41 research outputs found

    Homogenization of the vibro-acoustic transmission on periodically perforated elastic plates interacting with flow

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    We consider acoustic waves propagating in an inviscid fluid interacting with a rigid periodically perforated plate in the presence of permanent flows. The paper presents a model of an acoustic interface obtained by the asymptotic homogenization of a thin transmission layer in which the plate is embedded. To account for the flow, a decomposition of the fluid pressure and velocity in the steady and fluctuating parts is employed. This enables for a linearization and an efficient use of the homogenization method which leads to a model order reduction effect. The dependence of an extended Helmholtz equation on the permanent flow introduces a locally periodic velocity field in the perforated plate vicinity, so that the coefficients of the homogenized interface depend on the flow. The derived model extended by natural coupling conditions provides an implicit Dirichlet-to-Neumann operator. Numerical simulations of wave propagation in a waveguide illustrate the flow speed influence on the acoustic transmission. Also some geometrical aspects are explored

    Computational homogenization for two-scale modeling of perfused tissues

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    We developed a two-scale approach for modeling large-deforming perfused media with the 3-compartment microstructure. An incremental formulation based on the updated Lagrangian configuration and the Biot-type continuum model is introduced. Equations of the model express mechanical equilibrium and the volume fluid redistribution (the Darcy law), assuming both the fluid and solid phases are incompressible. This linearized system was treated by the homogenization method assuming locally periodic structures. The local reference cell involving geometrical representations of the blood vessels evolves in time due to large deformation. The homogenized model is implemented using a finite element code and a numerical example is presented

    Homogenization of the fluid-saturated piezoelectric porous metamaterials

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    The paper is devoted to the homogenization approach in modelling of peri- odic porous media constituted by piezoelectric porous skeleton with pores saturated by viscous fluid. The representative volume element contains the piezoelectric solid part (the matrix) and the fluid saturated pores (the channels). Both the matrix and the channels form connected subdomains. The mathematical model describing the material behaviour at the microscopic scale involves the quasi-static equilibrium equation governing the solid piezoelectric skeleton, the Stokes model of the viscous fluid flow in the channels and the coupling interface conditions on the transmission interface. The macroscopic model is derived using the unfolding method of homogenization. The effective material coefficients are computed using characteristic responses of the porous microstructure. The consti- tutive law for the upscaled piezo-poroelastic material involves a coefficient coupling the electric field and the pore pressure. A numerical example illustrates different responses of the porous medium subject to the drained and undrained loading

    Multiscale modelling of flow due to the peristaltic wave in deforming poro-piezoelectric medium

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    The paper reports on the homogenization based modelling of fluid saturated poroelastic materials containing locally controlable piezoelectric (PZ) actuators. This option provides metamaterial properties which enable to convert the electric power into the fluid transport due to the peristaltic deformation wave induced by the propagating voltage wave. A quasi-linear PZ-poroelastic material model is proposed to respect dependence of the effective medium parameters on the deformation at the microstructure (pore) level. Due to the sensitivity analysis of the homogenized coefficient, the two-scale modelling avoids any need to update the local microconfigurations. Numerical studies has been performed as the proof of the concept

    Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

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    Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

    The brain infarct core delineation using computed tomography angiography source images in acute stroke patients

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    Background and Purpose: Ischemic stroke is the 3rd most common cause of death and most common cause of permanent disability in developed countries. Rapid diagnostic work-up with reliable assessment of infarcted brain tissue and potentionally salvageable brain tissue is critical for acute stroke management. The first aim of this study is to asses delineation of infarct core in acute stroke patients using whole brain perfused blood volume (PBV) maps. These maps are calculated by automatic processing from computed tomography angiography source images (CTA-SI) and non-contrast computed tomography (NCCT) data. The second aim is to determine optimal quantitative threshold of PBV for infarct core identification in acute stroke setting. Material and methods: PBV maps were constructed using prototype software from NCCT and CTA-SI data in 37 acute ischemic stroke patients with angiographically proved recanalization after intravenous thrombolytic treatment. These PBV maps were automatically compared with final infarct extension on follow-up NCCT. The anatomic pixel-by-pixel correlation was assessed using Matthew's correlation coefficient (MCC) for infarct core delineation using different critical values of PBV. The optimal threshold with the best correlation was used for infarct volume computation. Minimal PBV..
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