Size-resolved aerosol fluxes above a temperate broadleaf forest

Aerosol fluxes were measured by eddy-correlation for 8 weeks of the summer and fall of 2011 above a temperate broadleaf forest in central Ontario, Canada. These size-resolved measurements apply to particles with optical diameters between 50 and 500 nm and are the first ones reported above a temperate deciduous forest. The particle spectrometer was located on top of the flux tower in order to reduce signal dampening in the tube and thus maximize measurement efficiency. The 8-week data set extends into autumn, capturing leaf senescence and loss, offering a rare opportunity to investigate the influence of leaf area index on particle transfer. A distinct pattern of emission and deposition that depends on the particle size is highlighted: while the smallest particles (dp  100 nm) are preferentially deposited (62% of the time). For the size bins with detection efficiency above 50% (68–292 nm), the median transfer velocity for each bin varies between +1.34 and −2.69 mm s−1 and is equal to −0.21 mm s−1 for the total particle count. The occurrence of the upward fluxes shows a marked diurnal pattern. Possible explanations for these upward fluxes are proposed. The measurements, and their comparison with an existing model, highlight some of the key drivers of the particle transfer onto a broadleaf forest: particle size, friction velocity, leaf area index and atmospheric stability.We are grateful to the Haliburton forest staff and owner for their support, as well as Ting Zheng and Jing Ming Chen (Dept of Geography, Univ. of Toronto) for sharing the TRAC instrument LAI data. The UHSAS and SMPS instruments were contributed by the Canadian Aerosol Research Network, funded by the Canada Foundation for Innovation. (Canada Foundation for Innovation)First author draf

The effect of flowering stage in wheat on the infection efficiency of Ustilago tritici

Dans l'ouest du Canada, la détermination du niveau de résistance de lignées de blé (Triticum aestivum) à l’ Ustiiago tritici est habituellement faite par inoculation lorsque les plantes atteignent le stade mi-anthèse du développement de l'épi. Par contre, il n'est pas toujours possible de faire les inoculations à ce stade, ainsi des inoculations sont parfois faites quelques jours avant ou après la mi-anthèse. L'objectif de cette étude était de déterminer si l'inoculation, par la méthode du vide partiel, d'épis de blé avec l’U. tritici à différents stades du développement de l'épi pouvait avoir un effet sur le nombre de grains viables par épi et, ultérieurement, sur le pourcentage de plantes cariées issues de grains inoculés. À chaque année durant 5 ans, quatre lignées de blé ont été inoculées au champ à trois différents stades du développement de l'épi. Les stades du développement de l'épi étudiés étaient la pré-anthèse, la mi-anthèse (les anthères à chaque extrémité de l'épi sont déhiscentes alors que celles du centre sont jaunes) et la post-anthèse (toutes les anthères sont déhiscentes). Il y avait des différences significatives entre les quatre lignées de blé et les 5 années de l'étude quant au nombre de grains viables par épi et le pourcentage de plantes cariées. Un nombre de grains viables par épi plus grand et un pourcentage plus faible de plantes cariées ont été significativement obtenus avec l'inoculation post-anthèse. Nous concluons que l'inoculation de l’Ustilago tritici par la méthode du vide partiel doit être faite au stade préanthèse ou mi-anthèse du développement de l'épi de blé afin de minimiser les effets négatifs de la maturité sur l'efficacité d'infection.In general, in western Canada, the inoculation of wheat (Triticum aestivum) lines to determine the level of resistance to Ustiiago tritici occurs when the plants are at the mid-anthesis stage of spike development. However, it is not always possible to inoculate at this stage so occasionally inoculations are done a few days before or after mid-anthesis. The objective of this study was to determine if inoculation of wheat spikes with U. tritici at different stages of spike development using the partial-vacuum method affected the number of viable seed per spike and subsequent percentage of smutted plants grown from inoculated seed. Four lines of wheat were inoculated at three different stages of spike development in the field each year for 5 years. The stages of spike development studied were preanthesis, mid-anthesis (anthers at either end of the spike were dehisced while those in the middle of the spike were yellow), and post-anthesis (all anthers dehisced). There were significant differences among the four wheat lines and the 5 years of the study for the number of viable seed per spike and the percent of smutted plants. Inoculation at post-anthesis resulted in a significantly greater number of viable seed per spike and lower percentage of smutted plants. We conclude that the partial-vacuum method of inoculation with Ustiiago tritici should be done at the pre- or midanthesis stage of wheat head development to minimize the negative effect of maturity on infection efficiency

Two-step magnetization reversal FORC fingerprint of coupled bi-segmented Ni/Co magnetic nanowire arrays

First Order Reversal Curve (FORC) analysis has been established as an appropriate method to investigate the magnetic interactions among complex ferromagnetic nanostructures. In this work, the magnetization reversal mechanism of bi-segmented nanowires composed by long Co and Ni segments contacted at one side was investigated, as a model system to identify and understand the FORC fingerprint of a two-step magnetization reversal process. The resulting hysteresis loop of the bi-segmented nanowire array exhibits a completely different magnetic behavior than the one expected for the magnetization reversal process corresponding to each respective Co and Ni nanowire arrays, individually. Based on the FORC analysis, two possible magnetization reversal processes can be distinguished as a consequence of the ferromagnetic coupling at the interface between the Ni and Co segments. Depending on the relative difference between the magnetization switching fields of each segment, the softer magnetic phase induces the switching of the harder one through the injection and propagation of a magnetic domain wall when both switching fields are comparable. On the other hand, if the switching fields values differ enough, the antiparallel magnetic configuration of nanowires is also possible but energetically unfavorable, thus resulting in an unstable magnetic configuration. Making use of the different temperature dependence of the magnetic properties for each nanowire segment with different composition, one of the two types of magnetization reversal is favored, as demonstrated by FORC analyses

Sedimentary dynamics and high-frequency sequence stratigraphy of the southwestern slope of Great Bahama Bank

New geophysical data from the leeward slope of Great Bahama Bank show how contour currents shape the slope and induce re-sedimentation processes. Along slope segments with high current control, drift migration and current winnowing at the toe of slope form a deep moat. Here, the slope progradation is inhibited by large channel incisions and the accumulation of large mass transport complexes, triggered by current winnowing. In areas where the slope is bathed by weaker currents, the accumulation of mass transport complexes and channel incision is rather controlled by the position of the sea level. Large slope failures were triggered during the Mid-Pleistocene transition and Mid-Brunhes event, both periods characterized by changes in the cyclicity or the amplitude of sea-level fluctuations. Within the seismic stratigraphic framework of third order sequences, four sequences of higher order were identified in the succession of the upper Pleistocene. These higher order sequences also show clear differences in function of the slope exposure to contour currents. Two stochastic models emphasize the role of the contour currents and slope morphology in the facies distribution in the upper Pleistocene sequences. In areas of high current influence the interplay of erosional and depositional processes form a complex fades pattern with downslope and along strike facies alterations. In zones with lower current influence, major facies alternations occur predominately in downslope direction, and a layer-cake pattern characterizes the along strike direction. Therefore, this study highlights that contour currents are an underestimated driver for the sediment distribution and architecture of carbonate slopes

A Macroscope for Global History. Seshat Global History Databank: a methodological overview

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Digital Humanities Quarterly following peer review. The final published version is available online at: http://www.digitalhumanities.org/dhq/vol/10/4/000272/000272.html This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 LicenseThis article introduces the ‘Seshat: Global History’ project, the methodology it is based upon and its potential as a tool for historians and other humanists. The article describes in detail how the Seshat methodology and platform can be used to tackle big questions that play out over long time scales whilst allowing users to drill down to the detail and place every single data point both in its historic and historiographical context. Seshat thus offers a platform underpinned by a rigorous methodology to actually do 'longue durée' history and the article argues for the need for humanists and social scientists to engage with data driven ‘longue durée' history. The article argues that Seshat offers a much needed infrastructure in which different skills sets and disciplines can come together to analyze the past using long timescales. In addition to highlighting the theoretical and methodological underpinnings, the potential of Seshat is demonstrated by showcasing three case studies. Each of these case studies is centred around a set of long standing questions and historiographical debates and it is argued that the introduction of a Seshat approach has the potential to radically alter our understanding of these questions.Peer reviewedFinal Accepted Versio

Lameness in cattle: recent research to inform clinical practice

Lameness in cattle has significant consequences for welfare, health and productivity. More research is now being done on lameness and this article, the first in a two-part series, provides an update on research-based advances in the field published from around the world over the past five years. These developments have improved our understanding of lameness in cattle and can inform clinical practice and the control of lameness on-farm. The second article, to be published in a subsequent issue of In Practice, will cover the understanding and management of claw health and claw horn lesions

Prospects for observations of high-energy cosmic tau neutrinos

We study prospects for the observations of high-energy cosmic tau neutrinos (E \geq 10^6 GeV) originating from proton acceleration in the cores of active galactic nuclei. We consider the possibility that vacuum flavor neutrino oscillations induce a tau to muon neutrino flux ratio greatly exceeding the rather small value expected from intrinsic production. The criterias and event rates for under water/ice light Cerenkov neutrino telescopes are given by considering the possible detection of downgoing high-energy cosmic tau neutrinos through characteristic double shower events.Comment: 10 pages, Revtex, 3 figures included with eps