1,720,983 research outputs found
Topology optimization for chiral elastic bodies
No full textThe topology optimization problem is dealt with for linearly elastic chiral micropolar bodies. The maximum global stiffness is taken as objective function, and the material density as design variable. According to the SIMP model, the constitutive tensors are assumed to be smooth functions of the density. Optimal material distributions are obtained for several significant cases. Comparisons in terms of optimal configurations are made with classical Cauchy materials and centrosymmetric materials
Extrema of the strain energy density for anisotropic micropolar solids
No full textThe paper deals with any 2D solid of prescribed shape and elastic properties, consisting of an orthotropic micropolar material. The conditions are determined under which the global stiffness of the solid is maximized, taking the orientation of the material symmetry axes to the local extreme strains as design variable. Unlike Cauchy solids, it is shown that the maximum stiffness problem for micropolar solids is not fulfilled by ‘trivial’ solutions, at which full collinearity of the material symmetry axes and the directions of the extreme strains is achieved. The paper closes with the determination of the optimal orientations for a special elasticity problem
Numerical Assessment of the Performance of Elastic Cloaks for Transient Flexural Waves
Full text linkA relevant application of transformation elastodynamics has shown that flexural waves in a Kirchhoff-Love plate can be diverted and channeled to cloak a region of the ambient space. To achieve the goal, an orthotropic meta-structural plate should be employed. However, the corresponding mathematical transformation leads to the presence of an unwanted strong compressive prestress, likely beyond the buckling threshold of the structure, with a set of in-plane body forces to warrant equilibrium. In addition, the plate must possess, at the same time, high bending stiffnesses, but a null twisting rigidity. With the aim of estimating the performance of cloaks modelled with approximate parameters, an in-house finite element code, based on a subparametric technique, is implemented to deal with the cloaking of transient waves in orthotropic thin plates. The tool allows us to explore the sensitivity of specific stiffness parameters that may be difficult to match in a real cloak design. In addition, the finite element code is extended to investigate a meta-plate interacting with a Winkler foundation, to confirm how the subgrade modulus should transform in the cloak region
Ottimizzazione topologica per solidi micropolari
No full textThe theory of micropolar continua is an extension of the classical theory of Cauchy’s continua. In this paper a procedure is proposed for the topological optimization of structures made of micropolar solids in view of the maximization of their elastic stiffness. The minimum flexibility problem, with a constraint on the volume fraction, is solved through an augmented Lagrangian functional. Some numerical examples are shown, focusing in particular on structural interfaces. The results show that the obtained optimal topologies agree with the real shape of biological tissues and indicate that the proposed procedure can be employed in the definition of the optimal topology of structures made of nonlocal artificial materials
Low levels of cobalamin, epidermal growth factor, and normal prions in multiple sclerosis spinal cord
No full textWe have previously demonstrated that multiple sclerosis (MS) patients have abnormal cerebrospinal fluid (CSF) levels of the key myelin-related molecules cobalamin (Cbl), epidermal growth factor (EGF), and normal cellular prions (PrPCs), thus confirming that some CSF abnormalities may be co-responsible for remyelination failure. We determined the levels of these three molecules in post-mortem spinal cord (SC) samples taken from MS patients and control patients. The control SC samples, almost all of which came from non-neurological patients, did not show any microscopic lesions of any type. All of the samples were supplied by the U.K. MS Tissue Bank. The Cbl, EGF, and PrPC levels were determined using enzyme-linked immunosorbent assays. The SC total homocysteine level was determined using a competitive immunoenzymatic assay. CSF samples, taken from a further group of MS patients, were used for the assay of holo-transcobalamin (holo-TC) levels. The Cbl, EGF, and PrPC levels were significantly decreased in MS SCs in comparison with controls and, paradoxically, the decreased Cbl levels were associated with decreased SC levels of homocysteine, a biochemical marker of Cbl deficiency. The trends of EGF and PrPC levels paralleled those previously found in CSF, whereas that of Cbl was the opposite. There was no significant difference in CSF holo-TC levels between the MS patients and the controls. Given that we have previously demonstrated that Cbl positively regulates central nervous system EGF levels, it is conceivable that the low EGF levels in the MS SC may be causally related to a local decrease in Cbl levels. Only PrPC levels were invariably decreased in both the SC and CSF regardless of the clinical course of the disease. These findings suggest that the simultaneous lack of Cbl, EGF, and PrPCs may greatly hamper the remyelination process in MS patients, because they are key molecules of the machinery for remyelination
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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