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

We recently proposed a new methodology called VOLARE for using video lectures. The methodology essentially consists in replacing frontal lectures given in class with video recordings (with synchronized slides) of the same, and using the available time in class with activities where the students can be more protagonist of their learning process. In the present paper we report an assessment in-itinere of the methodology, and we find it to be effective and well accepted by the students.

Assessing a new methodology for using video-lectures.

Support to e-learning activities has undergone a transition from simple web-based solutions to complete and integrated Learning Management Systems. Such transformation had an important, maybe unwanted and probably almost unnoticed side-effect: the closure to the outside world. We discuss why that happens and whether it is a desirable or necessary feature. We outline the consequences of such fact on e-learning in general, and on the dream of an open society in particular. Finally, we propose some solutions that allow keeping the necessary protection features while allowing for a more open sharing of learning resources.

Should Learning Management Systems be considered harmful? The vanishing dream of an open cultural exchange.

The ubiquitous nature of the Web has rendered a vast amount of information accessible on demand transforming itself to be the primary hub of personal and collective knowledge. Consequently it is becoming more challenging to manage such information effectively as we face the era of information overload, a.k.a. infobesity. The most popular way of managing web pages is bookmarking. Bookmarks, however, would serve little purpose if they cannot be easily organized or found for re-use. In this paper, we discuss the pros and cons of current folder and tag-based tools and highlight the role user context plays in information retrieval. Then we propose "MemoryLane", a bookmarking tool that offers context-specific tags to help organize and allows navigation of bookmarks by any context users remember.

Contextualizing bookmarks: an approach based on user context to improve organization and retrieval of bookmarks

Lectures On DEmand: the architecture of a system for delivering traditional lectures over the Web

The annotation of web pages, and the possibility to share the notes with others, seems to be a powerful tool. Although several tools already provide such possibility, they are not as widely popular as one would expect them to be. We try to explain this fact, and propose a novel architectural approach that is, in our view, particularly suited to some particular domain such as e-learning. We also present a tool that implements the proposed architecture.

/pdf/why-web-pages-annotation-tools-are-not-killer-applications-a-18os9579tw.pdf

Marco Ronchetti

Papers

Assessing a new methodology for using video-lectures.

Should Learning Management Systems be considered harmful? The vanishing dream of an open cultural exchange.

Contextualizing bookmarks: an approach based on user context to improve organization and retrieval of bookmarks

Lectures On DEmand: the architecture of a system for delivering traditional lectures over the Web

Why web pages annotation tools are not killer applications? A new approach to an old problem.