69 research outputs found
OSSOS. V. Diffusion in the Orbit of a High-perihelion Distant Solar System Object
We report the discovery of the minor planet 2013 SY, on an
exceptionally distant, highly eccentric orbit. With a perihelion of 50.0 au,
2013 SY's orbit has a semi-major axis of au, the largest
known for a high-perihelion trans-Neptunian object (TNO), well beyond those of
(90377) Sedna and 2012 VP. Yet, with an aphelion of au,
2013 SY's orbit is interior to the region influenced by Galactic tides.
Such TNOs are not thought to be produced in the current known planetary
architecture of the Solar System, and they have informed the recent debate on
the existence of a distant giant planet. Photometry from the
Canada-France-Hawaii Telescope, Gemini North and Subaru indicate 2013 SY
is km in diameter and moderately red in colour, similar to other
dynamically excited TNOs. Our dynamical simulations show that Neptune's weak
influence during 2013 SY's perihelia encounters drives diffusion in its
semi-major axis of hundreds of astronomical units over 4 Gyr. The overall
symmetry of random walks in semi-major axis allow diffusion to populate 2013
SY's orbital parameter space from the 1000-2000 au inner fringe of the
Oort cloud. Diffusion affects other known TNOs on orbits with perihelia of 45
to 49 au and semi-major axes beyond 250 au, providing a formation mechanism
that implies an extended population, gently cycling into and returning from the
inner fringe of the Oort cloud.Comment: First reviewer report comments incorporated. Comments welcom
Morphometric comparison between hatchery-reared and wild-caught megalopae of the mangrove crab
Dynamic protein methylation in chromatin biology
Post-translational modification of chromatin is emerging as an increasingly important regulator of chromosomal processes. In particular, histone lysine and arginine methylation play important roles in regulating transcription, maintaining genomic integrity, and contributing to epigenetic memory. Recently, the use of new approaches to analyse histone methylation, the generation of genetic model systems, and the ability to interrogate genome wide histone modification profiles has aided in defining how histone methylation contributes to these processes. Here we focus on the recent advances in our understanding of the histone methylation system and examine how dynamic histone methylation contributes to normal cellular function in mammals
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo
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OSSOS. XXVI. On the Lack of Catastrophic Collisions in the Present Kuiper Belt
We investigate different conditions, including the orbital and size-frequency distribution (SFD) of the early Kuiper Belt, that can trigger catastrophic planetesimal destruction. The goal of this study is to test if there is evidence for collisional grinding in the Kuiper Belt that has occurred since its formation. This analysis has important implications for whether the present-day SFD of the cold classical trans-Neptunian objects (TNOs) is a result of collisional equilibrium or if it reflects the primordial stage of planetesimal accretion. As an input to our modeling, we use the most up-to-date debiased OSSOS++ ensemble sample of the TNO population and orbital model based on the present-day architecture of the Kuiper Belt. We calculate the specific impact energies between impactor-target pairs from different TNO groups and compare our computed energies to catastrophic disruption results from smoothed particle hydrodynamics simulations. We explore different scenarios by considering different total primordial Kuiper Belt masses and power slopes of the SFD and allowing collisions to take place over different timescales. The collisional evolution of the Kuiper Belt is a strong function of the unknown initial mass in the trans-Neptunian region, where collisional grinding of planetesimals requires a total primordial Kuiper Belt mass of M > 5 M ⊕, collision speeds as high as 3 km s−1, and collisions over at least 0.5 Gyr. We conclude that presently, most of the collisions in the trans-Neptunian region are in the cratering rather than disruption regime. Given the low collision rates among the cold classical Kuiper Belt objects, their SFD most likely represents the primordial planetesimal accretion. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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Col-OSSOS: The Distribution of Surface Classes in Neptune's Resonances
The distribution of surface classes of resonant trans-Neptunian objects (TNOs) provides constraints on the protoplanetesimal disk and giant planet migration. To better understand the surfaces of TNOs, the Colours of the Outer Solar System Origins Survey acquired multiband photometry of 102 TNOs and found that the surfaces of TNOs can be well described by two surface classifications: BrightIR and FaintIR. These classifications both include optically red members and are differentiated predominantly based on whether their near-infrared spectral slope is similar to their optical spectral slope. The vast majority of cold classical TNOs, with dynamically quiescent orbits, have the FaintIR surface classification, and we infer that TNOs in other dynamical classifications with FaintIR surfaces share a common origin with the cold classical TNOs. Comparison between the resonant populations and the possible parent populations of cold classical and dynamically excited TNOs reveal that the 3:2 has minimal contributions from the FaintIR class, which could be explained by the ν 8 secular resonance clearing the region near the 3:2 before any sweeping capture occurred. Conversely, the fraction of FaintIR objects in the 4:3 resonance, 2:1 resonance, and the resonances within the cold classical belt suggest that the FaintIR surface formed in the protoplanetary disk between ≳34.6 and ≲47 au, though the outer bound depends on the degree of resonance sweeping during migration. The presence and absence of the FaintIR surfaces in Neptune’s resonances provides critical constraints for the history of Neptune’s migration, the evolution of the ν 8, and the surface class distribution in the initial planetesimal disk. © 2023. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
OSSOS. XVII. An upper limit on the number of distant planetary objects in the Solar System
International audienceBeyond the giant planets there is a collection of bodies left over from the epoch of planet formation. The objects that are just beyond Neptune are more easily detected than those that journey hundreds of au away; all such highly eccentric objects have been observed inside 150 au. We are interested here in a population of Pluto to Mars-sized planets that were almost certainly present in the early Solar System, some of which may now be stranded in the distant Solar System. Using data from the Outer Solar System Origins Survey (OSSOS), which covers ~167 square degrees down to r ~25, we searched for objects beyond 300 au using a rarely used search technique. To find such objects we created catalogues of all the sources that were stationary (to the level of the astronomical seeing) in three images taken over 2 h. We then searched for which such 'stationary' objects were not present days/weeks/months before and after. Although other astronomical phenomena (e.g. supernovae) were discovered, no slow moving Solar System object was found. From the null detection and using a survey simulator, we obtain a model-dependent 95% upper limit of ~1000 on the number of 'planetary' objects (with absolute magnitudes, H r , <2) in the distant Solar System. To our knowledge this is the first published limit for objects of this scale beyond 300 au. We show that if there are a small number of Mars-scale objects still in the distant Solar System, despite being brighter they may have escaped detection in other surveys due to their slow rates of motion
Brain stem auditory evoked potentials in patients with multiple system atrophy with progressive autonomic failure (Shy-Drager syndrome).
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