4,214 research outputs found
High-frequency diffraction of an electromagnetic plane wave by an imperfectly conducting rectangular cylinder at grazing incidence
We derive new results for the electromagnetic scattered far wave field produced when a high-frequency plane E-polarized wave is at grazing incidence on an imperfectly conducting rectangular cylinder. The solution to the problem is obtained by using the geometrical theory of diffraction, multiple diffraction methods, the canonical solution for the problem of the diffraction of a plane wave by a right-angled impedance wedge, in conjunction with a novel analytic approach
Fundamental groups, Alexander invariants, and cohomology jumping loci
We survey the cohomology jumping loci and the Alexander-type invariants
associated to a space, or to its fundamental group. Though most of the material
is expository, we provide new examples and applications, which in turn raise
several questions and conjectures.
The jump loci of a space X come in two basic flavors: the characteristic
varieties, or, the support loci for homology with coefficients in rank 1 local
systems, and the resonance varieties, or, the support loci for the homology of
the cochain complexes arising from multiplication by degree 1 classes in the
cohomology ring of X. The geometry of these varieties is intimately related to
the formality, (quasi-) projectivity, and homological finiteness properties of
\pi_1(X).
We illustrate this approach with various applications to the study of
hyperplane arrangements, Milnor fibrations, 3-manifolds, and right-angled Artin
groups.Comment: 45 pages; accepted for publication in Contemporary Mathematic
Uniformizing surfaces via discrete harmonic maps
We show that for any closed surface of genus greater than one and for any
finite weighted graph filling the surface, there exists a hyperbolic metric
which realizes the least Dirichlet energy harmonic embedding of the graph among
a fixed homotopy class and all hyperbolic metrics on the surface. We give
explicit examples of such hyperbolic surfaces through a new interpretation of
the Nielsen realization problem for the mapping class groups.Comment: 31 pages, 5 figure
Loop exponent in DNA bubble dynamics
Dynamics of DNA bubbles are of interest for both statistical physics and
biology. We present exact solutions to the Fokker-Planck equation governing
bubble dynamics in the presence of a long-range entropic interaction. The
complete meeting time and meeting position probability distributions are
derived from the solutions. Probability distribution functions reflect the
value of the loop exponent of the entropic interaction. Our results extend
previous results which concentrated mainly on the tails of the probability
distribution functions and open a way to determining the strength of the
entropic interaction experimentally which has been a matter of recent
discussions. Using numerical integration, we also discuss the influence of the
finite size of a DNA chain on the bubble dynamics. Analogous results are
obtained also for the case of subdiffusive dynamics of a DNA bubble in a
heteropolymer, revealing highly universal asymptotics of meeting time and
position probability functions.Comment: 24 pages, 11 figures, text identical to the published version; v3 -
updated Ref. [47] and corrected Eqs. (3.6) and (3.10
Multi-soliton dynamics in the Skyrme model
We exhibit the dynamical scattering of multi-solitons in the Skyrme model for
configurations with charge two, three and four. First, we construct maximally
attractive configurations from a simple profile function and the product
ansatz. Then using a sophisticated numerical algorithm, initially
well-separated skyrmions in approximately symmetric configurations are shown to
scatter through the known minimum energy configurations. These scattering
events illustrate a number of similarities to BPS monopole configurations of
the same charge. A simple modification of the dynamics to a dissipative regime,
allows us to compute the minimal energy skyrmions for baryon numbers one to
four to within a few percent.Comment: latex, 10 pages, plus 5 figures (as gif files
A Lagrangian effective field theory
We have continued the development of Lagrangian, cosmological perturbation
theory for the low-order correlators of the matter density field. We provide a
new route to understanding how the effective field theory (EFT) of large-scale
structure can be formulated in the Lagrandian framework and a new resummation
scheme, comparing our results to earlier work and to a series of
high-resolution N-body simulations in both Fourier and configuration space. The
`new' terms arising from EFT serve to tame the dependence of perturbation
theory on small-scale physics and improve agreement with simulations (though
with an additional free parameter). We find that all of our models fare well on
scales larger than about two to three times the non-linear scale, but fail as
the non-linear scale is approached. This is slightly less reach than has been
seen previously. At low redshift the Lagrangian model fares as well as EFT in
its Eulerian formulation, but at higher the Eulerian EFT fits the data to
smaller scales than resummed, Lagrangian EFT. All the perturbative models fare
better than linear theory.Comment: 19 pages, 3 figure
Thermodynamic metrics and optimal paths
A fundamental problem in modern thermodynamics is how a molecular-scale
machine performs useful work, while operating away from thermal equilibrium
without excessive dissipation. To this end, we derive a friction tensor that
induces a Riemannian manifold on the space of thermodynamic states. Within the
linear-response regime, this metric structure controls the dissipation of
finite-time transformations, and bestows optimal protocols with many useful
properties. We discuss the connection to the existing thermodynamic length
formalism, and demonstrate the utility of this metric by solving for optimal
control parameter protocols in a simple nonequilibrium model.Comment: 5 page
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