773 research outputs found
Designing by decorating: The use of pictures in primary school
Introduction. This paper concerns the concept of information use. The aim of the study is to understand how information use, as an activity, is shaped when project-based methods are used in primary school. The particular focus here is information use which involves visual information resources. It relates to the overarching aim of a set of studies describing and illustrating how information literacies are enacted and socially shaped in Swedish primary schools. Method. 25 booklets, produced by children at a Swedish primary school when working with project-based assignments, were collected during an ethnographical study. Analysis. An analysis of the relationships between pictures and text in the 25 booklets was conducted. Results. The analysis suggests that the pictures in the booklets are subordinated to written text and their functions are decorative and illustrative. Pictures are seldom used for explaining or narrating. Conclusions. An underpinning idea of the study is to understand information activities as purposeful within the settings where they take place. Given earlier research indicating that project-based working methods tend to be focused on the reproduction of facts and the making of products rather than on contents, it could be argued that the children's use of pictures in this study is purposeful. However, if this use of pictures is a desirable outcome could be a matter of discussion. The findings may be relevant for developing teaching in the multimodal aspects of information use
Constructing the Desirable Reader in Swedish Contemporary: Literature Policy
This study contributes to a growing number of critical studies of reading that are seeking to understand how reading is constructed socially and politically. It addresses issues concerning why certain types of reading are deemed more appropriate than others in various contexts and historical eras. The aim of the study is to explore constructions of reading, reading promotion, and readers that can be identified in Swedish literature policy 2012-2013 in order to make explicit the implicit assumptions embedded in the politics of readinğ This is achieved through a discourse analysis of the Swedish Government Commission report on Literature from 2012 and the subsequent Government Bill from 2013. The analysis focuses on the construction of the 'problem' that reading is supposed to solve, the subject-position of the reader, and the knowledge practices that underpin the construction of the 'problem'. The analysis reveals that the main 'problem' is the changing reading habits of the Swedish population and the decline in the reading ability of Swedish children and youth. This is seen as a threat to several important societal values, such as children's learning and development, democracy, “the culture of reading”, Sweden's economic competitiveness, and the market for literature. Responsibility for the problem is placed on the school system, parents, and the use of computers and the Internet. The remedy is seen as the promotion of the right kind of literature. Furthermore, the analysis illustrates how the subject position of the appropriate reader is formed around the notion of the harmful non-reader. Similar dividing practices are constructed around youth/adult, pupil/teacher, child/parent, and son/father where the latter is expected to make the former a reader and thereby a desirable subject. The analysis also shows how two contradictory knowledge practices are joined together in the policy texts, where seemingly rational, objective, and empirical research is paired with humanistic Bildung values
Correlations and superfluidity of a one-dimensional Bose gas in a quasiperiodic potential
We consider the correlations and superfluid properties of a Bose gas in an
external potential. Using a Bogoliubov scheme, we obtain expressions for the
correlation function and the superfluid density in an arbitrary external
potential. These expressions are applied to a one-dimensional system at zero
temperature subject to a quasiperiodic modulation. The critical parameters for
the Bose glass transition are obtained using two different criteria and the
results are compared. The Lifshits glass is seen to be the limiting case for
vanishing interactions.Comment: Published in PRA, typos correcte
Information Research
Introduction. This study explored how various meanings are attributed to the term facts in Swedish schools and how this may shape conditions for students' learning. The understanding of information activities as social, communicative, and discursive, which motivates the study, is informed by a sociocultural perspective of learning and information interaction. Method. The study re-analyses empirical data from four previous research projects, where material was collected through various qualitative methods, mainly interviews, observations, and document analysis. The material involved 14 classes from year 2 to year 12.Analysis. The data were analysed thematically. In the material, 565 occurrences of facts are identified and categorised. Results. The analysis generated three themes. Firstly, facts were associated with specific genres or modalities. Secondly, facts were seen as distinguishable, external, and tangible. Thirdly, facts came across as having strong connections to neutrality and they were viewed as evidence. Conclusions. The analysis showed variation in how the study participants talked about facts. Despite the dominant associations, each theme displayed more complex meanings of the term, which indicates that fact cannot be equated to how the term has been used as an analytical term in previous research. The frequent use of the term facts can be understood as a result of the strong focus on students seeking and using certain types of information for writing school reports. The results show how important it is that information researchers adopt an open and explorative approach to the meaning of the language used in school activities that they study
Ansatz from Non-Linear Optics Applied to Trapped Bose-Einstein Condensates
A simple analytical ansatz, which has been used to describe the intensity
profile of the similariton laser (a laser with self-similar propagation of
ultrashort pulses), is used as a variational wave function to solve the
Gross-Pitaevskii equation for a wide range of interaction parameters. The
variational form interpolates between the noninteracting density profile and
the strongly interacting Thomas-Fermi profile smoothly. The simple form of the
ansatz is modified for both cylindrically symmetric and completely anisotropic
harmonic traps. The resulting ground-state density profile and energy are in
very good agreement with both the analytical solutions in the limiting cases of
interaction and the numerical solutions in the intermediate regime.Comment: 4 pages, 3 figures, published versio
Superfluid-Insulator transition of ultracold atoms in an optical lattice in the presence of a synthetic magnetic field
We study the Mott insulator-superfluid transition of ultracold bosonic atoms
in a two-dimensional square optical lattice in the presence of a synthetic
magnetic field with p/q (p and q being co-prime integers) flux quanta passing
through each lattice plaquette. We show that on approach to the transition from
the Mott side, the momentum distribution of the bosons exhibits q precursor
peaks within the first magnetic Brillouin zone. We also provide an effective
theory for the transition and show that it involves q interacting boson fields.
We construct, from a mean-field analysis of this effective theory, the
superfluid ground states near the transition and compute, for q=2,3, both the
gapped and the gapless collective modes of these states. We suggest experiments
to test our theory.Comment: 4 pages, 4 figs; v
Relating two standard notions of secrecy
Two styles of definitions are usually considered to express that a security
protocol preserves the confidentiality of a data s. Reachability-based secrecy
means that s should never be disclosed while equivalence-based secrecy states
that two executions of a protocol with distinct instances for s should be
indistinguishable to an attacker. Although the second formulation ensures a
higher level of security and is closer to cryptographic notions of secrecy,
decidability results and automatic tools have mainly focused on the first
definition so far.
This paper initiates a systematic investigation of the situations where
syntactic secrecy entails strong secrecy. We show that in the passive case,
reachability-based secrecy actually implies equivalence-based secrecy for
digital signatures, symmetric and asymmetric encryption provided that the
primitives are probabilistic. For active adversaries, we provide sufficient
(and rather tight) conditions on the protocol for this implication to hold.Comment: 29 pages, published in LMC
Vortices in Bose-Einstein-Condensed Atomic Clouds
The properties of vortex states in a Bose-Einstein condensed cloud of atoms
are considered at zero temperature. Using both analytical and numerical methods
we solve the time-dependent Gross-Pitaevskii equation for the case when a cloud
of atoms containing a vortex is released from a trap. In two dimensions we find
the simple result that the time dependence of the cloud radius is given by
, where is the trap frequency. We calculate and
compare the expansion of the vortex core and the cloud radius for different
numbers of particles and interaction strengths, in both two and three
dimensions, and discuss the circumstances under which vortex states may be
observed experimentally.Comment: Revtex, 11 pages including 5 eps figures, submitted to Phys. Rev. A;
new reference added, remark added in Sec. IIIB, axis label added in Fig.
Betatron emission as a diagnostic for injection and acceleration mechanisms in laser-plasma accelerators
Betatron x-ray emission in laser-plasma accelerators is a promising compact
source that may be an alternative to conventional x-ray sources, based on large
scale machines. In addition to its potential as a source, precise measurements
of betatron emission can reveal crucial information about relativistic
laser-plasma interaction. We show that the emission length and the position of
the x-ray emission can be obtained by placing an aperture mask close to the
source, and by measuring the beam profile of the betatron x-ray radiation far
from the aperture mask. The position of the x-ray emission gives information on
plasma wave breaking and hence on the laser non-linear propagation. Moreover,
the measurement of the longitudinal extension helps one to determine whether
the acceleration is limited by pump depletion or dephasing effects. In the case
of multiple injections, it is used to retrieve unambiguously the position in
the plasma of each injection. This technique is also used to study how, in a
capillary discharge, the variations of the delay between the discharge and the
laser pulse affect the interaction. The study reveals that, for a delay
appropriate for laser guiding, the x-ray emission only occurs in the second
half of the capillary: no electrons are injected and accelerated in the first
half.Comment: 8 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1104.245
Phase diagram of quantized vortices in a trapped Bose-Einstein condensed gas
We investigate the thermodynamic stability of quantized vortices in a dilute
Bose gas confined by a rotating harmonic trap at finite temperature.
Interatomic forces play a crucial role in characterizing the resulting phase
diagram, especially in the large Thomas-Fermi regime. We show that the
critical temperature for the creation of stable vortices exhibits a maximum as
a function of the frequency of the rotating trap and that the corresponding
transition is associated with a discontinuity in the number of atoms in the
condensate. Possible strategies for approaching the vortical region are
discussed.Comment: Revtex, 4 pages, 2 figure
- …