301 research outputs found
Quantum Statistical Relation for black holes in nonlinear electrodynamics coupled to Einstein-Gauss-Bonnet AdS gravity
We consider curvature-squared corrections to Einstein-Hilbert gravity action
in the form of Gauss-Bonnet term in D>4 dimensions. In this theory, we study
the thermodynamics of charged static black holes with anti-de Sitter (AdS)
asymptotics, and whose electric field is described by nonlinear electrodynamics
(NED). These objects have received considerable attention in recent literature
on gravity/gauge dualities.
It is well-known that, within the framework of anti de-Sitter/Conformal Field
Theory (AdS/CFT) correspondence, there exists a nonvanishing Casimir
contribution to the internal energy of the system, manifested as the vacuum
energy for global AdS spacetime in odd dimensions. Because of this reason, we
derive a Quantum Statistical Relation directly from the Euclidean action and
not from the integration of the First Law of thermodynamics. To this end, we
employ a background-independent regularization scheme which consists in the
addition to the bulk action of counterterms that depend on both extrinsic and
intrinsic curvatures of the boundary (Kounterterm series). This procedure
results in a consistent inclusion of the vacuum energy and chemical potential
in the thermodynamic description for Einstein-Gauss-Bonnet AdS gravity
regardless the explicit form of the NED Lagrangian.Comment: 22 pages, no figures; 3 references and a subsection on Thermodynamic
Charges added; Final version for PR
Exact solutions for the Einstein-Gauss-Bonnet theory in five dimensions: Black holes, wormholes and spacetime horns
An exhaustive classification of certain class of static solutions for the
five-dimensional Einstein-Gauss-Bonnet theory in vacuum is presented. The class
of metrics under consideration is such that the spacelike section is a warped
product of the real line with a nontrivial base manifold. It is shown that for
generic values of the coupling constants the base manifold must be necessarily
of constant curvature, and the solution reduces to the topological extension of
the Boulware-Deser metric. It is also shown that the base manifold admits a
wider class of geometries for the special case when the Gauss-Bonnet coupling
is properly tuned in terms of the cosmological and Newton constants. This
freedom in the metric at the boundary, which determines the base manifold,
allows the existence of three main branches of geometries in the bulk. For
negative cosmological constant, if the boundary metric is such that the base
manifold is arbitrary, but fixed, the solution describes black holes whose
horizon geometry inherits the metric of the base manifold. If the base manifold
possesses a negative constant Ricci scalar, two different kinds of wormholes in
vacuum are obtained. For base manifolds with vanishing Ricci scalar, a
different class of solutions appears resembling "spacetime horns". There is
also a special case for which, if the base manifold is of constant curvature,
due to certain class of degeneration of the field equations, the metric admits
an arbitrary redshift function. For wormholes and spacetime horns, there are
regions for which the gravitational and centrifugal forces point towards the
same direction. All these solutions have finite Euclidean action, which reduces
to the free energy in the case of black holes, and vanishes in the other cases.
Their mass is also obtained from a surface integral.Comment: 31 pages, 1 figure, minor changes and references added. Final version
to be published in PR
Thermodynamics of Taub-NUT/Bolt-AdS Black Holes in Einstein-Gauss-Bonnet Gravity
We give a review of the existence of Taub-NUT/bolt solutions in Einstein
Gauss-Bonnet gravity with the parameter in six dimensions. Although
the spacetime with base space has curvature singularity at
, which does not admit NUT solutions, we may proceed with the same
computations as in the case. The investigation of
thermodynamics of NUT/Bolt solutions in six dimensions is carried out. We
compute the finite action, mass, entropy, and temperature of the black hole.
Then the validity of the first law of thermodynamics is demonstrated. It is
shown that in NUT solutions all thermodynamic quantities for both base spaces
are related to each other by substituting
. So no further information is given by investigating NUT
solution in the case. This relation is not true for bolt
solutions. A generalization of the thermodynamics of black holes to arbitrary
even dimensions is made using a new method based on the Gibbs-Duhem relation
and Gibbs free energy for NUT solutions. According to this method, the finite
action in Einstein Gauss-Bonnet is obtained by considering the generalized
finite action in Einstein gravity with an additional term as a function of
. Stability analysis is done by investigating the heat capacity and
entropy in the allowed range of , and . For NUT solutions
in dimensions, there exist a stable phase at a narrow range of . In
six-dimensional Bolt solutions, metric is completely stable for
, and is completely unstable for
case.Comment: 19 pages, 3 figures, some Refs. are added, Fig 1 is replaced, and
some corrections are don
Towards a state-space geometry of neural responses to natural scenes: A steady-state approach
Our understanding of information processing by the mammalian visual system has come through a variety of techniques ranging from psychophysics and fMRI to single unit recording and EEG. Each technique provides unique insights into the processing framework of the early visual system. Here, we focus on the nature of the information that is carried by steady state visual evoked potentials (SSVEPs). To study the information provided by SSVEPs, we presented human participants with a population of natural scenes and measured the relative SSVEP response. Rather than focus on particular features of this signal, we focused on the full state-space of possible responses and investigated how the evoked responses are mapped onto this space. Our results show that it is possible to map the relatively high-dimensional signal carried by SSVEPs onto a 2-dimensional space with little loss. We also show that a simple biologically plausible model can account for a high proportion of the explainable variance (~73%) in that space. Finally, we describe a technique for measuring the mutual information that is available about images from SSVEPs. The techniques introduced here represent a new approach to understanding the nature of the information carried by SSVEPs. Crucially, this approach is general and can provide a means of comparing results across different neural recording methods. Altogether, our study sheds light on the encoding principles of early vision and provides a much needed reference point for understanding subsequent transformations of the early visual response space to deeper knowledge structures that link different visual environments
Secretoglobin and Transferrin Expression in Bronchoalveolar Lavage Fluid of Horses with Chronic Respiratory Disease
Background: Lower expression of secretoglobin and transferrin has been found in the bronchoalveolar lavage fluid (BALF) of a small number of horses with experimentally induced signs of recurrent airway obstruction (RAO) compared to healthy controls.
Hypothesis/Objectives: Secretoglobin and transferrin BALF expression will be similarly decreased in horses with naturally occurring clinical signs of RAO and in horses with experimentally induced clinical signs of RAO as compared to healthy controls and intermediate in horses with inflammatory airway disease (IAD).
Animals: Recurrent airway obstruction-affected and control horses were subjected to an experimental hay exposure trial to induce signs of RAO. Client-owned horses with a presumptive diagnosis of RAO and controls from the same stable environments were recruited.
Methods: Pulmonary function and BALF were evaluated from control and RAO-affected research horses during an experimental hay exposure trial (n = 5 in each group) and from client-owned horses (RAO-affected horses, n = 17; IAD-affected horses, n = 19; healthy controls, n = 5). The concentrations of secretoglobin and transferrin in BALF were assessed using Western blots.
Results: Naturally occurring and experimentally induced RAO horses had similar decreases in BALF transferrin expression, but secretoglobin expression was most decreased in naturally occurring RAO. Secretoglobin and transferrin expression were both lower in BALF of RAO-affected horses than in IAD-affected and control horses.
Conclusions and Clinical Importance: Secretoglobin and transferrin expression is decreased in BALF of RAO-affected horses after both experimental and natural exposure. Secretoglobin and transferrin likely play clinically relevant roles in the pathophysiology of RAO, and may thus be used as biomarkers of the disease
Gauge Identities and the Dirac Conjecture
The gauge symmetries of a general dynamical system can be systematically
obtained following either a Hamiltonean or a Lagrangean approach. In the former
case, these symmetries are generated, according to Dirac's conjecture, by the
first class constraints. In the latter approach such local symmetries are
reflected in the existence of so called gauge identities. The connection
between the two becomes apparent, if one works with a first order Lagrangean
formulation. Our analysis applies to purely first class systems. We show that
Dirac's conjecture applies to first class constraints which are generated in a
particular iterative way, regardless of the possible existence of bifurcations
or multiple zeroes of these constraints. We illustrate these statements in
terms of several examples.Comment: 21 page
Short-term Clinical Outcomes of a European Training Programme for Robotic Colorectal Surgery
Background
Despite there being a considerable amount of published studies on robotic colorectal surgery (RCS) over the last few years, there is a lack of evidence regarding RCS training pathways. This study examines the short-term clinical outcomes of an international RCS training programme (the European Academy of Robotic Colorectal Surgery—EARCS).
Methods
Consecutive cases from 26 European colorectal units who conducted RCS between 2014 and 2018 were included in this study. The baseline characteristics and short-term outcomes of cases performed by EARCS delegates during training were analysed and compared with cases performed by EARCS graduates and proctors.
Results
Data from 1130 RCS procedures were collected and classified into three cohort groups (323 training, 626 graduates and 181 proctors). The training cases conversion rate was 2.2% and R1 resection rate was 1.5%. The three groups were similar in terms of baseline characteristics with the exception of malignant cases and rectal resections performed. With the exception of operative time, blood loss and hospital stay (training vs. graduate vs. proctor: operative time 302, 265, 255 min, p < 0.001; blood loss 50, 50, 30 ml, p < 0.001; hospital stay 7, 6, 6 days, p = 0.003), all remaining short-term outcomes (conversion, 30-day reoperation, 30-day readmission, 30-day mortality, clinical anastomotic leak, complications, R1 resection and lymph node yield) were comparable between the three groups.
Conclusions
Colorectal surgeons learning how to perform RCS under the EARCS-structured training pathway can safely achieve short-term clinical outcomes comparable to their trainers and overcome the learning process in a way that minimises patient harm
Hamilton-Jacobi Counterterms for Einstein-Gauss-Bonnet Gravity
The on-shell gravitational action and the boundary stress tensor are
essential ingredients in the study of black hole thermodynamics. We employ the
Hamilton-Jacobi method to calculate the boundary counterterms necessary to
remove the divergences and allow the study of the thermodynamics of
Einstein-Gauss-Bonnet black holes.Comment: 21 pages, LaTe
Does monitor position influence visual-motor performance during minimally invasive surgery?
Background: In minimally invasive surgery (MIS), the natural relationship between hand and eye is disrupted, i.e. surgeons typically control tools inserted through the patient’s abdomen while viewing the workspace on a remote monitor, which can be located in a variety of positions. This separates the location of visual feedback from the area in which a motor action is executed. Previous studies suggest that the visual display should be placed directly ahead of the surgeon (i.e. to preserve visual-motor mapping). However, the extent of the impact of this rotation on surgical performance is unknown. Methods: Eighteen participants completed an aiming task on a tablet PC within a surgical box trainer using a laparoscopic tool in a controlled simulated environment. Visual feedback was presented on a remote monitor located at 0°, ±45° and ±90°, with order randomised using the Latin Square method. Results: Movements were significantly slower when the monitor was 90° relative to midline, but spatial accuracy was unaffected by monitor position. Interestingly, the effect of reduced speed in the 90° condition was transient, decreasing over time, suggesting rapid adaptation to the rotation. Conclusions: We conclude that the angle of the visual display in the context of MIS may require a surgeon to adapt to a changed mapping between visual inputs and motor outputs. While this adaptation occurs relatively quickly, it may interfere with skilled actions (e.g. intracorporeal suturing) in complex surgical procedures
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