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

The Theory of Brown Dwarfs and Extrasolar Giant Planets

Straddling the traditional realms of the planets and the stars, objects below the edge of the main sequence have such unique properties, and are being discovered in such quantities, that one can rightly claim that a new field at the interface of planetary science and and astronomy is being born. In this review, we explore the essential elements of the theory of brown dwarfs and giant planets, as well as of the new spectroscopic classes L and T. To this end, we describe their evolution, spectra, atmospheric compositions, chemistry, physics, and nuclear phases and explain the basic systematics of substellar-mass objects across three orders of magnitude in both mass and age and a factor of 30 in effective temperature. Moreover, we discuss the distinctive features of those extrasolar giant planets that are irradiated by a central primary, in particular their reflection spectra, albedos, and transits. Aspects of the latest theory of Jupiter and Saturn are also presented. Throughout, we highlight the effects of condensates, clouds, molecular abundances, and molecular/atomic opacities in brown dwarf and giant planet atmospheres and summarize the resulting spectral diagnostics. Where possible, the theory is put in its current observational context.Comment: 67 pages (including 36 figures), RMP RevTeX LaTeX, accepted for publication in the Reviews of Modern Physics. 30 figures are color. Most of the figures are in GIF format to reduce the overall size. The full version with figures can also be found at: http://jupiter.as.arizona.edu/~burrows/papers/rm

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

Reaction hijacking inhibition of Plasmodium falciparum asparagine tRNA synthetase

Malaria poses an enormous threat to human health. With ever increasing resistance to currently deployed drugs, breakthrough compounds with novel mechanisms of action are urgently needed. Here, we explore pyrimidine-based sulfonamides as a new low molecular weight inhibitor class with drug-like physical parameters and a synthetically accessible scaffold. We show that the exemplar, OSM-S-106, has potent activity against parasite cultures, low mammalian cell toxicity and low propensity for resistance development. In vitro evolution of resistance using a slow ramp-up approach pointed to the Plasmodium falciparum cytoplasmic asparaginyl-tRNA synthetase (PfAsnRS) as the target, consistent with our finding that OSM-S-106 inhibits protein translation and activates the amino acid starvation response. Targeted mass spectrometry confirms that OSM-S-106 is a pro-inhibitor and that inhibition of PfAsnRS occurs via enzyme-mediated production of an Asn-OSM-S-106 adduct. Human AsnRS is much less susceptible to this reaction hijacking mechanism. X-ray crystallographic studies of human AsnRS in complex with inhibitor adducts and docking of pro-inhibitors into a model of Asn-tRNA-bound PfAsnRS provide insights into the structure-activity relationship and the selectivity mechanism

Pandora gas pipeline Palmer River to Townsville section

[Extract] The Australian Centre for Tropical Freshwater Research (ACTFR) undertook surveys to assess the environmental values of the Palmer River to Townsville section of the proposed route for the Pandora gas pipeline. This includes a corridor extending ten kilometres on both sides of the proposed route. The proposed pipeline corridor from the Palmer River to Townsville almost entirely traverses a bioregion in North Queensland known as the Einasleigh Uplands, apart from the very southern section near Townsville (Brigalow Belt) and the northern section between the Mitchell and Palmer Rivers (Gulf Plains). The surveys were conducted by three teams, one for each of the following: 1) Vegetation Survey and Mapping 2) Aquatic Habitats and Fauna 3) Terrestrial Fauna Fieldwork for these surveys were undertaken in the last two weeks of September 1996 and the first week of October 1996. The vegetation and terrestrial fauna teams travelled together for 14 days. The aquatic team travelled separately for a total of 9 days. After the ground-based fieldwork was complete, the leader of each of the three teams participated in three days of helicopter surveys, traversing the pipeline route, including corridor, from the Palmer River to Townsvill