Ecoulement pulsatoire dans une conduite comportant une paroi élastique très déformable

Résumé Devant la difficulté d'effectuer correctement des mesures sur un tuyau à priori entièrement souple parcouru par un débit pulsé, on a réalisé un canal dont une partie seulement est constituée par une feuille de caoutchouc déformable par gonflement. On a mesuré la céléritéC des ondes et établi une loi originale liantC à la pression moyennep, de la formeC ³=a ₁ p+a ₂, oùa ₁ eta ₂ sont des facteurs caractéristiques du canal.Une étude théorique fondée sur la méthode cas caractéristiques d'une part et sur les propriétés mécaniques des milieux élastiques à grande déformation non linéaire d'autre part, a permis de retrouver cette relation et de vérifier d'une manière très satisfaisante les propriétés générales de l'écoulement pulsé (répartition des pression eet des vitesses).Une technique précise de mesure des vitesses dans un liquide au moyen d'un anémomètre à film chaud a été élaborée.

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Summary As accurate measurements in a completely extensible pipe are difficult to obtain, a channel has been built where only one part was formed by flflexible rubber sheet. We have measured the wave speedC and established a law forC versus the differential pressurep, of the form:C ³=a ₁+a ₂, wherea ₁ anda ₂ are parameters depending on the channel properties.The results of a theoretical study based on the method of characteristics and on the non-linear theory of finite deformations was found in good agreement with the above relation, and with the general properties of pulsating flow (pressure and velocity distribution).A very accurate method for velocity measurements in a liquid with hot-film anemometry is described.

     

Improved Schemes for Visual Cryptography

A (k,n)-threshold visual cryptography scheme ((k,n)-threshold VCS, for short) is a method to encode a secret image SI into n shadow images called shares such that any k or more shares enable the visual recovery of the secret image, but by inspecting less than k shares one cannot gain any information on the secret image. The visual recovery consists of xeroxing the shares onto transparencies, and then stacking them. Any k shares will reveal the secret image without any cryptographic computation.In this paper we analyze visual cryptography schemes in which the reconstruction of black pixels is perfect, that is, all the subpixels associated to a black pixel are black. For any value of k and n, where 2 k n, we give a construction for (k,n)-threshold VCS which improves on the best previously known constructions with respect to the pixel expansion (i.e., the number of subpixels each pixel of the original image is encoded into). We also provide a construction for coloured (2,n)-threshold VCS and for coloured (n,n)-threshold VCS. Both constructions improve on the best previously known constructions with respect to the pixel expansion.     

Approximation of the Hilbert Transform on the real semiaxis using Laguerre zeros

The authors propose two new algorithms for the computation of Cauchy principal value integrals on the real semiaxis. The proposed quadrature rules use zeros of Laguerre polynomials. Theoretical error estimates are proved and some numerical examples are showed.     

Assigning vibrational spectra of ferryl-oxo intermediates of cytochrome C oxidase by periodic orbits and molecular dynamics

Complexity is inherent in biological molecules not only because of the large number of atoms but also because of their nonlinear interactions responsible for chaotic behaviours, localized motions, and bifurcation phenomena. Thus, versatile spectroscopic techniques have been invented to achieve temporal and spatial resolution to minimize the uncertainties in assigning the spectra of complex molecules. Can we associate spectral lines to specific chemical bonds or species in a large molecule? Can energy stay localized in a bond for a substantial period of time to leave its spectroscopic signature? These longstanding problems are investigated by studying the resonance Raman spectra of ferryl-oxo intermediates of cytochrome c oxidase. The difference spectra of isotopically substituted ferryl oxygen ((16)O minus (18)O) in the cytochrome c oxidase recorded in several laboratories show one or two prominent positive peaks which have not been completely elucidated yet. By applying the hierarchical methods of nonlinear mechanics, and particularly the study of periodic orbits in the active site of the enzyme, in conjunction with molecular dynamics calculations of larger systems which include the embraced active site by the protein and selected protonated/deprotonated conformations of amino acids, we translate the spectral lines to molecular motions. It is demonstrated that for the active site stable periodic orbits exist for a substantial energy range. Families of periodic orbits which are associated with the vibrations of Fe(IV)=O bond mark the regions of phase space where nearby trajectories remain localized, as well as assign the spectral bands of the active site in the protein matrix. We demonstrate that proton movement adjacent to active site, which occurs during the P --> F transition, can lead to significant perturbations of the Fe(IV)=O isotopic difference vibrational spectra in cytochrome c oxidase, without a change in oxidation state of the metal sites. This finding links spectroscopic characteristics to protonation events occurring during enzymatic turnover.     

Numerical treatment of second kind Fredholm integral equations systems on bounded intervals

In this paper the authors propose numerical methods to approximate the solutions of systems of second kind Fredholm integral equations. They prove that such methods are stable and convergent. Error estimates in weighted L^p$L^p$ norm, 1?p?+∞$1?p?+\infty$, are given and some numerical tests are shown.     

Probing the environment of cu(b) in heme-copper oxidases

Time-resolved step-scan FTIR (TRS2-FTIR) and density functional theory have been applied to probe the structural dynamics of CuB in heme-copper oxidases at room temperature. The TRS2-FTIR data of cbb3 from Pseudomonas stutzeri indicate a small variation in the frequency of the transient CO bound to CuB in the pH/pD 7-9 range. This observation in conjunction with density functional theory calculations, in which significant frequency shifts of the nu(CO) are observed upon deprotonation and/or detachment of the CuB ligands, demonstrates that the properties of the CuB ligands including the cross-linked tyrosine, in contrast to previous reports, remain unchanged in the pH 7-9 range. We attribute the small variations in the nu(CO) of CuB to protein conformational changes in the vicinity of CuB. Consequently, the split of the heme Fe-CO vibrations (alpha-, beta-, and gamma-forms) is not due to changes in the ligation and/or protonation states of the CuB ligands or to the presence of one or more ionizable groups, as previously suggested, but the result of global protein conformational changes in the vicinity of CuB which, in turn, affect the position of CuB with respect to the heme Fe.     

Measurement of CP-violating asymmetries in B0 decays to CP eigenstates

We present measurements of time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates. The measurement uses a data sample of 23x10(6) Upsilon(4S)-->BbarB decays collected by the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we find events in which one neutral B meson is fully reconstructed in a CP eigenstate containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the standard model is proportional to sin2beta, is derived from the decay time distributions in such events. The result is sin2beta = 0.34+/-0.20 (stat)+/-0.05 (syst).     

Improved worst-case complexity for the MIN 3-SET COVERING problem

We consider MIN SET COVERING when the subsets are constrained to have maximum cardinality 3. We propose an exact algorithm whose worst-case complexity is bounded above by O^*(1.3957^m), where m is the number of sets in the instance. This result improves upon the previously known bound of O^*(1.4391^m).