249 research outputs found
Advanced Compton Telescope Designs and SN Science
The Advanced Compton Telescope (ACT) has been suggested to be the optimal
next-generation instrument to study nuclear gamma-ray lines. In this work, we
investigate the potential of three hypothetical designs of the ACT to perform
SN science. We provide estimates of 1) the SN detection rate, 2) the SN Ia
discrimination rate, and 3) which gamma-ray lines would be detected from
specific supernova remnants. We find that the prompt emission from a SN Ia is
such that it is unlikely that one would be within the range that an
INTERMEDIATE ACT would be able to distinguish between explosion scenarios,
although such an instrument would detect a handful of SNRs.
We further find that the SUPERIOR ACT design would be a truly breakthrough
instrument for SN science. By supplying these estimates, we intend to assist
the gamma-ray astrophysics community in deciding the course of the next decade
of gamma-ray SN science.Comment: 10 pages, accepted for publication in New astronomy Reviews
(Astronomy with Radioactivities III
Optical and near-IR observations of SN 1998bw
SN 1998bw, especially after the discovery of GRB 030329/SN 2003dh, seems to
be the equivalent of the Rosetta stone for the SN/GRB connection. In this paper
I review optical and near IR observations that have been carried out for this
uncanny object, which has probably confirmed suspicions and ideas originally
formulated in the early seventies of last century.Comment: 9 pages, 7 figures. Invited review to the IAU Colloquium n. 192,
SUPERNOVAE: ten years of SN 1993J, Valencia (Spain
Variable-Speed-of-Light Cosmology from Brane World Scenario
We argue that the four-dimensional universe on the TeV brane of the
Randall-Sundrum scenario takes the bimetric structure of Clayton and Moffat,
with gravitons traveling faster than photons instead, while the radion varies
with time. We show that such brane world bimetric model can thereby solve the
flatness and the cosmological constant problems, provided the speed of a
graviton decreases to the present day value rapidly enough. The resolution of
other cosmological problems such as the horizon problem and the monopole
problem requires supplementation by inflation, which may be achieved by the
radion field provided the radion potential satisfies the slow-roll
approximation.Comment: 18 pages, LaTeX, revised version to appear in Phys. Rev.
The Role of Radioactivities in Astrophysics
I present both a history of radioactivity in astrophysics and an introduction
to the major applications of radioactive abundances to astronomy
A self-optimised approach to synthesising DEHiBA for advanced nuclear reprocessing, exploiting the power of machine-learning
In an effort to advance the development of hydrometallurgical reprocessing of used nuclear fuel across the globe, this work sets out to explore and identify an optimised, cost effective pathway to synthesise the ligand DEHiBA (N,N-di-(2-ethylhexyl)isobutyramide). Currently, very few chemical suppliers stock and distribute this specialist ligand, designed for selective uranium chelation and extraction from nuclear fuel. The current high cost of DEHiBA therefore restricts access to essential large-scale testing of this promising ligand designed to advance nuclear reprocessing. This work utilises an automated flow reactor platform for the efficient optimisation of four synthetic routes to DEHiBA. These optimisations focus on optimising cost, reagent efficiency, yield, and productivity target functions by exploiting the power of machine-learning algorithms for rapid process development. Ultimately, we have identified an efficient and cost-effective solvent-free route to DEHiBA from isobutyric anhydride and di-2-ethylhexylamine for 99%, at a purity of 76%, and a process mass intensity of 1.29 g gâ1, whilst alternative conditions demonstrated productivities >75 kg Lâ1 hâ1, all whilst maintaining a high level of process control with outlet temperatures not exceeding 35 °C
Quintessence and variation of the fine structure constant in the CMBR
We study dependence of the CMB temperature anisotropy spectrum on the value
of the fine structure constant and the equation of state of the dark
energy component of the total density of the universe. We find that bounds
imposed on the variation of from the analysis of currently available
CMB data sets can be significantly relaxed if one also allows for a change in
the equation of state.Comment: 5 pages, 3 figures. Several references added and a few minor typos
corrected in the revised versio
Superconducting fluctuation corrections to ultrasound attenuation in layered superconductors
We consider the temperature dependence of the sound attenuation and sound
velocity in layered impure metals due to superconducting fluctuations of the
order parameter above the critical temperature. We obtain the dependence on
material properties of these fluctuation corrections in the hydrodynamic limit,
where the electron mean free path is much smaller than the wavelength of sound
and where the electron collision rate is much larger than the sound frequency.
For longitudinal sound propagating perpendicular to the layers, the open Fermi
surface condition leads to a suppression of the divergent contributions to
leading order, in contrast with the case of paraconductivity. The leading
temperature dependent corrections, given by the Aslamazov-Larkin, Maki-Thompson
and density of states terms, remain finite as T->Tc. Nevertheless, the
sensitivity of new ultrasonic experiments on layered organic conductors should
make these fluctuations effects measurable.Comment: 13 pages, 6 figures. Accepted for PRB. Added discussion on incoherent
interlayer tunneling and other small modifications suggested by referee
Analytically Solvable Asymptotic Model of Atrial Excitability
We report a three-variable simplified model of excitation fronts in human
atrial tissue. The model is derived by novel asymptotic techniques \new{from
the biophysically realistic model of Courtemanche et al (1998) in extension of
our previous similar models. An iterative analytical solution of the model is
presented which is in excellent quantitative agreement with the realistic
model. It opens new possibilities for analytical studies as well as for
efficient numerical simulation of this and other cardiac models of similar
structure
Prospects for Studies of Stellar Evolution and Stellar Death in the JWST Era
I review the prospects for studies of the advanced evolutionary stages of
low-, intermediate- and high-mass stars by the JWST and concurrent facilities,
with particular emphasis on how they may help elucidate the dominant
contributors to the interstellar dust component of galaxies. Observations
extending from the mid-infrared to the submillimeter can help quantify the
heavy element and dust species inputs to galaxies from AGB stars. JWST's MIRI
mid-infrared instrument will be so sensitive that observations of the dust
emission from individual intergalactic AGB stars and planetary nebulae in the
Virgo Cluster will be feasible. The Herschel Space Observatory will enable the
last largely unexplored spectral region, the far-IR to the submillimeter, to be
surveyed for new lines and dust features, while SOFIA will cover the wavelength
gap between JWST and Herschel, a spectral region containing important fine
structure lines, together with key water-ice and crystalline silicate bands.
Spitzer has significantly increased the number of Type II supernovae that have
been surveyed for early-epoch dust formation but reliable quantification of the
dust contributions from massive star supernovae of Type II, Type Ib and Type Ic
to low- and high-redshift galaxies should come from JWST MIRI observations,
which will be able to probe a volume over 1000 times larger than Spitzer.Comment: 24 pages, 19 figures. To appear in `Astrophysics in the Next Decade:
JWST and Concurrent Facilities' (JWST Conference Proceedings), edited by H.
A. Thronson, M. Stiavelli and A. G. G. M. Tielens; Springer Series:
Astrophysics and Space Science Proceeding
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