Non-linear analysis of laminated metal matrix composites by an integrated micro/macro-mechanical model

The present paper describes an integrated micro/macro mechanical study of the elastic-viscoplastic behavior of unidirectional metal matrix composites (MMC). The micromechanical analysis of the elastic moduli is based on the Composites Cylinder Assemblage model (CCA) with comparisons also draw with a Representative Unit Cell (RUC) technique. These "homogenization" techniques are later incorporated into the Vanishing Fiber Diameter (VFD) model and a new formulation is proposed. The concept of a smeared element procedure is employed in conjunction with two different versions of the Bodner and Partom elastic-viscoplastic constitutive model for the associated macroscopic analysis. The formulations developed are also compared against experimental and analytical results available in the literature.

Numerical study on mixed convection in a horizontal flow past a square porous cavity using UNIFAES scheme

Mixed convection on the flow past a heated length and past a porous cavity located in a horizontal wall bounding a saturated porous medium is numerically simulated. The cavity is heated from below. The steady-state regime is studied for several intensities of the buoyancy effects due to temperature variations. The influences of Péclet and Rayleigh numbers on the flow pattern and the temperature distributions are examined. Local and global Nusselt numbers are reported for the heated surface. The convective-diffusive fluxes at the volume boundaries are represented using the UNIFAES, Unified Finite Approach Exponential-type Scheme, with the Power-Law approximation to reduce the computing time. The conditions established by Rivas for the quadratic order of accuracy of the central differencing to be maintained in irregular grids are shown to be extensible to other quadratic schemes, including UNIFAES, so that accuracy estimates could be obtained.

Solution of aerospace problems using structured and unstructured strategies

Products developed at industries, institutes and research centers are expected to have high level of quality and performance, having a minimum waste, which require efficient and robust tools to numerically simulate stringent project conditions with great reliability. In this context, Computational Fluid Dynamics (CFD) plays an important role and the present work shows two numerical algorithms that are used in the CFD community to solve the Euler and Navier-Stokes equations applied to typical aerospace and aeronautical problems. Particularly, unstructured discretization of the spatial domain has gained special attention by the international community due to its ease in discretizing complex spatial domains. This work has the main objective of illustrating some advantages and disadvantages of numerical algorithms using structured and unstructured spatial discretization of the flow governing equations. Numerical methods include a finite volume formulation and the Euler and Navier-Stokes equations are applied to solve a transonic nozzle problem, a low supersonic airfoil problem and a hypersonic inlet problem. In a structured context, these problems are solved using MacCormack’s implicit algorithm with Steger and Warming’s flux vector splitting technique, while, in an unstructured context, Jameson and Mavriplis’ explicit algorithm is used. Convergence acceleration is obtained using a spatially variable time stepping procedure.

Matrix Mind : on managerial reframing in multidimensional problem solving

Det är inte ovanligt att man i organisationer ställs inför problem som inte kan hanteras inom befintlig organisationsstruktur. Skälen kan vara att frågorna har många – ibland konflikterande – dimensioner och perspektiv som samtidigt måste beaktas. I den här avhandlingen studeras vilka tankemönster och föreställningar som fanns när grupper av chefer försökte lösa komplexa problem, som inte hade en naturlig organisatorisk hemvist och hur de omsatte dessa tankemönster i handling. Vad kännetecknade det ledarskap som utövades under problemlösningsprocessen? Avhandlingens empiri hämtas från ledarutvecklingsprogram i två internationellt verksamma företag i Sverige, och omfattar 14 verkliga affärsproblem i dessa företag och den process varigenom de löstes. De 14 seminarierna utgör exempel på hur mångdimensionella frågeställningar framgångsrikt hanteras utanför den befintliga organisationsstrukturen. Studien ger, genom att adressera frågor kring tankesätt och ledningsprocesser, en djupare förståelse för förutsättningarna för detta, och lyfter särskilt fram betydelsen av ett ledarskap som inbegriper begreppen intervention, förmåga och omtolkning. Som ett samlat begrepp introduceras bilden att utöva ledarskapet utifrån ett matrix mind. Att påverka strukturer (i vid mening) och därigenom de förmågor som utvecklas, är del i detta ledarskap. Det sker genom interventioner (ingrepp som påverkar relationer i t ex en grupp) och baserades i den aktuella empirin på uppfattningar om värdet av problematisering, erfarenhetsutbyte och av ett språk, som både beskriver och anger inriktning för aktiviteter. Interventioner i strukturer (och till dem knutna processer) beskriver dock bara delvis detta ledarskap. Att leda med ett matrix mind innefattar också ett nyfiket och kreativt förhållningssätt, och att utifrån detta leda omtolkning av problem. I empirin finns flera exempel på detta. Avhandlingen avser att ge ett bidrag inom såväl organisations- som ledarskapsteori.

Concanavalin A-reactive nuclear matrix glycoprotein

The binding capacity of concanavalin A (Con A) to condensed euchromatin and heterochromatin was investigated in chicken erythrocyte nuclei (CEN), mouse liver cells, Zea mays mays meristematic cells and Drosophila melanogaster polytene chromosomes after 4 N HCl hydrolysis to determine whether binding was preferentially occurring in bands and heterochromatin. Dry mass (DM) variation was investigated in CEN by interference microscopy. Feulgen and Con A reactions were employed for all materials to correlate the loci of the two reactions. Quantifications and topological verifications were carried out by video image analysis (high performance cytometry). It was observed that 4 N HCl hydrolysis caused an important DM loss in CEN leaving a level corresponding to the average DNA DM content. In this material, Con A binding was restricted to the nuclear envelope, which reinforces the idea of the absence of a nuclear matrix in these cells. The other cell types exhibited a correspondence of Feulgen-positive and Con A-reactive areas. The Con A reaction was highly positive in the condensed chromatin areas and heterochromatin. This fact led us to speculate that Con A-positive proteins may play a role in the chromatin condensation mechanism, endowing this structure with physico-chemical stability towards acid hydrolysis and contributing to its rheological properties.

Cellular and matrix interactions during the development of T lymphocytes

The thymus contains an extensive extracellular matrix. Although thymocytes express integrins capable of binding to matrix molecules, the functional significance of the matrix for T cell development is uncertain. We have shown that the matrix is associated with thymic fibroblasts which are required for the CD44+ CD25+ stage of double negative (CD4-8-) thymocyte development. The survival of cells at this stage is dependent on IL-7 and we propose that the role of fibroblasts is to present, via the matrix, IL-7 to developing T cells.

Expression of extracellular matrix components and their receptors in the central nervous system during experimental Toxoplasma gondii and Trypanosoma cruzi infection

Alterations in extracellular matrix (ECM) expression in the central nervous system (CNS) usually associated with inflammatory lesions have been described in several pathological situations including neuroblastoma and demyelinating diseases. The participation of fibronectin (FN) and its receptor, the VLA-4 molecule, in the migration of inflammatory cells into the CNS has been proposed. In Trypanosoma cruzi infection encephalitis occurs during the acute phase, whereas in Toxoplasma infection encephalitis is a chronic persisting process. In immunocompromised individuals such as AIDS patients, T. cruzi or T. gondii infection can lead to severe CNS damage. At the moment, there are no data available regarding the molecules involved in the entrance of inflammatory cells into the CNS during parasitic encephalitis. Herein, we characterized the expression of the ECM components FN and laminin (LN) and their receptors in the CNS of T. gondii- and T. cruzi-infected mice. An increased expression of FN and LN was detected in the meninges, leptomeninges, choroid plexus and basal lamina of blood vessels. A fine FN network was observed involving T. gondii-free and T. gondii-containing inflammatory infiltrates. Moreover, perivascular spaces presenting a FN-containing filamentous network filled with a4+ and a5+ cells were observed. Although an increased expression of LN was detected in the basal lamina of blood vessels, the CNS inflammatory cells were a6-negative. Taken together, our results suggest that FN and its receptors VLA-4 and VLA-5 might be involved in the entrance, migration and retention of inflammatory cells into the CNS during parasitic infections.

Regulatory roles of microtubule-associated proteins in neuronal morphogenesis. Involvement of the extracellular matrix

As a result of recent investigations, the cytoskeleton can be viewed as a cytoplasmic system of interconnected filaments with three major integrative levels: self-assembling macromolecules, filamentous polymers, e.g., microtubules, intermediate filaments and actin filaments, and supramolecular structures formed by bundles of these filaments or networks resulting from cross-bridges between these major cytoskeletal polymers. The organization of this biological structure appears to be sensitive to fine spatially and temporally dependent regulatory signals. In differentiating neurons, regulation of cytoskeleton organization is particularly relevant, and the microtubule-associated protein (MAP) tau appears to play roles in the extension of large neuritic processes and axons as well as in the stabilization of microtubular polymers along these processes. Within this context, tau is directly involved in defining neuronal polarity as well as in the generation of neuronal growth cones. There is increasing evidence that elements of the extracellular matrix contribute to the control of cytoskeleton organization in differentiating neurons, and that these regulations could be mediated by changes in MAP activity. In this brief review, we discuss the possible roles of tau in mediating the effects of extracellular matrix components on the internal cytoskeletal arrays and its organization in growing neurons.

Extracellular matrix molecules play diverse roles in the growth and guidance of central nervous system axons

Axon growth and guidance represent complex biological processes in which probably intervene diverse sets of molecular cues that allow for the appropriate wiring of the central nervous system (CNS). The extracellular matrix (ECM) represents a major contributor of molecular signals either diffusible or membrane-bound that may regulate different stages of neural development. Some of the brain ECM molecules form tridimensional structures (tunnels and boundaries) that appear during time- and space-regulated events, possibly playing relevant roles in the control of axon elongation and pathfinding. This short review focuses mainly on the recognized roles played by proteoglycans, laminin, fibronectin and tenascin in axonal development during ontogenesis.

Adhesion of the human pathogen Sporothrix schenckii to several extracellular matrix proteins

The pathogenic fungus Sporothrix schenckii is the causative agent of sporotrichosis. This subcutaneous mycosis may disseminate in immunocompromised individuals and also affect several internal organs and tissues, most commonly the bone, joints and lung. Since adhesion is the first step involved with the dissemination of pathogens in the host, we have studied the interaction between S. schenckii and several extracellular matrix (ECM) proteins. The binding of two morphological phases of S. schenckii, yeast cells and conidia, to immobilized type II collagen, laminin, fibronectin, fibrinogen and thrombospondin was investigated. Poly (2-hydroxyethyl methacrylate) (poly-HEMA) was used as the negative control. Cell adhesion was assessed by ELISA with a rabbit anti-S. schenckii antiserum. The results indicate that both morphological phases of this fungus can bind significantly to type II collagen, fibronectin and laminin in comparison to the binding observed with BSA (used as blocking agent). The adhesion rate observed with the ECM proteins (type II collagen, fibronectin and laminin) was statistically significant (P<0.05) when compared to the adhesion obtained with BSA. No significant binding of conidia was observed to either fibrinogen or thrombospondin, but yeast cells did bind to the fibrinogen. Our results indicate that S. schenckii can bind to fibronectin, laminin and type II collagen and also show differences in binding capacity according to the morphological form of the fungus.

Functions of the extracellular matrix and matrix degrading proteases during tumor progression

Cell interactions with extracellular matrices are important to pathological changes that occur during cell transformation and tumorigenesis. Several extracellular matrix proteins including fibronectin, thrombospondin-1, laminin, SPARC, and osteopontin have been suggested to modulate tumor phenotype by affecting cell migration, survival, or angiogenesis. Likewise, proteases including the matrix metalloproteinases (MMPs) are understood to not only facilitate migration of cells by degradation of matrices, but also to affect tumor formation and growth. We have recently demonstrated an in vivo role for the RGD-containing protein, osteopontin, during tumor progression, and found evidence for distinct functions in the host versus the tumor cells. Because of the compartmentalization and temporal regulation of MMP expression, it is likely that MMPs may also function dually in host stroma and the tumor cell. In addition, an important function of proteases appears to be not only degradation, but also cleavage of matrix proteins to generate functionally distinct fragments based on receptor binding, biological activity, or regulation of growth factors.

Alterations in proteins of bone marrow extracellular matrix in undernourished mice

The objective of the present study was to determine the effect of protein malnutrition on the glycoprotein content of bone marrow extracellular matrix (ECM). Two-month-old male Swiss mice were submitted to protein malnutrition with a low-protein diet containing 4% casein as compared to 20% casein in the control diet. When the experimental group had attained a 20% loss of their original body weight, we extracted the ECM proteins from bone marrow with PBS buffer, and analyzed ECM samples by SDS-PAGE (7.5%) and ECL Western blotting. Quantitative differences were observed between control and experimental groups. Bone marrow ECM from undernourished mice had greater amounts of extractable fibronectin (1.6-fold increase) and laminin (4.8-fold increase) when compared to the control group. These results suggest an association between fluctuations in the composition of the hematopoietic microenvironment and altered hematopoiesis observed in undernourished mice.

Meal-feeding scheme: twenty years of research in Brazil

Naomi Shinomiya Hell was the first researcher to investigate the physiological adaptations to a meal-feeding scheme (MFS) in Brazil. Over a period of 20 years, from 1979 to 1999, Naomi's group determined the physiological and metabolic adaptations induced by this feeding scheme in rats. The group showed the persistence of such adaptations even when MFS is associated with moderate exercise training and the performance to a session of intense physical effort. The metabolic changes induced by the feeding training were discriminated from those caused by the effective fasting period. Naomi made an important contribution to the understanding of the MFS but a lot still has to be done. One crucial question still remains to be satisfactorily answered: what is the ideal control for the MFS?

The extracellular matrix in multiple sclerosis: an update

Extracellular matrix (ECM) molecules play important roles in the pathobiology of the major human central nervous system (CNS) inflammatory/demyelinating disease multiple sclerosis (MS). This mini-review highlights some recent work on CNS endothelial cell interactions with vascular basement membrane ECM as part of the cellular immune response, and roles for white matter ECM molecules in demyelination and remyelination in MS lesions. Recent basic and clinical investigations of MS emphasize axonal injury, not only in chronic MS plaques, but also in acute lesions; progressive axonal degeneration in normal-appearing white matter also may contribute to brain and spinal cord atrophy in MS patients. Remodeling of the interstitial white matter ECM molecules that affect axon regeneration, however, is incompletely characterized. Our ongoing immunohistochemical studies demonstrate enhanced ECM versican, a neurite and axon growth-inhibiting white matter ECM proteoglycan, and dermatan sulfate proteoglycans at the edges of inflammatory MS lesions. This suggests that enhanced proteoglycan deposition in the ECM and axonal growth inhibition may occur early and are involved in expansion of active lesions. Decreased ECM proteoglycans and their phagocytosis by macrophages along with myelin in plaque centers imply that there is "injury" to the ECM itself. These results indicate that white matter ECM proteoglycan alterations are integral to MS pathology at all disease stages and that they contribute to a CNS ECM that is inhospitable to axon regrowth/regeneration.