Quantitative Composition, Distribution, Community Structure and Standing Stock of Sea Ice Microalgae in the Canadian Arctic

One hundred and ninety-six (196) species of microalgae were identified from the annual shore-fast sea ice samples collected from the Canadian Arctic between November and June in the years 1971 to 1978. The diatoms were represented by 189 species (21 centric and 168 pennate), the flagellates by three species, the dinoflagellates and chrysophytes by two species each. There were no blue-green algae. Species composition and distribution are tabulated. The dominant species of the microalgal communities in the bottom of the ice different from those found elsewhere in the ice. The sea ice microalgal communities and standing stock started to develop in late fall at the time of ice formation. They grew very slowly through the winter months, exponentially increased in early spring, reached a peak just prior to the thaw period in late spring or early summer, and declined rapidly in summer as ice melting occurred. Standing stock was greatest at the bottom of the sea ice, where it was one to two orders of magnitude larger than in other parts of the ice column, and 50 to 500 times greater than in the phytoplankton in the underlying waters. The ice communities consisted mainly of diatoms with a great majority of pennate forms. Large numbers of species and cells of diatoms were found at the bottom of the sea ice. Dinoflagellates, flagellates and chrysophytes occurred in relatively low numbers except in a few cases when ice blooms were observed. During May most of the sea ice microalgal blooms occurred in the bottom of the ice except for Phaeocystis pouchetii, which occurred elsewhere in the ice. Environmental factors controlling standing stock, growth and distribution of sea ice microalgae are discussed

Diel, Tidal and Vertical Variations of Phytoplankton and Its Environment in Frobisher Bay

Phytoplankton were collected and environmental measurements made at depths of 0, 1, 3, 5, 7, 10, 20 and 30 m at 3 h intervals through a tidal cycle in the summer in Frobisher Bay. Light, temperature, salinity and nutrients varied vertically. Concentration of chlorophyll a, species composition, number of species and diversity also exhibited a pronounced vertical variation, while phytoplankton cell numbers and the evenness of the variations in species diversity and evenness were minor under the existing environmental conditions, where only light fluctuated significantly. The integrated values of biomass, nutrients and mean temperature and salinity showed neither significant diel nor tidal variation.Key words: arctic phytoplankton, biomass, species composition, abundance, diversity, environmental factorsEn été, on a effectué des prélèvements de phytoplancton et procédé à des mesures environnementales à des profondeurs de 0, 1, 3, 5, 7, 10, 20 et 30 m, à des intervalles de 3 h, durant un cycle de marée, dans la baie Frobisher. La lumière, la température, la salinité et les éléments nutritifs variaient verticalement. La teneur en chlorophylle a, la variété des espèces, le nombre des espèces et la diversité montraient aussi une nette variation verticale, tandis que le nombre de cellules de phytoplancton et l’uniformité de la distribution des espèces  étaient les mêmes dans toute la colonne d’eau. La biomasse et la composition du phytoplancton changeaient considérablement en fonction du temps. Cependant, les variations nycthéméralesdans la diversité et l’uniformité des espèces étaient minimes dans les conditions ambiantes du moment, où seule la lumière fluctuait de façon significative. Les valeurs intégrées de la biomasse, des éléments nutritifs ainsi que de la température et de la salinité moyennes ne montraient pas de variations significatives, qu’elles soient nycthémérales ou dues à la marée.Mots clés: phytoplancton arctique, biomasse, variété des espèces, abondance, diversité. facteurs environnementau

The Growth of Arctic Marine Phytoplankton in Frobisher Bay

During the summers of 1977 and 1978, populations of phytoplankton collected in Frobisher Bay at depths of 0, 5, 10, 15, 20 and 25 m were enclosed in dialysis bags and incubated in situ at the depths from which they were collected. The greatest growth rate of the populations occurred at 10 m in July-August 1977 and at 5 m in late August-early September 1978. Exponential growth rates and generation times of dominant species of phytoplankton are tabulated. Growth rates ranged from 0.06 to 1.12 division/day and generation times varied from 21.4 to 404.7 hr/division. Light appears to be the major limiting factor for phytoplankton growth in this area; nutrients, temperature and salinity were not limiting in this experiment.Key words: growth rates, generation times, arctic marine phytoplankton, limiting factorsMots clés: les taux de croissance, les temps de génération, phytoplancton marine de l'arctique, des facteurs limitant

Mechanical properties, microstructure and crystallographic texture of magnesium AZ91-D alloy welded by Friction Stir Welding (FSW)

The objective of the study was to characterize the properties of a magnesium alloy welded by friction stir welding (FSW). The results led to a better understanding of the relationship between this process and the microstructure and anisotropic properties of alloy materials. Welding principally leads to a large reduction in grain size in welded zones due to the phenomenon of dynamic recrystallization. The most remarkable observation was that crystallographic textures appeared from a base metal without texture in two zones: the thermo-mechanically affected and stir welded zones. The latter zone has the peculiarity of possessing a marked texture with two components on the basal plane and the pyramidal plane. These characteristics disappeared in the TMAZ, which had only one component following the basal plane. These modifications have been explained by the nature of the plastic deformation in these zones, which occurs at a moderate temperature in the TMAZ and high temperature in the SWZ

Estimation of leaf nitrogen content using artificial neural network with cross-learning scheme and significant wavelengths

Reflectance from crops provides spectral information for non-destructive monitoring of their nutrition status. In order to develop a multi-spectral imaging system for remote sensing of the nitrogen content of crops, the significant wavelengths and calibration models were carefully evaluated in this study. The significant wavelengths in full band (4002500 nm) and a selected band (450-950 nm), which is suitable for silicon CCD cameras, were investigated. In this article, significant wavelengths for estimating nitrogen content of cabbage seedling leaves were first determined by SMLR (stepwise multi-linear regression) analysis. A proposed ANN (artificial neural network) model with cross-learning scheme (ANN-CL) was further developed to increase the prediction accuracy. To comply with the design of a practical multi-spectral imaging system using silicon CCD cameras and commercially available bandpass filters, an ANN-CL model with four inputs of spectral absorbance at 490, 570, 600, and 680 nm was developed. The calibration results (rc = 0.93, SEC = 0.873%, and SEV = 0.96001o) reduced the SEVabout 15% when compared with the SMLR method withfour wavelengths (SEV = 1.099%). In addition, the results were comparable to that of SMLR with seven wavelengths (rc = 0.94, SEC = 0.806010, and SEV = 0.993%) in the full band. These results indicated that the ANN model with cross-learning using spectral information at 490, 570, 600, and 680 nm could be used to develop a practical remote sensing system to predict nitrogen content of cabbage seedlings

Evaluation of plant seedling water stress using dynamic fluorescence index with blue LED-based fluorescence imaging

A dynamic fluorescence image index system capable of non-destructive assessment of water stress in cabbage seedlings was developed. The quenching curves of chlorophyll fluorescence characteristic to the plant's water stress status under reduced excitation energy were acquired via a multispectral imaging system. The dynamic fluorescence index (DR), a fluorescence index derived from quantitative modeling of the quenching curves in this study, was found superior to conventional indices such as the fluorescence decrease ratio (Rfd) in evaluating water stress status in cabbage seedlings, with respect to due mainly to its significantly reduced measuring time and enhanced precision of the chlorophyll fluorescence responses. The best results of the quantitative model to predict water stress status of seedlings using the dynamic fluorescence index were r = 0.944 and SEE = 0.286 MPa using the 720 nm channel. The blue (460 nm) LED-excited fluorescence multispectral imaging system (FMSIS) coupled with DFI provides a powerful research tool for plant physiology studies as well as for improving greenhouse and agriculture management practices where quantitative assessment of water potential in leafy plants is critical. (C) 2010 Elsevier B.V. All rights reserved

Intraoperative neuromonitoring for the early detection and prevention of RLN traction injury in thyroid surgery: A porcine model

Background Operative traction of the thyroid lobe is a necessary component of thyroid surgery. This surgical maneuver can cause traction injury of the recurrent laryngeal nerve (RLN), and this complication has been reported to be the most common mechanism of nerve injury. The goal of this study was to investigate the electromyographic (EMG) signal pattern during an acute RLN traction injury and establish reliable strategies to prevent the injury using intraoperative neuromonitoring (IONM). Methods Fifteen piglets (30 RLNs) underwent IONM via automated periodic vagal nerve stimulation and had their EMG tracings recorded and correlated with various models of nerve injury. Results In the pilot study, a progressive, partial EMG loss was observed under RLN tractions with different tension (n = 8). The changes in amplitudes were more marked and consistent than were the changes in latency. The EMG gradually gained partial recovery after the traction was relieved. Among the nerves injured with electrothermal (n = 4), clamping (n = 1), and transection (n = 1) models, the EMG showed immediate partial or complete loss, and no gradual EMG recovery was observed. Another 16 RLNs were used to investigate the potential of EMG recovery after different extents of RLN traction. We noted the EMG showed nearly full recovery if the traction stress was relieved before the loss of signal (LOS), but the recovery was worse if prolonged or repeated traction was applied. The mean restored amplitudes after the traction was relieved before, during, and after the LOS were 98 \ub1 3% (n = 6), 36 \ub1 4% (n = 4), and 15 \ub1 2% (n = 6), respectively. Conclusion RLN traction injury showed graded, partial EMG changes; early release of the traction before the EMG has degraded to LOS offers a good chance of EMG recovery. IONM can be used as a tool for the early detection of adverse EMG changes that may alert surgeons to correct certain maneuvers immediately to prevent irreversible nerve injury during the thyroid operation