Magnetoresistive effects ͑ ͑ ͑R͑0͒-R͑H͒͒ ͒ ͒͞R͑H͒ exceeding 500% are found at room temperature in a field of 7 mT in nanocontacts between Fe 3 O 4 crystallites. The shape of the I͑V͒ curve depends on field and the magnitude of the magnetoresistance is correlated with the resistance, the largest effects occurring when R . 100 kV. The explanation proposed involves hopping transport of spin-polarized electrons through a narrow domain wall pinned at the nanocontact; spin pressure on the domain wall pushes it out into the electrode, leading to the nonlinearity of the I͑V͒ characteristic. Application of current-induced wall motion in a simple fast-switching magnetic memory element is proposed. DOI: 10.1103/PhysRevLett.87.026601 PACS numbers: 72.25. -b, 73.63.Rt, 75.70. -i Conventional electronics ignores the spin of the electron. If the budding science of spin electronics is to bear fruit, devices have to be designed around effects which are large at room temperature. Half-metallic oxides are potential sources of fully spin-polarized electrons, and when they are used to inject electrons across thin tunnel barriers [1,2], grain boundaries [3], or interparticle contacts [4] large magnetoresistance effects are observed, at liquid helium temperatures. For reasons that remain uncertain, the spin polarization falls rapidly with increasing temperature and the magnetoresistance at room temperature in all-oxide structures is usually no more than 1%. In this Letter, we show that the conductivity of a nanocontact between two crystallites of magnetite (Fe 3 O 4 ) can increase sixfold at room temperature in an applied field of 7 mT (70 Oe). This large low-field effect is attributed to spin-polarized electrons hopping across a very narrow domain wall at the contact. Spin pressure on the domain wall at the nanocontact leads to nonlinearity of the I͑V ͒ characteristic, and the possibility of fast switching in a bistable two-or threeterminal device via current-induced wall motion.Magnetite, the ferrimagnetic inverse spinel Fe 3 O 4 , is the half-metallic oxide with the highest known Curie temperature (860 K). Carriers are small polarons in a minority spin 3d # ͑t 2g ͒ band [5] which hop among the B sites; the majority spin band is full [6]. Tiny magnetite crystals grown by chemical vapor transport are used for our experiments [7]. Two of them are glued in a simple piezoelectric device with vibration isolation that allows electrical contact to be made or broken in a controlled manner [8], following a method of Costa-Krämer et al. [9]. All measurements are carried out at room temperature (290 K) in ambient air. A magnetic field of up to 14 mT (140 Oe) can be applied in any direction in a plane by means of two pairs of Helmholtz coils.When the contact is broken rapidly in a relay (ഠ100 ms), the conductance falls in an irregular way. A histogram based on 500 such breaks shows a single weak peak near the quantum of conductance G 0 2e 2 ͞h ͑12.9 kV͒ 21 . There is much less structure than was found previously for contacts between crystal...

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Abstract. Streamflow variability and trends in Australia were investigated for 222 high-quality stream gauging stations having 30 years or more continuous unregulated streamflow records. Trend analysis identified seasonal, interannual and decadal variability, long-term monotonic trends and step changes in streamflow. Trends were determined for annual total flow, baseflow, seasonal flows, daily maximum flow and three quantiles of daily flow. A distinct pattern of spatial and temporal variation in streamflow was evident across different hydroclimatic regions in Australia. Most of the stations in southeastern Australia spread across New South Wales and Victoria showed a significant decreasing trend in annual streamflow, while increasing trends were retained within the northern part of the continent. No strong evidence of significant trend was observed for stations in the central region of Australia and northern Queensland. The findings from step change analysis demonstrated evidence of changes in hydrologic responses consistent with observed changes in climate over the past decades. For example, in the Murray-Darling Basin, 51 out of 75 stations were identified with step changes of significant reduction in annual streamflow during the middle to late 1990s, when relatively dry years were recorded across the area. Overall, the hydrologic reference stations (HRSs) serve as critically important gauges for streamflow monitoring and changes in long-term water availability inferred from observed datasets. A wealth of freely downloadable hydrologic data is provided at the HRS web portal including annual, seasonal, monthly and daily streamflow data, as well as trend analysis products and relevant site information.

Abstract:An investigation has been undertaken to quantify the uncertainty in statistically downscaled catchment precipitation and runoff projections due to different climate models. A significant component of the investigation was the assessment of climate model reproduction of the seasonal (i.e. monthly) cycle of the atmospheric predictors used by a statistical downscaling model. Four climate model simulations forced by the SRES A2 emission scenario were used: the CSIRO Mk3 GCM, the CSIRO Conformal-Cubic Atmospheric Model (CCAM, run at high spatial resolution over Australia with far-field forcing from the Mk3 GCM), the Hadley Centre HadAM3P GCM and the Max Planck Institute ECHAM4 GCM.The non-homogeneous hidden Markov model (NHMM), a stochastic downscaling model, was used to quantify the impacts of the projected climate change on multi-site, daily precipitation. A catchment water balance model (LUCICAT), calibrated under existing conditions, was driven by the downscaled precipitation to produce runoff projections. Land use and potential evaporation (evapotranspiration potential) were kept fixed for the future climate in order to assess the catchment response to differences in the downscaled precipitation series.Biases in climate model reproduction of the season cycles of the atmospheric predictors used in downscaling are shown to have significant impacts on simulated precipitation, and hence runoff. The downscaled CCAM and Mk3 results project reductions in annual precipitation ranging from 12 to 14% by mid century , resulting in a decline in runoff ranging from 30 to 44%. Downscaling the HadAM3P output, available at the daily time step only for the period 2070-2099, produces a precipitation decline of 24% and a runoff reduction of 69%. The ECHAM4 downscaled precipitation inadequately reproduced the observed annual cycle and so was not used for runoff projection.

A conceptual water balance model is presented to represent changes in monthly water balance following land use changes. Monthly rainfall runoff, groundwater and soil moisture data from four experimental catchments in Western Australia have been analysed. Two of these catchments, Ernies (control, fully forested) and Lemon (54% cleared) are in a zone of mean annual rainfall of 725 mm, while Salmon (control, fully forested) and Wights (100% cleared) are in a zone with mean annual rainfall of 1125 mm. At the Salmon forested control catchment, streamflow comprises surface runoff, base flow and interflow components. In the Wights catchment, cleared of native forest for pasture development, all three components increased, groundwater levels rose significantly and stream zone saturated area increased from 1% to 15% of the catchment area. It took seven years after clearing for the rainfallrunoff generation process to stabilise in 1984. At the Ernies forested control catchment, the permanent groundwater system is 20 m below the stream bed and so does not contribute to streamflow. Following partial clearing of forest in the Lemon catchment, groundwater rose steadily and reached the stream bed by 1987. The streamflow increased in two phases: (i) immediately after clearing due to reduced evapotranspiration, and (ii) through an increase in the groundwaterinduced stream zone saturated area after 1987. After analysing all the data available, a conceptual monthly model was created, comprising four inter-connecting stores: (i) an upper zone unsaturated store, (ii) a transient stream zone store, (ii) a lower zone unsaturated store and (iv) a saturated groundwater store. Data such as rooting depth, Leaf Area Index, soil porosity, profile thickness, depth to groundwater, stream length and surface slope were incorporated into the model as a priori defined attributes. The catchment average values for different stores were determined through matching observed and predicted monthly hydrographs. The observed and predicted monthly runoff for all catchments matched well with coefficients of determination (R 2 ) ranging from 0.68 to 0.87. Predictions were relatively poor for: (i) the Ernies catchment (lowest rainfall, forested), and (ii) months with very high flows. Overall, the predicted mean annual streamflow was within ±8% of the observed values.