169,848 research outputs found
Maçonnerie / par A. Demanet,...
No full textCollection : Bibliothèque des professions industrielles, commerciales et agricoles. Série C, Art de l'ingénieur ; 10Collection : Bibliothèque des professions industrielles, commerciales et agricoles ; 1
Cliniques de médecine interne :Hôpital Saint-Pierre
No full textSYL-006983 = Fascicule 1 ;SYL-006984 = Fascicule 2 ;SYL-006986 = Fascicule 4 ;SYL-006987 = Fascicule 5 ;SYL-006988 = Fascicule 6 ;SYL-006989 = Fascicule 7 ;SYL-006990 = Fascicule 8 ;SYL-006991 = Fascicule 10 ;SYL-006992 = Fascicule 13 ;SYL-006993 = Fascicule 14Fascicule 1 contient :Chapitre 1 :Les oedèmes /Demanet, Chapitre 2 :L'hypertension artérielle /Demanet -- Fascicule 2 contient :Les urémies diagnostic différentiel et mise au point des urémies /Demanet Paduart, Chapitre 4 :Les troubles électrolytiques / Demanet, Chapitre 5 :Les troubles du rythme /Bernard -- Fascicule 4 contient :Chapitre 6 :Les anticoagulants et les agents thrombolytiques en thérapeutique / Neve, Chapitre 7 :Le traitement médical de l'angor / M. Englert, Chapitre 8 :L'insuffisance respiratoire chronique /J. C. Yernault -- Chapitre 5 contient :L'antibiothérapie extra-hospitalière actualisation 1977 /J. Sternon -- Fascicule 6 :Les comas /Cornil, Coma neurologique /Franken, Les hémiplégies /Franken, Les vertiges /Gérard, Le syndrome méninge / Francken, Perte de connaissance de courte durée /Francken -- Fascicule 7 contient :Algies faciales unilatérales, Les méningites, Les troubles de la marche, Les algies des membres inférieurs -- Fascicule 8 contient :Diagnostic différentiel /Franken, Diabète, Classification, Classification du diabète selon l'âge, Le diabète -- Le Fascicule 10 contient :Thérapeutique des affections rhumatismales, Douleurs abdominales, Anémies hémolytiques, Insuffisance rénale aigue, Arrêt circulatoire, Hyperaldostéronisme, Syndrome néphrotique, Embolie pulmonaire -- Fascicule 13 contient :Séminaire technique d'électrocardiographie /Englert3 édition 4 tirage Année académique 1979-19804me Doctoratinfo:eu-repo/semantics/published
Compressive wave computation
No full textThis paper presents a method for computing the solution to the time-dependent wave equation from the knowledge of a largely incomplete set of eigenfunctions of the Helmholtz operator, chosen at random. While a linear superposition of eigenfunctions can fail to properly synthesize the solution if a single term is missing, it is shown that solving a sparsity-promoting ℓ 1 minimization problem can vastly enhance the quality of recovery. This phenomenon may be seen as “compressive sampling in the Helmholtz domain.”
An error bound is formulated for the one-dimensional wave equation with coefficients of small bounded variation. Under suitable assumptions, it is shown that the number of eigenfunctions needed to evolve a sparse wavefield defined on N points, accurately with very high probability, is bounded by C()logNloglogN where C(η) is related to the desired accuracy η and can be made to grow at a much slower rate than N when the solution is sparse. To the authors’ knowledge, the partial differential equation estimates that underlie this result are new and may be of independent mathematical interest. They include an L [superscript 1] estimate for the wave equation, an L [infinity symbol]−L[superscript 2] estimate of the extension of eigenfunctions, and a bound for eigenvalue gaps in Sturm–Liouville problems.
In practice, the compressive strategy is highly parallelizable, and may eventually lead to memory savings for certain inverse problems involving the wave equation. Numerical experiments illustrate these properties in one spatial dimension.National Science Foundation (U.S.
Curvelets, Wave Atoms, and Wave Equations
No full textWe argue that two specific wave packet families---curvelets and wave atoms---provide powerful tools for representing linear systems of hyperbolic differential equations with smooth, time-independent coefficients. In both cases, we prove that the matrix representation of the Green's function is sparse in the sense that the matrix entries decay nearly exponentially fast (i.e., faster than any negative polynomial), and well organized in the sense that the very few nonnegligible entries occur near a few shifted diagonals, whose location is predicted by geometrical optics.
This result holds only when the basis elements obey a precise parabolic balance between oscillations and support size, shared by curvelets and wave atoms but not wavelets, Gabor atoms, or any other such transform.
A physical interpretation of this result is that curvelets may be viewed as coherent waveforms with enough frequency localization so that they behave like waves but at the same time, with enough spatial localization so that they simultaneously behave like particles.
We also provide fast digital implementations of tight frames of curvelets and wave atoms in two dimensions. In both cases the complexity is O(N² log N) flops for N-by-N Cartesian arrays, for forward as well as inverse transforms.
Finally, we present a geometric strategy based on wave atoms for the numerical solution of wave equations in smoothly varying, 2D time-independent periodic media. Our algorithm is based on sparsity of the matrix representation of Green's function, as above, and also exploits its low-rank block structure after separation of the spatial indices. As a result, it becomes realistic to accurately build the full matrix exponential using repeated squaring, up to some time which is much larger than the CFL timestep. Once available, the wave atom representation of the Green's function can be used to perform 'upscaled' timestepping.
We show numerical examples and prove complexity results based on a priori estimates of sparsity and separation ranks. They beat the O(N^3) bottleneck on an N-by-N grid, for a wide range of physically relevant situations. In practice, the current wave atom solver can become competitive over a pseudospectral method in the regime when the wave equation should be solved several times with different initial conditions, as in reflection seismology.</p
Fast wave computation via Fourier integral operators
No full textThis paper presents a numerical method for ``time upscaling'' wave equations, i.e., performing time steps not limited by the Courant-Friedrichs-Lewy (CFL) condition. The proposed method leverages recent work on fast algorithms for pseudodifferential and Fourier integral operators (FIO). This algorithmic approach is not asymptotic: it is shown how to construct an exact FIO propagator by 1) solving Hamilton-Jacobi equations for the phases, and 2) sampling rows and columns of low-rank matrices at random for the amplitudes. The setting of interest is that of scalar waves in two-dimensional smooth periodic media (of class C∞ over the torus), where the bandlimit of the waves goes to infinity. In this setting, it is demonstrated that the algorithmic complexity for solving the wave equation to fixed time T ≃ 1 can be as low as O(N [superscript 2] log N) with controlled accuracy. Numerical experiments show that the time complexity can be lower than that of a spectral method in certain situations of physical interest
Scattering in Flatland: Efficient Representations via Wave Atoms
No full textThis paper presents a numerical compression strategy for the boundary integral equation of acoustic scattering in two dimensions. These equations have oscillatory kernels that we represent in a basis of wave atoms, and compress by thresholding the small coefficients to zero.
This phenomenon was perhaps first observed in 1993 by Bradie, Coifman, and Grossman, in the context of local Fourier bases (Bradie et al. in Appl. Comput. Harmon. Anal. 1:94–99, 1993). Their results have since then been extended in various ways. The purpose of this paper is to bridge a theoretical gap and prove that a well-chosen fixed expansion, the non-standard wave atom form, provides a compression of the acoustic single- and double-layer potentials with wave number k as O(k)-by-O(k) matrices with C ε δ k 1+δ non-negligible entries, with δ>0 arbitrarily small, and ε the desired accuracy. The argument assumes smooth, separated, and not necessarily convex scatterers in two dimensions. The essential features of wave atoms that allow this result to be written as a theorem are a sharp time-frequency localization that wavelet packets do not obey, and a parabolic scaling (wavelength of the wave packet) ∼ (essential diameter)2. Numerical experiments support the estimate and show that this wave atom representation may be of interest for applications where the same scattering problem needs to be solved for many boundary conditions, for example, the computation of radar cross sections
Sublinear Randomized Algorithms for Skeleton Decompositions
No full textA skeleton decomposition of a matrix A is any factorization of the form A[subscript :C]ZA[subscript R:], where A[subscript :C] comprises columns of A, and A[subscript R:] comprises rows of A. In this paper, we investigate the conditions under which random sampling of C and R results in accurate skeleton decompositions. When the singular vectors (or more generally the generating vectors) are incoherent, we show that a simple algorithm returns an accurate skeleton in sublinear O(ℓ[superscript 3]) time from ℓ ~ k log n rows and columns drawn uniformly at random, with an approximation error of the form O([n over ℓ]σ[subscript k]) whereσ[subscript k] is the kth singular value of A. We discuss the crucial role that regularization plays in forming the middle matrix U as a pseudoinverse of the restriction A[subscript RC] of A to rows in R and columns in C. The proof methods enable the analysis of two alternative sublinear-time algorithms, based on the rank-revealing QR decomposition, which allows us to tighten the number of rows and/or columns to k with error bound proportional to σ[subscript k].National Science Foundation (U.S.)Alfred P. Sloan Foundatio
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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