17,580 research outputs found
Cosmological perturbations in a gravity with quadratic order curvature couplings
We present a set of equations describing the evolution of the scalar-type
cosmological perturbation in a gravity with general quadratic order curvature
coupling terms. Equations are presented in a gauge ready form, thus are ready
to implement various temporal gauge conditions depending on the problems. The
Ricci-curvature square term leads to a fourth-order differential equation for
describing the spacetime fluctuations in a spatially homogeneous and isotropic
cosmological background.Comment: 5 pages, no figure, To appear in Phys. Rev.
The Origin of Structures in Generalized Gravity
In a class of generalized gravity theories with general couplings between the
scalar field and the scalar curvature in the Lagrangian, we can describe the
quantum generation and the classical evolution of both the scalar and tensor
structures in a simple and unified manner. An accelerated expansion phase based
on the generalized gravity in the early universe drives microscopic quantum
fluctuations inside a causal domain to expand into macroscopic ripples in the
spacetime metric on scales larger than the local horizon. Following their
generation from quantum fluctuations, the ripples in the metric spend a long
period outside the causal domain. During this phase their evolution is
characterized by their conserved amplitudes. The evolution of these
fluctuations may lead to the observed large scale structures of the universe
and anisotropies in the cosmic microwave background radiation.Comment: 5 pages, latex, no figur
A Codazzi-like equation and the singular set for smooth surfaces in the Heisenberg group
In this paper, we study the structure of the singular set for a
smooth surface in the -dimensional Heisenberg group . We
discover a Codazzi-like equation for the -area element along the
characteristic curves on the surface. Information obtained from this ordinary
differential equation helps us to analyze the local configuration of the
singular set and the characteristic curves. In particular, we can estimate the
size and obtain the regularity of the singular set. We understand the global
structure of the singular set through a Hopf-type index theorem. We also
justify that Codazzi-like equation by proving a fundamental theorem for local
surfaces in .Comment: 64 pages, 17 figure
Cosmological Gravitational Wave in a Gravity with Quadratic Order Curvature Couplings
We present a set of equations describing the cosmological gravitational wave
in a gravity theory with quadratic order gravitational coupling terms which
naturally arise in quantum correction procedures. It is known that the
gravitational wave equation in the gravity theories with a general term
in the action leads to a second order differential equation with the only
correction factor appearing in the damping term. The case for a
term is completely different. The gravitational wave is described by a fourth
order differential equation both in time and space. However, curiously, we find
that the contributions to the background evolution are qualitatively the same
for both terms.Comment: 4 pages, revtex, no figure
Evaluation of a Liquid Amine System for Spacecraft Carbon Dioxide Control
The analytical and experimental studies are described which were directed toward the acquisition of basic information on utilizing a liquid amine sorbent for in use in a CO2 removal system for manned spacecraft. Liquid amine systems are successfully used on submarines for control of CO2 generated by the crew, but liquid amines were not previously considered for spacecraft applications due to lack of development of satisfactory rotary phase separators. Developments in this area now make consideration of liquid amines practical for spacecraft system CO2 removal. The following major tasks were performed to evaluate liquid amine systems for spacecraft: (1) characterization, through testing, of the basic physical and thermodynamic properties of the amine solution; (2) determination of the dynamic characteristics of a cocurrent flow absorber; and (3) evaluation, synthesis, and selection of a liquid amine system concept oriented toward low power requirements. A low weight, low power system concept was developed. Numerical and graphical data are accompanied by pertinent observations
COBE constraints on inflation models with a massive non-minimal scalar field
We derive power spectra of the scalar- and tensor-type structures generated
in an inflation model based on a massive non-minimally coupled scalar field
with the strong coupling assumption. We make analyses in both the
original-frame and the conformally transformed Einstein-frame. We derive
contributions of both structures to the anisotropy of the cosmic microwave
background radiation, and compare the contributions with the four-year COBE-DMR
data. Previous study showed that sufficient amount of inflation requires a
small coupling parameter. In such a case the spectra become near Zeldovich
spectra, and the gravitational wave contribution becomes negligible compared
with the scalar-type contribution which is testable in future CMBR experiments.Comment: 4 pages, no figure, To appear in Phys. Rev.
Band gap renormalization in photoexcited semiconductor quantum wire structures in the GW approximation
We investigate the dynamical self-energy corrections of the electron-hole
plasma due to electron-electron and electron-phonon interactions at the band
edges of a quasi-one dimensional (1D) photoexcited electron-hole plasma. The
leading-order dynamical screening approximation is used in the calculation
by treating electron-electron Coulomb interaction and electron-optical phonon
Fr\"{o}hlich interaction on an equal footing. We calculate the
exchange-correlation induced band gap renormalization (BGR) as a function of
the electron-hole plasma density and the quantum wire width. The calculated BGR
shows good agreement with existing experimental results, and the BGR normalized
by the effective quasi-1D excitonic Rydberg exhibits an approximate
one-parameter universality.Comment: 11 pages, 3 figure
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