1,349 research outputs found
STEM + Art = STEAM
Science, Technology, Engineering and Math – the STEM subjects – alone will not lead to the kind of breathtaking innovation the 21st century demands...So what does it mean to add Art to turn STEM to STEAM
High-Energy Emission from Interacting Supernovae: New Constraints on Cosmic-Ray Acceleration in Dense Circumstellar Environments
Supernovae (SNe) with strong interactions with circumstellar material (CSM)
are promising candidate sources of high-energy neutrinos and gamma rays, and
have been suggested as an important contributor to Galactic cosmic rays beyond
1 PeV. Taking into account the shock dissipation by a fast velocity component
of SN ejecta, we present comprehensive calculations of the non-thermal emission
from SNe powered by shock interactions with a dense wind or CSM. Remarkably, we
consider electromagnetic cascades in the radiation zone and subsequent
attenuation in the pre-shock CSM. A new time-dependent phenomenological
prescription provided by this work enables us to calculate gamma-ray, hard
X-ray, radio, and neutrino signals, which originate from cosmic rays
accelerated by the diffusive shock acceleration mechanism. We apply our results
to SN IIn 2010jl and SN Ib/IIn 2014C, for which the model parameters can be
determined from the multi-wavelength data. For SN 2010jl, the more promising
case, by using the the latest Fermi Large Area Telescope (LAT) Pass 8 data
release, we derive new constraints on the cosmic-ray energy fraction,
<0.05-0.1. We also find that the late-time radio data of these interacting SNe
are consistent with our model. Further multi-messenger and multi-wavelength
observations of nearby interacting SNe should give us new insights into the
diffusive shock acceleration in dense environments as well as pre-SN mass-loss
mechanisms.Comment: 16 pages, 10 figures, 3 tables, accepted for publication in ApJ.
Results and conclusions unchange
Divergent Thinking | RISD President
Innovation happens when convergent thinkers—people who march straight ahead towards a clearly defined goal—combine forces with divergent thinkers, those who may wander professionally but who are comfortable being uncomfortable and who look for what is real. RISD harbors a lot of divergent, agile thinkers. . . . – John Maeda, RISD President 2008-13https://digitalcommons.risd.edu/risdxyz_fall2013/1004/thumbnail.jp
Cultural Context | RISD President
Art and design remind us to look at things from different angles and to value what is unique about ourselves and our culture… . John Maeda, RISD President 2008-12https://digitalcommons.risd.edu/risdxyz_springsummer2013/1003/thumbnail.jp
X-ray Measurements of the Particle Acceleration Properties at Inward Shocks in Cassiopeia A
We present new evidence that the bright non-thermal X-ray emission features
in the interior of the Cassiopeia A supernova remnant (SNR) are caused by
inward moving shocks based on Chandra and NuSTAR observations. Several bright
inward-moving filaments were identified using monitoring data taken by Chandra
in 2000-2014. These inward-moving shock locations are nearly coincident with
hard X-ray (15-40 keV) hot spots seen by NuSTAR. From proper motion
measurements, the transverse velocities were estimated to be in the range
2,100-3,800 km s for a distance of 3.4 kpc. The shock velocities
in the frame of the expanding ejecta reach values of 5,100-8,700 km
s, slightly higher than the typical speed of the forward shock.
Additionally, we find flux variations (both increasing and decreasing) on
timescales of a few years in some of the inward-moving shock filaments. The
rapid variability timescales are consistent with an amplified magnetic field of
0.5-1 mG. The high speed and low photon cut-off energy of the
inward-moving shocks are shown to imply a particle diffusion coefficient that
departs from the Bohm regime ( 3-8) for the few
simple physical configurations we consider in this study. The maximum electron
energy at these shocks is estimated to be 8-11 TeV, smaller than the
values of 15-34 TeV inferred for the forward shock. Cassiopeia A is
dynamically too young for its reverse shock to appear to be moving inward in
the observer frame. We propose instead that the inward-moving shocks are a
consequence of the forward shock encountering a density jump of 5-8
in the surrounding material.Comment: 16 pages, 8 figures, accepted for publication in Ap
Introduction: Immersed in Lithics
The idea of holding a conference to discuss how we can explore what affects our approaches to, and understanding of, lithic artefacts and their analysis emerged from a hands-on workshop entitled Northern Knap-in in November 2014. In that workshop we wanted to explore how prehistoric people in the north of England, which is perceived by many as being a (lithic)resource-poor region, might have adapted to the lack of good quality flint and chert for tool manufacture and so we experimented with the working of non-flint raw materials. Many things emerged from that day including how the experimental knapping of materials other than flint allowed us to think outside the conventional box, and how communal knapping and grinding demonstrated some of the different ways that people interacted and adapted to each other’s rhythm when making artefacts. We were also struck (excuse the pun) by how much non-lithic specialists contributed to the questions we raise in lithic analysis. This brought home to us the importance of finding other, sometimes non- conventional, ways in which we can engage with the past. This eventually led to the Immersed in Lithics Conference in February 2016
Relativistic Radiative Transfer for Spherical Flows
We present a new complete set of Lagrangian relativistic hydrodynamical
equations describing the transfer of energy and momentum between a standard
fluid and a radiation fluid in a general non-stationary spherical flow. The new
set of equations has been derived for a particular application to the study of
the cosmological Quark--Hadron transition but can also be used in other
contexts.Comment: 28 pages, 9 postscript figs, Plain Te
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