1,721,091 research outputs found
Parametric Design of Minimal Mass Tensegrity Bridges Under Yielding and Buckling Constraints
No full textThis study investigates the use of the most fundamental elements; cables for tension and bars for compression, in the search for the most efficient bridges. Stable arrangements of these elements are called tensegrity structures. We show herein the minimal mass arrangement of these basic elements to satisfy both yielding and buckling constraints. We show that the minimal mass solution for a simply-supported bridge subject to buckling constraints matches Michell's 1904 paper which treats the case of only yield constraints, even though our boundary conditions differ. The necessary and sufficient condition is given for the minimal mass bridge to lie totally above (or below) deck. Furthermore this condition depends only on material properties. If one ignores joint mass, and considers only bridges above deck level, the optimal complexity (number of elements in the bridge) tends toward infinity (producing a material continuum). If joint mass is considered then the optimal complexity is finite. The optimal (minimal mass) bridge below deck has the smallest possible complexity (and therefore cheaper to build), and under reasonable material choices, yields the smallest mass bridge
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
Static and Dynamic Behavior of Functionally Graded Carbon Nanotube-Reinforced Laminated Composite Doubly-Curved Shells: Higher-Order Structural Approaches
No full textShell structures are broadly employed in many engineering applications due to their efficiency in bearing with external loads, a high degree of resistance, remarkable stiffness and a high strength-to-weight ratio. These peculiar features are given by the doubly-curvature that defines their reference surface. Recently, the need of higher level performances has led to a greater use of innovative materials in shell design, such as fiber-reinforced composites, sandwiches and nanostructures. As a consequence, new materials have been introduced to design stiffer structural elements, without increasing their weight. Analogously, these advanced materials have allowed to improve their mechanical behavior, increasing for instance the safety requirements and the opposition to delamination phenomena. Advancements in manufacturing process have led to the consequent development of the so-called smart structures, which are currently the main topics of many researches and applications. A clear example of this aspect is given by the increasing use of Carbon Nanotubes (CNTs) as reinforcing phase of many composite materials. Nevertheless, since their first applications several mechanical models have been proposed to characterize these nanoparticles. A new micromechanical approach which deals with the agglomeration effect of CNTs is followed by the authors. The key point of this model consists in assuming that the distribution of CNTs in a polymer matrix is irregular. Consequently, their concentration is not uniform since they tend to concentrate in spherical shaped inclusions. The homogenization process based on the Mori-Tanaka scheme is used to compute the effective mechanical properties of such composites
THE COLLAPSE OF A MAGASIN À POUDRE DESCRIBED BY FRÉZIER: AN INTERESTING CASE STUDY FROM THE PAST
Full text linkIn his Treatise, Frézier describes the case of the collapse of a “magasin à poudre” built in 1732. Frézier tries to infer the cause of the incident by applying the geometrical rule by the De La Hire, which regards the minimum thickness of the piers. Then, he compares such a thickness with that of the actual piers. In his opinion, the collapse of the powder magazine occurred because of the weakness of the piers. In the present paper we return on this case, and we try to investigate the real cause of the collapse by comparing the results obtained by Frézier with those arising from an accurate application of De La Hire’s rule and from the methods and tools of modern limit analysis as well
Static and Dynamic Behavior of Functionally Graded Carbon Nanotube-Reinforced Laminated Composite Doubly-Curved Shells: Higher-Order Structural Approaches
No full textShell structures are broadly employed in many engineering applications due to their efficiency in bearing with external loads, a high degree of resistance, remarkable stiffness and a high strength-to-weight ratio. These peculiar features are given by the doubly-curvature that defines their reference surface. Recently, the need of higher level performances has led to a greater use of innovative materials in shell design, such as fiber-reinforced composites, sandwiches and nanostructures. As a consequence, new materials have been introduced to design stiffer structural elements, without increasing their weight. Analogously, these advanced materials have allowed to improve their mechanical behavior, increasing for instance the safety requirements and the opposition to delamination phenomena. Advancements in manufacturing process have led to the consequent development of the so-called smart structures, which are currently the main topics of many researches and applications. A clear example of this aspect is given by the increasing use of Carbon Nanotubes (CNTs) as reinforcing phase of many composite materials. Nevertheless, since their first applications several mechanical models have been proposed to characterize these nanoparticles. A new micromechanical approach which deals with the agglomeration effect of CNTs is followed by the authors. The key point of this model consists in assuming that the distribution of CNTs in a polymer matrix is irregular. Consequently, their concentration is not uniform since they tend to concentrate in spherical shaped inclusions. The homogenization process based on the Mori-Tanaka scheme is used to compute the effective mechanical properties of such composites
Free Vibration Analysis of Functionally Graded Carbon Nanotube-Reinforced Composite Plates with Arbitrary Domains and Discontinuities
No full textComposite plates are structural elements that are commonly used in many fields, such as civil, aerospace and mechanical engineering. The mechanical response of these structures has been enhanced by the advancements in the manufacturing processes that characterized the last decades. In particular, the attention of both the academic research and the industry improvement is focused on the development of new classes of materials that can reasonably increase the structural performances. For these purposes, the class of granular composites defined by a gradual variation of the mechanical properties along the thickness of the structures has been developed. In the literature, they are typically named as Functionally Graded Materials (FGMs). The idea on which these composites are based on is also employed to specify the spatial variation of an extremely innovative reinforcing phase made of carbon nanofibers, known as Carbon Nanotubes (CNTs). It has been proven that the insertion of these particles in a polymeric matrix can drastically change the structural response of many structural elements. Since their discovery in the nineties, CNTs have revolutionized the classical idea of composite structures. The term “nanostructure” has been introduced to refer to these structural elements
Free Vibration Analysis of Functionally Graded Carbon Nanotube-Reinforced Composite Plates with Arbitrary Domains and Discontinuities
No full textComposite plates are structural elements that are commonly used in many fields, such as civil, aerospace and mechanical engineering. The mechanical response of these structures has been enhanced by the advancements in the manufacturing processes that characterized the last decades. In particular, the attention of both the academic research and the industry improvement is focused on the development of new classes of materials that can reasonably increase the structural performances. For these purposes, the class of granular composites defined by a gradual variation of the mechanical properties along the thickness of the structures has been developed. In the literature, they are typically named as Functionally Graded Materials (FGMs). The idea on which these composites are based on is also employed to specify the spatial variation of an extremely innovative reinforcing phase made of carbon nanofibers, known as Carbon Nanotubes (CNTs). It has been proven that the insertion of these particles in a polymeric matrix can drastically change the structural response of many structural elements. Since their discovery in the nineties, CNTs have revolutionized the classical idea of composite structures. The term “nanostructure” has been introduced to refer to these structural elements
A MODERN REINTERPRETATION OF DURAND-CLAYE’S METHOD FOR THE STUDY OF EQUILIBRIUM CONDITIONS OF MASONRY DOMES
Full text linkThis paper aims at describing a modern reinterpretation of the Durand-Claye method for checking equilibrium of masonry revolution domes, able to account for a nonlinear stress distribution both in tension and compression. Our investigation is addressed to spherical and pointed masonry domes subject to symmetrical load conditions. The preliminary results obtained enable determining the dome minimum thickness versus the angle of embrace. A comparison with some results available in the literature is made, together with a critical examination of the state of the art
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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