1,382 research outputs found
Stable two-dimensional solitary pulses in linearly coupled dissipative Kadomtsev-Petviashvili equations
A two-dimensional (2D) generalization of the stabilized Kuramoto -
Sivashinsky (KS) system is presented. It is based on the Kadomtsev-Petviashvili
(KP) equation including dissipation of the generic (Newell -- Whitehead --
Segel, NWS) type and gain. The system directly applies to the description of
gravity-capillary waves on the surface of a liquid layer flowing down an
inclined plane, with a surfactant diffusing along the layer's surface.
Actually, the model is quite general, offering a simple way to stabilize
nonlinear waves in media combining the weakly-2D dispersion of the KP type with
gain and NWS dissipation. Parallel to this, another model is introduced, whose
dissipative terms are isotropic, rather than of the NWS type. Both models
include an additional linear equation of the advection-diffusion type, linearly
coupled to the main KP-NWS equation. The extra equation provides for stability
of the zero background in the system, opening a way to the existence of stable
localized pulses. The consideration is focused on the case when the dispersive
part of the system of the KP-I type, admitting the existence of 2D localized
pulses. Treating the dissipation and gain as small perturbations and making use
of the balance equation for the field momentum, we find that the equilibrium
between the gain and losses may select two 2D solitons, from their continuous
family existing in the conservative counterpart of the model (the latter family
is found in an exact analytical form). The selected soliton with the larger
amplitude is expected to be stable. Direct simulations completely corroborate
the analytical predictions.Comment: a latex text file and 16 eps files with figures; Physical Review E,
in pres
Detecting child grooming behaviour patterns on social media
Online paedophile activity in social media has become a major concern in society as Internet access is easily available to a broader younger population. One common form of online child exploitation is child grooming, where adults and minors exchange sexual text and media via social media platforms. Such behaviour involves a number of stages performed by a predator (adult) with the final goal of approaching a victim (minor) in person. This paper presents a study of such online grooming stages from a machine learning perspective. We propose to characterise such stages by a series of features covering sentiment polarity, content, and psycho-linguistic and discourse patterns. Our experiments with online chatroom conversations show good results in automatically classifying chatlines into various grooming stages. Such a deeper understanding and tracking of predatory behaviour is vital for building robust systems for detecting grooming conversations and potential predators on social media
Controlled dephasing of Andreev states in superconducting quantum point-contacts
We have studied the relaxation and dephasing processes in a superconducting
quantum point contact induced by the interaction with an electromagnetic
environment. Based on a density matrix approach we obtain the rates for the
dissipative dynamics as function of the transmission, the phase difference on
the contact and the external impedance. Our calculation allows to determine the
appropriate range of parameters for the observation of coherent oscillations in
the current through the contact.Comment: 8 pages, 2 figures. To appear in Physical Review
Influence of Gap Extrema on the Tunneling Conductance Near an Impurity in an Anisotropic Superconductor
Changes: figures added in postscript form, Eq. (7) and various typos
corrected. We examine the effect of an impurity on the nearby tunneling
conductance in an anisotropically-gapped superconductor. The variation of the
conductance has pronounced spatial dependence which depends strongly on the
Fermi surface location of gap extrema. In particular, different gap symmetries
produce profoundly different spatial features in the conductance. These effects
may be detectable with an STM measurement on the surface of a high-temperature
superconductor.Comment: 12 pages (revtex) + 3 figures (included - postscript), NSF-ITP-93-8
Continuous-distribution puddle model for conduction in trilayer graphene
An insulator-to-metal transition is observed in trilayer graphene based on
the temperature dependence of the resistance under different applied gate
voltages. At small gate voltages the resistance decreases with increasing
temperature due to the increase in carrier concentration resulting from thermal
excitation of electron-hole pairs. At large gate voltages excitation of
electron-hole pairs is suppressed, and the resistance increases with increasing
temperature because of the enhanced electron-phonon scattering. We find that
the simple model with overlapping conduction and valence bands, each with
quadratic dispersion relations, is unsatisfactory. Instead, we conclude that
impurities in the substrate that create local puddles of higher electron or
hole densities are responsible for the residual conductivity at low
temperatures. The best fit is obtained using a continuous distribution of
puddles. From the fit the average of the electron and hole effective masses can
be determined.Comment: 18 pages, 5 figure
Multiple Local Curvature Gabor Binary Patterns for Facial Action Recognition
Curvature Gabor features have recently been shown to be powerful facial texture descriptors with applications on face recognition. In this paper we introduce their use in facial action unit (AU) detection within a novel framework that combines multiple Local Curvature Gabor Binary Patterns (LCGBP) on different filter sizes and curvature degrees. The proposed system uses the distances of LCGBP histograms between neutral faces and AU containing faces combined with an AU-specific feature selection and classification process. We achieve 98.6% overall accuracy in our tests with the extended Cohn-Kanade database, which is higher than achieved previously by any state-of-the-artmethod
Design and Development of Ankle-Foot Rehabilitation Exerciser (AFRE) System Using Pneumatic Actuator
This research presents the design and development of a novel strategy for an Ankle-Foot Rehabilitation Exerciser (AFRE) system. AFRE system can be used Continuous Passive Motion (CPM) device and strength endurance training device for early stage functional rehabilitation. The designed mechanism can allow desired maximum and minimum Range of Motion (ROM) for dorsiflexion and plantar flexion (upwards and downwards stretching). This device consists of a new moveable mechanism design prototype using a new double acting Intelligent Pneumatic Actuator (IPA), embedded controller and communication protocol. The drive system consists of a nonlinear moving pneumatic actuator that controls the angle position, force and compliance for stiffness characteristic of the ankle-foot orthosis platform. In addition, the device can be configured through MATLAB via personal computer where the user can adjust the required ROM and resistance for the user in real-time. Analysis carried out during the system validation and testing through selected subjects are presented and discussed. This AFRE system is expected to substitute the traditional therapy and motorized rehabilitation device to increase the healing time of the patient specifically
Heat Kernel Coefficients for Laplace Operators on the Spherical Suspension
In this paper we compute the coefficients of the heat kernel asymptotic
expansion for Laplace operators acting on scalar functions defined on the so
called spherical suspension (or Riemann cap) subjected to Dirichlet boundary
conditions. By utilizing a contour integral representation of the spectral zeta
function for the Laplacian on the spherical suspension we find its analytic
continuation in the complex plane and its associated meromorphic structure.
Thanks to the well known relation between the zeta function and the heat kernel
obtainable via Mellin transform we compute the coefficients of the asymptotic
expansion in arbitrary dimensions. The particular case of a -dimensional
sphere as the base manifold is studied as well and the first few heat kernel
coefficients are given explicitly.Comment: 26 Pages, 1 Figur
Morphological and microstructural characterization of laser-glazedplasma-sprayed thermal barrier coatings
Laser glazing has been revealing a high potential for the improvement of plasma-sprayed (PS) thermal barrier coatings (TBCs) by
reducing surface roughness, eliminating open porosity on the surface and generating a controlled segmented crack network, although the
relationship of the processing parameters with the resultant properties has not yet been completely established. In this investigation, TBCs
consisting of atmospheric plasma-sprayed (APS) ZrO2–8wt.%Y2O3 were subjected to a CO2 continuous wave laser-glazing process in
order to seal its surface porosity, generating an external dense layer. For that purpose, different amounts of radiation resulting from different
scanning speeds were applied to the specimens as well as different track overlapping. Results have shown a significant decrease of the
surface roughness after the laser treatment. All specimens presented a fully dense and porous free external layer with a polyfaceted
columnar microstructure highly adherent to the plasma-sprayed coating. Controlled surface crack networks, extremely dependent on the
laser scanning speed and track overlapping, were achieved for each set of processing parameters. The cracks were found to have a
tendency to be oriented in two perpendicular directions, one in the direction of the laser-beam travel direction, the other perpendicular to it.
Moreover, the cracks parallel to the beam travel direction are found to be on the overlapping zone, coinciding with the edge of the
subsequent track. The cracks are perpendicular to the surface along the densified layer and tend to branch and deviate from the vertical
direction below it, within the porous PS coating. XRD results revealed mainly tV nontransformable tetragonal zirconia with a small
percentage of residual monoclinic zirconia for the as-sprayed coating. All glazed coatings presented only tV nontransformable tetragonal
zirconia with some variations on preferable crystal orientation. Grain sizes varied from 26 to 52 nm, increasing with an increase of laserirradiated
energy; microstrain behaved inversely.Fundação para a Ciência e a Tecnologia (FCT) - Project POCTI/CTM/44590/2002.União Europeia (UE). Fundo Europeu de Desenvolvimento Regional (FEDER)
A study of the centrally produced phiphi system in pp interactions at 450 GeV/c
The reaction pp to pfps(K+K-K+K-) in which the K+K-K+K- system is centrally
produced has been studied at 450 GeV/c. Phi phi production has been found to
dominate this reaction and is compatible with being produced by double Pomeron
exchange. An angular analysis of the phi phi system favours JPC = 2++ and its
dPT dependence is similar to that observed for glueball candidates.Comment: 11 pages, Latex, 4 Figure
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