3,025 research outputs found
Dynamical Stability and Habitability of Gamma Cephei Binary-Planetary System
It has been suggested that the long-lived residual radial velocity variations
observed in the precision radial velocity measurements of the primary of Gamma
Cephei (HR8974, HD222404, HIP116727) are likely due to a Jupiter-like planet
around this star (Hatzes et al, 2003). In this paper, the orbital dynamics of
this plant is studied and also the possibility of the existence of a
hypothetical Earth-like planet in the habitable zone of its central star is
discussed. Simulations, which have been carried out for different values of the
eccentricity and semimajor axis of the binary, as well as the orbital
inclination of its Jupiter-like planet, expand on previous studies of this
system and indicate that, for the values of the binary eccentricity smaller
than 0.5, and for all values of the orbital inclination of the Jupiter-like
planet ranging from 0 to 40 degrees, the orbit of this planet is stable. For
larger values of the binary eccentricity, the system becomes gradually
unstable. Integrations also indicate that, within this range of orbital
parameters, a hypothetical Earth-like planet can have a long-term stable orbit
only at distances of 0.3 to 0.8 AU from the primary star. The habitable zone of
the primary, at a range of approximately 3.1 to 3.8 AU, is, however, unstable.Comment: 25 pages, 7 figures, 3 tables, submitted for publicatio
Differential Solute Regulation in Leaf Blades of Various Ages in Salt-Sensitive Wheat and a Salt-Tolerant Wheat x Lophopyrum elongatum (Host) A. Love Amphiploid
Where are the Uranus Trojans?
The area of stable motion for fictitious Trojan asteroids around Uranus'
equilateral equilibrium points is investigated with respect to the inclination
of the asteroid's orbit to determine the size of the regions and their shape.
For this task we used the results of extensive numerical integrations of orbits
for a grid of initial conditions around the points L4 and L5, and analyzed the
stability of the individual orbits. Our basic dynamical model was the Outer
Solar System (Jupiter, Saturn, Uranus and Neptune). We integrated the equations
of motion of fictitious Trojans in the vicinity of the stable equilibrium
points for selected orbits up to the age of the Solar system of 5 billion
years. One experiment has been undertaken for cuts through the Lagrange points
for fixed values of the inclinations, while the semimajor axes were varied. The
extension of the stable region with respect to the initial semimajor axis lies
between 19.05 < a < 19.3 AU but depends on the initial inclination. In another
run the inclination of the asteroids' orbit was varied in the range 0 < i < 60
and the semimajor axes were fixed. It turned out that only four 'windows' of
stable orbits survive: these are the orbits for the initial inclinations 0 < i
< 7, 9 < i < 13, 31 < i < 36 and 38 < i < 50. We postulate the existence of at
least some Trojans around the Uranus Lagrange points for the stability window
at small and also high inclinations.Comment: 15 pages, 12 figures, submitted to CMD
An Overview of the 13:8 Mean Motion Resonance between Venus and Earth
It is known since the seminal study of Laskar (1989) that the inner planetary
system is chaotic with respect to its orbits and even escapes are not
impossible, although in time scales of billions of years. The aim of this
investigation is to locate the orbits of Venus and Earth in phase space,
respectively to see how close their orbits are to chaotic motion which would
lead to unstable orbits for the inner planets on much shorter time scales.
Therefore we did numerical experiments in different dynamical models with
different initial conditions -- on one hand the couple Venus-Earth was set
close to different mean motion resonances (MMR), and on the other hand Venus'
orbital eccentricity (or inclination) was set to values as large as e = 0.36 (i
= 40deg). The couple Venus-Earth is almost exactly in the 13:8 mean motion
resonance. The stronger acting 8:5 MMR inside, and the 5:3 MMR outside the 13:8
resonance are within a small shift in the Earth's semimajor axis (only 1.5
percent). Especially Mercury is strongly affected by relatively small changes
in eccentricity and/or inclination of Venus in these resonances. Even escapes
for the innermost planet are possible which may happen quite rapidly.Comment: 14 pages, 11 figures, submitted to CMD
Stability of Terrestrial Planets in the Habitable Zone of Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208
We have undertaken a thorough dynamical investigation of five extrasolar
planetary systems using extensive numerical experiments. The systems Gl 777 A,
HD 72659, Gl 614, 47 Uma and HD 4208 were examined concerning the question of
whether they could host terrestrial like planets in their habitable zones
(=HZ). First we investigated the mean motion resonances between fictitious
terrestrial planets and the existing gas giants in these five extrasolar
systems. Then a fine grid of initial conditions for a potential terrestrial
planet within the HZ was chosen for each system, from which the stability of
orbits was then assessed by direct integrations over a time interval of 1
million years. The computations were carried out using a Lie-series integration
method with an adaptive step size control. This integration method achieves
machine precision accuracy in a highly efficient and robust way, requiring no
special adjustments when the orbits have large eccentricities. The stability of
orbits was examined with a determination of the Renyi entropy, estimated from
recurrence plots, and with a more straight forward method based on the maximum
eccentricity achieved by the planet over the 1 million year integration.
Additionally, the eccentricity is an indication of the habitability of a
terrestrial planet in the HZ; any value of e>0.2 produces a significant
temperature difference on a planet's surface between apoapse and periapse. The
results for possible stable orbits for terrestrial planets in habitable zones
for the five systems are summarized as follows: for Gl 777 A nearly the entire
HZ is stable, for 47 Uma, HD 72659 and HD 4208 terrestrial planets can survive
for a sufficiently long time, while for Gl 614 our results exclude terrestrial
planets moving in stable orbits within the HZ.Comment: 14 pages, 18 figures submitted to A&
Anterior versus posterior approach in traumatic thoracolumbar burst fractures deemed for surgical management: Systematic review and meta-analysis
Uncertainties remain regarding the optimal surgical approach in the treatment of traumatic thoracolumbar burst fractures. We aim to compare the surgical, radiological and functional outcomes in anterior versus posterior approaches in patients with traumatic thoracolumbar burst fractures deemed for surgical management. A systematic review adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was performed. Qualitative analysis and where suitable, meta-analysis were performed to compute pooled estimates of the differences between anterior and posterior approaches. A total of six studies (three observational, one prospective non-randomized trial, two randomized controlled trials) were included. There were no cases of postoperative neurological decline. Meta-analysis demonstrates a longer duration (Mean Difference (MD) + 81.68, 95% CI 39.20 to 123.16, p < 0.001) and increased estimated blood loss (MD + 426.27, 95% CI 119.84 to 732.70, p = 0.006) for the anterior approach. No difference between approaches was found regarding length of hospital stay, late postoperative kyphotic angle, construct failure rate, instrumentation revision rate, rate of return to work, and total hospital charges. Limitations include the small number of, and heterogeneity across studies. Given the similarities in neurological, radiological and functional outcomes between the two approaches, the longer duration and estimated blood loss in the anterior approach should be a point of consideration when selecting the surgical approach. There is an urgent need for contemporary, high quality research in this area
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