Scalar Field Inhomogeneous Cosmologies

Some exact solutions for the Einstein field equations corresponding to inhomogeneous $G_2$ cosmologies with an exponential-potential scalar field which generalize solutions obtained previously are considered. Several particular cases are studied and the properties related to generalized inflation and asymptotic behaviour of the models are discussed.Comment: 21 pages LaTeX, 3 figures appended as a uuencoded compressed tar fil

Drag and lift forces on a counter-rotating cylinder in rotating flow

Results are reported of an experimental investigation into the motion of a heavy cylinder free to move inside a water-filled drum rotating around a horizontal axis. The cylinder is observed to either co- or, counter intuitively, counter-rotate with respect to the rotating drum. The flow was measured with particle image velocimetry (PIV), and it was found that the inner cylinder significantly altered the bulk flow field from the solid-body rotation found for a fluid filled drum. In the counter-rotation case, the generated lift force allowed the cylinder to freely rotate without contact with the drum wall. Drag and lift coefficients of the freely counter-rotating cylinder were measured over a wide range of Reynolds numbers, 2,500 $<$ Re $<$ 25,000, dimensionless rotation rates, 0.0$< \alpha <$1.2, and gap to cylinder diameter ratios 0.003 $< G/2a <$ 0.5. Drag coefficients were consistent with previous measurements on a cylinder in a uniform flow. However, for the lift coefficient considerable larger values were observed in the present measurements. We found the enhancement of the lift force to be mainly caused by the vicinity of the wall

Aero-acoustic oscillations inside large deep cavities

This investigation focuses on the pressure amplitude response, within two deep cavities characterized by their length over depth ratios (L/H = 0.2 and 0.41), under varying free stream velocity in a large wind tunnel. Experiments have shown that for deep rectangular cavities at low Mach number, oscillations of discrete frequencies can be produced. These oscillations appear when the free stream velocity becomes higher than a minimum value. In addition, as flow velocity is increased, upward jumps in oscillation frequency are observed in the two cavity configurations. Convection velocity of instabilities along the shear layer was measured using velocity cross-correlations. This study shows that the hydrodynamic modes of the cavity shear layer are correctly predicted by the Rossiter model when the convection velocity is determined and the empirical time delay is neglected. For L/H = 0.2 the first oscillation mode is observed on the spectrogram. For L/H = 0.41, both the first and the second mode have approximately the same amplitude. Time-resolved Particle image velocimetry measurements were performed to obtain the vorticity distribution during the oscillation cycle along the cavity shear layer. It is found that the number of structures in the cavity shear layer depends on the mode order of cavity oscillation

La poética del psicoanálisis y del exilio de Edmundo Gómez Mango (1940-2019)

Esta fue mi frase íntima en el momento de saber de su muerte y del asalto de la congoja, del adiós imposible, en ese tiempo suspendido, especial de descreencia, de sideración y dolor

Las sombras de Wuhan: Entre la melancolía y la ilusión mentirosa del yo

Estos párrafos fueron escritos a partir de una experiencia de estos días de confinamientos por la pandemia en que nos vemos enfrentados a lo que verdaderamente nos supera, porque estamos, creo, guiados por esos otros que llamamos los medios, en una situación oscilante entre la entrega a la catástrofe (y su fascinación oscura) y el ilusorio voluntarismo salvador del mundo. ¿Cómo podremos enfrentar-apartar la caída en la melancolía y el escepticismo, pero también la caída en la ilusión de la desmentida o lo que Badiou llamó, tan bien, «cuidarse de los llamados perentorios» a la vida y Daniel Gil: «las formas más comunes de degradación de la vida cotidiana: la desmentida»? (…