1,767 research outputs found
Anticipating a New Golden Age
The standard model of fundamental interactions is remarkably successful, but
it leaves an unfinished agenda. Several major questions seem ripe for
exploration in the near future. I anticipate that the coming decade will be a
Golden Age of discovery in fundamental physics.Comment: 25 pages, 15 figures. Version 3: Added references, caption to Figure
14 correcte
Turbulence and turbulent pattern formation in a minimal model for active fluids
Active matter systems display a fascinating range of dynamical states,
including stationary patterns and turbulent phases. While the former can be
tackled with methods from the field of pattern formation, the spatio-temporal
disorder of the active turbulence phase calls for a statistical description.
Borrowing techniques from turbulence theory, we here establish a quantitative
description of correlation functions and spectra of a minimal continuum model
for active turbulence. Further exploring the parameter space, we also report on
a surprising type of turbulence-driven pattern formation far beyond linear
onset: the emergence of a dynamic hexagonal vortex lattice state after an
extended turbulent transient, which can only be explained taking into account
turbulent energy transfer across scales.Comment: Supplemental videos available at https://youtu.be/gbf6cRho03w
https://youtu.be/n0qUUhAUJFQ https://youtu.be/LGmamkM012
Equation of State in a Strongly Interacting Relativistic System
We study the evolution of the equation of state of a strongly interacting
quark system as a function of the diquark interaction strength. We show that
for the system to avoid collapsing into a pressureless Boson gas at
sufficiently strong diquark coupling strength, the diquark-diquark repulsion
has to be self-consistently taken into account. In particular, we find that the
tendency at zero temperature of the strongly interacting diquark gas to
condense into the system ground state is compensated by the repulsion between
diquarks if the diquark-diquark coupling constant is higher than a critical
value . Considering such diquark-diquark repulsion, a positive
pressure with no significant variation along the whole strongly interacting
region is obtained. A consequence of the diquark-diquark repulsion is that the
system maintains its BCS character in the whole strongly interacting region.Comment: 9 pages, 7 figs, To appear in Phys. Rev.
Dissipation Layers in Rayleigh-B\'{e}nard Convection: A Unifying View
Boundary layers play an important role in controlling convective heat
transfer. Their nature varies considerably between different application areas
characterized by different boundary conditions, which hampers a uniform
treatment. Here, we argue that, independent from boundary conditions,
systematic dissipation measurements in Rayleigh-B\'enard convection capture the
relevant near-wall structures. By means of direct numerical simulations with
varying Prandtl numbers, we demonstrate that such dissipation layers share
central characteristics with classical boundary layers, but, in contrast to the
latter, can be extended naturally to arbitrary boundary conditions. We validate
our approach by explaining differences in scaling behavior observed for no-slip
and stress-free boundaries, thus paving the way to an extension of scaling
theories developed for laboratory convection to a broad class of natural
systems
Modeling space-time correlations of velocity fluctuations in wind farms
An analytical model for the streamwise velocity space-time correlations in
turbulent flows is derived and applied to the special case of velocity
fluctuations in large wind farms. The model is based on the Kraichnan-Tennekes
random sweeping hypothesis, capturing the decorrelation in time while including
a mean wind velocity in the streamwise direction. In the resulting model, the
streamwise velocity space-time correlation is expressed as a convolution of the
pure space correlation with an analytical temporal decorrelation kernel. Hence,
the spatio-temporal structure of velocity fluctuations in wind farms can be
derived from the spatial correlations only. We then explore the applicability
of the model to predict spatio-temporal correlations in turbulent flows in wind
farms. Comparisons of the model with data from a large eddy simulation of flow
in a large, spatially periodic wind farm are performed, where needed model
parameters such as spatial and temporal integral scales and spatial
correlations are determined from the large eddy simulation. Good agreement is
obtained between the model and large eddy simulation data showing that spatial
data may be used to model the full temporal structure of fluctuations in wind
farms.Comment: Submitted to Wind Energ
The Lundgren-Monin-Novikov Hierarchy: Kinetic Equations for Turbulence
We present an overview of recent works on the statistical description of
turbulent flows in terms of probability density functions (PDFs) in the
framework of the Lundgren-Monin-Novikov (LMN) hierarchy. Within this framework,
evolution equations for the PDFs are derived from the basic equations of fluid
motion. The closure problem arises either in terms of a coupling to multi-point
PDFs or in terms of conditional averages entering the evolution equations as
unknown functions. We mainly focus on the latter case and use data from direct
numerical simulations (DNS) to specify the unclosed terms. Apart from giving an
introduction into the basic analytical techniques, applications to
two-dimensional vorticity statistics, to the single-point velocity and
vorticity statistics of three-dimensional turbulence, to the temperature
statistics of Rayleigh-B\'enard convection and to Burgers turbulence are
discussed.Comment: Accepted for publication in C. R. Acad. Sc
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
Systematic Study Of Leptonic Mixing In A Class Of SU_H(2) Models
We perform a systematic analysis of the PMNS matrices which arise when one
assigns the three generations of leptons to the representation of a
horizontal symmetry. This idea has been previously explored by
Kuchimanchi and Mohapatra. However, we assume the neutrino mass matrix
results from leptonic couplings to triplet scalar fields and
hierarchies exist amongst lepton mass matrix elements which result from
couplings to scalar fields with different charges. Of the sixteen
candidate PMNS matrices which result it is found that only one is both
predictive and possesses a leading order structure compatible with experimental
data. The relevant neutrino mass matrix displays the symmetry
to leading order and we explore the perturbations required
to produce a realistic lepton spectrum. The effective mass in neutrinoless
double beta decay is required to lie in the range
, which is just below current
experimental bounds. is non-zero but not uniquely determined.Comment: To appear in Phys. Rev.
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