1,721,040 research outputs found
A piecewise conservative method for unconstrained convex optimization
No full textWe consider a continuous-time optimization method based on a dynamical system, where a massive particle starting at rest moves in the conservative force field generated by the objective function, without any kind of friction. We formulate a restart criterion based on the mean dissipation of the kinetic energy, and we prove a global convergence result for strongly-convex functions. Using the Symplectic Euler discretization scheme, we obtain an iterative optimization algorithm. We have considered a discrete mean dissipation restart scheme, but we have also introduced a new restart procedure based on ensuring at each iteration a decrease of the objective function greater than the one achieved by a step of the classical gradient method. For the discrete conservative algorithm, this last restart criterion is capable of guaranteeing a qualitative convergence result. We apply the same restart scheme to the Nesterov Accelerated Gradient (NAG-C), and we use this restarted NAG-C as benchmark in the numerical experiments. In the smooth convex problems considered, our method shows a faster convergence rate than the restarted NAG-C. We propose an extension of our discrete conservative algorithm to composite optimization: in the numerical tests involving non-strongly convex functions with l(1)-regularization, it has better performances than the well known efficient Fast Iterative Shrinkage-Thresholding Algorithm, accelerated with an adaptive restart scheme
On the asymptotic behaviour of anisotropic energies arising in the cardiac bidomain model
No full textConvergence of front propagation for anisotropic bistable reaction-diffusion equations
No full textWe study the convergence of the singularly perturbed anisotropic, nonhomogeneous reaction-diffusion equation epsilon partial derivative(t)u - epsilon(2) div T degrees(x,del u) + f(u) - epsilon(c(1)/c(0))g = 0, where f is the derivative of a bistable quartic-like potential with unequal wells, T degrees(x,) is a nonlinear monotone operator homogeneous of degree one and g is a given forcing term. More precisely, we prove that an appropriate level set of the solution satisfies an O(epsilon(3)\log epsilon\(2)) error bound (in the Hausdorff distance) with respect to a hypersurface moving with the geometric law V = (c - epsilon kappa(phi))n(phi) + g-dependent terms, where n(phi) is the so-called Cahn-Hoffmann vector and kappa(phi) denotes the anisotropic mean curvature of the hypersurface. We also discuss the connection between the anisotropic reaction-diffusion equation and the bidomain model, which is described by a system of equations modeling the propagation of an electric stimulus in the cardiac tissue
Combined treatment with chemotherapy and radiotherapy in high-risk FIGO stage III-IV endometrial cancer patients.
No full text
In silico modelling and analysis of the electrical and mechanical properties of in vitro cardiac cultures with different fiber architectures
No full textToday, in vitro cardiac cultures are widely exploited to investigate several aspects of the electromechanical behavior of the cardiac tissue. Thus, new forecasts may derive from modelling their properties. In particular, in this paper, we focus on the fiber architecture of cultures, i.e. on the way cellular sarcomeres are locally oriented, when they are designed to be cardiac patches. We employ a three-dimensional model to simulate the bioelectrical activity and the biomechanics of a multilayered culture made of ventricular cells and with four possible architectures consisting of: i) random fibers in all cells; ii) randomly rotating fibers among layers; iii) structurally rotating fibers from the bottom layer to the top one; iv) parallel fibers among layers. Our results suggest that the best configuration for a patch may be the architecture with structurally rotating fibers, which is the one that most approaches the anisotropic structure of the in vivo heart, thanks to its better electrical and mechanical performances
Combined treatment with chemotherapy and radiotherapy in high-risk FIGO stage III-IV endometrial cancer patients
No full textComputational modeling of the electromechanical response of a ventricular fiber affected by eccentric hypertrophy
No full textThe aim of this work is to study the effects of eccentric hypertrophy on the electromechanics of a single myocardial ventricular fiber by means of a one-dimensional finite-element strongly-coupled model. The electrical current flow model is written in the reference configuration and it is characterized by two geometric feedbacks, i.e. the conduction and convection ones, and by the mechanoelectric feedback due to stretch-activated channels. First, the influence of such feedbacks is investigated for both a healthy and a hypertrophic fiber in case of isometric simulations. No relevant discrepancies are found when disregarding one or more feedbacks for both fibers. Then, all feedbacks are taken into account while studying the electromechanical responses of fibers. The results from isometric tests do not point out any notable difference between the healthy and hypertrophic fibers as regards the action potential duration and conduction velocity. The length-tension relationships show increased stretches and reduced peak values for tension instead. The tension-velocity relationships derived from afterloaded isotonic and quick-release tests depict higher values of contraction velocity at smaller afterloads. Moreover, higher maximum shortenings are achieved during the isotonic contraction. In conclusion, our simulation results are innovative in predicting the electromechanical behavior of eccentric hypertrophic fibers
- …
