425 research outputs found
JointZone: users' view of an adaptive online learning resource for rheumatology
This paper describes an online learning resource for rheumatology that was designed for a wide constituency of users including primarily undergraduate medical students and health professionals. Although the online resources afford an informal learning environment, the site was pedagogically designed to comply with the general recommendations of the Standing Committee on Training and Education of EULAR (European League Against Rheumatism) for a rheumatology core curriculum. Any Internet user may freely browse the site content with optional registration providing access to adaptive features that personalize the user’s view, for example, providing a reading history and targeted support based on scores from completed case studies. The site has now been available since early 2003, and an online survey of site registrants indicates that well structured pedagogical materials that reflect a learners’ dominant ‘community of practice’ appear to be a successful aid to informal learning
The Application and Evaluation of Adaptive Hypermedia Techniques in Web-based Medical Education
This article discusses the design issues involved in delivering web-based learning materials. An existing application in the medical domain – JointZone - is used to illustrate how personalization and an interactive environment can be incorporated into web-based learning. This work applies the combination of an adaptive hypermedia, situated learning approach, and hypermedia linking concepts to facilitate online learning. A usability study was carried out on the work described and an evaluation was undertaken to measure the effect of personalization on various learning factors. The evaluation outcome was analyzed subjectively and objectively. The results proved to be contradictory but nevertheless, the work gives new insights into the use of technology to support learning
ARPES Spectra of the Hubbard model
We discuss spectra calculated for the 2D Hubbard model in the intermediate
coupling regime with the dynamical cluster approximation, which is a
non-perturbative approach. We find a crossover from a normal Fermi liquid with
a Fermi surface closed around the Brillouin zone center at large doping to a
non-Fermi liquid for small doping. The crossover is signalled by a splitting of
the Fermi surface around the point of the 2D Brillouin zone, which
eventually leads to a hole-like Fermi surface closed around the point M. The
topology of the Fermi surface at low doping indicates a violation of
Luttinger's theorem. We discuss different ways of presenting the spectral data
to extract information about the Fermi surface. A comparison to recent
experiments will be presented.Comment: 8 pages, 7 color figures, uses RevTeX
A note on cluster methods for strongly correlated electron systems
We develop, clarify and test various aspects of cluster methods dynamical
mean field methods using a soluble toy model as a benchmark. We find that the
Cellular Dynamical Mean Field Theory (C-DMFT) converges very rapidly and
compare its convergence properties with those of the Dynamical Cluster
Approximation (DCA). We propose and test improved estimators for the lattice
self energy within C-DMFT.Comment: 5 pages, 3 figures; major change
Towards analytical approaches to the dynamical-cluster approximation
I introduce several simplified schemes for the approximation of the
self-consistency condition of the dynamical cluster approximation. The
applicability of the schemes is tested numerically using the
fluctuation-exchange approximation as a cluster solver for the Hubbard model.
Thermodynamic properties are found to be practically indistinguishable from
those computed using the full self-consistent scheme in all cases where the
non-interacting partial density of states is replaced by simplified analytic
forms with matching 1st and 2nd moments. Green functions are also compared and
found to be in close agreement, and the density of states computed using
Pad\'{e} approximant analytic continuation shows that dynamical properties can
also be approximated effectively. Extensions to two-particle properties and
multiple bands are discussed. Simplified approaches to the dynamical cluster
approximation should lead to new analytic solutions of the Hubbard and other
models
Cluster Dynamical Mean Field Theories
Cluster Dynamical Mean Field Theories are analyzed in terms of their
semiclassical limit and their causality properties, and a translation invariant
formulation of the cellular dynamical mean field theory, PCDMFT, is presented.
The semiclassical limit of the cluster methods is analyzed by applying them to
the Falikov-Kimball model in the limit of infinite Hubbard interaction U where
they map to different classical cluster schemes for the Ising model.
Furthermore the Cutkosky-t'Hooft-Veltman cutting equations are generalized and
derived for non translation invariant systems using the Schwinger-Keldysh
formalism. This provides a general setting to discuss causality properties of
cluster methods. To illustrate the method, we prove that PCDMFT is causal while
the nested cluster schemes (NCS) in general and the pair scheme in particular
are not. Constraints on further extension of these schemes are discussed.Comment: 26 page
The Korringa-Kohn-Rostoker Non-Local Coherent Potential Approximation (KKR-NLCPA)
We introduce the Korringa-Kohn-Rostocker non-local coherent potential
approximation (KKR-NLCPA) for describing the electronic structure of disordered
systems. The KKR-NLCPA systematically provides a hierarchy of improvements upon
the widely used KKR-CPA approach and includes non-local correlations in the
disorder configurations by means of a self-consistently embedded cluster. The
KKR-NLCPA method satisfies all of the requirements for a successful cluster
generalization of the KKR-CPA; it remains fully causal, becomes exact in the
limit of large cluster sizes, reduces to the KKR-CPA for a single-site cluster,
is straightforward to implement numerically, and enables the effects of
short-range order upon the electronic structure to be investigated. In
particular, it is suitable for combination with electronic density functional
theory to give an ab-initio description of disordered systems. Future
applications to charge correlation and lattice displacement effects in alloys
and spin fluctuations in magnets amongst others are very promising. We
illustrate the method by application to a simple one-dimensional model.Comment: Revised versio
A minimum single-band model for low-energy excitations in superconducting KFeSe
We propose a minimum single-band model for the newly discovered iron-based
superconducting KFeSe. Our model is found to be numerically
consistent with the five-orbital model at low energies. Based on our model and
the random phase approximation, we study the spin fluctuation and the pairing
symmetry of superconducting gap function. The spin excitation
and the pairing symmetry are revealed. All of the results can
well be understood in terms of the interplay between the Fermi surface topology
and the local spin interaction, providing a sound picture to explain why the
superconducting transition temperature is as high as to be comparable to those
in pnictides and some cuprates. A common origin of superconductivity is
elucidated for this compound and other high-T materials.Comment: 5 pages, 4 figure
IGF2 is a potential factor in RAI-refractory differentiated thyroid cancer
Differentiated thyroid cancer (DTC) is the most frequent endocrine tumor with a good prognosis after primary treatment in most cases. By contrast, 30-40% of patients with metastatic DTC are unresponsive to I-131 radioactive iodide (RAI) treatment due to tumor dedifferentiation. Currently, underlying molecular mechanisms of dedifferentiation remain elusive and predictive biomarkers are lacking. Therefore, the present study aimed to identify molecular biomarkers in primary tumors associated with RAI refractoriness. A retrospective cohort was gathered consisting of RAI-sensitive patients with DTC and RAI-refractory patients with poorly DTC. In all patients, extensive intratumoral mutation profiling, gene fusions analysis, telomerase reverse transcriptase (TERT) promoter mutation analysis and formalin-fixed paraffin-embedded-compatible RNA sequencing were performed. Genetic analyses revealed an increased mutational load in RAI-refractory DTC, including mutations in AKT1, PTEN, TP53 and TERT promoter. Transcriptomic analyses revealed profound differential expression of insulin-like growth factor 2 (IGF2), with up to 100-fold higher expression in RAI-refractory DTC compared with in RAI-sensitive DTC cases. ELISA revealed significant lower IGF2 plasma concentrations after surgery and subsequent I-131 RAI therapy in patients with DTC compared with pretreatment baseline. Overall, the current findings suggested that the tumor-promoting growth factor IGF2 may have a potential role in acquiring RAI refractoriness.Diabetes mellitus: pathophysiological changes and therap
- …