Ecosystem dynamics at disturbed and undisturbed sites in North Queensland wet tropical rain forest. III. Nutrient returns to the forest floor through litterfall

The nutrient contents and accessions in litterfall over a period of 3 y are reported for undisturbed areas and at two sites disturbed by selective harvesting in tropical rain forest in North Queensland, Australia. Mean concentrations (mg g(-1) dry weight) of nutrients in litterfall ranged from 10 to 12 for nitrogen; 0.33 to 0.43 for phosphorus; 3.6 to 4.3 for potassium; 6.0 to 10.5 for calcium and 1.7 to 2.6 for magnesium. These concentrations are in the middle to lower part of the spectrum of values recorded for tropical forest. Accessions of nutrients in litterfall (kg ha(-1) y(-1)) ranged from 59 to 64 N; 1.9 to 2.4 P; 20 to 24K; 34 to 63 Ca; and 9 to 16 Mg. These rates, particularly for IN and P, are among the lowest recorded for tropical forests. There were no consistent between-site differences in total nutrient accessions in small litterfall. In terms of the contribution of litterfall to the accessions of nutrients to the forest floor, this suggests that the logged sites have recovered from the effects of selective harvesting within 25 y. Nutrient accessions at each site were distinctly seasonal, with maximum accessions occurring in the late dry season to late in the wet season. Leaf-fall accounted for the largest proportion of nutrient accessions over the study period, although at certain times accessions in both reproductive material and wood were significant. A cyclone which crossed the coast near the study sites resulted in large nutrient accessions over a short period but had little effect on the total annual accession. A comparison with previous studies of litterfall in Australian tropical rainforests indicates that nutrient return in litterfall is directly related to soil fertility.

Flush air data system calibration using numerical simulation

The use of computational fluid dynamics simulations for calibrating a flush air data system is described, In particular, the flush air data system of the HYFLEX hypersonic vehicle is used as a case study. The HYFLEX air data system consists of nine pressure ports located flush with the vehicle nose surface, connected to onboard pressure transducers, After appropriate processing, surface pressure measurements can he converted into useful air data parameters. The processing algorithm requires an accurate pressure model, which relates air data parameters to the measured pressures. In the past, such pressure models have been calibrated using combinations of flight data, ground-based experimental results, and numerical simulation. We perform a calibration of the HYFLEX flush air data system using computational fluid dynamics simulations exclusively, The simulations are used to build an empirical pressure model that accurately describes the HYFLEX nose pressure distribution ol cr a range of flight conditions. We believe that computational fluid dynamics provides a quick and inexpensive way to calibrate the air data system and is applicable to a broad range of flight conditions, When tested with HYFLEX flight data, the calibrated system is found to work well. It predicts vehicle angle of attack and angle of sideslip to accuracy levels that generally satisfy flight control requirements. Dynamic pressure is predicted to within the resolution of the onboard inertial measurement unit. We find that wind-tunnel experiments and flight data are not necessary to accurately calibrate the HYFLEX flush air data system for hypersonic flight.

Simulation and optimization of heated, inviscid flows in scramjet ducts

A space-marching code for the simulation and optimization of inviscid supersonic flow in three dimensions is described. The now in a scramjet module with a relatively complex three-dimensional geometry is examined and wall-pressure estimates are compared with experimental data. Given that viscous effects are not presently included, the comparison is reasonable. The thermodynamic compromise of adding heat in a diverging combustor is also examined. The code is then used to optimize the shape of a thrust surface for a simpler (box-section) scramjet module in the presence of uniform and nonuniform heat distributions. The optimum two-dimensional profiles for the thrust surface are obtained via a perturbation procedure that requires about 30-50 now solutions. It is found that the final shapes are fairly insensitive to the details of the heat distribution.

Surface oxide and the role of magnesium during the sintering of aluminum

The effect of trace additions of magnesium on the sintering of aluminum and its alloys is examined. Magnesium, especially at low concentrations, has a disproportionate effect on sintering because it disrupts the passivating Al2O3 layer through the formation of a spinel phase. Magnesium penetrates the sintering compact by solid-state diffusion, and the oxide is reduced at the metal-oxide interface. This facilitates solid-state sintering, as well as wetting of the underlying metal by sintering liquids, when these are present. The optimum magnesium concentration is approximately 0.1 to 1.0 wt pet, but this is dependent on the volume of oxide and, hence, the particle size, as well as the sintering conditions. Small particle-size fractions require proportionally more magnesium than large-size fractions do.

The spatial and temporal distribution of koala faecal pellets

Faecal pellets were collected under trees used by free-ranging koalas in south-western, central and southeastern Queensland to determine the spatial and temporal distribution of pellets with respect to the activity of koalas. Deposition of faecal pellets by koalas was analysed according to the time of day at which the tree was occupied. For free-ranging koalas, 47% of daily faecal pellet output was recovered using a collection mat of 8 x 8 m placed under a day-roost tree. The best predictor of pellet production was the presence of a koala in a tree between 1800 hours and midnight. For other periods, there was no relationship between period of tree occupancy and faecal pellet recovery. There was a significant relationship between the average length of tree occupancy and the time of day that a koala entered a tree.

Modeling the optical constants of GaP, InP, and InAs

An extension of the Adachi model with the adjustable broadening function, instead of the Lorentzian one, is employed to model the optical constants of GaP, InP, and InAs. Adjustable broadening is modeled by replacing the damping constant with the frequency-dependent expression. The improved flexibility of the model enables achieving an excellent agreement with the experimental data. The relative rms errors obtained for the refractive index equal 1.2% for GaP, 1.0% for InP, and 1.6% for InAs. (C) 1999 American Institute of Physics. [S0021-8979(99)05807-7].

Building better wildlife-habitat models

Wildlife-habitat models are an important tool in wildlife management toda?, and by far the majority of these predict aspects of species distribution (abundance or presence) as a proxy measure of habitat quality. Unfortunately, few are tested on independent data, and of those that are, few show useful predictive st;ill. We demonstrate that six critical assumptions underlie distribution based wildlife-habitat models, all of which must be valid for the model to predict habitat quality. We outline these assumptions in a mete-model, and discuss methods for their validation. Even where all sis assumptions show a high level of validity, there is still a strong likelihood that the model will not predict habitat quality. However, the meta-model does suggest habitat quality can be predicted more accurately if distributional data are ignored, and variables more indicative of habitat quality are modelled instead.

Biomodel-guided stereotaxy

OBJECTIVES: To simplify the practice of stereotactic surgery by using an original method, apparatus, and solid anatomic replica for trajectory planning and to validate the method and apparatus in a laboratory and clinical trial. METHODS: The patient is marked with fiducials and scanned by using computed tomography or magnetic resonance imaging. The three-dimensional data are converted to a format acceptable to stereolithography. Stereolithography uses a laser to polymerize photosensitive resin into a solid plastic model (biomodel). Stereolithography can replicate brood vessels, soft tissue, tumor, and bone accurately (

Flyash as support for Ni catalysts in carbon dioxide reforming of methane

A series of Ni catalysts supported on flyash treated by various chemical methods was tested for carbon dioxide reforming of methane. Ni catalyst on the flyash treated with CaO (Ni/Ash-CaO) shows high conversion and stability, being close to those of the well-reported Ni/Al2O3 and Ni/SiO2 catalysts with conversions approaching thermodynamic equilibrium levels.

Modeling the optical constants of AlxGa1-xAs alloys

The extension of Adachi's model with a Gaussian-like broadening function, in place of Lorentzian, is used to model the optical dielectric function of the alloy AlxGa1-xAs. Gaussian-like broadening is accomplished by replacing the damping constant in the Lorentzian line shape with a frequency dependent expression. In this way, the comparative simplicity of the analytic formulas of the model is preserved, while the accuracy becomes comparable to that of more intricate models, and/or models with significantly more parameters. The employed model accurately describes the optical dielectric function in the spectral range from 1.5 to 6.0 eV within the entire alloy composition range. The relative rms error obtained for the refractive index is below 2.2% for all compositions. (C) 1999 American Institute of Physics. [S0021-8979(99)00512-5].