Blaschke's problem for timelike surfaces in pseudo-Riemannian space forms

We show that isothermic surfaces and S-Willmore surfaces are also the solutions to the corresponding Blaschke's problem for both spacelike and timelike surfaces in pseudo-Riemannian space forms. For timelike surfaces both Willmore and isothermic, we obtain a description by minimal surfaces similar to the classical results of Thomsen.Comment: 10 page

A note about isothermic surfaces in Rn−j,j

In this note we survey our results on the description of ti-melike isothermic surfaces in Rn-j,j using the Grassmannian systems or U/K-systems. We give the natural extensions of the definition of Ribaucour and Darboux transformations for timelike isothermic surfaces and review how those transformations correspond to dressing actions of suitable simple elements.      &nbsp

Geodesic Lines in Fields of Velocity

This work is a purely syntactic geometric exploration of some few elements, which are our axioms, that in last instance it is the set of differential equations whose solutions give the geodesic lines of the Schwarzschild spacetime. We observe that non new physics principles or postulates will be introduced in this work. We only link the Bohr's atoms model with the Einstein's relativity through of a common geometric syntax. To obtain this common syntax, we will define the {\it extended Lorentz group}, which is defined to preserve the volume form of the Minkowski spacetime. The Schwarzschild spacetime will be defined as a manifold associated to a set of radial fields of velocities within of the four-dimensional Minkowski vectorially space form. Our procedure includes a comparison of the Newtonian and the Schwarzschild times along geodesic lines. Our constructions have strong influence of the Einstein paper about the energy content produced by fields, as well as by the Schr\"odinger digression about the annihilation of matter. We define the orbital associated to the Kepler's laws as a set of elliptical orbits, which have equal eccentricity and equal major semi-axis. Then identifying the eccentricity with the relativistic velocity we will obtain a thermodynamic equivalence between the increasing of mass in kinetic form in special relativity theory and an adiabatic process with degree of freedom equal to 2. The eccentricity will be the needed velocity to move the revolution ellipsoid and so to obtain a contraction of its major axis such that it converts into a sphere with radius given by the minor semi-axis. Therefore we can associate to the each class of equal eccentricity orbital an unique timelike unit vector, which is called {\it the observer} of class.Comment: 39 page

Bjorling Problem for Timelike Surfaces in the Lorentz-Minkowski Space

We solve the Bjorling problem for timelike surfaces in the Lorentz-Minkowski space through a split-complex representation formula obtained for this kind of surface. Our approach uses the split-complex numbers and natural split-holomorphic extensions. As applications, we show that the minimal timelike surfaces of revolution as well as minimal ruled timelike surfaces can be characterized as solutions of certain adequate Bjorling problems in the Lorentz-Minkowski space

Disjoining Potential and Spreading of Thin Liquid Layers in the Diffuse Interface Model Coupled to Hydrodynamics

The hydrodynamic phase field model is applied to the problem of film spreading on a solid surface. The disjoining potential, responsible for modification of the fluid properties near a three-phase contact line, is computed from the solvability conditions of the density field equation with appropriate boundary conditions imposed on the solid support. The equation describing the motion of a spreading film are derived in the lubrication approximation. In the case of quasi-equilibrium spreading, is shown that the correct sharp-interface limit is obtained, and sample solutions are obtained by numerical integration. It is further shown that evaporation or condensation may strongly affect the dynamics near the contact line, and accounting for kinetic retardation of the interphase transport is necessary to build up a consistent theory.Comment: 14 pages, 5 figures, to appear in PR

Hydrodynamic theory of de-wetting

A prototypical problem in the study of wetting phenomena is that of a solid plunging into or being withdrawn from a liquid bath. In the latter, de-wetting case, a critical speed exists above which a stationary contact line is no longer sustainable and a liquid film is being deposited on the solid. Demonstrating this behavior to be a hydrodynamic instability close to the contact line, we provide the first theoretical explanation of a classical prediction due to Derjaguin and Levi: instability occurs when the outer, static meniscus approaches the shape corresponding to a perfectly wetting fluid

Medidor de actividad eléctrica muscular cuatro canales electromiógrafo (EMG) inalámbrico

This article presents the multiple stages of the development of a low-power pocket four-channel electromyography prototype, able to record, display and process surface electromyographic signals that originate in the muscles in the top and bottom limbs. Wireless RS232 serial communication and XBee module in transparent mode were implemented for the transmission of data from the prototype to the computer. Finally, Continuous Wavelet Transform was applied to the electromyography signals via LabVIEW to obtain the main frequency spectrum, needed to detect patterns and muscle movements and identify any muscle weaknesses or inadequate performanceEste articulo presenta el desarrollo de un prototipo de registro electromiográfico de cuatro canales, portátil, inalámbrico y de bajo consumo, el cual está conformado por múltiples etapas de desarrollo, con la capacidad de registrar, visualizar y procesar señales electromiográficas superficiales de los músculos en extremidades superiores e inferiores del cuerpo humano. El tipo de comunicación que se implementó para la transmisión de datos desde el prototipo hacia el computador es la comunicación serial RS232 inalámbrica, por tal motivo se utiliza el módulo XBEE en modo transparente, finalmente a las señales electromiógraficas se aplica la Transformada Wavelet Continua por medio del programa de LabVIEW, para obtener el espectro de las frecuencias principales, característica necesarias para detectar patrones de movimientos de los músculos y detectar así posibles deficiencias o rendimiento muscular

Hydrodynamic bubble coarsening in off-critical vapour-liquid phase separation

Late-stage coarsening in off-critical vapour-liquid phase separation is re-examined. In the limit of bubbles of vapour distributed throughout a continuous liquid phase, it is argued that coarsening proceeds via inertial hydrodynamic bubble collapse. This replaces the Lifshitz-Slyozov-Wagner mechanism seen in binary liquid mixtures. The arguments are strongly supported by simulations in two dimensions using a novel single-component soft sphere fluid.Comment: 5 pages, 3 figures, revtex3.