27,818 research outputs found
Coupled rotor-body vibrations with inplane degrees of freedom
In an effort to understand the vibration mechanisms of helicopters, the following basic studies are considered. A coupled rotor-fuselage vibration analysis including inplane degrees of freedom of both rotor and airframe is performed by matching of rotor and fuselage impedances at the hub. A rigid blade model including hub motion is used to set up the rotor flaplag equations. For the airframe, 9 degrees of freedom and hub offsets are used. The equations are solved by harmonic balance. For a 4-bladed rotor, the coupled responses and hub loads are calculated for various parameters in forward flight. The results show that the addition of inplane degrees of freedom does not significantly affect the vertical vibrations for the cases considered, and that inplane vibrations have similar resonance trends as do flapping vibrations
A scattering theory of ultrarelativistic solitons
We construct a perturbative framework for understanding the collision of
solitons (more precisely, solitary waves) in relativistic scalar field
theories. Our perturbative framework is based on the suppression of the
space-time interaction area proportional to , where is the
relative velocity of an incoming solitary wave and . We calculate the leading order results for collisions of (1+1) dimensional
kinks in periodic potentials, and provide explicit, closed form expressions for
the phase shift and the velocity change after the collisions. We find excellent
agreement between our results and detailed numerical simulations. Crucially,
our perturbation series is controlled by a kinematic parameter, and hence not
restricted to small deviations around integrable cases such as the Sine-Gordon
model.Comment: v3: 43 pages, 10 figures, references added, matches version accepted
for publication in PR
Landscape Predictions from Cosmological Vacuum Selection
In BP models with hundreds of fluxes, we compute the effects of cosmological
dynamics on the probability distribution of landscape vacua. Starting from
generic initial conditions, we find that most fluxes are dynamically driven
into a different and much narrower range of values than expected from landscape
statistics alone. Hence, cosmological evolution will access only a tiny
fraction of the vacua with small cosmological constant. This leads to a host of
sharp predictions. Unlike other approaches to eternal inflation, the
holographic measure employed here does not lead to "staggering", an excessive
spread of probabilities that would doom the string landscape as a solution to
the cosmological constant problem.Comment: 15 pages, 6 figures, v4 prd format, minor editin
Flavor-Changing Top Quark Rare Decays in the Littlest Higgs Model with T-Parity
We analyze the rare and flavor changing decay of the top quark into a charm
quark and a gauge boson in the littlest Higgs model with T-parity (LHT). We
calculate the one-loop level contributions from the T-parity odd mirror quarks
and gauge bosons. We find that the decay in the LHT
model can be significantly enhanced relative to those in the Standard Model.
Our numerical results show that the top quark FCNC decay can be as large as
, and in the favorite parameter space in the LHT model.Comment: 12 pages, 3 figure
Non-linear supersymmetric Sigma-Model for Diffusive Scattering of Classical Waves with Resonance Enhancement
We derive a non-linear sigma-model for the transport of light (classical
waves) through a disordered medium. We compare this extension of the model with
the well-established non-linear sigma-model for the transport of electrons
(Schroedinger waves) and display similarities of and differences between both
cases. Motivated by experimental work (M. van Albada et al., Phys. Rev. Lett.
66 (1991) 3132), we then generalize the non-linear sigma-model further to
include resonance scattering. We find that the form of the effective action is
unchanged but that a parameter of the effective action, the mean level density,
is modified in a manner which correctly accounts for the data.Comment: 4 pages, 1 Figure, to be published in Europhysics Letter
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