Towards higher-order accurate mass lumping in explicit isogeometric analysis for structural dynamics

We present a mass lumping approach based on an isogeometric Petrov-Galerkin method that preserves higher-order spatial accuracy in explicit dynamics calculations irrespective of the polynomial degree of the spline approximation. To discretize the test function space, our method uses an approximate dual basis, whose functions are smooth, have local support and satisfy approximate bi-orthogonality with respect to a trial space of B-splines. The resulting mass matrix is ``close'' to the identity matrix. Specifically, a lumped version of this mass matrix preserves all relevant polynomials when utilized in a Galerkin projection. Consequently, the mass matrix can be lumped (via row-sum lumping) without compromising spatial accuracy in explicit dynamics calculations. We address the imposition of Dirichlet boundary conditions and the preservation of approximate bi-orthogonality under geometric mappings. In addition, we establish a link between the exact dual and approximate dual basis functions via an iterative algorithm that improves the approximate dual basis towards exact bi-orthogonality. We demonstrate the performance of our higher-order accurate mass lumping approach via convergence studies and spectral analyses of discretized beam, plate and shell models

Reduction in Renal Function After Renal Arteriography and After Renal Artery Angioplasty

AbstractObjective: to investigate the incidence and risk factors for renal function deterioration after renal angiography and angioplasty or stenting.Methods: a retrospective study of 85 consecutive patients undergoing selective renal artery arteriography (n=53) or renal artery angioplasty % (PTRA) stenting (n=32) for renal artery stenosis. Multivariate logistic regression analysis was used to determine independent predictors of deterioration of renal function, defined as an increase of serum creatinine by at least one third within 24h.Results: deterioration of renal function occurred in 13 patients (15%), [8/53 (15%) after angiography and 5/32 (16%) after PTRA/stenting]. Only pre-existing renal impairment (se-creatinine≥177μmol/l) (Odds ratio: 40; 95% confidence interval 1.2–72, p=0.02) and administered dosage of contrast agent (more than 225ml) (OR 67; 95% CI1 1.8–100, p=0.02) were independently associated with renal function deterioration.Conclusion: transient renal dysfunction after renal artery angiography or PTRA/stenting occurs in about 15% of patients, but persistent renal failure is uncommon. Pre-existing renal impairment and amount of contrast agent are independent risk factors. Endovascular treatment of renal artery stenosis is not associated with a higher risk of renal deterioration compared to selective renal angiography

An economic assessment of western Oregon's private forests with streamside management restrictions

Management restrictions are simulated on streamside acres owned by private interests in western Oregon to assess forest inventory and log market implications. A dynamic, nonlinear optimization model of western Oregon's softwood log market simulates the resource and economic impacts of set-aside and minimum harvest age restrictions on forest acreage within 40 meters of water on private lands from 1995 to 2045. Without restrictions, about 49 percent of log market surplus is attained by producers, while the consumers' (mills) portion is 17 percent and the trade sector earns the remaining 34 percent. Streamside management constraints take up to 19 percent of the forestland out of production. When this acreage is set-aside from harvest, periodic softwood harvest levels drop by 15 to 26 percent and log prices rise by 7 to 10 percent. The average value of a bare forest acre further than 40 meters from water rises by 13 percent. The increase in log prices and land values does not offset the loss in management choices. The present value of producers' surplus drops by 11 percent, while consumers' surplus drops by 30 percent

Successful Left Atrial Appendage Occlusion with the New Generation Amulet® Device after Late-Occurring Embolization of an Amplatzer® Cardiac Plug in a Patient with Repetitive Strokes

The Amplatzer Cardiac Plug (ACP) is one of the most commonly used devices for percutaneous left atrial appendage (LAA) closure in order to prevent a stroke in patients with atrial fibrillation and contraindication for long-term oral anticoagulation therapy. We have previously described a patient who had experienced an embolization of the ACP device about 12 months after implantation and the device could be percutaneously retrieved. A few years later, he suffered from a posterior stroke and a stroke located in the brainstem as well as a transischemic attack (TIA). In order to protect him from further cardioembolic events a reocclusion of the LAA with the new generation of ACP device, the Amplatzer Amulet, was performed. A stable position of the device within follow-up period could be confirmed and the patient was free of additional strokes/TIA or bleeding events. This case stresses the importance of proper LAA sizing in order to prevent device embolization and notes that LAA size is not static. Moreover, it demonstrates that repeated implantation of an LAA occlusion device was still possible; one should be aware of undersizing the LAA dimensions and that the modifications of new generation LAA occlusion devices may overcome limitations of first-generation devices in order to prevent a cardioembolic stroke

The matrix-free macro-element hybridized Discontinuous Galerkin method for steady and unsteady compressible flows

The macro-element variant of the hybridized discontinuous Galerkin (HDG) method combines advantages of continuous and discontinuous finite element discretization. In this paper, we investigate the performance of the macro-element HDG method for the analysis of compressible flow problems at moderate Reynolds numbers. To efficiently handle the corresponding large systems of equations, we explore several strategies at the solver level. On the one hand, we devise a second-layer static condensation approach that reduces the size of the local system matrix in each macro-element and hence the factorization time of the local solver. On the other hand, we employ a multi-level preconditioner based on the FGMRES solver for the global system that integrates well within a matrix-free implementation. In addition, we integrate a standard diagonally implicit Runge-Kutta scheme for time integration. We test the matrix-free macro-element HDG method for compressible flow benchmarks, including Couette flow, flow past a sphere, and the Taylor-Green vortex. Our results show that unlike standard HDG, the macro-element HDG method can operate efficiently for moderate polynomial degrees, as the local computational load can be flexibly increased via mesh refinement within a macro-element. Our results also show that due to the balance of local and global operations, the reduction in degrees of freedom, and the reduction of the global problem size and the number of iterations for its solution, the macro-element HDG method can be a competitive option for the analysis of compressible flow problems

Nonlinear dynamic analysis of shear- and torsion-free rods using isogeometric discretization, outlier removal and robust time integration

In this paper, we present a discrete formulation of nonlinear shear- and torsion-free rods based on \cite{gebhardt_2021_beam} that uses isogeometric discretization and robust time integration. Omitting the director as an independent variable field, we reduce the number of degrees of freedom and obtain discrete solutions in multiple copies of the Euclidean space $\left(\mathbb{R}^3\right)$, which is larger than the corresponding multiple copies of the manifold \left(\mathbb{R}^3 \cross S^2\right) obtained with standard Hermite finite elements. For implicit time integration, we choose a hybrid form of the mid-point rule and the trapezoidal rule that preserves the linear angular momentum exactly and approximates the energy accurately. In addition, we apply a recently introduced approach for outlier removal \cite{hiemstra_outlier_2021} that reduces high-frequency content in the response without affecting the accuracy, ensuring robustness of our nonlinear discrete formulation. We illustrate the efficiency of our nonlinear discrete formulation for static and transient rods under different loading conditions, demonstrating good accuracy in space, time and the frequency domain. Our numerical example coincides with a relevant application case, the simulation of mooring lines

Validation of Self-Reported Health Literacy Questions Among Diverse English and Spanish-Speaking Populations

BackgroundLimited health literacy (HL) contributes to poor health outcomes and disparities, and direct measurement is often time-intensive. Self-reported HL questions have not been validated among Spanish-speaking and diverse English-speaking populations.ObjectiveTo evaluate three self-reported questions: 1 "How confident are you filling out medical forms?"; 2 "How often do you have problems learning about your medical condition because of difficulty understanding written information?"; and 3 "How often do you have someone help you read hospital materials?" Answers were based on a 5-point Likert scale.DesignThis was a validation study nested within a trial of diabetes self-management support in the San Francisco Department of Public Health.ParticipantsEnglish and Spanish-speaking adults with type 2 diabetes receiving primary care.MethodsUsing the Test of Functional Health Literacy in Adults (s-TOFHLA) in English and Spanish as the reference, we classified HL as inadequate, marginal, or adequate. We calculated the C-index and test characteristics of the three questions and summative scale compared to the s-TOFHLA and assessed variations in performance by language, race/ethnicity, age, and education.Key resultsOf 296 participants, 48% were Spanish-speaking; 9% were White, non-Hispanic; 47% had inadequate HL and 12% had marginal HL. Overall, 57% reported being confident with forms "somewhat" or less. The "confident with forms" question performed best for detecting inadequate (C-index = 0.82, (0.77-0.87)) and inadequate plus marginal HL (C index = 0.81, (0.76-0.86); p<0.01 for differences from other questions), and performed comparably to the summative scale. The "confident with forms" question and scale also performed best across language, race/ethnicity, educational attainment, and age.ConclusionsA single self-reported HL question about confidence with forms and a summative scale of three questions discriminated between Spanish and English speakers with adequate HL and those with inadequate and/or inadequate plus marginal HL. The "confident with forms" question or the summative scale may be useful for estimating HL in clinical research involving Spanish-speaking and English-speaking, chronically-ill, diverse populations