Complex environmental gradients predict distributions of river-dependent plants in eastern Australia

We used principal components analysis and multiple logistic regression to investigate the relationships between environmental variables and the distributions of 71 species of river-dependent vascular plants in north-eastern New South Wales, Australia. Our analysis defined seven main environmental factors, summarised (in order of decreasing frequency of statistically significant association with species distributions) as exposure, salinity, stream size, stone scarcity, nutrient enrichment, grazing pressure and rockiness. The main environmental correlates of the presence or absence of macrophyte species in our study were broadly similar to those reported elsewhere, but the relatively low apparent importance of nutrients and grazing was unexpected. We were not able to fully separate the effects of climate-related and non-climatic environmental variables because variables of both types loaded strongly on some principal components, but we suggest that both types of variables should be included in models that aim to forecast potential shifts in plant distributions under projected climatic change. Vascular plants have been neglected in monitoring programs for Australian rivers and their conservation requires a better understanding of patterns and trends in distribution and abundance.     

Rock fracture compliance derived from time delays of elastic waves

The purpose of this study is to compare the reliability of various methods of estimating normal rock fracture compliance from elastic wave measurements. We compare ultrasonic through‐transmission laboratory measurements for a smooth fracture in a Westerly granite specimen with numerical simulations and analytical solutions. The focus is on deriving compliance from time delays. The influence of specimen and source transducer width was constrained using numerical wave simulations. We find that measured ultrasonic phase delays are better suited to estimate the fracture compliance than group delays. Using the frequency domain instead of the time domain increases the accuracy of the fracture compliance estimates. We further show that for cases where precise phase delay measurements are unavailable, employing first break times in conjunction with numerical simulations can be considered as an alternative.     

Comment on “Thermoluminescence of meteorites and their terrestrial ages”

Melcher (1981a) recently proposed a method to determine the terrestrial age of chondritic meteorites using thermoluminescence. This paper suggests that Melcher's analysis of the second-order thermoluminescence signals is inappropriate and hence his conclusions regarding the age estimates are wrong.     

Thermoluminescence spectra of igneous quartz and hydrothermal vein quartz

Variations in thermoluminescence spectra are reported for four types of geological quartz examined with a new spectrometer featuring dual imaging photon detectors that separately and simultaneously detect (1) uv-blue (200–450 nm) and (2) blue to near infrared (400–800 nm) emission. Samples show striking differences which appear to be characteristic of their geological origin. Volcanic quartz phenocrysts from acid volcanics show red thermoluminescence (TL) emission bands centered at 620–630 nm that are 100 times more intense than similar bands in other quartz, while a violet emission at 420–435 nm was observed exclusively in igneous quartz (volcanic and granitic). A broad emission band centered at 560–580 nm was observed only in quartz formed hydrothermally. Massive quartz from Li-rich pegmatite bodies shows narrow, intense 470 nm emission bands at 230° C apparently related to Al and to Ge defects detected with electron paramagnetic resonance (EPR), and emission bands at 330 and 280 nm, possibly related to recombination at oxygen vacancies. The common 380 nm emission band of quartz was observed in both volcanic and granitic quartz, but was not detected in either the pegmatitic or the hydrothermal vein quartz. Observed spectral variation is identified as a potential source of error in luminescence dating.     

Searching for multifractal scaling in gamma ray burst time series

We present a multifractal analysis of GRB time series used to quantify the variability of the light curve. We discuss the advantages and disadvantages of multifractal analysis, including sensitivity to noise, and burst intensity, and present results for a few sample bursts.     

Scattering attenuation and the fractal geometry of fracture systems

Scattering of seismic waves can be shown to have a frequency dependenceQ ^{–1 3–v} if scattering is produced by arrays of inhomogeneities with a 3D power spectrumW _3D(k) k ^–v. In the earth's crust and upper mantle the total attenuation is often dominated by scattering rather than intrinsic absorption, and is found to be frequency dependent according toQ ^–1 , where –1<–0.5. IfD ₁ is the fractal dimension of the surface of the 3D inhomogeneities measured on a 2D section, then this corresponds respectively to 1.5<D ₁1.75, since it can be shown that =2(D ₁–2). Laboratory results show that such a distribution of inhomogeneities, if due to microcracking, can be produced only at low stress intensities and slow crack velocities controlled by stress corrosion reactions. Thus it is likely that the earth's brittle crust is pervaded by tensile microcracks, at least partially filled by a chemically active fluid, and preferentially aligned parallel to the maximum principal compressive stress. The possibility of stress corrosion implies that microcracks may grow under conditions which are very sensitive to pre-existing heterogeneities in material constants, and hence it may be difficult in practice to separate the relative contribution of crack-induced heterogeneity from more permanent geological heterogeneities.By constrast, shear faults formed by dynamic rupture at critical stress intensities produceD ₁=1, consistent with a dynamic rupture criterion for a power law distribution of fault lengths with negative exponentD. The results presented here suggest empirically thatD ₁-1/2(D+1), thereby providing the basis for a possible framework to unify the interpretation of temporal variations in seismicb-value (b-D/2) and the frequency dependence of scattering attenuation ().This is PRIS contribution 046.     

Corporate management of the Northwestern Hawaiian Islands lobster fishery

Limited entry and biological quotas were implemented in the lobster fishery of the Northwestern Hawaiian Islands in 1991, during a period of declining stock abundance. A companion use-it-or-lose-it permit provision has had the perverse effect of increasing fishing effort during times of declining stocks. Despite its unfavorable short-term prospects, the fishery has the potential to be very lucrative for a small number of boats over the long term. This paper introduces a dramatically different management regime that would create ownership rights in a private management corporation for the current limited-entry permit holders. This corporation would function within a renewable operating contract with the government to protect the public interest in the conservation of the lobster population and its associated ecosystem. Published by Elsevier Science Ltd.