1,721,730 research outputs found
Principle of Virtual Work as Foundational Framework for Metamaterial Discovery and Rational Design|Le principe des puissances virtuelles comme cadre de base pour la découverte et la conception rationnelle des métamatériaux
No full textNovel theories are needed for the discovery of innovative and exotic metamaterial and for their rational design. The current practice of mechanical analyses based upon moribund classical theories and experimental trial-error campaigns is caught in an inescapable vortex and illusion of inductive reasoning. The needed novel research paradigm is one in which the formulation of theoretical concepts precede their experimental validation. In the absence of theoretical understanding, the design experiments and collection of experimental evidence will remain unavoidably circumscribed. History of science can provide us guidance in the search for the needed powerful tools required for discovery. The principle of virtual work provides the necessary framework for development of theories that can lead to novel metamaterials, as it was the unifying principle which allowed the French-Italian School, headed by D’Alembert, Lagrange and Gabrio Piola, to found modern continuum mechanics. Based upon this framework we have conceived a metamaterial synthesis schema that exploits micro-macro identification traceable to the early days of the formulation of continuum theories for deformable solids. The schema is illustrated with application to metamaterials with pantographic and granular motifs based upon higher-gradient and higher-order theories
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
Two-dimensional strain gradient damage modeling: a variational approach
No full textIn this paper, we formulate a linear elastic second gradient isotropic two-dimensional continuum model accounting for irreversible damage. The failure is defined as the condition in which the damage parameter reaches 1, at least in one point of the domain. The quasi-static approximation is done, i.e., the kinetic energy is assumed to be negligible. In order to deal with dissipation, a damage dissipation term is considered in the deformation energy functional. The key goal of this paper is to apply a non-standard variational procedure to exploit the damage irreversibility argument. As a result, we derive not only the equilibrium equations but, notably, also the Karush–Kuhn–Tucker conditions. Finally, numerical simulations for exemplary problems are discussed as some constitutive parameters are varying, with the inclusion of a mesh-independence evidence. Element-free Galerkin method and moving least square shape functions have been employed
Chirality in 2D Cosserat media related to stretch-micro-rotation coupling with links to granular micromechanics
Full text linkCosserat continuum model has attracted increasing interest for describing the mechanical behavior of microstructured solids. Existing formulation of Cosserat continuum model often overlooks chiral effects that arise from coupling between stretching deformations and the micro-rotation. Here, we introduce an extended Cosserat model that accounts for such a coupling. We discover the links of the extended model to the mechanics of granular materials and identify the continuum and grain-scale parameters that are the source of postulated chirality. The micro-rotation is shown to be related to the coupling of shear and normal responses of grain-pair interactions. The consequences of this chirality are then explicated with the aid of numerical examples. Through parametric studies we also demonstrate the possibility of measuring the effects of this type of chirality in experiments
A strain gradient variational approach to damage: a comparison with damage gradient models and numerical results
No full textThe global response of experimental uniaxial tests cannot be homogeneous, because of the unavoidable presence of localized deformations, which is always preferential from an energetic viewpoint. Accordingly, one must introduce some characteristic lengths in order to penalize deformations that are too localized. This is what leads to the concept of nonlocal damage models. The nonlocal approach employs nonlocal terms in the internal deformation energy in order to control the size of the localization region. In phase-field models and, in general, in gradient models, dependence of the internal energy upon the first gradient of damage is assumed, while in our approach the nonlocality is given by the dependence of the internal energy upon the second gradient of the displacement field. A discussion of the advantages and challenges of using the gradient of damage and of using the second gradient of the displacement field will be addressed in the present paper. A variational inequality is formulated and partial differential equations (PDEs), boundary conditions (BCs), and Karush-Kuhn- Tucker (KKT) conditions will be derived within the framework of 2D strain gradient damage mechanics. A novel dependence of the stiffness coefficients with respect to the damage field will also be discussed. Further, an explicit derivation of the damage field evolution in loading conditions will be provided. Finally, a numerical technique based on commercial software has been introduced and discussed for a couple of standard problems
Complex proximal humeral fractures in adults--a systematic review of management.
No full textWe performed a systematic review of the literature to compare the clinical outcomes of the management of three and four part fractures of the proximal humerus by conservative regimes, internal and external fixations and arthroplasty. We identified 147 reports of comparative trials and case series between 1969 and 1999. We selected only studies dealing exclusively with three and four part fractures of the proximal humerus, with at least 15 patients, treated within 48 h of injury by one of the three modalities studied, in which at least one of the outcomes of interest (pain, range of motion, infection and restoration of anatomy) was described. Also, to be included, studies had to have a follow-up period of at least 6 months, in which a minimum of 85% of patients were followed-up. Twenty four reports met our eligibility criteria. Conservatively managed patients had more pain and a poorer range of motion than those managed by either fixation or arthroplasty. Better restoration of anatomy was delivered in the fixation group. There was no significant difference in the functional range of motion between the arthroplasty and fixation groups, but there were very few studies available to compare infection rates in these two management modalities. The results from the present systematic review suggest that the data from the published literature are inadequate for evidence-based decision making with regards to the treatment of complex proximal humeral fractures
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