Bardeen black hole chemistry

In the present paper we try to connect the Bardeen black hole with the concept of the recently proposed black hole chemistry. We study thermodynamic properties of the regular black hole with an anti-deSitter background. The negative cosmological constant $\Lambda$ plays the role of the positive thermodynamic pressure of the system. After studying the thermodynamic variables, we derive the corresponding equation of state and we show that a neutral Bardeen-anti-deSitter black hole has similar phenomenology to the chemical Van der Waals fluid. This is equivalent to saying that the system exhibits criticality and a first order small/large black hole phase transition reminiscent of the liquid/gas coexistence.Comment: 16 pages, 4 figures, version in press on Physics Letters

Regular black holes in isothermal cavity

We examine the thermodynamic behavior of a static neutral regular (non-singular) black hole enclosed in a finite isothermal cavity. The cavity enclosure helps us investigate black hole systems in a canonical or a grand canonical ensemble. Here we demonstrate the derivation of the reduced action for the general metric of a regular black hole in a cavity by considering a canonical ensemble. The new expression of the action contains quantum corrections at short distances and concludes to the action of a singular black hole in a cavity at large distances. We apply this formalism to the noncommutative Schwarzschild black hole, in order to study the phase structure of the system. We conclude to a possible small/large stable regular black hole transition inside the cavity that exists neither at the system of a classical Schwarzschild black hole in a cavity, nor at the asymptotically flat regular black hole without the cavity. This phase transition seems to be similar with the liquid/gas transition of a Van der Waals gas.Comment: 10 pages, 4 figures, version appeared in Physics Letters

The role of advanced imaging in transcatheter aortic valve implantation

Aortic stenosis, currently the most prevalent valvular heart disease in Europe, is an important public health problem, affecting thousands of patients every year. While surgical aortic valve replacement is still considered the “gold standard” treatment, recent innovations in transcatheter valve therapies have offered an attractive alternative: transcatheter aortic valve implantation (TAVI). In 2002, Cribier et al. announced the first human case description of a percutaneously implanted heart valve in a patient suffering from severe aortic stenosis. Since then, the number of patients that undergo TAVI has increased exponentially. Preliminary early and midterm results following TAVI have been promising. However, despite satisfactory hemodynamic results, TAVI procedures still face important safety issues such as paravalvular leaks, vascular complications, stroke, conduction disorders and the need for pacemaker implantation. Currently, TAVI is offered only to patients who are considered high risk candidates for surgical aortic valve replacement. A fundamental characteristic of percutaneous interventions is the lack of direct visualization of the target organ/tissue. Consequently, interventional cardiology is greatly related to and depending on imaging. Especially in TAVI, which is entering the field of traditional valve surgery, the role of multimodality cardiac imaging is mandatory. Contrast aortography, multi slice computed tomography (MSCT), magnetic resonance imaging and echocardiography can provide a detailed characterisation of vascular anatomy, aortic root dimensions, aortic valve calcifications and left ventricular (LV) function. The use of these imaging techniques is invaluable for patient selection and planning of the procedure. In addition, some techniques can be used during the operation to guide the implantation, as well as after the procedure to evaluate the positioning and function of the prosthesis. TAVI is a fascinating technology but it is still in its infancy. Further studies are needed in order to understand and modulate TAVI. The aim of the present thesis is to investigate the role of advanced cardiac imaging for TAVI

‘What are the goals of kindergarten?’ Consistency of teachers’ and parents’ beliefs about kindergarten goals

The teachers’ perceptions of the curriculum or their beliefs about how children learn can influence the quality of the teaching activity and its final outcome. Furthermore, the importance of an extended cooperation and mutual understanding between the actors involved (kindergarten teachers – parents) seems to be a crucial issue in order to establish a supportive framework. The research is structured in two dimensions. We seek the beliefs of kindergarten teachers (K-teachers) and parents, as well as their mutual perceptions of each other’s beliefs, i.e., K-teachers for parents and parents for K-teachers, about the importance of kindergarten goals. The study was conducted in Greece, specifically in the region of Central Macedonia, in June 2021, after the re-opening of schools due to the Covid-19 pandemic. A sample of 330 K-teachers and 419 parents from public and private schools responded to closed-ended questionnaires, rating –on a 5-point Likert scale- the importance of 14 Kindergarten goals. We found that K-teachers generally underestimated parents’ beliefs about kindergarten goals relative to their own beliefs and overestimated parents’ beliefs about the ‘academic’ curriculum goals; a trend that was not confirmed by the parallel survey of parents’ beliefs. In contrast, parents appeared to express a more balanced perception between their own beliefs and those they perceived K-teachers to hold. We also found evidence of differentiation between private and public schools. According to the findings, a harmonized perception of kindergarten goals by K-teachers and parents in private versus public schools is apparent

Sparse Estimation using Bayesian Hierarchical Prior Modeling for Real and Complex Linear Models

In sparse Bayesian learning (SBL), Gaussian scale mixtures (GSMs) have been used to model sparsity-inducing priors that realize a class of concave penalty functions for the regression task in real-valued signal models. Motivated by the relative scarcity of formal tools for SBL in complex-valued models, this paper proposes a GSM model - the Bessel K model - that induces concave penalty functions for the estimation of complex sparse signals. The properties of the Bessel K model are analyzed when it is applied to Type I and Type II estimation. This analysis reveals that, by tuning the parameters of the mixing pdf different penalty functions are invoked depending on the estimation type used, the value of the noise variance, and whether real or complex signals are estimated. Using the Bessel K model, we derive a sparse estimator based on a modification of the expectation-maximization algorithm formulated for Type II estimation. The estimator includes as a special instance the algorithms proposed by Tipping and Faul [1] and by Babacan et al. [2]. Numerical results show the superiority of the proposed estimator over these state-of-the-art estimators in terms of convergence speed, sparseness, reconstruction error, and robustness in low and medium signal-to-noise ratio regimes.Comment: The paper provides a new comprehensive analysis of the theoretical foundations of the proposed estimators. Minor modification of the titl