11,890 research outputs found
Stacking the Equiangular Spiral
We present an algorithm that adapts the mature Stack and Draw (SaD) methodology for fabricating the exotic Equiangular Spiral Photonic Crystal Fiber. (ES-PCF) The principle of Steiner chains and circle packing is exploited to obtain a non-hexagonal design using a stacking procedure based on Hexagonal Close Packing. The optical properties of the proposed structure are promising for SuperContinuum Generation. This approach could make accessible not only the equiangular spiral but also other quasi-crystal PCF through SaD
Evolving temporal association rules with genetic algorithms
A novel framework for mining temporal association rules by discovering itemsets with a genetic algorithm is introduced. Metaheuristics have been applied to association rule mining, we show the efficacy of extending this to another variant - temporal association rule mining. Our framework is an enhancement to existing temporal association rule mining methods as it employs a genetic algorithm to simultaneously search the rule space and temporal space. A methodology for validating the ability of the proposed framework isolates target temporal itemsets in synthetic datasets. The Iterative Rule Learning method successfully discovers these targets in datasets with varying levels of difficulty
What is Holding Back Convnets for Detection?
Convolutional neural networks have recently shown excellent results in
general object detection and many other tasks. Albeit very effective, they
involve many user-defined design choices. In this paper we want to better
understand these choices by inspecting two key aspects "what did the network
learn?", and "what can the network learn?". We exploit new annotations
(Pascal3D+), to enable a new empirical analysis of the R-CNN detector. Despite
common belief, our results indicate that existing state-of-the-art convnet
architectures are not invariant to various appearance factors. In fact, all
considered networks have similar weak points which cannot be mitigated by
simply increasing the training data (architectural changes are needed). We show
that overall performance can improve when using image renderings for data
augmentation. We report the best known results on the Pascal3D+ detection and
view-point estimation tasks
Soliton turbulences in the complex Ginzburg-Landau equation
We study spatio-temporal chaos in the complex Ginzburg-Landau equation in
parameter regions of weak amplification and viscosity. Turbulent states
involving many soliton-like pulses appear in the parameter range, because the
complex Ginzburg-Landau equation is close to the nonlinear Schr\"odinger
equation. We find that the distributions of amplitude and wavenumber of pulses
depend only on the ratio of the two parameters of the amplification and the
viscosity. This implies that a one-parameter family of soliton turbulence
states characterized by different distributions of the soliton parameters
exists continuously around the completely integrable system.Comment: 5 figure
Stable circulation modes in a dual-core matter-wave soliton laser
We consider a model of a matter-wave laser generating a periodic array of
solitary-wave pulses. The system, a general version of which was recently
proposed in Ref. [5], is composed of two parallel tunnel-coupled cigar-shaped
traps (a reservoir and a lasing cavity), solitons being released through a
valve at one edge of the cavity. We report a stable lasing mode accounted for
by circulations of a narrow soliton in the cavity, which generates an array of
strong pulses (with 1,000 - 10,000 atoms in each, the array's duty cycle ~ 30%)
when the soliton periodically hits the valve.Comment: J. of Physics B: At. Mol. Opt. Physics, in pres
Fermionic bright soliton in a boson-fermion mixture
We use a time-dependent dynamical mean-field-hydrodynamic model to study the
formation of fermionic bright solitons in a trapped degenerate Fermi gas mixed
with a Bose-Einstein condensate in a quasi-one-dimensional cigar-shaped
geometry. Due to a strong Pauli-blocking repulsion among spin-polarized
fermions at short distances there cannot be bright fermionic solitons in the
case of repulsive boson-fermion interactions. However, we demonstrate that
stable bright fermionic solitons can be formed for a sufficiently attractive
boson-fermion interaction in a boson-fermion mixture. We also consider the
formation of fermionic solitons in the presence of a periodic axial
optical-lattice potential. These solitons can be formed and studied in the
laboratory with present technology.Comment: 7 pages, 7 ps figure
The dependence of the estimated luminosities of ULX on spectral models
Data from {\it Chandra} observations of thirty nearby galaxies were analyzed
and 365 X-ray point sources were chosen whose spectra were not contaminated by
excessive diffuse emission and not affected by photon pile up. The spectra of
these sources were fitted using two spectral models (an absorbed power-law and
a disk blackbody) to ascertain the dependence of estimated parameters on the
spectral model used. It was found that the cumulative luminosity function
depends on the choice of the spectral model, especially for luminosities ergs/s. In accordance with previous results, a large number () of the sources have luminosities ergs/s (Ultra-Luminous X-ray
sources) with indistinguishable average spectral parameters (inner disk
temperature keV and/or photon index ) with those of the
lower luminosities ones. After considering foreground stars and known
background AGN,we identify four sources whose minimum luminosity exceed
ergs/s, and call them Extremely Luminous X-ray sources (ELX). The
spectra of these sources are in general better represented by the disk black
body model than the power-law one. These ELX can be grouped into two distinct
spectral classes. Two of them have an inner disk temperature of keV and
hence are called ``supersoft'' ELX, while the other two have temperatures
keV and are called ``hard'' ELX. The estimated inner disk
temperatures of the supersoft ELX are compatible with the hypothesis that they
harbor intermediate size black holes, which are accreting at times
their Eddington Luminosity. The radiative mechanism for hard ELX, seems to be
Inverse Comptonization, which in contrast to standard black holes systems, is
probably saturated.Comment: Accepted for publication in Astrophysical Journal. 9 pages. Complete
long Tables 4 and 5 are given as tab4.tex and tab5.tex separatel
Dispersion control for matter waves and gap solitons in optical superlattices
We present a numerical study of dispersion manipulation and formation of
matter-wave gap solitons in a Bose-Einstein condensate trapped in an optical
superlattice. We demonstrate a method for controlled generation of matter-wave
gap solitons in a stationary lattice by using an interference pattern of two
condensate wavepackets, which mimics the structure of the gap soliton near the
edge of a spectral band. The efficiency of this method is compared with that of
gap soliton generation in a moving lattice recently demonstrated experimentally
by Eiermann et al. [Phys. Rev. Lett. 92, 230401 (2004)]. We show that, by
changing the relative depths of the superlattice wells, one can fine-tune the
effective dispersion of the matter waves at the edges of the mini-gaps of the
superlattice Bloch-wave spectrum and therefore effectively control both the
peak density and the spatial width of the emerging gap solitons.Comment: 8 pages, 9 figures; modified references in Section 2; minor content
changes in Sections 1 and 2 and Fig. 9 captio
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