The objective of this study was to determine whether the composite bond strength acquired using a single step self-etching bonding system is as or more effective when compared to the two step etch-rinse-bond system at clinically relevant in-vitro standards. A total of 80 extracted human deciduous with at least one intact smooth surface were collected with parental consent. Collected teeth were randomly assigned to one of four treatment protocols (n=20): single step self-etch (Adper Prompt L-Pop, 3M ESPE), two step etch (15s)-rinse-bond (Optibond Solo Plus, Kerr), single step self etch (Adper L Pop, 3M ESPE) with 30s pre-etch, and two step etch (30s)-rinse-bond (Optibond Solo Plus, Kerr). A composite cylinder of uniform shape was bonded to each tooth using the designated adhesive system and specimens were tested with a universal testing machine. Descriptive statistics and statistical analysis was performed. Median shear bond strengths for all specimens, regardless of treatment group, ranged from 3.25 MPa to 43.13 MPa. These values are above suggested minimum clinical required values of 3MPa. A Kruskal-Wallis analysis between treatment groups found statistical significance (p<0.05) for shear bond strength between the groups and both one step system protocols, had higher mean and median shear bond strength values than the two step systems. An adhesive remnant index (ARI) was analyzed to confirm uniform adhesive fracture between all four treatment groups. Both a Fisher’s exact test, and a Hantel-Haenszel statistic found no significant difference (p<0.05) between the samples. Based on these findings we concluded that: 1. The ARI score for all treatment groups was not statistically significant, suggesting that the type of bond breakage was consistent regardless of adhesive system used. 2. Both Optibond Solo Plus and Adper Prompt L-Pop systems achieve adequate shear bond strengths as described by current literature. 3. The use of a one-step system to save chair time and aid in patient behavior management may be clinically useful.

To date, most shear velocity heterogeneity models in the lower mantle have been derived using long period data. Comparatively little use has been made of the vast ISC database of shear wave arrival times, which covers the years 1964 to 1991. The aim of this study is to use this database to construct global models of shear wave heterogeneity in the lower mantle and compare it with existing P models using similar period data in order to evaluate the hypothesis that P and S heterogeneity are proportional. In order to reproduce the resolution operator inherent in these existing models, the same parameterization has been employed; lateral dependence is in terms of spherical harmonics up to degree and order 6, and radial dependence in terms of a quartic polynomial. The inversion uses data from over 4500 events selected according to criteria which minimize the bias introduced by uneven source receiver coverage. Despite having approximately one sixth of the amount of data the model correlates well with a P wave model computed using data from the same events, and this in turn is almost identical to models computed by other authors using similar inversion methods. Assuming proportionality of P and S heterogeneity, a joint inversion of the P and S data has been performed. The resultant model correlates extremely well with the P model of this study, and similar variance reductions are obtained for both the P and S datasets as were found in the original inversions. Several model parameterizations have been used to try to investigate the dependence of the model expansion on the results. Consequently, taking into account results from synthetic experiments and from experiments into trade-offs with other inversion parameters, the average ratio of relative S to P heterogeneity ^{d ln v_s}andfrasl;_{d ln v_p} throughout the lower mantle is constrained to be in the interval (1.8,2.1) with emphasis on higher values within these bounds. This value is in agreement with other studies using similar period data, and the upper bound is close to the optimum value of 2.27 obtained by Li et al., 1991 from normal mode data, suggesting that the ratio is at least only weakly dependent on frequency. In addition evidence is presented that the ratio is increasing with depth although attempts to extract specific gradients have failed because of the very poor distribution of S rays in the deepest mantle.

No description available.

The goal of the present work is a detailed and comprehensive study to assess the accuracy of the numerical simulation of the mixing processes in a lobed mixer flow field via a Reynolds-averaged solution method. To meet this goal, the first objective of the current work was to establish the suitability of various meshing strategies that would allow the complex mixer geometries found in current gas-turbine engine designs to be captured, together with the associated convoluted shear layers. A second objective was targeted at providing further insight and understanding of the capability of eddy-viscosity-based turbulence models in capturing the convoluted shear layers. Simplified mixer configurations selected from the literature were studied under incompressible isothermal flow conditions. Two solution algorithms were employed to model the mixer flow fields. The first consisted of a pressure-based structured grid methodology developed for incompressible flows. A density-based mixed-unstructured grid algorithm for compressible flows was also used, with extensions to low Mach number flows made possible through a low Mach number preconditioner. The effects of turbulence were modelled using ak-e turbulence model. The absence of this model in the code made available for the unstructured algorithm necessitated its implementation as a first step in the current work. The effects of unstructured mesh type on the prediction of flows with internal mixing layers were first assessed for an incompressible planar mixing layer. This simplified case was used as a benchmark case to help understand the effects on the convoluted shear layers arising within the lobed mixer flows. To quantify the capability of a Reynolds-averaged approach in simulating the turbulent mixer flow field, two variants of the two equation k-e model were employed. The first constituted the standard linear high Reynolds number k-e model of Launder and Spalding [62]. The second model was a quadratic non-linear version developed by Speziale [99] for the prediction of secondary flows in non-circular ducts. The relative merits of these two models was assessed through detailed comparisons with experimental data taken from the literature. Of particular importance in the mixer flow was the formation and subsequent evolution of the vorticity field. Consequently, this motivated a detailed study of the evolving vorticity field. The investigations thus far were based on a simplified mixer configuration with no temperature differences between the two streams. Therefore, as a final step, a realistic scarfed mixer was modelled in an attempt to model the temperature mixing. The main contribution of the present work is the assessment of a grid-based Reynolds-averaged solution procedure for the prediction of lobed mixer flows. The study revealed that capturing the initial mixing region proved to be most difficult. Firstly, unstruc-tured meshes employing non-hexahedral elements were very inefficient at simulating the mixing layer in the early stages. Secondly, the initial mixing region presented significant difficulties for the Reynolds-averaged solution method in which neither turbulence model was capable of correctly reproducing the turbulence field. Despite this, global parameters such as momentum thickness and streamwise circulation were well captured in the predictions.

Temperature changes occur in soils in a number of ways, e. g. landfill liners, around buried services and during sampling. An experimental programme was conducted to examine the effect of temperature (between 10 to 80 °C) on the volume change and shear behaviour of saturated clays. Testing included Liquid Limit (cone penetrometer), residual shear strength (modified Bromhead Ring Shear), laboratory vane shear ( at moisture contents between the Liquid and Plastic Limits) and oedometer tests. An extensive literature survey indicated that kaolinites and smectites would show extremes of thermal behaviour. To examine this two artificially pure clays were tested: English China Clay (a well crystallised kaolinite) and Wyoming Bentonite (a monovalent smectite). To supplement this four British soils were tested: Keuper Marl, Lower Lias Clay, London Clay and Oxford Clay. Full material data were obtained coupled with careful control of stress and thermal histories. It is concluded that two types of extreme thermal response exists: a thermomechanical and a thermo-physicochemical change exhibited by kaolinite and smectite respectively. The temperature sensitivity of clays relative to a particular parameter is positively related to its specific surface area. A quick and repeatable method to qualitatively assess this has been developed: the LUT method. Its advantages include that no temperature calibrations are needed and it has a relatively large operating temperature range, 10 to 80 °C having been successfully used. The consolidation pressure (in the oedometer) needed to change the nature of a soil's thermal response is negatively related to its specific surface area. This, it is postulated, occurs at the same 'critical' contact stress for all clays, i. e. the interparticle threshold stress at which a thermo-physicochemical response changes to a thermo-mechanical one. This threshold stress occurs at a anisotropic consolidation pressure of 60 kPa for a well crystallised kaolinite , at 250 kPa for reconstituted London Clay and at 480 kPa for a mono-valent smectite. Furthermore, greater parallel particle alignment or reconstituting a sample enhances a soil's temperature sensitivity in the oedometer. The thermal changes to consolidation and permeability coefficients can be typically predicted by the corresponding change to the dynamic viscosity of water. Deviations occur with smectites at normal stresses greater than 480 kPa, while for Keuper Marl this occurred at normal stresses of 50 kPa and greater than 850 kPa. Keuper Marl exhibits a greater temperature sensitivity of different parameters than predicted by index tests. This is strongly dependent on consolidation pressure and temperature. At elevated temperatures (>40 °C) and under increasing consolidation pressure, ped units tend to collapse, but once the pressure is removed ped reformation occurs. Thus knowledge of thermal and stress histories, coupled with full material data, is essential to effectively predict temperature effects on the engineering behaviour of soils with any degree of confidence.

Experimental and analytical research has been conducted to investigate the degradation of shear performance of beams due to bond deterioration and longitudinal bar cutoffs. To achieve the controlled rate of bond degradation, the method of adjustment of the rib height by machining was adopted. Bond behaviour of the milled bars were measured in tension stiffening tests with internally installed strain gauges. Maximum bond stresses for the milled bars were reduced by up to 50% compared to those for normal deformed bar. The bond behaviour of the milled bars were compared with those of the bars subjected to accelerated corrosion. It was confirmed that the stripped bar had the possibility to simulate corroded bars to some extent. Based on the calculations of average tensile stresses in the cracked concrete for each specimen, appropriate tension stiffening factors for each type of bar were suggested and then verified with the 2-dimensional nonlinear finite element analysis program VecTor2. Next, eight simply supported beams were tested. In four of them half of the longitudinal bars were cut off near the supports. Various combinations of normal and machined reinforcing bars were selected for both longitudinal and transverse reinforcement. The predicted shear failure load for the cutoff beam based on the general method for shear design in CSA A23.3-04 was unconservatively estimated. Cutoffs of longitudinal reinforcement resulted in much more significant drops of shear resistance than did bond deterioration of reinforcement. The inclinations of diagonal cracks for the cutoff series were larger than those for the no-cutoff series due to significant concentrations of longitudinal strains near the cutoff locations. Finally modifications to the general shear design method in CSA A23.3-04 were proposed based on the results of VecTor2 analyses for the beam tests. It was found that the influence of bond deterioration on the shear strength of reinforced concrete member can be accounted for by adjusting the tension stiffening factor applied to the equation for β. With respect to bar cutoffs, its influence on shear strength can be expressed by the strain concentration factor applied to the equation for ε_x.

Experimental and analytical research has been conducted to investigate the degradation of shear performance of beams due to bond deterioration and longitudinal bar cutoffs. To achieve the controlled rate of bond degradation, the method of adjustment of the rib height by machining was adopted. Bond behaviour of the milled bars were measured in tension stiffening tests with internally installed strain gauges. Maximum bond stresses for the milled bars were reduced by up to 50% compared to those for normal deformed bar. The bond behaviour of the milled bars were compared with those of the bars subjected to accelerated corrosion. It was confirmed that the stripped bar had the possibility to simulate corroded bars to some extent. Based on the calculations of average tensile stresses in the cracked concrete for each specimen, appropriate tension stiffening factors for each type of bar were suggested and then verified with the 2-dimensional nonlinear finite element analysis program VecTor2. Next, eight simply supported beams were tested. In four of them half of the longitudinal bars were cut off near the supports. Various combinations of normal and machined reinforcing bars were selected for both longitudinal and transverse reinforcement. The predicted shear failure load for the cutoff beam based on the general method for shear design in CSA A23.3-04 was unconservatively estimated. Cutoffs of longitudinal reinforcement resulted in much more significant drops of shear resistance than did bond deterioration of reinforcement. The inclinations of diagonal cracks for the cutoff series were larger than those for the no-cutoff series due to significant concentrations of longitudinal strains near the cutoff locations. Finally modifications to the general shear design method in CSA A23.3-04 were proposed based on the results of VecTor2 analyses for the beam tests. It was found that the influence of bond deterioration on the shear strength of reinforced concrete member can be accounted for by adjusting the tension stiffening factor applied to the equation for β. With respect to bar cutoffs, its influence on shear strength can be expressed by the strain concentration factor applied to the equation for ε_x.

No description available.

No description available.

The aim of this work was to use simulation as a tool to better understand areas of orthokinetic (shear-induced) aggregation which are still not well understood. These areas include aggregate structure, aggregate strength, breakup and restructuring and combined perikinetic/orthokinetic aggregation. Previous simulation studies were reviewed and it was concluded that the methodology of Chen and Doi (1989) was an appropriate starting point for this study. The modified simulation was validated by comparison with theoretical and experimental results. Orthokinetic aggregates were found to have a fractal structure with an estimated value of 1.65. Scaling exponents, which were shown to be indicative of fractal dimension, of 2.1-2.7 were also obtained. Flexible bonds allowed restructuring to occur which led to an increase in the co-ordination number, scaling exponent, aggregate strength and a reduction in aggregate size. Thus aggregate strength increases with fractal dimension. It was confirmed that both restructuring and breakup/reformation could lead to the formation of small, compact aggregates. The high shear conditions simulated favoured breakup/reformation, while restructuring was expected to dominate with more flexible bonds, possibly at lower shear rates. Taking some account of hydrodynamic interactions by the inclusion of Kirkwood-Riseman theory led to an increase in the compactness of the aggregates and the co-ordination numbers, as well as a decrease in size of the aggregates. The results showed that hydrodynamic interactions can not be ignored. The explanation for the dramatic effects was that particles/microflocs on the outer edges of the aggregates broke off and reformed in a more compact way. Erosion was found to dominate in all cases, thus supporting the theory that erosion dominates at higher fractal dimensions. The shearing range simulated was found to be relatively high (equivalent to &lt200s-1 for particles of 2-5??m), producing relatively small aggregates. Hence it is proposed that under high shear conditions, erosion dominates. It was shown by extension of the DLCA algorithmic restructuring work of Meakin and Jullien (1988, 1989) that the scattering patterns observed in gently sheared aggregating systems are consistent with the interpretation that the shearing causes partial restructuring at large length scales.