Université Paris 8

Abstract I present a finite-difference method for modeling P-SV wave propagation in heterogeneous media. This is an extension of the method I previously proposed for modeling SH-wave propagation by using velocity and stress in a discrete grid. The two components of the velocity cannot be defined at the same node for a complete staggered grid: the stability condition and the P-wave phase velocity dispersion curve do not depend on the Poisson's ratio, while the S-wave phase velocity dispersion curve behavior is rather insensitive to the Poisson's ratio. Therefore, the same code used for elastic media can be used for liquid media, where S-wave velocity goes to zero, and no special treatment is needed for a liquid-solid interface. Typical physical phenomena arising with P-SV modeling, such as surface waves, are in agreement with analytical results. The weathered-layer and corner-edge models show in seismograms the same converted phases obtained by previous authors. This method gives stable results for step discontinuities, as shown for a liquid layer above an elastic half-space. The head wave preserves the correct amplitude. Finally, the corner-edge model illustrates a more complex geometry for the liquid-solid interface. As the Poisson's ratio v increases from 0.25 to 0.5, the shear converted phases are removed from seismograms and from the time section of the wave field.

We show that, under a sparsity scenario, the Lasso estimator and the Dantzig selector exhibit similar behavior. For both methods, we derive, in parallel, oracle inequalities for the prediction risk in the general nonparametric regression model, as well as bounds on the ℓp estimation loss for 1≤p≤2 in the linear model when the number of variables can be much larger than the sample size.

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SUMMARY Much recent effort has sought asymptotically minimax methods for recovering infinite dimensional objects—curves, densities, spectral densities, images—from noisy data. A now rich and complex body of work develops nearly or exactly minimax estimators for an array of interesting problems. Unfortunately, the results have rarely moved into practice, for a variety of reasons—among them being similarity to known methods, computational intractability and lack of spatial adaptivity. We discuss a method for curve estimation based on n noisy data: translate the empirical wavelet coefficients towards the origin by an amount √(2 log n)σ/√n. The proposal differs from those in current use, is computationally practical and is spatially adaptive; it thus avoids several of the previous objections. Further, the method is nearly minimax both for a wide variety of loss functions—pointwise error, global error measured in Lp-norms, pointwise and global error in estimation of derivatives—and for a wide range of smoothness classes, including standard Holder and Sobolev classes, and bounded variation. This is a much broader near optimality than anything previously proposed: we draw loose parallels with near optimality in robustness and also with the broad near eigenfunction properties of wavelets themselves. Finally, the theory underlying the method is interesting, as it exploits a correspondence between statistical questions and questions of optimal recovery and information-based complexity.

Abstract Given a probability space ( X , μ) and a bounded domain Ω in ℝ d equipped with the Lebesgue measure |·| (normalized so that |Ω| = 1), it is shown (under additional technical assumptions on X and Ω) that for every vector‐valued function u ∈ L p ( X , μ; ℝ d ) there is a unique “polar factorization” u = ∇Ψ s , where Ψ is a convex function defined on Ω and s is a measure‐preserving mapping from ( X , μ) into (Ω, |·|), provided that u is nondegenerate, in the sense that μ( u −1 ( E )) = 0 for each Lebesgue negligible subset E of ℝ d . Through this result, the concepts of polar factorization of real matrices, Helmholtz decomposition of vector fields, and nondecreasing rearrangements of real‐valued functions are unified. The Monge‐Ampère equation is involved in the polar factorization and the proof relies on the study of an appropriate “Monge‐Kantorovich” problem.

At high-energy colliders, jets of hadrons are the observable counterparts of the perturbative concepts of quarks and gluons. Good procedures for identifying jets are central to experimental analyses and comparisons with theory. The kt family of successive recombination jet finders has been widely advocated because of its conceptual simplicity and flexibility and its unique ability to approximately reconstruct the partonic branching sequence in an event. Until now however, it had been believed that for an ensemble of N particles the algorithmic complexity of the kt jet finder scaled as N3, a severe issue in the high multiplicity environments of LHC and heavy-ion colliders. We here show that the computationally complex part of kt jet-clustering can be reduced to two-dimensional nearest neighbour location for a dynamic set of points. Borrowing techniques developed for this extensively studied problem in computational geometry, kt jet-finding can then be performed in NlnN time. Code based on these ideas is found to run faster than all other jet finders in current use.

Time reversal of ultrasonic fields represents a way to focus through an inhomogeneous medium. This may be accomplished by a time-reversal mirror (TRM) made from an array of transmit-receive transducers that respond linearly and allow the incident acoustic pressure to be sampled. The pressure field is then time-reversed and re-emitted. This process can be used to focus through inhomogeneous media on a reflective target that behaves as an acoustic source after being insonified. The time-reversal approach is introduced in a discussion of the classical techniques used for focusing pulsed waves through inhomogeneous media (adaptive time-delay techniques). Pulsed wave time-reversal focusing is shown using reciprocity valid in inhomogeneous medium to be optimal in the sense that it realizes the spatial-temporal matched filter to the inhomogeneous propagation transfer function between the array and the target. The research on time-reversed wave fields has also led to the development of new concepts that are described: time-reversal cavity that extends the concept of the TRM, and iterative time-reversal processing for automatic sorting of targets according to their reflectivity and resonating of extended targets.

Is calculation possible without language? Or is the human ability for arithmetic dependent on the language faculty? To clarify the relation between language and arithmetic, we studied numerical cognition in speakers of Mundurukú, an Amazonian language with a very small lexicon of number words. Although the Mundurukú lack words for numbers beyond 5, they are able to compare and add large approximate numbers that are far beyond their naming range. However, they fail in exact arithmetic with numbers larger than 4 or 5. Our results imply a distinction between a nonverbal system of number approximation and a language-based counting system for exact number and arithmetic.

SCISAT‐1, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earth's atmosphere. It was launched into low Earth circular orbit (altitude 650 km, inclination 74°) on 12 Aug. 2003. The primary ACE instrument is a high spectral resolution (0.02 cm −1 ) Fourier Transform Spectrometer (FTS) operating from 2.2 to 13.3 μm (750–4400 cm −1 ). The satellite also features a dual spectrophotometer known as MAESTRO with wavelength coverage of 285–1030 nm and spectral resolution of 1–2 nm. A pair of filtered CMOS detector arrays records images of the Sun at 0.525 and 1.02 μm. Working primarily in solar occultation, the satellite provides altitude profile information (typically 10–100 km) for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest, as well as atmospheric extinction profiles over the latitudes 85°N to 85°S. This paper presents a mission overview and some of the first scientific results.

International audience

AR = aortic regurgitation AS = aortic stenosis AVA = aortic valve area CSA = cross sectional area CWD = continuous wave Doppler D = diameter HOCM = hypertrophic obstructive cardiomyopathy LV = left ventricle LVOT = left ventricular outflow tract MR = mitral regurgitation MS = mitral stenosis MVA = mitral valve area ΔP = pressure gradient RV = right ventricle RVOT = right ventricular outflow tract SV = stroke volume TEE = transesophageal echocardiography T 1/2 = pressure half-time TR = tricuspid regurgitation TS = tricuspid stenosis V = velocity VSD = ventricular septal defect VTI =velocity time integral Valve stenosis is a common heart disorder and an important cause of cardiovascular morbidity and mortality. Echocardiography has become the key tool for the diagnosis and evaluation of valve disease, and is the primary non-invasive imaging method for valve stenosis assessment. Clinical decision-making is based on echocardiographic assessment of the severity of valve stenosis, so it is essential that standards be adopted to maintain accuracy and consistency across echocardiographic laboratories when assessing and reporting valve stenosis. The aim of this paper was to detail the recommended approach to the echocardiographic evaluation of valve stenosis, including recommendations for specific measures of stenosis severity, details of data acquisition and measurement, and grading of severity. These recommendations are based on the scientific literature and on the consensus of a panel of experts. This document discusses a number of proposed methods for evaluation of stenosis severity. On the basis of a comprehensive literature review and expert consensus, these methods were categorized for clinical practice as: It is essential in clinical practice to use an integrative approach when grading the severity of stenosis, combining all Doppler and 2D data, and not relying on one specific measurement. Loading conditions influence velocity and pressure gradients; therefore, these parameters vary depending on intercurrent illness of patients with low vs. high cardiac output. In addition, irregular rhythms or tachycardia can make assessment of stenosis severity problematic. Finally, echocardiographic measurements of valve stenosis must be interpreted in the clinical context of the individual patient. The same Doppler echocardiographic measures of stenosis severity may be clinically important for one patient but less significant for another. Level 1 Recommendation: an appropriate and recommended method for all patients with stenosis of that valve. Level 2 Recommendation: a reasonable method for clinical use when additional information is needed in selected patients. Level 3 Recommendation: a method not recommended for routine clinical practice although it may be appropriate for research applications and in rare clinical cases. Echocardiography has become the standard means for evaluation of aortic stenosis (AS) severity. Cardiac catheterization is no longer recommended 1–3 except in rare cases when echocardiography is non-diagnostic or discrepant with clinical data. This guideline details recommendations for recording and measurement of AS severity using echocardiography. However, although accurate quantitation of disease severity is an essential step in patient management, clinical decision-making depends on several other factors, most importantly This echocardiographic standards document not make recommendations for clinical are in the for of with heart The most common of AS are a aortic valve with stenosis of a and valve disease 1 In and the aortic valve disease for of all valve for of a valve for most of the with a cases of However, AS is stenosis of and AS of evaluation of the aortic valve is based on a of and to the number of and to and In addition, the of imaging and Doppler the of the of or imaging is although transesophageal echocardiography may be when is valve most of the right and left in a and with the of or of the right and in a right left with one of of the left and is is most when the are in with an may a tricuspid valve when a is may an or of the but these are less specific a In and a valve may be However, in stenosis of a aortic valve is to the number of of vs. tricuspid valve of a tricuspid aortic valve is most when the of and is in a of a or tricuspid the severity of valve can be of with or and with a The of valve is a of clinical AS is in a with and most the of the disease the mitral valve so that aortic valve disease is mitral valve or stenosis is stenosis based on the of the in velocity with or Doppler and on the of the outflow may be to a or with to the for with hypertrophic to that in severity ventricular with in in a velocity with with when ventricular are and when ventricular is stenosis is and is to a with or in the of aortic valve assessment to become important for patient and of the vs. and of the assessment of is for the of the TEE may be to echocardiography However, standards to be for data recording and measurement for AS quantitation for data recording and measurement for AS quantitation of AS severity for clinical appropriate in all patients with AS reasonable when additional information is needed in selected patients and not recommended for clinical use velocity LV outflow AS and and transesophageal stroke pressure pressure the pressure the aortic valve velocity of AS of the aortic valve AVA aortic valve AVA AVA valve the of to the AVA number of of AS severity for clinical appropriate in all patients with AS reasonable when additional information is needed in selected patients and not recommended for clinical use velocity LV outflow AS and and transesophageal stroke pressure pressure the pressure the aortic valve velocity of AS of the aortic valve AVA aortic valve AVA AVA valve the of to the AVA number of for Clinical 1 = appropriate in all patients with The primary parameters recommended for clinical evaluation of AS severity AS velocity gradient Valve area The velocity across the aortic or aortic is using Doppler data recording in to the velocity and or right most the or may be patient and of and are velocity measurement a the and of the of the aortic is and be AS velocity is the velocity a other are not The that the aortic velocity is in the and on in an individual patient. 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Abstract This book presents in a self-contained form the typical basic properties of solutions to semilinear evolutionary partial differential equations, with special emphasis on global properties. It considers important examples, including the heat, Klein-Gordon, and Schro"odinger equations, placing each in the analytical framework which allows the most striking statement of the key properties. With the exceptions of the treatment of the Schro"odinger equation, the book employs the most standard methods, each developed in enough generality to cover other cases. This new edition includes a chapter on stability, which contains partial answers to recent questions about the global behavior of solutions. The self-contained treatment and emphasis on central concepts make this text useful to a wide range of applied mathematicians and theoretical researchers.

Cryptochromes are flavoprotein photoreceptors first identified in Arabidopsis thaliana, where they play key roles in growth and development. Subsequently identified in prokaryotes, archaea, and many eukaryotes, cryptochromes function in the animal circadian clock and are proposed as magnetoreceptors in migratory birds. Cryptochromes are closely structurally related to photolyases, evolutionarily ancient flavoproteins that catalyze light-dependent DNA repair. Here, we review the structural, photochemical, and molecular properties of cry-DASH, plant, and animal cryptochromes in relation to biological signaling mechanisms and uncover common features that may contribute to better understanding the function of cryptochromes in diverse systems including in man.

The use of the risk-neutral probability measure has proved to be very powerful for computing the prices of contingent claims in the context of complete markets, or the prices of redundant securities when the assumption of complete markets is relaxed. We show here that many other probability measures can be defined in the same way to solve different asset-pricing problems, in particular option pricing. Moreover, these probability measure changes are in fact associated with numéraire changes, this feature, besides providing a financial interpretation, permits efficient selection of the numéraire appropriate for the pricing of a given contingent claim and also permits exhibition of the hedging portfolio, which is in many respects more important than the valuation itself. The key theorem of general numéraire change is illustrated by many examples, among which the extension to a stochastic interest rates framework of the Margrabe formula, Geske formula, etc.

In this article, we discuss the implications of the fact that adult second language learners (outside the classroom) universally develop a well-structured, efficient and simple form of language–the Basic Variety (BV). Three questions are asked as to (1) the structural properties of the BV, (2) the status of these properties and (3) why some structural properties of ‘fully fledged’ languages are more complex. First, we characterize the BV in four respects: its lexical repertoire, the principles according to which utterances are structured, and temporality and spatiality expressed. The organizational principles proposed are small in number, and interact. We analyse this interaction, describing how the BV is put to use in various complex verbal tasks, in order to establish both what its communicative potentialities are, and also those discourse contexts where the constraints come into conflict and where the variety breaks down. This latter phenomenon provides a partial answer to the third question,concerning the relative complexity of ‘fully fledged’ languages–they have devices to deal with such cases. As for the second question, it is argued firstly that the empirically established continuity of the adult acquisition process precludes any assignment of the BV to a mode of linguistic expression (e.g., ‘protolanguage’) distinct from that of ‘fully fledged’ languages and, moreover, that the organizational constraints of the BV belong to the core attributes of the human language capacity, whereas a number of complexifications not attested in the BV are less central properties of this capacity. Finally, it is shown that the notion of feature strength, as used in recent versions of Generative Grammar, allows a straightforward characterization of the BV as a special case of an I-language, in the sense of this theory. Under this perspective, the acquisition of an Ilanguage beyond the BV can essentially be described as a change in feature strength.

A significant no-load healing period is the generally accepted prerequisite for osseointegration in dental implantology. The aim of this article was to examine whether this no-load healing period is validated by the experimental literature. In vivo histological data was scrutinized to identify the effect of early loading protocols on the bone-implant interface. Several loading modes were identified. They were categorized into groups according to implant design and the type of prosthetic reconstruction, and by their ability to introduce a distinct magnitude of motion at the interface. Specific histologic responses of early loaded implants (i.e., fibrous repair or osseointegration) were suggested to be directly related to the specific combinations of the above parameters. Early loading per se was not found to be detrimental to osseointegration. Specifically, only excessive micromotion was directly implicated in the formation of fibrous encapsulation. The literature suggests that there is a critical threshold of micromotion above which fibrous encapsulation prevails over osseointegration. This critical level, however, was not zero micromotion as generally interpreted. Instead, the tolerated micromotion threshold was found to lie somewhere between 50 and 150 microns. Suggestions are made for the earliest loading time that achieves osseointegration.

Density estimation is a commonly used test case for nonparametric estimation methods. We explore the asymptotic properties of estimators based on thresholding of empirical wavelet coefficients. Minimax rates of convergence are studied over a large range of Besov function classes $B_{\sigma pq}$ and for a range of global $L'_p$ error measures, $1 \leq p' < \infty$. A single wavelet threshold estimator is asymptotically minimax within logarithmic terms simultaneously over a range of spaces and error measures. In particular, when $p' > p$, some form of nonlinearity is essential, since the minimax linear estimators are suboptimal by polynomial powers of n. A second approach, using an approximation of a Gaussian white-noise model in a Mallows metric, is used to attain exactly optimal rates of convergence for quadratic error $(p' = 2)$.

The ACS Virgo Cluster Survey consists of HST ACS imaging for 100 early-type galaxies in the Virgo Cluster, observed in the F475W (≈SDSS g ) and F850LP (≈SDSS z ) filters. We derive distances for 84 of these galaxies using the method of surface brightness fluctuations (SBFs), present the SBF distance catalog, and use this database to examine the three-dimensional distribution of early-type galaxies in the Virgo Cluster. The SBF distance moduli have a mean (random) measurement error of 0.07 mag (0.5 Mpc), or roughly 3 times better than previous SBF measurements for Virgo Cluster galaxies. Five galaxies lie at a distance of d ≈ 23 Mpc and are members of the W' cloud. The remaining 79 galaxies have a narrow distribution around our adopted distance of ⟨ d ⟩ = 16.5 ± 0.1 (random mean error) ±1.1 Mpc (systematic). The rms distance scatter of this sample is σ( d ) = 0.6 ± 0.1 Mpc, with little or no dependence on morphological type or luminosity class (i.e., 0.7 ± 0.1 and 0.5 ± 0.1 Mpc for the giants and dwarfs, respectively). The back-to-front depth of the cluster measured from our sample of early-type galaxies is 2.4 ± 0.4 Mpc (i.e., ±2 σ of the intrinsic distance distribution). The M87 (cluster A) and M49 (cluster B) subclusters are found to lie at distances of 16.7 ± 0.2 and 16.4 ± 0.2 Mpc, respectively. There may be a third subcluster associated with M86. A weak correlation between velocity and line-of-sight distance may be a faint echo of the cluster velocity distribution not having yet completely virialized. In three dimensions, Virgo's early-type galaxies appear to define a slightly triaxial distribution, with axis ratios of (1 : 0.7 : 0.5). The principal axis of the best-fit ellipsoid is inclined ~20°-40° from the line of sight, while the galaxies belonging to the W' cloud lie on an axis inclined by ~10°-15°.

Abstract The aim of this book is to offer a direct and self-contained access to some of the new or recent results in fluid mechanics. It gives an authoritative account on the theory of the Euler equations describing a perfect incompressible fluid. First of all, the text derives the Euler equations from a variational principle, and recalls the relations on vorticity and pressure. Various weak formulations are proposed. The book then presents the tools of analysis necessary for their study: Littlewood-Paley theory, action of Fourier multipliers on L spaces, and partial differential calculus. These techniques are then used to prove various recent results concerning vortext patches or sheets, essentially the persistence of the smoothness of the boundary of a vortex patch, even if that smoothness allows singular points, as well as the existence of weak solutions of the vorticity sheet type. The text also presents properties of microlocal (analytic or Gevrey) regularity of the solutions of Euler equations, and provides links of such properties to the smoothness in time of the flow of the solution vector field.

Brown adipocytes are thermogenic cells which play an important role in energy balance. Their thermogenic activity is due to the presence of a mitochondrial uncoupling protein (UCP). Until recently, it was admitted that in rodents brown adipocytes were mainly located in classical brown adipose tissue (BAT). In the present study, we have investigated the presence of UCP protein or mRNA in white adipose tissue (WAT) of rats. Using polymerase chain reaction or Northern blot hybridization, UCP mRNA was detected in mesenteric, epidydimal, retroperitoneal, inguinal and particularly in periovarian adipose depots. The uncoupling protein was detected by Western blotting in mitochondria from periovarian adipose tissue. When rats were submitted to cold or to treatment with a beta-adrenoceptor agonist, UCP expression was increased in this tissue as in typical brown fat. Moreover, the expression was decreased in obese fa/fa rats compared to lean controls. Morphological studies showed that periovarian adipose tissue of rats kept at 24 degrees C contained cells with numerous typical BAT mitochondria with or without multilocular lipid droplets. Immunocytochemistry confirmed that multilocular cells expressed mitochondrial UCP. Furthermore, the number of brown adipocytes and the density of mitochondrial cristae increased in parallel with exposure to cold. These results demonstrate that adipocytes expressing UCP are present in adipose deposits considered as white fat. They suggest the existence of a continuum in rodents between BAT and WAT, and a great plasticity between adipose tissue phenotypes. The physiological importance of brown adipocytes in WAT and the regulation of UCP expression remain open questions.