9,833 research outputs found
Wave envelopes with second-order spatiotemporal dispersion : I. Bright Kerr solitons and cnoidal waves
We propose a simple scalar model for describing pulse phenomena beyond the conventional slowly-varying envelope approximation. The generic governing equation has a cubic nonlinearity and we focus here mainly on contexts involving anomalous group-velocity dispersion. Pulse propagation turns out to be a problem firmly rooted in frames-of-reference considerations. The transformation properties of the new model and its space-time structure are explored in detail. Two distinct representations of exact analytical solitons and their associated conservation laws (in both integral and algebraic forms) are presented, and a range of new predictions is made. We also report cnoidal waves of the governing nonlinear equation. Crucially, conventional pulse theory is shown to emerge as a limit of the more general formulation. Extensive simulations examine the role of the new solitons as robust attractors
A Fast and Accurate Cost Model for FPGA Design Space Exploration in HPC Applications
Heterogeneous High-Performance Computing
(HPC) platforms present a significant programming challenge,
especially because the key users of HPC resources are scientists,
not parallel programmers. We contend that compiler technology
has to evolve to automatically create the best program variant
by transforming a given original program. We have developed a
novel methodology based on type transformations for generating
correct-by-construction design variants, and an associated
light-weight cost model for evaluating these variants for
implementation on FPGAs. In this paper we present a key
enabler of our approach, the cost model. We discuss how we
are able to quickly derive accurate estimates of performance
and resource-utilization from the design’s representation in our
intermediate language. We show results confirming the accuracy
of our cost model by testing it on three different scientific
kernels. We conclude with a case-study that compares a solution
generated by our framework with one from a conventional
high-level synthesis tool, showing better performance and
power-efficiency using our cost model based approach
Spanning trees for the geometry and dynamics of compact polymers
Using a mapping of compact polymers on the Manhattan lattice to spanning
trees, we calculate exactly the average number of bends at infinite
temperature. We then find, in a high temperature approximation, the energy of
the system as a function of bending rigidity and polymer elasticity. We
identify the universal mechanism for the relaxation of compact polymers and
then endow the model with physically motivated dynamics in the convenient
framework of the trees. We find aging and domain coarsening after quenches in
temperature. We explain the slow dynamics in terms of the geometrical
interconnections between the energy and the dynamics.Comment: 10 pages, 8 figure
Wave envelopes with second-order spatiotemporal dispersion: II. Modulational instabilities and dark Kerr solitons
A simple scalar model for describing spatiotemporal dispersion of pulses, beyond the classic “slowly-varying envelopes + Galilean boost” approach, is studied. The governing equation has a cubic nonlinearity and we focus here mainly on contexts with normal group-velocity dispersion. A complete analysis of continuous waves is reported, including their dispersion relations and modulational instability characteristics. We also present a detailed derivation of exact analytical dark solitons, obtained by combining direct-integration methods with geometrical transformations. Classic results from conventional pulse theory are recovered as-ymptotically from the spatiotemporal formulation. Numerical simulations test new theoretical predictions for modulational instability, and examine the robustness of spatiotemporal dark solitons against perturbations to their local pulse shape
Bayesian Cosmic Web Reconstruction: BARCODE for Clusters
We describe the Bayesian BARCODE formalism that has been designed towards the
reconstruction of the Cosmic Web in a given volume on the basis of the sampled
galaxy cluster distribution. Based on the realization that the massive compact
clusters are responsible for the major share of the large scale tidal force
field shaping the anisotropic and in particular filamentary features in the
Cosmic Web. Given the nonlinearity of the constraints imposed by the cluster
configurations, we resort to a state-of-the-art constrained reconstruction
technique to find a proper statistically sampled realization of the original
initial density and velocity field in the same cosmic region. Ultimately, the
subsequent gravitational evolution of these initial conditions towards the
implied Cosmic Web configuration can be followed on the basis of a proper
analytical model or an N-body computer simulation. The BARCODE formalism
includes an implicit treatment for redshift space distortions. This enables a
direct reconstruction on the basis of observational data, without the need for
a correction of redshift space artifacts. In this contribution we provide a
general overview of the the Cosmic Web connection with clusters and a
description of the Bayesian BARCODE formalism. We conclude with a presentation
of its successful workings with respect to test runs based on a simulated large
scale matter distribution, in physical space as well as in redshift space.Comment: 18 pages, 8 figures, Proceedings of IAU Symposium 308 "The Zeldovich
Universe: Genesis and Growth of the Cosmic Web", 23-28 June 2014, Tallinn,
Estoni
Bistable Helmholtz bright solitons in saturable materials
We present, to the best of our knowledge, the first exact analytical solitons of a nonlinear Helmholtz equation with a saturable refractive-index model. These new two-dimensional spatial solitons have a bistable characteristic in some parameter regimes, and they capture oblique (arbitrary-angle) beam propagation in both the forward and backward directions. New conservation laws are reported, and the classic paraxial solution is recovered in an appropriate multiple limit. Analysis and simulations examine the stability of both solution branches, and stationary Helmholtz solitons are found to emerge from a range of perturbed input beams
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