4,067 research outputs found
Projections and Dyadic Parseval Frame MRA Wavelets
A classical theorem attributed to Naimark states that, given a Parseval frame
in a Hilbert space , one can embed in
a larger Hilbert space so that the image of is the
projection of an orthonormal basis for . In the present work, we
revisit the notion of Parseval frame MRA wavelets from two papers of
Paluszy\'nski, \v{S}iki\'c, Weiss, and Xiao (PSWX) and produce an analog of
Naimark's theorem for these wavelets at the level of their scaling functions.
We aim to make this discussion as self-contained as possible and provide a
different point of view on Parseval frame MRA wavelets than that of PSWX.Comment: 19 page
The Radio Emission from the Ultra-Luminous Far-Infrared Galaxy NGC 6240
We present new radio observations of the ``prototypical'' ultra-luminous far-
infrared galaxy NGC~6240, obtained using the VLA at 20~cm in `B' configuration
and at 3.6~cm in `A' configuration. These data, along with those from four
previous VLA observations, are used to perform a comprehensive study of the
radio emission from NGC~6240. Approximately 70\% (~3 x 10 W~Hz)
of the total radio power at 20 cm originates from the nuclear region ( <~ 1.5
kpc), of which half is emitted by two unresolved (\alphaS_{\nu} \propto \nu^{-\alpha}). The
supernova rate required to power the diffuse component is consistent with that
predicted by the stellar evolution models of Rieke \etal (1985). If the radio
emission from the two compact cores is powered by supernova remnants, then
either the remnants overlap and form hot bubbles in the cores, or they are very
young ( <~ 100 yr). Nearly all of the other 30\% of the total radio power comes
from an ``arm-like'' region extending westward from the nuclear region. The
western arm emission has a steep spectrum (\alpha^{-14}$ erg/s/cm2 in the 2-10 keV band. No significant radio
emission is detected from or near the possible ultra-massive ``dark core''
hypothesized by Bland-Hawthorn, Wilson \& Tully (1991).Comment: 36 pages (text and tables) as an uuencoded compressed postscript file
(figures available upon request), accepted for the ApJ (20 Nov issue), STScI
preprint no. ?? -- May 199
Discrete Symmetries in Covariant LQG
We study time-reversal and parity ---on the physical manifold and in internal
space--- in covariant loop gravity. We consider a minor modification of the
Holst action which makes it transform coherently under such transformations.
The classical theory is not affected but the quantum theory is slightly
different. In particular, the simplicity constraints are slightly modified and
this restricts orientation flips in a spinfoam to occur only across degenerate
regions, thus reducing the sources of potential divergences.Comment: 8 pages, v2: Minor change
Loop quantum cosmology of Bianchi type IX models
The loop quantum cosmology "improved dynamics" of the Bianchi type IX model
are studied. The action of the Hamiltonian constraint operator is obtained via
techniques developed for the Bianchi type I and type II models, no new input is
required. It is shown that the big bang and big crunch singularities are
resolved by quantum gravity effects. We also present the effective equations
which provide modifications to the classical equations of motion due to quantum
geometry effects.Comment: 20 page
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Power-Ups in Digital Games: The Rewarding Effect of Phantom Game Elementson Player Experience
Power-ups are a type of game reward that allow the player tocustomise their experience by altering gameplay for a shortperiod of time. Despite the wide use of power-ups in videogames, little is known about their effect on gaming experiences.To explore this, we conducted an experimental study that compares the experiences of players depending on their exposureto power-ups in a recreational video game. The results show that players who collected power-ups felt significantly more immersed in the game, experienced more autonomy, but didnot feel more competent or challenged than those who played the game without these collectables. Interestingly, a similareffect was observed for those players who picked up ‘placebo ’power-ups, despite the items having no effect on the gameplay. We provide a discussion of these results and their implications both for games user researchers and game designers
Hybrid Quantization: From Bianchi I to the Gowdy Model
The Gowdy cosmologies are vacuum solutions to the Einstein equations which
possess two space-like Killing vectors and whose spatial sections are compact.
We consider the simplest of these cosmological models: the case where the
spatial topology is that of a three-torus and the gravitational waves are
linearly polarized. The subset of homogeneous solutions to this Gowdy model are
vacuum Bianchi I spacetimes with a three-torus topology. We deepen the analysis
of the loop quantization of these Bianchi I universes adopting the improved
dynamics scheme put forward recently by Ashtekar and Wilson-Ewing. Then, we
revisit the hybrid quantization of the Gowdy cosmologies by combining
this loop quantum cosmology description with a Fock quantization of the
inhomogeneities over the homogeneous Bianchi I background. We show that, in
vacuo, the Hamiltonian constraint of both the Bianchi I and the Gowdy models
can be regarded as an evolution equation with respect to the volume of the
Bianchi I universe. This evolution variable turns out to be discrete, with a
strictly positive minimum. Furthermore, we argue that this evolution is
well-defined inasmuch as the associated initial value problem is well posed:
physical solutions are completely determined by the data on an initial section
of constant Bianchi I volume. This fact allows us to carry out to completion
the quantization of these two cosmological models.Comment: 20 pages, version accepted for publication in Physical Review
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