ALBERT

Description: Optical spectra and properties of radio galaxies

Description: Two-stage temperature stabilized circuit using two transistors is described. Increase in temperature causes the base-to-emitter voltage of n-p-n transistor to become less positive whereas the base-to-emitter voltage of p-n-p transistor becomes less negative, so the temperature-induced variation in V sub 1 and V sub 2 cancel out.

Description: In this paper we review the IGS network as it currently exists and its effectiveness in supporting the IGS suite of precise products.

Description: The hydrographic conditions in the south-east Atlantic were investigated during the cruise of R/V Poseidon in April 1999. The area of investigation covers the two major eastern boundary currents of the Southern Atlantic and its convergence in the Angola-Benguela Frontal Zone (ABFZ). Hydrographic measurements have been carried out in combination with current measurements and are supplemented with remote sensing data of sea surface temperature (SST) and wind stress. The Angola Current transported in its surface part less saline water from the great rivers in the north towards the ABFZ. At the same time, south of the front, strong coastal upwelling in the Benguela was observed. At the beginning of April 1999 the ABFZ was found at an unusual southern position. The rapid dynamic response of the ABFZ to wind forcing is discussed on the basis of satellite SST images combined with hydrographic measurements.

Description: A multidisciplinary survey on board R.V. Poseidon off Angola and northern Namibia in April 1999 allowed a large-scale view of the South-East Atlantic boundary current system. The data set comprises meteorological, hydrographical, biological and chemical data. Sequences of satellite images of sea-surface temperature and wind stress provided additional synoptic information. Several mesoscale cyclonic gyres were observed embedded in a larger area of low dynamic height, known as the Angola Gyre. The most developed mesoscale feature was the subthermoclinal Angola Dome detected at 9 degreesS, 8.5 degreesE. At the beginning of April, the Angola-Benguela Frontal Zone (ABFZ) was found at an unusually southerly position near 19 degreesS. During the time of the cruise, the zone moved rapidly northward. The dynamics of this event are discussed in detail. The high-frequency temporal variations of the front were closely related to local wind forcing. Below the thermocline the conditions were more persistent. The ABFZ was represented as a front between different types of Central Water. The existence of a poleward undercurrent below the ABFZ, reported in recent publications, was not verified from direct current measurements. However, water mass distribution suggests overall poleward transport below the thermocline.

Description: In contrast to the situation observed in mammals and birds, a switching between different sex determination systems frequently occurred during the evolution of the teleost fish lineage. This might be due to a frequent turnover of sex-determining signals at the top of the sex determination cascade (master sex-determining genes in the case of genetic sex determination). Alternatively, different variations of a same master gene might decide the sex of individuals in different sex determination systems. In the medaka Oryzias latipes, a Y-specific copy of the putative transcription factor gene dmrt1 very likely corresponds to the master sex-determining gene inducing male formation [Nature 417 (2002) 559; Proc. Natl. Acad. Sci. U. S. A. 99 (2002) 11778]. This gene, alternately called dmY and dmrt1Y, has been formed by duplication of the autosomal dmrt1. In order to determine if an orthologue of dmrt1Y was also located in the sex determination region of the related platyfish Xiphophorus maculatus, Southern blot analysis was performed on genomic DNA from XY and YY males and WY and XX females using both medaka and human dmrt1 cDNA as probes. Using different restriction enzymes, no evidence for sex-specific dmrt-containing genomic fragments could be found in the platyfish. No dmrt gene could be detected by low-stringency Southern blot analysis of genomic inserts from 60 bacterial artificial chromosome (BAC) clones linked to the sex-determining locus on the X and Y chromosomes. Six different groups of BAC clones containing dmrt genes were isolated from a platyfish genomic library. X. maculatus dmrt1 gene and cDNA were characterised. In adult, expression of dmrt1 was detected only in testis. Phylogenetic analysis indicated that the duplication of dmrt1 that led to the formation of dmY/dmrt1Y within the medaka lineage clearly occurred after its divergence from the platyfish lineage. Hence, a dmY/dmrt1Y orthologue generated by this particular event of duplication does not correspond to the master sex-determining gene in the platyfish.