Wobbling of a liquid column between unequal discs

One of the most puzzling results of an experiment on the stability of long liquid columns under microgravity, performed aboard Spacelab-D2 in 1993 and named STACO, aiming at the analysis of deformations of nearly cylindrical liquid columns under several mechanical disturbances, is revisited here. It corresponds to the unexplained breakage of an 85 mm long liquid bridge of low viscosity silicone oil, established between unequal discs of 30 and 28 mm, intended to counterbalance the expected deformation by residual acceleration found in previous flights, and left idle because the vibrations and oscillations to be applied afterwards were not started, for fear of premature breakage. A detailed image analysis is performed to extract the maximum amount of data, to be able to check against available theories for axisymmetric and non-axisymmetric deformations of a liquid column

Generalized Poincaré-Sobolev inequalities

Poincaré-Sobolev inequalities are very powerful tools in mathematical analysis which have been extensively used for the study of differential equations and their validity is intimately related with the geometry of the underlying space. In particular, and since their applicability as part of the Moser iteration method, their weighted counterparts are of interest for applications. The goal of this dissertation is to present a self-contained study of Poincaré-Sobolev inequalities, weights and the combination of both under the framework of the abstract theory of generalized Poincaré-Sobolev inequalities. To this end, the basic aspects on the theory of Poincaré-Sobolev inequalities and the theory of Muckenhoupt weights is presented. In relation with these, the class of functions with bounded mean oscillations is studied, together with a new characterization of it through some boundedness properties of commutators of fractional integrals. A unified study of classical and fractional weighted Poincaré-Sobolev inequalities, as well as a study of Muckenhoupt weights in relation with functions with bounded mean oscillations is carried out by using new self-improving techniques.BERC 2014-2017, SEV-2013-032

Anisotropic Atom-Surface Interactions in the Casimir-Polder Regime

The distance-dependence of the anisotropic atom-wall interaction is studied. The central result is the 1/z^6 quadrupolar anisotropy decay in the retarded Casimir-Polder regime. Analysis of the transition region between non-retarded van der Waals regime (in 1/z^3) and Casimir-Polder regime shows that the anisotropy cross-over occurs at very short distances from the surface, on the order of 0.03 Lambda, where Lambda is the atom characteristic wavelength. Possible experimental verifications of this distance dependence are discussed.Comment: 5 pages, 2 figure

Optical absorption of divalent metal tungstates: Correlation between the band-gap energy and the cation ionic radius

We have carried out optical-absorption and reflectance measurements at room temperature in single crystals of AWO4 tungstates (A = Ba, Ca, Cd, Cu, Pb, Sr, and Zn). From the experimental results their band-gap energy has been determined to be 5.26 eV (BaWO4), 5.08 eV (SrWO4), 4.94 eV (CaWO4), 4.15 eV (CdWO4), 3.9-4.4 eV (ZnWO4), 3.8-4.2 eV (PbWO4), and 2.3 eV (CuWO4). The results are discussed in terms of the electronic structure of the studied tungstates. It has been found that those compounds where only the s electron states of the A2+ cation hybridize with the O 2p and W 5d states (e.g BaWO4) have larger band-gap energies than those where also p, d, and f states of the A2+ cation contribute to the top of the valence band and the bottom of the conduction band (e.g. PbWO4). The results are of importance in view of the large discrepancies existent in prevoiusly published data.Comment: 16 pages, 3 figures, 1 tabl

Synchronization of the Frenet-Serret linear system with a chaotic nonlinear system by feedback of states

A synchronization procedure of the generalized type in the sense of Rulkov et al [Phys. Rev. E 51, 980 (1995)] is used to impose a nonlinear Malasoma chaotic motion on the Frenet-Serret system of vectors in the differential geometry of space curves. This could have applications to the mesoscopic motion of biological filamentsComment: 12 pages, 7 figures, accepted at Int. J. Theor. Phy

Negative-index media for matter-wave optics

We consider the extension of optical meta-materials to matter waves. We show that the generic property of pulsed comoving magnetic fields allows us to fashion the wave-number dependence of the atomic phase shift. It can be used to produce a transient negative group velocity of an atomic wave packet, which results into a negative refraction of the matter wave. Application to slow metastable argon atoms Ar*(3P2) shows that the device is able to operate either as an efficient beam splitter or an atomic meta-lens. Implications of "meta-media" in atom optics are considered.Comment: 4 pages, 4 figures, submitted at PRL 4 November 200

HUMAN MOTION ANALYSIS AND SYNTHESIS USING GRAPHICAL BIOMECHANICS MODELS IN SPORTS ACTIVITIES

In many applications the study of human movement using a computer is very useful. One such application is the three-dimensional reconstruction of the structure of the human body and its movement using sequences of images and graphic models. For this reconstruction to be accurate and precise the person analyzed and the virtual human (humanoid) must have similar anthropometric characteristics. A process is therefore defined that attempts to adjust the humanoid to the morphology of the person, a process which can be very laborious and subjective if done manually or by selection of points. This article presents a process of semiautomatic matching between person and humanoid. Once this process is carried out we are ready to analyze and represent the movements under study. The study is adapted to specific sports activities. In these cases the adjustment process can be assisted by the computer. At present, it is used in indoor spaces, but its use in outdoor spaces is also intended. The system requires no markers or special clothing to be worn by the athlete or sports participant, and its range of application is therefore very wide. Also very important are its portability into domestic environments using VRML 2.0 and the H-anim standard for specification of virtual humanoids. This advantage is very important because experts can visualize movements on any personal computer with a commercial Internet browser

Social comparisons are associated with poorer and riskier financial decision making, no matter whether encounters are sporadic or repeated

Previous research suggests that social comparisons affect decision making under uncertainty. However, the role of the length of the social interaction for this relationship remains unknown. This experiment tests the effect of social comparisons on financial risk taking and how this effect is modulated by whether social encounters are sporadic or repeated. Participants carried out a computer task consisting of a series of binary choices between lotteries of varying profitability and risk, with real monetary stakes. After each decision, participants could compare their own payoff to that of a counterpart who made the same decision at the same time and whose choices/earnings did not affect the participants’ earnings. The design comprised three between-subjects treatments which differed in the nature of the social interaction: participants were informed that they would be matched with either (a) a different participant in each trial, (b) the same participant across all trials, or (c) a "virtual participant", i.e. a computer algorithm. Compared to the non-social condition (c), subjects in both social conditions (a and b) chose lotteries with lower expected value (z=-3.10, p<0.01) and higher outcome variance (z=2.13, p=0.03). However, no differences were found between the two social conditions (z=1.15, p=0.25 and z=0.35, p=0.73, respectively). These results indicate that social comparison information per se leads to poorer and riskier financial decisions, irrespective of whether or not the referent other is encountered repeatedly

On the influence of Marangoni convection on the stability of liquid bridge interfaces

This paper analyses the influence of the Marangoni flow on the stability of almost cylindrical liquid bridges by using bifurcation techniques. An analytical relation between the different parameters is found that allows the prediction of the variation of the maximum stable length. This variation although is qualitatively “larger” than that due to symmetric effects (f.i. volume variation, solid body rotation), can somehow be compensated with the other effects. By choosing adequately f.i. the disk diameter difference, the shortening in stability due to Marangoni convection can be almost completely cancelle