1,240 research outputs found
New torsion black hole solutions in Poincar\'e gauge theory
We derive a new exact static and spherically symmetric vacuum solution in the
framework of the Poincar\'e gauge field theory with dynamical massless torsion.
This theory is built in such a form that allows to recover General Relativity
when the first Bianchi identity of the model is fulfilled by the total
curvature. The solution shows a Reissner-Nordstr\"om type geometry with a
Coulomb-like curvature provided by the torsion field. It is also shown the
existence of a generalized Reissner-Nordstr\"om-de Sitter solution when
additional electromagnetic fields and/or a cosmological constant are coupled to
gravity.Comment: 14 pages, 0 figures, minor changes, references adde
Einstein-Yang-Mills-Lorentz black holes
Different black hole solutions of the coupled Einstein-Yang-Mills equations
have been well known for a long time. They have attracted much attention from
mathematicians and physicists since their discovery. In this work, we analyze
black holes associated with the gauge Lorentz group. In particular, we study
solutions which identify the gauge connection with the spin connection. This
ansatz allows one to find exact solutions to the complete system of equations.
By using this procedure, we show the equivalence between the Yang-Mills-Lorentz
model in curved space-time and a particular set of extended gravitational
theories.Comment: 10 pages, 0 figures, minor changes, references added. It matches the
version published in Eur. Phys. J.
Extended Reissner-Nordstr\"om solutions sourced by dynamical torsion
We find a new exact vacuum solution in the framework of the Poincar\'e Gauge
field theory with massive torsion. In this model, torsion operates as an
independent field and introduces corrections to the vacuum structure present in
General Relativity. The new static and spherically symmetric configuration
shows a Reissner-Nordstr\"om-like geometry characterized by a spin charge. It
extends the known massless torsion solution to the massive case. The
corresponding Reissner-Nordstr\"om-de Sitter solution is also compatible with a
cosmological constant and additional U(1) gauge fields.Comment: 12 pages, 0 figures, minor changes, references adde
Correspondence between Einstein-Yang-Mills-Lorentz systems and dynamical torsion models
In the framework of Einstein-Yang-Mills theories, we study the gauge Lorentz
group and establish a particular correspondence between this case and a certain
class of theories with torsion within Riemann-Cartan space-times. This relation
is specially useful in order to simplify the problem of finding exact solutions
to the Einstein-Yang-Mills equations. The applicability of the method is
divided into two approaches: one associated with the Lorentz group SO(1,n-1) of
the space-time rotations and another one with its subgroup SO(n-2). Solutions
for both cases are presented by the explicit use of this correspondence and,
interestingly, for the last one by imposing on our ansatz the same kind of
rotation and reflection symmetry properties as for a nonvanishing space-time
torsion. Although these solutions were found in previous literature by a
different approach, our method provides an alternative way to obtain them and
it may be used in future research to find other exact solutions within this
theory.Comment: 10 pages, 0 figures, minor changes, references added. It matches the
version published in Phys. Rev.
Stability in quadratic torsion theories
We revisit the definition and some of the characteristics of quadratic
theories of gravity with torsion. We start from the most general Lagrangian
density quadratic in the curvature and torsion tensors. By assuming that
General Relativity should be recovered when torsion vanishes and investigating
the behaviour of the vector and pseudovector torsion fields in the weak-gravity
regime, we present a set of necessary conditions for the stability of these
theories. Moreover, we explicitly obtain the gravitational field equations
using the Palatini variational principle with the metricity condition
implemented via a Lagrange multiplier
Fermion dynamics in torsion theories
In this work we have studied the non-geodesical behaviour of particles with
spin 1/2 in Poincar\'e gauge theories of gravity, via the WKB method and the
Mathisson-Papapetrou equation. We have analysed the relation between the two
approaches and we have argued the different advantages associated with the WKB
approximation. Within this approach, we have calculated the trajectories in a
particular Poincar\'e gauge theory, discussing the viability of measuring such
a motion.Comment: 17 pages, 2 figures, minor changes, conclusions unchanged. It matches
the version published in JCA
Neoker Single Crystal Alumina Fibers as reinforcement in Al-based MMC: first steps
α-Al2O3 whiskers are good candidates for use as strengtheners in advanced composites, specifically, single crystal -Al2O3 whiskers grown with c-axis orientation, because of their favorable fracture strength, stiffness, and creep resistance, even at high temperatures are optimum reinforces. Very few methods are currently available to obtain single-crystal α-Al2O3 whiskers, and these methods were too complex and expensive for use on an industrial scale. A novel method for obtaining c-axis alumina single-crystal whiskers (developed at the Institute of Ceramic Materials of Galicia) has been scaled-up to industrial production by Neoker, a Spin-Off of the of the University of Santiago de Compostela, Spain. The technology for the production of the whiskers involves the reaction between aluminum and powdered silica in Ar atmospheres containing metal vapors. Aluminum is the most popular matrix for the metal matrix composites (MMCs). The Al alloys are quite attractive due to their low density, their capability to be strengthened by precipitation, their good corrosion resistance, high thermal and electrical conductivity, and their high damping capacity. The reinforcement in AMCs could be in the form of continuous/discontinuous whiskers, whisker or particulates, in volume fractions ranging from a few percent to 70%. Properties of AMCs can be tailored to the demands of different industrial applications by suitable combinations of matrix, reinforcement and processing route. The composites studied in the present work were prepared by infiltration processes where the reinforcements were pressed into a preform that was then infiltrated by the molten Al allo
Access to HIV/STI testing among male and female Venezuelan migrants in Peru: evidence from a nationwide survey
Background: Human immunodeficiency virus (HIV) infection and sexually transmitted infections (STIs) are major global public health issues. Migrants represent a vulnerable group that faces multiple barriers to access to healthcare services, including HIV/STI testing. This study aimed to assess the factors associated with access to HIV/STI testing in male and female Venezuelan migrants in Peru. Methods: This was a cross-sectional study involving secondary data analysis of the 2022 Venezuelan Population Residing in Peru Survey. The study was conducted in the eight most populated cities inhabited by Venezuelan migrants and refugees. For each city, the sampling design was probabilistic, stratified, and independent. The outcome variable was whether participants had access to HIV or other STI testing during their stay in Peru. Statistical analysis was stratified by sex owing to potential effect modification. Crude and adjusted prevalence ratios were calculated using generalized linear models Poisson family with log link function. Confidence intervals were calculated to 95%. Results: A total of 3,723 male and 3,984 female migrants were included. Access to HIV/STI testing among male and female migrants was 19.85% and 25.16%, respectively. Among male migrants, being LGBTI, health insured, and married or cohabiting were associated with increased access to HIV/STI testing. Among females, those aged 18–44 years, those who were married or cohabiting and were health insured, and those residing for more than 1 year in Peru were significantly more likely to have access to HIV/STI testing. Moreover, physical/mental disability and unemployed status were associated with a lower probability of HIV/STI testing in females. Conclusions: Only two in ten Venezuelan migrants and refugees in Peru were screened for HIV/STI, with fewer males than females. Sex-specific sociodemographic, health-related, and migration-related variables were independently associated with access to HIV/STI testing
Professional competences as a key factor in the didactic methodology of organizational communication
[ES] Este estudio realiza una propuesta de metodología didáctica para las asignaturas sobre comunicación organizacional que se imparten en las Facultades de Ciencias de la Comunicación en las universidades españolas. Se utiliza el diseño de enfoque dominante o principal, en el que prevalece la Investigación Acción como método cualitativo, que favorece el cambio en los procesos educativos para la transformación social; y al que se le agrega el componente cuantitativo de la encuesta, para evaluar los resultados de la propuesta que aquí se realiza. A partir de la revisión de guías docentes y del análisis de ofertas de empleo se observa que, aunque existe correspondencia entre universidad y empresa en el reconocimiento de competencias como capacidad de análisis, redacción, edición, habilidades relacionales, estrategia y proactividad; no se enseñan habilidades relevantes que demanda el mercado laboral como el trabajo en equipo, la autonomía, el dominio del inglés y el manejo de herramientas tecn[EN] This study makes a proposal of didactic methodology for the subjects on organizational communication taught in the Degree in Journalism of Spanish universities. The dominant or main approach design is used, in which Action Research prevails as a qualitative method that favors change in the educational processes for social transformation; and to which the quantitative component of the survey is added, in order to evaluate the results of the proposal carried out here. From the revision of the teaching guides and the analysis of job vacancies it is observed that, even if there is correspondence in the recognition of competencies such as analytical capacity, writing, editing, relational skills, strategy and proactivity in the university and the companies, the university does not teach relevant skills demanded by the working market such as teamwork, autonomy, command of English and the use of technological tools of the network society. The intervention in the classroom and the students’ assGalarza Fernández, E.; Sosa Valcarcel, A.; Paniagua Rojano, F. (2019). Las competencias profesionales como factor clave en la metodología didáctica de la comunicación organizacional. REDU. Revista de Docencia Universitaria. 17(2):11-24. https://doi.org/10.4995/redu.2019.12475OJS1124172Aced, C. (2013). La comunicación corporativa: al otro lado de la información. Madrid: Cuadernos EVOCa.Alarcón, L., Montero, F. (2017). 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