The sustainability of Australian agricultural production systems: a realistic objective or simply a desirable aim?

Whilst the term sustainability has undergone considerable transformation from its original intended meaning, in the context of agriculture it is considered to have relevance to four aspects of the activity; the maintenance of production, financial returns, employment opportunities, and the stability of the ecosystem. This article's appraisal of market trends suggests that the key issue of substantially improved financial returns for Australian agriculturalists is at present unlikely for some enterprises. What is particularly discouraging is that downward trends have persisted, despite the many efficiency gains in agriculture. Further gains from technological developments and trade liberalisation will be limited for many agricultural sectors. Whilst initiatives to reduce land degradation have achieved a high public profile, greater effectiveness can be achieved in this area. There is some scope for significant improvements in the overall performance of agriculture, but the most achievable gains will probably be confined to those specific enterprises that can use geography to greatest advantage.     

Atmospheric chemistry of the monoterpene reaction products nopinone,camphenilone, and 4-acetyl-1-methylcyclohexene

Rate constants for the gas-phase reactions of OH radicals with nopinone (6,6-dimethylbicyclo[3.1.1]heptan-2-one) and camphenilone (3,3-dimethylbicyclo[2.2.1]heptan-2-one) and for the reactions of 4-acetyl-1-methylcyclohexene with OH and NO₃ radicals and O₃ have been measured at 296±2 K. The rate constants (cm³ molecule^–1 s^–1 units) obtained were, for reaction with the OH radical: nopinone, (1.43±0.37)×10^–11; camphenilone, (5.15±1.44)×10^–12; and 4-acetyl-1-methylcyclohexene, (1.29±0.33)×10^–10; for reaction with the NO₃ radical: 4-acetyl-1-methylcyclohexene, (1.05±0.38)×10^–11; and for reaction with O₃: 4-acetyl-1-methylcyclohexene, (1.50±0.53)×10^–16. These data are used to calculate the tropospheric lifetimes of these monoterpene atmospheric reaction products.     

Fan and playa areas in southern California and adjacent parts of Nevada

In bolsons in the desert regions of southern California and adjacent parts of Nevada, the area underlain by alluvial fan gravels and playa sediments is generally ?1·2 times the area being eroded to produce those sediments. In certain larger basins in the vicinity of Death Valley, however, the depositional area is only about half the size of the erosional area. This reflects the more active tectonic environment in these bolsons. Of the areas underlain by recent sediments in these bolsons, playas make up 2–6 per cent. Smaller playas are found in the Mojave region, and seem to be associated with sedimentary terranes. Conversely, igneous terranes support larger playas. Larger deviations of playa area from these averages are attributable to incorrect identification of bolson boundaries. Fine sediment is either able to pass through the bolson to the next down stream, or is being collected from areas upstream that were not considered to be part of the system. For example, the playa in Death Valley is unusually large. This is in part because the Death Valley playa has been deformed tectonically so parts of it are now eroding, and in part because the outlet of Lake Tecopa was downcut in the geologically recent past, so sediment once trapped there now reaches Death Valley. The size of the playa in Death Valley is still adjusting to these changes.     

Numerical modelling of the saline interface in coastal karstic aquifers within a conceptual model uncertainty framework

Numerical modelling is increasingly used as a tool for improving management strategies in aquifers and to support the design of comprehensive projects considering natural and anthropogenic processes. Overall, numerical simulation in karstic aquifers poses a major scientific challenge due to the non-Darcian groundwater flow dynamics. In specific cases, the equivalent porous medium approach has shown acceptable results, particularly in poorly karstified aquifers with regional/subregional scales such as this case. The Yucatan coastal karstic aquifer (Mexico) has been defined as a complex regional heterogeneous system, partially confined, thus allowing the discussion of multiple conceptual models. In this research, a two-dimensional numerical model of flow and transport was implemented using SEAWAT for the NW Yucatan aquifer. Four likely conceptual models were audited, calibrated and verified using hydrogeological field data, to select the best one, considering their fit and complexity. The numerical model accuracy was evaluated using the root-mean-square error, Nash Sutcliffe efficiency and the Pearson coefficient. The Akaike information criterion and Bayesian information criterion were included for evaluating the complexity of the numerical models. In addition, the signal of tide propagation into the aquifer was assessed as a proxy to improve the numerical calibration process. Results show that the most complex numerical model has a better calibration than the simpler models, but the model accuracy is worse when compared to less complex numerical models in the verification exercise. This research offers enhancement in the knowledge of numerical modelling in heterogeneous coastal aquifers within a conceptual-model uncertainty setting.

     

Timing and duration of partial melting and magmatism in the Variscan Montagne Noire gneiss dome (French Massif Central)

International Journal of Earth Sciences - Unravelling the detailed pressure–temperature–time-deformation (P–T–t-D) evolution of magmatic and metamorphic rocks provides...     

Further observations of quasars in ESO/SERC field 927

We present the spectra and redshifts of 62 quasars, from observations made with the Cerro Tololo Inter-American Observatory (CTIO) 4-m Blanco Telescope. These quasars form part of a total sample of 118 (with 56 having been published previously), which is being used for analysis of structure in the early universe. Quasars of particular interest are noted, including eight broad absorption line (BAL) quasars and two quasars with unusual emission spectra. Finally, we include a short summary of the present status of the large quasar group (LQG) that was discovered by Clowes & Campusano from the earlier observations. The quasars are from an area ∼25.3 deg² of ESO/SERC field 927, which is centred at (1950) 10^h40^m00^s, 05°00'00'.     

An examination on several key problems inChina's urbanization process

WithrapideconondcdevelopmentthroughoutChina,thecounnyhasenteredtheperiodofacceleratedothazahonprocess.Accompamedbyindustriallzahonandurbanhaonstep,mpidurbanrenovahonandimpoamboctUfeprojectFonstnJchon,social,econondcandspatialmctUreaxeexperiencinggrCatchanges.ThegreatchangeineconondcandspatialStrUctUreembodiestheinereasingnuInberofthecitiesanduIbanexpansioftMeanwhileitalsopresentStheincreasingroadnetdensityamongcihes,theincreasinghighguderoadsandrailwaysandareaexpansionforkeyprojectSfacili…     

Source/receiver array directivity effects on marine seismic attenuation measurements

Attenuation of seismic waves, quantified by the seismic quality factor Q, holds important information for seismic interpretation, due to its sensitivity to rock and fluid properties. A recently published study of Q, based on surface seismic reflection data, used a modified spectral ratio approach (QVO), but both source and receiver responses were treated as isotropic, based on simple raypath arguments. Here, this assumption has been tested by computing apparent attenuation generated by frequency-dependent directivity of typical marine source and receiver arrays and acquisition geometries. Synthetic wavelet spectra were computed for reflected rays, summed over the first Fresnel zone, from the base of a single interval, 50–3000 m thick and velocity 2000 m/s, overlying a 2200 m/s half-space, and for offsets of 71–2071 m. The source and receiver geometry were those of an actual survey. The modelled spectra are clearly affected by directivity, most strongly because of surface ghosts. In general, the strong high-frequency component, produced by the array design, leads to apparently negative attenuation in individual reflection events, though this is dependent on offset and target depth. For shallow targets (less than 400–500 ms two-way traveltime (TWT) depth), apparent Q-values as extreme as ?50 to ?100 were obtained. For deeper target depths, the directivity effect is far smaller. The implications of the model study were tested on real data. QVO was applied to 20 true-spectrum-processed CMPs, in a shallow (405–730 ms TWT) and a deeper (1000–1300 ms TWT) interval, firstly using a measured far-field source signature (effectively isotropic), and secondly using computed directivity effects instead. Mean interval Q^?1-values for the deeper interval, 0.029 ± 0.011 and 0.027 ± 0.018 for conventional and directional processing, respectively, suggested no directivity influence on attenuation estimation. For the shallow interval (despite poor spectral signal-to-noise ratios and hence scattered attenuation estimates), directional processing removed directivity-generated irregularities from the spectral ratios, resulting in an improvement from Q^?1_int = ?0.036 ± 0.130 to a realistic Q^?1_int = 0.012 ± 0.030: different at 94% confidence level. Equivalent Q-values are: for the deeper interval, 35 and 37 for conventional and directional processing, respectively, and ?28 and 86 for the shallow interval. These results support the conclusions of the model studies, i.e. that source/receiver directivity has a negligible effect except for shallow targets (e.g. TWT depth ≤ 500 ms) imaged with conventional acquisition geometry. In such cases directivity corrections to spectra are strongly recommended.