Stability of Agricultural Ecosystems: Application of a Simple Model for Soil Erosion Assessment

The stability of the erosion system in a tropical rain forest environment is investigated using the model previously described by Morgan, Morgan and Finney (1982) and validated by Morgan and Finney (1982). Simulations are carried out for the natural primary forest cover, commercial timber extraction and the agricultural ecosystems of rubber cultivation, shifting cultivation with sixteen-year, fourteen-year and four-year cycles, and continuous rotational cropping of groundnuts, maize and potatoes. The model is operated for five slope steepnesses using a hundred-year synthetic sequence of rainfall data generated by Monte Carlo analysis. Erosional stability is expressed in terms of changes in rooting or top soil depth. Using the model it is possible to distinguish between three broad states of biostasy, rhexistasy and homeostasy, representing increasing, decreasing and stable rooting depths respectively. Detailed examination of the magnitudes of the change in rooting depth in response to perturbations in the system and the length of time required for recovery can show the extent to which systems in a state of or close to homeostasy are potentially unstable

Stability of Agricultural Ecosystems: Documentation of a Simple Model for Soil Erosion Assessment

Documentation is presented of a model for assessing the stability of the soil erosion component of an agricultural ecosystem. The model uses a simplified version of the Meyer-Wischmeier approach to predict the annual rate of soil erosion by water on hillslopes and this is compared with the rates of weathering and top soil renewal to determine changes in the depth of the soil profile and the top soil or rooting layer. Erosion is taken to be the result of splash detachment and runoff transport. Splash detachment is related to rainfall energy and rainfall interception by the crop. Runoff volume and sediment transport capacity are estimated from equations first presented by Kirkby. The results of trials with the model in the Silsoe area of Bedfordshire, England, show that realistic values of runoff and erosion are obtained for a range of soil and crop conditions. The model can be used to assess the stability of the erosion system under existing landuse conditions and to determine what changes need to be made in the erosion system to produce stability when unstable conditions are predicted

Unusual Weather and River Bank Erosion in the Delta of the Colville River, Alaska

Reports correlation between weather conditions and erosion observed in this arctic coastal area in 1961. The summer's unusually high temperatures and precipitation, also strong and frequent west winds caused greater-than-normal flooding and collapse of river banks

B2.5-Eunomia simulations of Magnum-PSI detachment experiments: I. Quantitative comparisons with experimental measurements

Detachment experiments have been carried out in the linear plasma device Magnum-PSI by increasing the gas pressure near the target. In order to have a proper detailed analysis of the mechanism behind momentum and power loss in detachment, a quantitative match is pursued between B2.5-Eunomia solutions and experimental data. B2.5 is a multi fluid plasma code and Eunomia is a Monte Carlo solver for neutral particles, and they are coupled together to provide steady-state solution of the plasma and neutral distribution in space. B2.5-Eunomia input parameters are adjusted to produce a close replication of the plasma beam measured in the experiments without any gas puffing in the target chamber. Using this replication as an initial condition, the neutral pressure near the plasma beam target is exclusively increased during simulation, matching the pressures measured in the experiments. Reasonable agreement is found between the electron temperature of the simulation results with experimental measurements using laser Thomson scattering near the target. The simulations also reveal the effect of increased gas pressure on the plasma current, effectively reducing the current penetration from the plasma source. B2.5-Eunomia is capable of reproducing detachment characteristics, namely the loss of plasma pressure along the magnetic field and the reduction of particle and heat flux to the target. The simulation results for plasma and neutrals will allow future studies of the exact contribution of individual plasma-neutral collisions to momentum and energy loss in detachment in Magnum-PSI.</p

Stability of Agricultural Ecosystems: Validation of a Simple Model for Soil Erosion Assessment

Validation trials of the model described by Morgan, Morgan and Finney (1982) for assessing the stability of the soil erosion component of an agricultural ecosystem were carried out using data from published studies of soil loss for 67 sites in 12 countries. Correlation coefficients of 0.74 and 0.58 were obtained between predicted and observed values of runoff at 56 sites and soil loss at 67 sites respectively. If two poor predictions of very high erosion rates in China are omitted, the value of the correlation coefficient for soil loss rises to 0.67 and the slope of the reduced major axis regression line is not significantly different from unity. The success of the model was also evaluated against the criteria that it should predict whether or not there was likely to be an erosion problem and if there was, that it should predict the magnitude of the problem. Against these criteria, the model was successful on 59 per cent of the tests for runoff and 70 percent of the tests for soil loss. Considering only those sites for which high quality input data were available, the success rate for soil loss rose to 90 per cent. Guidelines are presented for the selection of parameter values for rainfall intensity, weathering rates, soil renewal rates and rooting depth

Do stronger school smoking policies make a difference? Analysis of the health behaviour in school-aged children survey

Background: Associations of the strength of school smoking policies with cigarette, e-cigarette and cannabis use in Wales were examined. Methods: Nationally representative cross-sectional survey of pupils aged 11–16 years (N=7376) in Wales. Senior management team members from 67 schools completed questionnaires about school smoking policies, substance use education and tobacco cessation initiatives. Multi-level, logistic regression analyses investigated self-reported cigarette, e-cigarette and cannabis use, for all students and those aged 15–16 years. Results: Prevalence of current smoking, e-cigarette use and cannabis use in the past month were 5.3%, 11.5% and 2.9%, respectively. Of schools that provided details about smoking policies (66/67), 39.4% were strong (written policy applied to everyone in all locations), 43.9% were moderate (written policy not applied to everyone in all locations) and 16.7% had no written policy. There was no evidence of an association of school smoking policies with pupils’ tobacco or e-cigarette use. However, students from schools with a moderate policy [OR = 0.47; 95% (confidence interval) CI: 0.26–0.84] were less likely to have used cannabis in the past month compared to schools with no written policy. This trend was stronger for students aged 15–16 years (moderate policy: OR = 0.42; 95% CI: 0.22–0.80; strong policy: OR = 0.45; 95% CI: 0.23–0.87). Conclusions: School smoking policies may exert less influence on young people’s smoking behaviours than they did during times of higher adolescent smoking prevalence. Longitudinal studies are needed to examine the potential influence of school smoking policies on cannabis use and mechanisms explaining this associatio

Damping signatures in future neutrino oscillation experiments

We discuss the phenomenology of damping signatures in the neutrino oscillation probabilities, where either the oscillating terms or the probabilities can be damped. This approach is a possibility for tests of non-oscillation effects in future neutrino oscillation experiments, where we mainly focus on reactor and long-baseline experiments. We extensively motivate different damping signatures due to small corrections by neutrino decoherence, neutrino decay, oscillations into sterile neutrinos, or other mechanisms, and classify these signatures according to their energy (spectral) dependencies. We demonstrate, at the example of short baseline reactor experiments, that damping can severely alter the interpretation of results, e.g., it could fake a value of $\sin(2\theta_{13})$ smaller than the one provided by Nature. In addition, we demonstrate how a neutrino factory could constrain different damping models with emphasis on how these different models could be distinguished, i.e., how easily the actual non-oscillation effects could be identified. We find that the damping models cluster in different categories, which can be much better distinguished from each other than models within the same cluster.Comment: 33 pages, 5 figures, LaTeX. Final version published in JHE

Strength Reduction in Electrical and Elastic Networks

Particular aspects of problems ranging from dielectric breakdown to metal insu- lator transition can be studied using electrical o elastic networks. We present an expression for the mean breakdown strength of such networks.First, we intro- duce a method to evaluate the redistribution of current due to the removal of a finite number of elements from a hyper-cubic network of conducatances.It is used to determine the reduction of breakdown strength due to a fracture of size $\kappa$.Numerical analysis is used to show that the analogous reduction due to random removal of elements from electrical and elastic networks follow a similar form.One possible application, namely the use of bone density as a diagnostic tools for osteorosporosis,is discussed.Comment: one compressed file includes: 9 PostScrpt figures and a text fil

Absence of lattice strain anomalies at the electronic topological transition in zinc at high pressure

High pressure structural distortions of the hexagonal close packed (hcp) element zinc have been a subject of controversy. Earlier experimental results and theory showed a large anomaly in lattice strain with compression in zinc at about 10 GPa which was explained theoretically by a change in Fermi surface topology. Later hydrostatic experiments showed no such anomaly, resulting in a discrepancy between theory and experiment. We have computed the compression and lattice strain of hcp zinc over a wide range of compressions using the linearized augmented plane wave (LAPW) method paying special attention to k-point convergence. We find that the behavior of the lattice strain is strongly dependent on k-point sampling, and with large k-point sets the previously computed anomaly in lattice parameters under compression disappears, in agreement with recent experiments.Comment: 9 pages, 6 figures, Phys. Rev. B (in press