High-redshift galaxies, their active nuclei and central black holes

We demonstrate that the luminosity function of the recently detected population of actively star-forming galaxies at redshift z  = 3 and the B -band luminosity function of quasi-stellar objects (QSOs) at the same redshift can both be matched with the mass function of dark matter haloes predicted by standard variants of hierarchical cosmogonies for lifetimes of optically bright QSOs anywhere in the range 10⁶ to 10⁸ yr. There is a strong correlation between the lifetime and the required degree of non-linearity in the relation between black hole and halo mass. We suggest that the mass of supermassive black holes may be limited by the back-reaction of the emitted energy on the accretion flow in a self-gravitating disc. This would imply a relation of black hole to halo mass of the form M _bh ∝  v ⁵_halo ∝  M ^5/3_halo and a typical duration of the optically bright QSO phase of a few times 10⁷ yr. The high integrated mass density of black holes inferred from recent black hole mass estimates in nearby galaxies may indicate that the overall efficiency of supermassive black holes for producing blue light is smaller than previously assumed. We discuss three possible accretion modes with low optical emission efficiency: (i) accretion at far above the Eddington rate, (ii) accretion obscured by dust, and (iii) accretion below the critical rate leading to an advection-dominated accretion flow lasting for a Hubble time. We further argue that accretion with low optical efficiency might be closely related to the origin of the hard X-ray background and that the ionizing background might be progressively dominated by stars rather than QSOs at higher redshift.     

Estuarine and coastal connectivity of an estuarine-dependent fishery species,Pomadasys commersonnii (Haemulidae)

Understanding the level of connectivity between estuarine and coastal waters is essential for appropriate management of estuarine-associated taxa. Most studies have focused on the role of a single estuary, while limited research exists on the importance of multiple estuaries to individuals of estuarine-associated species. This study used acoustic telemetry to assess the usage of multiple estuaries and coastal waters by the estuarine-dependent spotted grunter Pomadasys commersonnii. Twenty-six adult fish were tagged with acoustic transmitters in the Kariega and Bushmans estuaries, South Africa, and their movements along a 300-km stretch of Indian Ocean coastline were monitored for up to 17 months. Tagged individuals spent most of their time in the estuary where they were tagged (55% and 85% for fish tagged in the two estuaries, respectively), followed by time in the sea (30% and 15%) and in other estuaries (15% and <1%). The mean durations of sea trips for fish tagged in the Kariega Estuary or Bushmans Estuary, respectively, were 25 days (range 3–55) and 12 days (range 2–22). Of the fish that went to sea, 93% from the Kariega Estuary and 60% from the Bushmans Estuary visited other estuaries. Most visits were undertaken to the Swartkops, Bushmans and Kowie estuaries, although the longest durations were spent in the Sundays Estuary. Individuals moved to estuaries up to 130 km away. The total distance travelled between estuaries by an individual during the study was ～529 km, with means of 201 and 184 km, respectively, for fish tagged in the Kariega and Bushmans estuaries. Despite covering large distances between estuaries, individuals often returned to their tagging estuary. Residency in their tagging estuary, combined with frequent visits to a neighbouring estuary, highlights the importance of estuarine habitats for this popular fish species, even after reaching maturity.     

Automated AF-demagnetization on the 2G-Enterprises through-bore,cryogenic magnetometer

Since the early sixties, alternating field demagnetization (AFD) has been a standard laboratory technique for demagnetizing rocks to expose the multicomponent structure of their natural remanent magnetization (NRM). In the majority of AFD implementations, however, the procedure remains as labour-intensive as ever. The implementation that we have developed at the Australian Geological Survey Organisation, automates the procedure for AFD based on the static method, and results in significant productivity and efficiency gains without compromising data quality. A properly formulated procedure for static AFD may be the only method of retrieving higher-coercivity components of natural remanence in samples prone to developing gyroremanence at higher alternating fields (AFs). Our AFD environment comprises: a 2G-Enterprises through-bore, cryogenic magnetometer; 2G AF-coils and control equipment; and personal computer software, developed by us, to control all procedural aspects for a complete AFD of a sample including, importantly, a counteracting procedure to neutralize the effects of gyroremanence build-up at higher AFs. With our system, AFD of 8 samples/day, each of 20+ steps, requires only 20 min of user attention compared with a full day for conventional systems.     

Profligacy and scarcity: an analysis of water management in Australia

Without denying the physical relaity of water shortages during the 1982 Australia drought, it is argued that some of the difficulties arise not from climatic factors but from the way the water resource is managed. An attempt is made to explain why metropolitan Australia can continue to make profligate use of water, while rural Australia suffers scarcity. The system of administration is considered and the capacity planning and pricing policies of supply authorities analysed. Finally, a call is made for the introduction of an effective integrated management system.     

Stable Atmospheric Boundary-Layer Experiment in Spain (SABLES 98): A Report

This paper describes the Stable AtmosphericBoundary Layer Experiment in Spain (SABLES 98),which took place over the northern Spanish plateaucomprising relatively flat grassland,in September 1998. The main objectives of the campaign were to study the properties of themid-latitude stable boundary layer (SBL).Instrumentation deployed on two meteorologicalmasts (of heights 10 m and 100 m)included five sonic anemometers, 15 thermocouples,five cup anemometers and three propeller anemometers,humidity sensors and radiometers.A Sensitron mini-sodar and a tetheredballoon were also operated continuously. Atriangular array of cup anemometers wasinstalled to allow the detection ofwave events. Two nocturnal periods analysedon 14–15 and 20–21 September are used toillustrate the wide-ranging characteristics of the SBL.     

Responses of benthic macroinvertebrates to thin-layer disposal of dredged material in Mississippi Sound, USA

Benthic community responses to thin-layer disposal of dredged material were assessed at three sites in Mississippi Sound, USA. Community composition differed between disposal and reference sites (ANOSIM) for each disposal event. Oweniid sand worms, Amphinomid fire worms, and brittle stars (Ophiuriodea) contributed the most to community distinctions between disposal and reference sites (SIMPER), with higher abundances at the disposal sites. Total infaunal abundance was similar to pre-disposal and reference conditions within 3-10 months of thin-layer disposal. Distinctions in community composition between disposal and reference sites (nMDS) persisted throughout the 16-month study period, but were less pronounced at the site where sediment composition was unchanged by disposal. Size distributions of some taxa (e.g., gastropod and hemichordate) suggest adults recolonized the newly deposited sediments either through vertical migration or lateral immigration from adjacent areas. Thin-layer disposal offers a viable alternative to conventional open-water disposal practices and warrants further exploration for other areas with deeper bathymetries and different hydrodynamic regimes.     

Colloid particle sizes in the Mississippi River and some of its tributaries,from Minneapolis to below New Orleans

An on-board technique was developed that combined discharge-weighted pumping to a high-speed continuous-flow centrifuge for isolation of the particulate-sized material with ultrafiltration for isolation of colloid-sized material. In order to address whether these processes changed the particle sizes during isolation, samples of particles in suspension were collected at various steps in the isolation process to evaluate changes in particle size. Particle sizes were determined using laser light-scattering photon correlation spectroscopy and indicated no change in size during the colloid isolation process. Mississippi River colloid particle sizes from twelve sites from Minneapolis to below New Orleans were compared with sizes from four tributaries and three seasons, and from predominantly autochthonous sources upstream to more allochthonous sources downstream. © 1998 John Wiley & Sons, Ltd.