1,721,530 research outputs found
Transcatheter valve-in-valve implantation for degenerated aortic bioprostheses: Still not ready for prime-time
No full textThe progressively increasing experience with transcatheter aortic valve implantation (TAVI) together with the publication of new prospective randomized studies showing the non-inferiority and sometimes the superiority of this technique when compared to surgical aortic valve replacement (SAVR) also in low risk patients [1,2] has led to the expansion of the indications for TAVI. Consequently, there has also been a growing interest towards transcatheter bioprostheses implantation in the setting of structural deterioration of previously implanted aortic xenografts in order to avoid surgical reintervention. Valve-in-valve (ViV) procedure represents a micro-invasive approach [3] for patients with degenerated aortic bioprostheses since it enables to implant a new valve inside the malfunctioning one, on the beating heart, with no need for cardiopulmonary bypass, with no skin incision and with local anesthesia if performed through a transfemoral access. All these aspects make ViV particularly interesting as an alternative therapeutic option in patients with failing bioprostheses. In this issue of the IJC, Dr. Woitek and his colleagues from Leipzig, evaluate their results with conventional redo surgery (Re-SAVR) and with valve-invalve transfemoral TAVI (VinV-TFAVI) in 258 consecutive patients [4]. As authors have correctly pointed out, this study should not be considered a true comparison of these techniques since baseline characteristics are different in the two cohorts, but rather a “hypothesi
Topological Calculus: between Algebraic Topology and Electromagnetic Fields
No full textTopological behaviour of self-similar spectra for fractal domains is shown and applied to solve electromagnetic problems on fractal geometries, like for example the Sierpinski gasket.. Two different mathematical tools are employed: the Topological Calculus, which frames a topology-consistent, discrete counterpart to domains and operators and the Iterated Function Systems (IFSs) to produce fractals as limit sets of simple recursion mappings. Topological invariants and Analytical features of a set can be easily extracted from such a discrete model, even for complex geometries like fractal ones.One of the targets of this work is to show how recursion symmetries of a (pre-) fractal set, mathematically coded by "algebraic" relationships between its parts, are sole responsible for the self-similar distribution of its (laplacian) eigenvalues: no metric information is needed for this property to be observed.Another primary target is to show how Topological Calculus easily allows for an almost instantaneous discretization of contoinuum equations of any (topological) field theory. Investigating the natural modes of self-similar domains is important to many applications whose core geometry is prefractal or at least highly irregular. Most recently, transport and electromagnetic pehnomena were focused: IFS-generated waveguides, resonators and antennas(9) exhibiting multi-band properties. Such complex domains need careful mathematical formulations in order to transfer traditional-geometric properties to them; Topological Calculus is one of such discrete formulations
Spectral analysis of Šerpinskij carpet-like prefractal waveguides and resonators
No full textExact results on some modal properties of waveguides and resonators is studied, whose geometry is derived from "Šerpinskij carpet-like" prefractals (Serpinskij carpet and sponge; Menger sponge). The study is biased to the closed-form computation of specific resonances and eigenmodes (called "diaperiodic"), and to the relation existing between their topology and the existence of a finite set of transverse electromagnetic modes
Shifting a Paradigm of Cardiac Surgery: From Minimally Invasive to Micro-Invasive
No full textThe development of new techniques for the treatment of almost all structural heart pathologies that do not require cardiopulmonary bypass and aortic cross-clamping, such as transcatheter aortic valve replacement and transapical mitral chordae implantation, define a new age of our specialty: the micro-invasive (microICS) cardiac surgery era
Modelling stomatal uptake of ozone: data requirements and applicability of CONECOFOR permanent monitoring plots in Italy
No full textIt is accepted that ozone (O3) effects on vegetation depend mostly on the amount of O3 uptake rather than on exposure. As direct measurement of uptake is unfeasible under most forest conditions, modelling is needed. There are different modelling approaches (e.g. diagnostic and prognostic models) which follow the electric resistance analogue principle. Unfortunately, these models are data intensive and implementation can be difficult in sites which are not designed for canopy-atmosphere flux studies. The paper provides an overview on modelling approaches, identifies data requirements and evaluates the actual chance for implementing a flux approach in the CONECOFOR PMPs
Technique versus technology and the (r)evolution of cardiac surgery: A professional journey from classical surgery to embracing intervention
No full textCan you hear the fractal dimension of a drum?
No full textElectromagnetics and Acoustics on a bounded domain are governed by the
Helmholtz's equation; when such a domain is a [pre-]fractal described by means
of a `just-touching' Iterated Function System (IFS) spectral decomposition of
the Helmholtz's operator is self-similar as well. Renormalization of the
Green's function proves this feature and isolates a subclass of eigenmodes,
called ``diaperiodic'', whose waveforms and eigenvalues can be recursively
computed applying the IFS to the initiator's eigenspaces. The definition of
``spectral dimension'' is given and proven to depend on diaperiodic modes only
for a wide class of IFSs. Finally, asymptotic equivalence between box-counting
and spectral dimensions in the fractal limit is proven. As the `self-similar'
spectrum of the fractal is enough to compute box-counting dimension, positive
answer is given to title question
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