742 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.
Improving employees' performance through internal marketing and organizational learning: mediating role of organizational innovation in an emerging market
This study identifies a specific relationship between internal marketing and organizational learning as the key drivers of organizational innovation, which build employees performance in the context of the petroleum industry. A model of the antecedents of organizational innovation was examined in a survey conducted among managers and employed specialists working in the oil industry in Iran. Structural equation modelling via Smart PLS was employed to gain insight into the various influences and relationships. We empirically scrutinized relationships between these constructs by validating a conceptual model employing SEM. The results indicate that internal marketing and organizational learning are key drivers of organizational innovation, which they are build employees performance. As well as, the results clarify that it is possible to improve the level of employee performance even through the complementary partial mediating role of organizational innovation. Additionally, this study makes a managerial contribution to the understanding of internal marketing, organizational learning and innovation on employee performance
Rotating Solution of Einstein-Maxwell Dilaton Gravity with Unusual Asymptotics
We study electrically charged, dilaton black holes, which possess
infinitesimal angular momentum in the presence of one or two Liouville type
potentials. These solutions are neither asymptotically flat nor (anti)-de
Sitter. Some properties of the solutions are discussed.Comment: 11 pages, Accepted (Int. J. Theor. Phys.
Xenogenic demineralized bone matrix and fresh autogenous cortical bone effects on experimental bone healing: radiological, histopathological and biomechanical evaluation
Topological Black Holes in Lovelock-Born-Infeld Gravity
In this paper, we present topological black holes of third order Lovelock
gravity in the presence of cosmological constant and nonlinear electromagnetic
Born-Infeld field. Depending on the metric parameters, these solutions may be
interpreted as black hole solutions with inner and outer event horizons, an
extreme black hole or naked singularity. We investigate the thermodynamics of
asymptotically flat solutions and show that the thermodynamic and conserved
quantities of these black holes satisfy the first law of thermodynamic. We also
endow the Ricci flat solutions with a global rotation and calculate the finite
action and conserved quantities of these class of solutions by using the
counterterm method. We compute the entropy through the use of the Gibbs-Duhem
relation and find that the entropy obeys the area law. We obtain a Smarr-type
formula for the mass as a function of the entropy, the angular momenta, and the
charge, and compute temperature, angular velocities, and electric potential and
show that these thermodynamic quantities coincide with their values which are
computed through the use of geometry. Finally, we perform a stability analysis
for this class of solutions in both the canonical and the grand-canonical
ensemble and show that the presence of a nonlinear electromagnetic field and
higher curvature terms has no effect on the stability of the black branes, and
they are stable in the whole phase space.Comment: 14 page
Asymptotically Flat Radiating Solutions in Third Order Lovelock Gravity
In this paper, we present an exact spherically symmetric solution of third
order Lovelock gravity in dimensions which describes the gravitational
collapse of a null dust fluid. This solution is asymptotically (anti-)de Sitter
or flat depending on the choice of the cosmological constant. Using the
asymptotically flat solution for with a power-law form of the mass
as a function of the null coordinate, we present a model for a gravitational
collapse in which a null dust fluid radially injects into an initially flat and
empty region. It is found that a naked singularity is inevitably formed whose
strength is different for the and cases. In the case,
the limiting focusing condition for the strength of curvature singularity is
satisfied. But for , the strength of curvature singularity depends on
the rate of increase of mass of the spacetime. These considerations show that
the third order Lovelock term weakens the strength of the curvature
singularity.Comment: 15 pages, no figure, references added, two appendix adde
Phases of 4D Scalar-tensor black holes coupled to Born-Infeld nonlinear electrodynamics
Recent results show that when non-linear electrodynamics is considered the
no-scalar-hair theorems in the scalar-tensor theories (STT) of gravity, which
are valid for the cases of neutral black holes and charged black holes in the
Maxwell electrodynamics, can be circumvented. What is even more, in the present
work, we find new non-unique, numerical solutions describing charged black
holes coupled to non-linear electrodynamics in a special class of scalar-tensor
theories. One of the phases has a trivial scalar field and coincides with the
corresponding solution in General Relativity. The other four phases that we
find are characterized by the value of the scalar field charge. The causal
structure and some aspects of the stability of the solutions have also been
studied. For the scalar-tensor theories considered, the black holes have a
single, non-degenerate horizon, i.e., their causal structure resembles that of
the Schwarzschild black hole. The thermodynamic analysis of the stability of
the solutions indicates that a phase transition may occur.Comment: 18 pages, 8 figures, new phases, figures, clarifying remarks and
acknowledgements adde
Accelerated Expansion of the Universe in Gauss-Bonnet Gravity
We show that in Gauss-Bonnet gravity with negative Gauss-Bonnet coefficient
and without a cosmological constant, one can explain the acceleration of the
expanding Universe. We first introduce a solution of the Gauss-Bonnet gravity
with negative Gauss-Bonnet coefficient and no cosmological constant term in an
empty -dimensional bulk. This solution can generate a de Sitter
spacetime with curvature . We show that an
-dimensional brane embedded in this bulk can have an expanding feature
with acceleration. We also considered a 4-dimensional brane world in a
5-dimensional empty space with zero cosmological constant and obtain the
modified Friedmann equations. The solution of these modified equations in
matter-dominated era presents an expanding Universe with negative deceleration
and positive jerk which is consistent with the recent cosmological data. We
also find that for this solution, the derivative of the scale factor
with respect to time can be expressed only in terms of Hubble and deceleration
parameters.Comment: 12 pages, no figure, references added, typos corrected, Section 4
ammended, an appndix added, version to be appeared in Phys. Rev.
Sonification as a Reliable Alternative to Conventional Visual Surgical Navigation
Despite the undeniable advantages of image-guided surgical assistance systems in terms of accuracy, such systems have not yet fully met surgeons' needs or expectations regarding usability, time efficiency, and their integration into the surgical workflow. On the other hand, perceptual studies have shown that presenting independent but causally correlated information via multimodal feedback involving different sensory modalities can improve task performance. This article investigates an alternative method for computer-assisted surgical navigation, introduces a novel sonification methodology for navigated pedicle screw placement, and discusses advanced solutions based on multisensory feedback. The proposed method comprises a novel sonification solution for alignment tasks in four degrees of freedom based on frequency modulation (FM) synthesis. We compared the resulting accuracy and execution time of the proposed sonification method with visual navigation, which is currently considered the state of the art. We conducted a phantom study in which 17 surgeons executed the pedicle screw placement task in the lumbar spine, guided by either the proposed sonification-based or the traditional visual navigation method. The results demonstrated that the proposed method is as accurate as the state of the art while decreasing the surgeon's need to focus on visual navigation displays instead of the natural focus on surgical tools and targeted anatomy during task execution
KCNN2 mutation in autosomal-dominant tremulous myoclonus-dystonia
BACKGROUND: Despite recent advances in neurogenetics which have facilitated the identification of a number of dystonia genes, many familial dystonia syndromes remain without known cause. OBJECTIVE: To identify the cause of autosomal dominant tremulous myoclonus-dystonia in a UK kindred with affected individuals in three generations. METHODS: Known genetic causes of myoclonus-dystonia were excluded. We combined clinical and electrophysiological phenotyping with whole-exome sequencing and Sanger sequencing to identify candidate causal variants in a family with tremulous myoclonus-dystonia. RESULTS: The core phenotype consisted of childhood-onset dystonia predominantly affecting hands and neck, with a fast tremor with superimposed myoclonus, and in some, subtle cerebellar signs. We identified a novel missense variant in KCNN2 (NM_021614:c.1112G>A:p.(Gly371Glu)) which was the only variant we were able to identify segregating with the phenotype over three generations. This variant, which is absent from the most recent version of gnomAD, was predicted to be deleterious by SIFT and PolyPhen-2, and obtained an overall CADD score of 29.7. CONCLUSION: KCNN2 (potassium calcium-activated channel subfamily N member 2), a member of the KCNN family of potassium channel genes, is highly conserved across species and in humans is highly expressed in the brain, particularly the cerebellum. KCNN2 mutations have never been described as pathological in human disease, but are recognised abnormalities in two rodent models of fast, jerky tremor. Segregation, absence of the variant in the normal population and in silico prediction of a deleterious effect together with animal models compatible with the clinical phenotype are all in line with KCNN2 mutations being a plausible cause underlying myoclonus-dystonia
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