644 research outputs found
A Rectangular Area Filling Display System Architecture
A display system architecture which has rectangular area filling as its primitive operation is presented. It is shown that lines can be drawn significantly faster while rendition of filled boxes shows an O(n^2) speed improvement. Furthermore filled polygons can be rendered with an O(n) speed improvement.
Implementation of this rectangular area filling architecture is discussed and refined. A custom
VLSI integrated circuit is currently being designed to implement this rectangular area filling architecture
and at the same time reduce the display memory system video refresh bandwidth requirements
The Observational Signatures of Primordial Pair-Instability Supernovae
Massive Population III stars from 140 - 260 solar masses ended their lives as
pair-instability supernovae (PISNe), the most energetic thermonuclear
explosions in the universe. Detection of these explosions could directly
constrain the primordial IMF for the first time, which is key to the formation
of the first galaxies, early cosmological reionization, and the chemical
enrichment of the primeval IGM. We present radiation hydrodynamical
calculations of Pop III PISN light curves and spectra performed with the RAGE
code. We find that the initial radiation pulse due to shock breakout from the
surface of the star, although attenuated by the Lyman-alpha forest, will still
be visible by JWST at z ~ 10 - 15, and possibly out to z ~ 20 with strong
gravitational lensing. We have also studied metal mixing at early stages of the
explosion prior to breakout from the surface of the star with the CASTRO AMR
code and find vigorous mixing in primordial core-collapse explosions but very
little in PISNe. This implies that the key to determining progenitor masses of
the first cosmic explosions is early spectroscopy just after shock breakout,
and that multidimensional mixing is crucial to accurate low-mass Pop III SNe
light curves and spectra.Comment: 4 pages, 3 figures, proceedings of Deciphering the Ancient Universe
with Gamma-Ray Bursts, Kyoto, Japan, April 19 - 23, 201
Ionization Front Instabilities in Primordial H II Regions
Radiative cooling by metals in shocked gas mediates the formation of
ionization front instabilities in the galaxy today that are responsible for a
variety of phenomena in the interstellar medium, from the morphologies of
nebulae to triggered star formation in molecular clouds. An important question
in early reionization and chemical enrichment of the intergalactic medium is
whether such instabilities arose in the H II regions of the first stars and
primeval galaxies, which were devoid of metals. We present three-dimensional
numerical simulations that reveal both shadow and thin-shell instabilities
readily formed in primordial gas. We find that the hard UV spectra of
Population III stars broadened primordial ionization fronts, causing H2
formation capable of inciting violent thin- shell instabilities in D-type
fronts, even in the presence of intense Lyman-Werner flux. The high post- front
gas temperatures associated with He ionization sustained and exacerbated shadow
instabilities, unaided by molecular hydrogen cooling. Our models indicate that
metals eclipsed H2 cooling in I-front instabilities at modest concentrations,
from 0.001- 0.01 solar. We conclude that ionization front instabilities were
prominent in the H II regions of the first stars and galaxies, influencing the
escape of ionizing radiation and metals into the early universe.Comment: 13 pages, 11 figures, accepted by ApJ with minor revision
Indistinguishable Chargeon-Fluxion Pairs in the Quantum Double of Finite Groups
We consider the category of finite dimensional representations of the quantum
double of a finite group as a modular tensor category. We study
auto-equivalences of this category whose induced permutations on the set of
simple objects (particles) are of the special form of PJ, where J sends every
particle to its charge conjugation and P is a transposition of a
chargeon-fluxion pair. We prove that if the underlying group is the semidirect
product of the additive and multiplicative groups of a finite field, then such
an auto-equivalence exists. In particular, we show that for S_3 (the
permutation group over three letters) there is a chargeon and a fluxion which
are not distinguishable. Conversely, by considering such permutations as
modular invariants, we show that a transposition of a chargeon-fluxion pair
forms a modular invariant if and only if the corresponding group is isomorphic
to the semidirect product of the additive and multiplicative groups of a finite
near-field.Comment: 15 pages, arXiv:1006.5479 includes all results of this paper, v3:
fixed a typo in eq (11
Modeling Emission from the First Explosions: Pitfalls and Problems
Observations of the explosions of Population III (Pop III) stars have the
potential to teach us much about the formation and evolution of these
zero-metallicity objects. To realize this potential, we must tie observed
emission to an explosion model, which requires accurate light curve and spectra
calculations. Here, we discuss many of the pitfalls and problems involved in
such models, presenting some preliminary results from radiation-hydrodynamics
simulations.Comment: 6 pages, 3 figures, proceedings of 'The First Stars and Galaxies:
Challenges for the Next Decade", Austin, TX, March 8-11, 201
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