arXiv subjects

Joshua Wallace

Publications and source records attributed to Joshua Wallace.

4 recordsLinked to original sources

arXiv2024

Open-Source, Cost-Aware Kinematically Feasible Planning for Mobile and Surface Robotics

We present Smac Planner, an openly available, search-based planning framework that addresses the critical need for kinematically feasible path planning across diverse robot platforms. Smac Planner provides high-performance implementations of Cost-Aware A*, Hybrid-A*, and State Lattice planners that can be deployed for Ackermann, legged, and other large non-circular robots. Our framework introduces novel "Cost-Aware" variations that significantly improve performance in complex environments common to mobile robotics while maintaining kinematic feasibility constraints. Integrated as the standard planning system within the popular ROS 2 Navigation stack, Nav2, Smac Planner now powers thousands of robots worldwide across academic research, commercial applications, and field deployments.

cs.RO↗

arXiv2017

Collisional Fragmentation is Not a Barrier to Close-in Planet Formation

Collisional fragmentation is shown to not be a barrier to rocky planet formation at small distances from the host star. Simple analytic arguments demonstrate that rocky planet formation via collisions of homogeneous gravity-dominated bodies is possible down to distances of order the Roche radius ($r_\mathrm{Roche}$). Extensive N-body simulations with initial bodies ${\gtrsim}1700$ km that include plausible models for fragmentation and merging of gravity-dominated bodies confirm this conclusion and demonstrate that rocky planet formation is possible down to ${\sim}$1.1 $r_\mathrm{Roche}$. At smaller distances, tidal effects cause collisions to be too fragmenting to allow mass build-up to a final, dynamically stable planetary system. We argue that even differentiated bodies can accumulate to form planets at distances that are not much larger than $r_\mathrm{Roche}$.

astro-ph.EP↗

arXiv2016

Detecting the Supernova Breakout Burst in Terrestrial Neutrino Detectors

We calculate the distance-dependent performance of a few representative terrestrial neutrino detectors in detecting and measuring the properties of the $ν_e$ breakout burst light curve in a Galactic core-collapse supernova. The breakout burst is a signature phenomenon of core collapse and offers a probe into the stellar core through collapse and bounce. We examine cases of no neutrino oscillations and oscillations due to normal and inverted neutrino-mass hierarchies. For the normal hierarchy, other neutrino flavors emitted by the supernova overwhelm the $ν_e$ signal, making a detection of the breakout burst difficult. For the inverted hierarchy (IH), some detectors at some distances should be able to see the $ν_e$ breakout burst peak and measure its properties. For the IH, the maximum luminosity of the breakout burst can be measured at 10 kpc to accuracies of $\sim$30% for Hyper-Kamiokande (Hyper-K) and $\sim$60% for the Deep Underground Neutrino Experiment (DUNE). Super-Kamiokande (Super-K) and Jiangmen Underground Neutrino Observatory (JUNO) lack the mass needed to make an accurate measurement. For the IH, the time of the maximum luminosity of the breakout burst can be measured in Hyper-K to an accuracy of $\sim$3 ms at 7 kpc, in DUNE $\sim$2 ms at 4 kpc, and JUNO and Super-K can measure the time of maximum luminosity to an accuracy of $\sim$2 ms at 1 kpc. Detector backgrounds in IceCube render a measurement of the $ν_e$ breakout burst unlikely. For the inverted hierarchy, a measurement of the maximum luminosity of the breakout burst could be used to differentiate between nuclear equations of state.

astro-ph.HE↗

arXiv2014

Anisotropic Lyman-alpha Emission

As a result of resonant scatterings off hydrogen atoms, Lyman-alpha (Lya) emission from star-forming galaxies provides a probe of the (hardly isotropic) neutral gas environment around them. We study the effect of the environmental anisotropy on the observed Lya emission by performing radiative transfer calculations for models of neutral hydrogen clouds with prescriptions of spatial and kinematic anisotropies. The environmental anisotropy leads to corresponding anisotropy in the Lya flux and spectral properties and induces correlations among them. The Lya flux (or observed luminosity) depends on the viewing angle and shows an approximate correlation with the initial Lya optical depth in the viewing direction relative to those in all other directions. The distribution of Lya flux from a set of randomly oriented clouds is skewed to high values, providing a natural contribution to the Lya equivalent width (EW) distribution seen in observation. A narrower EW distribution is found at a larger peak offset of the Lya line, similar to the trend suggested in observation. The peak offset appears to correlate with the line shape (full width at half maximum and asymmetry), pointing to a possibility of using Lya line features alone to determine the systemic redshifts of galaxies. The study suggests that anisotropies in the spatial and kinematic distributions of neutral hydrogen can be an important ingredient in shaping the observed properties of Lya emission from star-forming galaxies. We discuss the implications of using Lya emission to probe the circumgalactic and intergalactic environments of galaxies.

astro-ph.CO↗