Construction of a giant vortex state in a trapped Fermi system

A superfluid atomic Fermi system may support a giant vortex if the trapping potential is anharmonic. In such a potential, the single-particle spectrum has a positive curvature as a function of angular momentum. A tractable model is put up in which the lowest and next lowest Landau levels are occupied. Different parameter regimes are identified and characterized. Due to the dependence of the interaction on angular momentum quantum number, the Cooper pairing is at its strongest not only close to the Fermi level, but also close to the energy minimum. It is shown that the gas is superfluid in the interior of the toroidal density distribution and normal in the outer regions. Furthermore, the pairing may give rise to a localized density depression in configuration space.Comment: 12 pages, 14 figure file

Turbulence in Binary Bose-Einstein Condensates Generated by Highly Non-Linear Rayleigh-Taylor and Kelvin-Helmholtz Instabilities

Quantum turbulence (QT) generated by the Rayleigh-Taylor instability in binary immiscible ultracold 87Rb atoms at zero temperature is studied theoretically. We show that the quantum vortex tangle is qualitatively different from previously considered superfluids, which reveals deep relations between QT and classical turbulence. The present QT may be generated at arbitrarily small Mach numbers, which is a unique property not found in previously studied superfluids. By numerical solution of the coupled Gross-Pitaevskii equations we find that the Kolmogorov scaling law holds for the incompressible kinetic energy. We demonstrate that the phenomenon may be observed in the laboratory.Comment: Revised version. 7 pages, 8 figure

Stability of the solutions of the Gross-Pitaevskii equation

We examine the static and dynamic stability of the solutions of the Gross-Pitaevskii equation and demonstrate the intimate connection between them. All salient features related to dynamic stability are reflected systematically in static properties. We find, for example, the obvious result that static stability always implies dynamic stability and present a simple explanation of the fact that dynamic stability can exist even in the presence of static instability.Comment: 7 pages, 1 figur

Phases of a rotating Bose-Einstein condensate with anharmonic confinement

We examine an effectively repulsive Bose-Einstein condensate of atoms that rotates in a quadratic-plus-quartic potential. With use of a variational method we identify the three possible phases of the system (multiple quantization, single quantization, and a mixed phase) as a function of the rotational frequency of the gas and of the coupling constant. The derived phase diagram is shown to be universal and the continuous transitions to be exact in the limit of weak coupling and small anharmonicity. The variational results are found to be consistent with numerical solutions of the Gross-Pitaevskii equation.Comment: 8 pages, 6 figure

Collecting and compiling: The activity of seeking pictures in primary school

Purpose: The aim of this study is to further understanding of the situated activity of seeking pictures. It relates to an ongoing discussion on how multimodal information literacies are enacted in different social practices. Design/methodology/approach: In order to understand the characteristics of the communication and interactions in the activity of seeking pictures, video recordings from an ethnographic study of primary school children working with problem-centred assignments have been analysed. Findings: The analysis reveals how the activity of seeking pictures is shaped by the assumption that pictures are different from facts and information; pictures are seen primarily as having decorative functions. The activity is also characterised by playful, yet efficient cooperation between the children; they make the activity meaningful by transforming it into a play and game activity where pictures become important as physical objects, but not as a semiotic means of learning. Research limitations/implications: The study is limited to the activity of seeking pictures in a specific primary school; however, it shows how modes other than textual modes can be included in the study of information activities. Practical implications: The study reveals the need for developing methods for enhancing children's possibilities to critically examine and learn from visual material, such as pictures. Originality/value: Research on information seeking and information literacies rarely focus on multimodal aspects of information activities or the seeking of pictures outside special collections, despite the increased significance of visual material in the contemporary media landscape. This paper shows how studies of multimodal information activities can be designed

Information and experience: Audiovisual observations of reading activities in Swedish comprehensive school classrooms 1967–1969

This study investigates reading activities in Swedish primary school classrooms during the late 1960s. Sound and video recordings of 223 Swedish lessons held between 1967 and 1969 are used to analyse the activity of reading as taught and performed. The results indicate that the practice of informational reading, often based on finding predetermined, explicit "facts" in textbooks through individual, silent reading, was common. The practice of experiential reading, based on fiction, imagination and the joy of reading, was not only less common, but also often compromised by instrumental concerns. In the national curriculum of the time, the practice of informational reading was related to study skills and was intended to prepare all pupils for higher-level education. While often appearing over-proportioned, superficial and fragmented, these reading practices were still intentional objects of learning and teaching, and were grounded in the democratic and egalitarian ideals of Swedish post-war educational policy

Reading as dialogical document work: possibilities for Library and Information Science

Purpose – The purpose of this paper is to introduce a dialogically based theory of documentary practices and document work as a promising framework for studying activities that are often conceptualised as information behaviour or information practices within Library and Information Science (LIS). Design/methodology/approach – An empirical example – a lesson on how to read railway timetables – is presented. The lesson stems from a research project including 223 Swedish lessons recorded in Swedish primary schools 1967-1969. It is argued that this lesson, as many empirical situations within LIS research, can fruitfully be regarded as documentary practices which include document work such as reading, rather than instances of information behaviour. Findings – It is found that the theoretical perspective of dialogism could contribute to the theory development within LIS, and function as a bridge between different subfields such as reading studies and documentary practices. Research limitations/implications – The framework is yet to be applied on a larger scale. This would require a willingness to go beyond the entrenched idea of information as the core theoretical concept and empirical object of study within LIS. Social implications – The theoretical framework offers a view of the relations between individuals, documents, and social contexts, through which it is possible to explore the social significance of core LIS concerns such as reading, literacy, and document work. Originality/value – The theoretical framework offers an alternative to the monologist, information-based theories and models of people’s behaviours and practices prevalent in LIS

The Surface of a Bose-Einstein Condensed Atomic Cloud

We investigate the structure and collective modes of a planar surface of a trapped Bose-Einstein condensed gas at zero temperature. In the long-wavelength limit we find a mode similar to the gravity wave on the surface of a fluid with the frequency $\omega$ and the wavenumber $q$ related by $\omega^2=Fq/m$. Here $F$ is the force due to the confining potential at the surface and $m$ is the particle mass. At shorter wavelengths we use a variational approach and find corrections to $\omega^2$ of order $q^4 \ln{q}$. We demonstrate the usefulness of the concept of an effective surface tension for describing both static and dynamic properties of condensed atomic clouds.Comment: 8 pages, REVTEX, submitted to Phys. Rev.