94 research outputs found
The dynamic characteristics of two-dimensional spoilers at low speeds
SIGLEAvailable from British Library Document Supply Centre- DSC:D73304/87 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
A computing environment for the application of system building in architecture : a computer based building system within a general computing environment for architectural practice
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCHBibliography: leaves 209-218.by Stefanos A. Kalligas.M.S
Decaying Dark Energy in Higher-Dimensional Gravity
We use data from observational cosmology to put constraints on
higher-dimensional extensions of general relativity in which the effective
four-dimensional dark-energy density (or cosmological "constant") decays with
time. In particular we study the implications of this decaying dark energy for
the age of the universe, large-scale structure formation, big-bang
nucleosynthesis and the magnitude-redshift relation for Type Ia supernovae. Two
of these tests (age and the magnitude-redshift relation) place modest lower
limits on the free parameter of the theory, a cosmological length scale L akin
to the de Sitter radius. These limits will improve if experimental
uncertainties on supernova magnitudes can be reduced around z=1.Comment: 11 pages, 5 figures, submitted to A&
Five-dimensional PPN formalism and experimental test of Kaluza-Klein theory
The parametrized post Newtonian formalism for 5-dimensional metric theories
with a compact extra dimension is developed. The relation of the 5-dimensional
and 4-dimensional formulations is then analyzed, in order to compare the higher
dimensional theories of gravity with experiments. It turns out that the value
of post Newtonian parameter in the reduced 5-dimensional Kaluza-Klein
theory is two times smaller than that in 4-dimensional general relativity. The
departure is due to the existence of an extra dimension in the Kaluza-Klein
theory. Thus the confrontation between the reduced 4-dimensional formalism and
Solar system experiments raises a severe challenge to the classical
Kaluza-Klein theory.Comment: 4 pages, 1 table, accepted for publication in Physics Letters
Cosmic Acceleration With A Positive Cosmological Constant
We have considered a cosmological model with a phenomenological model for the
cosmological constant of the form \Lambda=\bt\fr{\ddot R}{R}, \bt is a
constant. For age parameter consistent with observational data the Universe
must be accelerating in the presence of a positive cosmological constant. The
minimum age of the Universe is , where is the present Hubble
constant. The cosmological constant is found to decrease as . Allowing
the gravitational constant to change with time leads to an ever increasing
gravitational constant at the present epoch. In the presence of a viscous fluid
this decay law for is equivalent to the one with () provided \alpha=\fr{\bt}{3(\bt-2)}. The
inflationary solution obtained from this model is that of the de-Sitter type.Comment: a more revised versio
Gravitational conformal invariance and coupling constants in Kaluza-Klein theory
We introduce a generalized gravitational conformal invariance in the context
of non-compactified 5D Kaluza-Klein theory. It is done by assuming the 4D
metric to be dependent on the extra non-compactified dimension. It is then
shown that the conformal invariance in 5D is broken by taking an absolute
cosmological scale over which the 4D metric is assumed to be dependent
weakly on the 5th dimension. This is equivalent to Deser's model for the
breakdown of the conformal invariance in 4D by taking a constant cosmological
mass term in the theory. We set the scalar field to its
background cosmological value leading to Einstein equation with the
gravitational constant and a small cosmological constant. A dual Einstein
equation is also introduced in which the matter is coupled to the higher
dimensional geometry by the coupling . Relevant interpretations of
the results are also discussed.Comment: 10 pages, LaTeX, some cghanges in the tex
Cosmological Models with Variable Gravitational and Cosmological constants in Gravity
We consider the evolution of a flat Friedmann-Roberstson-Walker Universe in a
higher derivative theories, including terms to the
Einstein-Hilbert action in the presence of a variable gravitational and
cosmological constants. We study here the evolution of the gravitational and
cosmological constants in the presence of radiation and matter domination era
of the universe. We present here new cosmological solutions which are
physically interesting for model building.Comment: 14 pages, no figure. to be published in Int. J. Mod. Phys.
Wave Mechanics and General Relativity: A Rapprochement
Using exact solutions, we show that it is in principle possible to regard
waves and particles as representations of the same underlying geometry, thereby
resolving the problem of wave-particle duality
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