645 research outputs found
Fourier, Gauss, Fraunhofer, Porod and the Shape from Moments Problem
We show how the Fourier transform of a shape in any number of dimensions can
be simplified using Gauss's law and evaluated explicitly for polygons in two
dimensions, polyhedra three dimensions, etc. We also show how this combination
of Fourier and Gauss can be related to numerous classical problems in physics
and mathematics. Examples include Fraunhofer diffraction patterns, Porods law,
Hopfs Umlaufsatz, the isoperimetric inequality and Didos problem. We also use
this approach to provide an alternative derivation of Davis's extension of the
Motzkin-Schoenberg formula to polygons in the complex plane.Comment: 21 pages, no figure
Three-dimensional molecular dynamics simulations of void coalescence during dynamic fracture of ductile metals
Void coalescence and interaction in dynamic fracture of ductile metals have
been investigated using three-dimensional strain-controlled multi-million atom
molecular dynamics simulations of copper. The correlated growth of two voids
during the coalescence process leading to fracture is investigated, both in
terms of its onset and the ensuing dynamical interactions. Void interactions
are quantified through the rate of reduction of the distance between the voids,
through the correlated directional growth of the voids, and through correlated
shape evolution of the voids. The critical inter-void ligament distance marking
the onset of coalescence is shown to be approximately one void radius based on
the quantification measurements used, independent of the initial separation
distance between the voids and the strain-rate of the expansion of the system.
The interaction of the voids is not reflected in the volumetric asymptotic
growth rate of the voids, as demonstrated here. Finally, the practice of using
a single void and periodic boundary conditions to study coalescence is examined
critically and shown to produce results markedly different than the coalescence
of a pair of isolated voids.Comment: Accepted for publication in Physical Review
3D FEA modelling of laminated composites in bending and their failure mechanisms
keywords: 3D keywords: 3D keywords: 3D keywords: 3D keywords: 3DAbstract This paper developed three-dimensional (3D) Finite Element Analysis (FEA) to investigate the effect of fibre lay-up on the initiation of failure of laminated composites in bending. Tsai-Hill failure criterion was applied to identify the critical areas of failure in composite laminates. In accordance with the 3D FEA, unidirectional ([0]16), cross-ply ([0/90]4s) and angle-ply ([Âą45]4s) laminates made up of pre-preg Carbon Fibre Reinforced Plastics (CFRP) composites were manufactured and tested under three-point bending. The basic principles of Classical Laminate Theory (CLT) were extended to three-dimension, and the analytical solution was critically compared with the FEA results. The 3D FEA results revealed significant transverse normal stresses in the cross-ply laminate and in-plane shear stress in the angle-ply laminate near free edge regions which are overlooked by conventional laminate model. The microscopic images showed that these free edge effects were the main reason for stiffness reduction observed in the bending tests. The study illustrated the significant effects of fibre lay-up on the flexural failure mechanisms in composite laminates which lead to some suggestions to improve the design of composite laminates
Cellular buckling from mode interaction in I-beams under uniform bending
Beams made from thin-walled elements, whilst very efficient in terms of the
structural strength and stiffness to weight ratios, can be susceptible to
highly complex instability phenomena. A nonlinear analytical formulation based
on variational principles for the ubiquitous I-beam with thin flanges under
uniform bending is presented. The resulting system of differential and integral
equations are solved using numerical continuation techniques such that the
response far into the post-buckling range can be portrayed. The interaction
between global lateral-torsional buckling of the beam and local buckling of the
flange plate is found to oblige the buckling deformation to localize initially
at the beam midspan with subsequent cellular buckling (snaking) being predicted
theoretically for the first time. Solutions from the model compare very
favourably with a series of classic experiments and some newly conducted tests
which also exhibit the predicted sequence of localized followed by cellular
buckling.Comment: 23 pages, 15 figures and 6 table
Superconductors with Magnetic Impurities: Instantons and Sub-gap States
When subject to a weak magnetic impurity potential, the order parameter and
quasi-particle energy gap of a bulk singlet superconductor are suppressed.
According to the conventional mean-field theory of Abrikosov and Gor'kov, the
integrity of the energy gap is maintained up to a critical concentration of
magnetic impurities. In this paper, a field theoretic approach is developed to
critically analyze the validity of the mean field theory. Using the
supersymmetry technique we find a spatially homogeneous saddle-point that
reproduces the Abrikosov-Gor'kov theory, and identify instanton contributions
to the density of states that render the quasi-particle energy gap soft at any
non-zero magnetic impurity concentration. The sub-gap states are associated
with supersymmetry broken field configurations of the action. An analysis of
fluctuations around these configurations shows how the underlying supersymmetry
of the action is restored by zero modes. An estimate of the density of states
is given for all dimensionalities. To illustrate the universality of the
present scheme we apply the same method to study `gap fluctuations' in a normal
quantum dot coupled to a superconducting terminal. Using the same instanton
approach, we recover the universal result recently proposed by Vavilov et al.
Finally, we emphasize the universality of the present scheme for the
description of gap fluctuations in d-dimensional superconducting/normal
structures.Comment: 18 pages, 9 eps figure
Experimental Observations of Frictional Heating in Fiber-Reinforced Ceramics
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65540/1/j.1151-2916.1992.tb04162.x.pd
Human factors and missed solutions to Enigma design weaknesses
The German World War II Enigma suffered from design weaknesses that facilitated its large-scale decryption by the British throughout the war. The author shows that the main technical weaknesses (self-coding and reciprocal coding) could have been avoided using simple contemporary technology, and therefore the true cause of the weaknesses is not technological but must be sought elsewhere. Specifically, human factors issues resulted in the persistent failure to seek out more effective designs. Similar limitations seem to beset the literature on the period, which misunderstands the Enigma weaknesses and therefore inhibits broader thinking about design or realising the critical role of human factors engineering in cryptography
Legitimizing leisure experiences as emotional work: A post-humanist approach to gendered equine encounters
** From Crossref via Jisc Publications Router.
** Licence for VoR version of this article starting on 08-06-2018: http://onlinelibrary.wiley.com/termsAndConditions#vorThis is the peer reviewed version of the following article: Finkel, R. & Danby, P. (2018) Legitimizing leisure experiences as emotional work: A post-humanist approach to gendered equine encounters. Gender, Work & Organization, 26(3), pp. 377-391, which has been published in final form at https://doi.org/10.1111/gwao.12268. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Due to changes in lifestyle and work patterns, education and values associated with wellbeing, nonâhuman animals are now incorporated into a range of human experiences and environments. This research specifically focuses on humanâequine relations, examining blurred boundaries between therapeutic and recreational interspecies encounters. It is acknowledged that humanâequine relations are often gendered and this research focuses mainly on women's narratives. Viewed through the postâhumanist lens, horses now form kinship and companionship roles, particularly for women, where relations have become mutually emotionally dependent as a result of interspecies communication and embodied encounters. Research utilizes feminist postâhumanist and cultural politics of emotion frameworks associate with the coâagency on the coâagency of animals. Embedded in the concept of equiscapes, or postâhumanist leisure spaces, research methods employ qualitative approaches, including inâdepth interviews, participant diaries and multispecies ethnography. Findings reveal how women make considerable investments in equine activities, which develops mutual welfare and wellbeing. Yet, despite these benefits, emotional and other expenditures are justified in work discourses to legitimize them as valuable to themselves, their families and their communities.div_BaM26pub5397pub
Enhancement of wave damping within metamaterials having embedded negative stiffness inclusions
The wave dissipation properties of layered periodic structures are modelled by FE as well as analytical approaches. A linear oscillator incorporating a negative stiffness element and having exceptional energy dissipation properties is exhibited and incorporated within the modelled structures. The structural dynamic stability of both the oscillator and the modelled waveguides is discussed and ensured. The numerical results provide evidence of a drastic increase of several orders of magnitude for the damping ratio of the flexural waves propagating within the structures
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