1,720,974 research outputs found
Gedanken experiments for the determination of two-dimensional linear second gradient elasticity coefficients
No full textIn the present paper, a two-dimensional solid consisting of a linear elastic isotropic material, for which the deformation energy depends on the second gradient of the displacement, is considered. The strain energy is demonstrated to depend on 6 constitutive parameters: the 2 Lamé constants (λ and μ) and 4 more parameters (instead of 5 as it is in the 3D-case). Analytical solutions for classical problems such as heavy sheet, bending and flexure are provided. The idea is very simple: The solutions of the corresponding problem of first gradient classical case are imposed, and the corresponding forces, double forces and wedge forces are found. On the basis of such solutions, a method is outlined, which is able to identify the six constitutive parameters. Ideal (or Gedanken) experiments are designed in order to write equations having as unknowns the six constants and as known terms the values of suitable experimental measurements
The influence of different geometries of matrix/scaffold on the remodeling process of a bone and bioresorbable material mixture with voids
No full textSince internal architecture greatly influences crucial factors for tissue regeneration, such as nutrient diffusion, cell adhesion and matrix deposition, scaffolds have to be carefully designed, keeping in mind case-specific mechanical, mass transport and biological requirements. However, customizing scaffold architecture to better suit conflicting requirements, such as biological and mechanical ones, remains a challenging issue. Recent advances in printing technologies, together with the synthesis of novel composite biomaterials, have enabled the fabrication of various scaffolds with defined shape and controlled in vitro behavior. Thus, the influence of different geometries of the assemblage of the matrix and scaffold on the remodeling processes of living bone and artificial material should be investigated. To this end, two implant shapes are considered in this paper, namely a circular inclusion and a rectangular groove of different aspect ratios. A model of a mixture of bone tissue and bioresorbable material with voids was used to numerically analyze the physiological balance between the processes of bone growth and resorption and artificial material resorption in a plate-like sample. The adopted model was derived from a theory for the behavior of porous solids in which the matrix material is elastic and the interstices are void of material
A Ritz approach for the static analysis of planar pantographic structures modeled with nonlinear Euler–Bernoulli beams
No full textWe present a finite element discrete model for pantographic lattices, based on a continuous Euler–Bernoulli beam for modeling the fibers composing the pantographic sheet. This model takes into account large displacements, rotations and deformations; the Euler–Bernoulli beam is described by using nonlinear interpolation functions, a Green–Lagrange strain for elongation and a curvature depending on elongation. On the basis of the introduced discrete model of a pantographic lattice, we perform some numerical simulations. We then compare the obtained results to an experimental BIAS extension test on a pantograph printed with polyamide PA2200. The pantographic structures involved in the numerical as well as in the experimental investigations are not proper fabrics: They are composed by just a few fibers for theoretically allowing the use of the Euler–Bernoulli beam theory in the description of the fibers. We compare the experiments to numerical simulations in which we allow the fibers to elastically slide one with respect to the other in correspondence of the interconnecting pivot. We present as result a very good agreement between the numerical simulation, based on the introduced model, and the experimental measures
Parametric Experimentation on Pantographic Unit Cells Reveals Local Extremum Configuration
No full textPantographic metamaterials are known for their ability to have large deformation while remaining in the elastic regime. We have performed a set of experiments on 3D printed pantographic unit cells to parametrically investigate their response when undergoing tensile, compression, and shear loading with the aim of i) studying the role of each parameter in the resultant mechanical behavior of the sample, and ii) providing a benchmark for the mathematical models developed to describe pantographic structures. Results show the existence of local extrema in the space of the geometrical parameters, suggesting the use of optimization techniques to find optimal geometrical parameters resulting in desired functionalities. We have also performed tensile relaxation tests on the samples, with the results indicating the complexity of the dynamic behavior and the existence of multiple relaxation characteristic times. Such results can be used to for calibrating mathematical models describing pantographic structures under dynamic loadings
3D-measurements of 3D-deformations of pantographic structures
Full text linkSamples of differently sized so-called pantographic structures are subjected to large deformation loading tests up to rupture, while their response to the deformation is recorded by an optical 3D-measurement system. Digital image correlation is used to calculate the deformation that took place perpendicular to the reference plane by the help of a four-camera system. Results show that the deformation behavior is strongly non-linear and that the structures are capable to perform large (elastic) deformations without leading to complete failure
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Funkcjonalna adaptacja kości jako zagadnienie optymalnego sterowania
No full textThe functional adaptation of bone is a process of bone tissue remodeling induced by variable in time mechanical demands that the skeleton has to satisfy. It is a very complex but highly organized process composed of events at micro-level (molecular and cellular) but having effects in macro-scale (variation of bone internal structure and external shape). Mathematical models of this phenomenon proposed in the literature represent formulas postulated on the basis of the results of medical observations or laboratory investigations and describe locally the evolution of a material in space and time. In the present paper a use is made of the hypothesis of optimal response of bone, proposed earlier by the author, what enables derivation (instead of postulation) the remodeling rules from a very general and global assumption. It turns out that such a formulation has many similarities to engineering optimal control problems. The link between the postulated local adaptation rules and those derived from the global assumption is also discussed.Funkcjonalna adaptacja kości jest procesem polegającym na przebudowie tkanki kostnej wywołanej zmieniającymi się w czasie wymaganiami mechanicznymi, jakie musi spełniać szkielet kostny. Proces ten jest niezwykle złożony, ale doskonale zorganizowany i składa się z szeregu zjawisk zachodzących na poziomie mikro (molekularnym i komórkowym) lecz mających efekt na poziomie makro (zmiana zewnętrznego kształtu kości oraz jej struktury wewnętrznej). Matematyczne modele tego zjawiska, postulowane w oparciu o obserwacje medyczne i badania laboratoryjne, opisują lokalną ewolucję materiału w czasie i przestrzeni. W tej pracy zastosowano hipotezę optymalnej odpowiedzi kości zaproponowaną wcześniej przez autora w celu wyprowadzenia (zamiast postulowania) związków rządzących przebudową kości w oparciu o bardzo ogólne założenia. Okazuje się, że takie sformułowanie ma wiele wspólnego z zagadnieniami optymalnego sterowania. W pracy zaprezentowano przykład zastosowania omawianego podejścia oraz przeprowadzono krótką dyskusję na temat związków między postulowanymi modelami i wyprowadzonymi w oparciu o przyjętą hipotezę
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