3 research outputs found
Cosmic 21-cm Fluctuations as a Probe of Fundamental Physics
Fluctuations in high-redshift cosmic 21-cm radiation provide a new window for
observing unconventional effects of high-energy physics in the primordial
spectrum of density perturbations. In scenarios for which the initial state
prior to inflation is modified at short distances, or for which deviations from
scale invariance arise during the course of inflation, the cosmic 21-cm power
spectrum can in principle provide more precise measurements of exotic effects
on fundamentally different scales than corresponding observations of cosmic
microwave background anisotropies.Comment: 8 pages, 2 figure
f(R) theories
Over the past decade, f(R) theories have been extensively studied as one of
the simplest modifications to General Relativity. In this article we review
various applications of f(R) theories to cosmology and gravity - such as
inflation, dark energy, local gravity constraints, cosmological perturbations,
and spherically symmetric solutions in weak and strong gravitational
backgrounds. We present a number of ways to distinguish those theories from
General Relativity observationally and experimentally. We also discuss the
extension to other modified gravity theories such as Brans-Dicke theory and
Gauss-Bonnet gravity, and address models that can satisfy both cosmological and
local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in
Relativity, Published version, Comments are welcom
Numerical prediction of wind turbine noise
This paper develops and validates the first principle based numerical method for predicting the noise radiated from the rotating Horizontal-Axis Wind Turbine (HAWT) blades. The noise radiated to the far-field was predicted by the code based on Ffowcs Williams-Hawkings (FW-H) equation, using both original non-permeable formulation and permeable formulation. A commercially available CFD solver, ANSYS CFX 11.0, was used to calculate the flow parameters on and around the blade surface that are required for FW-H codes. A capability of the solver for modelling the flow field around the wind turbine blades was validated by comparing with the experimental results of NREL phase VI wind turbine blades. The FW-H codes were validated using acoustic results of UH-1H helicopter rotor in hover and Hartzell aircraft propeller in forward motion, which were measured in anechoic wind tunnel facility. Then the developed FW-H acoustic codes were applied to calculate the noise radiated from NREL Phase VI wind turbine blades. (C) 2010 Elsevier Ltd. All rights reserved