We have observed a metallic solid (Al-14-at.%-Mn) with long-range orientational order, but with icosahedral point group symmetry, which is inconsistent with lattice translations. Its diffraction spots are as sharp as those of crystals but cannot be indexed to any Bravais lattice. The solid is metastable and forms from the melt by a first-order transition.

Metallic Phase with Long-Range Orientational Order and No Translational Symmetry

This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.

Spin glasses: Experimental facts, theoretical concepts, and open questions

A high-intensity electron gun based on field emission from a film of aligned carbon nanotubes has been made. The gun consists of a nanotube film with a 1-millimeter-diameter grid about 20 micrometers above it. Field-emission current densities of about 0.1 milliampere per square centimeter were observed for applied voltages as low as 200 volts, and current densities greater than 100 milliamperes per square centimeter have been realized at 700 volts. The gun is air-stable, easy and inexpensive to fabricate, and functions stably and reliably for long times (short-term fluctuations are on the order of 10 percent). The entire gun is only about 0.2 millimeter thick and can be produced with virtually no restrictions on its area, from less than 1 square millimeter to hundreds of square centimeters, making it suitable for flat panel display applications.

http://science.sciencemag.org/content/sci/270/5239/1179.full.pdf

A Carbon Nanotube Field-Emission Electron Source

Bond-orientational order in molecular-dynamics simulations of supercooled liquids and in models of metallic glasses is studied. Quadratic and third-order invariants formed from bond spherical harmonics allow quantitative measures of cluster symmetries in these systems. A state with short-range translational order, but extended correlations in the orientations of particle clusters, starts to develop about 10% below the equilibrium melting temperature in a supercooled Lennard-Jones liquid. The order is predominantly icosahedral, although there is also a cubic component which we attribute to the periodic boundary conditions. Results are obtained for liquids cooled in an icosahedral pair potential as well. Only a modest amount of orientational order appears in a relaxed Finney dense-random-packing model. In contrast, we find essentially perfect icosahedral bond correlations in alternative "amorphon" cluster models of glass structure.

Bond-orientational order in liquids and glasses

PLUMED 2: New feathers for an old bird

Three-dimensional bond orientational order is studied via computer simulations of 864 particles interacting through a Lennard-Jones pair potential. Long-range orientational fluctuations appear upon supercooling about ten percent below the equilibrium melting temperature. The fluctuations suggest a broken icosahedral symmetry with extended correlations in the orientations of local icosahedral packing units.

Icosahedral Bond Orientational Order in Supercooled Liquids

M-learning is a quite new, exciting and promising field. Papers on this domain are spread through several conference and workshops proceedings, so it is rather difficult to have a complete view of the field. This paper aims at helping, by reviewing the existing work, and classifying the research directions that try to answer the questions of how m-learning will help reaching the goals of a better learning, and how it will be different from the rest of e-learning. Finally, we try to foresee some directions for successful m-learning research.

Where is Mobile Learning Going

Having worked for a long time with video-lectures, we devised a new teaching model that makes use of the recorded videos to free the teacher from part of his work and allowing him to concentrate his efforts on a more effective and involving teaching strategy.

/pdf/using-video-lectures-to-make-teaching-more-interactive-43vrz38u3q.pdf

Using video lectures to make teaching more interactive

Recently the problem of the glass transition has been further complicated by the discovery of a phase which forms under conditions similar to those required by the formation of metallic glasses. This new phase (the “quasicrystal”) seems to be structurally intermediate between the glass and the crystal phase, being characterized by long-range orientational order and quasiperiodic translational order. The aim of this paper is to provide an introductory overview of this new field of quasicrystals. Experimental results and theoretical models are briefly presented.

Marco Ronchetti

Papers

Bond-orientational order in liquids and glasses

Icosahedral Bond Orientational Order in Supercooled Liquids

Where is Mobile Learning Going

Using video lectures to make teaching more interactive

An introductory overview