21,311 research outputs found
A New Perspective on the Nonextremal Enhancon Solution
We discuss the nonextremal generalisation of the enhancon mechanism. We find
that the nonextremal shell branch solution does not violate the Weak Energy
Condition when the nonextremality parameter is small, in contrast to earlier
discussions of this subject. We show that this physical shell branch solution
fills the mass gap between the extremal enhancon solution and the nonextremal
horizon branch solution.Comment: 10 pages, 3 figures, reference adde
Polarized galactic synchrotron and dust emission and their correlation
We present an analysis of the level of polarized dust and synchrotron
emission using the WMAP9 and Planck data. The primary goal of this study is to
inform the assessment of foreground contamination in the cosmic microwave
background (CMB) measurements below from 23 to 353 GHz. We
compute angular power spectra as a function of sky cut based on the Planck 353
GHz polarization maps. Our primary findings are the following. (1) There is a
spatial correlation between the dust emission as measured by Planck at 353 GHz
and the synchrotron emission as measured by WMAP at 23 GHz with
or greater for and ,
dropping to for . (2) A simple foreground model
with dust, synchrotron, and their correlation fits well to all possible cross
spectra formed with the WMAP and Planck 353 GHz data given the current
uncertainties. (3) In the 50 cleanest region of the polarized dust map, the
ratio of synchrotron to dust amplitudes at 90 GHz for 50 110 is
. Smaller regions of sky can be cleaner although the
uncertainties in our knowledge of synchrotron emission are larger. A
high-sensitivity measurement of synchrotron below 90 GHz will be important for
understanding all the components of foreground emission near 90 GHz.Comment: 10 pages, 8 figures; Published in JCAP. Source masks updated, minor
change
Speed of reaction diffusion in embryogenesis
Reaction diffusion systems have been proposed as mechanisms for patterning during many stages of embryonic development. While much attention has been focused on the study of the steady state patterns formed and the robustness of pattern selection, much less is known about the time scales required for pattern formation. Studies of gradient formation by the diffusion of a single morphogen from a localized source have shown that patterning can occur on realistic time scales over distances of a millimeter or less. Reaction diffusion has the potential to give rise to patterns on a faster time scale, since all points in the domain can act as sources of morphogen. However, the speed at which patterning can occur has hitherto not been explored in depth. In this paper, we investigate this issue in specific reaction diffusion models and address the question of whether patterning via reaction diffusion is fast enough to be applicable to morphogenesis
Complex pattern formation in reaction diffusion systems with spatially-varying parameters
Spontaneous pattern formation in reactionâdiffusion systems on a spatially homogeneous domain has been well studied. However, in embryonic development and elsewhere, pattern formation often takes place on a spatially heterogeneous background. We explore the effects of spatially varying parameters on pattern formation in one and two dimensions using the GiererâMeinhardt reactionâdiffusion model. We investigate the effect of the wavelength of a pre-pattern and demonstrate a novel form of moving pattern. We find that spatially heterogeneous parameters can both increase the range and complexity of possible patterns and enhance the robustness of pattern selection
Resolving the large scale spectral variability of the luminous Seyfert 1 galaxy 1H 0419-577: Evidence for a new emission component and absorption by cold dense matter
An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 in
September 2002, when the source was in an extreme low-flux state, found a very
hard X-ray spectrum at 1-10 keV with a strong soft excess below ~1 keV.
Comparison with an earlier XMM-Newton observation when 1H 0419-577 was `X-ray
bright' indicated the dominant spectral variability was due to a steep power
law or cool Comptonised thermal emission. Four further XMM-Newton observations,
with 1H 0419-577 in intermediate flux states, now support that conclusion,
while we also find the variable emission component in intermediate state
difference spectra to be strongly modified by absorption in low ionisation
matter. The variable `soft excess' then appears to be an artefact of absorption
of the underlying continuum while the `core' soft emission can be attributed to
recombination in an extended region of more highly ionised gas. We note the
wider implications of finding substantial cold dense matter overlying (or
embedded in) the X-ray continuum source in a luminous Seyfert 1 galaxy.Comment: 34 pages, 15 figures, submitted to Ap
Endogenous Mechanisms and Nash Equilibrium in Competitive Contracting
We model strategic competition in a market with asymmetric information as a noncooperative game in which each firm competes for the business of a buyer of unknown type by offering the buyer a catalog of products and prices. The timing in our model is Stackelberg: in the first stage, given the distribution of buyer types known to all firms and the deducible, type-dependent best responses of the agent, firms simultaneously and noncooperatively choose their catalog offers. In the second stage the buyer, knowing his type, chooses a single firm and product-price pair from that firm's catalog. By backward induction, this Stackelberg game with asymmetric information reduces to a game over catalogs with payoff indeterminacies. In particular, due to ties within catalogs and/or across catalogs, corresponding to any catalog profile offered by firms there may be multiple possible expected firm payoffs, all consistent with the rational optimizing behavior of the agent for each of his types. The resolution of these indeterminacies depends on the tie-breaking mechanism which emerges in the market. Because each tie-breaking mechanism induces a particular game over catalogs, a reasonable candidate would be a tie-breaking mechanism which supports a Nash equilibrium in the corresponding catalog game. We call such a mechanism an endogenous Nash mechanism. The fundamental question we address in this paper is, does there exist an endogenous Nash mechanism - and therefore, does there exist a Nash equilibrium for the catalog game? We show under fairly mild conditions on primitives that catalog games naturally possess tie-breaking mechanisms which support Nash equilibria.common agency with adverse selection, endogenous contracting mechanisms, discontinuous games, catalog games, existence of Nash equilibrium, competitive contracting
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