330 research outputs found
Fluctuations around classical solutions for gauge theories in Lagrangian and Hamiltonian approach
We analyze the dynamics of gauge theories and constrained systems in general
under small perturbations around a classical solution (background) in both
Lagrangian and Hamiltonian formalisms. We prove that a fluctuations theory,
described by a quadratic Lagrangian, has the same constraint structure and
number of physical degrees of freedom as the original non-perturbed theory,
assuming the non-degenerate solution has been chosen. We show that the number
of Noether gauge symmetries is the same in both theories, but that the gauge
algebra in the fluctuations theory becomes Abelianized. We also show that the
fluctuations theory inherits all functionally independent rigid symmetries from
the original theory, and that these symmetries are generated by linear or
quadratic generators according to whether the original symmetry is preserved by
the background, or is broken by it. We illustrate these results with the
examples.Comment: 27 pages; non-essential but clarifying changes in Introduction, Sec.
3 and Conclusions; the version to appear in J.Phys.
Non-linear screening of external charge by doped graphene
We solve a nonlinear integral equation for the electrostatic potential in
doped graphene due to an external charge, arising from a Thomas-Fermi (TF)
model for screening by graphene's electron bands. In particular, we study
the effects of a finite equilibrium charge carrier density in graphene,
non-zero temperature, non-zero gap between graphene and a dielectric substrate,
as well as the nonlinearity in the band density of states. Effects of the
exchange and correlation interactions are also briefly discussed for undoped
graphene at zero temperature. Nonlinear results are compared with both the
linearized TF model and the dielectric screening model within random phase
approximation (RPA). In addition, image potential of the external charge is
evaluated from the solution of the nonlinear integral equation and compared to
the results of linear models. We have found generally good agreement between
the results of the nonlinear TF model and the RPA model in doped graphene,
apart from Friedel oscillations in the latter model. However, relatively strong
nonlinear effects are found in the TF model to persist even at high doping
densities and large distances of the external charge.Comment: 12 pages including 6 figure
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
Torsion induces Gravity
In this work the Poincare-Chern Simons and Anti de Sitter Chern Simons
gravities are studied. For both a solution that can be casted as a black hole
with manifest torsion is found. Those solutions resemble Schwarzschild and
Schwarzschild-AdS solutions respectively.Comment: 4 pages, RevTe
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
Patient-specific mental rehearsal with interactive visual aids: a path worth exploring?
Background
Surgeons of today are faced with unprecedented challenges; necessitating a novel approach to pre-operative preparation which takes into account the specific tests each case poses. In this study, we examine patient-specific mental rehearsal for pre-surgical practice and assess whether this method has an additional effect when compared to generic mental rehearsal.
Methods
Sixteen medical students were trained how to perform a simulated laparoscopic cholecystectomy (SLC). After baseline assessments, they were randomised to two equal groups and asked to complete three SLCs involving different anatomical variants. Prior to each procedure, Group A practiced mental rehearsal with the use of a pre-prepared checklist and Group B mental rehearsal with the checklist combined with virtual models matching the anatomical variations of the SLCs. The performance of the two groups was compared using simulator provided metrics and competency assessment tool (CAT) scoring by two blinded assessors.
Results
The participants performed equally well when presented with a “straight-forward” anatomy [Group A vs. Group B—time sec: 445.5 vs. 496 p = 0.64—NOM: 437 vs. 413 p = 0.88—PL cm: 1317 vs. 1059 p = 0.32—per: 0.5 vs. 0 p = 0.22—NCB: 0 vs. 0 p = 0.71—DVS: 0 vs. 0 p = 0.2]; however, Group B performed significantly better [Group A vs. B Total CAT score—Short Cystic Duct (SCD): 20.5 vs. 26.31 p = 0.02 η 2 = 0.32—Double cystic Artery (DA): 24.75 vs. 30.5 p = 0.03 η 2 = 0.28] and committed less errors (Damage to Vital Structures—DVS, SCD: 4 vs. 0 p = 0.03 η 2=0.34, DA: 0 vs. 1 p = 0.02 η 2 = 0.22). in the cases with more challenging anatomies.
Conclusion
These results suggest that patient-specific preparation with the combination of anatomical models and mental rehearsal may increase operative quality of complex procedures
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
Mental practice with interactive 3D visual aids enhances surgical performance
Background: Evidence suggests that Mental Practice (MP) could be used to finesse surgical skills. However, MP is cognitively demanding and may be dependent on the ability of individuals to produce mental images. In this study, we hypothesised that the provision of interactive 3D visual aids during MP could facilitate surgical skill performance. Methods: 20 surgical trainees were case-matched to one of three different preparation methods prior to performing a simulated Laparoscopic Cholecystectomy (LC). Two intervention groups underwent a 25-minute MP session; one with interactive 3D visual aids depicting the relevant surgical anatomy (3D-MP group, n = 5) and one without (MP-Only, n = 5). A control group (n = 10) watched a didactic video of a real LC. Scores relating to technical performance and safety were recorded by a surgical simulator. Results: The Control group took longer to complete the procedure relative to the 3D&MP condition (p = .002). The number of movements was also statistically different across groups (p = .001), with the 3D&MP group making fewer movements relative to controls (p = .001). Likewise, the control group moved further in comparison to the 3D&MP condition and the MP-Only condition (p = .004). No reliable differences were observed for safety metrics. Conclusion: These data provide evidence for the potential value of MP in improving performance. Furthermore, they suggest that 3D interactive visual aids during MP could potentially enhance performance, beyond the benefits of MP alone. These findings pave the way for future RCTs on surgical preparation and performance
The role of low-level image features in the affective categorization of rapidly presented scenes
It remains unclear how the visual system is able to extract affective content from complex scenes even with extremely brief (\u3c 100 millisecond) exposures. One possibility, suggested by findings in machine vision, is that low-level features such as unlocalized, two-dimensional (2-D) Fourier spectra can be diagnostic of scene content. To determine whether Fourier image amplitude carries any information about the affective quality of scenes, we first validated the existence of image category differences through a support vector machine (SVM) model that was able to discriminate our intact aversive and neutral images with ~ 70% accuracy using amplitude-only features as inputs. This model allowed us to confirm that scenes belonging to different affective categories could be mathematically distinguished on the basis of amplitude spectra alone. The next question is whether these same features are also exploited by the human visual system. Subsequently, we tested observers’ rapid classification of affective and neutral naturalistic scenes, presented briefly (~33.3 ms) and backward masked with synthetic textures. We tested categorization accuracy across three distinct experimental conditions, using: (i) original images, (ii) images having their amplitude spectra swapped within a single affective image category (e.g., an aversive image whose amplitude spectrum has been swapped with another aversive image) or (iii) images having their amplitude spectra swapped between affective categories (e.g., an aversive image containing the amplitude spectrum of a neutral image). Despite its discriminative potential, the human visual system does not seem to use Fourier amplitude differences as the chief strategy for affectively categorizing scenes at a glance. The contribution of image amplitude to affective categorization is largely dependent on interactions with the phase spectrum, although it is impossible to completely rule out a residual role for unlocalized 2-D amplitude measures
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