Refine
Year of publication
Institute
- Fachbereich Medizintechnik und Technomathematik (1563) (remove)
Has Fulltext
- no (1563) (remove)
Language
- English (1563) (remove)
Document Type
- Article (1311)
- Conference Proceeding (133)
- Book (43)
- Part of a Book (43)
- Doctoral Thesis (18)
- Other (6)
- Patent (4)
- Preprint (3)
- Habilitation (1)
- Talk (1)
Keywords
- LAPS (4)
- Natural language processing (4)
- CellDrum (3)
- Field-effect sensor (3)
- Light-addressable potentiometric sensor (3)
- Paired sample (3)
- hydrogen peroxide (3)
- impedance spectroscopy (3)
- Bacillus atrophaeus (2)
- Biocomposites (2)
- Boundary integral equations (2)
- Clustering (2)
- Conductive boundary condition (2)
- Empirical process (2)
- Force (2)
- Goodness-of-fit test (2)
- Incomplete data (2)
- Independence test (2)
- Information extraction (2)
- Iterative learning control (2)
- Limit analysis (2)
- Machine learning (2)
- Natural fibres (2)
- Parametric bootstrap (2)
- Polymer-matrix composites (2)
- Raman spectroscopy (2)
- Shakedown analysis (2)
- Stiffness (2)
- Stress concentrations (2)
- Transmission eigenvalues (2)
- biopotential electrodes (2)
- constructive alignment (2)
- damage (2)
- examination (2)
- field-effect sensor (2)
- frequency mixing magnetic detection (2)
- likelihood ratio test (2)
- locomotion (2)
- long-term retention (2)
- multimodal (2)
- muscle fascicle behavior (2)
- not identically distributed (2)
- practical learning (2)
- tobacco mosaic virus (TMV) (2)
- ultrasound (2)
- ultrasound imaging (2)
- (Bio)degradation (1)
- Acceleration (1)
- Achilles tendon (1)
- Active learning (1)
- Adaptive control (1)
- Afterload (1)
- Ageing (1)
- Agent-based simulation (1)
- AlterG (1)
- Alzheimer's disease (1)
- Anastomotic leakage (1)
- Anatomy (1)
- Annulus Fibrosus (1)
- Architectural gear ratio (1)
- Assistive technology (1)
- Asymptotic efficiency (1)
- Asymptotic relative efficiency (1)
- Autolysis (1)
- Automatic control (1)
- Bacillus atrophaeus spores (1)
- Bacillus sp (1)
- Balance (1)
- Biomechanical simulation (1)
- Biomolecular logic gate (1)
- Biosolubilization (1)
- Bladder (1)
- Bone sawing (1)
- Booster Station (1)
- Bootstrap (1)
- Bootstrapping (1)
- Boundary integral equations, (1)
- Brownian Pillow (1)
- CNOT (1)
- Calorimetric gas sensor (1)
- Capacitive field-effect (1)
- Capacitive model (1)
- Cardiac myocytes (1)
- Cardiac tissue (1)
- Categorial variable (1)
- Cell permeability (1)
- Cellular force (1)
- Cementoblast (1)
- Censored data (1)
- Chance constrained programming (1)
- Chemical images (1)
- Chemical imaging (1)
- Chemical imaging sensor (1)
- Chemical sensor (1)
- Circular Dichroism (1)
- Cloud Computing (1)
- Cloud Service Broker (1)
- Co-managed care (1)
- Coat protein (1)
- Coefficient of ocular rigidity (1)
- Collective risk model (1)
- Competitiveness (1)
- Complex System (1)
- Complex-valued eigenvalues (1)
- Compliance (1)
- Compression (1)
- Computational biomechanics (1)
- Concomitant (1)
- Conductive Boundary Condition (1)
- Conservation laws (1)
- Constitutive model (1)
- Contractile tension (1)
- Contractility (1)
- Corneo-scleral shell (1)
- Coverage probability (1)
- Cramér-von-Mises statistic (1)
- Cramér-von-Mises test (1)
- Cross border adjustment mechanism (1)
- Crámer–von-Mises distance (1)
- C–V method (1)
- DNA (1)
- DNA biosensor (1)
- DNA hybridization (1)
- DPA (dipicolinic acid) (1)
- Damage mechanics theory (1)
- Decomposition (1)
- Deep learning (1)
- Dehydrogenase (1)
- Diaphorase (1)
- Differential tonometry (1)
- Dimensional splitting (1)
- Disc Degeneration (1)
- Discontinuous fractures (1)
- Discrete Optimization (1)
- Drug simulation (1)
- Dry surfaces (1)
- E-Mobility (1)
- EEG (1)
- EIS capacitive sensor (1)
- ES-FEM (1)
- Eigenvalue trajectories (1)
- Elderly (1)
- Electrolyte–insulator–semiconductor (1)
- Electromagnetism (1)
- Electromechanical modeling (1)
- Elemental (1)
- End-to-end colorectal anastomosis (1)
- Endothelial cells (1)
- Endothelial dysfunction (1)
- Energy market design (1)
- Energy-intensive industry (1)
- Entropy solution (1)
- Enzymatic biosensor (1)
- Enzyme biosensor (1)
- Enzyme coverage (1)
- Enzyme logic gate (1)
- Enzyme nanocarrier (1)
- Equivalence test (1)
- Esophageal Doppler monitor (1)
- Evolution of damage (1)
- Exponential Euler scheme, (1)
- Exponential time differencing (1)
- Extension fracture (1)
- Extension strain criterion (1)
- External knee adduction moments (1)
- Eyeball (1)
- FGF23 (1)
- FS-FEM (1)
- Fall prevention (1)
- Field effect (1)
- Field-effect biosensor (1)
- Field-effect device (1)
- Finite difference methods (1)
- Finite element analysis (1)
- Finite element analysis (FEA) (1)
- Finite element modelling (1)
- Floor prices (1)
- Forces (1)
- Fracture configuration (1)
- Fracture simulation (1)
- Freeze–thaw process (1)
- Frequency adaption (1)
- Frequency mixing magnetic detection (1)
- Functional Delta Method (1)
- Gamma distribution (1)
- Glaucoma (1)
- Glucose biosensor (1)
- Glucose oxidase (1)
- Gold nanoparticle (1)
- Goodness-of-fit tests for uniformity (1)
- Grid Computing (1)
- Ground-level falls (1)
- Growth modelling (1)
- Hadamard differentiability (1)
- Haemodialysis (1)
- Handbike (1)
- Heart tissue culture (1)
- Helmholtz equation (1)
- Heterostructure (1)
- Higher-order codes (1)
- Hodgkin–Huxley models (1)
- Hoeffding-Blum-Kiefer-Rosenblatt independence test (1)
- Homogenization (1)
- Hotelling’s T² test (1)
- Human-Computer interaction (1)
- Hydrogen peroxide (1)
- Image Reconstruction (1)
- Impedance Spectroscopy (1)
- Impedance spectroscopy (1)
- Implicit methods (1)
- Induced pluripotent stem cells (1)
- Information Extraction (1)
- Inotropic compounds (1)
- Integrated empirical distribution (survival) function (1)
- Interior Neumann eigenvalues (1)
- Interior transmission eigenvalues (1)
- Interior transmission problem (1)
- Intervertebral Disc (1)
- Intradiscal Pressure (1)
- Inverse Scattering (1)
- Inverse dynamic problem (1)
- Inverse kinematic problem (1)
- Inverse scattering (1)
- Inverse spectral problem (1)
- Ion channels (1)
- Kinetic energy (1)
- Klotho (1)
- Knee (1)
- LPS (1)
- Lab-on-Chip (1)
- Label-free detection (1)
- Langevin theory (1)
- Layer-by-layer adsorption (1)
- LbL films (1)
- Light-addressable Potentiometric Sensor (1)
- Lipopolysaccharide (1)
- Liver (1)
- Load modeling (1)
- Long COVID (1)
- MOS (1)
- Magnetic nanoparticles (1)
- Manipulated variables (1)
- Marginal homogeneity (1)
- Marginal homogeneity test (1)
- Market modeling (1)
- Matrix exponential (1)
- Mechanical simulation (1)
- Mechanotransduction (1)
- Metascintillator (1)
- Microbial adhesion (1)
- Microcirculation (1)
- Micromagnetic simulation (1)
- Mild cognitive impairment (1)
- Mobility (1)
- Mobility tests (1)
- Mobility transition (1)
- Mohr–Coulomb criterion (1)
- Monotone methods (1)
- Multi-criteria decision analysis (1)
- Multi-dimensional partial differential equations (1)
- Multi-sample problem (1)
- Multianalyte detection (1)
- Multimode failure (1)
- Multiple TOF kernels (1)
- Muscle (1)
- Muscle Fascicle (1)
- Muscle Force (1)
- Muscle fibers (1)
- Musculoskeletal model (1)
- Musculoskeletal system (1)
- Myocardial infarction and cardiac death (1)
- NONOate (1)
- Natural Language Processing (1)
- Natural language understanding (1)
- Negative impedance convertor (1)
- Neural Network (1)
- Niacin (1)
- Nitric Oxide (1)
- Nitric Oxide Donor (1)
- Non-linear optimization (1)
- Non-parallel fissures (1)
- Nonequilibrium dynamics (1)
- Nonlinear Dynamics (1)
- Nonlinear PDEs (1)
- Nonlinear eigenvalue problems (1)
- Nucleus Pulposus (1)
- Numerical inversion of Laplace transforms (1)
- Numerical linear algebra (1)
- Numerics (1)
- O2 plasma (1)
- Ocular blood flow (1)
- Organic light-emitting diode display (1)
- PTH (1)
- Parabolic SPDEs (1)
- Paralympic sport (1)
- Passive stretching (1)
- Pelvic floor dysfunction (1)
- Pelvic muscle (1)
- Penicillin (1)
- Pharmacology (1)
- Phosphate (1)
- Physiology (1)
- Poly(allylamine hydrochloride) (1)
- Poly(d,l-lacticacid) (1)
- Polyimide (1)
- Post-COVID-19 syndrome (1)
- Potential theory (1)
- Potentiometry (1)
- Preference assessment (1)
- Pressure-volume relationship (1)
- Process model (1)
- Product-integration (1)
- Profile Extraction (1)
- Profile extraction (1)
- Proximal humerus fracture (1)
- Pulsations (1)
- Pump System (1)
- Query learning (1)
- RVA (1)
- Reaction-diffusion systems (1)
- Real distinct pole (1)
- Real-time monitoring (1)
- Recombinant activated protein C (1)
- Reconstruction (1)
- Regionalization (1)
- Rehabilitation Technology and Prosthetics (1)
- Rehabilitation engineering (1)
- Relation classification (1)
- Reliability analysis (1)
- Reliability of structures (1)
- Reproducible research (1)
- Resampling test (1)
- Resolvent Operator (1)
- Resonance-mode measurement (1)
- Retinal vessel analysis (1)
- Retinal vessels (1)
- Riboflavin (1)
- Robotic rehabilitation (1)
- Rotator cuff (1)
- Running (1)
- S-FEM (1)
- Sampling methods (1)
- ScaLAPACK (1)
- Semi-parametric random censorship model (1)
- Septic cardiomyopathy (1)
- Simulation (1)
- Simultaneous determination (1)
- Sleep EEG (1)
- Sn₃O₄ (1)
- Source term (1)
- Spleen (1)
- Steel industry (1)
- Sterilisation process (1)
- Stochastic programming (1)
- Surface microorganisms (1)
- Surgical Navigation and Robotics (1)
- Surgical staplers (1)
- Survival analysis (1)
- Swabbing (1)
- TMV adsorption (1)
- TOF PET (1)
- Ta₂O₅ gate (1)
- Technical Operations Research (TOR) (1)
- Tendon Rupture (1)
- Tendon properties (1)
- Tension (1)
- Text Mining (1)
- Text mining (1)
- Thiamine (1)
- Tinetti test (1)
- Tobacco mosaic virus (1)
- Tobacco mosaic virus (TMV) (1)
- Training (1)
- Transmission Eigenvalues (1)
- Trustworthy artificial intelligence (1)
- Uniaxial compression test (1)
- Ureter (1)
- Vapnik–Čhervonenkis class (1)
- Variable height stapler design (1)
- Vascular response (1)
- Vasomotions (1)
- Velocity (1)
- Visual field asymmetry (1)
- Vitamin A (1)
- Vitamin B (1)
- Vitamin D (1)
- Volterra integral equation (1)
- Volume of confidence regions (1)
- Volume status (1)
- Volumes of confidence regions (1)
- Workflow (1)
- Workflow Orchestration (1)
- XOR (1)
- acetoin (1)
- achilles tendon (1)
- actin cytoskeleton (1)
- adipose-derived stromal cells (ASCs) (1)
- adsorption (1)
- agility (1)
- allocation (1)
- anaesthetic complications (1)
- anisotropy (1)
- annealing (1)
- aortic perfusion (1)
- aquaculture (1)
- artificial olfactory image (1)
- asymptotic relative efficiency (1)
- barium strontium titanate (1)
- biaxial tensile experiment (1)
- biomechanics (1)
- biosensor (1)
- biosensors (1)
- bootstrap (1)
- calorimetric gas sensor (1)
- calorimetric gas sensor;hydrogen peroxide;wireless sensor system (1)
- capacitive field-effect biosensor (1)
- capacitive field-effect sensor (1)
- carbonized rice husk (1)
- cardiomyocyte biomechanics (1)
- catalytic metal (1)
- cell aerosolization (1)
- cell atomization (1)
- central symmetry test (1)
- cerebral small vessel disease (1)
- chance constrained programming (1)
- chemical sensor (1)
- chip-based sensor setup (1)
- cognitive impairment (1)
- community dwelling (1)
- complete block symmetry (1)
- computational fluid dynamics analysis (1)
- conditional excess distribution (1)
- conditional expectation principle (1)
- confidence interval (1)
- connective tissue (1)
- constitutive modeling (1)
- contactless conductivity sensor (1)
- correlation (1)
- coupled Néel–Brownian relaxation dynamics (1)
- covariance principle (1)
- dental trauma (1)
- dialysis (1)
- difficult airway (1)
- distorted element (1)
- double-lumen tube intubation (1)
- drop jump (1)
- eigensolvers (1)
- elastic scattering (1)
- electrical conductivity of liquids (1)
- electrolyte-insulator semiconductor sensor (EIS) (1)
- electromyography (1)
- electronic nose (1)
- endoluminal (1)
- endospores (1)
- energy absorption (1)
- energy dissipation (1)
- enzymatic (bio)degradation (1)
- enzyme cascade (1)
- enzyme immobilization (1)
- exchangeability test (1)
- extracorporeal membrane oxygenation (1)
- field-effect structure (1)
- force generation (1)
- forecast (1)
- forehead EEG (1)
- frequency mixing (1)
- functional data (1)
- gait (1)
- gas sensor (1)
- glucose oxidase (GOx) (1)
- goodness-of-fit test (1)
- healthy aging (1)
- heavy metals (1)
- hiPS cardiomyocytes (1)
- high-intensity exercise (1)
- high-k material (1)
- horseradish peroxidase (HRP) (1)
- huge dimensional data (1)
- humic acid (1)
- hydroxylation (1)
- hyper-gravity (1)
- hyperelastic (1)
- hypo-gravity (1)
- immobilization (1)
- in-ear EEG (1)
- in-situ monitoring (1)
- independence test (1)
- intraclass correlation coefficient (1)
- key performance indicators (1)
- lable-free detection (1)
- light-addressable potentiometric sensor (1)
- light-addressing technologies (1)
- lignite (1)
- limit analysis (1)
- lipopolysaccharide (1)
- magnetic actuation (1)
- magnetic beads (1)
- magnetic biosensing (1)
- magnetic nanoparticles (1)
- magnetic relaxation (1)
- magnetic sandwich immunoassay (1)
- magnetic sensing (1)
- magnetic separation (1)
- magnetic tweezers (1)
- magnetophoretic velocity (1)
- mechanical buffer (1)
- metal-oxide-semiconductor structure (1)
- method of fundamental solutions (1)
- microfluidics (1)
- micromagnetic simulation (1)
- multi-functional material (1)
- multinomial distribution (1)
- multiparametric immunoassays (1)
- multivariate normal distribution (1)
- muscle mechanics (1)
- nanobelts (1)
- non-simplex S-FEM elements (1)
- novel photoexcitation method (1)
- optical sensor setup (1)
- optical spore trapping (1)
- optical trapping (1)
- organosilanes (1)
- overload (1)
- parabolic flight (1)
- performance analysis (1)
- performance testing (1)
- physiology (1)
- plant virus detection (1)
- plug-based microfluidic device (1)
- poly(d, l-lactic acid) (1)
- portfolio risk (1)
- prevention (1)
- psychosocial (1)
- random effects (1)
- random effects meta-regression model (1)
- rehabilitation (1)
- reliability of structures (1)
- retinal microvasculature (1)
- retinal vessels (1)
- running (1)
- sEMG (1)
- sarcomere operating length (1)
- scanned light pulse technique (1)
- sensors (1)
- separable Hilbert space (1)
- series elastic element behavior (1)
- shakedown analysis (1)
- shoulder (1)
- silanization (1)
- simulation (1)
- smooth muscle contraction (1)
- spatial resolution (1)
- sprint start (1)
- standard error of measurement (1)
- sterilisation (1)
- sterilization (1)
- sterilization conditions (1)
- stiffness (1)
- stochastic programming (1)
- strain energy function (1)
- stretch reflex (1)
- stretch-shortening cycle (1)
- superparamagnetic bead (1)
- superparamagnetic nanoparticles (1)
- surface functionalization (1)
- surface modification (1)
- survival (1)
- temperature (1)
- tendon rupture (1)
- test-retest reliability (1)
- thermometry (1)
- tilted constant illumination (1)
- training simulator (1)
- tri-lineage differentiation (1)
- turnip vein clearing virus (TVCV) (1)
- twin-fluid atomizer (1)
- ultrasonography (1)
- uniformly most powerful invariant test (1)
- unloading (1)
- videolaryngoscopy (1)
- virgin passive (1)
- virtual reality (1)
- viscoelasticity (1)
- visualization (1)
- walking (1)
- walking gait (1)
Objective
Hemodialysis patients show an approximately threefold higher prevalence of cognitive impairment compared to the age-matched general population. Impaired microcirculatory function is one of the assumed causes. Dynamic retinal vessel analysis is a quantitative method for measuring neurovascular coupling and microvascular endothelial function. We hypothesize that cognitive impairment is associated with altered microcirculation of retinal vessels.
Methods
152 chronic hemodialysis patients underwent cognitive testing using the Montreal Cognitive Assessment. Retinal microcirculation was assessed by Dynamic Retinal Vessel Analysis, which carries out an examination recording retinal vessels' reaction to a flicker light stimulus under standardized conditions.
Results
In unadjusted as well as in adjusted linear regression analyses a significant association between the visuospatial executive function domain score of the Montreal Cognitive Assessment and the maximum arteriolar dilation as response of retinal arterioles to the flicker light stimulation was obtained.
Conclusion
This is the first study determining retinal microvascular function as surrogate for cerebral microvascular function and cognition in hemodialysis patients. The relationship between impairment in executive function and reduced arteriolar reaction to flicker light stimulation supports the involvement of cerebral small vessel disease as contributing factor for the development of cognitive impairment in this patient population and might be a target for noninvasive disease monitoring and therapeutic intervention.
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.
Dynamic retinal vessel analysis (DVA) provides a non-invasive way to assess microvascular function in patients and potentially to improve predictions of individual cardiovascular (CV) risk. The aim of our study was to use untargeted machine learning on DVA in order to improve CV mortality prediction and identify corresponding response alterations.
Biocompatibility, flexibility and durability make polydimethylsiloxane (PDMS) membranes top candidates in biomedical applications. CellDrum technology uses large area, <10 µm thin membranes as mechanical stress sensors of thin cell layers. For this to be successful, the properties (thickness, temperature, dust, wrinkles, etc.) must be precisely controlled. The following parameters of membrane fabrication by means of the Floating-on-Water (FoW) method were investigated: (1) PDMS volume, (2) ambient temperature, (3) membrane deflection and (4) membrane mechanical compliance. Significant differences were found between all PDMS volumes and thicknesses tested (p < 0.01). They also differed from the calculated values. At room temperatures between 22 and 26 °C, significant differences in average thickness values were found, as well as a continuous decrease in thicknesses within a 4 °C temperature elevation. No correlation was found between the membrane thickness groups (between 3–4 µm) in terms of deflection and compliance. We successfully present a fabrication method for thin bio-functionalized membranes in conjunction with a four-step quality management system. The results highlight the importance of tight regulation of production parameters through quality control. The use of membranes described here could also become the basis for material testing on thin, viscous layers such as polymers, dyes and adhesives, which goes far beyond biological applications.
Useful market simulations are key to the evaluation of diferent market designs existing of multiple market mechanisms or rules. Yet a simulation framework which has a comparison of diferent market mechanisms in mind was not found. The need to create an objective view on different sets of market rules while investigating meaningful agent strategies concludes that such a simulation framework is needed to advance the research on this subject. An overview of diferent existing market simulation models is given which also shows the research gap and the missing capabilities of those systems. Finally, a methodology is outlined how a novel market simulation which can answer the research questions can be developed.
The recent advances in microbiology have shed light on understanding the role of vitamins beyond the nutritional range. Vitamins are critical in contributing to healthy biodiversity and maintaining the proper function of gut microbiota. The sharing of vitamins among bacterial populations promotes stability in community composition and diversity; however, this balance becomes disturbed in various pathologies. Here, we overview and analyze the ability of different vitamins to selectively and specifically induce changes in the intestinal microbial community. Some schemes and regularities become visible, which may provide new insights and avenues for therapeutic management and functional optimization of the gut microbiota.
Vitamin D plays an essential role in calcium and inorganic phosphate (Pi) homeostasis, maintaining their optimal levels to assure adequate bone mineralization. Vitamin D, as calcitriol (1,25(OH)2D), not only increases intestinal calcium and phosphate absorption but also facilitates their renal reabsorption, leading to elevated serum calcium and phosphate levels. The interaction of 1,25(OH)2D with its receptor (VDR) increases the efficiency of intestinal absorption of calcium to 30–40% and phosphate to nearly 80%. Serum phosphate levels can also influence 1,25 (OH)2D and fibroblast growth factor 23 (FGF23) levels, i.e., higher phosphate concentrations suppress vitamin D activation and stimulate parathyroid hormone (PTH) release, while a high FGF23 serum level leads to reduced vitamin D synthesis. In the vitamin D-deficient state, the intestinal calcium absorption decreases and the secretion of PTH increases, which in turn causes the stimulation of 1,25(OH)2D production, resulting in excessive urinary phosphate loss. Maintenance of phosphate homeostasis is essential as hyperphosphatemia is a risk factor of cardiovascular calcification, chronic kidney diseases (CKD), and premature aging, while hypophosphatemia is usually associated with rickets and osteomalacia. This chapter elaborates on the possible interactions between vitamin D and phosphate in health and disease.
A generalized shear-lag theory for fibres with variable radius is developed to analyse elastic fibre/matrix stress transfer. The theory accounts for the reinforcement of biological composites, such as soft tissue and bone tissue, as well as for the reinforcement of technical composite materials, such as fibre-reinforced polymers (FRP). The original shear-lag theory proposed by Cox in 1952 is generalized for fibres with variable radius and with symmetric and asymmetric ends. Analytical solutions are derived for the distribution of axial and interfacial shear stress in cylindrical and elliptical fibres, as well as conical and paraboloidal fibres with asymmetric ends. Additionally, the distribution of axial and interfacial shear stress for conical and paraboloidal fibres with symmetric ends are numerically predicted. The results are compared with solutions from axisymmetric finite element models. A parameter study is performed, to investigate the suitability of alternative fibre geometries for use in FRP.
Virgin passive colon biomechanics and a literature review of active contraction constitutive models
(2022)
The objective of this paper is to present our findings on the biomechanical aspects of the virgin passive anisotropic hyperelasticity of the porcine colon based on equibiaxial tensile experiments. Firstly, the characterization of the intestine tissues is discussed for a nearly incompressible hyperelastic fiber-reinforced Holzapfel–Gasser–Ogden constitutive model in virgin passive loading conditions. The stability of the evaluated material parameters is checked for the polyconvexity of the adopted strain energy function using positive eigenvalue constraints of the Hessian matrix with MATLAB. The constitutive material description of the intestine with two collagen fibers in the submucosal and muscular layer each has been implemented in the FORTRAN platform of the commercial finite element software LS-DYNA, and two equibiaxial tensile simulations are presented to validate the results with the optical strain images obtained from the experiments. Furthermore, this paper also reviews the existing models of the active smooth muscle cells, but these models have not been computationally studied here. The review part shows that the constitutive models originally developed for the active contraction of skeletal muscle based on Hill’s three-element model, Murphy’s four-state cross-bridge chemical kinetic model and Huxley’s sliding-filament hypothesis, which are mainly used for arteries, are appropriate for numerical contraction numerical analysis of the large intestine.
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.