Impenetrable Boundaries Research Articles

An investigation of slip transmission during uniaxial tensile deformation of a coarse-grained copper via EBSD characterization and crystal plasticity modelling

This study explores the phenomenon of slip transmission across grain boundaries in coarse-grained copper. The associated effects on the deformation gradient are also investigated, using both experiment and simulation. An in-situ tensile test of a fully annealed copper specimen was conducted first using a scanning electron microscope (SEM). The deformation gradient and geometrically necessary dislocation (GND) maps at selected tensile strain values were obtained and characterized by electron backscatter diffraction (EBSD). In addition, a physically based strain gradient crystal plasticity finite element method model has been developed to simulate the early stage of tensile deformation behaviour of copper. In this model, slip transmission across the grain boundary is either allowed or blocked, depending on the alignment of adjacent grains. Slip transmission is allowed at grain boundaries between suitably aligned grains according to the Luster-Morris factor, residual Burgers vector is applied to consider the slip misalignment at GB region, and dislocation accumulation at grain boundaries is included following the Kocks-Mecking law. It was found that dislocation pile-up, lattice rotation and stress concentration were much higher near the impenetrable grain boundaries than at the penetrable ones. Due to the slip transmissions across grain boundaries, the stress and strain concentrations can be partially relaxed, and the slip transmission induced relaxation is associated with the number of active slip systems and shear strain on the best aligned slip systems. This study provides an effective strategy to investigate the early stage of plastic deformation, and a good agreement between experimental observations and simulation results has been achieved.

On the investigation of size effect in bcc α-iron under high strain rate and high temperature: Multiscale dislocations dynamics simulations

Size effect for BCC α-iron is investigated for micro-polycrystalline grains. MDDP simulations were performed to mimic impenetrable grain boundaries at sizes ranging between 0.5 μm and 2 μm at an applied rate of 105 s−1 at 300 K, 600 K and 900 K temperatures. For the three deformation temperatures, the Hall-Petch effect and the Orowan effect are reproduced. A comprehensive study of the microstructure evolution shows that screw dislocations control the plastic deformation of the polycrystalline materials via the activation of cross-slip mechanisms. Hardening is seen at low sizes for all temperatures at low strain range due to the dislocations pile up inside the grains prior to cross-slip activation. Once cross-slip is thermally activated, self-multiplication of dislocations is detected resulting in strain softening indicating that Orowan fit represented better the size effect in micro-polycrystalline BCC α-iron.

Canonical quantization on the half-line and in an interval based upon an alternative concept for the momentum in a space with boundaries

For a particle moving on a half-line or in an interval the operator $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{p}=\ensuremath{-}i{\ensuremath{\partial}}_{x}$ is not self-adjoint and thus does not qualify as the physical momentum. Consequently canonical quantization based on $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{p}$ fails. Based upon an alternative concept for a self-adjoint momentum operator ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{p}}_{R}$, we show that canonical quantization can indeed be implemented on the half-line and on an interval. Both the Hamiltonian $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{H}$ and the momentum operator ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{p}}_{R}$ are endowed with self-adjoint extension parameters that characterize the corresponding domains $D(\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{H})$ and $D({\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{p}}_{R})$ in the Hilbert space. When one replaces Poisson brackets by commutators, one obtains meaningful results only if the corresponding operator domains are properly taken into account. The alternative concept for the momentum is used to describe the results of momentum measurements of a quantum mechanical particle that is reflected at impenetrable boundaries, either at the end of the half-line or at the two ends of an interval.

Social Management: Epistemology Beyond Paradigms

Abstract The objective of this theoretical essay is to propose a new path for the epistemological debate in the field of social management that goes beyond the paradigmatic boundaries. Based on studies that deal with social management from different perspectives, a comparison was made between models based on the thesis of incommensurability by Thomas Kuhn – such as the Gibson Burrell and Gareth Morgan diagram of sociological paradigms – and an alternative to break away from the paradigmatic mentality: the circle of epistemic matrices. The study demonstrated that the logic of incommensurable paradigms is not adequate to guide social management studies due to its complexity and plurality. This was proven by the identification of multiple sociological approaches adopted in field studies, including hybrid approaches. In this sense, the circle of epistemic matrices proved to be more appropriate, because instead of impenetrable boundaries, it allows transit between the matrices and enables a dialogue between different sociological approaches.

Social Management: Epistemology Beyond Paradigms

Abstract The objective of this theoretical essay is to propose a new path for the epistemological debate in the field of social management that goes beyond the paradigmatic boundaries. Based on studies that deal with social management from different perspectives, a comparison was made between models based on the thesis of incommensurability by Thomas Kuhn – such as the Gibson Burrell and Gareth Morgan diagram of sociological paradigms – and an alternative to break away from the paradigmatic mentality: the circle of epistemic matrices. The study demonstrated that the logic of incommensurable paradigms is not adequate to guide social management studies due to its complexity and plurality. This was proven by the identification of multiple sociological approaches adopted in field studies, including hybrid approaches. In this sense, the circle of epistemic matrices proved to be more appropriate, because instead of impenetrable boundaries, it allows transit between the matrices and enables a dialogue between different sociological approaches.

Analysis of specific kinetic energy for the Birikh–Ostroumov shear diffusion flow

The article presents a new exact solution for stratified steady-state shear diffusion flows of a viscous fluid in an infinite horizontal layer with impenetrable boundaries. The announced exact solution belongs to the Ostroumov–Birikh family. Two components of the velocity vector depend on the vertical (transverse) coordinate. The concentration field and the pressure field are described by linear forms relative to horizontal (longitudinal) coordinates, with coefficients depending on the third coordinate. The components of the velocity field and the shear stress field are analyzed in detail, and the behavior of the specific kinetic energy is studied. It is shown that this exact solution is capable of describing the stratification of the shear stress field and the nonmonotonic behavior of flow velocity. The relation of flow velocities and shear stresses to the distribution of specific kinetic energy is revealed.

A call for the standardised reporting of factors affecting the exogenous loading of extracellular vesicles with therapeutic cargos.

Extracellular vesicles (EVs) are complex nanoparticles required for the intercellular transfer of diverse biological cargoes. Unlike synthetic nanoparticles, EVs may provide a natural platform for the enhanced targeting and functional transfer of therapeutics across complex and often impenetrable biological boundaries (e.g. the blood-brain barrier or the matrix of densely organised tumours). Consequently, there is considerable interest in utilising EVs as advanced drug delivery systems for the treatment of a range of challenging pathologies. Within the past decade, efforts have focused on providing standard minimal requirements for conducting basic EV research. However, no standard reporting framework has been established governing the therapeutic loading of EVs for drug delivery applications. The purpose of this review is to critically evaluate progress in the field, providing an initial set of guidelines that can be applied as a benchmark to enhance reproducibility and increase the likelihood of translational outcomes.

Lévy Flights in Steep Potential Wells: Langevin Modeling Versus Direct Response to Energy Landscapes

We investigate the non-Langevin relative of the L\'{e}vy-driven Langevin random system, under an assumption that both systems share a common (asymptotic, stationary, steady-state) target pdf. The relaxation to equilibrium in the fractional Langevin-Fokker-Planck scenario results from an impact of confining conservative force fields on the random motion. A non-Langevin alternative has a built-in direct response of jump intensities to energy (potential) landscapes in which the process takes place. We revisit the problem of L\'{e}vy flights in superharmonic potential wells, with a focus on the extremally steep well regime, and address the issue of its (spectral) "closeness" to the L\'{e}vy jump-type process confined in a finite enclosure with impenetrable (in particular reflecting) boundaries. The pertinent random system "in a box/interval" is expected to have a fractional Laplacian with suitable boundary conditions as a legitimate motion generator. The problem is, that in contrast to amply studied Dirichlet boundary problems, a concept of reflecting boundary conditions and the path-wise implementation of the pertinent random process in the vicinity of (or sharply at) reflecting boundaries are not unequivocally settled for L\'{e}vy processes. This ambiguity extends to fractional motion generators, for which nonlocal analogs of Neumann conditions are not associated with path-wise reflection scenarios at the boundary, respecting the impenetrability assumption.

Angular momentum transport by the GSF instability: non-linear simulations at the equator

We present an investigation into the nonlinear evolution of the Goldreich-Schubert-Fricke (GSF) instability using axisymmetric and three-dimensional simulations near the equator of a differentially rotating radiation zone. This instability may provide an important contribution to angular momentum transport in stars and planets. We adopt a local Boussinesq Cartesian shearing box model, which represents a small patch of a differentially rotating stellar radiation zone. Complementary simulations are also performed with stress-free, impenetrable boundaries in the local radial direction. The linear and nonlinear evolution of the equatorial axisymmetric instability is formally equivalent to the salt fingering instability. This is no longer the case in 3D, but we find that the instability behaves nonlinearly in a similar way to salt fingering. Axisymmetric simulations -- and those in 3D with short dimensions along the local azimuthal direction -- quickly develop strong jets along the rotation axis, which inhibit the instability and lead to predator-prey-like temporal dynamics. In 3D, the instability initially produces homogeneous turbulence and enhanced momentum transport, though in some cases jets form on a much longer timescale. We propose and validate numerically a simple theory for nonlinear saturation of the GSF instability and its resulting angular momentum transport. This theory is straightforward to implement in stellar evolution codes incorporating rotation. We estimate that the GSF instability could contribute towards explaining the missing angular momentum transport required in red giant stars, and play a role in the long-term evolution of the solar tachocline.

A mesoscale continuum approach of dislocation dynamics and the approximation by a Runge-Kutta discontinuous Galerkin method

We consider a mesoscale continuum model for the evolution of dislocation density in small-strain crystal plasticity. The model is based on the continuum dislocation dynamics theory and extended by a formulation for impenetrable grain boundaries. We introduce a fully coupled numerical method combining a conforming finite element approximation of elasto-plasticity with an implicit Runge-Kutta discontinuous Galerkin discretization of the dislocation microstructure which allows for 3d computations including multiple slip systems and dislocation interaction. In addition, a numerical representation of grain boundaries impenetrable to dislocation flux is considered within this framework. The formulation is applied to a tricrystal focusing on the analysis of dislocation stress interaction between different grains. The results are compared to discrete dislocation dynamics data from the literature.

Cultural capital and public relations

This article focuses on problems with correlating a value system to human activity. The author approaches analyzing this issue in terms of cultural capital. Subject to examination is the key component of social order, which can be described as “developing relations of the highest and lowest order”, as orientation towards oneself of one’s community in a social group or network. This work attempts to define what social capital consists of in terms of privileged and legitimized cultural practices. Presumably a culture of common values bears self-worth if it can be materialized within the boundaries of various types of relations. This allows for predicting trends of change in interpersonal relationships, by means of generalizing the results and conducting comparative analysis. Highlighted is the fact that such analysis makes sense if it were to be conducted in terms of cultural capital. As such, a special role is assigned to cultural competence. The ability and/or skills in practically using cultural achievements under certain conditions, with the goal of converting them into other types of capital later down the line, are especially valuable. Also noted is the fact that an understanding of cultural capital, as well as its transformations, is vital for analyzing actual practices which reflect the processes of the “achievements, approval or rejection, reproduction or transformation” dynamic. The author confirms the conclusion which had already been drawn by foreign scientists who are well-known in this field of knowledge, namely that there exists a certain pattern: either society brings forth specific channels for the flow of class cultures with their impenetrable boundaries, their peculiar and somewhat autonomous standards of purpose (of taste), or a dilution of class distinctions occurs. This inevitably has an effect on the decline of the role of cultural capital, and therefore on belonging to the elite. A hypothesis is brought forth about the need to define a person’s place within social networks, their affiliation with those who are typically considered to be members of “exclusive cultures”. Otherwise a connection to such networks implies the “lowest level of cultural competence” and an unfavorable place in the social hierarchy.

THE NOTION OF POWER OR WHAT IS LEFT OUT IN ROBERT GILPIN’S ‘TRICHOTOMOUS CATEGORISATION’: THEORETICAL AND PHILOSOPHICAL POSITIONS IN INTERNATIONAL POLITICAL ECONOMY AND THE GROUND FOR THEORETICAL MERGER

The article aims at contributing to philosophical understanding of issues in international political economy (IPE). The philosophical formations of different approaches to conducting research in IPE demonstrate that all its divisions are conditional, with permeable rather than impenetrable boundaries. To simplify introduction, some IPE textbooks follow Robert Gilpin’s “trichotomous categorisation”, or theoretical division of the field into realism, liberalism and Marxism/structuralism, which fails to clearly define cultural and historical roots, ignores alternative philosophical approaches to IPE, and denies the possibility of theoretical mergers. With the main focus on the notion of power, this article aims at exploring the possible ways to overcome this trichotomous theoretical division, making the attempt to find ground for theoretical merger. The paper concludes that the theoretical boundaries can be transcended by merging different concepts (a “horizontal” merger), or by approaching the same phenomena in different epistemological ways (a “vertical” merger).

Examining the intra-modal interference in an idealized oceanic wedge using scale-model experiments and acoustic propagation modeling

Scale-model tank experiments are beneficial because they offer a controlled environment in which to make underwater acoustic propagation measurements that can provide high-quality data for comparison with numerical models. This talk presents results from a 1:7500 scale model experiment for a wedge with a 10° slope fabricated from closed-cell polyurethane foam to investigate three-dimensional (3D) propagation effects. A 333 μs second long pulse allows the acoustic field to obtain a steady-state, continuous-wave signal. A computer controlled positioning system accurately moves the receiving hydrophone in 3D space to create a dense field of vertical line arrays, which are used to mode filter the measured time series. The single-mode fields show the classical interference pattern resulting from rays launched up and along the slope. The measured data are compared to an exact, closed-form solution for a point source in wedge with impenetrable boundaries. The finite size of the source and the departure from the ...

Transient sound radiation from an impulsively excited piezoelectric composite hollow sphere in a wedge-shaped acoustic domain

The exact 3D linear piezoelasticity theory, the linear acoustic wave equation, and the classical method of images are employed for the coupled acousto-elastodynamic time response analysis of an arbitrarily thick two-layered elasto-piezoelectric composite hollow sphere that is freely suspended in a perfect acoustic wedge with impenetrable (rigid/compliant) boundaries, while subjected to arbitrary (non-axisymmetric) non-stationary electro-mechanical excitations. Problem solution is attained by application of the method of eigen-function expansion, a revised form of translational addition theorems for modified spherical Bessel functions in Laplace transform domain, and Durbin’s numerical inversion algorithm with an advanced (modified Cesàro) convergence improvement scheme. Numerical simulations include selected radiated pressure time signatures of a water-submerged air-filled PZT4/aluminum spherical shell driven by a pair of external diametrical short duration mechanical pulses. The effects of sphere wall thickness, wedge opening (apex) angle (γ=π/6,π/4,π/2) and surface condition (hard or pressure-release) are examined. Also, some noteworthy features of the transient fluid/structure interaction are recognized through proper 2D visualizations of the internal and external sound fields. Lastly, accuracy of the proposed acousto-elastic model is confirmed with the help of a commercial FEA software in addition to comparison with the available data.

Three-dimensional underwater sound propagation: Proposed benchmark problems

A set of benchmark problems is suggested for testing the accuracy and efficiency of numerical solutions for three-dimensional (3D) underwater sound propagation. The physical causes of the 3D propagation conditions considered in this talk include out-of-plane reflections from medium boundaries and interfaces and horizontal refractions caused by changes of the index of refraction in the medium. Five different propagation scenarios are suggested: (1) sound propagation in a slope environment, (2) nonlinear internal wave waveguides, (3) submarine canyons, (4) seamounts, and (5) 3D waveguides with surface waves and/or seafloor sand waves. Both idealized and realistic environments will be considered. To allow theoretical closed-form solutions, the model environments will be simplified to create idealized problems, such as an impenetrable wedge/slope model and a semi-circular waveguide with impenetrable boundaries. For the problems which do not have closed-form solutions, different numerical solutions will be generated for comparisons. The numerical methods focused in this talk include 3D parabolic-equation, normal mode and finite element methods, and discussions on other numerical techniques, such as ray tracing, wavenumber integration, finite difference, and boundary element methods, will also be provided. [Work supported by the ONR.]

A Benchmark Model for Three-Dimensional Sound Propagation in an Ideal Wedge-Shaped Waveguide

A benchmark model is developed to compute the three-dimensional acoustic field excited by a harmonic point source in a homogeneous wedge-shaped waveguide with impenetrable boundaries. A derivation of the exact solution is presented based on Fourier synthesis, which reduces the three-dimensional ideal wedge problem to a sequence of two-dimensional line-source ideal wedge problems, to which the analytical solution is well established. The details of the numerical implementation of this solution are also provided. Our numerical results indicate that this model is efficient and capable of providing accurate three-dimensional acoustic fields for arbitrary receiver locations, and hence can serve as a benchmark model for sound propagation in a continental shelf environment.

Ghost-busting fashion: Symbolic boundaries and the politics of time in fashion journalism

This article examines the rhetorical tools that leading fashion journalists have used over the past 60 years when they seek to protect the idea of impenetrable temporal boundaries between contemporary fashionable dress and its history. Journalists have always taken a dim view of fashion practices that recycle historical styles in contemporary fashion design. Yet in the late 20th century they intensified this repudiation by the previously unseen use of negatively connoted temporal fashion words, like ‘retro’ and ‘nostalgia’. Journalists further combined such fashion words, declaring specific styles as passé or fashion-dead, with chronological designations to evoke the idea that such styles belong to an irretrievable chronological past. In doing so, they are ‘ghost-busting’ the presence of fashion history for the benefit of a cultural industry that is centred on a rhythmic transcendence of its own past in order to convince consumers of the apparent newness of fashion products.

Generalized Modal Expansion and Reduced Modal Representation of 3-D Electromagnetic Fields

A generalized modal expansion theory for investigating arbitrary 3-D bounded and unbounded electromagnetic fields is presented. When an inhomogeneity is enclosed with impenetrable boundaries, the field excited by arbitrary sources is expanded with a complete set of eigenmodes, which are classified into trapped modes and radiation modes. As the boundaries tend to infinity, trapped modes remain unchanged, while radiation modes form a continuum. To illustrate the theory, several real-life structures are investigated with a conformal finite-difference technique in the frequency domain. Perfectly matched layers (PMLs) are imposed at finite extent to emulate the unbounded problems. Numerical examples show that, only a few system modes are prominent in expanding an excited field, leading to a reduced modal picture which provides a quick guidance as well as useful physical insight for engineering design and optimization of electromagnetic devices and components.

Linking Micro‐ and Macroscopic Aspects of a Dislocation Based Continuum Model by Investigating the Dislocation Double Pileup

AbstractIn this contribution we discuss the problem of a dislocation double pileup at impenetrable boundaries which serves as a benchmark test to examine the continuum dislocation dynamics (CDD). We enhance a formulation for a numerical implementation and the mean‐field theory to account for the ‘long‐range’ stress field due to inhomogeneous plastic deformations by a suitable correction term. This allows us to handle the motion of dislocation densities at impenetrable boundaries and study the influence of dislocation interactions on a scale much smaller than the scale of the proposed mean‐field stress. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fast iterative solvers for boundary value problems on a local spherical region

Boundary value problems on local spherical regions arise naturally in geophysics and oceanography when scientists model a physical quantity on large scales. Meshless methods using radial basis functions provide a simple way to construct numerical solutions with high accuracy. However, the linear systems arising from these methods are usually ill-conditioned, which poses a challenge for iterative solvers. We construct preconditioners based on an additive Schwarz method to accelerate the solution process for solving boundary value problems on local spherical regions. References D. Crowdy. Point vortex motion on the surface of a sphere with impenetrable boundaries. Physics of Fluids, 18:036602 (2006). doi:10.1063/1.2183627. A. E. Gill. Atmosphere-Ocean Dynamics, International Geophysics Series Volume 30. Academic, New York (1982). R. Kidambi and P. K. Newton. Point vortex motion on a sphere with solid boundaries. Physics of Fluids, 12:581 (2000). doi:10.1063/1.870263. Q. T. Le Gia, I. H. Sloan, and T. Tran. Overlapping additive Schwarz preconditioners for elliptic PDEs on the unit sphere. Math. Comp., 78:79--101 (2009). doi:10.1090/S0025-5718-08-02150-9. C. Muller. Spherical Harmonics, Vol. 17 of Lecture Notes in Mathematics. Springer-Verlag, Berlin (1966). M. V. Nezlin. Some remarks on coherent structures out of chaos in planetary atmospheres and oceans. Chaos, 4:109--111 (1994). doi:10.1063/1.165997. T. Tran, Q. T. Le Gia, I. H. Sloan, and E. P. Stephan. Preconditioners for pseudodifferential equations on the sphere with radial basis functions. Numer. Math., 115:141--163 (2009). doi:10.1007/s00211-009-0269-8.