Continuous melting of a driven two-dimensional flux lattice with strong pins

The phase diagram of a driven two-dimensional vortex lattice in the presence of dense quasi-point pins is investigated. The transition from the crystal to the liquid is found continuous at intermediate inductions. The correlations in the pseudo random force that allow for an uncomplete unbinding of the dislocations is proposed as a key mechanism to account for the continuous transition.Comment: 7 pages, 8 figure

Transition to plastic motion as a critical phenomenon and anomalous interface layer of a 2D driven vortex lattice

The dynamic transition between the ordered flow and the plastic flow is studied for a two-dimensional driven vortex lattice, in the presence of sharp and dense pinning centers, from numerical simulations. For this system, which does not show smectic ordering, the lattice exhibits a first order transition from a crystal to a liquid, shortly followed by the dynamical transition to the plastic flow. The resistivity provides a critical order parameter for the latter, and critical exponents are determined in analogy with a percolation transition. At the boundary between a pinned region and an unpinned one, an anomalous layer is observed, where the vortices are more strongly pinned than in the bulk.Comment: 7 pages, 7 figure

A novel image reconstruction method applied to deep Hubble Space Telescope Images

We have developed a method for the linear reconstruction of an image from undersampled, dithered data, which has been used to create the distributed, combined Hubble Deep Field images -- the deepest optical images yet taken of the universe. The algorithm, known as Variable-Pixel Linear Reconstruction (or informally as "drizzling"), preserves photometry and resolution, can weight input images according to the statistical significance of each pixel, and removes the effects of geometric distortion both on image shape and photometry. In this paper, the algorithm and its implementation are described, and measurements of the photometric accuracy and image fidelity are presented. In addition, we describe the use of drizzling to combine dithered images in the presence of cosmic rays.Comment: Invited paper, to appear in Applications of Digital Image Processing XX, ed. A. Tescher, Proc. S.P.I.E. vol. 3164, in press; 6 pages, 4 included figures, SPIE LaTex style file include

The Way Forward: From Sanctions to Supports

The New York City Working Group on School Transformation brought together education practitioners, school reformers, policy-makers, advocates, and parent and student leaders to propose alternatives to the school closings policy of the New York City Department of Education (DOE). (See the list of Working Group members in Appendix 1.) The group was initiated by the New York City Coalition for Educational Justice and coordinated by the Annenberg Institute for School Reform following the fall 2011 conference Effective Alternatives to School Closings: Transforming Struggling Schools in New York City. This report presents the Working Group's conclusions about the limitations of school closings and a set of recommendations for systemic responses to the needs of struggling schools

Co-ordinating distributed knowledge: An investigation into the use of an organisational memory

This paper presents an ethnographically informed investigation into the use of an organisational memory, focusing in particular on how information was used in the performance of work. We argue that understanding how people make use of distributed knowledge is crucial to the design of an organisational memory. However, we take the perspective that an ‘organisational memory’ is not technology dependant, but is an emergent property of group interaction. In this sense, the technology does not form the organisational memory, but provides a novel means of augmenting the co-ordination of collaborative action. The study examines the generation, development and maintenance of knowledge repositories and archives. The knowledge and information captured in the organisational memory enabled the team members to establish a common understanding of the design and to gain an appreciation of the issues and concerns of the other disciplines. The study demonstrates why technology should not be thought of in isolation from its contexts of use, but also how designers can make use of the creative flexibility that people employ in their everyday activities. The findings of the study are therefore of direct relevance to both the design of knowledge archives and to the management of this information within organisations