1,236 research outputs found
Interfacial thermal transport with strong system-bath coupling: A phonon delocalization effect
We study the effect of system-bath coupling strength on quantum thermal
transport through the interface of two weakly coupled anharmonic molecular
chains using quantum self-consistent phonon approach. The heat current shows a
resonant to bi-resonant transition due to the variations in the interfacial
coupling and temperature, which is attributed to the delocalization of phonon
modes. Delocalization occurs only in the strong system-bath coupling regime and
we utilize it to model a thermal rectifier whose ratio can be non-monotonically
tuned not only with the intrinsic system parameters but also with the external
temperature.Comment: 7 pages, 7 figure
Parameter constraints in a near-equipartition model with multi-frequency \emph{NuSTAR}, \emph{Swift} and \emph{Fermi-LAT} data from 3C 279
Precise spectra of 3C 279 in the 0.5-70 keV range, obtained during two epochs
of
\emph{Swift} and \emph{NuSTAR} observations, are analyzed using a
near-equipartition model. We apply a one-zone leptonic model with a
three-parameter log-parabola electron energy distribution (EED) to fit the
\emph{Swift} and \emph{NuSTAR} X-ray data, as well as simultaneous optical and
\emph{Fermi}-LAT -ray data. The Markov Chain Monte Carlo (MCMC)
technique is used to search the high-dimensional parameter space and evaluate
the uncertainties on model parameters. We show that the two spectra can be
successfully fit in near-equipartition conditions, defined by the ratio of the
energy density of relativistic electrons to magnetic field
being close to unity. In both spectra, the observed X-rays are dominated by
synchrotron-self Compton photons, and the observed rays are dominated
by Compton scattering of external infrared photons from a surrounding dusty
torus.
Model parameters are well constrained. From the low state to the high state,
both the curvature of the log-parabola width parameter and the synchrotron peak
frequency significantly increase. The derived magnetic fields in the two states
are nearly identical (\ G), but the Doppler factor in the high state is
larger than that in the low state (28 versus 18). We derive that
the gamma-ray emission site takes place outside the broad-line region, at
0.1 pc from the black hole, but within the dusty torus. Implications
for 3C 279 as a source of high-energy cosmic-rays are discussed.Comment: accepted by MNRA
The application of manifold based visual speech units for visual speech recognition
This dissertation presents a new learning-based representation that is referred to as a Visual
Speech Unit for visual speech recognition (VSR). The automated recognition of human speech using only features from the visual domain has become a significant research topic that plays an essential role in the development of many multimedia systems such as audio visual speech recognition(AVSR), mobile phone applications, human-computer interaction (HCI) and sign language recognition. The inclusion of the lip visual information is opportune since it can improve the overall accuracy of audio or hand recognition algorithms especially when such systems are operated in environments characterized by a high level of acoustic noise.
The main contribution of the work presented in this thesis is located in the development of a new learning-based representation that is referred to as Visual Speech
Unit for Visual Speech Recognition (VSR). The main components of the developed Visual Speech Recognition system are applied to: (a) segment the mouth region of
interest, (b) extract the visual features from the real time input video image and (c) to identify the visual speech units. The major difficulty associated with the VSR systems resides in the identification of the smallest elements contained in the image sequences that represent the lip movements in the visual domain.
The Visual Speech Unit concept as proposed represents an extension of the standard viseme model that is currently applied for VSR. The VSU model augments the standard viseme approach by including in this new representation not only the data associated with the articulation of the visemes but also the transitory information between consecutive
visemes. A large section of this thesis has been dedicated to analysis the performance of the new visual speech unit model when compared with that attained for standard (MPEG-
4) viseme models. Two experimental results indicate that:
1. The developed VSR system achieved 80-90% correct recognition when the system has been applied to the identification of 60 classes of VSUs, while the
recognition rate for the standard set of MPEG-4 visemes was only 62-72%.
2. 15 words are identified when VSU and viseme are employed as the visual speech element. The accuracy rate for word recognition based on VSUs is 7%-12% higher than the accuracy rate based on visemes
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