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(203) Production(s) de l'année 2015


A possible explanation of the nature of dark matter by Newtonian mechanics
Auteur(s): OliviTran N., Cannat M
(Document sans référence bibliographique) 20151116
Ref HAL: hal01230773_v1
DOI: 10.13140/RG.2.1.2035.1448
Exporter : BibTex  endNote
Résumé: We calculate the trajectory of a moving object on earth and the trajectory of the earth around the sun in a fourdimensional space (x, y, z, t). We see that the trajectory has a mass: this is what is called dark matter which mass depends on the mass of the moving object. Indeed the deformation of space, the track, deviates light as we are at the hypersurface of the universe, and that is the method of measurement of the 'mass' of the universe.




From singleparticle to collective effective temperatures in an active fluid of selfpropelled particles
Auteur(s): Levis D., Berthier L.
(Article) Publié:
Epl, vol. 111 p.60006 (2015)
Ref HAL: hal01229483_v1
Ref Arxiv: 1506.08553
DOI: 10.1209/02955075/111/60006
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: We present a comprehensive analysis of effective temperatures based on fluctuationdissipation relations in a model of an active fluid composed of selfpropelled hard disks. We first investigate the relevance of effective temperatures in the dilute and moderately dense fluids. We find that a unique effective temperature does not in general characterize the nonequilibrium dynamics of the active fluid over this broad range of densities, because fluctuationdissipation relations yield a lengthscaledependent effective temperature. By contrast, we find that the approach to a nonequilibrium glass transition at very large densities is accompanied by the emergence of a unique effective temperature shared by fluctuations at all lengthscales. This suggests that an effective thermal dynamics generically emerges at long times in very dense suspensions of active particles due to the collective freezing occurring at nonequilibrium glass transitions.
Commentaires: 6 pages, 3 figs. Réf Journal: EPL 111, 60006 (2015)



High numerical aperture holographic microscopy reconstruction with extended z range
Auteur(s): Verrier N., Donnarumma D., Tessier G, Gross M.
(Article) Publié:
Applied Optics, vol. p. (2015)
Ref HAL: hal01225788_v1
Ref Arxiv: 1511.04263
DOI: 10.1364/AO.54.009540
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: An holographic microscopy reconstruction method compatible with high numerical aperture microscope objective (MO) up to NA=1.4 is proposed. After off axis and reference field curvature corrections, and after selection of the +1 grating order holographic image, a phase mask that transforms the optical elements of the holographic setup into an afocal device is applied in the camera plane. The reconstruction is then made by the angular spectrum method. The field is first propagated in the image half space from the camera to the afocal image of the MO optimal plane (plane for which MO has been designed) by using a quadratic kernel. The field is then propagated from the MO optimal plane to the object with the exact kernel. Calibration of the reconstruction is made by imaging a calibrated object like an USAF resolution target for different positions along z. Once the calibration is done, the reconstruction can be made with an object located in any plane z. The reconstruction method has been validated experimentally with an USAF target imaged with a NA=1.4 microscope objective. Nearoptimal resolution is obtained over an extended range (±50 µm) of z locations.




Bursting of Dilute EmulsionBased Liquid Sheets Driven by a Marangoni Effect
Auteur(s): Vernay C., Ramos L., Ligoure C.
(Article) Publié:
Physical Review Letters, vol. 115 p.198302 (2015)
Ref HAL: hal01225954_v1
Ref Arxiv: 1511.00451
DOI: 10.1103/PhysRevLett.115.198302
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: We study the destabilization mechanism of thin liquid sheets expanding in air and show that dilute oilinwater emulsionbased sheets disintegrate through the nucleation and growth of holes that perforate the sheet. The velocity and thickness fields of the sheet outside the holes are not perturbed by holes and hole opening follows a TaylorCulick law. We find that a prehole, which widens and thins out the sheet with time, systematically precedes the hole nucleation. The growth dynamics of the prehole follows the law theoretically predicted for a liquid spreading on another liquid of higher surface tension due to Marangoni stresses. Classical Marangoni spreading experiments quantitatively corroborate our findings.



Clogging of a single pore by colloidal particles
Auteur(s): Dersoir Benjamin, Robert de Saint Vincent Matthieu, Abkarian M., Tabuteau Hervé
(Article) Publié:
Microfluidics And Nanofluidics, vol. 19 p.953961 (2015)
Ref HAL: hal01225631_v1
DOI: 10.1007/s104040151624y
Exporter : BibTex  endNote
Résumé: The clogging of porous media by colloidal particles is a complex process which relies on many different physical phenomena. The formation and the structure of a clog results from the interplay between hydrodynamics (flow rate and pore geometry) and the DLVO forces (particle–particle and particle–wall). In order to get a better understanding of this process, we study the clogging of a microfluidic filter, at the single pore level, and determine the influence of each relevant parameter separately. We show that in order to form stable clogs, colloidal particles have to pile up over a length in the flow direction roughly equal to the width of the pore. We found that there are two clogging regimes, which depend on the applied pressure. In the first one, at low pressures, the length of the clog within the pore and the number of particles that pass through the pore prior to clogging are constant. In the second one, for higher pressures, both quantities increase with the pressure. We also show that a higher ionic strength accelerates the clog formation, keeping constant the length of the clog



The Influence of LongRange Surface Forces on the Contact Angle of Nanometric Droplets and Bubbles
Auteur(s): Stocco A., Moehwald H.
(Article) Publié:
Langmuir, vol. 31 p.11835–11841 (2015)
Ref HAL: hal01225317_v1
DOI: 10.1021/acs.langmuir.5b02922
Exporter : BibTex  endNote
Résumé: For a droplet or a bubble of dimensions below 100 nm, longrange surface forces such as longrange van der Waals forces can compete with capillarity, which leads to a size dependence of the contact angle. This is discussed in this work, where we also show that the effect cannot simply be described by a normalized line tension. We calculate interfacial profiles for typical values of van der Waals forces and discuss the role of longrange surface forces on the contact angle of nanobubbles and nanodrops.



Theta series, wallcrossing and quantum dilogarithm identities
Auteur(s): Alexandrov S., Pioline Boris
(Document sans référence bibliographique) 20151109
Ref HAL: hal01229341_v1
Ref Arxiv: 1511.02892
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: Motivated by mathematical structures which arise in string vacua and gauge theories with N=2 supersymmetry, we study the properties of certain generalized theta series which appear as Fourier coefficients of functions on a twisted torus. In CalabiYau string vacua, such theta series encode instanton corrections from $k$ NeveuSchwarz fivebranes. The theta series are determined by vectorvalued wavefunctions, and in this work we obtain the transformation of these wavefunctions induced by KontsevichSoibelman symplectomorphisms. This effectively provides a quantum version of these transformations, where the quantization parameter is inversely proportional to the fivebrane charge $k$. Consistency with wallcrossing implies a new fiveterm relation for Faddeev's quantum dilogarithm $\Phi_b$ at $b=1$, which we prove. By allowing the torus to be noncommutative, we obtain a more general fiveterm relation valid for arbitrary $b$ and $k$, which may be relevant for the physics of fivebranes at finite chemical potential for angular momentum.
Commentaires: 26 pages
