The mechanical responses of the comminuted ceramic under impact is important in understanding penetration resistance of the target, modeling the penetration process, developing ceramic models and designing better armor systems. To determine the dynamic compressive responses of ceramic rubbles, a novel loading/reloading feature in SHPB experiments was developed to produce two consecutive loading pulses in a single dynamic experiment with two strikers and two shapers. The first pulse pulverizes the intact specimen into rubble after characterizing the intact material. After unloading of the first pulse, a second pulse loads the comminuted specimen and gives the dynamic constitutive behavior of the rubble.With this new experimental technique, several series of experiments were conducted on an oxide ceramic -- alumina AD995 and a non-oxide ceramic--hot pressed silicon carbide, SiC-N, with different strain rates, various volume dilatations and damaged levels under 26 MPa, 56 MPa and 104 MPa confinement. The results show that the strength of the damaged ceramic is not very sensitive to strain rates within this research range and the pulse separation once the damage attains a critical level. When slightly damaged far below a critical level, the specimen remains nearly elastic; when transitionally damaged, the specimen strength gradually decrease from the slight damage level to the heavy damage level. Increasing confinement increases the strength of the ceramics. The crack patterns were dominantly axial splitting for the slight damage, axial splitting and fragmentation for the intermediate damage, and fragmentation and comminution for the heavy damage. For SiC-N, the volume dilatation history shows a delayed failure. SEM observations indicated that microstructural failure mechanism is intergranular fracture for alumina and transgranular fracture for SiC-N.Mohr-Coulomb criterion was successfully employed to describe the damaged ceramic and the parameters were determined. JH-1 model was employed to describe the failed SiC-N in the linearly segmentation description of the strength and the parameters were also determined. Through the analysis of JH-1 model for SiC-N, the critical damage level can be taken as D = 1.0. JH-2 model was used to describe analytically the damaged AD995 and the parameters were obtained. The critical damage value is 0.88 for alumina determined directly from JH-2 model. The description of JH-1 model is equivalent to Mohr-Coulomb criterion while it is unsuitable for JH-2 model due to the non-linear description. Based on the analysis of existing models and current experimental data, an empirical constitutive material model was developed for the damaged ceramic, which well described the completely damaged ceramic, but was unable to model the partially damaged ceramic.

This dissertation explores the changing role of material culture in the expression of identity, using the Philistine settlement at Tel Miqne-Ekron in the Iron I (12th-10th centuries BCE) as a test case. A diachronic analysis documenting strategies of maintenance and adaptation points to the transformation of materials from domestic tools to symbols of social status, which were used to define social boundaries and promote a distinct identity. This occurred in conjunction with the increasing strength of the Philistine presence in the southern Levant.My dissertation focuses on one excavation area, described as the 'elite' zone. I outlined two areas of investigation: the organization of space, and a spatial distribution of the artifact assemblage. Through this analysis, I reconstruct Buildings 351 and 350 as elite residences, and Buildings 353 and 354 as the loci of crafts activities. Furthermore, I suggest that activities associated with Buildings 351 and 350 included elite sponsored feasting, and argue that the interconnected construction of these buildings with Buildings 353 and 354 implies an integrated function.In the final part of my analysis, I interpret change over time by contextualizing the foreign, i.e. Philistine and local, i.e. Canaanite material culture assemblages as a means to investigate diachronic variation. My research demonstrates that the traditional focus on foreign origins has obscured our understanding of these objects by removing them from their local contexts. Developments included a shift in the role played by the Philistine pottery, from a domestic assemblage associated with an immigrant populations' adjustment of traditional methods of daily practices, to a fine-ware assemblage, where it was used to express a concept of elite identity. The model I propose views change as a reflexive process involving both group and individual interactions.

Synthesis and characterization of optical nanocrystals and nanostructures. An approach to transparent laser nanoceramicsMontserrat Galceran MestresEls materials nanocristal·lins són materials policristal·lins amb una mida de partícula en el rang dels nanòmetres. Presenten diferents propietats físiques, òptiques, electròniques, químiques i estructurals perquè tenen una proporció més elevada d'àtoms a la superfície que els materials en volum. La síntesi de nanocristalls és la primera etapa per fabricar materials nanoceràmics per a aplicacions làser. Són atractius per a làsers en estat sòlid perquè ofereixen avantatges com ara: baix cost, fabricació senzilla i bones propietats mecàniques i òptiques.Aquesta tesi tracta la síntesi i caracterització de nous nanomaterials òptics (KRE(WO4)2, RE2O3, KTiOPO4) dopats amb ions actius com les terres rares (RE), erbi, iterbi, holmi i europi com a primera etapa per sintetitzar noves ceràmiques làser Ho:Lu2O3. Per avaluar les qualitats d'aquests materials com a possibles làser en estat sòlid o materials d'òptica nolinear, s'ha dut a terme una caracterització estructural, òptica i espectroscòpica aquests nanomaterials (nanocristalls, nanoestructures i nanoceràmiques).Synthesis and characterization of optical nanocrystals and nanostructures. An approach to transparent laser nanoceramicsMontserrat Galceran MestresNanocrystalline materials are polycrystalline materials with a particle size in the nanometer range that have different physical, optical, electronic, chemical and structural properties because they have a larger fraction of surface atoms than larger-scale materials. The synthesis of nanocrystals is the first step in manufacturing nanoceramic laser materials; they are very attractive to solid state laser due to several advantages such as low cost, easy fabrication and good mechanical and optical properties.This thesis deals with the synthesis and characterization of new optical nanomaterials (KRE(WO4)2, RE2O3, KTiOPO4) doped with active rare earth (RE) ions as erbium, ytterbium, holmium and europium as a first step to synthesize a new Ho:Lu2O3 laser ceramics. An extensively structural, optical and spectroscopic characterization of the nanomaterials (nanocrystals, nanostructures and nanoceramics) was performed in order to evaluate these materials as a promising solid state laser or nonlinear optical materials.

Solid oxide fuel cells (SOFCs) are electrochemical devices that can convert a variety of fuels directly into electricity. Their commercialization requires efficient operation of its components. The sluggish kinetics for the oxygen reduction reaction (ORR) at the SOFC cathode contributes to the loss in the fuel cell efficiency. In this work, the ORR was investigated for the strontium-doped lanthanum manganite cathode (LSM) and yttria-stabilized zirconia electrolyte (YSZ) system. A combined mathematical modelling and experimental framework was developed to estimate, for the first time, the kinetics of the elementary processes of the ORR for porous LSM cathodes. The kinetics of each process was then analyzed to identify the contribution to the cathode resistance. The steady state and impedance response for polarized and unpolarized LSM cathodes was collected over a temperature range between 750C and 850C and two different oxygen partial pressure (pO2) ranges: (i) between 0.0001atm and 0.001atm, where LSM is considered to be stoichiometric with respect to oxygen and (ii) between 0.01atm and 0.21atm, where LSM is considered to be superstoichiometric with respect to oxygen. A mathematical model was developed to analyze both the steady state and impedance data. Two pathways for the ORR were considered: one where oxygen is transported in the gas phase and one where oxygen is transported along the surface of the LSM cathode. Rate constants, transport coefficients and their respective activation energies were obtained for the adsorption/desorption, surface diffusion and charge transfer processes. The experimental results indicated different polarization behavior between low and high pO2. It is hypothesized that the concentration of cation vacancies on the LSM surface changes with both pO2 and extent of polarization and that cation vacancies on the LSM surface can promote the ORR. Modelling results at low pO2 suggested that the adsorption reaction was slow and that thermodynamic limitations resulting in low equilibrium oxygen surface coverage can play an important role at both low and high polarizations. Modelling in high pO2 was complicated by the nature of the LSM surface in these conditions and suggests an electrochemical reaction at the gas/LSM interface and the transport of charged adsorbed oxygen atoms. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2009-12-31 11:53:23.535

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