Monte Carlo Simulation of Ising Models with Dipole Interaction

Recently, a new memory effect was found in the metamagnetic domain structure of the diluted Ising antiferromagnet $Fe_x Mg_{1-x} Cl_2$ by domain imaging with Faraday contrast. Essential for this effect is the dipole interaction. We simulate the low temperature behavior of diluted Ising-antiferromagnets by a Monte Carlo simulation considering long range interaction. The metamagnetic domain structure occurring due to the dipole interaction is investigated by graphical representation. In the model considered the antiferromagnetic state is stable for an external magnetic field smaller than a lower boundary $B_{c1}$ while for fields larger than an upper boundary $B_{c2}$ the system is in the saturated paramagnetic phase, where the spins are ferromagnetically polarized. For magnetic fields in between these two boundaries a mixed phase occurs consisting of ferromagnetic domains in an antiferromagnetic background. The position of these ferromagnetic domains is stored in the system: after a cycle in which the field is first removed and afterwards applied again the domains reappear at their original positions. The reason for this effect can be found in the frozen antiferromagnetic domain state which occurs after removing the field.Comment: Latex, 10 pages; 3 postsript-figures, compressed tar-file, uuencoded, report 10109

Coherent response of lakes in Ontario, Canada to reductions in sulphur deposition: the effects of climate on sulphate concentrations

International audienceSulphate deposition in south-central Ontario declined between 1976 and 2000 by more than 50%, whereas lake sulphate (SO42?) concentrations decreased by, on average, only half as much. To investigate the factors that controlled this slower than expected response, the temporal patterns in lake SO42? concentrations were compared with patterns in both deposition and climate, since climate has a major influence on the hydrological cycle in this part of the continent. To do this, the temporal coherence in SO42? concentrations between 9 lake basins was estimated using the intraclass correlation from a repeated-measures analysis of variance and two subsets of lakes were found (six in one group, four in the other), each with lakes having synchronous patterns. One subset (4 lakes) included the 3 with the longest water replenishment times (>3.4 yr) which are expected to respond to decreases in SO42? deposition more slowly. However, the average pattern reflecting the temporal changes of each of the two subsets was very similar. The response of both subsets of lakes to the decreasing SO42? deposition over two decades was independent of the degree of acidification or sensitivity to acidification of the lakes. In a determination of which factors best predicted each of those two subsets' SO42? time series, good predictive models were produced by regional/global-scale climate indices, specifically the Southern Oscillation Index (SOI) describing the El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation Index (NAOI), as well as by SO42? deposition indices. When the predictor variables were combined, models which described the long-term changes in lake SO42? concentration best included the SOI, the NAOI and SO42? deposition. Thus, large-scale climate factors play a major role in determining the response of aquatic systems to changes in SO42? deposition, perhaps through their influence on lake and/or catchment processes that effectively delay recovery. Keywords: Atmospheric deposition, lake recovery, temporal trends, climate, temporal coherenc

Buy High Sell Low: Redefining Bean Counting in the Coffee Industry for a Sustainable Future

Charles Manz returns to the JVBL providing ‒ together with several fellow researchers/writers ‒ a case study of a socially responsible business within the coffee industry. Familiar CSR concepts are examined such as Fair Trade and sustainability which foster parity in dealing with buyers while maintaining product quality and reasonable income. The practices of Dean’s Beans, a progressive coffee organization, are examined as a notable demonstration of how a business can fiscally succeed while maintaining a commitment to the triple-bottom-line considerations of people, planet, and profits

The impact of acid deposition and forest harvesting on lakes and their forested catchments in south central Ontario: a critical loads approach

International audienceThe impact of acid deposition and tree harvesting on three lakes and their representative sub-catchments in the Muskoka-Haliburton region of south-central Ontario was assessed using a critical loads approach. As nitrogen dynamics in forest soils are complex and poorly understood, for simplicity and to allow comparison among lakes and their catchments, CLs (A) for both lakes and forest soils were calculated assuming that nitrate leaching from catchments will not change over time (i.e. a best case scenario). In addition, because soils in the region are shallow, base cation weathering rates for the representative sub-catchments were calculated for the entire soil profile and these estimates were also used to calculate critical loads for the lakes. These results were compared with critical loads obtained by the Steady State Water Chemistry (SSWC) model. Using the SSWC model, critical loads for lakes were between 7 and 19 meq m-2yr-1 higher than those obtained from soil measurements. Lakes and forests are much more sensitive to acid deposition if forests are harvested, but two acid-sensitive lakes had much lower critical loads than their respective forested sub-catchments implying that acceptable acid deposition levels should be dictated by the most acid-sensitive lakes in the region. Under conditions that assume harvesting, the CL (A) is exceeded at two of the three lakes and five of the six sub-catchments assessed in this study. However, sulphate export from catchments greatly exceeds input in bulk deposition and, to prevent lakes from falling below the critical chemical limit, sulphate inputs to lakes must be reduced by between 37% and 92% if forests are harvested. Similarly, sulphate leaching from forested catchments that are harvested must be reduced by between 16 and 79% to prevent the ANC of water draining the rooting zone from falling below 0 ?eq l-1. These calculations assume that extremely low calcium leaching losses (9?27 ?eq l-1) from forest soils can be maintained without any decrease in forest productivity. Calcium concentrations in the three lakes have decreased by between ?10 and 25% over the past 20 years and calculations assume that calcium concentrations in lakes can fall to around 30% of their current values without any harmful effects on biota. Both these assumptions require urgent investigation. Keywords: acid deposition, calcium, critical loads, forests, harvesting, lakes</p

UCET Discussion paper on effective Continuing Professional Development

This report is based on the wealth of experience and scholarship shared by UCET colleagues. It reflects on key aspects of CPD-related policy, practice and research over the past 50 years and highlights the following principles: - Education professionals require an expanding range of competences over their career; these are often context-specific, unforeseen and go beyond any single framework - As well as being research-informed, CPD should engage educators in theory so they can adapt their learning creatively to enrich their own setting - Reflective practitioners are best cultivated by supporting teachers’ in conducting their own research - Effective CPD is built on trusted relationships between deliverers and learners and include a strong element of coaching and/or mentoring often by peers - For sustained impact, CPD needs to be sustained over time (at least across two terms), making use of multiple formats - By engaging teachers in their wider social, economic and environmental contexts, CPD will ensure responsible professionals in the fullest sense - Developing teachers’ agency will enable them to consider their practice critically, lead their own learning and thus maximise the positive impact they have on their learners - All CPD should be subject to robust quality assurance mechanisms

Role of climate change in recovery of acidified surface waters

International audienceSurface waters in Europe and North America have begun to recover in response to decreases in emissions of acidifying pollutants to the atmosphere. Variations in climate influence chemical and biological recovery. Part of the EU project Eurolimpacs (Integrated project to evaluate the impacts of global change on European freshwater ecosystems) focuses on the interactive effects of acid deposition and climate on freshwater ecosystems. This special issue of Hydrology and Earth System Sciences is devoted to this topic, and consists of studies conducted in 8 countries on aspects regarding episodes, nitrate, dissolved organic carbon, recovery and biological effects

Acidification and recovery of aquatic ecosystems in south central Ontario, Canada: regional application of the MAGIC model

International audienceThe dynamic model MAGIC was applied to 25 lakes in south-central Ontario, Canada using a regional modelling methodology. Soil and lake water chemistry for each lake catchment was simulated for the period 1850?2050. Sulphate (SO42?) deposition forecasts were derived from recently proposed emission reductions, which correspond roughly to a 50% reduction in SO42? deposition by 2010 from the 2000 baseline. Changes in SO42? deposition had a significant impact on lake chemistry. Simulated lake water chemistry showed a recovery potential under the current deposition scenario; by 2050 concentration levels recovered to values predicted for the early 1900s. Moreover, simulated future lake water chemistry showed significant recovery compared to 1975 levels. However, although regional simulations predict that base cation losses have decreased in recent years, soils in the region will continue to acidify with Ca2+ losses dominating depletion of the exchangeable pool. Base cation losses from the exchangeable pool are currently buffering lakes against the impacts of acid deposition; ultimately base cation inputs into the lakes will decrease as exchangeable base cation pools become depleted. Further emission reductions are necessary to ensure continued recovery from acidification. Keywords: regional dynamic model, sulphate, acid neutralising capacity, critical loads, lake chemistry, soil base saturatio

A Comparison of Three Systems of Milk Production With Different Land Use Strategies

Under the Luxemburg agreement FAPRI-Ireland (Breen & Hennessey 2003) projects that milk price will decrease by 5.0 to 5.5 c/l because of reductions in support for butter and skimmed milk powder. These changes mean that many dairy farmers need to reappraise their systems of milk production and consider necessary adjustments that will ensure viability in the longer term. The objective of this study was to model three different systems of milk production in scenarios where quota, cow numbers or land was restricted

Shape-dependent Depinning of a Domain Wall by a Magnetic Field and a Spin-Polarized Current

The effect of sample shape on the depinning of the domain wall (DW) driven by an applied magnetic field or a spin-polarized current is studied theoretically. The shape effect resulting from the modulation of the sample width (geometric pinning) can essentially affect the DW depinning. We found a good agreement between the ratios of the critical values of the magnetic field and the spin-polarized current predicted by the theory and measured in the experiment.Comment: 9 pages, 5 figure

The impacts of future climate change and sulphur emission reductions on acidification recovery at Plastic Lake, Ontario

International audienceClimate-induced drought events have a significant influence on sulphate export from forested catchments in central Ontario, subsequently delaying the recovery of surface waters from acidification. In the current study, a model chain that employed a statistical downscaling model, a hydrological model and two hydrochemical models was used to forecast the chemical recovery of Plastic Lake sub-catchment 1 (PC1) from acidification under proposed deposition reductions and the A2 emission scenario of the Intergovernmental Panel on Climate Change. Any predicted recovery in stream acid neutralising capacity and pH owing to deposition reductions were clearly offset by large acid effluxes from climate-induced drought events. By 2100, ANC is predicted to show large variations ranging between 10 and ?30 ?molc L?1. Similarly, predicted pH in 2100 is lower (>0.05 of a pH unit) than the value simulated for 2000 (pH 4.35). Despite emission reductions, the future scenario paints a bleak picture of reacidification at PC1 to levels commensurate with those of the late 1970s. The principal process behind this reacidification is the oxidation of previously stored (reduced) sulphur compounds in wetlands during periods of low-flow (or drought), with subsequent efflux of sulphate upon re-wetting. Simulated catchment runoff under the A2 emissions scenario predictes increased intensity and frequency of low-flow events from approximately 2030 onwards. The Integrated Catchments model for Carbon indicated that stream DOC concentrations at PC1 will also increase under the future climate scenario, with temperature being the principal driver. Despite the predicted (significant) increase in DOC, pH is not predicted to further decline (beyond the climate-induced oxidation scenario), instead pH shows greater variability throughout the simulation. As echoed by many recent studies, hydrochemical models and model frameworks need to incorporate the drivers and mechanisms (at appropriate time-scales) that affect the key biogeochemical processes to reliably predict the impacts of climate change