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Understanding the elastic material behavior of myocardium during the diastolic phase is critical for evaluating cardiac function and improving treatments for diastolic abnormalities. This study introduces a novel multi-objective optimization framework that incorporates both strain and volume measurements to enhance the accuracy of myocardial property assessments in Rheumatic Heart Disease (RHD) patients and healthy controls. By employing global volume and strain measurements instead of segmented strains from the sixteen AHA regions, we achieve a robust alignment with the Klotz curve across all groups, indicating an accurate simulation of end-diastolic pressure–volume relationships (EDPVRs). Our approach uniquely integrates combinations of longitudinal, circumferential, and radial strains, resulting in an unprecedented reduction in errors between clinical and simulated strain values, with less than one percent difference for targeted parameters. The results demonstrate that the alignment between computational predictions and clinical measurements depends significantly on the choice of optimization target. The study reveals significant differences in tissue mechanics between RHD patients and healthy controls, with notable variations in ventricular stiffness and fiber orientations across optimization targets, confirmed through rigorous statistical analyses. The observed variations in fiber angles, particularly the smaller angles for longitudinal strains and steeper angles for circumferential strains, underscore the intricate relationship between myocardial fiber architecture and cardiac deformation, offering deeper insights into ventricular biomechanics. By presenting qualitative and quantitative differences in stress and strain distributions, this research advances the understanding of myocardial mechanics, highlighting the clinical relevance of fiber orientation and material properties in modeling cardiac mechanics and distinguishing diseased from healthy myocardial behavior. [ABSTRACT FROM AUTHOR]

As part of the 2019 Southern oCean seAsonal Experiment (SCALE) Winter Cruise of the South African icebreaker SA Agulhas II, first-year ice was sampled at the advancing outer edge of the Antarctic marginal ice zone along a 150 km Good Hope Line transect. Ice cores were extracted from four solitary pancake ice floes of 1.83–2.95 m diameter and 0.37–0.45 m thickness as well as a 12×4 m pancake ice floe of 0.31–0.76 m thickness that was part of a larger consolidated pack ice domain. The ice cores were subsequently analysed for temperature, salinity, texture, anisotropic elastic properties and compressive strength. All ice cores from both solitary pancake ice floes and consolidated pack ice exhibited predominantly granular textures. The vertical distributions of salinity, brine volume and mechanical properties were significantly different for the two ice types. High salinity values of 12.6±4.9 PSU were found at the topmost layer of the solitary pancake ice floes but not for the consolidated pack ice. The uniaxial compressive strengths for pancake ice and consolidated pack ice were determined as 2.3±0.5 and 4.1±0.9 MPa, respectively. Young's and shear moduli in the longitudinal core direction of solitary pancake ice were obtained as 3.7±2.0 and 1.3±0.7 GPa, respectively, and of consolidated pack ice as 6.4±1.6 and 2.3±0.6 GPa, respectively. Comparing Young's and shear moduli measured in longitudinal and transverse core directions, a clear directional dependency was found, in particular for the consolidated pack ice. [ABSTRACT FROM AUTHOR]

The aim of this work is to significantly accelerate the process of parameter optimization of cardiac mechanics problems. This is achieved by coupling a reduced-order method, called the proper orthogonal decomposition with interpolation (PODI), with the frequently used Levenberg-Marquardt method (LVM). The PODI method involves a database to generate solution fields of the problem at hand. This database consists of precomputed solution fields such as displacement, strain, and stress fields that are associated with a parametric domain. When coupling PODI with LVM, the parametric domain of the database coincides with the parametric bounds of LVM. For each optimization step, the solutions corresponding to the updated set of parameters and their perturbations can then be obtained by using these data sets for the purpose of interpolation in the low-dimensional space. Two cardiac problems are investigated to compare the PODI-LVM method with a conventional approach where LVM makes use of full-scale simulations to compute the update of the parameters. Here, this is the element-free Galerkin method. In the first example, the diastolic filling of a left-ventricle heart model is considered and in the second one, a biventricle model is studied. In both cases, optimized values of the parameters of the cardiac constitutive equation are found that match the given diastolic pressure-volume curve. The PODI-LVM optimization procedure results in a computation speed-up factor of 900 on a standard desktop computer at high levels of accuracy. [ABSTRACT FROM AUTHOR]

A reduced order method (ROM) called the Proper Orthogonal Decomposition with Interpolation (PODI) is used to solve cardiac mechanics problems in an efficient manner such that the computation time and resources needed are drastically reduced. Here, PODI makes use of a precomputed set of simulations stored in a database which allows for the interpolation of the solution of the problem at hand in a low-dimensional space. For the case of a database being built from patient-specific heart models, the corresponding datasets are not compatible with each other and the Proper Orthogonal Modes extracted from selected ensemble of datasets are inadequate. To solve this problem, it is proposed to standardise the datasets utilising a template grid. Two types of templates are investigated, namely, a cube and a heart-shape grid. For the latter, the accurate standardisation requires that the datasets linked to a patient-specific heart anatomies are registered on the heart template heart geometry using the Coherent Point Drift (CPD) method coupled with a moving least square-based interpolation scheme. This facilitates the transfer of the given solution fields to the template where the PODI computation can be adequately performed. The suitability of the approach is demonstrated for the diastolic filling phase of a bi-ventricular heart model. It is shown that fast computation speeds and accurate results can be achieved. [ABSTRACT FROM AUTHOR]

In this research, a reduced order method (ROM) called the Proper Orthogonal Decomposition with Interpolation (PODI) is used to drastically reduce computation time of highly complex and non-linear problems as encountered in simulating the heart. The idea behind this method is to first construct a database of pre-computed full-scale solutions using the Element Free Galerkin method (EFG) and then project a selected subset of these solutions to a low dimensional space. Using the Moving Least Square method an interpolation is carried out for the problem at hand, before the resulting coefficients are projected back to the original high dimensional solution space. Computations are carried out on a bi-ventricle model to investigate the performance and accuracy varying the material parameters and to determine the sensitivity with respect to the parametric values. The PODI calculations are completed within 1.25 s on a normal desktop machine with the relative ℓ 2 error norm not exceeding 2.5 × 10 − 3 . Hence, it is demonstrated that real-time modelling of the heart can be successfully carried out at acceptable error levels. [ABSTRACT FROM AUTHOR]

Abstract: The Cosserat continuum falls into the group of so-called generalized continua which have the capacity to consider internal lengths and so describe a certain type of size effects. The paper addresses some aspects of the non-linear formulation of the Cosserat continuum and its meshfree approximation. The use of moving least square approximations [P. Lancaster, K. Salkauskas, Mathematics of Computations 37(155) (1981) 141–158] in a non-linear Cosserat continuum-based formulation gives rise to certain implications which are related to the essential boundary condition enforcement as well as to the updating of the rotation field. Here, the enforcement of the displacement boundary conditions is accomplished by modifying the initial variational principle or weak form of equations such that the essential boundary conditions appear as Euler–Lagrange equations. The updating of the rotational degrees of freedom in the meshfree code adopts a multiplicative scheme which is based on the spinor theory and has been already successfully applied to finite elements by the first author. The suitability of the proposed methodology is exemplified in modelling size-scale effects in elasticity. The impact of the Cosserat continuum-based formulation on small-scale structures is demonstrated and the comparison with a classical Green strain tensor-based approach reveals significant differences. [Copyright &y& Elsevier]

• A novel framework for anisotropic, micromorphic materials is presented. • Special focus is paid to fibrous materials such as soft tissues. • The proposed model is able to account for fiber reorientation and dispersion. • Essential micro-boundary conditions are applied to couple macro- and micro deformations. • The micromorphic theory and numerical examples are discussed. Materials exhibiting a heterogeneous and non-uniform composition in terms of elastic and anisotropic properties such as biological tissues require special efforts to accurately describe their constitutive behavior. In contrast to classical models, micromorphic formulations can predict the macroscopically observable material response as originated from distinct scale-dependent micro-structural deformation mechanisms. This is facilitated by additional independent degrees of freedom and associated additional strain and stress quantities. Here, a generalized continuum is mathematically constructed from a macro-continuum and a micro-continuum which are both adequately coupled on kinematics and constitutive levels as well as by micro-boundary conditions. In view of biomechanical modeling, the potential of the formulation is studied for a number of academic examples characterized by an anisotropic material composition to elucidate the micromorphic material response as compared with the one obtained using a classical continuum mechanics approach. The results demonstrate the ability of the generalized continuum approach to address non-affine elastic reorientation of the preferred material direction in the macro-space and its dispersion in the micro-space as affecting deformation, strain and stress on the macroscopic level. In particular, if the anisotropy in the micromorphic formulation is solely linked to the extra degrees of freedom and associated strain and stress measures, the deformation for small and large strains is shown to be distinctly different to the classical response. Together with the ability to implicitly account for scale-dependent higher-order deformation effects in the constitutive law the proposed generalized micromorphic formulation provides an advanced description, especially for fibrous biological materials. [ABSTRACT FROM AUTHOR]

Introduction: Rheumatic heart disease (RHD), degenerative aortic stenosis (AS), and congenital valve diseases are prevalent in sub-Saharan Africa. Many knowledge gaps remain in understanding disease mechanisms, stratifying phenotypes, and prognostication. Therefore, we aimed to characterise patients through clinical profiling, imaging, histology, and molecular biomarkers to improve our understanding of the pathophysiology, diagnosis, and prognosis of RHD and AS. Methods: In this cross-sectional, case–controlled study, we plan to recruit RHD and AS patients and compare them to matched controls. Living participants will undergo clinical assessment, echocardiography, CMR and blood sampling for circulatory biomarker analyses. Tissue samples will be obtained from patients undergoing valve replacement, while healthy tissues will be obtained from cadavers. Immunohistology, proteomics, metabolomics, and transcriptome analyses will be used to analyse circulatory- and tissue-specific biomarkers. Univariate and multivariate statistical analyses will be used for hypothesis testing and identification of important biomarkers. In summary, this study aims to delineate the pathophysiology of RHD and degenerative AS using multiparametric CMR imaging. In addition to discover novel biomarkers and explore the pathomechanisms associated with RHD and AS through high-throughput profiling of the tissue and blood proteome and metabolome and provide a proof of concept of the suitability of using cadaveric tissues as controls for cardiovascular disease studies. [ABSTRACT FROM AUTHOR]

Computational sea ice models have been developed to simulate sea ice formation, melt and motion characteristics on a regional scale. However, the highly dynamic sea ice behaviour in the Antarctic marginal ice zone (MIZ), the area where sea ice and ocean waves interact, still eludes reliable prediction. This is due to the complex sea ice composition consisting of relatively small and mobile ice floes governed by collision and fracture mechanisms. To improve the accuracy of sea ice models, the realistic sea ice distribution needs to be accounted for at a high resolution so that key aspects defining the interplay of ice motion and wave propagation can be suitably distinguished. In this work a computational fluid dynamics model based on the small-scale continuum approach has been developed to simulate the dynamics of a heterogeneous sea ice cover. The model makes use of a realistic sea ice layout and studies the mechanical behaviour of sea ice as affected by wave forcing and the specific material properties of ice floes and grease ice. Taking advantage of the continuum approach paired with a heterogeneous sea ice cover, the floe-grease ice interaction is elucidated by discussing detailed temporal and spatial distributions of the mechanical response of sea ice. Results show that the interplay between waves and the ice floe collision behaviour is directly controlled by sea ice inertia, where the frequency and severity of ice floe collisions increase with the wave period. Furthermore, the interaction of grease ice with ice floes through form drag at the interface leads to high localised grease ice strain rate gradients and low viscosity values due its shear thinning characteristics. • Wave induced velocity of sea ice and water are characterised by a significant phase shift due to the effect of inertia. • Floe collision patterns become more chaotic and violent for larger wave periods due to increasing wave energy and inertia. • Floe-grease ice interaction induces high localised grease ice velocities and strain rates, due to form drag at the interface. [ABSTRACT FROM AUTHOR]

Rheumatic heart disease (RHD) is the major cause of cardiovascular morbidity and mortality in children and young adults in low- and middle-income countries. Acute rheumatic fever (ARF) is characterised by multiorgan infl ammatory symptoms initiated through cross reaction of immune responses (IRs) to group A streptococcus (GAS) proteins to host proteins. Recurrence of these IRs targeting the heart valves may lead to permanent damage, a sequela which is termed RHD. Preliminary studies suggested genetic associations in RF reactions, but that other host factors are also involved, leaving the determinants of RHD progression incompletely understood. Previous clinical and recent epidemiological studies support differential clinical phenotypes, with varying history from different settings. This review summarises the protein-centric biomolecular changes in RHD and highlights outstanding molecular gaps where urgent focus is required to improve our understanding RHD pathophysiology. Numerous studies have confi rmed alterations in the expression of structural and immune response proteins, but the modifi cations giving rise to neo-epitopes and their involvement in RHD have not been established. As RHD is associated with poor living conditions, identifi cation of other factors driving infl ammation to enhance RHD progression is necessary to advance our knowledge and improve patient management. Furthermore, biomarkers for early identifi cation, disease stratifi cation, and alternative therapeutic strategies are necessary to improve treatment and prevention strategies in order to reduce the burden of RHD. Relevance: Despite the explosion of scientifi c innovation over the last few decades, fundamental scientifi c studies to understand the pathophysiological mechanisms of RHD remain in their infancy and the determinants of RHD progression thus remain uncertain. Moreover, inconsistency in natural history and phenotypic presentations are seen between Africans and other cohorts in which preliminary studies were conducted, implying that differences in genetic complexity and environmental factors may be responsible for the differential disease progression rates. [ABSTRACT FROM AUTHOR]

Rheumatic heart disease (RHD) is prevalent in sub-Saharan Africa, where the capacity for diagnosis and evaluation of disease severity and complications is not always optimal. While the medical history and physical examination are important in the assessment of patients suspected to have RHD, cardiovascular imaging techniques are useful for confirmation of the diagnosis. Echocardiography is the workhorse modality for initial evaluation and diagnosis of RHD. Cardiovascular magnetic resonance is complementary and may provide additive information, including tissue characteristics, where echocardiography is inadequate or non-diagnostic. There is emerging evidence on the role of computed tomography, particularly following valve replacement surgery, in the monitoring and management of RHD. This article summarises the techniques used in imaging RHD patients, considers the evidence base for their utility, discusses their limitations and recognises the clinical contexts in which indications and imaging with various modalities are expanding. • Diagnosis of RHD is based on medical history and physical examination; echocardiography is the first-line imaging modality. • Cardiovascular imaging techniques aid with diagnosis and comprehensive evaluation of severity and complications in RHD. • CT and CMR provide additive information above echocardiography but are not always available in resource-poor settings. • Improved understanding of the role of imaging modalities and their complementary role enhances management of RHD patients. [ABSTRACT FROM AUTHOR]

Antarctic sea ice shows a large degree of regional variability, which is partly driven by severe weather events. Here we bring a new perspective on synoptic sea ice changes by presenting the first in situ observations of an explosive extratropical cyclone crossing the winter Antarctic marginal ice zone (MIZ) in the South Atlantic. This is complemented by the analysis of subsequent cyclones and highlights the rapid variations that ice‐landing cyclones cause on sea ice: Midlatitude warm oceanic air is advected onto the ice, and storm waves generated close to the ice edge contribute to the maintenance of an unconsolidated surface through which waves propagate far into the ice. MIZ features may thus extend further poleward in the Southern Ocean than currently estimated. A concentration‐based MIZ definition is inadequate, since it fails to describe a sea ice configuration which is deeply rearranged by synoptic weather. Plain Language Summary: The extent of Antarctic sea ice is characterized by large regional variations that are in stark contrast with the alarming decreasing trends found in the Arctic. This is partly due to the presence of severe weather events, like extratropical cyclones travelling through the Southern Ocean and reaching the marginal ice zone (MIZ). The MIZ is a region where the ocean, atmosphere, and sea ice processes are closely interlinked. We provide direct evidence of how winter polar cyclones rearrange the MIZ and how their effects extend into the ice‐covered region as far as the Antarctic continent. We present the first observations of large ice drift, ice concentration, and temperature changes as an explosively deepening cyclone crosses the MIZ. This case study is complemented by analysis of subsequent but more frequent storms that confirms how storminess in the Southern Ocean maintains a sea ice surface that is less compact, more mobile, and more extended than previously anticipated. Our results urge the scientific community to revise the current definition of the MIZ and improve its representation in models to better include the role of polar cyclones in detecting Antarctic sea ice trends. Key Points: We present the first in situ measurements of an explosive polarcyclone crossing the Antarctic marginal ice zoneWarm air advection and wave propagation contribute to the maintenance of an unconsolidated sea ice surface far away from the ice edgePolar cyclones reshape the ice‐covered ocean, thus extending the marginal ice zone beyond current definitions [ABSTRACT FROM AUTHOR]

In this paper, we present results of a four‐field finite element formulation in the context of the Theory of Porous Media for the modeling of freezing processes. The primary solution variables are ice displacements, fluid pressure, temperature, and volume fraction ice. In detail, we show results on ice formation (mass transfer from liquid to solid constitutents) and temperature distribution. Special attention is given to the modeling of the heat of solidification. A thermodynamically consistent approach is used for the energetic effects to characterize and control the phase transition, see [1]. Finally, a numerical example of a freezing process with an inhomogeneous material distribution is shown. [ABSTRACT FROM AUTHOR]