Optical carrier wave shocking: detection and dispersion

Carrier wave shocking is studied using the Pseudo-Spectral Spatial Domain (PSSD) technique. We describe the shock detection diagnostics necessary for this numerical study, and verify them against theoretical shocking predictions for the dispersionless case. These predictions show Carrier Envelope Phase (CEP) and pulse bandwidth sensitivity in the single-cycle regime. The flexible dispersion management offered by PSSD enables us to independently control the linear and nonlinear dispersion. Customized dispersion profiles allow us to analyze the development of both carrier self-steepening and shocks. The results exhibit a marked asymmetry between normal and anomalous dispersion, both in the limits of the shocking regime and in the (near) shocked pulse waveforms. Combining these insights, we offer some suggestions on how carrier shocking (or at least extreme self-steepening) might be realised experimentally.Comment: 9 page

Analysis of longitudinal variations in North Pacific alkalinity to improve predictive algorithms

The causes of natural variation in alkalinity in the North Pacific surface ocean need to be investigated to understand the carbon cycle and to improve predictive algorithms. We used GLODAPv2 to test hypotheses on the causes of three longitudinal phenomena in Alk*, a tracer of calcium carbonate cycling. These phenomena are (a) an increase from east to west between 45°N and 55°N, (b) an increase from west to east between 25°N and 40°N, and (c) a minor increase from west to east in the equatorial upwelling region. Between 45°N and 55°N, Alk* is higher on the western than on the eastern side, and this is associated with denser isopycnals with higher Alk* lying at shallower depths. Between 25°N and 40°N, upwelling along the North American continental shelf causes higher Alk* in the east. Along the equator, a strong east-west trend was not observed, even though the upwelling on the eastern side of the basin is more intense, because the water brought to the surface is not high in Alk*. We created two algorithms to predict alkalinity, one for the entire Pacific Ocean north of 30°S and one for the eastern margin. The Pacific Ocean algorithm is more accurate than the commonly used algorithm published by Lee et al. (2006), of similar accuracy to the best previously published algorithm by Sasse et al. (2013), and is less biased with longitude than other algorithms in the subpolar North Pacific. Our eastern margin algorithm is more accurate than previously published algorithms

Biological and physical forcing of carbonate chemistry in an upwelling filament off northwest Africa: Results from a Lagrangian study

The Mauritanian upwelling system is one of the most biologically productive regions of the world's oceans. Coastal upwelling transfers nutrients to the sun-lit surface ocean, thereby stimulating phytoplankton growth. Upwelling of deep waters also supplies dissolved inorganic carbon (DIC), high levels of which lead to low calcium carbonate saturation states in surface waters, with potentially adverse effects on marine calcifiers. In this study an upwelled filament off the coast of northwest Africa was followed using drifting buoys and sulphur hexafluoride to determine how the carbonate chemistry changed over time as a result of biological, physical and chemical processes. The initial pHtot in the mixed layer of the upwelled plume was 7.94 and the saturation states of calcite and aragonite were 3.4 and 2.2, respectively. As the plume moved offshore over a period of 9 days, biological uptake of DIC (37 ?mol kg?1) reduced pCO2 concentrations from 540 to 410 ?atm, thereby increasing pHtot to 8.05 and calcite and aragonite saturation states to 4.0 and 2.7 respectively. The increase (25 ?mol kg?1) in total alkalinity over the 9 day study period can be accounted for solely by the combined effects of nitrate uptake and processes that alter salinity (i.e., evaporation and mixing with other water masses). We found no evidence of significant alkalinity accumulation as a result of exudation of organic bases by primary producers. The ongoing expansion of oxygen minimum zones through global warming will likely further reduce the CaCO3 saturation of upwelled waters, amplifying any adverse consequences of ocean acidification on the ecosystem of the Mauritanian upwelling system

The Role of Habitat Shaping Motion Detection in Two Songbirds

Double cones of birds are photoreceptors associated with motion perception, and perceiving motion is highly important to detect predators. Predation risks varies between habitats and may impose selective pressures that could affect organisms’ traits. There is evidence that birds show interspecific variations in visual system properties, such as the photoreceptor densities (single and double cones) and distribution across the retina. However, little is known about the relationship between the distribution of double cones and predator scanning strategies in birds living in different habitats. The goal of this study was to compare double cones distributions of birds that live in open vs. closed habitats. We measured the density and distribution of double cones in 2 species of the order Passeriformes. We found that the density of double cones in both species (open and closed habitat) is greater in the retina dorsal region. This result suggests that other visual traits might be taken into account in future work to better elucidate the relationship between habitat type and sensing motion. Moreover, the White-throated Sparrow had a more homogeneous distribution of double cones, result expected for this closed habitat species. Future work is suggested to be done using more individuals and more species to assess fully understand the evolution of predator- prey interactions and learn how prey can optimize vigilance strategies in different habitats with different predation pressure

Conodont (U-Th)/He thermochronology of the Mormon Mountains, Tule Spring Hills, and Beaver Dam Mountains, southeastern Nevada and southwestern Utah

ABSTRACT Although (U-Th)/He thermochronology is a well-established dating technique used to understand the temperature-time histories of rocks, the method is restricted to rocks that contain specific accessory minerals such as apatite or zircon. Marine carbonates and shales typically lack these accessory phases, and thus present a challenge for application of the method. Here, we explore the utility of biogenic apatite from conodonts as a (U-Th)/He thermochronometer at a well- studied calibration site located in eastern Nevada and southwestern Utah. We perform (U-Th)/He thermochronometry, laser ablation inductively coupled plasma mass spectrometry, X-ray micro-computed tomography, and scanning electron microscopy on specimens with conodont color alteration indices (CAI) of 1.5 – 3 extracted from carbonate rocks in the footwalls of low-angle normal faults in the Mormon Mountains, Tule Spring Hills, and Beaver Dam Mountains. (U-Th)/He (CHe) dates have high scatter; dates are commonly reproducible to 20% of sample means, but can deviate up to 150%. All CAI 1.5 – 2.5 conodonts produce CHe dates younger than 193 Ma, consistent with thermal resetting of samples; however, most CAI 3 conodonts give ages 2 – 3x older than Mississippian and Permian deposition. Average U, Th, and rare earth element (REE) concentrations depend on porosity and permeability differences between albid and hyaline conodont tissue and range from <10 to 100s of ppm in concentration. Parent isotope concentrations are especially low in CAI 3 conodonts, commonly <1 ppm, and there is an inverse relationship between these concentrations and CHe dates. The majority of parent U, Th, and Sm, and REEs are concentrated within the outer 5 μm of the conodont elements and consistently show 5 – 10x enrichment relative to cores. Margin enrichment is also depressed with increasing CAI. SEM imaging shows a shift in the orientation of apatite microcrystallites from perpendicular to parallel to the major axis of the conodont elements at CAI 3, and corrosion and recrystallization features on the surfaces of some CAI 2.5 and 3 conodonts. We propose these microstructural changes associated with increasing CAI influence CHe dates. Parent isotope loss occurs during the post-cooling stage, either in the outcrop or in the laboratory. Our hypothesis is that the double-buffered formic acid procedure for dissolving dolomitized carbonates may accelerate this loss in higher CAI conodonts

What drives the latitudinal gradient in open-ocean surface dissolved inorganic carbon concentration?

Previous work has not led to a clear understanding of the causes of spatial pattern in global surface ocean dissolved inorganic carbon (DIC), which generally increases polewards. Here, we revisit this question by investigating the drivers of observed latitudinal gradients in surface salinity-normalized DIC (nDIC) using the Global Ocean Data Analysis Project version 2 (GLODAPv2) database. We used the database to test three different hypotheses for the driver producing the observed increase in surface nDIC from low to high latitudes. These are (1) sea surface temperature, through its effect on the CO2 system equilibrium constants, (2) salinity-related total alkalinity (TA), and (3) highlatitude upwelling of DIC- and TA-rich deep waters. We find that temperature and upwelling are the two major drivers. TA effects generally oppose the observed gradient, except where higher values are introduced in upwelled waters. Temperature-driven effects explain the majority of the surface nDIC latitudinal gradient (182 of the 223 μmol kg1 increase from the tropics to the high-latitude Southern Ocean). Upwelling, which has not previously been considered as a major driver, additionally drives a substantial latitudinal gradient. Its immediate impact, prior to any induced air-sea CO2 exchange, is to raise Southern Ocean nDIC by 220 μmol kg1 above the average low-latitude value. However, this immediate effect is transitory. The long-term impact of upwelling (brought about by increasing TA), which would persist even if gas exchange were to return the surface ocean to the same CO2 as without upwelling, is to increase nDIC by 74 μmol kg1 above the low-latitude average

Autogenous Brachial—Brachial Fistula for Vein Access. Haemodynamic Factors Predicting Outcome and 1 Year Clinical Data

AbstractTwo-stage autogenous brachial vein–brachial artery access (ABBA) has been proposed as an option where adequate superficial vein is not available for the creation of conventional haemodialysis fistulae.MethodsThis report depicts the clinical outcome of a series of 17 consecutive patients who underwent ABBA in a single centre. Of the 17 patients, nine had had at least one previous arterioventricular (AV) fistula or graft, and eight were new to haemodialysis. Patencies were assessed using the Kaplan–Meier survival analysis.ResultsIn 14 patients, the brachial vein was transposed (82%) and the time to transposition ranged from 4 to 26 weeks (median time: 6 weeks). The functional patency rate was 45.75% at 12 months. After stage one, all fistulas that went on to develop well had a brachial vein flow of at least 900mlmin−1, and this was significantly higher than in fistulas that failed to develop (p=0.005). The maturation rate in our study was 65% and the median time to cannulation of the fistula was 8weeks from the stage 1. Of the 17 patients, 12 (71%) experienced at least one complication. Ten (59%) demonstrated moderate-to-severe stenoses; eight of which necessitated angioplasty and/or percutaneous mechanical thrombolysis.ConclusionsABBA was characterised by a high incidence of complications and a long period to achieve maturation. Despite close monitoring and a high rate of secondary interventions, the patency rate was low. With this experience, we now only consider it an alternative in patients without adequate superficial veins, who have had failed grafts or where there is a very high risk of infection