Gentrificación no es un nombre de señora: un proyecto de Left Hand Rotation

Left Hand Rotation es un colectivo artístico que desarrolla proyectos experimentales en múltiples formatos y soportes, como vídeo, instalaciones, intervenciones en el espacio público, etc. El proyecto/taller Gentrificación no es un nombre de señora surge como respuesta al análisis del papel de la cultura en los procesos de gentrificación, y persigue modificar la forma preestablecida en que los conflictos asociados a la gentrificación se perciben, difundiendo situaciones silenciadas y facilitando la articulación de las fuerzas de resistencia implicadas

Rotation and pseudo-rotation

Eigenvectors of stress-energy tensor (the source in Einstein's equations) form privileged bases in description of the corresponding space-times. When one or more of these vector fields are rotating (the property well determined in differential geometry), one says that the space-time executes this rotation. Though the rotation in its proper sense is understood as that of a timelike congruence (vector field), the rotation of a spacelike congruence is not a less objective property if it corresponds to a canonical proper basis built of the just mentioned eigenvectors. In this last case, we propose to speak on pseudo-rotation. Both properties of metric, its material sources, and space-time symmetries are considered in this paper.Comment: 13 pages, no figures, contains parts of the PhD Thesis of H. Vargas Rodr\'igue

On Rotation Curve Analysis

An analysis of analytical methods used for computing galactic masses on the basis of rotation curves (Saari 2015) is shown to be flawed

Rotation and differential rotation of active Kepler stars

We present rotation periods for thousands of active stars in the Kepler field derived from Q3 data. In most cases a second period close to the rotation period was detected, which we interpreted as surface differential rotation (DR). Active stars were selected from the whole sample using the range of the variability amplitude. To detect different periods in the light curves we used the Lomb-Scargle periodogram in a pre-whitening approach to achieve parameters for a global sine fit. The most dominant periods from the fit were ascribed to different surface rotation periods, but spot evolution could also play a role. Due to the large number of stars the period errors were estimated in a statistical way. We thus cannot exclude the existence of false positives among our periods. In our sample of 40.661 active stars we found 24.124 rotation periods $P_1$ between 0.5-45 days. The distribution of stars with 0.5 < B-V < 1.0 and ages derived from angular momentum evolution that are younger than 300 Myr is consistent with a constant star-formation rate. A second period $P_2$ within $\pm30$% of the rotation period $P_1$ was found in 18.619 stars (77.2%). Attributing these two periods to DR we found that the relative shear $\alpha=\Delta\Omega/\Omega$ increases with rotation period, and slightly decreases with effective temperature. The absolute shear $\Delta\Omega$ slightly increases between $T_{eff}=3500-6000$ K. Above 6000 K $\Delta\Omega$ shows much larger scatter. We found weak dependence of $\Delta\Omega$ on rotation period. Latitudinal differential rotation measured for the first time in more than 18.000 stars provides a comprehensive picture of stellar surface shear, consistent with major predictions from mean-field theory. To what extent our observations are prone to false positives and selection bias is not fully explored, and needs to be addressed using more Kepler data.Comment: 19 pages, 18 figures, accepted by A&A. A table containing all periods, KIC number, etc. can be found here: http://www.astro.physik.uni-goettingen.de/~reinhold/period_table.te

Rotation- and temperature-dependence of stellar latitudinal differential rotation

More than 600 high resolution spectra of stars with spectral type F and later were obtained in order to search for signatures of differential rotation in line profiles. In 147 stars, the rotation law could be measured, 28 of them are found to be differentially rotating. Comparison to rotation laws in stars of spectral type A reveals that differential rotation sets in at the convection boundary in the HR-diagram; no star that is significantly hotter than the convection boundary exhibits the signatures of differential rotation. Four late A-/early F-type stars close to the convection boundary and at vsini~100 km/s show extraordinarily strong absolute shear at short rotation periods around one day. It is suggested that this is due to their small convection zone depth and that it is connected to a narrow range in surface velocity. Detection frequencies of differential rotation were analyzed in stars with varying temperature and rotation velocity. Measurable differential rotation is more frequent in late-type stars and slow rotators. The strength of absolute shear and differential rotation are examined as functions of the stellar effective temperature and rotation period. The strongest shear is found at rotation periods between two and three days. In slower rotators, the strongest shear at a given rotation rate is given approximately by DOmega_max ~ P^{-1}. In faster rotators, alpha_max and DOmega_max diminish less rapidly. A comparison with differential rotation measurements in stars of later spectral type shows that F-stars exhibit stronger shear than cooler stars do, the upper boundary in absolute shear DOmega with temperature is consistent with the temperature scaling law found in Doppler Imaging measurements.Comment: 15 pages, accepted for publication in A&A, typos correcte