Local Realistic Theory for PDC Experiments Based on the Wigner Formalism

In this article we present a local hidden variables model for all experiments involving photon pairs produced in parametric down conversion, based on the Wigner representation of the radiation field. A modification of the standard quantum theory of detection is made in order to give a local realist explanation of the counting rates in photodetectors. This model involves the existence of a real zeropoint field, such that the vacumm level of radiation lies below the threshold of the detectors.Comment: 7 pages, no figure

Human oocytes and zygotes are ready for ultra-fast vitrification after 2 minutes of exposure to standard CPA solutions

Vitrification of human oocytes and embryos in different stages of development is a key element of daily clinical practice of in vitro fertilization treatments. Despite the cooling and warming of the cells is ultra-fast, the procedure as a whole is time consuming. Most of the duration is employed in a long (8–15 minutes), gradual or direct exposure to a non-vitrifying cryoprotectant solution, which is followed by a short exposure to a more concentrated vitrifying solution. A reduction in the duration of the protocols is desirable to improve the workflow in the IVF setting and reduce the time of exposure to suboptimal temperature and osmolarity, as well as potentially toxic cryoprotectants. In this work it is shown that this reduction is feasible. In silico (MatLab program using two-parameter permeability model) and in vitro observations of the oocytes’ osmotic behaviour indicate that the dehydration upon exposure to standard cryoprotectant solutions occurs very fast: the point of minimum volume of the shrink-swell curve is reached within 60 seconds. At that point, intracellular water ejection is complete, which coupled with the permeation of low molecular weight cryoprotectants results in similar intracellular and extracellular solute concentrations. This shows that prolonging the exposure to the cryoprotectant solutions does not improve the cytosolic glass forming tendency and could be avoided. To test this finding, human oocytes and zygotes that were donated for research were subjected to a shortened, dehydration-based protocol, consisting of two consecutive exposures of one-minute to two standard cryoprotectant solutions, containing ethylene glycol, dimethyl sulfoxide and sucrose. At the end of this two-minute dehydration protocol, the critical intracellular solute concentration necessary for successful vitrification was attained, confirmed by the post-warming survival and ability to resume cytokinesis of the cells. Further studies of the developmental competency of oocytes and embryos would be necessary to determine the suitability of this specific dehydration protocol for clinical practice, but based on our results, short times of exposure to increasingly hypertonic solutions could be a more time-efficient strategy to prepare human oocytes and embryos for vitrification

Le Postmodernisme latino-américain

Le concept de postmodernisme pose beaucoup de problèmes en Amérique latine. Pour certains auteurs, il s'agit d'un terme créé par des pays riches, libéraux et capitalistes qui y trouvent un appui théorique à leur désengagement politique. Quelques-uns se posent en effet la question suivante: comment pourrions-nous être postmodernes si nous ne sommes pas encore vraiment modernes? D'autres, par contre, défendent le fait d'un postmodernisme latino-américain pas plus réactionnaire que n'importe quel autre mouvement culturel, puisque tout dépend de l'usage que l'on en fait. Il y a aussi des écrivains qui défendent un postmodernisme latino-américain spécifique. Et il y a même ceux qui croient que tout le postmodernisme est né en Amérique latine sous l'influence de Borges. Dans cet article, nous exposons donc cette polémique et nous essayons de résumer les éléments de base permettant de reconnaître l'existence d'un mouvement postmoderniste spécifique à ce continent.The concept of postmodernism is a troubling one for Latin Americans. Some identify the term as a creation of the rich, liberal, capitalistic countries which find in it a theoretical justification for their political disengagement. As some authors put it: «How can we be postmodern when we have not yet become truly modern? Others by contrast defend the idea of a Latin American postmodernism as no more reactionary than any other cultural movement, since all depends on the use made of it. Still other writers favour the concept of a specifically Latin American form of postmodernism, with a number going so far as to proclaim its Latin American origins under the influence of Borges. The purpose of this article is to explore this polemic and to summarise the underlying traits which might serve as criteria of a postmodernist movement specific to the Latin American continent

Problem Definition and Hypothesis Generation by Recent Family Nurse Practitioner Graduates

Little is known about the effect of problem definition on hypothesis-generation accuracy in recent family nurse practitioner (FNP) graduates. The hypotheticodeductive-reasoning model served as the theoretical framework for the study. An alternating-treatment single-subject experimental design was used to examine the effects of problem definition on 8 recent FNP graduates\u27 ability to generate hypotheses to diagnose patient problems. Diagnostic-reasoning software provided web-delivered simulated-patient scenarios that described patient problems that were either ill defined or well defined. The independent variable was problem definition (ill-defined versus well-defined problems). The dependent variables were accuracy of the final diagnosis, the total number of diagnostic hypotheses generated, percent of the diagnostic hypotheses plausible, time from initial login to final diagnosis, and confidence in the final diagnosis. Analysis consisted of visual inspection of graphs and nonparametric tests for each of the dependent variables. Expected differences in accuracy between ill-defined and well-defined problems were not found. However, there were significant differences in time (p = .02) and confidence (p = .01) for diagnosing ill-defined and well-defined problems. One conclusion was that problem definition is a function of the individual problem solver\u27s experience. Hypotheticodeductive reasoning was not used by most problem solvers; instead pattern matching was observed in recent FNPs\u27 diagnosis of patient problems. Future studies should address individual perceptions of problem definition. Programs that educate FNPs should evaluate students\u27 understanding of the hypotheticodeductive reasoning model and individualize learning experiences to promote clinical decision-making