Three-dimensional fracture growth as a standard dissipative system: some general theorems and numerical simulations

Crack propagation in brittle materials has been studied by several authors exploiting its analogy with standard dissipative systems theory. In recent publications, minimum theorems were derived in terms of crack tip “quasi static velocity” for two-dimensional fracture mechanics. Following the cornerstone work of Rice on weight function theories, Leblond and coworkers proposed asymptotic expansions for stress intensity factors in three dimensions. In view of the expression of the expansions proposed by Leblond, however, symmetry of Ceradini’s theorem operators was not evident and the extension to 3D of outcomes proposed in 2D not straightforward. Following a different path of reasoning, minimum theorems have been finally derived. Moving from well-established theorems in plasticity, algorithms for crack advancing have been finally formulated. Their performance is here presented within a set of classical benchmarks

hypersingular formulation for boundary stress evaluation revisited part 1 smooth boundaries

This work focuses on the (HBIE) hypersingular boundary integral equation,also called traction equation, and on its use to evaluate the stress tensorin linear elasticity. When the field point is moved to the boundary, by meansof a limit process, free terms come into play. As a common belief, they aredue to the strongly singular kernel: indeed it is proved that the hypersingularkernel does not cause any free term when tractions are evaluated onsmooth boundaries with respect to the boundary surface normal (when theconcept of normal makes sense). The stress tensor along the boundary involvessurfaces with normal differing from the boundary normal, too. In thiscase, free terms are proved to be generated also by the hypersingular kernel,aside from the regularity of the boundary: their analysis is the main goal ofthe present work

hypersingular formulation for boundary stress evaluation revisited part 2 corners

This work focuses on the use of the hypersingular boundary integral equationto evaluate the linear elastic stress tensor on the boundary. A companionpaper [1] has been devoted to smooth boundaries: in the present work, thetraction equation is analyzed at a corner, in the presence of a Lipschitzboundary. Properties of the hypersingular and of the strongly singular operatorare discussed together with properties of the whole linear elastic integraloperator

A study on the VEGFR2-ligand multi-physics interactions in Angiogenesis.

Tumorgrowthissustainedbyangiogenesis,i.e. theformationofnewbloodvesselsfrompre-existing ones. Angiogenesis is modulated by the interaction between tyrosine kinase receptors (TKRs), expressed by endothelial cells (ECs), and extracellular ligands, produced by tumor cells. This interaction triggers the activation of intracellular signaling cascades and kinetic processes, including cell deformationandadhesion,whicheventuallycausecelldivisionandproliferation. VascularEndothelial Growth Factor Receptor-2 (VEGFR2) is a pro-angiogenic receptor expressed on ECs. Ligand stimulation induces the polarization of ECs and the relocation of VEGFR2 in cell protrusion or in the basal aspect in cells plated on ligand enriched extracellular matrix (ECM) [1]. EC response to angiogenic growth factors is regulated by distinct sets of inputs conveyed by TRKs and different co-receptors including integrins, membrane proteins that are responsible of stress fibers formation and cell contractility [2]. Although biochemical pathways following VEGFR2 activation are well established, knowledge about the receptor dynamics on the plasma membrane remains limited. A multi-physics model has been developed [3] to describe: i) the diffusion of VEGFR2 on the cellularmembrane;ii)thechemicalkineticsoftheligand-receptorbindingreaction;iii)themechanical adhesion and spreading of the cell onto a ligand-rich extracellular substrate, in finite strain. The identification of the multi-physics interactions that regulate receptor polarization could open new perspectives to develop innovative anti-angiogenic strategies through the modulation of EC activation

Nitrogen-Doped Zinc Oxide for Photo-Driven Molecular Hydrogen Production

Due to its thermal stability, conductivity, high exciton binding energy and high electron mobility, zinc oxide is one of the most studied semiconductors in the field of photocatalysis. However, the wide bandgap requires the use of UV photons to harness its potential. A convenient way to appease such a limitation is the doping of the lattice with foreign atoms which, in turn, introduce localized states (defects) within the bandgap. Such localized states make the material optically active in the visible range and reduce the energy required to initiate photo-driven charge separation events. In this work, we employed a green synthetic procedure to achieve a high level of doping and have demonstrated how the thermal treatment during synthesis is crucial to select specific the microscopic (molecular) nature of the defect and, ultimately, the type of chemistry (reduction versus oxidation) that the material is able to perform. We found that low-temperature treatments produce material with higher efficiency in the water photosplitting reaction. This constitutes a further step in the establishment of N-doped ZnO as a photocatalyst for artificial photosynthesis

Morphological alterations and gene and protein expression profiling of bladder tumor cells after treatment with gemcitabine.

Chemical agents used in cancer therapy are associated with cell cycle arrest, activation or deactivation of mechanisms\ud associated to DNA repair and apoptosis. However, due to the complexity of biological systems, the molecular\ud mechanisms responsible for these activities are not fully understood. Thus, studies about gene and protein expression\ud have shown promising results for understanding the mechanisms related to cellular responses and regression of cancer\ud after chemotherapy. This study aimed to evaluate the gene and protein expression profiling in bladder transitional cell\ud carcinoma (TCC) with different TP53 status after gemcitabine (1.56 μM) treatment. The RT4 (grade 1, TP53 wild\ud type), 5637 (grade 2, TP53 mutated) and T24 (grade 3, TP53 mutated) cell lines were used. PCR arrays and mass\ud spectrometry were used to analyze gene and protein expression, respectively. Morphological alterations were observed\ud using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results of PCR array\ud showed that gemcitabine activity was mainly related to CDKN1A, GADD45A and SERTDA1 overexpression, and BAX\ud overexpression only in the wild type TP53 cells. Mass spectrometry demonstrated that gemcitabine modulated the protein\ud expression, especially those from genes related to apoptosis, transport of vesicles and stress response. Analyses using SEM\ud and TEM showed changes in cell morphology independently on the cell line studied. The observed decreased number of\ud microvillus suggests low contact among the cells and between cell and extracellular matrix; irregular forms might indicate\ud actin cytoskeleton deregulation; and the reduction in the amount of organelles and core size might indicate reduced\ud cellular metabolism. In conclusion, independently on TP53 status or grade of bladder tumor, gemcitabine modulated\ud genes related to the cell cycle and apoptosis, that reflected in morphological changes indicative of future cell death.FAPESPCNP

Multi-physics interactions drive VEGFR2 relocation on endothelial cells.

Vascular Endothelial Growth Factor Receptor-2 (VEGFR2) is a pro-angiogenic receptor, expressed on endothelial cells (ECs). Although biochemical pathways that follow the VEGFR2 activation are well established, knowledge about the dynamics of receptors on the plasma membrane remains limited. Ligand stimulation induces the polarization of ECs and the relocation of VEGFR2, either in cell protrusions or in the basal aspect in cells plated on ligand-enriched extracellular matrix (ECM). We develop a mathematical model in order to simulate the relocation of VEGFR2 on the cell membrane during the mechanical adhesion of cells onto a ligand-enriched substrate. Co-designing the in vitro experiments with the simulations allows identifying three phases of the receptor dynamics, which are controlled respectively by the high chemical reaction rate, by the mechanical deformation rate, and by the diffusion of free receptors on the membrane. The identification of the laws that regulate receptor polarization opens new perspectives toward developing innovative anti-angiogenic strategies through the modulation of EC activatio

Numerical Prediction of Cavitation Inception in Centrifugal Impellers

Cavitation is a fundamental issue in pump design since it yields significant decrease of performances and pump life, damaging impeller surfaces and triggering harmful flow instabilities. This topic is usually addressed through costly experimental tests. The aim of this paper is to assess numerical methodologies for the correct evaluation and prediction of the cavitation inception in centrifugal impellers during the design phase. Preliminary analyses were performed to individuate the most promising approach by using two cavitation models on a 2D test case representing the NACA 0009 hydrofoil. Then, two CFD approaches were considered for the evaluation of the NPSHr in actual pumps. RANS two-phase calculations including the selected cavitation model were performed on a geometry provided by WEIR Gabbioneta srl. Monophase simulations have been performed as well and an in-house heuristic model has been proposed to evaluate the NPSHr curve from a non cavitating pressure field. The heuristic post-processor has been tuned using both the two-phase and the monophase data, and validated using the available experimental values provided by WEIR Gabbioneta srl

Influencia del tamaño de los cortes, la congelación, almacenamiento congelado y descongelación en la producción de exudado en patas de cerdo deshuesadas

En la industria de los chacinados se suele utilizar –para cubrir faltantes de materia prima nacional– carne de cerdo importada. La misma se adquiere congelada y se la descongela en el momento de su utilización. Dicho proceso se lleva a cabo –muchas veces– en condiciones de temperatura y de circulación del medio de calentamiento (aire o agua) muy poco controladas, generando un alto volumen de exudado y la posibilidad de contaminación (Mascheroni, 2001). La pérdida de peso resultante puede depender de distintos parámetros del proceso: Condiciones de congelación y de almacenamiento, peso de la muestra, tiempo de almacenamiento, condiciones de descongelación, etc. Las condiciones de congelación generalmente no pueden ser controladas por el comprador, pero las otras si. Por ello el objetivo de este trabajo fue estudiar la influencia de distintas características del producto y del proceso de almacenamiento congelado y descongelación en la producción de exudado en patas de cerdo deshuesadas.Facultad de Ingenierí

Potential role of low kV ex vivo micro-CT for 3D morphometry of paraffin embedded coronary vessels before histology

Purpose: Micro CT is an established tool for non destructive 3D inspection of small specimens. Aim of the study was to demonstrate that despite its limitations in differentiation of soft materials, micro CT can reliably display coronary vessel structure and surrounding tissues after paraffin embedding. Data were obtained from coronary specimens of pig, physical phantoms and numerical simulations. Preliminary images with dual-energy techniques are also shown. Methods: A micro CT scanner built by our group was used for the experiments. The x-ray tube was set up in the range of 20-50 kV; the voxel size was set to 21 μm. A phantom composed of formalin fixed fat and myocardium of rat, dehydrated and paraffin embedded, was used to measure the contrast of different tissues with respect to background. Similar acquisitions were simulated numerically. Real samples of pig excised coronary arteries were processed in the same way and acquired with the same settings; resulting images were compared to those obtained by histology. Results: In phantom, the myocardium contrast vs. paraffin varied from 40% at 20 kV to 29% at 50 kV. The fat contrast vs. background was 2% at 20 kV, whereas it was indistinguishable from the background at 50 kV; all the contrasts in phantom appeared lower than those expected from simulations, probably because of tissue shrinkage. In the samples from pig (see Figure), the vessel wall contrast was 25% greater than the myocardium contrast; the pericardium and a balloon induced stenosis were clearly distinguished. All micro CT scans were shorter than 1 hour. Conclusion: Micro CT is a useful complementary tool for the 3D morphometry of coronary vessels after paraffin embedding, and it can help for the preliminary identification of features of interest for subsequent histological analysis