718 research outputs found
Detection of the tagged or untagged photons in acousto-optic imaging of thick highly scattering media by photorefractive adaptive holography
We propose an original adaptive wavefront holographic setup based on the
photorefractive effect (PR), to make real-time measurements of acousto-optic
signals in thick scattering media, with a high flux collection at high rates
for breast tumor detection. We describe here our present state of art and
understanding on the problem of breast imaging with PR detection of the
acousto-optic signal
Transient behavior of surface plasmon polaritons scattered at a subwavelength groove
We present a numerical study and analytical model of the optical near-field
diffracted in the vicinity of subwavelength grooves milled in silver surfaces.
The Green's tensor approach permits computation of the phase and amplitude
dependence of the diffracted wave as a function of the groove geometry. It is
shown that the field diffracted along the interface by the groove is equivalent
to replacing the groove by an oscillating dipolar line source. An analytic
expression is derived from the Green's function formalism, that reproduces well
the asymptotic surface plasmon polariton (SPP) wave as well as the transient
surface wave in the near-zone close to the groove. The agreement between this
model and the full simulation is very good, showing that the transient
"near-zone" regime does not depend on the precise shape of the groove. Finally,
it is shown that a composite diffractive evanescent wave model that includes
the asymptotic SPP can describe the wavelength evolution in this transient
near-zone. Such a semi-analytical model may be useful for the design and
optimization of more elaborate photonic circuits whose behavior in large part
will be controlled by surface waves.Comment: 12 pages, 10 figure
Spectral imbalance and the normalized dissipation rate of turbulence
The normalized turbulent dissipation rate is studied in decaying
and forced turbulence by direct numerical simulations, large-eddy simulations,
and closure calculations. A large difference in the values of is
observed for the two types of turbulence. This difference is found at moderate
Reynolds number, and it is shown that it persists at high Reynolds number,
where the value of becomes independent of the Reynolds number, but
is still not unique. This difference can be explained by the influence of the
nonlinear cascade time that introduces a spectral disequilibrium for
statistically nonstationary turbulence. Phenomenological analysis yields simple
analytical models that satisfactorily reproduce the numerical results. These
simple spectral models also reproduce and explain the increase of
at low Reynolds number that is observed in the simulations
Saving Cultural Heritage with Digital Make-Believe: Machine Learning and Digital Techniques to the Rescue
The application of digital methods for content-based curation and dissemination of cultural heritage data offers unique advantages for physical sites at risk of damage. In areas affected by 2011 Arab spring, digital may be the only approach to create believable cultural experiences. We propose a framework incorporating computational methods such as: digital image processing, multi-lingual text analysis, and 3D modelling, to facilitate enhanced data archive, federated search, and analysis. Potential use cases include experiential search, damage assessment, virtual site reconstruction, and provision of augmented information for education and cultural preservation. This paper presents initial findings from an empirical evaluation of existing scene classification methods, applied to detection of cultural heritage sites in the Palmyra region. Results indicate that deep learning offers an appropriate solution to semantic annotation of publicly available cultural heritage image data
Genetic Rat Models of Parkinson's Disease
Parkinson's disease (PD) is a neurodegenerative disease characterized by a specific loss of dopaminergic neurons. Although the vast majority of PD cases are idiopathic in nature, there is a subset that contains genetic links. Of the genes that have been linked to PD, α-synuclein and leucine-rich repeat kinase 2 have been used to develop transgenic rat models of the disease. In this paper we focused on the various transgenic rat models of PD in terms of their ability to mimic key symptoms of PD in a progressive manner. In general, we found that most of these models provided useful tools for the early stages of PD, but the development of new transgenic rats that present significant neuropathologic and motoric deficits in a progressive manner that more accurately mimics PD is needed
Convergence of the Generalized Volume Averaging Method on a Convection-Diffusion Problem: A Spectral Perspective
A mixed formulation is proposed and analyzed mathematically for coupled convection-diïŹusion in heterogeneous medias. Transfer in solid parts driven by pure diïŹusion is coupled
with convection-diïŹusion transfer in ïŹuid parts. This study is carried out for translation-invariant geometries (general inïŹnite cylinders) and unidirectional ïŹows. This formulation brings to the fore a new convection-diïŹusion operator, the properties of which are mathematically studied: its symmetry is ïŹrst shown using a suitable scalar product. It is proved to be self-adjoint with compact
resolvent on a simple Hilbert space. Its spectrum is characterized as being composed of a double set of eigenvalues: one converging towards ââ and the other towards +â, thus resulting in a nonsectorial operator. The decomposition of the convection-diïŹusion problem into a generalized eigenvalue problem permits the reduction of the original three-dimensional problem into a two-dimensional one. Despite the operator being nonsectorial, a complete solution on the inïŹnite cylinder, associated to a step change of the wall temperature at the origin, is exhibited with the help of the operatorâs two sets of eigenvalues/eigenfunctions. On the computational point of view, a mixed variational formulation is naturally associated to the eigenvalue problem. Numerical illustrations are provided for axisymmetrical situations, the convergence of which is found to be consistent with the numerical discretization
Intermittency of velocity time increments in turbulence
We analyze the statistics of turbulent velocity fluctuations in the time
domain. Three cases are computed numerically and compared: (i) the time traces
of Lagrangian fluid particles in a (3D) turbulent flow (referred to as the
"dynamic" case); (ii) the time evolution of tracers advected by a frozen
turbulent field (the "static" case), and (iii) the evolution in time of the
velocity recorded at a fixed location in an evolving Eulerian velocity field,
as it would be measured by a local probe (referred to as the "virtual probe"
case). We observe that the static case and the virtual probe cases share many
properties with Eulerian velocity statistics. The dynamic (Lagrangian) case is
clearly different; it bears the signature of the global dynamics of the flow.Comment: 5 pages, 3 figures, to appear in PR
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