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When solving nonlinear algebraic equations that arise from discretization using the finite element method (FEM), it is often observed that the standard Newton-Raphson (N-R) iteration either fails to converge or necessitates a large number of iterations in the vicinity of critical points. This work proposes an additional numerical strategy, known as the Potra-Pták iterative cycle, to improve the efficiency of solving highly nonlinear structural problems. Therefore, the focus here is on making the nonlinear solver more robust and efficient, allowing the analysis of more complex nonlinear structures. In the Potra-Pták iterative cycle, two corrections of the objective function (energy function) are performed. The introduction of a second correction in the iterative cycle makes the Potra-Pták strategy more efficient than the standard or modified N-R iterations. This numerical strategy was implemented in the homemade Computational System for Advanced Structural Analysis (CS-ASA) program. The program is based on the FEM and is capable of performing static and dynamic nonlinear analysis of steel, concrete, and composite structures, and its efficiency is then verified through the analysis of slender frames and arches. The algorithm details for solving the nonlinear structural problem, characterized by the Potra-Pták scheme, are provided. [ABSTRACT FROM AUTHOR]

INTRODUCTION: The identification of COVID-19 pneumonia using chest radiography is challenging. OBJECTIVES: We investigate classification models to differentiate COVID-19-based and typical pneumonia in chest radiography. METHODS: We use 136 segmented chest X-rays to train and evaluate the performance of support vector machine (SVM), random forest (RF), AdaBoost (AB), and logistic regression (LR) classification methods. We use the PyRadiomics to extract statistical texture-based features in the right, left, and in six lung zones. We use a stratified k-folds (k=5) cross-validation within the training dataset, selecting the most relevant features with validation accuracy and relative feature importance. RESULTS: The AB model seems to be the best discriminant method, using six lung zones (AUC = 0.98). CONCLUSION: Our study shows a predominance of radiomic texture-based features related to COVID-19 pneumonia within the right lung, with a tendency within the upper lung zone. [ABSTRACT FROM AUTHOR]

Many researchers have studied building pounding to calculate the dissipated energy and impact force between two buildings during an earthquake. In this paper, a new equation is proposed to measure the impact force and energy dissipation. The results based on the proposed equation are compared with the results of available equations. Using a suggested link element, a new formula is presented to calculate the impact force and energy dissipation. In order to evaluate the results of dissipated energy, a new relation between CR and impact velocity is also suggested. Since there is a need to have a reference curve to select impact velocity, based on the coefficient of restitution, several impact velocities and CRs were evaluated. By using the latter curve, results could be evaluated. A new equation of motion is assumed to select the best impact velocity and coefficient of restitution. Finally, based on the coefficient of restitution and using the steady-state response of a single degree of freedom system, due to external force, a new equation of motion is suggested to calculate the impact damping ratio. [ABSTRACT FROM AUTHOR]

The article presents a study which aims to present criteria for determining the critical load of dynamic buckling of thin shell. The purpose of establishing the criteria is to guide engineers, scientists, and researchers dealing with the problem of dynamic stability. To illustrate the use of the criteria, two examples have been studied.