88,653 research outputs found
A new integrated approach to improve left ventricular electromechanical activation during right ventricular septal pacing
No full textAims The deleterious effects of apical right ventricular pacing has fostered the utilization of alternative pacing sites. Although right ventricular septal (RVS) sites are commonly used, the results have been controversial because of poor standardization of lead position by fluoroscopy. This study investigated the utility of a new RVS pacing technique based on the combination of fluoroscopy (F), and electrophysiological mapping (F + EP). Left ventricular (LV) electromechanical activation was determined in patients undergoing RVS pacing and the results of the F + EP approach were compared with those derived from standard F alone. Methods and results Between December 2008 and November 2010 we enrolled 156 consecutive patients undergoing permanent RVS pacing. The standard F approach was used in 93 patients and the F + EP technique was applied to 63 patients. Electromechanical activation was assessed by: (i) electromechanical latency (EML) interval measured from the QRS onset to the mechanical activation of the basal LV and (ii) intra-LV dyssynchrony measured as the interval from the earliest to the latest LV basal motion. Intra-LV dyssynchrony was found in 46.2% patients in the F group compared with 15.9% in the group F + EP (P < 0.001). The F group demonstrated a significantly higher degree of intra-LV dyssynchrony than F + EP group (43.9 +/- 24.3 vs. 26.5 +/- 15.4 ms; P < 0.001). The F group exhibited a significantly higher EML duration compared with the F + EP group (215.8 +/- 25.3 vs. 195.1 +/- 17.4 ms; P < 0.001). Conclusion During RVS pacing, the F + EP approach provides a more physiological LV activation than the standard F technique. The prognostic significance of these short-term findings needs to be correlated with long-term data
Under-resolved simulation of turbulent flows using a p-adaptive discontinuous galerkin method
No full textIn this work we present the main features of a p-adaptive Discontinuous Galerkin (DG) method, suited for the accurate and efficient simulation of turbulent flows. The method allows to locally adapt the polynomial degree of the solution within mesh elements (p-adaptation), obtaining significant reduction of the simulation time and memory, and, at the same time, preserving the high accuracy needed by Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). Adaptation is driven by a simple error indicator, obtained blending two simple indicators based on
the interface pressure jumps and on the decay of the coefficients of the modal expansion.
Moreover, a load-balancing strategy is adopted during adaptation to achieve good parallel performances. Preliminary results are presented for the under-resolved simulation of the turbulent flows (i) around the NACA 0018 airfoil, Rec = 100 000, M = 0.2 and angle of attack AoA = 10", and (ii) around a rounded leading-edge flat plate (the T3L test case of the ERCOFTAC suite)
Robustness and efficiency of an implicit time-adaptive discontinuous Galerkin solver for unsteady flows
No full textHigh-fidelity fluid dynamics simulations of unsteady flows are nowadays of great interest for many industrial fields. This class of simulations, as they are characterized by a wide range of temporal scales, requires robust, accurate and efficient long time integration strategies. These features can be achieved by an appropriate coupling of high-order time integration schemes and time-step adaptation algorithms. The adaptation algorithms are typically based on a local error estimator, which exploits the local truncation error of the time integration scheme and of its lower order embedded scheme. In literature few information are available to assess the benefits in terms of robustness, accuracy, and efficiency provided by the coupling between temporal schemes and adaptation strategies for unsteady CFD simulations. The aim of this work is to reduce this gap, presenting a numerical investigation of the performance for different adaptive time-step strategies, based on implicit Rosenbrock-type temporal schemes, in a high-order discontinuous Galerkin solver. The performance of the considered time integration strategies for the autonomous ODE system resulting from the DG space discretization of the Navier–Stokes equations is assessed for several test cases of increasing stiffness and difficulty, identifying the best scheme and algorithm: (i) the 2D laminar flow around a circular cylinder and around a tandem of cylinders at ReD=100; (ii) the 2D viscous flow through a porous media, modelled as an array of cylinders, at ReD=2100 and ReD=10,000; (iii) the 3D turbulent flow through a 4-wheels rudimentary landing gear (RLG) at ReD=1×106
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