Stable non-uniform black strings below the critical dimension

The higher-dimensional vacuum Einstein equation admits translationally non-uniform black string solutions. It has been argued that infinitesimally non-uniform black strings should be unstable in 13 or fewer dimensions and otherwise stable. We construct numerically non-uniform black string solutions in 11, 12, 13, 14 and 15 dimensions. Their stability is investigated using local Penrose inequalities. Weakly non-uniform solutions behave as expected. However, in 12 and 13 dimensions, strongly non-uniform solutions appear to be stable and can have greater horizon area than a uniform string of the same mass. In 14 and 15 dimensions all non-uniform black strings appear to be stable.Comment: 26 pages, 11 figures. V2: reference added, matches published versio

Understanding the spiral structure of the Milky Way using the local kinematic groups

We study the spiral arm influence on the solar neighbourhood stellar kinematics. As the nature of the Milky Way (MW) spiral arms is not completely determined, we study two models: the Tight-Winding Approximation (TWA) model, which represents a local approximation, and a model with self-consistent material arms named PERLAS. This is a mass distribution with more abrupt gravitational forces. We perform test particle simulations after tuning the two models to the observational range for the MW spiral arm properties. We explore the effects of the arm properties and find that a significant region of the allowed parameter space favours the appearance of kinematic groups. The velocity distribution is mostly sensitive to the relative spiral arm phase and pattern speed. In all cases the arms induce strong kinematic imprints for pattern speeds around 17 km/s/kpc (close to the 4:1 inner resonance) but no substructure is induced close to corotation. The groups change significantly if one moves only ~0.6 kpc in galactocentric radius, but ~2 kpc in azimuth. The appearance time of each group is different, ranging from 0 to more than 1 Gyr. Recent spiral arms can produce strong kinematic structures. The stellar response to the two potential models is significantly different near the Sun, both in density and kinematics. The PERLAS model triggers more substructure for a larger range of pattern speed values. The kinematic groups can be used to reduce the current uncertainty about the MW spiral structure and to test whether this follows the TWA. However, groups such as the observed ones in the solar vicinity can be reproduced by different parameter combinations. Data from velocity distributions at larger distances are needed for a definitive constraint.Comment: 18 pages, 21 figures, 4 tables; acccepted for publication in MNRA

Instability and new phases of higher-dimensional rotating black holes

It has been conjectured that higher-dimensional rotating black holes become unstable at a sufficiently large value of the rotation, and that new black holes with pinched horizons appear at the threshold of the instability. We search numerically, and find, the stationary axisymmetric perturbations of Myers-Perry black holes with a single spin that mark the onset of the instability and the appearance of the new black hole phases. We also find new ultraspinning Gregory-Laflamme instabilities of rotating black strings and branes.Comment: 5 pages, 5 figures. The instability of the black hole is argued to appear at the second zero mode. The first zero mode is not associated to a new branch of black hole solution

Absolute magnitudes and kinematics of CP stars from Hipparcos data

The position in the HR diagram and the kinematic characteristics of different kinds of CP stars of the upper main sequence are obtained using the LM method (Luri et al., 1996). Most of the CP stars are main sequence stars occupying the whole width of the sequence. From a kinematic point of view, they belong to the young disk population (ages < 1.5 Gyr). It has also been found that, on kinematic grounds, the behaviour of lambda Bootis stars is similar to the one observed for normal stars of the same spectral range. On the other hand, roAp and noAp stars show the same kinematic characteristics. The peculiar velocity distribution function has been decomposed into a sum of three dimensional gaussians and the presence of Pleiades, Sirius and Hyades moving groups has been clearly established. Finally, a small number of CP stars are found to be high-velocity objects.Comment: 8 pages, 1 figure, to appear in: Proc. of the 26th workshop of the European Working Group on CP stars, eds. P. North, A. Schnell and J. Ziznovsky, Contrib. Astr. Obs. Skalnate Pleso Vol. 27, No

Acreditación de programas en la Universidad de Puerto Rico: Análisis de las políticas para evidenciar un proceso de cambio exitoso, 2003-2014

A first-rate university should demonstrate the excellence and quality of its programs, including how they meet continuous and complex changes in areas such as technological advances, demographic changes, fiscal policies, and new contents in the academic offerings. In 2003, the University of Puerto Rico initiated a process to establish a culture of external scrutiny and evaluation of its programs to ensure that they could respond to the challenge of working with these complex topics. As part of said process, it required that all the programs with voluntary accreditation should be accredited. The project was a success, and 84 percent of those programs were accredited by the corresponding agencies. Taking as reference the model by John P. Kotter, a research specialist on large-scale transformation and change, this article describes the different stages that the programs went through to ensure accreditation. At the same time, it also confirms that the Kotter model is applicable to higher education. Cómo citar: Freytes-González, C. E., &amp; Figueras-Álvarez, C. (2017). Program accreditation at the University of Puerto Rico: Policy analysis to evidence a successful process of change, 2003-2014. Cuaderno de Investigación en la Educación, 32, 126-173. Recuperado a partir de https://revistas.upr.edu/index.php/educacion/article/view/16511Una universidad de primera debe demostrar la excelencia y calidad de sus programas, incluyendo cómo estos atienden cambios continuos y complejos, entre ellos, los adelantos tecnológicos, los cambios demográficos, políticas fiscales y los nuevos contenidos en la oferta académica. En 2003, la Universidad de Puerto Rico inició un proceso para establecer una cultura de evaluación y escrutinio externo que asegurara que sus programas sean de excelencia y capaces de enfrentar estos desafíos. Para ello, requirió la acreditación de todos los programas de acreditación voluntaria. El proyecto fue muy exitoso, y el 84 porciento de esos programas se acreditaron por las agencias correspondientes. Tomando como referencia el modelo de John P. Kotter, especialista en investigaciones sobre las transformaciones y cambios en ambientes a grandes escalas, este trabajo describe las etapas de los programas para acreditarse. Además, confirma que el modelo de Kotter es también aplicable a la educación superior. How to cite: Freytes-González, C. E., &amp; Figueras-Álvarez, C. (2017). Program accreditation at the University of Puerto Rico: Policy analysis to evidence a successful process of change, 2003-2014. Cuaderno de Investigación en la Educación, 32, 126-173. Retrieved from https://revistas.upr.edu/index.php/educacion/article/view/1651

Monolithic integration of Giant Magnetoresistance (GMR) devices onto standard processed CMOS dies

Giant Magnetoresistance (GMR) based technology is nowadays the preferred option for low magnetic fields sensing in disciplines such as biotechnology or microelectronics. Their compatibility with standard CMOS processes is currently investigated as a key point for the development of novel applications, requiring compact electronic readout. In this paper, such compatibility has been experimentally studied with two particular non-dedicated CMOS standards: 0.35 μm from AMS (Austria MicroSystems) and 2.5 μm from CNM (Centre Nacional de Microelectrònica, Barcelona) as representative examples. GMR test devices have been designed and fabricated onto processed chips from both technologies. In order to evaluate so obtained devices, an extended characterization has been carried out including DC magnetic measurements and noise analysis. Moreover, a 2D-FEM (Finite Element Method) model, including the dependence of the GMR device resistance with the magnetic field, has been also developed and simulated. Its potential use as electric current sensors at the integrated circuit level has also been demonstrated