Long wave generation by wave groups in the nearshore

This study investigates the forcing of leaky mode long wave by incident wave groups in the nearshore. Using both field and model data, two previously proposed generation models are evaluated: the bounded long wave of Longuet-Higgins and Stewart (1964), and the breakpoint-forced long wave of Symonds et al. (1982). New methods of parameterizing incident wave height modulations are proposed, including an amplitude time series and a clearly defined groupiness factor. Cross-correlations between observed amplitude and low frequency time series clearly document the release and shoreline reflection of a group-forced long wave. The shallow water amplification of the component identified as the bounded long wave is less than predicted by theory, but much larger than the shoaling of a free long wave. A time-variant numerical model is developed to further explain the observed cross-correlation signal, and to evaluate the relative importance of the two modes of long wave generation. The model simulates the forcing of leaky mode long waves by incident wave groups as they progress through the shoaling and breaking regions. New methods of modeling both short and long waves in the nearshore are proposed. Field observations are used to verify the model: the natural cross-correlation signal is exceedingly well predicted using model generated data. Simulated time series reveal that the modification of the cross-correlation signal toward shore is related to a fundamental change in bound wave dynamics, and not the addition of the breakpoint-forced wave as previously speculated. The relative importance of breakpoint-forced and bounded long waves is determined through a series of model tests with plane beaches and monochromatic wave groups. Consistent with field observations, the breakpoint-forced wave is secondary to the bounded long wave under almost all conditions, except at very low frequencies and with high beach slopes. Overall, model predictions indicate that the directly group-forced component accounts for approximately half the total long wave height found under field conditions. This is consistent with previous observations that both leaky and edge wave modes are energetic on natural beaches

Water resource problems of energy projects in the Colorado River Basin

The successful development of western coal and oil shale deposits is dependent, to a significant degree, on the availability of adequate water supplies. EQL is involved in a study of the aggregate effects of various energy activities in the upper Colorado River Basin on downstream water quantity and quality. These activities will tend to reduce the available water in the river, and could increase its salinity, which is already so high as to interfere with downstream domestic and agricultural use

The Silicon–Hydrogen Exchange Reaction: Catalytic Kinetic Resolution of 2-Substituted Cyclic Ketones

We have recently reported the strong and confined, chiral acid-catalyzed asymmetric ‘silicon−hydrogen exchange reaction’. One aspect of this transformation is that it enables access to enantiopure enol silanes in a tautomerizing σ-bond metathesis, via deprotosilylation of ketones with allyl silanes as the silicon source. However, until today, this reaction has not been applied to racemic, 2-substituted, cyclic ketones. We show here that these important substrates readily undergo a highly enantioselective kinetic resolution furnishing the corresponding kinetically preferred enol silanes. Mechanistic studies suggest the fascinating possibility of advancing the process to a dynamic kinetic resolution

Color Transparency at COMPASS energies

Pionic quasielastic knockout of protons from nuclei at 200 GeV show very large effects of color transparency as -t increases from 0 to several GeV^2. Similar effects are expected for quasielastic photoproduction of vector mesons.Comment: 9 pages, 4 figure

Barrier island breach evolution : alongshore transport and bay-ocean pressure gradient interactions

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: Oceans 121 (2016): 8720–8730, doi:10.1002/2016JC012029.Physical processes controlling repeated openings and closures of a barrier island breach between a bay and the open ocean are studied using aerial photographs and atmospheric and hydrodynamic observations. The breach site is located on Pea Island along the Outer Banks, separating Pamlico Sound from the Atlantic Ocean. Wind direction was a major control on the pressure gradients between the bay and the ocean to drive flows that initiate or maintain the breach opening. Alongshore sediment flux was found to be a major contributor to breach closure. During the analysis period from 2011 to 2016, three hurricanes had major impacts on the breach. First, Hurricane Irene opened the breach with wind-driven flow from bay to ocean in August 2011. Hurricane Sandy in October 2012 quadrupled the channel width from pressure gradient flows due to water levels that were first higher on the ocean side and then higher on the bay side. The breach closed sometime in Spring 2013, most likely due to an event associated with strong alongshore sediment flux but minimal ocean-bay pressure gradients. Then, in July 2014, Hurricane Arthur briefly opened the breach again from the bay side, in a similar fashion to Irene. In summary, opening and closure of breaches are shown to follow a dynamic and episodic balance between along-channel pressure gradient driven flows and alongshore sediment fluxes.2017-06-1

Walking within Film: Gilbertson and Tait and Insignificant Steps Within landscape

Two Scottish women film-makers, Jenny Gilbertson and Margaret Tait both encounter walking within 20th century Island culture. This study considers the function itself within cinema as an occurrence of landscape. To this end it treats their earlier work, investigating it through a Deleuzian cinematic framework. The predominantly visual field of film is demonstrated as rendering walking relatively invisible, with particular relevance to the action image. The wider investigative construct of affect is also observed as incompatible. Only in Tait’s later work does the cinema of chronology convey a satisfactory explanation of walking, but this is confined to the schema of ‘organic’ documentary. Finally, walking in relation to landscape is considered as conceptual act. This employs a model suggested by Jean-Luc Nancy that is only partially attainable through cinema, so that the role of the medium itself is open to doubt

Networks of lexical borrowing and lateral gene transfer in language and genome evolution

Like biological species, languages change over time. As noted by Darwin, there are many parallels between language evolution and biological evolution. Insights into these parallels have also undergone change in the past 150 years. Just like genes, words change over time, and language evolution can be likened to genome evolution accordingly, but what kind of evolution? There are fundamental differences between eukaryotic and prokaryotic evolution. In the former, natural variation entails the gradual accumulation of minor mutations in alleles. In the latter, lateral gene transfer is an integral mechanism of natural variation. The study of language evolution using biological methods has attracted much interest of late, most approaches focusing on language tree construction. These approaches may underestimate the important role that borrowing plays in language evolution. Network approaches that were originally designed to study lateral gene transfer may provide more realistic insights into the complexities of language evolution

Monte Carlo simulation of coagulation in discrete particle-size distributions. Part 2. Interparticle forces and the quasi-stationary equilibrium hypothesis

Hunt (1982) and Friedlander (1960a, b) used dimensional analysis to derive expressions for the steady-state particle-size distribution in aerosols and hydrosols. Their results were supported by the Monte Carlo simulation of a non-interacting coagulating population of suspended spherical particles developed by Pearson, Valioulis & List (1984). Here the realism of the Monte Carlo simulation is improved by accounting for the modification to the coagulation rate caused by van der Waals', electrostatic and hydrodynamic forces acting between particles. The results indicate that the major hypothesis underlying the dimensional reasoning, that is, collisions between particles of similar size are most important in determining the shape of the particle size distribution, is valid only for shear-induced coagulation. It is shown that dimensional analysis cannot, in general, be used to predict equilibrium particle-size distributions, mainly because of the strong dependence of the interparticle force on the absolute and relative size of the interacting particles

Monte Carlo simulation of coagulation in discrete particle-size distributions. Part 1. Brownian motion and fluid shearing

A method for the Monte Carlo simulation, by digital computer, of the evolution of a colliding and coagulating population of suspended particles is described. Collision mechanisms studied both separately and in combination are: Brownian motion of the particles, and laminar and isotropic turbulent shearing motions of the suspending fluid. Steady-state distributions are obtained by adding unit-size particles at a constant rate and removing all particles once they reach a preset maximum volume. The resulting size distributions are found to agree with those obtained by dimensional analysis (Hunt 1982)

Modeled alongshore circulation and force balances onshore of a submarine canyon

Author Posting. © American Geophysical Union, 2015. 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: Oceans 120 (2015): 1887–1903, doi:10.1002/2014JC010555.Alongshore force balances, including the role of nonlinear advection, in the shoaling and surf zones onshore of a submarine canyon are investigated using a numerical modeling system (Delft3D/SWAN). The model is calibrated with waves and alongshore flows recorded over a period of 1.5 months at 26 sites along the 1.0, 2.5, and 5.0 m depth contours spanning about 2 km of coast. Field observation-based estimates of the alongshore pressure and radiation-stress gradients are reproduced well by the model. Model simulations suggest that the alongshore momentum balance is between the sum of the pressure and radiation-stress gradients and the sum of the nonlinear advective terms and bottom stress, with the remaining terms (e.g., wind stress and turbulent mixing) being negligible. The simulations also indicate that unexplained residuals in previous field-based estimates of the momentum balance may be owing to the neglect of the nonlinear advective terms, which are similar in magnitude to the sum of the forcing (pressure and radiations stress gradients) and to the bottom stress.Funding was provided by a joint WHOI-USGS postdoctoral scholarship, NSF, ONR, and ASD(R&E).2015-09-2