411 research outputs found
Shock Breakout in 3-Dimensional Red Supergiant Envelopes
Using Athena++, we perform 3D Radiation-Hydrodynamic calculations of the
radiative breakout of the shock wave in the outer envelope of a red supergiant
(RSG) which has suffered core collapse and will become a Type IIP supernova.
The intrinsically 3D structure of the fully convective RSG envelope yields key
differences in the brightness and duration of the shock breakout (SBO) from
that predicted in a 1D stellar model. First, the lower-density `halo' of
material outside of the traditional photosphere in 3D models leads to a shock
breakout at lower densities than 1D models. This would prolong the duration of
the shock breakout flash at any given location on the surface to 1-2
hours. However, we find that the even larger impact is the intrinsically 3D
effect associated with large-scale fluctuations in density that cause the shock
to break out at different radii at different times. This substantially prolongs
the SBO duration to 3-6 hours and implies a diversity of radiative
temperatures, as different patches across the stellar surface are at different
stages of their radiative breakout and cooling at any given time. These
predicted durations are in better agreement with existing observations of SBO.
The longer durations lower the predicted luminosities by a factor of 3-10
(), and we derive the new
scalings of brightness and duration with explosion energies and stellar
properties. These intrinsically 3D properties eliminate the possibility of
using observed rise times to measure the stellar radius via light-travel time
effects.Comment: 12 pages, 13 figures, Accepted by Ap
Safely Learning Visuo-Tactile Feedback Policies in Real For Industrial Insertion
Industrial insertion tasks are often performed repetitively with parts that
are subject to tight tolerances and prone to breakage. In this paper, we
present a safe method to learn a visuo-tactile insertion policy that is robust
against grasp pose variations while minimizing human inputs and collision
between the robot and the environment. We achieve this by dividing the
insertion task into two phases. In the first align phase, we learn a
tactile-based grasp pose estimation model to align the insertion part with the
receptacle. In the second insert phase, we learn a vision-based policy to guide
the part into the receptacle. Using force-torque sensing, we also develop a
safe self-supervised data collection pipeline that limits collision between the
part and the surrounding environment. Physical experiments on the USB insertion
task from the NIST Assembly Taskboard suggest that our approach can achieve
45/45 insertion successes on 45 different initial grasp poses, improving on two
baselines: (1) a behavior cloning agent trained on 50 human insertion
demonstrations (1/45) and (2) an online RL policy (TD3) trained in real (0/45)
Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions
We update the capabilities of the software instrument Modules for Experiments
in Stellar Astrophysics (MESA) and enhance its ease of use and availability.
Our new approach to locating convective boundaries is consistent with the
physics of convection, and yields reliable values of the convective core mass
during both hydrogen and helium burning phases. Stars with
become white dwarfs and cool to the point where the electrons are degenerate
and the ions are strongly coupled, a realm now available to study with MESA due
to improved treatments of element diffusion, latent heat release, and blending
of equations of state. Studies of the final fates of massive stars are extended
in MESA by our addition of an approximate Riemann solver that captures shocks
and conserves energy to high accuracy during dynamic epochs. We also introduce
a 1D capability for modeling the effects of Rayleigh-Taylor instabilities that,
in combination with the coupling to a public version of the STELLA radiation
transfer instrument, creates new avenues for exploring Type II supernovae
properties. These capabilities are exhibited with exploratory models of
pair-instability supernova, pulsational pair-instability supernova, and the
formation of stellar mass black holes. The applicability of MESA is now widened
by the capability of importing multi-dimensional hydrodynamic models into MESA.
We close by introducing software modules for handling floating point exceptions
and stellar model optimization, and four new software tools -- MESAWeb,
MESA-Docker, pyMESA, and mesastar.org -- to enhance MESA's education and
research impact.Comment: 64 pages, 61 figures; Accepted to AAS Journal
Reconstruction of the metabolic network of Pseudomonas aeruginosa to interrogate virulence factor synthesis
Virulence-linked pathways in opportunistic pathogens are putative therapeutic targets that may be associated with less potential for resistance than targets in growth-essential pathways. However, efficacy of virulence-linked targets may be affected by the contribution of virulence-related genes to metabolism. We evaluate the complex interrelationships between growth and virulence-linked pathways using a genome-scale metabolic network reconstruction of Pseudomonas aeruginosa strain PA14 and an updated, expanded reconstruction of P. aeruginosa strain PAO1. The PA14 reconstruction accounts for the activity of 112 virulence-linked genes and virulence factor synthesis pathways that produce 17 unique compounds. We integrate eight published genome-scale mutant screens to validate gene essentiality predictions in rich media, contextualize intra-screen discrepancies and evaluate virulence-linked gene distribution across essentiality datasets. Computational screening further elucidates interconnectivity between inhibition of virulence factor synthesis and growth. Successful validation of selected gene perturbations using PA14 transposon mutants demonstrates the utility of model-driven screening of therapeutic targets
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