4,926 research outputs found
Higher Gauge Theory and Gravity in (2+1) Dimensions
Non-abelian higher gauge theory has recently emerged as a generalization of
standard gauge theory to higher dimensional (2-dimensional in the present
context) connection forms, and as such, it has been successfully applied to the
non-abelian generalizations of the Yang-Mills theory and 2-form
electrodynamics. (2+1)-dimensional gravity, on the other hand, has been a
fertile testing ground for many concepts related to classical and quantum
gravity, and it is therefore only natural to investigate whether we can find an
application of higher gauge theory in this latter context. In the present paper
we investigate the possibility of applying the formalism of higher gauge theory
to gravity in (2+1) dimensions, and we show that a nontrivial model of
(2+1)-dimensional gravity coupled to scalar and tensorial matter fields - the
model - can be formulated both as a standard gauge theory and
as a higher gauge theory. Since the model has a very rich structure - it admits
as solutions black-hole BTZ-like geometries, particle-like geometries as well
as Robertson-Friedman-Walker cosmological-like expanding geometries - this
opens a wide perspective for higher gauge theory to be tested and understood in
a relevant gravitational context. Additionally, it offers the possibility of
studying gravity in (2+1) dimensions coupled to matter in an entirely new
framework.Comment: 22 page
Iris Codes Classification Using Discriminant and Witness Directions
The main topic discussed in this paper is how to use intelligence for
biometric decision defuzzification. A neural training model is proposed and
tested here as a possible solution for dealing with natural fuzzification that
appears between the intra- and inter-class distribution of scores computed
during iris recognition tests. It is shown here that the use of proposed neural
network support leads to an improvement in the artificial perception of the
separation between the intra- and inter-class score distributions by moving
them away from each other.Comment: 6 pages, 5 figures, Proc. 5th IEEE Int. Symp. on Computational
Intelligence and Intelligent Informatics (Floriana, Malta, September 15-17),
ISBN: 978-1-4577-1861-8 (electronic), 978-1-4577-1860-1 (print
Dynamical Mean-Field Study of the Ferromagnetic Transition Temperature of a Two-Band Model for Colossal Magnetoresistance Materials
The ferromagnetic (FM) transition temperature (Tc) of a two-band
Double-Exchange (DE) model for colossal magnetoresistance (CMR) materials is
studied using dynamical mean-field theory (DMFT), in wide ranges of coupling
constants, hopping parameters, and carrier densities. The results are shown to
be in excellent agreement with Monte Carlo simulations. When the bands overlap,
the value of Tc is found to be much larger than in the one-band case, for all
values of the chemical potential within the energy overlap interval. A nonzero
interband hopping produces an additional substantial increase of Tc, showing
the importance of these nondiagonal terms, and the concomitant use of multiband
models, to boost up the critical temperatures in DE-based theories.Comment: 4 pages, 4 eps figure
Self-propulsion of a catalytically active particle near a planar wall: from reflection to sliding and hovering
Micron-sized particles moving through solution in response to self-generated
chemical gradients serve as model systems for studying active matter. Their
far-reaching potential applications will require the particles to sense and
respond to their local environment in a robust manner. The self-generated
hydrodynamic and chemical fields, which induce particle motion, probe and are
modified by that very environment, including confining boundaries. Focusing on
a catalytically active Janus particle as a paradigmatic example, we predict
that near a hard planar wall such a particle exhibits several scenarios of
motion: reflection from the wall, motion at a steady-state orientation and
height above the wall, or motionless, steady "hovering." Concerning the steady
states, the height and the orientation are determined both by the proportion of
catalyst coverage and the interactions of the solutes with the different
"faces" of the particle. Accordingly, we propose that a desired behavior can be
selected by tuning these parameters via a judicious design of the particle
surface chemistry
Performance estimation of interior permanent-magnet brushless motors using the voltage-driven flux-MMF diagram
The flux-magnetomotive force (flux-MMF) diagram, or "energy conversion loop," is a powerful tool for computing the parameters of saturated interior permanent-magnet brushless motors, especially when the assumptions underlying classical dq theory are not valid, as is often the case in modern practice. Efficient finite-element computation of the flux-MMF diagram is possible when the motor current is known a priori, but in high-speed operation the current regulator can lose control of the current waveform and the computation becomes "voltage-driven" rather than "current-driven." This paper describes an efficient method for estimating the motor performance-average torque, inductances-by solving the voltage-driven problem. It presents experimental validation for a two-pole brushless interior permanent-magnet motor. The paper also discusses the general conditions under which this method is appropriate, and compares the method with alternative approaches
The extent of dust in NGC 891 from Herschel/SPIRE images
We analyse Herschel/SPIRE images of the edge-on spiral galaxy NGC 891 at 250,
350 and 500 micron. Using a 3D radiative transfer model we confirm that the
dust has a radial fall-off similar to the stellar disk. The dust disk shows a
break at about 12 kpc from the center, where the profile becomes steeper.
Beyond this break, emission can be traced up to 90% of the optical disk in the
NE side. On the SW, we confirm dust emission associated with the extended,
asymmetric HI disk, previously detected by the Infrared Space Observatory
(ISO). This emission is marginally consistent with the large diffuse dust disk
inferred from radiative transfer fits to optical images. No excess emission is
found above the plane beyond that of the thin, unresolved, disk.Comment: Letter accepted for publication in A&A; final version after
shortening and language editin
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