Modeling Excitable Systems: Reentrant Tachycardia

Excitable membranes are an important type of nonlinear dynamical system and their study can be used to provide a connection between physical and biological circuits. We discuss two models of excitable membranes important in cardiac and neural tissues. One model is based on the Fitzhugh-Nagumo equations and the other is based on a three-transistor excitable circuit. We construct a circuit that simulates reentrant tachycardia and its treatment by surgical ablation. This project is appropriate for advanced undergraduates as a laboratory capstone project, or as a senior thesis or honors project, and can also be a collaborative project, with one student responsible for the computational predictions and another for the circuit construction and measurements.Comment: 9 pages, twocolumn, revised and published in American Journal of Physic

Effective Thermoelectric Power Generation in an Insulated Compartment

The Seebeck coefficient S is a temperature- and material-dependent property, which linearly and causally relates the temperature difference ΔT between the “hot” and “cold” junctions of a thermoelectric power generator (TEC-PG) to the voltage difference ΔV . This phenomenon is the Seebeck effect (SE), and can be used to convert waste heat into usable energy. This work investigates the trends of the effective voltage output ΔV (t ) and effective Seebeck coefficient S′(t ) versus several hours of activity of a solid state TEC-PG device. The effective Seebeck coefficient S′(t ) here is related to a device, not just to a material’s performance. The observations are pursued in an insulated compartment in various geometrical and environmental configurations. The results indicate that the SE does not substantially depend on the geometrical and environmental configurations. However, the effective Seebeck coefficient S′(t ) and the produced effective ΔV (t ) are affected by the environmental configuration, once the temperature is fixed. Heat transfer calculations do not completely explain this finding. Alternative explanations are hypothesized

Cigarette smoking and risk of gestational diabetes: a systematic review of observational studies

<p>Abstract</p> <p>Background</p> <p>Gestational diabetes is a prevalent disease associated with adverse outcomes of pregnancy. Smoking as been associated with glucose intolerance during pregnancy in some but not all studies. Therefore, we aimed to systematically review all epidemiological evidence to examine the association between cigarette smoking during pregnancy and risk of developing gestational diabetes mellitus.</p> <p>Methods</p> <p>We conducted a systematic review of articles published up to 2007, using PubMed, Embase, LILACS e CINAHL to identify the articles. Because this review focuses on studies of smoking during pregnancy, we excluded studies evaluating smoking outside pregnancy. Two investigators independently abstracted information on participant's characteristics, assessment of exposure and outcome, and estimates for the association under study. We evaluated the studies for publication bias and performed heterogeneity analyses. We also assessed the effect of each study individually through sensitivity analysis.</p> <p>Results</p> <p>We found and critically reviewed 32 studies, of which 12 met the criteria for inclusion in the review. Most of the studies provided only unadjusted measurements. Combining the results of the individual studies, we obtained a crude odds ratio of 1.03 (99% CI 0.85–1.25). Only 4 studies presented adjusted measurements of association, and no association was found when these alone were analyzed (OR 0.95; 99% CI 0.85–1.07). Subgroup analysis could not be done due to small sample size.</p> <p>Conclusion</p> <p>The number of studies is small, with major heterogeneity in research design and findings. Taken together, current data do not support an association between cigarette smoking during pregnancy and the risk of gestational diabetes.</p

Probing fundamental aspects of quantum mechanics with quantum computers

IBM quantum computers are used to perform a recently-proposed experiment testing the necessity of complex numbers in the standard formulation of quantum mechanics. While the noisier devices are incapable of delivering definitive results, it is shown that certain devices possess sufficiently small error rates to yield convincing evidence that a faithful description of quantum phenomena must involve complex numbers. The results are consistent with previous experiments and robust against daily calibration of these devices. This work demonstrates the feasibility of using freely-available, noisy, intermediate-scale quantum devices to test foundational features of quantum mechanics.Comment: 5 pages; 5 figures + supplementary informatio

Complex spatiotemporal pattern generated with increased stimulation time near the crossover between quiescent and synchronized steady-states.

<p>A fourth-order, five-point stencil was used for evaluation of the spatial derivative. Compare to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122401#pone.0122401.g011" target="_blank">Fig. 11</a>.</p