Search results for "Modell"
showing 10 items of 2134 documents
Distribution of Heavy Metals in Marine Sediments of Palermo Gulf (Sicily, Italy)
2008
Concentrations of Cr, Cu, Hg, Pb and Zn have been measured, by atomic absorption spectrophotometry, in the fine fraction (<63 μm) of surface sediments collected in 30 sites in the Palermo Gulf (Sicily, Italy) in order to assess the levels and the spatial distribution of these elements. Enrichment factors calculated with respect to clean areas have been considered to discriminate between levels due to background or to pollution contributions. The sampling stations, which form a grid inside these areas, are characterized by geographic proximity and by the presence of pollution sources. Ratio matching technique along with hierarchical clustering, minimum spanning tree and principal component a…
The nucleosome-remodeling ATPase ISWI is regulated by poly-ADP-ribosylation.
2008
ATP-dependent nucleosome-remodeling enzymes and covalent modifiers of chromatin set the functional state of chromatin. However, how these enzymatic activities are coordinated in the nucleus is largely unknown. We found that the evolutionary conserved nucleosome-remodeling ATPase ISWI and the poly-ADP-ribose polymerase PARP genetically interact. We present evidence showing that ISWI is target of poly-ADP-ribosylation. Poly-ADP-ribosylation counteracts ISWI function in vitro and in vivo. Our work suggests that ISWI is a physiological target of PARP and that poly-ADP-ribosylation can be a new, important post-translational modification regulating the activity of ATP-dependent nucleosome remodel…
Brittle failure in polycrystalline RVEs by a grain-scale cohesive boundary element formulation
2013
Polycrystalline materials are commonly employed in engineering structures. For modern applica- tions a deep understanding of materials degradation is of crucial relevance. It is nowadays widely recognized that the macroscopic material properties depend on the microstructure. The polycrystalline microstructure is characterized by the features of the grains and by the phys- ical and chemical properties of the intergranular interfaces, that have a direct influence on the evolution of the microstructural damage. The experimental investigation of failure mechanisms in 3D polycrystals still remains a challenging task. A viable alternative, or complement, to the experiments is Computational Microm…
A multiscale approach to polycrystalline materials damage and failure
2015
A two-scale three-dimensional approach for degradation and failure in polycrystalline materials is presented. The method involves the component level and the grain scale. The damageinduced softening at the macroscale is modelled employing an initial stress boundary element approach. The microscopic degradation is explicitly modelled associating Representative Volume Elements (RVEs) to relevant points of the macro continuum and employing a cohesive-frictional 3D grain-boundary formulation to simulate intergranular degradation and failure in the Voronoi morphology. Macro-strains are downscaled as RVEs' periodic boundary conditions, while overall macro-stresses are obtained upscaling the micro…
A cohesive boundary element approach to material degradation in three-dimensional polycrystalline aggregates
2013
A new three-dimensional grain-level formulation for intergranular degradation and failure in polycrystalline materials is presented. The polycrystalline microstructure is represented as a Voronoi tessellation and the boundary element method is used to express the elastic problem for each crystal of the aggregate. The continuity of the aggregate is enforced through suitable conditions at the intergranular interfaces. The grain-boundary model takes into account the onset and evolution of damage by means of an irreversible linear cohesive law, able to address mixed-mode failure conditions. Upon interface failure, a non-linear frictional contact analysis is introduced for addressing the contact…
A three-dimensional boundary element model for the analysis of polycrystalline materials at the microscale
2012
A three-dimensional multi-domain anisotropic boundary element formulation is presented for the analysis of polycrystalline microstructures. The formulation is naturally expressed in terms of intergranular displacements and tractions that play an important role in polycrystalline micromechanics, micro-damage and micro-cracking. The artificial morphology is generated by Hardcore Voronoi tessellation, which embodies the main statistical features of polycrystalline microstructures. Each crystal is modeled as an anisotropic elastic region and the integrity of the aggregate is restored by enforcing interface continuity and equilibrium between contiguous grains. The developed technique has been ap…
Formulation and test of an ice aggregation scheme for two-moment bulk microphysics schemes
2013
A simple formulation of aggregation for 2-moment bulk microphysical models is de-rived. The solution involves the evaluation of a double integral of the collection kernelweighted with the crystal size (or mass) distribution. This quantity is to be inserted intothe differential equation for the crystal number concentration which has classical form. The double integrals are evaluated numerically for log-normal size distributions overa large range of geometric mean masses. A polynomial fit of the results is given thatyields good accuracy. Various tests of the new parameterization are described: aggre-gation as stand-alone process, in a box-model, and in 2-D simulations of a cirrostratuscloud. …
A new constructive method using the theory of invariants to obtain material behavior laws
2006
International audience; The aim of this paper is to present a constructive method to derive mechanical behavior laws using the Theory of Invariants and Continuum Thermodynamics. More precisely, we want to construct, in a general way, the state or dissipation potential in a polynomial form given a set of variables V and the material symmetry group S. For this purpose, we show how to obtain a set of generators for the S-invariant polynomials of V. Then, using the Grœbner basis concept, we write all the decompositions of a polynomial of a given degree.
Nonmonotonic Pattern Formation in Three Species Lotka-Volterra System with Colored Noise
2005
A coupled map lattice of generalized Lotka-Volterra equations in the presence of colored multiplicative noise is used to analyze the spatiotemporal evolution of three interacting species: one predator and two preys symmetrically competing each other. The correlation of the species concentration over the grid as a function of time and of the noise intensity is investigated. The presence of noise induces pattern formation, whose dimensions show a nonmonotonic behavior as a function of the noise intensity. The colored noise induces a greater dimension of the patterns with respect to the white noise case and a shift of the maximum of its area towards higher values of the noise intensity.
A Machine Learning Model to Predict Intravenous Immunoglobulin-Resistant Kawasaki Disease Patients: A Retrospective Study Based on the Chongqing Popu…
2021
Objective: We explored the risk factors for intravenous immunoglobulin (IVIG) resistance in children with Kawasaki disease (KD) and constructed a prediction model based on machine learning algorithms.Methods: A retrospective study including 1,398 KD patients hospitalized in 7 affiliated hospitals of Chongqing Medical University from January 2015 to August 2020 was conducted. All patients were divided into IVIG-responsive and IVIG-resistant groups, which were randomly divided into training and validation sets. The independent risk factors were determined using logistic regression analysis. Logistic regression nomograms, support vector machine (SVM), XGBoost and LightGBM prediction models wer…