Nitrogen availability and transformations in Missisquoi Bay, Lake Champlain : effects on phytoplankton community structure and cyanobacterial blooms

L'objectif de l'étude était de déterminer la disponibilité de l'azote (N) et les transformations dans la colonne d'eau (WC) et l'interface eau-sédiments (SWI), et d'établir des liens avec les éclosions de cyanobactéries dans la baie Missisquoi du lac Champlain. Ces paramètres ont été évalués à l'embouchure de la rivière aux Brochets et dans le bassin central, afin d'obtenir un gradient environnemental pour étudier l'effet des décharges de nutriments sur le cycle de l'azote et la structure des communautés de phytoplancton (PCS). Les résultats portent à croire qu'en général, les nutriments ne limitent pas la productivité primaire, mais que l'azote peut la limiter à petite échelle. Contrairement à nos hypothèses, le phytoplancton semblait gérer les concentrations en nutriments, et non l'inverse. La PCS n'affectait pas la consommation en NH4+ dans la WC. De même, le taux de régénération du NH4+ dans la WC n'était pas relié à la PCS, ce qui réfute l'hypothèse que les cyanobactéries inhibent la régénération. Les sédiments agissaient comme un puits de NO3-, tel que prédit, mais étaient aussi une source de NH4+ vers la WC, contrairement aux hypothèses. Une biomasse élevée de cyanobactéries était associée avec une relâche subséquente de NO3- des sédiments, ce qui pourrait impliquer une stimulation de la nitrification. L'anammox explique de 6 à 10% de la production totale de diazote, mais la dénitrification en était le principal vecteur. Les taux de dénitrification étaient reliés à la concentration instantanée en azote de la WC, mais pas à ses fluctuations. On observe des relations similaires entre les flux de NO3- dans les sédiments et la dénitrification avec la biomasse cyanobactérienne antérieure. Cela suggère que des concentrations inférieures en azote dans la WC, à la suite de floraisons de cyanobactéries, ont rendu possibles des taux de dénitrifications inférieurs. Les données ne corroborent pas l'hypothèse selon laquelle la dénitrification mènerait à des conditions propices pour les cyanobactéries fixatrices d'azote. Au contraire, les résultats suggèrent que les conditions propices aux cyanobactéries fixatrices d'azote causent une réduction des taux de dénitrification. Le lac était un puits net d'azote dans un budget préliminaire calculé en utilisant le cycle du NH4+ dans la WC et les flux d'azote à l'SWI, comparés aux apports en azote estimés des affluents. Ces calculs révèlent une source d'azote « manquante », qui pourrait être la fixation d'azote dans la WC selon les résultats. Les taux observés de fixation d'azote dans la WC n'étaient pas différents de ceux des contrôles expérimentaux, mais même ces taux négligeables sont d'un ordre de grandeur plus élevé que ceux nécessaires pour combler l'azote « manquant ».\ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : cycle de l'azote, cyanobactéries, dénitrification, eutrophisation, budget d'azot

Evaluation of US Federal Guidelines (Primary Response Incident Scene Management [PRISM]) for Mass Decontamination of Casualties During the Initial Operational Response to a Chemical Incident

Study objective The aim of this study was to evaluate the clinical and operational effectiveness of US federal government guidance (Primary Response Incident Scene Management [PRISM]) for the initial response phase to chemical incidents. Methods The study was performed as a large-scale exercise (Operation DOWNPOUR). Volunteers were dosed with a chemical warfare agent simulant to quantify the efficacy of different iterations of dry, ladder pipe system, or technical decontamination. Results The most effective process was a triple combination of dry, ladder pipe system, and technical decontamination, which attained an average decontamination efficiency of approximately 100% on exposed hair and skin sites. Both wet decontamination processes (ladder pipe system and technical decontamination, alone or in combination with dry decontamination) were also effective (decontamination efficiency >96%). In compliant individuals, dry decontamination was effective (decontamination efficiency approximately 99%), but noncompliance (tentatively attributed to suboptimal communication) resulted in significantly reduced efficacy (decontamination efficiency approximately 70%). At-risk volunteers (because of chronic illness, disability, or language barrier) were 3 to 8 times slower than ambulatory casualties in undergoing dry and ladder pipe system decontamination, a consequence of which may be a reduction in the overall rate at which casualties can be processed. Conclusion The PRISM incident response protocols are fit for purpose for ambulatory casualties. However, a more effective communication strategy is required for first responders (particularly when guiding dry decontamination). There is a clear need to develop more appropriate decontamination procedures for at-risk casualties.Peer reviewedFinal Published versio

Health Behaviour Changes after Diagnosis of Chronic Illness Among Canadians Aged 50 or Older

Changes in health behaviors (smoking, physical activity, alcohol consumption, and fruit and vegetable consumption) after diagnosis of chronic health conditions (heart disease, cancer, stroke, respiratory disease, and diabetes) were examined among Canadians aged 50 or older. Results from 12 years of longitudinal data from the Canadian National Population Health Survey indicated relatively modest changes in behavior. Although significant decreases in smoking were observed among all groups except those with respiratory disease, at least 75% of smokers did not quit. No significant changes emerged in the percentage meeting physical activity recommendations, except those with diabetes, or in excessive alcohol consumption, except those with diabetes and respiratory disease. The percentage reporting the recommended minimum fruit and vegetable intake did not increase significantly among any group

H-alpha Spectral diversity of type II supernovae

We present a spectroscopic analysis of the H-alpha profiles of hydrogen-rich type II supernovae. A total of 52 type II supernovae having well sampled optical light curves and spectral sequences were analyzed. Concentrating on the H-alpha P-Cygni profile we measure its velocity from the FWHM of emission and the ratio of absorption to emission (a/e) at a common epoch at the start of the recombination phase, and search for correlations between these spectral parameters and photometric properties of the V-band light curves. Testing the strength of various correlations we find that a/e appears to be the dominant spectral parameter in terms of describing the diversity in our measured supernova properties. It is found that supernovae with smaller a/e have higher H-alpha velocities, more rapidly declining light curves from maximum, during the plateau and radioactive tail phase, are brighter at maximum light and have shorter optically thick phase durations. We discuss possible explanations of these results in terms of physical properties of type II supernovae, speculating that the most likely parameters which influence the morphologies of H-alpha profiles are the mass and density profile of the hydrogen envelope, together with additional emission components due to circumstellar interaction.Comment: Accepted for publication in ApJ letters. 9 pages, 3 figures, 2 table

UBVRIz Light Curves of 51 Type II Supernovae

We present a compilation of UBV RIz light curves of 51 type II supernovae discovered during the course of four different surveys during 1986 to 2003: the Cerro Tololo Supernova Survey, the Calan/Tololo Supernova Program (C&T), the Supernova Optical and Infrared Survey (SOIRS), and the Carnegie Type II Supernova Survey (CATS). The photometry is based on template-subtracted images to eliminate any potential host galaxy light contamination, and calibrated from foreground stars. This work presents these photometric data, studies the color evolution using different bands, and explores the relation between the magnitude at maximum brightness and the brightness decline parameter (s) from maximum light through the end of the recombination phase. This parameter is found to be shallower for redder bands and appears to have the best correlation in the B band. In addition, it also correlates with the plateau duration, being thus shorter (longer) for larger (smaller) s values.Comment: 110 pages, 9 Figures, 6 Tables, accepted in A

Vibrational Excitations in Weakly Coupled Single-Molecule Junctions: A Computational Analysis

In bulk systems, molecules are routinely identified by their vibrational spectrum using Raman or infrared spectroscopy. In recent years, vibrational excitation lines have been observed in low-temperature conductance measurements on single molecule junctions and they can provide a similar means of identification. We present a method to efficiently calculate these excitation lines in weakly coupled, gateable single-molecule junctions, using a combination of ab initio density functional theory and rate equations. Our method takes transitions from excited to excited vibrational state into account by evaluating the Franck-Condon factors for an arbitrary number of vibrational quanta, and is therefore able to predict qualitatively different behaviour from calculations limited to transitions from ground state to excited vibrational state. We find that the vibrational spectrum is sensitive to the molecular contact geometry and the charge state, and that it is generally necessary to take more than one vibrational quantum into account. Quantitative comparison to previously reported measurements on pi-conjugated molecules reveals that our method is able to characterize the vibrational excitations and can be used to identify single molecules in a junction. The method is computationally feasible on commodity hardware.Comment: 9 pages, 7 figure

Anatomy of a post-starburst minor merger: a multi-wavelength WFC3 study of NGC 4150

(Abridged) We present a spatially-resolved near-UV/optical study of NGC 4150, using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope. Previous studies of this early-type galaxy (ETG) indicate that it has a large reservoir of molecular gas, exhibits a kinematically decoupled core (likely indication of recent merging) and strong, central H_B absorption (indicative of young stars). The core of NGC 4150 shows ubiquitous near-UV emission and remarkable dusty substructure. Our analysis shows this galaxy to lie in the near-UV green valley, and its pixel-by-pixel photometry exhibits a narrow range of near-UV/optical colours that are similar to those of nearby E+A (post-starburst) galaxies. We parametrise the properties of the recent star formation (age, mass fraction, metallicity and internal dust content) in the NGC 4150 pixels by comparing the observed near-UV/optical photometry to stellar models. The typical age of the recent star formation (RSF) is around 0.9 Gyrs, consistent with the similarity of the near-UV colours to post-starburst systems, while the morphological structure of the young component supports the proposed merger scenario. The RSF metallicity, representative of the metallicity of the gas fuelling star formation, is around 0.3 - 0.5 Zsun. Assuming that this galaxy is a merger and that the gas is sourced mainly from the infalling companion, these metallicities plausibly indicate the gas-phase metallicity (GPM) of the accreted satellite. Comparison to the local mass-GPM relation suggests (crudely) that the mass of the accreted system is around 3x10^8 Msun, making NGC 4150 a 1:20 minor merger. A summation of the pixel RSF mass fractions indicates that the RSF contributes about 2-3 percent of the stellar mass. This work reaffirms our hypothesis that minor mergers play a significant role in the evolution of ETGs at late epochs.Comment: 28 pages, 2 tables, accepted for publication in Ap

HETDEX pilot survey for emission-line galaxies - I. Survey design, performance, and catalog

We present a catalog of emission-line galaxies selected solely by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivated as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 sq.arcmin with a 3500-5800 Ang. bandpass under 5 Ang. full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4-20 E-17 erg/s/sq.cm depending on the wavelength, and Ly-alpha luminosities between 3-6 E42 erg/s are detectable. This survey method complements narrowband and color-selection techniques in the search for high redshift galaxies with its different selection properties and large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complementary data. We find 104 galaxies via their high redshift Ly-alpha emission at 1.9<z<3.8, and the majority of the remainder objects are low redshift [OII]3727 emitters at z<0.56. The classification between low and high redshift objects depends on rest frame equivalent width, as well as other indicators, where available. Based on matches to X-ray catalogs, the active galactic nuclei (AGN) fraction amongst the Ly-alpha emitters (LAEs) is 6%. We also analyze the survey's completeness and contamination properties through simulations. We find five high-z, highly-significant, resolved objects with full-width-half-maximum sizes >44 sq.arcsec which appear to be extended Ly-alpha nebulae. We also find three high-z objects with rest frame Ly-alpha equivalent widths above the level believed to be achievable with normal star formation, EW(rest)>240 Ang.Comment: 45 pages, 36 figures, 5 tables, submitted to ApJ

The Seventh Data Release of the Sloan Digital Sky Survey

This paper describes the Seventh Data Release of the Sloan Digital Sky Survey (SDSS), marking the completion of the original goals of the SDSS and the end of the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most of the roughly 2000 deg^2 increment over the previous data release lying in regions of low Galactic latitude. The catalog contains five-band photometry for 357 million distinct objects. The survey also includes repeat photometry over 250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A coaddition of these data goes roughly two magnitudes fainter than the main survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2 in the Northern Galactic Cap, closing the gap that was present in previous data releases. There are over 1.6 million spectra in total, including 930,000 galaxies, 120,000 quasars, and 460,000 stars. The data release includes improved stellar photometry at low Galactic latitude. The astrometry has all been recalibrated with the second version of the USNO CCD Astrograph Catalog (UCAC-2), reducing the rms statistical errors at the bright end to 45 milli-arcseconds per coordinate. A systematic error in bright galaxy photometr is less severe than previously reported for the majority of galaxies. Finally, we describe a series of improvements to the spectroscopic reductions, including better flat-fielding and improved wavelength calibration at the blue end, better processing of objects with extremely strong narrow emission lines, and an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor correction