1,977 research outputs found
A simple preconditioned domain decomposition method for electromagnetic scattering problems
We present a domain decomposition method (DDM) devoted to the iterative
solution of time-harmonic electromagnetic scattering problems, involving large
and resonant cavities. This DDM uses the electric field integral equation
(EFIE) for the solution of Maxwell problems in both interior and exterior
subdomains, and we propose a simple preconditioner for the global method, based
on the single layer operator restricted to the fictitious interface between the
two subdomains.Comment: 23 page
Blind fluorescence structured illumination microscopy: A new reconstruction strategy
In this communication, a fast reconstruction algorithm is proposed for
fluorescence \textit{blind} structured illumination microscopy (SIM) under the
sample positivity constraint. This new algorithm is by far simpler and faster
than existing solutions, paving the way to 3D and/or real-time 2D
reconstruction.Comment: submitted to IEEE ICIP 201
A Metric for Gradient RG Flow of the Worldsheet Sigma Model Beyond First Order
Tseytlin has recently proposed that an action functional exists whose
gradient generates to all orders in perturbation theory the Renormalization
Group (RG) flow of the target space metric in the worldsheet sigma model. The
gradient is defined with respect to a metric on the space of coupling constants
which is explicitly known only to leading order in perturbation theory, but at
that order is positive semi-definite, as follows from Perelman's work on the
Ricci flow. This gives rise to a monotonicity formula for the flow which is
expected to fail only if the beta function perturbation series fails to
converge, which can happen if curvatures or their derivatives grow large. We
test the validity of the monotonicity formula at next-to-leading order in
perturbation theory by explicitly computing the second-order terms in the
metric on the space of coupling constants. At this order, this metric is found
not to be positive semi-definite. In situations where this might spoil
monotonicity, derivatives of curvature become large enough for higher order
perturbative corrections to be significant.Comment: 15 pages; Erroneous sentence in footnote 14 removed; this version
therefore supersedes the published version (our thanks to Dezhong Chen for
the correction
A characterization of Dirac morphisms
Relating the Dirac operators on the total space and on the base manifold of a
horizontally conformal submersion, we characterize Dirac morphisms, i.e. maps
which pull back (local) harmonic spinor fields onto (local) harmonic spinor
fields.Comment: 18 pages; restricted to the even-dimensional cas
Localization and chemical forms of cadmium in plant samples by combining analytical electron microscopy and X-ray spectromicroscopy
International audienceCadmium (Cd) is a metal of high toxicity for plants. Resolving its distribution and speciation in plants is essential for understanding the mechanisms involved in Cd tolerance, trafficking and accumulation. The model plant Arabidopsis thaliana was exposed to cadmium under controlled conditions. Elemental distributions in the roots and in the leaves were determined using scanning electron microscopy coupled with energy dispersive X-ray microanalysis (SEM-EDX), and synchrotron-based micro X-ray fluorescence (μ-XRF), which offers a better sensitivity. The chemical form(s) of cadmium was investigated using Cd LIII-edge (3538 eV) micro X-ray absorption near edge structure (μ-XANES) spectroscopy. Plant μ-XANES spectra were fitted by linear combination of Cd reference spectra. Biological sample preparation and conditioning is a critical point because of possible artifacts. In this work we compared freeze-dried samples analyzed at ambient temperature and frozen hydrated samples analyzed at −170 °C. Our results suggest that in the roots Cd is localized in vascular bundles, and coordinated to S ligands. In the leaves, trichomes (epidermal hairs) represent the main compartment of Cd accumulation. In these specialized cells, μ-XANES results show that the majority of Cd is bound to O/N ligands likely provided by the cell wall, and a minor fraction could be bound to S-containing ligands. No significant difference in Cd speciation was observed between freeze-dried and frozen hydrated samples. This work illustrates the interest and the sensitivity of Cd LIII-edge XANES spectroscopy, which is applied here for the first time to plant samples. Combining μ-XRF and Cd LIII-edge μ-XANES spectroscopy offers promising tools to study Cd storage and trafficking mechanisms in plants and other biological samples
A VIA CRUCIS DO DESEJO FEMININO: UM ESTUDO SOBRE A ESCRITA DE CLARICE LISPECTOR
Esta tese discute a presença do desejo feminino na ficção da escritora brasileira Clarice Lispector. O recorte da pesquisa é o polêmico livro A via crucis do corpo, publicado pela escritora em 1974. O volume foi mal recebido pela crÃtica da época de lançamento e foi pouco traduzido até hoje. Encomendada para falar de sexo, a obra é bastante crÃtica, elaborada num tom irônico por meio de narrativas que exibem a crueza e a complexidade humanas. Criticando o mercado literário, o livro utiliza o sexo como tema para tratar também de outras questões, como a violência e a opressão. Numa aproximação da psicanálise à literatura, a pesquisa aborda explicações sobre o desenvolvimento da sexualidade, considerando as teorias freudiana e lacaniana sobre a feminilidade. Ironizando temas complexos e perigosos, a começar pelo tÃtulo, A via crucis do corpo sugere traços de feminismo e de autobiografia nos seus textos de ficção. A tese faz um recorte da fortuna crÃtica e acadêmica da escritora e também retoma a crÃtica feminista de Hélène Cixous e Luce Irigaray sobre a escrita clariceana
Surgery and the Spectrum of the Dirac Operator
We show that for generic Riemannian metrics on a simply-connected closed spin
manifold of dimension at least 5 the dimension of the space of harmonic spinors
is no larger than it must be by the index theorem. The same result holds for
periodic fundamental groups of odd order.
The proof is based on a surgery theorem for the Dirac spectrum which says
that if one performs surgery of codimension at least 3 on a closed Riemannian
spin manifold, then the Dirac spectrum changes arbitrarily little provided the
metric on the manifold after surgery is chosen properly.Comment: 23 pages, 4 figures, to appear in J. Reine Angew. Mat
A Reilly formula and eigenvalue estimates for differential forms
We derive a Reilly-type formula for differential p-forms on a compact
manifold with boundary and apply it to give a sharp lower bound of the spectrum
of the Hodge Laplacian acting on differential forms of an embedded hypersurface
of a Riemannian manifold. The equality case of our inequality gives rise to a
number of rigidity results, when the geometry of the boundary has special
properties and the domain is non-negatively curved. Finally we also obtain, as
a by-product of our calculations, an upper bound of the first eigenvalue of the
Hodge Laplacian when the ambient manifold supports non-trivial parallel forms.Comment: 22 page
Fluorescence blind structured illumination microscopy: a new reconstruction strategy
International audienceIn this communication, a fast reconstruction algorithm is proposed for fluorescence blind structured illumination mi-croscopy (SIM) under the sample positivity constraint. This new algorithm is by far simpler and faster than existing solutions , paving the way to 3D and real-time 2D reconstruction
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