Adaptive local discontinuous Galerkin approximation to Richards’ equation

We propose a spatially and temporally adaptive solution to Richards’ equation based upon a local discontinuous Galerkin approximation in space and a high-order, backward difference method in time. We cast our approach in terms of a general, decoupled adaption algorithm based upon operators. We define non-unique instances of all operators to result in an adaption method from within the general class of methods that is defined. We formally decouple the spatial adaption from the temporal adaption using a method of lines approach and limit the temporal truncation error so that the total error is dominated by the spatial component. We use a multiple grid approach to guide adaption and support the data structures. Spatial adaption decisions are based upon error and regularity indicators, which are economical to compute. The resultant methods are compared for two test problems. The results show that the proposed adaption methods are superior to methods that adapt only in time and that in cases in which the problem has sufficient smoothness, adapting the order of the elements in addition to the grid spacing can further improve the efficiency of this robust solution approach.     

Extremely red galaxy counterparts to 7C radio sources

We present RIJHK imaging of seven radio galaxies from the 7C Redshift Survey (7CRS) which lack strong emission lines and we use these data to investigate their spectral energy distributions (SEDs) with models that constrain their redshifts. Six of these seven galaxies have extremely red colours ( R − K >5.5) and we find that almost all of them lie in the redshift range 1< z <2. We also present near-infrared spectroscopy of these galaxies which demonstrate that their SEDs are not dominated by emission lines, although tentative lines, consistent with H α at z =1.45 and z =1.61, are found in two objects. Although the red colours of the 7CRS galaxies can formally be explained by stellar populations that are either very old or young and heavily reddened, independent evidence favours the former hypothesis. At z ∼1.5 at least 1/4 of powerful radio jets are triggered in massive (> L *) galaxies, which formed the bulk of their stars several Gyr earlier, that is at epochs corresponding to redshifts z ≳5. If a similar fraction of all z ∼1.5 radio galaxies are old, then extrapolation of the radio luminosity function shows that, depending on the radio source lifetimes, between 10 and 100 per cent of the near-IR selected extremely red object (ERO) population undergo a radio outburst at epochs corresponding to 1< z <2. An ERO found serendipitously in the field of one of the 7CRS radio sources appears to be a radio-quiet analogue of the 7CRS EROs with an emission line likely to be [O  ii ] at z =1.20. The implication is that some of the most massive elliptical galaxies formed the bulk of their stars at z ≳5 and these objects probably undergo at least two periods of active galactic nucleus activity: one at high redshift during which the black hole forms and another one at an epoch corresponding to z ∼1.5.     

Fate and effects of picric acid and 2,6-DNT in marine environments: toxicity of degradation products

The toxicity of transformation products of 2,6-dinitrotoluene (2,6-DNT) and 2,4,6-trinitrophenol (picric acid) were assessed in spiked sandy and fine-grained marine sediments and in seawater. Toxicity of pore water from sediments spiked with 2,6-DNT decreased for the macro-alga, Ulva fasciata, zoospores as biotransformation proceeded, but increased for the copepod, Schizopera knabeni, nauplii. The primary biotransformation product of 2,6-DNT, 2-amino-6-nitrotoluene, was also more toxic than the parent compound to copepod nauplii, but not to alga zoospores, in spiked seawater tests. Two biotransformation products of picric acid, picramic acid and 2,4-DNP, were more toxic than their parent compound. Porewater toxicity from picric acid-spiked sediments decreased significantly at the end of six-months incubation. Fine-grained sediment spiked with either ordnance compound had lower toxicity than its sandy counterpart after six months, suggesting faster microbial transformation in the former and production of less toxic products. Photo-transformation of 2,6-DNT in seawater resulted in a reduction in toxicity.     

Tectonic significance of Late Neoproterozoic granites from the Tibesti massif in southern Libya inferred from Sr and Nd isotopes and U–Pb zircon data

The Neoproterozoic crust of the Tibesti massif was stabilized by magmatism that included subduction-generated batholithic suites and post-orogenic granite plutons. All of the magmatism occurred in a period of about 20 million years centered around 550 Ma, and nearly all of the granites have initial ⁸⁷Sr/⁸⁶Sr ratios of about 0.706. The Wadi Yebigue pluton has U–Pb zircon ages of 563 Ma and 558 Ma on two different phases and ε_Nd at 550 Ma from −0.5 to −2.2. These isotopic data and the geologic history of the massif suggest that granites in the Tibesti massif developed during and shortly after closure of a short-lived ocean basin that developed by fragmentation of pre-existing continental crust of the Saharan region.     

Part I. Decrepitation and degassing behaviour of quartz up to 1560 °C: Analysis of noble gases and halogens in complex fluid inclusion assemblages

Stepped heating and crushing experiments have been used to investigate the noble gas and halogen degassing behaviour of quartz in detail. Samples with diverse character were selected from the Eloise and Osborne, Iron Oxide Copper Gold (IOCG) ore deposits, and the Railway Fault, 13 km south of the Mt Isa Mine, in the Proterozoic Mt Isa Inlier of northeast Australia. Quartz has been shown to have a bimodal degassing profile. The first degassing mode at temperatures of <700 °C is caused by thermally induced mechanical decrepitation of fluid inclusions. Changes in the Br/Cl, I/Cl, Ar/Cl and ⁴⁰Ar/³⁶Ar composition of gas released at different temperatures up to 700 °C can be related to the decrepitation of different types of fluid inclusion observed by microthermometry. These variations with temperature permit deconvolution of the complex fluid inclusion assemblages associated with the IOCG samples; the ultra high salinity, multi solid (MS) and liquid-vapour-daughter (LVD) fluid inclusions, with a predominantly primary origin, decrepitate at higher temperatures than lower salinity liquid-vapour (LV) and monophase (M) fluid inclusions that have a predominantly secondary origin. Three of the IOCG samples have primary MS and LVD fluid inclusions characterized by molar Br/Cl values of between 0.25 × 10⁻³ and 0.66 × 10⁻³, I/Cl between 0.37 × 10⁻⁶ and 5.0 × 10⁻⁶, ⁴⁰Ar/³⁶Ar values of <1000 and low ³⁶Ar concentrations of 0.7-1.0 × 10⁻⁶ cm³ cm⁻³H₂O. These low values are most easily explained by the involvement of halite dissolution water in IOCG genesis. One of the IOCG samples has Br/Cl of 1.3-2.0 × 10⁻³ and I/Cl of 10 × 10⁻⁶, similar to juvenile magmatic fluids in Phanerozoic Porphyry Copper Deposits. This sample also has a higher ³⁶Ar concentration of 3.5 × 10⁻⁶ cm³ cm⁻³H₂O and a slightly elevated ⁴⁰Ar/³⁶Ar of 2236. Step heating reveals limited and non-systematic variation within the more homogenous population of LV fluid inclusions from the Railway Fault. The samples have mean values of 8.1 × 10⁻³ for Br/Cl; 9.4-12 × 10⁻⁶ for I/Cl; <2000 for ⁴⁰Ar/³⁶Ar; and 4.7-4.8 × 10⁻⁶ cm³ cm⁻³H₂O for ³⁶Ar concentration. The Br/Cl values are similar to those previously reported for basinal brines present in silicic alteration at the Mt Isa Mine and the additional data can be explained by interaction of such a bittern brine with fine grained sedimentary rocks in the sub-surface. The second mode of quartz degassing occurs between 1200 and 1450 °C and releases a greater volume of gas than the first degassing mode. Several lines of evidence, including microscope observations, indicate that the gas released at high temperature is also from the fluid inclusion reservoir. However, its release may be triggered by a metastable phase transition of quartz (∼1200 °C) and caution is required in interpretation of the fluid compositions obtained at these temperatures. The data provide an improved understanding of fluid inclusion decrepitation behaviour that is different to that obtained in lower temperatures experiments designed by other workers to investigate H-isotope fractionation.     

Measurement of the ozone concentration from 55 to 95 km at sunset

Three measurements of the concentration of ozone in the mesosphere and lower thermosphere at sunset have been made by the occultation technique from rocket payloads. Two of these were developmental flights made from Woomera in June 1966. Both produced useful results from 55 to 70 km, and the one flight giving results above 70 km indicated the presence of a secondary ozone layer with approximately uniform concentration between 72 and 92 km. The final flight, made from Fort Churchill Range in September 1969, revealed a minimum in the concentration near 80 km and a secondary maximum around 90 km.     

Toxicological and chemical assessment of ordinance compounds in marine sediments and porewaters

Toxicological and chemical studies were performed with a silty and a sandy marine sediment spiked with 2,6-dinitrotoluene (2,6-DNT), 2,4,6-trinitrophenylmethylnitramine (tetryl), or 2,4,6-trinitrophenol (picric acid). Whole sediment toxicity was analyzed by the 10-day survival test with the amphipod Ampelisca abdita, and porewater toxicity tests assessed macro-algae (Ulva fasciata) zoospore germination and germling growth, sea urchin (Arbacia punctulata) embryological development, and polychaete (Dinophilus gyrociliatus) survival and reproduction. Whole sediments spiked with 2,6-DNT were not toxic to amphipods. The fine-grained sediment spiked with tetryl was also not acutely toxic. The tetryl and picric acid LC50 values in the sandy sediment were 3.24 and 144 mg/kg dry weight, respectively. The fine-grained sediment spiked with picric acid generated a U-shaped concentration-response curve in the amphipod test, with increased survival both in the lowest and highest concentration. Grain-size distribution and organic carbon content strongly influenced the behavior of ordnance compounds in spiked sediments. Very low concentrations were measured in some of the treatments and irreversible binding and biodegradation are suggested as the processes responsible for the low measurements. Porewater toxicity varied with its sedimentary origin and with ordnance compound. The sea urchin embryological development test tended to be the least sensitive. Tetryl was the most toxic chemical in all porewater tests, and picric acid the least toxic. Samples spiked with 2,6-DNT contained a degradation product identified as 2-methyl-3-nitroaniline (also known as 2-amino-6-nitrotoluene), and unidentified peaks, possibly degradation products, were also seen in some of the picric acid- and tetryl-spiked samples. Degradation products may have played a role in observed toxicity.     

Geographic representation in spatial analysis

Spatial analysis mostly developed in an era when data was scarce and computational power was expensive. Consequently, traditional spatial analysis greatly simplifies its representations of geography. The rise of geographic information science (GISci) and the changing nature of scientific questions at the end of the 20th century suggest a comprehensive re-examination of geographic representation in spatial analysis. This paper reviews the potential for improved representations of geography in spatial analysis. Existing tools in spatial analysis and new tools available from GISci have tremendous potential for bringing more sophisticated representations of geography to the forefront of spatial analysis theory and application.