Numerical simulations of the type III migration:I. Disc model and convergence tests

We investigate the fast (type III) migration regime of high-mass protoplanets orbiting in protoplanetary disks. This type of migration is dominated by corotational torques. We study the details of flow structure in the planet's vicinity, the dependence of migration rate on the adopted disc model, and the numerical convergence of models (independence of certain numerical parameters such as gravitational softening). We use two-dimensional hydrodynamical simulations with adaptive mesh refinement,based on the FLASH code with improved time-stepping scheme. We perform global disk simulations with sufficient resolution close to the planet, which is allowed to freely move throughout the grid. We employ a new type of equation of state in which the gas temperature depends on both the distance to the star and planet, and a simplified correction for self-gravity of the circumplanetary gas. We find that the migration rate in the type III migration regime depends strongly on the gas dynamics inside the Hill sphere (Roche lobe of the planet) which, in turn, is sensitive to the aspect ratio of the circumplanetary disc. Furthermore, corrections due to the gas self-gravity are necessary to reduce numerical artifacts that act against rapid planet migration. Reliable numerical studies of Type III migration thus require consideration of both the thermal andthe self-gravity corrections, as well as a sufficient spatial resolution and the calculation of disk-planet attraction both inside and outside the Hill sphere. With this proviso, we find Type III migration to be a robust mode of migration, astrophysically promising because of a speed much faster than in the previously studied modes of migration.Comment: 17 pages, 15 figures, submitted to MNRAS. Comments welcom

A comfort comparison of travoprost BAK-free 0.004% versus latanoprost 0.005% in patients with primary open-angle glaucoma or ocular hypertension

David A Godfrey1, Lee S Peplinski2, Jeanette A Stewart3, William C Stewart31Glaucoma Associates of Texas, Dallas, TX, USA; 2Kentuckiana Institute for Eye Research, Louisville, KY, USA; 3PRN Pharmaceutical Research Network, LLC, Dallas, TX, USAPurpose: To determine the short-term comfort after a single dose of travoprost BAK-free compared to latanoprost in primary open-angle glaucoma or ocular hypertensive patients.Design: Prospective, double-masked, randomized comparison of two separate active agents dosed once in opposite eyes.Methods: At Visit 1, qualified patients began a glaucoma medicine-free period for three days. At Visit 2, patients were randomly assigned to travoprost BAK-free or latanoprost in opposite eyes. Following dosing in each eye, patients completed a visual analog scale (VAS score, 0–100 mm) at specified time intervals and a comfort survey.Results: In 54 completed subjects, no difference existed five seconds after dosing, in comfort on the VAS between latanoprost (7.1 ± 16.2 mm) and travoprost BAK-free (7.8 ± 16.1 mm, P = 0.53). Also no differences existed between treatments following dosing for discomfort at individual timepoints past five seconds, peak discomfort or the time required to return to baseline comfort (P > 0.05). In addition, the comfort survey demonstrated no difference between products for burning, stinging, foreign body sensation, overall comfort and general acceptance between the products, both for absolute levels and changes from baseline (P > 0.05).Conclusion: Following a single instillation, both latanoprost and travoprost BAK-free exhibit similar comfort scores.Keywords: comfort, travoprost BAK-free, latanoprost, glaucoma, ocular hypertensio

Numerical simulations of type III planetary migration: III. Outward migration of massive planets

We present a numerical study of rapid, so called type III migration for Jupiter-sized planets embedded in a protoplanetary disc. We limit ourselves to the case of outward migration, and study in detail its evolution and physics, concentrating on the structure of the co-rotation and circumplanetary regions, and processes for stopping migration. We also consider the dependence of the migration behaviour on several key parameters. We perform this study using global, two-dimensional hydrodynamical simulations with adaptive mesh refinement. We find that the outward directed type III migration can be started if the initial conditions support $Z > 1$, that corresponds to initial value M_\rmn{\Delta} \ga 1.5. Unlike the inward directed migration, in the outward migration the migration rate increases due to the growing of the volume of the co-orbital region. We find the migration to be strongly dependent on the rate of the mass accumulation in the circumplanetary disc, leading to two possible regimes of migration, fast and slow. The structure of the co-orbital region and the stopping mechanism differ between these two regimes.Comment: 18 pages, 13 figures, submitted to MNRA

Testing the COncept of Drift Shadow with X-Ray Absorption Imaging

X-ray absorption imaging experiments and measurements of inflow and outflow distribution provide quantitative and vistial evidence for capillary diversion around a drift and a drift-shadow effect. Test cells were constructed from volcanic tuff with either in-plane (one fracture parallel to the face of the test cell) or multi-fracture (with a grid of fractures perpendicular to the test cell) systems. Tracer solutions were dripped in the fractures at ports along the top of the test cell. Discharge along the bottom boundary and in the drift was monitored. Variables included flow rate and fracture aperture. X-ray absorption imaging allowed for visualization of flow paths through the system. Evidence for capillary diversion and drift shadow include: (1) very small (< 1 %,of inflow in most cases) measured discharge into the drift, (2) discharge less than expected under the drift and discharge greater than expected just beyond the drift, and (3) visualization of the tracer-solution flow path from above the drift, around the drift, and shedding beyond the drift. However, tracer was also observed in a natural fracture under the drift in one system. It is unclear whether these high concentrations are due to diversion around the drift and back under the drift or capillary spreading along the bottom boundary of the test cell. Future experiments will focus on using samples collected directly from Yucca Mountain and minimizing the capillary barrier effects along the lower boundary of the test cells. The implementation of the drift shadow effect, as supported by these experiments, could impact performance of the proposed Yucca Mountain repository

Crystal structure of Cu-Sn-In alloys around the {\eta} phase field studied by neutron diffraction

The study of the Cu-Sn-In ternary system has become of great importance in recent years, due to new environmental regulations forcing to eliminate the use of Pb in bonding technologies for electronic devices. A key relevant issue concerns the intermetallic phases which grow in the bonding zone and are determining in their quality and performance. In this work, we focus in the {\eta}-phase (Cu2In or Cu6Sn5) that exists in both end binaries and as a ternary phase. We present a neutron diffraction study of the constitution and crystallography of a series of alloys around the 60 at.% Cu composition, and with In contents ranging from 0 to 25 at.%, quenched from 300\degreeC. The alloys were characterized by scanning electron microscopy, probe microanalysis and high-resolution neutron diffraction. The Rietveld refinement of neutron diffraction data allowed to improve the currently available model for site occupancies in the hexagonal {\eta}-phase in the binary Cu-Sn as well as in ternary alloys. For the first time, structural data is reported in the ternary Cu-Sn-In {\eta}-phase as a function of composition, information that is of fundamental technological importance as well as valuable input data for ongoing modelisations of the ternary phase diagram.Comment: 8 pages, 10 figure

Vortex generation in protoplanetary disks with an embedded giant planet

Vortices in protoplanetary disks can capture solid particles and form planetary cores within shorter timescales than those involved in the standard core-accretion model. We investigate vortex generation in thin unmagnetized protoplanetary disks with an embedded giant planet with planet to star mass ratio $10^{-4}$ and $10^{-3}$. Two-dimensional hydrodynamical simulations of a protoplanetary disk with a planet are performed using two different numerical methods. The results of the non-linear simulations are compared with a time-resolved modal analysis of the azimuthally averaged surface density profiles using linear perturbation theory. Finite-difference methods implemented in polar coordinates generate vortices moving along the gap created by Neptune-mass to Jupiter-mass planets. The modal analysis shows that unstable modes are generated with growth rate of order $0.3 \Omega_K$ for azimuthal numbers m=4,5,6, where $\Omega_K$ is the local Keplerian frequency. Shock-capturing Cartesian-grid codes do not generate very much vorticity around a giant planet in a standard protoplanetary disk. Modal calculations confirm that the obtained radial profiles of density are less susceptible to the growth of linear modes on timescales of several hundreds of orbital periods. Navier-Stokes viscosity of the order $\nu=10^{-5}$ (in units of $a^2 \Omega_p$) is found to have a stabilizing effect and prevents the formation of vortices. This result holds at high resolution runs and using different types of boundary conditions. Giant protoplanets of Neptune-mass to Jupiter-mass can excite the Rossby wave instability and generate vortices in thin disks. The presence of vortices in protoplanetary disks has implications for planet formation, orbital migration, and angular momentum transport in disks.Comment: 14 pages, 15 figures, accepted for publication in A&

In situ visualization of large-scale turbulence simulations in Nek5000 with ParaView Catalyst

In situ visualization on high-performance computing systems allows us to analyze simulation results that would otherwise be impossible, given the size of the simulation data sets and offline post-processing execution time. We develop an in situ adaptor for Paraview Catalyst and Nek5000, a massively parallel Fortran and C code for computational fluid dynamics. We perform a strong scalability test up to 2048 cores on KTH’s Beskow Cray XC40 supercomputer and assess in situ visualization’s impact on the Nek5000 performance. In our study case, a high-fidelity simulation of turbulent flow, we observe that in situ operations significantly limit the strong scalability of the code, reducing the relative parallel efficiency to only ≈ 21 % on 2048 cores (the relative efficiency of Nek5000 without in situ operations is ≈ 99 %). Through profiling with Arm MAP, we identified a bottleneck in the image composition step (that uses the Radix-kr algorithm) where a majority of the time is spent on MPI communication. We also identified an imbalance of in situ processing time between rank 0 and all other ranks. In our case, better scaling and load-balancing in the parallel image composition would considerably improve the performance of Nek5000 with in situ capabilities. In general, the result of this study highlights the technical challenges posed by the integration of high-performance simulation codes and data-analysis libraries and their practical use in complex cases, even when efficient algorithms already exist for a certain application scenario

The dynamical role of the circumplanetary disc in planetary migration

Numerical simulations of planets embedded in protoplanetary gaseous discs are a precious tool for studying the planetary migration ; however, some approximations have to be made. Most often, the selfgravity of the gas is neglected. In that case, it is not clear in the literature how the material inside the Roche lobe of the planet should be taken into account. Here, we want to address this issue by studying the influence of various methods so far used by different authors on the migration rate. We performed high-resolution numerical simulations of giant planets embedded in discs. We compared the migration rates with and without gas selfgravity, testing various ways of taking the circum-planetary disc (CPD) into account. Different methods lead to significantly different migration rates. Adding the mass of the CPD to the perturbing mass of the planet accelerates the migration. Excluding a part of the Hill sphere is a very touchy parameter that may lead to an artificial suppression of the type III, runaway migration. In fact, the CPD is smaller than the Hill sphere. We recommend excluding no more than a 0.6 Hill radius and using a smooth filter. Alternatively, the CPD can be given the acceleration felt by the planet from the rest of the protoplanetary disc. The gas inside the Roche lobe of the planet should be very carefully taken into account in numerical simulations without any selfgravity of the gas. The entire Hill sphere should not be excluded. The method used should be explicitly given. However, no method is equivalent to computing the full selfgravity of the gas.Comment: 15 pages, 19 figures (most in color), in press in Astronomy and Astrophysic

A comparative study of disc-planet interaction

We perform numerical simulations of a disc-planet system using various grid-based and smoothed particle hydrodynamics (SPH) codes. The tests are run for a simple setup where Jupiter and Neptune mass planets on a circular orbit open a gap in a protoplanetary disc during a few hundred orbital periods. We compare the surface density contours, potential vorticity and smoothed radial profiles at several times. The disc mass and gravitational torque time evolution are analyzed with high temporal resolution. There is overall consistency between the codes. The density profiles agree within about 5% for the Eulerian simulations while the SPH results predict the correct shape of the gap although have less resolution in the low density regions and weaker planetary wakes. The disc masses after 200 orbital periods agree within 10%. The spread is larger in the tidal torques acting on the planet which agree within a factor 2 at the end of the simulation. In the Neptune case the dispersion in the torques is greater than for Jupiter, possibly owing to the contribution from the not completely cleared region close to the planet.Comment: 32 pages, accepted for publication in MNRA