The Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory is a second generation water Cherenkov detector designed to determine whether the currently observed solar neutrino deficit is a result of neutrino oscillations. The detector is unique in its use of D2O as a detection medium, permitting it to make a solar model-independent test of the neutrino oscillation hypothesis by comparison of the charged- and neutral-current interaction rates. In this paper the physical properties, construction, and preliminary operation of the Sudbury Neutrino Observatory are described. Data and predicted operating parameters are provided whenever possible.Comment: 58 pages, 12 figures, submitted to Nucl. Inst. Meth. Uses elsart and epsf style files. For additional information about SNO see http://www.sno.phy.queensu.ca . This version has some new reference

Image Analysis Techniques to Accompany a new In Situ Ichthyoplankton Imaging System

We have built a high resolution towed digital imaging system (ISIIS) capable of imaging water volumes sufficient to accurately quantify even rare plankton (e.g. larval fish) in situ. This imaging system produces very high resolution imagery at very high data rates necessitating automated image analysis. As we are interested in the identification and quantification of a large number of organisms, some of which are relatively similar to each other, we are developing an automated system for detection and recognition of organisms of interest using computer vision tools. Our method aims at (i) the detection of multiple regions (organisms) of interest automatically, while filtering out noise and out-of-focus organisms, and (ii) the classification of the detected organisms into pre-defined categories using shape and texture information. For the organisms detection, we use a probabilistic scheme based on image statistics to locate the regions of interest and -based on size and shape constraints - we filter out the noise, i.e., regions that are detected but do not correspond to organisms. For the classification of the detected organisms, we use the Scale Invariant Feature Transform (SIFT) for matching between the detected regions and the organism images in our database ("dictionary")

Impact of North Brazil Current rings on local circulation and coral reef fish recruitment to Barbados, West Indies

Early observations of the flow environment around the island of Barbados indicated frequent occurrence of strong current reversals associated with surface salinity fronts. Higher resolution spatial and temporal measurements of the flow regime in 1996 and 1997 provided a comprehensive view of the local surface circulation (0-100 m), revealing that external forcing by North Brazil Current (NBC) rings plays a dominant role in the near-field flow variability surrounding the island. NBC ring forcing had comparable effects on the velocity field during both years, indicating that the ring structure was retained while interacting with topography. In the present study, the interaction of NBC rings with coastal flow dynamics and the biological response of the system as measured by recruitment of coral reef fishes is examined. Our observations show that NBC rings can remain quite coherent as they pass the Tobago-Barbados ridge. Further, the flow direction and associated residence time in the vicinity of the island appear to vary depending on the orientation of the rings as they collide with the island. Concurrent biological samples revealed complex responses to the presence of rings in that during some of the events, larval fishes appeared to be rapidly advected away, resulting in a failure of larval settlement, whereas under other conditions larval retention was enhanced and was followed by a settlement pulse. Impingement by a ring did not alter the concentration of water column chlorophyll a (Chl a), but it did influence the depth of the Chl a maximum. Simultaneous changes were observed in the vertical distribution of fish larvae. Larval fish encountering ring waters exhibited reduced growth rates and longer larval periods, both potentially reducing survival and, ultimately, recruitment success. Overall, results demonstrate that NBC rings interfere with the islandscale flow dynamics around Barbados and interject considerable variability in the local recruitment signal of coral reef fishes

Patterns in larval reef fish distributions and assemblages, with implications for local retention in mesoscale eddies

Benthic marine populations are often replenished by a combination of larvae from local and distant sources. To promote retention of locally spawned larvae in strong, unidirectional boundary current systems, benthic marine organisms must utilize biophysical mechanisms to minimize advective loss. We examined patterns in larval fish abundance, age distribution, and assemblage in relation to environmental variables in the Straits of Florida to better understand the factors underlying larval transport and retention in a boundary current system. Depth was the primary structuring element; larval assemblages were more distinct across vertical distances of tens of metres than they were over horizontal distances of tens to hundreds of kilometres. However, depth distributions were species-specific, and larval assemblages inside and outside of mesoscale eddies were distinct. Age distributions were consistent with the hypothesis that mesoscale eddies provide opportunities for retention. Our data indicate that the effect of eddies on larval retention is likely taxon-specific and temporally variable, as synchronization of reproductive output, larval distribution, and timing of eddy passage are prerequisite to entrainment and subsequent retention of locally spawned larvae