58,693 research outputs found
The surface science of quasicrystals
The surfaces of quasicrystals have been extensively studied since about 1990. In this paper we review work on the structure and morphology of clean surfaces, and their electronic and phonon structure. We also describe progress in adsorption and epitaxy studies. The paper is illustrated throughout with examples from the literature. We offer some reflections on the wider impact of this body of work and anticipate areas for future development.
(Some figures in this article are in colour only in the electronic version
Geometric reasoning via internet crowdsourcing
The ability to interpret and reason about shapes is a peculiarly human capability that has proven difficult to reproduce algorithmically. So despite the fact that geometric modeling technology has made significant advances in the representation, display and modification of shapes, there have only been incremental advances in geometric reasoning. For example, although today's CAD systems can confidently identify isolated cylindrical holes, they struggle with more ambiguous tasks such as the identification of partial symmetries or similarities in arbitrary geometries. Even well defined problems such as 2D shape nesting or 3D packing generally resist elegant solution and rely instead on brute force explorations of a subset of the many possible solutions. Identifying economic ways to solving such problems would result in significant productivity gains across a wide range of industrial applications. The authors hypothesize that Internet Crowdsourcing might provide a pragmatic way of removing many geometric reasoning bottlenecks.This paper reports the results of experiments conducted with Amazon's mTurk site and designed to determine the feasibility of using Internet Crowdsourcing to carry out geometric reasoning tasks as well as establish some benchmark data for the quality, speed and costs of using this approach.After describing the general architecture and terminology of the mTurk Crowdsourcing system, the paper details the implementation and results of the following three investigations; 1) the identification of "Canonical" viewpoints for individual shapes, 2) the quantification of "similarity" relationships with-in collections of 3D models and 3) the efficient packing of 2D Strips into rectangular areas. The paper concludes with a discussion of the possibilities and limitations of the approach
Electron Doping of Cuprates via Interfaces with Manganites
The electron doping of undoped high- cuprates via the transfer of charge
from manganites (or other oxides) using heterostructure geometries is here
theoretically discussed. This possibility is mainly addressed via a detailed
analysis of photoemission and diffusion voltage experiments, which locate the
Fermi level of manganites above the bottom of the upper Hubbard band of some
cuprate parent compounds. A diagram with the relative location of Fermi levels
and gaps for several oxides is presented. The procedure discussed here is
generic, allowing for the qualitative prediction of the charge flow direction
at several oxide interfaces. The addition of electrons to antiferromagnetic Cu
oxides may lead to a superconducting state at the interface with minimal
quenched disorder. Model calculations using static and dynamical mean-field
theory, supplemented by a Poisson equation formalism to address charge
redistribution at the interface, support this view. The magnetic state of the
manganites could be antiferromagnetic or ferromagnetic. The former is better to
induce superconductivity than the latter, since the spin-polarized charge
transfer will be detrimental to singlet superconductivity. It is concluded that
in spite of the robust Hubbard gaps, the electron doping of undoped cuprates at
interfaces appears possible, and its realization may open an exciting area of
research in oxide heterostructures.Comment: 12 pages, 9 figure
Universality issues in surface kinetic roughening of thin solid films
Since publication of the main contributions on the theory of kinetic
roughening more than fifteen years ago, many works have been reported on
surface growth or erosion that employ the framework of dynamic scaling. This
interest was mainly due to the predicted existence of just a few universality
classes to describe the statistical properties of the morphology of growing
surfaces and interfaces that appear in a wide range of physical systems.
Nowadays, this prediction seems to be inaccurate. This situation has caused a
clear detriment of these studies in spite of the undeniable existence of
kinetic roughening in many different real systems, and without a clear
understanding of the reasons behind the mismatch between theoretical
expectations and experimental observations. In this chapter we aim to explore
existing problems and shortcomings of both the theoretical and experimental
approaches, focusing mainly on growth of thin solid films. Our analysis
suggests that the theoretical framework as yet is not complete, while more
systematic and consistent experiments need to be performed. Once these issues
are taken into account, a more consistent and useful theory of kinetic
roughening might develop.Comment: Review article to appear in ``Advances in Condensed Matter and
Statistical Mechanics", ed. E. Korutcheva and R. Cuerno. To be published by
Nova Science Publishers. 22 pages. 4 eps figure
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