Effect of gender on P-wave dispersion in asymptomatic populations

Background: Exercise testing is a diagnostic tool for evaluating the induction of stress-induced paroxysmal atrial fibrillation (PAF). Resting P-wave dispersion has been suggested to be greater in males versus females but if used by clinicians, gender difference in response to exercise must be determined. Methods: Sixteen healthy subjects (n=8 male, age: 21±0.3; n=8 female, age: 23±1.4) performed an incremental exercise test using the Bruce protocol. Electrocardiograms were recorded at rest, end-exercise, 1, 3, and 5 mins recovery. P-waves were measured in each lead with the maximum (P-max) and minimum (P-min) P-wave durations and dispersion calculated. Results: There was a significant decrease in P-max from rest to end-exercise in males and females [males, 118.3±7.4 (95%CI: 109.7 to 126.8ms) vs. 97.9±6.2 (89.3 to 106.4ms); females, 109.4±4.5 (100.8 to 117.9ms) vs. 94.3±4.6 (85.7 to 102.8ms); p=0.001 (5.7 to 29.8ms)]. Similarly, for P-min [males, 65.6±5.6 (57.4 to 73.9ms) vs. 50.8±2.7 (42.5 to 59.0ms); females, 58.4±3.3 (50.1 to 66.6ms) vs. 45.6±2.7 (37.4 to 53.9ms); p=0.01 (2.2 to 25.4ms)]. Irrespective of gender there was limited change in P-wave dispersion in response to exercise. Males had a longer P-max versus females during the protocol [109.6±2.3 (105.8 to 113.4ms) vs. 103.6±1.8 (99.8 to 107.4ms); p=0.03] but this was not stage-specific. There was no gender differences in either P-min (p=0.12) or P-wave dispersion (p=0.64) across the protocol or stage-specific. Conclusions: Results from this study indicate that in contrast to P-max and P-min, the P-wave dispersion may not be significantly influenced by the sympathetic nervous system in males and females. Therefore, this study suggests males and females should be evaluated in the same way using the P-wave dispersion for predicting the development of stress-induced PAF at rest and during exercise testing protocols

Semantically Rich Tools for Text Exploration

Literary scholarship is poised to benefit immensely from the emerging modular software frameworks that support deep and finely grained investigations of digital texts. Humanities research centers, such as the Brown University Women Writers Project, have invested substantially in enriching bodies of literary texts with semantic and structural information, using XML formats such as the Text Encoding Initiative (TEI). Recent innovations in scholarly software design offer opportunities to exploit the semantic depth of TEI collections by creating new tools for textual analysis and collaboration. To this end, the Brown University Scholarly Technology Group (STG) and the Brown University Women Writers Project (WWP) propose a new effort to create a prototype suite of software tools to explore TEI encoded texts in the new Software Environment for the Advancement of Scholarly Research (SEASR)

Morphodynamics of Atolls, Reef Flats, and the Islands Atop Them

The atolls that dot the tropical oceans of (primarily) the Pacific and Indian Oceans contain shallow and emergent coastal environments that often comprise the only subaerial, inhabitable land of many island chains and island nations. Created foremost by calcifying organisms, and composed of both biogenic rocky substrate and detrital sediment, these shallow environments are shaped by waves, currents, and tides. The low-lying, geomorphically active reef islands sitting atop of atolls face considerable hazards from climate change. I will present a series of recent and ongoing research projects addressing the formation mechanisms and potential climate change response of coastal atoll environments, including the “spurs and grooves” on the offshore fore-reef, the shallow reef flat itself, and the islands that can be found up on top

Exploring shoreface dynamics and a mechanistic explanation for a morphodynamic depth of closure

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Earth Surface 121 (2016): 442–464, doi:10.1002/2015JF003699.Using energetics-based formulations for wave-driven sediment transport, we develop a robust methodology for estimating the morphodynamic evolution of a cross-shore sandy coastal profile. In our approach, wave-driven cross-shore sediment flux depends on three components: two onshore-directed terms (wave asymmetry and wave streaming) and an offshore-directed slope term. In contrast with previous work, which applies shallow water wave assumptions across the transitional zone of the lower shoreface, we use linear Airy wave theory. The cross-shore sediment transport formulation defines a dynamic equilibrium profile and, by perturbing about this steady state profile, we present an advection-diffusion formula for profile evolution. Morphodynamic Péclet analysis suggests that the shoreface is diffusionally dominated. Using this depth-dependent characteristic diffusivity timescale, we distinguish a morphodynamic depth of closure for a given time envelope. Even though wave-driven sediment transport can (and will) occur at depths deeper than this morphodynamic closure depth, the rate of morphologic bed changes in response to shoreline change becomes asymptotically slow. Linear wave theory suggests a shallower shoreface depth of closure and much sharper break in processes than shallow water wave assumptions. Analyzing hindcasted wave data using a weighted frequency-magnitude approach, we determine representative wave conditions for selected sites along the U.S. coastline. Computed equilibrium profiles and depths of closure demonstrate reasonable similarities, except where inheritance is strong. The methodology espoused in this paper can be used to better understand the morphodynamics at the lower shoreface transition with relative ease across a variety of sites and with varied sediment transport equations.This research has been supported by the National Science Foundation grant CNH-0815875, the Strategic Environment Research and Development Program, and the Coastal Ocean Institute of the Woods Hole Oceanographic Institution.2016-08-2

Wave-angle control of delta evolution

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L13405, doi:10.1029/2011GL047630.Wave-influenced deltas, with large-scale arcuate shapes and demarcated beach ridge complexes, often display an asymmetrical form about their river channel. Here, we use a numerical model to demonstrate that the angles from which waves approach a delta can have a first-order influence upon its plan-view morphologic evolution and sedimentary architecture. The directional spread of incoming waves plays a dominant role over fluvial sediment discharge in controlling the width of an active delta lobe, which in turn affects the characteristic rates of delta progradation. Oblique wave approach (and a consequent net alongshore sediment transport) can lead to the development of morphologic asymmetry about the river in a delta's plan-view form. This plan-form asymmetry can include the development of discrete breaks in shoreline orientation and the appearance of self-organized features arising from shoreline instability along the downdrift delta flank, such as spits and migrating shoreline sand waves—features observed on natural deltas. Somewhat surprisingly, waves approaching preferentially from one direction tend to increase sediment deposition updrift of the river. This ‘morphodynamic groin effect’ occurs when the delta's plan-form aspect ratio is sufficiently large such that the orientation of the shoreline on the downdrift flank is rotated past the angle of maximum alongshore sediment transport, resulting in preferential redirection of fluvial sediment updrift of the river mouth.This research was supported by NSF grants EAR‐0952146 and OCE‐0623766, the Exxon‐Mobil Upstream Research Company, and the WHOI‐USGS postdoctoral fellowship

Reply to comment by M. Ortega-Sánchez et al. on “High-angle wave instability and emergent shoreline shapes : 1. Modeling of sand waves, flying spits, and capes”

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 113 (2008): F01006, doi:10.1029/2007JF000885

Rollover, drowning, and discontinuous retreat: Distinct modes of barrier response to sea-level rise arising from a simple morphodynamic model

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Earth Surface 119 (2014): 779–801, doi:10.1002/2013JF002941.We construct a simple morphodynamic model to investigate the long-term dynamic evolution of a coastal barrier system experiencing sea-level rise. Using a simplified barrier geometry, the model includes a dynamic shoreface profile that can be out of equilibrium and explicitly treats barrier sediment overwash as a flux. With barrier behavior primarily controlled by the maximum potential overwash flux and the rate of shoreface response, the modeled barrier system demonstrates four primary behaviors: height drowning, width drowning, constant landward retreat, and a periodic retreat. Height drowning occurs when overwash fluxes are insufficient to maintain the landward migration rate required to keep pace with sea-level rise. On the other hand, width drowning occurs when the shoreface response rate is insufficient to maintain the barrier geometry during overwash-driven landward migration. During periodic barrier retreat, the barrier experiences oscillating periods of rapid overwash followed by periods of relative stability as the shoreface resteepens. This periodic retreat, which occurs even with a constant sea-level rise rate, arises when overwash rates and shoreface response rates are large and of similar magnitude. We explore the occurrence of these behaviors across a wide range of parameter values and find that in addition to the maximum overwash flux and the shoreface response rate, barrier response can be particularly sensitive to the sea-level rise rate and back-barrier lagoon slope. Overall, our findings contrast with previous research which has primarily associated complex barrier behavior with changes in external forcing such as sea-level rise rate, sediment supply, or back-barrier geometry.This research has been supported by the National Science Foundation grant #CNH-0815875, the Strategic Environment Research and Development Program, and the Coastal Ocean Institute of the Woods Hole Oceanographic Institution.2014-10-0

Mechanics and rates of tidal inlet migration : modeling and application to natural examples

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Earth Surface 121 (2016): 2118–2139, doi:10.1002/2016JF004035.Tidal inlets on barrier coasts can migrate alongshore hundreds of meters per year, often presenting great management and engineering challenges. Here we perform model experiments with migrating tidal inlets in Delft3D-SWAN to investigate the mechanics and rates of inlet migration. Model experiments with obliquely approaching waves suggest that tidal inlet migration occurs due to three mechanisms: (1) littoral sediment deposition along the updrift inlet bank, (2) wave-driven sediment transport preferentially eroding the downdrift bank of the inlet, and (3) flood-tide-driven flow preferentially cutting along the downdrift inlet bank because it is less obstructed by flood-tidal delta deposits. To quantify tidal inlet migration, we propose and apply a simple mass balance framework of sediment fluxes around inlets that includes alongshore sediment bypassing and flood-tidal delta deposition. In model experiments, both updrift littoral sediment and the eroded downdrift inlet bank are sediment sources to the growing updrift barrier and the flood-tidal delta, such that tidal inlets can be net sink of up to 150% of the littoral sediment flux. Our mass balance framework demonstrates how, with flood-tidal deltas acting as a littoral sediment sink, migrating tidal inlets can drive erosion of the downdrift barrier beach. Parameterizing model experiments, we propose a predictive model of tidal inlet migration rates based upon the relative momentum flux of the inlet jet and the alongshore radiation stress; we then compare these predicted migration rates to 22 natural tidal inlets along the U.S. East Coast and find good agreement.National Science Foundation Grant Number: EAR-14247282017-05-1

Instability and finite-amplitude self-organization of large-scale coastline shapes

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of The Royal Society for personal use, not for redistribution. The definitive version was published in Philosophical Transactions of the Royal Society of London Series A-Mathematical Physical and Engineering Sciences 371 (2013):20120363, doi:10.1098/rsta.2012.0363.Recent research addresses the formation of patterns on sandy coastlines on alongshore scales that are large compared with the cross-shore extent of active sediment transport. A simple morphodynamic instability arises from the feedback between wave-driven alongshore sediment flux and coastline shape. Coastline segments with different orientations experience different alongshore sediment fluxes, so that curvatures in coastline shape drive gradients in sediment flux, which can augment the shoreline curvatures. In a simple numerical model, this instability, and subsequent finite-amplitude interactions between pattern elements, lead to a wide range of different rhythmic shapes and behaviours—ranging from symmetric cuspate capes and bays to alongshore migrating ‘flying spits’—depending on the characteristics of the input wave forcing. The scale of the pattern coarsens in some cases because of the merger of migrating coastline features, and in other cases because of non-local screening interactions between coastline protrusions, which affect the waves reaching other parts of the coastline. Features growing on opposite sides of an enclosed water body mutually affect the waves reaching each other in ways that lead to the segmentation of elongated water bodies. Initial tests of model predictions and comparison with observations suggest that modes of pattern formation in the model are relevant in nature

Rollover, drowning, and discontinuous retreat: Distinct modes of barrier response to sea-level rise arising from a simple morphodynamic model

We construct a simple morphodynamic model to investigate the long-term dynamic evolution of a coastal barrier system experiencing sea-level rise. Using a simplified barrier geometry, the model includes a dynamic shoreface profile that can be out of equilibrium and explicitly treats barrier sediment overwash as a flux. With barrier behavior primarily controlled by the maximum potential overwash flux and the rate of shoreface response, the modeled barrier system demonstrates four primary behaviors: height drowning, width drowning, constant landward retreat, and a periodic retreat. Height drowning occurs when overwash fluxes are insufficient to maintain the landward migration rate required to keep pace with sea-level rise. On the other hand, width drowning occurs when the shoreface response rate is insufficient to maintain the barrier geometry during overwash-driven landward migration. During periodic barrier retreat, the barrier experiences oscillating periods of rapid overwash followed by periods of relative stability as the shoreface resteepens. This periodic retreat, which occurs evenwith a constant sea-level rise rate, arises when overwash rates and shoreface response rates are large and of similar magnitude. We explore the occurrence of these behaviors across a wide range of parameter values and find that in addition to themaximum overwash flux and the shoreface response rate, barrier response can be particularly sensitive to the sea-level rise rate and back-barrier lagoon slope. Overall, our findings contrast with previous research which has primarily associated complex barrier behavior with changes in external forcing such as sea-level rise rate, sediment supply, or back-barrier geometry