THE MARINE RADIOCARBON BOMB PULSE ACROSS THE TEMPERATE NORTH ATLANTIC: A COMPILATION OF Delta C-14 TIME HISTORIES FROM ARCTICA ISLANDICA GROWTH INCREMENTS

Marine radiocarbon bomb-pulse time histories of annually resolved archives from temperate regions have been underexploited. We present here series of Delta C-14 excess from known-age annual increments of the long-lived bivalve mollusk Arctica islandica from 4 sites across the coastal North Atlantic (German Bight, North Sea; Tromso, north Norway; Siglufjordur, north Icelandic shelf; Grimsey, north Icelandic shelf) combined with published series from Georges Bank and Sable Bank (NW Atlantic) and the Oyster Ground (North Sea). The atmospheric bomb pulse is shown to be a step-function whose response in the marine environment is immediate but of smaller amplitude and which has a longer decay time as a result of the much larger marine carbon reservoir. Attenuation is determined by the regional hydrographic setting of the sites, vertical mixing, processes controlling the isotopic exchange of C-14 at the air-sea boundary, C-14 content of the freshwater flux, primary productivity, and the residence time of organic matter in the sediment mixed layer. The inventories form a sequence from high magnitude-early peak (German Bight) to low magnitude-late peak (Grimsey). All series show a rapid response to the increase in atmospheric Delta C-14 excess but a slow response to the subsequent decline resulting from the succession of rapid isotopic air-sea exchange followed by the more gradual isotopic equilibration in the mixed layer due to the variable marine carbon reservoir and incorporation of organic carbon from the sediment mixed layer. The data constitute calibration series for the use of the bomb pulse as a high-resolution dating tool in the marine environment and as a tracer of coastal ocean water masses.

Detection of intrastrain antigenic variation of Bacteroides fragilis surface polysaccharides by monoclonal antibody labelling

Bacteroides fragilis is a constituent of the normal resident microbiota of the human intestine and is the gram-negative obligately anaerobic bacterium most frequently isolated from clinical infection. Surface polysaccharides are implicated as potential virulence determinants. We present evidence of within strain immunochemical variation of surface polysaccharides in populations that are noncapsulate by light microscopy as determined by monoclonal antibody labelling. Expression of individual epitopes can be enriched from a population of an individual strain by use of immunomagnetic beads. Also, individual colonies in which either >94% or 94% of the bacteria carry a given epitope, there is no enrichment for other epitopes recognized by different polysaccharide-specific monoclonal antibodies. This intrastrain variation has important implications for the development of potential vaccines or immunodiagnostic tests.

Pulse shape measurements using single shot-frequency resolved optical gating for high energy (80 J) short pulse (600 fs) laser

Relevant to laser based electron/ion accelerations, a single shot second harmonic generation frequency resolved optical gating (FROG) system has been developed to characterize laser pulses (80 J, ∼600 fs) incident on and transmitted through nanofoil targets, employing relay imaging, spatial filter, and partially coated glass substrates to reduce spatial nonuniformity and B-integral. The device can be completely aligned without using a pulsed laser source. Variations of incident pulse shape were measured from durations of 613 fs (nearly symmetric shape) to 571 fs (asymmetric shape with pre- or postpulse). The FROG measurements are consistent with independent spectral and autocorrelation measurements. © 2010 American Institute of Physics.

Three-Dimensional Dynamics of Breakout Afterburner Ion Acceleration Using High-Contrast Short-Pulse Laser and Nanoscale Targets

Breakout afterburner (BOA) laser-ion acceleration has been demonstrated for the first time in the laboratory. In the BOA, an initially solid-density target undergoes relativistically induced transparency, initiating a period of enhanced ion acceleration. First-ever kinetic simulations of the BOA in three dimensions show that the ion beam forms lobes in the direction orthogonal to laser polarization and propagation. Analytic theory presented for the electron dynamics in the laser ponderomotive field explains how azimuthal symmetry breaks even for a symmetric laser intensity profile; these results are consistent with recent experiments at the Trident laser facility. © 2011 American Physical Society.

Mono-energetic ion beam acceleration in solitary waves during relativistic transparency using high-contrast circularly polarized short-pulse laser and nanoscale targets

In recent experiments at the Trident laser facility, quasi-monoenergetic ion beams have been obtained from the interaction of an ultraintense, circularly polarized laser with a diamond-like carbon target of nm-scale thickness under conditions of ultrahigh laser pulse contrast. Kinetic simulations of this experiment under realistic laser and plasma conditions show that relativistic transparency occurs before significant radiation pressure acceleration and that the main ion acceleration occurs after the onset of relativistic transparency. Associated with this transition are a period of intense ion acceleration and the generation of a new class of ion solitons that naturally give rise to quasi-monoenergetic ion beams. An analytic theory has been derived for the properties of these solitons that reproduces the behavior observed in kinetic simulations and the experiments. © 2011 American Institute of Physics.

Pulse-response TAP studies of the reverse water-gas shift reaction over a Pt/CeO2 catalyst

The temporal analysis of products (TAP) technique was successfully applied for the first time to investigate the reverse water-gas shift (RWGS) reaction over a 2% Pt/CeO2 catalyst. The adsorption/desorption rate constants for CO2 and H-2 were determined in separate TAP pulse-response experiments, and the number of H-containing exchangeable species was determined using D-2 multipulse TAP experiments. This number is similar to the amount of active sites observed in previous SSITKA experiments. The CO production in the RWGS reaction was studied in a TAP experiment using separate (sequential) and simultaneous pulsing Of CO2 and H-2. A small yield of CO was observed when CO2 was pulsed alone over the reduced catalyst, whereas a much higher CO yield was observed when CO2 and H-2 were pulsed consecutively. The maximum CO yield was observed when the CO2 pulse was followed by a H-2 pulse with only a short (1 s) delay. Based on these findings, we conclude that an associative reaction mechanism dominates the RWGS reaction under these experimental conditions. The rate constants for several elementary steps can be determined from the TAP data. In addition, using a difference in the time scale of the separate reaction steps identified in the TAP experiments, it is possible to distinguish a number of possible reaction pathways. (c) 2005 Elsevier Inc. All rights reserved.