1,721,057 research outputs found
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
Smooth Finite Element Methods with Polynomial Reproducing Shape Functions
Full text linkA couple of discretization schemes, based on an FE-like tessellation of the domain and polynomial reproducing, globally smooth shape functions, are considered and numerically explored to a limited extent. The first one among these is an existing scheme, the smooth DMS-FEM, that employs Delaunay triangulation or tetrahedralization (as approximate) towards discretizing the domain geometry employs triangular (tetrahedral) B-splines as kernel functions en route to the construction of polynomial reproducing functional approximations. In order to verify the numerical accuracy of the smooth DMS-FEM vis-à-vis the conventional FEM, a Mindlin-Reissner plate bending problem is numerically solved. Thanks to the higher order continuity in the functional approximant and the consequent removal of the jump terms in the weak form across inter-triangular boundaries, the numerical accuracy via the DMS-FEM approximation is observed to be higher than that corresponding to the conventional FEM. This advantage notwithstanding, evaluations of DMS-FEM based shape functions encounter singularity issues on the triangle vertices as well as over the element edges. This shortcoming is presently overcome through a new proposal that replaces the triangular B-splines by simplex splines, constructed over polygonal domains, as the kernel functions in the polynomial reproduction scheme. Following a detailed presentation of the issues related to its computational implementation, the new method is numerically explored with the results attesting to a higher attainable numerical accuracy in comparison with the DMS-FEM
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
Non-classical continuum models for solids using peridynamics and gauge theory
No full textThis thesis focuses on three areas of nonclassical continuum mechanics of solids. In the first part, we develop a few peridynamics (PD) models and solution strategies for discretized PD equations in the context of the mechanics of solids and structures. A strategy for removal of zero energy modes in PD correspondence models is presented in the second part of this thesis and a way of modelling solid continua with defects is outlined drawing upon analogies from gauge theory. In the last part, exploring conformal gauge symmetries in elastic solids, we show how several electromechanical and magnetomechanical phenomena can emerge solely from local conformal symmetry considerations of the Lagrangian.
We start with formulating a PD theory for thick linear elastic shells to model fracture and fragmentation in these structures. Effects of shear deformation and coupling between surface wryness with in-plane stress resultants and surface strain with moment resultants are considered. A few numerical simulations on thick plate, thick cylindrical shell and quasi-static fracture propagation on thick cylindrical shell are presented. Next, a reduced dimensional PD theory is developed for axisymmetric structures. Apart from reduction of computational burden, it eliminates stress singularity near the axis of symmetry due to the nonlocality in PD. We furnish a few numerical simulations on Taylor impact test with copper and steel specimens and compared them with experimental observations. After that, inelastic response of ceramics is investigated using phase field based PD theory to eliminate some of the limitations of Deshpande-Evans (DE) ceramics constitutive model. A macroscopic PD phase field based integro-differential damage evolution rule is used replacing DE crack growth law which removes possible mesh dependent solutions. We numerically solve a spherical cavity expansion problem using dimensional reduction and demonstrate evolution of damage and plastic fronts. Next, a general procedure for solving discretized PD continuum and atomic systems is presented using Hamilton-Jacobi theory and time-dependent perturbation techniques. Here, approximate analytical solutions of positions and momenta are obtained as functions of initial conditions and time with which separate analysis for each initial condition can be eliminated resulting in saving in computational time. A few simulations on linear discretized PD problems are furnished to demonstrate the efficacy of our method. We also solved graphene sheets under tension and shear loading using simplified Tersoff potential for given initial conditions. After that, flexoelectricity – an electromechanical coupling phenomenon is modeled in PD to investigate nanoscale fracture propagation in dielectrics. An analytical solution is presented for an infinite 3D body considering bond based case. Incorporating damage through phase field theory, we present a few numerical simulations on damage propagation in a flexoelectric plate.
In the second part of the thesis, we develop a sub-horizon based PD theory to eliminate zero-energy and other unphysical deformation modes from the correspondence framework of non-ordinary state based PD which requires only a minor alteration of the conventional PD correspondence equations and little additional computational demand. With this, one may study convergence of the solutions for a fixed horizon size with increasing particle density and obtain meaningful nonlocal solutions. We also outlined a way to model defective continua in this framework drawing upon analogies from a translation invariant gauge theory of solids.
In the last part, a conformal gauge theory of solids is laid out. We note that, if the pulled back metric of the current configuration (right Cauchy-Green tensor) is scaled with a constant, the volumetric part of Lagrange density changes but the isochoric part remains invariant. However, under a position dependent scaling, isochoric part loses its invariance. In order to restore invariance of the isochoric part, we introduce a 1-form compensating field and modify the definition of derivative to a gauge covariant one (minimal replacement). Noting close connection with Weyl geometry, we impose Weyl condition through the Lagrangian and for the evolution of 1-form, a minimal coupling is constructed. We obtain Euler-Lagrange equations from Hamilton’s principle and noticed a close similarity with flexoelectricity governing equations interpreting the exact part of 1-form with electric field and the anti-exact part with the polarization vector. Next, piezoelectricity and electrostriction phenomena are modeled through contraction of Weyl condition in various manners. We also modeled magnetomechanical phenomena applying Hodge decomposition theorem on the 1-form which leads to curl of a pseudo-vector field and a vector field. Identifying the pseudo-vector field with the magnetic potential and vector part with magnetization, flexomagnetism, piezomagnetism and magnetostriction phenomena are modeled
Space-Time Gauge Theories for Continuum Modelling of Viscoplasticity, Damage And Electro-Magneto-Mechanical Phenomena in Solids
No full textOver the years, sustained research efforts have aimed to understand the material behaviour
under a broad range of response regimes, especially from micromechanical or phenomenological
perspectives — via both continuum modeling and experiments conducted at different
scales. However, a review of the relevant literature has revealed that physics-based models
that can replicate experimental results are very few, and models depicting consistent coupling
phenomena observed in solids beyond elasticity are elusive. Symmetry-driven approaches to
continuum mechanics of solids typically have a unifying nature, combining the prediction
of diverse observed phenomena under a single umbrella. This thesis attempts to derive a
unified field theory for various physical phenomena in solids by exploring local symmetry,
which offers a framework to consistently arrive at the relations among polarization vector,
temperature, scalar potential, vector potential, and the electric and magnetic field for multiphysics
phenomena. Furthermore, this approach enables a consistent and robust coupling
among flow stress, strain rate, and other variables describing the kinematics of plasticity and
damage.
This thesis draws upon continuous and local symmetry-based principles of gauge theory
to arrive at continuum models for various electro-magneto-mechanical coupling phenomena
and inelastic responses involving plasticity and damage in solids. The specific local symmetries
we exploit in the process are conformal (scaling) and translational in space-time.
The work presented may thus be classed in two parts – one focusing on a unified continuum
description of multi-physics phenomena such as piezoelectricity, piezo-magnetism, coupled
thermoelasticity and flexoelectricity and the other on dissipative phenomena such as plasticity
and damage.
Under an inhomogeneous (local) action of the symmetry (gauge) group, invariance of the
energy density is lost. Minimal replacement is used to restore gauge invariance of the energy
density; this requires the definition of a gauge covariant operator in place of the ordinary
partial derivative. Minimal replacement introduces a non-trivial gauge compensating 1-form
field. The 1-form field is decomposed into an anti-exact part and the exact differential of a
scalar-valued function. The other essential ingredient of gauge theory is minimal couplin
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
A non-classical continuum approach to study the fragmentation of brittle solids
No full textIn this thesis, a non-local continuum approach coupled with the phase-field theory and Jones-Wilkins-Lee (JWL) equation of state (EOS) is proposed to model and simulate blast-induced fracture in brittle materials. Also, we study the evolution of field variables in the underground explosion of steel fiber reinforced concrete (SFRC). For numerical implementation, we have used a non-ordinary state-based peridynamic theory coupled with a diffusive phase-field damage approach. Moreover, JWL EOS from the family of isentropes has been formed, and finally, the constitutive relations have been arrived with the help of the JWL EOS. As the conventional equation of motion cannot capture the discontinuities in the damaged portion of the material, derivative-free integro-differential equations of motion have been used in line with the peridynamics approach to overcome the limitation of the conventional equation of motion. The motivation for using non-ordinary state-based (NOSB) peridynamics (PD) over the bond-stretch-based (BSB) or bond-energy-based (BEB) models comes from the fact that the applicability of BSB and BEB models are only limited to materials with Poisson's ratio 1/4.
We have introduced a dynamic failure mechanism due to blast-induced stress wave propagation in rock media, generated due to the pressure of a high-velocity gaseous detonator. Furthermore, an expansion of stress wave in the SFRC mass due to the underground explosion of highly pressurized detonators (Iregel 1175U) has been studied in this thesis. A program-burn algorithm inside the JWL EOS has been implemented to model rock fragmentation. A predictor-corrector explicit time integration scheme has been used to update the field variables at every time step. The phase-field damage can capture well the explosive-induced fracture in rock media and damage in the SFRC medium for the underground explosion. The current numerical approach suggests a versatile physics-oriented future model for this class of problems. The formulation proposed in the thesis has been validated against two numerical benchmark tests and has shown good predictive quality
Constitutive Theories for Polymers Using Non-Classical Continuum Mechanics
No full textThis thesis is on the development of a few constitutive theories characterising the thermo-mechanical response of polymers. In proposing the theories, some aspects of non-classical continuum mechanics are used. The first few constitutive theories predict the extrinsic and intrinsic mechanical behaviour of different types of polymers across a wide range of ambient temperature, loading rate, and/or solvent concentration. Varied response features characterised by strikingly contrasted timescales are observed as the conditions are altered. For example, for thermoplastics, hyperelastic response is observed for high temperatures or low loading rates. In contrast, the response is nearly viscoplastic at low temperatures or high loading rates. For a unified, seamless modelling approach to transitions across the timescale separated behavioural characteristics, a thermodynamic framework based on effective temperature is used. Separate theories have been constituted for thermoplastics, block-copolymers, and hydrogels, all within this thermodynamic setup. Here a thermodynamic system is split into configurational and kinetic-vibrational subsystems, which are weakly coupled by heat exchange. The configurational subsystems are characterized by states that evolve over larger time scales than the kinetic vibrational subsystem, which evolves with a time scale of atomic vibrations. One or more configurational subsystems are defined for describing submacroscopic phenomena involving multiple time scales or different relaxation rates. Depending on the relaxation processes, the configurational subsystems are chosen. While for thermorheologically simple thermoplastics, a single configurational subsystem is sufficient to capture relaxation, multiple configurational subsystems are necessary for thermorheologically complex polymers such as thermoplastic elastomers, especially to capture such complex phenomena as Mullin's effect. The rate of heat exchange between the configurational and kinetic vibrational subsystems is governed by the structural relaxation time. In the case of thermoplastics and block copolymers that do not contain a solvent, the structural relaxation time may be a function of the ambient temperature. However, for hydrogels, the relaxation time requires to be a function of the solvent concentration as well. All the three constitutive models are validated against experimental observations reported in the literature. They successfully capture the salient features of mechanical response across temperature or rate or solvent phase transition. Besides, the model for block-copolymers is shown to have features that enable it to be used as an effective design tool for the composition, given the requirement of an effective glass transition temperature. In addition to the viscoelastic theories, a brittle damage model for compressible elastomers is also developed. This theory is grounded in non-Euclidean geometry wherein the kinematic variables are derived considering the assumption that, upon damage, the material body no longer remains Euclidean but assumes the structure of a Riemannian manifold. Also, the energy of surface creation due to cracks is assumed to be a function of the Ricci curvature. The theory is used in several numerical simulations. The observations from some of these simulations are used to highlight the superior features of the geometry-driven approach vis-\'a-vis a second-order phase field theory involving a quadratic degradation function
A Smooth Finite Element Method Via Triangular B-Splines
Full text linkA triangular B-spline (DMS-spline)-based finite element method (TBS-FEM) is proposed along with possible enrichment through discontinuous Galerkin, continuous-discontinuous Galerkin finite element (CDGFE) and stabilization techniques. The developed schemes are also numerically explored, to a limited extent, for weak discretizations of a few second order partial differential equations (PDEs) of interest in solid mechanics. The presently employed functional approximation has both affine invariance and convex hull properties. In contrast to the Lagrangian basis functions used with the conventional finite element method, basis functions derived through n-th order triangular B-splines possess (n ≥ 1) global continuity. This is usually not possible with standard finite element formulations. Thus, though constructed within a mesh-based framework, the basis functions are globally smooth (even across the element boundaries). Since these globally smooth basis functions are used in modeling response, one can expect a reduction in the number of elements in the discretization which in turn reduces number of degrees of freedom and consequently the computational cost. In the present work that aims at laying out the basic foundation of the method, we consider only linear triangular B-splines. The resulting formulation thus provides only a continuous approximation functions for the targeted variables. This leads to a straightforward implementation without a digression into the issue of knot selection, whose resolution is required for implementing the method with higher order triangular B-splines. Since we consider only n = 1, the formulation also makes use of the discontinuous Galerkin method that weakly enforces the continuity of first derivatives through stabilizing terms on the interior boundaries. Stabilization enhances the numerical stability without sacrificing accuracy by suitably changing the weak formulation. Weighted residual terms are added to the variational equation, which involve a mesh-dependent stabilization parameter. The advantage of the resulting scheme over a more traditional mixed approach and least square finite element is that the introduction of additional unknowns and related difficulties can be avoided. For assessing the numerical performance of the method, we consider Navier’s equations of elasticity, especially the case of nearly-incompressible elasticity (i.e. as the limit of volumetric locking approaches). Limited comparisons with results via finite element techniques based on constant-strain triangles help bring out the advantages of the proposed scheme to an extent
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