170 research outputs found
Rotation of an immersed cylinder sliding near a thin elastic coating
It is known that an object translating parallel to a soft wall in a viscous
fluid produces hydro- dynamic stresses that deform the wall, which, in turn,
results in a lift force on the object. Recent experiments with cylinders
sliding under gravity near a soft incline, which confirmed theoretical
arguments for the lift force, also reported an unexplained steady-state
rotation of the cylinders [Saintyves et al. PNAS 113(21), 2016]. Motivated by
these observations, we show, in the lubrication limit, that an infinite
cylinder that translates in a viscous fluid parallel to a soft wall at constant
speed and separation distance must also rotate in order to remain free of
torque. Using the Lorentz reciprocal theorem, we show analytically that for
small deformations of the elastic layer, the angular velocity of the cylinder
scales with the cube of the sliding speed. These predictions are confirmed
numerically. We then apply the theory to the gravity-driven motion of a
cylinder near a soft incline and find qualitative agreement with the
experimental observations, namely that a softer elastic layer results in a
greater angular speed of the cylinder.Comment: 16 pages, 4 figure
Designing arrays of Josephson junctions for specific static responses
We consider the inverse problem of designing an array of superconducting
Josephson junctions that has a given maximum static current pattern as function
of the applied magnetic field. Such devices are used for magnetometry and as
Terahertz oscillators. The model is a 2D semilinear elliptic operator with
Neuman boundary conditions so the direct problem is difficult to solve because
of the multiplicity of solutions. For an array of small junctions in a passive
region, the model can be reduced to a 1D linear partial differential equation
with Dirac distribution sine nonlinearities. For small junctions and a
symmetric device, the maximum current is the absolute value of a cosine Fourier
series whose coefficients (resp. frequencies) are proportional to the areas
(resp. the positions) of the junctions. The inverse problem is solved by
inverse cosine Fourier transform after choosing the area of the central
junction. We show several examples using combinations of simple three junction
circuits. These new devices could then be tailored to meet specific
applications.Comment: The article was submitted to Inverse Problem
Historias de vida e historias lingüísticas : una aproximación a las identidades
Este texto se presentó como comunicación al II Congreso Internacional de Etnografía y Educación: Migraciones y Ciudadanías. Universidad Autónoma de Barcelona, Barcelona, 5-8 Septiembre 2008Desde una perspectiva etnográfica, a través de las historias de vida e historias lingüísticas de niños inmigrados, realizamos una aproximación a sus identidades, como parte constitutiva de la realidad escolar actual. Pretendemos conocer las situaciones de multiculturalidad y plurilingüismo, para formar identidades y contribuir al desarrollo de la convivencia en las escuelas, mediante una metodología interdisciplinar que combina las aportaciones de las Ciencias Sociales, Educativas y Lingüísticas. La aplicación de este estudio es principalmente de tipo educativo, para mejorar la formación inicial de los maestros. Esta comunicación forma parte de una investigación que se realiza en nuestro Departamento en la que, con un enfoque interdisciplinar, participan las áreas de conocimiento de Didáctica y Organización Escolar, Didáctica de la Lengua y Didáctica de las Ciencias Sociales. Adoptamos unas estrategias comunes para construir conocimiento, a fin de integrar las aportaciones procedentes de diversos ámbitos científicos, de manera globalizada y relacional (ALTAVA et al.,1999). Puesto que la realidad es compleja (MORIN, 1994) y que también lo es su conocimiento, asumimos que su aprendizaje requiere la convergencia de distintos clases de saberes procedentes de diferentes ámbitos científicos. En nuestro caso, realizamos aportaciones desde los campos disciplinares de la Lingüística, la Pedagogía y la Didáctica, y desde el conjunto de las Ciencias Sociales (Historia, Antropología, etc.). Nuestro objeto de estudio general es la situación escolar de los niños inmigrantes en la provincia de Castellón, las estrategias didácticas y organizativas que existen en la escuela respecto a la educación intercultural y al multilingüismo.Para lograrlo, en una perspectiva de indagación y acción, dicha investigación pretende dar respuesta a las situaciones de multiculturalidad y plurilingüismo en las escuelas actuales, dentro de la formación (inicial y permanente) de los maestros; todo ello bajo un planteamiento didáctico y académico de una mayor adaptación a la realidad y al proceso de armonización europeas en los programas y metodología docentes
Photoassociative creation of ultracold heteronuclear 6Li40K* molecules
We investigate the formation of weakly bound, electronically excited,
heteronuclear 6Li40K* molecules by single-photon photoassociation in a
magneto-optical trap. We performed trap loss spectroscopy within a range of 325
GHz below the Li(2S_(1/2))+K(4P_(3/2)) and Li(2S_(1/2))+K(4P_(1/2)) asymptotic
states and observed more than 60 resonances, which we identify as rovibrational
levels of 7 of 8 attractive long-range molecular potentials. The long-range
dispersion coefficients and rotational constants are derived. We find large
molecule formation rates of up to ~3.5x10^7s^(-1), which are shown to be
comparable to those for homonuclear 40K_2*. Using a theoretical model we infer
decay rates to the deeply bound electronic ground-state vibrational level
X^1\Sigma^+(v'=3) of ~5x10^4s^(-1). Our results pave the way for the production
of ultracold bosonic ground-state 6Li40K molecules which exhibit a large
intrinsic permanent electric dipole moment.Comment: 6 pages, 4 figures, submitted to EP
Surface and Bulk Relaxation of Vapour-Deposited Polystyrene Glasses
We have studied the liquid-like response of the surface of vapour-deposited
glassy films of polystyrene to the introduction of gold nanoparticles on the
surface. The build-up of polymer material was measured as a function of time
and temperature for both as-deposited films, as well as films that have been
rejuvenated to become normal glasses cooled from the equilibrium liquid. The
temporal evolution of the surface profile is well described by the
characteristic power law of capillary-driven surface flows. In all cases, the
surface evolution of the as-deposited films and the rejuvenated films are
enhanced compared to bulk and are not easily distinguishable from each other.
The temperature dependence of the measured relaxation times determined from the
surface evolution is found to be quantitatively comparable to similar studies
for high molecular weight spincast polystyrene. Comparisons to numerical
solutions of the glassy thin film equation provide quantitative estimates of
the surface mobility. For temperatures sufficiently close to the
glass-transition temperature, particle embedding is also measured and used as a
probe of bulk dynamics, and in particular bulk viscosity
Seasonal H1N1 2007 influenza virus infection is associated with elevated pre‐exposure antibody titers to the 2009 pandemic influenza A (H1N1) virus
AbstractThe new influenza strain detected in humans in April 2009 has caused the first influenza pandemic of the 21st century. A cross‐reactive antibody response, in which antibodies against seasonal H1N1 viruses neutralized the 2009 pandemic influenza A (H1N1) virus (2009 pH1N1), was detected among individuals aged >60 years. However, factors other than age associated with such a cross‐reactive antibody response are poorly documented. Our objective was to examine factors potentially associated with elevated pre‐exposure viro‐neutralization and hemagglutination‐inhibition antibody titers against the 2009 pH1N1. We also studied factors associated with antibody titers against the 2007 seasonal H1N1 virus. One hundred subjects participating in an influenza cohort were selected. Sera collected in 2008 were analysed using hemagglutination inhibition and viro‐neutralization assays for the 2009 pH1N1 virus and the 2007 seasonal H1N1 virus. Viro‐neutralization results were explored using a linear mixed‐effect model and hemagglutination‐inhibition results using linear‐regression models for interval‐censored data. Elevated antibody titers against 2009 pH1N1 were associated with seasonal 2007 H1N1 infection (viro‐neutralization, p 0.006; hemagglutination‐inhibition, p 0.018). Elevated antibody titers were also associated with age in the viro‐neutralization assay (p <0.0001). Seasonal 2007 H1N1 infection is an independent predictor of elevated pre‐exposure antibody titers against 2009 pH1N1 and may have contributed to lowering the burden of the 2009 pH1N1 pandemic
Large atom number dual-species magneto-optical trap for fermionic 6Li and 40K atoms
We present the design, implementation and characterization of a dual-species
magneto-optical trap (MOT) for fermionic 6Li and 40K atoms with large atom
numbers. The MOT simultaneously contains 5.2x10^9 6Li-atoms and 8.0x10^9
40K-atoms, which are continuously loaded by a Zeeman slower for 6Li and a
2D-MOT for 40K. The atom sources induce capture rates of 1.2x10^9 6Li-atoms/s
and 1.4x10^9 40K-atoms/s. Trap losses due to light-induced interspecies
collisions of ~65% were observed and could be minimized to ~10% by using low
magnetic field gradients and low light powers in the repumping light of both
atomic species. The described system represents the starting point for the
production of a large-atom number quantum degenerate Fermi-Fermi mixture
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