57 research outputs found
Parallel inexact Newton-Krylov and quasi-Newton solvers for nonlinear elasticity
In this work, we address the implementation and performance of inexact
Newton-Krylov and quasi-Newton algorithms, more specifically the BFGS method,
for the solution of the nonlinear elasticity equations, and compare them to a
standard Newton-Krylov method. This is done through a systematic analysis of
the performance of the solvers with respect to the problem size, the magnitude
of the data and the number of processors in both almost incompressible and
incompressible mechanics. We consider three test cases: Cook's membrane
(static, almost incompressible), a twist test (static, incompressible) and a
cardiac model (complex material, time dependent, almost incompressible). Our
results suggest that quasi-Newton methods should be preferred for compressible
mechanics, whereas inexact Newton-Krylov methods should be preferred for
incompressible problems. We show that these claims are also backed up by the
convergence analysis of the methods. In any case, all methods present adequate
performance, and provide a significant speed-up over the standard Newton-Krylov
method, with a CPU time reduction exceeding 50% in the best cases
Parallel Newton-Krylov-BDDC and FETI-DP deluxe solvers for implicit time discretizations of the cardiac Bidomain equations
Two novel parallel Newton-Krylov Balancing Domain Decomposition by
Constraints (BDDC) and Dual-Primal Finite Element Tearing and Interconnecting
(FETI-DP) solvers are here constructed, analyzed and tested numerically for
implicit time discretizations of the three-dimensional Bidomain system of
equations.
This model represents the most advanced mathematical description of the
cardiac bioelectrical activity and it consists of a degenerate system of two
non-linear reaction-diffusion partial differential equations (PDEs), coupled
with a stiff system of ordinary differential equations (ODEs).
A finite element discretization in space and a segregated implicit
discretization in time, based on decoupling the PDEs from the ODEs, yields at
each time step the solution of a non-linear algebraic system.
The Jacobian linear system at each Newton iteration is solved by a Krylov
method, accelerated by BDDC or FETI-DP preconditioners, both augmented with the
recently introduced {\em deluxe} scaling of the dual variables.
A polylogarithmic convergence rate bound is proven for the resulting parallel
Bidomain solvers.
Extensive numerical experiments on linux clusters up to two thousands
processors confirm the theoretical estimates, showing that the proposed
parallel solvers are scalable and quasi-optimal
Social anxiety and Internet gaming disorder: The role of motives and metacognitions
AbstractBackground and aimsIn recent years, Internet Gaming Disorder (IGD) has been recognized as a mental health problem. Although research has found that social anxiety, motives, the preference for online social interactions (POSI), and metacognitions about online gaming are independent predictors of IGD, less is known about their relative contribution to IGD. The aim of the current study was to model the relationship between social anxiety, motives, POSI, metacognitions about online gaming, and IGD.MethodsFive hundred and forty three Italian gamers who play more than 7 h a week (mean age = 23.9 years; SD = 6.15 years; 82.5% males) were included in the study. The pattern of relationships specified by the theoretical model was examined through path analysis.ResultsResults showed that social anxiety was directly associated with four motives (escape, coping, fantasy, and recreation), POSI, and positive and negative metacognitions about online gaming, and IGD. The Sobel test showed that negative metacognitions about online gaming played the strongest mediating role in the relationship between social anxiety and IGD followed by escape, POSI, and positive metacognitions. The model accounted for 54% of the variance for IGD.Discussion and conclusionsOverall, our findings show that, along with motives and POSI, metacognitions about online gaming may play an important role in the association between social anxiety and IGD. The clinical and preventive implications of these findings are discussed
Robust parallel nonlinear solvers for implicit time discretizations of the Bidomain equations
In this work, we study the convergence and performance of nonlinear solvers
for the Bidomain equations after decoupling the ordinary and partial
differential equations of the cardiac system. Firstly, we provide a rigorous
proof of the global convergence of Quasi-Newton methods, such as BFGS, and
nonlinear Conjugate-Gradient methods, such as Fletcher--Reeves, for the
Bidomain system, by analyzing an auxiliary variational problem under physically
reasonable hypotheses. Secondly, we compare several nonlinear Bidomain solvers
in terms of execution time, robustness with respect to the data and parallel
scalability. Our findings indicate that Quasi-Newton methods are the best
choice for nonlinear Bidomain systems, since they exhibit faster convergence
rates compared to standard Newton-Krylov methods, while maintaining robustness
and scalability. Furthermore, first-order methods also demonstrate
competitiveness and serve as a viable alternative, particularly for matrix-free
implementations that are well-suited for GPU computing
Social anxiety and Internet gaming disorder: The role of motives and metacognitions
AbstractBackground and aimsIn recent years, Internet Gaming Disorder (IGD) has been recognized as a mental health problem. Although research has found that social anxiety, motives, the preference for online social interactions (POSI), and metacognitions about online gaming are independent predictors of IGD, less is known about their relative contribution to IGD. The aim of the current study was to model the relationship between social anxiety, motives, POSI, metacognitions about online gaming, and IGD.MethodsFive hundred and forty three Italian gamers who play more than 7 h a week (mean age = 23.9 years; SD = 6.15 years; 82.5% males) were included in the study. The pattern of relationships specified by the theoretical model was examined through path analysis.ResultsResults showed that social anxiety was directly associated with four motives (escape, coping, fantasy, and recreation), POSI, and positive and negative metacognitions about online gaming, and IGD. The Sobel test showed that negative metacognitions about online gaming played the strongest mediating role in the relationship between social anxiety and IGD followed by escape, POSI, and positive metacognitions. The model accounted for 54% of the variance for IGD.Discussion and conclusionsOverall, our findings show that, along with motives and POSI, metacognitions about online gaming may play an important role in the association between social anxiety and IGD. The clinical and preventive implications of these findings are discussed
A clinical-in silico study on the effectiveness of multipoint bicathodic and cathodic-anodal pacing in cardiac resynchronization therapy.
Up to one-third of patients undergoing cardiac resynchronization therapy (CRT) are nonresponders. Multipoint bicathodic and cathodic-anodal left ventricle (LV) stimulations could overcome this clinical challenge, but their effectiveness remains controversial. Here we evaluate the performance of such stimulations through both in vivo and in silico experiments, the latter based on computer electromechanical modeling. Seven patients, all candidates for CRT, received a quadripolar LV lead. Four stimulations were tested: right ventricular (RVS); conventional single point biventricular (S-BS); multipoint biventricular bicathodic (CC-BS) and multipoint biventricular cathodic-anodal (CA-BS). The following parameters were processed: QRS duration; maximal time derivative of arterial pressure (dPdtmax); systolic arterial pressure (Psys); and stroke volume (SV). Echocardiographic data of each patient were then obtained to create an LV geometric model. Numerical simulations were based on a strongly coupled Bidomain electromechanical coupling model. Considering the in vivo parameters, when comparing S-BS to RVS, there was no significant decrease in SV (from 45 ± 11 to 44 ± 20 ml) and 6% and 4% increases of dPdtmax and Psys, respectively. Focusing on in silico parameters, with respect to RVS, S-BS exhibited a significant increase of SV, dPdtmax and Psys. Neither the in vivo nor in silico results showed any significant hemodynamic and electrical difference among S-BS, CC-BS and CA-BS configurations. These results show that CC-BS and CA-BS yield a comparable CRT performance, but they do not always yield improvement in terms of hemodynamic parameters with respect to S-BS. The computational results confirmed the in vivo observations, thus providing theoretical support to the clinical experiments
Adolescent gambling and impulsivity: does employment during high school moderate the association?
The aim of the present study was to examine the potential moderating relationships between adolescent gambling and impulsivity traits (negative urgency, positive urgency, lack of premeditation, lack of perseverance and sensation seeking) with employment status. High-school students (N=400; 69% male; mean age=18.35 years; SD=1.16; past year gamblers) were surveyed to provide data on impulsivity and employment. Multiple linear regression analysis was applied to examine associations with gambling and related problems. Positive urgency was associated with stronger scores of both gambling frequency and problem gambling. Students in employment had substantially higher frequency of gambling and greater problem gambling. Moreover, the combination of having a job and low perseverance was associated with a particularly high frequency on gambling. These findings further support the importance of positive urgency and employment status in adolescent gambling. The study highlights unique moderating relationship between gambling and lack of perseverance with employment status. Youth with a low perseverance and having a job may have particular need for interventions to reduce gambling
Psychological complications in patients with acromegaly: relationships with sex, arthropathy, and quality of life
Current treatment of acromegaly restores a normal life expectancy in most cases. So, the study of persistent complications affecting patients' quality of life (QoL) is of paramount importance, especially motor disability and depression. In a large cohort of acromegalic patients we aimed at establishing the prevalence of depression, to look for clinical and sociodemographic factors associated with it, and to investigate the respective roles (and interactions) of depression and arthropathy in influencing QoL
Unexpected impairment of INa underpins reentrant arrhythmias in a knock-in swine model of Timothy syndrome
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