4,821 research outputs found
Device for directionally controlling electromagnetic radiation Patent
Concentrator device for controlling direction of solar energy onto energy converter
Directional control of radiant heat
Surface with grooves having flat bases gives directional emissivities and absorptivities that can be made to approximate a perfect directional surface. Radiant energy can then be transferred in desired directions
Cosmology under Milne's shadow
Based on the magnitude--redshift diagram for the sample of supernovae Ia
analysed by Perlmutter et al. (1999), Davis & Lineweaver rule out the special
relativistic interpretation of cosmological redshifts at a confidence level of
23 sigma. Here, we critically reassess this result. Special relativity is known
to describe the dynamics of an empty universe, by means of the Milne kinematic
model. Applying only special-relativistic concepts, we derive the angular
diameter distance and the luminosity distance in the Milne model. In
particular, in this model we do not use the underlying metric in its
Robertson-Walker form, so our exposition is useful for readers without any
knowledge of general relativity. We do however, explicitly use the
special-relativistic Doppler formula for redshift. We apply the derived
luminosity distance to the magnitude--redshift diagram for supernovae Ia of
Perlmutter et al. (1999) and show that special relativity fits the data much
better than that claimed by Davis & Lineweaver. Specifically, using these data
alone, the Milne model is ruled out only at a 2 sigma level. Although not a
viable cosmological model, in the context of current research on supernovae Ia
it remains a useful reference model when comparing predictions of various
cosmological models.Comment: 5 pages, 1 figure; a didactic article; matches the version accepted
for publication in PAS
Dynamics of Massive Scalar Fields in dS Space and the dS/CFT Correspondence
Global geometric properties of dS space are presented explicitly in various
coordinates. A Robertson-Walker like metric is deduced, which is convenient to
be used in study of dynamics in dS space. Singularities of wavefunctions of
massive scalar fields at boundary are demonstrated. A bulk-boundary propagator
is constructed by making use of the solutions of equations of motion. The
dS/CFT correspondence and the Strominger's mass bound is shown.Comment: latex, 14 pages and 3 figure
On Lifshitz scaling and hyperscaling violation in string theory
We explore string/M-theory constructions of holographic theories with
Lifshitz scaling exponent and hyperscaling violation exponent ,
finding a range of -values. Some of these arise as effective metrics
from dimensional reduction of certain kinds of null deformations of
spacetimes appearing in the near horizon geometries of extremal D3-, M2- and
M5-brane theories. The solution in particular gives rise to
in (boundary) space dimensions. Other solutions arise as the IIA D2- and
D4-brane solutions with appropriate null deformations, and we discuss the phase
structure of these systems.Comment: Latex, 15pgs, v2: references, minor clarifications adde
Domain walls in Born-Infeld-dilaton background
We study the dynamics of domain walls in Einstein-Born-Infeld-dilaton theory.
Dilaton is non-trivially coupled with the Born-Infeld electromagnetic field. We
find three different types of solutions consistent with the dynamic domain
walls. For every case, the solutions have singularity. Further more, in these
backgrounds, we study the dynamics of domain walls. We qualitatively plot
various form of the bulk metrics and the potential encountered by the domain
walls. In many cases, depending upon the value of the parameters, the domain
walls show bouncing universe and also undergo inflationary phase followed by
standard decelerated expansion.Comment: 18 pages,6 figures,latex, References added, Some points clarifie
The Nearby Supernova Factory
The Nearby Supernova Factory (SNfactory) is an ambitious project to find and
study in detail approximately 300 nearby Type Ia supernovae (SNe~Ia) at
redshifts 0.03<z<0.08. This program will provide an exceptional data set of
well-studied SNe in the nearby smooth Hubble flow that can be used as
calibration for the current and future programs designed to use SNe to measure
the cosmological parameters. The first key ingredient for this program is a
reliable supply of Hubble-flow SNe systematically discovered in unprecedented
numbers using the same techniques as those used in distant SNe searches. In
2002, 35 SNe were found using our test-bed pipeline for automated SN search and
discovery. The pipeline uses images from the asteroid search conducted by the
Near Earth Asteroid Tracking group at JPL. Improvements in our subtraction
techniques and analysis have allowed us to increase our effective SN discovery
rate to ~12 SNe/month in 2003.Comment: 7 pages, 3 figures to be published in New Astronomy Review
de Sitter black hole with a conformally coupled scalar field in four dimensions
A four-dimensional black hole solution of the Einstein equations with a
positive cosmological constant, coupled to a conformal scalar field, is given.
There is a curvature singularity at the origin, and scalar field diverges
inside the event horizon. The electrically charged solution, which has a fixed
charge-to-mass ratio is also found. The quartic self-interacting coupling
becomes bounded in terms of Newton's and the cosmological constants.Comment: 5 pages, no figures, CECS style, energy conditions are discussed and
some references were added. To appear in Phys. Rev.
Archeops, mapping the CMB sky from large to small angular scales
Archeops is a balloon-borne experiment designed to measure the temperature
fluctuations of the CMB on a large region of the sky () with a high
angular resolution (10 arcminutes) and a high sensitivity ( per
pixel). Archeops will perform a measurement of the CMB anisotropies power
spectrum from large angular scales () to small angular scales
(). Archeops flew for the first time for a test flight in July
1999 from Sicily to Spain and the first scientific flight took place from
Sweden to Russia in January 2001. The data analysis is on its way and I present
here preliminary results, realistic simulations showing the expected accuracy
on the measurement of the power spectrum and perspectives for the incoming
flights (Winter 2001/2003).Comment: 6 pages, 6 figures, proceedings to TAUP2001 conference, LNGS, Italy,
Sept. 200
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