Origin and Dynamics of the Mutually Inclined Orbits of Upsilon Andromedae c and d

We evaluate the orbital evolution and several plausible origins scenarios for the mutually inclined orbits of Upsilon Andromedae c and d. These two planets have orbital elements that oscillate with large amplitudes and lie close to the stability boundary. This configuration, and in particular the observed mutual inclination, demands an explanation. The planetary system may be influenced by a nearby low-mass star, Upsilon And B, which could perturb the planetary orbits, but we find it cannot modify two coplanar orbits into the observed mutual inclination of ~30 deg. However, it could incite ejections or collisions between planetary companions that subsequently raise the mutual inclination to >30 deg. Our simulated systems with large mutual inclinations tend to be further from the stability boundary than Upsilon And, but we are able to produce similar systems. We conclude that scattering is a plausible mechanism to explain the observed orbits of Upsilon And c and d, but we cannot determine whether the scattering was caused by instabilities among the planets themselves or by perturbations from Upsilon And B. We also develop a procedure to quantitatively compare numerous properties of the observed system to our numerical models. Although we only implement this procedure to Upsilon And, it may be applied to any exoplanetary system.Comment: 19 pages, 5 figures, accepted to Astrophysical Journa

A Statistical Examination of the Short Term Stability of the Upsilon Andromedae System

Because of the high eccentricities (~0.3) of two of the possible planets about the star Upsilon Andromeda, the stability of the system requires careful study. We present results of 1000 numerical simulations which explore the orbital parameter space as constrained by the observations. The orbital parameters of each planet are chosen from a Gaussian error distribution, and the resulting configuration is integrated for 1,000,000 years. We find that 84% of these integrations are stable. Configurations in which the eccentricity of the third planet is 0.45 the system is always unstable, typically producing a close encounter between the second and third planets. A similar exercise with the gas giants in our own Solar System sampled with the same error distribution was performed. Approximately 81% of these simulations were stable for 10^6 years.Comment: 12 pages, 1 figure, submitted to Ap

The flattening and the orbital structure of early-type galaxies and collisionless N-body binary disk mergers

We use oblate axisymmetric dynamical models including dark halos to determine the orbital structure of intermediate mass to massive Coma early-type galaxies. We find a large variety of orbital compositions. Averaged over all sample galaxies the unordered stellar kinetic energy in the azimuthal and the radial direction are of the same order, but they can differ by up to 40 percent in individual systems. In contrast, both for rotating and non-rotating galaxies the vertical kinetic energy is on average smaller than in the other two directions. This implies that even most of the rotating ellipticals are flattened by an anisotropy in the stellar velocity dispersions. Using three-integral axisymmetric toy models we show that flattening by stellar anisotropy maximises the entropy for a given density distribution. Collisionless disk merger remnants are radially anisotropic. The apparent lack of strong radial anisotropy in observed early-type galaxies implies that they may not have formed from mergers of disks unless the influence of dissipational processes was significant.Comment: 14 pages, 8 figures; accepted for publication in MNRA

ROCKETSHIP: a flexible and modular software tool for the planning, processing and analysis of dynamic MRI studies

Background: Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a promising technique to characterize pathology and evaluate treatment response. However, analysis of DCE-MRI data is complex and benefits from concurrent analysis of multiple kinetic models and parameters. Few software tools are currently available that specifically focuses on DCE-MRI analysis with multiple kinetic models. Here, we developed ROCKETSHIP, an open-source, flexible and modular software for DCE-MRI analysis. ROCKETSHIP incorporates analyses with multiple kinetic models, including data-driven nested model analysis. Results: ROCKETSHIP was implemented using the MATLAB programming language. Robustness of the software to provide reliable fits using multiple kinetic models is demonstrated using simulated data. Simulations also demonstrate the utility of the data-driven nested model analysis. Applicability of ROCKETSHIP for both preclinical and clinical studies is shown using DCE-MRI studies of the human brain and a murine tumor model. Conclusion: A DCE-MRI software suite was implemented and tested using simulations. Its applicability to both preclinical and clinical datasets is shown. ROCKETSHIP was designed to be easily accessible for the beginner, but flexible enough for changes or additions to be made by the advanced user as well. The availability of a flexible analysis tool will aid future studies using DCE-MRI

The transition between hole-pairs and four-hole clusters in four-leg tJ ladders

Holes weakly doped into a four-leg \tj ladder bind in pairs. At dopings exceeding a critical doping of $\delta_c\simeq {1/8}$ four hole clusters are observed to form in DMRG calculations. The symmetry of the ground state wavefunction does not change and we are able to reproduce this behavior qualitatively with an effective bosonic model in which the four-leg ladder is represented as two coupled two-leg ladders and hole-pairs are mapped on hard core bosons moving along and between these ladders. At lower dopings, $\delta<\delta_c$, a one dimensional bosonic representation for hole-pairs works and allows us to calculate accurately the Luttinger liquid parameter \krho, which takes the universal value \krho=1 as half-filling is approached

Modelling tsunami inundation on coastlines with characteristic form

This paper provides an indication of the likely difference in tsunami amplification and dissipation between different characteristic coastal embayments, coastal entrances and estuaries. Numerical modeling is performed with the ANU/Geoscience Australia tsunami inundation model. Characteristic coastal morphology is represented by simpler generic morphological shapes which can be applied easily in the ANUGA model, such that key non-dimensional parameters (e.g. embayment depth/bay width) can be varied. Modeling is performed with a range of bay shapes, seabed gradient and different incident tsunami wave shapes and wave angles, including sine waves, solitary waves and leading depression Nwaves. The results show a complex pattern for both large and small embayments, with wave breaking an important control on the amplification of the wave between the 20m contour and the shore. For large embayments, the wave run-up can be amplified by a factor six in comparison to the amplitude at the model boundary. For small embayments, the amplification is dependent on the location of the ocean water line, or tidal stage

Sticking under wet conditions: the remarkable attachment abilities of the torrent frog, staurois guttatus

Tree frogs climb smooth surfaces utilising capillary forces arising from an air-fluid interface around their toe pads, whereas torrent frogs are able to climb in wet environments near waterfalls where the integrity of the meniscus is at risk. This study compares the adhesive capabilities of a torrent frog to a tree frog, investigating possible adaptations for adhesion under wet conditions. We challenged both frog species to cling to a platform which could be tilted from the horizontal to an upside-down orientation, testing the frogs on different levels of roughness and water flow. On dry, smooth surfaces, both frog species stayed attached to overhanging slopes equally well. In contrast, under both low and high flow rate conditions, the torrent frogs performed significantly better, even adhering under conditions where their toe pads were submerged in water, abolishing the meniscus that underlies capillarity. Using a transparent platform where areas of contact are illuminated, we measured the contact area of frogs during platform rotation under dry conditions. Both frog species not only used the contact area of their pads to adhere, but also large parts of their belly and thigh skin. In the tree frogs, the belly and thighs often detached on steeper slopes, whereas the torrent frogs increased the use of these areas as the slope angle increased. Probing small areas of the different skin parts with a force transducer revealed that forces declined significantly in wet conditions, with only minor differences between the frog species. The superior abilities of the torrent frogs were thus due to the large contact area they used on steep, overhanging surfaces. SEM images revealed slightly elongated cells in the periphery of the toe pads in the torrent frogs, with straightened channels in between them which could facilitate drainage of excess fluid underneath the pad

The spin-orbit interaction as a source of new spectral and transport properties in quasi-one-dimensional systems

We present an exact theoretical study of the effect of the spin-orbit (SO) interaction on the band structure and low temperature transport in long quasi-one-dimensional electron systems patterned in two-dimensional electron gases in zero and weak magnetic fields. We reveal the manifestations of the SO interaction which cannot in principle be observed in higher dimensional systems.Comment: 5 pages including 5 figures; RevTeX; to appear in Phys.Rev.B (Rapid Communications