Coastal areas of the North Sea are commercially important for fishing and tourism, and are subject to the increasingly adverse effects of harmful algal blooms, eutrophication and climate change. Monitoring phytoplankton in these areas using Ocean Colour Remote Sensing is hampered by the high spatial and temporal variation in absorption and scattering properties. In this paper we demonstrate a clustering method based on specificabsorption properties that give accurate water quality products from the Medium Resolution Imaging Spectrometer (MERIS). A total of 468 measurements of Chlorophyll a (Chla), Total Suspended Material (TSM), specific-(sIOP) and inherent optical properties (IOP) were measured in the North Sea between April 1999 and September 2004. Chla varied from 0.2 to 35 mg m-3 , TSM from 0.2 to 75 g m-3 and absorption properties of coloured dissolved organic material at 442 nm (a CDOM (442)) was 0.02 to 0.26 m-1. The variation in absorption properties of phytoplankton (a ph) and non-algal particles (a NAP) were an order of magnitude greater than that for a ph normalized to Chla (a ph *) and a NAP normalized to TSM (a NAP *). Hierarchical cluster analysis on a ph *, a NAP * and a CDOM reduced this large data set to three groups of high a NAP *-a CDOM , low a ph * situated close to the coast, medium values further offshore and low a NAP *-a CDOM , high a ph * in open ocean and Dutch coastal waters. The median sIOP of each cluster were used to parameterize a semi-analytical algorithm to retrieve concentrations of Chla, TSM and a CDOM (442) from MERIS data. A further 60 measurements of normalized water leaving radiance (nL w), Chla, TSM, a CDOM (442) and a NAP (442) collected between 2003 and 2006 were used to assess the accuracy of the satellite products. The regionalized MERIS algorithm showed improved performance in Chla and a CDOM (442) estimates with relative percentage differences of 29 and 8% compared to 34 and 134% for standard MERIS Chla and a dg (442) products, and similar retrieval for TSM at concentrations >1 gm-3 .
A prototype point-source integrating cavity absorption meter (PSICAM) is presented and compared with spectrophotometric absorption measurements. Different light collector assemblies of the PSICAM were tested regarding their capability to determine the absorption of water constituents accurately over a wide range of concentrations and scattering properties. The PSICAM setup with a radiance-type sensor showed the best performance. It was compared with a photometric absorption determination using nonscattering dye solutions. The mean difference between both methods was less than 2.4% in the spectral range of 400-700 nm. The absorption determination with the PSICAM, when equipped with a radiance sensor as a light collector, was only little affected by scattering and temperature. We conclude that the PSICAM can be used to determine the absorption of natural seawater samples at ambient temperatures.
A neutral trehalase gene, NTCI, from the human pathogenic yeast Candida albicans was isolated and characterized. An ORF of 2724 bp was identified encoding a predicted protein of 907 amino acids and a molecular mass of 104 kDa. A single transcript of approximately 3.2 kb was detected by Northern blot analysis. Comparison of the deduced amino acid sequence of the C. albicans NTCI gene product with that of the Saccharomyces cerevisiae NTHI gene product revealed 57% identity. The NTCl gene was localized on chromosome 1 or R. A null mutant (AntcIlAntcl) was constructed b y sequential gene disruption. Extracts from mutants homozygous for neutral trehalase deletion had only marginal neutral trehalase activity. Extracts from heterozygous mutants showed intermediate activities between extracts from the wild-type strain and from the homozygous mutants. The null mutant showed no significant differences in pathogenicity as compared to the wildtype strain in a mouse model of systemic candidiasis. This result indicates that the neutral trehalase of C. albicans is not a potential target for antifungal drugs.
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