5,908 research outputs found
The Complex Network of Evolutionary Computation Authors: an Initial Study
EC paper authors form a complex network of co-authorship which is, by itself,
a example of an evolving system with its own rules, concept of fitness, and
patterns of attachment. In this paper we explore the network of authors of
evolutionary computation papers found in a major bibliographic database. We
examine its macroscopic properties, and compare it with other co-authorship
networks; the EC co-authorship network yields results in the same ballpark as
other networks, but exhibits some distinctive patterns in terms of internal
cohesion. We also try to find some hints on what makes an author a sociometric
star. Finally, the role of proceeding editorship as the origin of long-range
links in the co-authorship network is studied as well.Comment: Sociometric study of the Evolutionary Computation community.
Submitted to Evolutionary Computation lette
Low-energy effective theory for a Randall-Sundrum scenario with a moving bulk brane
We derive the low-energy effective theory of gravity for a generalized
Randall-Sundrum scenario, allowing for a third self-gravitating brane to live
in the 5D bulk spacetime. At zero order the 5D spacetime is composed of two
slices of anti-de Sitter spacetime, each with a different curvature scale, and
the 5D Weyl tensor vanishes. Two boundary branes are at the fixed points of the
orbifold whereas the third brane is free to move in the bulk. At first order,
the third brane breaks the otherwise continuous evolution of the projection of
the Weyl tensor normal to the branes. We derive a junction condition for the
projected Weyl tensor across the bulk brane, and combining this constraint with
the junction condition for the extrinsic curvature tensor, allows us to derive
the first-order field equations on the middle brane. The effective theory is a
generalized Brans-Dicke theory with two scalar fields. This is conformally
equivalent to Einstein gravity and two scalar fields, minimally coupled to the
geometry, but nonminimally coupled to matter on the three branes.Comment: 16 pages, 1 figure, typos correcte
Hybrid integral transforms analysis of the bioheat equation with variable properties
Pennes’ equation is the most frequently employed model to describe heat transfer processes within living tissues, with numerous applications in clinical diagnostics and thermal treatments. A number of analytical solutions were provided in the literature that represent the temperature distribution across tissue structures, but considering simplifying assumptions such as uniform and linear thermophysical properties and blood perfusion rates. The present work thus advances such analysis path by considering a heterogeneous medium formulation that allows for spatially variable parameters across the tissue thickness. Besides, the eventual variation of blood perfusion rates with temperature is also accounted for in the proposed model. The Generalized Integral Transform Technique (GITT) is employed to yield a hybrid numerical–analytical solution of the bioheat model in heterogeneous media, which reduces to the exact solution obtained via the Classical Integral Transform Method for a linear formulation with uniform coefficients. The open source UNIT code (“Unified Integral Transforms”) is utilized to obtain numerical results for a set of typical values of the governing parameters, in order to illustrate the convergence behavior of the proposed eigenfunction expansions and inspect the importance of accounting for spatially variable properties in predicting the thermal response of living tissues to external stimulus.Indisponível
Determination of oscillator strength of confined excitons in a semiconductor microcavity
We have achieved a significant experimental Rabi-splitting (3.4 meV) for
confined polaritons in a planar semiconductor microcavity for only a
single quantum well (SQW) of GaAs (10 nm) placed at the antinode. The
Rabi-splitting phenomena are discussed in detail based on the semiclassical
theory, where two coupled harmonic oscillators (excitons and photons) are used
to describe the system. In this way, we can obtain the dispersion curve of
polaritons, the minimum value for the cavity reflectance and the oscillator
strength to reach the strong coupling regime. This approach describes an
ensemble of excitons confined in a SQW and includes a dissipation component.
The results present a weak coupling regime, where an enhanced spontaneous
emission takes place, and a strong coupling regime, where Rabi-splitting in the
dispersion curve can be observed. The theoretical results are confronted with
experimental data for the reflectance behavior in resonant and off-resonant
conditions and present a great accuracy. This allows us to determine the
oscillator strength of the confined excitons in the SQW with great precision.Comment: 11 pages, 7 figure
Loop and Path Spaces and Four-Dimensional BF Theories: Connections, Holonomies and Observables
We study the differential geometry of principal G-bundles whose base space is
the space of free paths (loops) on a manifold M. In particular we consider
connections defined in terms of pairs (A,B), where A is a connection for a
fixed principal bundle P(M,G) and B is a 2-form on M. The relevant curvatures,
parallel transports and holonomies are computed and their expressions in local
coordinates are exhibited. When the 2-form B is given by the curvature of A,
then the so-called non-abelian Stokes formula follows.
For a generic 2-form B, we distinguish the cases when the parallel transport
depends on the whole path of paths and when it depends only on the spanned
surface. In particular we discuss generalizations of the non-abelian Stokes
formula. We study also the invariance properties of the (trace of the) holonomy
under suitable transformation groups acting on the pairs (A,B).
In this way we are able to define observables for both topological and
non-topological quantum field theories of the BF type. In the non topological
case, the surface terms may be relevant for the understanding of the
quark-confinement problem. In the topological case the (perturbative)
four-dimensional quantum BF-theory is expected to yield invariants of imbedded
(or immersed) surfaces in a 4-manifold M.Comment: TeX, 39 page
Three-dimensional BF Theories and the Alexander-Conway Invariant of Knots
We study 3-dimensional BF theories and define observables related to knots
and links. The quantum expectation values of these observables give the
coefficients of the Alexander-Conway polynomial.Comment: 32 pages (figures available upon request); LaTe
- …