Virtual Learning Communities for Faculty members – does WhatsApp work?

There is evidence that being part of a learning community improves teaching practice and student outcomes.1 Developing a learning community for clinical educators working over a wide geographical area, in a variety of specialties, is challenging. We attempted to address this problem by developing a virtual learning community using a smart phone app. [Introduction

An empirical many-body potential energy function for modelling ytterbium

An empirical potential energy function, comprising two- and three-body terms, has been derived for the rare-earth element ytterbium, by fitting parameters to the phonon dispersion curves, elastic constants, lattice energy and lattice distance of the face-centred-cubic (fcc) phase of Yb. This potential reproduces the structural data for fcc Yb, including the negative Cauchy pressure, and correctly accounts for the metastable bcc phase. We predict the bcc phonon dispersion curves (not yet available in the literature) and the activation energy for the Bain transformation between the fcc and bcc phases. The surface energies and relaxations of the high-symmetry surfaces of fcc Yb ((111), (100) and (110)) are calculated for the first time. Furthermore, we predict that the (110) surface of Yb is stable with respect to the 1 × 2 'missing-row' reconstruction

Non-Sinusoidal Activity Can Produce Cross-Frequency Coupling in Cortical Signals in the Absence of Functional Interaction between Neural Sources

<div><p>The analysis of cross-frequency coupling (CFC) has become popular in studies involving intracranial and scalp EEG recordings in humans. It has been argued that some cases where CFC is mathematically present may not reflect an interaction of two distinct yet functionally coupled neural sources with different frequencies. Here we provide two empirical examples from intracranial recordings where CFC can be shown to be driven by the shape of a periodic waveform rather than by a functional interaction between distinct sources. Using simulations, we also present a generalized and realistic scenario where such coupling may arise. This scenario, which we term waveform-dependent CFC, arises when sharp waveforms (e.g., cortical potentials) occur throughout parts of the data, in particular if they occur rhythmically. Since the waveforms contain both low- and high-frequency components, these components can be inherently phase-aligned as long as the waveforms are spaced with appropriate intervals. We submit that such behavior of the data, which seems to be present in various cortical signals, cannot be interpreted as reflecting functional modulation between distinct neural sources without additional evidence. In addition, we show that even low amplitude periodic potentials that cannot be readily observed or controlled for, are sufficient for significant CFC to occur.</p></div

Experimental timeline describing cell seeding, induction and imaging time points.

<p>The total number of cells seeded on each scaffold was scaled up by scaffold volume to maintain a consistent density with previous work <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055696#pone.0055696-Kang1" target="_blank">[15]</a>.</p

Changes in cell redox ratio and density with time.

<p>A) Average cellular redox ratio at 0, 1, and 2 wks in perfusion compared to previously published static culture experiments <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055696#pone.0055696-Quinn1" target="_blank">[9]</a>. In both static and perfusion culture, no change in redox was observed between 0 and 1 wks, but the redox ratio decreased (p<0.001) from 1 to 2 wks. Although a significant decrease was observed in both cultures at wk 2, the redox ratio was signficantly higher in the perfusion cultures. B) Cell population measurements per image stack (238×238×40 µm volume) at 0, 1, and 2 wks in perfusion flow demonstrate an increase over time, but substantial sample-to-sample variability.</p

False colored redox maps of adipose tissues <i>in vitro</i> after 0, 1, and 2 wks within the perfusion environment.

<p>The grayscale structures in the images are the silk biomaterial 3D scaffolds, while the sparsely distributed colored objects are cells.</p

H&E stained images taken of the edges and middle of sacrificed adipose samples after 0, 1, and 2 wks in perfusion.

<p><b>Images were acquired at 10× and 40×.</b> The dark purple structures are part of the silk scaffold, the lighter purple is ECM, and the dark spots within elongated structures are nuclei within cells. The blue arrows and dashed line specify the location of the edges of the tissues. The red arrows point out ECM formation in at the 2 wk time point. 10× scale bars are 500 µm. 40× scale bars are 200 µm.</p

Statistical significance of phase-amplitude and phase-phase coupling for low-amplitude transients.

<p>A, Each pixel in the image represents the average p-value, across 100 repetitions, for a phase-amplitude CFC effect driven by adding a Gaussian spike train (inter-spike interval: 100 ms) of the given amplitude and width, to a background EEG signal featuring no initial CFC. The color scale corresponds not to the actual p-value, but to n = 0.05/p, i.e. the number of Bonferroni multiple-comparisons the effect “survives”, resulting in a simple linear scale of significance. The white outline indicates the cluster of significant pixels (n> = 1). Importantly, note that significant CFC occurs even for very low-amplitude transients (under 1 standard deviation). It can also be seen that the magnitude of CFC depends on the width of the transient waveform: very narrow transients do not contain enough energy to drive the phase of the slow-frequency component, while wide transients contain a weaker high-frequency component. B, Significance of phase-phase coupling between 10Hz and 20Hz is shown for the same range of transient amplitudes and widths. Since a parametric significance test was used, p-value tended to be very small and so the logarithmic scale n = log10(0.05/p) was used (such that n = 0 corresponds to p = 0.05, n = 1 to p = 0.005, etc.). White border indicates area where p<0.05. Note that the area indicated as significant in this analysis does not fully overlap that of the phase-amplitude coupling analysis (Fig 7A).</p

Preferred frequency-for-amplitude as a function of Gaussian spike width.

<p>Shaded area reflects one standard deviation of the preferred frequency across 100 iterations (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167351#sec002" target="_blank">Materials and Methods</a>).</p

Examples of CFC in eight simulated signals.

<p>The plots on the left of each column depict a trace from the original (background) signal used for the simulation (black), the added Gaussian train (red), and the compound signal after adding the potentials (blue). The blue trace is therefore the sum of the black and the red ones. Note the temporal jitter in the Gaussian periodicity (i.e. variability of the inter-peak interval). The image on the right in each column shows the comodulogram for the compound signal (blue to red color scale corresponds to 0 to 1 in all panels). Clusters of significant CFC in the comodulograms are marked with a black outline (p<0.01). Note that values in the bottom triangle of each plot are not shown as CFC is invalid for frequencies-for-amplitude lower than the frequency-for-phase. The left column shows results for EEG-based simulations with a 100-ms mean inter-peak interval; the right column shows results for pink-noise-based simulations with a 166-ms mean inter-peak interval. It can be easily seen that the periodicity determines the frequency-for-phase of the CFC (10Hz and 6Hz, respectively), as well as its harmonics. A, D, the raw background traces with no added spikes. B, F, added spikes with an amplitude of 3 STDs and a width of 10 ms (full-width at half-maximum). C, G, Same as B,F but with an amplitude of 1.5 STDs. Note the diminished magnitude of the effect. D, H, Same as B,F but with a width of 20 ms. Note the lower frequency-for-amplitude range for which CFC occurs.</p