1,354,365 research outputs found
On dynamic behavior of composite plates using a higher-order Zig-Zag theory and exponential basis functions
No full textIn this paper, a boundary node method is presented to study wave propagation in laminated composite plates. The Zig-Zag theory of Cho and Parmerter is used for deriving the governing equations of laminated plates. To the best of the authors’ knowledge, this study is the first one employing the theory in non-stationary dynamic plate problems addressing wave propagation issues. For this theory, there is no information about the Green’s functions and thus the presented method can be considered as an alternative to the boundary integral method. With the use of exponential basis functions (EBFs), the response of the structure is first found in the frequency domain and finally the time-domain response is obtained using inverse Fourier transformation. The EBFs are found so that they satisfy the governing equations in the frequency domain. For the first time, in this paper, we shall present explicit relations for the EBFs in the frequency domain for Cho and Parmerter’s Zig-Zag theory. The coefficients of the EBFs are found through the collocation of the boundary conditions. The dynamic analysis of some composite laminated plates is presented, and the results are compared to those obtained from the dynamic analysis of two-/three-dimensional finite element method (FEM). We shall discuss the capabilities and limitations of the theory and the solution method. The capability of the method, in the analysis of problems excited by high-frequency loads, is shown in the solution of wave propagation problems for which the FEM needs excessive number of elements and thus it is practically impossible to be applied
Peridynamic modeling of inelastic materials for aerospace applications
No full textStudy of the mechanical behavior of ductile materials is essential in engineering and materials science due to the widespread use of these materials in industry. Ductile materials are known for their ability to deform significantly before fracture, and this has contributed to their extensive adoption in many industrial sectors such as aerospace, automotive, and structural engineering.
Ductile materials undergo elastoplastic deformation prior to fracture. This process reduces the stiffness of the material before failure. When a material is loaded, it initially exhibits elastic behavior. A surface in the stress space known as the yield surface controls the initiation of the plastic deformation. Plastic deformation occurs when the stress in the material remains on the yield surface throughout the loading process. Furthermore, to reflect the real behavior observed in most ductile materials, the size of the yield surface is controlled by adding a hardening/softening assumption to the formulation.
The linear elastic fracture mechanics (LEFM) approach, which neglects yielding at the crack front, is not reliable for simulating the mechanical behavior of ductile materials that undergo significant deformation under service loads. In contrast, the elasto-plastic fracture mechanics (EPFM) approach considers the impact of yielding at crack tips and characterizes the plastic behavior of the material. Consequently, it is appropriate for analysing ductile materials.
Moreover, the deformation of all metals is, to some extent, time-dependent. This behavior can be effectively characterized by elasto-viscoplasticity. This framework accounts for the time-dependent inelastic strains observed in solids. The Perzyna constitutive law, with its simple formulation, accurately simulates the evolution of viscous effects and is thus widely employed in engineering applications.
Classical continuum mechanics is a theory that establishes the mathematical foundation for the study of the mechanical behavior of ductile materials. However, fracture analysis is challenging, especially when it is approached within the framework of the classical mechanics theory because this theory uses partial derivatives in the equation of motion, which require continuity of the displacement field. This assumption becomes problematic when dealing with discontinuities such as cracks.
Peridynamics is a nonlocal theory of solid mechanics designed for discontinuous problems. It is well suited to failure analysis because it uses integral equations rather than partial differential equations. It redefines the equation of motion and improves its suitability for solving problems involving cracks. However, since it is a recently introduced theory, Peridynamics is not equipped with all constitutive laws normally available for classical continuum mechanics.
Therefore, it is reasonable to develop a peridynamic elastoplastic model for the study of the mechanical behaviour of ductile materials. The main purpose of this dissertation is to develop peridynamic approaches to simulate both elastoplastic materials and elasto-viscoplastic materials with strain hardening. The elastoplastic model is based on the classical theory of plasticity. The model is capable of simulating the elastoplastic behavior of materials with isotropic, kinematic and combined hardening. The elasto-viscoplastic peridynamic model is based on the Perzyna constitutive law. For materials with hardening, the yield surface changes with any change in plastic strain, a behavior observed in most materials. This effect is duly taken into account in the proposed models. We shall briefly show that the proposed approaches are well suited for fracture analysis of ductile materials. Several examples, including 2D plane stress and plane strain, and 3D cases, are performed to demonstrate the capabilities of the proposed approaches
Effects of intracerebroventricular and intra-Arcuate nucleus injection of Ghrelin on pain behavioral responses and met-Enkephalin and β-endorphin concentrations in the periaqueductal gray area in rats
No full textGhrelin is an endogenous ligand for orphan growth hormone secretagogue receptors. Ghrelin receptors have been found in central nervous system (CNS) areas responsible for pain modulation and transmission. This study investigated the effects of intracerebroventricular (ICV) and intra-arcuate nucleus (ARC) injection of ghrelin on pain behavioral responses and levels of β-endorphin (β-EP) and met-enkephalin (MENK) in the periaqueductal gray area (PAG) during the formalin test in rats. Thirty-five male rats were studied in five groups. Ghrelin was injected into the left lateral ventricle (ICV, 5 μL) or into the ARC (1 μL). After 15 min, formalin (2.5%) was subcutaneously injected into the left hind paw. Behavioral nociceptive scores were recorded for 60 min. MENK and β-EP were collected by microdialysis in the PAG and determined by high-performance liquid chromatography (HPLC). ICV and ARC injection of ghrelin significantly reduced pain in all phases of the formalin test (p < 0.001). Dialysate concentrations of MENK and β-EP in the PAG increased in all the phases (p < 0.01). In conclusion, the present study shows that the ARC nucleus and the endogenous opioid system are involved in ghrelin-induced pain modulation
Supplemental Material - Implementation of a Population-Based Cancer Family History Screening Program for Lynch Syndrome
No full textSupplemental Material for Implementation of a Population-Based Cancer Family History Screening Program for Lynch Syndrome by Sayoni Lahiri, MS, Sara Pirzadeh-Miller, MS, Kelsey Moriarty, MS, and Nisa Kubiliun, MD in Cancer Control</p
Effects of a non-absorbing substrate on the magneto-optical Kerr response of plasmonic ferromagnetic nanodisks
No full textMagnetoplasmonics is an emerging field of intense research on materials combining magnetic and plasmonic functionalities. The novel optical and magneto-optical (MO) properties displayed by these materials could allow the design of a new class of magnetically controllable optical nano-devices. In this work, we investigate the effects of a non-absorbing (insulating) substrate on the MO activity of pure ferromagnetic disk-shaped nanostructures supporting localized plasmon resonances. We show that the red-shift of the localized plasmon resonance, related to the modification of the localization of the electromagnetic field due to the substrate, is not the only effect that the substrate has on the MO response. We demonstrate that the reflectivity of the substrate itself plays a key role in determining the MO response of the system. We discuss why it is so and provide a description of the modeling tools suitable to take into account both effects. Understanding the role of the substrate will permit a more aware design of magnetoplasmonic nanostructured devices for future biotechnological and optoelectronic applications. Ferromagnetic nickel nanodisk in vacuum (left) and on a non-absorbing substrate (right), illuminated by linearly polarized light. The polarization of the reflected field is changed in the first case due to a combination of intrinsic magneto-optical properties and the nanoconfinement of the material. In the second case, the polarization of the reflected light is affected also by the presence of the substrate. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No full text“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
No full textWe 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
A peridynamics elastoplastic model with isotropic and kinematic hardening for static problems
No full textThis study proposes a formulation equivalent to J2 plasticity with the associated flow rule to simulate the elastoplastic behavior of materials with isotropic or kinematic hardening in a peridynamic framework. The capabilities of the developed formulation are analysed through 2D and 3D case studies whose results (displacement and stress field) are compared with those obtained from the corresponding FEM models
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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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