Refine
Year of publication
- 2022 (46) (remove)
Institute
- Fachbereich Medizintechnik und Technomathematik (46) (remove)
Has Fulltext
- no (46) (remove)
Document Type
- Article (30)
- Conference Proceeding (8)
- Book (4)
- Part of a Book (3)
- Other (1)
Keywords
- Biocomposites (2)
- Natural fibres (2)
- Polymer-matrix composites (2)
- Stress concentrations (2)
- damage (2)
- Alzheimer's disease (1)
- Biomechanical simulation (1)
- Bootstrapping (1)
- Boundary integral equations (1)
- Categorial variable (1)
- Cementoblast (1)
- Chance constrained programming (1)
- Clustering (1)
- Collective risk model (1)
- Compression (1)
- Concomitant (1)
- Conductive boundary condition (1)
- Deep Learning (1)
- ES-FEM (1)
- Elektroenzephalographie (1)
- Empirical process (1)
- Evolution of damage (1)
- Extension fracture (1)
- Extension strain criterion (1)
- FGF23 (1)
- FS-FEM (1)
- Finite element analysis (1)
- Finite element analysis (FEA) (1)
- Forces (1)
- Fracture configuration (1)
- Fracture simulation (1)
- Haemodialysis (1)
- Handbike (1)
- Heterostructure (1)
- Image Reconstruction (1)
- Independence test (1)
- Information Extraction (1)
- Inverse spectral problem (1)
- Klotho (1)
- Limit analysis (1)
- Machine learning (1)
- Mechanotransduction (1)
- Metascintillator (1)
- Microcirculation (1)
- Mild cognitive impairment (1)
- Mohr–Coulomb criterion (1)
- Multiple TOF kernels (1)
- Myocardial infarction and cardiac death (1)
- Natural Language Processing (1)
- Niacin (1)
- PTH (1)
- Paralympic sport (1)
- Phosphate (1)
- Profile Extraction (1)
- Proximal humerus fracture (1)
- Psychiatrische Biomarker (1)
- Pulsations (1)
- Reliability of structures (1)
- Retinal vessel analysis (1)
- Retinal vessels (1)
- Riboflavin (1)
- Rotator cuff (1)
- S-FEM (1)
- Schlafspindeldetektion (1)
- Shakedown analysis (1)
- Stochastic programming (1)
- TOF PET (1)
- Tension (1)
- Text Mining (1)
- Thiamine (1)
- Tobacco mosaic virus (1)
- Transmission eigenvalues (1)
- Vasomotions (1)
- Vitamin A (1)
- Vitamin B (1)
- Vitamin D (1)
- acetoin (1)
- adipose-derived stromal cells (ASCs) (1)
- anaesthetic complications (1)
- anisotropy (1)
- aortic perfusion (1)
- biaxial tensile experiment (1)
- biopotential electrodes (1)
- bootstrap (1)
- capacitive field-effect biosensor (1)
- cell aerosolization (1)
- cell atomization (1)
- cerebral small vessel disease (1)
- chance constrained programming (1)
- cognitive impairment (1)
- computational fluid dynamics analysis (1)
- constitutive modeling (1)
- correlation (1)
- dental trauma (1)
- dialysis (1)
- difficult airway (1)
- distorted element (1)
- double-lumen tube intubation (1)
- endoluminal (1)
- enzyme immobilization (1)
- extracorporeal membrane oxygenation (1)
- force generation (1)
- forehead EEG (1)
- high-intensity exercise (1)
- hyperelastic (1)
- impedance spectroscopy (1)
- in-ear EEG (1)
- limit analysis (1)
- muscle fascicle behavior (1)
- non-simplex S-FEM elements (1)
- performance testing (1)
- reliability of structures (1)
- retinal vessels (1)
- sEMG (1)
- shakedown analysis (1)
- simulation (1)
- smooth muscle contraction (1)
- stochastic programming (1)
- strain energy function (1)
- survival (1)
- tendon rupture (1)
- tri-lineage differentiation (1)
- twin-fluid atomizer (1)
- ultrasound imaging (1)
- videolaryngoscopy (1)
- virgin passive (1)
- viscoelasticity (1)
- walking gait (1)
- · Psychiatrische Erkrankungen/Diagnostik (1)
When confining pressure is low or absent, extensional fractures are typical, with fractures occurring on unloaded planes in rock. These “paradox” fractures can be explained by a phenomenological extension strain failure criterion. In the past, a simple empirical criterion for fracture initiation in brittle rock has been developed. But this criterion makes unrealistic strength predictions in biaxial compression and tension. A new extension strain criterion overcomes this limitation by adding a weighted principal shear component. The weight is chosen, such that the enriched extension strain criterion represents the same failure surface as the Mohr–Coulomb (MC) criterion. Thus, the MC criterion has been derived as an extension strain criterion predicting failure modes, which are unexpected in the understanding of the failure of cohesive-frictional materials. In progressive damage of rock, the most likely fracture direction is orthogonal to the maximum extension strain. The enriched extension strain criterion is proposed as a threshold surface for crack initiation CI and crack damage CD and as a failure surface at peak P. Examples show that the enriched extension strain criterion predicts much lower volumes of damaged rock mass compared to the simple extension strain criterion.
Teamsitzungen, Arbeitsgruppentreffen, Kickoffs und Meetings – sie alle werden mit dem Ziel durchgeführt, innerhalb einer vorgegebenen Zeitspanne ein gemeinsames Arbeitsziel zu erreichen. Damit die Zielerreichung auch bei komplexeren Arbeitsaufträgen nicht vom Zufall abhängt, empfiehlt es sich, die Leitung des Ablaufs einem Moderator zu übertragen.
In diesem Beitrag einer mehrteiligen Serie wird beschrieben, über welches Mindset der Moderator verfügen sollte, welche grundsätzlichen Methoden hilfreich sind und was bei der Onlinemoderation im Besonderen zu beachten ist.
On the basis of bivariate data, assumed to be observations of independent copies of a random vector (S,N), we consider testing the hypothesis that the distribution of (S,N) belongs to the parametric class of distributions that arise with the compound Poisson exponential model. Typically, this model is used in stochastic hydrology, with N as the number of raindays, and S as total rainfall amount during a certain time period, or in actuarial science, with N as the number of losses, and S as total loss expenditure during a certain time period. The compound Poisson exponential model is characterized in the way that a specific transform associated with the distribution of (S,N) satisfies a certain differential equation. Mimicking the function part of this equation by substituting the empirical counterparts of the transform we obtain an expression the weighted integral of the square of which is used as test statistic. We deal with two variants of the latter, one of which being invariant under scale transformations of the S-part by fixed positive constants. Critical values are obtained by using a parametric bootstrap procedure. The asymptotic behavior of the tests is discussed. A simulation study demonstrates the performance of the tests in the finite sample case. The procedure is applied to rainfall data and to an actuarial dataset. A multivariate extension is also discussed.
FEM shakedown analysis of structures under random strength with chance constrained programming
(2022)
Direct methods, comprising limit and shakedown analysis, are a branch of computational mechanics. They play a significant role in mechanical and civil engineering design. The concept of direct methods aims to determine the ultimate load carrying capacity of structures beyond the elastic range. In practical problems, the direct methods lead to nonlinear convex optimization problems with a large number of variables and constraints. If strength and loading are random quantities, the shakedown analysis can be formulated as stochastic programming problem. In this paper, a method called chance constrained programming is presented, which is an effective method of stochastic programming to solve shakedown analysis problems under random conditions of strength. In this study, the loading is deterministic, and the strength is a normally or lognormally distributed variable.
The European Union's aim to become climate neutral by 2050 necessitates ambitious efforts to reduce carbon emissions. Large reductions can be attained particularly in energy intensive sectors like iron and steel. In order to prevent the relocation of such industries outside the EU in the course of tightening environmental regulations, the establishment of a climate club jointly with other large emitters and alternatively the unilateral implementation of an international cross-border carbon tax mechanism are proposed. This article focuses on the latter option choosing the steel sector as an example. In particular, we investigate the financial conditions under which a European cross border mechanism is capable to protect hydrogen-based steel production routes employed in Europe against more polluting competition from abroad. By using a floor price model, we assess the competitiveness of different steel production routes in selected countries. We evaluate the climate friendliness of steel production on the basis of specific GHG emissions. In addition, we utilize an input-output price model. It enables us to assess impacts of rising cost of steel production on commodities using steel as intermediates. Our results raise concerns that a cross-border tax mechanism will not suffice to bring about competitiveness of hydrogen-based steel production in Europe because the cost tends to remain higher than the cost of steel production in e.g. China. Steel is a classic example for a good used mainly as intermediate for other products. Therefore, a cross-border tax mechanism for steel will increase the price of products produced in the EU that require steel as an input. This can in turn adversely affect competitiveness of these sectors. Hence, the effects of higher steel costs on European exports should be borne in mind and could require the cross-border adjustment mechanism to also subsidize exports.
Reliable methods for automatic readability assessment have the potential to impact a variety of fields, ranging from machine translation to self-informed learning. Recently, large language models for the German language (such as GBERT and GPT-2-Wechsel) have become available, allowing to develop Deep Learning based approaches that promise to further improve automatic readability assessment. In this contribution, we studied the ability of ensembles of fine-tuned GBERT and GPT-2-Wechsel models to reliably predict the readability of German sentences. We combined these models with linguistic features and investigated the dependence of prediction performance on ensemble size and composition. Mixed ensembles of GBERT and GPT-2-Wechsel performed better than ensembles of the same size consisting of only GBERT or GPT-2-Wechsel models. Our models were evaluated in the GermEval 2022 Shared Task on Text Complexity Assessment on data of German sentences. On out-of-sample data, our best ensemble achieved a root mean squared error of 0:435.
Retinal vessels are similar to cerebral vessels in their structure and function. Moderately low oscillation frequencies of around 0.1 Hz have been reported as the driving force for paravascular drainage in gray matter in mice and are known as the frequencies of lymphatic vessels in humans. We aimed to elucidate whether retinal vessel oscillations are altered in Alzheimer's disease (AD) at the stage of dementia or mild cognitive impairment (MCI). Seventeen patients with mild-to-moderate dementia due to AD (ADD); 23 patients with MCI due to AD, and 18 cognitively healthy controls (HC) were examined using Dynamic Retinal Vessel Analyzer. Oscillatory temporal changes of retinal vessel diameters were evaluated using mathematical signal analysis. Especially at moderately low frequencies around 0.1 Hz, arterial oscillations in ADD and MCI significantly prevailed over HC oscillations and correlated with disease severity. The pronounced retinal arterial vasomotion at moderately low frequencies in the ADD and MCI groups would be compatible with the view of a compensatory upregulation of paravascular drainage in AD and strengthen the amyloid clearance hypothesis.
Edge-based and face-based smoothed finite element methods (ES-FEM and FS-FEM, respectively) are modified versions of the finite element method allowing to achieve more accurate results and to reduce sensitivity to mesh distortion, at least for linear elements. These properties make the two methods very attractive. However, their implementation in a standard finite element code is nontrivial because it requires heavy and extensive modifications to the code architecture. In this article, we present an element-based formulation of ES-FEM and FS-FEM methods allowing to implement the two methods in a standard finite element code with no modifications to its architecture. Moreover, the element-based formulation permits to easily manage any type of element, especially in 3D models where, to the best of the authors' knowledge, only tetrahedral elements are used in FS-FEM applications found in the literature. Shape functions for non-simplex 3D elements are proposed in order to apply FS-FEM to any standard finite element.
The mechanical behavior of the large intestine beyond the ultimate stress has never been investigated. Stretching beyond the ultimate stress may drastically impair the tissue microstructure, which consequently weakens its healthy state functions of absorption, temporary storage, and transportation for defecation. Due to closely similar microstructure and function with humans, biaxial tensile experiments on the porcine large intestine have been performed in this study. In this paper, we report hyperelastic characterization of the large intestine based on experiments in 102 specimens. We also report the theoretical analysis of the experimental results, including an exponential damage evolution function. The fracture energies and the threshold stresses are set as damage material parameters for the longitudinal muscular, the circumferential muscular and the submucosal collagenous layers. A biaxial tensile simulation of a linear brick element has been performed to validate the applicability of the estimated material parameters. The model successfully simulates the biomechanical response of the large intestine under physiological and non-physiological loads.
Image reconstruction analysis for positron emission tomography with heterostructured scintillators
(2022)
The concept of structure engineering has been proposed for exploring the next generation of radiation detectors with improved performance. A TOF-PET geometry with heterostructured scintillators with a pixel size of 3.0×3.1×15 mm3 was simulated using Monte Carlo. The heterostructures consisted of alternating layers of BGO as a dense material with high stopping power and plastic (EJ232) as a fast light emitter. The detector time resolution was calculated as a function of the deposited and shared energy in both materials on an event-by-event basis. While sensitivity was reduced to 32% for 100 μm thick plastic layers and 52% for 50 μm, the CTR distribution improved to 204±49 ps and 220±41 ps respectively, compared to 276 ps that we considered for bulk BGO. The complex distribution of timing resolutions was accounted for in the reconstruction. We divided the events into three groups based on their CTR and modeled them with different Gaussian TOF kernels. On a NEMA IQ phantom, the heterostructures had better contrast recovery in early iterations. On the other hand, BGO achieved a better contrast to noise ratio (CNR) after the 15th iteration due to the higher sensitivity. The developed simulation and reconstruction methods constitute new tools for evaluating different detector designs with complex time responses.