Linking teaching and research in undergraduate physical geography papers: The role of fieldwork     

Ian Fuller  Martin Brook  Kat Holt 《New Zealand geographer》2010,66(3):196-202

Undergraduate teaching should be informed by research. The extent to which this is the case and how this is best practised is the subject of this paper. Learning strategies that seek to embed research within the undergraduate programme from an introductory level are discussed. The degree of success in these strategies is informed by input from postgraduate students who have ‘come through the ranks’. Their views, obtained via a focus group, suggest that research is rigorously embedded at every level of the programme and is most clearly linked to teaching in research-based third-year papers with a strong fieldwork component.  相似文献   

Using data assimilation method to calibrate a heterogeneous conductivity field and improve solute transport prediction with an unknown contamination source   总被引：1，自引：1，他引：0  

Chunlin Huang  Bill X. Hu  Xin Li  Ming Ye 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(8):1155-1167

Hydraulic conductivity distribution and plume initial source condition are two important factors affecting solute transport in heterogeneous media. Since hydraulic conductivity can only be measured at limited locations in a field, its spatial distribution in a complex heterogeneous medium is generally uncertain. In many groundwater contamination sites, transport initial conditions are generally unknown, as plume distributions are available only after the contaminations occurred. In this study, a data assimilation method is developed for calibrating a hydraulic conductivity field and improving solute transport prediction with unknown initial solute source condition. Ensemble Kalman filter (EnKF) is used to update the model parameter (i.e., hydraulic conductivity) and state variables (hydraulic head and solute concentration), when data are available. Two-dimensional numerical experiments are designed to assess the performance of the EnKF method on data assimilation for solute transport prediction. The study results indicate that the EnKF method can significantly improve the estimation of the hydraulic conductivity distribution and solute transport prediction by assimilating hydraulic head measurements with a known solute initial condition. When solute source is unknown, solute prediction by assimilating continuous measurements of solute concentration at a few points in the plume well captures the plume evolution downstream of the measurement points.  相似文献   

The European Upper Mantle as Seen by Surface Waves     

Lapo Boschi  Bill Fry  Göran Ekström  Domenico Giardini 《Surveys in Geophysics》2009,30(4-5):463-501

We derive a global, three-dimensional tomographic model of horizontally and vertically polarized shear velocities in the upper mantle. The model is based on a recently updated global database of Love- and Rayleigh-wave fundamental-mode phase-anomaly observations, with a good global coverage and a particularly dense coverage over Europe and the Mediterranean basin (broadband stations from the Swiss and German seismic networks). The model parameterization is accordingly finer within this region than over the rest of the globe. The large-scale, global structure of our model is very well correlated with that of earlier shear-velocity tomography models, based both on body- and surface-wave observations. At the regional scale, within the region of interest, correlation is complicated by the different resolution limits associated to different databases (surface waves, compressional waves, shear waves), and, accordingly, to different models; while a certain agreement appears to exist for what concerns the grand tectonic features in the area, heterogeneities of smaller scale are less robustly determined. Our new model is only one step towards the identification of a consensus model of European/Mediterranean upper-mantle structure: on the basis of the findings discussed here, we expect that important improvements will soon result from the combination, in new tomographic inversions, of fundamental-mode phase-anomaly data like ours with observations of surface-wave overtones, of body-wave travel times, of ambient “noise”, and by accounting for an a-priori model of crustal structure more highly resolved than the one employed here.  相似文献   

Modelling the tidal mixing fronts and seasonal stratification of the Northwest European Continental shelf     

Jason Holt  Lars Umlauf 《Continental Shelf Research》2008

We investigate mixing processes under stratified conditions on the Northwest European Continental shelf using a numerical model (POLCOMS). Our results indicate that convection induced by vertical shearing of horizontal density gradients (‘shear-induced convection’) is a regularly occurring feature in the bottom and surface boundary layers in this open shelf-sea situation. Two types of turbulence models are investigated to study their capability for reproducing the observed location of tidal mixing fronts, and the physical processes occurring in seasonally stratified waters. The first model is a one-equation variant of the Mellor–Yamada model, whereas the second model combines a more recent second-momentum closure with a two-equation model. It is found that generally mean frontal positions (as estimated from ICES data) are predicted more accurately by the two-equation model. The one-equation model reproduces the mean frontal locations to 18.1 km (<3 grid spacings) and the two-equation model to 17.1 km; although in the Celtic Sea the accuracy is ∼33 and ∼12 km, respectively. Comparison with historical tide gauges, current metres, CTD stations, and thermistor chain data from the North Sea Project all show an improvement in accuracy when the two-equation model is used. This is particularly apparent in the model's ability to reproduce the spring–neap variability during stratification. We find that in the presence of shear-induced convection the routinely applied clipping of the turbulent length-scale, previously thought to be a minor ingredient in a turbulence model, has a dramatic effect on the results: if the length-scale clipping is not applied, substantial over-mixing is observed to occur. The causes and possible remedies of this effect are investigated. Overall our results demonstrate a sensitivity to the details of the turbulence model that is significantly greater than previously thought.  相似文献   

Diverse young stellar populations in the intermediate-redshift radio galaxies 3C 213.1 and 3C 459: implications for the evolution of the host galaxies     

K. A. Wills  C. Tadhunter  J. Holt  R. González Delgado  K. J. Inskip  J. Rodríguez Zaurín  R. Morganti 《Monthly notices of the Royal Astronomical Society》2008,385(1):136-146

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A sample of radio-loud QSOs at redshift ∼ 4     

J. Holt  C. R. Benn  M. Vigotti  M. Pedani  R. Carballo  J. I. González-Serrano  K.-H. Mack  B. García 《Monthly notices of the Royal Astronomical Society》2004,348(3):857-865

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Effects of Local Dispersion and Kinetic Sorption on Evolution of Concentration Variance in a Heterogeneous Aquifer     

Bill X. Hu  Changming He 《Mathematical Geology》2006,38(3):327-342

A Eulerian stochastic method is applied to develop a theory of concentration variance for solute transport in a heterogeneous medium. The study focuses on the effects of kinetic sorption and local dispersion on solute dissipation. Spatial distribution of the concentration variance is obtained by scaling the zero local dispersion form of σ_c ². The scaling function resulting from the local dispersion and kinetic sorption is derived in a closed integral form. It satisfies the measurement of total concentration variance resulting from the Eulerian mass balance using spatially integrated concentration moments. The spatially integrated moments bypass the need for classical closures applied to joint moments between concentration and velocity fields. The study results indicate that kinetic sorption reduces the total development of concentration variance in comparison with non-reactive solute transport. Kinetic sorption acts as a reduction mechanism, but not as a dissipating mechanism like the local dispersion. Kinetic sorption and local dispersion are not additive processes and their effects on the concentration variance depend on the stage of transport time.  相似文献   

Community structure of macrozooplankton in Trinity and Upper Galveston Bays     

Joan Holt  Kirk Strawn 《Estuaries and Coasts》1983,6(1):66-75

Macrozooplankton were sampled bi-weekly from October 1969 through May 1973 at 16 stations. Hydrological measurements, including water temperature and conductivity, accompanied each biological sample. Sampling sites and species were grouped by cluster analysis using Camberra-Metric measure of dissimilarity and flexible sorting. Two major seasons, based on taxon composition and abundance, were identified: A warm season (average water temperature above 22°C) dominated by larval and juvenile crustaceans, and a cool season with an abundance of larval fishes. Sites were more similar to each other within a year than they were between years. Differences between years correlated with variations in salinity and temperature. Community structure indices (Shannon-Weaver diversity, species richness and “evenness”) were applied to the seasonal data. Shannon diversity and “evenness” were positively correlated with each other, but richness values were often negatively correlated with the other two indices.  相似文献   

Stochastic study of solute transport in a nonstationary medium     

Hu BX 《Ground water》2006,44(2):222-233

A Lagrangian stochastic approach is applied to develop a method of moment for solute transport in a physically and chemically nonstationary medium. Stochastic governing equations for mean solute flux and solute covariance are analytically obtained in the first-order accuracy of log conductivity and/or chemical sorption variances and solved numerically using the finite-difference method. The developed method, the numerical method of moments (NMM), is used to predict radionuclide solute transport processes in the saturated zone below the Yucca Mountain project area. The mean, variance, and upper bound of the radionuclide mass flux through a control plane 5 km downstream of the footprint of the repository are calculated. According to their chemical sorption capacities, the various radionuclear chemicals are grouped as nonreactive, weakly sorbing, and strongly sorbing chemicals. The NMM method is used to study their transport processes and influence factors. To verify the method of moments, a Monte Carlo simulation is conducted for nonreactive chemical transport. Results indicate the results from the two methods are consistent, but the NMM method is computationally more efficient than the Monte Carlo method. This study adds to the ongoing debate in the literature on the effect of heterogeneity on solute transport prediction, especially on prediction uncertainty, by showing that the standard derivation of solute flux is larger than the mean solute flux even when the hydraulic conductivity within each geological layer is mild. This study provides a method that may become an efficient calculation tool for many environmental projects.  相似文献