2,781 research outputs found
Cover-Encodings of Fitness Landscapes
The traditional way of tackling discrete optimization problems is by using
local search on suitably defined cost or fitness landscapes. Such approaches
are however limited by the slowing down that occurs when the local minima that
are a feature of the typically rugged landscapes encountered arrest the
progress of the search process. Another way of tackling optimization problems
is by the use of heuristic approximations to estimate a global cost minimum.
Here we present a combination of these two approaches by using cover-encoding
maps which map processes from a larger search space to subsets of the original
search space. The key idea is to construct cover-encoding maps with the help of
suitable heuristics that single out near-optimal solutions and result in
landscapes on the larger search space that no longer exhibit trapping local
minima. We present cover-encoding maps for the problems of the traveling
salesman, number partitioning, maximum matching and maximum clique; the
practical feasibility of our method is demonstrated by simulations of adaptive
walks on the corresponding encoded landscapes which find the global minima for
these problems.Comment: 15 pages, 4 figure
Hybrid Courses in Aeronautical Science Curriculums
This article focuses on the need to address learning styles of NetGeners with an emphasis on aviation students. A brief history of aviation training generations as posited by Kearns (2010) is reviewed after which the author\u27s experience creating a university hybrid or blended course on Crew Resource Management is discussed. This article was supported in part by a grant from Embry-Riddle Aeronautical University\u27s Center for Teaching and Learning Excellence
The Moduli Space of the Supersymmetric Yang-Mills Theory
We present the hyper-elliptic curve describing the moduli space of the N=2
supersymmetric Yang-Mills theory with the gauge group. The exact
monodromies and the dyon spectrum of the theory are determined. It is verified
that the recently proposed solitonic equation is also satisfied by our
solution.Comment: Complete set of monodromies are included. To be published in
Phys.lett.
Holomorphic Anomaly in Gauge Theories and Matrix Models
We use the holomorphic anomaly equation to solve the gravitational
corrections to Seiberg-Witten theory and a two-cut matrix model, which is
related by the Dijkgraaf-Vafa conjecture to the topological B-model on a local
Calabi-Yau manifold. In both cases we construct propagators that give a
recursive solution in the genus modulo a holomorphic ambiguity. In the case of
Seiberg-Witten theory the gravitational corrections can be expressed in closed
form as quasimodular functions of Gamma(2). In the matrix model we fix the
holomorphic ambiguity up to genus two. The latter result establishes the
Dijkgraaf-Vafa conjecture at that genus and yields a new method for solving the
matrix model at fixed genus in closed form in terms of generalized
hypergeometric functions.Comment: 34 pages, 2 eps figures, expansion at the monopole point corrected
and interpreted, and references adde
Divergent Time Scale in Axelrod Model Dynamics
We study the evolution of the Axelrod model for cultural diversity. We
consider a simple version of the model in which each individual is
characterized by two features, each of which can assume q possibilities. Within
a mean-field description, we find a transition at a critical value q_c between
an active state of diversity and a frozen state. For q just below q_c, the
density of active links between interaction partners is non-monotonic in time
and the asymptotic approach to the steady state is controlled by a time scale
that diverges as (q-q_c)^{-1/2}.Comment: 4 pages, 5 figures, 2-column revtex4 forma
Patterning the insect eye: from stochastic to deterministic mechanisms
While most processes in biology are highly deterministic, stochastic
mechanisms are sometimes used to increase cellular diversity, such as in the
specification of sensory receptors. In the human and Drosophila eye,
photoreceptors sensitive to various wavelengths of light are distributed
randomly across the retina. Mechanisms that underlie stochastic cell fate
specification have been analysed in detail in the Drosophila retina. In
contrast, the retinas of another group of dipteran flies exhibit highly ordered
patterns. Species in the Dolichopodidae, the "long-legged" flies, have regular
alternating columns of two types of ommatidia (unit eyes), each producing
corneal lenses of different colours. Individual flies sometimes exhibit
perturbations of this orderly pattern, with "mistakes" producing changes in
pattern that can propagate across the entire eye, suggesting that the
underlying developmental mechanisms follow local, cellular-automaton-like
rules. We hypothesize that the regulatory circuitry patterning the eye is
largely conserved among flies such that the difference between the Drosophila
and Dolichopodidae eyes should be explicable in terms of relative interaction
strengths, rather than requiring a rewiring of the regulatory network. We
present a simple stochastic model which, among its other predictions, is
capable of explaining both the random Drosophila eye and the ordered, striped
pattern of Dolichopodidae.Comment: 24 pages, 4 figure
Possible indicators for low dimensional superconductivity in the quasi-1D carbide Sc3CoC4
The transition metal carbide Sc3CoC4 consists of a quasi-one-dimensional (1D)
structure with [CoC4]_{\inft} polyanionic chains embedded in a scandium
matrix. At ambient temperatures Sc3CoC4 displays metallic behavior. At lower
temperatures, however, charge density wave formation has been observed around
143K which is followed by a structural phase transition at 72K. Below T^onset_c
= 4.5K the polycrystalline sample becomes superconductive. From Hc1(0) and
Hc2(0) values we could estimate the London penetration depth ({\lambda}_L ~=
9750 Angstroem) and the Ginsburg-Landau (GL) coherence length ({\xi}_GL ~= 187
Angstroem). The resulting GL-parameter ({\kappa} ~= 52) classifies Sc3CoC4 as a
type II superconductor. Here we compare the puzzling superconducting features
of Sc3CoC4, such as the unusual temperature dependence i) of the specific heat
anomaly and ii) of the upper critical field H_c2(T) at T_c, and iii) the
magnetic hysteresis curve, with various related low dimensional
superconductors: e.g., the quasi-1D superconductor (SN)_x or the 2D
transition-metal dichalcogenides. Our results identify Sc3CoC4 as a new
candidate for a quasi-1D superconductor.Comment: 4 pages, 5 figure
Heisenberg Dimer Single Molecule Magnets in a Strong Magnetic Field
We calculate the static and dynamic properties of single crystal, single
molecule magnets consisting of equal spin or 5/2 dimers. The spins in
each dimer interact with each other via the Heisenberg exchange interaction and
with the magnetic induction via the Zeeman interaction, and
interdimer interactions are negligible. For antiferromagnetic couplings, the
static magnetization and specific heat exhibit interesting low temperature
and strong quantum effects. We calculate the frequency spectrum of
the Fourier transform of the real part of the time autocorrelation function
for arbitrary , and compare our results with
those obtained for classical spins. We also calculate the inelastic neutron
magnetic dynamical structure factor at arbitrary .Comment: 11 pages, 14 figures, submitted to Phys. Rev.
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