An affine continuum mechanical model for cross-linked F-actin networks with compliant linker proteins

Cross-linked actin networks are important building blocks of the cytoskeleton. In order to gain deeper insight into the interpretation of experimental data on actin networks, adequate models are required. In this paper we introduce an affine constitutive network model for cross-linked F-actin networks based on nonlinear continuum mechanics, and specialize it in order to reproduce the experimental behavior of in vitro reconstituted model networks. The model is based on the elastic properties of single filaments embedded in an isotropic matrix such that the overall properties of the composite are described by a free-energy function. In particular, we are able to obtain the experimentally determined shear and normal stress responses of cross-linked actin networks typically observed in rheometer tests. In the present study an extensive analysis is performed by applying the proposed model network to a simple shear deformation. The single filament model is then extended by incorporating the compliance of cross-linker proteins and further extended by including viscoelasticity. All that is needed for the finite element implementation is the constitutive model for the filaments, the linkers and the matrix, and the associated elasticity tensor in either the Lagrangian or Eulerian formulation. The model facilitates parameter studies of experimental setups such as micropipette aspiration experiments and we present such studies to illustrate the efficacy of this modeling approach

Automatic transcription of Turkish makam music

In this paper we propose an automatic system for transcribing/nmakam music of Turkey. We document the specific/ntraits of this music that deviate from properties that/nwere targeted by transcription tools so far and we compile/na dataset of makam recordings along with aligned microtonal/nground-truth. An existing multi-pitch detection algorithm/nis adapted for transcribing music in 20 cent resolution,/nand the final transcription is centered around the/ntonic frequency of the recording. Evaluation metrics for/ntranscribing microtonal music are utilized and results show/nthat transcription of Turkish makam music in e.g. an interactive/ntranscription software is feasible using the current/nstate-of-the-art.This work is partly supported by the European/nResearch Council under the European Union’s Seventh/nFramework Program, as part of the CompMusic project/n(ERC grant agreement 267583)

Comparison of two model frameworks for fiber dispersion in the elasticity of soft biological tissues

This study compares two models that are used to describe the elastic properties of fiber-reinforced materials with dispersed fibers, in particular some soft biological tissues such as arterial walls and cartilages. The two model approaches involve different constitutive frameworks, one being based on a generalized structure tensor (GST) and the other on the method of angular integration (AI). By using two representative examples, with the same number of parameters for each model, it is shown that the predictions of the two models are virtually identical for a significant range of large deformations, which contradicts conclusions contained in several papers that are based on faulty analysis. Additionally, each of the models is fitted to sets of uniaxial data from the circumferential and axial directions of the adventitia of a human aorta, both models providing excellent agreement with the data. While the predictions of the two models are comparable and exclusion of compressed fibers can be accommodated by either model, it is well known that the AI model requires more computational time than the GST model when used within a finite element environment, in particular if compressed fibers are excluded

Crack phase-field modeling of anisotropic rupture in fibrous soft tissues

The estimation of rupture in fibrous soft tissues has emerged as a central task in medical monitoring and risk assessment of diseases such as aortic dissection and aneurysms. In an attempt to address the challenges we have established a computational framework within the context of crack phase-field modeling and proposed an energy-based anisotropic failure criterion based on the distinction of isotropic and anisotropic material responses. Numerically we compare that criterion with other anisotropic failure criteria, in particular we analyze their capability to describe an admissible failure surface and how a crack can be propagated. A canonical rate-dependent setting of the crack phase-field model is formulated and solved in a weak sense by a standard Galerkin procedure featuring a one-pass operator-splitting algorithm on the temporal side. The anisotropic failure criteria are tested according to their performance on reflecting an admissible initiation, and crack propagation with an emphasis placed upon the aortic dissection

Development of enterococci and production of tyramine during the manufacture and ripening of Cheddar cheese

peer-reviewedThe effect of six strains of enterococci (three strains of Enterococcus faecalis, and one strain each of Ec. faecium, Ec. durans and Ec. casseliflavus) on flavour development and tyramine production in Cheddar cheese during manufacture and ripening was studied in two trials. No strain produced gelatinase or haemolysin and all of them grew well during manufacture reaching 107 colony forming units (cfu)/g in 6 h, after which they remained more or less constant during at least 48 weeks of ripening. There was no relationship between tyramine production in a broth containing tyrosine and tyramine production in the cheese. All strains, except Ec. casseliflavus, produced tyramine in the cheese, with the greatest concentration (162 mg/kg) being produced by Ec. durans after 9 months ripening at 8 ºC. There was no statistically significant difference (P > 0.05) between the flavour of the control cheese and any cheese containing an enterococcus. Nevertheless, cheese made with Ec. faecium E-24 received the best score in each trial at both time points. No off-flavours were found. Regarding proteolysis, only Ec. faecalis E-140 showed significant (P < 0.05) increases in both phosphotungstic acid and pH 4.6 soluble N. It is concluded that enterococci have little effect on the flavour of Cheddar cheese.This project was partly financed under FAIR Contract CT97-3078 from the E

Modeling of fibrous biological tissues with a general invariant that excludes compressed fibers

Dispersed collagen fibers in fibrous soft biological tissues have a significant effect on the overall mechanical behavior of the tissues. Constitutive modeling of the detailed structure obtained by using advanced imaging modalities has been investigated extensively in the last decade. In particular, our group has previously proposed a fiber dispersion model based on a generalized structure tensor. However, the fiber tension–compression switch described in that study is unable to exclude compressed fibers within a dispersion and the model requires modification so as to avoid some unphysical effects. In a recent paper we have proposed a method which avoids such problems, but in this present study we introduce an alternative approach by using a new general invariant that only depends on the fibers under tension so that compressed fibers within a dispersion do not contribute to the strain-energy function. We then provide expressions for the associated Cauchy stress and elasticity tensors in a decoupled form. We have also implemented the proposed model in a finite element analysis program and illustrated the implementation with three representative examples: simple tension and compression, simple shear, and unconfined compression on articular cartilage. We have obtained very good agreement with the analytical solutions that are available for the first two examples. The third example shows the efficacy of the fibrous tissue model in a larger scale simulation. For comparison we also provide results for the three examples with the compressed fibers included, and the results are completely different. If the distribution of collagen fibers is such that it is appropriate to exclude compressed fibers then such a model should be adopted

Classical and all-floating FETI methods for the simulation of arterial tissues

High-resolution and anatomically realistic computer models of biological soft tissues play a significant role in the understanding of the function of cardiovascular components in health and disease. However, the computational effort to handle fine grids to resolve the geometries as well as sophisticated tissue models is very challenging. One possibility to derive a strongly scalable parallel solution algorithm is to consider finite element tearing and interconnecting (FETI) methods. In this study we propose and investigate the application of FETI methods to simulate the elastic behavior of biological soft tissues. As one particular example we choose the artery which is - as most other biological tissues - characterized by anisotropic and nonlinear material properties. We compare two specific approaches of FETI methods, classical and all-floating, and investigate the numerical behavior of different preconditioning techniques. In comparison to classical FETI, the all-floating approach has not only advantages concerning the implementation but in many cases also concerning the convergence of the global iterative solution method. This behavior is illustrated with numerical examples. We present results of linear elastic simulations to show convergence rates, as expected from the theory, and results from the more sophisticated nonlinear case where we apply a well-known anisotropic model to the realistic geometry of an artery. Although the FETI methods have a great applicability on artery simulations we will also discuss some limitations concerning the dependence on material parameters.Comment: 29 page

Modeling and experimental investigations of the stress-softening behavior of soft collagenous tissues

This paper deals with the formulation of a micro-mechanically based dam-age model for soft collagenous tissues. The model is motivated by (i) a sliding filament model proposed in the literature [1] and (ii) by experimental observations from electron microscopy (EM) images of human abdominal aorta specimens, see [2]. Specifically, we derive a continuum damage model that takes into account statistically distributed pro- teoglycan (PG) bridges. The damage model is embedded into the constitutive framework proposed by Balzani et al. [3] and adjusted to cyclic uniaxial tension tests of a hu- man carotid artery. Furthermore, the resulting damage distribution of the model after a circumferential overstretch of a simplified arterial section is analyzed in a finite element calculation