Universality of vertex corrections to the electrical conductivity in models with elastically scattered electrons

We study quantum coherence of elastically scattered lattice fermions. We calculate vertex corrections to the electrical conductivity of electrons scattered either on thermally equilibrated or statically distributed random impurities. We demonstrate that the sign of the vertex corrections to the Drude conductivity is in both cases negative. Quantum coherence due to elastic back-scatterings always leads to diminution of diffusion.Comment: ReVTEX, 9 pages, 8 EPS figure

A formal descriptive theory of software-based creative practice

PhDCreative artefacts, from concert posters to architectural plans, are often created in entirely software-based workflows. Software tools can be easily made to record all user interactions, thereby capturing the observable part of creative practice. Although recording software-based creative practice is easy, analysing it is much harder. This is especially true if one wishes to analyse the cognitive process that underlies the recorded creative practice. There are currently no clear methods for the analysis of recorded creative practice, nor are there any suitable theories of the cognition underlying creative practice that can serve as the basis for the development of such methods. This thesis develops a formal descriptive theory of the cognition underlying software-based creative practice, with the aim of informing the development of analysis of recorded creative practice. The theory, called the Software-based Creative Practice Framework (SbCPF), fits with extended and predictive views of cognition. It characterises creative practice as a process of iteratively working from an abstract idea to a concrete artefact, whereby the required lowlevel detail to decide on action is imagined in flight, during practice. Furthermore, it argues that this iterative just-in-time imagination is necessary, because of the predictive nature of the mind. The SbCPF was developed through the use of a novel method for the analysis of creative practice displayed in video tutorials. This method is based on Grounded Theory, Rhetorical Structure Theory, Gesture Theory, Category Theory, and a novel taxonomy describing the relation of action to speech. The method is applied to produce a grounded theory of the creative practice of 3D modelling and animation with the Blender software. The grounded theory forms the basis of the aforementioned formal theory. Finally, the formal theory is further illustrated, evaluated, and explored by way of implementing a computational model.Queen Mary University of London, and the EPSRC Centre for Doctoral Training in Media and Arts Technology EP/G03723X/

A Semantic Web Annotation Tool for a Web-Based Audio Sequencer

Music and sound have a rich semantic structure which is so clear to the composer and the listener, but that remains mostly hidden to computing machinery. Nevertheless, in recent years, the introduction of software tools for music production have enabled new opportunities for migrating this knowledge from humans to machines. A new generation of these tools may exploit sound samples and semantic information coupling for the creation not only of a musical, but also of a "semantic" composition. In this paper we describe an ontology driven content annotation framework for a web-based audio editing tool. In a supervised approach, during the editing process, the graphical web interface allows the user to annotate any part of the composition with concepts from publicly available ontologies. As a test case, we developed a collaborative web-based audio sequencer that provides users with the functionality to remix the audio samples from the Freesound website and subsequently annotate them. The annotation tool can load any ontology and thus gives users the opportunity to augment the work with annotations on the structure of the composition, the musical materials, and the creator's reasoning and intentions. We believe this approach will provide several novel ways to make not only the final audio product, but also the creative process, first class citizens of the Semantic We

Self-dual Ginzburg-Landau vortices in a disk

We study the properties of the Ginzburg-Laundau model in the self-dual point for a two-dimensional finite system . By a numerical calculation we analyze the solutions of the Euler-Lagrange equations for a cylindrically symmetric ansatz. We also study the self-dual equations for this case. We find that the minimal energy configurations are not given by the Bogomol'nyi equations but by solutions to the Euler Lagrange ones. With a simple approximation scheme we reproduce the result of the numerical calculation.Comment: 8 pages, 4 figures, RevTex macro

Chiral boundary conditions for Quantum Hall systems

A quantum mesoscopic billiard can be viewed as a bounded electronic system due to some external confining potential. Since, in general, we do not have access to the exact expression of this potential, it is usually replaced by a set of boundary conditions. We discuss, in addition to the standard Dirichlet choice, the other possibilities of boundary conditions which might correspond to more complicated physical situations including the effects of many body interactions or of a strong magnetic field. The latter case is examined more in details using a new kind of chiral boundary conditions for which it is shown that in the Quantum Hall regime, bulk and edge characteristics can be described in a unified way.Comment: 16 pages, LaTeX, 2 figures, to be published in the Proceedings of the Minerva workshop on Mesoscopics, Fractals and Neural Networks, Phil. Mag. (1997

Точки роста в современной кардиологии и организация специализированной кардиологической помощи

Показаны приоритеты исследований в кардиологии и основные направления организации высокоспециализированной кардиологической помощи населению.The priorities of cardiology and main directions of organization of highly qualified cardiological aid are shown

Fluctuations of the local density of states probe localized surface plasmons on disordered metal films

We measure the statistical distribution of the local density of optical states (LDOS) on disordered semi-continuous metal films. We show that LDOS fluctuations exhibit a maximum in a regime where fractal clusters dominate the film surface. These large fluctuations are a signature of surface-plasmon localization on the nanometer scale

Coherent Backscattering of Ultracold Atoms

We report on the direct observation of coherent backscattering (CBS) of ultracold atoms, in a quasi-two-dimensional configuration. Launching atoms with a well-defined momentum in a laser speckle disordered potential, we follow the progressive build up of the momentum scattering pattern, consisting of a ring associated with multiple elastic scattering, and the CBS peak in the backward direction. Monitoring the depletion of the initial momentum component and the formation of the angular ring profile allows us to determine microscopic transport quantities. The time resolved evolution of the CBS peak is studied and is found a fair agreement with predictions, at long times as well as at short times. The observation of CBS can be considered a direct signature of coherence in quantum transport of particles in disordered media. It is responsible for the so called weak localization phenomenon, which is the precursor of Anderson localization.Comment: 5 pages, 4 figure

Vortex nucleation through edge states in finite Bose-Einstein condensates

We study the vortex nucleation in a finite Bose-Einstein condensate. Using a set of non-local and chiral boundary conditions to solve the Schr$\ddot{o}$dinger equation of non-interacting bosons in a rotating trap, we obtain a quantitative expression for the characteristic angular velocity for vortex nucleation in a condensate which is found to be 35% of the transverse harmonic trapping frequency.Comment: 24 pages, 8 figures. Both figures and the text have been revise