1,089 research outputs found
Learning Design: reflections on a snapshot of the current landscape
The mounting wealth of open and readily available information and the swift evolution of social, mobile and creative technologies warrant a re-conceptualisation of the role of educators: from providers of knowledge to designers of learning. This need is being addressed by a growing trend of research in Learning Design. Responding to this trend, the Art and Science of Learning Design workshop brought together leading voices in the field and provided a forum for discussing its key issues. It focused on three thematic axes: practices and methods, tools and resources, and theoretical frameworks. This paper reviews some definitions of Learning Design and then summarises the main contributions to the workshop. Drawing upon these, we identify three key challenges for Learning Design that suggest directions for future research
Incomplete approach to homoclinicity in a model with bent-slow manifold geometry
The dynamics of a model, originally proposed for a type of instability in
plastic flow, has been investigated in detail. The bifurcation portrait of the
system in two physically relevant parameters exhibits a rich variety of
dynamical behaviour, including period bubbling and period adding or Farey
sequences. The complex bifurcation sequences, characterized by Mixed Mode
Oscillations, exhibit partial features of Shilnikov and Gavrilov-Shilnikov
scenario. Utilizing the fact that the model has disparate time scales of
dynamics, we explain the origin of the relaxation oscillations using the
geometrical structure of the bent-slow manifold. Based on a local analysis, we
calculate the maximum number of small amplitude oscillations, , in the
periodic orbit of type, for a given value of the control parameter. This
further leads to a scaling relation for the small amplitude oscillations. The
incomplete approach to homoclinicity is shown to be a result of the finite rate
of `softening' of the eigen values of the saddle focus fixed point. The latter
is a consequence of the physically relevant constraint of the system which
translates into the occurrence of back-to-back Hopf bifurcation.Comment: 14 Figures(Postscript); To Appear in Physica D : Nonlinear Phenomen
Aging dynamics of ferromagnetic and reentrant spin glass phases in stage-2 CuCCl graphite intercalation compound
Aging dynamics of a reentrant ferromagnet stage-2
CuCoCl graphite intercalation compound has been studied
using DC magnetic susceptibility. This compound undergoes successive
transitions at the transition temperatures ( K) and
( K). The relaxation rate exhibits a
characteristic peak at below . The peak time as a
function of temperature shows a local maximum around 5.5 K, reflecting a
frustrated nature of the ferromagnetic phase. It drastically increases with
decreasing temperature below . The spin configuration imprinted at the
stop and wait process at a stop temperature () during the
field-cooled aging protocol, becomes frozen on further cooling. On reheating,
the memory of the aging at is retrieved as an anomaly of the
thermoremnant magnetization at . These results indicate the occurrence
of the aging phenomena in the ferromagnetic phase () as well
as in the reentrant spin glass phase ().Comment: 9 pages, 9 figures; submitted to Physical Review
Toward an Integrated Competence-based System Supporting Lifelong Learning and Employability: Concepts, Model, and Challenges
Miao, Y., Van der Klink, M., Boon, J., Sloep, P. B., & Koper, R. (2009). Toward an Integrated Competence-based System Supporting Lifelong Learning and Employability: Concepts, Model, and Challenges. In M. Spaniol, Q. Li, R. Klamma & R. W. H. Lau (Eds.), Proceedings of the 8th International Conference Advances in Web Based Learning - ICWL 2009 (pp. 265-276). August, 19-21, 2009, Aachen, Germany. Lecture Notes in Computer Science 5686; Berlin, Heidelberg: Springer-Verlag.Efficient and effective lifelong learning requires that people can make informed decisions about their continuous personal development in the different stages of their lives. In this paper we state that lifelong learners need to be characterized as decision-makers. In order to improve the quality of their decisions we propose the development of an integrated lifelong learning and employment support system, which traces learners’ competence development and provides a decision support environment. An abstract conceptual model has been developed and the main design ideas have been documented using Z notation. Moreover, we analyzed the main technical challenges for the realization of the target system: competence information fusion, decision analysis models, spatial indexing structures and browsing structures and visualization of competence related information objects.The work on this publication has been sponsored by the TENCompetence Integrated Project that is funded by the European Commission's 6th Framework Programme, priority IST/Technology Enhanced Learning. Contract 027087 [http://www.tencompetence.org
Dynamics of diluted magnetic semiconductors from atomistic spin dynamics simulations: Mn doped GaAs as a case study
The dynamical behavior of the magnetism of diluted magnetic semiconductors
(DMS) has been investigated by means of atomistic spin dynamics simulations.
The conclusions drawn from the study are argued to be general for DMS systems
in the low concentration limit, although all simulations are done for 5%
Mn-doped GaAs with various concentrations of As antisite defects. The
magnetization curve, , and the Curie temperature have been
calculated, and are found to be in good correspondence to results from Monte
Carlo simulations and experiments. Furthermore, equilibrium and non-equilibrium
behavior of the magnetic pair correlation function have been extracted. The
dynamics of DMS systems reveals a substantial short ranged magnetic order even
at temperatures at or above the ordering temperature, with a non-vanishing pair
correlation function extending up to several atomic shells. For the high As
antisite concentrations the simulations show a short ranged anti-ferromagnetic
coupling, and a weakened long ranged ferromagnetic coupling. For sufficiently
large concentrations we do not observe any long ranged ferromagnetic
correlation. A typical dynamical response shows that starting from a random
orientation of moments, the spin-correlation develops very fast ( 1ps)
extending up to 15 atomic shells. Above 10 ps in the simulations, the
pair correlation is observed to extend over some 40 atomic shells. The
autocorrelation function has been calculated and compared with ferromagnets
like bcc Fe and spin-glass materials. We find no evidence in our simulations
for a spin-glass behaviour, for any concentration of As antisites. Instead the
magnetic response is better described as slow dynamics, at least when compared
to that of a regular ferromagnet like bcc Fe.Comment: 24 pages, 15 figure
Determination of the basic timescale in kinetic Monte Carlo simulations by comparison with cyclic-voltammetry experiments
While kinetic Monte Carlo simulations can provide long-time simulations of
the dynamics of physical and chemical systems, it is not yet possible in
general to identify the inverse Monte Carlo attempt frequency with a physical
timescale. Here we demonstrate such an identification by comparing simulations
with experimental data. Using a dynamic lattice-gas model for the
electrosorption of Br on Ag(100), we measure the scan-rate dependence of the
separation between positive-and negative-going peaks in cyclic-voltammetry (CV)
and compare simulated and experimental peak separations. By adjusting the Monte
Carlo attempt frequency, good agreement between simulated and experimental peak
separations is achieved. It is also found that the uniqueness of such a
determination is dependent on the relative values of the adsorption/desorption
and diffusion free-energy barriers.Comment: Accepted for publication in Surface Science Letters,8 pages, 4
figure
Long Tailed Maps as a Representation of Mixed Mode Oscillatory Systems
Mixed mode oscillatory (MMO) systems are known to exhibit some generic
features such as the reversal of period doubling sequences and crossover to
period adding sequences as bifurcation parameters are varied. In addition, they
exhibit a nearly one dimensional unimodal Poincare map with a longtail. We
recover these common features from a general class of two parameter family of
one dimensional maps with a unique critical point that satisfy a few general
constraints that determine the nature of the map. We derive scaling laws that
determine the parameter widths of the dominant windows of periodic orbits
sandwiched between two successive states of RL^k sequence. An example of a two
parameter map with a unique critical point is introduced to verify the
analytical results.Comment: 13 pages and 8 figure
Aging dynamics in reentrant ferromagnet: CuCoCl-FeCl graphite bi-intercalation compound
Aging dynamics of a reentrant ferromagnet
CuCoCl-FeCl graphite bi-intercalation compound has
been studied using AC and DC magnetic susceptibility. This compound undergoes
successive transitions at the transition temperatures ( K) and
( K). The relaxation rate exhibits a characteristic
peak at close to a wait time below , indicating that
the aging phenomena occur in both the reentrant spin glass (RSG) phase below
and the ferromagnetic (FM) phase between and . The
relaxation rate () in the FM phase
exhibits two peaks around and a time much shorter than under
the positive -shift aging, indicating a partial rejuvenation of domains. The
aging state in the FM phase is fragile against a weak magnetic-field
perturbation. The time () dependence of around is well approximated by a stretched exponential relaxation:
. The exponent depends on
, , and . The relaxation time () exhibits a
local maximum around 5 K, reflecting a chaotic nature of the FM phase. It
drastically increases with decreasing temperature below .Comment: 16 pages,16 figures, submitted to Physical Review
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