653 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
Mapping the Region in the Nearest Star System to Search for Habitable Planets
Circumstellar planets within the alpha Centauri AB star system have been suggested through formation models and recent observations, and ACESat (Belikov et al. AAS Meeting #225, #311.01, 2015) is a proposed space mission designed to directly image Earth-sized planets in the habitable zones of both of these stars. The alpha Centauri system is billions of years old, so planets are only expected to be found in regions where their orbits are long-lived. We evaluate the extent of the regions within the alpha Centauri AB star system where small planets are able to orbit for billion-year timescales and we map the positions in the sky plane where planets on stable orbits about either stellar component may appear. We confirm the qualitative results of Wiegert & Holman (Astron. J. 113, 1445, 1997) regarding the approximate size of the regions of stable orbits, which are larger for retrograde orbits relative to the binary than for prograde orbits. Additionally, we find that mean motion resonances with the binary orbit leave an imprint on the limits of orbital stability, and the effects of the Lidov-Kozai mechanism are also readily apparent. Overall, orbits in the habitable zones near the plane of the binary are stable, whereas high-inclination orbits are short-lived
Treatment of secondary hyperparathyroidism in kidney disease: what we know and do not know about use of calcimimetics and vitamin D analogs
There is a growing understanding of the pathophysiology of secondary hyperparathyroidism (SHPT) and a recent emergence of new agents for SHPT treatment in patients with advanced kidney disease. At the same time, appreciation that mineral metabolic derangements promote vascular calcification and contribute to excess mortality, along with recognition of potentially important “non-classical” actions of vitamin D, have prompted the nephrology community to reexamine the use of various SHPT treatments, such as activated vitamin D sterols, phosphate binders, and calcimimetics. In this review, the evidence for treatment of SHPT with calcimimetics and vitamin D analogs is evaluated, with particular consideration given to recent clinical trials that have reported encouraging findings with cinacalcet use. Additionally, several controversies in the pathogenesis and treatment of SHPT are explored. The proposition that calcitriol deficiency is a true pathological state is challenged, the relative importance of the vitamin D receptor and the calcium sensing receptor in parathyroid gland function is summarized, and the potential relevance of non-classical actions of vitamin D for patients with advanced renal disease is examined. Taken collectively, the balance of evidence now supports a treatment paradigm in which calcimimetics are the most appropriate primary treatment for SHPT in the majority of end stage renal disease patients, but which nevertheless acknowledges an important role for modest doses of activated vitamin D sterols
A Blueprint for the Charles City Public School’s “Community Den”
Charles City County Public Schools (CCPS) submitted a Request for Assistance to work with a capstone team that would conduct a thorough analysis of the Community Den program and offer a blueprint that would sustain the Den’s efforts well into the future. To address this request, a doctoral Capstone team primarily utilized qualitative methods of data collection in a 3-phrase approach, including, an extensive process of literature review, asset mapping, which is a strength-based approach of connecting communities with resources, document analysis, site visits, interviews, and focus groups. These approaches allowed the capstone team to gain a better understanding of the resources available to the Community Den, the needs of the students and community members it serves, and existing best practices in rural community resource and support initiatives. Findings indicated that improving access to resources, prioritizing community connection, increasing student engagement, and optimizing the physical space as critical elements for the Community Den successful operation. Recommendations focused on opportunities for student engagement, marketing outreach, community engagement, improvements for data management, and physical spacing were formatted as initial steps within the blueprint to improve the overall operations of the Community Den
The Stability of the Suggested Planet in the nu Octantis System: A Numerical and Statistical Study
We provide a detailed theoretical study aimed at the observational finding
about the nu Octantis binary system that indicates the possible existence of a
Jupiter-type planet in this system. If a prograde planetary orbit is assumed,
it has earlier been argued that the planet, if existing, should be located
outside the zone of orbital stability. However, a previous study by Eberle &
Cuntz (2010) [ApJ 721, L168] concludes that the planet is most likely stable if
assumed to be in a retrograde orbit with respect to the secondary system
component. In the present work, we significantly augment this study by taking
into account the observationally deduced uncertainty ranges of the orbital
parameters for the stellar components and the suggested planet. Furthermore,
our study employs additional mathematical methods, which include monitoring the
Jacobi constant, the zero velocity function, and the maximum Lyapunov exponent.
We again find that the suggested planet is indeed possible if assumed to be in
a retrograde orbit, but it is virtually impossible if assumed in a prograde
orbit. Its existence is found to be consistent with the deduced system
parameters of the binary components and of the suggested planet, including the
associated uncertainty bars given by observations.Comment: 11 pages, 10 figures, 3 tables; Monthly Notices of the Royal
Astronomical Society (in press
- …