Rates of Sediment Accumulation, Bioturbation and Resuspension in Back Bay, Virginia, a Coastal Lagoon

Back Bay is the northernmost section of the Albemarle-Pamlico lagoon-estuary system. Back Bay lagoon and its associated barrier (Currituck Spit) are moving landward in response to post-glacial sea level rise (2.6 mm yr-1). The long term (100 year time scale) landward migration rate of Currituck Spit may be on the order of a meter per year. Sediment accumulation, resuspension and bioturbation are processes in Back Bay that control the residence time of organic matter in the bay floor. and therefore, effect the rate of nutrient release. As burial proceeds, nutrients in the zone of mixing may be remineralized and recycled back to to water column, or may pass downwards into the zone of permanent burial. X-radiographs indicate that Back Bay sediments are bioturbated by the community of insect larvae, polychaetes and oligochaetes that constitute the benthic infauna of this oligohaline water body. However, analysis of wind records suggests that in some respects, wave resuspension is a more important mixing process. Under mild to moderate conditions, waves in the bay are fetch limited. However, under hurricane conditions the bay surface saturates with breaking waves before peak winds are attained. For a 6 km fetch (a typical long fetch for the Bay), the resuspension threshold is 6 ms-1 (13.5 knots). This value is exceeded 35.7 percent of the time, and sediment is resuspended in about 40 events in a year. Radiogeochemical analyses suggest that long term (100 yr) accumulation rates are of the order of 2-3 mm yr-1. The Bay is floored by mud (silt and clay), with an admixture of sand. Sediment introduction probably occurs largely as a result of \u27wind pumping\u27. During winter storms, strong southerly winds set down southern Back Bay, and drive turbid water from Currituck Sound through the Knotts Island Passage. As the storm progresses, the wind shifts to the north and northwest, sets up lower Back Bay against the Knotts Island Passage, and flushes sediment and water back into Currituck Sound. In this model, Back Bay is a sediment-accumulating sink. The shallow (1-2 m) floor of Back Bay is controlled by an equilibrium between the rate of sediment supply and mean annual wave power. Concentration profiles of 210Pb and 137Cs measured in 1984 indicate that the short term (30 year) accumulation rate was then twice that of sea level rise. The period of record corresponds with Eurasian Milfoil invasion. The historically dense growth of this plant would have modified the equilibrium by damping wave currents, accelerating the sedimentation rate and shifting the Bay floor to a shallower equilibrium depth. The Bay floor appears to presently be undergoing a reduced rate of sedimentation with some local erosion, perhaps in conjunction with a return to an earlier regime

A mathematical model for the distribution of dissolved silicon in interstitial waters----an analytical approach

A mathematical model for the distribution of dissolved silicon in interstitial waters is studied. This model includes the input flux of particulate silicon, bioturbation, the dissolution of silicon particles, and the diffusion of dissolved silicon in the interstitial water. It is shown that the model reduces to a nonlinear eigenvalue problem. This problem is shown to have only one eigenvalue which is determined by the solution of a simple algebraic equation...

Imaging ultra thin layers with helium ion microscopy: Utilizing the channeling contrast mechanism

Background: Helium ion microscopy is a new high-performance alternative to classical scanning electron microscopy. It provides superior resolution and high surface sensitivity by using secondary electrons.\ud \ud Results: We report on a new contrast mechanism that extends the high surface sensitivity that is usually achieved in secondary electron images, to backscattered helium images. We demonstrate how thin organic and inorganic layers as well as self-assembled monolayers can be visualized on heavier element substrates by changes in the backscatter yield. Thin layers of light elements on heavy substrates should have a negligible direct influence on backscatter yields. However, using simple geometric calculations of the opaque crystal fraction, the contrast that is observed in the images can be interpreted in terms of changes in the channeling probability.\ud \ud Conclusion: The suppression of ion channeling into crystalline matter by adsorbed thin films provides a new contrast mechanism for HIM. This dechanneling contrast is particularly well suited for the visualization of ultrathin layers of light elements on heavier substrates. Our results also highlight the importance of proper vacuum conditions for channeling-based experimental methods\u

Asymptotic dynamics of three-dimensional bipolar ultrashort electromagnetic pulses in an array of semiconductor carbon nanotubes

We study the propagation of three-dimensional bipolar ultrashort electromagnetic pulses in an array of semiconductor carbon nanotubes at times much longer than the pulse duration, yet still shorter than the relaxation time in the system. The interaction of the electromagnetic field with the electronic subsystem of the medium is described by means of Maxwell’s equations, taking into account the field inhomogeneity along the nanotube axis beyond the approximation of slowly varying amplitudes and phases. A model is proposed for the analysis of the dynamics of an electromagnetic pulse in the form of an effective equation for the vector potential of the field. Our numerical analysis demonstrates the possibility of a satisfactory description of the evolution of the pulse field at large times by means of a three-dimensional generalization of the sine-Gordon and double sine-Gordon equations

Diffusion in two-component quasiparticle systems of liquid and solid mixtures of helium isotopes

An exact expression for the diffusion time which depends on the interaction rates for particles of not only different, but also of the same species, has been derived from the system of kinetic equations. The result is valid for particles with arbitrary statistics and energy-momentum relations. The derived general relations are valid for investigating diffusion in liquid and solid ³He-⁴He mixtures. The contribution of interaction between quasiparticles of the same type to the diffusion coefficient and effective thermal conductivity of superfluid solutions is analyzed. The calculated values are compared with experimental data. The calculated diffusion coefficient of ³He-⁴He solid solutions differs from the previous theoretical results. A comparison of the obtained diffusion coefficient with experimental data makes it possible to determine the numerical value of the energy band width for impurity quasiparticles.Виходячи з системи кiнетичних рiвнянь для компонент сумiшi отримано точний вираз для дифузiйного часу, що залежить вiд взаємодiї частинок не тiльки рiзних, а й одного типу. Отриманий результ справедливий для частинок з довiльною дисперсiєю і статистикою. Одержаний точний вираз використовується для дослiдження дифузiї у рiдких та твердих квантових розчинах ³He-⁴He. Проаналiзовано внесок взаємодiї мiж квазiчастинками однакових типiв у коефiцiєнт дифузiї та теплопровiдностi надплинних розчинiв. Обчисленi результати порiвнюються з iснуючими експериментальними даними. Отриманий коефiцiєнт дифузiї для твердих квантових розчинiв ³He-⁴He iстотно вiдрiзняється від попереднiх результатiв теорiї. Порiвняння цього результату з експериментальними даними дозволило дiстати числове значення для енергетичної зони квазiчастинок домiшки

Retention, Detention and Overland Flow for Pollutant Removal from Highway Stormwater Runoff, Volume II: Design Guidelines

DTFH61-85-C-00117This volume is the second in a two-volume report which developed design guidelines and specifications for measures to reduce or eliminate the impacts of highway runoff on surface waters. This report provides design guidelines and specifications for three types of management measures for the removal of pollutants from highway stormwater runoff. The three general types of management measures, determined through previous FHWA studies to be effective in treating highway runoff, are: retention systems (basins, trenches, and wells), detention basins (wet detention basins, dry extended detention basins, and wetlands), and overland flow (grassed channels and filter strips). These guidelines have been developed based on the experience of the project team, review of available literature, and bench-scale and field testing

Roadmap on superoscillations

Superoscillations are band-limited functions with the counterintuitive property that they can vary arbitrarily faster than their fastest Fourier component, over arbitrarily long intervals. Modern studies originated in quantum theory, but there were anticipations in radar and optics. The mathematical understanding—still being explored—recognises that functions are extremely small where they superoscillate; this has implications for information theory. Applications to optical vortices, sub-wavelength microscopy and related areas of nanoscience are now moving from the theoretical and the demonstrative to the practical. This Roadmap surveys all these areas, providing background, current research, and anticipating future developments

Varicella zoster virus glycoprotein C increases chemokine-mediated leukocyte migration

Varicella zoster virus (VZV) is a highly prevalent human pathogen that establishes latency in neurons of the peripheral nervous system. Primary infection causes varicella whereas reactivation results in zoster, which is often followed by chronic pain in adults. Following infection of epithelial cells in the respiratory tract, VZV spreads within the host by hijacking leukocytes, including T cells, in the tonsils and other regional lymph nodes, and modifying their activity. In spite of its importance in pathogenesis, the mechanism of dissemination remains poorly understood. Here we addressed the influence of VZV on leukocyte migration and found that the purified recombinant soluble ectodomain of VZV glycoprotein C (rSgC) binds chemokines with high affinity. Functional experiments show that VZV rSgC potentiates chemokine activity, enhancing the migration of monocyte and T cell lines and, most importantly, human tonsillar leukocytes at low chemokine concentrations. Binding and potentiation of chemokine activity occurs through the C-terminal part of gC ectodomain, containing predicted immunoglobulin-like domains. The mechanism of action of VZV rSgC requires interaction with the chemokine and signalling through the chemokine receptor. Finally, we show that VZV viral particles enhance chemokine-dependent T cell migration and that gC is partially required for this activity. We propose that VZV gC activity facilitates the recruitment and subsequent infection of leukocytes and thereby enhances VZ

Moral courage in the workplace: moving to and from the desire and decision to act

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72135/1/j.1467-8608.2007.00484.x.pd