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This work explores a feature of brain dynamics, metastability, by which transients are observed in functional brain data. Metastability is a balance between static (stable) and dynamic (unstable) tendencies in electrophysiological brain activity. Furthermore, metastability is a theoretical mechanism underlying the rapid synchronization of cell assemblies that serve as neural substrates for cognitive states, and it has been associated with cognitive flexibility. While much previous research has sought to characterize metastability in the adult human brain, few studies have examined metastability in early development, in part because of the challenges of acquiring adequate, noise free continuous data in young children. To accomplish this endeavor, we studied a new method for characterizing the stability of EEG frequency in early childhood, as inspired by prior approaches for describing cortical phase resets in the scalp EEG of healthy adults. Specifically, we quantified the variance of the rate of change of the signal phase (i.e., frequency) as a proxy for phase resets (signal instability), given that phase resets occur almost simultaneously across large portions of the scalp. We tested our method in a cohort of 39 preschool age children (age =53 ± 13.6 months). We found that our outcome variable of interest, frequency variance, was a promising marker of signal stability, as it increased with the number of phase resets in surrogate (artificial) signals. In our cohort of children, frequency variance decreased cross-sectionally with age (r = −0.47, p = 0.0028). EEG signal stability, as quantified by frequency variance, increases with age in preschool age children. Future studies will relate this biomarker with the development of executive function and cognitive flexibility in children, with the overarching goal of understanding metastability in atypical development.

Three-dimensional (3D) and two-dimensional (2D) depth-averaged (DA) large-eddy simulations (LES) are presented for three different shallow-water flows involving large-scale horizontal structures: a mixing layer, the flow around a circular cylinder, and the flow in a groyne field. The results are compared with each other and also with experiments. In the 3D-LES, most of the energy-containing turbulent motions, including the larger subdepth-scale motions, are resolved, while in the 2D-DA-LES the effect of the 3D subdepth-scale turbulence is represented by a quadratic bottom-friction model and a simple eddy-viscosity model. In the case of the mixing layer, an additional stochastic backscatter model is necessary to account for the energy transfer from the subdepth-scale turbulence to the 2D structures in order to generate the latter. The 3D-LES results are generally in good agreement with the experiments, including the evolution of the horizontal structures. The much more economic 2D-DA-LES are somewhat less realistic in detail but also produce results that are generally of sufficient accuracy for practical purposes. DOI: 10.1061/(ASCE)0733-9429(2007)133:8(857) CE Database subject headings: Flow simulation; Turbulent flow; Shallow water; Three-dimensional models; Two-dimensional models; Vortices.

In this paper, the non-reacting flow in a swirl burner is studied using large eddy simulation. The configuration consists of two unconfined coannular jets at a Reynolds number of 81,500. The flow is characterized by a Swirl number of 0.93. Two cases are studied in the paper differing with respect to the axial location of the inner pilot jet. It was observed in a companion experiment (Bender and Buchner, 2005, Proc. 12 Int. Cong. Sound and Vibration, Lisbon, Portugal) that when the inner jet is retracted the flow oscillations are considerably amplified. This is also found in the present simulations. Large-scale coherent structures rotating at a constant rate are observed when the inner jet is retracted. The rotation of the structures leads to vigorous oscillations in the velocity and pressure time signals recorded at selected points in the flow. In addition, the mean velocities, the turbulent fluctuations, and the frequency of the oscillations are in good agreement with the experiments. A conditional averaging procedure is used to perform a detailed analysis of the physics leading to the low-frequency oscillations. [DOI: 10.1115/1.2364198]

The flow around a low-pressure turbine rotor blade with periodically incoming wakes at a realistic Reynolds number is computed by means of large-eddy simulation (LES). The computed results are discussed in terms of phase-averaged and mean quantities. A comparison is made with an existing direct numerical simulation (DNS) for the same geometry and operating conditions. Particular attention is devoted to flow structures associated with the incoming wakes and their effect on the boundary layers. The analysis of the flowfield reveals patterns similar to those encountered in DNS and in LES of flow in the same geometry at a lower Reynolds number. Noticeable differences occur in the suction-side boundary layer, which exhibits a complete transition to turbulence for the present case.

Interatrial conduction block refers to a disturbance in the propagation of electrical impulses in the conduction pathways between the right and the left atrium. It is a risk factor for atrial fibrillation, stroke, and premature death. Clinical diagnostic criteria comprise an increased P wave duration and biphasic P waves in lead II, III and aVF due to retrograde activation of the left atrium. Machine learning algorithms could improve the diagnosis but require a large-scale, well-controlled and balanced dataset. In silico electrocardiogram (ECG) signals, optimally obtained from a statistical shape model to cover anatomical variability, carry the potential to produce an extensive database meeting the requirements for successful machine learning application. We generated the first in silico dataset including interatrial conduction block of 9,800 simulated ECG signals based on a bi-atrial statistical shape model. Automated feature analysis was performed to evaluate P wave morphology, duration and P wave terminal force in lead V1. Increased P wave duration and P wave terminal force in lead V1 were found for models with interatrial conduction block compared to healthy models. A wide variability of P wave morphology was detected for models with interatrial conduction block. Contrary to previous assumptions, our results suggest that a biphasic P wave morphology seems to be neither necessary nor sufficient for the diagnosis of interatrial conduction block. The presented dataset is ready for a classification with machine learning algorithms and can be easily extended.

Purpose: This study sought to assess risk compensation following voluntary medical male circumcision of young school-going men. Risk compensation is defined as an inadvertent increase in sexual risk behaviors and a corresponding decrease in self-perceived risk for contracting HIV following the application of a risk reduction technology.Methods: This study documented the sexual practices of circumcised (n = 485) and uncircumcised (n = 496) young men in 42 secondary schools at three time points (baseline and 6 and 12 months) in a sub-district of KwaZulu-Natal, South Africa. Study participants were aged from 16 to 24 years old.Results: At the end of the study period, there was no significant difference between the two cohorts concerning learners’ perceptions of being at risk of contracting HIV (interaction effect: b = −0.12, p = 0.40). There was also no significant difference in the number of sexual partners in the previous month (interaction effect: b = −0.23, p = 0.15). The proportion of learners who have never used a condom decreased significantly over time (time effect: b = −0.27, p = 0.01), and there was no difference between the circumcised and uncircumcised learners (interaction effect: b = −0.09, p = 0.91).Conclusions: Risk compensation, as evidenced in this study over a 1-year period, was not associated with undergoing voluntary medical male circumcision (VMMC) in our sample of young school-going men. However, it is of concern that at the end of this study, less than half of the sexually active sample in a high-HIV-prevalence community used condoms consistently in the previous month (39% for both study cohorts). The latter underscores the need to view VMMC as a potential entry point for planned HIV and sexuality education interventions targeting young men in this community. [ABSTRACT FROM AUTHOR]