Nonpersistence of resonant caustics in perturbed elliptic billiards

Caustics are curves with the property that a billiard trajectory, once tangent to it, stays tangent after every reflection at the boundary of the billiard table. When the billiard table is an ellipse, any nonsingular billiard trajectory has a caustic, which can be either a confocal ellipse or a confocal hyperbola. Resonant caustics —the ones whose tangent trajectories are closed polygons— are destroyed under generic perturbations of the billiard table. We prove that none of the resonant elliptical caustics persists under a large class of explicit perturbations of the original ellipse. This result follows from a standard Melnikov argument and the analysis of the complex singularities of certain elliptic functions.

Quantitative genetic modeling and inference in the presence of nonignorable missing data.

Natural selection is typically exerted at some specific life stages. If natural selection takes place before a trait can be measured, using conventional models can cause wrong inference about population parameters. When the missing data process relates to the trait of interest, a valid inference requires explicit modeling of the missing process. We propose a joint modeling approach, a shared parameter model, to account for nonrandom missing data. It consists of an animal model for the phenotypic data and a logistic model for the missing process, linked by the additive genetic effects. A Bayesian approach is taken and inference is made using integrated nested Laplace approximations. From a simulation study we find that wrongly assuming that missing data are missing at random can result in severely biased estimates of additive genetic variance. Using real data from a wild population of Swiss barn owls Tyto alba, our model indicates that the missing individuals would display large black spots; and we conclude that genes affecting this trait are already under selection before it is expressed. Our model is a tool to correctly estimate the magnitude of both natural selection and additive genetic variance.

Physicians' estimates of the 10 year cardiovascular risk in hypertensive patients: an evaluation in primary care physicians in training.

To evaluate how young physicians in training perceive their patients' cardiovascular risk based on the medical charts and their clinical judgment. Cross sectional observational study. University outpatient clinic, Lausanne, Switzerland. Two hundred hypertensive patients and 50 non-hypertensive patients with at least one cardiovascular risk factor. Comparison of the absolute 10-year cardiovascular risk calculated by a computer program based on the Framingham score and adapted for physicians by the WHO/ISH with the perceived risk as assessed clinically by the physicians. Physicians underestimated the 10-year cardiovascular risk of their patients compared to that calculated with the Framingham score. Concordance between methods was 39% for hypertensive patients and 30% for non-hypertensive patients. Underestimation of cardiovascular risks for hypertensive patients was related to the fact they had a stabilized systolic blood pressure under 140 mm Hg (OR = 2.1 [1.1; 4.1]). These data show that young physicians in training often have an incorrect perception of the cardiovascular risk of their patients with a tendency to underestimate the risk. However, the calculated risk could also be slightly overestimated when applying the Framingham Heart Study model to a Swiss population. To implement a systematic evaluation of risk factors in primary care a greater emphasis should be placed on the teaching of cardiovascular risk evaluation and on the implementation of quality improvement programs.

Evaluation à l'aide d'un livre de bord des compétences cliniques acquises par des stagiaires en médecine. [Evaluation using a logbook of mastering of clinical skills by medical students]

La maîtrise des compétences cliniques est extrêmement importante pour le médecin. Leur enseignement est aujourd'hui facilité grâce à la disponibilité du «Swiss Catalogue of Learning Objectives for Undergraduate Medical Training» où sont décrits les niveaux de compétence à atteindre au terme des études de médecine. Un carnet de bord a été préparé à la Faculté de biologie et de médecine de Lausanne à partir de ce document. Il a permis de mettre en évidence chez les étudiants une très nette amélioration de la maîtrise des compétences cliniques entre le début et la fin des stages en médecine interne, chirurgie/orthopédie, pédiatrie, gynécologie/obstétrique et psychiatrie. Un tel outil devrait permettre dans l'avenir de mieux guider l'apprentissage des étudiants et de suivre leurs progrès à chaque étape du curriculum. [Abstract] The mastering of the clinical skills is of utmost importance for the physician. The teaching of the skills is nowadays made easier with the <<Swiss Catalogue of Learning Objectives for Undergraduate Medical Training>> which lists all the skills and their respective level of expected mastering at graduation. In order to do a survey on how good the students are at those skills, a logbook based on this document has been setup at the Faculty of biology and medicine of the University of Lausanne. This has shown that students went through a clear progression of the mastering of the skills during their elective year in internal medicine, surgery/orthopaedics, paediatric, obstetric and gynaecology as well as psychiatry. Such an instrument should in the future help to better guide the learning process of the clinical skills and to do a better follow-up of their progress.

The European Board of Physical and Rehabilitation Medicine : the past, the present and the future [Europejska Rada Medycyny Fizykalnej i Rehabilitacji: przeszłość, teraźniejszość i perspektywy]

Right from the beginning of the development of the medical specialty of Physical and Rehabilitation Medicine (PRM) the harmonization of the fields of competence and the specialist training across Europe was always an important issue. The initially informal European collaboration was formalized in 1963 under the umbrella of the European Federation of PRM. The European Academy of PRM and the UEMS section of PRM started to contribute in 1969 and 1974 respectively. In 1991 the European Board of Physical and Rehabilitation Medicine (EBPRM) was founded with the specific task of harmonizing education and training in PRM in Europe. The EBPRM has progressively defined curricula for the teaching of medical students and for the postgraduate education and training of PRM specialists. It also created a harmonized European certification system for medical PRM specialists, PRM trainers and PRM training sites. European teaching initiatives for PRM trainees (European PRM Schools) were promoted and learning material for PRM trainees and PRM specialists (e-learning, books and e-books, etc.) was created. For the future the Board will have to ensure that a minimal specific undergraduate curriculum on PRM based on a detailed European catalogue of learning objectives will be taught in all medical schools in Europe as a basis for the general medical practice. To stimulate the harmonization of national curricula, the existing postgraduate curriculum will be expanded by a syllabus of competencies related to PRM and a catalogue of learning objectives to be reached by all European PRM trainees. The integration of the certifying examination of the PRM Board into the national assessment procedures for PRM specialists will also have to be promoted.

Supporting the reuse of effective CSCL learning designs through social structure representations

Distance and blended collaborative learning settings are usually characterized by different social structures defined in terms of groups' number, dimension, and composition; these structures are variable and can change within the same activity. This variability poses additional complexity to instructional designers, when they are trying to develop successful experiences from existing designs. This complexity is greatly associated with the fact that learning designs do not render explicit how social structures influenced the decisions of the original designer, and thus whether the social structures of the new setting could preclude the effectiveness of the reused design. This article proposes the usage of new representations (social structure representations, SSRs) able to support unskilled designers in reusing existing learning designs, through the explicit characterization of the social structures and constraints embedded either by the original designers or the reusing teachers, according to well-known principles of good collaborative learning practice. The article also describes an evaluation process that involved university professors, as well as the main findings derived from it. This process supported the initial assumptions about the effectiveness of SSRs, with significant evidence from both qualitative and qualitative data.

How are "teaching the teachers" courses in evidence based medicine evaluated? A systematic review.

BACKGROUND: Teaching of evidence-based medicine (EBM) has become widespread in medical education. Teaching the teachers (TTT) courses address the increased teaching demand and the need to improve effectiveness of EBM teaching. We conducted a systematic review of assessment tools for EBM TTT courses.To summarise and appraise existing assessment methods for teaching the teachers courses in EBM by a systematic review. METHODS: We searched PubMed, BioMed, EmBase, Cochrane and Eric databases without language restrictions and included articles that assessed its participants. Study selection and data extraction were conducted independently by two reviewers. RESULTS: Of 1230 potentially relevant studies, five papers met the selection criteria. There were no specific assessment tools for evaluating effectiveness of EBM TTT courses. Some of the material available might be useful in initiating the development of such an assessment tool. CONCLUSION: There is a need for the development of educationally sound assessment tools for teaching the teachers courses in EBM, without which it would be impossible to ascertain if such courses have the desired effect.

Assessment of a new MRI classification of spinal stenosis based on cross-sectional morphology of the dural sac : FM2

Introduction: Quantitative measures of degree of lumbar spinal stenosis (LSS) such as antero-posterior diameter of the canal or dural sac cross sectional area vary widely and do not correlate with clinical symptoms or results of surgical decompression. In an effort to improve quantification of stenosis we have developed a grading system based on the morphology of the dural sac and its contents as seen on T2 axial images. The grading comprises seven categories ranging form normal to the most severe stenosis and takes into account the ratio of rootlet/CSF content. Material and methods: Fifty T2 axial MRI images taken at disc level from twenty seven symptomatic lumbar spinal stenosis patients who underwent decompressive surgery were classified into seven categories by five observers and reclassified 2 weeks later by the same investigators. Intra- and inter-observer reliability of the classification were assessed using Cohen's and Fleiss' kappa statistics, respectively. Results: Generally, the morphology grading system itself was well adopted by the observers. Its success in application is strongly influenced by the identification of the dural sac. The average intraobserver Cohen's kappa was 0.53 ± 0.2. The inter-observer Fleiss' kappa was 0.38 ± 0.02 in the first rating and 0.3 ± 0.03 in the second rating repeated after two weeks. Discussion: In this attempt, the teaching of the observers was limited to an introduction to the general idea of the morphology grading system and one example MRI image per category. The identification of the dimension of the dural sac may be a difficult issue in absence of complete T1 T2 MRI image series as it was the case here. The similarity of the CSF to possibly present fat on T2 images was the main reason of mismatch in the assignment of the cases to a category. The Fleiss correlation factors of the five observers are fair and the proposed morphology grading system is promising.

English as a world language: its role as a lingua francaa sociolinguistic profile of students of secondary schools in Santiago Island, in the Archipelago of Cape Verde

Esta tese centra-se em aspectos relevantes do inglês como uma língua universal, no actual contexto globalizado e examina possíveis mudanças relacionadas com o seu uso, em especial no continente africano, particularmente no caso de Cabo Verde, no sentido de ponderar eventuais alternativas nas pedagogias linguísticas no ensino desta língua que impliquem uma adaptação à realidade contemporânea. Uma vez que, nos nossos tempos, o inglês é a língua de eleição para a comunicação intercultural entre povos com várias experiências culturais e linguísticas, o conhecimento deste idioma torna-se, a cada dia que passa, impreterível e indispensável, na interacção intercultural. Em África, as funções desempenhadas pelo inglês são complexas; além da língua inglesa ser usada para comunicação entre etnias, com o estatuto de língua franca, também tem o papel de preservar a identidade nacional e de estabelecer a unidade entre os povos da mesma nação. Por conseguinte, é de considerar talvez ainda com mais pertinência, a adopção de uma nova filosofia de pedagogia de ensino que permita dotar os seus cidadãos de capacidades que lhes possibilitem comunicar de forma inteligível com povos de outras culturas e línguas. O primeiro capítulo aborda aspectos teóricos relacionados com a expansão, comunicação e mudança associadas à língua inglesa e suas implicações no ensino em países onde esta não é língua nativa (L1). O segundo capítulo reflecte, em primeiro lugar, sobre a situação linguística em África e as línguas francas predominantes no continente, incluindo a língua inglesa. Considera também questões relacionadas com o multilinguismo e a identidade, bem como assuntos relacionados com as implicações da diversidade linguística para a educação dos povos africanos.

Delta(1232) isobar excitations and the ground state of nuclei

The influence of Delta isobar components on the ground-state properties of nuclear systems is investigated for nuclear matter as well as finite nuclei. Many-body wave functions, including isobar configurations and binding energies, are evaluated employing the framework of the coupled-cluster theory. It is demonstrated that the effect of isobar configurations depends in a rather sensitive way on the model used for the baryon-baryon interaction. As examples for realistic baryon-baryon interactions with explicit inclusion of isobar channels we use the local (V28) and nonlocal meson-exchange potentials (Bonn2000) but also a model recently developed by the Salamanca group, which is based on a quark picture. The differences obtained for the nuclear observables are related to the treatment of the interaction, the pi-exchange contributions in particular, at high momentum transfers.

Crystallization behaviour of some melt spun Nd-Fe-B alloys

The kinetics of crystallization of four amorphous (or partially amorphous) melt spun Nd-Fe-B alloys induced by thermal treatment is studied by means of differential scanning calorimetry and scanning electron microscopy, In the range of temperatures explored experimentally, the crystallization process is thermally activated and generally proceeds in various stages. The Curie temperature and the crystallization behavior have been measured. The apparent activation energy of crystallization of most of the crystallization stages has been determined for each melt spun alloy. The explicit form of the kinetic equation that best describes the first stage of crystallization has been found. It follows in general the Johnson-Mehl-Avrami-Erofe'ev model, but clear deviations to that model occur for one alloy. Scanning electron microscopy demonstrates that preferentially hetereogeneous nucleation occurs at the ribbon surface which was in contact with the wheel. From crystallization kinetics results the lower part of the experimental time-temperature-transformation curves for all studied alloys are deduced and extrapolated to the high temperature limit of their range of validity, also deduced.

Theory for correlation functions of processes driven by external colored noise

We study steady-state correlation functions of nonlinear stochastic processes driven by external colored noise. We present a methodology that provides explicit expressions of correlation functions approximating simultaneously short- and long-time regimes. The non-Markov nature is reduced to an effective Markovian formulation, and the nonlinearities are treated systematically by means of double expansions in high and low frequencies. We also derive some exact expressions for the coefficients of these expansions for arbitrary noise by means of a generalization of projection-operator techniques.

Intensity correlation functions of dye lasers: Comparison of colored-gain-noise and colored-loss-noise models

The intensity correlation functions C(t) for the colored-gain-noise model of dye lasers are analyzed and compared with those for the loss-noise model. For correlation times ¿ larger than the deterministic relaxation time td, we show with the use of the adiabatic approximation that C(t) values coincide for both models. For small correlation times we use a method that provides explicit expressions of non-Markovian correlation functions, approximating simultaneously short- and long-time behaviors. Comparison with numerical simulations shows excellent results simultaneously for short- and long-time regimes. It is found that, when the correlation time of the noise increases, differences between the gain- and loss-noise models tend to disappear. The decay of C(t) for both models can be described by a time scale that approaches the deterministic relaxation time. However, in contrast with the loss-noise model, a secondary time scale remains for large times for the gain-noise model, which could allow one to distinguish between both models.

Solvable dynamics in a system of interacting random tops

A new solvable model of synchronization dynamics is introduced. It consists of a system of long range interacting tops or magnetic moments with random precession frequencies. The model allows for an explicit study of orientational effects in synchronization phenomena as well as nonlinear processes in resonance phenomena in strongly coupled magnetic systems. A stability analysis of the incoherent solution is performed for different types of orientational disorder. A system with orientational disorder always synchronizes in the absence of noise.

Dynamics of transient domain structures in nematic liquid crystals: The splay Fréedericksz transition

We discuss the dynamics of the transient pattern formation process corresponding to the splay Fréedericksz transition. The emergence and subsequent evolution of the spatial periodicity is here described in terms of the temporal dependence of the wave numbers corresponding to the maxima of the structure factor. Situations of perpendicular as well as oblique field-induced stripes relative to the initial orientation of the director are both examined with explicit indications of the time scales needed for their appearance and posterior development.