connected boundaries.Comment: We include generalizations to higher dimensions due to the unknown
referee and Janko Latschev. We add examples of open sets with connected
boundary on which the shell capacity is not continuous. 3rd and 4th version:
minor changes, to appear in J. Fixed Point Theory App
Hepatocyte growth factor in human osteoarthritic cartilage
AbstractObjective Hepatocyte growth factor/scatter factor is a potent mitogen, morphogen and motogen for a variety of mainly epithelial cells. Hepatocyte growth factor is synthesized by mesenchymal cells and can be found in various tissues. The objective of this study was to investigate the expression and distribution patterns of this pleiotropic growth factor and its receptor, the product of the proto-oncogene c-met in normal and osteoarthritic human knee cartilage.Methods Five normal and 14 osteoarthritic human cartilage samples graded histomorphologically by Mankin Score, were studied by radioactive in-situ hybridization and immunohistochemistry for the expression of Hepatocyte growth factor and the c-met receptor.Results Hepatocyte growth factor could be found by immunohistochemistry in the territorial matrix surrounding the chondrocytes of calcified cartilage and within the deep zone of normal cartilage. Chondrocytes of these cartilage zones showed also positive c-met receptor-staining. Moreover, a small number of chondrocytes in the superficial and intermediate zone showed c-met staining. In accordance with the increased hepatocyte growth factor staining of osteoarthritic cartilage, an enhanced expression of hepatocyte growth factor-RNA by chondrocytes of the deep zone as well as the deeper mid zone was observed. Contrary to normal cartilage,c-met was identified immunohistochemically in osteoarthritic chondrocytes of all cartilage zones.Conclusion These results indicate that hepatocyte growth factor seems to be acting in an autocrine/paracrine manner in normal and osteoarthritic cartilage. The ubiquitous presence of the HGF/HGF-receptor complex in osteoarthritic chondrocytes suggests that hepatocyte growth factor may contribute to the altered metabolism in osteoarthritic cartilage.{copy
Probing single-photon ionization on the attosecond time scale
We study photoionization of argon atoms excited by attosecond pulses using an
interferometric measurement technique. We measure the difference in time delays
between electrons emitted from the and from the shell, at
different excitation energies ranging from 32 to 42 eV. The determination of
single photoemission time delays requires to take into account the measurement
process, involving the interaction with a probing infrared field. This
contribution can be estimated using an universal formula and is found to
account for a substantial fraction of the measured delay.Comment: 4 pages, 4 figures, under consideratio
Development of improved inhibitors of wall teichoic acid biosynthesis with potent activity against Staphylococcus aureus
A small molecule (1835F03) that inhibits Staphylococcus aureus wall teichoic acid biosynthesis, a proposed antibiotic target, has been discovered. Rapid, parallel, solution-phase synthesis was employed to generate a focused library of analogs, providing detailed information about structure–activity relationships and leading to the identification of targocil, a potent antibiotic
Status of the ALICE magnet system
ALICE is the LHC experiment dedicated to heavy ion (Pb, Ca) physics. ALICE will be installed in point 2 of LHC, the former point 2 of LEP. The luminosity at the interaction point will be in the order of 10 /sup 27/ (10/sup 31/ for p-p). Consequently, the radiation level in ALICE will be comparatively low. We will use the existing infrastructure. Therefore, no noticeable civil engineering work will be necessary. Minor modifications will be made to gain a second access to the experiment cavern-mainly for the union arm spectrometer. ALICE will reuse the L3 solenoid, which is already installed and has been used in LEP as spectrometer magnet. A dipole magnet with a very large aperture is in addition required for the Dimuon Arm spectrometer and will be installed next to the L3 solenoid. The detectors in ALICE are concentrated around the IP inside L3 (Barrel) and along the muon arm. Some small forward detectors will be located toward the injection area at a larger distance from IP (~100 m). After a review of the present status of both projects some important milestones will be highlighted in the conclusion. (9 refs)
Planetesimal fragmentation and giant planet formation: the role of planet migration
In the standard model of core accretion, the cores of the giant planets form by the accretion of planetesimals. In this scenario, the evolution of the planetesimal population plays an important role in the formation of massive cores. Recently, we studied the role of planetesimal fragmentation in the in situ formation of a giant planet. However, the exchange of angular momentum between the planet and the gaseous disk causes the migration of the planet in the disk. In this new work, we incorporate the migration of the planet and study the role of planet migration in the formation of a massive core when the population of planetesimals evolves by planet accretion, migration, and fragmentation.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
Planetesimal fragmentation and giant planet formation: the role of planet migration
In the standard model of core accretion, the cores of the giant planets form by the accretion of planetesimals. In this scenario, the evolution of the planetesimal population plays an important role in the formation of massive cores. Recently, we studied the role of planetesimal fragmentation in the in situ formation of a giant planet. However, the exchange of angular momentum between the planet and the gaseous disk causes the migration of the planet in the disk. In this new work, we incorporate the migration of the planet and study the role of planet migration in the formation of a massive core when the population of planetesimals evolves by planet accretion, migration, and fragmentation.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
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