25,795 research outputs found
PSI to turbulence during internal wave beam refraction through the upper ocean pycnocline
A numerical study based on large eddy simulation (LES) is performed to investigate the nonlinear interaction of a semidiurnal (M2) internal wave beam with an upper ocean pycnocline. During refraction through the pycnocline, the wave beam undergoes parametric subharmonic instability (PSI) with formation of waves with (1/2)M2 frequency. The three-dimensional LES enables new results that quantify the route to turbulence through PSI. The subharmonic waves generated from PSI have an order of magnitude smaller vertical scale and are susceptible to wave breaking. Convective instability initiates transition to turbulence, while shear production maintains it. Turbulence at points in the subharmonic wave paths is modulated at (1/2)M2 frequency. The beam suffers substantial degradation owing to PSI, reflected harmonics and ducted waves so that only about 30% of the incoming energy is transported by the main reflected beam.We are pleased to acknowledge
support through ONR N000140910287,
program manager Terri Paluszkiewicz,
ARC DECRA Fellowship DE140100089
for B.G., and helpful discussions with
Shaun Johnston, SIO
Non-perturbative unification in the light of LEP results
We consider an alternative to conventional GUTs originally proposed by
Maiani, Parisi and Petronzio, where owing to the existence of extra fermion
generations at some intermediate scale, the gauge couplings become large at
high energies. We first comment on how the non- supersymmetric version of this
scenario is ruled out; we then consider the two-loop evolution of the couplings
in the supersymmetric extension of this scenario, and check whether such a
scenario is feasible in the light of the precies values of couplings now
available from LEP.Comment: Latex file 7 pages+1 fig. (ps file appended after the latex file),
CERN-TH.6913/9
Modified theory of gravity and the history of cosmic evolution
A continuous transition from early Friedmann-like radiation era through to
late time cosmic acceleration passing through a long Friedmann-like matter
dominated era followed by a second phase of radiation era has been realized in
modified theory of gravity containing a combination of curvature squared term,
a linear term, a three-half term and an ideal fluid. Thus the history of cosmic
evolution is explained by modified theory of gravity singlehandedly. The second
phase of radiation-like era might provide an explanation to the hydrogen and
helium reionization at low redshift.Comment: 15 pages, 6 figures, Astrophys Space Sci (2014
Inner multipliers and Rudin type invariant subspaces
Let be a Hilbert space and be
the -valued Hardy space over the unit disc in
. The well known Beurling-Lax-Halmos theorem states that every
shift invariant subspace of other than
has the form , where is an
operator-valued inner multiplier in for some Hilbert space . In this
paper we identify with -valued Hardy
space and classify all such inner
multiplier for which is a Rudin type invariant subspace of
.Comment: 8 page
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