Bed morphology, flow structure, and sediment transport at the outlet of Lake Huron and in the upper St. Clair River

An integrated multibeam echo sounder and acoustic Doppler current profiler field survey was conducted in July 2008 to investigate the morphodynamics of the St. Clair River at the outlet of Lake Huron. The principal morphological features of the upper St. Clair River included flow-transverse bedforms that appear weakly mobile, erosive bedforms in cohesive muds, thin non-cohesive veneers of weakly mobile sediment that cover an underlying cohesive (till or glacio-lacustrine) surface, and vegetation that covers the bed. The flow was characterized by acceleration as the banks constrict from Lake Huron into the St. Clair River, an approximately 1500-m long region of flow separation downstream from the Blue Water Bridge, and secondary flow connected to: i) channel curvature; ii) forcing of the flow by local bed topography, and iii) flow wakes in the lee side of ship wrecks. Nearshore, sand-sized, sediment from Lake Huron was capable of being transported into, and principally along, the banks of the upper St. Clair River by the measured flow. A comparison of bathymetric surveys conducted in 2007 and 2008 identifies that the gravel bed does undergo slow downstream movement, but that this movement does not appear to be generated by the mean flow, and could possibly be caused by ship-propeller-induced turbulence. The study results suggest that the measured mean flow and dredging within the channel have not produced major scour of the upper St. Clair River and that the recent fall in the level of Lake Huron is unlikely to have been caused by these mechanisms.     

CREATING AND EVALUATING DIGITAL ELEVATION MODEL‐BASED STREAM‐POWER MAP AS A STREAM ASSESSMENT TOOL

As urban development increases, a need is emerging to understand and predict river behaviour in order to focus rehabilitation efforts and protect the natural river system while preserving urban infrastructure. Stream assessment methods are reviewed to demonstrate the need for a physically based and objective method that is also accessible in terms of time, data requirements and expertise. The case of Highland Creek near Toronto, Canada, is used to demonstrate a new type of initial stream assessment method that is based on the concept of stream power and performed entirely in a geographic information system using information from a digital elevation model (DEM). The results from this analysis are tested against existing information for Highland Creek. This includes a hydraulic model (Hydraulic Engineering Center's ‘River Analysis System’), field‐measured slopes, air photos and the geomorphic effects of an extreme flood. In addition, the results are presented in map form to demonstrate the effectiveness of visualizing the stream‐power distribution over the entire basin and also the usefulness of overlaying stream power onto other available information. The slopes extracted from the DEM are found to be statistically similar to those from a one‐dimensional hydraulic model and field‐measured slopes. Individual peaks in slope as well as locations of stream‐power maxima and minima are found to correlate to actual channel features as seen in air photos. The extreme flood event of August 2005 caused a dramatic change in channel form at the exact location of maximum energy predicted by the DEM‐based stream‐power analysis. The case of Highland Creek illustrates how this approach yields a useful outcome for understanding stream dynamics and stability as part of a stream assessment process. Copyright © 2011 John Wiley & Sons, Ltd.     

Reproducibility of MRI-based white matter tract estimation using multi-fiber probabilistic tractography: effect of user-defined parameters and regions

Objective

There is a pressing need to assess user-dependent reproducibility of multi-fibre probabilistic tractography in order to encourage clinical implementation of these advanced and relevant approaches. The goal of this study was to evaluate both intrinsic and inter-user reproducibility of corticospinal tract estimation.

Materials and methods

Six clinical datasets including motor functional and diffusion MRI were used. Three users performed an independent tractography analysis following identical instructions. Dice indices were calculated to quantify the reproducibility of seed region, fMRI-based end region, and streamline maps.

Results

The inter-user reproducibility ranged 41–93%, 29–94%, and 50–92%, for seed regions, end regions, and streamline maps, respectively. Differences in streamline maps correlated with differences in seed and end regions. Good inter-user agreement in seed and end regions, yielded inter-user reproducibility close to the intrinsic reproducibility (92–97%) and in most cases higher than 80%.

Discussion

Uncertainties related to user-dependent decisions and the probabilistic nature of the analysis should be considered when interpreting probabilistic tractography data. The standardization of the methods used to define seed and end regions is a necessary step to improve the accuracy and robustness of multi-fiber probabilistic tractography in a clinical setting. Clinical users should choose a feasible compromise between reproducibility and analysis duration.

     

Mechanosensation: swimming round in circles

Studies of inherited deafness disorders in mice and humans are providing new insights into the basis of hair-cell mechanosensitivity; this enterprise has been joined by large-scale genetic screening in the zebrafish, where a number of intriguing mutants defective in mechanosensation have recently been described.     

Selective heterogeneous hydrocarbon oxidation over oxide catalysts

The heterogeneously-catalysed oxidation of hydrocarbons over oxide catalysts is reviewed. The first section of the paper deals in a general way with the structural features of hydrocarbons and relates these to the selective oxidation products which may be obtained from them. The interaction of oxygen and hydrocarbons with oxides is also considered in a general context and the kinetics of heterogeneous oxidation of hydrocarbons are discussed. The second section of the paper deals in more detail with the selective oxidation of aromatic hydrocarbons with particular reference to vanadium oxide containing catalysts. Finally, an account is given of the selective oxidation of monoalkenes to 1,3 conjugated systems and ketones over mixed oxide catalysts. The information available is considered throughout with a view to revealing those features of such systems which give rise to the selectivity.     

Electrical and structural characteristics of non-stoichiometric Cu-based delafossites

Non-stoichiometric Cu^xGaO² polycrystalline ceramics were prepared using solid-state synthesis methods and their structural and electrical properties were characterized as a function of x. While single phase delafossite could only be confirmed for the stoichiometric composition, X-ray diffraction results show that the a and c lattice parameters were stable from Cu^0.98GaO² to Cu^1.02GaO². Below x = 0.97, the structure underwent a 0.4% decrease in cell volume. For compositions rich in Cu, the a parameter remained constant while the c parameter shrank at a constant rate. Despite these changes in cell dimensions, the results of current-voltage and impedance spectroscopy measurements indicate that both the conductivity and the activation energy do not vary with x. The absence of a change in electrical properties as well as the formation of secondary phases in non-stoichiometric compositions suggests that CuGaO² does not allow significant deviations from the ideal CuGaO² stoichiometry. This implies that the p-type conductivity is fixed by a defect species that does not vary with the Cu stoichiometry.     

The Need for Greater Transparency When Assessing the Performance and Prospects of Melbourne’s Rail Franchise Contracts

Among policymakers and researchers at an international level, there is great interest in the performance of the Melbourne rail franchise model. This review attempts to examine the Melbourne model in an international context and assess the performance of the system under current contracts. Potential flaws are highlighted including lack of information, concerns over performance and contestability, and the treatment of the potential long-term maintenance backlog under short-term contracts. The authors conclude with an overall stance of there needing to be far greater public information transparency to allow proper scrutiny of the effectiveness of these contracts for the public good.