No description available.

No description available.

No description available.

No description available.

No description available.

Master of Science / Department of Physics / Jeremy D. Schmit / Antibodies are large Y-shaped proteins which are used by immune system to identify and neutralize pathogens. Monoclonal antibody therapy is used to treat different patient conditions. There are problems associated with the manufacturability and deliverability of mAb solutions due to the viscous nature of the protein. The viscosity of antibody solutions increases with the increase in concentration and decreases with applied shear. We want to know why these behaviours are seen and to address this problem we have developed a theory describing the rapid viscosity increase with increasing concentration. We use the polymer theory to explain this behaviour. Here antibodies are treated as polymers. The length of the polymer depend on the aggregation. The reptation time increases approximately as the cubic power of size of aggregate (N³ ). We see the shear thinning behaviour is dependent on the Ab-Ab binding energy and find the relationship between the size of the aggregate and the binding energy. We find aggregate size and morphology using several models for Ab-Ab interaction sites. We use the head to head binding (fAb-fAb binding) model to describe aggregation state in our viscosity theory. The size of the aggregate and hence the reptation time is captured by the binding energy. When the binding energy increases the zero shear viscosity increases and the reptation time decreases. Likewise when the binding energy decreases the zero shear viscosity decreases and the reptation time increases. We have yet to find the correct exponents for the shear thinning behaviour of different mAbs which would be our future work.

Objective: To compare the adhesive strength in dentin of three universal adhesive systems in vitro by means of the shear test. Materials and methods: Seventy-five bovine teeth were selected and cut. Dentin was exposed from the buccal surface of the crowns with 220 grit sandpaper, and samples were then inserted in transparent acrylic bases (15x10mm). The samples were randomly divided in 3 groups (n=25): G1-Universal adhesive system Scotchbond™ Universal (3M ESPE-USA); G2-Universal adhesive system Peak Universal Bond (Ultradent); G3-Universal adhesive system Tetric N-Bond (Ivoclar Vivadent). The adhesive procedures were carried out according to the instructions of each manufacturer and the restorative procedures were carried out with micro-cylinders (made of Tygon type tubing 0.79x1.5mm) of the composite resin Filtek™ Z350XT-A2 (3M ESPE-USA). The samples were incubated at 37ºC (+/-5ºC) for 24 hours. Adhesive strength was evaluated in a universal test machine by means of the shear test (0.5mm/ min, 500N) and the resulting fracture type was evaluated with a Dinolite digital microscope (x200). The results were analyzed by descriptive statistics (Mean±SD), and inferential statistics by a one-way ANOVA. Results: No statistically significant differences were found between the universal adhesive systems evaluated G1 (14.91±4.76), G2 (16.90±4.11) and G3 (17.34±4.04)/(p=0.114). Conclusions: The shear test resulted in similar values of immediate adhesive strength of the three universal adhesive systems used. / Revisión por pares

No description available.

The effective shear strength of artificially overconsolidated clays with continuous fissures, or with discontinuous or partial fissuring, has been discussed from both the experimental and numerical points of view.Direct shear and triaxial tests have been conducted on a range of unfissured, partially and fully fissured specimens of artificially overconsolidated clay samples in the laboratory. Specimens subjected to direct shear tests have been prepared in three different preconsolidation pressures and two or three different Overconsolidation ratios (OCR) for unfissured, partially and fully fissured specimens. Specimens subjected to triaxial tests also were prepared for three different preconsolidation pressures and overconsolidation ratios. In order to investigate the effect of orientation of fissures, artificially overconsolidated fissured triaxial specimens were prepared in three different orientations at 30 degrees, 45 degrees and 60 degrees to the direction of minimum principal stress (sigma[subscript]3).For both direct shear and triaxial tests, special tools and devices were designed and constructed to prepare unfissured, partially and fully fissured specimens.Taking into account the number of parameters which influence the effective shear strength of overconsolidated clays, and the time which is needed to artificially prepare the overconsolidated specimens and to run drained tests, as well as the impossibility or impracticality of the laboratory simulations for some specific cases, numerical methods were used to complement the experimental component of the investigation.Numerical modelling of direct shear and triaxial specimens utilised the FLAC (Fast Lagrangian Analysis of Continua, Itasca, 1993) program for two dimensional simulation of the direct shear tests and the ANSYS (1996) program for three dimensional simulation of triaxial tests. The experimental ++ / results have been used to calibrate the coefficients of the numerical models and to verify the results obtained from numerical models.Strain softening behaviour was simulated numerically for unfissured and fully fissured specimens subjected to direct shear tests. Using the obtained experimental and numerical results of the study of direct shear tests with respect to the effects of different parameters on the effective shear strength of the spacing subjected to direct shear tests and also FLAC programming, FLACish (FISH), a model was written designated as the Homogenised Strain Softening Model (HSSM). In this model the effects of different parameters discussed in this thesis, are applied to the Mohr Coulomb parameters (c'[subscript]u and phi'[subscript]u) of unfissured specimens. This model was used to predict the effective shear strength of cases in which laboratory simulation was impractical or not feasible.The advantage of this model (HSSM) is that it relates the effective shear strength of the fissured mass to the corresponding Coulomb parameters (c'[subscript]u and phi'[subscript]u) of the intact or unfissured overconsolidated clay specimen with reduction functions relating to the parameters discussed in this thesis.The numerical models developed by ANSYS were calibrated and verified by the experimental results, and then used to predict or estimate the effects of confining pressure, orientation of fissures on the three dimensional modelling of the partially and fully fissured overconsolidated triaxial specimens.In this thesis the effects of the type of clay, preconsolidation (P'[subscript]c) pressure, Overconsolidation ratio (OCR), size of sample, rate of shearing and fissure parameters, such as spacing, width and orientation of fissure were discussed and identified or quantified to estimate the effective shear strength of the artificially overconsolidated ++ / fissured samples. These results are applicable for the estimation of the effective shear strength of the naturally overconsolidated fissured mass by homogenising the effects of the parameters on the Mohr Coulomb parameters (c'[subscript]u and phi'[subscript]u) of the intact or unfissured clay mass.

An experimental investigation into the direct shear behaviour of steel fibre reinforced composites utilising discrete fibres at pre-defined angles and fibres randomly distributed is described. The direct shear tests encompassed the complete range of loading from its initial application to failure of the double L-shaped push-off specimens. Hooked-ended and straight steel fibres were used in the tests with the fibres oriented at angles of ??75??, ??60??, ??45??, ??30??, ??15?? and 0?? with respect to a plane normal to the loading direction. The embedment lengths of the fibres, related to the total fibre length lf , each side of the shear plane were 0.5lf :0.5lf and 0.25lf :0.75lf . In addition to the single fibre tests, tests were conducted on randomly oriented steel fibre reinforced composites with fibre volumes of 0.005, 0.010, 0.015, and 0.020 with hooked-ended and straight steel fibres. In addition to the tests outlined above, a series of non-destructive tests employing radiographic techniques was carried out to produce photographic images of events taking place of fibres pulling out from a cementitious element. The tests consisted of hooked-ended steel fibres oriented at angles of -60??, -30??, 0??, +30?? and +60?? to the cracking plane and straight fibres oriented at angles of -60??, 0?? and +60??. The non destructive technique allowed the internal behaviour occurring within the specimen along the shear plane to be investigated without impacting on the direct shear tests. The angle of the fibre to the interface plane is an important parameter in determining the behaviour of the fibres under load and for the mode of failure; viz fibre pullout or fibre fracture. The effect of the end hook on behavioural aspects becomes increasingly less significant for more acute fibre angles where bending and snubbing effects become increasingly influential on the load versus displacement behaviour and mode of failure. Contrary to expectations, the fibre embedment length had little influence over the peak loads attained for the discrete fibre tests and, in a number of specimens, fibres pulled out from the longer embedded side. This observation is contrary to the generally accepted assumption that a fibre remains rigidly embedded on the long side and pulls out from short side. The traditional role that uniform bond stresses along a fibre length and friction have played in the description of fibre behaviour is not as significant as previously reported, other effects such as snubbing are more important in anchoring a fibre. Various models need to be revised with this observation in mind. The experimental results and observations from the discrete hooked-ended and straight steel fibres investigation are incorporated in the development of a behavioural model, the Variable Engagement Model II (VEMII). The VEMII describes the behaviour of randomly oriented discontinuous steel fibre reinforced composites loaded in shear. The model is verified against a series of randomly distributed fibre reinforced mortar specimens carried out in this study. Two forms of models are analysed: 1) a model based on the observation of lumped shear stresses at the fibre hook and in the snubbing zone; and 2) a uniform fibre bond stress applied along the embedded part of the fibre. The lumped bond stress approach and the uniform approach were found to give reasonable comparisons with the test data for the hooked-ended fibres but were conservative for the straight fibres. The VEMII confirms the applicability of the uniform bond approach adopted by previous researchers even though it does not correspond to the observations of fibre pullout behaviour of single fibres. The VEMII model provides a versatile approach that can also be applied to hybrid fibre combinations.