33 research outputs found
Topological Black Holes of (n+1)-dimensional Einstein-Yang-Mills Gravity
We present the topological solutions of Einstein gravity in the presence of a
non-Abelian Yang-Mills field. In () dimensions, we consider the
semisimple group as the Yang-Mills gauge group, and
introduce the black hole solutions with hyperbolic horizon. We argue that the
4-dimensional solution is exactly the same as the 4-dimensional solution of
Einstein-Maxwell gravity, while the higher-dimensional solutions are new. We
investigate the properties of the higher-dimensional solutions and find that
these solutions in 5 dimensions have the same properties as the topological
5-dimensional solution of Einstein-Maxwell (EM) theory although the metric
function in 5 dimensions is different. But in 6 and higher dimensions, the
topological solutions of EYM and EM gravities with non-negative mass have
different properties. First, the singularity of EYM solution does not present a
naked singularity and is spacelike, while the singularity of topological
Reissner-Nordstrom solution is timelike. Second, there are no extreme 6 or
higher-dimensional black holes in EYM gravity with non-negative mass, while
these kinds of solutions exist in EM gravity. Furthermore, EYM theory has no
static asymptotically de Sitter solution with non-negative mass, while EM
gravity has.Comment: 14 pages, 2 figures, accepted by Mod. Phys. Lett.
Spacetimes with Longitudinal and Angular Magnetic Fields in Third Order Lovelock Gravity
We obtain two new classes of magnetic brane solutions in third order Lovelock
gravity. The first class of solutions yields an -dimensional spacetime
with a longitudinal magnetic field generated by a static source. We generalize
this class of solutions to the case of spinning magnetic branes with one or
more rotation parameters. These solutions have no curvature singularity and no
horizons, but have a conic geometry. For the spinning brane, when one or more
rotation parameters are nonzero, the brane has a net electric charge which is
proportional to the magnitude of the rotation parameters, while the static
brane has no net electric charge. The second class of solutions yields a
pacetime with an angular magnetic field. These solutions have no curvature
singularity, no horizon, and no conical singularity. Although the second class
of solutions may be made electrically charged by a boost transformation, the
transformed solutions do not present new spacetimes. Finally, we use the
counterterm method in third order Lovelock gravity and compute the conserved
quantities of these spacetimes.Comment: 15 pages, no figur
Counterterm Method in Lovelock Theory and Horizonless Solutions in Dimensionally Continued Gravity
In this paper we, first, generalize the quasilocal definition of the stress
energy tensor of Einstein gravity to the case of Lovelock gravity, by
introducing the tensorial form of surface terms that make the action
well-defined. We also introduce the boundary counterterm that removes the
divergences of the action and the conserved quantities of the solutions of
Lovelock gravity with flat boundary at constant and . Second, we obtain
the metric of spacetimes generated by brane sources in dimensionally continued
gravity through the use of Hamiltonian formalism, and show that these solutions
have no curvature singularity and no horizons, but have conic singularity. We
show that these asymptotically AdS spacetimes which contain two fundamental
constants are complete. Finally we compute the conserved quantities of these
solutions through the use of the counterterm method introduced in the first
part of the paper.Comment: 15 pages, references added, typos correcte
Attitudes of medical instructors and students of Tabriz University of Medical Sciences towards Peer Assisted Learning (PAL) system
Introduction: Recently, there has been a shift of emphasis from teaching to creating an interactive and student-oriented atmosphere in education.  One of the method in creating student oriented atmosphere is Peer Assisted Learning (PAL), in which students play the role of teachers , assistant, and enhance other students’ learning. Regarding numerous benefits of this system, the present study aimed to survey the attitudes of teachers and students at Medical School of Tabriz University of Medical Sciences on Peer Assisted Learning.  Methods: Following a literature review, the researchers designed a questionnaire about benefits of peer assisted learning, and the stages of its content validity. Pilot study and reliability were followed. The collected data were analyzed by SPSS 16.  Results: The obtained results showed that an absolute maximum of the participants agreed with the potential benefits of performing the proposed system. Data analysis showed that students have significantly more agreement with PAL compare to the teacher-oriented method.  Conclusion: Regarding the obtained results, we concluded that teachers and students agreed with the benefits and application of PAL. Implementation of this active learning system would lead in productive and capable work force