720 research outputs found
Case Studies of Habitable Trojan Planets in the System of HD 23079
We investigate the possibility of habitable Trojan planets in the HD 23079
star-planet system. This system consists of a solar-type star and a
Jupiter-type planet, which orbits the star near the outer edge of the stellar
habitable zone in an orbit of low eccentricity. We find that in agreement with
previous studies Earth-mass habitable Trojan planets are possible in this
system, although the success of staying within the zone of habitability is
significantly affected by the orbital parameters of the giant planet and by the
initial condition of the theoretical Earth-mass planet. In one of our
simulations, the Earth-mass planet is captured by the giant planet and thus
becomes a habitable moon.Comment: 24 pages, 8 figures, 3 tables; International Journal of Astrobiology
(in press
Aluminum-induced de novo bone formation in the beagle. A parathyroid hormone-dependent event.
L'aluminium stimule la néo-ostéogenèse et produit un bilan osseux positif. Cependant cet effet semble dépendre de la disponibilité d'un pool d'ostéoblastes fonctionnels qui, s'il est réduit par la thyroparathyroïdectomie limite l'expression de la néoformation d'os provoquée par l'aluminium
The Instability Transition for the Restricted 3-Body Problem. III. The Lyapunov Exponent Criterion
We establish a criterion for the stability of planetary orbits in stellar
binary systems by using Lyapunov exponents and power spectra for the special
case of the circular restricted 3-body problem (CR3BP). The centerpiece of our
method is the concept of Lyapunov exponents, which are incorporated into the
analysis of orbital stability by integrating the Jacobian of the CR3BP and
orthogonalizing the tangent vectors via a well-established algorithm originally
developed by Wolf et al. The criterion for orbital stability based on the
Lyapunov exponents is independently verified by using power spectra. The
obtained results are compared to results presented in the two previous papers
of this series. It is shown that the maximum Lyapunov exponent can be used as
an indicator for chaotic behaviour of planetary orbits, which is consistent
with previous applications of this method, particularly studies for the Solar
System. The chaotic behaviour corresponds to either orbital stability or
instability, and it depends solely on the mass ratio of the binary components
and the initial distance ratio of the planet relative to the stellar separation
distance. Our theoretical results allow us to link the study of planetary
orbital stability to chaos theory noting that there is a large array of
literature on the properties and significance of Lyapunov exponents. Although
our results are given for the special case of the CR3BP, we expect that it may
be possible to augment the proposed Lyapunov exponent criterion to studies of
planets in generalized stellar binary systems, which is strongly motivated by
existing observational results as well as results expected from ongoing and
future planet search missions.Comment: 10 pages, 8 figures, 3 tables; accepted by Astronomy and Astrophysic
Multimodality Imaging of Abnormal Vascular Perfusion and Morphology in Preclinical 9L Gliosarcoma Model
This study demonstrates that a dynamic susceptibility contrast-magnetic resonance imaging (DSC-MRI) perfusion parameter may indicate vascular abnormality in a brain tumor model and reflects an effect of dexamethasone treatment. In addition, X-ray computed tomography (CT) measurements of vascular tortuosity and tissue markers of vascular morphology were performed to investigate the underpinnings of tumor response to dexamethasone.One cohort of Fisher 344 rats (N = 13), inoculated intracerebrally with 9L gliosarcoma cells, was treated with dexamethasone (i.p. 3 mg/kg/day) for five consecutive days, and another cohort (N = 11) was treated with equal volume of saline. Longitudinal DSC-MRI studies were performed at the first (baseline), third and fifth day of treatments. Relative cerebral blood volume (rCBV) was significantly reduced on the third day of dexamethasone treatment (0.65 ± .13) as compared to the fifth day during treatment (1.26 ±.19, p < 0.05). In saline treated rats, relative CBV gradually increased during treatment (0.89 ±.13, 1.00 ± .21, 1.13 ± .23) with no significant difference on the third day of treatment (p>0.05). In separate serial studies, microfocal X-ray CT of ex vivo brain specimens (N = 9) and immunohistochemistry for endothelial cell marker anti-CD31 (N = 8) were performed. Vascular morphology of ex vivo rat brains from micro-CT analysis showed hypervascular characteristics in tumors, and both vessel density (41.32 ± 2.34 branches/mm(3), p<0.001) and vessel tortuosity (p<0.05) were significantly reduced in tumors of rats treated with dexamethasone compared to saline (74.29 ± 3.51 branches/mm(3)). The vascular architecture of rat brain tissue was examined with anti-CD31 antibody, and dexamethasone treated tumor regions showed reduced vessel area (16.45 ± 1.36 µm(2)) as compared to saline treated tumor regions (30.83 ± 4.31 µm(2), p<0.001) and non-tumor regions (22.80 ± 1.11 µm(2), p<0.01).Increased vascular density and tortuosity are culprit to abnormal perfusion, which is transiently reduced during dexamethasone treatment
Planetary Candidates Observed by Kepler. VII. The First Fully Uniform Catalog Based on The Entire 48 Month Dataset (Q1-Q17 DR24)
We present the seventh Kepler planet candidate catalog, which is the first to
be based on the entire, uniformly processed, 48 month Kepler dataset. This is
the first fully automated catalog, employing robotic vetting procedures to
uniformly evaluate every periodic signal detected by the Q1-Q17 Data Release 24
(DR24) Kepler pipeline. While we prioritize uniform vetting over the absolute
correctness of individual objects, we find that our robotic vetting is overall
comparable to, and in most cases is superior to, the human vetting procedures
employed by past catalogs. This catalog is the first to utilize artificial
transit injection to evaluate the performance of our vetting procedures and
quantify potential biases, which are essential for accurate computation of
planetary occurrence rates. With respect to the cumulative Kepler Object of
Interest (KOI) catalog, we designate 1,478 new KOIs, of which 402 are
dispositioned as planet candidates (PCs). Also, 237 KOIs dispositioned as false
positives (FPs) in previous Kepler catalogs have their disposition changed to
PC and 118 PCs have their disposition changed to FP. This brings the total
number of known KOIs to 8,826 and PCs to 4,696. We compare the Q1-Q17 DR24 KOI
catalog to previous KOI catalogs, as well as ancillary Kepler catalogs, finding
good agreement between them. We highlight new PCs that are both potentially
rocky and potentially in the habitable zone of their host stars, many of which
orbit solar-type stars. This work represents significant progress in accurately
determining the fraction of Earth-size planets in the habitable zone of
Sun-like stars. The full catalog is publicly available at the NASA Exoplanet
Archive.Comment: Accepted to the Astrophysical Journal Supplement Series. 30 pages, 9
figures, 7 tables. We make the DR24 robovetter decision code publicly
available at http://github.com/JeffLCoughlin/robovetter, with input and
output examples provided using the same data as contained in the full paper's
table
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