1,437 research outputs found
On the small-scale structure of turbulence and its impact on the pressure field
Understanding the small-scale structure of incompressible turbulence and its
implications for the non-local pressure field is one of the fundamental
challenges in fluid mechanics. Intense velocity gradient structures tend to
cluster on a range of scales which affects the pressure through a Poisson
equation. Here we present a quantitative investigation of the spatial
distribution of these structures conditional on their intensity for
Taylor-based Reynolds numbers in the range [160, 380]. We find that the
correlation length, the second invariant of the velocity gradient, is
proportional to the Kolmogorov scale. It also is a good indicator for the
spatial localization of intense enstrophy and strain-dominated regions, as well
as the separation between them. We describe and quantify the differences in the
two-point statistics of these regions and the impact they have on the
non-locality of the pressure field as a function of the intensity of the
regions. Specifically, across the examined range of Reynolds numbers, the
pressure in strong rotation-dominated regions is governed by a
dissipation-scale neighbourhood. In strong strain-dominated regions, on the
other hand, it is determined primarily by a larger neighbourhood reaching
inertial scales.Comment: Accepted for publication by the Journal of Fluid Mechanic
Signature of exotic particles in light by light scattering
We discuss the implications on light by light scattering of two kind of
exotic particles: doubly charged scalar bosons and doubly charged fermions; the
virtual effects of a nonstandard singly charged gauge boson are also examined.
These particles, if their masses lie in the range 0.1--1.0 TeV, will have a
clear signature in the future linear colliders. The present analysis has the
advantage that it depends only on electromagnetic symmetry, so it is applicable
to any model which predicts this class of particles. In particular, our results
have interesting consequences on left-right models and their supersymmetric
extension.Comment: 6 eps figures. Requires elsevier.cl
Scaling of the superconducting transition temperature in underdoped high-Tc cuprates with a pseudogap energy: Does this support the anyon model of their superfluidity?
In earlier work, we have been concerned with the scaling properties of some
classes of superconductors, specifically with heavy Fermion materials and with
five bcc transition metals of BCS character. Both of these classes of
superconductors were three-dimensional but here we are concerned solely with
quasi-two-dimensional high-Tc cuprates in the underdoped region of their phase
diagram. A characteristic feature of this part of the phase diagram is the
existence of a pseudogap (pg). We therefore build our approach around the
assumption that kB Tc / E_pg is the basic dimensionless ratio on which to
focus, where the energy E_pg introduced above is a measure of the pseudogap.
Since anyon fractional statistics apply to two-dimensional assemblies, we
expect the fractional statistics parameter allowing `interpolation' between
Fermi-Dirac and Bose-Einstein statistical distribution functions as limiting
cases to play a significant role in determining kB Tc / E_pg and experimental
data are analyzed with this in mind.Comment: Phys. Chem. Liquids, to be publishe
Resolved energy budget of superstructures in Rayleigh-B\'{e}nard convection
Turbulent superstructures, i.e. large-scale flow structures in turbulent
flows, play a crucial role in many geo- and astrophysical settings. In
turbulent Rayleigh-B\'{e}nard convection, for example, horizontally extended
coherent large-scale convection rolls emerge. Currently, a detailed
understanding of the interplay of small-scale turbulent fluctuations and
large-scale coherent structures is missing. Here, we investigate the resolved
kinetic energy and temperature variance budgets by applying a filtering
approach to direct numerical simulations of Rayleigh-B\'{e}nard convection at
high aspect ratio. In particular, we focus on the energy transfer rate between
large-scale flow structures and small-scale fluctuations. We show that the
small scales primarily act as a dissipation for the superstructures. However,
we find that the height-dependent energy transfer rate has a complex structure
with distinct bulk and boundary layer features. Additionally, we observe that
the heat transfer between scales mainly occurs close to the thermal boundary
layer. Our results clarify the interplay of superstructures and turbulent
fluctuations and may help to guide the development of an effective description
of large-scale flow features in terms of reduced-order models
Gravitational Correction to Running of Gauge Couplings
We calculate the contribution of graviton exchange to the running of gauge
couplings at lowest non-trivial order in perturbation theory. Including this
contribution in a theory that features coupling constant unification does not
upset this unification, but rather shifts the unification scale. When
extrapolated formally, the gravitational correction renders all gauge couplings
asymptotically free.Comment: 4 pages, 2 figures; v2: Clarified awkward sentences and notations.
Corrected typos. Added references and discussion thereof in introduction.
Minor copy editting changes to agree with version to be published in Physical
Review Letter
Near-Zero Modes in Superconducting Graphene
Vortices in the simplest superconducting state of graphene contain very low
energy excitations, whose existence is connected to an index theorem that
applies strictly to an approximate form of the relevant Bogoliubov-deGennes
equations. When Zeeman interactions are taken into account, the zero modes
required by the index theorem are (slightly) displaced. Thus the vortices
acquire internal structure, that plausibly supports interesting dynamical
phenomena.Comment: 9 pages, to appear in Proceedings of the Nobel Symposium on Graphene
and Quantum Matte
Anomalous Dimensions of Anisotropic Gauge Theory Operators
The anomalous dimensions of the anisotropic dimension four operators in SU(N) gauge theory coupled to fermions are calculated to lowest order. The possibility of comparison with numerical simulations is pointed out
Energy Spectrum of Anyons in a Magnetic Field
For the many-anyon system in external magnetic field, we derive the energy
spectrum as an exact solution of the quantum eigenvalue problem with particular
topological constraints. Our results agree with the numerical spectra recently
obtained for the 3- and the 4-anyon systems.Comment: 11 pages in Plain LaTeX (plus 4 figures available on request), DFPD
92/TH/4
Classical Dynamics of Anyons and the Quantum Spectrum
In this paper we show that (a) all the known exact solutions of the problem
of N-anyons in oscillator potential precisely arise from the collective degrees
of freedom, (b) the system is pseudo-integrable ala Richens and Berry. We
conclude that the exact solutions are trivial thermodynamically as well as
dynamically.Comment: 19 pages, ReVTeX, IMSc/93/0
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