Temperature-based estimation of time of death (ToD) can be performed either with the help of simple phenomenological models of corpse cooling or with detailed mechanistic (thermodynamic) heat transfer models. The latter are much more complex, but allow a higher accuracy of ToD estimation as in principle all relevant cooling mechanisms can be taken into account. The potentially higher accuracy depends on the accuracy of tissue and environmental parameters as well as on the geometric resolution. We investigate the impact of parameter variations and geometry representation on the estimated ToD. For this, numerical simulation of analytic heat transport models is performed on a highly detailed 3D corpse model, that has been segmented and geometrically reconstructed from a computed tomography (CT) data set, differentiating various organs and tissue types. From that and prior information available on thermal parameters and their variability, we identify the most crucial parameters to measure or estimate, and obtain an a priori uncertainty quantification for the ToD.

Estimation of time of death based on a single measurement of body core temperature is a standard procedure in forensic medicine. Mechanistic models using simulation of heat transport promise higher accuracy than established phenomenological models in particular in nonstandard situations, but involve many not exactly known physical parameters. Identifying both time of death and physical parameters from multiple temperature measurements is one possibility to reduce the uncertainty significantly. In this paper, we consider the inverse problem in a Bayesian setting and perform both local and sampling-based uncertainty quantification, where proper orthogonal decomposition is used as model reduction for fast solution of the forward model. Based on the local uncertainty quantification, optimal design of experiments is performed in order to minimize the uncertainty in the time of death estimate for a given number of measurements. For reasons of practicability, temperature acquisition points are selected from a set of candidates in different spatial and temporal locations. Applied to a real corpse model, a significant accuracy improvement is obtained already with a small number of measurements.

Temperature-based death time estimation is based either on simple phenomenological models of corpse cooling or on detailed physical heat transfer models. The latter are much more complex but allow a higher accuracy of death time estimation, as in principle, all relevant cooling mechanisms can be taken into account.Here, a complete workflow for finite element-based cooling simulation is presented. The following steps are demonstrated on a CT phantom:Computer tomography (CT) scanSegmentation of the CT images for thermodynamically relevant features of individual geometries and compilation in a geometric computer-aided design (CAD) modelConversion of the segmentation result into a finite element (FE) simulation modelComputation of the model cooling curve (MOD)Calculation of the cooling time (CTE)For the first time in FE-based cooling time estimation, the steps from the CT image over segmentation to FE model generation are performed semi-automatically. The cooling time calculation results are compared to cooling measurements performed on the phantoms under controlled conditions. In this context, the method is validated using a CT phantom. Some of the phantoms' thermodynamic material parameters had to be determined via independent experiments.Moreover, the impact of geometry and material parameter uncertainties on the estimated cooling time is investigated by a sensitivity analysis.

Pulse thermography of concrete structures is used in civil engineering for detecting voids, honeycombing and delamination. Quantitatively realistic numerical 3D simulation is difficult due to the arising boundary layer at the heated surface and unreliable information about material parameters and environmental conditions. We address both issues by a semi-analytic reformulation of the heat transport problem and by parameter identification. Numerical results are compared with measurements of a test specimen.

Reasons for the failure of adaptive methods to deliver improved efficiency when integrating monodomain models for myocardiac excitation are discussed. Two closely related techniques for reducing the computational complexity of linearly implicit integrators, deliberate sparsing and splitting, are investigated with respect to their impact on computing time and accuracy.

The paper communicates simulation results (computations and visualizations) for the dynamics of ventricular fibrillation caused by irregular excitation in the frame of the monodomain model with an action potential model due to Aliev–Panfilov for a human 3D geometry. The numerical solution of this challenging multiscale reaction–diffusion problem is attacked by algorithms which are fully adaptive in both space and time (code library KARDOS). The obtained results clearly demonstrate an accurate resolution of the cardiac potential during the excitation and the plateau phases (in the regular cycle) as well as after a reentrant excitation (in the irregular cycle).

Computer Tomographic (CT) image data have become a standard basis for structural analyses of bony organs. In this context, regression functions between stiffness components and Hounsfields units (HU) from CT, related to X-ray attenuation coefficients, are widely used for the definition of the (actually inhomogeneous and anisotropic) material behavior inside the organ. Herein, we suggest to derive the functional dependence of the fully orthotropic stiffness tensors on the Hounsfield units from the physical information contained in the X-ray attenuation coefficients: (i) Based on voxel average rules for the X-ray attenuation coefficients, we assign to each voxel the volume fraction occupied by water (marrow) and that occupied by solid bone matrix. (ii) By means of a continuum micromechanics representation for bone, which is based on voxel-invariant (species and whole bone-specific) stiffness properties of solid bone matrix and of water, we convert the aforementioned volume fractions into voxel-specific orthotropic stiffness tensor components. The micromechanics model, in combination with the average rule for X-ray attenuation coefficients, predicts a quasi-linear relationship between axial Young's modulus and HU, and highly nonlinear relationships for both circumferential and radial Young's moduli as well as for the shear moduli in all principal material directions. Corresponding whole-organ Finite Element (FE) analyses of a partially edentulous human mandible characterized by atrophy of the alveolar ridge show that volumetric strain concentrations/peaks within the organ are decreased when considering material anisotropy, and increased when considering material inhomogeneity.

2D and 3D dynamic thermal simulations of building components in combination with transient climate boundary conditions can approximate the real behaviour of a building component The usual tools for multidimensional building component simulation are limited in the component geometry and can not be extended for multiphysics problems (e. g. hygrothermal analysis). For this reason, a toolbox for thermal component simulation, based on the FEM-tool KARDOS, was developed. This toolbox comprises a pre-processor which is able to define and to discretise 2D and 3D complex component models. Starting from these models, the input files of KARDOS are generated automatically. Some applications shall illustrate the operating principle of the toolbox.

Within the biomechanics of bony organs, individual tissue anisotropy and inhomogeneity are intensively discussed subjects. This paper is dedicated to the impact of a fully anisotropic and inhomogoneous material description on the structural behaviour of an elderly partially edentulous human mandible. Radial, axial, and circumferential trajectories of orthotropic elasticity were reconstructed from kind of inner skeleton derived from the organ's geometry and from coherent structures recognisable from the spatial distribution of the grey values coming from computer tomography (CT). Based on recent micromechanical research driven forward by the second author, CT numbers were transferred into inhomogeneous stiffness tensor components reflecting individual tissue properties. These coefficients were considered as local orthotropic elastic coefficients in reference to coordinate systems formed by the anisotropic trajectories of elasticity. For the sake of a complete anisotropic material description over the whole organ, the tensor components were transformed into a global base frame which allows assembling an overall patient‐specific stiffness matrix. Various sensitivity analysis revealed that the more the anisotropy is considered the more the mandible is spared from loading which indicates kind of mechanical optimality of the mandible with respect to tissue anisotropy. In the opposite, the consideration of individual inhomogeneous tissue properties resulted in intensification of load concentrations due to pathological alterations of the organ which gives rise to the suggestion of self‐energising processes of bone resorption. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The dynamics of ventricular fibrillation caused by irregular excitation is simulated in the frame of the monodomain model with an action potential model due to Aliev-Panfilov for a human 3D geometry. The numerical solution of this multiscale reaction-diffusion problem is attacked by algorithms which are fully adaptive in both space and time (code library KARDOS). The obtained results clearly demonstrate an accurate resolution of the cardiac potential during the excitation and the plateau phases (in the regular cycle) as well as after a reentrant excitation (in the irregular cycle).

This article is focused on the role of anisotropic elasticity in the simulation of the load distribution in a human mandible, due to a lateral bite on the leftmost premolar. Based on experimental evidence, orthotropy of the elastic properties of the bone tissue has been adopted. The trajectories of anisotropic elasticity are reconstructed from (i) the organ's geometry and (ii) from coherent structures which can be recognized from the spatial distribution of the grey values coming from computer tomography (CT). A sensitivity analysis comprising various three-dimensional (3D) finite element (FE) simulations reveals the relevance of elastic anisotropy for the load carrying behavior of a human mandible: comparison of the load distributions in isotropic and anisotropic simulations indicates that anisotropy seems to "spare" the mandible from loading. Moreover, a maximum degree of anisotropy leads to kind of load minimization of the mandible, expressed by a minimum of different norms of local volumetric strain, evaluated throughout the organ. The observed optimization with respect to volumetric rather than shear strain seems to confirm the frequently emphazised role of volumetric-strain-induced fluid flow for the stimulation of cellular activity.

The paper introduces and studies numerical methods that are fully adaptive in both three-dimensional (3D) space and time to challenging multiscale cardiac reaction-diffusion models. In these methods, temporal adaptivity comes via stepsize control in function space oriented linearly implicit time integration, while spatial adaptivity is realized within multilevel finite element methods controlled by a posteriori local error estimators. In contrast to other recent adaptivity approaches to cardiac modeling that discretize first in space and then in time (so-called method of lines), our method discretizes first in time and then in space (so-called Rothe method)---an approach that has already proven to be highly efficient in a number of challenging multiscale problems in science and technology (KARDOS code library). With this method, the evolution of a complete heartbeat, from the excitation to the recovery phase, is simulated both in the frame of the anisotropic monodomain models and in the more realistic anisotropic bidomain models, coupled with either a variant of the simple FitzHugh--Nagumo model or the more complex phase-I Luo--Rudy ionic model. The numerical results exhibit a rather satisfactory performance of our adaptive method for complex cardiac reaction-diffusion models on 3D domains up to moderate sizes. In particular, the method accurately resolves the evolution of the intra- and extracellular potentials, gating variables, and ion concentrations during the excitation, plateau, and recovery phases.

The aim of this study is to relieve scientists from the complex and time-consuming task of model generation by providing a model of a canine tooth and its periradicular tissues for Finite Element Method (FEM) simulations.This was achieved with diverse commercial software, based on a micro-computed tomography of the specimen.The Finite Element (FE) Model consists of enamel, dentin, nerve (innervation), periodontal ligament (PDL), and the surrounding cortical bone with trabecular structure. The area and volume meshes are of a very high quality in order to represent the model in a detailed form. Material properties are to be set individually by every user.The tooth model is provided for Abaqus®, Ansys®, HyperMesh®, Nastran® and as STL files, in an ASCII format for free download.This can help reduce the cost and effort of generating a tooth model for some research institutions, and may encourage other research groups to provide their high quality models for other researchers. By providing FE models, research results, especially FEM simulations, could be easily verified by others.

The paper extends affine conjugate Newton methods from convex to nonconvex minimization, with particular emphasis on PDE problems originating from compressible hyperelasticity. On the basis of well-known schemes from finite dimensional nonlinear optimization, three different algorithmic variants are worked out in a function space setting, which permits an adaptive multilevel finite element implementation. These algorithms are tested on two well-known 3D test problems and a real-life example from surgical operation planning.

Am Beispiel eines 18 jährigen Patienten mit ausgeprägter Mittelgesichtshypoplasie wird die 3D Planung einer Knochen verlagernden Korrekturoperation unter Berücksichtigung der funktioneilen und ästhetischen Rehabilitation demonstriert. Unterschiedliche Varianten einer Le Fort-I Ostéotomie zur Oberkiefermobilisierung wurden am 3D Modell geplant und die Verlagerung hinsichtlich der dentalen Okklusion und der resultierenden Gesichtsform bewertet. Zur räumlichen Weichgewebeprädiktion wird sowohl ein homogenens als auch ein inhomogenenes, volumetrisches Gewebemodell betrachtet und die jeweilige Simulationsgüte anhand postoperativer CT-Daten quantitativ überprüft.