1,720,959 research outputs found
The influence of different geometries of matrix/scaffold on the response of a bone and resorbable material mixture with voids
No full textA 2-D dimensional sample made of natural bone tissue and artificial bioresorbable material is numerically investigated in order to study the influence of different geometries of the assemblage of matrix and scaffold. With the specific tools of the Mixture theory we consider the solid matrix with evolving apparent mass densities (rb for bone and rm for material) to describe bone tissue synthesis and resorption when a bio-resorbable material of the kind used in bone reconstruction is present (see e.g. [1, 2, 3]). To take porosity effects in account the adopted model is derived from the Nunziato-Cowin theory developed
for porous solids in which the matrix material is linearly elastic and the interstices are void of material. In detail, to describe the mechanical phenomena which influence the porosity variation we introduce,
following the aforementioned theory [4], an independent kinematic degree of freedom, namely the change in volume fraction from the reference volume fraction, namely
x = (rb+rm)/rMax-(rb R+rmR)/rMax,
with rMax the maximal density without pores. It is well established that exercise results in increased bone mass, while unloading due to immobilization, bedrest, and weightlessness results in bone atrophy.
The strains induced by external loads are sensed by mechanoreceptors, primarily on osteocytes which essentially transduce the mechanical signals into biological signals. These biological signals are able to trigger bone remodeling by directing osteoblast activity and osteoclastic resorption.
[1] T. Lekszycki and F. dell’Isola. A mixture model with evolving mass densities for describing synthesis and resorption phenomena in bones reconstructed with bio-resorbable materials. J. Applied Math and
Mech. (ZAMM), 92:426–444, 2012.
[2] A. Madeo, T. Lekszycki, and F. dell’Isola. A continuum model for the bio-mechanical interactions between living tissue and bio-resorbable graft after bone reconstructive surgery. Comptes Rendus Mécanique, 339:625–640, 2011.
[3] A. Madeo, D. George, T. Lekszycki, M. Nierenberger, and Y. Rémond. A second gradient continuum model accounting for some effects of micro-structure on reconstructed bone remodeling. Comptes
Rendus M ́ecanique, 340:575–589, 2012.
[4] S. C. Cowin and J. W. Nunziato. Linear elastic materials with voids. J. Elasticity, 13:125–147, 1983
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
A continuum model of a mixture of bone tissue and bio-resorbable material for simulating mass density redistribution in a 2d sample
No full textThe bio-mechanical phenomena occurring in bones grafted with the inclusion of artificial materials demand the formulation of mathematical models which are refined enough to describe their non-trivial behavior. In this paper reference is made to earlier works, where a 3D model was proposed and numerical examples were performed in 1D space to investigate and explain some fundamental mechanisms possible during remodeling process. Herein possible effects resulting from 2D interactions are being discovered and examined which may not be present in 1D case so more realistic situations are approached and discussed. This model was used to numerically analyze the physiological balance between the processes of bone apposition and resorption and material resorption in a plate-like sample. The specimen was constituted by a portion of bone living tissue and one of bio-resorbable material and was acted by in-plane loading conditions. A range of load magnitude was identified within which a physiological state is established. A parametric analysis was carried out to evaluate the sensitivity of the model to changes of some critical quantities within physiological ranges
Numerical simulation of remodeling of bone tissue and bio-resorbable material mixture with voids under different loads
No full textA model of a mixture of bone tissue and bio-resorbable 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 linearly elastic and the interstices are void of material. The specimen was constituted by a region of bone living tissue and one of bio-resorbable material and was acted by different in-plane loading conditions, namely pure bending and shear. Ranges of load magnitudes were identified within which physiological states become possible. A parametric analysis was worked out to evaluate the sensitivity of the model to changes of the constitutive parameters of material varying within physiological ranges
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
I2V Highway and Urban Vehicular Networks: A Comparative Analysis of the Impact of Mobility on Broadcast Data Dissemination
No full textIn this paper, we consider the problem of disseminating data in Infrastructure-to-Vehicular (I2V) IEEE 802.11 networks. We analyze, with a comparative approach, the performance in highway and urban scenarios. In particular, after characterizing the mobility in these scenarios we analyze the performance in terms of data dissemination from a fixed Road Side Unit (RSU) to the vehicles passing in its proximity through a recently proposed multihop probabilistic broadcasting protocol, namely Irresponsible Forwarding (IF). In the case of highway-like Vehicular Ad-Hoc NETworks (VANETs), we first characterize a mobile scenario in such a way to make a direct comparison with a static scenario meaningful, taking into account a physical characterization of the network (e.g., in terms of vehicle spatial density). Then, we consider a few mobile urban scenarios, characterized by the presence of junctions regulated by Traffic Lights (TLs) and Roundabouts (Rs). Our results show that, from a single packet perspective, the vehicles’ mobility does not affect the behavior of the IF protocol, at least in the considered mobile scenarios (both highway and urban). However, different conclusions are reached when an information flow (i.e., a series of consecutive packets) is considered. In this context, we determine the maximum amount of data which can be transferred from the RSU to the mobile vehicles passing through a certain Region Of Interest (ROI) around the RSU
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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