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

With the advances in mobile technologies is now possible to support learners and teachers activities on the move. We analyzed the functionalities that should be provided by a general mobile learning platform and identified a problem that is weakly studied, namely support for offline usage of learning material, called hoarding. Hoarding can use some techniques used by caching and pre-fetching schemas, but in most cases the goal of the last two is to reduce latency time, bandwidth consumption and/or servers workload, while in hoarding the aim is to reduce the size of the hoarding set, keeping the accuracy very high. We want to study the parameters that could help hoarding algorithm to face the peculiarity in m-learning scenario and our final goal is to provide an efficient strategy, taking into account additional parameters, extracted automatically by the system.

/pdf/hoarding-content-in-m-learning-context-3fv9kh5tf1.pdf

Hoarding content in m-learning context

Proper reuse of learning objects depends both on the amount and quality of attached semantic metadata such as "learning objective"', "related concept", etc. Manually expressing such metadata is a time consuming and expensive task.. Here we present an approach based on a probabilistic model, which through the automatic classification of learning resources on a given taxonomic organization of the knowledge, allows to associate ontological metadata to the learning resources.

Automatic Generation of Metadata for Learning Objects

Mobile Learning is rather new, but rapidly growing research domain. This paper presents part of a study that we have performed to investigate the university students' readiness to utilize mobile learning. About 600 Italian and 200 Bulgarian students participated in an online questionnaire in June 2005. They were asked about the availability of devices, about their willingness to use m-learning, etc. We studied in depth also similar studies conducted in other countries and confronted the outcomes. The analyses show that the students are mainly positive to the prospective of accessing mobile learning. The attitude differs, depending mainly of their previous experience and current habits. Sometimes gender differences can be noticed and the availability of devices and students' income influence the student's attitude. Things like nationality or studied subject does not seem to influence the future of mobile learning.

http://www.wseas.us/e-library/conferences/2006venice/papers/539-476.pdf

Marco Ronchetti

Papers

Hoarding content in m-learning context

Automatic Generation of Metadata for Learning Objects

Determining Students' Readiness for Mobile Learning

Mobile ELDIT: Transition from an e-Learning to an m-Learning System

Monte Carlo calculation of the concentration of lattice vacancies by the method of overlapping distributions