2,399 research outputs found
A Newman-Penrose Calculator for Instanton Metrics
We present a Maple11+GRTensorII based symbolic calculator for instanton
metrics using Newman-Penrose formalism. Gravitational instantons are exact
solutions of Einstein's vacuum field equations with Euclidean signature. The
Newman-Penrose formalism, which supplies a toolbox for studying the exact
solutions of Einstein's field equations, was adopted to the instanton case and
our code translates it for the computational use.Comment: 13 pages. Matches the published version. The web page of the codes is
changed as https://github.com/tbirkandan/NPInstanto
Elastic moduli approximation of higher symmetry for the acoustical properties of an anisotropic material
The issue of how to define and determine an optimal acoustical fit to a set
of anisotropic elastic constants is addressed. The optimal moduli are defined
as those which minimize the mean squared difference in the acoustical tensors
between the given moduli and all possible moduli of a chosen higher material
symmetry. The solution is shown to be identical to minimizing a Euclidean
distance function, or equivalently, projecting the tensor of elastic stiffness
onto the appropriate symmetry. This has implications for how to best select
anisotropic constants to acoustically model complex materials.Comment: 20 page
Thermo-elasticity for anisotropic media in higher dimensions
In this note we develop tools to study the Cauchy problem for the system of
thermo-elasticity in higher dimensions. The theory is developed for general
homogeneous anisotropic media under non-degeneracy conditions.
For degenerate cases a method of treatment is sketched and for the cases of
cubic media and hexagonal media detailed studies are provided.Comment: 33 pages, 5 figure
2D and 3D cubic monocrystalline and polycrystalline materials: their stability and mechanical properties
We consider 2- and 3-dimensional cubic monocrystalline and polycrystalline
materials. Expressions for Young's and shear moduli and Poisson's ratio are
expressed in terms of eigenvalues of the stiffness tensor. Such a form is well
suited for studying properties of these mechanical characteristics on sides of
the stability triangles. For crystalline high-symmetry directions lines of
vanishing Poisson's ratio are found. These lines demarcate regions of the
stability triangle into areas of various auxeticity properties. The simplest
model of polycrystalline 2D and 3D cubic materials is considered. In
polycrystalline phases the region of complete auxetics is larger than for
monocrystalline materials.Comment: 9 pages, 3 figures, in proceedings of the Tenth International School
on Theoretical Physics, Symmetry and Structural Properties of Condensed
Matter, Myczkowce 200
Quasiharmonic elastic constants corrected for deviatoric thermal stresses
The quasiharmonic approximation (QHA), in its simplest form also called the
statically constrained (SC) QHA, has been shown to be a straightforward method
to compute thermoelastic properties of crystals. Recently we showed that for
non-cubic solids SC-QHA calculations develop deviatoric thermal stresses at
high temperatures. Relaxation of these stresses leads to a series of
corrections to the free energy that may be taken to any desired order, up to
self-consistency. Here we show how to correct the elastic constants obtained
using the SC-QHA. We exemplify the procedure by correcting to first order the
elastic constants of MgSiO-perovskite and MgSiO-post-perovskite, the
major phases of the Earth's lower mantle. We show that this first order
correction is quite satisfactory for obtaining the aggregated elastic averages
of these minerals and their velocities in the lower mantle. This type of
correction is also shown to be applicable to experimental measurements of
elastic constants in situations where deviatoric stresses can develop, such as
in diamond anvil cells.Comment: 4 figures, 1 table, submitted to Phys. Rev. B, July 200
A proposal of a UCN experiment to check an earthquake waves model
Elastic waves with transverse polarization inside incidence plane can create
longitudinal surface wave (LSW) after reflection from a free surface. At a
critical incidence angle this LSW accumulates energy density, which can be
orders of magnitude higher than energy density of the incident transverse wave.
A specially arranged vessel for storage of ultracold neutrons (UCN) can be used
to verify this effect.Comment: 8 pages 3 figures added a paragraph on vibrations along surface at
critical angl
Those wonderful elastic waves
We consider in a simple and general way elastic waves in isotropic and
anisotropic media, their polarization, speeds, reflection from interfaces with
mode conversion, and surface waves. Reflection of quasi transverse waves in
anisotropic media from a free surface is shown to be characterized by three
critical angles.Comment: 11 Figures 26 page
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“Tales and Adventures”: G.A. Henty’s Union Jack and the Competitive World of Publishing for Boys in the 1880s’
In the competitive publishing environment of the late nineteenth century, writers and magazines had to distinguish themselves carefully from potential rivals. This article examines how G.A. Henty’s quality boys’ weekly, Union Jack (1880-83), attempted to secure a niche in the juvenile publishing market by deliberately distinguishing itself from other papers as a literary, imperialist and “healthy” publication. The article explores the design and marketing techniques of the magazine, its status as a fiction paper, the high calibre of its contributors, and its aggressive rhetoric in targeting an exclusively masculine audience. It argues that while Union Jack was marketed as a niche publication, it eventually failed to distinguish itself sufficiently to survive in an extremely competitive environment
The Tolman VII solution, trapped null orbits and w - modes
The Tolman VII solution is an exact static spherically symmetric perfect
fluid solution of Einstein's equations that exhibits a surprisingly good
approximation to a neutron star. We show that this solution exhibits trapped
null orbits in a causal region even for a tenuity (total radius to mass ratio)
. In this region the dynamical part of the potential for axial w - modes
dominates over the centrifugal part.Comment: 5 pages revtex. 10 figures png. Further information at
http://grtensor.phy.queensu.ca/tolmanvii
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