Physical Constraints to Aquatic Plant Growth in New Zealand Lakes

The nature of aquatic plant communities often defines benthic habitat within oligotrophic and mesotrophic lakes and lake management increasingly recognizes the importance of maintaining plant diversity in order to sustain biological diversity and capacity within lakes. We have developed simple statistical relationships between key physical and vegetation variables that define the habitat requirements, or “habitat-templates”, of key vegetation types to facilitate management of plant communities in New Zealand lakes. Statistical relationships were derived from two datasets. The first was a multi-lake dataset to determine the effects of water level fluctuation and water clarity. The second dataset was from a comprehensive shoreline survey of Lake Wanaka, which allowed us to examine within-lake variables such as beach slope and wave action. Sufficient statistical relationships were established to develop a habitat template for each of the major species or assemblages. The relationships suggested that the extent and diversity of shallow-growing species was related to a combination of the extent of water level fluctuation and wave exposure. (PDF contains 9 pages.

Hydrogen absorption properties of amorphous (Ni0.6Nb0.4−yTay)100−xZrx membranes

Ni based amorphous materials have great potential as hydrogen purification membranes. In the present work the melt spun (Ni0.6Nb0.4−yTay)100−xZrx with y=0, 0.1 and x=20, 30 was studied. The result of X-ray diffraction spectra of the ribbons showed an amorphous nature of the alloys. Heating these ribbons below T < 400 °C, even in a hydrogen atmosphere (1−10 bar), the amorphous structure was retained. The crystallization process was characterized by differential thermal analysis and the activation energy of such process was obtained. The hydrogen absorption properties of the samples in their amorphous state were studied by the volumetric method, and the results showed that the addition of Ta did not significantly influence the absorption properties, a clear change of the hydrogen solubility was observed with the variation of the Zr content. The values of the hydrogenation enthalpy changed from ~37 kJ/mol for x=30 to ~9 kJ/mol for x=20. The analysis of the volumetric data provides the indications about the hydrogen occupation sites during hydrogenation, suggesting that at the beginning of the absorption process the deepest energy levels are occupied, while only shallower energy levels are available at higher hydrogen content, with the available interstitial sites forming a continuum of energy levels

M-grid: Using Ubiquitous Web Technologies to create a Computational Grid

There are many potential users and uses for grid computing. However, the concept of sharing computing resources excites security concerns and, whilst being powerful and flexible, at least for novices, existing systems are complex to install and use. Together these represent a significant barrier to potential users who are interested to see what grid computing can do. This paper describes m-grid, a system for building a computational grid which can accept tasks from any user with access to a web browser and distribute them to almost any machine with access to the internet and manages to do this without the installation of additional software or interfering with existing security arrangements

Dynamical Evolution of the Extra Dimension in Brane Cosmology

The evolution of the extra dimension is investigated in the context of brane world cosmology. New cosmological solutions are found. In particular, solutions in the form of waves travelling along the extra dimension are identified.Comment: Latex file, 10 page

Possible explanation for star-crushing effect in binary neutron star simulations

A possible explanation is suggested for the controversial star-crushing effect seen in numerical simulations of inspiraling neutron star binaries by Wilson, Mathews and Marronetti (WMM). An apparently incorrect definition of momentum density in the momentum constraint equation used by WMM gives rise to a post-1-Newtonian error in the approximation scheme. We show by means of an analytic, post-1-Newtonian calculation that this error causes an increase of the stars' central densities which is of the order of several percent when the stars are separated by a few stellar radii, in agreement with what is seen in the simulations.Comment: 4 pages, 1 figure, uses revetx macros, minor revision

Detection methods for non-Gaussian gravitational wave stochastic backgrounds

We address the issue of finding an optimal detection method for a discontinuous or intermittent gravitational wave stochastic background. Such a signal might sound something like popcorn popping. We derive an appropriate version of the maximum likelihood detection statistic, and compare its performance to that of the standard cross-correlation statistic both analytically and with Monte Carlo simulations. The maximum likelihood statistic performs better than the cross-correlation statistic when the background is sufficiently non-Gaussian. For both ground and space based detectors, this results in a gain factor, ranging roughly from 1 to 3, in the minimum gravitational-wave energy density necessary for detection, depending on the duty cycle of the background. Our analysis is exploratory, as we assume that the time structure of the events cannot be resolved, and we assume white, Gaussian noise in two collocated, aligned detectors. Before this detection method can be used in practice with real detector data, further work is required to generalize our analysis to accommodate separated, misaligned detectors with realistic, colored, non-Gaussian noise.Comment: 25 pages, 12 figures, submitted to physical review D, added revisions in response to reviewers comment

Binary-induced collapse of a compact, collisionless cluster

We improve and extend Shapiro's model of a relativistic, compact object which is stable in isolation but is driven dynamically unstable by the tidal field of a binary companion. Our compact object consists of a dense swarm of test particles moving in randomly-oriented, initially circular, relativistic orbits about a nonrotating black hole. The binary companion is a distant, slowly inspiraling point mass. The tidal field of the companion is treated as a small perturbation on the background Schwarzschild geometry near the hole; the resulting metric is determined by solving the perturbation equations of Regge and Wheeler and Zerilli in the quasi-static limit. The perturbed spacetime supports Bekenstein's conjecture that the horizon area of a near-equilibrium black hole is an adiabatic invariant. We follow the evolution of the system and confirm that gravitational collapse can be induced in a compact collisionless cluster by the tidal field of a binary companion.Comment: 9 Latex pages, 14 postscript figure

Impact of Increased Load Carriage Magnitude on the Dynamic Postural Stability of Men and Women

The impact of load carriage on dynamic postural stability affects the survivability of the Warfighter by influencing performance capabilities and injury incidence. Further, sex may interact with the relationship between load carriage and dynamic postural stability to further compromise survivability. PURPOSE: To investigate the effect of load carriage magnitude on dynamic postural stability of men and women and its relationship to jumping ability. METHODS: 32 subjects (16 men, 16 women) were investigated for maximum jump height and dynamic postural stability. Dynamic postural stability was assessed by subjects jumping a horizontal distance of 40% their height over a 30cm hurdle, landing on one leg on a force plate (sample rate = 1200 Hz). 3 trials were completed for 3 load conditions: +0, +20 and +30% body weight (BW). Dynamic postural stability was determined from ground reaction force data during landings, by calculation of the dynamic postural stability index (DPSI). Maximum jump height was assessed by subjects performing 3 countermovement jumps (sample rate = 1000 Hz). Two-way repeated measures ANOVA were used to compare mean DPSI scores between sexes and conditions (α = 0.05). Pearson’s Correlation Coefficients were used to determine the relationship between jump height and change in DPSI scores between conditions (α = 0.05). RESULTS: Load condition significantly affected DPSI (F = 100.304, p = 0.001). DPSI scores increased between the 0% (0.359 ± 0.041), 20% (0.396 ± 0.034) and 30% (0.420 ± 0.028) BW load conditions. No significant effect of sex on DPSI was found (F = 0.131). No significant sex by load interaction on DPSI was found (F = 0.393). No significant correlations were found between jump height and change in DPSI scores between conditions. CONCLUSION: Increased load was found to negatively affect dynamic postural stability, most likely as a result of modifying the demands of the task. Therefore, the dynamic postural stability of men and women changes comparably in response to increased load carriage magnitude. Future research should focus on the effects of load on dynamic postural stability under higher loads and during more military-specific tasks