Algal dynamics in tropical riverine water holes

Microalgae are key components of many aquatic food webs and of aquatic biodiversity, yet little is known of the dynamics of algal assemblages in tropical systems, where diversity is likely to be very high. This study investigated algal assemblages of remnant riparian water holes in the seasonal Australian tropics, and the natural and human influences on them. Phytoplankton and water sample sand in situ physico-chemical data were collected from sites in the Burdekin River catchment, one of the largest in tropical Australia. Sites in the catchment were chosen based on differing water chemistry and turbidity. Samples were collected at three times during the day (dawn, midday, afternoon) in two microhabitats within the waterhole (open water and macrophytes) at varying times within the year representing the wet and dry seasons and the change between seasons. Multivariate analyses demonstrated compositional differences between assemblages between seasons and rivers and showed that conductivity and turbidity were major physico-chemical determinants of the differences. Majority of the sites showed dominance in Chlorophyta, followed by Cyanophyta and Heterokontophyta (Bacillariophyceae). The differences related both to natural geological and edaphic factors and to land management regimes in the catchment. The results provide improved understanding of algal dynamics in seasonal tropical rivers and will be used to create models for site-specific assessment of water quality in a regional monitoring program

Planck scale effects in neutrino physics

We study the phenomenology and cosmology of the Majoron (flavon) models of three active and one inert neutrino paying special attention to the possible (almost) conserved generalization of the Zeldovich-Konopinski-Mahmoud lepton charge. Using Planck scale physics effects which provide the breaking of the lepton charge, we show how in this picture one can incorporate the solutions to some of the central issues in neutrino physics such as the solar and atmospheric neutrino puzzles, dark matter and a 17 keV neutrino. These gravitational effects induce tiny Majorana mass terms for neutrinos and considerable masses for flavons. The cosmological demand for the sufficiently fast decay of flavons implies a lower limit on the electron neutrino mass in the range of 0.1-1 eV.Comment: 24 pages, 1 figure (not included but available upon request), LaTex, IC/92/196, SISSA-140/92/EP, LMU-09/9

Tight-binding parameters for charge transfer along DNA

We systematically examine all the tight-binding parameters pertinent to charge transfer along DNA. The $\pi$ molecular structure of the four DNA bases (adenine, thymine, cytosine, and guanine) is investigated by using the linear combination of atomic orbitals method with a recently introduced parametrization. The HOMO and LUMO wavefunctions and energies of DNA bases are discussed and then used for calculating the corresponding wavefunctions of the two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO and LUMO energies of the bases are in good agreement with available experimental values. Our results are then used for estimating the complete set of charge transfer parameters between neighboring bases and also between successive base-pairs, considering all possible combinations between them, for both electrons and holes. The calculated microscopic quantities can be used in mesoscopic theoretical models of electron or hole transfer along the DNA double helix, as they provide the necessary parameters for a tight-binding phenomenological description based on the $\pi$ molecular overlap. We find that usually the hopping parameters for holes are higher in magnitude compared to the ones for electrons, which probably indicates that hole transport along DNA is more favorable than electron transport. Our findings are also compared with existing calculations from first principles.Comment: 15 pages, 3 figures, 7 table

Relativistic Laser-Matter Interaction and Relativistic Laboratory Astrophysics

The paper is devoted to the prospects of using the laser radiation interaction with plasmas in the laboratory relativistic astrophysics context. We discuss the dimensionless parameters characterizing the processes in the laser and astrophysical plasmas and emphasize a similarity between the laser and astrophysical plasmas in the ultrarelativistic energy limit. In particular, we address basic mechanisms of the charged particle acceleration, the collisionless shock wave and magnetic reconnection and vortex dynamics properties relevant to the problem of ultrarelativistic particle acceleration.Comment: 58 pages, 19 figure

A review of the freshwater fishes of the Kimberley region of Western Australia

This paper provides an overview of the freshwater fishes of the remote and sparsely populated Kimberley region of Western Australia, an area that has been subject to minimal scientific surveys, most of which have occurred in the last 30 years. A total of 49 freshwater fish species are reported from the region, but this number will likely grow as a result of future discoveries. It is an endemic hotspot, with similar to 40% of the species found nowhere else; many of which are known from only a few localities. The fauna is dominated by members of the Terapontidae (10 species) and Eleotridae (10 species), followed by the Plotosidae (five species), Melanotaeniidae (five species), Atherinidae (four species) and Ambassidae (four species). Additionally, in terms of freshwater fishes of the Kimberley, there are two species each in the Toxotidae and Ariidae, and a single species from each of the Anguillidae, Clupeidae, Hemiramphidae, Belonidae, Apogonidae, Gobiidae and Soleidae. There are currently no introduced fishes found in any major catchments of the Kimberley, however, there are records of the Eastern Mosquitofish (Gambusia holbrooki) from Cape Leveque (Morgan et al. 2004c) and the Redclaw Crayfish (Cherax quadquicarinatus), which have recently been found within the Ord River basin (Doupe et al. 2004)

Investigational piscivory of some juvenile Australian\ud freshwater fishes by the introduced Mozambique\ud tilapia Oreochromis mossambicus

Experimental tanks were used to observe predatory effects in three different size classes of Mozambique tilapia Oreochromis mossambicus (one of the world's most widespread exotic species and generally regarded to be a herbivore or both herbivore and detritivore) when tested against 10 juvenile Australian freshwater fish species, and significant levels of predation against all were recorded. There was a general trend for larger O. mossambicus to kill more prey and this was also reflected in a separate series of experiments using juvenile barramundi Lates calcarifer over a range of size classes. Predatory effects by O. mossambicus broadly reflected the accepted models of predator–prey interactions, being that mortality (and survival) was closely related to relative body size and mouth gape limitation. Experimental evidence for piscivory in O. mossambicus was supported by field sampling that detected prey fish remains in 16% of all fish surveyed (n = 176). The recognition of active piscivory by O. mossambicus in laboratory and field situations is the first such evidence, and suggests a need to re-evaluate the nature of their effects in introduced environments